Construction vehicle

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(12) Patent Go) SE 533 997 C2

Sweden (21) Patent application number: 0950589-2 (45) Patent granted: 22/02/2011 (41) Application generally available: 2009-09-04 (22) Patent application submitted: 21/28/2008 (24) Maturity date: 2008- 02-21

Completed international patent application with number: PCT / JP2008 / 052931 (51) International class:

F16H 61/40 (2010.01)

E02F 9/22 (2006.01)

F16H 61/66 (2006.01) (86) International filing date: 2008-02-21 (83) Deposit of microorganism: - (30) Priority information: 2007-04-26 JP 2007-116722

<td>(73) Patent holders:</td><td>KOMATSU LTD., 2-3-6, Akasaka, Minato-ku, 1078414 Tokyo JP</td>

<td>(72) Inventor:</td><td>Atsushi SHIRAO, Ishikawa JP Masanori IKARI, Ishikawa JP</td>

<td>(74) Agents:</td><td>Albihns.Zacco AB, Box 5581, 114 85 Stockholm SE</td>

<td>(54) Name:</td><td>Construction vehicles with device for avoiding wheel sizing and sudden acceleration</td>

<td>(56) Publications cited:</td><td>EP 1319763 A1</td>

(47) Summary:

The present invention provides a construction vehicle in which tire slip and sudden accelerations can be suppressed. In the construction vehicle of the present invention, a control unit may implement suppressive control of a rapid change of pump displacement to control the displacement of a transport hydraulic pump so that the oil pressure of a primary circuit reaches a maximum value equal to or less than a limiting pressure value when the vehicle has stopped, regardless of vehicle speed, and the displacement of the transport hydraulic pump gradually increases as the oil pressure of the primary circuit decreases from the maximum value.

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533 997

SUMMARY

The present invention provides a construction vehicle in which tire slip and sudden accelerations can be suppressed. In the construction vehicle of the present invention, a control unit may implement suppressive control of a rapid change of pump displacement to control the displacement of a transport hydraulic pump so that the oil pressure of a primary circuit reaches a maximum value equal to or less than a limiting pressure value when the vehicle has stopped, regardless of vehicle speed, and the displacement of the transport hydraulic pump gradually increases as the oil pressure of the primary circuit decreases from the maximum value.

533 997

Construction vehicles with device for avoiding hole slimming and sudden acceleration

FIELD OF ART

The present invention relates to a construction vehicle.

BACKGROUND TECHNOLOGY

An example of a construction vehicle is one in which the hydraulic pump is driven by a motor, and a transport hydraulic motor is driven by the pressure oil discharged from the hydraulic pump, which thereby causes the vehicle to be transported. In this type of construction vehicle, the speed and drive wheel force of the vehicle can be controlled by controlling the engine speed, hydraulic pump displacement, and transport hydraulic motor displacement (patent document 1).

The oil pressure characteristic of the pump displacement primary circuit, as shown in Fig. 14, is usually obtained in construction vehicles, such as that described above. The solid line L11 and the dashed lines L12 to L15 in this diagram are lines showing the oil pressure characteristic of the pump displacement primary circuit, which varies with respect to the engine speed. The oil pressure in the primary circuit is the oil pressure in a transport hydraulic circuit through which pressure oil flows which is discharged from the hydraulic pump and sent to the transport hydraulic motor. The dashed line L14 shows that the pump displacement decreases as the oil pressure in the primary circuit increases, and the pump displacement increases as the oil pressure in the primary circuit decreases. The plant vehicle is also provided with an oil pressure limiting component to protect the transport hydraulic circuit. The oil pressure limiting component is formed by a limiting valve or other component to reduce the oil pressure in the primary circuit so that the oil pressure in the primary circuit does not exceed a predetermined limit pressure value. The oil pressure characteristic of the pump displacement primary circuit shown by the dashed line L12 in FIG. 14, the limit valve acts in cases where the pump displacement is equal to or less than a predetermined pump displacement value Qx3, which causes the oil pressure in the primary circuit to decrease and remain constant at a limit pressure value Pit. Patent document 1: Japanese published patent application no. 2004-144254.

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DESCRIPTION OF THE INVENTION

However, in a construction vehicle, such as that described above, the pump displacement changes rapidly, and the wheels can slip or the vehicle can suddenly accelerate. For example, there may be times when the construction vehicle remains stationary, and cannot move forward, due to a large load when the vehicle is plowing snow or sediment. Therefore, in this state, assuming the driver fully depresses the accelerator pedal, the engine speed will be maintained at maximum rotational speed. In this case, as the oil pressure in the primary circuit has increased, the oil pressure limiting component acts to reduce the oil pressure in the primary circuit. At this time, the pump displacement and the oil pressure in the primary circuit reach the point Px1 in FIG. 14.1 this condition, the oil pressure in the primary circuit decreases as the load acting on the construction vehicle from the snow or sediment decreases. With the oil pressure characteristic of the pump displacement primary circuit, such as those shown by the solid line L11, the pump displacement and the oil pressure in the primary circuit change from point Px1 to point Px2, and the pump displacement changes rapidly from Qx1 to Qx2. Therefore, the wheels may slip or the construction vehicle may suddenly accelerate.

It is an object of the present invention to provide a construction vehicle in which it is possible to minimize wheel slip and sudden acceleration.

The construction vehicle according to a first aspect of the present invention comprises an engine, a transport hydraulic pump, a transport hydraulic circuit, a transport hydraulic motor, a transport wheel, a hydraulic pump for work equipment, a work equipment, a control unit, and an oil pressure limiting component. The transport hydraulic pump is a hydraulic pump driven by the engine. The transport hydraulic circuit is a circuit through which pressure oil flows out of the transport hydraulic pump. The transport hydraulic motor is a hydraulic motor driven by the oil pressure provided by the transport hydraulic circuit. The transport wheel is driven by the driving force of the transport hydraulic motor. The hydraulic pump for the work equipment is a hydraulic pump driven by the engine. The working equipment is powered by the pressure oil, which is discharged from the hydraulic pump for the working equipment. The control unit controls the engine speed, the transport hydraulic pump displacement, and the transport hydraulic motor displacement, to control the vehicle speed and the driving wheel force. The oil pressure limiting component limits the pressure of the transport circuit to not

533 997 exceeds a predetermined limit pressure value, the transport circuit pressure being the pressure of the pressure oil flowing through the transport hydraulic circuit. The control unit can implement a suppressive control of a rapid change of the pump displacement of the transport hydraulic pump, so that the transport circuit pressure reaches a maximum value equal to or less than the limit pressure value when the vehicle has stopped, regardless of engine speed, and the transport hydraulic pump displacement decreases the degree of displacement value.

In this construction vehicle, the suppressive control results in a rapid change of the pump displacement in the oil pressure characteristic of the pump displacement primary circuit, wherein the transport circuit pressure gradually changes according to changes in the oil pressure in the primary circuit, without the influence of the oil pressure limiting component. In this construction vehicle, rapid changes in pump displacement can thus be suppressed, and wheel slip and sudden acceleration can also be suppressed.

With this suppressive control of a rapid change in pump displacement, since the displacement of the transport hydraulic pump is controlled, the danger of affecting the output flow rate of other hydraulic pumps, for example the hydraulic pump for the work equipment is less than in cases where the engine speed is limited. Therefore, reductions in the operating speed of the work equipment can be suppressed while the suppressive control of a rapid change in pump displacement is implemented.

The plant vehicle according to a second aspect of the present invention comprises an engine, a transport hydraulic pump, a transport hydraulic circuit, a transport hydraulic motor, a transport wheel, a hydraulic pump for work equipment, a work equipment, a control unit, and an oil pressure limiting component. The transport hydraulic pump is a hydraulic pump driven by the engine. The transport hydraulic circuit is a circuit through which pressure oil flows out of the transport hydraulic pump. The transport hydraulic motor is a hydraulic motor driven by the oil pressure provided by the transport hydraulic circuit. The transport wheel is driven by the driving force of the transport hydraulic motor. The hydraulic pump for the work equipment is a hydraulic pump driven by the engine. The working equipment is powered by the pressure oil, which is discharged from the hydraulic pump for the working equipment. The control unit controls the engine speed, the transport hydraulic pump displacement, and the transport hydraulic motor displacement, to control the vehicle speed and the driving wheel force. The oil pressure limiting component limits the pressure of the transport circuit so as not to exceed a predetermined limit pressure value, the transport circuit pressure being the pressure of the pressure oil flowing through the transport hydraulic circuit. The control unit can implement a suppressive control of a rapid change of pump displacement to control the transport hydraulic pump displacement so that the transport hydraulic pump displacement gradually decreases as the transport circuit pressure increases, and the transport circuit pressure reaches a maximum value equal to or less than the set pressure value when the vehicle is set.

In this construction vehicle, the implementation of a suppressive control results in a rapid change of the pump displacement in the oil pressure characteristic of the pump displacement primary circuit, wherein the transport circuit pressure gradually changes according to changes in the oil pressure in the primary circuit, without the influence of the oil pressure limiting component. In this construction vehicle, rapid changes in pump displacement can thus be suppressed, and wheel slip and sudden acceleration can also be suppressed.

With this suppressive control of a rapid change in pump displacement, since the displacement of the transport hydraulic pump is controlled, the danger of affecting the output flow rate of other hydraulic pumps, for example the hydraulic pump for the work equipment is less than in cases where the engine speed is limited. Therefore, reductions in the operating speed of the work equipment can be suppressed while the suppressive control of a rapid change in pump displacement is implemented.

The construction vehicle according to a third aspect of the present invention is the construction vehicle according to the first and second aspects, which further comprises a transport circuit pressure detector for detecting the transport circuit pressure, and a motor speed detector for detecting the engine speed. The control unit controls the transport hydraulic pump displacement under the suppressive control of a rapid change of the pump displacement on the basis of the transport circuit pressure detected by the transport circuit pressure detector and the engine speed detected by the engine speed detector.

In this construction vehicle, the desired oil pressure characteristic of the pump displacement primary circuit can be obtained by controlling the transport hydraulic pump displacement on the basis of the transport circuit pressure detected by the transport circuit pressure detector and the torque detector detected by the engine speed detector. The suppressive control of a rapid change in the pump displacement described above can thus easily be carried out.

The construction vehicle according to a fourth aspect of the present invention is the construction vehicle of the first and second aspects, further comprising a vehicle speed detector for detecting vehicle speed, and a motor speed detector for detecting the engine speed. The control unit controls the transport hydraulic pump displacement on the basis of the vehicle speed, which is detected by the vehicle speed detector and the engine speed is detected by the engine speed detector under the suppressive control of a rapid change in the pump displacement.

In this construction vehicle, the displacement of the transport hydraulic pump is controlled against the background of the vehicle speed, which is detected by the vehicle speed detector and the engine speed is detected by the engine speed detector. In a vehicle having a mechanism where the transport hydraulic pump displacement decreases as the transport circuit pressure increases, the vehicle speed is a parameter correlated with the transport circuit pressure under conditions when the transport hydraulic motor displacement is constant and the engine speed is constant. Therefore, the preferred oil pressure characteristic of the pump displacement primary circuit can also be obtained by controlling the displacement of the transport hydraulic pump in the light of the vehicle speed and engine speed. The suppressive control of a rapid change in the pump displacement described above can thus easily be carried out.

The plant vehicle according to a fifth aspect of the present invention is the plant vehicle according to the first and second aspects, which comprises an electromagnetic proportional control valve, which can control the displacement of the transport hydraulic pump. The control unit controls the displacement of the transport hydraulic pump by electrically controlling the electromagnetic proportional control valve.

In this construction vehicle, the control unit electrically controls the electromagnetic proportional control valve, and can thus control the displacement of the transport hydraulic pump. With this construction vehicle, the displacement of the transport hydraulic pump can thus be controlled to obtain the desired oil pressure characteristic of the pump displacement primary circuit.

533 997 and the suppressive control of a rapid change in pump displacement can thus be easily carried out.

The plant vehicle according to a sixth aspect of the present invention is the plant vehicle according to the first or second aspect, which further comprises a pump displacement control mechanism for varying the transport hydraulic pump displacement in accordance with the pilot pressure provided, and a pressure control valve which can control the pilot pressure applied to the pump displacement control. The control unit controls the displacement of the transport hydraulic pump by electrically controlling the pressure control valve.

In this construction vehicle, the control unit controls the pressure control valve electrically, and can thus control the displacement of the transport hydraulic pump. With this construction vehicle, the displacement of the transport hydraulic pump can thus be controlled to obtain the desired oil pressure characteristic of the pump displacement primary circuit, and the suppressive control of a rapid change of the pump displacement can thus be easily carried out.

The construction vehicle according to a seventh aspect of the present invention is the construction vehicle according to the first or second aspect, wherein the control unit controls the transport hydraulic pump displacement under suppressive control of a rapid change of the pump displacement so that the maximum driving wheel force of the vehicle speed driving force characteristic is obtained at a lower speed than the maximum driving wheel force of the vehicle speed driving decrease driving force characteristic

In a conventional construction vehicle, the driving wheel force does not assume an extreme value when the vehicle speed is zero, but when the vehicle speed is in a low speed range, as in the vehicle speed driving wheel characteristic shown in FIG. 15.1 in this case, the driving wheel power increases in accordance with an increase in vehicle speed at a certain speed or less, and the driving wheel power then decreases in accordance with an increase in vehicle speed at a certain speed or greater, making the vehicle more difficult to handle for the driver.

533 997

However, in the construction vehicle of the seventh aspect of the present invention, under suppressive control of a rapid change of pump displacement, the maximum driving wheel force of the vehicle speed-driving force characteristic arises at a lower speed than the maximum driving wheel force of the down-speed driving force of the driving speed driving force. of the pump displacement is not carried out. Therefore, vehicle speed driving force characteristic under suppressive control of a rapid change in pump displacement is closer than monotonic reduction function in which the driving wheel power gradually decreases in accordance with the increase of vehicle speed, a vehicle speed driving wheel speed change of

The construction vehicle according to an eighth aspect of the present invention is the construction vehicle according to the first or second aspect, which further comprises a selector to allow a driver to choose the implementation of suppressive control of a rapid change in pump displacement. In this construction vehicle, the driver can arbitrarily choose whether suppressive control of a rapid change of pump displacement should be implemented by activating the selector. For example, the suppressive control of a rapid change of pump displacement can be selected when transported on snow-paved roads or other low-friction pavements, and the suppressive control of a rapid change of pump displacement can be selected during transport over normal road surfaces.

533 997

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side view of the construction vehicle;

Fig. 2 is a schematic view showing the structure of the hydraulic drive mechanism according to the first embodiment;

Fig. 3 is a block diagram of the construction vehicle;

Fig. 4 is a graph showing an example of oil pressure directional statistics of pump displacement primary circuit;

Fig. 5 is a graph showing an example of oil pressure characteristics of engine displacement primary circuit;

Fig. 6 is a graph showing the characteristics of vehicle speed-driving wheel force;

Fig. 7 is a graph showing oil pressure characteristic data of pump displacement primer for each engine speed under suppressive control of a rapid change of pump displacement;

Fig. 8 is a drawing showing the construction of the hydraulic drive mechanism in accordance with the second embodiment;

Fig. 9 is a graph showing data on characteristics of engine speed pilot pressure for each vehicle speed under suppressive control of a rapid change of pump displacement;

Fig. 10 is a graph showing the oil pressure characteristics of the pump displacement primary circuit for each engine speed under suppressive control of a rapid change of pump displacement;

Fig. 11 is a drawing showing the construction of a hydraulic drive mechanism in accordance with another embodiment;

Fig. 12 is a drawing showing the construction of a hydraulic drive mechanism in accordance with another embodiment;

Fig. 13 is a drawing showing the construction of a hydraulic drive mechanism in accordance with another embodiment;

Fig. 14 is a graph showing the oil pressure characteristics of the engine displacement primary circuit of a conventional plant vehicle; and

Fig. 15 is a graph showing the characteristics of the vehicle speed-driving wheel force of a conventional construction vehicle.

533 997

REFERENCE

In Construction Vehicles

Working device

4a, 4b Transport wheels

Engine

Transporthydraulpump

II Hydraulic pump for work equipment

Transporthydraulmotor

controller

Engine speed detector

20, 21 Primary Circuits (Transport Hydraulic Circuits)

Oil pressure detector for primary circuit (pressure detector for transport circuit)

Steering cylinder for pump displacement (steering mechanism for pump displacement)

Control valve for pump displacement (electromagnetic proportional control valve)

Decompression valve (pressure control valve)

Control valve (oil pressure limiting component)

Vehicle Speed ​​Sensor

Other voters (voters)

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) &lt;Overall Configuration&gt;

A side view of the construction vehicle 1 according to an embodiment of the present invention is shown in Fig. 1. The construction vehicle 1 is a wheel loader which can be propelled by means of tires 4a, 4b, and can also use a working equipment 3 to perform the desired work. The construction vehicle 1 includes a vehicle frame 2, a working equipment 3, tires 4a, 4b, and a cabin 5.

533 997

The vehicle frame 2 has a front frame 2a arranged on the front and a rear frame 2b arranged on the rear, and the front frame 2a and the rear frame 2b are interconnected in the middle of the vehicle frame 2 and can pivot to the right and left.

The working equipment 3 and a pair of front wheels 4a are fixed to the front frame 2a. The working equipment 3 is a device driven by pressure oil from a hydraulic pump 11 for the working equipment (see Fig. 2), and the working equipment has a lifting arm 37 mounted at the front part of the front frame 2a, a bucket 38 attached to the outer end of the lifting arm. 37, and a cylinder 26 for the working equipment (see Fig. 2) for driving these components. The pair of front wheels 4a are arranged on the side surfaces of the front frame 2a.

The cab 5, a pair of rear wheels 4b, and other components are provided at the rear frame 2b. The cab 5 is located at the upper portion of the vehicle frame 2, and inside the cab is a steering wheel, a accelerator pedal, and other operating components; a display unit for displaying the vehicle speed and other varying information, a driver's seat, and the like. The pair of rear wheels 4b are arranged on side surfaces of the vehicle frame 2b. A hydraulic fluid tank (not shown) is provided on the right side of the rear frame 2b, and the hydraulic fluid tank houses hydraulic fluid which is pressurized by various hydraulic pumps.

A hydraulic drive mechanism 7a for driving the tires 4a, 4b and the operating equipment 3 is installed on the vehicle frame 2. The structure of the hydraulic drive mechanism 7a is described below with reference to Fig. 2.

&lt;Hydraulic drive mechanism 7a&gt;

The hydraulic drive mechanism 7a primarily has a motor 8, a transport hydraulic pump 9, a charge pump 10, the hydraulic pump 11 for the work equipment, a transport hydraulic motor 12, a drive shaft 15, a control unit 16 (see Fig. 3), and uses a so-called HST system.

533 997

The engine 8 is a diesel engine and the output torque generated by the engine 8 is transmitted to the transport hydraulic pump 9, the charge pump 10, the hydraulic pump 11 for the work equipment, a control hydraulic pump (not shown), and other components. The engine 8 is equipped with a fuel injection device 17 for controlling the output torque and rotational speed of the engine 8, and the fuel injection device adjusts a guide value for the engine speed according to how much the throttle pedal is activated (hereinafter referred to throttle pedal position) and adjusts the amount of fuel injected. . The accelerator pedal is a means of indicating the target speed of the engine 8, and is provided with a position detector 18 for the accelerator pedal (see Fig. 3). The accelerator pedal position detector 18 is made up of a potentiometer or the like, and the accelerator pedal position detector detects the position of the accelerator pedal. The throttle pedal position detector 18 sends a position signal indicating the throttle pedal position for the controller 16, and a control signal is output from the controller 16 to the fuel injection device 17. Therefore, the driver can control the engine speed by adjusting how much the throttle is affected. The motor 8 is also provided with a motor speed detector 19 (see FIG. 3), which is composed of a speed sensor to detect the actual speed of the engine 8, and a speed signal from the engine speed detector 19 is input to the controller 16.

The transport hydraulic pump 9 is a variable displacement hydraulic pump, which can vary the displacement by varying the angle of inclination of a folding disc, and is driven by the motor 8. Pressure oil discharged from the transport hydraulic pump 9 is fed to the transport hydraulic motor 12 through the primary circuits 7 oil pressure detector 22 for the primary circuit (transport circuit pressure detector) (see FIG. 3) to detect the pressure (hereinafter referred to as primary circuit oil pressure) of the pressure oil passing through the primary circuits 20, 21. The primary pressure (transport circuit pressure) oil pressure corresponds to the driving oil pressure of the pressure oil to drive the transport hydraulic motor 12. A control cylinder 23 is connected to the pump terminal. the transport hydraulic pump 9 and a pump displacement control valve 24 can vary the inclination angle of the folding disc of the transport hydraulic pump 9. The pump displacement control valve 24 has a link unit 24a, which is interconnected with the cylinder unit 23a of the pump displacement control cylinder 23, and can control, as required, the position of the cylinder unit 23a against the background of a control signal from the control unit 16. Specifically, the pump displacement control valve 24 is an electromagnetically proportional control valve for controlling the pump displacement 23 of the pump displacement against the background of a control signal from the control unit 16, and can switch the direction of the oil supplied to the control cylinder 23 for the pump displacement as well as varying the pitch angle of the transverse angle of the tilt angle of the . Therefore, the control unit 16 can vary the displacement of the transport hydraulic pump 9 by electrically controlling the control valve 24 for the pump displacement.

The charge pump 10 is driven by the motor 8 and can provide pressure oil to drive the pump displacement control cylinder 23 to the pump displacement control valve 24. The charge pump 10 also provides pressure oil to drive a motor cylinder 29 to a motor control valve 30.

A limiting circuit 39 connected to a limiting valve 31 is also connected to a circuit to provide pressure oil from the charge pump 10 to the control cylinder 23 for the pump displacement. The restriction valve 31 is a decompression valve which can reduce the pilot pressure to the control cylinder 23 of the pump displacement to a set pressure via the balance between spring force and the force of the oil pressure of the primary circuit. The restriction valve 31 is designed to reduce the pilot pressure provided to the cylinder displacement control cylinder 23 in cases where the oil pressure of the primary circuit has become equal to or greater than a set limit pressure, and to limit the oil pressure of the primary circuit so as not to exceed the limit pressure value.

The hydraulic pump 11 for the work equipment is driven by the engine 8, whereby pressure oil discharged from the hydraulic pump 11 for the work equipment is supplied to the work equipment cylinder 16 of the work equipment 3 via a hydraulic circuit 25 for the work equipment, so that the work equipment cylinder 26 is driven.

The transport hydraulic motor 12 is a variable displacement hydraulic motor, which can vary the displacement by varying the angle of inclination of an angled shaft, and is driven by the pressure oil discharged from the transport hydraulic pump 9 to generate a driving force for transport. The transport hydraulic motor 12 is provided with a motor cylinder 29 for controlling the inclination angle of the transport hydraulic motor 12, and a motor control valve 30 (see Fig. 3) for controlling the motor cylinder 29. The motor control valve 30 is an electromagnetic control valve which is controlled against the background of a control signal from the control unit 16, and the displacement of the transport hydraulic motor 12 can be varied by controlling the motor cylinder 29.

533 997

The drive shaft 15 causes the tires 4a, 4b to rotate by transferring the driving force from the transport hydraulic motor 12 to the tires 4a, 4b (see Fig. 1). The drive shaft 15 is also provided with a vehicle speed detector 34 (see Fig. 3), which is composed of a vehicle speed sensor to detect the vehicle speed from the rotational speed of the drive shaft 15, and a vehicle speed signal from a vehicle speed detector 34 is input to the controller 16.

The control unit 16 controls the control valves and the fuel injection device 17 electronically in the light of output signals from the detectors, and the control unit can control the engine speed, the displacement of the hydraulic pumps 9 to 11, the displacement of the transport hydraulic motor 12, and other factors. For example, by electrically controlling the control valve 24 for the pump displacement, the control unit 16 can control the displacement of the transport hydraulic pump 9. The driving wheel force and vehicle speed thus vary continuously in the construction vehicle 1, and the vehicle speed can be automatically changed from zero to the maximum vehicle speed without a speed changing operation (see Fig. 6). The construction vehicle 1 comprises a first selector 35, and the operation of the first selector 35 by a driver causes the control unit 16 to implement limiting control of the driving wheel force to limit the maximum driving wheel force. The construction vehicle 1 also includes a second selector 36, and the operation of the second selector 36 by a driver causes the controller 16 to implement suppressive control of a rapid change in pump displacement. Transport control of the construction vehicle 1 is described in detail below.

&lt;Control of the transport hydraulic pump 9 and the transport hydraulic motor 12&gt;

The controller 16 processes the output signals from the engine speed detector 19 and the oil pressure detector 22 for the primary circuit and outputs directional signals regarding the pump displacement to the control valve 24 for the pump displacement. The controller 16 refers to the oil pressure characteristic data for the pump displacement primary circuit stored in the controller 16, sets the pump displacement from the value of the engine speed and the oil pressure value of the primary circuit, and outputs a pump displacement directive value corresponding to the set pump displacement 24. The use of pump displacement is hereinafter referred to as the displacement of the transport hydraulic pump 9. FIG. 4 shows an example of data for the oil pressure characteristics of

533 997 pump displacement primary circuit. The solid line L11 and the dashed lines L12 to L15 in the diagram are lines showing the oil pressure characteristics of the pump displacement primer circuit (hereinafter referred to as PQ characteristics), which vary according to the engine speed. The pump displacement control valve 24 varies the inclination angle of the transport hydraulic pump 9 by controlling the pump displacement control cylinder 23 in the light of the entered directional value for the pump displacement. The pump displacement is thereby controlled to correspond to the engine speed.

The controller 16 also processes output signals from the engine speed detector 19 and the oil pressure detector 22 for the primary circuit and outputs a directional signal for the engine displacement to the motor control valve 30. The controller 16 refers to the oil pressure characteristic of the engine displacement primary circuit stored in the controller 16, sets the engine displacement from the value of the engine speed and the value of the oil pressure of the primary circuit, and outputs an instruction regarding the slope angle change corresponding to the set motor control 30. shows an example of the oil pressure characteristic data of the engine displacement primary circuit. The solid line L21 in the diagram is a line at which the angle of inclination in relation to the oil pressure of the primary circuit is established, when the engine speed is at a certain speed. The slope angle is at a minimum (min) while the oil pressure of the primary circuit is at a specific value or less, with the slope angle gradually increasing (inclined portion L22 of the solid line) as the oil pressure of the primary circuit increases, and after the slope angle has reached a maximum (max) , the slope angle remains at the maximum slope angle Max even if the oil pressure increases. The inclined portion L22 of the solid line is set to increase or decrease according to the engine speed. Specifically, if the engine speed is low, the angle of inclination increases from a state of low oil pressure of the primary circuit, and the angle of inclination is controlled to reach the maximum angle of inclination in a state of less oil pressure of the primary circuit (reference to the inclined portion L23 of the lower dashed line. 5). Conversely, if the engine speed is high, the slope angle remains at the minimum slope angle Min until the oil pressure of the primary circuit increases further, and the slope angle is controlled to reach the maximum slope angle Max in a state of higher oil pressure of the primary circuit (reference L to 24). upper dashed line in Fig. 5).

533 997 &lt;Limiting control of drive wheel force&gt;

The controller 16 switches the maximum value of the slope angle of the transport hydraulic motor 12 against the background of an output signal from the first selector 35 and limits the maximum displacement of the transport hydraulic motor 12 to a predetermined limited value, thereby limiting the maximum driving wheel force. In the construction vehicle 1, the first selector 35 can be switched between a switched on state and a turned off state. The maximum drive wheel force in the on state can be varied between three levels: level A, level B, and level C. When the first selector 35 is in the off state, the maximum angle of inclination is present at the maximum position in Fig. 5, and the characteristic of the vehicle speed. The driving wheel force in this state is represented by the graph L1 in Fig. 6. This maximum inclination angle Max is a maximum value for the performance of the transport hydraulic motor 12. When the first selector 35 is turned to the on state, the maximum inclination angle changes to a value corresponding to the level of the set maximum drive wheel force. Specifically, when the maximum drive wheel force is set to level A at the on state, the maximum inclination angle is changed to Ma. Similarly, when the maximum drive wheel angle is set to Level B, the maximum slope angle changes to Mb, and when the maximum drive wheel force is set to Level C, the maximum slope angle changes to Mc. Thus, the maximum slope angle is changed to Ma, Mb, and Mc, which are smaller than Max, resulting in the characteristic of vehicle speed-driving wheel force, in which the maximum driving wheel force has decreased, as in the graphs La, Lb, and Lc in Fig. 6 . It is thereby possible to suppress the drive wheel force of the tires 4a, 4b to prevent slipping, even when the accelerator pedal position is set to maximum in order to ensure a workload performed by the work equipment 3 on soft roadways, snow-covered roadways, and other roadways, which have low roadways or in cases in which the weight of the assembled objects is relatively low. The graphs L1, La, Lb, and Lc all represent the characteristics of the vehicle speed driving force in a state when the accelerator pedal position is fully extended.

• «Suppressive control of a rapid change in pump displacement&gt;

The controller 16 can implement suppressive control of a rapid change of pump displacement against the background of the output of the second selector 36. Suppressive control of a rapid change of the pump displacement is performed to control

533 997 the pump displacement of the transport hydraulic pump 9, so that the displacement of the transport hydraulic pump 9 gradually changes according to the change in the oil pressure of the primary circuit while the oil pressure of the primary circuit is limited so as not to exceed the pressure limiting valve.

Under suppressive control of a rapid change of pump displacement, controller 16 determines the displacement of the transport hydraulic pump 9 against the graph shown in Fig. 7.1 this graph, the displacement of the transport hydraulic pump 9 has been determined in relation to the oil pressure of the primary circuit, and the lines L1T shows data for PQ characteristics, which vary according to engine speed. Considering the engine speeds, sequentially in relation to lines L1T to L15 'at N1, N2, N3, N4, N5, the speeds have the ratio N1&gt; N2&gt; N3&gt; N4&gt; N5. The data for the PQ characteristic shown in Figs. 7 is used in cases where suppressive control of a rapid change in pump displacement has been used, and there are also characteristics which differ from data on PQ characteristic L11 to L15 (reference to double dashed lines) in cases where suppressive control of a rapid change in pump displacement not selected. Reference symbols, which belong to PQ characteristic data, which have the same number, represent the same engine speed. For example, line L11 and LIT represent data for PQ characteristics at the same engine speed, and differ or not, depending on whether suppressive control of a rapid change in pump displacement has been selected. The controller 16 controls the displacement of the transport hydraulic pump 9 against the background of the oil pressure of the primary circuit, as detected by the oil pressure detector 22 of the primary circuit, the engine speed detected by the engine speed detector 19, and their data on PQ characteristics.

Specifically, in data on PQ characteristics shown in Fig. 7, the oil pressure of the primary circuit reaches a maximum value equal to or less than the limiting pressure value Pit when the vehicle has stopped, and the displacement of the transport hydraulic pump 9 gradually increases as the oil pressure of the primary circuit decreases. the maximum value. In other words, the displacement of the transport hydraulic pump 9 gradually decreases as the oil pressure of the primary circuit increases, and the oil pressure of the primary circuit reaches a maximum value equal to or less than the limit pressure value Pit when the vehicle has stopped. Therefore, data on PQ characteristics L1Γ to L14 'in cases where suppressive control of a rapid change in pump displacement is chosen differently from data on PQ characteristics L11 to L14 in cases

533 997 where suppressive control of a rapid change in pump displacement has not been selected. Specifically, for data on PQ characteristics L11 to L15, in cases where suppressive control of a rapid change in pump displacement has not been selected, data on PQ characteristics L11, L12 corresponding to engine speeds equal to or greater than a predetermined rotational speed have a horizontal line Lhz, in which the oil pressure of the primary circuit does not change even if the pump displacement does not change. In this section, the oil pressure of the primary circuit remains constant at the limiting pressure value Plt and the oil pressure of the primary circuit does not change even if the pump displacement does not change. This occurs because the limit circuit operates, which suppresses increases in the oil pressure of the primary circuit and maintains a constant oil pressure of the primary circuit at the limit pressure value Pit. With data on PQ characteristics L1T, L12 ', used in cases where suppressive control of a rapid change of pump displacement has been selected, no such aforementioned horizontal line exists independent of engine speed, and the pump displacement gradually changes according to changes in the oil pressure of the primary circuit. . For data on PQ characteristics L1Γ to L15 ', in cases where suppressive control of a rapid change in pump displacement has been selected, data on PQ characteristics L15' in the case of a relatively low engine speed, are the same as data on PQ characteristics in cases where suppressive control of a rapid change in pump displacement has not been selected.

Under a suppressive control of a rapid change of pump displacement, as described above, the displacement of the transport hydraulic pump 9 is controlled so that the oil pressure of the primary circuit and the pump displacement are changed along the lines shown by the PQ characteristic L1T to L15 'in Fig. 7. The characteristic of vehicle drive speed. , which is shown by the graph L2 in Fig. 6 is thereby obtained. This characteristic of vehicle speed-driving force is similar to the characteristic of vehicle speed driving force of a vehicle fitted with a torque converter (reference to graph L3). Characteristics of the vehicle speed-driving wheel force of a vehicle fitted with a torque converter constitute a monotonically decreasing function, and the maximum driving wheel power reaches a maximum at the time when the vehicle speed is zero. The graph Lc represents the characteristic of vehicle speed-driving force when level C for limiting control of the driving wheel force is carried out but when suppressive control of a rapid change of pump displacement is not carried out (a throttle pedal position of 100%). The graph L2 represents the characteristic of vehicle speed-driving wheel force when under-pressure control of a rapid change of pump displacement has been carried out together with level C for limiting control of the driving wheel force. In this graph L2, the maximum driving wheel force arising at a lower speed than the maximum driving wheel force is shown in the characteristic vehicle speed-driving wheel force shown by the graph Lc. Specifically, vehicle speed V1, where maximum driving wheel power occurs in the vehicle speed-driving force characteristic of suppressive control of a rapid change in pump displacement, is less than vehicle speed V2 where the maximum driving wheel power occurs in the characteristic of vehicle speed driving force when reference is made to downward driving force. a change in pump displacement does not occur, for example at 1 km / h.

Suppressive control of a rapid change in pump displacement can also be carried out along level B or level A for limiting the driving wheel force, instead of level C for limiting the driving wheel force.

Controller 16 terminates suppressive control of a rapid change of pump displacement in case the second selector 36 has been turned off.

&lt;Characteristics&gt;

(1)

In the construction vehicle 1, under suppressive control of a rapid change of pump displacement, conditions in which the oil pressure of the primary circuit is not altered, is suppressed, since the pump displacement control valve 24 is controlled so that the displacement of the transport hydraulic pump 9 changes gradually with the displacement of the primary circuit in accordance with the .

Therefore, rapid changes in pump displacement are suppressed. Rapid accelerations and occurrences of slip on roads with low friction can thus be reduced.

Vehicle Speed-Drive Wheel Characteristics Similar to vehicle speed-drive power characteristics of a vehicle equipped with a torque converter can be obtained by controlling the pump displacement control valve 24 as described above. Because one

533 997 vehicles fitted with a torque converter have a linear characteristic of vehicle speed driving force in which the driving wheel force reaches a maximum at a vehicle speed at zero and the driving wheel force decreases in accordance with the increase of the vehicle speed, obtaining similar characteristics of the vehicle speed driving wheel for a driver to easily carry out transport operations.

(2) the construction vehicle 1, since the displacement of the transport hydraulic pump 9 is controlled under the suppressive control of a rapid change of the pump displacement, there is little danger of affecting the displacement of other hydraulic pumps, for example of the hydraulic pump 11 for work equipment, in comparison with the engine speed 8 is limited. Therefore, it is possible to suppress reductions in drive speed of work equipment 3 while suppressing control of a rapid change in pump displacement.

(Second embodiment) &lt;Configuration&gt;

Fig. 8 shows the configuration of a hydraulic drive mechanism 7b of a plant vehicle 1 according to the second embodiment of the present invention.

In this hydraulic drive mechanism 7b, which is connected to the transport hydraulic pump 9, a directional valve 24 and a control cylinder 23 for the pump displacement can vary the inclination angle of the folding disc of the transport hydraulic pump 9. The control cylinder 23 for the pump displacement through the displacement through the displacement through the displacement pump the angle of inclination of the wobble of the transport hydraulic pump 9 in accordance with the pilot pressure provided. The directional valve 24 is an electromagnetic control valve for controlling the direction of pressure oil provided by the control cylinder 23 for pump displacement against the background of a control signal from the control unit 16. The action of the directional valve 24 allows the construction vehicle 1 to switch between transport forward and backward. A vehicle speed control valve 32 is provided on the circuit to provide pressure oil from the charge pump 1033 to the pump displacement control cylinder 23. The vehicle speed control valve 32 is an electromagnetic, proportional pressure control valve which can control, as required, the pilot pressure provided by the pump displacement control cylinder 23 in accordance with a control signal from the control unit 16. The vehicle speed control valve 32 can vary the displacement of the transport hydraulic pump 9 by is provided by the control cylinder 23 for the pump displacement.

As described above, the vehicle speed control valve 16 controls electrically the hydraulic drive mechanism 7b and controls the pilot pressure provided by pump displacement control cylinder 23, whereby the displacement of the transport hydraulic pump 9 can be varied as required.

In addition, the configuration is similar to that of the construction vehicle of the first embodiment.

&lt;Control of transport hydraulic pump 9 and transport hydraulic motor 12&gt;

In the following, control of the transport hydraulic pump 9 and the transport hydraulic motor 12 in this construction vehicle will be described.

The control unit 16 outputs a directional signal for the pump displacement to the control valve 32 for vehicle speed in accordance with the engine speed and oil pressure of the primary circuit. Referring to the characteristics of engine speed pilot pressure stored in control unit 16, controller 16 sets the pump displacement from the engine speed value and the oil pressure of the primary circuit and outputs a directive value corresponding to the set pump displacement of the control valve 32 for the vehicle speed. FIG. 9 shows an example of data on characteristics of engine speed pilot pressure. The solid line L21 and the dashed lines L22, L23 in the diagram are lines representing data on engine speed pilot pressure characteristics which change according to the oil pressure of the primary circuit. The vehicle speed control valve 32 varies the inclination angle of the transport hydraulic pump 9 by controlling the pump displacement control cylinder 23 against the directive value entered from the control unit 16. The displacement of the transport hydraulic pump 9 is thus controlled to correspond to the engine speed.

533 997

The controller 16 also processes outputs from the engine speed detector 19 and the oil pressure detector 22 for the primary circuit and outputs a directional signal for the engine displacement to the motor control valve 30. Referring to data on engine speed oil pressure characteristics of the primary circuit stored in the controller 16, the controller outputs a tilt angle variation command to the engine control valve 30 to increase the engine displacement from the actual value of the engine speed and the oil pressure value of the primary circuit.

In this construction vehicle, limitation control of the drive wheel force and suppressive control of a rapid change in pump displacement can be implemented, similar to the construction vehicle according to the first embodiment. Limit control of the driving wheel force is a control similar to that of the construction vehicle in accordance with the first embodiment and is therefore not described. Suppressive control of a rapid change in pump displacement is described below.

[Suppressive control of a rapid change in pump displacement]

The controller 16 can implement a suppressive control of a rapid change of the pump displacement in the light of the output of the second selector 36. Suppressive control of a rapid change in the pump displacement in this construction vehicle is most similar to that of the construction vehicle according to the first embodiment in that the displacement of the transport hydraulic pump 9 is controlled so that the displacement of the transport hydraulic pump 9 gradually changes according to changes in the oil pressure of the primary pressure of the primary pressure of the primary pressure. do not exceed the limit pressure value Pit. However, suppressive control of a rapid change in the pump displacement in this construction vehicle differs from the construction vehicle in accordance with the first embodiment in that the pump displacement is controlled by control of the vehicle speed control valve 32.

533 997

The pilot pressure provided by the pump displacement control cylinder 23 is determined against the background of the oil pressure of the primary circuit and the engine speed. For example, at the oil pressure Pma of the primary circuit, data on characteristics of engine speed pilot pressure, which is shown by line L21 in Fig. 9. At oil pressure Pmb of the primary circuit, data on characteristics of engine speed pilot pressure shown by line L22 in Fig. 9, and at the oil pressure Pmc of the primary circuit, data on the characteristics of engine speed pilot pressure are shown, which is shown by line L23 in Fig. 9. The ratio of these pressures is Pma&gt; Pmb&gt; Pmc. Characteristics of engine speed pilot pressure L21 to L23, when engine speed is equal to or greater than a predetermined value Nc, pilot pressure is set to increase as the oil pressure of the primary circuit decreases if engine speed remains the same. For example, the rotational speed N1 (&gt; Nc) is the pilot pressure Ppa at the oil pressure Pma of the primary circuit. The transport hydraulic pump 9 is thus driven by the oil pressure of the primary circuit and the pump displacement corresponding to the pump Pa in Fig. 10. With the same engine speed N1, the pilot pressure Ppb is at the oil pressure Pmb of the primary circuit. The transport hydraulic pump 9 is thereby driven by the oil pressure of the primary circuit and the pump displacement corresponding to the pump Pb. With the same engine speed N1, the pilot pressure is Ppc at the oil pressure Pmc of the primary circuit. The transport hydraulic pump 9 is thereby driven by the oil pressure of the primary circuit and the pump displacement corresponding to the point Pc. The prints have the ratio Ppa &lt;Ppb &lt;Ppc. PQ characteristics, such as those shown in FIG. 10 thus occurs. Under suppressive control of a rapid change in pump displacement, the control of the pilot pressure causes the PQ characteristic to occur which are similar data on the PQ characteristic L11 'to L15' in suppressing control of a rapid change of pump displacement according to the first embodiment shown in Fig. 10. . Vehicle speed driving characteristics, similar to those for suppressive control of a rapid change in pump displacement according to the first embodiment (see Fig. 6), are also exhibited thereby.

&lt;Characteristics&gt;

With this construction vehicle, the same effects can be exhibited as those of the construction vehicle according to the first embodiment described above.

533 997

In the present embodiment, under suppressive control of a rapid change of pump displacement, the pilot pressure provided to the pump displacement control cylinder 23 is controlled according to the strength of the oil pressure of the primary circuit, but the pilot pressure can also be controlled according to the vehicle speed instead of the oil pressure of the primary circuit. In this case, data on the characteristics of engine speed pilot pressure L21 are set to L23, as shown in FIG. 9, such that an engine speed equal to or greater than a predetermined value Nc, whereby the pilot pressure decreases as the vehicle speed decreases if the engine speed remains the same.

(Other Embodiments) (A)

In the embodiment described above, the present invention is applied to a wheel loader, but the present invention is not limited to a wheel loader and can be applied to any construction vehicle driven by a hydraulic motor and having an HST installed.

(B)

In the above embodiment, suppressive control is performed by a rapid change of pump displacement when selected by the second selector 36, but suppressive control of a rapid change of pump displacement can also be performed automatically without being selected by a driver. Nearly linear characteristics of vehicle speed driving force are thereby obtained during low speed operation, and the driver can thus operate the accelerator pedal more easily.

(C)

In the first embodiment described above, suppressive control is effected by a rapid change of pump displacement by electrically controlling the control valve 24 of the pump displacement, but other control means can be used if the displacement of the transport hydraulic pump 9 is controlled to obtain the characteristic of the oil pressure of the primary circuit pump displacement. is shown in Fig. 7.

533 997 (D)

In the second embodiment described above, the pilot pressure provided to the pump displacement control cylinder 23 is controlled by controlling the vehicle speed control valve 32 according to a control signal from the control unit 16. The upper limit of the pilot pressure corresponding to the engine speed, which is controlled by the vehicle speed control valve 32, can also be controlled. is controlled by controlling a decompression valve 28 according to a control signal from the control unit 16 shown in Fig. 11. The decompression valve 28 is an electromagnetic proportional pressure control valve for connecting the directional valve 24 and a pilot circuit 33 through which pressure oil discharged from the charge pump 10 passes, and the decompression valve 28 can control the pilot pressure provided to the cylinder displacement control 23 by a control signal from the control signal.

The position at which the decompression valve 28 is provided is also not limited by the aforementioned position. For example, the decompression valve 28 may be provided divergently from the pilot circuit 33 shown in Fig. 12. The decompression valve 28 may also be provided divergently from the limiting circuit 39, which is connected to the pilot circuit 33, shown in Fig. 13. Furthermore, the decompression valve is not limited to a single one. Two decompression valves may be provided, one being a forward transport decompression valve to provide forward pressure pilot pressure to the pump displacement control cylinder 23 and the other is a reverse transport decompression valve to provide reverse transport pilot pressure to the pump displacement control cylinder 23 and the pilot pressure provided. the pump displacement control cylinder 23 can be controlled in both decompression valves. In this case, the directional valve 24.1 in hydraulic circuits, such as these, fails, the pilot pressure provided to the pump displacement control cylinder 23 can be controlled to obtain characteristics of the oil pressure of the primary circuit pump displacement, such as those shown in Fig. 10.

(E)

In the first embodiment described above, the pump displacement is controlled against the background of the oil pressure of the primary circuit and the engine speed, but the vehicle speed can also be used as a factor instead of the oil pressure of the primary circuit.

533 997

INDUSTRIAL APPLICABILITY

The present invention makes it possible to suppress tire slip and sudden accelerations, and the present invention is useful as a construction vehicle.

533 997