GB2135385A

GB2135385A - Reciprocating piston crankcase compression machine

Info

Publication number: GB2135385A
Application number: GB08303920A
Authority: GB
Inventors: Anthony Willoughby Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-11
Filing date: 1983-02-11
Publication date: 1984-08-30
Also published as: GB8303920D0

Abstract

The reciprocating piston 12 is connected by means of a connecting rod 20 to a crank shaft arranged within a crank case with an intake port and a transfer port communicating with the crank case on opposite sides of the crank shaft. The arrangement is such that during the piston stroke the crank case is divided by the connecting rod 20 into two variable volume working chambers 204, 208. Upon rotation of the crank shaft the connecting rod 20 acts to draw in a charge through the intake port into the working chamber 204 to one side of the connecting rod and to expel the charge drawn into the working chamber during the preceding cycle on the other side, 208, of the connecting rod 20 out of the transfer port for delivery into the cylinder. <IMAGE>

Description

SPECIFICATION Reciprocating piston machine The present invention relates to reciprocating piston machines in general and to a two stroke engine.

In accordance with the invention in its broader aspect, there is provided a reciprocating piston machine comprising a piston connected by means of a connecting rod to a crank shaft arranged within a crank case, and an inlet port and an outlet port communicating with the crank case on opposite sides of the crank shaft; the arrangement being such that during the piston stroke the crank case is divided by the connecting rod into two variable volume working chambers and upon rotation of the crank shaft the connecting rod acts to draw in a fluid through the inlet port into the working chamber to one side of the connecting rod and to expel through the outlet port on the other side of the connecting rod the fluid drawn into the first working chamber during the previous cycle. Thus the crank case, crankshaft and connecting rod act together as a pump.

It may thus be seen that the invention proposes a means by which the connecting rod and crankshaft may, if constructed and arranged in a special way and used in a special casing, be used as a novel displacement pump whose pumping displacement is largely independent of, and may be isolated from, the volume displaced above the piston in the same machine.

One application of the invention is the provision of a two-stroke engine with improved control of its charging and scavenging.

In accordance with a second aspect of the present invention, there is provided a two stroke engine having a reciprocating piston connected by means of a connecting rod to a crank shaft arranged within a crank case, and an intake port and a transfer port communicating with the crank case on opposite sides of the crank shaft; the arrangement being such that during the piston stroke the crank case is divided by the connecting rod into two variable volume working chambers and upon rotation of the crank shaft the connecting rod acts to draw in a charge through the intake port into the working chamber to one side of the connecting rod and to expel through the transfer port the charge drawn into the working chamber during the preceding cycle on the other side of the connecting rod, for injection into a combustion chamber of the engine.

By dividing the crank case into two chambers, the special connecting rod, with its special crank case (and such other parts as may be necessary to create a sufficient seal) forms a vane type pump of which the displacement is not dependent upon, and is greater than the piston displacement of the engine. If then a valve controlling the admission of the charge into the combustion chamber is so arranged, or is of such a type, as to be capable of being closed after the exhaust valve, then the charge entering the combustion chamber can be compressed without the risk of its blowing out to waste through the exhaust port. By this means more mixture can be induced into the combustion chamber, and thus more power will be obtained from the engine than from other types of engine of similar displacement.

Conventional two stroke engines have a transfer port situated in the cylinder wall adjacent to the exhaust port and controlled, like the exhaust port, by the position of the piston. Because that port may not be opened before the exhaust port, so it must perforce close before it. Consequently, under many conditions a proportion of the fresh charge is wasted to atmosphere with the exhaust and there is considerable mixing of the incoming and the spent charge. Because of this, such engines have poor fuel economy and poor behaviour at idling and at part-throttle.

In one embodiment of the two stroke engine of the invention, the valve controlling the transfer of mixture from the crank case to the combustion chamber is placed at the opposite end of the cylinder to the exhaust port or ports. As a result, the incoming charge has to travel the full length of the cylinder before reaching the exhaust port or ports. Mixing and wastage are thus minimised and economy and idling and part-throttle operation may be as good as, or better than, in four stroke designs of similar power.

The compression ratio of the engine cylinder may be quite low since the incoming charge is already partly compressed. Accordingly, a side valve operated by a cam lobe on the crank shaft, with its virtues of mechanical simplicity and reliability, may be used without the disadvantage of an unacceptably high surface to volume ratio in the combustion chamber.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic partial section through an engine in accordance with the invention, and Figures 2A, B, C and D are schematic sections in a plane transverse to the crank shaft axis, showing the piston in different positions.

In Figure 1 , there is shown a two stroke internal combustion engine having a combustion chamber 10, a piston 12 and a cylinder 14. The piston 12 is connected to a crank shaft 1 8 by way of a connecting rod 20. The crank shaft runs in two anti-friction bearings 30, 32 each running in an oil bath and sealed from the crank case interior. In the usual manner a little end bearing 22 connects the piston 1 2 to the connecting rod 20 and a big end bearing 24 connects the connecting rod 20 to the crank shaft 1 8.

The engine in Figure 1 is a flat twin engine and a similar cyclinder is provided on the opposite side of the crank case. Those elements of the second cylinder which can be seen in Figure 1 have been designated by the same reference numerals and will not be described further.

Within the crank case, the charge is compressed in the manner described below and applied to a transfer port which also opens into the crank case. The transfer port is connected by a passage (not shown) which leads to the combustion chamber 10 and is controiled by a poppet valve 34. The poppet valve is opened and closed by a cam 36 on the crank shaft which displaces the valve 34 through the action of an adjustable cam follower 38. The valve 34 is urged into a closed position by a valve spring 40.

In entering the crank case, the connecting rod 20 passes through a slot in the crank case periphery whose sides are close to the sides of the rod and whose edges are shaped to obstruct the flow of gas past them. The sharp edges on the connecting rod 20 and the small clearance between the connecting rod and the crankshaft 1 8 permit the charge taken in to be pumped in the manner now to be described.

Figure 2A shows one possible shape of the connecting rod 20 and the rod is shown with the piston in the top dead centre position. Figure 2B shows the position of the connecting rod 20 after a rotation of 900 clockwise. It can be seen at this point that the crank case has been divided into two chambers 204, 208 by the connecting rod.

Chamber 204 communicates with the inlet port and chamber 208 with the transfer port.

The lower edge 202 remains in close proximity to the crank case surface 206 during further rotation. Thus, when the piston reaches bottom dead centre position, as shown in Figure 2C, the chamber 204 will have expanded consequently drawing a charge in through the inlet port to fill the chamber 204. In the meantime, the chamber 208 to the left of the connecting rod, as viewed, as a smaller volume than it had in Figure 2B and consequently within it the intake charge from the preceding cycle is compressed. The chamber 208 is in communication with the transfer port which leads by way of the previously described poppet valve 34 to the combustion chamber 1 0. In the position shown in Figure 2D, all the preceding intake charge has been compressed fully and applied to the transfer port.

During continued, rotation to return to the top dead centre position, the poppet valve 34 is closed and shortly before top dead centre the spark plug fires to ignite the charge. Meanwhile chamber 204 has increased to encompass almost the whole of the crank case space and also the cylinder volume below the piston. Now, the piston 12 and with it the connecting rod 20 descend once again resuiting in a repetition of the above described cycle during which the crank case is divided by the connecting rod 20 into two variable volume working chambers the first, 204, drawing in a fresh charge through the inlet port and the second, 208, pumping the previously drawn in charge out of the transfer port for application to the combustion chamber.

By virtue of the compression of the charge, the quantity of air introduced into the combustion chamber is increased. This permits the power of the engine to be increased. Furthermore, the engine is seen to operate in a uniflow mode in that a fresh charge is introduced at the top of the cylinder while the position of the exhaust port or ports is lower down the cylinder. Consequently, after the power stroke when the poppet valve 34 is opened again, the fresh charge entering the combustion chamber through the transfer port assists in pushing out the exhaust gases through the exhaust port 1 6 and thereby provides more efficient scavenging.

Though the preferred embodiment described above employs a poppet valve between the trasnfer port and the combustion chamber, it is alternatively possible to employ a rotary valve and this would enable an in-line multi-cylinder engine to be manufactured from relatively few components.

The invention in its broadest aspect provides a particular crank case and connecting rod construction which enables the crank case of a reciprocating piston machine to function as a displacement pump. In the particular embodiment described above this pump is used to compress the charge entering a combustion chamber on the same machine but this need not necessarily be the case in other embodiments of the invention. For example, the pump formed by the crank case of one cylinder of a multi-cylinder engine may be used to compress the charge for another cylinder.

It is not even essential to the invention that the pumping action of the crank case be used as part of or in conjunction with an internal combustion engine since it may alternatively be used to pump a gas, or liquid, for any other purpose.

Claims

1. A reciprocating piston machine comprising a piston connected by means of a connecting rod to a crank shaft arranged within a crank case, and an inlet port and an outlet port cominunicating with the crank case on opposite sides of the cranl < shaft; the arrangement being such that during the piston stroke the crank case is divided by the connecting rod into two variable volume working chambers and upon rotation of the crank shaft the connecting rod acts to draw in a fluid through the inlet port into the working chamber to one side of the connecting rod and to expel through the outlet port on the other side of the connecting rod the fluid drawn into the first working chamber during the previous cycle.

2. A two stroke engine having a reciprocating piston connected by means of a connecting rod to a crank shaft arranged within a crank case, and an intake port and a transfer port communicating with the crank case on opposite sides of the crank shaft; the arrangement being such that during the piston stroke the crank case is divided by the connecting rod into to variable volume working chambers and upon rotation of the crank shaft the connecting rod acts to draw in a charge through the intake port into the working chamber to one side of the connecting rod and to compress the charge drawn into the working chamber during the preceding cycle on the other side of the connecting rod, for injection into the cylinder through the transfer port.

3. A two stroke engine as claimed in claim 2, wherein the transfer port leads to a position in the combustion chamber above the exhaust port where a valve is provided together with a means of opening the valve before the exhaust port opens and of closing the valve after the exhaust port closes.

4. A two stroke engine as claimed in claim 3, wherein the transfer valve is a poppet side valve operated by a cam mounted directly on the crank shaft.

5. A two stroke engine as claimed in claim 3, wherein the transfer valve is a rotary valve.

6. A reciprocating piston machine constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.