Abstract:
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.

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a slide valve in a first specific embodiment in a part-sectional view. 
         FIG. 2  shows a slide valve in a second specific embodiment in a part-sectional view. 
         FIG. 3A  shows a slide valve in a third specific embodiment in a sectional view. 
         FIG. 3B  shows the slide valve from  FIG. 3A  having a 90° rotated sectional plane. 
         FIG. 4  shows the slide valve from  FIG. 3A  in an axial sectional view IV. 
         FIG. 5  shows a perspective representation of the slide valve from  FIG. 3A . 
         FIG. 6A  shows a first view of a slide element similar to that from  FIG. 3A . 
         FIG. 6B  shows a second view of the slide element from  FIG. 6A . 
         FIG. 6C  shows an axial longitudinal section of the slide element from  FIG. 6A . 
         FIG. 7  shows a perspective representation of a sectional view of a slide valve similar to that from  FIG. 3B . 
         FIG. 8  shows a schematic representation of an injection mold having two injection points. 
     
    
    
     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. 1  shows a slide valve  10  in a part-sectional view. In the present case, slide valve  10  is designed as a pressure regulating valve. It encompasses a housing  12  that has an axially stepped outer contour. A stepped bore  14  featuring a guide portion  16  having a constant diameter is provided in housing  12  and extends in the longitudinal direction thereof. Guide portion  16  has a cylindrical guide surface  18 . 
     Configured in guide portion  16  of stepped bore  14  is a cylindrical slide element  20  that is guided by a guide surface  18 . Slide element  20  has a peripheral surface  22  and, in the present case, two axially extending tongues  21 , of which only one is visible in the drawing. In addition, slide element  20  has a right end face  24  in  FIG. 1  and a left end face  26  in  FIG. 1 . A control edge  25  is configured between end face  24  and peripheral surface  22 , and a control edge  27  is configured between end face  26  and peripheral surface  22 . Thus, both control edges  25  and  27  extend radially peripherally, similarly to peripheral surface  22 . 
     A compression spring  28  rests against right end face  24  in  FIG. 1 , and the other end thereof is braced against a step of stepped bore  14  in housing  12 . A coupling pin  30  acts centrically on left end face  26  of slide element  20  in  FIG. 1  and is guided in a fluid-tight manner in a guide piece  32 . Thus, the center of end face  26  forms a functional surface for coupling pin  30 . An armature  34  of an electromagnetic actuating device  36  acts on the end of coupling pin  30  distal from slide element  20 . This electromagnetic actuating device  36  is flanged to housing  12  of slide valve  10 . 
     In the area of the right end of slide element  20  in  FIG. 1 , two mutually opposing, radially extending channels  38   a  and  38   b  penetrating housing  12  are provided in the region of guide portion  16 . The outlet of particular channel  38   a , respectively  38   b  leading to guide surface  18  forms a control port  40   a , respectively  40   b . Analogously, a pair of mutually opposing, radially extending channels  42   a  and  42   b  penetrating housing  12  are provided in the area of the left end of slide element  20  in  FIG. 1 . The outlets thereof leading to guide surface  18  form control ports  44   a  and  44   b . In the axial position of slide element  20  shown in  FIG. 1 , control ports  40   a ,  40   b ,  44   a  and  44   b  are sealed. 
     The two channels  42   a  and  42   b  communicate with a supply connection  46 , which, in turn, communicates with a pressure side of a hydraulic pump (not shown). The two channels  38   a  and  38   b  communicate with a return connection  48 , which, in turn, communicates with a low-pressure region of the hydraulic pump. At the right end in  FIG. 1 , housing  12  has a pressure-regulating port  50  that communicates with a control connection  52 . If slide valve  10  is 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 connection  52 , the pressure acting on the clutch via a hydraulic amplifier. 
     To seal supply connection  46 , return connection  48  and control connection  52 , O-ring seals  54  are configured in circumferential grooves on the exterior of slide valve  10 . A pressure chamber  56  is bounded, inter alia, by right end face  24  in  FIG. 1 , whereas a pressure chamber  58  is bounded, inter alia, by left end face  26  in  FIG. 1 . The two pressure chambers  56  and  58  of slide valve  10  are connected by two axially extending hydraulic channels, as are shown exemplarily in  FIGS. 3 and 4 . However, the hydraulic channels are not visible in the drawing in  FIG. 1 , and they are referred to here without reference numerals. Control ports  40   a ,  40   b ,  44   a  and  44   b  each have a circular cross section. In the present case, slide element  20  is fabricated from a fiberglass reinforced plastic. The majority of the elements of slide valve  10  shown in  FIG. 1  essentially have a rotationally symmetric design. 
     The operation of slide valve  10  is described in the following: To adjust a specific pressure level at control connection  52 , electromagnetic actuation device  36  is energized in a specific manner, coupling pin  30  pressing with a predetermined force toward slide element  20  (arrow  64  in  FIG. 1 ). Counteracting the same is the force of compression spring  28  on end face  24 . Due to the connection provided by the hydraulic channels, essentially the same pressure prevails in both pressure chambers  56  and  58 ; thus, slide element  20  is substantially pressure-compensated. 
     If the pressure at control connection  52  drops, the pressure prevailing in pressure chamber  58  and the hydraulic force at coupling pin  30  (arrow  66 ) acting equidirectionally with compression spring  28  also drop correspondingly. Slide element  20  in  FIG. 1  is hereby moved to the right, whereby the two control ports  44   a  and  44   b  approach control edge  27  assigned thereto or even emerge therefrom, allowing an intensified flow of pressurized hydraulic fluid into pressure chamber  58 . Thus, the pressure rises in pressure chamber  58  and, via the hydraulic channels, also in pressure chamber  56 , and, correspondingly, also in control connection  52 . 
     Slide element  20  thereby forms a pressure regulator, automatically ensuring that a predetermined pressure level is adjusted at control connection  52  in accordance with the current being supplied to electromagnetic actuation device  36 . A too high pressure at control connection  52  is reduced by a corresponding displacement of slide element  20  in  FIG. 1  to the left, and by a flowing off of the hydraulic fluid to return connection  48 . This is likewise achieved in that control edge  25  approaches control ports  40   a  and  40   b  or even releases the same in response to a movement of slide element  20  to the left. 
     In the case of illustrated slide valve  10 , leakage into control ports  40   a  and  40   b  from pressure chamber  56  and from control orifices  44   a  and  44   b  into pressure chamber  58  caused by the guide play is relatively minor. A reason for this is the relatively high precision to which slide element  20  is produced. 
     In the present case, slide element  20  was 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 element  20  is injection-molded using two injection points configured symmetrically at axial end faces  24  and  26 . Compression springs  21  feature axially extending binding seams  88 . This is explained in greater detail further below with reference to  FIG. 8 . 
     In excerpted form,  FIG. 2  shows a sectional view of another specific embodiment of slide valve  10 , respectively of slide element  20 . In the present case, slide element  20  features a centrical, axial cylindrical recess  74 . 
       FIG. 3A  shows a sectional view of a slide valve  10  in a specific embodiment similar to  FIG. 1 . In addition, slide valve  10  according to  FIG. 3A  features an axially extending rib  70  (“guide rib”). Coupling pin  30 , as well as compression spring  28  are not shown in the drawing of  FIG. 3 . 
     Guide surface  18  of housing  12  features an axially extending groove  72 , which, in the specific embodiment of  FIG. 3A , is subdivided by rib  70  into a first groove  72   a  in the upper region and a second groove  72   b  in the lower region of the drawing. It is also discernible that slide element  20  has a blind hole-type, centrical cylindrical recess  74 . An annular recess  76 , capable of receiving an end section of compression spring  28 , is configured in the right region of slide element  20  in the drawing of  FIG. 3A . 
       FIG. 3B  shows slide valve  10  of  FIG. 3A  in a sectional view having a sectional plane that is 90° rotated relative to  FIG. 3A . 
       FIG. 4  shows a sectional view of  FIG. 3A  in the direction of a line IV-IV. Rib  70  and groove  72 , respectively  72   a  and  72   b  are very readily discernible in this view. Slide element  20  and portions of guide surface  18 , respectively of housing  12  surrounding slide element  20  are mirror-inverted relative to axis  78  (vertically). Together, grooves  72   a  and  72   b  constitute one of two hydraulic channels  73  (“overflow channels”) required for operation of slide valve  10  through which fuel may flow axially along slide element  20 . It is also discernible from  FIG. 4  that control orifices  40   a ,  40   b ,  44   a  and  44   b  extend only via a limited distance in the circumferential direction of guide surface  18 , namely the diameter of control orifices  40   a ,  40   b ,  44   a  and  44   b . Control ports  40   a ,  40   b ,  44   a  and  44   b  are radially configured to feature an angle of approximately 90° relative to tongues  21 . 
       FIG. 5  shows a perspective view of slide valve  10  of  FIGS. 3A ,  3 B and  4 . 
       FIG. 6A  shows a view of slide element  20  similar to that of  FIG. 3 through 5 , the view of  FIG. 6A  being selected in such a way that both tongues  21  are visible on slide element  20 . Tongues  21  are rigidly joined to slide element  20 ; they may be produced in one piece with slide element  20 . 
       FIG. 6B  shows a view VIB of  FIG. 6A . 
       FIG. 6C  shows a view along a line VIC-VIC of  FIG. 6B . 
       FIG. 7  shows a perspective view of slide valve  10  similar to slide valve  10  according to  FIG. 3   b  in a part-sectional view. For the sake of better clarity, sectional planes of slide element  20  and of guide piece  32  deviate slightly from sectional plane of housing  12  in the present case. 
     It is discernible that slide element  20  of  FIG. 7  is axially displaceable (in the drawing, horizontally). Tongues  21 , which are radially guided in grooves  72 , prevent slide element  20  from being able to rotate about the longitudinal axis. A corresponding radial portion of peripheral surface  22  of slide element  20  is thereby always essentially facing a corresponding control ports  40   a  and  40   b , respectively  44   a  and  44   b .  FIG. 7  shows tongues  21 , however, not control ports  40   a  and  40   b .  FIG. 3A  shows control ports  40   a  and  40   b , however, not tongues  21 . 
       FIG. 8  shows a simplified schematic representation of a specific embodiment of an injection mold  80 , two end face-side injection points  86  being configured mutually symmetrically. Two injection points  86  may be configured at both end faces  24  and  26  of slide element  20 , respectively. This permits a greater precision of finished slide element  20  at regions of peripheral surface  22 , as well as of control edges  25  and  27  that are radially distal from binding seam  88 , thus at those regions that come in contact with control ports  40   a ,  40   b ,  44   a  and  44   b  during operation of slide valve  10 . The improved geometric properties are also obtained by the longitudinal orientation of the reinforcing fibers that arises during plastic injection molding.