Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1999-11-01
2001-10-23
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
Reexamination Certificate
active
06305489
ABSTRACT:
This application is based on patent application Ser. No. 10-319529 filed in Japan, the content of which is incorporated thereinto by reference.
TECHNICAL FIELD
The present invention relates to a power steering apparatus and, more particularly, to a so-called motor-driven hydraulic power steering apparatus which is adapted to generate a hydraulic pressure by driving an oil pump by an electric motor to assist a steering operation by the generated hydraulic pressure.
BACKGROUND ART
Motor-driven hydraulic power steering apparatuses are conventionally known which are adapted to rotate an oil pump by an electric motor and supply a working oil to a power cylinder from the oil pump to mitigate an operation force required for operating a steering wheel.
In a power steering apparatus of this type, a steering assist force is determined by the rotation speed of the electric motor. More specifically, a higher rotation speed of the electric motor increases the flow rate of the oil to increase the assist force, while a lower rotation speed of the electric motor reduces the flow rate of the oil to reduce the assist force.
On the other hand, the assist force is not required when the steering operation is not performed and, therefore, the rotation of the electric motor is stopped or kept in an idling state with an extremely low rotation speed for power saving.
Since loads on front wheels are apparently increased immediately after a vehicle is decelerated by pedaling a break just before a corner, the steering wheel tends to feel heavier. Immediately after the vehicle is accelerated, the loads on the front wheels are apparently reduced, so that the steering wheel tends to feel lighter. With the assist force being maintained at a constant level, the steering feeling changes at the acceleration and deceleration of the vehicle, so that the driver feels uncomfortable.
When the steering operation is suddenly started in a non-steering state, the rotation of the electric motor cannot follow the sudden start of the steering operation, so that the steering wheel temporarily feels heavier. Therefore, it is desirable that the rotation speed of the electric motor is steeply increased by predicting occurrence of the steering operation.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a power steering apparatus which ensures a consistent steering feeling even at acceleration and deceleration of a vehicle.
It is another object of the present invention to provide a power steering apparatus which constantly provides a consistent steering feeling by predicting occurrence of a steering operation.
In accordance with one aspect of present invention to achieve the aforesaid objects, there is provided a power steering apparatus which comprises: acceleration detection means for sensing a fore-and-aft acceleration of a motor vehicle which is expressed as a value prefixed with a sign; and control means for reducing a rotation speed of an electric motor to reduce an assist force in accordance with the acceleration if the value of the acceleration of the vehicle sensed by the acceleration detection means is positive, and increasing the rotation speed of the electric motor to increase the assist force in accordance with the acceleration if the value of the acceleration of the vehicle sensed by the acceleration detection means is negative.
The power steering apparatus allows a driver to constantly obtain a consistent steering feeling irrespective of the fore-and-aft acceleration.
In accordance with another aspect of the invention, there is provided a power steering apparatus which comprises: acceleration detection means for sensing a fore-and-aft acceleration of a motor vehicle which is expressed as a value prefixed with a sign; and control means for preliminarily setting a rotation speed of an electric motor at a rotation speed level sufficient for generation of an assist force in accordance with the acceleration if the value of the acceleration of the vehicle sensed by the acceleration detection means is not greater than a predetermined negative level when a steering operation is not performed.
In the power steering apparatus, the next occurrence of the steering operation can be predicted by detecting an acceleration level not greater than the predetermined negative level and, therefore, the assist force can smoothly be generated immediately after the steering operation is started. The aforesaid “predetermined negative level” is defined as a fore-and-aft acceleration level of the vehicle typically sensed when the driver consciously decelerates the vehicle before performing the steering operation. The aforesaid “rotation speed level sufficient for generation of an assist force” is defined as a rotation speed level required for generation of a force sufficient to assist the steering operation performed by the driver.
REFERENCES:
patent: 4762194 (1988-08-01), Morishita et al.
patent: 5381336 (1995-01-01), Shorkey
patent: 5558177 (1996-09-01), Inaguma et al.
patent: 5691900 (1997-11-01), Luckevich
patent: 6131693 (2000-10-01), Mukai et al.
Johnson Brian L.
Koyo Seiko Co. Ltd.
Lerner Avraham H.
Rabin & Champagne, P.C.
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