GB2167124A - Two stroke reciprocating internal combustion engine - Google Patents

Abstract

A cylinder 2 is divided into two by a slidable piston 7, one end of the cylinder being used for induction of fluid 9, the other end for combustion 8. A passage 24 formed in the piston linking the induction end to a port 15 formed in the side of the piston near its combustion end. A pocket 16 is provided in the cylinder wall which co-operates with the piston's port, for part of each operating cycle of the engine, to permit transfer of operating fluid from the induction end to the combustion end of the cylinder. The cylinder, which has an exhaust port 20 is enclosed by a cylinder head 3 and by a block 4 containing a one way valve 18. A bell crank 10 and links connect the piston to a crankshaft 12. Lubricant is pumped to bearings and is not required to be mixed with the fuel. Fuel may be injected into the pocket 16. <IMAGE>

Description

SPECIFICATION 2 stroke reciprocating internal combustion engine This invention relates to internal combustion engines, and more particularly to engines of the type variously known as two stroke or two cycle reciprocating internal combustion engines. Whilst two stroke engines have well recognized advantages in terms of simplicity of construction and relatively high power output per unit weight, known two stroke engines do suffer from various disadvantages.

More particularly, two stroke engines which operate by drawing a mixture of fuel, combustion air, and lubricant through the crank case of the engine prior to admission to the combustion chamber tend to have high fuel consumption in relation to the power produced, relatively poor torque characteristics at low revs, and tend to use an excessive amount of lubricant leading to objectionable exhaust smoke and odour.

According to one feature of the present invention there is provided a two stroke reciprocating internal combustion engine comprising a cylinder; a piston reciprocable within the cylinder and dividing the cylinder into a combustion chamber at one end of the cylinder and an inlet chamber at the other end of the cylinder; a pivotally mounted lever coupled to the piston to be alternately pivoted in opposite directions in response to reciprocating movement of the piston within the cylinder; a transfer passage formed in the piston for connecting the combustion chamber to the inlet camber; and a transfer pocket formed in the wall of the cylinder, which connects with a port formed in the side of the piston, during a portion of each operating cycle of the engine to permit transfer of fluid from the inlet chamber to the combustion chamber.

The preferred embodiment of the invention makes use of a pump fed pressurized lubricant system and thereby obviates the need to mix lubicating oil with the engine fuel. Since there is no direct fluid communication between the crank case and the combustion chamber consumption of lubricating oil is very small and a relatively clean and odour free exhaust is produced.Further, it is belived that by suitable selection of the operating characteristics of the engine a higher volumetric efficiency and good fuel consumption characteristics as compared withEthose of prior art two stroke engines may be obtained whilst at the same time the construction of the engine will involve the use of considerably fewer discrete components and moving parts than would be required for the construction of a conventional 4 stroke engine having comparable number of power strokes and output.

The above and further features and advantages of the invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings, wherein: Figure 1 is a cross sectional view through one cylinder of the preferred embodiment of the present invention; Figure 2 is a section on the line AA of Fig.

1; and Figure 3 illustrates a typical engine timing cycle for the engine of Figs. 1 and 2.

Referring firstly to Figs. 1 and 2 the two stroke internal combustion engine 1 shown includes a cylinder 2 closed at one end by a cylinder head 3 and closed at the other end by an inlet block 4. The cylinder 2 is of constant diameter throughout its length. It will be appreciated, however, that other arrangements are possible. For example, the cylinder may be formed by two seperate cylinder portions each of different diameters and secured to a central engine block.

A piston 7 is reciprocable within the cylinder 2 and divides the cylinder into a combustion chamber 8 and an inlet chamber 9.

Throughout this specification the terms Top Dead Centre (TDC): Bottom Dead Centre (BDC): forward stroke of the piston: and return stroke of the piston are all used to describe the position or motion of the piston 7 in relation to the combustion chamber 8.

Thus, as illustrated in Fig. 1 the piston is nearly at BDC and the volume of the inlet chamber 9 is at its near minimum. Movement of the piston to the left as viewed in Fig. 1 is a forward stroke of the piston and brings the piston to TDC when the volume of the combustion chamber 8 is at its minimum and the volume of the inlet chamber 9 is at its maximum.

A bell-crank lever 10 is pivotally mounted via a pivot pin 11 on the engine block and is connected at its lower end to a crankshaft 12 via a connecting rod 13. The upper end (as viewed in Fig. 1) of the bell crank is formed to take a pivot pin 5 which connects the bell crank with the piston 7 by way of pivoted link 6 and pivot pin 14. Accordingly, as the piston 7 reciprocates within the cylinder 2 the bell crank 10 is alternately pivoted clockwise and anti-clockwise about pivot pin 11.

An inlet manifold 17 connected, in the case of the embodiment illustrated in the drawings, to a carburettor, is connected to the inlet block 4 to supply to the inlet block a fuel/air mixture, for example a petrol/air mixture. An inlet valve 18 normally biased closed by thin flexible spring steel valve plates 19 controls flow of the air/fuel mixture into the inlet chamber 9. An exhaust port 20 is formed in the wall of the cylinder 2 and is connected to an exhaust manifold 21 in conventional man ner.

A transfer passage 24 connects the aperture 23 formed in the end of piston adjacent to inlet chamber 9, to a port 15 formed in the side of the piston 7 near the end adjacent the combustion chamber 8. A transfer pocket or pockets 16 formed in the wall of cylinder 2 is normally covered by the piston 7 and its sealing rings 28 in order to isolate the combustion chamber 8 from the transfer passage 24.

During a portion of each operating cycle of the engine, the piston 7 uncovers one end of the transfer pocket 16 in order to provide free communication between the transfer passage 24 and the combustion chamber 8.

Sealing of port 15 in the side of piston 7 to the wall of cylinder 2 adjacent to transfer passage 16 to prevent loss of transferring fluid, is by maintaining firm and constant contact of the piston to the cylinder wall in the direction of pocket 16. This is achieved by positioning pivot pin 14 connecting the piston to the bell crank 10 and crankshaft 12, offset from the essentially centre line forces of pressure and dynamics acting on the piston, so as to cause a reaction of forces to impart a small sideway loading on the piston in the direction of the port 15 and the transfer pocket 16.

A lubrication system comprising an oil sump, oil pump, galleries and drillings is provided to supply lubricant to the various bearings in conventional manner.

Operation of the above described engine is as follows: Just after the piston 7 passes the near BDC position illustrated in Fig. 1, clockwise rotation of the crankshaft 12 produces anticlockwise rotation of the lever 10 which causes the piston 7 to commence a forward stroke within the cylinder. Continued forward movement of the piston 7 causes a partial vacuum within the inlet chamber 9 and thereby moves the inlet plates 19 out of engagement with their associated seats to admit fuel/air mixture into the inlet chamber 9.

Shortly after forward movement of the piston 7 commences the transfer pocket and exhaust port 20 is closed by piston 7. Continued forward movement of the piston causes compression of the previously admitted combustion mixture within the combustion chamber 8 and at an appropriate point in the operating cycle the spark plug 25 is energized to ignite the combustion mixture. After the piston 7 passes TDC and commences its return stroke the bell crank level 10 is driven clockwise as viewed in Fig. 1 and drives the crankshaft 12.

At or slightly before TDC the inlet valve 18 closes due to a reversal of gas pressure acting on plates 19 and accordingly during the return stroke of the piston the combustion mixture trapped in the inlet chamber 9 and transfer passages 24 is partially compressed.

Just after the point in the return stroke where the piston 7 uncovers the exhaust port, permitting exhaust to commence the port 15 in the side of the piston 7 is aligned with the transfer pocket 16, and the piston uncovers the combustion chamber end of the transfer pocket 16 to permit the partially compressed combustion mixture to flow into the combustion chamber. The profile of the transfer pocket 16 is shaped to act with the deflector 27 formed on the piston crown to produce good scarifying of the exhaust gases during the transfer of combustion mixture from the transfer passage 24 to the combustion chamber 8. The volume of transfer pocket 16 can be adjusted to obtain the optimum pressure and velocity of the transferring fluid to give the best operating characteristics. The operating cycle of the engine then recommences as described above.

The above described engine provides various advantages. Firstly, because combustion mixture flows through the piston on its way to the combustion chamber excellent cooling of the piston is produced, thereby eliminating problems traditionally associated with hot pistons and leaving the way open to the use of piston rings made of non-metallic material.

Secondly, cooling of the piston produces corrseponding preheating of the combustion mixture. This pre-heating occurs to a large extent after the inlet valve 18 has closed, i.e.

after the full charge of combustion mixture is trapped within the inlet chamber 9 and transfer passage 24. Thus the pre-heating of the combustion mixture before admission to the combustion chamber does not reduce the volumetric efficiency of the engine as would be the case if a pre-heated inlet manifold was used. Good mixture preparation is further enhanced by the high turbulence imparted into the fuel/air mixture by positive high velocity transfer action.

The use of a oil sump and conventional pump lubricant systems obviates the need to run the engine on a fuel/oil mixture and accordingly markedly reduces the oil consumption and exhaust emission of the engine as compared with conventional two-stroke engines.

Other advantages of the engine will be clear to those skilled in the art.

Various modification of the above described engine may prove desirable. For example, rather than supplying a fuel/air mixture to the inlet manifold 17 air or other combustion supporting gas may be supplied to the inlet manifold 17 and fuel may be injected directly into the combustion chamber 8 via a suitable injection nozzle. A fuel injection engine'of this type can operate by spark or compression ignition.

Further, the air of fuel/air mixture supplied to the inlet manifold 17 may be supercharged or turbocharged to increase charging of the inlet chamber 9 during forward strokes of the piston. If it is desired to charge the cylinder 8 with a large volume of air or fuel/air mixture without resorting to use of a compressor the inlet chamber 9 can be made of a larger dia meter than the combustion chamber 8 whereby a large volume of air or fuel/air mixture will be drawn into the inlet chamber 9 during forward movement of the piston 7.

It may prove beneficial to inject fuel in a spray pattern directly into transfer pocket 16 during the transfer of fluid into the combustion chamber 8. The injection could be intermitant and timed so as to minimize the loss of fuel through the exhaust port. It may prove advantageous to use other mechanical means of converting the reciprocating action of the piston into rotary motion. These methods could for example include a sealing system on a connecting rod which drives a crankshaft via a crosshead or directly, a swashplate. The number of positioning of transfer pockets and exhaust ports can be varied to provide the best operating characteristics for the engine without affecting the basic operating principals.

Finally, refering to Fig. 3 a typical timing cycle for the above described engine is shown. Starting from TDC.29 the power stroke 30 lasts untill the piston uncovers the exhaust port to produce an exhaust phase 31 of approximately 1200. Thereafter the exhaust port is closed by the piston and a compression stroke 32 of approximately 1200 is produced prior to ignition at TDC. Initial tranfer 33 from the inlet chamber 9 to the transfer passage 24 extends for approximately 1800 from TDC, and induction 34 from the inlet manifold 17 to the inlet chamber 9, lasts for approximately 1800 before TDC. Secondary transfer 35 from the transfer passage 24 into the combustion chamber 8 is approximately co-extensive with the exhaust phase i.e. it extends from approximately 1200 after TDC to approximately 1200 before TDC. It will be appreciated however, that the timing cycle illustrated in Fig. 3 is given purely by way of example and that other timings may prove desirable under certain circumstances.

Claims (10)

1. A two stroke reciprocating internal combustion engine comprising a cylinder, a piston with sealing rings at each end, reciprocable within the cylinder and dividing the cylinder into a combustion chamber at one end of the cylinder and an induction chamber at the other end of the cylinder, a linkage coupled at one end to the piston and at the other end to a crankshaft so that the reciprocating movement of the piston within the cylinder is translated into a rotary motion, a transfer passage formed in the piston which connects the induction end of the piston with a port formed in the side of the piston near its opposite end, and a transfer pocket formed in the wall of the cylinder which connects with the port formed in the side of the piston, during a portion of each operating cycle of the engine to permit transfer of fluid from the induction chamber to the combustion chamber, fluid which having entered the induction chamber via a port, being prevented from leaving by a one way valve means located in the port.

2. A two stroke engine according to claim 1 with a cylinder divided into two by a slidable piston, one end of the cylinder being used for induction of combustionable fluid and the other end of the cylinder for combustion.

3. A two stroke engine according to claims 1 and 2 with a piston formed with an internal passage which connects one end of the piston with a port formed in the side of the piston near its opposite end.

4. A two stroke engine according to claims 1, 2 and 3 in which a pocket is formed in the wall of the cylinder and positioned so as to co-operate with a port formed in the side of a piston during a part of each operating cycle of the engine to permit transfer of fluid from one end of the cylinder to the other.

5. A two stroke engine according to claims 1, 2, 3 and 4 in which the supply of lubricant to bearing surfaces is by a pump fed system which obviates the need to mix lubricant with the engine's fuel.

6. A two stroke engine according to claims 1, 2, 3, 4, and 5 in which a piston formed with seals at each end reciprocates within a cylinder under the control of a link connecting from a pin in the piston's central postion to a bell crank, and from the bell crank to a connecting rod, and to a journal of a crankshaft, so that the reciprocating action of the piston is converted into rotary motion.

7. A two stroke engine according to preceding claims in which the fluid for combustion is transferred from an induction chamber to a combustion chamber via an internal passage formed in a piston, and a pocket formed in the wall of a cylinder, so as to generate turbulence in the fluid, and by taking up heat from the piston, pre-heat the fluid without detriment to the volumetric efficiency of the engine, to obtain conditions within the fluid which will result in its rapid and complete burning.

8. A two stroke engine according to claims 1, 2, 3, 4, 5, 6, and 7 in which the induction end of the piston can be formed with a larger diameter than the combustion end, to work in a similar sized cylinder to supercharge the combustion chamber, or to match the capacity of the combustion chamber in an opposed piston version of this engine.

9. A two stroke engine as claimed in any preceding claims in which fuel for combustion can be-added to transferring fluid by a suitable injector positioned to discharge into a transfer pocket formed in the cylinder wall, with the fuel injections being timed to occur late in the transfer cycle to prevent loss of fuel through the exhaust port.

10. A two stroke internal combustion en gine substantially as described herein with reference to figures 1, 2 and 3 of the accompanying drawings.