EP0558358B1 - Exhaust recirculation device for a compression ignition engine driven by the charge lever of the engine - Google Patents

Description

The invention relates to a device for recirculating exhaust gas from a compression-ignition engine controlled by all-or-nothing valves.

In the case of diesel engines, it is known to ensure the recirculation of part of the gases taken from an exhaust pipe of the engine, so as to reintroduce these gases in a pipe for the admission of fresh gas into the engine. The recirculation of exhaust gases makes it possible to reduce the emissions of nitrogen oxide and in particular of nitrogen monoxide NO which is chemically unstable and which transforms into NO₂ on contact with air. In the presence of water, NO₂ dioxide changes to nitric acid, so that NO nitrogen monoxide escaping from the engine is likely to turn into a dangerous polluting substance.

The recirculation of the exhaust gases makes it possible to reduce the emissions of polluting gases such as nitrogen oxides, on the one hand due to the reduction in the flow rate of the exhaust gases, part of which is reintroduced into the engine with the gases. on the other hand, the fact that the introduction of exhaust gases, and therefore of important specific heat molecules such as triatomic molecules of carbon dioxide or water, into the intake manifold of the engine causes a reduction in the maximum combustion temperature and therefore the quantity of nitrogen oxide formed which is all the more important the higher the combustion temperature.

The exhaust gases likely to contain the polluting substances are therefore less abundant and the proportion of polluting substances in these gases is also reduced, when a certain recirculation of the exhaust gases is carried out. Recirculation is carried out via a conduit ensuring the connection between an exhaust manifold or manifold and an intake manifold or manifold of the engine, on which is disposed. a valve making it possible to control the recirculation of the exhaust gases, as a function of the operating parameters of the engine and in particular as a function of the power level requested from the engine.

Such a valve, generally called an EGR valve, (corresponding to the designation in English Exhaust gas recirculation) has a relatively complex structure and operation, insofar as it is necessary to carry out exhaust gas recirculation only in certain engine operating phases. The EGR valve comprises a shutter which is associated with control means allowing, by displacement of the shutter, the opening or the closing of the valve, so as to ensure or, on the contrary, to prohibit the recirculation of the gases of exhaust, depending on the engine operating phases.

The shutter of the EGR valve must be placed in a closed position, so as to prevent gas recycling, especially when the engine is at full load.

Indeed, at full load, to obtain the required power and to preserve the performance of the engine, it is necessary to introduce into the engine fresh gases containing a high proportion of oxygen and therefore to avoid a mixture of these fresh gases. with exhaust gases.

The recirculation devices currently used on vehicles with a diesel engine include vacuum-operated EGR valves. The shutter of the valve is connected to a membrane which constitutes one of the walls of a chamber of the valve connected to a vacuum pump, by means of a solenoid valve with progressive opening or of all or nothing type.

When the vacuum level and the vacuum in the chamber are low, the shutter consisting of a valve is held in abutment by return means on a valve seat of the valve closing the passage of gases in the recirculation duct.

The valve can be opened by lifting the valve above the valve seat, creating a deeper vacuum in the chamber through the vacuum pump.

The communication between the vacuum pump and the chamber is ensured by opening the solenoid valve which is controlled by an electronic control unit, depending on parameters such as engine speed, air pressure at l intake and temperature of the cooling water and / or by a control unit depending on the engine load level.

Such a device is complex and requires the use of electrical control circuits or partially made in pneumatic form. A pneumatic converter is used, for example, connected to the load lever of the fuel injection pump using a linkage. This progressive converter provides a vacuum proportional to the position of the load lever. This vacuum is modulated by a solenoid valve controlled by an electronic unit which takes into account parameters such as engine speed and temperature.

Such complex, delicate and costly devices may be necessary to reduce the discharge of polluting engines to a very low level, so as to comply with extremely strict standards such as those prevailing in certain foreign countries.

In fact, compression ignition engines that are currently manufactured and that have benefited from certain technical improvements produce much less polluting emissions than engines using an older technique.

In this case, complex recirculation devices such as those which have been described above may prove to be superfluous and it may be desirable to use simpler devices and consequently much less expensive.

US-A-4,349,004 describes a device for recirculating the exhaust gas of a diesel engine which includes an EGR valve controlled by a vacuum source. An electromagnetic valve is used to control the communication of the vacuum source with the EGR valve or the isolation of the EGR valve, depending on the load level of the engine. A fuel injection pump control lever cooperates with contactors to close the EGR valve. Such a device has the disadvantage of not taking into account the temperature of the engine so that the recirculation device is likely to operate when the engine is cold.

US-A-4,157,081 describes a recirculation device in which a recirculation duct opens into an engine intake pipe downstream of the intake adjustment butterfly. An electromagnetic valve arranged on the recirculation duct can be controlled by a thermal contactor to close the recirculation duct, when the engine is cold. Such a device does not include an EGR valve for controlling the operation of the recirculation as a function of the engine load and requires the use of an independent additional valve for controlling the recirculation as a function of the engine temperature.

The object of the invention is therefore to propose a device for recirculating the exhaust gas of a compression-ignition engine comprising a recirculation duct connected, at one of its ends, to a means for recovering gases from exhaust of the engine and, at its other end, to a means for admitting fresh gas into the motor and an all-or-nothing recirculation valve, interposed on the recirculation duct and controlled, for its opening and closing, by a vacuum source connected to the recirculation valve by means of an all-or-one solenoid valve nothing associated with control means actuated by a member for adjusting the power of the engine, the member for adjusting the power of the engine being constituted by a load lever and the means for controlling the solenoid valve by at least one contactor electric disposed at the end of a displacement zone of the load lever and placed on a supply circuit of the solenoid valve, so that the load lever cooperates with the contactor to ensure the closing of the solenoid valve and of the recirculation valve, when the engine load becomes greater than a value corresponding to an average load intermediate between the zero load and the maximum engine load, the ele solenoid valve and the recirculation valve being open, when the load lever is in a position located below the contactor and corresponding to a motor load lower than the average load, this device being of a simple and inexpensive structure, usable in the case of low-emission engines and including means for adjusting the recirculation taking into account the load level and the engine temperature.

For this purpose, it includes a probe for measuring the temperature of the motor electrically connected to the electrical contactor actuated by the load lever, so as to prevent the opening of the solenoid valve, when the temperature of the motor is below a predetermined limit. .

In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, with reference to the appended figures, an embodiment of a device according to the invention.

Figure 1 is a schematic view of a diesel engine having an exhaust gas recirculation device according to the invention.

FIG. 2 is a view in elevation and in partial section of the recirculation valve of the device shown in FIG. 1.

Figure 3 is an engine operating diagram showing the limits of the load zones involved in adjusting the recirculation device.

Figure 4 is a view similar to that of Figure 1, of a diesel engine having a throttle valve at the intake.

In Figure 1, we see a compression engine 1 having an exhaust manifold 2 and an intake manifold 3. A turbo-compressor 4 is placed on the exhaust line 5, so as to be driven by the gases exhaust.

A recirculation duct in two parts 7, 8 is connected, at one of its ends, to the exhaust manifold 2 and, at its other end, to the inlet distributor 3. A recirculation valve or EGR valve 10 is interposed between the two parts 7 and 8 of the recirculation duct.

The EGR valve 10 can be controlled by vacuum, by means of a vacuum pump 20 and a conduit 22 for connection between the vacuum pump and the EGR valve, on which a solenoid valve 21 is arranged.

As can be seen in FIG. 2, the EGR valve 10 comprises a valve body 11 connected by its inlet end 11a to the part 7 of the recirculation duct connected to the exhaust manifold 2 and by its outlet end 11b, to part 8 of the recirculation duct connected to the inlet distributor 3. The body of the valve 11 therefore delimits a chamber which is placed in communication, via the end 11a of the body 11 with the part 7 of the duct engine recirculation valve connected to the exhaust manifold and, via the end 11b of the body 11, to the part 8 of the engine recirculation pipe connected to the intake distributor 3.

The valve 10 comprises a shutter 12 formed in the form of a valve coming to rest in the closed position, as shown in solid lines in FIG. 2, on a valve seat 11c machined in the internal surface of the body 11 of the valve. The seat 11c is flared, in the direction of circulation of the exhaust gases and the shutter 12 has a frustoconical bearing of corresponding shape. The part of the shutter 12 engaged in the terminal part of the inlet end 11a of the valve body, of diameter ⌀₁, has a diameter ⌀₂ <⌀₁ so that the opening of the valve is obtained when the shutter 12 is raised above the seat 11c and has its part of diameter ⌀₂ opposite the part with diameter ⌀₁ of the conduit 11. The valve 10 comprises, fixed by screws to the upper part of the body 11, a control unit 13 whose internal volume is separated into two superimposed chambers 14 and 15, by a flexible deformable membrane 16 disposed transversely inside the housing 13 and ensuring a tight closure of the chamber 14 which is completely isolated from the chamber 15. The chamber 15 is subjected to atmospheric pressure and the chamber 14 to a partial vacuum. The pipe 22 connecting the vacuum pump 20 to the EGR valve 10 opens into the chamber 14, so that the chamber 14 can be placed under vacuum relative to the chamber 15, by opening the solenoid valve 21.

The valve 12 is connected to the membrane 16 by means of a rod 17 the upper part of which is fixed to a part 18 in which the membrane 16 is engaged and fixed.

The rod 17 is slidably mounted in a guide piece ensuring the closure of the chamber of the body 11 of the valve at its upper part.

The valve 12 integral with the rod 17 can be moved between its fully closed position shown in solid lines in Figure 2 in which the valve 12 rests on the seat 11c of the body 11 and a full open position 12 'shown in dotted lines in FIG. 2, in which the valve is located above the seat 11c and frees the passage delimited by the seat 11c. The EGR valve 10 therefore operates on an all-or-nothing basis.

The permeability of the valve, in its open position, and therefore the circulation of the exhaust gases through the valve does not depend on the amplitude of the lifting of the shutter but only on the difference in diameter ⌀₁ - ⌀₂, so that dispersion effects due to differences in the characteristics of the valves obtained in a manufacturing process are avoided.

In FIG. 2, the positions 16 ′ and 18 ′ of the diaphragm 16 and of the clamping piece 18, respectively, corresponding to the open position 12 ′ of the valve 12, are also shown in dotted lines.

When the vacuum in the chamber 14 is little pushed, the solenoid valve 21 being closed, the valve 12 rests on the seat 11c and ensures complete closure of the recirculation duct.

The engine then operates without recirculation of exhaust gases.

The operation of the engine with exhaust gas recirculation can be obtained by establishing a higher level of vacuum and depression in the chamber 14, by opening the solenoid valve 21 so as to put the chamber 14 in communication with the vacuum pump. .

When a sufficient vacuum level is reached, the membrane 16 moves upward from its position shown in solid lines in Figure 2 to its position 16 'shown in dotted lines.

The upward movement of the membrane 16 causes, through the rod 17, the movement of the valve 12 from its closed position to its open position 12 '.

Part of the burnt gas from the engine coming from the exhaust manifold can then be introduced into the intake manifold, via the recirculation duct on which the valve 10 is inserted.

As can be seen in FIG. 1, the engine 1 includes an injection pump 25, the load lever 26 of which can be moved from a position 26a corresponding to the released position of the accelerator pedal of the vehicle to a position corresponding to the fully depressed position of the accelerator pedal, passing through an intermediate position 26b.

An electrical switch 28 is placed in the zone in which the load lever 26 moves, so as to be actuated by the load lever, when the latter reaches its intermediate position 26b.

The contactor 28 is interposed on a circuit 30 for supplying electrical power to the solenoid valve 21. The circuit 30 further comprises an electrical relay 31 interposed between the contactor 28 and the solenoid valve 21.

A temperature probe 32 is electrically connected to the electrical contactor 28.

The engine 1 also comprises glow plugs electrically connected to a power supply unit 36 itself connected to the circuit 30 and to the probe 32, which makes it possible to control the supply of the glow plugs as a function of the position of the load lever 26 and the engine cooling water temperature measured by probe 32.

In fact, the glow plugs can be used not only to obtain satisfactory cold starting conditions in all circumstances but also to improve the operation of the engine after starting, with regard to noise, misfires and pollution .

The glow plugs are then supplied not only before starting, in a timed manner, but also after starting, for a few minutes and in a timed manner. This provides post-heating after start-up.

It is nevertheless necessary, to avoid deterioration of the glow plugs, to cut off the supply current during the post-heating, when the engine load reaches a limit value between low and high loads; the position of the load lever is then position 26b.

In addition, post-heating should only be used when the engine is cold, that is to say when the temperature identified by the probe 32 is below a limit which can be 48 or 60 ° C.

After starting the engine, when the load lever 26 moves in the zone 33 between position 26a (pedal released) and position 26b (pedal depressed to a medium load position), the relay 31 in series with the contactor 28 and the thermal switch 32 ensures the supply and the opening of the solenoid valve, in the case where the temperature to which the thermal switch 32 is subjected is higher than a predetermined limit (48 or 60 ° C.).

The EGR valve is open, which allows recirculation of the exhaust gases towards the intake manifold 3.

In this case, the supply unit 36 of the glow plugs is inactive and the post-heating is not in operation.

Conversely, in the case where the temperature to which the thermoswitch 32 is subjected is lower than the predetermined limit, the lever 26 being in zone 33, the EGR valve is closed and the glow plugs are supplied.

In the case where the load lever reaches position 26b, it actuates the contactor 28 so that current no longer reaches relay 31 and the control of housing 36. The EGR valve is closed and the glow plugs do not are not supplied regardless of the temperature identified at the thermal switch 32.

When the lever 26 returns to the zone 33 while crossing the position 26b, it actuates the contactor 28 so as to supply the relay 31 and the control of the housing 36 as a function of the position of the thermal switch 32.

In Figure 3, there is shown, on a diagram giving the engine torque as a function of the speed (generally expressed in revolutions / minute), different curves corresponding to fixed positions of the pedal accelerator of a vehicle equipped with a diesel engine such as engine 1, that is to say curves corresponding to a fixed position of the load lever 26 of the engine.

Curve 40 corresponds to an engine running at idle (accelerator pedal released).

Curve 41 corresponds to an operation of the engine at full load.

All of the engine operating points are located between curves 40 and 41 which correspond respectively to a relaxation of the accelerator pedal and to maximum depressing of this pedal.

The first position also corresponds to position 26a of the load lever.

FIG. 3 also shows a curve 43 corresponding to the fixed position 26b of the load lever in which this lever actuates the contactor 28. The load or power supplied by the motor is then less than the maximum load. This load corresponding to the position 26b of the lever 26 is designated as an average load and constitutes a limit between the operation at low load and the operation at high load of the engine.

Curve 43 delimits in the engine operating zone between curves 40 and 41, two domains 46 and 47 corresponding respectively to an operation of the engine at low load and to an operation of the engine at high load.

The arrangement of the contactor 28 is such that this contactor is actuated in the opening or closing direction by the load lever, when the engine operating point passes from the domain 47 to the domain 46 or vice versa from the domain 46 to the domain 47.

In the case of idling, low load or partial load operation, the load lever 26 is in the zone 33, so that the solenoid valve is supplied with electric current. However, the solenoid valve 21 can be supplied with electric current ensuring its opening only if the probe 32 generally constituted by a thermal switch and connected to the contactor 28 emits a signal authorizing the passage of current. An authorization signal is issued if the engine water temperature is above a certain limit which is generally around 48 ° C. This avoids operating the recirculation device when the engine is cold.

In the case where the engine temperature is higher than the predetermined limit, the supply and the opening of the solenoid valve 21 are therefore ensured, so that the vacuum pump 20 is put in communication with the vacuum chamber of the EGR valve 10, via the connecting line 22.

On the other hand, the authorization signals are reversed as regards the control of the supply of the glow plugs, as explained above. The glow plugs are only supplied when the engine water temperature is below the predetermined limit.

In the event of an acceleration passing the engine operating point from domain 46 to domain 47, the load lever 26 actuates the contactor 28 so as to interrupt the supply of electric current to the solenoid valve 21 The solenoid valve 21 closes again, so as to isolate the vacuum pump 20 from the connection pipe 22 of the EGR valve 10. The vacuum chamber of the EGR valve 10 is vented through the connecting line 22, the pressure is restored very quickly in the chamber of the EGR valve which closes very quickly.

In the case of an acceleration in the vicinity of full load, this limits the response time of the turbocharger 4 which immediately receives the entire exhaust gas flow.

At the same time, the power supply to the glow plugs remains constantly cut.

It is obvious that if the accelerator pedal is released to return from domain 47 to domain 46, the movement of the load lever 26 makes it possible to release the contactor 28.

FIG. 4 shows a motor 1 similar to the motor represented in FIG. 1 and the corresponding elements of a device for adjusting the gas recirculation and the post-heating which bear the same references as the elements represented in the figure 1.

The engine 1 is an atmospheric engine. In this case, as is well known to those skilled in the art, the difference in gas pressure, during engine operation, between the intake manifold 3 and the exhaust manifold 2, is very small.

Exhaust gas recirculation hardly occurs and the amount of recirculated gas remains low.

The device shown in Figure 4 overcomes this drawback.

A butterfly valve 38 associated with a vacuum actuating device 39 is disposed in a supply conduit opening into the intake manifold.

The vacuum device 39 is connected by a pipe 37 to the pipe 22 connecting the EGR valve 10 to the vacuum pump 20. The actuation of the throttle valve 38 by means of the vacuum device 39 which is controlled by the solenoid valve 21 is therefore simultaneous with actuation of the EGR valve. The throttle valve 38 which can be placed in a partially closed position or in a fully open position lowers the pressure in the intake manifold 3, during the operation of the EGR valve. This increases the exhaust gas recirculation rate.

The recirculation device according to the invention which is of a simple embodiment and which only uses the engine load lever as an actuating member can be used to equip vehicles comprising a low-polluting diesel engine. The device has the advantage of being of moderate cost and of exhibiting entirely satisfactory operating characteristics. The control of the post-heating using the control means of the EGR valve makes it possible to further improve the operation of the engine.

The invention is not limited to the embodiment which has been described.

This is how the electrical contactors actuated by the charging lever can be of any type, that the engine temperature sensor can be constituted by a different element from a thermo-contact and that the electrical supply circuit of the 'solenoid valve can be made according to any embodiment adapted and integrated into the vehicle whose propulsion is provided by the engine.

The vacuum pump can be a pump driven by an electric motor powered by a vehicle power source or a pump driven directly by the engine.

The invention applies in the case of any compression ignition engine.

Claims (7)

1. Exhaust recirculation device for a compression-ignition engine (1) comprising a recirculation pipe (7, 8) connected at one of its ends to a means (2) of recovering the engine exhaust gases and, at its other end, to a means (3) of admitting fresh gas into the engine and a fully-open/fully-closed recirculation gate (10) interposed on the recirculation pipe (7, 8) with its opening and closing controlled by a source of negative pressure (20) connected to the recirculation gate (10) by means of a fully-open/fully-closed solenoid valve (21) associated with control means (28) actuated by a device (26) for adjusting the engine power, the device for adjusting the engine power consisting of a load lever (26) and the means (28) of controlling the solenoid valve (21) consisting of at least or a electrical contactor (28) disposed at the end of an area (33) in which the load lever (26) moves and placed on a circuit supplying the solenoid valve (21), so that the load lever (26) cooperates with the contactor (28) in order to close the solenoid valve (21) and the recirculation gate (10) when the load of the engine (1) is greater than a value corresponding to an average load intermediate between zero load and the maximum load of the engine, the solenoid valve (21) and the recirculation gate (10) being open when the load lever (26) is in a position before the contactor (28) and corresponding to an engine load lower than the average load, characterized by the fact that it has a sensor (32) for measuring the temperature of the engine (1) connected electrically to the electrical contactor (28) actuated by the load lever (26), so as to prevent the solenoid valve (21) from opening when the temperature of the engine (1) is lower than a predetermined limit.
2. Device according to Claim 1, characterized by the fact that the sensor (32) consists of a thermal switch.
3. Device according to either one of Claims 1 and 2, characterized by the fact that the recirculation gate (10) is connected to the negative-pressure source (20) by means of a connecting pipe (22) on which the solenoid valve (21) is interposed.
4. Device according to any one of Claims 1 to 3, characterized by the fact that the electrical control circuit for the solenoid valve (21) has an electrical relay (31).
5. Recirculation device according to any one of Claims 1 to 4, characterized by the fact that the source of negative pressure (20) connected to the recirculation gate (10) consists of a vacuum pump.
6. Device according to any one of Claims 1 to 5, in the case of an engine (1) having a set of glow plugs (35) associated with means (36) of supplying electric heating current effecting a postheating of the engine (1) subsequent to starting up, characterized by the fact that the supply means (36) for the glow plugs are connected to the electrical contactor (28) and to the sensor (32), so that the supply to the glow plugs (35) is actuated when the load lever (26) is in a position before the contactor (28) corresponding to an engine load lower than the average load and the temperature detected by the censor (32) is lower than a predetermined limit.
7. Device according to any one of Claims 1 to 6, characterized by the fact that, in a pipe connected to the inlet manifold (3), the engine (1) has a butterfly (38) associated with a negative-pressure control means (39) connected to the source of negative pressure (20) by means of the solenoid valve (21), so as to be moved between a position of complete opening and a position of partial closure of the pipe connected to the inlet manifold (3), in synchronism with the opening of the recirculation gate (10), in order to lower the gas pressure in the inlet manifold (3).

Images