Abstract:
A camshaft adjusting device including—a vane cell adjuster and—a central locking device ( 26 ) for locking the rotor ( 17 ) with respect to the stator ( 16 ), wherein—at least one first valve functional pin ( 46 ) is provided in the rotor hub ( 30 ), and the working chambers ( 20, 21, 22, 23 ) with different directions of action can be fluidically connected to one another via said valve functional pin,—in a first switch position, the first valve functional pin ( 46 ) fluidically connects at least two first working chambers ( 20, 21 ) with different directions of action to each other via a non-return valve ( 9, 10 ) during a movement from the direction “early” or “late” into the central locking position,—in a second switch position, the first valve function pin ( 46 ) fluidically separates the at least two first working chambers ( 20, 21 ) with different directions of action,—a bridging line ( 50 ) is provided for a fluid-free connection of the two first working chambers ( 20, 21 ), and—the bridging line ( 50 ) can be switched by a valve pin ( 45 ).

Description:
[0001]    The present invention relates to a camshaft adjusting device having.            
         [0002]    Camshaft adjusting devices are generally used in valve trains of internal combustion engines in order to alter the valve opening and closing times, as a result of which the consumption values of the internal combustion engine and the operating behavior may generally be improved. 
       BACKGROUND 
       [0003]    One specific embodiment of the camshaft adjusting device proven in practice includes a vane cell adjuster with a stator and a rotor, which delimit an annular space, which is subdivided by projections and vanes into multiple working chambers. The working chambers may be selectively acted upon by a pressure medium, which is fed in a pressure medium circuit via a pressure medium pump from a pressure medium reservoir into the working chambers on one side of the vanes of the rotor and is fed from the working chambers on the respective other side of the vanes back to the pressure medium reservoir. The working chambers, the volume of which is increased in the process, exhibit an operating direction which is opposite the operating direction of the working chambers, the volume of which is reduced. Accordingly, the operating direction means that a pressure medium acting upon each group of working chambers causes the rotor to rotate either clockwise or counterclockwise relative to the stator. The pressure medium flow, and therefore the adjusting movement, is controlled, for example, with the aid of a central valve having a complex structure of flow-through openings and control edges and a valve body displaceable in the central valve, which closes or unblocks the flow-through openings as a function of its position. 
         [0004]    One problem with such camshaft adjusting devices is that in a start phase they are not yet completely filled with pressure medium and may even be run dry, so that the rotor may carry out uncontrolled movements relative to the stator due to the alternating torques exerted by the camshaft, which may result in increased wear and an undesirable noise generation. To avoid this problem, it is known to provide a locking device between the rotor and the stator, which locks the rotor in a rotation angle position relative to the stator favorable for starting when the internal combustion engine is turned off In exceptional cases, however, for example, when the internal combustion engine stalls, it is possible that the locking device does not lock the rotor as intended, and it is necessary to operate the camshaft adjuster in the subsequent start phase with an unlocked rotor. However, since some internal combustion engines have a very poor start behavior when the rotor is not locked in the center position, the rotor must then be automatically rotated and locked in the center locking position in the start phase. 
         [0005]    Such an automatic rotation and locking of the rotor relative to the stator is known, for example, from DE 10 2008 011 915 A1 and from DE 10 2005 011 916 A1. The locking devices described in both publications include a plurality of spring-loaded locking pins, which lock successively in locking slots provided on the sealing cover or on the stator when the rotor is rotated and, in the process, allow the rotor in each case to rotate in the direction of the center locking position before reaching the center locking position, but which block a rotation of the rotor in the opposite direction. After the internal combustion engine is warmed up and/or the camshaft adjuster is filled completely with pressure medium, the locking pins, activated by the pressure medium, are forced out of the locking slots so that the rotor may be subsequently rotated as intended for adjusting the rotation angle position of the camshaft relative to the stator. 
         [0006]    One disadvantage of this approach is that the rotor can be locked only with multiple successively locking locking pins, which results in higher costs. In addition, the locking process presupposes that the locking pins lock successively in a functionally reliable manner. If one of the locking pins fails to lock, the locking process may be interrupted, since the rotor is therefore not locked on one side in the intermediate position and may rotate back. In addition, it must be ensured that the locking pins may be reliably forced out of the locking slots during a start of the internal combustion engine. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide a camshaft adjuster which includes a functionally reliable and cost-effective center locking of the rotor. 
         [0008]    According to the basic concept of the present invention, it is provided that a bridging line is provided for a fluidically-free connection of the first two working chambers, the bridging line being switchable by a valve pin. The first two working chambers are two working chambers of differing operating directions, which are used to automatically move the rotor from a direction “early” or “late” into the center locking position. For this purpose, the two first working chambers are fluidically connected to one another via a check valve during the movement of the rotor from the direction “early” or “late” into the center locking position when the internal combustion engine is switched off. A check valve having a first operating direction or a second operating direction is fluidically switched between the first working chambers as a function of whether the rotor is moved from the direction “early” or “late” into the center locking position. In this way, it is ensured that only one of the first working chambers increases its volume and thus enables the movement of the rotor relative to the stator only in the direction of the center locking position. When re-starting the internal combustion engine, the locking pins must be moved again out of the locking slot. This is achieved by the application of a pressure medium to the locking slot, causing the locking pin to move against the spring force back into the rotor hub. At the same time, one of the first two working chambers, as a result of the application of pressure medium, is acted upon by pressure medium, causing a torque to occur between the stator and the rotor; the remaining working chambers of different operating directions are fluidically short-circuited in this operating state by the first valve function pin. In this state, the locking pins have not yet been completely forced out of the locking slot, as a result of which at least one locking pin may jam on the locking slot as a result of the applied torque. Due to the clamping effect, the locking pin is unable to be moved or to be moved only belatedly out of the locking slot. With the bridging line according to the present invention, a direct fluidically free connection may be established in this state between the two first working chambers. A freely flowable pressure medium line in this context is understood to mean a pressure medium line, through which a pressure medium may flow unhindered or essentially unhindered in both flow directions; a pressure medium line with a check valve is therefore not freely flowable. No torque is created between the stator and the rotor in this operating state as a result of this fluidic short circuit, which is why the jamming of the locking pin on the locking slot is prevented. The bridging line in this case is controllable via a valve pin, the valve pin preferably being controllable by the pressure medium in the locking slot. The fluidic switching of the bridging line by a valve pin may ensure that the fluidic short circuit between the two first working chambers occurs only in the operating state in which a jamming is to be avoided, i.e., in the phase between the start of the internal combustion engine and normal operation. In all other operating states, the bridging line is not fluidically switched between the two first working chambers. The result of this is that a reliable unlocking from the center locking position is enabled during the start phase of the internal combustion engine. 
         [0009]    It is provided that a recess for accommodating the valve pin is provided in the locking slot. The advantage of the recess on the one hand is that the valve pin may assume an additional valve position. On the other hand, the valve pin may be moved into two switching positions when the locking slot is switched to zero pressure. The valve pin with a front surface facing the locking slot initially drags along a bottom surface of the locking slot when the rotor is moved in the direction of the center locking position relative to the stator, until it reaches the point at which the recess is provided. There, the valve pin is pushed by the spring force into the recess and thereby assumes the additional switching position. 
         [0010]    It is further provided that the recess is situated in a locking slot secured to the stator in such a way that the valve pin in the center locking position is movable with at least one end section into the recess. Thus, the specific arrangement of the recess offers the advantage that the additional switching position may only be reached in the center locking position. The additional switching position for the fluidically free connection of the two first working chambers via the bridging line need only occur in the center locking position during the start of the internal combustion engine. 
         [0011]    It is further advantageous if the bridging line is switched fluidically open between the two first working chambers when the end section is located completely in the recess. This ensures that the two first working chambers are fluidically freely connected only if a sufficient pressure level is not yet reached in the locking slot and a jamming of the locking pins is possible. The spring force of the locking pins in such a case need not be identical to the spring force of the valve pin. The spring force of the valve pin is preferably greater than that of the locking pins. In this way, it is the locking pins that are first moved out of the locking slot. If the locking pins have been moved so far out of the locking slot that a jamming is no longer possible, the valve pin is also moved against the spring force and, as a result, the free fluidic connection between the first two working chambers is interrupted. 
         [0012]    One end section of the valve pin projecting into the recess is preferably tapered in the direction of one end of the valve pin. The locking slot is not acted upon by pressure medium when the internal combustion engine is stopped, which is why, when the rotor is moved, the end of the valve pin drags from the direction “early” or “late” into the center locking position along the bottom surface until it has reached the recess. Because of the tapering, the frictional resistance between the end and the bottom surface is reduced and the penetration of the end section into the recess is facilitated. 
         [0013]    The tapering of the end section is further preferably formed by a conical shape or spherical shape. A spherical or conical shape is simple and cost-effective to manufacture and offers the advantage that the transition between the bottom surface and the recess is not sudden, but rather occurs steadily. Inherent to this is also the advantage that the valve pin may be more easily moved out of the recess in the case of an adjusting movement between the rotor and the stator. Thus, the valve pin may be moved out of the recess by a hydraulic force as well as by a mechanical force. 
         [0014]    It is advantageous if the shape of the recess is adapted to the outer contour of the end section in such a way that pressure medium is able to flow between the recess and the end section when the end section is located completely in the recess. This enables the valve pin to be moved by the pressure medium in the locking slot against the operating spring force out of the recess. Additional devices for again moving the valve pin out of the recess may therefore be omitted. 
         [0015]    It is further preferred that the valve pin is formed by the first valve function pin. The valve function pin is already provided in the camshaft adjusting device and is controlled by the pressure medium level in the locking slot. Thus, with a minimal design change, it is possible to fluidically switch the bridging line between the two first working chambers as a function of the switching position of the valve function pin. 
         [0016]    The first valve function pin in a third switching position preferably connects the first working chambers fluidically freely to one another via the bridging line. The third switching position of the valve function pin may only be reached if the camshaft adjusting device is located in the center locking position and, as a result, the valve function pin or the end section thereof may be moved into the recess. If the camshaft adjusting device is not in the center locking position, the valve function pin is then only able to assume the first or the second switching position. In the center locking position, the additional third switching position may only be reached if the valve function pin is not moved into the first or second switching position by the application of pressure medium in the locking slot. 
         [0017]    The valve pin may also be formed by an additional second valve function pin. The second valve function pin may therefore be controlled independently of the first valve function pin. However, the second valve function pin is preferably also controllable via the pressure medium level in the locking slot. In this specific embodiment of the present invention, the second valve function pin preferably has two switching positions. In a first switching position of the second locking device, the free fluidic connection between the two first working chambers is blocked. The first switching position of the second locking device is reached if the second valve function pin or the end section thereof is not pushed into the recess. In a second switching position of the second valve function pin, the two first working chambers are fluidically freely connected to one another via the bridging line; the second valve function pin in this switching position is pushed into the recess. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention is described in greater detail below with reference to a preferred exemplary embodiment. In the individual figures, in particular: 
           [0019]      FIG. 1  schematically shows a representation of a camshaft adjusting device according to the present invention with a circuit diagram of a pressure medium circuit in the center locking position having a first valve function pin in a third switching position; 
           [0020]      FIG. 2  schematically shows a representation of a camshaft adjusting device according to the present invention with a circuit diagram of a pressure medium circuit in the center locking position having a first valve function pin in a second switching position; 
           [0021]      FIG. 3  schematically shows a representation of a camshaft adjusting device according to the present invention with a circuit diagram of a pressure medium circuit in the center locking position having an additional second valve function pin in a second switching position. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    A camshaft adjusting device is apparent in  FIGS. 1 through 3 , having a known basic construction with a schematically depicted vane cell adjuster as the basic component, which includes a stator  16  drivable by a crankshaft not depicted and a rotor  17  rotatably fixedly connectable to a camshaft also not depicted having multiple vanes  11  and  12  extending radially outwardly therefrom. In the upper development drawing, the vane cell adjuster is apparent, whereas a detail of rotor  17  having a center locking device  26  is schematically apparent at the bottom left and a switching device in the form of a selector switch valve  7  for controlling the pressure medium flow is schematically apparent at the bottom right. Selector switch valve  7  includes an A-port, B-port and C-port, to which pressure medium lines  18 ,  27  and  28  are fluidically attached. In addition, selector switch valve  7  is fluidically connected to a pressure medium reservoir T and to a pressure medium pump P which, during an actuation of the camshaft adjusting device, conveys the pressure medium, once it is returned, again from pressure medium reservoir T in a pressure medium circuit. 
         [0023]    A pressure medium circuit is also apparent having a plurality of pressure medium lines  1 ,  3 ,  4 ,  6 ,  8 ,  13 ,  14 ,  15 ,  18 ,  27 ,  28 ,  29 ,  31 ,  32 ,  33 ,  34 ,  38 ,  39 ,  40 ,  41 ,  42 ,  48  and  49 , which are selectively fluidically connectable to pressure medium pump P or pressure medium reservoir T via selector switch valve  7 . 
         [0024]    Stator  16  includes a plurality of stator webs, which subdivide an annular space between stator  16  and rotor  17  into pressure chambers  24  and  25 . Pressure chambers  24  and  25 , in turn, are subdivided by vanes  11  and  12  of rotor  17  into working chambers  20 ,  21 ,  22  and  23 , into which pressure medium lines  1 ,  3 ,  4  and  6  open. Center locking device  26  includes two locking pins  2  and  5 , which are used for locking rotor  17  with respect to stator  16  in a locking slot  19  secured to the stator. Locking slot  19  may, for example, be situated in a sealing cover securely screwed to stator  16 . 
         [0025]    In principle, the rotation angle of the camshaft relative to the crankshaft during normal operation is adjusted in the direction “late,” for example, by applying pressure medium to working chambers  21  and  23  and thereby increasing their volume, while at the same time forcing the pressure medium out of working chambers  20  and  22  and reducing their volume. The stop position “early” is marked in the depictions with an F, and the stop position “late” is marked with an S. Working chambers  20 ,  21 ,  22  and  23 , the volume of which is increased each time in groups during this adjusting movement, are referred to within the context of the present invention as working chambers  20 ,  21 ,  22  and  23  of one operating direction, while working chambers  20 ,  21 ,  22  and  23 , the volume of which at the same time decreases, are referred to as working chambers  20 ,  21 ,  22  and  23  of the opposite operating direction. The volume change of working chambers  20 ,  21 ,  22  and  23  then result in rotor  17  with vanes  11  and  12  rotating with respect to stator  16 . In the upper development drawing of stator  16 , the volume of working chambers  21  and  23  is increased by an application of pressure medium via the B-port of selector switch valve  7  during a movement from “early” to “late,” whereas the volume of working chambers  20  and  22  is reduced at the same time by the backflow of the pressure medium via the A-port of selector switch valve  7 . This volume change results in a rotation of rotor  17  with respect to stator  16 , which results in a shift of the vanes  11  and  12 , in the development drawing of  FIG. 2  to the left, out of the shown center locking position. 
         [0026]      FIGS. 1 and 2  show a first specific embodiment of the present invention, whereas a second alternative specific embodiment is shown in  FIG. 3 , the first specific embodiment being preferably used in practice. 
         [0027]    In  FIGS. 1 through 3 , it is apparent that, according to the solution according to the present invention, a check valve  9  and  10 , respectively, is situated in a rotor hub  30  of rotor  17  in spatial proximity to locking pins  2  and  5 . Locking pin  2  is fluidically connected via pressure medium line  14  to pressure medium line  27 . In addition, pressure medium line  1  is fluidically connected via pressure medium lines  8  and  13  to an accommodating space  43  of locking pin  2 . Pressure medium lines  8  and  13  are fluidically connected in parallel. Pressure medium line  8  and  13  are fluidically connected to second pressure medium line  14  as a function of the switching position of a first valve device  36 . Thus, the first valve device  36  is formed by accommodating space  43  and locking pin  2  guided therein. In a first switching position, first valve device  36  fluidically connects pressure medium line  8  to pressure medium line  14  via pressure medium line  38  (see  FIG. 1 ). In a second switching position of first valve device  36 , the fluidic connection between pressure medium line  13  and pressure medium line  14  is established via pressure medium line  39  (see  FIG. 2 ). Check valve  9  in this case is situated in third pressure medium line  8 , the operating direction of check valve  9  being such as to enable a through-flow of pressure medium in the direction of working chamber  20 . This applies similarly to a second valve device  37 , which is formed by locking pin  5  mounted in an accommodating space  44 , accommodating space  44  being fluidically connected to pressure medium lines  33 ,  31  and  32 . In a first switching position, second valve device  37  fluidically connects pressure medium line  31  to pressure medium line  33  via pressure medium line  40  (see  FIG. 1 ). In a second switching position of second valve device  37 , the fluidic connection between pressure medium line  32  and pressure medium line  33  is established via pressure medium line  41  (see  FIG. 2 ). Pressure medium lines  31  and  32  in this case are fluidically connected in parallel. Check valve  10  is situated in pressure medium line  31 , the operating direction of check valve  10  being set in such a way that a through-flow of pressure medium is possible only in the direction of working chamber  21 . Alternatively to the arrangement of check valves  9  and  10  outside of locking pins  2  and  5  in rotor hub  30 , these check valves may also be provided directly in first and/or second valve device  36  and  37 . 
         [0028]      FIG. 1  shows a camshaft adjusting device according to the present invention, in which a valve pin  45  for switching a bridging line  50  is formed by a first valve function pin  46 . First valve function pin  46  is linearly displaceable and spring-loaded. It is also spring-loaded in the direction of the engagement position in locking slot  19  and is situated in rotor  17  in such a way that it does not hinder the rotational movement of rotor  17  with respect to stator  16 . First valve function pin  46  is just moved along. To enable the adjustment of rotor  17  with respect to stator  16 , center locking device  26  is first released by applying pressure medium via pressure medium pump P to locking slot  19  via pressure medium line  18  from the C-port of selector switch valve  7 . Due to the application of pressure medium to locking slot  19 , locking pins  2  and  5 , as well as first valve function pin  46 , are forced out of locking slot  19 , so that rotor  17  may subsequently rotate freely with respect to stator  16 . 
         [0029]      FIG. 1  shows the camshaft adjusting device in a center locking position during the start of the internal combustion engine. Pressure medium pump P in this operating state is fluidically connected to the B-port of selector switch valve  7 . The C-port of selector switch valve  7  in this switching position is fluidically connected to pressure medium reservoir T. 
         [0030]    The adjusting movement of the rotor into the center locking position is described below. The adjusting movement described below is completed chronologically before the state depicted in  FIG. 1 . When rotor  17  is moved with respect to stator  16  from the direction “early” into the center locking position, first valve device  36  is in the second switching position, whereas second valve device  37  is in the first switching position. Thus, check valve  10  is switched between the two first working chambers  20  and  21  so that the excessive pressure medium is only able to flow from working chamber  20  into working chamber  21  and, as a result, a movement may take place in the direction of the center locking position. With this adjusting movement into the center locking position, locking slot  19  is switched to zero pressure, as a result of which first valve function pin  46  is moved by a spring force from a second switching position into a first switching position. In the first switching position, pressure medium line  15  is fluidically connected to pressure medium line  34  via pressure medium line  42 , the fluidic connection between pressure medium lines  48  and  49  being blocked. In a second switching position, there is no fluidic connection between pressure medium lines  15  and  34  as well as between  48  and  49 . As long as the camshaft adjusting device is not in the center locking position, first valve function pin  46  is held in the first switching position by a bottom surface  51  of locking slot  19 . Thus, when rotor  17  is moved from the direction “early” into the center locking position, a fluidic connection is established between first working chambers  20  and  21  via pressure medium lines  1 ,  13 ,  39 ,  14 ,  27 ,  34 ,  42 ,  15 ,  33 ,  40 ,  31  and  3 . The pressure medium in this case flows via check valve  10 . The functional principle is to be applied similarly when rotor  17  is adjusted with respect to stator  16  from the direction “late” into the center locking position. First valve device  36  is then in the first switching position and second valve device  37  is in the second switching position. In this case, the flow from working chamber  21  into working chamber  20  takes place via pressure medium lines  3 ,  32 ,  41 ,  33 ,  15 ,  42 ,  34 ,  14 ,  38 ,  8  and  1 . The pressure medium in this adjustment direction flows via check valve  9 . 
         [0031]    If the camshaft adjusting device is in the center locking position (see  FIG. 1 ), then the backflow of pressure medium via check valve  9  and  10  is not possible. Thus, during a start of the internal combustion engine, the two first working chambers  20  and  21  are therefore fluidically freely connected via a bridging line  50 . Remaining working chambers  22  and  23  are fluidically short-circuited via pressure medium line  42  in first valve function pin  46 . During a start of the internal combustion engine, pressure is already applied by pressure pump P to working chambers  20 ,  21 ,  22  and  23  of one operating direction before locking pins  2  and  5  have been moved out of locking slot  19 . Without additional bridging line  50 , no pressure compensation could take place in first working chambers  20  and  21  due to check valves  9  and  10 , which is why a torque is created between stator  16  and rotor  17 . Locking pins  2  and  5  in this operating state project at least still partly into locking slot  19 , which could result in a jamming of at least of one locking pin  2  or  5  with locking slot  19 . 
         [0032]    In a first specific embodiment according to the present invention, bridging line  50  is provided in first valve function pin  46 , which may be fluidically connected between pressure medium lines  48  and  49  in an additional third switching position of first valve function pin  46 , see  FIG. 1 . In this way, first working chambers  20  and  21  may be fluidically freely short-circuited via pressure medium lines  1 ,  48 ,  50 ,  49  and  3 . A freely flowable pressure medium line in this context is understood to mean a pressure medium line, through which pressure media may flow unhindered or essentially unhindered in both flow directions; accordingly, a pressure medium line  8  or  31  with check valve  9  or  10  is not freely flowable. The result of this is that a jamming of locking pins  2  and  5  at locking slot  19  is prevented during the start of the internal combustion engine. 
         [0033]    The third switching position of first valve function pin  46  may be reached only if an end section  52  of first valve function pin  46  projects into a recess  35  provided therefor. Recess  35  is situated in locking slot  19  in such a way that end section  52  is only able to project into it in the center locking position. During the adjusting movement of rotor  17  from the direction “early” or “late” into the center locking position, first valve function pin  46  is moved by the spring force into the first switching position and held there in this first switching position by bottom surface  51 . Once the center locking position is reached, first valve function pin  46  is located at the position of recess  35 , so that end section  52  is moved by the spring force into recess  35 . End section  52  is tapered in the direction of the end of first valve function pin  46 , preferably, with a spherical shape, even more preferably with a conical shape. In this way, a sudden transitional movement of end section  52  into recess  35  is avoided. In addition, the contour of recess  35  is configured in such a way that when an end section  52  is located completely in the recess, the pressure medium is able to flow from locking slot  19  between recess  35  and end section  52 . This ensures that a force against the spring force is applied by the pressure medium to first valve function pin  46  and, as a result, the pin may be moved out of locking slot  19 . The pretensioning force of the springs of locking pins  2  and  5  in this case may differ from the pretensioning force of first valve function pin  46 . The pretensioning force of locking pins  2  and  5  is set preferably lower than that of valve pin  45 . The result of this is that initially locking pins  2  and  5  are moved so far out of locking slot  19  that a jamming of locking pins  2  and  5  with locking slot  19  is prevented. Once locking pins  2  and  5  have been moved so far out of locking slot  19  that a jamming is ruled out, first valve function pin  46  moves into the second switching position, as a result of which pressure medium lines  48  and  49 , as well as pressure medium lines  15  and  34  are fluidically blocked; this state is depicted in  FIG. 2 . Locking pins  2  and  5  in this operating state are also in the second switching position. Thus, all fluidic connections between working chambers  20 ,  21 ,  22  and  23  of different operating directions are blocked. Working chambers  21  and  23  are connected to pressure medium pump P via pressure medium lines  28  and  6 , as well as pressure medium lines  28 ,  29 ,  33 ,  41 ,  32  and  3  via the C-port of selector switch valve  7 . The excessive pressure medium of oppositely operating working chambers  20  and  22  may drain into pressure medium reservoir T via pressure medium lines  1 ,  13 ,  39 ,  14 ,  27  as well as via pressure medium lines  4  and  27  via the A-port of selector switch valve  7 . 
         [0034]      FIG. 3  shows a second specific embodiment of the present invention, in which valve pin  45  is formed by an additional second valve function pin  47 . Accordingly, first valve function pin  46  assumes only the already known first and second switching position; the third switching position is omitted. Second valve function pin  47  also has two switching positions. In a first switching position, the fluidically free connection of pressure medium lines  48  and  49  is blocked. In a second switching position, a fluidically free connection between first working chambers  20  and  21  may be established via bridging line  50 . In this way, the pressure medium may flow freely between first working chambers  20  and  21  via pressure medium lines  1 ,  48 ,  50 ,  49  and  3 . Similar to first valve function pin  46 , second valve function pin  47  may also reach the second switching position only if end section  52  of valve function pin  47  has been moved completely into recess  35 . Recess  35  in this case is situated in locking slot  19  in such a way that it may be reached by second valve function pin  47  only in the center locking position. If the C-port of selector switch valve  7  is switched to zero pressure and the center locking position is reached, second valve function pin  47  in this specific embodiment is in the second switching position, and thus forms a fluidically free connection between first working chambers  20  and  21 . At the same time, first valve function pin  46  is in the first switching position, as a result of which additional working chambers  22  and  23  having different operating directions are fluidically short-circuited. In this way, the blocking of the rotation of rotor  17  with respect to stator  16  is prevented during the freewheeling. The further functionality corresponds to that of the first exemplary embodiment from  FIGS. 1 and 2 . Thus, even in the second specific embodiment from  FIG. 3 , a jamming of locking pins  2  and  5  on locking slot  19  may be reliably prevented. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  pressure medium line 
           2  locking pin 
           3  pressure medium line 
           4  pressure medium line 
           5  locking pin 
           6  pressure medium line 
           7  selector switch valve 
           8  pressure medium line 
           9  check valve 
           10  check valve 
           11  vane 
           12  vane 
           13  pressure medium line 
           14  pressure medium line 
           15  pressure medium line 
           16  stator 
           17  rotor 
           18  pressure medium line 
           19  locking slot 
           20  working chamber 
           21  working chamber 
           22  working chamber 
           23  working chamber 
           24  pressure chamber 
           25  pressure chamber 
           26  center locking position 
           27  pressure medium line 
           28  pressure medium line 
           29  pressure medium line 
           30  rotor hub 
           31  pressure medium line 
           32  pressure medium line 
           33  pressure medium line 
           34  pressure medium line 
           35  recess 
           36  valve device 
           37  valve device 
           38  pressure medium line 
           39  pressure medium line 
           40  pressure medium line 
           41  pressure medium line 
           42  pressure medium line 
           43  accommodating space 
           44  accommodating space 
           45  valve pin 
           46  first valve function pin 
           47  second valve function pin 
           48  pressure medium line 
           49  pressure medium line 
           50  bridging line 
           51  bottom surface 
           52  end section