Patent Publication Number: US-9404544-B2

Title: Slave cylinder for a vibration-damped hydraulic force transmission system, particularly a hydraulic clutch actuating system for motor vehicles

Description:
FIELD OF THE INVENTION 
     The present invention relates to a slave cylinder for a vibration-damped hydraulic force transmission system and, in particular, to slave cylinders such as are in widespread use in hydraulic clutch actuating systems for motor vehicles. 
     DESCRIPTION OF THE PRIOR ART 
       FIG. 19  shows a conventional hydraulic clutch actuating system for motor vehicles in simplified illustration. The hydraulic clutch actuating system  10  comprises a master cylinder  12  mounted on a pedal block  11  of the motor vehicle and a slave cylinder  14  fixed in the motor vehicle in the vicinity of a transmission, the cylinders being hydraulically connected together by way of a hydraulic line  16  which, starting from the master cylinder  12 , here consists of a first pipe length  18 , a hose length  20  and a second pipe length  22 . The piston (not illustrated) of the master cylinder  12 , which is hydraulically connected with an equalizing reservoir  24 , is operatively connected with a clutch pedal  28  by way of a piston rod  26  so that the master cylinder  12  can be actuated by pressing down the clutch pedal  28 , which produces a displacement of the piston in the master cylinder  12 . As a result, a fluid column is pushed through the hydraulic line  16  in the direction of the slave cylinder  14  and hydraulically actuates the slave cylinder  14 . 
     The slave cylinder  14 , more specifically the piston (not shown here) thereof, is operatively connected by means of a piston rod  30  with a release mechanism  36  of a friction clutch  38  via a release lever  32  and a thrust bearing  34 . If for release of the friction clutch  38  the slave cylinder  14  is hydraulically loaded, then a clutch pressure plate  40  is separated by means of the release mechanism  36  from a clutch driven plate  44 , which is seated on a transmission shaft  42  and co-operates with a flywheel  43  carried by the crankshaft of the internal combustion engine (not illustrated), of the friction clutch  38  and thus also the internal combustion engine from the transmission (similarly not shown in more detail) of the motor vehicle. 
     If the clutch pedal  28  is relieved of load in order to re-engage the friction clutch  38  the slave cylinder  41 , more specifically the piston thereof, is as a consequence of inter alia the spring forces of the friction clutch  38  returned to its basic or starting setting, whereby the above-mentioned fluid column is pushed through the hydraulic line  16  back again in the direction of the master cylinder  12 . 
     In such a hydraulic clutch actuating system  10 —which is to be regarded as a quasi-static hydraulic force transmission system in which there is no continuous flow of the hydraulic fluid—vibrations of the internal combustion engine, particularly the crankshaft thereof, are transmitted by way of the components of the friction clutch  38 , the thrust bearing  34 , the release lever  32  and the slave cylinder  14  to the fluid column present between slave cylinder  14  and master cylinder  12  in the hydraulic line  16 , in which column the vibrations propagate as pressure pulses. It would be regarded as disadvantageous that these pressure pulses are felt as vibrations at the clutch pedal  28  by the driver particularly when his or her foot rests on the clutch pedal  28  in typical urban driving—so-called ‘contact tingling’—or the depressed clutch pedal  28  is held during, for example, a pause in front of traffic lights. 
     There is thus no lack of proposals in the state of the art as to how to counteract this problem (for example, DE 36 31 507 C2 ‘square helix’, DE 40 03 521 C2 ‘double line with line branches of different length’, DE 195 40 753 C1 ‘auxiliary vibrator’, DE 101 12 674 C1 ‘diaphragm damper cell’ and DE 103 51 907 A1 ‘damping device with labyrinth body’). It is common to these proposals that inserted or arranged in or parallel to the hydraulic line between master cylinder and slave cylinder is a separate subassembly for vibration damping, which does not interrupt the fluid column between master cylinder and slave cylinder and which is also generally capable of satisfactorily damping the pressure pulses. However, sufficient installation space for accommodation of such subassemblies is not always available in the engine bay. Moreover, this procedure increases the number of hydraulic connecting points (for example detent or screw connections) between the subassemblies involved and thus inevitably the risk of leakages as well as the assembly cost. 
     Against this background it was already proposed (for example DE 199 20 821 C1, DE 10 2005 044 582 A1) to accommodate an auxiliary vibrator or vibration damper in the housing of the master cylinder, more specifically in the pressure chamber thereof, for which purpose, however, it would be necessary to provide cylinder housings which are specially designed, thus incurring extra cost, and which in particular are extended in axial direction, with a special receiving and/or mounting capability for the auxiliary vibrator or vibration damper. Moreover, installation space is frequently restricted particularly at the pedal block or in the region of the splashboard in a motor vehicle, so that bulky master cylinders are not desirable. 
     In this connection closer account need not be taken of ‘double-acting’ valve mechanisms which are connected between master cylinder and slave cylinder (for example JP 59-89833 A, EP 1 719 921 A2) and which open with each displacement of the fluid column, i.e. not only on displacement in the direction of the slave cylinder, but also on displacement in the direction of the master cylinder, and close when the fluid column is not moved, so as to separate the master cylinder, or decouple it in terms of vibration, from the slave cylinder, since these valve mechanisms (a) are as a rule of dissimilar and expensive construction as constantly ‘pressure-medium-open’ damping devices not needing spring-biased valve bodies or the like, (b) oblige specific opening and closing pressures, which often undesirably increase return travel times and the system hysteresis, and finally (c) are provided with bypasses more susceptible to contaminations and accompanying losses in performance. 
     What is needed is a vibration-damped hydraulic force transmission system, particularly a hydraulic clutch actuating system for motor vehicles, where the vibration-damping measures are integrated in the force transmission system in the most economic and space-saving manner as possible. 
     SUMMARY OF THE INVENTION 
     According to the invention, provided in a slave cylinder for a vibration-damped hydraulic force transmission system, particularly a hydraulic clutch actuating system for motor vehicles, which comprises a cylinder housing, a piston received therein to be longitudinally displaceable and a pressure chamber which is bounded by the cylinder housing and the piston and can be selectably acted on by a pressure medium, by way of a pressure connection provided in the cylinder housing, in order to displace the piston in the cylinder housing, is an insert member which is inserted in the pressure chamber and secured in the pressure connection and which is equipped with a device for reducing pressure pulses, the device being constantly open to the pressure medium. 
     Due to the fact that the insert member equipped with the device for reducing pressure pulses is inserted into the pressure chamber of the slave cylinder—for which purpose no additional installation space has to be provided, since use can be made of the cylinder dead space present there anyway, as a consequence of which the axial length of the slave cylinder is unchanged by comparison with conventional constructions—the integration of the vibration-damping measures in the force transmission system is realized at the outset in highly space-saving manner; by contrast to the prior art, it is not necessary to provide and mount any vibration-damping subassemblies either in the hydraulic line between master cylinder and slave cylinder or in the master cylinder. Since, in addition, the insert member is secured in the pressure connection of the slave cylinder, it is not necessary to undertake any additional constructional measures for the installation/mounting of the insert member, but an existing slave cylinder such as known from, for example, EP 1 666 752 A2 of the applicant can be utilized unchanged in order to integrate the insert member. Through the arrangement of the device for reducing pressure pulses in the pressure chamber of the slave cylinder, i.e. in the immediate vicinity of the point of introduction of the vibrations into the fluid column, it is additionally ensured in advantageous manner that the pressure pulses cannot propagate at maximum amplitude in/through the hydraulic line between slave cylinder and master cylinder, so that the risk of the hydraulic line detaching from its fastening points at, for example, the bodywork of the motor vehicle due to vibration or shaking loose therefrom is also minimized. A further advantage of the arrangement of the device for reducing pressure pulses in the pressure chamber of the slave cylinder consists in that when a slave cylinder equipped in that manner is utilized in an otherwise conventional hydraulic clutch actuating system according to  FIG. 19  the second pipe length—near the slave cylinder—of the hydraulic line, which in order to reduce vibration would usually be constructed with a narrowed cross-section by comparison with the first pipe length, can be eliminated, i.e. the hose length of the hydraulic line can now be directly connected with the pressure connection of the slave cylinder, which on the one hand significantly reduces costs and the need for installation space (omission of the second pipe length, an associated mount and a plug connection) and on the other hand through elimination of the said plug connection results in a smaller size and more robust construction. 
     In a compact construction which is particularly simple in terms of production the insert member can be of substantially pot-shaped construction with a shroud section and a base, with which a substantially hollow-cylindrical extension inserted into the pressure connection of the cylinder housing is connected. 
     In principle, it is possible to fix the insert member in the pressure connection of the cylinder housing by force couple (for example, by means of a press fit) or material couple (for example by a welded or glued connection). However, it is preferred, particularly with respect to simple assembly, to secure the insert member in the pressure connection of the cylinder housing by axial mechanically positive couple, namely by means of a snap connection. In this regard, in an advantageous embodiment the extension of the insert member is provided at the outer circumference with an annular collar going out from its free end and is multiply longitudinally slotted for formation of a plurality of spring arms, wherein in the mounted state of the insert member the annular collar at the extension engages behind an annular end surface, which is remote from the pressure chamber, in the pressure connection of the cylinder housing. In that case it is particularly advantageous in terms of cost if the cylinder housing comprises a base body of plastics material provided with a bore in which a metallic guide sleeve for the piston is inserted, the annular end surface, behind which the insert member engages, in the pressure connection of the cylinder housing being formed by an end of the guide sleeve of the cylinder housing. 
     In a first variant, the device for reducing pressure pulses can comprise an additional conduit path in the form of a channel with an opening at the pressure chamber side and an opening at the pressure connection side, the channel having a length amounting to a multiple of the direct spacing between the two openings. The second pipe length according to  FIG. 19  is thus quasi integrated in the slave cylinder in a simple and very space-saving manner. Although various courses of the channel are conceivable, it is preferred particularly from production aspects if the channel has a helically extending helix section. In this connection, the helix section of the channel can be formed at the outer circumference of the shroud section of the insert member as a groove which is radially outwardly covered by an inner circumferential surface of the cylinder housing, which on the one hand is producible particularly simply and economically—for example by means of injection-molding of the insert member, the radially outwardly open groove of which is then ‘complemented’ to form the channel in extremely simple manner only at the time of insertion of the insert member into the pressure chamber of the slave cylinder by the cylinder wall present there in any case, and thus without use of sealing elements or the like—and on the other hand effects a deflection of the fluid column, which has proved advantageous with respect to good vibration damping with smallest possible throughflow resistance. In an advantageous embodiment the channel can in this regard have an end section which is formed by the extension of the insert member and which is connected with the helix section by a connecting section of the channel, the connecting section extending in the base of the insert member. With respect to a best possible damping action it has additionally proved advantageous if the helix section of the channel has a cross-section smaller than or equal to the minimum cross-section of the pressure connection. In order to ensure good deaeration of the slave cylinder with a flushing action for any air bubbles contained in the pressure chamber, the opening of the channel at the pressure chamber side is preferably disposed at the top adjacent to the inner circumferential surface of the cylinder housing in the installed position of the slave cylinder. 
     In a second variant, the device for reducing pressure pulses can comprise a volume receiving means which is mounted at the insert member and which is elastically deformable under pressure in order to damp or reduce vibrations. In this connection, for a particularly compact construction the volume receiving means can be mounted at the inner circumference of the shroud section of the insert member. The volume receiving means is preferably a rubber-elastic spool-shaped element with a passage bore and an annular recess at the outer circumferential side, which recess together with the inner circumference of the shroud section of the insert member bounds an annular air chamber. In such a construction of the volume receiving means, if a pressure amplitude runs into the passage bore, the spool-shaped element deforms against the spring effect of the rubber-elastic material, whereby the air volume in the annular air chamber is compressed so that the spool-shaped element—as the term “volume receiving means” indeed implies—experiences a defined expansion in the region of the passage bore, leading to a degree of ‘pressure relief’ of the pressure amplitude. In this regard, the spring effect of the rubber-elastic material and the compressed air volume ensures automatic restoration of the spool-shaped element to its initial form if the pressure of the pressure medium prevailing in the region of the passage bore of the spool-shaped element drops below a predetermined value. 
     It has proved particularly effective in terms of damping or reducing vibration if in the case of a combination of the two afore-described variants of the device for reducing pressure pulses the volume receiving means as seen from the pressure chamber of the slave cylinder is hydraulically connected upstream of the channel forming the additional conduit path, so that the pressure pulse propagating from the pressure chamber of the slave cylinder does not have to initially transit the additional conduit path in order to reach the volume receiving means. In this connection, in an embodiment of particularly short and compact construction the helix section of the channel can coaxially surround the volume receiving means. 
     The afore-described first variant of the device for reducing pressure pulses by means of an additional conduit path can appropriately develop the respective functional requirements in the manner that the insert member comprises an inner insert of substantially pot-shaped construction with an inner insert shroud section and an inner insert base, wherein formed between the shroud section of the insert member and the inner insert shroud section is a helically extending helix section prolongation of which one end thereof is in fluid connection with the helix section and the other end thereof in fluid connection with an interior space of the inner insert, which interior space in turn communicates with the pressure connection. As a result, the additional conduit path can thus be prolonged as desired or needed in simple manner without at the same time increasing the need for axial constructional volume. Here as well it is of advantage particularly with respect to an economic capability of manufacture by means of, for example, injection-molding from plastics material if the helix section prolongation is formed at the outer circumference of the inner insert shroud section as a groove, which is radially outwardly covered by an inner circumferential surface—present there anyway—of the shroud section of the insert member; sealing elements or the like are again superfluous in this embodiment. 
     In further pursuance of the concept of the invention a thermostatically operating bypass valve providing a direct fluid connection between the pressure chamber and the pressure connection at low temperatures and interrupting this fluid connection at higher temperatures can be provided in the insert member in hydraulically parallel connection with the device for reducing pressure pulses. In the case of low temperatures at which the hydraulic medium—usually brake fluid—is already relatively viscous this embodiment has the advantage on the one hand that the forces to be exerted on the clutch pedal in the event of quick actuation do not undesirably increase and on the other hand that the return speed of the clutch pedal does not undesirably decrease. Advantageously, the bypass valve in this regard comprises a thermostatic element received in the interior space of the inner insert between the base of the insert member and the inner insert base and operatively connected with a plunger which opens or closes an opening in the inner insert base in dependence on temperature in order to provide the direct fluid connection between the pressure chamber and the pressure connection at low temperatures and to interrupt this fluid connection at higher temperatures. 
     In a further, advantageous embodiment the insert member or the inner insert has at the end thereof at the pressure chamber side a fastening section which so co-operates with an extension of the piston at the pressure chamber side that the piston prior to filling with pressure medium or first actuation of the slave cylinder is fixed in a predetermined stroke setting with respect to the cylinder housing and is releasable relative to the cylinder housing by the pressure medium filling or first actuation of the slave cylinder. Through the temporary fastening of the piston relative to the cylinder housing by the fastening section at the insert member or the inner insert and the extension at the piston it is possible, inter alia, to mount the slave cylinder at its place of use substantially free of force, since in that case the spring element usually present at or in the slave cylinder and serving to reset the piston does not have to be compressed by pushing the piston rod, which is operatively connected with the piston, into the cylinder housing, but the piston and thus also the piston rod can be temporarily held by means of the fastening section and extension in a defined stroke setting—which is advantageous for mounting—with respect to the cylinder housing against the force of the spring element. Other purposes of use of this embodiment include avoidance of overfilling of a hydraulic system, which includes such a slave cylinder, at the time of prefilling thereof, wherein the fastening section and extension ensure that the slave cylinder prior to first actuation thereof can accept only a predetermined amount of hydraulic fluid, as well as safeguarding the slave cylinder of such a construction against transport damage, wherein the fastening section and extension during transport of the slave cylinder prevent excessive protrusion of the piston rod from the cylinder housing. With respect to simple and economic production and provision of the premounting position of the piston it is preferred if the fastening section of the insert member comprises a hollow cylinder, which is axially aligned with respect to a center axis of the pressure chamber, with an annular bead at the inner circumferential side, while the central extension at the piston is provided at the outer circumferential side with an annular collar which engages behind the annular bead in the manner of a snap connection when the piston is fixed to the insert member. 
     Basically, the insert member can be made of a metallic material, for example an aluminum alloy, for example by machining. Ultimately, however, it is conducive to, in particular, provision of a device favorable in cost if the insert member is injection-molded from a plastics material, as already mentioned. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below on the basis of preferred exemplifying embodiments and with reference to the accompanying, partly schematic drawings, in which identical reference numerals denote identical or corresponding parts and elastomeric parts are mostly shown in the undeformed state in order to simplify the illustration. In the drawings: 
         FIG. 1  shows a longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating system for motor vehicles, in the pressure chamber of which is inserted an insert member equipped with a device for reducing pressure pulses, the device being constantly open to the pressure medium and having in combination an additional conduit path in the form of a channel and a volume receiving means, according to a first embodiment of the invention, 
         FIG. 2  shows a perspective illustration, obliquely from the front, of the insert member which, in the case of the slave cylinder according to  FIG. 1 , is secured in the pressure connection, 
         FIG. 3  shows a side view of the insert member according to  FIG. 2 , 
         FIG. 4  shows a front view of the insert member according to  FIG. 2 , from the left in  FIG. 3 , 
         FIG. 5  shows a back view of the insert member according to  FIG. 2 , from the right in  FIG. 3 , 
         FIG. 6  shows a side view of the insert member according to  FIG. 2  in correspondence with the section line VI-VI in  FIG. 5 , 
         FIG. 7  shows an enlarged-scale illustration of the detail VII in  FIG. 6 , 
         FIG. 8  shows a perspective individual illustration, obliquely from the front, of the elastomeric volume receiving means which, in the case of the slave cylinder according to  FIG. 1 , is mounted in the insert member, 
         FIG. 9  shows a longitudinal sectional view of the volume receiving means according to  FIG. 8 , 
         FIG. 10  shows a broken-away longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating system for motor vehicles, in the pressure chamber of which is inserted an insert member equipped with a device for reducing pressure pulses, which device is constantly open to the pressure medium and has merely an additional conduit path in the form of a channel, according to a second embodiment of the invention, 
         FIG. 11  shows a broken-away longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating system for motor vehicles, in the pressure chamber of which is inserted an insert member equipped with a device for reducing pressure pulses, which device is constantly open to the pressure medium and has merely a volume receiving means, according to a third embodiment of the invention, 
         FIG. 12  shows a broken-away longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating system for motor vehicles, in the pressure chamber of which is inserted an insert member equipped with a device for reducing pressure pulses, which device is constantly open to the pressure medium and has an additional conduit path in the form of a channel, wherein the insert member comprises an inner insert which prolongs the channel and in which a thermostatically operating bypass valve is provided, according to a fourth embodiment of the invention, 
         FIG. 13  shows a longitudinal sectional view of the insert member, which in the case of the slave cylinder according to  FIG. 12  is secured in the pressure connection, with inner insert and bypass valve, 
         FIG. 14  shows a sectional view of the insert member according to  FIG. 13  in correspondence with the section line XIV-XIV in  FIG. 13 , 
         FIG. 15  to  FIG. 17  show broken-away perspective illustrations of the insert member according to  FIG. 13  for clarification of the pressure medium paths, which can be freed by a thermostatic element of the bypass valve, for a direct fluid connection between the pressure chamber and the pressure connection of the slave cylinder, 
         FIG. 18  shows a diagram in which the ratio of the acceleration measured at a piston rod of the master cylinder to the acceleration measured at a piston rod of the slave cylinder is recorded against frequency, as a result of a test in which a sinusoidal vibration with variable frequency and an amplitude of 1 g (9.81 m/s 2 ) was applied to the piston rod of the slave cylinder, for (1st) a hydraulic clutch actuating system without a device for reducing pressure pulses (marked by triangles), (2nd) a hydraulic clutch actuating system with a slave cylinder equipped in correspondence with  FIG. 1  (marked with empty squares), (3rd) a hydraulic clutch actuating system with a slave cylinder equipped in correspondence with  FIG. 10  (marked with lozenges) and (4th) a hydraulic clutch actuating system with a slave cylinder equipped in correspondence with  FIG. 11  (marked with small stars), and 
         FIG. 19  shows a diagrammatic illustration of a hydraulic clutch actuating system according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a slave cylinder  50  for a vibration-damped hydraulic force transmission system, namely a vibration-damped clutch actuating system for motor vehicles. The slave cylinder  5  has a cylinder housing which is denoted generally by  52  and in which a piston subassembly  54  is received to be longitudinally displaceable, the subassembly comprising a piston  56  and a piston rod  58  connected with the piston  56  at least rigidly in tension and compression, thus to be effective in terms of actuation. Disposed in the cylinder housing  52  is a pressure chamber  60  which is bounded on the lefthand side in  FIG. 1  in variable manner by the piston  56 , on the righthand side in  FIG. 1  in fixed manner by a housing base  62  of the cylinder housing  52 , and radially outwardly in fixed manner by a circumferential wall  64  of the cylinder housing  52 . The pressure chamber  60  can be selectably acted on by a pressure medium, for example brake fluid, by way of a pressure connection  66 , which is provided at the housing base  62  and which in the mounted state of the slave cylinder  50  is connected with a clutch master cylinder in a manner known per se (cf.  FIG. 19 ) via a pressure line (which by comparison with  FIG. 19  can optionally also be of different construction) in order to displace the piston  56  in the cylinder housing  52 . As is described in more detail in the following, inserted in the pressure chamber  60  to adjoin the housing base  62  is an insert member  68  which is secured in the pressure connection  66  and in the first embodiment illustrated here advantageously fulfils several functions. In this connection, the insert member  68  serves, in particular, as a support for a device  70  for reducing pressure pulses, the device being constantly open to the pressure medium, or is equipped with this device. 
     As will be explained in detail further below, the device  70  for reducing pressure pulses thus connected in the mounted state of the slave cylinder  50  between the pressure chamber  60  of the slave cylinder  50  and a pressure chamber of the master cylinder (cf. again  FIG. 19 ) comprises on the one hand an additional conduit path in the form of a channel  72 , which has an opening  74  at the pressure chamber side or slave cylinder side, an opening  76  at the pressure connection side or master cylinder side and intermediately a channel length amounting to a multiple of the direct spacing, i.e. the ‘straight line spacing’, between the two openings  74  and  76 , and on the other hand a volume receiving means  78  which is mounted at the insert member  68  and is resiliently deformable under pressure. As a result, the channel  72  and the volume receiving means  78  of the device  70  for reducing pressure pulses are combined in the cylinder housing  52  with maximum compactness to form a subassembly, wherein the insert member  68  at least in part together with the cylinder housing  52  bounds the channel  72 . 
     According to  FIG. 1  the cylinder housing  52  comprises a base body  80 , which is preferably injection-molded from plastics material and which is provided on the outer circumference with a fastening flange  82  for mounting of the slave cylinder  50  in the motor vehicle. The fastening flange  82  has two fastening bores  84  reinforced by means of slotted steel bushes  86 . Extending through the fastening bores  84 , which are lined by the steel bushes  86 , in the mounted state of the slave cylinder  50  are, for example, screws (not shown) serving for fastening the slave cylinder  50  to, for example, a transmission wall (not illustrated) in the motor vehicle. The base body  80  of the cylinder housing  52  additionally has, to the left of the fastening flange  82  in  FIG. 1 , a radial groove  88  at the outer circumference, into which an elastomeric protective cap  92  having a bellows section  90  surrounding the piston rod  58  is buttoned by an annular collar  94  at the inner circumference. The bellows section  90  of the protective cap  92  additionally surrounds a spring element, which is provided on the side of the piston  56  remote from the pressure chamber  60 , in the form of a helical compression spring  96  which at its end on the right in  FIG. 1  is supported at the cylinder housing  52  and by its end at the left in  FIG. 1  engages the piston rod  58  so that the helical compression spring  96  biases the piston subassembly  54  in a direction away from the housing base  62  in order to keep the piston rod  58 , in the mounted state of the slave cylinder  50 , in contact with a clutch lever (not shown). 
     At the inner circumferential side the base body  80  of the cylinder housing  52  has a stepped bore  98  open to the left in  FIG. 1 , in which a preferably metallic guide sleeve  100  as a further component of the cylinder housing  52  is inserted. The guide sleeve  100  has two hollow-cylindrical sleeve sections  102  and  104  of different diameter which are connected together at the housing base  62  of the cylinder housing  52  by way of an annular section  106 . Starting from the side at the left in  FIG. 1  the stepped bore  98  of the base body  80  now has four bore sections  108 ,  110 ,  112  and  114  of different diameter, which reduces in size in  FIG. 1  from the left to the right. 
     The first bore section  108  of the stepped bore  98  in the base body  80  has at its open end an undercut  116  serving for fixing an annular securing element  118 , which is slotted for mounting and preferably consists of plastics material, to the cylinder housing  52 , which securing element bears against the end surface of the guide sleeve  100  at the left in  FIG. 1  and thus secures the guide sleeve  100  in the base body  80  of the cylinder housing  52 . The larger-diameter sleeve section  102  of the guide sleeve  100  is tightly received in the second bore section  110  of the stepped bore  98  of the base body  80  and forms by its inner circumferential surface the circumferential wall  64  bounding the pressure chamber  60 . The third bore section  112  of the stepped bore  98  is connected with the second bore section  110  by way of an annular shoulder  120  against which the annular section  106  of the guide sleeve  100  bears. The smaller-diameter sleeve section  104  of the guide sleeve  100  is tightly received in the third bore section  112  of the stepped bore  98  in the base body  80 . In that case the sleeve section  104  is provided at the outer circumference with a radial groove  122  for reception of an O-ring  124  providing a static seal between the third bore section  112  of the base body  80  and the sleeve section  104  of the guide sleeve  100 . The fourth bore section  114  of the base body  80  is connected with the third bore section  112  by way of a further annular shoulder  126 , the dimensions of the smaller-diameter sleeve section  104  of the guide sleeve  100  on the one hand and the third and fourth bore sections  112  and  114  of the stepped bore  98  on the other hand being so matched to one another that an annular end surface  128  of the sleeve section  104  of the guide sleeve  100  has a small axial spacing from the annular shoulder  126  of the base body  80  and protrudes radially inwardly beyond this for securing, as described in more detail below, of the insert member  68  in the pressure connection  66 . The fourth bore section  114  of the stepped bore  98  in the base body  80  is additionally provided at the inner circumference with a plurality of—here, for example, four—radially inwardly protruding longitudinal ribs (not able to be seen in  FIG. 1 ) which extend in axial direction of the cylinder housing  52  and which are distributed non-uniformly or asymmetrically over the circumference of the fourth bore section  114  and serve for rotational angle orientation of the insert member  68  in the pressure connection  66 , as similarly will be explained below in more detail. Finally, a smaller-diameter pressure connecting bore  130  formed in the base body  80  opens into the fourth bore section  114  of the stepped bore  98  at the end of the fourth bore section  114  at the right in  FIG. 1 . 
     It is apparent from the above description that the pressure connecting bore  130 , the fourth bore section  114  of the stepped bore  98  and the sleeve section  104 , which is received in the third bore section  112  thereof, of the guide bore  100  are a component of the pressure connection  66 , by way of which the pressure chamber  60  of the slave cylinder  50  can be acted on by the pressure medium. As a consequence of the static sealing, which is produced by the O-ring  124 , at the outer circumference of the smaller-diameter sleeve section  104  of the guide sleeve  100  this experiences—when the pressure chamber  60  is loaded with pressure by way of the pressure connection  66 , in which the hydraulic pressure on the one hand acts on the annular end surface  128  of the sleeve section  104  and on the other hand on the larger-area end surface opposite thereto of the annular section  106  of the guide sleeve  100 , the latter end surface being remote from the pressure chamber  60 —a resultant force to the right in  FIG. 1 , which strives to keep the guide sleeve  100  in the stepped bore  98  of the base body  80 , thus relieving the fixing of the guide sleeve  100  in the base body  80  by means of the securing element  118 . 
     As can be further inferred from  FIG. 1 , the piston  56 , which is guided with small radial play in the larger-diameter sleeve section  102  of the guide sleeve  100  of the cylinder housing  52  and is metallic in the illustrated exemplifying embodiment, has at the outer circumference a radial groove  132  for receiving a groove ring  134 . The elastomeric groove ring  134  bears in a manner known per se, by its sealing lip at the outer circumference, under a degree of bias against the circumferential wall  64  of the cylinder housing  52  and thus ensures dynamic sealing of the pressure chamber  64  to the left in  FIG. 1 . 
     On the lefthand side in  FIG. 1  the piston  56  is further provided with a central recess  136  in which a ball head  138  formed at the end of the piston rod  58  at the right in  FIG. 1  is pivotably retained by means of a securing element  140  so that the piston rod  58  has a degree of angular movability with respect to the piston  56 . Instead of the form of the piston subassembly  54  shown in  FIG. 1  this could also be of integral construction with a piston outer surface which drops away conically or spherically towards the piston rod in order to guarantee angular mobility as is known in principle from DE 43 22 969 A1 or DE 43 31 241 A1. 
     The piston rod  58 , which is metallic in the illustrated exemplifying embodiment, has on the side at the left in  FIG. 1  a profiled end  142  on which an end piece  144  of plastics material is injection-molded, the end piece having a substantially spherical end surface  146  by way of which the piston rod engages the clutch lever (not illustrated) to be effective in terms of actuation. At the end of the end piece  144  at the right in  FIG. 1  this forms an annular collar  148  of the piston rod  58 , which on the one hand serves for coupling the protective cap  92  to the piston rod  58 , wherein the annular collar  148  engages in mechanically positive manner in an annular recess  150  of substantially complementary form in a fastening section  152  of the protective cap  92 , which fastening section is, on the side of the protective cap  92  remote from the pressure chamber  60 , connected with the bellows section  90  of the protective cap  92 . On the other hand, the annular collar  148  of the piston rod  58  forms by its end face facing the pressure chamber  50  a counter-bearing for the helical compression spring  96 , wherein also deriving from the end of the biased helical compression spring  96  facing the annular collar  148  is a degree of radial centering effect for the piston rod  58 , which is advantageous when mounting the slave cylinder  50  in the motor vehicle. 
     It is additionally evident from  FIG. 1  that the securing element  118  for retaining the guide sleeve  100  in the cylinder housing  52  is provided on its side remote from the pressure chamber  60  with an axial groove  154  which serves as a further counter-bearing and for centering the end, which faces the pressure chamber  60  and is on the right in  FIG. 1 , of the helical compression spring  96 , which spring widens substantially conically, thus is formed to be frusto-conical, in diameter towards the axial groove  154  starting from the annular collar  148  of the piston rod  58 . Through this ‘relocation’ of the helical compression spring  96  from the pressure chamber  60  and the guide sleeve  100  to the illustrated position between securing element  118  and annular collar  148  at the piston rod  58  the ratio of stroke volume to dead-space volume—or actual volume in the illustrated (installed) basic setting of the piston  56 —of the pressure chamber  60  can be advantageously reduced by comparison with prior constructions, which ultimately causes a very short axial constructional length of the actual cylinder housing  52 . In addition, since the pressure chamber  60  does not have to accommodate a piston restoring spring at which air bubbles could ‘settle’, the pressure chamber  60  when the piston  56  returns from an actuated setting to its basic setting is subjected to good flushing or evacuation by the pressure medium, which contributes to particularly good deaeration of the slave cylinder  50 . 
     Further details of the device  70  for reducing pressure pulses, namely with regard to the insert member  68  ( FIGS. 2 to 7 ) injection-molded from a suitable plastics material, for example from a polyamide  66  reinforced with glass fiber, and the elastomeric volume receiving means  78  ( FIGS. 8 and 9 ) incorporated therein, are evident from  FIGS. 2 to 9 . 
     According to, in particular,  FIGS. 1 and 6  the insert member  68  is of substantially pot-shaped construction with a shroud section  156 , the outer diameter of which substantially corresponds with the inner diameter of the circumferential wall  64  of the cylinder housing  52 , and a base  158 , with which a substantially hollow-cylindrical extension  160  is connected, the extension being inserted into the pressure connection  66  of the cylinder housing  52 . 
     More specifically, the insert member  68  is axially mechanically positively fastened in the pressure connection  66  of the cylinder housing  52 , specifically by means of a snap connection. For this purpose the extension  160  of the insert member  68  is provided at the outer circumference with a segmented annular collar  162  extending from its free end and is multiply slotted in order to form a plurality of spring arms  164  (see, in particular,  FIGS. 2, 3, 5 and 6 ), wherein according to  FIG. 1  a counter-bearing surface formed by the annular collar  162  of the extension  160  and facing the pressure chamber  60  engages in the manner of a snap hook behind the annular end surface  128 —which projects radially inwardly beyond the fourth bore section  114  of the stepped bore  98  in the base body  80  and which is formed by the smaller-diameter sleeve section  104  of the guide sleeve  100 —in the pressure connection  66  of the cylinder housing  52 . According to, in particular,  FIG. 5  there are four slots  166  which extend in longitudinal direction of the extension  160  and in the illustrated embodiment interrupt the extension  160  of the insert member  68  and the asymmetrical distribution of which over the circumference of the extension  160  corresponds with the distribution of the above-mentioned longitudinal ribs (not shown) in the fourth bore section  114  of the stepped bore  98  in the base body  80  of the cylinder housing  52 . In this connection, the slots  166  in the extension  160  of the insert member  68  on the one hand and the longitudinal ribs in the base body  80  of the cylinder housing  52  on the other hand are dimensionally matched to one another in such a manner that in the mounted state of the insert member  68  the longitudinal ribs at the housing side engage with small circumferential play in the slots  166 , but in that case do not protrude radially inwardly beyond the spring arms  164 . The asymmetrical, mutually matched circumferential distributions of the longitudinal ribs and the slots  166  ensure in simple manner a unique rotational angle orientation of the mounted insert member  68  in the slave cylinder  50 , specifically in such a manner that the opening  74 , which is at the pressure chamber side, of the channel  72  of the device  70  for reducing pressure pulses is, in the installed position of the slave cylinder  50 , disposed at the top near the inner circumferential surface of the cylinder housing  52  formed by the circumferential wall  64 , as shown in  FIG. 1 . 
     For preferably automatic production of the afore-described snap connection between the cylinder housing  52  and the insert member  68  oriented in angle with respect to the cylinder housing  52  the insert member is pushed, starting from the open end of the cylinder housing  52  lined with the guide sleeve  100 , into the guide sleeve  100  until the spring arms  164  of the extension  160  come into contact with a small incline between the annular section  106  and the inner circumference of the smaller-diameter sleeve section  104  of the guide sleeve  100 . On further axial relative displacement of the insert member  68  with respect to the cylinder housing  52  the spring arms  164  spring radially inwardly. As a consequence, the longitudinal ribs (not shown) in the fourth bore section  114  of the base body  80  of the cylinder housing  52  engage in the slots  166  of the extension  160  of the insert member  68  before the spring arms spring back radially outwardly and detent by their segmented counter-bearing surface  165  behind the annular end surface  128  of the sleeve section  104 . The base  158  of the insert member  68  comes into contact, by its end face facing the pressure connection  66 , with the end surface, which faces the pressure chamber  60 , of the annular section  106  of the guide sleeve  100  at substantially the same time. Since both the transition from the end surface, which faces the pressure connection  66 , of the spring arms  164  to the outer circumferential surface thereof and the transition of the end surface, which faces the pressure chamber  60 , of the longitudinal ribs (not illustrated) to the inner circumferential surface thereof are formed at right angles with only a broken edge, i.e. without incline, the insert member  68  can mate with the cylinder housing  52  only if there is correct angular orientation of these parts. In the event of an attempt to join the insert member to the cylinder housing  52  without angular orientation or with incorrect angular orientation the mutually facing end surfaces of the spring arms  164  on the one hand and the longitudinal ribs (not shown) on the other hand impinge on one another substantially over an area and thereby prevent further axial displacement of the insert member  68  with respect to the cylinder housing  52 . Since, moreover, the angular orientation of the insert member  68  with respect to the cylinder housing  52  has effect at the base body  80  thereof, a fixing, which acts in circumferential direction, of the guide sleeve  100  in the base body  80  is not required. 
     As evident, particularly from  FIGS. 1 and 6 , the channel  72  in the insert member  68  has a helically extending helix section  168  connected with an end section  172 , which is formed by the extension  160  of the insert member  68  and runs in axial direction, via a connecting section  170  extending in the base  158  of the insert member  68  in radial direction, so that the helix section  168  communicates not only with the channel opening  74  at the slave cylinder side, but also with the channel opening  76  at the master cylinder side. In that case the helix section  168  of the channel  72  is formed as a groove at the outer circumference of the shroud section  156  of the insert member  68  preferably by injection-molding, the groove in the mounted state of the insert member  68  being covered radially outwardly by the inner circumferential surface, which is formed by the circumferential wall  64 , of the cylinder housing  52 . In the illustrated embodiment the helix section  168  has five full turns; it is, however, evident that the helix section can have a greater or lesser number of turns in correspondence with the respective functional requirements, which can—as with other cross-sectional shapes of the helix section departing from the illustrated substantially rectangular cross-sectional shape—be readily managed by injection-molding. The cross-section or cross-sectional area of the helix section  168  of the channel  72  is preferably selected so that it is less than or equal to the minimum cross-section of the pressure connection  66 , which in the illustrated embodiment is defined by the pressure connection bore  130 . 
     According to, in particular,  FIGS. 1, 6 and 7  the insert member  68  additionally has at its end at the pressure chamber side a fastening section  174  which so co-operates with a projection  176  of the piston  56  at the pressure chamber side that the piston  56  prior to filling with pressure medium or first actuation of the slave cylinder  50  is fixed in a predetermined stroke setting with respect to the cylinder housing  52  and is releasable relative to the cylinder housing  52  by the pressure medium filling or first actuation of the slave cylinder  50 . More specifically, the fastening section  174  of the insert member  68  comprises a hollow cylinder  178 , which is connected with the shroud section  156  of the insert member at the left in  FIG. 1  and axially aligned with respect to a center axis of the pressure chamber  60 , with an annular bead  180  encircling at the inner circumference and protruding radially inwardly, the bead being shown to enlarged scale in  FIG. 7 , while the center extension  176  at the piston  56  is provided at the outer circumference with an annular collar  182  (see  FIG. 1 ) which has an outer surface slightly tapering towards the pressure connection  66  and which mechanically positively engages behind the annular bead  180  in the fixed state of the piston  56  at the insert member  68 . For this purpose the annular bead  180 , which according to  FIG. 7  in particular is rounded towards the pressure chamber  60 , on the one hand and the annular collar  182  on the other hand are dimensionally matched to one another in such a manner that the clear inner diameter of the annular bead  180  is slightly smaller than the largest outer diameter of the annular collar  182 , while the spacing thereof from the end surface of the piston  56  is slightly larger than the axial length of the annular bead  180 . 
     For fastening the piston subassembly  54  to the insert member  68  during assembly of the slave cylinder  50  the piston subassembly  54  is pushed into the cylinder housing  52  against the force of the helical compressions spring  96  in the sense of reducing the pressure chamber  60  until the projection  176  at the piston  56  comes into contact by its annular collar  182 , which is chamfered towards the insert member  68 , with the rounded annular bead  180  facing the pressure chamber  60 . On further axial relative displacement of the piston subassembly  54  with respect to the cylinder housing  52  in the direction of the pressure connection  66  the annular collar  182  at the piston extension  176  resiliently widens the annular bead  180  of the fastening section  174  in radially outward direction. After the annular bead  180  has been pushed past, this snaps into place behind the annular collar  182  as a consequence of the resilient properties of the material of the insert member  68 , thus into the annular gap between the annular collar  182  and the end surface of the piston  56  facing the pressure chamber  60 . The piston subassembly  54  is now mechanically positively fixed to the fastening section  174  of the insert member  68 . 
     Since the piston subassembly  54  is thus captive in a setting in which it is pushed as far as possible into the cylinder housing  52  the slave cylinder  50  requires only a small amount of space for storage, transport and mounting in the motor vehicle. In addition, the slave cylinder  50  can be mounted in the motor vehicle substantially free of force, because the helical compression spring  96  does not have to be compressed, instead being kept in a biased setting by the fastening of the piston subassembly  54  produced by the insert member  68 . 
     For the first actuation of the slave cylinder  50  mounted in the motor vehicle the pressure medium is fed to the pressure chamber  60  by way of the pressure connection  66 . As a consequence of the pressure which then builds up in the pressure chamber  60  and acts on the effective area of the piston  56  the piston  56  is subjected to a force which is directed to the left in  FIG. 1  and adds to the force of the helical compression spring  96 . If the sum of these forces exceeds the holding force of the connection between the extension  176  of the piston  56  and the fastening section  174  of the insert member  68  the annular bead  180  at the fastening section  174  is again widened out by way of the annular collar  182  at the extension  176 , whereupon the piston subassembly  54  comes free of the insert member  68 . A further fastening of the piston subassembly  54  in operation of the slave cylinder  50  is not intended and also cannot occur, since there is no longer a falling below of the axial spacing, as shown in  FIG. 1 , between the extension  176  at the piston  56  and the fastening section  174  at the insert member  68  in operation of the slave cylinder  50 . 
     It is apparent from the above description that the holding force of the connection between the extension  176  of the piston  56  and the fastening section  174  of the insert member  68  is constructionally designed in such a manner that on the one hand it is sufficiently larger than the spring force of the helical compression spring  96  in order to prevent unintended loosening of the fastening of the piston subassembly  54 , but on the other hand is sufficiently less than the holding force of the connection between the insert member  68  and the cylinder housing  52  so that on first actuation of the slave cylinder  50  the insert member  68  is not pulled out of the pressure connection  66 . 
     As further evident from  FIG. 1  the volume receiving means  78  is mounted at the inner circumference of the shroud section  156  of the insert member  68  so that the helix section  168  of the channel  72  coaxially surrounds the volume receiving means  78 . For this purpose the insert member  68  has a cylindrical blind bore  184  with which a conically widening introducing section  186 , at the left in  FIGS. 1 and 6 , for the volume receiving means  78  is connected, the introducing section terminating with a small step at the hollow cylinder  178 . 
     The volume receiving means  78  shown in more detail in  FIGS. 8 and 9  is a rubber-elastic substantially spool-shaped element having a passage bore  188  with a central cylinder section  190  and opening funnels  192  disposed on either side of the cylinder section  190 . The volume receiving means  78 , which is formed to be rotationally symmetrical with respect to its longitudinal axis and to have mirror symmetry with respect to a notional plane perpendicular to the longitudinal axis, is provided at the outer circumference with a fluted annular recess  194  which, according to  FIG. 1 , together with the inner circumference of the shroud section  156  of the insert member  68  bounds an annular air chamber  196  in the region of the blind bore  184 . The air chamber  196  is sealed on both sides, i.e. in  FIG. 1  to the right and the left, by annular sealing beads  198  (see  FIGS. 8 and 9 ) of the volume receiving means  78 . The functioning of this volume receiving means  78  was already explained in more detail in the introduction, so that further explanations with respect thereto at this point seem superfluous. In this connection, finally, mention is to be made of the fact that the illustrated arrangement or positioning of channel  72  and volume receiving means  78 , in which the volume receiving means  78  as seen from the pressure chamber  60  is hydraulically connected upstream of the channel  72  forming the additional conduit path, has proved particularly effective in terms of damping vibration. 
     The second, third and fourth embodiments will be described in the following with reference to  FIGS. 10 to 17  only to the extent that they differ from the afore-described first embodiment. 
     The second embodiment shown in  FIG. 10  differs from the first embodiment only in the respect that the device  70  for reducing pressure pulses has merely the channel  72  as additional conduit path, but a volume receiving means is not inserted in the blind bore  184  of the insert member  68 , which is unchanged by comparison with  FIGS. 1 to 7 . 
     By contrast, in the third embodiment illustrated in  FIG. 11  a volume receiving means  78  according to  FIGS. 8 and 9  is inserted in the blind bore  184  of the insert member  68 . In exchange, the device  70  for reducing pressure pulses is here not provided with a channel forming an additional conduit path in the afore-described sense; there is quasi a direct, unprolonged connection between pressure chamber  60  and pressure connection  66  and, in particular, by way of a cross-sectionally large annular space  200 , which is bounded at the inner circumference by the fastening section  174  and by the outer circumference—with the same outer diameter by comparison therewith—of the shroud section  156  of the insert member  68  and at the outer circumference by the circumferential wall  64  of the cylinder housing  52 , as well as by way of the sections  170  and  172  in the base  158  or projection  160  of the insert member  68 . In this regard the connecting section  170 , in the installed position of the slave cylinder  50 , opens into the annular space  200  at the top adjacent to the circumferential wall  64  of the cylinder housing  52  so as to ensure good deaeration of the pressure chamber  60 . 
     As expected, the devices  70  for reducing pressure pulses according to the embodiments of  FIGS. 1, 10 and 11  have different vibration damping characteristics, as evident from  FIG. 18 , which illustrates by way of example the result of tests in which (1st) a sinusoidal vibration with variable frequency and an amplitude of 1 g was applied to the piston rod  58  of the slave cylinder  50 , (2nd) the accelerations at a piston rod (not shown) of the master cylinder (not illustrated) hydraulically connected with the slave cylinder  50  and at the piston rod  58  were measured and (3rd) for the test evaluation were recorded, in relation to one another, against the excitation frequency in a diagram. In this connection, use was made of a slave cylinder  50  with an effective piston diameter of 22.20 mm and a master cylinder with an effective piston diameter of 19.05 mm, which were hydraulically connected together by way of—starting from the slave cylinder  50 —a pressure line arrangement consisting of (a) an elastomeric clutch hose (internal diameter: approximately 6 mm, external diameter: approximately 12 mm, length: approximately 250 mm, a fabric layer) and (b) a metallic clutch pipe (internal diameter: approximately 4.75 mm, wall thickness: approximately 0.7 mm, length: approximately 610 mm). In the embodiments according to  FIGS. 1 and 10  the length of the helix section  168  of the channel  72  of the device  70  for reducing pressure pulses was approximately 200 millimeters, with an open cross-section of approximately 6 mm 2 , while in the embodiments according to  FIGS. 1 and 11  use was made, as volume receiving means  78 , of a rubber sealing plug corresponding with  FIGS. 8 and 9  with an overall length of approximately 7.3 mm, a maximum external diameter of approximately 9.6 mm in the region of the sealing bead  198  and an internal diameter of approximately 3 mm in the region of the cylinder section  190 . 
     The different vibration damping capabilities of the various tested devices  70  for reducing pressure pulses as well as the effects thereof by comparison with the arrangement without a device for reducing pressure pulses (marked by triangles) are clearly apparent in  FIG. 18 : not only the case of the embodiment according to  FIG. 10  (marked with lozenges), but also in the embodiment according to  FIG. 11  (marked with small stars) there are a reduction and shifting of the first maximum (at approximately 65 Hz to lower frequencies), in which connection the volume receiving means  78  alone produces a better damping effect than the channel  72  alone; at higher frequencies the damping effect of the channel  72  tends to increase by comparison with the volume receiving means  78 . The combination of the two measures in correspondence with the embodiment according to  FIG. 1  (marked with empty squares) leads to an overall damping effect which in sum clearly exceeds the individual effects; all vibration maxima are strongly ‘depressed’, at least by approximately 50%, and here, too, a displacement of the first maximum towards lower frequencies takes place. It is clear to the expert that these results are to be understood only as exemplifying and the device  70  for reducing pressure pulses can be optimized as desired with respect to its vibration damping effect for the respective installation situation with regard to, obviously, the amplitude ratio or the frequency range to be damped, be it through selectable use of channel  72  and/or volume receiving means  78  or a change of the shape/dimensions of channel  72  or volume receiving means  78  or of the material of the volume receiving means  78 . 
     In the fourth embodiment illustrated in  FIGS. 12 to 17  the insert member  68 , which is again inserted in the pressure chamber  60  and secured in the pressure connection  66 , comprises an inner insert  202  of substantially pot-shaped construction, with (see, in particular,  FIGS. 13, 15 and 17 ) an inner insert shroud section  204  and an inner insert base  206 . Formed between the shroud section  156  of the insert member  68  and the inner insert shroud section  204  is a helically extending helix section prolongation  208 , one end of which is according to  FIGS. 13 and 15  in fluid connection with the (outer) helix section  168  by way of the connecting section  170  and the other end of which is in fluid connection with an interior space  210  of the inner insert  202  by way of a passage  209 , which interior space in turn communicates with the pressure connection  66  by way of the end section  172  in the extension  160 . In that case the helix section prolongation  208  is again formed at the outer circumference of the inner insert shroud section  204  as a groove, which is covered radially outwardly by an inner circumferential surface  212  of the shroud section  156  of the insert member  68 . The inner insert  202 , which is similarly injection-molded from a suitable plastics material, is so inserted into the insert member  68  and secured therein (for example glued or ultrasonically welded) that the inner insert shroud section  204  bears against the base  158  of the insert member  68 , whereby the mutually opposite bases  158  and  206  bound the interior space  210  in axial direction, while the interior space  210  is bounded radially outwardly by an inner circumferential surface  214  of the inner insert shroud section  204 . The hollow cylinder  178  of the fastening section  174  is formed at the inner insert  202  on the side of the inner insert base  206  facing the pressure chamber  60 . 
     As evident from a comparison of, for example,  FIGS. 1  ( 6 ) and  12  ( 13 ), in the fourth embodiment the channel  72  is significantly longer than the channel  72  in the first embodiment, due to the helix section prolongation  208  and the circumstance that the helix section  168  at the shroud section  156  of the insert member  68  includes a greater number of turns (here seven complete turns), and has in addition a smaller free cross-section. In such a construction of the channel  72  an undesired increase in the force, which is to be applied to the clutch pedal, in case of quick actuation and an equally undesired decrease in the return speed of the clutch pedal can occur, particularly at low temperatures at which the hydraulic medium—usually brake fluid—is relatively viscous, due to the higher flow resistance. In order to counteract this problem, provided in the insert member  68  is a thermostatically operating bypass valve  216  which is hydraulically connected in parallel with respect to the device  70  for reducing pressure pulses and which provides a direct fluid connection between the pressure chamber  60  and the pressure connection  66  at low temperatures and interrupts this fluid connection at higher temperatures. 
     As can be inferred particularly from  FIGS. 13, 15 and 17 , the bypass valve  216  comprises a thermostatic element  218 , which is accommodated in the interior space  210  of the inner insert  202  between the base  158  of the insert member  68  and the inner insert base  206  and which is operatively connected with a plunger  220  which opens and closes an opening  222  in the inner insert base  206  in dependence on temperature (the closed state is shown in the figures) in order to provide the direct fluid connection between the pressure chamber  60  and the pressure connection  66  at low temperatures and to interrupt this fluid connection at higher temperatures. In this regard the thermostatic element  218  is supported on the side, which is at the right in  FIG. 13 , on several projections  224  which are distributed over the circumference of the end section  172  and integrally formed at the insert member  68  and which keep the thermostatic element  218  at a spacing from the base  158  so that the hydraulic medium can pass through passages between the individual projections  224  from the interior space  210  to the end section  172  and conversely. On the side at the left in  FIG. 13  the thermostatic element  218  is held by a thickened end in a profile section  226  of the inner insert  202 , which has an approximately flower-shaped cross-section (see  FIG. 14 ) so that the hydraulic medium can flow through between the inner insert shroud section  204  and the outer circumference of the thermostatic element  218 . 
     It is apparent that a hydraulic connection is always present between the pressure chamber  60  and the pressure connection  66  in the fourth embodiment as well and in particular—starting from the pressure chamber  60 —by way of the opening  74  at the slave cylinder side, the helix section  168 , the connecting section  170 , the helix section prolongation  208 , the passage  209 , the free cross-sections between the thermostatic element  218  and the inner insert shroud section  204  or the base  158  of the insert member  68 , respectively, the end section  172  and finally the opening  76  at the master cylinder side. A change in length at the thermostatic element  218  occurs at low temperatures, whereby the plunger  220  is drawn in the direction of the interior space  210  out of the opening  222  in the inner insert base  206  so that a connection between the pressure chamber  60  and the pressure connection  66  is additionally created by way of the hollow cylinder  178 , the opening  222 , the profile section  226  and further as described above. 
     In connection with the fourth embodiment it is to be finally noted that in this embodiment as well a volume receiving means (not illustrated) similar to the afore-described volume receiving means  78  can be provided, for example with adapted dimensioning, in the hollow cylinder  178 . 
     A slave cylinder for a vibration-damped hydraulic force transmission system, particularly a hydraulic clutch actuating system for motor vehicles, is disclosed, with a cylinder housing, a piston received therein to be longitudinally displaceable and a pressure chamber, which is bounded by the cylinder housing and the piston and can be selectably acted on by a pressure medium via a pressure connection provided in the cylinder housing in order to displace the piston in the cylinder housing. In addition, an insert member inserted in the pressure chamber and secured in the pressure connection is provided, the insert member being equipped with a device, which is constantly open to the pressure medium, for reducing pressure pulses. As a result, the vibration-damping measures or means are integrated in the slave cylinder in a particularly economic and space-saving manner. 
     Other variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.