Track-type work machine

Abstract

To provide a crawler type working machine capable of inhibiting power loss of an engine being turning slowly.SOLUTION: When an operation amount of a steering lever 35 is larger than a first predetermined amount TH1 and smaller than a second predetermined amount TH2, a bulldozer 1 causes right and left steering clutches 40L and 40R to engage with each other, releases right and left steering brakes 50L and 50R, and causes a swivel motor 80 to drive so that a rotation speed of an inner output shaft 60IN becomes further lower than a rotation speed of an outer output shaft 60OUT as the operation amount of the steering lever 35 increases. When the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2, a controller 100 reduces an engagement rate of an inner steering clutch 40IN and causes an inner steering brake 50IN to perform braking operation.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a crawler-type work machine.

Background Art

[0002] Conventionally, a crawler-type work machine (for example, a bulldozer) including an input shaft that rotates by the power of an engine, left and right steering clutches that transmit or cut off rotational power from the input shaft to the left and right output shafts, and left and right steering brakes that brake the left and right output shafts is known (see, for example, Patent Document 1).

[0003] In the crawler-type work machine described in Patent Document 1, when the steering lever is operated in either the left or right direction during traveling, the steering clutch corresponding to the operation direction is released, and the steering brake corresponding to the operation direction is semi-braked to perform a slow turn.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the crawler-type work machine described in Patent Document 1, since a slow turn is executed using the braking force of the steering brake, power loss of the engine occurs.

[0006] An object of the present disclosure is to provide a crawler-type work machine capable of suppressing power loss of the engine during a slow turn.

Means for Solving the Problems

[0007] The crawler-type work machine according to one aspect of the present disclosure includes left and right planetary gear mechanisms, left and right steering clutches, left and right steering brakes, a swing motor, a steering lever, and a controller. The left and right planetary gear mechanisms are disposed between an input shaft and left and right output shafts. The left and right steering clutches are rotatable about the input shaft, and switch between transmission and interruption of rotational power from the input shaft to the left and right output shafts by the left and right planetary gear mechanisms. The left and right steering brakes brake the left and right output shafts. The swing motor rotates the left and right steering clutches so that a rotational speed difference occurs between the left and right output shafts. The steering lever is operable in a left turn direction and a right turn direction with reference to a neutral position. The controller controls the left and right steering clutches, the left and right steering brakes, and the swing motor according to the operation direction and operation amount of the steering lever. When the operation amount is greater than a first predetermined amount and less than a second predetermined amount, the controller engages the left and right steering clutches, releases the left and right steering brakes, and drives the swing motor so that the rotational speed of the inner output shaft corresponding to the operation direction among the left and right output shafts becomes lower than the rotational speed of the outer output shaft opposite to the operation direction as the operation amount increases. When the operation amount is equal to or greater than the second predetermined amount, the controller decreases the engagement rate of the inner steering clutch corresponding to the operation direction among the left and right steering clutches, and brakes the inner steering brake corresponding to the operation direction among the left and right steering brakes.

Advantages of the Invention

[0008] According to the technology of the present disclosure, it is possible to provide a crawler-type work machine capable of suppressing power loss of the engine during slow turning.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0010] (Configuration of Bulldozer 1) FIG. 1 is a perspective view of a bulldozer 1 which is an example of a crawler-type working machine. FIG. 2 is a cross-sectional configuration diagram of the power transmission system of the bulldozer 1. FIG. 3 is a schematic system configuration diagram of the power transmission system of the bulldozer 1.

[0011] As shown in FIG. 1, the bulldozer 1 includes left and right traveling devices 4L, 4R including left and right sprockets 2L, 2R and left and right crawlers 3L, 3R, a blade 5 provided at the front of the vehicle, and a ripper device 6 provided at the rear of the vehicle.

[0012] The bulldozer 1 can perform operations such as pushing soil with the blade 5 and operations such as crushing and excavation with the ripper device 6.

[0013] As shown in FIGS. 2 and 3, the bulldozer 1 has an engine 10, an engine power transmission unit 20, left and right planetary gear mechanisms 30L, 30R, left and right steering clutches 40L, 40R, left and right steering brakes 50L, 50R, left and right output shafts 60L, 60R, a turning motor 80, a motor power transmission unit 90, and a controller 100.

[0014] [Engine Power Transmission Unit] The engine power transmission unit 20 transmits the power from the engine 10 to the left and right planetary gear mechanisms 30L, 30R. The engine power transmission unit 20 includes a power take-off 21, a torque converter 22, a transmission 23, a pinion 24, a bevel gear 25, and an input shaft 26.

[0015] The power take-off device 21 transmits the power from the engine 10 to the torque converter 22. The torque converter 22 transmits the power of the engine 10 transmitted from the power take-off device 21 to the transmission 23 via a fluid. The transmission 23 has a plurality of speed-stage clutches for shifting the rotational power transmitted from the torque converter 22 and a direction-stage clutch for switching between forward and reverse. The transmission 23 is connected to the pinion 24. The power from the transmission 23 is transmitted to the input shaft 26 via the pinion 24 and the bevel gear 25. The input shaft 26 extends in the left-right direction. The axial direction of the input shaft 26 is synonymous with the left-right direction of the bulldozer 1.

[0016] [Planetary gear mechanism] The left and right planetary gear mechanisms 30L and 30R are arranged between the input shaft 26 and the left and right output shafts 60L and 60R. The left and right planetary gear mechanisms 30L and 30R 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.

[0017] The left and right ring gears 31L and 31R are connected to the input shaft 26. The left and right planetary gears 32L and 32R are arranged inside the left and right ring gears 31L and 31R in the radial direction perpendicular to the axial direction of the input shaft 26. 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 attached to the input shaft 26. The left and right sun gears 33L and 33R are arranged 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 sun gears 33L and 33R can be disengaged from and engaged with the motor power transmission unit 90 (specifically, the left and right clutch gears 91L and 91R described later) via the left and right steering clutches 40L and 40R. The left and right carriers 34L and 34R are connected to the left and right planetary gears 32L and 32R and the left and right output shafts 60L and 60R.

[0018] [Steering Clutch] The left and right steering clutches 40L and 40R are arranged between the left and right planetary gear mechanisms 30L and 30R and the motor power transmission unit 90. The left and right steering clutches 40L and 40R disengage and engage the left and right sun gears 33L and 33R of the left and right planetary gear mechanisms 30L and 30R and the left and right clutch gears 91L and 91R of the motor power transmission unit 90.

[0019] The left and right steering clutches 40L and 40R are driven by the supply of hydraulic oil. The left and right steering clutches 40L and 40R are constituted by wet multi-plate clutches that can be engaged and disengaged. In the present embodiment, the left and right steering clutches 40L and 40R are positive type hydraulic clutches. The left and right steering clutches 40L and 40R are disengaged when no hydraulic oil is supplied, partially engaged when the hydraulic pressure of the supplied hydraulic oil is less than a predetermined value, and fully engaged when the hydraulic pressure of the supplied hydraulic oil is equal to or greater than the predetermined value.

[0020] The hydraulic pressure of the hydraulic oil supplied to the left and right steering clutches 40L and 40R is controlled by the left and right clutch control valves 27L and 27R. The engagement ratio of the left and right steering clutches 40L and 40R varies from 0% to 100% (maximum value) according to the hydraulic pressure of the supplied hydraulic oil.

[0021] The left and right steering clutches 40L and 40R switch the transmission and interruption of the rotational power from the input shaft 26 by the left and right planetary gear mechanisms 30L and 30R to the left and right output shafts 60L and 60R.

[0022] Specifically, when the left steering clutch 40L is engaged, the rotation of the input shaft 26 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 is in a free rotation state, and the transmission of rotational power from the input shaft 26 to the left output shaft 60L is blocked. Similarly, the right steering clutch 40R switches the transmission and interruption of rotational power from the input shaft 26 to the right output shaft 60R according to its engagement and release.

[0023] Here, the left and right steering clutches 40L and 40R are rotatable about the input shaft 26. The left and right steering clutches 40L and 40R rotate in opposite directions to each other by the rotational power from the turning motor 80 transmitted via the motor power transmission unit 90.

[0024] For example, when the left and right steering clutches 40L and 40R are engaged, if the left steering clutch 40L rotates clockwise while the right steering clutch 40R rotates counterclockwise, the rotational speed of the left output shaft 60L becomes higher than that of the right output shaft 60R, and the bulldozer 1 makes a gentle right turn.

[0025] In this specification, a gentle turn means moving forward or backward in an arc with a relatively large turning radius by creating a rotational speed difference between the left and right output shafts 60L and 60R that rotate in the same direction.

[0026] Also, when the left steering clutch 40L is engaged and the right steering clutch 40R is released, if the left steering clutch 40L rotates clockwise, the rotation of the right output shaft 60R stops and the left output shaft 60L rotates, causing the bulldozer 1 to make a sharp right turn. However, when the bulldozer 1 makes a sharp right turn, as will be described later, the right steering brake 50R brakes the right output shaft 60R.

[0027] In this specification, "sharp turn" is a concept that includes true skid steering and quasi-true skid steering. True skid steering means turning around one of the crawlers on the other side while completely stopping the other crawler by rotating one of the left and right output shafts 60L and 60R and completely stopping the other. Quasi-true skid steering means turning while substantially stopping the crawler on the other side by rotating one of the left and right output shafts 60L and 60R while slightly allowing the rotation of the other.

[0028] As shown in FIG. 2, the right steering clutch 40R has a plurality of clutch plates 41, a plurality of clutch disks 42, and a clutch piston 43.

[0029] Each clutch plate 41 is attached to the right clutch gear 91R. Each clutch disk 42 is fixed to the right sun gear 33R. Each clutch plate 41 and each clutch disk 42 are alternately arranged in the axial direction.

[0030] When the clutch piston 43 moves leftward with the supply of hydraulic oil, each clutch plate 41 and each clutch disk 42 are pressed into contact with each other, and the right steering clutch 40R is engaged. As a result, the right sun gear 33R of the right planetary gear mechanism 30R and the right clutch gear 91R of the motor power transmission unit 90 are joined.

[0031] On the other hand, when the clutch piston 43 moves rightward with the discharge of hydraulic oil, each clutch plate 41 and each clutch disk 42 are separated, and the right steering clutch 40R is released. As a result, the right sun gear 33R of the right planetary gear mechanism 30R and the right clutch gear 91R of the motor power transmission unit 90 are separated.

[0032] Note that the left steering clutch 40L has the same configuration as the right steering clutch 40R.

[0033] [Steering Brake] The left and right steering brakes 50L and 50R are driven by the supply of hydraulic oil. The left and right steering brakes 50L and 50R are constituted by wet multi-plate clutches that can be engaged and disengaged. In the present embodiment, the left and right steering brakes 50L and 50R are negative-type hydraulic brakes. The left and right steering brakes 50L and 50R are fully engaged when no hydraulic oil is supplied, partially engaged when the hydraulic pressure of the supplied hydraulic oil is less than a predetermined value, and disengaged when the hydraulic pressure of the supplied hydraulic oil is equal to or greater than the predetermined value. When the left and right steering brakes 50L and 50R are engaged (fully engaged or partially engaged), braking force is generated in the left and right steering brakes 50L and 50R.

[0034] The hydraulic pressure of the hydraulic oil supplied to the left and right steering brakes 50L and 50R is controlled by the left and right brake control valves 28L and 28R. When the left and right steering brakes 50L and 50R are engaged (fully engaged or partially engaged), braking force is generated in the left and right steering brakes 50L and 50R. The braking force of the left and right steering brakes 50L and 50R varies from 0% to 100% (maximum value) according to the hydraulic pressure of the supplied hydraulic oil.

[0035] The left and right steering brakes 50L and 50R brake the rotation of the left and right output shafts 60L and 60R.

[0036] Specifically, when the left steering brake 50L is engaged, the rotation of the left output shaft 60L is braked, whereby the rotation of the left sprocket 2L is reduced. On the other hand, when the right steering brake 50R is engaged, the rotation of the right output shaft 60R is braked, whereby the rotation of the right sprocket 2R is reduced.

[0037] As shown in FIG. 2, the right steering brake 50R has a rotating member 51, a brake housing 52, a plurality of fixed plates 53, a plurality of brake disks 54, and a brake piston 55.

[0038] The rotating member 51 is fixed to the right output shaft 60L and rotates together with the right output shaft 60R. The brake housing 52 is fixed to the rotating member 51. Each fixing plate 53 is attached to the brake housing 52. Each brake disk 54 is fixed to the rotating member 51. Each fixing plate 53 and each brake disk 54 are alternately arranged in the axial direction.

[0039] When the brake piston 55 moves leftward as the hydraulic oil is filled, each fixing plate 53 and each brake disk 54 separate from each other, and the right steering brake 50R is released. On the other hand, when the brake piston 55 moves rightward as the hydraulic oil is discharged, each fixing plate 53 and each brake disk 54 are pressed against each other, and a braking force is generated on the right steering brake 50R.

[0040] Note that the left steering brake 50L has the same configuration as the right steering brake 50R.

[0041] [Slewing motor] The slewing motor 80 is driven by the power of the engine 10. The slewing motor 80 rotates in either the forward rotation direction or the reverse rotation direction. The rotation direction and the rotation speed of the slewing motor 80 are controlled by the controller 100. The rotation speed of the slewing motor 80 changes from 0% to 100% (maximum value) according to the power transmitted from the engine 10.

[0042] 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. The slewing motor 80 rotates the left and right steering clutches 40L and 40R so that a rotational speed difference occurs between the left and right output shafts 60L and 60R. For example, when the bulldozer 1 gently slews to the right, if the slewing motor 80 rotates the left and right steering clutches 40L and 40R in the reverse direction, the rotational speed of the left output shaft 60L becomes higher than that of the right output shaft 60R. Also, when the bulldozer 1 makes a powered turn to the right, the slewing motor 80 rotates the left and right steering clutches 40L and 40R in the reverse direction, but the right steering clutch 40R is released and the right steering brake 50R is braked, so the right output shaft 60R does not rotate and only the left output shaft 60L rotates.

[0043] [Motor power transmission unit] The motor power transmission unit 90 is disposed between the slewing motor 80 and the left and right steering clutches 40L and 40R. The motor power transmission unit 90 transmits the rotational power of the slewing motor 80 to the left and right steering clutches 40L and 40R.

[0044] The motor power transmission unit 90 includes left and right clutch gears 91L and 91R, a first transfer gear 92, a countershaft 93, a second transfer gear 94, an idler gear 95, and a pinion gear 96.

[0045] The left and right clutch gears 91L and 91R can be engaged with and disengaged from the left and right sun gears 33L and 33R via the left and right steering clutches 40L and 40R. The left and right clutch gears 91L and 91R are rotatable about the axial direction of the input shaft 26. The left clutch gear 91L meshes with the idler gear 95. The right clutch gear 91R is connected to the idler gear 95 via the first transfer gear 92, the countershaft 93, and the second transfer gear 94. When the slewing motor 80 rotates, the left and right clutch gears 91L and 91R rotate in opposite directions to each other.

[0046] The idler gear 95 meshes with the left clutch gear 91L, the second transfer gear 94, and the pinion gear 96. The idler gear 95 is rotatable about the axial direction of the input shaft 26.

[0047] The pinion gear 96 meshes with the idler gear 95. The pinion gear 96 is rotatable about the pinion shaft 96a. The pinion gear 96 rotates by the rotational power of the turning motor 80 transmitted via the pinion shaft 96a.

[0048] [Controller] The controller 100 is connected to the steering lever 35 used for the steering operation of the bulldozer 1. The steering lever 35 is operable in the left turning direction P2 and the right turning direction P3 respectively with respect to the neutral position P1. The operator can turn the bulldozer 1 gently and sharply (semi-precision turning and precision turning) left and right by adjusting the operation direction and operation amount of the steering lever 35.

[0049] The controller 100 controls the rotational speed of the engine 10 and the speed-stage clutch and direction-stage clutch of the transmission 23 in order to drive the bulldozer 1.

[0050] During the running of the bulldozer 1, the controller 100 controls the left and right steering clutches 40L, 40R, the left and right steering brakes 50L, 50R, and the turning motor 80 according to the operation direction and operation amount of the steering lever 35 in order to turn the bulldozer 1.

[0051] The controller 100 switches the running mode of the bulldozer 1 to any one of the "straight running mode", "gentle turning mode", "semi-precision turning mode", and "precision turning mode" according to the operation amount of the steering lever 35.

[0052] When the operation amount of the steering lever 35 is equal to or less than the first predetermined amount TH1, the controller 100 sets the traveling mode of the bulldozer 1 to the straight traveling mode. When the operation amount of the steering lever 35 is greater than the first predetermined amount TH1 and less than the second predetermined amount TH2, the controller 100 sets the traveling mode of the bulldozer 1 to the gentle turning mode. When the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2 and less than the third predetermined amount TH3, the controller 100 sets the traveling mode of the bulldozer 1 to the semi-precise turning mode. When the operation amount of the steering lever 35 is equal to or greater than the third predetermined amount TH3, the controller 100 sets the traveling mode of the bulldozer 1 to the precise turning mode.

[0053] The second predetermined amount TH2 is greater than the first predetermined amount TH1. The third predetermined amount TH3 is greater than the second predetermined amount TH2. Each of the first to third predetermined amounts TH1 to TH3 can be set to a desired value. The first predetermined amount TH1 may be "0".

[0054] In this specification, the "semi-precise turning mode" and the "precise turning mode" may be collectively referred to as the "sharp turning mode".

[0055] · Straight traveling mode In the straight traveling mode, the controller 100 controls the left and right clutch control valves 27L and 27R to engage the left and right steering clutches 40L and 40R. The engagement rate of the left and right steering clutches 40L and 40R is set to 100%.

[0056] In the straight traveling mode, the controller 100 controls the left and right brake control valves 28L and 28R to release the left and right steering brakes 50L and 50R. The braking force of the left and right steering brakes 50L and 50R is set to 0%.

[0057] In the straight traveling mode, the controller 100 stops the turning motor 80. The rotation speed of the turning motor 80 is set to 0%.

[0058] · Gentle turning mode In the slow turning mode, the controller 100 controls the left and right clutch control valves 27L and 27R to engage the left and right steering clutches 40L and 40R. The engagement ratio of each of the left and right steering clutches 40L and 40R does not have to be particularly limited as long as it is a sufficiently high value, but 90% or more is preferable, 95% or more is more preferable, and 100% is particularly preferable.

[0059] In the slow turning mode, the controller 100 controls the left and right brake control valves 28L and 28R to release the left and right steering brakes 50L and 50R. The braking force of the left and right steering brakes 50L and 50R is set to 0%.

[0060] In the slow turning mode, as the operation amount of the steering lever 35 increases, the controller 100 drives the turning motor 80 so that the rotation speed of the inner output shaft 60 IN becomes lower than the rotation speed of the outer output shaft 60 OUT .

[0061] The inner output shaft 60 IN is the output shaft corresponding to the operation direction of the steering lever 35 (i.e., the turning direction) among the left and right output shafts 60L and 60R. The outer output shaft 60 OUT is the output shaft opposite to the operation direction of the steering lever 35 among the left and right output shafts 60L and 60R.

[0062] The controller 100 increases the rotation speed of the turning motor 80 as the operation amount of the steering lever 35 increases. For example, the controller 100 may gradually increase the rotation speed of the turning motor 80 in proportion to the operation amount of the steering lever 35, or may increase the rotation speed of the turning motor 80 step by step according to the operation amount of the steering lever 35.

[0063] The rotation speed of the turning motor 80 when the operation amount of the steering lever 35 is the second predetermined amount TH2 does not have to be particularly limited as long as it is sufficiently high, but 90% or more is preferable, 95% or more is more preferable, and 100% (maximum value) is particularly preferable.

[0064] ·Quasi-gyroscopic turning mode In the quasi-gyroscopic turning mode, the controller 100 controls the left and right clutch control valves 27L, 27R to reduce the engagement ratio of the inner steering clutch 40 IN below the engagement ratio in the slow turning mode and maintain the engagement ratio of the outer steering clutch 40 OUT at about the same level as the engagement ratio in the slow turning mode.

[0065] The inner steering clutch 40 IN is the steering clutch corresponding to the operation direction of the steering lever 35 among the left and right steering clutches 40L, 40R. The outer steering clutch 40 OUT is the steering clutch opposite to the operation direction of the steering lever 35 among the left and right steering clutches 40L, 40R.

[0066] The inner steering clutch 40 IN The target value of the engagement ratio does not need to be particularly restricted as long as it is sufficiently low, but it is preferably 50% or less, more preferably 10% or less, and particularly preferably 0%. The controller 100 may gradually reduce the engagement ratio of the inner steering clutch 40 IN in inverse proportion to the operation amount of the steering lever 35, or may stepwise reduce the engagement ratio of the inner steering clutch 40 IN according to the operation amount of the steering lever 35. Alternatively, the controller 100 may reduce the engagement ratio of the inner steering clutch 40 IN to the target value when the operation amount of the steering lever 35 reaches the second predetermined amount TH2.

[0067] The outer steering clutch 40 OUT The engagement ratio does not need to be particularly restricted as long as it is sufficiently high, but it is preferably 90% or more, more preferably 95% or more, and particularly preferably 100%.

[0068] In the quasi-gyroscopic turning mode, the controller 100 controls the left and right brake control valves 28L, 28R to control the inner steering brake 50 INApply braking and release the outer steering brake 50 OUT Release it.

[0069] The inner steering brake 50 IN is the steering brake corresponding to the operation direction of the steering lever 35 among the left and right steering brakes 50L and 50R. The outer steering brake 50 OUT is the steering brake opposite to the operation direction of the steering lever 35 among the left and right steering brakes 50L and 50R.

[0070] The controller 100 preferably increases the braking force of the inner steering brake 50 IN as the operation amount of the steering lever 35 increases. The controller 100 may increase the braking force of the inner steering brake 50 IN in proportion to the operation amount of the steering lever 35, or may increase the braking force of the inner steering brake 50 IN step by step according to the operation amount of the steering lever 35.

[0071] When the operation amount of the steering lever 35 is the third predetermined amount TH3, the braking force of the inner steering brake 50 IN is not particularly limited as long as it is sufficiently high, but 90% or more is preferable, 95% or more is more preferable, and 100% is particularly preferable. The braking force of the outer steering brake 50 OUT is 0% as in the slow turning mode.

[0072] In the quasi-accurate turning mode, the controller 100 maintains the rotation speed of the turning motor 80 at approximately the same level as that in the slow turning mode. The rotation speed of the turning motor 80 is not particularly limited as long as it is sufficiently high, but 90% or more is preferable, 95% or more is more preferable, and 100% is particularly preferable.

[0073] ·Accurate turning mode In the accurate turning mode, the controller 100 controls the left and right clutch control valves 27L and 27R to control the inner steering clutch 40 INand the outer steering clutch 40 OUT Maintain the engagement rate of each to be approximately the same as the engagement rate in the accurate turning mode. The engagement rate of the inner steering clutch 40 IN is lower than the engagement rate in the slow turning mode.

[0074] The inner steering clutch 40 IN The target value of the engagement rate is not particularly limited as long as it is sufficiently low, but preferably 50% or less, more preferably 10% or less, and particularly preferably 0%. The engagement rate of the outer steering clutch 40 OUT is not particularly limited as long as it is sufficiently high, but preferably 90% or more, more preferably 95% or more, and particularly preferably 100%.

[0075] In the accurate turning mode, the controller 100 controls the left and right brake control valves 28L, 28R to fully engage the inner steering brake 50 IN and release the outer steering brake 50 OUT The braking force of the inner steering brake 50 IN is 100%, and the braking force of the outer steering brake 50 OUT is 0%.

[0076] In the accurate turning mode, the controller 100 maintains the rotational speed of the turning motor 80 to be approximately the same as the rotational speed in the accurate turning mode. The rotational speed of the turning motor 80 is not particularly limited as long as it is sufficiently high, but preferably 90% or more, more preferably 95% or more, and particularly preferably 100%.

[0077] (Turning control method) Next, the turning control method executed by the controller 100 will be described assuming that the operation amount of the steering lever 35 gradually increases from 0.

[0078] FIG. 4 is a flowchart for explaining the turning control method. FIG. 5 is a graph showing an example of the state of the bulldozer 1.

[0079] In step S1, when the operation amount of the steering lever 35 is equal to or less than the first predetermined amount TH1, the controller 100 causes the bulldozer 1 to travel in a straight-ahead mode.

[0080] Specifically, the controller 100 engages the left and right steering clutches 40L and 40R, releases the left and right steering brakes 50L and 50R, and stops the turning motor 80. Thereby, the bulldozer 1 travels straight ahead.

[0081] In step S2, when the operation amount of the steering lever 35 is greater than the first predetermined amount TH1 and less than the second predetermined amount TH2, the controller 100 causes the bulldozer 1 to turn in a slow-turning mode in the operation direction of the steering lever 35.

[0082] Specifically, the controller 100 engages the left and right steering clutches 40L and 40R, releases the left and right steering brakes 50L and 50R, and drives the turning motor 80 so that the rotational speed of the inner output shaft 60 IN becomes lower than the rotational speed of the outer output shaft 60 OUT as the operation amount of the steering lever 35 increases. Thereby, the bulldozer 1 slowly turns in the operation direction of the steering lever 35.

[0083] In the example shown in FIG. 5, the rotational speed of the turning motor 80 gradually increases from 0% to 100% in proportion to the operation amount of the steering lever 35.

[0084] In step S3, when the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2 and less than the third predetermined amount TH3, the controller 100 causes the bulldozer 1 to turn in an accurately-turning mode in the operation direction of the steering lever 35.

[0085] Specifically, the controller 100 reduces the engagement ratio of the inner steering clutch 40 IN and brakes the inner steering brake 50 IN and the rotational speed of the inner output shaft 60 IN is the outer output shaft 60OUT The turning motor 80 is driven so as to have a rotational speed lower than that of . As a result, the bulldozer 1 turns accurately in the direction of operation of the steering lever 35.

[0086] In the example shown in FIG. 5, the engagement ratio of the inner steering clutch 40 IN decreases in two steps from 100% to 0% according to the operation amount of the steering lever 35, and the braking force of the inner steering brake 50 IN increases in two steps from 0% to 100% according to the operation amount of the steering lever 35.

[0087] In step S4, when the operation amount of the steering lever 35 is equal to or greater than the third predetermined amount TH3, the controller 100 turns the bulldozer 1 in the fixed-turning mode in the direction of operation of the steering lever 35.

[0088] Specifically, the controller 100 maintains the engagement ratios of the inner steering clutch 40 IN and the outer steering clutch 40 OUT at approximately the same level as the engagement ratio in the accurate-turning mode, fully engages the inner steering brake 50 IN and releases the outer steering brake 50 OUT . Further, the controller 100 maintains the rotational speed of the turning motor 80 at approximately the same level as the rotational speed in the accurate-turning mode. As a result, the bulldozer 1 turns in the direction of operation of the steering lever 35.

[0089] (Feature) [1] When the operation amount of the steering lever 35 is greater than the first predetermined amount TH1 and smaller than the second predetermined amount TH2, the controller 100 engages the left and right steering clutches 40L and 40R, releases the left and right steering brakes 50L and 50R, and as the operation amount of the steering lever 35 increases, the rotational speed of the inner output shaft 60 IN is lower than that of the outer output shaft 60 OUTThe turning motor 80 is driven so as to be lower than the rotational speed of . As a result, the bulldozer 1 slowly turns in the operation direction of the steering lever 35.

[0090] When the operation amount of the steering lever 35 is equal to or greater than a second predetermined amount TH2, the controller 100 reduces the engagement rate of the inner steering clutch 40 IN and brakes the inner steering brake 50 IN . As a result, the bulldozer 1 makes a sharp turn (a field turn or a semi-field turn) in the operation direction of the steering lever 35.

[0091] In this way, by controlling the left and right steering clutches 40L, 40R, the left and right steering brakes 50L, 50R, and the turning motor 80, both slow turning and sharp turning can be performed.

[0092] During slow turning, the left and right steering brakes 50L, 50R are released. Therefore, compared with the case where slow turning is performed using the braking force of the left and right steering brakes 50L, 50R, the power loss of the engine 10 can be suppressed. Further, since the left and right steering brakes 50L, 50R are not used during slow turning, the left and right steering brakes 50L, 50R can have a longer service life.

[0093] [2] When the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2, it is preferable for the controller 100 to set the rotational speed of the turning motor 80 to 100% (maximum value). Thereby, it is possible to further suppress a decrease in the center vehicle speed of the bulldozer 1 during a sharp turn.

[0094] [3] When the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2 and smaller than a third predetermined amount TH3, the inner steering brake 50 INIt is preferable to increase the braking force of the turning wheel 14. This allows a quasi-pivot turn to be interposed between the gentle turn and the pivot turn, thereby improving the controllability of the bulldozer 1 when switching from the gentle turn to the pivot turn.

[0095] [4] The controller 100 controls the inside steering brake 50 when the operation amount of the steering lever 35 is the third predetermined amount TH3. IN It is preferable to set the braking force to 100% (maximum value). This allows a wider adjustment range for the turning radius during a quasi-pivot turn.

[0096] [5] When the operation amount of the steering lever 35 is equal to or larger than the second predetermined amount TH2, the controller 100 controls the inner steering clutch 40 IN It is preferable to set the engagement rate to 0%, which allows for a smaller turning radius during sharp turns (especially semi-pivot turns).

[0097] [6] Since the controller 100 drives the swing motor 80 during a sharp turn, the swing radius of the bulldozer 1 during a sharp turn can be reduced.

[0098] (Modification of the embodiment) The present invention is not limited to the above-described embodiments, and various modifications and alterations are possible without departing from the scope of the present invention.

[0099] (Variation 1) In the above embodiment, in the quasi-pivot turn mode, the controller 100 controls the inside steering brake 50 as the operation amount of the steering lever 35 increases. IN The braking force of the inside steering brake 50 IN The braking force may be maintained at a predetermined value greater than 0%.

[0100] (Variation 2) In the above-described embodiment, the controller 100 is configured to interpose a quasi-creeping mode between the creeping mode and the field turning mode. However, the creeping mode and the field turning mode may be directly connected without interposing the quasi-creeping mode. In this case, a sharp turn would only mean a field turn.

[0101] (Modification Example 3) In the above-described embodiment, the controller 100 is configured to switch from the creeping mode to the sharp turn mode (quasi-field turning mode and field turning mode) according to the operation amount of the steering lever 35. However, the present invention is not limited to this. The controller 100 may switch from the creeping mode to the sharp turn mode in response to the operation amount of the steering lever 35 being greater than the first predetermined amount TH1 and receiving a sharp turn instruction from the operator.

[0102] Here, FIG. 6 is a schematic system configuration diagram of the power transmission system provided in the bulldozer 1a according to this modification example. The bulldozer 1a has the same configuration as the bulldozer 1 according to the above-described embodiment, except that it is provided with a sharp turn button 36.

[0103] The sharp turn button 36 is connected to the controller 100. The sharp turn button 36 receives a sharp turn instruction from the operator. When the sharp turn button 36 is pressed by the operator, a sharp turn instruction is transmitted to the controller 100. The sharp turn button 36 may transmit a sharp turn instruction to the controller 100 while it is being pressed by the operator, or may continue to transmit a sharp turn instruction to the controller 100 until it is pressed again by the operator.

[0104] When the operation amount of the steering lever 35 is equal to or less than the first predetermined amount TH1, the controller 100 sets the traveling mode of the bulldozer 1 to the straight traveling mode as described in the above-described embodiment.

[0105] When the operation amount of the steering lever 35 is greater than the first predetermined amount TH1 and no sharp turn instruction is received, the controller 100 sets the traveling mode of the bulldozer 1 to the gentle turn mode. The control of the controller 100 in the gentle turn mode is as described in the above embodiment.

[0106] However, in the above embodiment, when the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2, the sharp turn mode is set. In this modified example, even when the operation amount of the steering lever 35 is equal to or greater than the second predetermined amount TH2, the sharp turn mode is not set. Therefore, in this modified example, the steering lever 35 is used only for gently turning the bulldozer 1.

[0107] When the operation amount of the steering lever 35 is greater than the first predetermined amount TH1 and a sharp turn instruction is received, the controller 100 sets the traveling mode of the bulldozer 1 to the sharp turn mode. The control of the controller 100 in the sharp turn mode is as described in the above embodiment.

[0108] In the above embodiment, it is switched from the semi-precise ground turn mode to the precise ground turn mode according to the operation amount of the steering lever 35. In this modified example, the controller 100 sets the semi-precise ground turn mode for a predetermined time after receiving the sharp turn instruction, and then sets the precise ground turn mode after the predetermined time has elapsed. However, in this modified example, the controller 100 may directly connect the gentle turn mode and the precise ground turn mode without intervening the semi-precise ground turn mode.

[0109] (Modified Example 4) In the above embodiment, the left and right steering clutches 40L and 40R are positive type hydraulic clutches, but they may be negative type hydraulic clutches.

[0110] (Modified Example 5) In the above embodiment, the left and right steering brakes 50L and 50R are negative type hydraulic brakes, but they may be positive type hydraulic clutches.

[0111] (Modification Example 6) In the above embodiment, the left and right output shafts 60L and 60R are connected to the left and right sprockets 2L and 2R. However, left and right final reduction gears may be interposed between the left and right output shafts 60L and 60R and the left and right sprockets 2L and 2R.

[0112] (Modification Example 7) In the above embodiment, the controller 100 drives the turning motor 80 in the sharp turning mode (semi-fixed turning mode and fixed turning mode), but it is not limited thereto. The controller 100 may not drive the turning motor 80 in the semi-fixed turning mode, or may not drive the turning motor 80 in the fixed turning mode.

Explanation of Reference Numerals

[0113] 1 Bulldozer 10 Engine 20 Engine Power Transmission Unit 26 Input Shaft 30L, 30R Left and Right Planetary Gear Mechanisms 31L, 31R Left and Right Ring Gears 32L, 32R Left and Right Planetary Gears 33L, 33R Left and Right Sun Gears 34L, 34R Left and Right Carriers 40L, 40R Left and Right Steering Clutches 50L, 50R Left and Right Steering Brakes 60L, 60R Left and Right Output Shafts 80 Turning Motor 90 Motor Power Transmission Unit 91L, 91R Left and Right Clutch Gears 92 First Transfer Gear 93 Countershaft 94 Second Transfer Gear 95 Idler Gear 96 Pinion Gear 98 Fixed Member 99 Turning Motor 100 Controller

Claims

1. Left and right planetary gear mechanisms disposed between an input shaft and left and right output shafts, Left and right steering clutches that are rotatable about the input shaft and switch the transmission and interruption of rotational power from the input shaft to the left and right output shafts by the left and right planetary gear mechanisms, Left and right steering brakes that brake the left and right output shafts, A turning motor that rotates the left and right steering clutches so that a rotational speed difference occurs between the left and right output shafts, A steering lever that can be operated in a left turning direction and a right turning direction with reference to a neutral position, A controller that controls the left and right steering clutches, the left and right steering brakes, and the turning motor according to an operation direction and an operation amount of the steering lever, Comprising, The controller, When the operation amount is greater than a first predetermined amount and less than a second predetermined amount, engage the left and right steering clutches, release the left and right steering brakes, and drive the turning motor so that the rotational speed of the inner output shaft corresponding to the operation direction among the left and right output shafts becomes lower than the rotational speed of the outer output shaft opposite to the operation direction as the operation amount increases, When the operation amount is greater than or equal to the second predetermined amount, reduce the engagement ratio of the inner steering clutch corresponding to the operation direction among the left and right steering clutches, brake the inner steering brake corresponding to the operation direction among the left and right steering brakes, and drive the turning motor constantly, A crawler-type work machine.

2. The controller sets the rotational speed of the turning motor to a maximum value when the operation amount is greater than or equal to the second predetermined amount, The crawler-type work machine according to Claim 1.

3. The controller increases the braking force of the inner steering brake as the operation amount increases when the operation amount is greater than or equal to the second predetermined amount and less than a third predetermined amount, The crawler-type work machine according to Claim 1 or 2.

4. The controller sets the braking force of the inner steering brake to a maximum value when the operation amount is the third predetermined amount, The crawler-type work machine according to Claim 3.

5. The controller sets the engagement ratio of the inner steering clutch to 0% when the operation amount is greater than or equal to the second predetermined amount, The crawler-type work machine according to any one of Claims 1 to 4.

6. Left and right planetary gear mechanisms disposed between an input shaft and left and right output shafts, Left and right steering clutches that are rotatable about the input shaft and switch the transmission and interruption of rotational power from the input shaft to the left and right output shafts by the left and right planetary gear mechanisms, Left and right steering brakes that brake the left and right output shafts, A turning motor that rotates the left and right steering clutches so that a rotational speed difference occurs between the left and right output shafts, A steering lever that can be operated in the left turning direction and the right turning direction with reference to the neutral position, A controller that controls the left and right steering clutches, the left and right steering brakes, and the turning motor according to the operation direction and operation amount of the steering lever, Comprising, The controller, When the operation amount is greater than a first predetermined amount and no sharp turn instruction is received from the operator, the left and right steering clutches are engaged, the left and right steering brakes are released, and as the operation amount increases, the rotational speed of the inner output shaft corresponding to the operation direction among the left and right output shafts becomes lower than the rotational speed of the outer output shaft opposite to the operation direction, and the turning motor is driven accordingly, When the operation amount is greater than the first predetermined amount and the sharp turn instruction is received, the engagement rate of the inner steering clutch corresponding to the operation direction among the left and right steering clutches is decreased, the inner steering brake corresponding to the operation direction among the left and right steering brakes is braked, and the turning motor is constantly driven, A crawler-type work machine.

7. The controller, when the operation amount is greater than the first predetermined amount and the sharp turn instruction is received, sets the rotational speed of the turning motor to the maximum value, The crawler-type work machine according to claim 6.

8. The controller, when the operation amount is greater than the first predetermined amount and the sharp turn instruction is received, sets the braking force of the inner steering brake to the maximum value, The crawler-type work machine according to claim 6 or 7.

9. The controller, when the operation amount is greater than the first predetermined amount and the sharp turn instruction is received, sets the engagement rate of the inner steering clutch to 0%, The crawler-type work machine according to any one of claims 6 to 8.

10. Comprising a sharp turn button for receiving a sharp turn instruction from the operator, The crawler-type work machine according to any one of claims 6 to 9.

11. Each of the left and right planetary gear mechanisms, a ring gear connected to the input shaft; a sun gear rotatably attached to the input shaft and connected to the steering clutch; a planetary gear disposed between the ring gear and the sun gear; a carrier connected to the planetary gear and the output shaft; having the crawler-type work machine according to any one of claims 1 to 10.

12. left and right clutch gears that can be disengaged from and engaged with the sun gears of the respective left and right planetary gear mechanisms via the left and right steering clutches and rotate in opposite directions to each other; an idler gear that transmits the rotational power of the turning motor to the left and right clutch gears; comprising the crawler-type work machine according to claim 11.

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