US20100307437A1

US20100307437A1 - Rocker arm for a valve train of an internal combustion engine

Info

Publication number: US20100307437A1
Application number: US12/783,604
Authority: US
Inventors: Robert Kamm; Rainer Schwinn
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: SCAHEFFLER TECHNOLOGIES & Co KG GmbH; Schaeffler Technologies AG and Co KG
Priority date: 2009-06-05
Filing date: 2010-05-20
Publication date: 2010-12-09

Abstract

A rocker arm (1 a to 1 f) for a valve train of an internal combustion engine is provided having an elongate lever body (2 a to 2 f) formed out of sheet metal and including a first end section (3), a second end section (5) and a center section (4) formed by two spaced apart, parallel side walls (6 a to 6 f), having aligned axle-receiving bores (7). The first end section includes a crossbar (11 a to 11 f) connecting the side walls to each other and two contact surfaces (12) for a simultaneous actuation of two gas exchange valves of the internal combustion engine, and the first end section is configured substantially wider than the center section. The contact surfaces extend on the crossbar while being spaced in transverse direction from the side walls.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/184,426, filed Jun. 5, 2009, which is incorporated herein by reference as if fully set forth.

BACKGROUND

The invention concerns a rocker arm of a valve train of an internal combustion engine. The rocker arm comprises an elongate lever body formed out of a sheet metal and comprising a first end section, a second end section and a center section formed by two spaced apart, parallel side walls comprising aligned axle-receiving bores, the first end section comprising a crossbar connecting the side walls to each other and two contact surfaces for a simultaneous actuation of two gas exchange valves of the internal combustion engine, and said first end section is configured substantially wider than the center section.
A double rocker arm of the above-noted type is known from the document DE 196 18 417 A1, which is considered to be generic, and, besides the low manufacturing costs incurred by using a shaping method, it is characterized by an advantageous high-quality light-weight characteristic because the lever body possesses a width matched to the distance between the two gas exchange valves only on the valve-side first end section, whereas the remaining lever geometry corresponds to that of a standard rocker arm for actuation of only one gas exchange valve i.e., of a single rocker arm. In contrast, the double rocker arm proposed in the document DE 43 36 360 C2 possesses a clearly larger mass and a correspondingly high mass moment of inertia about its fulcrum because the considerable valve-side width of the lever extends over the first end section and over the entire center section up to the second end section.
A drawback of the generic double rocker arm of the first-cited document, however, is the arrangement of the contact surfaces actuating the gas exchange valves on the valve-side lower edges of the side walls of the lever body. This arrangement requires namely that the wall thickness of the side walls must be matched to the required width of the contact surfaces and thus to the diameter of the valve stems in contact therewith. Starting from the typical ratio of the valve stem diameter to the lever wall thickness in an order of magnitude of 2:1 in standard single rocker arms, the wall thickness of the generic double rocker arm would be clearly too large either locally in the region of the contact surfaces or uniformly all-over. Whereas the required local enhancement of the wall thickness by a shaping method would be at least considerably difficult, the uniform wall thickness would result in an overdimensioning of the lever with regard to its mechanical strength with a correspondingly superfluous mass.

SUMMARY

The object of the present invention is therefore to improve a rocker arm of the above-noted type, so that the aforesaid drawback is eliminated with simple measures and the rocker arm, while retaining its simple manufacturability, possesses a high-quality light-weight characteristic.
This objective is achieved according to the invention, with advantageous developments and further features of the invention being described in detail below and in the claims. According to the invention, the contact surfaces extend on the crossbar while being spaced in transverse direction from the side walls. As a result, the dimensioning of the side wall thickness can be completely uncoupled from the required width of the contact surfaces and matched first and foremost to the required strength/rigidity of the lever body.
According to a further aspect of the invention, the second end section of the lever body comprises a joint socket for mounting the rocker arm on a stationary joint head arranged in the internal combustion engine, the rocker arm comprising a roller mounted on a roller axle fixed in the axle-receiving bores. While the present embodiment concerns the currently predominantly used valve train kinematics including a rocker arm frequently also referred to as a roller finger lever (as known, the roller serves as a low-friction contact surface for a cam of a camshaft), it is possible, alternatively, to also use a centrally mounted rocker arm whose axle-receiving bores engage around a stationary rocker arm axle arranged in the internal combustion engine, said rocker arm then comprising, on its second end section, a cam-contacting surface likewise in the form of a roller or a rigid sliding contacting surface.
Besides this, as viewed in perpendicular direction to the contact surfaces, the lever body can have a substantially T-shaped configuration in that the crossbar comprises an inner section which is connected to lower edges of the side walls facing the gas exchange valves while extending between the side walls, and further comprises two outer sections which are connected to upper edges of the side walls turned away from the gas exchange valves and extend away from each other.
The inner ends of the outer sections can be bent through 180° and connected to the upper edges of the side walls while extending parallel to the side walls and slightly spaced from or in bearing relationship to the side walls. For achieving an enhanced bending strength of the outer sections in direction of the gas exchange valves, the inner ends of the outer sections are welded to the side walls in the region of the lower edges of the side walls.
Should a guidance of the rocker arm be required in transverse direction, this can be realized on one or both of the valve stems, in the first case particularly through provision of valve guiding webs known form the prior art on both sides of one of the contact surfaces. In the second case, it is possible either to use an inner guidance of the rocker arm through valve guiding webs extending within the intermediate space between the valve stems on their opposing inner sides, or an outer guidance of the rocker arm using valve guiding webs extending outside of the intermediate space between the valve stems on their outer sides turned away from each other. In the case of inner guidance, the side walls can serve as valve guiding webs engaging between the inner sides of the valve stems and, in the case of outer guidance, the valve guiding webs can be formed by bending the outer ends of the outer sections of the crossbar at a right angle in direction of the gas exchange valves to engage around the gas exchange valves and serve as a transverse guide of the rocker arm relative to the gas exchange valves.
In an alternative embodiment of the rocker arm, the first end section, together with the side walls widening into a T-shape and the crossbar, forms a substantially H-shaped or U-shaped cross-sectional profile. With regard to the aforesaid outer guidance of the rocker arm, the invention preferably proposes that the U-shaped cross-sectional profile be open in direction of the gas exchange valves to engage around the gas exchange valves and serve as a transverse guide of the rocker arm relative to the gas exchange valves.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention will become apparent from the following description and the appended drawings which illustrate examples of embodiment of the invention. In the drawings:

FIG. 1 is a perspective view of an embodiment of a rocker arm according to the invention.

FIG. 2 is a perspective view of another embodiment of a rocker arm according to the invention.

FIG. 3 is a perspective view of another embodiment of a rocker arm according to the invention.

FIG. 4 is a perspective view of another embodiment of a rocker arm according to the invention.

FIG. 5 is a perspective view of another embodiment of a rocker arm showing only the lever body.

FIG. 6 is a perspective view of another embodiment of a rocker arm according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

If not otherwise stated, identical or functionally identical features or components are designated by the same reference numerals, or the reference numerals of these features or components are omitted in individual figures.
The rocker arms identified at la to if in FIGS. 1 to 6 serve for a simultaneous actuation of two gas exchange valves of an internal combustion engine and comprise respectively, an elongate lever body 2 a to 2 f formed in one piece by cold shaping out of sheet metal and comprising a first end section 3, a center section 4 and a second end section 5. The center section 4 is formed by two side walls 6 a to 6 f which, in this region, extend parallel to each other and comprise aligned axle receiving bores 7, (see FIG. 5). A roller axle 8 is fixed by staking, in a manner known per se, in the axle receiving bores 7. The roller axle 8 serves to mount a roller 9 as a low-friction contacting surface for a cam of a camshaft. The second end section 5 comprises a semispherical joint socket 10 for a pivotal mounting of one end of the rocker arm 1 a-1 f on a semispherical joint head of a support element that is arranged stationary in the internal combustion engine. The first end section 3 comprises a crossbar 11 a to 11 f which connects the side walls 6 a-6 f and comprises two contact surfaces 12 for the valve stems. The contact surfaces 12 extending in the figures on the underside of the crossbars 11 a to 11 f are configured with a convex shape, in a manner known per se, in the longitudinal direction of the lever bodies 2 a-2 f and, according to the invention, extend spaced from the side walls 6 a to 6 f in transverse direction.
Viewed in a direction perpendicular to the contact surfaces 12, i.e. in a top view, all the lever bodies 2 a-2 f are T-shaped due to the fact that the first end section 3 is substantially wider than the center section 4. The width of the center section 4 is comprised only of the width of the roller 9, the axial lash of the roller 9 between the side walls 6 a to 6 f and twice the wall thickness of the side walls 6 a to 6 f. In contrast, as will be elucidated later in connection with the rocker arms 1 b, 1 d and 1 e, the width of the first end section 3 corresponds at least to the sum of the distance between the gas exchange valves, their valve stem diameters and, where appropriate, also the valve guiding webs.
In the rocker arms 1 a-1 d, the crossbar 11 a-11 d is formed by one inner section 13 a to 13 d and two outer sections 14 a to 14 d. The inner section 13 a-13 d extends between the side walls 6 a to 6 d and connects these to each other in that it is connected to lower edges of the side walls 6 a to 6 d facing the gas exchange valves. The two outer sections 14 a-14 d which comprise a profile corresponding to the convex contact surfaces 12 (see, in particular, FIG. 1) are connected to upper edges of the side walls 6 a-6 d turned away from the gas exchange valves and extend away from each other in transverse direction of the rocker arm.
While the outer sections 14 a, 14 b of the lever bodies 2 a, 2 b are bent through 90° from the upper edges of the side walls 6 a, 6 b, the lever bodies 2 c, 2 d comprise outer sections 14 c, 14 d whose inner ends, bent through 180° , are connected to the upper edges of the side walls 6 c, 6 d and extend at first in parallel and in bearing relationship to the side walls 6 c, 6 d down to the level of the inner sections 13 c, 13 d. A gaping-open of the double-backed sheet metal produced by the valve forces acting on the outer sections 14 c, 14 d is prevented by the fact that the inner ends of the outer sections 14 c, 14 d are welded to the lower edges of the side walls 6 c, 6 d. The weld joint identified at 15 in FIG. 4 is represented only symbolically.
The rocker arm 1 e of FIG. 5—represented is only its lever body 2 e—comprises side walls 6 e which widen in the region of the first end section 3 into a T-shape and, together with the crossbar 11 e which extends between the side walls 6 e and is connected to the upper edges of the side walls 6 e, form a U-shaped cross-sectional profile which is open toward the gas exchange valves. The guidance of the rocker arm le in transverse direction is affected through outer guidance by the fact that the U-shaped cross-sectional profile of the lever body 2 e engages around the valve stems.
The invention also provides an outer guidance relative to the gas exchange valves in the case of the rocker arms 1 b and 1 d. For this purpose, the outer ends of the outer sections 14 b, 14 d are bent at right angles in direction of the gas exchange valves to serve as valve guiding webs engaging around the outer sides of the valve stems. In contrast, the transverse guidance of the rocker arm la is realized through inner guidance on the side walls 6 a which engage in the region of the first end section 3 between the inner sides of the valve stems.
The rocker arm if illustrated in FIG. 6 comprises a beam-like straight crossbar 11 f that is connected to the lower edges of the side walls 6 f.

LIST OF REFERENCE NUMERALS

1 Rocker arm
2 Lever body
3 First end section
4 Center section
5 Second end section
6 Side wall
7 Axle-receiving bore
8 Roller axle
9 Roller
10 Joint socket
11 Crossbar
12 Contact surface
13 Inner section of crossbar
14 Outer section of crossbar
15 Weld joint

Claims

1. A rocker arm for a valve train of an internal combustion engine, comprising an elongate lever body formed of sheet metal and including a first end section, a second end section and a center section formed by two spaced apart, parallel side walls having aligned axle-receiving bores, the first end section including a crossbar connecting the side walls to each other and two contact surfaces for a simultaneous actuation of two gas exchange valves of the internal combustion engine, said first end section being configured substantially wider than the center section, and the contact surfaces extend on the crossbar while being spaced in a transverse direction from the side walls.

2. The rocker arm according to claim 1, wherein the second end section of the lever body comprises a joint socket for mounting the rocker arm on a stationary joint head arranged in the internal combustion engine, the rocker arm further comprising a roller mounted on a roller axle fixed in the axle-receiving bores.

3. The rocker arm according to claim 1, wherein the lever body has a substantially T-shaped configuration viewed in a direction perpendicular to the contact surfaces.

4. The rocker arm according to claim 3, wherein the crossbar comprises an inner section which is connected to lower edges of the side walls facing the gas exchange valves while extending between the side walls and further comprises two outer sections which are connected to upper edges of the side walls turned away from the gas exchange valves and extend away from each other.

5. The rocker arm according to claim 4, wherein inner ends of the outer sections are bent through 180° and connected to the upper edges of the side walls while extending parallel to the side walls and slightly spaced from or in bearing relationship to the side walls.

6. The rocker arm according to claim 5, wherein the inner ends of the outer sections are welded to the side walls in a region of the lower edges of the side walls.

7. The rocker arm according to claim 4, wherein outer ends of the outer sections are bent at a right angle in a direction of the gas exchange valves to engage around the gas exchange valves and serve as a transverse guide of the rocker arm relative to the gas exchange valves.

8. The rocker arm according to claim 3, wherein the first end section, together with the side walls widening into a T-shape and the crossbar, forms a substantially H-shaped or U-shaped cross-sectional profile.

9. The rocker arm according to claim 8, wherein the U-shaped cross-sectional profile is open in a direction of the gas exchange valves to engage around the gas exchange valves and serves as a transverse guide of the rocker arm relative to the gas exchange valves.