Abstract:
A valve of an accumulator device, which is formed by an accumulator cylinder and an accumulator piston guided therein, includes a valve sealing body. The valve sealing body is configured to selectively open and close a valve opening at a valve seat. The valve also includes an opening mechanism configured to selectively raise the valve sealing body from the valve seat. The opening mechanism is held by a spring element, and the spring element is formed by a punched and bent part.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. 10 2012 218 553.4, filed on Oct. 11, 2012 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The disclosure relates to a valve of an accumulator device, which is formed by means of an accumulator cylinder and an accumulator piston guided therein. The valve comprises a valve sealing body for selective opening and closure of a valve opening at a valve seat and having an opening means for selectively raising the valve sealing body from the valve seat, which opening means is held by means of a spring element. The disclosure furthermore relates to the use of a valve of this kind in an accumulator device, in particular for a hydraulic unit of a vehicle brake system. 
         [0003]    Accumulator devices of the type in question are used particularly in vehicle brake systems and serve to provide temporary storage for pressure medium in the form of brake fluid. In this case, the pressure medium is returned from wheel brake cylinders or fed in from a main accumulator of the vehicle brake system, e.g. in vehicle brake systems with an antilock brake system (ABS) and an electronic stability program (ESP). 
         [0004]    Valves in accumulator devices of hydraulic units, in particular of vehicle brake systems, are used to control the quantity of pressure medium within the associated accumulator device. 
         [0005]    The accumulator devices comprise an accumulator cylinder and an accumulator piston which is guided therein and by means of which an accumulator volume for the pressure medium is delimited. The pressure medium can be delivered from the accumulator volume into a brake circuit when required. If the accumulator volume decreases, the accumulator piston travels into the accumulator cylinder to a depth such that, by means of an opening means, it opens a valve closed in a spring-assisted manner. Pressure medium then flows into the accumulator cylinder again through the opened valve. 
         [0006]    Conventionally employed opening means are configured as a pin which is inserted, in particular press-fitted, in an accurately fitting manner at a fixed location in the accumulator piston. Manufacture with an accurate fit is necessary since the opening means must strike the valve sealing body correctly in order to raise it. In general, the pin-shaped opening means is passed through the valve opening to the valve sealing body from the piston side. For this purpose, high precision in the component geometry and in the stroke motion of the accumulator piston is necessary. Precise component geometry can be achieved only by very dimensionally accurate and hence expensive components, manufacture and assembly. A precise stroke motion entails a complex configuration with, for example, additional guide rings and a long length of guidance for the accumulator piston. 
       SUMMARY 
       [0007]    According to the disclosure, a valve is provided for an accumulator device formed by means of an accumulator cylinder and an accumulator piston guided therein. The valve is provided with a valve sealing body for selective opening and closure of a valve opening at a valve seat. The valve furthermore has an opening means for selectively raising the valve sealing body from the valve seat, in which the opening means is held by means of a spring element. The spring element is formed by means of a punched and bent part. 
         [0008]    The spring element according to the disclosure is deformed by virtue of its spring properties when a force is exerted, and reassumes its original shape when the force acting upon it ceases. Here, the spring element holds the opening means accurately and robustly in position on the valve sealing body. At the same time, it also gives the opening means a defined freedom of movement so that, when the piston moves, it is taken along by the latter and pushed against the valve closing body. When moved in this way, the opening means raises the valve sealing body from the valve seat by pressure contact and opens the valve. 
         [0009]    According to the disclosure, the spring element is formed by means of a punched and bent part, which can be produced in a particularly simple and economical manner and in large quantities by machine by punching and bending a suitable material. A suitable material which is preferably used is a metal sheet, in particular spring steel, which is very robust and exhibits little wear. Moreover, functional elements or functional regions that are required during production in and/or on the spring element can be integrated into the punched and bent part in a particularly simple and economical manner, preferably in a single step by means of punching and/or bending. 
         [0010]    For assembly, the opening means with the associated punched and bent part can preferably simply be inserted and clipped into or clipped onto the accumulator device. 
         [0011]    Moreover, as a relatively small precision component, the punched and bent part together with the opening means can be produced at low cost. The opening means with the punched and bent part is furthermore preferably configured as an individual component, which is advantageously produced in advance and is held nonpositively and/or positively on the accumulator device with little effort by means of the spring element as a punched and bent part. 
         [0012]    In comparison with conventional accumulator devices, the overall result is lower accuracy requirements on the manufacture of the opening means and the mounting thereof on the accumulator device. Thus, in addition to the low-cost production of the spring element as a punched and bent part, the effort involved in manufacture and manufacturing costs for the accumulator device are reduced overall. 
         [0013]    As a particularly preferred option, the opening means is held on the accumulator cylinder or the cylinder by means of the punched and bent part. By being held in this way, the opening means is held on the component at which the valve closing body also rests on its valve seat, at least indirectly. Therefore, the position of these components relative to one another is then particularly precise. The opening means can furthermore be mounted very easily on the cylinder simply by being clipped in. 
         [0014]    As an alternative, the opening means is advantageously held on the accumulator piston or the piston by means of the punched and bent part. Here too, simple clip mounting is possible. In this development, it is furthermore possible to use a simple standard accumulator piston without the need for a particularly precise interference fit for an opening means on said piston. A relatively simple piston geometry can therefore be chosen. Moreover, the risk of abraded shavings or of deformation due to compressive forces is almost completely avoided. 
         [0015]    Particularly precise positioning of the opening means held in accordance with the disclosure is possible if the associated punched and bent part is arranged directly on the component forming the valve seat, in particular a valve seat body. Together with the opening means, the punched and bent part of this kind can then also be of particularly small dimensions. Integral configuration of the punched and bent part with the component forming the valve seat is advantageous. It is furthermore also advantageous likewise to make the valve sealing body integral with the opening means and the punched and bent part. Here, it is possible, in particular, to make use of the high strength of spring steel for the valve seat and/or the valve sealing body too. With a “combination part” of this kind, it is also possible to make the surrounding pump housing particularly small. 
         [0016]    The opening means is preferably configured with a pin element for engagement, in particular for slightly eccentric engagement, on the valve sealing body. In this case, the pin element is formed by means of a pin which is punched out of a reference plane of the punched and bent part and bent out of said reference plane. A pin of this kind as an opening means can advantageously extend through the valve opening in order then, on the one hand, to engage on the valve sealing body and, on the other hand, to be actuated by the accumulator piston. For this purpose, the end of the pin facing the valve sealing body can be specially adapted, in particular configured with an oblique contact surface, to ensure that the valve sealing body is not deformed at its surface when the opening means makes contact. 
         [0017]    That end of the pin which is directed toward the valve sealing body is furthermore preferably configured with at least two points of engagement by means of which the pin engages on the valve sealing body when opening the valve. Using at least two points of engagement stabilizes the direction of motion during engagement and as the valve sealing body is pushed open, especially where the valve sealing body is a ball. For the ball, at least three points of support are formed by two points of engagement together with a point of contact or point of rolling contact on an associated valve seat of a valve seat body, and therefore the position of the ball is fixed in a definite and stable manner. 
         [0018]    Moreover, the opening means preferably engages on the valve sealing body with a slight eccentricity, thereby making separation and raising of the valve sealing body from the valve seat easier. The valve sealing body is then raised in a slightly asymmetric manner, as a result of which the flow cross section of the valve opening is increased quickly and more fluid can flow through per unit time. 
         [0019]    As an alternative, the pin is manufactured as an individual part and connected to the punched and bent part as a spring element. As a particularly preferred option, the end of the pin facing the punched and bent part has a shoulder formation which can be fitted into a recess of complementary shape on the punched and bent part. The pin is preferably fitted in a particularly stable and non-detachable manner on the punched and bent part, in particular by means of an interference fit. In an alternative variant, the pin is advantageously connected releasably to the punched and bent part, thus enabling the pin to be replaced individually in a simple manner as a wearing part. 
         [0020]    It is furthermore advantageous if the pin is held by means of a radially directed arm. As a portion of the punched and bent part, the radially directed arm forms a resilient connection radially from the outside to the inside, wherein the pin is positioned radially on the inside. With this connection, the pin is held in a very simple manner in the center of an otherwise circular-cylindrical cylinder-piston arrangement by means of a spring force defined by the arm. The valve opening can advantageously be arranged there in the center, thereby making it possible to achieve a symmetrical and largely laminar flow through the valve according to the disclosure. 
         [0021]    Moreover, the arm is advantageously configured with two subarms, which are punched out of the reference plane of the punched and bent part and extend substantially radially, in particular in parallel. The subarms are spaced apart, thus forming a through opening for the brake fluid. The brake fluid flows through the through opening during operation, thus advantageously enabling brake fluid to be delivered with little resistance. Moreover, the spring force of the individual subarm can be adapted individually according to operating requirements, in particular by varying the thickness and/or length of the individual subarm. It is advantageous if the subarms have a lower spring force overall, in particular because of the through opening, than a single compact arm without a through opening having otherwise identical thickness and length dimensions. By means of the lower spring force, a lower resistance of the spring element to displacement by the accumulator piston is provided. 
         [0022]    Moreover, a bead, in particular a concave bead or a convex bead, is preferably formed at the transition from the arm to the pin, stabilizing and/or reinforcing the pin in a simple manner and without an additional material. Forces which would otherwise lead to wear arise particularly at the transition from the arm to the pin. 
         [0023]    For stabilization, the pin is, additionally or alternatively, preferably configured with at least one flange punched out of the reference plane of the punched and bent part and bent out of said reference plane. The flange is thus formed on at least one outer edge of the pin and, as a particularly preferred option, points radially in the direction of the arm. A particularly stable and simultaneously compact pin is thereby provided. 
         [0024]    According to the disclosure, a valve in which the spring element is configured with an annular holding portion is furthermore advantageously provided. Here, the annular holding portion is formed by means of an annular disk, which is punched out of an abovementioned reference plane of the punched and bent part and in which, in particular, at least one through opening is punched. By means of the annular disk as an annular holding portion, the spring element can be mounted very simply in an accurately fitting manner and in a fixed location, in particular on the accumulator cylinder or accumulator piston of circular-cylindrical shape. Moreover, brake fluid can flow through the at least one through opening punched out of the annular disk. As a result, brake fluid can flow into the accumulator device and out of the accumulator device particularly easily and with particularly little resistance, and therefore the exchange of fluid is facilitated. 
         [0025]    It is furthermore advantageous if the spring element is configured with at least one axial spacer facing the accumulator cylinder. In this case, the axial spacer is formed by means of a tab punched out of an above-described reference plane of the punched and bent part and bent out of said reference plane. This tab forms a spacing between the accumulator cylinder and the spring element, allowing fluid to flow through there. Moreover, the spacing avoids hydraulic sticking of the spring element on the accumulator cylinder, which would otherwise occur. In addition or as an alternative, an axial spacer facing the accumulator piston is preferably punched out of the reference plane of the punched and bent part and, from this reference plane, is formed as a bent-out tab. With the axial spacer formed in this way, a spacing is created between the spring element and the accumulator cylinder and preferably, at the same time, between the spring element and the accumulator piston. According to the disclosure, brake fluid can thus flow with particularly little resistance around the spring element. 
         [0026]    The spring element is furthermore preferably configured with an axial protrusion facing the accumulator piston. The axial protrusion is formed by means of an arm punched out of an aforementioned reference plane of the punched and bent part and bent out of said reference plane. The protrusion of this kind forms a spacer between the accumulator piston and the opening means. This allows particularly simple adaptation of the arrangement according to the disclosure to different types of accumulator cylinder and/or accumulator piston. In particular, a simple, low-cost standard accumulator piston can be used, which has a flat piston end face. When the accumulator piston moves in the direction of the spring element, this piston end face is the first to press against the arm bent out of the reference plane of the punched and bent part and actuates the pin held in this way. In this way, a particularly short response time can be achieved. 
         [0027]    The disclosure is furthermore directed to a use of such a valve according to the disclosure in an accumulator device, in particular for a hydraulic unit of a vehicle brake system, in which the accumulator piston, in particular, is configured with an axial protuberance facing the opening means. This configuration is particularly advantageous if the opening means is mounted with the spring element according to the disclosure on the accumulator cylinder or on the valve seat body. 
         [0028]    The protuberance on the piston end face facing the opening means is preferably configured at least approximately in the form of a spherical segment. The center of the spherical segment is advantageously the point around which the accumulator piston can turn or pivot slightly within the accumulator cylinder when it deviates from its theoretically linear motion. The offset of this kind of the accumulator piston in the accumulator cylinder then to a large extent no longer has an effect on the actuation of the opening means. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Illustrative embodiments of the solution according to the disclosure are explained in greater detail below by means of the attached schematic drawings, in which: 
           [0030]      FIG. 1  shows part of a hydraulic circuit diagram of a vehicle brake system having an accumulator device in accordance with the prior art, 
           [0031]      FIG. 2  shows the detail II in  FIG. 1 , 
           [0032]      FIG. 3  shows a longitudinal section through an accumulator device in accordance with  FIG. 1 , 
           [0033]      FIG. 4  shows a longitudinal section through a first variant of an accumulator device having a spring element according to the disclosure, 
           [0034]      FIG. 5  shows a perspective view of a first illustrative embodiment of a spring element for a valve according to the disclosure, 
           [0035]      FIG. 6  shows a first side view of the spring element in accordance with  FIG. 5 , 
           [0036]      FIG. 7  shows a plan view of the spring element in accordance with  FIG. 5 , 
           [0037]      FIG. 8  shows an enlarged plan view of the spring element in accordance with  FIG. 5 , 
           [0038]      FIG. 9  shows a second side view of the spring element in accordance with  FIG. 5 , 
           [0039]      FIG. 10  shows the detail X in  FIG. 4 , 
           [0040]      FIG. 11  shows a perspective view of a second illustrative embodiment of a spring element according to the disclosure, 
           [0041]      FIG. 12  shows the section XII according to  FIG. 11 , 
           [0042]      FIG. 13  shows a perspective view of a third illustrative embodiment of a spring element for a valve according to the disclosure, 
           [0043]      FIG. 14  shows a perspective view of a fourth illustrative embodiment of a spring element for a valve according to the disclosure, 
           [0044]      FIG. 15  shows the section XV according to  FIG. 14 , 
           [0045]      FIG. 16  shows a perspective view of a fifth illustrative embodiment of a spring element according to the disclosure, 
           [0046]      FIG. 17  shows the section XVII according to  FIG. 16 , 
           [0047]      FIG. 18  shows the detail XVIII in  FIG. 17 , and 
           [0048]      FIG. 19  shows a longitudinal section through a second variant of an accumulator device having a spring element according to the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]      FIG. 1  illustrates a vehicle brake system  10 , which comprises a brake pedal  12  that can be actuated by a driver of an associated four-wheeled vehicle. The brake pedal  12  acts on a brake booster  14 , by means of which pressure on a fluid in the form of brake fluid can be produced at an associated brake master cylinder  16 . The brake master cylinder  16  is connected to various fluid lines  18 , by means of which, in particular, a changeover valve  20 , a pump element  22  with associated drive motor  24 , an inlet valve  26  for the rear left hand side, and inlet valve  28  for the front right hand side, an outlet valve  30  for the rear left hand side, an outlet valve  32  for the front right hand side, a brake cylinder  34  for the rear left hand side and a brake cylinder  36  for the front right hand side are selectively connected together fluidically. An accumulator device  38  for temporary storage of brake fluid is furthermore inserted into the fluid lines  18 . 
         [0050]    The accumulator device  38  is illustrated by a relatively rough schematic diagram in  FIG. 2  and by a more detailed schematic diagram in  FIG. 3 . The accumulator device  38  comprises a cup-shaped, circular-cylindrical accumulator cylinder  40 , in which an accumulator piston  42  is movably mounted. In this case, the accumulator piston  42  is sealed off in a fluid tight but, at the same time, movable manner on the inside of the accumulator cylinder  40  by means of a piston seal  44  arranged in a fixed location on the accumulator piston  42 . A piston spring  46  urges the accumulator piston  42  mounted movably in this way into the cup shape of the accumulator cylinder  40 , thereby forming in the interior of the latter a pressure space for the temporary storage of brake fluid under pressure. 
         [0051]    A valve  48 , by means of which brake fluid can be admitted selectively into the interior of the accumulator cylinder  40 , is formed on the accumulator cylinder  40  at the bottom surface  47  of the cup shape of said cylinder, said bottom surface lying opposite the accumulator piston  42 . The valve  48  is actuated by means of the accumulator piston  42  when the latter moves far into the accumulator cylinder  40  and thus approaches the valve  48 . For this purpose, the valve  48  is configured with a valve sealing body  50  which is urged against a valve seat  54  in the direction of the accumulator piston  42  by means of a valve spring  52 . The valve seat  54  is formed on a valve seat body  56  and there surrounds a valve opening  58 . The valve seat body  56  can be of single-part configuration, of multi-part configuration with a valve seat and a valve seat carrier or integrated as a fastening in the accumulator cylinder  40 . 
         [0052]    An opening means  60  in the form of a pin is formed on the accumulator piston  42 , said pin being pressed in an interference fit  62  on the accumulator piston  42  opposite the valve opening  58  and being held there in a fixed location. The interference fit  62  serves to position the pin-shaped opening means  60  very precisely, especially in the axial direction of the accumulator piston  42 , relative to the valve sealing body  50  resting against the valve seat  54 . Precise positioning is required to ensure that the accumulator piston  42  raises the valve sealing body  50  at a precisely defined point from the valve seat  54  and in this way opens the valve  48  as it moves into the accumulator piston  42 . 
         [0053]      FIG. 4  illustrates an accumulator device  38  according to the disclosure which very largely comprises the elements which have already been described in detail in  FIG. 3 . In addition, a filter  63  for filtering brake fluid flowing into the accumulator device  38  is fitted in the valve  48 . Moreover, there is no conventional opening means  60  in the form of a pin arranged by means of an interference fit  62  in an accumulator piston  42  shaped especially for this purpose. Instead, a spring element  64  according to the disclosure is provided, in the present case said spring being positioned between the accumulator piston  42  and the bottom surface  47  of the accumulator piston  40 . 
         [0054]      FIG. 5  to  FIG. 18  show various illustrative embodiments of the spring element  64  according to the disclosure in detail. Common to all the illustrative embodiments is the fact that the spring element  64  is formed as a punched and bent part, in the present case from spring steel, and has a reference plane  65 . In this reference plane  65 , an annular holding portion  66  of the spring element  64  is formed by punching an annular disk  67  out of the reference plane  65 . The annular holding portion  66  serves to hold a radially directed arm  68  which, for its part, holds a pin  69 . Both the arm  68  and the pin  69  are punched out of the reference plane  65  of the punched and bent part and are bent in such a way that the pin  69  points upward (relative to the figure). When installed in the accumulator device  38 , the pin  69  projects in the direction of the accumulator cylinder  40  and hence in the direction of the valve sealing body  50 . The pin  69  forms an opening means  70 , by means of which the valve sealing body  50  is pushed off the valve seat  54  and hence the valve  48  is opened when the accumulator piston  42  moves into the accumulator cylinder  40  ( FIG. 4  and  FIG. 19 ). 
         [0055]    In its radially inward-directed extent, the arm  68  extends beyond the center of the annular disk  67 , with the result that the pin  69  held by the arm  68  engages eccentrically on the valve sealing body  50  through the valve opening  58  ( FIG. 4  and  FIG. 19 ). 
         [0056]    The arm  68  is furthermore bent in the direction of the accumulator piston  42 , with the result that an axial protrusion  71  of the spring element  64  in the direction of the accumulator piston  42  is formed. If the accumulator piston  42  moves toward the spring element  64 , the accumulator piston  42  touches the axial protrusion  71  first of all. The arm  68  and the pin  69  connected thereto are immediately pushed in the direction of the valve sealing body  50 , and the valve  48  is opened particularly quickly. 
         [0057]    Moreover, the arm  68  is configured with two parallel subarms  72 , which are punched and bent out of the reference plane  65  and point radially inward approximately in parallel. A through opening  74  is formed between the subarms  72 , attenuating the spring action of the spring element  64  and allowing the brake fluid to flow through. 
         [0058]    The through flow of the brake fluid is additionally facilitated by means of at least one through opening  76 , which is punched out of the annular disk  67 . In the present illustrative embodiments, there are 5 to 6 such through openings  76 . 
         [0059]    In addition, a total of six tabs is punched out of the annular disk  67 . Of the six tabs, three tabs are bent out of the reference plane  65  in such a way that three axial spacers  78  facing the bottom surface  47  of the accumulator cylinder  40  are formed. The other three tabs are bent in the opposite direction and thus form three axial spacers  80  facing the accumulator piston  42 . By means of the spacing formed by the spacers  78  and  80 , particularly easy and resistance-free through flow of the brake fluid is additionally enabled. Moreover, any hydraulic sticking of a conventional spring element or holder for an opening pin on the accumulator cylinder  40  and/or the accumulator piston  42 , which would otherwise occur, is avoided. 
         [0060]      FIG. 5  to  FIG. 10  illustrate a first illustrative embodiment of a spring element  64  according to the disclosure in detail in various views. In this case, the pin  69  has a bifurcated shape with two engagement rods  82 . By means of these two engagement rods  82 , the pin  69  engages reliably and without twisting on a ball serving as a valve closing body  50 . The individual engagement rod  82  has an oblique, in particular rounded, contact surface  84 , which touches the valve closing body  50  when the valve  48  is opened ( FIG. 10 ). 
         [0061]      FIG. 11  and  FIG. 12  show an illustrative embodiment in which a bead  86  shaped convexly in the direction of the radial arm  68  is formed at a transition  85  from the arm  68  to the pin  69 , i.e. at a pin bend, and between the two engagement rods  82 . The bead  86  stabilizes the transition  85  and simultaneously stabilizes the pin  69 . 
         [0062]    In another illustrative embodiment in accordance with  FIG. 13 , the pin  69  is additionally stabilized by means of two flanges  88 , which extend axially along respective outer edges of the pin  69  and point radially in the direction of the arm  68 . In this way, a particularly stable and simultaneously compact pin  69  is advantageously formed. 
         [0063]      FIG. 14  and  FIG. 15  illustrate an illustrative embodiment in which a bead  90  which is concave when viewed in the direction of the radial arm  68  is formed at the transition  85 . The concave bead  90  is thus situated on the outside of the pin bend, i.e. on a rounded portion of the pin  69  formed during the bending of that punched-out portion of the annular disk  67  provided for the arm  68  and the pin  69 . By means of the concave bead  90 , the pin  69  is, first of all, stabilized and, secondly, is shaped in such a way that two points of engagement for the sealing body  50  are created. There is no need here for two engagement rods  82  of the kind described in the illustrative embodiments shown in  FIG. 5  to  FIG. 13  to be specially formed. 
         [0064]    In another illustrative embodiment in accordance with  FIG. 16  to  FIG. 18 , the pin  69  is shaped as a separate pin with two engagement rods  82 , each of which forms an oblique contact surface  84 . This pin  69  furthermore has a shoulder formation  92 , by means of which the pin  69  is pressed by means of an interference fit into a complementary aperture  94  provided in the punched and bent part. As an alternative, the pin  69  can be connected to the spring element  64  by means of soldering, welding and/or deformation of the pin. 
         [0065]    As illustrated in  FIGS. 4 and 19 , the pin  69  projects through the associated valve opening  58  and ends with the, generally obliquely oriented, contact surface  84 , which is provided for the purpose of striking against the associated valve sealing body  50 . The positioning of the opening means  70  thus corresponds to that of the opening means  60  according to the prior art. At the same time, however, the opening means  70  is not arranged rigidly but is arranged resiliently on another body of the accumulator device  38 . In this way, it can be arranged directly or indirectly on the accumulator cylinder  40 , in particular resiliently, thereby making possible simple and, at the same time, precise positioning relative to the valve sealing body  50 . 
         [0066]      FIG. 4  shows an illustrative embodiment in which the spring element  64  is clipped onto the inside of the accumulator cylinder  40  by means of its holding portion  66  and, in this way, is mounted there in a fixed location. 
         [0067]    In an alternative illustrative embodiment (not shown), the spring element  64  is held by means of its annular holding portion  66  on a correspondingly shaped valve seat body  56  and hence in the immediate vicinity of the valve seat  54 . 
         [0068]    The opening means  70  held resiliently on the accumulator cylinder  40  or on the valve seat body  56  in this way is moved against the valve sealing body  50  by means of the accumulator piston  42  in order to be able to raise said body from the valve seat  54  as already explained above. For this purpose, a protuberance  98 , by means of which the accumulator piston  42  strikes against the spring element  64  during its movement into the accumulator cylinder  40 , is formed centrally on a piston end face  96  facing the spring element  64 . In the illustrative embodiment in accordance with  FIG. 4 , the protuberance  98  is in the form of an obliquely stepped elevation on a simple accumulator piston  42 . In a variant illustrated in  FIG. 19 , the protuberance  98  is in the form of a spherical segment and has a radius  100  which is chosen in such a way that, when it pivots slightly or performs a nonlinear movement within the accumulator cylinder  40 , the accumulator piston  42  pivots about the central point  102  at which the radius  100  has its origin. Irrespective of the nonlinear movement of the accumulator piston  42 , the opening means  70  is thus always urged reliably toward the valve sealing body  50 .