Working machinery

Abstract

To provide a work machine that can improve operation stability.SOLUTION: After recognizing that a bulldozer 1 is transferred from a first running state to a stopping state, a controller 100 generates a double engagement state by engaging a velocity-stage clutch 23c in an opened state in the running state while maintaining an engagement state of a velocity-stage clutch 23d in an engagement state in the running state, and releases left and right service brakes 50L and 50R by supplying hydraulic pressure to the brakes.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This disclosure relates to a work machine.

Background Art

[0002] Conventionally, a work machine including a transmission having a plurality of clutches and left and right service brakes that brake left and right output shafts connected to left and right drive wheels is known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a method of engaging one or more clutches included in a transmission when shifting from a traveling state to a stop state by switching the transmission to a neutral state and operating the left and right service brakes. According to the method described in Patent Document 1, it is possible to suppress the work machine from slipping down when stopped on a slope.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in a work machine, from the viewpoint of safety, a negative-type brake that is released by supplying pressure oil is used as the left and right service brakes. Therefore, when shifting from a stop state to a traveling state, it is necessary to supply pressure oil to both the direction step clutch of the transmission and the left and right service brakes, resulting in competition for pressure oil and instability in the operation of the work machine.

[0006] An object of this disclosure is to provide a work machine capable of improving operation stability.

Means for Solving the Problems

[0007] A working machine relating to one aspect of this disclosure includes a forward and reverse directional clutch, a transmission having at least a first speed clutch and a second speed clutch, left and right output shafts rotated by power from the transmission, left and right service brakes that brake the rotation of the left and right output shafts, and a controller that controls the transmission and the left and right service brakes. The left and right service brakes are negative type brakes that are released by the supply of pressurized oil. The first speed clutch and the second speed clutch have a relationship in which, in the driving state, one is in an open state and the other is in an engaged state. After transitioning from the driving state to the stopped state, the controller maintains the engaged state of the one speed clutch that was in the engaged state in the driving state, and engages the other speed clutch that was in the open state in the driving state to create a double-engaged state, and also supplies hydraulic pressure to the left and right service brakes to release them. [Effects of the Invention]

[0008] The technology described herein can provide a work machine capable of improving operational stability. [Brief explanation of the drawing]

[0009] [Figure 1] This is a side view of a bulldozer according to an embodiment. [Figure 2] This is a schematic system configuration diagram of a bulldozer according to an embodiment. [Figure 3] This table shows the control details provided by the controller according to the embodiment. [Figure 4] This is a schematic system configuration diagram of a bulldozer related to Modification Example 1. [Modes for carrying out the invention]

[0010] (Exterior configuration of Bulldozer 1) Figure 1 is a side view of bulldozer 1, an example of a work machine.

[0011] As shown in Figure 1, the bulldozer 1 comprises a vehicle body 2, a working device 3, and a pair of left and right track devices 1A.

[0012] The vehicle body 2 comprises a cab 4, an engine compartment 5, and a vehicle frame (not shown). The cab 4 is located at the upper rear of the vehicle body 2. The engine compartment 5 is located in front of the cab 4.

[0013] The working device 3 is attached to the vehicle body 2. The working device 3 includes a blade 6, a frame 7, an angle cylinder 8, and a lifting cylinder 9. The blade 6 is an example of the “working device” according to this disclosure. The blade 6 is positioned in front of the vehicle body 2. The blade 6 is supported by the frame 7. The front end of the frame 7 is rotatably attached to the rear surface of the blade 6. The rear end of the frame 7 is rotatably supported on the side of the vehicle body 2.

[0014] The blade 6 is driven by an angle cylinder 8 and a lifting cylinder 9. The angle cylinder 8 and the lifting cylinder 9 are examples of "working machine cylinders" according to this disclosure.

[0015] The front end of the angle cylinder 8 is rotatably supported on the rear surface of the blade 6. The rear end of the angle cylinder 8 is rotatably supported on the side of the vehicle body 2. The blade 6 tilts in the front-rear direction as the angle cylinder 8 extends and retracts by hydraulic pressure.

[0016] The lower end of the lifting cylinder 9 is rotatably supported on the upper surface of the frame 7. The middle part of the lifting cylinder 9 is rotatably supported on the side of the vehicle body 2. The blade 6 moves vertically as the lifting cylinder 9 extends and retracts by hydraulic pressure.

[0017] The pair of left and right track units 1A are the running gear of the bulldozer 1. The pair of left and right track units 1A are positioned so as to sandwich the vehicle body 2.

[0018] Each of the left and right track systems 1A comprises a track 2A, a drive wheel (sprocket) 3A, a idler wheel (idler) 4A, and a track frame 5A.

[0019] The crawler 2A is configured in an annular ( endless ) shape and is wound around the drive wheel 3A and the idler wheel 4A. The crawler 2A is engaged with the drive wheel 3A and rotates by the rotational drive of the drive wheel 3A.

[0020] Each of the drive wheel 3A and the truck frame 5A is attached to the side portion of the vehicle body 2. The drive wheel 3A is arranged to be rotatably driven behind the truck frame 5A. The pair of left and right drive wheels 3A are supported by the left and right final reduction gears 70L, 70R described later. The idler wheel 4A is rotatably arranged at the front end of the truck frame 5A.

[0021] (Internal structure of the bulldozer 1) FIG. 2 is a schematic system configuration diagram of the bulldozer 1.

[0022] As shown in FIG. 2, the bulldozer 1 includes an engine 10, a torque converter 15, a transmission 20, a differential steering mechanism 30, left and right service brakes 50L, 50R, left and right output shafts 60L, 60R, left and right final reduction gears 70L, 70R, and a controller 100.

[0023] The engine 10 is a power source of the bulldozer 1. The torque converter 15 transmits the power of the engine 10 to the transmission 20 via a fluid.

[0024] [Transmission 20] The transmission 20 shifts the rotational motion transmitted from the torque converter 15. The transmission 20 according to the present embodiment is a planetary gear type transmission.

[0025] The transmission 20 includes a plurality of planetary gear mechanisms 21a to 21f, forward and reverse direction clutches 22 ( including a reverse clutch 22a and a forward clutch 22b ), a plurality of speed clutches 23a to 23d, an input shaft 24, and an output shaft 25.

[0026] The multiple planetary gear mechanisms 21a to 21f are arranged in this order from the input side to the output side.

[0027] The planetary gear mechanism 21a includes a sun gear 111, a plurality of planetary gears 112, a ring gear 113, and a carrier 114. The sun gear 111 is positioned radially outward from the input shaft 24. The sun gear 111 rotates about the input shaft 24. Each planetary gear 112 meshes with the sun gear 111. Each planetary gear 112 is positioned radially outward from the sun gear 111. Each planetary gear 112 is supported by the carrier 114. Each planetary gear 112 revolves around the sun gear 111 while rotating on its own axis. The ring gear 113 meshes with each planetary gear 112. The ring gear 113 is fixed to a carrier 124 (described later) and rotates integrally with the carrier 124. A reverse clutch 22a is connected to the carrier 114. The rotation of the carrier 114 is slowed by the engagement of the reverse clutch 22a.

[0028] The planetary gear mechanism 21b includes a sun gear 121, a plurality of planetary gears 122, a ring gear 123, and a carrier 124. The sun gear 121, planetary gears 122, and ring gear 123 have the same configuration as the sun gear 111, planetary gear 112, and ring gear 113 described above, respectively. Each planetary gear 122 is supported by the carrier 124. A forward clutch 22b is connected to the ring gear 123. The rotation of the ring gear 123 is braked by the engagement of the forward clutch 22b. The carrier 124 supports each planetary gear 122.

[0029] The planetary gear mechanism 21c includes a sun gear 131, a plurality of planetary gears 132, and a ring gear 133. The sun gear 131, planetary gears 132, and ring gear 133 have the same configuration as the sun gear 111, planetary gear 112, and ring gear 113 described above, respectively. The sun gear 131 is positioned radially outward from the output shaft 25. The sun gear 131 rotates around the output shaft 25. Each planetary gear 132 is supported by a carrier 124. The ring gear 133 is fixed to a carrier 144, which will be described later, and rotates integrally with the carrier 144. A speed stage clutch 23a is connected to the ring gear 133. The rotation of the ring gear 133 is braked by the engagement of the speed stage clutch 23a.

[0030] The planetary gear mechanism 21d includes a sun gear 141, a plurality of planetary gears 142, a ring gear 143, and a carrier 144. The sun gear 141, planetary gears 142, and ring gear 143 have the same configuration as the sun gear 131, planetary gears 132, and ring gear 133 described above, respectively. A speed stage clutch 23b is connected to the ring gear 143. The rotation of the ring gear 143 is braked by the engagement of the speed stage clutch 23b. The carrier 144 supports each planetary gear 142.

[0031] The planetary gear mechanism 21e includes a sun gear 151, a plurality of planetary gears 152, and a ring gear 153. The sun gear 151, planetary gears 152, and ring gear 153 have the same configuration as the sun gear 131, planetary gear 132, and ring gear 133 described above. Each planetary gear 152 is supported by a carrier 144. The ring gear 153 is fixed to a carrier 164, which will be described later, and rotates integrally with the carrier 164. A speed stage clutch 23c is connected to the ring gear 153. The rotation of the ring gear 153 is braked by the engagement of the speed stage clutch 23c.

[0032] The planetary gear mechanism 21f includes a sun gear 161, a plurality of planetary gears 162, a ring gear 163, and a carrier 164. The sun gear 161, planetary gears 162, and ring gear 163 have the same configuration as the sun gear 131, planetary gears 132, and ring gear 133 described above, respectively. A speed stage clutch 23d is connected to the ring gear 163. The rotation of the ring gear 163 is braked by the engagement of the speed stage clutch 23d. The carrier 164 supports each planetary gear 162.

[0033] The power from the engine 10 is input to the input shaft 24 via the torque converter 15. The power, whose rotational speed has been varied by multiple planetary gear mechanisms 21a to 21f, is output from the output shaft 25. The output shaft 25 is located coaxially with the input shaft 24.

[0034] Here, the reverse clutch 22a, the forward clutch 22b, and the multiple speed step clutches 23a to 23d are positive-type wet multi-plate hydraulic clutches that are engaged by the supply of pressurized oil. The engagement and disengagement of the reverse clutch 22a, the forward clutch 22b, and the multiple speed step clutches 23a to 23d are controlled by the controller 100. The forward and reverse (F, R) movement of the bulldozer 1 is switched by controlling the engagement and disengagement of the reverse clutch 22a and the forward clutch 22b. The speed steps (1ST, 2ND, 3RD, 4TH) of the bulldozer 1 are switched by controlling the engagement and disengagement of the multiple speed step clutches 23a to 23d. While the bulldozer 1 is running, one of the multiple speed step clutches 23a to 23d is engaged, and the remaining clutches are disengaged.

[0035] The output shaft 25 is connected to the differential steering mechanism 30 via a pinion 27 and a bevel gear 28. The power output from the transmission 20 is input to the differential steering mechanism 30 via the pinion 27 and the bevel gear 28.

[0036] [Differential steering mechanism 30] The differential steering mechanism 30 is positioned between the transmission 20 and the left and right output shafts 60L and 60R. The differential steering mechanism 30 includes an input shaft 30a, left and right planetary gear mechanisms 30L and 30R, left and right steering clutches 40L and 40R, a slewing motor 80, and a motor power transmission unit 90.

[0037] The left and right planetary gear mechanisms 30L and 30R each have left and right ring gears 31L and 31R, left and right planetary gears 32L and 32R, left and right sun gears 33L and 33R, and left and right carriers 34L and 34R.

[0038] The left and right ring gears 31L and 31R are connected to the input shaft 30a. The left and right planetary gears 32L and 32R are positioned inside the left and right ring gears 31L and 31R in the radial direction centered on the input shaft 30a. The left and right planetary gears 32L and 32R mesh with the left and right ring gears 31L and 31R and the left and right sun gears 33L and 33R. The left and right sun gears 33L and 33R are rotatably mounted relative to the input shaft 30a. The left and right sun gears 33L and 33R are positioned inside the left and right planetary gears 32L and 32R in the radial direction. The left and right sun gears 33L and 33R are connected to the left and right steering clutches 40L and 40R. The left and right carriers 34L and 34R, which support the left and right planetary gears 32L and 32R, are connected to the left and right output shafts 60L and 60R. The left and right service brakes 50L and 50R, which will be described later, are attached to the left and right carriers 34L and 34R.

[0039] The left and right steering clutches 40L and 40R are either positive-type wet multi-plate hydraulic clutches engaged by the supply of pressurized oil, or negative-type wet multi-plate hydraulic clutches released by the supply of pressurized oil. The left and right steering clutches 40L and 40R can engage and disengage with the left and right sun gears 33L and 33R. The engagement and disengagement of the left and right steering clutches 40L and 40R are controlled by the controller 100.

[0040] The left and right steering clutches 40L and 40R switch the transmission and interruption of rotational power from the input shaft 30a and the swing motor 80 to the left and right output shafts 60L and 60R via the left and right planetary gear mechanisms 30L and 30R.

[0041] Specifically, when the left steering clutch 40L is engaged, unless the sub-shaft 93 (details described later) is in a free-rotating state, the rotation of the input shaft 30a is transmitted to the left output shaft 60L via the left ring gear 31L, the left planetary gear 32L, and the left carrier 34L. On the other hand, when the left steering clutch 40L is released, the left sun gear 33L becomes free-rotating, and the transmission of rotational power from the input shaft 30a to the left output shaft 60L is interrupted. Similarly, the right steering clutch 40R switches the transmission and interruption of rotational power from the input shaft 30a to the right output shaft 60R depending on its engagement and disengagement.

[0042] Here, the left and right steering clutches 40L and 40R are connected to the left and right clutch gears 91L and 91R, and are rotatable with respect to the left and right clutch gears 91L and 91R around the input shaft 30a. The left and right clutch gears 91L and 91R rotate in opposite directions due to the rotational power from the swing motor 80 transmitted via the motor power transmission unit 90.

[0043] The slewing motor 80 is driven by the power of the engine 10. The slewing motor 80 rotates in either the forward or counter-rotation direction. The rotation direction and rotation speed of the slewing motor 80 are controlled by the controller 100. The slewing motor 80 may be a hydraulic motor or an electric motor.

[0044] The rotational power of the slewing motor 80 is transmitted to the left and right steering clutches 40L and 40R via the motor power transmission unit 90. When both the left and right steering clutches 40L and 40R are engaged, the slewing motor 80 rotates the left and right clutch gears 91L and 91R in opposite directions, thereby creating a difference in rotational speed between the left and right output shafts 60L and 60R. The motor power transmission unit 90 includes left and right clutch gears 91L and 91R, a first transfer gear 92, a sub-shaft 93, a second transfer gear 94, an idler gear 95, a pinion gear 96, and a differential lock brake 97.

[0045] The left and right clutch gears 91L and 91R can engage and disengage from the left and right sun gears 33L and 33R via the left and right steering clutches 40L and 40R. The left clutch gear 91L meshes with the idler gear 95. The right clutch gear 91R meshes with the first transfer gear 92. The first transfer gear 92 and the second transfer gear 94 are connected to each other by the sub-shaft 93. The second transfer gear 94 meshes with the idler gear 95. The rotation of the idler gear 95 is transmitted directly to the left clutch gear 91L and also to the right clutch gear 91R via the second transfer gear 94, the sub-shaft 93, and the first transfer gear 92. The left and right clutch gears 91L and 91R rotate in opposite directions due to the rotation transmitted from the idler gear 95.

[0046] The idler gear 95 meshes with the left clutch gear 91L, the second transfer gear 94, and the pinion gear 96, transmitting the rotation of the pinion gear 96 to the left clutch gear 91L and the second transfer gear 94. The pinion gear 96 is connected to the rotation axis 80a of the swing motor 80. The pinion gear 96 rotates around the rotation axis 80a.

[0047] The differential lock brake 97 is mounted on the rotating shaft 80a. The differential lock brake 97 is a positive-type wet multi-plate hydraulic clutch that is engaged by the supply of pressurized oil. The engagement and disengagement of the differential lock brake 97 are controlled by the controller 100. When the differential lock brake 97 is engaged, the rotating shaft 80a becomes immobile, and when the differential lock brake 97 is disengaged, the rotating shaft 80a becomes rotatable.

[0048] [Left and right service brakes 50L, 50R] The left and right service brakes 50L and 50R brake the rotation of the left and right output shafts 60L and 60R. The left and right service brakes 50L and 50R are negative-type wet multi-plate hydraulic brakes that are released by the supply of pressurized oil. The engagement and release of the left and right service brakes 50L and 50R are controlled by the controller 100. The left and right service brakes 50L and 50R are released when pressurized oil is supplied and engaged when pressurized oil is not supplied.

[0049] [Left and right output shafts: 60L, 60R] The left and right output shafts 60L and 60R are rotated by power from the transmission 20. The rotation of the left and right output shafts 60L and 60R is braked when the left and right service brakes 50L and 50R are engaged, and unbraked when the left and right service brakes 50L and 50R are released.

[0050] [Left and right final deceleration units 70L, 70R] The left and right final reduction gears 70L and 70R are mounted on the left and right output shafts 60L and 60R. Drive wheels 3A are mounted on each of the left and right final reduction gears 70L and 70R.

[0051] [Controller 100] The controller 100 controls the engine 10 and the transmission 20 to operate the bulldozer 1. The controller 100 controls the transmission 20 and the left and right service brakes 50L and 50R to stop the bulldozer 1.

[0052] The controller 100 controls the left and right steering clutches 40L and 40R, the left and right service brakes 50L and 50R, and the swing motor 80 in order to make the bulldozer 1 turn while it is in motion.

[0053] In this disclosure, turning is a form of driving state. Turning is a concept that includes slow turning, pivot turning, and super-pivot turning. Slow turning means that the bulldozer 1 turns left or right by rotating the left and right track units 1A at different rotational speeds. Pivot turning means that the bulldozer 1 turns around a predetermined turning center by stopping one of the left and right track units 1A and rotating the other. Super-pivot turning means that the bulldozer 1 turns in place by rotating the left and right track units 1A in opposite directions at the same rotational speed.

[0054] In a gentle turn, both the left and right steering clutches 40L and 40R are engaged, the slewing motor 80 rotates the left and right output shafts 60L and 60R in the same direction but at different speeds, and both the left and right service brakes 50L and 50R are released. In a pivot turn, only the steering clutch opposite to the turning side of the left and right steering clutches 40L and 40R is engaged, the slewing motor 80 rotates only the output shaft opposite to the turning side of the left and right output shafts 60L and 60R, and only the service brake on the turning side of the left and right service brakes 50L and 50R is engaged. In a super pivot turn, both the left and right steering clutches 40L and 40R are engaged, the slewing motor 80 rotates the left and right output shafts 60L and 60R in different directions but at the same speed, and both the left and right service brakes 50L and 50R are released.

[0055] Figure 3 is a table showing the control performed by the controller 100 when the bulldozer 1 transitions from the first driving state to the stopped state, and then from the stopped state to the second driving state. In Figure 3, the first and second driving states are assumed to be states in which the bulldozer moves forward without steering operation at the 1ST speed. That is, in Figure 3, the state is assumed to be when the bulldozer moves straight in first gear, stops, and then moves straight again in first gear.

[0056] In the first and second driving states, the forward clutch 22b and the speed gear clutch 23d are engaged, while the reverse clutch 22a, speed gear clutches 23a to 23c, the left and right service brakes 50L and 50R, and the differential lock brake 97 are released.

[0057] The stopped state is when the speed gear clutch 23d is engaged, and the forward clutch 22b, speed gear clutches 23a to 23c, and differential lock brake 97 are released.

[0058] Here, after the controller 100 recognizes that the bulldozer 1 has transitioned from the first driving state to the stopped state, it engages the speed clutch 23c and the differential lock brake 97, and supplies hydraulic pressure to the left and right service brakes 50L and 50R to release them.

[0059] In this way, by maintaining the engaged state of the speed stage clutch 23d, which was engaged in the driving state, and engaging the speed stage clutch 23c, which was disengaged in the driving state, a double engagement state is created by the speed stage clutch 23c and speed stage clutch 23d. As a result, the bulldozer 1 can be kept in a stopped state even when the left and right service brakes 50L and 50R are released. In particular, when the bulldozer 1 is stopped on a slope, there is a risk that the bulldozer 1 will slide down if only the speed stage clutch 23d is engaged, but by double-engaging the speed stage clutch 23c and speed stage clutch 23d, the sliding of the bulldozer 1 can be suppressed. In addition, since the left and right service brakes 50L and 50R are released before transitioning from the stopped state to the second driving state, there is no need to supply pressurized oil to the left and right service brakes 50L and 50R when transitioning from the stopped state to the second driving state. Therefore, since pressurized oil only needs to be supplied to the forward clutch 22b, there is no competition for pressurized oil between the forward clutch 22b and the left and right service brakes 50L and 50R. As a result, it is possible to suppress the instability of the bulldozer 1's operation when transitioning from a stopped state to a second travel state.

[0060] The above effects are particularly effective when the second travel state is a pivot turn, that is, when transitioning from a stationary state to a pivot turn. Specifically, by suppressing the downward sliding of the bulldozer 1 in the stationary state, it is possible to transition from a stationary state to a stable pivot turn. In addition, since it is not necessary to supply pressurized oil to the left and right service brakes 50L and 50R when transitioning to a pivot turn, it is possible to quickly transition to a pivot turn in response to the operator's operation.

[0061] Furthermore, by engaging the differential lock brake 97, the left and right output shafts 60L and 60R become immobile. Therefore, even if an unbalanced load is applied to the left and right track devices 1A, the differential action of the differential steering mechanism 30 can prevent the bulldozer 1 from rotating.

[0062] In the above-described embodiment, a differential lock brake 97 was mentioned, but the differential lock brake 97 is not necessarily required. If the differential action of the differential mechanism 30 can be stopped by the rotational resistance of the slewing motor 80 alone when the slewing motor 80 is not rotating (i.e., if the differential action can be stopped by the braking force of the slewing motor 80 alone), then the differential lock brake 97 is unnecessary.

[0063] Furthermore, although the above-described embodiment has left and right steering clutches 40L and 40R, left and right steering clutches 40L and 40R are not necessarily required.

[0064] (Modified version of the embodiment) The present invention is not limited to the embodiments described above, and various modifications or alterations are possible without departing from the scope of the present invention.

[0065] (Variation 1) In the above embodiment, the bulldozer 1 is provided with a differential steering mechanism 30, but it is not necessary to provide a differential steering mechanism 30.

[0066] For example, as shown in Figure 4, the bulldozer 1a may be equipped with an input shaft 30b, left and right steering clutches 41L, 41R, and left and right carriers 42L, 42R.

[0067] The left and right steering clutches 41L and 41R are connected to both ends of the input shaft 30b. The left and right steering clutches 41L and 41R are positive-type wet multi-plate hydraulic clutches that are engaged by the supply of pressurized oil, or negative-type wet multi-plate hydraulic clutches that are released by the supply of pressurized oil. The left and right clutch drums 42L and 42R connect the left and right steering clutches 41L and 41R to the left and right output shafts 60L and 60R. The left and right service brakes 50L and 50R are attached to the left and right clutch drums 42L and 42R. As described in the above embodiment, the left and right service brakes 50L and 50R are negative-type wet multi-plate hydraulic brakes.

[0068] Thus, even in a bulldozer 1a that does not have a differential steering mechanism 30, by controlling the various clutches and service brakes 50L and 50R as explained in Figure 3, it is possible to suppress the instability of the bulldozer 1's operation when transitioning from a stopped state to a second driving state.

[0069] (Modification 2) In the above embodiment, the differential steering mechanism 30 includes left and right planetary gear mechanisms 30L and 30R, but it does not need to include left and right planetary gear mechanisms 30L and 30R.

[0070] (Variation 3) In the above embodiment, the controller 100 prevents the left and right output shafts 60L and 60R from rotating by engaging the differential lock brake 97, but the method of preventing the left and right output shafts 60L and 60R from rotating is not limited to this. For example, the left and right output shafts 60L and 60R may be prevented from rotating by mechanically fixing the idler gear 95 or the pinion gear 96.

[0071] (Modification 4) In the above embodiment, the controller 100 is configured to double-engage the speed step clutch 23c and the speed step clutch 23d, but the combination of clutches to be double-engaged is not limited to this. After transitioning from a driving state to a stopped state, the controller 100 may double-engage a speed step clutch that is engaged in the driving state and a speed step clutch that is disengaged in the driving state from among the multiple speed step clutches. The speed step clutch that is engaged in the driving state is the "first speed step clutch" according to this disclosure, and the speed step clutch that is disengaged in the driving state is the "second speed step clutch" according to this disclosure. The first speed step clutch and the second speed step clutch have a relationship in which, in the driving state, one is disengaged and the other is engaged.

[0072] (Variation 5) In the above embodiment, the transmission 20 has speed step clutches 23a to 23d, but is not limited thereto. The transmission 20 only needs to have at least two speed step clutches. For example, if the transmission 20 has two speed step clutches, one of the speed step clutches that is engaged in the driving state is the "first speed step clutch" according to this disclosure, and the other speed step clutch that is disengaged in the driving state is the "second speed step clutch" according to this disclosure.

[0073] (Experimental variation 6) In the above embodiment, the controller 100 engages the differential lock brake 97 after the bulldozer 1 transitions from a driving state to a stopped state; however, the differential lock brake 97 may be engaged simultaneously with the transition from a driving state to a stopped state. [Explanation of symbols]

[0074] 1,1a,1b Bulldozer 10 Engines 20 Transmission 22 Directional clutch 23a~23d Speed ​​Clutch 30 Differential steering mechanism 40L, 40R left and right steering clutches 50L, 50R Left and Right Service Brakes 60L, 60R left and right output shafts 80,81 Swivel motor 100 controllers

Claims

1. A transmission having forward and reverse directional clutches, and at least a first speed clutch and a second speed clutch, The left and right output shafts rotate by power from the aforementioned transmission, The service brakes on the left and right sides brake the rotation of the aforementioned left and right output shafts, A controller that controls the transmission and the left and right service brakes, Equipped with, The aforementioned left and right service brakes are negative-type brakes that are released by the supply of pressurized oil. The first speed gear clutch and the second speed gear clutch are in a relationship such that, in the driving state, one is in an open state and the other is in an engaged state. The controller, after transitioning from a driving state to a stopped state, maintains the engaged state of one of the speed gear clutches that was engaged in the driving state, while engaging the other speed gear clutch that was disengaged in the driving state to create a double-engaged state, and also supplies hydraulic pressure to the left and right service brakes to release them. Agricultural machinery.

2. The transmission is equipped with a differential steering mechanism positioned between the left and right output shafts, The controller disables the rotation of the left and right output shafts simultaneously with or after the transition from the driving state to the stopped state. The work machine according to claim 1.

3. The differential steering mechanism is, Input axis and, A planetary gear mechanism is positioned between the input shaft and the left and right output shafts, Left and right steering clutches that switch the transmission and interruption of rotational power from the input shaft to the left and right output shafts via the left and right planetary gear mechanisms, A slewing motor that generates a difference in rotational speed between the left and right output shafts by causing the left and right steering clutches to rotate in opposite directions, It has, When the controller transitions from the driving state to the stopped state, it prevents the left and right output shafts from rotating by fixing the output shaft of the swing motor. The working machine according to claim 2.

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