Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1999-09-16
2001-11-06
Olszewski, Robert P. (Department: 2167)
Motor vehicles
Steering gear
With fluid power assist
C180S446000, C701S041000
Reexamination Certificate
active
06311799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering apparatus which applies a steering assist force to a steering mechanism by a hydraulic pressure generated by a pump driven by an electric motor.
2. Description of Related Art
Power steering apparatuses are conventionally used which assist operation of a steering wheel by supplying a working oil from an oil pump to a power cylinder coupled to a steering mechanism. In such a power steering apparatus, the oil pump is driven by an electric motor such as a brushless motor, and a steering assist force is generated by the power cylinder in accordance with the rotation speed of the electric motor.
Drive control of the electric motor is performed, for example, on the basis of a steering angular speed which is a time-related change amount of a steering angle observed when a steering wheel is operated. As shown in
FIG. 6
, if a steering angular speed W&thgr; is not greater than a first threshold W
1
, a motor rotation speed R is kept at a first rotation speed R
1
. If the steering angular speed W&thgr; is not smaller than a second threshold W
2
which is greater than the first threshold W
1
, the motor rotation speed R is kept at a second rotation speed R
2
which is greater than the first rotation speed R
1
. If the steering angular speed V&thgr; is within a range between the first threshold W
1
and the second threshold W
2
, the motor rotation speed R is varied generally linearly with the steering angular speed W&thgr; between the first rotation speed R
1
and the second rotation speed R
2
.
Thus, a greater steering assist force is generated as the steering wheel is operated more quickly. Hence, the steering assist can properly be provided.
When the steering wheel is returned to a steering angle midpoint (a steering angle which corresponds to an angular position of the steering wheel in straight traveling) after having been turned in one direction, a self-alignment torque is exerted on the steering mechanism due to a reverse input from tires to return the steering wheel to the steering angle midpoint. Therefore, a great steering assist force as required to turn the steering wheel is not necessary.
Nevertheless, the conventional power steering apparatus is adapted to perform the aforesaid control irrespective of the direction of the operation of the steering wheel. Even if a great steering assist force is not required, the rotation speed of the electric motor is increased in response to abrupt operation of the steering wheel. Therefore, wasteful energy consumption is inevitable.
Further, smooth return of the steering wheel to the steering angle midpoint by utilizing the self-alignment torque may be prevented in the conventional power steering apparatus.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power steering apparatus which features an enhanced energy saving.
It is another object of the present invention to provide a power steering apparatus which ensures smooth return of a steering wheel to a steering angle midpoint.
The power steering apparatus according to the present invention, which is adapted to generate a steering assist force to be applied to a steering mechanism by a hydraulic pressure generated by a pump driven by an electric motor, comprises: steering direction detection means for sensing a direction of steering operation of the steering mechanism; steering angular speed detection means for sensing a steering angular speed when the steering mechanism is operated; and motor control means for determining a rotation speed of the motor in accordance with the steering angular speed sensed by the steering angular speed detection means and controlling driving of the electric motor on the basis of an output of the steering direction detection means so that the motor rotation speed is set at a lower value when the steering mechanism is operated toward a steering angles midpoint than when the steering mechanism is operated away from the steering angle midpoint.
In accordance with the present invention, the motor rotation speed is set at a lower value when the steering mechanism is operated toward the steering angle midpoint than when the steering mechanism is operated away from the steering angle midpoint. This prevents the power steering apparatus from applying an excessively great steering assist force to the steering mechanism when the steering mechanism is operated toward the steering angle midpoint, thereby enhancing the energy saving of the apparatus.
The motor control means preferably determines the motor rotation speed with respect to the steering angular speed sensed by the steering angular speed detection means in accordance with a first characteristic line which defines a relationship between the steering angular speed and the motor rotation speed for the steering operation away from the steering angle midpoint, and in accordance with a second characteristic line which defines a relationship between the steering angular speed and the motor rotation speed for the steering operation toward the steering angle midpoint. In this case, it is preferable that the second characteristic line defines the relationship such that the steering angular speed with respect to the motor rotation speed is greater than that defined by the first characteristic line.
In this case, the first and second characteristic lines may each be defined so that the motor rotation speed varies generally linearly with the steering angular speed.
The first and second characteristic lines may be parallel to each other (or the second characteristic line may be obtained through parallel shift of the first characteristic line). Particularly where the first and second characteristic lines are linear, these characteristic lines may have different inclinations. Where the first and second characteristic lines have different inclinations, the second characteristic line preferably has a smaller inclination than the first characteristic line. Alternatively, the second characteristic line may be obtained, for example, by shifting the first characteristic line in parallelism and changing the inclination of the resulting characteristic line.
Where a lower limit is set for the rotation speed of the electric motor, a range of the steering angular speed for which the motor is to be rotated at the lower limit motor rotation speed may be changed. More specifically, the first characteristic line and the second characteristic line may respectively have thresholds which each define a boundary between the range of the steering angular speed for which the motor is to be rotated at the lower limit motor rotation speed and a range of the steering angular speed for which the motor rotation speed is varied in accordance with an increase in the steering angular speed (e.g., generally linearly with an increase in the steering angular speed).
Similarly, where an upper limit is set for the rotation speed of the electric motor, a range of the steering angular speed for which the motor is to be rotated at the upper limit motor rotation speed may be changed. More specifically, the first characteristic line and the second characteristic line may respectively have thresholds which each define a boundary between the range of the steering angular speed for which the motor is to be rotated at the upper limit motor rotation speed and the range of the steering angular speed for which the motor rotation speed is varied in accordance with an increase in the steering angular speed (e.g., generally linearly with an increase in the steering angular speed).
In accordance with the present invention, the steering angular speed with respect to the motor rotation speed is set greater on the second characteristic line than on the first characteristic line which is to be employed for the steering operation away from the steering angle midpoint. Therefore, when the steering mechanism is operated toward the steering angle midpoint, the motor rotation speed with respect to the steering angular speed is determined in accordanc
Fischer Andrew J.
Koyo Seiko Co. Ltd.
Olszewski Robert P.
Rabin & Berdo P.C.
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