FR2888884A1 - METHOD AND SYSTEM FOR MONITORING THE AIR SUPPLY OF AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE - Google Patents

Abstract

The invention relates to a method for controlling the supercharging of a motor vehicle internal combustion engine equipped with a turbocharger (14) supercharged driven by the engine exhaust gas. The boost pressure is regulated around a set value developed from state variables including the air pressure (Pave) upstream of the turbocharger (14). In addition, the boost pressure is regulated from a measurement (Ncomp) of the rotational speed of the turbocharger.

Description

METHOD AND SYSTEM FOR CONTROLLING THE AIR SUPPLY OF A MOTOR

  INTERNAL COMBUSTION OF MOTOR VEHICLE

  The invention relates to the air supply of internal combustion engines and, in particular, the control of the air supercharging of an internal combustion engine equipped with a turbocharger.

  More particularly, the invention relates to controlling the turbocharger to achieve a boost pressure setpoint while eliminating any risk of deterioration of the turbocharger.

  Known in the state of the art, various techniques for controlling the operation of a turbocharger supercharging to effectively regulate the air pressure admitted into the intake manifold of the engine while avoiding any deterioration of the turbocharger.

  In this respect, reference may be made to French patent application No. 2,829,530.

  According to the pressure regulation technique described in this document, the pressure in the intake manifold is regulated around a first pressure reference value and the pressure prevailing upstream of the turbine of the turbocharger is regulated around a second pressure setpoint value corresponding to a maximum authorized pressure value upstream of the turbine of the turbocharger. The control of the turbocharger is thus effected by means of two regulators receiving, one, a boost pressure measurement or a measurement of the pressure prevailing in the intake manifold and, the other, a measurement of pressure prevailing in upstream of the turbocharger turbine.

  The disadvantage of this technique is that the measured values as well as the setpoints consist only of thermodynamic values which do not directly translate the operating conditions of the turbocharger. In other words, a turbocharger failure detected from pressure measurements will only be identified late.

  The object of the invention is therefore to overcome this disadvantage and to allow control of the air supercharging of an internal combustion engine to effectively regulate the pressure of the air admitted into the intake manifold of the engine while improving the detection of malfunctions of the turbocharger.

  The subject of the invention is therefore a method for controlling the air supercharging of an internal combustion engine of a motor vehicle equipped with a supercharging turbocharger driven by the exhaust gases of the engine, comprising the regulation of the pressure of supercharging around a setpoint developed from state variables including the air pressure upstream of the turbocharger.

  According to this method, the boost pressure is further regulated from a measurement of the rotational speed of the turbocharger.

  The rotational speed of the turbocharger is directly related to the conditions of malfunction or malfunction of the turbocharger. This is an operating parameter of a constituent element of the turbocharger, namely the turbine. Thus, any malfunction of the turbocharger can be immediately detected.

  In one embodiment, the rotational speed measurement of the turbocharger is used to develop a maximum pressure value downstream of the turbocharger.

  According to this embodiment, the maximum pressure value downstream of the turbocharger can be extracted from a map in which is stored the evolution of the pressure ratio of the turbocharger as a function of the air flow through the compressor, for different Turbocharger speed values, from the air pressure upstream of the turbocharger and the speed of rotation of the turbocharger.

  A boost pressure setpoint is then developed from state variables representative of the operation of the engine, the minimum value between the boost pressure setpoint and the maximum pressure value extracted from the mapping is calculated and regulated. the boost pressure using the calculated minimum value.

  According to another implementation of the method according to the invention, a boost pressure setpoint and a turbocharger rotation speed setpoint are developed and the boost pressure is regulated by means of a first supercharging pressure regulator. and a second turbocharger speed controller arranged in cascade.

  For example, the boost pressure setpoint is developed from variables characteristic of the operating state of the engine such as the engine torque or engine speed.

  The speed reference can also be developed from variables characteristic of the operating state of the engine, such as the engine torque or speed.

  Advantageously, the control method further comprises a step of controlling the rotational speed of the turbocharger by comparing the speed with at least one threshold value for detecting a malfunction.

  For example, to do this, under transient conditions, the deceleration of the turbocharger is compared with a first threshold value and the rotational speed with a second threshold value.

  For example, the or each threshold value is developed from a map, as a function of the ratio of turbocharger pressures and air flow.

  According to another aspect, the subject of the invention is also a system for controlling the supercharging of an internal combustion engine of a motor vehicle equipped with a turbocharger, comprising means for measuring state variables comprising the air pressure upstream of the turbocharger and regulating means for regulating the charge air pressure around a set value developed from the state variables.

  According to a general characteristic of this control system, it further comprises means for measuring the rotational speed of the turbocharger, the control means being further adapted to regulate the boost pressure from the measured speed.

  In one embodiment, this control system comprises, stored in memory, a map in which is stored the evolution of the pressure ratio of the turbocharger as a function of the air flow through the compressor, for different values of rotation speed of the turbocharger, the regulation means comprising calculation means for calculating a minimum value between the boost pressure setpoint value and a maximum pressure value extracted from the map, the boost pressure being regulated using the calculated minimum value.

  In another embodiment, the system comprises a first regulator for regulating the supercharging pressure from a boost pressure setpoint and a second regulator for regulating the turbocharger rotation speed from a pressure regulator. rotational speed setpoint, said boost pressure and rotation speed setpoint values being developed from variables characteristic of the operating state of the engine, the first and second regulators being arranged in cascade.

  Other objects, features and advantages of the invention will appear on reading the following description, given solely by way of nonlimiting example, and with reference to the appended drawings in which: FIG. 1 schematically illustrates the general structure of an internal combustion engine of a motor vehicle provided with a control system according to the invention; FIG. 2 illustrates a first supercharging pressure regulation mode according to the invention; FIG. 3 is an example of implementation of a regulator according to this first regulation mode; FIG. 4 illustrates another mode of boost pressure regulation according to the invention; FIG. 5 illustrates an exemplary implementation of a regulator according to this second embodiment; Figure 6 shows a curve explaining the step of controlling the rotational speed of the turbocharger for the detection of a sub-speed of the turbocharger; - Figure 7 shows a curve explaining the step of controlling the rotational speed of the turbocharger for the detection of an overspeed; and FIG. 8 is a flowchart showing the main phases of the turbocharger rotation speed control step.

  In Figure 1, there is shown schematically the general structure of an internal combustion engine 10 of a motor vehicle and its fresh air intake and exhaust manifolds.

  As seen in this figure, the fresh air intake circuit in the engine 10 essentially comprises an air filter 12 supplying, via a turbocharger 14 and appropriate ducts 16, the intake manifold. 18 of the motor 10 (arrows F).

  With regard to the exhaust manifold 20, the latter collects the exhaust gases resulting from the combustion and discharges these outwards, via the turbocharger 14 and a particulate filter 22 arranged on the exhaust line 24 of the engine to reduce the amount of particles, including soot, released into the environment (Arrows F ').

  A heat exchanger 26 equipping the feed line 16 intake manifold 18 fresh air allows cooling of the charge air.

  Furthermore, the engine 10 is associated with an exhaust gas recirculation circuit 28 for injecting a part of these gases into the intake manifold 18 so as, in particular, to limit the quantity of oxide of produced while avoiding the formation of smoke in the exhaust.

  This circuit 28 essentially comprises a recirculation valve EGR disposed between the turbocharger 14 and the collector 18, on the pipe 16 and communicating with the exhaust manifold 20 via a pipe 32.

  The turbocharger 14 essentially comprises a turbine 34 driven by the exhaust gas and a compressor 36 mounted on the same axis as the turbine and providing a compression of the air distributed by the air filter 12, in order to increase the amount of air admitted into the engine cylinders.

  Finally, it can be seen in FIG. 1 that the recirculation circuit 30 and the turbocharger 14 are controlled by a central unit comprising a first regulation stage 38 for regulating the quantity of recirculated exhaust gas by acting on the valve 30 and on a admission flap 31 arranged upstream of the EGR valve to control the flow of fresh air and a second control stage 40 for regulating the boost pressure acting on a solenoid valve 42 driving a pneumatic actuator 44 acting on the turbocharger 14. Although these stages are shown separately in Figure 1, it is conceivable that they can be arranged in the form of two stages or software modules incorporated in the same calculation means.

  The first stage 38 comprises a module 38-a for calculating a fresh air setpoint and a regulation module 38-b producing control signals for the EGR valve 30 and the admission flap 31.

  As will be described in detail below, the second regulation stage includes a 40-a module for generating a boost pressure setpoint and a 40-b pressure regulation module delivering control signals to a solenoid valve. 42.

  Finally, the system described in FIG. 1 is completed by a set of measurement sensors delivering regulation signals to regulation stages 38 and 40 for the implementation of the regulations.

  Thus, the boost pressure control stage 40 receives, in particular, the following signals: a signal Q for measuring the air flow through the turbocharger 40; a signal Tavc for measuring the temperature upstream of the compressor; a signal Pavc for measuring the pressure prevailing upstream of the compressor; a Psuralim signal for measuring the boost pressure, which also corresponds to the pressure prevailing in the manifold and, at the load drop near generated by the cooler 26, to the pressure downstream of the turbocharger; a signal Nmot for measuring the speed of rotation of the motor; the motor torque Cmot; an Ncomp signal for measuring the rotational speed of the turbocharger.

  The first regulation stage 38 receives, meanwhile, a signal Q 'for measuring the flow of fresh air at the inlet of the turbocharger 14 delivered by a flowmeter 46 and a signal P for measuring the position of the EGR valve 30.

  Referring to FIG. 2, a first embodiment of the regulation of the supercharging pressure implemented by the supercharging pressure regulation stage 40 will now be described.

  As seen in this FIG. 2, in this embodiment, the regulation is essentially based on the use of a map C stored in memory in the central unit giving the evolution of the pressure ratio itc, constituted by the ratio between the pressure downstream of the compressor and the pressure upstream of the compressor, as a function of the air flow Q passing through the compressor, for different values Ncomp turbocharger rotation speed.

  The stored data constitute a compression field and are specific to each turbocharger fitted to the vehicle.

  From this compression field, the central unit extracts a curve C linking the pressure ratio itc as a function of the speed Ncomp of rotation of the turbo, from a measurement Q of the air flow in the compressor (Phase I).

  By using the pressure measurement Pavc upstream of the compressor, the central unit deduces a maximum pressure value Pape downstream of the compressor not to exceed to avoid damage to the turbocharger (Phase II).

  In the following phase III, the central unit translates the maximum pressure value extracted from the map into a maximum pressure value Pcolmax for the collector, based on the pressure drop generated by the charge air cooler 26.

  In the following phase IV, the central unit makes a comparison between the maximum setpoint Pcolmax developed from the map and a setpoint value Pcol developed from state variables representative of the operation of the engine, such as the torque of the engine. engine or its operating speed, the air temperature, .... The minimum value between these setpoints Pcolmax and Pcol is calculated to develop the setpoint Cons used to regulate the boost pressure.

  It should be noted that it is also possible, as a variant, to convert the maximum manifold pressure into a maximum value of the boost pressure setpoint, by using the level of pressure drop generated by the cooler 26 and to compare this pressure level. maximum boost with a boost pressure setpoint developed from state variables representative of the operation of the engine and thus develop the setpoint Cons.

  Referring now to FIG. 3, in one embodiment of the pressure regulating stage 40 corresponding to the first embodiment, the first module 40-a uses the pressure ratio nc, the flow rate Q in the compressor, the pressure prevailing upstream of the compressor, the speed of the engine, the temperature upstream of the compressor and the speed of rotation of the compressor to extract a curve C of the compression field a maximum pressure value Papc downstream of the corresponding compressor at a limit value of the speed of rotation of the compressor to avoid any risk of alteration of the compressor. This maximum pressure value Papc is converted by means of a conversion module 48 into a corresponding value of maximum pressure in the collector Pcolmax. A calculation module 50 calculates the minimum value between the pressure setpoint Pcol produced from the variables representing the operating state of the engine and the maximum pressure value in the collector Pcolmax to develop the setpoint value Cons. A comparator 52 then makes a comparison between this setpoint value Cons and the measured value of the pressure in the collector Pcolmes. The regulation error E is then presented at the input of the regulation module 40-b to develop the command signal Comm for the turbine 34 of the turbocharger 14.

  A second embodiment of the control method according to the invention will now be described with reference to FIG. In these figures, the arrows F and F 'respectively represent the supply of the collector 18 in fresh air and the recovery of the exhaust gases and their evacuation to the outside.

  As indicated above, according to this embodiment, the regulation consists of using two regulators 54 and 56 arranged in cascade.

  In FIG. 4, in which elements identical to those of FIG. 1 are designated by the same reference numerals, the motor M, its air supply means and its exhaust gas exhaust means are recognized. In this figure, only the portion of the CPU UCE for regulating the turbocharger 14 has been resumed. It incorporates the first and second regulation modules 54 and 56 arranged in cascade.

  The first control module 54 is associated with a module 58 for calculating a boost pressure setpoint and a second module 60 for calculating a turbocharger speed setpoint. These setpoint values are calculated, in a manner known per se, from variables representative of the operating state of the engine, such as the engine torque (Cmot), the operating speed, the air temperature, etc. . The first control module 54 retrieves a Psuralim measurement value from the boost pressure or the pressure in the manifold and delivers a regulation signal S to the second stage 56. The latter generates, at the output, a control signal Comm at from a Ncomp measurement of rotational speed of the turbocharger.

  In Figure 5, there is shown an embodiment of such a control system.

  This system comprises the two regulators 54 and 56.

  As regards the first regulator 54, a comparator 62 makes a comparison between a measured value of the Psuralim supercharging pressure and the set value Psuralim_cons coming from the calculation module 58. The regulation error E is presented at the input of the first regulator 54.

  The output of this regulator delivers a setpoint value Ncomp_cons for the speed of the turbocharger which is compared by means of a comparator 64 with a corresponding measured value Ncomp.

  The resulting regulation error s is presented at the input of the second regulator 56 for the development of the COMM command.

  To do this, an RCO control signal is delivered to the solenoid valve 42 (FIG. 1) which controls the pneumatic actuator 44 acting on the turbocharger 14.

  Furthermore, according to the invention, a phase of control of the rotation speed of the turbocharger is also implemented in order to detect the occurrence of malfunction defects. In particular, this procedure, implemented by means of hardware and software of the central unit duly programmed, makes it possible to detect a malfunction either from a drop in speed (FIG. 6) of the turbocharger or from a overspeed (Figure 7).

  Referring first to Figure 6, the detection of a low speed corresponding to the beginning of weakness of the turbocharger can be used to diagnose, for example, the coking of the oil, lubrication defects, fouling of the crankcase. compressor, to detect an oil pollution, or even a rupture of the rotating assembly. But this under-speed can also detect a malfunction of the exhaust gas recirculation (EGR) circuit.

  This detection consists in verifying that the turbocharger speed Ncomp remains within a predetermined operating zone Z bounded by upper and lower limits Bsup and Binf.

  In steady state of operation, at two points of the engine load regime, an average speed is set for the turbocharger with a predetermined dispersion, for example more than at least 5,000 rpm. For example, a point is set at 90 km / h and the other at 130 km / h.

  Over a time window, a maximum difference between the measured speed and the target speed is analyzed. In the case where the difference thus obtained is greater than a first threshold value, a decrease in the performance of the turbocharger is detected, but without any critical effect. It is then possible to implement procedures to compensate for the detected problem, for example by acting on the vanes of the turbine or by limiting the fuel flow injected.

  On the contrary, if the measured difference exceeds a second threshold value greater than the first threshold value, a degraded operating mode is implemented.

  In transient mode, it monitors the evolution of the acceleration or deceleration of the turbocharger and its speed.

  The acceleration of the turbocharger is thus calculated and compared with a first threshold value. Likewise, the speed of the turbocharger is compared with a second threshold value. The occurrence of a malfunction is considered if the deceleration of the turbocharger is greater than the first threshold value and if its speed is lower than the second threshold value.

  Referring to Figure 7, it is also implemented an overspeed detection for the turbocharger. Such overspeed may be due to a number of malfunctions, such as clogging of the air filter, blockage in the open position of the EGR valve, breakage of a turbocharger fin, malfunction of the pressure sensor in the collector, .... As before, a distinction is made according to the operating conditions.

  In steady state, the procedure is identical to the sub-speed detection procedure. In fact, on two points of regime in load of the engine, one fixes an average objective of speed of the turbocharger, for example a point with 90 km / h and with 130 km / h, with a predetermined dispersion, for example of more or less 5,000 rpm. Over a time window, a maximum difference between the measured speed and the target speed is analyzed. If this difference exceeds a first threshold value, a decrease in turbocharger performance is detected. Measures to restore the speed are then taken, for example by lowering the boost pressure setpoint. On the contrary, if this difference exceeds a second threshold value greater than the first threshold value, a degraded operating mode is implemented.

  Under transient conditions, a speed threshold is developed based on the compression ratio and the air flow in the turbocharger. Similarly, the acceleration of the turbocharger is determined. The malfunction is then detected if the acceleration is greater than a first threshold value and the rotational speed is greater than the threshold value developed from the compression ratio and the air flow rate.

  Referring to Figure 8, we will now describe the main phases of the procedure for controlling the rotational speed of the turbocharger.

  During a first phase 70, a check is made of activation conditions of the speed control procedure. This check is carried out, for example, on the state of the pressure sensor in the manifold, on the state of the solenoid valve 42, and on the rolling conditions.

  The speed of the turbocharger is checked on the one hand when the pressure sensor in the manifold and the solenoid valve is operating correctly and when the recirculation of the exhaust gas is inactive or, on the other hand, when the exhaust gas recirculation is active and the system is operating in steady state or low dynamic range.

  The speed control procedure is then implemented (step 72) according to the procedure described above with reference to FIGS. 6 and 7, from the engine speed and load (Nmot), the speed of rotation of the compressor (Ncomp). ), compressor inlet air temperature (Tavc), turbocharger airflow (Q), compressor upstream pressure, boost pressure or manifold pressure (Pavc, Psuralim, Pcol). Degraded operating modes, alert messages, are then developed (step 74) according to the result of the speed control procedure.

Claims (13)

  1. A method for controlling the air supercharging of a motor vehicle internal combustion engine equipped with a turbocharger (14) supercharged driven by the engine exhaust gas, including the regulation of the supercharging pressure around the engine. a set value developed from state variables comprising the air pressure (Pave) upstream of the turbocharger (14), characterized in that the boost pressure is further regulated from a measurement (Ncomp) the rotational speed of the turbocharger.   2. Method according to claim 1, characterized in that the speed measurement (Ncomp) of rotation of the turbocharger is used to develop a maximum pressure value (Pape) downstream of the turbocharger.   3. Method according to claim 2, characterized in that the maximum pressure value downstream of the turbocharger is extracted from a map in which is stored the change in the pressure ratio (1tc) of the turbocharger (14) as a function of the flow rate. of air passing through the compressor, for different turbocharger speed values, from the air pressure (Pave) of the turbocharger and the rotational speed of the turbocharger.   4. Method according to claim 3, characterized in that a boost pressure setpoint is developed from state variables representative of the operation of the engine, the minimum value is calculated between the supercharging pressure setpoint (Pcol). and the pressure value (Pcolmax) extracted from the map and the boost pressure is adjusted using the calculated minimum value.   5. Method according to claim 1, characterized in that one develops a boost pressure setpoint (Psuralim_cons) and a set speed of rotation of the turbocharger (Ncomp_Cons) and regulates the boost pressure by means of a first boost pressure regulator (54) and a second turbocharger speed controller (56) arranged in cascade.   6. Method according to claim 5, characterized in that the boost pressure setpoint is developed from variables characteristic of the operating state of the engine, such as the engine torque or speed.   7. Method according to one of claims 6 and 5, characterized in that the speed reference is developed from variables characteristic of the operating state of the engine, such as the engine torque or operating speed.   8. Method according to any one of claims 1 to 7, characterized in that it further comprises steps of controlling the rotational speed of the turbocharger (14) by comparing the speed with at least a threshold value of detecting a malfunction.   9. The method of claim 8, characterized in that in transient regime, the deceleration of the turbocharger is compared with a first threshold value and the rotational speed with a second threshold value.   10. Method according to one of claims 8 and 9, characterized in that the or each threshold value is developed from a map, according to the ratio of turbocharger pressures and air flow.   11. A system for controlling the supercharging of an internal combustion engine of a motor vehicle equipped with a turbocharger, comprising means for measuring state variables comprising the air pressure (Pavc) upstream of the engine. turbocharger and regulating means for regulating the supercharging air pressure around a set value developed from the state variables, characterized in that it further comprises means for measuring the speed of rotation of the turbocharger, the regulating means being further adapted to regulate the supercharging pressure from the measured speed.   12. System according to claim 11, characterized in that it comprises, stored in memory, a map in which is stored the evolution of the pressure ratio (7tc) of the turbocharger as a function of the air flow through the compressor, for different speed values, the regulation means comprising calculation means for calculating a minimum value between the boost pressure setpoint value and a maximum pressure value extracted from the map, the boost pressure being regulated using the minimum value calculated.   13. System according to claim 11, characterized in that it comprises a first regulator for regulating the supercharging pressure from a boost pressure setpoint and a second regulator ensuring the regulation of the rotational speed of the turbocharger. from a rotation speed setpoint, said boost pressure and rotation speed setpoint values being developed from variables that are characteristic of the operating state of the engine, the first and second regulators being arranged in cascade.