Roller rocker arm for actuating a gas exchange valve of an internal combustion engine

Abstract

Roller rocker arm (1) for actuating a gas exchange valve of an internal combustion engine, comprising a lever (2) pivotably supported at one end, at the other end of which a support (7) for a valve stem end of the gas exchange valve is formed, and comprising a cam roller (3) against which a cam of a camshaft engages during operation of the internal combustion engine and which is mounted on an axle pin (24) by means of a needle bearing having a needle ring (10), wherein the axle pin (24) is arranged in bores of spaced-apart side walls (5 and 6) of the lever (2), and wherein the axial dimension of the needle ring (10) is greater than the width of the cam roller (3) at its cam contact surface (20) facing the cam, characterized in that the needle ring (10) protrudes on one side beyond a first end face of the cam roller (3) and ends directly adjacent to the corresponding one side wall (6) of the lever (2).that the needle ring (10) terminates at its other end with an end face of the cam roller (3), while the other side wall (5), starting from its sections located in the region of a calotte (8) serving to support and pivot the lever (2) and the support (7), is cranked inwards, wherein one side wall (6) has an outwardly cranked course in the region of the needle ring (10) projecting axially beyond the cam roller (3).

Description

[0001] The invention relates to a roller rocker arm for actuating a gas exchange valve of an internal combustion engine, having a lever pivotably supported at one end, at the other end of which a support for a valve stem end of the gas exchange valve is formed, and having a cam roller, against which a cam of a camshaft runs during operation of the internal combustion engine and which is mounted on an axle bolt by means of a needle bearing having a needle ring, wherein the axle bolt is arranged in bores of spaced-apart side walls of the lever and wherein the axial dimension of the needle ring is greater than the width of the cam roller at its cam contact surface facing the cam. Field of the invention

[0002] Roller rocker arms are arranged within the valve train in internal combustion engines with an overhead camshaft as transmission elements between the cams and the gas exchange valves to be actuated. They consist of a single-armed lever, one end of which is supported on a usually hydraulically adjustable support element, and the other end of which engages the gas exchange valve to be opened via a valve stem support. A cam roller is arranged in the middle section of the lever, which rolls along the circumference of the respective cam. The use of this cam roller significantly reduces friction in the valve train, thus enabling a significant reduction in fuel consumption during operation of the internal combustion engine. As an alternative to these valve trains with roller rocker arms, there are designs of internal combustion engines with an overhead camshaft in which rocker arms or bucket tappets are used as cam followers.Some of these cam followers are also equipped with a cam roller.

[0003] A roller rocker arm of the type described in the preamble of patent claim 1 is known from DE 101 21 798 A1. This roller rocker arm has a cam roller that fills the entire space between the spaced-apart side walls of the arm. This allows the raceways for a needle bearing used to support the cam roller on an axle pin to be wide in order to reduce the surface pressure (Hertzian pressure) on the corresponding raceways. The roller rocker arm is intended for a variable-stroke valve train in which at least two cams with different outer contours and a uniform cam base circle are provided for each gas exchange valve to be actuated. The different cam contours also include differences in the cam lobe, i.e., there is a cam with a large cam lobe and a cam with a small cam lobe, whereby the cam package is arranged displaceably on the camshaft so that one of the two cams selectively engages the outer circumference of the cam roller. On its outer circumference, the cam roller is provided with circumferential recesses in the edge area, creating a space in which the cam with a large cam lobe can move freely when the adjacent cam with a small cam lobe actuates the roller rocker arm on the cam roller. With this design of the cam roller, its raceways are therefore wider than its contact surface provided on the outer circumference.

[0004] The document DE 10 2010 024 196 A1 relates to a rocker arm for actuating a gas exchange valve of an internal combustion engine. The rocker arm has a lever pivotably supported at one end and configured at its other end with a valve stem support for a valve stem end of a gas exchange valve. Furthermore, the rocker arm has a cam roller against which a cam of a camshaft engages during operation of the internal combustion engine and which is mounted on an axle pin by means of a needle roller and a cage. The cage is arranged in bores in spaced-apart side walls of the lever, and to reduce Hertzian pressure, an axial dimension of the needle roller and cage is larger than the width of the cam roller at its cam contact surface facing the cam.A first end of the needle roller and cage should protrude on one side beyond a first end face of the cam roller and end directly adjacent to or in contact with the corresponding side wall of the lever. Furthermore, the needle roller and cage should essentially be flush with a second end face of the cam roller at its second end. A spacer sleeve should be arranged between this second end of the needle roller and the side wall facing it.

[0005] Furthermore, the prior art documents EP 1 548 145 A1, DE 10 2005 047 234 A1, DE 10 2007 012 734 A1, DE 10 2004 002 290 A1 and DE 10 2010 005 606 A1 are known. Object of the invention

[0006] The invention is based on the object of developing a roller rocker arm of the type mentioned at the outset in such a way that the weight of this arm and its manufacturing costs are reduced. Summary of the invention

[0007] This object is achieved according to the characterizing part of patent claim 1 in that the needle roller and cage projecting on one side beyond a first end face of the cam roller and ending immediately adjacent to the corresponding side wall of the lever, that the needle roller and cage essentially terminate at its other end with an end face of the cam roller, and that one side wall has an outwardly cranked profile in the region of the needle roller and cage projecting axially beyond the cam roller, while the other side wall is cranked inwards starting from its sections located in the region of a calotte serving to support and pivot the lever and the support. In contrast to the generic prior art, the needle roller and cage-guided needle roller bearing is intended to project on one side beyond the cam roller.The basis for this inventive design is the fact that the Hertzian pressure is significantly greater on the inner raceway, which has a small radius of curvature, than on the outer raceway, which has a large radius of curvature. Therefore, the needles that protrude beyond the outer raceway are designed to roll along the inner raceway over their entire length. This effectively reduces the surface pressure on the inner raceway.

[0008] On the side of the cam roller where the needle roller and cage protrude axially, the necessary clearance is created by offsetting the corresponding side wall outward. In this area, the opposite side wall is offset inward, so that it runs close to the end face of the cam roller.

[0009] In a further embodiment of the invention, the needles of the needle roller and cage are to be guided in a sliding manner along the end faces of the side walls. The outer ring of the cam roller can also be guided in a sliding manner along this inwardly bent section of the side wall.

[0010] Furthermore, an inner raceway for the needle roller and cage needles can be formed directly on the axle pin. The needle rollers, which protrude axially beyond the cam roller, roll along the axle pin along their entire length. Alternatively, a separate inner ring can be arranged on the axle pin, forming the inner raceway with the width of the needle roller and cage.

[0011] In a further embodiment of the invention, the lever is U-shaped in cross-section, with the side walls being connected to one another by a transverse wall in which a recess is arranged to accommodate the cam roller, and with the longitudinal center planes of the rectangular recess, the calotte serving to support the lever, and the support having an identical course. This lever profile has sufficient rigidity and can advantageously be produced from a punched sheet metal blank using a non-cutting forming process, in particular by cold forming. The cam roller can be guided on the end face along the edges of the recess. In addition, the correspondingly designed roller rocker arm should be arranged in the valve train such that the open U-shaped profile faces away from the support element and the gas exchange valve.Consequently, the cap and the support, which acts directly on the end of a valve stem, are formed on an outer surface of the transverse wall.

[0012] The transverse wall can extend radially to the needle roller and cage assembly, thus creating sufficient clearance for the roller and not compromising the lever's rigidity. Alternatively, it is possible to provide a rectangular recess for the protruding needles next to the roller recess. This recess extends to the side wall and is larger in the longitudinal direction of the lever than the inner diameter of the outer ring of the cam roller.

[0013] Furthermore, in a further development of the teaching according to the patent claim, the axial dimension of the needle roller assembly should be 30% to 60% larger than the width of the cam roller. A corresponding ratio of the width of the cam roller to the width of the needle roller assembly results in a sufficient reduction in Hertzian pressure, while the structural dimensions of the roller rocker arm still allow for its space-saving arrangement in the valve train.

[0014] Finally, the roller rocker arm is provided for a switchable valve train in which at least two axially movable cams with different cam contours roll selectively on the outer circumference of the cam roller on the camshaft. A corresponding valve train is explained in detail in DE 100 54 623 A1. The asymmetrical design of the lever with its inwardly cranked side wall creates the necessary clearance for a cam designed with a large cam lobe when the roller rocker arm is actuated via the cam with the smaller cam lobe. If, due to the width of the cams of the cam pair, appropriate clearance for the large cam cannot be achieved solely by the inwardly cranked side wall, this side wall can be provided with a flattened area or recess. Short description of the drawing

[0015] For further explanation of the invention, reference is made to the drawing, which shows a simplified embodiment. Shown are: Fig. 1 a plan view of a roller rocker arm according to the invention, Fig. 2 a side view of the roller rocker arm according to Fig. 1, Fig. 3 a view from below of the roller rocker arm after Fig. 1 and Fig. 4 a longitudinal section through the roller rocker arm according to Fig. 1 according to line IV-IV. Detailed description of the drawing

[0016] In the Fig. In the drawings 1 to 4, 1 denotes a roller-type rocker arm, which essentially consists of a U-shaped lever 2 and a cam roller 3. The U-shaped lever 2 is designed as a non-cutting sheet metal part, whereby, as part of the forming process, a blank is first punched out of sheet metal and then cold-formed. Thus, the lever 2 has a transverse wall 4 and side walls 5 and 6 extending therefrom.

[0017] At one end of the lever 2, the transverse wall 4 is designed as a support 7, with which the lever 2 rests on one end of a valve stem (not shown in detail) of a gas exchange valve. At the opposite end of the lever 2, as can be seen in particular from the Fig. 1, Fig. 3 and Fig. 4, a cap 8 is formed into the transverse wall 4, via which the lever 2 used in the valve train is supported on a support element (also not shown). This support element is preferably designed to be hydraulically variable in length, so that the pivot point of the lever 2 can be changed in such a way that any valve clearance that may occur can be compensated for. In the area of ​​the cap 8, the distance between the side walls 5 and 6 is increased to create sufficient space for their arrangement.

[0018] As in particular the Fig. 1 and Fig. 3 can be removed, the cam roller 3 is arranged in a recess 9 in the transverse wall 4 which is essentially designed with a rectangular outer contour. Fig. 1 a needle roller 10, of which in the illustration according to Fig. 1, individual needles 11 are visible, projecting on one side over the axial extent of the cam roller 3. The ends of the needles 11 extend to an inner circumferential surface 12 of the side wall 6 and are guided along it in a sliding manner. In this area, this side wall 6 has an outward offset 13, creating sufficient space for the protruding needle roller assembly 10.

[0019] The opposite side wall 5, however, is provided in this area with an inwardly directed offset 14, whereby a circumferential surface 15 of this side wall 5 is guided up to an end face 16 of the cam roller 3. Both the recess 9 and the cam roller 3 arranged therein have a Fig. 1, which runs centrally through the support 7 and the calotte 8. Since, as already explained, the side walls 5 and 6 are provided with outward and inward offsets 13 and 14, the lever 2 is designed asymmetrically. This creates sufficient space for the movement of a large cam, which is part of a longitudinally displaceable cam assembly. Furthermore, the Fig. 1 that a spray opening 17 directed towards the cam roller 3 is provided on the calotte 8, through which lubricating oil is applied to the cam roller 3. In the area of ​​the projecting ends of the needle roller 10, as can be seen from the Fig. 3, the transverse wall 4 is provided with a bulge 18 downwards, ie the transverse wall 4 runs radially to the needle ring 10 and thus creates sufficient space for the protruding needles 11.

[0020] In the side view and in the sectional view of the roller rocker arm 1 according to the invention according to the Fig. 2 and Fig. 4 shows that the cam roller 3 has an outer ring 19 with a cam contact surface 20 and an outer raceway 21 for the needle roller and cage assembly 10. Furthermore, the needles 11 of the needle roller and cage assembly are guided on an inner raceway formed on an inner ring, with this inner ring and thus the entire cam roller 3 being mounted relative to the side walls 5 and 6 by means of an axle bolt 24.

[0021] The side walls 5 and 6 are also provided with flattened areas 25 so that, in a switchable valve train with a pair of cams that can be moved longitudinally on a camshaft, sufficient clearance for the large cam is ensured. Furthermore, the side walls 5 and 6 have grooves 26 and 27 in the area of ​​the calotte 8, in which a clamp (not shown) can be fixed to the side walls 5 and 6. This clamp serves to connect the roller rocker arm 1 to the support element to form a pre-assembled unit that can be delivered for installation in the corresponding cylinder head. To guide the roller rocker arm 1 at the valve stem end of the gas exchange valve, the lever 2 is provided in the area of ​​the support 7 with tabs 28 and 29, which extend from the side walls 5 and 6 and are bent down to below the transverse wall 4. These bent tabs 28 and 29 are spaced apart from each other by a distance that corresponds approximately to the diameter of the valve switching end.

[0022] The Fig. 1 to 4, it can be seen that the relatively narrow cam roller 3 is provided with a considerably wider needle roller and cage assembly 10, which projects beyond the cam roller 3 on one side, so that the surface pressure of the rolling elements, designed as needles 11, on the inner ring can be significantly reduced. For this purpose, the lever 2 is designed asymmetrically, i.e., an outward offset 13 of the side wall 6 creates sufficient space for the protruding needle roller and cage assembly 10. List of reference symbols 1 roller rocker arm 2 levers 3 cam roller 4 cross wall 5 Side wall 6 Side wall 7th edition 8 dome 9 Recess 10 needle roller 11 needles 12 inner surface of 6 13 Outward offset 14 Inward crank 15 lateral surface of 5 16 frontal area of ​​3 17 Spray opening 18 bulge of 4 19 Outer ring 20 Cam contact surface 21 outdoor track 24 axle bolts 25 flattenings 26 grooves 27 grooves 28 tab 29 tab

Claims

[1] Roller rocker arm (1) for actuating a gas exchange valve of an internal combustion engine, having a lever (2) pivotably supported at one end, at the other end of which a support (7) for a valve stem end of the gas exchange valve is formed, and having a cam roller (3) against which a cam of a camshaft runs during operation of the internal combustion engine and which is mounted on an axle pin (24) by means of a needle bearing having a needle ring (10), wherein the axle pin (24) is arranged in bores of spaced-apart side walls (5 and 6) of the lever (2) and wherein the axial dimension of the needle ring (10) is greater than the width of the cam roller (3) at its cam contact surface (20) facing the cam, characterized bythat the needle ring (10) projects on one side beyond a first end face of the cam roller (3) and ends immediately adjacent to the corresponding one side wall (6) of the lever (2), that the needle ring (10) terminates at its other end with an end face of the cam roller (3), while the other side wall (5), starting from its sections lying in the region of a calotte (8) serving to support and pivot the lever (2) and the support (7), is cranked inwards, wherein the one side wall (6) has an outwards cranked course in the region of the needle ring (10) projecting axially beyond the cam roller (3). [2] Roller rocker arm according to claim 1, characterized by that needles (11) of the needle roller and cage (10) are guided on the front side in a sliding manner on the side walls (5 and 6). [3] Roller rocker arm according to claim 2, characterized bythat an inner raceway for the needles (11) of the needle roller and cage (10) is formed on an inner ring arranged on the axle bolt (24), which inner ring projects on one side beyond the cam roller (3). [4] Roller rocker arm according to claim 1, characterized by that the lever (2), seen in cross-section, is U-shaped, wherein the side walls (5 and 6) are connected to one another by a transverse wall (4) in which a recess (9) serving to receive the cam roller (3) is arranged, and wherein a longitudinal center plane of the rectangular recess (9) extends centrally through the calotte (8) and the support (7). [5] Roller rocker arm according to claim 4, characterized bythat the transverse wall (4) has a bulge (18) in the region of the projecting needles (11) which extends to the side wall (6) and whose radius, related to a longitudinal axis of the axle bolt (24), is greater than a radius of an outer raceway (21) on the outer ring (19) of the cam roller (3). [6] Roller rocker arm according to claim 1, characterized by that the lever (2) is designed as a non-cutting sheet metal part. [7] Roller rocker arm according to claim 4, characterized by that the transverse wall (4) of the U-shaped lever (2) is provided with the cap (8) and the support (7) on its outer surface facing away from the open profile of the lever (2). [8] Roller rocker arm according to claim 1, characterized by that the axial dimension of the needle roller and cage (10) is 30% to 60% larger than the width of the cam roller (3).

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