EP1561019A1

EP1561019A1 - Method for testing at least three sensors, which detect a measurable variable for an internal combustion engine

Info

Publication number: EP1561019A1
Application number: EP03776812A
Authority: EP
Inventors: Rainer Buck; Andreas Krautter; Dirk Foerstner; Michael Walter; Juergen Sojka; Matthias Stegmaier
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-10-23
Filing date: 2003-10-20
Publication date: 2005-08-10
Also published as: JP2006504113A; JP4490913B2; US7275425B2; WO2004040104A1; US20060137436A1

Abstract

The invention relates to a method for testing at least three sensors (191, 192, 193, 194, 195), which detect a measurable variable for an internal combustion engine (100). A measurement for the sensor signal (S1, S2, S3, S4, S5) of the respective sensor (191, 192, 193, 194, 195) to be tested is compared with a reference signal (M, S1, S2, S3, S4, S5), which is obtained from at least some of the sensor signals (S1, S2, S3, S4, S5) of the sensors (191, 192, 193, 194, 195) to be tested. A sensor (191, 192, 193, 194, 195) is identified as defective by means of a comparison of the measurement for the sensor signal (S1, S2, S3, S4, S5) with the reference signal (M, S1, S2, S3, S4, S5). The reference signal (M, S1, S2, S3, S4, S5) is formed, for example, from a mean value (M) of the measurement of the sensor signals (S1, S2, S3, S4, S5) of at least some of the sensors to be tested (191, 192, 193, 194, 195), whereby the individual sensor signals (S1, S2, S3, S4, S5) can be weighted differently by means of correction factors (K1, K2, K3, K4, K5) during the formation of the mean value. The sensors (191, 192, 193, 194, 195) are for example, temperature sensors or pressure sensors, which can be located in an induction zone (105) of the internal combustion engine (100), in the internal combustion engine (100) itself, in an exhaust gas zone (110) and/or in an exhaust gas post-treatment system (115).

Description

Method for checking at least three sensors that detect a measurement variable in the area of an internal combustion engine

The invention relates to a method for checking at least three sensors, which detect a measured variable in the area of an internal combustion engine, according to the preamble of the independent claim.

In order to comply with exhaust gas limit values, exhaust gas aftertreatment systems are used in internal combustion engines which contain, for example, a catalytic converter, a particle filter or other components suitable for exhaust gas aftertreatment. The components used often only work optimally in a certain temperature range. If the components have storage properties with respect to at least one exhaust gas component, monitoring of the loading condition with the exhaust gas component is generally necessary.

Temperature sensors are used to record the measured variable, which can be arranged both in the intake area, on the internal combustion engine itself and in the exhaust gas area. Pressure sensors, which can be used, for example, to determine the loading state of a particle filter, are used to record the measured variable. The pressure sensors record the pressure difference that occurs at the particle filter, which is a measure of the loading condition. Further

Pressure sensors can be arranged in the intake area of the internal combustion engine.

If a sensor provides a faulty sensor signal, faulty control of the internal combustion engine and the exhaust gas aftertreatment system can occur. The The consequences are increased fuel consumption of the internal combustion engine and increased exhaust gas emissions.

Proper working of the entire device is only ensured if the sensors used provide a reliable sensor signal. From DE 101 12

139 AI, a method for monitoring sensors has become known that detect a measured variable of an internal combustion engine. These can be temperature sensors, pressure sensors or other sensors. The individual sensor signals are compared with a reference signal, which is provided by another sensor, which is itself not included in the diagnosis. The sensor, which is not included in the diagnosis, is arranged at an installation location at which a comparatively low sensor load occurs, such as in the intake area, in which a temperature sensor is exposed to smaller temperature fluctuations than if it were used in the exhaust gas area. By forming the differences between the individual sensor signals of the sensors to be monitored and the reference signal of the sensor and

Faulty sensors are identified by comparisons with predefined threshold values. If no error was detected in the previous method steps, a plausibility test is carried out at the end by forming differences between the sensors to be monitored and comparing them with threshold values.

The invention is based on the object of specifying a method for checking at least three sensors which record a measured variable in the area of an internal combustion engine and which provides a reliable result with a simple checking effort.

The object is achieved by the features specified in the independent claim.

Advantages of the invention

According to the method according to the invention, it is provided that a measure for the sensor signal of the sensor to be checked in each case is compared with a reference signal, that the reference signal is obtained from at least some of the sensor signals of the sensors to be checked and that a sensor is identified as faulty on the basis of a comparison the measure for the sensor signal and the reference signal. The method according to the invention initially has the advantage that all sensors are included in the diagnosis. A further significant advantage is that a faulty sensor can be recognized immediately in the underlying check of at least three sensors with simple comparison operations.

Advantageous further developments and refinements of the method according to the invention result from the dependent claims.

One embodiment provides that the reference signal is formed from an average of a measure of the sensor signals of at least some of the sensors to be checked. The measure enables a very simple provision of the reference signal. An advantageous further development of this embodiment provides that the sensor signals are weighted with a predetermined factor each when averaging. The inclusion of a weighting factor enables the importance and the installation location of the individual sensors to be taken into account.

A simple check is possible in that a sensor is recognized as faulty if the difference between the measure for the sensor signal and the reference signal exceeds a predetermined threshold value.

If the reference signal is falsified by at least one defective sensor, the embodiment that the sensor whose measurement for the sensor signal is furthest from the reference signal is recognized as defective can nevertheless ensure reliable detection of a defective sensor.

A further development of the method according to the invention provides that the check is carried out in a stationary operating state or at a standstill or after a cold start of the internal combustion engine. The development ensures that the sensor signals of the at least three sensors to be checked have at least approximately a stationary value, so that the check leads to a reliable statement. During a standstill or after a cold start of the internal combustion engine, the sensor signals have a value that is predetermined by the ambient conditions. With temperature sensors, the sensor signals will largely reflect the ambient temperature. The measure that the standstill of the internal combustion engine is detected, a timer being provided that is started when a detected standstill and that the check is provided after a predetermined time, ensures that a steady state of the sensor signals when the internal combustion engine is at a standstill also actually exists.

Another measure that ensures that the stationary operating state, the standstill or the cold start of the internal combustion engine is present provides a comparison between a sensor signal of at least one selected sensor, which has a slow rate of change, and a sensor signal of a sensor to be tested. The selected sensor is arranged on a component that has the greatest possible inertia with regard to the sensor signal. A temperature sensor is a component with a high thermal capacity.

A further development of the method according to the invention provides that the sensor signal of a sensor identified as faulty is not taken into account when determining the reference signal. The exclusion of the faulty sensor during further checks ensures that the reference signal is not falsified. Another measure provides that a check is no longer carried out if the number of sensors identified as defective exceeds a predetermined number.

Further advantageous refinements and developments of the method according to the invention result from further dependent claims and from the following description.

drawing

Fig. 1 shows a block diagram of an internal combustion engine and a controller and the

FIGS. 2-5 show flow diagrams of different configurations of a method according to the invention. The internal combustion engine 100 is supplied with fresh air via an intake area 105. The exhaust gases of internal combustion engine 100 pass through an exhaust gas area 110. An exhaust gas aftertreatment system 115 is arranged in exhaust gas area 110. This can be a catalyst and / or a particle filter. Exhaust aftertreatment system 115 may have multiple catalysts for different

Contain pollutants or combinations of at least one catalyst and a particle filter.

Furthermore, a control unit 170 is provided, which contains at least one engine control unit 175 and an exhaust gas aftertreatment control unit 172.

Alternatively, the engine control unit 175 and the exhaust gas aftertreatment control unit 172 can also be arranged separately. The engine control unit 175 applies control signals to a fuel metering system 180. Furthermore, the engine control unit 175 and / or the exhaust gas aftertreatment control unit 172 provide signals for the other unit and / or further control units.

Furthermore, sensors are provided which supply the exhaust gas aftertreatment control unit 172 and the engine control unit 175 with signals. A first sensor 191 provides a sensor signal S1 that characterizes the state of the fresh air. A second sensor

192 provides a sensor signal S2 that characterizes the state of the fuel metering system 180. A third sensor 193 provides a sensor signal S3 that characterizes the state of the exhaust gas upstream of the exhaust gas aftertreatment system 115. A fourth sensor 194 provides a sensor signal S4 that characterizes the state of the exhaust gas aftertreatment system 115. A fifth sensor 195 adjusts

Sensor signal S5 ready, which characterizes the state of the exhaust gases after the exhaust gas aftertreatment system 115. All five sensors 191, 192,

193, 194, 195 record a single measured variable in the area of internal combustion engine 100. The measured variable is, for example, the temperature. Alternatively, the measured variable can be the pressure. Other measured variables such as acceleration or speed are also conceivable.

Depending on the embodiment, all sensors 191, 192, 193,

194, 195 may be provided. In alternative configurations, the minimum number of three sensors or even more than the five sensors 191, 192, 193, 194, 195 shown.

The method according to the invention for checking at least three sensors 191, 192, 193, 194, 195, which detect a measured variable in the area of internal combustion engine 100, works as follows:

On the basis of sensor signals S1, S2, S3, S4, S5, the engine control 175 calculates a control signal to act upon the fuel metering system 180. The fuel metering system 180 then measures the corresponding amount of fuel

Internal combustion engine 100 too. The toxic exhaust gas components formed during the combustion are converted into harmless components in one or more catalysts which are contained in the exhaust gas aftertreatment system 115. A particle filter can be contained in the exhaust gas aftertreatment system 115 to remove the particles contained in the exhaust gas. A catalytic converter works optimally in a certain temperature range. A particle filter is also optimally regenerated in a certain temperature range. The sensors 191, 192, 193, 194, 195 designed as temperature sensors detect the temperature at different points. With these sensors 191, 192, 193, 194, 195, the exhaust gas temperature of the internal combustion engine 100 can be set to a predetermined level

Temperature level or be kept in a predetermined temperature range. The sensors 191, 192, 193, 194, 195 designed as pressure sensors determined the pressures occurring in the intake area 105, on the internal combustion engine 100 and / or in the exhaust gas area 110. For example, the loading condition of the particle filter can be determined on the basis of the pressure difference that occurs. The first sensor 191 arranged in the suction area 105 detects, for example, the air pressure, which can be taken into account when determining the air-fuel mixture.

A check of the correct functioning of the at least three sensors 191, 192, 193, 194, 195 ensures that the internal combustion engine 100 and in particular the exhaust gas aftertreatment system 115 work properly.

FIG. 2 shows a first embodiment according to the invention on the basis of a flow chart. A first query 200 checks whether there are operating states in which a check is possible. Such operating conditions are in particular when the internal combustion engine 100 is in a stationary operating state, when the internal combustion engine 100 is switched off and is at a standstill, or when the internal combustion engine 100 has just been started and is still in the cold start phase.

An advantageous embodiment provides that the standstill of the internal combustion engine 100 is detected. For this purpose, a timer provided emits a signal after a predetermined time has elapsed, and if it occurs, the internal combustion engine 100 can be assumed to be at a standstill for a sufficiently long time. If a starting process of the internal combustion engine 100 occurs after a sufficiently long standstill, one can

Cold start can be accepted.

An advantageous embodiment, which detects a stationary operating state, the standstill and / or the cold start of the internal combustion engine 100, provides that the sensor signal S1, S2, S3, S4, S5 of a selected sensor 191, 192, 193, 194, 195, which has a slow rate of change with which the sensor signal S1, S2, S3, S4, S5 of at least one other sensor 191, 192, 193, 194, 195 is compared. If the sensors 191, 192, 193, 194, 195 are temperature sensors, the sensor signal of the sensor 191, 192, 193, 194, 195 which detects the temperature of the medium which has the greatest heat capacity is used. In the exemplary embodiment shown, it is preferably the second sensor 192 that detects the temperature of the fuel metering system 180. This configuration determines whether the entire device is in a steady state, which is in a steady operating state, the standstill or when the internal combustion engine 100 is cold started. It is irrelevant whether the sensor 191, 192, 193,

194, 195 has a high thermal capacity per se or the medium, the temperature of which is recorded. A stationary operating state, a standstill or a cold start of the internal combustion engine 100 is present when the difference between the sensor signal of the selected sensor 191, 192, 193, 194, 195 and the at least one other sensor 191, 192, 193, 194, 195 is one falls below the predetermined threshold.

A further development of this embodiment provides that the sensor signals of two selected sensors 191, 192, 193, 194, 195, which are slow Have rate of change, are used for comparison. It is sufficient here if at least one difference fulfills the criterion.

After it has been determined in the first query 200 whether such an operating state is present, an average value M of a measure is determined in a first function block 210

Sensor signals S1, S2, S3, S4, S5 of the sensors 191, 192, 193, 194, 195 to be checked are formed. In this exemplary embodiment, the mean value M is the reference signal. A weighting of the individual sensor signals S1, S2, S3, S4, S5 is preferably provided when averaging. The weighting is taken into account with the correction factors K1, K2, K3, K4, K5. With the weighting, it is possible to take into account the importance of the individual sensors 191, 192, 193, 194, 195 and / or the installation location. A significant advantage results in the weighting that the weighting of those sensors 191, 192, 193, 194, 195 can be reduced which, in a stationary operating state, at a standstill or during the cold start of the internal combustion engine 100, have different sensor signals depending on the ambient conditions provide. For example, it could occur that the first sensor 191 detects a different temperature in a sunny weather at the same ambient temperature than when it is cloudy, provided the internal combustion engine 100 is arranged in a motor vehicle. Nevertheless, even in this case there is a stationary operating state, a standstill or a cold start of the internal combustion engine 100, in which the checking according to the invention of the sensors 191, 192, 193, 194, 195 is enabled.

In a subsequent second function block 220, the differences Dn of the individual sensor signals Sn are based on those determined in the first function block 210

Average M determined. In a second query 230, the individual differences Dn are compared with a threshold value SW. The difference Dn that exceeds the threshold value SW leads to the sensor 191, 192, 193, 194, 195, which is likely to be faulty.

An alternative embodiment is shown in FIG. First, the determination of the differences Dn between the individual sensor signals Sn and the mean value M is again provided in the second function block 220. The maximum difference Max Dn is determined in a subsequent third function block 240. In the subsequent third query 250, it is checked whether the determined maximum difference Max Dn exceeds a predetermined threshold SW. If this is the case, this sensor 191, 192, 193, 194, 195 with the maximum difference is likely to be faulty. The advantage of this alternative embodiment is that a faulty sensor 191, 192, 193, 194, 195, the sensor signal S1, S2, S3, S4, S5 of which can falsify the mean value M determined in the first function block 210, does not result in the

Check in the second query 230 too many sensors 191, 192, 193, 194, 195 are erroneously classified as faulty.

A further alternative embodiment is shown in FIG. In this embodiment, the reference signal is obtained from a measure of a sensor signal S1, S2, S3, S4, S5 from a single sensor 191, 192, 193, 194, 195 to be checked. In the simplest case, the reference signal is identical to the sensor signal S1, S2, S3, S4, S5. This case is shown in Figure 4. Furthermore, for reasons of clarity, the exemplary embodiment according to FIG. 4 is shown limited to checking three sensors 191, 192, 193.

The first query 200 already described again detects whether there is an operating state of the internal combustion engine 100 in which monitoring is permitted. If this is the case, then a function difference 510 shows a first difference Dl between the sensor signal S1 of the first sensor 191 and the sensor signal S2 of the second sensor

192 determined. In the subsequent function block 520, a second difference D2 between the sensor signal S1 of the first sensor 191 and the sensor signal S3 of the third sensor 193 is determined.

The subsequent query 530 checks whether the first difference D1 is greater than a first

Threshold value is SW1. If this is the case, a further query 540 checks whether the second difference D2 is greater than a second threshold value SW2. If this is not the case, the first sensor S1 is recognized as faulty in a function block 560. If it is determined in query 540 that the second difference D2 is greater than the second threshold value SW2, then the second sensor S2 is recognized as faulty in a function block 262.

If it is determined in query 530 that the first difference D1 is not greater than the first threshold value SW1, a query 550 checks whether the second difference D2 is greater than the second threshold value SW2. If this is the case, then in one Function block 264 the third sensor S3 recognized as faulty. If the differences D1, D2 are smaller than the threshold values SW1 and SW2, it is recognized in a function block 266 that there is no error.

It is preferably provided that the threshold values SW1 and SW2 assume the same value. However, it can also be provided that the threshold values SW1, SW2 can assume different values.

Another embodiment is shown in FIG. In this embodiment, the reference signal is also obtained from a measure of a sensor signal S1, S2, S3, S4, S5 from a single sensor 191, 192, 193, 194, 195 to be checked. In the simplest case, the reference signal is identical to the sensor signal S1, S2, S3, S4, S5. This case is shown in Figure 5. Furthermore, for reasons of clarity, this exemplary embodiment according to FIG. 5 is also shown limited to the checking of three sensors 191, 192, 193.

The difference between the exemplary embodiment according to FIGS. 4 and 5 lies in the fact that, in the exemplary embodiment according to FIG. 5, the differences D1, D2, D3 are formed between all sensor signals S1, S2, S3. The amount of deviation between the individual sensor signals S1, S2, S3 is determined in each case. Are all

Differences Dl, D2, D3 below a threshold SW1, so are all sensors

51, S2, S3 recognized as error-free. If one of the differences D1, D2, D3 is greater than the threshold value SW1, an error is recognized. The error can not be a sensor Sl,

52, S3 can be assigned. If two differences are greater than the threshold value SW1, then the sensor S1, S2, S3 is recognized as faulty, which in both calculations of the

Differences is used. In this embodiment, an error can not only be recognized, it can also be assigned to a specific sensor S1, S2, S3.

In the first query 200, it is checked again, as in the previous exemplary embodiments, whether a stationary operating state, a standstill or a cold start

Internal combustion engine 100 is present. In a subsequent function block 410, a first difference Dl is formed between the first and second sensor signals S1, S2. As with all the previously described differences, the amount of the difference is preferably also formed here. In a functional block 420, a second difference D2 is formed, which is the amount of the difference between the first and the third Sensor signal S1, S3 corresponds. In a further function block 430, a third difference D3 is formed, which corresponds to the amount of the deviation between the second and third sensor signals S2, S3.

In the subsequent query 440, it is checked whether the difference Dl is greater than that

Threshold is SWl. If this is the case, a query 445 checks whether the second difference D2 is greater than a threshold value SW2. If this is the case, the first sensor 191 is incorrectly recognized in function block 260. If this is not the case, a query 448 checks whether the third difference D3 is greater than a threshold value SW3. If this is the case, the second sensor is in the function block

192 recognized as faulty. If this is not the case, an error is identified in a function block 268 that cannot be assigned.

If it is recognized in query 440 that the difference D1 is not greater than the threshold value SW1, then it is checked in query 450 whether the second difference

D2 is greater than the threshold value SW2. If this is not the case, then fault-free sensors 191, 192, 193 are recognized in function block 266. If this is the case, it is checked in query 455 whether the third difference D3 is greater than the threshold value SW2. If this is the case, the third sensor 193 is recognized as faulty in function block 264. If this is not the case, then in the function block 268

Error detected that cannot be assigned.

Claims

Expectations

1. A method for checking at least three sensors (191, 192, 193, 194, 195) which detect a measurement variable in the area of an internal combustion engine (100), characterized in that a measure for the sensor signal (S1, S2, S3, S4, S5) of the sensor to be checked (191, 192, 193, 194, 195) with a

Reference signal (M, Sl, S2, S3, S4, S5) is compared, that the reference signal (M, Sl, S2, S3, S4, S5) from at least some of the sensor signals (Sl, S2, S3, S4, S5) the sensors to be checked (191, 192, 193, 194, 195) is obtained and that a sensor (191, 192, 193, 194, 195) is recognized as faulty by comparing the measure for the sensor signal (S1, S2, S3 , S4, S5) and the

Reference signal (M, Sl, S2, S3, S4, S5).

2. The method according to claim 1, characterized in that the reference signal (M,

51, S2, S3, S4, S5) from an average (M) of a measure of the sensor signals (S1, S2, S3, S4, S5) of at least some of the sensors (191, 192,

193, 194, 195) is formed.

3. The method according to claim 2, characterized in that the sensor signals (Sl,

52, S3, S4, S5) when averaging, each with a predetermined factor (Kl, K2, K3, K4, K5).

4. The method according to claim 1, characterized in that a sensor (191, 192, 193, 194, 195) is recognized as faulty if the difference (Dn, Dl, D2, D3) between the measure for the sensor signal (Sl, S2, S3, S4, S5) and the reference signal (M, Sl, S2, S3, S4, S5) a predetermined threshold value (SW, SW1, SW2, SW3).

5. The method according to claim 1, characterized in that the sensor (191, 192, 193, 194, 195) is recognized as faulty, the measure of the sensor signal (Sl, S2, S3, S4, S5) furthest from the reference signal ( M, Sl, S2, S3, S4, S5) is removed.

6. The method according to claim 1, characterized in that the reference signal (M, Sl, S2, S3, S4, S5) from a measure of a sensor signal (Sl, S2, S3, S4, S5) of a single sensor to be checked (191, 192, 193, 194, 195) is obtained.

7. The method according to claim 1, characterized in that the check is carried out in a stationary operating state or at a standstill or after a cold start of the internal combustion engine (100).

Method according to Claim 7, characterized in that the standstill of the internal combustion engine (100) is detected, that a timer is provided which is started when a standstill is detected and that the check is provided after a predetermined time has elapsed.

9. The method according to claim 7, characterized in that the stationary operating state, the standstill or the cold start of the internal combustion engine (110) is detected on the basis of a comparison between a sensor signal (S1, S2, S3, S4, S5) of at least one selected sensor (191 , 192, 193, 194, 195), which has a slow rate of change, and a sensor signal (S 1,

S2, S3, S4, S5) of a sensor to be checked (191, 192, 193, 194, 195).

10. The method according to claim 1, characterized in that the sensor signal (S12, S2, S3, S4, S5) of a sensor (191, 192, 193, 194, 195) identified as faulty when determining the reference signal (M, Sl, S2, S3, S4, S5) is not taken into account.

11. The method according to claim 1, characterized in that a check is no longer carried out when the number of sensors identified as defective (191, 192, 193, 194, 195) exceeds a predetermined number.

12. The method according to claim 1, characterized in that the measured variable is a temperature.