A Tappet Assembly for an Internal Combustion Engine

Europaisches Patentamt J) European Patent Office © Publication number: 0 376 445 Office europeen des brevets A1

EUROPEAN PATENT APPLICATION

Applicant: FORD-WERKE AKTIENGESELLSCHAFT Werk Koln-Niehl Henry-Ford-Strasse Postfach 60 40 02 D-5000 Koln 60(DE) © DE

© An engine tappet is constructed with flat, essentially parallel or conformal bearing walls (36,40) inter- 1A nal of its case for the introduction during no-load operation of a lubricant under pressure to the space between the surfaces, the pressure level of the lubricant being greater than the force necessary to re- lash in the to create oil CO move system, thereby an film between the walls (36,40) that is partially squeezed out during load operations of the cam (20) event to in effect float one part upon the other to UJ reduce rotational friction. FIG.2

Xerox Copy Centre 1 EP 0 376 445 A1 2

A TAPPET ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE

This invention relates in general to an auto- cam event and the contact becomes loaded but the motive type internal combustion engine, and more oil cannot be squeezed out in the time allowed by particularly, to the construction of a tappet assem- the event. Accordingly, the tappet can rotate freely, bly to reduce friction between the rotating parts. which reduces friction. Cam/tappet friction can be reduced by promot- 5 It is a primary object of the invention, therefore, ing tappet rotation. The ideal rotation speed would to provide an automotive engine tappet construc- be that at which the surface velocities of the cam tion that utilises a squeeze film of lubricant princi- and tappet surfaces are the same. Friction is re- ple to reduce frictional resistance to rotation be- duced in two ways: (1) By increasing the oil film tween the parts. thickness, thus decreasing the degree of contact 70 It is another object of the invention to provide a between the cam and tappet surfaces, and (2) by tappet of the construction described above in which introducing a rolling motion between the surfaces, a thin film of lubricant is introduced between two coefficients of rolling friction being lower than those smooth bearing surfaces to in effect floatingly of sliding friction. This will be true for a wide range mount the parts relative to each other to reduce of valve train geometries, including the centre pivot 75 friction. rocker arm example shown in Fig. 1 . According to the invention there is provided a This invention promotes tappet rotation by re- tappet assembly for the valve train of an internal ducing the frictional resistance to tappet rotation. combustion engine having an element (12) of the This is accomplished by introducing a squeeze film valve train engaged by the tappet (18) for moving bearing between the relative rotating parts, such as 20 the same, the tappet having an outer cup-shaped the end cap and the check valve body in a hydrau- case member (30) with side walls and an essen- lic type tappet. tially flat bottom wall adapted to be engaged by a Squeeze films are lubricating films between rotating cam member (20), the cam member hav- two bearing surfaces. These can be produced in ing a circumferential base circle no-load portion several ways: by forcing oil between the surfaces 25 (24) and a contoured cam circumferential load por- at a pressure large enough to overcome the load tion (26), the cam member (20) engaging the bot- on the bearing surfaces, or by allowing oil to flow tom wall to one side of its centre to impart a into the area between the bearing when the bearing rotative torque on the case, the case slidably and is unloaded. When the bearing is loaded or when rotatably receiving therein in back-to-back relation- the pressure forcing oil into the gap is less than the 30 ship first and second channel-like members (32,38) pressure on the bearing, the oil is squeezed out of each having spaced side walls joined by a continu- the bearing. As the oil film becomes thin, the rate ous essentially flat end wall, the first member (38) at which it is squeezed out becomes progressively being engageable by a portion of the engine ele- less. Accordingly, such films can last for a consid- ment (12), the flat end walls (36,40) of the mem- erable time. If the bearing surfaces are smooth, 35 bers being adjacent one another and movable rela- very thin oil films can completely separate the two tive to each other to at times form a fluid chamber bearing surfaces. This allows the surface to move (46) therebetween, a fluid inlet (48) to the chamber easily, i.e., with low friction relative to one another. and a source of fluid lubricant under pressure con- The invention to be described to reduce friction nected to the inlet for supplying lubricant at a by improving tappet rotation, as stated previously, 40 pressure level greater than the force of the element relies on a squeeze film of engine oil between two (12) and cam member (20) against the first mem- bearing surfaces inside the tappet. In the case of a ber (38) and case to thereby effect separation of mechanical tappet, the load over the base circle is the end walls (36,40) by a film of lubricant thereby nearly zero. Therefore, only a small bearing area is reducing frictional resistance to rotation between needed to form an oil film. In the case of a hydrau- 45 the parts, the fluid under pressure being introduced lic tappet, a significant load is produced when the during the no-load operation of the valve train when cam/tappet contact is on the base circle because of the case bottom wall is in contact with the base the hydraulic pressure in the tappet used to pump circle portion (24) of the cam member (20), the up the tappet to maintain contact with the cam fluid being partially squeezed from the chamber base circle. The invention takes advantage of this 50 (46) during the load condition of operation of the by using this oil under pressure to force oil be- valve train when the case bottom wall is in contact tween two smooth bearing surfaces incorporated in with the contoured cam portion (26) of the cam the bearing. member (20) to provide a thin film of lubricant After an oil film is formed at the load bearing between the flat end walls. surface, the cam/tappet contact moves over the Fig. 1 schematically illustrates a side

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elevational view of a valve train embodying the allows the squeeze film to last longer before the oil invention; film thickness becomes comparable in dimensions The invention will now be described further, by to the surface roughness. Fig.. 4 illustrates the rate way of example, with reference to the accompany- of collapse of an oil film thickness with time and its ing drawings, in which : 5 approach to the surface roughness of the adjacent Fig. 2 is a cross-sectional schematic view of parts. a mechanical tappet embodying the invention; After an oil film is formed at the load bearing Fig. 3 is a cross-sectional schematic view of surfaces 36, 40 in chamber 46, the cam/tappet a hydraulic tappet embodying the invention; and contact moves over the cam event in which the Figs. 4, 5 and 6 are graphical illustrations 10 contoured cam portion 26 of the cam member showing various squeeze film characteristics. moves the tappet assembly through its load opera- Fig. 1 illustrates an essentially conventional tion, causing higher loads to be applied to the valve train assembly consisting of a rocker arm 10 tappet assembly. The oil film then is gradually oscillatable about a fulcrum 12 to reciprocate the squeezed out by means of leakage past the side stem 14 of a valve 16 in the usual manner. The 75 portions 42 of the end cap, to decrease the oil film opposite end of the rocker arm is actuated by a thickness. It will be clear, however, that such leak- tappet assembly 18 that rides on the surface of a age is not necessary for operation under this prin- cam member 20 fixed for rotation on a camshaft ciple to reduce friction. having an axis 22. The cam member in this case Fig. 3 illustrates schematically a hydraulic tap- has a base circle portion 24 and a contoured cam 20 pet construction with the squeeze film bearing prin- surface portion 26 for loading the tappet against ciple incorporated. In this case, the tappet is con- the rocker arm to actuate the valve. The structed in a manner similar to a conventional hy- cam/tappet contact would be made off centre of draulic tappet, with an outer cylindrical case 50 the tappet face to impose a turning torque on the receiving therein with a press-fit a cylindrical tappet upon rotation of the cam member. 25 channel-shaped check valve body 52. The latter Fig. 2 illustrates a mechanical tappet 18' con- has an axial or central opening 54 for the flow of oil struction that employs the squeeze film lubricant or lubricant past a ball-type pressure relief valve 56 principle. As shown, the tappet includes an outer controlling the inlet of lubricant to a chamber 58. tubular channel or cup-shaped case 30 within An end cap member 60, slidably received within which is fixed a second tubular channel or cup- 30 the check valve body 52, is adapted to engage the shaped member 32 having side leg portions 34 and end of the rocker arm shown in Fig. 1. a flat, smooth round bottom portion 36. Facing the The opposite end of the case 50 contains a bottom portion 36 is a cylindrical cap member 38 second cylindrical end cap member 62 slidably having a mating flat round bottom plate 40 and received within the end of the tappet case 52, as side and top surface portions 42, 44. The channel 35 shown. It has opposite flat or crowned, round faces member 32 in this case is shown with a press fit; 64 and 66 and side walls 68, forming a hollow hat- however, it will be clear that it could be secured in shaped element. The bottom round face 70 of the the outer case 30 by other methods. check valve body is also made flat in a manner The cap member 38 is slidably received within mating that of the bottom or end plate 64, the two the outer case 30 and movable with respect to the 40 being ground smooth in a manner similar to that member 32 to define a fluid lubricant or oil cham- described in connection with the solid tappet. ber 46 between the two flat bearing surfaces 36, An oil or lubricant supply hole 74 is provided in 40. An oil or lubricant supply hole 48 is adapted to the side of the tappet case as an inlet for the oil or be connected to a suitable source of lubricant lubricant under pressure. The pressure level must under pressure, such as the engine oil pump, for 45 be sufficient to pump up the tappet by admitting oil example. past the pressure relief valve so that the end caps The pressure level of the lubricant entering the 60, 62 engage the ends of the rocker arm and cam chamber 46 required must be sufficient to provide in a manner eliminating lash. It will also be clear a force greater than the forces pressing the tappet that the pressure level in the chamber 76 defined against the end of the rocker arm when the tappet so between the two end plates 70 and 64 must pro- contacts the cam on the base circle. Also, the two vide a force greater than just the forces exerted by facing end surfaces 36, 40 should be made the cam on the tappet against the rocker arm smooth. In the case illustrated, the bottom 40 of the sufficient to eliminate the lash, thereby providing a end cap 38 and the bottom 36 of the channel- squeeze film of lubricant between the two facing shaped member 32 are made flat, then polished to 55 end plates 70 and 64. This in effect floatingly a surface finish of about 2 micro inches with a very mounts the end cap 62 with respect to the check slight crown. A slight crown is desirable to avoid valve body 52 on a thin film of lubricant or oil. A contact at sharp edges. The fine surface finish load that is produced by this oil under pressure

3 5 EP 0 376 445 A1 6 times the area of the end cap separates the com- reasonable large, the tappets should normally fill in ponents and creates the oil film. a fraction of the time available on the base circle. The thickness of the oil film in this configura- As the squeeze film thickness becomes small, the tion is dictated by the valve lash. Oil pressures rate of film collapse becomes slower. normally encountered in engines, about 10 psi at 5 low idle, higher at higher speeds, are more than adequate to create this oil film. As the contact Claims moves off the base circle and over the cam event, the load on the cam tappet contact increases and 1 . A tappet assembly for the valve train of an becomes greater than the load produced by the oil w internal combustion engine having an element (12) pressure. The oil is then squeezed out of the of the valve train engaged by the tappet (18) for contact. However, if the surface finish is sufficiently moving the same, the tappet having an outer cup- smooth, the oil film endures until the contact is shaped case member (30) with side walls and an once again on the base circle. At that point, the essentially flat bottom wall adapted to be engaged process is repeated. Experimental results were ob- 75 by a rotating cam member (20), the cam member tained in a cam/tappet friction rig derived from an having a circumferential base circle no-load portion engine with a centre pivot rocker arm geometry. (24) and a contoured cam circumferential load por- Fig. 5 shows that the internal squeeze film tappet tion (26), the cam member (20) engaging the bot- described above produced much higher rotational tom wall to one side of its centre to impart a speeds. In Fig. 5, the curve labelled "flat cap" 20 rotative torque on the case, the case slidably and denotes results for a standard or conventional pro- rotatably receiving therein in back-to-back relation- duction tappet. The cam event is over the interval ship first and second channel-like members (32,38) of approximately - 65 to + 65 degrees. The point each having spaced side walls joined by a continu- of maximum lift is at 0 degrees. Fig. 6 shows ous essentially flat end wall, the first member (38) friction torque as a function of cam angle. The 25 being engageable by a portion of the engine ele- internal squeeze film tappet shows lower friction ment (12), the flat end walls (36,40) of the mem- losses. bers being adjacent one another and movable rela- One limitation on tappet speed is the rotational tive to each other to at times form a fluid chamber inertia of the tappet. That is, at higher speeds, the (46) therebetween, a fluid inlet (48) to the chamber tappet cannot change rotational speed fast enough 30 and a source of fluid lubricant under pressure con- to follow the motion of the cam. This limits the nected to the inlet for supplying lubricant at a degree of friction reduction obtainable at higher pressure level greater than the force of the element speeds. Fig. 3 shows an approach to extending the (12) and cam member (20) against the first mem- speed range by reducing the rotational inertia and ber (38) and case to thereby effect separation of how this may be incorporate into a hydraulic tappet 35 the end walls (36,40) by a film of lubricant thereby configuration. This is done by having the separate reducing frictional resistance to rotation between rotating tappet face in the tappet, which has a the parts, the fluid under pressure being introduced lower rotational inertia, and a balance of forces on during the no-load operation of the valve train when the base circle, which pumps-up the hydraulic tap- the case bottom wall is in contact with the base pet while also creating the oil film required for the 40 circle portion (24) of the cam member (20), the squeeze film. The balance of forces in this particu- fluid being partially squeezed from the chamber lar design is obtained by sizing the squeeze film (46) during the load condition of operation of the bearing larger than the end cap area so that on the valve train when the case bottom wall is in contact base circle the rotating tappet face is forced up with the contoured cam portion (26) of the cam against the squeeze film stops 80, creating the oil 45 member (20) to provide a thin film of lubricant film needed, while the end cap 60 is forced up between the flat end walls. against the rocker arm, taking up any valve lash. 2. A tappet assembly as claimed in Claim 1, Experimental data have not been obtained for this the first member comprising an end cap closed at design. both ends, the second member being hollow and Test data obtained on a construction of this 50 including an opening in its end wall containing a type were obtained with the ASTM 20W30 refer- spring closed pressure relief valve operable above ence oil HR4. Oil viscosity would have only a minor a predetermined pressure in the chamber to admit effect on performance of the squeeze film bearing lubricant to the interior of the second member , the over the range of viscosities found for practical opposite end of the second member slidably re- engine oils at operating temperatures. Hydraulic 55 ceiving therein a second end cap member having a valves often are not completely pumped up at very flat bottom wall actuated by the lubricant admitted low ambient temperatures until the oil is warm. to the interior to move the second end cap against Since the passages used to fill the tappets are the valve train element to reduce the lash between

4 EP 0 376 445 A1 the element and cam member. 3. A tappet assembly as claimed in Claim 1, wherein the case and first and second members constitute a solid tappet. 4. A tappet assembly as claimed in Claim 2, 5 wherein the case and other members constitute a hydraulic tappet. 5. A tappet assembly as claimed in Claim 2, including means between one of the members and the case limiting the sliding relative movement be- w tween the one member and the case. 6. A tappet assembly as claimed in Claim 1, wherein the adjacent end walls are smooth.

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FIG.6 European Patent Application Number EUROPEAN SEARCH REPORT Office

EP 89 31 0681 DOCUMENTS CONSIDERED TO BE RELEVANT Category Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION ant. Cl.S ) FR-A-920444 (LAGO) 1. 3 F01L1/14 * page 1, line 56 - page 2, line 35; figures 1, F01L1/16 2 * F01L1/32 F01L1/24 EP-A-80175 (NISSAN) 1, 3, 6 * page 6, line 24 - page 7, line 22; figures 3, 4 *

EP-A-128748 (AUTOMOTIVE ENGINF) * page 3, line 13 - page 3, line 33 * * page 4, Hnp 13 - page 4, line 25; figure 1 *

A GB-A-513805 (JENNFR)

A FR-A-2550273 (PEUGEOT)

TECHNICAL FIELDS SEARCHED (Int. ci.S )

FOIL F01M

The present search report has been drawn up for aH claims Place of search Dale of completion of the search Examiner THE HAGUE 23 MARCH 1990 LEFEBVRE L.J.F.

CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure A : member of the same patent family, corresponding P : intermediate document document