Steering device

1. A steering device, comprising:

an operation unit operable by a driver to steer steerable wheels;

a target turning angle determination device which determines a target turning angle of said steerable wheels according to an operation amount of said operation unit;

a turning angle measuring device which measures an actual turning angle of said steerable wheels;

a turning actuator which turns said steerable wheels according to a deviation between said target turning angle and said actual turning angle;

a reaction force determination device which determines a reaction force to apply to said operation unit; and

a reaction force actuator which applies said reaction force,

wherein a rate of increase of said reaction force

remains unchanged when said target turning angle approaches a maximum turning angle during a period in which a deviation between said actual turning angle and said target turning angle is not less than a predetermined level, and

is raised when said actual turning angle approaches the maximum turning angle.

2. A steering device according to claim 1 , wherein said target turning angle is changed according to the operation amount of said operation unit when said actual turning angle approaches said maximum turning angle.

3. A steering device according to claim 1 , wherein when said target turning angle approaches said maximum turning angle during a period in which a deviation between said actual turning angle and said target turning angle is not less than a predetermined level, a preliminary reaction force, which is smaller than a reaction force applied when said actual turning angle approaches said maximum angle, is applied to said operation unit.

4. A steering device according to claim 1 , wherein when the direction of operation of the unit is reversed upon the condition of the actual turning angle approaching said maximum turning angle, said target turning angle is changed according to the actual steering angle.

5. A steering device according to claim 1 , wherein

upon operation of the operation unit, the reaction force actuator applies an initial reaction force to the operation unit, the initial reaction force being substantially constant over time for increasing actual turning angle, and

when said target turning angle approaches said maximum turning angle during a period in which a deviation between said actual turning angle and target turning angle is not less than a predetermined level, a substantially constant preliminary reaction force is applied to said operation unit, the preliminary reaction force comprising a force which is greater than the initial reaction force, and which is smaller than a reaction force applied when said actual angle approaches said maximum turning angle.

6. A steering device according to claim 1 , wherein the steering reaction force is maintained at a substantially constant level between the time when the target turning angle has reached said maximum turning angle and the time when the actual turning angle has reached said maximum turning angle.

7. A steering device according to claim 1 , wherein the steering reaction force is maintained at s substantially constant level between the time when the target turning angle has reached said maximum turning angle and the time when the actual turning angle has reached said maximum turning angle, and when the actual angle reaches said maximum turning angle then said steering reaction force rapidly increases.

8. A method of controlling a steer-by-wire steering device, the steering device comprising:

an operation unit operable by a driver to steer steerable wheels; a target turning angle determination device which determines a target turning angle of said steerable wheels according to an operation amount of said operation unit;

a turning angle measuring device which measures an actual turning of said steerable wheels;

a turning actuator which turns said steerable wheels according to a deviation between said target turning angle and said actual turning angle;

a reaction force determination device which determines a reaction force to apply to said operation unit; and

a reaction force actuator which applies said reaction force, wherein the steering device is controlled such that:

when the difference between the actual turning angle and the target turning angle is less than a predetermined level, and when the target turning angle reaches a maximum turning angle, then the steering reaction force is rapidly increased; and

when the difference between the actual turning angle and the target turning angle is greater than a predetermined level, and when the target turning reaches a maximum turning angle, then the steering reaction force remains substantially unchanged.

9. The method of claim 8 , wherein the steering device is further controlled such that:

when the difference between the actual turning angle and the target turning angle is greater than a predetermined level, and when the target turning reaches a maximum turning angle, then the steering reaction force remains substantially unchanged until the actual angle reaches the maximum turning angle, at which time the steering reaction force is rapidly increased.

10. The method of claim 8 , wherein when the direction of the steering unit is reversed upon the condition of the actual turning angle approaching said maximum turning angle, said target turning angle is changed according to the actual steering angle.

11. The method of claim 8 , wherein upon operation of the operation unit, the reaction force actuator applies an initial reaction force, and wherein when said target turning angle approaches said maximum turning angle during a period in which a deviation between said actual turning angle and said target turning angle is not less than a predetermined level, a preliminary reaction force is applied to said operation unit, the preliminary reaction force comprising a force which is greater than the initial reaction force, and which is smaller than a reaction force applied when said actual when said actual turning angle approaches said maximum turning angle.

12. A method of controlling a steer-by-wire steering device, the steering device comprising:

an operation unit operable by a driver to steer steerable wheels;

a target turning angle determination device which determines a target turning angle of said steerable wheels according to an operation amount of said operation unit;

a turning angle measuring device which measures an actual turning angle of said steerable wheels;

a turning actuator which turns said steerable wheels according to a deviation between said target turning angle and said actual turning angle;

a reaction force determined device which determines a reaction force to apply to said operation unit; and

a reaction force actuator which applies said reaction force, wherein the steering device is controlled such that:

when the operation unit is operated by the driver, the reaction force actuator applies an initial steering reaction force to the operation unit, the initial steering reaction force being substantially constant over time for an increasing actual turning angle;

when the difference between the actual turning angle and the target turning angle is less than a predetermined level, and when the target turning angle reaches a maximum turning angle, then the steering reaction force is rapidly increased; and

when the difference between the actual turning angle and the target turning angle is greater that a predetermined level, and when the target angle turning reaches the maximum turning angle, then the steering reaction force is increased to a level of force which is greater than the initial steering reaction force and substantially maintained at that force level unit the actual turning angle reaches the maximum turning angle, at which time the steering reaction force is rapidly increased.