GB2091806A - Four-stroke engine with charging by the engine pistons - Google Patents

Abstract

The cylinders L and R are charged alternately through the inlet valves 21 with air or mixture compressed in the crankcase 10 or in spaces (42), Figure 2 (not shown), beneath the pistons 17 which are partitioned from the crankcase. The compression in the crankcase 10 or in the spaces (42) may be adjusted by a piston 29. <IMAGE>

Description

SPECIFICATION Engine This invention relates to internal combustion engines, which may be spark ignition engines or compression ignition engines.

Various arrangements have already been proposed for propelling air or air/fuel mixture positively into the cylinders of internal combustion engines, but in general these involve the provision of auxiliary equipment, e.g. in the form of compressors, turbo-chargers or superchargers. These arrangements, of course, necessitate the provision of appropriate mountings for the equipment and means for applying drive thereto with consequential adaptation of the engine design and additional expense.

An object of the present invention is to provide a construction of engine which has provision for the positive propulsion of air or air/fuel mixture into its cylinders without the need for providing auxiliary equipment, the propulsion being achieved with the use of components which must necessarily be present as part of the engine in any event.

With this object in view, the present invention provides an internal combustion engine comprising at least one pair of cylinders with respective pistons reciprocable therein, air inlet means providing for air or air/fuel mixture to pass or be drawn into the spaces beneath the pistons upon each compression stroke and exhaust stroke of the pair of pistons, and valved inlet ports to the cylinders, providing for each said cylinder to be opened to the said spaces upon the induction stroke of its piston for air or air/fuel mixture to be positively charged therein by the pressure increasing action, on the air or air/fuel mixture in said spaces, of the two pistons performing respectively their induction and expansion strokes.

The spaces below the pistons may be open to a crankcase of the engine, or the arrangement may be such that each cylinder is blanked off below its piston by a partition or closure through which a respective linearly-movable connecting rod of the piston extends.

The inlet means may conveniently comprise an inlet connection connecting with one of the cylinders near to the base of said cylinder. The arrangement may then be such that this inlet connection is closed at the end of each induction and expansion stroke of the piston in said one of the cylinders. Alternatively the inlet may be controlled by a valve.

The construction of the engine of the invention may be such that a fuel/air mixture is supplied by way of the air inlet means. In this instance, the air inlet means may lead from a carburettor.

Alternatively the arrangement may be such that only air (preferably filtered) is supplied to the air inlet means and in this case the engine will, naturally, comprise injectors for injecting fuel directly into the cylinders, into the spaces beneath the pistons, or into the inlet ports of the cylinders.

For enabling the effective weight of air or fuel/air mixture propelled into each cylinder upon its induction stroke to be varied within limits, the arrangement is preferably such that the effective compression can be varied. This may conveniently be achieved by the provision of a supplementary cylinder communicating with the spaces beneath the pistons and accommodating a volume-varying piston whose position can be varied as desired, to adjust the compression effect.

The invention will be described further, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic sectional elevation illustrating a two-cylinder engine constructed in accordance with the invention; and Figure 2 is a view similar to Figure 1, but illustrating a modification.

The engine illustrated in Figure 1 comprises a crankcase 10 surmounted by two parallel upright cylinders 11 which are illustrated for convenience as being integral with the crankcase 10 but in practice will, of course, be separately formed and appropriately mounted to the crankcase 10. In the case where the engine is an air-cooled engine, each cylinder will, in practice, be formed with cooling fining which is omitted for simplification of the drawing.

Mounted within the crankcase 10 by bearings 12 and 13 (which are shown as being plain bearings but may, in practice comprise heavy-duty roller or ball bearings) is a crankshaft 14, crankpins 15 of which are connected to respective connecting rods 16 connecting with respective pistons 17 reciprocable within the respective cylinders 11.

Assuming the engine to be a spark-ignition petrol fuelled engine, each cylinder 11 is fitted at or near its head with a respective spark plug (not shown) connected with an appropriate ignition system to generate sparks in the respective cylinder 11 in conventional manner.

The crankcase 10 is sealed to prevent unintentional gaseous leakage therefrom and is connected by a passage 18 to a transfer duct 19 which joins with an inlet port 20 of each of the cylinders 11, these ports 20 being fitted in traditional manner with respective inletvalves, indicated diagrammatically at 21, actuated by appropriate mechanism (not shown) which may for instance include one or more camshafts.

Each cylinder 11 also has a respective exhaust port 22 fitted with a respective exhaust valve 23 connected to an exhaust duct 24 which directs exhaust gases by way of an exhaust pipe 25 to a silencer (not shown).

One of the cylinders 11, that is to say the right hand one indicted by the letter R in the drawing, is fitted with air inlet means in the form of an air inlet duct 26 opening through the wall of the cylinder 11 and effectively valved by the respective piston 17, being closed when the piston approaches its bottom dead centre position. This duct 26 has a carburettor (not shown) connected thereto.

The crankcase 10 has connected thereto a secondary cylinder body 27 which is shown projecting downwardly in the figure but may be in any convenient position. This cylinder body 27 accommodates a crankcase volume adjusting piston 29 whose piston rod 30 projects externally to enable the position of the piston 29 to be adjusted, correspondinglyto adjust the overall combined volume of the crankcase 10 and the cylinder body 27.

The manner of operation of the engine will readily be understood from the foregoing description. To distinguish the two cylinders, as has already been mentioned the right hand cylinder has been designated with the letter R, whilst the left hand cylinder has been designated with the letter L.

Considering firstly the right hand cylinder R, its piston 17 is shown at the bottom dead centre position and just at the end of a combustion stroke, accordingly, in its next stroke, this piston 17 performs its exhaust stroke, discharging combustion gases past the respective exhaust valve 23 through the exhaust duct 24 to the exhaust pipe 25. At the beginning of this exhaust stroke, the piston 17 opens the air inlet duct 26 and this provides for an air/fuel mixture to be drawn into the space under the right hand piston 17 and then into the spaces under the two pistons 17 and into the crankcase 10 as a result of the pressure reduction generated in the crankcase 10 by the upward movement of both of the pistons 17. This upward movement of the piston 17 of the left hand cylinder L is a compression stroke, both the valves 23 and 21 of this cylinder L being closed.

At approximately top dead centre, ignition occurs in the left hand cylinder L to drive its piston 17 downwards in an expansion or power stroke, whilst the downward movement of the piston 17 of the right hand cylinder R is an induction stroke, its valve 21 being open and fuellair mixture being both drawn into the cylinder R by such downward movement of the respective piston and positively propelled into the cylinder under pressure by the compressing effect created in the crankcase 10 by the downward movement of both of the pistons 17.

At bottom dead centre, the pistons 17 commence moving upwards again. This time, the right hand piston 17 is performing its compression stroke (in the same way as described above for the left hand piston 17) and the left hand piston 17 is correspondingly performing its exhaust stroke; these strokes are then followed respectively by their power or combustion stroke, and induction stroke.

The engine accordingly runs afterthe manner of a conventional twin-cylinder engine, with each cylinder performing a power or combustion stroke whilst the other is performing its induction stroke and so on. At each induction, the fuel/air mixture is positively displaced into the respective cylinder by the compressive effect achieved by the simultaneous receiprocation of the pistons, so that the fuel/air supply (and the extra compression thereof) is in direct proportion to the rotational speed of the engine. It will readily be appreciated that this positive displacement of the air/fuel mixture into the cylinders is achieved using only the components which are necessarily present to constitute an engine.

The secondary cylinder piston arrangement 27, 29, 30 is optional and when present enables the weight of the air/fuel mixture propelled into the cylinder upon each induction stroke to be adjusted. Downward movement of the piston 29 from its illustrated position increases the effective overall volume of the crankcase 10 and consequently reduces the extent to which the air/fuel mixture therein is compressed by the movement of the pistons, correspondingly reducing the weight of an air/fuel mixture passing to the cylinders, as may be desired, e.g. in the practical running of the engine.

Figure 2 illustrates, diagrammatically, the upper part of a second embodiment of the engine of the invention in which the connecting rods 16 of the pistons 17 extend through guide seals 40 provided in respective partitions or closures 41 present across the lower end of each cylinder 11. In the operation of the engine, therefore, these connecting rods 16 perform linear motion; and this is converted to rotary motion in any suitable manner and by any suitable mechanism in the lower part (not illustrated) of the engine, below the partitions or closures 41.

These partitions or closures 41 accordingly define, beneath the respective pistons 17, corresponding spaces 42 which are isolated from any crankcase which may be present. These spaces 42 are, however, connected by respective radial bores 43 with the passage 18 and thus connect with the transfer duct 20.

Inlet duct 26 connects with the space 42 under the piston 17 of the right hand cylinder R and incorporates a mechanically-operated valve indicated schematically at 44.

This embodiment of the engine operates in substantially the same way as the embodiment described above with reference to Figure 1, with the exceptions, of course, that the fuel/air mixture entry by way of the duct 26 is not piston controlled but is controlled by the valve 43, and that the compression occurring in the spaces 42 beneath the pistons 17 on the downwards strokes thereof is not shared in any way with any crankcase which the engine may have.

In this embodiment the secondary cylinder and piston arrangement 27, 29 and 30 can, again, be provided to permit adjustment of the achieved compression effect. As has already been stated, the drawings are purely diagrammatic, to illustrate the principles involved in the engine of the invention, and the dimensions of the various components will be selected to be as near as possible to optimum with the piston 29 merely providing for relatively fine adjustment.

The invention is not confined to the precise details of the foregoing example and variations may be made thereto. Thus, for example in the illustrated cases the arrangement may be such that only air enters the engine by way of the duct 26, fuel being injected directly into the cylinders 11 or being introduced at the inlet ports 21 in known manner. If the fuel is diesel fuel, sparking plugs will, of course, be omitted from the engine.

Although the engine has been described above in relation to two cylinder engines it will be appreciated that such a construction is likely to be the simplest form thereof and the invention can, of course, be applied to an engine comprising any practical even numbers of cylinders, these being arranged in pairs substantially as described above.

Claims (12)

1. An internal combustion engine comprising at least one pair of cylinders with respective pistons reciprocable therein, air inlet means providing for air or air/fuel mixture to pass or to be drawn into the spaces beneath the pistons upon each compression stroke and exhaust stroke of the pair of pistons, and valved inlet ports to the cylinders, providing for each said cylinder to be opened to the said spaces upon the induction stroke of its piston for air or air/fuel mixture to be positively charged therein by the pressure increasing action, on the air or air/fuel mixture in said spaces, of the two pistons performing respectively their induction and expansion strokes.

2. An engine as claimed in claim 1 wherein the said spaces are open to a crankcase of the engine.

3. An engine as claimed in claim 1 wherein each piston has a linearly-movable connecting rod which extends through and is sealed relative to a partition below the respective piston.

4. An engine as claimed in claim 1,2 or 3 wherein the inlet means comprises an inlet connection connecting with one of the cylinders near to the base of said cylinder.

5. An engine as claimed in claim 4 wherein the inlet cnnection is disposed so as to be closed at the end of each induction and expansion stroke of the piston in said one of the cylinders.

6. An engine as claimed in claim 4 wherein the inlet means comprises a port controlled by a valve.

7. An engine as claimed in any preceding claim in which a fuel/air mixture is supplied by way of the air inlet means.

8. An engine as claimed in claim 7 wherein the air inlet means leads from a carburettor.

9. An engine as claimed in any of claims 1 to 6 wherein only air is supplied to the air inlet means and the engine comprises injectors for injecting fuel directly into the cylinders or into the said spaces.

10. An engine as claimed in any preceding claim wherein the effective volume of the said spaces can be varied.

11. An engine as claimed in claim 10 and having a supplementary cylinder communicating with the said spaces and accommodating a volume-varying piston whose position can be varied as desired, to adjust the combined volume of the said spaces and supplementary cylinder.

12. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.