Patent Publication Number: US-2012031361-A1

Title: Internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This U.S. patent application claims priority to German Patent Application DE102010036899.7, filed Aug. 6, 2010, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to an internal combustion engine having a plurality of cylinders. 
     BACKGROUND OF THE INVENTION 
     In modern internal combustion engines, variable valve timing mechanisms are used to optimize the charge movement in the combustion chamber, by way of which variable valve timing mechanisms different valve strokes can be set for the gas exchange valves of the internal combustion engine. DE 196 11 641 C1, which is incorporated by reference herein, has disclosed a valve timing mechanism of an internal combustion engine, by way of which valve timing mechanism the actuation of a gas exchange valve with a plurality of different lifting cams is made possible. To this end, a sliding cam with a plurality of cam tracks is mounted fixedly on the camshaft so as to rotate with it but so as to be displaceable axially, which sliding cam has a lifting contour, into which an actuating element engages in the form of a pin for generating an axial displacement of the cam. As a result of the axial displacement of the cam, a different valve stroke is set for the respective gas exchange valve. 
     DE 10 2007 027 979 A1, which is incorporated by reference herein, has described a valve timing mechanism for gas exchange valves of an internal combustion engine with a camshaft tunnel bearing, which valve timing mechanism comprises cam pieces which can be displaced on a camshaft, a radial bearing of the camshaft being positioned between two sliding-cam pieces which are provided for the actuation of gas exchange valves of a cylinder. The previously known mountings of a valve timing mechanism with a sliding-cam assembly are complicated and afford restricted flexibility. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a simplified arrangement of a valve timing mechanism in a cylinder head of an internal combustion engine, in particular with regard to the positioning and the mounting of a sliding-cam system in the cylinder head. 
     According to one aspect of the invention, an internal combustion engine has a plurality of cylinders, a crankcase, a cylinder head and a cylinder-head cover, the cylinder head being formed from a cylinder-head lower part and a camshaft housing which is positioned between the cylinder-head cover and the cylinder-head lower part, and at least one camshaft and one sliding cam which can be displaced axially on the camshaft and has a slotted-guide section being provided for actuating gas exchange valves of the internal combustion engine, an actuator with an actuable pin being provided for bringing about an axial displacement of the sliding cam, characterized in that the camshaft and the sliding cam are positioned in the camshaft housing, it being possible for the camshaft which is mounted rotatably for valve actuation to be assembled with the axially displaceable sliding cam in the camshaft housing in such a way that the camshaft, the sliding cam and the camshaft housing form one preassembled unit which can be attached to the cylinder-head lower part. 
     The internal combustion engine is distinguished by the fact that the camshafts and the sliding cams are positioned in the camshaft housing, it being possible for the camshaft which is mounted rotatably for valve actuation to be assembled with the axially displaceable sliding cam in the camshaft housing in such a way that the camshaft, the sliding cam and the camshaft housing together form one preassembled unit which can be attached to the cylinder-head lower part. Advantageous accommodation of a valve timing mechanism therefore takes place with a compact sliding-cam device for the actuation of the gas exchange valves of a cylinder in a camshaft housing, which can be preassembled before the attachment of the camshaft housing to the cylinder-head lower part is carried out. This leads to simplified assembly of the internal combustion engine and therefore makes reliable, quality-assured and inexpensive production of the internal combustion engine possible on account of the simplified handling and the unit which is tested in advance and is preassembled. 
     As claimed in one refinement of the invention, the actuators which are provided for bringing about the axial displacement of the sliding cam are arranged in a lateral region of the camshaft housing. To this end, a lateral wall of the camshaft housing is expediently provided with a plurality of openings arranged in it for receiving the actuators. As a result of the lateral arrangement of the actuators, they can be introduced into the camshaft housing with less outlay than previously and the construction tolerances can be reduced, the said actuators then being accommodated in such a way that an overall height of a cylinder head is reduced to a minimum. This therefore brings about a particularly compact and simplified arrangement of the internal combustion engine, the connecting options of the actuators, for example to a control unit of the internal combustion engine, being simplified by the lateral openings which are provided to accommodate the actuators. Moreover, the design of the cylinder-head cover, in particular, can be of simplified configuration. 
     As claimed in one preferred refinement of the invention, each sliding cam is assigned an individual actuator per cylinder for the actuation of the inlet-side or outlet-side gas exchange valves. In particular, the sliding cam and the actuator are positioned in the camshaft housing spatially between two bearing points of the camshaft. At least two or three gas exchange valves can preferably be actuated by way of one sliding cam per cylinder, the slotted-guide section which is arranged on the sliding cam being positioned between two cam sections which in each case serve for the actuation of the gas exchange valves and in each case have a plurality of cam tracks. As a result, there is a compact sliding-cam form, by way of which the actuation of two gas exchange valves which are positioned close to one another can be brought about in a functionally reliable manner. 
     In a further refinement of the invention, the camshaft adjusting device and the drive wheel are connected to the camshaft, are arranged in the camshaft housing and advantageously form a part of the preassembled unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and combinations of features result from the description. Concrete exemplary embodiments of the invention are shown in simplified form in the drawing and are explained in greater detail in the following description. In the drawing: 
         FIG. 1  shows a diagrammatically illustrated internal combustion engine of the boxer type, 
         FIG. 2  shows a sectional view of the cylinder head of the internal combustion engine from  FIG. 1 , 
         FIG. 3  shows a further sectional view of the cylinder head of the internal combustion engine from  FIG. 1 , 
         FIG. 4  shows a perspective view of a camshaft housing of the internal combustion engine from  FIG. 1  according to a first embodiment, 
         FIG. 5  shows a further perspective view of the internal combustion engine from  FIG. 1  according to the first embodiment, 
         FIG. 6  shows a perspective view of a camshaft housing of the internal combustion engine as shown in  FIG. 1 , according to a second embodiment, and 
         FIG. 7  shows a perspective view of the camshaft housing of the internal combustion engine as shown in  FIG. 1 , with bearing devices which are configured integrally on the camshaft housing. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an internal combustion engine  1  of the boxer type which is formed from two cylinder rows  1   a  and  1   b  which are arranged horizontally. The internal combustion engine  1  comprises a crankcase  2  and in each case one cylinder head  3  per cylinder row  1   a  and  1   b , which cylinder head  3  is delimited to the outside by a cylinder-head cover  4 . The cylinder head  3  is assembled from a cylinder-head lower part  5  and a camshaft housing  6 . 
     As shown in  FIG. 2 , an inlet camshaft  7  and an outlet camshaft  8  are mounted in the camshaft housing  6  for controlling gas exchange valves of the internal combustion engine  1 . The camshaft housing  6  is attached as one preassembled unit to the cylinder-head lower part  5  and is screwed to the latter. After the mounting of the camshaft housing  6  on the cylinder-head lower part  5 , the cylinder-head cover  4  is attached to the camshaft housing  6 . A plurality of bolts  12  are provided for fastening the cylinder-head cover  4  to the camshaft housing  6 . 
     Two inlet valves  9  and two outlet valves  10  are provided per cylinder, the inlet valves  9  being actuated in a controlled manner by the inlet camshaft  7  in a known way. The outlet valves  10  are actuated in a controlled manner by the outlet camshaft  8 . To this end, the inlet camshaft  7  and the outlet camshaft  8  mounted in the camshaft housing  6  in each case have a plurality of sliding cams  13 .  FIG. 3  shows a sectional view through the inlet camshaft  7  which actuates the two inlet valves  9  with the aid of roller drag levers  21 . As shown in  FIG. 3 , the sliding cam  13  is formed from a slotted-guide section  15  which is positioned in the center and two outer cam sections  14 . Each outer cam section  14  comprises three cam tracks  17 , by way of each of which a different valve stroke is set. As an alternative, two cam tracks can be arranged instead of three on each outer cam section  14 . 
     As can be seen in  FIG. 4  or  5 , each sliding cam  13  is assigned an actuator  16  which has an extendable pin (not shown) which interacts with the slotted-guide section  15 . As a result, an axial displacement of the sliding cam  13  takes place in a region between two camshaft bearings. As a result of the axial displacement of the sliding cam  13 , the respective valve is actuated in a targeted manner by way of a defined cam track, with the result that a different valve stroke setting takes place. The function of the displaceable cam  13  can be designed, for example, as described in document DE 196 11 641 C1. 
     The sliding cam  13  which is shown in  FIG. 3  comprises three cam tracks  17  which are axially displaceable for each valve. As an alternative, two cam tracks instead of three can be arranged for each valve. In each case one camshaft adjusting device  18  and one drive wheel  19  as shown in  FIG. 4  are attached at one end of each camshaft  7 ,  8 . The camshaft adjusting device  18  is actuated hydraulically or electrically, by way of which a camshaft angle is adjusted, in order to change the control times of the internal combustion engine. The drive wheel  19  is configured as a chain sprocket and serves to drive the respective camshaft. To this end, the drive wheel  19  is coupled via a drive chain (not shown) to a crankshaft (not shown) of the internal combustion engine  1 . 
     In order to mount the camshafts  7  and  8 , in each case three radial bearing devices  20  are provided, for example, which comprise a lower bearing-ring body  23  which is configured in one piece with the camshaft housing  6 . In the case of an internal combustion engine of V design with 8 cylinders, four radial bearing devices  20  are provided, for example. Furthermore, each radial bearing device  20  comprises an individual bearing cap  22  which is fastened with the lower ring to the camshaft housing  6  with the aid of, for example, two bolts. As an alternative, the individual bearing caps as shown in  FIG. 7  are configured in one piece with the camshaft housing  6 . In this case, there is a tunnel-like radial bearing device  20   a . Here, the respective camshaft  7  or  8  is pushed in through a corresponding opening  28  for mounting on the camshaft housing  6 . The sliding cams  13  are brought into position at the corresponding point between the respective radial bearing devices  20   a , in such a way that the respective camshaft  7  or  8  is then pushed into them. 
     The camshafts  7  and  8  are preassembled on the camshaft housing  6  and are connected to the respective camshaft adjuster  18  and the drive wheel  19 . After this, there is a preassembled camshaft housing unit which is attached to the cylinder-head lower part  5  in a single mounting step. 
     The camshaft housing  6  comprises two end sections  24  and  25 , between which two lateral walls or edge parts  26  and  27  extend. The camshafts  7  and  8  extend in the axial direction parallel to the lateral walls  26  and  27  and are delimited in the axial direction by the two end sections  24  and  25 . 
       FIG. 4  shows a first exemplary embodiment of the present invention.  FIG. 4  shows the preassembled camshaft housing  6  together with the camshafts  7  and  8 . The parts cylinder-head cover  4 , camshaft housing  6  and cylinder-head lower part  5  which are screwed together are shown in  FIG. 2 . In each case one individual sliding cam  13  is provided for each cylinder both on the inlet camshaft  7  and on the outlet camshaft  8 , between which sliding cam  13  and the respective gas exchange valve in each case one roller drag lever  21  is arranged. 
     The sliding cams  13  which are connected fixedly to the respective camshaft so as to rotate with it make a valve stroke adjustment possible. The camshaft angle can be changed by the respective camshaft adjusting device. The camshaft  7  and  8  is driven by the drive wheel  19 . Depending on the operating point of the internal combustion engine  1 , targeted adjustment of the valve stroke and/or of the camshaft angle is performed, in order to achieve a best possible degree of efficiency of the internal combustion engine  1  at the respective operating point. 
     In the exemplary embodiment which is shown in  FIG. 4  and  FIG. 5 , the actuators  16  are positioned laterally in the camshaft housing  6 , preferably in the respective lateral wall  26  and  27 . To this end, as shown in  FIG. 5 , in each case one corresponding opening  29  is provided on the lateral wall  26  and  27  of the camshaft housing  6 , through which opening  29  the respective actuator  16  is pushed in. As a result of the lateral arrangement of the actuators  16 , an overall height of the camshaft housing  6  is reduced to a minimum. An arrangement of this type is advantageous, in particular, in boxer engines, since they have cylinders which lie horizontally in the vehicle and require more installation space in the width direction than, for example, inline engines or V engines. 
       FIG. 6  shows a second exemplary embodiment of the present invention, in which the actuators  16  are positioned in the camshaft housing  6  above the camshafts  7  and  8 . An arrangement of this type is suitable, in particular, for internal combustion engines of V design or inline design. 
     The alternative which is shown in  FIG. 7  is suitable for both exemplary embodiments of the invention. Here, the individual bearing caps as shown in  FIG. 7  are configured in one piece with the camshaft housing  6 , with the result that the respective radial bearing device is of tunnel-like configuration. 
     A three-stage sliding-cam system for an internal combustion engine  1  with simplified assembly is provided by way of the present invention, in which sliding-cam system a sufficient bearing width of the radial bearings  20  can be provided for the camshafts  7  and  8  in the case of low or small valve and cylinder spacings. As a result of the accommodation of the actuators  16  in the camshaft housing  6 , the tolerances for the function of the sliding cams  13  can be kept low, since the machining of the camshaft bearings  20  and the machining operations for receiving the actuator system and the camshaft adjusting device  18  can be carried out in one component. Moreover, the camshaft housing  6  can be delivered with the preassembled camshafts  7 ,  8  and actuators  16  as one unit during the production of the internal combustion engine  1 .