WO2011131884A1

WO2011131884A1 - Method for controlling an egr valve that is resistant to dispersion

Info

Publication number: WO2011131884A1
Application number: PCT/FR2011/050718
Authority: WO
Inventors: Mohammed Jerouane
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2010-04-23
Filing date: 2011-03-31
Publication date: 2011-10-27
Also published as: FR2959276A1; FR2959276B1

Abstract

The invention relates to a method for controlling an electric motor (14) driving a rotating stopper (13) of an exhaust-gas recycling valve (10) of an internal combustion engine, which includes the steps of: determining the angular position Θ of the stopper (13); generating an angular position setting 9c of the stopper (13) according to the activation of an accelerator control of the internal combustion engine; generating a supply setting for the electric motor on the basis of a reference control intensity Iref determined by: Formula (I) where Ks is a constant strictly higher than 0, J is the rotational inertia of the mobile elements of the valve, Km is the torque of the electric motor, and Kr is a value modelling operating dispersions of the valve.

Description

METHOD FOR CONTROLLING AN EGR VALVE, ROBUST AGAINST

Dispersions

The present invention claims the priority of the French application 1053143 filed April 23, 2010 whose content (text, drawings and claims) is here incorporated by reference.

The invention relates to the admission of air into an internal combustion engine, and in particular the intake air distribution devices introducing fresh air and air from the exhaust system. in the combustion chamber of the engine.

The recycling of the exhaust gas reduces the level of nitrogen oxides emitted in the exhaust gas. Exhaust gas recirculation involves introducing fresh air and exhaust into the combustion chamber of the engine. For diesel engines, it is common to see recycling rates of the order of 50%, which means that half of the gases drawn by a cylinder of an internal combustion engine are recirculated exhaust gas. Increasingly stringent emission standards for pollutants have led to the generalization of EGR exhaust gas recirculation systems for diesel engines. However, the use of EGR for spark ignition engines is also growing.

The recycling of exhaust gas is controlled via a valve. The valve allows to take a variable amount of exhaust gas to mix with fresh air to be introduced into the combustion chamber. The valve regulates the exhaust gas recirculation flow to the engine inlet at each combustion cycle.

This recycling requires to slave the flow of exhaust gas reinjected, and thus the position of the shutter of the EGR valve to a set value that varies over time. The setpoint is supplied by the engine control unit to control an electric motor operating the shutter.

[0006] It is technically difficult to position the shutter precisely in a precise manner over the entire operating range. required. The pressure differences between upstream and downstream of the EGR valve have a strong influence on the accuracy of the servo. In addition, the valves generally include return springs bringing the shutter to a position of equilibrium intermediate between the opening and the total closure. The action of these springs disrupts the dynamic operation of the valve. In addition, the operation of the shutter is strongly non-linear.

Servo imperfections generally have the following consequences: an increase in the shutter response time inducing a degradation of the performance of the engine, or the generation of large oscillations of the shutter inducing its inefficiency. These consequences generally result in an increase in fuel consumption and the production of nitrogen oxides.

A number of solutions proposed so far synthesize the control law of the shutter via a feedback corrector called "PID" (for Proportional, Integral, Derived). The method of synthesis consists mainly in determining the error between the measured position of the shutter and the set position (proportional action), in calculating the speed of change of the error (derivative action) and the time integral of the error (integral action) and to develop a position control signal sum of these three actions.

Such solutions are not very robust vis-à-vis the external disturbances encountered or variations in the characteristics of the components. Such solutions also require long and difficult calibration methods to be developed.

Document FR2881536 describes a servo-control process having increased robustness, that is to say a lower sensitivity to external disturbances. This document proposes to perform a prepositioning of the EGR valve in open loop, as a function of a set point value, a pressure variation between the upstream and downstream and properties of the return spring.

[001 1] This solution also has drawbacks. This solution requires a number of sensors that increase the cost of the valve EGR. In addition, the positioning of the shutter is not very robust in the face of errors on the parameters taken into account, in particular the variation of pressure or the properties of the return spring. Furthermore, the control law proposed by this solution is only valid for the regulation around a single equilibrium position. To ensure satisfactory regulation over the entire range of the shutter, this solution assumes the use of a large number of separate control laws for the different positions of the shutter. Indeed, each control law is linear and is only fair on a small part of the race of the shutter whose behavior is non-linear. This solution is therefore difficult to develop because of the number of operating points to be tested and because of the number of permutations to be performed in real time between the different control laws.

The invention aims to solve one or more of these disadvantages. The invention thus relates to a method of controlling an electric motor for driving a rotary shutter of an exhaust gas recycling valve of an internal combustion engine, comprising the steps of:

- determine the angular position Θ of the shutter;

generating an angular position reference 9c of the shutter as a function of the actuation of an accelerator control of the internal combustion engine;

generating an electric motor supply instruction based on a reference control intensity Iref determined by:

With Ks a constant strictly greater than 0, J the rotational inertia of the movable elements of the valve, Km the torque of the electric motor, and Kr a value modeling the operating dispersions of the valve. According to a variant, a return spring which remembers the shutter towards a rest position closing the flow of recycled exhaust gas in the absence of excitation of the electric motor.

According to another variant, said supply setpoint is calculated by transforming said reference control intensity into a pulse width modulation signal applied to a control input of the electric motor.

According to another variant, the transformation comprises a clipping of the reference control intensity.

According to yet another variant, the transformation comprises the multiplication of the clipped signal by the engine torque Km.

According to a variant, Ks is a gain value for adjusting the operation of the valve.

[0019] The invention also relates to an internal combustion engine, comprising:

an exhaust gas recirculation circuit comprising a controlled valve for regulating the flow of recycled exhaust gas therethrough, the valve comprising a shutter element rotatably mounted in an exhaust passage and comprising an engine electric driving the shutter element;

a control module of the electric motor adapted to:

- Obtain an angular position value Θ of the shutter;

J * (Dua) UKr

With Ks a constant strictly greater than 0, J the rotational inertia of the movable elements of the valve, Km the torque of the electric motor, and Kr a value modeling the operating dispersions of the valve.

According to a variant, the engine comprises a return spring reminding the shutter to a position of interruption of the flow of exhaust gas through the valve.

According to another variant, the control module generates a power supply command of the electric motor by transforming said reference control intensity into a pulse width modulation signal, and the control module applies the modulation signal. pulse width on a control input of the electric motor.

Other features and advantages of the invention will become apparent from the description which is given below, by way of indication and in no way limiting, with reference to the accompanying drawings, in which:

• Figure 1 illustrates the principle of determination of the set position of the EGR valve depending on the support on an accelerator pedal;

FIG. 2 is a schematic representation of an EGR valve;

FIG. 3 represents a processing diagram generating a motor intensity reference of the EGR valve;

FIG. 4 is a diagram illustrating the intensity conversion for controlling the motor of the EGR valve in pulse width modulation or pulse width modulation.

[0024] Figure 1 illustrates the principle of determining a set position of an EGR valve. The user applies an acceleration command, for example via a pedal. This control is measured as a depression level of an accelerator pedal identified by a value Ac and translates a torque demand to the internal combustion engine. A first engine control map 21 converts this value into a fuel flow setpoint. inject Qinj for a given engine speed Nmot. A second map 22 converts this setpoint value into an intake air flow setpoint Qac.

Figure 2 schematically illustrates an EGR valve 10. In known manner, the EGR valve comprises a valve body 1 1 defining a fluid passage. A sealing member 13 is disposed in this fluid passage for regulating the flow rate of the recycled exhaust gas. The closure member 13 is pivotally mounted about an axis 15 in the fluid passage. The angular position of this shutter element in the passage makes it possible to close or open the passage, partially or completely. The shutter member may be a valve having a head cooperating with a seat in the fluid passage and attached to a drive shaft. In the example of FIG. 2, the drive shaft 12 of an electric motor 14 drives the shutter element 13 in rotation about the axis 15.

The electric motor 14 and its shaft 12 thus constitute means for positioning the shutter element 13. The electric motor 14 is powered by a signal of variable intensity in time, delivered by a servo system . The servo system is for example integrated in an engine control computer. The servo system comprises an angular position sensor 16 detecting the angular position of the shaft 12 and generating a corresponding signal sur on its output 18.

Reminder springs (not shown) urge the closure member to a rest position. The return torque exerted by the spring is opposite to the torque exerted by the electric motor during operation. The rest position of the return element corresponds to a total closure of the fluid passage therewith. Thus, in case of malfunction of the EGR valve, the exhaust gas recirculation will stop.

The electrical and mechanical behavior of the valve 10 can generally be modeled by means of the following equations

U = R * I + L * - {1)

dt

J * (ë) = K _m * I - K _r {2) Equation 1 corresponds to an electrical modeling of the electric motor 14 of the valve. Equation 2 corresponds to a mechanical modeling of the shutter element of the valve.

U corresponds to the voltage at the terminals of the electric motor, R corresponds to its electrical resistance, I corresponds to the intensity therethrough and L corresponds to its inductance.

J corresponds to the overall rotational inertia of the valve, Θ corresponds to the angular position of the motor shaft (measured by the sensor 16, or determined numerically by a computer), Km corresponds to the engine torque, and Kr corresponds to the resistive torque (including in particular the viscous torque, the spring return torque, the pair of abutments, etc.) and also represents a set of dispersions on the system formed by the valve (friction, noise, estimation of model error ...).

We define beforehand the following values: er = e- 0c

^• _ ά - θο)

e ^{r ~} _dt

Corresponding respectively to the tracking error and the time derivative of the tracking error, 9c corresponding to the desired angular position of the drive shaft.

We consider a dynamic error variable S defined by the following relation:

·· ·

S = er + Ks * er

With Ks a constant strictly greater than 0, corresponding to a calibrated gain value. This gain value is calibrated to adjust the control applied to the motor 14. If the dynamic variable S is 0 or tends to zero, then the tracking error er tends to 0, which is the goal for the regulation of the angular position of the drive shaft.

Calculations make it possible to determine the minimum intensity Iref to be applied to the electric motor to cancel the dynamic variable S. The intensity Iref is expressed as follows:

The regulation of the valve being carried out with a feedback, it is possible to replace this intensity value in equation (2), to arrive at the relation:

·· ·

er = - Ks * er

This relation is solved with a continuation value of the form er = E _n * e -Ks * t

E0 being a constant and t the time.

The tracking error converges to 0 in time. Moreover, this convergence is obtained independently of the parameter Kr of resistant torque. Thus, the control with the determined intensity Iref is robust with respect to this parameter Kr. The parameter Kr can be determined by tests on the valve 10.

In addition, such a control can be generated with a reduced number of sensors, increasing the reliability and lowering the cost of the exhaust gas recirculation loop. Moreover, such a control can be used for the entire race of the closing element, without requiring the use of a multiplicity of models. In addition, such a command may be implemented with relatively short calibration methods and easy to develop via a single parameter Ks.

FIG. 3 is a diagram illustrating the parameters and the operations implemented for the calculation of the control intensity Iref of the motor 14.

The module 31 calculates the difference between Θ and 9c. The module 32 calculates the time derivative of the output signal of the module 31. The module 33 multiplies the output signal of the module 32 not a factor (-Ks). The module 38 calculates the second time derivative of 9c. The module 34 adds the output signals of the modules 33 and 38. The module 35 multiplies the output signal of the module 34 by the factor J. The module 36 adds the output signal of the module 35 to the value Kr. The module 37 multiplies the output signal of the module 36 by a factor (1 / Km) to generate the intensity control signal Iref.

FIG. 4 is a diagram illustrating the transformation of the intensity control Iref into a pulse width modulation control, to apply a cyclic voltage ratio between the power supply terminals of the motor 14, and thus dispose of a simplified order adapted to the CMM HW.

The module 41 achieves a saturation of the calculated Iref value. The module 42 multiplies the output signal of the module 41 by the factor Km to convert the intensity into voltage, the module 43 multiplies the output of the module 42 by a value UBat corresponding to a battery voltage (for example 12V corresponding to a voltage connected to the on-board network), the module 44 multiplies the output of the module 43 by a gradation value (for example 1/100) of the control signal, to generate the control signal Upwm.

Claims

1. A method of controlling an electric motor (14) for driving a rotary shutter (13) of an exhaust gas recirculation valve (10) of an internal combustion engine, comprising the steps of:

-determine the angular position Θ of the shutter (13);

generating a setpoint of angular position 9c of the shutter (13) as a function of the actuation of an accelerator control of the internal combustion engine;

generating a power supply instruction of the electric motor based on a reference control intensity Iref determined by:

Control method according to claim 1, wherein a return spring recalls the shutter (13) to a rest position closing the flow of recycled exhaust gas in the absence of excitation of the electric motor (14).

A control method according to claim 1 or 2, wherein said power setpoint is calculated by transforming said reference control intensity into a pulse width modulated signal (Upwm) applied to a control input of the electric motor ( 14).

A control method according to claim 3, wherein the transform comprises a clipping of the reference control intensity.

A control method according to claim 4, wherein the transformation comprises multiplying the clipped signal by the engine torque Km.

A control method as claimed in any one of the preceding claims, wherein Ks is a gain value for adjusting the operation of the valve (10).

7. Internal combustion engine, characterized in that it comprises:

an exhaust gas recirculation circuit comprising a controlled valve for regulating the flow of recycled exhaust gas therethrough, the valve (10) comprising a shutter element (13) rotatably mounted in a gas passage; exhaust system comprising an electric motor driving the shutter member;

a control module (17) for the electric motor adapted to:

obtaining an angular position value Θ from the shutter (13);

generating a power supply command of the electric motor (14) based on a reference control intensity Iref determined by:

An internal combustion engine as claimed in claim 7 including a return spring biasing the shutter member (13) to a position to interrupt the flow of exhaust gas through the valve.

Internal combustion engine according to claim 7 or 8, wherein the control module (17) generates a power supply command of the electric motor (14) by converting said reference control intensity into a pulse width modulated signal. (Upwm), and wherein the control module (17) applies the pulse width modulated signal to a control input of the electric motor.