JP4673338B2 - Shift control device for hydraulic transmission - Google Patents

Description

  According to the present invention, in a work vehicle in which a first hydraulic transmission and a second hydraulic transmission, each of which performs transmission by selective engagement of a plurality of hydraulic clutches, are provided in series, The present invention relates to a control device that controls the operation of a hydraulic clutch at the time of gear shift switching of the transmission.

  In a work vehicle in which a first hydraulic transmission and a second hydraulic transmission, each of which performs transmission by selective engagement of a plurality of hydraulic clutches, are connected in series, the first and second hydraulic transmissions are provided. The number of gears obtained by the transmission is the number of gears obtained by multiplying the number of gears of the first hydraulic transmission and the number of gears of the second hydraulic transmission, and such a multi-stage gear shift can be performed by a switching valve that is easy to operate. It will be possible.

  By the way, when shifting operations of both hydraulic transmissions, there are a case where one hydraulic clutch is engaged and a case where two hydraulic clutches are engaged depending on the gear stage before the shift and the gear stage after the shift. is there. That is, according to the shift stage before and after the shift, the engaged hydraulic clutch of the first or second hydraulic transmission is kept engaged, and the engaged hydraulic clutch of the other hydraulic transmission is disconnected. In the case of engaging the hydraulic clutch and in both the first hydraulic transmission and the second hydraulic transmission, the engaged hydraulic clutch is disconnected and a new hydraulic clutch is engaged, that is, the two hydraulic clutches are connected. There is a case where it is interrupted. The time until the hydraulic oil is filled with the hydraulic clutch to be engaged from a single hydraulic pump is longer when two hydraulic clutches are engaged than when only one hydraulic clutch is engaged. It takes a long time. Accordingly, the increase in the hydraulic pressure after the hydraulic oil is filled is slower when the two hydraulic clutches are engaged than when only one hydraulic clutch is engaged.

A control method that compensates for such a time difference required for filling hydraulic oil to the hydraulic clutch has not yet been provided. Although a technique for gradually increasing the hydraulic pressure of the hydraulic oil supplied to the hydraulic clutch from the time when the engagement command for the hydraulic clutch is applied is well known, this technique does not solve the problem of the time difference required to fill the hydraulic oil. Therefore, until now, poor transmission feeling based on the time difference has been overlooked.
JP-A-8-20257

  Therefore, the main object of the present invention is to solve the problem of the time difference required for filling the hydraulic clutch with hydraulic oil when engaging only one hydraulic clutch and when engaging two hydraulic clutches during the shifting operation. Accordingly, it is an object of the present invention to provide a novel shift control method and control apparatus that improve the shift feeling despite this time difference.

Means for solving the problems of the present invention are as follows.
In claim 1, a first hydraulic transmission (17) and a second hydraulic transmission (20), each of which performs transmission by selective engagement of a plurality of hydraulic clutches, are connected in series. In a certain work vehicle, a plurality of electromagnetic switching valves (VL, VM,...) That are connected to the hydraulic clutches (57, 58, 59, 66, 67, 68), respectively, and control the supply and discharge of hydraulic oil to and from the hydraulic clutches. VH, V1, V2, V3; VAL, VAM, VAH, VA1, VA2, VA3) and operation control means (80, 85) for selectively giving an engagement command and a disconnection command to each of the electromagnetic switching valves. , 86) and pressure control means (VL, VM, VH, V1, V2, etc.) for gradually increasing the hydraulic pressure of the hydraulic oil supplied to the hydraulic clutch over time from the time when the engagement command is given to the electromagnetic switching valve. V3,8 110), and a disconnection command for the electromagnetic switching valve connected to the hydraulic clutch that is disconnected from the point of time when the engagement command for the electromagnetic switching valve connected to the hydraulic clutch to be engaged is applied to the operation control means. set the time interval between the time of grant s interval setting means (88, 90) set only the in the time s interval setting means (88, 90), the time when to Nyudan the hydraulic clutch of one addressed s A time setting circuit (90) is provided for setting the time interval relatively long and setting the time interval relatively long when the two hydraulic clutches are engaged and disengaged .

According to a second aspect of the present invention, the time setting circuit (90) sets the time interval when shifting up relatively long and sets the time interval when shifting down relatively short .

According to a third aspect of the present invention, the time interval set in the time interval setting means (88, 90) is determined from the application time point (t0) of the engagement command to the electromagnetic switching valve connected to the hydraulic clutch to be engaged. The clutch is filled with oil, and the working oil pressure for the hydraulic clutch is greater than the time interval until the point (ta) at which the oil pressure increases to the piston holding pressure (pa).

In claim 4, a first hydraulic transmission (17) and a second hydraulic transmission (20) , each of which performs transmission by selective engagement of a plurality of hydraulic clutches , are connected in series. In a certain work vehicle, a plurality of electromagnetic switching valves (VL, VM,...) That are connected to the hydraulic clutches (57, 58, 59, 66, 67, 68), respectively, and control the supply and discharge of hydraulic oil to and from the hydraulic clutches. VH, V1, V2, V3; VAL, VAM, VAH, VA1, VA2, VA3) and operation control means (80, 85) for selectively giving an engagement command and a disconnection command to each of the electromagnetic switching valves. , 86) and pressure control means (VL, VM, VH, V1, V2, etc.) for gradually increasing the hydraulic pressure of the hydraulic oil supplied to the hydraulic clutch over time from the time when the engagement command is given to the electromagnetic switching valve. V3,8 110), and provided with pressure setting means (Va, 89; 111) for setting a lowering characteristic of the working oil pressure after the disengagement command is given to the hydraulic clutch to be disengaged in the operation control means, The means (Va, 89; 111) reduces the lowering of the working hydraulic pressure with respect to the hydraulic clutch to be disconnected when the two hydraulic clutches are engaged / disengaged than when the one hydraulic clutch is engaged / disengaged. Be gentle .

In claim 5, wherein the pressure setting means (Va, 89; 111) is a reduction of the working oil pressure for the hydraulic clutch to be cut, thereby variably slowly performed.

In claim 6, the pressure setting means (Va, 89; 111) is a reduction of the working oil pressure for the hydraulic clutch to be cut more slowly made so that the person at the time of shift-down than during upshift.

In claim 7, the pressure setting means (Va, 89; 111) is a reduction of the working oil pressure for the hydraulic clutch to be disconnected, the relatively gently done so in a low speed rotating state than the rated rotation state of the engine .

In claim 8, wherein the pressure setting means (Va, 89; 111) is a reduction of the working oil pressure for the hydraulic clutch to be cut, than slowly performed so that as the rotational speed is low according to the rotational speed of the engine.

In claim 9 , the pressure setting means (Va, 89; 111) compares the detected value of the tachometer (83) for detecting the engine speed with the rated engine speed, and is cut off. A pressure setting circuit (89) for setting a lowering characteristic of the working hydraulic pressure with respect to the clutch is provided.

In the claims 10, wherein the electromagnetic switching valve, the electromagnetic proportional selector valve which also serves as a pressure control means (VL, VM, VH, V1 , V2, V3) and that.

  The transmission control device for a hydraulic transmission according to the present invention includes a first hydraulic transmission (17) and a second hydraulic transmission (20) that perform transmission by selective engagement of a plurality of hydraulic clutches. In a work vehicle connected in series, a plurality of electromagnetics connected to the hydraulic clutches (57, 58, 59, 66, 67, 68) and controlling supply / discharge of hydraulic oil to / from the hydraulic clutches. Switching valve (VL, VM, VH, V1, V2, V3; VAL, VAM, VAH, VA1, VA2, VA3), an operation for selectively giving an engagement command and a disconnection command to each of the electromagnetic switching valves Control means (80, 85, 86) and pressure control means (VL, VM, etc.) for gradually increasing the hydraulic pressure of the hydraulic oil supplied to the hydraulic clutch over time from the time when the engagement command is given to the electromagnetic switching valve. VH V1, V2, V3, 87; 110), and is connected to the hydraulic clutch that is disconnected from the application control means when the engagement command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be engaged. Time interval setting means (88, 90) for setting the interval until the application time of the disconnection command for the electromagnetic switching valve, or pressure setting for setting the lowering characteristic of the working oil pressure after the disconnection command is applied to the hydraulic clutch to be disconnected At least one of the means (Va, 89; 111) is provided.

When the engagement command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be engaged with the operation control means (80, 85, 86) that selectively applies the engagement command and the disconnection command to each of the electromagnetic switching valves. According to the configuration in which the time interval setting means (88, 90) for setting the interval until the application time of the disconnection command to the electromagnetic switching valve connected to the hydraulic clutch to be disconnected is provided by this time interval setting means For example, the time interval when the hydraulic clutch addressed to one is engaged is set relatively short, and the time interval when the hydraulic clutch addressed to two is engaged is set relatively long, As described above, the shift control method of the present invention can be implemented.
Further, the operation control means (80, 85, 86) is provided with pressure setting means (Va, 89; 111) for setting a lowering characteristic of the working hydraulic pressure after giving a disconnection command to the hydraulic clutch to be disconnected. For example, this pressure setting means, for example, lowers the working oil pressure for the hydraulic clutch to be disconnected more slowly when the two hydraulic clutches are engaged / disconnected than when the one hydraulic clutch is engaged / disengaged. The shift control method of the present invention can be implemented as described above.
If both the time interval setting means (88, 90) and the pressure setting means (Va, 89; 111) are provided, various controls can be performed as shown in the embodiments described later.

  When providing the time interval setting means (88, 90), the time for setting the time interval at the time of upshifting relatively long and setting the time interval at the time of downshifting relatively short when the time interval setting means (88, 90) is provided. A setting circuit (90) is preferably provided. Further, when the pressure setting means (Va, 89; 111) is provided, the means is configured to cause the working hydraulic pressure to be lowered with respect to the hydraulic clutch to be disconnected more slowly during the downshift than during the upshift. It is preferable to do this. According to such a configuration, the region where the hydraulic clutches to be engaged and disengaged in common are slip-engaged can be made smaller at the time of downshifting than at the time of upshifting, and energy efficiency can be improved as described above.

  It is preferable that the pressure setting means (Va, 89; 111) causes the hydraulic pressure of the hydraulic clutch to be cut to decrease relatively slowly in the low-speed rotation state than in the rated rotation state of the engine. That is, when the engine is running at a low speed, the number of revolutions of the hydraulic pump decreases and the discharge flow rate of the pump decreases. Therefore, it takes a long time to fill the hydraulic clutch with oil. It is compensated by the inflow.

  More generally, it is preferable that the pressure setting means (Va, 89; 111) lowers the working hydraulic pressure with respect to the hydraulic clutch to be disconnected more gradually as the rotational speed is lower according to the rotational speed of the engine. . Such pressure setting means (Va, 89; 111) compares the detected value of the tachometer (83) for detecting the engine speed with the rated engine speed, and acts on the hydraulic clutch to be disconnected. A pressure setting circuit (89) for setting the lowering characteristic can be configured.

  The electromagnetic switching valve is preferably configured as an electromagnetic proportional switching valve (VL, VM, VH, V1, V2, V3) that also serves as the pressure control means. At this time, it is not necessary to provide pressure control means for gradually increasing the hydraulic pressure by arranging the individual hydraulic clutches.

  Other features and advantages of the present invention can be clearly understood from the following description with reference to the accompanying drawings.

  FIG. 1 shows a transmission mechanism of a tractor equipped with an embodiment of the present invention. A driving shaft 12 connected to an engine 10 mounted on the foremost portion of the tractor body via a buffer joint 11 is provided at the front portion of the body. From the driving shaft 12, a traveling transmission mechanism and a PTO transmission mechanism are provided. And have been branched.

  The traveling transmission mechanism includes a hydraulic forward / reverse switching device 14 provided between the drive shaft 12 and the output shaft 13 below the first drive connected to the output shaft 13 disposed on an extension line of the output shaft 13. A first hydraulic transmission 17 provided between the shaft 15 and a hollow first transmission shaft 16 disposed on an extension line of the driving shaft 12, and an extension line of the first transmission shaft 16 disposed on the first transmission shaft 16. A second hydraulic transmission device 20 provided between a hollow second drive shaft 18 connected to the second drive shaft 18 and a second transmission shaft 19 disposed on an extension line of the first drive shaft 15, and an extension line thereof. And a mechanical transmission 23 including a hollow intermediate shaft 21 disposed on an extension line of the second drive shaft 18. The mechanical transmission 23 is provided between the propeller shaft 22 and the propeller shaft 22. A small bevel gear 24 is formed at the rear end of the propeller shaft 22, and this small bevel gear 24 is meshed with a large input bevel gear 26 of a differential device 25 for left and right rear wheels. The left and right output shafts 27 of the differential device 25 are connected to the left and right rear wheels 30 via the left and right brakes 28 and the planetary gear type speed reducer 29. A differential lock clutch 31 is provided on the output shaft 27 on one side. It is provided.

  In addition to the two-wheel drive of the left and right rear wheels 30 by the transmission mechanism described above, the vehicle can be driven by a four-wheel drive by selectively driving the left and right front wheels (not shown). That is, two gears 36 that are rotationally driven from two gears 34 and 35 that rotate integrally on the intermediate shaft 33 from a gear 32 for taking out the front wheel driving force on the propeller shaft 22. 37 is installed loosely on the front wheel driving force take-out shaft 38. The front wheel driving force take-out shaft 38 is connected in the front wheel direction (not shown), and a hydraulic clutch mechanism 39 for selectively coupling the gears 36 and 37 to the take-out shaft 38 is provided on the front wheel driving force take-out shaft 38. It is provided. When the gear 37 is coupled to the front wheel driving force take-out shaft 38, the front wheel is driven at a speed synchronized with the rear wheel 30, and when the gear 36 is coupled, the front wheel is driven at a higher speed than the rear wheel 30.

  The PTO transmission mechanism includes a transmission shaft 40 connected to the rear end of the drive shaft 12 and penetrating through the hollow first transmission shaft 16, the second drive shaft 18 and the intermediate shaft 21, and the rear end of the transmission shaft 40. A transmission shaft 41 connected to the transmission shaft 41, a transmission shaft 43 arranged on an extension line of the transmission shaft 41 and connected to the transmission shaft 41 via a hydraulic PTO clutch 42, and parallel to the transmission shaft 43 and extending out of the tractor body A PTO shaft 44 and a mechanical PTO transmission 45 provided between the transmission shaft 43 and the PTO shaft 44 are provided. A power take-out shaft 49 is provided that is driven from the transmission shaft 41 through gear trains 46, 47, and 48. Depending on the power take-out shaft 49, the hydraulic pump 50 is driven.

  The first hydraulic transmission 17 in the traveling transmission mechanism includes three gears 51, 52, 53 that are loosely installed on the first drive shaft 15 and three gears that are fixedly installed on the first transmission shaft 16. The corresponding ones of 54, 55, and 56 are meshed with each other, and the gears 51, 52, and 53 are alternatively connected to the first drive shaft by three hydraulic clutches 57, 58, and 59 provided on the first drive shaft 15. 15 to obtain a three-stage shift. The second hydraulic transmission device 20 in the traveling transmission mechanism includes three gears 60, 61, 62 fixed on the second drive shaft 18 and three loosely installed on the second transmission shaft 19. The corresponding gears 63, 64, 65 are meshed with each other, and the gears 63, 64, 65 are alternatively shifted by the three hydraulic clutches 66, 67, 68 provided on the second transmission shaft 19. It is configured to be coupled to the shaft 19 to obtain a three-stage shift. Therefore, by operating the hydraulic clutches 57, 58 to 59 addressed to one of the first hydraulic transmission 17 and the hydraulic clutches 66, 67 to 68 addressed to one of the second hydraulic transmission 20, a total of 9 stages are achieved. Can be obtained.

The gear ratio of the meshed gears in the first and second hydraulic transmissions 17 and 20 is based on the alternative operation of the hydraulic clutches 57, 58, 59 and the alternative operation of the hydraulic clutches 66, 67, 68. Thus, the gear ratio of 1-9 speed shown in Table 1 is set.

  FIG. 2 shows a hydraulic circuit for operating the hydraulic clutches 57, 58, 59 of the first hydraulic transmission 17 and the hydraulic clutches 66, 67, 68 of the second hydraulic transmission 20. The six hydraulic clutches of the first and second hydraulic transmissions 17 and 20 are connected to an oil supply circuit 70 for supplying hydraulic hydraulic oil set by a pressure regulating valve 69 by the hydraulic pump 50 shown in FIG. Six electromagnetic proportional switching valves VL, VM, VH and V1, V2, V3 connected to 57, 58, 59 and 66, 67, 68, respectively, are provided. Each electromagnetic proportional switching valve VL, VM, VH, V1, V2, V3 is configured as a two-position valve having a neutral position and an operating position as shown in the figure, and solenoids L, M, H, 1, 2, 3 It is displaced from the neutral position to the working position by excitation. A pressure sensor 71 is connected to a connection circuit between each electromagnetic proportional switching valve VL, VM, VH, V1, V2, V3 and each hydraulic clutch 57, 58, 59, 66, 67, 68. A secondary pressure regulating valve 72 for setting lubricating oil pressure is connected to the oil discharge side of the pressure regulating valve 69, and a lubricating oil circuit 73 is led out between the pressure regulating valves 69, 72, and the hydraulic clutches 57, 58, 59, 66, 67. , 68 is supplied with lubricating oil.

  Note that a line filter 76 and a relief valve 77 as a bypass valve are inserted in parallel with each other in an oil suction circuit 75 extending from the oil tank 74 to the hydraulic pump 50. The relief valve 77 performs a relief operation when the line filter 76 is clogged, and keeps the oil flow to the hydraulic pump 50. As shown in FIG. 1, the hydraulic forward / reverse switching device 14 has a forward hydraulic clutch 14F and a reverse hydraulic clutch 14R. These hydraulic clutches 14F and 14R are driven by a hydraulic pump 78 driven by the driving shaft 12. The oil suction circuit 79 connected to the hydraulic pump 78 is connected to the oil suction circuit 75 as shown in FIG.

  FIG. 3 is a block diagram showing an electric control circuit for controlling the operation of the electromagnetic proportional switching valves VL, VM, VH, V1, V2 and V3. A logic circuit 80 is provided. On the input side of the logic circuit 80, the lever angle and the rotation direction of the shift lever 81 that is rotated to the 1st speed position-9th speed position 1-9 as shown in the figure are detected. A potentiometer 82, a tachometer 83 for detecting the number of revolutions of the engine 10 (FIG. 1), a road traveling / working changeover switch 84, and six pressure sensors 71 (FIG. 2) are connected. A solenoid drive circuit 85 for driving the solenoids L, M, H, 1, 2, 3 of the electromagnetic proportional switching valves VL, VM, VH, V1, V2, V3 in the excitation direction and a solenoid drive circuit 86 for driving in the demagnetization direction; Is provided. First, the output side of the logic circuit 80 is directly connected to the solenoid drive circuit 85 via a pressure setting circuit 87 for setting the hydraulic pressure increase patterns of the electromagnetic proportional switching valves VL, VM, VH, V1, V2, and V3. It is connected. The output side of the logic circuit 80 is also connected to the solenoid drive circuit 86 via a delay circuit 88 and a pressure setting circuit for setting the hydraulic pressure drop pattern of the electromagnetic proportional switching valves VL, VM, VH, V1, V2, V3. The delay circuit 88 is connected to the delay circuit 88 via the time setting circuit 90.

  As shown in FIG. 4, the electromagnetic proportional switching valves VL, VM, VH, V1, V2, and V3 are actuated from the time point t0 when the ON signal is applied to the solenoids L, M, H, 1, 2, and 3, respectively. Control is performed so as to gradually increase the hydraulic pressure p to the normal hydraulic pressure p1. In FIG. 4, time ta is the time when the oil chamber of the hydraulic clutch is filled with oil and the hydraulic pressure p rises to the piston holding pressure pa. At this time point ta, the hydraulic pressure p rapidly rises to a corresponding value on a relatively gentle rise waveform a set in advance, and then rises along the rise waveform a until time point tb. The oil pressure at the time point tb is a value at which the hydraulic clutch is completely engaged, and thereafter, the oil pressure p is raised to the normal oil pressure p1 along a relatively steep rise waveform b in preparation for an unexpected situation. In FIG. 4, curve C1 is for road driving, curve C2 is for work, and during work with a large travel load, the initial oil pressure at time t0 and the oil pressure at time tb shown by the broken lines are low in travel load. It is set higher than that when driving on the road. The logic circuit 80 shown in FIG. 3 indicates a signal indicating the position after the shift of the speed change lever 81 detected by the potentiometer 82 and whether the traveling mode or working mode is detected by the road / work switching switch 84. A signal is applied to the solenoid drive circuit 85, and the latter signal is applied to the pressure setting circuit 87, and a hydraulic pressure increase curve is set by the circuit 87 to be applied to the solenoid drive circuit 85. The solenoid drive circuit 85 corresponds. The solenoid L, M, H, 1, 2 or 3 is driven.

  Each electromagnetic proportional switching valve VL, VM, VH, V1, V2, V3 corresponds from time t0 when an OFF signal is given to the solenoid L, M, H, 1, 2, 3 as illustrated in FIG. Control is performed so that the working oil pressure of the hydraulic clutch to be lowered from the normal oil pressure p1 to zero. This decrease in the hydraulic pressure is caused by rapidly decreasing the hydraulic pressure p to a certain value as illustrated by the curves C2 and C3, as well as when the hydraulic pressure p is rapidly decreased to the piston holding pressure pa or lower as shown by the curve C1. After the fact, it includes the case of a relatively slow decline. In order to gradually reduce the hydraulic pressure, variable throttles in the electromagnetic proportional switching valves VL, VM, VH, V1, V2, and V3 are used. In FIG. 2, the variable throttle is taken out of the electromagnetic proportional switching valve and indicated by reference numeral Va. The logic circuit 80 shown in FIG. 3 gives a signal indicating the position before the shift at the time of shifting the shift lever 81 detected by the potentiometer 82 to the solenoid drive circuit 86, and also sends a curve determination signal to the pressure setting circuit according to the logic described later. Is applied to 89 and a hydraulic pressure drop curve is set by the circuit 89 and applied to the solenoid drive circuit 86, and the solenoid drive circuit 86 drives the corresponding solenoid L, M, H, 1, 2 or 3.

  When shifting operation of the first and second hydraulic transmissions 17 and 20 by the transmission lever 81 shown in FIG. 3, as can be seen from Table 1 above, the first or second hydraulic transmission 17 or When one hydraulic clutch of only 20 is newly operated and one hydraulic clutch being operated is disengaged, one hydraulic clutch addressed to one of the first and second hydraulic transmissions 17 and 20 is newly operated. There is a case where the hydraulic clutch addressed to one in operation is disconnected. In the former case, for example, in order to shift up from the third speed to the fifth speed, in the first hydraulic transmission 17, the hydraulic clutch 58 of the second hydraulic transmission 20 is operated by continuing the operation of the hydraulic clutch 58. In order to shift down from the 6th speed to the 4th speed, the second hydraulic transmission 20 continues to operate the hydraulic clutch 67 as it is, and the operation is performed such that the hydraulic clutch 66 that is newly operated is operated. The operation is such that the hydraulic clutch 57 of the one-hydraulic transmission 17 is newly operated and the hydraulic clutch 59 in operation is disengaged. In the latter case, for example, in order to shift up from the second speed to the sixth speed, the hydraulic clutch 59 of the first hydraulic transmission 17 and the hydraulic clutch 67 of the second hydraulic transmission 20 are newly operated. An operation is performed such as disengaging the hydraulic clutch 58 of the first hydraulic transmission 17 and the hydraulic clutch 66 of the second hydraulic transmission 20, and the first hydraulic transmission is used to shift down from the 9th gear to the 5th gear. The hydraulic clutch 58 of the device 17 and the hydraulic clutch 67 of the second hydraulic transmission 20 are newly operated to disconnect the hydraulic clutch 59 of the first hydraulic transmission 17 and the hydraulic clutch 68 of the second hydraulic transmission 20. Will be operated. As described above, when only one hydraulic clutch is newly operated and when two hydraulic clutches are newly operated, the time required for the oil chamber of the hydraulic clutch to be filled with oil is the latter. Almost doubles. Therefore, the present invention tries to divide the hydraulic control that compensates for this time difference into four cases: up-shifting and down-shifting at the rated engine speed, up-shifting and down-shifting at a low engine speed. Is.

FIG. 6 shows a hydraulic control mode at the time of upshifting in the engine rated speed state. The tachometer 83 shown in FIG. 3 inputs to the logic circuit 80 that the engine is in the rated rotation state. Further, the potentiometer 82 inputs the position of the shift lever 81 before and after the up-shifting to the logic circuit 80, and whether the logic circuit 80 newly operates only one hydraulic clutch or two hydraulic clutches. judge. The upper graph in FIG. 6 shows a control mode when only one hydraulic clutch is newly operated. Therefore, only one hydraulic clutch is disengaged and the other one operating hydraulic clutch has the normal hydraulic pressure p1. It continues to act as it is. The working oil pressure p of the hydraulic clutch to be cut is rapidly lowered to the piston holding pressure pa or less, and this oil pressure lowering curve is set by the pressure setting circuit 89 shown in FIG.
The lower graph in FIG. 6 shows a control mode in the case where two hydraulic clutches are newly operated. Therefore, the working hydraulic pressure p of the two hydraulic clutches is lowered. This decrease in hydraulic pressure is also performed along a rapid decrease curve set by the pressure setting circuit 89 in FIG. The hydraulic pressure increase curve is exactly the same when only one hydraulic clutch is newly operated (upper graph in FIG. 6) and when two hydraulic clutches are newly operated (lower graph in FIG. 6). And is set by the pressure setting circuit 87 shown in FIG.

  When operating only one hydraulic clutch and disconnecting one hydraulic clutch (upper graph in FIG. 6), when operating two hydraulic clutches and disconnecting two hydraulic clutches (lower side in FIG. 6) The graph) also shows the hydraulic clutch that has been operating until the time when the engagement command is applied to the hydraulic clutch to be newly operated (the ON signal is applied to the solenoid L, M, H, 1, 2, or 3) t0. The cutting command application time point (off signal application time point to solenoid L, M, H, 1, 2, or 3) ts is delayed by a certain time. This time is set by the time setting circuit 90 according to the output signal of the logic circuit 80 shown in FIG. 3, and is obtained by delaying the solenoid driving time point applied to the solenoid driving circuit 86 by the delay circuit 88 by a predetermined amount. It is done. Then, as shown in the graph of FIG. 6, when two hydraulic clutches are operated and two hydraulic clutches are disconnected from the delay time Δt1 when only one hydraulic clutch is operated and one hydraulic clutch is disconnected. The delay time Δt2 is increased by approximately the time difference corresponding to the time difference between the time when one hydraulic clutch to be newly filled is filled with oil and the time when two hydraulic clutches are filled with oil. .

  Accordingly, a newly actuated region (upper graph) in which one hydraulic clutch to be newly operated and one hydraulic clutch that has been operated so far are slip-engaged in common with hatching in FIG. The area (lower graph) in which the two hydraulic clutches and the two hydraulic clutches that have been operated in common are slip-engaged is made substantially equal in area. The common slip engagement region or the area thereof is selected so that the shift of the shift stage is performed most smoothly, both when the hydraulic clutch addressed to one is turned on and off and when the hydraulic clutch addressed to two is turned on and off. The shift feeling is good without being influenced by the capacity of the hydraulic pump 50.

  FIG. 7 shows a hydraulic control mode at the time of downshifting in the engine rated speed state. The upper graph shows the hydraulic control mode when only one hydraulic clutch is operated and one hydraulic clutch is disconnected, and the lower graph is when two hydraulic clutches are operated and two hydraulic clutches are disconnected. The hydraulic control mode is shown. The hydraulic control in this case is basically the same as in the case of FIG. 6, and the time point ts at which the working hydraulic pressure decreases along the rapid decrease curve set by the pressure setting circuit 89 in FIG. When the hydraulic clutch addressed to one is turned on / off from the hydraulic oil supply start time t0, it is delayed by a time interval Δt1 ′, and when the hydraulic clutch addressed to two is turned on / off, the time interval Δt2 ′ is longer. An area (upper graph) in which one newly engaged hydraulic clutch and one previously operated hydraulic clutch are slip-engaged with a delay, and are hatched in FIG. The areas of the two hydraulic clutches operated in the same manner and the region (lower graph) in which the two hydraulic clutches operated so far are slip-engaged in common are made substantially equal.

  However, the time intervals Δt1 ′ and Δt2 ′ shown in FIG. 7 are smaller than the time intervals Δt1 and Δt2 shown in FIG. That is, the delay times Δt1 ′ and Δt2 ′ set by the time setting circuit 90 by the downshift signal input by the logic circuit 80 in FIG. 3 are made shorter than the delay times Δt1 and Δt2 set by the setting circuit 90 at the time of upshifting. -ing This is in consideration of inertia when the vehicle travels, and since the energy required to decelerate is smaller than the energy required to accelerate the traveling vehicle, it is newly engaged. The energy efficiency is improved by actively reducing the area where the hydraulic clutch and the hydraulic clutch to be disconnected are slip-engaged at the time of deceleration.

  In the control shown in FIGS. 6 and 7, the time intervals Δt1, Δt2, Δt1 ′, Δt2 ′ are changed from the time t0 when the engagement command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be engaged to the hydraulic clutch. Is greater than the time interval until time ta when the working oil pressure with respect to the hydraulic clutch rises to the piston holding pressure pa, thereby facilitating control.

  FIG. 8 shows a hydraulic control mode at the time of upshifting in the engine low-speed rotation state (a state in which the engine rotates at an idling rotation or a rotational speed close thereto). Therefore, the tachometer 83 shown in FIG. 3 inputs to the logic circuit 80 that the engine is in a low speed rotation state. The upper graph in FIG. 8 shows the hydraulic control mode when only one hydraulic clutch is operated and one hydraulic clutch is disengaged, and the lower graph is operated when two hydraulic clutches are operated and two hydraulic clutches are operated. The hydraulic control mode when turning off is shown. As in the case of FIG. 6, the hydraulic control in this case is also the time point when the hydraulic pressure of the hydraulic clutch to be disconnected is lowered (disconnection command application time point) ts, when the hydraulic oil supply start time to the new hydraulic clutch starts or the engagement command application time point. When the hydraulic clutch addressed to one is turned on and off, the time delay is delayed by Δt1, and when the hydraulic clutch addressed to two is turned on and off, the time delay is delayed by Δt2. However, in the hydraulic control in FIG. 8, the variable throttle Va in each of the electromagnetic proportional switching valves VL, VM, VH, V1, V2, and V3 is used, and the hydraulic pressure of the hydraulic clutch to be disconnected is rapidly increased to a certain value. After the fact, it is gradually lowered.

  That is, as apparent from the comparison of the graph of FIG. 8 with the graph of FIG. 6, in the case of FIG. 8, the time required for the hydraulic clutch to fill with oil due to the low speed rotation of the hydraulic pump 50 corresponding to the low speed rotation of the engine. In order to compensate for this long time, the hydraulic pressure reduction curve set by the pressure setting circuit 89 in FIG. The area of the slip engagement common to the hydraulic clutches to be secured is almost equal to the case of FIG. Then, when the two hydraulic clutches are turned on and off (the lower side in FIG. 8), the decrease in the hydraulic pressure is made slower than when the one hydraulic clutch is turned on and off (the upper side in FIG. 8). The area of the slip-engaged area of the hydraulic clutch to be newly engaged and the hydraulic clutch to be disconnected is made approximately equal between the case where the hydraulic clutch destined for the individual is turned on and off and the case where the hydraulic clutch destined for the second is engaged. ing.

  FIG. 9 shows a hydraulic control mode at the time of downshifting in the engine low speed rotation state. The upper graph shows the hydraulic control mode when only one hydraulic clutch is operated and one hydraulic clutch is disconnected, and the lower graph is when two hydraulic clutches are operated and two hydraulic clutches are disconnected. The hydraulic control mode is shown. The hydraulic control in this case is basically the same as in the case of FIG. 8, and it is assumed that the hydraulic pressure decrease curve of the hydraulic clutch to be disconnected can be moderately reduced, and the oil filling time for the newly operated hydraulic clutch is long. Dealing with becoming. Similarly to the case of FIG. 7, the delay times .DELTA.t1 'and .DELTA.t2' set by the time setting circuit 90 by the downshift signal input by the logic circuit 80 of FIG. The energy efficiency is improved by making it shorter than Δt1 and Δt2.

  As shown in FIG. 2, the hydraulic pressure in the connection circuit between each electromagnetic proportional switching valve VL, VM, VH, V1, V2, V3 and each hydraulic clutch 57, 58, 59, 66, 67, 68 is detected. As shown, the six pressure sensors 71 connected to the input side of the logic circuit 80 are connected to the hydraulic clutch for a predetermined time or longer due to a hydraulic system trouble after the pressure of the hydraulic clutch to be disconnected receives a disconnection command. If the pressure value continues to be higher than the pressure value corresponding to the allowable absorption energy value of the friction plate lining, the solenoids L, M, H, 1, of all the electromagnetic proportional switching valves are operated by the logic circuit 80 and the solenoid drive circuits 85, 86. The engagement command for 2 and 3 is refused to prevent abnormal double meshing, and the gears and hydraulic clutch are prevented from being damaged.

  1, the forward / reverse switching device 14 is provided with a reverse gear train 92 including a forward gear train 91 and an idle gear 92a between the drive shaft 12 and the output shaft 13, and these gears. The gears loosely fitted to the drive shaft 12 in the rows 91 and 92 are coupled to the drive shaft 12 by the selective operation of the forward hydraulic clutch 14F and the reverse hydraulic clutch 14R, and are connected to the output shaft 13 in the forward direction and It is configured to selectively give a reverse rotation.

  The mechanical transmission 23 connects the intermediate shaft 21 to the second transmission shaft 19 via a reduction gear train, and fixedly installs two transmission gears 93 and 94 on the intermediate shaft 21. A transmission gear 96 connected to the side gear 94 via a reduction gear mechanism 95 is provided outside the intermediate shaft 21, and gears 97, 98, 99 meshed with the transmission gears 93, 94, 96 are placed on the propeller shaft 22. It is configured to be loosely installed. Two compound clutches 100, 101 are provided on the propeller shaft, and the gears 98, 99 can be selectively coupled to the propeller shaft 22 by the compound clutch 100, and the gear 97 is connected to the propeller shaft by the compound clutch 101. The second transmission shaft 19 and the propeller shaft 22 can be directly connected to each other. Therefore, the mechanical transmission 23 has four shift speeds.

  In the above embodiment, the hydraulic control at the time of up-shifting and the hydraulic control at the time of down-shifting in the engine rated speed state are respectively addressed by two rather than the time intervals Δt1 and Δt1 ′ when the hydraulic clutch addressed to one is switched on and off. The control of increasing the time intervals Δt2 and Δt2 ′ when the hydraulic clutch was turned on and off was used. In another embodiment, the time interval when the hydraulic clutch addressed to one is turned on and off is equal to the time interval when the hydraulic clutch addressed to two is turned on and off, for example, at time intervals Δt1 and Δt1 ′. When the number of hydraulic clutches to be addressed is two, the same effect can be controlled by gradually reducing the hydraulic pressure for the hydraulic clutch to be disconnected. 10 and 11 each show another embodiment in which such hydraulic control is performed.

  FIG. 10 shows the hydraulic control at the time of upshifting in the engine rated speed state, with one time interval between the application command application time t0 for the new hydraulic clutch and the disconnection command application time ts for the active hydraulic clutch. Another embodiment is shown in which Δt1 is set equal even when the destination hydraulic clutch is turned on and off and when the two destination hydraulic clutches are turned on and off. In this control, when the hydraulic clutch addressed to one is turned on and off (upper graph in FIG. 10), the working hydraulic pressure for the hydraulic clutch to be cut is rapidly reduced as in the case of the control in FIG. On the other hand, when the two hydraulic clutches are turned on and off (the lower graph in FIG. 10), the hydraulic pressure for the hydraulic clutch to be cut is lowered along a lowering curve having a portion having a gradual lowering characteristic. I am letting you. A region where the newly engaged hydraulic clutch and the disconnected hydraulic clutch are slip-engaged in common when the one hydraulic clutch is turned on and off and when the second hydraulic clutch is turned on and off is substantially Are equal.

  FIG. 11 shows the hydraulic control at the time of downshifting in the engine rated speed state with one time interval between the time t0 at which the engagement command is applied to the new hydraulic clutch and the time ts at which the disconnection command is applied to the operating hydraulic clutch. Another embodiment is shown in which Δt1 ′ is equally set when the destination hydraulic clutch is turned on and off and when the second hydraulic clutch is turned on and off. Similarly to the control of FIG. 10, when the hydraulic clutch addressed to one is turned on and off (the upper graph in FIG. 11), the working hydraulic pressure is rapidly reduced for the hydraulic clutch to be disconnected, In the case of turning on and off (lower graph in FIG. 11), the working hydraulic pressure is gradually lowered for the hydraulic clutch to be cut, and the case of turning on and off the one hydraulic clutch and turning on and off the two hydraulic clutches. In some cases, the region in which the newly engaged hydraulic clutch and the disconnected hydraulic clutch are slip-engaged in common is substantially the same.

  Furthermore, it is possible to perform control so that the application time point of the disconnection command for the hydraulic clutch in operation is equal to the application time point t0 of the engagement command for the new hydraulic clutch. FIG. 12 shows an embodiment designed in such a manner at the time of upshifting in the engine rated speed state. In this embodiment, the decrease in the working hydraulic pressure for the hydraulic clutch to be disconnected is determined when the hydraulic clutch destined for one is turned on and off (upper graph in FIG. 12) and when the hydraulic clutch destined for two is turned on and off (lower in FIG. 12). (The graph on the side) is also performed slowly, and the hydraulic pressure is lowered more slowly in the latter case than in the former case, and the hydraulic clutch addressed to one and the hydraulic clutch addressed to two The region where the newly engaged hydraulic clutch and the disconnected hydraulic clutch are slip-engaged in common is made substantially equal in the case of turning on and off.

  Control of securing a predetermined slip engagement region by compensating for the difference between the original time interval Δt1 and the reduced time interval by gradually reducing the hydraulic pressure by decreasing the time interval Δt1 shown in FIG. Is possible. FIG. 13 shows such hydraulic control.

  FIG. 14 shows an embodiment in which the hydraulic circuit shown in FIG. 2 is changed to a more basic circuit. That is, the electromagnetic proportional switching valves VL, VM, VH, V1, V2, and V3 are replaced with electromagnetic switching valves VAL, VAM, VAH, VA1, VA2, and VA3, and the oil supply circuit 70 is electromagnetically connected to these electromagnetic switching valves. They are connected by a circuit in which a proportional valve 110 is inserted. An electromagnetic control valve 111 is connected to the tank ports of the electromagnetic switching valves VAL, VAM, VAH, VA1, VA2, and VA3.

  Each electromagnetic proportional valve 110 has a neutral position N and an action position I. In the neutral position N, the connection between the oil supply circuit 70 and each electromagnetic switching valve VAL, VAM, VAH, VA1, VA2, VA3 is cut off and each electromagnetic switching is performed. The valve VAL, VAM, VAH, VA1, VA2, VA3 is connected to the oil tank, and the oil supply circuit 70 is connected to each electromagnetic switching valve VAL, VAM, VAH, VA1, VA2, VA3 at the operation position I moved by the excitation of the solenoid. On the other hand, the working hydraulic pressure for each of the hydraulic clutches 57, 58, 59, 66, 67, 68 is gradually increased through the electromagnetic switching valves that are connected to the working position at the same time as described above. Each electromagnetic control valve 111 is moved by each solenoid switching valve VAL, VAM, VAH, VA1, VA2, VA3 to the oil tank without squeezing the oil, and discharged by an internal variable throttle 111a. And a position B for squeezing oil. In order to make the variable aperture 111a easy to see, in FIG. 14, it is drawn outside the electromagnetic control valve 111.

  Therefore, the hydraulic circuit of FIG. 14 can also be used for each hydraulic control according to FIGS. 6-13. That is, the electromagnetic proportional valves 110 corresponding to the electromagnetic switching valves VAL, VAM, VAH, VA1, VA2, and VA3 are simultaneously moved to the operating position to gradually increase the clutch operating hydraulic pressure, and the electromagnetic control valves 111 are respectively corresponding to the electromagnetic valves. When the switching valves VAL, VAM, VAH, VA1, VA2, and VA3 are moved from the operating position to the neutral position, oil is discharged from the corresponding hydraulic clutches 57, 58, 59, 66, 67, and 68, and the hydraulic clutch is moved. In this case, in order to moderate the decrease in hydraulic pressure, the hydraulic pressure is variably and gradually decreased by the variable throttle 111a that moves to the position B by excitation of the solenoid and changes the throttle degree by the current value that is conducted to the solenoid. obtain.

  In the above embodiment, the speed change control is performed by dividing the rotation state of the engine 10 into the rated rotation state and the low-speed rotation state. However, the speed change control is continuously performed according to the rotation speed of the engine 10 without dividing into two. Of course, it is possible to control the hydraulic pressure to be gradually lowered with respect to the hydraulic clutch that is disconnected as the rotational speed is lower. That is, the variable throttle Va as the pressure setting means and the pressure setting circuit 89 or the electromagnetic proportional valve 110 cause the working hydraulic pressure to be lowered with respect to the hydraulic clutch to be disconnected more gradually according to the engine speed as the engine speed decreases. It is composed. Specifically, for example, the pressure setting circuit 89 compares the detected value of the tachometer 83 that detects the engine speed with the rated engine speed, and sets the operating oil pressure drop characteristic for the hydraulic clutch to be disconnected. To make things. As a result, the time required to fill the hydraulic clutch with oil according to the engine speed can be continuously compensated according to the speed.

  The shift control method for a hydraulic transmission according to the present invention includes a first hydraulic transmission and a second hydraulic transmission that are connected in series, each of which performs transmission by selective engagement of a plurality of hydraulic clutches. In a certain working vehicle, the hydraulic oil pressure supplied to one or two hydraulic clutches to be engaged is gradually increased over time, while the hydraulic oil discharged from one or two hydraulic clutches to be disconnected is increased. Change the hydraulic pressure degradation characteristics over time when the number of hydraulic clutches to be disconnected is one and two, and when one hydraulic clutch is engaged and when two hydraulic clutches are engaged and disengaged The region in which the hydraulic clutch to be engaged and disengaged in both cases is slip-engaged in common is set to be substantially equal to each other. The time-dependent decrease characteristic of the hydraulic pressure of the hydraulic oil discharged from the hydraulic clutch to be disconnected refers to the time when the hydraulic pressure of the hydraulic clutch starts to decrease due to the application of the disconnection command of the hydraulic clutch to be disconnected, and the hydraulic pressure after the disconnection command is applied Including both of the lowering characteristics.

  Changing the time-dependent decrease characteristic of the hydraulic pressure of the hydraulic oil discharged from the disconnected hydraulic clutch between when the number of disconnected hydraulic clutches is one and when the number of disconnected hydraulic clutches is, for example, the hydraulic pressure to be engaged The interval from the time when the clutch engagement command is applied to the time when the hydraulic clutch disconnection command is applied is relatively short when the one hydraulic clutch is engaged or disengaged. When it is cut off, it is obtained by setting it relatively long. In this case, the oil filling time is longer due to the problem of the time difference required to fill the hydraulic clutch with hydraulic oil when only one hydraulic clutch is engaged and when two hydraulic clutches are engaged. In the case of two hydraulic clutches, this is dealt with by increasing the interval from the application time point of the engagement command of the hydraulic clutch to be engaged to the application time point of the disconnection command of the hydraulic clutch to be disconnected.

  It is also possible to change the hydraulic pressure of the hydraulic oil discharged from the hydraulic clutch to be changed between the case of one hydraulic clutch to be disconnected and the case of two hydraulic clutches to be disconnected. The lowering of the working hydraulic pressure with respect to can also be obtained by relatively slowly performing the engagement / disengagement of the two hydraulic clutches rather than the engagement / disengagement of the one hydraulic clutch. In this case, the problem of the time difference is addressed by relatively slowly decreasing the hydraulic pressure with respect to the hydraulic clutch to be disconnected in the case of two hydraulic clutches that require a longer oil filling time. This method can also be implemented in combination with the above-described method of changing the time interval.

  In any case, the present invention gradually increases the hydraulic pressure of the hydraulic oil supplied to one or two hydraulic clutches to be engaged with time and discharges from one or two hydraulic clutches to be disconnected. When the hydraulic pressure of hydraulic oil is changed over time when one hydraulic clutch is disconnected and when two hydraulic clutches are combined, a combination of connecting and disconnecting the hydraulic clutch addressed to one Since the common slip-engagement areas of the hydraulic clutches that are engaged and disengaged when the two hydraulic clutches are engaged and disengaged are set to be substantially equal to each other, the common slip area is shifted to shift stage switching. As long as it is selected to be performed most smoothly, it depends on the capacity of the hydraulic pump to be used, whether the hydraulic clutch destined for one is engaged or not. Without shifting -Ring will be good.

  It is preferable that the region where the hydraulic clutches to be engaged / disengaged are slip-engaged in common is set smaller at the time of downshifting than at the time of upshifting. In other words, considering the inertia when the vehicle is traveling, the energy required to decelerate is smaller than the energy necessary to increase the speed of the traveling vehicle. The area is actively reduced when decelerating to improve energy efficiency.

It is a mechanism figure which shows the transmission mechanism of the tractor equipped with the Example of this invention. It is a circuit diagram which shows the hydraulic circuit for operating the hydraulic clutch of a 1st and 2nd hydraulic transmission. It is a block diagram which shows the electric control circuit for controlling the action | operation of the electromagnetic proportional switching valve shown in FIG. It is a graph which shows the oil pressure gradual increase characteristic of each electromagnetic proportional switching valve. It is a graph which shows the hydraulic pressure fall characteristic of each electromagnetic proportional switching valve. It is a graph which shows the hydraulic control mode at the time of shift up in an engine rated rotation state. It is a graph which shows the hydraulic control mode at the time of downshift in an engine rated rotation state. It is a graph which shows the hydraulic control mode at the time of upshifting in an engine low-speed rotation state. It is a graph which shows the hydraulic control mode at the time of downshift in an engine low-speed rotation state. It is a graph which shows the hydraulic control aspect according to the other Example at the time of up-shifting in an engine rated rotation state. It is a graph which shows the hydraulic control aspect according to the other Example at the time of downshift in an engine rated rotation state. It is a graph which shows the hydraulic-pressure control aspect according to the further another Example at the time of the shift up in an engine rated rotation state. It is a graph which shows the hydraulic-control aspect according to another Example at the time of up-shifting in an engine rated rotation state. FIG. 6 is a circuit diagram showing a hydraulic circuit according to another embodiment for operating a hydraulic clutch of the first and second hydraulic transmissions.

VL, VM, VH Solenoid proportional switching valve V1, V2, V3 Solenoid proportional switching valve L, M, H Solenoid 1, 2, 3 Solenoid Va Variable throttle VAL, VAM, VAH Solenoid switching valve VA1, VA2, VA3 Solenoid switching valve 10 Engine 17 First hydraulic transmission 20 Second hydraulic transmission 50 Hydraulic pump 57, 58, 59 Hydraulic clutch 66, 67, 68 Hydraulic clutch 80 Logic circuit 81 Shift lever 82 Potentiometer 83 Tachometer 85 Solenoid drive circuit 86 Solenoid drive Circuit 87 Pressure setting circuit 88 Delay circuit 89 Pressure setting circuit 90 Time setting circuit 110 Proportional solenoid valve 111 Electromagnetic control valve 111a Variable throttle

Claims (10)

In a work vehicle in which a first hydraulic transmission (17) and a second hydraulic transmission (20) each performing transmission transmission by selective engagement of a plurality of hydraulic clutches are connected in series, A plurality of electromagnetic switching valves (VL, VM, VH, V1, V2, connected to the hydraulic clutches (57, 58, 59, 66, 67, 68), respectively, for controlling the supply and discharge of the hydraulic oil to and from the hydraulic clutches. V3; VAL, VAM, VAH, VA1, VA2, VA3), operation control means (80, 85, 86) for selectively applying an engagement command and a disconnection command to each of the electromagnetic switching valves, and hydraulic pressure Pressure control means (VL, VM, VH, V1, V2, V3, 87; 110) for gradually increasing the hydraulic pressure of hydraulic oil supplied to the clutch over time from the time when the engagement command is given to the electromagnetic switching valve. And be prepared In the operation control means, an interval from the time when the engagement command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be engaged to the time when the cutting command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be disconnected is set. time s interval setting means (88, 90) set only the that, the time s interval setting means (88, 90), said time s relatively short setting the interval of the case of Nyudan the hydraulic clutch of one addressed A shift control apparatus for a hydraulic transmission , provided with a time setting circuit (90) for setting the time interval relatively long when the two hydraulic clutches are engaged and disengaged . 2. The hydraulic transmission according to claim 1, wherein the time setting circuit (90) sets the time interval when shifting up relatively long and sets the time interval when shifting down relatively short . Shift control device. The hydraulic clutch is filled with oil from the time (t0) when the engagement command is applied to the electromagnetic switching valve connected to the hydraulic clutch to be engaged for the time interval set in the time interval setting means (88, 90). 2. The transmission control device for a hydraulic transmission according to claim 1, wherein the hydraulic pressure applied to the hydraulic clutch is greater than a time interval until a time point (ta) at which the hydraulic pressure to the piston holding pressure (pa) increases . In a work vehicle in which a first hydraulic transmission (17) and a second hydraulic transmission (20) each performing transmission transmission by selective engagement of a plurality of hydraulic clutches are connected in series, A plurality of electromagnetic switching valves (VL, VM, VH, V1, V2, connected to the hydraulic clutches (57, 58, 59, 66, 67, 68), respectively, for controlling the supply and discharge of the hydraulic oil to and from the hydraulic clutches. V3; VAL, VAM, VAH, VA1, VA2, VA3), operation control means (80, 85, 86) for selectively applying an engagement command and a disconnection command to each of the electromagnetic switching valves, and hydraulic pressure Pressure control means (VL, VM, VH, V1, V2, V3, 87; 110) for gradually increasing the hydraulic pressure of hydraulic oil supplied to the clutch over time from the time when the engagement command is given to the electromagnetic switching valve. And be prepared The operation control means is provided with pressure setting means (Va, 89; 111) for setting a lowering characteristic of the working oil pressure after the disconnection command is given to the hydraulic clutch to be disconnected, and the pressure setting means (Va, 89; 111). ) Is a hydraulic shift that causes a lowering of the hydraulic pressure applied to the disconnected hydraulic clutch to be performed more slowly when the two hydraulic clutches are engaged / disengaged than when the one hydraulic clutch is engaged / disengaged. Gear shift control device. It said pressure setting means (Va, 89; 111) is, the shift control device of the hydraulic transmission according to claim 4 in which the reduction of the working oil pressure for the hydraulic clutch to be cut, thereby variably slowly performed. 5. The hydraulic transmission according to claim 4 , wherein the pressure setting means (Va, 89; 111) causes the hydraulic pressure of the hydraulic clutch to be disconnected to decrease more gradually during downshifting than during upshifting. Shift control device. 5. The hydraulic transmission according to claim 4 , wherein the pressure setting means (Va, 89; 111) causes the hydraulic pressure of the hydraulic clutch to be cut to decrease relatively slowly in a low speed rotation state than in a rated rotation state of the engine. Gear shift control device. 5. The hydraulic transmission according to claim 4 , wherein the pressure setting means (Va, 89; 111) causes the working hydraulic pressure of the hydraulic clutch to be disconnected to decrease more gradually as the rotational speed decreases in accordance with the rotational speed of the engine. Shift control device. The pressure setting means (Va, 89; 111) is compared with the detected value of the tachometer (83) for detecting the engine speed and the rated engine speed, and the working oil pressure for the hydraulic clutch to be cut is reduced. The transmission control device for a hydraulic transmission according to claim 8 , further comprising a pressure setting circuit (89) for setting the characteristics . The hydraulic type according to any one of claims 1 to 9, wherein the electromagnetic switching valve is an electromagnetic proportional switching valve (VL, VM, VH, V1, V2, V3) that also serves as the pressure control means. A transmission control device for a transmission.

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