US3161112A - Speed compensated variable compression ratio piston and valve - Google Patents

Description

1954 w. A. WALLACE ETAL 3,161,112

SPEED COMPENSATED VARIABLE COMPRESSION RATIO PISTON AND VALVE Filed June 26, 1963 FIG. /0 2 .l I e 7 5 e2 32 l l i 34 l o4 we /02 a 92 oo 5::

INVENTORS WILLIAM A. WALLACE 6 THOMAS J. PEARSALL ATTORNEYS tates atent Ofiice 3,161,112 SPEED COMPENSATED VARIABLE COMPRESSION RATEO RlS'llON AND VALVE William A. Wallace, Grosse Pointe Woods, and Thomas .1. Pearsali, Grosse Pointe Farms, Mich, and Wilfred P. Mansfield, 7 Merton Road, Slough, England; said Wallace and said liearsall assignors to Continental Aviation and Engineering Corporation, Detroit, Mich, a

corporation of Virginia Filed June 26, 1963, Ser. No. 290,705 13 Claims. (Cl. 92-82) This invention relates to improvements in pressure regulating valves and pistons, and more particularly to an improved valve for a reciprocating piston of the variable compression ratio (VCR) type disclosed in US. Patents Nos. 2,742,027, dated April 17, 195.6, 3,014,468, dated December 26, 1961, and 3,038,458, dated June 12, 1962, all issued in the name of Wilfred P. Mansfield.

The aforesaid Mansfield patents disclose various forms of VCR pistons which may be employed in the cylinder or cylinders of an internal combustion engine for varying the compression ratio thereof by varying the clearance volume of the cylinder in order to increase the efficiency of the engine and/ or to reduce the weight and structural cost of the engine without a reduction in horsepower in a simple, eflicient and economical manner. It is desirable that a VCR piston operate to limit as uniformly as possible the maximum combustion chamber pressure throughout the speed range of the engine. However, it

has been found that when conventional spring loaded valves are employed to release pressure fluid from the fluid chamber in the VCR piston, the combustion chamber pressure rises above the maximum desired limit as the speed of the engine increases. For example, combustion chamber pressure may rise above a maximum design limit of about 1500 psi. to about 2000 p.-s.i. as engine rpm. increases from about 1200 to 2800 rpm.

One object ofthe present invention is to provide an improved VCR piston which is operable to regulate maximum combustion chamber pressures in a more uniform manner than hitherto obtainable.

Another object is to provide an improved valve for use in a VCR piston which is speed compensated to thereby regulate fluid pressure in the piston chamber in a manner which insures more uniform maintenance of the maximum desired combustion chamber pressure by the piston.

A further object is to provide an improved VCR piston construction which provides compensating pressure fiuid to a valve of the above character to thereby enable the piston to uniformly regulate combustion chamber pressure regardless of engine speed.

Other objects, features and advantages of the present invention will become apparent in the following description taken in conjunction with the accompanying drawing wherein:

trate details of one embodiment of the improved valve of the invention. I

FIG. 3 is a fragmentary horizontal section taken on the line 3-3 of FIG. 1, with a portion broken away,

illustrating one-way supply valves for the upper and lower. I

pressure fluid chambers of the piston.

FIG. 4 is a horizontal sectional view similar to FIG. 2 but illustrating a modified valve of the invention,

Referring to FIG. 1, there is shown by way of example a preferred embodiment of a VCR piston 10 adapted for reciprocation in the bore of each cylinder of a fourstroke cycle internal combustion engine. Piston 10 comprises an outer piston 12 and an inner piston 14, outer piston 12 having a crown 16 which serves as the head of piston 10 and forms the movable wall of the cylinder combustion chamber. Inner piston 14 is slidable within and axially of outer piston 12 and carries rings 20 and 22 which have a fluid sealing engagement with the outer piston. Inner piston 14 is attached in a conventional manner by a wrist pin 24 to the small end 26 of a connecting rod 28.

An upper pressure fluid chamber 30 is formed between the upper surface of inner piston 14 and the interior surface of crown 16. A lower annular pressure fluid chamber 32 is formed by the upper surface of a retaining and sealing ring 34 threadably secured in the skirt of outer piston 12 and by the under surfaces 36 and 38 of pistons 12 and 14 disposed above ring 34. The control of movei merit between outer and inner pistons 12 and 14 is obtained by controlling the flow of an incompressible fluid into and out of upper and lower chambers 30 and 32.

The incompressible pressure fluid preferably comprises oil supplied to the piston from the pressurized lubricating oil supply of the engine viaan oil passage 40 in rod 28. Passage 40 communicates with a crankshaft oil supply passage (not shown) and extends lengthwise of rod 28 to end 26 thereof where it communicates with an outlet 42 via annular groove 44 encircling wrist pin 24. Oil under engine lubricating pressure flows upwardly via passages 40, '44, 42 into a cavity 46 of a seal cap 48 which is urged downwardly by a spring 50 into sliding sealed engagement with the upper end 26 of rod 28. Oil passes through an axial hole 52 in cap 48 into a spring chamber 54 and thence via a passage 55, a supply valve 56 (one-way check-type) and a passage 57 to lower chamber 32. Oil also flows from chamber 54 via a passage 58 past a second one-way supply valve 58a (FIG, 3) and thence via a passage 59 leading upwardly to the upper chamber 30.

Forces tending to move outer piston 12 upwardly relative' to inner piston 14 (as viewed in FIG. 1) increase oil Pressure in lower chamber 32, and hence this movement is controlled so as to occur in small increments over'several cycles by permitting discharge of oil from' lower chamber 32 at a restricted rate. This bleed may take place through an adjustable discharge orifice provided in ring 34 such as that disclosed in the aforesaid Mansfield Patent 2,742,027, or through a clearance provided between ring 34 and the skirt of inner piston 14. Preferably however, oil .is discharged from the lower chamber back up the supply passage 57 through a casing port 57a of valve 56 which leads to the interior of valve 56, port 57a being open at all times. The oil then flows at a predetermined rate from the spring chamber behind valve 56 via a restricted orifice 57b, calculated to provide,

. application of William A. Wallace, co-inventor herein,

and Robert F. Pecha, Ser. No. 290,706, filed June 26, 1963, assigned to the ass-ignee of the present application and entitled Variable Compression Ratio Piston.

Discharge of oil from upper chamber 30 takes place 2 via an outlet passage 60 leading to an improved spring- Patented Dec. 1.5, 1964 loaded, speed compensated pressure regulating valve 62 of the present invention which is mounted in inner piston 14, and thence via a drain passage 64 leading to the underside of inner piston 14 where the oil is free to drain downwardly to the engine crankcase.

The operation of the improved VCR piston as thus far described is similar to that of the VCR pistons disclosed in the aforesaid Mansfield Patent 2,740,027 to which reference may be made for a more detailed explanation of the theory and various uses of VCR pistons. Assuming that combustion chamber pressure is below a predetermined maximum value, as inner piston 14 decelerates in approaching the top dead center position at the end of the exhaust stroke and then accelerates in the opposite direction on the intake stroke, the momentum of outer piston 12 forces it upwardly relative to inner piston 14, causing valve 56 to close and forcing a predetermined amount of oil out of lower chamber 32 via the restricted discharge path 5711-57 This permits outer piston 12 to move a very small distance (in the order of a few thousandths of an inch) upwardly relative to inner piston 14. This in turn increases the volume of, and consequently reduces fluid pressure in, chamber 30 so that a proportionate amount of oil flows from chamber 54 through passage 58, the one-way upper chamber supply valve and passage 59 into upper chamber 30. This added oil is trapped in chamber 30 by the one-way supply valve, and prevents outer piston 12 from moving back downwardly relative to the inner piston until oil pressure in chamber 30 exceeds the predetermined pressure at which outlet valve 62 is set to open against the pressure of its spring. Hence upward relative movement of the outer piston will occur for several cycles until the cylinder clearance voltime has been reduced to the point where combustion chamber pressure reaches a predetermined maximum value which produces said predetermined pressure in chamber 30. Thereafter, a state of relative equilibrium exists wherein the outer piston moves up and down very slightly relative to the inner piston on each cycle, its mean relative position being that producing the maximum combustion chamber pressure as determined by the opening pressure of valve 62. 7

If the combustion chamber pressure is suddenly increased, as by opening the engine throttle or increasing the load on the engine, valve 62 rapidly discharges a correspondingly greater amount of oil from upper chamber 30 so that the outer piston 12 moves dovmwardly a correspondingly greater distance, thereby increasing the cylinder clearance volume and thus returning the maximum cylinder pressure to the predetermined value. Valve 62 is designed to permit outer piston 12 to move downwardly more rapidly than it can move upwardly in each cycle in order to provide more rapid drop to the maximum combustion chamber pressure and to limit oil pumping losses resulting from the relative movement of the inner and outer pistons.

The above operation assumes that the VCR piston is reciprocating at a constant speed. However, as noted previously, it has been found that when a conventional spring loaded pressure regulating valve is used to control pressure in chamber 30, combustion chamber pressure tends to creep above the desired maximum limit as the speed of the piston increases. The present invention overcomes this problem by providing the improved speed complensated relief valve 62 in a novel arrangement in piston 10 which enables it to maintain substantially uniform combustion chamber pressure regardless of engine speed.

As shown in FIG. 2, valve 62 is a self-contained unit enclosed in a valve casing 66 mounted in a blind bore 67 in inner piston 14 with its axis perpendicular to the direction of piston reciprocation and parallel to the axis of wrist pin 24. Outlet passage 60 communicates via a tubular conduit 61 with an axial passage 68 in casing 66 which in turn communicates via an annular chamber 69, radial passages 70 and an external groove 72 in casing 66 with drain passage 64. A valve member 74 slides axially in a bore 75 in casing 66 and a beveled end 76 thereof seats on a conical valve seat 77 in passage 68 to thereby open and close communication between passages 60 and 64. A spherical opposite end 78 of member 74 extends into a counterbore 80 and butts against the end face 82 of a compensating piston 84 which slides axially in counterbore 80. A coil compression spring 86 is also disposed in counterbore 80 and butts at one end against a vented screw plug 88 and at the other against piston 84. A passage 90 in inner piston 14 communicates at one end with the oil chamber 54 and at the other end with an annular external groove 92 of casing 66 which in turn communicates via a series of radial ports 94 with a chamber 96 formed in counterbore 80' by piston 84, the adjacent end of the counterbore and end 78 of the valve member.

The end face 82 of piston 84 has a working area larger than the effective working area of the end 78 of valve member 74, and both areas are constantly exposed to fluid pressure in oil supply chamber 54. Hence, the effective difference in these areas, e.g., the cross-sectional area of piston 84 minus that of member 78, produces a net compensating force on piston 84 opposite to the valveclosing force exerted by spring 86. This compensating force is always less than the spring force and is derived from the velocity-related variation in oil pressure in chamber 54 which occurs as a result of momentum forces exerted on the oil in this chamber by the column of oil contained in connecting rod passages 40, 42 and 44. This mass of oil moving with rod 28 exerts an upward force as inner piston 14 decelerates in approaching top dead center and then accelerates in the opposite direction after passing top dead center. The resulting pressure variation is proportional to the square of engine r.p.m. and is additive to lubricating system pressure which varies directly with engine r.p.m. Hence, valve compensating chamber 96 is supplied with fluid under a pressure which varies with engine r.p.m., increasing at higher speeds and decreasing at lower speeds, as well as with the cyclical variation in the position of piston 10. The latter variation occurs at double the frequency of, but substantially in phase with, the cyclical variation in combustion chamber pressure, both pressures peaking when piston 10 is in the vicinity of top dead center. Since compensating piston 84 provides the force transmitting connection between spring 86 and valve member 74, the fluid pressure acting on face 82 of piston 84 opposes the valve closing force of spring 86, thereby reducing the net force urging member 74 towards seat 77. Hence the force required to open valve member 74 is reduced as engine r.p.m. increases. This compensating action of piston 84 has been found effective to overcome the problem of non-uniform regulation of oil pressure in upper chamber 30 which in turn overcomes the problem of non-uniform regulation of the combustion chamber pressure by the VCR piston.

It is believed that the above speed compensation of valve member 74 permits it to be opened by pressure fluid in passages 60, 68 and in chamber 30 at a lower pressure at high speeds than at low speeds. Hence valve 74 is open for discharging oil from chamber 30 for a longer period of time at high engine speeds than would otherwise be the case. This enables valve 74 to discharge the required volume of oil from chamber 30 for balancing a unit increase in combustion chamber pressure regardless of piston speed. In addition, the speed compensating pressure fluid acting on piston 84 offsets the speed-related variation in force required to open valve 74.

In any event, by providing a compensating member such as piston 84 for developing a force in opposition to the valve closing force which increases with an increase in engine speed and vice-versa, the desired maximum combustion chamber pressure will be maintained by piston 10 at a more uniform value than hitherto obtainable. By obtaining this opposing force from the fluid pressure variations occurring in spring chamber 54, a properly phased and proportioned force is provided in a very simple and economical manner without significantly aflecting the incoming supply of oil for chamber 30.

Referring to FIG. 4, a modified form of pressure regulating valve 100 is shown also in accordance with the present invention. Valve 100 differs from valve 62 in that the compensating member comprises a flange 102 integral with the spring end of a movable valve member 104 which functions in the same manner as valve member 74. The variable fluid pressure in chamber 96 acts on a surface 106 of flange 102 exposed thereto to develop a force in opposition to the force exerted by spring 86 on flange 102, thereby providing a net valve-closing force which varies inversely with engine speed. Although the modified construction simplifies the structure of valve member 104 and compensating member 106 by uniting them, the previously described embodiment of FIG. 2 is preferred. The provision of valve member 74 and compensating piston 84 as two separate parts in simple contacting engagement allows the parts to be axially misaligned without introducing sticking or leakage problems, thereby permitting larger concentricity tolerances between bore 75 and counterbore 80 in casing 66.

Another feature common to both embodiments is the connection of the valve outlet ports '70 to the low (crankcase) pressure drainage passage 64 via the peripheral groove 72 of valve casing 66 at a point spaced from casing groove 2. The pressure drop from ports 70' to passage 64 when valve member 74 is opened is sufficiently low to insure that the high pressure fluid released by valve member '74 flows directly into passage 64 rather than working its way back to groove 92 via the clearance space between casing 66 and bore 67. This clearance Space results from the provision of a slip fit between casing 66 and bore 6'7 to permit assembly of the casing endwise into the bore. This clearance is small enough to restrict leakage of compensating fluid from groove 92 togroove 72 and outlet 64 so that the operation of compensating piston 84 is not impaired. However, the maximumfluid pressure in chamber 54 may be on the order of 200'p.s.i. whereas in chamber 30 it may be 2000 p.s.i., and hence the potential pressure fluid flow from groove 72 to groove 92, rather than in the reverse direction, presents the more serious problem. The provision of low pressure drain 64 adjacent groove 7 2 and the portion of casing 66 intervening between grooves 72 and 92 overcomes the latter problem in a simple manner.

We claim:

1. In an internal combustion engine piston having first and second parts movable relative to one another in response to reciprocation of the piston and a pressure fluid containing chamber within said piston which varies in internal volume in response to said relative movement and to variations in the quantity of pressure fluid therein, the combination therewith of means forming a first fluid flow passage communicating with said chamber, a valve member movable to open and close said first passage for controlling flow of fluid therethrough to thereby vary the quantity of fluid in said chamber, means for yieldably biasing said valve member towards closed position to thereby regulate the pressure of the fluid in said chamber, means forming a second passage communicating with a source of pressure fluid which varies in pressure with the velocity of said piston and compensating means exposed to pressure fluid in said second passage and having an operable connection to said valve member for translating a velocity-related pressure variation in said source into a compensating force acting on said valve member so that it is operable to provide substantially uniform regulation of the fluid pressure in said chamber regardless of the velocity of said piston.

2. The combination set forth in claim 1 including a casing for said valve member and a chamber in said casing communicating with said second passage, said compensating means comprising a piston disposed in said case ing and operable to form a movable wall of said casing chamber and arranged to provide said compensating force.

3. The combination set forth in claim 1 wherein said compensating means comprises a member interposed between said biasing means and'said valve member to provide a force transmitting connection therebetween, said compensating member having a surface exposed to pressure fluid in said second passage for developing said compensating force.

4. The combination set forth in claim 1 including a casing adapted to form a portion of said first passage and to support said valve member therein for said movement thereof, said biasing means comprising a spring member disposed in said casing with one end thereof fixed and the other end operably connected to said valve member for urging it towards closed position, said casing having a chamber communicating with said second passage, said compensating means comprising a member slidably received in said casing chamber and forming a movable wall thereof exposed to pressure fluid therein for developing said compensating force.

5. The combination set forth in claim 4 wherein said compensating member comprises a flange integral with said valve member.

6. The combination set forth in claim 4 wherein said compensating member is disposed between and in abutting contacting relation with said valve and spring members to thereby provide said operable connection as well as the opertaive force transmitting connection between said valve and spring members, said compensating and valve members having their adjacent ends exposed to pressure fluid in said casing chamber, said end of said compensating member having a larger elfective working surface eX- posed to pressure fluid in said casing chamber than said end of said valve member.

7. The combination set forth in claim 1 including a connecting rod operably connected to said piston for converting reciprocating movement thereof into rotary motion in the engine, an oil passage in said rod extending lengthwise thereof for supplying oil from a lubrication system of the engine to said piston, said piston having a fluid supply passage communicating with said connecting rod passage and said piston chamber, said second passage communicating with said supply passage.

8. In combination, means forming a chamber containing pressure fluid subjected to periodic pressure changes of varying frequency, means forming a fluid flow passage communicating with the chamber, a valve member movable in said passage means for opening and closing said fluid flow passage, means biasing said valve member closed and yieldable to permit said valve member to open in response to chamber pressure fluid acting on said valve member, a compensating member having an operable connection-with said valve member for opposing the closing force acting on said valve member, and means for applying force to said compensating member in phase with pressure variations occurring in the chamber and in proportion to the rate of change of pressure therein so that said compensating member is effective to modulate opening and closing movement of said valve member to thereby control flow via said passage of substantially equal pressure regulating increments of said pressure fluid regardless of the rate of change of pressure in the chamher.

9. The combination set forth in claim 8 wherein said biasing means comprises a spring member and said compensating member is interposed between said valve and spring members to provide the biasing connection therebetween.

10. The combination set forth in claim 9 wherein said force applying means includes a fluid pressure chamber associated with said compensating member, one surface of said compensating member engaging said spring and an opposite surface thereof forming a movable wall of said last-mentioned chamber.

11. A fluid pressure regulating valve for a variable compression ratio piston comprising a casing having a fluid flow passage therein adapted for connection to a ratio-controlling pressure fluid chamber of the piston, said casing having a valve seat in said passage, a valve member slidably mounted in said casing for movement axially thereof and having one end adapted to engage said seat for closing said passage, said casing having a bore extending axially from one end thereof towards said valve member, a coil compression spring extending axially within said bore, means for supporting the end of said spring remote from said valve member, piston means movable in said bore and interposed between the adjacent ends of said spring and said valve member for transmitting force between said spring and valve member, said piston means dividing said bore into a chamber for receiving said spring and a fluid pressure chamber, said casing having a second passage communicating with said fluid pressure chamber for supplying pressure fluid thereto to modulate the force transmitted from said spring to said valve member via said piston means.

12. In a variable compression ratio piston having one part adapted for connection to a connecting rod of an engine and a second part movable relative to said first part adapted to serve as a variable boundary of the piston on the side thereof remote from the connecting rod, the combination therewith of means adapted to control said relative movement of said piston parts comprising a high prcs+ sure fluid chamber in said piston, a bore in one of said piston parts, a valve casing fitted in said bore and having a fluid flow passage therein with an inlet and an outlet at the exterior of said casing, a high pressure fluid conduit in said one part connecting said chamber with said passage inlet, a drainage passage in said one part communicating with said bore adjacent said passage outlet and adapted to conduct pressure fluid at low pressure therefrom, a valve member movable in said casing and adapted to open and close said casing passage between said inlet and outlet thereof, means in said casing for biasing said valve member towards closed position, compensating means disposed in said casing between said biasing means and said valve member for transmitting force therebetween, said compensating means cooperating with said casing to define a compensating chamber therein on the side of said compensating means remote from said biasing means, and means for supplying compensating pressure fluid to said casing chamber including a conduit in said one part opening to said bore at a point spaced axially from said passage outlet, said casing having a port communicating with said compensating conduit and said casing chamber.

13. A variable compression rato composite piston comprising outer and inner pistons movable axially relative to one another in response to reciprocation of the composite piston, said outer and inner pistons defining a pressure fluid chamber therebetween which varies in internal volume in response to said relative movement and to variations in the quantity of pressure fluid therein, said composite piston having inlet and outlet fluid flow passages communicating with said chamber, a valve member movable to open and close one of said passages for controlling flow of fluid therethrough to thereby vary the quantity of fluid in said chamber, means for yieldably biasing said valve member towards closed position to thereby regulate the pressure of the fluid in said chamber, said composite piston having a compensating passage communicating with a source of pressure fluid in said composite piston which varies in pressure with the velocity of said composite piston and compensating means exposed to pressure fluid in said compensating passage and having an operable connection to said valve member for translating a velocityrelated pressure variation in said source into a compensating force acting on said valve member so that it is operable to provide substantially uniform regulation of the fluid pressure in said chamber regardless of the velocity of said composite piston.

No references cited.

Claims (1)

1. IN AN INTERNAL COMBUSTION ENGINE PISTON HAVING FIRST AND SECOND PARTS MOVABLE RELATIVE TO ONE ANOTHER IN RESPONSE TO RECIPROCATION OF THE PISTON AND A PRESSURE FLUID CONTAINING CHAMBER WITHIN SAID PISTON WHICH VARIES IN INTERNAL VOLUME IN RESPONSE TO SAID RELATIVE MOVEMENT AND TO VARIATIONS IN THE QUANTITY OF PRESSURE FLUID THEREIN, THE COMBINATION THEREWITH OF MEANS FORMING A FIRST FLUID FLOW PASSAGE COMMUNICATING WITH SAID CHAMBER, A VALVE MEMBER MOVABLE TO OPEN AND CLOSE SAID FIRST PASSAGE FOR CONTROLLING FLOW OF FLUID THERETHROUGH TO THEREBY VARY THE QUANTITY OF FLUID IN SAID CHAMBER, MEANS FOR YIELDABLY BIASING SAID VALVE MEMBER TOWARDS CLOSED POSITION TO THEREBY REGULATE THE PRESSURE OF THE FLUID IN SAID CHAMBER, MEANS FORMING A SECOND PASSAGE COMMUNICATING WITH A SOURCE OF PRESSURE FLUID WHICH VARIES IN PRESSURE WITH THE VELOCITY OF SAID PISTON AND COMPENSATING MEANS EXPOSED TO PRESSURE FLUID IN SAID SECOND PASSAGE AND HAVING AN OPERABLE CONNECTION TO SAID VALVE MEMBER FOR TRANSLATING A VELOCITY-RELATED PRESSURE VARIATION IN SAID SOURCE INTO A COMPENSATING FORCE ACTING ON SAID VALVE MEMBER SO THAT IT IS OPERABLE TO PROVIDE SUBSTANTIALLY UNIFORM REGULATION OF THE FLUID PRESSURE IN SAID CHAMBER REGARDLESS OF THE VELOCITY OF SAID PISTON.

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