Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-01-20
2001-04-10
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S402000
Reexamination Certificate
active
06213248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering control apparatus for turning steered wheels in accordance with rotation of a steering wheel. More particularly, the invention concerns a steering control apparatus wherein a steering shaft connected to the steering wheel is mechanically separated from a turning mechanism for turning the steered wheels and wherein the turning mechanism is controlled an electric control by device.
2. Related Background Art
An example of the steering control apparatus of this type is disclosed, for example, in Japanese Patent Publication No. 6-98931 and the structure thereof is shown in
FIG. 6. A
steering shaft motor
122
is attached to a steering shaft
121
mounted with a steering wheel
120
, so that the steering shaft motor
122
can rotate the steering shaft
121
. When a turning shaft motor
130
rotates a turning shaft
132
, a rack shaft
134
in mesh with a pinion
131
provided at the tip of the turning shaft is displaced along the axial direction, whereby tires
133
are turned in synchronism with the motion of this rack shaft
134
. At this time a turning shaft motor control circuit
141
controls driving of the turning shaft motor
130
so that a turning amount detected by a turning displacement amount sensor
137
may be coincident with a target control amount calculated by a steering displacement amount arithmetic unit
144
. At the same time as it, a turning reaction force sensor
138
detects turning reaction force exerted on the turning shaft
132
upon this turning operation and a steering effort sensor
124
detects a steering effort exerted on the steering shaft
121
. A steering shaft motor control circuit
140
drives the steering shaft motor
122
, based on a deviation between the steering effort and the turning reaction force detected by the two sensors
124
,
138
.
In this way the control of driving of the steering shaft
121
is carried out based on the deviation between the steering effort detected by the steering effort sensor
124
and the turning reaction force detected by the turning reaction force sensor
138
. This turning reaction force is, however, detected as a result of such operation that a steering angle sensor
123
first detects a steering angle, the turning shaft motor
130
rotates the turning shaft
132
according to this steering angle, the rotation of the turning shaft
132
displaces the rack shaft
134
to actually turn the tires
133
, and the actual turning of tires generates axial force. Therefore, no turning reaction force exists in the initial stage of steering, and the steering effort is thus reflected in the control of rotation of steering shaft
121
as it is. This results in increasing the rotation amount of steering shaft
121
by the steering shaft motor
122
, so that the steering reaction force is small. After a while, the tires
133
are actually turned to generate the axial force (turning reaction force) so as to decrease the deviation between the steering effort and the turning reaction force, whereupon the rotation of steering shaft
121
is restrained, thereby increasing the steering reaction force. There appears a phase shift (a temporal shift) between the steering amount of steering wheel
120
and the steering reaction force as described above. This degraded the steering feeling of driver, so as to raise the incompatible steering feeling.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above problem and an object of the invention is to provide a steering control apparatus that can relieve the incompatible steering feeling as described above and thus improve the steering feeling.
A steering control apparatus of the present invention comprises: a steering shaft on which a steering effort is exerted through a steering wheel; steering angle detecting means for detecting a steering angle which is an angle of rotation of the steering shaft; steering shaft driving means for rotating the steering shaft; steering effort detecting means for detecting the steering effort exerted on the steering shaft through the steering wheel; turning means for turning a steered wheel, based on the steering angle, the turning means being mechanically separated from the steering shaft; turning reaction force detecting means for detecting a turning reaction force exerted on the steered wheel; and turning amount detecting means for detecting a turning amount of the steered wheel; wherein the steering shaft driving means drives the steering shaft, taking account of the steering effort, the turning reaction force, the steering angle, and the turning amount.
The steering shaft driving means desirably drives the steering shaft, based on a deviation between a force proportional to the steering effort, and the turning reaction force and a deviation between a target control amount based on the steering angle, and the turning amount. Further, the steering shaft driving means desirably drives the steering shaft, based on a control amount obtained by subtracting a value based on the deviation between the target control amount based on the steering angle, and the turning amount from a value based on the deviation between the force proportional to the steering effort, and the turning reaction force.
In the initial stage of steering the increase in the turning reaction force tends to lag because of a delay of response of the turning operation. This makes the deviation between the force proportional to the steering effort, and the turning reaction force greater than necessary. The steering control apparatus of the present invention can restrain the undesired increase in the deviation between the force proportional to the steering effort, and the turning reaction force, appearing in the initial stage of steering, by utilizing the deviation between the target control amount based on the steering angle, and the turning amount. This can drive the steering shaft with appropriate steering reaction force.
The steering shaft driving means may be one wherein the steering shaft driving means drives the steering shaft, based on a control amount obtained by subtracting a value based on the deviation between the target control amount based on the steering angle, and the turning amount and a value based on the change rate of the deviation between the target control amount based on the steering angle, and the turning amount from a value based on the deviation between the force proportional to the steering effort, and the turning reaction force.
This can restrain the undesired increase in the deviation between the force proportional to the steering effort, and the turning reaction force, occurring in the initial stage of steering, by also utilizing the change rate of the deviation between the target control amount based on the steering angle, and the turning amount, thereby preventing abrupt steering.
The steering shaft driving means may also be one for driving the steering shaft, taking account of the steering effort, turning reaction force, and steering angle. In this case, the undesired increase in the deviation between the force proportional to the steering effort, and the turning reaction force, appearing in the initial stage of steering, can be restrained by utilizing the steering angle.
This permits the steering shaft drive control with appropriate steering reaction force to be carried out even for small steering amounts.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention wi
Kawaguchi Hiroshi
Sugitani Nobuyoshi
Cuff Michael
Oliff & Berridg,e PLC
Swann J. J.
Toyota Jidosha & Kabushiki Kaisha
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