JP7502234B2 - Power transmission device for work vehicle - Google Patents

Description

The present invention relates to a power transmission device for a work vehicle.

Patent document 1 shows a power transmission device including a planetary gear mechanism driven by a hydraulic motor and a speed change mechanism with three speed stages.

JP 2012-40944 A

There is a need to prevent a decrease in efficiency when switching gears in the power transmission device of Patent Document 1.

The power transmission device according to the first aspect of the present disclosure includes a planetary gear mechanism, a first shaft, a second shaft, a third shaft, a reverse transmission mechanism, a first forward transmission mechanism, a second forward transmission mechanism, and an additional transmission mechanism. The planetary gear mechanism has a sun gear, a planetary gear, and an internal gear. A first gear among the sun gear, the planetary gear, and the internal gear is rotated by an engine. A second gear other than the first gear among the sun gear, the planetary gear, and the internal gear is rotated by a hydraulic motor of a hydraulic transmission driven by an engine. The first shaft is a rotation axis of a third gear other than the first gear and the second gear among the sun gear, the planetary gear, and the internal gear. The second shaft is configured to transmit a rotational force to the traveling device. The third shaft is interposed between the first shaft and the second shaft. The reverse transmission mechanism is configured to transmit the rotational force of the first shaft to the third shaft in order to drive the traveling device in the backward direction. The first forward transmission mechanism is provided between the reverse transmission mechanism and the planetary gear mechanism in the axial direction of the first shaft. The first forward transmission mechanism is configured to transmit the rotational force of the first shaft to the third shaft at a first transmission ratio as a rotational force in the opposite direction to the reverse transmission mechanism in order to drive the traveling device in the forward direction. The second forward transmission mechanism is provided between the reverse transmission mechanism and the planetary gear mechanism in the axial direction. The second forward transmission mechanism is configured to transmit the rotational force of the first shaft to the third shaft at a second transmission ratio smaller than the first transmission ratio as a rotational force in the opposite direction to the reverse transmission mechanism in order to drive the traveling device in the forward direction. The additional speed change mechanism is configured to change the speed of the rotational force of the third shaft and transmit it to the second shaft.

The configuration disclosed in this application is capable of reducing the decrease in efficiency when switching speeds during forward travel by providing a first forward transmission mechanism and a second forward transmission mechanism.

FIG. 1 is a side view showing the entire tractor. FIG. 2 is a plan view showing the entire tractor. FIG. 3 is a skeleton diagram showing the power transmission device. FIG. 4 is a sectional front view showing the branch transmission mechanism. FIG. 5 is a cross-sectional side view showing the planetary gear mechanism, the reverse rotation transmission mechanism, the first forward rotation transmission mechanism, and the second forward rotation transmission mechanism. FIG. 6 is a sectional front view showing the planetary gear mechanism. FIG. 7 is a sectional front view showing the reverse transmission mechanism. FIG. 8 is a block diagram showing a gear shifting device. FIG. 9 is a graph showing a vehicle speed vs. efficiency of the power transmission device according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings showing embodiments thereof. In the drawings, the same reference numerals indicate corresponding or substantially identical components.
<Embodiment>
<Overall composition>

1 is a side view showing the entire tractor 1 according to an embodiment of the present invention. FIG. 2 is a plan view showing the entire tractor 1 according to an embodiment of the present invention. The tractor 1 is an example of a work vehicle. Referring to FIGS. 1 and 2, the tractor 1 according to an example of a work vehicle includes a pair of left and right front wheels 2a that can be steered and driven, a pair of left and right rear wheels 2b that can be driven, an engine room 3 in which an engine 3a is housed at the front of the vehicle body, a driver's compartment 4 having a seat 4a at the rear of the vehicle body, and a vehicle body frame 5 that supports the engine room 3 and the driver's compartment 4. The tractor 1 further includes a link mechanism 6 having a pair of left and right lift arms 6a that can be swung up and down and are provided on both sides of the rear end of the vehicle body frame 5, and a PTO shaft 7 that protrudes from the rear end of the vehicle body frame 5 to the rear of the vehicle body. The front wheels 2a and the rear wheels 2b are collectively referred to as the traveling device 2. In FIG. 2, the traveling device 2 is realized by wheels, but all or part of the traveling device 2 may be realized by crawlers.

The tractor 1 can be configured as a riding tiller by connecting a rotary tiller (not shown) to the rear of the vehicle body via a link mechanism 6 so that it can be raised and lowered freely, and by transmitting the output of the engine 3a to the rotary tiller from the PTO shaft 7. In addition, the tractor 1 can be configured as various riding work machines by connecting various work devices to the rear of the vehicle body so that they can be raised and lowered freely and driven.

The vehicle body frame 5 includes a clutch housing 10 connected to the rear of the engine 3a, a continuously variable transmission case 20a whose front part is detachably connected to the rear of the clutch housing 10, a transmission case 11 connected to the rear of the continuously variable transmission case 20a, and a front wheel support frame 12 connected to the lower part of the engine 3a. The transmission case 11 includes a front transmission case 11a whose front part is detachably connected to the rear of the continuously variable transmission case 20a, and a rear transmission case 11b whose front part is detachably connected to the rear of the front transmission case 11a. The vehicle body frame 5 includes a front wheel drive case 13 attached to the front wheel support frame 12, and supports a pair of left and right front wheels 2a drivably via the front wheel drive case 13. The vehicle frame 5 has a pair of left and right rear wheel drive cases 14 arranged sideways on either side of the rear transmission case 11b, and supports the pair of left and right rear wheels 2b so that they can be driven freely via the pair of left and right rear wheel drive cases 14.

In the embodiment of the present application, the front-rear direction (front direction/rear direction) of the tractor 1 means the front-rear direction (front direction/rear direction) as seen by an operator seated in the seat 4a of the driver's seat 4. The left direction, right direction, and width direction of the tractor 1 mean the left direction, right direction, left and right directions, respectively, as seen by the operator. The up direction, down direction, and height direction of the tractor 1 mean the up direction, down direction, and height direction as seen by the operator. The front-rear/left-right (width)/up-down (height) directions of the tractor 1 respectively correspond to the front-rear/left-right (width)/up-down (height) directions as seen by the operator.

3 is a skeleton diagram showing a power transmission device 8 configured to transmit the driving force output by the engine 3a to the front wheels 2a and the rear wheels 2b. In FIG. 3, the power transmission system that transmits the driving force output by the engine 3a to the PTO shaft 7 is omitted. As shown in FIG. 3, the power transmission device 8 is configured to transmit the driving force output by the engine 3a from the output shaft 3b to the hydrostatic speed change mechanism 20 and the planetary gear mechanism 30 via the main clutch mechanism 15 and the branch transmission mechanism 16. The power transmission device 8 is configured to transmit the driving force output from the first shaft 38 that outputs the rotational force of the planetary gear mechanism 30 to the additional speed change mechanism 55 via one of the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50. The power transmission device 8 is further configured to transmit power from the second shaft 54, which is the output shaft of the additional speed change mechanism 55, to the rear wheel differential mechanism 25, and from the second shaft 54 to the front wheel differential mechanism 26 via the gear transmission mechanism 61, the front wheel transmission mechanism 70, and the rotating shaft 27. In other words, the second shaft 54 is configured to transmit rotational force to the traveling device 2. As described above, the power transmission device 8 includes the planetary gear mechanism 30, the first shaft 38, the second shaft 54, the reverse transmission mechanism 40, the first forward transmission mechanism 45, the second forward transmission mechanism 50, and the additional speed change mechanism 55.

The hydraulic transmission mechanism 20 is housed in a continuously variable transmission case 20a that is connected to the front part of the front transmission case 11a. The planetary gear mechanism 30, reverse transmission mechanism 40, first forward transmission mechanism 45, and second forward transmission mechanism 50 are arranged in the front transmission case 11a. The additional transmission mechanism 55, rear wheel differential mechanism 25, and gear transmission mechanism 61 are arranged in the rear transmission case 11b. The branch transmission mechanism 16 is provided in the front part of the continuously variable transmission case 20a. Each mechanism will be explained in detail below.

As shown in Figures 3 and 4, the branch transmission mechanism 16 includes an engine side gear 17 and a pair of transmission gears 18, 19 rotatably provided inside a transmission mechanism case 16a connected to a continuously variable transmission case 20a. The engine side gear 17 is provided at the end of the output shaft 15a of the main clutch mechanism 15 so as to be rotatable as one unit. The engine side gear 17 is supported so as to be rotatable with the output shaft 15a as the rotation axis. When the main clutch mechanism 15 is in a connected state, the engine side gear 17 is linked to the engine 3a side, and is rotated by the driving force output from the output shaft 3b of the engine 3a. When the main clutch mechanism 15 is in a disconnected state, the engine side gear 17 is not rotated by the engine 3a.

The pair of transmission gears 18, 19 are arranged such that the rotating shafts 18a, 19a of the pair of transmission gears 18, 19 are positioned at a height equal to or lower than the rotating shaft 17a of the engine side gear 17 and are in mesh with the engine side gear 17. The rotating shaft 18a of one transmission gear 18 is positioned at a height lower than the rotating shaft 19a of the other transmission gear 19. One transmission gear 18 is rotatably connected as one unit to the front end of a shaft 23 serving as an input shaft in the fore-and-aft direction of the vehicle body and provided in a pump 21 constituting the hydraulic speed change mechanism 20. The other transmission gear 18 is rotatably connected as one unit to the extending end of an engine output introduction shaft 24 that extends from the planetary gear mechanism 30 toward the front of the vehicle body, penetrating the continuously variable speed change case 20a.

The branch transmission mechanism 16 is disposed on the vehicle body front side with respect to the hydraulic pump 21 and hydraulic motor 22 that constitute the hydraulic transmission mechanism 20. The hydraulic transmission mechanism 20 is a hydrostatic continuously variable transmission mechanism. The branch transmission mechanism 16 is configured to branch the driving force output from the output shaft 3b of the engine 3a to the hydraulic transmission mechanism 20 side and the planetary gear mechanism 30 side by the engine side gear 17 and a pair of transmission gears 18, 19 on the vehicle body front side of the hydraulic transmission mechanism 20. The branch transmission mechanism 16 is configured to transmit the driving force branched to the hydraulic transmission mechanism 20 side to the hydraulic transmission mechanism 20 by the pump shaft 23, and to transmit the driving force branched to the planetary gear mechanism 30 side to the planetary gear mechanism 30 by the engine output introduction shaft 24.

The hydraulic transmission mechanism 20 includes a continuously variable transmission case 20a provided in front of the front transmission case 11a, and a hydraulic pump 21 and a hydraulic motor 22 arranged inside the continuously variable transmission case 20a so as to be positioned on the vehicle body front side with respect to the planetary gear mechanism 30. The hydraulic pump 21 is a variable capacity, axial plunger type hydraulic pump. The hydraulic motor 22 is an axial plunger type hydraulic motor. The hydraulic transmission mechanism 20 can change the gear ratio by changing the angle of the swash plate of the hydraulic pump 21. The hydraulic pump 21 is driven by the rotation of the engine 3a, and outputs pressurized oil to the hydraulic motor 22 through an oil passage (not shown). The hydraulic motor 22 is thus driven by the hydraulic pump 21 to rotate the motor output shaft 28.

Figure 5 is a cross-sectional view showing the planetary gear mechanism 30, the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50. Figure 6 is a cross-sectional side view showing the planetary gear mechanism 30. Referring to Figures 5 and 6, the planetary gear mechanism 30 has a sun gear 31, a plurality of planetary gears 32, and an internal gear 33. The sun gear 31 is rotatably supported by the first support portion 30a of the front transmission case 11a via a bearing B1. The plurality of planetary gears 32 are positioned at equal intervals around the sun gear 31. The internal gear 33 is configured to mesh with the three planetary gears 32. The planetary gear mechanism 30 further includes a carrier 35 and a first shaft 38. The carrier 35 rotatably supports each planetary gear 32 via a support shaft 34.

The carrier 35 is supported rotatably relative to the sun gear 31 via a pair of bearings B2 on the first boss portion 31a of the sun gear 31. The support shaft 34 of each planetary gear 32 is connected to the carrier 35. The planetary gear mechanism 30 further has an annular support plate 36. The support plate 36 connects the three support shafts 34 on the side opposite to the side where the carrier 35 is located relative to the planetary gear 32. As shown in FIG. 6, the support plate 36 prevents the support shafts 34 from tilting relative to the carrier 35, and maintains the sun gear 31 and the meshing state of the planetary gear 32 with the sun gear 31 in a normal state so that the planetary gear 32 does not tilt relative to the sun gear 31 and the internal gear 33.

By engaging the splines on the first boss portion 31a of the sun gear 31 with the splines on the motor output shaft 28, the sun gear 31 is connected to rotate integrally with the motor output shaft 28, which is the output shaft of the hydraulic transmission mechanism 20.

The engine output introduction shaft 24 is connected to an input gear 37 that is rotatably supported via a bearing B5 on the first support portion 30a of the front transmission case 11a. The input gear 37 has a through hole therein through which the engine output introduction shaft 24 passes, and the through hole and the outer periphery of the engine output introduction shaft 24 are provided with splines that mesh with each other. The engine output introduction shaft 24 and the input gear 49 are rotatably connected as a single unit by a spline fit. The carrier 35 has teeth formed on its outer periphery that are configured to mesh with the input gear 49.

The boss portion 33a of the internal gear 33 is rotatably supported by the second support portion 30b of the front transmission case 11a via a bearing B3, and is rotatably supported by the second boss portion 31b of the sun gear 31 via a bearing B4. The inner circumference of the boss portion 33a of the internal gear 33 is formed with a spline that meshes with a spline formed on the outer circumference of the first shaft 38. The internal gear 33 is connected to the first shaft 38 so as to rotate integrally with the first shaft 38 by the engagement of these splines. The first shaft 38 is rotatably supported by the second support portion 30b of the front transmission case 11a via a bearing B6, and is rotatably supported by the third support portion 30c of the front transmission case 11a via a bearing B7. The first shaft 38 has a central axis Ax1 and is rotatable around the central axis Ax1. Here, the direction along the central axis Ax1 is called the axial direction Dx.

The planetary gear mechanism 30 has the above configuration. As a result, the driving force output from the engine 3a from the output shaft 3b is input to the input gear 37 via the engine side gear 17, the transmission gear 19, and the engine output introduction shaft 24, so that the driving force from the engine 3a is input to the carrier 35 without being subjected to the speed change action of the hydraulic speed change mechanism 20. Furthermore, the driving force output from the motor output shaft 28 by the hydraulic speed change mechanism 20 is input to the sun gear 31. Then, the driving force from the hydraulic speed change mechanism 20 and the driving force from the engine 3a that is not subjected to the speed change action of the hydraulic speed change mechanism 20 are combined, and the combined driving force is output to the first shaft 38 connected to the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50.

Therefore, the power transmission device 8 branches the driving force output from the engine 3a through the output shaft 3b to the hydraulic transmission mechanism 20 side and the planetary gear mechanism 30 side by the branch transmission mechanism 16 at a location located on the vehicle body front side with respect to the hydraulic transmission mechanism 20. The power transmission device 8 then inputs the driving force branched to the hydraulic transmission mechanism 20 side to the hydraulic pump 21 of the hydraulic transmission mechanism 20 through the shaft 23, converts it to a driving force in the forward rotation direction and a driving force in the reverse rotation direction by the speed change action of the hydraulic pump 21 and the hydraulic motor 22 of the hydraulic transmission mechanism 20, and outputs it from the motor output shaft 28 with stepless speed change regardless of whether it is converted to a driving force in the forward rotation direction or the reverse rotation direction. The power transmission device 8 inputs the driving force output from the motor output shaft 28 of the hydraulic speed change mechanism 20 to the sun gear 31 of the planetary gear mechanism 30, and inputs the driving force branched to the planetary gear mechanism 30 side by the branch transmission mechanism 16 to the carrier 35 of the planetary gear mechanism 30 via the engine output introduction shaft 24 and the input gear 37. In the planetary gear mechanism 30, the driving force from the engine 3a and the driving force from the hydraulic speed change mechanism 20 are combined, and the combined driving force is output from the first shaft 38 to the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50.

Here, the planetary gear 32 rotated by the carrier 35 is called the first gear. The sun gear 31 rotated by the hydraulic motor 22 is called the second gear. The internal gear 33 rotating integrally with the first shaft 38 is called the third gear. In this case, it can be said that the first gear (planetary gear 32) of the sun gear 31, planetary gear 32, and internal gear 33 is rotated by the engine 3a. It can be said that the second gear (sun gear 31) other than the first gear (planetary gear 32) of the sun gear 31, planetary gear 32, and internal gear 33 is rotated by the hydraulic motor 22 of the hydraulic speed change mechanism 20 driven by the engine 3a. It can be said that the first shaft 38 is the rotation axis of the third gear other than the first gear and the second gear of the sun gear 31, planetary gear 32, and internal gear 33.

3, the reverse transmission mechanism 40 includes a transmission gear 41, a reverse gear 42, a reverse output gear 43, and a reverse clutch 44. The reverse transmission mechanism 40 is configured to transmit the rotational force of the first shaft 38 to the third shaft 39 to drive the traveling device 2 in the reverse direction. The power transmission device 8 includes a third shaft 39. The third shaft 39 is interposed between the first shaft 38 and the second shaft 54. The third shaft 39 is rotatably supported by the second support portion 30b of the front transmission case 11a via a bearing B8, and is rotatably supported by the third support portion 30c of the front transmission case 11a via a bearing B9. The third shaft 39 has a central axis Ax3 and is rotatable around the central axis Ax3. The central axis Ax3 is substantially parallel to the central axis Ax1. Thus, the third shaft 39 extends in the axial direction Dx. The reverse clutch 44 is configured to connect and disconnect the first shaft 38 and the third shaft 39 via the reverse transmission mechanism 40. The reverse clutch 44 is provided on the first shaft 38. As shown in FIG. 7, the transmission gear 41 engages with the reverse gear 42, and the reverse gear 42 meshes with the reverse output gear 43. The transmission gear 41 does not mesh with the reverse output gear 43. Note that in FIG. 7, some components in the power transmission device 8 other than the transmission gear 41, the reverse gear 42, and the reverse output gear 43 are not shown.

When the reverse clutch 44 is switched to an engagement state, the driving force of the first shaft 38 is transmitted in the order of the transmission gear 41, the reverse gear 42, the reverse output gear 43, and the third shaft 39. At this time, the third shaft 39 rotates so as to drive the front wheels 2a and the rear wheels 2b in the reverse direction. Since the transmission gear 41 is rotatably supported by the first shaft 38 via the bearing B10, when the reverse clutch 44 is switched to a disengagement state, the transmission gear 41 rotates independently of the first shaft 38. The reverse output gear 43 is formed integrally with the third shaft 39. The transmission gear 41 is engaged with the reverse output gear 43 via the reverse gear 42. Therefore, the transmission gear 41, the reverse gear 42, and the reverse output gear 43 rotate together with the third shaft 39.

The first forward transmission mechanism 45 includes a first transmission gear 46, a first forward output gear 47, and a first forward clutch 48. The first forward transmission mechanism 45 is provided between the reverse transmission mechanism 40 and the planetary gear mechanism 30 in the axial direction Dx of the first shaft 38. The first forward transmission mechanism 45 is configured to transmit the rotational force of the first shaft 38 to the third shaft 39 at a first speed transmission ratio as a rotational force in the opposite direction to that of the reverse transmission mechanism 40 in order to drive the traveling device 2 in the forward direction. The first forward clutch 48 is configured to connect and disconnect the first shaft 38 and the third shaft 39 via the first forward transmission mechanism 45. The first forward clutch 48 is provided on the first shaft 38.

When the first forward clutch 48 is switched to the on state, the driving force of the first shaft 38 is transmitted in the order of the first transmission gear 46, the first forward output gear 47, and the third shaft 39. The third shaft 39 rotates to drive the front wheels 2a and the rear wheels 2b in the forward direction. The above-mentioned first speed transmission ratio is a value obtained by dividing the number of teeth of the first forward output gear 47 by the number of teeth of the first transmission gear 46. Since the first transmission gear 46 is rotatably supported by the first shaft 38 via a needle bearing NB1, when the first forward clutch 48 is switched to the off state, the first transmission gear 46 rotates independently of the first shaft 38. The first forward output gear 47 is formed integrally with the third shaft 39, is provided on the third shaft 39, and is configured to rotate together with the third shaft 39. The first transmission gear 46 is provided on the first shaft 38 and is engaged with the first forward output gear 47. As a result, the first transmission gear 46 and the first forward output gear 47 rotate together with the third shaft 39.

The second forward transmission mechanism 50 includes a second transmission gear 52, a second forward output gear 51, and a second forward clutch 53. The second forward transmission mechanism 50 is provided between the reverse transmission mechanism 40 and the planetary gear mechanism 30 in the axial direction Dx. More specifically, the second forward transmission mechanism 50 is provided between the planetary gear mechanism 30 and the first forward transmission mechanism 45 in the axial direction Dx. The second forward transmission mechanism 50 is configured to transmit the rotational force of the first shaft 38 to the third shaft 39 at a second transmission ratio smaller than the first transmission ratio as a rotational force in the opposite direction to that of the reverse transmission mechanism 40 in order to drive the traveling device 2 in the forward direction. The second forward clutch 53 is configured to couple and release the first shaft 38 and the third shaft 39 via the second forward transmission mechanism 50. The second forward clutch 53 is provided on the third shaft 39. In other words, the first forward clutch 48 and the second forward clutch 53 are provided on different shafts, the first shaft 38 and the third shaft 39. When the second forward clutch 53 is switched to the engaged state, the driving force of the first shaft 38 is transmitted in the order of the second transmission gear 52, the second forward output gear 51, and the third shaft 39. The third shaft 39 rotates to drive the front wheels 2a and the rear wheels 2b in the forward direction.

The second speed transmission ratio described above is the value obtained by dividing the number of teeth of the second forward output gear 51 by the number of teeth of the second transmission gear 52. The second speed transmission ratio is smaller than the first speed transmission ratio, specifically, by (1) the number of teeth of the first transmission gear 46 being smaller than the number of teeth of the second transmission gear 52, and (2) the number of teeth of the first forward output gear 47 being greater than the number of teeth of the second forward output gear 51. However, either (1) or (2) may not be realized. Since the second forward output gear 51 is rotatably supported by the third shaft 39 via the needle bearing NB2, when the second forward clutch 53 is switched to the off state, the second forward output gear 51 rotates independently of the third shaft 39. Since the second transmission gear 52 is spline-fitted with the first shaft 38, it is provided on the first shaft 38 and configured to rotate together with the first shaft 38. The second transmission gear 52 is provided on the third shaft 39 and engages with the second forward output gear 51. Therefore, the second transmission gear 52 and the second forward output gear 51 rotate together with the first shaft 38.

The reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 are hydraulic clutches having a well-known configuration including a cylinder, a piston, a rotation transmission source clutch disc, a rotation transmission destination clutch disc, and a spring that presses the piston to separate the rotation transmission source clutch disc and the rotation transmission destination clutch disc. For this reason, detailed descriptions of these clutches are omitted. In the second forward clutch 53, an oil passage 53c for hydraulically pressing the piston 53p pressed by the spring 53s from the opposite side is provided in the housing of the second forward clutch 53 and the second support part 30b of the front transmission case 11a, but is not provided in the third shaft 39.

The reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 are switched between their engaged and disengaged states by the shift lever or switch on the driver's seat 4, and an electronic circuit (not shown) controls the opening and closing of a control valve that controls whether or not hydraulic oil is supplied to one of the reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 corresponding to the operation of the shift lever or switch. The electronic circuit controls the reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 so that two or more of the reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 are not engaged at the same time. In other words, the electronic circuit controls one of the reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 to be engaged and the remaining clutch to be disengaged, or controls all of the reverse clutch 44, the first forward clutch 48, and the second forward clutch 53 to be disengaged.

The additional transmission mechanism 55 is configured to change the rotational force of the third shaft 39 and transmit it to the second shaft 54. As shown in FIG. 3, the additional transmission mechanism 55 includes a fourth shaft 39a connected to the third shaft 39 via a joint JT so as to be rotatable together with the fourth shaft 39a, a first gear 57 and a second gear 59 provided on the fourth shaft 39a so as to be rotatable together with the first gear 57, a low-speed gear 56 provided on the second shaft 54 so as to be rotatable relative to the first gear 57, a high-speed gear 58 provided on the second shaft 54 so as to be rotatable relative to the second shaft 54, and a transmission cylinder shaft 60 provided on the second shaft 54 so as to be rotatable together with the first gear 57 and the second gear 59. The first gear 57 and the second gear 59 are rotatable together with the third shaft 39. The second shaft 54 has a spline 54s for engaging with the transmission cylinder shaft 60. The inner surface of the transmission cylinder shaft 60 has a spline inner wall that engages with the spline 54s. The fourth shaft 39a may be formed integrally with the third shaft 39. The transmission cylinder shaft 60 has a first engagement portion that can engage with the high-speed gear 58 on a surface other than the inner surface, and a second engagement portion that can engage with the low-speed gear 56 on a surface other than the inner surface.

When the transmission cylinder shaft 60 is moved in the axial direction of the fourth shaft 39a by a shift fork (not shown) and the transmission cylinder shaft 60 engages with the boss of the low-speed gear 56, the driving force transmitted from the reverse transmission mechanism 40, the first forward transmission mechanism 45, or the second forward transmission mechanism 50 is transmitted to the second shaft 54 via the first gear 57, the low-speed gear 56, and the transmission cylinder shaft 60. In this case, the low-speed state is achieved regardless of whether the driving force is transmitted from the reverse transmission mechanism 40, the first forward transmission mechanism 45, or the second forward transmission mechanism 50. When the transmission cylinder shaft 60 is moved in the axial direction of the fourth shaft 39a by a shift fork (not shown) and the transmission cylinder shaft 60 engages with the high-speed gear 58, the driving force transmitted from any of the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50 is transmitted to the second shaft 54 via the second gear 59, the high-speed gear 58, and the transmission cylinder shaft 60. In this case, the high-speed state is achieved regardless of whether the driving force is transmitted from the reverse transmission mechanism 40, the first forward transmission mechanism 45, or the second forward transmission mechanism 50.

8 is a block diagram showing a speed change device 80 for changing the speed of the power transmission device 8. As shown in FIG. 8, the speed change device 80 for changing the speed of the power transmission device 8 includes a speed change operation unit 29, which is a cylinder that changes the direction of the swash plate of the hydraulic pump 21 of the hydraulic transmission mechanism 20, a control device 81 linked to the first forward clutch 48, the second forward clutch 53, and the reverse clutch 44, a speed change lever 82, a speed change detection sensor 83 that detects the operation position of the speed change lever 82, an engine rotation sensor 84 that detects the output speed of the engine 3a, a forward/reverse lever 85, a forward/reverse detection sensor 86 that detects the operation position of the forward/reverse lever 85, a switching lever 87 that selects whether the transmission cylinder shaft 60 is engaged with the boss portion of the low-speed gear 56 or the boss portion of the high-speed gear 58, and a switching detection sensor 88 that detects the operation position of the switching lever 87. As shown in FIG. 2, the shift lever 82 is attached to a lever support 91 connected to the front of an armrest 90 installed to the side of the seat 4a of the driver's seat 4 so that it can be freely swung back and forth.

The shift detection sensor 83 is composed of a rotary potentiometer whose rotary operation part is linked to the shift lever 82. The forward/reverse detection sensor 86 is composed of a rotary potentiometer whose rotary operation part is linked to the forward/reverse lever 85. The control device 81 is composed of a microcomputer, and includes a travel shift control circuit 89A and a forward/reverse control circuit 89B. The switch detection sensor 88 is composed of a rotary potentiometer whose rotary operation part is linked to the switch lever 87.

The traveling speed change control circuit 89A detects the output speed of the engine 3a when the engine 3a is in the accelerator set state based on the detection information from the engine rotation sensor 84, determines the operation position to which the speed change lever 82 is operated based on the detection information from the speed change detection sensor 83, and controls the hydraulic speed change mechanism 20 via the speed change operation unit 29 so as to produce a vehicle speed corresponding to the operation position of the speed change lever 82 based on the detected output speed of the engine 3a and the determined operation position of the speed change lever 82. In addition, the traveling speed change control circuit 89A can change whether the transmission cylinder shaft 60 is engaged with the boss portion of the low-speed gear 56 or the boss portion of the high-speed gear 58 based on the detection information from the switching detection sensor 88. Specifically, when the low-speed gear 56 is engaged, the speed range realized by the power transmission device 8 is a speed range mainly intended for work driving, so the switching lever 87 is operated in a direction to set it. When engaging the high-speed gear 58, the speed range achieved by the power transmission device 8 is a speed range intended primarily for driving on farm roads, so the switching lever 87 is operated in the direction that sets this.

The forward/reverse control circuit 89B determines the operating position to which the forward/reverse lever 85 is operated based on the detection information from the forward/reverse detection sensor 86, and based on this determination result, switches and controls the reverse transmission mechanism 40, the first forward transmission mechanism 45, and the second forward transmission mechanism 50 so that the operating state corresponds to the operating position of the forward/reverse lever 85.
<Actions and Effects of the Embodiments>

9 is a vehicle speed-efficiency diagram of the power transmission device 8 according to the embodiment. In FIG. 9, "Work Lo" represents the correspondence relationship between vehicle speed and efficiency when the first forward transmission mechanism 45 outputs the driving force to the third shaft 39 when the switching lever 87 is switched to work driving. "Work Lo" represents the correspondence relationship between vehicle speed and efficiency when the first forward transmission mechanism 45 outputs the driving force to the third shaft 39 when the switching lever 87 is switched to work driving. "Work Hi" represents the correspondence relationship between vehicle speed and efficiency when the second forward transmission mechanism 50 outputs the driving force to the third shaft 39 when the switching lever 87 is switched to work driving. "Driving Lo" represents the correspondence relationship between vehicle speed and efficiency when the first forward transmission mechanism 45 outputs the driving force to the third shaft 39 when the switching lever 87 is switched to farm road driving. "Driving Hi" represents the relationship between vehicle speed and efficiency when the second forward transmission mechanism 50 outputs driving force to the third shaft 39 when the switching lever 87 is switched to farm road driving.

Figure 9 also shows the vehicle speed-efficiency curve of the power transmission device according to JP 2012-040944 A. In the power transmission device according to JP 2012-040944 A, in the auxiliary transmission mechanism corresponding to the additional transmission mechanism 55 of the embodiment, the transmission tubular shaft is configured to be able to be fitted into one of three gears: high-speed gear, medium-speed gear, or low-speed gear. "Conventional Lo" in Figure 9 represents the relationship between vehicle speed and efficiency when the transmission tubular shaft in the power transmission device according to JP 2012-040944 A is fitted into the low-speed gear. "Conventional Mid" in Figure 9 represents the relationship between vehicle speed and efficiency when the transmission tubular shaft in the power transmission device according to JP 2012-040944 A is fitted into the medium-speed gear. "Conventional Hi" in Figure 9 represents the relationship between vehicle speed and efficiency when the transmission cylinder shaft in the power transmission device disclosed in JP 2012-040944 A is engaged with a high-speed gear.

9, in the conventional power transmission device, efficiency is reduced when switching between low-speed gear and medium-speed gear, and when switching between medium-speed gear and high-speed gear. However, in the power transmission device 8 according to the present embodiment, since four-stage shifting is possible, the efficiency reduction during switching can be suppressed more than in the past. More specifically, when the transmission cylinder shaft 60 is engaged with the low-speed gear 56, the difference between the efficiency when switching from the first forward transmission mechanism 45 to the second forward transmission mechanism 50 and the maximum efficiency when the rotational force of the first shaft 38 is transmitted to the third shaft 39 by the second forward transmission mechanism 50 is suppressed more than in the past. When the transmission cylinder shaft 60 is engaged with the high-speed gear 58, the difference between the efficiency when switching from the first forward transmission mechanism 45 to the second forward transmission mechanism 50 and the maximum efficiency when the rotational force of the first shaft 38 is transmitted to the third shaft 39 by the second forward transmission mechanism 50 is suppressed more than in the past.

Furthermore, the gear change by the additional speed change mechanism 55 using the change lever 87 must be performed after the tractor 1 is stopped. Work driving includes rotary plowing, plowing, and fertilization work. In the conventional power transmission device, the tractor 1 must be stopped at the start of work and set to low-speed gear for rotary plowing (or plowing), and set to medium-speed gear for fertilization work (or plowing). When driving on a farm road, the high-speed gear must be set. Furthermore, when plowing, efficiency decreases even if the low-speed gear or medium-speed gear is set. In the power transmission device 8 according to this embodiment, whether the work driving is rotary plowing, plowing, or fertilization work, the tractor 1 is stopped at the start of work and the change lever 87 is set for work driving in which the transmission cylinder shaft 60 is engaged with the low-speed gear 56. This operation is easier for the user to understand than the conventional operation, and the operation is facilitated.

In this application, the words "comprise" and their derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the words "have," "include," and their derivatives.

The terms "member," "part," "element," "body," and "structure" can have multiple meanings, such as a single part or multiple parts.

Ordinal numbers such as "first" and "second" are merely terms used to identify a configuration and have no other meaning (such as a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

Words expressing degree, such as "substantially," "about," and "approximately," can mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values described in this application can be interpreted to include words such as "substantially," "about," and "approximately."

In this application, the phrase "at least one of A and B" should be interpreted to include A only, B only, and both A and B.

In view of the above disclosure, it is clear that various changes and modifications of the present invention are possible. Therefore, the present invention may be implemented in a manner different from the specific disclosure of this application without departing from the spirit of the present invention.

Claims (12)

a planetary gear mechanism having a sun gear, planetary gears, and an internal gear, in which a first gear of the sun gear and the planetary gears is rotated by an engine , and a second gear of the sun gear and the planetary gears other than the first gear is rotated by a hydraulic motor of a hydraulic transmission mechanism driven by the engine;
a first shaft configured to rotate with the internal gear;
A second shaft configured to transmit a rotational force to the running device;
a third shaft interposed between the first shaft and the second shaft;
a reverse transmission mechanism configured to transmit a rotational force of the first shaft to the third shaft in order to drive the traveling device in a reverse direction;
a first forward transmission mechanism that is provided between the reverse transmission mechanism and the planetary gear mechanism in the axial direction of the first shaft and is configured to transmit the rotational force of the first shaft to the third shaft at a first speed transmission ratio as a rotational force in a direction opposite to that of the reverse transmission mechanism in order to drive the traveling device in a forward direction;
a second forward transmission mechanism that is provided between the reverse transmission mechanism and the planetary gear mechanism in the axial direction and is configured to transmit the rotational force of the first shaft to the third shaft at a second transmission ratio smaller than the first transmission ratio as a rotational force in a direction opposite to that of the reverse transmission mechanism in order to drive the traveling device in the forward direction;
an additional transmission mechanism configured to change the speed of a rotational force of the third shaft and transmit the rotational force to the second shaft;
A first bearing that rotatably supports the internal gear;
a second bearing that rotatably supports the first shaft between the first forward rotation transmission mechanism and the first bearing in the axial direction;
Equipped with
the internal gear includes a boss portion supported by the first bearing and configured to fit onto the first shaft;
the second forward transmission mechanism includes a second forward clutch that is provided on the third shaft and is configured to couple and release the coupling between the first shaft and the third shaft via the second forward transmission mechanism;
At least a portion of the second forward clutch is provided between the first bearing and the second bearing in the axial direction .
A power transmission device for a work vehicle.
The second forward transmission mechanism is provided between the planetary gear mechanism and the first forward transmission mechanism in the axial direction.
The power transmission device according to claim 1 .
the reverse transmission mechanism includes a reverse clutch configured to couple and disengage the first shaft and the third shaft via the reverse transmission mechanism;
the first forward transmission mechanism includes a first forward clutch configured to couple and disengage the first shaft and the third shaft via the first forward transmission mechanism;
the second forward transmission mechanism includes a second forward clutch configured to couple and disengage the first shaft and the third shaft via the second forward transmission mechanism;
The reverse clutch is provided on the first shaft,
The first forward clutch and the second forward clutch are provided on different shafts of the first shaft and the third shaft.
The power transmission device according to claim 1 or 2.
the first forward clutch is provided on the first shaft,
the second forward clutch is provided on the third shaft;
The power transmission device according to claim 3.
The first forward rotation transmission mechanism includes:
a first forward output gear provided on the third shaft and configured to rotate with the third shaft;
a first transmission gear provided on the first shaft and engaged with the first forward output gear;
Equipped with
The second forward transmission mechanism includes:
a second transmission gear provided on the first shaft and configured to rotate together with the first shaft;
a second forward output gear provided on the third shaft and engaged with the second transmission gear;
The number of teeth of the first transmission gear is smaller than the number of teeth of the second transmission gear.
5. The power transmission device according to claim 4.
The second transmission gear is spline-fitted with the first shaft.
6. The power transmission device according to claim 5.
7. The power transmission device according to claim 5, wherein the first transmission gear is rotatably supported on the first shaft via a needle bearing.
The number of teeth of the first forward output gear is greater than the number of teeth of the second forward output gear.
8. A power transmission device according to claim 5.
the first forward output gear is integrally formed with the third shaft;
The power transmission device according to claim 8.
10. The power transmission device according to claim 5, wherein the second forward output gear is rotatably supported on the third shaft via a needle bearing.
The power transmission device according to claim 1 , wherein the additional speed change mechanism performs only two-stage speed change.
The additional transmission mechanism includes:
a first gear and a second gear rotatable together with the third shaft;
a low-speed gear provided on the second shaft so as to be relatively rotatable while meshing with the first gear;
a high-speed gear provided on the second shaft in a state of meshing with the second gear so as to be relatively rotatable;
a transmission cylinder shaft provided on the second shaft so as to be integrally rotatable;
Equipped with
The transmission cylindrical shaft has a first engagement portion engageable with the high speed gear and a second engagement portion engageable with the low speed gear.
A power transmission device according to any one of claims 1 to 11.

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