Abstract:
A stator ( 20 ) for a camshaft adjuster ( 4 ). The stator ( 20 ) has an outer part ( 50 ) for concentrically holding a rotor ( 22 ) with vanes ( 34 ) arranged around the rotor ( 22 ) and a segment ( 52 ) projecting from the outer part ( 50 ) for engaging between two vanes ( 34 ) of the rotor ( 22 ), in order to form, together with the two vanes ( 22 ), pressure chambers ( 44 ) of the camshaft adjuster ( 4 ). Here, the segment ( 52 ) has a cavity ( 70 ) for holding a hydraulic fluid from the pressure chambers ( 44 ).

Description:
INCORPORATION BY REFERENCE 
     The following documents are incorporated herein by reference as if fully set forth: German Patent Application No. 10 2012 201 566.3, filed Feb. 2, 2012. 
     FIELD OF THE INVENTION 
     The invention relates to a stator for a camshaft adjuster, the camshaft adjuster, and an internal combustion engine with the camshaft adjuster. 
     BACKGROUND 
     Camshaft adjusters are technical assemblies for adjusting the phase positions between a crankshaft and a camshaft in an internal combustion engine. 
     From WO 2011 032 805 A1, it is known to arrange a volume accumulator in a camshaft adjuster, wherein, in the case of an under-pressure, hydraulic fluid can be drawn from this accumulator by the pressure chambers. 
     SUMMARY 
     The object of the invention is to improve the known camshaft adjusters. 
     This objective is met by the features of the invention. Preferred improvements are described below and in the claims. 
     The invention provides forming the volume accumulator in the stator of the camshaft adjuster. 
     This is based on the idea that the stator of a camshaft adjuster has segments that form the pressure chambers together with the vanes of the rotor of the camshaft adjuster. These segments can have hollow constructions, for example, for saving material and weight. 
     However, the invention is also based on the knowledge that the cavities of these segments are usually not functionally utilized. The use of these cavities as volume accumulators would therefore impart an additional function to these segments, without requiring great increases in the installation space of the camshaft adjuster. 
     The invention therefore provides a stator for a camshaft adjuster that comprises an outer part for concentrically holding a rotor with vanes arranged on the rotor and a segment projecting from the outer part for engaging between two vanes of the rotor, in order to form pressure chambers of the camshaft adjuster together with the two vanes. Here, the segment has a cavity for holding a hydraulic fluid from the pressure chambers. The outer part can have, in particular, a ring shape, wherein the segments project inward in the radial direction. The vanes can be arranged around the rotor and project away from this rotor in the radial and/or axial direction. The cavity in the segment thus can be used as a volume accumulator that holds hydraulic fluid coming from the pressure chamber via a corresponding supply port, wherein, in the case of an under-pressure, the pressure chamber can draw the discharged hydraulic fluid via a discharge port connected to the pressure chamber. 
     In one refinement of the invention, the stator has a front cover placed on the ring-shaped outer part in the axial direction and/or a back cover placed on the ring-shaped outer part in the axial direction. These covers close an interior space of the ring-shaped outer part of the stator and allow the pressure chambers to be defined with the vanes of the rotor. 
     In an alternative construction of the invention, the cavity in the indicated stator can be formed, instead of in the segment, also in one of the two covers or in both covers. 
     In an additional refinement, a supply line for supplying the cavity with hydraulic fluid is guided from the pressure chambers through the front cover and/or through the back cover. Because the covers are already locked in rotation with the stator, the supply of the cavity with the hydraulic fluid can be implemented in a technically very favorable way. 
     In one alternative or additional refinement of the invention, a discharge line for bleeding hydraulic fluid from the cavity is guided through the front cover and/or through the back cover. In this way, the volume accumulator formed by the cavity can be connected via the discharge line directly to the tank connection of the camshaft adjuster. 
     In another refinement of the invention, the specified stator comprises a pressure equalization line between the cavity and an outer side of the segment directed in the peripheral direction for supplying the pressure chamber with the hydraulic fluid, so that the pressure chamber can draw hydraulic fluid from the pressure chamber. 
     In one special refinement of the invention, the indicated stator comprises a non-return valve in the pressure equalization line that allows a flow of hydraulic fluid from the cavity, in order to balance an under-pressure in one of the pressure chambers. In this way, a flow of hydraulic fluid from the pressure chamber into the volume accumulator is prevented when the pressure in the pressure chamber is greater than that in the volume accumulator. The non-return valve thus makes sure that the volume accumulator is used only for equalizing an under-pressure in the pressure chamber. 
     The invention also provides a camshaft adjuster for setting a phase shift between a crankshaft driven by an internal combustion engine and a camshaft controlling the internal combustion engine. The indicated camshaft adjuster comprises an indicated stator for transferring rotational energy from the crankshaft and a rotor held concentrically in the stator for receiving the rotational energy to the camshaft. Through the indicated stator, the indicated camshaft adjuster can be formed with more functions and with a comparatively low increase in installation space. 
     In one refinement of the invention, the indicated camshaft adjuster comprises a central valve for connecting at least one pressure chamber formed between the rotor and the stator to the cavity in the segment of the stator. The central valve thus makes sure that the pressure chamber is either filled with hydraulic fluid from a pressure connection or is emptied via the volume accumulator. 
     The invention also provides an internal combustion engine that comprises a combustion chamber, a crankshaft driven by the combustion chamber, a camshaft for controlling the combustion chamber, and an indicated camshaft adjuster for transferring rotational energy from the crankshaft to the camshaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be explained in more detail below with reference to a drawings in which 
         FIG. 1  is a schematic diagram of an internal combustion engine with camshaft adjusters, 
         FIG. 2  is a section view of a camshaft adjuster from  FIG. 1  with a stator, 
         FIG. 3  is a section view of an example for the stator from  FIG. 2 , 
         FIG. 4  is a section view of another example for the stator from  FIG. 2 , and 
         FIG. 5  is a section view of yet another example for the stator from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the figures, identical elements are provided with identical reference symbols and will be described only once. 
       FIG. 1  will be referenced that shows a schematic diagram of an internal combustion engine  2  with camshaft adjusters  4 . 
     In a known way, the internal combustion engine  2  comprises a combustion chamber  6  that can be opened and closed by valves  8 . The valves are driven by cams  10  on corresponding camshafts  12 . In the combustion chamber  6 , a reciprocating piston  14  is also held that drives a crankshaft  16 . The rotational energy of the crankshaft  16  is transferred on its axial end via driving means  18  to the camshaft adjuster  4 . 
     The camshaft adjusters  4  are each placed axially on one of the camshafts  12 , receive the rotational energy from the driving means  18 , and transfer this energy to the camshafts  12 . Here, the camshaft adjusters  4  can delay or accelerate the rotation of the camshafts  12  relative to the crankshaft  14  in terms of time, in order to change the phase position of the camshafts  12  relative to the crankshaft  16 . 
       FIG. 2  will be referenced that shows a section view of one of the camshaft adjusters  4  from  FIG. 1  with a stator  20 . 
     In addition to the stator  20 , the camshaft adjuster  4  has a rotor  22  held in the stator  20 , a spiral spring  24  biasing the stator  20  relative to the rotor  22 , a spring cover  26  covering the spiral spring, a central valve  28  held centrally in the camshaft adjuster  4 , and a central magnet  30  actuating the central valve  28 . 
     The rotor  22  is held concentrically in the stator  20  and has, shown in  FIGS. 3 to 5 , vanes  34  projecting from a hub  32  of the rotor. The rotor  22  is held concentrically on a central screw  36  of the central valve  28  that can be screwed into one of the camshafts  12  and in which a control piston  38  is held so that it can move in the axial direction and can be moved by a tappet  40  of the central magnet in the axial direction into the central screw  36  and can be pressed outward from the central screw  36  by a spring  42  in the axial direction. Depending on the position of the control piston  38  in the central screw  36 , pressure chambers  44  of the camshaft adjuster  4  shown in  FIGS. 3 to 5  are connected in a known way to a pressure connection  46  or to a volume accumulator connection  48  by which a hydraulic fluid can be pumped out into the pressure chambers  44  or can be bled from these chambers. 
     The stator  20  has a ring-shaped outer part  50  that can be seen well in  FIGS. 3 to 5 , with four segments  52  projecting inward in the radial direction from this outer part. The ring-shaped outer part  50  is closed in the axial direction with a front cover  54  and a back cover  56 , wherein the covers  54 ,  56  are held on the ring-shaped outer part  50  by screws  58 . One of the screws  58  has an axial extension  60  that is used as a mounting point for the spiral spring  24 . A peripheral groove  62  is further formed in the back cover  56  on the axial side opposite the ring-shaped outer part  50 . The spring cover  26  is clamped in this peripheral groove. Teeth  64  in which the driving means  18  can engage are formed on the radial periphery of the ring-shaped outer part  50 . 
     The central screw  36  has radial holes  66  as volume accumulator connections  48 , with axial channels  68  through the front cover  54  being placed on these holes. The channels  68  are set in the radial direction on a peripheral groove  71  on the radial inner side of the front cover  54  directed toward the central screw  36 , in order to allow a flow of hydraulic fluid in any position of the central screw  36  locked in rotation with the rotor  22  relative to the stator  20  between the radial holes  66  and the channels  68 . 
     The channels  68  lead into cavities  70  that are formed in the segments  52  and through which the screws  58  are also guided. The cavities  70  are opened by non-return valves  72  to the pressure chambers  44  of the camshaft adjuster  4 , wherein the flow of hydraulic fluid is possible only from the cavity  70  to the pressure chamber  44 , so that the pressure chamber  44  can draw hydraulic fluid stored in the cavity  70  in the case of an under-pressure. If the cavity  70  is overflowing with too much hydraulic fluid, then the excess of hydraulic fluid is discharged via a tank connection  74 , for example, to a not-shown oil pan. The cavities  70  in the segments  52  are therefore used as volume accumulators for equalizing an under-pressure in the pressure chambers  44  of the camshaft adjuster  4  of the internal combustion engine  2 . 
       FIG. 3  will be referenced that shows a section view of an example for the stator from  FIG. 2 . 
     As can be seen from  FIG. 3 , the non-return valves  72  can be constructed, for example, as ball non-return valves. 
       FIG. 4  will be referenced that shows a section view of another example for the stator from  FIG. 2 . 
     As can be seen from  FIG. 4 , the balls of the non-return valves  72  can be held in the non-return valves  72  by springs. In this way, the dynamic response of the non-return valves  72  can be increased during the opening and/or closing of the non-return valves  72 . 
       FIG. 5  will be referenced that shows a section view of yet another example for the stator from  FIG. 2 . 
     As can be seen from  FIG. 5 , the non-return valves  72  can be constructed, for example, as plate non-return valves. In this way, the non-return valves can be installed in the camshaft adjuster  4  with a particularly small amount of installation space. 
     In the present construction, the cavities  70  are constructed in the segments  52 . Alternatively or additionally, the cavities  70  could also be formed in the covers  54 ,  56 . Accordingly, the described supply lines or discharge lines for the hydraulic fluid are then alternatively or additionally guided through the covers, wherein the non-return valves are then alternatively or additionally also to be mounted on the covers. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               2  Internal combustion engine 
               4  Camshaft adjuster 
               6  Combustion chamber 
               8  Valve 
               10  Cam 
               12  Camshaft 
               14  Reciprocating piston 
               16  Crankshaft 
               18  Driving means 
               20  Stator 
               22  Rotor 
               24  Spiral spring 
               26  Spring cover 
               28  Central valve 
               30  Central magnet 
               32  Hub 
               34  Vane 
               36  Central screw 
               38  Control piston 
               40  Tappet 
               42  Spring 
               44  Pressure chamber 
               46  Pressure connection 
               48  Volume accumulator connection 
               50  Ring-shaped outer part 
               52  Segment 
               54  Front cover 
               56  Back cover 
               58  Screw 
               60  Axial extension 
               62  Groove 
               64  Tooth 
               66  Radial hole 
               68  Channel 
               70  Cavity 
               71  Peripheral groove 
               72  Non-return valve 
               74  Tank connection