Engine Management System
Direct injection
Direct injection of petrol gives advantages such as low fuel consumption, low emissions and high power.
Injection takes place directly in the cylinder at high pressure, between 3-20 MPa (30-200 bar). To achieve these high pressures, a mechanical fuel pump driven by the exhaust camshaft is used. The fuel pump supplies the fuel rail with fuel under high pressure. The fuel is distributed on to the fuel injectors, which are controlled by the engine control module (ECM).
Excess fuel from the high pressure pump is returned to the inlet of the high pressure pump. The fuel system has thus no separate return line to the tank. Injection into the cylinder is either by:
- An injection during the compression stroke, so-called stratified combustion.
- Two injections, one during the induction stroke and one during the compression stroke, so-called semi-stratified combustion.
- An injection during the compression stroke, so-called homogeneous combustion.
- Stratified combustion
- Semi stratified combustion
- Homogeneous combustion
Stratified combustion
Injection takes place during the compression stroke's second half. When all of the drawn in air is not involved in combustion, a portion of the air is used to isolate and concentrate the optimum stoichiometric air-fuel mixture (14.7:1) to the spark plug and the piston combustion chamber, which creates a stable combustion.
(coolant temperature/catalyst temperature). In colder conditions semi stratified combustion is also used during the starter motor sequence.
Stratified combustion is used during the period when the starter motor is activated and the fuel pressure has reached at least approx. 3 MPa (30 bar). When the engine has started, the engine's operating mode shifts to semi stratified combustion in cases where catalyst heating is required. Stratified combustion is used in all conditions at temperatures above -20 °C.
The concentration of the fuel air mixture to the spark plug and piston occurs by the airflow created through the inlet ports' and combustion chamber's shape, as well as the fuel injector's position relative to the piston. When combustion has been initiated, the fuel air mixture is said to be 30:1 or even leaner for the entire cylinder.
Semi-stratified combustion
Injection takes place through two injections. The first takes place during the first half of the induction stroke and the other during the second half of the compression stroke. The fuel quantity is distributed so that the largest amount of fuel is injected during the induction stroke and the remainder during the compression stroke. This provides a lateral and stable combustion with low peak pressure and low temperature, resulting objects in low NOx emissions. With the low walls impingement and efficient combustion with lean fuel-air mixture (lambda >1), HC emissions are also low.
Semi-stratified combustion is used during catalytic converter heating when the engine has started. The time in this operating mode can be anything from 0 seconds when the engine coolant is at operating temperature and the catalytic converter is warm to approximately 30 seconds when both the coolant and catalytic converter are cold. Important parameters for the calculation of time by the engine control module (ECM) are the signals from the coolant temperature sensor and a calculation model for catalytic converter temperature. When the catalytic converter is considered sufficiently hot, the engine operating mode changes to homogeneous combustion.
Homogeneous combustion
Injection occurs in the first half of the induction stroke compared to conventional port injection. The incoming air is cooled by the fuel evaporation. This gives high knock tolerance.
Direct injection also gives slight wall impingement which results in low HC emissions. Homogeneous combustion is used during the driving cycle except in the above conditions.
Miscellaneous
- If the fuel pressure in the fuel rail at start has fallen to 0 kPa (0 bar) it takes approx. 2-3 pump strokes before the pressure reaches 3 MPa (30 bar). 3 pump strokes corresponds to 1.5 crankshaft revolutions.
- During the period of stratified combustion, 4-20 injections occur.
- During the period of semi-stratified combustion, the idle speed is raised to approx. 1200 (varies depending on market)
- During the period of semi-stratified combustion the exhaust camshaft is controlled to a later position. This means that the hot exhaust gases reach the exhaust manifold which gives reduced HC emissions. Together with late ignition the catalytic converter is rapidly heated.
- During the period of stratified and semi-stratified combustion, fuel injection occurs at approx. 5-10° crankshaft degrees before ignition occurs.
- For all strategies the injection time is adapted depending on the different parameters such as load, engine speed, operating mode and injected fuel volume.
Engine Control Module (ECM)
Supplier is Denso. The control modules for the diesel engine and the petrol engines are identical in terms of:
- External geometry
- The time critical signals regarding shift quality, torque limitation and drive mode, amongst other things, are sent via PT CAN.
- Shift requests and transmission temperature, amongst other things, are sent via HS CAN.
- Connector
- The time critical signals regarding shift quality, torque limitation and drive mode, amongst other things, are sent via PT CAN.
- Shift requests and transmission temperature, amongst other things, are sent via HS CAN.
- Circuit board
- The time critical signals regarding shift quality, torque limitation and drive mode, amongst other things, are sent via PT CAN.
- Shift requests and transmission temperature, amongst other things, are sent via HS CAN.
- The communication with the transmission control module (TCM) takes place via PT (Power Train) CAN at a speed of 500 kBs and via HS CAN.
- The time critical signals regarding shift quality, torque limitation and drive mode, amongst other things, are sent via PT CAN.
- Shift requests and transmission temperature, amongst other things, are sent via HS CAN.
- the software that controls when the automatic transmission normal shifts should occur based on accelerator pedal position, drive mode, operating conditions etc. and when the lock-up function must be activated.
- integrated sensor that registers the air pressure.
- integrated temperature sensor.
- handling the refined wheelspin control at Launch Mode.
Example of components and functions with similar function principles are:
- DC/DC-converter that increases the battery voltage from approx. 12 V to approx. 40-50 V. A condenser stores the voltage required to control components that require voltage greater than 12 V. • Two High-side drivers that supply voltage to two injectors each.
- four low-side drivers that each close the circuit for an injector.
- H-bridges that are used to control current in two directions, i.e. change the polarity in a component. Used, amongst other things, to control electric motors such as the ETA (Electronic Throttle Actuator).
Data capacity
- CPU (Central Processing Unit) 200MHz, 32 bit
- RAM (Random Access Memory) 256kB
- EEPROM (Electrically Erasable Programmable Read-Only Memory) flash memory 128 kB
Position sensor crankshaft
The sensor consists of four hall sensors, one permanent magnet and internal electronics. The sensor has different signal characteristics depending on the crankshaft's direction of rotation.
The signal to the engine control module (ECM) is a quadratic pulse between approx. 0.5 V and 4.5 V. Increased rotation speed gives increased frequency with fixed timed low signal.
During forward rotation the time period for the low signal is 45 μs (1) and at backwards rotation 90 μs (2). The engine control module (ECM) stores the engine position during the current driving cycle. This means that the engine control module (ECM) knows which cylinder is next in turn for injection and ignition at the next start, after the engine has been switched off during Start/Stop.
The engine can therefore be started without having to search for a synchronizing position between crankshaft and camshafts. This gives shorter starting phases with reduced load on the battery and starter motor, especially important when starting during Start/Stop sequence. If the driving cycle is interrupted the stored crankshaft position also disappears from the engine control module (ECM). The crankshaft position sensor's signal is also used for misfire diagnosis.
The sensors for the exhaust and inlet camshafts are identical. The sensor consists of one hall sensor, one permanent magnet and internal electronics. The sensor has only one type of signal characteristic, i.e. the engine control module (ECM) cannot identify the direction of rotation. The signal is a quadratic pulse between approx. 0.5 V and 4.5 V. High signal corresponds to "peak" on the trigger wheel, and "valley" corresponds to low signal.
Synchronizing crankshaft and camshafts
The crankshaft lock ring has a "gap" and gives the crankshaft position sensor 60-4=56 pulses per crankshaft revolution. When the engine control module (ECM) has identified the gap, the engine control module (ECM) can determine the exact position of the crankshaft by counting pulses. The engine control module (ECM) compares the crankshaft position sensor's signal with that of the camshaft position sensors when the crankshaft and "gap" have rotated 90° after Top Dead Centre. If the signals correspond with those expected the components are synchronized. The values for this initial synchronization are saved in the engine control module (ECM).
Because the crankshaft position sensor changes signal with direction of rotation (and the engine control module (ECM) can therefore "always" identify the crankshaft position) the next start can occur without requiring new synchronizing. This gives a significantly shorter start process in that the lock ring "gap" does not need to pass the crankshaft position sensor for the engine control module (ECM) to be able to identify the position.
The engine control module (ECM) also uses the signals from the crankshaft position sensor and exhaust camshaft position sensor to identify the fuel pump (pump piston) position.