US2468332A - Tappet construction - Google Patents

Description

Ap 26, 1949. c, E JOHNSON 2,468,332

TAPPET CONSTRUCTION Filed April 29, 1946 \NvsNToR "m; QM

AIIQRNEIQ Patented Apr. 26 1949 TAPPET CONSTRUCTION Charles E. Johnson, North Muskegon, Mich., as-

signor to Johnson Products, Inc., Muskegon Heights, Mich., a corporation of Michigan Application April 29, 1946, Serial No. 665,705

8 Claims. 1

The present invention relates to an improved hydraulic tappet construction, by means of which hydraulic tappets are usable with the same cam shafts and cams which operate mechanical tappets. This permits the replacement of mechanical tappets by hydraulic tappets in engines initially supplied with the mechanical tappets, without the necessity of simultaneously replacing the cam shafts by different shafts having cams thereon which will properly operate hydraulic tappets; or of regrinding the cams of the original cam shafts for hydraulic tappet operation. With my invention, through an improvement in the hydraulic tappet, no special or different design of cams to operate the hydraulic tappets is needed.

The cams on a cam shaft which actuates tappets to lift valves, either intake or exhaust, for the cylinders of an internal combustion engine, each has a projecting portion which moves the tappet and the valve against a strong spring which holds the valve tightly closed except when the tappet lifts it. For'a major portion of the rotation of a cam shaft, the valve is closed and in order to insure that it shall be tightly closed, in the adjustment of a mechanical tappet, a clearance is left between the upper end of the tappet and the lower end of the valve stem, varying slightly with different manufacturers of engines but normally approximately ten to fifteen thousandths of an inch. Therefore, the cam is designed so that a portion of its periphery in which, during its rotation, it is inactive to lift the valve, is given a radius dimension which is ten to fifteen thousandths of an inch less than required for snug engagement of the tappet with both the cam and the lower end of the valve stem. When the cam in its rotation, has its lifting projecting portion approaching the valve stem to lift the valve, there is a progressive change in the contour of the cam from its lesser radius arc-shaped dwell portion, at each end thereof, to the inclined fiat surfaces of the cam projection, whereby the slack or clearance mentioned as approximating ten or fifteen thousandths of an inch, is taken up and the valve is started in its lifting with the opposite ends of the tappet in firm pressure engagement with the cam and the lower end of the valve stem, respectively.

Such design or periphery or outer contour of a cam is unsatisfactory with the normal hydraulic tappet. A hydraulic tappet is selfadjusting, operating automatically with the operation of the engine and maintaining the upper end of the tappet at all times against the lower end of the for mechanical tappets, the ten to fifteen thousandths of an inch decrease in radius of the cam is reached, oil is automatically taken within the tappet to elongate it sufflciently that its upper end will continually bear against the lower end of the valve stem, whereupon on the progressive increase of the radius of the cam over the short distance described coming to the tappet, the valve'is cracked, that is, is slightly lifted off of its seat prior to the timethat it should be lifted at all. Similarly, on the closing of the valve, with a dropping off progressively from the larger radius to the dwell portion of the tappet having a radius of ten to fifteen thousandths of an inch less, the valve closing is imperfect, re-

sulting with intake valves in losses of compression and of fuel, and with exhaust valves in-the very high temperature of the burning fuel mixture and gases passing the valve and its seat, with damaging consequences in burning to both. This has required, for hydraulic tappets, a different form of periphery or outer surface for the cams to operate them properly, thus preventing easy installation of hydraulic tappets in place of mechanical tappets, or in some :cases the replacement of hydraulic tappets by mechanical tappets, without simultaneously removing and replacing the cam shafts or regrinding the cams at heavy expense.

My invention, in a very practical and effective manner, solves the problem through an improvement of the hydraulic tappet itself so that such tappets are usable with the same cams that actuate mechanical tappets.

An understanding of preferred constructions embodying the invention, may be had from the following description, taken in connection with the accompanying drawings, in which Fig. 1 is a vertical section through my improved tappet in its position between the lower end of a valve stem and its operating cam when thevalve is closed.

Fig. 2 is a similar vertical section showing the tappet immediately prior to the valve being opened by the cam rotation.

Fig. 3 is an enlarged central vertical section through the improved piston of the hydraulic tappet.

Fig. 4 is an enlarged elevation of the cam, such cam being of the design long used for actuating mechanical tappets and with which, with my invention, hydraulic tappets may be equally well used.

Fig. is a fragmentary section similar to Figs. 1 and 2 2} trating a difierent form of structure embod yi the invention equivalent to the form shown a (1 having a less number of parts.

Like reference characters refer to like parts in the difierent figures of the drawings.

For the mounting and installation of a hydraulic tappet, cylindrical guides are made in the block of the engine I, or a fixture attached to said engine block, in which the tappet barrel 2, closed at its lower end as indicatedat 3, is mounted for slidable movement in most internal combustion engines. The barrel 2 of the tappet is open at its upper end and, between its upper and lower ends, has an integral partition 4, with a central opening 5 connecting the lower chamber shown with the space above the partition 4. Such recess is of cylindrical shape and has a piston I fitting therein but movable in an outward direction. The upper end of the opening 5 is normally closed by a valve actuated by a light spring as indicated at 6. The chamber below the horizontal partition 4 is maintained full of oil under the pressure of the lubricating system of the engine, the valve 6 lifting to supply oil under piston I on upward movements thereof, but operating as a check valve to prevent oil returning. A spring split ring 8 seated in an annular groove within and at the upper end of the tappet barrel is provided to prevent accidental disassembly of the piston springs and valve from the tappet barrel. Between the piston I, which is recessed at its lower end, and the upper side of the partition 4, a coiled compression spring 9 is located, the force of which is directed toward moving the piston upwardly in the vertical installation shown. The strength of the spring 8 is much less than the strength of the spring which holds an engine intake or exhaust valve in closed position.

The cam III, which turns with a cam shaft in the usual manner in internal combustion engines,

is located at the lower end of the barrel 2 with distance until the inclined converging sides of the cam projection are reached the radius is of a dimension equal to the radius of the longer arc II plus the ten to fifteen thousandths of an inch, or any other approximate amount which the engine designer has fixed upon to be the clearance between the lower end of an engine valve stem which bears upon the upper end of a mechanical tappet and the surface of the arc I I against which the lower end of the tappet bears, this to insure that the engine intake or exhaust valve shall be completely closed and tightly held in closed position by its actuating spring between intake or exhaust openings of the valve. At the ends of the approximate half circle arc II, the cam surface progressively increases in radius, as from approximately the points I3 to a larger radius at I2. This is a conventional design of cam for mechanical tappets.

In the previous hydraulic tappets the piston I above its lower portion has been solid, and the lower end of the valve stem has been in engagement with the upper end of such solid piston. In the present invention, in one form shown, the upper end portion of the piston I is interiorly' bored leaving a horizontal partition I4 approximately midway between the upper and lower ends of said piston I. Within the cylindrical recess above the partition I4, an auxiliary or supplementary piston I5 is mounted, at its upper side and centrally thereof having a projection I6 of a diameter less than that of the body of the piston, and against the upper end of which the lower end of the valve stem I1 is in bearing contact engagement. The piston I5 is recessed upwardly from its lower side stopping short of the upper end of the projection I6. Within the recess made, a coiled compression spring I8 is located, resting at its lower end upon the upper side of the partition I4 and acting on the piston to move it upwardly until stopped by a split spring ring I9 seated in a groove nearthe upper end and within said-piston I. The spring I8 is of greater strength than the springd plus whatever oil pressure there may be added to the force of the spring 9 to move the piston 1 in an upward direction, but such strength of the spring I8 is materially less than the strength of the intake or exhaust valve spring which exerts its force upon an intake or exhaust valve and its stem H in a downward direction. The piston I5-has a limited movement. When in its uppermost position (Figs. 1 and 3) and stopped against further movement by the split ring I9, there is a space 20 between the lower side of the piston I5 and the upper side of the partition I4 equal in dimension to the ten to fifteen thousandths of an inch or other approximate clearance amount, d by which the radius of the cam surface I I i ecreased from the radius of the cam surfaces beginning at I2 and extending therefrom to the converging fiat sides of the cam projection I8.

With this construction, it being understood that the engine lubricating oil fills all spaces within the barrel underneath and the partition 4 and I4, the upper end of the projections I6 is held pressed at all times against the lower end of the valve stem IT. With the cam rotating in a clockwise direction (Fig. 1), the spring I8, stronger than the spring 9 plus the oil pressure, holds the piston I5 at its upper position while the arc Ii. of the cam is bearing against the lower end of the tappet barrel. But when the progressively increasing radius of the cam between the points I3 and I2 comes underneath the tappet, the heavier force of the intake or exhaust valve spring to which the tappet is subjected overcomes the strength of v the spring I8, and piston I5 is progressively forced down to its lowest position, as in Fig. 2, closing the narrow space at 20. The tappet, therefore, has its parts thus located during the lifting of the intake or exhaust valve and while the projecting part of the cam is riding underneath the lower end of the tappet barrel. But as soon as the point I2 is reached at the opposite side of the cam, the intake or exhaust valve spring having moved the valve back substantially, if not completely, to its closed position, as soon as the intake or exhaust valve is completely closed and its force is removed from the spring I8, said spring pushes the piston I5 in an upward direction and, through the trapped oil, maintains the lower end of the tappet barrel in bearing engagement against the reduced radius surface at I I without cracking the engine valve. The lower side of the piston I5 separate from the upper side of the partition I4 until t e larger radius portion of the cam is again brought underneath the lower end of the tappet barrel 2.

In Fig. 5, the piston 1 at its upper side is recessed to make a shallow circular depression in which a disk 2| concave at its upper side and convex at its lower side is located. Said disks are of spring material so that it may flex in a downward direction upon sufflcient pressure applied thereto at its upper side. The space 22 between the under side of the disk and the bottom of the recess in which it is located is equivalent to the space 20 between the piston l5 and the partition 14, that is the clearance dimension of approximately ten to fifteen thousandths of an inch. The disk 2| when flattened so as to bear at its under side against the recess in which it is located will therefore have a yielding movement the same as the movement of the piston l5 when the bottom is against the upper side of the partition I on compression of spring I8.

In this construction the lower end of the valve stem l1 bears against the upper side of disk 2|. The resistance of the disk 2| to distortion and flattening is greater than the strength of the spring 9 plus the oil pressure. In other words the yielding resistance of the disk 2| is equivalent to or the'same as the resistance of the spring l8. Similarly the strength or resistance of disk 2| to flattening is less than the strength of the valve spring associated with the engine valve, the stem of which is shown at IT.

This provides an embodiment of the invention operating upon identical principles with the first described form, but in some ways it may be preferred as more economical to produce and assemble and of a lesser number of parts, therefore simpler and less liable to getting out of order.

The constructions described are readily manufactured, easily installed and operate perfectly, acting in function to prevent excess oil from entering the chamber above the partition 4 which it would do if the valve stem I! pressed directly against the piston l as in previous practice, and thereby causing a cracking open of a valve too soon, or its closure too late. One design of cam only is required for both mechanically adjusted and self-adjusting hydraulic tappets,

It is to be understood that the dimensions referred to many times, namely, ten to fifteen thousandths of an inch substantially covers the range between the large and the small radius arcs of a cam surface, but the invention is to be in no sense restricted because of the practical example given in the way of dimensions in cam surfaces between the long dwell arc of the shorter radius and the shorter arcs of the slightly larger radius. Each engine designer or tappet adjuster may select, and does select the clearance or play which is to be, and which in practice, a workman adjusting a mechanical tappet does by inserting a feeler gage of the selected dimension between the lower end of a valve stem and the upper end of a tappet which he is adjusting with respect to said valve stem. The invention is the same irrespective of the particular and specific dimensions of the clearance or play which is used.

The invention is directed to the tappet structure as disclosed, or in such variations as may be equivalent thereto, within the scope of the appended claims which define the invention.

I claim:

1. A hydraulic tappet, adapted to be located between a cam on an engine cam shaft and the end of the stem of a spring closed poppet valve having a barrel, a piston in the outer end of the barrel, spring means to move the piston outwardly, means for supplying liquid to and trapping it against its return located at the inner end of the piston, a member carried at the outer end of the piston against which the inner end of said valve stem is adapted to bear, said member normally being spaced from the piston a preselected distance When the valve connected with said valve stem is closed, and movable toward the piston when said valve is moved from its seat and having associated yielding resistance means of less strength than the engine valve spring, and of greater strength than the spring means lifting said piston.

2. A hydraulic tappet, adapted to be located between a cam on an engine cam shaft and the end of the stem of a spring closed poppet valve having a barrel, a piston in the outer end of the barrel, spring means to move the piston outwardly and means for supplying liquid to and trapping it against its return located at the inner end of the piston, a concave disc member bearing at its edges against the outer end of the piston and spaced from the piston at its intermediate portion a preselected distance, said concave member being of spring material and having a resistance against flattening greater than the force exerted by the spring means moving said piston, and less than said spring closing said engine poppet valve, the stem of which is adapted to bear against said member.

'3. A hydraulic tappet having a barrel, a piston in the outer end of the barrel, spring means to move the piston outwardly, and means for sup plying liquid to and trapping it against return at the inner end of the piston, said piston in the outer end portion thereof having a cylindrical recess, a second piston located within said recess, spring means for moving said second piston outwardly with respect to the first piston, the strength of said spring means being greater than the strength of the first mentioned spring means normally moving the first piston outward, and means to stop the movement of said second piston in said cylindrical recess to a preselected amount.

4. A hydraulic tappet, adapted to be located between a cam on an engine cam shaft and the end of the stem of a spring closed poppet valve, having a barrel with a cylinder at its outer portion and a piston mounted in said cylinder with a spring normally moving the piston outward and means for supplying liquid under pressure to and prevented from escape at the inner end of said piston, said piston having a horizontal partition across it between its ends outwardly of which said cylindrical recess is located, a second piston within the said cylindrical recess, a spring means between said second piston and the horizontal partition of the first piston normally acting to move said second piston outwardly, stop means for stopping said second. piston at a predetermined outer position, in which its inner end is spaced a preselected distance from the outer side of said partition, said spring means acting upon the second piston being greater in strength than the spring acting on the first piston plus the oil pressure acting upon said first piston, and said second spring means being of less strength than the poppet valve spring, the inner end of the stem of which valve is adapted to bear against the outer end of said second piston.

5. A hydraulic tappet having a cylindrical barrel closed at its inner end and adapted to ride at said inner end on a cam of an engine cam shaft, said barrel in the outer portion thereof having a movable piston reciprocably mounted therein, said piston being of substantially tubular form and having a, transverse partition across it between its sides between its inner and outer ends, a spring hearing at its outer end against the inner side of the partition, said hydraulic tappet having means for conducting liquid under pressure to said piston at the inner side of the partition and to prevent return of such liquid, a second piston located outwardly of said partition, said second piston having a recess at its inner side, a coiled compression spring of greater strength than the first mentioned spring located in said recess and bearing at its inner end against the partition of the first piston, and stop means in the outer end portion of the first piston to stop outward movement of said second piston when its inner side has separated from the outer side of said partition a preselected limited amount.

6. In a hydraulic tappet having a barrel, a liquid and spring actuated piston in its outer end portion and means for supplying liquid under 1 pressure at the inner end of said piston and for trapping said liquid against return, said piston in its outer portion having a cylindrical recess, a second piston within said recess, spring means stronger than the means acting on the first piston between said second piston and the bottom of said cylindrical recess in which it is located, and means for stopping outward movement of said second piston carried by the first piston and limiting the extent of separation of the inner end of the second piston from the bottom of the recess in which it is located to a preselected small amount.

'7. A construction as defined in claim 3, said second piston comprising, an inner portion of an exterior diameter closely approximating the interior diameter of the cylindrical recess in which the piston is located, and having an outer portion 01' a smaller diameter extending from the inner portion, said recess for receiving the spring acting upon said second piston being centrally located, and extending from the inner side 01' said inner larger portion of the piston into, but stopping short oi, the outer end of said small diameter upper portion.

8. A hydraulic tappet, adapted to be placed between a cam on an engine cam shaft and the end of a spring closed poppet valve, having a barrel, 8. piston in the outer end of the barrel, spring means to move the piston outwardly, means for supplying liquid to and trapping it against its return located at the inner end of the piston, a spring affected member carried by said piston at its outer portion against which the inner end of said poppet valve is adapted to bear, said spring aifected member carried by said piston having a preselected range of movement whereby the outer end of the piston and the end of the valve may be at variable distances from each other within such range of movement, and resisting such movement with a force greater than the strength of said spring means for moving the piston and less than the strength of the valve closing spring,

CHARLES E. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain June 29, 1921

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