FR2944317A3 - GAS INTAKE AND EXHAUST SYSTEM OF AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE - Google Patents

Abstract

The system has a high pressure recirculation loop (30) of exhaust gas comprising a branch (32) between an outlet of an exhaust manifold (16) and an inlet of an intake manifold (14). A flow sensor (58) measures entering of the air flow. A temperature sensor (54) measures temperature of gases in the intake manifold. A pressure sensor (56) measures pressure of the gases in the intake manifold. A valve (72) is arranged in the outlet of an exhaust (44) of a motor vehicle. A control unit (74) controls the valve relative to the sensors measurements.

Description

GAS INTAKE AND EXHAUST SYSTEM OF AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE FIELD OF THE INVENTION

The present invention relates to low and high pressure loop exhaust recirculation systems in a motor vehicle internal combustion engine, and more particularly to the management of the impact of such recirculation on the operation of devices. of exhaust gas pollution whose operation is impacted by that of the recirculation of the exhaust gas.

STATE OF THE ART In FIG. 1, an internal combustion engine vehicle engine of the state of the art is illustrated under the general reference 10.

The engine 10 comprises a cylinder block 12, supplied with fresh gas by an intake manifold 14 and whose exhaust gas is collected at an exhaust manifold 16.

The air is admitted into the engine 10 via an air inlet 18 and, after passing through an air filter 20, is directed at the inlet of the compressor part 22 of a variable geometry turbocharger 24 to be compressed. The outlet of the compressor part 22 is also connected to the intake manifold 14 through a heat exchanger 26 cooling the compressed gases.

A high pressure exhaust gas recirculation loop 30 is further provided and includes a bypass 32 connecting the outlet 34 of the exhaust manifold 16 to the inlet manifold inlet 36 and a valve controllable valve 38 regulating the flow of exhaust gases recirculated by this high pressure loop 30.

The turbine portion 40 of the variable geometry turbocharger 24 is in turn mounted downstream of the high pressure bypass 30 and supplies the energy to the compressor 22 by the expansion of the exhaust gas. As is known in itself, the turbine portion 40 comprises orientable vanes for modifying the flow rate and the pressure of the gases towards the turbine itself, in particular to increase the reactivity of the compressor 22 at low speeds.

An exhaust gas treatment device 42, such as an oxidation catalyst or a nitrogen oxide trap (or NOx), is further provided downstream of the turbine portion 40. The output of the device 42 is connected to the exhaust outlet 44 of the vehicle and to a low pressure recirculation loop 46 of the exhaust gas.

This low pressure recirculation loop 46 comprises a bypass 48, connecting the output of the device 42 to the inlet of the compressor part 22, an exchanger 50 for cooling the gases flowing in the bypass 48, and a controllable valve 52 regulating the flow gases in the bypass 48.

As is known per se, the recirculation of the exhaust gas has the effect of reducing the generation of pollutants, including NOx, while the turbocharging produced by the turbocharger increases the power of the engine.

In a manner known per se, the control of the valves 38 and 52 of the low and high pressure loops and the turbine portion 40 is carried out as a function of the measurement of the temperature T ~ 1 mes and Pool me gas pressure in the collector intake 14, respectively delivered by a temperature sensor 54 and a pressure sensor 56 arranged in the manifold 14, and the measurement of the incoming airflow Qair mes, delivered by a flowmeter 58 mounted at the outlet of the air filter 20 .

This control of the valves 38 and 52 and the turbine part 40, implemented by an information processing unit 60 connected thereto and to the sensors 54, 56, 58, essentially aims at controlling the air masses and burnt gases entering the cylinders as well as the temperature and pressure of these gases. Usually setpoints for the pressure and temperature of the gases in the manifold and a setpoint for the incoming air flow are determined a priori and stored in maps according to engine speed and torque values. The control of the valves 38, 52 and the turbine part 40 then aims to obtain said instructions. For example, reference may be made to document US 2007/0079614 for such control of the state of the art.

However, an exhaust gas treatment device, such as an oxidation catalyst or a NOx trap, needs to be primed for operation with a minimum of efficiency. This means in particular that the temperature and the volume flow rate of the gases at the inlet thereof have minimum values. The effectiveness of an oxidation catalyst, for example in terms of treated unburned hydrocarbon levels (in particular HC and CO), is represented in FIG. 2. As can be seen in this figure, the efficiency of the Oxidation catalyst depends both on the temperature and the flow rate of the gases entering it. In particular, the effectiveness of the catalyst increases as the temperature increases and when the flow rate decreases. It is thus necessary to respect ranges of temperatures and flow rates for minimum catalyst operation, a similar remark can be made for a NOx trap.

However, there are often situations of defusing the treatment device, and more particularly in transient situations. Indeed, since the evolution of the temperature of the gases in the intake manifold is slow compared to the evolution of the pressure of these and the flow of air entering, the follow-up of the transient instructions can lead to bad input conditions of the treatment device and even a defusing of the latter. For example, following the driver pressing the accelerator pedal, monitoring the temperature setpoint may cause the high-pressure loop valve to close too much, which increases the exhaust gas flow rate. at the input of the treatment device and thus decreases its effectiveness.

Usually, the manufacturers make a compromise between a satisfactory follow-up of the instructions and a satisfactory operation of the processing device. The arbitration between these conflicting constraints generally depends on the regulatory constraints in force.

On this point, one can for example refer to WO 2007/085944 which describes the influence of the high pressure loop on the performance of an oxidation catalyst. This document notably discloses a control of the valves 38 and 52 during a release of foot to ensure that the temperature of the oxidation catalyst remains in a satisfactory range, while releasing the constraints on the follow-up of the instructions.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a turbocharged system with high and low pressure loops for recirculating the exhaust gases of an internal combustion engine which reduces the antagonism between the setpoint tracking and the efficiency of the aftertreatment device. thus allowing both engine over-fueling and more efficient gas handling.

For this purpose, the subject of the invention is an intake and exhaust gas system of an internal combustion engine of a motor vehicle, comprising: an air inlet; a variable geometry turbocharger, the turbine portion of which is arranged at the outlet of the exhaust manifold of the engine and the compressor portion of which is arranged between the air intake and the inlet of the engine intake manifold; an exhaust treatment device arranged between the turbine portion of the turbocharger and the vehicle exhaust outlet and requiring predetermined temperature and / or gas flow conditions for satisfactory operation; a high pressure exhaust gas recirculation loop, having a bypass between the exhaust manifold outlet and the intake manifold inlet, and a controllable valve arranged in said manifold; a low-pressure exhaust gas recirculation loop, having a bypass between the output of the treatment device and the air inlet, and a controllable valve arranged in said bypass; and a flow sensor for measuring the flow of incoming air; a temperature sensor for measuring the temperature of the gases in the intake manifold; a pressure sensor for measuring the gas pressure in the intake manifold; and a control unit for the valves of the high pressure and low pressure loops and turbocharger turbine part as a function of the measurements of the flow rate, temperature and pressure sensors.

According to the invention, this system further comprises a controllable valve arranged in the exhaust outlet of the vehicle, said control unit being able to control said valve according to the measurements of said sensors.

In other words, a valve is added at the exhaust outlet. Two actuators are thus present in the system to distribute the flow rates between the exhaust and the low pressure recirculation loop of the exhaust gases. When these two actuators are not in abutment, it is thus obtained an additional degree of freedom because the system is then characterized by three instructions to follow, that is to say the inflow of air, temperature and pressure. gases in the intake manifold, and four actuators, that is to say the valves of the high and low pressure loops, the turbine part and the valve at the exhaust outlet.

According to embodiments of the invention, the system comprises one or more of the following features. The control unit is able to implement a quadratic linear control law for controlling the valves and the turbine part as a function of the temperature, pressure and flow rate measurements. The control unit comprises:

first means for calculating a control signal of the valve of the high pressure mouth, a control signal of the turbine part and a signal of

valve control of the low pressure loop according to the measurements of

temperature, pressure and flow; and

second means for calculating a control signal of the outlet valve

based on the control signal of the valve of the low pressure mouth so as to close the valve at the exhaust outlet as the

Low pressure loop valve opens. Especially :

the first calculation means comprise:

a first block for calculating the control signal of the valve of the high-pressure mouth, the control signal of the turbine part, and a flow setpoint for the low-pressure loop as a function of the temperature, pressure and flow rate measurements; ;

o a second block of calculation of an unsaturated control signal for the valve

the low pressure loop as a function of the flow setpoint and a measurement or estimation of the flow rate in the low pressure loop by implementing a servo-control of said setpoint on said measurement or flow rate estimation;

o a saturation block of the unsaturated control signal to form the control signal of the valve of the low-pressure loop, and

the second calculation means are able to calculate the control signal of the valve at the exhaust outlet as a decreasing function of the difference between the control signal of the valve of the low pressure loop and the control signal saturated with it.

The second calculation means are capable of calculating the control signal of the valve at the exhaust outlet according to the relationship: ## EQU1 ## where Ueeh is the control signal of the valve at the exhaust outlet, Uegrtbp is the unsaturated control signal of the low-pressure loop valve, Uegr bp is the control signal of the low-pressure loop valve, and a is a predetermined positive-speed setting parameter. closing the valve at the exhaust outlet.

The enslavement of the flow instruction is of the PID type.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended drawings, in which like references designate identical or similar elements, and in which: FIG. 1 is a diagrammatic view of an intake and exhaust system of an exhaust gas recirculation double circulation internal combustion engine of the state of the art already discussed above; Fig. 2 is a graph of curves illustrating the relationship between the efficiency of an oxidation catalyst and the temperature and volume flow rate of the inlet exhaust gas thereof, already discussed above; FIG. 3 is a schematic view of an intake and exhaust system of an internal combustion engine with a double exhaust gas recirculation loop according to the invention; FIG. 4 is a schematic view of a first embodiment according to the invention of a control unit for the valves and the turbine part of the system of FIG. 3; and FIG. 5 is a schematic view of a second embodiment according to the invention of a control unit for the valves and the turbine part of the system 30 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 schematically illustrates a system 70 for admitting and exhausting a turbocharged internal combustion engine with a double exhaust gas recirculation loop according to the invention.

The system 70 differs essentially from that of the state of the art described in connection with FIG. 1 in that a controllable valve 72 is arranged at the exhaust outlet, that is to say downstream of the low loop. recirculation pressure 46, and by the information processing unit 74 which controls the valves 38, 52 and 72 as well as the turbine portion 40 as a function of the temperature and pressure measurements of the sensors 54, 56 and the flow rate. sensor air 58.

FIG. 4 is a schematic view of a first embodiment of the information processing unit 74, the blocks represented in FIG. 4 represent, for example, the software functions implemented by this unit.

According to this first embodiment, the unit 74 implements a quadratic linear control, or LQ command. It comprises a block 80 forming a map receiving as input the values of the speed N and the engine torque C and evaluating, according to these, a predetermined map for determining the setpoints of the incoming air flow Qair cons, pressure in the collector intake 14 Pool cons, and temperature in intake manifold Taoi cons.

A subtracter 82, connected to the mapping block 80, forms the difference between the setpoint vector (Qair cons, Pool cons, Pool eons) T and the vector (Qair mes, Pool mes, Teem mes) T corresponding flow measurements. air, pressure and temperature in the intake manifold 14, the symbol T here representing the transposed.

The difference between these vectors is then integrated by an integrator 84, then multiplied by a matrix gain 86 of predetermined value L1 of dimension 3 * 3. A subtracter 88 also receives a vector L2X and subtracts it from the output of the gain 86 to form the vector (Uegr hp, Uegr bp, Ueeh, Ugt) T of the control signal Uegr hp of the valve 38 of the high loop. pressure 30, the control signal Uegr bp of the valve 52 of the low-pressure loop 46, the control signal Uech of the valve 75 at the exhaust outlet and the control signal Ugt of the turbine portion 40 of the turbocharger with geometry variable 24.

A state estimator 90 also receives the vector (Uegr hp, Uegr bp, Ueeh, Ugt) T of the control signals and the vector (Qah mes, Pool mes, Teoi mes) T of the measurements and estimates the vector of state x of a predetermined linear model of the intake and exhaust system having for input the commands (Uegr hp, Uegr bp, Ueeh, Ugt) T and output measures (Qah mes, Pool mes, Tcoi mes) T according to the relationships: x = Ax + Bu y = Cx where u is the vector of the control signals, y is the vector of measurements, A is a predetermined square matrix of dimension n * n, B is a predetermined matrix of dimension 4 * n and C is a predetermined matrix of dimension n * 3.

A matrix gain 92 of predetermined value L2 of dimension n * 3 is further connected to the estimator 90 and multiplies the estimate of the state vector by the gain L2 to form the vector L2X at the input of the subtractor 88. The information processing unit 74 thus calculates a vector (Uegr hp, Uegr bp, Uech, Ut) T of control signals according to the relationship: The estimator 90 uses, for example, Kalman filtering to estimate the vector. state x, and the matrix gains L1 and L2 are obtained during the synthesis of the LQ control law and allow in particular to adjust the relative importance of the actuators 20 of the system, as is known per se of the state of the technique.

Fig. 5 is a schematic view of a second embodiment of the information processing unit 74.

The unit 74 comprises, as for the first embodiment described above, a block 80 forming a map determining according to the values of the speed and the engine torque the vector of the instructions (QPT air cons, col cons, col cons) T.

The unit 74 also comprises a control block 100 receiving the vector of the setpoints (Qair cons, Pcoi cons, Tcoi cons) T as well as the vector of the measurements (Qair mes, Peoi mes, Tcoi mes) T and determining according to these a first vector of three control signals, namely the control signals Uegr hp and the valve 30 of the high-pressure loop 30 and the turbine part 40, as well as an intermediate control signal Qegr_bp_cons of the volume flow rate of the low-pressure loop 46. (U \ egr hp (/ Q \ (air cons VA _ `C my Uegrbp L1 f Pcol cons Pcol mes ù L2x Uech \ \ Tcolcons / \ TU columns / 35 The command block 100 sets implementing a square control with three setpoints and three control signals, such as a control of the status return observer type for example, so as to satisfy the conventional constraints of the engine gas supply The flow instruction Qegr_bp_cons of the low-pressure loop 46 is satisfied by the controlling the valves 58 of the low pressure loop 46 and the valve 72 at the exhaust outlet.

More particularly, the unit 74 further comprises a subtracter 102 receiving the flow instruction Qegr_bp_cons as well as an estimate Qegr_bp_est of the volume flow in the low pressure loop 46 and forming the difference Qegr_bp_cons - Qegr bp is between these, as well as a derivative integral proportional corrector (PID) 104 receiving said difference. The output of the PID thus forms a raw control signal Uegrtbp of the valve 58, that is to say without taking into account its operating range. The estimate Qegr_bp_est of the volume flow of the low pressure loop is obtained in a manner known per se, for example using a Kalman estimator or a state observer based on a linear model of the system. having for input the vector (Ueg hp, Qegr bp, U, gt) T, the exhaust valve 72 being considered completely open, and for output the vectors of the measurements (Qair mes, Peoi mes, Teol mes) T. Alternatively, a flowmeter is arranged in the branch 48 of the low pressure loop 46 upstream of the exchanger 50. The PID is connected to a saturation block 106 which saturates the raw control signal Uegrtbp to values corresponding to the minimum openings. and maximum of the valve 58 to form the control signal Uegr bp delivered to the valve 58. The control signal Uech of the valve 72 at the exhaust outlet is formed with the aid of two subtractors 108, 110 , a unit gain 112 and a gain 114 in the ratio: = 77 raw Uech ù 1 ù a (Uegr bp ù Uegr bp) where a is a predetermined positive parameter setting the closing speed of the valve 72 output exhaust. As can thus be noted, as long as the valve 58 of the low pressure loop is not in high saturation, that is to say completely open, the valve 72 at the exhaust outlet remains completely open as well. Once the valve 58 is saturated, any additional flow request can not be satisfied, Uegr bp remaining constant and equal to the high saturation value. On the other hand, this additional request for bit rate results in a signal Uegrtbp increasing beyond the high saturation value. The signal Uech then decreases, that is to say that the valve 72 at the exhaust outlet 5 closes. The flow of gas, which was initially discharged outside the vehicle by the exhaust outlet, is thus diverted to the low pressure loop, which is equivalent to changing the pressure drop of the exhaust to find the freedom of control on the low pressure branch.

Although a PID corrector has been described, any other type of zero static error corrector would be suitable.

Claims (6)

REVENDICATIONS1. An intake and exhaust gas system of an internal combustion engine of a motor vehicle, comprising: an air inlet (18); a variable geometry turbocharger (24), the turbine portion (40) of which is arranged at the outlet of the exhaust manifold (16) of the engine and the compressor portion (22) of which is arranged between the air intake (18) and the inlet of the intake manifold (14) of the engine; an exhaust treatment device (42) arranged between the turbine part (40) of the turbocharger (24) and the exhaust outlet (44) of the vehicle and requiring predetermined temperature and / or flow rate conditions; gas for satisfactory operation; an exhaust gas recirculation loop (30) having a bypass (32) between the exhaust manifold outlet (16) and the intake manifold inlet (14), and a controllable valve (38) arranged in said lead (32); a low pressure recirculation loop (46) of the exhaust gas, having a bypass (48) between the outlet of the treatment device (42) and the air inlet (18), and a controllable valve (52) arranged in said lead (46); and a flow sensor (58) for measuring the flow of incoming air; a temperature sensor (54) for measuring the temperature of the gases in the intake manifold (14); a pressure sensor (56) for measuring the pressure of the gases in the intake manifold (14); and a control unit (74) of the valves (38, 52) of the high pressure and low pressure loops (30, 46) and turbine part (40) of the turbocharger (24) depending on the measurements of the flow sensors ( 58), temperature (54) and pressure (56), characterized in that it further comprises a controllable valve (72) arranged in the exhaust outlet (44) of the vehicle, said control unit (74) being able to drive said valve (72) according to the measurements of said sensors (54, 56, 58). 2. System according to claim 1, characterized in that the control unit (74) is adapted to implement a quadratic linear control law for controlling the valves (38, 52, 72) and the turbine part (40). depending on temperature, pressure and flow measurements. 3. System according to claim 2, characterized in that the control unit (74) comprises: first means (100, 102, 104, 106) for calculating a control signal of the valve (38) of the loop high pressure (30), a control signal of the turbine part (40) and a control signal of the valve (38) of the low pressure loop (46) according to the temperature, pressure and flow rate measurements ; and second means (108, 110, 112) for calculating a control signal of the valve (72) at the exhaust outlet (44) as a function of the control signal of the valve (52) of the low loop. pressure (46) to close the valve (72) at the exhaust outlet (44) as the valve (52) of the low pressure loop (46) opens. 4. System according to claim 3, characterized in that: the first calculation means (100, 102, 104, 106) comprise: a first calculation block (100) of the control signal of the valve (38) of the loop; high pressure (30), the control signal of the turbine portion (40), and a flow rate setpoint for the low pressure loop (46) as a function of temperature, pressure and flow rate measurements; a second calculation block (102, 104) of an unsaturated control signal for the valve (52) of the low-pressure loop (46) as a function of the flow setpoint and a flow measurement or estimate in the low pressure loop (30) by implementing a servo (102, 104) of said setpoint on said measurement or flow rate estimate; a saturation block (106) of the unsaturated control signal for forming the control signal of the valve of the low pressure loop, and the second calculation means (108, 110, 112) are able to calculate the signal of controlling the valve (72) at the exhaust outlet (44) as a decreasing function of the difference between the control signal of the valve (52) of the low pressure loop (46) and the control signal saturated with that -this. 5. System according to the relation 4, characterized in that the second means (108, 110, 112) of calculation are able to calculate the control signal of the valve (72) at the exhaust outlet according to the relationship: gross Uech = 1a (uegr bp ù Uegr bp) where Uech is the control signal of the valve at the exhaust outlet, Ugrtbt, is the unsaturated control signal of the valve of the low-pressure loop, Uegr hp is the control signal of the valve of the low pressure loop, and a is a predetermined positive parameter regulating the closing speed of the valve at the exhaust outlet. 6. System according to claim 4 or 5, characterized in that the servocontrol of the flow instruction is of the PID type.