US 2665669 A
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`fan. 12, 1954 L. B. ELLIS HYDRAULIC LASH ADJUSTER Filed June 11, 1948 Patented Jan. 12, 1954 HYDRAULIC LASH ADJUS'IER Lockwood B. Ellis, Birmingham, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 11, 1948, Serial No. 32,404
(Cl. 12S-90) 12 Claims.
The present invention relates to internal combustion engines and more particularly to hydraulc tappets for automatically taking up lash or play in internal combustion engine valve operating mechanisms.
Valve operating mechanisms of internal combustion engines generally comprise a valve train of several engaging parts which transfer mction from an eccentric cam to a poppet valve. As the operating clearances between the cngaging parts of the train vary to a considerable extent because of temperature variations and wear it is difcult to effect a stable silent and efficient operation of the engine. Accordingly it is desirable to incorporate means in the train for automatically compensating for such conditions.
Hydraulic tappets are a particularly effective device for automatically adjusting the clearances in such valve trains7 however, the cost of manufacture and assembly has heretofore limited the extent of their use to the more expensive engines.
It is therefore an object of the present invention to provide an improved and simplified hydraulic tappet which may be constructed and assembled at a cost which adapts it to use in `all engines.
It is another object to provide a hydraulic tappet of a minimum number of simply formed parts which be easily and efficiently assembled into a compact unit.
Other objects and advantages of the invention will appear from the following description taken in connection with the drawing I rining a part of the specification and in which Figure 1 is a longitudinal sectional view of a fragmentary portion of an internal combustion engine provided with hydraulic tappets of the type cmbcdying the present invention; Figure 2 is an enlarged longitudinal sectional view of the tappet; Figure 3 is an enlarged cross-sectional view of the tappet along the line 3-3 of Figure 2; Figure 4 is a perspective View of a valve cage forming part of the tappet assembly and Figure 5 is an enlarged longitudinal sectional View of another form of hydraulic tappet embodying the present invention.
Referring now to the drawing and particularly te Figure l., there is illustrated a hydraulic tappet lo embodying the present invention in the valve train or operating gear of a typical internal combustion engine. In Figure 1, a cam l2 which is one of several spaced along the camshaft of the engine `supplies the motion for raising the poppet valve i4 against the pressure of a spring IG which in turn, returns valve I4 to its seat when permitted by the cam motion. As shown, the motion of the cam is transmitted to the stem of the poppet valve through the hydraulic tappet which automatically compensates for any clearance that may develop in the valve train due to Wear or temperature variations. The tappet is guided for reciprocating movement in a cylindrical opening it in the engine block Eil. A communicating passage 22 is provided in the engine block to supply the tappet with oil from the pressure lubricating system, not shown, thereby insuring an adequate supply of oil for operating the tappet and lubricating the Working parts of the tappet mechanism.
As shown in Figure 2 the valve tappet iii comprises a generally cylindrical member 24 with one end closed yand a piston reciprocably mounted within the cylindrical member. With the piston and cylindrical member assembled in this manner there is formed an interior chamber 2B which when supplied With oil from the lubricating system provides a liquid column upon which the piston rests and through which motion applied to the cylindrical member by the cam is transmitted to the pcppet valve. The mechanism for controlling the volume of liquid in the chamber 28 and thus the position of the piston in the cylindrical member to automatically compensate for any lash or clearance that may develop in the valve train and the introduction of oil to the chamber Will be explained hereinafter in connection with the description of the piston and the operation of the tappet.
The cylindrical member 24 is formed with grooves 30 and 32 in its external and internal Walls respectively, and a port 34 which connects the respective grooves through the Wall of the cylindrical member and provides for the fiow of oil from the communicating passage .22 to the piston 25. An enlarged section 36 is formed in the internal Wall of the cylindrical member adjacent to the closed end thereof. In connection with groove 3B it is preferred that the groove be of suicient Width to remain in register with the `communicating passage 22 throughout the entire working stroke of the cylindrical member. However, it is not necessary that this groove remain in register with the communicating passage throughout the entire working stroke of the cylindrical member as the tappet will function efiiciently Where registration occurs throughout substantially only the first 30% of the Working stroke. To resist Wear caused by the rubbing aton of the cam on the closed end of the cylindrical member 2t, the member is made of steel or cast which may be heat-treated or chilled .respectively and the face which engages the cam is hardened by such treatment.
The piston E@ is formed with a cavity 36 which is in communication with the internal chamber 2t of the tappet through a passage i0 controlled vby a one-way ball valve 42. The cavity 38 serves as a reservoir for supplying oil to the internal chamber 23 and preferably should be of a size or capacity to insure the proper operation of the tappet mechanism for periods when oil 'is not being delivered to cavity 39 from the communicating passage 22. Such periods may occur during the starting of a cold Vengine when the oil is most viscous and therefore does not flow readily until a substantial pressure is built up in the lubricating system. Further, such periods may occur when the supply of oil to the tappets of a thoroughly heated engine may be temporarily restricted or cut of. During such periods, the cavity will continue to supply oil to the internal chamber for a substantial period of time thus insuring efficient operation of the tappet as long as oil remains in the cavity 38. Ports 44 are provided in the wall of the piston 25 for establishing communication between the cavity 38 and the communicating passage 22 through port 34 of the cylindrical member. Ports 41?. are positioned in the wall of the piston at a height suiicient to insure maximum capacity for the cavity 38. A groove d6 formed in the external wall of the piston 25 adjacent ports Mi is adapted to form a continuous oil passageway between ports 34 and it regardless of their angular or radial relationship. This groove also serves to collect oil which has been forced by the pressure in the internal chamber 23 upwardly along the engaging surfaces of the piston and cylindrical member for return to cavity 3B through ports Alli. This collecting groove 46 provides for the return to the cavity of a substantial portion of the oil forced erably not less than .007 and not more than out of the internal chamber 28 thus establishing an oil recirculating system for the tappet mechanism within the tappet itself.
Under the temperature conditions to which the tappet is exposed in an operating engine, hard films of oil residue resembling solidified varnish form on areas of the piston and cylinder walls which are not in continuous contact with each other. Where the pston varies only slightly from its normal operating position, as shown, to take up lash or clearance in the valve train, such hard lms do not interfere with the operation of the tap-pet. However, where the piston undergoes considerable change of position, as for example, when the engine is not running and the pressure of spring it forces the piston into abutting relationship with the end wall of the cylinder, the hard films become wedged between the walls of the piston and cylinder causing a binding of the parts which renders the tappet inoperative. Grooves 32 and 45 and enlarged section 36 are of sufficient depth and width to prevent formations of hard films from interfering with the operation of the tappet. In addition, groove 32 is arranged in cylinder 2li to overlap groove 46 in piston 26 in the manner shown with the piston in its operating position in the cylinder. Further the enlarged section 36 is arranged to overlap the shoulder of the piston formed at the junction of the piston wall and reduced end section in the manner shown. With this groove arrangement the binding of the parts is prevented as the movement of the piston to its non-operative position is away .010. As the valve seat is superficially hardened by heat treatment to resist wear it is preferred that the curvature of the face engaging the ball be not less than the above limit to prevent overstressing'any point on the seat where a particle might become lodged between the ball while the ball is subjected to the high pressures developed within the internal cavity 8. With sufcient material adjacent the edge of the valve seat obtained by the aforesaid .007 minimum radius, the edge forms a hard surface on which iioating particles in the oil which collect on the seat may be crushed by the action of the ball when it seats without damaging the seat by overstressing causing fractures on the surface.
The ball valve i2 is held in recess 50 by a cupshaped cage 54 shown in perspective in Figure 4. The cage is formed with an annular flange 56 and ports 58 to permit passage of oil to the interior cavity 28. The diameter of the cup is of such a dimension that the cage lits loosely for rotation about the reduced section 48. The depth of the cup is preferably slightly less than the length of the reduced section so that the cage may be fitted on the reduced section with a gap 60 between the flange 56 and the shoulder G2 4formed at the junction of the walls of the piston and its reduced section. The valve cage 54 is held in position on the reduced section of the piston by the pressure of a spring 64 which is bottomed on the end wall of the cylindrical member and has its other end engaging the flange 56 of the cage. To maintain the eiliciency of operation that is desirable in a hydraulic tappet a clearance of .005 to 008" is preferred between the ball d2 and the seat 52. If
Athe clearance is under .005 there is a delay in time in transferring oil from the cavity 38 to interior chamber 293 when the oil is very viscous vand flows slowly due to low temperature creating lash in the valve train and consequently noise. If the clearance is greater than .012 the time element in returning the ball to the seat is such that oil is pushed back through the orifice into cavity 38 creating lash and noise when the oil is extremely uid or thin due to high temperature.
In order that the Valve clearance may be maintained substantially constant within the above mentioned limits, the valve cage 54 is loosely fitted to the reduced section in the manner hereinabove described so that a certain amount of wear will occur on the end face of the reduced section and the corresponding face of the cage. As the cage will turn on the reduced section due to the rotary motion of parts of the tappet assembly when in operation, wear will occur on the engaging faces of the cage and reduced section due to the rubbing action. This wear will compensate for any wear which occurs on the face of the valve seat and at the contact point `of ball to cage thus maintaining the clearance between the ball and valve seat necessary to the efficient operation ofthe tappet. The cage 54 is preferably hardened by heat treatment to prevent` excessive wear and thus over-compensate for any corresponding wear on the valve seat.
A cap 66 is provided for covering the open end of the piston and is formed with a semi-spherical recess B8 to engage the ball end of the stern of 'the valve I4.
The tappet I is assembled as a unit by inserting the spring 64 then the piston and ball valve assembly. The parts are maintained in assembled relationship by the split ring 'I0 which snaps into a corresponding groove 'I2 in the wall of the `cylindrical member 24. The split `ring 'I0 is provided with diametrically opposed straight portions 'I4 shown in Figure 3 which permit the use of a cap 66 having a diameter such that its peripheral edge will not engage the wall of the cylindrical member to cause wear in the wall while still retaining the aforesaid parts assembled.
In Figure 5 there is illustrated a modification of the tappet o-f the present invention adapted for use in engines which have removable guide brackets for the hydraulic tappets. The tappet mechanism of the modification is substantially the same as the mechanism hereinabove described in connection with Figure 2. The structure differs in that the open end of the piston is closed by a cap 'I8 provided with an upwardly extending portion Bt which engages the valve stem. In addition the end of the cylindrical .member 82 is provided with an enlarged section 84 for engines having relatively large cams.
In operation, with the tappet I0 resting on the base circle of the cam I2 oil under pressure is introduced to the cavity 38 of the piston 26 from the communicating passage 22 of the lubricating system through the registering ports and grooves in the walls of the piston and cylindrical member. The oil is then forced into the internal chamber 28 through passage 4U and past ball valve 42 by the pressure of the system and the action of spring 64 in forcing the piston upwardly to take up any lash or clearance in the valve train. As the cam I2 rotates `and the action of the eccentric portion is transmitted to the tappet the tappet is forced upwardly against the pressure of spring I6. A pressure is built up in the internal chamber 2B which forces the ball valve 42 against the valve seat 52 thereby providing a column of oil between the piston and cylindrical member which transmits the motion of the cam to the valve. Of course, with the relatively high pressure in the interior chamber 28 some oil is forced upwardly along the engag ing walls of the piston and cylindrical member where it is collected in groove 4S and returned to cavity 38 through passages 44. As the cam continues to rotate the direction of the tappet changes following the face of the cam. On the return stroke the pressure of spring |16 continues to supply sufficient force to the piston to maintain a seated or closed condition of the ball valve until the tappet is again riding on the base circle. Any clearance that may have developed in. the valve train during the complete cycle of valve operation is automatically compensated by the action of spring 64 in forcing the piston upwardly to take up the clearance. With this action the ball valve opens and oil is again introduced into interior chamber 28 to fill the chamber for the next complete cycle of valve operation.
Along with the reciprocating movement mparted to the tappet IIJ by cam I2 and spring I6 a denite and controlled rotary force is imparted to the cylindrical member 24 by cam I2. rIhis rotary force is utilized in the tappet of the present invention to maintain a clearance between the ball 42 and valve seat 52 desirable for the most efficient operation of the tappet. To eect a rotary movement of the cylindrical member 24 its cam engaging surface is formed with a spherical curvature and the cooperating cam surface Vis formed with a tapered or conical surface. In assembling the tappet in the engine it is arranged with respect to the cam so that the cam and cylindrical member engage at a point slightly offset from the central axis of the tappet. With this arrangement a definite and controlled rotary force is imparted to the cylindrical meinber and it in turn is transmitted through the gripping action of spring 64 to the cage 554. As hereinbefore mentioned this rotary movement of cage 54 on piston `26 effects a wearing of the surfaces between the cage and piston which compensates for the wearing action of the ball on the valve seat of the piston. In this manner the clearance between the ball and valve seat is effectively maintained within limits most desirable for efficient operation of the tappet.
The tappet of the present invention is particularly adapted to operate quietly at maximum efliciency over long periods of time without attention, thereby providing for the most efficient engine operation. In addition, the simplicity of the component parts and the assembly makes it particularly adapted to low cost manufacturing and assembly operations. Further the cost of a tappet such as the hereinabove described makes its use in all types of vehicle engines feasible.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. In a hydraulic tappet, a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, a passage in said piston providing communication between the closed end of said cylinder and the interior of said piston, a valve for controlling said passage, a valve cage limiting opening movement of said valve and mounted to rotatively bear on the end of said piston and a spring positioned between said valve cage and the bottom of said cylinder to transmit rotation from said cylinder to said cage.
2. In a hydraulic tappet, a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston having a reduced end and a passage providing communicam tion between the interior of said tappet and the interior of said piston, a recess in said reduced end communicating with said passage, a ball valve positioned in said recess for controlling said passage, a cup-shaped valve cage mounted for rotation on said reduced end to maintain the open position of said ball valve with respect to said passage substantially constant, said cage being provided with an outwardly extending flange spaced apart from said piston and diamet rically opposed apertures offset from its central axis, and a helical spring positioned between said cage and the bottom of said cylinder with its ends in frictional engagement with said flange and said bottom to transmit rotary motion from said cylinder to said cage,
3. In a hydraulic tappet, a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston being provided with a central cavity and a uniformly re duced end, a groove in the external wail of said piston in `communication with said cavity for collecting and returning oil thereto, a recess in said reduced end connected by a passageway to said cavity, a ball valve positioned in said recess for controlling said passageway, a cup-shaped valve cage mounted for rotation on said reduced end to maintain the open position of said valve substantially constant with respect to said passageway, said cage having an outwardly extending flange spaced apart from said piston and diametricaliy opposed apertures oiset from its central axis, and a helical spring positioned between said cage and the bottom of said cylinder with its ends in frictional engagement with said ange and said bottom to transmit rotary motion from said cylinder to said cage.
4. In an actuating system for a reciprocated member, a hydraulic tappet including a cylinder provided with a closed end, means for simultaneously reciprocating and. rotating said cylinder, a piston mounted for reciprocation in said cylinder, said piston having a passage therein providing communication between the internal chamber formed by mounting said piston in said cylinder and an external source of liquid, means for restraining rotation of said piston in said cylinder, a valve for controlling said passage, a valve positioning cage rotatively mounted on the end oi' said piston and a spring positioned in said cylinder with its ends in engagement with said cage and the closed end of said cylinder to transmit rotary movement from said cylinder to said cage.
5. In an internal combustion engine having a valve and means for actuating said valve, a hydraulic tappet interposed between said valve and said means comprising a, cylinder with a closed end operatively engaging said means for simultaneous reciprocation and rotation thereby, a piston mounted in said cylinder and operatively connected to said valve to transmit reciprocating movement to said valve while being substantially restrained from rotation with said cylinder, said piston having a passage therein providing communication between the internal chamber of said tappet and an external source of liquid, a Valve for controlling said passage, a Valve cage rotatively mounted on the end of said piston for positioning said valve and a spring positioned between the closed end of said cylinder and said cage for yieldingly urging said cage into engagement with said piston and to transmit rotary movement from said cylinder to said cage.
6. In a hydraulic tappet, a cylinder provided with a closed end and an internal annular groove having one side dened by said closed end and a piston mounted for reciprocation in said cylinder with a substantial portion of one end of its cylinder engaging surface overlapped by said groove, said piston having a reduced diameter portion extending from said one end, and a cup rotatively receiving said portion, said cup being formed with an external nange at its open end of substantially the diameter of the cylinder engaging surface of the piston.
7. In a hydraulic tappet, a cylinder provided with a closed end and an internal annular groove in its wall connected by a communicating passage with the exterior of said cylinder, a piston mounted for reciprocation in said cylinder, said piston having an external annular groove overlapped by said internal annular groove, a passage in said piston providing communication between the internal chamber formed by mounting said piston in said cylinder and said external annular groove and a valve for controlling said passage.
8. In a hydraulic tappet, a cylinder provided with a closed end and a plurality of internal annular grooves in its wall, one of said grooves being connected by a communicating port with the exterior of said cylinder, a piston mounted for reciprocation in said cylinder with a substantial portion of one end of its cylinder engaging surface overlapped by one of said internal annular gro0ves, said piston being provided with an external annular groove in overlapping relation with the internal annular groove connected by said communicating port, a passage providing communication between the internal chamber formed by mounting said piston in said cylinder and said external annular groove and a valve con trolling said passage.
9. In a hydraulic tappet having a cylinder adapted to be reciprocated and rotated in operation and provided with a closed end, a hollow piston mounted for reciprocation in the cylinder, said piston having a reduced diameter end portion opposite the closed end of the cylinder, said portion having a passage extending therethrough from the interior of the piston and terminating in an enlargement open to the closed end of the cylinder, a valve seat on the piston at the juncture of said enlargement and said passage, a ball valve Within said enlargement and engageable with said seat4 to close said passage against now of fluid into the piston from the closed end of the cylinder, said enlargement being of sufficient depth that a predetermined clearance exists between the ball and the end of said reduced portion when the ball is engaged with said seat, a cup having its side walls loosely journaled on the periphery of said reduced portion and its end Wall abutting the end of said reduced portion to maintain said ball clearance, said cup being of less depth than the length of said reduced portion and having an external flange formed on its side walls, and a coil compression spring having its opposite ends thrustably engaging said flange and the closed end of said cylinder.
10. In combination, an axially rotatable and reciprocable cylinder, a piston therein, said piston having a passage for conducting fluid into one end of the cylinder, a check valve movable to open and close said passage, a seat on the piston engaged by the valve when in closed relation with said passage, a member limiting opening movement of the valve, said member and piston having oppositely disposed end faces rotatably abutting each other, and a resilient member biasing said iirst named member axially of the cylinder to maintain said faces in abutment with each other and rotatively couple said first named member to the cylinder, whereby relative rotation and resultant Wear of said faces at least partially compensates for Wear of said valve on said seat and said first named member and tends to maintain the limit of valve opening movement constant during re ciprocation of the cylinder.
l1. In a hydraulic tappet, a cylinder mounted for rotation and reciprocation and provided interiorly thereof with an abutment facing one end of the cylinder, a coil spring disposed within the cylinder and resting on said abutment, a piston slidably fitting said cylinder and terminating at its inner end within said spring, a cup resting on said `Spring and frictionally coupled thereby for rotation with said cylinder, said piston end bottoming in said cup and having a valve seat spaced from the bottom of the cup, a check valve-having a predetermined freedom of movement between said seat and the bottom of said cup, and a member engaging the other end of the piston and restraining its rotation whereby wear of said cup bottom resulting from its rotation on said rst named end of the piston tends to compensate for wear of said check 'valve and seat.
12. In combination, a cylinder, guiding means accommodating reciprocation and rotation of the cylinder, a piston in the cylinder, means for introducing fluid into one end of the cylinder including a passage in the piston, a check valve movable to close and open said passage, a seat on the piston engageable by the valve when in closing relation with said passage, and a member rotatively coupled to the cylinder limiting opening movement of the valve, said member having a rotary bearing engagement with said piston end for effecting wear of the engaging surfaces of said member and piston end to compensate for wear of the valve and seat during relative rotation of the cylinder and piston.
LOCKWOOD B. ELLIS.
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