Download File

Electronic Fuel Injection
Roger Bortignon
1
Electronic Fuel Injection
• during the late 1970’s and early 1980’s, government imposed minimum fuel
mileage standards and tougher pollution control standards meant the end of the
carburetor
• Electronic Fuel Injection (EFI), was developed to help manufacturers build vehicles
that use less fuel, run cleaner and perform better
2
What is EFI?
• EFI uses a computer called a Powertrain Control Module (PCM) to determine how
much fuel the engine needs
• the computer turns on a fuel injector which sprays fuel, under pressure, into the
intake manifold or directly into the cylinder
3
Hey Roger, this new technology is amazing!
4
3 main types of fuel injection…
1) Throttle body injection (TBI)
• uses 1 or 2 injectors mounted on top of the throttle (fig. a)
• performs better than a carburetor
• unequal fuel distribution with some condensation
• looks similar to a carburetor (fig. b)
• low manufacturing costs
• not as common today (used a lot in the 1980s)
fig. a
fig. b
5
3 main types of fuel injection…
2) Multi-port or multi-point injection (MPFI)
• uses 1 injector for each cylinder
• much more common than TBI
• delivers the fuel more precisely than TBI
• more complex and costly compared to TBI
• intake manifold only delivers air so it can be designed for max. air flow
• improves low speed torque
6
3 main types of fuel injection…
• 3) Direct injection (newest design) injects the fuel directly into the combustion
chamber
7
How EFI Works
Input
Engine sensors
Processing
Computer
Output
Fuel quantity
Idle speed
Spark timing
Emission controls
8
Input Section
• these sensors provide engine information to the PCM…
 engine speed sensor
 throttle position sensor
 coolant temperature sensor
 air temperature sensor
 engine load sensor
 knock (detonation) sensor
 oxygen sensor
9
Input Section – Engine Speed
• engine speed, measured in RPM’s, is provided to the PCM
by either…
 the distributor’s pick-up coil (vehicles with
distributors) or…
 crankshaft position sensor (used on distributor-less &
direct ignition)
10
Input Section – Throttle Position
• throttle position sensor (TPS) tells the PCM how much pressure the driver is
putting on the throttle
• TPS is a variable resistor
11
Input Section – TPS
• a 5 volt signal is sent to the TPS. A return signal is sent back to the PCM that
corresponds with throttle position.
• idle: ≈ .5 volt
• ½ throttle: ≈ 2.5 volts
• wide open throttle ≈4.5 volts
• PCM interprets these return voltages as specific throttle positions.
• PCM can then adjust the quantity of fuel needed accordingly.
12
TPS & PCM Wiring
• throttle position determines what portion of the 5 volt signal is at the PCM’s
signal terminal
PCM
13
Input Section – Engine Temperature
• a coolant temperature sensor (CTS) is used to provide the PCM with the
temperature of the coolant
• the PCM can then inject more fuel the colder the engine is or less fuel as the
engine warms up
• the CTS is a temperature sensitive resistor (thermistor). As the temperature
increases, its resistance decreases
14
Input Section – Air Temperature
• an air temperature sensor is used to provide the PCM with the temperature of the
air entering the intake manifold
• the PCM can then inject more fuel the colder the engine is or less fuel as the engine
warms up
• the air temperature sensor is a temperature sensitive resistor
 as the temperature increases, its resistance decreases
15
Input Section – Measuring Engine Load #1
• a manifold absolute pressure sensor (MAP sensor) senses engine vacuum and
uses this signal as an indicator of the engine load
• light engine load = higher vacuum = lower manifold pressure
• heavy engine load = lower vacuum = higher manifold pressure
• PCM responds by injecting more fuel into the engine during heavy loads, or less
fuel at light loads
16
Input Section – Measuring Engine Load #2
• another way to measure engine load is to
measure how much air is flowing into the engine
• mass airflow sensor (MAF) “tells” the
computer how much load is being placed on the
engine
• MAF measures airflow into the engine in
grams/second
17
Input Section – Measuring Engine Load #3
• air flow can also be measured with an air flow meter
• uses a moveable flap
18
Input Section – Spark Knock
• knock sensor can detect detonation & PCM will respond by retarding the ignition
timing
 detonation is combustion of the fuel that wasn’t initiated by the spark plug
 this can be caused by excessive heat, carbon build-up or low octane fuel
19
Input Section – Oxygen Sensor
• the key to EFI’s ability to provide excellent fuel economy & low emissions is the
oxygen sensor (O2 sensor)
• the O2 sensor “tells” the PCM if the air-fuel mixture is too rich or too lean. PCM
then adjusts the AFM to keep it at the ideal ratio of 14.7:1
Tech Tip:
too rich means too much fuel
too lean means too little fuel
20
How does the O2 sensor do that?
• the O2 sensor screws into the exhaust pipe
• as the exhaust gases leave the engine, the O2 sensor compares oxygen in the atmosphere to
oxygen left in the exhaust gases
• if there is little oxygen left over, this means the mixture is too rich
• if there is lots of oxygen left over, then the mixture is too lean
21
O2 Sensor Communication with the PCM
•
if the mixture is too rich = little oxygen is left over in the exhaust gases
 O2 sensor produces ≈ 1 volt
•
if the mixture is too lean = lots of oxygen left over in the exhaust gases
 O2 sensor produces a low voltage ≈ .1 volt
•
if the mixture is perfect (14.7:1), then the O2 sensor will produce .5 volt
22
Output Section
23
Output Section – Fuel Delivery
• once the PCM has received all the data from the input sensors, it then decides how
much fuel to give the engine by varying how long the injector is turned on
• injector on-time is called pulse width
 (measured in milliseconds)
24
25
26
Output Section – Idle Speed Control
• the PCM is also responsible for controlling the idle speed of the engine with an
idle speed motor…
27
28
PCM Output Control
• in addition to fuel quantity & idle speed control, the PCM also controls
emission control devices
 we’ll discuss these after spring break
29
Fuel Delivery System
• a fuel pump draws fuel from the tank and pressurizes
• the fuel pump and fuel pressure regulator work together to maintain…
 TBI injection operates at lower pressures ≈ 15psi (using an electric fuel pump)
some multiport pressures are higher than 35psi (using an electric fuel pump)
direct injection can be in the 400 – 1500psi range (using a mechanical fuel pump)
30
Electric Fuel Pump
31
Returnless Fuel Supply System
•
•
•
•
used since the mid 90’s
uses an in-tank fuel pump & pressure regulator module
reduces fuel evaporative losses
PCM can vary fuel supply by modifying fuel pump pulse width
Return-type
Return-less-type
32
Direct Injection Fuel Supply
• direct injection engines use an engine driven, high pressure mechanical fuel
pump…
• 35psi, as is found on port injection is insufficient for direct injection
• direct injection pressures must overcome compression pressures
45 sec.
33
Gasoline Fuel Injection
• optimal (more better) way of delivering fuel to a spark ignition engine when
compared to carburetors
 more exact control of fuel delivery
 AFM ratio better matched to the engine working conditions
 better fuel economy
 fewer emissions
 less cylinder wear (less chance of fuel washing oil off cylinder)
 better performance (driveability)
34
Electronic Throttle Control - AKA Drive-by-wire
•
•
•
•
•
throttle cable is eliminated
PCM controls air flow into engine – not the driver
TPS is still used
Pedal Position Sensor (PPS) added
DC servo motor opens/closes throttle plate
PPS
35