US2897804A

US2897804A - Means to vary the compression ratio of an internal combustion engine during operation

Info

Publication number: US2897804A
Application number: US709048A
Authority: US
Inventors: William R Crooks
Original assignee: Cooper Bessemer Corp
Current assignee: Cooper Bessemer Corp
Priority date: 1958-01-15
Filing date: 1958-01-15
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04

Description

Filed Jan. 15, 1958 Aug. 4, 1959 w. R. CROOKS 2,897,804 MEANS TO VARY OMPRESSION I O OF INTERNAL COMBU ENGINE DURI OPERA N 3 Sheets-Sheet l Aug. 4, 1959 w. R. CROOKS 2,897,304

MEANS TO VARY THE COMPRESSION RATIO OF AN INTERNAL COMBUSTION ENGINE DURING OPERATION Filed Jan. 15, 1958 3 Sheets-Sheet 2 3/ -30 7 F153 I I ma, W/mm fiw i is V i W 30 BY (@1429 Q0! [III 2,897,804 MEANS 'ro VARY THE COMPRESSION RATIO OF AN INTERNAL Aug. 4, 1959 w. R. CROOKS COMBUSTION ENGINE DURING OPERATION 3 Sheets-Sheet 3 Filed Jan. 15, 1958 w w A INVENTOR.

WlY/fam K Crab/rs BY A ITORNEYJ Uni d State w- Otis.

MEANS TO VARY THE COMPRESSION RATIO OF AN INTERNAL COMBUSTION ENGINE DURING OPERATION William R. Crooks, Mount Vernon, Ohio, assignor to The Cooper-Bessemer Corporation, Mount Vernon, Ohio, a corporation of Ohio f v Application January 15, 1958, Serial No. 709,048

' 6 claims. tor. 123-48) This invention relates to improved controls for varying the compression ratio of internal combustion engines during operation and more particularly to such controls that may be made responsive to a selected oil pressure such as the a pressure of-"t-he engine lubricating systems.

The horsepower of modern diesel and gas engines is being increased as rapidly as the strength of engine components and improvements in supercharging equipment will permit. The strength of engine components is increased by such factors as improved designs, more high- 1y skilled engineering, and stronger metals. Supercharging or turbo-charging equipment is also continually being improved to force more and more air into the engine cylinders. More air is advantageous because it enables more fuel to be burned without developing excessive combustion temperatures. However, an increase in the intake air pressure, as is necessary to increase the amount of air, also results in higher compression pressures for a given engine. The compression pressures are thereby increased closer and closer to the maximum pressure limit that is permitted, as determined by the strength of the engine. Consequently, there is a smaller margin between the compression pressure and the limiting preslower intake pressure at low loads, however, it is desure that can be utilized for pressure increase during the combustion process. This situation results in the necessity of setting the fuel injection timing late to prevent the combustion, pressure from being excessive. Thus late timing brings about-loss in efficiency and load carrying ability of the engine. Tests have shown that there is an optimum inlet manifold pressure for an engine, above which the fuel injection timing must be retarded to the extent that the beneficial efiects of the additional air are lost. 1

The load pulling ability of an engine is also known to increase with a decrease in compression ratio, for any given limiting firing pressure. For example, tests conducted with one engine showed that the highest available mean eflective pressure, which is proportional to the load carrying ability, was increased 22% when the compression ratio was reduced from 12:1 to 8 /211. Thus, under heavy loads there is a beneficial eflect in reducing the compression ratio of an engine as the intake pressure is increased. At lower loads, however, mean effective pressures are not as critical and higher compression ratios are desirable to obain the advantages resulting therefrom. Therefore, the optimum compression ratios of a given engine at some high loads will be considerably'be'low the high ratios desired at low loads and may be so low that the engine will not even fire satisfactorily at low loads. or when idling.

The above factors show a definite need for varying the compression ratio according to the load to which an engine is subjected. Thus, for agiven engine and intake pressure, it is desirable to maintain a relatively low compression ratio at high loads, in order that a higher mean eflective pressure can be obtained during firing and the load pulling ability of the engine can be increased. For the same engine and the correspondingly of the lubricating system. When the shell has been sirable to maintain a high compression ratio, when a high mean efiective pressure and load pulling ability are not as important, and suitable conditions for fuel ignition must be maintained.

In the operation of a turbocharged engine it happens that whenthe speed and load of the engine are high, the exhaust gas energy available to drive the turbochargeris also high so that this unit operates at high speed'and'increases the intake manifold pressure. The high manifold pressure results in a high compression pressure; thus it is desirable to reduce the compression ratio so that the firing pressure will not exceed the design maximum for which the engine is built. As the speed and load decrease the intake pressure from the turbocharger decreases, and a higher compression ratio is desirable since compression starts from a lower cylinder pressure.

The present invention proposes a control for varying the compression ratio of an internal combustion engine in response to varying loads and one which is operative while the engine is running. Theoretically, the optimum compression ratio will vary for each load'. As a practical matter, however, two predetermined ratios will sufiice in most instances with the lower ratio employed when the load is above a predetermined amount and the higher ratio employed when the load is below a predetermined amount. A control according to the invention is operated in response to some oil pressure which changes as the load changes such as the oil pressure of the lubricating system. Thus, when a heavier load causes the oil pressure to exceed a predetermined amount, the control of the present invention will shift to provide a lower engine compression ratio and when the load decreases and the oil pressure falls below the predetermined amount, the control will shift to provide a higher engine compression ratio,

lnsuch installations as in locomotives, ships, trucks or the like, an increase in load is accompanied by an increase in engine speed. Since the lubricating oil pressure is developed by an engine driven pump in these engines, the discharge pressure is higher at higher speeds so that, in efiect, an increase in load on the engine will be accompanied by an increase in the oil pressure in the lubricating system." In installations where a constant speed ,or isochronous governor is used, a separate governor control may be used to control a lubricating oil pump discharge valve regulator so that the regulated oil pressure increases as the load increases.

A control according to the invention is also more reliable and more practical than previously known devices. This is primarily due to the fact that the components of the control are relatively simple and positive acting. The heart of the control is in an eccentric bearing shell that is interposed between each connecting rod and its crank throw. The eccentric shell is adjustable between two or more positions and in each posi-' tion causes a different relationship between the head of the cylinder and the piston crown. When the thickest portion *ofthe eccentrieshell is disposed on the side of the crank throw toward the connecting rod and piston, the piston crown will extend fartherest into the cylinder and produce the highest compression ratio. When the thinnest portion of the eccentric shell is disposed on the side of the crank throw toward the connecting rod and piston, the piston crown will not enter as far into the cylinder and will thus produce the lowest compression ratio. The position of the eccentric shell can be controlled by a suitable gear train that is driven by a simple hydraulic motor whose direction of rotation is determined by a hydraulic valve controlled by oil pressure rotated to a predetermined position, it is locked in that position by the gear train. Alternately, the position of the shell can be controlled by two hydraulic latching devices that free the shell for rotation on thecrankshaft until it reaches a predetermined position. One of the latches then operates to latch the shell in place. In either case, the control can be provided for each connecting rod or each crankshaft throw.

It is, therefore, an object of the invention to vary the compression ratio in an internal combustion engine while it is operating, to maintain a lower ratio at higher loads and a higher compression ratio at lower loads, said control being responsive to an oil pressure which changes with load such as the pressure of the lubricating system of the engine.

Another object of the invention is to provide a reliable and practical control for changing the compression ratio of an engine according to the load thereon.

Other objects of the invention will be suggested from the following detailed description of a preferred embodiment thereof, reference being made to the accompanying drawings in which:

Fig. 1 is a somewhat diagrammatic view, with parts broken away, of a supercharged diesel engine embodying a control according to the present invention,

Fig. 2 is a detailed view, partially in cross section, of the control shown in Fig. 1,

Fig. 3 is a detailed, fragmentary view in cross section of a hydraulic valve and motor embodied in the control shown in Figs. 1 and 2, and

Fig. 4 is a view partially in cross section, of an alternate control that embodies the principles of the invention.

A control according to the invention basically comprises eccentric bearing shells interposed between connecting rods of an engine and the throws of a crankshaft of the engine. Each shell is locked in either of two or more selected positions with progressively thicker portions of the shell being disposed toward the cylinder as the compression ratio is increased. This movement of the eccentric shell is accomplished by any suitable means such as one or more hydraulic cylinders and pistons which are actuated when a selected oil pressure rises above or falls below a predetermined amount. A discussion of two specific embodiments of the invention follows.

Fig. 1 shows an outline, diagrammatic view of a supercharged diesel engine 11 and a fragmentary view of a portion thereof including a piston 12, a cylinder 13, a connecting rod 14, a bearing cap 15, a crankshaft 16, shown in cross section, and a control generally indicated at 17. The present invention resides primarily in the combination of elements including the control 17.

Referring more particularly to Fig. 2, one form of the control 17 includes an eccentric bearing shell 18 that is located between a throw of the crankshaft 16 and the connecting rod 14 and the lower bearing cap 15. The shell 18 extends beyond one side of the conneccting rod 14 and the cap 15 and has a spur gear 19 attached thereto which is concentric with the outer surface of the shell 18. The gear 19 is engaged by a pinion spur gear 20 whose shaft is journalled in a housing 21 suitably attached to the bearing cap 15. The pinion gear 20 is driven by a hydraulic motor 22 through a worm 23 and worm wheel. 24. The worm 23 is driven in turn by a shaft 25 connected to an impeller 26 of the motor 22. The impeller 26 and a coacting impeller 27 are, in turn, driven in one direction or the other by hydraulic fluid admitted through either of orifices 28 or 29. When the oil is admitted through the orifice 29, the

impellers

26 and 27 rotate in a direction to drive the bearing shell 18 in a clockwise direction, as shown in Fig. 2, until the teeth of the pinion spur gear 20 contact the last of the teeth on the spur gear 19 near the thickest portion of the shell 18. In this position, the thinnest portion of the shell 18 is on the opposite side of the crankshaft 16 from the control 17, toward the connecting rod 14 and the cylinder head of the engine. The hydraulic fluid admitted through the orifice 29 continues to exert torque on the impeller 26, which torque is transmitted to the pinion spur gear 20 and thereby maintains the spur gear 19 and the shell 18 in a locked position. The effective length of the connecting rod 14 is now shortened and the piston carried thereby does not approach the cylinder head as closely as when the shell 18 is turned to another position. The compression ratio of the engine is thus lowered.

When hydraulic fluid is admitted through the orifice 28, located on the opposite side of the

impellers

26 and 27, the impellers are caused to rotate in the directions shown in Fig. 3 and drive the spur gear 19 in a counterclockwise direction until the teeth of the gear 20 contact the last of the teeth of the gear 19 near the thinnest portion of the shell 18. At this time the shell 18 will have rotated 180 with the thickest portion of the shell 18 on the opposite side of the crankshaft 16 from the control 17, toward the connecting rod 14. The effective length of the connecting rod 14 is now lengthened so that the associated piston penetrates farther into the cylinder and the compression ratio is increased.

Fluid is supplied to the orifices 28 and 29 through

passages

30 and 31 that are connected to a four-way valve 32. Oil is supplied through a passage 33 from any suitable source which carries oil at a pressure that changes as the load changes. Such a pressure is available from the lubricating system of the engine 11 and flows to an end of a cylindrical housing 34 of the valve 32 and also through a branch passage 35 to a central portion of the housing 34. A spool valve 36 is located in the housing 34 and is urged upwardly by a spring 37 located at the end of the housing 34 opposite the passage 33. The

passages

30 and 31 communicate with the valve housing 34 on either side ofthe branch passage 35 and are equally spaced therefrom. The spool valve 36 has two wide

annular grooves

38 and 39 that enable either of the

passages

30 and 31 to be connected with the passage 35. When the valve 36 is in a lower position as shown in Fig. 2, the

' passage 35 is connected with the passage 31 by means of the annular groove 38; when the piston 36 is in an upper position as shown in Fig. 3, the passage 35 communicates with the passage 30 by means of the annular groove 39. In either case, the other of the

passages

30 and 31 communicates with either of

drain lines

40 and 41 formed in the valve housing and connected to a drain 42.

The present invention is particularly applicable to engine installations in which an increase in load is accomplished by an increase in engine speed as, for example, in locomotive, marine service or trucks. In operation, assuming a heavy load to be applied to the engine 11, the engine speed is increased and the oil pressure in the lubricating system will build up. The resulting increase in pressure in passage 33 which contains oil at system pressure drives the valve 36 downwardly against the spring 37 when the oil pressure exceeds a predetermined amount, say 15 p.s.i. When this occurs, oil from passage 33 flows through the branch passage 35, the groove 38, and the passage 31. The oil is admitted through the orifice 29 and drives the

impellers

26 and 27. The impeller 26 rotates the shaft 25, the worm 23, and the gear 20 and causes the eccentric shell 18 to move to the position shown in Fig. 2 in which the compression ratio is lowered. The oil, after striking the im-'

pellers

26 and 27, flows through the orifice 28, through the line 30, around the groove 39, through the drain line 41, and out the drain 42. The force of the oil on the impeller 26 is continually transmitted to the gear 20 and thereby firmly maintains the shell 18 in a fixed position with the thinnest portion of the shell 18 extending toward the connecting rod 14 to establish a low compression ratio.

When the load on the engine 11 decreases, the oil pressure in the lubricating oil system decreases and exerts less pressure on the valve 36. When the force exerted by the oil on the valve 36 is less than the force exerted by the spring 37, the valve will move to the upper position as shown in Fig. 3. The oil from the lubricating system then flows through the branch passage 35, the groove 39, the supply passage 30, and the orifice 28. The oil then strikes the

impellers

26 and 27 from the opposite direction and rotates the shaft 25, the worm 23, the spur gear '26 and, hence, the spur gear 19 in the opposite directions. Rotation of the gear 19 and the eccentric shell 18 continue until the shell has been rotated 180 and the teeth of the gear Zll reach the opposite end of the teeth on the gear 19. The thickest portion of the shell 18 is then disposed toward the connecting rod 14 and establishes a high compression ratio. The oil in this case flows out of the orifice 29, through the passage 31, around the wide annular groove 38 in the spool valve 36, through the drain line 40, and out the drain 42..

Fig. 4 shows an alternate control for varying the compression ratio of an engine which, as in the case of the form above described may operate in response to oil pressure in the engine lubricating system. A fragment of a connecting rod 51 and a lower bearing cap 52 are shown around a throw of a crankshaft 53 with an eccentric bearing shell 54 disposed therebetween. In this case, two hydraulically actuated

latches

55 and 56 are disposed 180 apart in the bearing cap 52 and in a portion of the connecting rod 51 respectively. The latch 55 includes a cylinder 57 and a piston 58 connected to a stem 59 that can move into latching relation to an indentation 66 in the bearing shell 54. The piston 58 is urged outwardly by a spring 61 and is urged inwardly by the pressure of oil in a passage 62 communicating with the outer end of the cylinder 57 and a portion of the lubrication system, for example, between the bearing shell 54- and the bearing cap 52. The latch 56 includes a cylinder 63 and a piston 64 that has a stem 65 similar to the stem 59. The piston 64 is urged inwardly by a spring 66 and is urged outwardly by the pressure of oil in a passage 67 communicating with the inner end of the cylinder 63 and a portion of the lubricating system, for example, between the shell 54 and the connecting rod 51.

The springs 61 and 66 are designed to withstand a given pressure, for example 15 p.s.i., on the respective pistons 58 and 64.; when this pressure is exceeded, the springs will be compressed. If the oil pressure, for example the pressure of the lubricating system, is above this amount, the piston 58 will be moved inwardly against the spring 61, and move the stem 59 against the shell 54 and into latching engagement in the indentation 60, whenever the indentation is aligned with the stem 59. The latch 55 and the indentation 66 are then positioned so that the shell 54- will be locked with the thinnest portion of the shell located upwardly toward the connecting rod 51. The same oil pressure is exerted upwardly on the piston 64 and urges the piston 64 upwardly against the spring 66. This moves the stem 65 to a position away from the shell 54 and maintains it in that position until the pressure decreases. If the load now drops so that the oil pressure falls below the predetermined amount, the pressure on the piston 58 will be correspondingly decreased and the spring 61 will move the piston 58 and the stem 59 outwardly and the stem 59 will thereby be disengaged from the indentation 60. The shell 54 is then free to move around the throw of the crankshaft 53. It has been found that the shell when freed of both latches will creep around the crankshaft in the direction of crankshaft rotation as the engine continues to'operate. The present invention takes advantage of this natural motion to reposition the sleeve when the compression ratio is to be changed.

When the oil pressure of the engine drops, the oil pressure in the cylinder 63 is also decreased and enables the spring 66 to move the piston 64 inwardly so that stem 65 presses against the surface of the shell 54. The stem 65 then engages the indentation 60 when the two are .aligned and prevents further rotation of the shell 54. The latch 56 and the indentation 60 are then positioned so that the thickest portion of the. shell 54 is now located toward the connecting rod 51 and remains so until the stem 65 is again disengaged from the indentation 60, which will occur when the oil pressure again exceeds the strength of the spring 66 and moves the piston 64 and the stem 65 outwardly. The shell 54 will then again be free and will rotate around the throw of the crankshaft 53 until the indentation 60 is aligned with and engaged by the stem 59.

It will be readilyseen that the invention provides an efiective way for changing compression ratios according to the load on an engine. Apparatus designed according to the invention basically comprises an eccentric bearing shell located between a throw of a crankshaft and a connecting rod and cap, and means responsive to oil pressure for locking the shell in at least two positions, in which positions the thinnest and thickest portions of the shell are located on the side of the crankshaft throw toward the connecting rod and piston. The thinnest portion of the shell is located on the side of the crankshaft throw toward the connecting rod and piston when the load on the engine is above a predetermined amount thus giving a lower compression ratio,

and the thickest portion of the shell is located on the side of the crankshaft throw toward the connecting rod and piston when the load is below a predetermined amount, thus giving a higher compression ratio.

Various modifications and changes of the abovediscussed, preferred embodiments of the control for rotating the eccentric shell will be suggested from the above description. Such modifications and changes may be incorporated without departing fromthe invention as defined in the appended claims.

What I claim is:

1. Apparatus for varying the compression ratio of an internal combustion engine, said apparatus comprising an eccentric shell interposed between a throw of a crankshaft and a connecting rod of the engine for varying the effective length of the connecting rod and thus the stroke of a piston connected thereto with respect to a cylinder of the engine, and means responsive to an oil pressure in the engine for locking said shell in at least two different positions with respect to a throw of the crankshaft, whereby a thick portion of said shell will be locked in a position on the side of the crankshaft throw toward the connecting rod and the piston of the engine when the pressure is low and a thin portion of said shell will be locked in a position on the side of the crankshaft toward the connecting rod and the piston of the engine when the pressure is high.

2. Apparatus for varying the compression ratio of an internal combustion engine in response to the load thereon, said apparatus comprising an eccentric shell interposed between a throw of a crankshaft and a connecting rod of the engine for varying the stroke of the connecting rod and a piston connected thereto with respect to a cylinder of the engine, means for locking said shell in at least two different positions with respect to a throw of the crankshaft, and means responsive to an oil pressure that varies in proportion to the load on the engine for actuating said locking means, whereby a thick portion of said shell will be locked in a position on the side of the crankshaft throw toward the connecting rod and the piston of the engine when the load and hence said oil pressure is low and a thin portion of said shell will be 3. Apparatus for varying the compression ratio of an internal combustion engine in response to the load thereon, said apparatus comprising an eccentric shell interposed between a throw of a crankshaft and a connecting rod of the engine for varying the effective length of the connecting rod and thus the stroke of a piston connected thereto with respect to a cylinder of the engine, pressure operated latch means operatively associated with said shell for maintaining said shell inlocked positions with respect to said connecting rod when any one of said latch means is in a latching position, one biased toward a latching position and the other biased away from the latching position whereby pressure above a predetermined amount releases one latch means and pressure below a predetermined amount releases the other latch means, and means to impose a pressure on said latch means that increases as the load on the engine increases.

4. Apparatus for varying the compression ratio of an internal combustion engine having a piston, a crankshaft and a connecting rod operated thereby, said apparatus comprising an eccentric shell interposed between a throw of said crankshaft and its connecting rod, and means to hold said shell in at least two selected positions with respect to said connecting rod, one position presenting a thicker portion of said shell on the side of said crank throw toward said connecting rod whereby the compression ratio of the engine is increased, and another position presenting a thinner portion of said shell on the side of said crank throw toward said connecting rod whereby the compression ratio of the engine is decreased, said means including a reversible fluid motor, connections to supply driving fluid to said motor in one direction when the load on the engine is above a predetermined value and in the opposite direction when the load on the engine is below said predetermined value, and pressure responsive valve means responsive to pres sure in the engine lubricating system to direct fluid to said connections.

5. Apparatus for varyingthe compression ratio of an internal combustion engine having a piston, a crankshaft and a connecting rod operated thereby, said apparatus comprising an eccentric shell adapted to be interposed between a throw of said crankshaft and its connecting rod, means to hold said shell in at least two selected positions with respect to said connecting rod,

than

one position presenting a thicker portion of said shell on .the side of said crank throw toward said connecting rod whereby thecompression ratio of the engine is increased, and another position presenting a thinner portion of said/she ll on the side of said crank throw toward said connecting rod whereby the compression ratio of the engine is decreased, said means including a gear attached vto said 'shell at one side of said connecting rod, a hydraulic motor for driving said gear, and a hydraulic, I four-way valve responsive to an oil pressure in the engine for supplying driving fluid to said motor in one direction when the load on the engine is above a predetermined value and in the opposite direction when the load on the engine is below said predetermined value.

6. Apparatus for varying the compression ratio of an internal combustion engine having a piston, a crankshaft, and a connecting rod operated thereby, said apparatus comprising an eccentric shell interposed between 'a throw of said crankshaft and its connecting rod, means to hold said shell in at least two selected positions with respect to said connecting rod, one position presenting a thicker portion'of said shell on the side of said crank throw "toward said connecting rod whereby the compress'ion ratio of the engine is increased, and another position presenting a thinner portion of said shell on the side of said crank throw toward said connecting rod whereby the compression ratio of the engine is decreased, 'said means including a gear attached to said eccentric shell at one side of said crankshaft, a housing attached -to'said connecting rod adjacent said shell, a gear train associated with said housing for driving said gear, a hydraulic motor for driving said gear train, supply conduits connected to opposite sides of said motor, and a hydraulic, four-way valve responsive to oil pressure in the lubricating system of said engine for supplying oil from said lubricating system through one conduit to said motor when the load on the engine is above a predetermined value and through the other conduit to said motor when the load on the engine is below a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS