US3618574A

US3618574A - Variable cam and follower assembly

Info

Publication number: US3618574A
Application number: US819627A
Authority: US
Inventors: Merlin J Miller
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1969-04-28
Filing date: 1969-04-28
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09

Abstract

An adjustable cam and follower assembly capable of varying cam timing, amount of lift and duration of lift wherein the cam has an axially and radially varying contour and the follower has the a flat cam engaging face free to rock and maintain line contact with the cam contour throughout its entire range of adjustment. The assembly is particularly useful in operating internal combustion engine poppet valves where it can be made sensitive to engine speed to achieve optimum flow of exhaust and intake for each engine condition thereby minimizing pollutants in engine exhaust and preventing dilution of fuel intake with residues.

Description

United States Patent [72] inventor Merlin J. Miller Cleveland, Ohio [21] Appl. No. 819,627

[22] Filed Apr. 28, 1969 [45] Patented Nov. 9, 1971 [73] Assignee TRW Inc.

Cleveland, Ohio [54] VARIABLE CAM AND FOLLOWER ASSEMBLY 7 Claims, 12 Drawing Figs.

[52] U.S. Cl 123/90.l8, 123/90.27, 123/90.42, 123/90.44, 123/905 [51] lnt.Cl F011 l/34, F011 1/18 [50] Field ofSearch 123/90,

Primary Examiner- Al Lawrence Smith Attorney-Hill, Sherman, Meroni, Gross and Simpson ABSTRACT: An adjustable cam and follower assembly capable of varying cam timing, amount of lift and duration of lift wherein the cam has an axially and radially varying contour and the follower has the a flat cam engaging face free to rock and maintain line contact with the cam contour throughout its entire range of adjustment. The assembly is particularly useful in operating internal combustion engine poppet valves where it can be made sensitive to engine speed to achieve optimum flow of exhaust and intake for each engine condition thereby minimizing pollutants in engine exhaust and preventing dilution of fuel intake with residues.

VARIABLE CAM AND FOLLOWER ASSEMBLY FIELD OF THE INVENTION This invention relates generally to adjustable cam and follower assemblies and particularly to internal combustion engine valve operating means and while the invention will hereinafier be specifically embodied in such valve operating means it will be understood that the cam and follower combinations of the invention are not limited to such particular usage but are generally applicable for varying timing, extent of movement, and duration of movement of mechanical parts.

DESCRIPTION OF THE PRIOR ART Speed sensitive adjustable cam and follower assemblies for internal combustion engines are known in the art as for example in the Sampietro, US. Pat. No. 2,980,089 dated Apr. 18, 1961. In the Sampietro patent however the cam and follower only have point contact relationship and high-speed, high-load usage results in rapid wear, skiving and galling of the contacting surfaces thus soon destroying the efficiency of the engine. This wear has forced the return to fixed or nonadjustable cam and follower combinations which will maintain line contact relationship but which cannot provide the highly desirable variation in valve operation for different engine conditions. Flxed cam internal combustion engines therefore have valve settings providing what is known as free-flowing valving invariably resulting in overlapping of intake and exhaust valve events. During the scavenging of burned residues from the engine cylinder, the exhaust valve closes late to permit the inertia of exhaust gases at high speed to continue to flow from the cylinder. To insure free flow of the intake mixture, the intake valve is opened early to provide adequate flow area for highspeed operation. Unfortunately, there is only one speed at which a fixed arbitrary timing is satisfactory, At low speeds the compromised valve timing will allow burned residues to be drawn back into the intake manifold and at high speed unburned residues will be discharged with attendant contamination of the atmosphere.

SUMMARY OF THE INVENTION The present invention now provides an adjustable or variable timed valve operating means which can use the speed sensitive cam adjusting mechanisms of the prior art such as are disclosed in the aforesaid Sampietro, US. Pat. No. 2,980,089, but the cams and followers of this invention are so designed and corelated as to maintain line contact relationship throughout their entire range of adjustment thereby eliminating the heretofore encountered wear, galling and skiving problems.

To achieve smooth continuous cam action and quiet operation, the velocity of the follower must reach its peak before the cam nose engages the follower and again before the follower engages the cam base circle. To maintain full line contact between the cam and follower for avoiding the wear problems while at the same time providing for variable timing, and valve lift, it has now been found that the follower must be free to roll or tip in a plane coincidental to the axis of the cam. In the present invention this rolling or tipping is accommodated by a rocker arm having one end supported by a pivot providing a fixed tilting center while the other end is supported by a slidable pivot. The follower is thus free to tilt about an axis which maintains its lateral placement relative to the cam. The cam, on the other hand, has a relatively wide axially extending surface portion defining a base circle, an opening flank, a nose, and a closing flank. The surfaces lying in the flanks and the nose have three dimensions in space being inclined both radially and axially along the width of the cam to engage the follower along a straight line and to skew the line contact with the follower in opposite straight line directions on opposite sides of the nose. The cam engaging follower surface is flat and the cam surfaces are contoured to provide uniform velocity and acceleration gradient movements of the follower as the cam and follower are relatively shifted along the width of the cam.

It is then an object of this invention to provide a cam and follower assembly which is adjustable to vary timing and extent of lift while maintaining the line contact relationship therebetween in all positions of adjustment.

Another object of this invention is to provide valve operating mechanism for internal combustion engines which varies the valve contact between cam and follower surfaces throughout all positions of adjustment.

Another object of this invention is to provide a cam and follower assembly for internal combustion engines including an axially shiftable cam shaft and rocker arms that can tilt and skew to maintain line contact relationship with the cams throughout all positions of axial adjustment of the shaft.

A further object of the invention is to provide a wide cam contour which will maintain straight line engagement with a flat surfaced cam follower as it is shifted axially to vary the velocity and acceleration of the follower in uniform gradients along its width.

Another object of the invention is to provide an overhead cam shaft and rocker arm assembly for the poppet valves of internal combustion engines wherein the shaft is axially shiftable to change the positions of the cams relative to their followers for varying the timing, extent and duration of valve lift and wherein each follower is free to tilt for maintaining line contact relationship with its cam throughout the extent of axial shifting of the cam shaft.

Other and further objections of this invention will become apparent to those skilled in this art from the following detailed description of the annexed sheets of drawings which, by way of preferred examples only, illustrate several embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat diagrammatic fragmentary view of a section of an internal combustion engine illustrating one form of valve operating mechanism according to this invention;

FIG. 2 is a fragmentary view taken generally along the lines IlIIofFlG. 1;

FIG. 3 is a bottom plan view of a valve stem seating ring used in the assembly of FIGS, 1 and 2;

FIG. 4 is a elevational view of semispherical button carried by the seating ring;

FIG. 5 is a fragmentary plan view of the engine cam shaft and a plurality of rocker arms actuated by the cams of the shafts in engines of FIGS. 1 and 2;

FIG. 6 is a bottom plan view of one of the rocker arms shown in FIGS. 1 and 5;

FIG. 7 is a view similar to FIG. 1 but illustrating a modified valve operating mechanism of this invention;

FIG. 8 is a fragmentary view taken generally along the lines VIII-VIII of FIG. 7;

FIG. 9 is a fragmentary view taken generally along the lines lX-IX of FIG. 7;

FIG. 10 is a bottom plan view of the rocker arm of the assembly ofFIG. 7;

FIG. 11 is a perspective view of one of the cams of this invention; and

FIG. 12 is a diagrammatic view illustrating the line contacts between the cam and follower as the cam operates through a full cycle on the follower.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 the reference numeral 10 designates generally a valve in head engine equipped with the variable timed valve operating mechanism 11 of this invention. The engine 10 has a cylinder head 12 with a valve port 13 controlled by a poppet valve 14 which has a head 15 coacting with a valve seat 16 in the head and stem 17 slidable in a guide 18 arid urged to closed position by a spring 19 compressed between the cylinder head and a retainer 20 locked on the valve stem.

The valve operating mechanism 11 includes a cam shaft 21 with a plurality of wide earns 22 each acting on a rocker arm 23. Each rocker arm 23 has a flat pad 24 on its top face. a forwardly extending rounded nose portion 25 with a semispherical recess 26 in its bottom face and an elongated narrow tail portion 27 with a semispherical recess 28 in its bottom face at the rear extremity thereof. A pivot support 29 carried by the engine head 12 has a semispherical head 30 seated in the recess 28 and providing a fixed pivot support for the rocker arm 23. The pivot support is maintained in good seated engagement in the socket provided by the recess 28 by means of a hydraulic or otherwise actuated lash adjustor 31 seated in the engine head 12 and acting on the support 29 to accommodate expansion and contraction of the valve linkage to take up clearance and prevent backlash in the assembly.

The tip end 170 of the valve stem 17 extends above the retainer and receives a collar 32 therearound. This collar 32 has a circular beveled recess 32a projecting beyond the valve stem tip 170 and freely receiving therein a hemispherical button 33 with a flat bottom end slidably seated on the end of the valve stem and with the semispherical head thereof seated in the socket provided by the recess 26 in the nose of the rocker arm. Since the button 33 is loose in the collar 32 and slides over the valve stem tip, the rocker arm 23 is free to tilt about an axis that is coincidental with the axis of the cam shaft 21 while, of course, rocking about the fixed pivot support 29 under the influence of the cam 22 to open and close the valve 14.

As shown in FIG, 2, the cam 22 has full line contact with the pad 24 of the rocker arm 23.

The cam 22 has a base circle portion 22aside flanks 22b, and a nose 220. The cam 22 varies in height along its axial length on the flanks and nose so as to provide a low lift end 34 and a high lift end 35.

As shown in FIG. 5, a plurality of cams 22 are provided on the cam shaft 21 with each cam having a cooperating rocker arm follower 23 and with the cam shaft being axially adjustable as indicted by the arrows to vary the axial positioning of the earns 22 over the pads 24 of the rocker arm. The cam shaft 21 can be axially shifted by any suitable mechanism preferably of the speed sensitive type such a fly ball governor 36 driven from an engine driven gear 37 and more fully illustrated at 54 in the aforesaid Sampietro U.S. Pat. No. 2,980,089. Thus, the high end of the cam will operate on the follower at high speeds and the low end of the cam will operate on the follower at low speeds with commensurate variations therebetween.

It should be especially understood that since the rocker arm 23 only has a fixed pivot at one end thereof and is free to slide relative to the valve tip 17athrough the loose button 33, the pad 24 is free to skew and follow the cam contour along it entire axial length so as to maintain a line contact relationship in all positions of the cam as it is shifted by the cam shaft.

In the modified arrangement shown in FIGS. 7 to 10 parts identical with parts described in FIGS. 1 to 6 have been marked with the same reference numerals. However, as shown in FIG. 7 the valve operating assembly llahas a modified rocker arm 40 and the tip end of the valve stem 17 has a ball head 41. The rocker arm 40 has the same flat pad 24 as the arm 23 with a similar front nose 25 having a semispherical recess 26 in its bottom face and a similar elongated tail portion 27. However, the the tail portion 27 has an axially elongated channel 42 in its bottom face with a cylindrical transverse section receiving the head of the pivot support 29. The ball head 41 of the valve stem 17 seats directly in the recess 26 and provides the fixed pivot axis for the rocker arm 40 while the elongated channel 42 permits sliding of the rocker arm relative ro the support 29.

Thus, in the assembly of FIGS. 7 to 10 the fixed pivot axis of the rocker arm 40 is the valve stem 17 instead of pivot support 28 as in the embodiment of FIGS. 1 to 6. However, the assembly of FIGS. 7 to 10 operates in the identical manner as described above in connection with the first embodiment of FIGS. 1 to 6.

FIG. 11 illustrates how the cam 22 of this invention provides a variation of the amount of offset for any angle of cam rotation in accordance with the longitudinal position of the follower along the cam axis and how the contact between the cam and cam follower traces a straight line across the surface of the cam As shown in FIG. 11, the line AD represents the contact line between the cam surface and the cam follower, This is a straight line and the amount of offset from the cam axis to this line is shown at BF at section 1 and CE at section 2. For any cam rotation angle and placement of the follower on the surface of the cam, the offset between the surface contact and cam axis at all sections of the cam, on either side of sections 1 and 2, forms a straight line across the surface. When the rotation of the cam is such that the follower contact is at the nonlift or base circle of the cam, then this contact line is parallel with the cam axis. At all cam angles where lift occurs, such as on the shank areas 22band on the nose 22cthe contact line is not parallel with the cam axis.

The cam contour gives smooth continuous action to the follower at sections 1 and 2 and is contoured for straight line contact so that the action of the follower when placed anywhere along the cam axis will have smooth continuous engagement with the cam.

The beginning of the cam lift occurs at a point where line BF or CE begins to take on dimension. When the cam follower is riding on the base circle, the contact line is parallel with the cam axis and the lengths oflines BF and CE is 0. To achieve a difference in cam timing between sections 1 and 2, the contact at one section continues directly above the cam axis (0 offset) as cam rotation progresses, while contact at the early opening sections is permitted to extend its offset in a smooth continuous action. The contact line begins to tilt as rise at one end occurs and will began to skew with respect to the cam axis as the contact offset (dimension CE) begins to increase from 0. At a desired index angle the contact at the previously nonrising cam section may rise in a fashion to achieve the desired lift at that section. Cam timing to suit the condition of engine speed and load may be adjusted by moving either the cam or its follower to a position to feel the effective action at any section along the width of the cam.

The variable timed cam design of this invention permits not only a variation in the amount of the valve opening, but also provides a freedom to select opening and closing points for the valve independently. The wide event portion (section 2) of the cam permits higher cam rise and will act as the high per formance end of the cam. The short event portion (section 1) will control undesirable backflow of exhaust gases into the cylinder and into the intake manifold. This results in minimum dilution of the combustible mixture with consequent cleaner burning.

It should be understood that the cam follower, 23 of FIG. 1 and 40 of FIG. 7 always has freedom to tilt as wall as rock but it is restrained from moving sideways. One end of the follower is supported by a pivot and provides a fixed pivot centerline while the other end is slidable. In the embodiment of FIGS. 1 to 4 the sliding motion occurs between the valve stem tip and the hemispherical button member 33, but side movement of the rocker is restrained by the thrust block 32 surrounding the valve tip and confined within a channel at the end of the cam follower. In the alternate arrangement of FIG. 7, the sliding pivot is a radius channel 42 at the pivot support end of the follower.

FIG. 12 illustrates the line contacts of the

cam follower

23 or 40 with the cam 22. The curve represents the lift action of the cam with areas 1-2 and 4-5 representing the lift imparted by the flanks 22b of the cam, with area 2-3 representing the lift side of the nose 22cand with area 3-4 representing the closing side of the nose.

In the flank area 1-2 the line contact between the cam and follower starts with a line 50 parallel to the cam axis at the and 4 of the nose it swings to the left where as illustrated at 53 the line contact is inclined considerably to the left. Next, as the follower rises on the cam on the descending flanks side from 4 to 5 the contact line swings back to the base circle position 50. This diagram is intended to illustrate how straight line engagement with all surfaces of the cam is maintained and how the flank surfaces 220 of the cam are contoured to skew the contact lines in opposite straight line directions on opposite sides of the nose 22c. This cam contour provides unifonn velocity and acceleration gradients along the length of linear adjustment of the cam and, of course, the cam follower is free to rock to maintain the contact lines.

The rolling of the rocker arm or follower gives an average of the lift or a mean"lift without affecting the lift or the duration of lift.

From the above descriptions it will therefor be understood that the invention now provides a variable timed cam and follower assembly having a wide range of adjustment while always maintaining a full contact line between the cam and follower.

Although various minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. A variable timed cam and follower assembly which comprises: a cam having a base circle portion, an opening flank portion, a nose portion and a closing flank portion, said portions having axial dimensions establishing adjustment width for the cam, said nose and flank portions being axially inclined along said width, a rocker arm riding on said cam, means for relatively shifting the cam and rocker arm to vary the axial position of the cam on the rocker arm, said rocker arm being free to tilt about an axis transverse to the cam axis for maintaining line contact with all of said cam portions, said line contact being parallel to the cam axis on the base circle portion, skewed in one direction to the cam axis on the opening flank portion, and skewed in the opposite direction on the closing flank portion, the direction and degree of skew of the line contact being a function of the lift and velocity components of the cam contour.

2. An adjustable cam and follower combination which comprises: a cam having an axial width dimension with a base circle portion an opening flank portion, a nose portion, and a closing flank portion, said flank portions and nose portion being axially displaced along the width of the cam to vary timing, duration of lift and degree of lift, a cam follower having a flat surface engaging said portions along a contact line, said cam follower being free to rock in a plane coincidental to the axis of the cam as it rides on said cam for maintaining line contact therewith, and said cam and follower being relatively shiftable to (vary the) effect said variation in timing. duration, and degree of (rise) lift imparted to the follower.

3. The combination of claim 2 including speed sensitive means for shifting the cam and follower.

4. An overhead cam shaft and follower assembly for the valves of an internal combustion engine which comprises: a cam shaft having a plurality of cams appreciable axial width along the length thereof, cam followers underlying each of the cams on the said cam shaft having flat surfaces riding on said cams, one end of each of said followers acting on an engine valve to open and close the valve, the other end of each of said followers being pivotally supported from the engine, one end of each follower being free to shift and the other end of each follower having a fixed pivot axis, said followers being free to rock transversely of the cam shaft axis, and each of said cams having a contour for varying the duration and timing of the valve operation depending upon the axial alignment of the cams with the flat surfaces of the followers, said cam shaft and followers being axially shiftable to vary the area of the cam engaged by the follower, and said followers maintaining a line contact engagement with the cam throughout all positions of the adjustment.

5. A variable timed cam and follower assembly which comprises: a cam having a base circle portion, an open flank portion, a nose portion and a closing flank portion, said portions having axial dimensions establishing adjustment width for the cam, said nose and flank portions being axially inclined along said width, a follower having a flat surface riding on said cam. means for relatively shifting the cam and follower to vary the axial positioning of the cam on the follower, said follower being free to tilt about an axis transverse to the cam axis for maintaining line contact with all of said cam portions, said line contact being parallel to the cam axis on the base circle portion, skewed in one direction to the cam axis on the opening flank portion, and skewed in the opposite direction on the closing flank portion, the direction and degree of skew of the line contact being a function of the lift and velocity components of the cam contour.

6. A variable timed cam and follower assembly which comprises: a cam having a base circle portion, an opening flank portion, a nose portion and a closing flank portion, said portions having axial dimensions establishing adjustment width for the cam, said nose and flank portions being axially inclined along said width, a follower which is a rocker arm having one end on a fixed pivot with the other end free to slide and a central portion riding on said cam, means for relatively shifting the cam and follower to vary the axial positioning of the cam on the follower, said follower being free to tilt about an axis transverse to the cam axis for maintaining line contact with all of said cam potions, said line contact being parallel to the cam axis on the base circle portion, skewed in one direction to the cam axis on the opening flank portion, and skewed in the opposite direction on the closing flank portion, the direction and degree of skew of the line contact being a function of the lift and velocity components of the cam contour.

7. Valve operating mechanism for internal combustion engine which comprises: a cam shaft having a plurality of cams of appreciable axial width surfaces contoured to vary timing and duration of valve lift, a follower for each cam, said cam shaft and followers being relatively shiftable to vary the contact regions thereof, and said followers being rocker arms acting on valves each having a fixed pivot accommodating rolling a rocking about an axis transverse to the cam shaft axis for maintaining line contact with the cam throughout the extent of relative axial adjustment between the cams and followers.

Claims

2. An adjustable cam and follower combination which comprises: a cam having an axial width dimension with a base circle portion, an opening flank portion, a nose portion, and a closing flank portion, said flank portions and nose portion being axially displaced along the width of the cam to vary timing, duration of lift and degree of lift, a cam follower having a flat surface engaging said portions along a contact line, said cam follower being free to rock in a plane coincidental to the axis of the cam as it rides on said cam for maintaining line contact therewith, and said cam and follower being relatively shiftable to (vary the) effect said variation in timing, duration, and degree of (rise) lift imparted to the follower.

5. A variable timed cam and follower assembly which comprises: a cam having a base circle portion, an opening flank portion, a nose portion and a closing flank portion, said portions having axial dimensions establishing adjustment width for the cam, said nose and flank portions being axially inclined along said width, a follower having a flat surface riding on said cam, means for relatively shifting the cam and follower to vary the axial positioning of the cam on the follower, said follower being free to tilt about an axis transverse to the cam axis for maintaining line contact with all of said cam portions, said line contact being parallel to the cam axis on the base circle portion, skewed in one direction to the cam axis on the opening flank portion, and skewed in the opposite direction on the closing flank portion, the direction and degree of skew of the line contact being a function of the lift and velocity components of the cam contour.

7. Valve operating mechanism for internal combustion engine which comprises: a cam shaft having a plurality of cams of appreciable axial width surfaces contoured to vary timing and duration of valve lift, a follower for each cam, said cam shaft and followers being relatively shiftable to vary the contact regions thereof, and said followers being rocker arms acting on valves each having a fixed pivot accommodating rolling and rocking about an axis transverse to the cam shaft axis for maintaining line contact with the cam throughout the extent of relative axial adjustment between the cams and followers.