Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2000-04-25
2001-08-21
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
C180S403000, C180S429000, C091S37500R
Reexamination Certificate
active
06276487
ABSTRACT:
FIELD OF THE INVENTION
The invention refers to a rotary or slide valve for power steering systems of motor vehicles. The rotary shift valve contains two valve elements, which are coaxially flexibly arranged, with maximum rotation relative to each other being limited by the rotational travel of a backlash clutch. The first valve element, which is linked to a valve input element, is designed as a radial, outer rotary slide. The second valve element forms a rotation-fixed link with a valve output element and is designed as a radial, inner control bush, which is guided in an axial bore of the rotary slide. Both valve elements feature longitudinal control grooves whose axial length is at least partially limited and which cooperate in the control of the flow of a pressure medium to and from two working spaces of a servomotor. A torsion rod spring returns the two valve elements from their deflected positions to their neutral positions.
BACKGROUND OF THE INVENTION
A centering device is arranged between the rotary slide and the valve output element in support of the torsion rod spring. This device contains two centering elements, which are rotatable against each other, and there is at least one anti-friction element located between the two centering elements. One of the centering elements forms a rotationfixed link with a reaction piston.
Such a rotary shift or slide valve is known from DE-A1-44 33 599. The advantage of this rotary shift valve is that the outer dimensions of the entire valve can be very small, which is due to the particular arrangement of the control bush inside the rotary slide. With this rotary shift valve, centering is effected via the torsion rod spring. The particular feature of a torsion rod spring is that the return effected by the torsion rod spring in the actual center area of the rotary shift valve is only minimal. Therefore, the torsion rod spring is supplemented by a centering device, which allows precise centering, especially in the center area of the rotary shift valve. In this version, extra space in axial direction is required for the additional centering device, and especially for longitudinal guidance of one of the centering elements.
Since the centering device is arranged between the rotary slide and the valve output element, it is possible for a prefixed position to be determined for one centering element of the centering device together with the valve output element. As a result, it is possible to set centering force and position of the centering device after production of the individual parts. Since the reaction piston rotates together with the rotary slide, a relative motion results between the reaction piston and a valve housing. The reaction piston must be sealed off against the valve housing, and therefore friction arises, which directly affects the manual force to be applied to a hand wheel.
BRIEF SUMMARY OF THE INVENTION
The task of the invention is to improve the known rotary shift valve in such a way that friction is reduced. At the same time, the length of the rotary shift valve is to be shortened.
This task is solved by the rotary shift valve described in hereinbelow. Beneficial and purposeful features of the invention are also described hereinbelow.
The solution in the generic rotary shift valve is brought about by a rotation-fixed but axially displaceable link between the valve output element and the centering element, which is firmly linked to the reaction piston. The other centering element is in a predetermined position and forms a rotation-fixed and non-displaceable link with the rotary slide. The reaction piston in the area of the centering unit is deposed radially around the rotary slide and projects in axial direction into the area of the rotary slide.
In the invented arrangement, the reaction piston forms a rotation-fixed but axially displaceable link with the valve output element. As a result, sealing ring friction between reaction piston and valve housing is transferred from the primary side to the secondary side of the rotary shift valve. Backlash-free reaction torque can be generated, which results in precise function. With regard to the return of the rotary shift valve to its neutral position, no extra hysteresis is generated by the friction on the sealing ring of the reaction piston. By intra-positioning reaction piston and rotary slide, i.e. as a result of the reaction piston projecting into the area of the slide valve, a compact and short design is achieved.
The axial dimensions of the rotary shift valve are further reduced if the rotation-fixed link between the reaction piston and the valve output element is formed by a metal bellows. The latter is installed radially outside the centering elements so that here, too, intra-positioning cuts back axial length.
The purpose of the metal bellows is mainly to bring about torsion rigidity of the reaction piston in relation to the valve output element. By means of additional pre-load of the metal bellows, through which the metal bellows also acts as a spring, the valve characteristics can be directly influenced.
Torsion rigidity of the reaction piston is particularly easy to bring about if metal bellows and reaction piston are firmly linked to each other. Then, following adjustment of the centering device, the metal bellows only needs to be firmly linked to the valve output element by form- or friction-locking means.
If in the process of assembly of rotary shift valve and centering device, linking of the metal bellows to the valve output element is to be omitted, a bush can be affixed to the metal bellows, with this bush having an adhesive or friction lining, which in cooperation with an adhesive or friction lining on a surface of the reaction piston brings about a rotation-fixed friction and/or adhesive link, due to the pre-load of the metal bellows and/or the hardening of the adhesive. Then, there is no need for the metal bellows to be mounted stationary.
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Bieber Jurgen
Breitweg Werner
Schanzel Rainer
Larson & Taylor PLC
Swann J. J.
Zeender F.
ZF Friedrichshafen AG
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