Control device and control method for transmission with clutch

Technical Field

The present invention relates to a control device and a control method for a transmission with a clutch, and the invention particularly relates to a control device and a control method for a transmission with a clutch, which is preferable for a construction vehicle such as a wheel loader, in which tires are used.

Background Art

Japanese Laid-open Patent No. 62-132060 has been proposed as a control method for a transmission by which a clutch of the transmission is smoothly engaged. The configuration of the proposed clutch hydraulic control device is shown in a sectional view in Fig. 8 and a hydraulic circuit diagram in Fig. 9. In Fig. 9, a clutch hydraulic control device 50 operates a clutch hydraulic control valve 52 in response to a command from a controller 51, and sends pressure oil from a hydraulic pump 53 to a clutch chamber 54 to achieve smooth engagement. The clutch hydraulic control valve 52 includes valves for a forward gear 52A, a reverse gear 52B, a first speed gear, a second speed gear, and the like.

The clutch hydraulic control valve 52 includes a pressure control valve 60 for controlling clutch oil pressure, a flow rate detecting valve 70 for detecting the pressure oil flowing from the hydraulic pump 53 to the clutch chamber 54 through the pressure control valve 60 and the flow rate detecting valve 70, and a filling completion detecting sensor 80 (hereinafter, called a filling sensor 80) for detecting that the clutch chamber 54 is filled with oil, that is, the filling is completed. The pressure control valve 60 is controlled by the controller 51, and a detection signal from the filling sensor 80 is inputted into the controller 51.

The pressure control valve 60, the flow rate detecting valve 70, and the filling sensor 80 are mounted on a body 90 as shown in Fig. 8. The body 90 is provided with a pump port 91 into which pressure oil flows from the hydraulic pump 53, an output port which supplies pressure oil into the clutch chamber 54, and drain ports 93 and 94 shown in Fig. 8, which return oil returning or leaking from the clutch chamber 54 to a tank 95. The pressure control valve 60 includes a pressure control valve spool 61 (hereinafter, called a control valve spool 61), a piston 62, a proportional solenoid 63, and a first spring 64. The right end portion of the control valve spool 61 is abutted to a plunger 63a of the proportional solenoid 63, and a spring 64 is abutted to the left end portion thereof, thereby pressing the control valve spool 61 to the proportional solenoid 63 side. The pressure in an oil passage 67 (the pressure to the clutch chamber 54) acts on an oil chamber 65 inside the spool, which is formed by being divided by the control valve spool 61 and the piston 62 through an oil passage 66 formed inside the control valve spool 61.

The flow rate detecting valve 70 includes a flow rate detecting valve spool 71 (hereinafter, called a detecting valve spool 71), a second spring 72, and a third spring 73. Three of raised portions are formed at the detecting valve spool 71, and these raised portions divisionally form a first oil chamber 74, a second oil chamber 75, and a third oil chamber 76. A hole 77 is provided in the raised portion of the detecting valve spool 71 between the second oil chamber 75 and the third oil chamber 76. The detecting valve spool 71 has three different pressure receiving areas Aa, Ab, and Ac, and allows these areas to have relationships Aa + Ac > Ab, and Ab > Ac. The second spring 72 is abutted to and inserted into the left end portion of the detecting valve spool 71, and the third spring 73 is abutted to and inserted into the right end portion thereof. When pressure is not generated in the second oil chamber 75 and the third oil chamber 76, the detecting valve spool 71 is held in a neutral position where the second spring 72 and the third spring 73 respectively have free length. Accordingly, when the detecting valve spool 71 is not operated (the illustration shows a situation in which it is operated), the pressure oil flowing into the flow rate detecting valve 70 trough the pump port 91 stays in the first oil chamber 74. In the above, the second spring 72 and the third spring 73 work as springs for returning the detecting valve spool 71, and when the pressure oil is not supplied, the detecting valve spool 71 is designed to be in the neutral position.

The filling sensor 80 includes a sensing pin 81, a first resistance Ra and a second resistance Rb which are connected in series, and an insulator 82. The sensing pin 81 is attached at the body 90 with the insulator between them in the position where the detecting spool 71 abuts to the right end portion thereof when it is moved. A lead wire 83 is extended from the sensing pin 81, and the lead wire 83 is connected to a point between the first resistance Ra and the second resistance Rb. Predetermined direct voltage is applied to these first resistance Ra and the second resistance Rb, and the body 90 is grounded by means of a ground wire 84.

Next, the operation in the aforesaid configuration will be explained. When the clutch of an applicable speed gear is engaged, the controller 51 inputs a current Ia (time Ta) of a trigger command to the proportional solenoid 63 of the pressure control valve 60. Thereafter, the controller 51 lowers command current Ia to initial pressure command current Ip corresponding to initial pressure Pp of the clutch oil pressure, and waits until the filling is finished in this state.

As a result of inputting the current Ia of the trigger command, the plunger 63a of the proportional solenoid 63 moves the control valve spool 61 in the leftward direction in the drawing. Thereby, the pressure oil from the hydraulic pump 53 flows into the second oil chamber 75 of the detecting valve spool 71 through the pump port 91, the control valve spool 61, and the oil passage 67 (the arrow Ya shown in Fig. 8). The pressure oil which has flown into the second oil chamber 75 flows into the clutch chamber 54 through the hole 77 of the detecting valve spool 71, the third oil chamber 76, and the output port 92. At this time, the hole 77 causes differential pressure between the second oil chamber 75 and the third oil chamber 76, thereby moving the detecting valve spool 71 in the leftward direction in the drawing. As a result, the first oil chamber 74 and the second oil chamber 75, which are closed to each other by the body 90, are opened to each other. The pressure oil from the hydraulic pump 53 then passes through the opened portion (Yb), merges with oil Ya from the aforesaid control valve spool 61, and flows into the clutch chamber 54 through the hole 77 of the detecting valve spool 71, the third oil chamber 76, and the output port 92. The pressure oil continues to flow until the clutch chamber 54 becomes full.

When the clutch chamber 54 is filled with oil, the filling is finished, oil does not flow any more, and the differential pressure in the hole 77 between the second oil chamber 75 and the third oil chamber 76 does not exist. Thereby, the detecting valve spool 71 is moved to the rightward direction, and returned to the neutral position. Further, at this time, due to the relationship among the areas of the pressure receiving areas of the detecting valve spool 71, that is, Aa + Ac > Ab, and the force to which the returning force of the second spring 72 is added, the detecting valve spool 71 is moved to the rightward direction. When the detecting valve spool 71 is returned, the pressure oil from the hydraulic pump 53 fills the clutch chamber 54, and causes chute pressure. Further, the detecting valve spool 71 is moved in the rightward direction, thereby bringing the detecting valve spool 71 into contact with the sensing pin 81. By this contact, it is detected that the clutch chamber 54 is filled with oil, and that the filling is finished.

As described above, in the aforesaid art, at a point in time when the clutch chamber 54 is completely filled, peak pressure occurs as a result of a delay in the response of the pressure control valve 60 and the flow rate detecting valve 70. The peak pressure doesn't matter in a higher throttle area at higher engine speed. However, a disadvantage in that a shock or a noise occurring to the vehicle to thereby make the operator feel uncomfortable, occurs especially in a low throttle area at lower engine speed in a construction vehicle using tires, such as a wheel loader which requires smooth engagement of the clutch in both of the forward and reverse movements. In order to eliminate the disadvantage, it is suitable to reduce the flow rate of the pressure oil supplied to a clutch chamber 8 before the clutch chamber 8 (see Fig. 1) proposed by the present invention is filled with the pressure oil, thereby achieving smooth engagement of the clutch. However, unless the engagement of the clutch is achieved in a certain period of time, a disadvantage occurs, thereby giving the operator uncomfortable feeling that a slow start is made. When a control is to be carried out to smoothly engage the clutch in a certain period of time for the aforesaid reason, the following difficulties occur. Specifically, the first one is that the volume of the clutch chamber is not fixed, but "varied" according to manufacturing errors of the components such as a clutch disc, a clutch piston, or a piston case. The second one is that the clutch disc is worn, thereby varying the volume of the clutch chamber.

Fig. 10 is a graph for explaining the above description, and shows a situation in that the engine speed is lower. An elapsed time T when filling the clutch chamber 54 is plotted in the axis of abscissa, and volume V of the clutch chamber 54 is plotted in the axis of ordinates. In the graph, a line L represents pressure oil supply to the clutch chamber 54, the supply flow rate is larger in a line LA from engaging time 0 to time Ta, and smaller supply flow rate is shown in a solid line LB from the time Ta. The gradient of the solid line LB from the time Ta shows the increase ratio of supply rate of the pressure oil which does not cause a shock or a noise in the vehicle. The portion between the times Tb and Tc shows allowable engaging time when the engine speed is lower. The portion between the volumes Vb and Vc of the clutch chamber 54 shows variations of the volume of the clutch chamber 54. The clutch is assembled in the volume Vd between the variations Vb and Vc of the volume of the clutch chamber 54. It is difficult to match a point of completing the engagement of the clutch, that is, a completion point Ps of the solid line LB, to the volume Vd as well as to the allowable engaging times Tb to Tc. Specifically, it is followed by a difficulty to place the completion point Ps within the range between the points PA and PB of the solid line LC. In addition, even if the point PS temporally falls in a right place, when the clutch disc is worn out, the engaging time goes out of the range between the allowable engaging times Tb to Tc, which becomes a disadvantage.

Disclosure of the Invention

The present invention is made to eliminate the aforesaid disadvantages of the prior art, and its object is to provide a control device and a method for a transmission with a clutch by which adjustment is facilitated and a clutch is smoothly coupled without generating a shock, a noise caused by coupling the clutch, or the like in a vehicle even when the engine speed is low.

A first configuration of a control device for a transmission with a clutch according to the present invention is, in a transmission with a clutch which supplies oil from a hydraulic pump to a clutch chamber selected from a plurality of speed gears, moves a clutch piston in the selected clutch chamber, and which allows the clutch piston to press to engage a clutch to thereby transmit engine power by the selected speed gear, a control device for a transmission with a clutch supplying oil into the selected clutch chamber through a pressure control valve and a flow rate detecting valve of a clutch control valve, detecting that the selected clutch chamber is filled with oil by means of the flow rate detecting valve, and smoothly engaging the clutch by means of the pressure control valve on receiving a speed change command from a controller, characterized in that <ul id="ul0001" list-style="none" compact="compact"><li>the clutch chamber is supplied with oil from the hydraulic pump and has predetermined volume in which the clutch piston is moved, and</li><li>the controller <ul id="ul0002" list-style="none" compact="compact"><li>outputs a great trigger command value for a first predetermined period of time to supply a large flow rate initially and supplies a first predetermined quantity to the clutch chamber from the pressure control valve through the flow rate detecting valve, changes the great trigger command value to a smaller command value, supplies smaller flow rate than that at the time of the first predetermined quantity before the clutch piston completes its movement, and detects that the clutch chamber becomes full by means of the flow rate detecting valve, and</li><li>outputs to the pressure control valve a second predetermined period of time corrected by increasing or decreasing the first predetermined period of time so as to cause a period of time required for making the clutch chamber full to fall within a predetermined time, when the period of time from the time at which the speed change command is received until the clutch chamber becomes full does not fall within the predetermined time.</li></ul></li></ul>

According to the aforesaid configuration, a large quantity of oil is initially supplied to the clutch chamber having predetermined volume and an extremely small quantity of oil is supplied thereto by changing the quantity, before the clutch chamber becomes full, therefore the clutch can be engaged very smoothly. A shock occurring at the time of engagement or a noise made by engaging the clutch, which is propagated to the operator, is eliminated. In addition, even when an extremely small quantity of oil is supplied by changing the quantity, the quantity is changed from a large quantity to the extremely small quantity in accordance with the variation of the clutch volume, or the clutch volume changing according to the abrasion while being used, therefore the period of time required for engaging the clutch can be made fall within the predetermined time. Thereby, the operator doesn't feel a delay in engaging the clutch. Especially in a construction vehicle such as a wheel loader, in which tires are used and a shock, a noise, or the like occurring to the vehicle is easily propagated, the clutch is engaged with an extremely small quantity of oil , therefore the vehicle is smoothly started, and the speed is smoothly changed. Further, in the vehicle, the clutch can be smoothly coupled without generating a shock, a noise, or the like which is felt when the engine speed is lower. The period of time required for engaging the clutch is made to fall within a predetermined standardized time at predetermined intervals, automatically or by adjusting by the operator, therefore the clutch can be adjusted easily.

A second configuration of a control device for a transmission with a clutch according to the present invention is, in a transmission with a clutch which supplies oil from a hydraulic pump to a clutch chamber selected from a plurality of speed gears, moves a clutch piston in the selected clutch chamber, and which allows the clutch piston to press to engage the clutch to thereby transmit engine power by the selected speed gear, a control device for a transmission with a clutch supplying oil to the selected clutch chamber through a pressure control valve which receives a speed change command, and including a controller for controlling the pressure control valve to smoothly engage the clutch, characterized by including <ul id="ul0003" list-style="none" compact="compact"><li>a fullness detecting sensor for detecting that the clutch chamber is filled with pressure oil from pressure, and characterized in that</li><li>the clutch chamber is supplied with oil from the hydraulic pump and has predetermined volume in which the clutch piston is moved, and in that</li><li>the controller <ul id="ul0004" list-style="none" compact="compact"><li>passes a great trigger command value to the pressure control valve for a first predetermined period of time to supply a large flow rate initially and supplies a first predetermined quantity to the clutch chamber,</li><li>changes the great trigger command value to a smaller command value and supplies a smaller flow rate than that at the time of the first predetermined quantity to make the clutch chamber full, before the clutch piston completes its movement, and detects that the clutch chamber becomes full by means of the fullness detecting sensor, and</li><li>outputs to the pressure control valve a second predetermined period of time corrected by increasing or decreasing the first predetermined period of time so as to cause a period of time required for making the clutch chamber full to fall within a predetermined time, when the period of time from the time at which the speed change command is received until the clutch chamber becomes full does not fall within the predetermined time.</li></ul></li></ul>

According to the above configuration, the operational effects as in the aforesaid first configuration is obtained. Further, an ordinary pressure control valve and a pressure detector can be used.

A control method for a transmission with a clutch according to the present invention is <ul id="ul0005" list-style="none" compact="compact"><li>a control method for a transmission with a clutch which supplies oil from a hydraulic pump to a clutch chamber selected from a plurality of speed gears through a pressure control valve which receives a speed change command, moves a clutch piston in the selected clutch chamber, and which allows the clutch piston to press to engage a clutch to thereby transmit engine power by the selected speed gear, and is characterized by including the steps of</li><li>on supplying oil from the hydraulic pump, passing a great trigger command value to the flow control valve for a first predetermined period of time to initially flow a large flow rate to the clutch chamber having predetermined volume in which the clutch piston is moved,</li><li>changing the great trigger command value to a smaller command value and supplying smaller flow rate than that at the time of the trigger command value to make the clutch chamber full, before the clutch piston completes its movement, and</li><li>controlling a period of time required for making the clutch chamber full to fall within a predetermined time by increasing or decreasing the first predetermined period of time by a predetermined unit time when the period of time from the time at which the speed change command is outputted until the clutch chamber becomes full does not fall within the predetermined time.</li></ul>

According to the aforesaid method, the operational effects as in the first configuration of the aforesaid device is obtained.

Brief Description of the Drawings

<ul id="ul0006" list-style="none" compact="compact"><li>Fig. 1 is a schematic diagram of a control device for a transmission with a clutch according to an embodiment of the present invention;</li><li>Fig. 2 is a sectional view of a clutch hydraulic control valve according to the embodiment of the present invention;</li><li>Fig. 3 is a time chart of a command signal to the clutch hydraulic control valve in Fig. 2;</li><li>Fig. 4 is a flowchart of part of a control according to the embodiment of the present invention;</li><li>Fig. 5 is part of flowchart continued from Fig. 4;</li><li>Fig. 6 is another part of flow chart continued from Fig. 4;</li><li>Fig. 7 is a diagram showing the relationship between a clutch volume and a time required for engaging the clutch according to the embodiment of the present invention;</li><li>Fig. 8 is a sectional view of a clutch hydraulic control valve of the prior art;</li><li>Fig. 9 is a schematic diagram of a control device for a transmission with a clutch of the prior art; and</li><li>Fig. 10 is a diagram showing the relationship between the clutch volume and the time required for engaging the clutch to explain the disadvantages of the prior art.</li></ul>

Best Mode for Carrying out the Invention

A preferred embodiment of the present invention will now be described with reference to the attached drawings.

In Fig. 1, a control device 1 for a transmission with a clutch (hereinafter, called a control device 1) is mounted on a wheeled type of wheel loader having a working device which is not illustrated. The controller 1 includes a controller 2, a clutch hydraulic control valve 3, and a hydraulic pump 4. A signal from an accelerator lever 5 and a signal from a transmission lever 6 for selecting a forward or a reverse gear, or a speed gear of the transmission are inputted. The accelerator lever 5 and the transmission lever 6 are respectively provided with position sensors 5a and 6a.

In the aforesaid configuration, an operator sets the speed of an engine 7 by means of the accelerator lever 5, and makes a selection with the transmission lever 6 to run the wheel loader. At this time, in the control device 1, the clutch hydraulic control valve 3 is operated in response to a command from the controller 2, and the pressure oil from the hydraulic pump 4 is sent to a clutch chamber 8, thereby achieving smooth engagement without causing a shock or making a noise or the like to allow the wheel loader to travel with the clutch being smoothly coupled. The clutch includes a multiple disc clutch, which is pressed by a clutch piston 8A in the clutch chamber 8, slidably moved by receiving the pressure oil in the clutch chamber 8, and which is engaged when the pressure of the clutch chamber 8 is risen to predetermined pressure. The clutch chamber 8 has predetermined volume Vx (corresponding to the slashed portion shown by a symbol 8B) according to the movement of the piston 8A, from the time the piston 8A contacts the clutch by receiving the pressure oil from the hydraulic pump 4 until it presses the clutch and starts coupling.

In Figs. 1 and 2, the clutch hydraulic control valve 3 includes a pressure control valve 10 controlling the clutch oil pressure, a flow rate detecting valve 20 detecting the flow of the pressure oil flowing into the clutch chamber 8 from the hydraulic pump 4 through the pressure control valve 10 and the flow rate detecting valve 20, and a filling sensor 80A detecting the completion of filling. The pressure control valve 10 is controlled by the controller 2, and a detection signal from the filling sensor 80A is inputted into the controller 2. The pressure control valve 10, which is configured as in the prior art, includes a pressure control valve spool 61 (hereinafter, called a control valve spool 61), a piston 62, a proportional solenoid 63, and a first spring 64.

The flow rate detecting valve 20, which is configured as in the prior art, includes a flow rate detecting valve spool 21 (hereinafter, called a detecting valve spool 21), a second spring 72, and a third spring 73. Three of protruded portions are formed at the detecting valve spool 21, and these protruded portions divisively form a first oil chamber 22, a second oil chamber 23, and a third oil chamber 24. A hole 77 is provided in the protruded portion of the detecting valve spool 21 between the second oil chamber 23 and the third oil chamber 24. The detecting valve spool 21 has three different pressure receiving areas Aa, Ab, and Ac, as in the prior art, and allows these areas to have relationships, Aa + Ac &gt; Ab, and Ab &gt; Ac.

The filling sensor 80A includes a sensing pin 81, insulator 82, a first resistance Ra connected to the sensing pin 81, and a power source 85. The sensing pin 81 is attached at the body 90 with the insulator 82 between them in the position at which the sensing pin 81 is brought into contact with the right end portion of the detecting valve spool 21 when the detecting valve spool 21 is moved. Further, a lead wire 83 is extended from the sensing pin 81, and the lead wire 83 is connected to the first resistance Ra. Predetermined direct voltage is applied to the first resistance Ra, and the body 90 is grounded by a ground wire 84. According to the aforesaid configuration, when the detecting valve spool 21 is brought into contact with the sensing pin 81, current from the power source 85 flows through the first resistance Ra. The potential difference between the portions before and after the first resistance Ra is detected, thereby detecting that the clutch chamber 8 is filled.

Next, the difference between the configurations of the prior art and the embodiment of the present invention will be explained.

In the prior art, as described above, the pressure oil from the hydraulic pump 53 flows into the second oil chamber 75 of the detecting valve spool 71 through the pump port 91, the control valve spool 61, and the oil passage 67. The pressure oil flown into the second oil chamber 75 flows into the clutch chamber 54 through the hole 77 of the detecting valve spool 71, the third oil chamber 76, and the output port 92. At this time, the hole 77 causes differential pressure between the second oil chamber 75 and the third oil chamber 76, thereby moving the spool 71 in the leftward direction in the drawing. As a result, the first oil chamber 74 and the second oil chamber 75, which are closed to each other by the body 90, are opened to each other. The pressure oil from the hydraulic pump 53 then passes through the opened portion, merging with oil Ya from the aforesaid control valve spool 61, and flows into the clutch chamber 54 through the hole 77 of the detecting valve spool 71, the third oil chamber 76, and the output port 92. The pressure oil continues to flow until the clutch chamber 54 is filled. However, explaining with use of Figs. 8 and 9 of the prior art, in the present embodiment, the first oil chamber 74 and the second oil chamber 75 are closed to each other. Accordingly, oil in the prior art, which is "the pressure oil from the hydraulic pump 53, passing through the opened portion, merging with oil Ya from the aforesaid control valve spool 61, and flowing into the clutch chamber 54" doesn't exist. Specifically, the oil flow shown by the arrow Yb is eliminated.

Returning to Figs. 1 and 2 in the present embodiment, the pressure oil from the hydraulic pump 4 flows into the second oil chamber 23 of the detecting valve spool 21 through the pump port 91, the control valve spool 61, and the oil passage 67 (shown by the arrow Ya). The pressure oil flown into the second oil chamber 23 flows into the clutch chamber 8 through the hole 77 of the detecting valve spool 21, the third oil chamber 24, and the output pot 92. When the clutch chamber 8 is filled with oil, the filling is finished, and oil does not flow any more, therefore the differential pressure, which is caused by the hole 77 between the second oil chamber 23 and the third oil chamber 24, does not exist. Thereby, the detecting valve spool 21 is moved in the rightward direction to return to the neutral position, and further moved in the rightward direction as in the aforesaid prior art. From this movement, filling sensor 80A detects that the clutch chamber 8 is filled with oil and that the filling is completed as in the prior art.

As described above, as a result that the flow rate into the clutch chamber 8 is controlled by the control valve spool 61, the increase ratio in the supply rate of the pressure oil into the clutch chamber 8 from the hydraulic pump 4 has the gradient of a solid line LB from time Ta as shown in Fig. 7. Thereby, the clutch is smoothly engaged, and the wheel loader is allowed to travel with the clutch being smoothly coupled without generating a shock, a noise, or the like.

The controller 2 inputs signals from the accelerator lever 5 and the transmission lever 6, and outputs a command for supplying the clutch chamber 8 with the pressure oil from the hydraulic pump 4 to the clutch hydraulic control valve 3 for a forward or a reverse gear, or a speed gear of the transmission, which is selected by the operator with the transmission lever 6. As for a command from the controller 2, a command current I is outputted as shown in Fig. 3. In Fig. 3, time T is plotted in the axis of abscissa, and the command current I outputted by the controller 2 is plotted in the axis of ordinates. As for the symbols in Fig. 3, time Tf represents speed change command output time, the command current Ia from the time Tf to time Tg represents a trigger command value, the time ta from the time Tf to the time Tg, in which the command current is passed, represents trigger time, time Th represents filling completion time, and time tb from the time Tf to the time Th represents filling time.

The operation in the aforesaid configuration will be explained. Fig. 4 to Fig. 6 are flowcharts of a method for controlling the clutch hydraulic control valve 3 which within a predetermined period of time controls the period of time between when a command for engaging the clutch is issued and when the filling is finished. Fig. 7 is an explanatory diagram for engaging the clutch within a predetermined period of allowable time for engaging a clutch of the present embodiment, and the diagram corresponds to Fig. 10.

The following is an adjusting method to control the period of time taken to engage the clutch within a predetermined time in a situation in that the clutch chamber 8 has predetermined volume Vx, using the vehicle after it is assembled, or with the clutch disc being worn out. Here, the predetermined volume Vx = a clutch chamber area Ac × moving quantity Sx of the clutch piston.

In step 1, the controller 2 recognizes that the temperature of the oil of the transmission (the temperature of the oil for the torque converter when the oil of the torque converter is shared) falls within a range of a predetermined value. In step 2, when the operator sets the engine 7 at predetermined engine speed by manipulating the accelerator lever 5, the controller 2 recognizes the engine speed range. In step 3, the controller 2 reads a lower limit value Tq and an upper limit value Tr of the optimum set filling time corresponding to the oil temperature and the engine speed, which is previously stored with a map or the like, as the optimum set filling times Tq and Tr in this situation.

In step 4, the operator sends a signal of a selected speed gear of the transmission to the controller 2 by manipulating the transmission lever 6 (from the neutral gear N to the forward first speed gear F1, from the neutral gear N to the forward second speed gear F2, from the neutral gear N to the reverse gear R, or the like). In step 5, the controller 2 receives the selected signal from the transmission lever 6, issues a command to operate to the corresponding clutch hydraulic control valve 3 of the control device 1, and stores speed change command output time Tfa at which the command is outputted. Alternatively, the controller 2 starts to count the elapsed time from the speed change command output time Tfa at which it outputs the command. The command is outputted in accordance with the time chart in Fig. 3. In step 6, by a command in accordance with the time chart, the clutch hydraulic control valve 3 is switched, and the clutch hydraulic control valve 3 supplies the pressure oil from the hydraulic pump 4 to the clutch chamber 8.

Further explanation will be made with reference to Fig. 7. In the present embodiment, the controller 2 first outputs the trigger command value Ia of the current to the proportional solenoid 63 of the pressure control valve 10 of the clutch hydraulic control valve 3 for trigger time taa in terms of time. Thereby, the control valve spool 61 of the pressure control valve 10 is greatly moved in the leftward direction, and thereby the pressure oil from the hydraulic pump 4 flows into the clutch chamber 8 from a portion MA widely opened at the control valve spool 61 through the second oil chamber 23 of the detecting valve spool 21, the hole 77 of the detecting valve spool 21, and the third chamber 24, and the output port 92. The quantity flowing into the clutch chamber 8 is large since a gradient α of the increase ratio is great. This is the supply of the pressure oil to the clutch chamber 8 shown by the line LA in Fig. 7, in which larger quantity is supplied to the clutch chamber 8 from the speed change command output time Tfa (engaging time 0) to the time Ta, specifically, for the trigger time taa.

Next, when the trigger time taa has been elapsed, the controller 2 outputs a command value Ib from which the command current is subtracted to the proportional solenoid 63 of the pressure control valve 10. Thereby, the amount of the movement of the control valve spool 61, which has moved greatly in the leftward direction, is decreased. For this reason, the pressure oil from the hydraulic pump 4 flows into the clutch chamber 8 from a portion MB slightly opened at the control valve spool 61 through the second oil chamber 23 of the detecting valve spool 21, the hole 77 of the detecting valve spool 21, the third oil chamber 24, and the output port 92. The quantity flowing into the clutch chamber 8 is small since a gradient β of the increase ratio is small. This is the supply of the pressure oil to the clutch chamber 8 shown by the line LB in Fig. 7, which shows an increase ratio of the pressure oil supply which does not cause a shock or a noise in the vehicle.

The pressure oil fills the clutch chamber 8 (the situation represented by a point PS), the filling sensor 80A detects that filling completion time Tha has come, and a signal is sent to the controller 2. Incidentally, it is suitable to read the terminal value of the counted elapsed time from the speed change command output time Tfa, which has started in response to the command in step 5. The controller 2 may output a command value Ic from which command current is further subtracted at filling competion time Th of the clutch chamber 8. Thereafter, due to the engagement of the clutch, the pressure in the clutch chamber 8 is risen, thereby the clutch is smoothly engaged with less slippage.

Returning to the flow, in step 7, the controller 2 obtains the filling time tb based on the filling completion time Tha in step 6 and the speed change command output time Tfa in step 5. In step 8, it is determined whether the obtained filling time tb falls within a period of set filling time which is set in accordance with the temperature range and the engine speed range at a point in time when the speed is changed (from the lower limit value Tq to the upper limit value Tr) or not. Specifically, it is determined whether the filling time tb is in the lower limit value Tq of the set filling time ≦ the filling time tb ≦ the upper limit value Tr of the set filling time, or not. When the filling time tb falls within a period of time of the set filling time (from the lower limit value Tq to the upper limit value Tr), a command is given to go to step 9. In step 9, the controller 2 outputs the same command value to the proportional solenoid 63 of the pressure control valve 10 for the next speed change.

In step 8, when the filling time tb is greater than the upper limit value Tr of the set filling time, a command is given to go to step 10. In step 10, the controller 2 adds a trigger time Δ ta of a predetermined value to the trigger time taa of the previous time, and obtains new trigger time tab (= taa + Δ ta. In step 11, the controller 2 outputs the trigger command value Ia of current to the proportional solenoid 63 of the pressure control valve 10 with the new trigger time tab, and stores the time Tfb. In step 12, the clutch hydraulic control valve 3 is switched in response to a command of the new time chart, and as in step 6, the clutch hydraulic control valve 3 supplies the pressure oil from the hydraulic pump 4 to the clutch chamber 8. The filling sensor 80A detects the filling completion time Thb.

In step 13, the controller 2 obtains filling time tc from the filling completion time Thb in step 12 and the speed change command output time Tfb in step 11. In step 14, it is determined whether the obtained filling time tc is in tc ≦ the upper limit value Tr, or not. If it is not, a command is given to return to step 10, and step 10 to step 14 are repeated until tc ≦ the upper limit value Tr. In step 14, when tc ≦ Tr, a command is given to go to step 15, and the controller 2 stores the new time chart, and issues a command to the proportional solenoid 63 of the pressure control valve 10 in accordance therewith. Specifically, control is performed according to the new trigger time tab.

When the filling time tb &lt; the lower limit value Tq in step 8, a command is given to step 16, and the controller 2 obtains a new trigger time tac (= taa - Δ ta) by subtracting a trigger time Δ ta of a predetermined value from the previous trigger time taa. In step 17, the controller 2 outputs a trigger command value Ia of current to the proportional solenoid 63 of the pressure control valve 10 with the new trigger time tac, and stores time Tfc thereof. In step 18, the clutch hydraulic control valve 3 is switched in response to a command of a new time chart, and as in step 6, the clutch hydraulic control valve 3 supplies the pressure oil from the hydraulic pump 4 to the clutch chamber 8. The filling sensor 80A detects filling completion time Thc.

In step 19, the controller 2 obtains filling time td from the filling completion time Thc in step 18 and the speed change command output time Tfc in step 17. In step 20, it is determined whether the obtained filling time td is in td ≧ the lower limit value Tq, or not. If it is not, a command is given to return to step 16, and step 16 to step 20 are repeated until td ≧ Tq. When td ≧ Tq, a command is given to go to step 21, and the controller 2 stores the new time chart and issues a command to the proportional solenoid 63 of the pressure control valve 10 in accordance therewith. Specifically, control is performed according to the new trigger time tac.

According to the above, the filling time tb falls at the filling times tc and td between the lower limit value Tq and the upper limit value Tr of the set filling time, and the clutch is smoothly engaged without causing a shock, a noise, or the like, thereby allowing the wheel loader to travel with the clutch being smoothly coupled.

The above description shows an example in which the determination in step 8, specifically, the determination whether the measured filling time tb falls within a set period of filling time, is made only once. However, as is shown in steps 22 and 23, it is suitable to make the determination a plurality of times, and to give a command to go to step 10 or step 16 if each result is out of the period of set filling time at each of the plurality of times. Further, it is suitable to set the trigger time taa to output the trigger command value Ia in consideration of variations of the volume of the clutch chamber 8 when manufactured, if it is set after the vehicle is assembled. For example, it is suitable to collect the errors of the components and cause the filling completion time Th to fall within a period of set filling time Tq to Tr when the the volume is at the minimum. When the vehicle is used, or when the vehicle is used with the clutch disc being worn out, it is suitable to store the previous trigger time taa, and add the trigger time Δ ta of a predetermined value thereto.

In the above, the flow rate and the pressure are controlled by means of the pressure control valve 10, and the completion of filling the clutch chamber 8 is detected by means of the detecting valve spool 21 of the flow rate detecting valve 20, but as for the completion of filling the clutch chamber 8, it is suitable to detect a change of the pressure by means of a pressure sensor (fullness detecting sensor) 97 shown in Fig. 1. It is suitable to change the trigger time ta to output the trigger command value Ia by an operator with use of a reset lever 98 after predetermined time, and it is also suitable to make the above change by the operator with the reset lever 98 when he or she feels a delay in engaging the clutch. Further, it is suitable to automatically make the above change at predetermined time intervals in response to the command from the controller 2 irrespective of the operator.

Industrial Availability

The present invention is useful as a control device and a control method of a transmission with a clutch, which are easily adjusted and smoothly couple the clutch without causing a shock, a noise of clutch engaging, or the like in the vehicle, even when the engine speed is lower.