VARIABLE VOLUME INTERNAL COMBUSTION ENGINE FIELD OF THE INVENTION

[0001] The present subject matter relates generally to an internal combustion engine and more particularly, pertains to a variable volume combustion chamber for an internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] A conventional internal combustion engine in a saddle type vehicle converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The said engine has a cylinder comprising a cylinder head and a piston reciprocating in the cylinder. Other components necessary for the function of the engine such as intake and exhaust valves, rocker arms, rocker arm camshaft, piston rings, crankshaft, connecting rod etc. are also present. The cylinder head is atop the cylinder and receives a reciprocating piston from the bottom. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft and setting the vehicle into motion. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft rotation then drives the vehicle.

[0003] The compression ratio of an engine is the ratio of the total internal volume between the top surface of the piston and the inner surface of top wall of the combustion chamber of a cylinder head when the piston is at bottom dead center to the clearance volume of the cylinder when the piston is at top dead center. Generally the cylinder bore diameter, piston stroke length and combustion chamber volume are constant within a conventional engine. Hence it operates at a constant compression ratio. This means that the piston can reciprocate within a fixed range i.e. the top dead center and the bottom dead center positions are static for the piston of such an engine. Since the compression ratio is static, it results in compression pressure varying with the operating conditions for the engine. Consequently the thermal efficiency of the engine varies under varying operating conditions. The compression ratio is generally optimized for full throttle opening so that the engine derives more energy from the air-fuel mixture. However this results in a drop in performance in part throttle conditions where the compression ratio is less than optimal, leading to overall reduced efficiency.

[0004] The present invention is directed to overcoming one or more problems as set forth above. It is therefore an object of the present invention to disclose a low cost, compact mechanism for achieving an increased thermal efficiency in an internal combustion engine so that optimum performance can be obtained under all operating conditions. It is yet another object of the present invention to provide an internal combustion engine with variable compression ratio under varying operating conditions by adjusting the combustion chamber volume thereby improving the engine efficiency through a simple, cost effective mechanism. Another object of the present invention is to present a mechanism to vary combustion chamber volume and based on ease of manufacturability with a minimum modification to the cylinder head design.

SUMMARY OF THE INVENTION

[0005] To this end, the present subject matter discloses an internal combustion engine in which the compression ratio is varied during operation, comprising a cylinder having a cylinder head, a major piston in the cylinder, a minor piston ensconced in a groove in the cylinder head and adjacent to an intake and an exhaust valve, the minor piston being angularly disposed with respect to the major cylinder long axis, the minor piston further comprising belleville spring pack and a retainer ring in such a way that the retainer ring faces the combustion chamber where, when the engine is in operation, maximum compression ratio is obtained at part throttle conditions and minimum compression ratio is obtained at full throttle conditions.

[0006] According to an aspect of the present invention, the minor piston is made of aluminium or aluminium alloy.

[0007] The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

Figure 1 illustrates a cylinder head of an internal combustion engine incorporating the present invention.

Figure 2 depicts a cut section view of the engine block including the cylinder head when the throttle is at partially open position.

Figure 3 depicts a cut section view of the engine block including the cylinder head when the throttle is at fully open position.

DETAILED DESCRIPTION OF THE INVENTION

[0009] In the ensuing exemplary embodiments, the engine is an internal combustion engine which can be incorporated in an on-road vehicle, off-road vehicle, tractor, excavator, generator sets or the like. Various other features of the internal combustion engine according to the present subject matter here will be discernible from the following further description thereof, set out hereunder. The detailed explanation of the constitution of parts other than the subject matter which constitutes an essential part has been omitted at suitable places.

[00010] Before proceeding to the present invention, it would be proficient to know the working of a conventional internal combustion engine. An internal combustion engine may either be a spark ignition or a compression ignition engine. It may also be differentiated into a two stroke or a four stroke engine. A conventional four stroke engine goes through a combustion cycle in four phases, the induction stroke, compression stroke, explosion stroke and exhaust stroke. Initially the piston is at the bottom of the cylinder (bottom dead centre) and the air-fuel mixture has already been introduced to it. The piston moves up the cylinder to compress this air-fuel mixture and the compression pressure is built up in the cylinder. This is called the compression stroke. When the piston reaches the top of its stroke (top dead centre), a spark plug emits a spark to ignite the fuel due to which the air-fuel mixture in the cylinder explodes driving the piston down. This is called the explosion stroke. Once the piston reaches bottom dead centre, an exhaust valve allows the exhaust to leave the cylinder through a tail pipe. Then, as the piston moves back up the cylinder, the exhaust is pushed out of the cylinder through exhaust valve. This is called the exhaust stroke. Finally, when the piston reaches the top dead centre, intake valve opens to let more air-fuel mixture enter the cylinder. As the piston moves down the cylinder, the chamber is filled with the air-fuel mixture. This is called the induction stroke.

[00011] Further compression ratio is the ratio between the volume of the cylinder above the piston when the piston is at bottom dead centre and the volume when the piston is at the top dead centre. A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher efficiency is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature.

[00012] A conventional internal combustion engine is usually designed such that the compression ratio is optimal for full throttle, to allow the engine to operate at maximum efficiency at high r.p.m and large throttle opening. Therefore the compression ratio for a conventional engine is constant. Since the efficiency is generally optimized for full throttle operation, the average efficiency is low. At any part-throttle condition, the compression ratio is less than optimal, leading to reduced efficiency.

[00013] All this happens because the volume of the combustion chamber above the top dead centre of the piston does not change. Hence the present invention provides a simple means to alter the volume of the combustion chamber thereby achieving variable compression ratio of the engine in part throttle condition. It attempts to provide a low combustion chamber volume (hence high compression ratio) at part throttle condition and high combustion chamber volume (hence low compression ratio) at full throttle condition so that optimum performance can be obtained in all operating conditions. ••

[00014] An embodiment of the present invention is now described with reference to the drawings. In the drawings, the same reference numerals are given to members and parts having the same functions. Typically an internal combustion engine includes an engine block defining one or more combustion cylinders. For the purpose of simplicity, only one combustion cylinder is shown in the drawings. At one end of the combustion cylinder, a cylinder head is attached to the block in which the cylinder resides.

[00015] Figure 1 partially illustrates a cylinder head of an engine incorporating the present invention in the form of a variable volume cylinder head 103 placed over a combustion chamber. The variable volume is achieved by the use of a minor piston 106 in the cylinder head 103. The minor piston is angularly disposed adjacent to the intake 101 and exhaust 102 ports.

[00016] Figure 2 illustrates a cut section view of the engine block including the cylinder head along the A-A axis comprising at least two pistons, a major piston 201 in the major cylinder 202 and a minor piston 106 in the cylinder head of the aforementioned internal combustion engine. The major piston 201 is reciprocally disposed within the combustion cylinder (major cylinder) 202 and movable between a top dead centre position adjacent to the cylinder head and a bottom dead centre position at an opposing end of the combustion cylinder 202. It consists of compression and oil rings 204. The space between the major piston and the combustion cylinder head at top dead centre is known as the combustion chamber 203 where the combustion of air-fuel mixture takes place. A piston pin (gudgeon pin) connects the major piston to a crankshaft (not shown) through a connecting rod (not shown).

[00017] The cylinder head 103 includes a groove 108, angularly disposed, and located close to the intake 101 and exhaust 102 ports and one of the side of the groove is in communication with combustion chamber 203 of the major cylinder 202. The minor piston 106 is reciprocally disposed in the said groove 108. The groove carrying the minor piston 106 may be positioned in an oblique fashion with respect to the major cylinder longitudinal axis. The cylinder head 103 thus includes the minor piston 106. The minor piston 106 must incorporate compression rings, lubrication channels etc. to function but such items are well known in the prior art, and are not part of the invention herein and therefore, the detailed explanation of the constitution of parts other than the minor piston which constitutes an essential part is omitted in this description.

[00018] A disk type spring known as belleville spring 105 is provided in the minor piston 106 opposite to the end facing the combustion chamber 203. The belleville spring 105 is a metal disk stamped into a conical shape and carries extremely high loads under very small deflections. It is largely self-damping due to its nature. The belleville spring 105 has a specific pre-load when assembled with the minor piston 106. A retainer ring 107 is also provided at the minor piston head to cushion the minor piston's return back to the original position. The retainer ring 107 faces the combustion chamber 203. The minor piston 106 is sandwiched between the retainer ring 107 on one side and the belleville spring 105 on the other side.

[00019] The functioning of the present invention will now be explained briefly. Figure 2 shows the working of the minor piston when the throttle is partly open. Initially during the induction stroke, when the throttle is at minimum position the minor piston 106 is at its lowest position towards the combustion chamber 203 whereas the major piston 201 is at the bottom dead centre. The minor piston 106 is inwards towards the combustion chamber 203 due to the belleville spring force and held in position by the retainer ring 107.

[00020] Figure 3 shows the position of the minor piston when the throttle is full open. As the throttle is pulled towards the rider, more air-fuel mixture is injected into the major cylinder 202 through the intake valve. The major piston 201 moves up towards the top compressing the air-fuel mixture while the minor piston 106 remains down. The mixture is then ignited by the spark plug. The resulting explosion places an upward force upon the minor piston 106 and downward force on the major piston 201. Consequentially the huge compression force acts against the spring force (provided by the belleville spring) displacing the minor piston in upward direction. The movement of the minor piston is depicted by the arrow in Figure 3. This increases the combustion chamber volume which correspondingly lowers the compression ratio. The space between within the groove 108 and below the minor piston 106 is added to the clearance volume of the engine in computing the compression ratio. As the minor piston goes upward, the clearance volume is reduced and the compression ratio is decreased.

[00021] The major piston 201 moves to the bottom transferring the energy to the crankshaft. Thus at full throttle, the combustion chamber volume is largest and the compression ratio is least. The major piston 201 again comes up for the exhaust stroke to take place. As soon as the exhaust escapes the combustion chamber, the combustion chamber pressure drops due to which the minor piston sent back to original position by the belleville spring.

[00022] When the throttle goes down away from the rider (part throttle), the minor piston 106 is moved inwards due to less compression force and the subsequent combined effect of the belleville spring and retainer ring. The combustion chamber volume decreases and maximum compression ratio is obtained. Thus the compression ratio is varied by means of a minor piston. Without the minor piston, the compression ratio would remain constant. Moreover the minor piston motion is self regulated by spring force and compression forces, giving continuous variable compression ratio with respect to throttle opening. The compression is thus varied by means of a minor piston engulfed in a groove in the cylinder head of an internal combustion engine. Under part throttle conditions, the minor piston moives down to increase the compression ratio. Thus under part throttle conditions the engine compression ratio is increased to run in a more fuel efficient manner whereas under full throttle conditions, the engine compression ratio is lowered.

[00023] The present subject matter and its equivalent thereof offer many advantages, including those which have been described henceforth. It provides a low cost, compact mechanism for a variable compression ratio engine. The simple means for varying the compression ratio leads to ease in manufacturing of the present invention and also the engine assembly. The said means provides a self-adjusting and self-positioning mechanism and thereby avoids the need of extra controlling units. The cross-sectional area and the stroke length of the major and minor piston can be selected to provide the desired variation in compression ratio. The shape of the minor piston can be selected to allow it to fit conveniently into the cylinder head, avoiding intake and exhaust valves.

[00024] In a two wheeler vehicle being ridden in the city, the vehicle remains in part throttle conditions for a longer duration. Thus the high compression ratio obtained during part throttle conditions increases its efficiency. The fuel efficiency of an engine is directly proportional to compression ratio, so the fuel economy of the vehicle is also increased during part throttle conditions. The vehicle is seldom used in full throttle under city conditions, hence overall fuel efficiency of the vehicle increases. The present invention may be also used for a multi cylinder engine by deploying several minor pistons along with the belleville spring and the retainer ring in the respective minor cylinders.

[00025] The present subject matter is thus described. In this description, the terms 'engine' and 'internal combustion engine' have been used interchangeably and both denote the same meaning. The description is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:

1. An internal combustion engine in which the compression ratio is varied during operation, comprising: a cylinder having a cylinder head, a major piston in the cylinder, a minor piston ensconced in a groove in the cylinder head and adjacent to an intake and an exhaust valve, the minor piston being angularly disposed with respect to the major cylinder long axis, the minor piston further comprising belleville spring pack and a retainer ring in such a way that the retainer ring faces the combustion chamber where, when the engine is in operation, maximum compression ratio is obtained at part throttle conditions and minimum compression ratio is obtained at full throttle conditions.

2. The internal combustion engine as claimed in claim 1 wherein the said minor piston is made of aluminum or aluminum alloy.

3. A two wheeler comprising the said internal combustion engine as claimed in any of the preceding claims.

4. An internal combustion engine substantially as herein described and illustrated by accompanying drawings.