Method for assessing a mode of operation of an injection valve in the event of an activation voltage being applied, and corresponding evaluation device

p0001The invention relates to a method for evaluating an operation of an injection valve when a drive voltage is applied. The invention further relates to an evaluation device for evaluating an operation of an injection valve when a drive voltage is applied.

p0002The <patcit id="pcit0001" dnum="DE102006013166"><text>DE 102006013166</text></patcit> Describes a method and a control device for determining an opening voltage of an injector with a piezoactuator. In this case, the opening of the injector is determined by interrupting the current supply at a holding voltage and subsequently measuring a voltage change applied to the piezoelectric actuator and comparing it with a comparison voltage rise.

p0003Further, the <patcit id="pcit0002" dnum="EP1146216A"><text>EP 1146 216 A</text></patcit> A method for controlling the exhaust gas temperature. For this purpose, an engine operating parameter target value is calculated from the air-fuel ratio and the rotational speed. Starting from this engine operating parameter target value, a positional conductance value for an actuator, in particular a throttle valve, is calculated.

p0004An injection valve, for example a common-rail injector (CRI), often has at least one actuator. The at least one actuator can, for example, be a piezoactuator. For injection of a fuel into an internal combustion engine, a drive voltage is applied to the at least one actuator in this case. The at least one actuator then undergoes an expansion due to the applied drive voltage and, at the same time, exerts a pressure on a shifting chain which is arranged on the at least one actuator and has, for example, a hydraulic coupler. A shift valve arranged behind the shift chain, possibly a hydraulic servovalve, is moved into an opening position in this way. When the switching valve is in its opening position, the fuel from the fuel tank can flow into the internal combustion engine.

p0005For precise metering of the fuel injected into the internal combustion engine, the control voltage should be selected in such a way that the switching valve is displaced into its opening position with a defined force excess. It must be taken into account here that the control voltage for shifting the switching valve into its opening position is dependent on a rail pressure.

p0006Frequently, the control voltage during injector manufacture is determined individually for each injection valve. A characteristic curve of the drive voltage determined for opening the injection valve as a function of the respective rail pressure is subsequently stored in an injection control device for controlling the injection valve. This is also referred to as an injector-specific voltage matching (ISA).

p0007However, both the at least one actuator and the switching chain are subject to drift during their service life. This also results in a deviation in the drive voltage required for opening the injection valve from the original characteristic curve during the operation of the injection valve in a vehicle.

p0008It is therefore advantageous if during the operation of the injection valve the characteristic curve of the drive voltage necessary to open the injection valve is checked. In particular, this check should be carried out taking account of the respective rail pressure. However, according to the prior art, no possibilities are yet known to carry out this check without a driver's penalty for the driver, for example as a result of noise formation, or a significant influence on the driving behavior of the vehicle.

p0009The invention provides a method with the features of claim 1 and an evaluation device with the features of claim 10.

p0010The method according to the invention is based on the recognition that the number and the volume of the noises generated during an assessment of the functioning of the injection valve when a drive voltage is applied is significantly reduced when the respective drive voltage for a non-torque-forming injection to the at least one actuator of the Injection valve. Such a non-torque-forming injection is often also referred to as post-injection.

p0011On the other hand, in the method according to the invention, there is hardly any noise formation in the case of a non-torque-forming injection. Likewise, the driving behavior of the vehicle during the execution of the method according to the invention is hardly influenced during a journey. The method according to the invention can thus be carried out regularly during a journey without this being connected to a driver's cab by the driver.

p0012Furthermore, the method according to the invention is based on the recognition that a non-torque-forming injection which has already taken place can be detected with a sensor device, which has already been conventionally installed on the vehicle, for determining a fuel content in the exhaust gas tract. Therefore, it is not necessary to provide another sensor device in the internal combustion engine or in the exhaust gas tract for carrying out the method. This saves the cost and the space for a further sensor device. The measured fuel content can be a fuel / air ratio or a quantity of fuel in the exhaust gas tract. The non-torque-forming injection can thus also be detected after an ignition of the fuel in the engine.

p0013It is preferably determined that the application of the drive voltage to the at least one actuator does not cause the injection valve to open if the determined fuel content is less than the comparison value and that the application of the drive voltage to the at least one actuator causes the injection valve to open, Is greater than the comparison value. In this way it is easy to determine whether a drift of the at least one actuator or of the shift chain is present at the injection valve.

p0014In a preferred embodiment of the method, the fuel content in the exhaust gas tract is determined by means of a lambda tail end. Conventionally, almost all vehicles with a weight of more than 1,500 kg are equipped with a lambda probe which is intended to ensure that the given emission limit values ​​are maintained<u>become one</u> Such lambda probe allows reliable detection of a non-torque-forming injection.

p0015Preferably, the application of the drive voltage to the at least one actuator is carried out at a piston position, in which no torque is released when a fuel injected into the engine is burned. In this way, noise generation can be almost completely prevented in carrying out the method.

p0016In a preferred embodiment, the application of the drive voltage to the at least one actuator is performed at a piston position at which the fuel injected into the engine is no longer ignited. This prevents the process from causing combustion noise or heat. This embodiment of the method is therefore particularly suitable for carrying out during a journey.

p0017In addition, a rail pressure can be measured and the functioning of the injection valve can be evaluated as a function of the rail pressure. The method therefore also takes account of the relation between the drive voltage necessary for opening the injection valve and the currently available rail pressure.

p0018In a further development of the method, an output value for the drive voltage is predetermined at the beginning of the method. Such an output value can be, for example, the drive voltage predefined by the manufacturer for the newly produced injection valve at the current rail pressure.

p0019In a preferred development, if the determined fuel content is smaller than the comparison value, the drive voltage is increased by a first predetermined voltage difference, and the method is repeated at least once again in order to determine a drive voltage as a newly determined drive voltage Opening of the injection valve. The method can thus be used not only to determine whether a drift is present on the at least one actuator or on the injection valve's chain. In addition, as soon as such a situation is established, a drive voltage suitable for opening the injection valve can be re-determined.

p0020Likewise, if the determined fuel content is greater than the comparison value, the drive voltage can be reduced by a second predetermined voltage difference, the method can be repeated at least once again, and the smallest drive voltage can then be determined as a newly determined drive voltage; upon application to the at least one actuator An opening of the injection valve is determined. The second voltage difference can be selected to be significantly lower than the first voltage difference. Thus, the smallest control voltage which causes the injection valve to be opened can be determined relatively precisely. The present invention thus makes it possible after an extended operation of an injection valve to newly determine the drive voltage to be applied to the actuator for a safe injection with a minimum tolerance range during the normal driving operation. The drive voltage to be applied to the respective actuator can in this case be newly determined as a function of the rail pressure. The correction values ​​determined can subsequently be stored individually in a correction field.

p0021In a further development of the method, a characteristic curve for an optimum drive voltage as a function of the rail pressure is determined on the basis of the newly determined drive voltage. In the application of the injection valve, a number of empty points are defined which permit a sufficiently clear identification of the actuator. In order to check the installed actuators, the empty points with their drive voltage variations are successively measured in the presence of the corresponding releases, which are, for example, a rail pressure, an exhaust gas temperature or further stationarities. If all empty points of the actuator are measured, the fingerprint thus produced is compared with the minimum voltage requirement values ​​originally stored for this actuator and stored in the characteristic field. These characteristic values ​​are then available for a correction of the charge voltage control of the individual actuators.

p0022The abovementioned advantages of the method according to the invention also apply to a corresponding evaluation device. A drift correction of the actuators mounted on an injection valve can also be carried out by means of this evaluation device, which ensures a perfect functioning of the actuators during the entire operation.

p0023Further possible applications and advantages of the invention are given in the following descriptions of exemplary embodiments, which are illustrated in the drawings. Show it:<dl id="dl0001"><dt>FIG. 1:</dt><dd>FIG. 10 is a flowchart of a first embodiment of the method of judging an operation of an injection valve upon application of a driving voltage; FIG.</dd><dt>FIG. 2:</dt><dd>5 is a flowchart of a second embodiment of the method; and</dd><dt>FIG. 3:</dt><dd>4 shows a schematic structure for illustrating a function of the evaluation device for judging an operation of an injection valve when a drive voltage is applied.</dd></dl>

p0024<figref idrefs="f0001">FIG</figref> 10 is a flowchart showing a first embodiment of the method for judging an operation of an injection valve upon application of a driving voltage.

p0025Before a real start of the process, a comparison value R0 for a fuel content in an exhaust gas tract is specified (step SO). The comparison value R0 is, for example, a fuel quantity or a fuel / air ratio. In this case, the comparison value R0 corresponds to a fuel content in the exhaust gas tract after a non-torque-forming injection of fuel into the associated internal combustion engine.

p0026Preferably, the step S0 is executed by the manufacturer before the injection valve is put into operation. The single-point valve is then installed in a vehicle.

p0027In a step S1, a drive voltage U for a non-torque-forming injection is applied to the at least one actuator of the injection valve, for example during a travel of the vehicle. In a preferred embodiment, the at least one actuator is a piezoactuator. The application of the control voltage U is effected, for example, in the case of a piston position in which no torque is released when a fuel which is injected into the engine is burnt. Advantageously, the piston position can be selected in such a way that a fuel which is possibly injected into the engine is no longer ignited.

p0028The control voltage U is, for example, the drive voltage predetermined by the manufacturer of the injection valve at the currently present rail pressure p. In addition, the control voltage U can also be selected with regard to a current exhaust gas temperature.

p0029In a further step S2, a fuel content R (U) in the exhaust gas tract is determined after the application of the control voltage U to the at least one actuator. The fuel content R (U) can be, for example, a fuel quantity or an air / fuel ratio in the exhaust gas tract.

p0030Subsequently, the fuel content R (U) is compared with the comparison value R0 in step S3. In this way, it is to be determined whether, when the drive voltage U is applied to the at least one actuator, the injection valve is opened and a fuel is injected into the internal combustion engine.

p0031If the measured fuel content R (U) is smaller than the comparison value R0, it is determined in step S4 that the application of the control voltage U to the at least one actuator does not cause the injection valve to open. If the injection valve is not opened when the drive voltage U is applied, this indicates a probable drift of the at least one actuator or of the switching chain. In this case, it is necessary to newly determine the drive voltage U required for opening the injection valve so that the desired injection quantities are reliably maintained during further operation of the injection valve. A corresponding message is then output.

p0032If the measured fuel content R (U) is above the comparison value R0, the application of the drive voltage U to the actuator causes the injection valve to be opened and thus an injection of fuel into the internal combustion engine. This is determined in step S5. A corresponding message is also output in this case.

p0033<figref idrefs="f0002">FIG</figref> 14 is a flowchart showing a second embodiment of the method of judging an operation of an injection valve upon application of a driving voltage.

p0034In a step S10 preceding the method, an output drive voltage U0, a voltage difference ΔU and the previously described comparison value R0 for a fuel content in the exhaust gas tract are specified. In a preferred embodiment, this step S10 is executed by the manufacturer of the injection valve before its commissioning.

p0035The output drive voltage U0 is, for example, a drive voltage suitable for opening the new injection valve, which is determined by the manufacturer specifically for this injection valve. The voltage difference ΔU will be discussed in more detail below.

p0036During a journey of the vehicle, the method is started in a step Sla to examine the at least one actuator and the injection valve's chain for a possible drift. A current rail pressure p is measured. Depending on the current rail pressure p, a drive voltage U is selected from the provided output drive voltages U0 (step S11).

p0037In a further step S12, the control voltage U for a non-torque-forming injection is applied to the at least one actuator of the injection valve. It is particularly advantageous if the control voltage U is applied to the at least one actuator of the injection valve only when the pistons are in a position in which a fuel which is possibly injected into the engine is no longer ignited. A possible injection of fuel into the engine thus hardly influences the functioning of the engine. Possible noise changes, such as engine noise or combustion noises, are avoided during injection initiated as a post-injection. Likewise, no torque change is caused, which is why the method is also applicable during the normal driving operation.

p0038In a subsequent step S13, a fuel content R (U), for example a fuel quantity or a fuel / air ratio, is determined in the exhaust gas tract. In a preferred embodiment, the fuel content R (U) is determined by measuring the air / fuel ratio in the exhaust gas tract by means of the Lambda probe end and then evaluating it with the measured value of an air quantity meter installed within the air supply. Since the air flow meter and the lambda probe are conventionally already installed in many vehicles, this embodiment of step S13 can be carried out without an additional sensor having to be installed on the vehicle.

p0039In a further step S14, the determined fuel content R (U) is compared with the comparison value R0. If the fuel content R (U) is smaller than the comparison value R0, it is determined that the injection valve is not opened when the drive voltage U is applied to the at least one actuator. This indicates a drift of the at least one actuator or the shift chain of the injection valve. It is therefore advantageous if the control voltage U for opening the injection valve is newly determined in this situation.

p0040In a subsequent method step S15, the drive voltage U is increased by the voltage difference ΔU. Subsequently, the process steps S12 to S14 for the newly determined drive voltage U are carried out again. If again the determined fuel content R (U) is below the comparison value R0, the process steps S15 and S12 to S14 are repeated. This takes place until a fuel content R (U) is determined, which is above the comparison value R0.

p0041With a fuel content R (U) above the comparison value R0, it is determined that when the control voltage U is applied to the at least one actuator, the injection valve is opened (in <figref idrefs="f0002">FIG</figref> But not shown). In a further method step S16, the smallest drive voltage U at which a fuel content R (U) is determined to be greater than the comparison value R0 is then determined as a newly determined drive voltage Un (p). A fingerprint for the respective drift of the at least one actuator and / or the switching chain can subsequently be determined on the basis of this newly determined drive voltage Un (p). Subsequently, a new characteristic curve for a suitable drive voltage U for opening the switching valve can be defined based on the respective rail pressure p using this fingerprint.

p0042In a further development of the method, after the step S14, if the measured fuel content is greater than the comparison value R0, the drive voltage U can be reduced by a predetermined minimum voltage difference. The minimum voltage difference is preferably significantly smaller than the voltage difference ΔU. Steps S12 to S14 are then carried out until a fuel content R (U) is measured again under the comparison value R0. In this way, the smallest drive voltage U can be determined in which just a fuel content R (U) is determined above the comparison value R0. Such an iteration step may be performed to establish an even more accurate drive voltage Un (p). The newly determined drive voltage Un (p) can subsequently be evaluated and / or used to operate the injection valve, as described above. However, it is also possible to dispense with such an iterative step for more precisely determining the new-determined drive voltage Un (p), by specifying a relatively small voltage difference ΔU.

p0043As an alternative to the fuel / air ratio, the fuel content can also be determined as the air / fuel ratio. In this case, opening of the injection valve can be ascertained, provided the air / fuel ratio determined is less than a predetermined comparison value. A non-opening of the injection valve, despite the application of a drive voltage, is then determined if the determined air / fuel ratio is greater than a predetermined comparison value. In the<figref idrefs="f0001">FIG</figref> and <figref idrefs="f0002">2</figref> But this is not shown.

p0044<figref idrefs="f0003">FIG</figref> Shows a schematic structure for illustrating a function of the evaluation device for judging an operation of an injection valve when a drive voltage is applied to an actuator of the injection valve.

p0045The injection valve 10 to be examined is arranged between a fuel tank 12 and a combustion engine 14. When the injection valve 10 is opened, a fuel from the fuel tank 12 is injected into the internal combustion engine 14.

p0046The internal combustion engine 14 is also connected to an air supply 16. An air flow meter 18 is arranged within the air feed 16 and measures the air quantity filled into the internal combustion engine 14 and provides a corresponding first sensor signal 20.

p0047Furthermore, the internal combustion engine 14 has an outlet to an exhaust gas tract 22. A lambda sensor 24 is arranged within the exhaust gas tract 22. The lambda sensor 24 is designed to determine a fuel / air ratio in the exhaust gas tract 22 and to provide a corresponding second sensor signal 26.

p0048In addition, an engine sensor system 28 is arranged on the internal combustion engine 14, with which a piston position can be determined. A third sensor signal 30 provided by the motor sensor system 28 includes the angle after the upper dead point and is output to an injection controller 32.

p0049The injection control device 32, after receiving the third sensor signal 30 with the angle after the upper dead point, is designed by the motor sensor system 28 to control the injection valve 10 by means of a voltage signal applied to at least one actuator (not shown) in such a way that the injection valve 10, A certain angle after the upper dead point 30 is opened or closed.

p0050The mode of operation of an evaluation device 36 for judging an operation of the injection valve 10 when a drive voltage U is applied is explained below:<ul><li>The evaluation device 36 receives a fourth sensor signal 40 with a rail pressure p determined by a vehicle-specific pressure sensor 38 via a receiving device 36a. An output device 36b of the evaluation device 36 then outputs a control voltage U corresponding to the rail pressure p as control signal 42 to the injection control device 32. The injection control device 32 is controlled by the control signal 42 in such a way that it applies a voltage signal 34 corresponding to the control voltage U for a non-torque-forming injection to the actuator of the injection valve 10. For example, the injection control device 32 waits for an angle after the upper dead point at which a fuel injected into the internal combustion engine 14 is no longer ignited.</li></ul>

p0051In an alternative embodiment, the motor sensor system 28 can also output the third sensor signal 30 with the ascertained angles after the upper dead point 30 to the evaluation device 36. In this case, the evaluation device 36 outputs the control signal 42 to the injection control device 32 only at a certain angle after the upper dead point.

p0052The evaluation device 36 receives from the lambda sensor 24 the second sensor signal 26 with the measured air-fuel ratio in the combustion train 22. In addition, the evaluation device 36 receives from the air-volume meter 18 the first sensor signal 20 with the air quantity filled in the internal combustion engine 14. A comparison device 36c of the evaluation device 36 then uses this data to determine the amount of fuel filled into the internal combustion engine 14. Subsequently, the calculated fuel quantity is compared with a comparison value R0. If the fuel quantity injected into the internal combustion engine 14 is above the comparison value R0, the evaluation device 36 recognizes that the injection valve 10 is opened to the at least one actuator when the respective drive voltage U is applied.

p0053If, however, the calculated fuel quantity is smaller than the comparison value R0, the evaluation device 36 recognizes that the application of the control voltage U to the at least one actuator of the injection valve does not cause the injection valve 10 to open. The respective control voltage U is thus unsuitable for opening the injection valve 10. If this control voltage U corresponds to the value prescribed by the manufacturer for the new injection valve 10, then a drift of the at least one actuator and / or the shift chain is present.

p0054Furthermore, the minimum required voltage requirement can be repeated by the evaluation device 36, in that the described measuring method is repeated with changed drive voltages U. The minimum required drive voltage U for an injection, determined in this way, is subsequently stored in individual individual cylinders in characteristic fields and is thus available for the drift compensation of the actuators.