US2047446A - Scavenging tappet - Google Patents

Description

July 14, 19 6- J. 1.. TAYLOR SCAVENGING TAPPE Filed Dec, 24, 1931 F- 5. far

INVENTOR'. Jbfin Leonard Fly/a1:

AT RNEY.

Patented July 14, 1936 UN I TE D STAT ES ATE NT O-FF' 9 Claims.

This invention relates to valve tappets for use particularly in oil-burning engines, or other internal combustion engines.

Anobject of the invention is to generally improve the constructionand operation of devices of this class.

A further object is to provide for the impositive actuation of a valve, and further objects are to provide the following:

A valve actuating device of a collapsible nature arranged to store energy from: a cam for later actuation of a valve.

A device arranged for actuating a valve in response to both a cam, and the pressure in the cylinder controlled by the valve.

An extremely simple cam mechanism which will vary the timing of a scavenging air valve in response to cylinder conditions.

A device which will provide for reversing. an engine without special reversing mechanism.

An arrangement for actuating a plurality of. valves at different distances from a rocker arm.

Qtherexpe'dients for the practicev of the invention, and the accomplishment of the. above objects.

The means and manner of accomplishment of these objects are fully set forth in thefollowing specification and accompanying drawing in which:

Fig. 1 is a.sectionalelevationtaken online |-l' of Fig. 2.

Fig. 2 is a top plan of Fig. 1, drawn to' a reduced scale.

Figs- 3, 4, and 5 are perspective views or parts and assemblies indicated in Fig.1-

Fig. 6 is a. modification of a rocker arm element.

Similar reference characters apply to. like parts Ehroughout. the several views and the specifica- Applicant has devised. atappet for a twostroke cycle engine in which. the scavenging air is introduced through the cylinder head through appropriate volves while the exhaust gases are discharged through ports opened by the piston at the bottom of its stroke. In' this type of engine the cylinder pressure will be highest when the piston is approximately at top dead center, but it will diminish progressively as the piston recedes and expansion of the contents of the cylinder takes place. As the exhaust port opens near bottom dead center there will ordinarily be a decided drop in pressure, and it is at this point where the exhaust pressure falls below a predc-- terminedvalue that it is desirable to have the scavenging air' admitted.

It is: undesirable, however, to have the valves open before: the pressure has been reduced to a value below, or at least equal to that of the 5 scavenging air supply, since otherwise some of the exhaust gases would be forced into the air supply an'd'later returned to the engine to dilute the fresh air.

Applicant has devised a construction in which 10 the valves are operated by a cam, but impositively so that if at the time that the cam would opmate the valves the cylinder pressure is higher than desired, the resulting resistance to movement of the valves will maintain them closed, and they will open: subsequently to the action of the cam when the exhaust port has been open long enough to reduce the pressure in the cylinder tothe desired value; the valves being allowed by the 0am to close at the most desirable" point in the cycle.

The closing point would preferably be slightly after the closing point of the exhaust port in order togive a slight supercharging effect, as is desirable in this type of engine, and in the event of reverse rota-tion, the fall of the cam becoming therise, theva'lves would be opened too early if it were not for the impositiveor yielding actu-' atingv mechanism, which as above explained permits the valves to remain closed beyond the point of actuation by the cam. In laying out the cam, therefore, all that need be considered is the desired closing points, and these may be made correct for engine operation in either direction, the opening movement taking place automatically at the. correct point in the cycle, andreversal of the engine being accomplished without shifting the cam or making any changes except in the time of combustion.

Referring to the drawing, and particularly 40 Figs. 1 and 2, R is a compound rocker whose pivotalshaft or fulcrum P, is disposed in familiar manner between air valves and tappet' assemblies, the latter being arranged in suitable relation to a cam-shaft for actuation thereby. The scavenging-air valves are here indicated by their stems S-S", which extend upwardly through an air manifold M, a portion of which is shown in Fig. 1. I

In the illustrated embodiment the valve stem or stems are pressed down by the rocker, and returned by springs such as Sp, interposed be tween manifold M and washers'or abutmentsW disposed about the stems and held in place by means of pins Pi in the stems.

The rocker has arms RI and the singular arm R2 oppositely extending from the fulcrum P, the rocker being provided with a bearing construction including caps rr integral or otherwise fixed with a spacing half-sleeve R3 which encloses the aforesaid shaft P. The arm R2 has a socket portion to receive the spherical head I of a push rod 2 provided with an adjusting nut 3, also provided with a spherical head that rests in a similar socket formed in the upper end of a hollow reciprocating stem 4, axially central in the novel tappet means here concerned. The elements I, 2 and 3 form a thrust-link that is free to accommodate itself to the arcuate swing of the rocker arm R2 which occurs due to the reciprocation of the aforesaid stem 4.

Fig. 6 diagrammatically illustrates another form of rocker R1", similar to R except that the arms RI are here extended to serve four instead of two scavenging valves; two of said four, S2 and S3, being shown in the figure. The difference in travel between the portion of the arm above stem S2 and that above S3 is compensated for by a spiral spring D, the stiifness of which is less than the initial load on the valve spring, spring D collapsing against itself after a given movement of arm R1" and thereafter acting as a rigid member for depressing the valve-stems S3, thereby taking up the lost motion between the arm and stem without clatter.

The tappet means, itself consists of a depending sleeve 5 fixed with the housing H of a cam shaft C and having a cap 6, said sleeve being fastened by means such as similar flanges, 5' and 6 respectively. Within the bore of sleeve 5 is slidably located a spring cage I, closed at the top by a spider element 8 having annularly arranged apertures 8', which serve to lighten the piece and provide spannerwrench holes for tightening it. Spider 8 has an axial bore 8 guiding a tubular stem 4 whose upward movements are limited by a flange or abutment 4' which shoulders against the underside of the spider. The cap 6 has a bushing 9 closely fitted to stem 4. The fit of said stem in said bushing is further sealed against oil leakage by packing material IIJ pressed between bushing 9 and a washer II by means of a compression spring I2. The spring I2 also functions to depress the parts I and 8 which action keeps a roller I4 resiliently contacting the face Cb of a cam Ca. The spring-cage 'I has a bottom wall I between which latter and the flange 4' is compressed a power or tappet spring I3. Spring cage I provides, beneath the bottom I an open ended chamber 7" wherein is mounted the cam-roller I4 having a pintle' I5 stationary in sleeve 1 but extending to dispose flat portions I5 for reciprocative movement in slots 5", formed in the depending skirt of the outer sleeve 5. The bottom edge of the said sleeve may be cut away at a: if necessary for clearance for the cam Ca upon which the roller I4 rides. The said roller is prevented from leaving its associated parts, in the event sleeve 5 and its attached parts, or cam shaft C is removed from the engine, by machining the skirt of the sleeve 5 to form the walls 5w (Fig. 5) through which is passed a cotter-pin I6 that shoulders under the ledge I5" formed in either one or both of the flats I5 of the rollerpintle IS.

The housing H is exposed to the splash of crankcase oil, so that the several elements of the tappet assembly are kept lubricated through suitable apertures and bores a, b, and c in the several elements.

Adjustment of the clearance between the tappet and rocker and stem S is provided by the threaded push rod 2 and its associated nut 3. Also, one of the arms RI is provided with a screw I1 and a suitable nut I8 for adjusting the clearance between the stem and arm to permit obtaining equal clearance for the two stems.

Because of the control of the scavenging timing exerted by the cylinder pressure, cam Ca may be made symmetrical, so as to properly operate the scavenging valves in either direction of rotation of shaft C. As the rise of the cam encounters the roller I4, the roll and its attached parts, shaft I5, and sleeve or cage I, are forced upwardly, but because of the pressure normally obtaining in the engine cylinder, and the consequent resistance to movement of valve stems S, stem 4 will be prevented from moving, and spring I3 will be compressed, storing energy for later actuation of the valves. After the opening of the exhaust port, in the normal operation of the engine, the cylinder pressure falls, and when it becomes equal to, or slightly less than that in manifold M, the total resistance to movement of the valves becomes less than the force exerted by the compressed spring I3, and the valves are opened. This takes place sometime during the contact of roller I4 with the dwell portion Cb of cam Ca. At the proper time in the cycle, the dwell portion passes out from under roller I4, and the roller, cage, spring, and stem 4, all move downwardly, allowing the valves to close in the ordinary manner. The point at which the rise of the cam strikes the roller is therefore not critical, and since the normal opening point of the valves is slightly nearer bottom dead-center in the travel of the engine piston, than the closing point, the fall of the cam, for rotation in one direction, may be the rise for rotation in the opposite direction, and the fact that it raises the roller a little earlier in the cycle than the desired opening point of the valves is of no consequence in the operation of the engine. Of course the parts might be arranged within the contemplation of the invention so that the rise of the roller I4 would correspond accurately with the opening of the exhaust port, if desired, spring I3 then allowing the valves to remain closed during part of the exhaust period, or until the cylinder pressure falls to or below that of the scavenging air.

In the event that it is desirable to provide an additional valve or valves in the engine cylinder,

it may be done by lengthening either or both of arms R1 and using the construction shown in Fig. 6, with the spring D interposed between the arm and stem S3.

The above being a complete description of an illustrative embodiment of the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a valve actuating mechanism the combination of a cam, a rocker arm and connections between said cam and said arm arranged to actuate said arm, a fulcrum for said arm, and a plurality of valve stems actuated from said rocker arm, arranged for equal movement, but unequally spaced from said fulcrum, resilient means urging said stems in one direction one of said valve stems relatively near said fulcrum being substantially in contact with said rocker arm in the position of the parts corresponding to the closed position of said valves, and another of said valve stems relatively distant from said fulcrum being substantially spaced from said rockerarm whereby t'o-receive only an amount of-movement substantially equal to that of the above mentioned valve stem, and a. spiral spring interposed between the-last mentioned stem and said rocker arm and proportioned so that the coils thereof close and form a positive actuating means between said rocker arm andsaid valve stem at a point in the movement of said rocker arm such that the remaining movement of the rocker arm will impart movement to the second valve substantially equal to that of the first valve.

2'. In a tappet mechanism the combination of a camhaving a roller actuating surface and a cam follower including a guldemember having a substantiallycylindrical bore and'provided with an axial slot arranged substantially on a diameter of saidbore perpendicular to the direction of movement of said roller actuating surface, a plunger guided in said bore and having a roller receiving recess, said plunger-being provided with a bore transverse to said recess, a pin in said bore and having a reduced end portion extending into said slot to prevent rotation of said plunger in said cylindrical bore while permitting axial displacement of said plunger, and a roller journaled on said pin within said recess and cooperating with said roller actuating surface.

3. In a tappet mechanism for a valve subject to a varying resistance to movement, the combination of a cam for moving said valve, a follower cooperating with said cam and including a sleeve, guiding means for said sleeve providing a bore in which said sleeve is slidable, a cam contacting element at one end of said sleeve, and a resilient element arranged to urge said sleeve in a direction to maintain said contacting element in contact with said cam, a valve actuating rod guided in said guiding means and projecting into said sleeve, an abutment on said rod within said sleeve, a stop member on said sleeve and positioned to cooperate with said abutment to prevent removal of said rod from said sleeve, and a resilient element in said sleeve and acting in a direction toyieldingly maintain said abutment against said stop, and to yield and permit movement of said sleeve under the influence of said cam at such times as there is sumcient resistance to the movement of said valve to prevent actuation thereof through said resilient element, and to maintain said abutment against said stop and to actuate said valve at such times as there is insufficient resistance to the movement of said valve to cause said resilient element to be compressed.

4. In a tappet mechanism for a valve subject to varying resistance to movement, the combination with a valve, of a relatively light valve spring arranged for operating said valve in the direction of said resistance, a cam for moving said valve, a follower cooperating with said cam, and connections from said follower to said valve including resilient means positioned between said cam follower and said valve, and arranged to receive and absorb the full movement of said follower caused by said cam at times when said valve strongly resists opening, and to operate said valve upon reduction of the resistance to the operation of said valve below an amount sufficient to cause said resilient means to be compressed, said resilient means being of a strength superior to said relatively light valve spring, whereby said valve spring will not interfere with operation of said valve by said cam through said resilient means,

except-when assisted by the above mentioned resistance to: movement of said valve.

5. In a tappet mechanism for a valve subject to varying resistance to-movement, the combination with a valve, of a relatively light valve spring arranged: for operating said valve in the direction of' said resistance, a camfor moving said valve, a follower cooperating with said cam and including a sleeve,means for guiding said sleeve for reciprocatingmovement in response to movement of said cam, a valve actuating rod extending into said sleeve, and a tappet spring disposed in said sleeve and" arranged to-exert resilient pressure against said rod, said spring being disposed between a portion of said sleeve and said rod so astoconstitute the actuating means for said rod wherebyto be compressed and to receive energy from said cam at such times as sufficient resistance i'soffered' tomovement of said valve and rod to cause said tappet spring to be compressed, F

and to release said energy and move' said valve upon reduction of said resistance below such an amount, said tappet spring being of a strength substantially greater than said valve spring.

6. In a tappet mechanism for a valve subject to varying resistance to movement, the combination with a valve, of a relatively light valve spring arranged for operating said valve in the direction of said resistance, a cam for moving said valve, a follower cooperating with said cam and including a sleeve, means for guiding said sleeve for reciprocating movement in response to movement of said cam, a Valve actuating rod extending into said sleeve, an abutment on said rod within said sleeve, a stop on said sleeve positioned to prevent withdrawal of said rod from said sleeve, and a tappet spring within said sleeve and. compressed between a portion thereof and said valve actuating rod to yieldingly maintain said abutment in contact with said stop, said tap-pet spring being of a strength such that said valve spring does not interfere with operation of said valve except when assisted by the above mentioned resistance to movement of said valve, but to yield and permit movement of said sleeve in response to said cam independently of said valve actuating rod when the combined force of said resistance and said valve spring exceeds the strength of said tappet spring.

'7. In an actuating mechanism for a valve subject to varying resistance to movement, the combination with said valve, of a cam, a cam follower, and connections from said follower arranged to operate said valve, said connections including a spring interposed between said follower and said valve, and having a capacity for yielding at least equal to the full lift of said cam at the point of introduction of said spring into said connections when said resistance is at a maximum, and of a stiffness suflicient to actuate said valve through the full range of movement of said valve when said resistance to movement is at a minimum, whereby said cam may move said valve through its full range of movement upon cessation of said maximum resistance to movement, and whereby said cam may move said follower through its full range of movement Without moving said valve at times of maximum resistance to movement of said valve.

8. In a tappet mechanism for a valve subject to varying resistance to movement, the combination with a valve, of a relatively light valve spring arranged for operating said valve in the direction of said resistance, a cam for moving said valve, a follower cooperating with said cam and including a sleeve, guiding means for said sleeve providing a bore in which said sleeve is slidable, a cam contacting element at one end of said sleeve, and a resilient element arranged to urge said sleeve in a direction to maintain said contacting element in contact with said cam, a valve actuating rod guided in said guiding means and projecting into said sleeve, an abutment on said rod within said sleeve, a stop member on said sleeve and positioned to cooperate with said abutment to prevent removal of said rod from said sleeve, and a resilient element in said sleeve and acting in a direction to yieldingly maintain said abutment against said stop, said element being of a strength such that said valve spring does not interfere with operation of said valve except when assisted by said resistance to movement of said valve, but to yield and permit movement of said sleeve under the influence of said cam at such times as there is resistance to the movement of said valve.

9. In a tappet mechanism for an intake valve for an internal combustion engine having an exhaust port opened by extreme outward travel of the piston thereof, the combination with a valve of a relatively light valve spring arranged to close the valve, a cam for moving said valve, a follower cooperating with said cam, and connections from said follower to said valve including resilient means positioned between said cam follower and said valve, and arranged to receive and absorb the full movement of said follower caused by said cam in the event that said valve is prevented from moving, said cam having a rise portion, a dwell, and a fall portion, said portions being symmetrical about a point of contact of said follower with said cam representing the extreme outward travel of the piston of said engine, whereby the action of said valve will be coordinated with the opening of said exhaust port in either direction of operation of said engine.

JOHN LEONARD TAYLOR.

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