Slide valve having a housing and a slide element guided within the housing

A slide valve having a housing and a slide element guided within the housing, at least two hydraulic connections being present on the housing, and at least one of the hydraulic connections communicating hydraulically with at least one control port in a cylindrical guide surface that guides the slide element, the control port extending only over a limited distance in the circumferential direction of the guide surface and cooperating with a control edge of the slide element assigned thereto, the slide element having an essentially cylindrical outer contour and at least one end face, and the slide element being produced by injection molding, and at least one injection point being configured on the end face.

RELATED APPLICATION INFORMATION

The present application claims priority to and the benefit of German patent application no. 10 2011 006 855.4, which was filed in Germany on Apr. 6, 2011, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a slide valve, as well as to a method in accordance with the description herein.

BACKGROUND INFORMATION

In modern automatic transmissions in motor vehicles, hydraulically actuated clutches are used for gear shifting. To enable these gearshift operations to be carried out imperceptibly to the driver, the utmost precision must be used to adjust the hydraulic pressure in the clutches in accordance with predefined pressure ramps. Electromagnetically actuated pressure control valves are used to adjust these pressure ramps.

SUMMARY OF THE INVENTION

It is, therefore, an object of the exemplary embodiments and/or exemplary methods of the present invention to provide a slide valve according to the description herein, as well as a method according to the description herein. Advantageous further refinements are delineated in the dependent claims. Important features of the exemplary embodiments and/or exemplary methods of the present invention are set forth in the following description and in the drawings, the features important to the exemplary embodiments and/or exemplary methods of the present invention being able to be considered, both alone, as well as in different combinations, without having to refer explicitly thereto again.

It is an advantage of the exemplary embodiments and/or exemplary methods of the present invention that a slide element of a slide valve may be produced cost-effectively by injection molding, it being possible to maintain low dimensional tolerances of the slide element surfaces important to functioning. Any gaps that arise and resultant leakage flows of a hydraulic fluid between the slide element and a cylindrical guide surface of a slide housing (“housing”) remain relatively insignificant.

The slide valve according to the present invention features a housing having at least two hydraulic connections. At least one of the hydraulic connections communicates hydraulically with at least one control port in a cylindrical guide surface of the housing that guides the slide element. In particular, the control port extends only over a limited distance in the circumferential direction of the guide surface. The control port cooperates with a control edge of the slide element assigned thereto. The slide element has an essentially cylindrical outer contour and at least one end face, and is produced by injection molding. At least one injection point (sprue) required for the injection molding is configured on the end face of the slide element. At least two injection points may be configured on both end faces of the slide element, respectively.

More than one injection point may be configured on the end face of the slide element, which may be symmetrically to a longitudinal axis of the slide element, respectively of the slide valve. The symmetry achieved in the injection molding process makes possible an especially uniform demolding of the slide element, and thus excellent geometrical accuracy.

This eliminates the need for postprocessing operations, such as machining.

It is provided, in particular, that the slide valve encompass means for limiting a rotation of the slide element relative to the housing. Combining the property of the at least one control port, whereby it extends only over a limited distance in the circumferential direction of the guide surface, with the means for limiting rotation, makes it possible to ensure that the control port(s) is/are only able to cooperate with the designated radial portions of the slide element. Thus, it suffices when particular precision is used only in the injection molding of these radial portions of the slide element, as will be explained further below. Any potential leakage may be thereby minimized.

One embodiment of the slide valve provides that the means for limiting the rotation encompass at least one guide device in accordance with the tongue and groove principle, a radial angle of the groove being equal to or greater than a radial angle of the tongue guided in the groove. Such a guide device, which functions in accordance with the tongue and groove principle, may be manufactured very simply and to adequate precision. Costs may be thereby saved and the fatigue strength of the slide valve enhanced.

In particular, the guide device design may provide for the slide element to feature at least one axially extending tongue, and for the guide surface, respectively the housing to feature at least one axially extending groove. The tongue may be smaller in axial length than the slide element. This configuration is particularly useful when, at the same time, each groove is a radial portion of an axially extending hydraulic channel (“overflow channel”). Thus, the functions of the groove and of the overflow channel are advantageously combined. The design of the slide valve is thereby simplified, making it possible to save costs.

One embodiment of the present invention provides that the groove be formed at least at one of two axially extending bounding surfaces by an axially extending rib of the guide surface, respectively of the housing. Additional design options are thereby derived for the overflow channel(s). This makes it possible to obtain an adequate cross section of the overflow channels and, at the same time, limit a rotation of the slide element relative to the housing.

Another embodiment of the present invention provides that the slide element feature two approximately 180° mutually offset tongues, the first tongue cooperating with the corresponding groove to limit a clockwise rotation of the slide element, and the second tongue cooperating with the corresponding groove to limit a counterclockwise rotation of the slide element. Thus, once again, other structural design options for realizing the overflow channels, on the one hand, and the groove, on the other hand, are described. For example, the longitudinal rib may be configured within the overflow channel, whereby the overflow channel is subdivided into at least two radial regions. Thus, the tongue configured on the slide element may glide by a bounding surface axially along the rib, the other respective axial bounding surface of the tongue not featuring any limit stop. Thus, using at least two approximately 180° mutually radially offset tongues configured on the slide element, one of the tongues is configured for acting on one direction of rotation, respectively, so that, in sum, both directions of rotation are provided for. This means that the radial play of the slide element in the groove may be kept relatively small. The precision of the slide valve according to the present invention may be thereby enhanced. The tongues may be radially configured at an approximately 90° angle relative to the control ports of the housing. It is noted that the present designation “clockwise direction” is only for comparison purposes and does not connote a requisite direction of rotation.

The slide valve is very inexpensive to manufacture when the slide element and/or the guide surface, respectively the housing are fabricated from a high-strength or reinforced plastic and/or from a fiberglass reinforced plastic. This makes it possible to attain an ease of manufacture, minimal contraction, a low rate of wear, adequate insensitivity to a hydraulic fluid that is used, and, in each case, desired thermal properties.

Due to the stringent requirements for the operating temperatures—for example, up to 150° C.—and the mechanical strength—for example, acting pressures of up to 20 bar—reinforced plastics having a high temperature resistance and a high resistance to the hydraulic oil used are particularly advantageous. The reinforcing fibers may be glass fibers, carbon fibers or other types of fibers, for example organic fibers, such as aromatic polyamides. Alternatively or additionally, inorganic filler material having an acicular, plate-like or spherical shape may be used.

The fibrous additives result in a relatively pronounced anisotropy of the slide element properties that, in particular, are conditional upon the geometry and/or the position of the injection points. Nevertheless, the present invention makes it possible for the slide element of the slide valve to be manufactured with adequate precision and small gap dimensions in the injection molding process.

A method is also provided for producing the slide valve, the slide element being manufactured by injection molding, and the slide element being injection-molded using at least one injection point on at least one end face of the slide element. At least two injection points may be configured at both end faces of the slide element, respectively. The slide element, injection-molded in this manner, thereby features an especially uniform and symmetrical shape having optimal roundness. It is possible to effectively approach a cylindrical shape, in particular at those radial portions of the slide element that cooperate with the control ports. This applies, in particular, to fiberglass reinforced plastics where, generally, the strength is greater and the thermal expansion coefficient is smaller. This makes it possible to improve the functioning of the slide valve and to minimize leakage.

In a first embodiment for that purpose, the slide element is injection-molded using at least two casting molds of an injection mold, the first casting mold being designed as a hollow cylindrical body, and the second casting mold as a punch that axially bounds the hollow cylindrical body. This embodiment is especially suited for those slide valves whose slide element has a comparatively small axial length. The slide element produced by injection molding may be advantageously axially demolded from the particular injection mold. The advantage is that the slide element may be designed to be radially symmetric, no axially extending binding seams being formed. In a second embodiment for that purpose, the slide element is injection-molded using at least three casting molds of an injection mold, the first and the second casting mold being designed as two elements of an axially cut hollow cylindrical body (“shape-forming cavity”), and the third casting mold as a punch that axially bounds the hollow cylindrical body. Thus, those slide elements having a comparatively long axial length may also be produced. For example, a first and a second part of the mold tool correspond to the axially cut halves of the hollow body. Thus, in some instances, 180° mutually radially offset burs may form on the slide element.

Another embodiment of the method provides that the slide element be injection-molded using two injection points configured symmetrically at the axial end face thereof. The two injection points may be radially adjacent to those portions of the peripheral surface of the slide element that cooperate with the control ports. This is particularly advantageous when a particular hydraulic connection of the slide valve features a pair of 180° mutually radially offset control ports. This enables the slide element to operate very precisely.

In particular, it is provided that burs forming during injection molding of the slide element on the peripheral surface thereof are formed outside of a region of the at least one control port. Together with the arrangements according to the exemplary embodiments and/or exemplary methods of the present invention for limiting a rotation of the slide element relative to the housing, it is achieved that the control ports of the housing cooperate only with the very precisely produced radial portions of the slide element, a contact with the burs of the slide element being thereby avoided.

Exemplary specific embodiments of the present invention are clarified in the following with reference to the drawing.

DETAILED DESCRIPTION

The same reference numerals are used for functionally equivalent elements and quantities in all of the figures, even for different specific embodiments.

FIG. 1shows a slide valve10in a part-sectional view. In the present case, slide valve10is designed as a pressure regulating valve. It encompasses a housing12that has an axially stepped outer contour. A stepped bore14featuring a guide portion16having a constant diameter is provided in housing12and extends in the longitudinal direction thereof. Guide portion16has a cylindrical guide surface18.

Configured in guide portion16of stepped bore14is a cylindrical slide element20that is guided by a guide surface18. Slide element20has a peripheral surface22and, in the present case, two axially extending tongues21, of which only one is visible in the drawing. In addition, slide element20has a right end face24inFIG. 1and a left end face26inFIG. 1. A control edge25is configured between end face24and peripheral surface22, and a control edge27is configured between end face26and peripheral surface22. Thus, both control edges25and27extend radially peripherally, similarly to peripheral surface22.

A compression spring28rests against right end face24inFIG. 1, and the other end thereof is braced against a step of stepped bore14in housing12. A coupling pin30acts centrically on left end face26of slide element20inFIG. 1and is guided in a fluid-tight manner in a guide piece32. Thus, the center of end face26forms a functional surface for coupling pin30. An armature34of an electromagnetic actuating device36acts on the end of coupling pin30distal from slide element20. This electromagnetic actuating device36is flanged to housing12of slide valve10.

In the area of the right end of slide element20inFIG. 1, two mutually opposing, radially extending channels38aand38bpenetrating housing12are provided in the region of guide portion16. The outlet of particular channel38a, respectively38bleading to guide surface18forms a control port40a, respectively40b. Analogously, a pair of mutually opposing, radially extending channels42aand42bpenetrating housing12are provided in the area of the left end of slide element20inFIG. 1. The outlets thereof leading to guide surface18form control ports44aand44b. In the axial position of slide element20shown inFIG. 1, control ports40a,40b,44aand44bare sealed.

The two channels42aand42bcommunicate with a supply connection46, which, in turn, communicates with a pressure side of a hydraulic pump (not shown). The two channels38aand38bcommunicate with a return connection48, which, in turn, communicates with a low-pressure region of the hydraulic pump. At the right end inFIG. 1, housing12has a pressure-regulating port50that communicates with a control connection52. If slide valve10is installed in an automatic transmission of a motor vehicle, for example, in order to actuate clutches for gear shifting, a hydraulic clutch actuation would take place via control connection52, the pressure acting on the clutch via a hydraulic amplifier.

To seal supply connection46, return connection48and control connection52, O-ring seals54are configured in circumferential grooves on the exterior of slide valve10. A pressure chamber56is bounded, inter alia, by right end face24inFIG. 1, whereas a pressure chamber58is bounded, inter alia, by left end face26inFIG. 1. The two pressure chambers56and58of slide valve10are connected by two axially extending hydraulic channels, as are shown exemplarily inFIGS. 3 and 4. However, the hydraulic channels are not visible in the drawing inFIG. 1, and they are referred to here without reference numerals. Control ports40a,40b,44aand44beach have a circular cross section. In the present case, slide element20is fabricated from a fiberglass reinforced plastic. The majority of the elements of slide valve10shown inFIG. 1essentially have a rotationally symmetric design.

The operation of slide valve10is described in the following: To adjust a specific pressure level at control connection52, electromagnetic actuation device36is energized in a specific manner, coupling pin30pressing with a predetermined force toward slide element20(arrow64inFIG. 1). Counteracting the same is the force of compression spring28on end face24. Due to the connection provided by the hydraulic channels, essentially the same pressure prevails in both pressure chambers56and58; thus, slide element20is substantially pressure-compensated.

If the pressure at control connection52drops, the pressure prevailing in pressure chamber58and the hydraulic force at coupling pin30(arrow66) acting equidirectionally with compression spring28also drop correspondingly. Slide element20inFIG. 1is hereby moved to the right, whereby the two control ports44aand44bapproach control edge27assigned thereto or even emerge therefrom, allowing an intensified flow of pressurized hydraulic fluid into pressure chamber58. Thus, the pressure rises in pressure chamber58and, via the hydraulic channels, also in pressure chamber56, and, correspondingly, also in control connection52.

Slide element20thereby forms a pressure regulator, automatically ensuring that a predetermined pressure level is adjusted at control connection52in accordance with the current being supplied to electromagnetic actuation device36. A too high pressure at control connection52is reduced by a corresponding displacement of slide element20inFIG. 1to the left, and by a flowing off of the hydraulic fluid to return connection48. This is likewise achieved in that control edge25approaches control ports40aand40bor even releases the same in response to a movement of slide element20to the left.

In the case of illustrated slide valve10, leakage into control ports40aand40bfrom pressure chamber56and from control orifices44aand44binto pressure chamber58caused by the guide play is relatively minor. A reason for this is the relatively high precision to which slide element20is produced.

In the present case, slide element20was injection-molded using three casting molds of an injection mold, the first and the second casting mold being designed as two elements of an axially cut hollow cylindrical body, and the third casting mold as a punch that axially bounds the hollow cylindrical body. Slide element20is injection-molded using two injection points configured symmetrically at axial end faces24and26. Compression springs21feature axially extending binding seams88. This is explained in greater detail further below with reference toFIG. 8.

In excerpted form,FIG. 2shows a sectional view of another specific embodiment of slide valve10, respectively of slide element20. In the present case, slide element20features a centrical, axial cylindrical recess74.

FIG. 3Ashows a sectional view of a slide valve10in a specific embodiment similar toFIG. 1. In addition, slide valve10according toFIG. 3Afeatures an axially extending rib70(“guide rib”). Coupling pin30, as well as compression spring28are not shown in the drawing ofFIG. 3.

Guide surface18of housing12features an axially extending groove72, which, in the specific embodiment ofFIG. 3A, is subdivided by rib70into a first groove72ain the upper region and a second groove72bin the lower region of the drawing. It is also discernible that slide element20has a blind hole-type, centrical cylindrical recess74. An annular recess76, capable of receiving an end section of compression spring28, is configured in the right region of slide element20in the drawing ofFIG. 3A.

FIG. 3Bshows slide valve10ofFIG. 3Ain a sectional view having a sectional plane that is 90° rotated relative toFIG. 3A.

FIG. 4shows a sectional view ofFIG. 3Ain the direction of a line IV-IV. Rib70and groove72, respectively72aand72bare very readily discernible in this view. Slide element20and portions of guide surface18, respectively of housing12surrounding slide element20are mirror-inverted relative to axis78(vertically). Together, grooves72aand72bconstitute one of two hydraulic channels73(“overflow channels”) required for operation of slide valve10through which fuel may flow axially along slide element20. It is also discernible fromFIG. 4that control orifices40a,40b,44aand44bextend only via a limited distance in the circumferential direction of guide surface18, namely the diameter of control orifices40a,40b,44aand44b. Control ports40a,40b,44aand44bare radially configured to feature an angle of approximately 90° relative to tongues21.

FIG. 6Ashows a view of slide element20similar to that ofFIG. 3 through 5, the view ofFIG. 6Abeing selected in such a way that both tongues21are visible on slide element20. Tongues21are rigidly joined to slide element20; they may be produced in one piece with slide element20.

FIG. 6Cshows a view along a line VIC-VIC ofFIG. 6B.

FIG. 7shows a perspective view of slide valve10similar to slide valve10according toFIG. 3bin a part-sectional view. For the sake of better clarity, sectional planes of slide element20and of guide piece32deviate slightly from sectional plane of housing12in the present case.

It is discernible that slide element20ofFIG. 7is axially displaceable (in the drawing, horizontally). Tongues21, which are radially guided in grooves72, prevent slide element20from being able to rotate about the longitudinal axis. A corresponding radial portion of peripheral surface22of slide element20is thereby always essentially facing a corresponding control ports40aand40b, respectively44aand44b.FIG. 7shows tongues21, however, not control ports40aand40b.FIG. 3Ashows control ports40aand40b, however, not tongues21.

FIG. 8shows a simplified schematic representation of a specific embodiment of an injection mold80, two end face-side injection points86being configured mutually symmetrically. Two injection points86may be configured at both end faces24and26of slide element20, respectively. This permits a greater precision of finished slide element20at regions of peripheral surface22, as well as of control edges25and27that are radially distal from binding seam88, thus at those regions that come in contact with control ports40a,40b,44aand44bduring operation of slide valve10. The improved geometric properties are also obtained by the longitudinal orientation of the reinforcing fibers that arises during plastic injection molding.