US 6,155,377 A · Variable gear ratio steering system · patentgrep

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Abstract

In a variable gear ratio steering system, a control unit determines the steering angle ratio which is to be achieved by the steering angle ratio varying unit according to a condition of the vehicle with respect to a given road condition. Such vehicle conditions may include a road surface frictional coefficient so that an excessive steering may be avoided on slippery road surfaces by increasing the steering gear ratio under such conditions. Such vehicle conditions may also include a side force utilization ratio of the steerable wheels so that an excessive steering may be avoided when there is little margin in the available side force for the steerable wheels. The steering system may include a CCD camera for determining the lateral position of the vehicle relative to the current driving lane and a control unit for determining the predicted lateral travel of the vehicle, typically from the steering input angle and the vehicle speed, so that the steering gear ratio may be increased when the vehicle has traveled or drifted sideways more than predicted. Thereby, the vehicle is prevented from inadvertently drifting out of the driving lane.

Claims30

Dependent claims

A variable gear ratio steering system for a vehicle which can vary a ratio of a steering input angle of a steering wheel to a steering output angle of steerable wheels, comprising:

an input shaft rotatably supported by a casing for receiving a steering input;
an output shaft rotatably supported by said casing adapted to transmit a steering output to the steerable wheels of the vehicle;
a variable ratio gear unit interposed between said input shaft and said output shaft for transmitting rotative power from said input shaft to said output shaft;
steering angle ratio varying means associated with said variable ratio gear unit to vary said steering angle ratio;
control means for determining said steering angle ratio which is to be achieved by said steering angle ratio varying means according to a condition of the vehicle with respect to a given road condition;
and
means for detecting a road surface frictional coefficient, said control means increasing said steering angle ratio when a road surface frictional coefficient lower than a reference value is detected, wherein said steering gear ratio progressively increase with a decrease in the detected road surface frictional coefficient.

4 more elements

A variable gear ratio steering system for a vehicle which can vary a ratio of a steering input angle of a steering wheel to a steering output angle of steerable wheels, comprising:

an input shaft rotatably supported by a casing for receiving a steering input;
an output shaft rotatably supported by said casing adapted to transmit a steering output to the steerable wheels of the vehicle;
a variable ratio gear unit interposed between said input shaft and said output shaft for transmitting rotative power from said input shaft to said output shaft;
steering angle ratio varying means associated with said variable ratio gear unit to vary said steering angle ratio;
control means for determining said steering angle ratio which is to be achieved by said steering angle ratio varying means according to a condition of the vehicle with respect to a given road condition;
and
means for detecting a road surface frictional coefficient, said control means increasing said steering angle ratio when a road surface frictional coefficient lower than a reference value is detected, wherein the detected road surface frictional coefficient is measured from a reaction received by the steering device from the road surface.

4 more elements

A variable gear ratio steering system for a vehicle which can vary a ratio of a steering input angle of a steering wheel to a steering output angle of steerable wheels, comprising:

an input shaft rotatably supported by a casing for receiving a steering input;
an output shaft rotatably supported by said casing adapted to transmit a steering output to the steerable wheels of the vehicle;
a variable ratio gear unit interposed between said input shaft and said output shaft for transmitting rotative power from said input shaft to said output shaft;
steering angle ratio varying means associated with said variable ratio gear unit to vary said steering angle ratio;
control means for determining said steering angle ratio which is to be achieved by said steering angle ratio varying means according to a condition of the vehicle with respect to a given road condition;
and
means for determining a side force utilization ratio of said steerable wheels, said control means increasing said steering angle ratio when a side force utilization ratio approaches one.

4 more elements

A variable gear ratio steering system for a vehicle which can vary a ratio of a steering input angle of a steering wheel to a steering output angle of steerable wheels, comprising:

an input shaft rotatably supported by a casing for receiving a steering input;
an output shaft rotatably supported by said casing adapted to transmit a steering output to the steerable wheels of the vehicle;
a variable ratio gear unit interposed between said input shaft and said output shaft for transmitting rotative power from said input shaft to said output shaft;
steering angle ratio varying means associated with said variable ratio gear unit to vary said steering angle ratio;
control means for determining said steering angle ratio which is to be achieved by said steering angle ratio varying means according to a condition of the vehicle with respect to a given road condition;
and
lateral space computing means for computing a maximum lateral travel which keeps said vehicle within a current drive lane, and means for predicting a lateral travel of said vehicle, said control means increasing said steering angle ratio as a ratio of said predicted lateral travel of said vehicle to said maximum lateral travel increases.

4 more elements

A variable gear ratio steering system for a vehicle which can vary a ratio of a steering input angle of a steering wheel to a steering output angle of steerable wheels, comprising:

an input shaft rotatably supported by a casing for receiving a steering input;
an output shaft rotatably supported by said casing adapted to transmit a steering output to the steerable wheels of the vehicle;
a variable ratio gear unit interposed between said input shaft and said output shaft for transmitting rotative power from said input shaft to said output shaft;
steering angle ratio varying means associated with said variable ratio gear unit to vary said steering angle ratio;
control means for determining said steering angle ratio which is to be achieved by said steering angle ratio varying means according to a condition of the vehicle with respect to a given road condition;
and
means for determining a target position of said vehicle relative to a current driving lane and means for predicting a position of said vehicle according to a current driving condition, said control means increasing said steering angle ratio as a deviation of said predicted vehicle position from a determined target vehicle position decreases.

4 more elements

Dependencies are inferred from the claim text.