toyota training course t874 engine control systems II ch08

The ECM controls engine idle speed with the Idle Air Control Valve IACV.. • Dual VVT-i controls both intake and exhaust valve timing.. VVT-i uses the crankshaft position sensor and Varia

Air Induction Systems

Section 8

Slide 109

L852f809

Without an Electronic Throttle Control System, the throttle valve position and opening rate is controlled directly by the driver through a mechanical system (accelerator cable or linkage) The ECM controls engine idle speed with the Idle Air Control Valve (IACV) Under command from the ECM, the IACV allows a certain amount of air to bypass the closed throttle valve Use of an IACV allows idle speed to be stabilized under varying engine loads and, in some applications, provides cold fast idle Electronic Throttle Control System-intelligent (ETCS-i) gives the ECM complete control of the throttle valve position and opening rate

ETCS-i controls throttle operation based on driver input and other vehicle operating conditions ETCS-i allows systems such as Vehicle Skid

Control (VSC) to adjust throttle valve angle to help maintain traction A

“limp home” feature allows the vehicle to be driven at reduced speed if the system malfunctions

Electronic Throttle

Control System

Overview

In linkless ETCS-i, there is no mechanical cable connection between the driver’s foot and the throttle body Major system components include:

• Accelerator Pedal Position Sensor (APPS): The APPS is mounted

at the accelerator pedal As the driver moves the accelerator pedal, the APPS signal voltage changes to indicate pedal position There are two voltage output signals from the APPS The ECM uses these two signals to calculate the desired throttle valve angle Also, by using two signals the ECM is able to compare and detect if there is anything wrong with APPS performance

• Throttle Position Sensor (TPS): The TPS detects the actual angle

of the throttle valve This system uses a dual-output TPS

• Throttle Control Motor: The throttle control motor is a DC motor

controlled by the ECM The ECM controls the direction and the amperage of the current through the motor The circuit is pulsewidth modulated (duty ratio cycle regulated) If there is a malfunction, the ECM shuts the circuit OFF and the return springs close the throttle valve The ECM will turn the motor OFF if there is not enough or too much amperage in the motor circuit Unlike the link type, there

is no magnetic clutch between the throttle control motor and the throttle valve

• Fail-Safe: If ETCS-i malfunctions, the MIL will illuminate to alert

the driver If the failure is in either one of the APPS or TPS signals, the ECM will attempt to use the second signal to continue limited electronic throttle control If all four of these signals malfunction, the vehicle can be operated only at idle speed (there is no “limp mode” lever) ISC and cruise control systems will not operate

Operation

Slide 110

208EG44/241EG28

Without variable valve timing, engine valve timing is a compromise between the needs to produce maximum torque (horsepower) at low to medium speeds, idle stability, fuel economy, low emissions, and maximum horsepower output Continuously adjusting when the valves open and close, called variable valve timing, yields significant improvements in all these areas The ECM, according to driving conditions such as engine speed and load, will advance or retard the camshaft, changing when the valves open and close This system is called the Variable Valve Timing-intelligent (VVT-i) system

There are two types of VVT-i:

• VVT-i controls intake valve timing only (as shown)

• Dual VVT-i controls both intake and exhaust valve timing

Both systems use an ECM-controlled oil pressure system to alter camshaft position

Variable Valve Timing

Systems (VVT-i)

Slide 111

T852f285/T852f286

VVT-i provides a variety of benefits:

• Smooth Idle: At idle RPM, valve overlap is eliminated by retarding

the camshaft There is no blowback of exhaust gases to the intake side Combustion is more stable because of the clean air/fuel mixture

• Torque Improvement in Low to Medium Speed Range: In the low

to medium speed range with a heavy load, the camshaft is advanced, increasing the valve overlap This has two effects First, the exhaust gases help pull in the intake mixture Second, by closing the intake valve early, the air/fuel mixture taken into the cylinder is not discharged This improves volumetric efficiency and increases torque (and therefore horsepower) in the low and midrange RPM range

• EGR Effect: VVT-i eliminates the need for an Exhaust Gas

Recirculation (EGR) valve by increasing valve overlap

• Better Fuel Economy: A VVT-i equipped engine is more efficient

and provides better fuel economy from a variety of factors Without VVT-i, the engine would have to be larger and heavier to produce the same horsepower Smaller pistons, connecting rods, and crankshaft reduce friction and mechanical losses A lighter engine improves vehicle fuel economy Also, it takes less energy to move the piston downward on the intake stroke

• Improved Emission Control Performance: VVT-i increases the

valve overlap, creating an internal EGR effect Another benefit

is that hydrocarbons (HCs) are reduced Some of the unburned air/fuel mixture from the previous cycle returns to the cylinder for combustion Finally, CO2 is reduced because of the decrease in fuel consumption

Effects of VVT-i

Benefits of VVT-i Air Induction Systems

Slide 112

VVT-i uses the crankshaft position sensor and Variable Valve Timing (VVT) sensors (camshaft position sensor) to measure the amount of camshaft movement This feedback is necessary for the ECM to know how much and which direction to move the camshaft, and for diagnosis

A continuously variable valve timing mechanism, called a controller or actuator, is used to adjust the camshaft from one end of its adjustment range to the other

A camshaft timing Oil Control Valve (OCV), controlled by the ECM, directs engine oil pressure to the advance or retard side of the VVT-i controller Two types of controller have been used: helical and vane All Dual VVT-i systems use vane type controllers

When trying to determine the cause of a VVT system issue, check the Freeze Frame data and duplicate the conditions Use the Technical Information System (TIS) for Repair Manual (RM) and Electrical Wiring Diagram (EWD) information, and look for applicable Technical Service Bulletins (TSBs)

Active tests can be performed to check the VVT system Different active tests will be available depending on the VVT system Typically, when the valve timing is changed at idle with an active test, the engine will run rough or may die Refer to the Repair Manual for the proper VVT active test response and diagnostic procedure

Check the vehicle service history If the vehicle has been repaired in the past, check for improperly installed timing belts, components, etc

Construction

Diagnosis

Active Tests

Slide 113

T852f296/T852f297

NOTE:

The Oil Control Valve (OCV) is controlled by the ECM to direct engine oil pressure to the advance or retard side of the VVT-i controller The OCV spool valve position is determined by a varying magnetic field strength opposing a constant spring strength:

• Advance: To advance timing, the ECM increases the pulsewidth (duty

ratio) This strengthens the magnetic field, overcoming spring pressure and moving the spool valve to send more oil to the advance side

• Retard: To retard the timing, the ECM decreases the pulsewidth

Spring pressure overcomes the weaker magnetic field and the spool valve moves toward the retard position

• Hold: When the camshaft is in the desired position, the ECM sends

a pulsewidth that moves the spool valve to the hold position In the hold position, the oil is trapped in the controller, maintaining the desired camshaft position When the engine is stopped, the spring pushes the spool valve to the most retarded position (intake) or the most advanced position (exhaust)

Oil Control Valves

Slide 114

T852f288/T852f289

The helical VVT-i controller has an outer gear driven by the timing belt,

an inner gear affixed to the camshaft, and a movable piston that is placed between the outer gear and inner gear As the piston moves laterally (axially), the helical splines on the piston and inner gear force the camshaft to move in relation to the timing gear

Oil pressure from the OCV is directed to one or the other side of the piston to advance, retard, or maintain valve timing:

• Advance: When the ECM commands the OCV to advance timing,

hydraulic pressure is applied from the left side of the piston, moving the piston to the right The twist in the helical splines on the inside diameter of the piston causes the intake camshaft to rotate in the advance direction in relation to the camshaft timing pulley

• Retard: When the ECM commands the OCV to retard timing,

hydraulic pressure is applied to the right side of the piston, moving the piston to the left The camshaft rotates in the retard direction

• Hold: To hold the desired camshaft position, the OCV shuts off the

oil passages This maintains the hydraulic pressure on both sides of the piston, and camshaft position does not change

Controller (Helical)

Slide 115

T852f293/T852f294/T852f295

Oil pressure from the OCV is directed to one or the other vane chamber

to advance, retard, or maintain valve timing:

• Advance: When the ECM commands the OCV to advance timing,

hydraulic pressure is applied to the timing advance side vane chamber The camshaft rotates in the advance direction

• Retard: When the ECM commands the OCV to retard timing,

hydraulic pressure is applied to the timing retard side vane chamber The camshaft rotates in the retard direction

• Hold: To hold the desired camshaft position, the OCV shuts off the

oil passages This maintains the hydraulic pressure in both vane chambers, and camshaft position does not change

Special care should be taken when installing VVT-i controllers Always refer to the Repair Manual for vehicle specific procedures

Controller (Vane)

Slide 116

T852f298/T852f299/T852f300/T852f301/T852f302/T852f303

VVT-i Controller (Vane) Air Induction Systems

NOTE:

Dual VVT-i uses OCVs and vane controllers to set both intake and exhaust camshaft timing Separate control of intake and exhaust valve timing allows varying amounts of valve overlap based on engine operating conditions:

• No overlap: There is no overlap during engine starting/stopping,

idling, low temperature, or light load operation Blowback is prevented on the intake side for improved starting, stabilized RPM, and improved fuel economy

• Maximum overlap: There is maximum overlap during medium

load and low to medium speed operation with heavy load Overlap

is maximized to reduce pumping loss and improve volumetric efficiency for increased torque, better emission control, and improved fuel economy

• Moderate overlap: There is moderate overlap during high speed

operation Overlap is moderate to improve volumetric efficiency for increased power output

Dual VVT-i Operation

Slide 117

Acoustic Control Induction System (ACIS) Air Induction Systems

Slide 118

T852f316

The Acoustic Control Induction System (ACIS) improves torque throughout the engine speed range (especially at low speeds) by changing the intake manifold length in stages The ECM commands intake air control valve(s) to change the length of the intake manifold based on engine speed and throttle valve opening

ACIS is tuned for each type of engine Vacuum stored in the vacuum chamber is applied to the intake air control valve through the VSV The VSV is switched ON and OFF by the ECM The intake air control valve

is switched according to engine speed and load

The air flow in the intake pipe pulsates due to opening and closing of the engine intake valves When an intake valve closes, the air near the valve

is compressed by inertia This compressed air pushes off the intake valve

at high speed toward the intake chamber If the intake manifold length and intake chamber shape are set to cause the compressed air to return

to an engine intake valve during the intake stroke, the intake air volume

is increased, improving volumetric efficiency This is called the intake

"inertia effect", and it improves torque and horsepower

Acoustic Control

Induction System

(ACIS)

The Exhaust Gas Recirculation (EGR) system is used for reducing oxides

of nitrogen (NOx) and for engine knock control Recirculating a controlled amount of exhaust gases into the intake air/fuel mixture lowers combustion temperature and pressure This, in turn, reduces the amount of NOx emission, helps prevent engine knock, and allows for more advanced ignition timing Under the following conditions, EGR is cut to maintain driveability

• Before the engine is warmed up

• During deceleration (throttle valve closed)

• Light engine load (amount of intake air very small)

• High engine RPM

• Wide open throttle (WOT)

• Engine idling The EGR valve opens and closes the passage between the exhaust manifold and intake manifold Vacuum is used to move the EGR valve Inside the vacuum actuated EGR valve is a valve, diaphragm, and spring When vacuum

is applied to the diaphragm, it lifts the valve off its seat, allowing exhaust gases into the intake air stream When vacuum is removed, the spring forces the diaphragm and valve downward, closing the exhaust passage

For proper engine operation, the EGR valve must open to the proper height, and when closed seal the intake manifold from exhaust gases Some EGR valves are water cooled to cool the exhaust gases Cooling the exhaust gases increases their effectiveness in reducing NOx and controlling engine knock

Exhaust Gas

Recirculation (EGR)

Slide 120

T852f250

In the Cutoff Control EGR system, the amount of exhaust gas to be recirculated is controlled by the EGR vacuum modulator The EGR vacuum modulator compensates for changes in engine vacuum and exhaust backpressure due to changes in throttle position and engine load The EGR vacuum modulator provides vacuum to the EGR valve so that

it opens to the correct height regardless of variations in engine vacuum or exhaust backpressure The ECM controls the EGR VSV to allow or block this modulated vacuum from reaching the EGR valve When the ECM turns the VSV ON, vacuum is blocked from reaching the EGR valve When the ECM turns the VSV OFF, vacuum is allowed to reach the EGR valve through the EGR vacuum modulator

The ECM uses the EGR temperature sensor signal for EGR operation detection If the temperature is too low (cold) there is little or no flow If the temperature is high (hot) when the EGR valve is supposed to be OFF, the EGR valve is leaking

EGR Operation

(Cutoff Control)

Slide 121

T852f251

EGR Operation (Cutoff Control) Air Induction Systems

This type of ECM controlled EGR system uses a Vacuum Control Valve (VCV), an EGR VSV, and an EGR valve position sensor to regulate exhaust gas flow

The VCV regulates the intake manifold vacuum applied to the VSV to a constant level

The EGR valve position sensor is a potentiometer sensor mounted on the EGR valve As the EGR valve opens, the voltage signal of the EGR valve position sensor increases

The ECM uses the EGR valve position sensor signal to control EGR valve position height EGR valve height is controlled by the strength

of the vacuum signal, and the ECM controls vacuum signal strength by varying the pulsewidth signal sent to the EGR VSV If greater EGR flow

is needed, the ECM increases the pulsewidth signal to the EGR VSV This applies more vacuum to the EGR valve

The ECM uses the EGR temperature sensor signal for EGR operation detection If the temperature is too low (cold) there is little or no flow If the temperature is high (hot) when the EGR valve is supposed to be OFF, the EGR valve is leaking

EGR Operation

(Constant Vacuum)

Slide 122

T852f255