GB1587842A

GB1587842A - Internal combustion piston engine

Info

Publication number: GB1587842A
Application number: GB2395977A
Authority: GB
Original assignee: Rae W L S
Current assignee: Rae W L S
Priority date: 1978-04-04
Filing date: 1978-04-04
Publication date: 1981-04-08

Description

(54) INTERNAL COMBUSTION PISTON ENGINE (71) I, WILLIAM LILLICO STEPHEN RAE, a British subject of 10 Brandon Drive, Bearsden, Glasgow G61 3LN, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an internal combustion piston engine.

Previous proposals directed towards improving the specific fuel consumption of internal combustion piston engines have related to: (a) Improvements in materials and design to reduce friction losses and reciprocating mass losses.

(b) Improvements in mechanical design to reduce the amount of unburnt hydrocarbons in the exhaust gases by means of increased swirl or turbulence.

(c) Changes to the cylinder head and/or piston shape to increase the compression ratio of the engine.

(d) Changes to the cam-shaft shape and settings to alter the angular position of the engine shaft at which the valves open and close in order to vary the amount of exhaust gas retained in the cylinder to be mixed with the following inlet charge, thereby achieving some pre-heating of the inlet charge and re-cycling a proportion of the exhaust mixture which may contain a proportion of unburnt fuel.

(e) Changes to cylinder head design (stratified charge) to permit running on a weak mixture thereby reducing unburnt fuel content in the exhaust gases.

These previous proposals are all designed to reduce "secondary" energy losses in order to approach as closely as possible the theoretical thermal efficiency determined by the " Otto Cycle" on which petrol and gas engines operate. and the "Diesel Cycle" on which the diesel engines operate. Both cycles determine the "primary" energy losses calculated by the heat rejected from the engine at the end of the expansion stroke. Both cycles also depend upon the equality of the compression and expansion ratios. although in practice. the exhaust valve in real engines usually opens before completion of the expansion stroke, causing the effective expansion ratio of the engine to be smaller than the compression ratio thereby increasing the "primary" energy lost with the exhaust gas.

It is well known that an increase in the compression ratio gives an improvement to the efficiency of the thermal cycle. but there is an upper limit imposed by the flash-point temperature of the fuel. Thus the disadvantage of the above-mentioned previous proposals is that none of them can reduce the "primary energy losses in the working cycle.

It is also well known that there is a theoretical cycle known as the Atkinson cycle which allows a greater proportion of work to be extracted from the hot gases than is possible in the Otto (or Diesel) cycles. The principal feature is an expansion ratio which is greater than the compression ratio. It has long been accepted that an engine operating in an "Atkinson" type of cycle would have lower primary energy losses and hence an improved thermal efficiency. The practical difficulties in designing an engine to operate on this cycle have never been resolved in a form acceptable to engine manufacturers.

It is an aim of the present invention to provide an internal combustion piston engine in which the primarv losses set by the Otto and Diesel cycles are reduced by means of a simple mechanical modification which converts the engine to operate on a thermal cycle similar to the Atkinson cycle. By operating the engine of the present invention on a fundamentally more efficient thermal cycle. an improvement in the specific fuel consumption may be achieved.

Accordingly, this invention provides an internal combustion engine of the type having at least one reciprocating piston and cylinder arrangement and at least one inlet valve controlled by cam means, the internal combustion engine having (1) shaped inlet cam means adapted to delay the closure of the inlet valve thereby spilling induced air or fuel-air mixture from the cylinder prior to inlet valve closure and compression, and (2) a cylinder head having at least one raised lip portion and/or the piston having at least one raised crown portion for reducing the minimum cylinder volume such that the internal combustion engine has an expansion ratio which is greater than its effective compression ratio (as herein defined), and the internal combustion engine being such that during operation its valve timing does not alter.

As used herein, the term "effective compression ratio" means that ratio of the volume of the cylinder above the piston at the point reached when the inlet valve closes to the volume above the cylinder when the piston reaches top dead centre.

Preferably the inlet cam means has a protuberance which is flat at its apex.

The cylinder head may have a pair of raised lip portions which define therebetween a recessed area on the cylinder head. The lip portions give a squish effect near the end of a compression stroke when the piston approaches closely to the head. Gas is driven rapidly inwards towards the combustion recess as the piston approaches the lips. This rapid movement of gas causes extra turbulence in the combustion chamber to promote more complete combustion.

The or each piston may have a continuous raised crown portion which extends entirely around the periphery of the crown of the piston and which defines a recessed portion.

The engines of the present invention may be reciprocating piston engines operating on a 4-stroke cycle, or air-purged engines operating on a 2-stroke cycle. The inventive concept is applicable to new engines and to existing engines which can have existing components replaced and/or modified as necessary.

The effective compression ratio will normally be within the limit set by the fuel flash-point characteristics. More specifically, the compression and expansion ratio of a typical petrol engine may be 10:1. Fuel characteristics prevent this being raised much above 12:1. The engine of the present invention would allow an effective compression ratio to be maintained at 10:1 together with an expansion ratio of 20:1, a value normally only achieved in diesel engines. Modern diesel engines may have a compression ratio and an expansion ratio of 20:1 (some diesel engines have reached about 25:1), but the engine of the present invention would allow an expansion ratio of over 40:1 to be achieved while retaining an effective compression ratio of 20:1. Preferably, in the engine of the present invention, the ratio of expansion ratio to effective compression ratio lies in the range of 1.4:1 to 2:1.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows valve timing in relating to the angle of the main engine shaft and the cam shaft; Figure 2 shows the appearance of both a typical known cam profile and a modified cam profile as employed in an engine of the present invention, the modified cam profile giving the required inlet valve timing.

Figure 3 shows a full engine cycle for a known engine and an engine of the present invention Figures 4 and 5 are part sectional and plan view of a modified cylinder head, Figure 4 also showing a piston and cylinder of an engine; Figure 6 shows a section through a modified piston; Figure 7 is a top plan view of the modified piston shown in Figure 6; Figure 8 shows a known 4-stroke petrol engine cycle; and Figure 9 shows a modified engine cycle from an engine of the present invention.

In order to achieve the required high efficiency thermal cycle, a combination of a modification to the cam shaft and a modification to the cylinder head and/or pistons are employed.

Modification to the cam shaft The objective is to extend the period during which the inlet valves are open in order to draw in the maximum volume of fuel air mixture, then drive a proportion of this volume back out of each cylinder before the inlet valve closes.

-In Figure 1, there is shown the valve timing in relation to the angle of the main engine shaft and the cam shaft. The valve timing does not alter during operation of the engine.

Note that the cam shaft rotates at exactly half the speed of the main engine shaft. The modification required is to extend the angle of the inlet cams.

In Figure 2, there is shown the appearance of both a typical cam profile and the modified version. Since the maximum cam radii and position on the cam shaft remain as before, no change is required to the cam shaft mounting arrangements. In the modified version, it will be seen that the inlet cam means has a protuberance which is flat at its apex.

In Figure 3, there is shown the full engine cycle for standard and new versions, illustrating the points in the cycle at which the valves start to open and reach full closure.

The cam shaft modification alone will give a dual ratio displacement cycle, but since the compression starts at half the maximum volume, the effective compressidn ratio is reduced to half the original. The combined effect of the low effective compression ratio and the dual ratio cycle would give only a small improvement in efficiency and a significant reduction in peak power developed.

Modification to the cylinder head or pistons The objective of this modification is to reduce the compressed volume in proportion to the amount spilled to recover the original compression ratio. In this way, full advantage can be taken of the new thermal cycle efficiency and peak engine power is maintained.

In Figures 4 and 5 there is shown one method in which both "depth" and effective "diameter" of the combustion chamber have been reduced. Swirl will be enhanced by the additional "squish"-lip effect around the combustion chamber.

More specifically, in Figure 4, there is shown part of an internal combustion engine comprising a piston 2 which reciprocates on a connecting rod 4 in a cylinder 6 defined by a cylinder wall 8. The piston 2 has a pair of piston rings 10, 12 which sit in grooves in the piston 2. The cylinder 6 is closed by a cylinder head 14 which houses a sparking plug 16 and a valve 18. The valve 18 has a valve head 20 for opening and closing an inlet port 22. The valve 18 opens and closes the port 22 under the control of a modified cam shaft 24 which has inlet cam means 25 and exhaust cam means 27. The profile of the cam means 25 and 27 is most clearly seen in Figure 2.

The cylinder head 14 is modified as shown most clearly in Figure 5. In Figure 5, it will be seen that the cylinder head 14 is provided with "squish" lips 26 which define a recessed area 28.

Modification to the piston or pistons In order to modify an existing engine, it may be less expensive to fit modified pistons instead of a new cylinder head. An example of a modified piston is illustrated in Figures 6 and 7 wherein there is shown a piston 30 having grooves 32, 34 for receiving piston rings (not shown). The piston 30 has a connecting pivot point 36 for connecting to a connecting rod (not shown).

The piston 30 is modified by having a raised crown portion 38 which defines a recessed portion 40. The valves and the sparking plug (not shown) associated with the piston 30 are received in the recessed crown portion 40. The raised crown portion 38 in effect forms raised "squish" lips.

Principle of operation: Consider a standard known 4-stroke petrol engine (unmodified), illustrated in Figure 8 with a compression ratio of 10:1.

Inlet Stroke: Piston moves from A to B, where the inlet valve closes.

Compression: Piston moves from B to A, compressing volume VE to VO where VE/VO = 10:1.

Expansion: Piston moves again from A to B where the expansion ratio is VE/Vo = 10:1 approx.

Exhaust: Piston moves again from B to A, exhausting up to 90% of the exhaust gases.

The modified cycle is illustrated in Figure 9.

Inlet: The piston moves from Ar to B, drawing in the fuel/air mixture, but then starts to reject some of the mixture as it moves back to C, at which point the modified cam shaft closes the inlet valve.

Compression: The piston continues upwards from C to A1 compressing the volume V1 to V .

The cylinder head is modified to reduce the compressed volume from its original volume VO so as to maintain an effective compression ratio of 10:1 i.e. V1/VlO = 10:1.

Expansion: After ignition, the piston is driven from A] to B and the expansion ratio is VE/V1o Thus V1 = BVE, V O = 2VO and the expansion ratio = 2 times the effective compression ratio = 20:1.

Exhaust: The piston moves from B to A1, driving out up to 95% of the exhaust gases.

Advantages (a) A higher thermal efficiency can be achieved, i.e. less fuel is required per brake horsepower hour.

(b) The exhaust gases are emitted at a substantially lower temperature and pressure.

(c) For a given power requirement, the quantity of exhaust gas emitted is reduced compared to an unmodified engine.

(d) The exhaust noise is reduced due to the lower exhaust pressure and the small quantity of gas emitted.

(e) The means of achieving the dual ratio operating cycle requires modification to conventional engine parts only. No additional parts are required and the modified parts are suited to conventional methods of manufacture and maintenance.

At first sight it may appear that a modified engine in accordance with the invention would not be capable of producing the same peak power output as a similar unmodified engine.

However, the power developed depends upon the volume of mixture retained in the cylinder under dynamic operating conditions together with the efficiency with which the fuel is converted into useful work.

Theoretical analysis shows that a modified engine in accordance with the invention will develop substantially the same maximum power as an unmodified engine under the same operating conditions. In addition the modified engine will exhibit a smaller variation in torque developed at varying engine speeds when compared with an unmodified engine.

It is to be appreciated that the embodiment of the invention described above has been given by way of example only and that modifications may be effected. Thus, for example, the ratio of expansion ratio to effective compression ratio may be varied provided this ratio is greater than 1.0. The invention may also be applied to engines incorporating proposals to reduce secondary energy losses.

WHAT I CLAIM IS: 1. An internal combustion engine of the type having at least one reciprocating piston and cylinder arrangement and at least one inlet valve controlled by cam means, the internal combustion engine having (1) shaped inlet cam means adapted to delay the closure of the inlet valve thereby spilling induced air or fuel-air mixture from the cylinder prior to inlet valve closure and compression, and (2) a cylinder head having at least one raised lip portion and/or the piston having at least one raised crown portion for reducing the minimum cylinder volume such that the internal combustion engine has an expansion ratio which is greater than its effective compression ratio (as herein defined), and the internal combustion engine being such that during operation its valve timing does not alter.

2. An internal combustion engine according to claim 1 in which the inlet cam means has a protuberance which is flat at its apex.

3. An internal combustion engine according to claim 1 or claim 2 in which the cylinder head has a pair of raised lip portions which define therebetween a recessed area on the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Principle of operation: Consider a standard known 4-stroke petrol engine (unmodified), illustrated in Figure 8 with a compression ratio of 10:1. Inlet Stroke: Piston moves from A to B, where the inlet valve closes. Compression: Piston moves from B to A, compressing volume VE to VO where VE/VO = 10:1. Expansion: Piston moves again from A to B where the expansion ratio is VE/Vo = 10:1 approx. Exhaust: Piston moves again from B to A, exhausting up to 90% of the exhaust gases. The modified cycle is illustrated in Figure 9. Inlet: The piston moves from Ar to B, drawing in the fuel/air mixture, but then starts to reject some of the mixture as it moves back to C, at which point the modified cam shaft closes the inlet valve. Compression: The piston continues upwards from C to A1 compressing the volume V1 to V . The cylinder head is modified to reduce the compressed volume from its original volume VO so as to maintain an effective compression ratio of 10:1 i.e. V1/VlO = 10:1. Expansion: After ignition, the piston is driven from A] to B and the expansion ratio is VE/V1o Thus V1 = BVE, V O = 2VO and the expansion ratio = 2 times the effective compression ratio = 20:1. Exhaust: The piston moves from B to A1, driving out up to 95% of the exhaust gases. Advantages (a) A higher thermal efficiency can be achieved, i.e. less fuel is required per brake horsepower hour. (b) The exhaust gases are emitted at a substantially lower temperature and pressure. (c) For a given power requirement, the quantity of exhaust gas emitted is reduced compared to an unmodified engine. (d) The exhaust noise is reduced due to the lower exhaust pressure and the small quantity of gas emitted. (e) The means of achieving the dual ratio operating cycle requires modification to conventional engine parts only. No additional parts are required and the modified parts are suited to conventional methods of manufacture and maintenance. At first sight it may appear that a modified engine in accordance with the invention would not be capable of producing the same peak power output as a similar unmodified engine. However, the power developed depends upon the volume of mixture retained in the cylinder under dynamic operating conditions together with the efficiency with which the fuel is converted into useful work. Theoretical analysis shows that a modified engine in accordance with the invention will develop substantially the same maximum power as an unmodified engine under the same operating conditions. In addition the modified engine will exhibit a smaller variation in torque developed at varying engine speeds when compared with an unmodified engine. It is to be appreciated that the embodiment of the invention described above has been given by way of example only and that modifications may be effected. Thus, for example, the ratio of expansion ratio to effective compression ratio may be varied provided this ratio is greater than 1.0. The invention may also be applied to engines incorporating proposals to reduce secondary energy losses. WHAT I CLAIM IS:

1. An internal combustion engine of the type having at least one reciprocating piston and cylinder arrangement and at least one inlet valve controlled by cam means, the internal combustion engine having (1) shaped inlet cam means adapted to delay the closure of the inlet valve thereby spilling induced air or fuel-air mixture from the cylinder prior to inlet valve closure and compression, and (2) a cylinder head having at least one raised lip portion and/or the piston having at least one raised crown portion for reducing the minimum cylinder volume such that the internal combustion engine has an expansion ratio which is greater than its effective compression ratio (as herein defined), and the internal combustion engine being such that during operation its valve timing does not alter.

cylinder head.

4. An internal combustion engine according to any one of claims 1 to 3 in which the or each piston has a continuous raised crown portion which extends entirely around the periphery of the crown of the piston and which defines a recessed portion.

5. An internal combustion engine according to claim 1 and substantially as herein described with reference to the accompanying drawings.