HIGH STIFFNESS LOW MASS ROCKER ARM

Abstract

A cam-follower rocker arm is provided comprising a flat single plate body containing an axle that extends perpendicular from the vertical wall area for making contact with a valve and a second pivot point axle. The pivot point for the cam-follower rocker arm may be located centrally or at the end of the cam-follower rocker arm that is opposite the cam-follower rocker arm valve arm. An external cam-follower bearing is mounted on the axle and extends on each side of the flat plate wall. The cam-follower 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 flat plate cross-section relative to conventional prior art cam-follower rocker arms that have a U-shape or a dual wall cross-section.

Description

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 cam-follower rocker arm characterized by relatively reduced mass and increased stiffness and has enhanced bearing quality provided by cam-follower bearings, also known as roller bearings, positioned outside the cam-follower rocker arm body.

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 contributed 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 cam-follower rocker arm. Two key design factors for enhancing cam-follower rocker arm performance are stiffness and mass. Reducing the moving mass of the cam-follower rocker arm allows more aggressive valve lift profiles, which in turn can improve engine power, raise limiting speed, and reduce hydrocarbon emissions.

With reference to related prior art, Mills U.S. Pat. No. 4,825,717, at column 1, lines 13-17, for example, describes the advantages of a lightweight cam-follower rocker arm. Increased stiffness can improve high-speed valve train system stability, valve train component durability and noise, vibration, and harshness (NVH) performance. At column 1, lines 26-28, of that patent the importance of a stiffer cam-follower rocker arm is described and at column 4, lines 18-45 the functioning of a rocker arm is described. U.S. Pat. No. 6,230,676 Pryba teaches the use of a central aperture that extends from the body to receive a tubular section at any angle to the body ranging from 90° to acute column 5 lines 14-23. In that arrangement the tubular section is mounted over a fixed shaft from which the rocker arm pivots about. The present invention differs from the arrangement disclosed by Pryba in that the tubular section is not used as pivot but instead the outer surface of the tubular section is used to support cam-follower bearings mounted on either side of rocker arm body making this a cam-follower rocker arm type. The outer surface of the cam-follower bearings is in contact with an overhead rotating cam.

U.S. Pat. No. 6,691,657 Hendriksma uses a body that provides a passage between socket and pad for receiving a mating portion of a slider member. The body is provided with a bore for which to receive roller bearings and pass a shaft through and to mount roller followers on opposite ends column 3 lines 35-46. The Herdriksma arrangement involves a two-step cam-follower rocker arm allowing the overhead rotating cam to engage the outer cam-follower bearings only during specific times during the engine operating event. The present invention differs from Herdriksma because the cam-follower bearings are always in contact with overhead rotating cam and must be designed to handle the full range of engine loads. These prior art disclosures are indicative that while various cam-follower rocker arm configurations of the prior art may have referenced efforts to improve on the mass and stiffness design factors but a need still exists for an improved advancement in cam-follower 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 cam-follower 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 cam-follower rocker arm vertical wall. The cam-follower 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 utilize 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 cam-follower rocker arm's stiffness and mass. From the analysis results, improved stiffness and reduced mass can be achieved through the use of a flat plate cross section for the cam-follower rocker arm body instead of the conventional U-shape cross section. The unique design of the cam-follower 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 cam-follower 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 cam-follower rocker arm with a rotatable bearing positioned on the cam-follower rocker arm at a point between the valve contact end and the opposite last adjuster end of the cam-follower 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 is a plain view of the cam-follower rocker arm of the invention comprising a flat body 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 difference of U-shape cross-sectional configuration of prior art cam-follower rocker arm bodies.

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

FIG. 5 is an exploded perspective view of the components of the cam-follower rocker arm of the invention that includes the main flat plate 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 cam-follower rocker arm of the invention that includes the bearing plate and an arrangement of roller bearing needles around the axle that passes through the flat plate rocker arm body.

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

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

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

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

FIG. 11 illustrates the alternative cam-follower rocker arm positioned in FIG. 10 containing a rotatable cam on one end of the cam-follower rocker arm.

FIG. 12 is an alternative perspective view similar to that of FIG. 1 in which the cam-follower 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 cam-follower rocker arm shown in the assembly of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

The cam-follower rocker arm of the invention comprises a cam-follower rocker arm characterized by having a substantially reduced mass and increased stiffness for use with a valve train assembly that includes a cam and cam-follower rocker arm. Illustrated in FIG. 1 is a valve train assembly 10 comprising a rocker arm 14 of the cam-follower type 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 cam-follower 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 26 of the cam-follower 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 cam-follower rocker arm 14. Oil or other lubricating fluid is supplied through a central passage (not shown) from which it flows to the intermediate surface of the cam-follower 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 cam-follower rocker arm.

Conventional details of the peripheral elements functioning in conjunction with the cam-follower 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.

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 cam-follower rocker arm 14. The cam-follower rocker arm 14 is in contact with the camshaft cam 11. As the camshaft cam 11 rotates the camshaft lobe 11a actuates the cam-follower rocker arm 14, i.e., the cam-follower rocker arm 14 pivots relative to the hydraulic lash adjuster 12, and the cam-follower rocker arm 14 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 flat plate cross-sectional configuration of the rocker arm body 20 of the invention as distinguished from the conventional prior art U-shaped cross-sectional rocker arm body 40 construction illustrated by FIG. 3 wherein sectional views FIGS. 3A, 3B and 3C, corresponding to those of FIG. 2, illustrate the comparative difference. The assembled elements of the prior art rocker arm body 40 illustrated in FIG. 3 are shown in perspective in FIG. 4 comprising a U-shape cross-section body 40 having a pivot end 41, a pad end 42, an axle 43 and a cam-follower bearing 44. It is seen that the prior art rocker arm body 40 comprises two parallel sides 40a and 40b as shown in FIG. 3 and FIG. 4 and distinguish markedly from the single flat plate rocker arm body 20 of the invention shown as 14 in FIGS. 1, 7 and 8 and as 20 and 20a in FIGS. 5 and 6 respectively.

Referring to FIG. 5, the rocker arm body 20 of the invention comprising essentially a flat plate (as distinguished from a U-shape cross section of the type shown in FIG. 3 and FIG. 4). The opposite vertical side walls 21 and 22 of the flat plate rocker arm of the invention is provided 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 the pivot end 23 and pad end 24. The cam-follower bearings 26, of the journal bearing type, are mounted on either of the outboard sides of the body 20 with bearing plates 27 on both of the outboard sides of the body 20 and bearings 26 and are provided with a retaining pin 28 which holds the assembled components of bearings 26, bearing plates 27 together on the body 20.

A cam-follower rocker arm assembly of the needle bearing type as shown in FIG. 6 has the same configuration as the journal bearing type shown in FIG. 5 with comparable functioning parts designated with the same reference numerals as in FIG. 3, except that the reference numbers are 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 body 20a.

FIG. 7 illustrates the assembled cam-follower rocker arm of FIG. 5. and FIG. 8 illustrates the cam-follower rocker arm 14 of FIG. 7 of the invention in position on a valve train.

FIG. 9 illustrates in comparison to FIG. 8, the prior art cam-follower rocker arm 45 configuration in a valve train. The reference numbered elements, other than the cam-follower 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 cam-follower rocker arm of the invention comprising a flat plate cross-section body has been found to be substantially advantageous. The journal bearing configuration of the cross-section cam-follower rocker arm requires fewer components, functions with less vibration tendency and is easier to assemble. The alternative needle bearing configuration illustrated by FIG. 6 is viewed as offering a performance benefit in reduced fiction at low speeds. In this embodiment, the bearing needles should meet engineering requirements of greater length than diameter. Absent this needle ratio, the needles may lockup and interfere with a smooth rotation of the bearing.

As illustrated in FIGS. 10 and 12, the cam-follower rocker arm of the invention may be mounted with the axle centrally (FIG. 10) or it may be mounted with the axle at the end (opposite the valve end) of the cam-follower rocker arm as shown in FIG. 12.

FIG. 11 illustrates a cam-follower rocker arm 51 configured to have the cam-follower bearings 56 located at one end of the cam-follower rocker arm body 52 with a hollow tube 59 for the mounting shaft which extends outwards from both sides of the body 52 and located between the pad end 55 and cam-follower bearings 56. In FIG. 10 the cam-follower rocker arm 51 of FIG. 11 is shown assembled in a valve train system comprised of a valve 13a, valve spring 15a, cam 58, cam lobe 11a, and a stationary mounting shaft 53 for mounting the cam-follower rocker arm 51. The cam-follower rocker arm 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 the cam-follower rocker arm 61 of the invention configured to have the cam-follower bearings 66 located centrally in the cam-follower rocker arm body 62 with a hollow tube 69 for the mounting shaft extending outwards from both sides positioned at the end of the body 62 opposite the pad end 65. FIG. 12 illustrates the cam-follower rocker arm of FIG. 13 assembled 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 cam-follower rocker arm 61. The cam-follower rocker arm 61, mounted on shaft 63 is held in place by bolts (not shown) in holes 64 in the shaft 63.

Though the invention has been described with respect to the preferred embodiments thereof, variations and modifications will become apparent to those skilled in the art prior the present disclosure. It is therefore the intention that the claims be interpreted as broadly as possible in view of the prior art, to include all such variations and modifications.

Claims

1. A cam-follower rocker arm characterized by relatively high stiffness and low mass comprising: a. a flat plate rocker arm body having a valve end, a mounting pivot and a cam-follower bearing point;b. the cam-follower bearing point comprising an axle positioned transversely through said axle having an extension on either side of the body; 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; andiii. a retaining pin for securing said cam-follower bearings and bearing plates to provide an integrated cam-follower rocker arm assembly.

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

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

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

5. The cam-follower rocker arm of claim 2 in which one end of the flat plate body is provided with a pivot end and the opposite end of said body is provided with a valve pad.

6. The cam-follower rocker arm of claim 3 in which one end of the flat plate body is provided with a pivot end and the opposite end of said body is provided with a valve pad.

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