Apparatus for operating engine valve

Abstract: A camshaft (18) has, for each valve lifter (32), a high-lift cam (26) between two low-lift cams (24), the high-lift cam (26) fitting within the envelope of the low-lift cams (24). The lifter (32) comprises an outer tappet (36) elongated in the direction of the camshaft (18) and slidably mounted in an elongated bore (30) in a cam carrier (10). The outer tappet (36) is contacted by both low-lift cams (24) and operates two valves (40) simultaneously. An elongated bore (54) extending transverse of the outer tappet (36) carries an elongated inner tappet (38) which is contacted by the high-lift cam (26). A hydraulically actuated locking mechanism (74) couples the tappets (36,38) for movement together for high-lift operation and unlocks for low-lift operation to allow the inner tappet (38) to idle in the outer tappet (36).

Description: This invention relates to apparatus for operating one or more valves in an internal combustion engine. The intake and exhaust valves of an engine ideally are operated by cams and return springs to open at the right time and for a correct amount and duration to achieve the desired engine operation. Since the optimum cam profile for one engine condition, eg low speed, is usually very different to the optimum profile for other conditions, eg high speed, various arrangements have been proposed to vary the valve opening as a function of the engine speed, load, or other parameters. One such prior art proposal is to employ separate low-lift and high-lift cams with separate lifters, each lifter being independently mounted in a carrier block and acting on an individual valve. In particular, two low-lift tappets, one on either side of a single high-lift tappet, operates each of two valves independently. The low-lift tappets would always be operatively coupled to the valves while the high-lift tappets would just idle during low speed operation. For high speed conditions, a locking mechanism couples the low- and high-lift tappets such that the action of the high-lift cam overrides the low-lift cams to control the low-lift tappet and the valves for movement together. The locking mechanism comprises pins in the low-lift tappets which must slide into holes in the high-lift tappet, thereby requiring tight tolerances in the three cooperating tappets. Further, tight tolerance requirements apply to the cam carrier which must have accurately positioned bores for each of the three tappets. Prior art in accordance with the preamble of claim 1 is disclosed in EP-A-0265282. The present invention seeks to provide improved apparatus for operating a valve of an engine. Apparatus in accordance with the present invention is characterised over EP-A-0265282 by the features specified in the characterising portion of claim 1. In a practical embodiment, there is provided a valve operating mechanism for two-step lifter operation comprising carrier means for movably holding a valve lifter; a camshaft supported by the carrier and including high-lift and low-lift cam means; and a two-step valve lifter supported by the carrier for selective operation by the high-lift cam means and the low-lift cam means; the lifter including a first lifter element mounted for reciprocating movement on the carrier means for engagement by the low-lift cam means, a bore in the first lifter element, a second lifter element mounted in the bore for reciprocating movement in the bore and for engagement by the high-lift cam means, and locking means for selectively locking the second lifter element to the first lifter element, whereby when the locking means is in a locked condition the first lifter element is controlled by the high-lift cam means, and when the locking means is in an unlocked condition the first lifter element is controlled by the low-lift cam means. The invention can provide a two-step cam arrangement having only two tappets for each set of cams, in which only one of the tappets is slidably supported by a cam carrier. It can also provide a lifter assembly having two tappets in which the tappets can be locked together without sliding a pin into a hole. It may also provide a camshaft configuration for a two-step cam arrangement which is easily machined with accuracy. The invention can also provide ease of manufacture of the carrier and the lifter with accurate tolerances, improved synchronous valve operation due to a single lifter operating two valves, improved lash adjustment capability for a two-step lifter, and improved locking of high-lift and low-lift tappets. The present invention will now be described, by way of illustration only, with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional side view of the front portion of a cam carrier and cover including a camshaft and valve lifter; Figure 2 is a plan view of the assembly of Figure 1 with the camshaft and cover removed; Figure 3 is an isometric view of the lifter of Figure 1 and valves; Figures 4 and 5 are cross-sectional side and end views, respectively, of the lifter of Figure 3; Figure 6 is a bottom view of the lifter of Figure 3; Figure 7 is a cross-sectional end view of the assembly of Figure 1; Figure 8 is a cross-sectional side view of a valve lifter according to a first embodiment of the invention which replaces the lifter of Figures 1 to 7; Figures 9 to 11 are cross-sectional end views of the lifter of Figure 8 for valve-closed, low-lift valve-open, and high-lift valve-open conditions of the lifter; and Figure 12 is a partial cross-sectional view of a camshaft, valve lifter, valves and engine head according to a second embodiment of the invention. The ensuing description is directed to a valve operating mechanism especially designed for an overhead camshaft engine having four valves per cylinder, the intake valves operating in unison and the exhaust valves likewise operating in unison, each pair of valves being actuated by a single lifter. A set of two low-lift cams and one high-lift cam, operating on the lifter, actuate either the intake valves or the exhaust valves. It will be apparent that the embodiments described are not limited to that specific application. For example, the lifter could be used to operate a single valve for two-step valve control in an engine having two valves per cylinder. Also, they could be adapted to cam-in-head engines and to cam-in-block engines with push rods, for example. Referring to Figures 1 and 2 of the drawings, a camshaft carrier 10 supported on a cylinder head, not shown, has an upper side 12 closed by a cover 14. Together, the carrier 10 and cover 14 enclose a camshaft compartment 16 sealed at the joint by suitable means and containing an overhead camshaft 18. The camshaft is rotatably supported on webs 20, 22 of the carrier 12 and cover 14 respectively. Camshaft bearings, not shown, may be formed by machined portion of the webs or, if desired, could comprise separate inserts. Camshaft 18 includes a plurality of low-lift cams 24 and high-lift cams 26. The low-lift cams 24 are arranged in pairs on opposite sides of the high-lift cams 26. Beneath each set of cams 24, 26, the carrier 10 contains an elongated bore 28 having semi-cylindrical ends 30 and its major axis extending parallel to the camshaft 18. The semi-cylindrical ends preferably subtend an arc greater than 180 degrees. Between the ends 30, the bore has a midsection 31 which joins each end 30 at a waisted portion thereof and curves outwardly in a cylindrical surface to become larger in the centre 34, having a width comparable to or larger than the diameter of the ends 30. A valve lifter 32 resides in the bore 28 and can be slideably moved therein in reciprocating manner. As shown in Figure 3, the valve lifter 32 comprises two lift elements or tappets: an outer tappet 36 which is operably engaged at its upper end by the cams 24, and an inner tappet 38 which is operably engaged at its upper surface by the cam 26. The bottom of the outer tappet 36 bears against the stems of a pair of valves 40. The outer tappet 36 is elongated to fit lengthwise in the bore 28 (that is substantially parallel to the camshaft) and has semi-cylindrical ends 42 which slidably fit against the ends 30 of the bore 28. The mid-section 44 of the tappet 36 is shaped somewhat like the mid-section 31 of the bore 28 but is sufficiently smaller to ensure that there is a spacing between mid-sections of the bore 28 and the tappet 36, as can be clearly seen in Figure 2. Thus, the only contact between the bore 28 and the outer tappet 36 is at the semi-cylindrical ends 30 and 42 which are readily fabricated to the correct tolerance. The resulting half-cylinder bearing surfaces are able to take lateral thrust in any direction to assure a stable operation. The lateral forces imposed by cam action on the tappet 36 are taken up by side thrust on both ends of the spaced bearing surfaces. Since the bore 28 and tappet 36 are elongated, the tappet 36 is held against rotation. Further, since all the major surfaces are cylindrical, machining or other fabrication of the bore 28 is simplified. Figures 4, 5 and 6 show the outer tappet 36 with top 46 supporting a depending skirt 48 which extends around the periphery of the upper surface 46 of the tappet 36. An elongated bore 50 in the centre of the tappet 36 formed by a bore wall portion 51 has its major axis extending perpendicularly to the axis of the camshaft. The bore 50 has semi-cylindrical ends 52 connected by planar sides 54. The inner tappet 38 has the same shape as the bore 50 and fits slidably within the bore 50. The tappet 38 has a top 56 and sidewalls 58 which engage the bore 50. A sheet metal spring retainer 60 is secured across the bottom of the bore 50 by being welded to the bottom of bore wall 51, for example, or by use of corner tabs (not shown) which are bent over a rib on the wall 51. The retainer 60 has a central aperture 62 surrounded by an upturned flange 64. A coil spring 66 within the tappet 38 fits over the flange 64 and sits against the retainer 60 at one end and bears against the tappet top 56 at the other end so as to bias the tappet 38 upwardly against the cam 26. In the absence of a locking mechanism, to be described, the inner tappet 38 is thus free to reciprocate in the bore 50 under action of the high-lift cam 26. To selectively lock the inner and outer tappets together, a lock arrangement is provided which comprises a pair of cylindrical recesses 68 formed within the tappet 36 and extending from the bore wall portion 51 to the respective end walls 42. The recesses 68 each have a stepped bore providing a shoulder 70 and a reduced diameter portion 72 at the inner end of the recess. A locking pin 74 slidably located in each recess 68 has a body portion which slidably fits in the reduced diameter portion 72 and a head 76 which slidably fits in the outer end of its associated recess 68. A coil spring 78 disposed around the body of the pin 74 bears against the shoulder 70 and the head 76 to bias the pin outwardly. An annular stopper 80 at the outer end of each recess 68 limits the travel of the pin 74 out of the recess 68 to retain the pin in the recess 68. The outer end of each recess terminates in a vertically oblong oil passage 82 in the end 42 of the outer tappet 36 which communicates with an oil gallery in the carrier 10 to be described. The side walls 58 of the inner tappet 38 are shaped to form saddle-shaped stops 84. The stops 84 are located above the recesses 68 when the tappet 38 is in its upper position marginally to clear the pins 74 when the pins 74 are extended into the inner tappet 38. When the pins 78 are extended by application of oil pressure to passage 82, the stops 84 engage the pins 74 so that the inner tappet is no longer able to reciprocate in the bore 50 and the outer tappet 36 is locked to the inner tappet 38 for movement together under action of the high-lift cam 26. As shown in Figure 5, the circular portion 86 of the high-lift cam 26 is smaller than the circular portions 88 of the low-lift cams 24 and the profile of the high-lift cam 26 fits within the profiles of the two low-lift cams 24. This provides a distinct manufacturing advantage since it is desirable that the two low-lift cams 24 be the same and they can be ground at the same time for improved accuracy without interfering with the high-lift cam 26. Since the circular portion 86 is smaller than the circular portion 88, the tappet 38 sits above the tappet 36 when both are in contact with the circular portion of their cam 24, 26. Wear pads 90, 92 are set in recesses in the tops of the low-lift and high-lift tappets 36, 38. The cams slidably contact the wear pads which are preferably alloys for optimum wear. The pad 92 is also useful for lash compensation for the high-lift tappet 38. The compensation is effected by selecting a pad thickness which is sufficient to take up undesired clearance. Of course, the wear pads 90 could be selected for lash compensation in the low-lift cams, but it is preferred to use lash caps 94 which are inserted between the bottom of the tappet 36 and the tops of the valves 40, the caps being of a size adapted to compensate for the low-lift lash. Each lash cap 94 is a cylindrical element with a recess 96 in its lower surface for receiving the upper end of a valve stem. The lash caps are not secured to the lifter 32 but are shown in Figure 4 to illustrate the location of the caps when the valve train is assembled. It can thus be seen that the caps are equally spaced from the ends 42 of the outer tappet 36 and outboard of the bore 50. Thus, the forces on the lifter 32 tend to be balanced. The valves 40 are spaced equidistantly from the centre of the lifter 32. The cam force is delivered either by the high-lift cam 26 at the centre of the lifter 32 or by the two low-lift cams 24 equidistant from the centre. Referring to Figures 1, 2 and 7, an oil passage 100 in the carrier 10 is supplied continuously with pressurized engine oil to lubricate the camshaft bearings. A second oil passage 102 in the carrier 10 feeds oil to the passages 82 in the outer tappet 36 for lubricating the locking mechanism 74. The oil pressure from the passage 100 is admitted by a solenoid controlled valve 104 to the passage 102 when the solenoid is energized. In the deenergized state, the valve 104 isolates the passage 100 from passage 102 and relieves oil pressure from the passage 102 to a drain 106. The main extent of the oil passage 102 is lower than the drain 106 to prevent draining excess oil from that passage, thereby keeping the passage filled and ready for rapid application of pressure when the solenoid valve 104 is energized. Thus, energizing valve 104 causes oil pressure to advance the locking pins 74 into the inner tappet 38 beneath the saddle-like stops 84 when both tappets are in contact with the circular portions of their respective cams. Since the profile of the high-lift cam 26 provides a higher lift than that of the low-lift cams 24, the high-lift cam 26 will control the movement of both the outer and inner tappets 36, 38 to obtain maximum opening of the valves 40, as shown in Figure 1. Deenergising the valve 104 relieves the pressure, allowing the springs 78 to retract the pins 74 from the stops 84 when the tappets are in contact with the circular portions of their respective cams 26, to unlock the tappets so that only the low-lift cams 24 are then effective to move the outer tappet 36 and the valves 40. When unlocked, the inner tappet 38 still moves in response to the high-lift cam 26 but it merely idles in the bore 50 and has no effect on the outer tappet 36. Regardless of the cam angle at which the valve is actuated, the actual switching between high and low-lift occurs only when the tappets are in engagement with their respective circular portions, thereby avoiding sudden impacts or changes in velocity of valve train components which can produce unacceptable noise and wear of components. A similar tappet arrangement but with a locking mechanism in accordance with the present invention is shown in Figures 8-11. The outer tappet configuration is the same as described above and includes the wear pads 90, 92 to contact the cams. The outer tappet 110 has a web 112 across the tappet body near its bottom and a central aperture 114 in the web which retains the lower end of a cylindrical sleeve 116. The upper end of the sleeve 116 extends into the inner tappet 118. The sleeve 116 has a closed lower end and an oil passage 120 in the lower end which is coupled through radial ports 122 to oil passages 124 in the web 112 which passages extend to the ends of the tappet 110 (best seen in Figure 8). A spool 126 which is axially slidable in the sleeve 116 has an inner stem 127, a radially extending upper flange 128 extending across the sleeve bore and a lower head 130 extending across the sleeve bore, the lower head having an upper ramp surface 132 sloping towards the stem 127. Lateral apertures 134 (one shown) are located in the sleeve 116 opposite the stem 127 when the spool 126 is in its lower position in the sleeve 116. A ball 136 partially fits in each aperture, the diameter of the ball being greater than the thickness of the sleeve 116 such that the ball 136 may partially reside adjacent the stem 127 between the upper flange 128 and the ramp-surface 132. A coil spring 138 compressed between the top of the spool 126 and the inner surface of the top of the inner tappet 118 biases the spool to its lower position. An outer sleeve 140 slidably surrounding the sleeve 116 in telescoping manner is urged against the top of the inner tappet 118 by a coil spring 142 which is seated on the web 112. When the inner tappet 118 is in contact with the circular portion of the high-lift cam 26, the lower end of the sleeve 140 terminates just below the centreline of the aperture 134 in the sleeve 116 and contains at the end an internal annular relieved portion which slopes upward and inward to form a pocket 144 adapted partially to receive the balls 136 when the balls are pushed out of the sleeve 116 (best seen in Figure 1). In operation, when no oil pressure is applied to the passage 124, the spool 126 remains in its lower position and the balls 136 remain in the confines of the sleeve 116 or are pushed in by the sloping wall of the pocket 144. Then, as the high-lift cam 26 pushes down on the inner tappet 118, the outer sleeve 140 becomes free to telescope over the inner sleeve 116 as shown in Figure 10 and the motion of the tappet 110 is controlled by the low-lift cam. When, however, oil pressure is applied to the passage 124 and into the passage 120, the spool is pushed by the pressure upwardly in the sleeve 116 and the ramp surface 132 pushes the balls 136 out of the inner sleeve 116 and partially into the pocket 144 (assuming the circular portions of the cams 24, 26 are in contact with their respective pad 90, 92). Then, the balls engage both the aperture 134 of the inner sleeve 116 and the pocket 144 of the outer sleeve 140 to lock the sleeve and aperture together, thus to lock the tappets 110,118 together, as is shown in Figure 11. In that case, the outer tappet 110 will move under control of the high-lift cam. Figure 12 shows a lifter 150 employing essentially the same locking mechanism as described above for Figures 8 - 11 but having other features of interest. The outer tappet 152, rather than being contained in a bore of the cam carrier, is supported for vertical movement on two posts 154 extending from the head 156 and sliding in vertical bores 158 near either end of the tappet 152. The posts 154 are located outboard of the valves 40, which engage the bottom of the outer tappet 152. Valve springs 40' provide the force to urge the lifter 150 against the cams 24' and 26' of the camshaft 18. In this version, part of the high-lift cam 26' extends beyond the envelope of the low-lift cams 24'. Roller followers 160 are mounted on the outer tappet 152 and the inner tappet 162, instead of wear pads, for low friction contact with the cams. The inner tappet 162 comprises an outer sleeve 164 reciprocably slidable in a bore 166 of the outer tappet 152. Roller follower 160 is mounted near the top of the sleeve 164 by means of a roller axle 168 which extends through holes 170 in the sleeve to a compression spring 172 which pushes on the axle to urge the tappet 162 against the cam 26'. The spring 172 is contained in an annular groove 174 surrounding the bore 166 in the outer tappet 152. The locking mechanism is similar to that of Figure 8. A web 176 extends across the sleeve interior to provide a spring seat for spring 138 which depresses spool 126 against the bottom of an inner sleeve 116'. The lower end of the outer sleeve 164 has a pocket 144 which can partially receive balls 136 which partially reside in an aperture in the sleeve 164. A hole 178 in the bottom of the sleeve 116' communicates with oil passages 180 which extend through the tappet 152 to the bores 158. Each post 154 contains an oil passage 182 which connects to an oil gallery (not shown) in the head 156. When oil pressure is applied the spool 126 moves up to force the balls partially into the pocket 144 thereby to lock the outer sleeve against movement relative to the outer tappet so that the high-lift cam 26' controls the lifter movement. When oil pressure is removed, the balls return to the inner sleeve 116' to allow free reciprocation of the inner tappet 162 within the outer tappet 152.

Claims: Apparatus for operating one or more valves in an internal combustion engine comprising a camshaft (18) including first and second cam means (24,26); a two-step valve lifter assembly (32) supported adjacent the camshaft by a support (10) and selectively operable by the first and second cam means (24,26); the valve lifter assembly being coupled to one or more valves and including a first lifter element (110) movable by one of the first and second cam means so as to slide reciprocably on the support, and a second lifter element (118) reciprocably movable by the other of the first and second cam means, wherein the first cam means (24) is adapted to provide a first, relatively smaller lift of the valve or valves, and the second cam means (26) is adapted to provide a second, relatively greater lift of the valve or valves; and mechanical locking means adapted selectively to lock the second lifter element (118) to the first lifter element (110), whereby when the locking means is in a locked condition the first and second lifter elements are movable by the second cam means (26), and when the locking means is in an unlocked condition one of the first and second lifter elements is movable by the first cam means (24); the switching of the locking means between the locked and the unlocked conditions causing a change in the extent of lift of the valve or valves and a change in engine operation; characterised in that the second valve lifter element (118) is reciprocably movable in a bore of the first valve lifter element (110) and in that the mechanical locking means includes an actuator (126) slidable in one of the first and second lifter elements and a ball (136) movable by the actuator (126) into engagement between the first and second lifter elements to lock the second lifter element (118) to the first lifter element (110). Apparatus according to claim 1, wherein the locking means includes a first sleeve (140) movable with the second lifter element (118); a second sleeve (116) secured to the first lifter element (110) and telescopically slidable within the first sleeve, the second sleeve (116) comprising an aperture (134), the first sleeve (140) comprising a pocket (144) adapted to be aligned with the aperture (134) when the first and second lifter elements (110,118) are in abutment with the circular portions or with circular portions of their respective cam means; the ball (136) being capable of residing partially within the aperture, the actuator (126) being disposed within the second sleeve and operative to move the ball into the pocket to lock the first and second sleeves together, thereby locking the second lifter element to the first element. Apparatus according to claim 2, wherein the actuator (126) comprises a spool axially slidable in the second sleeve (116) which is biased towards an unlocked position in which the first and second sleeves are unlocked and is hydraulically movable to a locked position in which the first and second sleeves are locked together, and comprises a recess for partially receiving the ball and a surface (132) adapted to slope towards the pocket (144) so as to urge the ball into the pocket on movement of the spool to the locked position. Apparatus according to any preceding claim, wherein the first lifter element (110) is adapted to be moved by the first cam means (24) and the second lifter element (118) is adapted to be moved by the second cam means (26). Apparatus according to any preceding claim, wherein the first lifter element (110) has an oblong shape and comprises spaced cam contact portions (90) disposed on opposite sides of the first lifter element relative to the bore; the second cam means (26) comprises a single second cam (26) adapted to abut the second lifter element (118); and the first cam means (24) comprises a pair of first cams (24) disposed on respective sides of the second cam and adapted to abut the cam contact portions of the first lifter element. Apparatus according to claim 5, wherein the profile of each of the first cams (24) comprises a first circular portion, the profile of the second cam being disposed within the profile of the first cam and comprising a second circular portion having a smaller diameter than the first circular portion of the first cams; wherein, when the first and second lifter elements are in contact with the circular portions of their respective cams, the second lifter element extends beyond the contact portions of the first lifter element. Apparatus according to claim 6, wherein the second lifter element (118) comprises a cam contact portion (92) extending beyond the contact portions (90) of the first lifter element when the first and second lifter elements are in contact with the circular portions of their respective cams. Apparatus according to any preceding claim, wherein the second lifter element comprises lash adjusting means for adjusting lash comprising a wear pad on the surface of the second lifter element for abutment with the second cam means, the thickness of the wear pad being selected to compensate for lash. Apparatus according to any preceding claim, wherein the first lifter element (110) has an oblong shape, the support (10) comprising an oblong aperture (31) within which the first lifter element is slidably received; the bore of the first lifter element (36) having an oblong shape, the longitudinal axis thereof being substantially perpendicular to the longitudinal axis of the first lifter element; the second lifter element being oblong in shape.

Inventors: CARROLL MICHAEL EDWARD MC, CASTELLANA JOHN, GIANNONE GUY ERNEST, KUNZ TIMOTHY WILTON, SHOST MARK ANTHONY, SPATH MARK JAMES, CARROLL, MICHAEL EDWARD MC, CASTELLANA, JOHN, GIANNONE, GUY ERNEST, KUNZ, TIMOTHY WILTON, SHOST, MARK ANTHONY, SPATH, MARK JAMES
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1991
Main classification: F01L1
IPC codes: F01L13, F01L1