Work vehicle

Abstract

To provide a work vehicle for enabling an electric motor to be appropriately returned into a neutral position in a neutral state while enabling a trunnion shaft of a hydrostatic continuously variable transmission to be turnably operated by the electric motor.SOLUTION: The work vehicle includes: a gear engagement type link mechanism 5A for linking an output shaft of a transmission operating electric motor 4 to a trunnion shaft 12b; a shift angle sensor 6 for detecting a turning angle of the trunnion shaft 12b; a motor sensor 43 for detecting the turning angle of the output shaft; and a control device 101 for controlling the actuation of the electric motor 4. The control device 101 can switch between a neutral mode to control the electric motor 4 so that a detection value of the motor sensor 43 becomes a neutral target value and a target value updating mode to update the neutral target value, and sets the neutral target value in the target value updating mode on the basis of a detection value of the shift angle sensor 6 and the detection value of the motor sensor 43, which are changed with the actuation of the electric motor 4 so as to turn to the neutral position.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a work vehicle in which a trunnion shaft of a hydrostatic continuously variable transmission is operated by an electric motor.

Background Art

[0002] Conventionally, as this type of work vehicle, the output shaft of an electric motor and the trunnion shaft of a hydrostatic continuously variable transmission are interlocked via a gear meshing type linkage mechanism, and the detection value of a shift angle sensor that detects the rotation angle of the trunnion shaft is set to the target value set by the operation of the main shift lever. The electric motor was configured to be controlled (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The angle of the swash plate of a hydrostatic continuously variable transmission and the rotation angle of the trunnion shaft correspond one-to-one. To precisely control the shift state, it is necessary to precisely control the rotation angle of the trunnion shaft. For example, to control a hydrostatic continuously variable transmission to a neutral state, it is necessary to stop the trunnion shaft within a very narrow range. There is room for improvement in the form of controlling an electric motor based on the detection value of a displacement angle sensor as in the above prior art.

[0005] An object of the present invention is to provide a work vehicle capable of rotating and operating a trunnion shaft of a hydrostatic continuously variable transmission by an electric motor and capable of appropriately returning the hydrostatic continuously variable transmission to a neutral state in the neutral state.

Means for Solving the Problems

[0006] The characteristic configuration of the work vehicle according to the present invention includes a hydrostatic continuously variable transmission for power output, an electric motor for shift operation, a gear meshing type linkage mechanism that links the output shaft of the electric motor and the trunnion shaft of the hydrostatic continuously variable transmission, a biasing mechanism that rotationally biases the trunnion shaft to return it to the neutral position, a shift angle sensor that detects the rotation angle of the trunnion shaft, a target value setting means that sets a shift target value by manual operation, a motor sensor that detects the rotation angle of the output shaft, and a control device that controls the operation of the electric motor. The control device can be switched between a shift operation mode in which the electric motor is controlled so that the rotation angle of the trunnion shaft detected by the shift angle sensor becomes the shift target value, a neutral mode in which the electric motor is controlled so that the rotation angle of the output shaft detected by the motor sensor becomes the neutral target value, and a target value update mode in which the neutral target value is updated. In the target value update mode, the neutral target value is set based on the detection value of the shift angle sensor and the detection value of the motor sensor that change as the electric motor is operated so that the trunnion shaft rotates toward the neutral position.

[0007] According to the present invention, the control device that controls the electric motor can be switched between a shift operation mode that performs control based on the rotation angle of the trunnion shaft detected by the shift angle sensor and a neutral mode that performs control based on the rotation angle of the output shaft detected by the motor sensor. The output shaft of the motor and the trunnion shaft are linked by a gear meshing type linkage mechanism, and the amount of rotation of the output shaft of the motor is larger than the amount of rotation of the corresponding trunnion shaft. Therefore, according to the neutral mode, more precise control of the trunnion shaft becomes possible than in the shift operation mode.

[0008] Since the angular range of the trunnion shaft for the hydrostatic continuously variable transmission to be in the neutral state is very small, if the control to the neutral state is performed in the shift operation mode, the control may become unstable or it may take time to reach stability. In this configuration, the control of the hydrostatic continuously variable transmission to the neutral state is facilitated by switching to the neutral mode. Further, since a return biasing force acts on the hydrostatic continuously variable transmission toward the neutral side and there is backlash in the gear meshing type linkage mechanism, there is an advantage that the allowable range of the rotational position of the output shaft of the electric motor becomes relatively large.

[0009] And in the target value update mode, by operating the electric motor, the trunnion shaft is rotated from a position other than the neutral position toward the neutral position, and the detected values of the shift angle sensor and the motor sensor that change with the rotation are detected, and a neutral target value is set based on these detected values. When reaching the neutral position, the rotation of the trunnion shaft stops due to the biasing force of the biasing mechanism, and accordingly, the output fluctuation of the shift angle sensor stops. At this time, if the output shaft of the electric motor continues to rotate, there is backlash, so the output shaft of the electric motor continues to rotate. And at the position where it rotates by the amount of play of the backlash, the output shaft of the electric motor and the trunnion shaft become in a state where they can be interlocked, and the output of the displacement angle sensor fluctuates again. Therefore, it is possible to obtain the detected value of the motor sensor (neutral target value) when the output shaft is at the appropriate neutral position from the information of the detected value of the shift angle sensor and the detected value of the motor sensor. By using the neutral target value updated in the target value update mode in the neutral mode, the output shaft of the electric motor can be surely moved to the appropriate neutral position, and the hydrostatic continuously variable transmission can be surely returned to the neutral state.

[0010] Therefore, it has become possible to provide a work vehicle that can rotate the trunnion shaft of the hydrostatic continuously variable transmission by an electric motor and can appropriately return the hydrostatic continuously variable transmission to the neutral state in the neutral state.

[0011] In the present invention, in the target value update mode, as the electric motor is operated so that the trunnion shaft rotates from the forward state toward the neutral position, when it is detected by the detection value of the shift angle sensor that the trunnion shaft has reached the neutral position, the detection value of the motor sensor at this time is detected as the forward detection value. As the electric motor is operated so that the trunnion shaft rotates from the reverse state toward the neutral position, when it is detected by the detection value of the shift angle sensor that the trunnion shaft has reached the neutral position, the detection value of the motor sensor at this time is detected as the reverse detection value. It is preferable to set the neutral target value based on the forward detection value and the reverse detection value.

[0012] According to this configuration, when the trunnion shaft rotates from the forward state toward the neutral position, the rotation position at which the trunnion shaft stops rotating and the forward detection value is detected corresponds to one end of the backlash allowance, and when the trunnion shaft rotates from the reverse state toward the neutral position, the rotation position at which the trunnion shaft stops rotating and the reverse detection value is detected corresponds to the other end of the backlash allowance. Therefore, the neutral target value can be appropriately set by using the forward detection value and the reverse detection value of the motor sensor.

[0013] In the present invention, in the target value update mode, it is preferable that the control device controls the operation of the electric motor so that the rotation angle of the output shaft changes by a set unit angle every set time.

[0014] According to this configuration, the electric motor does not operate continuously, but changes by a set unit angle every set time. As a result, after operating by only the set unit angle, for example, it is possible to operate the electric motor while checking whether the trunnion shaft has stopped at the neutral position, and the rotation angle of the output shaft can be appropriately adjusted without being affected by the return biasing force and causing an error.

[0015] In the present invention, the linkage mechanism is configured such that a driving gear provided on the output shaft and a driven gear provided on the trunnion shaft mesh with each other and are interlocked. When the trunnion shaft is not in the neutral position, it is preferable that the driven gear is pressed and biased by the biasing mechanism so that the tooth surfaces contact each other in a rotational direction opposite to the rotational direction of the driving gear.

[0016] According to this configuration, when the trunnion shaft is not in the neutral position, the driven gear is pressed and biased in a rotational direction opposite to the rotational direction of the driving gear, so that it is possible to avoid a deviation in the rotation angle and appropriately control the electric motor.

[0017] In the present invention, the biasing mechanism includes a swing arm having a cam and swinging integrally with the trunnion shaft, an operating body having a cam follower and swinging around an axis parallel to the axis of the trunnion shaft, and a biasing spring for biasing the cam follower toward the cam. It is preferable that the swing arm is swing-biased in a direction to return to the neutral position along with the pressing action of the biasing spring and the cam follower on the cam.

[0018] According to this configuration, by using a cam-type biasing mechanism, it is possible to bias the trunnion shaft appropriately back to the neutral position with a simple structure.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0020] Hereinafter, an example of an embodiment of the work vehicle according to the present invention will be described based on the description of the drawings. The mode for carrying out the present invention will be described with reference to the drawings. In the following description, unless otherwise specified, the direction of arrow F in the figure is defined as "front", the direction of arrow B is defined as "rear", the direction of arrow L is defined as "left", and the direction of arrow R is defined as "right".

[0021] 〔Overall Configuration〕 FIG. 1 is a side view showing the whole of a tractor which is an example of a work vehicle according to an embodiment of the present invention. As shown in this figure, the tractor includes a vehicle body 1 equipped with left and right front wheels 1F that can be steered and driven, and left and right rear wheels 1R that can be driven. A prime mover 2 is provided at the front part of the vehicle body 1, and a driving part 3 with a driver's cab 30 is provided at the rear part of the vehicle body 1. The vehicle body 1 includes a vehicle body frame 10 that supports the prime mover 2 and the driving part 3 on the front wheels 1F and the rear wheels 1R. Although not shown, side brakes that individually apply a braking action to the left and right rear wheels 1R are provided.

[0022] The vehicle body frame 10 has a monocoque structure including an engine mounting frame 10F supported by the front wheels 1F, an engine 20 provided in the power unit 2, a transmission case 11 whose front end is connected to the rear part of the engine 20, a hydrostatic continuously variable transmission (hereinafter abbreviated as continuously variable transmission) 12 whose front end is connected to the rear end of the transmission case 11, and a transmission case 13 whose front end is connected to the rear end of the continuously variable transmission 12. A link mechanism 15 having a pair of left and right lift arms 14 provided at the rear part of the transmission case 13 so as to be swingable up and down, and a power take-out shaft 16 provided at the rear part of the vehicle body frame 10 are provided.

[0023] Inside the driver's cab 30 of the driver's section 3, there are provided a driver's seat 31, a steering wheel 32 as a steering operation tool, a main shift lever 33 as a target value setting means for setting a shift target value by manual operation, left and right brake pedals 21 capable of individually braking the left and right side brakes, a shuttle lever 34 for switching forward and backward, and various other operation tools. The main shift lever 33 is disposed on the front surface of the left rear wheel fender 37 among the left and right rear wheel fenders 37. The shuttle lever 34 is equipped on the left side of the handle post 38 to which the steering wheel 32 is attached.

[0024] When turning, the left and right brake pedals 21 can be individually operated to brake the rear inner wheel 1R during turning, thereby increasing the turning force. On the other hand, when decelerating during straight running, the left and right brake pedals 21 can be simultaneously depressed, and when parking, the left and right brake pedals 21 can also be held in a state where they are simultaneously depressed.

[0025] In the continuously variable transmission 12 to which the power of the engine 20 is transmitted, an axial plunger type hydraulic pump (not shown) and a hydraulic motor (not shown) are provided. By changing and adjusting the swash plate angle (not shown) of the hydraulic pump, the rotational speed of the output shaft (not shown) output from the hydraulic motor (not shown) is changed. The power of the output shaft after being shifted is configured to be transmitted to the transmission case 13.

[0026] The change of the swash plate angle of the hydraulic pump is performed by the forward and reverse rotation operations of the trunnion shaft 12b protruding laterally outward from the outer wall 12a of the continuously variable transmission 12. The rotation operation of the trunnion shaft 12b is performed by an electric motor 4 capable of forward and reverse rotation provided outside the continuously variable transmission 12. The control configuration of the electric motor 4 will be described later.

[0027] 〔Relay operating device〕 As shown in FIGS. 1 to 3, a relay operating device 5 for transmitting the speed change operation by the electric motor 4 to the hydrostatic continuously variable transmission 12 is attached to the outer wall 12a on the right lateral side of the continuously variable transmission 12.

[0028] As shown in FIGS. 2 and 3, the relay operating device 5 includes a linkage mechanism 5A that links the output shaft 41 provided in the electric motor 4 and the trunnion shaft 12b of the continuously variable transmission 12 to transmit the speed change operation of the electric motor 4 to the trunnion shaft 12b, and a biasing mechanism 5B that rotationally biases the trunnion shaft toward the neutral position. These linkage mechanism 5A and biasing mechanism 5B are housed in a common casing 50. The casing 50 is detachably fixed to the outer wall 12a of the hydrostatic continuously variable transmission 12 using a fixture such as a set bolt 17.

[0029] The linkage mechanism 5A includes a drive gear 42 as a first linkage portion G1 linked to the output shaft 41 of the electric motor 4, and a driven gear 52 as a second linkage portion G2 linked to the trunnion shaft 12b.

[0030] The electric motor 4 is provided with a motor case 40 that houses a rotor and a stator, an output shaft 41 protruding from the motor case 40, and a motor sensor 43 that detects the rotation angle of the output shaft 41. The motor case 40 is connected and fixed to the outside of a casing lid portion 50b, which will be described later, of the casing 50. The output shaft 41 protruding from the motor case 40 penetrates the casing lid portion 50b and is installed in a state of protruding into the casing body 50a of the casing 50.

[0031] The drive gear 42 is provided in a state of being externally fitted to the output shaft 41 so as to rotate forward and backward integrally with the axis P1 of the output shaft 41. The driven gear 52 meshing with the drive gear 42 is formed at the end of a swing arm 51 that swings integrally with the trunnion shaft 12b. That is, the swing arm 51 is mounted so as to swing integrally with the trunnion shaft 12b around the axis P2 of the trunnion shaft 12b. A gear having a pitch circle centered on the axis P2 of the trunnion shaft 12b is formed at the edge portion of the swing arm 51 at a position away from the axis P2 of the trunnion shaft 12b, and this constitutes the driven gear 52.

[0032] The biasing mechanism 5B includes a swing arm 51 that swings integrally with the trunnion shaft 12b, and an operating body 55 that swings around an axis P3 parallel to the axis P2 of the trunnion shaft 12b. A cam 51a for guiding a cam follower 56 provided on the operating body 55 is formed on the swing arm 51. This cam 51a is formed at a position closer to the axis P2 of the trunnion shaft 12b than the position where the driven gear 52 is formed on the swing arm 51. The cam 51a is formed to be line-symmetrical with respect to a virtual line segment a1 connecting the axis P2 of the trunnion shaft 12b and the axis P1 of the output shaft 41 as shown in FIGS. 3 and 4 when the trunnion shaft 12b of the hydrostatic continuously variable transmission 12 is in the neutral position.

[0033] The above swing arm 51 is composed of a single member, and both the driven gear 52 and the cam 51a are formed at locations where the positions in the axial direction of the trunnion shaft 12b are different from each other. That is, as shown in FIGS. 2 and 3, the swing arm 51 is composed of a plate-like member mounted on the trunnion shaft 12b and extending toward the side where the output shaft 41 is present, and is a stepped plate material with a plate thickness closer to the axis P2 of the trunnion shaft 12b being thicker than the plate thickness farther from the axis P2.

[0034] Then, a cam 51a is formed at a stepped portion that serves as a boundary between a thick-walled portion with a large plate thickness near the axis P2 of the trunnion shaft 12b and a thin-walled portion with a small plate thickness far from the axis P2. A driven gear 52 is formed at the edge portion of the swing arm 51 at a location farther from the axis P2 of the trunnion shaft 12b than the location where the cam 51a exists.

[0035] The operating body 55 is supported by a shaft portion 53 having an axis P3 parallel to the axis P2 of the trunnion shaft 12b. An eccentric wheel portion 54 is integrally formed on the shaft portion 53. The operating body 55 is provided with a biasing spring 57 that biases a cam follower 56 toward the cam 51a. The biasing spring 57 is constituted by a torsion spring, is mounted on the shaft portion 53 with the intermediate portion wound around the eccentric wheel portion 54, one end portion is wound around the shaft portion 56a of the cam follower 56, and the other end portion abuts against the inner surface of the peripheral wall of the casing 50. With this structure, the inner surface of the peripheral wall of the casing 50 serves as a reaction force receiver for the other end portion of the biasing spring 57, and one end portion of the biasing spring 57 biases the cam follower 56 in a direction of always pressing it against the cam 51a.

[0036] The biasing force of the biasing spring 57 does not have a biasing force that forcibly swings the swing arm 51 to return the trunnion shaft 12b to the neutral position, but has a biasing force that can swing the swing arm 51 by the amount of backlash between the driving gear 42 and the driven gear 52.

[0037] As shown in FIG. 4, the axis P3 serving as the swing fulcrum of the operating body 55 is provided within the interval between a line segment b2 passing through the axis P2 of the trunnion shaft 12b and a line segment b1 passing through the axis P1 of the output shaft 41 in a direction orthogonal to the virtual line segment a1 connecting the axis P2 of the trunnion shaft 12b and the axis P1 of the output shaft 41.

[0038] An eccentric wheel portion 54 is integrally formed on a shaft portion 53 that supports the operating body 55. By rotating the eccentric wheel portion 54 around the axis P3, the biasing direction of the biasing spring 57 mounted in a state of winding around the eccentric wheel portion 54 can be finely adjusted, and the corresponding position of the cam follower 56 with respect to the cam 51a can be finely adjusted.

[0039] As shown in FIGS. 3 and 4, the casing 50 housing the linking mechanism 5A and the biasing mechanism 5B includes a casing main body 50a having a peripheral wall portion and a lid-shaped casing lid portion 50b that closes the open side thereof. As shown in FIG. 3, the casing 50 is fixed to the continuously variable transmission 12 in a state where the bottom of the casing main body 50a faces the outer wall 12a of the continuously variable transmission 12. The electric motor 4 is fixed to the casing lid portion 50b and can be detached from and attached to the continuously variable transmission 12 together with the casing 50. As shown in FIG. 4, an internal viewing portion 58 that enables visual inspection of the inside of the casing 50 is provided in a part of the casing lid portion 50b.

[0040] [Operation of the Relay Operating Device] Based on FIGS. 3 to 6, the operation of the relay operating device 5 when transmitting the speed change operation of the electric motor 4 to the trunnion shaft 12b will be described.

[0041] When a neutral state is commanded, the electric motor 4 operates the trunnion shaft 12b to the neutral position as shown in FIG. 3. In this state, the acting direction of the biasing force f1 of the biasing spring 57 that biases the cam follower 56 of the relay operating device 5 toward the cam 51a coincides with the line segment a1 connecting the axis P2 of the trunnion shaft 12b and the axis P1 of the output shaft 41, and faces the side where the axis P2 of the trunnion shaft 12b exists.

[0042] At this time, the direction of the reaction force of the cam 51a at the position where it contacts the cam follower 56 is the direction of the reaction forces f2, f2 shown in FIG. 4. Since the acting directions of the reaction forces f2, f2 cross each other at substantially equal angles in opposite directions across the line segment a1, the swing arm 51 does not swing clockwise or counterclockwise around the axis P2 of the trunnion shaft 12b and is kept in the neutral position.

[0043] When the speed increase on the forward side is commanded instead of being neutral, the electric motor 4 rotates the drive gear 42 counterclockwise as shown in FIG. 5, and accordingly, the swing arm 51 swings clockwise. As a result, the trunnion shaft 12b also rotates clockwise to change the swash plate angle of the continuously variable transmission 12 by a predetermined amount, and forward travel is performed. At this time, the direction of the reaction force of the cam 51a at the position where it contacts the cam follower 56 is the direction of the reaction force f2 shown in FIG. 6.

[0044] The acting direction of the reaction force f2 faces one side of the line segment a1, to the left side in FIG. 5. At this time, since the distance from the axis P3 of the operating body 55 to the cam follower 56 is constant, it acts to pull the swing arm 51 relatively to the right in the direction opposite to the direction (left direction) of the reaction force f2 acting on the cam follower 56. As shown in the enlarged portion in the figure, the driven gear 52 on the swing arm 51 side is pulled in the direction fa in which it contacts the tooth surface of the drive gear 42, and this position is maintained. That is, during forward travel, the driven gear 52 on the swing arm 51 side is always driven in a state of being in contact with the tooth surface of the drive gear 42, and is driven with almost no backlash.

[0045] When the speed increase on the reverse side is commanded instead of being neutral, the electric motor 4 rotates the drive gear 42 clockwise as shown in FIG. 6, and accordingly, the swing arm 51 swings counterclockwise. As a result, the trunnion shaft 12b also rotates counterclockwise to change the swash plate angle of the continuously variable transmission 12 by a predetermined amount, and reverse travel is performed. At this time, the direction of the reaction force of the cam 51a at the position where it contacts the cam follower 56 is the direction of the reaction force f2 shown in FIG. 5.

[0046] The acting direction of the reaction force f2 is on one side of the line segment a1, towards the right side in FIG. 6. At this time, since the distance from the axis P3 of the operating body 55 to the cam follower 56 is constant, it acts to push the swing arm 51 relatively towards the left direction, contrary to the direction (right direction) of the reaction force f2 acting on the cam follower 56, and as shown in the enlarged portion in the figure, it is drawn towards the direction fa in which the driven gear 52 on the swing arm 51 contacts the tooth surface of the driving gear 42, and it is in a state of maintaining this position. That is, during reverse travel, the driven gear 52 on the swing arm 51 is always driven in a state of contacting the tooth surface of the driving gear 42, and is driven with almost no backlash occurring.

[0047] 〔Control Configuration〕 The tractor (working vehicle) according to this embodiment includes a shift angle sensor 6 that detects the rotation angle of the trunnion shaft 12b, a motor sensor 43 that detects the rotation angle of the output shaft 41, a control device (motor control unit 101) that controls the operation of the electric motor 4, and a target value setting unit 100 as a target value setting means for setting a shift target value of the continuously variable transmission 12 according to the manual operation received by the operating tool S (main shift lever 33, shuttle lever 34, brake pedal 21). The control device (motor control unit 101) can be switched between a shift operation mode for controlling the electric motor 4 so that the rotation angle of the trunnion shaft 12b detected by the shift angle sensor 6 becomes the shift target value, a neutral mode for controlling the electric motor 4 so that the rotation angle of the output shaft 41 detected by the motor sensor 43 becomes a neutral target value as a preset set value, and a set value update mode as a target value update mode for updating the neutral target value. In the set value update mode, the neutral target value is set based on the detection value of the shift angle sensor 6 and the detection value of the motor sensor 43 that change as the electric motor 4 is operated so that the trunnion shaft rotates towards the neutral position.

[0048] A specific configuration will be described. As shown in FIGS. 3 and 4, a potentiometer-type shift angle sensor 6 for detecting the rotation state of the trunnion shaft 12b is mounted on the casing lid portion 50b. By detecting the rotation angle of the trunnion shaft 12b that is rotationally operated as the swing angle of the swing arm 51 changes, this shift angle sensor 6 can detect the swash plate angle of the continuously variable transmission 12.

[0049] As shown in FIG. 7, a lever operation angle sensor 33a composed of a potentiometer is provided at the swing fulcrum portion of the main shift lever 33, and a forward / backward detection sensor 34a for detecting the operation position of the shuttle lever 34 is provided at the swing fulcrum portion of the shuttle lever 34. Also, a brake sensor 22 for detecting that both the left and right brake pedals 21 have been depressed is provided.

[0050] The main shift lever 33 is configured to be able to perform a stepless shift operation to an arbitrary shift position between the lowest speed position Ls where the speed is zero and the highest speed position Hs. The operation position of the main shift lever 33 is detected by the lever operation angle sensor 33a. The shuttle lever 34 can be switched between forward, neutral, and reverse, and is configured to be able to switch the operation position to three preset positions: the forward position FF, the neutral position NN, and the reverse position RR. The forward / backward detection sensor 34a detects to which of the three positions the shuttle lever 34 has been switched.

[0051] The electric motor 4 is configured using, for example, a servo motor, and can rotationally adjust and fix the rotation angle of the trunnion shaft 12b to an arbitrary angle. Inside the motor case 40 of the electric motor 4, a motor sensor 43 capable of detecting the rotation angle of the output shaft 41 is integrally provided. The motor sensor 43 is configured using, for example, a rotary encoder, and can detect the rotation angle of the output shaft 41.

[0052] As shown in Fig. 7, the detection results of the shift angle sensor 6, the lever operation angle sensor 33a, the forward / backward movement detection sensor 34a, the brake sensor 22, and the motor sensor 43 are input to the ECU 23. The ECU 23 includes a microcomputer and is configured to execute various operations in the form of a control program. When the program is executed, the functions of each functional unit are realized.

[0053] The ECU 23 includes, as functional units, a target value setting unit 100 that sets a shift target value for the continuously variable transmission 12, and a motor control unit 101 as a control device that controls the operation of the electric motor 4.

[0054] Based on the detection results of the lever operation angle sensor 33a, the forward / backward movement detection sensor 34a, and the brake sensor 22 (i.e., the manual operation received by the operating tool S), when a non-neutral state is commanded, the target value setting unit 100 sets a shift target value corresponding to the traveling speed commanded by the lever operation angle sensor 33a in the traveling direction (either forward or backward) commanded by the forward / backward movement detection sensor 34a. When neutral is commanded, a neutral corresponding value (zero speed) corresponding to the neutral state of the continuously variable transmission 12 is set as the shift target value.

[0055] When the shift target value is not the neutral corresponding value, the motor control unit 101 controls the electric motor 4 so that the rotation angle of the trunion shaft 12b detected by the shift angle sensor 6 becomes the shift target value. As a result, when the aircraft travels forward or backward, the continuously variable transmission 12 can be shifted so that the speed commanded by the operator's operation of the main shift lever 33 is achieved.

[0056] When the shift target value is the neutral corresponding value, the motor control unit 101 controls the electric motor 4 so that the rotation angle of the output shaft 41 detected by the motor sensor 43 becomes the motor neutral value as a preset set value.

[0057] The control of the electric motor 4 by the ECU 23 will be specifically described based on the control flowcharts of Figs. 8 to 10. If the control mode is not the set value update mode described later, the detection values of the lever operation angle sensor 33a, the forward / backward detection sensor 34a, and the brake sensor 22 are read (steps #1, #2). Next, a shift target value is set (step #3). The set value update mode will be described later.

[0058] When setting the shift target value, as shown in FIG. 9, when the main shift lever 33 is in the lowest speed position Ls (step #31), the shuttle lever 34 is in the neutral position NN (step #32), and further, it is detected that both the left and right brake pedals 21 are depressed by the brake sensor 22 (step #33), a neutral corresponding value (zero speed) is set as the shift target value (step #34). If any of steps #31 to #33 is determined to be false, a value corresponding to the operation position of the main shift lever 33 is set as the shift target value (step #35). Note that the shift target value setting process may be configured such that when it is detected that the main shift lever 33 is in the lowest speed position Ls (step #31) and the shuttle lever 34 is in the neutral position NN (step #32), a neutral corresponding value (zero speed) is set as the shift target value (step #34). The shift target value setting process may be configured such that when it is detected that the shuttle lever 34 is in the neutral position NN (step #32), a neutral corresponding value (zero speed) is set as the shift target value (step #34).

[0059] Next, if a neutral corresponding value (zero speed) is not set as the shift target value (step #4: No), the electric motor 4 is controlled so that the rotation angle of the trunion shaft 12b detected by the shift angle sensor 6 becomes the shift target value (steps #5, #6). At this time, duty control is performed as the control of the electric motor 4. That is, the operation of the electric motor 4 is controlled in such a state that the duty ratio of the pulse current to the electric motor 4 is increased as the deviation between the shift target value and the current rotation angle of the trunion shaft 12b detected by the shift angle sensor 6 increases. As a result, when the deviation is large, the operation is performed quickly.

[0060] When the neutral corresponding value (zero speed) is set as the shift target value (Step #4: Yes), the operation of the electric motor 4 is stopped to maintain the neutral state (Step #7). When the neutral state continues for the set time (about 1 second) (Step #8: Yes), the detected value of the motor sensor 43 is read (Step #9), and the electric motor 4 is controlled so that the detected value of the motor sensor 43 becomes the preset neutral target value (motor neutral value) (Step #10). At this time, one-shot control is executed to control the operation of the electric motor 4 so that the rotation angle of the output shaft 41 of the electric motor 4 changes by the set unit angle (for example, 60 degrees) every set time (for example, 1 second). The control in Steps #5 and #6 corresponds to the shift operation mode, and the control in Steps #7 to #12 corresponds to the neutral mode. Note that the set time and the set unit angle in the one-shot control are not limited to the illustrated values and can be variously changed and implemented.

[0061] [Regarding the set value update mode (target value update mode)] The motor control unit 101 is configured to be switchable to a set value update mode for updating the motor neutral value as the neutral target value. As shown in FIG. 7, a mode switch 24 is provided that can switch the motor control unit 101 to the set value update mode based on a manual operation. When this mode switch 24 is operated and switched to the set value update mode, the motor control unit 101 executes the following update process.

[0062] Note that the processing in this set value update mode is carried out by a maintenance worker when the tractor is produced at the factory or when repairs, replacements, etc. are carried out due to long-term use, and is not carried out by an ordinary user.

[0063] As shown in FIG. 10, when starting the set value update process, first, the electric motor 4 is operated so that the trunnion shaft 12b reaches a predetermined position (rotation position) on the forward side (Step #131). The predetermined position on the forward side is a rotation position where the detected value detected by the shift angle sensor 6 has rotated forward by a predetermined angle (several degrees to about 10 degrees) from the value corresponding to the neutral state in advance.

[0064] Next, the electric motor 4 is operated by a unit angle toward the neutral side (step #132). Hereinafter, this operation is referred to as unit angle rotation processing. When the unit angle rotation processing is first executed, since the trunnion shaft 12b is not in the neutral position, the driven gear 52 on the swing arm 51 side is in contact with the tooth surface of the drive gear 42 (see FIG. 6). Therefore, when the electric motor 4 operates and the drive gear 42 rotates, the driven gear 52 will rotate in conjunction and follow the rotation by the biasing force of the biasing mechanism 5B. As a result, it is detected that the detection value of the shift angle sensor 6 has changed (the determination becomes YES) (step #133). Therefore, the unit angle rotation processing is executed again (step #132).

[0065] When the unit angle rotation processing is repeatedly executed until the trunnion shaft 12b reaches a position corresponding to the neutral position, the driven gear 52 will stop rotating without following the rotation even if the unit angle rotation processing is executed. As a result, the detection value of the shift angle sensor 6 does not change in step #133 (the determination becomes No). At this time, the driven gear 52 is in a state of being slightly separated from the tooth surface of the drive gear 42. Therefore, the detection values of the shift angle sensor 6 and the motor sensor 43 at that time are stored as the forward side detection values (step #134). The determination as to whether or not the detection value of the shift angle sensor 6 does not change may be based on the condition that it continues for a predetermined time (about several seconds).

[0066] Next, the electric motor 4 is operated so that the trunnion shaft 12b reaches a predetermined position (rotation position) on the reverse side (step #135). The predetermined position on the reverse side is a rotation position where the detection value detected by the shift angle sensor 6 rotates by a predetermined angle (several degrees to about 10 degrees) to the reverse side from the value corresponding to the neutral state in advance.

[0067] Also on the reverse side, similar to the forward side, the unit angle rotation processing is executed toward the neutral side, and the unit angle rotation processing is repeatedly executed until the detection value of the shift angle sensor 6 no longer changes (steps #136, #137). When the detection value of the shift angle sensor 6 does not change, the detection values of the shift angle sensor 6 and the motor sensor 43 at that time are stored as the reverse side detection values (step #138).

[0068] Due to the backlash between the gears, a difference occurs between the forward detection value of the motor sensor 43 and the reverse detection value of the motor sensor 43. Therefore, the average value of these is set as the motor neutral value and stored in a storage device (not shown) (step #139). This motor neutral value is used as the target value for the operation of the electric motor 4 in step #11.

[0069] Also, due to measurement errors of the shift angle sensor 6, etc., when shifting from the forward operation range to the neutral side and when shifting from the reverse operation range to the neutral side, the shift angle determined to be neutral may be different values. Therefore, the average value of the forward detection value and the reverse detection value of the shift angle sensor 6 is set as the neutral corresponding value and stored in a storage device (not shown), and is used as the neutral corresponding value in step #4.

[0070] 〔Another Embodiment〕 (1) In the above embodiment, the control device (motor control unit 101) is configured to control the operation of the electric motor 4 so that the rotation angle of the output shaft 41 changes by the set unit angle every set time in the set value update mode. Instead of this configuration, the electric motor 4 may be operated so that the rotation angle of the output shaft 41 rotates continuously.

[0071] (2) In the above embodiment, in the set value update mode (target value update mode), the average value of the forward detection value and the reverse detection value is set as the neutral target value (motor neutral value). Instead of this configuration, a value shifted by the set amount to the forward side with respect to the average value (median value) of the forward detection value and the reverse detection value may be set as the neutral target value to increase the sensitivity of the forward shift operation. Also, a value shifted by the set amount to the reverse side with respect to the average value (median value) of the forward detection value and the reverse detection value may be set as the neutral target value to increase the sensitivity of the forward shift operation.

[0072] (3) In the above-described embodiment, the electric motor 4 is operated so that the trunnion shaft 12b rotates from the forward state toward the neutral position to detect the forward-side detection value, and the electric motor 4 is operated so that the trunnion shaft 12b rotates from the reverse state toward the neutral position to detect the reverse-side detection value. However, instead of this configuration, for example, the electric motor 4 may be operated so that the trunnion shaft 12b rotates in one direction from the forward state through the neutral position to the reverse state, and the forward-side detection value may be detected at the position where the trunnion shaft 12b stops during the rotation, and then the reverse-side detection value may be detected at the position where the trunnion shaft 12b starts to rotate. Alternatively, it may be configured to rotate in one direction from the reverse side.

[0073] (4) In the above-described embodiment, as the linking mechanism 5A, an example is shown in which a swing arm 51 that swings integrally with the trunnion shaft 12b has a driven gear 52 and a cam 51a formed thereon. However, instead of this configuration, for example, various configurations can be adopted, such as a configuration in which the swing arm 51 is provided with a cam follower 56 and the operating body 55 is provided with a cam 51a, a configuration in which the driven gear 52 is attached to a member different from the swing arm 51, a configuration in which the driven gear 52 is directly attached to the trunnion shaft 12b and a cam 51a is formed on the swing arm 51 provided separately therefrom.

[0074] (5) In the above-described embodiment, a torsion spring is used as the biasing spring 57. However, not limited to the torsion spring, an appropriate spring such as a coil spring can be adopted.

Industrial Applicability

[0075] The present invention can be applied to various work vehicles such as tractors, combines, rice transplanters, and transport vehicles, as well as work vehicles in which the trunnion shaft of a hydrostatic continuously variable transmission is operated by an electric motor.

Explanation of Reference Numerals

[0076] 4 Electric motor 5A Linking mechanism 5B Biasing mechanism 6 Transmission angle sensor 12 Hydrostatic continuously variable transmission 12b Trunion axis 41 Output shaft 42 Driving gear 43 Motor sensor 51 Rocking arm 51a Cam 52 Driven gear 55 Operating body 56 Cam follower 57 Biasing spring 100 Target value setting unit (target value setting means) 101 Motor control unit (control device)

Claims

1. A hydrostatic continuously variable transmission for power output, an electric motor for shift operation, a gear meshing type linkage mechanism that links the output shaft of the electric motor and the trunion shaft of the hydrostatic continuously variable transmission, a biasing mechanism that rotationally biases the trunion shaft to return toward the neutral position, a shift angle sensor that detects the rotation angle of the trunion shaft, a target value setting means for setting a shift target value by manual operation, a motor sensor that detects the rotation angle of the output shaft, a control device that controls the operation of the electric motor, and is provided with, The control device, a shift operation mode for controlling the electric motor so that the rotation angle of the trunion shaft detected by the shift angle sensor becomes the shift target value, a neutral mode for controlling the electric motor so that the rotation angle of the output shaft detected by the motor sensor becomes a neutral target value, a target value update mode for updating the neutral target value, and is switchable to, and In the target value update mode, a work vehicle that sets the neutral target value based on the detection value of the shift angle sensor and the detection value of the motor sensor that change as the electric motor is operated so that the trunion shaft rotates toward the neutral position.

2. The control device, in the target value update mode, As the electric motor is operated so that the trunion shaft rotates from the forward state toward the neutral position, when it is detected by the detection value of the shift angle sensor that the trunion shaft has reached the neutral position, the detection value of the motor sensor at that time is detected as the forward side detection value, As the electric motor is operated so that the trunion shaft rotates from the reverse state toward the neutral position, when it is detected by the detection value of the shift angle sensor that the trunion shaft has reached the neutral position, the detection value of the motor sensor at that time is detected as the reverse side detection value, The work vehicle according to claim 1, wherein the neutral target value is set based on the forward side detection value and the reverse side detection value.

3. The control device, in the target value update mode, controls the operation of the electric motor so that the rotation angle of the output shaft changes by a set unit angle every set time. The work vehicle according to claim 2.

4. The linkage mechanism is configured such that a drive gear provided on the output shaft and a driven gear provided on the trunion shaft are meshed and interlocked. When the trunnion axis is not in the neutral position, the driven gear is urged by the biasing mechanism so that the tooth surfaces contact each other in the rotational direction opposite to the rotational direction of the driving gear. The working vehicle according to any one of claims 1 to 3.

5. The biasing mechanism includes a swing arm having a cam and swingable integrally with the trunnion axis, an operating body having a cam follower and swingable about an axis parallel to the axis of the trunnion axis, and a biasing spring for biasing the cam follower toward the cam. The working vehicle according to claim 4, wherein the swing arm is swingably biased in a direction to return to the neutral position along with the pressing action of the biasing spring and the cam follower on the cam.

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