Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1999-02-04
2001-06-12
Mai, Lanna (Department: 3619)
Motor vehicles
Steering gear
With electric power assist
C180S446000, C701S041000, C701S042000
Reexamination Certificate
active
06244373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering control apparatus for vehicle provided with a transmission ratio varying mechanism for varying a transmission ratio between a steering amount of a steering wheel and a turn amount of wheels.
2. Related Background Art
An example of the steering control apparatus provided with the transmission ratio varying mechanism of this type is disclosed in Japanese Laid-open Patent Application No. Sho 63-227472, for example. As disclosed in this application, the transmission ratio varying mechanism is provided with a driving motor and is constructed in such structure that a prescribed gear mechanism connects an input shaft connected to the steering wheel side to an output shaft connected to the tie rod side and that the transmission ratio of rotations between the input shaft and the output shaft can be changed by driving the gear mechanism by the driving motor.
On this occasion, the driving motor is controlled so that a rotational position of the driving motor detected by a rotational angle sensor approaches a target position computed based on the steering angle of the steering wheel and the transmission ratio.
SUMMARY OF THE INVENTION
Since the position control of the driving motor was carried out based on deviation from the target position as described above, the driving motor might be driven by the degree corresponding to remaining deviation even in the cases where steering operation was stopped after abrupt steering operation and where abrupt switching-back operation of the steering wheel was carried out. An example thereof is illustrated in FIG.
8
. When the abrupt switching-back operation of the steering wheel is carried out, the target rotational position of the driving motor varies as indicated by a solid line. In contrast with it, at a point of time t1 when the steering wheel is switched back, the deviation e1 due to a delay in follow-up remains with respect to an actual rotational position of the driving motor indicated by a dashed line. As the steering direction of the steering wheel is switched back after this point, steering torque is also switched so that the direction of the steering torque becomes opposite to the rotating direction of the driving motor. Therefore, the steering torque comes to act in the direction to assist the rotation of the driving motor. This steeply increases the rotating speed of the driving motor. At time t2 the rotational position of the driving motor agrees with the target rotational position. Although the control of the driving motor is desired to stop there, a large overshoot e2 appears at time t3 because of the inertia of the driving motor and the rotational speed of the driving motor increased. This phenomenon resulted in giving a driver such incompatible steering feeling that the steering direction of the steering wheel is not coincident with the steered direction of the wheels.
The present invention has been accomplished in order to solve this problem and an object thereof is to provide a steering control apparatus for vehicle that can improve the steering feeling by adequately suppressing occurrence of the above-stated overshoot due to the inertia of motor.
The present steering control apparatus for vehicle is a steering control apparatus for vehicle adapted to change a transmission ratio between a steering amount and a turn amount by driving a transmission ratio varying mechanism by an actuator, the steering control apparatus for vehicle comprising: transmission ratio setting means for setting the transmission ratio according to a running condition of a vehicle; steering speed detecting means for detecting a steering speed of a steering wheel; driving speed setting means for setting a target driving speed for the actuator, based on the transmission ratio set by the transmission ratio setting means and the steering speed detected by the steering speed detecting means; and speed control means for controlling a speed of the actuator to the target driving speed set by the driving speed setting means.
The speed control means carries out the speed control of the actuator according to increase or decrease of the steering speed during manipulation of the steering wheel. For example, in the preceding example of
FIG. 8
, this control decreases the driving speed of the actuator with decreasing steering speed toward the time to and then nulls the driving speed of the actuator at the point of the time t1 at which the steering speed is zero. This adequately suppresses occurrence of the overshoot due to the inertia of motor.
The steering control apparatus may further comprise limiting means for limiting the target driving speed to the magnitude within a predetermined range.
When the target driving speed of the actuator is limited by the limiting means, for example when the limit is defined by the operation limit speed of the actuator, the speed of the actuator is always controlled within the range not more than the operation limit speed, which can prevent occurrence of the overshoot with reliability.
The steering control apparatus for vehicle may further comprise: driving speed detecting means for detecting the driving speed of the actuator; and failure determining means for determining whether a failure occurs, based on the driving speed detected by the driving speed detecting means and the target driving speed limited by the limiting means.
Since the target driving speed is limited to the magnitude in the predetermined range by the limiting means, the deviation between the target driving speed and the driving speed detected becomes smaller than predetermined deviation. Therefore, the failure determining means determines that a failure occurred in a control system, for example, when this deviation is greater than a predetermined value.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus 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 will become apparent to those skilled in the art from this detailed description.
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Kawamuro Junji
Kojo Takahiro
Matsuda Morihiro
Shindo Masahiko
Mai Lanna
Oliff & Berridg,e PLC
To Toan
Toyota Jidosha & Kabushiki Kaisha
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