Motor vehicles – Steering gear – With fluid power assist
Patent
1994-11-15
1996-07-02
Hill, Mitchell J.
Motor vehicles
Steering gear
With fluid power assist
91449, B62D 508, B62D 5083
Patent
active
055312861
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an auxiliary power steering unit, especially for motor vehicles. Such an auxiliary power steering has a control valve--made as a rotary slide valve--for controlling a pressure medium that is conveyed to and from the pressure chambers of a servomotor from a tank by a servopump. The rotary slide valve has two feedback chambers that are connected to the pressure line of the servopump via one, each, fixed throttle and via one common throttle. The feedback pressure that takes effect in the feedback chambers is limited to a maximum value by means of at least one cutoff valve.
2. Description of the Prior Art
Such an auxiliary power steering is known from EP-B1-0198824.
If the cutoff valve mentioned in this publication is made in the form of a seat valve, which is frequently the case, then the pressure medium stream regulated upon the valve's response is diverted directly into the tank. As a result, the pressure medium volume that is available for the servomotor of the auxiliary power steering is reduced considerably. Besides, flow and oscillation noises are generated during the diversion of the pressure medium screen. The switching pressure is also tolerance-tainted by unavoidable production tolerances.
The purpose of the invention is so to improve an auxiliary power steering known according to the state of the art that one can most extensively prevent a loss of pressure medium upon response of the cutoff valve and that the tolerances of the response pressures of the cutoff valve can, if at all possible, be avoided entirely.
SUMMARY OF THE INVENTION
This problem is solved by the auxiliary power steering of the present invention. The cutoff valve is made in the form of a pressure balance whose response pressure can be adjusted from the outside without dismantling. Besides, the cutoff valve is inserted in the pressure line of the servopump between the servopump and the feedback chambers. By using the pressure balance design and as a result of the arrangement in the pressure line, no connection is opened from the pressure line to the tank as the cutoff valve responds. Instead, the connection from the pressure line to the feedback chambers is increasingly blocked off so that the entire pressure medium stream, moved by the servopump, will continue to be available to the servomotor of the auxiliary power steering. Because the response pressure of the cutoff valve can be adjusted from the outside without dismantling, one can eliminate all of the production tolerances of the cutoff valve and one can compensate for additional tolerances in the other steering parts.
Practical and advantageous versions of the invention are given in the subclaims.
But the invention is not confined to the combinations of features given in the claims. The expert will find additional meaningful ways of combining claims and individual claim features from the problem statement.
The response pressure of the cutoff valve can be adjusted in a particularly simple fashion if the valve body of the cutoff valve consists of two parts whose inside-lying part is so made that it cannot be turned and whose axially movable and outside-lying part is made rotatably and axially immovable in the valve borehole. The inside-lying part is connected with the outside-lying part by means of a screw thread. If the outside-lying part is turned by an adjusting device that is accessible from the outside, then a pressure spring located inside the valve body is compressed more or less strongly. Because the pressure spring acts upon the control piston located inside the valve body, one can very accurately set the response pressure of the cutoff valve.
If the common throttle is so made that it reveals a throughflow cross section that can be altered as a function of the vehicle speed, then one can attain differing feedback forces as a function of the speed.
If the common throttle is made with a constant throughflow cross section, then this throttle can be arranged either in the valve body or in
REFERENCES:
patent: 5092418 (1992-03-01), Suzuki et al.
patent: 5133424 (1992-07-01), Fox et al.
patent: 5186272 (1993-02-01), Smith
patent: 5419235 (1995-05-01), Gilbert et al.
patent: 5447209 (1995-09-01), Sasaki et al.
Majer Hans-Werner
Schanzel Rainer
Schoffel Jorgen
Hill Mitchell J.
ZF Friedrichshafen AG
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