3A and 3B. The steering member 45 is a lever such as a joy stick. Alternatively, the steering member 45 may be a member other than a lever. For example, the steering member 45 may be a steering wheel.

The steering member 45 is connected to an operation sensor 51. The operation sensor 51 is included in the work machine 1. The operation sensor 51 outputs a steering operation signal that indicates an operation on the steering member 45 by the operator.

The articulating lever 55 is operable by the operator for turning the front frame 11 with respect to the rear frame 12. The articulating lever 55 is a lever such as a joystick. Alternatively, the articulating lever 55 may be a member other than a lever. The articulating lever 55 is connected to an operation sensor 60. The operation sensor 60 is included in the work machine 1. The operation sensor 60 outputs an articulating operation signal that indicates an operation on the articulating lever 55 by the operator.

The leaning lever 63 is operable by an operator for leaning the front wheels 3A and 3B. The leaning lever 63 is a lever such as a joy stick. Alternatively, the leaning lever 63 may be a member other than a lever. The leaning lever 53 is connected to an operation sensor 52. The operation sensor 52 outputs a leaning operation signal that indicates an operation on the leaning lever 63 by the operator.

The work implement operating member 35 is operable by the operator in order to change the orientation of the work implement 5. The work implement operating member 35 includes, for example, a plurality of operating levers. Alternatively, the work implement operating member 35 may be another member such as a switch or a touch screen. The work implement operating member 35 outputs a signal that indicates an operation on the work implement operating member 35 by the operator.

The shift member 53 is operable by the operator for switching between forward travel and reverse travel of the work machine 1. The shift member 53 includes, for example, a shift lever. Alternatively, the shift member 53 may be another member such as a switch or a touch screen. The shift member 53 outputs a signal that indicates an operation on the shift member 53 by the operator.

The accelerator operating member 36 is operable by an operator for controlling the travel of the work machine 1. The accelerator operating member 36 includes, for example, an accelerator pedal. Alternatively, the accelerator operating member 36 may be another member such as a switch or a touch screen. The accelerator operating member 36 outputs a signal that indicates an operation on the accelerator operating member 36 by the operator.

The work machine 1 includes a steering angle sensor 40, an articulate angle sensor 30, and a leaning angle sensor 62. The steering angle sensor 40 is used for detecting a steering angle θ1 of the front wheels 3A and 3B (example of steering control wheel). The steering angle sensor 40 outputs a steering angle signal (first angle signal) that indicates the steering angle θ1. The steering angle signal is, for example, the stroke amounts of the plurality of steering actuators 41A and 41B. The steering angle sensor 40 may directly detect the steering angle θ1.

The steering angle θ1 is defined as described below. FIGS. 5A and 5B are top views of the front part of the work machine 1. In FIGS. 5A and 5B, the articulate angle is zero, that is, the work machine 1 is illustrated in a state in which the front frame 11 is not bent with respect to the rear frame 12.

As illustrated in FIG. 5A, the work machine 1 includes a first steering shaft 43A and a second steering shaft 43B. The first steering shaft 43A and the second steering shaft 43B are the turning shafts of the front wheels 3A and 3B respectively.

The first steering shaft 43A and the second steering shaft 43B are provided to the front frame 11. The first steering shaft 43A and the second steering shaft 43B extend in the up-down direction. The first steering shaft 43A and the second steering shaft 43B turnably support the front wheels 3A and 3B respectively.

The steering angle θ1 is the angle that the front wheels 3A and 3B turn with respect to the front frame 11 about the first steering shaft 43A and the second steering shaft 43B respectively. For example, the steering angle θ1 is the turning angle of the front wheels 3A and 3B with respect to the front-back direction of the front frame 11.

Specifically, a center line L1 is defined on the front frame 11. The center line L1 is the center line of the front frame 11 that extends in the front-back direction of the front frame 11. The center line L1 passes through a below mentioned articulate shaft 44 as seen in a top view of the work machine 1. The steering angle θ1 is the turning angle of the front wheels 3A and 3B in reference to the center line L1.

The steering angle θ1 changes from a neutral position to the left or right due to the stroke motions of the plurality of steering actuators 41A and 41B. The steering angle θ1 at the neutral position is zero degrees. The front wheels 3A and 3B are disposed parallel to the first center line L1 of the front frame 11 at the neutral position. In FIGS. 5A, 3A′ and 3B′ represent the front wheels while turned by the steering angle θ1 from the neutral position to the left. In FIGS. 5B, 3A′ and 3B′ represent the front wheels while turned by the steering angle θ1 from the neutral position to the right.

The articulate angle sensor 30 is used to detect the articulate angle of the front frame 11 with respect to the rear frame 12. The articulate angle sensor 30 outputs an articulate angle signal that indicates the articulate angle. The articulate angle signal is, for example, the stroke amounts of the left articulate cylinder 27 and the right articulate cylinder 28. The articulate angle sensor 30 may detect the articulate angle directly.

The articulate angle is defined as described below. As illustrated in FIGS. 5A and 5B, the work machine 1 includes the articulate shaft 44. The articulate shaft 44 is connected to the front frame 11 and the rear frame 12. The articulate shaft 44 extends in the up-down direction. The front frame 11 and the rear frame 12 are connected to each other so as to allow turning about the articulate shaft 44. The articulate angle is the angle that the front frame 11 turns with respect to the rear frame 12 about the articulate shaft 44.

The leaning angle sensor 62 is used for detecting a leaning angle θ2 of the front wheels 3A and 3B. The leaning angle sensor 62 outputs a leaning angle signal (second angle signal) that indicates the leaning angle θ2. The leaning angle signal is, for example, the stroke amount of the leaning actuator 61. The leaning angle sensor 62 may detect the leaning angle θ2 directly.

The leaning angle θ2 is defined as described below. As illustrated in FIGS. 6A and 6B, the leaning angle θ2 is the tilting angle in the left-right direction of the front wheels 3A and 3B as seen from the front of the vehicle body 2. For example, the leaning angle θ2 is the tilting angle in which the front wheels 3A and 3B respectively tilt about the leaning shafts 54A and 54B as seen from the front of the vehicle body 2. In the following explanation, the state (3A and 3B depicted with solid lines) in which the front wheels 3A and 3B are perpendicular to a horizontal plane H1 is referred to as the neutral state of the front wheels 3A and 3B. The leaning angle θ2 is zero degrees while the front wheels 3A and 3B are in the neutral state.

In FIG. 6A, the front wheels 3A and 3B are changed from the neutral state by the leaning angle θ2 to the left (3A″ and 3B″ depicted with dashed lines). In FIG. 6B, the front wheels 3A and 3B are changed from the neutral state (3A and 3B depicted with solid lines) by the leaning angle θ2 to the right (3A″ and 3B″ depicted with dashed lines).

As illustrated in FIG. 4, the work machine 1 includes a controller 37. The controller 37 includes a storage device 38 and a processor 39. The processor 39 is, for example, a CPU and executes a program for controlling the work machine 1. The storage device 38 includes a memory such as a RAM or a ROM, and an auxiliary storage device such as an SSD or an HDD. The storage device 38 stores programs and data for controlling the work machine 1.

The controller 37 controls the power transmission device 33 in response to an operation of the shift member 53. As a result, the traveling direction of the work machine 1 switches between forward travel and reverse travel. Alternatively, the shift member 53 may be mechanically connected to the power transmission device 33. The action of the shift member 53 may be mechanically transmitted to the power transmission device 33 whereby the gears for forward travel and reverse travel of the power transmission device 33 may be switched.

The controller 37 controls the driving source 31 and the power transmission device 33 in response to an operation on the accelerator operating member 36. As a result, the work machine 1 is able to travel. The controller 37 controls the hydraulic pump 32 and the work implement valve 34 in response to an operation on the work implement operating member 35. Consequently, the work implement 5 is operated.

The controller 37 acquires the operating amount of the steering member 45 from the steering operation signal from the operation sensor 51. The controller 37 causes the plurality of steering actuators 41A and 41B to extend and contract by controlling the steering valve 42A in accordance with the steering operation signal. As a result, the controller 37 changes the steering angle θ1 of the front wheels 3A and 3B. The controller 37 acquires the steering angle signal from the steering angle sensor 40. The controller 37 calculates the steering angle θ1 of the front wheels 3A and 3B based on the steering angle signal.

The controller 37 acquires the operating amount of the articulating lever 55 from the articulating operation signal from the articulating lever 55. The controller 37 controls the articulating valve 42B. For example, the controller 37 controls the articulating valve 42B in accordance with the articulating operation signal thereby causing the left articulate cylinder 27 and the right articulate cylinder 28 to extend and contract. As a result, the controller 37 changes the articulate angle. The controller 37 acquires the articulate angle signal from the articulate angle sensor 30. The controller 40 calculates the articulate angle based on the articulate angle signal.

The controller 37 acquires the operating amount of the leaning lever 63 by means of the leaning operation signal from the leaning lever 63. The controller 37 controls the leaning valve 42C. For example, the controller 37 controls the leaning valve 42C in accordance with the leaning operation signal thereby causing the leaning actuator 61 to extend and contract. As a result, the controller 37 changes the leaning angle θ2 in accordance with the operation of the leaning lever 63 by the operator. The controller 37 acquires the leaning angle signal from the leaning angle sensor 62. The controller 37 calculates the leaning angle θ2 based on the leaning angle signal.

The controller 37 executes an automatic leaning control for changing the leaning angle θ2 in accordance with the steering angle θ1. The following discussion pertains to the automatic leaning control. In the automatic leaning control, the controller 37 controls the leaning valve 42C in accordance with the steering angle θ1 thereby causing the leaning actuator 61 to extend and contract. As a result, the controller 37 automatically changes the leaning angle θ2 without depending upon the operation of the leaning lever 63. FIGS. 7A and 7B are flow charts illustrating processing of the automatic leaning control.

In step S101, the controller 37 acquires the current steering angle θ1.

In step S102, the controller 37 acquires the traveling direction of the vehicle body 2. In step S103, the controller 37 determines whether the traveling direction of the vehicle body 2 is the forward travel direction.

If the traveling direction of the vehicle body 2 is the forward travel direction (Yes in S103), the controller 37 acquires, in step S104, first table data as target leaning angle table data. The first table data is stored in the storage device 38.

The first table data defines the relationship between the steering angle θ1 of the front wheels 3A and 3B when the vehicle body 2 is traveling forward and a target leaning angle θ_T2. FIG. 8A illustrates an example of the first table data. As illustrated in FIG. 8A, in the first table data, when the steering angle θ1 of the front wheels 3A and