FR2845732A1 - Control system for recirculation of i.c. engine exhaust gases comprises central computer calculating recorded gas recirculation value as function of engine operating point and control part for exhaust gas recirculation valve displacement - Google Patents

Abstract

The system for controlling the quantity of re-circulated exhaust gas comprises a central computer (28) for calculating a recorded value of the re-circulated exhaust gas as a function of the operating point of the engine. There is a control part for the displacement of an exhaust gas recirculation valve (26) which is displaced as a function of the recorded value in order to position the valve. The movement of the valve displacement control part comprises a first movement part for the control of the valve displacement and a second movement part for the displacement of a fresh air inlet control valve (30). An Independent claim is included for a method for controlling the exhaust gas recirculation.

Description

Control system for the operation of an internal combustion engine and

  recirculation control method

  exhaust gases by means of such a control system.

  The invention relates to gas recirculation circuits

  exhaust from internal combustion engines.

  More particularly, the invention relates to a system of

  control of the operation of an internal combustion engine allowing a control of the quantity of recirculated exhaust gases, as well as a corresponding control method.

  As we know, motor vehicles, and in particular

  Diesel type motor vehicles are often equipped with an exhaust gas recirculation circuit which is intended to reinject the exhaust gases into the engine's intake manifold.

  We know that such recirculation makes it possible to reduce

  nitrogen oxide emissions from the engine, which are particularly harmful chemical species. The amount of nitrogen oxide is in fact strongly linked to the composition of the reactive mixture in the engine cylinders, in air, in fuel, and in inert gas.

  Thus, by providing for recirculation of the exhaust gases, inert gases are injected into the engine cylinders, which make it possible to reduce the amount of nitrogen oxide produced by the engine. This recirculation is however likely to significantly increase the quantity of fumes in the exhaust gases if it is not properly adjusted, and, in particular,

  if the quantity of recirculated exhaust gases is too large.

  Furthermore, under certain conditions, in particular when the driver of the motor vehicle requires frank acceleration,

  exhaust gas recirculation must be shut off.

  Thus, the exhaust gas recirculation circuit is provided with a valve for adjusting the flow of recirculated gases. An electronic computer, responsible for managing the amount of fuel to be injected into the engine cylinders, calculates a set value for the amount of recirculated exhaust gas as a function of the engine operating point and controls the valve. setting

  to regulate the percentage of recirculated gases.

  However, the maximum flow rate of recirculated gases, for a given operating point, is obtained when the recirculation valve is opened to the maximum. This flow is limited by the pressure difference between the exhaust manifold and the distributor

of admission.

  In order to further increase the amount of recirculated gas, it has been proposed to provide the fresh air intake line in the cylinders, upstream of the intake manifold, with an intake control valve of recirculated gases. In normal operation, this valve is fully open. However, when it is desired to increase the quantity of fresh air, this valve is operated in the closing direction so as to increase the differential pressure on either side of the gas recirculation duct and thus increase

the amount of recirculated gas.

  In this regard, reference may be made to documents US-A-006 138 20 651, and EP-A-1 002 947, which describe different arrangements of

  exhaust gas recirculation systems.

  This technique, although making it possible to effectively increase the quantity of recirculated gases, has a major drawback, insofar as it requires, either respective control devices 25 for the exhaust gas recirculation valve and for the exhaust valve. fresh air intake control, i.e. to mechanically link the

  two valves to use only one control system.

  The object of the invention is therefore to overcome this drawback.

  Thus, according to the invention, there is provided a system for controlling the operation of an internal combustion engine by controlling the quantity of recirculated exhaust gases, comprising a central computer adapted to calculate a setpoint quantity of exhaust gas recirculated according to the engine operating point and a control member for the movement of an exhaust gas recirculation valve displaceable according to the set value of recirculated gas for positioning

said valve.

  According to a general characteristic of this system, the member for controlling the movement of the valve comprises a first stroke part intended for controlling the movement of said valve, and a second stroke part intended for movement of a

fresh air intake control.

  According to another characteristic, the control member 10 comprises a control axis driven in rotation by motor means controlled by the central computer and whose rotation causes

  the angular displacement of said valves.

  In one embodiment, the valves are mounted on the control axis in a freely rotatable manner and in this said axis carries a stop bearing on the valves to cause their displacement Elastically deformable means can be provided to urge the exhaust gas recirculation valve and the fresh air intake control valve in the open position According to another characteristic, the system according to the invention 20 further comprises a stop for limiting the angular displacement of the recirculation valve of exhaust gas on which this

  recirculation valve rests in the open position.

  According to the invention, there is also proposed a method for controlling the recirculation of exhaust gases from an internal combustion engine, by developing a set value for the quantity of recirculated exhaust gases and controlling the displacement. an exhaust gas recirculation valve and a valve for controlling the admission of fresh air into the engine cylinders, characterized in that the displacement of the recirculation valve and of the control valve d fresh air are admitted by means of a common control member, the stroke of this control member comprising a first stroke part intended for controlling the movement of the exhaust gas recirculation valve and a second part of the race intended for

  moving the fresh air intake control valve.

  Other objects, characteristics and advantages of the invention

  will appear on reading the following description, given only 5 by way of nonlimiting example, and made with reference to the drawings

  attached, in which: - Figure 1 is a schematic view of an internal combustion engine equipped with an exhaust gas recirculation circuit and provided with a control system according to the invention; Figure 2 is a detail view of the engine of Figure 1 showing the arrangement of the exhaust gas recirculation valve and the fresh air intake control valve; and - Figures 3 to 6 illustrate the operation of the system according to the invention, in different respective positions of the exhaust gas recirculation valve and the control valve

fresh air intake.

  In Figure 1, there is shown, schematically, the general structure of an internal combustion engine of a vehicle

  automotive, designated by the general reference 10.

  In the embodiment considered, the motor 10 is

  provided with four cylinders 12 in line.

  The cylinders 12 are supplied with air via a

  intake manifold 14, itself supplied by a line 16 provided with an air filter (not shown), and, if necessary, with a turbocharger for supercharging the engine with air.

  An exhaust manifold 20 collects the exhaust gases from the combustion and evacuates them to

  outside, passing through an exhaust line 22.

  An exhaust gas recirculation circuit 24 extends between the exhaust line 22, downstream of the exhaust manifold, and the intake pipe 16, upstream of the intake manifold 14, and recovers a part of the exhaust gas to reinject it into the intake manifold 14, so as in particular to limit the quantity of nitrogen oxide produced while avoiding the formation of

smoke in exhaust fumes.

  As can also be seen in FIG. 2, this exhaust gas recirculation circuit 24 essentially comprises an exhaust gas recirculation valve (EGR), designated by the

  general reference 26.

  Furthermore, the motor 10 is provided with a computer 28, duly programmed to control the operation of the motor 10, in particular for adjusting its parameters of

operation.

  In particular, the computer 28 produces a set value for the quantity of recirculated gases and controls the EGR valve as a function of the set value, by means of a

control unit.

  As is known, the quantity of recirculated gases depends on the pressure difference between the exhaust line 22, downstream of the exhaust manifold 10, and the supply line 16, in

  upstream of the intake distributor 14.

  In order to increase the quantity of recirculated gases, when the recirculation valve 26 is fully open, the supply line 16 is provided with a valve 30 for controlling the admission of fresh air, also controlled by the computer 28, and arranged upstream of the zone into which the exhaust gases open. This control valve 30 is intended to be closed in order to lower the pressure on the intake side and thus increase the quantity of

recirculated gases.

  As seen in Figure 2, the control valve

  fresh air intake 30 and the recirculation valve 26 are both carried by a common shaft or axis 32 and are mounted on it freely in rotation. Motor means (not shown), controlled by the computer 28 cause the angular displacement of the axis 22 and the consecutive opening or closing of the valves 26 and 30. Springs 34 and 36 stress these valves in the open position.

  A stopper, produced in the form of a longitudinal rib. 38 carried by the axis 32, and on which the valves are intended to come to bear, is used to cause the angular displacement of the valves 32 and 36 (FIGS. 2 to 6). This stop and the springs 34 and 36 exert antagonistic forces. Thus, from an initial position, visible in FIG. 3, in which the EGR valve 26 is closed and bears on the stop of the axis 32 and the fresh air intake valve 30 is open, after rotation of the axis 32, the EGR valve 26, released, is moved 10 in the closing direction under the action of the spring 36 (Figure 4), to a fully open position, in which it comes bearing against a stop 40 carried for example by the wall of the

  exhaust gas recirculation line (Figures 4 and 5).

  Continuing its rotation, the axis 32, and in particular the stop 38 15 which it carries, bears against the fresh air intake control valve 30 and causes the latter to rotate in the direction of the closing to a completely closed position, visible in FIG. 6. This movement is exerted against the force exerted by the corresponding return spring 34. The pressure upstream of the inlet distributor 14 is then reduced, and the quantity of gas

  recirculated is increased accordingly.

  When the axis 32 is rotated by the drive means in the other direction, that is to say from a position corresponding to that visible in FIG. 6, the inlet control valve 25 fresh air 30 thus released, is first of all repositioned in its initial state, under the action of the corresponding spring 34. After reaching its fully open position, the stop 38 comes to bear against the EGR valve 26 which is then repositioned in its

  closed initial position, against spring 36.

  Note that all the intermediate positions between the positions shown in Figures 3, 4, 5 and 6 can be used

  and constitute stable positions.

  As will be appreciated, the invention which has just been described uses, for the displacements of the EGR valve and of a valve for controlling the admission of fresh air, a single control member, including a first stroke part is used to move the EGR valve, and a second stroke part of which is used to move

  the fresh air intake control valve.

  Thus, the EGR valve can be opened or closed independently of the intake flap, insofar as the axis is rotated in one or the other direction, only as regards its first part of the stroke. On the contrary, the air intake control flap can only be closed if the EGR valve 10 is fully opened. Indeed, the air intake valve is mainly used to increase the rate of gases recirculated by vacuum, when the EGR valve 26 is fully opened. The fact of not being able to control the closing of the air intake control valve 30 is therefore not an unacceptable drawback. 15

Claims (4)

  1-System for controlling the operation of an internal combustion engine, by controlling the quantity of recirculated exhaust gases, the system comprising a central computer (28) adapted to calculate a set value for the quantity of exhaust gas exhaust recirculated as a function of the engine operating point and a control member (32) for the movement of an exhaust gas recirculation valve (26) displaceable as a function of the set value of recirculated gases for positioning said valve, 10 characterized in that the stroke of the valve movement control member comprises a first stroke part intended for controlling the movement of said valve (26) and a second stroke part intended for moving a valve ( 30)   fresh air intake control.   2-control system according to claim 1, characterized in that the control member comprises a control axis (32) driven in rotation by motor means controlled by the central computer and whose rotation causes the angular displacement of said valves. 3- control system according to claim 2, characterized in that the valves are mounted on the control axis in free rotation and in that said axis carries a stop (38) bearing   on the valves to cause them to move.   4-System according to any one of claims 1 to 3, 25 characterized in that elastically deformable means (34, 36)   stress the exhaust gas recirculation valve and the valve   fresh air intake control in the open position.   -System according to any one of claims 1 to 4,   characterized in that it further comprises a stop (40) for limiting the angular displacement of the exhaust gas recirculation valve on which this recirculation valve rests open position.   6-Method for controlling the recirculation of exhaust gas from an internal combustion engine by developing a set value for the quantity of recirculated exhaust gases and controlling the movement of a recirculation valve (26) exhaust gas and a valve (30) for controlling the intake of fresh air into the engine cylinders, characterized in that the movement of the recirculation valve and the intake control valve d fresh air is produced by means of a common control member (32), the stroke of this control member comprising a first stroke part intended for controlling the movement of the exhaust gas recirculation valve and a 15 second part of the stroke intended for the displacement of the valve fresh air intake control.