Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-05-11
2001-11-20
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C091S399000
Reexamination Certificate
active
06318232
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of German application number 19921552.7 filed Nov. 5, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a pressure-cutoff arrangement for an auxiliary power steering system in the end positions of the steering lock.
2. Description of Related Art
Pressure-cutoff arrangements of this type are known from the prior art. Thus, for example, EP 0321756 A2 indicates a recirculating ball steering system in which the working piston carries two seat valves which can be actuated in the axial direction and which strike against the housing in the end positions of the admissible steering lock and, in doing so, reduce the working pressure occurring in the working space which has been acted upon by pressure. As a result of this, the auxiliary power assistance is eliminated when this impingement occurs, so that further turning of the steering system is not possible.
A generic auxiliary power steering system, in which cutoff valves are likewise associated with the working piston, is also known from Spanish Patent Application P9202046. In the extreme positions, the cutoff valves impinge on a stop in the form of a pin which is pretensioned in the direction of the valves by a spring. The pin can be locked in the radial direction with the aid of a clamping screw. In order to set the opening point of the cutoff valves, and thereby set the stop limits, it is necessary, in this steering system, to undo the clamping screw and to actuate the steering system manually, with the wheels relieved of load, until the maximum admissible turning angle is reached. As a result of this, the cutoff valve will press the spring-loaded pin inwards into the required position. The pin can then be locked in this position and is thereby permanently set.
Finally, the nearest prior art is known from DE 4127610, in which stop means in the form of a bolt or bush form the end stops of the cutoff valves. The pistons or bushes are seated, with a press fit, on ribs constructed in the peripheral direction and can be pressed, when the front wheels are relieved of load for the purpose of setting the steering system manually, that is to say without auxiliary power assistance, into the required position, in which they are fixed automatically because of the press fit. In this form of embodiment, manual fixing, such as is known from Spanish Patent Application P9202046, is not necessary. However, the press fit of the piston or bush on the one hand necessitates very precise manufacture of the corresponding structural elements, and on the other hand permits, at most, very few repeated setting operations, since the fit becomes loose in the event of repeated changing and the retaining force falls below the opening force of the cutoff valve.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a pressure-cutoff device for an auxiliary power steering system, which device is capable of repeated setting and sets itself by simple manual turning of the steering system.
Because the stop means are fixed by means of a spring which acts in the radial direction and has a retaining force that exceeds the opening force of the cutoff valves, they can be brought to the required setting by manually moving the cutoff valves against the stop means. Even repeated displacement of the stop means does not lead to a substantial drop in the retaining force of the radial spring. In this connection, it is advantageous if the stop means has a substantially round shaft region and the spring surrounds the said shaft region in the form of a ring. In addition to satisfactory retaining force, this also brings about a distribution of the said retaining force which is uniform over the periphery, and also a certain guidance of the stop means. If the spring is a circumferential coil spring with a wave-like profile in the peripheral direction, particularly high retaining force can be achieved with simultaneous centring of the stop means.
For simple resetting of the stop means, it is advantageous if the latter are guided, in each case, in a bore, for example a through-bore in the steering housing or else a bore in a separate holder, each through-bore preferably having a removable fluid-tight and pressure-tight closure, after the removal of which, one end of the particular stop means, which end faces away from the steering housing, is accessible from outside. The stop means can then be moved manually into a basic position from which setting takes place.
Finally, it is advantageous, for reliable and mechanically stable mounting, if the spring is enclosed in an annular groove associated with the through-bore or with the shaft region, and is fixed in the axial direction. The spring is then fixed either in the steering housing or on the stop means and can be easily brought into this defined position on assembly.
REFERENCES:
patent: 4625624 (1986-12-01), Adams
patent: 5419235 (1995-05-01), Gilbert et al.
patent: 5803201 (1998-09-01), Sheppard
patent: 41 27 610 A1 (1992-02-01), None
patent: 195 06 995 A1 (1995-08-01), None
patent: 0 321 756 A2 (1988-12-01), None
patent: P 9202046 (1992-10-01), None
Gutzlaff Markus
Lemke Norbert
Kershteyn Igor
Look Edward K.
Mercedes Benz Lenkungen GmbH
Woodbridge Richard C.
Woodbridge & Associates P.C.
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