Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1999-06-28
2001-05-01
Hurley, Kevin (Department: 3619)
Motor vehicles
Steering gear
With electric power assist
C180S404000
Reexamination Certificate
active
06223851
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rear wheel steering device which is driven by an electric motor, and in particular to a rear wheel steering device which is provided with means for reliably restoring and firmly retaining a neutral position.
BACKGROUND OF THE INVENTION
Various proposals have been made in regard to the technology of front and rear wheel steering devices which improve the handling of the vehicle by steering the rear wheels in a certain relationship to the front wheel steering angle (Japanese patent laid open publication No. 9-58515). Such a front and rear wheel steering device is typically incorporated with a fail-safe device for automatically restoring the steering angle to the neutral position (straight ahead position) in case of a failure of the steering sensor (or upon stopping the engine).
According to a known fail-safe device, a return spring is used for forcing the steering rod back to the neutral position when a normal steering angle control is not possible (see Japanese patent laid open publication No. 8-301131, for instance).
However, according to this conventional device, because the steering rod is constantly subjected to the spring force of a return spring which is powerful enough to restore the steering to the neutral position and allow the vehicle to move straight ahead even when the steering sensor has failed and it is no longer possible to determine the neutral position, the motor for producing the steering angle must be powerful enough to oppose the spring force of the return spring in addition to overcoming the resistance from the road surface. This factor has prevented a compact design of the electric motor and the drive circuit for the motor.
Japanese patent laid open publication No. 5-69834 discloses an arrangement which comprises a primary and secondary drive units, and clutches for selectively coupling the drive units to the steering device so that the rear wheel steering angle may be restored to the neutral position with the secondary steering device in case of a failure of the primary steering device. However, the steering angle sensor must be able to determine the neutral position at all times, and the need for the secondary drive unit which is needed only at the time of a failure undesirably adds to the size of the overall system.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide a rear wheel steering device which is capable of restoring the neutral position at the time of a failure in a reliable manner without increasing the size of the overall system.
A second object of the present invention is to provide a rear wheel steering device which is capable of maintaining the neutral position both accurately and firmly.
A third object of the present invention is to provide a rear wheel steering device which is reliable in operation, and simple in structure.
According to the present invention, these and other objects of the present invention can be accomplished by providing a rear wheel steering device, comprising: a slide shaft supported by a casing so as to be axially slidable; a rotary shaft supported by the casing in parallel with the slide shaft so as to be rotatable around its axial line, and provided with a pair of threaded sections of mutually opposite senses; an electric motor adapted to turn the rotary shaft in either direction; a pair of slide members supported in a rotationally fast manner, and having threaded sections which engage the corresponding threaded sections of the rotary shaft so as to be moveable in mutually opposite axial directions as the rotary shaft is turned in either direction; a pair of clutch units each interposed between a corresponding one of the slide members and the slide shaft for selectively coupling them in an axially fast manner; and at least one actuator for selectively engaging either one of the clutch units.
Thus, the steering direction can be determined by selectively engaging either one of the clutch units, and the magnitude of the steering angle can be determined by turning the rotary shaft with the electric motor in either direction. In particular, when it is desired to bring the steering device to the neutral position, it can be achieved simply by turning the electric motor in a prescribed direction without regard to the current state of the steering device. This is particularly beneficial when the restoration of the neutral position is required as a fail-safe measure in case of a failure for monitoring the state of the steering device because the device is unable to properly monitor the state of the steering device at such a time. Also, this device does not require a spring member or the like which constantly applies a load to the steering device for restoring the neutral position in case of a device failure so that the resulting reduction in the load acting on the motor reduces the required capacity of the output of the electric motor.
The slide shaft may be provided with a projection which is adapted to be held between the slide members when the slide members are moved axially toward each other as a preferred arrangement for forcing the slide shaft to the neutral position. In particular, if the casing comprises a projection which is adapted to be held between the slide members when the slide members are moved axially toward each other, jointly with the projection provided in the slide shaft, so as to firmly define a neutral position for the slide shaft, the neutral position can be accurately defined, and, once the neutral position is retained, can be held in a highly firm fashion.
The slide members may consist of a sleeve member fitted onto the slide shaft so that the device may have a mechanically durable structure, and capable of a stable operation. According to a preferred embodiment of the present invention adapted to the use of such sleeve members, each of the clutch units may comprise a clutch inner which is attached to the slide shaft and a clutch outer which is attached to a corresponding one of the slide members so as to be respectively axially fast but relatively rotatable by a prescribed angle, each of the clutch units comprising a spring member which relatively urges the clutch outer and the clutch inner in an angular direction, the actuator being adapted to relatively turn the clutch outer and the clutch inner in an opposite angular direction against a biasing force of the spring member; the clutch outer and the clutch inner being provided with radial projections which selectively allow transmission of an axially outward movement of a corresponding one of the slide members to the slide shaft depending on an angular position of the clutch outer relative to the clutch inner.
The steering device may be formed in various forms. For instance, it can be constructed as a parallel-shaft arrangement, in which the rotary shaft comprises a threaded rod rotatably supported by the casing next to the slide shaft, and having a pair of threaded sections of opposite senses on either side of an axially central part thereof, each of the slide members including a first annular part having an internal thread engaging a corresponding one of the threaded sections of the threaded rod and a second annular part fitted onto the slide shaft with the clutch unit interposed between them.
Once the slide members have moved away from the neutral position, it is essential that the applicable clutch unit is kept engaged for the steering device to operate properly, in particular to regain the neutral position. As a measure against the failure of the actuator for selectively engaging the clutch and/or as a measure for eliminating the need for keeping the actuator energized at all times except for when the steering device is at the neutral position, it is preferably to provide means for keeping one of the clutches engaged after the slide members have left the neutral position. As a preferred arrangement for achieving this, the clutch inner may be rotatable relative to the slide shaft, and provided with an arm which is e
Furumi Hiroshi
Kakizaki Yoshio
Shirakawa Kunio
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Honda Giken Kogyo Kabushiki Kaisha
Hurley Kevin
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