Solenoid valve control device and work vehicle

Abstract

To switch a solenoid valve at an appropriate timing.SOLUTION: A solenoid valve control device which controls a first solenoid valve 52A and a second solenoid valve 52B by an electric current value based on a target gear ratio 72, includes: a present gear ratio acquiring unit 64 for acquiring a present gear ratio 76 which is a ratio of an output rotation speed 74 of a drive unit 4 and an output rotation speed 75 of a transmission; a present electric current value acquiring unit 65 for acquiring a present electric current value 78 which is an electric current value to be input in the first solenoid valve 52A or the second solenoid valve 52B; and a switch control unit 67 for performing a switch control of the solenoid valve for switching whether a pump inclined panel is controlled using the first solenoid valve 52A or a pump inclined panel is controlled using the second solenoid valve 52A based on the present electric current value 78 and a gear ratio difference 79 which is a difference between a target gear ratio 72 and the present gear ratio 76.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a solenoid valve control device that controls a hydrostatic continuously variable transmission via a solenoid valve, and to a work vehicle that controls a hydrostatic continuously variable transmission by means of a solenoid valve control device. [Background technology]

[0002] The work vehicle (tractor) shown in Patent Document 1 includes a hydrostatic continuously variable transmission (stepless transmission unit), a planetary transmission (compound planetary transmission unit, transmission output unit), a forward / reverse switching device, a speed change operating device (speed change lever), and a forward / reverse switching device (forward / reverse lever). The continuously variable transmission receives power output from the engine and changes the speed of the input power before outputting it. The planetary transmission combines the power output from the engine and the power output from the continuously variable transmission and outputs the combined power. The planetary transmission also changes the speed of the combined power output by changing the speed of the continuously variable transmission. The forward / reverse switching device switches between a forward transmission state in which the combined power output from the planetary transmission is converted into forward power and output toward the traveling device (front wheels, rear wheels), and a reverse transmission state in which the combined power from the planetary transmission is converted into reverse power and output toward the traveling device. The speed change device controls the vehicle speed by changing the speed of the continuously variable transmission, and the forward / reverse switch device switches between forward and reverse.

[0003] In a work vehicle (tractor) configured as described above, the vehicle speed is determined by the rotational speed (rpm) of the combined power, i.e., the ratio (gear ratio) between the engine rpm and the output shaft rpm. The rotational speed of the combined power is determined by the gear range of the planetary transmission and the power (swash plate angle) output from the continuously variable transmission. The gear range is determined by the operation of the clutch of the planetary transmission. The swash plate angle of the continuously variable transmission is tilted back and forth between a maximum inclination on one side (-MAX) and a maximum inclination on the other side (+MAX), with the neutral position in between. In other words, the continuously variable transmission alternates between forward and reverse rotation. Each time the gear range is shifted, the tilt direction of the swash plate angle switches, switching between forward and reverse rotation, gradually changing the rotational speed of the combined power.

[0004] The swash plate angle of a continuously variable transmission is controlled by hydraulic oil supplied from a hydraulic cylinder. The hydraulic cylinder is controlled by two solenoid valves. The solenoid valves are controlled by the current value of a control signal. One solenoid valve controls the swash plate angle on the forward rotation side from the neutral position via a hydraulic cylinder, while the other solenoid valve controls the swash plate angle on the reverse rotation side from the neutral position via a hydraulic cylinder. In this case, the solenoid valves are switched when the swash plate is in the neutral position. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-95058 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the solenoid valve is switched and the swash plate of the continuously variable transmission begins to tilt, the current value (start-up current value) input to the solenoid valve can vary from one solenoid valve to another depending on the load on the axle (input shaft and output shaft of the continuously variable transmission), the temperature of the operating oil, the engine speed, etc. As a result, the gear ratio may not be controlled appropriately near the neutral position of the swash plate.

[0007] For example, there are cases where the target gear ratio is not reached even when the solenoid valve is switched and the current value controlling the solenoid valve is set to a predetermined rising current value, or where the target gear ratio is reached before the rising current value is reached. Also, depending on the configuration of the hydraulic circuit, there may be a problem of a delay between when the solenoid valve is controlled and when the swash plate actually starts to tilt.

[0008] The present invention aims to switch the solenoid valve at an appropriate time. [Means for solving the problem]

[0009] In order to achieve the above object, an electromagnetic valve control device according to one embodiment of the present invention is a solenoid valve control device for a transmission in which power output from a drive unit is changed in speed by a gear transmission and a hydrostatic continuously variable transmission and then output. The electromagnetic valve control device controls a first solenoid valve that controls a pump swash plate on the forward rotation side from a neutral position and a second solenoid valve that controls the pump swash plate on the reverse rotation side from a neutral position with respect to the hydrostatic continuously variable transmission based on a target gear ratio, and includes: a current gear ratio acquisition unit that acquires a current gear ratio, which is the ratio of the output speed of the drive unit to the output speed of the transmission; a current current value acquisition unit that acquires a current current value, which is the current value input to the first solenoid valve or the second solenoid valve; and a switching control unit that performs solenoid valve switching control to switch between controlling the pump swash plate using the first solenoid valve or controlling the pump swash plate using the second solenoid valve, based on a gear ratio difference, which is the difference between the target gear ratio and the current gear ratio, and the current current value.

[0010] A work vehicle according to one embodiment of the present invention comprises a drive unit, a hydrostatic continuously variable transmission that changes the speed of the power output from the drive unit and outputs the power, a gear transmission that combines the power output from the drive unit and the power output from the hydrostatic continuously variable transmission and changes the speed of the combined power and outputs the combined power, a first solenoid valve in the hydrostatic continuously variable transmission that controls the pump swash plate on the forward rotation side from the neutral position and a second solenoid valve in the hydrostatic continuously variable transmission that controls the pump swash plate on the reverse rotation side from the neutral position, and the solenoid valve control device.

[0011] With the above configuration, solenoid valve switching control can be performed according to the state in which the pump swash plate is controlled by the first solenoid valve and the second solenoid valve, which is determined by the gear ratio difference, so that the solenoid valve can be switched at the appropriate time.

[0012] The switching control unit may perform the solenoid valve switching control when the current current value is equal to or less than a predetermined current threshold and the gear ratio difference is equal to or greater than a predetermined gear ratio difference threshold.

[0013] With this configuration, the solenoid valve can be switched at an appropriate timing with greater accuracy, taking into consideration the current current value and the gear ratio difference.

[0014] The pump may further include a memory unit that stores a rising current value, which is the current value at which the pump swash plate begins to tilt from the neutral position, and the switching control unit may perform the solenoid valve switching control when the value obtained by subtracting the rising current value from the current current value is equal to or less than a predetermined first current threshold value corresponding to a current threshold value, and the gear ratio difference is equal to or greater than a predetermined first switching target deviation corresponding to a gear ratio difference threshold value.

[0015] With this configuration, the solenoid valve can be switched early if the gear ratio difference is large, even if the current current value has not yet reached the rising current value, taking into account the rising current value that varies depending on the axle load, operating oil temperature, engine speed, etc. As a result, the solenoid valve can be switched at an appropriate time.

[0016] In addition, the switching control unit may perform the solenoid valve switching control when the current current value is equal to or less than the rising current value and the gear ratio difference is equal to or greater than a predetermined second switching target deviation that is smaller than the first switching target deviation and corresponds to the gear ratio difference threshold value.

[0017] With this configuration, even if the current current value is not the rising current value, the solenoid valve is switched if the current gear ratio is different from the target gear ratio by a predetermined amount or more, so that the solenoid valve can be switched appropriately.

[0018] Furthermore, the switching control unit may perform the solenoid valve switching control when the value obtained by subtracting the current current value from the rising current value is equal to or less than a predetermined second current threshold, and the gear ratio difference is equal to or greater than a predetermined third switching target deviation that is smaller than the second switching target deviation and corresponds to the gear ratio difference threshold.

[0019] With this configuration, solenoid valve switching control can be performed before the current current value reaches the rising current value, so that the solenoid valve can be switched at the appropriate time and the appropriate gear ratio can be controlled early.

[0020] In addition, the switching control unit may maintain the current value when the value obtained by subtracting the current current value from the rising current value is equal to or less than the second current threshold and the gear ratio difference is smaller than the third switching target deviation.

[0021] With this configuration, the current current value is maintained, and then the solenoid valve switching control is resumed when the gear ratio difference becomes greater than a predetermined value, thereby making it possible to switch the solenoid valve at an appropriate time.

[0022] The switching control unit may prohibit the electromagnetic valve switching control until a predetermined time has elapsed after the electromagnetic valve switching control is performed.

[0023] Even when the solenoid valve is switched, there may be a delay before the control signal (current value) is actually input to the solenoid valve, or a delay in tilting the swash plate. Furthermore, repeated switching of the solenoid valve in a short period of time may cause the operation of the continuously variable transmission to become unstable. The above configuration prevents the solenoid valve from being switched in a short period of time, and the control signal (current value) and tilting of the swash plate are performed appropriately, ensuring stable operation of the continuously variable transmission. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a side view showing an example of the configuration of a tractor. [Figure 2] FIG. 1 is a schematic diagram illustrating a configuration example of a power transmission device. [Figure 3] FIG. 2 is a schematic diagram showing a configuration example of a planetary transmission unit. [Figure 4] 1 is a hydraulic circuit diagram illustrating a continuously variable transmission and an operating structure of the continuously variable transmission. [Figure 5] 4A and 4B are diagrams illustrating a vehicle speed change performed by a speed change control means. [Figure 6]FIG. 2 is a diagram illustrating a configuration for performing electromagnetic valve switching control. [Figure 7] 4 is a diagram illustrating an example of information used for electromagnetic valve switching control. FIG. [Figure 8] FIG. 10 is a diagram illustrating an example of a rising current value. [Figure 9] FIG. 10 is a diagram illustrating a flow of electromagnetic valve switching control. [Figure 10] FIG. 10 is a diagram illustrating a flow of electromagnetic valve switching control. DETAILED DESCRIPTION OF THE INVENTION

[0025] A tractor, which is an example of a work vehicle of the present invention, will be described below with reference to the drawings. In the following description, with respect to the tractor, the direction of arrow F shown in Fig. 1 is referred to as the "front side of the vehicle body," the direction of arrow B shown in Fig. 1 is referred to as the "rear side of the vehicle body," the direction of arrow U shown in Fig. 1 is referred to as the "upper side of the vehicle body," the direction of arrow D shown in Fig. 1 is referred to as the "lower side of the vehicle body," the direction toward the front of the paper in Fig. 1 is referred to as the "left side of the vehicle body," and the direction toward the back of the paper in Fig. 1 is referred to as the "right side of the vehicle body."

[0026] [Overall tractor] As shown in FIG. 1, a tractor includes a traveling body 3 supported by a pair of steerable and drivable front wheels 1 (traveling gear) and a pair of drivable rear wheels 2 (traveling gear). A prime mover 5 equipped with an engine 4 (drive unit) is provided at the front of the traveling body 3. A driver's section 6, where a driver sits and operates the vehicle, and a link mechanism 7, which connects a work implement such as a rotary tiller so that the implement can be raised and lowered, are provided at the rear of the traveling body 3. The driver's section 6 includes a driver's seat 8, a steering wheel 9 for steer- ing the front wheels 1, and a cabin 10 that covers the passenger space. A body frame 11 of the traveling body 3 includes the engine 4, a transmission case 12 whose front portion is connected to the rear of the engine 4, and a front-wheel support frame 13 connected to the bottom of the engine 4. A power takeoff shaft 14 is provided at the rear of the transmission case 12, which extracts and transmits power from the engine 4 to the work implement connected by the link mechanism 7.

[0027] [Power transmission device for driving] As shown in Fig. 2, the tractor includes a power transmission device 15 for traveling. The power transmission device 15 transmits power from the engine 4 to the front wheels 1 and the rear wheels 2. The power transmission device 15 includes a transmission 18 that changes the speed of the power from the engine 4 and transmits it to the rear wheel differential mechanism 16 and the front wheel differential mechanism 17. The transmission 18 is housed in the transmission case 12.

[0028] As shown in FIG. 2 , the transmission 18 is provided with an input shaft 20, a main speed change unit 21, a forward / reverse switching device 23, a gear mechanism 24, and a front wheel transmission unit 25. The input shaft 20 is provided at the front of the transmission case 12, and transmits power from the output shaft 4a of the engine 4. The main speed change unit 21 receives the power of the input shaft 20, changes the speed of the input power, and outputs it. The forward / reverse switching device 23 receives the output of the main speed change unit 21, and switches the rotation direction of the power output from the main speed change unit 21 between forward and reverse. The gear mechanism 24 transmits the output of the forward / reverse switching device 23 to the input shaft 16a of the rear wheel differential mechanism 16. The front wheel transmission unit 25 receives the output of the forward / reverse switching device 23, changes the speed of the input power, and outputs it to the front wheel differential mechanism 17.

[0029] [Main transmission section] As shown in Figure 2, the main transmission section 21 includes a continuously variable transmission 28 to which the power of the input shaft 20 is input, and a planetary transmission 31 (gear transmission) to which the power of the input shaft 20 and the output of the continuously variable transmission 28 are input.

[0030] The continuously variable transmission 28 is a hydrostatic continuously variable transmission (hydrostatic transmission (HST)) and includes a variable displacement hydraulic pump P and a hydraulic motor M. The continuously variable transmission 28 changes the speed of the power input from the input shaft 20 to forward rotation power or reverse rotation power according to the swash plate angle by changing the swash plate angle of the hydraulic pump P. Furthermore, the continuously variable transmission 28 continuously changes the rotation speed (number of revolutions) of the forward rotation power or reverse rotation power according to the swash plate angle and outputs it from the motor shaft 28b. As shown in FIG. 2 , the hydraulic pump P has a rotating shaft 26 whose front end is connected to the input shaft 20, and a pump shaft 28a connected to the input shaft 20 via a first gear mechanism 27 connected to the rear end of the rotating shaft 26. The hydraulic motor M outputs power according to the pressure oil supplied from the hydraulic pump P to the motor shaft 28b.

[0031] As shown in FIG. 2, the planetary transmission 31 includes a planetary transmission unit 31A and an output unit 31B. The planetary transmission unit 31A receives the power of the input shaft 20 and the output of the continuously variable transmission 28. The output unit 31B outputs the output of the planetary transmission unit 31A in four stages across a speed range. As shown in FIGS. 2 and 3, the planetary transmission unit 31A includes a first planetary transmission unit 32 and a second planetary transmission unit 33. The first planetary transmission unit 32 includes a first sun gear 32a, a first planetary gear 32b meshing with the first sun gear 32a, and a first ring gear 32c having internal teeth meshing with the first planetary gear 32b. The second planetary transmission unit 33 is located rearward of the first planetary transmission unit 32. The second planetary transmission unit 33 has a second sun gear 33a, a second planetary gear 33b that meshes with the second sun gear 33a, a second ring gear 33c that has internal teeth that mesh with the second planetary gear 33b, and a second carrier 33d that supports the second planetary gear 33b.

[0032] As shown in Fig. 2, a second gear mechanism 30 is provided between the first sun gear 32a and the motor shaft 28b of the continuously variable transmission 28, and the output of the continuously variable transmission 28 is input to the first sun gear 32a via the second gear mechanism 30. A third gear mechanism 29 is provided between the first ring gear 32c and the input shaft 20, and the power of the input shaft 20 is input to the first ring gear 32c via the third gear mechanism 29. As shown in Figs. 2 and 3, the first planetary transmission unit 32 is provided with an interlocking gear 32d that meshes with the first planetary gear 32b, and the interlocking gear 32d and the second planetary gear 33b are interlocked and connected by a connecting member 33e. The first planetary transmission unit 32 and the second planetary transmission unit 33 constitute a so-called compound planetary transmission unit.

[0033] 2 and 3, the output section 31B includes a triple-shaft structure including a first input shaft 34a, a second input shaft 34b, and a third input shaft 34c, and an output shaft 35 positioned parallel to the first input shaft 34a. 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. The first input shaft 34a is connected to a first range gear mechanism 36a, and a first clutch CL1 is provided between the first range gear mechanism 36a and the output shaft 35. The third input shaft 34c is connected to a second range gear mechanism 36b, and a second clutch CL2 is provided between the second range gear mechanism 36b and the output shaft 35. A third range gear mechanism 36c is connected to the second input shaft 34b, and a third clutch CL3 is provided between the third range gear mechanism 36c and the output shaft 35. A fourth range gear mechanism 36d is connected to the third input shaft 34c, and a fourth clutch CL4 is provided between the fourth range gear mechanism 36d and the output shaft 35.

[0034] In the main transmission unit 21, the power output from the engine 4 is input to the hydraulic pump P of the continuously variable transmission 28 via the input shaft 20, the rotating shaft 26, and the first gear mechanism 27. The power input to the hydraulic pump P is output from the motor shaft 28b by the continuously variable transmission 28 as forward rotation power or reverse rotation power. The rotation speed (number of rotations) of the output forward rotation power or the rotation speed (number of rotations) of the output reverse rotation power is changed continuously by the continuously variable transmission 28. The output of the continuously variable transmission 28 is input to the first sun gear 32a of the first planetary transmission unit 32 via the second gear mechanism 30, and the power output from the engine 4 is input to the first ring gear 32c of the first planetary transmission unit 32 via the input shaft 20 and the third gear mechanism 29. The power output from the continuously variable transmission 28 input to the first ring gear 32c and the power output from the engine 4 are combined by the first planetary transmission unit 32 and the second planetary transmission unit 33 of the planetary transmission unit 31A, and the combined power is transmitted from the second planetary transmission unit 33 to the output unit 31B and output from the output shaft 35.

[0035] In main transmission unit 21, when first clutch CL1 is engaged, the combined power generated by planetary transmission unit 31A is shifted to first-speed range power by first range gear mechanism 36a and first clutch CL1 of output unit 31B. The shifted first-speed range power is transmitted from second ring gear 33c to first input shaft 34a of output unit 31B. Furthermore, in this state, continuously variable transmission 28 is operated to change speed, so that the first-speed range power is continuously changed and output from output shaft 35.

[0036] When the second clutch CL2 is engaged, the combined power generated by the planetary transmission unit 31A is shifted to second-speed range power by the second range gear mechanism 36b of the output unit 31B and the second clutch CL2. The shifted second-speed range power is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. Furthermore, in this state, the continuously variable transmission 28 is operated to change speed, so that the second-speed range power is continuously changed and output from the output shaft 35.

[0037] When third clutch CL3 is engaged, the combined power generated by planetary transmission unit 31A is shifted to third-speed range power by third range gear mechanism 36c of output unit 31B and third clutch CL3. The shifted third-speed range power is transmitted from second carrier 33d to second input shaft 34b of output unit 31B. Furthermore, when continuously variable transmission 28 is operated to change speeds in this state, the third-speed range power is continuously changed and output from output shaft 35.

[0038] When the fourth clutch CL4 is engaged, the combined power generated by the planetary transmission unit 31A is shifted to fourth-speed range power by the fourth range gear mechanism 36d of the output unit 31B and the fourth clutch CL4. The shifted fourth-speed range power is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. Furthermore, in this state, the continuously variable transmission 28 is operated to change speeds, so that the fourth-speed range power is continuously changed and output from the output shaft 35.

[0039] [Forward / forward switching device] As shown in Fig. 2, the forward / reverse switching device 23 includes an input shaft 23a, an output shaft 23b, a forward gear interlock mechanism 23c, and a reverse gear interlock mechanism 23d. The input shaft 23a is connected to the output shaft 35 of the planetary transmission 31. The output shaft 23b is provided parallel to the input shaft 23a. A forward clutch CLF and a reverse clutch CLR are provided on the input shaft 23a. The forward gear interlock mechanism 23c is provided between the forward clutch CLF and the output shaft 23b. The reverse gear interlock mechanism 23d is provided between the reverse clutch CLR and the output shaft 23b.

[0040] When the forward clutch CLF is engaged, it connects the input shaft 23a to the forward gear interlock mechanism 23c, creating a forward transmission state in which the power of the input shaft 23a is transmitted to the output shaft 23b via the forward gear interlock mechanism 23c. When the reverse clutch CLR is engaged, it connects the input shaft 23a to the reverse gear interlock mechanism 23d, creating a reverse transmission state in which the power of the input shaft 23a is transmitted to the output shaft 23b via the reverse gear interlock mechanism 23d.

[0041] In the forward / reverse switching device 23, the output of the planetary transmission 31 is input to the input shaft 23a, and when the forward clutch CLF is engaged, the power of the input shaft 23a is converted into forward power by the forward clutch CLF and the forward gear interlock mechanism 23c and transmitted to the output shaft 23b. When the reverse clutch CLR is engaged, the power of the input shaft 23a is converted into reverse power by the reverse clutch CLR and the reverse gear interlock mechanism 23d and transmitted to the output shaft 23b. The forward power and reverse power of the output shaft 23b are transmitted to the rear wheel differential mechanism 16 and the front wheel transmission part 25 by the gear mechanism 24.

[0042] In the rear wheel differential mechanism 16, the forward or reverse power transmitted from the forward / reverse switching device 23 is transmitted from the left and right output shafts 16b to the left and right rear wheels 2. The power of the left output shaft 16b is transmitted to the left rear wheel 2 via a planetary reduction mechanism 37. A steering brake 38 is provided on the left output shaft 16b. Although not shown, the transmission system from the right output shaft 16b to the right rear wheel 2 is also provided with a planetary reduction mechanism 37 and a steering brake 38, similar to the transmission system to the left rear wheel 2. The traveling vehicle body 3 (see FIG. 1) can be easily turned depending on the braking states of the left and right steering brakes 38.

[0043] [Front wheel transmission section] As shown in Fig. 2, the front wheel transmission unit 25 includes an input shaft 25a connected to the output shaft 24a of the gear mechanism 24, and an output shaft 25b positioned parallel to the input shaft 25a. A constant speed clutch CLT and an accelerating clutch CLH positioned rearward of the constant speed clutch CLT are provided on the input shaft 25a. A constant speed gear mechanism 40 is provided between the constant speed clutch CLT and the output shaft 25b. A accelerating gear mechanism 41 is provided between the accelerating clutch CLH and the output shaft 25b. A parking brake 39 is provided on the output shaft 24a of the gear mechanism 24.

[0044] In the front wheel transmission unit 25, when the constant speed clutch CLT is engaged, the power of the input shaft 25a is transmitted to the output shaft 25b by the constant speed clutch CLT and the constant speed gear mechanism 40. A constant speed transmission state is established by the constant speed gear mechanism 40, and power for driving the front wheels 1 is output from the output shaft 25b in a state in which the peripheral speed of the front wheels 1 is the same as the peripheral speed of the rear wheels 2. When the speed-up clutch CLH is engaged, the power of the input shaft 25a is transmitted to the output shaft 25b by the speed-up clutch CLH and the speed-up gear mechanism 41. A front wheel speed-up transmission state is established by the speed-up gear mechanism 41, and power for driving the front wheels 1 is output from the output shaft 25b in a state in which the peripheral speed of the front wheels 1 is higher than the peripheral speed of the rear wheels 2. The output from the output shaft 25 b is input to the front wheel differential mechanism 17 via a rotary shaft 42 that connects the output shaft 25 b and the input shaft 17 a of the front wheel differential mechanism 17 .

[0045] When the constant velocity clutch CLT is engaged, the traveling vehicle body 3 (see FIG. 1) enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven in a state in which the average peripheral speed of the left and right front wheels 1 is the same as the average peripheral speed of the left and right rear wheels 2, and when the speed-up clutch CLH is engaged, the traveling vehicle body 3 enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven in a state in which the average peripheral speed of the left and right front wheels 1 is faster than the average peripheral speed of the left and right rear wheels 2. As a result, when the speed-up clutch CLH is engaged, the traveling vehicle body 3 can turn with a turning radius that is smaller than the turning radius when the constant velocity clutch CLT is engaged.

[0046] [Hydraulic circuit] The continuously variable transmission 28 is controlled by a hydraulic circuit as shown in Fig. 4. The hydraulic circuit includes a hydraulic cylinder 50, a speed change operation valve 52 formed by an electromagnetically operated valve, and a hydraulic pump 54. The continuously variable transmission 28 is controlled by changing (tilting) the angle (swash plate angle) of a swash plate 49 (pump swash plate) of a hydraulic pump P, and power corresponding to the swash plate angle of the hydraulic pump P is output from a hydraulic motor M. The swash plate 49 of the hydraulic pump P is controlled by the amount and hydraulic pressure (operating hydraulic pressure) of operating oil supplied from the hydraulic pump 54 via a hydraulic cylinder 50, and the operating oil supplied (discharged) from the hydraulic cylinder 50 is controlled by the speed change operation valve 52.

[0047] As shown in Figure 4, hydraulic cylinder 50 is connected to swash plate 49 of hydraulic pump P. Hydraulic cylinder 50 has two oil chambers, oil chamber 50A and oil chamber 50B. Speed ​​change operation valve 52 is connected to hydraulic cylinder 50 via operation oil passage 51 and controls hydraulic cylinder 50 to cause hydraulic pump P to discharge operation oil. Hydraulic pump 54 is connected to speed change operation valve 52 via oil supply passage 53. In addition, an emergency relief valve 56 is connected to drive oil passage 55 that connects hydraulic pump P and hydraulic motor M of continuously variable transmission 28.

[0048] In this hydraulic circuit, the speed change operation valve 52 is switched to discharge the operating oil supplied from the hydraulic pump 54 from one of two oil chambers of the hydraulic cylinder 50. The speed change operation valve 52 includes a first solenoid valve 52A and a second solenoid valve 52B. The first solenoid valve 52A discharges the operating oil from the oil chamber 50A of the hydraulic cylinder 50, thereby tilting the swash plate 49 of the hydraulic pump P on the forward rotation side from the neutral position. The second solenoid valve 52B discharges the operating oil from the oil chamber 50B of the hydraulic cylinder 50, thereby tilting the swash plate 49 of the hydraulic pump P on the reverse rotation side from the neutral position. In this way, the continuously variable transmission 28 is operated to change speed by switching the first solenoid valve 52A and the second solenoid valve 52B of the transmission control valve 52 with the neutral position of the swash plate 49 (the continuously variable transmission 28 is in a neutral state) as the boundary, thereby tilting the swash plate 49 to an inclination angle corresponding to the operating position of the transmission control valve 52.

[0049] [Vehicle speed change] Next, referring to FIG. 2, a configuration for changing the vehicle speed by the main transmission unit 21 will be described using FIG. 5. The vertical axis of FIG. 5 represents the calculated gear ratio G (current gear ratio) and the rotation speed V of the input shaft 16a (corresponding to the vehicle speed). The calculated gear ratio G is the ratio of the rotation speed of the input shaft 16a to the rotation speed of the input shaft 20. The horizontal axis of FIG. 5 represents the speed change state of the continuously variable transmission 28, with [N] representing the neutral state and [-MAX] representing the speed change state in which the highest speed reverse power is output (maximum swash plate angle in reverse rotation). [+MAX] representing the speed change state in which the highest speed forward rotation power is output (maximum swash plate angle in forward rotation). [G1], [G2], [G3], and [G4] represent preset set gear ratios.

[0050] With the first clutch CL1 engaged, the continuously variable transmission 28 is shifted from [-MAX] to [+MAX], and the rotation speed V increases continuously from zero speed [0] in the first speed range. In the first speed range, the calculated gear ratio G when the continuously variable transmission 28 is in a neutral state is set to [C1N]. When the calculated gear ratio G reaches [G1], the shift control means 48 switches the first clutch CL1 to off and switches the second clutch CL2 to on. With the second clutch CL2 engaged, the rotation speed V increases continuously in the second speed range as the continuously variable transmission 28 is shifted from [+MAX] to [-MAX]. In the second speed range, the calculated gear ratio G when the continuously variable transmission 28 is in a neutral state is set to [C2N]. When the calculated gear ratio G reaches [G2], the shift control means 48 switches the second clutch CL2 off and the third clutch CL3 on. When the continuously variable transmission 28 is shifted from [-MAX] to [+MAX] with the third clutch CL3 engaged, the rotational speed V increases continuously in the third-speed range. In the third-speed range, the calculated gear ratio G when the continuously variable transmission 28 is in a neutral state is set to [C3N]. When the calculated gear ratio G reaches [G3], the shift control means 48 switches the third clutch CL3 off and the fourth clutch CL4 on. As the continuously variable transmission 28 is shifted from [+MAX] to [-MAX] with the fourth clutch CL4 engaged, the rotational speed V increases continuously in the fourth-speed range. In the fourth-speed range, the calculated gear ratio G when the continuously variable transmission 28 is in a neutral state is set to [C4N].

[0051] [Speed ​​control] The configuration for performing the speed change control will be described using FIG. 6 while referring to FIGS.

[0052] As a speed change operating tool for changing the speed of the continuously variable transmission 28, for example, a speed change pedal 45 is provided on the driving section 6. The operating position of the speed change pedal 45 is detected by a potentiometer 46. In this embodiment, the potentiometer 46 is used, but instead of the potentiometer 46, various operating position detection mechanisms such as those using a detection switch can be used.

[0053] The gear shift operation is controlled by a control unit 60 in accordance with the operating position of a gear shift pedal 45. The control unit 60 is equipped with a processor such as a CPU or an ECU. The control unit 60 is linked to the continuously variable transmission 28 via a first solenoid valve 52A or a second solenoid valve 52B. The control unit 60 is also linked to each of the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4 of the planetary transmission 31 (gear transmission). When the gear shift pedal 45 is operated, the control unit 60 detects that a gear shift operation has been performed based on detection information from a potentiometer 46 and performs gear shifting on the continuously variable transmission 28. At this time, the control unit 60 performs control (solenoid valve switching control) to switch the gear shift operation valve 52, which controls the swash plate angle, between the first solenoid valve 52A and the second solenoid valve 52B each time the swash plate 49 of the hydraulic pump P tilts across the neutral position. The control unit 60 also controls the switching operations of the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4.

[0054] The control unit 60 is linked to the rotation speed detection unit 4A, the rotation speed detection unit 31C, the stage number detection unit 31D, the current detection unit 52C, and the current detection unit 52D.

[0055] The rotation speed detection unit 4A detects the rotation speed of the engine 4 (engine output rotation speed 74) and transmits it to the control unit 60. The rotation speed detection unit 31C detects the output rotation speed of the transmission 18 (gear output rotation speed 75) and transmits it to the control unit 60. For example, the rotation speed detection unit 31C may detect the rotation speed of the input shaft 16a of the rear wheel differential mechanism 16, or may detect the rotation speed of the output shaft 35 of the planetary transmission 31 (gear transmission). When detecting the rotation speed of the input shaft 16a of the rear wheel differential mechanism 16, the rotation speed detection unit 31C may be configured to detect the rotation speed of a transmission gear 63 provided on the input shaft 16a.

[0056] The gear number detection unit 31D detects the gear range, detects which of the first clutch CL1, second clutch CL2, third clutch CL3 and fourth clutch CL4 is switched on, and transmits the detection result to the control unit 60.

[0057] The current detection unit 52C measures the current value of the current (control signal) input to the first solenoid valve 52A and transmits it to the control unit 60. The current detection unit 52D measures the current value of the current (control signal) input to the second solenoid valve 52B and transmits it to the control unit 60.

[0058] The control unit 60 functions as a solenoid valve control device, and as part of the speed change operation of the continuously variable transmission 28, performs solenoid valve switching control to switch the first solenoid valve 52A and the second solenoid valve 52B on and off based on information acquired from the rotation speed detection unit 4A, etc., and a switching table 70. The control unit 60 also determines the value of current to be input to the first solenoid valve 52A or the second solenoid valve 52B that has been switched on, and outputs it to the first solenoid valve 52A or the second solenoid valve 52B.

[0059] [Solenoid valve switching control] The configuration for controlling the switching of the electromagnetic valve will be described with reference to FIGS. 1 and 2 and with reference to FIGS. 6 to 8. FIG.

[0060] The control unit 60 includes a data communication unit 61, a target gear ratio acquisition unit 62, a current gear ratio acquisition unit 64, a current current value acquisition unit 65, a switching control unit 67, and a storage unit 69. The control unit 60 also includes a gear shift control unit 68 that performs gear shift control together with the switching control unit 67.

[0061] The data communication unit 61 is connected in a state capable of data communication with the potentiometer 46, the rotation speed detection unit 4A, the rotation speed detection unit 31C, the gear number detection unit 31D, the current detection unit 52C, the current detection unit 52D, etc. The data communication unit 61 also transmits control signals to the first solenoid valve 52A, the second solenoid valve 52B, the planetary transmission 31 (gear transmission), etc.

[0062] The memory unit 69 pre-stores rising current values ​​71 (hereinafter sometimes referred to as (b)) for the first solenoid valve 52A and the second solenoid valve 52B, as well as a switching table 70. The rising current value 71 is the current value of the control signal at which the gear ratio begins to change in each of the first solenoid valve 52A and the second solenoid valve 52B, and is the current value at which the swash plate 49 begins to tilt (pivot) from the neutral position. In other words, in each speed range, the point at which the gear ratio changes as the current is gradually increased is taken as the rising current point, which is the point at which the swash plate 49 starts to move, and the current value at this point is taken as the rising current value 71.

[0063] The target gear ratio acquisition unit 62 calculates (acquires) a target gear ratio 72 (hereinafter sometimes referred to as (c)) corresponding to the operating position of the speed change pedal 45 acquired from the potentiometer 46 via the data communication unit 61, and stores it in the memory unit 69.

[0064] The current gear ratio acquisition unit 64 acquires the engine output rotation speed 74 acquired by the rotation speed detection unit 4A and the gear output rotation speed 75 acquired by the rotation speed detection unit 31C via the data communication unit 61, and calculates a current gear ratio 76 (hereinafter, may be referred to as (d)). The current gear ratio acquisition unit 64 stores the calculated current gear ratio 76 in the memory unit 69.

[0065] The current current value acquiring unit 65 acquires the current values ​​detected by the current detecting units 52C and 52D via the data communication unit 61. The current current value acquiring unit 65 stores the larger of these current values ​​in the memory unit 69 as a current current value 78 (hereinafter, may be referred to as (a)), which is the current value related to the control signal controlling the hydraulic pump P. The stored current current value 78 is linked to information which is the current value of the current detecting unit 52C or the current detecting unit 52D, that is, information on whether the current value is related to the control signal on the forward rotation side or the control signal on the reverse rotation side.

[0066] The switching control unit 67 calculates a gear ratio difference 79 (hereinafter sometimes referred to as (f)) which is the difference between the target gear ratio 72 and the current gear ratio 76, and stores the calculated value in the memory unit 69. The switching control unit 67 performs solenoid valve switching control to switch the first solenoid valve 52A and the second solenoid valve 52B on and off based on a current current value 78 and a switching table 70. For example, the switching control unit 67 performs solenoid valve switching control based on a rising current value 71, the current current value 78, the gear ratio difference 79, and the switching table 70, as will be described later.

[0067] The memory unit 69 also stores a gear position 73 acquired from the gear position detection unit 31D via the data communication unit 61. The gear position 73 corresponds to the clutch of the output unit 31B that has been switched on, and corresponds to a speed range. That is, the gear position 73 "1" corresponds to the first speed range in which the first clutch CL1 has been switched on, the gear position 73 "2" corresponds to the second speed range in which the second clutch CL2 has been switched on, the gear position 73 "3" corresponds to the third speed range in which the third clutch CL3 has been switched on, and the gear position 73 "4" corresponds to the fourth speed range in which the fourth clutch CL4 has been switched on.

[0068] The respective start-up current values ​​71 of the first solenoid valve 52A and the second solenoid valve 52B are calculated in advance for each gear stage 73 as follows when the engine 4 is warmed up and the transmission oil temperature is 50°C, and are stored in the memory unit 69.

[0069] First, with the gear position 73 set to "1," as shown in FIG. 8, the target current value for the first solenoid valve 52A is gradually swept from a state in which the continuously variable transmission 28 is in a neutral position and the current gear ratio 76 is C1N. Accordingly, the current current value 78 increases, and the current gear ratio 76 begins to change from the value (C1N) indicating the neutral position. The current value at which the current gear ratio 76 changes from C1N is set as the rising current value 71 for the first solenoid valve 52A at which the swash plate 49 begins to tilt. Thereafter, the rising current value 71 for the second solenoid valve 52B is similarly calculated. Furthermore, the gear position 73 is switched, and the rising current values ​​71 for the first solenoid valve 52A and the second solenoid valve 52B are calculated for each gear position 73. In Figure 8, the change in the current gear ratio according to the target current value supplied to the first solenoid valve 52A is shown by a solid line, and the change in the current gear ratio according to the target current value supplied to the second solenoid valve 52B is shown by a dashed line.

[0070] Furthermore, a switching table 70 stored in the storage unit 69 stores switching conditions for the solenoid valve switching control, and a first switching target deviation 70b (hereinafter may be referred to as (F1)), a second switching target deviation 70c (hereinafter may be referred to as (F2)), and a third switching target deviation 70a (hereinafter may be referred to as (F3)), which are gear ratio difference thresholds among the switching thresholds for each clutch (gear stage 73) that has been switched on, are determined and stored in advance. Note that the first switching target deviation 70b, the second switching target deviation 70c, and the third switching target deviation 70a are determined in advance for each gear stage 73 based on the gear ratio in the neutral state of the continuously variable transmission 28, the range of fluctuation of the gear ratio, and the like, and have the relationship third switching target deviation 70a<second switching target deviation 70c<first switching target deviation 70b. 6, a first current threshold 70f (hereinafter may be referred to as (A1)) and a second current threshold 70g (hereinafter may be referred to as (A2)) are determined in advance and stored as current thresholds among the switching thresholds. The switching table 70 may further store information such as a gear ratio corresponding to a pre-estimated neutral position (neutral point) of the continuously variable transmission 28, a gear ratio variation range, and a gear ratio width that is the width of the gear ratio variation range.

[0071] [Switching control section] The operational configuration of the switching control unit 67 in the solenoid valve switching control will be described using FIGS. 6 to 10 with reference to FIGS.

[0072] As described above, the switching table 70 and the rising current value 71 are determined in advance and stored in the storage unit 69 (step #1 in FIG. 9).

[0073] In order to perform gear change control, including solenoid valve switching control, while the vehicle is traveling, the target gear ratio acquisition unit 62 continuously acquires the operating position of the gear change pedal 45 from the potentiometer 46 of the gear change pedal 45 via the data communication unit 61. The target gear ratio acquisition unit 62 calculates a target gear ratio 72 corresponding to the acquired operating position of the gear change pedal 45 and stores the calculated target gear ratio in the memory unit 69 (step #2 in FIG. 9).

[0074] Furthermore, the current gear ratio acquisition unit 64 continuously acquires an engine output rotation speed 74 from a rotation speed detection unit 4A of the engine 4 via the data communication unit 61. Similarly, the current gear ratio acquisition unit 64 continuously acquires a gear output rotation speed 75, which is the output rotation speed of the planetary transmission 31, from a rotation speed detection unit 31C of the planetary transmission 31 via the data communication unit 61. The current gear ratio acquisition unit 64 then obtains a current gear ratio 76 by dividing the gear output rotation speed 75 by the engine output rotation speed 74 and multiplying the result by 10,000, and stores the result in the storage unit 69 (step #3 in FIG. 9 ). Furthermore, the current gear ratio acquisition unit 64 obtains a gear position 73 from a gear position detection unit 31D of the planetary transmission 31 via the data communication unit 61 and stores the result in the storage unit 69.

[0075] Furthermore, the current current value acquiring unit 65 continuously acquires the current values ​​of the control signals sent to the first solenoid valve 52A and the second solenoid valve 52B from the current detecting units 52C and 52D via the data communication unit 61. The control unit 60 then determines which solenoid valve is being used to control the swash plate 49 of the continuously variable transmission 28, and stores the current value input to the solenoid valve used for control as the current current value 78 in the memory unit 69 (step #4 in FIG. 9).

[0076] It should be noted that steps #2 to #4 in FIG. 9 are executed as needed while the vehicle is running or while the engine 4 is operating, and are not necessarily executed in this order.

[0077] Next, the switching control unit 67 calculates the difference between the target gear ratio 72 and the current gear ratio 76 as a gear ratio difference 79 and stores it in the storage unit 69 (step #5 in FIG. 9). The gear ratio difference 79 is the absolute value of the value obtained by subtracting the current gear ratio 76 from the target gear ratio 72.

[0078] Then, the switching control unit 67 performs solenoid valve switching control based on the switching table 70, the rising current value 71, the current current value 78, and the gear ratio difference 79 (step #6 in FIG. 9). That is, the switching control unit 67 determines how close the current current value 78 has decreased to the rising current value 71 and how far the current gear ratio 76 is from the target gear ratio 72, taking into account the number of gear stages 73, and performs solenoid valve switching control to switch the first solenoid valve 52A and the second solenoid valve 52B on and off.

[0079] By performing this control, the tilt state of the swash plate 49, taking the axle load into consideration, can be determined using the difference between the current current value 78 and the rising current value 71. Furthermore, based on the relationship between the target gear ratio 72 and the current gear ratio 76, it can be determined whether the swash plate 49 is being controlled toward the neutral position or is being controlled to accelerate beyond the neutral position. By controlling the solenoid valve switching in consideration of the tilt state of the swash plate 49 taking the axle load into consideration, delays in the switching timing can be suppressed, enabling smooth switching. Furthermore, if the swash plate 49 is being controlled to accelerate beyond the neutral position, switching can be performed early. As a result, the solenoid valve can be switched at an appropriate time.

[0080] The electromagnetic valve switching control will be specifically described below.

[0081] First, the switching control unit 67 determines whether the value obtained by subtracting the rising current value 71 from the current current value 78 is equal to or less than a predetermined first current threshold value 70f ((a)-(b)≦(A1)) stored in the switching table 70 (step #61 in FIG. 10). For example, the first current threshold value 70f is 20 mA.

[0082] If it is determined that the value obtained by subtracting the rising current value 71 from the current current value 78 is equal to or less than the first current threshold value 70f (Yes in step #61 in FIG. 10), the switching control unit 67 determines that the current current value 78 is somewhat close to the rising current value 71. Then, taking into account the gear position 73, the switching control unit 67 determines whether the gear ratio difference 79 is equal to or greater than a predetermined first switching target deviation 70b ((f)≧(F1)) stored in the switching table 70 and determined according to the gear position 73 (step #62 in FIG. 10).

[0083] If it is determined that the gear ratio difference 79 is greater than or equal to the first switching target deviation 70b (Yes in step #62 of FIG. 10), the switching control unit 67 performs solenoid valve switching control, switching the first solenoid valve 52A or the second solenoid valve 52B that is turned on to off, and switching the first solenoid valve 52A or the second solenoid valve 52B that is turned off to on (step #63 of FIG. 10).

[0084] When the current current value 78 and the rising current value 71 are close to each other and the gear ratio difference 79 is larger than a certain level, it is difficult to approach the appropriate gear ratio even if solenoid valve switching control is performed after the current current value 78 reaches the rising current value 71. With the above configuration, solenoid valve switching control can be performed before the current current value 78 reaches the rising current value 71, and the solenoid valve can be switched at the appropriate time, allowing control to be performed to the appropriate gear ratio early.

[0085] In step #62, if it is determined that the gear ratio difference 79 is not greater than the first switching target deviation 70b (No in step #62 in Figure 10), the switching control unit 67 determines whether the current current value 78 is less than or equal to the rising current value 71 ((a)≦(b)) (step #64 in Figure 10).

[0086] If it is determined that the current current value 78 is equal to or less than the rising current value 71 (Yes in step #64 in FIG. 10), the switching control unit 67 determines whether the value obtained by subtracting the current current value 78 from the rising current value 71 is equal to or less than a predetermined second current threshold value 70g stored in the switching table 70 (step #65 in FIG. 10). For example, the second current threshold value 70g is 40 mA.

[0087] If it is determined that the value obtained by subtracting the current current value 78 from the rising current value 71 is equal to or less than the second current threshold 70g (Yes in step #65 of Figure 10), the switching control unit 67 takes into account the gear stage number 73 and determines whether the gear ratio difference 79 is equal to or greater than the third switching target deviation 70a, which is smaller than the first switching target deviation 70b (step #66 of Figure 10).

[0088] If it is determined that the gear ratio difference 79 is equal to or greater than the third switching target deviation 70a (Yes in step #66 in FIG. 10), the switching control unit 67 performs solenoid valve switching control (step #63 in FIG. 10).

[0089] In this way, when the gear ratio difference 79 is relatively small while the current current value 78 is relatively close to the rising current value 71, the switching control unit 67 executes solenoid valve switching control even if the current current value 78 has not yet reached the rising current value 71. In other words, switching is necessary when the current current value 78 and the rising current value 71 are fairly close and the gear ratio difference 79 is relatively large. The same applies when the current current value 78 falls below the rising current value 71. However, as will be described later, if switching is performed when the gear ratio difference 79 is very small (less than or equal to the third switching target deviation 70a), the continuously variable transmission 28 cannot make very fine movements near the neutral position, and the solenoid valve will switch frequently due to load fluctuations. Therefore, switching is intentionally not performed when the gear ratio difference 79 is very small (less than or equal to the third switching target deviation 70a). This allows the solenoid valve to be switched at an appropriate time and controlled to an appropriate gear ratio early.

[0090] In step #66, if it is determined that the gear ratio difference 79 is not greater than or equal to the third switching target deviation 70a (No in step #66 in Figure 10), the switching control unit 67 does not perform solenoid valve switching control, but controls the current current value 78 to be maintained (step #67 in Figure 10).

[0091] When the current current value 78 decreases to close to the rising current value 71 and the gear ratio difference 79 becomes relatively small, the current current value 78 is small, which may result in the swash plate 49 not tilting much. Therefore, in this state, the current current value 78 is maintained, and then, when the gear ratio difference 79 becomes larger than a predetermined value, the solenoid valve switching control is resumed. This allows the solenoid valve to be switched at an appropriate time.

[0092] In step #65, if it is determined that the value obtained by subtracting the current current value 78 from the rising current value 71 is not less than the second current threshold 70g (No in step #65 of Figure 10), the switching control unit 67 takes into account the gear stage number 73 and determines whether the gear ratio difference 79 is greater than or equal to the second switching target deviation 70c, which is greater than the third switching target deviation 70a and smaller than the first switching target deviation 70b (step #68 of Figure 10).

[0093] If it is determined that the gear ratio difference 79 is equal to or greater than the second switching target deviation 70c (Yes in step #68 in FIG. 10), the switching control unit 67 performs solenoid valve switching control (step #63 in FIG. 10).

[0094] In this way, when the current current value 78 is equal to or less than the rising current value 71 and the gear ratio difference 79 is equal to or greater than the second switching target deviation 70c, the switching control unit 67 performs solenoid valve switching control. As a result, even if the current current value 78 is not equal to the rising current value 71, the solenoid valve is switched if the current gear ratio 76 is different by a predetermined amount or more, so that the solenoid valve can be switched appropriately.

[0095] If the answer is No in step #61, No in step #64, and No in step #68, the process continues from step #61.

[0096] [Another embodiment] (1) In the above embodiment, the switching control unit 67 may control the solenoid valve so that it does not switch until a predetermined time has elapsed after switching the solenoid valve, even if the switching conditions are met. The predetermined time is, for example, 150 milliseconds.

[0097] Even when the solenoid valve is switched, there is a time lag before a control signal (current value) is actually input to the solenoid valve. There is also a time lag between when the solenoid valve is switched and when the swash plate 49 actually begins to tilt. Therefore, if the switching conditions are met immediately after the solenoid valve is switched, the solenoid valve will be switched again accordingly. In such cases, the control signal (current value) may not be input appropriately, or the swash plate 49 may not tilt appropriately. Furthermore, repeated switching of the solenoid valve in a short period of time may cause the operation of the continuously variable transmission 28 to become unstable.

[0098] With the above configuration, after switching the solenoid valve, solenoid valve switching control is not performed until a predetermined time has elapsed, so the control signal (current value) and tilt of the swash plate 49 are performed appropriately, and the continuously variable transmission 28 operates stably.

[0099] (2) In each of the above embodiments, the switching thresholds (gear ratio difference thresholds) stored in the switching table 70 are not limited to the three, i.e., the third switching target deviation 70a, the first switching target deviation 70b, and the second switching target deviation 70c, but may be set to two or less, or four or more, switching thresholds. In this case as well, the switching control unit 67 executes solenoid valve switching control for each gear stage 73 in accordance with the relationship between the current current value 78 and the rising current value 71 and these switching thresholds.

[0100] This allows the solenoid valve switching control to be performed appropriately in accordance with the transmission 18, the surrounding environmental conditions, and the like.

[0101] (3) In each of the above embodiments, the switching threshold value is not limited to being stored in the switching table 70, but may be set as a function including the current current value 78 and the rising current value 71 according to the gear position 73. Such a function may be set by linearly interpolating predetermined values, or by other methods.

[0102] This makes it possible to more easily control the switching of the electromagnetic valve.

[0103] (4) In each of the above embodiments, the control unit 60 is not limited to being configured with the above-described functional blocks, but may be configured with any functional blocks. For example, each functional block of the control unit 60 may be further subdivided, or conversely, some or all of the functional blocks may be combined. Furthermore, the functions of the control unit 60 are not limited to the above-described functional blocks, and may be realized by a method executed by any functional block. Furthermore, some or all of the functions of the control unit 60 may be configured with software. A program related to the software is stored in any storage device such as the storage unit 69, and is executed by a processor such as a CPU included in the control unit 60 or a separately provided processor.

[0104] (5) In each of the above embodiments, the planetary transmission 31 is configured to divide the combined power into four speed ranges, but the planetary transmission 31 may also be configured to divide the speed range into three or fewer or five or more speed ranges.

[0105] (6) In each of the above embodiments, an example is shown in which the tractor is equipped with front wheels 1 and rear wheels 2, but the tractor may also use a crawler running device or a combination of a mini crawler and wheels as the running device.

[0106] (7) In each of the above embodiments, an example was shown in which the speed change pedal 45 was provided, but this is not limiting, and the tractor may also employ a speed change lever as a speed change operating tool.

[0107] (8) In each of the above embodiments, the solenoid valve control device can be mounted not only on a tractor but also on various types of work vehicles such as agricultural vehicles. [Industrial Applicability]

[0108] The present invention can be applied to a solenoid valve control device that controls a solenoid valve for a continuously variable transmission, and to a work vehicle equipped with a solenoid valve control device. [Explanation of symbols]

[0109] 4 Engine (drive unit) 18 Transmission 28 Continuously variable transmission (hydrostatic continuously variable transmission) 31 Planetary transmission (gear transmission) 49 Swash plate (pump swash plate) 52A First solenoid valve 52B Second solenoid valve 60 Control unit (solenoid valve control device) 64 Current gear ratio acquisition section 65 Current current value acquisition unit 67 Switching control section 69 Memory section 70 Switching Table 70a Third switching target deviation (F3) 70b First switching target deviation (F1) 70c Second switching target deviation (F2) 70f First current threshold (A1) 70g Second Current Threshold (A2) 71 Rising current value 72 Target gear ratio 73 gears 74 Engine output RPM 75 Gear output speed 76 Current gear ratio 78 Current value 79 Gear ratio difference

Claims

1. A solenoid valve control device for a transmission that changes the speed of power output from a drive unit using a gear transmission and a hydrostatic continuously variable transmission and outputs the power, the solenoid valve control device controlling, based on a target gear ratio, a first solenoid valve that controls a pump swash plate on a forward rotation side from a neutral position and a second solenoid valve that controls the pump swash plate on a reverse rotation side from the neutral position with respect to the hydrostatic continuously variable transmission, using current values, a current gear ratio acquisition unit that acquires a current gear ratio, which is a ratio between an output rotation speed of the drive unit and an output rotation speed of the transmission; a current value acquiring unit that acquires a current value that is the current value input to the first solenoid valve or the second solenoid valve; a switching control unit that performs solenoid valve switching control to switch between controlling the pump swash plate using the first solenoid valve and controlling the pump swash plate using the second solenoid valve based on a gear ratio difference, which is the difference between the target gear ratio and the current gear ratio, and the current current value.

2. The solenoid valve control device according to claim 1 , wherein the switching control unit performs the solenoid valve switching control when the current current value is equal to or less than a predetermined current threshold and the gear ratio difference is equal to or greater than a predetermined gear ratio difference threshold.

3. a storage unit configured to store a rising current value, which is the current value at which the pump swash plate starts to tilt from the neutral position; 2. The solenoid valve control device according to claim 1, wherein the switching control unit performs the solenoid valve switching control when a value obtained by subtracting the rising current value from the current current value is equal to or less than a predetermined first current threshold value corresponding to a current threshold value, and the gear ratio difference is equal to or greater than a predetermined first switching target deviation corresponding to a gear ratio difference threshold value.

4. 4. The solenoid valve control device according to claim 3, wherein the switching control unit performs the solenoid valve switching control when the current current value is equal to or less than the rising current value and the gear ratio difference is equal to or greater than a predetermined second switching target deviation that is smaller than the first switching target deviation and corresponds to the gear ratio difference threshold value.

5. 5. The solenoid valve control device according to claim 4, wherein the switching control unit performs the solenoid valve switching control when a value obtained by subtracting the current value from the rising current value is equal to or less than a predetermined second current threshold, and the gear ratio difference is equal to or greater than a predetermined third switching target deviation that is smaller than the second switching target deviation and corresponds to the gear ratio difference threshold.

6. 6. The solenoid valve control device according to claim 5, wherein the switching control unit maintains the current value when a value obtained by subtracting the current current value from the rising current value is equal to or less than the second current threshold value and the gear ratio difference is smaller than the third switching target deviation.

7. The solenoid valve control device according to any one of claims 1 to 6, wherein the switching control unit prohibits the solenoid valve switching control until a predetermined time has elapsed after the solenoid valve switching control has been performed.

8. A drive unit; a hydrostatic continuously variable transmission that changes the speed of the power output from the drive unit and outputs the power; a gear transmission that combines the power output from the drive unit and the power output from the hydrostatic continuously variable transmission, and that changes the speed of the combined power before outputting it; a first solenoid valve for controlling a pump swash plate on a forward rotation side from a neutral position in the hydrostatic continuously variable transmission, and a second solenoid valve for controlling the pump swash plate on a reverse rotation side from the neutral position; A work vehicle comprising the solenoid valve control device according to claim 1.

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