US2711161A - Hydraulic tappet - Google Patents

Description

June 21, 1955 A. w. RICKENBACH 2,711,161

HYDRAULIC TAPPET Filed Sept. 16, 1952 2 Sheets-Sheet 1 AUGUST. w. R/CKENBACH.

ATTORNEYS.

\ INVEN TOR. 1

June 21-, 1955 A. w. RICKENBACH 2,711,161

HYDRAULIC TAPPET Filed Sept. 16. 1952 2 Sheets-Sheet 2 V INVENTOR. I

AUGUST W. RICKENBACH.

a/fin ATTORNEYS.

United States PatentO HYDRAULIC TAPPET August W. Rickenbach, Wiliiamsport, Avco Manufacturing Corporation, corporation of Delaware Pan, assignor to Cincinnati, Ohio, :1

The present invention relates to a component of an internal combustion engineand, more specifically, to an improved hydraulic tappet for use in an internal combustion engine having valves for controlling the intake or exhaust of gases from a cylinder of the engine.

A problem frequently encountered in the construction and operation of internal combustion engines is that of maintaining proper adjustment of the mechanical elements which actuate the inlet and exhaust valves. This problem is aggravated by thermal expansion and contraction of the engine which make it ditficult to maintain adjustment of the valve actuating elements. As is well-known to those skilled in this art, proper adjustment is important, for it assures that the valves will seat fully and prevents the actuating elements or valve linkage from holding the valves in an open position in which burning of the valves would occur.

Becauseof the importance of proper adjustment, bydraulic tappets are often incorporated in engines." Basically, a hydraulic tappet incorporates a piston and cylinder assembly which is expanded by high pressure oil, supplied by the engine, to take up the clearance within the valve linkage. The areas within the tappet assembly on which the oil acts and the pressure of the oil used, are such that the tappet itself cannot open the valves; thus proper adjustment is maintained and the valves are not prevented from seating properly. Hydraulic tappets, therefore, make it possible to avoid many of the difficulties previously encountered.

On the other hand, hydraulic tappets are not entirely satisfactory since their inherent operation is such that all clearance is eliminated from the valve linkage. This being the case, even slight spurious movements of the associated cam shaft are transmitted through the linkage to the valves, causing the valves to open erratically and leading to backfiring and rough running of the engine.

The source of such spurious movements is not entirely clear at this time, but it is thought that such movements might result-from whipping, i. e., flexing of the cam shaft, or shifting of the cam shaft because of excessive cam shaft bearing clearances. On the other hand, it is thought possible that the tappet may tend to bounce on its associated cam, particularly during high speed operation. Regardless of the source of spurious motions, it is a fact that difliculty has been encountered in operation of engines having hydraulic tappets, the difliculty manifesting L itself in rough running of the engine, backfiring, and generally unsatisfactory performance.

The present invention eliminates all of these'difiiculties and assures that hydraulic tappets can be used without concern for any spurious movements delivered to the rappers. Briefly stated, the present invention comprises a spring-type washer disposed between two components of. the hydraulic tappet through which motion must be transferred when the cam shaft acts on the tappetto move the valve linkage. This spring-type washer permits a small amount of motion between the tappet components before movement is transferred to the valve linkage and, in, this Z,7ll,li P t-iterated June 21, 1955 way, slight spurious movements delivered to. the tappet are not transferred to the valves.

In view of the foregoing, it will be appreciated that it is an object of the present invention to provide an improved hydraulic tappet.

Another object of the invention is to provide means for improving hydraulic tappet operation which can be readily added to existing tappets at very little cost.

It is also an object of the invention to provide a hydraulic tappet which will prevent the transmission of very small movements to the valve linkage. Stated otherwise, it is an object of the invention to provide a hydraulic tappet, the components of which must undergo a slight relative movement before the tappet will be effective to transfer motion from a camshaft to an associated valve.

A still further object of the invention is the provision of animprovement for a hydraulic tappet which will significantly improve its performance without jeopardizing any of its well-known desirable characteristics.

Another object of the invention is the provision of a hydraulic tappet which will preclude the transmission of spurious cam shaft motions regardless of the position assumed by the tappet while in use. This is a particularly important feature of the invention since hydraulic tappets are widely used in the aircraft'field in which engines commonly assume a wide variety of positions while in use.

. The novel features that are considered characteristic of the invention are set forth in theappended claim; the inventionitself, however, both as to its organization and method of operation,

and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which: I

Figure l is an enlarged longitudinal sectional view of a hydraulic tappet incorporating a spring washer in keeping with the novel teaching of the present invention;

Figure 2 is a greatly enlarged cross sectional view of the spring washer used within the tappet assembly; and

Figure 3 is a longitudinal sectional view through one cylinder and its associated valve actuating system of an internal combustion engine, certain parts of the engine being broken away to facilitate a description ofits internal construction.

As illustrated in Figure 3, a hydraulic tappet, generally designated 1, is slidably positioned in the crankcase 2 of an internal combustion engine, generally designated 3. Cylinder 4 of the engine is bolted to the crankcase, the cylinder including a cylinder head 5 in which isformed a rocker box 6 covered by rocker box cover 7. Hydraulic tappet 1 cooperates with a valve linkage, generally designated 8, the valve linkage including rocker arm 9, pivoted as at 10, within rocker box 6. The rocker arm transfers motion venience of illustration, is an inlet valve for admitting a combustible charge to cylinder 4. Asis conventional, an inlet pipe 12 is connected to intake port 13 from which the combustible charge is admitted to the cylinder by valve 11.

The engine is conventional in its provision of a re ciprocating piston 14 connected to a connecting rod 15 which,.in turn, is rotatably secured to a crank pin id of crankshaft 17. A spark plug 18 isalso provided for igniting the combustible charge within the cylinder, the energy resulting from combustion being transferred to piston 14 and crankshaft 17.

together with additional objects to valve 11 which, for con imparts a periodic reciprocating movement to the hydraulic tappet which, in turn, transfers this motion to valve linkage 8 which operates valve 11 through the rocker arm 9. Valve springs 22 are provided within the rocker box, the springs being engaged with thevalve washer 23 which is locked at 24 to the stem of the valve. The springs act to hold the valve closed against its seat 25 at all times, and, thus, the valve linkage must overcome the load of these springs in addition to the net gas forces acting on the valve before the valve can be forced open.

The particular form of engine used is not of importance to this invention, although the invention has found most widespread use in 4-cycle engines. In atypical engine of this type, the inlet valve is opened during every other revolution of the crankshaft, the inlet valve remaining closed during the time that combustion occurs within the cylinder and the exhaust gases are expelled therefrom. It will be appreciated that if the valve lifts off of its seat during the time that combustion is taking place, a loss of pressure from the cylinder will occur and the charge within pipe 12 may be ignited with highly undesirable backfiring and danger of fire.

It has been observed that in 4-cycle engines incorporating conventional hydraulic tappets rough running and backfiring is apt to occur. it has been deduced that very slight movements of the cam shaft, in the order of .003 to .005 of an inch, occur, possibly from the flexing of the cam shaft, or possibly from movement of the cam shaft within its bearings. Since the hydraulic tappet, as will be explained more fully hereinafter, takes up any clearance in the valve linkage, such movements, although small, are transmitted directly to the valves and it is thought that these movements cause the faulty engine operation encountered. The present invention was devised to eliminate this difiiculty and has been applied practically to engines with excellent results.

The invention is illustrated particularly well in Figurel in which is shown a hydraulic tappet including an outer sleeve 26 slidably retaining a cylinder member 27 within which is slidably disposed a piston 28. An oil port 29 is provided in the side wall of sleeve 26. Oil under pressure is supplied to port 29 through a high pressure oil channel 30 (see Figure 3), the oil passing into internal volume 3. from which it is supplied through tube 32 to the interior of cylinder 27. The oil flows past a check valve 33, comprising a's'teel ball 34 which cooperates with a seat 35 formed integrally with tube 32. Under certain conditions of operation, as will be described, oil passing through tube 32 lifts ball 34 and enters cylinder27 beneath piston 23. The oil pressure, acting on the piston, cooperates with a spring 36 in urging piston 28 towards the right, as viewed in Figure i. It will be noted that spring 36 is engaged with cylinder 27 and piston 28.

During that part of the engine cycle during which valve 11 should remain closed, oil pressure, entering through port 29 and passing through check valve 33, acts to move piston 28 outwardly of the hydraulic tappet thereby taking up any looseness, or clearance, in the valve linkage, or between the rocker arm and valve stem. When cam 20, in the course of its rotation, imparts motion to the tappet during its normal operation, force is transferred through the tappet, piston 28 of the tappet assembly delivering the force to the valve linkage. As a result, the tappet assembly constitutes a load transferring member momentarily placed under compression.

The force exerted on piston 28 is opposed by the oil trapped within cylinder 27. Compression of the oil forces ball 34 of the check valve tightly against its seat. During the time that this compressive load exists, a slight amount of leakage occurs between the wall of piston 28 and the" interior of cylinder 27, although the leakage is not large enough to adversely affect the usefulness of the tappet as a compression member. After cam 20 advances far enough to relieve the load from the tappet, springs 22 return the valve 11 to a fully seated position and check valve 33 again admits oil to the interior of cylinder 27 to expand V the length of the tappet and thereby take up any clearance in the system.

The foregoing description outlines briefly the oper- Figure 2. It will be noted that the faces of the Washer 39 and 40 define conical surfaces inclined at an angle to This type washer per se is not the axis of the washer. novel. It is characteristic of this washer that it can be deflected from its normal position shown in Figure 2 into a flexed position in which faces 39 and 40 lie within paral-' lel planes perpendicular to the central axis. Deflection of the washer into such a position requires a compressive I load; the washer will return to the position ofFigure 2 whenever released from this load.

Inasmuch as cylinder 27 is slidably' retained within sleeve 26, it will be appreciated that washer 37 will be flattened into its loaded position before motion is transmitted to piston 28. This can be assured by designingthe washer with a low spring rate. Movements impartedto sleeve 26 must be of greater magnitude than the motion required to flatten washer 37 before any movement is transferred to piston 28. This motion, for the hydraulic tappet illustrated, is in the order of magnitude of .006

of an inch. Thus, stray movements of .004 of an inch,-

or less, are not transmitted through the tappet assembly and do not affect in any way the operation of the engine.

On the other hand, when sizable movements are trans? ferred to the tappet, as by the normal rotation of the cam shaft, the washer 37 is first flattened and then thenormal lift of the cam is transferred to the valve'through the re: lated linkage system.

It will be apparent to those skilled in the art thatthis is an extremely simple structure to accomplish'a highly desirable result, and one which can be readily added to- 7 conventional hydraulic tappets to improve their operation.

Another thing that will become apparent is that the oper-. ation of the improved tappet is by no way influenced by V its position, as is the case in other devices designed to attain the same purpose.

Inasmuch as the spring washer is not flexed beyondits elastic limit, it always returns to its unstressed-position shown in Figure 1 when the load imposed by the cam 20 I is released. At such time, the spring washer returns to, its

unloaded position and the oil entering the tappet from g port 29 causes it to takeup the clearance in the system in a perfectly conventional manner. It will benoted that the spring washer flexes-as required to offset the effect of any stray motions imparted to the valve linkage system from any source. On the other hand,

the washer flattens and acts as a load transferring component of the tappet during the time that the associated valve is being opened in the course of normal operation.

It will be appreciated by those skilled in the art thatthis invention, although sirnplein construction, is highly novel and representsa very significant advance in the artoftappet design and one which improves the performance of engines containing hydraulic tappets.

Havingdescribed a specific embodiment of my-1nvention, I claim:

nuIar faces defining an annular space between them, and a conoidal spring-type washer in the annular space maintaining predetermined clearance between said annular faces, said spring-type washer when deflected coming into bearing engagement with said annular faces whereby it serves as a compression member between said shell and said cylinder.

UNITED STATES PATENTS Truesdell Mar. 16, Daisley May 10, Voorhies Mar. 6, Johnson Apr. 26, Johnson May 6,

Engemann Mar. 31,

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