Abstract:
A guide ring for a pump element of a hydraulic unit of a vehicle brake system is configured to guide a pump piston in a pump housing when the pump piston is displaced along the axis thereof in the pump housing. On the inner side of the guide ring facing the pump piston, the guide ring includes a first step that has a first inner diameter and a second inner diameter.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2013/062758, filed on Jun. 19, 2013, which claims the benefit of priority to Serial No. DE 10 2012 214 355.6, filed on Aug. 13, 2012 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a guide ring for a pump element of a hydraulic unit of a vehicle brake system for guiding a pump piston in a pump housing when the pump piston is displaced along its axis in the pump housing. The disclosure further relates to the use of such a guide ring in a hydraulic unit module for vehicle brake systems. 
     Hydraulic units are used in vehicle brake systems in order to provide a controlled brake pressure in associated brake circuits. For controlling the brake pressure the hydraulic unit comprises, among other things, at least one pump element, the pump piston of which is displaceable in a pump cylinder. In the area where brake fluid is admitted into the pump cylinder the pump piston is further guided in a pump housing, in which an eccentric drive for the pump piston is also located. A sealing arrangement, which is formed by a sealing ring, a support ring and a guide ring, is generally provided between the eccentric drive and the admission area. The sealing ring produces a largely fluid-tight seal between the admission area, representing an area exposed to slight pressure, and the eccentric drive, representing an area largely free of pressure. The support ring supports the sealing ring. The guide ring serves to guide the pump piston relative to the pump housing and thereby also relative to the pump cylinder. This guidance occurs at that end area of the pump piston where lateral forces are introduced to the pump piston by the eccentric drive. These lateral forces are absorbed by the guide ring. Moreover, the guide ring defines the overall space for the sealing ring and the support ring in an axial direction, in such a way that a sealing effect is achieved with a degree of play necessary for the reciprocating movement of the piston. A sealing arrangement of this type is disclosed by DE10 2006 036 442 A1, for example. 
     Hydraulic units of different capacities are needed for different types of vehicles and different functions in a vehicle. These various capacity classes are achieved by means of different pump elements and in particular here by different pump piston diameters. For this purpose the pump housings must be matched to the different pump piston diameters, making it necessary to produce a plurality of different pump housing variants. 
     SUMMARY 
     According to the disclosure a guide ring is created for a pump element of a hydraulic unit of a vehicle brake system, for guiding a pump piston in a pump housing when the pump piston is displaced along its axis in the pump housing. The guide ring is designed with a first step having a first inside diameter and a second inside diameter on its inner side facing the pump piston. 
     Here the first inside diameter of the guide ring is slightly larger than the diameter of the pump piston and guides the pump piston with a requisite guide clearance in the guide ring. Together with the second inside diameter, which is larger than the first inside diameter, the disclosure creates a stepped internal contour of the guide ring. This stepped internal contour or step forms a free space or empty space in the form of a sleeve between the pump piston and this portion of the guide ring. At least one further component of the pump element, which is thereby confined and held both in an axial direction and in a radial direction, may be arranged in this sleeve. 
     A sealing ring, which with its radially outer side bears on the guide ring to form a seal, and with its radially inner side bears on the pump piston or piston to form a seal, is preferably accommodated as further component in the sleeve. It is especially preferred if in addition to the sealing ring a support ring, which is likewise confined radially outwards by the guide ring according to the disclosure, is accommodated in the step according to the disclosure in an axial direction between the sealing ring and the guide ring. A complete sealing arrangement is thereby advantageously also held radially in the guide ring according to the disclosure. 
     Here the guide ring holds the sealing ring in a bore of the pump housing, in which the pump element is arranged. With pump elements of different capacities and hence different pump piston diameters, the guide ring according to the disclosure means that this bore can always have the same diameter. For this purpose it is merely necessary to adapt the internal contour of different types of guide rings to the individual pump piston diameters and/or sealing ring diameters, their external contour remaining the same. According to the disclosure, therefore, the component variance of pump housings for different pump piston diameters is shifted to the guide rings. In production it is substantially more cost-effective to vary the shape of the different types of guide rings than to vary the pump housing. They are preferably manufactured simply by means of injection molding from brake fluid-resistant plastic. 
     In an advantageous development of the guide ring according to the disclosure this is designed with a second step having a third inside diameter on its inner side facing the pump piston. Here the third inside diameter is adapted to hold a further component compactly and stably in a radial direction. A filter, adjoining the sealing ring in an axial direction, for filtering fluid, especially brake fluid, in the admission area or low-pressure area of a pump inlet, preferably serves as the further component. This allows filters of different sizes to be easily and cost-effectively fitted by varying the third inside diameter, particularly where the external contour of the guide ring and hence the shape of the bore of the pump housing remain unchanged. 
     The guide ring is furthermore preferably designed with a third step having a first outside diameter and a second outside diameter on its outer side facing the pump housing. With the third step on its outer side the guide ring is held not only in a radial direction but also in an axial direction in the pump housing, particularly by means of a stepped configuration designed to complement the third step. 
     In addition, the guide ring is preferably designed with a tapered portion on its outer side facing the pump housing. Designed in this way, the guide ring according to the disclosure can be precisely positioned externally by just one step in the pump housing and internally still comprises multiple steps for the arrangement of the filter and the seal. 
     The disclosure is furthermore directed towards a use of such guide rings according to the disclosure in a hydraulic unit module for vehicle brake systems having one type of pump housing, at least two types of pump pistons and at least two types of guide rings. Here the one type of pump housing has only one internal contour facing the associated guide ring. At the same time at least the two types of pump pistons have different outside diameters. At least the two types of guide rings are adapted on the one hand for arrangement on the one internal contour of the one type of pump housing and on the other for arrangement on the different outside diameters of at least the two types of pump pistons. 
     Adapted in this way, at least the two types of guide rings have a different internal contour, which at least largely bears on the external contour of the associated type of pump piston with the respective outside diameter. Furthermore, at least the two types of guide rings have an identical external contour, which is adapted to the internal contour or bore of the one type of pump housing. One type of pump housing can therefore advantageously be used for different pump piston outside diameters and hence for piston pumps of different capacity classes. The number of pump housing variants needed is reduced compared to the conventional number, so that larger quantities of each variant can be produced. Considerably lower unit manufacturing costs are thereby achieved due to a lower handling cost and a reduced design and testing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the solution according to the disclosure are explained in more detail below with reference to the schematic drawings attached, of which: 
         FIG. 1  shows a longitudinal section of an exemplary embodiment of a pump element having a guide ring according to the state of the art, 
         FIG. 2  shows a longitudinal section of an exemplary embodiment of a pump element having a first variant of a guide ring according to the disclosure and 
         FIG. 3  shows an enlarged longitudinal section of a second variant of a guide ring according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a pump element  10  of a hydraulic unit, which is arranged in a block-shaped pump housing  12 . The hydraulic unit allows an associated vehicle brake system, especially an antilock, a traction control and a driving dynamics control function (ABS, ASR and ESP) on vehicle brakes. 
     A stepped bore  14 , in which the pump element  10  is arranged, is formed in the pump housing  12 . The stepped bore  14  has three offsets  16 ,  18  and  20 , which serve progressively to reduce the diameter of the bore  14  in steps from the outside inwards and to form an internal contour  21  of the pump housing  12 . The pump element  10  has a substantially complementary external contour  22  to the internal contour  21 . The pump element  10  further comprises a multipart pump cylinder  23 , which with its outside diameter  25  encloses a likewise multipart pump piston  24 . 
     The multipart pump cylinder  23  comprises an annular filter  26 , to which brake fluid, through the inlet  28 , can be fed radially inwards through the pump housing  12 . Adjoining the filter  26  and facing axially outwards is a cylindrical cup  30 , which encloses a delivery chamber  32 . Situated then at the very outside is a cylinder cover  34 , which is caulked so that it is fluid-tight to the pump housing  12  and which serves to retain the filter  26  and the cylindrical cup  30  and thereby the entire pump element  10  in the stepped bore  14 . An outlet valve  36 , which serves for the controlled discharge of brake fluid, under pressure, from the delivery chamber  32  into an outlet  38 , is situated in the cylinder cover  34 . 
     The multipart pump piston  24  is designed with a circular cylindrical piston tappet  40 , which is situated in the axially innermost area of the bore  14 . With its outside diameter the piston tappet  40  forms the outside diameter  25  of the pump piston  24  relevant here. Furthermore, at one end face  42  the piston tappet  40  can be moved in an axial direction out of the bore  14  by an eccentric  44 . Abutting the other end face  46  of the piston tappet  40  is a piston sleeve  48 , through which the brake fluid, admitted through the inlet  28  and the filter  26 , can flow further radially inwards. A piston gasket  50  then axially abuts the piston sleeve  48 , an inlet valve  52  being situated between the piston sleeve  48  and the piston gasket  50  for feeding the admitted brake fluid into the delivery chamber  32 . 
     As part of the pump piston  24  the piston tappet  40  is guided in the inner part of the stepped bore  14  by means of a guide ring  54 , a support ring  56  and a sealing ring  58 . The sealing ring  58  is embodied as a low-pressure sealing ring and seals off a low-pressure area  60  prevailing at the filter  26  from an entirely pressureless eccentric area  62  prevailing at the eccentric  44 . The support ring  56  supports the sealing ring  58  and protects the latter against mechanical damage. The guide ring  54  absorbs and buffers lateral forces occurring during the operation of the eccentric  44 . At the same time the guide ring  54  serves as bearing surface for the piston tappet  40 , allows a reciprocal sliding movement of the piston tappet  40  free from fiction in the pump housing  12  and thereby prevents abrasive wear. 
     According to  FIG. 1  the conventional guide ring  54  is arranged between the third offset  20  of the bore  14  and the support ring  56  in a purely cylindrical area  64  of the bore  14 . The sealing ring  58  is also positioned in the purely cylindrical area  64  adjoining the support ring  56  in an axial direction. The guide ring  54  thereby confines and holds the sealing ring  58  and the support ring  56  in a first axial direction. In the opposite direction to the first axial direction the sealing ring  58  and hence also the support ring  56  are confined by means of the filter  26 , which bears with its inner end face on the second offset  18  of the stepped bore  14  and is supported against the latter. Supported in this way, the pump element  10  is also fixed in the stepped bore  14 . 
     The guide ring  54  together with the sealing ring  58  and the support ring  56  forms a sealing arrangement  66 . 
       FIG. 2  and  FIG. 3  illustrate a guide ring  54  according to the disclosure. With its inner side  68  the guide ring  54  according to the disclosure faces the piston tappet  40  of the multipart piston pump  24 . In a first variant of the guide ring  54  the inner side  68  comprises a first step  70  having a first inside diameter  72  and a second inside diameter  74  ( FIG. 2 ). Here the first inside diameter  72  is slightly larger than the diameter of the piston tappet  40  and extends over a first length  73 . There the guide ring  54 , with its inner side  68 , forms a sliding surface for the reciprocating sliding movement of the piston tappet  40  during operation. The second inside diameter  74  is larger than the first inside diameter  72 , so that with the first step  70  a hollow cylindrical portion  76  or a sleeve is formed over a second length  75 . The support ring  56  and the sealing ring  58  are accommodated there and according to the disclosure are confined and held not only axially but also radially outwards by the guide ring  54 . Overall, this creates an especially compact and stable sealing arrangement  66 . 
     In a second variant of the guide ring  54  according to  FIG. 3  a second step  78  having a third inside diameter  80 , which is larger than the second inside diameter  74 , is formed on its inner side  68 . Formed in this way, it is possible to accommodate a further component, which has a larger diameter than the sealing ring  58 . The further component is advantageously the filter  26  of corresponding size. 
     On its outer side  82  the guide ring  54  comprises a third step  84  having a first outside diameter  86  and a larger, second outside diameter  88 . This third step  84  advantageously serves to hold the guide ring  54  against the third offset  20  of the bore  14  of the pump housing  12 . 
     In the second variant according to  FIG. 3  the outer side  82  further comprises a tapered portion  90 , which is designed to complement the second offset  18  of the bore  14 . 
     The crucial aspect of the solution according to the disclosure is that the guide ring  54  with its outer side  82  always has the same external contour irrespective of the size of the piston tappet  40  or of the sealing ring  58  and/or the support ring  56 . One type of pump housing  12  can then be used for different types of pump elements  10  having pump pistons  24  of different sizes and hence different capacity classes, affording exceptional savings in both time and costs. It is merely necessary to adapt the internal contour of the guide ring  54  to the pump piston  24 .