A Gasoline Direct Injection Internal Combustion Engine

The present invention relates to a gasoline direct injection internal combustion engine.

It is important in a gasoline direct injection internal combustion engine to ensure good mixing of the injected fuel with air in the combustion chamber.

The present invention provides an internal combustion engine comprising: a variable volume combustion chamber formed by a piston reciprocating in a cylinder; a gasoline direct injector for injecting gasoline fuel directly into the combustion chamber; a plurality of intake valves via which air is introduced into the combustion chamber; a spark plug for igniting fuel in the combustion chamber; at least one exhaust valve via which combusted gases leave the combustion chamber; and a valve operating mechanism for opening and closing the intake valves and the exhaust valve (s); wherein: a gasoline direct injector is located in an upper surface of the cylinder; and the valve operating mechanism can operate the first and second intake valves such that in an engine cycle a valve opening time and a valve closing time of the first intake valve differ from a valve opening time and a valve closing time of the second intake valve and thereby a swirl of air is created in the combustion chamber into which the direct fuel injector delivers fuel.

The primary advantage is that increased turbulence is set up in the combustion chamber to the benefit of fuel atomisation and vaporisation and hence combustion efficiency.

The present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a simplified illustration of a combustion chamber of an engine according to the present invention, showing disposition of an injector and a spark plug;

Figure 2 is a schematic illustration of the combustion chamber of Figure 1 showing the disposition of inlet valves in the engine;

Figure 3 is a graphical illustration of the valve lifts of the intake and exhaust valves of the engine of Figure 2, operating according to the Otto cycle;

Figure 4 is a graphical illustration of the valve lifts of the intake and exhaust valves of the engine of Figure 2 , operating according to the Miller cycle; and Figure 5 is a graphical illustration of the valve lifts of the intake and exhaust valves of the engine of Figure 3 , operating according to the Atkinson cycle.

Turning first to Figure 1, there can be seen a variable volume combustion chamber 10 formed by a piston 11 sliding in a cylinder 12. A gasoline injector 16 is mounted substantially vertically, i.e. substantially aligned with an axis of the cylinder 12. The injector 16 is located centrally in the top of the combustion chamber 10. The injector 16 sprays gasoline directly into the combustion chamber 10. The injector 16 is located adjacent a spark plug 13. The spark plug 13 and injector 16 are located in a

plane lying along a crankshaft axis of a conventional multi- cylinder bank.

Turning now to Figure 2, there can be seen in the Figure a cylindrical combustion chamber 10. The chamber 10 is defined between a piston 11 and a surrounding cylinder 12. The piston 11 reciprocates in the cylinder 12 and thereby varies the volume of the combustion chamber 10. The piston 11 is connected by a connecting rod 13 to a crankshaft 14. The cylinder 12 and the cylindrical combustion chamber 10 have a principal axis 15. An injector

16 is located on the principal axis 15 and delivers fuel and air to the combustion chamber 10 centrally to the combustion chamber. The injector 16 opens onto a central part of the hemispherical closed end surface of the cylinder 12.

In the Figure 1 there can be seen a pair of intake valves 17 and 18. These valves are poppet valves. These valves control flow into the combustion chamber 10 of air from a pair of inlet runners 19 and 20. The inlet valves 17 and 18 are biased into abutment with valve seats surrounding the intake ports of the engine by valve springs 21 and 22.

Also in Figure 1 there can be seen a pair of exhaust valves 23 and 24 which open and close exhaust ports at the end of two exhaust runners 25 and 26. Like the inlet valves

17 and 18, the exhaust valves 23 and 24 are each biased into a closed position by one of a pair of valve springs 27 and 28.

Each of the poppet valves 17, 18, 23 and 24 is open and closed by one of four hydraulic actuators 29, 30, 31 and 32.

All of the hydraulic actuators are identical to each other and therefore the operation of only one actuator 29, will be described and it can be assumed that the other three actuators operate in an identical fashion.

The actuator 29 comprises a piston 33 movable in a cylinder 34. The piston 33 has a stem member 35 which abuts the top of the stem of the poppet valve 17. The piston 33 defines with the cylinder 34 an upper and a lower chamber in the cylinder 34. These chambers are both connected to an electrically operated servo-valve 36. The servo-valve 36 is connected by piping both to a pump 37 which supplies pressurised hydraulic fluid and to a sump 38 for hydraulic fluid. The pump 37 draws hydraulic fluid from the sump 38 and pressurises the drawn hydraulic fluid. The valve 36 can operate to either (a) supply hydraulic fluid to the upper chamber of actuator 29 while allowing hydraulic fluid to flow from the lower chamber (so that the piston 33 moves downward and opens the inlet valve 17) or (b) so that pressurised hydraulic fluid is supplied to the lower chamber of the actuator 29 and hydraulic fluid is allowed to flow out of the upper chamber to the sump 38 (so that the piston 33 moves upwardly to allow the inlet valve 17 to close under the action of the valve spring 21) .

The hydraulic servo-valve 36 will meter the flow of hydraulic fluid into and out of the chambers of the actuator 29 in order to control the speed of motion of the piston 33 and the position of the piston 33 (and thereby to control the speed of motion and position of the inlet valve 17) .

The actuators 30, 31 and 32 have associated therewith servo-valves 39, 40 and 41 which operate in the same way as the servo-valve 36 already described. The four servo-valves 36, 39, 40 and 41 are controlled by electrical signals generated by an electronic controller 42. The electronic controller 42 receives from four position transducers 43, 44,45 and 46, signals indicating the position of the pistons in the actuators 29, 30, 31 and 32 and hence the position of the valves 17 18, 23 and 24. These position signals provide feedback signals in the closed position control feedback loop.

In Figure 2 it is shown that the electronic controller 42 also receives a signal from a rotational sensor 47 connected to the crankshaft 14 which will indicate the position of the piston 11 in the cylinder 12. The electronic controller 42 will be a digital controller which will operate according to a pre-programmed set of instructions in dependence on the various signals received thereby. The electronic controller 42 will receive signals from sensors which are not shown, such sensors indicating for instance the temperature of the engine, the position of the accelerator pedal used to control the engine, the load on the engine and the speed of the engine .

In Figure 2 the injector 16 receives fuel via a line 49. The line 49 will be connected to a fuel pump (not shown) which will either be an electrical or mechanical fuel pump .

The valve train mentioned above is capable of operating the valves intake and exhaust with different lifts and/or

opening durations at different engine speeds and/or loads. The valve motion appropriate for low speed and low load operation will be different to the valve motion appropriate for high speed and high load operation.

The applicant has realised that at low speeds and low loads in particular it is important to create a swirl motion in the combustion chamber in order to ensure good atomisation and vaporisation of a fuel injected into the cylinder prior to ignition. At higher speeds and higher loads the time available to create such swirl conditions is less and also the kinetic energy of the air flowing into the combustion chamber is greater so that there is a greater amount of turbulence in the combustion chamber anyway.

The present invention proposes that the inlet valves are controlled such that one intake valve has a opening time and closing time different to those of the other intake valve. In this way, the flow of air into the combustion chamber naturally gives rise to a swirl within the combustion chamber and it is into this swirling mixture that fuel is directly injected. The increased turbulence in the combustion chamber has a primary advantage that it leads to better fuel atomisation and vaporisation and hence combustion efficiency.

It is envisaged that the intake valves will be operated differently only at certain engine speeds and loads and at other engine speeds and loads the valve opening times and valve closing times of both intake valves will be identical to each other.

In the embodiment illustrated the swirl will be set up in the chamber approximately centred on the cylinder axis and it is for this reason that the fuel injector 15 and the spark plug 53 are located centrally in the upper surface of the cylinder.

The swirl can react with the spray in different ways. If the spark plug and the injector are disposed such that the chamber is asymmetric, for instance with the spark plug and injector located in a plane lying along the crankshaft axis in a conventional multi-cylinder bank, then the injection of the spray into the charge air will differ depending upon the detail of the swirl and the injection core. This is shown in Figure 1.

In Figure 3, there is shown graphically the opening times and closing times of a pair of intake valves in an engine operated with an Otto cycle and operated according to the present invention. Only the intake and compression strokes of the engine are shown graphically, but it will be appreciated that the engine is operating a four-stroke cycle of intake, compression, power and then exhaust. In the figure the line 100 shows that a first intake valve opens earlier in the cycle than the second intake valve whose motion is indicated by a line 101. It can also be seen that the first intake valve with the motion indicated by line 100 closes at a closing time before the closing time of the intake valve whose motion is indicated by line 101. The Figure 3 operation is operation according to an Otto cycle, in which the compression ratio of the engine is effectively equivalent to the expansion ratio of the engine.

In an alternative operation an engine is operated according to a Miller cycle with an expansion ratio greater than the effective compression ratio of the engine. This is shown in Figure 4 where the line 200 shows the movement of a first intake valve and the line 201 shows the movement of a second intake valve . As with Figure 3 , the valve opening time and closing time of one valve differs to the valve opening time and closing time of the valve. Unlike Figure 3, one of the valves (that with the motion indicated by line 201) closes not during the intake stroke, but during the beginning of the compression stroke. Thus, air drawn into the combustion chamber during the intake stroke is expelled via the intake valve at the beginning of the compression stroke in order to reduce the compression ratio effective in the engine.

Figure 5 shows the engine operating with an Atkinson cycle. In this operation the intake valves again have opening times which differ to each other and closing times which differ to each other (as indicated by the lines 300 and 301) . However, unlike the cycles above, both intake valves are closed prior to the end of the intake stroke. This means that air drawn into the combustion chamber during the intake stroke is then expanded after the intake valves are closed with the expanded air then being pressurised in a subsequent compression stroke. This reduces the effective compression ration of the engine and leads to an engine with an expansion ratio greater than the compression ratio.

Whilst the engine described above has two intake valves and one spark plug, the engine could have any number of spark plugs or any number of intake valves as long there are

_ Q _

at least two intake valves. The number of exhaust valves are not important .

The injector 16 could inject fuel to create a homogeneous mixture or a stratified mixture. Injector 16 could be a pressure swirl injector and could be any of a multi-hole injector, a multi-spray injector, a piezoelectric injector and/or an outward-opening injector.

The injector 16 is preferably set at a "bend angle" as illustrated in Figure 1. Preferably the injector 16 is set at an angle in the range 0° to 15° from the cylinder axis, more preferably 5° to 15° from the cylinder axis and most preferably 10° to 15° from the cylinder axis. By setting the bend angle the cone of spray issued by the injector 16 is oriented in relation to the cylinder axis as can be seen in Figure 1 and the setting of the bend angle can influence the interaction of the fuel with the swirling gas down the cylinder bore.

Above the injector 16 and spark plug 53 have been described as lying in a plane containing also the crankshaft ( this means that in a two inlet valve and two exhaust valve per cylinder engine with a conventional valve layout the valves are asymmetrical about the plane with both inlet valve lying on one side and both exhaust valves on the other), but in an alternative embodiment the injector and spark plug can be configured so that they lie on a plane at right angles to the crankshaft axis (in which case in the conventional four valve per cylinder engine the arrangement is symmetrical with the arrangement of one inlet and one exhaust valve on one side of the plane the mirror image of

the arrangement of one inlet valve and one exhaust valve on the other side of the plane) . This still means that swirl interaction is set up, but the interaction of the spray with the air through the two inlet valves can be mirrored.

Whilst above electrohydraulic actuators have been described controlling the operation of the valves and this is preferable to allow for full variation of valve movement over all engine operating conditions, mechanical systems can be used instead. For instance, cam profile switching systems can be used which at certain engine speeds and loads drive the intake valves using first cams of a first profile and at other engine speeds and loads drive the intake valves using different cams of different profiles. Such systems can be used in combination with cam phasing arrangements.

Asymmetric intake ports can be used to further guide the air in a swirl motion. Similarly, shrouding can be provided in the combustion chamber or port to increase the swirl. Tumble flaps could be included in each intake port to influence swirl and tumble within the chamber.

The engine of the invention could be used with any type of fuel, liquid or gaseous or bi-phase.

Above the engine has been described operating a four- stroke cycle, but the invention of the current application is also applicable to any engine operating cycle, e.g. two- stroke, six-stroke, etc.

The present invention is applicable in multi-cylinder engines even though only one cylinder is depicted above. It

could also be used in a single cylinder engine and could be used in a radial engine or a Boxer engine.

Although above the spark plug and the injector are described as close spaced and central, they can be wide spaced with the spark plug only central . This may in some circumstances be advantageous with the fuel delivered to the faster moving periphery of the vortex in the cylinder.