Fluid handling – Processes – Cleaning – repairing – or assembling
Reexamination Certificate
2000-03-09
2001-07-31
Chambers, A. Michael (Department: 3753)
Fluid handling
Processes
Cleaning, repairing, or assembling
C137S625230, C091S37500R
Reexamination Certificate
active
06267133
ABSTRACT:
The invention concerns a method for the assembly of a steering valve with a centering device for hydraulic power steering systems, in particular for motor vehicles, in accordance with the nomen collectivum of claim
1
. The steering valve contains a first valve element and a second valve element, with both valve elements being rotatable in relation to each other. The centering unit contains a first centering element and a second centering element, with both elements being rotatable and axially displaceable in relation to each other. At least one of the two centering elements can be actuated by means of a spring toward the other centering element. The centering elements have essentially radially arranged grooves facing each other, in which anti-friction elements can be inserted.
A steering valve with a centering device to which above method refers is known from EP-B1-646 080. With such steering valves, the two valve elements as well as the two centering elements must be very precisely aligned and fixed in relation to each other, for the mechanical center of the centering unit to correspond to the hydraulic center of the steering valve.
With the known steering valve with a centering unit, the second valve element forms a single part with the second centering element. Alignment of the mechanical center of the centering unit with the hydraulic center of the valve elements is effected by aligning the first centering element relative to the first valve element. To this end, the first centering element is initially rotatable relative to the axial lock. After alignment, rotation-locked connection of the parts is brought about. Connecting the parts by means of welding, however, may result in undesirable local warm-up.
The suggestion has been made, therefore, to separately produce the second centering element and the second valve element and to connect both during assembly. According to the proposal, after placement and alignment of the second centering element, the second valve element is to be connected to the second centering element by deforming a ring-shaped flange provided on the second valve element. This, however, involves the risk that the second valve element might not only be deformed in the area of its ring-shaped flange but also on its circumference and in the area of its control grooves. Moreover, such an assembly requires correct positioning of the first centering element relative to the first valve element to be followed by the alignment of the two centering elements relative to each other. This alignment is impaired by the friction between the second centering element and the second valve element. Such a combination of assembly, positioning, alignment and fixation by deforming components generally requires complex equipment.
The task of the invention is to present a precise and cost-effective assembly method. This task is solved by the method described in claim
1
. The method involves the following steps:
The two valve elements of the steering valve—without centering unit—are hydraulically or pneumatically centered, and when aligned in their central position they are linked to each other by means of a torsion bar spring.
Separate from the steering valve, the two centering elements of the centering unit are pre-assembled in an assembly fixture and aligned in their mechanical center position together with the anti-friction elements, e.g. by applying an axial force.
The two centrally aligned valve elements of the steering valve are linked to the two centering elements (aligned in their mechanical center position) of the centering unit. To this end, the first centering element is aligned relative to the first valve element by means of a rotation-fixed axial guide element, and non-rotatable but axially displaceable connection is established. Then, by means of axial displacement of the entire centering unit along the non-rotatable axial guide element, the second centering element is linked to the second valve element via longitudinal press fit.
With this method, alignment of the centering elements relative to each other does not result in reaction torque from the centering unit acting on the steering valve, which could affect the centering of the valve elements.
The subordinate claims state the advantages and purpose-specific features of the invention. Assembly, for example, is facilitated if the second centering element has a radial, external circumferential groove for easy insertion of the assembly tool. The circumferential groove can be replaced by an assembly flange providing the same benefit. Circumferential groove or assembly flange are used for the alignment of parts and for assembly or pressing-on. It is of particular advantage if the circumferential groove, on its wall not facing the second valve element, features an insertion taper facilitating insertion of the assembly tool and if its wall facing the second valve element features an essentially flat surface for safe support of the assembly tool. To rule out the possibility that assembly of the press fit might have an influence on the sealing gap between the two valve elements, an anti-friction bearing—e.g. in the form of a needle bearing—may be disposed between the first and the second valve element in the axial area of the second centering element.
REFERENCES:
patent: 5575193 (1996-11-01), Bareis et al.
patent: 5769121 (1998-06-01), Breitweg
patent: 5957027 (1999-09-01), Gilbert et al.
patent: 6026858 (2000-02-01), Gilbert
patent: 6052900 (2000-04-01), Campbell
patent: 39 34 468 A1 (1990-04-01), None
patent: 44 20 744 C2 (1997-07-01), None
Hofmann Hans
Kruttschnitt Andreas
Walter Wolfgang
Chambers A. Michael
Larson & Taylor PLC
ZF Friedrichshafen AG
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