WO1989000643A1

WO1989000643A1 - Internal combustion engine

Info

Publication number: WO1989000643A1
Application number: PCT/GB1988/000576
Authority: WO
Inventors: Graham Beverley
Original assignee: Graham Beverley
Priority date: 1987-07-18
Filing date: 1988-07-18
Publication date: 1989-01-26

Abstract

There is disclosed a spark ignition engine having at least one cylinder (10), a piston (11) linearly reciprocable in the cylinder so as to effect induction, compression, combustion and exhaust of an air/fuel mixture supplied to the engine, an intake (12a) to the cylinder (10) for admitting an air/fuel mixture, an output (14) from the cylinder (10) for venting exhaust products from the cylinder, and a control device (16) for supplying the air/fuel mixture to said intake (12a), said control device being controllable by an operator in order to lessen or increase the quantity of air/fuel mixture applied to the engine to meet a particular load demand. In order to convert the engine to operate according to the Atkinson cycle, but without the complicated mechanical means normally required, the engine is modified so that the ratio of volume Y swept by the piston (11) during its stroke to the volume X defined between the piston at the top of its stroke and the cylinder head is considerably greater e.g. 12 to 20 than that normally used for spark ignition of a charge in said volume X, and the control device includes means (17, 18) for restricting the supply of air/fuel mixture to the intake (12a), independently of operator control of the control device (16), so as effectively to reduce the compressive ratio applied to the charge by the compression stroke of the piston (11).

Description

INTERNAL COMBUSTION ENGINE

This invention relates to an internal combustion engine.

The invention has been developed primarily, though not exclusively, in connection with a spark ignition engine which is intended to operate with volatile liquid fuels, such as petrol, and gaseous fuels, and seeks to improve the operating efficiency to approach, or even exceed, the efficiencies obtainable with compression ignition engines.

It has been recognised for many years that the compression ignition or "diesel" engine has superior operating efficiency, as compared with a spark ignition or petrol engine operating on the OTTO cycle, and virtually all heavy duty vehicles are, and have been for many years fitted with diesel engines, from the viewpoint of fuel ecomony.

However, until fairly recently, diesel engines have not been widely accepted by customers for motorcars, at least in the United Kingdom, although there is a larger market in some European countries. The main disadvantages of diesel engines, for use in motorcars, are their relatively low power output, greater noise and tendency to emit smoke, a weight penalty and increased cost, as compared with petrol engines. ^• Despite all these disadvantages, there is a growing perception among customers of an advantage as to fuel costs, and long term durability of diesel engines for use in motorcars, which has resulted in an increasing availability of diesel- engined options for motorcars.

Nevertheless, the disadvantages of diesel engines, as compared with petrol engines, remain substantial, and there is a potential market for any possible improvement to the design of petrol engine so as to approach the operating efficiency of a diesel engine, while retaining to a large extent the inherent advantages of a petrol engine, namely less noise, less smoke and lower cost.

According to the invention there is provided a spark ignition engine having at least one cylinder, a piston linearly reciprocable in said cylinder so as to effect induction, compression, combustion and exhaust of an air/fuel mixture supplied to the engine, an intake to the cylinder for admitting an air-fuel mixture, an output from the cylinder for venting exhaust products from the cylinder, and a control device for supplying the air/fuel mixture to said intake, said control device being controllable by an operator in order to lessen or increase the- quantity of air/fuel mixture applied to the engine to meet a particular load demand, in which: the ratio of volume swept by the piston during its stroke to the volume defined between the piston at the top of its stroke and the cylinder head is considerably greater than that normally used for spark-ignition of a charge in said volume; and, the control device includes means for restricting the supply of air/fuel to the intake, independently of operator control of the control device, so as effectively to reduce the compressive ratio applied to the charge by the compression stroke of the piston.

Preferably, the engine operates on a four stroke cycle, though it is envisaged that the invention will be also applicable to a spark ignition engine operating on the two stroke cycle.

Effectively, in an internal combustion engine according to the invention, the theoretical compression ratio is significantly greater than that normally used for normal satisfactory spark-induced combustion of a compressed charge e.g. a compression ratio in the range 12 to 20, but said independently operating means of the control device restricts the amount of air/fuel admitted to the cylinder during the induction stroke, whereby the effective compression ratio is reduced to a lower level e.g. 8 to 12, suitable for sustaining normal spark-induced combustion of the charge.

However, by virtue of the two characterising features applied to an internal combustion engine according to the invention, there is provided by simple means an effective simulation of an Atkinson cycle engine. As will be well known, the Atkinson cycle was developed pre-1900, and depended upon a fundamentally different concept of the essential parameters to be considered in the efficient operation of a spark-ignition engine.

Conventional wisdom takes the view that the "compression ratio" shall be the same as the expansion ratio. Thus the expansion ratio is limited to the allowable value of compression ratio. The Atkinson cycle adopted complicated mechanical means to ensure that the combustion or expansion stroke of the piston was much greater than the induction stroke. This larger expansion stroke of the piston enables the compressed charge of fuel to undergo more complete combustion, and/or expansion and therefore results in more efficient use of the fuel. However, the mechanical complexity of the Atkinson cycle engine has been such that it has not been accepted for use on a mass production basis.

The invention, by contrast, provides more simple means whereby an otherwise conventional spark-ignition engine may be modified so as to simulate the operation of an engine operating according to the Atkinson cycle, such means comprising increasing the theoretical compression ratio of the engine (by reducing the volume defined above the piston head at the top of its stroke), and restricting the supply of fuel-air to the engine by an appropriate amount so that the actual compression ratio is in line with acceptable values for an unmodified engine.

The engine may run on petrol or other volatile liquid fuel, or a gaseous fuel, and the intake of air or fuel/air mixture is restricted in a controlled manner so as to allow the use of higher compression/ expansion ratio than could be used in an unrestricted engine, with consequent improvement in efficiency.

One preferred means for effecting controlled restriction may comprise limiting the opening of the controlling device, usually referred to as the "throttle plate". Thus, although maximum intake of air or fuel/air mixture may be requested (as for instance in a road vehicle where^" the driver has his foot hard down on the accelerator pedal), whereas this would normally result in the controlling device (throttle plate) being wide open, in an engine modified according to the invention with a theoretically higher compression. ratio and resulting higher efficiency, there would be a tendency for "pinking" or pre- ignition to occur, and therefore the controlling device (throttle plate) has its opening controlled by any suitable means so as to limit the opening thereof. This would restrict the intake of air or fuel/air mixture so that pinking or pre-ignition would not occur.

Another preferred means for restricting the intake of air or fuel/air mixture may comprise a secondary throttle plate, or other restrictive device, which would be operable to effect a controlled restriction, even though the normal restricting device (throttle plate) may be operated to a wide open position.

A further means for restricting the intake of air or fuel/air mixture may comprise an arrangement whereby the inlet valve associated with the or each cylinder may be arranged to close earlier than normal.

A still further way of achieving a required restriction in supply of air / fuel to the intake, independently of operator control of the control device (so as effectively to reduce the compression ratio applied to the charge by the compression stroke of the piston, while allowing an effectively larger expansion stroke), may comprise an arrangement whereby the inlet valve associated with the or each cylinder may be caused to close later than normal .

This will be particularly suitable for use in a multi- cylinder arrangement, in that by the late closing of the inlet valve of any particular cylinder, a portion of the air / fuel charge introduced into the cylinder during the induction stroke will be returned to the inlet manifold during the early part of the compression stroke, but this returned charge portion will be available in the manifold to be drawn by an induction stroke of the or other cyl inders.

Another way of achieving the desired objective of the invention comprises an arrangement whereby a controlled quantity of exhaust gas is returned to the inlet manifold, or to the intake to the or each cylinder, to mix with the air / fuel mixture and to be drawn into the cylinder(s) during each induction stroke. This will have the effect of diluting the air / fuel mixture, so as to reduce the mass of air / fuel which can be admitted into any particular cylinder during an induction stroke.

In this specification, reference is made to control over the opening and closing of an inlet valve associated with a respective cylinder of an internal combustion engine, but of course for engines having more than one inlet valve per cylinder, evidently the opening and closing control may be exercised over a single one of the valve, some, or all of the valves associated with each cylinder.

It is intended that an engine, modified according to the invention, would normally be operated in the restricted, high efficiency mode. This would result in the torque output being restricted, as compared with an unmodified engine of the same size, but there will still remain the advantage of more efficient use of the fuel and, in any event, the power output will still be generally comparable with that obtainable by a diesel engine.

It is envisaged that it may be possible to provide further modification to the engine such as to offer a second mode of operation, in which there would be little or no restriction of the intake of air or fuel/air mixture, a-nd the tendency for resulting "pinking" (as a result of the- increased compression ratio) would be avoided, or at least limited, by retarding the ignition by a suitable amount. Depending on how high a compression ratio is used torque outputs could then be similar to those of a normal unrestricted engine. Maximum pressure would occur substantially after the piston has reached the top of its stroke and would lower the effective expansion ratio, and there would be a consequent reduction of efficiency. However, the efficiency, it is believed, could still be comparable with that of a normal unrestricted engine.

One embodiment of spark ignition engine according to the invention will now be described in detail, by way of example only, with reference to the acompanying schematic drawing.

Referring now to the drawing, there is shown schematically a spark ignition engine having at least one cylinder and modified according to the invention. For ease of illustration only, the engine shown in the drawing has a^" single cylinder, though it should be appreciated that the invention is applicable to single or multicylinder engines. The engine has a cylinder 10 and a piston 11 linearly reciprocable between the TDC (top dead centre) position designated by reference 11a and BDC (bottom dead centre) position designated by reference lib. The volume defined above the piston 11 at top dead centre is designated by reference X and the volume Y swept by the piston 11 during its travel from top dead centre to bottom dead centre is such as to give a compression ratio ^X^^Λ which is much greater than that normally required for a petrol engine. Thus, ^L^^Λ may be in the range 12 to 20, whereas a spark ignition petrol engine normally operates with a compression ration somewhat in the range between 8.0 and 10.0. A position lie of the piston 11 represents a typical bottom dead centre position for an unmodified engine.

The cylinder 10 has a usual inlet valve 12 for controlling the input from an intake 12a of an air/fuel mixture to the cylinder space above the piston 11, and an exhaust valve 13 leading via an exhaust manifold to an exhaust pipe 14. Following the compression stroke of the piston 11, a. spark is generated via a spark plug or the like 15 under suitable timed control with the operation o'f the engine. A control device in the form of a standard throttle plate 16 is arranged in an input supply to the engine, and will be under the direct control of the driver for altering the engine speed to meet current or anticipated load demand.

Given that the compression ratio of the engine is considerably increased, as compared with that normally required for satisfactory operation of a spark ignition petrol engine, and when supplied with similar fuel there would be a very substantial tendency for "pinking" or pre- ignition to occur. However, although the volume swept by the piston during its travel along the induction stroke is substantially greater, means is provided for deliberately restricting the amount of air and fuel admitted during the induction stroke, so that effectively the compression ratio is reduced to a lower level at which pinking or pre- ignition will not occur. The purpose of this is to then allow a substantial volume in which expansion can take place during and/or after combustion of the fuel, and this will result in more complete combustion and/or expansion of the fuel/air mixture with corresponding increase in efficiency.

Therefore, the control device 16 is controlled by an operator in order to lessen or increase the quantity of air/fuel mixture supplied to the engine to meet a particular load demand, but a separate and independently operating means is provided for restricting the actual amount supplied, despite a particular demand setting made by the control device 16.

Therefore, as mentioned above, the ratio of volume swept by the piston during its stroke to the volume defined between the piston and the cylinder head at top dead centre is considerably greater than that required for spark- ignition of a charge of air/fuel in this volume, but the control device which controls the operation of the engine Includes means for restricting the supply of air/fuel to tfce inlet valve 12 independently of operation of the control device 16, so as effectively to reduce the compressive ratio applied to the charge by the compression stroke of the piston. For illustration purposes only, there is shown schematically this control means by reference 17, which comprises some suitable arrangement for restricting the flow along the intake to the cylinder. This may comprise, for example, a secondary throttle plate 18 which has its opening controlled by some suitable independent control means operating on suitable parameters that have been pre-set to suit operating requirements.

Therefore, by this relatively simple means (17, 18), there is provided an effective simulation of an engine operating according to the Atkinson cycle; in the Atkinson cycle complicated mechanical means is provided so that the expansion stroke (combustion stroke) of the piston is considerably greater than the compression stroke.

The embodiment shown in the drawings is an engine operating on the four stroke cycle, but it is envisaged that the engine modification according to the invention disclosed herein may be applied, with suitable changes, to an engine operating on the two stroke cycle.

A modified engine according to the invention (operating in the high efficiency mode) will produce less torque, and therefore also less power, than an unmodified engine having the same swept volume, but the operating efficiency will be improved so as to approach, or even exceed those obtainable by diesel engines, while retaining most of the inherent advantages of a petrol or other volatile fuel engine.

While there has been described above an embodiment of the invention in the form of a linearly reciprocating piston type internal combustion engine, it should be appreciated that the features of increase of expansion ratio over the actual value of compression ratio may also be applied with advantage to a rotary piston (wankel) engine.

Claims

1. A spark ^■ ignition engine having at least one cylinder (10), a piston (11) linearly reciprocable in said cylinder so as to effect induction, compression, combustion and exhaust of an air/fuel mixture supplied to the engine, an intake (12a) to the cylinder for admitting an air/fuel mixture, an output (14) from the cylinder for venting exhaust products from the cylinder, and a control device (16) for supplying the air/fuel mixture to said intake (12a), said control device being controllable by an operator in order to lessen or increase the quantity of air/fuel mixture applied to the engine to meet a particular load demand, in which: the ratio of volume (Y) swept by the piston (11) during its stroke to the volume (X) defined between the piston at the top of its stroke and the cylinder head is considerably greater than that normally used for spark- ignition of a charge in said volume (X); and, the control device includes means (17, 18) for restricting the supply of air/fuel to the intake (12a) independently of operator control of the control device (16) so as effectively to reduce the compressive ration applied to the charge by the compression stroke of the piston.

2. An engine according to Claim 1 and operating on the four stroke cycle.

3. An engine according to Claim 1 or 2, in which said control means (17, 18) is operative to limit the opening of a throttle plate (16) controllable by the operator.

4. An engine according to Claim 1 or 2, in which said control means (17, 18) includes a secondary throttle plate ⁽18) which is operable to effect a controlled restriction in supply of air to the throttle plate (16) controllable by the operator.

5. An engine according to Claim 1 or 2, in which said control means comprises an arrangement whereby the inlet valve (12) associated with the or each cylinder is arranged to close earlier than normal.

6. An engine according to Claim 1 or 2, in which said control means comprises an arrangement whereby the inlet valve (12) associated with the or each cylinder is caused to close later than normal.

7. An engine according to Claim 1 or 2, in which a control means (17, 18) comprises an arrangement whereby a controlled quantity of exhaust gas is returned to the inlet manifold (12a) or to the intake to the or each cylinder, to mix with the air/fuel mixture and to be drawn into the cylinder(s) during each induction stroke.

8. An engine according to any one of the preceding claims and having more than one inlet valve associated with the or each cylinder, in which said control means (17, 18) is operative to control the opening and closing over a single one of the valves, some of the valves, or all of the valves associated with each cylinder in order to restrict the supply of fuel/air mixture to the cylinder.

9. An engine according to Claim 1 or 2, in which said control means (17, 18) is arranged to retard the ignition.