GB2393758A

GB2393758A - An auto-ignited homogeneous charge four stroke engine

Info

Publication number: GB2393758A
Application number: GB0217534A
Authority: GB
Inventors: James William Griffith Turner
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2002-07-29
Filing date: 2002-07-29
Publication date: 2004-04-07
Anticipated expiration: 2022-07-29
Also published as: GB2393758B; GB0217534D0

Abstract

With reference to Figure 1, the present invention provides a method of operating a four-stroke internal combustion engine in which combustion is achieved at least partially by an auto-ignition process and in which flow of fuel/air charge into and flow of combusted gases from at least one combustion chamber (12) is regulated by valve means (15, 16) in order to ensure that the fuel/air charge is mixed with the combusted gases so as to generate conditions in the combustion chamber (12) suitable for operation of an auto-ignition process. The valve means (15,16) used comprises an inlet valve means (15) controlling flow of fuel/air mixture into the combustion chamber (12) from an inlet passage (13) and exhaust valve means (16) controlling exhaust of combusted gases from the combustion chamber (12) to an exhaust passage (14). During a single four-stroke cycle the inlet valve means (15) is opened for two separate periods, with the inlet valve means (15) being opened during an exhaust stroke of the engine so that combusted gases are expelled from the combustion chamber (12) into the inlet passage (13) and then closed prior to a subsequent opening of the inlet valve means (15) to allow the combustion gases previously expelled from the combustion chamber (12) to be drawn back into the combustion chamber (12) during an intake stroke along with a fresh charge of air or fuel/air mixture.

Description

- 1 - AN AUTO-IGNITED HOMOGENEOUS CHARGE FOUR STROKE ENGINE

The present invention relates to a four-stroke internal combustion engine.

Increasingly, stringent fuel economy and emissions targets are being imposed by government legislation. These and consumer pressures continually force the automotive industry to investigate new ways 10 of improving the combustion process of the internal combustion engine.

One such approach is the auto-ignition (AI) process. In this process a mixture of combusted gases, 15 air and fuel is created which ignites without the need for a spark during compression. The process is sometimes called self-ignition. It is a controlled process and thus differs from the undesirable pre-

ignition which has been known in some spark-ignition 20 engines. It differs from compression ignition in diesel engines because in a diesel engine the diesel fuel ignites immediately on injection into a pre-

compressed high temperature charge of air, whereas in the auto-ignition process the fuel and air and 25 combusted gases are mixed together prior to combustion. Use of the auto-ignition process in two-

stroke engines is well known. The present invention relates to the application of this process to a four-

stroke internal combustion engine.

In US 6082342 there is described a four-stroke internal combustion engine which provides for auto-

ignition by controlling the motion of the inlet and exhaust valves of a combustion chamber to ensure that 35 a fuel/air charge is mixed with combusted gases to generate conditions suitable for auto-ignition. US 6082342 describes an engine with a mechanically cam

- 2 - actuated exhaust valve which is closed later in the four-stroke cycle than usual in a normal four-stroke engine to allow for the exhaust valve to be simultaneously open with an intake valve and to allow 5 previously expelled combusted gases to be drawn back into the combustion chamber. Additionally, there is described an engine in which an exhaust valve is closed early in the exhaust stroke to trap combusted gases for subsequent mixing with an intake of fuel and 10 air mixture. In both engines the exhaust valve is opened only once in each four-stroke cycle.

The present invention provides a method of operating a four-stroke internal combustion engine in 15 which combustion is achieved at least partially by an auto-ignition process and in which flow of fuel/air charge into and flow of combusted gases from at least one combustion chamber is regulated by valve means in order to ensure that the fuel/air charge is mixed with 20 the combusted gases so as to generate conditions in the combustion chamber suitable for operation of an auto-ignition process, wherein the valve means used comprises an inlet valve means controlling flow of fuel/air mixture into the combustion chamber from an 25 inlet passage and exhaust valve means controlling exhaust of combusted gases from the combustion chamber to an exhaust passage characterized in that: during a single four-stroke cycle the inlet valve means is opened for two separate periods, with the 30 inlet valve means being opened during an exhaust stroke of the engine so that combusted gases are expelled from the combustion chamber into the inlet passage and then closed prior to a subsequent opening of the inlet valve means to allow the combusted gases 35 previously expelled from the combustion chamber to be drawn back into the combustion chamber along with a fresh charge of air or fuel/air mixture.

The double opening during an intake stroke of the inlet valve means in a single four-stroke cycle reliably creates the conditions necessary for auto-

ignition in the combustion chamber.

Preferred embodiments of the present invention will be described with reference to the following figures: Figure 1 is a schematic illustration of a first 10 embodiment of single cylinder four-stroke engine according to the present invention; Figures 2a and 2b are valve timing diagrams for the exhaust and inlet valves of a single cylinder four-stroke internal combustion engine operating 15 according to a conventional method of operation; and Figures 3a, 3b and 3c are valve timing diagrams for the exhaust and inlet valves of a single cylinder four-stroke internal combustion engine operating according to the method of the present invention, in a 20 first regime.

For simplicity, the detailed description

following will address the method of the present invention in its application to a single cylinder 25 four-stroke internal combustion engine, although it should be appreciated that the present invention is equally applicable to a multicylinder four-stroke internal combustion engine.

30 A schematic representation of a first embodiment of a single-cylinder four-stroke internal combustion engine is given in Figure 1. In the figure a piston 10 is movable in a cylinder 11 and defines with the cylinder 11 a variable volume combustion chamber 12.

An intake passage 13 supplies a mixture of fuel and air into the combustion chamber 12. The flow of

- 4 the fuel/air charge into the combustion chamber 12 is controlled by an intake valve 15.

Combusted gases can flow from the combustion 5 chamber 12 via an exhaust passage 14 and flow of combusted gases through the exhaust passage 14 is controlled by the exhaust valve 15.

Combusted gases can flow from the combustion 10 chamber 12 via an exhaust passage 14 and flow of combusted gases through the exhaust passage 14 is controlled by the exhaust valve 16.

The inlet valve 15 and the exhaust valve 16 are 15 hydraulically actuated. It can be seen in the figure that the stem 17 of the inlet valve 15 has provided thereon a piston 18 which is movable in a cylinder 19.

Similarly, the stem 20 of the exhaust valve 16 has a piston 21 provided thereon which is movable in a 20 cylinder 22.

Flow of hydraulic fluid to the cylinder 19 is controlled by a servo-valve 23. The servo-valve 23 is electrically controlled. The servo-valve 23 is 25 controlled by control signals generated by the electronic controller 24. The servo-valve 23 can control hydraulic fluid to flow into an upper chamber 25 of an arrangement of the piston 18 and the cylinder 19 whilst controlling flow of hydraulic fluid out of a 30 lower chamber 26. The servo-valve 23 can also control flow of hydraulic fluid to and from the cylinder 19 such that hydraulic fluid is delivered to the bottom chamber 26 whilst hydraulic fluid is expelled from the upper chamber 25. The fluid supplied to and expelled 35 from the cylinder 19 is metered, so as to control exactly the position and/or velocity of the inlet valve 15.

- 5 In a similar fashion, a servo-valve 27 is provided to control flow of hydraulic fluid to and from the cylinder 22. The servo-valve 27 is controlled electrically by the electronic controller 24. The 5 servovalve 27 can operate to supply hydraulic fluid under pressure to an upper chamber 28 of a cylinder 22 whilst allowing hydraulic fluid to be expelled from the lower chamber 29 of the cylinder 22. Conversely, the servo-valve 27 can allow pressurised hydraulic 10 fluid to be supplied to the lower chamber 29 whilst allowing hydraulic fluid to be expelled from the upper chamber 28. The servo-valve 27 meters the flow of hydraulic fluid to and from the cylinder 22 in order to control the position and/or the velocity of the 15 exhaust valve 16.

Both of the servo-valves 23 and 27 are connected to a pump 30 and a sump 31. Hydraulic fluid under pressure is supplied by the pump 30 and when hydraulic 20 fluid is expelled from either or both of the cylinders 19 and 22 it is expelled to the sump 31. The pump 30 will in practice draw fluid from the sump 31 to pressurise the fluid and then supply the pressurised fluid to the servo-valves 23 and 27.

The electronic controller 24 will control the movement of the inlet valve 15 and exhaust valve 16 having regard to the position of the inlet and exhaust valves 15 and 16 as measured by two position 30 transducers 32 and 33. The controller 24 will also have regard to the position of the engine, which will be measured by a rotation sensor 34 which is connected to a crank shaft 35 of the internal combustion engine, the crank shaft 35 being connected by a connecting rod 35 36 to the piston 10 reciprocable in the cylinder 11.

The engine of the present invention has an

- 6 - hydraulically controlled valve train with an electronic controller 24 which is programmable and hydraulically controls the opening and closing of both the inlet 15 and exhaust 16 valves. This enables 5 control of the motion of the inlet 15 and exhaust 16 valves and in particular the time (in terms of the engine cycle) when the inlet 15 and exhaust 16 valves open and the duration of time for which they are open.

10 Conventional four-stroke internal combustion engines have cam shafts which drive the inlet and exhaust valves. The cam shafts have cam profiles which are designed to maximise the gas flow through the engine. Such engines rely on a spark plug to 15 ignite the mixture. They also rely on an intake throttle to reduce gas flow and therefore control the power output of the engine.

In an engine according to the present invention 20 the movement of the inlet 15 and exhaust 16 valves will be used for total gas flow management, controlling both the amount of air flowing into and out of the combustion chamber 12 during each stroke of the engine and also controlling the internal mixing 25 process between the different gas species inside the combustion chamber 12 and also to an extent inside the inlet passage 13 and exhaust passage 14. The valve motion in the internal combustion engine according to the present invention will be very different from the 30 motion of inlet and exhaust valves controlled by a conventional mechanical cam shaft. The valve motion will comprise different duration valve opening periods, different height lifts and a different number of lifts in each stroke. This will allow the engine 35 valves 15 and 16 to control gas flow, engine load/power and also the timing of combustion within the engine. There will therefore be a reduced need for

( - 7 - a throttle system and a reduced need for a spark plug.

It may be that a spark plug is used only on start up of the engine or at low temperatures or in high load/high speed operating conditions.

In Figure 1 there can be seen a throttle 40 which is rotated by a motor 41 controlled by the controller 24. Whilst the throttle 40 can be used to control power output of the engine in a conventional manner it 10 is used in an unusual fashion in the present invention to fully close the inlet passage 13 in certain circumstances, as will be described later.

In Figure 1 there can also be seen a fuel 15 injector 50 which delivers fuel in a spray into the inlet passage 13. The fuel injector 50 is controlled by the electronic controller 24.

The auto-ignition process is already well-known 20 in two stroke engines. It provides improved fuel consumption, a lower engine emission (principally lower hydrocarbons and carbon monoxide) and improved combustion stability. The two-stroke engine is an ideal engine for autoignition because auto-ignition 25 relies upon the retention of some exhaust gas in the combustion chamber and a two-stroke engine can easily facilitate this, because the process of scavenging exhaust gases can be controlled to leave the required residual amount of exhaust gas in the mixture of fuel 30 and air ready for combustion. Auto-ignition can provide reproducible combustion time after time.

Control of the motion of the inlet valve 15 and exhaust valve 16 in accordance with the present 35 invention is illustrated with reference to Figures 3a, 3b and 3c, with Figures 2a and 2b giving an operating regime of normal camshaft operated valves for

- 8 comparison. Figures 2a and 2b show typical valve motion in a standard four-stroke internal combustion engine. The 5 zero degree position is the beginning of the expansion stroke of the engine. Figure 2a shows that the exhaust valve opens in the expansion stroke roughly 30 degrees before bottom dead centre and Figure 2b shows that the exhaust valve remains open through the exhaust stroke 10 to close at the beginning of the induction stroke at roughly 10 degrees after top dead centre. Figure 2a also shows that the inlet valve begins to open at the end of the exhaust stroke about 10 degrees before top dead centre, remains open throughout the induction 15 stroke and Figure 2b shows that the inlet valve closes in the beginning of the compression stroke at about 45 degrees after bottom dead centre. A fuel/air charge is introduced into the combustion chamber via the open inlet valve. Then the fuel/air charge is ignited by 20 sparks compressed and then as the combustion occurs and the gases expand in the power stroke.

Figures 3a, 3b and 3c illustrate an operating regime according to the present invention. In this 25 operating regime the inlet valve 15 is opened and closed twice during each 360 degree rotation of the crankshaft 35. The inlet valve 15 is opened during an engine cycle at roughly 30 degrees after bottom dead centre in the beginning of the exhaust stroke (see 30 Figure 3a). The inlet valve 15 is then closed at approximately 90 degrees after bottom dead centre. The inlet valve 15 is then opened again at the end of the exhaust stroke and remains open for the whole of the intake stroke, closing roughly 45 degrees after bottom 35 dead centre in the compression stroke.

( - 9 - The exhaust valve 14 is opened as in normal operation in the expansion stroke roughly 30 degrees before bottom dead centre, then remains open for the while of the exhaust stroke and closes at top dead 5 centre point of the piston 10 at the end of the exhaust stroke.

In the operating regime of the present invention the inlet valve 15 is opened twice during a single 10 four stroke engine cycle. During one period of opening combusted gases are expelled from the combustion chamber to the inlet passage 13. During the other period of opening previously exhausted combusted gases are drawn back into the combustion chamber from the 15 inlet passage 13 at the same time as fuel/air charge is drawn into the combustion chamber 12 through the inlet passage 13. Thus mixing of combusted gases and fresh fuel/air charge is achieved in the inlet passage 13 and also throughout induction of the fresh charge 20 into the combustion chamber. This promotes the correct conditions for auto-ignition. Auto-ignition of the mixture of combusted gases, fuel and air occurs after compression of the mixture during the compression stroke. The combustion of the mixture then causes the 25 gases to expand in the power stroke. The four stroke cycle then starts again.

It should be noted that the maximum lift of the inlet valve 16 is less when opened early in the 30 exhaust stroke in each engine cycle.

In the operation of the engine the electrically operated throttle 40 will be fully closed when the inlet valve IS is opened early in the exhaust stroke, 35 in order to prevent expulsion of the exhausted gases past the throttle valve 40 to atmosphere.

( The inlet passage 13, at least the part of the inlet passage 13 between the throttle valve 13 and the inlet valve 15 will be defined by a material resistant to the heat of the expelled combusted gases.

There could be a heat resistant plenum chamber located between the inlet valve 15 and the throttle 40 and combusted gases could be expelled into the plenum chamber for mixture in the chamber prior to re 10 introduction to the combustion chamber 12.

The high temperature exhaust gases expelled into the inlet passage 13 could assist transition of liquid fuel to vapour in the case that the fuel is injected 15 by the injector 40 on to the back of the inlet valve 14. The timing of delivery of the fuel by the injector 50 will be controlled by the controller 23 to occur only after the inlet valve 15 is closed during the exhaust stroke.

If there are two inlet valves per cylinder and if motion of each inlet valve is separately controlled then it may be preferable to open only one intake valve to receive combusted gases early in the exhaust 25 stroke and then the other (if there is an intake passage common to both intake valves) during the intake stroke or both during the intake stroke.

If there are two inlet valves per cylinder and if 30 the motion of each inlet valve is separately controlled then the inlet valves could be controlled to have differing motions and thereby create swirl of the gases in the combustion chamber to promote mixing and to promote the correct conditions for auto 35 ignition.

As mentioned above, whilst the simple engine

( 11 -

shown above does not have a spark plug, it may prove necessary to use a spark plug to complement the auto-

ignition process, particularly in start-up conditions.

Also it may also prove preferable to rely on auto 5 ignition only in partload/low speed operating conditions and to use spark ignition during high load/high speed operating conditions.

Whilst the inlet valve 15 and exhaust valve 16 in 10 the above embodiments are both hydraulically actuated, they could be valves actuated purely electrically or by electromagnetic forces.

With the engine of the present invention it will 15 not be necessary to pre-heat the fuel/air charge prior to admission into the combustion chamber in order to achieve auto-ignition.

Claims

- 12 CLAIMS

1. A method of operating a four-stroke internal combustion engine in which combustion is achieved at 5 least partially by an auto-ignition process and in which flow of fuel/air charge into and flow of combusted gases from at least one combustion chamber is regulated by valve means in order to ensure that the fuel/air charge is mixed with the combusted gases 10 so as to generate conditions in the combustion chamber suitable for operation of an auto-ignition process, wherein: the valve means used comprises an inlet valve means controlling flow of fuel/air mixture into the 15 combustion chamber from an inlet passage and exhaust valve means controlling exhaust of combusted gases from the combustion chamber to an exhaust passage; characterized in that: during a single four-stroke cycle the inlet valve 20 means is opened for two separate periods, with the inlet valve means being opened during an exhaust stroke of the engine so that combusted gases are expelled from the combustion chamber into the inlet passage and then closed prior to a subsequent opening 25 of the inlet valve means to allow the combustion gases previously expelled from the combustion chamber to be drawn back into the combustion chamber during an intake stroke along with a fresh charge of air or fuel/air mixture.

2. A method as claimed in claim 1 wherein the flow of gases through the inlet passage is throttled by use of a throttle in the inlet passage and wherein the method comprises controlling the throttle to fully 35 close the inlet passage whilst combusted gases are expelled into the inlet passage via the open inlet valve means during the exhaust stroke.

l

( - 13

3. A method as claimed in claim 1 or claim 2 wherein the inlet valve means and the exhaust valve means are simultaneously open during at least part of the period during which the inlet valve means is open in the 5 exhaust stroke.

4. A method as claimed in any one of claims 1 to 3 wherein the inlet valve means used comprises at least two independently movable inlet valves, a first inlet 10 valve which is opened during the exhaust stoke to allow the combusted gases to be expelled to the inlet passage and a second inlet valve which is opened only during the period of opening of the inlet valve means which allows a charge of air or fuel/air mixture to be 15 drawn into the combustion chamber.

5. A method as claimed in any one of the preceding claims comprising in the four-stroke cycle delivery of fuel to the inlet passage only after the inlet valve 20 means has closed subsequent to allowing combusted gases to be expelled to the inlet passage whereby the delivered fuel mixes in the inlet passage with the expelled combusted gases.

25

6. A method as claimed in any one of the preceding claims wherein the combustion chamber is a variable volume chamber defined in a cylinder by a piston reciprocating in the cylinder and wherein the opening and closing of the valve means is controlled by an 30 electronic processor which operates according to a programme of instructions and which receives an input signal indicative of the position of the piston reciprocating in the cylinder.

35

7. A method as claimed in claim 6 wherein the valve means comprises hydraulically actuated valves controlled by the electronic processor.

/

8. A method as claimed in claim 7 wherein the hydraulically actuated valves are poppet valves.

9. A method as claimed in any one of the preceding 5 claims comprising the step of pressuring the fuel/air mixture by supercharging or turbocharging prior to admitting the fuel/air mixture into the combustion chamber. 10

10. A four-stroke internal combustion engine operated according to a method as claimed in any one of the preceding claims.