Variable gear ratio hydraulic power steering device

1. A variable gear ratio hydraulic power steering device having a variable ratio transmission mechanism for varying the rotation transmission ratio V 2 /V 1 between the rotational angle V 1 of a first steering shaft coupled to a steering handle and the rotational angle V 2 of a second steering shaft coupled to a pinion shaft, a transmission ratio controlling controller for controlling the variable ratio transmission mechanism, a flow volume control valve for controlling the discharge flow volume of an oil pump which circulates operating fluid which provides an assist force to the steering device, and a valve controlling controller for controlling the flow volume control valve, wherein:

the variable ratio transmission mechanism is provided with a lock mechanism for restricting relative rotation between the first steering shaft and the second steering shaft;

the valve controlling controller is provided with a memory for storing main and secondary flow volume control maps each mapping various flow volume control values for controlling the flow volume control valve, and a detector adapted to detect the operational state of the lock mechanism; and

the valve controlling controller is constructed to control the flow volume control valve by the use of the main flow volume control map when the lock mechanism permits the relative rotation between the first and second steering shafts and to control the flow volume control valve by the use of the secondary flow volume control map when the lock mechanism restricts the relative rotation between the first and second steering shafts.

2. The variable gear ratio hydraulic power steering device as set forth in claim 1 , wherein the detector is adapted to receive a reference signal related to the operational state of the lock mechanism for restricting the relative rotation between the first and second steering shafts and to detect the operational state regarding whether the lock mechanism restricts or permits the relative rotation between the first and second steering shafts, based on the reference signal.

3. The variable gear ratio hydraulic power steering device as set forth in claim 2 , wherein the reference signal is a control signal for controlling the lock mechanism.

4. The variable gear ratio hydraulic power steering device as set forth in claim 1 , wherein:

the transmission ratio controlling controller is constructed to vary a transmission ratio control target value for the rotation transmission ratio V 2 /V 1 of the variable ratio transmission mechanism within a predetermined range including value 1 in dependence on a traveling state; and

in a control range in which transmission ratio control target values smaller than value 1 are set by the transmission ratio controlling controller,various flow volume control values which are mapped in the secondary flow volume control map are set to more increase the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do; and

in another control range in which transmission ratio control target values larger than value 1 are set by the transmission ratio controlling controller, various flow volume control values which are mapped in the secondary flow volume control map are set to more suppress the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do.

5. The variable gear ratio hydraulic power steering device as set forth in claim 2 , wherein:

the transmission ratio controlling controller is constructed to vary a transmission ratio control target value for the rotation transmission ratio V 2 /V 1 of the variable ratio transmission mechanism within a predetermined range including value 1 in dependence on a traveling state; and

in a control range in which transmission ratio control target values smaller than value 1 are set by the transmission ratio controlling controller, various flow volume control values which are mapped in the secondary flow volume control map are set to more increase the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do; and

in another control range in which transmission ratio control target values larger than value 1 are set by the transmission ratio controlling controller, various flow volume control values which are mapped in the secondary flow volume control map are set to more suppress the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do.

6. The variable gear ratio hydraulic power steering device as set forth in claim 3 , wherein:

the transmission ratio controlling controller is constructed to vary a transmission ratio control target value for the rotation transmission ratio V 2 /V 1 of the variable ratio transmission mechanism within a predetermined range including value 1 in dependence on a traveling state; and

in a control range in which transmission ratio control target values smaller than value 1 are set by the transmission ratio controlling controller, various flow volume control values which are mapped in the secondary flow volume control map are set to more increase the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do; and

in another control range in which transmission ratio control target values larger than value 1 are set by the transmission ratio controlling controller, various flow volume control values which are mapped in the secondary flow volume control map are set to more suppress the discharge flow volume of the oil pump than various flow volume control values mapped in the main flow volume control map do.

7. The variable gear ratio hydraulic power steering device as set forth in claim 1 , wherein the transmission ratio controlling controller is integrated with the flow volume controlling controller.

8. The variable gear ratio hydraulic power steering device as set forth in claim 2 , wherein the transmission ratio controlling controller is integrated with the flow volume controlling controller.

9. The variable gear ratio hydraulic power steering device as set forth in claim 3 , wherein the transmission ratio controlling controller is integrated with the flow volume controlling controller.

10. The variable gear ratio hydraulic power steering device as set forth in claim 4 , wherein the transmission ratio controlling controller is integrated with the flow volume controlling controller.