US3157166A

US3157166A - Variable dwell and lift mechanism for valves

Info

Publication number: US3157166A
Application number: US213174A
Authority: US
Inventors: John H Macneill
Original assignee: SOROBAN ENGINEERING Inc
Current assignee: SOROBAN ENGINEERING Inc
Priority date: 1962-07-30
Filing date: 1962-07-30
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

NOV; 17, J H, MaCNEILL VARIABLE DWELL AND LIFT MECHANISM FOR VALVES Filed July 30, 1962 3 Sheets-Sheet 1 IN VENTOR JOHN H. MACNElLL ATTORNEY 5 NOV. 17, 1964 MacNElLL VARIABLE DWELL AND LIFT MECHANISM FOR VALVES Filed July 30, 1962 5 Sheets-Sheet 2 INVENTOR JOHN H. MACNEILL ATTORNEYS Nov. 17, 1964 J. H. M NEILL v VARIABLE DWELL. AND LIFT MECHANISM FOR VALVES FiledJuly so. 1962 3 Sheets-Sheet 5 ATTORNEYS United States Patent 3,157,166 VARIABLE Ell ELL AND LET NEQHANISP FOR VALVEE;

John H. MacNeill, Endialanti-c, Fla, assignor to Sorohan Engineering, Inc, Melbourne, Fla, a corporation of Florida Filed .l'uly 30, 1962, Ser. No. 213,174 9 Claims. (Cl. lZ3-tl) The present invention relates to valve mechanisms for internal combustion engines and more particularly to a valve assembly including a mechanism for varying the dwell and lift characteristics of the valve.

It is well known that the valve dwell and lift characteristics that produce the most efficient operation of engines operating at high speeds produce inefficient operation of an engine operating at low speeds, and vice versa. When an engine is operating under high performance or high power conditions, the interval of the Valve opening; that is, dwell, should be long and the amount of valve lift should be great, whereas when operating in the low performance or low power condition, the dwell time can be short relative to the dwell time set forth above and the amount of lift should be less than that for the high performance condition since less fuel is required. The long dwell time is desirable for high performance operation since it is desired to have the intalre valve open for a short time while the exhaust valve is still open so as to maximize the charge to the cylinder. At slow speeds valve overlap is undesirable due to exhaust back into the cylinder of exhaust gases due in part to opening of exhaust valves associated with other cylinders. Thus, it is desirable to be able to vary the dwell of the intake and/or exhaust valves so as to provide overlap at high speeds and prevent overlap at low speeds.

Referring now to the valve lift characteristics, the valve lift should be less during low perfomance operation than during high performance operation since, due to the slower relative movement of the piston, the air is drawn in at a relatively low speed and in low quantity. If the valve has a high lift, the flow into the chamber is almost laminar and results in poor mixing of fuel and air. On the other hand, if the valve lift is small, even though the rate of intake is small, the velocity past the unseated valve is great and sufiicient turbulence is produced' to provide the necessary mixing of the fuel and air.

A number of mechanisms have been proposed for permitting variable valve dwell and lift and some have been employed in racing vehicles. In many of these devices, the spacing between the end of the valve stem and the valve actuating mechanism varies with the performance desired and results in impact between the valve stem and actuating mechanism, materially shortening the life of both. In some of the other prior art devices, the impact is avoided during the opening of the valve but occurs during the seating of the valve which merely transfers the destructive impacts from the valve stem to the valve itself. Other mechanisms have been employed which accomplish results similar to those of the present invention but they are relatively complex and are not trouble free particularly under the extreme environments in which such devices are normally employed; that is, in racing and other high performance vehicles.

It is therefore an object of the present invention to provide a valve mechanism permitting variation of both dwell time and amount of lift of the cam which mechanism does not introduce impact loading into the system and which is relatively simple in structure and therefore easily maintained under operating conditions.

It is another object of the present invention to provide a variable dwell and lift mechanism for valves employed "ice in internal combustion engines which does not introduce impact loading into the system.

It is another object of the present invention to provide a relatively simple mechanism requiring the movement of only a few parts to effect variable dwell and lift of a valve mechanism of an internal combustion engine.

It is still another object of the present invention to provide a variable dwell and lift mechanism for internal combustion engines in which two distinct parameters of the system are varied by the movement of a single element of the system, each of the two parameters having a distinct but cumulative effect upon changes in dwell and lift of the valve mechanism.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a partial sectional'diagram in elevation of the valve mechanism in the low performance valve close position;

FIGURE 2 shows the mechanism of FIGURE 1 in the valve open position;

FIGURE 3 is a schematic view in elevation partially in section of the apparatus of the present invention in the high performance valve close position;

FIGURE 4 illustrates the apparatus in the high performance position with the valve open;

FIGURE 5 is a set of graphs showing the opening and closing cycles of the valve in the low and high performance positions;

FIGURE 6 is a schematic diagram in elevation of a modification of the apparatus of FIGURE 1 permitting overcenter operation of the drive linkage;

FIGURE 7 is a graph of the opening and closing cycles of the valve of the apparatus of FIGURE 6; and

FIGURE 8 is a schematic diagram in elevation of a further embodiment of the invention providing positive drive of the drive linkage in both directions.

Referring now specifically to FIGURE 1 of the accompanying drawings, the apparatus of the present invention is illustrated in the low power position; that is, in a position in which the duration of valve opening and amount of valve lift is at a minimum. There is provided an internal combustion engine generally designated by the reference numeral 1, only those portions being illustrated which are essential to the understanding of the operation of the apparatus of the present invention. The engine is of the overhead cam type and includes a combustion chamber 2, only a portion of which is illustrated, a piston 3 adapted to reciprocate in the chamber 2, and an intake valve 4 adapted to cooperate with an annular valve seat 6. When the valve 4 is in the position illustrated, it seals a passage betv vn the chamber 2 and a passage 7 in the engine block. The passage 7 communicates with an intake manifold, not illustrated.

The engine is also provided with an exhaust valve 8 but the operation of this valve is completely conventional and since its operation forms no part of the present invention, none of its operating mechanism is illustrated. On the other hand, if it is desired to control the operation of the exhaust valve then the apparatus of the present invention may be applied thereto.

The inlet or intake valve 4- has a valve stem 9 adapted to reciprocate in a sleeve 11 pressed into the cylinder head. The upper end, as viewed in FIGURE 1, of the valve stem 9 extends above the upper end of the sleeve 11 and is provided in this region with a removable, flared spring retainer 12 adapted to hold a pair of compression springs 13 under high compression between itself and a flat surface 14 on the cylinder head. The valve 4 is thus norad mally biased upwardly so as to be seated against the valve seat 6 and close the opening between the chamber 2 and the passage 7 which communicates with the inlet manifold.

The upper end of the valve stem 9 is adapted to be engaged by a rocker arm 16 pivoted about a shaft 17 at its end opposite to the end which engages the valve stem d. Rotation about the shaft 17 is imparted to the rocker arm 16 by means of a toggle arrangement comprising a first link 18, a second link 19 and a cam follower Zll. The

links

18 and 19 have adjacent ends pivotally connected to a shaft about which the cam follower it is rotatable. One end of the link 18 is pivotally connected to the rocker arm 16 by means of a shaft 23 and a remote end of the link 19 is pivoted about a stationary shaft 24. A hairpin spring 26 has a single turn taken about the shaft 24, has one end seated against a fixed stop 27 and its other end 28 engaging the shaft 22 to urge it in a clockwise direc tion about the shaft 24. As a result, the cam follower 7:1 is biased into engagement with a timing cam 23 of the rotatable cam shaft 29 driven by the engine.

With the apparatus in the position illustrated, rotation of the cam 28 causes the cam follower 21 to oscillate about the shaft 24 thereby altering the angle between the links 13 and 19. As the angle between these two links decreases, the rocker arm in is caused to rotate counterclockwise about the shaft 1'7, thereby pressing downwardly against the valve stem 9 and causing the valve 4 to move downwardly into the chamber 2 opening the passage between the chamber 2 and the passage 7. This condition is illustrated in FIGURE 2 of the accompanying drawings and it will be noted that the opening provided between valve 4 and the valve seat is quite s hall.

As previously indicated, it is an object of the present invention to provide an apparatus for permitting control of the opening between the valve 4 and the valve is and also to control the length of time of such opening. This mechanism includes the already recited

elements

13, 19, 21, 22, 23, 24, 26, 2'7 and 28 and further includes an adjusting pinion 31 adapted to engage a rack 32 which carries at its left end, as viewed in FIGURE 1, the shaft 17 about which the right end of the rocker arm is pivoted. The pinion 31 is carried on a shaft 33 and then upon rotation of the shaft 33, the rack 32 is caused to translate parallel to its elongated dimension as viewed in FIGURE 1. The apparatus of FIGURE 1 is illustrated in a position in which the rack 32 has been moved as far as possible toward the left and therefore further adjustment of the rack 3-2 must be in a direction necessary to move the rack to the right and cause the rocker arm 16 to move towards the right. This position is ih ustrated in FIGURE 3 of the accompanying drawings. It will be noted that in this position, the

links

18 and 19 are no longer almost in line but the angle therebetween has been reduced by roughly The illustration in FIGURE 3 is taken when the mechanism is in its high power position; that is, the rocker arm 15 has been moved to the extreme right.

Upon rotation of the cam 28 under these conditions, rapid downward movement of the left end of the rocker arm is initiated almost immediately and the valve 4 assumes the position illustrated in FIGURE 4 in its fully open position. It will be noted that under these circumstances, the passage between the valve 4 and the valve seat 6 is quite large and further, the interval during which the opening occurs is considerably greater. It will be noted that the rocker arm 16 is in engagement with the top of the rod 9 when the apparatus is in both the low and high performance conditions. Actually, the surface of the rocker arm 16 adjacent the rod 9 is contoured so that, at all positions between and including the extreme positions, a proper relationship is ma ntained between these two members which in practice requires a slight clearance therebetween when the valve is closed.

In further explanation of the apparatus, reference is now made to FIGURES l, 2 and 5, the latter figure comprising timing diagrams illustrating the interval during which the valves are open and the amount of opening of the valves. Referring again for the moment only to PHGURES 1 and 3, the surface of the cam 28 above a horizontal line 3% through its center is of constant radius over its upper 180 surface. The surface of the cam below its horizontal center line 3% gradually increases in diameter and reaches a maximum at a distance from the horizontal; that is, in the precise vertical position as illustrated in FIGURES 1 and 3. Engagement between the cam follower 2.1 and the cam 28 over its upper half of the surface produces no motion of the cam follower 21 and during this interval the valve d is in engagement with the Valve seat 5. This interval is not illustrated in the graphs of FIGURE 5.

In FIGURE 5, graph A illustrates the low performance operation of the valve and graph B represents the high erformance operation. The Zero degree position of the graphs is the position with the cam 28 rotated so that it intersects or engages the cam follower 21 along the center line 3t) of the cam. The cam must be rotated about 15 counterclockwise in FIGURES l and 3 to obtain this position.

In operation, the cam 28 rotates clockwise with the portion of the cam 28 having the maximum radius engaging the cam follower 21 after 90 of rotation. Due to the fact that the

links

18 and 19 are almost aligned in the low performance condition illustrated in FIGURE 1, very little motion is imparted to the cam during the initial periods of rotation of the cam and the amount of opening of the valve is so small that substantially no fluid is admitted to the cylinder throu h the valve opening between the valve and the valve seat. However, after about 15 of rotation of the cam 28, the opening between the valve and its seat admits significant amounts of the fuel mixture and thereafter the opening increases in size until the cam has rotated about 90. Thereafter, the valve begins to close and reaches very nearly full closing at roughly of rotation of the cam relative to its initial position. Complete closing is achieved at of rotation of the cam 28 and complete closure of the valve 4 is maintained for the next 180 until the cam again assumes the initial position set forth above. The interval of effective opening of the valve in the above example covers about 150 of rotation of the cam shaft.

The operation of the apparatus in the high performance position is quite different and this is illustrated in FIGURE 4 and Graph B of FIGURE 5. The maximum opening of the valve is more than twice as great as the opening during low performance operation. In addition, the knee or the angle between the

links

18 and 19 is relatively large during the inoperative period of the valve and consequently, movement of the cam follower to the left, as illustrated in the figures, almost immediately produces a relatively large movement of the valve 4. This is shown clearly from a comparison of Graphs A and B. The valve 4 is moved a sufficient amount to produce an effective opening between the valve and the seat almost instantaneously in the high performance position of Graph B, whereas almost 15 of rotation of the cam 23 is required to produce an effective opening in the low performance condition of Graph A. Further due to the large opening between the valve and the seat in the high performance position considerably more of the fuel mi);- ture may pass into the cylinder during high performance operation than during low performance operation.

The differences in performance between these two extremes and the range of intermediate positions is the result of two distinct but concurrent variations in the physical arrangement. The first variation relates to changes in the lever arm of the mechanism, being longest in the high performance position, FIGURE 3, and shortest in the low performance position, FIGURE 1. In consequence, the mechanical amplification of the movement of the upper end of the link 18 is varied as between the various positions of the apparatus and changes the amount of movement of the valve 4 as a function thereof.

The second variation in the system is of the angle between links 13 and 19 which changes the amount of translatory motion imparted to the upper end of link 18 as a result of the action of cam 28. When the angle between the links is a maximum; that is, 180, little translatory motion is imparted to the upper end of ling 18 during the rotation of the cam follower 21 about shaft 24. However, if the angle between

links

18 and 19 is reduced, for instance, to 150, the amount of rotation of cam 21, produced by cam 28, imparts a large translatory motion to the upper end of link 18. These relationships are, in fact, controlled by the sine function.

It is apparent from the above that the apparatus of the invention produces, in additive relationship, variations in the amount of movement of the upper end of the link 18 and in the amount of amplification of this movement effected by the lever 16, resulting in large variations in effective dwell and lift of the valve. The term effective dwe is employed above to denote the fact that the valve begins to open at the same time regardless of the position of the arm 16 but the opening of the valve is initially so slight when operating under low performance conditions that its initial opening may be considered to take effect only after about 15 of rotation of the cam shaft from its zero position as defined above.

The true dwell time of the valve may be actually decreased and the maximum opening further decreased during low performance operation by moving the rack 32 and the rocker arm 15 even further to the left than is illustrated in FIGURE 3, this being illustrated in FIG- URE 6. The additional movement causes the pin 23 to move to the left of the extension of the center line of the link 19. This movement causes the rocker arm 16 to be depressed slightly and in order to prevent a slight unseating of the valve 6, the rocker arm 16 is slightly recessed as at 34 in this embodiment of the invention. The recess is formed such that the desired normal clearance is maintained between the valve stem and the rocker arm as the rocker arm is moved to the left.

In this embodiment of the invention, the high performance characteristics are not altered relative tothe characteristics of the devices illustrated in FIGURES 1-4. The low performance characteristic is altered and is illustrated in FIGURE 7.

During low performance operation, the rocker arm is initially raised as a result of straightening of the

links

18 and 19 as the follower 21 moves over center to the left. As the

links

18 and 19 break over center to the left, the rocker arm 16 moves downward, contacts the upper end of the valve stem 9 and opens the valve. The motion of the valve 9 is plotted in FIGURE 7. The valve does not start to open until 15 of rotation of the cam shaft and the total opening of the valve is less than in FIGURE 45A. The valve is subsequently closed at 150 of rotation of the cam shaft so that the total dwell time of the valve 4 is 120 rather than the 180 dwell provided by the apparatus of FIGURES l-4.

In the embodiment of the invention thus far described, the pivot point of the link 18 has been moved as a result of movement of the rocker arm in order to vary the angle between the

links

18 and 19. The same result can be obtained by varying the position of the shaft 24 so as to vary the pivot point for the link 19 and concurrently vary the angle between the

links

18 and 19.

It is preferred to vary the location of the rocker arm in order to vary the position of shaft 23 for two reasons: First of all, the region in which the shaft 24 is located is not very large and it is difficult to obtain room for suflicient movement of the shaft 24 to provide the desired variation in valve lift. Secondly, the movement of the rocker arm 16 changes the lever arm between the pivot pin 17 and the valve stem 9 and also alters the lift characteristics of the mechanism. Thus, the movement of the rocker arm 16 provides a variable mechanical multiplying function which is not available if the shaft 24 is moved. The variation in lever arm in conjunction with the change of angle between the

links

18 and 19 provides a mechanism having a high degree of flexibility in that by varying the relative effects of these two interrelated quantities many different lift characteristics may be obtained. For instance, if the mechanism is arranged such that the knee between the

links

18 and 19 is displaced toward the cam 28 rather than away from it then the change in length of the lever arm of the member 16 is opposite to the effect produced on the linkage by movement of the lever arm resulting in a more gradual change of characteristics with movement of the rack 32.

There are a number of permissible variations in design of the various apparatus illustrated within the scope of the present invention. For instance, the rack 32 and pinion 31 may be replaced by a lever arrangement and the apparatus may be employed with equal facility in engines which do not employ overhead cams and the rocker arms are operated by push rods. Also the variable opening and/ or dwell apparatus may be applied to the exhaust valves as well as to the intake valves particularly where wide variations in valve overlap are required.

In engines operating at very high r.p.rn.s it may be desirable to eliminate the springs 26 so as to prevent resonant effects. This may be accomplished by employing the apparatus illustrated in FIGURE 8 of the accompanying drawings. Referring specifically to FIGURE 8, in which elements identical to those of FIGURES 14 bear the same reference numerals, the link 18 is eliminated and its function is provided by an arm 36 of a bell crank 37 pivoted about a stud 33. The upper end of arm 36 is connected to the pivot pin 22 which carries the cam follower 21 and one end of the link 19.

The bell crank has a second arm 39 extending upwardly to the right as viewed in FIGURE 8 and carries at its upper end a pivot pin 41 which pivotally supports a cam follower 42. The cam follower 42 contacts a cam 43 of a cam shaft 44. The shaft 44 is synchronized with the shaft 29 and the cam 42 is complementary to the cam 28. In consequence, the bell crank is positively driven in both directions about its pivot 38 and springs are not required to maintain contact between the cam followers 21 and cams 28.

The dual cam arrangement may be eliminated by contouring the upper half of the cam 28 as viewed in FIG- URE 8 to be a complement of the lower half thereof. In such a case, the cam follower 42 may operate off of the right side of the cam 28 and the cam 43 and cam shaft 44 may be eliminated. The pivot pin 33 of hell crank 37 would be moved under the shaft 29 and the angle between and length of arms 36 and 39 would be altered to accommodate the new geometry.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of .the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A variable dwell and lift mechanism for valves comprising a valve, a valve stem, a valve seat, means for biasing said valve into engagement with said valve seat, a valve actuator for engaging said valve stem and moving said valve relative .to said valve seat, a toggle comprising a pair of links pivotally connected together at one end of each, the other end of a link of said pair of links being pivoted about a pivot point on said valve actuator, the other end of another of said pair of links being pivoted about a pivot point remote from said actuator means, means for selectively moving one of said pivot points to alter the angle between said links and means for periodically reciprocating the point of pivotal connection between said links to alter the angle between said links so as to vary the length of said toggle and reciprocate said valve actuator.

2. A variable dwell and lift mechanism for valves comprising a valve, a valve stem, a valve seat, means for a biasing said valve into engagement with said valve seat, a lever arm having a surface in juxtaposition to said valve stem, a pair of links pivotally connected together at one end of each, the other end of a first of said pair of links being pivoted about a pivot point on said lever arm, the other end of another of said pair of links being pivoted about a pivot point remote from said lever arm, means for selectively moving said lever arm so as to rotate said first link about the pivotal connection between said links, said surface of said lever arm being contoured to maintain the position of said lever arm relative to said valve stem approximately the same along the direction of movement of said valve stem, and means for periodically moving the point of pivotal connection between said links to oscillate said lever arm and reciprocate said valve.

3. The combination according to claim 2 wherein said means for selectively moving said lever arm comprises a rack and pinion gear, said lever arm having an end remote from said valve stem pivotally connected to said rack.

4. The combination according to claim 2 wherein said means for periodically moving comprises a cam follower secured to said links at the point of pivotal connection between said links, a rotatable shaft lying parallel to the pivotal axis of said links and a cam secured to said shaft and engaging said cam follower.

5. A variable dwell and lift mechanism for valves comprising a valve, 21 valve stem, a valve seat, means for biasing said valve into engagement with said valve seat, a

lever arm having a surface in juxtaposition to said valve stem, a pair of links pivotally connected together at one end of each, the other end of a first of said pair of links being pivoted about a pivot point on said lever arm, the other end of another of said pair of links being pivoted about a pivot point remote from said lever arm, means for selectively moving the other end of one of said links so as to rotate said one of said links about the pivotal connection between said links and means for periodically reciprocating the point of pivotal connection between said links to periodically alter the distance between the other ends of said links, oscillate said lever arm and reciprocate said valve.

6. A variable dwell and lift mechanism for valves comprising a valve, a valve stem, a valve seat, means for biasing said valve into engagement with said valve seat, a lever arm having a surface in juxtaposition to said valve stem, a pair of links pivotally connected together at one end of each, the other end of a first of said pair of links being pivoted about a pivot point on said lever arm, the other end of another of said pair of links being pivoted about a pivot point remote from said lever arm, means for selectively moving said other end of said first of said pair of links so as to rotate said first link about the pivotal connection between said links and alter the angle therebetween and means for periodically moving the point of pivotal connection between said links so as to cyclically decrease and increase the distance between said other ends of said links thereby to oscillate said lever arm and reciprocate said valve.

7. A variable dwell and lift mechanism for valves comprising a valve, a valve stem, 21 valve seat, means for biasing said valve into engagement with said valve seat, a lever arm having a surface in juxtaposition to said valve stem, a toggle comprising a pair of links extending between a fixed pivot point and said lever arm, means for selectively adjusting the initial angle between said links, means for periodically buckling said toggle and means for returning said toggle to its initial position.

8. A variable dwell and lift mechanism for valves comprising a valve, a valve stem, a valve seat, means for biasing said valve into engagement with said valve seat, a lever arm having a surface in juxtaposition to said valve stem, a toggle comprising a pair of links extending generally perpendicular to said lever arm between a fixed pivot and said lever arm, means for selectively adjusting the initial angle between said links, means for periodically buckling said toggle and means for returning said toggle to said initial angle between said links.

9. The combination according to claim 8 wherein said means for selectively adjusting comprises means for shifting said lever arm, said lever arm being contoured to maintain relatively constant the spacing between said lever arm and said valve stem.

References Cited in the file of this patent UNITED STATES PATENTS 1,395,851 McLean Nov. 1, 1921 2,834,330 Weaving May 13, 1958 2,934,052 Longenecker Apr, 26, 1960 2,977,943 Lieberherr Apr. 4, 1961 FOREIGN PATENTS 333,729 France Sept. 29, 1903

Claims

1. A VARIABLE DWELL AND LIFT MECHANISM FOR VALVES COMPRISING A VALVE, A VALVE STEM, A VALVE SEAT, MEANS FOR BIASING SAID VALVE INTO ENGAGEMENT WITH SAID VALVE SEAT, A VALVE ACTUATOR FOR ENGAGING SAID VALVE STEM AND MOVING SAID VALVE RELATIVE TO SAID VALVE SEAT, A TOGGLE COMPRISING A PAIR OF LINKS PIVOTALLY CONNECTED TOGETHER AT ONE END OF EACH, THE OTHER END OF A LINK OF SAID PAIR OF LINKS BEING PIVOTED ABOUT A PIVOT POINT ON SAID VALVE ACTUATOR, THE OTHER END OF ANOTHER OF SAID PAIR OF LINKS BEING PIVOTED