The following is from one of my textbooks and refers to ignition timing – fig 10-17 shows a timing and dwell map (a similar method is used to determine engine fuelling.
The F1 issue seems to be that the FIA regulations say that the ‘looked up’ (vertical axis) should be set so as to produce maximum torque at all times when the driver requests it from the throttle pedal.
F1 systems are complex but this should help:
The basic ignition advance angle is obtained from a memorized cartographic map. This is held in a ROM chip within the ECU. The parameters for this are:
- Engine rpm – given by the flywheel sensor.
- Engine load /Inlet air pressure – given by the manifold absolute pressure sensor.
The above two parameters (speed and load) give the basic setting but to ensure optimum advance angle the timing is corrected by:
- Coolant temperature.
- Air temperature.
- Throttle position.
Figure 1017 Engine timing and dwell maps
The ignition is set to a predetermined advance during the starting phase. Figure 10.17 shows a typical advance map and a dwell map used by the Motronic system. These data are held in ROM. For full ignition control, the electronic control unit has first to determine the basic timing for three different conditions:
- Under idling conditions, ignition timing is often moved very quickly by the ECU in order to control idle speed. When timing is advanced, engine speed will increase within certain limits.
- Full load conditions require careful control of ignition timing to prevent combustion knock. When a full load signal is sensed by the ECU (high manifold pressure) the ignition advance angle is reduced.
- Partial throttle is the main area of control and, as already stated, the basic timing is set initially by a programme as a function of engine speed and manifold pressure.
Corrections are added according to:
- Operational strategy.
- Knock protection.
- Phase correction.
The ECU will also control ignition timing variation during overrun fuel cut-off and reinstatement and also ensure anti-jerk control. When starting, the ignition timing plan is replaced by a specific starting strategy. Phase correction is when the ECU adjusts the timing to take into account the time taken for the HT pulse to reach the spark plugs. To ensure good drivability the ECU can limit the variations between the two ignition systems to a maximum value, which varies according to engine speed and the basic injection period.
A three-dimensional cartographic map, shown in Figure 9.25, is used to represent how the information on an engine’s fuelling requirements is stored. This information forms part of a read only memory (ROM) chip in the ECU. When the ECU has determined the look-up value of the fuel required (injector open time), corrections to this figure can be added for battery voltage, temperature, throttle change or position and fuel cut off.
Figure 925 Cartographic map used to represent how the information on an engine’s fuelling requirements are stored