Low-mass, direct-acting hydraulic valve-lifter

Abstract: A direct-acting hydraulic valve-lifter (10) features in a preferred embodiment a follower (15) assembled with a thin wall metal shell (18) and a light plastics baffle (19) to support a lash-adjusting hydraulic element assembly (16). An inlet riser chamber (38) has sufficient cross-section to minimize oil flow restriction in cold oil conditions. Dead space between the shell (18) and the baffle (19) is filled with a strong lightweight foam (20) to support and retain the baffle (19) and to displace oil for low mass.

Description: This invention relates to hydraulic valve-lifters (HVL's) for engines and, in more particular embodiments, to direct-acting HVL's of light weight for use in relatively high-speed overhead cam (OHC) automotive engines and the like. HVL's may also be referred to as hydraulic tappets and sometimes are called hydraulic-lash adjusters, and direct-acting hydraulic valve-lifters (DAHVL's) are sometimes called bucket tappets, however these various names are not necessarily of equivalent scope. In particular, this invention relates to a follower for a hydraulic valve-lifter as specified in the preamble of claim 1, for example as disclosed in DE-A-3623638. It is known in the art relating to overhead cam (OHC) internal combustion engines to provide a direct-acting hydraulic valve-lifter (DAHVL) that is contacted by a cam and directly actuates one or more valves of the engine. One such arrangement which has been used in production engines is shown in United States patent 4,745,888 issued May 24, 1988. In that patent disclosure, a camshaft 18 supported in an aluminium camshaft carrier 11 has cams 22, each of which directly engages a DAHVL (tappet 23) that in turn engages the stem 34 of a poppet valve conventionally carried in a cylinder head, not shown, to actuate the valve. Each lifter 23 includes a cup-like follower having a cam-engaging alloy cast iron upper end 24 diffusion-bonded to a cold-formed steel baffle shell including an annular outer wall (skirt 26) and an inwardly-supported central wall 27. The central wall includes a radial supporting baffle and an axial annular cylinder portion in which a hydraulic element assembly (HEA) (hydraulic-lash adjuster 28) is reciprocably supported. The HEA is supplied with hydraulic fluid (engine oil) through an annular oil feed chamber 30 which is fed at its lower edge through an opening 32 via an external groove 31. The follower construction is thin-walled to maintain a low reciprocating weight for the lifter 23 as is desirable for operation at higher engine speeds. However, the chamber 30 is filled with a significant volume of oil which increases the reciprocating mass of the lifter in operation. Also, the oil in the chamber 30 may drain from the lifter when the engine is stopped so that, upon starting, the oil supply must again fill the chamber 30 before a dependable feed of oil is again provided to the HEA 28. During this period, the HEA must rely upon an internal oil reservoir for its oil supply. In addition, air may enter the system such as through draining of the chamber 30 when the engine is stopped or foaming of the oil supply during engine operation. This air may enter the HEA through an inlet from the chamber 30, resulting in unwanted tappet noise and/or improper valve actuation for an extended period until the air is removed from the lifter by escape through the clearances apart from or along with the escaping oil. Co-pending European patent application Serial No.91202790.1 (EP-A-0 485 007) discloses DAHVL's in which oil is displaced from the chamber 30 by oil-resistant foam which reduces the operating reciprocating mass of the lifter and supports or assists in supporting the axial cylinder portion of the central wall that in turn supports the HEA. Reference to that patent application, which is incorporated herein by reference, as well as to corresponding applications elsewhere will further explain the background of the additional features included in the present invention. A hydraulic valve-lifter according to the present invention is characterised by the features specified in the characterising portion of claim 1. The present invention involves direct-acting hydraulic valve lifters (DAHVL's) which utilize the foam filler and other features of the aforementioned European patent application 91202790.1 (EP-A-0 485 007) whilst providing improvements in the cam follower construction that can reduce mass and complexity with potentially lower manufacturing cost. Among the improved features of the invention are: A follower having an optional single-piece shell combined with a light plastics baffle retained by the foam filler for low mass and cost; suitable for use with conventional hydraulic element assemblies (HEA's) or other piston arrangements. A preferred polymer material for the baffle having low mass and good stability characteristics. A riser chamber that provides a fluid inlet path and sufficient volume for maintaining pressure under cold flow. This can be formed as part of the plastics baffle and/or within the supporting foam. Sealing and assembly means and methods for reliability and efficiency of manufacture. These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings; in which:- Figure 1 is a cross-sectional view of an engine valve train incorporating a direct-acting hydraulic valve-lifter (DAHVL) having a riser chamber and other features according to the present invention; Figure 2 is a top view of a plastics baffle member shown in Figure 1; Figure 3 is a pictorial view of the plastics baffle member shown in Figures 1 and 2; Figure 4 is an enlarged view of the circled portion of Figure 1 showing an optional "crush edge" sealing feature; Figure 5 is a cross-sectional view of an alternative embodiment of the invention, having other optional features; Figure 6 is a cross-sectional view of another embodiment of follower formed with a lost core shown prior to removal; Figure 7 is a top end view of a baffle for the embodiment of Figure 6 showing the lost core in place prior to assembly into a shell; and Figure 8 is a pictorial view of the baffle of Figures 6 and 7 with the lost core in position for assembly. Referring now to Figures 1-4 of the drawings in detail, numeral 10 generally indicates a preferred embodiment of direct-acting hydraulic valve lifter (DAHVL) according to the present invention. Lifter 10 is somewhat similar in its general construction to the tappets or lifters described in the previously cited U.S.patent 4,745,888 and in European patent application 91202790.1 (EP-A-0 485 007) and is adapted to be reciprocably mounted between a cam 11 and a stem 12 of a cylinder poppet valve in an engine 14 in a conventional manner as shown, for example, in the cited U.S patent. The lifter 10 comprises a cam follower 15 and a hydraulic element assembly (HEA) 16. The follower 15 includes a cup-like outer shell 18, an inner baffle 19 and a foam filler 20. The shell 18 has an annular skirt-like outer wall 22 with an open bottom end 23 and a cam-engaging head 24 closing the upper end. (The head 24 is often referred to as a foot for consistency with other valve-lifters, including historical direct-acting types, in which the lifter rides on top of the cam). For some applications, the head 24 may be formed of steel integral with the outer wall 22. However, where an alloy cast iron or other head material is preferred, the head 24 may be separately formed and attached to the wall 22 in any suitable manner such as, for example, by diffusion-bonding or laser-welding. The shell outer wall 22, as shown in Figure 1, is of circular cross-section centred on an axis 26, however it may be oval, rectangular or another suitable shape, if desired. Between its ends, an inwardly-extending annular groove 27 is formed, as by rolling or machining. An oil inlet opening 28 passes through the shell 18 on the upper side of the groove 27, as shown in Figure 1. The baffle 19 is formed separately from the shell 18, and is of a suitable lightweight material and construction and is retained in the upper portion of the shell 18. Baffle 19 includes an upstanding inner wall 30 that preferably extends to the head 24 of the shell 18. The upper portion of the wall 30 forms an annular recess 31 similar to a counterbore in appearance. Below the recess, the wall 30 defines an inner cylinder 32 which is preferably of circular cross-section to receive therein a conventional HEA. A flange 34 extends outwards from the cylinder, preferably at the bottom of the wall 30. In the illustrated embodiment, the flange 34 extends radially for part of its diameter and then slopes downwards to engage the shell outer wall 22 inwards of the oil groove 27. The raised central portion of the flange 34 provides clearance for associated valve train components. The flange includes a fill hole 35 and a smaller vent hole 36 to be later discussed. Along one side of the inner wall 30 and aligned with the inlet opening 28 are auxiliary wall means defining a riser chamber 38 extending axially along the inner wall 30 from the flange 34 to the head 24 of the shell. In the Figure 1-4 embodiment, the wall means include spaced lateral walls 39 and 40 that extend radially outwards from the inner wall 30, and a boundary wall 42 that connects outer edges of the lateral walls 39,40 between the inner and outer walls 30, 22 to define the outer extent of the riser chamber 38. Walls 39, 40, 42 also engage the inner side of the head 24 and extend to the flange 34 below. An inlet hole 43 through the boundary wall 42 near the flange 34 is aligned with the opening 28 in the wall 22. When assembled, the shell 18 and the baffle 19 define an annular first space 44 between the inner and outer walls. This space is filled with a foam filler 20 except for the riser chamber 38 which is open to the passage of oil. A passage 46 formed through the foam between the inlet opening 28 and the inlet hole 43 allows oil flow from the oil groove 27 into the riser chamber 38. A slot 47 through the upper portion of the inner wall 30 connects the riser chamber 38 with a second space 48 within the inner wall and a shallow recess 50 in the head 24 permits oil to flow from the chamber 38 through the slot 47 and recess 50 to an inner reservoir 51 in the HEA. The features of the HEA form no part of the present invention since they are of known conventional form or are disclosed in the prior co-pending European patent application 91202790.1 (EP-A-0 485 007). Detailed discussion of the HEA is not therefore required. In general, however, the HEA comprises a closed end piston 52 internally carrying a plunger 54 engagable with the head 24 and having a check-valve-controlled orifice 55 that allows one-way oil flow from the reservoir 51 to a pressure chamber 56 between the piston and plunger. Re-circulation holes 58 in the plunger 54 and clearance means formed as a flat on the piston or as a groove 60 across the cylinder 32 surface provide optional re-circulation and vent means as described and claimed in the aforesaid European patent application 91202790.1 (EP-A-0 485 007). Another optional feature shown in Figure 4, which shows an enlarged view of the circled area 4 of Figure 1, is a crush edge 62 at the lower outer edge of the baffle flange 34. Formed as a sharp edge 62 (shown in dashed lines) in the plastics material prior to assembly, the edge 62 is deformed by interference fitting within the smaller inner diameter of the outer wall 22 adjacent the oil groove 27. This tight-fitting, crushed edge 62 forms a seal against the escape of the foam filler during its installation in the follower first space 44. Figure 5 shows a DAHVL 63 similar to that of Figure 1 wherein like numerals designate like parts. Several optional features are included in a modified follower 64. A two-piece shell 66 is provided having a thin steel outer wall 67 attached, such as by diffusion-bonding, to an alloy cast iron head 68. The two-piece construction is optional and similar to prior commercial valve lifters such as that shown in the aforementioned U.S. patent 4,745,888. A baffle 70 similar to that of Figures 1-4 is also provided having two other modifications. An inner wall 71 has at its upper end a lip 72 extending outwards and engaging an inner side of the head 68. The lip can assist in preventing leakage of foam into the second space 48 containing the HEA 16. A modified riser chamber 74 is also formed by providing an outward extension 75 from the lower portions of auxiliary walls 76 to form an enlarged inlet portion 78. This extends the riser chamber 74 outward and further reduces resistance to fluid flow from the inlet opening 28 to the second space 48. In this Figure 5 embodiment, the joint between the baffle 70 and the outer wall 67, at the location of the riser chamber inlet portion 78, is sealed against oil leakage by the close fitting of the parts and, optionally, by a crushed edge 62 forming seal means as shown in Figure 4. However, it does not have the additional sealing effect of the foam filler at this location as does the Figure 1-4 embodiment. If desired, other types of seals could be provided as seal means to control leakage at this joint. Also, such seals as resilient rings or gaskets could be used around the baffle edges to control foam leakage during filling. Figure 6 illustrates another embodiment of follower 80 for a DAHVL according to the present invention. The shell 18 is optionally like that of Figure 1 but baffle 82 is modified to eliminate auxiliary walls. Instead, a lost core 83 is applied during manufacture as shown in Figures 6-8. The core 83 fits within the annular recess 31 of the inner wall 30 of baffle 82 closing the upper part of the second space 48. A small radial segment 84 of the core extends through the slot 47 in the wall 30 out to the outer wall 22 and down to the flange 34 of the baffle at the inlet opening 28 to prevent the inflow of foam filler 20 to the cored volume during the filling process. The core is subsequently removed, as will be discussed later, forming a riser chamber 86 in the first space that is bordered by the foam filler 20 and connects the inlet opening 28 with the second space 48. In operation of the described embodiments, oil admitted through the opening 28 passes through the riser chamber 38, 74, 86, slot 47 and recess 50 to the reservoir 51. From there, it is allowed to pass through the check-valved orifice 55 and to re-fill the pressure chamber 56 at each cycle as the HEA 16 operates to adjust the valve-lash in known manner, urging the follower head 24, 68 lightly against the cam 11 and the HEA piston 52 against the valve stem 12. Then, as the rotating cam 11 forces the follower 15, 64, 80 downwards, the HEA piston 52 opens the valve by forcing down the stem 12 and spring seat 87 against the force of the spring 88, further cam rotation again allowing the valve to close and the replacement of oil which has leaked from the pressure chamber 56. Under warmed-up engine operation, oil flows freely into the inlet passages. However, the riser chamber 38, 74, 86 is made with sufficient cross-section transverse to the direction of oil flow to avoid substantial resistance to cold oil flow and to encourage normal filling of the pressure chamber even under cold starting conditions when the oil is more viscous. The recirculation holes 58 and vent groove 60, if provided, operate to minimize the entry of oil-entrained air into the reservoir 51. In manufacture of a lifter follower as in Figures 1-4, the shell 18 may be cold-formed from a conventional hardenable steel with the oil groove 27 being roll-formed or machined therein as desired. The baffle 19 is preferably moulded of a low-mass polymer plastics material having good dimensional control, thermal expansion stability and chemical resistance. A presently preferred example is Fortron® 6165, a highly glass-reinforced and mineral-filled polyphenylene sulphide (PPS) moulding material available from Hoechst Celanese, Engineering Plastics Division, Summit, New Jersey, U.S.A. The groove 60, if used, may be moulded into the cylinder 32, or the cylinder 32 and groove 60 may be machined for clearance control if desired. Alternatively, the baffle 19 may be made from any suitable material which selected, for example, from among the thermoplastic and thermosetting reinforced and filled engineering plastics materials. Among the needed or desired characteristics of such baffle materials are durability in a lubricating oil environment at temperatures from -40° to 150°C., a coefficient of linear thermal expansion closely matched to the mating metallic components, resistance to lubricating oil contaminants and an ability to be moulded with close tolerance and low warp. After assembly of the baffle 19 into the shell 18, the foam filler is installed as a liquid into the first space 44 through a nozzle inserted into the fill hole 35 in the flange 34. The filler foams and hardens in place, with air escaping from the space 44 through the vent hole 36. Leakage of foam into the second space 48 and the riser chamber 38 may be prevented if necessary by pressurizing these spaces through the inlet hole 43, the bottom of the cylinder 32 being sealed off during the process. However, the joints may be adequately sealed by engagement of the baffle and shell members, possible with the aid of crush edges such as 62 acting as seal means. After hardening, the foam filler has sufficient strength and adhesion to retain the plastics baffle in position within the shell under engine operating conditions. A preferred selection of foam filler material is a modified polyurethane foam provided by System-Chardonol Division of Cook Composites and Polymers Co. (formerly the Freeman Chemical Company) of port Washington, Wisconsin, U.S.A. and having a mix ration of 100 parts by weight Chempol® 030-A944-70 resin to 200 parts by weight Chempol® 030-2416 Isocyanate. At present, a preferred process for assembling the lifter follower includes the following steps: 1. Provide a follower shell and plastics baffle as described above, both of which should be clean and dry. 2. Heat the shell to 66°C (150°F). This helps to assure proper expansion and correct physical and mechanical properties of the cured foam. 3. Assemble the baffle into the shell, orienting the baffle riser chamber with the shell inlet opening. 4. In a fixture, clamp the baffle in the shell and seal the baffle at the shell inner diameter. 5. Mix the two-part foam and inject through the baffle foam fill hole. 6. When foam expansion begins, apply air pressure to baffle interior volume to prevent foam seepage thereinto. 7. Heat the follower assembly with the clamped baffle at 66°C (150°F) until the foam is cured and set. 8. When complete, remove the baffle from the clamping fixture. Manufacture of the Figure 5 embodiment can be essentially as above, whilst the embodiment of Figures 6-8 differs in the previously described use of the lost core 83. Any suitable core material can be used which can be removed after assembly of the lifter follower. Possible examples are oil or water-soluble foam materials, ice, etc. Whilst the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made to the disclosed embodiments within the scope of the following claims.

Claims: A hydraulic valve-lifter comprising a cup-like shell (18;66) with a peripheral outer wall (22;67) substantially parallel to an axis of reciprocation (26) and having a closed end (24) and an open end (23); a separate baffle (19;70;82) received within said shell (18;66), said baffle (19;70;82) including an inner wall (30;71) defining an inner cylinder (32), said inner cylinder (32) being parallel with the axis (26) and spaced within the outer wall (22;67) to define a first space (44) therebetween, and a flange (34) extending outwards from the cylinder (32) towards the outer wall (22;67) to form, at least in part, a floor for said first space (44); inlet means (28,38,43,46,47;74,78;86) for admitting hydraulic fluid through said first space (44) to a second space (48) extending radially within the cylinder (32) and adjacent the closed end (24) of the shell; and filler means (20) filling a substantial portion of said first space (44) to block the entry of hydraulic fluid to the filled portion; characterised in that said filler means (20) comprises a lightweight oil-resistant foam. A hydraulic valve-lifter according to claim 1, in which said foam adheres to both the baffle (19) and the shell (18) to aid in retaining the baffle (19) within the shell. A hydraulic valve-lifter according to claim 1, in which said flange (34) extends outwards to the outer wall (22), and said foam is retained between the baffle (19) and the shell (18). A hydraulic valve-lifter according to claim 1, including seal means (62) sealing a joint between the flange (34) of the baffle (19) and the outer wall (22) of the shell (18). A hydraulic valve-lifter according to claim 4, in which the seal means includes a crush edge (62) comprising a narrow projecting lip on the flange (34), said lip being crushed during assembly of the baffle (19) and the shell (18) to form a tight sealing fit at said joint. A hydraulic valve-lifter according to claim 1, in which said inner wall (30) of the baffle (19) extends axially to the closed end (24) of the shell (18). A hydraulic valve-lifter according to claim 1, in which said inner wall (71) of the baffle (70) includes a lip (72) extending outwards against the closed end (24) of the shell (66). A hydraulic valve-lifter according to claim 1, in which said baffle (19) is formed from a synthetic plastics material. A hydraulic valve-lifter according to claim 8, in which the synthetic plastics material forming the baffle (19) is selected from the group consisting of re-inforced and filled thermoplastic and thermosetting engineering plastics materials. A hydraulic valve-lifter according to claim 1, in which the synthetic plastics material forming the baffle is a mineral/glass-filled polyphenylene sulphide polymer. A hydraulic valve-lifter according to claim 1, in which the foam is a modified polyurethane foam. A hydraulic valve-lifter according to claim 1, in which said inlet means includes an inlet opening (28) through the outer wall (22) intermediate the ends (23,24) thereof, and passage means (38,43,46,47) through said first space (44) and connecting the inlet opening (28) to the second space (48) near the closed end (24) of the shell (18). A hydraulic valve-lifter according to claim 12, in which the passage means includes a riser chamber (38;74;86) extending axially in the first space (44) between the inlet opening (28) and the closed end (24) of the shell (18), the riser chamber (38;74;86) being relatively narrow but of adequate transverse cross-section to avoid substantial resistance to cold oil flow and being connected to the second space (48) near said closed end (24). A hydraulic valve-lifter according to claim 13, in which the riser chamber (86) is formed by a lost core (83) during the formation of the foam filler (20) after which the lost core (83) is removed. A hydraulic valve-lifter according to claim 14, in which a portion of the second space (48) adjacent the closed end (24) of the shell (18) is also formed by the lost core (83).

Inventors: ENGEL DONALD GEORGE, GAUTHIER DANIEL GEORGE, KRIEG JOHN JOSEPH, WARDEN MICHAEL JON, ENGEL, DONALD GEORGE, GAUTHIER, DANIEL GEORGE, KRIEG, JOHN JOSEPH, WARDEN, MICHAEL JON
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: F01L1
IPC codes: F01L1