Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2000-05-02
2001-06-26
Rivell, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S625210, C091S37500R
Reexamination Certificate
active
06250333
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a servovalve, in particular for hydraulic power-assisted steering systems of motor vehicles, in the form of a rotary spool valve with a rotary spool and a control bush, which coaxially surrounds the rotary spool and can be rotated against spring force relative to the rotary spool.
Such servovalves are, for example, known from DE 42 34 571 A1 and U.S. Pat. No. 4,966,192. In the case of a power-assisted steering system, the rotary spool and the control bush form parts of a train of shafts which mechanically connects a manual steering wheel to the steered vehicle wheels. In this arrangement, a shaft part, which is torsionally connected to the control bush, and a shaft part, which supports or includes the rotary spool, are connected together by a torsion bar so that they are axially secured but torsionally flexible. The rotary spool and the control bush are deflected relative to one another from a relative central position to a greater or lesser extent corresponding to the forces and torques effective between the manual steering wheel and the vehicle steering wheels. This rotary travel between the control bush and the rotary spool has the effect that a hydraulic servomotor controlled by the servovalve is acted upon in a controllable manner by hydraulic pressure or by a hydraulic pressure difference in one or the other direction, depending on the direction of the relative twist between the control bush and the rotary spool supports the respective steering manoeuvre, i.e. the manual force to be applied to the manual steering wheel is correspondingly reduced.
The spring force is typically generated by a torsion bar which mechanically connects the rotary spool to the control bush. In order to accommodate the torsion bar, the rotary spool and the parts of the control bush axially abutting it or the elements torsionally connected to the control bush have a tubular configuration.
In DE 196 15 543 A, published after the claimed priority date, a servovalve, of the type mentioned at the beginning, is described in which a first axial extension is arranged eccentrically to the axis of the rotary spool valve at one end face of the control bush.
An end surface, which faces towards the aforesaid end face, has a further extension of the same type as the first extension and has the same radial distance from the axis of the rotary spool valve as the first extension. The end face is arranged at an axial distance from the free end of this extension on a part which is torsionally connected to the rotary spool, and the total axial length of the extensions is somewhat shorter than the axial distance between the end face of the control bush and the end surface.
A C-spring, which surrounds the rotary spool and whose free ends are clamped against the extensions and try to force the latter into a mutually aligned position, is arranged between the said end face of the control bush and the said end surface.
This realizes the general idea of arranging, axially between an end face of the control bush and a part at the rotary spool end, a ring-type spring, which surrounds a section of the rotary spool and which is bent open to a greater or lesser extent during relative rotations between the control bush and the rotary spool because the extensions then move away from one another in the peripheral direction of the rotary spool section.
A particular advantage of this design is the ease of assembly of the C-spring. In addition, the C-spring can also be configured with preload in such a way that a specified spring loading is still present when the pins are mutually aligned.
In accordance with this older patent application, provision is usually made for the rotary spool and the control bush to be additionally connected by way of a torsion bar, which is accommodated within a tubular inner space of the rotary spool and is firmly connected at one end to the rotary spool, for example by pinning, and is firmly connected at its other end to the control bush or parts connected to the latter. This torsion bar, as well as the aforesaid C-spring, effects an increasing restoring force in the case of relative rotations between the control bush and the rotary spool.
In addition, the torsion bar is used to secure the control bush and the rotary spool axially relative to one another.
SUMMARY OF THE INVENTION
The object of the invention is to ensure a fixed axial position of the rotary spool and the control bush relative to one another in a simple design manner, in a servovalve of the type mentioned at the beginning, even when no torsion bar is provided.
This object is achieved, in accordance with the invention, by firmly connecting the control bush to a sleeve on the same axis and arranging or configuring a bearing axially between the control bush and the sleeve, which bearing secures the control bush and the rotary spool axially relative to one another.
The invention is based on the general idea of integrating a bearing into the rotary spool valve and, to achieve a simple arrangement or configuration, of combining the control bush with a sleeve axially abutting it in order to form a tubular part which surrounds the bearing and which can be dismantled.
As a result, it is then possible to achieve an arrangement which can be assembled by pushing parts axially onto one another or by placing them axially on one another.
Provision is preferably made to force the spool bush and the rotary spool into a central rotational position relative to one another by means of a preloaded C-spring. In this connection, it is expedient for a first axial extension to be arranged eccentrically to the axis of the rotary spool valve at the end face of the sleeve facing away from the control bush. An end surface, which faces towards the end face, has a further extension of the same type as the first extension, and has the same radial distance from the axis of the rotary spool valve as the first extension, is arranged at an axial distance from the free end of this extension on a part which is torsionally connected to the rotary spool. The total axial length of the extensions are somewhat shorter than the axial distance between the end face of the sleeve and the end surface of the part which is torsionally connected to the rotary spool, and the C-spring is arranged between the end face of the sleeve and the end surface of the part torsionally connected to the rotary spool in such a way that this C-spring surrounds a section of the rotary spool and its free ends are clamped against the extensions.
In addition to easier assembly, this construction offers the advantage that it permits a rotational adjustment of the control bush relative to the sleeve and therefore to the sleeve-end extension when the control bush and the sleeve are connected, which extension, together with the other extension in interaction with the C-spring, in turn specifies the central rotational position or initial position of the rotary spool valve.
With respect to preferred features of the invention, reference is otherwise made to the claims and the following explanation of the drawings, by which particularly preferred embodiments of the invention are described.
REFERENCES:
patent: 4488475 (1984-12-01), Masuda et al.
patent: 4799514 (1989-01-01), Tanaka et al.
patent: 4905572 (1990-03-01), Devaud et al.
patent: 5058696 (1991-10-01), Prebay et al.
patent: 5797309 (1998-08-01), Eberhart
patent: 5845557 (1998-12-01), Speidel et al.
patent: 42 34 571 (1994-04-01), None
patent: 196 15 543 (1997-10-01), None
patent: 0 072 712 (1983-02-01), None
patent: 2496583 (1982-06-01), None
Breuning Edwin
Schiek Bernd
Speidel Gerd
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Mercedes-Benz Lenkungen GmbH
Rivell John
Schoenfeld Meredith H.
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