Work vehicle

Abstract

To provide a work vehicle capable of performing control of a vehicle speed with good accuracy.SOLUTION: A work vehicle includes: an engine rotation sensor 61 for detecting the rotational frequency of an engine; a hydraulic motor rotation sensor 63 for detecting the rotational frequency of a hydraulic motor; an input rotation sensor 62 for detecting input rotational frequency NI which is the rotational frequency of power inputted into a frontward / backward switching device; and a control device 47. The control device 47 includes: an input rotational frequency calculation part 67 for calculating the input rotational frequency NI based on a detection value of the engine rotation sensor 61 and a detection value of the hydraulic motor rotation sensor 63; and a vehicle speed control part 48 capable of switching between a first vehicle speed control mode for controlling a vehicle speed based on a detection value of the input rotation sensor 62 and a second vehicle speed control mode for controlling the vehicle speed based on a calculation value of the input rotational frequency calculation part 67.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Conventionally, as a work vehicle, for example, a work vehicle described in Patent Document 1 is known. The work vehicle described in Patent Document 1 includes a hydraulic pump (referred to as "hydraulic pump

[50] " in the document) driven by power from an engine (referred to as "engine [6]" in the document), and a hydraulic motor (referred to as "hydraulic motor

[51] " in the document) driven by pressure oil from the hydraulic pump. It has a hydrostatic continuously variable transmission device (referred to as "continuously variable transmission section

[21] " in the document) that shifts and outputs the power from the engine, and a planetary transmission device (referred to as "compound planetary transmission section

[22] " in the document) into which the power from the engine and the power from the continuously variable transmission device are input and which combines and outputs the power from the engine and the power from the continuously variable transmission device, and a forward and reverse switching device (referred to as "forward and reverse switching device

[30] " in the document) that can switch the power from the planetary transmission device to a forward power and output it to a traveling device (referred to as "front wheels [4], rear wheels [5]" in the document), and a reverse power and output it to the traveling device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In conventional work vehicles, the rotational speed of the input shaft of the forward / reverse switching device (referred to as "input shaft

[95] " in the literature) is detected by a sensor, and the vehicle speed is controlled by controlling the rotational speed of the input shaft of the forward / reverse switching device to a target rotational speed. However, in conventional work vehicles, depending on the rotational speed of the input shaft, the sensor may not be able to detect the rotational speed of the input shaft properly, so there is room for improvement in terms of accurately controlling the vehicle speed.

[0005] In light of the above situation, there is a need for a work vehicle capable of precisely controlling its speed. [Means for solving the problem]

[0006] The features of this invention are: A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit is switchable between a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit. 、 The vehicle speed control unit executes the second vehicle speed control mode in the low-speed range. It is the matter.

[0007] According to this configuration, the vehicle speed control unit is configured to be switchable between a first vehicle speed control mode and a second vehicle speed control mode. Therefore, if the input rotational speed cannot be properly detected by the input rotational speed sensor, the vehicle speed control unit can switch to the second vehicle speed control mode, thereby controlling the vehicle speed based on the value calculated by the input rotational speed calculation unit. This enables accurate control of the vehicle speed.

[0008]

[0009] Also, When the vehicle speed is low, the input rotation speed is also low. In such cases, the input rotation speed sensor may not be able to properly detect the input rotation speed. With this feature configuration, when the vehicle speed is low, the vehicle speed control unit switches to the second vehicle speed control mode, allowing the vehicle speed to be controlled based on the value calculated by the input rotation speed calculation unit. This enables accurate vehicle speed control even when the input rotation speed is low.

[0010] Furthermore, the present invention The characteristics are , A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit is switchable between a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit. As a threshold for the rotational speed at the input shaft of the forward / reverse switching device,A first threshold value for switching from the second vehicle speed control mode to the first vehicle speed control mode and a second threshold value for switching from the first vehicle speed control mode to the second vehicle speed control mode are set. The second threshold value is set to a value smaller than the first threshold value. It is .

[0011] According to this configuration, the vehicle speed control unit is configured to be switchable between a first vehicle speed control mode and a second vehicle speed control mode. Therefore, if the input rotational speed cannot be properly detected by the input rotational speed sensor, the vehicle speed control unit can switch to the second vehicle speed control mode, thereby controlling the vehicle speed based on the value calculated by the input rotational speed calculation unit. This enables accurate control of the vehicle speed. Also, According to this characteristic configuration, the vehicle speed control unit can be prevented from frequently switching between the first vehicle speed control mode and the second vehicle speed control mode.

[0012] Furthermore, in the present invention, the control device has a failure determination unit that determines whether the hydraulic motor rotation sensor has failed, when it is determined by the failure determination unit that the hydraulic motor rotation sensor has failed, it is preferable that the vehicle speed control unit does not execute the second vehicle speed control mode.

[0013] According to this characteristic configuration, when the hydraulic motor rotation sensor has failed, it is possible to avoid the inconvenience of the vehicle speed control unit executing the second vehicle speed control mode.

[0014] Furthermore, in the present invention, the control device has a failure determination unit that determines whether the engine rotation sensor has failed, when it is determined by the failure determination unit that the engine rotation sensor has failed, it is preferable that the vehicle speed control unit does not execute the second vehicle speed control mode.

[0015] According to this characteristic configuration, when the engine rotation sensor has failed, it is possible to avoid the inconvenience of the vehicle speed control unit executing the second vehicle speed control mode.

[0016] Furthermore, in the present invention, the control device has a failure determination unit that determines whether the input rotation sensor has failed, If the fault detection unit determines that the input rotation sensor is faulty, it is preferable that the vehicle speed control unit does not execute the first vehicle speed control mode.

[0017] This feature configuration avoids the inconvenience of the vehicle speed control unit executing the first vehicle speed control mode when the input rotation sensor is malfunctioning.

[0018] Furthermore, the present invention The characteristics are , A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, Sub-transmission unit that changes the speed of power from the aforementioned forward / reverse switching device. and , A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit is switchable between a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit. The vehicle speed control unit executes the second vehicle speed control mode when the sub-transmission unit is in the lowest gear. It is .

[0019] According to this configuration, the vehicle speed control unit is configured to be switchable between a first vehicle speed control mode and a second vehicle speed control mode. Therefore, if the input rotational speed cannot be properly detected by the input rotational speed sensor, the vehicle speed control unit can switch to the second vehicle speed control mode, thereby controlling the vehicle speed based on the value calculated by the input rotational speed calculation unit. This enables accurate control of the vehicle speed. Also, With this feature configuration, when the vehicle speed is low, the vehicle speed control unit switches to a second vehicle speed control mode, allowing the vehicle speed to be controlled based on the value calculated by the input rotation speed calculation unit. This enables accurate vehicle speed control even when the input rotation speed is low. [Brief explanation of the drawing]

[0020] [Figure 1] This is a side view of the tractor. [Figure 2] This is a schematic diagram of a power transmission system. [Figure 3]This is a schematic diagram of the planetary gearbox. [Figure 4] This is a control configuration cylinder. [Figure 5] This is an explanatory diagram of vehicle speed change controlled by a control device. [Figure 6] This is a flowchart of the control system operated by the vehicle speed control unit. [Figure 7] This is a flowchart of the control system operated by the vehicle speed control unit. [Modes for carrying out the invention]

[0021] Hereinafter, an embodiment of the present invention will be described based on the drawings. In the following explanation, with respect to the tractor (an example of a "work vehicle"), the direction of arrow F in Figure 1 is referred to as the "front of the vehicle," the direction of arrow B in Figure 1 is referred to as the "rear of the vehicle," the direction of arrow U in Figure 1 is referred to as the "top of the vehicle," the direction of arrow D in Figure 1 is referred to as the "bottom of the vehicle," the direction of the front side of Figure 1 is referred to as the "left side of the vehicle," and the direction of the back side of Figure 1 is referred to as the "right side of the vehicle."

[0022] [Overall view of the tractor] Figure 1 shows a tractor. This tractor has a vehicle body 3 supported by a pair of steerable and drivable front wheels 1 (running gear) and a pair of drivable rear wheels 2 (running gear). A drive unit 5 containing an engine 4 is provided at the front of the vehicle body 3. At the rear of the vehicle body 3 is a driver's compartment 6 where the operator sits and operates the vehicle, and a link mechanism 7 that connects to work equipment such as a rotary tiller so that it can be raised and lowered. The driver's compartment 6 is equipped with a driver's seat 8, a steering wheel 9 for steering the front wheels 1, and a cabin 10 that covers the passenger space. The vehicle body frame 11 of the vehicle body 3 is composed of an engine 4, a transmission case 12 whose front end is connected to the rear of the engine 4, and a front wheel support frame 13 connected to the bottom of the engine 4. At the rear of the transmission case 12 is a power take-off shaft 14 that extracts power from the engine 4 and transmits it to the work equipment connected by the link mechanism 7.

[0023] [Power transmission system for traction] As shown in Figure 2, the power transmission device 15 for driving, which transmits power from the engine 4 to the front wheels 1 and rear wheels 2, includes a transmission 18 that shifts the power from the engine 4 and transmits it to the rear differential mechanism 16 and the front differential mechanism 17. The transmission 18 is housed in a transmission case 12.

[0024] As shown in Figure 2, the transmission 18 includes an input shaft 20 located at the front of the transmission case 12 to which power from the output shaft 4a of the engine 4 is transmitted; a main transmission unit 21 that receives power from the input shaft 20 and outputs the input power after shifting the speed; a forward / reverse switching device 23 to which the output of the main transmission unit 21 is received; a gear mechanism 24 that transmits the output of the forward / reverse switching device 23 to the input shaft 16a of the rear wheel differential mechanism 16; and a front wheel transmission unit 25 that receives the output of the forward / reverse switching device 23 and outputs the input power after shifting the speed to the front wheel differential mechanism 17.

[0025] [Main transmission unit] 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.

[0026] 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 speed of the forward and reverse rotational power is continuously varied and output from the motor shaft 28b. In other words, the continuously variable transmission 28 changes the speed of the power from the engine 4 and outputs it. The continuously variable transmission 28 is a hydrostatic continuously variable transmission. The hydraulic pump P is driven by power from the engine 4. The hydraulic motor M is driven by pressurized oil from the hydraulic pump P.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] [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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [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.

[0040] 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.

[0041] 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.

[0042] [Control Configuration] 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.

[0043] 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 vehicle speed control unit 48. When the gear shift pedal 45 is operated, the vehicle speed control unit 48 detects that a gear shift has been performed based on the detection information from the first potentiometer 46 and performs a gear shift operation on the continuously variable transmission 28.

[0044] 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 vehicle speed control unit 48 to switch between the first clutch CL1, second clutch CL2, third clutch CL3, and fourth clutch CL4.

[0045] 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. The first switching valve (not shown) connected to the first clutch CL1, the second switching valve (not shown) connected to the second clutch CL2, the third switching valve (not shown) connected to the third clutch CL3, and the fourth switching valve (not shown) connected to the fourth clutch CL4 are linked to the control device 47, enabling the vehicle speed control unit 48 to switch the first, second, third, and fourth switching valves.

[0046] As shown in Figure 4, an engine rotation sensor 61 for detecting the rotational speed of engine 4, an input rotation sensor 62 for detecting the rotational speed of input shaft 23a, and a hydraulic motor rotation sensor 63 for detecting the rotational speed of hydraulic motor M are linked to the control device 47. As shown in Figure 2, the input rotation sensor 62 detects the rotational speed of gear 59 provided on input shaft 23a as the rotational speed of input shaft 23a. That is, the input rotation sensor 62 detects the input rotational speed NI, which is the rotational speed of the power input to the forward / reverse switching device 23. The hydraulic motor rotation sensor 63 detects the rotational speed of gear 60 provided on motor shaft 28b as the rotational speed of hydraulic motor M. Gear 60 is included in the second gear mechanism 30.

[0047] The vehicle speed control unit 48 calculates the gear ratio (rotational speed of input shaft 23a / engine rotational speed) of the variable transmission between the engine 4 and the input shaft 23a based on the values ​​detected by the engine rotation sensor 61 and the input 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 23a. The rotational speed V of the input shaft 23a corresponds to (is proportional to) the vehicle speed. The vehicle speed control unit 48 is configured to control the vehicle speed by controlling the rotational speed of the input shaft 23a to a target rotational speed.

[0048] Figure 5 is an explanatory diagram of the vehicle speed change by the vehicle speed control unit 48. The vertical axis of Figure 5 shows the calculated gear ratio G and the rotational speed V of the input shaft 23a (corresponding to the vehicle speed). The horizontal axis of Figure 5 shows the shift state of the continuously variable transmission 28. [N] indicates the neutral state, and [-MAX] indicates the shift state that outputs the maximum speed reverse power. [+MAX] indicates the shift state that outputs the maximum speed forward power. [-K] indicates the shift state for clutch switching on the reverse side (the shift state just before [-MAX]), and [+K] indicates the shift state for clutch switching on the forward side (the shift state just before [+MAX]). [G1], [G2], [G3], and [G4] are preset gear ratios.

[0049] 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 vehicle speed control unit 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 vehicle speed control unit 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 vehicle speed control unit 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.

[0050] 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.

[0051] As shown in Figure 4, the control device 47 and the forward / reverse switching device 23 are linked. The control device 47 includes a forward / reverse switching unit 66. When the forward / reverse lever 64 is operated, the forward / reverse switching unit 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]]. The forward clutch CLF and the reverse clutch CLR are configured as hydraulically operated clutches that are engaged when operating hydraulic pressure is supplied and disengaged when operating hydraulic pressure is discharged. A forward operating valve (not shown) connected to the forward clutch CLF and a reverse operating valve (not shown) connected to the reverse clutch CLR are linked to the control device 47, enabling the forward operating valve and the reverse operating valve to be operated by the forward / reverse switching unit 66, thereby enabling the forward / reverse switching operation of the forward / reverse switching device 23 by the forward / reverse switching unit 66.

[0052] As shown in Figure 4, the control device 47 includes a vehicle speed control unit 48, a forward / reverse switching unit 66, an input rotation speed calculation unit 67, and a fault detection unit 68.

[0053] The input rotation speed calculation unit 67 calculates the input rotation speed NI based on the value detected by the engine rotation sensor 61 (the rotation speed of the engine 4 detected by the engine rotation sensor 61) and the value detected by the hydraulic motor rotation sensor 63 (the rotation speed of the hydraulic motor M detected by the hydraulic motor rotation sensor 63). Specifically, the input rotation speed calculation unit 67 calculates the input rotation speed NI based on the value detected by the engine rotation sensor 61, the value detected by the hydraulic motor rotation sensor 63, and the gear ratio (specifically, the gear ratio of the third gear mechanism 29, the second gear mechanism 30, and the planetary transmission 31). The vehicle speed control unit 48 is configured to switch between a first vehicle speed control mode, which controls the vehicle speed based on the value detected by the input rotation sensor 62 (the input rotation speed NI detected by the input rotation sensor 62), and a second vehicle speed control mode, which controls the vehicle speed based on the value calculated by the input rotation speed calculation unit 67 (the input rotation speed NI calculated by the input rotation speed calculation unit 67). The fault determination unit 68 determines whether or not the hydraulic motor rotation sensor 63 is faulty.

[0054] As shown in Figure 6, when the first clutch CL1 is engaged (S1), and the rotational speed V (vehicle speed) of the input shaft 23a is increasing from zero speed [0] in the first gear range (S2), and the rotational speed V (vehicle speed) of the input shaft 23a is less than the first threshold V1 (S3, Yes), and the fault determination unit 68 does not determine that the hydraulic motor rotation sensor 63 is faulty (S4, No), the vehicle speed control unit 48 executes the second vehicle speed control mode (S5). That is, the vehicle speed control unit 48 executes the second vehicle speed control mode in the low-speed range of the rotational speed V (vehicle speed) of the input shaft 23a (in this embodiment, the range where the rotational speed V (vehicle speed) of the input shaft 23a is less than the first threshold V1).

[0055] Furthermore, if the rotational speed V (vehicle speed) of the input shaft 23a is not less than the first threshold V1 (S3, No), the vehicle speed control unit 48 executes the first vehicle speed control mode (S6). Also, even if the rotational speed V (vehicle speed) of the input shaft 23a is less than the first threshold V1 (S3, Yes), if the fault detection unit 68 determines that the hydraulic motor rotation sensor 63 is faulty (S4, Yes), the vehicle speed control unit 48 executes the first vehicle speed control mode (S6). In other words, if the fault detection unit 68 determines that the hydraulic motor rotation sensor 63 is faulty (S4, Yes), the vehicle speed control unit 48 does not execute the second vehicle speed control mode (S6).

[0056] Here, as shown in Figure 2, the input rotation sensor 62 is positioned close to the front wheel 1 (see Figure 1) and the rear wheel 2, so it can directly detect the vehicle speed. Therefore, at normal vehicle speeds, the vehicle speed is controlled based on the value detected by the input rotation sensor 62 (first vehicle speed control mode). However, at low speeds (around 0 vehicle speed), the vehicle speed is slow (i.e., the input shaft 23a rotates slowly), which raises concerns that the rotation speed update cycle will be slow and the control will not be stable. Therefore, in the low vehicle speed range, in order to obtain an accurate rotation speed within a certain time, the vehicle speed is controlled based on the detection values ​​of sensors other than the input rotation sensor 62 (specifically, the engine rotation sensor 61 and the hydraulic motor rotation sensor 63) (second vehicle speed control mode).

[0057] As shown in Figure 7, when the vehicle speed control unit 48 is executing the first vehicle speed control mode (S1), if the rotational speed V (vehicle speed) of the input shaft 23a falls below the second threshold V2 (S2, Yes), and the fault determination unit 68 does not determine that the hydraulic motor rotation sensor 63 is faulty (S3, No), the vehicle speed control unit 48 switches to the second vehicle speed control mode (S4).

[0058] Furthermore, if the rotational speed V (vehicle speed) of the input shaft 23a is not less than the second threshold V2 (S2, No), the vehicle speed control unit 48 continues the first vehicle speed control mode (S5). Also, even if the rotational speed V (vehicle speed) of the input shaft 23a is less than the second threshold V2 (S2, Yes), if the fault detection unit 68 determines that the hydraulic motor rotation sensor 63 is faulty (S3, Yes), the vehicle speed control unit 48 continues the first vehicle speed control mode (S5). In other words, if the fault detection unit 68 determines that the hydraulic motor rotation sensor 63 is faulty (S3, Yes), the vehicle speed control unit 48 does not execute the second vehicle speed control mode (S5).

[0059] As shown in Figure 5, the first threshold V1 and the second threshold V2 are thresholds related to the rotational speed V (vehicle speed) of the input shaft 23a. The first threshold V1 is the threshold for switching from the second vehicle speed control mode to the first vehicle speed control mode. The first threshold V1 is set to a value smaller than the rotational speed VN (vehicle speed) of the input shaft 23a, which corresponds to the neutral state N of the continuously variable transmission 28 in the first gear range. For example, the first threshold V1 may be set to the rotational speed V (vehicle speed) of the input shaft 23a, which corresponds to the median (or approximate median) between the neutral state N of the continuously variable transmission 28 and the maximum reverse power -MAX in the first gear range, or it may be set to the rotational speed V (vehicle speed) of the input shaft 23a, which corresponds to the median (or approximate median) between the neutral state N of the continuously variable transmission 28 and the shift state -K for clutch switching on the reverse side in the first gear range. The second threshold V2 is the threshold at which the vehicle speed control mode switches from the first vehicle speed control mode to the second vehicle speed control mode. The second threshold V2 is set to a smaller value than the first threshold V1. This prevents frequent switching between the first vehicle speed control mode and the second vehicle speed control mode, which would otherwise cause discontinuities, in the low-speed range.

[0060] [Another embodiment] (1) In the above embodiment, the input rotation sensor 62 detects the rotational speed of the input shaft 23a. However, the input rotation sensor 62 may also detect the rotational speed of the output shaft 35.

[0061] (2) In the above embodiment, the second threshold V2 is set to a value smaller than the first threshold V1. However, the second threshold V2 may be set to the same value as the first threshold V1.

[0062] (3) In the above embodiment, if the fault detection unit 68 determines that the hydraulic motor rotation sensor 63 is faulty, the vehicle speed control unit 48 does not execute the second vehicle speed control mode. However, if the fault detection unit 68 determines that the engine rotation sensor 61 is faulty, the vehicle speed control unit 48 does not have to execute the second vehicle speed control mode. Alternatively, if the fault detection unit 68 determines that the input rotation sensor 62 is faulty, the vehicle speed control unit 48 does not have to execute the first vehicle speed control mode.

[0063] (4) In the above embodiment, the transmission 18 may include a sub-transmission unit that changes the speed of the power from the forward / reverse switching device 23. In this case, it is preferable that the vehicle speed control unit 48 executes the second vehicle speed control mode when the sub-transmission unit is in the lowest gear. [Industrial applicability]

[0064] This invention can be used in work vehicles. [Explanation of Symbols]

[0065] 1. Front wheels (running gear) 2. Rear wheels (running gear) 4 engines 23 Forward / forward switching device 28 Continuously Variable Transmission 31 Planetary gearbox 47 Control device 48 Vehicle speed control unit 61 Engine speed sensor 62 Input rotation sensor 63 Hydraulic motor rotation sensor 67 Input rotation speed calculation unit 68 Failure determination section NI input rotational speed M Hydraulic motor P Hydraulic pump V1 First threshold V2 Second threshold

Claims

1. A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit has a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit, and is switchable between these modes. The vehicle speed control unit is a work vehicle that executes the second vehicle speed control mode in the low-speed range.

2. A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit has a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit, and is switchable between these modes. A first threshold value for the rotational speed at the input shaft of the forward / reverse switching device is set, which is the threshold value for switching from the second vehicle speed control mode to the first vehicle speed control mode, and a second threshold value for switching from the first vehicle speed control mode to the second vehicle speed control mode. The second threshold is set to a value smaller than the first threshold. The vehicle speed control unit is a work vehicle that executes the second vehicle speed control mode in the low-speed range.

3. A hydrostatic continuously variable transmission having a hydraulic pump driven by power from an engine and a hydraulic motor driven by pressurized oil from the hydraulic pump, which outputs power from the engine in a variable speed manner, A planetary transmission receives power from the engine and power from the continuously variable transmission, and outputs a combined power from the engine and power from the continuously variable transmission. A work vehicle equipped with a forward / reverse switching device capable of switching between a forward transmission state, which switches the power from the planetary transmission to forward power and outputs it to the running gear, and a reverse transmission state, which switches the power from the planetary transmission to reverse power and outputs it to the running gear, An engine speed sensor for detecting the rotational speed of the engine, A hydraulic motor rotation sensor for detecting the rotational speed of the hydraulic motor, An input rotation sensor detects the input rotation speed, which is the rotation speed of the power input to the forward / reverse switching device, A sub-transmission unit that changes the speed of the power from the forward / reverse switching device, A control device is provided, The control device is An input rotation speed calculation unit calculates the input rotation speed based on the detected value of the engine rotation sensor and the detected value of the hydraulic motor rotation sensor, The vehicle speed control unit has a first vehicle speed control mode that controls the vehicle speed based on the detected value of the input rotation sensor and a second vehicle speed control mode that controls the vehicle speed based on the calculated value of the input rotation speed calculation unit, and is switchable between these modes. The vehicle speed control unit is a work vehicle that executes the second vehicle speed control mode when the sub-transmission unit is in the lowest gear.

4. The control device has a fault determination unit that determines whether or not the hydraulic motor rotation sensor is malfunctioning. The work vehicle according to any one of claims 1 to 3, wherein if the fault detection unit determines that the hydraulic motor rotation sensor is faulty, the vehicle speed control unit does not execute the second vehicle speed control mode.

5. The control device has a fault determination unit that determines whether or not the engine rotation sensor is malfunctioning. The work vehicle according to any one of claims 1 to 3, wherein if the fault detection unit determines that the engine speed sensor is faulty, the vehicle speed control unit does not execute the second vehicle speed control mode.

6. The control device has a fault determination unit that determines whether or not the input rotation sensor is malfunctioning. The work vehicle according to any one of claims 1 to 3, wherein if the fault detection unit determines that the input rotation sensor is faulty, the vehicle speed control unit does not execute the first vehicle speed control mode.

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