Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois
Chapter 22 Gasoline Injection Fundamentals
Contents Gasoline injection fundamentals Gasoline injection classifications Throttle body and multiport injection Gasoline injection controls Electronic fuel injection Engine sensors Injector pulse width (Continued)
Contents Throttle body injection Engine idle speed control Continuous throttle body injection Electronic multiport injection Air-fuel emulsion injector Unitized multiport injection (Continued)
Contents Injector resistor pack Airflow-sensing multiport EFI Pressure-sensing multiport EFI Hydraulic-mechanical continuous injection system Fuel accumulator Direct gasoline injection
Gasoline Injection Fundamentals Uses pressure from an electric fuel pump to spray fuel into the engine’s intake manifold Provides the engine with the correct air-fuel mixture for specific operating conditions
Advantages Improved atomization Better fuel distribution Smoother idle Improved fuel economy Lower emissions Better cold-weather driveability Increased engine power Simpler
Atmospheric Pressure Formed by the air surrounding the earth At sea level, the atmosphere exerts 14.7 psi (103 kPa)
Vacuum Lower than atmospheric pressure Less than 14.7 psi (103 kPa) at sea level Sometimes called suction
Differences in Pressure Cause Flow An engine uses differences in pressure to force fuel and air into its cylinders The engine acts as a vacuum pump, producing low pressure, or vacuum, in the intake manifold
Intake Manifold Vacuum Closed throttle, high vacuum Open throttle, reduced vacuum
Engine Throttle Valve Controls airflow and gasoline engine power output When opened, airflow, fuel flow, and power increase
Throttle-by-Wire System Uses a pedal sensor, the ECU, and an actuator to operate the engine throttle valve The ECU regulates engine speed to improve fuel economy Some systems provide sport and comfort modes
Gasoline Injection Classifications There are many types of gasoline injection systems A gasoline injection system is commonly called a fuel injection system A diesel injection system is also a fuel injection system
Throttle Body and Multiport Injection
Throttle Body Injection Injector nozzles are mounted in a throttle body assembly on top of the engine Multiport Injection Injectors are mounted in the intake ports going to each cylinder
Indirect Injection Sprays fuel into the intake manifold. Most gasoline systems are indirect. Direct Injection Sprays fuel directly into the engine’s combustion chambers. Used in all diesel injection systems.
Gasoline Injection Controls Electronic fuel injection Hydraulic fuel injection Mechanical fuel injection Injection timing Injector opening relationship
Electronic Fuel Injection Uses various engine sensors and a control module to regulate the opening and closing of the fuel injectors This is the most common type of gasoline injection system
Hydraulic Fuel Injection Uses hydraulic control devices moved by air or fuel pressure Airflow sensor and fuel distributor meter gasoline (continuous injection) the fuel distributor is a hydraulic valve mechanism that meters fuel into the engine
Mechanical Fuel Injection Uses throttle linkage, mechanical pump, and governor to control injection volume Old, seldom-used system used on high-performance gasoline and diesel engine applications
Injection Timing Intermittent injection Timed injection opens and closes injectors independent of engine intake valves Timed injection sprays fuel into the engine just before or as the intake valve opens Continuous injection sprays fuel into the intake manifold at all times
Injector Opening Relationship Simultaneous Injection all the injectors open at the same time pulsed on and off together Sequential Injection injectors open one after the other injection matches the firing order of the engine
Injector Opening Relationship Group Injection Several but not all injectors open at the same time V-8 engine–one group of four injectors open at one time, another group of four open at a different time
Electronic Fuel Injection (EFI) EFI system can be divided into four subsystems: fuel delivery system air induction system sensor system computer control system
Systems Overview
Fuel Delivery System Components electric fuel pump fuel filter fuel pressure regulator injectors
Fuel Delivery System
Electric Fuel Pump Draws gasoline out of the tank Forces it to the fuel rail
Fuel Pressure Regulator Controls the pressure entering the injector(s) Returns excess fuel to the tank Vacuum may be ported into the regulator lower pressure at idle increasing pressure at higher load
Fuel Pressure Regulator Low vacuum, high load High vacuum, low load
Injectors Solenoid-operated fuel valve Electrical terminals Armature Injector body Needle valve Fuel inlet Inlet screen Return spring Coil windings Spray mist Solenoid-operated fuel valve When current flows, magnetism attracts the armature to open the injector valve
Air Induction System Air filter Throttle valve(s) Sensors Ducts traps dust and debris Throttle valve(s) controls airflow through the throttle body Sensors sense airflow and throttle position Ducts route clean air to the throttle body
Air Induction System
Sensor System Inputs to the control module Signals the following operating conditions: temperature position pressure or vacuum speed
Computer Control System Uses data from the sensors to control fuel injectors Wiring harness connects computer to sensors and injectors
Electronic Control Module Commonly mounted behind the instrument panel
Engine Sensors Oxygen (O2) Manifold absolute pressure (MAP) Throttle position (TP) Engine coolant temperature(ECT) Airflow
Engine Sensors Intake air temperature (IAT) Crankshaft position (CKP) Fuel pressure Fuel temperature
Oxygen Sensor Measures oxygen content in the exhaust In OBD I vehicles, the sensor is threaded into the exhaust manifold before the catalytic converter OBD II equipped vehicles use at least two oxygen sensors one before and one after catalytic converter the sensor located after the converter monitors catalyst efficiency
Oxygen Sensor Operation Increase in exhaust oxygen from lean mixture causes oxygen sensor voltage to decrease Decrease in exhaust oxygen from rich mixture causes oxygen sensor voltage to increase
Oxygen Sensor Construction
Open Loop Injection system does not use exhaust gas oxygen as an indicator of air-fuel mixture Operation is from information stored in the computer Cold engines operate in open loop
Closed Loop Computer uses information from the oxygen sensor as a main input for air-fuel mixture control Normally, hot engines operate in closed loop
Information Flow Open Loop Closed Loop
MAP Sensor Senses engine load by measuring pressure, or vacuum, inside the intake manifold High pressure (low vacuum) indicates high load Low pressure (high vacuum) indicates low load
Often mounted on the engine or in the engine compartment MAP Sensor Often mounted on the engine or in the engine compartment
Piezo-resistor chip converts pressure change into resistance change MAP Sensor Theory Piezo-resistor chip converts pressure change into resistance change
Manifold vacuum flexes the chip, altering its resistance MAP Sensor Side View Manifold vacuum flexes the chip, altering its resistance
Throttle Position Sensor Senses throttle position Variable resistor connected to the throttle plate As the throttle opens or closes, sensor resistance changes, signaling throttle position
Throttle Position Sensor Variable resistor signals throttle position
Engine Coolant Temperature Sensor Senses engine coolant temperature At low temperatures, sensor resistance may be high computer will richen mixture At high temperatures, sensor resistance changes computer will deliver leaner mixture
Airflow Sensor Measures amount of air entering engine Air flap or door operates a variable resistor Airflow opens the flap, changing position of the variable resistor and changing the signal voltage to the computer
Airflow Sensor Operation This airflow sensor operates a variable resistor
Intake Air Temperature Sensor Measures the temperature of the air entering the engine Air temperature affects air density Cooler air is more dense, requiring more fuel Helps the computer compensate for changes in outside air temperature
Crankshaft Position Sensor Detects engine speed and position Information is used by computer for fuel injection operation
Fuel Pressure Sensor Measures fuel pressure inside the fuel rail Signals to ECU to compensate for variations in fuel system pressure Often used in returnless fuel injection systems
Fuel Temperature Sensor Measures fuel temperature in the fuel rail Signals to ECU to adjust fuel metering, timing, and other parameters In some vehicles, sensor is combined with the fuel pressure sensor in a single housing
Other Sensors Several other sensors may be used: A/C compressor sensor transmission sensor EGR sensor vehicle speed sensor knock sensor
Digital Signals Signal is on or off Voltage goes from maximum to minimum instantly Crankshaft position sensor output may be a digital signal
Analog Signals Signal varies in voltage or strength May be produced by change in resistance of a sensor as temperature, pressure, or position changes
Injector Pulse Width Pulse width is the amount of time an injector is energized At wide open throttle, computer lengthens injector pulse to richen mixture At low load, computer shortens pulse width
Pulse width controls the amount of fuel injected Injector Pulse Width Pulse width controls the amount of fuel injected
Throttle Body Injection Components: throttle body housing TBI injector TBI pressure regulator throttle positioner (idle speed control) throttle position sensor throttle plates
TBI Overview
Fuel enters the regulator before passing into the injector TBI Assembly Fuel enters the regulator before passing into the injector
Throttle Body Housing Bolted to the intake manifold Holds the injector(s), throttle plates, throttle position sensor, fuel pressure regulator, and idle speed control device
TBI Injector Components: solenoid coil armature or plunger ball or needle valve seat Injector spring
This injector uses a ball-type valve instead of a pointed needle valve TBI Injector This injector uses a ball-type valve instead of a pointed needle valve
Injector Operation When the computer energizes the injector, a magnetic field is produced in the coil Magnetism pulls the plunger and valve up to open the injector Fuel can then squirt through the injector nozzle Fuel is sprayed above the throttle valve
TBI Pressure Regulator Contains a fuel valve, diaphragm, and spring Spring holds the fuel valve closed, causing pressure increase as fuel flows in from the electric fuel pump When preset pressure is reached, fuel pressure acting on the diaphragm forces the fuel valve open, allowing fuel to flow back to the tank
TBI System Cutaway
Engine Idle Speed Control There are several different types of idle speed control devices: fast idle thermo valve idle air control motor throttle positioner
Fast Idle Thermo Valve Thermowax plunger contracts when cold to allow more airflow at idle Plunger expands when the engine warms, closing valve and reducing airflow
Fast Idle Thermo Valve Idle air control valve and the thermo valve affect air that bypasses the throttle valve to alter idle speed
Computer controlled solenoid- or servomotor-operated air bypass valve Idle Air Control Motor Computer controlled solenoid- or servomotor-operated air bypass valve
Throttle Positioner Computer controlled motor opens or closes the throttle plates In this way, the computer can maintain a precise idle speed with changes in temperature, load, and other conditions
Continuous Throttle Body Injection (CTBI) Sprays a solid stream of fuel into the air horn Does not pulse the injectors on and off to control the air-fuel mixture System alters pressure applied to the throttle body nozzles to control mixture
Electronic Multiport Injection Uses a computer, sensors, and one solenoid injector for each cylinder Components: multiport throttle body multiport pressure regulator fuel rail
Multiport Fuel Injection Controls
Multiport Fuel Injection Air Delivery
Multiport Fuel Injection Fuel Delivery
Injection Components Throttle body Multiport pressure regulator contains throttle plates and a throttle position sensor Multiport pressure regulator mounted on the fuel rail, maintains pressure at the inlet to the injectors by acting as a bypass
Injection Components Fuel rail Multiport fuel Injector connects the main fuel line to the inlet of each injector Multiport fuel Injector sprays fuel into the intake port, below the throttle valve
Injection Components
Injection Components
Multiport Fuel Injector Solenoid opens the injector when current flows through the coil
Air-Fuel Emulsion Injector Mixes air with the fuel creating a slurry Slurry is injected into the intake manifold Atomizes the fuel and improves combustion Low pressure air from the air injection pump may be used
Air-Fuel Emulsion Injector
Unitized Multiport Injection Mounts all of the injectors into a single assembly A multi-pin terminal connects each injector to the control module
Unitized Multiport Injection Components
Unitized Multiport Injection Components Fuel injection transfer lines connect each injector to its poppet valve Fuel injection poppet valve spring loaded valve that prevents fuel leakage between injector pulses when the fuel injector opens, fuel pressure forces the poppet valve open, spraying fuel into the intake port
Note the fitting for the plastic transfer line Unitized Injector Note the fitting for the plastic transfer line
Injector Resistor Pack Set of low-ohm resistors Resistors control current flow to each injector coil Resistors protect windings from excess current Usually 5-7 ohms Often mounted in the engine compartment
Injector Circuit Circuit contains resistor pack Each pin corresponds to a resistor
Airflow-Sensing Multiport EFI Uses an airflow sensor as a main control Airflow sensor is placed at the inlet to the intake manifold Sensor converts airflow into an electrical signal for the computer
Airflow-Sensing Multiport EFI
Airflow Sensor Operation Throttle moved open for more power, increased flow pushes sensor flap open Throttle almost closed, sensor detects little airflow
Pressure-Sensing Multiport EFI Uses intake manifold pressure (vacuum) as a primary control Pressure sensor is connected to the intake manifold Sensor converts changes in manifold pressure into changes in resistance Computer uses this data
Pressure-Sensing Multiport EFI
Hydraulic-Mechanical Continuous Injection System
Continuous Injection System (CIS) Hydraulic-mechanical system Uses a mechanical airflow sensor to operate a hydraulic fuel distributor Continuous injectors spray fuel anytime the engine is running
Continuous Injection System (CIS)
Continuous Fuel Injector
Cold Start Injector Extra fuel injector Sprays fuel into the intake plenum for cold engine starting and running Improves cold operation by enriching the air-fuel mixture Controlled by a thermo-time switch or control module
Cold Start Injector
Fuel Accumulator Damps pressure pulses May maintain pressure when shut down to aid restarting
Fuel Accumulator Components and Operation Engine running, fuel pressure compresses diaphragm spring Engine off, spring pressure on diaphragm maintains system pressure
Direct Gasoline Injection Used in high-efficiency engines Fuel injector sprays fuel directly into combustion chamber Permits more precise control over fuel economy
Piezo Gasoline Injectors Crystalline ceramic material used instead of an electromagnet to open injector valve Piezo crystal converts electrical energy directly into motion Smaller, lighter construction allows for quick and accurate operation
Direct Gasoline Injection System