HIGH STIFFNESS LOW MASS ROCKER ARM

Abstract

A rocker arm is provided that includes a body which is comprised of a single vertical wall having an I-shape cross section and an axle that extends perpendicular from the vertical wall area for making contact with a valve and a pivot point. The pivot point for the rocker arm may be located centrally or at the end of the rocker arm that is opposite the rocker arm valve arm. An external cam follower bearing is mounted on the axle on each side of a single vertical wall. The rocker arm of the invention is characterized by a relatively reduced mass and has a stiffness that exceeds limits achieved by known prior art designs for an overhead cam and cam follower valve train; the gain in stiffness being attributed to the body's I-shape cross-section relative to conventional prior art rocker arms having a U-shape or dual vertical wall cross-section.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. Nonprovisional application Ser. No. 11/277,439 filed on Mar. 24, 2006.

FIELD OF THE INVENTION

The invention relates to a valve train system using a cam and cam-follower rocker arm for an internal combustion engine. More particularly, the invention relates to an improved rocker arm characterized by relatively reduced mass and increased stiffness and has enhanced bearing quality provided by cam-follower bearings positioned outside the rocker arm.

BACKGROUND OF THE INVENTION

Efforts to improve engine power and performance are directed to improvements to the valve train. The introductions of cam phasing, valve deactivation and variable lift technology have all contributions to improved engine power and performance. However, these technologies are relatively expensive and cannot ordinarily be fitted into an existing engine without modifications to the engine. One critical area of the valve train is the rocker arm. Two key design factors for enhancing rocker arm performance are stiffness and mass. Reducing the moving mass of the rocker arm allows more aggressive valve lift profiles, which in turn can improve engine power, raise limiting speed, and reduce hydrocarbon emissions. Mills U.S. Pat. No. 4,825,717, at column 1, lines 13-17, for example, describes the advantages of a lightweight rocker arm. Increased stiffness can improve high-speed valve train system stability, valve train component durability and noise, vibration, and harshness (NVH) performance. U.S. Pat. No. 4,825,717, at column 1, lines 26-28, also describes the importance of a stiffer rocker arm and at column 4, lines 18-45 teaches the art of a rocker arm. Pryba et. al. U.S. Pat. No. 6,230,676, at column 7, lines 18-34 describes a flat rocker arm with a tube extending from the sides to be assembled onto a fixed shaft with a bearing contained within the rocker arm. Many rocker arm configurations of the prior art have been used in efforts to improve on the mass and stiffness design factors but a need still exists for an improved advancement in rocker arm construction that surpasses current design goals, has favorable cost and can be packaged into today's existing conventional valve trains.

SUMMARY OF THE INVENTION

The rocker arm of the invention characterized by improved applicability comprises a body having a vertical wall; an axle that extends perpendicular from and through the vertical wall of the body, an area for making contact with a valve, and an opposite pivoting area that engages and is pivotally actuated by a lash adjuster. An external cam-follower bearing is mounted at the axle on each side of the rocker arm vertical wall. The rocker arm of the invention is characterized by a relatively reduced mass and has a stiffness that exceeds limits achieved by known prior art designs for a valve train that utilizes a cam-follower rocker arm. Commercially available computer aided engineering analysis tools are used to compare different cross sectional shapes and provide results to optimize the rocker arm's stiffness and mass. From the analysis results, improved stiffness and reduced mass can be achieved through the use of an I-shape cross section for the rocker arm body instead of the conventional U-shape cross section. The unique design of the rocker arm of the present invention provides a substantial increase in stiffness and reduction in effective mass. The result of the modified cross section and the external cam-follower bearing arrangement provide the capability for valve train and engine performance levels substantially above that normally attainable with conventional rocker arm designs

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates schematically a cam and cam-follower rocker arm valve train design that includes an overhead cam, hydraulic lash adjuster, valve, valve spring and rocker arm with a rotatable bearing positioned on the rocker arm at a point between the valve contact end and the opposite last adjuster end of the rocker arm.

FIG. 1A illustrates the cam riding on the external cam-follower bearing in a cross section along A-A of FIG. 1.

FIG. 2 illustrates the I-shape cross-sectional configuration of the rocker arm body of the invention with FIGS. 2A, 2B and 2C being cross-sectional views along lines A-A, B-B and C-C respectively of FIG. 2.

FIGS. 3, 3A, 3B and 3C illustrate U-shape cross-sectional views corresponding to those of FIG. 2 to illustrate the U-shape cross-sectional configuration of prior art rocker arm bodies.

FIG. 4 is a perspective view of the U-shape cross-section prior art rocker arm body.

FIG. 5 is an exploded perspective view of the components of the rocker arm of the invention that includes the main body, the cam-follower bearings, the bearing plates and a retaining pin.

FIG. 6 is an alternative exploded perspective view of the components of the rocker arm of the invention that includes the bearing plate and an arrangement of needles around the axle of the body.

FIG. 7 is a perspective view of the rocker arm of the invention comprising the assembled components of FIG. 5.

FIG. 8 is a perspective view of the rocker arm of the invention depicting FIG. 7 in a valve train.

FIG. 9 shows the prior art U-shape cross-section rocker arm of FIG. 4 in a valve train.

FIG. 10 is an alternative embodiment illustrating the rotatable cam positioned at one end of the rocker arm as distinguished from the central position shown in FIG. 8.

FIG. 11 illustrates the alternative rocker arm containing a rotatable cam on one end of the rocker arm.

FIG. 12 is an alternative perspective view similar to that of FIG. 1 in which the rocker arm of the invention is arranged so as to pivot about a fixed shaft instead of engaging a hydraulic lash adjuster.

FIG. 13 is a perspective view of the rocker arm shown in the assembly of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

The rocker arm of the invention pertains to a rocker arm of reduced mass and increased stiffness for use with a valve train assembly that comprises a cam and cam-follower rocker arm. Illustrated in FIG. 1 is an assembly 10 comprising a rocker arm of the cam-follower type 14 that has one end portion on a lifter post 12a extending upwardly from a lash adjuster 12 of an internal combustion engine (not shown) and the other end portion of the rocker arm 14 engages the upper end 13a of a valve stem 13. The valve stem 13 extends upwardly from a cylinder head (not shown) through a coiled compression spring 15 which is conventionally seated against the cylinder head and against a retainer ring mounted on the valve stem 13. An overhead cam 11 engages an intermediate portion, the cam-follower bearing of the rocker arm 14 to cause a valve located at the lower end of the valve stem 13 to open and close as the stem is moved longitudinally by the rocker arm 14. Oil or other lubricating fluid is supplied through a central passage from which it flows to the intermediate surface of the rocker arm 14 for lubricating purposes.

The lash adjuster 12 is slidably carried in a chamber (not shown) and is urged upwardly by fluid such as oil under pressure in its chamber. The lash adjuster 12 thereby can yield somewhat when the cam 11 rotates. In practice, the lash adjuster 12 is devised to move corresponding to movement of the high lobe 11a of the cam 11 which rotates to provide a zero lash adjustment for the rocker arm.

Additional conventional details of the peripheral elements functioning in conjunction with the rocker arm of the invention may be found in the disclosure of aforementioned U.S. Pat. No. 4,825,717, the description of which is incorporated herein by reference thereto.

As noted, the assembly includes an overhead cam 11 provided with lobe 11a mounted on camshaft 16, a hydraulic lash adjuster 12, valve stem 13 and rocker arm 14. The rocker arm 14 is in contact with the camshaft cam 11. As the camshaft cam 11 rotates the camshaft lobe 11a it displaces the rocker arm, i.e., the rocker arm pivots relative to the hydraulic lash adjuster 12 fixed in a pocket in the head, and the rocker arm translates rotating motion of camshaft 11 into linear motion which opens and closes the valve via valve stem 13.

Shown in FIG. 2 is a plan view followed by sectional views FIGS. 2A, 2B and 2C illustrating the I-shape cross-sectional configuration of the rocker arm of the invention as distinguished from the conventional prior art U-shaped cross-sectional construction illustrated by FIG. 3.

FIG. 3 is a plan view of a prior art rocker arm with sectional view FIGS. 3A, 3B and 3C corresponding to those of FIG. 2 to illustrate the comparative difference. The assembled elements of the prior art rocker arm illustrated in FIG. 3 are shown in perspective in FIG. 4 which comprises a lash adjuster contact, a U-shape cross-section having a pivot end 41, a pad end 42, an axle 43 and a cam follower bearing 44.

The prior art rocker arm body comprises two parallel sides 40a and 40b as shown in FIG. 3 and FIG. 4 as distinguished from the single I-shape rocker arm body of the invention.

As shown in FIG. 5, the rocker arm of the invention comprises essentially an I-shape cross sectional body 20 (as distinguishes from a U-shape cross section of the type shown in FIG. 3 and FIG. 4). The U-shape cross-section rocker arm of the invention with opposite vertical side walls 21 and 22 with a pivot 23 preferably having a generally concave configuration at one end, a valve pad 24 at the other end and an axle portion 25 which extends outwards from both sides of the body 20 and located between rocker arm pivot end and pad end. The journal bearing comprises the cam-follower bearings 26 on either of the outboard sides of the body 20, bearing plates 27 on both of the outboard sides of the body and bearings 26 and a retaining pin 28 which holds the assembled components of bearings 26, bearing plates 27 together on the body 20.

A rocker arm assembly of the needle bearing type as shown in FIG. 6 has the same configuration as the journal type shown in FIG. 5 with comparable functioning parts designated with the same reference numerals as in FIG. 3, except followed by the lower case “a” and except for the addition of multiple needles 30 circumventing the outer diameter of the axle 25a on both sides of the rocker arm 20a.

FIG. 7 illustrates the assembled rocker arm of FIG. 5. FIG. 8 illustrates the rocker arm of FIG. 7 of the invention in position on a valve train.

FIG. 9 illustrates in comparison to FIG. 8, the prior art rocker arm configuration in a valve train. The reference numbered elements, other than the rocker arms in FIG. 8 and FIG. 9, are similar to the like numbered components described with reference to FIG. 1.

From a manufacturing and performance perspective, a journal bearing configuration in the rocker arm of the invention comprising an I-shape cross-section body has been found advantageous. The journal bearing configuration of the cross-section rocker arm requires fewer components and is easier to assemble. While the needle bearing configuration illustrated by FIG. 6 may offer a performance benefit in reduced fiction at low speeds, the needles should meet engineering requirements of greater length than diameter. Without this needle ratio, the needles could lockup and interfere with the rotation of the bearing.

As illustrated in FIGS. 10-13, the rocker arm of the invention may be mounted centrally (FIGS. 10 and 11) or it may be mounted at the end (opposite the valve end) of the rocker arm.

FIG. 11 illustrates a rocker arm assembly 51 configured to have the cam follower bearings 56 located at one end of the rocker arm body 52 with a hollow tube 59 for mounting the rocker arm which extends outwards from both sides in the rocker arm centered body 52. FIG. 10 illustrates the rocker arm in a valve train system comprised of a valve 13a, valve spring 15a, cam 58, cam lobe 11a, and a stationary shaft 53 for mounting the rocker arm assembly 51. The rocker arm assembly 51 is mounted onto a shaft 53 which is held in place by bolts (not shown) secured in holes 54 in the shaft 53.

FIG. 13 illustrates a rocker arm assembly 61 configured to have the cam follower bearings 66 located centrally in the rocker arm body 62 with a hollow tube 69 which extends outwards from both sides positioned at the end of the body 62 opposite the valve end. FIG. 12 illustrates the rocker arm of FIG. 13 in a valve train system comprised of a cam 68, cam lobe 11b, valve 13b, valve spring 15b, and a stationary shaft 63 for mounting the rocker arm assembly 61. The rocker arm assembly 61 mounted onto a shaft 63 is held in place by bolts (not shown) in holes 64 in the shaft 63.

Although the invention has been described in terms of specific test and embodiments, one skilled in the art can substitute other tests and embodiments and these are meant to be included herein. The invention is only to be limited by the scope of the appended claims.

Claims

1. A rocker arm characterized by relatively high stiffness and low mass comprising:

a. an elongated lever body having an I-shape cross-section, and having a first valve end, a mounting pivot point and a cam follower bearing point;

b. the cam follower point comprising an axle positioned transversely through said lever at said point, said axle having an extension on either side of the lever; i. a rotatable cam-follower bearing mounted on said axle and extending from each of the sides of the lever; ii. bearing plates mounted on said axle outboard of each of said cam-follower bearings to retain the cam-follower bearings on the axle; and iii. a retaining pin for securing said cam-follower bearings and bearing plates to provide an integrated rocker arm assembly.

2. The rocker arm of claim 1 wherein the cam follower bearing is centrally located on the rocker arm.

3. The rocker arm of claim 1 wherein the cam follower is located at one end of the rocker arm.

4. The rocker arm of claim 1 in which the transverse axle is provided with circumventing needles over which said cam-follower bearing are mounted to reduce bearing friction.

5. The rocker arm of claim 2 in which one end of the vertical I-shape body is provided with a pivot end and the opposite end of said body is provided with a valve pad.

6. The rocker arm of claim 3 in which one end of the vertical I-shape body is provided with a pivot end and the opposite end of said body is provided with a valve pad.

7. The rocker arm of claim 5 wherein the pivot end comprises a generally concave configuration.