Electricity: motive power systems – Automatic and/or with time-delay means – Movement – position – or limit-of-travel
Reexamination Certificate
1999-12-21
2001-05-29
Masih, Karen (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Movement, position, or limit-of-travel
C701S072000, C701S041000, C180S193000
Reexamination Certificate
active
06239568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering control apparatus which carries out control of steering reaction force.
2. Related Background Art
A conventionally known example of the apparatus for the control of steering reaction force is a so-called power steering system in which an assisting force produced by driving force of an electric motor or by an oil pressure is exerted on a steering system according to a steering torque detected, during steering operation. In this case, the steering reaction force decreases with increasing assisting force, whereas the steering reaction force increases with decreasing assisting force (Japanese Patent Application Laid-Open No. Sho63-306972 etc.).
SUMMARY OF THE INVENTION
FIG. 1
shows the relation between steering-wheel angle &thgr; of the steering wheel and steering reaction force MT acting on the steering wheel. The characteristic of steering-wheel angle &thgr; versus steering reaction force MT illustrated in
FIG. 1
is the result of detection in which a vehicle equipped with the power steering system was driven on the slalom course so as to vary the steering-wheel angle &thgr; sinusoidally and in which transition of the steering reaction force MT on that occasion was detected. In the figure, a characteristic curve indicated by a solid line represents the result of the detection where the vehicle was driven at medium speed, and a characteristic curve indicated by a dotted line the result of the detection where the vehicle was driven at high speed.
There is a phase difference between steering-wheel angle &thgr; and steering reaction force MT. And the phase of steering reaction force MT leads the steering-wheel angle &thgr;. For that reason the two characteristic curves are Lissajous loops which are convex up. Noting hysteresis widths of these Lissajous loops, the hysteresis width at high speed is smaller than that at medium speed and, particularly near the neutral position of steering angle (near the steering-wheel angle &thgr;=0), the hysteresis width wh at high speed is considerably smaller than the hysteresis width wm at medium speed.
To keep a fixed driving direction of the vehicle, a driver needs to keep holding forces constant on the steering wheel so as to keep a fixed steering-wheel angle. This is, however, not easy in practice, as empirically known. Even if there occurs a little change in a balance of the holding forces or even if an external force from road wheels is exerted on the steering wheel to finely change the steering reaction force, the steering wheel will keep the same steering-wheel angle as long as such change of force is within the magnitude of hysteresis as illustrated. In other words, if the hysteresis width is small, small change in the steering force or the external force will appear as change of the steering-wheel angle &thgr;. Therefore, when the hysteresis width becomes smaller at higher speed as illustrated in
FIG. 1
, the steering-wheel angle &thgr; reacts sensitive to even small change in the steering force or the external force, so that steering feeling varies depending upon vehicle speed.
The hysteresis width can be increased by enhancing transmission rigidity between the steering wheel and the tires (steered road wheels), but in this case greater vibration will be transmitted from the road surface to the vehicle body, which will degrade the ride quality of the car.
The present invention has been accomplished in order to solve the problem described above and an object of the invention is to provide a steering control apparatus capable of adjusting the hysteresis width in the characteristic of the steering-wheel angle versus steering reaction force without use of mechanical techniques which can sacrifice the ride quality.
The steering control apparatus of the present invention is a steering control apparatus for control of steering reaction force, which comprises an actuator interposed in a steering system between a steering wheel and steered road wheels, for supplying driving force to the steering system, and phase control means for controlling a phase of steering reaction force acting on the steering wheel through the steering system, by controlling driving of the actuator.
Since the driving force of the actuator acts upon the steering wheel in addition to the frictional force of the steering system and the external force from the road wheels. The frictional force of the steering system and the external force from the road wheels are the original components of the steering reaction force. A resultant force of these forces acts as a steering reaction force on the steering wheel. Accordingly, the phase of the steering reaction force acting on the steering wheel can be changed by controlling the driving force of the actuator. The phase control means controls the phase of the steering reaction force acting on the steering wheel, by controlling the driving of the actuator.
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.
REFERENCES:
patent: 4669745 (1987-06-01), Miki et al.
patent: 5365439 (1994-11-01), Momose et al.
patent: 5754966 (1998-05-01), Ichikawa et al.
patent: 5964819 (1999-10-01), Naito
patent: 63-291769 (1988-11-01), None
patent: 63-306972 (1988-12-01), None
patent: 3-14771 (1991-01-01), None
Kawaguchi Hiroshi
Sugitani Nobuyoshi
Masih Karen
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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