Abstract:
A piston-type internal-combustion engine having deactivatable, mechanically actuated cylinder valves that are respectively actuated by at least one camshaft via a roller drag lever ( 5 ) comprising two partial levers ( 5.1, 5.2 ) that are hinged to one another via an articulated shaft ( 6 ), on which the roller ( 7 ) associated with a cam ( 8 ) of the camshaft is rotatably seated. A locking mechanism ( 13 ) is provided to selectively couple or decouple the two partial levers ( 5.1, 5.2 ) to activate or deactivate the force transmission between the camshaft and the cylinder valve. The free end  5.11  of one partial lever ( 5.1 ) is supported on the cylinder valve ( 2 ), and the free end  5.21  of the other partial lever ( 5.2 ) is supported on the engine block ( 11 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application is a continuation application of the international patent application PCT/EPO1/08624, filed Jul. 26, 2001, which international patent application includes the designation of the USA and which international patent application is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     In a piston-type internal combustion engine having mechanically actuated cylinder valves that are actuated with the aid of at least one camshaft via roller drag levers, it is possible to deactivate the cylinder valves of a portion of the cylinders in order to operate the engine in partial-load operation, for example, operations which only some of the cylinders are fired, whereas the cylinders having deactivated cylinder valves are not fired, but are idle. The cylinder valves can be deactivated cyclically, so other cylinders can always be fired, taking into consideration running smoothness. The active cylinders can then be fired under full-load conditions, and thus under optimum operating conditions, with the piston-type internal-combustion engine only delivering a partial load overall. 
     The arrangements known to this point for deactivating the cylinder valves have a very complicated design, and require a considerable amount of space. 
     It is the object of the invention to provide a piston-type internal-combustion engine having deactivatable cylinder valves and a simple valve-gear design. 
     SUMMARY OF THE INVENTION 
     This object generally is achieved according to the invention with a piston-type internal-combustion engine having deactivatable, mechanically actuated cylinder valves that are respectively actuated by at least one camshaft via of a roller drag lever with a roller. The lever is configured from two partial levers that are hinged to one another via an articulated shaft, on which the roller associated with a cam of the camshaft is rotatably seated, and having a locking mechanism that can be switched to act between the two partial levers and is used to activate or deactivate the force transmission between the camshaft and the cylinder valve. The free end of the one partial lever is supported on the cylinder valve, and a support is provided on the engine block for the free end of the other partial lever. The engine further has a restoring spring that is effective between the two partial levers, and presses the roller along the cam when the partial levers are unlocked. The fact that the articulated shaft for the two partial levers simultaneously acts as a bearing for the roller greatly simplifies the design of the valve gear. The restoring spring ensures that, when the cylinder valve is deactivated, the two partial levers are guided with the roller along the cam contour, so the roller remains in contact with the cam in this operating mode. At the same time, it is ensured that, after the piston-cylinder unit has been set to zero pressure, the two partial levers assume their extended position for as long as the roller is in contact with the base circle of the cam, and the locking element can extend into its receptacle and lock the two partial elements together. 
     A particularly advantageous embodiment of the invention provides that the partial lever associated with the cylinder valve has an extension that faces the support and extends past the articulated shaft. The extension overlaps a region of the partial lever associated with the support in scissors fashion, and the latching mechanism is associated with the region in which the two partial levers overlap like scissors. 
     A further advantageous embodiment of the invention provides that the locking mechanism is formed by a piston-cylinder unit that can be supplied with compressed oil and is disposed in the partial lever associated with the support. The piston-cylinder unit further has a locking element that can be displaced parallel to the articulated shaft, and that has a piston portion and a bar portion. The bar portion and the piston portion can be formed as separate components or, in an advantageous embodiment of the invention, they can be connected to one another in one piece. It is practical to provide a restoring spring that holds the locking element in its latched position, so in normal operation, the two partial levers are locked together and are not unlocked until the piston-cylinder unit is supplied with compressed oil, and the corresponding cylinder valve is thus deactivated. 
     A further advantageous embodiment of the invention provides that the piston-cylinder unit is supplied with compressed oil via a hydraulic play-compensation element that forms the support. This type of hydraulic play-compensation element is present anyway in the arrangement of the roller drag levers, so in order to supply compressed oil to the piston-cylinder unit, it is only necessary to provide a corresponding compressed-oil conduit in the partial lever resting on the compensation element, the conduit being connected to the cylinder of the piston-cylinder unit. The spring force of the restoring spring of the piston-cylinder unit is selected such that the spring is not compressed at the pressure level required for the play compensation, and with the given piston surface, so the roller of the roller drag lever remains in constant contact with the cam. If a cylinder valve is to be deactivated, the pressure in the compressed-oil supply of the play-compensation elements is increased to the point that the restoring spring of the locking element compresses, thus releasing the lockup of the two partial levers. If the relevant cylinder valve is to be re-activated, the oil pressure is reduced correspondingly, so the restoring spring re-engages the locking element with the other partial lever, and locks the two partial levers together. 
     A still further advantageous further embodiment of the invention provides that at least the partial lever that is associated with the cylinder valve is formed in a claw or u-shaped jaw shape or u-shaped jaw, and extends laterally around the roller in the region of the articulated shaft, with one jaw part forming the extension. This embodiment offers a very stable, compact construction of the roller drag lever, which simultaneously permits the articulated shaft and the roller to be seated properly. 
    
    
     The invention is explained in detail using schematic drawings of an exemplary embodiment. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a cylinder valve that can be actuated by via a cam and roller drag levers according to the invention, in the activated state. 
     FIG. 2 shows the cylinder valve according to FIG. 1, in the deactivated state. 
     FIG. 3 is a horizontal section through the roller drag lever along the line III—III in FIG. 1, on an enlarged scale. 
     FIG. 4 is a partial vertical section, on an enlarged scale, through the compressed-oil supply of the locking mechanism effected by a hydraulic valve alignment. 
     FIG. 5 shows an embodiment having a rigid support and a mechanical play compensation. 
     FIG. 6 is a section through the locking region along the line VI—VI in FIG.  5 . 
     FIG. 7 shows a modified embodiment of the locking means. 
     FIG. 8 is a partial longitudinal section, along the line VIII—VIII in FIG. 7, in the locked position. 
     FIG. 9 is a partial longitudinal section of the unlocked position according to FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a mechanical cam-valve gear for actuating a cylinder valve  1 . The stem  2  of the cylinder valve  1  is provided with a spring plate  3  that is supported on a valve spring  4  that holds the valve  1  in its closed position as shown. 
     A roller drag lever  5 , which is essentially formed by a partial lever  5 . 1  and a partial lever  5 . 2 , is provided for actuating the cylinder valve  1 . The two partial levers  5 . 1  and  5 . 2  are hinged to one another via an articulated shaft  6 , on which a roller  7 , which rests on the cam  8  of the associated camshaft, is seated to rotate freely. 
     The roller drag lever  5  is supported at its free end  5 . 11  associated with the partial lever  5 . 1  on the end of the valve stem  2 . The free end  5 . 21  of the drag lever  5  associated with the partial lever  5 . 2  supports the roller drag lever  5 , via a spherical cap  5 . 23 , on the moving part  9  of a hydraulic play-compensation element  10  of a known design. The play-compensation element  10  is permanently connected to the engine block  11 , and is connected to a compressed-oil supply via a corresponding conduit arrangement  12  in the engine block. 
     A switchable locking mechanism  13 , whose design and function will be described in detail below, is provided between the two partial levers  5 . 1  and  5 . 2 . In the illustrated locked position, the two partial levers  5 . 1  and  5 . 2  are locked together via the locking mechanism  13  to constitute a rigid unit, so that when the cam  8  rotates, the cylinder valve  1  is opened and closed, corresponding to the stroke height of the cam  8 . 
     If the relevant cylinder valve is to be deactivated, the locking mechanism  13  is actuated and the two partial levers  5 . 1  and  5 . 2  are unlocked, so the roller drag lever  5  “buckles” or articulates in the region of the roller  7  as shown in FIG. 2, and no force can be transmitted onto the cylinder valve. A restoring spring  14 , which is disposed between the two partial levers  5 . 1  and  5 . 2 , and is only indicated schematically here, ensures that the two partial levers are spread apart around the articulated shaft  6 , so the roller  7  remains in contact with the contour of the cam  8  when the two partial levers are unlocked, and follows the contour. When the roller drag lever  5  is deactivated or unlocked, the two partial levers can swing or rotate around the articulated shaft  6  and their supports at the end  2 . 1  of the valve stem, on the one hand, and at the support, here the moving part  9  of the hydraulic compensation element, on the other hand. 
     If the two partial levers  5 . 1  and  5 . 2  are to be locked with one another again, the locking mechanism  13  is correspondingly set at zero pressure, as will be explained in detail below, so a restoring spring can re-engage the locking mechanism  13  in the phase when the roller  7  rests against the base-circle region  8 . 1  of the cam  8 . 
     FIG. 3 shows the roller drag lever  5  in a horizontal section and on a larger scale. In this embodiment, the partial levers  5 . 1  and  5 . 2  are embodied like claws or u-shaped jaws, and extend on the lateral sides around the articulated shaft  6  and the roller  7 . An extension  5 . 3  on the partial lever  5 . 1  overlaps the partial lever  5 . 2  laterally, so the two partial levers can pivot about the articulated shaft  6  scissors-like relative to one another when unlocked. 
     The locking mechanism  13  is seated in the partial lever  5 . 2 . In the illustrated embodiment, the mechanism comprises a cylinder  15  that is formed in the wall of the lever portion  5 . 2  facing the extension  5 . 3  of the partial lever  5 . 1 , in which a piston portion  16  is seated to be displaced in a direction parallel to the longitudinal axis of the shaft  6 . In a corresponding recess  17  in the side wall of the extension  5 . 3  of the partial lever  5 . 1  and facing the cylinder  15 , a bar portion  18  is seated to be displaced in a direction parallel to the longitudinal axis of the shaft  6  counter to the force of a restoring spring  19 . 
     A supply conduit  20  connects the cylinder  15  to a compressed-oil supply. If compressed oil is supplied to the cylinder  15  with correspondingly high pressure, the piston portion  16  pushes the bar portion  18  back, counter to the force of the restoring spring  19 , until it stops in its recess  17 . The length of the bar portion  18  is selected such that, in the unlocked state illustrated here, the bar portion  18  is wholly within the recess  17  and permits the scissors-like relative movement of the two partial levers  5 . 1  and  5 . 2 , during which the end faces of the bar portion  18  and the piston portion  16  glide across each other. 
     If the cylinder  15  is set at zero pressure, the restoring spring  19  pushes the bar portion  18  and the piston portion  16  back into the cylinder  15  while the roller  7  rolls on the base circle  8 . 1  of the cam. The bar portion  18  thus extends into the portion of the cylinder  15  vacated by the piston  16 , and securely locks the two partial levers  5 . 1  and  5 . 2  together. The restoring force must be sufficient to push the locking element back very quickly. 
     The locking element can be modified such that the bar element  18  simultaneously functions as a piston. For this purpose, it is necessary to alter the direction of the spring restoring force and the compressed oil, and to configure the piston differently. A restoring spring disposed in the cylinder  15  presses the piston  16  into the recess  17  and locks the two partial levers together in the zero-pressure setting or when the oil pressure is low. If the part of the bar element that is configured as a piston is acted upon by pressure in the opposite direction of the force of the restoring spring, the part is pushed back into the cylinder  15 , and the locking part that is securely connected to the piston is pulled out of the recess  17 , thereby releasing the partial lever  5 . 1  from the partial lever  5 . 2 . 
     FIG. 4 is a vertical, partial section, on an enlarged scale, of the support of the partial lever  5 . 2  on the play-compensation element  10  via the free end  5 . 21 . The play-compensation element  10  essentially comprises a cylinder  10 . 1 , in which the hollow support  9  is guided in the manner of a piston. The supply line  12  introduces compressed oil into the interior of the moving hollows support  9  at a predetermined, low pressure, which assures the contact of the roller  7  against the cam  8  and ensures that the free end  5 . 11  of the partial lever  5 . 1  rests on the end  2 . 1  of the valve stem  2 , at any temperature. In the region where the free end  5 . 21  of the partial lever  5 . 2  is supported on the support  9 , the moveable hollow support  9  has a throughgoing bore  21 , which is connected to the supply conduit  20  and terminates into the cylinder  15 , as shown in FIG.  3 . If the cylinder valve  1  is to be deactivated, as described above, the play-compensation element  10  is acted upon with a correspondingly increased pressure that suffices to compress the restoring spring  17  formed in accordance with FIG. 3, and to push the bar portion  18  completely into its recess  17  in the extension  5 . 3  of the partial lever  5 . 1 , thus disengaging the two partial levers  5 . 1  and  5 . 2 . 
     In the other described embodiment, the increased pressure causes the piston  16  provided with a shoulder as a bar portion to be pushed back into the cylinder  15 , counter to the force of a restoring spring, so the shoulder attached to the piston  16  is pulled out of the recess  17 . 
     FIG. 5 illustrates a modification of the embodiment according to FIG.  1 . In this embodiment, the roller drag lever  5  is securely supported on the engine block via a support pin  10 . 1 . The support pin  10 . 1  is provided with a flow conduit  11 . 1 , which is connected to the conduit arrangement  12  of the compressed-oil supply. The support of the roller drag lever  5  and the actuation of the locking mechanism  13  are effected as in the above-described embodiment shown in FIGS. 1, etc. The design and function are identical so that reference is directed to the above description, where identical components are provided with identical reference characters. 
     The arrangement of the restoring spring  14  allows a hydraulic valve-play compensation element to be omitted, and thus results in a valve gear having mechanical play without the use of a drag-lever shaft. The arrangement of the restoring spring  14  also permits the contact between the roller  7  and the cam  8  to be maintained in both the base circle and the region of the cam ramp, even if the partial levers are locked together. To achieve this, as shown in FIG. 6, the end region of the cylinder  15  is provided with a groove-like extension  15 . 1  that extends in the direction of the pivoting movement of the two partial levers  5 . 1  and  5 . 2 . FIG. 6 illustrates this arrangement, in the locked position, in a section along the line VI—VI in FIG.  5 . The bar portion  18  extends into the groove-like extension  15 . 1  and is held in the locked position by the restoring spring  19 , as described in conjunction with FIG.  3 . Because of the groove-like extension  15 . 1 , whose length approximately corresponds to the magnitude of the anticipated valve play, it is possible for the two partial levers  5 . 1  and  5 . 2  to be displaced relative to one another in the directions of the arrows  21  and  22 . The restoring spring  14  ensures that roller  7  always rests against the curve  8 . 1  of the cam  8 . Both thermal and wear-induced changes in length of the valve shaft are compensated, so the valve spring  4  reliably holds the valve in its closed position as long as the roller  7  is rolling on the base-circle region  8 . 1  of the cam  8 . As soon as the roller  7  rolls onto the cam contour  8 . 2 , the bar  18  comes to rest against the groove-shaped extension  15 . 1 , so the cam can open the valve counter to the force of the valve spring  4 . 
     If the relevant valve is supposed to be deactivated, the oil pressure pushes the piston  16  forward, counter to the force of the restoring spring  19 , which breaks the locked connection of the two partial levers  5 . 1  and  5 . 2 . 
     FIG. 7 shows an embodiment of the locking mechanism  13  that is modified with respect to FIG.  3 . The modification initially lies in the connection of the bar portion  18 . 1  and the piston portion  16 . 1  by a web  16 . 2  with a reduced cross-sectional dimension to form a one-piece construction. In this embodiment, the cylinder  15  and the unitary piece  16 . 1 ,  16 . 2 ,  18 . 1  are located wholly within the partial lever  5 . 2 , which is shaped like a u-shared jaw. The partial lever  5 . 1 , however, extends on all four sides around the roller  7 . The partial lever  5 . 1  has, at its end facing the locking element  13 , an extension or bar latch  5 . 4 , whose width allows it to pivot through the empty space adjacent the web  16  between the piston portion  16 . 1  and the bar portion  18 . 1  in the unlocked position shown in FIG. 7, when the cylinder  15  is supplied with compressed oil. If the cylinder  15  is set at zero pressure, the restoring spring  19  presses the bar portion  18 . 1 , along with the piston portion  16 . 1 , back into the cylinder  15 , so the bar portion  18 . 1  can extend beneath and block the bar latch  5 . 4  as soon as the roller  7  passes through the base-circle region  8 . 1  in the cam  8 . 
     FIG. 8 is a sectional representation of the arrangement in the locked position. It can be seen from FIG. 8 how the bar latch  5 . 4  is supported on the bar portion  18 . 1  in the locked position. It can readily be seen that, when the bar portion  18 . 1  is displaced into the position shown in FIG. 7, the bar latch  5 . 4  is released and the two partial levers  5 . 1  and  5 . 2  can pivot downward toward one another in the directions of the two arrows, as shown in FIG.  9 . The restoring spring is not shown here in order to simplify the drawing. 
     The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.