Materials handling vehicle estimating a speed of a movable assembly from a lift motor speed

BACKGROUND ART

0001<patcit id="pcit0001" dnum="US7344000B2"><text>U.S. Patent No. 7,344,000 B2</text></patcit> discloses a materials handling vehicle comprising a base, such as a power unit, and a carriage assembly, such as a platform assembly, wherein the carriage assembly is movable relative to the base. The vehicle further comprises a cylinder coupled to the base to effect movement of the carriage assembly relative to the base and a hydraulic system to supply a pressurized fluid to the cylinder. The hydraulic system includes an electronically controlled valve coupled to the cylinder. The vehicle further comprises control structure to control the operation of the valve such that the valve is closed in the event of an unintended descent of the carriage assembly in excess of a commanded speed.

0002<patcit id="pcit0002" dnum="US2006060409A"><text>US 2006/060409 A</text></patcit> discloses a materials handling vehicle according to the preamble of claim 1, comprising an electronically controlled valve coupled to a lift cylinder which, in turn, is coupled to a carriage assembly, wherein the valve is controlled so as to close in the event of an unintended descent of the carriage assembly.

DISCLOSURE OF INVENTION

0003In accordance with the present invention, a materials handling vehicle is provided comprising: a support structure including a fixed member; a movable assembly coupled to the support structure; a hydraulic system and a control structure. The support structure further comprises lift apparatus to effect movement of the movable assembly relative to the support structure fixed member. The lift apparatus includes at least one ram/cylinder assembly. The hydraulic system includes a motor, a pump coupled to the motor to supply a pressurized fluid to the at least one ram/cylinder assembly, and an electronically controlled valve associated with the at least one ram/cylinder assembly. The materials handling vehicle comprises a control structure to estimate a speed of the movable assembly from a speed of the motor and to calculate an updated pump volumetric efficiency using the estimated movable assembly speed and a determined movable assembly speed.

0004The control structure may determine the updated volumetric efficiency using the following equation: <maths id="math0001" num=""><math display="block"><mrow><mi>updated volumetric efficiency</mi><mo>=</mo><mfenced separators=""><mi>determined movable assembly speed</mi><mo>*</mo><mi>current volumetric efficiency</mi></mfenced><mo>/</mo><mi>estimated movable assembly speed</mi><mn>.</mn></mrow></math><img file="EP2865635B1_D0001.tif" /></maths>

0005The current volumetric efficiency may be derived based on one or more of a speed of the materials handling vehicle, a direction of rotation of the pump, and a pressure, a temperature, and/or a viscosity of the pressurized fluid.

0006The fixed member may comprise a fixed mast weldment coupled to a power unit.

0007The lift apparatus may further comprise at least one movable mast weldment and the movable assembly may comprise a fork carriage assembly which moves relative to the support structure fixed member.

BRIEF DESCRIPTION OF DRAWINGS

0008<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a top view of a materials handling vehicle in which a monomast is incorporated;</li><li><figref idref="f0002">Fig. 2</figref> is a front view of the vehicle illustrated in <figref idref="f0001">Fig. 1</figref> with a fork carriage apparatus elevated;</li><li><figref idref="f0003">Fig. 3</figref> is an enlarged top view of the monomast illustrated in <figref idref="f0001">Fig. 1</figref>;</li><li><figref idref="f0004">Fig. 4</figref> is a side view, partially in cross section, of an upper portion of the monomast;</li><li><figref idref="f0005">Fig. 5</figref> is a perspective side view, partially in cross section, of the monomast upper portion;</li><li><figref idref="f0006">Fig. 6</figref> is a side view, partially in cross section, of the monomast;</li><li><figref idref="f0007">Fig. 7</figref> is a perspective side view illustrating the monomast and a portion of the fork carriage apparatus;</li><li><figref idref="f0008">Fig. 8</figref> is a perspective side view illustrating the fork carriage apparatus coupled to the monomast illustrated in <figref idref="f0001">Fig. 1</figref>;</li><li><figref idref="f0009">Fig. 9</figref> is a schematic diagram illustrating the motor, pump, controller, electronic normally closed ON/OFF solenoid-operated valve, first and second electronic normally closed proportional solenoid-operated valves, mast weldment lift structure and fork carriage apparatus lift structure;</li><li><figref idref="f0010">Figs. 10A</figref> and <figref idref="f0011">10B</figref> provide a flow chart illustrating process steps implemented by a controller not forming a part of the present invention;</li><li><figref idref="f0012">Fig. 11</figref> is test data from a vehicle constructed in accordance with the present invention;</li><li><figref idref="f0013">Fig. 12</figref> is an exploded view of a mast assembly, a mast weldment lift structure and a fork carriage apparatus lift structure of a vehicle of a second embodiment of the present invention;</li><li><figref idref="f0014">Fig. 13</figref> is a schematic diagram illustrating the motor, pump, controller, electronic normally closed ON/OFF solenoid-operated valve, first, second and third electronic normally closed proportional solenoid-operated valves, mast weldment lift structure and fork carriage apparatus lift structure of the vehicle of the second embodiment of the present invention; and</li><li><figref idref="f0015">Fig. 14</figref> provides a flow chart illustrating process steps not forming a part of the present invention.</li></ul>

MODES FOR CARRYING OUT THE INVENTION

0009<figref idref="f0001">Fig. 1</figref> illustrates a top view of a materials handling vehicle 100 comprising a rider reach truck 100. A monomast 200, a mast weldment lift structure 220, a fork carriage apparatus 300 and a fork carriage apparatus lift structure 400, constructed in accordance with a first embodiment of the present invention, are incorporated into the rider reach truck 100, see also <figref idref="f0003">Figs. 3</figref> and <figref idref="f0009">9</figref>.

0010The truck 100 further includes a vehicle power unit 102, see <figref idref="f0001">Figs. 1</figref> and <figref idref="f0002">2</figref>. The power unit 102 houses a battery (not shown) for supplying power to a traction motor coupled to a steerable wheel (not shown) mounted near a first corner at the rear 102A of the power unit 102. Mounted to a second corner at the rear 102A of the power unit 102 is a caster wheel (not shown). A pair of outriggers 202 and 204 are mounted to a monomast frame 210, see <figref idref="f0002">Fig. 2</figref>. The outriggers 202 and 204 are provided with supports wheels 202A and 204A. The battery also supplies power to a lift motor 301, which drives a hydraulic lift pump 302, see <figref idref="f0009">Fig. 9</figref>. As will be discussed in further detail below, the lift pump 302 supplies pressurized hydraulic fluid to the fork carriage apparatus lift structure 400 and the mast weldment lift structure 220. While not illustrated, a further motor and pump may be provided to supply pressurized hydraulic fluid to accessory mechanisms, such as a side-shift mechanism, a tilt mechanism and/or a reach mechanism.

0011The vehicle power unit 102 includes an operator's compartment 110. An operator standing in the compartment 110 may control the direction of travel of the truck 100 via a tiller 120. The operator may also control the travel speed of the truck 100, and height, extension, tilt and side shift of first and second forks 402 and 404 via a multifunction controller 130, see <figref idref="f0001">Fig. 1</figref>. The first and second forks 402 and 404 form part of the fork carriage apparatus 300.

0012The monomast 200 may be constructed as set out in <patcit id="pcit0003" dnum="US20100065377A1" dnum-type="L"><text>U.S. Patent Application Publication No. 2010/0065377 A1, entitled "Monomast for a Materials Handling Vehicle," filed on September 10, 2009</text></patcit>. Briefly, the monomast 200 comprises a fixed first stage mast weldment 230 (also referred to herein as a fixed member), a second stage mast weldment 240 positioned to telescope over the first stage weldment 230 and a third stage mast weldment 250 positioned to telescope over the first and second stage weldments 230 and 240, see <figref idref="f0001">Figs. 1</figref> and <figref idref="f0003 f0004 f0005">3-5</figref>. The mast weldment lift structure 220 effects lifting movement of the second and third stage weldments 240 and 250 relative to the fixed first stage weldment 230, see <figref idref="f0009">Fig. 9</figref>.

0013Support structure is defined herein as comprising the power unit 102, the fixed first mast weldment 230 and lift apparatus. Lift apparatus is defined herein as comprising the second and third mast weldments 240 and 250, the mast weldment lift structure 220 and the fork carriage apparatus lift structure 400.

0014The mast weldment lift structure 220 comprises a hydraulic ram/cylinder assembly 222 comprising a cylinder 222A and a ram 222B, see <figref idref="f0004 f0005 f0006">Figs. 4-6</figref>. The cylinder 222A is fixedly coupled to a base 1239 forming part of the first stage weldment 230, see <figref idref="f0006">Fig. 6</figref>. Hence, the cylinder 222A does not move vertically relative to the vehicle power unit 102.

0015An engagement plate 1300 of a pulley assembly 302 is coupled to an end portion 1222B of the ram 222B, see <figref idref="f0004">Fig. 4</figref>. The pulley assembly 302 further comprises first and second vertical plates 1310 and 1312, which are fixed to the engagement plate 1300 by welds. A pulley or roller 314 is received between and rotatably coupled to the first and second vertical plates 1310 and 1312. The pulley assembly 302 is fixedly coupled to the second stage weldment 240 by coupling structure (not shown). First and second chains 500 and 502 are coupled at first ends (only the first end 500A of the first chain 500 is clearly illustrated in <figref idref="f0006">Fig. 6</figref>) to chain anchors (not shown) which, in turn, are bolted to a bracket 510 fixedly welded to the cylinder 222A of the hydraulic ram/cylinder assembly 222, see <figref idref="f0006">Fig. 6</figref>. Opposing second ends of the first and second chains 500 and 502 (only the second end 500B of the first chain 500 is clearly illustrated in <figref idref="f0006">Fig. 6</figref>) are coupled to a lower section of the third stage weldment 250 via coupling anchors 504 and 506, see <figref idref="f0002">Figs. 2</figref> and <figref idref="f0006">6</figref>. The first and second chains 500 and 502 extend over the pulley or roller 314 of the pulley assembly 302, see <figref idref="f0004">Fig. 4</figref>. When the ram 222B is extended, it causes the pulley assembly 302 to move vertically upward such that the pulley 314 pushes upwardly against the first and second chains 500 and 502. As the pulley 314 applies upward forces on the chains 500 and 502, the second stage weldment 240 moves vertically relative to the first stage weldment 230 and the third stage weldment 250 moves vertically relative to the first and second stage weldments 230 and 240. For every one unit of vertical movement of the second stage weldment 240 relative to the first stage weldment 230, the third stage weldment 250 moves vertically two units relative to the first stage weldment 230.

0016The fork carriage apparatus 300, also referred to herein as a movable assembly, is coupled to the third stage weldment 250 so as to move vertically relative to the third stage weldment 250, see <figref idref="f0007">Fig. 7</figref>. The fork carriage apparatus 300 also moves vertically with the third stage weldment 250 relative to the first and second stage weldments 230 and 240. The fork carriage apparatus 300 comprises a fork carriage mechanism 310 to which the first and second forks 402 and 404 are mounted, see <figref idref="f0008">Fig. 8</figref>. The fork carriage mechanism 310 is mounted to a reach mechanism 320 which, in turn, is mounted to a mast carriage assembly 330, see <figref idref="f0007">Figs. 7</figref> and <figref idref="f0008">8</figref>. The mast carriage assembly 330 comprises a main unit 332 having a plurality of rollers 334 which are received in tracks 350 formed in opposing outer sides surfaces 250B and 250C of the third stage weldment 250, see <figref idref="f0003">Figs. 3</figref> and <figref idref="f0007">7</figref>. As noted above, accessory mechanisms, such as a side-shift mechanism, a tilt mechanism and/or a reach mechanism may be provided to laterally move, tilt and/or extend the forks 402 and 404.

0017The fork carriage apparatus lift structure 400 comprises a hydraulic ram/cylinder assembly 410 including a cylinder 412 and a ram 414, see <figref idref="f0007">Fig. 7</figref>. The cylinder 412 is fixedly coupled to a side section 257D of the third stage weldment 250. First and second pulleys 420 and 422 are coupled to an upper end of the ram 414, see <figref idref="f0007">Fig. 7</figref>. A lift chain 440 extends over the first pulley 420 and is coupled at a first end 440A to the cylinder 412 via chain anchors and a bracket 441 welded to the cylinder 412 and at its second end 440B to the mast carriage assembly 330, see <figref idref="f0007">Fig. 7</figref>. Vertical movement of the ram 414 effects vertical movement of the entire fork carriage apparatus 300 relative to the third stage weldment 250. For every one unit of vertical movement of the ram 414 and the first pulley 420 relative to the third stage weldment 250, the fork carriage apparatus 300 moves vertically two units relative to the third stage weldment 250.

0018The materials handling vehicle 100 comprises a hydraulic system 401 comprising the lift motor 301, which drives the hydraulic lift pump 302, as noted above. The lift motor 301 comprises a velocity (RPM) sensor. The pump 302 supplies pressurized hydraulic fluid to the hydraulic ram/cylinder assembly 222 of the mast weldment lift structure 220 and the hydraulic ram/cylinder assembly 410 of the fork carriage apparatus lift structure 400.

0019The hydraulic system 401 further comprises a hydraulic fluid reservoir 402, see <figref idref="f0009">Fig. 9</figref>, which is housed in the power unit 102, and fluid hoses/lines 411A-411C coupled between the pump 302 and the mast weldment lift structure hydraulic ram/cylinder assembly 222 and the fork carriage apparatus lift structure hydraulic ram/cylinder assembly 410. The fluid hoses/lines 411A and 411B are coupled in series and function as supply/return lines between the pump 302 and the mast weldment structure hydraulic ram/cylinder assembly 222. The fluid hoses/lines 411A and 411C are coupled in series and function as supply/return lines between the pump 302 and the fork carriage apparatus lift structure hydraulic ram/cylinder assembly 410. Because the fluid hose/line 411A is directly coupled to both fluid hoses/lines 411 B and 411C, all three lines 411A-411C are always at the substantially the same fluid pressure.

0020The hydraulic system 401 also comprises an electronic normally closed ON/OFF solenoid-operated valve 420 and first and second electronic normally closed proportional solenoid-operated valves 430 and 440. The valves 420, 430 and 440 are coupled to an electronic controller 1500 for controlling their operation, see <figref idref="f0009">Fig. 9</figref>. The electronic controller 1500 forms part of a "control structure." The normally closed ON/OFF solenoid valve 420 is energized by the controller 1500 only when one or both of the rams 222B and 414 are to be lowered. When de-energized, the solenoid valve 420 functions as a check valve so as to block pressurized fluid from flowing from line 411A, through the pump 302 and back into the reservoir 402, i.e., functions to prevent downward drift of the fork carriage apparatus 300, yet allows pressurized fluid to flow to the cylinders 222A and 412 via the lines 411A-411C during a lift operation.

0021The first electronic normally closed proportional solenoid-operated valve 430 is located within and directly coupled to a base 1222A of the cylinder 222A of the mast weldment lift structure hydraulic ram/cylinder assembly 222, see <figref idref="f0009">Fig. 9</figref>. The second electronic normally closed proportional solenoid-operated valve 440 is located within and directly coupled to a base 412A of the cylinder 412 of the fork carriage apparatus lift structure hydraulic ram/cylinder assembly 410. The first normally closed proportional solenoid-operated valve 430 is energized, i.e., opened, by the controller 1500 when the ram 222B is to be lowered. The second normally closed proportional solenoid-operated valve 440 is energized, i.e., opened, by the controller 1500 when the ram 414 is to be lowered. When de-energized, the first and second normally closed proportional solenoid-operated valves 430 and 440 function as a check valves so as to block pressurized fluid from flowing out of the cylinders 222A and 412. The valves 430 and 440, when functioning as check valves, also permit pressurized hydraulic fluid to flow into the cylinders 222A and 412 during a lift operation.

0022When a lift command is generated by an operator via the multifunction controller 130, both the cylinder 412 of the fork carriage apparatus lift structure 400 and the cylinder 222A of the mast weldment lift structure 220 are exposed to hydraulic fluid at the same pressure via the lines 411A-411C. Because the ram 414 of the fork carriage apparatus lift structure 400 and the ram 222B of the mast weldment lift structure 220 include base ends having substantially the same cross sectional areas and for all load conditions, the fork carriage apparatus lift structure 400 requires less pressure to actuate than the mast weldment lift structure 220, the ram 414 of the fork carriage apparatus lift structure 400 will move first until the fork carriage apparatus 300 has reached its maximum height relative to the third stage weldment 250. Thereafter, the second and third stage weldments 240 and 250 will begin to move vertically relative to the first stage weldment 230.

0023When a lowering command is generated by an operator via the multifunction controller 130, the electronic controller 1500 causes the electronic normally closed ON/OFF solenoid-operated valve 420 to open. Presuming the rams 222B and 414 are fully extended when a lowering command is generated, the first proportional valve 430 is energized by the controller 1500, causing it to fully open in the illustrated embodiment to allow fluid to exit the cylinder 222A of the mast weldment lift structure 220, thereby allowing the second and third stage weldments 240 and 250 to lower. Once the second and third stage weldments 240 and 250 near their lowermost positions, the controller 1500 causes the second proportional valve 440 to substantially fully open and the first proportional valve 430 to partially close. Partially closing the first valve 430 causes the fluid pressure in the lines 411A-411C to lower. By opening the second valve 440 and partially closing the first valve 430, the ram 414 begins to lower, while the ram 222B continues to lower. After the ram 222B reaches its lowermost position, the ram 414 continues to lower until the fork carriage apparatus 300 reaches its lowermost position. Except for the partial closure of the first proportional valve 430 when the second and third stage weldments 240 and 250 near their lowermost positions, the speed at which fluid is metered from the cylinder 222A of the mast weldment lift structure 220 and the cylinder 412 of the fork carriage apparatus lift structure 400 is generally controlled by the pump 302.

0024First and second encoder units 600 and 602, respectfully, also forming part of the "control structure," are provided and may comprise conventional friction wheel encoder assemblies or conventional wire/cable encoder assemblies, see <figref idref="f0009">Fig. 9</figref>. In the illustrated embodiment, the first encoder unit 600 comprises a first friction wheel encoder assembly mounted to the third stage weldment 250 such that a first friction wheel engages and moves along the second stage weldment 240. Hence, as the third stage weldment 250 moves relative to the second stage weldment 240, the first friction wheel encoder generates pulses to the controller 1500 indicative of the third stage weldment movement relative to the second stage weldment 240.

0025Also in the illustrated embodiment, the second encoder unit 602 comprises a second friction wheel assembly mounted to the fork carriage apparatus 300 such that a second friction wheel engages and moves along the third mast stage weldment 250. Hence, as the fork carriage apparatus 300 moves relative to the third stage weldment 250, the second friction wheel encoder generates pulses to the controller 1500 indicative of the fork carriage apparatus 300 movement relative to the third stage weldment 250.

0026As noted above, the first and second encoder units 600 and 602 generate corresponding pulses to the controller 1500. The pulses generated by the first encoder unit 600 are used by the controller 1500 to determine the position of the third stage weldment 250 relative to the second stage weldment 240 as well as the speed of movement of the third stage weldment 250 relative to the second stage weldment 240. The controller 1500 also determines the speed and position of the third stage weldment 250 relative to the fixed first stage weldment 230, wherein the speed of the third stage weldment 250 relative to the first stage weldment 230 is equal to twice the speed of the third stage weldment 250 relative to the second stage weldment 240. Further, the distance from a reference point on the third stage weldment 250 to a reference point on the first stage weldment 230 is twice the distance from the reference point on the third stage weldment 240 to a reference point on the second stage weldment 230, wherein the reference point on the second stage weldment 240 is at a location corresponding to the reference point location on the first stage weldment 230. The pulses generated by the second encoder unit 602 are used by the controller 1500 to determine the position of the fork carriage apparatus 300 relative to the third mast stage weldment 250 as well as the speed of movement of the fork carriage apparatus 300 relative to the third mast stage weldment 250. By knowing the speed and position of the third stage weldment 250 relative to the first stage weldment 230 and the speed and position of the fork carriage apparatus 300 relative to the third stage weldment 250, the controller 1500 can easily determine the speed and position of the fork carriage apparatus 300 relative to the first stage weldment 230.

0027During a lowering command, the controller 1500 compares a determined or sensed speed of the fork carriage apparatus 300 relative to the first stage weldment 230 to first and second threshold speeds. This involves the controller 1500 determining a first speed comprising a determined or sensed speed of the third stage weldment 250 relative to the first stage weldment 230, determining a second speed comprising a determined or sensed speed of the fork carriage apparatus 300 relative to the third stage weldment 250 and adding the first and second determined speeds together to calculate a third determined speed. The third determined speed is equal to the determined or sensed speed of the fork carriage apparatus 300 relative to the first stage weldment 230.

0028As noted above, for every one unit of vertical movement of the second stage weldment 240 relative to the first stage weldment 230, the third stage weldment 250 moves vertically two units relative to the first stage weldment 230. In order to determine the first speed, the controller 1500 determines the speed of third stage weldment 250 relative to the second stage weldment 240 using the pulses from the first encoder unit 600, as noted above, and multiplies the determined speed of movement of the third stage weldment 250 relative to the second stage weldment 240 by "2". Hence, this provides the first speed, i.e., the determined speed of the third stage weldment 250 relative to the first stage weldment 230.

0029The second speed is equal to the determined speed of movement of the fork carriage apparatus 300 relative to the third mast stage weldment and is found using the pulses generated by the second encoder unit 602 as noted above.

0030During a lowering command, the controller 1500 may compare the third determined speed, i.e., the determined speed of the fork carriage apparatus 300 relative to the first stage weldment 230, to the first and second threshold speeds. In the illustrated embodiment, the comparison of the third determined speed to the first and second threshold speeds may be made by the controller 1500 once every predefined time period, e.g., every 5 milliseconds. The comparison of the third determined speed to the first and second threshold speeds is referred to herein as a "comparison event." If the third determined speed is greater than the first threshold speed during a predefined number of sequential comparison events, e.g., between 1-50 comparison events, or greater than the second threshold speed during a single comparison event, then the electronic controller 1500 implements a response routine, wherein the controller de-energizes the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 so as to prevent further downward movement of the rams 222B and 414. The controller 1500 may cause the first and second valves 430 and 440 to move from their powered open positions to their closed positions immediately or over an extended time period, such as from about 0.3 second to about 1.0 second. By causing the first and second valves 430 and 440 to close over an extended time period, the magnitude of pressure spikes within the cylinders 222A and 412, which occur when the pistons 222B and 414 stop their downward movement within the cylinders 222A and 412, is reduced. Further, closing of the first and second valves 430 and 440 by the controller 1500 may comprise partially closing the first and second valves 430 and 440, i.e., not fully closing the first and second valves 430 and 440, so as to allow the fork carriage apparatus 300 and the second and third stage weldments 240, 250 to lower slowly to the ground. It is presumed that when the third determined speed is greater than one of the first and second threshold speeds, the fork carriage apparatus 300 is moving too quickly relative to the first stage weldment 230, i.e., at an unintended descent speed, which condition may occur when there is a loss of hydraulic pressure in the fluid being metered from one or both of the cylinders 222A and 412. Loss of hydraulic pressure may be caused by a breakage in one of the fluid lines 411A-411C.

0031In a further embodiment, the controller 1500 compares the third determined speed, i.e., the determined speed of the fork carriage apparatus 300 relative to the first stage weldment 230, to only the first threshold speed. The comparison of the third determined speed to the first threshold speed is made by the controller 1500 once every predefined time period, e.g., every 5 milliseconds. The comparison of the third determined speed to the first threshold speed is also referred to herein as a "comparison event." If the third determined speed is greater than the first threshold speed, during a predefined number of sequential comparison events, e.g., between 1-50 comparison events, then the electronic controller 1500 implements a response routine, wherein the controller 1500 de-energizes the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 so as to prevent further downward movement of the rams 222B and 414.

0032The first threshold speed may be determined by the electronic controller 1500 as follows. First, the controller 1500 may estimate the magnitude of a combined lowering speed of the ram 222B of the mast weldment lift structure 220 and the ram 414 of the fork carriage apparatus lift structure 400 from a speed of the lift motor 301. As discussed above with respect to a lowering operation, with the fork carriage apparatus 300 and the second and third stage weldments 240 and 250 fully extended, the ram 222B begins to lower first, then the rams 222B and 414 lower simultaneously during a staging part of the lowering operation until the ram 222B reaches its lowermost position. Thereafter, the ram 414 continues its downward movement until it reaches its lowermost position.

0033First, the controller 1500 converts the lift motor speed into a lift pump fluid flow rate using the following equation: <maths id="math0002" num=""><math display="block"><mrow><mi>pump fluid flow rate</mi><mspace width="1em" /><mfenced separators=""><mi>gallons</mi><mo>/</mo><mi>minute</mi></mfenced><mo>=</mo><mfenced open="[" close="]" separators=""><mfenced separators=""><mi>lift motor speed</mi><mfenced><mi>RPM</mi></mfenced></mfenced><mo>*</mo><mfenced separators=""><mrow><mi>lift pump displacement</mi><mspace width="1em" /></mrow><mfenced separators=""><mi>cc</mi><mo>/</mo><mi>revolution</mi></mfenced></mfenced><mo>*</mo><mfenced><mi>lift motor volumetric efficiency</mi></mfenced></mfenced><mo>/</mo><mfenced separators=""><mn>3786</mn><mrow><mspace width="1em" /><mi>cc</mi></mrow><mo>/</mo><mi>gal</mi></mfenced></mrow></math><img file="EP2865635B1_D0002.tif" /></maths>

0034The controller 1500 may then determine an estimated downward linear speed (magnitude) of the fork carriage apparatus 300 relative to the first stage weldment 230 using the following equation, which equation is believed to be applicable during all phases of a lowering operation, including staging when both the rams 222B and 414 are being lowered simultaneously: <maths id="math0003" num=""><math display="block"><mrow><mi mathvariant="normal">estimated linear speed of the fork carriage apparatus</mi><mspace width="1em" /><mn mathvariant="normal">300</mn><mspace width="1em" /><mi mathvariant="normal">relative to the first weldment</mi><mspace width="1em" /><mn mathvariant="normal">230</mn><mspace width="1em" /><mfenced separators=""><mi mathvariant="normal">inches</mi><mo>/</mo><mi mathvariant="normal">second</mi></mfenced><mo>=</mo><mfenced open="[" close="]" separators=""><mfenced separators=""><mi mathvariant="normal">pump fluid flow rate</mi><mfenced separators=""><mi mathvariant="normal">gallons</mi><mo>/</mo><mi mathvariant="normal">minute</mi></mfenced></mfenced><mo>*</mo><mrow><mfenced separators=""><mn mathvariant="normal">231</mn><mspace width="1em" /><msup><mi mathvariant="normal">in</mi><mn mathvariant="normal">3</mn></msup><mo>/</mo><mi mathvariant="normal">gallon</mi></mfenced><mo>*</mo><mfenced><mi mathvariant="normal">speed ratio</mi></mfenced></mrow></mfenced><mo>/</mo><mfenced open="[" close="]" separators=""><mfenced separators=""><mrow><mi mathvariant="normal">inside area of cylinder</mi><mspace width="1em" /></mrow><mfenced><msup><mi mathvariant="normal">in</mi><mn mathvariant="normal">2</mn></msup></mfenced></mfenced><mo>*</mo><mfenced separators=""><mn mathvariant="normal">60</mn><mrow><mspace width="1em" /><mi mathvariant="normal">seconds</mi></mrow><mo>/</mo><mi mathvariant="normal">minute</mi></mfenced></mfenced></mrow></math><img file="EP2865635B1_D0003.tif" /></maths> wherein, <ul id="ul0002" list-style="none" compact="compact"><li>"inside area of cylinder" = cross sectional area of cylinder 222B, which equals the cross sectional area of cylinder 412 (only the cross sectional area of a single cylinder is used in the equation);</li><li>"speed ratio" = (the third weldment speed/first weldment speed) = (fork carriage apparatus speed/third weldment speed) = 2/1 in the illustrated embodiment.</li></ul>

0035In the illustrated embodiment, the first threshold speed is equal to the estimated speed of the fork carriage apparatus 300 relative to the first weldment 230 times either a first tolerance factor, e.g., 1.6, or a second tolerance factor, e.g., 1.2. Once an operator gives a command via the multi-function controller 130 to lower the fork carriage apparatus 300, the controller 1500 executes a ramping function within its software so as to increase the magnitude of the downward lowering speed of the fork carriage apparatus 300 in a controlled manner at a predetermined rate, e.g., a speed change of from about 4 feet/minute to about 40 feet/minute every 16 milliseconds, based on the position of the multifunction controller 130, until the commanded downward speed is reached. The first tolerance factor is used when the fork carriage apparatus lowering speed is in the process of being ramped to the commanded speed, i.e., the controller 1500 is still executing the ramping function, and the second tolerance factor is used when the controller 1500 is no longer increasing the speed of the lift motor 301, i.e., the controller 1500 has completed the ramping function. The first tolerance factor is greater than the second tolerance factor to account for the physical lag time occurring between when an operator commands a speed change and the speed of the fork carriage apparatus actually occurs. It is also contemplated that in an alternative embodiment, the first threshold speed may equal the estimated speed of the fork carriage apparatus 300 relative to the first weldment 230.

0036The controller 1500 may use the determined downward speed of the fork carriage apparatus relative to the first stage weldment, the estimated fork carriage apparatus downward speed relative to the first weldment and the current pump volumetric efficiency to generate an updated pump volumetric efficiency, which updated pump volumetric efficiency may be used by the controller 1500 the next time it converts lift motor speed into a lift pump fluid flow rate. The controller 1500 may determine the updated pump volumetric efficiency using the following equation: <maths id="math0004" num=""><math display="block"><mrow><mi>updated pump volumetric efficiency</mi><mo>=</mo><mfenced separators=""><mi>determined fork carriage apparatus speed</mi><mo>*</mo><mi>current volumetric efficiency</mi></mfenced><mo>/</mo><mfenced><mi>estimated fork carriage apparatus speed</mi></mfenced><mn>.</mn></mrow></math><img file="EP2865635B1_D0004.tif" /></maths>

0037An initial pump volumetric efficiency, i.e., one used when the controller 1500 is first activated and one applied in the above equation as the "current volumetric efficiency" the first time an updated pump volumetric efficiency is calculated, e.g., the first time after a lowering operation is commenced, may equal 95% or any other appropriate value. The initial pump volumetric efficiency may be stored in memory associated with the controller 1500Rather than using a single initial pump volumetric efficiency, multiple volumetric efficiency points that correspond to, for example, the speed of the truck 100, although other vehicle conditions could be used, such as hydraulic fluid pressure, hydraulic fluid temperature, hydraulic fluid viscosity, direction of rotation of the hydraulic lift pump 302, etc., may be stored in a data or look up table. The correct volumetric efficiency point based on a corresponding one or more of the vehicle condition(s) may be looked up in the data table and applied as the initial pump volumetric efficiency to calculate an updated pump volumetric efficiency. It is noted that using the initial pump volumetric efficiency is not intended to be limited to only being used once per lowering operation. That is, the initial pump volumetric efficiency may be used in generating an updated pump volumetric efficiency for several implementations of the above equation. For example, the initial pump volumetric efficiency may be used in generating an updated pump volumetric efficiency for a predefined time period, such as, for example, the first 0.5 seconds after a lowering operation is commenced.

0038The second threshold speed may comprise a fixed speed, such as 300 feet/minute. When the fork carriage apparatus 300 is moving at a speed equal to or greater than 300 feet/minute, it is presumed to be moving at an unintended, excessive speed.

0039Referring to <figref idref="f0010">Figs. 10A</figref> and <figref idref="f0011">10B</figref>, a flow chart illustrates a process 700 implemented by the controller 1500 for controlling the operation of the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 during a lowering command. At step 701, when the vehicle 100 is powered-up, the controller 1500 reads non-volatile memory (not shown) associated with the controller 1500 to determine a value stored within a first "lockout" memory location. If, during previous operation of the vehicle 100, the controller 1500 determined that a "concern-count," to be discussed below, exceeded a "concern-max" count, e.g., 40, the controller 1500 will have set the value in the first lockout memory location to 1. If not, the value in the first lockout memory location would remain set at 0.

0040If the controller 1500 determines during step 701 that the value in the first lockout memory location is 0, the controller 1500 next determines, during step 702, if the magnitude of the third determined speed is greater than a fixed lower threshold speed, e.g., 60 feet/minute, and whether the direction of movement of the lift motor 301, as indicated by the velocity sensor (noted above) associated with the motor 301, indicates that the fork carriage apparatus 300 is being lowered. If the answer to either or both of these queries is NO, then the "concern-count" value is set equal to 0, see step 703, and the controller 1500 returns to step 702. Step 702 may be continuously repeated once every predetermined time period, e.g., every 5 milliseconds. If the answer to both queries is YES, then the controller 1500 determines, in step 704, if an operator commanded lowering speed for the fork carriage apparatus 300 is being ramped, i.e., the ramping function is still being executed. If the answer is YES, then the first tolerance factor is used and the first threshold speed is equal to the estimated speed of the fork carriage apparatus 300 relative to the first weldment 230 times the first tolerance factor, see step 705. If the answer is NO, then the second tolerance factor is used and the first threshold speed is equal to the estimated speed of the fork carriage apparatus 300 relative to the first weldment 230 times the second tolerance factor, see step 706.

0041After the first threshold speed has been calculated, the controller 1500 determines, during step 707, whether the third determined speed is greater than the first threshold speed. If NO, the controller 1500 sets the "concern-count" value to 0 and returns to step 704. If YES, i.e., the controller 1500 determines that the third determined speed exceeds the first threshold speed, the controller 1500 increments the "concern-count" by "1," see step 709. At step 711, the controller 1500 determines if the "concern-count" is greater than the "concernmax" count or whether the third determined speed is greater than the second threshold speed. If the answer to both queries is NO, then the controller 1500 returns to step 704. Steps 704 and 707 may be continuously repeated once every predetermined time period, e.g., every 5 milliseconds. If the answer to one or both queries is YES, then the controller 1500 implements a response routine, wherein the controller 1500 de-energizes the first and second electronic normally closed proportional solenoid-operated valves 430 and 440, see step 713. As noted above, the valves 430 and 440 may be closed over an extended time period, e.g., from about 0.3 second to about 1.0 second.

0042Once the valves 430 and 440 have been closed, the controller 1500 determines, based on pulses generated by the encoder units 600 and 602, the height of the fork carriage apparatus 300 relative to the first stage weldment 430 and defines that height in non-volatile memory as a first "reference height," see step 714. The controller 1500 also sets the value in the first lockout memory location to "1," see step 716, as an unintended descent fault has occurred. As long as the value in the first lockout memory location is set to 1, the controller 1500 will not allow the valves 430 and 440 to be energized such that they are opened to allow descent of the fork carriage apparatus 300. However, the controller 1500 will allow, in response to an operator-generated lift command, pressurized fluid to be provided to the cylinders 222A and 412, which fluid passes through the valves 430 and 440.

0043If, after an unintended descent fault has occurred and in response to an operator-generated command to lift the fork carriage apparatus 300, one or both of the rams 222A and 414 are unable to lift the fork carriage apparatus 300, then the value in the first lockout memory location remains set to 1. On the other hand, if, in response to an operator-generated command to lift the fork carriage apparatus 300, one or both of the rams 222A and 414 are capable of lifting the fork carriage apparatus 300 above the first reference height plus a first reset height, as indicated by signals generated by the encoder units 600 and 602, the controller 1500 resets the value in the first lockout memory location to 0, see steps 718 and 720. Thereafter, the controller 1500 returns to step 702 and, hence, will allow the valves 430 and 440 to be energized such that they can be opened to allow controlled descent of the fork carriage apparatus 300. Movement of the fork carriage apparatus 300 above the first reference height plus a first reset height indicates that the hydraulic system 401 is functional. The first reset height may have a value of 0.25 inch to about 4 inches.

0044If the controller 1500 determines during step 701 that the value in the first lockout memory location is 1, the controller 1500 continuously monitors the height of the fork carriage apparatus 300, via signals generated by the encoder units 600 and 602, to see if the fork carriage apparatus 300 moves above the first reference height, which had previously been stored in memory, plus the first reset height, see step 718.

0045<figref idref="f0012">Fig. 11</figref> illustrates data collected during operation of a vehicle constructed in accordance with the present invention. The data comprises an operator-commanded speed (as commanded via the multifunction controller 130), a third determined speed, i.e., a sensed speed of the fork carriage apparatus 300 relative to the first stage weldment 230, and a threshold speed. An estimated speed of the fork carriage apparatus 300 relative to the first stage weldment 230 was determined, wherein the estimated speed was calculated using the lift motor speed, as discussed above. The third determined speed was compared to the operator-commanded speed every 5 milliseconds. Also, the third determined speed was compared to the threshold speed every 5 milliseconds. The threshold speed was calculated by multiplying the estimated speed by 1.2. During each comparison event, when the third determined speed was greater than the operator-commanded speed, an "old concern-count" was incremented. Also during each comparison event, when the third determined speed was greater than the threshold speed, a "new concern-count" was incremented. When either the new concern count or the old concern count exceeded 50 counts, the controller 1500 implements a response routine, wherein the controller 1500 de-energized the first and second electronic normally closed proportional solenoid-operated valves 430 and 440. As is apparent from <figref idref="f0012">Fig. 11</figref>, the comparison between the third determined speed and the threshold speed resulted in zero events where the valves 430 and 440 were de-energized. However, the comparison between the third determined speed and the operator-commanded speed resulted in two events where the number of old concern-counts exceeded 50; hence, the controller 1500 de-energized the first and second valves 430 and 440. It is believed that the comparison of the third determined speed to the operator-commanded speed was less accurate than the comparison between the third determined speed with the threshold speed. This is believed to be because of inherent delays that occur in the vehicle from when an operator commands a fork carriage apparatus speed change via the multifunction controller 130 and pressurized fluid enters or exits the cylinders 222A and 412.

0046In the illustrated embodiment, during a lowering command, the controller 1500 compares a determined speed of the fork carriage apparatus 300 relative to the first stage weldment 230 to first and second threshold speeds. It is also contemplated that, during a lowering command, the controller 1500 may separately compare the first speed, i.e., the determined speed of the third stage weldment 250 relative to the first stage weldment 230, to the first and second threshold speeds and separately compare the second speed, i.e., the determined speed of the fork carriage apparatus 300 relative to the third stage weldment 250, to the first and second threshold speeds. During staging, it is contemplated that reduction of the first and second threshold speeds may be required. If the first determined speed is greater than the first threshold speed during a predefined number of sequential comparison events, e.g., between 1-50 comparison events, or greater than the second threshold speed during a single comparison event, then the electronic controller 1500 may de-energize the first and second electronic normally closed proportional solenoid-operated valves 430 and 440. If the second determined speed is greater than the first threshold speed during a predefined number of sequential comparison events, e.g., between 1-50 comparison events, or greater than the second threshold speed during a single comparison event, then the electronic controller 1500 may de-energize the first and second electronic normally closed proportional solenoid-operated valves 430 and 440.

0047The first threshold speed as calculated above may be used by the controller 1500 when comparing the first speed to the first threshold speed and the second speed to the first threshold speed.

0048Additionally, an electric current consumed or generated by the lift motor 301, i.e., an electric current flow into or out of the lift motor 301, may be monitored. The monitored electric current flow into or out of the lift motor 301 may be used to change one or more operating parameters of the truck 100. For example, in some conditions, particularly with cold hydraulic fluid, it is possible that there is too much pressure drop in the hydraulic system 401 to allow the lift motor 301 to drive the hydraulic lift pump 302 at a speed at which the fork carriage apparatus 300 is lowered at a predetermined, desired lowering speed, e.g., 240 feet/ minute. Specifically, the hydraulic lift pump 302 requires a minimum operating pressure to ensure that the hydraulic lift pump 302 is completely filled with hydraulic fluid, and is not rotating faster than it can fill with the hydraulic fluid, which may result in cavitation of the hydraulic fluid.

0049It has been determined that if the monitored electric current flow into or out of the lift motor 301 rises above a predetermined threshold value, the minimum operating pressure of the hydraulic lift pump 302 may not be met, which may be indicative of the hydraulic lift pump 302 rotating faster than it can fill with the hydraulic fluid and thus leading to cavitation of the hydraulic fluid, as noted above. When this condition is sensed, i.e., when the monitored electric current flow into or out of the lift motor 301 rises above the predetermined threshold value, the speed of the lift motor 301 is reduced until the electric current flow into or out of the lift motor 301 is back below the threshold value. Once the monitored electric current flow into or out of the lift motor 301 drops below the threshold value, the lift motor 301 can be adjusted back up to its normal operating speed. By monitoring the electric current flow into or out of the lift motor 301 and adjusting the operating speed of the lift motor 301, the cavitation of the hydraulic fluid in the hydraulic lift pump 302 can be prevented.

0050<figref idref="f0015">Fig. 14</figref> illustrates a flow chart for monitoring the electric current flow into or out of the lift motor 301 and adjusting an operating parameter of the truck 10, as envisaged herein. The steps may be carried out or implemented by the controller 1500, which controller 1500 may receive signals representative of the electric current flow into or out of the lift motor 301.

0051At step 800, the electric current flow into or out of the lift motor 301 is monitored. This step 800 may be implemented, for example, every 5 milliseconds, and may be implemented continuously during a lowering operation as described herein.

0052At step 802, it is determined whether the electric current flow into or out of the lift motor 301 is at or above a predetermined upper threshold value. By way of example, where the method is being employed in a regenerative lowering operation, the threshold value may be 0 amps, but may be other suitable values, or may be a percentage of a maximum or minimum current flow into or out of the lift motor 301.

0053If the electric current flow into or out of the lift motor 301 is determined at step 802 to be below the predetermined upper threshold value, the lift motor 301 is maintained at a normal operating speed at step 804. This cycle of steps 800-804 is repeated during a lowering operation until the electric current flow into or out of the lift motor 301 is determined to be at or above the predetermined upper threshold value.

0054If the electric current flow into or out of the lift motor 301 is determined at step 802 to be at or above the predetermined upper threshold value, the speed of the lift motor 301 is reduced at step 806 to a reduced operating speed. Reducing the speed of the lift motor 301 to the reduced operating speed causes a corresponding reduction in the rotating speed of the hydraulic lift pump 302. Step 806 is implemented to reduce or avoid cavitation of the hydraulic fluid in the hydraulic lift pump 302, as discussed above.

0055The lift motor 301 is maintained at the reduced operating speed at step 808 until the electric current flow into or out of the lift motor 301 is determined to be below a predetermined lower threshold value.

0056Upon the electric current flow into or out of the lift motor 301 dropping below the predetermined lower threshold value, the speed of the lift motor 301 is increased at step 810 back up to the normal operating speed.

0057Further, a pressure of the hydraulic fluid in the truck 100 may be monitored and compared with a threshold pressure T_P during the implementation of lifting and/or lowering commands, or during other vehicle operation procedures. The monitored pressure may be measured by a transducer T_D (see <figref idref="f0009">Fig. 9</figref>) or other sensing structure located in hydraulic structure within the truck 100, i.e., within a component of the hydraulic system 401 or within the cylinder 222A of the mast weldment lift structure 220 or the cylinder 412 of the fork carriage apparatus lift structure 400. The transducer T_D sends a signal to the controller 1500 that represents the measured pressure within the hydraulic structure.

0058The threshold pressure T_P may comprise a variable that is dependent on one or more parameters, such as the height of a portion of the truck 10, e.g., a maximum lift height of the movable assembly, e.g., the maximum height of the tops of the forks 402, 404 relative to the ground, or a maximum height of the top of the third stage mast weldment 250 relative to the ground, and the weight of a load 250A that is carried on the forks 402, 404. According to one example, these values, i.e., the height of the truck portion and the weight of the load that is carried on the forks 402, 404, can be used to determine the threshold pressure T_P according to the following equation: <maths id="math0005" num=""><math display="block"><mrow><msub><mi mathvariant="normal">T</mi><mi mathvariant="normal">P</mi></msub><mfenced><mi mathvariant="normal">psi</mi></mfenced><mo>=</mo><mfenced open="[" close="]" separators=""><mi mathvariant="normal">A</mi><mfenced separators=""><mi mathvariant="normal">psi</mi><mo>/</mo><mi mathvariant="normal">pound</mi></mfenced><mo>*</mo><mi mathvariant="normal">Load</mi><mfenced><mi mathvariant="normal">pounds</mi></mfenced></mfenced><mo>/</mo><mn mathvariant="normal">100</mn><mfenced><mi mathvariant="normal">unitless</mi></mfenced><mo>+</mo><mfenced open="[" close="]" separators=""><mi mathvariant="normal">Height</mi><mfenced><mi mathvariant="normal">inches</mi></mfenced><mo>*</mo><mn mathvariant="normal">100</mn><mfenced><mi mathvariant="normal">unitless</mi></mfenced></mfenced><mo>/</mo><mi mathvariant="normal">B</mi><mfenced separators=""><mi mathvariant="normal">inches</mi><mo>/</mo><mi mathvariant="normal">psi</mi></mfenced></mrow></math><img file="EP2865635B1_D0005.tif" /></maths> where T_P is the threshold pressure (psi), A is a system gain defined by a numerical constant equal to 10 (psi/pound) in the illustrated example, Load is the weight of the load carried on the forks 402, 404 (pounds), 100 is a unitless scaling factor, Height is the maximum lift height of the movable assembly (inches), 100 is a unitless scaling factor, and B is a system offset defined by a numerical constant equal to 600 (inches/psi) in the illustrated example.

0059According to one example, the comparison of the monitored pressure of the hydraulic fluid in the hydraulic structure to the threshold pressure T_P may be made by the controller 1500, e.g., when the truck 10 is implementing a lowering command or a lifting command, once every predefined time period, e.g., every 5 milliseconds. If the monitored pressure of the hydraulic fluid in the hydraulic structure falls below the threshold pressure T_P, it may be an indication that the hydraulic structure has lost its load-holding ability, e.g., as a result of a break in one of the fluid lines 411A-411C. If the monitored pressure of the hydraulic fluid in the hydraulic structure falls below the threshold pressure, the controller 1500 implements a response routine by de-energizing the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 so as to prevent further downward movement of the rams 222B and 414. The controller 1500 may cause the first and second valves 430 and 440 to move from their powered open positions to their closed positions immediately or over an extended time period, such as from about 0.3 second to about 1.0 second. By causing the first and second valves 430 and 440 to close over an extended time period, the magnitude of pressure spikes within the cylinders 222A and 412, which occur when the pistons 222B and 414 stop their downward movement within the cylinders 222A and 412, is reduced. Further, closing of the first and second valves 430 and 440 by the controller 1500 may comprise partially closing the first and second valves 430 and 440, i.e., not fully closing the first and second valves 430 and 440, so as to allow the fork carriage apparatus 300 and the second and third stage weldments 240, 250 to lower slowly to the ground.

0060In one example, so as to avoid false trips when the monitored pressure is compared to the threshold pressure T_P, the response routine is only implemented by the electronic controller 1500 if it is also determined that the fork carriage apparatus 300 is moving at a speed greater than a predetermined speed relative to the first stage weldment 230, wherein the speed of the fork carriage apparatus 300 relative to the first stage weldment may be determined as described in detail herein. The predetermined speed may be greater than or equal to about 90 feet/minute.

0061It is noted that the comparison of the monitored pressure of the hydraulic fluid in the hydraulic structure to the threshold pressure T_P can be performed by the controller 1500 to implement a response routine in addition to or instead of one or more of the other comparisons described herein, such as the comparison of the determined or sensed speed of the fork carriage apparatus 300 relative to the first stage weldment 230 to the first and/or second threshold speeds and/or the comparison of the monitored electric current flow into or out of the lift motor 301 to the predetermined threshold (current) value.

0062Moreover, alternate response routines to the response routines previously described herein can be implemented by the controller 1500 if a comparison event, e.g., the comparison of the determined or sensed speed of the fork carriage apparatus 300 relative to the first stage weldment 230 to the first and/or second threshold speeds, the comparison of the monitored electric current flow into or out of the lift motor 301 to the predetermined threshold (current) value, and/or the comparison of the monitored pressure of the hydraulic fluid in the hydraulic structure to the threshold pressure T_P, yields an outcome that requires that a response routine be implemented. For example, the controller 1500 could initially implement a step decrease in electric current to the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 to a level at or slightly above a breakout current. The breakout current is 250 milliamps in one example and is the minimum current that will effect hydraulic fluid through the valve. The controller 1500 may then increase the current to the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 in stepwise fashion to a level below a maximum commanded current. The maximum commanded current is 600 milliamps in one example and is the current that fully opens the valves 430 and 440. The controller 1500 may then ramp the current to the first and second electronic normally closed proportional solenoid-operated valves 430 and 440 down to the breakout current over a time period of, for example, approximately 400 milliseconds. By causing the first and second valves 430 and 440 to close over an extended time period, the magnitude of pressure spikes within the cylinders 222A and 412, which occur when the first and second valves 430 and 440 are abruptly closed, is reduced. Further, controlling the first and second valves 430 and 440 in this manner, e.g., not fully closing the first and second valves 430 and 440 abruptly, improves response time and reduces oscillations in the fork carriage apparatus 300 that may otherwise occur as a result of a velocity fuse event, while allowing the fork carriage apparatus 300 and the second and third stage weldments 240, 250 to slow their descent to the ground in a controlled manner.

0063In accordance with a second embodiment of the present invention, a materials handling vehicle is provided comprising, for example, a stand-up counter balance truck or like vehicle, including a power unit (not shown), a mast assembly 1000, a mast weldment lift structure 1100, a fork carriage apparatus (not shown) and a fork carriage apparatus lift structure 1200, see <figref idref="f0013">Fig. 12</figref>. The mast assembly 1100 comprises, in the illustrated embodiment, first, second and third mast weldments 1002, 1004 and 1006, see <figref idref="f0013">Fig. 12</figref>, wherein the second weldment 1004 is nested within the first weldment 1002 and the third weldment 1006 is nested within the second weldment 1004. The first weldment 1002 is fixed to the vehicle power unit. The second or intermediate weldment 1004 is capable of vertical movement relative to the first weldment 1002. The third or inner weldment 1006 is capable of vertical movement relative to the first and second weldments 1002 and 1004.

0064The mast weldment lift structure 1100 comprises first and second lift ram/cylinder assemblies 1102 and 1104, which are fixed at their cylinders 1102B and 1104B to the first weldment 1002, see <figref idref="f0013">Fig. 12</figref>. Rams 1102A and 1104A extending from the cylinders 1102B and 1104B are fixed to an upper brace 1004A of the second weldment 1004.

0065A first chain 1211 is fixed to the cylinder 1102B of the first ram/cylinder assembly 1102 and a second chain 1213 is fixed to the cylinder 1104B of the second ram/cylinder assembly 1104. The first chain 1211 extends over a first pulley 1004B coupled to an upper end of the second mast weldment 1004 and is coupled to a lower portion 1006A of the third weldment 1006, see <figref idref="f0013">Fig. 12</figref>. The second chain 1213 extends over a second pulley 1004C coupled to an upper end of the second mast weldment 1004 and is also coupled to the third weldment lower portion 1006A. When the rams 1102A and 1104A of the assemblies 1102 and 1104 are extended, the rams 1102A and 1104A lift the second weldment 1004 vertically relative to the fixed first weldment 1002. Further, the first and second pulleys 1004B and 1004C fixed to an upper end of the second weldment 1004 apply upward forces on the chains 1211 and 1213 causing the third weldment 1006 to move vertically relative to the first and second weldments 1002 and 1004. For every one unit of vertical movement of the second weldment 1004, the third weldment 1006 moves vertically two units.

0066The fork carriage apparatus comprises a pair of forks (not shown) and a fork carriage mechanism upon which the forks are mounted. The fork carriage mechanism may be mounted for reciprocal movement directly to the third mast weldment 1006. Alternatively, the fork carriage mechanism may be mounted to a reach mechanism (not shown), which is mounted to a mast carriage assembly (not shown), which is mounted for reciprocal movement to the third mast weldment 1006.

0067The fork carriage apparatus lift structure 1200 is coupled to the third weldment 1006 and the fork carriage apparatus to effect vertical movement of the fork carriage apparatus relative to the third weldment 1006. The lift structure 1200 includes a ram/cylinder assembly 1210 comprising a cylinder 1212 fixed to the third mast weldment 1006 such that it moves vertically with the third weldment 1006. A ram 1211, see <figref idref="f0014">Fig. 13</figref>, is associated with the cylinder 1212 and is capable of extending from the cylinder 1212 when pressurized hydraulic fluid is provided to the cylinder 1212. Third and fourth pulleys 1216 and 1218 are coupled to an upper end of the ram 1211, see <figref idref="f0013">Fig. 12</figref>. A pair of lift chains (not shown) are fixed at one end to the cylinder 1212, extend over the third pulley 1216 and are coupled to a lower portion (not shown) of the fork carriage apparatus. When pressurized fluid is provided to the cylinder 1212, its ram 1211 is extended causing the pulley 1216 to move vertically relative to the third weldment 1006. Vertical movement of the pulley 1216 causes the lift chains to raise the fork carriage assembly relative to the third weldment 1006.

0068The materials handling vehicle of the second embodiment includes a hydraulic system 1300 as illustrated in <figref idref="f0014">Fig. 13</figref>, wherein elements that are the same as those illustrated in <figref idref="f0009">Fig. 9</figref> are referenced by the same reference numerals. The hydraulic system 1300 comprises a lift motor 301, which drives a hydraulic lift pump 302. The pump 302 supplies pressurized hydraulic fluid to the mast weldment lift structure 1100 comprising the first and second lift ram/cylinder assemblies 1102 and 1104 and the fork carriage apparatus lift structure 1200 comprising the ram/cylinder assembly 1210.

0069The hydraulic system 1300 further comprises a hydraulic fluid reservoir 402, which is housed in the power unit, and fluid hoses/lines 411A-411D coupled between the pump 302 and the mast weldment lift structure 1100 comprising the first and second lift ram/cylinder assemblies 1102 and 1104 and the fork carriage apparatus lift structure 1200 comprising the ram/cylinder assembly 1210. The fluid hoses/lines 411A and 411B are coupled in series and function as supply/return lines between the pump 302 and the mast weldment structure first hydraulic ram/cylinder assembly 1102. The fluid hoses/lines 411A and 411C are coupled in series and function as supply/return lines between the pump 302 and the fork carriage apparatus lift structure hydraulic ram/cylinder assembly 1210. The fluid hoses/lines 411A and 411D are coupled in series and function as supply/return lines between the pump 302 and the mast weldment structure second hydraulic ram/cylinder assembly 1104. Because the fluid hose/line 411A is directly coupled to the fluid hoses/lines 411B-411D, all four lines 411A-411C are always at the substantially the same fluid pressure.

0070The hydraulic system 401 also comprises an electronic normally closed ON/OFF solenoid-operated valve 420 and first, second and third electronic normally closed proportional solenoid-operated valves 1430, 1435 and 1440. The valves 1420, 1430, 1435 and 1440 are coupled to an electronic controller 1500 for controlling their operation, see <figref idref="f0014">Fig. 13</figref>. The electronic controller 1500 forms part of a "control structure." The normally closed ON/OFF solenoid valve 420 is energized by the controller 1500 only when one or more of the rams 1211, 1102A and 1104A are to be lowered. When de-energized, the solenoid valve 420 functions as a check valve so as to block pressurized fluid from flowing from line 411A, through the pump 302 and back into the reservoir 402, i.e., functions to prevent downward drift of the fork carriage apparatus, yet allows pressurized fluid to flow to the cylinders 1212, 1102B and 1104B via the lines 411A-411D during a lift operation.

0071The first electronic normally closed proportional solenoid-operated valve 1430 is located within and directly coupled to a base 1102C of the cylinder 1102B of the mast weldment lift structure first hydraulic ram/cylinder assembly 1102, see <figref idref="f0014">Fig. 13</figref>. The second electronic normally closed proportional solenoid-operated valve 1435 is located within and directly coupled to a base 1104C of the cylinder 1104B of the mast weldment lift structure second hydraulic ram/cylinder assembly 1104. The third electronic normally closed proportional solenoid-operated valve 1440 is located within and directly coupled to a base 1212A of the cylinder 1212 of the fork carriage apparatus lift structure hydraulic ram/cylinder assembly 1200. The first and second normally closed proportional solenoid-operated valves 1430 and 1435 are energized, i.e., opened, by the controller 1500 when the rams 1102A and 1104A are to be lowered. The third normally closed proportional solenoid-operated valve 1440 is energized, i.e., opened, by the controller 1500 when the ram 1211 is to be lowered. When de-energized, the first, second and third normally closed proportional solenoid-operated valves 1430, 1435 and 1440 function as check valves so as to block pressurized fluid from flowing out of the cylinders 1102B, 1104B and 1212. The valves 1430, 1435 and 1440, when functioning as check valves, also permit pressurized hydraulic fluid to flow into the cylinders 1102B, 1104B and 1212 during a lift operation.

0072When a lift command is generated by an operator via a multifunction controller, the cylinder 1212 of the fork carriage apparatus lift structure 1200 and the cylinders 1102B and 1104B of the mast weldment lift structure 1100 are exposed to hydraulic fluid at the same pressure via the lines 411A-411D. The ram 1211 of the fork carriage apparatus lift structure 1200 has a base end with a cross sectional area and each of the rams 1102A and 1104A of the mast weldment lift structure 1100 includes a base end having a cross sectional area equal to about ½ of the cross sectional area of the ram 1211 of the fork carriage apparatus lift structure 1200. Hence, the combined cross sectional areas of the rams 1102A and 1104A equals the cross sectional area of the ram 1211. As a result, for all load conditions, the fork carriage apparatus lift structure 1200 requires less pressure to actuate than the mast weldment lift structure 1100. As a result, the ram 1211 of the fork carriage apparatus lift structure 1200 will move first until the fork carriage apparatus has reached its maximum height relative to the third stage weldment 1006. Thereafter, the second and third stage weldments 1004 and 1006 will begin to move vertically relative to the first stage weldment 1002.

0073When a lowering command is generated by an operator via the multifunction controller 130, the electronic controller 1500 causes the electronic normally closed ON/OFF solenoid-operated valve 420 to open. Presuming the rams 1211, 1102A and 1104A are fully extended when a lowering command is generated, the first and second proportional valves 1430 and 1435 are energized by the controller 1500, causing them to fully open in the illustrated embodiment to allow fluid to exit the cylinders 1102B and 1104B of the mast weldment lift structure 1100, thereby allowing the second and third stage weldments 1004 and 1006 to lower. Once the second and third stage weldments 1004 and 1006 near their lowermost positions, the controller 1500 causes the third proportional valve 1440 to substantially fully open and the first and second proportional valves 1430 and 1435 to partially close. Partially closing the first and second valves 1430 and 1435 causes the fluid pressure in the lines 411A-411D to lower. By opening the third valve 1440 and partially closing the first and second valves 1430 and 1435, the ram 1211 begins to lower, while the rams 1102A and 1104A continue to lower. After the rams 1102A and 1104A reach their lowermost position, the ram 1211 continues to lower until the fork carriage apparatus reaches its lowermost position.

0074First and second encoder units 600 and 602, respectfully, also forming part of the "control structure," are provided and may comprise conventional friction wheel encoder assemblies or conventional wire/cable encoder assemblies, see <figref idref="f0014">Fig. 13</figref>. In the illustrated embodiment, the first encoder unit 600 comprises a first friction wheel encoder assembly mounted to the third stage weldment 1006 such that a first friction wheel engages and moves along the second stage weldment 1004. Hence, as the third stage weldment 1006 moves relative to the second stage weldment 1004, the first friction wheel encoder generates pulses to the controller 1500 indicative of the third stage weldment movement relative to the second stage weldment.

0075Also in the illustrated embodiment, the second encoder unit 602 comprises a second friction wheel assembly mounted to the fork carriage apparatus such that a second friction wheel engages and moves along the third mast stage weldment 1006. Hence, as the fork carriage apparatus moves relative to the third stage weldment 1006, the second friction wheel encoder generates pulses to the controller 1500 indicative of the fork carriage apparatus movement relative to the third stage weldment 1006.

0076As noted above, the first and second encoder units 600 and 602 generate corresponding pulses to the controller 1500. The pulses generated by the first encoder unit 600 are used by the controller 1500 to determine the position of the third stage weldment 1006 relative to the second stage weldment 1004 as well as the speed of movement of the third stage weldment 1006 relative to the second stage weldment 1004. Using this information, the controller 1500 determines the speed and position of the third stage weldment 1006 relative to the fixed first stage weldment 1002. The pulses generated by the second encoder unit 602 are used by the controller 1500 to determine the position of the fork carriage apparatus relative to the third mast stage weldment 1006 as well as the speed of movement of the fork carriage apparatus relative to the third mast stage weldment 1006. By knowing the speed and position of the third stage weldment 1006 relative to the first stage weldment 1002 and the speed and position of the fork carriage apparatus relative to the third stage weldment 1006, the controller 1500 can easily determine the speed and position of the fork carriage apparatus relative to the first stage weldment 1002.

0077During a lowering command, the controller 1500 compares a determined or sensed speed of the fork carriage apparatus relative to the first stage weldment 230 to first and second threshold speeds. This involves the controller 1500 determining a first speed comprising a determined or sensed speed of the third stage weldment 1006 relative to the first stage weldment 1002, determining a second speed comprising a determined or sensed speed of the fork carriage apparatus relative to the third stage weldment 1006 and adding the first and second determined speeds together to calculate a third determined speed. The third determined speed is equal to the determined or sensed speed of the fork carriage apparatus relative to the first stage weldment 1002.

0078As noted above, for every one unit of vertical movement of the second stage weldment 1004 relative to the first stage weldment 1002, the third stage weldment 1006 moves vertically two units relative to the first stage weldment 1002. In order to determine the first speed, the controller 1500 determines the speed of third stage weldment 1006 relative to the second stage weldment 1004 using the pulses from the first encoder unit 600, as noted above, and multiplies the determined speed of movement of the third stage weldment 1006 relative to the second stage weldment 1004 by "2". Hence, this provides the first speed, i.e., the speed of the third stage weldment 1006 relative to the first stage weldment 1002.

0079The second speed is equal to the determined speed of movement of the fork carriage apparatus relative to the third mast stage weldment and is found using the pulses generated by the second encoder unit 602 as noted above.

0080During a lowering command, the controller 1500 may compare the third determined speed, i.e., the determined speed of the fork carriage apparatus relative to the first stage weldment 1002, to the first and second threshold speeds. In the illustrated embodiment, the comparison of the third determined speed to the first and second threshold speeds may be made by the controller 1500 once every predefined time period, e.g., every 5 milliseconds. The comparison of the third determined speed to the first and second threshold speeds is referred to herein as a "comparison event." If the third determined speed is greater than the first threshold speed during a predefined number of sequential comparison events, e.g., between 1-50 comparison events, or greater than the second threshold speed during a single comparison event, then the electronic controller 1500 implements a response routine, wherein the controller 1500 de-energizes the first, second and third electronic normally closed proportional solenoid-operated valves 1430, 1435 and 1440 so as to prevent further downward movement of the rams 1102A, 1104A and 1211. The controller 1500 may cause the first, second and third valves 1430, 1435 and 1440 to move from their powered open positions to their closed positions immediately or over an extended time period, such as from about 0.3 second to about 1.0 second. Further, as discussed above, the valves 1430, 1435 and 1440 could only be partially closed so as to allow the fork carriage apparatus and the second and third stage weldments 1004, 1006 to lower slowly to the ground. It is presumed that when the third determined speed is greater than one of the first and second threshold speeds, the fork carriage apparatus is moving too quickly relative to the first stage weldment 1002, i.e., at an unintended descent speed, which condition may occur when there is a loss of hydraulic pressure in the fluid being metered from one or more of the cylinders 1102B, 1104B and 1212. Loss of hydraulic pressure may be caused by a breakage in one of the fluid lines 411A-411D.

0081The first threshold speed may be determined by the electronic controller 1500 as follows. First, the controller 1500 may estimate a combined speed of the rams 1102A, 1104A of the mast weldment lift structure 1100 and the ram 1211 of the fork carriage apparatus lift structure 1200 from a speed of the lift motor 301. As discussed above, with respect to a lowering operation with the fork carriage apparatus and the second and third stage weldments 1004 and 1006 fully extended, the rams 1102A and 1104A begin to lower first, then the rams 1102A, 1104A and 1211 lower simultaneously during a staging part of the lowering operation until the rams 1102A and 1104A reach their lowermost position. Thereafter, the ram 1211 continues its downward movement until it reaches its lowermost position.

0082First, the controller 1500 converts the lift motor speed into a lift pump fluid flow rate using the following equation:<maths id="math0006" num=""><math display="block"><mrow><mi mathvariant="normal">pump</mi><mspace width="1em" /><mi mathvariant="normal">fluid</mi><mspace width="1em" /><mi mathvariant="normal">flow</mi><mspace width="1em" /><mi mathvariant="normal">rate</mi><mspace width="1em" /><mfenced separators=""><mi mathvariant="normal">gallons</mi><mo>/</mo><mi mathvariant="normal">min</mi><mi mathvariant="normal">u</mi><mi mathvariant="normal">t</mi><mi mathvariant="normal">e</mi></mfenced><mo>=</mo><mfenced open="[" close="]"><mrow><mrow><mfenced separators=""><mi mathvariant="normal">lift</mi><mspace width="1em" /><mi mathvariant="normal">motor</mi><mspace width="1em" /><mi mathvariant="normal">speed</mi><mspace width="1em" /><mrow><mfenced separators=""><mi mathvariant="normal">R</mi><mi mathvariant="normal">P</mi><mi mathvariant="normal">M</mi></mfenced></mrow></mfenced><mo>*</mo></mrow><mrow><mfenced separators=""><mi mathvariant="normal">lift</mi><mspace width="1em" /><mi mathvariant="normal">pump</mi><mspace width="1em" /><mi mathvariant="normal">displacement</mi><mfenced separators=""><mi mathvariant="normal">c</mi><mi mathvariant="normal">c</mi><mo>/</mo><mi mathvariant="normal">revolution</mi></mfenced></mfenced><mo>*</mo><mfenced separators=""><mi mathvariant="normal">lift</mi><mspace width="1em" /><mi mathvariant="normal">motor</mi><mspace width="1em" /><mi mathvariant="normal">volumetric</mi><mspace width="1em" /><mi mathvariant="normal">efficiency</mi></mfenced></mrow></mrow></mfenced><mo>/</mo><mfenced separators=""><mn mathvariant="normal">3786</mn><mspace width="1em" /><mi mathvariant="normal">c</mi><mi mathvariant="normal">c</mi><mo>/</mo><mi mathvariant="normal">g</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">l</mi></mfenced></mrow></math><img file="EP2865635B1_D0006.tif" /></maths>

0083The controller 1500 may then determine an estimated linear speed of the fork carriage apparatus relative to the first stage weldment 1002 using the following equation, which equation is believed to be applicable during all phases of a lowering operation, including staging when the rams 1102A and 1104A and ram 1211 are being lowered simultaneously: <maths id="math0007" num=""><math display="block"><mrow><mi>estimated linear speed of the fork carriage apparatus relative to the first weldment</mi><mspace width="1em" /><mn>1002</mn><mspace width="1em" /><mfenced separators=""><mi>inches</mi><mo>/</mo><mi>second</mi></mfenced><mo>=</mo><mfenced open="[" close="]" separators=""><mfenced separators=""><mi>pump fluid flow rate</mi><mfenced separators=""><mi>gallons</mi><mo>/</mo><mi>minute</mi></mfenced></mfenced><mo>*</mo><mrow><mfenced separators=""><mn>231</mn><mspace width="1em" /><msup><mi>in</mi><mn>3</mn></msup><mo>/</mo><mi>gallon</mi></mfenced><mo>*</mo><mfenced><mi>speed ratio</mi></mfenced></mrow></mfenced><mo>/</mo><mfenced open="[" close="]" separators=""><mfenced separators=""><mrow><mi>cylinder inside area</mi><mspace width="1em" /></mrow><mfenced><msup><mi>in</mi><mn>2</mn></msup></mfenced></mfenced><mo>*</mo><mfenced separators=""><mn>60</mn><mrow><mspace width="1em" /><mi>seconds</mi></mrow><mo>/</mo><mi>minute</mi></mfenced></mfenced></mrow></math><img file="EP2865635B1_D0007.tif" /></maths> wherein, <ul id="ul0003" list-style="none" compact="compact"><li>"cylinder inside area" = summation of the cross sectional areas of cylinders 1102B and 1104B = the cross sectional area of cylinder 1212 (only the summation of the cross sectional areas of cylinders 1102B and 1104B or only the cross sectional area of cylinder 1212 is used in the equation);</li><li>"speed ratio" = (the third weldment speed/first weldment speed) = (fork carriage apparatus speed/third weldment speed) = 2/1 in the illustrated embodiment.</li></ul>

0084In the illustrated embodiment, the first threshold speed is equal to the estimated speed of the fork carriage apparatus relative to the first weldment 1002 times either a first tolerance factor, e.g., 1.6, or a second tolerance factor, e.g., 1.2. As noted above with regards to the embodiment illustrated in <figref idref="f0009">Fig. 9</figref>, the first tolerance factor is used when the fork lowering speed is in the process of being ramped to the commanded speed, i.e., the controller 1500 is still executing a ramping function, and the second tolerance factor is used when the controller 1500 is no longer increasing the speed of the lift motor 301, i.e., the controller 1500 has completed the ramping function.

0085As noted above, the controller 1500 may use the determined downward speed of the fork carriage apparatus relative to the first stage weldment, the estimated fork carriage apparatus downward speed relative to the first weldment and the current pump volumetric efficiency to generate an updated pump volumetric efficiency, which updated pump volumetric efficiency may be used by the controller 1500 the next time it converts lift motor speed into a lift pump fluid flow rate. Or, as noted above, the controller 1500 may use the initial pump volumetric efficiency, i.e., a predefined stored initial pump volumetric efficiency or an appropriate volumetric efficiency point that corresponds to one or more vehicle conditions, e.g., speed, hydraulic fluid pressure, temperature, and/or viscosity, direction of rotation of the hydraulic lift pump 302, etc., stored in a data or look up table, the next time it converts lift motor speed into a lift pump fluid flow rate.

0086The second threshold speed may comprise a fixed speed, such as 300 feet/minute.

0087The process 700 set out in <figref idref="f0010">Figs. 10A</figref> and <figref idref="f0011">10B</figref> may be used the controller 1500 for controlling the operation of the first, second and third electronic normally closed proportional solenoid-operated valves 1430, 1435 and 1440 during a lowering command, with the following modifications being made to the process.

0088At step 711, the controller 1500 determines if the "concern-count" is greater than the "concern-max" count or whether the third determined speed is greater than the second threshold speed. If the answer to one or both queries is YES, then the controller 1500 implements a response routine, wherein the controller 1500 de-energizes the first, second and third electronic normally closed proportional solenoid-operated valves 1430, 1435 and 1440.

0089Once the valves 1430, 1435 and 1440 have been closed, the controller 1500 determines, based on pulses generated by the encoder units 600 and 602, the height of the fork carriage apparatus relative to the first stage weldment 1002 and defines that height in non-volatile memory as a first "reference height," see step 714. The controller 1500 also sets the value in the first lockout memory location to "1," see step 716, as an unintended descent fault has occurred. As long as the value in the first lockout memory location is set to 1, the controller 1500 will not allow the valves 1430, 1435 and 1440 to be energized such that they are opened to allow descent of the fork carriage apparatus. However, the controller 1500 will allow, in response to an operator-generated lift command, pressurized fluid to be provided to the cylinders 1102B, 1104B and 1212, which fluid passes through the valves 1430, 1435 and 1440.

0090If, after an unintended descent fault has occurred and in response to an operator-generated command to lift the fork carriage apparatus, one or more of the rams 1102A, 1104A and 1211 are unable to lift the fork carriage apparatus, then the value in the first lockout memory location remains set to 1. On the other hand, if, in response to an operator-generated command to lift the fork carriage apparatus, one or more of the rams 1102A, 1104A and 1211 are capable of lifting the fork carriage apparatus above the first reference height plus a first reset height, as indicated by signals generated by the encoder units 600 and 602, the controller 1500 resets the value in the first lockout memory location to 0, see steps 718 and 720. Thereafter, the controller 1500 returns to step 702 and, hence, will allow the valves 1430, 1435 and 1440 to be energized such that they can be opened to allow controlled descent of the fork carriage apparatus. Movement of the fork carriage apparatus above the first reference height plus a first reset height indicates that the hydraulic system 1300 is functional.

0091If the controller 1500 determines during step 701 that the value in the first lockout memory location is 1, the controller 1500 continuously monitors the height of the fork carriage apparatus, via signals generated by the encoder units 600 and 602, to see if the fork carriage apparatus moves above the first reference height plus the first reset height, see step 718.

0092It is further contemplated that the monomast 200 illustrated in <figref idref="f0001">Fig. 1</figref> may comprise only a first fixed mast weldment and a second movable mast weldment and the mast assembly 1000 illustrated in <figref idref="f0013">Fig. 12</figref> may include only a first fixed mast weldment and a second movable mast weldment.

0093While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the scope of the invention, which is defined by the appended claims.