FR3072418A1 - METHOD FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE WITH COMMON IGNITION, IN THE UNLIMITED STATE - Google Patents

Abstract

The invention relates to a method of controlling a spark-ignition engine equipped with a partial recirculation circuit of the exhaust gas at the engine intake. The engine can be atmospheric or supercharged. According to the invention, when the engine is running in the unlit state, in the absence of fuel injection and ignition of the spark plugs, and a throttle-throttle body of the the amount of air admitted into the engine is open to limit pumping losses, the position of a valve is further adjusted so as to increase the recirculation of the gases from the engine at the intake. This reduces the supply of oxygen to a catalyst for engine pollution, so that the restart of the engine, it limits emissions of nitrogen oxides.

Description

METHOD FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE WITH CONTROLLED IGNITION, IN THE UNIT LIT

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for controlling an internal combustion engine, of the spark-ignition type, when it is operating in the unlit state. It finds an advantageous application on hybrid motor vehicles, in which the internal combustion engine (internal combustion engine) is associated with an electric machine, under operating conditions where the entire torque necessary for driving the vehicle is provided by the electric machine, and more generally for any motor vehicle fitted with at least one heat engine, under operating conditions where the driver releases the vehicle's accelerator pedal.

STATE OF THE ART

As part of the reduction of polluting emissions linked to the operation of thermal engines of motor vehicles, legal standards (for example the European standard "euro6") have led manufacturers to integrate into the exhaust line of these engines several kinds of catalytic devices for depolluting the combustion gases of said engines.

More particularly known are the three-way catalysts of spark-ignition engines (of the type operating in particular with petrol) which make it possible to oxidize unburnt hydrocarbons (HC) and carbon monoxide (CO), and to reduce oxides of nitrogen (NO _X ) emitted by the engine.

It is also known that the heat engines of certain motor vehicles can be associated with reversible electric machines that can operate in engine mode or in generator mode. In generator mode, the electric machine is an alternator which supplies an electric current intended to be stored in a storage battery; in engine mode, on the contrary, it is supplied with current previously stored in the storage battery and it provides engine torque which is added to that of the heat engine to be transmitted to the wheels of the vehicle.

In certain use cases, such an internal combustion engine of the ignition type

-2controlled is made to operate in the non-ignited state, more precisely without injecting fuel into the engine or ignition itself (i.e. without sparking sparks across the spark plugs of the engine) . This case arises when a computer or supervisor on board the vehicle requires a zero torque setpoint from the engine.

For example, in the case where the heat engine is the only one to drive the vehicle, without being associated with an electric machine, it is known to operate the engine in the unlit state in the case of a lift of the driver's foot , that is to say when the driver releases the accelerator pedal completely, for example when the vehicle approaches a steep downhill slope. In this case, the engine continues to run in the unlit state. Driven by the inertia of the vehicle, it delivers a resistant torque corresponding to the compression energy of the gases in the engine. Preferably, an air intake valve, or throttle valve, of the motor is opened so as to minimize the pumping energy. But this opening of the throttle body causes a large influx of clean air at the engine exhaust, so that the engine catalyst is charged with oxygen. When the engine is restarted, combustion resumes normally in the cylinders, and due to the excess oxygen in the catalyst, there is a peak in emissions, in particular of nitrogen oxides by massive oxidation of base emissions. .

Also known from the unexamined patent application FR 17 52680 by the applicant is a method for controlling a positive-ignition engine of the supercharged type and associated with at least one partial recirculation circuit of the exhaust gases at the intake of the engine, implemented when the driver of the vehicle releases the accelerator pedal, and successively comprising steps during which: a valve for adjusting the flow of recycled gases is closed without closing the throttle body; the fuel injection is cut into at least one engine cylinder; the throttle body is almost completely closed after a predetermined period corresponding to the transfer time of the recycled gases; and, we cut the fuel injection in the remaining cylinders.

The aim of such a method is to solve operating problems in transient mode of the engine before it is restarted and combustion resumes in the engine cylinders. Since the throttle valve ends up being closed, it limits the supply of oxygen to the catalyst but it considerably increases the energy loss linked to the gas pumping effort in the engine.

In the case where the engine is associated with an electric machine, it is known to

-3operate the engine in the unlit state when the entire torque required for driving the vehicle, corresponding to a given depressing of the accelerator pedal by the driver, is provided by the only electric machine. A computer can force such an operating mode into purely electric mode, for example during a cold start of the vehicle, before the catalyst has been sufficiently heated to reach its priming temperature, or when the engine efficiency is deemed insufficient. , or when it is planned to discharge the battery of the electric machine, etc. Such examples are not limitative.

Document EP-A1-2 563 633 in particular discloses a hybrid vehicle equipped with a heat engine and an electric machine. It is expected that the heat engine will operate in the unlit state as long as the efficiency of its pollution control device is too low, that is to say as long as a starting temperature is not reached. In other words, during a cold start of the vehicle, the latter is driven entirely by the electric machine. First, an engine precatalyst is electrically heated. Then, in a second step, when we anticipate that we will need, or that we may imminently need the heat engine to drive the vehicle, for example because a torque request from the conductor will exceed the capacity of the single electric machine, so we also heat a main engine catalyst which is mounted downstream of the pre-catalyst. This is achieved by opening a throttle valve housing of the engine, the engine remaining in the non-ignited state, so that the heat of the pre-catalyst is transmitted to the catalyst thanks to the flow of compressed air compressed in the engine and then heated in the pre-catalyst. In such a method, the treatment efficiency of the depollution device of a spark-ignition engine in the non-ignited state is improved, but the catalyst cannot be loaded with oxygen, so that on restarting the engine, there is a peak in nitrogen oxide emissions.

SUMMARY OF THE INVENTION

The invention proposes to remedy the shortcomings of known methods for controlling spark-ignition engines in the non-ignited state, in the particular case where the engine is associated with a partial recirculation circuit of the exhaust gases at the intake, whose interest is well known, on such spark-ignition engines, for increasing the combustion efficiency thanks to a decrease in the combustion temperature due to the dilution of the gases, and on the other hand for reducing the

-4 losses by pumping, the charge of fresh air necessary for the production of the engine torque can often be modified thanks to a supply of recycled gas rather than by actuating a throttle body of the engine.

More specifically, it aims to avoid peaks of nitrogen oxide emissions when restarting such an engine while minimizing the pumping energy of the intake gases into the engine.

It concerns all internal combustion engines with positive ignition, whether they are of the atmospheric type (naturally aspirated) or of the supercharged type, provided that partial recirculation of the exhaust gases at the intake is possible.

It therefore proposes a method for controlling a positive-ignition engine associated with at least one partial recirculation circuit of the exhaust gases at the intake of the engine originating upstream of an exhaust gas pollution control device of the engine, said engine being mounted on a motor vehicle, and being able to be further associated with a reversible electric machine able to operate according to a generator mode or according to an engine mode in which it participates in the driving torque of the vehicle, said method including:

A step in which a torque is required for the vehicle to be driven by a driver of the vehicle;

A step during which an engine torque setpoint is determined;

A step during which it is checked whether said engine torque setpoint is zero;

If said torque setpoint is zero, a step during which the injection of fuel into the engine is stopped and the ignition by the engine spark plugs is stopped; and,

If said torque setpoint is zero, a step during which a motor throttle unit is opened, said method being characterized in that it further comprises, when said torque setpoint is zero, a step of adjusting the position a valve capable of increasing the recirculation of gases from the engine when the engine is admitted.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will appear on reading a non-limiting embodiment thereof, with reference to the appended drawings in which:

Figure 1 is a schematic view illustrating a motor device according to the invention; and, Figure 2 is a flowchart illustrating the different steps of a method of controlling an engine of the motorization device of Figure 1 according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 represents a motorization device 1 suitable for implementing the method according to the invention, which in particular is fitted to a motor vehicle. It comprises at least one heat engine 2, more specifically an internal combustion engine of the spark-ignition type (operating in particular on petrol), which is here in a non-limiting manner in the form of a four-cylinder in-line engine. supercharged.

In a variant not shown, it can be an atmospheric engine, that is to say a naturally aspirated engine.

For its operation, such a heat engine 2 sucks air in the direction of arrow F1 via an intake circuit 3, and evacuates its combustion gases by an exhaust circuit 4 in order to direct towards a pollution control system 5 of the combustion gases from the engine, and evacuate them into the external atmosphere in the direction of arrow F2. The pollution control device 5 generally comprises at least one three-way catalyst 5, the engine being of the spark-ignition type and operating in a manner known per se generally at richness 1 at most of its operating points, the catalyst 5 thus making it possible to oxidize unburnt hydrocarbons and carbon monoxide, as well as reduce nitrogen oxides, which are emitted in engine combustion gases.

The engine also consumes fuel, for example petrol (but it can also be other fuels such as alcohol or gas), which is brought to the engine thanks to an injection system (partially not shown), for example a direct injection system which may include a supply rail common to the cylinders and at least one fuel injector 6 per cylinder capable of injecting fuel directly into each of the cylinders, more precisely into each

-6 combustion chamber delimited in each cylinder. In a variant not shown, each cylinder can be supplied by an injector which injects the fuel into an intake pipe upstream of each cylinder. A spark plug (not shown in Figure 1) also opens into each of the engine’s combustion chambers.

In the air intake circuit 3, an air filter 7 eliminates the dust contained in the air. With regard to FIG. 1 of a supercharged engine 2, the engine 2 also comprises a turbocharger 8, the compressor 9 of which is mounted downstream of the air filter 7. In addition, it is possible that a temperature exchanger 10 is arranged downstream of the compressor 8. The intake circuit 3 also comprises, downstream of the compressor 8, a first regulating valve 11 for the flow rate of the gases entering the engine 2, or throttle body 11, and a manifold intake 12, or distributor 12, of the engine. An intake gas pressure sensor 13 Pcoll and an intake gas temperature sensor Tcoll are interposed in the intake circuit 3 between the throttle body 11 and the intake manifold 12. They can also be mounted on the intake manifold 12. In a manner known per se, knowing the opening angle of the throttle body, the intake pressure and the intake temperature makes it possible to determine the amount of air ( in mass flow unit, for example in kg / h) present in the engine. Of course, in a variant not shown, it is also possible to have a flow meter to measure this quantity of air.

The compressor 9 is driven by a turbine 15 of the turbocharger, which is interposed in the exhaust pipe 4 between the engine 2 and the three-way catalyst 5. The turbine 15 is mounted in the exhaust circuit 4 of the engine, downstream an exhaust manifold 16 of the engine, more precisely between the exhaust manifold 16 and the catalyst 5. Conventionally, the turbine 15 can be associated with an exhaust bypass pipe (not shown) which bypasses the turbine 15 and which includes an exhaust discharge valve (also called a waste waste valve) in order to be able to adjust the energy supplied by the exhaust gases to the turbine 15, and therefore to be able to adjust the pressure delivered by the compressor 9.

In addition, in the context of the invention, the heat engine 2 comprises at least one partial recirculation circuit of the exhaust gases at the intake, also known by the abbreviation EGR circuit (EGR designating the acronym in English). for "Exhaust Gas Recycling"). The EGR circuit includes a

-7 recirculation 17 which here originates at a point in the exhaust circuit 4 located upstream of the turbine 15, and the other end of which opens downstream of the compressor 9. The recirculation line 17 is provided with a recirculation valve 18, or EGR valve, which allows the amount of recycled gas to be adjusted.

The engine of FIG. 1 being of the supercharged type, the EGR circuit is more precisely a partial recirculation circuit at high pressure of the exhaust gases at the intake, also known by the abbreviation EGR circuit HP, insofar as the exhaust gases are taken upstream of the turbine 15, that is to say at a point in the exhaust circuit where they are not yet expanded, and that they are returned downstream of the compressor 9, c ' that is to say at a point in the intake circuit where the engine intake gases are already compressed.

In a variant not shown, if the engine is of the atmospheric type, the motorization device 1 is identical in all respects to that of FIG. 1, except that it does not include the turbocharger 8 nor the exchanger 10. The partial exhaust gas recirculation circuit is nevertheless present in the context of the invention, but it is not a high pressure partial recirculation circuit. It originates between the exhaust manifold 16 and the catalyst 5, and its other end opens out between the air filter 7 and the throttle body 11.

The exhaust gases can circulate in the direction of arrow F indicated in FIG. 1 under operating conditions where the pressure prevailing downstream of the compressor 9 is lower than the pressure prevailing upstream of the turbine 15. It is possible that the exhaust circuit 4 is also provided, for example downstream of the catalyst 5, with an exhaust valve 19 capable of facilitating the circulation of said gases when this condition is not met or when the difference of pressure between the downstream of the compressor and the upstream of the turbine is too low to obtain a sufficient flow of recirculated gases: by closing the exhaust valve 19, a sufficiently large pressure drop is created to greatly increase the pressure upstream of the turbine, which forces the circulation of exhaust gases in line 17.

In a manner known per se, the heat engine 2 produces an engine torque, called the thermal torque Ct, which results from the combustion of a mixture of fresh air (to which recycled exhaust gases can be added) and fuel in quantities well defined by a computer of engine 2. In a manner known per se, the richness of the mixture is generally adjusted in stoichiometric proportions (ie with richness 1) using the indications of at least one oxygen sensor (not shown) .

In a first embodiment of the invention, the motorization device 1 according to the invention also comprises a reversible electric machine 20, as illustrated in FIG. 1.

The electric machine 20, for example an alternator-starter 20 separated from the flywheel of the heat engine 2, and a rotary shaft 21 of which is coupled via transmission means 22 to a rotary shaft 23 of the heat engine 2, for example a crankshaft, is capable of operating in "engine" mode or in "generator" mode, under the supervision of a control unit 24. Other architectural variants can be provided without departing from the scope of the invention.

In “generator” mode, the electric machine 20 is an alternator which supplies an electric current intended to be stored in an accumulator battery 25 by taking a resistant electric torque C _e ; in “engine” mode, it is on the contrary supplied by current previously stored in the battery 20 and it provides an electrical torque C _th motor which is added to that Ct of the heat engine to be transmitted to the wheels of the vehicle.

The general operating mode of the motorization device 1 is as follows: The depressing of the accelerator pedal (not shown) of the vehicle by the driver is translated by a computer (not shown) into a torque setpoint C to be transmitted to the vehicle wheels. The torque C can then be obtained either in the form of thermal torque Ct, or in the form of electrical torque C _e , or in the form of a combination of the two. In all cases, the value of the torque C is equal to the algebraic sum of the values of the thermal torque Ct and the electrical torque C _e , the latter taking a positive value in "motor" mode and a negative value in "generator" mode of the electric machine 20, the computer performing the distribution according to different parameters of the vehicle and / or of the motorization device 1

It may be that the entire torque necessary for driving the vehicle is supplied by the only electric machine, the supervisor 24 imposing a setpoint of thermal torque Ct zero, for example when the battery 25 is full and must be discharged, or when the catalyst 5 of the heat engine is cold and has too low a treatment efficiency, etc.

According to known operating modes, in the event of a zero thermal torque setpoint, the fuel injection in the heat engine 2 is then cut, the ignition is also interrupted by the spark plugs, and the throttle body 11 is opened. heat engine 2 is then driven empty by the electric machine 20 and does not deliver

-9that a low resistive torque corresponding to the pumping energy of the air in the cylinders.

In a second embodiment of the invention, the motorization device 2 is in all respects similar to the device represented in FIG. 1, with the exception of the fact that the heat engine 2 is not associated with an electric machine 20 but to a conventional alternator 20, the rotary shaft 21 of which is coupled to the engine via transmission means 22, for example an accessory belt.

In the same way as for the first mode, the depressing of the accelerator pedal (not shown) of the vehicle by the driver is translated by a computer (not shown) into a torque setpoint C to be transmitted to the wheels of the vehicle, but here, this torque C is obtained only in the form of thermal torque Ct of the motor 2.

In such a device, it may also happen that the thermal torque setpoint is zero, more particularly during a lifting of the foot by the driver of the vehicle, that is to say when the latter completely raises the foot the vehicle's accelerator pedal, for example when the vehicle is going downhill. The known operating modes in such a case are similar to those of the first embodiment of the device: the fuel injection in the cylinders and the ignition is cut off, and the throttle body 11 is opened so as to limit the energy. pumping.

FIG. 2 illustrates the various stages of a method for controlling an ignition engine as it has just been described with the support of FIG. 1.

The method begins with a step 100 during which the driver requires a torque C for driving the vehicle, for example by depressing the accelerator pedal. The depressing of the pedal is a representative value of this request. The rotation speed N of engine 2 is also noted.

The process continues with a step 200 of determining a thermal torque setpoint Ct, that is to say a torque setpoint imposed on the motor 2, and if necessary, if the motor 2 is associated with a electrical engine 20, of an electrical torque setpoint C _e . The driving torque of the vehicle can be provided entirely by the engine, or entirely by the electric machine, or in combination by the two together in variable proportions, under the action of an engine computer. Of course, if the motor is not associated with an electric machine, the electric torque setpoint is then always equal to zero.

The process continues with a step 300 for adjusting the motor 2, in which

- the engine 2 computer determines an air flow, a flow of recirculated exhaust gas at the intake and a fuel flow for the production of the thermal torque Ct. This results in the adjustment of an angular position a _pap of the butterfly housing 11, an angular position Oegr of the high-pressure recirculation valve 18 (and / or the exhaust valve 19), a time of injection ti _n j of fuel into the engine cylinders and an ignition advance AA. The richness r of the air / fuel mixture is most often set in a closed loop around the value 1.

In a test step 400, it is checked whether the set value Ct of the thermal torque is zero. As already explained above, this case can arise in particular during a foot lift in the case of a heat engine 2 alone, or when the computer causes the vehicle to operate in pure electric mode, in the case of a heat engine 2 associated with an electric machine 20.

If said setpoint Ct is not zero, the method resumes at step 100. Otherwise, the method directs towards a step 500 in which the heat engine 2 goes to an unstarted state, resulting in stopping fuel injection, in other words an injection time ti _n j zero, and stopping the production of sparks capable of initiating the combustion of the air / fuel mixture, across the spark plugs of the motor.

The process continues with a step 600 during which the recirculation valve 18 is open, preferably at its maximum opening position, so as to promote as much as possible the recirculation of the exhaust gases from the exhaust manifold 16 to the engine intake. In other words, it is a question of limiting the transfer of the gases coming from the engine towards the catalyst 5. The proportion of the recirculated gases naturally depends on the permeability of the EGR circuit and of the catalyst 5.

As a variant of step 600, or in combination with the opening of the EGR valve 18, it is also possible to cause the valve to close at the exhaust 19. This creates a back pressure capable of considerably increasing the proportion of gases from the engine flowing in line 17.

The method also includes a step 700 in which the position a _pap of the butterfly housing is open. More precisely, it can be kept unchanged with respect to the last non-zero thermal torque setpoint position Ct, or else, in a particularly advantageous manner, be adjusted to its maximum opening position, so as to minimize the pumping effort. of the motor.

- 11 The process then resumes iteratively in step 100.

It is understood from the foregoing, and more particularly from steps 600 and 700, that the method makes it possible to pump clean air into the engine during its operation in the unlit state and to recycle most of this air at 5 the engine intake without passing through the catalyst 5, which avoids loading the catalyst with oxygen. Thus, when the engine 2 is restarted, combustion resumes normally without producing a peak of nitrogen oxide emissions.

Of course, the invention is not limited to the embodiment which has just been described. As a variant, it is possible, for example, to modify the order of steps 500, 600 and 10,700 without departing from the scope of the invention. For example, one can first open the butterfly housing 11 if priority is given to the pumping effort, then then open the recirculation valve 18. These two openings can also be carried out simultaneously.

Claims (7)

1. Method for controlling a spark-ignition engine (2) associated with at least one high-pressure partial recirculation circuit of the exhaust gases at the intake of the engine originating upstream of a pollution control device (5 ) engine exhaust gas, said engine being mounted on a motor vehicle, and being able to be further associated with a reversible electric machine (20) capable of operating according to a generator mode or according to an engine mode in which it participates in vehicle driving torque, said method comprising: A step (100) in which a torque (C) is required for the vehicle to be driven by a driver of the vehicle; A step (200) during which a torque setpoint (Ct) of the motor (2) is determined; A step (300) during which it is checked whether said torque setpoint (Ct) of the motor is zero; If said torque setpoint (Ct) is zero, a step (500) during which the injection of fuel into the engine is stopped and the ignition by the engine spark plugs is stopped; and, If said torque setpoint (Ct) is zero, a step (700) during which a throttle unit (11) of the engine (2) is opened, CHARACTERIZED IN THAT It further comprises, when said setpoint (Ct) is zero, a step (600) of adjusting the position of a valve (18,19) capable of increasing the recirculation of gases from the engine (2) to the engine intake. 2. Method according to claim 1, characterized in that said adjustment step (600) comprises the opening of a recirculation valve (18) mounted on a pipe (17) for partial recirculation of the exhaust gases at l engine intake. 3. Method according to one of claims 1 or 2, characterized in that said adjustment step (600) comprises closing a valve (19) at the exhaust of the exhaust circuit (4) of the mounted engine downstream of the engine's pollution control device (5). 4. Method according to any one of the preceding claims, characterized - 13in that said adjustment step (600) is carried out after the step in which the throttle body (11) of the engine is open. 5. Method according to any one of the preceding claims, characterized in that the step (300) of verifying the setpoint value (Ct) of 5 engine torque (2) determines that it is zero due to the fact that a driver of the vehicle completely releases the foot of the accelerator pedal of the vehicle. 6. Method according to any one of claims 1 to 4, characterized in that the step (300) of verifying the setpoint value (Ct) of the torque of the 10 engine (2) determines that it is zero following the fact that an engine computer (2) supervises the driving of the vehicle by the only electric machine (20) associated with the engine (2).