Motor vehicles – Steering gear – Power assist alarms or disablers
Reexamination Certificate
2000-08-09
2001-06-26
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
Power assist alarms or disablers
C180S417000
Reexamination Certificate
active
06250416
ABSTRACT:
The invention relates to a hydraulic power steering system with
a steering wheel, also
steerable vehicle wheels positively coupled to the latter for steering adjustment, and
a double-acting hydrostatic servomotor positively coupled to the steerable vehicle wheels and/or the steering wheel,
a hydraulic pressure-generating device,
a relatively pressureless hydraulic reservoir,
a control-valve arrangement which has two parallel three-way pressure-reducing valves assigned in each case to one side or connecting line of the servomotor and which makes it possible to connect both sides of the servomotor to the hydraulic reservoir and, in each case, one side of the servomotor to the pressure-generating device,
a sensor for detecting forces or movements transmitted between the steering wheel and the steerable vehicle wheels, and also
an electronic control device which is connected, on the input side, to the sensor and which controls the control-valve arrangement as a function of the forces or moments transmitted between the steering wheel and steerable vehicle wheels, in such a way that the servomotor generates a boosting force in order to reduce a manual force perceptible on the steering wheel.
BACKGROUND
A power steering system of this type is known from U.S. Pat. No. 5 553 683. This known power steering system possesses three valves, the opening state of which is controlled by an electronic control by means of pulse-width modulation. In this case, the opening and closing behaviour of the valves is controlled directly, and incorrect settings of the boosting force may occur at least temporarily.
According to the periodical O +P “Ölhydraulik und Pneumatik” [“Oil Hydraulics and Pneumatics”] 40 (1996) No. 6, page 409, closed-center hydraulic power steering systems are known, a high peak power being available if a hydraulic pressure accumulator arranged as a pressure source is dimensioned appropriately. It is advantageous, furthermore, that the hydraulic steering system consumes energy only when a steering adjustment of the steerable vehicle wheels is assisted by a boosting force. By contrast, in the case of a steady-state steering situation without any manual force, no hydraulic energy is required.
In a power steering system known from EP-A 0 427 029, the control-valve arrangement is formed by proportionally working control valves which are urged by spring force into a position connecting the respective side of the servomotor to the hydraulic reservoir and by a controllable electromagnet, counter to the spring force, into a position connecting the respective side of the servomotor to the pressure accumulator.
It is known from U.S. Pat. No. 4,562,710 to provide hydraulic blocking of the servomotor of a power steering system as an immobilizer.
In power steering systems of the type specified in the introduction, a sensitive control of the boosting force may present difficulties.
SUMMARY OF THE INVENTION
The object of the invention is, in a steering system of the type specified in the introduction, to make it possible to improve the control of the boosting force.
This object is achieved, according to the invention, in that
the pressure-generating device has a hydraulic pressure accumulator,
the three-way pressure-reducing valves are provided with a controllable motor-pressure desired value, and
the control-valve arrangement is controlled by controlling the motor-pressure desired values of the pressure-reducing valves.
The invention is based on the general concept of actuating the control-valve arrangement indirectly by means of the electronic control device, in that only the desired value of a motor pressure to be set at the respective motor connection is predetermined and the valve arrangement otherwise works automatically as a function of the desired/actual-value deviation of the pressure at the respective motor connection. The control device thus acts as a desired-value generator working as a function of parameters.
In the invention, it is advantageous that the respective motor-pressure desired values also constitute a measure of the desired value of the boosting force to be set in each case, that is to say the pressure-reducing valves work automatically as a function of the desired/actual-value deviation of the boosting force.
This, on the one hand, ensures that the boosting force is controlled without any delay and as required and, on the other hand, means that no “overreactions” in the control of the boosting forces are to be expected, even in the event of a rapid change in the operating conditions.
A particular benefit of the invention is that no hydraulic control members having seals subject to friction have to be arranged in or on the mechanical drive train or in or on the positive connection between the steering wheel or steering wheel and the vehicle wheels steered thereby. The invention accordingly ensures a steering system with low hysteresis in steering manoeuvres with successive steering changes.
Moreover, as regards preferred features of the invention, reference is made to the claims and to the following explanation of the drawing, by means of which particularly preferred embodiments are described.
REFERENCES:
patent: 4562710 (1986-01-01), Lipschutz
patent: 5048627 (1991-09-01), Eguchi et al.
patent: 5449186 (1995-09-01), Gerl et al.
patent: 5553683 (1996-09-01), Wenzel et al.
patent: 6012541 (2000-01-01), Nishioka et al.
patent: 6018691 (2000-01-01), Yamamoto et al.
patent: 195 19 875 (1995-10-01), None
patent: 196 41 899 (1996-07-01), None
Pluschke Albrecht
Stehli Thomas
Crowell & Moring , L.L.P.
Johnson Brian L.
Luby Matthew
Meredes-Benz Lenkungen GmbH
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