Motor vehicles – Steering gear – Each wheel steerable
Reexamination Certificate
2001-04-11
2003-01-14
Boehler, Anne Marie (Department: 3611)
Motor vehicles
Steering gear
Each wheel steerable
C180S445000, C180S446000
Reexamination Certificate
active
06505700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to rear wheel steering devices for use in four wheel steered vehicles (4WS) and, more particularly, to rear wheel steering devices driven by an electric motor.
2. Description of the Related Art
In recent years, 4WS or four-wheel steering has become popular because it improves motion characteristics of a vehicle by steering rear wheels in conjunction with front wheel steering. It is essential for such 4WS to install a rear wheel steering device to steer rear wheels in conjunction with front wheel steering. This type of rear wheel steering device is disclosed in Japanese Patent Laid-Open Publication No. 2000-79881 filed by the applicant of the present application.
The aforementioned rear wheel steering device is shown in
FIGS. 13A
to
13
C hereof. An operation of the aforementioned rear wheel steering device will be described below with reference to those drawings.
In
FIG. 13A
, a lifting screw
102
is rotated by an electric motor
101
, thereby moving left and right slide blocks
103
L and
103
R to the left and right sides, respectively.
Since the left slide block
103
L remains in a clutch off state, the left side block
103
L is moved to the left side with the position of left clutch ring
104
L remaining unchanged.
The right slide block
103
R remains in a clutch-on state, and consequently, a plurality of internal teeth
105
R, which inwardly project from an inner periphery of the right slide block
103
R, may push a plurality of external teeth
114
R which outwardly project from an outer periphery of the right clutch ring
104
R. Therefore, sliding forth is sequentially transmitted to the right slide block
103
R, to right clutch ring
104
R, to right lock ring
106
R and then to steering shaft
107
, moving a steering shaft
107
to the right direction as shown by arrow to steer rear wheels.
In such a condition, left and right arms
110
L and
110
R, which project outwardly from outer peripheries of the left and right clutch rings
104
L and
104
R, respectively, and which engage in a guide slot
109
(shown in the upper portion of
FIG. 13A
) formed in an inner periphery of a case (not shown), are movable to the right direction, so that they do not interrupt an axial movement of the steering shaft
107
.
An incremental stroke value relative to the center of the steering shaft
107
can be adjusted without any restraint by rotating the electric motor
101
, and can be measured by a steering angle sensor
112
. Since the steering angle corresponds to a deflected angle of the wheel (designated by reference character &thgr; in
FIG. 14
) and the steering angle is obtained by converting the incremental stroke value into an angle, a stroke sensor will be referred to as a steering angle sensor
112
.
The incremental stroke value of the left slide block
103
L can be measured with a driving angle sensor
113
. Since the driving angle is determined by converting the incremental stroke of the slide block
103
L into an angle, a stroke sensor will be referred to as a driving angle sensor
113
.
FIG. 13B
shows that the right clutch ring
104
R has been moved to the right direction by the internal teeth
105
R in abutting engagement with the external teeth
114
R.
FIG. 13C
shows a relationship between the right slide block
103
R, after the electric motor
101
in
FIG. 13A
has been rotated in a reversed direction, and the central flange
115
that radially protrudes in a central area of an axial direction of the steering shaft
107
. By rotating the lifting screw
102
in a reverse direction, the right slide block
103
R is moved leftward to cause the right slide block
103
R to directly push the central flange
115
leftward.
FIG. 14
shows an operational principle of the conventional rear wheel steering device. A control device
117
receives the steering angle control data and starts the electric motor
101
responsive to the control data. When the lifting screw
102
is rotated by the electric motor
101
, the left and right slide blocks
103
L and
103
R are moved away from each other. The steering shaft
107
is moved to the right direction by the right slide block
103
R. The control device
117
compares the steering angle data delivered from the steering angle sensor
112
with the steering angle control data (produced by the front wheel steering system, not shown)and controls the steering angle &thgr; based on the steering angle control data such that, when the steering angles &thgr; of the rear wheels
118
L and
118
R coincide with the steering angle control data, the operation of the electric motor
101
is stopped.
The electric motor
101
must generate output power sufficient enough to steer the rear wheels to a specified direction immediately. The more output power is required, the larger the external diametrical dimensions (external dimension and length) of the electric motor become. Larger external diametrical dimensions interrupt miniaturization of the rear wheel steering device. Generally, small-sized electric motors can be mass produced and hence are inexpensive. On the other hand, production volume of large-sized electric motors is too small to be cost effective. The electric motor
101
has a large rated output power and hence is expensive. This prevents cost reduction of the rear wheel steering device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a rear wheel steering device which is compact in construction and low in manufacturing cost by rendering electric motors compact in size and low in cost.
According to an aspect of the present invention, there is provided a rear wheel steering device for use in a vehicle, which device comprises two electric motors serving as drive sources for steering rear wheels of the vehicle, and a rear wheel steering control device for controlling the two electric motors to drive in case both of the two electric motors are judged to operate in a normal condition on the basis of motor condition signals indicative of how the two electric motors are working.
The rear wheel steering device is driven by two electric motors. If output power is reduced by 50%, it becomes possible to employ small sized and low cost electric motors This results in achieving the desired miniaturization and cost reduction of the rear wheel steering device.
Desirably, the rear wheel steering device further includes a vehicle speed sensor for detecting a vehicle speed. The rear wheel steering device may be designed such that when one of the electric motors is in an abnormal state while the other one of the electric motors is in a normal state and when the vehicle speed detected by the vehicle speed sensor exceeds a give speed, it controls steering of the rear wheels using only the one electric motor being in normal state. That is, even when one of the electric motors goes out of a normal condition, the rear wheels can be steered using only the other electric motor remaining in normal condition as long as a given condition is satisfied. The given condition may be when the vehicle speed exceeds a predetermined speed. When the vehicle speed is below the predetermined value, the resulting steering torque is large and this will act as an overload on the electric motor of ½ (50%) output power. Thus, the rear wheels are steered only by the normal electric motor when the vehicle speed exceeds the given vehicle speed.
Preferably, the rear wheel steering device further comprises a vehicle speed sensor for detecting a vehicle speed. When one of the electric motors is in an abnormal state while the other one of the electric motors is in a normal state and when the vehicle speed detected by the vehicle speed sensor exceeds a given speed, the rear wheel steering control device controls, using only the in-normal-state electric motor, steering of the rear wheels to cause the rear wheels to be returned to a neutral position. That is, when a certain condition is satisfied, the rear wheels can be returned to the neutral position using only the nor
Furumi Hiroshi
Shirakawa Kunio
Boehler Anne Marie
Honda Giken Kogyo Kabushiki Kaisha
Merchant & Gould P.C.
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