Patent Publication Number: US-8522733-B2

Title: Device for variably adjusting control times of gas exchange valves of an internal combustion engine

Description:
This application is a 371 of PCT/EP2008/066065 filed Nov. 24, 2008, which in turn claims the priority of DE 10 2007 058 491.3 filed Dec. 5, 2007, the priority of both applications is hereby claimed and both applications are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a device for variably adjusting the timing control of gas exchange valves of an internal combustion engine, comprising a drive element, an output element, a rotation angle limiting device and a control valve, at least two counter-working pressure chambers being provided, it being possible to bring about a phase adjustment between the output element and the drive element by charging one of the pressure chambers with pressure medium while simultaneously discharging the other pressure chamber, the rotation angle limiting device preventing the phase relation from being altered when in a locked state and the rotation angle limiting device allowing the phase relation to be altered when in an unlocked state, it being possible to switch the rotation angle limiting device from the locked to the unlocked state by charging same with pressure medium, the control valve comprising a valve housing and a control piston, exactly one inflow port, at least one outflow port, one control port and two working ports being embodied on the valve housing, the inflow port being connected to a pressure source, the outflow port to a tank, the control port to the rotation angle limiting device and the working ports each being connected to a respective pressure chamber, and the control valve being arranged in a central receptacle of the output element. 
     BACKGROUND OF THE INVENTION 
     In modern internal combustion engines, devices for variably adjusting the timing control of gas exchange valves are used to configure the phase relation between crankshaft and camshaft variably between a maximum advance and a maximum retard position within a defined angular range. For this purpose the device is integrated in a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train may be implemented, for example, as a belt drive, chain drive or gear drive. 
     The device includes at least two counter-rotatable rotors, one rotor being in driving connection to the crankshaft and the other rotor being connected non-rotatably to the camshaft. The device includes at least one pressure chamber which is subdivided into two counter-working pressure chambers by means of a movable element. The movable element is operatively connected to at least one of the rotors. By supplying pressure medium to the pressure chambers or discharging pressure medium from the pressure chambers, the movable element is displaced within the pressure chamber, whereby a specified rotation of the rotors with respect to one another, and therefore of the camshaft with respect to the crankshaft, is effected. 
     The inflow of pressure medium to the pressure chambers and the discharge of pressure medium therefrom is controlled by means of a control unit, as a rule a hydraulic directional valve (control valve). The control unit is in turn controlled by means of a controller which determines the actual and reference position of the camshaft relative to the crankshaft (phase relation) with the aid of sensors and compares one to the other. When a difference between the two positions is detected, a signal is transmitted to the control unit which adapts the flows of pressure medium to the pressure chambers to this signal. 
     In order to ensure the functioning of the device, the pressure in the pressure medium circuit of the internal combustion engine must exceed a given value. Because the pressure medium is as a rule made available by the oil pump of the internal combustion engine and the available pressure therefore rises synchronously with the rotational speed of the internal combustion engine, below a given rotational speed the oil pressure is still too low to change or retain the phase relation of the rotors in a specified manner. This may be the case, for example, during the start phase of the internal combustion engine or during idling phases. 
     During these phases the device would execute uncontrolled oscillations, leading to increased noise emissions, greater wear, more uneven running and increased raw emissions of the internal combustion engine. In order to prevent this, there may be provided mechanical locking devices which couple the two rotors non-rotatably to one another during the critical operating phases of the internal combustion engine, it being possible to cancel this coupling by charging the locking device with pressure medium. In this case the locking position may be provided at one of the end positions (maximum advance position and maximum retard position) or between the and positions. 
     A device of this type is known, for example, from U.S. Pat. No. 6,684,835 B2. In this embodiment the device has a vane-cell construction, an outer rotor being mounted rotatably on an inner rotor in the form of a vane wheel. In addition, two rotation angle limiting devices are provided, a first rotation angle limiting device, when in the locked state, allowing the inner rotor to be adjusted with respect to the outer rotor within an interval between a maximum retard position and a defined central position (locking position). The second rotation angle limiting device, when in the locked state, allows the inner rotor to be rotated with respect to the outer rotor within an interval between the central position and the maximum advance position. When both rotation angle limits are in the locked position, the phase relation of the inner rotor to the outer rotor is limited to the central position. 
     Each of the rotation angle limiting devices consists of a spring-loaded locking pin which is arranged in a receptacle of the outer rotor. Each locking pin is loaded with a force in the direction of the inner rotor by means of a spring. A guide track, which is located opposite the locking pins in certain operating positions of the devices, is formed on the inner rotor. In these operating positions the pins can engage in the guide track. In this case the respective rotation angle limiting device is switched from the unlocked to the locked state. Each of the rotation angle limiting devices can be switched from the locked to the unlocked state by charging the guide track with pressure medium. In this case the pressure medium forces the locking pins back into their receptacles, whereby the mechanical coupling of the inner rotor to the outer rotor is cancelled. 
     The charging of the pressure chambers and the guide track with pressure medium is effected by means of a control valve, two working ports which communicate with the pressure chambers, and a control port which communicates with the locking groove, being formed, inter alia, on the control valve. Further control valves of this type are known from U.S. Pat. No. 6,779,500 B2. These control valves consist essentially of a conventional 4/3-way directional-proportional control valve which directs the pressure medium flows to and from the pressure chambers, and a 2/2-way directional control valve which controls the flows of pressure medium to and from the rotation angle limiting devices, the part-valves being arranged in series. In this case the two part-valves have a common control piston and a common valve housing. 
     A disadvantage of these embodiments is the large space requirement of the control valve, above all in the axial direction of the valve housing. In addition, the high number of control structures, which have to be formed on the control piston, is disadvantageous. This entails increased cost and increased space requirement. A further disadvantage is that these control valves are not suited to being used as a central valve which is arranged in a central receptacle of the inner rotor. Firstly, the control valves have two inflow ports to which pressure medium must be supplied via the inner rotor of the device. This increases the complexity and susceptibility to error of the device. Furthermore, the device must be constructed wide in the axial direction in order that all five ports of the valve are covered by the receptacle of the inner rotor. This entails increased cost in manufacturing the device. In addition, the space requirement and weight thereof are increased. 
     OBJECT OF THE INVENTION 
     It is the object of the invention to specify a device for variably adjusting the timing control of gas exchange valves of an internal combustion engine with a control valve, whereby a construction of the control valve as simple and cost-effective as possible is to be achieved. In addition, the space requirement of the control valve is to be minimized. 
     The object is achieved according to the invention in that the inflow port is arranged outside the output element and the drive element in the axial direction, and in that the working ports and the control port, depending on the position of the control piston within the valve housing, can be selectively connected to the inflow port or disconnected therefrom. In a concrete embodiment of the invention, it is provided that the working ports, the inflow port and the control port are configured as radial openings in the valve housing. 
     In this case the ports may be offset axially from one another and arranged in the sequence: inflow port, working port, outflow port, working port, control port, or: inflow port, control port, outflow port, working port, working port. 
     In a development of the invention, it is provided that a further outflow port is embodied on the valve housing as an axial port. 
     In addition, it may be provided that the control piston is configured to be hollow and that the interior of the control piston communicates with the inflow port in every position of the control piston relative to the valve housing. 
     In a concrete embodiment of the invention, it is proposed that the interior of the control piston can be connected to each of the working ports and to the control port by appropriate positioning of the control piston within the valve housing. 
     It may be provided that the control valve can adopt a first control position in which the first working port communicates exclusively with the outflow port, the second working port communicates exclusively with the inflow port and the control port communicates exclusively with the axial outflow port. 
     In a development of the invention, it is proposed that the control valve can adopt a second control position in which the first working port communicates exclusively with the outflow port, and the second working port and the control port communicate exclusively with the inflow port. 
     In this case it may be provided that the control valve can adopt a third control position in which the control port communicates exclusively with the inflow port while the working ports communicate neither with the inflow port nor with either of the outflow ports. 
     It is further proposed that the control valve can adopt a fourth control position in which the second working port communicates exclusively with the outflow port and the first working port and the control port communicate exclusively with the inflow port. 
     The device has an actuating device in the form of a hydraulic actuator and a hydraulic system which supplies the actuating device with pressure medium. The actuating device may be, for example, of the vane-cell or axial-piston type, as in the prior art. In the latter configuration a pressure piston which separates two pressure chambers from one another is displaced in an axial direction by the application of pressure medium. In this case the movement of the pressure piston causes a relative phase rotation between the output element and the drive element via two pairs of helical toothings. In addition, mechanical means (rotation angle limiting device) are provided to couple the output element to the drive element mechanically in a particular phase relation. The coupling may be such, for example, that the possible phase angles are limited to an angle range, or that a non-rotatable coupling between the output element and the drive element can be established in a defined phase relation. The rotation angle limiting device(s) may adopt a locked state (coupling established) and an unlocked state (no coupling). The transition from the locked to the unlocked state is effected by applying pressure medium to the rotation angle limiting device(s). 
     By charging one chamber or one group of pressure chambers with pressure medium while simultaneously discharging the other pressure chamber or pressure chambers, a phase adjustment of the inner rotor  23  relative to the outer rotor  22  is produced when the rotation angle limiting device(s) is/are in the unlocked state. In the locked state of the rotation angle limiting device(s), the phase adjustment takes place only within the range allowed by the rotation angle limiting device(s). 
     The hydraulic system has a control valve with a valve housing and a control piston. The valve housing may be configured to be substantially hollow-cylindrical. In this case the ports may be in the form of openings in the cylindrical surface. Within the valve housing a control piston can adopt a plurality of positions relative thereto, whereby a plurality of control positions can be realized. In this case it may be provided that the control piston can be displaced by means of an actuating unit relative to the valve housing in the axial direction thereof. The actuating unit may be, for example, of an electromagnetic or hydraulic type. In each control position a defined connection of the different ports is produced. The ports, in the form of openings in the lateral surface of the valve housing, are arranged offset to one another. The control piston and the valve housing can therefore be configured to be substantially rotationally symmetrical, whereby production can be considerably simplified. 
     The control piston has a plurality of control structures. There is provided a first control chamber which communicates, on the one hand, with the inflow port in all positions of the control piston and, on the other, can be connected to one of the working ports and to the control port (or the other working port). In this case there may be provided positions of the control piston in which the first control chamber communicates exclusively with the working port or the control port (or the other working port). In addition, there may be provided positions in which the first control chamber communicates with both ports. Through the activation of the working port and the control port (or the other working port) by means of a control chamber, the complexity of the control piston can be reduced. Fewer control elements are required, as a result of which costly machining thereof can be dispensed with and production costs can therefore be reduced. Furthermore, the reduction in the number of necessary control elements brings with it a reduction in the axial space requirement, so that use also as a central valve is possible. By virtue of a suitable arrangement on the valve housing of the control structures which cooperate with the first control chamber, the desired control logic of the control valve can be defined. 
     The control chambers may be configured, for example, as annular grooves in the outer lateral surface of the control piston. It would also be possible to form partial annular grooves. 
     The connection between the first control chamber and the inflow port may be effected via the interior of the hollow control piston. Pressure medium entering via the inflow port can reach the interior of the control piston via piston openings. In addition, there may be provided further piston openings which connect the first and/or the second control chamber to the interior of the piston. 
     Through the arrangement of the ports in the sequence: inflow port, working port (or control port), outflow port, working port, control port (or working port), the control valve may be provided for central valve applications. Because of the sequence of the ports, the pressure medium supply of the control valve can be arranged outside the actuating device. In this case the control valve projects from the inner rotor in the axial direction, the inflow port being located outside the inner rotor. The width of the inner rotor therefore needs to correspond only to the maximum distance between the working ports, the control port and the outflow port. The inner rotor, and therefore the actuating device, can therefore be made narrower. Furthermore, no pressure medium lines are required inside the inner rotor to conduct the pressure medium to the inflow port or ports, whereby the architecture of the actuating device is simplified and manufacturing costs are therefore reduced. The central valve solution leads to a more rigid hydraulic clamping of the vane in the pressure chamber. 
     It may be further provided that the control valve can adopt a first control position in which the working port communicates exclusively with the tank, the second working port communicates exclusively with the inflow port and the control port communicates exclusively with the tank. In addition, a second control position may be provided in which the first working port communicates exclusively with the tank and the second working port and the control port communicate exclusively with the inflow port. In addition, a third control position may be provided in which the control port communicates exclusively with the inflow port while the working ports communicate neither with the inflow port nor with either of the outflow ports. In addition, a fourth control position may be provided in which the second working port communicates exclusively with the tank and the first working port and the control port communicate exclusively with the inflow port. 
     Therefore, during starting of the internal combustion engine, in which the control valve adopts the first control position, the control port, and therefore the rotation angle limiting device(s), are connected to the tank. During the start, therefore, the coupling between inner rotor and outer rotor is ensured. Control positions two to four allow a phase adjustment in the direction of advanced or retarded timing, or a hydraulic fixing of the phase relation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the invention are apparent from the following description and from the drawings, in which an exemplary embodiment of the invention is represented in simplified form. In the drawings: 
         FIG. 1  shows an internal combustion engine only very schematically; 
         FIG. 2   a  is a top view of a device according to the invention for varying the timing control of gas exchange valves of an internal combustion engine with a hydraulic circuit, the control valve being represented only schematically; 
         FIG. 2   b  shows a longitudinal section through the device of  FIG. 2   a  along the line II B-II B, with the control valve; and 
         FIGS. 3   a - 3   d  each show longitudinal sections through the control valve of  FIG. 2   b  in different control positions thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a sketch of an internal combustion engine  1 , a piston  3  mounted on a crankshaft  2  in a cylinder  4  being indicated. In the embodiment illustrated, the crankshaft  2  is connected to an inlet camshaft  6  and an exhaust camshaft  7  via a traction drive  5  in each case, it being possible for a first and second device  10  to induce relative rotation between crankshaft  2  and camshafts  6 ,  7 . Cams  8  of the camshafts  6 ,  7  actuate one or more gas exchange inlet valves  9   a  and one or more gas exchange outlet valves  9   b . It may also be provided that only one of the camshafts  6 ,  7  is provided with a device  10 , or that only one camshaft  6 ,  7  equipped with a device  10  is provided. 
       FIGS. 2   a  and  2   b  show an embodiment of a device  10  according to the invention in a top view and in longitudinal section respectively. 
     The device  10  includes an actuating device  11  and a hydraulic system  12 . The actuating device  11  has a drive element (outer rotor  22 ), an output element (inner rotor  23 ) which is connected non-rotatably to the camshaft  6 ,  7  and two side covers  24 ,  25 . The inner rotor  23  is in the form of a vane wheel and has a substantially cylindrical hub element  26 , from the outer cylindrical surface of which, in the embodiment shown, five vanes  27  extend outwardly in the radial direction. In this case the vanes  27  may be formed integrally with the hub element  26 . Alternatively, the vanes  27  may be formed separately, as shown in  FIG. 2   a , and be arranged in axially extending vane grooves  28  formed on the hub element  26 , the vanes  27  being subjected to a radially outwardly directed force by means of spring elements (not shown) arranged between the bases of the vane grooves  28  and the vanes  27 . 
     Starting from an outer circumferential wall  29  of the outer rotor  22 , a plurality of projections  30  extend radially inwards. In the embodiment illustrated, the projections  30  are formed integrally with the circumferential wall  29 . Embodiments in which, instead of the projections  30 , vanes mounted on the circumferential wall  29  and extending radially inwards are provided are, however, also possible. The outer rotor  22  is mounted rotatably relative to the inner rotor  23  on the inner rotor  23  by means of circumferential walls of the projections  30  located radially inwards. 
     Formed on an outer lateral surface of the circumferential wall  29  is a sprocket  21 , by means of which torque can be transmitted from the crankshaft  2  to the outer rotor  22  via a chain drive (not shown). The sprocket  21  may be configured as a separate component and connected non-rotatably to the inner rotor  23 , or may be formed integrally therewith. Alternatively, a belt drive or gear drive may be provided. 
     The side covers  24 ,  25  are arranged one on each of the axial side faces of the outer rotor  22  and fixed non-rotatably thereto. For this purpose an axial opening  31  is provided in each of the projections  30 , a fastening element  32 , for example a pin or a screw, passing through each axial opening  31 , which fastening element  32  serves to fix the side covers  24 ,  25  non-rotatably to the outer rotor  22 . 
     Inside the device  10  a pressure chamber  33  is formed between each two projections  30  adjacent in the circumferential direction, which pressure chamber  33  is delimited in the circumferential direction by opposite, substantially radially extending boundary walls  34  of adjacent projections  30 , in the axial direction by the side covers  24 ,  25 , radially inwards by the hub element  26  and radially outwards by the circumferential wall  29 . Projecting into each of the pressure chambers  33  is a vane  27 , the vanes  27  being configured in such a manner that they rest against both the side walls  24 ,  25  and the circumferential wall  29 . Each vane  27  therefore divides the respective pressure chamber  33  into two counter-working pressure chambers  35 ,  36 . 
     The outer rotor  22  is arranged to be rotatable within a defined angular range with respect to the inner rotor  23 . The angular range is limited in one direction of rotation of the inner rotor  23  by the abutment of each vane  27  against a boundary wall  34  of the pressure chamber  33  configured as an advance stop  34   a  (advance timing control). Analogously, the angular range is limited in the other direction of rotation by the abutment of each vane  27  against the other boundary wall  34  of the pressure chamber  33 , which serves as a retard stop  34   b  (retard timing control). Alternatively, a rotation limiting device, which limits the rotation angle range of the outer rotor  22  with respect to the inner rotor  23 , may be provided. 
     By pressurizing one group of pressure chambers  35 ,  36  and depressurizing the other group, the phase relation of the outer rotor  22  with respect to the inner rotor  23 , and therefore of the camshaft  6 ,  7  with respect to the crankshaft  2 , can be varied. By pressurizing both groups of pressure chambers  35 ,  36 , the phase relation of the two rotors  22 ,  23  with respect to one another can be maintained constant. Alternatively, it may be provided that neither of the pressure chambers  35 ,  36  is charged with pressure medium during phases of constant phase relation. The lubricating oil of the internal combustion engine  1  is generally used as the hydraulic pressure medium. 
     During starting of the internal combustion engine  1  or during idling phases, the pressure medium supply of the device  10  may not be sufficient to ensure hydraulic clamping of the vanes  27  inside the pressure chambers  33 . In order to prevent uncontrolled oscillation of the inner rotor  23  with respect to the outer rotor  22 , there is provided a locking mechanism  41  which establishes a mechanical connection between the two rotors  22 ,  23 . The locking position may be located at one of the end positions of the inner rotor  23  relative to the outer rotor  22 . In this case a rotation angle limiting device  42  is provided, a locking pin  44  being arranged in one of the rotors  22 ,  23  and a guide track  45  adapted to the locking pin  44  being arranged in the other rotor  22 ,  23 . When the inner rotor  23  is in the locking position, the locking pin  44  can engage in the guide track  45  and thus establish a mechanical non-rotatable connection between the two rotors  22 ,  23 . 
     It has proved advantageous to select the locking position such that, in the locked state of the device  10 , the vanes  27  are located in a position between the advance stop  34   a  and the retard stop  34   b . Such a locking mechanism  41  is shown in  FIG. 2   a . This mechanism consists of a first and a second rotation angle limiting device  42 ,  43 . In the embodiment illustrated, each of the rotation angle limiting devices  42 ,  43  consists of an axially displaceable locking pin  44 , each of the locking pins  44  being received in a bore of the inner rotor  23 . In addition, two guide tracks  45  in the form of grooves extending in the circumferential direction are formed in the first side wall  24 . These guide tracks  45  are indicated in  FIG. 2   a  in the form of broken lines. Each of the locking pins  44  is loaded with a force in the direction of the first side cover  24  by means of a spring element  46 . When the inner rotor  23  adopts a position with respect to the outer rotor  22  in which a locking pin  44  is opposite the associated guide track  45  in the axial direction, said locking pin  44  is forced into the guide track  45  and the respective rotation angle limiting device  42 ,  43  is switched from an unlocked to a locked state. In this case the guide track  45  of the first rotation angle limiting device  42  is configured such that the phase relation of the inner rotor  23  with respect to the outer rotor  22 , with the first rotation angle limiting device  42  locked, is restricted to a range between a maximum retard position and the locking position. When the inner rotor  23  is in the locking position relative to the outer rotor  22 , the locking pin  44  of the first rotation angle limiting device  42  rests against a stop formed in the circumferential direction by the guide track  45 , whereby further adjustment in the direction of more advanced timing is prevented. 
     Analogously, the guide track  45  of the second rotation angle limiting device  43  is designed in such a manner that, with the second rotation angle limiting device  43  locked, the phase relation of the inner rotor  23  relative to the outer rotor  22  is restricted to a range between a maximum advance position and the locking position. 
     In order to switch the rotation angle limiting devices  42 ,  43  from the locked to the unlocked state, it is provided that the respective guide track  45  is charged with pressure medium. The respective locking pin  44  is thereby forced back into the bore against the force of the spring element  46  and the rotation angle limit is thus cancelled. 
     To supply the actuating device  11  with pressure medium, a plurality of pressure medium lines  38   a,b , control lines  48 , a control valve  37 , a pressure medium pump  47  and a tank  49  are provided. 
     First and second pressure medium lines  38   a ,  38   b  are provided within the inner rotor  23 . The first pressure medium line  38   a  extend, starting from the first pressure chambers  35 , to a central receptacle  40  of the inner rotor  23 . The second pressure medium line  38   b  likewise extend to the central receptacle  40 , starting from the second pressure chambers  36 . For reasons of clarity, the pressure medium lines  38   a,b  are shown for only two pressure chambers  33  in  FIG. 2   a.    
     To charge the rotation angle limiting devices  42 ,  43  with pressure medium, there are provided control lines  48  which, starting from a first annular groove  50  in the central receptacle  40  of the inner rotor  23 , extend via the first side cover  24  to the guide tracks  45 . In this case the first annular groove  50  communicates with the guide tracks  45  in all phase relations of the device  10 . 
     Arranged within the receptacle  40  of the inner rotor  23  is a control valve  37 . In the embodiment illustrated, the control valve  37  is received in a hollow camshaft  6 ,  7  which passes through the receptacle  40  of the inner rotor  23 . In this case the inner rotor  23  is connected non-rotatably to the camshaft  6 ,  7 , for example by means of a non-positive or material joint. 
     The control valve  37  has a first and a second working port A, B, an inflow port P, a third working port (control port S) and outflow ports T, T a . Pressure medium can be supplied to the control valve  37  by a pressure medium pump  47  via the inflow port P. The first and second working ports A, B communicate respectively with the first and second pressure medium lines  38   a,b . The control port S communicates with the control lines  48 . Pressure medium can be discharged by the control valve  37  to a tank  49  via the outflow ports T, T a . 
     In addition, the control valve  37  can be switched to four control positions S 1 -S 4  ( FIG. 2   a ). In the first control position S 1  the second working port B communicates with the inflow port P, while both the first working port A and the control port S are connected to the outflow ports T, T a . This control position S 1  is adopted during the start phase of the internal combustion engine  1 . In this phase the hydraulic clamping of the vanes  27  inside the pressure chambers  33  is generally not ensured because of insufficient system pressure. Because the guide tracks  45  of both rotation angle limiting devices  42 ,  43  are connected to the tank  49  via the control lines  48  and the control valve  37 , both rotation angle limiting devices  42 ,  43  adopt the locked state. The inner rotor  23  is therefore connected mechanically to the outer rotor  22 , whereby the phase relation is fixed in the locking position. Because the rotation angle limiting devices  42 ,  43  are connected not to the pressure medium pump  47  but to the tank  49  in this position of the control valve  37 , there is no danger of unwanted unlocking. The starting ability of the internal combustion engine  1  is therefore ensured and at the same time exhaust gas emissions are reduced. 
     The control positions S 2 -S 4  of the control valve  37  represent the regulating positions of the device  10  in which adjustment in the direction of retarded timing (second control position S 2 ) or adjustment in the direction of advanced timing (fourth control position S 4 ) is made, or the timing is maintained constant (third control position S 3 ). In these control positions S 2 -S 4  the guide tracks  45  of the rotation angle limiting devices  42 ,  43  are connected to the pressure medium pump  47  via the control lines  48  and the control valve  37 . System pressure is therefore present at the end faces of the locking pins  44 , as a result of which the rotation angle limiting devices  42 ,  43  adopt the unlocked state and allow a phase adjustment of the inner rotor  23  relative to the outer rotor  22 . 
     In the second control position S 2  both the second working port B and the control port S communicate with the inflow port P, while the first working port A is connected to the outflow port T. Pressure medium is therefore supplied by the pressure medium pump  47  to the second pressure chambers  36  via the control valve  37  and the second pressure medium lines  38   b . At the same time, pressure medium is discharged from the first pressure chambers  35  via the first pressure medium lines  38   a  and the control valve  37  to the tank  49 . The vanes  27  are therefore moved inside the pressure chambers  33  in the direction of the retard stops  34   b . This results in a relative change of the phase relation of the camshaft  6 ,  7  with respect to the crankshaft  2  in the direction of retarded timing. 
     In the third control position S 3  only the control port S communicates with the inflow port P, while the first and second working ports A, B are connected neither to the tank  49  nor to the outflow ports T, T a . Pressure medium is therefore neither conducted to the pressure chambers  35 ,  36  nor discharged therefrom. The vanes  27  are hydraulically clamped, whereby the phase relation of the inner rotor  23  relative to the outer rotor  22 , and therefore of the camshaft  6 ,  7  relative to the crankshaft  2 , is fixed. 
     In the fourth control position S 4 , both the first working port A and the control port S communicate with the inflow port P, while the second working port B is connected to the outflow port T. Pressure medium is therefore supplied by the pressure medium pump  47  to the first pressure chambers  35  via the control valve  37  and the first pressure medium lines  38   a . At the same time, pressure medium is discharged from the second pressure chambers  36  via the second pressure medium lines  38   b  and the control valve  37  to the tank  49 . The vanes  27  are therefore moved within the pressure chambers  33  in the direction of the advance stops  34   a . This results in a relative change of the phase relation of the camshaft  6 ,  7  with respect to the crankshaft  2  in the direction of advanced timing. 
     The control valve  37  is represented in  FIGS. 3   a - d . It consists of an actuating unit (not shown) and a hydraulic section  51 . The hydraulic section  51  consists of a substantially hollow-cylindrical valve housing  52  and a control piston  54 . The valve housing  52  has ports A, B, P, S, T, T a . With the exception of the axial outflow port T a , the ports A, B, P, S, T are in the form of openings in the cylindrical wall of the valve housing  52  which open into annular grooves formed in the outer lateral surface of the valve housing  52 . The working ports A, B communicate via openings in the camshaft  6 ,  7  respectively with the first and second pressure medium lines  38   a, b . The control port S communicates via openings in the camshaft  6 ,  7  with the first annular groove  50  of the inner rotor  23 , into which the control lines  48  open. 
     The outflow port T communicates via further openings in the camshaft  6 ,  7  with the second annular groove  53 , which is formed in the receptacle  40  of the inner rotor  23 . In this case the second annular groove  53  is connected to the exterior of the actuating device  11  via an axial bore  39 . 
     The ports A, B, P, S, T are offset axially from one another and arranged in the sequence: inflow port P, first working port A, outflow port T, second working port B, control port S. In this case, apart from the inflow port P, all the ports are arranged inside the receptacle  40  ( FIG. 2   b ). The inflow port P projects from the actuating device  11  in the axial direction. As a result, the pressure medium can be supplied to the control valve  37  outside the actuating device  11 . The need to provide a supply line, via which the pressure medium reaches the control valve  37 , inside the inner rotor  23  is thus eliminated. The architecture of the inner rotor  23  is thereby considerably simplified. 
     The axial outflow port T a  is embodied as an axial opening of the valve housing  52 . 
     The control piston  54  has a substantially hollow-cylindrical configuration and is arranged axially displaceably within the valve housing  52 . In this case, the axial position of the control piston  54  can be adjusted continuously by means of the actuating unit (not shown). The actuating unit acts against the force of a spring  55  which moves the control piston  54  to a starting position when the actuating unit is inactive. The spring  55  bears against a sheet-metal spring support  55   a  which is fastened in the axial opening that forms the axial outflow port T a . The actuating unit  50  may be in the form, for example, of an electrical actuating unit. 
     The control piston  54  has four control chambers  56   a,b,c,d  spaced axially from one another. In the embodiment illustrated the control chambers  56   a,b,c,d  are in the form of annular grooves in the outer lateral surface of the control piston  54 . With the exception of the fourth control chamber  56   d , the control chambers  56   a,b,c  communicate with the interior of the control piston  54  via piston openings  57   a,b,c . The control chambers  56   a - d  are each delimited by two annular webs  58   a - e . Here, the first annular web  58   a  delimits the first control chamber  56   a  in the direction of the axial outflow port T a  and the fifth annular web  58   e  delimits the inflow port P in the direction of the actuating unit (not shown). The second annular web  58   b  separates the first control chamber  56   a  from the fourth control chamber  56   d . The third annular web  58   c  separates the fourth control chamber  56   d  from the second control chamber  56   b . The fourth annular web  58   d  separates the second control chamber  56   b  from the third control chamber  56   c.    
     Depending on the relative position of the control piston  54  in relation to the valve housing  52 , the control chambers  56   a - d  communicate with different ports A, B, P, S, T, T a . 
     The first control chamber  56   a  is arranged in such a manner that communication can be established with the second working port B and the control port S. 
     The second control chamber  56   b  is arranged in such a manner that communication can be established with the first working port A. 
     The third control chamber  56   c  communicates with the inflow port P in all positions of the control piston  54 . 
     The fourth control chamber  56   d  is arranged in such a manner that communication can be established with the second working port B or with the first working port A. In this case the fourth control chamber  56   d  always communicates with the outflow port T. 
     The operation of the control valve  37  is explained with reference to  FIGS. 3   a - d . The figures differ with regard to the relative position of the control piston  54  in relation to the valve housing  52 . In  FIG. 3   a  the control valve  37  is shown in a state in which the actuating unit is inactive. The spring  55  urges the control piston  54  to the starting position in which it rests against a first stop  59 . In the following  FIGS. 3   b - c  the control piston  54  is offset relative to the valve housing  52  by an increasing travel distance against the force of the spring  55 . 
     In the state of the control valve  37  represented in  FIG. 3   a , pressure medium reaches the interior of the control piston  54  via the inflow port P, the third control chamber  56   c  and the third piston openings  57   c . From there, the pressure medium reaches the second working port B via the first piston openings  57   a  and the first control chamber  56   a . At the same time, a pressure medium flow to the control port S and the first working port A is blocked by the second and third annular webs  58   b,c  respectively. The first working port A is connected by means of the fourth control chamber  56   d  to the outflow port T, and the control port S is connected to the axial outflow port T a . 
     Consequently, pressure medium from the pressure medium pump  47  reaches the second pressure chambers  36  via the control valve  37 , while pressure medium is discharged to the tank  49  from the guide tracks  45  and the first pressure chambers  35 . The rotation angle limiting devices  42 ,  43  are therefore in the locked state and thus prevent a phase adjustment of the inner rotor  23  relative to the outer rotor  22 . 
     In  FIG. 3   b  the control piston  54  has been displaced by the distance x 1  relative to the valve housing  52  against the force of the spring  55 . Pressure medium which is supplied to the control valve  37  via the inflow port P reaches the first control chamber  56   a  via the interior of the control piston  54 , and from there reaches the second working port B and the control port S. At the same time a pressure medium flow to the first working port A is blocked by the third annular web  58   c . The first working port A continues to be connected to the outflow port T by means of the fourth control chamber  56   d . The first annular web  58   a  separates the control port S from the axial outflow port T a . 
     Consequently, pressure medium from the pressure medium pump  47  reaches the second pressure chambers  36  and the guide tracks  45  via the control valve  37 , while pressure medium is discharged to the tank  49  from the first pressure chambers  35 . 
     The rotation angle limiting devices  42 ,  43  are therefore switched to the unlocked state. At the same time, a phase adjustment in the direction of retarded timing takes place as a result of the pressure medium flow to the second pressure chambers  36  and the pressure medium discharge from the first pressure chambers  35 . 
     In  FIG. 3   c  the control piston  54  has been displaced by the distance x 2 &gt;x 1  relative to the valve housing  52  against the force of the spring  55 . Pressure medium which is supplied to the control valve  37  via the inflow port P reaches the first control chamber  56   a  via the interior of the control piston  54 , and from there reaches the control port S. At the same time a pressure medium flow to the two working ports A, B is blocked by the second and third annular webs  58   b,c  respectively. At the same time, the second and third annular webs  58   b,c  block the connection between each of the working ports A, B and the outflow port T. The first annular web  58   a  continues to separate the control port S from the axial outflow port T a . 
     Consequently, pressure medium from the pressure medium pump  47  reaches the guide tracks  45  via the control valve  37 , while pressure medium is neither supplied to the pressure chambers  35 ,  36  nor discharged therefrom. The actuating device  11  is therefore clamped hydraulically; that is to say, no phase adjustment takes place between the inner rotor  23  and the outer rotor  22 . 
     In  FIG. 3   d  the control piston  54  has been displaced by the distance x 3 &gt;x 2  relative to the valve housing  52  against the force of the spring  55 . Pressure medium which is supplied to the control valve  37  via the inflow port P reaches the first control chamber  56   a  via the interior of the control piston  54 , and from there reaches the control port S. At the same time, the pressure medium reaches the second control chamber  56   b  via the interior of the control piston  54  and the second piston openings  57   b , and from there reaches the first working port A. A connection between the inflow port P and the second working port B is blocked by the second annular web  58   b . Likewise, a pressure medium flow from the first working port A to the outflow port T is blocked by the third annular web  58   c . The second working port B is connected to the outflow port T by means of the fourth control chamber  56   d . The first annular web  58   a  continues to separate the control port S from the axial outflow port T a . 
     Consequently, pressure medium from the pressure medium pump  47  reaches the first pressure chambers  35  and the guide tracks  45  via the control valve  37 , while pressure medium is discharged from the second pressure chambers  36  to the tank  49 . 
     The rotation angle limiting devices  42 ,  43  are therefore switched to the unlocked state. At the same time, a phase adjustment in the direction of retarded timing takes place as a result of the pressure medium flow to the first pressure chambers  35  and the pressure medium discharge from the second pressure chambers  36 . 
     The control valve  37  illustrated serves, firstly, to regulate the phase relation of the inner rotor  23  relative to the outer rotor  22 . In addition, the locking states of the rotation angle limiting devices  42 ,  43  can be controlled by a separate control port S. By way of the separation of the control port S from the working ports A, B, the danger of unwanted locking or unlocking of the rotation angle limiting devices  42 ,  43  is reduced. In addition, the control logic regarding the control port S can be executed independently of those of the working ports A, B, and can therefore be tailored to the particular application. As a result of the pressure medium supply to one of the working ports B and to the control port S via a common control chamber  56   a , the structure of the control piston  54  is simplified. Instead of the five or six control chambers required in the prior art, the control valve  37  has only four control chambers  56   a - d  while having the same functionality. This leads to a significant simplification of the control piston  54 . Furthermore, the number of control edges (boundaries of the control chambers  56   a - d ), which are complex to produce, is reduced to a minimum. The control piston  54  can therefore be produced at lower cost and with greater process reliability. In addition, the control piston  54  can be designed shorter in the axial direction, considerably reducing the space requirement of the control valve  37 , which is located in space-critical regions of the internal combustion engine  1 . This applies both to embodiments as a plug-in valve (control valve  37  arranged outside the actuating device  11 ), in which the actuating unit and the hydraulic section  51  are connected to one another, and to central valve applications ( FIG. 2   b ), in which the hydraulic section  51  is embodied separately from the actuating unit and is arranged in the receptacle  40  of the actuating unit  11 . 
     Embodiments in which the first working port A and the control port S are reversed are also possible. 
     Reference Symbols 
     
         
           1  Internal combustion engine 
           2  Crankshaft 
           3  Piston 
           4  Cylinder 
           5  Traction drive 
           6  Inlet camshaft 
           7  Exhaust camshaft 
           8  Cam 
           9   a  Inlet gas exchange valve 
           9   b  Outlet gas exchange valve 
           10  Device 
           11  Actuating device 
           12  Hydraulic system 
           21  Sprocket 
           22  Outer rotor 
           23  Inner rotor 
           24  Side cover 
           25  Side cover 
           26  Hub element 
           27  Vane 
           28  Vane grooves 
           29  Circumferential wall 
         - 
           31  Axial opening 
           32  Fastening element 
           33  Pressure chamber 
           34  Boundary wall 
           34   a  Advance stop 
           34   b  Retard stop 
           35  First pressure chamber 
           36  Second pressure chamber 
           37  Control valve 
           38   a  First pressure medium line 
           38   b  Second pressure medium line 
           39  Axial bore 
           40  Receptacle 
           41  Locking mechanism 
           42  Rotation angle limiting device 
           43  Rotation angle limiting device 
           44  Locking pin 
           45  Guide track 
           46  Spring element 
           47  Pressure medium pump 
           48  Control line 
           49  Tank 
           50  First annular groove 
           51  Hydraulic section 
           52  Valve housing 
           53  Second annular groove 
           54  Control piston 
           55  Spring 
           55   a  Sheet-metal spring support 
           56   a  First control chamber 
           56   b  Second control chamber 
           56   c  Third control chamber 
           56   d  Fourth control chamber 
           57   a  First piston opening 
           57   b  Second piston opening 
           57   c  Third piston opening 
           58   a  First annular web 
           58   b  Second annular web 
           58   c  Third annular web 
           58   d  Fourth annular web 
           58   e  Fifth annular web 
           59  Stop 
         A First working port 
         B Second working port 
         P Inflow port 
         S Control port 
         T Outflow port 
         T a  Axial outflow port 
         x 1 -x 4  Displacement 
         S 1  First control position 
         S 2  Second control position 
         S 3  Third control position 
         S 4  Fourth control position