EP2430298B1 - Estimation of the nitrogen oxide (nox) concentration in an internal combustion engine - Google Patents

Description

The invention relates to the estimation and the regulation of at least one output parameter of an internal combustion engine comprising a plurality of cylinders.

In particular, the invention relates to the estimation of an output parameter of the internal combustion engine carried out from a measurement of the internal pressure of a cylinder of the engine, as well as the regulation of this output parameter from of this estimate.

Antipollution standards and lower consumption are becoming more and more important issues for car manufacturers. It is therefore necessary to control the combustion phase of vehicle engines to limit polluting emissions such as nitrogen oxides NO _x , carbon dioxide CO ₂ , carbon monoxide CO, unburned fuels HC and PM particles. , especially for diesel engines.

This necessarily requires perfect control of combustion without neglecting fuel consumption and engine performance.

In addition, during the tuning of the engines leaving the assembly lines, a single engine adjustment is carried out according to the emission standards. This single adjustment must therefore take into account the worst cases so that all engines can meet these standards, which obliges manufacturers to take safety margins large enough not to exceed these standards.

As is known, many sensors are generally embedded in vehicles for measuring a plurality of quantities and state variables, which entails a non-negligible cost in the manufacture of vehicles.

Reference may be made, for example, to the Japanese patent application JP2002371893 , in which an estimate of the emission of nitrogen oxides NO _x is made from a measurement of the internal pressure of a cylinder and a quantity of fresh air admitted into the engine. However, the estimation model used is based on a chemical kinetic approach of the combustion process which is complex and expensive.

We can also refer to the document WO 2008/108212 which describes a controller of an internal combustion engine capable of estimating a concentration of nitrogen oxides.

The document FR 2 915 241 A1 shows the calculation of the indicated average torque or the indicated average pressure from the measurements of the internal pressure of the cylinder at given times.

One of the aims of the invention is therefore to provide a system according to claims 1-4 and a method according to claims 7-10 for estimating an output parameter of the engine using a minimum of direct measurements of states. of the engine and with a minimum of variable calculations.

Another object of the invention is to provide a system according to claims 5-6 and a method according to claims 11-12 for regulating an output parameter of the engine from its estimate.

According to one aspect of the invention, there is proposed a system for estimating at least one output parameter of an internal combustion engine comprising at least one cylinder, a movable piston driven by means of a crankshaft, means for measuring the temporal variations of the angle of the crankshaft and of the internal pressure of said cylinder.

This system comprises calculating means for calculating a plurality of combustion parameters, such as internal cylinder pressures characteristic of combustion, internal cylinder pressure variations and engine cycle times, from said measurements of the cylinder. angle of the crankshaft and the internal pressure of the cylinder and estimating means for estimating at least one output parameter of the engine from said combustion parameters.

Thus, it is possible to provide a means for estimating an output parameter of the engine which takes into account only characteristic values of the internal pressure of a cylinder. Furthermore, the number of sensors used and the complex calculations of numerous intermediate engine state variables are limited.

Advantageously, the measurement of the internal pressure of the cylinder can be carried out by means of a pressure sensor. It is to highlight that each cylinder can be equipped with such a pressure sensor or more simply, a single cylinder of the engine.

The characteristic output parameters of the engine can be chosen among pollutant emissions, combustion noise, fuel consumption, engine torque and in general all the parameters that represent a condition emitted directly or indirectly by combustion in the engine.

According to the invention, the estimation means estimates at least one output parameter of the engine from a weighted sum of said combustion parameters.

In addition, an estimation means is provided which is simple and which requires few calculations.

The system may include a means for measuring a quantity of oxygen admitted into the engine and the calculating means is able to calculate said combustion parameters from, moreover, the quantity of oxygen admitted into the engine.

The system may also include a means for measuring a flow rate of fuel admitted into the engine and the calculating means is able to calculate said combustion parameters from, moreover, the flow rate of fuel admitted into the engine.

The system may also include a means for measuring a flow of fresh air admitted into the engine and the calculation means is able to calculate said combustion parameters from, in addition, the flow of fresh air admitted into the engine.

Using additional measuring means, the estimation of the output parameters of the engine is specified.

According to another aspect, there is proposed a device for regulating an output parameter of an internal combustion engine, comprising means for developing a setpoint for the output parameter of the engine, an actuator capable of controlling the output parameter of the engine. engine, an estimation system for estimating the output parameter of the engine, the regulating device being able to generate a command for said actuator from a difference between said setpoint and said estimate of the output parameter of the engine in order to regulate the motor output parameter.

Thus, a means is provided for closed-loop regulation of an engine output parameter by means of a measurement of the internal pressure of the cylinder.

This closed-loop regulation makes it possible to adapt the settings concerning the antipollution standards according to each engine, and therefore to reduce the dispersion from one engine to another during their manufacture.

This reduction in engine dispersion makes it possible to reduce the safety margins of the manufacturers and in particular to dimension the pollutant emission post-treatment systems as accurately as possible, and advantageously to reduce their volume.

In addition, the devices for post-treatment of polluting emissions generally include precious metals, such a reduction in their volume allows savings in the cost of a vehicle.

According to one embodiment, the device comprises means for generating a command setpoint for said actuator and means for calculating a command difference, between said command setpoint and said processed command, intended for said actuator.

It will thus be possible to take into account the constraints on one of the combustion parameters in order to regulate the output parameter of the engine. It is possible, for example, to take into account a constraint on the air flow admitted into the engine.

According to another aspect, there is proposed a method for estimating at least one output parameter emitted by an internal combustion engine comprising at least one cylinder, a movable piston driven by means of a crankshaft, comprising a step for measuring the temporal variations of the angle of the crankshaft and of the internal pressure of the cylinder.

This method comprises a step of calculating a plurality of combustion parameters, such as internal pressures of the cylinder characteristic of combustion, variations in internal cylinder pressure and engine cycle times, from said measurements of the cylinder. angle of the crankshaft and of the internal pressure of said cylinder and a step of estimating the output parameter of the engine from said combustion parameters.

According to the invention, at least one output parameter of the engine is estimated from a calculation of a weighted sum of said combustion parameters.

The method may include a step of measuring a quantity of oxygen admitted into the engine, and during the calculation step, said combustion parameters are calculated from, in addition, the quantity of oxygen admitted into the engine. engine.

The method can also comprise a step of measuring a flow rate of fuel admitted into the engine, and during the calculation step, said combustion parameters are calculated from, in addition, the flow rate of fuel admitted into the engine.

The method may also include a step of measuring a flow of fresh air admitted into the engine, and during the calculation step, said combustion parameters are calculated from, in addition, the flow of fresh air admitted. in the engine.

According to another aspect, there is provided a method of regulating an output parameter of an internal combustion engine, comprising a preparation of a setpoint of the output parameter of the engine, an estimation of the output parameter of the engine, and regulation of the output parameter of the engine on the basis of a difference between said setpoint and said estimate of the output parameter of the engine.

Advantageously, during the regulation step, a command is produced for an actuator controlling the output parameter of the motor, and in addition an actuator control setpoint is produced and a control difference is calculated between said setpoint of command and said processed command, intended for said actuator.

• la figure 1 illustre un mode de réalisation d'un système d'estimation d'au moins un paramètre de sortie d'un moteur à combustion interne ;
• la figure 2 illustre un mode de réalisation d'un dispositif de régulation d'un paramètre de sortie d'un moteur à combustion interne ; et
• la figure 3 illustre un autre mode de réalisation d'un dispositif de régulation d'un paramètre de sortie d'un moteur à combustion interne.

Other objects, characteristics and advantages of the invention will become apparent on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

• the figure 1 illustrates an embodiment of a system for estimating at least one output parameter of an internal combustion engine;
• the figure 2 illustrates an embodiment of a device for regulating an output parameter of an internal combustion engine; and
• the figure 3 illustrates another embodiment of a device for regulating an output parameter of an internal combustion engine.

On the figure 1 , there is schematically shown a system for estimating at least one output parameter of an internal combustion engine 1.

The characteristic output parameters of engine 1 can be chosen from among polluting emissions, combustion noise, fuel consumption, engine torque and generally all the parameters which represent a state emitted directly or indirectly by combustion. in engine 1.

It is possible, for example, to apply such an estimation system to estimate a rate of nitrogen oxides emitted during combustion in the engine 1.

The internal combustion engine 1 comprises a cylinder 2 in which a piston 3 moves via a connecting rod 4 connecting the piston 3 to a crankshaft 5 for driving the connecting rod 4. A combustion chamber 6 is delimited by said cylinder 2, said piston 3 and a cylinder head 7. The cylinder head 7 is provided with at least two valves 8 and 9 which make it possible to connect the combustion chamber 6 with respectively an intake manifold 10, for air possibly mixed with part of the exhaust gases, and an exhaust gas manifold 11. The engine 1 also comprises a fuel injector 12 arranged so as to inject fuel into the combustion chamber 6.

The estimation system comprises two measurement sensors 20, 21 as well as an electronic control unit 22 (ECU) which comprises a calculation means 23 and an estimation means 24. These means 23, 24 can be included in software form or in the form of logic circuits embedded in the ECU 22.

The sensor 21 makes it possible to measure the angle of the crankshaft θ at any time. The sensor 20 makes it possible to measure at any time the internal pressure P _cyl of the cylinder 2 which corresponds to the pressure inside the combustion chamber 6. These sensors 20 and 21 each emit a time measurement signal, transmitted respectively by connections 25 and 26, towards the calculation means 23.

In addition, the estimation system can comprise other means 27 to 29 for measuring engine state variables in order to specify the estimate of the output parameter of the engine PSe.

The estimation system can comprise, the measuring means 27 for measuring an amount of oxygen admitted into the engine 1, the measuring means 28 for measuring a flow of fuel admitted into the engine 1 and the measuring means 29 for measuring a flow of fresh air admitted into the engine 1. The means 27 for measuring the quantity of oxygen admitted into the engine 1 can be an oxygen sensor located in the intake manifold 10 or in the exhaust gas manifold 11. The measurement of the flow of fuel admitted into the engine 1 can be a fuel instruction sent to the injector 12. The means 29 for measuring the flow of fresh air admitted into the engine 2 can be an air flow meter located on the intake manifold 10, preferably upstream of the recovery of part of the exhaust gases. These measurement means 27 to 29 each emit a time measurement signal, transmitted respectively by connections 30 to 32, in the direction of the calculation means 23.

The calculation means 23 makes it possible to calculate a certain number of combustion parameters Xi from the input time signals θ , P _cyl . In addition, this calculation means 23 can also calculate said combustion parameters Xi from the additional time signals coming from the measuring means 27 to 29.

The combustion parameters Xi can be chosen from the start time of combustion, the duration of combustion, the maximum cylinder internal pressure, the angle of the crankshaft at which the pressure is maximum in the cylinder, the angle of the crankshaft for which a given fraction of the fuel has been burnt, the temperature of the exhaust gases, the pressure of the gases to the exhaust. Other parameters can be considered insofar as they are in direct or indirect relation with the combustion phase in the cylinder.

Preferably, the combustion parameters Xi are chosen as being only characteristic values of the internal pressure of the cylinder such as internal pressures of the cylinder characteristic of combustion P _cyl i, variations in internal pressure of the cylinder ∇P _cyl i and engine _{cycle time} t _cycle i.

The internal pressures of the cylinder characteristic of combustion P _cyl i can be, for example, the internal pressure of the maximum cylinder P _cyl max, the internal pressure of the cylinder at the instant of the start of combustion, the internal pressure of the cylinder for an angle of the crankshaft characteristic of combustion (that is to say an angle at which a given fraction of the fuel has been burned), the internal pressure of the cylinder when the angle of the crankshaft is equal to 80 ° after the top dead center of the piston.

It should be noted that the angles of the crankshaft characteristic of combustion are well known to those skilled in the art and are generally calculated as a function of the apparent release of energy in the cylinder.

The internal pressure variations of the cylinder ∇P _cyl i can be, for example, the maximum gradient of the internal pressure of the cylinder, the minimum gradient of the internal pressure of the cylinder (∇P _cyl ) _min , the maximum gradient of the internal pressure of the cylinder between the first controlled injection and the injection at the start of combustion.

avec ∇P_cyl représentant le gradient de la pression interne du cylindre et P_cyl représentant la pression interne du cylindre.The engine _{cycle times} t _cycle i can be, for example, the time elapsed between CA05 and CA50, or the time elapsed between CA05 and CA90, or the time elapsed between CA05 and the time when the maximum cylinder internal pressure is reached , or the time during which the internal pressure of the cylinder is greater than a threshold, or the time during which the internal pressure of the cylinder is equal to the maximum value of the ratio $\frac{P_{\mathit{cyl}}}{\nabla P_{\mathit{cyl}}}$

with ∇P _cyl representing the gradient of the internal pressure of the cylinder and P _cyl representing the internal pressure of the cylinder.

Note that the references CAx correspond to the angles of the crankshaft where x% of the fuel has been burnt.

The calculation means 23 is able to sample the measurements of the internal pressure of the cylinder P _cyl as a function of the measurements of the angle of the crankshaft θ . Preferably, the sampling interval of the internal pressure of the cylinder P _cyl is greater than or equal to 0.5 degrees of the angle of the crankshaft θ . Then, for each cycle of the combustion, the calculation means 23 saves in memory the sampled values of the internal pressure of the cylinder P _cyl .

From these sampled values, the calculation means 23 calculates the combustion parameters Xi, described above, and transmits them, via connections 40, to the estimation means 24.

This estimation means 24 makes it possible to estimate an output parameter PSe of the engine, for example a rate of nitrogen oxides NOx _e , from said calculated combustion parameters Xi. In addition, it sends the estimated result PSe through a connection 41.

Estimation means 24 can use several models to estimate the motor output parameter. Preferably, the models are capable of estimating the output parameter of the engine from a weighted sum of said combustion parameters Xi.

• N : nombre de paramètres de combustion Xi calculés par le moyen de calcul 23 ;
• α_i : constante de pondération qui varie selon le paramètre de combustion Xi ; et
• i : indexe d'identification du paramètre de combustion.

According to a first embodiment, which is not part of the invention, the estimation means 24 comprises a first model capable of calculating the output parameter PSe according to the following equation (1): $$\mathit{PSe}={\displaystyle \sum _{i=1}^{\mathrm{NOT}}{\mathrm{\alpha }}_i\cdot \mathit{Xi}}$$

• N: number of combustion parameters Xi calculated by the calculation means 23;
• α _i : weighting constant which varies according to the combustion parameter Xi; and
• i: identification index of the combustion parameter.

• exp : fonction mathématique exponentielle.

According to a second embodiment, which is not part of the invention, the estimation means 24 comprises a second model capable of calculating the output parameter PSe according to the following equation (2): $$\mathit{PSe}=\exp \left({\displaystyle \sum _{i=1}^{\mathrm{NOT}}{\alpha }_i\cdot \mathit{Xi}}\right)$$

• exp: exponential mathematical function.

• ω : vitesse angulaire du moteur 1 obtenue à partir des mesures de l'angle du vilebrequin θ.

The estimation means 24 according to the invention comprises a third model capable of calculating the output parameter PSe according to the following equation (3): $$\mathit{PSe}=\omega \cdot \exp \left({\displaystyle \sum _{i=1}^{\mathrm{NOT}}{\alpha }_i\cdot \mathit{Xi}}\right)$$

• ω: angular speed of engine 1 obtained from measurements of the angle of the crankshaft θ .

Moreover, this estimation means 24 uses models whose weighting constants α _i have been determined by prior tests.

On the figure 2 , there is schematically shown an embodiment of a device 50 for regulating an output parameter of an internal combustion engine 1. Reference has also been made to this figure 2 certain elements described in figure 1 .

The regulation device 50 comprises a means 51 for developing a setpoint for the output parameter of the motor Cons_PS, a regulation means 52 and an estimation module 53. These means 51, 52 and this module 53 can be included in software form. or in the form of logic circuits embedded in the ECU 22.

The estimation module 53 comprises the calculation means 23 and the estimation means 24 as described in section figure 1 , moreover, it estimates an output parameter PSe which it then transmits via the connection 41 to a calculation means 59 of the regulation means 52.

The calculation means 59 further receives, via a connection 54, the setpoint of the output parameter of the motor Cons_PS developed by the means 51. This calculation means 59 calculates a difference d between said setpoint Cons_PS and said estimate PSe of the output parameter of the engine and transmits this difference d via a connection 55 towards a correction means 56 of the regulation means 52.

The correction means 56 can be a corrector of the proportional integral type PI, or of the proportional integral derivative type PID, or any other type of corrector known to those skilled in the art. This correction means 56 develops a command Cmde from the difference d received, and transmits this command Cmde via a connection 57 to an actuator 58.

The actuator 58 makes it possible to control the real value of the output parameter of the motor which is to be regulated. This actuator 58 can be any means for modifying the values of the output parameters of the engine, such as for example a fuel injector, an air flap mounted on the intake manifold 10, a valve for recirculating part of the gases. exhaust.

This regulation device 50 makes it possible to regulate the output parameter of the engine via the actuator 58 as a function of a comparison between the setpoint Cons_PS and the estimate PSe of the output parameter of the engine.

On the figure 3 , there is schematically shown another embodiment of a device 50 for regulating an output parameter of an internal combustion engine 1. Reference has also been made to this figure 3 certain elements described in previous figures 1 and 2.

In this other embodiment, the regulation device 50 comprises a means 60 for generating a control setpoint Cons_Cmde and a second calculation means 61.

This second calculation means 61 receives, on the one hand the command Cmde produced by the regulation means 50 and which is transmitted by the connection 57, and on the other hand the command setpoint Cons_Cmde which is transmitted by a connection 62 from the means 60. The second calculation means 61 calculates a difference in command DiffCmde between the command Cmde and the setpoint of. command Cons_Cmde and transmits the result via a connection 63 towards the actuator 58.

For example, the output parameter of the engine can be the rate of nitrogen oxides to be regulated, the actuator 58 can be an air flap mounted on the intake manifold 10, Cons_Cmde and Cmde respectively represent a setpoint of air flow rate and a correction of this air flow rate, the regulating device 50 thus ensuring the reduction of dispersion of nitrogen oxides emitted by the engine.

It is thus possible to estimate a rate of nitrogen oxides in real time using a minimum of calculations and sensors.

Taking into account the measurement of the internal pressure of the cylinder allows a better estimation of the output parameters of the engine in comparison with the use of a mapping of the output parameter according to the engine speed and the fuel injected into the chamber combustion.

Closed-loop regulation makes it possible to reduce dispersion on the engines and to reduce the manufacturing costs of the engines, in particular by reducing the volume of the pollutant emission post-treatment systems.

Claims (12)

1. System for estimating at least one output parameter (PSe) of an internal combustion engine (1) comprising at least one cylinder (2), a moveable piston (3) driven via a crankshaft (5), means (20, 21) for measuring the temporal variations of the crankshaft angle and of the internal pressure of said cylinder, a computation means (23) for calculating, by using the measurements of the internal pressure of the cylinder as a function of the crankshaft angle (θ), a plurality of combustion parameters (Xi), comprising quantities from among internal pressures of the cylinder at characteristic moments of the combustion, internal pressure gradients of the cylinder and cycle times of the engine representing times elapsed between two predefined phases of the engine cycle, characterized in that the estimation system comprises an estimation means (24) configured to estimate at least the output parameter of the engine (PSe) as a product of an angular speed (ω) of the engine by an exponential function of a weighted sum of said combustion parameters (Xi) with weighting constants (αi), the angular speed (ω) being obtained from measurements of the crankshaft angle (θ), the weighting constants (αi) varying as a function of said combustion parameters (Xi).
2. System according to Claim 1, comprising a means (27) for measuring a quantity of oxygen admitted into the engine and in which the computation means (23) is also configured to calculate combustion parameters (Xi) used in the weighted sum from the quantity of oxygen admitted into the engine.
3. System according to either one of Claims 1 and 2, comprising a means (28) for measuring a fuel flow rate admitted into the engine and in which the computation means (23) is also configured to calculate combustion parameters (Xi) used in the weighted sum from the fuel flow rate admitted into the engine.
4. System according to any one of Claims 1 to 3, comprising a means (29) for measuring a fresh air flow rate admitted into the engine and in which the computation means (23) is also configured to calculate combustion parameters (Xi) used in the weighted sum from the fresh air flow rate admitted into the engine.
5. Device for regulating an output parameter of an internal combustion engine (1), comprising a means (51) for generating an engine output parameter setpoint (Con_PS), an actuator (58) capable of controlling the engine output parameter, an estimation system (53) according to one of Claims 1 to 4 for estimating the engine output parameter (PSe), the regulation device being able to generate a command (Cmde) for said actuator (58) from a difference (d) between said setpoint (Cons_PS) and said estimation of the engine output parameter (PSe) in order to regulate the engine output parameter.
6. Device according to Claim 5, comprising a means (60) for generating a command setpoint (Cons_Cmde) of said actuator (58) and a means (61) for calculating a command difference (DiffCmde), between said command setpoint (Cons_Cmde) and said generated command (Cmde), intended for said actuator (58).
7. Method for estimating at least one output parameter (PSe) emitted by an internal combustion engine (1) comprising at least one cylinder (2), a moveable piston (3) driven via a crankshaft (5), comprising a step of measuring temporal variations of the crankshaft angle and of the internal pressure of the cylinder, a step of calculation, by using the measurements of the internal pressure of the cylinder as a function of the crankshaft angle (θ), of a plurality of combustion parameters (Xi), comprising quantities from among internal pressures of the cylinder at characteristic moments of the combustion, internal pressure gradients of the cylinder and cycle times of the engine representing times elapsed between two predefined phases of the engine cycle, the method being characterized by comprising a step of estimation of the engine output parameter (PSe) as a product of an angular speed of the engine by an exponential function of a weighted sum of said combustion parameters (Xi) with weighting constants (αi), the angular speed (ω) being obtained from measurements of the crankshaft angle (θ), the weighting constants (αi) varying as a function of said combustion parameters (Xi).
8. Method according to Claim 7, comprising a step of measurement of a quantity of oxygen admitted into the engine, and, in the calculation step, combustion parameters (Xi) used in the weighted sum are also calculated from the quantity of oxygen admitted into the engine.
9. Method according to either one of Claims 7 and 8, comprising a step of measurement of a fuel flow rate admitted into the engine, and, in the calculation step, combustion parameters (Xi) used in the weighted sum are also calculated from the fuel flow rate admitted into the engine.
10. Method according to any one of Claims 7 to 9, comprising a step of measurement of a fresh air flow rate admitted into the engine, and, in the calculation step, combustion parameters (Xi) used in the weighted sum are also calculated from the fresh air flow rate admitted into the engine.
11. Method for regulating an output parameter of an internal combustion engine (1), comprising a generation of an engine output parameter setpoint (Cons_PS), an estimation according to one of Claims 7 to 10 of the engine output parameter (PSe), and a regulation of the engine output parameter from a difference (d) between said setpoint (Cons_PS) and said estimation of the engine output parameter (PSe).
12. Method according to Claim 11, wherein, in the regulation step, a command (Cmde) is generated for an actuator (58) controlling the engine output parameter, and which comprises a generation of a command setpoint (Cons_Cmde) of the actuator (58) and a calculation of a command difference (DiffCmde), between said command setpoint (Cons_Cmde) and said generated command (Cmde), intended for said actuator (58).

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