FR3085425A1 - Method for releasing the tightening of an electromagnetic metering valve - Google Patents

Abstract

Title: Method for releasing the jamming of an electromagnetic metering valve Method (100) for releasing the jamming of the electromagnetic metering valve of a metering system for metering a urea solution, for an SCR catalyst in the exhaust gas channel exhaust from an internal combustion engine. According to the method, the metering valve is actuated by a predefined pressure with the urea solution (120). Figure 1

Description

Description

Title of the invention: Method for releasing the clamping of an electromagnetic metering valve

FIELD OF THE INVENTION The present invention relates to a method for releasing the tightening of an electromagnetic metering valve as well as a computer program for implementing the method and a memory medium readable by a machine and containing the program as well as an electronic control device for the execution of the program.

STATE OF THE ART In the field of automotive technology, SCR catalyst systems are known (that is to say catalysts applying selective catalytic reduction) to reduce nitrogen oxides by injecting (metering) a aqueous urea solution (HWL) also called urea solution. The future regulations for protection against harmful emissions require monitoring of the quality of the HWL urea solution using a urea quality sensor, in particular to detect a possible faulty filling of the tank by the driver. These regulatory requirements concerning the accuracy of quality monitoring correspond to an accuracy of the measurements made by the sensor which is ± 1% of the mass fraction of urea in the HWL urea solution. The target value for the urea content of an HWL urea solution is typically 32.5%.

The dosing of the HWL urea solution by the dosing module is done using a needle valve. This needle is continuously monitored to ensure that the dosing module is working properly.

The urea solution known under the name adBlue® (AUS32) which is used in DNOX systems to denitrify the exhaust gases from internal combustion engines crystallizes at around -11 ° C. To avoid damage caused by freezing of the system and its components, the urea solution is drawn back into the tank when the engine is stopped. The re-aspiration of the urea solution concerns in particular the injection valve of the dosing module. But there is still a small amount left in the injector. According to the state of the art, this residue is immediately aspirated after the engine has stopped. As the metering module is installed in the exhaust gas system, it is heated by the heat accumulated in the exhaust gas installation. The heat released which is thus supplied to the dosing module is all the higher as the engine load has been high during the movement of the vehicle (warm stop). In the case of a dosing needle

DNOX which is blocked, it is mainly assumed that after the engine has stopped and the emptying / rebreathing phase, there remains in the metering valve, a residual quantity of urea solution between the valve needle and the interval of guidance, that is to say at the level of the valve stroke. However, due to the significant calorific contribution by the installation of exhaust gases after stopping, this residual quantity of liquid is transformed into solid crystals of urea whose development inside the injector can block the valve needle, so that on the next restart, there will be no injection.

The problems associated with valve needles blocked in the context of denitrification of smoke (DNOX) both for commercial vehicles and for passenger vehicles have been known for a long time. But, as until now it has not been possible to know exactly the reasons which thus produce a permanent blockage of the valve needle, it is necessary to definitively resolve these problems. The procedure for releasing the valve needle as it has been used to date by heating it by the coil has not always been successful. Only increasing the calorific intake by raising the temperature and increasing the duration of application of the electric current does not translate into a significant improvement insofar as only the heating duration fixed by the regulations concerning the heating system is respected. surveillance.

According to the state of the art, the metering valve is operated without pressure and without liquid to monitor it and diagnose the movement of the valve before the pressure is applied. For this purpose, using the evolution of the current in the metering valve, we expect a variation in inductance when the valve arrives against its mechanical stop. The start of injection determined by this procedure, i.e. the start of injection BIP (English name) and the associated BIP imprint, are used to determine if the movement of the valve needle corresponds to a sufficient BIP quality and that the valve is thus functional or, conversely, the valve is blocked.

If the BIP footprint is not sufficient, the DNOX system begins to heat the valve spool to decompose the urea crystals deposited in the valve and allow the valve needle to move again. For this, we supply electric current to the valve coil to heat it and reach a coil temperature of around 110 ° C. During the heating time of the valve which is, for example, of the order of 240 s, the valve is continuously controlled to check and note whether the BIP footprint is sufficient and whether the heating of the valve needle has success.

If at the end of the heating time, the valve is not released or does not move, a fault is recorded in the control unit. This recorded defect prohibits, during the entire driving cycle, a further rise in pressure and thus the metering of the urea solution (AdBlue®) as well as the reduction of nitrogen oxides NOx.

In another SCR catalyst system according to the prior art, the urea solution is measured in the exhaust gas using an electromagnetically controlled valve needle. This metering valve is controlled by a control device. If the valve opens, its current curve exhibits a characteristic bend generated by the counter-inductance of the displaced valve needle. This bend in the current curve is detected by the control unit which transforms it, by calculation, into a numerical value. This value can be used to detect a fault in the metering valve. This means that for a value higher than this, the valve is considered to have switched while for a lower value, it indicates that the valve has not switched and that it is blocked. The imprint of this bend in the current curve is however influenced by certain factors. One of these is the degree of magnetic saturation at the time of opening. This depends on the current level, i.e. the electromagnetic force which produces the movement of the needle. The needle is held against its seat by a spring and by the hydraulic pressure of the urea solution. This force must be overcome by the electromagnet. In the current applications of this fault diagnosis, it is possible, for example, to have a very cold coil which switches and which does not translate sufficiently in the current curve or to be used. The value which is calculated from there is too low even though the metering valve has switched. This results in the risk of wrongly detecting that the valve is blocked. Such a misdiagnosis is particularly likely in the case of cold coils, combined with a high battery voltage as well as high spring forces and / or pressures.

Document DE 10 2011 004 150 A1 describes a method for releasing the tightening of a metering valve from a metering system for the urea solution for an SCR catalyst of an internal combustion engine; according to this method, the clamping is released by adding heat to the metering valve. This heat supply (temperature rise) is done by feeding the electromagnetic coil of the electromagnetic metering valve.

Document DE 10 2007 017 459 A1 describes a thawing process for a metering valve, possibly blocked by the gel and which is intended to observe the metering rate of the urea solution in the gas channel d exhaust from an internal combustion engine. The frozen state of the electromagnetic metering valve is detected by the rise of the current supplying the coil of the metering valve. The rising edge of the current curve is monitored to detect the presence of characteristic variations in intensity produced by the variation in inductance of the magnetic circuit concerned during the movement of the needle of the metering valve.

We can have a deposit of urea crystals of the urea solution. The deposition of urea crystals occurs in particular if the dosing system reaches temperatures above, for example, 100 ° C and if after the SCR system has stopped, there is a determined cooling time. For example, it may happen that after a cooling time of around 0.5 hours, depending on the installation of exhaust gases, crystals of urea are formed. These urea crystals can in particular block or block the metering valve. The metering valve needle (movable needle) may lock in the open, closed or in an intermediate position, which will prevent the correct metering. In this case, because of the defective dosage, the on-board diagnosis records a fault. Document DE 10 2007 011 686 A1 describes a metering valve which doses a reactive agent into the exhaust gas channel of the internal combustion engine. Channels are provided in the valve body to cool the metering valve. These channels are crossed by a refrigerant.

Presentation and advantages of the invention The present invention relates to a method for releasing the blockage of the electromagnetic metering valve of a metering system for a urea solution, for an SCR catalyst in the channel exhaust gas from an internal combustion engine, this process being characterized in that the metering valve is urged by a predefined pressure with the urea solution.

For a utility vehicle, the pressure is preferably between 4.5 bars and 8.5 bars; for a passenger vehicle, this pressure is between 4.5 bars and 11 bars.

It advantageously follows that the urea crystals deposited mainly between the valve needle and the guide gap, that is to say over the stroke of the valve, will be at least partially dissolved thanks to the good migration characteristics of the urea solution (AdBlue®).

According to a preferred embodiment, in addition to loosening by applying to the metering valve the urea solution to release the clamping, applying heat to the metering valve. Loosening or unblocking by adding heat to the metering valve is preferably done before or at the same time as the tightening is released by urging the metering valve with the urea solution. The heat supply to the metering valve is preferably done by heating the coil of the metering valve, by its electrical supply.

This new concept allows motor vehicles to be able to perform in the same driving cycle, the metering with reduction of nitrogen oxides NOx. In addition, repairs and / or replacements of blocked, temporarily defective metering valves are avoided.

According to a preferred development, the metering valve is controlled for a predefined duration and an evaluated value of the BIP footprint is determined using the evolution of the current measured after the start of the predefined duration in the valve. dosing.

The predefined duration is included, preferably between 20 and 30 seconds. The order can be made according to a work report.

The start of the BIP injection determined by this characteristic and the corresponding evaluated value of the BIP imprint are advantageously used to determine whether the movement of the valve needle has a sufficient BIP quality, that is to say - say if the metering valve is working or if the valve needle is blocked.

The control of the valve coil generates a magnetic force exerted on the needle to try to move the needle. This produces an even better advance of the urea solution (AdBlue®) in the intermediate spaces of the valve needle and allows the needle to move.

If the evaluated value of the BIP footprint is less than a predefined threshold, that is to say if there is a blockage of the valve needle, then, according to another preferred development, it is sucked back the urea solution from the metering valve. The aspiration is preferably done cyclically. The re-suction allows the urea crystals already detached from the intermediate spaces in the valve to be evacuated from the metering valve. This accelerates the transformation process of the crystals from their crystalline state to their dissolved state as well as the release of the valve needle.

If the evaluated value of the BIP fingerprint is greater than a predefined threshold, that is to say if there is no tightening or blocking of the valve needle, we can successfully complete the present process.

According to a preferred development, re-aspiration is applied for a period of between 3 and 5 seconds. This period advantageously makes it possible to effectively remove the urea crystals from the metering valve.

According to a preferred development, after rebreathing, the metering valve is again controlled for a predefined period and with the aid of another evolution of the current measured after the start of the operation in the metering valve, another evaluation value of the BIP footprint is determined.

The predefined duration is between approximately 20 and 30 seconds. The order can also be made by a work report or work cycle.

The re-aspiration in connection with the last characteristic cited produces a back and forth movement of the urea solution (AdBlue®), which makes it possible, first of all, to reduce the disturbing air cushion in the valve by a mixing effect so that the fraction of liquid increases slowly in the valve to the furthest urea crystals in the guide interval and whose valve stroke zone causing the dissolution of the urea crystals. After the back and forth movement of the urea solution (AdBlue®), the evaluated value of the BIP footprint is determined again. If the evaluated value is still below the predefined threshold, the process is continued. If the evaluated value is at the predefined threshold, the successful process is terminated.

According to another preferred development, the re-aspiration and control steps of the metering valve are carried out several times to fill the metering valve with the HWL urea solution and the determination of the evaluated value of the BIP imprint; this means that these operations are carried out at least twice successively. The corresponding back and forth movements of the urea solution (AdBlue®) accentuate the mixing effect mentioned above so that the fraction of liquid in the valve progresses further to the most distant urea crystals in the guide interval and in the valve stroke area which results in better dissolution of the urea crystals. According to another development, the steps mentioned above are repeated until the evaluated value of the BIP imprint shows that there is no longer any tightening of the valve.

According to a preferred development, the urea solution is heated before requesting the metering valve. This is preferably done during the filling operations of the metering valve.

Thanks to this characteristic, by activating the heating of the pressure line, an additional calorific supply is produced to the metering valve by the urea solution (AdBlue®). This heating of the HWL urea solution allows better dissolution of the urea crystals.

According to another preferred development, the evolution of the temperature of the metering valve is used for the method of releasing the tightening of the electromagnetic metering valve, for example, by the intensity and the duration of the liberation programs. of the valve needle as described above.

A valve needle release program consists, for example, of filling the metering valve with the urea solution under pressure and then re-aspirating this solution.

This makes it possible to determine the functional relationship between the intensity and the duration of the valve needle release programs described above and the release of the tightening of the valve needle or else the probability of release of the tightening. valve needle.

The regeneration of the diesel particulate filter (DPF filter) carried out in the previous driving cycle with the high temperatures of the exhaust gases which then occur, as well as by the high temperatures of the injector existing at the time of l vehicle stop can be used to characterize the intensity and duration of the valve needle release programs described above. The temperature of the exhaust gases is in particular between 600 ° C and 800 ° C. The maximum temperature applied to the valve is in particular between 90 ° C and 190 ° C.

According to a preferred development, if the metering valve is tightened or blocked in the open state, then the process is terminated. This characteristic is related to the risks of a valve blocked in the open position. The reason is that a valve needle is blocked in the closed or open state. If the valve needle is blocked in the open state, i.e. if the tip of the valve needle is pushed against the valve seat by the valve spring, then when filling the valve valve with the urea solution (Adblue®) the liquid cannot reach the exhaust gas installation. But if the valve needle is blocked in the open position, i.e. if the tip of the valve needle is not pushed against the valve seat, for example in the case of the valve spring broken or if there are particles between the tip of the valve needle and the valve seat, then when filling the valve with urea solution (Adblue®) large quantities of liquid arrive in the installation. exhaust gases and cause a slip of ammonia / NH3 with the consequence, poisoning, which this characteristic of the invention avoids.

If the evaluated value of the BIP footprint which was determined in the previous driving cycle, after the shutdown of the internal combustion engine equipped with the SCR catalyst metering system, is less than a predefined value, then, according to a preferred embodiment, the process is stopped. The BIP footprint is preferably determined directly after the internal combustion engine has been switched off. Preferably, the movement of the control needle is controlled 2 to 3 times.

If the evaluated value of the BIP footprint is greater than the predefined value, it can be assumed with a very high probability that, in the following driving cycle, the tight valve is blocked in the closed position. If, immediately after stopping the internal combustion engine, for example, due to a valve spring break, you can no longer detect a BEEP, you no longer carry out the valve needle release program to a valve tightened, in the following circulation cycle because, in this case, there is a risk of poisoning.

This characteristic minimizes the risk of poisoning mentioned above.

According to another preferred development, the process is stopped if the power or the measured speed of the transfer pump of the urea solution HWL is greater than a power or a predefined speed of the transfer pump of the urea solution HWL .

Insofar as the metering valve remains blocked in the open position, the transfer pump must apply, at constant pressure, a transfer power considerably higher than if the valve was blocked in the closed position and for the same pressure. It is thus possible to use the power or the speed of the transfer pump as a decision criterion for judging whether the valve is blocked in the open position or in the closed position. This means that as soon as the speed of the transfer pump for the pressure in the system is above the normal threshold, i.e. at a predefined value, it must be assumed that the metering valve is blocked in the open position and if necessary, restrictions must be launched during the rest of the release process.

This monitoring of the power or the speed of the transfer pump is advantageously done to detect the valve blocked in the open position.

The computer program is designed to execute the steps of the process, in particular when the program is applied by an electronic control device or a computer. This allows the process to be implemented in a conventional control device without having to make constructive changes. The computer program is, for this purpose, stored in a memory readable by a machine. By executing the computer program with a conventional electronic control device, one obtains an electronic control device designed to perform a method of releasing the tightening of an electromagnetically actuated metering valve.

Presentation of the drawing The present invention will be described below, in more detail using an embodiment of the method shown in the accompanying drawing in which: [fig-1] diagram of the flowchart of an embodiment of the method of the invention.

Description of the embodiment of the invention The method 100 according to Figure 1 for releasing the tightening (blocking) of an electromagnetic metering valve begins at step 102 by an interrogation to know if the user activated the ignition of the motor vehicle. For this, the electrical signal is interrogated on the particular terminal (generally called terminal 15) of the ignition key. If this is not the case, the method returns to step 102. If this is the case, the method continues with step 104. In this one, it is checked whether an evaluation value of the BIP fingerprint has been determined for an internal combustion engine fitted with an SCR catalyst dosing system after the previous driving cycle has been stopped, to determine whether this value is less than a predefined value.

If the query receives a positive response, the process continues with step 144 in which the process is stopped and a fault message is issued. The fault message thus issued indicates that the dosing module is locked in the open position and that the driver of the vehicle must go to a workshop. If the request in step 104 receives a negative response, the process continues with step 106.

The figure uses a check mark for the positive response to an interrogation and a cross for the negative response to an interrogation.

In step 106, the metering valve is controlled for three dry cycles. For a usual control frequency of 3.33 Hz, for the dosing mode, in the field of commercial and passenger vehicles, this gives a control duration of about 1 second.

A dry cycle means that the valve was ordered in an extremely short manner without HWL urea solution to determine BIP, the tip of the valve arriving dry on the valve seat.

In the following step 108, the evaluated value of the BIP fingerprint is determined. In the next step 110, it is asked whether the evaluated value of the BIP footprint is less than a predefined threshold. If this is the case, the method continues with step 112. If this is not the case, the method continues with steps 140 and 141; in step 140, the transfer pump is operated with the usual pump parameters to fill the metering valve at the usual high pressure with the urea solution (Adblue®); in step 141, the HWL urea solution is measured in the exhaust gas line. Then the method 100 is terminated to release the tightening or blockage of the electromagnetic metering valve and a message is sent indicating that the metering valve is operating correctly.

In step 112, the metering valve is heated for 240 seconds at a temperature of 110 ° C. In the next step 114, the metering valve is controlled for 25 seconds. In the following step 116, the evaluated value of the BIP fingerprint is again determined. In the next step 118, it is asked whether the evaluated value of the BIP footprint is less than the predefined threshold. If this is the case, the method continues with step 120. If this is not the case, the method continues with steps 140 and 141 as mentioned above.

In step 120, the metering valve is heated for 240 seconds at a temperature of 110 ° C. and at the same time the transfer pump is operated with the parameters according to which the pump usually fills the metering valve under high pressure. pressure with urea solution (AdBlue®).

During the time of step 120, in step 122, the question is asked whether the speed of rotation of the transfer pump of the urea solution HWL is greater than the predefined speed of the transfer pump of the urea solution HWL . If this is the case, the process continues with step 124. If this is not the case, the process continues with step 144.

In step 124, we ask if the system pressure is lower than a predefined pressure. If this is the case, the process continues with step 144; if this is not the case, the process continues with step 126.

If the request made in step 122 constantly receives a negative response, the process continues with the dough 126 at the end of the time required in step 120.

In step 126, the metering valve is controlled again for 25 seconds. In the next step 128, an evaluated value of the BIP footprint is determined. In the following step 130, it is checked whether the evaluated value of the BIP footprint is less than a predefined threshold. If this is the case, the method continues with step 132. If this is not the case, the method continues with steps 140 and 141 mentioned above.

In step 132, the HWL urea solution is aspirated for a period of 4 seconds in the metering valve.

In step 134, the number of times that the metering valve for the current test for releasing the tightening of the metering valve is determined, that is to say in the current driving cycle, has already been used with strong pressure. In the next step 136, it is asked if the determined number is greater than the predefined threshold. If this is the case, the process continues with step 144. If this is not the case, the process returns to step 112.

Using another exemplary embodiment which uses several analogous blocks, the method will be explained in a simple manner. This variant of the method comprises the following blocks: first block in which the signal from terminal 15 is awaited, a second block which gives the BIP determination of the previous cycle, a third block which presents a BIP determination of the current cycle, a fourth block in wherein the metering valve is controlled with valve heating and a BIP determination, a fifth block in which the metering valve is controlled with valve heating and application of pressure by the HWL solution and a BIP determination and a sixth block in which we suck up and repeat the process.

The first block corresponds to step 102 of the embodiment of Figure 1. The second block corresponds to step 104 of the embodiment of Figure 1. The third, the fourth and the fifth blocks are analogous for the process and differ only in different values. The process flow according to blocks 3-5 is described in sufficient detail. The sixth block corresponds to steps 132-136 of the exemplary embodiment of FIG. 1.

Blocks 3 to 5 each have four stages. In the first step, the metering valve is controlled. Thus, in the third block, the metering valve is controlled without there being heating of the valve coil or application of the HWL urea solution. There are two to four controls of the metering valve. In the fourth block, the metering valve is only subjected to valve heating. This is preferably done 240 seconds. In the fifth block, the metering valve is controlled with a single stress by the HWL urea solution. This is preferably done for 25 seconds.

In a second step of blocks 3-5, BIP is determined. In a third step of blocks 3-5, it is asked whether the number of evaluations of the BIP footprint is less than a predefined threshold. If this is not the case, we continue with steps 140 and 141 as in the embodiment of FIG. 1. If this is the case, the process continues with four steps in which we have an interrogation depending on the number blocks. For block 3, it is asked whether 2 to 4 metering valve commands have already been carried out. In block 4, we ask if the 240 seconds mentioned above have passed. In block 5 we ask if the above 25 seconds have ended.

Claims (1)

Claims [Claim 1] Method (100) for releasing the blockage of the electromagnetic metering valve of a metering system for metering a urea solution, for an SCR catalyst, in the exhaust gas channel of an internal combustion engine, method characterized in that the metering valve is urged by a predefined pressure with the urea solution (120). [Claim 2] Method (100) according to claim 1, characterized in that in addition to releasing the clamp by urging the metering valve with the urea solution, the clamp is released by supplying heat to the metering valve (112, 120). [Claim 3] Method (100) according to claim 1 or 2, characterized in that the metering valve is controlled (106, 114, 126) for a predefined duration and using the current curve in the metering valve, measured after the start of the predefined duration, an evaluation value of the BIP imprint (108, 116, 128). [Claim 4] Method (100) according to claim 3, characterized in that if the evaluated value of the BIP footprint is less than a predefined threshold, the urea solution is aspirated (132) from the metering valve. [Claim 5] Method (100) according to claim 4, characterized in that it is sucked in (132) for a period of between 3 and 5 seconds. [Claim 6] Method (100) according to claim 4 or 5, characterized in that after the rebreathing (132), the metering valve is again controlled (106) for a predefined duration and using the evolution of the current in the metering valve after the beginning of the predefined duration, it is determined (108 ) another evaluated value of the BIP footprint. [Claim 7] Method (100) according to one of the preceding claims, characterized in that the evolution of the temperature of the metering valve is used to characterize the present method of releasing the tightening of the electromagnetic metering valve. [Claim 8] Method (100) according to one of the preceding claims, characterized in that the process (100) is terminated (104, 124) if the metering valve locks in the open state. [Claim 9] Method (100) according to one of the preceding claims, characterized in that the process is stopped (104) if the evaluated value of the BIP footprint which was determined in the previous driving cycle after the shutdown of the internal combustion engine equipped with the SCR catalyst metering system, is less than a predefined value. [Claim 10] Method (100) according to claim 8 or 9, characterized in that the method is stopped (122, 124) if the measured power or the speed of rotation of the transfer pump of the urea solution HWL is greater than a predefined power or speed of the transfer pump of the urea solution HWL. [Claim 11] Computer program product comprising program code instructions recorded on a medium readable by a computer and comprising programming means readable by a computer for executing the steps of the method (100) according to any one of claims 1 to 10. 1/1