Work vehicle

Abstract

To enable switching between forward and backward travel while suppressing switching shock and enable quick switching between forward and backward travel, in a service vehicle that combines power from an engine and power from a continuously variable transmission by a planetary transmission, and changes combined power into forward power and backward power by a forward and backward travel switching device and transmits it to a travel device.SOLUTION: A service vehicle comprises: a restraining vehicle speed setting unit 71 that sets a set restraining vehicle speed for restraining the switching of a forward and reverse switching device 23; and switching restraining means 70 that allows the switching of the forward and reverse switching device 23 when a detected vehicle speed is slower than the set restraining vehicle speed, and restrains the switching of the forward and reverse switching device 23 when the detected vehicle speed is higher than or equal to the set restraining vehicle speed. The restraining vehicle speed setting unit 71 can change the set restraining vehicle speed.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a work vehicle.

Background Art

[0002] As shown in Patent Document 1, there is a work vehicle (tractor) including a hydrostatic continuously variable transmission (continuously variable transmission unit) that inputs power from an engine and outputs the input power after shifting, a planetary transmission (compound planetary transmission unit, transmission output unit) that inputs power from the engine and power from the continuously variable transmission, combines the input engine power and the input continuously variable transmission power to output a combined power, and shifts the combined power output when the continuously variable transmission is shifted, a forward and reverse switching device that can switch between a forward transmission state in which the combined power from the planetary transmission is switched to forward power and output to a traveling device (front wheels, rear wheels) and a reverse transmission state in which the combined power from the planetary transmission is switched to reverse power and output to the traveling device, a transmission operation tool (transmission lever) for operating the continuously variable transmission, and a forward and reverse switching tool (forward and reverse lever) for switching the forward and reverse switching device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above-mentioned work vehicle changes the drive speed of the running gear by changing the speed of the continuously variable transmission (CVT) using a gear shifting device, thereby changing the speed of the combined power output by the planetary transmission. The drive of the running gear is also switched between forward and reverse by switching the forward / reverse switch using a forward / reverse switch. In other words, the driving speed during forward and reverse movement is changed by changing the speed of the CVT using a gear shifting device, and the forward / reverse movement is switched by switching the forward / reverse switch using a forward / reverse switch. In this type of work vehicle, in order to suppress the switching shock when the forward / reverse gear selector switches from one state to the other, it is necessary to set the vehicle speed at which the forward / reverse gear selector can be switched to a low speed. When the vehicle speed at which the switch can be switched is set to a low speed, when performing work that frequently switches the vehicle's forward / reverse movement, such as bulldozer work, the amount of deceleration that must be made to enable the switching of the forward / reverse gear selector becomes wider, and the time required for the forward / reverse switching becomes longer.

[0005] The present invention provides a work vehicle that can switch between forward and reverse movement while suppressing the shock of switching between the two, and that can quickly switch between forward and reverse movement by narrowing the reduction range required to enable the switching between the two. [Means for solving the problem]

[0006] The work vehicle according to the present invention is A hydrostatic continuously variable transmission (CVT) that receives power from an engine and outputs the input power after changing its speed; a planetary transmission that receives power from the engine and power from the CVT, combines the input power from the engine and the input power from the CVT to output a combined power, and changes the speed of the combined power output by the CVT changing its speed; a forward transmission state in which the combined power from the planetary transmission is switched to forward power and output toward the running gear, and a reverse transmission state in which the combined power from the planetary transmission is switched to reverse power and output toward the running gear. The vehicle is equipped with a switchable forward / reverse switching device, a shifting device for operating the continuously variable transmission, a forward / reverse switching device for switching the forward / reverse switching device, a vehicle speed detection mechanism for detecting vehicle speed, a deterrent vehicle speed setting unit for setting a set deterrent vehicle speed to deter the switching of the forward / reverse switching device, and a switching deterrent means that allows the switching of the forward / reverse switching device when the vehicle speed detected by the vehicle speed detection mechanism is lower than the set deterrent vehicle speed, and deters the switching of the forward / reverse switching device when the detected vehicle speed is higher than or equal to the set deterrent vehicle speed, wherein the deterrent vehicle speed setting unit is capable of changing the set deterrent vehicle speed. Furthermore, when the forward / reverse selector is operated, if the detected vehicle speed is higher than or equal to the set deterrent vehicle speed, the continuously variable transmission is provided with a deceleration control means that automatically controls the deceleration of the continuously variable transmission based on the detected vehicle speed and the set deterrent vehicle speed so that the detected vehicle speed becomes lower than the set deterrent vehicle speed. .

[0007] With this configuration, the set deterrent speed can be changed to either a low-speed or high-speed setting. If the set deterrent speed is set to a low-speed setting, the forward / reverse switching device, based on the operation of the forward / reverse switching mechanism, will be switched at a lower speed compared to when the set deterrent speed is set to a high-speed setting, thus enabling forward / reverse switching with less switching shock. If the set deterrent speed is set to a high-speed setting, the forward / reverse switching device, based on the operation of the forward / reverse switching mechanism, will be switched at a higher speed compared to when the set deterrent speed is set to a low-speed setting, thus enabling a narrower deceleration range to enable forward / reverse switching and allowing for quicker forward / reverse switching.

[0008]

[0009] With this configuration, when the forward / reverse selector is operated, the vehicle speed is reduced by the deceleration control means to a vehicle speed at which the forward / reverse selector can be switched. This eliminates the need for any special effort to reduce the vehicle speed, making it easy to switch between forward and reverse.

[0010] In the present invention, The forward / reverse switching device preferably comprises a forward clutch that, when switched to the "on" position, creates the forward transmission state, and a reverse clutch that, when switched to the "on" position, creates the reverse transmission state, and is equipped with a speed control mechanism that can adjust the switching speed of the forward clutch and the reverse clutch.

[0011] With this configuration, the speed adjustment mechanism can be adjusted to either delay the switching of the forward and reverse clutches or to speed them up. Therefore, when the set deterrent speed is set to high speed, the forward and reverse switching device switches at high speed, but the switching of the forward and reverse clutches is delayed, suppressing the switching shock. When the set deterrent speed is set to low speed, the forward and reverse switching device switches at low speed, but the switching of the forward and reverse clutches is speedy, allowing for quick forward and reverse switching.

[0012] In the present invention, The forward / reverse switching device preferably comprises a forward clutch that, when switched to the "on" position, creates the forward transmission state, and a reverse clutch that, when switched to the "on" position, creates the reverse transmission state, and is equipped with a clutch pressure adjustment mechanism that can adjust the pressure of the forward clutch and the reverse clutch when they are engaged.

[0013] According to this configuration, the forward clutch and the reverse clutch are adjusted by a clutch pressure adjusting mechanism so as to engage at a low pressure, enabling quick direction change of the traveling vehicle body. Also, it is possible to adjust the forward clutch and the reverse clutch by the clutch pressure adjusting mechanism so as to engage at a high pressure, allowing the direction of the traveling vehicle body to be changed even when the traveling vehicle body is in a high-speed state.

Brief Description of the Drawings

[0014] [Figure 1] It is a side view of the tractor. [Figure 2] It is a schematic diagram of the power transmission device. [Figure 3] It is a schematic diagram of the planetary transmission section. [Figure 4] It is a block diagram showing the shift control device. [Figure 5] It is a hydraulic circuit diagram showing the continuously variable transmission device and the operation structure of the continuously variable transmission device. [Figure 6] It is an explanatory diagram of vehicle speed shifting by the shift control means. [Figure 7] It is a flowchart of the restraint control for forward and reverse switching. [Figure 8] It is a flowchart of the deceleration control. [Figure 9] It is a graph showing the measurement results of clutch switching and vehicle speed change when the forward and reverse switching device is switched from the forward traveling state to the reverse traveling state.

Mode for Carrying Out the Invention

[0015] Hereinafter, an embodiment which is an example of the present invention will be described based on the drawings. In the following description, regarding the traveling vehicle body of a tractor (an example of a "working vehicle"), the direction of the arrow F shown in FIG. 1 is the "front side of the vehicle body", the direction of the arrow B shown in FIG. 1 is the "rear side of the vehicle body", the direction of the arrow U shown in FIG. 1 is the "upper side of the vehicle body", the direction of the arrow D shown in FIG. 1 is the "lower side of the vehicle body", the direction on the front side of the paper surface of FIG. 1 is the "left side of the vehicle body", and the direction on the back side of the paper surface of FIG. 1 is the "right side of the vehicle body".

[0016] 〔Overall of the Tractor〕 Figure 1 shows a tractor. This tractor includes a running vehicle body 3 supported by a pair of left and right steerable and drivable front wheels 1 (running devices) and a pair of left and right drivable rear wheels 2 (running devices). A power unit 5 equipped with an engine 4 is provided at the front part of the running vehicle body 3. At the rear part of the running vehicle body 3, a driver's cab 6 where an operator rides to perform driving operations and a link mechanism 7 for connecting a working device such as a rotary tiller device in a liftable and lowerable manner are provided. The driver's cab 6 is equipped with a driver's seat 8, a steering wheel 9 for steering the front wheels 1, and a cab 10 covering the riding space. The vehicle frame 11 of the running vehicle body 3 is composed of an engine 4, a transmission case 12 whose front part is connected to the rear part of the engine 4, a front wheel support frame 13 connected to the lower part of the engine 4, and the like. At the rear part of the transmission case 12, a power take-off shaft 14 for taking out and transmitting the power from the engine 4 to the working device connected by the link mechanism 7 is provided.

[0017] 〔Power transmission device for running〕 As shown in Figure 2, a power transmission device 15 for running that transmits the power from the engine 4 to the front wheels 1 and the rear wheels 2 includes a transmission 18 that shifts the power from the engine 4 and transmits it to a rear wheel differential mechanism 16 and a front wheel differential mechanism 17. The transmission 18 is housed in the transmission case 12.

[0018] As shown in Figure 2, the transmission 18 includes an input shaft 20 provided at the front part of the transmission case 12 and to which the power of the output shaft 4a of the engine 4 is transmitted, a main transmission part 21 into which the power of the input shaft 20 is input and that shifts and outputs the input power, a forward and reverse switching device 23 into which the output of the main transmission part 21 is input, a gear mechanism 24 that transmits the output of the forward and reverse switching device 23 to the input shaft 16a of the rear wheel differential mechanism 16, and a front wheel transmission part 25 into which the output of the forward and reverse switching device 23 is input and that shifts the input power and outputs it to the front wheel differential mechanism 17.

[0019] 〔Main transmission part〕 As shown in Figure 2, the main transmission unit 21 includes a continuously variable transmission 28 to which the power from the input shaft 20 is input, and a planetary transmission 31 to which the power from the input shaft 20 and the output of the continuously variable transmission 28 are input.

[0020] As shown in Figure 2, the continuously variable transmission 28 comprises a variable displacement hydraulic pump P, which 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, and a hydraulic motor M driven by pressurized oil from the hydraulic pump P. By changing the swash plate angle of the hydraulic pump P, the power from the input shaft 20 is changed into forward and reverse rotational power, and the rotational speeds of the forward and reverse rotational power are continuously varied and output from the motor shaft 28b. The continuously variable transmission 28 is a hydrostatic continuously variable transmission.

[0021] As shown in Figure 2, the planetary gearbox 31 includes a planetary gearbox 31A to which the power from the input shaft 20 and the output from the continuously variable transmission 28 are input, and an output unit 31B that outputs the output of the planetary gearbox 31A in four speed ranges. As shown in Figures 2 and 3, the planetary gearbox 31A includes a first planetary gearbox 32 which has a first sun gear 32a, a first planetary gear 32b that meshes with the first sun gear 32a, and a first ring gear 32c with internal teeth that meshes with the first planetary gear 32b. The planetary gear shifting unit 31A is located behind the first planetary gear shifting unit 32 and includes a second planetary gear shifting unit 33 which has a second sun gear 33a, a second planetary gear 33b that meshes with the second sun gear 33a, a second ring gear 33c with internal teeth that meshes with the second planetary gear 33b, and a second carrier 33d that supports the second planetary gear 33b.

[0022] As shown in Figure 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 Figures 2 and 3, the first planetary gear shifting 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 by a connecting member 33e. The first planetary gear shifting unit 32 and the second planetary gear shifting unit 33 constitute a so-called composite planetary gear shifting unit.

[0023] As shown in Figures 2 and 3, the output unit 31B comprises a triple-shaft structure consisting of 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, etc. The first input shaft 34a is connected to a second ring gear 33c, the second input shaft 34b is connected to a second carrier 33d, and the third input shaft 34c is connected to a second sun gear 33a. A first range gear mechanism 36a is connected to the first input shaft 34a, and a first clutch CL1 is provided spanning the first range gear mechanism 36a and the output shaft 35. A second range gear mechanism 36b is connected to the third input shaft 34c, and a second clutch CL2 is provided spanning 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.

[0024] In the main transmission unit 21, power from the engine 4 is input to the hydraulic pump P via the input shaft 20, the rotating shaft 26, and the first gear mechanism 27, and is converted into forward and reverse power by the continuously variable transmission 28 and output from the motor shaft 28b, and the rotational speed of the output forward and reverse power is continuously varied. 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 power 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, and the power from the continuously variable transmission 28 and the power 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.

[0025] In the main transmission unit 21, when the continuously variable transmission 28 is shifted with the first clutch CL1 engaged, the combined power generated by the planetary transmission unit 31A is transmitted from the second ring gear 33c to the first input shaft 34a of the output unit 31B. In the output unit 31B, the first range gear mechanism 36a and the first clutch CL1 generate power that shifts continuously in the first gear range, which is then output from the output shaft 35.

[0026] When the continuously variable transmission 28 is shifted while the second clutch CL2 is engaged, the combined power generated by the planetary gear shifting unit 31A is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. At the output unit 31B, the second range gear mechanism 36b and the second clutch CL2 convert the power into a continuously variable force in the second gear range, which is then output from the output shaft 35.

[0027] When the continuously variable transmission 28 is shifted while the third clutch CL3 is engaged, the combined power generated by the planetary gear shifting unit 31A is transmitted from the second carrier 33d to the second input shaft 34b of the output unit 31B. At the output unit 31B, the third range gear mechanism 36c and the third clutch CL3 generate power that shifts continuously in the third range, which is then output from the output shaft 35.

[0028] When the continuously variable transmission 28 is shifted while the fourth clutch CL4 is engaged, the combined power generated by the planetary gear shifting unit 31A is transmitted from the second sun gear 33a to the third input shaft 34c of the output unit 31B. At the output unit 31B, the fourth range gear mechanism 36d and the fourth clutch CL4 generate power that shifts continuously in the fourth gear range, which is then output from the output shaft 35.

[0029] [Forward / forward switching device] As shown in Figure 2, the forward / reverse switching device 23 comprises an input shaft 23a connected to the output shaft 35 of the planetary transmission 31, and an output shaft 23b provided parallel to the input shaft 23a. The input shaft 23a is provided with a forward clutch CLF and a reverse clutch CLR. A forward gear interlocking mechanism 23c is provided between the forward clutch CLF and the output shaft 23b, and a reverse gear interlocking mechanism 23d is provided between the reverse clutch CLR and the output shaft 23b.

[0030] When the forward clutch CLF is operated to the "engage" position, it connects the input shaft 23a to the forward gear interlocking mechanism 23c, creating a forward transmission state in which the power from the input shaft 23a is transmitted to the output shaft 23b via the forward gear interlocking mechanism 23c. When the reverse clutch CLR is operated to the "engage" position, it connects the input shaft 23a to the reverse gear interlocking mechanism 23d, creating a reverse transmission state in which the power from the input shaft 23a is transmitted to the output shaft 23b via the reverse gear interlocking mechanism 23d.

[0031] 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 operated to engage, the power of the input shaft 23a is converted into forward power by the forward clutch CLF and the forward gear interlocking mechanism 23c and transmitted to the output shaft 23b. When the reverse clutch CLR is operated to engage, the power of the input shaft 23a is converted into reverse power by the reverse clutch CLR and the reverse gear interlocking mechanism 23d and transmitted to the output shaft 23b. The forward and reverse power of the output shaft 23b are transmitted to the rear wheel differential mechanism 16 and the front wheel transmission unit 25 by the gear mechanism 24.

[0032] In the rear wheel differential mechanism 16, 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. Power from the left output shaft 16b is transmitted to the left rear wheel 2 via the 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.

[0033] [Front wheel transmission] As shown in Figure 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 located parallel to the input shaft 25a. The input shaft 25a is provided with a constant-speed clutch CLT and a speed-increasing clutch CLH located behind the constant-speed clutch CLT. A constant-speed gear mechanism 40 is provided across the constant-speed clutch CLT and the output shaft 25b. A speed-increasing gear mechanism 41 is provided across the speed-increasing clutch CLH and the output shaft 25b. A parking brake 39 is provided on the output shaft 24a of the gear mechanism 24.

[0034] In the front wheel transmission unit 25, when the constant-velocity clutch CLT is operated to engage, the power from the input shaft 25a is transmitted to the output shaft 25b by the constant-velocity clutch CLT and the constant-velocity gear mechanism 40, and the constant-velocity transmission state is created by the constant-velocity gear mechanism 40, so that power to drive the front wheel 1 is output from the output shaft 25b when the peripheral speed of the front wheel 1 is the same as the peripheral speed of the rear wheel 2. When the speed-increasing clutch CLH is operated to engage, the power from the input shaft 25a is transmitted to the output shaft 25b by the speed-increasing clutch CLH and the speed-increasing gear mechanism 41, and the front wheel speed-increasing transmission state is created by the speed-increasing gear mechanism 41, so that power to drive the front wheel 1 is output from the output shaft 25b when the peripheral speed of the front wheel 1 is faster than the peripheral speed of the rear wheel 2. The output from the output shaft 25b is input to the front wheel differential mechanism 17 via the rotating shaft 42 that connects the output shaft 25b and the input shaft 17a of the front wheel differential mechanism 17.

[0035] When the constant-speed clutch CLT is engaged, the vehicle body 3 enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven at a speed equal to the average circumferential speed of the left and right front wheels 1, and when the speed-increasing clutch CLH is engaged, the vehicle body 3 enters a four-wheel drive state in which the front wheels 1 and rear wheels 2 are driven at a speed higher than the average circumferential speed of the left and right rear wheels 2. As a result, when the speed-increasing clutch CLH is engaged, the vehicle body 3 can be driven with a smaller turning radius than when the constant-speed clutch CLT is engaged.

[0036] [Regarding the transmission control system] A gear shift pedal 45 (see Figure 4) is provided in the driver's unit 6 as a gear shift operating device for shifting gears in the continuously variable transmission 28. As shown in Figure 4, the operating position of the gear shift pedal 45 is detected by a first potentiometer 46, and the first potentiometer 46 is linked to a control device 47. In this embodiment, a first potentiometer 46 is used, but various operating position detection mechanisms, such as those using a detection switch, can be used instead of the first potentiometer 46.

[0037] As shown in Figure 4, the control device 47 and the continuously variable transmission 28 are linked. The control device 47 is configured using a microcomputer and includes a gear shift control means 48. When the gear shift pedal 45 is operated, the gear shift control means 48 detects that a gear shift operation has been performed based on the detection information from the first potentiometer 46 and operates the continuously variable transmission 28 to shift gears.

[0038] The gear shift operation of the continuously variable transmission 28 by the gear shift control means 48 is made possible by the operation structure shown in Figure 5. Specifically, as shown in Figure 5, the continuously variable transmission 28 is equipped with a hydraulic cylinder 50 connected to the swash plate 49 of a hydraulic pump P, and a gear shift operation valve 52 is connected to the hydraulic cylinder 50 via an operating oil passage 51. A hydraulic pump 54 is connected to the gear shift operation valve 52 via an oil supply passage 53. By switching the gear shift operation valve 52, the operating hydraulic pressure supplied by the hydraulic pump 54 is supplied to one or the other of the two oil chambers of the hydraulic cylinder 50 to operate the hydraulic cylinder 50, and the hydraulic pressure supply to the hydraulic cylinder 50 is stopped to stop the hydraulic cylinder 50. When the gear shift operation valve 52 is switched, the continuously variable transmission 28 is operated by tilting the swash plate 49 by the hydraulic cylinder 50 in the forward or reverse direction corresponding to the operating position of the gear shift operation valve 52. The speed control valve 52 is composed of an electromagnetically operated valve, and the electromagnetically operated part 52a of the speed control valve 52 is linked to the control device 47. An emergency relief valve 56 is connected to the drive oil passage 55 that connects the hydraulic pump P and the hydraulic motor M of the continuously variable transmission 28.

[0039] As shown in Figure 4, the control device 47 is linked to each of the first clutch CL1, second clutch CL2, third clutch CL3, and fourth clutch CL4, enabling the switching operation of the first clutch CL1, second clutch CL2, third clutch CL3, and fourth clutch CL4 by the gear shift control means 48.

[0040] Specifically, the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4 are each composed of hydraulically operated clutches. As shown in Figure 4, the first switching valve 57 connected to the first clutch CL1, the second switching valve 58 connected to the second clutch CL2, the third switching valve 59 connected to the third clutch CL3, and the fourth switching valve 60 connected to the fourth clutch CL4 are linked to the control device 47, enabling the switching operation of the first switching valve 57, the second switching valve 58, the third switching valve 59, and the fourth switching valve 60 by the gear shift control means 48.

[0041] As shown in Figure 4, an engine rotation detection mechanism 61 for detecting the rotational speed of the engine 4 and an input shaft rotation sensor 62 for detecting the rotational speed of the input shaft 16a of the rear wheel differential mechanism 16 are linked to the control device 47. As shown in Figure 2, the input shaft rotation sensor 62 detects the rotational speed of the transmission gear 63 provided on the input shaft 16a as the rotational speed of the input shaft 16a.

[0042] The gear shift control means 48 calculates the gear ratio (rotational speed of input shaft 16a / engine rotational speed) for the gear shift transmission between the engine 4 and the input shaft 16a based on the detection information from the engine rotation detection mechanism 61 and the detection information from the input shaft rotation sensor 62. Based on the calculated gear ratio G and the shift state of the continuously variable transmission 28, it switches the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4 to control the rotational speed V of the input shaft 16a. The rotational speed V of the input shaft 16a corresponds to the vehicle speed.

[0043] Figure 6 is an explanatory diagram of vehicle speed shifting by the shift control means 48. The vertical axis of Figure 6 shows the calculated gear ratio G and the rotational speed V of the input shaft 16a (corresponding to the vehicle speed). The horizontal axis of Figure 6 shows the shifting state of the continuously variable transmission 28. [N] indicates the neutral state, and [-MAX] indicates the shifting state that outputs the maximum speed reverse power. [+MAX] indicates the shifting state that outputs the maximum speed forward power. [-K] indicates the shifting state for clutch switching on the reverse side (the shifting state just before [-MAX]), and [+K] indicates the shifting state for clutch switching on the forward side (the shifting state just before [+MAX]). [G1], [G2], [G3], and [G4] are preset gear ratios.

[0044] In other words, with the first clutch CL1 engaged, as the continuously variable transmission 28 shifts from [-MAX] to [+MAX], the rotational speed V increases steplessly from zero speed [0] in the 1st gear range. When the continuously variable transmission 28 becomes [+K] and the calculated gear ratio G becomes [G1], the shift control means 48 switches the first clutch CL1 to disengage and switches the second clutch CL2 to engage. With the second clutch CL2 engaged, as the continuously variable transmission 28 shifts towards [-MAX], the rotational speed V increases steplessly in the 2nd gear range. When the continuously variable transmission 28 becomes [-K] and the calculated gear ratio G becomes [G2], the shift control means 48 switches the second clutch CL2 to disengage and switches the third clutch CL3 to engage. When the continuously variable transmission 28 is shifted toward [+MAX] with the third clutch CL3 engaged, the rotational speed V increases steplessly in the 3rd gear range. When the continuously variable transmission 28 becomes [+K] and the calculated gear ratio G becomes [G3], the shift control means 48 switches the third clutch CL3 to disengage and the fourth clutch CL4 to engage. As the continuously variable transmission 28 shifts toward [-MAX] with the fourth clutch CL4 engaged, the rotational speed V increases steplessly in the 4th gear range.

[0045] A forward / reverse lever 64 (see Figure 4) is provided in the driver's unit 6 as a forward / reverse switching device for operating the forward / reverse switching device 23. As shown in Figure 4, the operating position of the forward / reverse lever 64 is detected by a second potentiometer 65, and the second potentiometer 65 is linked to the control device 47. In this embodiment, a second potentiometer 65 is used, but various operating position detection mechanisms such as detection switches can be used instead of the second potentiometer 65.

[0046] As shown in Figure 4, the control device 47 and the forward / reverse switching device 23 are linked. The control device 47 is equipped with a forward / reverse switching means 66. When the forward / reverse lever 64 is operated, the forward / reverse switching means 66 detects that a switching operation has been performed based on the detection information from the second potentiometer 65 and switches the forward / reverse switching device 23 to a forward transmission state or a reverse transmission state corresponding to the operating position of the forward / reverse lever 64 [forward position [f], reverse position [r]]. Each of the forward clutch CLF and reverse clutch CLR is configured as a hydraulically operated clutch, which is engaged by the supply of operating hydraulic pressure and disengaged by the discharge of operating hydraulic pressure. As shown in Figure 4, the forward operating valve 67 connected to the forward clutch CLF and the reverse operating valve 68 connected to the reverse clutch CLR are linked to the control device 47, enabling the forward and reverse switching means 66 to operate the forward and reverse operating valves 67 and 68, thereby enabling the forward and reverse switching operation of the forward and reverse switching device 23 by the forward and reverse switching means 66.

[0047] As shown in Figure 4, the control device 47 includes a switching deterrent means 70, a deterrent vehicle speed setting unit 71, and a deceleration control means 73. A deterrent vehicle speed setting device 72 is linked to the control device 47.

[0048] The deterrent speed setting unit 71 is configured to set a set deterrent speed [SV] to deter the switching of the forward / reverse switching device 23, and the set deterrent speed [SV] is changed by the deterrent speed setting device 72.

[0049] Specifically, as shown in Figure 4, the deterrent speed setting device 72 is equipped with a dial-type operating tool 72a that can be rotated within the adjustment range W. The deterrent speed setting unit 71 can steplessly change the set deterrent speed [SV] within a change range corresponding to the adjustment range W of the deterrent speed setting device 72, and each time the deterrent speed setting device 72 is adjusted, the unit sets a new set deterrent speed [SV] corresponding to the speed value of the adjustment position of the deterrent speed setting device 72, based on the setting command from the deterrent speed setting device 72, replacing the previously set set deterrent speed [SV]. The deterrent speed setting unit 71 sets a higher set deterrent speed [SV] the higher the adjustment position of the deterrent speed setting device 72 is. In this embodiment, a dial-type deterrent speed setting device 72 is used, but various types of deterrent speed setting devices can be used, such as those with a slide-type or touch-panel operating tool.

[0050] The switching restraint means 70 uses the input shaft rotation sensor 62 as a vehicle speed detection mechanism, inputs the rotational speed of the input shaft 16a detected by the input shaft rotation sensor 62 as the detected vehicle speed [KV], and restrains the switching of the forward / reverse switching device 23 based on the detected vehicle speed [KV] and the set restraint vehicle speed [SV] set by the restraint vehicle speed setting unit 71.

[0051] In other words, as shown in Figure 7, when the switching restraint means 70 detects that the forward / reverse lever 64 has been switched from one forward position [f] to the other position [r] based on the detection information from the second potentiometer 65, it inputs the rotational speed detected by the input shaft rotation sensor 62 of the input shaft 16a as the detected vehicle speed [KV], and also inputs the set restraint vehicle speed [SV] from the restraint vehicle speed setting unit 71, and compares the detected vehicle speed [KV] and the set restraint vehicle speed [SV]. If it is determined that the detected vehicle speed [KV] is faster than or equal to the set restraint speed [SV], it restrains the switching of the forward / reverse switching device 23 by the forward / reverse switching means 66, that is, the switching of the forward clutch CLF and the reverse clutch CLR. If it is determined that the detected vehicle speed [KV] is lower than the set deterrent speed [SV], the forward / reverse switching means 66 is allowed to switch the forward / reverse switching device 23, that is, to switch between the forward clutch CLF and the reverse clutch CLR.

[0052] As shown in Figure 8, when the deceleration control means 73 detects that the forward / reverse lever 64 has been switched from one forward position [f] to the other based on the detection information from the second potentiometer 65, it inputs the rotational speed of the input shaft 16a detected by the input shaft rotation sensor 62 as the detected vehicle speed [KV], and also inputs the set restraint vehicle speed [SV] from the restraint vehicle speed setting unit 71, and compares the detected vehicle speed [KV] and the set restraint vehicle speed [SV]. If it is determined that the detected vehicle speed [KV] is higher than or equal to the set restraint speed [SV], it decelerates the continuously variable transmission 28 in priority to the gear shift control means 48, and stops the deceleration operation of the continuously variable transmission 28 when the detected vehicle speed [KV] becomes lower than the set restraint vehicle speed [SV]. If the detected vehicle speed [KV] is compared with the set deterrent speed [SV] and it is determined that the detected vehicle speed [KV] is not higher than the set deterrent speed [SV], the continuously variable transmission 28 is not decelerated and is maintained in the gear state it was in when the forward / reverse lever 64 was detected to have been operated.

[0053] As shown in Figure 4, a clutch adjustment mechanism 76 is linked to the forward clutch CLF and the reverse clutch CLR. The clutch adjustment mechanism 76 consists of a speed adjustment mechanism 76A that can adjust the switching speed of the forward clutch CLF and the reverse clutch CLR, and a clutch pressure adjustment mechanism 76B that can adjust the pressure when the forward clutch CLF and the reverse clutch CLR are engaged.

[0054] Figure 9 is a graph showing the measured clutch switching and vehicle speed changes when the forward / reverse switching device 23 is actually switched from forward to reverse driving mode on a tractor (without any work equipment attached). The horizontal axis of the upper and lower graphs represents time. The vertical axis to the right of the upper graph represents the system pressure applied to the forward clutch CLF and reverse clutch CLR by the actuators. Line f in the upper graph represents the forward instruction, and line r in the upper graph represents the reverse instruction. Line fp in the upper graph represents the change in system pressure applied to the forward clutch CLF, and line rp in the upper graph represents the change in system pressure applied to the reverse clutch CLR. The vertical axis to the left of the lower graph represents the rotational speed on the axle side of the forward / reverse switching device 23. Line a in the lower graph represents the change in rotational speed on the axle side of the forward / reverse switching device 23.

[0055] When the instruction switches from forward command f to reverse command r, the actuator that drives the reverse clutch CLR engages and disengages the reverse clutch CLR by raising or lowering the system pressure with a proportional pressure reducing valve. By setting the pressure to an intermediate level, the reverse clutch CLR is made to slip. (This pressure varies depending on the total weight and load of the tractor and coupling work equipment.) Therefore, from the time t when the instruction changes from forward command to reverse command until time tw has elapsed, the maximum pressure SP1 is applied to the gap in the reverse clutch CLR to inject oil into the reverse clutch CLR and fill it almost completely. However, it is almost full, and almost no torque is transmitted yet. Switching occurs between forward and neutral, or between reverse and neutral, and the size of the gap in the clutch differs depending on the length of time between switches, and the elapsed time tw is changed according to the size of the gap. After time tw has elapsed, the pressure is gradually increased as shown by the inclined part rpk of the line rp so that the reverse clutch CLR transmits torque and the direction of travel is changed. At this time, as shown by line a in the lower graph, the rotational speed (vehicle speed) on the axle side of the forward / reverse switching device 23 gradually changes from the forward rotational speed Vf, passing through zero, to the reverse rotational speed. The switch to reverse driving is completed at point t1 when the reverse clutch CLR is fully engaged. The rotational speed (vehicle speed) on the axle side of the forward / reverse switching device 23 becomes the reverse rotational speed Vr. The same occurs when the instruction changes from reverse to forward and the forward / reverse switching device 23 is switched from the reverse driving state to the forward driving state.

[0056] Therefore, when the speed control mechanism 76A switches the instruction from one forward or reverse command to the other, it fills the gaps of the forward clutch CLF and reverse clutch CLR, which should be switched to the engaged position, with oil. However, from the time t when the instruction is switched until the elapsed time tw has elapsed, the forward clutch CLF and reverse clutch CLR are almost completely filled with oil, so that torque can be quickly transmitted when the forward clutch CLF and reverse clutch CLR are switched. This oil filling operation of the speed control mechanism 76A remains constant regardless of the "travel speed when the clutch is switched" or the "clutch switching sensitivity that determines the strength of the clutch switching." (This is because if the oil is not filled quickly, the forward clutch CLF and reverse clutch CLR will not be able to transmit torque.)

[0057] The clutch pressure adjustment mechanism 76B adjusts the pressure of the proportional pressure reducing valve to adjust the clutch shifting sensitivity more sensitively or less sensitively, taking into account the actual change in vehicle speed according to the "travel speed," "clutch shifting sensitivity," and "total weight and load of the tractor and coupling work device." The clutch pressure adjustment mechanism 76B adjusts the pressure increase of the proportional pressure reducing valve within the elapsed time th to be faster in order to make the clutch shifting sensitivity more sensitive (so that the elapsed time th from the point t2 after the elapsed time tw has elapsed to the point t1 when the forward clutch CLF and reverse clutch CLR are fully engaged) and to be slower in order to make the clutch shifting sensitivity less sensitive (so that the elapsed time th is longer).

[0058] More specifically, the forward clutch CLF and reverse clutch CLR each include a clutch chamber (not shown) to which hydraulic fluid is supplied, and clutch plates (not shown) that are pressed by the hydraulic fluid supplied to the clutch chamber and become engaged. The forward clutch CLF and reverse clutch CLR are engaged when the clutch plates are engaged (fully engaged) and disengaged when the clutch plates are released.

[0059] By adjusting the "pressure" of the supplied hydraulic fluid, the clutch can be controlled to either slip or not, thereby changing the engagement state of the clutch plates. In other words, when the hydraulic fluid pressure is increased from a disengaged state, oil flows into the clutch chamber, eliminating the gap between the clutch plates. Once the gap is gone, the oil flow stops. After that, the pressure determines whether the clutch slips or not. If there is little load, the clutch plates will engage at low pressure, but if the load is heavy, the pressure must be increased for them to engage. Therefore, initially, the amount of hydraulic fluid determines how long it takes to fill the gap, and after the gap is gone, the engagement state of the clutch plates changes depending on the pressure.

[0060] The clutch adjustment mechanism 76 is provided in the operating oil passage 75 that supplies operating hydraulic pressure from the hydraulic pump 74 to the forward operating valve 67 of the forward clutch CLF and the reverse operating valve 68 of the reverse clutch CLR, respectively.

[0061] When the speed control mechanism 76A changes the instruction from one forward or reverse command to the other, it fills the forward clutch CLF or reverse clutch CLR that is to be switched to the engaged position with oil as quickly as possible, almost to full capacity, and then gradually increases the oil pressure with the proportional pressure reducing valve to switch the forward clutch CLF or reverse clutch CLR to the engaged position (fully engaged). When the speed control mechanism 76A is adjusted to a lower speed, it adjusts the time it takes to gradually increase the oil pressure with the proportional pressure reducing valve to delay the switching of the forward clutch CLF or reverse clutch CLR to the engaged position.

[0062] When the speed control mechanism 76A is adjusted to the high-speed side, it fills the forward clutch CLF or reverse clutch CLR that is to be switched to the engaged position with oil as quickly as possible, almost to full capacity, and then adjusts the time it takes for the oil pressure to gradually increase using the proportional pressure reducing valve to speed up the switching of the forward clutch CLF or reverse clutch CLR to the engaged (fully engaged) position.

[0063] The clutch pressure adjustment mechanism 76B, when adjusted to the high-pressure side, adjusts the pressure of the supplied hydraulic fluid to the high-pressure side, adjusting the clutch plates to a connected state that does not slip even under high drive loads, and adjusting the on (engagement) of the forward clutch CLF and reverse clutch CLR so that power can be transmitted even under high drive loads.

[0064] The clutch pressure adjustment mechanism 76B, when adjusted to the low-pressure side, adjusts the pressure of the supplied hydraulic fluid to the low-pressure side, adjusting the clutch plates to a connected state that does not slip even under low drive loads, and adjusting the on (engagement) of the forward clutch CLF and reverse clutch CLR so that power can be transmitted even under low drive loads.

[0065] The control device 47 is equipped with a clutch control means 77. Based on information from the deterrent vehicle speed setting unit 71, the clutch control means 77 determines whether the set deterrent vehicle speed [SV] is set to the low speed side or the high speed side. If it determines that the set deterrent vehicle speed [SV] is set to the low speed side, it adjusts the speed adjustment mechanism 76A to the high speed side and adjusts the clutch pressure adjustment mechanism 76B to the low pressure side. If it determines that the set deterrent vehicle speed [SV] is set to the high speed side, it adjusts the speed adjustment mechanism 76A to the low speed side and adjusts the clutch pressure adjustment mechanism 76B to the high pressure side. The clutch control means 77 activates the speed adjustment mechanism 76A and the clutch pressure adjustment mechanism 76B when the forward / reverse switching means 66 switches between the forward clutch CLF and the reverse clutch CLR.

[0066] In this embodiment, the speed adjustment mechanism 76A and the clutch pressure adjustment mechanism 76B are configured to be operated by the clutch control means 77. However, it is possible to configure the system so that the speed adjustment mechanism 76A and the clutch pressure adjustment mechanism 76B are operated by an operator without providing the clutch control means 77.

[0067] In the power transmission device 15, power from the engine 4 and power from the continuously variable transmission 28 are input to the planetary transmission section 31A of the planetary transmission 31 and combined, and the combined power is output from the output section 31B of the planetary transmission 31. The output combined power is input to the forward / reverse switching device 23 and converted into forward or reverse power and transmitted to the rear wheel differential mechanism 16 and the front wheel differential mechanism 17, which are then transmitted from the rear wheel differential mechanism 16 to the left and right rear wheels 2, and from the front wheel differential mechanism 17 to the left and right front wheels 1. Power transmission from the forward / reverse switching device 23 to the front wheel differential mechanism 17 is performed via the front wheel transmission section 25. As a result, the left and right front wheels 1 and the left and right rear wheels 2 are driven, and the vehicle body 3 moves forward or backward.

[0068] By operating the gear shift pedal 45, the gear shift control means 48 shifts the continuously variable transmission 28 based on the detection information from the first potentiometer 46, and based on the gear shift state of the continuously variable transmission 28, the detection information from the input shaft rotation sensor 62, and the detection information from the engine rotation detection mechanism 61, the gear shift control means 48 switches the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4, and the combined power is transmitted from the output unit 31B to the forward / reverse switching device 23 in a state where the combined power shifts steplessly from the 1st gear range to the 4th gear range. If the forward / reverse lever 64 is switched to the forward position [f], the forward / reverse switching means 66 engages the forward clutch CLF based on the detection information from the second potentiometer 65, switching the forward / reverse switching device 23 to the forward transmission state, and the combined power from the planetary transmission 31 is converted into forward power by the forward / reverse switching device 23 and transmitted to the rear wheel differential mechanism 16 and the front wheel differential mechanism 17. As a result, the rear wheels 2 and front wheels 1 are driven forward, causing the vehicle to shift gears and travel in the forward direction. When the forward / reverse lever 64 is switched to the reverse position [r], the forward / reverse switching means 66 engages the reverse clutch CLR based on the detection information from the second potentiometer 65, switching the forward / reverse switching device 23 to the reverse transmission state. The combined power from the planetary transmission 31 is converted into reverse power by the forward / reverse switching device 23 and transmitted to the rear wheel differential mechanism 16 and the front wheel differential mechanism 17. As a result, the rear wheels 2 and front wheels 1 are driven in the reverse direction, causing the vehicle to shift gears and travel in the reverse direction.

[0069] For example, if forward and reverse switching is not performed frequently, the deterrent speed setter 72 is adjusted to the low speed side. Then, the deterrent speed setting unit 71 sets the low-speed set deterrent speed [SV] corresponding to the adjustment position of the deterrent speed setter 72, and even if the forward / reverse lever 64 is switched from one position [f] to the other, if the detected speed [KV] is high enough to be above the set deterrent speed [SV], the switching of the forward clutch CLF and reverse clutch CLR by the forward / reverse switching means 66 is deterred by the switching deterrent means 70, and the forward / reverse switching device 23 does not switch. Then, the deceleration control means 73 performs a deceleration operation on the continuously variable transmission 28. When the detected vehicle speed [KV] becomes lower than the set deterrent vehicle speed [SV] due to this deceleration operation, the switching deterrent means 70 allows the forward clutch CLF and reverse clutch CLR to be switched by the forward / reverse switching means 66, and the forward / reverse switching device 23 is switched by the forward / reverse switching means 66 to a forward transmission state or reverse transmission state corresponding to the forward position [f] or reverse position [r] when the forward / reverse lever 64 is operated. Since the vehicle speed at which the switching of the forward / reverse switching device 23 is permitted is low, the forward / reverse switching can be performed with minimal switching shock.

[0070] Thus, when the set deterrent speed [SV] is set to a low speed, the forward / reverse switching device 23 can be switched with less switching shock, so the speed adjustment mechanism 76A is adjusted to the high speed side by the clutch control means 77 and the forward clutch CLF or reverse clutch CLR is switched to engage quickly (fully engaged). In this case, since the forward clutch CLF and reverse clutch CLR are switched at a low vehicle speed, the clutch pressure adjustment mechanism 76B is adjusted to the low pressure side by the clutch control means 77, and the forward clutch CLF or reverse clutch CLR is turned on (engaged) so that the clutch plates are engaged at low pressure, allowing for quick changes in the direction of the vehicle. The speed control mechanism 76A always operates in the same way when charging oil into the forward clutch CLF and reverse clutch CLR on the side that is being switched to the engaged position, filling them almost completely as quickly as possible. Then, by adjusting the oil pressure of the actuators that drive the forward clutch CLF and reverse clutch CLR on the side that is being switched to the engaged position to be increased quickly, the forward clutch CLF and reverse clutch CLR are switched to the engaged position more quickly.

[0071] For example, in operations that involve frequent switching between forward and reverse, such as bulldozer work, the deterrent vehicle speed setter 72 is adjusted to the high-speed side. Then, the deterrent speed setting unit 71 sets the high-speed set deterrent speed [SV] corresponding to the adjustment position of the deterrent speed setting device 72, and even if the forward / reverse lever 64 is switched from one position [f] and the reverse position [r] to the other, if the detected speed [KV] is higher than or equal to the set deterrent speed [SV], the switching of the forward / reverse switching means 66 of the forward clutch CLF and the reverse clutch CLR is deterred by the switching deterrent means 70, and the forward / reverse switching device 23 does not switch. Then, the deceleration operation of the continuously variable transmission 28 by the deceleration control means 73 is performed, and the detected speed [KV] becomes lower than the set deterrent speed [SV], and the switching deterrent means 70 allows the switching of the forward / reverse switching means 66 of the forward clutch CLF and the reverse clutch CLR, and the forward / reverse switching of the forward clutch CLF and the reverse clutch CLR When the forward / reverse switching device 23 is switched by the forward / reverse switching means 66 to the forward / reverse transmission state corresponding to the forward position [f] or reverse position [r] when the forward / reverse lever 64 is operated, the forward / reverse switching device 23 is switched by the forward / reverse switching means 66. In this case, the deceleration range by the deceleration control means 73 is narrower than the deceleration range when the deterrent vehicle speed setter 72 is adjusted to the low speed side, and the forward / reverse switching means 70 allows the forward / reverse switching means 66 to switch the forward / reverse switching device 23 to the forward / reverse transmission state corresponding to the forward position [f] or reverse position [r] when the forward / reverse lever 64 is operated, after the forward / reverse switching means 66 has switched the forward / reverse switching device 23 to the forward / reverse transmission state corresponding to the forward position [f] or reverse position [r] when the forward / reverse lever 64 is operated. In other words, the forward / reverse switching device 23 can be switched at a vehicle speed faster than when the set deterrent vehicle speed [SV] is set to the low speed side.

[0072] Thus, when the set deterrent speed [SV] is set to the high-speed side, the forward / reverse switching device 23 is switched at a higher speed than when the set deterrent speed [SV] is set to the low-speed side. As a result, the speed adjustment mechanism 76A is adjusted to the low-speed side by the clutch control means 77, and the forward clutch CLF or reverse clutch CLR is switched to engage later (fully engaged), suppressing the switching shock of the forward / reverse switching device 23. In this case, since the forward clutch CLF and reverse clutch CLR are switched to the high-pressure side by the clutch control means 77, the forward clutch CLF or reverse clutch CLR is switched to the "on" (engaged) state where the clutch plates are engaged at high pressure, allowing the vehicle to change direction even when the vehicle is traveling at high speed. The speed control mechanism 76A always operates in the same way when charging oil into the forward clutch CLF and reverse clutch CLR on the side that is being switched to the engaged position, filling them almost completely as quickly as possible. Then, by adjusting the pressure increase of the oil in the actuators that drive the forward clutch CLF and reverse clutch CLR on the side that is being switched to the engaged position to a slower degree, the forward clutch CLF and reverse clutch CLR are switched to the engaged position with a delay.

[0073] [Another embodiment] (1) In the above-described embodiment, an example with a deceleration control means 73 was shown, but it is also possible to not have a deceleration control means 73. That is, if the forward / reverse lever 64 is operated but the forward / reverse switching means 66 does not switch the forward / reverse switching device 23, the driver may operate the gear shift pedal 45 to the deceleration side so that the detected vehicle speed [KV] is lower than the set deterrent vehicle speed [SV], thereby causing the forward / reverse switching device 23 to switch.

[0074] (2) In the above-described embodiment, the planetary gearbox 31 was shown as being configured to divide the combined power into four speed ranges, but it may also be configured to divide it into three or fewer speed ranges or five or more speed ranges.

[0075] (3) In the above embodiment, the deterrent vehicle speed setting unit 71 is configured to set the set deterrent vehicle speed [SV] by changing it in a stepless manner, but it may also be configured to set the set deterrent vehicle speed [SV] by changing it in a stepwise manner.

[0076] (4) In the above embodiment, an example was shown in which a deterrent vehicle speed setting device 72 equipped with a dial-type operating device 72a was used. However, the deterrent vehicle speed setting device 72 may be equipped with a slide-type operating device or a touch panel type, etc.

[0077] (5) In the above-described embodiment, an example was shown in which a speed control mechanism 76A and a clutch pressure adjustment mechanism 76B are provided. However, an embodiment may be provided in which neither the speed control mechanism 76A nor the clutch pressure adjustment mechanism 76B is provided, or in which either the speed control mechanism 76A or the clutch pressure adjustment mechanism 76B is provided.

[0078] (6) In the above-described embodiment, an example was shown in which a clutch control means 77 for operating the speed adjustment mechanism 76A and the clutch pressure adjustment mechanism 76B is provided. However, the clutch control means 77 may not be provided, and the speed adjustment mechanism 76A and the clutch pressure adjustment mechanism 76B may be operated by an operator.

[0079] (7) In the embodiments described above, an example with front wheels 1 and rear wheels 2 was shown, but the running gear may be a crawler running gear or a combination of mini crawlers and wheels.

[0080] (8) In the above embodiment, an example in which a gear shift pedal 45 is provided was shown, but the invention is not limited to this, and a gear shift lever may be used as the gear shifting device.

[0081] (9) In the above-described embodiment, an example was shown in which a forward / reverse lever 64 is provided, but the embodiment is not limited to this, and a forward / reverse pedal may be used as the forward / reverse switching device. [Industrial applicability]

[0082] The present invention can be applied to a work vehicle comprising: a hydrostatic continuously variable transmission that changes the speed of power from an engine and outputs it; a planetary transmission that receives power from the engine and power from the continuously variable transmission, combines the input power from the engine and power from the continuously variable transmission to output combined power, and changes the speed of the combined power output by changing the speed of the continuously variable transmission; and a forward / reverse switching device that outputs the combined power from the planetary transmission toward the running gear. [Explanation of Symbols]

[0083] 1. Front wheels (running gear) 2. Rear wheels (running gear) 4 engines 23 Forward / forward switching device 28 Continuously Variable Transmission 31 Planetary gearbox 45 Gear shifting mechanism 62. Input shaft rotation sensor (vehicle speed detection mechanism) 64. Forward / reverse lever (forward / reverse selector) 70 Switching check means 71 Restricted vehicle speed setting section 73 Deceleration control means 76A Speed ​​adjustment mechanism 76B Clutch pressure adjustment mechanism CLF forward clutch CLR Reverse Clutch

Claims

1. A hydrostatic continuously variable transmission that receives power from the engine, changes the speed of the input power, and outputs it. A planetary transmission receives power from the engine and power from the continuously variable transmission, combines the input power from the engine and the input power from the continuously variable transmission to output combined power, and changes the speed of the combined power output by the shifting of the continuously variable transmission. A forward / reverse switching device capable of switching between a forward transmission state, which switches the combined power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the combined power from the planetary transmission to reverse power and outputs it to the running gear, A gear shifting device for operating the aforementioned continuously variable transmission, A forward / reverse switching device for operating the forward / reverse switching device, A vehicle speed detection mechanism that detects vehicle speed, A deterrent vehicle speed setting unit sets a set deterrent vehicle speed to deter the switching of the forward / reverse switching device, The system is provided with a switching restraint means that, when the vehicle speed detected by the vehicle speed detection mechanism is lower than the set restraint vehicle speed, allows the switching of the forward / reverse switching device, and when the detected vehicle speed is higher than or equal to the set restraint vehicle speed, restrains the switching of the forward / reverse switching device. The aforementioned deterrent vehicle speed setting unit allows for the setting of the deterrent vehicle speed, A work vehicle equipped with a deceleration control means that, when the forward / reverse switching device is operated, if the detected vehicle speed is higher than or equal to the set restraining vehicle speed, automatically controls the deceleration of the continuously variable transmission based on the detected vehicle speed and the set restraining vehicle speed so that the detected vehicle speed becomes lower than the set restraining vehicle speed.

2. The forward / reverse switching device comprises a forward clutch that, when switched to the "on" position, creates the forward transmission state, and a reverse clutch that, when switched to the "on" position, creates the reverse transmission state. The work vehicle according to claim 1, further comprising a switching speed adjustment mechanism capable of adjusting the switching speed of the forward clutch and the reverse clutch.

3. The forward / reverse switching device comprises a forward clutch that, when switched to the "on" position, creates the forward transmission state, and a reverse clutch that, when switched to the "on" position, creates the reverse transmission state. The work vehicle according to claim 1, further comprising a clutch pressure adjustment mechanism capable of adjusting the pressure at which the forward clutch and the reverse clutch are engaged.

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