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Part 3

14 COMPREHENSIVE COMPONENTS MONITORING Contd.

14.7 Air mass measurement with mass air flow (MAF) sensor - single MAF Sensor system

Applicable only for test groups






14.7.1 General Description
In order to achieve optimum engine operation regarding torque requirements and exhaust-gas emissions, the air mass that enters the combustion chamber during one combustion cycle must be measured precisely. The measured mass air flow is proportional to the molar mass of the oxygen contained in it, and it is used to determine the molar oxygen mass available per cylinder charge. On the basis of this mass air flow the fuel quantity required to be injected for an optimum combustion is determined.

The drawn in air mass is measured with a mass air flow sensor in the intake manifold. The mass air flow sensor is a flow meter which measures the air mass per time unit passing through it (mass flow). Moreover, a mass air flow model value is calculated from the throttle position and the engine speed.

14.7.2 Measured MAF irrationally high / low, P0101

Monitoring Strategy
The measured mass air flow value is compared to a modeled upper / lower rationality threshold value.

Enable Conditions
- Number of camshaft revolutions greater than threshold value

Malfunction Criteria
A mass air flow model value is continuously calculated from the throttle position and the engine speed. Taking all component-related and system-related tolerances into account, a minimum and a maximum mass air flow are derived from this model, which provide the lower and upper rationality threshold values.

If the mass air flow value measured by the mass air flow sensor exceeds the modeled maximum mass air flow value, an irrationally high mass air flow is detected and a fault is registered in the fault memory.

If the mass air flow value measured by the mass air flow sensor falls below the modeled minimum mass air flow value, an irrationally low mass air flow is detected and a fault is registered in the fault memory.






14.7.3 Measured MAF irrationally high / low compared to load adaptation and fuel adaptation, P0101

Monitoring Strategy
The multiplicative parts of the load adaptation and the fuel adaptation are each compared to a defined threshold value.

Enable Conditions
- Engine speed in defined range
- Coolant temperature greater than defined threshold value
- Intake air temperature less than defined threshold value
- Mass air flow in defined range
- Engine load in defined range
- Ratio of intake manifold air pressure to ambient pressure less than defined threshold value
- Canister purge valve closed
- Lambda control loop closed

Malfunction Criteria
The multiplicative parts of the load adaptation and the fuel adaptation are each compared to a defined threshold value. During high engine load/engine speed, the fuel adaptation values are calculated by integrating the mean value deviations of the lambda control factors from the neutral position. The multiplicative part of the load adaptation is calculated from the deviation of the measured mass air flow from the modeled mass air flow.

If the multiplicative part of the load adaptation is greater than a defined threshold value AND the multiplicative part of the fuel adaptation is less than a defined threshold value, a faulty mass air flow sensor is detected and registered in the fault memory.

If the multiplicative part of the load adaptation is less than a defined threshold value AND the multiplicative part of the fuel adaptation is greater than a defined threshold value, a faulty mass air flow sensor is detected and registered in the fault memory.






14.7.4 Measured MAF too low / high, compared to throttle position, P0068

Monitoring Strategy
The modeled mass air flow value is compared to the value determined by the mass air flow sensor.

Enable Conditions
- Engine speed in defined range
- Coolant temperature greater than defined threshold value
- Intake air temperature less than defined threshold value
- Mass air flow in defined range
- Engine load in defined range
- Ratio of intake manifold air pressure to ambient pressure less than defined threshold value
- Canister purge valve closed
- Lambda control loop closed

Malfunction Criteria
A mass air flow model value is continuously calculated from the throttle position and the engine speed. The quotient of the measured mass air flow and the modeled mass air flow is evaluated.

If the quotient is less than a defined threshold value, an irrationally low measured mass air flow compared to the mass air flow modeled from the throttle position is detected and a fault is stored in the fault memory.

If the quotient is greater than a defined threshold value, an irrationally high measured mass air flow compared to the mass air flow modeled from the throttle position is detected and a fault is stored in the fault memory.






14.8 Air mass measurement with intake Manifold Absolute Pressure (MAP) Sensor

Applicable only for test groups






14.8.1 General description
In order to achieve optimum engine operation regarding torque requirements and exhaust-gas emissions, the air mass that enters the combustion chamber during one combustion cycle must be measured precisely. The measured mass air flow is proportional to the molar mass of the oxygen contained in it, and it is used to determine the molar oxygen mass available per cylinder charge. On the basis of this mass air flow the fuel quantity required to be injected for an optimum combustion is determined.

The drawn in air mass is determined with a pressure sensor in the intake manifold. The pressure sensor measures the absolute pressure in the intake manifold immediately after the throttle blade. The mass of the air per time unit (mass flow) that flows into the combustion chambers is calculated based on this absolute pressure, the ambient pressure and the air temperature. Moreover, a mass air flow model and MAP model are calculated from the throttle position and the engine speed.

The manifold absolute pressure sensor (MAP sensor) is monitored over the entire working range for electrical and rationality failures. The rationality monitor of the manifold absolute pressure (MAP) sensor consists of three different and independent checks.
- Measured MAP to Modeled MAP check
- Measured MAP and Measured Ambient Pressure at Engine Start check
- Evaluation of the adaptation value check

The MAP sensor is used for the engine load calculation and any deviation of the sensor might cause a Lambda deviation, which is compensated by the Lambda adaptation, being monitored by the fuel system diagnostic. If none of the MAP sensor specific monitors detects an error although a higher deviation of the MAP sensor is present, the fuel system diagnostic will detect this failure finally before emissions exceed the applicable OBD thresholds.






Figure 159 shows the entire working range of the MAP sensor and identifies the monitoring functions for failure detection. The working ranges of the different monitoring function overlap each other. The check with the quickest failure detection is shown here.

14.8.2 MAP Rationality check low / high, P0106

Monitoring Strategy
The pressure value determined by the MAP sensor is compared to the modeled MAP (and the measurement value of the ambient air pressure sensor for Rationality check low). The adaptation value of the MAP sensor is evaluated during one of three defined engine operating ranges.

Typical Enable Conditions
For the comparison of the measured MAP with the modeled MAP:
- None

For the comparison of the measured MAP with the measured ambient pressure at engine start (only for Rationality check low):
- Engine speed less than defined threshold value
- Time since engine start less than defined threshold value

For the evaluation of the adaptation value:
- Number of times the three engine operating ranges have each been reached greater than defined threshold value, to make sure that the required number of intake manifold pressure adaptations for the monitor is available for the evaluation.
- Evaporative system monitoring not active (only for Rationality check low)
- Engine speed within defined range
- MAP greater than defined threshold value
- Ratio of MAP to ambient pressure less than defined threshold value

For engine operating range 1:
- Engine speed less than defined threshold value
- Mass air flow within defined range (only for Rationality check low)
- Change of adaptation value for operating range 1 less than defined threshold value for a defined time period

For engine operating range 2:
- Engine speed greater than defined threshold value
- MAP less than defined threshold value
- Change of adaptation value for operating range 2 less than defined threshold value for a defined time period

For engine operating range 3:
- Mass air flow greater than defined threshold value
- MAP greater than defined threshold value
- Change of adaptation value for operating range 3 less than defined threshold value for a defined time period

Malfunction Criteria for the Comparison of Measured MAP to Modeled MAP
A MAP model value is continuously calculated from the throttle position, the engine speed and the ambient air pressure. Taking the total sum of all the system's tolerances that can have an influence on the MAP into account, a minimum and a maximum manifold absolute pressure are calculated from this model value. This way, an upper and a lower threshold are imposed upon the rational range of the MAP. If the value measured by the MAP sensor falls below the modeled minimum MAP, an irrationally low MAP is detected and a fault is stored in the fault memory. If the value measured by the MAP sensor exceeds the modeled maximum MAP, an irrationally high MAP is detected and a fault is stored in the fault memory.






Malfunction Criteria for the Comparison of Measured MAP and Measured Ambient Pressure at Engine Start (only for Rationality check low)
At engine start the measurement value of the MAP sensor is compared to the measurement value of the ambient pressure sensor. If the deviation between these two values is greater than a defined threshold value (e.g. 60 hPa), a fault is stored in the fault memory.
To ensure that the monitoring function is not influenced by a manifold being still evacuated due to a fast engine restart, the time after last engine stop has to be greater than a calibrated value (e.g. 5 seconds).






Malfunction Criteria for the evaluation of the adaptation value
At low intake manifold pressures, the intake manifold pressure model must take large tolerances into account particularly for the throttle valve. To run the diagnostics, it must be ensured that the influence of other disturbance variables is minimized. For this purposes an adaptation value check is implemented. A defective intake manifold pressure sensor is learnt by the adaptation as an offset. This offset must be distinguished from a leakage in the intake manifold as well as from various tolerances with large mass flow rates (e.g. ambient pressure sensor tolerances, camshaft tolerances, etc.).

In each of three defined engine operating ranges an adaptation value is calculated from the difference between the measured MAP and the modeled MAP in order to correct the mass air flow. The modeled MAP value is assumed as the correct value. The adaptation values are continuously updated whenever the respective operating range is active, once the respective enable conditions are fulfilled. The fault monitor is started when at least a minimum number of MAP adaptations have been completed in each of the three engine operating ranges.

In engine operating range 1 - at low engine speeds and low mass air flow rates - adaptation values are calculated that are mainly influenced by the tolerances of the throttle blade adjustment mechanism.

In engine operating range 2 - at MAPs below a defined threshold value and engine speeds greater than a threshold value, adaptation values are calculated that are mainly influenced by the tolerances of the MAP sensor.

In engine operating range 3 - at high intake manifold absolute pressure and high mass air flows, adaptation values are calculated that are mainly influenced by tolerances of the ambient air pressure sensor.

The adaptation values are calculated for diagnostic purposes only. They are always taken into account for all engine operating ranges of mass air flow calculation from the throttle valve model. They have no influence on the engine load calculation from MAP-sensor.






In the ranges, the following effects have a dominant influence:

Range 1: Leakage in the intake manifold
At the same throttle valve angel, the mass air flow rate calculated for the intake manifold sensor increases while the mass flow rate from the throttle valve remains constant. At higher mass air flow rates, the magnitude of a leakage on the entire mass air flow decreases.

Range 2: manifold pressure sensor error
A deviation of the intake manifold sensor has a constant influence on the mass air flow calculation from the pressure sensor signal. The relative influence is greater at lower intake manifold pressures. In operating "range 2", a pressure sensor deviation differs from a leakage in the intake manifold. In this range, detection of a manifold absolute pressure sensor error is possible.

Range 3: Influence caused by tolerances of the ambient pressure sensor, camshaft, etc.
With greater mass air flow rates through the throttle valve, the influences of tolerances for the ambient pressure sensor and the camshafts affect the mass flow rate calculations significantly. The magnitude of leakages and small pressure sensor deviations decreases at higher mass air flow rates.

The physical incorporation of the values allows the system to adapt to the individual influences in accordance with their physical effect and therefore allows a distinction between the individual influences

The adaptation of a value is conducted as follows:
As long as the enable and operating conditions are met for an adaptation value within a dedicated range, the actual deviation of both mass flow rates is learnt for the relevant adaptation value. The time counter is running in parallel while the adaptation is carried out. Once a calibrated time (such as 1 second / 8 seconds / 5 seconds) has elapsed for each range, the system evaluates the change in the adaptation value. If the change is minimal (e.g. 0.1 kg/h or 3 hPa), the adaptation value is reliable. The "adaptation counter" for a successful adaptation within the actual range is increased, if the counters of the other ranges are greater than or equal to the actual counter. This ensures that an evaluation of the adaptation values is carried out only, if the areas were run separately and the adaptation values in every range have been stabilised.

The adaptation sequence for the first adaptation in a driving cycle is predefined (range1, 2, 3). Only if the adaptation value in the previous ranges is reliable, the subsequent range can be adapted. This prevents unnecessary adaptation of deviations for the mass air flow rates by tolerances affecting all operating ranges.

If the change in the adaptation values within the time period is larger than a calibrated value (e.g. greater than 0.4 kg/h or 10hPa), all counters are reset and the entire adaptation process is started again from the beginning. This is necessary to ensure that all adaptation areas are reactivated if large deviations occur suddenly before the evaluation of the adaptation values is completed.

The adaptation value from "range 2" is monitored to evaluate the intake manifold sensor. To ensure that all influences are separated into the relevant adaptation values, an evaluation is valid only, if the adaptation counters of all ranges exceeding a calibrated value (e.g. 2).

If this adaptation value falls below a defined threshold value an irrationally low measured MAP is detected and a fault is stored in the fault memory. If this adaptation value exceeds a defined threshold value an irrationally high measured MAP is detected and a fault is stored in the fault memory.






In-Use Monitor Performance Ratio

Incrementing the numerator:
The numerator is incremented by one when one of the three parts of the diagnostic has been entirely completed.

The adaptation value stabilization may require a longer time for the adaptation phase based on the actual engine operating condition in customer's hand. For this reason the "adaptation and time counters" are doubled ("Shadow Counters") to trigger incrementing of the numerator according to the "worst case duration" of the adaptation process.

As required for a successful adaptation within a specific range, the IUMPR related "time counters" are individually calibrated for each adaptation range (e.g. 5 seconds / 20 seconds/ 17 seconds). If the IUMPR related "adaptation counters" exceed their individually calibrated value (e.g. 5), incrementing of the numerator is allowed.

The "shadow counter" calibration accounts for the possible "adaptation counter reset event" caused by greater (implausible) changes in the adaptation value.

Incrementing the denominator:
The denominator is incremented by one when the conditions for incrementing the general denominator according to CCR (d) (4.3.2) are fulfilled.

14.8.3 MAP, Signal Range Fault, Signal too low / high, P0107 / P0108

Monitoring Strategy
The measured MAP is compared to a defined lower / upper threshold value.

Typical Enable Conditions
- None

Malfunction Criteria
The measured MAP is compared to a defined lower / upper threshold value. If the measurement result is less than / greater than this defined threshold, the fault "MAP signal too low / too high" is detected and is stored in the fault memory.






In-Use Monitor Performance Ratio

Incrementing the numerator:
The numerator is incremented by one when the monitor has been entirely completed once.

Incrementing the denominator:
The denominator is incremented by one when the conditions for incrementing the general denominator according to CCR (d) (4.3.2) are fulfilled.

14.8.4 Mass Air Flow from MAP irrationally constant, P0106

Monitoring Strategy
The change of the MAP between two engine operating ranges is compared to a defined threshold value.

Typical Enable Conditions
General Enable Conditions:
- Coolant temperature greater than defined threshold value

Engine operating range 1:
- Engine speed less than defined threshold value
- Throttle position greater than defined threshold value
- Time of engine running in operating range 1 greater than defined threshold value

Engine operating range 2:
- Engine speed greater than defined threshold value
- Throttle position less than defined threshold value
- Time of engine running in operating range 2 greater than defined threshold value

Malfunction Criteria
The MAP is measured in two defined engine operating ranges and the pressure change between the two engine operating ranges is evaluated. If the difference of the two MAPs is less than a defined threshold value, an irrationally constant pressure is detected and a fault is stored in the fault memory.

In-Use Monitor Performance Ratio

Incrementing the numerator:
The numerator is incremented by one when the monitor has been entirely completed once.

Incrementing the denominator:
The denominator is incremented by one when the conditions for incrementing the general denominator according to CCR (d) (4.3.2) are fulfilled.






14.8.5 Cross Check - MAP irrationally low/high, P0106

Monitoring Strategy
The measured values of all air pressure sensors are compared to each other at engine-on after a sufficiently long engine-off time.

Typical Enable Conditions
- Engine-off time greater than defined threshold value
- Engine speed less than defined threshold value

Malfunction Criteria
At engine-on, a mean value is calculated from the current measured values of all air pressure sensors used in the vehicle. This mean value is subtracted from the current measured value. If the resulting difference is less than / greater than a defined negative threshold value, an irrationally low / high MAP is detected and a corresponding fault is registered in the fault memory.

In-Use Monitor Performance Ratio

Incrementing the numerator:
The numerator is incremented by one when the monitor has been entirely completed once.

Incrementing the denominator:
The denominator is incremented by one when the conditions for incrementing the general denominator according to CCR (d) (4.3.2) are fulfilled.






14.8.6 Circuit Monitoring of the MAP Sensor

Short to Battery/Ground or Open Circuit

Monitoring Strategy
The signal voltage of the MAP sensor is continuously monitored.

Typical Enable Conditions
- None

Malfunction Criteria
Short to ground, P0107:
If the signal voltage of the MAP sensor is less than a defined threshold value (e.g. 0.2 V) for a defined time period (e.g. one second), a short to ground is detected and a fault is stored in the fault memory.

Short to battery or open circuit, P0108:
If the signal voltage of the MAP sensor is greater than a defined threshold value (e.g. 4.86 V) for a defined time period (e.g. one second), a short to battery or an open circuit is detected and a fault is stored in the fault memory.
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