Abstract:
A hydraulic camshaft adjuster, including a rotor and a stator and a hydraulic medium management system, by which at least two chambers separated by a rotor-fixed vane can be or are connected to a hydraulic medium supply device and/or hydraulic medium discharge device by an interposed hydraulic valve, wherein the vane contains a switchable hydraulic medium control device designed for selective release and interruption of a fluid connection from one chamber to the other chamber. A locking device for excluding a rotational movement between the rotor and the stator locks the rotor to the stator in a vane position in which the volume of the two chambers is approximately equal, and includes a pin, interlockable with a stator-fixed component, designed to control the inflow and/or outflow of hydraulic medium to/from a chamber.

Description:
[0001]    The present invention relates to a vane-type hydraulic camshaft adjuster, which includes a rotor and a stator as well as a hydraulic medium conducting system, such as an oil conducting system, which has at least one first, second and third hydraulic medium line, at least two chambers separated by a rotor-fixed vane being connectable or connected to a hydraulic medium supply and/or hydraulic medium discharge device with the aid of the oil conducting system by interposing a hydraulic valve, a switchable hydraulic medium control device being furthermore present in the vane, which is designed to selectively release and interrupt a fluid connection, such as a line, a channel or an opening, from one chamber to the other chamber, a locking device being additionally present for preventing a rotational movement between the rotor and the stator, the locking device being designed to lock the rotor to the stator in a vane position, in which the vane is situated between the two end stop positions, i.e., between ADVANCE and RETARD, and/or in which the two chambers have a volume of approximately the same size, i.e., the vane is in a central position, and the locking device including at least one pin which is able to establish a form-locked fit with a stator-fixed component or is engaged therewith, such as a locking pin, a locking bolt, a locking piston or a locking journal. 
       BACKGROUND 
       [0002]    A locking bolt in a vane-type camshaft adjuster is already known from the prior-art EP 1 371 818 A2. 
         [0003]    A vane-type hydraulic camshaft adjuster is also known from WO 2009/114500 A1, a center-locking mechanism, in which the vane is locked in a central position, being implemented with the aid of a locking pin. 
         [0004]    Hydraulic camshaft adjuster systems having center-locking mechanisms as well as hydraulic camshaft adjuster systems which operate according to the vane principle are thus known. They make it possible to adjust the control times of an internal combustion engine during engine operation. 
         [0005]    When starting the engine, if the oil pressure in the engine has not yet been built up, a hydraulic camshaft adjuster must be mechanically fixed. This is necessary to prevent uncontrolled oscillation and thus a noise development. “Startup rattling” should also be mentioned in this connection, which should be stopped. An end stop locking in a so-called “RETARD” or “ADVANCE” position is standard practice here. The vane of the rotor strikes the stator. The movement in the other rotation direction is prevented by a mechanical locking element. This element may be placed axially or radially in the camshaft adjuster. 
         [0006]    A mechanical fixing of the rotor between the two RETARD and ADVANCE end stops is rarely implemented but is being required more and more of automotive manufacturers. One speaks of a center-locking mechanism in this case. Due to the fact that few energy sources may be tapped during the center-locking process, and the initial position may be on the retard or advance side, a center-locking is much more difficult to implement than an end stop locking in the retard or advance position. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide an improvement in the area of center-locking, in particular such an improvement that a better control is achieved at lower rotational speeds, resulting in a good control which may be implemented independently of the engine control unit. 
         [0008]    The fact that the adjustment is greatly dependent on the existing camshaft alternating torque during engine operation is to be prevented. This may present a problem at negative engine oil temperatures, i.e., when temperatures are far below 0° C. Namely, the friction in the camshaft bearing increases significantly in this state, so that in sum a camshaft alternating torque undergoes a unilateral shift. This means that an extremely pronounced camshaft alternating torque is present in the adjusting direction toward RETARD, while a very small camshaft alternating torque is present in the other adjusting direction, namely toward ADVANCE. The center-locking mechanism built into this adjusting system works only in connection with a so-called CTA system (Camshaft Torque-Actuated System). At present, this function cannot be integrated into a conventional hydraulic camshaft adjusting system (OPA system—Oil Pressure-Actuated System), a situation which, however, is to be changed. 
         [0009]    The present invention provides a hydraulic camshaft adjuster having a pin, preferably assembled as a locking or control piston, to control the inflow and/or outflow of hydraulic medium to/from a chamber. 
         [0010]    In this way, a reliable center-locking mechanism is implemented, so that the engine, i.e., the internal combustion engine, may always start the next time the engine is started. The rotor may be locked relative to the stator in its center-locking position while the internal combustion engine is stopped, independently of the angle position of the vane in the stator prior to stopping the internal combustion engine and within the shortest period of time. No adjustment at the engine control unit is required. Furthermore, no additional installation space outside the camshaft adjuster is needed. 
         [0011]    In this way, a hydraulic freewheeling locking mechanism is ultimately implemented. It is activated when the hydraulic valve is deenergized. The freewheeling locking mechanism is deactivated again as soon as the hydraulic valve is energized for the purpose of an adjustment. The hydraulic valve may be activated by an engine control unit by interposing a magnet of variably determinable strength. 
         [0012]    Advantageous specific embodiments are explained in greater detail below. 
         [0013]    It is thus advantageous if the locking device includes two locking pins, namely an advance locking pin and a retard locking pin. In this way, a movement of the vane into the advance chamber and also into the retard chamber is preventable. 
         [0014]    To achieve a mechanically loadable locking, it is advantageous if the stator-fixed component is designed as a sealing cover which includes at least one or two preferably kidney-shaped recesses for the form-locked accommodation of one or both locking pins at least on one side. The kidney shape has advantages for the engagement of one or both pins with this/these recess(es) to facilitate a problem-free resting of the corresponding pin against the recess/recesses on at least one side. In this way, at least one form-locked fit is forced in one rotation direction. 
         [0015]    It has also proven to be advantageous if the advance locking pin is designed to engage with the stator-fixed component when the vane is in an ADVANCE adjustment position or in a central position, and/or when the retard locking pin is designed to engage with the stator-fixed component when the vane is in a RETARD adjustment position or in the central position. Instead of an engagement from the front, an engagement from behind may also be desired. 
         [0016]    To ensure a failsafe adjustability even if the oil pressure drops, it is advantageous if the locking pin is spring-loaded in such a way that it is pushed out of the rotor in the absence of a counter-force. 
         [0017]    It is also advantageous for the function if the advance locking pin is designed to interrupt a first hydraulic medium line to a chamber, for example the advance chamber, in its state extended from the rotor. 
         [0018]    The hydraulic medium control device may be designed to be particularly cost-effective if the switchable hydraulic medium control device includes a control piston having an oil conducting groove running around its outer circumferential surface. 
         [0019]    If the control piston is spring-preloaded in such a way that it is pushed into a position which releases the fluid connection in the absence of a counter-force, and/or via a second hydraulic medium line to the control piston upon the provision of hydraulic pressure, it is pushed into a position which interrupts the fluid connection, and/or the second hydraulic medium line is also designed, situated or connected for conducting hydraulic medium to one or both locking pins, for the purpose of providing a counter-force against the existing spring. The spring is a mechanical spring, such as a tension spring or a pressure spring, in particular a helical spring, which may also be used elsewhere to provide spring force. 
         [0020]    One advantageous exemplary embodiment is also characterized in that a first check valve is situated on or in the fluid connection in the vane to prevent the hydraulic medium flow from the one chamber into the other chamber, preferably from the advance chamber into the retard chamber, and/or a second check valve is present in another vane in the opposite active direction to the first check valve. In the first of the two cases, a progression of the vane in the ADVANCE direction is achieved, while in the second of the two cases, a progression in the RETARD direction is ensured. 
         [0021]    For a good force distribution, it is advantageous if four or five vanes are present, distributed equally on the rotor. 
         [0022]    In other words, one could also say that the hydraulic camshaft adjusting system having a center-locking mechanism includes a hydraulic camshaft adjuster and a hydraulic valve. The hydraulic valve may be designed as a cartridge valve or a central valve. 
         [0023]    In addition to the known standard components, such as a rotor and a stator, the camshaft adjuster also has a (further) locking unit, a check valve and a control piston unit in each vane. Each control piston unit, in turn, includes a control piston, a pressure spring and a guiding element. A bore is introduced into the control piston itself. Parallel thereto, bores are also provided in each vane, which connect an advance chamber (chamber A) to a retard chamber (chamber B) in each chamber pair. This connection is also interruptible by the control pistons. For this purpose, oil pressure must be applied to the control pistons, which must be pushed against the pressure spring. A check valve is situated in or on one of the multiple existing vanes. A check valve may be designed as a ball check valve or a plate check valve. Similar types of check valves may also be used. This prevents the oil, which is used as the hydraulic medium, from flowing out of first chamber A into a first chamber B, i.e., from the advance chamber into the retard chamber. 
         [0024]    In the other vanes connected to the rotor, the oil may flow in both directions. In one modification, however, a check valve may also be installed therein, which also operates, as needed, in an active direction other than that of the first check valve. It is advantageous if a first check valve, which acts in a first direction, is inserted into a first vane, and a second check valve, which acts opposite the active direction of the first check valve, is inserted into a second vane. 
         [0025]    Two locking pins are inserted into the locking device. 
         [0026]    A first locking pin is referred to as the advance locking pin, and a second locking pin is referred to as the retard locking pin. The retard locking pin prevents an oscillation of the vane in the RETARD direction and conversely the advance locking pin prevents an oscillation in the ADVANCE direction. It is, however, worth noting that the advance locking pin, which could also be referred to as the locking piston, has a circumferential groove, with the aid of which an additional switching function is achievable, using the hydraulic medium, such as oil. 
         [0027]    In the locked state, the advance locking pin separates the oil line between the hydraulic valve and the advance chamber (chamber A 1 ). In the unlocked state, this connection is reestablished. The other chambers (A n ) remain unaffected by this interruption and are always connected to the hydraulic valve. 
         [0028]    The hydraulic valve is a proportional valve having five ports and four piston positions. The ports are the oil feed, the oil discharge, chamber ports A and B and control line C. All ports are either open or closed, depending on the piston position in the hydraulic valve. 
         [0029]    The strategy in this process is that the camshaft adjuster finds the center-locking position itself and remains there until it is unlocked again. The locking action is initiated by the “ignition off” signal when the internal combustion engine, i.e., the motor, stops. 
         [0030]    Directly afterwards, the hydraulic valve is deenergized, and the camshaft adjuster begins to move in the direction of the center-locking position. If the camshaft adjuster was in the adjustment angle between RETARD and the center-locking position, the adjustment must take place in the ADVANCE direction. However, if the camshaft adjuster was in the angle position between ADVANCE and the center-locking position, the adjustment must take place in the RETARD direction. Depending on the adjusting direction, the adjustment takes place in different ways. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The adjusting system and the principle are explained in greater detail below with the aid of a drawing. The different exemplary embodiments are illustrated therein. 
           [0032]      FIG. 1  shows a schematic function representation of a hydraulic camshaft adjuster, including components participating in the functioning, during the locking operation from RETARD while the engine is stopped; 
           [0033]      FIG. 2  shows the hydraulic camshaft adjuster from  FIG. 1  during the locking operation from ADVANCE with a center stop; 
           [0034]      FIG. 3  shows the camshaft adjuster from  FIGS. 1 and 2  during a normal adjustment from ADVANCE to RETARD in an operating internal combustion engine; 
           [0035]      FIG. 4  shows the camshaft adjuster in the first exemplary embodiment in  FIGS. 1 through 3  during an adjustment from RETARD to ADVANCE while the internal combustion engine is running; 
           [0036]      FIG. 5  shows the camshaft adjuster from the first exemplary embodiment in a locked center-locking position; 
           [0037]      FIG. 6   a  shows a partially transparent representation of a camshaft adjuster according to the present invention in the first specific embodiment; 
           [0038]      FIG. 6   b  shows a partial sectional perspective view of the hydraulic camshaft adjuster in the first exemplary embodiment, from a front side; 
           [0039]      FIG. 7  shows a perspective view of the camshaft adjuster from  FIG. 6  from a rear side; 
           [0040]      FIG. 8  shows a section of the camshaft adjuster from  FIGS. 6 and 7  in the area of a hydraulic medium control device accommodating a control piston; 
           [0041]      FIG. 9  shows a representation of the camshaft adjuster in a view from the front; 
           [0042]      FIG. 10   a  shows a sectional view of the camshaft adjuster from  FIG. 9  along line X, when the camshaft adjuster is in the locked state; 
           [0043]      FIG. 10   b  shows a sectional view of the camshaft adjuster from  FIG. 9  along line X, when the latter is in the unlocked state; 
           [0044]      FIG. 11   a  shows a sectional view of the camshaft adjuster from  FIG. 9  along line XI, when a fluid connection in the vane, e.g., a bore, a line, a channel or an opening, is unblocked; 
           [0045]      FIG. 11   b  shows a sectional view of the camshaft adjuster from  FIG. 9  along line XI, when the fluid connection is blocked; 
           [0046]      FIG. 12   a  shows a sectional view of the camshaft adjuster from  FIG. 9  along line XII, in the locked state; 
           [0047]      FIG. 12   b  shows a sectional view along line XII of the camshaft adjuster from  FIG. 9  along line XII in the unlocked state; 
           [0048]      FIG. 13  shows a cross section of the camshaft adjuster from  FIG. 11   a  along line XIII; 
           [0049]      FIG. 14  shows a sectional view of the camshaft adjuster from  FIG. 11   b  along line XIV, a transverse bore in the vane, namely the fluid connection, being blocked, unlike in the switching position shown in  FIG. 13 ; 
           [0050]      FIG. 15  shows a longitudinal sectional view of the camshaft adjuster from  FIG. 11   a  or  11   b  along line XV; 
           [0051]      FIG. 16  shows a second exemplary embodiment of a hydraulic camshaft adjuster according to the present invention, in which a second check valve is mounted in a second vane, which acts in a direction other than that of a first check valve in a first vane, the camshaft adjuster being shown during the locking operation from RETARD while the engine is stopped; 
           [0052]      FIG. 17  shows a representation of the camshaft adjuster from  FIG. 16  in a switching position during the locking operation from ADVANCE while the engine is stopped; and 
           [0053]      FIG. 18  shows the representation of the camshaft adjuster from the second exemplary embodiment during a normal adjustment from ADVANCE to RETARD while the internal combustion engine is running. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    The figures are only schematic and are used only for the sake of understanding the present invention. Identical elements are provided with identical reference numerals. Not all important elements are illustrated, and certain elements are illustrated which are not absolutely necessary for the present invention. 
         [0055]      FIG. 1  shows a first specific embodiment of a hydraulic camshaft adjuster  1 . This camshaft adjuster  1  is of the vane type and uses a hydraulic medium, such as oil. A hydraulic conducting system  2  is present, which could also be referred to as an oil conducting system. It includes a first hydraulic medium line  3 , a second hydraulic medium line  4  and a third hydraulic medium line  5 . 
         [0056]    Camshaft adjuster  1  has, as usual, a stator  6  and a rotor  7 . 
         [0057]    A hydraulic medium supply and/or hydraulic medium discharge device  8  is connected to one end of first, second, third hydraulic medium lines  3  through  5 . Hydraulic medium supply and/or hydraulic medium discharge device  8  includes an oil supply device  9  and an oil discharge device  10 . A hydraulic valve  11  is connected between hydraulic medium conducting system  2  and hydraulic medium supply and/or hydraulic medium discharge device  8 . Hydraulic valve  11  is situated between a spring element  12  and an electromagnet  13 . Electromagnet  13  is supplied with variable current via an engine control unit, whereby the hydraulic valve or a piston in hydraulic valve  11  is movable. 
         [0058]    Chambers  14  divided by vanes  15  are provided between stator  6  and rotor  7 . An advance chamber  16  is present on the one side of each vane  15 , and a retard chamber  17  is present on the other side of particular vane  15 . 
         [0059]    A hydraulic medium control device  18  is present in each vane  15 . Hydraulic medium control device  18  includes at least one control piston  19 . Control piston  19  is situated in all vanes in such a way that it is hydraulically actuatable and is resettable by a spring  20 , and a fluid connection  21  between the two chambers  16  and  17  may selectively open or close. For this purpose, control piston  19  has a circumferential groove, which may be present inside control piston  19  or on its circumference. A straight channel may also be formed, which may have a partially open or closed cross section. 
         [0060]    A first check valve  22  is also present in at least one vane  15 . 
         [0061]    As shown in the second exemplary embodiment, with reference to  FIG. 16 , a second check valve  23  may also be inserted into another vane  15 , this second check valve  23  acting in the opposite direction than first check valve  22 , i.e., it closes instead of opens when oil flows from retard chamber  17  into advance chamber  16 . 
         [0062]    To return to  FIG. 1 , let it be noted that a locking device  24  is present, which includes two locking pins  25 . Locking pins  25  may establish a form-locked fit with a recess  26  or multiple recesses  26 , as illustrated in  FIGS. 6   a  and  6   b.    
         [0063]    Recess  26  may also be kidney-shaped for each of the two locking pins  25 . There is also a locking pin  25  to be referred to as advance locking pin  27  as well as a locking pin  25  to be referred to as retard locking pin  28 . These two locking pins  25  may come into form-locked contact with locking contour  29  on a stator-fixed component, such as a sealing cover. Both locking pins  25  are spring-preloaded via a spring  30 . A feed line of the second hydraulic medium line is present on the side of the locking pins facing away from the spring to be able to build up counter-pressure to spring  30 . 
         [0064]    Advance locking pin  27  is provided with hydraulic medium conducting contours, in particular for interrupting first hydraulic medium line  3 , as illustrated in  FIG. 1 . 
         [0065]    Advance locking pin  27  may also be provided with reference letter F, just as retard locking pin  28  may be provided with reference letter S. First hydraulic medium line  3  may also be designated by capital letter A, while second hydraulic medium line  4  may be designated by capital letter C and third hydraulic medium line  5  may be designated by capital letter B. 
         [0066]    Advance locking pin  27  is movably supported in rotor  7 , namely in the axial direction of the assembly, as is retard locking pin  28 . They may also be radially movably supported. 
         [0067]    By deenergizing the hydraulic valve in the case of the adjustment from the retard side when the engine is stopped, for the purpose of reaching a center-locking position and establishing a lock therein, oil pressure is applied to all retard chambers  17  in camshaft adjuster  1 . At the same time, all advance chambers  16  (i.e., all A chambers) are closed off by hydraulic valve  11 . No more oil is able to flow out of advance chambers  16  into a tank, i.e., reach oil discharge device  10 . 
         [0068]    In addition, the C port on the hydraulic valve is connected to the tank port, i.e., to oil discharge device  10 . As a result, all control pistons  19  move into the position in which no oil pressure is applied and release the short-circuit bores between the two chambers  16  and  17 . 
         [0069]    Parallel thereto, the locking gates are also depressurized. Consequently, the two locking pistons  25 , i.e., advance locking pin  27  and retard locking pin  28 , are able to drop into the locking gates. In the case of an adjustment angle on the retard side, however, only advance locking piston  27  is able to do this. Retard locking piston  28  is not situated opposite its locking gate and remains pressed back in rotor  7 . Since advance locking piston  27  is designed as a switching element, the oil line between chambers A 1  and A 2  is again interrupted. This is necessary to completely close chamber A 1 . 
         [0070]    Camshaft adjuster  1  now begins to oscillate, due to the still existing camshaft alternating torque. Its oscillation in the desired ADVANCE adjusting direction presses the oil out of retard chambers  17  into advance chambers  16  via fluid connections  21  in vanes  15 , which are designed as (short-circuit) bores. 
         [0071]    An oscillation in the negative RETARD direction is not possible. Check valve  22  in first advance chamber  16  is closed during this movement, and the camshaft alternating torque may be supported on the oil cushion in advance chamber A 1 . On the whole, this results in a kind of freewheeling movement. Rotor  7  progresses from an arbitrary retard position in the ADVANCE direction until advance locking piston  27  comes to a stop at the locking gate or locking contour  29 . At the same time, retard locking piston  28  is opposite an open locking position and may also lock therein. 
         [0072]    Camshaft adjuster  1  is now locked or mechanically fixed in a predefined lock position. Since the time between “ignition off” and the engine coming to a stop may be too short, and the camshaft adjuster may be unable to reach the center-locking position, a brief engine after-run of, e.g., 0.2 seconds may assist here. The exact time depends on the engine and must be ascertained through testing. 
         [0073]    Another option is to overcome the residual adjustment angle when restarting the engine. The starter of the internal combustion engine alone generates sufficient camshaft alternating torques, which set the freewheeling in motion and adjust camshaft adjuster  1  in the direction of the center-locking position. 
         [0074]    The oil pressure is also built up again when the engine starts. This helps to fill the supporting oil chamber, i.e., advance chamber  16  (A 1 ), with oil and support the camshaft alternating torque in the ADVANCE direction. 
         [0075]      FIG. 2  shows the adjustment from the advance side to the retard side while the engine is stopped, for the purpose of locking in the middle of the locking position. The adjustment in the RETARD direction differs from the adjustment in the ADVANCE direction primarily due to two features: 
         [0076]    For a start, retard locking piston  28  is now locked and advance locking piston  27  is still pressed back in rotor  7 . As a result, the oil line to chamber A 1 , i.e., to advance chamber  16 , is not interrupted. Consequently, rotor  7  may also no longer be supported on the oil cushion in chamber A 1 . 
         [0077]    The second distinguishing feature is the adjustment itself. The friction torque of the camshaft in the bearings is used for the adjustment. This friction torque always and reliably acts in the RETARD direction. Only the level of the friction torque is dependent on the engine oil temperature, which, in turn, affects the adjustment time. Should camshaft adjuster  1  fail to lock in the center-locking position (CLP), the locking operation is automatically resumed the next time the engine restarts and is locked until the first ignition spark. 
         [0078]      FIGS. 3 and 4  show the adjustment in both adjusting directions while the internal combustion engine is running During the engine operation, camshaft adjuster  1  may be adjusted in both adjusting directions via the center-locking positions. Port C on hydraulic valve  11  is permanently connected to oil supply P, i.e., to oil supply device  9 . All control pistons  19  in vane  15  are thereby pressed into vanes  15  and interrupt the short-circuit bores, i.e., fluid connections  21 . An oil exchange between advance and retard chambers  16  and  17  may take place. At the same time, locking pistons  25 , i.e., advance locking pin  27  and retard locking pin  28 , are pressed into rotor  7 . Advance chamber  16  (A 1 ) is thus connected to hydraulic valve  11 , as are the other A chambers. 
         [0079]    When camshaft adjuster  1  is fixed in the center-locking position, i.e. when it is locked, both locking pins  25 , i.e., both advance locking pin  27  and retard locking pin  28 , are in contact with locking contour  29 . Locking contour  29  is situated between the two. 
         [0080]    A camshaft adjuster, including a central valve, is depicted from both sides, partially in a sectional view and partially in a transparent view, in  FIGS. 6   a ,  6   b  and  7 . A first check valve  22 , made of sheet metal and having a sheet thickness of 0.25 mm, is situated on the advance chamber side of vane  15 . Advance locking pin  27  may also be designated as locking piston F and is designed as a switching element. Four control pistons  19 , including a spring  20  and a guiding element, are situated in equal distribution in camshaft adjuster  1 , namely in rotor  7 , and explicitly in vanes  15 . Screwed-on sealing cover  31  is also readily apparent in  FIG. 7 , as is toothing  32  situated on the outside of the stator. 
         [0081]      FIG. 8  shows a detail in a longitudinal sectional view of the camshaft adjuster from  FIGS. 6   a  through  7 , special attention having been given to control piston  19  as part of hydraulic medium control device  18 . 
         [0082]      FIG. 9  shows a view of the camshaft adjuster along the longitudinal axis, screw connections  33 , which may also be designed as rivet connections, being provided on inwardly extending projections  34  of stator  6 . 
         [0083]    In  FIGS. 10   a  and  10   b , the locked state of camshaft adjuster  1  is visualized on the one hand, and the unlocked state of camshaft adjuster  1  is visualized on the other hand. A locking spring  35  is supported on a cartridge  36 , and on particular locking pin  25 , i.e., on a locking piston  25 , represented here, in particular, as retard locking pin  28 . 
         [0084]      FIGS. 11   a  and  11   b  show, firstly, the state in which fluid connection  21  designed as a bore is unblocked ( FIG. 11   a ) and, secondly, the state in which it is blocked ( FIG. 11   b ). Control piston  19  supports spring  20 , which may also be referred to as the control piston spring, on one side in such a way that the control piston spring is caught between a guiding element  37  and control piston  19 . 
         [0085]      FIG. 12   a  shows the locked state, while  FIG. 12   b  shows the unlocked state. Advance locking pin  27  is illustrated. 
         [0086]    Fluid connection  21  is designed as a transverse bore, as is readily apparent from  FIGS. 13 and 14 . In  FIG. 13 , the transverse bore is open, although the camshaft adjuster is in the locked state. In  FIG. 14 , the camshaft adjuster is in the locked state, and the transverse bore is blocked. 
         [0087]    The potential adjusting directions from ADVANCE to RETARD or from RETARD to ADVANCE are apparent from  FIG. 15 , reference being made to rubbing sealing elements  38  on the outer circumference of vanes  15 . 
         [0088]      FIGS. 16 through 18  show a second exemplary embodiment, which differs from the first exemplary embodiment primarily in that second check valve  23  is inserted into a different vane  15  than first check valve  22 . 
         [0089]    The flow directions of the hydraulic medium, i.e., the oil, are shown by double-thick arrows over fluid connections  21  and particular hydraulic medium lines  3  through  5 . The active principle corresponds to that of the first exemplary embodiment; however, a progression of the rotor into a position, i.e., the placement of vanes  15  into a center-locking position, is now possible in both directions. A hydraulic freewheeling in two directions is thus provided, which is selectively actuatable. 
         [0090]    It is worth noting that retard locking pin  28  is also designed to interrupt a hydraulic medium line, namely third hydraulic medium line  5 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  camshaft adjuster 
           2  hydraulic medium conducting system 
           3  first hydraulic medium line 
           4  second hydraulic medium line 
           5  third hydraulic medium line 
           6  stator 
           7  rotor 
           8  hydraulic medium supply and/or hydraulic medium discharge device 
           9  oil supply device 
           10  oil discharge device 
           11  hydraulic valve 
           12  spring element 
           13  electromagnet 
           14  chamber 
           15  vane 
           16  advance chamber 
           17  retard chamber 
           18  hydraulic medium control device 
           19  control piston 
           20  spring 
           21  fluid connection 
           22  first check valve 
           23  second check valve 
           24  locking device 
           25  locking pin/piston 
           26  recess 
           27  advance locking pin/locking piston 
           28  retard locking pin/locking piston 
           29  locking contour/locking gate 
           30  spring of the locking pin/locking piston 
           31  sealing cover 
           32  toothing 
           33  screw connection 
           34  projection 
           35  locking spring 
           36  cartridge 
           37  guiding element 
           38  sealing element