FR3026138A1 - DEVICE AND METHOD FOR MONITORING THE OPERATING STATE OF A VARIABLE GEOMETRY AIR INTAKE SYSTEM - Google Patents

Abstract

This device for controlling the operating state of a variable geometry air intake system in the cylinders (2) of an internal combustion engine (1) comprises means (20) of comparison for comparing the value of a signal representative of the richness of the air-fuel mixture admitted into the engine cylinders and at least a threshold value of detection of a malfunction of the air intake system.

Description

The invention relates, in general, to the regulation of the richness of the air-fuel mixture injected into the cylinders of an air intake system. internal combustion engine, in particular of a motor vehicle. More particularly, the invention relates to controlling the operating state of a variable geometry air intake system. As is known, an internal combustion engine operates with a mixture of air and fuel, the proportions of which are defined by an engine management calculator for each operating point of the engine. For a quantity of fresh air admitted into the engine intake manifold, the computer defines a quantity of fuel injected, for a given operating point of the engine. The amount of fuel to be injected into the engine is defined by the richness, which is the ratio between the amount of air admitted and the amount of fuel injected into each cylinder. Some engines are equipped with a variable geometry air intake system, which has variable length ducts. In this respect reference may be made to US Pat. No. 7,270,103 which describes a variable intake system in which the length of the fresh air intake ducts is modified according to the operating conditions of the engine, in particular its load and its speed. The diameter of the duct is also changed when the length varies. It is also possible to refer to the document EP 0 747 584. The variable admission systems are generally equipped with an actuator which makes it possible to shorten the length of the pipes at high speed of the engine and to lengthen them at low speeds, to optimize the filling. engine cylinders in air.

The shortening of the length of the air intake ducts, at high speed, makes it possible to increase the richness and the power of the engine. However, it is necessary to avoid, and therefore to diagnose, any failure of the air intake system in order to finely control the differences in the exhaust richness and thus limit polluting emissions in the environment. In the state of the art, the control of the operating state of the variable admission systems is based on the use of sensors allowing each moment to know the exact length of the intake ducts. As soon as a difference is found between a setpoint and the measured position, the intake system is considered to be faulty. As we conceive, this solution requires the provision of a specific sensor. The object of the invention is therefore to overcome this disadvantage and to diagnose the operating state of a variable air intake system for the injection of fresh air into the cylinders of an engine with increased accuracy.

The object of the invention is therefore, according to a first aspect, a device for controlling the operating state of a system with variable geometry for the admission of air into the cylinders of an internal combustion engine comprising means for comparison for comparing the value of a signal representative of the richness of an air-fuel mixture admitted into the engine cylinders and at least a threshold value of detection of a malfunction of the air intake system. In one embodiment, the comparison means are constituted by means for comparing a signal for measuring the oxygen concentration of the engine exhaust gases with at least one malfunction detection threshold value. The device according to the invention may also comprise closed-loop control means for the richness of the air-fuel mixture.

In this case, the comparison means may comprise means for comparing a signal produced by the control loop with at least one malfunction detection threshold value. According to yet another characteristic of the device according to the invention, the signal produced by the regulation loop is the average value of a correction term of the fuel injection time in the cylinders. The subject of the invention is also, according to a second aspect, a method of controlling the operating state of a system with variable geometry of air intake in the cylinders of an internal combustion engine, in which one compares the value of a signal representative of the richness of the air-fuel mixture admitted into the engine cylinders with at least a threshold value of detection of a malfunction of the air intake system.

Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example, and with reference to the appended drawings, in which: FIG. 1 is a block diagram illustrating the general architecture of an internal combustion engine equipped with a control device according to the invention; FIGS. 2a and 2b illustrate the principle of regulating the richness of the mixture admitted into the engine cylinders; FIGS. 3a and 3b illustrate the principle of controlling the operating state of the system with variable geometry of air intake; and FIG. 4 is a flowchart illustrating the main phases of a control method according to the invention. Referring firstly to Figure 1 which schematically illustrates the general structure of an internal combustion engine of a motor vehicle, designated by the general numerical reference 1. In the embodiment shown, the motor 1 is provided with four cylinders 2 arranged in lines.

The cylinders 2 are supplied with air via an intake distributor 3, itself fed by an intake pipe 4 provided with an air filter 6 and a turbocharger 7 of the engine supercharger. air.

The inlet distributor is here a variable geometry distributor and comprises ducts whose length can be modified by an actuator, for example an electric motor, not shown. An exhaust manifold 8 recovers the exhaust gases from the combustion and discharges the latter outwards, through a turbine 9 of the turbocharger 7, for example a turbine with fixed geometry, associated with a bypass circuit 10 equipped with a control valve 11, and by a system 12 for treating gaseous effluents, for example a catalyst, a particulate filter, or any other suitable treatment device to ensure a clean-up of the exhaust gas. As can be seen, the intake pipe 4 is equipped, upstream of the distributor 3, with an air cooler 13 and a throttle valve, that is to say a valve 14 for controlling the flow rate gases admitted to the engine. The assembly is completed by sensors for measuring engine operating parameters, such as sensors 15 and 16 for measuring the Tsural supercharging temperature and the Psural supercharging pressure.

Sensors 17 furthermore make it possible to measure the pressure Pcoll and the temperature Tcoll of the gases in the inlet distributor. The set of sensors as well as the various controllable elements of the engine are connected to a central control unit 20. With regard to the regulation of the richness, the central control unit 20 calculates, for each operating point of the engine, a richness reference value from signals for measuring the oxygen concentration present in the flue gases delivered by a lambda probe 21 mounted upstream of the flue gas treatment system 12. For this purpose, the computer 20 is programmed so as to implement a regulation of the richness of the mixture.

In order to improve the accuracy of the regulation, a second optional lambda probe 22 is placed downstream of the treatment system 12. For each operating point of the engine, that is to say for each torque regime / charging, and knowing the position of the various actuators of the fresh air supply chain, and in particular the throttle valve 14, the valve 11 and the length of the variable length ducts 18 of the distributor 3, the central unit control 20 determines the air filling of the engine and deduces the air mass enclosed in each cylinder.

It may for example be to extract the air mass enclosed in the cylinders from a map stored in memory. From the air mass enclosed in the cylinders, and from a richness reference, for example equal to 1 in the case of a spark ignition engine (gasoline engine), the central unit 20 determines the amount of fuel to be injected. It may also be, for example, to extract these data from a map. The lambda probe 21 makes it possible, from the measurement of the quantity of oxygen present in the flue gases, to control that the setpoint of richness is reached.

This control can be carried out by implementing regulation either in open loop or in closed loop. In the case where the central unit 20 implements an open-loop control, the signal for measuring the amount of oxygen present in the flue gases makes it possible to control that the setpoint of richness is reached. In the case where the central unit 20 implements an open loop regulation, the signal for measuring the amount of oxygen present in the flue gases, representative of the richness of the air-fuel mixture admitted into the engine cylinders, is compared to a wealth setpoint. The difference between the measured richness and the richness setpoint is then compared to a malfunction detection threshold value of the variable geometry air intake system. For example, if the central unit 20 imposes on the air intake system an intake duct length equal to Li and the system fails and is locked to a length L2, while the length Li is the position of the variable admission system for which the filling efficiency is optimal for the operating point in question, the blocking of the system at the L2 position leads to a degradation of the filling efficiency. For example, if the length L2 is less than the length Li, the quantity of air enclosed in the cylinder is smaller than the expected quantity and the richness, measured at the level of the exhaust line, is increased to the extent that the injection setpoint remains unchanged with respect to the nominal operation imposed by the computer 20. The signal delivered by the lambda probe 21 is used to calculate the difference between the expected wealth value and the measured wealth value. Beyond a certain threshold of difference in wealth, it is considered that the variable admission system is faulty, insofar as diagnoses are also implemented to confirm that the operation of the fuel injection system corresponds to the nominal state imposed by the computer.

The richness error measured as a function of the filling error of the cylinders is given by the following relationships: M ess M ess Wealth error = measured Ri - Ri set point = K x K x M air_realized air set either Wealth error = K xM ess X air achieved setpoint with: K = Stoichiometric ratio Mess = Mass of fuel Mair = Mass of fresh air admitted R measured = Measured richness Ri setpoint = Setpoint of richness Mair performed = Mass of fresh air measured Mair setpoint = Set point of fresh air mass. Reference will now be made to FIGS. 2a, 2b, 3a and 3b to explain the detection of a malfunction of the air intake system in the case of closed-loop richness control.

In FIG. 2a, the signal S corresponds to the wealth measurement signal delivered by the lambda probe 21. In the example considered, the output voltage of the probe 21 changes as a function of time between phases such that I corresponding to a rich mixture and II corresponding to a lean mixture. With reference to FIG. 2b, the regulation loop implemented by the central unit 20 produces a signal S 'for correcting the fuel injection time in the cylinders. The output signal of the lambda probe 21, which is a voltage representative of the richness of the mixture, is subtracted from a target voltage representative of the richness setpoint, for example equal to 1 for a stoichiometric air-fuel mixture. In FIG. 2a, the setpoint voltage is here equal to 450 millivolts. If the voltage is below the set point, the gases are considered as poor, which requires enriching the mixture. In the context of a closed-loop control, this enrichment is achieved by a regulator, for example of the proportional-integral type PI which receives as input an error value corresponding to the difference between the actual output voltage of the probe lambda and a setpoint voltage and applies the entire proportional term of the regulator to the error, then the integral term. It deduces therein the correction signal S 'to be added to the predetermined basic injection time during the development of the engine.

If the voltage is higher than the set point, the gases are considered rich, which, on the contrary, requires depleting the mixture. In this case, the depletion is achieved by decreasing, in the same way, the amount of gasoline injected.

Referring to FIGS. 3a and 3b, which respectively illustrate the evolution of the output voltage S of the lambda probe 21 and the signal S 'of correction of the fuel injection duration managed by the computer 20, it can be seen that during phases 1 and 2, which respectively correspond to a rich mixture and to a lean mixture, the signal for correcting the fuel injection time in the cylinders is used to cancel the wealth drift at the exhaust. The average value of this correction term is normally equal to 0. The CPU 20 calculates the average value of this correction term and compares it with a malfunction detection threshold value. Thus, if during phase III, the signal S 'exceeds the threshold value of the detection of malfunction, the air intake system 18 is considered to be defective. It will be noted that the procedure just described applies equally to a variable or continuously discontinuous air intake system, that is to say able to take a limited number of predetermined positions. The method just described also applies to a different application of the variable air intake system. For example, for a spark ignition engine, the variable air intake system can be used to penalize engine air filling. This will further open the throttle valve 14 to maintain the same performance, which reduces the losses by pumping and thus optimize the overall efficiency of the engine. In this case, in both open loop and closed loop, the fault detection thresholds are duplicated. This will use relatively high and low thresholds of malfunction detection.

Finally, reference will be made to FIG. 4 to describe the main phases of a method of controlling the operating state of the air intake system 18 according to the invention. In this figure, step 23 corresponds to the start of the engine. Step 24 corresponds to the operating phase of the engine during which the integrity of the fuel injection system is checked. In the next step 25, the value of the output voltage of the lambda probe 21, which corresponds to the richness of the exhaust, is acquired. In the case where the central unit 20 implements an open-loop control, in the next step 26, the computer 20 measures the richness of the exhaust via the amplitude of the acquired signal. It then compares the measured wealth with the expected wealth to obtain a gap measure value (step 27). On the other hand, in the case of a closed-loop control, after the acquisition step 25, the computer 20 provides a closed loop control of the injection time (step 26a) and calculates the average value of the corrective term of the time. injection (step 27a).

In the following step 28, the computer 20 compares the difference retained at the end of step 27, where the average value of the corrective term obtained at the end of step 27a at the detection threshold values of malfunction. If the threshold values are exceeded, it is considered that the variable admission system has failed (step 29). If this is not the case, it is considered that the operation of the intake system is correct (step 30) before terminating the diagnosis of the admission system (step 31).

Claims (6)

REVENDICATIONS1. Device for controlling the operating state of an air intake system with variable geometry in the cylinders (2) of an internal combustion engine (1), characterized in that it comprises comparison means (20) for comparing the value of a signal (S ') representative of the richness of the air-fuel mixture admitted into the engine cylinders and at least a threshold value of detection of a malfunction of the intake system of air. 2. Device according to claim 1, wherein the comparison means are constituted by means for comparing a signal for measuring the oxygen concentration of the engine exhaust gas with at least one malfunction detection threshold value. 3. Device according to claim 1, comprising means (20) for closed-loop control of the richness of the air / fuel mixture. 4. Device according to claim 3, wherein comparison means comprise means for comparing a signal produced by the control loop with at least one malfunction detection threshold value. 5. Device according to claim 4, wherein said signal produced by the control loop is the average value of a correction term of the fuel injection time in the cylinders. 6. A method of controlling the operating state of a variable geometry air intake system in the cylinders (2) of an internal combustion engine (1), in which the value of a signal (S ') representative of the richness of the air-fuel mixture admitted into the engine cylinders with at least one threshold value of detection of a malfunction of the air intake system.