Transmission and work vehicle

Abstract

To provide a technique capable of handling a high load while suppressing an increase in capacity of hydraulic drive means in a transmission of a work vehicle.SOLUTION: An exemplary transmission is for a work vehicle in which drive force of a drive source is transmitted to a traveling drive shaft. The transmission comprises: a first continuously variable transmission and a second continuously variable transmission into which the drive force is input; a straight-movement power transmission mechanism which transmits the drive force output from the first continuously variable transmission as straight-movement drive force; a turning-movement power transmission mechanism which transmits the drive force output from the second continuously variable transmission as turning-movement drive force; an output adjustment mechanism which outputs the straight-movement drive force and the turning-movement drive force to the traveling drive shaft after adjusting both drive force; an assist power transmission mechanism which assists the straight-movement drive force; and a switching mechanism which switches a destination of drive force output from the second continuously variable transmission from the turning-movement power transmission mechanism to the assist power transmission mechanism.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, there is known a traveling work machine including a transmission capable of arbitrarily adjusting the driving speed and driving direction of left and right traveling crawlers by adjusting the output of a hydraulic driving means for traveling and a hydraulic driving means for turning (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in work vehicles, there has been an increasing demand for higher horsepower and higher speeds. Accordingly, the transmissions provided in work vehicles are often used under high loads. In order to cope with such use under high loads, in the transmission as disclosed in Patent Document 1, the capacity of the hydraulic driving means has been increased. However, such a measure causes problems such as an increase in the manufacturing cost and a larger size of the transmission.

[0005] An object of the present invention is to provide a technique capable of coping with high loads while suppressing an increase in the capacity of a hydraulic driving means in a transmission for a work vehicle.

Means for Solving the Problems

[0006] An exemplary transmission of the present invention is a transmission for a work vehicle that transmits the driving force of a driving source to a traveling drive shaft. The transmission includes a first continuously variable transmission and a second continuously variable transmission to which the driving force is input, a straight-ahead power transmission mechanism that transmits the power output from the first continuously variable transmission as straight-ahead power, a turning power transmission mechanism that transmits the power output from the second continuously variable transmission as turning power, an output adjustment mechanism that adjusts the straight-ahead power and the turning power and outputs them to the traveling drive shaft, an assist power transmission mechanism that assists the straight-ahead power, and a switching mechanism that switches the transmission destination of the power output from the second continuously variable transmission from the turning power transmission mechanism to the assist power transmission mechanism.

Advantages of the Invention

[0007] According to an exemplary aspect of the present invention, in a transmission for a work vehicle, it is possible to cope with high loads while suppressing an increase in the capacity of the hydraulic driving means.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0010] The work vehicle according to an embodiment of the present invention is a combine harvester. However, this is merely an example, and the present invention is also applicable to work vehicles other than combine harvesters. Examples of work vehicles other than combine harvesters to which the present invention is applicable include, for example, agricultural work vehicles such as tractors and transplanters, and construction and civil engineering work vehicles such as excavators and bulldozers. Further, the work vehicle to which the present invention is applied is not limited to a crawler-type work vehicle, and may be a wheel-type work vehicle.

[0011] The present invention may be applied to, for example, an articulated type work vehicle, an Ackermann type work vehicle, a three-wheeled work vehicle, a caster wheel type work vehicle, a triangular crawler type work vehicle, a zero-turn (ZTR) type riding lawn mower vehicle, and the like.

[0012] In addition, in this specification, the directions are defined as follows. First, the direction in which a combine harvester as a work vehicle travels during work is defined as "front", and the opposite direction is defined as "rear". Also, the right side is defined as right and the left side is defined as left when facing the traveling direction of the combine harvester. Then, the direction perpendicular to the front-rear direction and the left-right direction of the combine harvester is defined as the up-down direction. At this time, the direction of gravity is defined as down, and the opposite side is defined as up. Note that the above directions are merely names used for explanation purposes and are not intended to limit the actual positional relationship and direction.

[0013] <1. Overview of the Work Vehicle> FIG. 1 is a side view showing a schematic configuration of a combine harvester 100 according to an embodiment of the present invention. FIG. 2 is a plan view showing a schematic configuration of the combine harvester 100 according to an embodiment of the present invention. Note that the reference numeral 200 in FIG. 1 is the ground.

[0014] As shown in FIGS. 1 and 2, the combine 100 includes a traveling body 1 that is supported by the traveling unit 2 so as to be capable of traveling. At the front of the traveling body 1, a harvesting device 3 that takes in while cutting cereal straws is mounted so as to be vertically adjustable around a harvesting input case 16 via a single-acting lifting hydraulic cylinder 4. On the traveling body 1, a threshing device 5 having a feed chain 6 and a grain tank 7 that stores grains taken out from the threshing device 5 are mounted side by side. A driver's cab 9 is provided on the right side of the harvesting device 3 and in front of the grain tank 7.

[0015] The driver's cab 9 is provided with a steering wheel 10 which is an example of a control device, a driver's seat 11, a main speed change lever 12 and a sub speed change lever 13 as speed change operating devices, a threshing clutch lever 14 for operating the engagement and disengagement of the threshing clutch, and a harvesting clutch lever 15 for operating the engagement and disengagement of the harvesting clutch. Below the driver's seat 11, an engine 17 as a drive source is mounted. In front of the engine 17, a transmission 18 that appropriately changes the power of the engine 17 and transmits it to the left and right traveling crawlers 2 is arranged.

[0016] As can be seen from the above description, the combine (work vehicle) 100 includes an engine (drive source) 17 and a transmission 18. Note that the engine 17 is only an example of a drive source, and the drive source may be other than an engine. The drive source may be, for example, a motor.

[0017] As shown in FIGS. 1 and 2, the traveling unit 2 is specifically composed of a pair of left and right crawlers. The configurations of the left crawler 2 and the right crawler 2 are the same. For this reason, hereinafter, the configuration of the crawler 2 will be described using the case of the right crawler 2 shown in FIG. 1 as a representative example.

[0018] The crawler 2 includes a track frame 21 extending in the front-rear direction. On the front side of the track frame 21, a drive sprocket 22 attached to a traveling drive shaft 19 (see also FIG. 3 described later) protruding outward in the left-right direction (here, the right side) from a mission case constituting the transmission 18 is disposed as a drive wheel. At the rear part of the track frame 21, an idler 23 is disposed as a driven wheel. The idler 23 is rotatably supported by the track frame 21. Between the drive sprocket 22 and the idler 23 of the track frame 21, a plurality (four in this example) of tumbler wheels 24 are rotatably supported. The crawler 2 is configured by winding a crawler belt 25 around the drive sprocket 22, the idler 23, and the plurality of tumbler wheels 24.

[0019] When the power of the engine 17 is transmitted to the traveling drive shaft 19 via the transmission 18, the drive sprocket 22 rotates together with the traveling drive shaft 19. Along with the rotation of the drive sprocket 22, the crawler belt 25 rotates, enabling the combine 100 to travel by the traveling unit 2. That is, the combine (work vehicle) 100 includes a traveling unit 2 driven by the traveling drive shaft 19.

[0020] <2. Transmission> The transmission 18 is a power transmission device for a work vehicle that transmits the driving force of the engine (drive source) 17 to the traveling drive shaft 19. In other words, the transmission 18 is a hydraulic transmission. FIG. 3 is a power transmission system diagram of the transmission 18 according to an embodiment of the present invention. Note that, for easy understanding, elements other than the transmission 18 (for example, the engine 17, the drive sprocket 22, etc.) are also shown in FIG. 3.

[0021] As shown in FIG. 3, the transmission 18 includes a first continuously variable transmission 31, a second continuously variable transmission 32, a straight-ahead power transmission mechanism 40, a turning power transmission mechanism 50, an output adjustment mechanism 60, a switching mechanism 70, and an assist power transmission mechanism 80.

[0022] [2-1. First Continuously Variable Transmission and Second Continuously Variable Transmission] The first continuously variable transmission 31 and the second continuously variable transmission 32 are input with the driving force of the engine (driving source) 17. Specifically, the first continuously variable transmission 31 and the second continuously variable transmission 32 are hydraulic continuously variable transmissions. More specifically, the first continuously variable transmission 31 and the second continuously variable transmission 32 are HST (Hydraulic Static Transmission). Note that the first continuously variable transmission 31 and the second continuously variable transmission 32 are not limited to HST, and may be, for example, HMT (Hydro Mechanical Transmission).

[0023] The first continuously variable transmission 31 is electrically or mechanically associated with the main transmission lever 12 so that control linked to the operation of the main transmission lever 12 is performed. The first continuously variable transmission 31 is a straight-ahead HST for traveling speed change. Hereinafter, the first continuously variable transmission 31 is expressed as the straight-ahead HST 31. Also, the second continuously variable transmission 32 is electrically or mechanically associated with the steering wheel 10 so as to be linked to the operation of the steering wheel 10. The second continuously variable transmission 32 is a swivel HST for steering. Hereinafter, the second continuously variable transmission 32 is expressed as the swivel HST 32. Although details will be described later, in the present embodiment, the swivel HST 32 is also used for purposes other than steering.

[0024] When the main transmission lever 12 is operated to a position other than the neutral position and the steering handle 10 is at the neutral position, the straight - travel HST 31 is electrically or mechanically controlled so that the traveling machine body 1 travels straight ahead in the forward or backward direction according to the position of the main transmission lever 12 and the vehicle speed. Also, assume that with the main transmission lever 12 operated to a position other than the neutral position, the steering handle 10 is being pivotally operated to a position other than the neutral position. In this case, the straight - travel HST 31 and the turning HST 32 are electrically or mechanically controlled so that the traveling machine body 1 turns left or right with a smaller turning radius as the amount of the pivotal operation is larger, and the vehicle speed (turning speed during forward or backward movement) of the traveling machine body 1 decreases as the turning radius becomes smaller. Also, regardless of whether the main transmission lever 12 is operated in the forward or backward direction, the turning HST 32 is electrically or mechanically controlled so that the direction of the pivotal operation of the steering handle 10 coincides with the turning direction of the traveling machine body 1. For example, the turning HST 32 is controlled so that when the steering handle 10 is turned to the right, the traveling machine body 1 turns right, and when the steering handle 10 is turned to the left, the traveling machine body 1 turns left. Also, when the main transmission lever 12 is at the neutral position, the turning HST 32 is electrically or mechanically controlled so that no turning function is exhibited even when the steering handle 10 is pivotally operated. Incidentally, when the main transmission lever 12 is at the neutral position, the turning HST 32 may be electrically or mechanically controlled so that a super - close turning (spin - in - place) is performed according to the pivotal operation of the operation handle 10.

[0025] The straight - travel HST 31 has a straight - travel pump 311 and a straight - travel motor 312. The turning HST 32 has a turning pump 321 and a turning motor 322. The first straight - travel shaft 311a, which is the pump shaft of the straight - travel pump 311, and the first turning shaft 321a, which is the pump shaft of the turning pump 321, are each gear - connected to the transmission input shaft 181 of the transmission 18. The power output from the output shaft 171 of the engine 17 is transmitted to the first straight - travel shaft 311a and the first turning shaft 321a via the pulley - belt transmission system 20 and the transmission input shaft 181.

[0026] In the straight travel HST 31, hydraulic oil is appropriately fed from the straight travel pump 311 toward the straight travel motor 312 by the power transmitted to the first straight travel shaft 311a. Similarly, in the swing HST 32, hydraulic oil is appropriately fed from the swing pump 321 toward the swing motor 322 by the power transmitted to the first swing shaft 321a. Note that a charge pump 30 for supplying hydraulic oil to the straight travel pump 311, the straight travel motor 312, the swing pump 321, and the swing motor 322 is attached to the first swing shaft 321a.

[0027] In the straight travel HST 31, the swash plate angle of the straight travel pump 311 is changed and adjusted electrically or mechanically according to the operation amount of the main transmission lever 12, whereby the discharge direction and discharge amount of the hydraulic oil to the straight travel motor 312 are changed. As a result, the rotation direction and rotation speed of the second straight travel shaft 312a, which is the motor shaft protruding from the straight travel motor 312, are arbitrarily adjusted.

[0028] Also, in the swing HST 32, the swash plate angle of the swing pump 321 is changed and adjusted electrically or mechanically according to the operation amount of the steering handle 10, whereby the discharge direction and discharge amount of the hydraulic oil to the swing motor 322 are changed. As a result, the rotation direction and rotation speed of the second swing shaft 322a, which is the motor shaft protruding from the swing motor 322, are arbitrarily adjusted. Note that in the present embodiment, as will be described in detail later, even when the steering handle 10 is not operated (in the neutral position), the swash plate angle of the swing pump 321 is adjusted in the swing HST 32, and the second swing shaft 322a, which is the motor shaft of the swing motor 322, may rotate to output power.

[0029] [2-2. Power transmission mechanism for straight travel] The straight-ahead power transmission mechanism 40 transmits the power output from the straight-ahead HST (first continuously variable transmission) 31 as straight-ahead power. As shown in FIG. 3, the rotational power of the second straight-ahead shaft 312a is input to the straight-ahead power transmission mechanism 40. The straight-ahead power transmission mechanism 40 transmits the input rotational power as straight-ahead power to an output adjustment mechanism 60, the details of which will be described later. As will be described below, the straight-ahead power transmission mechanism 40 is configured as a speed reduction mechanism including a plurality of rotating shafts to which gears are attached.

[0030] Specifically, the rotational power of the second straight-ahead shaft 312a is transmitted to the third straight-ahead shaft 41 via an assist power transmission mechanism 80, the details of which will be described later. The rotational power of the third straight-ahead shaft 41 is transmitted to a sub-shift gear mechanism 42. The sub-shift gear mechanism 42 includes a sub-shift low-speed gear 421 and a sub-shift high-speed gear 422 that are switched by a sub-shift shifter 43. The sub-shift shifter 43 is pivotally supported by a fourth straight-ahead shaft 44, which is a sub-shift output shaft located on the output side of the sub-shift gear mechanism 42. By operating the sub-shift lever 13 arranged in the operation control unit 9, the output rotational speed of the second straight-ahead shaft 312a, which is the motor shaft of the straight-ahead motor 312, can be selectively switched to one of two shift stages: low speed or high speed. The rotational power from the sub-shift gear mechanism 42 is transmitted from a sub-shift output gear 45 attached to the fourth straight-ahead shaft 44 to an output adjustment mechanism 60, which functions as a left and right differential mechanism, the details of which will be described later.

[0031] Note that the number of gear stages that can be switched by operating the sub-shift lever 13 is not limited to two, and the number can be changed as appropriate. Also, in this embodiment, the power transmitted to the third straight-ahead shaft 41 is transmitted to a PTO shaft 46 that is gear-connected to the third straight-ahead shaft 41. The rotational power of the PTO shaft 46 is transmitted to a cutting input shaft (not shown) that is inserted and supported in the cutting input case 16. Further, a parking brake 47, such as a drum type, is provided on the fourth straight-ahead shaft 44. Also, a straight-ahead pulsar 48 is provided on the fourth straight-ahead shaft 44. A first rotation sensor RS1 for detecting the rotational speed of the straight-ahead power is disposed opposite the outer peripheral side of the straight-ahead pulsar 48.

[0032] [2-3. Rotary power transmission mechanism] The swing power transmission mechanism 50 transmits the power output from the swing HST (second continuously variable transmission) 32 as swing power. As shown in FIG. 3, the rotational power of the second swing shaft 322a, which is the motor shaft of the swing motor 322, is input to the swing power transmission mechanism 50. The swing power transmission mechanism 50 transmits the input rotational power as swing power to an output adjustment mechanism 60, the details of which will be described later.

[0033] Specifically, the rotational power of the second swing shaft 322a is transmitted to the swing power transmission mechanism 50 via a first clutch 71 included in a switching mechanism 70, the details of which will be described later. Depending on the set state of the first clutch 71, the rotational power of the second swing shaft 322a may or may not be input to the swing power transmission mechanism 50.

[0034] The swing power transmission mechanism 50 includes a swing brake 51 such as a wet multi-plate type provided on the second swing shaft 322a, a third swing shaft 53 connected to the second swing shaft 322a via an upstream reduction gear 52, and a fourth swing shaft 55 connected to the third swing shaft 53 via a downstream reduction gear 54. The rotational power of the second swing shaft 322a is transmitted to the third swing shaft 53 via the upstream reduction gear 52. The rotational power of the third swing shaft 53 is transmitted to the fourth swing shaft 55 via the downstream reduction gear 54.

[0035] The rotational power of the fourth swing shaft 55 is transmitted to the output adjustment mechanism 60, the details of which will be described later, as reverse rotational power via a left intermediate gear 56 and a reverse gear 57 provided on the fourth swing shaft 55. Also, the rotational power of the fourth swing shaft 55 is transmitted to the output adjustment mechanism 60, the details of which will be described later, as forward rotational power via a right intermediate gear 58 provided on the fourth swing shaft 55.

[0036] In this embodiment, a swing pulsar 59 is provided on the third swing shaft 53. A second rotation sensor RS2 for detecting the rotational speed of the swing power is disposed opposite to the outer peripheral side of the swing pulsar 59.

[0037] [2-4. Output Adjustment Mechanism] The output adjustment mechanism 60 adjusts the straight-ahead power from the straight-ahead power transmission mechanism 40 and the turning power from the turning power transmission mechanism 50, and outputs the adjusted power to the traveling drive shaft 19. As described above, the output adjustment mechanism 60 functions as the left and right differential mechanisms. Specifically, the output adjustment mechanism 60 includes a pair of left and right planetary speed change mechanisms 60L and 60R.

[0038] The pair of left and right planetary speed change mechanisms 60L and 60R are arranged symmetrically with respect to the left and right. The left and right planetary speed change mechanisms 60L and 60R share a center gear 61 that meshes with the sub-speed change output gear 45 and a sun gear shaft 62 to which the center gear 61 is attached at an intermediate portion in the axial direction. Further, each of the pair of left and right planetary speed change mechanisms 60L and 60R includes a sun gear 63 attached to an axial end portion of the sun gear shaft 62, a plurality of planetary gears 64 that mesh with the sun gear 63, a ring gear 65 that meshes with the plurality of planetary gears 64, and a planetary carrier 66 that rotatably arranges the plurality of planetary gears 64 on the same circumference. The left and right planetary carriers 66 face each other at appropriate intervals on the same axis (the axis of the sun gear shaft 62 and the forced differential output shaft 67).

[0039] The left and right ring gears 65 are arranged concentrically with the sun gear shaft 62 in a state where the internal teeth on the inner peripheral surface mesh with the plurality of planetary gears 64. The external teeth on the outer peripheral surfaces of the left and right ring gears 65 are connected to the fourth turning shaft 55 via the left and right intermediate gears 56, 58 and the reverse gear 57. Each ring gear 65 is rotatably fitted onto the left and right forced differential output shafts 67 that project outward from the outer surface of the planetary carrier 66 to the left and right. The left and right traveling drive shafts (axles) 19 are connected to the left and right forced differential output shafts 67 via a final gear mechanism 68.

[0040] When the sub-speed change gear mechanism 42 is set to neutral, the power transmission from the straight-ahead motor 312 to the left and right planetary speed change mechanisms 60L and 60R is blocked. When the sub-speed change gear mechanism 42 is set to a gear position other than neutral, power is transmitted from the straight-ahead motor 312 to the left and right planetary speed change mechanisms 60L and 60R via the sub-speed change gear mechanism 42.

[0041] Assume that power is transmitted from the straight - ahead motor 312 to the left and right planetary speed - change mechanisms 60L and 60R, and there is no input of turning power from the turning power - transmission mechanism 50 to the left and right planetary speed - change mechanisms 60L and 60R. In this case, the rotational power transmitted from the auxiliary speed - change gear mechanism 42 that constitutes the straight - ahead power - transmission mechanism 40 to the left and right planetary speed - change mechanisms 60L and 60R is equally transmitted to the left and right forced differential output shafts 67. For this reason, rotational power in the same direction and at the same rotational speed is transmitted from the left and right traveling drive shafts 19 to the respective drive sprockets 22. As a result, the left and right traveling crawlers 2 are driven in the same direction and at the same rotational speed, and the traveling body 1 moves straight ahead (forward or backward).

[0042] On the other hand, when there is an input of turning power from the turning power - transmission mechanism 50 to the left and right planetary speed - change mechanisms 60L and 60R, the turning power is transmitted to the left and right ring gears 65. Then, the left and right ring gears 65 to which the turning power is transmitted rotate at the same rotational speed in opposite directions. That is, when the straight - ahead power from the straight - ahead motor 312 and the turning power from the turning motor 322 are input to the left and right planetary speed - change mechanisms 60L and 60R, different turning powers are input between the left and right planetary speed - change mechanisms 60L and 60R. For this reason, the adjustment results of the straight - ahead power and the turning power are different between the left and right planetary speed - change mechanisms 60L and 60R, and a difference occurs in the power transmitted between the left and right drive sprockets 22. According to the difference in the transmitted power between the left and right drive sprockets 22, the vehicle speed (traveling speed) and the traveling direction of the traveling body 1 are determined.

[0043] When a straight-ahead operation in the longitudinal direction is performed and the steering wheel 10 is in the neutral state, the turning brake 51 is engaged, and the power transmission from the turning power transmission mechanism 50 to the left and right planetary speed change mechanisms 60L and 60R is blocked. On the other hand, when the steering wheel 10 is in a state other than neutral, the turning brake 51 is disengaged, and the power transmission from the turning power transmission mechanism 50 to the left and right planetary speed change mechanisms 60L and 60R is enabled. Also, depending on the rotational direction of the steering wheel 10 from the neutral position, the rotational directions of the left and right ring gears 65 that rotate in opposite directions to each other change. And depending on the rotational direction of the steering wheel 10 from the neutral position, the traveling direction (turning direction) of the traveling body 1 is determined.

[0044] [2-5. Switching mechanism] The switching mechanism 70 switches the transmission destination of the power output from the turning HST (second continuously variable transmission) 32. The switching mechanism 70 switches the transmission destination of the power from the turning power transmission mechanism 50 to the assist power transmission mechanism 80. Also, the switching mechanism 70 switches the transmission destination of the power from the assist power transmission mechanism 80 to the turning power transmission mechanism 50. That is, the switching mechanism 70 switches the transmission destination of the power between the turning power transmission mechanism 50 and the assist power transmission mechanism 80.

[0045] Normally, the transmission destination of the power output from the turning HST 32 is the turning power transmission mechanism 50. Under specific situations described later, the transmission destination of the power output from the turning HST 32 is switched from the turning power transmission mechanism 50 to the assist power transmission mechanism 80 using the switching mechanism 70. Also, when the specific situations disappear, the transmission destination of the power output from the turning HST 32 is returned from the assist power transmission mechanism 80 to the turning power transmission mechanism 50 using the switching mechanism 70.

[0046] Specifically, the switching mechanism 70 includes a first clutch 71 and a second clutch 72. The first clutch 71 switches between a power transmission state (clutch ON) in which the power of the second turning shaft 322a is transmitted to the turning power transmission mechanism 50 and a cutoff state (clutch OFF) in which the power of the second turning shaft 322a is not transmitted to the turning power transmission mechanism 50. The second clutch 72 switches between a power transmission state (clutch ON) in which the power of the second turning shaft 322a is transmitted to the switching shaft 73 to which gears are connected and a cutoff state (clutch OFF) in which the power of the second turning shaft 322a is not transmitted to the switching shaft 73.

[0047] Normally, the first clutch 71 is in the "clutch ON" state and the second clutch 72 is in the "clutch OFF" state, and the power of the second turning shaft 322a is input to the turning power transmission mechanism 50. Normally, the power of the second turning shaft 322a is not transmitted to the switching shaft 73. Under specific circumstances, the first clutch 71 is in the "clutch OFF" state and the second clutch 72 is in the "clutch ON" state, and the power of the second turning shaft 322a is transmitted to the assist power transmission mechanism 80 via the switching shaft 73 and the switching gear 74 attached to the switching shaft 73. Under specific circumstances, the power of the second turning shaft 322a is not transmitted to the turning power transmission mechanism 50.

[0048] Note that the first clutch 71 and the second clutch 72 are, for example, electromagnetic clutches. However, the first clutch 71 and the second clutch 72 may be hydraulic or mechanical clutches.

[0049] [2-6. Assist Power Transmission Mechanism] The assist power transmission mechanism 80 assists the straight-ahead power. The assist power transmission mechanism 80 receives power from the turning HST 32 via the switching mechanism 70. Then, the assist power transmission mechanism 80 inputs the input power as assist power for assisting the straight-ahead power to the straight-ahead power transmission mechanism 40.

[0050] In this embodiment, the assist power transmission mechanism 80 is a planetary speed change mechanism. According to such a configuration, a mechanism for synthesizing the output of the turning HST 32 with the output of the straight-ahead power transmission mechanism 40 that transmits the output of the straight-ahead HST 31 can be configured compactly. Note that the assist power transmission mechanism is not limited to a planetary speed change mechanism, and may be any other mechanism as long as it can appropriately synthesize powers with a rotational difference without difficulty. The assist power transmission mechanism may be, for example, a configuration using a so-called differential gear.

[0051] Specifically, the assist power transmission mechanism 80 of this embodiment has a sun gear shaft 81 that is gear-connected to a second straight-ahead shaft 312a, which is the motor shaft of the straight-ahead motor 312. The assist power transmission mechanism 80 also has a sun gear 82 attached to the axial end of the sun gear shaft 81, a plurality of planetary gears 83 meshing with the sun gear 82, a ring gear 84 meshing with the plurality of planetary gears 83, and a planetary carrier 85 that rotatably arranges the plurality of planetary gears 83 on the same circumference.

[0052] The ring gear 84 is arranged concentrically with the sun gear shaft 81 in a state where the internal teeth on the inner peripheral surface mesh with the plurality of planetary gears 83. The external teeth on the outer peripheral surface of the ring gear 84 are connected to the switching gear 74. The ring gear 84 is rotatably fitted onto a third straight-ahead shaft 41 that protrudes from the outer surface of the planetary carrier 85.

[0053] The rotational power of the second straight-ahead shaft 312a, which is the motor shaft of the straight-ahead motor 312, is transmitted to the third straight-ahead shaft 41 via the gear-connected sun gear shaft 81. Here, it is assumed that the switching mechanism 70 is set so that the rotational power of the second turning shaft 322a, which is the motor shaft of the turning motor 322, is transmitted to the switching shaft 73. In this case, since the rotational power of the second turning shaft 322a is transmitted to the ring gear 84 connected to the switching gear 74, the power synthesized with the power input to the ring gear 84 with respect to the rotational power of the second straight-ahead shaft 312a is transmitted to the third straight-ahead shaft 41. By adjusting the rotational direction of the second turning shaft 322a, power that assists (boosts) the rotational power of the second straight-ahead shaft 312a can be transmitted to the third straight-ahead shaft 41.

[0054] In addition, when the switching mechanism 70 is set so that the rotational power of the second turning shaft 322a is not transmitted to the switching shaft 73, power is not input to the ring gear 84 connected to the switching gear 74. For this reason, only the rotational power of the second straight-ahead shaft 312a is transmitted to the third straight-ahead shaft 41.

[0055] As can be understood from the above description, in the transmission 18 of the present embodiment, normally, the output from the straight-ahead HST (first continuously variable transmission) 31 is transmitted to the straight-ahead power transmission mechanism 40, and the output from the turning HST (second continuously variable transmission) 32 is transmitted to the turning power transmission mechanism 50. For this reason, by adjusting the outputs of the straight-ahead HST 31 and the turning HST 32, the speed and traveling direction of the combine 100 can be determined.

[0056] On the other hand, when an abnormal state in which the output from the turning HST 32 is transmitted to the assist power transmission mechanism 80 is selected in the switching mechanism 70, the output from the turning HST 32 is not input to the turning power transmission mechanism 50, so the combine 100 does not turn. Then, the output from the turning HST 32 is combined with the output from the straight-ahead HST 31 via the assist power transmission mechanism 80 and transmitted as straight-ahead power. For this reason, the straight-ahead power can be made a high output. As a result, the running performance of the combine 100 during straight-ahead travel can be improved. For example, when the place where the combine 100 travels is muddy or on a slope, the running load becomes a high load, but even in such a place, the combine 100 can travel using the assist function of the straight-ahead power.

[0057] In the transmission 18 of the present embodiment, it is possible to increase the output of the straight-ahead performance without improving the continuously variable transmission itself, such as increasing the HST capacity. That is, according to the present embodiment, it is possible to realize a transmission that can cope with high loads while suppressing an increase in the capacity of the hydraulic drive means (HST).

[0058] In addition, in the present embodiment, as a preferred form, the assist power transmission mechanism 80 is configured to be provided on a rotation axis that is at least one upstream side from the rotation axis that is the most downstream in power transmission among the plurality of rotation axes included in the straight-ahead power transmission mechanism 40. Specifically, the assist power transmission mechanism 80 is provided on the third straight-ahead shaft 41 that exists on the upstream side from the fourth straight-ahead shaft 44. If the assist power transmission mechanism 80 is configured to be provided on the rotation axis on the upstream side as much as possible, the power transmitted by the assist power transmission mechanism 80 can be combined on the upstream side of the speed reduction mechanism as much as possible. As a result, the torque of the straight-ahead power on the traveling drive shaft 19 can be increased. Note that the assist power transmission mechanism 80 may be configured to be provided on, for example, the fourth straight-ahead shaft 44 or the sun gear shaft 62.

[0059] <3. Assist control of straight-ahead power> Next, control related to the assist of the straight-ahead power using the assist power transmission mechanism 80 (assist control of the straight-ahead power) will be described.

[0060] [3-1. Control system] FIG. 4 is a block diagram showing an outline of a control system that performs assist control of straight-ahead power. Note that the control system shown in FIG. 4 is included in the transmission 18. However, at least some elements of the control system shown in FIG. 4 may be regarded as a device separate from the transmission 18. In this case, the control system shown in FIG. 4 may be regarded as the control system of the combine (work vehicle) 100, or may be regarded as the control system of the traveling drive device including the transmission 18.

[0061] As shown in FIG. 4, the control system includes a controller 91, a storage device 92, a sensor 93, an inclined plate actuator 94, a first clutch 71, and a second clutch 72. As can be understood from this, the transmission 18 includes the controller 91 and the sensor 93.

[0062] The controller 91 includes an arithmetic circuit, a memory, and an input / output unit. The arithmetic circuit is, for example, a processor or a microprocessor. The memory may be the storage device 92, or may be a device separate from the storage device 92. The functions of the controller 91 are realized, for example, by the arithmetic circuit executing arithmetic processing according to a program stored in the memory or the like. The controller 91 is disposed at an appropriate position of the aircraft 1. The controller 91 may be disposed at a position away from the transmission case that constitutes the transmission 18.

[0063] Note that the controller 91 may be constituted by one piece of hardware, or may be constituted by a plurality of pieces of hardware capable of communicating with each other. The functions of the controller 91 may be realized by the arithmetic circuit executing arithmetic processing according to a program as described above, that is, by software, or may be realized by other methods. At least some of the functions of the controller 91 may be realized using, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or the like. That is, at least some of the functions of the controller 91 may be realized by hardware using a dedicated IC or the like. Also, at least some of the functions of the controller 91 may be realized by using software and hardware in combination.

[0064] In the present embodiment, as shown in FIG. 4, the controller 91 controls the operations of the first clutch 71 and the second clutch 72 described above. In other words, the controller 91 controls the switching mechanism 70. Also, the controller 91 controls the swash plate actuator 94. Details thereof will be described later.

[0065] The memory device 92 is a main memory device such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The memory device 92 may further include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). Various programs, data, etc. are stored in the memory device 92. The memory device 92 is arranged in the vicinity of the controller 91 although there is no intention of particular limitation.

[0066] The sensor 93 detects information enabling switching determination in the switching mechanism 70 and outputs it to the controller 91. By providing such a sensor 93, it becomes possible to automatically determine the timing of using the output from the turning HST (second continuously variable transmission) 32 for assisting the straight - ahead driving power.

[0067] In the present embodiment, the sensor 93 includes a pressure sensor 93a, a rotation sensor 93b, and a turning determination sensor 93c. Note that there is no intention that all of these three sensors 93a to 93c must necessarily be included in the sensor 93. For example, a configuration may be adopted in which at least one of the pressure sensor 93a and the rotation sensor 93b is included in the sensor 93.

[0068] Specifically, the pressure sensor 93a detects the hydraulic pressure in the straight - ahead HST (first continuously variable transmission) 31. The pressure sensor 93a is attached at an appropriate position of the straight - ahead HST 31. When the traveling load increases while the combine 100 is traveling straight, the hydraulic pressure of the straight - ahead HST 31 tends to increase. Therefore, by adopting a configuration in which the pressure sensor 93a is included in the sensor 93, the controller 91 can detect that the traveling load has increased. Then, when the traveling load increases, the controller 91 can perform the switching process of the switching mechanism 70 and transmit the output of the turning HST 32 to the assist power transmission mechanism 80. That is, when the traveling load increases, the assist of the straight - ahead driving power can be automatically performed.

[0069] The rotation sensor 93b detects the rotational speed of the rotation based on the power output from the straight travel HST (the first continuously variable transmission) 31. In the present embodiment, the rotation sensor 93b is provided in the straight travel power transmission mechanism 40. Specifically, the rotation sensor 93b is the first rotation sensor RS1 disposed on the outer peripheral side of the straight travel pulsar 48 provided on the fourth straight travel shaft 44 described above. However, the position where the rotation sensor 93b is provided may be other positions. The rotation sensor 93b may be configured to detect the rotational speed of a rotation shaft other than the fourth straight travel shaft 44 that constitutes the straight travel power transmission mechanism 40.

[0070] When the traveling load increases while the combine 100 is traveling straight, the rotational speed of the rotation based on the power output from the straight travel HST 31 tends to decrease. Therefore, by adopting a configuration in which the sensor 93 includes the rotation sensor 93b, the controller 91 can detect that the traveling load has increased. Then, when the traveling load increases, the controller 91 can perform the switching process of the switching mechanism 70 to transmit the output of the turning HST 32 to the assist power transmission mechanism 80. That is, when the traveling load increases, the assist of the straight travel power can be automatically performed.

[0071] As can be understood from the above description, both the pressure sensor 93a and the rotation sensor 93b are provided to detect an increase in the traveling load. Therefore, a configuration may be adopted in which only one of the pressure sensor 93a and the rotation sensor 93b is provided. However, if two sensors 93a and 93b are provided as in the present embodiment, the necessity of the assist of the power accompanying the increase in the traveling load can be more appropriately determined.

[0072] The turning determination sensor 93c can determine the operating state of the turning power transmission mechanism 50. In the present embodiment, the turning determination sensor 93c is a rotation sensor provided in the turning power transmission mechanism 50. Specifically, the rotation sensor is the second rotation sensor RS2 disposed on the outer peripheral side of the turning pulsar 59 provided on the third turning shaft 53 described above. However, the turning determination sensor 93c may be other than the second rotation sensor RS2. The turning determination sensor 93c only needs to be able to determine the operating state of the turning power transmission mechanism 50. For example, it may be a sensor that detects the movement of the turning operation unit (the steering handle 10 in the present embodiment).

[0073] By providing the turning determination sensor 93c, the controller 91 can determine whether the output of the turning HST 32 is used as turning power. Thereby, the controller 91 can transmit the output of the turning HST 32 to the assist power transmission mechanism 80 at a timing when the output of the turning HST 32 is not used as turning power. That is, it is possible to automatically and appropriately determine the timing for using the output of the turning HST 32 for assisting the straight-ahead power.

[0074] The swashplate actuator 94 is an actuator that operates the swashplate angle of the turning pump 321. The swashplate actuator 94 changes and adjusts the swashplate angle in accordance with an instruction from the controller 91. When the assist power transmission mechanism 80 assists the straight-ahead power, since the combine 100 is traveling straight, the steering handle 10 is in the neutral position. For this reason, the turning HST 32 does not perform an output according to the operation of the steering handle 10. The controller 91 controls the swashplate angle of the turning pump 321 to output power from the turning HST 32 at a timing (high load) when assistance for the straight-ahead power is required.

[0075] [3-2. Control Flow] FIG. 5 is a flowchart showing the control flow of the assist control for straight-ahead power. At the start of the flow shown in FIG. 5, the first clutch 71 is set to clutch ON, the second clutch 72 is set to clutch OFF, and the combine 100 is traveling straight. That is, at the start of the flow shown in FIG. 5, the combine 100 is traveling straight with the output of the turning HST 32 input to the turning power transmission mechanism 50 and not input to the assist power transmission mechanism 80.

[0076] In step S1, the controller 91 determines whether the running load is an overload. Whether the running load is an overload is determined based on information input from the pressure sensor 93a and the rotation sensor 93b (first rotation sensor RS1). When the pressure value detected by the pressure sensor 93a is equal to or greater than a preset pressure threshold and the rotational speed detected by the rotation sensor 93b is equal to or less than a preset rotational speed threshold, the controller 91 determines that it is an overload. Note that it may be determined to be an overload when at least one of the pressure value being equal to or greater than the pressure threshold and the rotational speed being equal to or less than the rotational speed threshold is satisfied. When it is determined to be an overload (Yes in step S1), the process proceeds to the next step S2. When it is not determined to be an overload (No in step S1), since assist for straight-ahead power is not required, the process proceeds to step S6. Note that the running load becomes an overload when the place where the combine 100 travels is muddy or on a slope.

[0077] In step S2, the controller 91 determines whether a turning operation is being performed. Whether a turning operation is being performed is determined based on information from the turning determination sensor 93c. In the present embodiment, when the rotational speed obtained from the second rotation sensor RS2, which is the turning determination sensor 93c, is zero, it is determined that no turning operation is being performed. When the rotational speed obtained from the second rotation sensor RS2 is not zero, it is determined that a turning operation is being performed. When no turning operation is being performed (No in step S2), the process proceeds to the next step S3. When a turning operation is being performed (Yes in step S2), since assist for straight-ahead power cannot be performed, the process proceeds to step S6.

[0078] In step S3, the controller 91 turns the first clutch 71 off and turns the second clutch 72 on. As a result, the output of the turning HST 32 is input to the assist power transmission mechanism 80 and is not input to the turning power transmission mechanism 50. When the process of step S3 is completed, the process proceeds to the next step S4.

[0079]

[0078] In step S4, the controller 91 controls the swash plate actuator 94 to drive the turning HST 32 (turning motor 322) in order to enable the assist of the straight-ahead power using the output from the turning HST 32. As a result, the output from the turning motor 322 is combined with the output from the straight-ahead motor 312 via the assist power transmission mechanism 80, and the assist of the straight-ahead power is performed. Note that the swash plate angle (adjusted by the swash plate actuator 94) that determines the magnitude of the power output from the turning HST 32 may be a constant angle regardless of the magnitude of the traveling load, or may be changed according to the traveling load. When the turning HST 32 is driven, the process proceeds to the next step S5.

[0080] In step S5, the controller 91 checks whether there is a control end cause such as the stop of the engine 17. If there is a control end cause (Yes in step S5), the control flow shown in FIG. 5 ends. Particularly, if there is no control end cause (No in step S5), the process returns to step S1, and the processes after step S1 are performed.

[0081] In step S6, the controller 91 turns on the first clutch 71 and turns off the second clutch 72. If the straight-ahead power assist using the assist power transmission mechanism 80 is not being performed, then in step S6, the current states of the first clutch 71 and the second clutch 72 will be maintained. On the other hand, if the straight-ahead power assist using the assist power transmission mechanism 80 was being performed, then in step S6, the current states of the first clutch 71 and the second clutch 72 will be changed. When the settings of the first clutch 71 and the second clutch 72 are completed, the process proceeds to step S5 described above, and the process of step S5 will be performed.

[0082] <4. Precautions, etc.> The various technical features disclosed in this specification can be variously modified without departing from the gist of the technical creation. Also, the plurality of embodiments and modification examples shown in this specification may be implemented in combination within the possible range.

[0083] <5. Supplementary Note> The exemplary transmission of the present invention is a transmission for a work vehicle that transmits the driving force of a drive source to a traveling drive shaft, and includes a first continuously variable transmission and a second continuously variable transmission to which the driving force is input, a straight-ahead power transmission mechanism that transmits the power output from the first continuously variable transmission as straight-ahead power, a turning power transmission mechanism that transmits the power output from the second continuously variable transmission as turning power, an output adjustment mechanism that adjusts the straight-ahead power and the turning power and outputs them to the traveling drive shaft, an assist power transmission mechanism that assists the straight-ahead power, and a switching mechanism that switches the transmission destination of the power output from the second continuously variable transmission from the turning power transmission mechanism to the assist power transmission mechanism (a first configuration).

[0084] In the transmission of the first configuration described above, the assist power transmission mechanism may be a planetary transmission mechanism (a second configuration).

[0085] In the transmission having the first or second configuration, the straight-ahead power transmission mechanism is configured as a speed reduction mechanism including a plurality of rotating shafts to which gears are attached, and the assist power transmission mechanism may be configured to be provided on a rotating shaft that is at least one upstream side from the rotating shaft that is the most downstream in power transmission among the plurality of rotating shafts (third configuration).

[0086] The transmission having any one of the first to third configurations may further include a controller that controls the switching mechanism, and a sensor that detects information enabling switching determination in the switching mechanism and outputs the information to the controller (fourth configuration).

[0087] In the transmission having the fourth configuration, the first continuously variable transmission is a hydraulic continuously variable transmission, and the sensor may include a pressure sensor that detects the hydraulic pressure in the first continuously variable transmission (fifth configuration).

[0088] In the transmission having the fourth or fifth configuration, the sensor may include a rotation sensor that detects the number of rotations of the rotation based on the power output from the first continuously variable transmission (sixth configuration).

[0089] In the transmission having any one of the fourth to sixth configurations, the sensor may include a turning determination sensor that enables determination of the operating state of the turning power transmission mechanism (seventh configuration).

[0090] An exemplary work vehicle of the present invention may include the drive source, a transmission having any one of the first to seventh configurations, and a traveling unit driven by the traveling drive shaft (eighth configuration).

Explanation of Reference Numerals

[0091] 2 ··· Traveling unit 17 ··· Engine (drive source) 18 ··· Transmission 19 ··· Traveling drive shaft 31 ··· First continuously variable transmission, straight travel HST 32 ··· Second continuously variable transmission, turning HST 40 ··· Power transmission mechanism for straight travel 50 ··· Power transmission mechanism for turning 60 ··· Output adjustment mechanism 70 ··· Switching mechanism 80 ··· Power transmission mechanism for assist 91 ··· Controller 93 ··· Sensor 93a ··· Pressure sensor 93b ··· Rotation sensor 93c ··· Turning determination sensor 100 ··· Work vehicle

Claims

1. A transmission for a work vehicle that transmits the driving force of a drive source to a traveling drive shaft, a first continuously variable transmission and a second continuously variable transmission to which the driving force is input, a straight-ahead power transmission mechanism that transmits the power output from the first continuously variable transmission as straight-ahead power, a turning power transmission mechanism that transmits the power output from the second continuously variable transmission as turning power, an output adjustment mechanism that adjusts the straight-ahead power and the turning power and outputs them to the traveling drive shaft, an assist power transmission mechanism that assists the straight-ahead power, a switching mechanism that switches the transmission destination of the power output from the second continuously variable transmission from the turning power transmission mechanism to the assist power transmission mechanism, A transmission comprising:

2. The transmission according to claim 1, wherein the assist power transmission mechanism is a planetary transmission mechanism.

3. The straight-ahead power transmission mechanism is configured as a speed reduction mechanism including a plurality of rotating shafts to which gears are attached, The transmission according to claim 2, wherein the assist power transmission mechanism is provided on a rotating shaft that is at least one upstream side from the rotating shaft that is the most downstream in power transmission among the plurality of rotating shafts.

4. A controller that controls the switching mechanism, A sensor that detects information enabling switching determination in the switching mechanism and outputs it to the controller, The transmission according to claim 1, further comprising:

5. The first continuously variable transmission is a hydraulic continuously variable transmission, The transmission according to claim 4, wherein the sensor includes a pressure sensor that detects the hydraulic pressure in the first continuously variable transmission.

6. The transmission according to claim 4, wherein the sensor includes a rotation sensor that detects the number of rotations of the rotation based on the power output from the first continuously variable transmission.

7. The transmission according to claim 4, wherein the sensor includes a turning determination sensor that enables determination of the operating state of the turning power transmission mechanism.

8. The drive source, The transmission according to any one of claims 1 to 7, A traveling unit driven by the traveling drive shaft, A work vehicle comprising:

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