Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2003-04-24
2004-12-28
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S625690
Reexamination Certificate
active
06834676
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application, Serial No. 102 18 759.2, filed Apr. 26, 2002, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to a pneumatic slide valve for regulating a flow or pressure fluid between various ports.
It is to be understood by persons skilled in the art that the term “slide valve” is used here in a generic sense and the principles described in the following description are equally applicable to valves which generally follow the concepts outlined here, such as, for example, piston valve, gate valve, directional control valve and the like. A typical pneumatic slide valve of a type involved here includes a valve housing which is made of injection-molded plastic material and has a valve bore for accommodating a slide member, also called valve spool, for displacement in axial direction, whereby the valve bore is interrupted by pressure fluid compartments which are disposed in spaced-apart relationship along the valve bore and are fluidly connected with outer ports of the valve housing. In general, the valve housing of pneumatic slide valves is either made of multiple parts or of single-piece configuration. Multipart valve housings are used to simplify assembly of components to be fitted in the valve housing and are normally split in the plane of the slide member, whereby both housing portions are connected to one another, after installation of internal valve components, through a screw connection and sealed against one another by an interposed housing seal. Pneumatic slide valves with such multipart valve housing are bulky with substantial dimension in width because of a need for a certain material thickness to provide a support surface for the housing seal.
On the other hand, there is an ever increasing demand on the manufacturers to produce pneumatic gate valves of smaller size because the provision of small single valves enables the production of an overall compact valve unit composed of a multiplicity of adjoining single valves. Therefore, the use of a single-piece valve housing is more and more desired as the overall width can hereby significantly be reduced, without causing an excessive decrease in throughflow of pressure fluid. However, single-piece valve housings must be re-finished by a complicated material cutting process, after their production through injection molding, especially as far as the interior valve bore for accommodation of the slide member is concerned. The finishing process of the valve bore involves the provision of a particularly smooth surface and the formation of various slanted run-on surfaces and rounded control edges.
German patent publication DE 197 45 802 A1 describes a single-piece valve housing including individual, pre-fabricated valve bushings which form the valve bore and are molded around with plastic material as the valve housing is injection molded. In order to secure the valve bushings in axial direction, each valve bushing is provided on its outer circumference with at least one ring-shaped groove or, at least in predetermined sections, with a ring-shaped bump, to effect a form-fitting engagement with the valve housing, after the valve housing is molded around the valve bushings. The valve bushings, which are made of metallic material, are placed into the injection mold before the injection molding process and held in place at the appropriate positions by rams. After injection molding, the valve bushings are secured in form-fitting relationship with the valve housing.
Although this approach may appear to be sound, practice has shown that when a multiway valve of this type is used over an extended period or exposed to extreme temperature fluctuations, a clearance between the valve bushings and the valve housing may form that adversely affects the operation of the gate valve. In extreme situations, the emergence of a gap may lead to an inadvertent migration of pressure fluid to an area between neighboring pressure fluid compartments. To tackle this problem, the arrangement of a sealing element in the form of an O-ring between the valve bushing and the valve housing has been proposed. However, as plastic material is molded around the valve bushings as the valve housing is injection-molded, the sealing elements are pushed out of the intended position so that the valve housing cannot be manufactured at reliable reproducibility. Furthermore, the use of valve bushings results in a great number of individual parts, thereby further complicating the manufacturing process of the valve housing.
It would therefore be desirable and advantageous to provide an improved pneumatic slide valve which obviates prior art shortcomings and which is reliable in operation even when subjected to extreme stress, while still allowing a production of the valve housing in a simple manner.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a pneumatic slide valve includes a valve housing made of injection-molded plastic material and having a valve bore and a plurality of external ports, wherein the valve housing has an outer housing portion, which is made of reinforced plastic and is determinative for a geometric outer dimension of the valve housing, and an inner housing portion, which is made of non-reinforced plastic and extends continuously within the valve housing to define a plurality of pressure fluid compartments in fluid communication with the ports and to define the valve bore at least in a region which is positioned in the area of the pressure fluid compartments, with the valve bore interrupted in axial direction by the pressure fluid compartments, wherein the outer housing portion is molded around the inner housing portion, and a slide member, accommodated in the valve bore of the valve housing for displacement in the direction of the axis, for regulating a flow of compressed air between the ports.
The present invention resolves prior art problems by enabling the use of materials for making the valve housing to best suit the mechanical demands on the valve housing. The running surfaces of the valve bore have a particularly high service life, as the inner housing portion is made of non-reinforced plastic which exhibits elasticity and superior surface quality and thus is especially suitable for application in connection with the mechanical demands upon the valve bore. On the other hand, as the outer housing portion, which encapsulates the inner housing portion, is made of reinforced plastic, the tendency for creepage is relatively low as a consequence of the fillers contained in the reinforced plastic. This fact is especially advantageous in conjunction with a securement of the valve housing to a carrier or securement of peripheral components of the slide valve to the valve housing. Compared to the conventional structure with several valve bushings for configuration of the valve bore through insert molding, the valve housing of the slide valve in accordance with the present invention is comprised of only two components. As the outer housing portion is molded around the inner housing portion, the securement of the inner housing portion within the injection mold becomes less complicated, when compared with the conventional approach to integrate several individual valve bushings.
As a result of the material union between the inner housing portion and the outer housing portion, the formation of gap between these two housing portions is precluded. The material union is realized directly during the encapsulation of the inner housing portion, i.e. in a same process step, and combined with a form-fitting connection. The tight material union can easily be implemented, when the materials of both housing portions to be connected have a same melting temperature. Thus, a detachment of the inner housing portion within the valve housing is positively prevented.
According to another feature of the present invention, passageways between the pressur
Bosch Rexroth AG
Feiereisen Henry M.
Michalsky Gerald A.
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