US3823698A

US3823698A - Mechanical lash adjuster

Info

Publication number: US3823698A
Application number: US00218806A
Authority: US
Inventors: Deberg W Van
Original assignee: F Jos Lamb Co
Current assignee: Lamb Technicon Corp
Priority date: 1972-01-18
Filing date: 1972-01-18
Publication date: 1974-07-16
Anticipated expiration: 1991-07-16
Also published as: DE2302093C2; CA994193A; DE2302093A1; BR7300413D0

Abstract

In an internal combustion engine having a lash adjuster, the usual shortening of the valve train occurs during the opening stroke of the valve (to introduce excessive lash or clearance), then the train is lengthened at the end of the closing stroke to remove all lash. In this invention, the motion for shortening the train is derived from the inherent unwinding of the helical valve spring when compressed to open the valve. This unwinding turns a screw within a nut of a threaded connection in the tappet or valve lifter thereby shortening the train and introducing lash. The screw can turn in the nut because the nut is prevented from following the rotating spring either by counter rotational urge of an offset cam on the lifter or by a one-way clutch holding the lifter. The turning of the valve spring also winds up a restoring spring between the screw and the nut. When the valve closes, the force of the valve spring is removed from the lifter. The lifter (and nut) are then allowed to rotate in the opposite sense and the connection is threaded out by the restoring spring to remove all lash.

Description

United States Patent 1191 Van Deberg MECHANICAL LASH ADJUSTER Inventor: Walter H. Van Deberg, Berkley,

Mich.

Assignee: F. Jos. Lamb Company, Warren,

Mich.

Filed: Jan. 18, 1972 Appl. N0.: 218,806

[52] US. Cl 123/9054, 123/9028, 123/9029,

123/903, 123/9019 Int. Cl F011 1/20 Field of Search 123/9054, 90.28, 90.29,

281,954 12/1970 U.S.S.R..' ..123/90.54 371,353 4/1932 GreatBritain ..123/90.54

[ 1 July 16, 1974 Primary Examiner-Manuel A. Antonakas Assistant Examiner-Daniel J. OConnor Attorney, Agent, or Firm-Barnes, Kisselle, Raisch & Choate [5 7] ABSTRACT In an internal combustion engine having a lash adjuster, the usual shortening of the valve train occurs during the opening stroke of the valve (to introduce excessive lash or clearance), then the train is lengthened at the end of the closing stroke to remove all lash. In this invention, the motion for shortening the train is derived from the inherent unwinding of the helical valve spring when compressed to open the valve. This unwinding turns a screw within a nut of a threaded connection in the tappet or valve lifter thereby shortening the train and introducing lash. The screw can turn in the nut because the nut is prevented from following the rotating spring either by counter rotational urge of an offset cam on the lifter or by a one-way clutch holding the lifter. The turning of the valve spring also winds up a restoring spring between I the screw and the nut. When the valve closes, the force ofthe valve spring is removed from the lifter. The lifter (and nut) are then allowed to rotate in the opposite sense and the connection is threaded out by the restoring spring to remove all lash.

17 Claims, 7 lrew egl su s 54 as so 40 232 36 l 5; 42 I I 22 44 52 I PATENTED JUL 1 61974 sunaur'z IFOzmj Z 2 8 MECHANICAL LASH ADJUSTER THE PROBLEM SOLVED BY THE INVENTION In internal combustion engines, it is usual to have reciprcating T-shaped poppet valves constantly urged to close against their seats by helical compression springs surrounding the valve stems. The valves are periodically opened, that is lifted from the seats, against the force of the springs by individual cams rotated by a common cam shaft. The cam exerts opening or lifting force against the valve stem either directly or through any one of many types of. actuators including rocker arms and tappets, placed between the cam and the valve stem. t y

In the art, the term valve train is used in various ways to mean the apparatus which operates or influences the position of the valve. This includes various parts according to the ideas of the particular writer or to the problem involved. For reasons which will be apparent I use the term valve train to include all movable parts between the cam face and the valve face proper which determine or influence the relationship between the cam face and valve face, that is the time of seating and unseating of the valve, and the position and direction of motion of the valve at any instant. Thus in my usage valve train includes the body of the valve head on which the active valve face is found, the valve stem, valve-seating spring, all connections between the spring and the stem, and all operators (e.g. tappets, rocker arms and lash adjusters) between the cam and the valve stem. The term does not include the cam, engine body nor valve seat, for although the cam primarily operates the valve and the other engine elements change from time to time, due to temperature and wear and therefore do influence timing and the position of the valve face relative to the valve seat, these are the elements to which the valve train must conform, and with respect to which its adjustments must be made.

The basic factor with respect to which the trainmust conform is the distance from a plane representing the surface of the valve seat to the center line of the cam shaft. This distance changes slowly, but not with the cyclical operation of the valve, that is; it remains substantially constant throughout'a fewcycles of valve operation. The movement of the cam face, toward and away from that plane opens and closes the valve by alternately pushing the valve train and releasing it. If this distance were constant, the valve train should ideally maintain a constant length, in order that the valve will open and close at the precise instants required. In so doing it is important that at particular instants there be no lash or clearance between adjacent elements of the train for this would cause objectionable wear and rattle noise, and changing lash would cause opening of the valve at the wrong time.

It is well known that the camshaft-seat distance changes with engine temperature and wear, so that the length of the valve train must be changed, if lash is to be avoided. Also the length of the valve train itself changes importantly with temperature and wear. Different parts of the valve train change temperature and consequently length at different rates. Therefore it is difficult or impossible without some form of lash adjuster, to make a valve train which will maintain the constantly changing relationship which will assure 2 proper time of valve opening and closing and maintain freedom from rattle and excessive wear.

In previous attempts to solve this problem hydraulic lash adjusters are widely used. During each cycle of valve movement such adjusters alternately lengthen and shorten a hydraulic chamber placed in the valve train. They shorten the valve trains to introduce lash during opening of the valve so that there is at one instant too much lash, then after closing of the valve, lengthen the train to remove all lash. Then there is no clearance in the train when the valve is next to be opened. An example is shown in the Thompson U.S. Pat. No. 2,865,352 in 1958. Such adjusters or tappets operate extremely well within certain limitations. Millions of them are in satisfactory use in automobiles. However they have known inherent disadvantages which have encouraged the development of purely mechanical lash adjusters, for example those shown in the U.S. Pat. No. to Thompson 3,087,475 in 1963, and Goodwin 2,131,507 in 1938. Such mechanical lash adjusters as have come to my attention, if operative, are difficult or expensive to make and install in engines or are unreliable or of short life in operation or both. Their necessary size and arrangement makes them unsuitable in existing engines with overhead cam shafts in which the cam, valve and valve-spring are all in alignment and close together.

-' THE INVENTION It is an object of this invention to provide an improved fully mechanical lash adjuster of few parts and of short length which is particularly adaptable to existing overhead camshaft engines.

It is also an object to provide an improved mechanical lash adjuster in which the linear force which opens the valve generates a rotaty force which turns a thread to shorten the valve train to introduce lash between the cam and the train, and which also loads a restoring spring which restoring spring automatically turns the thread oppositely to remove all lash when the valve opening force is removed.

It is an object to remove this rotary threading force from the threaded connection the instant the valve is closed andto turn the thread to remove all lash in the interval between the closing of the valve and the next application of opening force.

It is an object to use the inherent rotation or unwinding of a helical spring while being compressed to provide the necessary rotary movement which both turns the threaded connection to change the length of the valve train and stores energy in a restoring spring which threads the connection in the opposite direction when the force of the helical spring is removed.

It is particularly an object to use the customary valve spring to provide the necessary rotary movement to turn the thread whenever the spring is compressed to open the valve.

Another object is to provide a lash adjuster in which the adjusting mechanism is located in a very small space between the end of the valve stem and the bottom of a cup which surrounds the stem and valve spring and bears on the cam. These and otherobjects and advantages of the invention will be apparent from the following description and from the annexed drawings which disclose, by way of example and not in any limiting sense, several forms of the invention.

In the accompanying drawings:

incorporated. I

FIG. 3 is an elevation of the cam and part of a tappet as seen from the right of FIG. 1, as from a plane represented by the line 22.

FIG. 3 is an enlarged section of the parts shown in FIG. 1, the lash adjuster and associated parts of the valve train being shown at the beginning of the opening stroke of the valve. The section is taken in the the paper of FIG. 1.

FIG. 4 is a section corresponding to FIG. 3 but showing the parts in the relationship in which they are installed in the engine.

FIG. 5 is a perspective view of a valve spring extended and wound as it is when the valve is closed.

FIG. 6 is a view corresponding to FIG. 5 showing the spring compressed and unwound as it is when the valve is open; and

FIG. 7 shows a modified form, corresponding to the view in FIG. 1.. v I

plane of In FIG. 3 the cam is about to start opening the valve. Further rotation of the cam in the direction of the arrow opens the valve by depressing the valve stem 16 (and compressing the spring 18) through the parts between the cam and stem, namely cap 20, nut 30, screw 36 and clutch face 38. This compresses the spring from the condition shown in FIG. 5 to that shown in FIG. 6. The lower end 48 of the spring is prevented from turning by the rough surface 49 of the spring seat in the enthe clutch faces 38, 40'together so that the unwinding of the'spring turns the screw 36.

As shown in FIG. 1 an engine 10 has a valve seat 12 and a valve head 14 fixed to a valve stem 16 which reciprocates in a bore in the engine. The valve is urged against its seat by a helical compression spring 18 which urges upward both the stem and a tappet including a cap or cup 20 slidable in a bore 22. The cap is periodically moved down against the force of the spring by the lobe of a rotary cam 24 mounted on the customary cam shaft 26. I sometimes refer to the cap as a base. If desired the. spring 18 may be provided with the customary harmonic friction vibration damping spring 28 helically wound in the hand oppositeto the spring 18 and in frictional contact with the inner surface of its convolutions. As shown in FIG. 2 the cam 24 engages cap 20 on one side of its center. Friction due to wiping of the rotating cam against the cap urges the base to turn in the bore 22. I

As so far described the structure is conventional except for particulars of the cap 20.

As shown particularly in FIGS; 3 and 4 a threaded nut 30 is placed loosely within the cap, being resiliently centered by an O-ring 32 while being prevented from turning in the cap and held against its top by a pin 34. Threaded into the nut 30 is a screw 36 having an internal conical clutch face 38 which cooperates with an external conical clutch face 40 on the valve stem 16. The screw 36 can thread in the nut 30 between an innermost position shown in FIG. 4 (in which the train is shortest) and in outermost position shownin FIG. 3 (in which the train is longest). The valve stem 16 is normally urgedagainst the screw 36 by the valve spring 18,

I bringing the clutch faces 38 and 40 into engagement with each other. The spring is confined by a valve re-- threaded down in the nut toward the bottom of FIG. 3,

and the valve trail will have its greatest length;

The cup '20 is prevented from turning or following the screw by any suitable means, for example by the above mentioned counter rotational urge of the friction between the cap 20 and the cam 24 'orby a one-way clutch represented by the sprag 54, between the cap and the engine. This causes the screw 36 to turn in the nut 30 and to move axially a small amount from the posit-ion shown in FIG. 3 toward the position shown in FIG. 4. Teis shortens the valve train slightly and introduces a small amount of lash into the system.

As the screw 36 turns into the nut 30 it further winds a pre-stressed restoring spring 56 anchored at one end 58 in the screw 36 and anchored at its other end 60 in the nut 30. On each opening stroke of the valve the valve spring 18 shortens the valvetrain to introduce lash into the system by making a. clearance along the length of the valve train and thus making the valve train too short. When the peak of the lobe on the cam 24 has passed contact with the cap '20 and the cap 20 under the urging of the spring 18 is following the receding face of the cam, the valve moves toward closed position and the spring 18 begins. to extend and to wind up again. This does not change the relative positions of the screw and nut for two reasons. First, although the spring may for a time hold the clutch faces 38-40 in engagement with each other and thus may for a time turn the screw 36 in the opposite sense, the nut 30 and the cap 20 turn following the winding spring and so preserve the relative rotative positions of the screw and nut. In fact when the receding face of the cam is thus traveling along the cap, the cam will assist the cap in rotating in the same sense.

Second, the helix angle of the threads is steep, that is a relatively large axial movement is produced by relatively small rotation. The threads may have multiple starts. The helix angle is preferablyslightly less than the friction angle, or the angle of repose of the screw in the nut underaxial force of the valve spring. Thus the axial force between the valve stem andthe screw when the valve is being opened can almost, but not quite, turn 7 the screw in the nut. Therefore only a small turning force across the clutch is required to turn thescrew toward .shorteningthe valve train. But greater turning force: will be required to turn the screw to lengthen the train than will be required to turn the screw to shorten the train. However whatever turning vforce may exist across the clutch when the valve spring is extending and winding up cannottum the screw in the nut because the nut turns with it. This arrangement prevents the stem from unscrewing the screw out of the nut and thus cancelling the previous shortening of the train during the winding of the spring. This holds the train shortened and keeps the restoring spring loaded as indicated in FIG. 4 until the cap approaches the base circle of the cam as shown at FIG. 4.

Throughout the closing stroke the force of compression of the spring (which is the activating clutch force) is progressively diminishing. As soon as the valve seats, the spring 18 is confined by the spring retainer 42 and cannot exert force on the lashadjuster. Now the screw can be turned in the nut by the unwinding torsion spring 56, which was wound up in the opening stroke of the valve, to lengthen the valve train.

If clearances permit the restoring spring can expand .from the position shown in FIG. 4 to that shown in FIG.

3. This would turn the screw out fartherthan the valve spring 18 can turn it in. This is because when the device was assembled in the engine the restoring spring was wound through an angular displacement greater than the maximum angular displacement of the upper tip of the valve spring 18. Therefore, after the valve closes the restoring spring continues to urge the cap 20 against receding face of the cam 24 and against its base circle so that the cap follows the cam without any lash whatever. Thus during each cycle of the valve operation the valve spring 18 shortens the valve train very slightly by turning the screw 36 in the nut until there is too much lash in the system and subsequently allows the spring-56 to remove all the lash from thesystem by lengthening the valve-train again.

When the valve train is first assembled the screw 36 is threaded into the nut 30 in the position of FIG. 4 by any suitable tool, winding the restoring spring. The spring is held' wound and pre-stressed by a pin 62, shown in phantom lines, inserted through a hole 64 into a slot 66 in the screw. When the valve train has been assembled, the pin is removed. The excessive travel built into the device accommodates necessary tolerances in mass production and eliminates the necessity for selection from categories of tolerance for fitting in assembly.

Some of the features of the invention can be used to I advantage in engines having a rocker arm between the cam shaft and the tappet. FIG. 7 illustrates such an application of theinvention. The tappet 20, valve stem 16, and valve spring 18 are all arranged as shown in FIGS. 3 and 4, but instead of having the tappet depressed by the cam, the cam 24"operates a rocker arm 70 which bears at one end on a fulcrum 72 and at its other end on the tappet 20. In this application of the invention the cam does not provide the counter rotating urge to oppose the unwinding of the spring and it is necessary to'have the one-way clutch represented by the sprag 54 between the tappet and the engine.

I claim as my invention: 7

I. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in com bination with a valve train for exerting valve-opening force between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring constantly exerting valve-seating force on the stem and having a maximum compressed length when the valve is seated, the spring having the characteristic of unwinding to rotate its convolutions when the spring is axially compressed and of winding to rotate the convolutions oppositely when the spring is axially extended, and means operated by rotation of the force between the cam and the valve, th e train including a valve stem secured to the valve, a helical compression spring constantly exerting valve-closing force on the stem and having a maximum compressed length when the valve is seated, the spring having the characteristic of unwinding to rotate its convolutions when the spring is axially compressed and of winding to rotate the convolutions oppositely when the spring is axially extended, and means operated by rotation of the convolutions when the valve spring is compressed to a length sufficient to permit the valve to open fully or changing the length of the train by a given increment in one sense and responsive to expansion of the valve spring toward its maximum length for changing the length of the train oppositely.

- 3. A'valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring surrounding the stem and constantly exerting seating force on the stem, the spring being adapted to unwind when compressed, and means operated by the unwinding motion of the spring for changingthe length of the train in one sense and operated by the winding motion of the spring for changing the length of the train oppositely.

4. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve and a helical compression spring surrounding the stem and constantly exerting seating force on the stem, the spring being adapted to unwindwhen compressed and means operated by unwinding motion of the valve spring fon changing the length of the train by one amount in one sense and operated by winding motion of the valve spring for changing the length of the train oppositely by a greater amount.

5. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring surrounding the stem and constantly exerting seating force on the stem,

the spring being adapted to unwind when compressed, and means operated by the-unwinding motion of the spring for changing the length of thetrain in one sense and operated by the winding motion of the spring for changing the length of the train oppositely the valve train being further characterized by a base for transmitting force between the cam and thestem, said base being restrained a'gainsttuming about the axis of the stem in one sense of rotation but permitted to'turn oppositely, a threaded element rotationally fixed in the base, a second element threaded into the first and adapted to engage the stem so that the amount of interengagement of the threaded element determines the length of the valve train, clutch means between the valve stem and the second element whereby compression and resultant unwinding of the spring turns the second element in said one sense of rotation with re- ,is rotary and in its engagement with the base constitutes means for opposing turning of the base in one sense of rotation upon compression of the valve spring and assists turning of the base in the opposite sense of rotation during expansion of the spring.

7. Apparatus as defined in claim 5 in which the valve train also includes a restoring spring between the threaded elements adapted to be stressed by the turning of.-the second element upon unwinding of the valve spring whereby when force between the cam and the stem is removed, the second element is turned oppositely to change the length of the valve train oppositely to the first mentioned change of length.

8.- Apparatus as defined in claim 7 in which the unwinding of the spring shortens the valve train and release of the restoring spring lengthens the valve train.

9. Apparatus as defined in claim 5 in which the valve also includes a pre-stressed restoring spring between the threaded elements adapted to be stressed further by turning of the second element in response to unwinding ofthe spring, whereby when the force between the cam and the stem is removed the second element is turned oppositely to change the length of the valve train oppositely to the first mentioned change by an amount greater than thefirst mentioned change.

. 8 10. Apparatus as defined in claim '5 which includes means for opposing turning of one end of the spring.

11. A valvelifter adapted to be placed in a valve train which has a helicalcompression spring for seating a valve mounted on a valve stem comprising in combination a first threaded element, a second element in threaded engagement with the first so that the distance which one element is threadedinto the other deter- Y mines the length of the valve train and means responsive to'rotation of convolutions of the valve spring about the axis of they spring for rotating the threaded I elements relative to each other.

12. Apparatus as defined in claim 11 in which there is means for urging the elements to rotate relative to each other oppositely to the rotation imparted by the valve spring.

13. Apparatus as defined in claim 12 in which one of the threaded elements includes a clutch member for engaging the valve stem. l

14. Apparatus as defined in claim 12 in which a helical restoring spring has its opposite ends anchored to the threaded elements respectively.

15. Apparatus as defined in claim 11 in'which one of the threaded elements includes a 'clutch'member for engaging the valve stem of the valve train.

16. Apparatus as defined in claim 15 in which a helical restoring spring has its opposite ends anchored to the threaded elements respectively.

17. Apparatus as defined in claims 11 in which a heli-;

cal restoring spring has its opposite ends anchored to the threaded elements respectively.

Claims

1. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train for exerting valve-opening force between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring constantly exerting valve-seating force on the stem and having a maximum compressed length when the valve is seated, the spring having the characteristic of unwinding to rotate its convolutions when the spring is axially compressed and of winding to rotate the convolutions oppositely when the spring is axially extended, and means operated by rotation of the convolutions when the valve spring is compressed to a shorter length for changing the length of the train in one sense and operated by rotation of the convolutions responsive to expansion of the spring toward its maximum length for changing the length of the train oppositely.

2. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train for exerting valve-opening force between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring constantly exerting valve-closing force on the stem and having a maximum compressed length when the valve 15 seated, the spring having the characteristic of unwinding to rotate its convolutions when the spring is axially compressed and of winding to rotate the convolutions oppositely when the spring is axially extended, and means operated by rotation of the convolutions when the valve spring is compressed to a length sufficient to permit the valve to open fully or changing the length of the train by a given iNcrement in one sense and responsive to expansion of the valve spring toward its maximum length for changing the length of the train oppositely.

3. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring surrounding the stem and constantly exerting seating force on the stem, the spring being adapted to unwind when compressed, and means operated by the unwinding motion of the spring for changing the length of the train in one sense and operated by the winding motion of the spring for changing the length of the train oppositely.

4. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve and a helical compression spring surrounding the stem and constantly exerting seating force on the stem, the spring being adapted to unwind when compressed and means operated by unwinding motion of the valve spring for changing the length of the train by one amount in one sense and operated by winding motion of the valve spring for changing the length of the train oppositely by a greater amount.

5. A valve adapted to be reciprocated against and away from a seat by a cyclically operable cam, in combination with a valve train between the cam and the valve, the train including a valve stem secured to the valve, a helical compression spring surrounding the stem and constantly exerting seating force on the stem, the spring being adapted to unwind when compressed, and means operated by the unwinding motion of the spring for changing the length of the train in one sense and operated by the winding motion of the spring for changing the length of the train oppositely the valve train being further characterized by a base for transmitting force between the cam and the stem, said base being restrained against turning about the axis of the stem in one sense of rotation but permitted to turn oppositely, a threaded element rotationally fixed in the base, a second element threaded into the first and adapted to engage the stem so that the amount of interengagement of the threaded element determines the length of the valve train, clutch means between the valve stem and the second element whereby compression and resultant unwinding of the spring turns the second element in said one sense of rotation with respect to the first element to change the length of the train.

6. Apparatus as defined in claim 5 in which the cam is rotary and in its engagement with the base constitutes means for opposing turning of the base in one sense of rotation upon compression of the valve spring and assists turning of the base in the opposite sense of rotation during expansion of the spring.

7. Apparatus as defined in claim 5 in which the valve train also includes a restoring spring between the threaded elements adapted to be stressed by the turning of the second element upon unwinding of the valve spring whereby when force between the cam and the stem is removed, the second element is turned oppositely to change the length of the valve train oppositely to the first mentioned change of length.

8. Apparatus as defined in claim 7 in which the unwinding of the spring shortens the valve train and release of the restoring spring lengthens the valve train.

9. Apparatus as defined in claim 5 in which the valve also includes a pre-stressed restoring spring between the threaded elements adapted to be stressed further by turning of the second element in response to unwinding of the spring, whereby when the force between the cam and the stem is removed the second element is turned oppositely to change the length of the valve train oppositely to the first mentioned change by an amount greater than the first mentioned change.

10. Apparatus as defined in claim 5 which includes means for opposing turning of one end of the spring.

11. A valve lifter adapted to be placed in a valve train which has a helical compression spring for seating a valve mounted on a valve stem comprising in combination a first threaded element, a second element in threaded engagement with the first so that the distance which one element is threaded into the other determines the length of the valve train and means responsive to rotation of convolutions of the valve spring about the axis of the spring for rotating the threaded elements relative to each other.

13. Apparatus as defined in claim 12 in which one of the threaded elements includes a clutch member for engaging the valve stem.

15. Apparatus as defined in claim 11 in which one of the threaded elements includes a clutch member for engaging the valve stem of the valve train.

17. Apparatus as defined in claims 11 in which a helical restoring spring has its opposite ends anchored to the threaded elements respectively.