Patent Abstract:
The invention relates to a piston having a valve arrangement for a vehicle hydraulic brake system comprising a piston channel penetrating the piston, a valve seat formed around an opening of the piston channel, and a valve element, which is displaceable relative to the piston and which for sealing the piston channel is positionable in a fluid-tight manner against the valve seat, wherein the valve seat takes the form of an annular projection on a sealing component, which comprises an elastic sealing element and a support element, which stabilizes the sealing element, and wherein the support element is designed in a region close to the sealing projection with a corresponding annular recess.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of International Application No. PCT/EP03/13962 filed Dec. 9, 2003, the disclosures of which are incorporated herein by reference, and which claimed priority to German Patent Application No. 102 58 790.6 filed Dec. 16, 2002, the disclosures of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a piston with a valve arrangement for a vehicle hydraulic brake system comprising a piston channel penetrating the piston, a valve seat formed around an opening of the piston channel, and a valve element, which is displaceable relative to the piston and for sealing the piston channel is positionable in a fluid-tight manner against the valve seat, wherein the sealing seat takes the form of an annular projection on a sealing component, which comprises an elastic sealing element and a support element, which stabilizes the sealing element. 
   Such a piston is known from EP 0 607 370 B2, and corresponding U.S. Pat. No. 5,473,896 which is incorporated by reference herein, and according to this background art is installed in a master brake cylinder of a vehicle brake system. The piston together with the master brake cylinder encloses a pressure chamber. In a ready position prior to a brake actuation, the valve arrangement is in an open position, in which the pressure chamber communicates with a hydraulic fluid reservoir. When a driver of the vehicle initiates a braking operation, the piston is displaced inside the master brake cylinder. In said case, the valve arrangement closes in that the valve element positions itself in a fluid-tight manner against the sealing seat, thereby interrupting the fluidic connection between the pressure chamber and the hydraulic fluid reservoir. Consequently, a high hydraulic pressure builds up in the pressure chamber and leads to actuation of the vehicle brake circuit and to activation of the vehicle brakes. On completion of the braking operation, the piston is moved back into its ready position, wherein the valve arrangement opens and the pressure in the pressure chamber reduces. 
   In modern vehicle brake systems, in addition to the previously described braking-induced pressure increase, considerable pressure increases moreover arise in the pressure chamber when automatic brake pressure generating systems, such as e.g. a vehicle traction control system or a vehicle stability control system, are activated. Such automatic brake pressure generating systems are used for selective actuation of a brake circuit independently of an active braking operation by the driver in order to activate individual wheel brakes for increased vehicle safety. The pressure increase in the pressure chamber is effected, for example, by means of an additional hydraulic pump. The pressure thus increased then has to be reduced by opening the valve arrangement. 
   It has been shown that the elastic sealing element according to the background art in the region, in which it is exposed to the pressurized hydraulic fluid in the pressure chamber, has a tendency to deform elastically and, especially given high hydraulic pressures, to “flow”. If, given high hydraulic pressure in the pressure chamber, the piston is moved back into its ready position, then, as the valve arrangement starts to open, i.e. as the valve element starts to move, the sealing element deforms in the region of the sealing seat under the action of the hydraulic pressure in such a way that the sealing seat expands and moves, for part of the lift of the valve element, together with this valve element. Allowance has to be made for this behaviour of the sealing element when designing the valve arrangement. It is therefore necessary to provide a large enough lift to guarantee reliable opening of the valve arrangement despite the pressure-related deformation of the valve seat. The valve element however has to complete this lift also during initiation of a braking operation, thereby delaying the response of the brake system. 
   In order to prevent such pressure-induced deformations at the sealing element, it is further known from EP 0 607 370 B2 to provide an additional valve, which during a pressure build-up separates the pressure chamber from the valve arrangement and therefore prevents high hydraulic pressures at the valve arrangement. This solution is however considerably more costly to manufacture and more susceptible to faults when in operation. 
   DE 39 32 248 A1 and U.S. Pat. No. 2,136,835 each disclose a piston with valve arrangement, in which piston the valve element during a pressure build-up is pressed by an annular bead into the sealing element. These solutions are susceptible to wear owing to the high mechanical loads acting upon the sealing element. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a piston of the initially described type which, while being of a simple design and highly resistant to wear, allows a rapid pressure build-up in the pressure chamber. 
   This object is achieved according to the invention by a piston with a valve arrangement for a vehicle hydraulic brake system, wherein the piston comprises a piston channel penetrating the piston, a valve seat formed around an opening of the piston channel, and a valve element, which is displaceable relative to the piston and, for sealing the piston channel, is positionable in a fluid-tight manner against the valve seat, wherein the sealing seat takes the form of an annular projection on a sealing component, which comprises an elastic sealing element and a support element, which stabilizes the sealing element. To achieve the previously stated object, according to the invention it is further provided that the support element is designed in a region close to the sealing projection with a corresponding annular recess. 
   The purpose of the annular recess is to receive the material of the sealing element that is deformed under high pressure in the region of the sealing seat and hence to direct the deformation towards the support element. This is achieved in particular also in that the surface of the support element in the region of the annular recess effects a better stabilization of the material of the sealing element and keeps it dimensionally more stable than is the case with the previously described background art. A better reinforcement of the elastic material of the sealing element is achieved by the enlargement of the surface of the support element by means of the annular recess than is the case with the background art. 
   A further increase of the dimensional stability of the sealing element is achievable according to the invention in that the sealing element is connected adhesively to the support element. This further reduces the deformability of the sealing element and stabilizes the sealing element as a whole. The adhesive connection may be effected by glueing or by vulcanizing the sealing element onto the support element. 
   In a development of the invention, it is provided that the annular sealing projection, viewed in cross section, has a round contour with a shallow flank trailing in the direction of the pressure chamber. The round and continuous run of the cross-sectional contour of the sealing projection prevents pressure peaks from occurring at the sealing projection and leading to locally concentrated extreme mechanical stress. The shallow trailing flank, precisely in the region subject to high pressure, ensures a well-balanced pressure distribution over a relatively large area and therefore leads to a reduction of the deformation. 
   In order to distribute pressure- and deformation-induced mechanical loads as uniformly as possible in the material of the sealing element also by means of the configuration of the annular recess, in a development of the invention it is provided that the annular recess, viewed in cross section, has a round, preferably circular-segment-round, contour. 
   Alternatively, it may however be provided that the annular recess, viewed in cross section, has a polygonal, preferably trapezoidal, contour. In the latter case, the sides serve as mechanical resistance to a deformation or flowing of the elastic sealing element material. 
   It was explained above that by means of the shape of the annular recess the deformation- and flow behaviour of the material of the sealing element may be influenced. As a further measure for purposefully controlling the deformation of the sealing element under pressure load, in a development of the invention it is provided that the annular recess is disposed, in relation to the sealing projection, closer to the opening of the piston channel. In other words, this means that the sealing projection lies, in relation to the annular recess, closer to the pressure chamber. If there is a high pressure in the pressure chamber, then a relatively high pressure difference exists at the sealing element between pressure chamber and piston channel. This pressure difference leads to a deformation of the material of the valve element in the region of the sealing projection in the direction of the piston channel. By virtue of the offset arrangement of sealing projection and annular recess, the material of the sealing projection is pressed initially in radial direction into the annular recess, so that an undesirable lift-increasing deformation of the sealing element in axial direction—as is the case with the background art—may be prevented. 
   With regard to the valve arrangement, in a development of the invention it is provided that the valve element comprises a valve tappet, which is guided in a guide element, and a valve disc, which interacts with the sealing seat. It may further be provided that the guide element is disposed in a receiving channel provided in the sealing component and that the valve disc has a substantially flat surface, which interacts with the sealing seat. Thus, the valve element and the sealing component, while being highly functional, are of a simple design and inexpensive to manufacture. With regard to the detailed construction of the guide element, in a development of the invention it is provided that the guide element comprises a guide bush, which guides the valve tappet, wherein the guide bush is held, preferably centrally, in the sealing component by means of at least one retaining web and wherein a fluid channel is formed between the guide bush and the sealing component. 
   To guarantee reliable and rapid closing of the valve arrangement during a braking operation, according to the invention it may further be provided that the valve element is biased by biasing means into a sealing position, in which it lies in a fluid-tight manner against the valve seat. In the ready position of the piston the valve element is then displaced out of its sealing position, so that the valve arrangement opens. The valve element is held in this open position until the piston is moved for the pressure build-up in the pressure chamber. The biasing means then effect a transfer of the valve element to the sealing position, simultaneously reducing the risk of jamming or blocking. 
   According to the invention, the sealing element may be formed from a flexible plastics material, in particular from an elastomer, and the support element may be formed from a material that is harder than the flexible plastics material, in particular from a metal material. 
   The invention further relates to a master brake cylinder arrangement comprising a master cylinder, a piston of the previously described type guided displaceably in the master cylinder, stop means defining a predetermined normal position of the piston, and biasing means biasing the piston into the normal position, wherein the piston together with the master cylinder encloses a pressure chamber, wherein moreover in the normal position the valve element is lifted off the sealing seat and the pressure chamber is connected by the piston channel fluidically to the fluid reservoir and wherein, upon displacement of the piston from its normal position counter to the action of the biasing means, the valve element positions itself against the sealing seat and a brake pressure builds up in the pressure chamber. 
   Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below by way of example with reference to the accompanying drawings. The drawings show: 
       FIG. 1  an axis-containing partial section of a master cylinder arrangement according to the invention; 
       FIG. 2  a plan view of the piston from the left, and 
       FIG. 3  an enlarged detail view of the valve element denoted by III in  FIG. 1 . 
       FIG. 4  an enlarged detail view of an alternate embodiment of the valve element. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a piston according to the invention is illustrated in an axis-containing part-sectional view and generally denoted by  10 . The piston  10  is guided movably in the direction of the axis A in a cylinder housing  12  of a master cylinder. The piston  10  is designed with a stepped piston channel  14 , which penetrates the piston axially. A sealing component  16 , comprising a sealing element  18  and a support element  20 , is installed with press fit adhesion in the piston channel  14 . The design of the sealing component  16  is additionally described in detail below. 
   The sealing component  16  is designed likewise with a central stepped through-channel  22 , in which a guide element  24  is received and press-fitted such as to be locked against displacement. In the guide element  24  a valve element  26  is guided in an axially displaceable manner. The valve element  26  comprises a valve tappet  28  and a valve disc  30 . For guiding the valve element  26  in the guide element  24 , the valve tappet  28  is accommodated with slight play in a corresponding guide bush  32  of the guide element  24  (see  FIG. 2 ). The guide bush  32  is pressed into and held axially in the through-channel  22  of the sealing component  16  by means of retaining webs  34 . By means of a restoring spring  35 , which is disposed between the guide bush  32  and the free end of the valve tappet  28  that is provided with a lock washer  37 , the valve element  26  is biased in such a way that the valve disc  30  is pressed with its underside  36  into abutment on a valve seat  38  on the end  40  facing the valve disc  30 . 
   For a closer description of the sealing component  16 , reference is made to  FIG. 3 , which is an enlarged view of the partial detail of  FIG. 1  denoted by III. The sealing component  16  comprises the sealing element  18  and the support element  20 . Both are connected adhesively to one another at their common contact surface  42 , e.g. by vulcanizing the sealing element  18  onto the support element  20  or by glueing them to one another. 
   The sealing element  18  on its end face  40  has the valve seat  38  in the form of an annular sealing projection. Its contour—viewed in the axis-containing cross section—from the radially inner side facing the through-channel  22  extends substantially in the shape of a segment of a circle and then tapers off with a sloping flank in the region denoted by  46 . The sealing element  18  on its outer peripheral surface  44  further comprises a plurality of bead-shaped sealing projections  48  running round in peripheral direction as well as a bead-shaped support projection  50  running round in peripheral direction and disposed close to the valve seat. The sealing projections  48  are used to enable the sealing component  16  to be pressed with a press fit and in a fluid-tight manner into the piston  10 , as shown in  FIG. 1 . The support projection  50  additionally stabilizes the region of the end  40  of the sealing element  18  by being supported against the inner wall of the piston channel  14 . 
   The support element  20  in its end region  52  facing the end  40  has an annular recess  54  extending in peripheral direction around the axis. The annular recess  54 —viewed in the axis-containing cross section—possesses, for the most part, a contour that is round like a segment of a circle with harmonically rounded-off transitions. Alternatively, as shown in  FIG. 4 . it may however be provided that the annular recess  54 ′, viewed in cross section, has a polygonal, preferably trapezoidal, contour. In the latter case, the sides serve as mechanical resistance to a deformation or flowing of the elastic sealing element material. The annular recess  54  is filled up with elastic material of the sealing element  18 . In its radially outer region, the support element  20  has a circumferential stabilizing edge  56 , which stabilizes the radially outer region of the sealing element  18 . In the radially inner region of the sealing component  16 , an end face portion  58  of the support element  20  is not covered by the material of the sealing element  18 . 
   Returning to  FIG. 1 , it may be seen that the piston  10  is accommodated in a cylindrical cavity  60  of the cylinder housing  12 , which is closed at one end, and together with the cylinder housing  12  encloses a pressure chamber  61  filled with hydraulic fluid. The piston  10  is biased by a spring  62  in  FIG. 1  to the right into its ready position shown in  FIG. 1  and is therefore applied under bias against a stop bolt  64 , which extends transversely through the cylinder housing  12  and is fixed therein. In the cylinder housing  12  a connection port  66  is provided, by which the cavity  60  communicates with a non-illustrated fluid reservoir. The cylinder housing  12  further comprises a non-illustrated further connection port, by which the pressure chamber  61  is connected to the brake circuit of a motor vehicle. 
   At the outer periphery of the piston  10  a fluid seal  68  is provided, which prevents a flow of fluid along the outer periphery of the piston  10  upon axial movement of the piston  10  in the cylinder housing  12  and hence allows fluid-tight guidance of the piston in the cylinder. 
   The arrangement according to  FIG. 1  operates as follows. Prior to initiation of a braking operation by the driver, the piston  10  is situated in its ready position shown in  FIG. 1 . In this ready position, the piston  10  is pressed by the spring  62  against the stop bolt  64 . In said case, the valve tappet  28  presses with its free end against the stop bolt  64 . The spring force of the spring  62  exceeds the spring force of the restoring spring  35 , so that the valve element  26  occupies its open position shown in  FIG. 1 , in which the valve disc  30  is lifted off the valve seat  38 . The pressure chamber  61  is therefore fluidically connected to the end of the piston channel  14  remote from the pressure chamber. 
   Upon an actuation of the brake, the piston  10  is displaced in  FIG. 1  according to arrow P 1  to the left. In said case, the valve disc  30  moves closer and closer to the valve seat  38  until finally they both come into contact. From then on, upon further piston movement in the direction of arrow P 1 , an above-atmospheric pressure builds up in the pressure chamber  61  and is transmitted to the brake circuit. On completion of the braking operation, the piston  10  moves according to arrow P 2  back into its normal position shown in  FIG. 1 . In said case, the valve element  26  again occupies its open position shown in  FIG. 1 . 
   Under the growing hydraulic pressure the valve element  26 , or more precisely its valve disc  30 , is pressed with increasing strength onto the valve seat  38 , with the result that the valve seat  38  deforms under this pressure. The hydraulic fluid under the above-atmospheric pressure moreover acts upon the flank region  46 , which is in contact with this hydraulic fluid and therefore likewise deforms. Given very high hydraulic pressures, a flowing of the material of the sealing element  18  may even occur in this region. 
   Because of the shape of the flank region  46  and the end region  52  of the support element  20 , the previously mentioned deformation does not however lead to the effect whereby upon lifting of the valve disc  30  off the sealing seat  38  under high pressure in the pressure chamber  61  the sealing seat  38  deforms in axial direction according to arrow P 1  and because of this axially directed deformation prevents a rapid disengagement of valve disc underside  36  and sealing seat  38  for the purpose of a rapid pressure reduction in the pressure chamber  61 . Instead of this, the material of the sealing element  18  deforms under the pressure of the hydraulic pressure in the pressure chamber  61  in such a way that it penetrates into the annular recess  54  and is displaced by it further in a radially inward direction. The shallow course of the flank  46  moreover brings about a rapid disengagement of valve disc underside  36  and valve seat  38 . Thus, even given high hydraulic pressures in the pressure chamber  61 , the invention guarantees a rapid lifting of the valve disc  30  off the valve seat  38  also with a small lift of the valve element  26 . In this way, the response characteristic of the brake system may be improved. 
   The invention discloses a simple yet effective way of designing the piston plus central valve for a vehicle brake system that, even given high hydraulic pressures in the pressure chamber—optionally caused by an automatic system such as e.g. a traction control system or a stability program, guarantees a rapid pressure reduction on completion of the braking operation. This is achieved in particular by measures relating to the shape of the valve seat, so that an unwanted hydraulic-pressure-related deformation of the valve seat may be extensively suppressed. 
   In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Technology Classification (CPC): 1