GB2349418A - Crankcase-supercharged four-stroke i.c. engine with at least one pair of cylinders - Google Patents

Abstract

An internal combustion engine including at least one pair of cylinders ( 8 , 28 ) and pistons ( 9, 27 ) operating each in a four stroke cycle with two strokes off-set and reciprocating in phase in the respective cylinders. Air charging means ( 2, 14, 17, 18, 22, 34) associated with the crank case interior including an air inlet means (12, 13, 23, 24 ) to the interior which communicates through a passage (1) with both cylinders so as to cause air displaced by both pistons on a working and induction stroke to charge into one cylinder performing the induction stroke. The cylinders may be arranged parallel, at an angle or opposed. The pistons may be connected to a common crankshaft or to a pair of crankshafts 15, 19.

Description

Index of Items Reference Drawing Figure 1 1. Fuel/air Transfer Pipe 2. Combustion Chamber Inlet Valve (No. 2 cylinder) 3. Spark Plug (No. 2 cylinder) 4. Exhaust Valve (No. 2 cylinder) 5. Exhaust Pipe (No. 2 cylinder) 6. Exhaust Port 7. Combustion Cavity (No. 2 cylinder) 8. No. 2 Cylinder 9. Piston (No. 2 cylinder) 10. Connecting Rod 11. Lower Side of Piston (No. 2 cylinder) 12. Crankcase Induction Pipe 13. Variable Throttle Control (Carburettor) 14. Crankcase Inlet Check Valve 15. Crank Shaft 16. Crank 17. Transfer Check Valve 18. Variable Volume Crankcase Cavity 19. Crank Shaft 20. Crank 21. Crankcase 22. Crankcase Inlet Check Valve 23. Crankcase Induction Pipe 24. Variable Throttle Control (Carburettor) 25. Lower Side of Piston (No. 1 cylinder) 26. Connecting Rod 27. Piston (No 1 cylinder) 28. No. 1 Cylinder 29. Combustion Cavity (No. 1 Cylinder) 30. Exhaust Port 31. Exhaust Pipe (No. 1 Cylinder) 32. Exhaust Valve (No. 1 Cylinder) 33. Spark Plug 34. Combustion Chamber Inlet Valve (No. 1 Cylinder) TITLE :-Intemal Combustion Enaine Descfiption The invention relates to internal combustion engines. Charging of engines thus fare has been accomplished by superchargers driven mechanically by the engine or turbochargers driven by exhaust gas flow. Both forms of charging require considerable additional equipment increasing engine mass and complexity.

The invention provides an internal combustion engine including at least one pair of cylinders and pistons operating each in a four stroke cycle with two strokes off-set and reciprocating in phase in the respective cylinders and air charging means having an air inlet means into a space below the pair of pistons which communicates with both cylinders so as to cause air displaced by both pistons on working and induction stroke to be charged into one cylinder performing an induction stroke.

Conveniently the respective pistons and cylinders of the pair are arranged parallel, at an angle or opposed and pistons are operable in synchronism by a pair of crankshafts or by a common crankshaft.

Preferably the aircharging means includes valves permitting induction into the space below the pistons and expulsion of air out of the space to the cylinders and space communicates with the crank case interior providing a very simple arrangement.

Drainas Figure 1 shows the items refered to in the text. Figures 2 to 5 show a schematic section through an engine of the invention in successive operation phases. The diagrams show a"Mid stroke"position.

Example of Invention With reference to an engine shown in the drawings, a crankcase 21 houses a pair of crank shafts 15 and 19. Crank portions 16 and 20 are provided respectively upon the crank shaft 15 and 19. connecting rods 10 and 26 have one end excentrically and pivotably connected to the crank 16 and 20 respectively, the other ends being connected to pistons 9 and 27. Each of the pistons 9 and 27 reciprocates in cylinders 8 and 28 to rotate the crank shafts 15 and 19. The pistons 9 and 27 reach their upper and lower most positions simultaneously as they are constantly in phase with one another. Each of the cylinders 8 and 28 opens at one end into the crankcase 21 such that the periphery of the crankcase 21 and the lower surfaces 11 and 25 of the pistons 9 and 27 define a cavity 18 whose volume is determined by the axial position of the pistons 9 and 27.

The engine operates in four distinct phases. Phase one (figure 2) illustrates the initial stages of the cycle in which the pistons 9 and 27 move up in the cylinders 8 and 28. The piston 9 exhausts contents of combustion cavity 7 of the cylinder 8 through the exhaust port 6 to the exhaust line 5 past a valve 4. The piston compresses the contents of the combustion cavity 29 of the cylinder 28, being contained by the closed valves 32 and 34. The upward motion of the piston 9 and 27 increases the volume of the cavity 18 and reduces the internal pressure of the cavity 18. With check valves 14 and 22 open, air mixture is drawn into the cavity 18 along the supply lines 12 and 23 at a rate controlled by choke valves 13 and 24. When the pistons 9 and 27 reach the upmost position, the check valves 14 and 22 close and valve 4 is actuated closed whilst the valve 2 is actuated open. Valves 2 and 34 control communication between the pre-compressed air mixture supply line 1 and the cavity 18 and the combustion cavities 7 and 29 with a further check valve 17 preventing reverse flow. Spark plug 33 next ignites the fuel/air mixture in combustion cavity 29, causing both pistons to move downward In phase two (figure 3) The decent of the pistons cause air/fuel mixture to be transfered into cavity 7 whilst piston 27 is forced down on a power stroke. With valves 14 and 22 closed, the motion of the pistons 9 and 27 compresses the contents of cavity 18 into the combustion cavity 7 via supply line 1 past valves 2 and 17. At the end of phase two when the pistons 9 and 27 reach the lowest position, the valve 17 closes and valve 2 is actuated closed whilst valve 32 actuated is open. The valve 32 controls the communication between the combustion cavity 29 and the exhaust line 31.

In phase three (figure 4) the pistons 9 and 27 move upwards causing air/fuel to be drawn once more into the cavity 18. The piston 27 now performs an exhaust stroke. the contents of the cavity 29 are forced out through exhaust port 30 and the exhaust line 31. The piston 9 this time performs a compression stroke during which the precompressed contents of the combustion cavity 7 are further compressed prior to combustion. The contents of the combustion cavity 7 are isolated by the closure of valves 2 and 4. At the end of phase three the pistons 9 and 27 reach the uppermost position and the valve 32 closes and valve 34 opens. The valve 34 controls communication between the pre-compressed air/fuel mixture supply line 1 and the combustion cavity 29.

In phase four (figure 5) spark plug 3 ignites the contents of combustion cavity 7 causing the piston 9 to move down on a power stroke together with piston 27 which now performs a pre-compression transfer phase for cavity 29. With the valves 14 and 22 closed, the motion of pistons 9 and 27 once more compress the contents of cavity 18 into the combustion chamber 29 of cylinder 28 via the supply line 1. At the end of phase four when the pistons 9 and 27 are lowermost the valves 17 and 34 close and the cycle can be repeated.

Whilst the pistons rise and secondly jointly the four stroke cycle performed by the respective pistons are two strokes out of phase. This results in the compression in one cylinder while the other is exhausted. Furthermore on the downward strokes, the volume corresponding to the displacement of two cylinders is charged into the single cylinder which is descending but not performing the working stroke. Thus the air/ fuel mixture is charged at a ratio of up to twice that of an uncharged system. The pair of cylinders are effectively charged in a two stroke cycle. each slug of air/fuel mixture entering the engine experiences five stokes before being exhausted.

1) Induction into the crankcase cavity.

2) Pre-compression and transfer into the combustion cavity.

3) Secondary compression in the combustion cavity.

4) Ignition and expansion.

5) Exhaust.

Whilst the construction described uses check valves, these valves may be actuated in synchronisation with crankshaft rotation. Whilst the carburettor type is used in this case for each inlet passages 12 and 23 to cause air/fuel mixture to be charged, the system can also operate with a single inlet passage or with a joint carburettor, adding fuel after air compression, in the passage 1, or fuel can be injected into the individual cylinders.

The crank case may be shared by more than two cylinders still suitably paired, but arranged so as to minimise the crankcase volume and maximise the compression. The pistons may be arranged parallel as illustrated but may also be opposed operating by a common crankshaft.

Supercharging can be achieved in this way without an external supercharging mechanism in a simple manner providing a high power to weight ratio, making the engine particularly suitable in motocycle applications.

As an additional safety device it may be nessasary to include some form of pressure relief valve in the transfer pipe 1 to avoid damage in the event of a"Back fire"of the engine.

Claims (8)

1. Claims 1. An internal combustion engine including at least one pair of cylinders and pistons operating each in a four stroke cycle with two stokes off-set and reciprocating in phase in the respective cylinders and air charging means having an air inlet into a space below the pair of pistons which communicates with both cylinders so as to cause air displaced by both pitons on a working and induction stroke to be charged into one cylinder performing the induction stroke.
2. 2. An engine according to claim 1 in which the respective pistons and cylinders of the pair are arranged parallel, at an angle or opposed.
3. 3. An engine according to claim 1 or claim 2 in which the pistons are operable in synchronism by a pair of crank shafts or by a common crank shaft.
4. 4. An engine according to any of the preceding claims in which the air charging means includes valves permitting induction into the space below the pistons and expulsion of air out of the space to the cylinders.
5. 5. An engine according to claim 4 in which the valves are check or one way valves or are operable by an actuating mechanism with the crank shaft or shafts.
6. 6. An engine according to any of the preceding claims in which the space communicates with the crank case interior.
7. 7. An engine according to any of the preceding claims in which the air inlet means inclues one or two passages provided with means for admixing fuel.
8. 8. An internal combustion engine substantially as described and shown by reference to the drawings.