Fail-safe rear wheel steering system for vehicle

Claim 2

A rear wheel steering control system for a vehicle, comprising: a hydraulic actuator for receiving control fluid pressure and varying a rear wheel steer angle in accordance with said control fluid pressure, a control valve for varying said control fluid pressure in accordance with a control signal, main controller means for producing said control signal to control said rear wheel steer angle, and fail-safe means for varying said control fluid pressure gradually to a predetermined fail-safe value when said control system fails, said fail-safe means comprising a fail-safe valve, comprising a solenoid, disposed between said control valve and said hydraulic actuator for closing and opening a control fluid pressure passage connecting said control valve and said actuator, and fail-safe controller means for placing said fail-safe valve in a closed position to close said control fluid pressure passage in response to a failure detection signal, wherein said control valve is an electromagnetic valve, and said fail-safe controller means includes means which, upon receipt of said failure detection signal, first places said fail-safe valve in said closed position, and then cuts off an electric current supplied to said electromagnetic valve.

Claim 3

A rear wheel steering control system for a vehicle, comprising: a hydraulic actuator for receiving control fluid pressure and varying a rear wheel steer angle of said vehicle in accordance with said control fluid pressure; an electromagnetic control valve for varying said control fluid pressure; main controller means for controlling said electromagnetic control valve to control said rear wheel steer angle; a fail-safe valve disposed between said electromagnetic control valve and said hydraulic actuator, said fail-safe valve having an open position and a closed position; and fail-safe controller means for opening and closing said fail-safe valve, said fail-safe controller means including means which, when said main controller means becomes unable to control said electromagnetic control valve, cuts off a supply of said fluid pressure to said actuator by closing said fail-safe valve, and then cuts off a supply of exciting current to said electromagnetic control valve.

Claim 4

A rear wheel steering control system for a vehicle, comprising: a hydraulic actuator for receiving control fluid pressure and varying a rear wheel steer angle of said vehicle in accordance with said control fluid pressure; an electromagnetic control valve for varying said control fluid pressure; main controller means for controlling said electromagnetic control valve to control said rear wheel steer angle; a fail-safe valve disposed between said electromagnetic control valve and said hydraulic actuator, said fail-safe valve having an open position and a closed position; and fail-safe controller means for opening and closing said fail-safe valve, said fail-safe controller means including means which, when said main controller means becomes unable to control said electromagnetic control valve, cuts off a supply of said fluid pressure to said actuator by closing said fail-safe valve, and then cuts off a supply of exciting current to said electromagnetic control valve.

Claim 5

A control system according to claim 2 wherein said fail-safe valve includes means for allowing fluid under said fluid pressure to gradually leak out from said hydraulic actuator when said fail-safe valve is in a closed position.

Claim 6

A control system according to claim 3 wherein said fail-safe controller means is separate from said main controller means.

Claim 7

A control system according to claim 4, wherein said fail-safe controller means is connected with a power source which is separate from a power source of said main controller means.

Claim 8

A control system according to claim 2 wherein said fail-safe valve includes a first solenoid and is held in said closed position when said solenoid is not energized.

Claim 9

A control system according to claim 6 wherein upon receipt of said failure detection signal, said fail-safe controller means first deenergizes said solenoid of said fail-safe valve to place said fail-safe valve in said closed position, and then varies said control signal to a neutral level to allow said rear wheel steer angle to decrease to zero.

Claim 10

A control system according to claim 6, wherein said electromagnetic control valve is actuated by a second solenoid, and said fail-safe controller means includes means which, upon receipt of said failure detection signal, deenergizes said first solenoid of said fail-safe valve immediately, and holds said second solenoid of said control valve energized for a predetermined limited time length.

Claim 11

A control system according to claim 1, wherein said fail-safe controller means includes means which, upon receipt of a failure detection signal, first places said fail-safe valve in said closed position, and then cuts off said current supplied to said electromagnetic control valve.

Claim 12

A rear wheel steering control system for a vehicle, comprising: a hydraulic actuator for receiving control fluid pressure and varying a rear wheel steer angle in accordance with said control fluid pressure, a control valve for varying said control fluid pressure in accordance with a control signal, main controller means for producing said control signal to control said rear wheel steer angle, and fail-safe means for varying said control fluid pressure gradually to a predetermined fail-safe value when said control system fails, said fail-safe means comprising a fail-safe valve, comprising a first solenoid, disposed between said control valve and said hydraulic actuator for closing and opening a control fluid pressure passage connecting said control valve and said actuator, and fail-safe controller means for placing said fail-safe valve in a closed position to close said control fluid pressure passage in response to a failure detection signal, wherein said fail-safe valve is held in said closed position when said first solenoid is not energized, and wherein said control valve is an electromagnetic valve actuated by a second solenoid, and said fail-safe controller means includes means which, upon receipt of said failure detection signal, deenergizes said first solenoid of said fail-safe valve immediately, and holds said second solenoid of said control valve energized for a predetermined limited time length.

Claim 13

A rear wheel steering control system for a vehicle, comprising: a hydraulic actuator for receiving control fluid pressure and varying a rear wheel steer angle in accordance with said control fluid pressure, a control valve for varying said control fluid pressure in accordance with a control signal, main controller means for producing said control signal to control said rear wheel steer angle, and fail-safe means for varying said control fluid pressure gradually to a predetermined fail-safe value when said control system fails, said fail-safe means comprising a fail-safe valve, comprising a first solenoid, disposed between said control valve and said hydraulic actuator for closing and opening a control fluid pressure passage connecting said control valve and said actuator, and fail-safe controller means for placing said fail-safe valve in a closed position to close said control fluid pressure passage in response to a failure detection signal, wherein said fail-safe valve is held in said closed position when said first solenoid is not energized, and wherein said control valve is an electromagnetic valve actuated by a second solenoid, and said fail-safe controller means includes means which, upon receipt of said failure detection signal, deenergizes said first solenoid of said fail-safe valve immediately, and holds said second solenoid of said control valve energized for a predetermined limited time length.