US2907310A - Dampening fluid - Google Patents

Description

' Addi-liva Oct. 6, 1959 w. s. GLEl-:soN ErAL ,2,907,310

DAMPENING FLUID Filed sept. 1, 1955 will e Unlted States Patent C i ce f www v Patented Oct. 6, 1959 We have now found that substantially improved results are obtained in hydraulically operated clearance regu- 2 907 310 lators by employing, as the hydraulic fluid, amixture of a di-methyl polysiloxane polymer and an ester type plas- DAMPENING FLUID 5 ticizer, specifically the compound di-Z-ethylhexyl adipate. William S. Gleeson, Euclid, and 'Edward W. Stevens, Spclflcaul" [.he combmzilogfcgt egsltnghglglsl North Madison, Ohio, assignors to Thompson Ramo p0 ymer avmgoa Vlsfosl .y 1 Wooldridge Inc. a corporation of Ohio at 25 C. (77 F.) havmg added thereto at'least 0% by welght, and preferably about 20% `by weight of the .Application September 1, '1955, Serial N0- 532,091 10 compound di-2-ethylhexyl adipate produces a more nearly l uniform viscosity characteristic in the temperature range 1 Clam' (CL 12J 90) from about minus 60 to about 300 F. This temperature range includes and indeed exceeds the normal operating temperature range of an internal combustion engine The present invention deals with improved clearance tappet assembly, regulators, lash adiustors, 0r the like and nds particular A further description of the present invention will applicability t0 ille eld 0f hydraulically Operated aPPeS be made in conjunction with a specic embodiment of the type employed for opening and closing poppet thereof as illustrated in the attached drawings. valves in internal combustion engines. The invention In the drawings; is also directed to an improved hydraulic iluid C-OmpOSiv Figure l is a view in elevation of a complete tappet tion particularly useful in such clearance regulators. mechanism employed with an internal combustion engine Automic clearance regulators, of which valve tappetS poppet valve; and are the best example, are designed to counteract loose- Figure 2 is a longitudinal cross-sectional view ofthe ness or play in a mechanical linkage system whether tappet barrel assembly illustrated in Figure l; these irregularities are caused b-y mechanical diliiculties Figure 3 is a graph comparing leak-down rates with or due to the eiiects of thermal expansion and contracrespect to temperature between a silicon fluid of the prior tion. In the operation of the regulators, it is important art and a dampening tluid according to theV present innot only that the clearance regulator be operative to vention. compensate for looseness in the system, but they must As shown in the drawings; not over control the linkage to produce an undesirable Reference numeral 10 indicates generally the tappet tightness, which, in the case of automatic tappets, would assembly of the present invention whose movement is prevent full seating of the valve during operation. controlled by means of a cam 11, supported on a suit- In order to operate effectively, an automatic tappet able cam shaft 12 of the internal combustion engine. must have substantially the same characteristics, regard- The vertical movement of the elements in the tappet less of the temperature at which it is employed; Thus assembly 10 is transmitted to a poppet valve 13 in the the tappet must be readily operable under low temperaengine block by acting on'the tip 14 of the valve stem ture conditions encountered when starting the engine in 13a. A spring retainer 15 is locked on the valve stem cold weather and should operate eifectively, without sub- 13a to bottom a valve spring 16 surrounding the valve stantial change of characteristics, even under the high stem and compressed between the retainer 15 and thev temperature conditions encountered after prolonged use 40 engine block. in a high speed engine. Thetappet mechanism itself includes a cylindrical To a large extent, the response characteristics of a barrel 17 having an open top and the closed bottom indihydraulically operated tappet are dependent upon the cated at 17a. A relatively light, cylindrical coiled spring type of hydraulic fluid contained within the unit. It is 18 is disposed at the base of the hollow cylinder 17 and particularly important that the uid employed have a exerts a relatively light force on a choke ring 19 which reasonably constant viscosity characteristic along an exhas `a smaller outer diameter than the inner diameter of tended range of temperatlues. This characteristic is dethe barrel 17. The choke ring 19 prefelably has a gensirable in the hydraulic iluid, but is rarely achieved. For crally triangular cross-section so that it provides an inner example, a typical hydraulic fluid presently being emtapering valve seating face 19a along its inner surface. ployed in tappets has a viscosity of `about 950 centistokes Also included within the barrel 17 is an elastomeric at a temperature of about 40 F., but this viscosity falls synethetic rubber cup seal member 21 which engages to a value of less than 200 as the temperature is raised the walls of the barrel 17. The rubber cup member 21 to 200 F; As a result, the operation in the hydraulic has a central bore therethrough which receives the shank tappet may be sluggish at low temperatures or excessively 22a of a valve member 22. The Valve member 22 also fast at high temperatures. has an enlarged head portion formed with a valve seat- We have now found that the viscosity characteristics ingtsurface 22h which is arranged to become seated of the hydraulic fluid can be stabilized, where the fluid in the valve seat surface 19a of the choke ring 19. is a polysiloxane polymer, by the addition thereto of cer- The shank 22a of the valve member 22 is also slidably tain ester type plasticizers and that when such mixtures received within a lower plunger member 24 having an are used in hydraulic tappets, the leak-downtime of the enlarged annular flange portion 24a bottomed against tappet becomes practically constant, at constant load, the upper surface of the rubber cup member 21. irrespective of temperature. An upper plunger member 26 is press fitted or other- Accordingly, an object of the present invention is to wise secured to the top end of the shank 22. The upper provide an improved hydraulically controlled clearance plunger member 26 has a relieved portion 26a which reregulator whose operational characteristics are not varied 55 ceives an elastomeric sealing ring such as a synthetic substantially by extreme changes in temperature. rubber circular seal 28 in sealing relation against the Another object of the invention is to provide a hysurfaces of the barrel 17 so `as to prevent dirt and other draulically operated, automatic tappet' for internal comcontaminants from entering the interior of the tappet bustion engines with an improved type of hydraulic fluid. mechanism.

Still another object of the invention is to provide an improved hydraulic fluid having general utility in various elds of application.

The upper plunger member 26 is also provided with a relieved shoulder portion 26h which serves to provide a means for containing a helical return spring 27 which normally separates the upper plunger member 26 from the llower plunger member 24. The spring 27 is preferably heavier and stiier than the spring 18.

In accordance with the present invention, the bottom portion of the tappet barrel 17, up to the upper cup member 21 is filled with a 'hydraulic uid 25 comprising prferably a vmixture of a methyl polysiloxane polymer having a viscosity in the range from about 100,000 to about 1,000,000 centistokes at 25 C., having dissolved therein from l to 50% by weight and preferably about by weight of the compound di-2-ethylhexyl adipate.

The choke ring 19 and the valve head 22h divide the lower portion of the tappet assembly into a lower pressure compartment A and a storage compartment B about the level of the valve and its valve seat. The return spring 27 bottoms the cup member 2l against the fluid in the compartment B.

In the operation of the tappet mechanism, when the cam 11 is in a position for moving the tappet 10, the load of the valve spring 16 is transmitted to the valve member 22 and through this valve member 22 to the choke ring 19. Since the choke ring rests on the body of hydraulic iluid 25 in the compartment A, the lifting pressure from the tappet barrel will be transmitted through the trapped oil in compartment A to the valve member 22 and finally to the engine valve 13. Some leak-down occurs between the outer periphery of the choke ring 19 and the inner wall of the barrel 17 thereby causing the hydraulic fluid to flow =from compartment A to the storage compartment B. As this leak-down occurs, the tappet valve 22 drops in the barrel, thereby shortening the assembly.

When the cam 11 has moved to a position in which it no longer applies a valve opening load on the valve spring 16, the tappet return spring 27 takes over and expands to force the upper plunger 26 upwardly through the open end of the barrel 17. As this occurs, the valve seating face 22b of the valve element 22 becomes unseated with respect to the valve seating face 19a of the choke ring 19. As the valve element'is opened, the cornpartment A is placed in full fluid communication with the storage compartment B. At the same time, the duid in the compartment B is under the compressive force exerted by the expanding return spring 27 through the lower plunger member 24 and the cup member 21, thereby forcing iluid from compartment B to compartment A. A condition of pressure equilibrium is promptly reached between the two compartments, and the valve seating face 22h will be seated, or very nearly seated, upon the valve seating face 19a of the choke ring 19.

Tests have indicated that the use of the improved hydraulic fluid of the present invention provides a substantially constant leak-down rate, at constant load, over a wide range of temperatures. In this characteristic, the duid differs very radically from the same siloxane polymer when employed in the absence of the diester additive. For example, it was 'found that at a temperature of about 0 F., a tappet assembly employing a polymer without the additive required a leak-down time of about 300 seconds at a given load. The same polysiloxane fluid containing 20% by weight of di-Z-ethylhexyl adipate required a leak-down rate of only about l5 seconds at 0 F. At increases in temperature, the siloxane polymer containing no additive exhibited a very rapid decrease in the leak-down time required, and at a temperature of about 250 F., the leak-down time had been reduced to about 20 seconds. In contrast, the leak-down time for the iluid containing the additive was fairly constant from a temperature of minus 30 to 300 F., and never exceeded aboutseconds, nor fell below 10 seconds.

The results of the tests described above are depicted in graphical form in Figure 3 of the drawings, wherein the curve labelled silicone fluid with 20% additive demonstrates how the fluid of the present invention eX- hibits substantially constant leak-down characteristics throughout a normal operating range of temperature.

Additional tests also indicated clearly that the iluid.

containing the diester additive possesses a viscosity Lstabilityrboth statically and dynamically under load which is not present in the uid without the additive.

The improved behaviour of the fluid under widely varying temperature conditions indicates that the Huid may be employed not only in clearance regulators, but

also in other systems where such characteristics are desirable. Speciiically the uid may b'e employed in lhydraulic systems of hydraulically operated brakes lo'w temperature hydraulic systems, and damping 'or dash p'o'rt type mechanisms.

It should be evident that various modilications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

An automatic clearance regulator for an internal com-v bustion engine comprising first and second relatively movable parts togethery forming a fluid reservoir and having a leak-down passage through which dampening fluid in said reservoir is forced upon relative movement of said first and second parts, and a dampenin'g fluid in said reservoir comprising a di-methyl polysiloxane polymer having a viscosity of at least about 100,000 centi- Stokes at 25 C. and having added thereto in amount of 10% to 50% by Weight the compound di-2-ethylheXyl adipate and said dampening fluid exhibiting substantially constant leak-down characteristics in a temperature range in the order of from about 30 F. to +300 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,570,853 Pierce Oct. 9, 1951 2,570,854 Pierce Oct. 9, 1951 2,583,604 Sirianni et al. Ian. 29, 1952 2,642,395 Currie lune 16, 1953 2,684,336 Moreton July 20, 1954 2,698,837 Gamrath et al. Jan. 4, 19'55 2,742,030 Gleeson Apr. 17, 1956 2,742,031 Tauschek Apr. 17, 1956 FOREIGN PATENTS 502,064 Belgium Apr. 14, 1951

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