EP1636472A1

EP1636472A1 - Method for control of a propulsion system comprising a diesel engine and a nitrogen oxides trap

Info

Publication number: EP1636472A1
Application number: EP04767329A
Authority: EP
Inventors: Laurent Philippe; Jérôme Cruchet
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2003-06-23
Filing date: 2004-06-11
Publication date: 2006-03-22
Also published as: JP4421610B2; US20070271909A1; FR2856432B1; KR20060018899A; JP2007514886A; WO2005003539A1; US7818962B2; FR2856432A1

Abstract

The invention relates to a propulsion system, comprising a diesel engine (1), an air inlet circuit (11, 13, 14) and an exhaust circuit (16, 3, 4), for exhaust gases coming from the engine. The inlet circuit comprises adjustment means (22, 23) to control the air flow (D) into the engine (1) and the exhaust circuit comprises a nitrogen oxides trap (3) for storage of the nitrogen oxides contained in the exhaust gases. During a regeneration mode in which the exhaust gases are provided with reducing agents for regeneration of the nitrogen oxides trap (3), a set point is determined for the air flow (D), according to the operating status of the engine, the adjustment means (22, 23) are controlled to obtain an air flow (D) close to the set point, a main fuel injection (Qp) is carried out and a secondary fuel injection (Qs) is carried out during a power phase such as to maintain the exhaust gas in a reducing state.

Description

Method of control of a diesel engine motorization system and nitrogen oxide trap.

The invention relates to a method for controlling a diesel engine drive system equipped with a nitrogen oxide trap, in particular when

.the system is also equipped with particle filtration.

Due to pollution standards, vehicle engine systems are now equipped with pollution control lines. In

^• _. such line, a ^' nitrogen oxide trap aims to capture nitrogen oxides in the exhaust gas of an internal combustion engine. For a Diesel engine, the pollution control line can be supplemented by a particle filter. It is even envisaged to provide a depollution device integrating the two functions.

For operation of the trap with a nitrogen-oxides' Diesel engine, it is known to operate ^• ent cycliqύe the engine so that the exhaust gases are reducing agents, for discharging the nitrogen oxide .piège . This works _. is for example described in the document EP 560 991.

During normal operation, combustion in a diesel engine takes place with excess air. As a result, nitrogen oxides are formed and these are captured and stored by the nitrogen oxide trap.

However, as the storage capacity is limited, it is necessary to regularly discharge the nitrogen oxide trap, which is done by the operation ^' generating reducing gases. This operation is also called ^• rich mixture operation. The exhaust gases contain, in this phase, unburnt hydrocarbons, carbon monoxide or hydrogen which will react with the nitrogen oxides stored in the nitrogen oxide trap to eliminate them.

To obtain this operation, document EP 560 ^' 991 proposes - for example an intake flap on an - intake duct making it possible to reduce the amount of air ^' admitted into a combustion chamber, and the injection of a additional amount of fuel, so that the combustion is carried out with a rich mixture. •

However ^ when switching the operation to blend ^• rich - it is desirable that the torque delivered - by -the ^engine remains substantially constant, so that the driver does not need to rehabilitate the de- torque demand during the transition .

It is therefore an objective - of the invention to propose a method for controlling a system of

.motorization ^' with, diesel engine equipped with an oxide trap'. of nitrogen so that 'the engine delivers an identical torque>' even- during the transition in the regeneration phase of the nitrogen oxide trap.

With this. ^' objective in view, the subject of the invention is a method ^' of controlling a de-motorization system comprising a diesel engine, an air intake circuit, a gas exhaust circuit exhaust in. from the engine, the intake circuit .. comprising adjustment means for controlling the flow of air entering the engine, the. Circuit '.échappement comprising an oxide trap 5. nitrogen to store ^the nitrogen oxides contained es les in exhaust gas, in which method operating in a regeneration mode to regenerate the trap oxides nitrogen by providing reducing exhaust gases. 0 According to the invention, during the regeneration mode, an air flow setpoint is determined according to the operating point of the engine, it is controlled. the. adjustment means to obtain an air flow close to. the instruction, a main fuel injection and a secondary injection are carried out, the secondary injection being adapted to maintain the exhaust gases in the reducing state.

Thus, the desired torque can be obtained, essentially by determining the main injection, while the richness of the exhaust gases is adjusted accordingly by the quantity of fuel injected during the secondary injection. ^The main injection is carried out when the piston -is near the, while the secondary injection is carried out when the piston has largely exceeded the top dead center, for example when the crankshaft has rotated in the order from- 60 ° -after said top dead center, during the expansion phase. ₀ In the case of a pollution control line comprising- for example a particle filter, there is a variable exhaust back pressure in line ^' . ^' de-pollution. Consequently, even with a predetermined air flow and quantity of fuel, the torque delivered varies as a function of this exhaust back pressure. Indeed, -5- ^" this- counter-pressure, increases in particular the resistance; to the exhaust of the burnt gases, and therefore the resistance. Opposite on a piston during the exhaust phase.

.a point, of determined operation, the

10. air flow setpoint • remains constant. However, when the back pressure increases, it is necessary to increase the quantity of fuel for the injection - main to maintain the torque, even with the constant air flow. The quantity of

15 fuel- - of- ^' secondary injection - will be reduced, ... to-- maintain the same level of richness of exhaust gas ^' -d'. We see in this case that the amount ^'smoke - emitted increases, this increase being due to la- decrease gas temperature at the end

20 ^'Phase • d ^ exhaust and decreasing consecutively ^ds ^{post-oxidation} reactions smoke ..

It is therefore another objective of the invention to improve the; motorization system so that the

25- engine delivers identical torque, even in the presence of a variable exhaust back pressure, and without increasing _. - the level of smoke emitted. For this, when the ^• motorization system includes an .accessory. _; generating a variable back pressure in

_.30 the ^"circuit, exhaust, -the air flow set is -from ^'preference -augmentée with said counter pressure-exhaust. Thus-, - admission- the increase in. air flow, losses; couple ^' due. efforts ^'suction of -' alr -are ..diminuées, which reduces the ^amount: -. of; ^, Fuel injection ^main. In addition -5, / -pôu-r-- .. ^' - ^{•' •} maintain the richness of the exhaust gases, -.- ^'• the ^• fuel quantity of the secondary injection is increased, which raises the temperature ^' from ^' -gas to ^' the end of the. relaxation phase. ^'Thus: 1a post ⁱ cόmbustion smoke is improved. 0- - In - ^'• : -le ..- ^' . ^' -.case ^• of an exhaust line comprising- -.a- ^'' particle-filter, the air flow set point es _. 0corrigée by a point on the function de- factor ^'one operation and state of loading of the particle filter. 5 - uήè ^"specific .manière, -. The state of loading of the particle filter is evaluated by the _debit-of / ^gases -.d'échappement therethrough and

• difference - in pressure / - between inlet and outlet.

In another way, the loading state0 '. of the particulate filter is evaluated by a measurement of

• the pressure in ^'' - upstream - of the particulate filter by

• ratio ^' to flow ^' - ^' - ^' from exhaust gas.

. L. ' invention ^' "will be better understood and others

- special features _. .ët _. - ^' àvantages will appear on reading 5 - • from 0.1a _: ' - _. ^' description ^' which will follow, the ^' description doing _. - reference to the drawings ^of annexes including ^•: ^'

- Figure 1 is ^a schematic view of a drive system according to the invention; 0 ' _. . _-. The Figure- "2 'is - a graph showing how fuel flow rates. and air as a function _o f against pressure ^• • ^'to the exhaust in a first de-.mode .réalisation e the invention;

- ^• .- la.;. ^' .figure 03. is a diagram showing the evolution ^" 5- - ^••' of the quantity of smoke emitted as a function of the exhaust back pressure in the first • embodiment;

• - the figure -. '4- ^' is ^' a diagram similar to the figure

2 .- for ^' .; a ^'second embodiment of .10 the invention; ^'

- ^• ..the.-Figure -5 ^"'' is- a diagram similar to the figure

3 for the second embodiment.

.The -from a motor according to the invention, -such ^as' shown in Figure 1, comprises a

15, -, engine ..1 - _. of. . ^'' Diesel type supercharged by a turbocharger 2 and whose exhaust gases are

• making treaties by ^a nitrogen oxide .piège 3 and then through a filter. with particles 4. The engine is supplied with air by an air circuit comprising an air intake 11,

20 a compressor 12 of the turbocharger 2, a line. discharge- 13 and an intake manifold 14

^• opening, .in engine combustion chambers

-1, a single chamber 15 being shown. The engine comprises for each combustion chamber 15 a

25- injector ^' .'20. -for supplying fuel in room- 15 • according to a sequence determined by means of ^the control 24.

The- exhaust gases produced by the

, - combustion -are- evacuated from the chamber 15 by a

30;; _. tube ^'' exhaust 16, through a turbine 17

_. turbocharger, then the nitrogen oxide trap 3 and the particulate filter 4. A recycling circuit

^. exhaust gas, has a nozzle 18 on the exhaust manifold, a valve 19 allowing the passage of gases. exhaust to the discharge line via line 21.

A valve 22 is inserted into the air circuit between the output line 21 and the inlet of the intake manifold 14. The valve 22 makes it possible to .varier ^'• the air passage section between an opening complete and partial throttling. An actuator. 23 acts on the valve 22 to determine the degree of opening thereof. It receives an opening position instruction from the control means 24.

• Sensors provide information on the - drive system. Among these sensors, a flow meter 26 delivers information on the admitted air flow rate D as well as information on the air temperature ^' Tair. A richness probe 28 gives information on the richness λ of the exhaust gases. A differential pressure sensor 30 measures the pressure difference DP between the inlet and the outlet of the particle filter 4. All this information is received by the control means 24.

The control means 24 determine the opening position setpoint and the fuel injection sequence according to the information received _. of the motorization system, such as those

• - mentioned above, and in addition the engine temperature • Tmσt, the rotation speed N of the engine, a value representative of the load demand α of the engine - such as the positioning of an accelerator pedal, and atmospheric pressure Patm.

During normal engine operation, the

-valve 22 is completely open, which ensures maximum filling of the combustion chambers with air. The amount of fuel injected at each

- - cycle - is such that the ratio between the mass of fuel and the mass of air is less than the stoichiometric ratio, that is to say in excess of air. These conditions are also expressed by stating that the richness of combustion is less than 1. The exhaust gases from this combustion contain oxygen which was not consumed by combustion, and we also speak of richness exhaust gas less than 1.

Under these operating conditions, it is observed that nitrogen oxides are formed in the

- burnt gases, which oxides are then absorbed by the nitrogen oxide trap 3. The nitrogen oxides may be reduced during operation in regeneration mode, in which the richness is greater than 1.

Consider a motorization system with or

. without particulate filter 4. To control the regeneration mode, according to a first embodiment of the invention, an intake air setpoint is determined as a function of the engine operating point, and the valve 22 is piloted so that the measurement of the air flow rate D 'by the flow meter 26 corresponds to the set point thus determined. At the same time, an amount of fuel to be injected during a main injection is also determined to obtain a torque corresponding to the demand α, expressed for example ^• by the. position of the accelerator pedal.

To obtain exhaust gases with a richness greater than 1, the main injection is completed by a secondary injection. The quantity of

, ^' 5 ^' χ, .- fuel during secondary injection is

^'' determined - by a regulation comparing a setpoint

.. ^' - • ^• - ^• de-richness and a measure λ of the- richness probe

^'' 28-. ^•

The air flow setpoint is determined by 10 ^' . example- by. - the intermediary of a cartography taking into account, the. engine rotation speed N, demand α, ^" engine temperature Tmot, intake air temperature - air and atmospheric pressure Patir

15 In the case of a drive system with a particulate filter 4, the back pressure at

1 the CPE exhaust changes as a function of the loading state of the particle filter 4. The diagram in FIG. 2 '. shows the evolution of the quantities of

20. fuel injected - Q with the evolution of said back pressure ^' CPE, for the same point of

-operation. Curve 40 represents the quantity

0- of.-. fuel injected during QP ^• of. injection

-principale, -courbe 41 represents the quantity of

25 fuel injected Qs during the secondary injection,

_. so that curve 42 represents the air flow

^' admitted D.

'The point _.. -of operation being the same, the

-flow rate -air does not change according to the counter-

30 pressure at ... the CPE exhaust. However, to keep the torque delivered by the engine constant when the CPE back pressure changes, the main quantity of fuel Qp is adjusted, for example by an action of the driver on the accelerator pedal. The regulation of wealth then to - consequently decreasing the amount of secondary ^fuel Qs. Figure 3 illustrates by curve 44 an increase in the amount of fumes emitted ^'with the increase in pressure against CPE.

In a second embodiment, preferred to the first, the air flow setpoint is calculated by taking into account the loading state of the particle filter. For example, a correction is added to the calculation of the setpoint according to the first embodiment as a function of the pressure difference DP between the inlet and the outlet of the particulate filter and a conventional estimate of the exhaust gas flow rate.

The diagram in FIG. 4 shows the evolution of the quantities of fuel injected Q with the evolution e 'of said CPE back pressure, for the same operating point. Curve 50 represents the amount of fuel Qp injected during the main injection, the ^'curve 51 represents the amount of

- fuel injected .Qs during the secondary injection, while curve 52 represents the admitted air flow D. It can be seen that the air flow increases with the CPE back pressure, while the main injection quantity Qp remains constant, to maintain a constant torque. To keep the richness of the exhaust gases constant, the quantity of fuel for the secondary injection must increase, as shown in curve 51 in the figure. 4. FIG. 5 shows by curve 54 a decrease in the quantity of fumes emitted with the increase in the CPE back pressure.

The invention is not limited to the embodiments • realization that ^'-.ont been described as examples. The oxide and nitrogen trap and the particulate filter can be combined ^• in a single device. The CPE back pressure can be measured directly before the turbine 17 or before the particulate filter and intake. into account in • the calculation of the air flow setpoint.

Claims

• -, 1. ^• ; -. Process. ^' for controlling a motorization system, ^' - ^' comprising a Diesel engine (1), a

Circuit ^{• • '} • intake ^' - of air (11, 13, 14), a circuit

^' exhaust ^' -. (I6 ₇ ..3, - 4) of exhaust gas in

5 from "-from: .- engine, intake circuit

• • comprising- adjustment means (22, 23) for '.. ^' , control the- ^' air flow (D.) ^' entering- the engine

- (1) - the, circuitry ^'exhaust comprising a trap

• -. oxides -of nitrogen- (3). to store nitrogen oxides 10 ^' . contained -.- in ^' lès -gas ^' of exhaust, - process according to which one-- operated in a regeneration mode

.to ^' regenerate _. - the nitrogen oxide trap (3) in

^' _. providing. -de. ^'' exhaust gas ^' reducers, characterized process -en.- .. ^' : what ,. during the mode of

15 .. '. Regeneration, - on _: .determines a flow rate setpoint

- _. - " ^{• '} '-d'air^' - (. D). According to ^' - leJ.p ^' anointed with engine operation, control- _. -, les -means of adjustment (22, 23) for

- - get;., A- Speed ^'• -' air ^"(D) close to the setpoint, there is provided a main fuel injection de- (Qp) _and.

20 injection "- secondary (Qs), secondary injection

^' (Qs) - being .. carried out during a relaxation phase and

•. suitable for ^' maintaining exhaust gases in the reducing state.

• '20 - Process, according to claim 1, in 25- - which, when '.- motorization system includes - ^' _{. '.} an • accessory- (4) ,. generating a back pressure (CPE) .variable in • the. ' exhaust circuit, the setpoint for - air flow "- is increased with said exhaust back pressure (CPE).

3. Method according to claim 2, wherein- 1 accessory generating a back pressure (CPE) • variable is a particle filter (4), the set point. air flow being corrected by a factor 5 - function - of the point - of operation and of the loading state of the ^' particulate filter (4).

0 ^• 4. .A method according to claim 3, in

. ..: which 1- ^' ' state-de. ^' .loading the particulate filter

•. (4) is. evaluated ^• •• by the exhaust gas flow on

• 10 crossing •• .and • there. difference in pressure (DP) between inlet-.and outlet.

-5. .. The method of claim 3, wherein the state of. loading of. particle filter

(4.) is evaluated by measuring the pressure upstream

15 of the ^' filter ^' to. particles (4) with respect to the flow of exhaust gases.

60 -Power system implementing the method of one of claims 1 to 5.