Control systems, work vehicles, control methods, and computer programs

Abstract

To reduce a time required for switching shift stages.SOLUTION: A control system controls an operation of a power transmission device of a work vehicle. The control system comprises: a storage device that stores data indicating a relation between a ratio between a rotational speed of a predetermined component on a power transmission path that transmits the rotation of a planetary transmission device to wheels and a rotational speed of an internal combustion engine, and a plurality of switching points that are points at which shift stages of the planetary transmission device are switched; and a control device that controls a hydraulic clutch mechanism so as to switch the shift stages. When the ratio changes and reaches a first value corresponding to a first switching point, or when the shift stages are switched after the ratio reaches the first value, the control device controls the hydraulic clutch mechanism to start filling oil for switching the shift stages before the ratio reaches the first value.SELECTED DRAWING: Figure 9

Description

Technical Field

[0005]

[0001] The present disclosure relates to a control system, a work vehicle, a control method, and a computer program.

Background Art

[0002] As a work vehicle such as an agricultural tractor, there is a work vehicle equipped with an internal combustion engine and a hydrostatic continuously variable transmission (for example, see Patent Document 1). The rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are combined by a planetary transmission and transmitted to the wheels. The switching of the gear stage of the planetary transmission can be performed using a clutch mechanism.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If it takes time to switch the gear stage of the planetary transmission during the running of the work vehicle, the operator may feel a large shift shock.

[0005] There is a demand to reduce the time required for switching the gear stage.

Means for Solving the Problems

[0006] A control system according to one embodiment of the present disclosure is a control system for controlling the operation of a power transmission device of a work vehicle, the power transmission device comprising: a hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump; a planetary transmission that transmits rotation generated by the internal combustion engine and rotation generated by the hydrostatic continuously variable transmission and generates multiple types of rotation corresponding to multiple gears; and a hydraulic clutch mechanism for switching the gears of the planetary transmission, the control system comprising a predetermined part on the power transmission path that transmits the rotation of the planetary transmission to the wheels The system includes a storage device that stores data showing the relationship between the ratio of the rotational speed of the product and the rotational speed of the internal combustion engine and a plurality of switching points which are points for switching gears of the planetary transmission, and a control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, wherein the plurality of switching points include a first switching point, and when the ratio changes and approaches a first value corresponding to the first switching point, the control device estimates a first time until the ratio reaches the first value, and controls the hydraulic clutch mechanism to start filling with oil for switching gears before the ratio reaches the first value based on the estimated first time.

[0007] A control method according to one embodiment of the present disclosure is a control method for controlling the operation of a power transmission device of a work vehicle, wherein the power transmission device comprises a hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of a swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, a planetary transmission that transmits rotation generated by the internal combustion engine and rotation generated by the hydrostatic continuously variable transmission and generates multiple types of rotation corresponding to multiple gears, and a hydraulic clutch mechanism that switches the gears of the planetary transmission, and the control method is a power transmission that transmits the rotation of the planetary transmission to the wheels The control method includes controlling the hydraulic clutch mechanism to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the path and the rotational speed of the internal combustion engine and a plurality of switching points which are points for switching gears of the planetary transmission, wherein the plurality of switching points include a first switching point, and the control method further includes estimating a first time until the ratio reaches a first value when the ratio changes and approaches a first value corresponding to the first switching point, and based on the estimated first time, controlling the hydraulic clutch mechanism to start filling with oil for switching gears before the ratio reaches the first value.

[0008] A computer program according to one embodiment of the present disclosure is a computer program that causes a computer to execute control of the operation of a power transmission device of a work vehicle, wherein the power transmission device comprises a hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of a swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, a planetary transmission that transmits rotation generated by the internal combustion engine and rotation generated by the hydrostatic continuously variable transmission and generates multiple types of rotation corresponding to multiple gears, and a hydraulic clutch mechanism that switches the gears of the planetary transmission, and the computer program transmits the rotation of the planetary transmission to the wheels The computer is instructed to control the hydraulic clutch mechanism to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the delivery path and the rotational speed of the internal combustion engine, and a plurality of switching points which are points for switching gears of the planetary transmission, wherein the plurality of switching points include a first switching point, and the computer program further instructs the computer to estimate a first time until the ratio reaches the first value when the ratio changes and approaches a first value corresponding to the first switching point, and to control the hydraulic clutch mechanism to start filling with oil for switching gears before the ratio reaches the first value based on the estimated first time.

[0009] A control system according to one embodiment of the present disclosure is a control system for controlling the operation of a power transmission device of a work vehicle, the power transmission device comprising: a hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil corresponding to the angle of a swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump; a planetary transmission that transmits rotation generated by the internal combustion engine and rotation generated by the hydrostatic continuously variable transmission and generates multiple types of rotation corresponding to multiple gears; and a hydraulic clutch mechanism for switching gears of the planetary transmission, the control system comprising: a storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch gears of the planetary transmission, and the ratio The system includes a control device that controls the hydraulic clutch mechanism to switch gears based on a ratio and the data, wherein the plurality of switching points include a first switching point, and the control device controls the hydraulic clutch mechanism to start filling the gear shift oil when the ratio changes to a first value corresponding to the first switching point, or when switching gears after the ratio has reached the first value, before the ratio reaches the first value, and the control device determines when to start filling the gear shift oil based on the time from when it starts filling the oil to switch from the current gear to the next gear until the clutch of the next gear is engaged.

[0010] A control system according to one embodiment of the present disclosure is a control system for controlling the operation of a power transmission device of a work vehicle, the power transmission device comprising: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil corresponding to the angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission that receives rotation generated by the internal combustion engine and rotation generated by the hydrostatic continuously variable transmission and generates multiple types of rotation corresponding to multiple gears; and a hydraulic clutch mechanism for switching the gears of the planetary transmission, the control system controls predetermined components on the power transmission path that transmits the rotation of the planetary transmission to the wheels The device includes a storage device that stores data showing the relationship between the ratio of the rotational speed and the rotational speed of the internal combustion engine and a plurality of switching points which are points for switching gears of the planetary transmission, and a control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, wherein the plurality of switching points include a first switching point, and the control device predetermines the angle of the swash plate at the first switching point and changes the rotational speed of the rotation generated by the hydraulic motor by controlling the angle of the swash plate, and when the ratio changes and approaches a first value corresponding to the first switching point, the control device stops the control of changing the angle of the swash plate before the ratio reaches the first value. [Effects of the Invention]

[0011] When shifting gears, it takes time to fill the clutch of the next gear to be shifted to with oil. If the oil filling process begins only after the ratio between the rotational speed of a specific rotating part and the rotational speed of the internal combustion engine reaches the value corresponding to the shift point, it will take time to engage the clutch of the next gear to be shifted to. Because the time during which the change in the above ratio is stopped is longer, the occupant may perceive a large shift shock.

[0012] According to one embodiment of the present disclosure, oil filling is started before the ratio reaches a value corresponding to the switching point. This allows the gear shift to be completed in a short time when the ratio reaches a value corresponding to the switching point, and by reducing the time during which the ratio change is stopped, the shift shock felt by the occupant can be reduced. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic side view showing an example of a work vehicle. [Figure 2] Figure 2 is a schematic diagram showing the power transmission system installed in a work vehicle. [Figure 3] Figure 3 is a schematic diagram of a planetary gearbox. [Figure 4] Figure 4 is a schematic diagram illustrating a hydrostatic continuously variable transmission. [Figure 5A] Figure 5A is a schematic diagram showing an example of a clutch in a hydraulic clutch mechanism. [Figure 5B] Figure 5B is a schematic diagram illustrating an example of a clutch in a hydraulic clutch mechanism. [Figure 5C] Figure 5C is a schematic diagram illustrating an example of a clutch in a hydraulic clutch mechanism. [Figure 5D] Figure 5D is a schematic diagram illustrating an example of a clutch in a hydraulic clutch mechanism. [Figure 6] Figure 6 is a block diagram showing an example of a control system installed in a work vehicle. [Figure 7] Figure 7 shows an example of the gear shifting operation of a work vehicle. [Figure 8] Figure 8 shows an example of a ratio that changes in response to the user's operation of the gear shift pedal. [Figure 9] Figure 9 illustrates the operation of switching gears in a planetary transmission. [Modes for carrying out the invention]

[0014] Hereinafter, a control system according to an embodiment of the present disclosure and a work vehicle equipped with the control system will be described with reference to the drawings. In the description of the embodiments, like components are denoted by like reference numerals, and when there is duplication, the description thereof will be omitted. The symbols F, Re, U, and D attached to the drawings represent front, rear, upper, and lower, respectively. In the following description of the embodiments, a tractor is exemplified as an example of the work vehicle. The technology of the present disclosure is not limited to tractors and can also be applied to other types of work vehicles. The following embodiments are illustrative, and the technology of the present disclosure is not limited to the following embodiments.

[0015] (Work vehicle) FIG. 1 is a side view schematically showing an example of a work vehicle 10. The work vehicle 10 shown in FIG. 1 is a tractor, and a work implement (implement) can be mounted on one or both of the rear and front portions. The work vehicle 10 can travel in a field while performing farm work according to the type of the work implement. The work vehicle 10 may travel in or outside the field without mounting a work implement.

[0016] The work vehicle 10 includes a vehicle body 101, an internal combustion engine (engine) 102, and a transmission case 103. The vehicle body 101 is provided with a pair of front wheels 104, a pair of rear wheels 105, and a cab 106. The internal combustion engine 102 can be, for example, a diesel engine. A power transmission device 15 (FIG. 2) is housed in the transmission case 103. Inside the cab 106, a driver's seat 108, a steering device 107, and a switch group for operations are provided. When the work vehicle 10 performs work travel in a field, one or both of the front wheels 104 and the rear wheels 105 may be a plurality of wheels (crawlers) equipped with endless tracks instead of wheels with tires.

[0017] The steering device 107 includes a steering wheel, a steering shaft connected to the steering wheel, and a power steering device that assists steering by the steering wheel. The front wheels 104 are steering wheels, and the traveling direction of the work vehicle 10 can be changed by changing the steering angle (also referred to as the "steering angle").

[0018] A coupling device 109 is provided at the rear of the vehicle body 101. The coupling device 109 allows the implement to be attached to and detached from the work vehicle 10. The coupling device 109 is equipped with, for example, a PTO shaft and can transmit power from the internal combustion engine 102 to the implement. The work vehicle 10 can pull the implement and have the implement perform a predetermined task. The coupling device 109 may also be provided at the front of the vehicle body 101. In that case, the implement can be connected to the front of the work vehicle 10.

[0019] (Power transmission device) Figure 2 is a schematic diagram showing the power transmission device 15 provided by the work vehicle 10.

[0020] At least a portion of the power transmission device 15 is housed in the transmission case 103 (Figure 1). The power transmission device 15 transmits the output of the internal combustion engine 102 to the front wheels 104 and the rear wheels 105.

[0021] The power transmission device 15 comprises an input shaft 20, a main transmission 21, a forward / reverse selector 23, a gear mechanism 24, a front wheel transmission mechanism 25, a rear wheel differential mechanism 16, and a front wheel differential mechanism 17. The rotation of the output shaft 102a of the internal combustion engine 102 is transmitted to the input shaft 20. The rotation of the output shaft 102a of the internal combustion engine 102 is transmitted to the input shaft 20, for example, via a damper disc. The rotation of the input shaft 20 is transmitted to the main transmission 21.

[0022] The main transmission 21 includes a hydrostatic continuously variable transmission (HST) 28 and a planetary transmission unit 30. The planetary transmission unit 30 includes a planetary transmission 31 and a hydraulic clutch mechanism 29. The rotation of the input shaft 20 is transmitted to the HST 28. The rotation of the input shaft 20 and the rotation generated by the HST 28 are transmitted to the planetary transmission 31. The planetary transmission 31 generates multiple types of rotation corresponding to multiple gears. The hydraulic clutch mechanism 29 switches the gears of the planetary transmission 31.

[0023] The HST28 comprises a hydraulic pump P, a hydraulic motor M, a pump shaft 28a, an output shaft 28b, and a swash plate 49. A rotary shaft 26 is connected to the rear end of the input shaft 20. A first gear mechanism 27A is connected to the rear end of the rotary shaft 26. The rotation of the input shaft 20 is transmitted to the pump shaft 28a via the rotary shaft 26 and the first gear mechanism 27A. The pump shaft 28a is connected to the hydraulic pump P, and the rotation of the input shaft 20 is transmitted to the hydraulic pump P. The hydraulic pump P is a variable displacement hydraulic pump. The hydraulic pump P, which receives the rotation of the input shaft 20, discharges oil according to the angle of the swash plate 49. The oil discharged by the hydraulic pump P is supplied to the hydraulic motor M, which generates rotation. By changing the angle of the swash plate 49, the speed of rotation generated by the hydraulic motor M can be changed steplessly. Furthermore, by changing the direction in which the swash plate 49 is tilted, the direction of rotation generated by the hydraulic motor M can be switched between forward rotation and reverse rotation.

[0024] The rotation generated by the hydraulic motor M is output from the output shaft 28b. A second gear mechanism 27B is provided between the output shaft 28b and the planetary transmission 31. The rotation of the output shaft 28b is transmitted to the planetary transmission 31 via the second gear mechanism 27B. The rotation of the input shaft 20 and the rotation of the output shaft 28b of the HST 28 are transmitted to the planetary transmission 31.

[0025] Figure 3 is a schematic diagram of the planetary gearbox 31. The planetary gearbox 31 comprises a first planetary gearbox 32 and a second planetary gearbox 33. The planetary gearbox 31 has a compound planetary gear mechanism.

[0026] The first planetary gearbox 32 comprises a first sun gear 32a, a first planetary gear 32b, a first ring gear 32c, and a linkage gear 32d. The second planetary gearbox 33 comprises a second sun gear 33a, a second planetary gear 33b, a second ring gear 33c, and a second carrier 33d.

[0027] The first sun gear 32a meshes with the first planetary gear 32b. The first ring gear 32c is provided with internal teeth that mesh with the first planetary gear 32b. The second planetary transmission 33 is positioned behind the first planetary transmission 32. The second sun gear 33a meshes with the second planetary gear 33b. The second ring gear 33c is provided with internal teeth that mesh with the second planetary gear 33b. The second carrier 33d supports the second planetary gear 33b. The interlocking gear 32d meshes with the first planetary gear 32b. The interlocking gear 32d and the second planetary gear 33b are connected by a connecting member 33e and interlock with each other.

[0028] As shown in Figures 2 and 3, the rotation of the output shaft 28b of the HST28 is transmitted to the first sun gear 32a via the second gear mechanism 27B. A third gear mechanism 27C is provided between the input shaft 20 and the first ring gear 32c. The rotation of the input shaft 20 is transmitted to the first ring gear 32c via the third gear mechanism 27C.

[0029] The planetary speed changer 31 includes an output device 37 (Figure 2) that outputs rotation. The output device 37 includes a first input shaft 34a, a second input shaft 34b, a third input shaft 34c, and an output shaft 35. The first input shaft 34a is connected to the second ring gear 33c, the second input shaft 34b is connected to the second carrier 33d, and the third input shaft 34c is connected to the second sun gear 33a.

[0030] The output device 37 further comprises a first range gear mechanism 36a, a second range gear mechanism 36b, a third range gear mechanism 36c, and a fourth range gear mechanism 36d. The hydraulic clutch mechanism 29 comprises a first clutch CL1, a second clutch CL2, a third clutch CL3, and a fourth clutch CL4.

[0031] The first range gear mechanism 36a is connected to the first input shaft 34a, and the rotation of the first input shaft 34a is transmitted to it. A first clutch CL1 is provided between the first range gear mechanism 36a and the output shaft 35. When the first clutch CL1 is engaged, the rotation of the first range gear mechanism 36a is transmitted to the output shaft 35 via the first clutch CL1. When the first clutch CL1 is disengaged, the rotation of the first range gear mechanism 36a is not transmitted to the output shaft 35.

[0032] The second range gear mechanism 36b is connected to the third input shaft 34c, and the rotation of the third input shaft 34c is transmitted to it. A second clutch CL2 is provided between the second range gear mechanism 36b and the output shaft 35. When the second clutch CL2 is engaged, the rotation of the second range gear mechanism 36b is transmitted to the output shaft 35 via the second clutch CL2. When the second clutch CL2 is disengaged, the rotation of the second range gear mechanism 36b is not transmitted to the output shaft 35.

[0033] The third range gear mechanism 36c is connected to the second input shaft 34b, and the rotation of the second input shaft 34b is transmitted to it. A third clutch CL3 is provided between the third range gear mechanism 36c and the output shaft 35. When the third clutch CL3 is engaged, the rotation of the third range gear mechanism 36c is transmitted to the output shaft 35 via the third clutch CL3. When the third clutch CL3 is disengaged, the rotation of the third range gear mechanism 36c is not transmitted to the output shaft 35.

[0034] The fourth range gear mechanism 36d is connected to the third input shaft 34c, and the rotation of the third input shaft 34c is transmitted to it. A fourth clutch CL4 is provided between the fourth range gear mechanism 36d and the output shaft 35. When the fourth clutch CL4 is engaged, the rotation of the fourth range gear mechanism 36d is transmitted to the output shaft 35 via the fourth clutch CL4. When the fourth clutch CL4 is disengaged, the rotation of the fourth range gear mechanism 36d is not transmitted to the output shaft 35.

[0035] As described above, the rotation of the output shaft 28b of the HST28 is transmitted to the first sun gear 32a. The rotation of the internal combustion engine 102 is transmitted to the first ring gear 32c via the input shaft 20. The planetary transmission 31 combines these transmitted rotations and outputs the combined rotation from the output shaft 35.

[0036] When the first clutch CL1 is engaged and the second-fourth clutches CL2-CL4 are disengaged, the rotation of the second ring gear 33c is transmitted to the output shaft 35 via the first input shaft 34a, the first range gear mechanism 36a, and the first clutch CL1. When the first clutch CL1 is engaged and the second-fourth clutches CL2-CL4 are disengaged, the gear position of the planetary transmission 31 is "first gear". The output shaft 35 outputs the rotation corresponding to first gear.

[0037] When the second clutch CL2 is engaged and the first, third, and fourth clutches CL1, CL3, and CL4 are disengaged, the rotation of the second sun gear 33a is transmitted to the output shaft 35 via the third input shaft 34c, the second range gear mechanism 36b, and the second clutch CL2. When the second clutch CL2 is engaged and the first, third, and fourth clutches CL1, CL3, and CL4 are disengaged, the gear position is "second gear". The output shaft 35 outputs the rotation corresponding to second gear.

[0038] When the third clutch CL3 is engaged and the first, second, and fourth clutches CL1, CL2, and CL4 are disengaged, the rotation of the second carrier 33d is transmitted to the output shaft 35 via the second input shaft 34b, the third range gear mechanism 36c, and the third clutch CL3. When the third clutch CL3 is engaged and the first, second, and fourth clutches CL1, CL2, and CL4 are disengaged, the gear is in "third gear". The output shaft 35 outputs the rotation corresponding to third gear.

[0039] When the fourth clutch CL4 is engaged and the first to third clutches CL1-CL3 are disengaged, the rotation of the second sun gear 33a is transmitted to the output shaft 35 via the third input shaft 34c, the fourth range gear mechanism 36d, and the fourth clutch CL4. When the fourth clutch CL4 is engaged and the first to third clutches CL1-CL3 are disengaged, the gear is in "fourth gear". The output shaft 35 outputs the rotation corresponding to fourth gear.

[0040] The rotation of the output shaft 35 is transmitted to the forward / reverse switching device 23. The forward / reverse switching device 23 comprises an input shaft 23a, an output shaft 23b, a forward gear interlocking mechanism 23c, a reverse gear interlocking mechanism 23d, a forward clutch CLF, and a reverse clutch CLR.

[0041] The rotation of the output shaft 35 is transmitted to the input shaft 23a. The input shaft 23a is equipped with a forward clutch CLF and a reverse clutch CLR.

[0042] When the forward clutch CLF is engaged, the rotation of the input shaft 23a is transmitted to the output shaft 23b via the forward clutch CLF and the forward gear interlocking mechanism 23c. From the forward gear interlocking mechanism 23c, rotation in the direction that moves the work vehicle 10 forward is transmitted to the output shaft 23b.

[0043] When the reverse clutch CLR is engaged, the rotation of the input shaft 23a is transmitted to the output shaft 23b via the reverse clutch CLR and the reverse gear interlocking mechanism 23d. From the reverse gear interlocking mechanism 23d, rotation in the direction that moves the work vehicle 10 in reverse is transmitted to the output shaft 23b.

[0044] The rotation of the output shaft 23b is transmitted via the gear mechanism 24 to the input shaft 16a of the rear wheel differential mechanism 16 and the input shaft 25a of the front wheel transmission mechanism 25.

[0045] The rotation of the input shaft 16a of the rear wheel differential mechanism 16 is transmitted to the left and right rear wheels 105 via the output shaft 16b. In Figure 2, only the left rear wheel 105 is shown. A brake 38A is provided on the output shaft 16b, and the rotation of the output shaft 16b is transmitted to the rear wheel 105 via the planetary reduction mechanism 38B. The power transmission structure to the right rear wheel 105 is the same as that to the left rear wheel 105.

[0046] The front wheel transmission mechanism 25 comprises an input shaft 25a, an output shaft 25b, a constant speed gear mechanism 40, a speed-increasing gear mechanism 41, a constant speed clutch CLT, and a speed-increasing clutch CLH. The input shaft 25a is connected to the output shaft 24a of the gear mechanism 24. The rotation of the output shaft 23b of the forward / reverse selector 23 is transmitted to the input shaft 25a. A parking brake 39 is provided on the output shaft 24a of the gear mechanism 24. The input shaft 25a of the front wheel transmission mechanism 25 is equipped with a constant speed clutch CLT and a speed-increasing clutch CLH.

[0047] When the constant-speed clutch CLT is engaged, the rotation of the input shaft 25a is transmitted to the output shaft 25b via the constant-speed clutch CLT and the constant-speed gear mechanism 40. When the speed-increasing clutch CLH is engaged, the rotation of the input shaft 25a is transmitted to the output shaft 25b via the speed-increasing clutch CLH and the speed-increasing gear mechanism 41. The rotation of the output shaft 25b is transmitted to the front wheels 104 via the rotating shaft 42 and the input shaft 17a of the front wheel differential mechanism 17.

[0048] When the constant-velocity clutch CLT is engaged, rotation is transmitted to the front wheel 104 such that its peripheral speed is the same as that of the rear wheel 105. When the speed-increasing clutch CLH is engaged, rotation is transmitted to the front wheel 104 such that its peripheral speed is greater than that of the rear wheel 105. When the speed-increasing clutch CLH is engaged, the turning radius of the work vehicle 10 can be reduced compared to when the constant-velocity clutch CLT is engaged.

[0049] The power transmission device 15 (Figure 2) is equipped with multiple rotation sensors 70 for detecting the rotation of various components. The rotational speed (rotational speed) of various components can be calculated using the output signals of these rotation sensors 70. The multiple rotation sensors 70 include, for example, a rotation sensor for detecting the rotation of the output shaft 28b of the HST 28, a rotation sensor for detecting the rotation of the output shaft 35 of the planetary transmission 31, a rotation sensor for detecting the rotation of the output shaft 23b of the forward / reverse switching device 23, and a rotation sensor for detecting the rotation of the input shaft 16a of the rear wheel differential mechanism 16. The internal combustion engine 102 is equipped with a rotation sensor 71 for detecting the rotation of the internal combustion engine 102. The rotation sensor 71 detects, for example, the rotation of the output shaft 102a. The rotational speed of the internal combustion engine 102 can be calculated using the output signals of the rotation sensor 71.

[0050] Figure 4 is a schematic diagram of the HST28. A hydraulic cylinder 90 is connected to the swash plate 49 of the hydraulic pump P. A speed control valve 92 is connected to the hydraulic cylinder 90 via an operating oil passage 91. A hydraulic pump 94 is connected to the speed control valve 92 via an oil supply passage 93. An emergency relief valve 96 and a pressure sensor 97 are provided in the closed circuit 95 connecting the hydraulic pump P and the hydraulic motor M. The pressure sensor 97 detects the hydraulic pressure in the closed circuit 95. A temperature sensor 74 is provided in the closed circuit 95. The temperature sensor 74 can be used to detect the temperature of the oil supplied to the hydraulic motor M.

[0051] Hydraulic fluid is supplied from the hydraulic pump 94 to the hydraulic cylinder 90 via the speed control valve 92, causing the hydraulic cylinder 90 to operate. By operating the hydraulic cylinder 90, the tilt angle of the swash plate 49 can be changed. By switching the ports of the speed control valve 92, the oil chamber to which hydraulic fluid is supplied among the two oil chambers of the hydraulic cylinder 90 can be switched. The speed control valve 92 is, for example, an electromagnetic valve, and port switching can be performed by operating the solenoid 92a of the speed control valve 92. By stopping the supply of hydraulic fluid to the hydraulic cylinder 90, the position of the hydraulic cylinder 90 can be maintained.

[0052] The HST28 can change the direction in which the swash plate 49 is tilted by switching the port of the speed control valve 92, thereby switching the direction of rotation generated by the hydraulic motor M between forward and reverse rotation. The HST28 can continuously change the speed of rotation generated by the hydraulic motor M by operating the hydraulic cylinder 90 to change the tilt angle of the swash plate 49.

[0053] The hydraulic cylinder 90 is equipped with, for example, a position sensor 72 for detecting the position of the cylinder of the hydraulic cylinder 90. The tilt direction and tilt angle of the swash plate 49 can be calculated using the output signal of the position sensor 72. A sensor for detecting the tilt direction and tilt angle of the swash plate 49 may also be provided on the swash plate 49.

[0054] Figures 5A to 5D schematically show examples of clutches provided in the hydraulic clutch mechanism 29 (Figure 2). Each of the first to fourth clutches CL1 to CL4 may have, for example, the structure of clutch CL shown in Figures 5A to 5D.

[0055] The clutch CL is provided with a hydraulic chamber 135. A hydraulic pump 141 and an oil tank 142 are connected to the hydraulic chamber 135 via an oil passage 145. An on-off valve 143 is provided between the hydraulic chamber 135 and the hydraulic pump 141. An on-off valve 144 is provided between the hydraulic chamber 135 and the oil tank 142. On-off valves 143 and 144 are, for example, solenoid valves. A temperature sensor 73 is provided on the hydraulic pump 141. The temperature sensor 73 detects the temperature of the oil supplied to the hydraulic chamber 135. The position of the temperature sensor 73 is arbitrary.

[0056] Figure 5A shows the clutch CL in the released state. When the clutch CL is in the released state, opening valve 143 and closing valve 144 supplies oil from the hydraulic pump 141 to the hydraulic chamber 135, and as shown in Figure 5B, the piston 133 moves in the direction of arrow 137 while pushing plate 131. As the piston 133 moves in the direction of arrow 137 while pushing plate 131, plate 131 comes into contact with plate 132, as shown in Figure 5C, and the clutch CL becomes engaged. The contact between plate 131 and plate 132 can be detected, for example, using a pressure sensor 136.

[0057] When the clutch CL is engaged, closing valve 143 and opening valve 144 causes the piston 133 to move in the direction of arrow 138 by the return spring 134, as shown in Figure 5D, and the oil in the hydraulic chamber 135 is discharged into the oil tank 142. As the piston 133 moves in the direction of arrow 138, plate 131 separates from plate 132, and the clutch CL is released. The piston 133 is pushed by the return spring 134 and returns to the position shown in Figure 5A.

[0058] (Control system) The work vehicle 10 is equipped with a control system that controls the operation of the work vehicle 10. Figure 6 is a block diagram showing an example of the control system 200 provided by the work vehicle 10. Figure 6 shows components that are relatively highly related to the gear shifting operation of the work vehicle 10, and other components are not shown.

[0059] The control system 200 includes a control device 210 and a storage device 220. The control device 210 may be implemented by a computer including a processor, such as an electronic control unit (ECU) installed in the work vehicle 10. The control device 210 may be implemented by one ECU or by multiple ECUs. For example, if the control device 210 is implemented by multiple ECUs, these multiple ECUs may be distributed and arranged within the work vehicle 10. Part of the control device 210 may be implemented by a user terminal device and / or a server computer that communicates with the work vehicle 10.

[0060] The control device 210 controls the operation of the power transmission device 15 based on user operations to the operating device 120 and output signals from sensors 70-74. The operating device 120 includes user-operated devices such as a gear shift pedal 121 and a forward / reverse lever 122. The control device 210 controls the travel speed of the work vehicle 10 according to the amount of user operation of the gear shift pedal 121, and switches the work vehicle 10 between forward and reverse according to user operation of the forward / reverse lever 122.

[0061] The storage device 220 is a storage device that includes any storage medium, such as a semiconductor storage medium, a magnetic storage medium, or an optical storage medium. The storage device 220 may be a collection of multiple storage devices. The storage device 220 may be a device independent of the control device 210, or it may be included in the control device 210. For example, if the ECU functions as the control device 210, the memory provided by the ECU may function as the storage device 220. The storage device 220 stores computer programs executed by the control device 210 and various types of information generated by the control device 210.

[0062] Figure 7 shows an example of the gear shifting operation of the work vehicle 10. The vertical axis in Figure 7 represents the ratio α. The ratio α is the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the output shaft 35 of the planetary transmission 31 to the wheels 104 and 105, to the rotational speed of the internal combustion engine 102. The predetermined component is any component located between the output shaft 35 and the wheels 104 and 105, and may be, for example, the input shaft 16a and output shaft 23b shown in Figure 2, but is not limited to these. The predetermined component may be any of the output shaft 35, wheels 104 and 105. Here, as an example, the predetermined component is assumed to be the input shaft 16a. When the rotational speed of the internal combustion engine 102 is constant, the travel speed of the work vehicle 10 increases as the ratio α increases.

[0063] The horizontal axis in Figure 7 shows the state of the HST28. "N" represents the neutral state of the HST28, where the swash plate 49 is in the neutral position. "+MAX" represents the state of the HST28 when the hydraulic motor M generates rotation in the forward direction at maximum speed, where the swash plate 49 is tilted significantly towards the side corresponding to forward rotation. "-MAX" represents the state of the HST28 when the hydraulic motor M generates rotation in the reverse direction at maximum speed, where the swash plate 49 is tilted significantly towards the side corresponding to reverse rotation. "+K" represents the state of the HST28 at the point where the gear ratio of the planetary transmission 31 is switched on the forward rotation side. "-K" represents the state of the HST28 at the point where the gear ratio of the planetary transmission 31 is switched on the reverse rotation side. Switching points S1, S2, and S3 are the points where the gear ratio of the planetary transmission 31 is switched.

[0064] The storage device 220 pre-stores data showing the relationship between the ratio α and the switching points S1, S2, and S3. This data includes, for example, information about the ratio α1 corresponding to switching point S1, the ratio α2 corresponding to switching point S2, and the ratio α3 corresponding to switching point S3. The control device 210 reads this data from the storage device 220. Based on the read data and the detected ratio α values, the control device 210 performs control to switch the gears of the planetary transmission 31.

[0065] The control device 210 can change the tilt angle of the swash plate 49 by, for example, controlling the operation of the speed control valve 92 (Figure 4) of the HST 28. The speed at which the swash plate 49 tilts can be controlled, for example, using a flow control valve. The control device 210 can switch between the engaged and disengaged states of clutches CL1-CL4 by, for example, controlling the operation of the on-off valves 143 and 144 (Figures 5A-5D) of clutches CL1-CL4, respectively.

[0066] At the start of the work vehicle 10, the control device 210 controls the swash plate 49 to achieve an inclination angle corresponding to "-K", and also controls the hydraulic clutch mechanism 29 to engage the first clutch CL1.

[0067] When the user operates the gear shift pedal 121 to accelerate the work vehicle 10, the control device 210 changes the inclination angle of the swash plate 49 from the "-MAX" side to the "+MAX" side. During the process of accelerating the work vehicle 10, the control device 210 controls the internal combustion engine 102 so that the rotational speed of the internal combustion engine 102 remains constant. As the inclination angle of the swash plate 49 changes, the counter-rotational speed generated by the hydraulic motor M gradually decreases, and at the neutral position, the rotational speed becomes zero. By further changing the inclination angle of the swash plate 49 from the neutral position toward the "+MAX" side, the hydraulic motor M generates rotation in the forward direction, and the forward rotational speed generated by the hydraulic motor M gradually increases. In this way, the ratio α increases steplessly as the inclination angle of the swash plate 49 is changed.

[0068] When the inclination angle of the swash plate 49 changes and reaches the switching point S1, the control device 210 engages the second clutch CL2 and releases the first clutch CL1. As a result, the gear ratio of the planetary transmission 31 switches from first gear to second gear. The state of the HST 28 reaching each switching point S1-S3 can be detected, for example, from the value of the ratio α and / or the inclination angle of the swash plate 49.

[0069] With the transmission in second gear, the control device 210 changes the inclination angle of the swash plate 49 from the "+MAX" side to the "-MAX" side. As the inclination angle of the swash plate 49 is changed, the ratio α increases steplessly.

[0070] When the inclination angle of the swash plate 49 changes and reaches the switching point S2, the control device 210 engages the third clutch CL3 and releases the second clutch CL2. As a result, the gear ratio of the planetary transmission 31 switches from second gear to third gear.

[0071] With the transmission in third gear, the control device 210 changes the inclination angle of the swash plate 49 from the "-MAX" side to the "+MAX" side. As the inclination angle of the swash plate 49 is changed, the ratio α increases steplessly.

[0072] When the inclination angle of the swash plate 49 changes and reaches the switching point S3, the control device 210 engages the fourth clutch CL4 and releases the third clutch CL3. As a result, the gear ratio of the planetary transmission 31 switches from third gear to fourth gear.

[0073] With the transmission in fourth gear, the control device 210 changes the inclination angle of the swash plate 49 from the "+MAX" side to the "-MAX" side. As the inclination angle of the swash plate 49 is changed, the ratio α increases steplessly.

[0074] Figure 8 shows an example of a ratio α that changes in response to the user's operation of the gear shift pedal 121. During the period when the planetary gear shifter 31 is switching gears, the change in ratio α is constant, or the value of ratio α decreases.

[0075] When engaging the clutch, oil is filled into the clutch's hydraulic chamber 135 (Figures 5A-5D). When switching gears in the planetary transmission 31, it takes time to fill the clutch of the next gear to be switched to with oil. If oil filling begins only after the ratio α reaches the value corresponding to the switching point, it takes time to engage the clutch of the next gear to be switched to, and the time during which the change in ratio α is stopped becomes longer, which may cause the occupant to feel a large shift shock.

[0076] In this embodiment, the filling of oil for engaging the clutch of the next gear is started before the ratio α reaches the value corresponding to the switching point. This allows the gear shift to be completed in a short time when the ratio α reaches the value corresponding to the switching point, thereby reducing the shift shock felt by the occupant. The details of this operation in this embodiment will be described below.

[0077] Figure 9 illustrates the operation of switching gears in the planetary transmission 31. Here, as an example, the operation of switching gears from first gear to second gear in the planetary transmission 31 is explained. The operation of switching between other gears is the same. This gear switching operation can also be applied to the operation of downshifting (for example, switching from second gear to first gear).

[0078] The “CL2 valve” shown in Figure 9 represents the state of the on-off valves 143 and 144 (Figures 5A-5D) of the second clutch CL2. When the “CL2 valve” is “ON”, it means that the on-off valve 143 of the second clutch CL2 is open and the on-off valve 144 is closed. Oil is supplied from the hydraulic pump 141 to the hydraulic chamber 135, and the second clutch CL2 becomes engaged. When the “CL2 valve” is “OFF”, it means that the on-off valve 143 of the second clutch CL2 is closed and the on-off valve 144 is open. The oil in the hydraulic chamber 135 is discharged to the oil tank 142, and the second clutch CL2 becomes disengaged.

[0079] The “CL1 valve” indicates the state of the on-off valves 143 and 144 of the first clutch CL1. When the “CL1 valve” is “ON”, it means that the on-off valve 143 of the first clutch CL1 is open and the on-off valve 144 is closed. Oil is supplied from the hydraulic pump 141 to the hydraulic chamber 135, and the first clutch CL1 is engaged. When the “CL1 valve” is “OFF”, it means that the on-off valve 143 of the first clutch CL1 is closed and the on-off valve 144 is open. The oil in the hydraulic chamber 135 is discharged to the oil tank 142, and the first clutch CL1 is released.

[0080] "CL2 sensor output" indicates the output signal of the pressure sensor 136 of the second clutch CL2. When the second clutch CL2 is engaged, "CL2 sensor output" indicates "HIGH", and when the second clutch CL2 is disengaged, "CL2 sensor output" indicates "LOW". "CL1 sensor output" indicates the output signal of the pressure sensor 136 of the first clutch CL1. When the first clutch CL1 is engaged, "CL1 sensor output" indicates "HIGH", and when the first clutch CL1 is disengaged, "CL1 sensor output" indicates "LOW".

[0081] In the graph shown in the lower part of Figure 9, the horizontal axis represents time, and the vertical axis represents the ratio α. This graph shows the change in ratio α when the planetary transmission 31 switches from first gear to second gear.

[0082] In this embodiment, the gear shift is switched when the ratio α changes and reaches a first value α1 (ratio α1) corresponding to the switching point S1, or after the ratio α has reached the first value α1. At this time, the control device 210 controls the hydraulic clutch mechanism 29 to start filling with oil for gear shifting before the ratio α reaches the first value α1. The control device 210 estimates the time T1 (first time) until the ratio α reaches the first value α1 from its current value. Based on the estimated time T1, the control device 210 can start filling the hydraulic chamber 135 of the second clutch CL2 with oil before the ratio α reaches the first value α1.

[0083] Furthermore, the control device 210 obtains the value of time T2 (second time), which is the time from when it starts filling the oil to switch from the current gear (first gear) to the next gear (second gear) until the second clutch CL2 is engaged. Based on time T2, the control device 210 can determine the time point P1 (first time point) at which it will start filling the oil to switch gears.

[0084] The control device 210 periodically calculates the value of the ratio α using the output signals from sensors 70 and 71. The control device 210 can estimate time T1 based on the rate of change of ratio α per unit time, the current value of ratio α, and a first value α1. For example, when time T1 is estimated from the rate of change of ratio α per unit time at a certain time point P0, it can be estimated that the ratio α reaches the first value α1 at time point P2. The rate of change of ratio α per unit time may be the average value over a certain period.

[0085] Furthermore, time T1 can be considered as the interval from ratio α0 to ratio α1, which corresponds to the starting point (time P0) of time T1, and the control device 210 starts filling the hydraulic chamber 135 of the second clutch CL2 with oil within the interval from ratio α0 to ratio α1.

[0086] Furthermore, if a work implement is connected to the work vehicle 10, it is necessary to accelerate or decelerate the work vehicle 10 including the work implement. On the other hand, if no work implement is connected to the work vehicle 10, the load to be accelerated or decelerated will be smaller. For this reason, the values ​​of the ratios α1-α3 corresponding to the switching points S1-S3 may change depending on whether or not a work implement is connected to the work vehicle 10. For this reason, the period (interval) in which the operation to switch the valve from "OFF" to "ON" is performed may be determined from the values ​​of the ratios α1-α3 that change depending on whether or not a work implement is connected, the current gear stage of the planetary transmission 31, and the time from when the valve is turned "ON" until the output signal of the pressure sensor 136 indicates "HIGH". Time T1 (or the interval from ratio α0 to ratio α1) is the period (or interval) in which the operation to switch the valve from "OFF" to "ON" is performed.

[0087] The control device 210 controls the second clutch CL2 so that the second clutch CL2 is engaged simultaneously with or after a predetermined time T3 (second predetermined time) has elapsed since the ratio α reached a first value α1 (ratio α1). The predetermined time T3 is, for example, 1 to 20 milliseconds, but is not limited thereto. The predetermined time T3 may also be zero.

[0088] The time T2 from the start of filling the second clutch CL2 with oil in the released state until the second clutch CL2 is engaged is predetermined, and the data for time T2 is stored in the storage device 220. The control device 210 can determine, for example, the time point P1 to start filling the second clutch CL2 with oil based on times T1, T2, and T3.

[0089] Alternatively, the time Ta from turning the valve "ON" until the output signal of the pressure sensor 136 indicates "HIGH" may be measured in advance, and the measured time Ta may be stored in the memory device 220. The control device 210 may compare time T1 and time Ta, and when time T1 becomes shorter than time Ta, it may start filling the hydraulic chamber 135 of the second clutch CL2 with oil. This corresponds to the control device 210 starting to fill the hydraulic chamber 135 of the second clutch CL2 with oil when the difference between the current value of ratio α and the first value α1 becomes smaller than the difference between ratio α at the time P1 when the CL2 valve is turned "ON" and ratio α when the output signal of the CL2 sensor indicates "HIGH". This makes it possible to suppress the output signal of the pressure sensor 136 from indicating "HIGH" before reaching the point where the planetary transmission 31 switches gears (for example, the first value α1), and thus reduce the shift shock felt by the occupant. However, if there are disturbances such as slight shaking of the work vehicle 10, the output signal of the pressure sensor 136 may not show "HIGH" after time Ta has elapsed since the valve was turned ON. For this reason, a certain amount of time T3 may be allocated as a margin to determine the timing (time P1) for turning the valve ON.

[0090] At time point P1, the control device 210 opens the on-off valve 143 of the second clutch CL2 and closes the on-off valve 144. This initiates the supply of oil from the hydraulic pump 141 to the hydraulic chamber 135 of the second clutch CL2.

[0091] At time point P2, the ratio α reaches the first value α1, and at time point P5, the second clutch CL2 is engaged. When the second clutch CL2 is engaged, the output signal of the pressure sensor 136 of the second clutch CL2 changes from "LOW" to "HIGH". When the output signal of the pressure sensor 136 of the second clutch CL2 changes from "LOW" to "HIGH", the control device 210 releases the first clutch CL1. The control device 210 closes the on-off valve 143 of the first clutch CL1 and opens the on-off valve 144. Discharge of oil from the hydraulic chamber 135 of the first clutch CL1 begins, and at time point P6, the first clutch CL1 is released.

[0092] By starting the oil filling process for engaging the second clutch CL2 before the ratio α reaches the first value α1 corresponding to the switching point S1, the gear shift can be completed in a short time when the ratio α reaches the first value α1. By reducing the time during which the change in ratio α is paused, the shift shock felt by the occupant can be reduced.

[0093] The time T2 from the start of filling the second clutch CL2 with oil while it is in the released state until the second clutch CL2 is engaged may be changed depending on the state of the second clutch CL2. For example, the control device 210 changes the length of time T2 based on the time elapsed since the second clutch CL2 was last engaged and then released.

[0094] If the elapsed time since the second clutch CL2 was last engaged and then released is short, there may be oil remaining in the hydraulic chamber 135 of the second clutch CL2. If the oil filling of the hydraulic chamber 135 is started in this state, the second clutch CL2 will engage in a short time. Therefore, if the elapsed time since the second clutch CL2 was last engaged and then released is short, the control device 210 sets the time T2 to a shorter value.

[0095] For example, a predetermined time T4 (first predetermined time) is set for the time from when control to release the second clutch CL2 in the engaged state is started until the oil in the hydraulic chamber 135 has completely drained. If the elapsed time is less than time T4, the control device 210 sets time T2 to be shorter than if it is T4 or longer. This prevents the second clutch CL2 from engaging before the ratio α reaches the first value α1.

[0096] Furthermore, setting a shorter time T2 can be considered as bringing the ratio α, which corresponds to the starting point of time T2 (the point P1 at which oil is to be filled into the second clutch CL2 in the released state), closer to the first value α1.

[0097] Time T4 may be changed according to the temperature of the oil supplied to the hydraulic chamber 135. The temperature of the oil supplied to the hydraulic chamber 135 can be detected using the temperature sensor 73. When the oil temperature is high, the viscosity decreases, and the oil will drain from the hydraulic chamber 135 more quickly. For example, the control device 210 may set time T4 shorter when the temperature of the oil being filled to engage the second clutch CL2 is high than when the temperature is low.

[0098] After estimating that the ratio α will reach a first value α1 at time P2, the gear shifting may be stopped before the ratio α reaches the first value α1. For example, the amount of change in the ratio α per unit time may decrease due to factors such as the user releasing the operation of the gear shift pedal 121 or an increase in the load on the work vehicle 10. Based on the calculated amount of change in the ratio α per unit time, the control device 210 determines that the ratio α no longer reaches the first value α1 at time P2, and stops the gear shifting.

[0099] The control device 210 may set a reference time point P3 (third time point), make a decision on whether or not to cancel the gear shift at a stage prior to time point P3, and not make a new decision on whether or not to cancel the gear shift at a stage after time point P3. For example, the control device 210 sets time point P3 to a time point T5 (third predetermined time) prior to time point P2. The predetermined time T5 is, for example, 20-50 milliseconds, but is not limited to that. If the control device 210 decides to cancel the gear shift at a stage prior to time point P3, it cancels the gear shift.

[0100] The control device 210 executes the gear change if it has decided not to cancel the gear change after time point P3. For example, the control device 210 executes the gear change even if a factor that would cause the gear change to be canceled occurs during the period between time point P3 and time point P2. This reduces control lag. After executing the gear change, the control device 210 decides whether or not to switch back to the original gear (first gear). For example, if the ratio α after executing the gear change is less than or equal to a predetermined value less than or equal to the first value α1, the control device 210 switches back to first gear. If the ratio α after executing the gear change is not less than or equal to a predetermined value less than or equal to the first value α1, the gear after the switch (second gear) is maintained.

[0101] The control device 210 may change the length of the predetermined time T5 according to the temperature of the oil being filled into the second clutch CL2 for shifting gears. For example, if the temperature of the oil being filled into the second clutch CL2 is high, the control device 210 sets the predetermined time T5 to be longer than when the temperature is low. That is, if the oil temperature is high, the time point P3 is set to an earlier time than when the temperature is low. When the oil is hot, its viscosity decreases, and the oil may be filled faster. By setting the time point P3 to an earlier time, smooth control can be performed even if the second clutch CL2 is engaged early.

[0102] Next, we will explain control that takes into account the overrun of the swash plate 49. For example, when the work vehicle 10 is accelerated and the ratio α changes and approaches a first value α1, the inclination angle of the swash plate 49 changes continuously. At this time, inertia acts on the swash plate 49 in the direction that changes the inclination angle. For this reason, even if the control that changes the inclination angle of the swash plate 49 to the forward rotation side is stopped when the ratio α changes and reaches the first value α1, the inclination angle of the swash plate 49 may continue to change to the forward rotation side due to inertia. If the inclination angle of the swash plate 49 continues to change to the forward rotation side, acceleration after switching to second gear may not be smooth.

[0103] In this embodiment, if the ratio α changes and approaches the first value α1, the control that changes the inclination angle of the swash plate 49 to the forward rotation side may be stopped before the ratio α reaches the first value α1.

[0104] The tilt angle θ1 of the swash plate 49 is predetermined when the ratio α is a first value α1. The value of the tilt angle θ1 may also be predetermined by the control device 210. Here, after stopping the control that changes the tilt angle of the swash plate 49 toward the forward rotation side, it is assumed that the tilt angle of the swash plate 49 continues to change by an angle θ2 toward the forward rotation side due to inertia. In this case, when the tilt angle of the swash plate 49 becomes an tilt angle θ3 which is an angle θ2 smaller than the tilt angle θ1, the control device 210 stops the control that changes the tilt angle of the swash plate 49 toward the forward rotation side. This makes it possible to suppress the overrun of the swash plate 49.

[0105] The memory device 220 has data pre-stored showing the relationship between the tilt angle of the swash plate 49 and the ratio α. Based on this data, the control device 210 can determine the value of the ratio αi when the tilt angle of the swash plate 49 is θ3. The value of the ratio αi may also be pre-stored in the memory device 220. In the process of the ratio α changing and approaching the first value α1, the control device 210 stops the control that changes the tilt angle of the swash plate 49 to the positive rotation side at point P4 when the ratio α becomes the ratio αi.

[0106] The control device 210 may change the time point P4 at which control is stopped based on the rate of change of the ratio α per unit time. For example, if the rate of change of the ratio α per unit time is large, the control device 210 sets the time point P4 to an earlier time than if it were small. If the rate of change of the ratio α per unit time is large, the inertia acting on the swash plate 49 increases, and the amount of overrun of the swash plate 49 may increase. If the rate of change of the ratio α per unit time is large, the overrun of the swash plate 49 can be suppressed by stopping the control that changes the tilt angle of the swash plate 49 to the positive rotation side earlier.

[0107] When the angle θ2 is large, the inclination angle θ3 becomes small, and the value of the ratio αi decreases. When the value of the ratio αi decreases, time point P4 becomes earlier. At time point P4, when the ratio α becomes equal to the ratio αi, the control device 210 can suppress the overrun of the swash plate 49 by stopping the control that changes the inclination angle of the swash plate 49 to the positive rotation side.

[0108] Data showing the relationship between the rate of change of ratio α per unit time and angles θ2 and θ3 may be pre-stored in the storage device 220. Similarly, data showing the relationship between the rate of change of ratio α per unit time and ratio αi may be pre-stored in the storage device 220. The control device 210 may use this data to stop the control that changes the tilt angle of the swash plate 49 to the positive rotation side.

[0109] The control device 210 may change time point P4 based on the temperature of the oil supplied to the hydraulic motor M. For example, if the temperature of the oil supplied to the hydraulic motor M is high, the control device 210 sets time point P4 to an earlier time than if the temperature is low. When the oil is hot, the viscosity decreases, which can increase the amount of overrun of the swash plate 49. When the oil is hot, the overrun of the swash plate 49 can be suppressed by stopping the control that changes the tilt angle of the swash plate 49 to the forward rotation side earlier.

[0110] Furthermore, the control device 210 may change the time point P4 according to the pressure in the closed circuit 95 of the HST 28. For example, if a force (internal pressure) is applied in the direction that the swash plate 49 is being pushed (chased from behind), the time point P4 may be set to an earlier time, and if a force is applied in the direction that the swash plate 49 is being pushed back (a direction in which the brakes are trying to stop it from the front), the time point P4 may be set to a later time. This makes it possible to more effectively suppress the overrun of the swash plate 49.

[0111] In the above description, it was assumed that the work vehicle 10 would be driven by a user, but the work vehicle 10 may also be equipped with an autonomous driving function. The technology of this disclosure can also be applied to gear shifting in autonomous driving.

[0112] If the control device 210 is implemented by multiple ECUs, an ECU (ECU1) that monitors the user's operation of the gear shift pedal 121 and an ECU (ECU2) that performs gear shifting may be provided separately. In this case, ECU1 may send a command to ECU2 to switch gears based on the operation state of the gear shift pedal 121, and ECU2, upon receiving the command, may begin preparing to switch gears. For example, ECU2 can reduce the total amount of computation by starting to calculate the amount of change of the ratio α per unit time after receiving the command.

[0113] The control system, including the control device and storage device in the above embodiment, can also be retrofitted to a work vehicle. Such a system can be manufactured and sold independently of the work vehicle. Computer programs used in such systems can also be manufactured and sold independently of the work vehicle. The computer programs can be provided, for example, stored in a computer-readable non-temporary storage medium. The computer programs can also be provided by download via a telecommunications line (e.g., the Internet).

[0114] As described above, this disclosure includes the control system, work vehicle, control method, and computer program described in the following items.

[0115] [Item 1] A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device is When the ratio changes and approaches a first value corresponding to the first switching point, the first time until the ratio reaches the first value is estimated. A control system that controls the hydraulic clutch mechanism to start filling the oil for shifting the gears before the ratio reaches the first value, based on the estimated first time.

[0116] [Item 2] The control system according to item 1, wherein the control device estimates the first time based on the amount of change of the ratio per unit time.

[0117] [Item 3] The control system according to item 1 or 2, wherein when the ratio reaches the first value, or when the current gear is switched to the next gear while the ratio has reached the first value, the control device determines a first time to start filling the oil for switching gears based on a second time from when the filling of the oil for switching gears begins until the clutch of the next gear is engaged.

[0118] [Item 4] The control system according to item 3, wherein the control device changes the length of the second time based on the elapsed time since the clutch of the next gear was last engaged and then released.

[0119] [Item 5] The control device, according to item 4, sets the second time to be shorter than the first predetermined time if the elapsed time is shorter than the first predetermined time.

[0120] [Item 6] The control system according to item 5, wherein the control device sets the first predetermined time to be shorter when the temperature of the oil to be filled to engage the clutch of the next gear is a first temperature than when the temperature is a second temperature lower than the first temperature.

[0121] [Item 7] The control system according to item 3, wherein the control device determines a first time point at which the oil filling begins, such that the clutch of the next gear is engaged at the same time as the ratio reaches the first value or after a second predetermined time has elapsed thereafter.

[0122] [Item 8] The control system according to item 7, wherein the second predetermined time is 1 to 20 milliseconds.

[0123] [Item 9] The control system according to item 7, wherein the control device performs control to release the clutch of the gear shift before the switch after the ratio reaches the first value.

[0124] [Item 10] The control device is A decision is made whether or not to discontinue the gear shifting at a third predetermined time before the second time point in time when the ratio is estimated to reach the first value, or before the third time point. A control system according to any of items 1 to 9, which, if it is decided to cancel, cancels the gear shifting.

[0125] [Item 11] The control system according to item 10, wherein the control device has decided not to cancel the gear shifting after the third time point has passed, and performs the gear shifting.

[0126] [Item 12] The control device, according to item 11, performs the gear shift even if a factor that would cause the gear shift to be canceled occurs during the period from the third time point to the second time point.

[0127] [Item 13] The control device, after performing the gear shift change, determines whether or not to switch back to the original gear, as described in item 12.

[0128] [Item 14] The control device changes the third predetermined time according to the temperature of the oil that is filled in order to switch the gear ratio, as described in item 10.

[0129] [Item 15] The control device, according to item 14, sets the third predetermined time to be longer when the temperature of the oil to be filled in order to switch the gear ratio is the third temperature than when the temperature is lower than the third temperature (the fourth temperature).

[0130] [Item 16] The control device is The angle of the swash plate is predetermined when the ratio is the first value. By controlling the angle of the swash plate, the rotational speed of the rotation generated by the hydraulic motor is changed. A control system according to any one of items 1 to 15, wherein if the ratio changes and approaches the first value, the control of changing the angle of the swash plate is stopped before the ratio reaches the first value.

[0131] [Item 17] The control system according to item 16, wherein the control device changes a fourth time point at which the control of changing the angle of the swash plate is stopped, based on the amount of change of the ratio per unit time.

[0132] [Item 18] The control device is the control system according to item 17, wherein when the amount of change in the ratio per unit time is the first amount of change, the fourth time point is set to an earlier time point than when the second amount of change is smaller than the first amount of change.

[0133] [Item 19] The control system according to item 17, wherein the control device further modifies the fourth time point based on the temperature of the oil supplied to the hydraulic motor.

[0134] [Item 20] The control system according to item 19, wherein the control device sets the fourth time point earlier when the temperature of the oil supplied to the hydraulic motor is a fifth temperature than when the oil is a sixth temperature which is lower than the fifth temperature.

[0135] [Item 21] A work vehicle comprising a control system described in any of items 1 to 20, the internal combustion engine, and the power transmission device.

[0136] [Item 22] A control method for controlling the operation of a power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control method described above is The hydraulic clutch mechanism is controlled to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points that are points for switching gears of the planetary transmission. Includes, The aforementioned multiple switching points include the first switching point, The control method described above is When the ratio changes and approaches a first value corresponding to the first switching point, estimate the first time until the ratio reaches the first value. Based on the estimated first time, the hydraulic clutch mechanism is controlled to begin filling with oil for shifting gears before the ratio reaches the first value. A control method that further includes the following.

[0137] [Item 23] A computer program that causes a computer to control the operation of the power transmission system of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The aforementioned computer program, The hydraulic clutch mechanism is controlled to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points that are points for switching gears of the planetary transmission. The computer is made to execute the above, The aforementioned multiple switching points include the first switching point, The aforementioned computer program, When the ratio changes and approaches a first value corresponding to the first switching point, estimate the first time until the ratio reaches the first value. Based on the estimated first time, the hydraulic clutch mechanism is controlled to begin filling with oil for shifting gears before the ratio reaches the first value. A computer program that further causes the aforementioned computer to execute the following.

[0138] [Item 24] A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device controls the hydraulic clutch mechanism to start filling the oil for switching the gear when the ratio changes and reaches a first value corresponding to the first switching point, or when the gear shift is switched after the ratio has reached the first value, before the ratio reaches the first value. The control device is a control system that determines the timing for starting the oil to switch gears based on the time from when the oil to switch gears is started until the clutch of the next gear is engaged.

[0139] [Item 25] The control system according to item 24, wherein the control device changes the length of time from the start of oil filling until the clutch of the next gear is engaged, based on the elapsed time since the clutch of the next gear was last engaged and then released.

[0140] [Item 26] The control device, when the elapsed time is shorter than a first predetermined time, sets the time from the start of oil filling until the clutch of the next gear shift is engaged to be shorter than when the elapsed time is longer.

[0141] [Item 27] The control system according to item 26, wherein the control device sets the first predetermined time to be shorter when the temperature of the oil to be filled to engage the clutch of the next gear is a first temperature than when the temperature is a second temperature lower than the first temperature.

[0142] [Item 28] The control system according to item 24 or 25, wherein the control device determines the time at which the oil filling begins so that the clutch of the next gear is engaged at the same time as the ratio reaches the first value or after a second predetermined time has elapsed thereafter.

[0143] [Item 29] The control system according to item 28, wherein the second predetermined time is 1 to 20 milliseconds.

[0144] [Item 30] The control system according to item 28, wherein the control device performs control to release the clutch of the gear shift before the switch after the ratio reaches the first value.

[0145] [Item 31] A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device is The angle of the swash plate at the first switching point is determined in advance, By controlling the angle of the swash plate, the rotational speed of the rotation generated by the hydraulic motor is changed. A control system that, when the ratio changes and approaches a first value corresponding to the first switching point, stops controlling the angle of the swash plate before the ratio reaches the first value.

[0146] [Item 32] A work vehicle comprising a control system described in any of items 24 to 31, the internal combustion engine, and the power transmission device. [Industrial applicability]

[0147] The technology disclosed herein is particularly useful in the field of vehicle transmission technology. [Explanation of Symbols]

[0148] 10: Work vehicle, 15: Power transmission device, 20: Input shaft, 21: Main transmission, 23: Forward / reverse selector, 28: Hydrostatic continuously variable transmission (HST) 28a: Pump shaft, 28b: Output shaft, 29: Hydraulic clutch mechanism, 30: Planetary transmission unit, 31: Planetary transmission, 35: Output shaft, 36a: First range gear mechanism, 36b: Second range gear mechanism, 36c: Third range gear mechanism, 36d: Fourth range gear mechanism, 37: Output device, 49: Swashplate, 70: Rotation sensor, 71: Rotation sensor, 72: Position sensor, 73: Temperature sensor, 74: Temperature sensor, 90: Hydraulic cylinder, 91: Operating oil passage, 92: Transmission valve, 92a: Solenoid, 93: Oil supply passage, 94: Hydraulic pump, 95: Closed circuit, 96: Emergency relief valve, 97: Pressure sensor, 101: Vehicle body, 102: Internal combustion engine, 102a: Output shaft, 103: Transmission case, 104: Front wheels, 105: Rear wheels, 106: Cabin, 107: Steering gear, 108: Driver's seat, 109: Coupling device, 120: Gear shifting device, 121: Gear shift pedal, 122: Forward / reverse lever, 131: Plate, 132: Plate, 133: Piston, 134: Return spring, 135: Hydraulic chamber, 136: Pressure sensor, 141: Hydraulic pump, 142: Oil tank, 143: On / off valve, 144: On / off valve, 145: Oil passage, 200: Control system, 210: Control device, 220: Memory device, CL: Clutch, CL1: First clutch, CL2: Second clutch, CL3: Third clutch, CL4: Fourth clutch, M: Hydraulic motor, P: Hydraulic pump

Claims

1. A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device is When the ratio changes and approaches a first value corresponding to the first switching point, the first time until the ratio reaches the first value is estimated. A control system that controls the hydraulic clutch mechanism to start filling the oil for shifting the gears before the ratio reaches the first value, based on the estimated first time.

2. The control system according to claim 1, wherein the control device estimates the first time based on the amount of change of the ratio per unit time.

3. The control system according to claim 1 or 2, wherein when the ratio reaches the first value, or when the current gear is switched to the next gear while the ratio has reached the first value, the control device determines a first time to start filling the oil for switching gears based on a second time from when the filling of the oil for switching gears is started until the clutch of the next gear is engaged.

4. The control system according to claim 3, wherein the control device changes the length of the second time based on the elapsed time since the clutch of the next gear was last engaged and then released.

5. The control system according to claim 4, wherein the control device sets the second time to be shorter than the first predetermined time if the elapsed time is shorter than the first predetermined time.

6. The control system according to claim 5, wherein the control device sets the first predetermined time to be shorter when the temperature of the oil to be filled to engage the clutch of the next gear is a first temperature than when the temperature is a second temperature lower than the first temperature.

7. The control system according to claim 3, wherein the control device determines a first time point at which it starts filling the oil so that the clutch of the next gear is engaged at the same time as the ratio reaches the first value or after a second predetermined time has elapsed thereafter.

8. The control system according to claim 7, wherein the second predetermined time is 1 to 20 milliseconds.

9. The control system according to claim 7, wherein the control device performs control to release the clutch of the gear shift before switching after the ratio reaches the first value.

10. The control device is A decision is made whether or not to stop the gear shifting at a third time point, which is a third predetermined time before the second time point when the ratio is estimated to reach the first value, or before the third time point. The control system according to claim 1 or 2, wherein if it is decided to cancel, the gear shifting is canceled.

11. The control system according to claim 10, wherein the control device has decided not to cancel the gear shifting after the third time point has passed, and performs the gear shifting.

12. The control system according to claim 11, wherein the control device performs the gear shift even if a factor that causes the gear shift to be canceled occurs during the period from after the third time point until the second time point is reached.

13. The control system according to claim 12, wherein the control device determines whether or not to switch back to the original gear after performing the gear shift.

14. The control system according to claim 10, wherein the control device changes the third predetermined time according to the temperature of the oil that is filled in order to switch the gear ratio.

15. The control system according to claim 14, wherein the control device sets the third predetermined time to be longer when the temperature of the oil to be filled in order to switch the gear shift is the third temperature than when the temperature is lower than the third temperature (fourth temperature).

16. The control device is The angle of the swash plate is predetermined when the ratio is the first value. By controlling the angle of the swash plate, the rotational speed of the rotation generated by the hydraulic motor is changed. The control system according to claim 1 or 2, wherein if the ratio changes and approaches the first value, the control of changing the angle of the swash plate is stopped before the ratio reaches the first value.

17. The control system according to claim 16, wherein the control device changes a fourth time point at which it stops controlling the angle of the swash plate based on the amount of change in the ratio per unit time.

18. The control system according to claim 17, wherein the control device sets the fourth time point earlier when the amount of change of the ratio per unit time is a first change, compared to when the second change is smaller than the first change.

19. The control system according to claim 17, wherein the control device further changes the fourth time point based on the temperature of the oil supplied to the hydraulic motor.

20. The control system according to claim 19, wherein the control device sets the fourth time point earlier when the temperature of the oil supplied to the hydraulic motor is a fifth temperature than when the oil is a sixth temperature which is lower than the fifth temperature.

21. A work vehicle comprising the control system according to claim 1 or 2, the internal combustion engine, and the power transmission device.

22. A control method for controlling the operation of a power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control method described above is The hydraulic clutch mechanism is controlled to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points that are points for switching gears of the planetary transmission. Includes, The aforementioned multiple switching points include the first switching point, The control method described above is When the ratio changes and approaches a first value corresponding to the first switching point, estimate the first time until the ratio reaches the first value. Based on the estimated first time, the hydraulic clutch mechanism is controlled to begin filling the oil for shifting the gear before the ratio reaches the first value. A control method that further includes the following.

23. A computer program that causes a computer to control the operation of the power transmission system of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The aforementioned computer program, The hydraulic clutch mechanism is controlled to switch gears based on the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points that are points for switching gears of the planetary transmission. The computer is made to execute the above, The aforementioned multiple switching points include the first switching point, The aforementioned computer program, When the ratio changes and approaches a first value corresponding to the first switching point, estimate the first time until the ratio reaches the first value. Based on the estimated first time, the hydraulic clutch mechanism is controlled to begin filling the oil for shifting the gear before the ratio reaches the first value. A computer program that further causes the aforementioned computer to execute the following.

24. A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device controls the hydraulic clutch mechanism to start filling the oil for switching the gear when the ratio changes and reaches a first value corresponding to the first switching point, or when the gear shift is switched after the ratio has reached the first value, before the ratio reaches the first value. The control device determines the time to start filling the oil for switching gears based on the time from when it starts filling the oil for switching gears from the current gear to the next gear until the clutch of the next gear is engaged. The control device is a control system that changes the length of time from the start of oil filling until the clutch of the next gear is engaged, based on the elapsed time since the clutch of the next gear was last engaged and then released.

25. The control system according to claim 24, wherein if the elapsed time is shorter than a first predetermined time, the control device sets the time from the start of oil filling until the clutch of the next gear shift is engaged to be shorter than if the elapsed time is longer.

26. The control system according to claim 25, wherein the control device sets the first predetermined time to be shorter when the temperature of the oil to be filled to engage the clutch of the next gear is a first temperature than when the temperature is a second temperature lower than the first temperature.

27. The control system according to claim 24, wherein the control device determines the time at which it starts filling the oil so that the clutch of the next gear is engaged at the same time as the ratio reaches the first value or after a second predetermined time has elapsed thereafter.

28. The control system according to claim 27, wherein the second predetermined time is 1 to 20 milliseconds.

29. The control system according to claim 27, wherein the control device performs control to release the clutch of the gear shift before switching after the ratio reaches the first value.

30. A control system for controlling the operation of the power transmission device of a work vehicle, The power transmission device is A hydrostatic continuously variable transmission having a hydraulic pump that transmits rotation generated by an internal combustion engine and discharges oil according to the angle of the swash plate, and a hydraulic motor that generates rotation when the oil is supplied from the hydraulic pump, A planetary transmission that transmits the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission, and generates multiple types of rotation corresponding to multiple gears, A hydraulic clutch mechanism for switching the gear ratio of the planetary transmission, Equipped with, The control system is A storage device that stores data showing the relationship between the ratio of the rotational speed of a predetermined component on the power transmission path that transmits the rotation of the planetary transmission to the wheels and the rotational speed of the internal combustion engine, and a plurality of switching points which are points that switch the gears of the planetary transmission, A control device that controls the hydraulic clutch mechanism to switch gears based on the ratio and the data, Equipped with, The aforementioned multiple switching points include the first switching point, The control device is The angle of the swash plate at the first switching point is determined in advance, By controlling the angle of the swash plate, the rotational speed of the rotation generated by the hydraulic motor is changed. A control system that, when the ratio changes and approaches a first value corresponding to the first switching point, stops controlling the angle of the swash plate before the ratio reaches the first value.

31. A work vehicle comprising the control system according to any one of claims 24, 25, 26, or 30, the internal combustion engine, and the power transmission device.

Images