Patent Publication Number: US-6701879-B2

Title: Internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention is directed to an internal combustion engine. 
     BACKGROUND INFORMATION 
     An internal combustion engine referred to in German Published Patent Application No. 198 26 074 includes an electrohydraulic valve control device, including valve actuators configured as hydraulic actuators, each of these actuating one of the gas-exchange valves. Each hydraulic actuator may have a double-acting working cylinder in which an operating piston may be guided in an axially displaceable manner. The operating piston may be rigidly connected to a piston rod, which may be guided out of the working cylinder and, itself, may be rigidly connected to the valve tappet of a gas-exchange valve or may be formed in one piece with it. 
     SUMMARY OF THE INVENTION 
     An exemplary internal combustion engine according to the present invention may provide two gas-exchange valves that are operated using a single valve actuator. In this context, the closing and opening of both gas-exchange valves may be reliably ensured, regardless of any existing component tolerances. In particular, it may be ensured that the valve elements of both gas-exchange valves in the valve closed position tightly abut the valve seat, so that the combustion chamber of the combustion cylinder may be reliably sealed. By economizing one valve actuator per combustion cylinder, the manufacturing costs for the internal combustion engine&#39;s valve control device may be reduced. 
     According to one exemplary embodiment of the present invention, the valve actuator may have a double-acting hydraulic working cylinder, including an operating piston that may be guided in the working cylinder in an axially displaceable manner, as well as a piston rod that may be rigidly connected to the operating piston and led through the working cylinder. The coupling element may be fastened to the piston rod&#39;s rod section which is led through the working cylinder by a swivel bearing, a swiveling axis being oriented transversely to the stroke direction of the operating piston. 
     The flexible connection sites may be formed so that the gas-exchange valves in the connection sites may perform at least a pendulum motion and a translatory shifting motion in each case relative to the coupling element and transversely to the stroke direction of the operating piston. In the case of two gas-exchange valves actuated by the valve actuator, the connection sites for both gas-exchange valves may be located on the coupling element on both sides of the swivel bearing. This structural configuration may ensure that both gas-exchange valves are reliably closed, even if due to component tolerances and thermal expansions, the valve elements of both gas-exchange valves do not simultaneously place themselves against their associated valve seat in the combustion cylinder. 
     If the valve element of the one gas-exchange valve abuts on the valve seat, the operating piston may not be blocked in its stroke motion and may move further due to the swivel bearing between the piston rod and coupling element, with result that the coupling element performs a swiveling motion until the valve element of the second gas-exchange valve also abuts the valve seat. In this context, the pendulum and translatory shifting support of the valve stems of both gas-exchange valves in the connection sites may prevent a blockage of the swiveling motion of the coupling element since the coupling element may position itself at an angle with respect to the valve stems without lateral forces being applied to the valve stems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows, in cutaway portions, a longitudinal section of a combustion cylinder of an internal combustion engine having two gas-exchange valves, as well as a block diagram of an electrohydraulic valve control device for the gas-exchange valves. 
     FIG. 2 shows, in cutaway portions, an enlarged display of a coupling element between a valve actuator of the valve control device and the gas-exchange valves. 
    
    
     DETAILED DESCRIPTION 
     The internal combustion engine for a motor vehicle may have four or more combustion cylinders  10 . One of these is shown schematically in a longitudinal section, in cutaway portions, in FIG. 1. A combustion chamber  11 , provided with gas-exchange valves  12  for controlling an intake and discharge cross-section, is formed in combustion cylinder  10 . Of gas-exchange valves  12 , the exemplary embodiment of FIG. 1 shows two discharge valves controlling a discharge cross-section of combustion chamber  11 . For the sake of clarity, the intake valves likewise present on combustion chamber  11  for controlling an intake cross-section were omitted in FIG.  1 . Both gas-exchange valves  12  are actuated synchronously, i.e. simultaneously opened and closed. Each gas-exchange valve  12  has a valve element  122  including a valve closing member  124 , which is seated on an axially displaceably guided valve stem  121  and which cooperates with a valve seat  123  enclosing the discharge cross-section in combustion cylinder  10 . By displacing valve stem  121  in one or the other axial direction, valve closing member  124  lifts off from valve seat  123  or places itself on it. 
     Both gas-exchange valves  12  are actuated by an electrohydraulic valve control device  13  shown in the block diagram in FIG.  1 . The valve control device has a valve actuator  14 , also known as a hydraulic actuator, which is controllable by control valves  15 ,  16 , and to which both gas-exchange valves  12  are linked by a coupling element  18 . Also belonging to valve control device  13  are a pressure supply device  19  which includes, for example, an adjustable high-pressure pump  20  which delivers fluid from a fluid reservoir  23 , a return valve  21  and an accumulator  22  for pulsation attenuation and energy storage. At outlet  191  of pressure supply device  19 , a permanent adjustable high pressure may be present. 
     Valve actuator  14  is configured as a double-acting working cylinder  32 , including a cylinder housing  28  and an operating piston  27  guided therein in an axially displaceable manner, which subdivides the interior space of cylinder housing  28  into a first pressure chamber  29  and a second pressure chamber  30 . First pressure chamber  29  is connected to a first pressure line  25 , and second pressure chamber  30  both to a second pressure line  26  as well as to a return line  31 . Both pressure lines  25 ,  26  are connected via a common return valve  24  to outlet  191  of pressure supply device  19 . First control valve  15  is connected into second pressure line  26  and second control valve  16  is connected into return line  31  which runs into fluid reservoir  23 . Both control valves  15 ,  16  are configured as 2/2 diverter solenoid valves. 
     As shown in FIG. 1, first control valve  15  is closed, and second control valve  16  is opened. The high pressure prevailing in first pressure chamber  29  may ensure that operating piston  27  is located in the top dead-center position, so that gas-exchange valves  12  are kept in their closed position. If control valves  15 ,  16  are switched over, second pressure chamber  30  is shut off from return line  31 , and the high pressure at outlet  191  of pressure supply device  19  is applied to second pressure chamber  30 . Since the area of operating piston  27  that limits second pressure chamber  30  is greater than the area of operating piston  27  limiting first pressure chamber  29 , operating piston  27  moves downwards, and both gas-exchange valves  12  are opened. In this context, the magnitude of the opening stroke depends on the formation of the electrical control signal applied to first control valve  15 , and the opening speed depends on the fluid pressure injected by pressure supply device  19 . 
     Coupling element  18 , which may be formed as a rectangular plate, is fastened at the end of a piston rod  33  that is rigidly joined to operating piston  27  and led through cylinder housing  28  of working cylinder  32  by a swivel bearing  34 , with a swiveling axis  341  oriented transversely to the stroke direction of operating piston  27 . As may be recognized from the enlarged sectional view of coupling element  18  in FIG. 2, the rod end of piston rod  33  dips into a recess  35  centrally disposed in coupling element  18  where swivel bearing  34  is positioned. To enable a swiveling motion of coupling element  18  on piston rod  33 , recess  35  is formed in such a manner that it tapers towards the end of piston rod  33 . Swivel bearing  34  is integrated in recess  35  and is made up of a cylinder pin  36  which is inserted into bore holes aligned with one another in piston rod  33  and in coupling element  18 . In FIG. 2, only bore hole  37  which is introduced into piston rod  33  may be seen. Bore hole  37  is positioned between cylinder pin  36  and bore hole wall  37  in a manner that provides some play, enabling the rotary motion of coupling element  18 . The fit between cylinder pin  36  and the bore holes in coupling element  18  may be an interference fit, so that the pin may not drift out of the bore holes. 
     The connection of both gas-exchange valves  12  to coupling element  18  is handled flexibly for tolerance compensation, connection sites  38 ,  39  being disposed between valve stems  121  of gas-exchange valves  12  and coupling element  18  on both sides of swivel bearing  34  at the same distance from swivel bearing  34 . In this context, each connecting site  38 ,  39  is formed so that valve stem  121  of gas-exchange valve  12  in connecting site  38 ,  39  may perform at least a swiveling or pendulum motion and a translatory shifting motion, in each case relative to coupling element  18  and transversely to the stroke direction of operating piston  27 . 
     As may be seen in the enlarged sectional view, in cutaway portions in FIG. 2, of valve stems  121  of gas-exchange valves  12  and piston rod  33  of working cylinder  32 , in each connecting site  38 ,  39 , coupling element  18  has an elongated hole  40  extending transversely to the stroke direction of piston rod  33  through which is guided a valve stem  121  of one of gas-exchange valves  12 . Valve stem  121  is accommodated with a stem section  121   a  disposed at a distance from the end of valve stem  121  in a pendulum bearing  41  and bears a spring plate  42  on a stem section  121   b  disposed at the stem end of valve stem  121 . Between spring plate  42  and coupling element  18 , a compression spring  43  slid over valve stem  121  is supported with prestressing action. 
     In stem section  121   a  accommodated by pendulum bearing  41  and also in stem section  121   b  supporting spring plate  42  of valve stem  121  of each gas-exchange valve, grooves  44  or rather  45  are recessed, this being in the exemplary embodiment of FIG. 2 in each case three grooves  44  or rather  45 . Pendulum bearing  41  has two half-rings  461  and  462  enclosing stem section  121   a  which meet at the end faces and are joined to form a closed ring  46  held together by a tension ring  47 . 
     Formed on the inner surface of both half-rings  461 ,  462 , are radially protruding semicircular ring lands  461   a  or rather  462   a , which are set apart from one another in the axial direction and which engage with clearance in grooves  44  in stem section  121   a  of valve stem  121  in manner that allows valve stem  121  to execute a rotary motion about its longitudinal axis. Ring  46  is non-positively placed by compression spring  43  against lower face  182  of coupling element  18  turned away from spring support surface  181 . 
     Spring plate  42  includes a collar  48  on which radially outwards-facing support surfaces  481  are formed. Collar  48  is slid in a positive locking manner on a cone  49  having a diameter that increases towards the stem end of valve stem  121 . Cone  49  is made up of two groove wedges  491 ,  492  which are held together by a slid-on collar  48 . Provided on each groove wedge  491 ,  492 , are three radially protruding, semicircular ring lands  491   a  or rather  492   a , which are set apart from one another in the axial direction and extend with clearance into grooves  45  in stem section  121   b  of valve stem  121  in such a manner that the rotary mobility of valve stem  121  about its longitudinal axis is retained. 
     Due to the prestressing force of compression spring  43 , collar  48  is pressed upwards far enough to produce a secure connection between groove wedges  491 ,  492  and valve stem  121 . Compression spring  43  is prestressed in such a manner that gas-exchange valve  12 , as long as it does not abut valve seat  123  with its valve element  121 , follows the motion of coupling element  18 . Because of pendulum bearing  41  and the associated possibility of a pendulum motion of valve stem  121 , elongated hole  40  which enables a translatory displacement of valve stem  121  within couple element  18 , and because of the deformability of compression spring  43 , a swiveling motion of coupling element  18  in swivel bearing  34  may be possible in a limited range and may not be blocked or cramped by valve stems  121 . 
     If, due to change-over of control valves  15 ,  16 , operating piston  27  moves downwards out of its top dead-center position shown in FIG. 1, then both gas-exchange valves  12  with their valve closing members  124  are lifted off of valve seats  123  via coupling element  18  and opened synchronously. To close gas-exchange valves  12 , control valves  15 ,  16  are returned to the position shown in FIG.  1 . In this manner, second pressure chamber  30  is connected to return line  31  and depressurized. Operating piston  27  moves upwards in FIG. 1, and, via coupling element  18 , gas-exchange valves  12  are actuated in the closing direction in such a manner that valve elements  122  are drawn upwards and valve closing members  124  place themselves on valve seats  123 . Due to component tolerances and heat expansions, however, valve closing members  124  of both valve elements  122  may not place themselves simultaneously on the associated valve seats  123 . 
     If valve closing member  124  of the one gas-exchange valve  12  abuts valve seat  123 , operating piston  27  may nevertheless move further since coupling element  18  may perform a swiveling motion in its swivel bearing  34  which may not be hindered by the flexible connection of valve stems  121  in connection sites  38 ,  39 . It thus may be ensured that, at the end of the stroke of operating piston  27 , both valve closing members  124  of gas-exchange valves  12  abut their associated valve seat  123  and, in this manner, gas-exchange valves  12  may be reliably closed. The symmetrical configuration of connection sites  38 ,  39  with respect to swiveling axis  341  of swivel bearing  34  may ensure equal closing forces on both gas-exchange valves  12 . 
     Alternatively, for example, gas-exchange valves  12  synchronously controlled by coupling element  18  may not have to be associated with one single combustion cylinder  10 . Instead, they may also be mounted on combustion chambers  11  of different combustion cylinders  10 . When using gas-exchange valves  12  as discharge valves, for example, in a four-cylinder internal combustion engine, the discharge valves of the first and the third combustion cylinder may be connected in the described manner to coupling element  18  for common actuation by a valve actuator  14  of valve control device  13 . 
     The jointly actuated gas-exchange valves  12  may have the function of intake valves, as well as of discharge valves.