Abstract:
The invention relates to a device that is always open for the pressure medium for reducing pressure pulsations and that can be switched between a pressure chamber of a slave cylinder and a pressure chamber of a master cylinder of a hydraulic force transmission system for motor vehicles. The device has an additional line section in the form of a channel having an opening on the slave cylinder side, an opening on the master cylinder side, and a channel length equaling a multiple of the direct distance between the two openings, and a volume receiver that can be elastically deformed under pressure, wherein the channel and the volume receiver are combined into an assembly in a housing. The result according to the invention is a device that not only has very good vibration dampening properties, but is also very compact and has a cost-effective design.

Description:
TECHNICAL FIELD 
     The present invention relates to a device for reducing pressure pulsations, the device being connectible between a pressure chamber of a slave cylinder and a pressure chamber of a master cylinder of a hydraulic force transmission system and being constantly open to the pressure medium. In particular, the invention relates to such devices for reducing pressure pulsations, such as are used on a large scale in hydraulic clutch actuating devices for motor vehicles. 
     PRIOR ART 
       FIG. 23  shows a conventional hydraulic clutch actuating device  10  for motor vehicles in a simplified illustration. The hydraulic clutch actuating device  10  comprises a master cylinder  12 , which is mounted on a pedal block  11  of the motor vehicle, and a slave cylinder mounted in the motor vehicle in the vicinity of a transmission, the cylinders being hydraulically interconnected by way of a hydraulic line  16  which in this case starts has, seen from the master cylinder  12 , a first pipe section  18 , a hose section  20  and a second pipe section  22 . The piston (not illustrated) of the master cylinder  12  hydraulically connected with a fluid 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 displacement of the piston in the master cylinder  12 . In this connection, a fluid column hydraulically loading the slave cylinder  14  is displaced through the hydraulic line  16  in the direction of the slave cylinder  14 . 
     The slave cylinder  14 , more precisely the piston (not shown here) thereof, is disposed in operative connection with a release mechanism  36  of a friction clutch  38  by way of a piston rod  30  via a release lever  32  and a release bearing  34 . If the slave cylinder  14  is hydraulically loaded for release of the friction clutch  38 , then the release mechanism  36  separates a clutch pressure plate  40  from a clutch drive disc  44 , which is seated on a transmission shaft  42  and which co-operates with a flywheel  43  carried by the crankshaft of the internal combustion engine (not illustrated), of the friction clutch  38 . The internal combustion engine is therefore also separated from the transmission (similarly not shown in more detail) of the motor vehicle. 
     If the clutch pedal  28  is released in order to re-engage the friction clutch  38 , the slave cylinder  14 , specifically the piston thereof, is returned to its basic or initial setting as a consequence of, inter alia, the spring forces of the friction clutch  38 , in which case the above-mentioned fluid column is displaced through the hydraulic line  16  back again in the direction of the master cylinder  12 . 
     In such a hydraulic clutch actuating in device  10 —which is to be regarded as a quasi-static hydraulic force transmission system in which a continuous flow of hydraulic fluid is not present—vibrations of the internal combustion engine, particularly the crankshaft thereof, are transmitted by way of the components of the friction clutch  38 , the release bearing  34 , the release lever  32  and the slave cylinder  14  to the liquid column, which is present in the hydraulic line  16 , between the slave cylinder  14  and the master cylinder  12 , the vibrations propagating in the column as pressure pulsations. It was already regarded as disadvantageous that the pressure pulsations are tracked by the driver at the clutch pedal  28  as vibrations particularly when the driver&#39;s foot rests on the clutch pedal in typical city driving—so-called “rest tingling”- or the depressed clutch pedal  28  is held, for example during a stop in front of traffic lights. 
     There is no lack of proposals in the prior art for counteracting this problem, for example DE 36 31 507 C2 “Square helix”, DE 40 03 521 C2 “Double line with line branches of different length”, U.S. Pat. No. 5,816,046 “Auxiliary oscillator”, U.S. Pat. No. 6,647,722 B2 “Diaphragm damper cell”, DE 100 06 542 A1 or U.S. Pat. No. 7,107,768 B2 “Damping device with labyrinth body”. It is common to these proposals that inserted into or arranged parallel to the hydraulic line between master cylinder and slave cylinder is a separate subassembly, which does not interrupt the fluid column between master cylinder and slave cylinder, for vibration damping, the subassembly being capable in general of also satisfactorily damping the pressure pulsations. However, the previously known solutions partially claim a relatively large amount of installation space, which is not always available in the engine compartment of the motor vehicle to a sufficient extent, and/or give rise to a comparatively complex and accordingly expensive construction of the device, which is not desirable for mass production. 
     “Double-acting” valve mechanisms connected between master cylinder and slave cylinder (for example, JP 59-89833 A, U.S. Pat. No. 7,578,378 B2) will not be considered in more detail in this connection, which mechanisms open when each displacement of the liquid column occurs, i.e. not only in the case of displacement in the direction of the slave cylinder, but also in the case of a displacement in the direction of the master cylinder, and close when the liquid column is not moving, so as to screen or decouple in terms of vibration the master cylinder from the slave cylinder, since these valve mechanisms (a) are usually of even considerably more complicated construction than damping devices which are constantly “open to the pressure medium” and do not require spring-biased valve bodies or the like, (b) require specific opening and closing pressures which often undesirably increase the return times and the system hysteresis, and finally (c) are provided with bypasses susceptible to contaminations and thus accompanying losses in performance. 
     What is desired is to provide a device for reducing pressure pulsations, connectible between a pressure chamber of a slave cylinder and a pressure chamber of a master cylinder of a hydraulic force transmission system, particularly a hydraulic clutch actuating device for motor vehicles, and constantly open to the pressure medium, and which device in conjunction with improved vibration-damping characteristics by comparison with the prior art is of compact and economic construction. 
     SUMMARY OF THE INVENTION 
     According to the invention a device, which is connectible between a pressure chamber of a slave cylinder and a pressure chamber of a master cylinder of a hydraulic force transmission system, particularly a hydraulic clutch actuating means for motor vehicles, and which is constantly open to the pressure medium, for reducing pressure pulsations comprises, in combination, an additional conduit in the form of a channel having a helix section, defining an opening at the slave cylinder side and an opening at the master cylinder side, and having a channel length which is multiple of the direct spacing between the two openings, and a volume receiver which is resiliently deformable under pressure, the channel and the volume receiver being combined into a subassembly in a housing in such a way that the helix section, which extends in the manner of a screw thread, and the volume receiver are arranged in the housing in a mutually coaxial positional relationship with one substantially surrounding the other. 
     Investigations have led to the unexpected result that the two afore-described measures for vibration damping—namely an additional conduit in the form of a channel on the one hand and a volume receiver on the other hand—are in combination capable of reducing pressure pulsations to an extent going well beyond the vibration damping effect of the respective measures individually, so that the vibration damping characteristics of the device according to the invention can be categorized as highly effective. Since, in addition, the channel and the volume receiver are combined into a subassembly in one and the same housing, wherein in addition the channel length is a multiple of the direct spacing between the two channel openings, the device according to the invention is on the one hand of very compact construction and on the other hand the channel and the volume receiver can be disposed in fluid connection with very little outlay on sealing and connection, thus very economically. A further advantage of the device according to the invention consists in that in the case of use of the device in a hydraulic clutch actuating device according to  FIG. 23 , which is otherwise conventional, the second pipe section, which is near the slave cylinder, of the hydraulic line which was usually constructed with a cross-section narrowed relative to the first pipe section for the purpose of reduction in vibrations, can be eliminated, i.e. the hose section of the hydraulic line can now be directly connected with the pressure connection of the slave cylinder, in which case the second pipe section according to  FIG. 23  can be quasi integrated into the device according to the invention in simple and very space-saving manner. Further, from production aspects it is of advantage that the helix section extends in the manner of a screw thread. Finally, since the helix section and the volume receiver are arranged in the housing in a mutually coaxial positional relationship with one substantially surrounding the other, the device is of particularly short and compact construction. In this connection, the helix section of the channel can surround the volume receiver at least partly coaxially. However, alternatively thereto the volume receiver can also at least partly coaxially surround the helix section of the channel. 
     It has proved to be particularly effective in terms of damping or reducing vibration if the volume receiver is hydraulically connected upstream of the channel, which forms the additional conduit, as seen in a direction from the slave cylinder to the master cylinder, so that the pressure pulsations propagating from the pressure chamber of the slave cylinder do not have to firstly pass through the additional conduit in order to reach the volume receiver. 
     In an embodiment of the device according to the invention with particular cost advantages an insert member can be inserted in the housing and bounds, at least partly together with the housing, the channel, which also facilitates assembly of the device. 
     In this regard, the helix section of the channel can be formed at the outer circumference of the insert member as a groove which is covered radially outwardly by an inner circumferential surface of the housing, which on the one hand can be produced particularly simply and economically—for example, by injection-molding of the insert member, the radially outwardly open groove of which is “completed” in extremely simple manner to form the channel, only on insertion of the insert member into the housing, by the housing wall which is present there in any case, and, in particular, without use of sealing elements or the like—and on the other hand produces a deflection of the fluid column, which has proved advantageous with respect to good vibration damping with smallest possible throughflow resistance. In addition, the helix section can have a helix reversal dividing the helix section into a subsection running in righthanded direction and a subsection running in lefthanded direction, whereby, in particular, the axial installation space requirement for the helix section is reduced. 
     In a compact embodiment which is particularly simple in terms of production the insert member can be of substantially pot-shaped construction with a casing section and a base. Advantageously, in this regard the helix section, which is formed at the outer circumference of the casing section of the insert member, of the channel can communicate with the opening of the channel at the master cylinder side by way of a connecting section of the channel extending in the base of the insert member. 
     The volume receiver is preferably mounted at the inner circumference of the sleeve section of the insert member, which on the one hand is required for a compact construction of the device and on the other hand enables a simple plug mounting of the volume receiver. It is in addition preferred if the volume receiver is a rubber-elastic bobbin-shaped element with a passage bore and, at the outer circumferential side, an annular recess which together with the inner circumference of the sleeve section of the insert member bounds an annular air chamber. With such a design of the volume receiver, if a pressure amplitude runs into the passage bore the bobbin-shaped element deforms against the spring effect of the rubber-elastic material, in which case the air volume in the annular air chamber is compressed so that the bobbin-shaped element—as the term “volume receiver” already implies—experiences a defined expansion in the region of the passage bore, which leads to a specific “relieving” of the pressure amplitude. In this connection, the spring effect of the rubber-elastic material and the compressed air volume ensures automatic return of the bobbin-shaped element to its original form when the pressure, which is present in the region of the passage bore of the bobbin-shaped element, of the pressure medium drops below a predetermined value. 
     In an alternative embodiment of the volume receiver this can moreover be a tubular element of a resilient plastics material which separates a radially inner pressure medium chamber from a radially outer air chamber in the housing. The volume receiver is thus advantageously capable of injection molding, in which case the length and cross-sectional profile can be formed to be relatively simple. In this embodiment of the volume receiver, if a pressure amplitude runs into the inner pressure medium chamber the tubular element slightly deforms against the spring effect of the plastics material, whereby the air volume in the radially outer air chamber is compressed so that the tubular element experiences a predetermined expansion which in turn leads to “relieving” of the pressure amplitude. In that case, the spring effect of the plastics material and—to a far smaller extent—the compressed air volume in the radially outer air chamber ensure automatic return of the tubular element to its original form when the pressure, which is present in the inner pressure medium chamber, of the pressure medium drops below a defined value. In this alternative of the device the substantially pin-shaped insert member can advantageously be inserted into a central bore, which communicates with the pressure medium chamber, in the housing. 
     Alternatively thereto, the volume receiver can be a substantially hose-shaped element of a rubber-elastic material which bounds a radially inner pressure medium chamber in the housing and bears by its outer circumferential surface against an inner circumferential surface of the housing, in which case the outer circumferential surface of the volume receiver is provided with a profiling for formation of cavities between the volume receiver and housing. Thus, in particular, the volume take-up of the system can advantageously be limited in defined manner. 
     However, as a further alternative for the volume receiver an embodiment is also conceivable in which there is formed in the housing or insert member a smaller cylinder space in which a spring-biased small piston is accommodated to be longitudinally displaceable in such a manner that in the case of a pressure amplitude the piston is displaced against its spring bias and through the thus-produced volume take-up a “relieving” of the pressure amplitude is again produced. The automatic return of the piston when a predetermined pressure of the pressure medium is fallen below would, in the case of such an embodiment, be produced by the spring operatively connected with the piston, for example a metallic helical compression spring, the characteristic and bias of which could in a given case also be settable in correspondence with the respective constructional conditions or requirements, but in each instance would be clearly defined and in addition advantageously substantially independent of the ambient temperature. 
     In one possible variant of the device it is provided that the housing is a separate housing which, provided with a slave connection and a master connection, is connectible into a hydraulic line between slave cylinder and master cylinder so that the slave connection and the master connection communicate with the pressure medium chamber formed in the interior space of the housing. This variant enables a substantially free placing, or a placing adapted to the respective constructional requirements or preconditions, of the device in the hydraulic line between slave cylinder and master cylinder. In this regard, the separate housing preferably has two parts, which, when fastened to one another, bound the interior space in which the insert member and the volume receiver are arranged. However, an embodiment is also conceivable in which the insert member and/or—in the case of the tubular element—the volume receiver is or are formed integrally with one of the housing halves so as to further reduce the parts count. The volume receiver preferably separates the pressure medium chamber from an air chamber in the interior space of the separate housing. The insert member is preferably axially clamped in place between the two parts of the separate housing so that there is no need for additional measures for fastening of the insert member. In analogous manner the tubular or hose-shaped element can also be clamped in place between the two parts of the separate housing. 
     In another variant of the device the housing is a cylinder housing of the slave cylinder (more preferred) or the master cylinder (less preferred), which has a pressure connection. Through arrangement of the device in the cylinder housing, particularly in the pressure chamber of the slave cylinder—where for this purpose no additional installation space has to be provided, since the cylinder dead space present here in any case can be utilized, so that the axial constructional length of the slave cylinder compared with conventional constructions does not change—the integration of the vibration-damping measures in the hydraulic force transmission system is similarly undertaken in very space-saving manner, wherein in a given case even an existing slave cylinder such as known from, for example, U.S. Pat. No. 7,287,376 B2 of the applicant can be adopted unchanged for integration of the device according to the invention. Through the arrangement of the device according to the invention in the pressure chamber of the slave cylinder, i.e. in the immediate vicinity of the location of the introduction of vibrations into the liquid column, it is in addition advantageously ensured that the pressure pulsations cannot propagate at maximum amplitude in or through the hydraulic line between slave cylinder and master cylinder, so that there is also minimization of the risk that the hydraulic line due to vibration detaches from its fastening points at, for example, the bodywork of a motor vehicle or shakes loose at these. 
     In an alternative, which is particularly favorable in terms of maintenance, to the arrangement of the device in the pressure chamber of the cylinder housing, the channel and volume receiver of the device can be contained in a pressure connecting section of the cylinder housing. In an advantageous embodiment the insert member is then inserted into the pressure connecting section and held there by connecting member. With respect to, in particular, simple mounting and capability of exchange it is in that regard advantageous if the insert member and the connecting member are constructed integrally. 
     With respect to a best possible damping effect it has also proved advantageous if the helix section of the channel has a cross-section which is smaller than or equal to the minimum cross-section of the slave and/or master connection of the separate housing or of the pressure connection of the cylinder housing, whereby a specific throttling effect is also provided. 
     In principle, the insert member and/or the housing of the device can be made of a metallic material, for example an aluminum alloy, such as by machining. However, is beneficial particularly for creation of an economic device if the insert member and preferably also the housing are injection-molded, as already mentioned, from a plastics material. 
     In a further variant of the device, finally, an additional path section can branch off the channel and open into a closed chamber in order to further influence the damping characteristics. In this regard, the afore-mentioned volume receiver or an additional volume receiver can be accommodated in the closed chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail in the following on the basis of preferred exemplifying embodiments with reference to the accompanying, partly schematic drawings, in which the same reference numerals denote the same or corresponding parts and elastomeric parts are, for simplification of illustration, mostly shown in undeformed state and in which: 
         FIG. 1  shows a longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating device for motor vehicles, into the pressure chamber of which is inserted an insert member equipped with a device for reducing pressure pulsations, the device being constantly open to the pressure medium and comprising in combination an additional conduit in the form of a channel and a volume receiver, as a first embodiment of the device according to the invention, 
         FIG. 2  shows a perspective individual illustration, obliquely from the front, of the pot-shaped insert member fastened, in the case of the slave cylinder according to  FIG. 1 , 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 sectional view of the insert member according to  FIG. 2  in correspondence with the section line VI-VI in  FIG. 5 , 
         FIG. 7  shows an illustration, to enlarged scale, of the detail VII in  FIG. 6 , 
         FIG. 8  shows a perspective individual illustration, obliquely from the front, of the elastomeric volume receiver mounted at the insert member in the case of the slave cylinder as shown in  FIG. 1 , 
         FIG. 9  shows a longitudinal sectional view of the volume receiver according to  FIG. 8 , 
         FIG. 10  shows a diagram in which for (1) a hydraulic clutch actuating device without the device according to the invention for reducing pressure pulsations (marked by triangles) and (2) a hydraulic clutch actuating device with a slave cylinder equipped in correspondence with  FIG. 1  (marked by blank squares) 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, 
         FIG. 11  shows a side view of a device according to the invention for reducing pressure pulsations in accordance with a second embodiment, which has an own housing, i.e. separate from the cylinder housing, but is otherwise similar to the first embodiment, 
         FIG. 12  shows a longitudinal sectional view of the device according to  FIG. 11 , 
         FIG. 13  shows a side view of a device according to the invention for reducing pressure pulsations in accordance with a third embodiment, which similarly has an own housing, i.e. separate from the cylinder housing, but differs from the second embodiment with respect to the construction and physical arrangement of the additional conduit and volume receiver, 
         FIG. 14  shows a longitudinal sectional view of the device according to  FIG. 13 , 
         FIG. 15  shows a perspective individual illustration, obliquely from the front, of a pin-shaped insert member inserted into the device according to  FIGS. 13 and 14 , particularly for illustration of a groove helically extending at the outer circumference of the insert part and forming a helix section of a channel, which is provided as an additional conduit of the device, 
         FIG. 16  shows a diagram analogous to that of  FIG. 10  in which for (1) a hydraulic clutch actuating in device without a device according to the invention for reducing pressure pulsations (marked by triangles) and (2) a hydraulic clutch actuating means device into which a device corresponding with  FIGS. 13 to 15  is connected into the hydraulic line between master cylinder and slave cylinder (marked by blank squares), 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 the result of a test in which a sinusoidal vibration at a variable frequency and an amplitude of 1 g (9.81 m/s 2 ) was applied to the piston rod of the slave cylinder, 
         FIG. 17  shows a longitudinal sectional view of a device according to the invention for reducing pressure pulsations in accordance with a variant of the third embodiment, in which—by comparison with  FIG. 14 —in particular the volume receiver is of different construction, 
         FIG. 18  shows an illustration, to enlarged scale, of the detail XVIII in  FIG. 17 , 
         FIG. 19  shows a longitudinal section view of a device according to the invention for reducing pressure pulsations in accordance with a variant of the second embodiment, which differs from  FIG. 12  particularly in the respect that a further path section branches off the additional conduit and opens into a closed chamber in which a second volume receiver can be arranged, 
         FIG. 20  shows a broken-away longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating means for motor vehicles, in the pressure connecting section of which a volume receiver and an insert member with an additional duct in the form of a channel are inserted, which in combination form a device—which is always open to the pressure medium—for reducing pressure pulsations and which are held in the pressure connecting section by a connecting member, similar to of the first embodiment according to the invention, 
         FIG. 21  shows a perspective individual illustration, obliquely from the front, of the insert member inserted into the pressure connecting section in the case of the slave cylinder according to  FIG. 20 , 
         FIG. 22  shows a broken-away longitudinal sectional view of a slave cylinder for a hydraulic clutch actuating means for motor vehicles, in which—similarly to  FIG. 20 —the device, which consists of volume receiver and an additional conduit in the form of a channel, for reducing pressure pulsations is accommodated in the pressure connecting section, wherein by contrast to  FIG. 20  the insert member and connecting member are constructed integrally, again similar to the first embodiment according to the invention, and 
         FIG. 23  shows a basic illustration of a hydraulic clutch actuating means according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a slave cylinder  50  for a vibration-damped hydraulic force transmission system, namely a vibration-damped hydraulic clutch actuating device for motor vehicles. The slave cylinder  50  has a cylinder housing which is denoted in general 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  which is connected at least tension-resistantly and compression-resistantly, thus effective in terms of actuation, with the piston  56 . Disposed in the cylinder housing  52  is a pressure chamber  60  which is variably bounded on the side on the left in  FIG. 1  by the piston  56 , fixedly bounded on the side on the right in  FIG. 1  by a housing base  62  of the cylinder housing  52  and fixedly bounded radially outwardly by a circumferential wall  64  of the cylinder housing  52 . The pressure chamber  60  is selectably loadable 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 in a manner known per se (cf.  FIG. 23 ) by way of a pressure line (which by comparison with  FIG. 23  can also be of different construction) with a clutch master cylinder—by a pressure medium, for example brake fluid, in order to displace the piston  56  in the cylinder housing  52 . As will be described in more detail in the following, inserted into the pressure chamber  60  adjoining the housing base  62  is an insert member  68  which is secured in the pressure connection  66  and in the first exemplifying embodiment illustrated here advantageously fulfils a plurality of functions. In this regard, the insert member  68  serves, in particular, as a support for a device  70 , which is constantly open to the pressure medium, for reducing pressure pulsations or is equipped with this. 
     As is similarly explained in detail further below, the device  70 , which in the mounted state of the slave cylinder  50  is therefore connected between the pressure chamber  60  of the slave cylinder  50  and a pressure chamber of the master cylinder (cf. again  FIG. 23 ) for reducing pressure pulsations comprises on the one hand an additional conduit 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 therebetween a channel length amounting to a multiple of the direct spacing, i.e. the “straight line spacing”, between the two openings  74 ,  76 , and on the other hand a volume receiver  78  which is mounted at the insert member  68  and which is resiliently deformable under pressure. As a result, the channel  72  and the volume receiver  78  of the device  70  for reducing pressure pulsations are combined in the cylinder housing  52  with the highest degree of compactness to form a subassembly, in which case the insert member  68  at least partly 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 at the outer circumferential side with a fastening flange  82  for mounting the slave cylinder  50  in the motor vehicle. The fastening flange  82  has two fastening bores  84 , which are reinforced by slotted steel bushes  86 . Extending through the fastening bores  84  lined by the steel bushes  86  are, in the mounted state of the slave cylinder  50 , for example, screws (not shown) which serve for fastening the slave cylinder  50  to, for example, a transmission wall (not illustrated) in the motor vehicle. In  FIG. 1  on the left of the fastening flange  82  the base body  80  of the cylinder housing  52  moreover has at the outer circumferential side a radial groove  88  into which an elastomeric protective cap  92 , which has a bellows section  90  surrounding the piston rod  58 , is clipped by an annular collar  94  at the inner circumferential side. The bellows section  90  of the protective cap  92  additionally encloses a spring element in the form of a helical compression spring  96 , which is provided on the side of the piston  56  remote from the pressure chamber  60  and which is supported at its end on the right in  FIG. 1  at the cylinder housing  52  and engages at its end at the left in  FIG. 1  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  so as to keep the piston rod  58  in contact with a clutch lever (not shown) in the mounted state of the slave cylinder. 
     At the inner circumferential side the base body  80  of the cylinder housing  52  has a stepped bore  98  which is open towards the left in  FIG. 1  and into 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 ,  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  which are of different diameter reducing 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  which serves for the fixing at the cylinder housing  52  of an annular securing element  118  preferably of plastics material, which is slotted for mounting and which bears against the end face 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  116  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 circumferential side with a radial groove  122  for reception of an O-ring  124 , which ensures static sealing between the third bore section  112  with 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 ,  114  of the stepped bore  98  on the other hand are 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 shoulder  126  for fastening, which will be described in more detail, 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 circumferential side with a plurality—here for example four—of longitudinal ribs (not able to be seen in  FIG. 1 ) which extend in axial direction of the cylinder housing  52  and which protrude radially inwardly and are non-uniformly or asymmetrically distributed over the circumference of the fourth bore section  114 . The ribs serve for rotational angle orientation of the insert member  68  in the pressure connection  66  as will be similarly explained in more detail in the following. Finally, a smaller-diameter pressure connection bore  130 , which is formed in the base body  80 , in the fourth bore section  114  opens at the end, which is at the right in  FIG. 1 , of the fourth bore section  114  of the stepped bore  98 . 
     It is evident from the above description that the pressure connection 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 sleeve  100  are a component of the pressure connection  66 , by way of which the pressure chamber  60  of the slave cylinder  50  can be loaded with 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, in the case of a pressure loading of the pressure chamber  60  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—which is opposite thereto and faces the pressure chamber  60 —of the annular section  106  of the guide sleeve  100 , a resulting force to the right in  FIG. 1  which endeavors to keep the guide sleeve  100  in the stepped bore  98  of the base body  80 , thus relieves of load the fastening of the guide sleeve  100  in the base body  80  by the securing element  118 . 
     As can be further inferred from  FIG. 1 , the piston  56 , which is guided with a small radial play in the larger-diameter sleeve section  102  of the guide sleeve  100  of the cylinder housing  52  and in the illustrated embodiment is metallic, has at the outer circumference a radial groove  132  for reception of a groove ring  134 . The elastomeric groove ring  134  bears, in a manner known per se, by its outer circumferential sealing lip under a defined bias against the circumferential wall  64  of the cylinder housing  52  and thus ensures dynamic sealing of the pressure chamber  60  towards the left in  FIG. 1 . 
     The piston  56  is additionally provided on the side at the left in  FIG. 1  with a central recess  136  in which a ball head  138 , which is formed at the end of the piston rod  58  at the right in  FIG. 1 , is pivotably retained by a securing element  140  so that the piston rod  58  has a defined capability of angular movement 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 decreases conically or spherically towards the piston rod, for ensuring the capability of angular movement, 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 embodiment has on the side at the left in  FIG. 1  a profiled end  142  onto which an end member  144  of plastics material is injection-molded, the end member having a substantially spherical end surface  146  by way of which the piston rod  58  engages the clutch lever (not shown) to be effective in terms of actuation. At the end of the end member  144  at the right in  FIG. 1  this forms an annular collar  148  of the piston rod  58  which serves on the one hand for coupling the protective cap  92  to the piston rod  58 , wherein the annular collar  148  is mechanically positively engaged in an annular recess  150  of substantially complementary form in a fastening section  152  of the protective cap  92 , which is connected on the side of the protective cap  92  remote from the pressure chamber  60  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 towards the pressure chamber  60  a counter-bearing for the helical compression spring  96 , wherein a defined radial centering effect, which is of advantage when mounting the slave cylinder  50  in the motor vehicle, also derives from the end of the biased helical compression spring  96  facing the annular collar  148 . 
     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 of the end, which faces the pressure chamber  60  and is at the right in  FIG. 1 , of the helical compression spring  96 , which starting from the annular collar  148  of the piston rod  58  substantially conically widens in diameter towards the axial groove  154 , thus is of frusto-conical construction. Through this “outward redisposition” of the helical compression spring from the pressure chamber  60  and the guide sleeve  100  to the illustrated setting between securing element  118  and annular collar  148  at the piston rod  58  it is possible to advantageously reduce by comparison with previously known constructions the ratio of stroke volume to dead-space volume—or actual volume in the illustrated (installed) basic setting of the piston rod  56 —of the pressure chamber  60 , which ultimately produces a very short axial constructional length of the actual cylinder housing  52 . Moreover, since the pressure chamber  60  does not have to receive a piston restoring spring at which air bubbles could ‘settle’, the pressure chamber  60  on return of the piston rod  56  from an actuating setting to a basic setting thereof is effectively flushed or evacuated by the pressure medium, which contributes to very good ventilation of the slave cylinder  50 . 
     Further details of the device  70  for reducing pressure pulsations are evident from  FIGS. 2 to 9 , in particular with respect to the insert member  68  ( FIGS. 2 to 7 ) injection-molded from a suitable plastics material, for example from a glass-fiber-reinforced polyamide  66 , and the elastomeric volume receiver  78  ( FIGS. 8 and 9 ) contained therein. 
     According to, in particular,  FIGS. 1 and 6 , the insert member  68  is of substantially pot-shaped construction, with a casing 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 projection  160  is connected, the projection being inserted into the pressure connection  66  of the cylinder housing  52 . 
     More precisely, the insert member  68  is axially mechanically positively fastened in the pressure connection  66  of the cylinder housing  52 , namely by a snap connection. For this purpose the projection  160  of the insert member  68  is provided, going out from its free end at the outer circumference, with a segmented annular collar  162  and has multiple longitudinal slotting for formation of a plurality of spring arms  164  (see, in particular,  FIGS. 2, 3, 5 and 6 ), wherein a counter-bearing surface  165 , which is foimed by the annular collar  162  of the projection  160  and faces towards the pressure chamber  60 , according to  FIG. 1  engages in the pressure connection  66  of the cylinder housing  52  in the manner of a snap hook behind the annular end surface  128 , which protrudes radially inwardly into the base body  80  beyond the fourth bore section  114  of the stepped bore  98  and is formed by the smaller-diameter sleeve section  104  of the guide sleeve  100 . According to, in particular,  FIG. 5 , there are four slots  166 , which extend in longitudinal direction of the projection  160  and which in the illustrated embodiment interrupt the projection  160  of the insert member  68  and the asymmetrical distribution of which over the circumference of the projection  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 regard, the slots  166  in the projection  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 so matched to one another in terms of dimensions that in the mounted state of the insert member  68  the longitudinal ribs at the housing side engage with a 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 distribution of the longitudinal ribs and slots  166  ensures in simple manner a unique rotational angle orientation of the mounted insert member  68  in the slave cylinder  50 , in particular 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 pulsations 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 , which is oriented in terms of 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 projection  160  come into contact with a small chamfer 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  enter the slots  166  of the projection  160  of the insert member  68  before the spring arms spring radially outwardly again and detent by their segmented counter-bearing surface  165  behind the annular end surface  128  of the sleeve section  104 . At substantially the same time the base  158  of the insert member  168  comes into contact by its end face towards the pressure connection  66  with the end surface, which faces the pressure chamber  60 , of the annular section  106  of the guide sleeve  100 . Since not only the transition from the end surface, which faces the pressure connection  56 , of the spring arms  164  to the outer circumferential surface thereof, but also the transition of the end surface, which faces the pressure chamber  60 , of the longitudinal ribs (not illustrated) to the inner circumferential surface thereof is formed to be right-angular only with a broken edge, i.e. without a chamfer, the insert member  68  can be joined to the cylinder housing  52  only in the case of correct angular orientation of these parts relative to one another. In the event of an attempt to join the insert member  68  without angular orientation or with incorrect angular orientation to the cylinder housing  52  the mutually facing end surfaces at the spring arms  164  on the one hand and at the longitudinal ribs (not shown) on the other hand hit one another substantially by an area and thus 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  takes place 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 necessary. 
     As evident particularly from  FIGS. 1 and 6 , the channel  72  in the insert member  68  has a helically extending helix section  168 , which is connected by way of a connecting section  170 , which extends in radial direction in the base  158  of the insert member  68 , with an end section  172  formed by the projection  160  of the insert member  68  and extending in radial direction, so that the helix section  168  communicates not only with the opening  74  at the slave cylinder side, but also with the opening  76  at the master cylinder side, of the channel  72 . In that case the helix section  168  of the channel  72  is formed at the outer circumference of the casing section  156  of the insert member  68 , preferably by injection molding, as a groove which in the mounted state of the insert member  68  is covered radially outwardly by the inner circumferential surface of the cylinder housing  52  formed by the circumferential wall  64 . In the illustrated embodiment, the helix section  168  has five complete turns; however, it will be evident that the helix section can have also more or less turns in correspondence with the respective functional requirements, which—just as other cross-sectional shapes of the helix section departing from the illustrated substantially rectangular cross-sectional shape—can be easily managed by injection molding. The cross-section or the cross-sectional area of the helix section  168  of the channel  72  is preferably to be selected so that it is smaller than or equal to the minimum cross-section of the pressure connection  66 , which in the illustrated embodiment is defined by the pressure connecting 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 captive section  174  which co-operates with a projection  176  of the piston  56  at the pressure chamber side in such a manner that the piston  56  prior to pressure-medium filling 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 precisely, the captive section  174  of the insert member  68  comprises a hollow cylinder  178 , which is connected at the left in  FIG. 1  with the casing section  156  of the member and is axially aligned with respect to a center axis of the pressure chamber  60 , with a radially inwardly projecting annular bead  180  which extends at the inner circumferential side and which is shown in  FIG. 7  to enlarged scale, while the central projection  176  at the piston  56  is provided at the outer circumferential side with an annular collar  182  (see  FIG. 1 ) which has an outer surface slightly tapering in direction towards the pressure connection  66  and 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, in particular,  FIG. 7  is radiused towards the pressure chamber  60 , on the one hand and the annular collar  182  on the other hand are so matched to one another in terms of dimensions that the clear inner diameter of the annular bead  180  is slightly smaller than the largest outer diameter of the annular collar  182 , whilst the spacing thereof from the end surface of the piston  56  is slightly larger than the axial length of the annular bead  180 . 
     For rendering the piston subassembly  54  captive at the insert member  68  when the slave cylinder  50  is assembled the piston subassembly  54  is pushed against the force of the helical compression spring  96  into the cylinder housing  58  in the sense of reduction of 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 radiused 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  68  the annular collar  182  at the piston projection  176  resiliently widens the annular bead  180  of the captive section  174  in radially outward direction. After pressing beyond the annular bead  180  this snaps behind the annular collar  182  as a consequence of the resilient characteristics 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 captive 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. Moreover, the slave cylinder  50  can be mounted substantially free of force in the motor vehicle, because the helical compression spring  96  does not have to be compressed, but is kept in a biased setting by means of the capture 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 thereby builds up in the pressure chamber  60  and acts on the effective area of the piston  56 , the piston  56  experiences a force which is directed to the left in  FIG. 1  and which 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 projection  176  of the piston  56  and the captive section  174  of the insert member  68  the annular bead  180  at the captive section  174  is further expanded beyond the annular collar  182  at the projection  176 , whereupon the piston subassembly  54  is released from the insert member  68 . Further capturing of the piston subassembly  54  in operation of the slave cylinder  50  is not intended and also cannot take place, since the axial spacing, which is shown in  FIG. 1 , between the projection  176  of the piston  56  and the captive section  174  at the insert member  68  is, in operation of the slave cylinder  50 , always maintained. 
     It is apparent from the above description that the holding force of the connection between the projection  176  of the piston  56  and the captive section  174  of the insert member  68  is constructionally designed in such a manner that it is on the one hand sufficiently larger than the spring force of the helical compression spring  96  so as to prevent unintended release of the captivation of the piston subassembly  54 , but on the other hand sufficiently smaller than the holding force of the connection between the insert member  68  and the cylinder housing  52  so that the insert member  68  on first actuation of the slave cylinder  50  is not pulled out of the pressure connection  66 . 
     As is further evident from  FIG. 1 , the volume receiver  78  is mounted at the inner circumference of the casing section  156  of the insert member  68  so that the helix section  168  of the channel  72  coaxially surrounds the volume receiver  78 . For this purpose the insert member  68  has a cylindrical blind bore  184  with which at the left in  FIGS. 1 and 6  a conically widening joining section  186  for the volume receiver  78 , which ends with a small step at the hollow cylinder  178 , is connected. 
     The volume receiver  78  shown in more detail in  FIGS. 8 and 9  is a rubber-elastic substantially bobbin-shaped element which has a passage bore  188  with a central cylinder section  190  and opening funnels  192  disposed on either side of the cylinder section  190 . At the outer circumferential side the volume receiver  78 , which is rotationally symmetrical with respect to its longitudinal axis and which is formed with mirror symmetry with respect to a notional plane perpendicular to the longitudinal axis, is provided with a channel-shaped annular recess  194  which according to  FIG. 1  bounds, in the region of the blind bore  184  and together with the inner circumference of the casing section  156  of the insert member  68 , an annular air chamber  196 . The air chamber  196  is sealed at both sides, i.e. to the right and left in  FIG. 1 , by annular sealing beads  198  (see  FIGS. 8 and 9 ) of the volume receiver  78 . The function of this volume receiver  78  was already explained in more detail in the introduction, so that further explanations with respect thereto at this point appear redundant. In this connection it is finally still to be mentioned that the illustrated arrangement or positioning of channel  72  and volume receiver  78 , in which the volume receiver  78  is upstream in hydraulic terms of the channel  72 —which forms the additional conduit—as seen from the pressure chamber  60 , has proved particularly effective in terms of damping vibrations. 
     The vibration-damping characteristics of the afore-described device  70  for reducing pressure pulsations can be readily seen in  FIG. 10 , which illustrates by way of example the result of tests in which (1) a sinusoidal vibration with variable frequency and an amplitude of 1 g was applied to the piston rod  58  of the slave cylinder  50 , (2) the accelerations of the piston rod (not shown) of the master cylinder (not illustrated) hydraulically connected with the slave cylinder  50  and of the piston rod  58  were measured and (3) were, for the test evaluation, recorded in a diagram placed in relationship to one another against excitation frequency. In this regard use was made of a slave cylinder  50  with an effective piston effective diameter of 22.20 mm and a master cylinder with an effective piston effective diameter of 19.05 mm, which were hydraulically interconnected by way of, starting from the slave cylinder  50 , (a) an elastomeric coupling hose section (inner diameter: approx. 6 mm; outer diameter: approx. 12 mm; length: approx. 250 mm, one fabric layer) and (b) a metallic coupling pipe section (inner diameter: approx. 4.75 mm; wall thickness: approx. 0.7 mm; length: approx. 610 mm) of an existing pressure line arrangement. The length of the helix section  168  of the channel  72  of the device  70  for reducing pressure pulsations was approximately 200 mm with an open cross-section of approx. 6 mm 2 . As volume receiving means  78  use was made of a rubber sealing plug in correspondence with  FIGS. 8 and 9  with an overall length of approx. 7.3 mm, a maximum outer diameter of approx. 9.6 mm in the region of the sealing bead  198  and an inner diameter of approx. 3 mm in the region of the cylinder section  190 . 
     The vibration-damping capability of the tested device  70  for reduction of pressure pulsations (marked by blank squares) by comparison with the arrangement without a device for reducing pressure pulsations (marked by triangles) is clearly apparent in  FIG. 10 : a substantial reduction in and displacement of the first maximum (at approx. 65 Hz) towards lower frequencies occurred; in addition, the further vibration maxima are strongly ‘depressed’, by at least approx. 50%. It is clear to the expert that these results are to be understood as only by way of example and the device  70  for reduction of pressure pulsations can obviously be optimized as desired with respect to its vibration-damping action for the respective installation situation such as in respect of the amplitude behavior or the frequency range to be damped, whether through change in the shape/dimensions of the channel  72  or volume receiver  78  or selection of a different material for the volume receiver  78 . 
     The second and third embodiments shall be described in the following with reference to  FIGS. 11 to 16  only to the extent that they differ from the afore-described first embodiment. In these figures the same or corresponding parts were provided with the same reference numerals supplemented by an apostrophe (′) for the second embodiment or two apostrophes (″) for the third embodiment (not listed in the Reference Numeral List at the end). 
     The second embodiment illustrated in  FIGS. 11 and 12  differs from the first embodiment principally in that the housing for receiving the channel  72 ′ and the volume receiver  78 ′ is a separate housing  200 ′, i.e. a housing separate from the cylinder housing of the slave or master cylinder, which, provided with a slave connection  202 ′ and a master connection  204 ′, is connectible into the hydraulic line (not illustrated) between slave cylinder and master cylinder so that the slave connection  202 ′ and the master connection  204 ′ (the latter by way of the channel  72 ′) communicate with a pressure medium chamber  208 ′ formed in an interior space  206 ′ of the housing  200 ′. In the illustrated embodiment the separate housing  200 ′ has two parts  210 ′,  212 ′, which are injection-molded from a suitable plastics material and which when fastened to one another bound the interior space  206 ′, in which the modified insert member  68 ′, similarly injection-molded from a suitable plastics material, corresponding with  FIG. 12  and the volume receiver  78 ′ according to  FIGS. 8 and 9  of the first embodiment are arranged. The latter separates, analogously to the first embodiment, the pressure medium chamber  208 ′ from an annular air chamber  196 ′ in the interior space  206 ′ of the housing  200 ′. 
     At the housing part  210 ′ at the left in  FIG. 12  the slave connection  202 ′ is executed as a plug part with a plug geometry known per se, comprising a central passage bore  214 ′ for the pressure medium chamber  208 ′ and two axially spaced-apart radial grooves  216 ′,  218 ′, of which the outer radial groove  216 ′ serves for reception of an O-ring  220 ′ for sealing with respect to the (receiving) counter-part (not shown), while the second radial groove  218 ′ in the mounted state of the device  70 ′ receives a securing element (not illustrated), which is fastened to the (receiving) counter-part, of spring steel wire. At the housing part  212 ′ on the right in  FIG. 12 , thereagainst, the master connection  204 ′ is constructed as a receiving part with a receiving geometry known per se, comprising a recess  222 ′ into which the (plug) counter-part (not shown) is insertable, and a securing element  224 ′ of spring steel wire, which is arranged at the outer circumferential side and which passes through a plug slot  226 ′, which extends transversely to the longitudinal axis of the master connection  204 ′, in order in the mounted state of the device  70 ′ to secure the (plug) counter-part in the recess  222 ′ in a manner known per se. 
     The righthand housing part  212 ′, which is connected with the master connection  204 ′ at the left in  FIG. 12 , is of substantially pot-shaped construction, with a base  228 ′ through which the end section  172 ′ of the channel  72 ′ extends in order to ensure a central hydraulic connection between the connecting section  170 ′ in the base  158 ′ of the insert member  68 ′ and the recess  222 ′ of the housing part  212 ′, and a casing section  230 ′, which at the inner circumferential side forms the circumferential wall  64 ′ radially outwardly covering the helix section  168 ′ of the channel  72 ′. By contrast to the first embodiment, the insert member  68 ′ in the second embodiment does not have at the base  158 ′ any projection for fastening in the housing  200 ′, but instead is axially clamped between the two housing parts  210 ′,  212 ′. In that case the insert member  68 ′ in  FIG. 12  at the right bears by its base  158 ′ over an area against the base  228 ′ of the housing part  212 ′, whilst the insert member  68 ′ is retained on the side at the left in  FIG. 12  in the interior space  206 ′ of the housing  200 ′ by means of a projection  232 ′—which is centrally hollowed in hollow-cylindrical manner and plugged into the casing section  230 ′ of the righthand housing part  212 ′ and which bears against the insert member  68 ′—of the lefthand housing part  210 ′. In the region of the projection  232 ′ the two housing parts  210 ′,  212 ′, which here tightly engage one in the other, are preferably glued together or ultrasonically welded together; alternatively thereto, however, a screw connection could also be provided. 
     As already mentioned in the introduction, the thus-constructed device  70 ′ for reducing pressure pulsations can be arranged largely freely in the hydraulic line between slave cylinder and master cylinder, for example between a hose section, which is at the slave cylinder side, and a pipe section which is at the master cylinder side, of the hydraulic line. The function or manner of effect of the device  70 ′ in this regard corresponds with that of the device  70  according to the first embodiment. 
     In the case of the third embodiment illustrated in  FIGS. 13 to 15  firstly the slave connection  202 ″ and the master connection  204 ″ of the two-part housing  200 ″ are constructed differently from the case of the second embodiment, namely mutually reversed so that the slave connection  202 ″ is formed as receiving part whilst the slave connection  204 ″ is constructed as plug part. In this regard the recess  222 ″ of the slave connection  202 ″ is in fluid connection with the pressure medium chamber  208 ″ via a passage  234 ″ in the housing part  210 ″ at the left in  FIG. 14 . 
     The central passage bore  214 ″, which communicates with the pressure medium chamber  208 ″ by way of the channel  72 ″, thereagainst has in the housing part  212 ″ on the right in  FIG. 14  a stepped bore section  236 ″ into which the substantially pin-shaped insert member  68 ″ is inserted. As a result, the helix section  168 ″—which again is formed at the outer circumference of the insert member  68 ″ as a groove in accordance with, in particular,  FIG. 15 —of the channel  72 ″ is covered radially outwardly by an inner circumferential surface  64 ″ of the bore section  236 ″ of the housing  200 ″. The ends  238 ″ of the insert member  68 ″ injection-molded from a suitable plastics material are respectively planoparallelly flattened in order to ensure a free passage to the pressure medium chamber  208 ″ or to the end, at the right in  FIG. 14 , of the passage bore  214 ″. The insert member  68 ″ can, for example, be dimensioned/matched in, for example, outer diameter with respect to the inner diameter at the circumferential wall  64 ″ in such a manner that it is fixed by pressing into the passage bore  214 ″. Transverse bores with very small cross-section can be provided (indicated in  FIG. 14  by dashed lines) in order to ensure better ventilation of the channel  72 ″ with respect to the pressure medium channel  208 ″ particularly in the case of filling of the device  70 ″ with hydraulic fluid. In the case of this embodiment as well, the helix section  168 ″ of the channel  72 ″ has a cross-section—here substantially rectangular—smaller than the minimum free cross-section of the master connection  204 ″ (in the end of the passage bore  214 ″ at the right in  FIG. 14 ). 
     According to  FIG. 14  the two housing parts  210 ″,  212 ″ are additionally provided at  240 ″ with annular structures of complementary construction, which mechanically positively interengage and at which the two housing parts  210 ″,  212 ″ are welded or glued for formation of the housing  200 ′. The righthand housing part  210 ″ and the lefthand housing part  212 ″ are formed with an annular recess  242 ″ and  244 ″, respectively, which together receive the volume receiver  78 ″ so that the volume receiver  78 ″ is clamped between the two housing parts  210 ″,  212 ″. 
     The volume receiver  78 ″ itself is a tubular element of a resilient plastics material, for example injection-molded polyamide  66  without glass-fiber reinforcement, which separates the radially inner pressure medium chamber  208 ″ from the radially outer air chamber  196 ″ in the somewhat spherically formed housing  200 ″. O-rings  246 ″ at the end and between the volume receiver  78 ″ and the respective housing part  210 ″,  212 ″ in that regard seal the pressure medium chamber  208 ″ relative to the air chamber  196 ″. In the case of this embodiment as well the helix section  168 ″ of the channel  72 ″ and the volume receiver  78 ″ in the housing  200 ″ are arranged in a mutual coaxial positional relationship with one substantially surrounding the other, so that the housing  200 ″ is of relative short construction, but here designed so that the volume receiver  78 ″ at least partly coaxially surrounds the helix section  168 ″ of the channel  72 ″. 
     It will be apparent to the expert that the volume take-up of a volume receiver  78 ″ designed in that manner can easily be appropriately matched to the respective installation and functional requirements by suitable selection of the parameters of material, wall thickness, diameter and/or length of the hollow-cylindrical pipe section so as to take into account, for example, the respective operating pressure of an actuating path. The function or manner of effect of the device  70 ″ overall was already explained in more detail in the introduction so that further explanations with respect thereto at this point appear superfluous. 
     Tests were also carried out with respect to the third embodiment, the result of which is illustrated in  FIG. 16  by way of example. The actual performance of the test corresponded with that which was already described further above with reference to  FIG. 10 . However, in the present case use was made of a slave cylinder with an effective piston effective diameter of 19.05 mm and a master cylinder with an effective piston effective diameter of 15.87 mm, which—analogously to  FIG. 23 —were hydraulically connected together by way of, starting from the slave cylinder, (a) a metallic clutch pipe section (inner diameter: approx. 4.75 mm; wall thickness: approx. 0.7 mm; length: approx. 300 mm), (b) an elastomeric clutch hose section (inner diameter: approx. 6 mm; outer diameter: approx. 12 mm; length: approx. 250 mm, one fabric layer) and (c) a metallic clutch pipe section (inner diameter: approx. 6 mm, wall thickness: approx. 0.7 mm; length: approx. 400 mm) of an existing pressure line arrangement. The (developed) length of the helix section  168 ″ of the channel  72 ″ of the device  70 ″ for reducing pressure pulsations, which was arranged between the clutch hose section and the clutch pipe section at the master cylinder side, again amounted to approx. 200 mm, with a free cross-section of approx. 3.6 mm 2 . As volume receiver  78 ″ use was made of a pipe section of an unreinforced polyamide  66  with an overall length of approx. 40 mm, an outer diameter of approx. 18 mm and an inner diameter of approx. 15.4 mm. 
     The vibration damping capability of the tested device  70 ″ for reducing pressure pulsations (marked by blank squares) by comparison with the arrangement without a device for reduction of pressure pulsations (marked by triangles) is clearly evident from  FIG. 16 : there is a substantial reduction particularly of the first maximum (at approx. 60 Hz), but without displacement in the frequency range. It is also to be noted that these results are to be understood as only by way of example: the device  70 ″ for reducing pressure pulsations can be optimized as desired with respect to its vibration-damping effect for the respective installation situation such as in respect of the amplitude behavior or the frequency range to be damped, whether by changing the shape/dimensions of channel  72 ″ or volume receiver  78 ″ and/or the selection of a different material for the volume receiver  78 ″. 
       FIGS. 17 and 18  show a variant of the third embodiment according to  FIGS. 13 to 15 , which will be described in the following only to the extent that it differs from the third embodiment. 
     In the first instance, in  FIG. 17 —by comparison with  FIG. 14 —the insert member  68 ″ is turned through 90° about its longitudinal axis so that the free passages to the pressure medium chamber  208 ″ or to the passage bore  214 ″ are not visible. Moreover, the housing  200 ″ is not of spherical construction in correspondence with  FIG. 14 , but such that the inner circumferential surface  248 ″, which is formed by the housing parts  210 ″,  212 ″ and surrounds the volume receiver  78 ″, of the housing  200 ″ is substantially cylindrical. 
     Moreover, an air chamber corresponding with  FIG. 14  (there reference number  196 ″) is not present between the outer circumferential surface  250 ″ of the volume receiver  78 ″, which for simplification of the illustration is shown in undeformed state, and the inner circumferential surface  248 ″ of the housing  200 ″. Instead, the volume receiver  78 ″ bears by its outer circumferential surface  250 ″ against the inner circumferential surface  248 ″ of the housing  200 ″. For that purpose, the substantially hose-shaped volume receiver  78 ″, made from a rubber-elastic material such as EPDM (elastomer on the basis ethylene-propylene-diene rubber), is profiled (profiling  251 ″) at its outer circumferential surface  250 ″ so that it does not bear over the whole area against the inner circumferential surface  248 ″ of the housing  200 ″, but only so as to leave comparatively small cavities. In the illustrated embodiment (see  FIG. 18 ) these cavities are formed by a plurality of annular grooves  252 ″ which are separated from one another by encircling webs  254 ″. As a consequence of this design, the volume receiver  78 ″ can, in the case of pressure loading by the housing  200 ″, more specifically the inner circumferential surface  248 ″ thereof, be compressed, with comparatively small volume take-up in the pressure medium chamber  208 . Through suitable selection of the geometry—groove or grooves with rounded or polygonal cross-section, other recesses serving to leave nubs, etc. —and/or the dimensions—depth, width and/or number of grooves or recesses, etc. —of the profiling  251 ′, the volume take-up of the device  70 ″ can be limited in defined manner in correspondence with the respective use requirements and the damping characteristics of the device  70 ″ influenced. 
     As can, moreover, be seen particularly in  FIG. 18 , the pressure medium chamber  208 ″ is sealed between the ends of the volume receiver  78 ″ and the housing  200 ″. More precisely in the illustrated embodiment the volume receiver  78 ″ is integrally formed at its end, which is at the right in  FIG. 18 , at the inner circumferential side with a sealing bead  256 ″ which is received in an associated annular groove  258 ″ of the housing part  212 ″. Thereagainst, at the end, which is at the left in  FIG. 18 , of the volume receiver  78 ″ there is provided an O-ring  260 ″ which bears against the substantially cylindrical inner circumference of the volume receiver  78 ″ and is in turn received in an associated annular groove  262 ″ of the housing part  210 ″. In principle, however, also both ends of the volume receiver can be provided at the inner circumference with a respective sealing bead or be provided at both ends of the volume receiver at the inner circumference with a respective O-ring. 
       FIG. 19  shows a device variant with respect to the second embodiment according to  FIGS. 11 and 12 , such as can in principle also be used in the first embodiment according to  FIGS. 1 to 10  and which in the following will be described only to the extent that it differs from the afore-described embodiments. 
     According to  FIG. 19  the housing parts  210 ′,  212 ′ of the housing  200 ′ are firstly formed to be axially prolonged by comparison with  FIGS. 11 and 12  so as to create space in the housing part  210 ′ for a receiving space  264 ′, which is connected with the passage bore  214 ′ and has a larger diameter by comparison therewith, for reception of the volume receiver  78 ′. The receiving space  264 ′ is terminated in  FIG. 19  at the left by a radially inwardly protruding annular bead  266 ′ which ensures that the volume receiving member  78 ′ cannot, in operation, migrate out of the receiving space  264 ′. 
     Moreover, inserted into the insert member  68 ′ arranged in the housing part  212 ′ is a substantially pot-shaped inner insert  268 ′ with a closed base  270 ′, which faces the housing part  210 ′, and a casing section  272 ′ bearing at the end against the base  158 ′ of the insert member  68 ′. The base  270 ′ and the casing section  272 ′ of the inner insert  268 ′ bound together with the base  158 ′ of the insert part  68 ′ a closed chamber  274 ′ having a single step in diameter. An additional volume receiver  278 ′ can be provided, as illustrated, in the larger diameter chamber section  276 ′ of the chamber  274 ′ in addition to the afore-described volume receiver  278 ′. However, alternatively thereto also only the volume receiver  78 ′ can be provided in the receiving space  264 ′, while no volume receiver is arranged in the chamber  274 ′, or the volume receiver  278 ′ can be provided in the chamber  274 ′ instead of the volume receiver  78 ′ in the receiving chamber  264 ′. 
     The smaller-diameter chamber section  280 ′ of the chamber  274 ′ is disposed in fluid connection by way of a connecting bore  282 ′ with a helix section  284 ′ which is formed at the outer circumference of the inner insert  268 ′, more precisely the casing section  272 ′ thereof, analogously to the helix section  168 ′, which is at the outer circumference, of the insert member  68 ′. The helix section  284 ′ is in turn hydraulically connected by way of a further connecting bore  286 ′ with the helix section  168 ′ of the insert member  68 ′. As a result, the connecting bore  286 ′ in the insert member  68 ′, the helix section  284 ′ formed between insert member  68 ′ and inner insert  268 ′ and the connecting bore  282 ′ in the inner insert  268 ′ form a further path section  288 ′, which branches off the additional conduit or the channel  72 ′, of the device  70 ′ for reducing pressure pulsations, which path section has a length which is a multiple of the direct spacing between the connecting bores  282 ′ and  286 ′ and which path section opens in the manner of a dead end in the closed chamber  274 ′ with or without volume receiver  278 ′. This represents a further possibility of appropriately adapting the device  70 ′ with respect to its damping characteristics to the respective use requirements. 
     It remains to be mentioned with respect to this variant that the inner insert  286 ′ is held in the insert member  68 ′ with the help of annularly segmental webs  290 ′ which in integral construction with the housing part  210 ′ or the inner insert  268 ′ and distributed uniformly over the circumference follow the annular bead  266 ′ on the left in  FIG. 19 . 
       FIGS. 20 to 22  finally show two variants similar to the first embodiment which was described above with reference to  FIGS. 1 to 10  and which will be described in the following only to the extent that they differ from the first embodiment. 
     It is common to these variants that the device  70  for reducing pressure pulsations is again integrated in the cylinder housing  52  of the slave cylinder  50 ; however this time it is not in the pressure chamber  60 , but in a pressure connection section  292 , which is physically separate or spaced from the pressure chamber  60 , of the cylinder housing  52 , which in the illustrated variants extends, starting from the housing base  62  of the cylinder housing  52 , away from the housing base  62  at approx. 40° to the housing longitudinal axis. 
     In this regard, the pressure connecting section  292  is provided, starting from its upper end at the right in  FIGS. 20 and 22 , with a stepped bore  294  which ultimately opens into the pressure connecting bore  130  of the pressure connection  66  to the pressure chamber  60 . More precisely, the stepped bore  294 , starting from the pressure connecting bore  130 , has a plurality of bore sections with increasing diameter from section to section, namely: 
     a. a connecting section  296  to the pressure connecting bore  130 , 
     b. a first receiving section  298  for reception of the volume receiver  78  (cf., for details of the latter,  FIGS. 8 and 9  with associated description) and a tubular projection  300  of the insert member  68 , 
     c. a second, optionally again slightly stepped (see  FIG. 22 ), second receiving section  302  for the main part of the insert member  68  and a plug end or plug section  304  of a connecting member  306 , which retains the insert member  68  in the pressure connecting section  292 ,
 
d. a fastening section  308  for fastening the connecting member  306  in the pressure connecting section  292 , provided—in  FIG. 20 —with an internal thread which co-operates with an external thread  310  at the connecting member  306 ; in  FIG. 22 , thereagainst, provided with an annular groove  312  into which a slotted plastics material ring  314  is inserted for formation of a snap connection with an associated annular groove  315  in the connection member  306 , and
 
e. optionally a joining chamfer  316  (see  FIG. 20 ) for the connecting member  306 .
 
     The connecting member  306  itself has, analogously to the second embodiment described in the foregoing with reference to, in particular,  FIG. 12 , a master connection  204  with receiving geometry known per se, having the recess  222  ending at the opening  76  of the channel  72  at the master cylinder side, the securing element  224  and the insertion slot  226  for that purpose. In addition, the plug end or plug section  304  is provided with an annular groove for reception of an O-ring  318  which seals relative to the second receiving section  302  of the stepped bore  294 . 
     The insert member  68  bearing against the annular shoulder  320  formed between the first receiving section  298  and the second receiving section  302  of the stepped bore  294  similarly has at the outer circumference of the projection  300  an annular groove  322  (cf.  FIG. 21 ) in which a further O-ring  324  is received, which seals relative to the first receiving section  298  of the stepped bore  294 . Finally, the insert member  68 , starting from the free end of the projection  300 , is provided with a blind bore  326  which as a component of the channel  72  forms at one end thereof the opening  74  at the slave cylinder side and at the other end thereof is hydraulically connected with the helix section  168  of the insert member  68  by way of a connecting bore  328  to be regarded as similar to the channel  72  and extending transversely to the insert member  68 . 
     The helix section  168  of the insert member  68  additionally has, in this variant according to  FIG. 21 , the feature that at  330  it possesses a helix reversal having the effect that the hydraulic fluid, which on actuation of the hydraulic clutch actuating means comes from the opening  76  at the master cylinder side and which initially flows with respect to the longitudinal axis of the insert member  68  in clockwise sense through the helix section  168  of the channel  72 , changes its direction of movement at the helix reversal  330 , which is formed in the manner of a switchback turn, and flows from the helix reversal  330  through the helix section  168  in counter-clockwise sense. In other words, the helix reversal  330  divides the helix section  168  into a subsection  332  running in the manner of a righthand thread and a subsection  334  running in the manner of a lefthand thread. As a result, by comparison with the helix section without helix reversal, on the one hand a slightly larger throughflow resistance increasing the damping effect of the device  70  arises and on the other hand the axial space requirement of the thus-formed helix section  168  is smaller. A helix reversal of that kind can obviously also be provided in the other embodiments. 
     Otherwise, the variants according to  FIGS. 20 and 22  additionally differ—apart from the different material for the cylinder housing  52  (light metal in  FIG. 20 ; plastics material in  FIG. 22 )—in that in the case of the variant according to  FIG. 22  the insert member  68  and the connection member  306  are of integral construction, preferably by means of injection molding from plastics material. 
     A device, which is connectible between a pressure chamber of a slave cylinder and a pressure chamber of a master cylinder of a hydraulic force transmission system, particularly a hydraulic clutch actuating means for motor vehicles, and which is constantly open to the pressure medium, for reducing pressure pulsations is disclosed. This device comprises an additional conduit in the form of a channel, which has a helix section, an opening at the slave cylinder side, an opening at the master cylinder side and a channel length which is a multiple of the direct spacing between the two openings, and a volume receiver which is resiliently deformable under pressure, wherein the channel and the volume receiver are combined in a housing to form a subassembly in such a way that the helix section, which extends in the manner of a screw thread, and the volume receiver are arranged in the housing in a mutually coaxial positional relationship surrounding the other. As a result, a device is created which not only has very good vibration damping characteristics, but is also constructed very compactly and has an economic construction.