Part 2

City Safety (only XC60)
City Safety is a function that helps the driver in case of high collision risk at speeds below 30 km/h, by preventing or minimizing the effects of collisions by reducing the speed. The Engine control module (ECM) can, upon request, perform torque limitation.
For a further information about the function, see Design and Function, Closing velocity module (CVM).

Engine Drag Control (EDC) (only XC60)
Engine Drag Control (EDC) is a function that is part of the DSTC function. The function ensures that the vehicle speed is not greater than the speed of the driven wheels. i.e. if the vehicle loses traction on the surface. The Engine control module (ECM) can increase the wheel torque on request so that the vehicle regains traction.
For a further information about the function, see Design and Function, Brake control module (BCM).

Fuel trim





Overview
Fuel trim reduces exhaust emissions. Fuel trim reduces nitrous oxides (NOx), carbon monoxide (CO) and hydrocarbon (HC) emissions.
Theoretically, if the correct amount of oxygen is added during combustion, fuel can be converted to water (H2O) and carbon dioxide (CO2). Emissions would then be completely safe.
In practice considerable amounts of hydro-carbons (HC) and varying amounts of carbon monoxide (CO) and carbon dioxide (CO2) remain.




Due to the high temperature and pressure, nitrous oxides such as NO and NO2 are also formed. The common designation for these gases is nitrous oxides NOx.




By speeding up the reaction between the remaining reactive components using a catalytic converter, these can be converted to water (H2O), carbon dioxide (CO2) and nitrogen (N2).
However this can only happen if the balance of hydro-carbons (HC), carbon monoxide (CO), oxygen (O2) and nitrous oxides (NOx) is exactly right in the exhaust. This happens when the fuel air mixture before combustion is 14.7 kg of air per kg of fuel. The Lambda value is then said to be one, (lambda=1).




A base program in the engine control module (ECM) calculates the injection period based on data about load, i.e. the measured air mass and engine speed (rpm). The calculated injection time (from the base program) is then modified by a circuit (short-term fuel trim). The signal from the heated oxygen sensor (HO2S) is used to finely adjust the injection period so that lambda=1 is reached. The short-term fuel trim is a circuit that finely adjusts the injection period so that the fuel/air mixture is optimized (lambda=1). The control module also used the signals from the front and rear heated oxygen sensors (HO2S) to correct the front heated oxygen sensor (HO2S) (offset adjustment) and thereby the injection period. This gives a higher degree of accuracy during fuel trim. Fuel trim is a rapid process which may take place several times a second. Adjustment of the injection period calculated in the base program is limited.

Adaptive functions




Certain factors, for example, tolerance deviations on certain components such as mass air flow (MAF) sensor and injectors, air leakage on the intake side, fuel pressure etc. affect the fuel / air mix. In order to compensate for this, the engine control module (ECM) has adaptive (self learning) functions. When the engine is new the short term fuel trim varies cyclically around a nominal central line (A) 1.00, with, for example, a ±5% change of injection time when fuel trim is in operation.
If there is air leakage for example, the short-term fuel trim will quickly be offset to a new position (B) and will then work for example between 1.10 (+10%) and 1.20 (+20%), although still at an amplitude of 5%, but with an offset in relation to the original center line (A). The injection period has then been increased to compensate the increase in the amount of air.
The adaptive functions will correct the change, so that the short-term fuel trim will work around the new center line (B) where it will again have its full range of control available.
Put simply, fuel trim is a measurement of the difference (C) between the original short-term fuel trim center line (A) and the new center line (B).
The adaptive functions are split into various operational ranges based on the load and speed of the engine.
The different adaption ranges can be read off.
The adaptive adjustments of injection time are continuously stored in the engine control module (ECM). This means that, at different operating ratios, the correct mixture ratio is achieved before the heated oxygen sensor (HO2S) reaches operating temperature.
The diagnostic trouble code (DTC) is stored in the engine control module (ECM) if any adaption value is too high or too low.

Fuel pressure regulation




General
Fuel pressure regulation for demand controlled fuel pumps means that the fuel pressure/flow is controlled steplessly by varying the output of the fuel pump. The design of the system means that the fuel pressure can be regulated between 300 and 500 kPa. The high pressure is used in extreme situations, such as heavy engine load for example and hot starts.

The following components are used for fuel pressure regulation:
- engine control module (ECM) (4/46)
- fuel pump control module (4/83)
- fuel pressure sensor with fuel temperature sensor (7/156)
- fuel pump (FP) (6/33).
The time taken for the engine start procedure can be reduced by rapidly increasing the pressure in the fuel rail when the engine control module (ECM) receives a signal about the position of the start control module (SCU) from the central electronic module (CEM).
The engine control module (ECM) is better able to calculate the injection period because the signal from the fuel pressure sensor provides information about the fuel pressure and actual fuel temperature. This particular improves the cold starting characteristics of the engine.
The advantages of varying the output of the fuel pump so that it is not always at full power are:
- the total power consumption of the fuel pump (FP) is reduced, reducing the load on the power supply system and reducing fuel consumption
- the service life of the fuel pump (FP) is increased
- fuel pump noise is reduced.
Control
The engine control module (ECM) calculates the desired fuel pressure. A signal is then transmitted to the fuel pump control module indicating the desired fuel pressure. Serial communication between the engine control module (ECM) and the fuel pump control module is used to carry the signal. The fuel pump control module then operates the fuel pump unit to obtain the desired pressure using a pulse width modulation (PWM) voltage on the ground lead. The fuel pump (FP) can be controlled steplessly by changing the pulse ratio of the pulse width modulation (PWM) signal. Only that pressure which is required at that specific time will then be released to the fuel rail/injectors. The value of the pulse width modulation (PWM) signal is a measurement of the operational load of the fuel pump (FP) (% duty, 100% = maximum pressure).
The engine control module (ECM) continuously monitors the fuel pressure using the signal from the fuel pressure sensor. This allows the desired fuel pressure to be reached, and if necessary a signal is transmitted to the fuel pump control module requesting that the fuel pressure is adjusted. The engine control module (ECM) regulates stable fuel pressure (approximately 400 kPa relative to the atmospheric pressure with the engine running).
Passive safety
For safety reasons, central electronic module (CEM) shuts off the fuel pump (FP) if the supplemental restraint system module (SRS) detects a collision.

Knock control




Knock occurs in the combustion chamber when the fuel and air mixture self ignites. This can occur either before or after the spark plug has produced an ignition spark. In both cases the gas in two or more places ignites in the combustion chamber.
This results in an extremely fast combustion process with flames from several directions. When these flames collide, the pressure in the cylinder increases rapidly and there is a mechanical knocking sound.
If any cylinder knocks, then certain types of vibrations in the engine block. These vibrations are transmitted to the knock sensors (7/23-24), which are bolted in the engine block.
One knock sensor detects knock on cylinders 1, 2, 3. The other knock sensor detects knock on cylinders 4, 5, and 6.
The mechanical stress generated in the knock sensors' piezo-electric materials result in generation of a voltage. The Engine control module (ECM) (4/46) can then, using the camshaft sensors (7/172-173) and the impulse sensor (7/25), decide which cylinder is knocking.
The knock sensors (KS) also interpret a proportion of normal engine sound. The control module is able to recognize the vibrations which correspond to knocking by filtering, amplifying and using software to evaluate the signal.
If the knock sensors (KS) detect knocking in the engine above a certain threshold value, the ignition timing is first retarded and then the fuel / air mixture is enriched to eliminate knocking.

Ignition control





The following components are used for ignition control:
- engine speed sensor (7/25)
- camshaft sensor (7/172-173)
- mass air flow (MAF) sensor (7/17)
- engine coolant temperature (ECT) sensor (7/16)
- throttle position (TP) sensor on the electronic throttle unit (6/120)
- knock sensor (KS) (7/23-24)
- transmission control module (TCM) (4/28)
- spark plugs with ignition coils (20/3-8).
The engine control module (ECM) calculates the optimum ignition advance based on the software and information from the sensors. The engine control module (ECM) cuts the current to the ignition coil mounted on the cylinder to be ignited and produces a spark.
During the starting phase the engine control module (ECM) produces a fixed ignition setting. When the engine has started and the vehicle is being driven, the engine control module (ECM) calculates the optimum ignition setting, taking factors such as the following into account:
- engine speed
- load
- temperature.
The engine control module (ECM) analyses the signal from the knock sensors (KS) when the engine reaches operating temperature. If any of the cylinders knock, the ignition is retarded for that specific cylinder until the knocking ceases.
The ignition then advanced to the normal position or until the knock recurs.
Before the Transmission control module (TCM) is going to shift, sometimes it sends a request for torque limitation to the Engine control module (ECM). Which then lowers the ignition momentarily to reduce the torque and thus give smoother shifting and reduced load on the transmission.
Lowering of ignition can be done in several levels, where the levels depend on the signals from the Transmission control module (TCM). The return signal from the Engine control module (ECM) to the Transmission control module (TCM) confirms that the signal reached the Engine control module (ECM).
For further information, also see: Misfire diagnostic, B6324S4 Misfire Diagnostics
The engine misfires if the fuel does not ignite correctly. For further information, also see: Misfire diagnostic, B6324S4 Misfire Diagnostics