Patent Publication Number: US-6666179-B2

Title: Camshaft for the operation of valves of an internal-combustion engine

Description:
This application claims the priority of German application 100 33 291.9, filed Jul. 7, 2000, the disclosure of which is expressly incorporated by reference herein. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a camshaft for the operation of valves of an internal-combustion engine including a device for hydraulic adjustment of a relative rotating position of the camshaft for influencing a timing of the valves. The device has a drive wheel for the camshaft, a cell wheel, and an impeller which, by way of radial vanes, is disposed within cells of the cell wheel and is able to carry out a relative motion. A locking arrangement, operative in a starting phase of the internal-combustion engine, is provided between the cell wheel and the impeller. The locking arrangement is formed by an axially spring-loaded, hydraulically operated piston, which is accommodated in one of the vanes of the impeller, and a corresponding receiving device for the piston, which is provided in a constructional unit consisting of the drive wheel and the cell wheel. 
     German Patent Document DE 39 37 644 A1 concerns a known camshaft of the type mentioned above. A locking arrangement is provided in this known camshaft. In the starting phase of the internal-combustion engine, the locking arrangement fixes the impeller relative to the cell wheel to avoid uncontrolled movements of the two wheels with respect to one another. Such uncontrolled movements, among other things, can cause disturbing sounds. The locking arrangement comprises a slidably movable locking sleeve arranged coaxially between the cell wheel and the impeller. The locking sleeve non-rotatably connects the above-mentioned wheels with one another in a first position and separates them from one another in a second position. 
     In German Patent Document DE 1 96 23 818 A1, a corresponding locking device is provided between a vane-type extension of an impeller and a cover of the cell wheel. The locking arrangement is provided with a spring-loaded axially movable piston. In the starting phase of the internal-combustion engine, this piston engages in a receiving device of the cover. 
     It is an object of this invention to improve a locking arrangement of a device for adjusting the relative rotating position of a camshaft such that it can easily be integrated in the device and functions well. 
     According to the invention, this object is achieved by providing a piston which has a locking section projecting into the receiving device and guided in one of the vanes of the device. An operating element with which the piston cooperates is provided. The piston is acted upon by a first pressure space, and the operating element is acted upon by a second pressure space. Additional characteristics and further developments of the invention are reflected in the claims. 
     The principal advantages achieved by the invention are that the piston and the operating element cooperating therewith, which can be acted upon from separate pressure spaces, ensure a reliable and immediate effect of the locking arrangement of the device for adjusting the relative rotating position of the camshaft. The operating element, constructed as a pin, and the piston can be integrated in a simple and spatially favorable manner in the vane of the impeller of the device. Furthermore, the piston and the pin are components which can be produced at acceptable expenditures and mounted easily. 
     The drawings illustrate an embodiment of the invention which will be described in detail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a schematically illustrated internal-combustion engine with camshafts for operating valves; 
     FIG. 2 is an enlarged sectional view along line II—II of FIG. 1; 
     FIG. 3 is an enlarged view of a detail X of FIG. 2; and 
     FIG. 4 is a sectional view along line IV—IV of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An internal-combustion engine  1  of the Otto type is illustrated only schematically in FIG.  1  and comprises several cylinders  2 ,  3  and  4 , two camshafts  5  and  6 , and, for example, two inlet valves  7  and  8  and two outlet valves  9  and  10  per cylinder. The inlet valves  7 ,  8  and the outlet valves  9 ,  10  are accommodated, in a V-shape, in a cylinder head (not shown) of the internal-combustion engine  1 . The two camshafts  5 ,  6  are connected with one another by way of an endless drive  11 . The endless drive may be a belt, a chain or the like, and winds around corresponding drive wheels. The endless drive  11  is operative adjacent to faces  12 ,  13  of the above-mentioned camshafts. Devices  14 ,  15  for hydraulically adjusting the relative rotating position of these camshafts are coaxially connected to the faces  12 ,  13  of the camshafts  5 ,  6 . Each device such as the device  14  is constructed as a vane cell pump. The timing of the valves  7 ,  8  is influenced, specifically in order to optimize the operation of the internal-combustion engine, among other things, with respect to the emission of exhaust gas. 
     The device  14  has a circular-cylindrical configuration and constructionally corresponds to the device  15 . The device  14  comprises a drive wheel  16  constructed as a chain wheel for the camshaft  5 , a cell wheel  17 , and an impeller  19  equipped with radial vanes  18 . The drive wheel  16 , the cell wheel  17  and the impeller  19  are arranged coaxially with respect to the camshaft  5 . The drive wheel  16  and the cell wheel  17  form a firmly mutually connected constructional unit  20 . In contrast, the impeller  19 , which can be swivelled about an axis of rctation  21 , is housed by the vanes  18  in chamber-type cells  22  of the cell wheel  17 . A total of five cells per device is provided. Each cell  22  is equipped with a first stop face  23  and a second stop face  24  for corresponding first and second stop faces  25 ,  26  of the vane  18 . All stop faces  23 ,  24  and  25 ,  26  extend radially with respect to the axis of rotation  21 , but the angle α, which is enclosed by the stop faces  23 ,  24 , is larger than the corresponding angle β of the stop faces  25 ,  26  of the vane  18 . 
     The cell  22  is also bounded by a circular surface  27 . A circular surface  28  of the vane  18  extends toward the circular surface  27 . Both circular surfaces  27  and  28  act as sealing surfaces. At reference number  29 , circular surfaces  30 ,  31 , forming comparable sealing surfaces, are provided between the impeller  19  and the cell wheel  17 . Adjacent to the circular surfaces  27  and  30 , the contact surfaces  23 ,  24  are provided with chamber-shaped recesses  32 ,  33  and  34 ,  35  by way of which hydraulic medium is admitted for acting upon the stop faces  25 ,  26  of the vane  18  of the impeller  19 . 
     In the starting phase of the internal-combustion engine  1 , the impeller  19  is fixed on the constructional unit  20  formed by the drive wheel  16  and the cell wheel  17 , for the purpose of which a locking arrangement  36  is provided. The locking arrangement  36  comprises a piston  37  which can be displaced in a guide bore  38  of the vane  18  of the impeller  19  in the axial direction of the axis of rotation  21 . By way of a locking section  39 , the piston cooperates with a corresponding receiving device  40  in a hub body  41  of the constructional unit  20 . The piston  37 , which is made in one piece with the locking section  39 , is acted upon from a first pressure duct  42  which is connected to a first pressure space  43 . An operating element  44 , which is operated by way of a second pressure duct  45 , is operatively connected with the piston  37 . The second pressure duct  45  is connected with a second pressure space  46 . Both pressure spaces  43  and  46 , which are separated from one another, are connected to the hydraulic system of the device  14 . 
     The operating element  44  is formed by a pin  47 , shown in FIG. 4, which is guided to a stop  48  of the piston  37 . The pin  47  is arranged in a guide bore  49  and extends parallel to the piston  37 . The pin is supported on a ring surface  50  which represents the stop  48  and which is provided on a piston head  52  on a side  51  facing away from the locking section  39 . The locking section  39  guided in the guide bore  38  has a diameter which is smaller than the diameter of the piston head  52 . The guide bores  38  and  49  of the piston  37  and of the pin  47 , respectively, extend at a distance from one another which is as small as possible. As FIG. 3 shows, the guide bores are situated in a common radial plane A—A. 
     The piston  37  and the pin  47  are connected by faces  53  and  54  to pressure chambers  55  and  56  which are situated away from the ring surface  50 . The pressure chamber  55  is connected with the first pressure duct  42 . The pressure chamber  56  is connected with the second pressure duct  45 . Furthermore, a pressure spring  59  is operative between a free side  57  of the piston head  52  and a supporting part  58  of the vane  18 . The pressure spring  59  rests in sections in a recess  60  of the piston head  52  and surrounds a journal  61  of the supporting part  58 , which is constructed as a spring plate. 
     When the internal-combustion engine is not in operation, its hydraulic system, including the device  14 , is without pressure. As a result, the pressure spring  59  holds the locking section  39  of the piston  37  in position in the receiving device  40 , and a relative movement of the impeller  19  in the cell wheel for adjustment of the camshaft  5  cannot take place. This condition is at first maintained in the starting phase of the internal-combustion engine  1  with a defined pressure level in the hydraulic system. After the above-mentioned pressure level has been exceeded, the piston  37  and the pin  47  are acted upon by hydraulic medium by way of the faces  53  and  54 , respectively, and the locking section  39  is led out of the receiving device  40  against the effect of the pressure spring  59 . The impeller  19 , or rather the camshaft  5 , can now be adjusted as a function of parameters (rotational speed, load) of the internal-combustion engine. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.