Abstract:
a cam adjuster for adjusting the angle-of-rotation positions of a cam shaft relative to a crankshaft. The cam shaft adjuster has at least two operating chambers to which pressure oil can be supplied to change the angle-of-rotation position. At least one of the operating chambers can be deactivated depending on an operating parameter by blocking the pressure oil supply.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This applications is a 371 of PCT/EP2010/053343 filed Mar. 16, 2010, which in turn claims the priority of DE 10 2009 015 882.0 filed Apr. 1, 2009. 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 camshaft adjuster. Furthermore, the invention relates to a method for adjusting the angle-of-rotation position of a camshaft relative to a crankshaft for an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     DE 100 84 408 B4 discloses a camshaft adjuster of vane cell design, the driving clement of which, in the form of a driving toothed wheel, is driven by a crankshaft via a traction element, such as a chain or a belt. A “stator,” in which a rotor is arranged rotatably in order to produce an actuating angle, is connected to the driving wheel for rotation therewith. The rotor is connected to a camshaft for rotation therewith. A relative angular position between the camshaft and driving wheel, and therefore the crankshaft, can be influenced according to the actuating angle, this being associated with a change in the engine timings. In an embodiment of vane cell design, the rotor has vanes which are displaceable in the circumferential direction, depending on a hydraulic pressure in control chambers of the stator, in order to produce an actuating angle. On the side facing away from the camshaft, the stator is formed by a disk which delimits the control chambers in the axial direction. The ratios of force between the rotor and stator can influenced, in addition to the hydraulic ratios in the region of the vanes, by a torsion spring, the base points of which are supported on the stator and on the rotor. The torsion spring is arranged on that side of the disk which faces away from the rotor, with a plurality of turns about the longitudinal axis. The radially outer base point is supported in relation to the stator via screws which serve at the same time to fasten the disk in the stator. The radially inner base point of the torsion spring is bent in a U-shaped manner and engages in a form-fitting manner around a rectangular partial cross-section of a supporting element. The supporting element furthermore has a cylindrical extension with which said supporting element extends through a central bore in the disk so as to permit relative rotation. The extension is connected in the stator to the camshaft for rotation therewith, in particular via an end side of the rotor. 
     A pin which is referred to in the document as a locking pin is guided displaceably in a bore of the rotor parallel to the longitudinal axis of the camshaft adjuster, wherein the axial position of the pin can be influenced by the ratios of force of a compression spring and/or the hydraulic ratios in the region of end surfaces of the pin. The disk of the stator has a corresponding recess which is oriented in the axial direction and is in the form of a blind hole. For an activated position of the pin, in particular a starting position, intermediate position, central position, advanced or retarded position, the pin emerges with an end region out of the rotor and enters the recess of the disk of the stator such that the degree of freedom of rotation between the rotor and stator is limited. 
     OBJECT OF THE INVENTION 
     The present invention is based on the object of providing a camshaft adjuster which requires particularly little oil. It is a further object of the invention to provide a corresponding method for adjusting the angle-of-rotation position of a camshaft relative to a crankshaft. 
     SUMMARY OF THE INVENTION 
     According to the invention, the object directed towards a camshaft adjuster is achieved by the provision of a camshaft adjuster for adjusting the angle-of-rotation position of a camshaft relative to a crankshaft, with at least two working chambers to which pressure oil can be supplied to change the angle-of-rotation position, wherein at least one of the working chambers can be cut off depending on an operating parameter by the supply of pressure oil being blocked. 
     The invention is based on the finding that the pressure transmission ratio, which is at the basis of the torque, which is imparted by the pressure oil, for rotating the camshaft, is decisively determined by ratios at a low pressure. The pressure transmission ratio of a camshaft adjuster is selected in such a manner that reliable adjustment is still possible even at a low engine oil pressure. The pressure transmission ratio follows here from the size and number of the working chambers and the size of the operative surfaces of the actuating elements, i.e. the vane surfaces in the case of a vane cell adjuster. As the engine oil pressure rises, a higher actuating torque therefore occurs. In this case, the actuating torque exceeds a value which would actually be sufficient for reliable and sufficiently rapid adjustment. Therefore, by definition of the requirement at low oil pressure, resources are given away at a higher oil pressure. In particular, it is endeavored to configure the oil pump of an internal combustion engine to be as small as possible, this being limited by the requirement of the oil consumers. A lower oil requirement in the adjustment of a camshaft would therefore be advantageous. 
     The invention now achieves this by at least one of the working chambers of the camshaft adjuster being configured so as to be able to be cut off. That is to say, depending on an operating parameter, in particular the oil pressure, the supply of oil to one of the working chambers is prevented and, as a result, the oil requirement is reduced. In an operating state in which the torque provided for adjusting the camshaft is sufficient even without said working chamber, the reduction of the quantity of oil does not result in any impairment of the operation. 
     The camshaft adjuster is advantageously of vane cell design, each working chamber being divided by a respective vane into two sub chambers, and the pressure oil being supplied to one of the two chambers, depending on the desired direction of the change in the angle-of-rotation position, in such a manner that said sub chamber is increased and the second sub chamber is reduced. Owing to the fact that a vane cell adjuster is in any case divided into a plurality of working chambers, this construction is particularly suitable for being adapted to an operating state because of the possibility of cutting off a working chamber. 
     The supply of pressure oil can preferably be blocked by an actuating body, the actuating position of which is determined by the pressure of the pressure oil. The actuating body furthermore preferably has a resetting spring, the spring force of which is directed counter to the actuating effect of the pressure oil. This configuration results in a particularly simple mechanism for cutting off the working chamber. The rising pressure of the pressure oil acts here directly on the actuating body in such a manner that, from a certain pressure, said actuating body prevents the supply of pressure oil to the working chamber. The resetting force of a spring serves to set the cut-off value for the pressure. 
     Preferably, when the working chamber is cut off, a short-circuiting pressure oil connection is produced at the same time between the two sub chambers of said working chamber. This ensures that the cut-off working chamber does not cause any impermissible delay in the adjusting operation because of the oil which continues to remain therein. The short-circuiting pressure oil connection permits the movement of the actuating element, driven by the other working chambers which remain active, within the cut-off working chamber. In this case, the actuating element displaces oil via the short-circuit between the two sub chambers of the working chamber without being impermissibly severely braked as a result. The cutting off of the working chamber and the short-circuit of the pressure oil are furthermore preferably brought about simultaneously by an actuating body. 
     Preferably, at least two working chambers can be cut off, the first working chamber being able to be cut off at a first value of the operating parameter, and the second working chamber being able to be cut off at a second value of the operating parameter, which value is greater than the first value. By means of this configuration, it is possible to even more finely adapt the oil required to the particular operating state. As the pressure rises and therefore the torque available for the adjustment operation also rises, first of all a first working chamber and then a second chamber or even further chambers can be cut off. When the cut-off mechanism is configured as described above with the actuating body and resetting spring, this gradual adaptation can be realized in a simple manner by a dedicated cut-off mechanism having a resetting spring of respectively differing strength being provided for each working chamber. 
     The actuating body is preferably of double-action design in such a manner that, depending on the direction of the change in the angle-of-rotation position, the working chamber can be cut off by the supply of pressure oil either to the first or second sub chamber being blocked. A mechanism is therefore provided by means of which both the first and the second sub chamber can be cut off. It is therefore possible to use a single cut-off mechanism for both possible actuating directions to cut off the working chamber. 
     A locking mechanism is preferably provided, by means of which an adjustment of the angle-of-rotation position can be blocked, wherein the blocking of the supply of pressure oil can also be set by the locking mechanism. Furthermore preferably, at a first oil pressure, the locking mechanism releases the supply of pressure oil counter to the force of a first spring and, at a second, higher oil pressure, blocks the supply of pressure oil counter to the force of a second spring. Therefore, both locking of the adjuster and cutting off of the working chamber are brought about by a single mechanism. 
     According to the invention, the object directed towards a method is achieved by provision of a method for adjusting the angle-of-rotation position of a camshaft relative to a crankshaft, in which pressure oil can be supplied into the working chambers of a camshaft adjuster having at least two working chambers to change the angle-of-rotation position, wherein the supply of pressure oil to at least one of the working chambers is blocked if a predetermined pressure of the pressure oil is exceeded, while the supply of pressure oil to at least one of the remaining working chambers remains open. 
     The advantages of a method of this type correspond to the advantages of the camshaft adjuster described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail by way of example with reference to the drawing, in which: 
         FIG. 1  shows a three-dimensional illustration of a half-longitudinal section of a camshaft adjuster; 
         FIG. 2  shows a rotor of a camshaft adjuster; 
         FIG. 3  shows a three-dimensional illustration of a cross-section through a rotor of a camshaft adjuster; 
         FIG. 4  shows a longitudinal section through a rotor of a camshaft adjuster; 
         FIG. 5  shows a cross-section through a rotor of a camshaft adjuster with a cut-off mechanism; 
         FIG. 6A  shows a cut-off mechanism with a short-circuit effect for the sub chambers; 
         FIG. 6B  shows a schematic illustration for cutting off a working chamber by means of the cut-off device according to  FIG. 6A  in the cut-off position; 
         FIG. 7A  shows a double-action cut-off mechanism with a short-circuit effect for the sub chambers; 
         FIG. 7B  shows a schematic illustration for cutting off a working chamber by means of the cut-off device according to  FIG. 7A  in the cut-off position; 
         FIG. 7C  shows a schematic illustration for cutting off a working chamber by means of the cut-off device according to  FIG. 7A  in the working position; and 
         FIG. 8  shows a cut-off mechanism which is designed at the same time as a locking mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a camshaft adjuster  1 . The camshaft adjuster  1  is by way of example a camshaft adjuster of vane cell design, although, in principle, any other type of camshaft adjuster, in which the adjustment takes place via the supply of pressure medium into a plurality of working chambers, can be used. 
     The camshaft adjuster  1  has a driving wheel  2  via which said camshaft adjuster is connected in terms of drive to a crankshaft. The driving wheel  2  is connected to a stator  3  for rotation therewith, the stator being formed with a pot-shaped housing  4  and a housing cover  5 . The interior, which is delimited by the housing  4  and housing cover  5 , is divided into two sub spaces located axially next to each other via a circular-ring-shaped disk  6  which is oriented transversely with respect to a longitudinal axis  7 - 7  of the camshaft adjuster  1 . The sub space facing the camshaft accommodates, in a manner not illustrated and with the formation of control chambers, the rotor  8  which has vanes and which is connected or braced to a threaded bore on the end side of the camshaft with the use of a central screw (not illustrated). A torsion spring  16  which extends with multiple turns about the longitudinal axis  7 - 7  is connected in between the stator  3  and rotor  8 . The sub space arranged on that side of the disk  6  which faces away from the camshaft forms an annular space  10  encircling around the longitudinal axis  7 - 7 . The annular space  10  is sealed in the contact region between the housing  4  of the stator  3  and housing cover  5  by the interconnection of a sealing plate  11  which can be braced between the housing  4  and housing cover  5  by fastening screws  12  being tightened. 
       FIG. 2  shows the rotor  8  of a camshaft adjuster  1 . The outer circumference of the rotor  8  has five vanes  21 . Each of said vanes  21  is arranged in a working chamber  41  (not illustrated specifically here), said working chambers being formed by the stator  2  (not illustrated) and the rotor  8 . A vane  21  divides the particular working chamber thereof into two sub chambers  41 A,  41 B. The working and sub chambers are illustrated schematically further on in  FIG. 4 . Each sub chamber  41 A,  41 B can be supplied with oil by an oil duct  29 ,  31  or can be emptied via said oil duct  29 ,  31 . In order to adjust the camshaft in a first actuating direction, oil is supplied for this purpose, for example, to each sub chamber  41 A on the left of a vane  21 , while the other sub chamber  41 B in each case is opened towards the tank and emptied. In the reverse, second actuating direction, the supply and removal of oil take place the other way around. In this case, the oil is supplied to and removed from the camshaft via the rotor hub. In the view in  FIG. 2 , a first cut-off mechanism  25  and a second cut-off mechanism  27  can be seen. Said cut-off mechanisms  25 ,  27  are each connected upstream of the oil duct  29 ,  31  of a sub chamber  41 A,  41 B. Corresponding cut-off mechanisms which act for the other actuating direction, are provided on the opposite side (not visible) of the rotor. The function of the cut-off mechanisms  25 ,  27  is described in more detail with reference to  FIG. 3 . 
     It becomes clear in  FIG. 3  in the cross-section through the rotor from  FIG. 2  how a cut-off mechanism is advantageously constructed. An actuating body  35  is pressed into a basic position by means of a spring  33 , which sits on a spring support  26 , and, by means of an annular groove  36  arranged in the surface of the actuating body, opens up the oil duct  29  to supply oil to a sub chamber  41 A. A bypass  37  branches off here from the oil duct  29  and opens out into a recess  39 . The actuating body  35  is adjacent to said recess  39 . When pressure oil is supplied via the oil duct  29 , a force is therefore also exerted on the actuating body  35 , said force being directed counter to the spring force of the spring  33 . As the pressure rises, the actuating body  35  is displaced counter to the spring force and, in the process, by displacement of the opening annular groove  36 , gradually closes the oil duct  29  until, finally, the supply of oil is cut and the working chamber  41  is therefore cut off. The value for the oil pressure at which the cutting off takes place can be set in a simple manner by selecting the spring constants of the spring  33 . According to the configuration in  FIG. 2 , two working chambers can thereby be cut off. In this case, the spring constant of the first cut-off mechanism  25  is selected to be smaller than the spring constant of the otherwise structurally identical second cut-off mechanism  27 . A graduated cutting off of the two working chambers thereby occurs: at a first, lower oil pressure, the first working chamber  41  cuts off while, at a second, higher oil pressure, the second working chamber  41  is additionally cut off. The oil requirement can thereby be set in a manner adapted to the operating state. 
     It can be seen in  FIG. 4  how respective cut-off mechanisms  25  for sub chambers  41 A,  41 B are respectively arranged on the front side and on the rear side of the rotor  8  according to the particular actuating direction. The arrangement of the cut-off mechanism as described above is illustrated once again in a cross-section in  FIG. 5 . 
       FIG. 6A  shows a further configuration of the cut-off mechanism in a cross-section, wherein here, as illustrated schematically in  FIG. 6B , only a single cut-off mechanism is provided for both sub chambers  41 A,  41 B. In this case, the actuating body  35  has an annular groove  67  in such a manner that, upon displacement of the actuating body  35  by increasing oil pressure, the supply of oil from an oil duct  51  is cut and at the same time a short-circuit line  65 , which connects the two sub chambers  41 A,  41 B to each other in terms of flow, is opened. By this means, the working chamber  41  is cut off, but at the same time, in spite of the lack of flow of oil out of the working chamber, the vane  21  is prevented from being hydraulically fixed. An adjustment via the action of the other working chambers  41  continues to be possible since the oil in the cut-off working chamber  41  can be displaced from one sub chamber  41 A,  4113  into the other sub chamber  41 A,  41 B via the short-circuit connection  65 . 
     The cut-off mechanism in  FIG. 6A  is advantageously of double-action design such that cutting off is possible for both actuating directions. This is illustrated in  FIG. 7A , The actuating body is now arranged between two springs  33  and has a plurality of grooves  67 A,  67 B in such a manner that the supply of oil firstly to the sub chamber  41 A and the next time to the sub chamber  41  B is blocked in both directions of displacement, wherein, in both cases, a short-circuit connection  65  between the sub chambers  41 A,  41 B is set by the blocking of the supply of oil and therefore the cutting off of the working chamber  41 . The switching state “working chamber in operation” is shown schematically in  FIG. 7C  and the switching state “working chamber cut off” is shown schematically in  FIG. 7B . 
     Finally,  FIG. 8  shows a further configuration of a cut-off mechanism  25 , wherein only part of the spring  33  and of the spring support  26  are shown. A locking pin  73  is in engagement with the spring support  26  and, at a first oil pressure, is released counter to the spring force of a locking spring  71  from a slotted locking link  75  arranged in a side cover  77 , and therefore opens up the camshaft adjuster for an adjustment. As the oil pressure rises further, the cutting off of a working chamber  41  follows as in the manner described above. The cut-off mechanism  25  is therefore connected in a simple manner structurally to a locking mechanism. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  Camshaft Adjuster 
           2  Driving Wheel 
           3  Stator 
           4  Housing 
           5  Housing Cover 
           6  Disk 
           7  Longitudinal Axis 
           8  Rotor 
           10  Annular Space 
           11  Sealing Plate 
           12  Fastening Screw 
           21  Vane 
           25  Cut-Off Mechanism 
           26  Spring Support 
           27  Cut-Off Mechanism 
           29  Oil Duct 
           31  Oil Duct 
           33  Spring 
           35  Actuating Body 
           37  Bypass Duct 
           39  Recess 
           41  Working Chamber 
           41 A Sub Chamber 
           41 B Sub Chamber 
           51 ,  53  Inflow/Outflow 
           61 ,  63  Chamber Inflow/Outflow 
           67  Annular Groove 
           67 A Annular Groove 
           67 B Annular Groove 
           65  Short-Circuit Duct 
           71  Locking Spring 
           73  Locking Pin 
           75  Slotted Locking Link 
           77  Side Cover