FR2942511A1 - DEVICE FOR INJECTING AN ADDITIVE PRODUCT IN THE EXHAUST SYSTEM OF A MOTOR VEHICLE. - Google Patents

Abstract

This device for injecting a liquid additive comprises an additive tank (3) connected by an additive duct (4) to an injector (5) placed in the exhaust system of the vehicle concerned. There is provided, on the additive duct (4), a suction and displacement displacement pump (6), comprising a cylinder (7) and a piston (8) which delimits a pressurizing chamber (11) in the cylinder (11). . An electric actuator (9) is coupled to the piston (8) to cause a recoil with suction of the additive into the chamber (11) from the reservoir (3) and simultaneous compression of a spring (10) acting on the piston . Thanks to the spring (10), the advance of the piston (8) with discharge of the additive to the injector is carried out under controlled pressure. Application to the injection of a mixture of water and urea, in the case of vehicles with engine using diesel fuel.

Description

The present invention relates to a device for injecting an additive product in the liquid state, such as urea, into the exhaust system of a motor vehicle with a heat engine, in particular a motor using diesel fuel as the fuel.

In motor vehicles using diesel as fuel, it is known, for the sake of combating pollution, to add urea to the exhaust gases, in particular for the reduction of nitrogen oxides. . More specifically, the urea is stored in a tank, in diluted form in water, and the additive thus formed is injected into the vehicle exhaust line, at an appropriate point of this line, that is, that is upstream of the catalytic converter in which the reduction of the nitrogen oxides takes place. It is therefore necessary to pump the additive, from the reservoir in which it is stored, in a properly dosed manner, and to inject this additive pumped into the exhaust line, with sufficient pressure. The logical solution here is the addition of a metering pump, located on the additive reservoir or between this reservoir and an additive injector placed on the exhaust line (see for example the patent documents FR 2 879 239 and WO 00/21881). Such a solution involves the implementation of a relatively powerful pump, necessary to pressurize a relatively large volume, for example 15 liters, corresponding to the capacity of the additive reservoir, while the flow rate of additive to be delivered remains very low and should only be injected periodically. Another solution, for removing the pump, is to store the additive in a flexible bag, associated with a device performing a pressurization of the bag, this device may comprise a spring maintained in compression and supported on said pocket to see the document FR 2 870 172 or its equivalent WO 2005/113279, in particular FIG. 2. However, such a system itself can not control the flow rate or the pressure of the additive and, in particular, it not adapt the pressure of the injected additive to the instantaneous needs. As for the amount of additive injected, in other words the dosing function, the addition of a solenoid valve controlled by a computer is necessary at the level of the injector.

In practice, the pressurizing and dosing additive devices, currently used in combination with exhaust systems, comprise a tank containing the additive, a pump (non-metering) for pressurizing this additive, and a dosing means constituted by an electromagnetic injector, which at each received electrical pulse sends a calculated amount of additive. To achieve the dosage, the electromagnetic pulse can be of varying frequency and duration. In such a device, the additive pressure supplied by the pump must be regulated in order to guarantee a good accuracy of the volume of injected additive. The pump, which operates continuously, must therefore be sized on the basis of its largest flow and, when the injector delivers little additive, that is to say when the operating point of the heat engine is low. pollution, the excess of the additive flow must be recycled, which in itself represents a loss of energy. In addition, the current achievements of these devices are such that, to ensure their operation when the vehicle starts in extreme cold, typically at a temperature below -11 ° C which corresponds to the freezing point of the water-urea mixture, it is necessary to provide a sequence of emptying the additive circuit at the stop of the vehicle, and also locally provide heating means in the additive tank and in the pipes. Current achievements do not make it possible to easily solve the problem of controlling the movements of the additive from the reservoir to the injector and also vice versa, in the purge phase, from the injector to the reservoir, and this regardless of the fact that the engine thermal vehicle rotates or does not rotate. Moreover, the volume of additive to be sucked up, corresponding to the volume of the pipe leading to the injector, is inevitably variable depending on the vehicles, and a universal device is thus desirable.

A solution already envisaged (French patent application No. 08.05185 filed on September 22, 2008 in the name of the Applicant) provides, on the additive circuit, a pressurizing member of the additive (member advantageously constituted by a piston mounted slidably in a cylinder) which is connected by a pressure sampling line to the fuel supply duct of the vehicle. Such a pumping device is therefore dependent on the fuel pressure in a pipe, which pressure is itself related to the rotation of the engine, and disappears when the engine is stopped, so that a battery of pressure should be considered. The present invention aims at eliminating the various disadvantages described above, by providing an injection device for an additive product, with pumping means adapted to the operating conditions and requirements, without being dependent on a fuel pressure or the like, these means being also adapted for the purge function, while constituting a relatively simple and economical solution to the problem of pressurizing and dosing the additive.

For this purpose, the subject of the invention is a device for injecting an additive product in the liquid state, such as a mixture of water and urea, into the exhaust system of a motor vehicle. with a heat engine, the additive injection device comprising an additive tank connected by an additive duct to at least one injector placed in the exhaust system, and means for pumping the additive being provided on the additive duct between the additive reservoir and the injector, these means being able to cyclically distribute metered quantities of pressurized additive, the device being essentially characterized by the fact that the pumping means are constituted by a suction and pressure displacement pump, comprising a cylinder, a piston mounted to move in translation in the cylinder and delimiting in this cylinder a pressurizing chamber, an electromechanical motor or actuator coupled to the piston so as to move in translation, and spring means acting on the piston in the direction of the discharge of the additive out of the cylinder, so that actuation of the motor or actuator in one direction causes a recoil of the piston with suction of the additive in the pressurizing chamber from the additive tank and with simultaneous compression of the spring means, while the advance of the piston with discharge of the additive to the injector is carried out under controlled pressure thanks to said spring means.

Thus, the solution proposed by the invention uses motorized pumping means. Advantageously, the motor of the positive displacement pump is here a DC electric motor, which has the advantage of being able to rotate in both directions of rotation, this without difficulty, and to have a high torque at startup, which makes it possible to easily put the spring in compression, and also to release this spring easily.

Such an electric motor is advantageously connected, by means of a gear reduction gear, to a rotating worm mounted along the axis of the cylinder of the pump, and cooperating with the piston shaped nut, or with a nut connected to the piston, the piston and / or the nut being immobilized in rotation. A sealing membrane, of the type that can be unrolled, can be mounted between the piston and the cylinder of the pump in order to seal the pressurizing chamber while taking into account the volume variations of this chamber. According to an important aspect of the invention, the electromechanical drive means is combined with a spring, which in practice is a helical compression spring, mounted within the cylinder of the pump and acting on the piston, on the opposite side to the pressurizing chamber. The displacement of the piston in the direction of suction of the additive product is effected, with the aid of the motor or actuator, whose power must be sufficient to compress the spring and simultaneously ensure the filling of the pressurizing chamber of the pump, this in a short time that is to say in a few seconds, for example in about five seconds. The displacement of the same piston in the opposite direction, for the delivery of the additive in the conduit leading to the injector, is carried out under controlled pressure thanks to the spring, the latter being dimensioned so as to obtain a small variation of effort over the entire stroke of the piston, so that the instantaneous flow rate of the injector varies little on this stroke of the piston. The spring plays, in a way, a role of pressure regulator and flow of the additive during the injection.

In a preferred embodiment of the additive injection device, object of the invention, there is provided on the discharge side of the positive displacement pump, a three-way solenoid valve whose control allows to direct the additive selectively to the injector, or conversely to the reservoir to drain the additive duct. The solenoid valve manages the suction functions of the additive with filling of the pressurizing chamber, the delivery of the additive, and also the emptying of the pipes. The device thus has an additional purge function, performed simply, that is to say a referral of the additive to the reservoir which prevents the blockage of the pipes by the gel of the water-urea mixture. For this function of emptying the additive duct, it is further provided, in combination with the aforementioned solenoid valve, a vent valve placed on the duct near the injector.

The cylinder of the positive displacement pump may comprise heating means, in particular by circulation of a hot fluid in the wall of this cylinder, to the right of the pressurizing chamber; these means provide a local heating of the additive, at the level of the pressurizing chamber defined by the cylinder and the piston of the pump. Advantageously, the aforementioned three-way solenoid valve is integrated in the pump, or contiguous to the cylinder of this pump, and it can also take advantage of the above-mentioned heating means that ensure the thawing of the additive. On the connection between the additive reservoir and the positive displacement pump, there may be inserted an additive auxiliary reservoir in the form of an annular chamber surrounding the cylinder of the pump in the zone provided with the heating means, so that this auxiliary reserve benefits from also the thaw effect. Thanks to these arrangements, the additive injection device is rapidly put into action, even in very cold conditions, with priority heating of the water-urea mixture contained in the pump and in the immediate vicinity, it being understood that the heating means use a fluid, present on the vehicle, whose temperature rise is itself fast, for example diesel on the fuel return line, or a cooling fluid of the heat engine itself heated by heat exchange. The additive auxiliary reserve makes it possible to make the best use of the heat returned by the heat exchanger formed by the heating means thus traversed by a hot fluid. Preferably, this additive auxiliary reserve has a volume substantially equivalent to the amount of additive injected into an operating cycle of the pump, more particularly a filling cycle of the pipe connecting the pump to the injector. In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of examples, some embodiments of this device for injecting an additive product. in the exhaust system of a motor vehicle: Figure 1 is a block diagram of an additive injection device according to the present invention, in a position of the operating cycle; Figure 2 is a diagram similar to Figure 2 but illustrating another position in the operating cycle; Figure 3 and 4 are diagrams similar to the previous ones, and illustrating the operation of the purge device; Figure 5 is a detailed view, in longitudinal section of the positive displacement pump of this device, in a particular embodiment; Figure 6 is a sectional view similar to Figure 5 but showing another position of the positive displacement pump; Figure 7 is a sectional view similar to the previous, showing another embodiment of the positive displacement pump; Referring first to FIGS. 1 to 4, it is very schematically shown a portion of the exhaust line 2 of a motor vehicle with a combustion engine, in particular a diesel engine, line into which a additive with a depolluting function, in particular a mixture of water and urea. The additive is stored in an additive reservoir 3 which is connected, by an additive duct 4, to an additive injector 5 placed on the exhaust line 2. On the additive duct 4 is interposed a suction pump and suction pump, designed to suck the additive stored in the tank 3 and to pressurize this additive, for the purpose of spraying by means of the injector 5 in the exhaust line 2.

The positive displacement pump 6 comprises a pump cylinder 7, in which is slidably mounted a pump piston 8 which divides the cylinder into two chambers. An electromechanical actuator 9 is coupled to the piston 8 so as to move it in translation, in one direction or the other, inside the cylinder 7.

In one of the chambers delimited by the piston 8 inside the cylinder 7 is mounted a helical compression spring 10, which bears on one face of the piston 8 so as to push it towards the right (with reference to the drawing) . The other chamber 11 delimited by the piston 8 and the cylinder 7 constitutes a pressurizing chamber of the additive. The pressurizing chamber 11 is connected to the additive conduit 4 via a three-way solenoid valve 12. Two end-of-travel sensors 13 and 14 are provided on the pump cylinder 7 to detect the arrival of the piston 8 in one or other of its end positions.

Finally, a vent valve 15 is placed on the additive duct 4, close to the additive injector 5.

FIGS. 1 and 2 illustrate the basic operation of the device, that is to say the cycle allowing the injection of additive into the exhaust line 2. More particularly, FIG. 1 shows the suction phase, in which the three-way solenoid valve 12 is controlled so as to put the additive reservoir 3 in communication with the pump 6, more particularly with the pressurizing chamber 11 of this pump. The electromechanical actuator 9 is then activated to move the piston 8 to the left, the piston 8 thus describing a suction stroke, while progressively compressing the spring 10. At the end of the stroke, the pressurizing chamber 11 is filled additive while the spring 10 is compressed to the maximum. The electromechanical actuator 9 is then stopped. Then, the three-way solenoid valve 12 is switched, so as to put the pump 6, more particularly the pressurizing chamber 11, in communication with the section of the additive duct 4 leading to the injector 5 - see FIG. 2. The electromechanical actuator 9 is then restarted, in the opposite direction, so as to release the piston 8 which, now subjected to the action of the spring 10, describes a discharge stroke (to the right), thereby pressurizing the additive contained in the chamber 11, the pressurized additive being made available in the portion of the additive duct 4 leading to the injector 5. The electromechanical actuator 9 is stopped either after a certain predefined operating time, ie after having described a certain predefined number of revolutions, this actuator 9 being in particular an electric motor with two directions of rotation (as specified hereinafter). The arrival of the pump piston 8 at the end of the discharge stroke, detected by the sensor 14, triggers the start of a new cycle identical to the previous one, with a new switching of the solenoid valve 12 and new suction of the additive in the tank 3, and so on ... Each cycle of operation, the device prepares a constant amount of additive, which corresponds to the displacement of the displacement pump 6, knowing that the stroke of the pump piston 8 is here constant. Moreover, the control system of the additive injector 5 makes it possible to know, by adding the injected unit quantities, the total amount of additive taken from the tank 3, thus also by a simple calculation the instantaneous position of the piston 8 compared to its total stroke. The electronic computer (not shown) which controls the device can then make a correction on the value of the additive pressure, related to the variation of force of the spring 10 on the stroke of the piston 8. Referring now to the following figures 3 and 4, we will describe the purge cycle provided to prevent the risk of blockage in very cold weather and in particular at a temperature below -11 ° C which corresponds to the solidification of the water-urea mixture used. For this, the water-urea mixture is returned to the tank 3, using the same volumetric pump 6. At the shutdown of the vehicle, and according to the outside temperature detected, the three-way solenoid valve 12 is controlled so as to first put the chamber 11 of the pump 6 in communication with the reservoir 3. Thus, the piston 8 is already pushing towards the reservoir 3 the amount of additive that was in the pump 6 at the time of setting stopping the vehicle. Then, the piston 8 having reached the end of the stroke, the solenoid valve 12 is switched which places the chamber 11 of the pump 6 in communication with the section of the duct 4 leading to the injector 5 - see FIG. 3. The actuator 9 is activated so as to move the piston 8 to the left, so that the additive contained in the relevant section of the conduit 4 is sucked by the pump 6, knowing that the valve 15 then allows the entry of air into the conduit 4, replacing the aspired additive.

The actuator 9 is stopped when the piston 8 has reached its recoil end position detected by the sensor 13. Then the solenoid valve 12 is switched and the actuator 9 is restarted in the opposite direction, so as to allow the displacement of the piston 8 to the right, with the aid of the spring 10. The additive previously sucked by the pump 6 is then transferred into the reservoir 3. The emptying is thus performed, by discharging the additive from the conduit 4 to 3. Figures 5 and 6 show, in detail, a part of the additive injection device, in particular the displacement pump 6 and its electromechanical actuator 9, in a particular embodiment, the elements corresponding to those described. previously identified by the same numerical references. The actuator 9 here comprises a direct current electric motor 16, with two directions of rotation, attached to the pump cylinder 7. The output shaft 17 of the electric motor 16 is connected via a gear reduction gear 18 , to a worm 19 rotatably mounted along the axis A of the pump cylinder 7. The worm 19 cooperates with a nut 20 integral with the pump piston 8, the latter being immobilized in rotation relative to the pump cylinder 7. Thus, the rotation of the electric motor 16, in one direction or the other, causes, via the gear 18 and the screw-nut mechanism 19, the axial translation of the piston 7, to the left or to the right, as the worm 19 is screwed or unscrewed in the nut 20, so as to repress or suck the additive. In this embodiment, an expandable flexible sealing membrane 21 is mounted between the pump piston 8 and the pump cylinder 7 to seal at least one side of the pressurizing chamber 11. In the zone of this pressurizing chamber 11, the wall of the pump cylinder 7 is provided with heating means, in the form of a circuit 22 traversed by a sufficiently hot fluid existing in the vehicle concerned, an arrival of this fluid being provided at 23. The fluid in question is, for example, fuel such as gas oil returning to the fuel tank of the vehicle concerned. The circuit 22 produces a heat exchanger which firstly heats the additive contained in the pump 6, in order to obtain a quick reactivation of the injection device of this additive.

Around the zone of the pressurizing chamber 11, there is still provided an annular chamber 24 which constitutes an additive auxiliary reserve, receiving at its inlet 25 the additive supplied from the reservoir 3 via the conduit 4. This annular chamber 24, so the adjoining additive reserve it contains may benefit from the reheating effect resulting from the circulation of a fluid in the circuit 22, since it surrounds this circuit 22. At the output 26 of the annular chamber 24, the optionally heated additive is directed to the three-way solenoid valve, which is here dissociated from the positive displacement pump 6. In a variant, illustrated in Figure 7, the three-way solenoid valve 12 is on the contrary integrated in the positive displacement pump 6, and more particularly placed at the end of the pump cylinder 7 adjacent to the pressurizing chamber 11. Thus, the solenoid valve 12 and the additive it contains may also benefit from the effect heating, obtained by the circulation of a fluid in the circuit 22.

The displacement of the displacement pump 6 will be defined, in each case of practical application, according to the desired autonomous for the device (expressed in kilometers traveled by the vehicle) and the volume of the pipes that are to be drained; for example, 30 cm3 correspond to 30 km traveled. The spring 10 of the positive displacement pump 6 is sized to have a small variation of force over the entire stroke of the piston 8, so that the instantaneous flow rate of the injector 5 varies little. This flow rate is a function of the square root of the pressure, which itself is regulated, for example at a value between 3 and 6 bar, by the spring 10. Finally, it will be noted that in the operation of the injection device of additive previously described, when the vehicle concerned is stopped, the pump 6 can be immobilized either in a position with pressurizing chamber 11 filled with additive, the piston 8 being moved back, or in a position with chamber empty pressure, that is to say with the piston 8 advanced to the end position (right). The choice of the immobilization position depends here on the strategy adopted for heating and thawing of the additive. As is obvious, and as a result of the foregoing, the invention is not limited to the embodiments of this additive injection device which have been described above, as examples ; it embraces, on the contrary, all variants of implementation and application respecting the same principle. In particular, one would not depart from the scope of the invention: - For driving the pump, replacing the DC motor by a motor of another type, such as an electric motor not to not, or any other electromechanical actuator; - By replacing the single three-way solenoid valve by any equivalent means, such as two controlled valves respectively controlling the inlet and the outlet of the pump; - By modifying the detail of the operating sequences; - Realizing the heating of the additive by the circulation of any available fluid, for example the coolant of the engine, or by using electric heating means, in particular of the resistive type; Modifying the detailed forms of the components of the device, for example those of the pump piston, and by sealing around this piston by any appropriate means, such as simple annular seals; - By adjusting the injection pressure of the additive to each particular case of application; - By using the device with any type of additive tank, this tank can be rigid or on the contrary made as a flexible bag; - By targeting the same device to the injection of any kind of liquid additive, for example ceria, in connection with any type of engine and fuel, on all kinds of vehicles.

Claims (11)

REVENDICATIONS1. Device for injecting an additive product in the liquid state, such as a mixture of water and urea, into the exhaust system (2) of a motor vehicle with a heat engine, the device for additive injection comprising an additive tank (3) connected by an additive duct (14) to at least one injector (5) placed in the exhaust system (2) and pumping means (6) of the additive being provided on the additive duct (4) between the additive reservoir (3) and the injector (5), these means (6) being able to cyclically dispense metered quantities of pressurized additive , characterized in that the pumping means are constituted by a positive displacement pump and displacement pump (6) comprising a cylinder (7), a piston (8) mounted to move in translation in the cylinder (7) and delimiting in this cylinder (7). ) a pressurizing chamber (11), a motor (16) or electromechanical actuator (9) coupled to the piston (8) so as to move it in translation, and spring means acting on the piston (9) in the direction of the discharge of the additive out of the cylinder (7), so that the actuation of the motor (16) or actuator (9) in one direction causes a recoil of the piston (8) with aspiration of the additive into the pressurizing chamber from the additive reservoir (3) and with simultaneous compression of the spring means (10), while the advance of the piston (8) with discharge of the additive to the injector (5) is carried out under controlled pressure, by means of said spring means (10). 2. Additive injection device according to claim 1, characterized in that the motor of the positive displacement pump (6) is a direct current electric motor (16) with two directions of rotation. An additive injection device according to claim 2, characterized in that the electric motor (16) is connected by means of a reduction gear (18) to a rotatably mounted worm (19). along the axis (A) of the cylinder (7) of the pump (6), and cooperating with the piston (8) shaped as a nut, or with a nut (20) connected to the piston (8), the piston (8) and / or the nut (20) being immobilized in rotation. 4. An additive injection device according to any one of claims 1 to 3, characterized in that a sealing membrane (21), of unrollable type, is mounted between the piston (8) and the cylinder (7). ) of the pump (6) to seal the pressurizing chamber (11) while taking into account the volume variations of this chamber (11). 5. Additive injection device according to any one of claims 1 to 4, characterized in that the spring means, acting on the piston (8) in the direction of the discharge of the additive out of the cylinder (7). ), are constituted by a helical compression spring (10) mounted inside the cylinder (7) and acting on the piston (8), on the opposite side to the pressurizing chamber (11). Additive injection device according to one of Claims 1 to 5, characterized in that a three-way solenoid valve (12) is provided on the discharge side of the positive displacement pump (6). the control makes it possible to direct the additive selectively towards the injector (5) or vice versa in the tank (3) to drain the additive duct (4). An additive injection device according to claim 6, characterized in that for the drain function of the additive line (4), in combination with the aforementioned solenoid valve (12), a damping valve is provided. in the air (15) placed on this conduit (4) near the injector (5). 8. Additive injection device according to any one of claims 1 to 7, characterized in that the cylinder (7) of the positive displacement pump (6) comprises heating means (22), in particular by circulation of a hot fluid in the wall of this cylinder (7), to the right of the pressurizing chamber (11), these heating means (22) thawing the additive. 9. An additive injection device according to claims 6 and 8, characterized in that the three-way solenoid valve (12) is integrated with the pump (6), or contiguous to the cylinder (7). this pump (6), so as to take advantage of the heating means (12) above. Additive injection device according to Claim 8 or 9, characterized in that, on the connection between the additive reservoir (3) and the positive displacement pump (6), an additive auxiliary reserve ( 24) in the form of an annular chamber surrounding the cylinder (7) of the pump (6) in the zone provided with the heating means (22), so that this auxiliary reserve (24) also benefits from the thaw effect. An additive injection device according to claim 10, characterized in that the auxiliary additive reservoir (24) has a volume substantially equivalent to the amount of additive injected into an operating cycle of the pump (6). , more particularly a filling cycle of the pipe connecting the pump (6) to the injector (5).