Ignition and Control Systems, Sensors and Actuators

In this article is detail on the type of current generation systems in both gasoline and diesel engines, the requirements current power trains have for ignition systems, fuel control, sensors and actuators, driver interface controls, engine controls and the emission control system. Please feel free to skip to the part most relevant to you.

For current gasoline internal combustion engines, they have the following current generation systems:

  • A 12 volt electrical system.
  • An ignition system, that is distributorless, that uses solid state coils. This are usually one coil per spark plug or pairs of spark plugs. This is timed to the engine crankshaft.
  • A starter motor, battery and alternator.
  • The control of fuel injection, spark ignition and emissions control electronically.
  • Multiple sensors for air mass, camshaft position, clutch, transmission and throttle position.
  • To reduce emissions further, a catalytic converter.
  • An interface with many non-powertrain systems.

    For current diesel internal combustion engines, they have the following current generation systems:
    • A 12 volt electrical system just like the gasoline engines have.
    • Diesels require larger batteries to get the engine going from a cold start.
    • The fuel injectors are times to the engine crankshaft electronically.
    • Diesels have a range of emissions control such as catalytic converters, exhaust gas recirculation and turbocharger control.
    • Like with gasoline, there are multiple sensors.
    • Diesels are generally more complex and expensive than gasoline control systems.
    Current powertrains have the following system requirements:
    • Ignition system - This compromises of a 12 volt battery, alternator to charge the battery, solid state direct ignition system (DIS) coils, a sensor to detect the crankshaft position and spark plugs.
    Looking at battery technology, most cars still use lead acid cells because they are well proven technology, cheap, have a long life and higher reliable. Lead acid cell batteries typically consist of 6x2.4 volt cells that are connected in series in a polypropylene casing. The lead plates would be submerged within sulphuric acid.

    Alternators have the objective of supplying electricity for all of the electrical systems on the car as well as charging up the battery at 14.4 volts. 

    The starter motor has the aim of starting the motor (turning it over) in all sorts of conditions. This ranges from -40 degrees to 55 degrees celsius (basically, anywhere on Earth)! It needs to start the engine quickly, smoothly and quietly. The starter motor gets its power from the battery. Once the engine is idling, the alternator will start generating electricity to charge the battery up so that it is ready to be uses again when the starter motor is requested.
    • Fuel control - This involves components in the fuel system such as fuel injectors, spark plugs and coils as well as the electronic control unit (ECU).
    The fuel injectors are very accurate solenoid valves which allow a very precise amount of fuel into the combustion chamber to burn.Of course, the amount of fuel allowed into the combustion chamber is dependent on how long the valve is open for. 

    Considering that the one of the main limitations of engines is how quickly it can get the fuel into the combustion chamber, the fuel is pressurised by a fuel pump into a pipe called a fuel rail. The injectors are opened based on how long the ECU applies voltage to the solenoid coil connected to the injectors. This means fuel efficiency can be improve since fuel into the combustion can vary every single stroke automatically.

    The spark plugs are located in the combustion chamber of gasoline engines and have the purpose of providing a very precisely timed spark in time with the crankshaft rotation. The electrodes (where the spark jumps) are often made of platinum since platinum will increase reliability as the sparks are in their tens of thousands of volts and will melt most materials away over time.As the pressure inside the combustion chamber increases, the energy that is required to produce the spark increases significantly.

    The electronic control system is a solid state computer module that contains coding to control the engine and how it operates. This involves 3D calibrated mapping for the spark ignition timing.
    • Sensors and actuators - There are many many sensors and acutators that are used on modern vehicles highlighted below.
    Wheel speed sensor for traction control, air conditioning switch, cylinder head temperature sensor, heated exhaust gas oxygen sensor (HEGO), knock sensor, engine oil temperature sensor, gear shift position sensor, clutch position sensor, engine coolant temperature sensor (ECT sensor), exhuast manifold temperature sensor, intake manifold temperature sensor, ambient air temperature sensor (ATS), manifold air pressure sensor (MAP sensor), barometric air pressure sensor (BAP sensor), mass air flow sensor (MAF sensor), camshaft position sensor, throttle position sensor (TPS) and crankshaft position sensor (CPS).

    Controller Area Network (CAN) is used to transmit the signals along wires. This helps to simplify the wiring harness, reduces connectors used, improves reliability, reduces cable length, provides easier installation, reduces warranty and is used industry wide.
    • Driver interface controls - These consist of a throttle pedal, clutch/gear shift position sensors and cruise control.
    The throttle pedal needs to be highly resistant to failure due to mechanic or corrosion defects and involves the throttle position sensor.
    The clutch/gear shift position sensors sense when the clutch is used or a gear is selected. 
    Cruise control consists of a throttle control that uses a servo system to maintain the predetermined speed.

    As well as this, there is also newer systems the driver can interface with:
    • Adaptive cruise control - This uses RADAR detection to maintain a certain distance to the car in front resulting in the car accelerating and potentially braking automatically based on the speed of traffic in front.
    • The combination of wheel speed sensors to be used on anti lock brakes as well as brake and throttle control.
    • Traction/dynamic skid control - This uses wheel speed sensors as well as the yaw rate sensor to detect when the wheel has lost traction. The steering system then provides throttle/brake intervention to help the wheel regain traction.
    • Engine controls - This consists of the throttle position sensor, which determines the power demanded by the driver. This then links in with the calibration of the fuel/spark map in the ECU as well as the required fuel injection and ignition timing of spark plugs.
    • Emissions control system - Emission control is very important to modern cars. This involves a closed loop control of fuel and spark to meet very strict legal limits of NOx (oxides of nitrogen), HC (unburnt hydrocarbons), CO (carbon monoxide), particulates (microscopic soot particles) and, of course, carbon dioxide  which is a direct equivalence for fuel economy.