Electronic Gasoline Injection system
L Jetronic

© Dr. Amr Ibrahim, 2010, all rights reserved. The commercial use of these...
Principle of electronic injection systems:
The electronic injection systems control the amount of injected
fuel electronic...
Schematic of L Jetronic
Fuel supply system
Solenoid operated fuel injection valves:

when the injector opens for longer time,
more fuel is injected
• when the inject...
Fuel pressure regulator:

• the regulator maintains the
pressure difference between fuel
pressure and intake manifold
pres...
Electronic control unit:

• the ECU, which consists of electronic components, receives electric
signals from all engine se...
Air flow sensor:

• the air flow sensor reports the amount of engine air flow to the ECU
• assuming flowing a specific air quantity via the air flow sensor
(point Q)
• this results in a specific angular
position...
Calculating engine speed:
• Information about engine speed is calculated from the number of
electric signals induced by th...
Basic injection fuel quantity:
• Both the air flow and engine speed signals are the main
variables to determine the basic ...
Total injection duration:
• The total injection duration (the duration of electric current
flow in the injector solenoid w...
• Tu= the pulse duration extension according to engine battery
voltage
• the pick up time of fuel injection valves depends...
Engine temperature sensor:

• it reports the engine temperature to
the ECU
• it consists of an NTC (negative
temperature c...
Throttle valve switch:

• it is mounted on the
throttle body and connected
to the throttle valve shaft

• it reports to th...
Engine cold start fuel enrichment:
• fuel enrichment during cold start can be achieved by either:
o extending the injectio...
warm up fuel enrichment:

• fuel enrichment is needed during
engine warm up to compensate for fuel
condensation
• the amou...
Auxiliary air device:
• it is used to increase the amount of air fuel mixture during idling
when the engine is cold to ove...
Engines fitted with a 3-way catalyst:
• the engine must operate at almost stoichiometric mixture in order
for the catalyst...
Lambda sensor:
Supplementary functions
Overrun fuel cutoff:
• the ECU cuts off fuel injection when the throttle valve is closed
while the...
L jetronic
L jetronic
L jetronic
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L jetronic

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L jetronic

  1. 1. Electronic Gasoline Injection system L Jetronic © Dr. Amr Ibrahim, 2010, all rights reserved. The commercial use of these slides without permission is strictly prohibited.
  2. 2. Principle of electronic injection systems: The electronic injection systems control the amount of injected fuel electronically Electronic injection system consists mainly of: • Sensors • Electronic Control Unit (ECU) • Actuators (e.g. solenoid operated fuel injection valves)
  3. 3. Schematic of L Jetronic
  4. 4. Fuel supply system
  5. 5. Solenoid operated fuel injection valves: when the injector opens for longer time, more fuel is injected • when the injector opens for shorter time, less fuel is injected • the valve opening duration (injection period) is controlled by the ECU • all injectors inject the fuel once every crankshaft revolution
  6. 6. Fuel pressure regulator: • the regulator maintains the pressure difference between fuel pressure and intake manifold pressure constant
  7. 7. Electronic control unit: • the ECU, which consists of electronic components, receives electric signals from all engine sensors in order to determine the fuel injection duration
  8. 8. Air flow sensor: • the air flow sensor reports the amount of engine air flow to the ECU
  9. 9. • assuming flowing a specific air quantity via the air flow sensor (point Q) • this results in a specific angular position for the sensor flap (point A) • this leads to a specific voltage to be produced by the potentiometer (point B) • the ECU receives the voltage signal and calculates the basic injected fuel quantity (point C) • the basic injected fuel quantity (point C) must be equivalent to the theoretical injected fuel quantity (point D) as determined by the required airfuel ratio
  10. 10. Calculating engine speed: • Information about engine speed is calculated from the number of electric signals induced by the ignition system to produce sparks • assuming 4-stroke-cycle 4-cylinder engine, 4 spark signals are produced for 2 crankshaft revolutions • that means f=2n, where f= number of sparks produced per second, n= number of crankshaft revolutions per second
  11. 11. Basic injection fuel quantity: • Both the air flow and engine speed signals are the main variables to determine the basic fuel quantity injected for each crankshaft revolution. For a 4 stroke cycle engine: N (rev/min) no of thermodynamic cycles (cycle/min)  2  m a (kg/min) m a (kg/cycle)  N/2 (cycle/min) F mf (kg/cycle)  ma (kg/cycle) A mf, inj (kg/rev)  mf (kg/cycle)/ 2 • the basic injection duration, Tp, is proportional to the basic amount of injected fuel calculated from the main variables
  12. 12. Total injection duration: • The total injection duration (the duration of electric current flow in the injector solenoid winding) determined by the ECU, Ti, is calculated as follows: Ti = Tp + Tm + Tu • Tm = the pulse duration extension as determined according to engine operating conditions such as: o engine cold start o engine warm up o engine load condition (idling or full load) • Tm is a measure of fuel enrichment
  13. 13. • Tu= the pulse duration extension according to engine battery voltage • the pick up time of fuel injection valves depends very much on the battery voltage • the lower the battery voltage, the longer the time which is needed to build the magnetic field to open the injector • without voltage compensation, low battery voltage would result in the injector opening duration to be too short • the battery voltage is fed to the ECU in order for the Tu to be calculated
  14. 14. Engine temperature sensor: • it reports the engine temperature to the ECU • it consists of an NTC (negative temperature coefficient) resistor • when the temperature increases, the electrical resistance of the NTC resistor decreases
  15. 15. Throttle valve switch: • it is mounted on the throttle body and connected to the throttle valve shaft • it reports to the ECU whether the throttle valve is closed (idling) or fully open (full load)
  16. 16. Engine cold start fuel enrichment: • fuel enrichment during cold start can be achieved by either: o extending the injection duration , or o using a cold start valve & a thermo time switch
  17. 17. warm up fuel enrichment: • fuel enrichment is needed during engine warm up to compensate for fuel condensation • the amount of fuel enrichment depends on the engine initial temperature Atmospheric temp=22o C
  18. 18. Auxiliary air device: • it is used to increase the amount of air fuel mixture during idling when the engine is cold to overcome engine friction
  19. 19. Engines fitted with a 3-way catalyst: • the engine must operate at almost stoichiometric mixture in order for the catalyst to operate efficiently • lambda sensor is used in order to measure the oxygen concentration in the exhaust gas • the value of λ is fed to the ECU • the ECU controls the fuel injection duration in order to keep λ=1
  20. 20. Lambda sensor:
  21. 21. Supplementary functions Overrun fuel cutoff: • the ECU cuts off fuel injection when the throttle valve is closed while the engine speed is higher than the idling speed during braking or downhill driving • the fuel injection starts again when engine speed reaches to the idling speed value • this reduces engine fuel consumption and emissions Maximum engine speed limitation: • the ECU cuts off fuel injection when engine speed increases above the maximum speed limit specified by the manufacturer • fuel injection starts again when engine speed is reduced below the maximum limit

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