Power transmission equipment

Abstract

DEPCT68 It is designed as a power transmission device capable of enclosing each shaft and gear, bearings, and Other similar devices are securely attached to each shaft inside the mechanism housing. The main power transmission device 31 of the power transmission equipment 100 includes the drive shaft of the main power transmission device 31a shaft. According to the main power transmission equipment, 31b is the first main power transmission gear, and 31c is the second main power transmission gear. 31e Sub-power transmission mechanism 32 incorporates the drive shaft of sub-power transmission device 32a the driven shaft of The secondary power transmission device consists of 32b, the first secondary power transmission gear 32c, and the second secondary power transmission gear 32d. Input shafts 23 and 24, driven shafts of the main power transmission device 31b, and the second main power transmission gear 31e. The drive shaft of sub-transmission device 32a and the first sub-transmission gear 32c are arranged using axes. Together with the first axis A1, the drive shaft of the main power transmission device 31a and the first main power transmission gear. 31c is positioned using a common axis with the second axis A2, the follow shaft of the sub-power transmission device. The 32b and the second sub-power transmission gear 32d are positioned using a common axis with the third axis A3. The second axis A2 and the third axis A3 are positioned lower than the first axis A1;

Description

power transmission device

[0001] The present invention relates to a power transmission device for transmitting power from a prime mover.

[0002] Conventionally, a power transmission device for transmitting power from a prime mover is known, for example, as disclosed in Patent Document 1. This device includes a transmission case, a traveling system transmission, a PTO (Power Take Off) system transmission, etc. The traveling system transmission housed in the transmission case includes a main transmission mechanism and an auxiliary transmission mechanism. Power from the prime mover is input to the main transmission mechanism and is changed in speed. The power changed in speed by the main transmission mechanism is input to the auxiliary transmission mechanism and is further changed in speed. In this way, the power from the prime mover is changed in speed via the main transmission mechanism and the auxiliary transmission mechanism, and is transmitted to the wheels of a traveling vehicle. This allows the traveling vehicle to travel appropriately.

[0003] JP 2006-97742 A (Fig. 1 etc.)

[0004] In the device disclosed in Patent Document 1, power from the prime mover is input to the main transmission mechanism via a shaft (hereinafter sometimes referred to as the "input shaft"). The input shaft is arranged to extend in the front-to-rear direction of the transmission case. The shafts of the main transmission mechanism and the auxiliary transmission mechanism are arranged parallel to the input shaft. The main transmission mechanism and the auxiliary transmission mechanism are provided with gears, bearings, and the like associated with each shaft as components. The components of the main transmission mechanism and the auxiliary transmission mechanism are located in different directions relative to the input shaft. In other words, the shafts and the gears, bearings, and the like associated with each shaft are arranged in various directions around the axis of the input shaft. The device disclosed in Patent Document 1 leaves much room for improvement in terms of compactly accommodating the traveling transmission within the case.

[0005] In view of the above, an object of the present invention is to provide a power transmission device in which each shaft and the gears, bearings, etc. associated with each shaft can be housed compactly inside a case.

[0006] The technical means of the present invention for solving this technical problem is characterized as follows: The power transmission device of the present invention includes an input shaft arranged coaxially with a first axis, configured to be able to input power from a prime mover provided in a traveling vehicle from a first direction side of the first axis, and rotating around the first axis when power from the prime mover is input, a first input gear arranged on the input shaft on a second direction side opposite to the first direction, configured to be able to rotate integrally with the input shaft, and rotating around the first axis when the input shaft rotates, and a third input gear arranged on the first axis in a third direction perpendicular to each of the first direction and the second direction. a second input gear arranged coaxially with the second shaft parallel to the first shaft and configured to mesh with the first input gear, and rotate about the second shaft when the first input gear rotates; a main transmission mechanism configured to be able to input power from the second input gear and to be able to change the speed of the input power and to output the power after the speed change; an auxiliary transmission mechanism configured to be able to input power output from the main transmission mechanism and to be able to change the speed of the input power and to output the power after the speed change; and a secondary transmission mechanism arranged on the traveling vehicle and configured to be able to input power output from the main transmission mechanism and to be able to change the speed of the input power and to output the power after the speed change. a case that accommodates a shaft, the first input gear, the second input gear, the main transmission mechanism, and the auxiliary transmission mechanism therein, wherein the main transmission mechanism is arranged coaxially with the second shaft and is configured to be able to input power from the second input gear from the first direction side of the second shaft, and when power from the second input gear is input, a main transmission drive shaft that rotates around the second shaft; and a case that accommodates the main transmission drive shaft, the first input gear, the second input gear, the main transmission mechanism, and the auxiliary transmission mechanism therein, wherein the main transmission mechanism is arranged coaxially with the second shaft and is configured to be able to rotate integrally with the main transmission drive shaft, and when the main transmission drive shaft rotates, a first main transmission gear that rotates in the same direction as the first shaft; a second main transmission gear that is arranged coaxially with the first shaft and configured to mesh with the first main transmission gear, and that rotates about the first shaft when the first main transmission gear rotates; and a main transmission driven shaft that is arranged coaxially with the first shaft and configured to be rotatable integrally with the second main transmission gear, and that rotates about the first shaft when the second main transmission gear rotates and that outputs power in the second direction relative to the second main transmission gear, and the auxiliary transmission mechanism is arranged coaxially with the first shaft,an auxiliary transmission drive shaft configured to be able to input power from the main transmission driven shaft from the first direction side of the first shaft, and to rotate about the first axis when power of the main transmission driven shaft is input; a first auxiliary transmission gear arranged coaxially with the first shaft, configured to be rotatable integrally with the auxiliary transmission drive shaft, and to rotate about the first axis when the auxiliary transmission drive shaft rotates; a third shaft located on the third direction side of the first shaft, arranged coaxially with the third shaft parallel to the first shaft and the second shaft, configured to mesh with the first auxiliary transmission gear, and to rotate about the third axis when the first auxiliary transmission gear rotates; and an auxiliary transmission driven shaft arranged coaxially with the third shaft, configured to be rotatable integrally with the second auxiliary transmission gear, and to rotate about the third axis when the second auxiliary transmission gear rotates, and to output power to the second direction side of the second auxiliary transmission gear.

[0007] In the power transmission device of the present invention, the second input gear is configured to input power to the end of the main transmission drive shaft on the first direction side.

[0008] In the power transmission device of the present invention, the case is provided with a partition wall portion that divides the internal space into a space on the first direction side and a space on the second direction side, the partition wall portion having a first insertion hole arranged coaxially with the first axis and a second insertion hole arranged coaxially with the second axis, the main transmission driven shaft has its end on the first direction side engaged with the first insertion hole of the partition wall and arranged so as to be rotatable relative to the partition wall, the main transmission drive shaft is engaged with the second insertion hole of the partition wall and its end on the first direction side is located in the first direction side space partitioned by the partition wall and arranged so as to be rotatable relative to the partition wall, the second input gear is arranged in the first direction side space partitioned by the partition wall, and the first main transmission gear and the second main transmission gear are arranged in the second direction side space partitioned by the partition wall.

[0009] In the power transmission device of the present invention, the first main transmission gear is composed of at least four gears, each of which has a different number of teeth and is arranged coaxially with the second shaft, and only one selected from each of the gears is configured to rotate integrally with the main transmission drive shaft, and the second main transmission gear is composed of the same number of gears as the number of the first main transmission gears, and each of the gears of the above configuration is arranged coaxially with the first shaft and is configured to mesh with each gear of the first main transmission gear.

[0010] In the power transmission device of the present invention, the case further includes a first bearing portion that rotatably supports the auxiliary transmission driven shaft on the first direction side of the third shaft, and a second bearing portion that rotatably supports the auxiliary transmission driven shaft on the second direction side of the third shaft, and the second auxiliary transmission gear is arranged between the first bearing portion and the second bearing portion.

[0011] In the power transmission device of the present invention, the second auxiliary transmission gear is composed of at least four gears, each of which has a different number of teeth and is arranged coaxially with the third shaft, and only one selected from among the gears is configured to rotate integrally with the auxiliary transmission driven shaft, and the first auxiliary transmission gear is composed of gears the same number as the number of the second main transmission gears, and each of the gears of the above configuration is arranged coaxially with the first shaft and is configured to mesh with each gear of the second auxiliary transmission gear.

[0012] In the power transmission device of the present invention, the traveling vehicle has front wheels on the first direction side and rear wheels on the second direction side, and the sub-transmission driven shaft outputs power on the second direction side of the gears that make up the second sub-transmission gear, and the output power is transmitted so as to be converted into rotational force for the rear wheels.In addition, the sub-transmission driven shaft is configured to output power from between two adjacent gears that make up the second sub-transmission gear, and the output power is transmitted so as to be converted into rotational force for the front wheels.

[0013] In the power transmission device of the present invention, the power transmission device is configured to include a first PTO input shaft that is arranged coaxially with the first shaft, is configured to be able to input power from the prime mover from a first direction side of the first shaft, and rotates around the first shaft when power from the prime mover is input; and two gears, each gear of the configuration is arranged coaxially with the first shaft, is configured to be able to rotate integrally with the first PTO input shaft, and rotates around the first shaft when the first PTO input shaft rotates; and a second PTO gear that is arranged coaxially with a fourth shaft that is parallel to the first shaft and the third shaft, and is configured so that one of the two gears and one of the first PTO gears mesh with each other, and rotates around the fourth shaft when the first PTO gear rotates. a second PTO input shaft arranged coaxially with the third axis, configured to be rotatable integrally with the second PTO gear, and configured to rotate about the fourth axis when the second PTO gear rotates; a PTO output shaft arranged coaxially with the third axis, configured so that the first direction side of the third shaft is housed inside the case while the second direction side of the third shaft protrudes outside the case and rotates about the third axis to output power toward a working device connected to the traveling vehicle; and a third PTO gear consisting of two gears, each gear of which meshes with the other of the first PTO gears and the other of the second PTO gears, and which is arranged coaxially with the third axis, and configured so that only one selected from the respective gears rotates integrally with the PTO output shaft.

[0014] According to the present invention, the shafts and the gears, bearings, etc. associated with the shafts can be concentrated on the first shaft and on the same side of the first shaft, and can be housed compactly inside the case.

[0015] Fig. 1 is an overall schematic view of a tractor to which a power transmission device according to a first embodiment of the present invention is applied. Fig. 2 is a rear perspective view of the tractor shown in Fig. 1. Fig. 3 is a cross-sectional view of the power transmission device shown in Fig. 1. Fig. 4 is an enlarged cross-sectional view of the vicinity of a power input mechanism provided in the power transmission device shown in Fig. 1. Fig. 5 is an enlarged cross-sectional view of the vicinity of a main speed change mechanism provided in the power transmission device shown in Fig. 1. Fig. 6 is an enlarged cross-sectional view of the vicinity of an auxiliary speed change mechanism provided in the power transmission device shown in Fig. 1. Fig. 7 is an enlarged cross-sectional view of a PTO-system transmission provided in a power transmission device according to a second embodiment of the present invention.

[0016] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0017] [First embodiment] Fig. 1 is an overall schematic diagram of a tractor 1 to which a power transmission device 100 according to a first embodiment of the present invention is applied. Fig. 2 is a rear perspective view of the tractor 1 including the rear end of the power transmission device 100. The left and right, up and down, and front and rear arrows appropriately indicated in each figure correspond to the leftward and rightward directions, the upward and down directions, and the frontward and rearward directions, respectively. Note that, although the tractor 1 is used as the traveling vehicle in this embodiment, the traveling vehicle is not limited to a tractor as long as the power transmission device 100 can be applied.

[0018] <Overall Overview of Tractor> As shown in FIGS. 1 and 2 , the tractor 1 includes front wheels 2, rear wheels 3, a prime mover 4, a hydraulic lifting device 5, and a power transmission device 100. The front wheels 2 and rear wheels 3 are connected to the left and right ends of the respective axles, forming a pair. That is, the tractor 1 of this embodiment is a two-axle, four-wheel type. The prime mover 4 is a drive source, such as a diesel engine, and is provided at the front of the tractor 1. A power transmission device 100 is provided at the rear of the prime mover 4, and power generated by the prime mover 4 can be input to the power transmission device 100. The input power is shifted by the power transmission device 100 and transmitted to the axles of the rear wheels 3 (or the front wheels 2 and rear wheels 3) and to a PTO output shaft 42 for operating the implement. The configuration of the power transmission device 100 will be described in detail later.

[0019] As shown in FIG. 2 , the hydraulic lifting device 5 is provided on the upper rear side of the power transmission device 100 of the tractor 1. The hydraulic lifting device 5 has one lift arm 5a on each side, and the ends of each lift arm 5a protrude rearward. In the hydraulic lifting device 5, hydraulic pressure is controlled by, for example, spool displacement caused by lever operation by the driver, causing the rear ends of the lift arms 5a to swing up and down. A working device (not shown) can be connected to the hydraulic lifting device 5 via the rear ends of the lift arms 5a and a three-point link (not shown). In other words, the working device is connected to the rear end of the tractor 1.

[0020] At the rear end of the tractor 1, a PTO output shaft 42 protrudes rearward while being exposed from the rear transmission case 12 of the power transmission device 100. When a work implement is coupled to the tractor 1, the rear end of the PTO output shaft 42 protruding rearward is connected to the work implement, and the PTO output shaft 42 is capable of transmitting power from the prime mover 4 to the work implement. The work implement is, for example, a rotary tiller, but the type and form are not limited as long as it is coupled to a traveling vehicle and driven by power transmitted from the PTO output shaft 42.

[0021] As shown in FIG. 1 , a driver's seat 1a is provided approximately in the center in the left-right direction between the fenders 3a that cover the vicinity of the upper surfaces of the left and right rear wheels 3. A steering wheel 1b is located in front of the driver's seat 1a. Various control levers, pedals, switches, etc. are also located around the driver's seat 1a. These can be operated by the driver while seated in the driver's seat 1a. With this configuration, the driver can steer the front wheels 2, control the rotation speed of the prime mover 4, change gears and switch between forward and reverse travel in the power transmission device 100, raise and lower the lift arm 5a, turn the PTO on and off, etc.

[0022] <Configuration of Power Transmission Device> As shown in Figure 3, the power transmission device 100 includes a case 10, a power input mechanism 20 housed in the case 10, various transmissions, etc. The case 10 is provided on the tractor 1 so as to extend in the longitudinal direction, and is made up of a front transmission case 11 on the front side and a rear transmission case 12 connected to the rear side. Furthermore, partitions that define the internal space and bearings for supporting the various shafts are provided on the inner walls of the case 10.

[0023] In the power transmission device 100, a first direction, a second direction, and a third direction are defined. In this embodiment, the first direction is the forward direction. The second direction is the direction opposite to the first direction and is the rearward direction in this embodiment. The third direction is a direction perpendicular to each of the first and second directions and is the downward direction in this embodiment.

[0024] In the power transmission device 100, a first axis A1, a second axis A2, and a third axis A3 are defined. The first axis A1 is an axis parallel to the front-to-rear direction. The second axis A2 is an axis parallel to the first axis A1 and is located lower than the first axis A1 (in the third direction). The third axis A3 is an axis parallel to the first axis A1 and the second axis A2 and is located lower than the first axis A1 (in the third direction). The third axis A3 is located slightly higher than the second axis A2.

[0025] <<Power Input Mechanism>> As shown in FIG. 3 , the front side of the front transmission case 11 is closed by a front end 11a and is partitioned by a partition wall 11b located rearward of the front end 11a. The partition wall 11b has a thickness in the front-to-rear direction and is shaped like a flat plate extending in the up-down and left-to-right directions. The power input mechanism 20 includes a flywheel 21, a clutch 22, a first input shaft 23, a second input shaft 24, a first input gear 25, and a second input gear 26. The flywheel 21 and the clutch 22 are housed in a front space partitioned by the partition wall 11b. The first input gear 25 and the second input gear 26 are located rearward of the partition wall 11b. The first input shaft 23 and the second input shaft 24 extend coaxially with the first axis A1 from the front to the rear, passing through a through-hole in the partition wall 11b.

[0026] The flywheel 21 is disposed coaxially with the first axis A1 so as to face the inner wall of the front end portion 11a. The flywheel 21 rotates about the first axis A1 in response to the operation of the prime mover 4, thereby suppressing torque fluctuations of the prime mover 4. In this embodiment, the flywheel 21 is the upstream end of the power transmission of each transmission, which will be described later. The clutch 22 is fixed to the rear side of the flywheel 21 and is housed in the same space as the flywheel 21. The clutch 22 can input power from the flywheel 21 to the front side of the second input shaft 24.

[0027] As shown in Figures 3 and 4, the front end of the first input shaft 23 is connected to the center of the flywheel 21 and is rotatable integrally with the flywheel 21. The second input shaft 24 has a hollow structure, and the first input shaft 23 is fitted inside it. The first input shaft 23 on the radially inner side and the second input shaft 24 on the radially outer side are rotatable relative to each other. The first input shaft 23 and the second input shaft 24 are configured to rotate about the first axis A1 when power from the prime mover 4 is input via the flywheel 21 and the clutch 22.

[0028] A partition wall 11c is provided behind the partition wall 11b. The partition wall 11c is arranged parallel to the partition wall 11b, has a thickness in the front-to-rear direction, and is shaped like a flat plate extending in the up-down and left-to-right directions. The partition wall 11c divides the interior of the front transmission case 11 into a front space and a rear space. In this embodiment, the power input mechanism 20 is disposed in the front space divided by the partition wall 11c.

[0029] The partition wall 11c has a first insertion hole 11c1 arranged coaxially with the first axis A1 and a second insertion hole 11c2 arranged coaxially with the second axis A2. The first input shaft 23, which penetrates the partition wall 11b, is inserted into the first insertion hole 11c1 and extends into the space behind the partition wall 11c. The second input shaft 24, which surrounds the first input shaft 23, penetrates the partition wall 11b and extends to the partition wall 11c. The rear end of the second input shaft 24 is journaled via a bearing on the front side of the first insertion hole 11c1.

[0030] A first input gear 25 is disposed in the space behind the second input shaft 24, behind the partition wall 11b and in front of the partition wall portion 11c. The first input gear 25 is disposed coaxially with the first axis A1. The first input gear 25 is configured to be rotatable integrally with the second input shaft 24, and rotates about the first axis A1 when the second input shaft 24 rotates.

[0031] A second input gear 26 is disposed in the space behind the partition wall 11b and in front of the partition wall portion 11c. The second input gear 26 is disposed coaxially with the second axis A2. In this embodiment, the second input gear 26 is a spline gear and includes a cylindrical boss gear 26a and a spline shaft 26b. The boss gear 26a is disposed coaxially with the second axis A2 so that its external teeth mesh with the first input gear 25. The spline shaft 26b is fitted into the boss gear 26a, so that the internal teeth of the boss gear 26a and the gear portion of the spline shaft 26b mesh with each other.

[0032] The front end of the spline shaft 26b is journaled via a bearing in a recess on the rear side of the partition wall 11b. The rear end of the spline shaft 26b is journaled via a bearing on the front side of the second insertion hole 11c2. The main transmission drive shaft 31a is engaged with the second insertion hole 11c2 and journaled via a bearing on the rear side of the second insertion hole 11c2 so as to be rotatable relative to the partition wall 11c. The front end of the main transmission drive shaft 31a is located in the space in front of the partition wall 11c. The rear end of the spline shaft 26b is engaged with the front end of the main transmission drive shaft 31a, so that the spline shaft 26b and the main transmission drive shaft 31a can rotate together.

[0033] When the second input shaft 24 rotates, the first input gear 25 rotates integrally about the first axis A1, and the boss gear 26a, spline shaft 26b, and main transmission drive shaft 31a also rotate integrally about the second axis A2. In this manner, the second input gear 26 is configured to input power to the front end of the main transmission drive shaft 31a. In other words, the power of the second input shaft 24 is speed-shifted according to the number of teeth of the first input gear 25 and the second input gear 26, respectively, and is input to the main transmission drive shaft 31a.

[0034] <<Main Transmission Mechanism>> As shown in Figure 3, each transmission is arranged in the rear space partitioned by the partition wall 11c. Each transmission has various shafts, gears, etc., and is made up of a traveling transmission 30 and a PTO transmission 40. The traveling transmission 30 is housed in the front transmission case 11, and the PTO transmission 40 is located behind the traveling transmission 30 and housed in the rear transmission case 12. The traveling transmission 30 includes a main transmission mechanism 31, an auxiliary transmission mechanism 32, a propeller shaft 33, and gear shafts 34 and 35.

[0035] 3 and 5, the main transmission mechanism 31 includes a main transmission drive shaft 31a, a main transmission driven shaft 31b, a first main transmission gear 31c, a main transmission shifter 31d, and a second main transmission gear 31e. The main transmission drive shaft 31a is disposed coaxially with the second axis A2, and is configured so that power can be input from the second input gear 26 to its front end. When power is input from the second input gear 26, the main transmission drive shaft 31a rotates about the second axis A2.

[0036] The main transmission drive shaft 31a is fitted into the second insertion hole 11c2, and its front end is located in the front space defined by the partition wall 11c and is arranged so as to be rotatable relative to the partition wall 11c (see FIG. 4). The vicinity of the front end of the main transmission drive shaft 31a is journaled via a bearing on the rear side of the second insertion hole 11c2. The rear end of the main transmission drive shaft 31a is journaled via a bearing at the bearing portion 11d. The bearing portion 11d is arranged rearward of the partition wall 11c and forward of the subtransmission mechanism 32.

[0037] The main transmission driven shaft 31b is disposed coaxially with the first axis A1 and is configured to be rotatable integrally with the second main transmission gear 31e. When the second main transmission gear 31e rotates, the main transmission driven shaft 31b rotates about the first axis A1 and outputs power to the rear side of the second main transmission gear 31e.

[0038] The main transmission driven shaft 31b has a hollow structure, and the first input shaft 23 is fitted inside it. The first input shaft 23 on the radially inner side and the main transmission driven shaft 31b on the radially outer side are rotatable relative to each other. The front end of the main transmission driven shaft 31b is fitted into a first insertion hole 11c1 of the partition wall portion 11c and is arranged so as to be rotatable relative to the partition wall portion 11c (see FIG. 4). The front end of the main transmission driven shaft 31b is journaled via a bearing on the rear side of the first insertion hole 11c1. The vicinity of the rear end of the main transmission driven shaft 31b is journaled via a bearing in the bearing portion 11e. The bearing portion 11e is arranged rearward of the partition wall portion 11c and forward of the subtransmission mechanism 32.

[0039] As shown in FIG. 5, the first main transmission gear 31c is composed of four gears 31c1, 31c2, 31c3, and 31c4. Each gear 31c1 to 31c4 is cylindrical, engages with the main transmission drive shaft 31a, and has external teeth on its outer surface. The number of teeth on the external teeth varies among the gears 31c1 to 31c4. In this embodiment, the number of teeth on gear 31c1 is greater than the number of teeth on gear 31c2, greater than the number of teeth on gear 31c3, and greater than the number of teeth on gear 31c4. The four gears 31c1, 31c2, 31c3, and 31c4 are arranged in parallel from front to rear in this order between the partition wall 11c and the bearing 11d, and are each arranged coaxially with the second axis A2.

[0040] Each of the gears 31c1 to 31c4 is rotatable relative to the main transmission drive shaft 31a, and only one of the gears 31c1 to 31c4 is selected and rotates integrally with the main transmission drive shaft 31a by operation of a main transmission shifter 31d (described later). In this embodiment, the number of first main transmission gears 31c is four, but more than four may be used.

[0041] The main transmission shifter 31d is composed of two shifters 31d1 and 31d2. Each shifter 31d1 and 31d2 is cylindrical and has the main transmission drive shaft 31a fitted therein. The shifter 31d1 is disposed between the gears 31c1 and 31c2, and the shifter 31d2 is disposed between the gears 31c3 and 31c4, and they are arranged coaxially with the second axis A2. Each shifter 31d1 and 31d2 can be displaced forward or backward from a neutral position in response to lever operation by the driver. When each shifter 31d1 and 31d2 is displaced forward or backward from the neutral position, the gears 31c1 to 31c4 adjacent to the shifter 31d1 and 31d2 are engaged with the displaced shifter 31d1 and 31d2 and fixed to the main transmission drive shaft 31a.

[0042] In this embodiment, the main transmission mechanism 31 has a four-speed shift function. In the neutral state, each of the shifters 31d1 and 31d2 is located in a neutral position, and the main transmission drive shaft 31a rotates relative to each of the gears 31c1 to 31c4. In other words, no power is transmitted between the main transmission drive shaft 31a and each of the gears 31c1 to 31c4. When the driver operates the main transmission mechanism 31 to select first speed from this state, the shifter 31d1 remains in the neutral position, while the shifter 31d2 moves rearward from the neutral position. The rearwardly moved shifter 31d2 fixes the gear 31c4 to the main transmission drive shaft 31a. As a result, of the gears 31c1 to 31c4, only the gear 31c4 rotates integrally with the main transmission drive shaft 31a, and the other gears 31c1, 31c2, 31c3 rotate relative to the main transmission drive shaft 31a.

[0043] When the driver operates the transmission to select second gear from first gear, shifter 31d1 remains in the neutral position, while shifter 31d2 moves forward from the rear through the neutral position. The forward-moving shifter 31d2 fixes gear 31c3 to the main transmission drive shaft 31a, instead of gear 31c4. As a result, of the gears 31c1 to 31c4, only gear 31c3 rotates integrally with the main transmission drive shaft 31a, while the other gears 31c1, 31c2, and 31c4 rotate relative to the main transmission drive shaft 31a.

[0044] When the driver operates the transmission to select third gear from second gear, shifter 31d1 moves rearward from the neutral position, while shifter 31d2 moves forward to the neutral position. Shifter 31d1, which has moved rearward, fixes gear 31c2 to main transmission drive shaft 31a. As a result, of gears 31c1 to 31c4, only gear 31c2 rotates integrally with main transmission drive shaft 31a, while the other gears 31c1, 31c3, and 31c4 rotate relative to main transmission drive shaft 31a.

[0045] When the driver operates the transmission to select fourth gear from third gear, shifter 31d1 moves from rearward through the neutral position to forward, while shifter 31d2 is maintained in the neutral position. The forward-moving shifter 31d1 fixes gear 31c1 to main transmission drive shaft 31a instead of gear 31c2. As a result, of the gears 31c1 to 31c4, only gear 31c1 rotates integrally with main transmission drive shaft 31a, while the other gears 31c2, 31c3, and 31c4 rotate relative to main transmission drive shaft 31a.

[0046] The second main transmission gear 31e is composed of four gears 31e1, 31e2, 31e3, and 31e4. Each of the gears 31e1 to 31e4 has a cylindrical shape, an inner wall surface connected to the outer surface of the main transmission driven shaft 31b, and external teeth on the outer surface of each of the gears 31e1 to 31e4. The number of teeth on the external teeth differs for each of the gears 31e1 to 31e4. In this embodiment, the relationship is as follows: number of teeth on gear 31e4 > number of teeth on gear 31e3 > number of teeth on gear 31e2 > number of teeth on gear 31e1. The four gears 31e1, 31e2, 31e3, and 31e4 are arranged in parallel from front to rear in this order between the partition wall portion 11c and the bearing portion 11e, and are each arranged coaxially with the first axis A1.

[0047] Each of the gears 31e1 to 31e4 is rotatable integrally with the main transmission driven shaft 31b and is adapted to mesh with each of the gears 31c1 to 31c4. The gears 31e1 and 31c1, the gears 31e2 and 31c2, the gears 31e3 and 31c3, and the gears 31e4 and 31c4 are adapted to be constantly meshed with each other. In this embodiment, the number of second main transmission gears 31e is four, but the number may be greater than or equal to the number of first main transmission gears 31c.

[0048] When the gear is in first gear, only the gear 31c4 rotates integrally with the main transmission drive shaft 31a, and the gear 31e4 meshing with the gear 31c4 rotates integrally with the main transmission driven shaft 31b. The gears 31e1, 31e2, and 31e3 also rotate integrally with the main transmission driven shaft 31b, and the gears 31c1, 31c2, and 31c3 meshing with the gears 31e1, 31e2, and 31e3, respectively, rotate relative to the main transmission drive shaft 31a.

[0049] When the gear is in second gear, only the gear 31c3 rotates integrally with the main transmission drive shaft 31a, and the gear 31e3 meshing with the gear 31c3 rotates integrally with the main transmission driven shaft 31b. The gears 31e1, 31e2, and 31e4 also rotate integrally with the main transmission driven shaft 31b, and the gears 31c1, 31c2, and 31c4 meshing with the gears 31e1, 31e2, and 31e4, respectively, rotate relative to the main transmission drive shaft 31a.

[0050] When the gear is in third gear, only the gear 31c2 rotates integrally with the main transmission drive shaft 31a, and the gear 31e2 meshing with the gear 31c2 rotates integrally with the main transmission driven shaft 31b. The gears 31e1, 31e3, and 31e4 also rotate integrally with the main transmission driven shaft 31b, and the gears 31c1, 31c3, and 31c4 meshing with the gears 31e1, 31e3, and 31e4, respectively, rotate relative to the main transmission drive shaft 31a.

[0051] When the gear is in fourth gear, only the gear 31c1 rotates integrally with the main transmission drive shaft 31a, and the gear 31e1 meshing with the gear 31c1 rotates integrally with the main transmission driven shaft 31b. The gears 31e2, 31e3, and 31e4 also rotate integrally with the main transmission driven shaft 31b, and the gears 31c2, 31c3, and 31c4 meshing with the gears 31e2, 31e3, and 31e4, respectively, rotate relative to the main transmission drive shaft 31a.

[0052] In this way, the power of the main transmission drive shaft 31a is changed in speed according to the number of teeth of the gears 31c4, 31e4, gears 31c3, 31e3, gears 31c2, 31e2, and gears 31c1, 31e1 in the combinations corresponding to first, second, third, and fourth speeds. The power after the speed change is output to the main transmission driven shaft 31b rearward of the second main transmission gear 31e. The output power is input to the front end of the sub-transmission drive shaft 32a of the sub-transmission mechanism 32.

[0053] <<Sub-transmission Mechanism>> As shown in Figures 3 and 6, the sub-transmission mechanism 32 includes a sub-transmission drive shaft 32a, a sub-transmission driven shaft 32b, a first sub-transmission gear 32c, a second sub-transmission gear 32d, and a sub-transmission shifter 32e. The sub-transmission drive shaft 32a is disposed coaxially with the first axis A1 and is configured to be rotatable integrally with the first sub-transmission gear 32c. The sub-transmission drive shaft 32a is configured to be able to input power from the main transmission driven shaft 31b from the front side of the first axis A1. When power is input from the main transmission driven shaft 31b, the sub-transmission drive shaft 32a rotates about the first axis A1.

[0054] The auxiliary transmission drive shaft 32a has a hollow structure, and the first input shaft 23 is fitted inside it. The first input shaft 23 on the radially inner side and the auxiliary transmission drive shaft 32a on the radially outer side are rotatable relative to each other. The vicinity of the front end of the auxiliary transmission drive shaft 32a is journaled by bearing 11f via a bearing. Bearing 11f is located rearward of bearing 11e. The front end of the auxiliary transmission drive shaft 32a and the rear end of the main transmission driven shaft 31b are located between bearings 11e and 11f and are connected to each other via a coupling. This allows the auxiliary transmission drive shaft 32a and the first auxiliary transmission gear 32c to rotate integrally with the main transmission driven shaft 31b. The vicinity of the rear end of the auxiliary transmission drive shaft 32a is journaled by bearing 11g via a bearing. Bearing 11g is located forward of the differential device 3b of the rear wheels 3.

[0055] The auxiliary transmission driven shaft 32b is disposed coaxially with the third axis A3 and is configured to rotate integrally with the second auxiliary transmission gear 32d. When the second auxiliary transmission gear 32d rotates, the auxiliary transmission driven shaft 32b rotates around the third axis A3 and outputs power to the differential device 3b located rearward of the second auxiliary transmission gear 32d.

[0056] As shown in FIG. 6 , the first auxiliary transmission gear 32c is composed of four gears 32c1, 32c2, 32c3, and 32c4. Each of the gears 32c1 to 32c4 has a cylindrical shape, an inner wall surface connected to the outer surface of the auxiliary transmission drive shaft 32a, and external teeth on the outer surface of each of the gears 32c1 to 32c4. The number of teeth on the external teeth varies among the gears 32c1 to 32c4. In this embodiment, the relationship is as follows: number of teeth of gear 32c1 > number of teeth of gear 32c4 > number of teeth of gear 31c3 > number of teeth of gear 31c2. The four gears 32c1, 32c2, 32c3, and 32c4 are arranged in parallel in this order from front to rear between the bearings 11g and 11f, and are each arranged coaxially with the first axis A1. Each of the gears 32c1 to 32c4 is rotatable integrally with the sub-transmission drive shaft 32a. In this embodiment, the number of first sub-transmission gears 32c is four, but it may be configured with more than four.

[0057] The traveling system transmission 30 is also provided with a gear shaft 34, which is arranged coaxially on an axis that is parallel to but different from the first axis A1, the second axis A2, and the third axis A3. A gear 34a that can rotate integrally with the gear shaft 34 is configured to mesh with only the gear 32c3 of the first auxiliary transmission gear 32c. Therefore, when the gear 32c3 rotates, the gear 34a rotates integrally with the gear shaft 34.

[0058] The case 10 also includes a first bearing 11h and a second bearing 11i. The first bearing 11h rotatably supports the auxiliary transmission driven shaft 32b on the front side of the third axis A3. The second bearing 11i rotatably supports the auxiliary transmission driven shaft 32b on the rear side of the third axis A3. More specifically, the front end of the auxiliary transmission driven shaft 32b is supported by the first bearing 11h via a bearing, and the rear end of the auxiliary transmission driven shaft 32b is supported by the second bearing 11i via a bearing. The first bearing 11h is located rearward of the bearing 11d. The second bearing 11i is located forward of the differential device 3b of the rear wheels 3.

[0059] The second auxiliary transmission gear 32d is composed of four gears 32d1, 32d2, 32d3, and 32d4. Each gear 32d1 to 32d4 is cylindrical, engages with the auxiliary transmission driven shaft 32b, and has external teeth on its outer surface. The number of teeth on the external teeth varies among the gears 32d1 to 32d4. In this embodiment, the number of teeth on the gear 32d2 is greater than the number of teeth on the gear 32d4, greater than the number of teeth on the gear 32d3, and greater than the number of teeth on the gear 32d1. The four gears 32d1, 32d2, 32d3, and 32d4 are arranged in parallel from front to rear in this order between the first bearing portion 11h and the second bearing portion 11i, and are each arranged coaxially with the third axis A3.

[0060] Each of the gears 32d1 to 32d4 is rotatable relative to the auxiliary transmission driven shaft 32b and is adapted to mesh with each of the gears 32c1 to 32c4. The gears 32d1 and 32c1, the gears 32d2 and 32c2, the gears 32d3 and 32c3, and the gears 32d4 and 32c4 are adapted to be constantly meshed with each other. Note that only the gears 32d3 and 32c3 are indirectly meshed with each other via the gear 34a of the gear shaft 34. The gears 32d1 to 32d4 are adapted so that only one selected from the gears 32d1 to 32d4 rotates integrally with the auxiliary transmission driven shaft 32b by the operation of the auxiliary transmission shifter 32e, which will be described later. In this embodiment, the number of second auxiliary transmission gears 32d is four, but the number may be greater than or equal to the number of first auxiliary transmission gears 32c.

[0061] The auxiliary transmission shifter 32e is composed of two shifters 32e1 and 32e2. Each of the shifters 32e1 and 32e2 has a cylindrical shape and is fitted with the auxiliary transmission driven shaft 32b. The shifter 32e1 is disposed between the gears 32d1 and 32d2, and the shifter 32e2 is disposed between the gears 32d3 and 32d4, and they are arranged coaxially with the third axis A3. Each of the shifters 32e1 and 32e2 can be displaced forward or backward from a neutral position in response to lever operation by the driver. When each of the shifters 32e1 and 32e2 is displaced forward or backward from the neutral position, the gears 31d1 to 31d4 adjacent to the shifter 32e1 and 32e2 are engaged with the displaced shifter 32e1 and 32e2 and fixed to the auxiliary transmission driven shaft 32b.

[0062] In this embodiment, the auxiliary transmission mechanism 32 has a four-speed shift function. In the neutral state, the shifters 32e1 and 32e2 are each located in a neutral position, and the auxiliary transmission driven shaft 32b rotates relative to the gears 32d1 to 32d4. That is, no power is transmitted between the auxiliary transmission driven shaft 32b and the gears 32d1 to 32d4. When a low speed of the auxiliary transmission mechanism 32 is selected by the driver's operation from this state, the shifter 32e2 is maintained in the neutral position, while the shifter 32e1 is displaced rearward from the neutral position. The rearward displaced shifter 32e1 fixes the gear 31c2 to the auxiliary transmission driven shaft 32b. As a result, of the gears 32d1 to 32d4, only the gear 32d2 rotates integrally with the auxiliary transmission driven shaft 32b, and the other gears 32d1, 32d3, 32d4 rotate relative to the auxiliary transmission driven shaft 32b.

[0063] When the driver operates the vehicle to select a medium speed from a low speed state, shifter 32e2 moves rearward from the neutral position, while shifter 32e1 moves from rearward to the neutral position. Shifter 32e2, which has moved rearward, fixes gear 32d4 to auxiliary transmission driven shaft 32b. As a result, of gears 32d1 to 32d4, only gear 32d4 rotates integrally with auxiliary transmission driven shaft 32b, while the other gears 32d1, 32d2, and 32d3 rotate relative to auxiliary transmission driven shaft 32b.

[0064] When the driver operates the vehicle to select a high speed from a medium speed, shifter 32e2 moves from the rear to the neutral position, while shifter 32e1 moves forward from the neutral position. Shifter 32e1, which has moved forward, fixes gear 32d1 to auxiliary transmission driven shaft 32b. As a result, of gears 32d1 to 32d4, only gear 32d1 rotates integrally with auxiliary transmission driven shaft 32b, while the other gears 32d2, 32d3, and 32d4 rotate relative to auxiliary transmission driven shaft 32b.

[0065] When the driver operates the vehicle to select reverse gear from a low to high gear position, the shifter 32e2, which was in the rearward or neutral position, moves forward, while the shifter 32e1, which was in the forward or neutral position, moves to the neutral position or remains in the neutral position. The forward-moving shifter 32e2 fixes the gear 32d3 to the auxiliary transmission driven shaft 32b. As a result, of the gears 32d1 to 32d4, only the gear 32d3 rotates integrally with the auxiliary transmission driven shaft 32b, while the other gears 32d1, 32d2, and 32d4 rotate relative to the auxiliary transmission driven shaft 32b.

[0066] When the gear position is low, only the gear 32d2 rotates integrally with the auxiliary transmission driven shaft 32b, and the gear 32c2 meshing with the gear 32d2 rotates integrally with the auxiliary transmission drive shaft 32a. The gears 32c1, 32c3, and 32c4 also rotate integrally with the auxiliary transmission drive shaft 32a, and the gears 32d1, 32d3, and 32d4 meshing with the gears 32c1, 32c3, and 32c4, respectively, rotate relative to the auxiliary transmission driven shaft 32b. Note that only the gear 32d3 meshes indirectly with the gear 32c3 via the gear 34a of the gear shaft 34, and therefore rotates relatively in the opposite direction to the rotation of the gears 32d1 and 32d4.

[0067] When the gear position is medium, only the gear 32d4 rotates integrally with the auxiliary transmission driven shaft 32b, and the gear 32c4 meshing with the gear 32d4 rotates integrally with the auxiliary transmission drive shaft 32a. The gears 32c1, 32c2, and 32c3 also rotate integrally with the auxiliary transmission drive shaft 32a, and the gears 32d1, 32d2, and 32d3 meshing with the gears 32c1, 32c2, and 32c3, respectively, rotate relative to the auxiliary transmission driven shaft 32b. In this case, only the gear 32d3 rotates relatively in the direction opposite to the rotation of the gears 32d1 and 32d2.

[0068] When the gear position is high, only the gear 32d1 rotates integrally with the auxiliary transmission driven shaft 32b, and the gear 32c1 meshing with the gear 32d1 rotates integrally with the auxiliary transmission drive shaft 32a. The gears 32c2, 32c3, and 32c4 also rotate integrally with the auxiliary transmission drive shaft 32a, and the gears 32d2, 32d3, and 32d4 meshing with the gears 32c2, 32c3, and 32c4, respectively, rotate relative to the auxiliary transmission driven shaft 32b. In this case, only the gear 32d3 rotates relatively in the direction opposite to the rotation of the gears 32d2 and 32d4.

[0069] When the gear is in reverse, only the gear 32d3 rotates integrally with the auxiliary transmission driven shaft 32b, and the gear 32c3, which meshes with the gear 32d3 via the gear 34a, rotates integrally with the auxiliary transmission drive shaft 32a. The gears 32c1, 32c2, and 32c4 also rotate integrally with the auxiliary transmission drive shaft 32a, and the gears 32d1, 32d2, and 32d4, which mesh with the gears 32c1, 32c2, and 32c4, respectively, rotate relative to the auxiliary transmission driven shaft 32b. In this case, the auxiliary transmission driven shaft 32b rotates in the opposite direction to the rotation direction when the gear is in the low to high speed range.

[0070] In this way, the power of the auxiliary transmission drive shaft 32a is changed in speed according to the number of teeth of each of the combinations of gears 32c2, 32d2, gears 32c4, 32d4, gears 32c1, 32d1, and gears 32c3, 32d3 (and 34a) corresponding to low speed, medium speed, high speed, and reverse. The power after the speed change is output to the auxiliary transmission driven shaft 32b rearward of the second auxiliary transmission gear 32d. The output power is input to the differential device 3b of the rear wheels 3 and transmitted so as to be converted into rotational force for the rear wheels 3. When the gear is in low to high speed, the auxiliary transmission driven shaft 32b rotates in one direction, and the rear wheels 3 are rotationally driven in the forward direction. On the other hand, when the gear is in reverse, the auxiliary transmission driven shaft 32b rotates in the opposite direction, and the rear wheels 3 are rotationally driven in the reverse direction.

[0071] The traveling system transmission 30 is also provided with a propeller shaft 33, which is arranged coaxially on an axis that is parallel to but different from the first axis A1, the second axis A2, and the third axis A3. A gear 33a that can rotate integrally with the propeller shaft 33 is provided at the rear end of the propeller shaft 33. A shifter 33b is provided in front of the gear 33a. The shifter 33b is configured to fix the gear 33a to the propeller shaft 33 or to separate it from the propeller shaft 33 in response to operation by the driver. The front end of the propeller shaft 33 is configured to output power toward the front wheels 2.

[0072] The traveling system transmission 30 is also provided with a gear shaft 35, which is arranged coaxially on an axis that is parallel to but different from the first axis A1, the second axis A2, and the third axis A3. A gear 35a that can rotate integrally with the gear shaft 35 is adapted to mesh with a gear 33a of the propeller shaft 33.

[0073] A gear 32f is provided on the auxiliary transmission driven shaft 32b between the adjacent gears 32d2 and 32d3. The gear 32f is disposed coaxially with the third axis A3 and is rotatable integrally with the auxiliary transmission driven shaft 32b. The gear 32f meshes with a gear 35a of the gear shaft 35. That is, when the auxiliary transmission driven shaft 32b rotates, the gear 32f rotates integrally with the auxiliary transmission driven shaft 32b, and the gear 33a of the propeller shaft 33 rotates via the gear 35a.

[0074] When the gear 33a is fixed to the propeller shaft 33 by the shifter 33b, and when the gear position of the auxiliary transmission mechanism 32 is between low and high, the auxiliary transmission driven shaft 32b rotates in one direction, and the propeller shaft 33 also rotates in one direction together with the gear 33a. This drives the front wheels 2 to rotate in the forward direction. Also, when the gear position of the auxiliary transmission mechanism 32 is reverse, the auxiliary transmission driven shaft 32b rotates in the reverse direction, and the propeller shaft 33 also rotates in the reverse direction together with the gear 33a. This drives the front wheels 2 to rotate in the reverse direction. In other words, speed change and forward / reverse switching can be performed in four-wheel drive.

[0075] In this way, the auxiliary transmission driven shaft 32b outputs power rearward of the gears constituting the second auxiliary transmission gear 32d, and the output power is transmitted so as to be converted into rotational power for the rear wheel 3. In addition, power is output from between two adjacent gears 32d2, 32d3 of the gears constituting the second auxiliary transmission gear 32d, and the output power is transmitted so as to be converted into rotational power for the front wheel 2.

[0076] On the other hand, when the gear 33a is disconnected from the propeller shaft 33 by the shifter 33b, the gear 33a rotates relative to the propeller shaft 33 in accordance with the rotation of the auxiliary transmission driven shaft 32b, regardless of the gear position of the auxiliary transmission mechanism 32. As a result, power is not transmitted to the front wheels 2, but only to the rear wheels 3. In other words, speed change and forward / reverse switching can be performed in two-wheel drive.

[0077] As described above, in the power transmission device 100, the power of the prime mover 4 is transmitted to only the rear wheels 3, or to both the front wheels 2 and the rear wheels 3, after being shifted through the power input mechanism 20 and the main transmission mechanism 31 and the sub-transmission mechanism 32 of the traveling transmission 30.

[0078] <<PTO Transmission>> As shown in FIG. 3, the PTO transmission 40 is housed in the rear transmission case 12 and includes a first PTO input shaft 41, first PTO gears 41a, 41b, a PTO output shaft 42, PTO output gears 42a, 42b, and a PTO shifter 42c.

[0079] The rear end 12a of the rear transmission case 12 is generally flat and closed by bolts fastened from the rear. The rear end of the first PTO input shaft 41 is supported by a bearing on the inner wall of the rear end 12a. The first PTO input shaft 41 is disposed coaxially with the first axis A1 and extends forward from the rear end 12a, passing through the bearing portion 12b. The bearing portion 12b is located forward of the rear end 12a and rearward of the differential device 3b of the rear wheels 3. The front end of the first PTO input shaft 41 is connected to the rear end of the first input shaft 23 via a coupling. This allows the first PTO input shaft 41 to rotate integrally with the first input shaft 23 around the first axis A1. That is, the first PTO input shaft 41 is configured to receive power from the prime mover 4 via the first input shaft 23 from the front side of the first axis A1. When power is input from the prime mover 4, it rotates around the first axis.

[0080] The first PTO gears 41a, 41b are composed of two gears, and each gear 41a, 41b is arranged coaxially with the first axis A1. The first PTO gears 41a, 41b are configured to be rotatable integrally with the first PTO input shaft 41. When the first PTO input shaft 41 rotates, the first PTO gears 41a, 41b rotate about the first axis A1.

[0081] The first PTO gears 41a, 41b each have a cylindrical shape, with their inner wall surfaces connected to the outer surface of the first PTO input shaft 41. The outer surfaces of the gears 41a, 41b have external teeth. The number of teeth on the external teeth differs between the gears 41a, 41b. In this embodiment, the number of teeth on the gear 41a is greater than the number of teeth on the gear 41b. The two gears 41a, 41b are arranged side by side in this order from rear to front between the rear end 12a and the bearing 12b.

[0082] The PTO output shaft 42 is disposed coaxially with the third axis A3, and the front side of the PTO output shaft 42 on the third axis A3 is housed inside the rear transmission case 12. The front end of the PTO output shaft 42 is journaled at the bearing portion 12c via a bearing. The bearing portion 12c is located forward of the rear end portion 12a and rearward of the differential device 3b of the rear wheels 3. The rear side of the PTO output shaft 42 on the third axis A3 protrudes rearward outside the rear transmission case 12 through the insertion hole 12a1 in the rear end portion 12a. With the PTO output shaft 42 inserted through the insertion hole 12a1, the PTO output shaft 42 is rotatable about the third axis A3. By rotating about the third axis A3, the PTO output shaft 42 outputs power to a work implement connected to the tractor 1.

[0083] The PTO output gears 42a, 42b are composed of two gears, and each gear 42a, 42b is arranged coaxially with the third axis A3 so as to mesh with the first PTO gears 41a, 41b, respectively. The PTO output gears 42a, 42b are configured so that only one of the gears 42a, 42b is selected by the operation of a PTO shifter 42c, which will be described later, to rotate integrally with the PTO output shaft 42.

[0084] Each of the PTO output gears 42a, 42b has a cylindrical shape, the PTO output shaft 42 is engaged therewith, and external teeth are formed on the outer surface. The number of teeth on the external teeth differs between the gears 42a, 42b. In this embodiment, the number of teeth on the gear 42b is greater than the number of teeth on the gear 42a. The two gears 42a, 42b are arranged side by side in this order from rear to front between the rear end 12a and the bearing portion 12c.

[0085] The PTO shifter 42c has a cylindrical shape, and the PTO output shaft 42 is fitted inside the PTO shifter 42c. The PTO shifter 42c is disposed between the PTO output gears 42a and 42b and is disposed coaxially with the third axis A3. The PTO shifter 42c can be displaced in either the forward or rearward direction from a neutral position in response to lever operation by the driver. When the PTO shifter 42c is displaced forward or rearward from the neutral position, the PTO output gears 42a and 42b adjacent to the PTO shifter 42c are engaged with the displaced PTO shifter 42c and fixed to the PTO output shaft 42.

[0086] In this embodiment, the PTO transmission 40 has a two-speed shift function. In the neutral state, the PTO shifter 42c is located in a neutral position, and the PTO output shaft 42 rotates relative to the PTO output gears 42a, 42b. That is, no power is transmitted between the PTO output shaft 42 and the PTO output gears 42a, 42b. From this state, when a low speed of the PTO transmission 40 is selected by the driver, the PTO shifter 42c is displaced forward from the neutral position. The displaced PTO shifter 42c fixes the PTO output gear 42b to the PTO output shaft 42. As a result, of the PTO output gears 42a, 42b, only the gear 42b rotates integrally with the PTO output shaft 42, while the other gear 42a rotates relative to the PTO output shaft 42.

[0087] When the driver operates the PTO shifter 42c to select a high gear from a low gear position, the PTO shifter 42c moves from the front to the neutral position and then rearward. The rearward-moving PTO shifter 42c fixes the PTO output gear 42a to the PTO output shaft 42. As a result, of the PTO output gears 42a, 42b, only the gear 42a rotates integrally with the PTO output shaft 42, while the other gear 42b rotates relative to the PTO output shaft 42.

[0088] When the gear position is low, only the PTO output gear 42b rotates integrally with the PTO output shaft 42, and the first PTO gear 41b meshing with the gear 42b rotates integrally with the first PTO input shaft 41. The first PTO gear 41a also rotates integrally with the first PTO input shaft 41, and the PTO output gear 42a meshing with the gear 41a rotates relative to the PTO output shaft 42.

[0089] When the gear position is high, only the PTO output gear 42a rotates integrally with the PTO output shaft 42, and the first PTO gear 41a meshing with the gear 42a rotates integrally with the first PTO input shaft 41. The first PTO gear 41b also rotates integrally with the first PTO input shaft 41, and the PTO output gear 42b meshing with the gear 41b rotates relative to the PTO output shaft 42.

[0090] In this way, the power of the first PTO input shaft 41 is shifted in speed according to the number of teeth of the gears 41b, 42b and the gears 41a, 42a, which correspond to the low and high speed combinations. The shifted power is output to the PTO output shaft 42 rearward of the PTO output gears 42a, 42b. The output power is input to the implement connected to the tractor 1 and transmitted so as to be converted into driving force for the implement. Whether the gear is low speed or high speed, the PTO output shaft 42 rotates in one direction.

[0091] As described above, in the power transmission device 100, the power of the prime mover 4 is transmitted to the working device via the PTO output shaft 42 after being shifted in the PTO transmission 40.

[0092] <Effects of the Embodiment> As described above, the power transmission device 100 according to the first embodiment of the present invention includes the first input shaft 23, the second input shaft 24, the first input gear 25, the second input gear 26, the main transmission mechanism 31, the auxiliary transmission mechanism 32, and the case 10. The main transmission mechanism 31 includes the main transmission drive shaft 31a, the main transmission driven shaft 31b, the first main transmission gear 31c, and the second main transmission gear 31e. The main transmission drive shaft 31a is arranged coaxially with the second axis A2 and is configured to be able to input power from the second input gear 26 from the front side (first direction side) of the second axis A2. The main transmission drive shaft 31a rotates about the second axis A2 when power from the second input gear 26 is input. The first main transmission gear 31c is arranged coaxially with the second axis A2 and is configured to be able to rotate integrally with the main transmission drive shaft 31a. The first main transmission gear 31c rotates about the second axis A2 when the main transmission drive shaft 31a rotates. The second main transmission gear 31e is arranged coaxially with the first axis A1 and is configured to mesh with the first main transmission gear 31c. The second main transmission gear 31e rotates about the first axis A1 when the first main transmission gear 31c rotates. The main transmission driven shaft 31b is arranged coaxially with the first axis A1 and is configured to be rotatable integrally with the second main transmission gear 31e. When the second main transmission gear 31e rotates, the main transmission driven shaft 31b rotates about the first axis A1 and outputs power rearward (in the second direction) of the second main transmission gear 31e.

[0093] The auxiliary transmission mechanism 32 includes an auxiliary transmission drive shaft 32a, an auxiliary transmission driven shaft 32b, a first auxiliary transmission gear 32c, and a second auxiliary transmission gear 32d. The auxiliary transmission drive shaft 32a is arranged coaxially with the first axis A1 and is configured to be able to input power from the main transmission driven shaft 31b from the front side (first direction side) of the first axis A1. The auxiliary transmission drive shaft 32a rotates about the first axis A1 when power is input from the main transmission driven shaft 31b. The first auxiliary transmission gear 32c is arranged coaxially with the first axis A1 and is configured to be able to rotate integrally with the auxiliary transmission drive shaft 32a. The first auxiliary transmission gear 32c rotates about the first axis A1 when the auxiliary transmission drive shaft 32a rotates. The second auxiliary transmission gear 32d is disposed coaxially with the third axis A3 and is configured to mesh with the first auxiliary transmission gear 32c. When the first auxiliary transmission gear 32c rotates, the second auxiliary transmission gear 32d rotates about the third axis A3. The auxiliary transmission driven shaft 32b is disposed coaxially with the third axis A3 and is configured to be rotatable integrally with the second auxiliary transmission gear 32d. When the second auxiliary transmission gear 32d rotates, the auxiliary transmission driven shaft 32b rotates about the third axis A3 and outputs power rearward (in the second direction) of the second auxiliary transmission gear 32d.

[0094] According to the above configuration, the main transmission driven shaft 31b and the auxiliary transmission drive shaft 32a are arranged coaxially with the first axis A1. The main transmission drive shaft 31a is arranged coaxially with the second axis A2, which is located below (in the third direction) the first axis A1. The auxiliary transmission driven shaft 32b is arranged coaxially with the third axis A3, which is located below (in the third direction) the first axis A1. In other words, the main transmission drive shaft 31a and the auxiliary transmission driven shaft 32b are located on the same side of the first axis A1. Therefore, each shaft and its associated gears, bearings, etc. can be arranged on the first axis A1 and on the same side of the first axis A1.

[0095] For example, in the prior art, the components of the main transmission mechanism and the sub-transmission mechanism are positioned in different directions relative to the first axis A1, and the shafts and the gears, bearings, etc. associated with each shaft are sometimes distributed in various directions around the first axis A1. In contrast, according to the first embodiment of the present invention, the shafts and the gears, bearings, etc. associated with each shaft are concentrated on the first axis A1 and in the same direction relative to the first axis A1, allowing them to be housed compactly inside the case 10.

[0096] In the first embodiment of the present invention, the second input gear 26 is configured to input power to the front end of the main transmission drive shaft 31 a. Specifically, the spline shaft 26 b is engaged with the front end of the main transmission drive shaft 31 a.

[0097] According to the above configuration, even if the first main transmission gear 31c is provided on the main transmission drive shaft 31a along the second axis A2, the second input gear 26 can be easily added. Therefore, the speed change of the power input to the main transmission mechanism 31 can be easily adjusted without significantly changing the configuration of the main transmission mechanism 31. For example, even if the prime mover 4 connected to the power transmission device 100 is available in a variety of outputs, the second input gear 26 configured as described above can achieve a speed change rate appropriate for the output of the prime mover 4 without significantly changing the configuration of the main transmission mechanism 31. Furthermore, the first input gear 25 and the second input gear 26, in addition to the main transmission mechanism 31 and the subtransmission mechanism 32, can further reduce the overall speed.

[0098] In the first embodiment of the present invention, the case 10 includes a partition wall 11c that divides the internal space into a front space and a rear space. The partition wall 11c has a first insertion hole 11c1 that is coaxial with the first axis A1 and a second insertion hole 11c2 that is coaxial with the second axis A2. The main transmission driven shaft 31b has its front end engaged with the first insertion hole 11c1 and is arranged to be rotatable relative to the partition wall 11c. The main transmission drive shaft 31a has its front end engaged with the second insertion hole 11c2 and is located in the front space divided by the partition wall 11c and is arranged to be rotatable relative to the partition wall 11c. The second input gear 26 is arranged in the front space partitioned by the partition wall portion 11c, and the first main transmission gear 31c and the second main transmission gear 31e are arranged in the rear space partitioned by the partition wall portion 11c.

[0099] According to the above configuration, with the first main transmission gear 31c and the second main transmission gear 31e housed in the space behind the partition wall 11c, the second input gear 26 can be added to the front end of the main transmission drive shaft 31a from the front side of the partition wall 11c. Therefore, there is no need to secure space for the input gear in the accommodation space of the main transmission mechanism 31. Furthermore, because the main transmission driven shaft 31b and the main transmission drive shaft 31a are journaled by the first insertion hole 11c1 and the second insertion hole 11c2, respectively, there is no need to provide additional bearings in the accommodation space of the main transmission mechanism 31. In other words, the partition wall 11c can serve as both a partition wall and a bearing. As a result, the main transmission mechanism 31 can be accommodated compactly.

[0100] In the first embodiment of the present invention, the first main transmission gear 31c is composed of four gears, 31c1, 31c2, 31c3, and 31c4, each of which has a different number of teeth and is arranged coaxially with the second axis A2. The first main transmission gear 31c is configured so that only one selected from the gears 31c1 to 31c4 rotates integrally with the main transmission drive shaft 31a. The second main transmission gear 31e is composed of the same number of gears as the first main transmission gears 31c, and the gears 31e1, 31e2, 31e3, and 31e4 are arranged coaxially with the first axis A1. The second main transmission gear 31e is configured to mesh with each of the gears 31c1 to 31c4 of the first main transmission gear 31c.

[0101] According to the above configuration, the main transmission mechanism 31 can be housed compactly, and the number of gear stages in the main transmission mechanism 31 can be increased. Therefore, fine gear changes can be realized when the tractor 1 is traveling.

[0102] In the first embodiment of the present invention, the case 10 (front transmission case 11) includes a first bearing 11h and a second bearing 11i. The first bearing 11h rotatably supports the auxiliary transmission driven shaft 32b on the front side of the third axis A3. The second bearing 11i rotatably supports the auxiliary transmission driven shaft 32b on the rear side of the third axis A3. The second auxiliary transmission gear 32d is disposed between the first bearing 11h and the second bearing 11i.

[0103] According to the above configuration, the second auxiliary transmission gear 32d can be disposed between the bearings on both ends of the auxiliary transmission driven shaft 32b, resulting in a so-called double-supported structure. For example, if the gear is disposed forward of the first bearing 11h or rearward of the second bearing 11i, this results in a so-called cantilevered structure. Compared to the cantilevered structure, the double-supported structure described above can improve the reliability of the second auxiliary transmission gear 32d. Furthermore, it is possible to suppress so-called gear tilt, in which the second auxiliary transmission gear 32d tilts relative to the auxiliary transmission driven shaft 32b, thereby reducing noise.

[0104] In the first embodiment of the present invention, the second auxiliary transmission gear 32d is composed of four gears 32d1, 32d2, 32d3, and 32d4, each of which has a different number of teeth and is arranged coaxially with the third axis A3. The second auxiliary transmission gear 32d is configured so that only one selected from the gears 32d1 to 32d4 rotates integrally with the auxiliary transmission driven shaft 32b. The first auxiliary transmission gear 32c is composed of the same number of gears as the number of second main transmission gears 32d, and the gears 32c1, 32c2, 32c3, and 32c4 are arranged coaxially with the first axis A1. The first auxiliary transmission gear 32c is configured to mesh with each of the gears 32d1 to 32d4 of the second auxiliary transmission gear 32d.

[0105] According to the above configuration, the sub-transmission mechanism 32 can be housed compactly while having a large number of gears. The sub-transmission mechanism 32 can have, for example, three forward gears and one reverse gear. In this case, by setting the main transmission mechanism 31 to have four gears as described above, the power transmission device 100 as a whole has 12 forward gears and four reverse gears. Therefore, when the tractor 1 is traveling, even finer gear changes can be achieved in both forward and reverse.

[0106] Furthermore, in the first embodiment of the present invention, the tractor 1 has front wheels 2 on the front side and rear wheels 3 on the rear side. The auxiliary transmission driven shaft 32b is configured to output power rearward of the gears 32d1 to 32d4 of the second auxiliary transmission gear 32d, and the output power is transmitted so as to be converted into rotational power for the rear wheels 3. In addition, the auxiliary transmission driven shaft 32b is configured to output power from between two adjacent gears 32d2, 32d3 of the gears 32d1 to 32d4 of the second auxiliary transmission gear 32d, and the output power is transmitted so as to be converted into rotational power for the front wheels 2.

[0107] According to the above configuration, the gear 32f for driving the front wheels 2 can be interposed between the plurality of second auxiliary transmission gears 32d. Therefore, the space between the second auxiliary transmission gears 32d can be utilized to provide a mechanism for driving the front wheels 2. Therefore, there is no need to secure a separate space for arranging the gear 32f, and the auxiliary transmission mechanism 32 can be housed compactly while still being able to drive the front wheels. Furthermore, since the gear 32f is interposed between the two adjacent gears 32d2 and 32d3, interference between the gears 32d2 and 32d3 can be suppressed, eliminating the need for a separate collar or the like.

[0108] In the first embodiment, the gear 32f for driving the front wheels 2 is interposed between two adjacent gears 32d2 and 32d3 of the second auxiliary transmission gear 32d. Alternatively, for example, the gear 32f may be interposed between two adjacent gears 32d1 and 32d2 or between two adjacent gears 32d3 and 32d4. This also achieves the same effect as described above.

[0109] Second Embodiment A power transmission device 100 according to a second embodiment of the present invention differs from the first embodiment described above in the following respects. In the PTO transmission 40 of the first embodiment, the PTO output shaft 42 rotates in one direction. Instead, in the second embodiment, the PTO output shaft 42 is rotatable in one direction and in the reverse direction, allowing the rotation direction to be switched. The second embodiment differs from the first embodiment described above only in this respect, and is otherwise the same as the first embodiment. Only the differences between the second embodiment and the first embodiment will be described below.

[0110] 7 is an enlarged cross-sectional view of the PTO transmission 40 included in the power transmission device 100 according to the second embodiment of the present invention. In FIG. 7, parts that are the same as or equivalent to those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof will be omitted.

[0111] The PTO transmission 40 of the second embodiment is housed in the rear transmission case 12, as in the first embodiment, and includes a first PTO input shaft 41, first PTO gears 41a, 41b, a PTO output shaft 42, PTO output gears 42a, 42b, and a PTO shifter 42c. The PTO transmission 40 of the second embodiment also includes a second PTO input shaft 43 and second PTO gears 43a, 43b. In the second embodiment, the PTO output gears 42a, 42b correspond to the third PTO gear.

[0112] The second PTO input shaft 43 is disposed coaxially with the fourth axis A4 and is configured to rotate integrally with the second PTO gears 43a, 43b. When the second PTO gears 43a, 43b rotate, the second PTO input shaft 43 rotates about the fourth axis A4. The fourth axis A4 is parallel to but offset from the first axis A1 and the third axis A3. The rear end of the second PTO input shaft 43 is journaled at the rear end 12a via a bearing. The front end of the second PTO input shaft 43 is journaled at the bearing 12d via a bearing. The bearing 12d is located forward of the rear end 12a and rearward of the differential device 3b of the rear wheels 3.

[0113] The second PTO gears 43a, 43b are configured to rotate integrally with the second PTO input shaft 43. Each of the second PTO gears 43a, 43b is arranged coaxially with the fourth shaft A4.

[0114] The second PTO gears 43a, 43b each have a cylindrical shape, and their inner wall surfaces are connected to the outer surface of the second PTO input shaft 43. The outer surfaces of the gears 43a, 43b have external teeth. The number of teeth on the external teeth differs between the gears 43a, 43b. In this embodiment, the number of teeth on the gear 43b is greater than the number of teeth on the gear 43a. The two gears 43a, 43b are arranged side by side in this order from rear to front between the rear end 12a and the bearing 12d.

[0115] One of the second PTO gears 43a, 43b, the gear 43b, is meshed with one of the first PTO gears 41a, 41b, the gear 41a, so that when the first PTO gears 41a, 41b rotate, the second PTO gears 43a, 43b rotate around the fourth axis A4.

[0116] One gear 42b of the PTO output gears 42a, 42b is configured to mesh with the other gear 41b of the first PTO gears 41a, 41b. The other gear 42a of the PTO output gears 42a, 42b is configured to mesh with the other gear 43a of the second PTO gears 43a, 43b. Only one of the PTO output gears 42a, 42b is selected by operation of the PTO shifter 42c and is configured to rotate integrally with the PTO output shaft 42.

[0117] In this embodiment, the PTO transmission 40 has a function of switching the rotation direction of the PTO output shaft 42. In the neutral state, the PTO shifter 42c is located in a neutral position, and the PTO output shaft 42 rotates relative to the PTO output gears 42a, 42b. That is, no power is transmitted between the PTO output shaft 42 and the PTO output gears 42a, 42b. From this state, when the driver selects rotation of the PTO output shaft 42 in one direction, the PTO shifter 42c is displaced forward from the neutral position. The displaced PTO shifter 42c fixes the PTO output gear 42b to the PTO output shaft 42. As a result, of the PTO output gears 42a, 42b, only the gear 42b rotates integrally with the PTO output shaft 42, while the other gear 42a rotates relative to the PTO output shaft 42.

[0118] When the PTO output shaft 42 rotates in one direction, and the driver operates the PTO shifter 42c to select rotation in the opposite direction, the PTO shifter 42c moves from the front to the neutral position and then rearward. The rearward-moving PTO shifter 42c fixes the PTO output gear 42a to the PTO output shaft 42. As a result, of the PTO output gears 42a, 42b, only the gear 42a rotates integrally with the PTO output shaft 42, while the other gear 42b rotates relative to the PTO output shaft 42.

[0119] When the rotation direction of the PTO output shaft 42 is unidirectional, only the PTO output gear 42b rotates integrally with the PTO output shaft 42, and the first PTO gear 41b meshing with the gear 42b rotates integrally with the first PTO input shaft 41. The first PTO gear 41a also rotates integrally with the first PTO input shaft 41, and the second PTO gear 43b meshing with the gear 41a rotates integrally with the second PTO input shaft 43. The second PTO gear 43a also rotates integrally with the second PTO input shaft 43, and the PTO output gear 42a meshing with the gear 43a rotates relative to the PTO output shaft 42 in the opposite direction.

[0120] When the rotation direction of the PTO output shaft 42 is reversed, only the PTO output gear 42a rotates integrally with the PTO output shaft 42, and the second PTO gear 43a meshing with the gear 42a rotates integrally with the second PTO input shaft 43. The second PTO gear 43b also rotates integrally with the second PTO input shaft 43, and the first PTO gear 41a meshing with the gear 43b rotates integrally with the first PTO input shaft 41. The first PTO gear 41b also rotates integrally with the first PTO input shaft 41, and the PTO output gear 42b meshing with the gear 41b rotates relative to the PTO output shaft 42 in the reverse direction.

[0121] In this way, the speed of the power of the first PTO input shaft 41 is changed according to the number of teeth of each of the gears 41b and 42b. The power after the speed change causes the PTO output shaft 42 to rotate in one direction. Furthermore, when the rotation direction of the PTO output shaft 42 is switched from one direction to the reverse direction, the speed of the power of the first PTO input shaft 41 is changed according to the number of teeth of each of the gears 41a, 43b, 43a, and 42a. The power after the speed change causes the PTO output shaft 42 to rotate in the reverse direction.

[0122] As described above, in the PTO transmission 40 of the power transmission device 100, the PTO output shaft 42 is rotatable in one direction and in the reverse direction, and the rotation direction can be switched. With the above configuration, the rotation direction of the rotation mechanism in the working device can also be freely switched by switching the rotation direction of the PTO output shaft 42. Therefore, a variety of working modes can be achieved with the working device.

[0123] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0124] DESCRIPTION OF SYMBOLS 1: Tractor 2: Front wheel 3: Rear wheel 4: Prime mover 10: Case 11: Front transmission case 11c: Partition wall portion 11c1: First insertion hole 11c2: Second insertion hole 11h: First bearing portion 11i: Second bearing portion 12: Rear transmission case 20: Power input mechanism 21: Flywheel 22: Clutch 23: First input shaft 24: Second input shaft 25: First input gear 26: Second input gear 26a: Boss gear 26b: Spline shaft 30: Traveling system transmission 31: Main transmission mechanism 31a: Main transmission drive shaft 31b: Main transmission driven shaft 31c: First main transmission gear 31c1: First main transmission gear 31c2: First main speed change gear 31c3: First main speed change gear 31c4: First main speed change gear 31d: Main speed change shifter 31d1: Main speed change shifter 31d2: Main speed change shifter 31e: Second main speed change gear 31e1: Second main speed change gear 31e2: Second main speed change gear 31e3: Second main speed change gear 31e4: Second main speed change gear 32: Auxiliary speed change mechanism 32a: Auxiliary speed change drive shaft 32b: Auxiliary speed change driven shaft 32c: First auxiliary speed change gear 32c1: First auxiliary speed change gear 32c2: First auxiliary speed change gear 32c3: First auxiliary speed change gear 32c4 : First auxiliary transmission gear 32d : Second auxiliary transmission gear 32d1 : Second auxiliary transmission gear 32d2 : Second auxiliary transmission gear 32d3 : Second auxiliary transmission gear 32d4 : Second auxiliary transmission gear 32e : Auxiliary transmission shifter 32e1 : Auxiliary transmission shifter 32e2 : Auxiliary transmission shifter 32f : Gear 33 : Propeller shaft 40 : PTO transmission 41 : First PTO input shaft 41a : First PTO gear 41b : First PTO gear 42 : PTO output shaft 42a : PTO output gear 42b : PTO output gear 42c : PTO shifter 43 : Second PTO input shaft 43a : Second PTO gear 43b : Second PTO gear 100 : Power transmission device A1 : First shaft A2 : Second shaft A3 : Third shaft A4 : Fourth shaft

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