WO2016097526A1

WO2016097526A1 - Method for heating a catalytic converter in a hybrid engine device

Info

Publication number: WO2016097526A1
Application number: PCT/FR2015/053352
Authority: WO
Inventors: Guillaume CHABARD; Florent GRIMALDI
Original assignee: Renault S.A.S.
Priority date: 2014-12-16
Filing date: 2015-12-07
Publication date: 2016-06-23
Also published as: EP3233599A1; FR3029972A1; FR3029972B1

Abstract

The invention relates to a method for heating a catalytic converter (6) mounted on the exhaust of a heat engine (2) capable of driving at least one drive wheel of a motor vehicle, said engine being associated with a reversible electric machine (15) which can operate in a generating mode or in an engine mode in which said electric machine (15) supplies part of the drive torque (C) of the vehicle, comprising: a step of starting (100) the vehicle in which a drive torque (C) of the vehicle is required; and a step of heating (600) the catalytic converter (6) until a starting temperature (θ_amo) of minimum effectiveness of the catalytic converter; CHARACTERISED IN THAT it also includes a step (400) of preheating the catalytic converter (6), in which the drive torque (C) of the vehicle is produced by the electric machine (15) operating in engine mode, the heat engine (2) being rotated, in the non-started state and with no fuel injection, by the electric machine (15).

Description

METHOD FOR HEATING A CATALYST IN A DEVICE

HYBRID MOTORIZATION

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method of heating a catalyst integrated in the exhaust line of an internal combustion engine. It also relates to a hybrid drive device capable of implementing such a method.

STATE OF THE ART

As part of the reduction of polluting emissions related to the operation of motor vehicle engines, the 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 cleaning up the combustion gases of said engines.

More particularly known are the three-way catalysts of spark ignition engines (operating on gasoline) which can oxidize unburnt hydrocarbons (HC) and nitric oxide, and reduce nitrogen oxides (NO _x ) emitted by the engine. Oxidation catalysts of compression-ignition engines (of the diesel type) which make it possible to oxidize unburned hydrocarbons and nitric oxide emitted by the engine operating in a lean mixture are also known.

In known manner, such a catalyst operates continuously. Its treatment efficiency, which is defined for each type of pollutant (HC, CO or NO _x ) as the conversion rate of the amount of pollutant entering the catalyst, depends primarily on the catalyst temperature. It is known, as shown in Figure 1, that the conversion rate begins to reach acceptable values, for example between 50% and 90% for example, when the catalyst temperature is for example between about 250 ° C and 300 ° C.

These temperatures are commonly reached and exceeded during the continuous operation of a heat engine. On the other hand, during a cold start of the heat engine, the temperature of the catalyst generally does not exceed the ambient temperature, for example 20 ° C., unless it is a restart after a very short stoppage. during which the catalyst does not have time to cool.

At room temperature, the catalyst is not primed, i.e. its effectiveness is nil. It also appears from FIG. 1 that the efficiency of the catalyst is zero as long as the temperature has not reached a value of the order of 150 ° C. When starting a combustion engine, it is therefore necessary to take measures to prevent the vehicle from emitting too much polluting emissions into the outside atmosphere. Conventionally, it is possible, for example, to provide an electrical resistance for heating the metal casing of the catalyst, or for carrying out delayed combustions inside the engine cylinders, relative to the normal operation of the engine, in particular by injecting the fuel more later in the engine cylinders, so as to degrade the combustion efficiency and increase the thermal losses of the engine.

These methods allow to quickly initiate a catalyst, that is to say to elevate its temperature from the temperature in the cold until a threshold temperature of about 250 ° C, said initiation temperature T _amo , to which it has a given minimum efficiency, for example 50%. But they lead to a significant overconsumption of fuel.

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

Several methods for controlling the temperature of a thermal engine catalyst associated with such an electric machine have been proposed. For example, there is known from US6057605-A1 a process in which, to increase the temperature of such a catalyst, the heat engine is operated at a higher torque than the torque required for driving the vehicle. The electric machine operates in generator mode by absorbing the surplus of unnecessary thermal torque to the vehicle. Such a method, applicable to the initiation of a catalyst, makes it possible not to degrade the combustion efficiency of the engine at its operating point, unlike the processes in which the combustion is delayed. Nevertheless the additional thermal losses caused to heat the catalyst lead to an additional consumption of fuel. SUMMARY OF THE INVENTION

The invention proposes to remedy the defects of the known methods of starting a thermal engine catalyst in a hybrid drive device, that is to say in the case where the heat engine is associated with an electric machine.

It proposes for this a method of heating a catalyst mounted on the exhaust of a heat engine adapted to drive at least one drive wheel of a motor vehicle, said motor being associated with a reversible electric machine that can operate in a manner generator or in a motor mode in which said electric machine participates in the driving torque of the vehicle, the method comprising:

a vehicle start step in which a driving torque of the vehicle is required; and,

a step of heating the catalyst to a minimum catalyst initiation temperature.

The main characteristic of the process according to the invention is that it also comprises a step of preheating the catalyst, in which the driving torque of the vehicle is entirely produced by the electric machine operating in engine mode, the heat engine being driven in rotation, in the un-started state and without fuel injection, by the electric machine.

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, described above, is a graph showing the efficiency of a catalyst as a function of its operating temperature;

Figure 2 is a schematic view illustrating a motorization device according to the invention;

Figure 3 is a flowchart illustrating the various steps of a method of heating a catalyst according to one embodiment of the invention; and, FIG. 4 is a graph which illustrates the evolution of the temperature of a catalyst from a cold temperature to a preheating temperature during a preheating stage of the process according to the invention.

DETAILED DESCRIPTION OF THE FIGURES As can be seen in FIG. 1, the motorization device 1 according to the invention can equip a vehicle, notably a motor vehicle. It comprises a heat engine 2, that is to say an internal combustion engine, for example a gasoline engine or a diesel engine, which is presented here in a non-limiting manner in the form of a four-cylinder engine. supercharged line. Of course, the engine may also be of the naturally aspirated type without departing from the scope of the invention.

For its operation, such a heat engine 2 draws air in the direction of the arrow F1 through an intake pipe 3, and rejects its exhaust gas through an exhaust pipe 4 in order to The depollution device 5 comprises a catalyst 6, for example a three-way catalyst 6 if the engine is of the gasoline type or an oxidation catalyst 6 if the engine is of the diesel type. It may further comprise one or more other gas purification systems 7, for example a second catalyst 7, a nitrogen oxide trap 7, a particulate filter 7, etc. At the outlet of the pollution control device 7, the exhaust gases are discharged into the outside atmosphere in the direction of the arrow F2.

The engine also consumes fuel, for example gasoline or diesel fuel, which is fed to the engine by means of an injection system (not shown), for example a direct injection system which includes a common supply rail to the engines. cylinders and at least one fuel injector per cylinder adapted to inject the fuel directly into each of the cylinders.

In the air intake duct 3, in a nonlimiting manner, there can be found an air filter 8 which makes it possible to eliminate the dust contained in the air, a flow meter 9 which makes it possible to determine the mass flow rate of air charge admitted in the engine 2, and an air intake flap 10, or throttle body 10, which regulates the flow admitted into the engine 2 by more or less obstructing the intake pipe 3.

Referring to FIG. 1, of a supercharged engine 2, the heat engine 2 also comprises a turbocharger 1 1 whose compressor 12 is interposed in the intake duct 3 between the compressor 12 and the intake flap 10 In addition, it is possible for a heat exchanger 13 to be arranged in the intake duct 3, between the compressor 12 and the intake flap 10, so that cool the compressed air by the compressor 12.

The compressor 12 is driven by the turbine 14 of the turbocharger, which is interposed in the exhaust pipe 4 between the engine 2 and the depollution device 5. In addition, the heat engine 2 may comprise one or more gas recirculation circuits. intake exhaust (not shown), more particularly a so-called high pressure EGR circuit and / or a low pressure EGR (EGR) circuit, without impair the generality of the invention.

In a manner known per se, the heat engine 2 produces a motor torque, said thermal torque C _t , which results from the combustion of a mixture of fresh air (to which can be added recycled exhaust gases recycled to the intake) and fuel in well-defined quantities by a calculator of engine 2.

The motorization device 1 according to the invention also comprises a reversible electric machine 15, as illustrated in FIG.

The electric machine 15, for example an alternator-starter 15 separate from the flywheel of the heat engine 2, and a rotary shaft 16 is coupled via transmission means 17 to a rotary shaft 18 of the engine 2, for example a crankshaft, is capable of operating in "engine" mode or in "generator" mode, under the supervision of a control box 19.

In "generator" mode, the electrical machine 15 is an alternator which supplies an electric current for storage in a battery 20 of accumulators by taking a strong electrical torque C _e ; in "motor" mode, it is instead powered by current previously stored in the battery 20 and provides an electric torque C _e engine that is added to that C _t of the engine to be transmitted to the wheels of the vehicle.

The operating mode of the motorization device 1 is as follows: The depression 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. The torque C can then be obtained either in the form of a thermal torque, or in the form of electric torque, 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 C _t and of 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 15, the calculator performing the distribution according to different parameters of the vehicle and / or the device of motorisation 1.

For the implementation of the process according to the invention, the catalyst may be equipped with means for determining a parameter representative of the temperature Θ of the exhaust gases passing through it, for example the temperature Θ of the catalyst itself, measured by a temperature sensor 21.

FIG. 2 illustrates the various steps of a method of heating the catalyst 6 according to one embodiment of the invention, using a motorization device 1 as just described, in which the temperature Θ of the trap catalyst 6 up to a priming temperature 9 _am o at which it has a predefined minimum treatment efficiency. For example, the targeted efficiency can be of the order of 50%, and the corresponding initiation temperature can be close to 250 ° C as seen in Figure 1.

The process begins with a step 100 of starting the vehicle. It can be materialized by the fact that the driver puts the ignition and requires a torque C for driving the vehicle, for example by pressing the accelerator pedal.

The process continues, iteratively, by a step 200 of determining the temperature Θ of the catalyst 6, then by a step 300 of comparing said temperature with a temperature threshold 9 _S , said preheating temperature, lower than the temperature boot 9 _am o ■ for example, the preheat temperature is between 60 ° C and 100 ° C.

As long as the temperature Θ of the catalyst 6 is lower than the preheating temperature 9 _S , the process leads to a step of preheating the catalyst 400 in which the torque C necessary for driving the vehicle is entirely supplied by the electric machine 15. This is generally the case for several seconds after the vehicle is started when the vehicle has been stopped for a long time. On the other hand, it may be that after a short stop, the temperature of the catalyst at the restart of the vehicle did not have time to fall below the preheating temperature because of the thermal inertia. In this case, step 400 of preheating the catalyst does not take place.

At this step 400, the heat engine 2 is not started. It does not produce a thermal torque. No fuel injection is performed in the cylinders. The heat engine 2 is rotated by the electric machine 15, and the successive cycles of compression of the air in the cylinders make it possible to increase the temperature at the exhaust and thus to heat the catalyst 6, until the reaching the preheating temperature 9 _S. Particularly advantageously, this step 400 can be performed by completely closing the air intake flap 10. This results in an acceleration of the temperature rise of the catalyst 6. Thus, with reference to FIG. made by the Applicant have shown that from a cold catalyst temperature of 20 ° C, it is possible to reach a preheating temperature of 60 ° C in about 30 seconds of operation of the vehicle in electrical mode, throttle body 10 closed, a temperature of 80 ° C in about 120 seconds and a temperature of 100 ° C in about 210 seconds.

It is understood from the foregoing that depending on the charge of the battery 20, one can adjust the value of the preheating temperature to account for the operating autonomy of the vehicle in purely electric mode.

When the temperature Θ of the catalyst 6 reaches the preheating temperature 9 _S , the process is directed to a step 500 for authorizing the starting of the heat engine 2. In other words, the torque C required for driving the vehicle can then produced by the heat engine 2, the electric machine 15, or a combination of both, under the supervision of the control box 19.

The method continues with a step 600 to end heating of the catalyst, capable of raising the temperature Θ of the catalyst 6 from the preheating temperature 9 _S to its light-off temperature 9 _amo ■ For example, this step 600 may consist conventionally to achieve delayed combustion of fuel, compared to combustion carried out normal operation of the engine. In a manner known per se, it is possible, for example, to perform late fuel injections into the engine cylinders.

Referring again to FIG. 1, it can be seen that step 400 of preheating the catalyst does not by itself make it possible to increase the efficiency of the catalyst. The efficiency being zero up to a temperature Θ of the order of 150 ° C, it remains zero until the end of the preheating step 400 because the temperature 9 _S does not reach such a value, even in prolonging the preheating time.

On the other hand, this preheating step advantageously makes it possible to shorten the duration of the heating of the catalyst up to its ignition temperature O _amo by the known processes used in step 600, thus reducing the fuel consumption necessary for priming. catalyst at this stage.

Of course, the invention is not limited to the embodiment just described. In a variant, for example, it would be impossible to measure the temperature Θ of the catalyst 6 and maintain the operation of the vehicle in purely electric mode for a predetermined fixed time, for example 30 seconds. It should then be that the step 600 end of heating is maintained for a predefined duration long enough to ensure that in all cases, the ignition temperature 9 _am o is reached.

Alternatively also, the method could be applied to any other exhaust gas depollution system requiring a minimum operating temperature for treating or storing pollutants, such as for example a nitrogen oxide trap 7 or a particulate filter 7, without departing from the scope of the invention.

Claims

A method of heating a catalyst (6) mounted at the exhaust of a motor (2) heat adapted to drive at least one drive wheel of a motor vehicle, said motor being associated with a reversible electric machine (15) operating in a generating mode or in a motor mode in which said electric machine (15) participates in the driving torque (C) of the vehicle, comprising:

a starting step (100) of the vehicle in which a driving torque (C) of the vehicle is required; and,

a step of heating (600) the catalyst (6) to a priming temperature (9 _am o) of minimal catalyst efficiency;

CHARACTERIZED IN THAT

it further comprises a step (400) for preheating the catalyst (6), in which the driving torque (C) of the vehicle is entirely produced by the electric machine (15) operating in engine mode, the heat engine (2) being rotated, in the un-started state and without fuel injection, by the electric machine (15).

Method according to claim 1, characterized in that during the preheating step (400) of the catalyst, an air intake flap (10) of the engine (2) is in the closed position.

Method according to one of the preceding claims, characterized in that the preheating step (400) takes place as long as the temperature (Θ) of the catalyst (6) is lower than a preheating temperature (9 _S ) of the catalyst (6). ).

Process according to Claim 3, characterized in that the preheating temperature (9 _S ) of the catalyst is below its priming temperature

Process according to one of Claims 3 or 4, characterized in that the preheating temperature (9 _S ) is between 60 ° C and 100 ° C.

Method according to one of claims 1 or 2, characterized in that the preheating step (400) takes place during a fixed predetermined time.

Process according to any one of the preceding claims, characterized in that the heating stage (600) of the catalyst is carried out by delayed combustion in the engine cylinders relative to the normal operation of the engine (2).

The method of any of the preceding claims, wherein the heat engine (2) is a spark ignition type engine, and the catalyst (6) is a three-way catalyst.

The method of any of the preceding claims, wherein the heat engine (2) is a compression ignition type engine, and the catalyst (6) is an oxidation catalyst.