Abstract:
A camshaft adjuster ( 11 ) for a camshaft ( 35 ), by which cylinder valves ( 12 ) of an internal combustion engine are actuated, wherein through the use of the camshaft ( 35 ) late torques act on the camshaft adjuster ( 11 ) in a direction of later cylinder valve opening times when the cam is running-on, and opposing early torques act on the camshaft adjuster ( 11 ) in a direction of earlier opening times when the cam is running-off. The feeding and draining of pressure medium can be controlled by a control unit ( 20 ), wherein a torque mode or a pump mode can be selectively adjusted by the control unit ( 20 ), wherein primarily camshaft torques are used for building up pressure in the first partial chamber A or in the second partial chamber B in the torque mode, while the pressure build-up in the first partial chamber A or in the second partial chamber B in the pump mode is primarily by pressure medium provided by a pressure medium pump P.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a device for variably adjusting the timing of gas exchange valves of an internal combustion engine, having a hydraulic phase adjustment unit, wherein the phase adjustment unit can be placed in drive connection with a crankshaft and with a camshaft and has at least one advance chamber and at least one retardation chamber, to and from which pressure medium can be supplied and discharged via pressure medium lines, wherein a phase position of the camshaft relative to the crankshaft can be adjusted by means of a supply of pressure medium to the adjustment chambers. 
       BACKGROUND 
       [0002]    In modern internal combustion engines, devices for variably adjusting the timing of gas exchange valves are used to enable variable configuration of the phase position of a camshaft relative to a crankshaft within a defined angular range between a maximum advanced position and a maximum retarded position. For this purpose, a hydraulic phase adjustment unit of the device is integrated into a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train can be implemented for example as a belt, chain or gear drive. The phase adjustment speed and the pressure medium requirement are significant parameters of such devices. To enable the phase position to be adapted in an optimum manner to the various driving situations, high phase adjustment speeds are desirable. In the context of measures for reducing consumption, there is furthermore a demand for an ever smaller pressure medium requirement so as to enable the pressure medium pump of the internal combustion engine to be of smaller design or to enable the delivery rate to be reduced when using regulated pressure medium pumps. 
         [0003]    A device of this type is known for example from EP 0 806 550 A1. The device comprises a vane-type phase adjustment unit with a drive input element, which is in drive connection with the crankshaft, and a drive output element, which is connected to the camshaft for conjoint rotation therewith. A plurality of pressure spaces is formed within the phase adjustment unit, wherein each of the pressure spaces is divided into two oppositely acting pressure chambers by means of a vane. The vanes are moved within the pressure spaces by means of a supply of pressure medium to or discharge of pressure medium from the pressure chambers, which brings about a change in the phase position between the drive output element and the drive input element. In this case, the pressure medium required for phase adjustment is provided by a pressure medium pump of the internal combustion engine and is directed selectively to the advance or retardation chambers by means of a control valve. The pressure medium flowing out of the phase adjustment unit is directed into a pressure medium reservoir, the oil sump of the internal combustion engine. Phase adjustment is thus accomplished by means of the system pressure provided by the pressure medium pump of the internal combustion engine. 
         [0004]    A further device is known for example from U.S. Pat. No. 5,107,804 A. In this embodiment, the phase adjustment unit is likewise of the vane type, and a plurality of advance and retardation chambers is provided. In contrast to EP 0 806 550 A1, phase adjustment is not accomplished by supplying pressure medium to the pressure chambers by means of a pressure medium pump; instead, alternating moments acting on the camshaft are used. The alternating moments are caused by the rolling movements of the cams on the gas exchange valves, each of which is preloaded by a valve spring. In this case, the rotary motion of the camshaft is braked during the opening of the gas exchange valves and accelerated during closure. These alternating moments are transmitted to the phase adjustment unit, with the result that the vanes are periodically subjected to a force in the direction of the retardation stop and of the advance stop. As a result, pressure peaks are produced alternately in the advance chambers and the retardation chambers. If the phase position is supposed to be held constant, pressure medium is prevented from flowing out of the pressure chambers. In the case of a phase adjustment in the direction of earlier timing, pressure medium is prevented from flowing out of the advance chambers, even at times at which pressure peaks are being produced in the advance chambers. If the pressure in the retardation chambers rises owing to the alternating moments, this pressure is used to direct pressure medium out of the retardation chambers into the advance chambers, using the pressure of the pressure peak generated. Phase adjustment in the direction of later timing is accomplished in a similar way. In addition, the pressure chambers are connected to a pressure medium pump, although only to compensate for leaks from the phase adjustment unit. Phase adjustment is thus accomplished by diverting pressure medium out of the pressure chambers to be emptied into the pressure chambers to be filled, using the pressure of the pressure peak generated. 
         [0005]    Another device is known from US 2009/0133652 A1. In this embodiment, phase adjustment in the case of small alternating moments is accomplished, in a manner similar to the device in EP 0 806 550 A1, by supplying pressure to the advance chambers or the retardation chambers by means of a pressure medium pump while simultaneously allowing pressure medium to flow out of the other pressure chambers to the oil sump of the internal combustion engine. In the case of high alternating moments, these are used, as in the device in U.S. Pat. No. 5,107,804 A, to direct the pressure medium under high pressure out of the advance chambers (retardation chambers) into the retardation chambers (advance chambers). During this process, the pressure medium expelled from the pressure chambers is fed back to a control valve, which controls the supply of pressure medium to or discharge of pressure medium from the pressure chambers. The pressure medium passes via check valves within the control valve to the inlet port, which is connected to the pressure medium pump, wherein some of the pressure medium is expelled into the pressure medium reservoir of the internal combustion engine. 
         [0006]    EP 2 075 421 A1 discloses a valve for a camshaft adjuster. The valve comprises a valve piston which is arranged in a rotatable manner in a valve housing. Inlets and outlets for pressurized oil are arranged such that, by adjusting the valve piston, pressurized oil can be conducted to the adjustment chambers and to a locking mechanism. Here, the locking mechanism can be activated not only in an end position of the camshaft adjuster, that is to say at a stop in the retarded or advanced position, but also in an intermediate position. This permits mid-position locking, which may be expedient depending on the engine application. 
         [0007]    DE 198 50 947 presents a device for controlling the timing of an internal combustion engine, having at least one drive means, at least one camshaft with cams, at least one hydraulically actuable adjustment unit for adjusting the angle of relative rotation between the drive means and the camshaft, at least one hydraulic fluid supply device for charging the adjustment unit, and at least one positive control unit by means of which the hydraulic charging of the adjustment unit can be influenced at least at times and/or at least in part as a function of the absolute angle of rotation of the camshaft and/or of the cams. Here, a flow connection to the adjustment chambers is shut off in a targeted manner when pressure fluctuations caused by torques arise which would be imparted back to the adjustment chambers by the camshaft when cams are running on or running off. 
         [0008]    U.S. Pat. No. 6,186,104 B1 discloses a vane-type valve timing control device for an internal combustion engine, in which, between the pressure cells and the control valve which actuates them, there is connected a pressure distributor device which serves to suppress disturbance camshaft torques. For this purpose, for example during a retardation, the oil supply to the pressure cells is shut off when an advance torque arises. Conversely, during an advance, the oil supply to the pressure cells is shut off when a retardation torque arises. Similarly to DE 198 50 947, therefore, a return swing of the adjustment unit is suppressed owing to the adjustment of opposing camshaft torques. 
       SUMMARY 
       [0009]    The invention is based on the object of providing a device for variably adjusting the timing of gas exchange valves of an internal combustion engine, which device, while exhibiting a high phase adjustment speed, should have a lower oil requirement. 
         [0010]    The objective is met according to the invention by specifying a camshaft adjuster for a camshaft which serves to actuate cylinder valves of an internal combustion engine, wherein retardation torques in the direction of retarded cylinder valve opening times are imparted back to the camshaft adjuster by the camshaft when cams are running on, and oppositely directed advance torques in the direction of advanced cylinder valve opening times are imparted back to the camshaft adjuster by the camshaft when cams are running off, 
         [0011]    having a pressure chamber and having an adjusting means arranged in the pressure chamber, 
         [0012]    wherein the adjusting means divides the pressure chamber into a first chamber part and a second chamber part, 
         [0013]    wherein pressure medium can be supplied to the first and the second chamber part and pressure medium can be discharged from the first chamber part and second chamber part, 
         [0014]    such that the adjusting means can be moved by a pressure difference between the first chamber part and second chamber part, resulting in a rotation of the camshaft, 
         [0015]    wherein, when a relatively high pressure prevails in the first chamber part, the camshaft is rotated in the direction of advanced cylinder valve opening times, and when a relatively high pressure prevails in the second chamber part, the camshaft is rotated in the direction of retarded cylinder valve opening times, 
         [0016]    and wherein the supply and discharge of pressure medium can be controlled by means of a control device, 
         [0017]    wherein a torque mode or a pump mode can be selectively set by means of the control device, 
         [0018]    wherein in the torque mode, predominantly camshaft torques are utilized to build up pressure in the first chamber part or in the second chamber part, 
         [0019]    whereas in the pump mode, the pressure build-up in the first chamber part or in the second chamber part is realized predominantly by means of pressure medium provided by a pressure medium pump. 
         [0020]    In the prior art, two strategies have hitherto been followed for hydraulic camshaft adjustment: firstly, a provision of pressure medium by means of a pressure medium pump, generally an oil pump of an engine oil lubricating circuit, or a utilization of camshaft torques for generating the required adjustment pressure. The first strategy is also referred to as “oil pressure actuated” (OPA) and the second is referred to as “cam torque actuated” (CTA). The invention is now based on the realization that respective advantages of OPA and CTA methods can be expediently combined with one another as a function of an operating state of the internal combustion engine. In operating states in which a high pump pressure of the pressure medium pump is provided, the pump mode, that is to say an OPA method, is expediently selected, whereas in the event of low pump pressures but high camshaft torques, the torque mode, that is to say the CTA method, is used. Here, it is self-evidently possible for an adjustment in the CTA method to be assisted by the pressure medium pump in addition to the utilization of the camshaft torques, and vice versa. 
         [0021]    Here, the invention is not restricted to a particular design of camshaft adjuster, that is to say, for example, use may be made of a vane-type adjuster in which multiple pairs of chamber parts are formed, wherein the adjustment means is a vane which divides the chamber parts and which is for example formed in one piece from a rotor or plugged into said rotor. 
         [0022]    The control device preferably comprises a valve piston which is arranged in a valve housing, wherein the valve piston is rotatable and axially displaceable relative to the valve housing, wherein the torque mode or the pump mode can be set by means of axial relative displacement of the valve piston with respect to the valve housing, whereas the supply and discharge of pressure medium to and from the chamber parts can be controlled by means of relative rotation of the valve piston with respect to the valve housing. 
         [0023]    The switching positions for the pump mode and torque mode are thus realized in a structurally simple manner by means of an axial displacement of the valve piston relative to the valve housing. In a respective axial switching position, the actual regulation of the adjustment, that is to say the supply and discharge of pressure medium to and from the chamber parts, is then possible by means of a rotation of the valve piston relative to the valve housing. It is advantageous if, for the axial displacement, the valve piston is moved relative to a positionally fixed cylinder head, for example by means of a magnet and a restoring spring, whereas the relative rotation is performed by the valve housing, which rotates for example together with the camshaft. This embodiment is used in particular in a preferred central valve configuration in which the control valve, formed from valve piston and valve housing, of the control device is arranged centrally in the camshaft adjuster and furthermore preferably simultaneously, as a screw, connects said camshaft adjuster to the camshaft. In a further preferred embodiment, the restoring spring of the valve piston is in the form of a compression spring and mounted by means of rolling bearings with respect to the valve housing, or is in the form of a tensile spring and connected directly or indirectly to the magnet. 
         [0024]    It is preferable for first orifices and second orifices to be arranged in the valve housing so as to be distributed over the circumference of the valve housing, wherein the first orifices correspond with the second chamber part and the second orifices correspond with the first chamber part, and wherein the surface of the valve piston forms an orifice cover such that the first orifices and second orifices can be at least partially closed off by the orifice cover in accordance with the axial position and angular position of the valve piston relative to the valve housing. The orifice cover is thus for example a surface which is situated radially further outward than the rest of the valve piston body and which adjoins the valve housing. 
         [0025]    It is furthermore preferable for the first orifices and the second orifices to be arranged relative to one another on the circumference at an angular interval, in each case spaced apart uniformly, and arranged in the correct phase with respect to the orifice cover, such that a relative rotation of the valve piston with respect to the valve housing by the angular interval leads to a geometrically identical arrangement. It is furthermore preferable for the orifice cover to be designed so as to be adapted with regard to an asymmetrical displacement of camshaft torques in relation to the zero line. Such an asymmetrical displacement occurs in particular as a result of a friction torque which acts on the camshaft in the retardation direction in an angle-independent manner. In this way, the approximately sinusoidal curve of the camshaft profile is thus displaced, as a whole, by a magnitude corresponding to the friction torque. It may thus be advantageous for the respective local widths of the orifice cover to be adapted to the now shortened or lengthened effective times of an advance or retardation torque. For example, an orifice cover illustrated in a “developed” view would no longer correspond to a symmetrical rectangular waveform curve with maximum and minimum phases of equal length, but rather would have in each case different lengths for the maximum and minimum phases. 
         [0026]    This arrangement makes it possible in particular, without further structural measures such as for example check valves, for an adjustment process coordinated with the camshaft torques to be carried out solely on the basis of the geometric arrangement of the valve housing and valve piston. Since the camshaft torques arise in a fixed geometrical phase position owing to the arrangement of the cams, it is for example possible through corresponding arrangement of the orifices and orifice cover to achieve that, in a CTA method mode, torques acting in the correct direction for an adjustment are utilized by virtue of orifices being opened up, and torques acting in the wrong direction for an adjustment are suppressed by virtue of orifices being closed. 
         [0027]    It is preferable for the orifice cover to be formed from a first cover part for the first orifices and a second cover part for the second orifices, wherein the first cover part and the second cover part have in each case an edge situated axially at the outside on the valve piston and an axially inner edge, wherein the inner edges have an approximately crown-like profile in the circumferential direction with an axial position which alternates along the circumference. 
         [0028]    The inner edges thus run for example in a zigzag-like manner, a crown-like manner or in the form of a rectangular waveform curve in the circumferential direction, that is to say the inner edges run at a first axial position in regions and at an axially spaced apart position in further regions. This makes it possible, by means of the orifice cover, for the orifices in the valve housing to be entirely or partially opened up or blocked as a function of the relative rotation of valve piston and valve housing. Here, as described above, said opening up and blocking is geometrically coupled to the phase position of the camshaft torques. 
         [0029]    It is preferable if, for the relative axial position of the valve piston, five switching positions can be set, wherein 
         [0030]    in a first position, the pump mode is set for an adjustment of the camshaft in the direction of retarded cylinder valve opening times, 
         [0031]    in the second, axially subsequent switching position, the torque mode is set for an adjustment of the camshaft in the direction of advanced cylinder valve opening times, 
         [0032]    in the third, axially subsequent switching position, a camshaft adjustment is blocked, 
         [0033]    in the fourth, axially subsequent switching position, the torque mode is set for an adjustment of the camshaft in the direction of retarded cylinder valve opening times, and 
         [0034]    in the fifth, axially subsequent switching position, the pump mode is set for an adjustment of the camshaft in the direction of advanced cylinder valve opening times. 
         [0035]    These five switching positions thus generally yield adequate adjustment possibilities, in a manner adapted to the respective engine operating state. For example: whereas, when there is adequate pressure from the pressure medium pump, a retardation of the camshaft takes place in switching position one and an advance takes place in switching position five, it is possible in the case of low pressure, utilizing the camshaft torques, for a retardation to take place in switching position two and an advance to take place in switching position four. The middle position, switching position three, can be utilized for a blocking of the adjustment. 
         [0036]    These five switching positions are preferably realized as follows: 
         [0037]    Preferably, in the first switching position, upon the occurrence of retardation torques, a relative angular position of the valve housing and valve piston is set such that the first orifices are predominantly opened up by the orifice cover for a supply of pressure medium from the pressure medium pump, 
         [0038]    while the second orifices are open for a discharge of pressure medium, 
         [0039]    wherein, upon the occurrence of advance torques, a relative angular position of the valve housing and valve piston is set such that the first orifices are opened up by the orifice cover for a supply of pressure medium from the pressure medium pump, while the second orifices are opened up for a supply of pressure medium from the pressure medium pump and simultaneously for a discharge of pressure medium. 
         [0040]    Preferably, in the second switching position, upon the occurrence of advance torques, a relative angular position of the valve housing and valve piston is set such that the second orifices are predominantly opened up by the orifice cover for a supply of pressure medium from the first chamber part and the first orifices are open for a discharge of pressure medium from the first chamber part into the second chamber part, wherein, upon the occurrence of retardation torques, a relative angular position of the valve housing and valve piston is set such that the second orifices are blocked by the orifice cover, while the first orifices are substantially opened up for a supply of pressure medium from the pressure medium pump. 
         [0041]    Preferably, in the third switching position, a relative angular position of the valve housing and valve piston is set such that the first orifices are blocked by the orifice cover upon the occurrence of advance torques and the second orifices are blocked by the orifice cover upon the occurrence of retardation torques. 
         [0042]    Preferably, in the fourth switching position, upon the occurrence of retardation torques, a relative angular position of the valve housing and valve piston is set such that the first orifices are predominantly opened up by the orifice cover for a supply of pressure medium from the second chamber part, while the second orifices are open for a discharge of pressure medium from the second chamber part into the first chamber part, wherein, upon the occurrence of advance torques, a relative angular position of the valve housing and valve piston is set such that the first orifices are blocked by the orifice cover, while the second orifices are substantially opened up for a supply of pressure medium from the pressure medium pump. 
         [0043]    Preferably, in the fifth switching position, upon the occurrence of advance torques, a relative angular position of the valve housing and valve piston is set such that the second orifices are predominantly opened up by the orifice cover for a supply of pressure medium from the pressure medium pump, while the first orifices are open for a discharge of pressure medium, wherein, upon the occurrence of retardation torques, a relative angular position of the valve housing and valve piston is set such that the first orifices are opened up by the orifice cover for a supply of pressure medium from the pressure medium pump and simultaneously for a discharge of pressure medium, while the second orifices are opened up for a supply of pressure medium from the pressure medium pump. 
         [0044]    The feature, specified for the above switching positions, of an orifice being predominantly opened up means that the predominant part of its cross section is not blocked by the orifice cover. This corresponds to an intensely dethrottled state. This embodiment is not imperatively necessary but rather is merely a preferred embodiment, in particular with the advantage that, owing to the substantially unrestricted pressure medium throughflow, there is no risk of air induction. In this way, hydraulic rigidity is ensured, and the generation of disturbing noises is also prevented. In contrast to conventional systems in which an axial displacement of a control piston generally causes an orifice to be opened up to a continuously increasing extent corresponding to the axial actuating movement, the rotation of the orifice cover over or away from a relatively large orifice in the valve housing results in the abrupt opening-up of a large cross section, and therefore the desired dethrottling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    Further features of the invention will emerge from the following description and from the drawings, which illustrate exemplary embodiments of the invention in simplified form. In the drawings: 
           [0046]      FIG. 1  shows, highly schematically, an internal combustion engine, 
           [0047]      FIG. 2  is a schematic illustration of a control valve, 
           [0048]      FIG. 3  shows a valve piston and a valve housing, 
           [0049]      FIG. 4  is an illustration of the camshaft torques as a function of the rotational angle of the camshaft, 
           [0050]      FIGS. 5-14  are schematic illustrations of the different switching positions in the case of an OPA method, 
           [0051]      FIG. 15  is an illustration of the change in flow rates at different control edges as a function of the switching position in the OPA method, 
           [0052]      FIG. 16  is an illustration of the opening of the control edges as a function of the switching position in the OPA method, 
           [0053]      FIGS. 17-20  are schematic illustrations of the different switching positions in the case of a CTA method, 
           [0054]      FIG. 21  is an illustration of the change in the flow rates at different control edges as a function of the switching position in the CTA method, and 
           [0055]      FIG. 22  is an illustration of the opening of the control edges as a function of the switching position in the CTA method. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0056]      FIG. 1  illustrates an internal combustion engine  1 , with a piston  3  which is connected to a crankshaft  2  being indicated in a cylinder  4 . In the illustrated embodiment, the crankshaft  2  is connected via in each case one traction mechanism drive  5  to an intake camshaft  6  and an exhaust camshaft  7 , wherein a first and a second camshaft adjuster  11  for variably adjusting the timing of gas exchange valves  9 ,  10  of an internal combustion engine can effect a relative rotation between the crankshaft  2  and the camshafts  6 ,  7 . Cams  8  of the camshafts  6 ,  7  actuate one or more intake gas exchange valves  9  or one or more exhaust gas exchange valves  10 . The intake gas exchange valves  9  and the exhaust gas exchange valves  10  will hereinafter be referred to for short as cylinder valves  12 . It may likewise be provided that only one of the camshafts  6 ,  7  is equipped with a device  11 , or only one camshaft  6 ,  7  is provided, which is equipped with a camshaft adjuster  11 . The intake camshaft  6  and the exhaust camshaft  7  will hereinafter be summarized under the expression “camshaft  35 ”. 
         [0057]      FIG. 2  is a schematic illustration of a control device  20 . The control device  20  comprises a valve housing  29  and a valve piston  27  arranged therein. In the example shown, the control valve  20  is arranged with one end in a camshaft  35 . There, the valve piston  27  is acted on by a restoring spring  31 . The restoring spring  31  is mounted by means of an axial bearing arrangement  33  in the form of a rolling bearing. The valve piston  27  is connected, at its end remote from the camshaft  35 , to a magnet piston  23  which can be moved axially by an electromagnet  21 . A rotation prevention means  25  connects the magnet piston  23  to the valve piston  27  such that the latter cannot rotate. It is self-evidently also conceivable for an axial movement to be performed by the valve housing  29  and a rotational movement to be performed by the valve piston  27 , with a correspondingly changed configuration of the surroundings. 
         [0058]      FIG. 3  shows the valve piston  27  and the valve housing  29  in a perspective view. The valve housing  29  has first orifices  41  distributed about its circumference. Arranged axially offset with respect to the first orifices  41  and approximately in the center of the valve housing  29  are circumferentially distributed third orifices  45 . Following these with an axial offset are, in turn, second orifices  43  which are arranged at the same position in the circumferential direction as the first orifices  41 . The valve piston  27  is inserted in the correct rotational position into the hollow valve housing  29 . The valve piston  27  has, on its surface  53 , an orifice cover  51  which is formed by a radially elevated part of the surface  53 . The orifice cover has, at one axial end of the valve piston  27 , a first cover part  51 A, and at the opposite end, a second cover part  51 B. The two cover parts  51 A,  51 B are of crown-like design, that is to say they form a ring around the surface  53  with a respective outer edge BT, AT. The outer edge BT of the first cover part  51 A simultaneously forms one axial end of the valve piston  27 , whereas the outer edge AT of the second cover part  51 B simultaneously forms the other axial end of the valve piston  27 . That inner edge PB, PA of the cover parts  51 A,  51 B which is directed axially toward the center of the surface  53  has a rectangular serration. Here, in each case one crown serration  52  of a cover part  51 A,  51 B is oriented in the circumferential direction so as to lie between two crown serrations  52  of the other cover part  51 B,  51 A, wherein there is however an axial spacing between the inner edges PB, PA. 
         [0059]    The valve piston  27  should now be arranged in the valve housing  29  in the correct rotational position such that the orifice cover  51  opens up and blocks the first orifices  41  and second orifices  43 , respectively, for the correct phase position in each case. A supply of pressure medium to chamber parts of a pressure chamber, and therefore also the adjustment of the phase position of the camshaft, is controlled in this way. This will be explained in detail further below. 
         [0060]      FIG. 4  shows, based on the example of a four-cylinder engine, the profile of the camshaft torques, plotted in the y direction, versus the rotational position of the camshaft, plotted in the x direction. A constant torque resulting from friction of the camshaft at a constant rotational speed is neglected here. Camshaft torques greater than zero correspond to a torque in the direction of an advance, that is to say in a direction which leads to earlier opening of the cylinder valves  12 . Camshaft torques less than zero correspond to a torque in the direction of a retardation, that is to say in a direction which leads to later opening of the cylinder valves  12 . It can be seen that the camshaft torques have an approximately sinusoidal profile as a function of the rotational position of the camshaft. At fixed angular positions in each case, advance torques arise, which alternate with retardation torques. This is now utilized in a targeted manner for the adjustment of the camshaft. 
         [0061]    In  FIG. 5 , a switching position for the adjustment of the camshaft is schematically plotted such that the orifice cover  51  of the valve piston  27  is illustrated in a developed view in a plane. The first cover part  51 A thus yields a rectangular profile with the inner edge PB and a straight outer edge BT. Illustrated opposite, then, is the second cover part  51 B with the inner edge PA and the outer edge AT. At the outer edge AT, the valve piston  27  is connected to the restoring spring  31 , which presses the valve piston  27  against a magnet  21  (not illustrated here). 
         [0062]    Also schematically illustrated are the first orifices  41  and the second orifices  43 , as they are arranged relative to the orifice cover  51  corresponding to the axial position and rotational position of the valve housing  29  relative to the valve piston  27 . The first orifices  41  correspond to a second chamber part B, and the second orifices  43  correspond to a first chamber part A. The chamber parts A, B are divided by a vane  67  which forms an adjustment means  67  and which divides a pressure chamber  69  into the chamber parts A, B. The vane  67  is connected to a rotor  65  of a camshaft adjuster  11 . The pressure chamber  69  is formed in a stator  63  of the camshaft adjuster  11 . A first oil duct  71  leads to the first chamber part A, a second oil duct  73  leads to the second chamber part B. Only a detail of the camshaft adjuster  11  is shown here. The camshaft adjuster  11  is designed as a vane-type adjuster and has a plurality of pressure chambers, chamber parts, vanes and supply ducts, which are not illustrated here for the sake of clarity. 
         [0063]    In the example of  FIG. 5 , an adjustment of the camshaft takes place in the direction of later opening times of the cylinder valves  12 : pressurized oil is supplied to the second chamber part B and is discharged from the first chamber part A. In the switching position shown here, the first cover part  51  substantially opens up the first orifices  41  by means of the inner edge PB, such that pressurized oil passes from a pump P via the third orifices  45  in the valve housing  29  to the second chamber part B. At the same time, the second orifices  43  are opened up slightly by the outer edge AT of the second cover part  51 B, such that oil can be discharged from the first chamber part A into a tank T. The pressure difference thus generated between the chamber parts A, B leads to a force being exerted on the vane  67  and therefore on the rotor  65  in a rotational direction to the left. The rotor  65  is connected to the camshaft  35 . The camshaft  35  is thus rotated in the “retardation” direction. 
         [0064]    As a result of the great extent to which the first orifices  41  are opened up, intense dethrottling is attained, as a result of which the risk of air induction is greatly reduced. Discharge control is realized through the lesser opening-up of the second orifices  43  to the tank. 
         [0065]      FIG. 5  shows, on the right adjacent to the schematic illustration of the valve piston  27  and the first and second orifices  41 ,  43  of the valve housing, the profile, known from  FIG. 4 , of the camshaft torques as a function of the rotational angle of the camshaft  35 . The valve housing  29  and therefore the first and second orifices  41 ,  43  now rotate in a defined manner relative to said camshaft profile, as shown by the juxtaposition. The first and second orifices in  FIG. 5  are therefore precisely synchronous with a retardation camshaft torque. This has the effect that the second orifices  43  receive a pressure peak in the direction of a retardation, as a result of which the oil situated in the first chamber part A can be quickly discharged. Furthermore, the oil pressure of the pump P acts via the widely opened, intensely dethrottled first orifices  41  into the second chamber part B. The result is a very fast adjustment of the camshaft  35 . A fast adjustment in the advance direction is also realized in a corresponding way. 
         [0066]      FIG. 6  shows an image corresponding to  FIG. 5 , but here, the first and second orifices  41 ,  43  have been rotated relative to the orifice cover  51 . This corresponds in terms of time to the occurrence of an advance camshaft torque. The first orifices  41  are opened up only to a small extent by the first cover part  51 A, whereas the second orifices  43  are opened up to a great extent for the supply of pressure from the pump P. The pump P acts on both chamber parts A, B. In chamber part B, said pump now acts counter to an advance torque, as a result of which compensation is substantially attained, and no adjustment takes place. Chamber part A is traversed by a flow of pressure medium and emptied into the tank T. 
         [0067]      FIGS. 5 and 6  show a switching position for a “retardation” adjustment, in which an adjustment method based on the “oil pressure actuated” (OPA) principle is realized, specifically in a retardation adjustment direction. This switching position, which thus predominantly utilizes the adjustment force of the pump and in which camshaft torques have merely an assisting action, is realized by means of the illustrated axial position of the valve piston  27 . The axial switching position is set by means of the magnet  21 . In the example shown, this is the basic position without energization of the electromagnet  21 . As explained, in the axial switching position, different rotational positions of the valve piston  27  relative to the valve housing  29  are realized, and in this way the corresponding camshaft torques are additionally utilized.  FIGS. 7 and 8  show the corresponding illustration for an “advance” adjustment. Here, the actions for the chamber parts A, B are interchanged, but otherwise the explanations made with regard to  FIGS. 5 and 6  apply analogously. 
         [0068]      FIG. 9  shows an intermediate position in which, upon the occurrence of a retardation torque, the second orifices  43  are completely blocked. In this way, an adjustment is blocked. Correspondingly,  FIG. 10  shows complete blocking of the first orifices  41  upon the occurrence of an advance torque.  FIGS. 9 and 10  therefore depict an axial switching position of the valve piston  27  in which an adjustment of the camshaft  35  should be prevented, that is to say said camshaft should be held in a defined relative angular position with respect to the crankshaft. 
         [0069]      FIGS. 5 to 10  show switching positions in which a high pressure of the pump P is available, that is to say generally an operating state of the internal combustion engine at high rotational speeds. If, however, the available pressure of the pump P is not high, in particular is considerably lower than the pressure exerted by camshaft torques, a suitable OPA method can be set through the selection of further switching positions. This will be described on the basis of  FIGS. 11-14 . 
         [0070]      FIG. 11  corresponds to  FIG. 5 . It is thus sought to realize an adjustment in the “retardation” direction. Here, the retardation torque aids the adjustment. In  FIG. 12 , upon the occurrence of an advance torque, it is clear that, owing to the axial position of the valve piston  27  which has now changed in relation to  FIG. 6 , complete coverage of the first orifices  41  is attained. Whereas, therefore, in  FIG. 6  only a high pump pressure was available for compensating the advance torque with the first orifices  41  slightly open, in the case of a low pump pressure the advance torque is suppressed by a complete blockage of the first orifices  41 .  FIGS. 13 and 14  again show the corresponding illustration in the case of an “advance” adjustment. 
         [0071]    The switching positions illustrated above can thus be summarized as follows: two OPA adjustment methods are provided, one in the case of low pump pressure and one in the case of high pump pressure. The axial switching positions can be abbreviated as follows: 
         [0072]    Switching position I: high pump pressure, retardation adjustment,  FIGS. 5 ,  6   
         [0073]    Switching position II: low pump pressure, retardation adjustment,  FIGS. 11 ,  12   
         [0074]    Switching position III: blocked adjustment,  FIGS. 9 ,  10   
         [0075]    Switching position IV: low pump pressure, advance adjustment,  FIGS. 13 ,  14   
         [0076]    Switching position V: high pump pressure, advance adjustment,  FIGS. 7 ,  8   
         [0077]    The advantage of this adjustability lies in particular in the fact that, by means thereof, in the case of high pump pressure and a torque which counteracts the desired adjustment direction, the inflow openings  41  and  43  to the respective chamber parts A, B are not fully closed, as a result of which the pump power, which is higher than the relatively low camshaft torque, can nevertheless still be utilized for adjustment despite the oppositely acting camshaft torque. The times at which oppositely acting camshaft torques arise can thus be utilized for the adjustment, resulting in a fast adjustment. If, however, the pump power is lower than the camshaft torques, the oppositely acting torques are suppressed by means of the completely closed orifices  41  and  43 , such that no reverse adjustment takes place. 
         [0078]      FIG. 15  illustrates how the throughflow of pressure medium at the respective inner and outer edges PA, PB, BT, AT changes as a function of the switching position. Here, dashed lines illustrate profiles at times with a camshaft torque in the advance direction, and solid lines illustrate profiles at times with camshaft torques in the retardation direction. The line for the inner edge of the first cover part  51 A, PB, will be explained by way of example: In the case of camshaft torques in the retardation direction, the throughflow at the inner edge PB is high in all axial positions, whereas in the case of torques in the advance direction, from switching position I to switching position II and subsequent switching positions, said throughflow falls quickly to zero. 
         [0079]      FIG. 16  schematically shows, for switching positions I-V, the degree of opening of the orifices  41 ,  43  as viewed from the respective inner edges PB, PA and outer edges BT, AT as a function of the switching positions I-V and the adjusting direction. Fully hatched fields correspond to a completely blocked orifice  41 ,  43 , fully white fields correspond to a completely open orifice  41 ,  43 , and partially hatched fields correspond to a partially blocked orifice  41 ,  43 . 
         [0080]    The statements made up to this point relate to an adjustment method in which adjustment is carried out predominantly by means of the pressure provided by the pump P and in which pressure generated by camshaft torques has an assisting action in suitable switching positions. It is now sought below to describe, in addition to a pump mode of said type, a torque mode in which predominantly the pressure peaks generated by camshaft torques are utilized for adjustment, while the pressure provided by the pump P possibly assists the adjustment. 
         [0081]      FIG. 17  shows an illustration corresponding to the illustrations of  FIGS. 5-14 , for the purpose of explaining a retardation adjustment by means of the utilization of the retardation torques. Here, the orifice cover  51  is set by means of the axial position of the valve piston  27  such that, upon the occurrence of a retardation torque, a connection of the two chamber parts A and B is created via the first and second orifices  41 ,  43 . Here, the first orifices  41  are opened to a great extent, such that intense dethrottling, and therefore a low risk of air induction, are again attained. The second orifices  43  are opened to a small extent in order to realize discharge control from the first chamber part A. As a result of the camshaft torque which causes rotation in the retardation direction, a pressure peak is now built up which, by means of the different opening ratios of the first and second orifices  41 ,  43 , generates a higher pressure in the first chamber part A than in the second chamber part B, and therefore, with a displacement of oil from the first chamber part A into the second chamber part B, causes a displacement of the vane  67  and therefore an adjustment of the camshaft  35  in the retardation direction. Oil from the pump P which arrives via the third orifices  45  assists said adjustment and compensates for leakage losses. 
         [0082]      FIG. 18  shows the same axial switching position as  FIG. 17 , but here, the relative rotational position between the valve piston  27  and valve housing  29  has been changed, because now the camshaft  35  is in a rotational position in which an advance torque arises. Since it is still sought to realize a retardation adjustment (unchanged axial position of the valve piston  27 ), said advance torque must be suppressed with regard to its adjustment action. For this purpose, the first cover part  51 A completely blocks the first orifices  41 . Oil therefore cannot escape from the second chamber part B, and no adjustment takes place. The complete shut-off prevents a return swing. Via fully open second orifices  43 , and therefore in an intensely dethrottled manner, the pump P pumps oil in an adjustment-neutral manner into the first chamber part A. Induction of air is prevented in this way. 
         [0083]      FIGS. 19 and 20  show positions corresponding to  FIGS. 18 and 19 , but for the opposite advance adjustment direction. 
         [0084]    A particularly expedient sequence of switching positions can now be established by selecting axially successive switching positions as follows: 
         [0085]    Switching position I: pump mode (OPA), retardation adjustment,  FIGS. 5 ,  6   
         [0086]    Switching position II: torque mode (CTA), advance adjustment,  FIGS. 19 ,  20   
         [0087]    Switching position III: blocked adjustment,  FIGS. 9 ,  10   
         [0088]    Switching position IV: torque mode (CTA), retardation adjustment,  FIGS. 17 ,  18   
         [0089]    Switching position V: pump mode (OPA), advance adjustment,  FIGS. 7 ,  8   
         [0090]    It is therefore possible, depending on the presence either of a dominating pressure of the pump P or of dominating camshaft torques for the camshaft adjustment, to set either a pump mode or a torque mode.  FIG. 21  again illustrates, for said sequence of switching positions, how the throughflow of pressure medium at the respective control edges, that is to say inner and outer edges PA, PB, AT, BT varies as a function of the axial position of the valve piston  27  and of the valve housing  29 , that is to say the switching positions I-V. 
         [0091]      FIG. 22  schematically shows, for the switching positions I-V, the degree of opening of the orifices  41 ,  43  as viewed from the respective inner edges PB, PA and outer edges BT, AT as a function of the switching positions I-V and the adjustment direction. Fully hatched fields correspond to a completely blocked orifice  41 ,  43 , fully white fields correspond to a completely open orifice  41 ,  43 , and partially hatched fields correspond to a partially blocked orifice  41 ,  43 . 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Internal combustion engine 
           2  Crankshaft 
           3  Piston 
           4  Cylinder 
           5  Traction mechanism drive 
           6  Intake camshaft 
           7  Exchaust camshaft 
           8  Cam 
           9  Intake gas exchange valve 
           10  Exhaust gas exchange valve 
           11  Camshaft adjuster 
           12  Cylinder valve 
           20  Control device 
           21  Magnet 
           23  Magnet piston 
           25  Rotation prevention means 
           27  Valve piston 
           29  Valve housing 
           31  Restoring spring 
           33  Axial bearing arrangement 
           35  Camshaft 
           41  First orifices 
           43  Second orifices 
           45  Third orifices 
           51  Orifice cover 
           51 A First cover part 
           51 B Second cover part 
           52  Crown serrations 
           53  Valve piston surface 
           63  Stator 
           65  Rotor 
           67  Vane 
           69  Pressure chamber 
           71  First oil duct 
           73  Second oil duct 
         A First chamber part 
         B Second chamber part 
         P Pressure medium pump 
         T Tank 
         PA Inner edge of the second cover part  51 B 
         PB Inner edge of the first cover part  51 A 
         AT Outer edge of the second cover part  51 B 
         BT Outer edge of the first cover part  51 A