Method and device for monitoring the actuating function of an actuator

Abstract

Method for monitoring the actuating function of an actuator (3, 4, 6, 7) of an air system of an internal combustion engine, wherein the air system exhibits a flow behavior that depends on a position of the actuator (3, 4, 6, 7), and wherein the flow behavior is observed to monitor the actuating function of the actuator, characterized in that the actuator (3, 4, 6, 7) is controlled at two different times with control commands for two predefined actuating positions, wherein the actuating function is monitored by observing a first flow behavior and a second flow behavior at the two predefined actuating positions of the actuator (3, 4, 6, 7), and wherein a malfunction of the actuating function of the actuator (3, 4, 6, 7) is excluded if the first flow behavior is within a first tolerance range and the second flow behavior is within a second tolerance range.that the actuator is only controlled with the control commands for one of the two predefined positioning positions if exhaust emission requirements are met in that one of the predefined positioning positions, that a malfunction of the actuator function (3, 4, 6, 7) is excluded if the ratio of the first path behavior to the second path behavior is within a ratio tolerance range, and that the first path behavior and the second path behavior are represented by a measured physical quantity of the air system.

Description

[0001] The actuators in the air systems of internal combustion engines are required to adjust defined operating conditions. Only precise adherence to these defined operating conditions ensures compliance with legally required emission limits. Modern internal combustion engines, for example, contain throttle valves, exhaust gas recirculation valves, swirl level adjusters, turbochargers, and various coolers, whose unrestricted control functionality is required.

[0002] Methods for monitoring the actuating function of actuators that are based exclusively on monitoring control deviations of the parameters to be adjusted are generally very inaccurate and in any case only of limited use for monitoring individual components. For example, the actuating function of an actuator can be monitored by observing the process behavior of an air system influenced by the actuator and then evaluating the actuating function of the actuator based on the observed process behavior. However, this only ensures rough monitoring of the actuating functionality of the actuator. Therefore, the monitoring of actuators in the air systems of internal combustion engines is usually carried out using special additional sensors, for example limit switches, position sensors or other displacement sensors. However, this is disadvantageous because the additional sensors are cost-intensive.

[0003] DE 35 09 444 C2 describes a method for controlling an internal combustion engine in which a signal from a throttle angle sensor is compared with the signal from an air flow sensor. The result of this comparison is a correction signal for correcting the throttle angle sensor.

[0004] DE 34 38 428 A1 discloses a method for controlling an internal combustion engine in which the signal from a throttle angle sensor is corrected. In this case, the correction is performed using the signal from a pressure sensor. Disclosure of the invention

[0005] One object of the invention is to provide a method and a device that provide a simple, cost-effective, and at the same time accurate way of monitoring the actuating function of an actuator in an air system. In general, the object of the invention is to improve the methods and devices known from the prior art for monitoring the actuating function of an actuator in an air system.

[0006] The object is achieved by a method for monitoring the actuating function of an actuator of an air system of an internal combustion engine, wherein the air system has a system behavior that is dependent on a position of the actuator, and wherein the system behavior is observed in order to monitor the actuating function of the actuator, characterized in that the actuator is controlled at two different times with control commands for two predefined actuating positions, wherein the actuating function is monitored by observing a first system behavior and a second system behavior at the two predefined actuating positions of the actuator.

[0007] The invention enables improved monitoring of the actuating function of an actuator in an air system, since the evaluation of the system behavior at different actuating positions of the actuator also detects deviations in the actuating functionality of the actuator from the ideal behavior that might otherwise go unnoticed. When evaluating the system behavior with only one actuating position of the actuator, less information is available than with the method according to the invention. By selecting the predefined actuating positions of the actuator, special conditions for the system behavior can be selected under which a malfunction of the actuator can be easily detected. The two predefined actuating positions are advantageously selected such that a malfunction of the actuator is detected.The invention is not limited to using only two predefined actuating positions of the actuator, but the invention also encompasses methods in which three or more predefined actuating positions of the actuator are controlled and three or more system behaviors are observed in each case.

[0008] The actuator is only controlled with the control commands for one of the two predefined control positions if the exhaust gas requirements are essentially met or are met in this one of the predefined control positions. This offers the advantage that exhaust gas requirements can always be met. Specially selected operating points for complying with exhaust gas requirements include, for example, overrunning operation of the internal combustion engine or normal operation of the internal combustion engine. The predefined control positions advantageously correspond to the ideal control positions at certain, predefined operating points of the internal combustion engine. This offers the advantage that the control function can be monitored without interfering with the ideal conditions of the internal combustion engine.A malfunction of the actuator's control function is ruled out if the first process behavior lies within a first tolerance range and the second process behavior lies within a second tolerance range. The two tolerance ranges are predefined and selected, so that if the tolerance ranges are maintained, proper control function of the actuator can be assumed.

[0009] A malfunction of the actuating function of the actuator is ruled out if the ratio of the first process behavior to the second process behavior lies within a ratio value tolerance range. For example, a certain factor can be specified between two process behavior parameters, and correct actuating function of the actuator can be assumed if this factor is maintained. Particularly preferred is a combination of the aforementioned check, which checks whether the first process behavior lies within a first tolerance range and the second process behavior lies within a second tolerance range, with the latter check function, which forms a ratio of the two process behaviors. A combination of these two methods offers a particularly high level of reliability for monitoring the actuating function of an actuator.

[0010] The first and second system behaviors are represented by a measured physical quantity of the air system. Likewise, multiple measured physical quantities of the air system can be used to describe the first and second system behaviors.

[0011] The actuator can be a throttle valve, an exhaust gas recirculation valve, a swirl level adjuster, a turbocharger, or a cooler of the internal combustion engine. The method is not limited to monitoring just one of these actuators. Rather, it is also intended that a plurality of these actuators can be monitored. This can be achieved, for example, by changing only one of the aforementioned actuators between the first predefined position and the second predefined position and observing the respective system behavior. This offers the advantage of eliminating any influence from adjusting the other actuators.

[0012] The measured physical quantity can preferably be the intake pressure, the fresh air mass flow, the pressure in front of a turbocharger turbine or similar measurable physical quantities of the air system.

[0013] The invention offers particular advantages if the actuator is monitored exclusively by observing the system behavior. This eliminates the need for additional sensors on the actuator. This offers the particular advantage that the actuator can be monitored cost-effectively.

[0014] A further independent subject matter of the invention is a device, in particular a control unit for an internal combustion engine, which is designed to carry out one of the methods according to the invention or advantageous methods described above.

[0015] Another independent subject matter of the invention is a computer program with program code for carrying out all steps of such a method when the program is executed in a computer. Short description of the drawings

[0016] An embodiment of the present invention is explained in more detail below with reference to the accompanying drawings. In the drawings: Fig. 1 schematically shows an air system in which a method according to the invention can be used; and Fig. 2 a flowchart of an embodiment of a method according to the invention. Embodiments of the invention

[0017] In Fig. 1 shows an air system, more precisely a combustion chamber 1 of an internal combustion engine with a connected air system. The air system comprises an exhaust tract 2 in which the exhaust pressure P 3 prevails. Exhaust gas is guided via the exhaust tract to the turbine of a turbocharger 3, which generates a boost pressure for the combustion chamber 1. Furthermore, a controllable exhaust gas recirculation valve 4 branches off from the exhaust tract 2. The exhaust gas recirculation valve 4 guides exhaust gas back into an intake tract 5 in which an intake pressure P 22 prevails. In addition to the compressor of the turbocharger 3, a throttle valve 6 and a swirl flap 7 are also arranged in the intake tract, the latter serving to control the air supplied to the combustion chamber 1. Pressure sensors are arranged in the intake tract 5 and in the exhaust tract 2 in order to measure the intake pressure P 22 and the exhaust pressure P 3.Furthermore, the air system is equipped with state-of-the-art sensors to determine, for example, the fresh air mass flow.

[0018] In the following description of the Fig. 2 is referred to in Fig. 1, where like reference numerals designate like parts. Fig. Figure 2 shows a diagram used to describe various preferred embodiments of the invention. The steps performed are similar to one another, with the preferred embodiments differing only in that different parameters are monitored to verify the function of various actuators.

[0019] The first preferred embodiment of the invention relates to the monitoring of the throttle valve 6. The method begins with a step 11. Subsequently, in a step 12, a check is carried out to determine whether the internal combustion engine is at a defined operating point. In this embodiment, it is provided that a check is carried out to determine whether, among other things, the engine speed is within a defined interval. If the check shows that the internal combustion engine is not operating within a desired parameter interval, i.e. is not being operated at the desired operating point, the method ends in a step 13. If, on the other hand, the internal combustion engine is operating at a desired operating point, then following step 12, in a step 14, the exhaust gas recirculation valve 4 is closed and the throttle valve 6 is fully opened. In a step 15, the intake pressure P22 in the intake tract 5 is measured as the first system behavior.Then, in step 16, the throttle valve 6 is closed to a defined ratio of 80%. By closing the throttle valve 6, the intake pressure P22 in the intake tract 5 is lowered and, at the same time, the fresh air mass flow is reduced, since at a lower intake pressure P22 the internal combustion engine also draws less air from the intake tract 5. Subsequently, in a step 17, the intake pressure P22 is measured again. A check is then carried out in a step 18 to determine whether the intake pressure P22 was within a given tolerance range when the throttle valve 6 was in the open position and whether the intake pressure P22 after the throttle valve 6 has closed is within a second tolerance range that does not overlap with the first tolerance range.If the check in step 18 reveals that the conditions specified there are not met, it is determined in step 19 that the actuator, in this example, throttle valve 6, is not functioning correctly. If, however, the check in step 18 reveals that the conditions are met, it is determined in step 21 that the actuating function of the throttle valve 6 actuator is correct. The process then ends in step 22.

[0020] A further preferred embodiment of the invention relates to the monitoring of the exhaust gas recirculation valve 4. This monitoring is analogous to the monitoring of the throttle valve 6 described above. In step 12, the conditions for the correct working pressure are again checked to check the actuating function of the exhaust gas recirculation valve 4. The same conditions apply here as in the exemplary embodiment for monitoring the throttle valve 6 described above. In contrast to the exemplary embodiment described above, however, in the second preferred exemplary embodiment now described, the throttle valve 6 is moved to a defined position and then the exhaust gas recirculation valve 4 is opened (first actuating position) and closed (second actuating position). The intake pressure P22 is again measured in each case.The opening and closing of the exhaust gas recirculation valve 4 and the measuring of the intake pressure P22 occur in steps 14 to 17 analogously to the first exemplary embodiment described above. Again, the actuating function of the exhaust gas recirculation valve 4 is assessed as correct if it is determined in step 18 that the intake pressure P22 in the open position lies within a first given tolerance range and after closing within a second given, non-overlapping tolerance range. Alternatively or additionally, provision can be made to calculate the ratio of the respectively measured intake pressures P22 and to check whether this ratio lies within a specific tolerance range. Furthermore, as an alternative to the procedure described above, the fresh air mass flow with the exhaust gas recirculation valve open and closed can also be used instead of the intake pressure P22.The two previously described embodiments and alternatives utilize the knowledge that the development of the intake pressure P22 and the fresh air mass flow are strongly dependent on the position of the exhaust gas recirculation valve 4 and the throttle valve 6.

[0021] A third preferred embodiment of the invention serves to monitor the actuating function of the swirl flap 7. Such monitoring can be carried out if, again, defined conditions for the operating point of the internal combustion engine are present. Among other things, the engine speed must be within a defined range (step 12). Under these conditions, the exhaust gas recirculation valve 4 is closed and the throttle valve 6 is fully opened. Subsequently, in steps 14 to 17, the swirl flap 7 is fully opened, the air mass flow is recorded, the swirl flap 7 is fully closed, and the air mass flow is recorded a second time. In this way, a first and a second system behavior of the air system is determined for different actuating positions of the swirl flap 7 as the actuator to be monitored.Again, in step 18 and the following steps, the swirl flap 7 is assessed as functional if the air mass flow for the open and closed swirl flap 7 is within defined, non-overlapping tolerance ranges. Alternatively or additionally, the ratio of the air mass flows can be observed. Another option is to measure the intake pressure P22 and evaluate it accordingly.

[0022] In a fourth preferred embodiment, the actuating function of the turbocharger 3 is monitored as an actuator. The system behavior is represented by the pressure P3 upstream of the turbine of the turbocharger 3. Otherwise, the method proceeds analogously to the other preferred embodiments described above, with all other actuators remaining in defined actuating positions, while the turbocharger 3 is controlled with two different defined actuating positions, at each of which the system behavior is observed.

[0023] In a fifth preferred embodiment, the actuating function of an exhaust gas recirculation cooler bypass valve is tested. The actuating function of this valve can be tested with the exhaust gas recirculation flap 4 open and the throttle valve 6 fully open. Again, in steps 14 to 17, the intake pressure P22 is measured with the exhaust gas recirculation cooler bypass valve open and closed, and it is checked whether the measured values ​​are within previously defined tolerance ranges.

[0024] In all preferred embodiments, it is provided that the operating conditions in the air system are only modified in such a way that emissions regulations are still met. Therefore, the method according to the invention only needs to be carried out at specific operating points of the internal combustion engine. A particularly preferred operating point is overrun operation of the internal combustion engine, since this results in low exhaust emissions. The described preferred embodiments represent only a selection, since the invention is generally also suitable for monitoring the control functions of other actuators in the air system.

Claims

[1] Method for monitoring the actuating function of an actuator (3, 4, 6, 7) of an air system of an internal combustion engine, wherein the air system has a system behavior which is dependent on a position of the actuator (3, 4, 6, 7), and wherein the system behavior is observed in order to monitor the actuating function of the actuator, characterized bythat the actuator (3, 4, 6, 7) is controlled at two different times with control commands for two predefined actuating positions, wherein the actuating function is monitored by observing a first system behavior and a second system behavior at the two predefined actuating positions of the actuator (3, 4, 6, 7), and that a malfunction of the actuating function of the actuator (3, 4, 6, 7) is excluded if the first system behavior lies within a first tolerance range and the second system behavior lies within a second tolerance range, that the actuator is only controlled with the control commands for one of the two predefined actuating positions if exhaust gas requirements are met in this one of the predefined actuating positions, that a malfunction of the actuating function of the actuator (3, 4, 6, 7) is excluded,if the ratio of the first path behavior to the second path behavior is within a ratio tolerance range, and that the first path behavior and the second path behavior are represented by a measured physical quantity of the air system. [2] Method according to claim 1, characterized by that the actuator (3, 4, 6, 7) is a throttle valve (6), an exhaust gas recirculation valve (4), a swirl level adjuster (7), a turbocharger (3) or a cooler of the internal combustion engine. [3] Method according to one of the preceding claims, characterized by that the measured physical quantity is an intake pressure, the fresh air mass flow or a pressure in front of a turbine of a turbocharger (3) of the internal combustion engine. [4] Method according to one of the preceding claims, characterized by that the monitoring of the actuator (3, 4, 6, 7) is carried out exclusively by observing the system behavior. [5] Device, in particular control device, which is designed to carry out a method according to one of claims 1 to 4. [6] A computer program comprising program code for performing all the steps of any one of claims 1 to 4 when the program is executed in a computer.

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