FR3101112A1 - Thermal management method of an exhaust line depollution device - Google Patents

Abstract

The present invention relates to a method of thermal management of a pollution control device (23) of an exhaust line (21) of a heat engine (10), the exhaust line (21) comprising a first exhaust duct (22) of the gases emerging at the inlet of the pollution control device (23), which method comprises the steps of estimating an operating state of the engine from engine parameters representative of an injection cut-off of fuel with the engine running, for example when the foot is lifted and, in the event of detection of a fuel injection cut-off with the engine running, the opening of an intake butterfly valve (12) of the engine, and the opening of an exhaust valve (26) regulating the passage of air between the exhaust manifold (13) and a second exhaust duct (25) opening to the outside air so as to evacuate the fresh air to the outside and diverting said fresh air from the exhaust line (21). Figure for the abstract: figure 1

Description

Process for thermal management of an exhaust line pollution control device

The field of the invention relates to a method for managing a pollution control device for a heat engine exhaust line.

Due to the increased requirements of pollution control standards, the control of the organs forming the exhaust line has become an essential component of the control strategies of motor vehicle powertrains. Among these organs, the catalysts constitute the basis of the depolluting functions. These catalysts require operating within a specific temperature range to be effective. Typically, the temperature rise is controlled by electrical heating equipment or by the temperature of the combustion gases escaping from the engine.

Document US2019/0063352A1 is known describing a system and method for thermal management of a three-way catalyst where the exhaust line is provided with an electrically heated catalyst upstream of the three-way catalyst allowing thermal pre-conditioning of the three-way catalyst before starting the engine. To this end, the system provides a fresh air injection duct directly at the inlet of the exhaust line. The additional duct includes a pump and a valve controlling the fresh air inlet in thermal pre-conditioning.

Recent powertrains, possibly hybrid ones, are configured to trigger the fuel injection cut-off of the internal combustion engine at running speed as soon as an opportunity arises, for example during the lifting phase, with the aim of reducing fuel consumption.

To limit pumping losses during foot lift phases, it is known to open the intake throttle valve so as to allow a flow of fresh air to flow between the intake line and the exhaust line. This strategy increases the potential for electrical energy harvesting. However, this strategy has the effect of cooling the depollution elements and significantly degrading the pollutant treatment performance. Moreover, to date, gasoline engine applications have high pumping losses because the throttle valve at the engine intake must close when you get up from your feet. Remember that the work of pumping the air is a function of the pressure difference between the intake and the exhaust. Reducing this difference by controlling an intake airflow flow reduces fuel consumption.

One objective of the invention is to overcome the aforementioned problems and aims to prevent a temperature defusing of one or more depollution elements of the exhaust line during the kick-off phase. Another objective is to increase the vehicle's energy recovery capabilities and reduce fuel consumption by reducing pumping losses.

More specifically, the invention relates to a process for thermal management of a device for depolluting an exhaust line of a heat engine, the exhaust line comprising a first gas exhaust duct opening out at the inlet of the device depollution. According to the invention, the method comprises the following steps:

• the estimation of an operating state of the engine from engine parameters representative of a fuel injection cut-off with the engine running, for example in a situation of lifting the foot,
• in the event of detection of a fuel injection cut-off with the engine running:
• the opening of an engine inlet butterfly valve,
• the opening of an exhaust valve regulating the passage of air between the exhaust manifold and a second exhaust duct opening out to the outside air so as to evacuate the fresh air to the outside and divert said fresh air from the exhaust line.

According to a variant, the method further comprises a step of forced extraction of fresh air through the second duct from the exhaust manifold to the outside air.

According to a variant, the method further comprises the following successive steps:

• stopping the heat engine at zero speed,
• in the event of detection of a request to start the engine, the pumping of fresh air prior to starting through the second duct so as to control the injection of fresh air directly into the first duct towards the pollution control unit,
• heating the air for a predetermined time,
• starting the heat engine,
• stopping said pumping.

The invention also provides a thermal management system for a device for depolluting an exhaust line of a combustion engine comprising an exhaust manifold, a first exhaust duct connecting the exhaust manifold and the inlet of the depollution device, a second exhaust duct connecting the exhaust manifold and a passage open to the outside air and a means for estimating an operating state of the engine from engine parameters representative of a fuel injection cut-off with engine running. According to the invention, the method further comprises an exhaust valve between the exhaust manifold and the second duct depending on said operating state, and means for regulating the flow of fresh air configured to, in the event of detection of a fuel injection cut-off with the engine running, open an air intake butterfly valve to the engine and open the exhaust valve so as to evacuate the fresh air circulating through the engine to the outside air and diverting said fresh air from the first exhaust duct.

According to a variant of the system, the exhaust valve is monostable, the stable position being the closing of the second duct.

According to a variant of the system, it further comprises a pump housed in the second duct arranged to at least suck in the fresh air coming out of the exhaust manifold.

According to a variant, the pump is reversible.

The invention also provides a motor vehicle comprising a powertrain comprising a heat engine, an exhaust line equipped with a pollution control device and a thermal management system of said pollution control device according to any one of the preceding embodiments. According to the invention, the vehicle comprises a control unit of said powertrain configured to implement the thermal management method according to any one of the preceding embodiments.

The invention makes it possible to reduce polluting gas emissions through improved thermal management of the pollution control units and better energy management of the powertrain, in particular by reducing pumping losses.

Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description comprising embodiments of the invention given by way of non-limiting examples and illustrated by the appended drawings, in which:

represents more precisely the internal combustion engine, the intake line, the air evacuation line during the lifting phase in accordance with the invention and the combustion gas exhaust line.

represents a flowchart illustrating a first algorithm of the thermal management method according to the invention.

In Figure 1, there is shown the heat engine 10 of a motor vehicle powertrain in accordance with the invention comprising an intake line 11 with fresh air supplying the intake manifold whose air flow is regulated by a member intake throttle valve 12. In a manner known per se, the fresh air passes through an air filter, not shown in FIG. 1, before being brought to the intake manifold of the engine 10. The engine 10 comprises an exhaust manifold 13 of the exhaust gases opening at least towards the exhaust line 21 which comprises a first combustion gas exhaust duct 22 at the outlet of the exhaust manifold, then, downstream of the duct 22, a depollution device 23 being able to be equipped with one or more depollution devices represented here by way of non-limiting example, three in number. In this example, the depollution device 23 comprises, in the direction of flow of the exhaust gases, a catalyst 231 capable of being thermally heated by electrical means, then a three-way catalyst 232, then a particle filter 233, then a exhaust duct 24 for the treated gases to the outside air.

The terms upstream and downstream will be defined in the description taking as reference the direction of circulation of the exhaust gases or the air leaving the exhaust manifold towards the air outside the engine.

The main objective of the invention is to avoid on the one hand the thermal defusing of each or part of the depollution members 231, 232, 233 during phases of foot lifting and on the other hand the reduction of losses by pumping of the engine 10. It is recalled that during a lifting phase, the drive shaft of the heat engine is rotating, driven by the wheels of the vehicle, and controlled in fuel injection cut-off. In this configuration of the kinematic chain of the powertrain, the engine is mechanically connected and in a state of transmission with the wheels, the clutch is closed and the gearbox has an engaged gear. This configuration of the kinematic chain can be detected by the powertrain control unit based in particular on engine operating parameters (fuel injection cut-off, engine speed), the accelerator pedal position and all of the components of the powertrain, or even from the state of a parameter specifically dedicated to the detection of a fuel injection cut-off. The injection cut-off state parameter is a two-state variable which is stored in the memory of the heat engine control unit, for example a Boolean-type variable, the value of which is determined according to whether the injection fuel is shut off (TRUE) or not (FALSE).

More specifically, to avoid thermal defusing of the pollution control unit, the powertrain comprises a second exhaust duct 25 provided to evacuate fresh air exiting from the exhaust manifold 13 and to divert this fresh air from the duct 22 during the lifting phase. The inlet of the exhaust duct 25 is connected downstream of the exhaust manifold 13 and upstream of the duct 22. In addition, a means 26 for regulating the air flow passing through the duct 25, for example a monostable valve, is positioned at the inlet of conduit 25. This conduit 25 opens at its other end to the outside air. Duct 25 is sized for the circulation of fresh air only, and excludes the circulation of exhaust gases. It is therefore excluded that the second duct 25 can be a gas recirculation duct towards the engine intake, such as an EGR (Exhaust Gas Recirculation) duct or through a circuit fitted with a turbocharger.

The valve 26 is therefore preferably a monostable valve where the stable position, in the absence of electrical control, is the closed position. A situation of emission of exhaust gases in the open air without passing through the exhaust line 21 is thus excluded. The valve 26 is controlled by a command which is a function of an operating state of the engine, based on engine parameters, representative of a cut-off of fuel injection with the engine running, in particular in a situation of lifting the foot. The damper control, for example electric control, is controlled by the heat engine control unit.

The duct 25 is, in a first variant, equipped only with the valve 26. Due to the absence of obstacles in the duct 25, unlike the exhaust line 21, the air will escape naturally through the duct 25. In a second variant, provision is made for the exhaust duct 25 to include a pump 27 for extracting the air from the outlet of the exhaust manifold 13. The pump provides forced extraction avoiding any passage of fresh air leaving the manifold to the exhaust line 21 when the intake throttle 12 and valve 26 are open at the same time.

In a third variant, the exhaust duct 25 comprises an air filter 28 on its end where the exhaust opening opening to the outside air is located. The air filter is provided to filter any residue likely to be evacuated from the intake line 11, from inside the engine casing 10, from the exhaust manifold 13 and finally from the duct 25.

In a fourth variant, the pump 27 is a reversible pump capable of sucking fresh air from the outside air to inject it directly into the exhaust line 21 without passing through the heat engine 10. The air filter 28 is then present to avoid the introduction of residues or external particles inside the exhaust line 21. In summary, the pump is able to extract the air leaving the exhaust manifold 13 to operate a first mode thermal management activated during the lifting phase, and optionally to introduce fresh air directly into the exhaust line 21 via the duct 25. This air is then heated by the catalyst 231 to operate a second thermal management mode activated during the engine starting phase to thermally precondition the three-way catalyst 232.

Finally, the engine control unit, the valve 26, and possibly the pump 27 constitute means for regulating the flow of air in the duct 25 controlled according to the state parameter representative of a cut-off of injection of running fuel.

We now describe in figure 2, the thermal management process of a depollution device of the exhaust line in the lifting phase implemented by the control unit of the combustion engine. The control unit is provided with an integrated circuit computer and electronic memories, the computer and the memories being configured to carry out the thermal management process. But this is not mandatory. Indeed, the computer could be external to the control unit, while being coupled to the latter. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program, for example. Consequently, the control unit, according to the invention, can be produced in the form of software (or computer (or even “software”)) modules, or else of electronic circuits (or “hardware”), or even of a combination of electronic circuits and software modules.

At a first step 30 of the method, the assumption is made that the thermal engine is rotating in fuel injection during which the conventional combustion cycle is operated. The exhaust gases flow from the exhaust manifold to the exhaust line. The valve 26 regulating the passage of air to the exhaust duct 25, with reference to Figure 1, is closed. If it is a monostable valve, no electrical command is sent to the valve 26. The pollution control devices operate in the optimum temperature range.

At each instant, the method comprises in a step 31 the estimation of an operating state of the engine, from engine parameters, representative of a fuel injection cut-off with the engine running, for example in a situation of lifting foot. One of these engine parameters is for example the fuel injection cut-off state parameter.

In the event of detection of a fuel injection cutoff with the engine running, indicated by the TRUE state of the injection cutoff parameter for example, the method controls a step 32 of opening the inlet butterfly valve of the engine so as to allow a flow of air through the engine generated by the natural aspiration of the engine. The motor is driven by the wheels possibly. In this way, in the lifting phase, the air flow reduces pumping losses and indirectly fuel consumption due to the increased capacity for recovering electrical energy via an alternator or electrical machine capable of being driven by the motor shaft of the heat engine (for example electric traction machine).

At the same time, to prevent defusing of the exhaust line pollution control devices, the method comprises a step 33 of opening the valve 26 so as to evacuate the fresh air to the outside and divert said fresh air from the exhaust line. exhaust 21. An electrical opening command issued by the engine control unit actuates the opening of the valve. The air circulation is therefore as follows: fresh air enters through the engine intake, passes through the intake manifold, then through the engine by natural aspiration generated by the pistons and then out of the intake manifold. exhaust, this fresh air circulates via the exhaust duct 25 to the outside air.

Preferably, to increase the flow rate of the circulation of fresh air through the duct 25, the method comprises a step of controlling forced extraction 34 of the fresh air to the outside. The pump 28 is controlled at a predetermined rotating speed value. In addition, the air extraction also ensures a further reduction in pumping losses caused by the forced extraction air flow stream.

The method comprises a step 35 of estimating at each instant the operating state of the engine representative of a fuel injection cut-off with the engine running. In the event of detection of an injection request, synonymous with an end of the lifting of the foot, the method comprises a step 36 of stopping the forced extraction, then a step of closing 37 of the valve 26. The method then returns to step 30 assuming that the heat engine is again operating in the combustion cycle.

On the contrary, as long as the injection cut-off is controlled, the engine butterfly valve is open, the access valve to the exhaust duct 25 is open and optionally the pump 27 is at rotating speed.

Another variant of the thermal management process is provided, allowing the implementation of a thermal pre-conditioning mode for the exhaust line pollution control devices before engine start. This thermal pre-conditioning mode provides for reversing the air flow in the duct 25 with respect to the first thermal management mode.

More precisely, according to this second mode, the engine is controlled when stationary at zero speed, for example a situation of stopping and extinguishing the engine, either while driving in the case of a hybrid powertrain architecture, or at the complete stop of the vehicle. It is assumed that the depollution devices are no longer in an optimal state of action.

Then, in the event of detection of a request to start the engine (still while driving or stationary), the method comprises the pumping of fresh air prior to starting through the duct 25 beforehand by passing the filter to air, and the opening of the valve regulating the flow of air through the duct 25, with reference to Figure 1, so as to control the injection of fresh air directly into the first duct 22 towards the pollution control unit 23. The method comprises a step of heating the air for a predetermined duration, ten seconds for example. The air is heated by the electric catalyst 231. Then once the flow of the predetermined duration is detected, the start of the heat engine is controlled. The valve 26 is closed during the start-up procedure to prevent combustion gases from escaping to the pipe 25. The method also controls the stopping of said pumping. The heating is kept activated for a few seconds following the end of the start-up procedure, the instant at which idle speed is reached.

The invention applies to conventional powertrains with internal combustion engines only (gasoline and diesel), as well as to hybrid powertrains.

Claims (8)

Process for thermal management of a pollution control device (23) of an exhaust line (21) of a combustion engine (10), the exhaust line (21) comprising a first exhaust duct (22) gases emerging at the inlet of the depollution device (23), characterized in that it comprises the following steps:

• the estimation (31) of an operating state of the engine from engine parameters representative of a cut-off of fuel injection with the engine running, for example in a situation of lifting the foot,
• in the event of detection of a fuel injection cut-off with the engine running:
• the opening (32) of an inlet butterfly valve (12) of the engine,
• the opening (33) of an exhaust valve (26) regulating the passage of air between the exhaust manifold (13) and a second exhaust duct (25) opening to the outside air so as to evacuating fresh air to the outside and diverting said fresh air from the exhaust line (21).

Method according to claim 1, characterized in that it further comprises a step of forced extraction (34) of fresh air through the second duct (25) from the exhaust manifold (13) to the air outside. Method according to any one of claims 1 to 2, characterized in that it further comprises the following successive steps:

• Shutting down the heat engine (10) at zero speed,
• In the event of detection of a request to start the engine (10), the pumping of fresh air prior to starting through the second duct (25) so as to control the injection of fresh air directly into the first duct ( 22) to the depollution unit (23),
• Heating the air for a predetermined time,
• Starting the heat engine (10),
• Stopping said pumping.

Thermal management system for a pollution control device (23) for an exhaust line (21) of a heat engine (10) comprising an exhaust manifold (13), a first exhaust duct (22) connecting the exhaust manifold (13) and the inlet of the depollution device (23), a second exhaust duct (25) connecting the exhaust manifold (13) and a passage open to outside air and a means for estimating an operating state of the engine from engine parameters representative of a fuel injection cut-off with the engine running, characterized in that it further comprises an exhaust valve (26) between the exhaust manifold (13) and the second duct (25) depending on said operating state, and means for regulating the flow of fresh air configured to, in the event of detection of a fuel injection cut-off with the engine running , opening an air intake butterfly valve (12) to the engine and opening the exhaust valve (26) so as to evacuate the fresh air circulating through the engine to the outside air and divert said fresh air from the first exhaust duct (22). Thermal management system according to Claim 4, characterized in that the exhaust valve (26) is monostable, the stable position being the closing of the second duct (25). Thermal management system according to Claim 4 or 5, characterized in that it further comprises a pump (27) housed in the second duct (25) arranged to at least suck in the fresh air leaving the exhaust manifold (13 ). Thermal management system according to Claim 6, characterized in that the pump (27) is reversible. Motor vehicle comprising a powertrain comprising a heat engine, an exhaust line equipped with a pollution control device and a thermal management system of said pollution control device according to any one of Claims 4 to 7, characterized in that it comprises a control unit of said powertrain configured to implement the thermal management method according to any one of claims 1 to 3.