Traction control for steering articulated power machine

1. An articulated power machine comprising:

a front frame member;

a rear frame member;

an articulation joint rotatably coupling the front and rear frame members;

an articulation angle actuator configured to turn the power machine by changing an articulation angle of the articulation joint;

a hydraulic steering circuit comprising:

a drive pump;

left side drive motors coupled to the drive pump and configured in series to receive hydraulic fluid flow from the drive pump to rotate left side tractive elements;

right side drive motors coupled to the drive pump and configured in series to receive hydraulic fluid flow from the drive pump to rotate right side tractive elements; and

a steering control unit configured to control the articulation angle actuator to change the articulation angle of the articulation joint when a turning operation is underway, wherein the steering control unit is further configured to generate a control signal to control the hydraulic steering circuit to allow the left and right side tractive elements to rotate independently when controlling the articulation angle actuator to change the angle of the articulation joint during the turning operation, and not when a turning operation is not underway,

wherein the hydraulic steering circuit further comprises a cross-feed loop configured to selectively provide a fluid path from a connection between the left side drive motors to a connection between the right-side drive motors, wherein the steering control unit is configured to generate the control signal to control the fluid path through the cross-feed loop such that the fluid path through the cross-feed loop is provided only when controlling the articulation angle actuator to change the angle of the articulation joint during the turning operation, and not when the turning operation is not underway, wherein the cross-feed loop includes a first hydraulic pathway coupled to the connection between the left side drive motors, a second hydraulic pathway coupled to the connection between the right side drive motors, and a control valve coupled between the first hydraulic pathway and the second hydraulic pathway, the control valve selectively providing the fluid path from the connection between the left side drive motors to the connection between the right side drive motors responsive to the control signal.

2. The articulated power machine of claim 1 , wherein the left side drive motors are configured in series with each other to receive hydraulic fluid flow from the drive pump to rotate the left side tractive elements, wherein the right side drive motors are configured in series with each other to receive hydraulic fluid flow from the drive pump to rotate right side tractive elements, and wherein the right side drive motors are coupled to the drive pump in parallel with the left side drive motors.

3. The articulated power machine of claim 2 , wherein the drive pump is coupled in parallel with the first and second right-side drive motors and with the first and second left side drive motors.

4. The articulated power machine of claim 1 , and further comprising a steering input device configured to be manipulated by an operator to control turning operations by responsively generating steering input signals, wherein the steering control unit is configured to control the articulation angle actuator and to generate the control signal responsive to the steering input signals.

5. The articulated power machine of claim 1 , and further comprising a traction lock circuit having a first solenoid-controlled valve coupled between one of the left side drive motors and the drive pump and having a second solenoid-controlled valve coupled between one of the right side drive motors and the drive pump.

6. The articulated power machine of claim 5 , wherein the traction lock circuit further comprises a first restricting orifice coupled between the one of the first and second left side drive motors and the drive pump and a second restricting orifice coupled between the one of the first and second right side drive motors and the drive pump.

7. The articulated power machine of claim 1 , wherein the first left side drive motor is a left front drive motor and the second left side drive motor is a left rear drive motor and the first right side drive motor is a right front drive motor and the second right drive motor is a right rear drive motor, wherein the steering control unit is configured such that when controlling the articulation angle actuator to change the articulation angle of the articulation joint when a turning operation is underway but the articulated power machine is not moving forward or backward, the steering control unit generates the control signal to control the hydraulic steering circuit to allow the left front drive motor and the left rear drive motor to turn in an opposite direction from the corresponding right front drive motor and right rear drive motor, thus preventing or reducing any skidding action by the associated tractive elements.

8. An articulated power machine comprising:

a front frame member;

a rear frame member;

an articulation joint rotatably coupling the front and rear frame members;

an articulation angle actuator configured to turn the power machine by changing an articulation angle of the articulation joint;

a drive pump;

left side drive motors coupled to the drive pump and configured in series with each other to receive hydraulic fluid flow from the drive pump to rotate left side tractive elements, the left side drive motors including a left front drive motor and a left rear drive motor;

right side drive motors coupled to the drive pump and configured in series with each other to receive hydraulic fluid flow from the drive pump to rotate right side tractive elements, the right side drive motors including a right front drive motor and a right rear drive motor and being coupled to the drive pump in parallel with the left side drive motors;

a cross-feed loop including a control valve and selectively providing a fluid path from a connection between the left side drive motors to a connection between the right side drive motors and a restriction positioned between the connection between the left side drive motors and the connection between the right side drive motors; and

a steering control unit in communication with a user controlled steering input and configured to control the articulation angle actuator to change the articulation angle of the articulation joint when a turning operation is underway, wherein the steering control unit is further configured to generate a control signal to control the control valve to provide the fluid path through the cross-feed loop in response to a signal received from the user controlled steering input when controlling the articulation angle actuator to change the angle of the articulation joint during the turning operation, wherein providing the fluid path through the cross-feed loop allows the left front drive motor and the left rear drive motor to turn in an opposite direction from the corresponding right front drive motor and right rear drive motor when the articulated power machine is not moving forward or backward, the control valve blocking the fluid path through the cross-feed loop when a turning operation is not underway.

9. The articulated power machine of claim 8 , wherein the cross-feed loop includes a first hydraulic pathway coupled between the connection between the left side drive motors and the control valve, and a second hydraulic pathway coupled between the connection between the right side drive motors and the control valve, the control valve selectively providing the fluid path from the connection between the left side drive motors, through the first and second fluid pathways, to the connection between the right side drive motors responsive to the control signal.

10. The articulated power machine of claim 8 , wherein the connection between the left side drive motors is a series connection between the left side drive motors, and wherein the connection between the right side drive motors is a series connection between the right side drive motors.

11. The articulated power machine of claim 8 , and further comprising a traction lock circuit having a first solenoid-controlled valve coupled between one of the left side drive motors and the drive pump and having a second solenoid-controlled valve coupled between one of the right side drive motors and the drive pump.

12. The articulated power machine of claim 11 , wherein the traction lock circuit further comprises a first restricting orifice coupled between the one of the left side drive motors and the drive pump and a second restricting orifice coupled between the one of the right side drive motors and the drive pump.

13. The articulated power machine of claim 8 , wherein the restriction is an orifice sized to prevent a free flow path between the connection between the left side drive motors and the connection between the right side drive motors.

14. A method of controlling an articulated power machine, the articulated power machine having a front frame member, a rear frame member, an articulation joint rotatably coupling the front and rear frame members, an articulation angle actuator configured to turn the power machine by changing an articulation angle of the articulation joint, and a steering circuit configured to control steering of the articulated power machine, the steering circuit including a drive pump, first and second left side drive motors connected in series, the first and second left side drive motors coupled to the drive pump and configured to receive hydraulic fluid flow from the drive pump to rotate the left side tractive elements, and first and second right side drive motors connected in series, the first and second right side drive motors coupled to the drive pump and configured to receive hydraulic fluid flow from the drive pump to rotate the right side tractive elements, the method comprising:

determining from a user controlled steering input whether a turning operation is underway;

using a steering control unit to control the articulation angle actuator to change the articulation angle of the articulation joint when a turning operation is underway;

using the steering control unit to control the steering circuit, having the left side drive motors connected in series and the right side drive motors connected in series, to allow left and right side tractive elements of the articulated power machine to rotate independently when controlling the articulation angle actuator to change the angle of the articulation joint during the turning operation, and not when a turning operation is not underway, comprising:

directing hydraulic fluid from the drive pump through the first left side drive motor and through the second left side drive motor before returning to the drive pump; and

directing hydraulic fluid from the drive pump through the first right side drive motor and through the second right side drive motor before returning to the drive pump.

15. The method of claim 14 , wherein the first left side drive motor is a left front drive motor and the second left side drive motor is a left rear drive motor and the first right side drive motor is a right front drive motor and the second right drive motor is a right rear drive motor, wherein using the steering control unit to control the steering circuit to allow the left and right side tractive elements to rotate independently further comprises using the steering control unit to allow the left front drive motor and the left rear drive motor to turn in an opposite direction from the corresponding right front drive motor and right rear drive motor when the articulated power machine is not moving forward or backward while the turning operation is underway.

16. The method of claim 14 , wherein the steering circuit further includes a cross-feed loop configured to selectively provide a fluid path from a first connection between the series connected left side drive motors to a second connection between the series connected right-side drive motors, wherein using the steering control unit to control the steering circuit to allow the left and right side tractive elements of the articulated power machine to rotate independently further comprises using the steering control unit to generate a control signal to control a control valve of the cross-feed loop to provide the fluid path through the cross-feed loop during the turning operation and to not provide the fluid path through the cross-feed loop when a turning operation is not underway.

17. The method of claim 16 , wherein using the steering control unit to generate the control signal further comprises using the steering control unit to generate the control signal in response to the user controlled steering input.

18. The method of claim 16 , wherein using the steering control unit to generate the control signal to control the control valve of the cross-feed loop to provide the fluid path through the cross-feed loop during the turning operation further comprises using the steering control unit to allow the left front drive motor and the left rear drive motor to turn in an opposite direction from the corresponding right front drive motor and right rear drive motor when the articulated power machine is not moving forward or backward during the turning operation.