Hydraulic lash adjuster

Abstract

 An hydraulic lash adjuster (10) for internal combustion valve gear having a body (12) defining a bore (14) with a plunger (16) slidably received in the bore (14) forming a relatively small volume high pressure hydraulic chamber (27). A valving orifice (38) is provided in the plunger for supplying hydraulic fluid to the chamber (27) upon relaxation of valve event forces and a one-way check ball valve (92) closes the orifice and the hydraulic chamber upon application of valve event forces to the plunger. The check ball has a diameter not greater than 34-1/2% of the plunger diameter, thereby enabling a smaller valve member and smaller chamber for a given body envelope. The smaller hydraulic chamber volume, when filled results in decreased volume of entrained air within the hydraulic fluid retained therein and therefore less shortening of the lash adjuster under valve event forces applied by the engine valve gear. The compactness permits addition of a roller follower without requiring increase in overall tappet size.

Description

BACKGROUND OF THE INVENTION

[0001] In designing valve gear for opening and closing the combustion chamber valves in an internal combustion engine in timed relationship to the combustion events, it is desirable to provide a way or means of compensating for slack or lash in the train of valve gear components. It has been found particularly satisfactory to employ a lash adjustment device which utilizes the change in volume of a hydraulic fluid chamber to provide for changes in length of the hydraulic lash adjustment link in the valve train. Such devices or hydraulic lash adjusters, as they are sometimes called, generally utilize a one-way check valve to permit hydraulic fluid to enter the chamber at the end of a plunger or piston, upon relaxation of the cyclic forces in the valve train, and upon application of the valve gear forces to close thereby trapping the fluid in the chamber thereby maintaining the adjusted length of the hydraulic link.

[0002] In engines having valve gear of the type wherein a movable tappet or follower has one end face thereof frictionally riding against the surface of a rotating cam lobe, considerable power is required to rotate the cam against the tappet surface and to overcome the force imparted by the valve closing spring.

[0003] In an attempt to reduce the valve gear power required for opening and closing the combustion chamber valves, it has been found satisfactory to incorporate a roller in the end of the tappet such that the surface of the roller contacts the rotating cam in rolling engagement rather than the sliding engagement of the tappet end face against the cam lobe. This expedient has been found particularly suitable for redesigning the valve gear of an existing engine configuration in order to increase the efficiency of the existing engine valve gear arrangement. However, where it is desired to add a roller follower' to an existing engine valve gear tappet, it has been found necessary to shorten the length of the plunger and hydraulic portions of the tappet in order to accommodate the roller on the cam end of the tappet. This has proven to be particularly troublesome where it is not feasible to enlarge the tappet or increase the length of the tappet without completely redesigning the valve gear and relocating the cam shaft on the engine.

[0004] Consequently, it has long been desired to find a way or means of providing a hydraulic lash adjusting tappet designed for a particular engine valve gear wherein the lash adjusting component and hydraulic chamber comprise less of the overall-length of the tappet to permit installation of a roller follower on the cam end of the tappet without increasing the overall length of the tappet.

[0005] Examination of Prior Art hydraulic lash adjusting tappets has shown that known hydraulic tappets have minimum envelope requirements as dictated by the ratio of check valve ball diameter to plunger diameter. Measurements of several commercially available hydraulic lash adjusting tappets for production engines as shown in table I and Figure 5 have determined that the Prior Art devices have the ratio of check ball diameter to plunger diameter in excess of 0.3₄5. The relationship of these parameters, as practiced in the known art makes it quite difficult to reduce the tappet size for.any given valve gear force load.

[0006] Additionally, in designing hydraulic lash adjusters for engine valve gear, it is also known that for a given tappet plunger, or piston, diameter, the cyclically applied maximum load of the valve gear train will produce a certain amount of lengthwise or longitudinal compression of the lash adjuster due to air in the hydraulic fluid entrained by circulation through the engine oil pump and galleries. This results in an overall bulk modulus of compression for the hydraulic chamber which is somewhat less than the bulk modulus of compression of the hydraulic fluid as measured in a static condition not having been circulated through the engine pump and oil supply. This lengthwise cyclic compression detracts from the lash-adjusted length of the tappet and is absorbed as lost motion in the valve train. As is known in the art, oil circulated by the engine oil pump contains about 5% by volume of entrained air. See publication "Valve Gear Technical Brief, No. 82-1", W.T. Mihalic, published by Eaton Corporation, Engine Components Division, Eaton Center, 1111 Superior Avenue, Cleveland, Ohio 44114. Thus, it has long been desired to find a way to decrease the amount of tappet plunger displacement due to air in the hydraulic fluid.

SUMMARY OF THE INVENTION

[0007] The present invention provides an hydraulic lash adjuster for the valve gear of an internal combustion engine of the type employing a tappet guided for reciprocating movement in a precision bore in the engine. The lash adjusting tappet of the present invention preferably employs a roller follower mounted on the end thereof for contacting the lobe of the engine cam shaft. The hydraulic lash adjuster of the present invention is of the type intended to be supplied with a continuous supply of pressurized hydraulic fluid and particularly from the engine oil galleries.

[0008] The lash adjuster of the present invention provides a unique construction whereby an existing hydraulic lash adjusting tappet for an engine valve gear having a friction face for contacting the cam lobe may be replaced with a tappet having a roller follower therein without the necessity for redesigning the valve gear to accommodate a larger tappet in order to include the roller follower. In particular, the hydraulic tappet of the present invention employs a reduced volume high pressure chamber for lash adjustment when compared with the tappet design practice heretofore known. The hydraulic tappet of the present invention employs a reduced diameter passage or orifice for supplying oil from the galleries or reservoir to the one-way ball check valve and a for supplying the high pressure chamber. The reduced diameter orifice permits a smaller check valve ball and consequently an axially shorter hydraulic pressure chamber and thus a more compact configuration.

[0009] The tappet of the present invention maintains the diameter of the check valve orifice to a ratio preferably less than 18=1/2% of the diameter of the tappet hydraulic plunger. A tappet made in accordance with the present invention has the ratio "R" of the check ball diameter "_D" to the diameter "Ø" of the hydraulic plunger maintained less than 0.345. The reduced volume of the hydraulic fluid in the high pressure chamber increases the hydraulic stiffness of the tappet, such that, for a given valve gear load on the plunger a reduced amount of compression or shortening of length of the tappet is experienced in operation. The increased hydraulic stiffness, or reduced amount of compression of the tappet under load, is attributed to the reduction in the amount of entrained air within the high pressure hydraulic chamber by virtue of the lower volume of hydraulic fluid containing such entrained air.

[0010] The present invention thus provides a unique hydraulic lash adjuster enabling a compact design in which a roller follower may be employed; and, the hydraulic lash adjusting function of the tappet is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

FIGURE 1 is a side view of the tappet with the plunger shown fully collapsed in solid outline and fully extended in dashed outline;

FIGURE 2 is a view similar to FIGURE 1 with the tappet body and plunger broken away to show the valve and high pressure chamber;

FIGURE 3 is a plot of applied valve gear load F plotted as a function of the plunger diameter Ø;

FIGURE 4 is a plot of the ratio of residual chamber volume V to plunger area as a function of the percent plunger displacement with load F; and

FIGURE 5 is a plot of the ratio of check valve ball diameter D to plunger diameter J6 plotted as a function of the ratio of the residual chamber volume _V to the plunger area.

DETAILED DESCRIPTION

[0012] Referring now to FIGURE 1 and FIGURE 2, the invention tappet is indicated generally at 10 and has a generally cylindrical body 12 with the outer cylinderical periphery thereof formed to precision dimensions for being slidably received in a guide bore in closely fitting relationship as is well known in the art. The body has a blind bore 14 provided in one end thereof in which is received a plunger 16 in precision sliding arrangement. The surfaces of the bore 14 and the cylindrical periphery of the plunger 16 are dimensioned with minimum clearance and tight tolerances to provide a precision fit to maintain a controlled leak-down of the hydraulic fluid in the tappet.

[0013] A collector groove 18 is formed in the outer periphery of the plunger and, if desired, an optional corresponding shallow collector groove 20 may be provided in the wall of the body bore 14. The collector groove 18 is supplied by a passage 22 provided through the wall of the body and communicating with the exterior collector groove 24 provided on the outer periphery of the body.

[0014] The plunger 16 is biased in a direction outwardly of the bore 14, or in a rightward direction in FIGURE 2, by a return spring 26 acting against the end of the plunger and the bottom 28 of the bore 14. The plunger is retained and limited in its outward movement by a suitable cap or spring clip 30 received over the flange 32 provided on the end of the body.

[0015] The plunger 16 has a cavity 32 provided therein with the end thereof sealed by a plunger plug or cap 34 which is retained thereon in a suitable manner as for example by crimping,interference press fit or welding about the periphery thereof. The cap 34 and cavity 32 define a hydraulic fluid reservoir 33. The plunger cap 34 has a suitable orifice 36 provided in the end thereof which communicates with the reservoir 33 for supplying oil to an adjacent valve gear component, as for example, a rocker arm or push rod. The reservoir 33 is supplied by a passageway 36 provided through the wall of the plunger which is fed by communication with the collector grooves 18 and 20.

[0016] The plunger has a fluid passage in the form of an orifice 38 provided in the end thereof which communicates with a counter bore 40 opening to the end of the tappet plunger. The shoulder of the orifice 38 and the bottom of the counter bore 40 form a valve seat. A check ball 42 received over the valve seat and is retained for limited movement therefrom by a cage 44 pressed into counter bore 40. A check ball spring 46 is registered against the underside of the cage and urges the check ball against the seat.

[0017] The bottom and side walls of the body bore 28 and the end of the plunger 16 adjacent thereto thus provide the wall of a high pressure chamber 27 for retaining hydraulic fluid therein to provide the lash adjusting function of the tappet.

[0018] An axle 48 is received transversely through the tappet body in a bore 50 formed therethrough adjacent the cam end of the tappet, and is retained therein by any suitable expedient as for example staking or welding. The body has a clearance recess or cutout 52 provided in the region surrounding the axle in which is received a suitable hardened roller follower 54 journaled over the axle on a suitable bearing arrangement such as the plurality of rollers 56 disposed about the axle.

[0019] In operation, it will be understood that the tappet is received in a suitable guide bore in the engine and supplied with oil through a gallery communicating with passage 22. The oil passes directly through passage 36 and into the reservoir 33 for supplying the check valve 42 and supplying the other valve gear component through orifice 36. The roller follower 54 is in contact with the surface of a cam lobe (not shown) and the end of plug 34 contacts associated valve gear components (not shown) for transmitting the cyclically applied forces of the cam lobe opening and closing of the combustion chamber valves in the engine.

[0020] As the roller follower is lifted by the cam lobe and the axial force increases on the plunger, the plunger is compressed in the bore 14 and relatively high pressure is created in the hydraulic fluid trapped in the chamber 27 by the closing of check ball 42. Any further appreciable displacement of the plunger with respect to the body, or shortening of the overall tappet length, is prevented by the bulr stiffness of the hydraulic fluid in the high pressure chamber. As the cam shaft is rotated and relaxes the load on the roller follower, the return spring 26 causes the plunger to displace a small amount rightwardly with respect to Fig. 2 to take up any lash in the valve gear. This small displacement of the plunger draws open check ball 42 and additional fluid enters the high pressure chamber to accommodate the extension of the plunger for lash adjustment. This manner of operation of a hydraulic lash adjuster is well known in the art and in this regard the tappet of the present invention is typical of such devices.

[0021] An important aspect of the invention will now be described with reference to TABLE I below wherein the diameter of the orifice 38 is denoted "d", the diameter of the plunger 16 denoted Ø, the check ball diameter denoted "D", and the corresponding ratio D/Ø is denoted "R". Values of these parameters as measured from production samples are listed for various commercially available Prior Art tappets denoted A through G; and, the corresponding values for a tappet made in accordance with the teachings of the present invention are also listed.

[0022] One embodiment of a tappet employing the teachings of the present invention employs a diameter for check ball orifice 38 of 0.11" (2.8 mm), a plunger diameter of 0.615" (15.6 mm), a check ball 42 having a diameter of 0.156 inches (3.95mm) which provides a D/Ø ratio "R" equal 0.254.

[0023] It will be noted from TABLE I that all of the commercially available tappets, for which measurements were taken to compile TABLE I, have a ratio "R" substantially in excess of that of the tappet of the present invention the lowest ratio R for prior art tappets being 0.345. This unique ratio "R" aspect of the invention permits the use of a smaller check ball and lower cage height; and, therefore a reduced axial length of the high pressure chamber which in turn reduces the volume of hydraulic fluid therein and the amount of entrained air in the high pressure chamber. The reduced amount of entrained air in the high pressure chamber in turn reduces the amount of displacement of the plunger when the check ball is closed and therefore increases the stiffness of the tappet in response to axially applied valve gear loads. Thus it will be seen that reducing the volume of the high pressure chamber results in a corresponding reduction in the amount of entrained air and increased stiffness of the hydraulic lash adjuster.

[0024] Referring now to FIGURE 3, for a given valve gear applied load F, and assuming a 40 psi hydraulic fluid supply pressure to passage 22 (see Fig. 2) and a 1200 psi maximum in the high pressure chamber, the diameter Ø of the plunger is found from the graph directly. Having determined the plunger diameter Ø, the residual hydraulic chamber volume V may be determined with reference to Fig. 4. It will be understood that the residual hydraulic chamber volume _V (in3) is the volume of the hydraulic chamber 27 with the plunger 16 "bottomed out" or in the furthest leftward displaced position, as shown in solid outline in Fig. 2 for the plunger end plug 34.

[0025] With the plunger diameter Ø known, the graph in FIGURE 4 is entered for a known permissible amount of plunger displacement, or tolerable lost motion in the valve gear, to determine the value of the ratio of the residual high pressure chamber volume V. With the ratio V/ TT/4 Ø 2 high pressure chamber volume V to plunger area known, the residual chamber volume V is readily computed. Having determined residual chamber volume V, the dimensions of the parts of the tappet are established to provide the desired value V, by suitable procedures, as will be known to those skilled in the art with the understanding that the tappet plunger diameter is fixed at the value of Ø as already determined by the above described procedure.

[0026] With reference to Fig. 5, having determined the residual chamber volume V and the plunger diameter Ø, the ratio R of the check ball diameter D, to plunger diameter Ø is obtained by entering the lower plot line of the graph at the appropriate value of V/ π/4 ز. It will be noted that the lower plot line labelled "present invention" in Fig. 5 is essentially linear, where the value of "R" can be expressed as R=3.₂2 (V/π/_µØ²)+.112. The lowest plotted point on the plot line of Fig. 5 represents the values for the present tappet form from Table I. It will be seen that the Prior Art tappets, as shown by the upper line faired through the points plotted and identified for the tappets measured to compile Table I, that the Prior Art tappets have a value of R substantially greater than tappets made in accordance with the present invention. This will be understood to mean that for a given ratio of V/π/₄ ø2 a larger ball diameter.has been used; and, therefore, the tappets have required a greater overall physical envelope. In other words, tappets made in accordance with the prior art teachings could not be made as small as tappets made in accordance with the present invention.

[0027] It will be seen from the foregoing procedure that if ratio of "R" is in excess of the teachings of the present invention it will be virtually impossible to reduce the size of the tappet for a given valve gear load application and still provide a tappt capable of providing satisfactory lash adjustment.

[0028] Thus the present invention provides a unique hydraulic lash adjusting tappet having a reduced volume high pressure hydraulic fluid chamber for lash adjustment which permits the tappet to have a foreshortened and compact envelope. Furthermore, tappets made in accordance with the present inventions exhibit an increased longitudinal stiffness and resistance to compression under applied forces from the adjacent engine valve gear components. The present invention provides this improved lash adjustment function by the unique and novel and structural arrangement wherein the ratio of the diameter of the check valve ball diameter to the hydraulic plunger diameter is maintained less than 0.345. The reduced diameter orifice permits a smaller check valve ball to be employed and thus further improves the compactness of the tappet. The compactness is particularly important where it is desired to replace an existing friction faced tappet with a tappet having a roller follower without increasing the envelope of the tappet.

[0029] Although the invention has hereinabove been described with respect to the illustrated embodiment, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.

Claims

1. An hydraulic lash adjuster for use in the valve gear of an internal combustion engine comprising:

(a) body means defining a force input surface at one end thereof adapted for receiving cyclically applied valve event forces from the engine valve gear and defining a blind bore therein extending generally in the direction of the applied forces;

(b) plunger means slidably received in said bore and defining in cooperation with said bore a hydraulic pressure chamber, said plunger means defining a reaction surface adapted for transmitting said valve event forces, said plunger means including an orifice communicating with said chamber and including one-way valve means comprising a check ball operative to permit fluid to flow into said chamber upon relaxation of said valve event forces and operative to close said chamber upon application of said valve event forces;

(c) said plunger means and said check ball, the ratio R of the diameter of said check ball to the diameter of said plunger less than 0.345 for any given level of valve event force; and

(d) means defining an oil supply passage to said one-way valve means.

2. The lash adjuster defined in Claim 1, wherein the ratio of the valve event design force to the transverse section area of said plunger means in said bore is not greater than 1200 for a given design valve gear force.

3. The lash adjuster described in Claim 1 (1) wherein said force input surface comprises the surface of a roller rotatably received on one end of said body means.

4. The method of lash adjustment in the valve gear of an internal combustion engine of the type subjected to cyclic maximum valve event forces and supplied with hydraulic fluid comprising the steps of:

(a) providing an hydraulic link in the force transmission train of the valve gear;

(b) providing a movable plunger in said link forming an hydraulic chamber and providing supply orifice for said chamber with a check ball valve for said orifice;

(c) sizing said plunger to have the hydraulic piston area thereof not less than one twelve hundredth (1/1200) the value of the design valve gear force of said valve gear train: and

(d) sizing said ball to have the diameter thereof not greater than 34-1/2 percent (%) of the diameter of said plunger.

Drawing