GB2394314A

GB2394314A - Method for controlling the torque of an intemal-combustion engine running on supercharged air

Info

Publication number: GB2394314A
Application number: GB0321716A
Authority: GB
Inventors: Gaetan Monnier
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2002-09-20
Filing date: 2003-09-17
Publication date: 2004-04-21
Anticipated expiration: 2023-09-17
Also published as: FR2844829A1; FR2844829B1; ITMI20031792A1; GB2394314B; GB0321716D0; DE10342887A1

Abstract

The present invention relates to a method for controlling the torque of an internal-combustion engine 10 running on supercharged air, said engine comprising a combustion chamber 16, at least one intake valve 20, at least one exhaust valve 24 and a fuel injection means 26, a method wherein the desired torque to be generated by this engine is determined and wherein the set value of the intake pressure of the supercharging air to be admitted in the combustion chamber and the fuel injection time required to obtain the fuel mixture allowing the desired torque to be obtained are determined from the desired torque. According to the invention, the fuel injection time is maintained at a constant value as soon as the pressure of the supercharging air exceeds its set value and for all the time during which this pressure is higher than this set value.

Description

1 2394314

FIELD OF THE INVENTION

The present invention relates to a method for controlling the torque of an internal-

combustion engine running with supercharged air.

It applies more particularly, but not exclusively, to direct-injection and spark-

5 ignition supercharged engines.

BACKGROUND OF THE INVENTION

The torque delivered by an internal-combustion engine depends on the amount of air fed into the combustion chamber of this engine, this amount of air being proportional to the density of this air. This air is mixed with a fuel to produce a fuel mixture which is 10 ignited, for example by a spark produced by a plug.

In cases where a high torque is required, it is obtained, for the same cylinder capacity and the same rotating speed, by compression of the air before it is fed into the engine cylinder, more commonly referred to as supercharging.

Supercharging is generally obtained by means of a turbosupercharger whose turbine 15 is driven by the exhaust gas of the engine. A computing unit which is generally included in this engine determines a set value for the pressure of the supercharged air to be fed into the combustion chamber of the engine as a function of the required torque.

This turbosupercharger is generally actuated when a high torque is required. More precisely, by way of example, when an action is exerted on the accelerator pedal until it 20 rests against the floor (pedal pressed down completely), this information is transmitted to the computing unit which translates it into a high torque demand.

By means of predetermined calibrations in the mapping of this computing unit, it determines the torque to be generated by this engine so as to meet the demand.

In order to obtain the required torque, this computing unit acts directly or indirectly on the control units of the various actuators used for engine running, such as the fuel 5 injector and/or the turbosupercharger.

Depending on the required torque, the computing unit sends instructions to the control unit of the turbosupercharger so that it delivers, during the intake phase of the engine running cycle, supercharging air in the combustion chamber with a predetermined set pressure value. This supercharging air mixes, as it is introduced, with 10 a fuel injected into the combustion chamber by a fuel injector so as to obtain a fuel mixture. The amount of fuel injected into the combustion chamber results from the injection time, i.e. the time during which the fuel injector is open to feed, directly or indirectly, fuel into the combustion chamber. This injection time depends on the mass of air 15 injected or present in the combustion chamber and it allows to obtain the desired fuel/air ratio required for a combustion meeting the torque demand and for complete use of the fuel available.

This fuel mixture is then compressed by the engine piston and ignited, notably by a plug of this engine. It is thus the combustion of this compressed fuel mixture which 20 provides the required torque.

In order to regulate the set pressure value desired for the supercharging air, it is well-known to use a waste gate allowing to control the amount of exhaust gas driving

the turbine of the turbosupercharger into rotation and, consequently, the pressure of the air leaving the supercharger.

However, despite actuation of the waste gate when the set pressure value of the supercharging air is reached, the turbosupercharger continues to increase the pressure of S this air because of the inertia inherent in this turbosupercharger and this waste gate. The delivered pressure of the air is thus higher than the pressure required to obtain the desired torque. The amount of air admitted and the fuel injected in the combustion chamber are therefore increased, and the fuel mixture obtained provides, during combustion, a torque that is higher than the required torque, which is detrimental to the 10 good running order ofthe engine and can cause degradation thereof.

The present invention aims to overcome the aforementioned problems by providing a method which allows to obtain a desired engine torque in a simple, reliable and economic way.

SUMMARY OF THE INVENTION

15 The invention thus relates to a method for controlling the torque of an internal combustion engine running with supercharged air, said engine comprising a combustion chamber, at least one intake valve, at least one exhaust valve and a fuel injection means, a method wherein: - the desired torque to be generated by this engine is determined, 20 - the set value of the intake pressure of the supercharging air to be admitted in the combustion chamber and the fuel injection time required to obtain the fuel mixture allowing the desired torque to be obtained are determined from the desired torque, characterized in that:

- the fuel injection time is maintained at a constant value as soon as the pressure of the supercharging air exceeds its set value and for all the time during which this pressure is higher than the set value.

Uncarbureted supercharging air can be advantageously admitted at the beginning of 5 each intake phase of the engine.

Said air can be admitted by overlap of the intake and exhaust valves.

Preferably, the supercharging air can be produced by a turbosupercharger.

The pressure of the supercharging air can be controlled by the turbosupercharger waste gate control.

10 Alternatively, the supercharging air can be produced by a driven mechanical compressor. BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will be clear from reading the description hereafter, given by way of non limitative example, with reference to the

15 accompanying drawings wherein: - Figure 1 shows an internal-combustion engine and its supercharging device, - Figure 2 illustrates the various engine torque control stages, and - Figure 3 is a graph showing the evolution of the various parameters required to control the engine torque.

DETAILED DESCRIPTION

Figure 1 shows an internal-combustion engine 10 and a supercharging device 12 such as a turbosupercharger.

The engine comprises at least one cylinder 14 comprising a combustion chamber 16 5 in which combustion of a fuel mixture takes place.

This cylinder comprises air intake means with at least one intake tubulure 18 associated with a throttling means such as an intake valve 20 and exhaust gas discharge means, here at least one exhaust manifold 22 whose opening/closing is controlled by a throttling means such as an exhaust valve 24.

10This cylinder also comprises a device for feeding the fuel into the combustion chamber, such as a fuel injector 26, and a device intended for ignition of the fuel mixture in this chamber, here a spark plug 28.

The engine should also comprise, as it is well-known in the art, a means for controlling passage of the intake air in intake manifold 18, such as a butterfly type valve 15 30 usually contained in a throttle box.

Intake valves 20, exhaust valves 24, fuel injector 26, plug 28, butterfly valve 30 are controlled by control units 32, 34, 36, 38 and 40 respectively.

Turbosupercharger 12 comprises a turbine 42 which drives a compressor 44 by means of a transmission shaft 46.

20 Turbine 42 is driven in rotation by exhaust gas carried by a line 48 coming from exhaust manifold 22 and opening onto the inlet of this turbine. Once this gas has flowed

through the turbine, it is discharged through a line 50 to any known device such as the exhaust line.

Line 48 comprises, upstream from turbine 42, a waste gate 52 allowing to circulate, in open position, all or part of the exhaust gas out of turbine 42 by means of a bypass 5 line 54 starting at this waste gate and ending downstream from the turbine.

This waste gate is also controlled by a control unit 56.

Compressor 44 comprises an inlet connected to an air intake line 58, this air being generally exterior air, and an outlet connected to a line 60, referred to as supercharging air supply line, which opens into intake manifold 18 after running through the throttle 10 box containing butterfly valve 30.

Supply line 60 comprises a pressure detector 62 which allows to continuously know the pressure of the supercharging air. This detector can also be arranged in intake manifold 18.

The various control units 32, 34, 36, 38, 40 and 56 receive control instructions from 15 a computing unit 64 such as a computer generally associated with an engine.

This computer also receives information from detectors arranged in the engine such as, for example, the engine knock detector, and information on the pressure of the supercharging air via detector 62.

It also receives information on an engine torque requirement which, in the example 20 of Figure 1, is provided by a control device such as an accelerator pedal 66 of a motor vehicle.

Thus, by way of example, when a high torque is required from the engine by pressing down on accelerator pedal 66 so that it rests against the floor (pedal pressed down completely), displacement detector 68 intended for this pedal, such as a potentiometer, sends a signal to computing unit 64, this signal allowing to determine the 5 required torque level, notably as a function of the rate at which this pedal is pressed dowry The computing unit translates this signal into a torque to be generated by the engine and, as a function of mappings contained in this computing unit, it translates this torque demand into actions to be exerted on the various actuators of the engine, such as the fuel 10 injection time, actuation of butterfly valve 30 and the pressure of the supercharging air to be admitted in the combustion chamber.

More precisely, with reference to Figure 2, in stage a), the computing unit will detect that a high torque is required and determines the value of this torque.

By means of its mapping, the computing unit mainly determines that, in order to 15 obtain this torque value, the supercharging pressure has to be at a set value and the fuel injection time has to be at a determined value to obtain the desired fuel/air ratio in the combustion chamber.

In stages b) and c), this computing unit determines the control parameters of the various actuators 20, 24, 26, 28, 30 and 52 and sends the necessary instructions to all or 20 part of control units 32, 34, 36, 38, 40 and 56 associated with these actuators.

In the example described, this procedure consists, for stage b), in closing all or part of waste gate 52 by means of control unit 56 so that the exhaust gas passes into turbine 42 to drive compressor 40 at a higher speed.

During this stage, instructions are sent, on the one hand, to control units 32 and 34 5 to open or close, at a given time and for a time determined by computing unit 64, intake and exhaust valves 20 and 24 and, on the other hand, to control unit 40 to control quasi-

total opening of butterfly valve 30 allowing passage of the supercharging air into intake manifold 18.

Advantageously, valve overlap is provided at the beginning of the intake phase of 10 each combustion cycle, i.e. simultaneous opening of the exhaust and intake valves so as to discharge by scavenging the residual burnt gas contained in the dead volume of the combustion chamber in order to replace it by fresh supercharging air containing no fuel, as described, by way of example, in French patent No.2,781,011 filed by the applicant.

In stage c), as a result of the closing of the waste gate, the pressure of the 15 supercharging air leaving compressor 44 is increased and instructions are sent to control unit 36 of fuel injector 26 for injecting fuel into the combustion chamber with a predetermined injection time, so as to obtain a fuel mixture with a predetermined fuel/air ratio corresponding to that contained in the mapping of the computing unit.

By means of detector 62, the computing unit checks, in stage d), if the set value of 20 the supercharging air pressure determined by computing unit 64 to obtain the required torque is reached so as to obtain the desired torque. If not, this computing unit sends instructions to all or part of the control units of the actuators defined in stage c) to increase the pressure of the air in order to obtain this set pressure value, to continue to

inject fuel according to the injection time determined and to maintain butterfly valve 30 in the fully open position.

If the set pressure value is reached, which means that the value of the theoretical torque required is obtained, the computing unit sends instructions to control unit 36 of S injector 26 so as to block the fuel injection time, i.e. to maintain the fuel injection time at a constant value. More precisely, the injection time remains at the same value as the value it had when the pressure of the supercharging air has reached its set value V. This allows to "unloop" the fuel/air ratio so as not to make the amount of fuel injected dependent on the amount of air admitted. Instructions are also sent to control unit 56 to 10 partly open waste gate 52 (stage e)). By means of this action, the amount of exhaust gas flowing through turbine 42 decreases so that the pressure of the supercharging air decreases and progressively reaches its set value again (stage f)).

Once this set value reached, fuel injection is again managed (stage g)) according to the injection time contained in the computer so that the time during which the injector is 15 open is again a function of the mass of air injected or present in the combustion chamber. The waste gate is held in position to stabilize the pressure of the supercharging air at the set value throughout the torque demand.

A fuel mixture allowing to obtain the desired torque during the combustion phase of this mixture is thus obtained.

20 In order to explain more in detail all that has been written so far, Figure 3 illustrates the evolution of the parameters used for the combustion during a predetermined engine running period. These parameters are notably the intake pressure of the supercharging air (curve A), the engine torque (curve B), the fuel injection time (curve C), the intake

fueVair ratio (curve D) and the combustion fueVair ratio (curve E), as a function of time (in seconds, as abscissa) and of the evolution of the set value (in %, as ordinate), this set value being designated by V in the graph.

This figure illustrates, by way of example, the evolution of the parameters during 5 running of the engine for about 2.3 seconds and at approximately 6000 rpm.

From the torque demand, the pressure of the supercharging intake air and the fuel injection time are established so as to obtain an increasing torque and an intake (or exhaust) fueVair ratio at set value V and which is substantially equal to the combustion fuel/air ratio, i.e. the fuel/air ratio of the fuel mixture contained in the combustion 10 chamber.

Between time To and time T. when butterfly valve 30 opens and waste gate 52 closes, thus allowing passage of the exhaust gas through turbine 42, the intake pressure goes to the value of the pressure at the compressor outlet, which is higher than the atmospheric pressure whereas the intake (or exhaust) and combustion fuel/air ratio 15 remains at the set value.

As a result of the closing of waste gate 52, the intake pressure increases up to set value V associated with the progression of the injection time, between T' and T2. This allows to obtain, during the same period, a progression of the torque up to set value V and maintenance of the intake fuel/air ratio at the set value.

20 From time To, a phase shift of the intake (or exhaust) fuel/air ratio in relation to the combustion fueVair ratio occurs, where the combustion fuel/air ratio exceeds the intake

(or exhaust) fueVair ratio and increases substantially regularly up to T2 whereas the intake (or exhaust) fuel/air ratio remains at its set value.

This phenomenon is due to the bypassing by uncarbureted fresh supercharging air at the beginning of each intake phase of the engine where valve overlap occurs when the 5 intake pressure is higher than the exhaust pressure, a phenomenon encountered in supercharged engines, notably at low engine speed, and in engines equipped with mechanical compressors.

This bypassing of the intake air directly at the exhaust without passing through combustion is possible because of the absence of fuel in the bypassed air, notably in the 10 case of direct fuel injection, which allows to decouple the intake (or exhaust) fuel/air ratio and the combustion fuel/air ratio.

As soon as the pressure of the supercharging air has reached the set value at the time T2 to obtain the desired torque, the injection time is blocked, i.e. it is kept at a value corresponding to the time when the supercharging air pressure has reached its set 1 5 value.

From this time, which corresponds to the opening of the waste gate so as to reduce passage of the exhaust gas in turbine 42, the pressure of the supercharging air continues to increase, it exceeds the set value and reaches a maximum essentially due to the inertia of the turbosupercharger as described above, then it decreases from this 20 maximum and reaches the set value at the time T3.

Between times T2 and T3, the injection time is maintained at the value it had at the time T2, which has the effect of decreasing the intake fuel/air ratio until the

supercharging air intake pressure has reached its maximum, then of increasing this intake fuel/air ratio to reach the set value when the intake pressure decreases down to its set value.

Simultaneously, the combustion fuel/air ratio decreases progressively from time T2 5 and reaches its set value at time T3 by the combined actions of the waste gate and of the valve overlap decrease, during the intake phase of each cycle, while remaining higher than the set value of the intake (or exhaust) fuel/air ratio.

From time T3 where the supercharging air pressure has reached its set value again, the injection time is looped again so as to make the fuel injection time again dependent 10 on the mass of air injected or present in the combustion chamber. This allows to obtain a combustion fuel/air ratio meeting the set value. The pressure of the supercharging air is stabilized at this set value until the end of the torque demand.

We thus obtain, within a very short period of time, a situation where the fuel mixture enclosed in the cylinder meets a given fuel/air ratio so as to obtain the desired 1 5 torque.

The present invention is not limited to the example described and it involves all variants. Notably, the turbosupercharger can be replaced by a mechanically driven compressor which has the same drawbacks as regards exceeding the set value of the 20 supercharging air pressure.

Besides, control units 32 and 34 of the intake 20 and exhaust 24 valves can be combined in a single device such as a variable distribution of electrohydraulic or electromagnetic type.

Furthermore, the invention can be applied to a method of controlling the torque of 5 an indirect-injection supercharged engine.

Claims

1. A method for controlling the torque of an internal-combustion engine running with supercharging air, said engine comprising a combustion chamber, at least one 5 intake valve, at least one exhaust valve and a fuel injection means, a method wherein: the desired torque to be generated by this engine is determined, the set value of the intake pressure of the supercharging air to be admitted in the combustion chamber and the fuel injection time required to obtain the fuel mixture allowing the required torque to be obtained are determined from the desired torque, 10 wherein: the fuel injection time is maintained at a constant value as soon as the pressure of the supercharging air exceeds its set value and for all the time during which this pressure is higher than the set value.

15

2. A method as claimed in Claim 1, wherein uncarbureted supercharging air is

admitted at the beginning of each intake phase of the engine.

3. A method as claimed in Claim I or 2, wherein said air is admitted by overlap of the intake and exhaust valves.

4. A method as claimed in Claim 1 or 2, wherein the supercharging air is produced by a turbosupercharger.

5. A method as claimed in Claim 4, wherein the pressure of the supercharging air 25 is controlled by control of waste gate of the turbosupercharger.

6. A method as claimed in Claim I or 2, wherein the supercharging air is produced by a driven mechanical compressor.

30

7. A method as substantially herein described with reference to the drawings.