Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 28-1Chapter 28 Prepared by Martin Restoule Algonquin College Electronic Fuel Injection

Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 28-1Chapter 28

Prepared byMartin Restoule

Algonquin College

Electronic Electronic Fuel InjectionFuel Injection

2828


ObjectivesObjectives

• Explain the difference between throttle body and port injection systems.

• Describe the difference between a sequential fuel injection (SFI) system and a multi-port fuel injection (MFI) system.

• Explain the design, purpose, and operation of major EFI components.

continued…



• Describe the inputs used by the computer to control the idle air control and idle air control by-pass air motors.

• Describe how the computer supplies the correct air/fuel ratio on a throttle body injection (TBI) system.

continued…



• Explain how the clear flood mode operates on a TBI system.

• Explain why manifold vacuum is connected to the pressure regulator in an MFI system.

• Describe the operation of the pressure regulator in a returnless EFI system.

continued…



• Describe the operation of the central injector and poppet nozzles in a central port injection (CPI) system.

• Describe the operation of direct gasoline injection systems.

continued…


Electronic Fuel Injection ComponentsElectronic Fuel Injection Components

• Powertrain Control Module– The heart of the fuel injection system is the

computer or powertrain control module (PCM).

– The PCM receives signals from all the system sensors, processes them, and transmits programmed electrical pulses to the fuel injectors.

– Both incoming and outgoing signals are sent through a wiring harness and a multiple-pin connector.

continued…



• Fuel Injectors – Fuel injectors are electromechanical

devices that meter and atomize fuel so it can be sprayed into the intake manifold.

– When the injector is electrically energized, a fine mist of fuel sprays from the injector tip.

– Two different valve designs are commonly used, a nozzle or needle valve and a ball valve.

– Both operate similarly with magnetic fields unseating the valves and a spring seats or closes the valve.

continued…



A typical fuel injector and its components

continued…



Examples of top and bottom feed injectors

continued…



• Idle Air Control– Engine idle speed is controlled by

bypassing a certain amount of airflow past the throttle valve in the throttle body housing.

– Two types of air bypass systems are used; auxiliary air valves and idle air control (IAC) valves.

continued…



• Idle Air Control (concluded)– The IAC system consists of an PCM

controlled stepper motor or actuator that extends or retracts the idle air control valve in the air bypass channel. around the throttle valve.

– The PCM calculates the amount of air needed for smooth idling based on input data such as coolant temperature, engine load, engine speed, and battery voltage.

continued…



An idle air control system

continued…


Types of Fuel Injection SystemsTypes of Fuel Injection Systems

• Throttle Body Injection (TBI)– The throttle body unit is similar in size and

shape to a carburetor, and, like a carburetor, it is mounted on the intake manifold.

– The injector(s) sprays fuel down into a throttle body chamber leading to the intake manifold.

– The intake manifold feeds the air/fuel mixture to all cylinders.

continued…



• Throttle Body Injection (TBI) (concluded)– Four-cylinder engines have a single– throttle body assembly with one injector and

throttle, whereas V6 and V8 engines are equipped with dual injectors and 2 throttles on a common throttle shaft.

– The throttle body assembly contains a pressure regulator, injector or injectors, TP sensor, idle speed control motor, and throttle shaft and linkage assembly.

continued…



A dual throttle body assembly

continued…



• Port Fuel Injection (PFI)– PFI systems use one injector at each

cylinder. – They are mounted in the intake manifold

near the cylinder head, where they can inject a fine, atomized fuel mist as close as possible to the intake valve.

– Fuel lines run to each cylinder from a fuel manifold, usually referred to as a fuel rail.

– Since each cylinder has its own injector, fuel distribution is exactly equal.

continued…



Port injection sprays fuel into the intake port and fills the port with fuel vapour before the valve opens

continued…



• Types of Port Fuel Injection– While all port injection systems operate

using an injector at each cylinder, they do not fire the injectors in the same manner.

– In multiport injection (MPI) systems, the injectors are arranged and turned on in pairs or groups.

– When the injectors are split into 2 equal groups, the groups are fired alternately (one group firing during each engine revolution).

continued…



• Types of Port Fuel Injection– Sequential fuel injection (SFI) systems

control each injector individually so that it is opened just before the intake valve opens.

– This means that the mixture is never static in the intake manifold and mixture adjustments can be made almost instantaneously between the firing of one injector and the next.

– Sequential firing is the most accurate and desirable method of regulating port injection.

continued…



Grouped injectors in multiport injection

continued…



• Central Port Injection (CPI)– In a central port (CPI) or central multiport

fuel injection (CMFI) system, a central injector assembly is mounted in the lower half of the intake manifold.

– This system uses one injector to control the fuel flow to 6 (on six cylinder engines) individual poppet nozzles.

– Each nozzle contains a check ball and extension spring that regulates the injector discharge.

continued…



Central multiport fuel injection components in the lower half of the intake manifold

continued…



• Gasoline direct injection (GDI)– With gasoline direct-injection, the gasoline

is injected directly into the combustion chamber.

– To prevent the heat from igniting the fuel in the injector, the injectors are designed to completely seal after the fuel is sprayed.

– The injectors must also be able to spray the fuel at a much higher pressure than what is in the cylinder.

continued…



• Gasoline direct injection (GDI) (concluded)– GDI allows for very lean operation (as much as

35:1) during cruising. – Under heavy loads, the system provides near-

stoichiometric air/fuel ratios. – With these lean ratios, the engine’s fuel economy is

increased by nearly 30% and the emission levels are substantially decreased.

– Volumetric efficiency is improved because the intake manifold and port only deliver air to the cylinders.

continued…



Component layout for a GDI system

continued…


Common Input SensorsCommon Input Sensors

• Volume Airflow Sensors– The airflow sensor (commonly called an

airflow meter or vane airflow sensor), measures airflow, or air volume.

– As air is drawn into the engine, a flap is deflected against a spring.

– A potentiometer attached to the flap shaft monitors the flap movement and produces a voltage signal.

– Signal strength increases as the flap opens.continued…



• Volume Airflow Sensors (concluded)– A Karman Vortex sensor is another design of

airflow sensor.– Air entering the airflow sensor passes

through vanes arranged around the inside of a tube and begins to swirl.

– The swirling air exerts high pressure against the outside of the housing and a low-pressure area in the centre of the intake tube.

– Two pressure-sensing tubes and an electronic sensor counts how many times the low-pressure area is sensed.

continued…



A typical airflow sensor

continued…



• Intake Air Temperature (IAT) Sensor– Cold, dense air can burn more fuel than the

same volume of warm air because it contains more oxygen.

– Airflow sensors that only measure air volume must have their readings adjusted to account for air temperature.

continued…



• Intake Air Temperature (IAT) sensor– An air temperature sensor mounted in the

induction system can measure air temperature and send an electronic signal to the control computer.

– The computer uses this input along with the air volume input in determining the amount of oxygen entering the engine.

continued…



• Mass Airflow Sensor (MAF)– By measuring air mass, a mass airflow

sensor does the job of a volume airflow sensor and an air temperature sensor.

– The mass of a given amount of air is calculated by multiplying its volume by its density.

– From a measurement of mass, the electronic control unit adjusts the fuel delivery for the oxygen content in a given volume of air.

– The accuracy of air/fuel ratios is greatly enhanced when matching fuel to air mass.

continued…



A Mass Airflow Sensor

continued…



• Mass Airflow Sensor (MAF) (concluded)– The mass airflow sensor converts air flowing

past a heated sensing element into an electronic signal.

– The strength of this signal is determined by the energy needed to keep the element at a constant temperature.

– As the volume and density (mass) of airflow across the heated element changes, the temperature of the element is affected and the current flow to the element must be adjusted.

continued…



Components of a hot wire-type mass airflow sensor

continued…



• Manifold Air Pressure (MAP)– The MAP sensor measures changes in the

intake manifold pressure that result from changes in engine load and speed.

– The pressure measured by the MAP sensor is the difference between barometric and manifold pressure.

– At idle, the engine produces a low MAP value.

– At wide-open throttle, manifold and barometric pressure are equal and a high value is produced.

continued…



A MAP Sensor

continued…



• Oxygen Sensor– The signals from the exhaust gas oxygen

sensor (O2S), or lambda sensor, are used by the PCM to monitor the air/fuel mixture.

– The signal from an oxygen sensor is based on the amount of oxygen in the exhaust gas.

– When the sensor’s signal indicates a lean mixture (more oxygen), the computer enriches the air/fuel mixture to the engine.

– When the sensor reading is rich (less oxygen), the computer leans the air/fuel mixture.

continued…



• Coolant Temperature Sensor – The coolant temperature sensor signals

the PCM when the engine needs cold enrichment, as it does during warm-up.

– This adds to the base pulse, but decreases to zero as the engine warms up.

continued…



• Throttle Position Sensor – The PCM uses throttle position sensor

information to determine throttle position, the rate of throttle opening and closing, and to determine if the throttle is closed or wide open.

continued…



• Crankshaft Position Sensor – The crankshaft position sensor (engine

speed) can provide engine data directly to the PCM or through the ignition system.

– This also times the start of the injection according to the intake stroke cycle.

continued…



• Cranking Enrichment – The starter circuit sends a signal for fuel

enrichment during cranking operations even when the engine is warm. This is independent of any cold start fuel enrichment demands.

continued…


Basic Fuel Injection SystemBasic Fuel Injection System

• Input sensors– Give engine operating condition

information to the computer.

• Control module– Determines how much fuel the engine

needs and controls the fuel injectors.

• Fuel injectors– Meter and atomize the fuel entering the

intake manifold or intake port.

continued…


Control Module Operating ModesControl Module Operating Modes

• Open loop mode– The computer uses pre-programmed

values and basic sensor information to determine injector pulse length.

• Closed loop mode– In addition to the other input sensors, the

computer uses signals from the exhaust oxygen sensor to determine injector pulse length.

continued…


Open and Closed LoopOpen and Closed Loop

continued…


Operating ModesOperating Modes

• Clear flood mode– The computer cuts off the fuel injectors

when throttle position is high (wide open) and RPM is low (cranking speed).

• Acceleration enrichment mode– The computer adds extra fuel during rapid

changes in throttle position and manifold vacuum or air flow.

continued…


SummarySummary

• There are three types of electronic fuel injection systems: throttle body, port, and central multi-port.

• Port injection systems use one of four firing systems: grounded single fire, grouped double fire, simultaneous double fire, or sequential fire.

continued…


SummarySummary

• The airflow sensor determines the amount of air entering the engine.

• The heart of the fuel injection system is the electronic control unit.

• Two types of fuel injectors are currently in use: top feed and bottom feed.

continued…


SummarySummary

• In a speed-density EFI system, the computer uses manifold pressure and engine rpm inputs to calculate the amount of air entering the engine.

• In an EFI system, the computer supplies the proper air/fuel ratio by controlling injector pulse width.

continued…


SummarySummary

• In an SFI system, each injector is controlled individually by the computer.

• The pressure regulator maintains the specified fuel system pressure and returns excess fuel to the fuel tank.

continued…


SummarySummary

• In a returnless fuel system, the pressure regulator and filter assembly is mounted with the fuel pump and gauge sending unit assembly in the fuel tank.

• A central multi-port injection system has one central injector and a poppet nozzle in each intake port.

continued…


SummarySummary

• GDI systems inject gasoline directly into the combustion chamber and allow for very lean operation.

• EFI systems rely on inputs from various sensors; these include airflow, air temperature, mass airflow, manifold absolute pressure, oxygen, coolant temperature, and throttle position sensors.

Documents

Copyright © 2007 by Nelson, a division of Thomson Canada Limited. 28-1Chapter 28 Prepared by Martin Restoule Algonquin College Electronic Fuel Injection