Abstract:
A radial piston machine includes a housing, rotor, first braking member, and brake ring with a second braking member. The rotor is mounted in the housing to be rotatable relative to an axis of rotation, and has an end face facing in a direction of the axis of rotation. The first braking member is positioned on the end face. The housing has a body defining a ring-shaped extension relative to the axis of rotation. The brake ring is positioned to surround the extension and is configured to be movable in the direction of the axis of rotation so as to bring the second braking member into braking engagement with the first braking member. The brake ring is further configured to positively engage with an inner radial side of the extension to limit a twisting between the housing and brake ring.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2015 222 291.8, filed on Nov. 12, 2015 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
         [0002]    The disclosure relates to a radial piston machine. 
       BACKGROUND 
       [0003]    U.S. Pat. No. 5,115,890 discloses a radial piston machine having braking means which are in the form of a multi-disk brake. Some of the brake disks are secured against twisting on the housing. 
         [0004]    U.S. Pat. No. 5,209,064 discloses a radial piston machine having braking means in which a first rotary bearing rests directly on an end face of the rotor. The braking means are arranged away from this end face. 
         [0005]    U.S. Pat. No. 3,690,097 discloses a radial piston machine in which two rotors are coupled to one another selectively by means of a dog clutch. 
       SUMMARY 
       [0006]    One advantage of the present disclosure is that the anti-twist safeguard required for the braking means can be provided by unmachined cast surfaces. Nevertheless, there is no risk of jamming or tilting of the braking means during operation. Moreover, the radial piston machine is of particularly compact design. The abovementioned selectable dog clutch can be used without reservations as a braking means, the said clutch forming a holding brake which is preferably engaged or disengaged when shut down. 
         [0007]    According to this disclosure, the housing has an extension, which is ring-like in relation to the axis of rotation and which is surrounded by a separate brake ring, wherein the brake ring is movable in the direction of the axis of rotation, wherein it has second braking means, which can be brought into braking engagement with the first braking means by a movement of the brake ring in the direction of the axis of rotation, wherein the brake ring engages positively on the radially inner side thereof in the ring-like extension in such a way that twisting between the housing and the brake ring is at least limited. The positive engagement between the brake ring and the ring-like extension can thus be arranged in immediate spatial proximity to the engagement between the first and the second braking means. Thus, tilting of the brake ring is excluded, even when the positive engagement bears on only one location of the circumference of the ring-like extension. Consequently, the corresponding positive engagement contours can be produced with large dimensional tolerances of the kind that are typical for the casting process. 
         [0008]    The housing preferably has a first and a second fluid connection, wherein a fluid distributing device is arranged in the housing, the said device being designed in such a way that each first fluid chamber can be fluidically connected selectively to the first or the second fluid connection by turning the rotor. The control surface preferably has a cross-sectional profile which is designed so as to be constant along the axis of rotation. The radial piston machine is intended for use with a pressurized fluid, which is preferably a liquid and most preferably hydraulic oil. The ring-like extension preferably surrounds the rotor, in particular the drive shaft thereof. The radial piston machine is preferably a radial piston motor, although it can also be a radial piston pump. 
         [0009]    Advantageous developments and improvements of the disclosure are given in the claims, description, and drawings. 
         [0010]    Provision can be made for a first rotary bearing, in which the rotor is mounted so as to be rotatable relative to the axis of rotation, to be accommodated on the radially inner side of the ring-like extension. The corresponding radial piston machine is of particularly compact design. Moreover, the first rotary bearing is in immediate spatial proximity to the engagement between the first and the second braking means and to the positive engagement between the ring-like extension and the brake ring. 
         [0011]    Elastic deformations of the radial piston machine caused by the forces which arise during braking are thereby minimized. As a result, the risk that the brake ring will tilt is low. In addition to the first rotary bearing, further rotary bearings can be arranged between the housing and the rotor. The first rotary bearing is preferably mounted on the drive shaft of the rotor. 
         [0012]    Provision can be made for the first rotary bearing to be supported in the direction of the axis of rotation on the end face of the rotor. This makes it possible to arrange the first rotary bearing particularly close to the engagement between the first and the second braking means, thus minimizing the abovementioned deformations even further. 
         [0013]    Provision can be made for the end face of the rotor, with the exception of the first braking means, to be of flat design, wherein it is aligned perpendicularly to the axis of rotation. Thus, the end face can be used directly as a contact surface for the first rotary bearing. Moreover, it can be produced easily and at low cost. The end face can be interrupted by slots, channels or the like in order to divert leaks past the first rotary bearing. 
         [0014]    At least one spring can be provided, which is installed under a preload between the brake ring and the housing in such a way that the brake ring is pushed towards the end face of the rotor in the direction of the axis of rotation. Thus, the first and the second braking means are in engagement as long as the brake ring is not moved counter to the force of the at least one spring. Particularly in the case of a malfunction, this ensures that the radial piston machine cannot move. The at least one spring is preferably accommodated in each case in an associated first recess in the housing. The at least one spring is preferably designed as a helical spring, the central axis of which is aligned parallel to the axis of rotation. The at least one spring can also be designed as a wave spring or as a diaphragm spring. The first recess is preferably of circular-cylindrical design, wherein it is arranged parallel to the axis of rotation. The at least one spring is preferably arranged adjacent to the brake ring on the side remote from the rotor in the direction of the axis of rotation. 
         [0015]    Provision can be made for a second fluid chamber to be provided, which is arranged in a ring-like manner around the brake ring and which is partially delimited by the housing, wherein the brake ring can be moved in the direction of the axis of rotation by pressurizing the second fluid chamber. Thus, the brake ring can be moved hydraulically counter to the force of the at least one spring. The corresponding pressure force acts in a uniformly distributed manner over the circumference of the brake ring, thus avoiding tilting of the brake ring. The direction of movement of the brake ring when the second fluid chamber is pressurized is preferably away from the end face of the rotor. 
         [0016]    Provision can be made for the second fluid chamber to be partially delimited by a separate closure ring, which is arranged in a ring-like manner around the brake ring, wherein the closure ring rests fluidtightly against the housing on its radially outer side. Thus, the brake ring can be installed before the closure ring is inserted, wherein the installation of both components mentioned can take place from the inside of the housing. Any leaks which occur there flow into the interior of the housing and do not get into the environment of the radial piston machine. 
         [0017]    Provision can be made for the housing to have a separate cam ring, on which the control surface is arranged, wherein the closure ring is supported on the cam ring in the direction of the axis of rotation. Thus, the position of the closure ring is defined by positive engagement, while, at the same time, the installation of the closure ring and of the cam ring is possible without problems. Because of the wave-like design of its control surface, the cam ring has end face components which project into the interior of the housing and can serve as a contact surface for the closure ring. 
         [0018]    Provision can be made for the second fluid chamber to be partially delimited by the brake ring. In this embodiment, the closure ring rests by means of its radially inner side against the brake ring, preferably fluidtightly. When viewed in cross section, the brake ring is preferably of L-shaped design. It preferably rests fluidtightly by means of its radially outer side and in a manner which allows sliding movement against the housing. Particularly at this contact location, tilting is avoided by the present disclosure. 
         [0019]    A separate annular piston can be provided, which is held on the brake ring so as to be rotatable relative to the axis of rotation, wherein it is supported on the brake ring in the direction of the axis of rotation, wherein the annular piston partially delimits the second fluid chamber. In this embodiment, the closure ring rests on its radially inner side against the annular piston, preferably fluidtightly. When viewed in cross section, the annular piston is preferably of L-shaped design. The annular piston and the closure ring are preferably arranged on opposite sides of the second fluid chamber. The annular piston preferably rests by means of its radially outer side fluidtightly and in a manner which allows sliding movement against the housing. Particularly at this contact location, tilting is avoided by the present disclosure. 
         [0020]    Provision can be made for the housing to have a sealing surface which is circular-cylindrical in relation to the axis of rotation, wherein a section of the sealing surface delimits the second fluid chamber. The closure ring preferably rests on its radially outer side in a sealing manner against the sealing surface. The brake ring or the annular piston preferably rests fluidtightly against the sealing surface. 
         [0021]    Provision can be made for the first braking means to be formed by a multiplicity of first extensions, which face the brake ring in the direction of the axis of rotation, wherein they are arranged in a uniformly distributed manner around the axis of rotation at a pitch, wherein the second braking means are formed by a multiplicity of second extensions, which face the first extensions in the direction of the axis of rotation, wherein they are arranged in a uniformly distributed manner around the axis of rotation at the said pitch. The first and the second braking means are thus designed in the manner of a dog clutch. The pitch is preferably made small to ensure that the first and the second braking means can engage in one another in as many different rotational positions as possible. The pitch is preferably between 4° and 15°, being 9°, for example. It is also conceivable for the first and the second braking means to be designed as friction linings. The side faces of the first and of the second extensions can be of sloping and/or rounded design to ensure that the dog clutch opens from a predetermined torque. 
         [0022]    Provision can be made for the brake ring to have, on its radially inner side, at least two third extensions, which are arranged in a manner distributed around the axis of rotation, wherein they engage in respective matching second recesses on the ring-like extension. Twisting of the brake ring relative to the housing is thereby limited by positive engagement. The third extensions preferably engage with play in the respectively associated second recess. The third extensions and the second recesses preferably have an unmachined cast surface. The said clearance is preferably made such that it is present irrespective of the dimensional tolerances which arise during casting. The second recesses are preferably designed to be open radially outwards and axially towards the rotor in order to simplify mounting of the brake ring on the housing. The third extensions preferably face radially inwards. 
         [0023]    Provision can be made for the at least one spring to be in each case arranged in the region of a second recess. Thus, the spring can in each case be supported on a third extension of the brake ring. The brake ring can thus be made thin and consequently in a manner which saves materials away from the third extensions. 
         [0024]    It is self-evident that the features mentioned above and those which remain to be explained below can be used not only in the respectively indicated combination but also in other combinations or in isolation without exceeding the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The disclosure is explained in greater detail below with reference to the attached drawings, in which: 
           [0026]      FIG. 1  shows a longitudinal section through a radial piston machine according to a first embodiment of the disclosure; 
           [0027]      FIG. 2  shows a cross section through the radial piston machine shown in  FIG. 1 , wherein the section plane passes through the center of the pistons; 
           [0028]      FIG. 3  shows a perspective view of the cylinder drum of the radial piston machine shown in  FIG. 1 ; 
           [0029]      FIG. 4  shows a perspective view of the first housing part of the radial piston machine shown in  FIG. 1 ; 
           [0030]      FIG. 5  shows an enlarged partial view of  FIG. 1  in the region of the brake ring; 
           [0031]      FIG. 6  shows a perspective view of the brake ring of the radial piston machine shown in  FIG. 1 ; 
           [0032]      FIG. 7  shows a view corresponding to  FIG. 5  of a second embodiment of the disclosure; and 
           [0033]      FIG. 8  shows an exploded view of the brake ring and of the annular piston of the axial piston machine shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  shows a longitudinal section through a radial piston machine  10  in accordance with a first embodiment of the disclosure. The radial piston machine  10  has a housing  20 , which is made up of a first housing part  21 , a second housing part  22  and a cam ring  30 , wherein the cam ring  30  is installed in a fixed manner between the first and the second housing part  21 ,  22 . Accommodated in the first housing part  21  are a first and a second rotary bearing  41 ;  42 , which are preferably designed as radial rolling bearings and, for example, as taper roller bearings. A drive shaft  47  is supported so as to be rotatable relative to an axis  11  of rotation in the first and the second rotary bearing  41 ;  42 . The drive shaft  47  projects with a drive means  50  from the housing  20 . The drive means  50  can be one or more gearwheels, for example. Arranged between the drive shaft  47  and the first housing part  21  is a seal  51 , which is designed as a radial shaft sealing ring, for example. It should be noted here that the housing  20  surrounds an interior  18  which is closed off in a substantially fluidtight manner. 
         [0035]    The drive shaft  47  is part of a rotor  40 , which furthermore comprises a cylinder drum  48 . In the present case, the drive shaft  47  and the cylinder drum  48  are designed as separate components, which are connected to one another for conjoint rotation with respect to the axis  11  of rotation by means of a splined profile (No.  49  in  FIG. 3 ). The drive shaft  47  and the cylinder drum  48  have minimal capacity for movement relative to one another in the direction of the axis  11  of rotation, thus avoiding stress in the first and the second rotary bearing  41 ;  42 . However, it is likewise conceivable for the drive shaft  47  and the cylinder drum  48  to be of integral design. 
         [0036]    A plurality of pistons  60  is accommodated in the rotor  40  so as to be movable radially with respect to the axis  11  of rotation. The cam ring  30  surrounds the cylinder drum  48 , wherein it has a control surface  31  which faces the cylinder drum  48 . The control surface  31  delimits the radially outward path of movement of the pistons  60 . Moreover, a first fluid chamber  15  is associated with each piston  60  on the radially inner side thereof. By pressurizing the first fluid chamber  15 , the respective piston  60  can be pressed against the control surface  31 , as a result of which rotary motion relative to the axis  11  of rotation is imparted to the rotor  40 . During this process, some of the pistons  60  are pushed radially inwards by the control surface  31 , thus reducing the volume of the corresponding first fluid chambers  15 . 
         [0037]    A first and a second fluid connection are provided on the second housing part  22 , although only the first fluid connection  17  is visible in  FIG. 1 . Also accommodated in the second housing part  22  is a fluid distribution device  13 , which is provided with a flat distribution surface  19  aligned perpendicularly to the axis  11  of rotation. Twelve outlet openings, for example, are arranged in the distribution surface  19  in a manner distributed around the axis  11  of rotation, wherein they are connected fluidically either to the first  17  or the second fluid connection. One fluid passage  52  for each first fluid chamber  15  is arranged in the cylinder drum  48 , the said passage extending substantially parallel to the axis  11  of rotation. Depending on the rotational position of the rotor  40 , this passage opens into one of the outlet openings mentioned, but it can also be blocked by the distribution surface  19 . Thus, each first fluid chamber  15  can be fluidically connected selectively to the first  17  or to the second fluid connection by rotating the rotor  40 . 
         [0038]      FIG. 2  shows a cross section through the radial piston machine  10  shown in  FIG. 1 , wherein the section plane passes through the center of the pistons  60 . The control surface  31  runs continuously and without interruption around the axis  11  of rotation. The cross-sectional profile, shown in  FIG. 2 , of the control surface  31  is of constant design in the direction of the axis  11  of rotation over the entire width of the cam ring  60 . The spacing between the control surface  31  and the axis  11  of rotation varies periodically along the circumference. In this case, six locations with a minimum and a maximum spacing, respectively, are provided, for example, with the result that a piston  60  performs six strokes for one revolution of the rotor  40 . 
         [0039]    The pistons  60  are of identical design to one another, wherein they are embodied as stepped pistons. They are each accommodated in a matching cylinder bore  43  in the cylinder drum  48 , the said bore being designed as a stepped bore. Accommodated in each piston  60  is a circular-cylindrical roller  61 , which rolls on the control surface  31 . It should be noted here that all the pistons are shown in the same radial position in  FIG. 2 , although they are pressed against the control surface  31  by the pressure in the first fluid chamber  15  during operation, and therefore the pistons occupy different radial positions. When the corresponding first fluid chamber  15  is pressurized, the pistons  60  denoted by reference numeral  63  bring about an anticlockwise rotation of the rotor  40 . The first fluid chambers  15 , which are associated with the pistons  60  denoted by the reference numeral  64 , decrease in size during this rotary motion. In the rotational position, shown in  FIG. 2 , of the rotor  40 , the pistons  65  are in an extreme position. 
         [0040]    The axes of rotation of the rollers  61  are aligned parallel to the axis  11  of rotation. The rollers  61  can be supported on the respectively associated piston  60  via a hydrostatic pressure field. 
         [0041]      FIG. 3  shows a perspective view of the cylinder drum  48  of the radial piston machine shown in  FIG. 1 . The cylinder drum  48  has a flat end face  44 , which is aligned perpendicularly to the axis  11  of rotation, wherein it faces the first rotary bearing (No.  41  in  FIG. 1 ). First braking means  45  are provided on the end face  44 . The first braking means  45  comprise a multiplicity of first extensions  46 , which are arranged in a uniformly distributed manner at a constant pitch  12  around the axis  11  of rotation. The first extensions  46  are of identical design to one another, wherein the spacing thereof with respect to the axis  11  of rotation is likewise identical. The side faces  53  thereof engage positively between the second extensions (No.  72  in  FIG. 6 ), which form the second braking means. The said side faces  53  can be of flat and sloping design, with the result that the said positive engagement is canceled when a predetermined torque is exceeded. For this purpose, the side faces  53  can also be of rounded design. 
         [0042]    Grooves or channels (not shown), by means of which fluid leaks can be guided past the first rotary bearing, can be provided in the end face  44 . 
         [0043]    Two retention rings  62  are arranged on the outer circumferential surface of the cylinder drum  48 , the positive engagement of the said rings preventing the pistons (No.  60  in  FIG. 2 ) from falling out of the respectively associated cylinder bore (No.  43  in  FIG. 2 ) while the cylinder drum  48  is not mounted on the remainder of the radial piston machine. The retention rings  62  are arranged on opposite lateral rims of the cylinder drum  48  in the direction of the axis  11  of rotation. 
         [0044]    As already explained, the cylinder drum  48  is provided with a splined profile  49 , which engages positively in the drive shaft (No.  47  in  FIG. 1 ). 
         [0045]      FIG. 4  shows a perspective view of the first housing part  21  of the radial piston machine shown in  FIG. 1 . The first housing part  21  is of substantially pot-type design.  FIG. 4  shows the side of the first housing part  21  which faces the cam ring (No.  30  in  FIG. 1 ). On the one hand, it is possible to see the circular bore  28  in the bottom surface of the first housing part  21 , through which the drive shaft (No.  47  in  FIG. 1 ) passes. Arranged around the bore  28  is an extension  23 , which is ring-like in relation to the axis of rotation (No  11  in  FIG. 1 ) and projects into the interior (No.  18  in  FIG. 1 ) of the housing. The first rotary bearing (No.  41  in  FIG. 1 ), in particular the corresponding outer ring, is mounted on the radially inner side of the ring-like extension  23 . The bearing seat  27  at that location is of circular-cylindrical design in relation to the axis of rotation (No.  11  in  FIG. 1 ). 
         [0046]    In the present case, a total of ten second recesses  25  is provided on the radially outer side of the ring-like extension  23 , wherein the number mentioned is largely a matter of free choice. The recesses  25  are designed to be open toward the cylinder drum (No.  48  in  FIG. 1 ) in the direction of the axis of rotation. Moreover, they are designed to be open radially outwards. When viewed in the direction of the axis of rotation, they have a rectangular or slightly trapezoidal cross-sectional profile. Third extensions (No.  73  in  FIG. 6 ) on the brake ring engage in the second recesses  25 , and therefore twisting of the brake ring relative to the housing is at least limited. One advantage of the present disclosure is that the second recesses  25  and the third extensions can have cast surfaces, which do not have to be finish-machined. They can therefore be embodied in a relatively imprecise and therefore low-cost way. Nevertheless, there is no risk that the brake ring will tilt. 
         [0047]    Each second recess  25  is associated with a first recess  24 , which is of circular-cylindrical design, wherein it is arranged in alignment with the relevant second recess  25  in the direction of the axis of rotation. The first recesses  24  extend parallel to the axis of rotation, wherein they have a constant depth. A spring (No.  14  in  FIG. 5 ) is accommodated in each of the first recesses  24 . 
         [0048]      FIG. 5  shows an enlarged partial view of  FIG. 1  in the region of the brake ring  70 . The outer ring of the first rotary bearing  41  is mounted on the inside on the already discussed bearing seat  27  of the ring-like extension  23 . The corresponding inner ring is mounted on the drive shaft  47 , wherein it is supported on the end face  44  of the cylinder drum  48  in the direction of the axis of rotation. 
         [0049]    Arranged around the ring-like extension  23  and hence around the first rotary bearing  41  is the brake ring  70 , which is shown in greater detail in  FIG. 6 . On its right-hand side in  FIG. 5 , the brake ring  70  has second braking means  71 , which are arranged exactly opposite the first braking means  45  on the cylinder drum  48  in the direction of the axis of rotation. The springs  14  rest against the left-hand side of the brake ring  70  in  FIG. 5 . In the present case, these springs are each designed as helical springs, although it is likewise conceivable to use diaphragm springs or wave springs. The springs  14  are very largely accommodated in a respectively associated first recess  24  in the first housing part  21 , with the result that their position is fixed. The springs  14  are installed under a preload between the housing  20  and the brake ring  70 , with the result that the brake ring  70  is pressed onto the cylinder drum  48 . The corresponding path of movement is limited by the closure ring  80 , which is supported on the cam ring  30  in the direction of the axis of rotation. In this case, the closure ring  80  is preferably designed in such a way that the tips of the second braking means  71  cannot come into contact with the end face  44 . 
         [0050]    It should be noted that  FIG. 5  shows a position of the brake ring  70  in which the second fluid chamber  16  is supplied with fluid pressure, with the result that the brake ring  70  is in an end position in which the second braking means  71  do not engage in the first braking means  45 . The corresponding end position is defined by a stop  29  on the first housing part  21 . If the second fluid chamber  16  is not supplied with fluid pressure, the brake ring  16  rests on the closure ring  80 , wherein the second braking means  71  engage in the first braking means  45 . 
         [0051]    The second fluid chamber  16  is partially delimited by a sealing surface  26  on the first housing part  21 , the said sealing surface being of circular-cylindrical design in relation to the axis of rotation. Both the brake ring  70  and the closure ring  80  rest sealingly against the sealing surface  26 , wherein a corresponding sealing ring is provided in each case. When viewed in cross section, the brake ring  70  is of L-shaped design. One leg of the L forms a side wall of the second fluid chamber  16 , the pressurization of which brings about a movement of the brake ring  70 . The other leg of the L forms a radially inner wall, opposite the sealing surface  26 , of the second fluid chamber  16 , the pressurization of which does not bring about any movement of the brake ring  70 . 
         [0052]    The closure ring  80  rests sealingly against the said radially inner wall, wherein a corresponding sealing ring is arranged there. The closure ring  80  likewise forms a side wall of the second fluid chamber. The pressurization of the said chamber gives rise to a force, which is supported by positive engagement on the cam ring  30 , with the result that the closure ring  80  does not move during operation. For this purpose, the closure ring  80  is provided with a narrow nose  81 , ensuring that it does not touch the cylinder drum  48  in any rotational position. With the cross-sectional profile shown in  FIG. 5 , the closure ring  80  is of rotationally symmetrical design in relation to the axis of rotation. The second fluid chamber  16  is likewise of rotationally symmetrical design in relation to the axis of rotation. 
         [0053]      FIG. 6  shows a perspective view of the brake ring  70  of the radial piston machine shown in  FIG. 1 . On the end face facing the cylinder drum (No.  48  in  FIG. 1 ), the brake ring  70  is provided with second braking means  71 . The second braking means  71  comprise a multiplicity of second extensions  72 , which are arranged in a uniformly distributed manner around the axis  11  of rotation at a constant pitch  12 . The second extensions  72  are of identical design to one another, wherein the spacing thereof with respect to the axis  11  of rotation is likewise identical. The side faces  74  thereof engage positively between the first extensions (No.  46  in  FIG. 3 ), which form the first braking means. The said side faces  74  can be of flat and sloping design, with the result that the said positive engagement is canceled when a predetermined torque is exceeded. For this purpose, the side faces  74  can also be of rounded design. The second extensions  72  are of identical design to the first extensions (No.  46  in  FIG. 3 ). The pitch  12  of the first and the second braking means  71  is of identical design. 
         [0054]    The third extensions  73 , which have already been mentioned, are provided on the inner circumferential surface of the brake ring  70 , the said extensions engaging in the second recesses (No.  25  in  FIG. 4 ) in order to secure the brake ring  70  positively against twisting around the axis  11  of rotation. It should be noted that the free space between the third extensions  73  does not pass through the brake ring in the direction of the axis  11  of rotation over the entire width, and therefore it does not intersect the second braking means  71 . At the opposite end, the said free space is of open design to enable the brake ring  70  to be brought into engagement with the first housing part (No.  21  in  FIG. 4 ). 
         [0055]    With the cross-sectional shape shown in  FIG. 5 , the outer circumferential surface of the brake ring  70  is of rotationally symmetrical design in relation to the axis  11  of rotation. The rear end face of the brake ring  70 , which is not visible in  FIG. 6 , is designed to be flat and perpendicular to the axis  11  of rotation. 
         [0056]      FIG. 7  shows a view corresponding to  FIG. 5  of a second embodiment of the disclosure. Apart from the differences described below, the second embodiment is of identical design to the first embodiment, and, to this extent therefore, reference can be made to the statements relating to  FIGS. 1 to 6 . Here, identical or corresponding parts in  FIGS. 1 to 8  are provided with the same reference numerals. In particular, the cylinder drum  48  shown in  FIG. 3 , the first housing part  21  shown in  FIG. 4  and the closure ring  80  shown in  FIG. 5  are of identical design in both embodiments. 
         [0057]    Instead of the integral brake ring in the first embodiment, a brake ring  70 ′ and a separate annular piston  90  are provided in the second embodiment. The annular piston  90  delimits the second fluid chamber  16  in the same way as the brake ring (No.  70  in  FIG. 5 ) in the first embodiment. The annular piston  90  is mounted on the brake ring  70 ′ so as to be rotatable relative to the axis of rotation. Owing to the friction forces in the corresponding seals, the annular piston  90  does not rotate relative to the housing  20  and the closure ring  80  during operation, although twisting relative to the axis of rotation is possible in principle. There is therefore no risk of wear on the said seals. During operation, the brake ring  70 ′ can perform small rotary movements about the axis of rotation relative to the housing  20  since the engagement between the second recesses (No.  25  in  FIG. 4 ) and the third extensions (No.  73  in  FIG. 8 ) preferably exhibits some play. This rotary movement leads only to a relative movement between the brake ring  70 ′ and the annular piston  90 . There are no wear-prone seals arranged there. 
         [0058]    The brake ring  70 ′ according to the second embodiment is likewise of L-shaped design, wherein the leg of the L which is vertical in  FIG. 7  brings about positive coupling between the annular piston  90  and the brake ring  70 ′. The springs  14  also rest against this leg of the L. The stop  29  preferably enters into contact with the vertical leg  20  of the L. The leg of the L which is horizontal in  FIG. 7  forms a bearing surface for the annular piston  90  which is circular-cylindrical in relation to the axis of rotation. With the cross-sectional shape shown in  FIG. 7 , the annular piston  90  is of rotationally symmetrical design in relation to the axis of rotation. 
         [0059]      FIG. 8  shows an exploded view of the brake ring  70 ′ and of the annular piston  90  of the axial piston machine shown in  FIG. 7 . The inner circumferential surface of the brake ring  70 ′ with the third extensions  73  is of identical design to the inner circumferential surface of the brake ring (No.  70  in  FIG. 6 ) according to the first embodiment. The same applies to the second braking means  71 . The end face of the brake ring  70 ′ opposite the second braking means  71  is designed so as to be flat and perpendicular to the axis of rotation. 
       REFERENCE SIGNS 
       [0000]    
       
           10  radial piston machine (first embodiment) 
           10 ′ radial piston machine (second embodiment) 
           11  axis of rotation 
           12  pitch 
           13  fluid distribution device 
           14  spring 
           15  first fluid chamber 
           16  second fluid chamber 
           17  first fluid connection 
           18  interior 
           19  distribution surface 
           20  housing 
           21  first housing part 
           22  second housing part 
           23  ring-like extension 
           24  first recess 
           25  second recess 
           26  sealing surface 
           27  bearing seat 
           28  bore 
           29  stop 
           30  cam ring 
           31  control surface 
           40  rotor 
           41  first rotary bearing 
           42  second rotary bearing 
           43  cylinder bore 
           44  end face 
           45  first braking means 
           46  first extension 
           47  drive shaft 
           48  cylinder drum 
           49  splined profile 
           50  drive means 
           51  seal 
           52  fluid passage 
           53  side face of the first extension 
           60  piston 
           61  roller 
           62  retention ring 
           63  driving piston 
           64  driven piston 
           65  piston in the extreme position 
           70  brake ring (first embodiment) 
           70 ′ brake ring (second embodiment) 
           71  second braking means 
           72  second extension 
           73  third extension 
           74  side face of the second extension 
           80  closure ring 
           81  nose 
           90  annular piston