FR2724976A1 - Rotary valve controlling exhaust gas recirculation in IC engine - Google Patents

Abstract

The motor casing (1) is mounted on the valve body (2) on spacers (5), to reduce heat transfer. The e.g. stepping type motor has a shaft (20) with a spring-steel teed drive-bar (24) fitting in notches (17) in the raised rim (16) of one ceramic disk (13), which it presses against a similar fixed disk (11), seated in a cylindrical opening (10) connected to the exhaust manifold. The amt. of gas recirculated is controlled by the degree to which shaped apertures in the disks coincide, the shapes being designed to provide uniformly increasing common area as the driven disk rotates. Gas admitted to an outer chamber (15) passes by a port (9) to the inlet manifold.

Description

Control unit for the quantity of exhaust gas recycled
in an exhaust gas recirculation system
an internal combustion engine
The present invention relates to a unit for controlling the quantity of exhaust gas recycled in an exhaust gas recirculation system of an internal combustion engine.

Exhaust gas recirculation (EGR) systems are already known intended, in internal combustion engines, to recycle part of the exhaust gases at the intake into the cylinders. Such recycling of gases, generally inert, and therefore not participating in combustion, makes it possible to lower the combustion temperature, which has the effect of reducing the rate of nitrogen oxides (NOx) present in exhaust, and therefore to limit the pollution caused by such an engine.

However, for the engine to function satisfactorily, such recirculation must only occur under normal engine operating conditions and therefore be interrupted in all non-nominal circumstances, namely, essentially, cold, under heavy load, and idling. In these latter cases, no recirculation is permitted while, in normal operation, recirculation of up to 25% by weight of the admitted gases is permitted. Regulation is therefore necessary.

Until now, this regulation has been obtained by having a needle valve in the recirculation circuit in which the position of the latter was controlled by a membrane subjected to a more or less significant vacuum. This control vacuum was controlled by a solenoid valve located between a vacuum source and the needle and diaphragm valve. The solenoid itself was supplied with alternating current, the duty cycle of which was determined by a computer to which was supplied, for example, the temperature of the coolant, the load and the speed of rotation of the engine.

These known needle valve systems had a number of drawbacks due in large part to the non-linearity of the variation in the flow rate of the valve as a function of its opening. Indeed, a needle valve has the characteristic of allowing the start of its opening a relatively large flow.

 It follows first of all that such a system is not very progressive in that, as soon as a low rate of recirculation could be authorized, this rate is in fact immediately relatively high.

Because of this not very progressive character, critical at low flow rates, the needle valve should also have a small passage diameter. However, such a small diameter is incompatible with the high flow rates desired under normal conditions.

In addition, these systems are relatively imprecise, especially at low flow rates.

In fact, because of the above, a very small variation in the opening can lead to considerable variations in the recirculation rate.

Furthermore, needle valves have the disadvantage of not being self-cleaning, and therefore of clogging very quickly. Again, this results in uncontrolled flow variations.

Finally, if you want good accuracy, such a system must be enslaved. It is in fact not possible to determine precisely what the duty cycle of the signal applied to the solenoid must be to cause a given opening of the needle valve. It is therefore necessary to have a sensor to know the degree of opening of the valve. In addition, such a sensor gives only an approximate indication that does not have a precise zero, due to the poorly understood expansions due to variations in temperature of the valve.

The present invention aims to overcome these drawbacks.

To this end, the invention relates to a unit for controlling the quantity of exhaust gas recycled into an exhaust gas recirculation system of an internal combustion engine, characterized in that it comprises a valve of the type comprising a mobile disk in rotation and provided with a light cooperating with a fixed orifice, and motor means for driving in rotation of said mobile disk.

As will be seen below, the use of a movable disc valve fitted with a passage light makes it possible to reconcile progressiveness and precision at low flow rates, with the possibility of obtaining high flow rates.

In a particular embodiment, there is provided a stop arranged to limit the movement of the movable disc while the valve is in the closed position, a non-zero rotational stroke being provided for said movable disc between its stop position and the start of the opening of the valve.

By bringing the valve into abutment, there is a zero which then makes it possible, knowing the rotation of the motor, to know with precision the angle by which the movable disc has turned. Such an arrangement has the advantage of being insensitive to temperature variations. In addition, the "dead" range of rotation makes it possible to start opening the valve with a precision of one motor step.

In a particular embodiment of the invention, the lumen has an increasing radial dimension in the direction of opening of the valve.

This allows great progressiveness to be obtained at the start of valve opening. It is thus possible to obtain non-linear operation at low flow rates in the direction opposite to the non-linearity of the needle valves, that is to say in a favorable direction. One can, for example, obtain, for the first third of the rotational travel of the movable disc, only 5% of the maximum flow rate of the valve.

The disc and the support piece, where the fixed orifice is formed, are preferably made of ceramic.

This material allows first of all to obtain an excellent seal between the upstream and downstream of the valve. Due to their lightness, these parts have less inertia and are less subject to vibrations. They can also be produced with great precision and, due to their shape, be self-cleaning. Finally, the arrangement according to the invention makes it possible to obtain a particularly compact unit.

The movable disc can be mounted on the shaft of the drive means by means of a spreader elastically engaged in at least one housing of a disc support member.

Thus, a given rotation of the motor from the stop corresponds to a precise position of the disc, whether this has been obtained in one direction of rotation or in the other of the motor.

More particularly, the lifter may have a C-shaped section, with dimensions in the free state slightly greater than those of said housing.

In a particular embodiment, the lifter is engaged at its two ends in two diametrically opposite housings and applies the disc elastically to its support piece.

In a particular embodiment of the invention, the motor means comprise a controlled motor with variable duty cycle (torque motor) associated with a return spring.

Such a solution has the advantage of benefiting from a control system similar to that of the solenoid needle valve. It can therefore be implemented relatively simply on engines of existing type.

In addition, it is possible with such an arrangement to carry out automatic returns using the large torque of the spring.

In another embodiment, the motor means comprise a stepping motor.

The use of a stepping motor makes it possible to obtain the desired precision without slaving.

In addition, a stepping motor is supplied only when it is desired to modify the flow rate. Its energy consumption is therefore lower and its lifespan is longer.

A particular embodiment of the invention will now be described by way of nonlimiting example, with reference to the accompanying drawings in which: - Figure 1 is an axial sectional view along line II of Figure 3, of a unit according to the invention, - Figure 2 is an elevational view, - Figure 3 is a top view, - Figure 4 is an exploded perspective view of the functional elements of the valve of this unit, - the FIG. 5 is a diagram illustrating the mounting of this unit on a motor, - FIG. 6 is a diagram illustrating the operating characteristic of the invention, in the case of the use of a stepping motor, and - the Figure 7 shows a particular form of the movable disc of the invention.

The control unit shown in FIG. 1 comprises a torque motor 1 of any suitable type, associated with a return spring, and a valve 2. The motor 1, being known, will not be described in more detail.

The valve 2 is contained in a valve housing 3, closed by a cover 4.

Four spacers 5 are made in one piece with the cover 4 and allow a certain distance to be provided between the valve 2 and the motor 1, in order to prevent the latter from being subjected to excessive heating. The housing 3, the cover 4 and the motor 1 are assembled using screws 6 passing through corresponding holes in the housing 3 and referred to in a cover 7 of the engine 1. Thus, the housing 3 is held in abutment on the cover 4 and the free ends of the spacers 5 are held in abutment on the cover 7.

A seal 8 is arranged between the housing 3 and the cover 4 and also participates in the thermal insulation of the motor 1 relative to the valve 2.

The valve housing 3, the section of which can be seen in FIG. 3, has a lateral exhaust port 9 and a central intake port 10. The intake port 9 is intended to be connected to the exhaust manifold of the engine and the exhaust port 10 is intended to be connected to the intake manifold of the engine. Thus, valve 2 regulates the flow of recycled gases from the exhaust manifold to the engine intake manifold.

The periphery of the intake orifice 10 forms a seat for a support piece 11, here in the form of a disc, fixed by any suitable means, for example by gluing on this seat. The support piece 11 is made of ceramic and has a semicircular opening 12.

A disc 13 movable in rotation is disposed in abutment on the support piece II.

The disc 13 is guided by the periphery of the orifice 10. The disc 13 has a semicircular lumen 14 which, in a certain angular position of the disc 13 can come to be superimposed on the fixed orifice 12 while, in the offset angular position 180 degrees, the light 14 and the orifice 12 are completely offset. In this latter position, the interior chamber 15 of the valve 2, on the side of which the disc 13 is located, is completely isolated from the outside of the valve, on the side of which the support piece 11 is located. The disc 13 is also made of ceramic and the faces opposite the disc 13 and the part 11 are polished, so as to ensure sealing.

The disc 13 is made in one piece with a cylindrical drive member 16 carrying, diametrically opposite, two forks 17 each delimiting a housing 18 for the ends of a drive spreader 19 mounted in its central part, by all suitable means, for example by riveting, at the end of the shaft 20 of the motor 1. For this purpose,
The shaft 20 passes through the cover 4 through a sealed bearing 21.

The lifter 19 has its C-shaped ends 22. They have dimensions slightly larger than those of the housings in the free state. Thus, when the ends 22 of the lifter 19 are engaged in the housings 18, the slots 23 that they delimit tighten and an assembly is thus produced without play. It follows that, knowing the angular position of the motor 1, we know precisely the angular position of the movable disc 13, whatever the direction of movement by which arrived at this position.

On the other hand, the central part 24 of the lifter is substantially planar and perpendicular to the shaft 20. The shaft 20 has a length such that, when the ends 22 of the lifter 19 are engaged at the bottom of the housings 18, the central part 24 of the spreader is bent elastically, which has the effect of applying the disc 13 on the support member 11, thus increasing the tightness of the valve 2. It will also be noted that this application of the disc 13 on the part d support 11 is also provided by the vacuum prevailing under the exhaust orifice relative to the pressure inside the chamber 15.

The lifter 19 is made of a material of the spring steel type.

Also formed in one piece with the disc 13 is a stop 25 external to the cylindrical drive member 16 and capable of cooperating with a fixed stop 26 formed in one piece with the housing 3 inside room 15.

Alternatively, the fixed stop 26 is formed not on the housing 3 but on the support piece 11, which avoids having to index this part relative to the housing.

We see in Figure 5 the engine 25 with its intake manifold 26 and its exhaust manifold 27. The intake manifold 26 is connected to an air intake 28 via the air filter 29. The Figure 5 also shows the butterfly valve 30 disposed in the intake manifold in a conventional manner.

We see in this figure that the inlet port 10 of the valve 2 is connected by a tube 31 to the exhaust manifold 27 of the engine 25 while the exhaust port 9 of the valve 2 is connected by a tube 32 to the intake manifold 26 downstream of the butterfly valve 30.

The engine 1 is controlled by a computer 33, which receives as input information on the engine rotation speed, its load and the temperature of the coolant, in order to determine from these parameters what should be the opening of the valve 2 and to supply the motor 1 for this purpose with alternating current at a suitable duty cycle.

FIG. 6 represents the flow-opening characteristic of the valve 2, in the case where a torque motor is not used, but a stepping motor. Given that the motor zero is precisely known, corresponding in the simplest case to the exactly closed position of valve 2, we know that the characteristic 34 of this valve is between the two lines 35 and 36, each starting at half a step from motor 1 on either side of zero, from which the theoretical characteristic 37 begins.

However, in a preferred embodiment, the orifices 12 and 14 are not exactly semi-circles but segments of a circle, so that there is an entire angular zone for the disc 13 in which the lumen 14 and the orifice 12 do not overlap at any point. The position of the stops 25 and 26 is such that, when the disc 13 is in abutment, one is in this zone at a number of steps N known to the motor 1. Thus, at the start of operation, the computer 33 brings the disc 13 in stop and thus knows precisely that the valve begins to open at the end of N steps, to within half a step. The best possible accuracy is thus obtained while having relatively simple stepping motor control.

FIG. 7 represents other shapes for the light 14 and the orifice 12, making it possible to obtain a non-linear characteristic for better progressiveness at low flow rates, and which can be used with one or the other type of motor. The orifice 12 'is here circular, while the lumen 14' has a radial dimension r which increases in the opposite direction to the direction of rotation of opening of the disc 13 'represented by the arrow O. The lumen 14' ends, on the side of its largest dimension, by a semi-circular part 38 equivalent to a half-orifice 12 '.

If the position shown in solid lines of the light 14 corresponds to the position in abutment of the disc 13 ', it is seen that it is necessary to perform a rotation of an angle CL between the position in abutment and the start of the opening.

Then this opening will start to grow very slowly due to the small radial dimension of the light 14 'in this area. The opening, and consequently the flow, will then increase more and more quickly up to a maximum corresponding to a flow surface equal to that of the orifice 12 ', when the light is in its position in phantom. . The corresponding characteristic is represented at 39 in FIG. 6.

Claims (9)

1. Unit for controlling the quantity of exhaust gas recycled into an exhaust gas recirculation system of an internal combustion engine, characterized in that it comprises a valve (2) of the type comprising a disc (13) movable in rotation and provided with a light (14) cooperating with a fixed orifice (12), and motor means (1) for driving in rotation said mobile disc. 2. Unit according to claim 1, comprising a stop (25, 26) arranged to limit the movement of the movable disc while the valve is in the closed position, a non-zero rotation stroke being provided for said movable disc between its position in abutment and the start of valve opening. 3. Unit according to any one of claims 1 and 2, wherein said lumen has an increasing radial dimension in the opposite direction to the opening direction of the valve. 4. Unit according to any one of claims 1 to 3, wherein said disc and the support part (11) where said fixed orifice is formed are made of ceramic. 5. Unit according to any one of claims 1 to 4, wherein said movable disc is mounted on the shaft of the drive means by means of a lifter (19) resiliently engaged in at least one housing (18) d 'a disc support member (16). 6. Unit according to claim 5, wherein said spreader has a C-shaped section of dimensions in the free state slightly greater than those of said housing. 7. Unit according to any one of claims 5 and 6, wherein the lifter is engaged at its two ends in two diametrically opposite housings and elastically applies the movable disc on its support piece. 8. Unit according to any one of claims 1 to 7, in which the motor means comprise a controlled motor with variable duty cycle (torque motor) associated with a return spring. 9. Unit according to any one of claims 1 to 7, in which the motor means comprise a stepping motor.