Control system, work vehicle, control method and computer program

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]

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

[0002] There are work vehicles such as agricultural tractors that are equipped with an internal combustion engine and a hydrostatic continuously variable transmission (see, for example, Patent Document 1). The rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are combined in a planetary transmission and transmitted to the wheels. The gear stages of the planetary transmission can be changed using a clutch mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-96208 Summary of the Invention [Problem to be solved by the invention]

[0004] If it takes a long time for the planetary transmission to change gears while the work vehicle is traveling, the driver may feel a large shift shock.

[0005] There is a demand for reducing the time it takes to change gears. [Means for solving the problem]

[0006] A control system according to an 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 including a hydrostatic continuously variable transmission having a hydraulic pump to which rotation generated by an internal combustion engine is transmitted and which discharges oil according to an angle of a swash plate, and a hydraulic motor to which the oil is supplied from the hydraulic pump and which generates rotation, a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted and which generates a plurality of types of rotation corresponding to a plurality of gear stages, and a hydraulic clutch mechanism for switching the gear stages of the planetary transmission, the control system controlling a predetermined portion on a power transmission path which transmits the rotation of the planetary transmission to wheels. and a control device that controls the hydraulic clutch mechanism to switch the gear stage based on the ratio and the data, the multiple switching points including 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 based on the estimated first time to start filling oil for switching the gear stage before the ratio reaches the first value.

[0007] A control method according to an embodiment of the present disclosure is a control method 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 to which rotation generated by an internal combustion engine is transmitted and which discharges oil according to an angle of a swash plate, and a hydraulic motor to which the oil is supplied from the hydraulic pump and which generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted and which generates a plurality of types of rotation corresponding to a plurality of gear stages; and a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; and the control method includes a power transmission control device for transmitting the rotation of the planetary transmission to wheels. The method includes controlling the hydraulic clutch mechanism to change the gear stage based on a relationship between a ratio between the rotational speed of a specified part on a path and the rotational speed of the internal combustion engine, and a plurality of switching points which are points at which the gear stages of the planetary transmission are changed, the plurality of switching points including a first switching point, and the control method further includes, when the ratio changes and approaches a first value corresponding to the first switching point, estimating a first time until the ratio reaches the first value, and controlling the hydraulic clutch mechanism to start filling oil to change the gear stage before the ratio reaches the first value based on the estimated first time.

[0008] A computer program according to an embodiment of the present disclosure is a computer program for causing a computer to execute control of the operation of a power transmission device of a work vehicle, the power transmission device including: a hydrostatic continuously variable transmission having a hydraulic pump to which rotation generated by an internal combustion engine is transmitted and which discharges oil according to an angle of a swash plate, and a hydraulic motor to which the oil is supplied from the hydraulic pump and which generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted and which generates a plurality of types of rotation corresponding to a plurality of gear stages; and a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; and the computer program includes a power transmission device for transmitting the rotation of the planetary transmission to wheels. The computer program further causes the computer to control the hydraulic clutch mechanism to change the gear stage based on a relationship between a ratio between a rotational speed of a specific part on a reach path and a rotational speed of the internal combustion engine, and a plurality of switching points which are points at which the gear stages of the planetary transmission are changed, the plurality of switching points including a first switching point, and the computer program further causes 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 to change the gear stage before the ratio reaches the first value based on the estimated first time.

[0009] A control system according to an 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 including: a hydrostatic continuously variable transmission having a hydraulic pump to which rotation generated by an internal combustion engine is transmitted and which discharges oil according to an angle of a swash plate, and a hydraulic motor to which the oil is supplied from the hydraulic pump and which generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted and which generates a plurality of types of rotation corresponding to a plurality of gear stages; and a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; the control system includes a storage device that stores data indicating the relationship between the ratio between the rotation speed of a predetermined part on a power transmission path that transmits the rotation of the planetary transmission device to wheels and the rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission device are switched; and a control device that controls the hydraulic clutch mechanism to change the gear stage based on a ratio and the data, the multiple changeover points including a first changeover point, and the control device controls the hydraulic clutch mechanism to start filling with oil for changing the gear stage when the ratio changes and reaches a first value corresponding to the first changeover point, or before the ratio reaches the first value, if the gear stage is changed after the ratio reaches the first value, and the control device determines the point in time to start filling with oil for changing the gear stage based on the time from when filling with oil for changing from a current gear stage to a next gear stage starts to when the clutch of the next gear stage 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 to which rotation generated by an internal combustion engine is transmitted and which discharges oil according to an angle of a swash plate, and a hydraulic motor to which the oil is supplied from the hydraulic pump and which generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted and which generates a plurality of types of rotation corresponding to a plurality of gear stages; and a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; and the control system controls a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels. The system includes a storage device that stores data indicating the relationship between a ratio between a rotational speed of the hydraulic motor and the rotational speed of the internal combustion engine, and a plurality of switching points which are points at which the gear stages of the planetary transmission are switched, and a control device that controls the hydraulic clutch mechanism to switch the gear stages based on the ratio and the data, the plurality of switching points including a first switching point, 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 to change 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 to change the angle of the swash plate before the ratio reaches the first value. Effect of the Invention

[0011] When shifting gears, it takes time to fill the oil in order to engage the clutch of the next gear to be shifted to. If oil filling starts after the ratio between the rotation speed of a specific rotating part and the rotation speed of the internal combustion engine reaches a value corresponding to the shift point, it takes time to engage the clutch of the next gear to be shifted to, and the time required to stop changing the ratio becomes longer, which may cause the passenger to feel a large shift shock.

[0012] According to an embodiment of the present disclosure, oil filling is started before the ratio reaches a value corresponding to the switching point, so that the gear shift can be completed in a short time when the ratio reaches a value corresponding to the switching point, and the time for stopping the change of the ratio is shortened, thereby reducing the shift shock felt by the occupant. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a side view that diagrammatically illustrates an example of a work vehicle. [Diagram 2] FIG. 2 is a diagram illustrating a schematic diagram of a power transmission device provided in a work vehicle. [Diagram 3] FIG. 3 is a diagram showing a schematic diagram of a planetary transmission. [Figure 4] FIG. 4 is a schematic diagram of a hydrostatic continuously variable transmission. [Figure 5A] FIG. 5A is a diagram illustrating an example of a clutch included in the hydraulic clutch mechanism. [Figure 5B] FIG. 5B is a diagram illustrating an example of a clutch included in the hydraulic clutch mechanism. [Figure 5C] FIG. 5C is a diagram illustrating an example of a clutch included in the hydraulic clutch mechanism. [Figure 5D] FIG. 5D is a diagram illustrating an example of a clutch included in the hydraulic clutch mechanism. [Figure 6] FIG. 6 is a block diagram showing an example of a control system provided in a work vehicle. [Figure 7] FIG. 7 is a diagram showing an example of a gear shift operation of a work vehicle. [Figure 8] FIG. 8 is a diagram showing an example of a ratio that changes in response to the operation of the speed change pedal by the user. [Figure 9] FIG. 9 is a diagram illustrating the operation of switching the gear position of the planetary transmission. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, similar components are given similar reference symbols, and if there is overlap, their description will be omitted. The symbols F, Re, U, and D in the drawings represent front, rear, top, and bottom, respectively. In the description of the embodiments below, a tractor is used as an example of a work vehicle. The technology of the present disclosure is not limited to tractors and can be applied to other types of work vehicles. The following embodiments are examples, and the technology of the present disclosure is not limited to the following embodiments.

[0015] (Work vehicle) FIG. 1 is a side view showing a schematic example of a work vehicle 10. The work vehicle 10 shown in FIG. 1 is a tractor, and can be fitted with a work implement at either or both of the rear and front. The work vehicle 10 can travel within a field while performing agricultural work according to the type of work implement. The work vehicle 10 may also travel within or outside a field without a work implement attached.

[0016] The work vehicle 10 includes a vehicle body 101, an internal combustion 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 cabin 106. The internal combustion engine 102 may be, for example, a diesel engine. The transmission case 103 houses a power transmission device 15 (FIG. 2). A driver's seat 108, a steering device 107, and a group of switches for operation are provided inside the cabin 106. When the work vehicle 10 travels for work in a field, one or both of the front wheels 104 and the rear wheels 105 may be multiple wheels (crawlers) equipped with 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 steerable wheels, and the traveling direction of the work vehicle 10 can be changed by changing the turning angle (also referred to as the "steering angle").

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

[0019] (Power transmission device) FIG. 2 is a diagram showing a schematic diagram of the power transmission device 15 provided in the work vehicle 10. As shown in FIG.

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

[0021] The power transmission device 15 includes an input shaft 20, a main speed change device 21, a forward / reverse switching device 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 an output shaft 102a of an internal combustion engine 102 is transmitted to the input shaft 20 via, for example, a damper disc. The rotation of the input shaft 20 is transmitted to the main speed change device 21.

[0022] The main transmission 21 includes a hydrostatic continuously variable transmission (HST: Hydro Static Transmission) 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 a plurality of types of rotation corresponding to a plurality of gear stages. The hydraulic clutch mechanism 29 switches the gear stages of the planetary transmission 31.

[0023] The HST 28 includes a hydraulic pump P, a hydraulic motor M, a pump shaft 28a, an output shaft 28b, and a swash plate 49. A rotating 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 rotating shaft 26. The rotation of the input shaft 20 is transmitted to the pump shaft 28a via the rotating 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 to which the rotation of the input shaft 20 is transmitted 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, and the hydraulic motor M generates rotation. By changing the angle of the swash plate 49, the speed of the rotation generated by the hydraulic motor M can be changed steplessly. Furthermore, by changing the tilt direction of the swash plate 49, the direction of rotation generated by the hydraulic motor M can be switched between a forward rotation direction and a reverse rotation direction.

[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] 3 is a diagram showing a schematic diagram of the planetary transmission 31. The planetary transmission 31 includes a first planetary transmission 32 and a second planetary transmission 33. The planetary transmission 31 has a compound planetary gear mechanism.

[0026] The first planetary transmission 32 includes a first sun gear 32a, a first planetary gear 32b, a first ring gear 32c, and an interlocking gear 32d. The second planetary transmission 33 includes 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 has internal teeth that mesh with the first planetary gear 32b. The second planetary transmission 33 is disposed rearward of the first planetary transmission 32. The second sun gear 33a meshes with the second planetary gear 33b. The second ring gear 33c has 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 are interlocked with each other.

[0028] 2 and 3, the rotation of the output shaft 28b of the HST 28 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 transmission 31 includes an output device 37 (FIG. 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 includes 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 includes 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 the first range gear mechanism 36a. 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 released, 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 the second range gear mechanism 36b. 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 released, 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 the third range gear mechanism 36c. 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 released, 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 receives the rotation of the third input shaft 34c. 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 released, 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 HST 28 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 to fourth clutches CL2 to 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 to fourth clutches CL2 to CL4 are disengaged, the gear position of the planetary transmission 31 is "first gear." The output shaft 35 outputs 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 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 position is "third gear." The output shaft 35 outputs rotation corresponding to third gear.

[0039] When the fourth clutch CL4 is engaged and the first and 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 and third clutches CL1-CL3 are disengaged, the gear position is "fourth gear." The output shaft 35 outputs a rotation corresponding to the 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 includes 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 provided 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. Rotation in a direction that moves the work vehicle 10 forward is transmitted from the forward gear interlocking mechanism 23c 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. Rotation in a direction that moves the work vehicle 10 backward is transmitted from the reverse gear interlocking mechanism 23d to the output shaft 23b.

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

[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. Of the left and right rear wheels 105, only the left rear wheel 105 is shown in Fig. 2. 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 a 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 includes an input shaft 25a, an output shaft 25b, a constant speed gear mechanism 40, an increasing speed gear mechanism 41, a constant speed clutch CLT, and an increasing speed clutch CLH. The input shaft 25a is connected to the output shaft 24a of the gear mechanism 24. Rotation of the output shaft 23b of the forward / reverse switching device 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 provided with the constant speed clutch CLT and the increasing speed 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 such that the peripheral speed of the front wheels 104 is the same as the peripheral speed of the rear wheels 105 is transmitted to the front wheels 104. When the speed-increasing clutch CLH is engaged, rotation such that the peripheral speed of the front wheels 104 is greater than the peripheral speed of the rear wheels 105 is transmitted to the front wheels 104. When the speed-increasing clutch CLH is engaged, the turning radius of the work vehicle 10 can be made smaller than when the constant velocity clutch CLT is engaged.

[0049] The power transmission device 15 (FIG. 2) is provided with a plurality of rotation sensors 70 that detect the rotation of various components. The rotation speeds (revolutions per minute) of the various components can be calculated using output signals from these rotation sensors 70. The plurality of rotation sensors 70 include, for example, a rotation sensor that detects the rotation of the output shaft 28b of the HST 28, a rotation sensor that detects the rotation of the output shaft 35 of the planetary transmission 31, a rotation sensor that detects the rotation of the output shaft 23b of the forward / reverse switching device 23, and a rotation sensor that detects the rotation of the input shaft 16a of the rear wheel differential mechanism 16. The internal combustion engine 102 is provided with a rotation sensor 71 that detects the rotation of the internal combustion engine 102. The rotation sensor 71 detects, for example, the rotation of the output shaft 102a. The rotation speed of the internal combustion engine 102 can be calculated using the output signal from the rotation sensor 71.

[0050] 4 is a diagram showing a schematic diagram of the HST 28. A hydraulic cylinder 90 is connected to the swash plate 49 of the hydraulic pump P. A speed change operation valve 92 is connected to the hydraulic cylinder 90 via an operation oil passage 91. A hydraulic pump 94 is connected to the speed change operation valve 92 via an oil supply passage 93. An emergency relief valve 96 and a pressure sensor 97 are provided in a closed circuit 95 connecting the hydraulic pump P and the hydraulic motor M. The pressure sensor 97 detects the hydraulic pressure of 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 oil is supplied to the hydraulic cylinder 90 from a hydraulic pump 94 via a speed change operation valve 92, and the hydraulic cylinder 90 operates. By operating the hydraulic cylinder 90, the tilt angle of the swash plate 49 can be changed. By switching the port of the speed change operation valve 92, it is possible to switch between the two oil chambers of the hydraulic cylinder 90 to which hydraulic oil is supplied. The speed change operation valve 92 is, for example, an electromagnetically operated valve, and port switching can be performed by operating a solenoid 92a of the speed change operation valve 92. By stopping the supply of hydraulic oil to the hydraulic cylinder 90, the position of the hydraulic cylinder 90 can be maintained.

[0052] The HST 28 can change the direction in which the swash plate 49 is tilted by switching the port of the speed change operation valve 92, and can switch the direction of rotation generated by the hydraulic motor M between forward and reverse rotation. The HST 28 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 provided with, for example, a position sensor 72 that detects the position of the hydraulic cylinder 90. The inclination direction and inclination angle of the swash plate 49 can be calculated using an output signal from the position sensor 72. A sensor for detecting the inclination direction and inclination angle of the swash plate 49 may be provided on the swash plate 49.

[0054] 5A to 5D are diagrams showing examples of clutches included in the hydraulic clutch mechanism 29 (FIG. 2). Each of the first to fourth clutches CL1 to CL4 may have the structure of the clutch CL shown in FIGS. 5A to 5D, for example.

[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. The on-off valves 143 and 144 are, for example, solenoid valves. The hydraulic pump 141 is provided with a temperature sensor 73. 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] Fig. 5A shows the clutch CL in a released state. When the clutch CL is in a released state, if the on-off valve 143 is opened and the on-off valve 144 is closed, oil is supplied from the hydraulic pump 141 to the hydraulic chamber 135, and the piston 133 moves in the direction of the arrow 137 while pushing the plate 131, as shown in Fig. 5B. When the piston 133 moves in the direction of the arrow 137 while pushing the plate 131, the plate 131 comes into contact with the plate 132, as shown in Fig. 5C, and the clutch CL enters an engaged state. The contact between the plates 131 and 132 can be detected by using, for example, a pressure sensor 136.

[0057] When the clutch CL is in the engaged state, if the on-off valve 143 is closed and the on-off valve 144 is opened, as shown in Fig. 5D, the piston 133 moves in the direction of the arrow 138 by the return spring 134, and the oil in the hydraulic chamber 135 is discharged to the oil tank 142. As the piston 133 moves in the direction of the arrow 138, the plate 131 moves away from the plate 132, and the clutch CL enters the released state. The piston 133 is pushed by the return spring 134 and returns to the position shown in Fig. 5A.

[0058] (Control System) The work vehicle 10 is equipped with a control system that controls the operation of the work vehicle 10. Fig. 6 is a block diagram showing an example of a control system 200 equipped in the work vehicle 10. Fig. 6 shows components that are relatively closely related to the gear shifting operation of the work vehicle 10, and other components are omitted from the illustration.

[0059] The control system 200 includes a control device 210 and a storage device 220. The control device 210 may be realized by a computer including a processor, such as an electronic control unit (ECU) provided in the work vehicle 10. The control device 210 may be realized by one ECU, or may be realized by multiple ECUs. For example, when the control device 210 is realized by multiple ECUs, the multiple ECUs may be distributed and disposed within the work vehicle 10. A portion of the control device 210 may be realized 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 the user's operation of the operating device 120 and the output signals of the sensors 70-74. The operating device 120 includes devices operated by the user, such as a speed change 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 operation of the speed change pedal 121 by the user, and switches between forward and reverse movement of the work vehicle 10 according to the operation of the forward / reverse lever 122 by the user.

[0061] The storage device 220 is a storage device including 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 may be included in the control device 210. For example, when an ECU functions as the control device 210, a memory provided in the ECU may function as the storage device 220. The storage device 220 stores a computer program executed by the control device 210 and various information generated by the control device 210.

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

[0063] The horizontal axis in FIG. 7 indicates the state of the HST 28. "N" indicates the neutral state of the HST 28, and the swash plate 49 is in the neutral position. "+MAX" indicates the state of the HST 28 in which the hydraulic motor M generates rotation in the forward direction at the maximum speed, and the swash plate 49 is largely inclined toward the side corresponding to the forward rotation. "-MAX" indicates the state of the HST 28 in which the hydraulic motor M generates rotation in the reverse direction at the maximum speed, and the swash plate 49 is largely inclined toward the side corresponding to the reverse rotation. "+K" indicates the state of the HST 28 at the point where the gear stage of the planetary transmission 31 is switched on the forward rotation side. "-K" indicates the state of the HST 28 at the point where the gear stage of the planetary transmission 31 is switched on the reverse rotation side. The switching points S1, S2, and S3 are points where the gear stage of the planetary transmission 31 is switched.

[0064] The storage device 220 prestores data indicating the relationship between the ratio α and the switching points S1, S2, and S3. The data includes, for example, information regarding the ratio α1 corresponding to the switching point S1, the ratio α2 corresponding to the switching point S2, and the ratio α3 corresponding to the switching point S3. The control device 210 reads out the data from the storage device 220. The control device 210 performs control to switch the gear stages of the planetary transmission 31 based on the read out data and the detected value of the ratio α.

[0065] The control device 210 can change the tilt angle of the swash plate 49, for example, by controlling the operation of a shift operation valve 92 (FIG. 4) of the HST 28. The speed at which the swash plate 49 tilts can be controlled, for example, by using a flow control valve. The control device 210 can switch between the engaged state and the released state of each of the clutches CL1-CL4, for example, by controlling the operation of opening / closing valves 143 and 144 (FIGS. 5A-5D) of each of the clutches CL1-CL4.

[0066] When the work vehicle 10 starts moving, the control device 210 controls the swash plate 49 so that the inclination angle corresponds to "-K," and also controls the hydraulic clutch mechanism 29 so that the first clutch CL1 is engaged.

[0067] When accelerating the work vehicle 10 in response to the user's operation of the speed change pedal 121, the control device 210 changes the inclination angle of the swash plate 49 from the "-MAX" side toward the "+MAX" side. In the process of accelerating the work vehicle 10, the control device 210 controls the internal combustion engine 102 so that the rotation speed of the internal combustion engine 102 is constant. As the inclination angle of the swash plate 49 changes, the rotation speed of the reverse rotation generated by the hydraulic motor M gradually decreases, and the rotation speed becomes zero in the neutral position. 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 rotation direction, and the rotation speed of the forward rotation generated by the hydraulic motor M gradually increases. In this manner, in the process of changing the inclination angle of the swash plate 49, the ratio α increases steplessly.

[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 disengages the first clutch CL1. This causes the planetary transmission 31 to shift from first gear to second gear. The fact that the state of the HST 28 has reached each of the switching points S1-S3 can be detected from, for example, the value of the ratio α and / or the inclination angle of the swash plate 49.

[0069] When the gear shift stage is switched to second gear, the control device 210 changes the inclination angle of the swash plate 49 from the "+MAX" side toward the "-MAX" side. In the process of changing the inclination angle of the swash plate 49, 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 disengages the second clutch CL2, thereby switching the gear position of the planetary transmission 31 from second gear to third gear.

[0071] When the gear shift stage is switched to third gear, the control device 210 changes the inclination angle of the swash plate 49 from the "-MAX" side toward the "+MAX" side. In the process of changing the inclination angle of the swash plate 49, 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 disengages the third clutch CL3, thereby switching the gear position of the planetary transmission 31 from third gear to fourth gear.

[0073] When the gear shift stage is switched to fourth gear, the control device 210 changes the inclination angle of the swash plate 49 from the "+MAX" side toward the "-MAX" side. In the process of changing the inclination angle of the swash plate 49, the ratio α increases steplessly.

[0074] 8 is a diagram showing an example of the ratio α that changes in response to the user's operation of the speed change pedal 121. During the period in which the planetary transmission 31 is switching gear positions, the change in the ratio α remains constant or the value of the ratio α decreases.

[0075] When a clutch is engaged, oil is filled into the hydraulic chamber 135 (FIGS. 5A-5D) of that clutch. When shifting gears in the planetary transmission 31, it takes time to fill the oil to engage the clutch of the next gear to be shifted to. If filling of oil starts after the ratio α reaches a value corresponding to the shift point, it takes time to engage the clutch of the next gear to be shifted to, and the time required to stop changing the ratio α becomes longer, which may cause the passenger to feel a large shift shock.

[0076] In this embodiment, before the ratio α reaches a value corresponding to the switching point, the oil for engaging the clutch of the next gear stage starts to be filled. This allows the gear stage to be switched in a short time when the ratio α reaches a value corresponding to the switching point, and reduces the shift shock felt by the passenger. The details of this operation in this embodiment are described below.

[0077] 9 is a diagram for explaining the operation of switching the gear stages of the planetary transmission 31. Here, as an example, the operation of switching the gear stages of the planetary transmission 31 from first gear to second gear will be explained. The same applies to the switching operations between other gear stages. This operation of switching the gear stages can also be applied to the operation of lowering the gear stage (for example, the operation of switching from second gear to first gear).

[0078] The "CL2 valve" shown in Figure 9 represents the state of the opening and closing valves 143, 144 (Figures 5A-5D) of the second clutch CL2. When the "CL2 valve" is "ON", this indicates a state in which the opening and closing valve 143 of the second clutch CL2 is open and the opening and closing valve 144 is closed. Oil is supplied from the hydraulic pump 141 to the hydraulic chamber 135, and the second clutch CL2 is in an engaged state. When the "CL2 valve" is "OFF", this indicates a state in which the opening and closing valve 143 of the second clutch CL2 is closed and the opening and closing valve 144 is open. The oil in the hydraulic chamber 135 is discharged to the oil tank 142, and the second clutch CL2 is in a released state.

[0079] The "CL1 valve" represents the state of the opening and closing valves 143, 144 of the first clutch CL1. When the "CL1 valve" is "ON", this indicates a state in which the opening and closing valve 143 of the first clutch CL1 is open and the opening and closing valve 144 is closed. Oil is supplied from the hydraulic pump 141 to the hydraulic chamber 135, and the first clutch CL1 is in an engaged state. When the "CL1 valve" is "OFF", this indicates a state in which the opening and closing valve 143 of the first clutch CL1 is closed and the opening and closing valve 144 is open. The oil in the hydraulic chamber 135 is discharged to the oil tank 142, and the first clutch CL1 is in a released state.

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

[0081] 9, the horizontal axis represents time, and the vertical axis represents the ratio α. This graph shows the change in the ratio α when the gear stage of the planetary transmission 31 is shifted from first gear to second gear.

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

[0083] The control device 210 also acquires the value of time T2 (second time) from when oil filling for switching from the current gear stage (first gear) to the next gear stage (second gear) starts until the second clutch CL2 is engaged. Based on time T2, the control device 210 can determine a time point P1 (first time point) for starting to fill with oil for switching the gear stage.

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

[0085] Time T1 can also be regarded as the section from ratio α0 to ratio α1, which corresponds to the start point (time point P0) of time T1, and the control device 210 starts filling oil into the hydraulic chamber 135 of the second clutch CL2 within the section from ratio α0 to ratio α1.

[0086] When a work machine is connected to the work vehicle 10, it is necessary to accelerate and decelerate the work vehicle 10 by the load of the work vehicle 10 including the work machine. On the other hand, when a work machine is not connected to the work vehicle 10, the load to be accelerated and decelerated is small. Therefore, the value of the ratio α1-α3 corresponding to the switching point S1-S3 may change depending on whether or not a work machine is connected to the work vehicle 10. Therefore, the period (section) for executing the operation of switching the valve from "OFF" to "ON" may be determined from the value of the ratio α1-α3 which changes depending on whether or not a work machine is connected, the current gear stage of the planetary transmission 31, and the time from when the valve becomes "ON" to when the output signal of the pressure sensor 136 indicates "HIGH". Time T1 (or the section from the ratio α0 to the ratio α1) is the period (or section) for executing the operation of switching the valve from "OFF" to "ON".

[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 the 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 be zero.

[0088] A time T2 from when the filling of oil into the released second clutch CL2 starts until the second clutch CL2 is engaged is set in advance, and data on the time T2 is stored in the memory device 220. The control device 210 can determine a time point P1 at which the filling of oil into the second clutch CL2 starts, for example, based on the times T1, T2, and T3.

[0089] Also, the time Ta from when the valve is turned "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 storage device 220. The time T1 may be compared with the time Ta, and when the time T1 becomes shorter than the time Ta, the control device 210 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 the ratio α and the first value α1 becomes smaller than the difference between the ratio α at the time point P1 when the CL2 valve is turned "ON" and the 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 the point at which the gear stage of the planetary transmission 31 is changed (for example, the first value α1) is reached, and the shift shock felt by the passenger can be reduced. However, if there is some disturbance such as slight shaking of the work vehicle 10, the output signal of the pressure sensor 136 may not indicate "HIGH" when the time Ta has elapsed since the valve was turned ON. For this reason, the timing for turning the valve ON (time point P1) may be determined by securing a certain amount of time T3 as a margin.

[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 starts the supply of oil from the hydraulic pump 141 to the hydraulic chamber 135 of the second clutch CL2.

[0091] At time P2, the ratio α reaches the first value α1, and at time 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 opening / closing valve 143 of the first clutch CL1 and opens the opening / closing valve 144. Discharge of oil from the hydraulic chamber 135 of the first clutch CL1 begins, and the first clutch CL1 is released at time P6.

[0092] By starting to fill the oil for engaging the second clutch CL2 before the ratio α reaches the first value α1 corresponding to the shift point S1, it is possible to complete the shift of the gear position in a short time when the ratio α reaches the first value α1. By shortening the time for which the change of the ratio α is stopped, it is possible to reduce the shift shock felt by the passengers.

[0093] The time T2 from when the second clutch CL2 in the released state starts to be filled with oil until the second clutch CL2 is engaged may be changed according to the state of the second clutch CL2. For example, the control device 210 changes the length of the time T2 based on the elapsed time since the second clutch CL2 was released after being engaged the previous time.

[0094] If the time that has elapsed since the second clutch CL2 was previously engaged and then released is short, oil may remain in the hydraulic chamber 135 of the second clutch CL2. If oil starts to be filled into the hydraulic chamber 135 in this state, the second clutch CL2 will be engaged in a short time. Therefore, if the time that has elapsed since the second clutch CL2 was previously engaged and then released is short, the control device 210 sets the time T2 to be short.

[0095] For example, a time T4 (first predetermined time) from when control to release the second clutch CL2 in an engaged state is started until the oil in the hydraulic chamber 135 is completely drained is set in advance. When the elapsed time is less than time T4, the control device 210 sets time T2 to be shorter than when the elapsed time is equal to or greater than time T4. This makes it possible to prevent the second clutch CL2 from being engaged before the ratio α reaches the first value α1.

[0096] Setting the time T2 to be short can also be considered as bringing the ratio α at the start point of the time T2 (time point P1 at which filling of the second clutch CL2 in the released state with oil begins) 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 temperature sensor 73. When the temperature of the oil is high, the viscosity is low and the oil will drain more quickly from the hydraulic chamber 135. For example, when the temperature of the oil filled to engage the second clutch CL2 is high, the control device 210 may set time T4 to be shorter than when the temperature of the oil is low.

[0098] After estimating that the ratio α will reach the first value α1 at time point P2, the shifting of the gear stage 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 become small due to factors such as the user loosening the operation of the gear shift pedal 121 or an increase in the load on the work vehicle 10. When the control device 210 determines that the ratio α has not reached the first value α1 at time point P2 based on the calculated amount of change in the ratio α per unit time, it stops the shifting of the gear stage.

[0099] The control device 210 may set a reference time point P3 (third time point), determine whether or not to cancel the gear shift before time point P3, and not determine again whether or not to cancel the gear shift after time point P3. For example, the control device 210 sets the time point P3 to a time point a predetermined time T5 (third predetermined time) before time point P2. The predetermined time T5 is, for example, 20-50 milliseconds, but is not limited to this. If the control device 210 determines to cancel the gear shift before time point P3, it cancels the gear shift.

[0100] When it is determined that the shifting of the gear stage is not to be stopped when the time point P3 has passed, the control device 210 executes the shifting of the gear stage. For example, the control device 210 executes the shifting of the gear stage even if a cause for canceling the shifting of the gear stage as described above occurs during the period from the time point P3 to the time point P2. This can reduce sluggishness of control. After executing the shifting of the gear stage, the control device 210 determines whether or not to switch back to the original gear stage (first gear). For example, if the ratio α after the shifting of the gear stage is smaller than the first value α1 by a predetermined value or more, the control device 210 executes the switch back to first gear. If the ratio α after the shifting of the gear stage is not smaller than the first value α1 by a predetermined value or more, the gear stage 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 filled into the second clutch CL2 to switch the gear stage. For example, when the temperature of the oil filled into the second clutch CL2 is high, the control device 210 sets the predetermined time T5 longer than when the temperature is low. In other words, when the oil temperature is high, the time point P3 is set earlier than when the oil temperature is low. When the oil is hot, the viscosity is low and the oil may be filled more quickly. By setting the time point P3 earlier, smooth control can be performed even if the second clutch CL2 is engaged early.

[0102] Next, control that takes into consideration the overrun of the swash plate 49 will be described. For example, when the work vehicle 10 is accelerated and the ratio α changes to approach the first value α1, the inclination angle of the swash plate 49 changes continuously. At this time, inertia acts on the swash plate 49 in a direction that changes the inclination angle. Therefore, even if the control for changing the inclination angle of the swash plate 49 to the forward rotation side is stopped when the ratio α changes to reach 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 the gear shift to second speed may not be smooth.

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

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

[0105] Data indicating the relationship between the inclination angle of the swash plate 49 and the ratio α is stored in advance in the storage device 220. The control device 210 can determine the value of the ratio αi when the inclination angle of the swash plate 49 is θ3 based on the data. The value of the ratio αi may be stored in advance in the storage device 220. In the process in which the ratio α changes and approaches the first value α1, the control device 210 stops the control for changing the inclination angle of the swash plate 49 to the forward rotation side at a time point P4 when the ratio α becomes the ratio αi.

[0106] The control device 210 may change the point P4 at which the control is stopped based on the amount of change in the ratio α per unit time. For example, when the amount of change in the ratio α per unit time is large, the control device 210 sets the point P4 earlier than when the amount of change in the ratio α per unit time is small. When the amount of change in the ratio α per unit time is large, the inertia acting on the swash plate 49 becomes large, and the amount of overrun of the swash plate 49 may become large. When the amount of change in the ratio α per unit time is large, the control for changing the inclination angle of the swash plate 49 to the positive rotation side is stopped earlier, thereby suppressing overrun of the swash plate 49.

[0107] When the angle θ2 is large, the inclination angle θ3 becomes small and the value of the ratio αi becomes small. When the value of the ratio αi becomes small, the time point P4 becomes earlier. At the time point P4 when the ratio α becomes equal to the ratio αi, the control device 210 stops the control for changing the inclination angle of the swash plate 49 to the forward rotation side, thereby preventing the swash plate 49 from overrunning.

[0108] Data indicating the relationship between the amount of change in ratio α per unit time and the angles θ2 and θ3 may be stored in advance in the storage device 220. Also, data indicating the relationship between the amount of change in ratio α per unit time and the ratio αi may be stored in advance in the storage device 220. The control device 210 may use these data to stop the control of changing the inclination angle of the swash plate 49 to the forward rotation side.

[0109] The control device 210 may change the point in time P4 based on the temperature of the oil supplied to the hydraulic motor M. For example, when the temperature of the oil supplied to the hydraulic motor M is high, the control device 210 sets the point in time P4 to an earlier point in time than when the temperature of the oil supplied to the hydraulic motor M is low. When the oil is hot, the viscosity of the oil decreases, and the amount of overrun of the swash plate 49 may increase. When the oil is hot, the control for changing the inclination angle of the swash plate 49 to the positive rotation side is stopped early, thereby suppressing the overrun of the swash plate 49.

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

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

[0112] When the control device 210 is realized by a plurality of ECUs, an ECU (ECU1) that monitors the operation of the shift pedal 121 by the user and an ECU (ECU2) that switches the gear position may be provided separately. In this case, the ECU1 may transmit a command to the ECU2 to switch the gear position based on the operation state of the shift pedal 121, and the ECU2 that receives the command may start preparations to switch the gear position. For example, the ECU2 may start calculating the amount of change in the ratio α per unit time after receiving the command, thereby reducing the total amount of calculation.

[0113] A control system including the control device and storage device in the above embodiment can also be installed in a work vehicle later. Such a system can be manufactured and sold independently of the work vehicle. A computer program used in such a system can also be manufactured and sold independently of the work vehicle. The computer program can be provided, for example, by being stored in a computer-readable non-transitory storage medium. The computer program can also be provided by downloading via a telecommunication line (for example, the Internet).

[0114] As described above, the present 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 an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; The control device includes: If the ratio changes and approaches a first value corresponding to the first switching point, estimating a first time until the ratio reaches the first value; a control system that controls the hydraulic clutch mechanism to start filling oil to change the gear position before the ratio reaches the first value based on the estimated first time.

[0116] [Item 2] 2. The control system according to claim 1, wherein the control device estimates the first time based on an amount of change in 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 shift stage is to be shifted to the next gear shift stage while the ratio has reached the first value, the control device determines a first point in time at which to start filling the oil for the gear shift stage, based on a second time from when filling of the oil for the gear shift stage is started to when the clutch of the next gear stage is engaged.

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

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

[0120] [Item 6] 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 of the oil is a second temperature lower than the first temperature.

[0121] [Item 7] The control device determines the first time point at which to start filling the oil so that the clutch of the next gear stage is engaged simultaneously with or after a second predetermined time has elapsed since the ratio reaches the first value.

[0122] [Item 8] 8. The control system of claim 7, wherein the second predetermined time is between 1 and 20 milliseconds.

[0123] [Item 9] 8. The control system according to item 7, wherein the control device performs control to release the clutch of the gear before the shift after the ratio reaches the first value.

[0124] [Item 10] The control device includes: determining whether to cancel the shifting of the gear position at a third time point that is a third predetermined time before a second time point at which the ratio is estimated to reach the first value or before the third time point; 10. The control system according to any one of items 1 to 9, wherein the shifting of the gear stage is cancelled if it is determined to be cancelled.

[0125] [Item 11] Item 11. The control system according to item 10, wherein the control device executes the shifting of the gear stage when it has been determined not to cancel the shifting of the gear stage when the third time point has passed.

[0126] [Item 12] Item 12. The control system according to item 11, wherein the control device executes the shifting of the gear stage even if a factor for canceling the shifting of the gear stage occurs during the period from the third point in time until the second point in time.

[0127] [Item 13] Item 13. The control system according to item 12, wherein the control device determines whether or not to switch back to the original gear after executing the gear shift.

[0128] [Item 14] Item 11. The control system according to item 10, wherein the control device changes the third predetermined time period depending on a temperature of the oil filled to switch the gear position.

[0129] [Item 15] Item 15. The control system according to item 14, wherein when the temperature of the oil filled to switch the gear stage is a third temperature, the control device sets the third predetermined time longer than when the temperature of the oil filled to switch the gear stage is a fourth temperature lower than the third temperature.

[0130] [Item 16] The control device includes: determining in advance an angle of the swash plate when the ratio is the first value; By controlling the change in the angle of the swash plate, the rotation speed of the rotation generated by the hydraulic motor is changed; 16. The control system according to any one of items 1 to 15, wherein, when the ratio is changing and approaching the first value, control of changing the angle of the swash plate is stopped before the ratio reaches the first value.

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

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

[0133] [Item 19] Item 18. The control system of item 17, wherein the control device varies the fourth point in time further based on a temperature of the oil supplied to the hydraulic motor.

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

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

[0136] [Item 22] A control method for controlling an operation of a power transmission device of a work vehicle, comprising: The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control method includes: controlling the hydraulic clutch mechanism to switch the gear stage based on a relationship between a ratio of a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels to a rotation speed of the internal combustion engine and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; Including, the plurality of switch points includes a first switch point; The control method includes: if the ratio is changing and approaching a first value corresponding to the first switch point, estimating a first time until the ratio reaches the first value; controlling the hydraulic clutch mechanism to start filling oil for changing the gear position before the ratio reaches the first value based on the estimated first time; The control method further comprises:

[0137] [Item 23] A computer program for causing a computer to execute control of an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The computer program comprises: controlling the hydraulic clutch mechanism to switch the gear stage based on a relationship between a ratio of a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels to a rotation speed of the internal combustion engine and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; causing the computer to execute the plurality of switch points includes a first switch point; The computer program comprises: if the ratio is changing and approaching a first value corresponding to the first switch point, estimating a first time until the ratio reaches the first value; controlling the hydraulic clutch mechanism to start filling oil for changing the gear position before the ratio reaches the first value based on the estimated first time; The computer program further causes the computer to execute the above steps.

[0138] [Item 24] A control system for controlling an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; The control device controls the hydraulic clutch mechanism to start filling oil for switching the gear stage when the ratio changes and reaches a first value corresponding to the first switching point, or when the gear stage is switched after the ratio reaches the first value, before the ratio reaches the first value; The control device determines the point in time to start filling the oil to shift the gear stage based on the time from when the filling of the oil to shift from the current gear stage to the next gear stage starts to when the clutch of the next gear stage is engaged.

[0139] [Item 25] Item 25. The control system according to item 24, wherein the control device changes the length of time from when the oil starts to be filled until the clutch of the next gear shift stage is engaged, based on the elapsed time since the clutch of the next gear shift stage was previously engaged and then released.

[0140] [Item 26] 26. The control system according to item 25, wherein the control device sets the time from when the oil filling starts to when the clutch of the next gear shift stage is engaged to a shorter time when the elapsed time is shorter than a first predetermined time than when the elapsed time is longer.

[0141] [Item 27] 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 of the oil is a second temperature lower than the first temperature.

[0142] [Item 28] 26. The control system according to claim 24 or 25, wherein the control device determines the time to start filling the oil so that the clutch of the next gear stage is engaged simultaneously with or after a second predetermined time has elapsed since the ratio reaches the first value.

[0143] [Item 29] Item 30. The control system of item 28, wherein the second predetermined time is between 1 and 20 milliseconds.

[0144] [Item 30] 29. The control system according to item 28, wherein the control device performs control to release the clutch of the gear before the shift after the ratio reaches the first value.

[0145] [Item 31] A control system for controlling an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; The control device includes: The angle of the swash plate at the first switching point is determined in advance; By controlling the change in the angle of the swash plate, the rotation speed of the rotation generated by the hydraulic motor is changed; a control system that, when the ratio is changing and approaching a first value corresponding to the first switching point, stops controlling the change in angle of the swash plate before the ratio reaches the first value.

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

[0147] The techniques of the present disclosure are particularly useful in the technical field of vehicle transmissions. [Explanation of symbols]

[0148] 10: work vehicle, 15: power transmission device, 20: input shaft, 21: main transmission device, 23: forward / reverse switching device, 28: hydrostatic continuously variable transmission (HST), 28a: pump shaft, 28b: output shaft, 29: hydraulic clutch mechanism, 30: planetary transmission unit, 31: planetary transmission device, 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: swash plate, 70: rotation sensor, 71: rotation sensor, 72: position sensor, 73: temperature sensor, 74: temperature sensor, 90: hydraulic cylinder, 91: operation oil passage, 92: speed change operation 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 (engine), 102a: output shaft, 103: transmission case, 104: front wheels, 105: rear wheels, 106: cabin, 107: steering device, 108: driver's seat, 109: coupling device, 120: gear shift operation 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: storage 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 an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; The control device includes: If the ratio changes and approaches a first value corresponding to the first switching point, estimating a first time until the ratio reaches the first value; a control system that controls the hydraulic clutch mechanism to start filling oil for changing the gear position 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 an amount of change in the ratio per unit time.

3. 3. The control system according to claim 1, wherein when the ratio reaches the first value, or when the current gear shift stage is to be shifted to the next gear shift stage while the ratio has reached the first value, the control device determines a first point in time at which to start filling the oil for the gear shift stage based on a second time from when filling of the oil for the gear shift stage is started to when the clutch of the next gear stage is engaged.

4. 4. The control system according to claim 3, wherein the control device changes the length of the second time period based on an 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 when the elapsed time is shorter than a first predetermined time than when the elapsed time is longer than the first predetermined time.

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

7. 4. The control system according to claim 3, wherein the control device determines the first time point at which to start filling the oil so that the clutch of the next gear stage is engaged simultaneously with or after a second predetermined time has elapsed since the ratio reaches the first value.

8. 8. The control system of claim 7, wherein the second predetermined time is between 1 and 20 milliseconds.

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

10. The control device includes: determining whether or not to cancel the shifting of the gear position at a third time point that is a third predetermined time before a second time point at which 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 the shifting of the gear stage is cancelled when it is determined to be cancelled.

11. The control system according to claim 10 , wherein the control device executes the shifting of the gear position when it has been determined not to cancel the shifting of the gear position when the third time point has passed.

12. The control system according to claim 11, wherein the control device executes the shifting of the gear position even if a factor for canceling the shifting of the gear position occurs during a period from the third point in time until the second point in time.

13. The control system of claim 12 , wherein the control device determines, after performing the gear shift, whether to shift back to the original gear.

14. The control system according to claim 10 , wherein the control device changes the third predetermined time period in accordance with a temperature of the oil filled for switching the gear position.

15. 15. The control system according to claim 14, wherein the control device sets the third predetermined time longer when the temperature of the oil filled to switch the gear stage is a third temperature than when the temperature of the oil filled to switch the gear stage is a fourth temperature lower than the third temperature.

16. The control device includes: determining in advance the angle of the swash plate when the ratio is at the first value; By controlling the change in the angle of the swash plate, the rotation speed of the rotation generated by the hydraulic motor is changed; 3. The control system according to claim 1, wherein, when the ratio is changing and approaching the first value, control of changing the angle of the swash plate is stopped before the ratio reaches the first value.

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

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

19. 20. The control system of claim 17, wherein the controller varies the fourth point in time further based on a temperature of the oil supplied to the hydraulic motor.

20. 20. The control system according to claim 19, wherein the control device sets the fourth point in time earlier when the temperature of the oil supplied to the hydraulic motor is a fifth temperature than when the temperature of the oil is a sixth temperature 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 an operation of a power transmission device of a work vehicle, comprising: The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control method includes: controlling the hydraulic clutch mechanism to switch the gear stage based on a relationship between a ratio of a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels to a rotation speed of the internal combustion engine and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; Including, the plurality of switch points includes a first switch point; The control method includes: if the ratio is changing and approaching a first value corresponding to the first switch point, estimating a first time until the ratio reaches the first value; controlling the hydraulic clutch mechanism to start filling oil for changing the gear position before the ratio reaches the first value based on the estimated first time; The control method further comprises:

23. A computer program for causing a computer to execute control of an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The computer program comprises: controlling the hydraulic clutch mechanism to switch the gear stage based on a relationship between a ratio of a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels to a rotation speed of the internal combustion engine and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; causing the computer to execute the plurality of switch points includes a first switch point; The computer program comprises: if the ratio is changing and approaching a first value corresponding to the first switch point, estimating a first time until the ratio reaches the first value; controlling the hydraulic clutch mechanism to start filling oil for changing the gear position before the ratio reaches the first value based on the estimated first time; The computer program further causes the computer to execute the above steps.

24. A control system for controlling an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; When the ratio changes and reaches a first value corresponding to the first switching point, or when the gear stage is switched after the ratio reaches the first value, the control device controls the hydraulic clutch mechanism to start filling oil for switching the gear stage before the ratio reaches the first value; The control device determines the point in time to start filling the oil to shift the gear stage based on the time from when the filling of the oil to shift from the current gear stage to the next gear stage starts to when the clutch of the next gear stage is engaged.

25. 25. The control system of claim 24, wherein the control device changes the length of time from when the oil starts to be filled to when the clutch of the next gear shift stage is engaged based on the elapsed time since the clutch of the next gear shift stage was previously engaged and then released.

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

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

28. 26. The control system of claim 24 or 25, wherein the control device determines the time to start filling the oil so that the clutch of the next gear stage is engaged simultaneously with or after a second predetermined time has elapsed since the ratio reaches the first value.

29. 30. The control system of claim 28, wherein the second predetermined period of time is between 1 and 20 milliseconds.

30. 29. The control system according to claim 28, wherein the control device performs control to release the clutch of the gear before the shift after the ratio reaches the first value.

31. A control system for controlling an operation of a power transmission device of a work vehicle, The power transmission device includes: a hydrostatic continuously variable transmission having a hydraulic pump that receives rotation generated by an internal combustion engine and discharges oil according to an angle of a swash plate, and a hydraulic motor that receives the oil from the hydraulic pump and generates rotation; a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic continuously variable transmission are transmitted, and which generates a plurality of types of rotation corresponding to a plurality of gear stages; a hydraulic clutch mechanism for switching the gear stages of the planetary transmission; Equipped with The control system includes: a storage device that stores data indicating a relationship between a ratio between a rotation speed of a predetermined component on a power transmission path that transmits the rotation of the planetary transmission to wheels and a rotation speed of the internal combustion engine, and a plurality of switching points that are points at which the gear stages of the planetary transmission are switched; a control device that controls the hydraulic clutch mechanism so as to switch the gear stage based on the ratio and the data; Equipped with the plurality of switch points includes a first switch point; The control device includes: The angle of the swash plate at the first switching point is determined in advance; By controlling the change in the angle of the swash plate, the rotation speed of the rotation generated by the hydraulic motor is changed; a control system which, when the ratio is changing and approaching a first value corresponding to the first switching point, stops controlling the change in angle of the swash plate before the ratio reaches the first value.

32. A work vehicle comprising the control system according to any one of claims 24, 25, 26, 27 and 31, the internal combustion engine, and the power transmission device.

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