WO2013110873A1

WO2013110873A1 - Method for the thermal protection of the components of the exhaust line of a heat engine

Info

Publication number: WO2013110873A1
Application number: PCT/FR2013/050072
Authority: WO
Inventors: Guillaume Allegre; Efstratios KRETZAS
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2012-01-26
Filing date: 2013-01-11
Publication date: 2013-08-01
Also published as: FR2986264A1; EP2807353A1; CN104246160B; FR2986264B1; BR112014017533B1; BR112014017533A2; CN104246160A; EP2807353B1; BR112014017533A8

Abstract

The invention relates to a method for the thermal protection of the components of the exhaust line of a heat engine according to which the temperatures of the exhaust gases and the walls of the exhaust line are predetermined and according to which, when the component of the exhaust line has reached the maximum temperature limit thereof, this is detected. According to the invention, the method consists of: - determining (54) a setpoint temperature (T3_setpoint) of the exhaust gases at the outlet of said engine, and - developing (56) a setpoint richness (ϕsetpoint) used to ensure said setpoint temperature of the exhaust gases.

Description

METHOD OF THERMALLY PROTECTING COMPONENTS OF THE EXHAUST LINE OF A

The present invention relates to a method of thermal protection of the components of the exhaust line of a heat engine whose fuel is gasoline, whether the engine is supercharged or not and that it is direct injection or indirect.

The components of the exhaust line of a heat engine are constituted by the elements in the exhaust gas evacuation circuit, starting, in the direction of evacuation of gases, by the valves of exhaust, passing successively through the exhaust manifold, the turbocharger for supercharged engines, the catalyst equipped with probes (oxygen probes for example), and ending with the silencer. The components can be more or less hot depending on the operating conditions of the engine. If the temperature of the exhaust gas is too high, the temperature of a component may possibly exceed a critical temperature from which the component may be damaged. It is therefore important to control the temperature in the exhaust line to avoid damaging a component and therefore not exceeding the critical temperature.

The temperature control of a catalyst placed in the exhaust line is for example described in several documents. More particularly, JP4060106 (A) relates to a device for comparing the measurement of the exotherm of a catalyst, by a temperature sensor, with the estimation of this exotherm to determine the aging state of the catalyst. If the exotherm does not correspond to that estimated, it can be deduced that the catalyst is deteriorated. This device does not concern the protection of a component of an exhaust line by thermal limitation. JP5312074 (A) relates to a method of compensating an oxygen sensor exhaust, downstream of the catalyst, depending on the catalyst temperature and the oxygen stored in the catalyst. However, this document does not concern the thermal protection of the exhaust line by enriching the combustion.

US6691507 (B1) describes a device for heating and maintaining temperature of a post-treatment element of nitrogen oxides, and the regeneration of this device by alternating rich / poor operation of the control of the richness of the fuel / air combustion mixture. This patent does not concern the thermal protection of a component by playing on wealth.

Patent FR2141049 (A5) relates to the determination of the input richness of a catalyst to optimize the aftertreatment of the exhaust gas.

However, none of the aforementioned documents relates to the thermal protection of the components of an exhaust line by enriching the fuel / air combustion mixture for cooling the exhaust gas.

The present invention provides a method for thermally protecting the components of an exhaust line by controlling the wealth.

More specifically, the invention relates to a method of thermal protection of the components of the exhaust line of a heat engine according to which the temperatures of the exhaust gas and the walls of the exhaust line are determined. (estimated or measured) and that the component of the exhaust line having reached its maximum temperature limit is detected. According to said method,

a target temperature T 3 is determined _{with respect} to exhaust gases at the output of said engine, and a setpoint of richness is developed (Setpoint for ensuring the said setpoint temperature of the exhaust gases.

Said setpoint of wealth (Setpoint is determined within the limit of the maximum wealth acceptable by the engine.

[00010] According to one mode of implementation preferred, said set temperature T3 _con sign of engine output in the exhaust gas is determined by presetting the reference temperature and by controlling, said prepositioning delivering a basic set temperature T3 (x) base determined using mappings based on engine operating point and x component to be protected. Said maps can be load-engine speed mappings with parameter T3 motor output temperature. Said regulation is preferably of the proportional and integral type which delivers a corrective term. Said corrective term is added to the prepositioning value T3 (x) base to provide said temperature T3 _CO nsign-

[0001 1] Instead of actuating said prepositioning and said regulation, it is possible to choose a default value for said setpoint temperature T3 _CO nsigne exhaust gas engine output.

According to another embodiment, said setpoint temperature T3 _CO nsigne exhaust gas engine output can be determined by inversion of the models of the exhaust line.

In order to produce said setpoint of richness (Setpoint, a temperature of the exhaust gas at engine output T3 _{is determined} for a richness φ .T3 said temperature T3 _is tim is determined from a temperature T3 _es tim <|> = i as a function of the different engine parameters and for a richness φ = 1, said temperature T3 _is tim <|> = i being corrected by means of a correction function f (Q _eC h _> Φ) determined by mapping (flow rate Q _eC h of the exhaust gases - setpoint richness φ). [00014] Advantageously, said temperature T3 _is tim is determined from the relation:

and said protection setpoint richness of the component x is determined from the relation:

Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, given by way of non-limiting examples and with reference to the accompanying drawings which show:

- Figure 1, the diagram of an exhaust line with thermally protected points by an adaptation of the engine control;

- Figure 2, the architecture of the thermal protection function;

- Figure 3, the illustration of the calculation of the exhaust temperature setpoint;

- Figure 4, the representation of a direct model of exhaust gas temperature and wealth dependence; and

- Figure 5, the representation of the inverse model for determining the protection of a component of the exhaust line.

[00016] FIG. 1 schematically represents an exhaust line 10 of a heat engine 12 with its cylinder head 14. The exhaust gases leave the cylinders 16 via the exhaust valves 18 to enter the exhaust manifold 20 The gases then pass successively by a turbocharger 22 (for a supercharged engine) provided with a turbine 24 and a bypass 26 ("waste gate"), a catalyst 28 with an upstream oxygen sensor 30 and a downstream probe 32, and The points to be thermally monitored, and the components that it is desired to thermally protect, are mainly the upstream 40 of the turbocharger 22, the upstream 42 and the downstream 44 of the catalyst 28 with the probes 30 and 32. as well as the interior 46 of the catalyst 28 and the collector 20 (the monitored point of the collector is designated 48 in FIG. 1). According to the invention the components are thermally protected by an adaptation of the control of the engine. The aim is that the temperatures at the monitored points do not exceed a critical value for which and beyond which the components (here the turbocharger and the catalyst with its probes) could be damaged.

Briefly, the invention consists in limiting the temperature of the exhaust gas at the engine outlet, by determining the enrichment necessary to not exceed the critical temperature of the component having reached this critical temperature, by reversal of the thermal models of the exhaust line.

According to the method of the invention, a target temperature is determined at the engine output T3 _con sign and wealth (Setpoint to ensure said setpoint temperature.

[00019] Figure 2 schematically illustrates the main steps of the method. The first two steps, corresponding to the modules 50 and 52, are generally known, the scope of the invention concerning the following two modules 54 and 56 surrounded by the rectangle 55.

The module 50 can estimate, using one or more model (s), the temperatures in the exhaust line according to various parameters such as the engine speed, the load, the advance on ignition and the temperature outside the vehicle. The module 50 provides Tech tim _es temperatures of the gas and the walls of the exhaust line, which are modeled separately or may be measured by sensors.

The module 52 makes it possible to detect, in other words to identify among the components of the exhaust line that it is desired to protect thermally, from the Tech _es tim information provided by the module 50, the component having reached its critical temperature (temperature from which the component may be damaged). For this purpose, it is possible to use a known monitor that scans all the monitored temperatures and indicates the element to be protected. Module 52 provides three pieces of information:

- x which is the index of the element detected as having reached its critical temperature (detection is done using models);

- Tech (x) _max which is the maximum temperature allowed by component x which has been detected as having reached its temperature limit, and

- Tech (x) estimate which is the current temperature (at the moment considered) of the component x.

These three pieces of information are then supplied to a module 54 which generates a target temperature T3 _CO nsign (also indicated in FIG. 1) which is the target temperature of the exhaust gases at the output of the heat engine and therefore at the output exhaust manifold 20. The detailed description of the module 54 will be made hereinafter with reference to FIG.

This setpoint temperature T3 _{with a} sign is supplied to a module 56 which generates a setpoint of richness (reference to be applied to the motor controller.) The detailed description of the module 56 will be made hereinafter with reference to FIGS. .

The method, object of the present invention, can be summarized as follows:

- exhaust and wall temperatures in the exhaust line are estimated (module 50) or measured;

the component of the exhaust line having reached its maximum temperature limit is detected (module 52);

a target temperature of the exhaust gases at the output of the engine (cylinder head outlet) is determined (module 54); and

- within the limit of the maximum acceptable wealth on the engine, a wealth is determined in order to respect the temperature setpoint exhaust gas at the output of the previously defined engine (module 56). The maximum allowable wealth of the engine is the limit below which the quality of combustion is acceptable (stability of combustion).

The temperature setpoint of the exhaust gas at the engine outlet, T3 _CO nsigne represents the temperature of the exhaust gas to be met at the output of the engine not to exceed the maximum limit of critical temperature Tech [x] max of the identified element x. The difference between the two temperatures, T3 _CO nsign and Tech [x] max can be defined by a transfer function that takes into account the heat exchange in the exhaust line between the motor output and the element x. However, such a transfer function is complex to model. FIG. 3 shows in detail an advantageous mode of implementation of the process concerning the elaboration of the temperature setpoint of the exhaust gas at the outlet of the engine, T3 _con sign (module 54), making it possible to avoid modeling such a transfer function. There are two steps here: on the one hand, the prepositioning of the target temperature (illustrated by the rectangle 58) which provides, for the element x, a base temperature T3 (x) base (the temperature T3 is the temperature exhaust gas at the engine outlet, more precisely at the outlet of the exhaust manifold) and, on the other hand, a temperature regulation (rectangle 60) which provides a temperature correction term T3 (x) base ■

The prepositioning allows to initiate the regulation from a base temperature T3 (x) base close to the temperature setpoint of the exhaust gas output of the desired engine, which allows a faster regulation. For the prepositioning, it is possible to use maps 62, mapping by element x (only one element is monitored at a time, the element x). The index x of the element to be monitored is introduced by the input 64 of a selector 66 which selects the mapping of the element x. The maps advantageously represent the air load of the motor 76 on the ordinate according to the engine speed 74 on the abscissa, with parameter temperature T3. The mapping relating to the element x gives the temperature T3 (x) base in open loop that is refined using the regulator 60. The regulator 60 is preferably of the proportional and integral type, although another type could be used (eg proportional, integral and derivative or proportional and derivative type or more complex type). It provides a corrective term for the temperature T3 (x) base. The controller consists of a proportional control 68 and an integral control 70. These two commands receive information 72 which represents the temperature error of the component x to to protect, this error being equal to (Tech (x) _max - Tech (x) _es tim) - The two commands 68 and 70 also receive the engine speed 74 and the air load 76. The proportional command 68 delivers a corrective term 78 which is proportional to the error 72 and the integral control 70 provides a correction term 80 which represents the integration of the error as a function of time so as to converge the error signal. The correction terms 78 and 80 are added in an adder 82 which provides the corrective term 84. The latter is added with the temperature T3 (x) base provided by the prepositioning 58, in an adder 86. The regulated temperature (T3 (x) _aS + b e the corrective term) is provided to an input 88 of a selector 90. This allows to choose either the regulated temperature, a T _default temperature value is necessary (supplied by a module 92 values temperatures without protection) when the protection is not active. The choice between these two inputs is made by means of a signal "activation protection component" applied to the input 94 of the module 90. The latter delivers the temperature of the desired exhaust gas T3 _CO nsign-

In summary, the calculation of the exhaust temperature setpoint T3 _CO nsigne to achieve the protection of the components of the exhaust line can be composed by: a prepositioning (or open loop) mapped according to the engine operating point and the element to be protected (rectangle 58);

a proportional-integral type regulator whose gains depend on the operating point and the element to be protected (rectangle 60); and an arbitration (rectangle 90) making it possible to choose between:

^* a default value (high value) when the protection is not active, and

^* the sum of the prepositioning and the corrective term coming from the regulator. According to an alternative embodiment of the invention, the embodiment shown schematically in Figure 3 (prepositioning and regulator) can be replaced by an inversion of the models of the exhaust line. This variant makes it possible to reduce the calibration time as well as the number of calibrations. However, it has the disadvantages of being complex to implement and not to offer a degree of freedom in the calibration for controlling the behavior of the system. The mode of implementation illustrated in FIG. 3 is then preferred.

[00030] FIGS. 4 and 5 schematically represent an embodiment of the development of a setpoint of richness (module 56 of FIG. 2), FIG. 4 schematically showing a direct model of the temperature of the exhaust gases. and wealth dependence and Figure 5 illustrating an inverse model for the determination of wealth for the protection of components. [00031] In FIG. 4, the temperature T3 _is tim <|> = i of the exhaust gas, estimated for a setpoint combustion richness φ equal to 1 and for a considered operating point, is delivered by the module 100 depending on the different engine parameters (operating point, water temperature, ignition advance degradation, position of the camshafts, etc ....) - Mapping 102, obtained at the test bench and representing ordinate flow Q _eC h exhaust gas and abscissa wealth φ, provide a function correction f () of the exhaust temperature as a function of the flow Qech exhaust gas and wealth φ. The correction function f () is delivered to a multiplier 104. The latter delivers at its output the temperature T3 _es tim which is the estimated temperature of the exhaust gas at the engine output (output of the exhaust manifold) for a richness φ, which which is expressed by:

Since the function f () is bijective over the richness interval [1 ^ _m ax], where φ ₃ χ is the maximum limit of richness below which the quality of the combustion is acceptable (stability of the combustion), it is possible determine the richness to respect an exhaust temperature for a given operating point. Indeed:

Λ

J

With:

T3 _CO nsigne: the set temperature of the exhaust gas at the engine output, and

f ¹ (): the inverse function of f () with respect to wealth. This function f ¹ () is provided by a mapping resulting from the inversion of the map of f ().

This inverse model is illustrated in FIG. 5. A divider 106 (it is indeed a divider since the multiplier 104 of FIG. 4 is inverted) receives on one of its inputs the temperature T3 _CO nsign (given by the module 54 of FIG. 2) and on another input the estimated temperature T3 _is tim <|> = i estimated at the output of the engine for the richness φ = 1. Module 50 of Figure 2 (estimation of temperatures in the exhaust line) provides this temperature directly T3 _es tim <|> = i -

In comparison with existing solutions, the present invention allows a reduction of C0 ₂ emissions since it defines a just needed enrichment. In addition, it allows a good performance of limiting the temperature of the components of the exhaust line resulting in either a possibility of reducing the cost of the components by allowing operation at temperatures closer to the limits of the materials (dimensioning at most fair ), or by reducing C0 ₂ emissions by not anticipating activation of the function. The invention also allows a gain calibration cost: in fact, the direct models are already calibrated, no additional testing is necessary since it is sufficient to digitally invert the maps of direct models.

Claims

1. A method of thermal protection of the components of the exhaust line of a heat engine according to which the temperatures of the exhaust gas and the walls of the exhaust line are determined and according to which the component of the exhaust line having reached its maximum temperature limit is detected, said method being characterized in that it consists of:

determining (54) a set temperature T3 _∞ denoting the exhaust gases at the output of said engine, and

- Develop (56) a richness setpoint (Setpoint for providing said exhaust gas setpoint temperature.

2. Method according to claim 1, characterized in that said wealth instruction (Setpoint is determined within the limit of the maximum wealth acceptable by the engine.

3. Method according to one of the preceding claims, characterized in that said _con sign T3 setpoint engine output of the exhaust gas is determined by pre-positioning (58) of the set temperature and by regulating (60).

4. Method according to claim 3 characterized in that said prepositioning (58) delivers a basic setpoint temperature

T3 (x) base determined using maps (62) according to the engine operating point and the component x to be protected.

5. Method according to claim 4 characterized in that said maps are load-engine speed maps with the engine output temperature parameter T3 as parameter.

6. Method according to one of claims 3 to 5 characterized in that said regulation (60) is of the proportional type (68) and integral (70) which delivers a correction term (84).

7. Method according to one of claims 3 to 6 characterized in that said corrective term (84) is added (86) to the prepositioning value T3 (x) base to provide said temperature T3 _∞ nsign-

8. Method according to one of claims 1 and 2 characterized in that said set temperature T3 _∞ nsigne exhaust gas engine output is determined by inversion of the models of the exhaust line.

9. Method according to one of the preceding claims characterized in that, in order to develop said wealth guideline (Setpoint, it determines a temperature of the exhaust gas engine output T3 _es tim for a richness φ.

10. Method according to claim 9 characterized in that said temperature T3 _is tim is determined from a temperature T3 _is tim <|> = i as a function of the different engine parameters (100) and for a richness φ = 1, said temperature T3 _is tim <|> = i being corrected by means of a correction function f (Q _eC h _> Φ) determined by mapping flow rate Q _eC h of the exhaust gases - setpoint φ.

11. The method of claim 10 characterized in that said temperature T3 _is tim is determined from the relation:

stimai ^X f (Qech>)

12. The method of claim 10 or 1 1 characterized in that said engine parameters consist of at least one of the following parameters: operating point, water temperature, degradation of the ignition advance and positioning timing of camshafts.

13. The method of claim 1 1 characterized in that said protection setpoint of the component x is determined from the relation: f

V

J

T3 _CO NSIGN _e being the setpoint temperature of the exhaust gas at the engine outlet, and

r-1

f ^" () being the inverse function of f () with respect to richness.