Work vehicle

Abstract

To actualize a desired work vehicle for allowing appropriate turning operation of a trunnion shaft of a hydrostatic continuously variable transmission all the time with an electric motor.SOLUTION: The work vehicle includes: a gear engagement type link mechanism 5A for linking an output shaft of a shift operation electric motor 4 with a trunnion shaft 12b of a hydrostatic continuously variable transmission; a shift angle sensor 6 for detecting the turning angle of the trunnion shaft 12b; a motor sensor 43 for detecting a 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 first control state of controlling the electric motor 4 so that the turning angle of the trunnion shaft 12b to be detected by the shift angle sensor 6 becomes a shift target value and a second control state of controlling the electric motor 4 so that the turning angle of the output shaft to be detected by the motor sensor 43 becomes a predetermined set value.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 a target value set by operating a main shift lever. The electric motor was configured to be controlled so as to be (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, and in order to precisely control the shift state, it is necessary to precisely control the rotation angle of the trunnion shaft. For example, in order 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 appropriately rotating and operating a trunnion shaft of a hydrostatic continuously variable transmission by an electric motor.

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 transmission 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 transmission angle sensor that detects the rotation angle of the trunnion shaft, a motor sensor that detects the rotation angle of the output shaft, a control device that controls the operation of the electric motor, and a target value setting unit that sets a transmission target value according to a manual operation received by an operating tool. The control device can switch between a first control state in which the electric motor is controlled so that the rotation angle of the trunnion shaft detected by the transmission angle sensor becomes the transmission target value, and a second control state in which the electric motor is controlled so that the rotation angle of the output shaft detected by the motor sensor becomes a preset value.

[0007] According to the present invention, the control device that controls the electric motor can be switched between a first control state in which control is performed based on the rotation angle of the trunnion shaft detected by the transmission angle sensor, and a second control state in which control is performed 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 second control state, more precise control of the trunnion shaft becomes possible compared to the first control state. In other words, when it is necessary to precisely control the trunnion shaft and switch to the second control state, it becomes possible to increase the stability (margin) of control and quickly shift to the control target value compared to always using the first control state.

[0008] Therefore, it has become possible to provide a work vehicle capable of appropriately rotating the trunnion shaft of a hydrostatic continuously variable transmission by an electric motor.

[0009] In the present invention, it is preferable that the control device switches to the first control state when the transmission target value is not a neutral corresponding value, and switches to the second control state when the transmission target value is the neutral corresponding value.

[0010] Since the angular range of the trunnion shaft in which the hydrostatic continuously variable transmission is in the neutral state is very small, if the control to the neutral state is performed in the first control state, the control may become unstable or may take time to become stable. In this configuration, when the shift target value is the neutral corresponding value, the control is performed in the second control state, so that the control to the neutral state becomes easy. Further, since the hydrostatic continuously variable transmission has a return biasing force acting toward the neutral side and there is backlash in the gear meshing type linkage mechanism, the allowable range of the rotation position of the output shaft of the electric motor becomes relatively large. Therefore, the rotation of the trunnion shaft of the hydrostatic continuously variable transmission by the electric motor is performed more appropriately.

[0011] In the present invention, 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 in the second control state.

[0012] According to this configuration, the electric motor does not operate until the output shaft continuously reaches the set value, but changes by a set unit angle every set time. As a result, after operating by only the set unit angle, the electric motor can be operated while checking the rotation state of the gear on the other side (trunnion shaft side), that is, whether the trunnion shaft is stopped at the neutral position, and the rotation angle of the output shaft can be appropriately adjusted in a state where no error occurs due to the influence of the return biasing force.

[0013] In the present invention, it is preferable that a biasing mechanism is provided to bias the trunnion shaft to rotate back toward the neutral position, the linkage mechanism is configured such that a drive gear provided on the output shaft and a driven gear provided on the trunnion shaft mesh and interlock with each other, and when the trunnion shaft is not in the neutral position, the driven gear is pressed and biased by the biasing mechanism so that the tooth surfaces contact each other in a rotation direction opposite to the rotation direction of the drive gear.

[0014] According to this configuration, when the trunion axis 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 the occurrence of a deviation in the rotation angle, and the electric motor can be appropriately controlled.

[0015] In the present invention, the biasing mechanism preferably includes a swing arm having a cam and swinging integrally with the trunion axis, an operating body having a cam follower and swinging around an axis parallel to the axis of the trunion axis, and a biasing spring for biasing the cam follower toward the cam, and 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.

[0016] According to this configuration, by using a cam-type biasing mechanism, it is possible to bias the trunion axis to appropriately return to the neutral position while having a simple structure.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0018] Hereinafter, an example of an embodiment of the work vehicle according to the present invention will be described based on the description in the drawings. The embodiments 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 drawings 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".

[0019] 〔Overall Configuration〕 FIG. 1 is a side view showing the overall 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.

[0020] 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 prime mover 2, a transmission case 11 having its front end connected to the rear part of the engine 20, a hydrostatic continuously variable transmission (hereinafter abbreviated as continuously variable transmission) 12 having its front end connected to the rear end of the transmission case 11, and a transmission case 13 having its front end 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 swingably and vertically operable, and a power take-off shaft 16 provided at the rear part of the vehicle body frame 10 are provided.

[0021] Inside the driver's cab 30 of the driving unit 3, there are various operating tools such as a driver's seat 31, a steering wheel 32 as a steering operation tool, a main transmission lever 33 as a shift operation tool, left and right brake pedals 21 that can separately brake-operate the left and right side brakes, a shuttle lever 34 for switching forward and reverse, etc. The main transmission 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.

[0022] When turning, the left and right brake pedals 21 can be separately operated to brake the inner rear 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 the state of being simultaneously depressed.

[0023] The continuously variable transmission 12 to which the power of the engine 20 is transmitted is provided with an axial plunger type hydraulic pump (not shown) and a hydraulic motor (not shown). 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.

[0024] The change of the swash plate angle of the hydraulic pump is performed by the forward and reverse rotation operation 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 provided outside the continuously variable transmission 12 that can rotate forward and reverse. The control configuration of the electric motor 4 will be described later.

[0025] 〔Relay operating device〕 As shown in FIGS. 1 to 3, a relay operating device 5 that transmits the shift 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.

[0026] As shown in FIGS. 2 and 3, the relay operation device 5 includes a linkage mechanism 5A that links the output shaft 41 provided on 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.

[0027] The linkage mechanism 5A includes a drive gear 42 as a first linkage portion G1 that links to the output shaft 41 of the electric motor 4, and a driven gear 52 as a second linkage portion G2 that links to the trunnion shaft 12b.

[0028] The electric motor 4 is provided with a motor case 40 that houses a rotor and a stator, an output shaft 41 that protrudes 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 that protrudes from the motor case 40 penetrates the casing lid portion 50b and is installed in a state of protruding into the inside of the casing body 50a of the casing 50.

[0029] 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 that meshes 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. And 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.

[0030] The urging 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-symmetric 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.

[0031] The above swing arm 51 is composed of a single member, and both the driven gear 52 and the cam 51a are formed at positions 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 attached to the trunnion shaft 12b and extending toward the side where the output shaft 41 exists, and is a stepped plate material in which the plate thickness on the side closer to the axis P2 of the trunnion shaft 12b is thicker than the plate thickness on the side farther from the axis P2.

[0032] The cam 51a is formed at a stepped portion that is the boundary between a thick portion with a large plate thickness near the axis P2 of the trunnion shaft 12b and a thin portion with a small plate thickness far from the axis P2, and the driven gear 52 is formed at the edge portion of the swing arm 51 at a position farther from the axis P2 of the trunnion shaft 12b than the position where the cam 51a exists.

[0033] 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, and an eccentric portion 54 is integrally formed on the shaft portion 53. The operating body 55 is provided with a biasing spring 57 that biases the 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 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 constantly pressing it against the cam 51a.

[0034] The biasing force of the biasing spring 57 does not have a biasing force sufficient to forcibly swing the swing arm 51 to return the trunnion shaft 12b to the neutral position, but has a biasing force sufficient to swing the swing arm 51 by the amount of backlash between the drive gear 42 and the driven gear 52.

[0035] 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.

[0036] An eccentric portion 54 is integrally formed on the shaft portion 53 that supports the operating body 55. By rotating the eccentric portion 54 around the axis P3, the biasing direction of the biasing spring 57 mounted in a state of being wound around the eccentric 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.

[0037] As shown in FIGS. 3 and 4, the casing 50 that houses the connection 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 attached to and detached from the continuously variable transmission 12 together with the casing 50. As shown in FIG. 4, an internal viewing portion 58 that allows visual inspection of the inside of the casing 50 is provided in a part of the casing lid portion 50b.

[0038] 〔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.

[0039] 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 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.

[0040] 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 intersect 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.

[0041] When the speed increase is commanded on the forward side rather than 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.

[0042] The acting direction of the reaction force f2 faces to 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, contrary to the direction of the reaction force f2 (left direction) acting on the cam follower 56, it acts to attract the swing arm 51 relatively to the right direction, and as shown in the enlarged portion in the figure, the driven gear 52 on the swing arm 51 side is attracted in the direction fa of contacting the tooth surface of the drive gear 42, and is in a state of maintaining this position. That is, during forward travel, the driven gear 52 on the swing arm 51 side is always driven in a state of contacting the tooth surface of the drive gear 42, and is driven with almost no backlash.

[0043] When the speed increase is commanded on the reverse side rather than 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.

[0044] The acting direction of the reaction force f2 is on one side of the line segment a1, and in FIG. 6, it is directed to the right side. At this time, since the distance from the axis P3 of the operating body 55 to the cam follower 56 is constant, contrary to the direction of the reaction force f2 acting on the cam follower 56 (right direction), it acts to push the swing arm 51 relatively leftward. As shown in the enlarged portion in the figure, it is biased in the direction fa in which the driven gear 52 on the swing arm 51 contacts the tooth surface of the driving gear 42, and 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.

[0045] 〔Control Configuration〕 The tractor (work 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 that sets a shift target value of the continuously variable transmission 12 according to a 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 first control state in which the electric motor 4 is controlled so that the rotation angle of the trunnion shaft 12b detected by the shift angle sensor 6 becomes the shift target value, and a second control state in which the electric motor 4 is controlled so that the rotation angle of the output shaft 41 detected by the motor sensor 43 becomes a preset set value. And the control device (motor control unit 101) switches to the first control state when the shift target value is not the neutral corresponding value, and switches to the second control state when the shift target value is the neutral corresponding value.

[0046] 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. This shift angle sensor 6 can detect the swash plate angle of the continuously variable transmission 12 by detecting the rotation angle of the trunnion shaft 12b that is rotationally operated as the swing angle of the swing arm 51 changes.

[0047] 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 and reverse 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. Further, a brake sensor 22 for detecting that both the left and right brake pedals 21 have been depressed is provided.

[0048] The main shift lever 33 is configured to be capable of continuously variable shifting to an arbitrary shift position between the lowest speed position Ls where the vehicle 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 is capable of switching 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 and reverse detection sensor 34a detects to which of the three positions the shuttle lever 34 has been switched.

[0049] The electric motor 4 is configured using, for example, a servo motor, and is capable of rotationally adjusting and fixing 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 is capable of detecting the rotation angle of the output shaft 41.

[0050] As shown in FIG. 7, the detection results of the shift angle sensor 6, the lever operation angle sensor 33a, the forward and reverse 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. By executing the program, the functions of each functional unit are realized.

[0051] The ECU 23 includes, as functional units, a target value setting unit 100 for setting a shift target value of the continuously variable transmission 12 and a motor control unit 101 as a control device for controlling the operation of the electric motor 4.

[0052] When the non-neutral state is commanded based on the detection results of the lever operation angle sensor 33a, the forward / backward detection sensor 34a, and the brake sensor 22 (i.e., the manual operation received by the operating tool S), the target shift 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 detection sensor 34a is set. When neutral is commanded, the neutral corresponding value (zero speed) corresponding to the neutral state of the continuously variable transmission 12 is set as the target shift value.

[0053] When the target shift 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 target shift value. As a result, when the aircraft is traveling forward or backward, the continuously variable transmission 12 can be shifted so as to reach the speed commanded by the operator's operation of the main shift lever 33.

[0054] When the target shift value is the neutral corresponding value, the electric motor 4 is controlled 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.

[0055] 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, the target shift value is set (step #3). The set value update mode will be described later.

[0056] 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, when it is detected that both the left and right brake pedals 21 are depressed by the brake sensor 22 (step #33), the 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, the value corresponding to the operation position of the main shift lever 33 is set as the shift target value (step #35). Incidentally, 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), the shift target value setting process may be configured so that the neutral corresponding value (zero speed) is set as the shift target value (step #34). The shift target value setting process may be configured so that when it is detected that the shuttle lever 34 is in the neutral position NN (step #32), the neutral corresponding value (zero speed) is set as the shift target value (step #34).

[0057] Next, if the 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 becomes larger. As a result, when the deviation is large, the operation is performed quickly.

[0058] When a 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 a preset 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 a set unit angle (for example, 60 degrees) every set time (for example, 1 second). The control in steps #5 and #6 corresponds to the first control state, and the control in steps #7 to #12 corresponds to the second control state. 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.

[0059] [Regarding the set 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 a set 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.

[0060] Note that the processing in this set value update mode is performed by a maintenance worker when the tractor is produced at the factory or when repairs, replacements, etc. are performed due to long-term use, and is not performed by an ordinary user.

[0061] 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 rotates forward by a predetermined angle (several degrees to about 10 degrees) from the value corresponding to the neutral state in advance.

[0062] 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 due to the biasing force of the biasing mechanism 5B. As a result, it is detected that the detected 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).

[0063] When the unit angle rotation processing is repeatedly executed until the trunnion shaft 12b reaches a position corresponding to the neutral position, even if the unit angle rotation processing is executed, the driven gear will not rotate followingly and the rotation will stop. As a result, the detected 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 detected values of the shift angle sensor 6 and the motor sensor 43 at that time are stored as the forward side detected values (step #134). The determination as to whether or not the detected 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).

[0064] 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 detected 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.

[0065] 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 detected value of the shift angle sensor 6 no longer changes (steps #136, #137). When the detected value of the shift angle sensor 6 no longer changes, the detected values of the shift angle sensor 6 and the motor sensor 43 at that time are stored as the reverse side detected values (step #138).

[0066] 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.

[0067] Also, due to measurement errors of the shift angle sensor 6, etc., the shift angle determined to be neutral may be different when shifting from the forward operation range to the neutral side and when shifting from the reverse operation range to the neutral side. Therefore, the average value of the forward detection value of the shift angle sensor 6 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.

[0068] 〔Alternative Embodiment〕 The following lists alternative embodiments.

[0069] (1) In the above embodiment, the control device (motor control unit 101) is configured to control the operation of the electric motor 4 such that the rotation angle of the output shaft 41 changes by a set unit angle every set time in the second control state. Instead of this configuration, the electric motor 4 may be continuously operated so that the rotation angle of the output shaft 41 becomes a set value (motor neutral value).

[0070] (2) In the above embodiment, the control device (motor control unit 101) is configured to switch to the first control state when the shift target value is not the neutral corresponding value, and to switch to the second control state when the shift target value is the neutral corresponding value. Instead of this configuration, the control device (motor control unit 101) may appropriately switch the control state according to the difference in the working conditions. For example, even when the shift target value is not the neutral corresponding value, when a malfunction occurs in the shift angle sensor 6, etc., the control may be executed in the second control state.

[0071] (3) In the above-described embodiment, when the target setting unit sets the shift target value, the operating tool S that is the target of accepting operations is configured to be the lever operation angle sensor 33a, the forward / reverse detection sensor 34a, and the brake sensor 22. However, as the operating tool S, only the lever operation angle sensor 33a and the forward / reverse detection sensor 34a may be used, only the forward / reverse detection sensor 34a and the brake sensor 22 may be used, or only the lever operation angle sensor 33a and the brake sensor 22 may be used. Further, any one of the above three sensors may be used alone.

[0072] (4) In the above-described embodiment, as the linking mechanism 5A, an example is given of a structure in which a driven gear 52 and a cam 51a are formed on a swing arm 51 that swings integrally with the trunnion shaft 12b. However, instead of this configuration, for example, 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 a separately provided swing arm 51, etc., various configurations can be adopted.

[0073] (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

[0074] The present invention can be applied to various work vehicles such as tractors, combines, rice transplanters, and transport vehicles, as a work vehicle in which the trunnion shaft of a hydrostatic continuously variable transmission is operated by an electric motor.

Explanation of Reference Numerals

[0075] 4 Electric motor 5A Linking mechanism 5B Biasing mechanism 6 Shift angle sensor 12 Hydrostatic continuously variable transmission 12b Trunnion shaft 41 Output shaft 42 Driving gear 43 Motor sensor 51 Swing arm 51a Cam 52 Driven gear 55 Operating body 56 Cam follower 57 Biasing spring 100 Target value setting unit 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 trunnion shaft of the hydrostatic continuously variable transmission, a shift angle sensor that detects the rotation angle of the trunnion shaft, a motor sensor that detects the rotation angle of the output shaft, a control device that controls the operation of the electric motor, and a target value setting unit that sets a shift target value of the hydrostatic continuously variable transmission according to a manual operation received by an operating tool, wherein the control device has a first control state 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, and a second control state in which the electric motor is controlled so that the rotation angle of the output shaft detected by the motor sensor becomes a preset set value, and the work vehicle is switchable between the two states.

2. The work vehicle according to claim 1, wherein the control device switches to the first control state when the shift target value is not a neutral corresponding value, and switches to the second control state when the shift target value is the neutral corresponding value.

3. The work vehicle according to claim 1, wherein in the second control state, 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.

4. The work vehicle is provided with a biasing mechanism that biases the trunnion shaft to rotate back toward the neutral position, 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 and interlock with each other, and when the trunnion shaft is not in the neutral position, the biasing mechanism presses and biases the driven gear so that the tooth surfaces contact each other in a rotation direction opposite to the rotation direction of the driving gear.

5. The biasing mechanism includes a swing arm that has a cam and swings integrally with the trunnion shaft, an operating body that has a cam follower and swings around an axis parallel to the axis of the trunnion shaft, and a biasing spring that biases the cam follower toward the cam. The work vehicle according to claim 4, wherein the swing arm is biased to swing in a direction to return to the neutral position due to the pressing action of the biasing spring and the cam follower on the cam.

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