GB1599696A - Internal combustion engine with stepped piston supercharger - Google Patents

Description

(54) INTERNAL COMBUSTION ENGINE WITH STEPPED PISTON SUPERCHARGER (71) We, DANA CORPORATION, a corporation of the State of Virginia, United States of America, of 4500 Dorr Street, Toledo, Ohio, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to reciprocating piston internal combustion engines.

Trends in engine design are always for more horsepower for a given engine displacement, size and weight. At the same time fuel efficiency is, in many applications, an important consideration. As is well known to those skilled in this art, a typical two-stroke cycle engine delivers significantly more horsepower per cubic inch displacement at a given rpm than any production, naturally aspirated four-stroke cycle engine, but the two-stroke cycle is substantially less efficient. Super-charged four-stroke cycle engines represent a compromise of sorts providing more power per unit weight than unsupercharged four-stroke cycle engines and better fuel economy than two-stroke cycle engines. Super-chargers, however are generally expensive and have found substantial use only in the racing car field.

According to the present invention there is provided a four-stroke reciprocating internal combustion engine comprising a combustion chamber, defined by a working cylinder and a piston slidable therein, and a crankcase, the piston having a compressor portion which defines with a conpressor cylinder a compressor chamber, the swept volume of which is greater than one half of the swept volume of the combustion chamber, means being provided for admitting a charge of air or fuel/air mixture to the compressor chamber from the crankcase on the intake and power strokes of the piston and for supplying each charge to an intermediate chamber, two such charges being supplied to the intermediate chamber during each operating cycle of the engine, the combustion chamber, during the intake stroke of the engine. receiving air or fuel/air mixture from the intermediate chamber whereby the pressure of the air or fuel/air mixture delivered to the combustion chamber is greater than the pressure of the air or fuel/air mixture received from the crankcase.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1 to 4 are sectional views showing, respectively, intake, compression, power and exhaust strokes of a four-stroke cycle reciprocating piston engine; Figure 5 is a fragmentary cross-section of the engine of Figures 1 to 4 showing in detail a preferred construction for part of the engine; Figure 6 is a timing diagram illustrating the operation of the engine of Figures 1 to 4; Figure 7 is a fragmentary sectional side view of a piston and cylinder arrangement for a multi-cylinder engine.

Figure 8 is a fragmentary sectional end view of the arrangement of Figure 7.

Figure 9 is a perspective view of a piston of the arrangement of Figures 7 and 8; and Figure 10 is a fragmentary sectional view of part of the piston of Figure 9.

The engine of Figures 1 to 4 has a single cylinder in which is slidable a piston 10 having an enlarged stepped portion 12 at its lower end. The piston 10 is arranged to drive a crankshaft 14 through a connecting rod 16 and a gudgeon pin 17, as is conventional. The upper portion of the piston 10 reciprocates within a combustion chamber cylinder 18 and includes grooves for receiving upper and lower piston rings 19 and 19a. The annular stepped portion 12 of the piston is carried by and preferably is formed integrally with the upper portion of the piston and sides within an enlarged area cylinder defined by a wall 20.The stepped portion 12 of the piston includes passageways 22 for the admission of a fuel-air mixture from a crankcase 23 of the engine into the compressor chamber defined by the wall 20, the annular stepped portion 12 and an annular shoulder 25 at the lower end of the cylinder wall 18. The passageways 22 are closed by one-way check valves 24. Passageways 26 are provided through the stepped portion 25 of the cylinder and are closed by one way check valves 27.

At least one passageway 26 and check valve 27 is provided, and preferably a plurality is provided, approximately evenly spaced about the shoulder 25, the number depending on the size and performance characteristic of the engine.

Passageways communicate between the compressor chamber and a manifold typically comprising an annular collector chamber 28 adjacent the shoulder 25 and in open communication with an intermediate chamber in the form of an accumulator/manifold 29.

One end of the manifold 29 is in periodic communication with the combustion chamber of the engine via an intake valve 30. The valve 30 may take any desired form; for many applications it will preferably be in the form of a rotary valve as shown to take advantage of the known benefits of such a valve. Poppett and other types of valves may also be used depending on the application and the preferences of the designer. Exhaust gases from the combustion chamber are also controlled by the rotary valve 30 which is shown in Figure 4 in a portion of the exhaust cycle as will hereinafter be explained in more detail.

Fuel air mixture may be provided via a carburettor or the like (not shown) through a passageway 32. Check valves 34 are optionally, but preferably, used to prevent backflow to the carburettor. Alternatively fuel injectors, not shown, can be used to inject fuel into the combustion chamber in the known manner, charge air being admitted to the crank case; e.g., for a Diesel engine.

A preferred arrangement for the portion of the engine block defining the collector chamber 28 is shown in more detail in Figure 5. The combustion chamber cylinder is provided as part of the engine block and is connected to an outer wall 36 thereof by the shoulder 25. An open-topped annular cavity 38 is thus provided. A plurality of the passageways 26 are provided in the shoulder 25 and the check valve 27 is an annular disc fitting in the bottom of the cavity 28. A particularly preferred form of check valve 27 comprises an upper disc 27a of rubber or the like and a lower disc 27b of thin beryllium alloy spring stock.

The inner circumference of the disc 27 is clamped to the shoulder 25 by a sleeve 40 and more particularly by a reduced diameter cylindrical portion 41 thereof which is a sliding fit over the cylinder 18. The cylindrical portion 41 terminates at its upper end in a radial shoulder 42 which bridges to an enlarged diameter cylindrical portion 43. The cylindrical portion 43 is a sliding fit within the outer wall 36 and sealingly engages a cylinder head gasket 46 disposed between the engine block and a valve containing cylinder head 48.

Because the sleeve 40 is sealed at each end it divides the cavity 38 into two separate cavities, the collector chamber 28 and an annular cavity 50 which is connected to a source of circulating cooling water.

Figure 6 illustrates the operation of the engine through a complete combustion cycle. In order to illustrate the operation of the compressor, the operation of the engine from top dead centre to top dead centre is represented by 1800 on the timing diagram rather than the usual 360". Thus a full combustion cycle is comprised of an engine intake stroke generally occurring in the first quadrant (I) of the timing diagram, a compression stroke (quadrant II) a power stroke (quadrant III) and an exhaust stroke (quadrant IV).

The specific preferred embodiment associated with the timing diagram of Figure 5 is a high performance engine having substantial valve overlap. More particularly, the intake valve opens 42" before top dead centre and closes 70" after bottom dead centre while the exhaust valve opens 64" before bottom dead centre of the power stroke and does not close until 36 after top dead centre on the exhaust stroke.

The operation of the compressor section of the engine is also shown in Figure 6. The check valves for the compressor are controlled only by the gas forces on them, inertia and the movement of the piston. Thus they will open and close at substantially the top and bottom dead centre positions of the piston.

It will, by now, be appreciated that the compressor section of the engine provides two charges of combustion mixture to the combustion chamber for each combustion stroke. The fuel/air mixture in the crankcase 23 is typically admitted from a carburettor (not shown) through the passageway 32 and past the check valves 34 at substantially atmospheric pressure (14.7 PSIA) although, as mentioned above, the fuel may be provided separately to the combustion chamber.

Assuming the provision of an atmospheric fuel-air mixture to the crankcase, the compressor section is initially filled with a combustion mixture at 14.7 PSIA. Two "charges" of the compressor are provided to the combustion chamber on each engine cycle.

Thus the theoretical charge pressure, assuming no valve overlap, is given by: PE = 2 V 14.7 PSIA VE where PE is the engine combustion chamber pressure, VE is the engine combustion chamber swept volume Ve is the compressor swept volume. It will be apparent that supercharging occurs for any engine geometry wherein the compressor swept volume is greater than one-half the combustion chamber swept volume. Typically a lower limit for a practical engine will be a compressor swept volue equal to approximately three-fourths the swept volume of the combustion chamber.

In the preferred embodiment illustrated the swept volumes of the engine combustion chamber and the compressor are equal, making the theoretical (assuming no valve overlap) charge pressure about 29 PSIA. In actual practice, because of the valve timing as shown in Figure 6, a charge pressure of somewhat less than this can be expected but even with the relatively high valve overlap (indicated by "B" for blowdown on Figure 6) chosen for this embodiment a substantial amount of supercharging is provided.

Figures 7 through 9 illustrate a preferred multicylinder embodiment in diagrammatic form. To minimize the size and weight of such an engine it is preferred to utilize the minimum spacing between adjacent combustion cylinders. To this end, as shown in Figure 9, the stepped portion 12a is elongate with an axial extent (along the line of cylinders) equal to the piston diameters and extending transversely of the engine. Thus, as shown in Figure 7, the adjacent pistons can be axially adjacent without the need for any additional spacing to accomodate the stepped portion of the piston. As shown in Figure 8 a collector chamber 28a is preferably provided above each stepped portion. Manifolding in any convenient way suitable to the overall engine geometry is provided to communicate between the collector chambers 28a and the combustion chamber.In some applications it will be preferred to provide a relief in the cylindrical body of the main portion of the piston just above the stepped portion 12a, thereby allowing the use of a single collector 28a.

Figure 10 illustrates a preferred seal arrangement for the stepped portion 12 or 12a. A circumferential groove 50 is provided in the piston periphery of the portion 12, this groove 50 including a stepped area 51 of reduced radial depth. An "0" ring 52 of any suitable rubber or rubber-like material fits within the groove 50 and provides a resilient biasing of a seal element 53 comprising a continuous ribbon of rectangular cross-section of polytetraf luoroethylene or the like.

Reference is made again to Figures 1 to 4 for a description of the operating cycle of the engine. In Figure 1, the piston 10 is at its lowermost position just prior to starting the compression stroke. During the previous 1800 of crankshaft revolution the piston was moving downwardly from the top dead centre position and the check valve 24 was open, permitting air or a fuel-air mixture from the crankcase to enter the compressor. During the same stroke, the inlet portion of rotary valve 30 was opened and the charge previously contained in the manifold 26 was aspirated into the cylinder 18.In Figure 2, the crankshaft has rotated 90" from the position of Figure 1, the valves 24 and 30 have closed and the stepped portion 12 of the piston 10 is on its first of two compression strokes of the engine combustion cycle delivering a compressed fuel-air mixture to the manifold 29 through the now opened valve 27. In Figure 3, the charge in the main cylinder has been ignited and the piston has started its downward power stroke causing the check valve 24 to open for the admission of a fresh charge or air or fuel-air mixture into the compressor. Figure 4 illustrates the piston at top dead centre position at the conclusion of the exhaust stroke of the cycle which is also the completion of the second stroke. Thus, it will be seen that there are two compression strokes of the stepped portion of the piston per combustion cycle of the engine.It is not believed that there is any critical ratio between the volumes of the compressor and that of the combustion chamber of the engine. The relative volumes can be varied as required to provide the degree of supercharge desired. The one to one volume ratio of the chamber volumes and consequent two to one compression ratio is preferred.

The volume of the manifold affects the operation primarily as it determines the time required to reach the same steady state operating pressure. In other words, if the manifold volume is relatively small, the same operating pressure will be reached with fewer strokes than if the manifold volume, for example, is substantially greater than the volume of the compression cylinder. The end result, however, is the same for any given engine in that the same pressure is always reached regardless of manifold size or engine speed. It is preferred that the manifold volume be of the same order of magnitude as the compressor and the combustion chamber Many variations of the present invention will occur to those skilled in the art. For example, and as mentioned briefly above, the supercharger of the present invention can be used with fuel injected gasoline engines or diesel engines. While a rotary valve assembly has been shown and described, it will be obvious that other known valve structures can be substituted. Similarly the engine timing, amount of supercharge and many other features of the overall engine can vary from the foregoing description of the preferred embodiments without departing from the spirit and scope of the invention as defined in the following

Claims (5)

claims. WHAT WE CLAIM IS:

1. A four-stroke reciprocating internal combustion engine comprising a combustion chamber, defined by a working cylinder and a piston slidable therein, and a crankcase, the piston having a compressor portion which defines with a compressor cylinder a compressor chamber, the swept volume of which is greater than one half of the swept volume of the combustion chamber, means being provided for admitting a charge of air or fuel/air mixture to the compressor chamber from the crankcase on the intake and power strokes of the piston and for supplying each charge to an intermediate chamber, two such charges being supplied to the intermediate chamber during each operating cycle of the engine, the combustion chamber, during the intake stroke of the engine, receiving air or fuel/air mixture from the intermediate chamber, whereby the pressure of the air of fuel/air mixture delivered to the combustion chamber is greater than the pressure of the air of fuel/air mixture received from the crankcase.

2. An engine as claimed in claim 1, wherein the swept volumes of the compressor chamber and of the combustion chamber are approximately equal.

3. An engine as claimed in claim 1 or 2, wherein the portion of the piston which is slidable in the working cylinder is circular in cross-section and wherein the compressor portion is elongate having a minor dimension which is substantially the same as the diameter of the portion which is slidable in the working cylinder.

4. An engine as claimed in claim 1, wherein the means for admitting a charge of air or fuel/air mixture to the compressor chamber comprises a passageway in the compressor portion extending between the crankcase and the compressor chamber and including a check valve permitting one-way flow from the former to the latter.

5. A four-stroke reciprocating internal combustion engine substantially as described herein with reference to and as shown in the accompanying drawings.