Engine Management System Flashcards
What does the EMS enable?
Fully control of engine through varying speeds and loads
Maintain current manufacturers emission regulations
Communication between other systems
Stopped under certain safety conditions
What is the EMS structure ?
Engine sensors that send ecu inputs to the ECU, which send ecu outputs to the engine actuators
What is ROM?
Read only memory
Pre programmed by the manufacturer and cannot be altered unless a re map is carried out
What is RAM
Random access memory
Variable information about the engine, it changes all the time and is compared to the rom in order to decide what action to take
What are sensors ?
Turns mechanical movements into electrical signals for the ÉCU to read
What are actuators ?
Turns electrical signals from ECU into mechanical movement
What is the lambda sensor ?
Measure oxygen in exhaust gases
Measure the content before the catalytic converter and after
Where is the closed loop signal being used?
Engine idling Cruising speed (constant speed)
Where is open loop scenarios being used?
Acceleration
Deceleration (engine braking)
Cold start
What is the throttle position sensor?
Informs the ECU of the position of the throttle
Can be a potentiometer or contact type switch
What does an air flow sensor do?
Informs the ECU of the amount of air entering the system
What are the 2 types of air flow sensors?
Mechanical type- measures the amount of air by VOLUME
Electronic type- Measures amount of air by MASS
How does the mechanical air flow sensor work?
Air deflects the flap and rotates the spindle which turns a wiper on the potentiometer- change in resistance
Adjust fuel to maintain correct ratio
What is the bypass port used for on an airflow operation ?
Allow air flow when idling
How does the electrical airflow sensor work?
ECU applies a small current to a wire , the cooling effect of the air causes the resistance to change in the wire, this determines the air temperature
The amount of current can determine whats happening to the air
What is a MAP sensor ?
Measure the amount of air entering the intake manifold in order to tell the ECU how much load is on the engine
Does this by measuring the vacuum created by acceleration - depression pulls diaphragm up causing the wiper to change the resistance
What is the crank angle sensor ?
Informs the ECU of the position and rotational speed of the crankshaft
RPM
Where can the CAS be located ?
Near the front pulley or on the bell housing
How does the CAS operate?
When the reluctor tooth is not level , voltage is produced which is detected by the ECU, when the tooth is level no voltage is lost
The pulses are counted per minute and this calculates the rpm
What is a knock sensor ?
Detect pressure changes in the cylinder block due to pre ignition and pre detonation
How does the knocking sensor work?
Voltage fed to piezoelectric crystal
Detonation occurs
This bends with shock wave and changes the resistance and the voltage changes
It uses this to retard the ignition timing or injection
What is the fuel injector valve?
Control the flow of fuel into the engine
Uses a solenoid, which produces a magnetic field and this attracts the nozzle causing the fuel to be injected and when the voltage is removed the nozzle returns to its seat
