Method and device for diagnosing an auxiliary heating function of an air mass sensor

Abstract

Method for diagnosing the functionality of an auxiliary heater (26) in an air mass sensor (2) in an engine system with an internal combustion engine, wherein the auxiliary heater (26) serves to prevent contamination of a sensor area (21), wherein the air mass sensor (2) is configured to communicate an air mass value via a signal line (4) during a sensor operating mode and to activate the auxiliary heater (26) upon detection of a defined state on the signal line (4), comprising the following steps: - Setting (S4) the state of the signal line (4) to the specified state for a predetermined time period (t2) in an auxiliary heating mode; - Acquisition (S3, S5) and transmission of a first temperature reading before entering auxiliary heating mode and a second temperature reading via the signal line after the specified time period (t2) has elapsed; - Detect (S7, S8) the functionality of the auxiliary heater (26) depending on the difference between the first temperature reading and the second temperature reading.

Description

Technical field

[0001] The invention relates to air mass sensors, in particular hot-film air mass sensors, with an auxiliary heater to prevent contamination of a sensor area. The invention further relates to measures for checking the functionality of the auxiliary heater of an air mass sensor. State of the art

[0002] An air mass sensor is used in the engine system of a motor vehicle to measure the mass flow rate of fresh air drawn in by an internal combustion engine. In air-cooled internal combustion engines, the measured air mass flow rate serves as the input parameter for calculating the amount of fuel to be injected.

[0003] A hot-film air mass sensor (HFM sensor) has a heated sensor area positioned within an airflow. Cooling caused by the airflow is compensated for by a supplied heating element, thus maintaining the sensor area at a constant temperature. The required heating element depends on the airflow rate. Alternatively, the cooling effect of the airflow across the sensor membrane can be measured, and the corresponding temperature difference can be used to indicate the airflow rate.

[0004] To keep contaminants away from the sensor area, an auxiliary heater can be provided in the air mass sensor. Such an air mass sensor with a heated sensor area is known from German patent application DE 101 11 840 C2. This auxiliary heater can be operated in such a way that thermal gradient vortices are formed in the area of ​​the auxiliary heater, leading to the deposition of contaminants in the airflow in the area of ​​the auxiliary heater, away from the sensor area. These contaminants can originate, for example, from the ambient air or from oil vapors introduced into the air supply system from a crankcase when the engine is switched off.

[0005] From DE 10 2011 002 502 A1 a method for diagnosing an exhaust gas sensor is also known, in which the cooling behavior of the sensor is analyzed after a heating phase in order to conclude that there is an impermissible thermal inertia, for example due to soot deposits.

[0006] A failure of the auxiliary heater leads to a slow contamination of the sensor area, which can lead to a progressive deterioration of the measurement and ultimately to unusable readings. Disclosure of the invention

[0007] It is a method for performing a diagnosis of an auxiliary heater in an air mass sensor according to claim 1, a device and a motor system according to the dependent claims.

[0008] Further details are specified in the dependent claims.

[0009] According to a first aspect, a method for diagnosing the functionality of an auxiliary heater in an air mass sensor in an engine system with an internal combustion engine is provided, wherein the auxiliary heater serves to prevent contamination of a sensor area. The air mass sensor is configured to communicate an air mass reading via a signal line during sensor operation and to activate the auxiliary heater upon detecting a defined condition on the signal line, with the following steps: - Setting the state of the signal line to the specified state for a predetermined period of time in an auxiliary heating mode; - Capturing and transmitting an initial temperature reading before entering auxiliary heating mode and a second temperature reading via the signal line after the specified time period has elapsed; - Determining the functionality of the auxiliary heater depending on the difference between the first temperature reading and the second temperature reading.

[0010] The auxiliary heater in the air mass sensor is typically activated by a signal level on the signal line, as determined by the control unit. For this purpose, the electrical potential of the signal line can be pulled by the control unit to the specified potential, such as ground potential.

[0011] Conventional diagnostic methods can only check whether the auxiliary heater in the mass airflow sensor is actually activated by the control unit, based on the presence of the specified potential on the signal line. It cannot be determined whether the auxiliary heater in the mass airflow sensor is actually activated depending on the signal level on the signal line.

[0012] In contrast, the above method allows the control unit to detect the functionality of the auxiliary heater. This enables early detection of an auxiliary heater failure, allowing the air mass sensor to be replaced during routine maintenance before contamination of the sensor area degrades or renders the readings unusable. This prevents the air mass sensor from failing due to an auxiliary heater defect, which would otherwise necessitate unscheduled repairs.

[0013] The above procedure for diagnosing the auxiliary heater involves determining the internal temperature of the mass airflow sensor before and after a predetermined period, i.e., a test period, during which the auxiliary heater is activated. If the auxiliary heater is functioning, the internal temperature of the mass airflow sensor is expected to have increased. A significant temperature increase indicates that the auxiliary heater is functioning. Otherwise, it can be assumed that the auxiliary heater is not working.

[0014] Furthermore, the defined state can correspond to a defined potential on the signal line.

[0015] It may be provided that the set potential on the signal line is detected if a signal applied to the signal line by the air mass sensor does not change the set potential.

[0016] According to one embodiment, the auxiliary heating mode can be activated after the engine system has been switched off.

[0017] It may be provided that the proper functioning of the auxiliary heater is recognized when the difference between the first temperature reading and the second temperature reading exceeds a predetermined threshold.

[0018] Furthermore, a defect in the auxiliary heater can be detected if the difference between the first temperature reading and the second temperature reading, recorded after the engine system has been switched off, falls below the specified threshold one or more times.

[0019] After the specified time period has elapsed, the sensor operating mode can be activated, at least briefly. During sensor operating mode, information can be transmitted via the signal line by not setting a defined state on the signal line.

[0020] According to another aspect, a control unit is provided for diagnosing the functionality of an auxiliary heater to prevent contamination of a sensor area in an air mass sensor in an engine system with an internal combustion engine. The air mass sensor is designed to communicate an air mass reading via a signal line and, upon detecting a defined condition on the signal line, to activate the auxiliary heater, comprising: - an input stage configured to provide an input impedance and to establish a defined state on the signal line, - a control unit logic that is trained to - to control the input stage so that the state of the signal line is set to the specified state in an auxiliary heating mode for a predetermined period of time; - to receive an initial temperature reading before switching to auxiliary heating mode and a second temperature reading after the specified time period has elapsed; - to recognize the functionality of the auxiliary heater depending on the difference between the first temperature reading and the second temperature reading.

[0021] Furthermore, the control unit logic can be designed to activate the input stage after a signal indicating that the engine system has been switched off, so that the potential of the signal line is set to the specified potential for the specified duration in the auxiliary heating mode.

[0022] According to another aspect, an engine system is provided with an internal combustion engine and an air mass sensor, which is designed to send an air mass reading via a signal line to the control unit above. Brief description of the drawings

[0023] The embodiments are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a sensor system comprising a hot-film air mass sensor and a control unit connected to the air mass sensor; and Fig. 2 a method for performing a diagnosis of the auxiliary heating of the air mass sensor; Fig. 3 the temporal course of the signal level on the signal line during the transition from a sensor operating mode to an auxiliary heating operating mode. Description of embodiments

[0024] Fig. Figure 1 shows a schematic representation of a sensor system 1 with an air mass sensor 2 and a control unit 3, which are connected to each other via a signal line 4, in particular (apart from a separate power supply) a single-core line.

[0025] The air mass sensor 2 has a sensor area 21 which is arranged in an airflow within an air guide 22, so that the airflow is directed over the sensor area 21. The sensor area 21 can be heated by means of an electric heating device 23, which, for example, has a resistive layer, and the temperature of the sensor area 21 can be measured by means of a temperature sensor 27.

[0026] A sensor logic 24 is provided that continuously measures the air mass flow rate. During measurement operation, the heating device is controlled by the sensor logic 24 by specifying a heating current. As the airflow passes, it cools the sensor area 21, which is heated by the heating device 23. The sensor logic 24 regulates the sensor area temperature, as detected by the temperature sensor 27, to a predetermined setpoint temperature and adjusts the heating current accordingly. The set heating current can then be used as a reference for the air mass flow rate through the flow guide 22. Other methods for determining the air mass flow rate are also conceivable. For example, a temperature difference caused by the airflow in the heating area can be determined and used as a reference for the air mass flow rate through the flow guide 22.

[0027] The air mass flow rate is processed appropriately in a sensor logic 24 and transmitted to the control unit 3 via the signal line 4. Possible transmission methods include serial digital transmission, such as using a SENT protocol, FAS transmission where the temperature is transmitted as a frequency signal, or transmission of an analog electrical quantity.

[0028] Another piece of information transmitted to the control unit 3 by the sensor logic 24 is the internal temperature of the air mass sensor 2. This is determined as a temperature reading using another temperature measuring device 25 and can, for example, represent a measure of the ambient temperature.

[0029] An electrically operated auxiliary heater 26 can be provided, which can be activated via the sensor logic 24. The auxiliary heater 26 is located near the sensor area 21 and, when activated, causes turbulence in the air above the sensor area 21, thus preventing the deposition of contaminants, such as dust particles or oil vapors, on the sensor area 21. This prevents degradation of the sensor's performance caused by contamination of the sensor area 21.

[0030] In addition to the air mass flow rate, the sensor logic 24 can also be configured to transmit the temperature information via the internal sensor temperature to the control unit 3 via the signal line 4, e.g. coded in the form of serially successive signal levels.

[0031] The auxiliary heater 26 is only activated when the combustion engine is switched off, as a proper measurement of the airflow passing through the air mass sensor 2 cannot be performed when the auxiliary heater 26 is active. The control unit 3 signals to the air mass sensor 2 that the combustion engine has been switched off by setting the signal line 4 to a specific electrical potential, in particular a ground potential, so that the sensor logic 24 cannot send any data via the signal line 4.

[0032] The sensor logic 24 is designed to recognize that no data can be transmitted via signal line 4 and therefore recognizes that the auxiliary heater 26 should be activated. Since no signal transmission from the air mass sensor 2 to the control unit 3 is possible in the deactivated state, a direct diagnosis of the auxiliary heater 26 is not possible.

[0033] To provide the specified electrical potential on the signal line, the control unit 3 includes an input stage 31, which comprises an input circuit capable of pulling the signal line 4 to the specified electrical potential, in particular a ground potential. For example, such an input circuit can have a pull-up resistor coupled to a pull-down transistor, which is controlled by a control unit logic 32 to apply the specified electrical potential to the signal line 4.

[0034] Furthermore, the control unit logic 32 executes a procedure for diagnosing the auxiliary heater 26 in the air mass sensor 2. Fig. Figure 2 is a flowchart illustrating the procedure for performing the diagnosis of the auxiliary heater 26 in the air mass sensor 2. Fig. Figure 3 shows the time course of the signal level on the signal line during the transition from a sensor operating mode to an auxiliary heating operating mode.

[0035] In step S1, the air mass sensor 2 is in sensor operating mode and records air mass data, temperature data, and the like for transmission to the control unit 3 via signal line 4. The sensor operating mode is shown in the signal diagram of the Fig. 3 during a time period t1. In step S1, at least the temperature reading in the air mass sensor 2 is determined and transmitted to the control unit 3 via the signal line 4.

[0036] In step S2, it is checked whether an auxiliary heating mode has been activated due to the combustion engine being switched off, as indicated by the special signal level on signal line 4 from control unit 3. If this is not the case, the process returns to step S1; otherwise (alternatively: yes), the procedure continues with step S3.

[0037] In step S3, the last recorded temperature reading is stored in the control unit 3. The auxiliary heater 26 is then activated in an auxiliary heating mode, and in step S4, a specific predefined time period t2 is observed. After this time period t2 has elapsed, the auxiliary heating mode is deactivated.

[0038] Sensor logic 24 can now transmit the last recorded temperature reading back to control unit 3. The first temperature reading recorded after the end of the auxiliary heating mode is stored in control unit 3 in step S5.

[0039] In step S6, it is checked whether the boundary conditions for performing the diagnosis are met. These boundary conditions can include the engine and / or ambient temperature being within a predefined temperature range. Furthermore, it can be checked whether the heating time of the auxiliary heater 26 was sufficiently long during the auxiliary heater operating mode to achieve a sufficient temperature difference, assuming the auxiliary heater 26 is functioning correctly. If the boundary conditions for performing the diagnosis are not met (alternative: no), the process returns to step S1; otherwise (alternative: yes), the procedure continues with step S7.

[0040] In step S7, it is checked whether the difference, in particular the difference between the temperature values ​​stored before and after the auxiliary heating mode is activated, exceeds a predefined temperature threshold. If this is the case, the auxiliary heater 26 is recognized as functional and the procedure continues with step S1; otherwise (alternative: no), the auxiliary heater 26 is recognized as non-functional and this is signaled accordingly.

[0041] Since a failure of the auxiliary heater 26 does not immediately lead to a failure of the air mass sensor 2, the fault type of the failed auxiliary heater 26 can be appropriately stored in a fault memory in order to replace the air mass sensor 2 during the next maintenance.

[0042] It may also be possible to debounce the diagnostic procedure and only signal a corresponding fault of the auxiliary heater 26 after a predetermined number of exceedances of the specified threshold value detected in step S7. In particular, the diagnosis of the auxiliary heater 26 can be carried out during a start / stop operation of the engine system in motor vehicles.

[0043] Furthermore, during a run-up phase of the engine system, the diagnostic procedure described above can be carried out several times in succession and the diagnostic results can be evaluated accordingly.

Claims

[1] Method for diagnosing the functionality of an auxiliary heater (26) in an air mass sensor (2) in an engine system with an internal combustion engine, wherein the auxiliary heater (26) serves to prevent contamination of a sensor area (21), wherein the air mass sensor (2) is configured to communicate an air mass value via a signal line (4) during a sensor operating mode and to activate the auxiliary heater (26) upon detection of a defined state on the signal line (4), comprising the following steps: - Setting (S4) the state of the signal line (4) to the specified state for a predetermined time period (t2) in an auxiliary heating mode; - Acquisition (S3, S5) and transmission of a first temperature reading before entering auxiliary heating mode and a second temperature reading via the signal line after the specified time period (t2) has elapsed; - Detect (S7, S8) the functionality of the auxiliary heater (26) depending on the difference between the first temperature reading and the second temperature reading. [2] Method according to claim 1, wherein the defined state corresponds to a defined potential on the signal line (4). [3] Method according to claim 2, wherein the set potential on the signal line (4) is detected when a signal applied to the signal line by the air mass sensor (2) does not change the set potential. [4] Method according to any one of claims 1 to 3, wherein the auxiliary heating mode is entered after the engine system has been switched off. [5] Method according to any one of claims 1 to 4, wherein proper functioning of the auxiliary heater (26) is recognized when the difference between the first temperature reading and the second temperature reading exceeds a predetermined temperature threshold. [6] Method according to any one of claims 1 to 5, wherein a defect of the auxiliary heater (26) is detected when the difference between the first temperature reading and the second temperature reading, as recorded after the engine system has been switched off, falls below the specified temperature threshold for one or more times. [7] Method according to any one of claims 1 to 6, wherein after the specified time period the sensor operating mode is assumed at least briefly, during which information can be transmitted via the signal line (4) by not setting a defined state on the signal line (4). [8] Control unit (3) for diagnosing the functionality of an auxiliary heater (26) for preventing contamination of a sensor area (21) in an air mass sensor (2) in an engine system with an internal combustion engine, wherein the air mass sensor (2) is configured to communicate an air mass value via a signal line (4) and to activate the auxiliary heater (26) when a defined condition is detected on the signal line (4), comprising: - an input stage (31) configured to provide an input impedance and to set a defined state on the signal line (4), - a control unit logic (32) that is trained to - to control the input stage (31) so that the state of the signal line (4) is set to the specified state for a predetermined time period (t2) in an auxiliary heating operating mode; - to receive a first temperature reading before entering auxiliary heating mode and a second temperature reading after the specified time period (t2) has elapsed; - to recognize the functionality of the auxiliary heater (26) depending on the difference between the first temperature reading and the second temperature reading. [9] Control unit (3) according to claim 8, wherein the control unit logic (32) is configured to control the input stage (31) after a signal indicating that the engine system has been switched off, so that the potential of the signal line (4) is set to the specified potential for the specified time period in the auxiliary heating mode. [10] Engine system comprising an internal combustion engine, an air mass sensor (2) configured to communicate an air mass value via a signal line (4) to a control unit (3) according to one of claims 8 and 9 and to activate the auxiliary heater (26) when a defined state is detected on the signal line. [11] Computer program which, when executed on a control unit according to claim 8 or 9, is configured to perform all steps of a method according to any one of claims 1 to 7. [12] Machine-readable storage medium on which a computer program according to claim 11 is stored.

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