US2878795A - Valve timing gear for reciprocating engines such as internal combustion engines - Google Patents

Description

March 1959 F K E. MANNERSTEDT 2,878,795

VALVE TIMING dEAiz FOR RECIPROCATING ENGINES. su'" A3 INTERNAL COMBUSTION ENGINES Filed Nov. 15, 195 1 United States Patent VALVE TIMING GEAR FOR RECIPROCATIN G EN- gUCH AS HWTERNAL COMBUSTION Folke Karl Erik Mannerstedt, Hagersten, Sweden Application November 15, 1954, Serial No. 468,984

Claims priority, application Sweden May 25, 1954 3 Claims. (Cl. 123-90) Among four-stroke-cycle internal combustion engines the so-called valve motor is the dominating one to-day. This designation refers to the fact that the supply and removal of gases (for the sake of brevity this notion also comprises vapors in the following) to and from an engine cylinder take place through openings in the wall of the combustion chamber, said openings being, constructively, kept either closed or, when a passage of gas is to take place, more or less open by means of valves of the so-called disk or mushroom type. This method is sometimes also made use of in connection with twostroke-cycle engines, in which case the present invention may be utilized to advantage on certain conditions. In the following, an application of the invention will be treated substantially only in connection with four-stroke-. cycle engines; this account will also explain the way of applying the invention to other types of reciprocating engines as well.

Depending on the location of the valves in the cylinder, two main types of four-stroke-cycle engines, that is to say, engines with side valves and engines with top valves, are distinguished between. The latter type is now strongly dominating, and this is the type the present invention primarily refers to; the invention is also applicable to side valve systems, however.

If the engine cylinder is conceived of as taking a vertical position with an underlying crank shaft, a socalled top valve is seated in the top portion of the combustion chamber, which as a rule constitutes a portion of a removable cylinder head. The valve stem is then directed upwardly, either vertically or forming, as a rule, an angle of 35 at the most with the cylinder axis. As a, rule, the control of such a valve takes place either from an overhead camshaft or from a camshaft located in the crankcase of the engine; in both cases, the camshaft is driven from the engine shaft at exactly half the number of revolutions of the latter. The valve is pressed against its seat by a spring acting at a certain bias between a seat in the stationary part of the engine and a seat rigidly connected to the valve stem.

If an overhead camshaft is made use of, it is arranged to actuate each valve either directly, so that a cam formed on the shaft forces the valve stem to move axially against the action of said spring at the rotation of the shaft, or indirectly, so that the cam acts upon a rocker, one end of which acts in turn on the valve stem. The expression valve stem is taken to include any existing steering plunger connected. to the stem and adapted to, relieve the valve stem of all non-axial stresses.

If the camshaft is located in the crankcase, the cam generally acts upon a short so-called valve pusher, which as a rule is formed as an axially movable piston mounted in the crankcase and having the open end thereof turned away from the cam. One end of a push rod bears on the. inner side of the piston bottom, while the other end of; said push rod bears on one end of a two-armed valve rocker mounted on the cylinder cover, the other end of said. valve rocker acting in turn. on thevalve stem, so:

2,878,795 Patented Mar. 24, 1959 2. that the valve is opened. There are many variants of this mechanism, but in principle the above description is characteristic'of all of them.

At a moderate maximum number of revolutions (below approximately 3000 revolutions per minute) of the engine, all of the means described hereinabove for the control of top valves are comparatively good both from the point of view of durability and with respect to noise, but the more the number of revolutions is augmented, the more conspicuous will their drawbacks be. These drawbacks primarily originate in the circumstance that the cam will at every moment of activity slide for a considerable distance over the part of the construction actuated thereby, and that the contact pressure grows very rapidly with an increasing maximum number of revolutions. This is so because the valve spring pressure will have to be increased practically proportionately tothe square of the number of revolutions in order to be able to accelerate the swinging masses of the system powerfully enough to prevent the system from leaving hold of the cam, as this behaviour is generally expressed. Add to this that hitherto it has not been possible, in connection with high numbers of revolutions, to provide any method of lubricating said points of a sliding contact, where steel acts against steel, in an entirely satisfactory manner; consequently, it is natural enough that a most abnormal wear manifests itself in the parts cooperating towards said sliding contact.

In this respect, the system with an overhead camshaft is the better one by reason of lower values of the swinging masses in the same, but on the other hand it is considerably more expensive in manufacture and increases the height of the engine, and it is not relieved of the consequences of a sliding contact without a satisfactory lubrication of the sliding surfaces.

The present invention refers to a valve timing gear, which is primarily intended for top valves and wherein the disadvantages touched upon are practically altogether eliminated. It is less expensive in manufacture than the conventional rod-rocker-system with an underlying cam shaft, and it has small swinging masses and mass forces and consequently requires only relatively weak valve springs while being practically without all. points of a sliding contact with: an insuilicient lubrication protection. Furthermore, it is particularly well adapted for standardization, whereby a specialized manufacture with a few standard types of the arrangement can cover the need of a great number of different engines of varying sizes. As an example of the very good properties oftheinvention might be mentioned that it was at one time secretly applied to a Swedish experimental motor cycle by which the driver won the Grand Prix of France for motorcycles in a superior manner.

As the main principle of the invention might be stated that the movement imparted to a valve through the same is not based on a conventional camshaft but on an eccentric shaft provided with a circular eccentric. One end of a motion-transforming member is mounted entirely or in part about said eccentric by means of a sliding or antifriction bearing, said member having a con-. tinuously reciprocating function and being for the sake of brevity designated as a connecting rod in the following. The other end of said connecting rod is connected by a joint to a cam rocker mounted on the cylinder top, which rocker may be single-armed or two-armed. The cam rocker is formed in such manner that a suitably shaped part of the same cooperates with the valve stem or with a steering plunger actuating the valve stem, in such a manner that within a certain sector of the revolution of the eccentric the system of the eccentric, the connecting rod. and the camrocker impartsan axial movement to the valve stem, whereby the valve is opened initial position and during its return movement permits closure of the valve with a variation of the closing speed. reversed in comparison with the opening movement, during the movement of closure. The latter movement may be effected in known manner by means of an ordinary valve spring, but the invention also permits a construction through which the motion of the valve closure becomes positively controlled, entirely or in part, and determined by the motion of the driving eccentric. This will take place, when the large end of the connecting rod is mounted entirely about the eccentric with a very small allowance, and when the small end of the connecting rod is likewise mounted in its entirety in the cam rocker with a very small allowance, while the cam rocker is also, in the axial direction of the valve stem, connected to the latter or to the steering plunger connected to the same, in such a manner that only an extremely small play can set in between the operative surface of the cam rocker facing the valve and the surface of the valve stem or the steering plunger actuated thereby; a construction of this type may also comprise a relatively weak valve closing spring.

The connecting rod comprised in the invention may function either as a pull rod or as a push rod in an embodiment wherein the valve is closed by means of spring power in the conventional manner. In all forms of embodiment, the construction may comprise one or more suitably located return springs.

It is characteristic of the invention that with a suit able configuration of the active surface of the cam rocker both the degree of the sector of the engine revolution in which the valve is open and the opening level of the valve can be varied in a certain measure through an alteration of the geometry of the system. Nothing prevents a construction whereby such an alteration can be carried into effect also during the operation of the engine, either manually through an intervention on the part of the engine attendant or automatically by means of a' governor, for instance in a certain relation to the nums ber of revolutions of the engine.

After the above general account of the main features of the invention it is believed to be entirely clear to any one skilled in the art that the invention is applicable, with respect to the formation of the details of the valve system, in many, more or less different manners, particularly in regard to the curvature of the active surface of the cam rocker and the cooperating active end surface of the valve stem or of the steering plunger connected thereto. Within the scope of the invention, the designer is at liberty to form these surfaces as he desires-to make them fiat, concave or convex with a constant radius of curvature or one varying along the surface-aiming at making their relative movement approach the concept of rolling as far as possible. As it is easy to maintain a layer of lubricant between said contact surfaces, the wear thereat will be exceedingly small with a suitable formation of the surfaces. Furthermore, since no difficulty is experienced in providing an effective lubrication of the contact points of the system, the durability of a well constructed valve system according to the invention may certainly be expected to become very great. It has been found in testing high speed experimental engines wherein the invention was applied that the durability of their valve systems is far superior to the durability of conventional valve systems at corresponding numbers of revolutions. In part this also depends on the fact that the acceleration of the principal masses of a.- system according to the invention only amounts to 035- 0.40 of the corresponding acceleration in a conventional cam-pushrod-rocker system.

To illustrate the simplicity of a valve timing gear ac 4 cording to the invention, in the annexed drawing, Fig. l is a vertical sectional view of an embodiment of such a gear for a top valve intended for a four-stroke-cycle internal combustion engine of the reciprocating type, the drawing being in a certain measure diagrammatic, details of the engine non-essential for the invention being simplified or omitted; and

Fig. 2 is a fragmentary top view of the embodiment shown in Fig. l as seen with the top casing removed.

In the drawing, which represents a cross section through the engine, 1 designates the cylinder body, 2 the crankcase, 3 the engine shaft with the crank pin 4. 5 denotes a connecting rod cooperating with the piston 6. 7 is a top valve controlled according to the invention, said top valve being provided with the valve stem 8 and the steering plunger 9. 10 is a valve spring, which in its position of rest keeps the valve pressed against the valve seat under a certain bias, and against the tension of which the valve is opened. 11 designates an eccentric shaft, driven in known manner (not shown) from the engine shaft 3 at a reduction of the number of revolutions in the exact ratio of 2: 1, said shaft being provided with a circular eccentric 12 rotating with the shaft 11. Mounted on the eccentric is the one end of a motion-transforming member, here taking the form of a connecting rod. Threaded into the other end of this connecting rod is an adjusting pin 14, the free end of which is ball-shaped. Pertaining to the threaded connection is a lock nut 15. 16 designates the rocker which was called the cam rocker hereinbefore.

spring 19 acting on the cam rocker in the direction of rotation indicated by the arrow. The whole valve mechanism is encased in an oil tight manner within a casing 20, and is lubricated in known manner, preferably with pressurized oil from an oil pump (not shown) driven by the engine.

A description of the function beyond the general account hereinabove is believed to be unnecessary. On the other hand, it is appropriate further to touch upon a few details in certain embodiments of the invention.

It is obvious from the nature of the construction shown in the drawing that with a certain formation and adjustment of the pressing surface 18 of the cam rocker 16 there is no constructive cause of hindering the existence of an infinitely small play between the pressing surface of the cam rocker and the steering plunger during the period in which the valve is closed. The question, whether a larger play should be used is substantially a question of thermal expansion. However, this question may-but need not necessarilyalso present itself in a form of embodiment wherein a desire of being able during the operation of the engine to vary that number of degrees of the crankshaft during which the valve does not bear on its seat is realized. An arrangement to this end may be undertaken in many ways known per se. For example, the pin 17 may be incorporated into the mechanism in a manner to make it displaceable by some fraction of a millimeter approximately in the axial direction of the cylinder or the valve stem. If the pin 17 be raised somewhat in the construction according to the drawing, the number of crankshaft degrees during which the valve is more or less open will be reduced, while the valve lift is at the same time reduced to a small extent. The level of the pin may be adapted to be determined by an eccentric mounting, by a positive guidance with the aid of screws, or by hydraulic pressure, or in some other known way. It is readily understood that the variation of said level may be adapted to be manually effected by an engine attendant or by means of an automatically acting governor, for instance with the number of revolutions as an influential factor. The variation may also be effected by a lateral displacement of the pin in the drawing, in this case also with the alternatives of a manual actuation or an automatic actuation from a governor. The latter also holds true for an arrangement wherein the connecting rod 13 is made in two parts in tandem, with the parts connected by a joint connected to the free end of a swinging arm extending approximately at right angles to the connecting rod, the pivot bearing of which arm is displaceably secured to the stationary part of the engine, in such a manner that an immaterial variation of the distance between the centers of the ball 14 and the eccentric 12 sets in at a small displacement of the pivot hearing. If said distance is shortened, then, with a suitable formation of the pressing surface 18 of the cam rocker, the angle of rotary movement of the crank shaft during which the valve is open will be reduced. Other embodiments comprising known machine elements are also conceivable within the scope of the invention.

Obviously, the motion-transforrning member 13 may on certain conditions have both a pulling and a pushing function allotted to the same for the purpose of actuating one and the same valve both for an opening and a closing movement. Then a connection must be provided in known manner between the member 13 and the rocker 16 on the one hand and the rocker 16 and the steering plunger 9 on the other hand, said connection being such that a positive control will be effected in both swinging directions.

It is also evident that the member 13 may be given both a pulling and a pushing function for the purpose of controlling a certain valve in one case and another valve in another case, with a phase displacement between the motion schemes of these valves as necessitated by the construction. On the whole, the invention is of such a nature, as stated hereinbefore, that a multiplicity of embodiments are possible within the scope of the same. it is not possible to describe all these facilities within a reasonable space, they should, all of them, be considered as falling within the scope of the invention, without being specially mentioned.

Obviously, the invention may also be made use of for the timing of valves of a cylinder operating according to the two-stroke-cycle principle; in this case the eccentric shaft is driven from the engine shaft at the number of revolutions of the latter shaft.

What is claimed is:

1. A valve gear for actuating a valve in an internal combustion engine comprising, in combination, a rotatable valve control shaft, a crank on said shaft, a rocker arm, a connecting rod between said crank and said rocker arm for converting the rotary motion of said valve control shaft into rocking motion of said rocker arm, means engaged by said rocker arm and reciprocated in response to rocking movements of said rocker arm, said means being disposed between said rocker arm and said valve, whereby rocking movements of said rocker arm are transmitted to said valve, said rocker arm and said reciprocating means being formed with interengaging cam surfaces, and said surfaces being formed to undergo during operation a predominantly rolling motion relatively to each other, a first spring means biasing said valve toward its closed position, a second spring means biasing said rocker arm toward said connecting rod, said shaft, rocker arm, connecting rod and reciprocating means being enclosed in an oil-tight casing for continuous lubrication.

2. A valve gear according to claim 1, wherein the crank end of said connecting rod only partially encircles said crank.

3. A valve gear for actuating a valve in an internal combustion engine comprising, in combination, a rotatable valve control shaft, a crank on said shaft, a rocker arm, a connecting rod between said crank and said rocker arm for converting the rotary motion of said valve control shaft into rocking motion of said rocker arm, means ongaged by said rocker arm and reciprocated in response to rocking movements of said rocker arm, said means being disposed between said rocker arm and said valve, whereby rocking movements of said rocker arm are transmitted to said valve, said rocker arm and said reciprocating means being formed with interengaging cam surfaces, and said surfaces being formed to undergo during operation a predominantly rolling motion relatively to each other, spring means biasing said valve toward its closed position and means for maintaining contact between said connecting rod and said rocker arm independently of said spring means, said shaft, rocker arm, connecting rod and reciprocating means being enclosed in an oil-tight casing for continuous lubrication.

References Cited in the file of this patent UNITED STATES PATENTS 863,922 Housum et al Aug. 20, 1907 1,182,044 Setz May 9, 1916 2,015,135 Brady Sept. 24, 1935 2,097,883 Johansson Nov. 2, 1937 2,200,152 Burkhardt May 7, 1940 2,720,873 Pick Oct. 18, 1955 FOREIGN PATENTS 8,200 Great Britain Apr. 13, 1908 183,078 Germany May 26, 1906 600,309 Germany July 19, 1934 388,108 France Aug. 3, 1908 1,038,516 France May 6, 1953 425,657 Italy Dec. 3, 1946

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