M Idle Speed Control

8/13/2019 M Idle Speed Control

1/14

Purpose of ECU ControlledIdle Speed Control Systems

The Idle Speed Control (ISC) systemregulates engine idle speed by adjusting the

volume of air that is allowed to by-pass theclosed throttle valve. The ECU controls theIdle Speed Control Valve (ISCV) based oninput signals received from various sensors.The system is necessary to providestabilization of curb idle when loads areapplied to the engine and to provide cold fastidle on some applications. The Idle SpeedControl system regulates idle speed underat least one or more of the followingconditions, depending on application:

Fast Idle Warm Curb Idle Air Conditioner Load Electrical Load Automatic Transmission Load

Difference BetweenMechanical Air Valvesand ECU Controlled ISCV

The ECU controlled ISC systems addressedin this chapter should not be confused with

the mechanical air valves which wereaddressed in Chapter 2, "Air InductionSystem." The ISC valve is totally controlled bythe ECU based on inputs received from thevarious sensors, and it controls manydifferent idle speed parameters.

The Wax type and Bi-metal mechanical airvalves are used only to regulate cold enginefast idle and are not ECU controlled.

There are some engines which utilize amechanical air valve, for cold fast idle control,in combination with an ECU controlled ISCVacuum Switching Valve (VSV) to controlwarm curb idle.

ENGINE CONTROLS PART #3 - IDLE SPEED CONTROL

Page 1 Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.


2/14

Four Different ECU ModulatedIdle Speed Control Systems (ISC)

There are four different types of ECU con-

trolled ISC systems used on Toyota engines.These systems are referred to as:

Stepper motor type

Rotary solenoid type

Duty control ACV type

On-off control VSV type

Step Motor Type ISC Valve

The Step Motor type ISCV is located on theintake air chamber or throttle body. Itregulates engine speed by means of astepper motor and pintle valve which controls

the volume of air by-passing the closedthrottle valve. The ISCV throttle air by-passcircuit routes intake air past the throttle valvedirectly to the intake manifold through avariable opening between the pintle valve andits seat.

The valve assembly consists of four electricalstator coils, a magnetic rotor, a valve andvalve shaft. The valve shaft is screwed intothe rotor so that as the rotor turns, the valveassembly will extend and retract.




3/14

The ECU controls movement of the pintlevalve by sequentially grounding the fourelectrical stator coils. Each time current ispulsed through the stator coils, the shaftmoves one 44 step." Direction of rotation isreversed by reversing the order with whichcurrent is passed through the stator coils.

The pintle valve has 125 possible positions,from fully retracted (maximum air by-pass) tofully extended (no air by-pass). In the eventthat the ISCV becomes disconnected orinoperative, its position will become fixed atthe step count where it failed. Because thestepper idle speed control motor is capableof controlling large volumes of air, it is usedfor cold fast idle control and is not used incombination with a mechanical air valve.




4/14

Primary Controlled Parameters

Initial Set-up

Engines equipped with the stepper type ISCVuse an ECU controlled EFI main relay which

delays system power down for about twoseconds after the ignition is turned off.During these two seconds, the ECU fullyopens the ISCV to 125 steps from seat,improving engine stability when it is started.This reset also allows the ECU to keep trackof the ISCV position after each engine restart.

Engine Starting ControlWhen the engine is started, rpm increasesrapidly because the ISCV is fully open. ThisISCV position is represented by point A onthe graph, 125 steps from seat.

When 500 rpm is reached, the ECU drivesthe ISCV to a precise number of steps fromseat based on the coolant temperature attime of start-up. This information is stored ina look up table in the ECU memory and isrepresented by point B on the graph.

Engine Warm-up Control

As the engine coolant approaches normaloperating temperature, the need for cold fastidle is gradually eliminated. The ECUgradually steps the ISCV toward its seatduring warmup. The warm curb idle positionis represented by point C on the graph. By

the time the coolant temperature reaches176'F (80'C), the cold fast idle program has

ended.

Feedback Idle Speed Control

The ECU has a pre-programmed target idlespeed which is maintained by the ISCVbased on feedback from the Ne signal.Feedback idle speed control occurs any timethe throttle is closed and the engine is atnormal operating temperature. The target idle

speed is programmed in an ECU look uptable and varies depending on inputs fromthe A/C and NSW signals. Any time actualspeed varies by greater than 20 rpm fromtarget idle speed, the ECU will adjust the ISCvalve position to bring idle speed back ontarget.




5/14

Engine Load/Speed ChangeEstimate Control

To prevent major loads from changingengine speed significantly, the ECUmonitors signals from the Neutral Start

Switch (NSW) and the Air Conditioner switch(A/C) and re-establishes target idle speedsaccordingly. ISCV position is adjusted veryquickly as the status of the A/C or NSWinputs change. Before a change in enginespeed can occur, the ECU has moved theISCV to compensate for the change inengine load. This feature helps to maintain astable idle speed under changing loadconditions.

The following chart shows typical target idlespeeds which can be found in New CarFeature books. These speed specificationscan be useful when troubleshootingsuspected operational problems in the steptype idle speed control system or relatedinput sensor circuits.

Other Controlled Parameters

Electrical Load Idle-up

Whenever a drop in voltage is sensed at theECU +B or IG S/W terminals, the ECU

responds by increasing engine idle speed.This strategy ensures adequate alternatorrpm to maintain system voltage at safeoperational levels.

Deceleration Dashpot Control

Some ECUs use a deceleration dashpotfunction to allow the engine to gradually idledown. This strategy helps improveemissions control by allowing more air intothe intake manifold on deceleration. Thisextra air is available to mix with any fuel whichmay have evaporated during the low manifoldpressure conditions of deceleration.

Learned Idle Speed Control

The idle speed control program is based onan ECU stored look up table which lists pintlestep positions in relation to specific enginerpm values. Over time, engine wear and othervariations tend to change theserelationships. Because this system iscapable of feedback control, it is alsocapable of memorizing changes in therelationship of step position and engine rpm.The ECU periodically rewrites the look uptable to provide more rapid and accurateresponse to changes in engine rpm.




6/14

The Rotary Solenoid ISCV is mounted to thethrottle body. This small, lightweight andhighly reliable valve controls the volume ofintake air which is allowed to by-pass theclosed throttle valve. Air volume control isaccomplished by means of a movable rotaryvalve which blocks or exposes the air by-pass port based on signals received fromthe ECU.

Because the Rotary Solenoid ISCV has largeair volume capability, it is used to control coldfast idle as well as other idle speedparameters. Although this ISCV is not usedin combination with a mechanical air valve,models equipped with air conditioning dorequire the use of a separate A/C idle-updevice.

The valve assembly consists of two electricalcoils, a permanent magnet, a valve and valveshaft. A fail-safe bi-metallic coil is fitted to theend of the shaft to operate the valve in theevent of electrical failure in the ISCV system.




7/14

The ECU controls movement of the valve byapplying a 250 Hz duty cycle to coils T1 andT2. The electronic circuitry in the ECU isdesigned to cause current to flow alternatelyin coil T1 when the duty cycle signal is low

and in coil T2 when the signal is high. Byvarying the the duty ratio (on time comparedto off time), the change in magnetic fieldcauses the valve shaft to rotate.

As duty ratio exceeds 50%, the valve shaftmoves in a direction that opens the air by-pass passage. At a duty ratio less than 50%,the shaft moves in a direction which closesthe passage. If the electrical connector is

disconnected or the valve fails electrically,the shaft will rotate to a position whichbalances the magnetic force of thepermanent magnet with the iron core of thecoils. This default rpm will be around 1000 to1200 rpm once the engine has reachednormal operating temperature.

Rotary ISCV Controlled Parameters

Engine Starling, Warm-upand Feedback Control

When the engine is started, the ECU opens

the ISCV to a pre-programmed positionbased on coolant temperature and sensedrpm. The higher the commanded rpm, thelonger the duty ratio will be. As the engineapproaches normal operating temperature,engine speed is gradually reduced.

Once the engine is fully warmed up, the ECUutilizes a feedback idle speed control strategywhich functions identically with the steppermotor ISC system. Different target idlespeeds are established depending on thestatus of load sensor inputs.

Turbo Charger Idle Down Control

On the 3S-GTE engine, the ISCV remains at ahigher idle air by-pass rate for a short periodof time after high speed or heavy loadoperation. This strategy prevents damage tothe turbocharger center shaft bearings bymaintaining an elevated engine oil pressure.

All other controlled parameters for the RotarySolenoid ISC system are the same as thewith the Stepper type ISCV. Idle loadstabilization is maintained when input fromthe neutral safety switch (NSW), headlights orrear window defogger (ELS) indicateadditional engine load.

As with the Stepper type ISC system, theRotary Solenoid system utilizes a learned

idle speed control strategy. The ECUmemorizes the relationship between enginerpm and duty cycle ratio and periodicallyupdates its look up tables. Both systemsutilize current supplied by the BATT terminalof the ECU to retain this learned memory. Ifthe battery is disconnected, the ECU mustrelearn target step positions and duty cycleratios.




8/14

Duty Control Air Control Valve (ACV) ISC

The Duty Control ACV is typically mounted onthe intake manifold. It regulates the volumeof air by-passing the closed throttle valve by

opening and closing an air by-pass. Valveopening time is a function of a duty cyclesignal received from the ECU.

The ACV is incapable of flowing largevolumes of air; therefore, a separatemechanical air valve is used for cold fast idleon engines equipped with this system.

The Duty Control ACV consists of anelectrical solenoid and a normally closed(N/C) valve which blocks passage of fresh airfrom the air cleaner to the intake manifold.The ECU controls the valve by applying a 10Hz variable duty ratio to the solenoid, causingthe valve to pass varying amounts of air intothe manifold. By increasing the duty ratio, theECU holds the air by-pass circuit openlonger, causing an increase in idle speed.

Duty Control ACV Controlled Parameters

Starting and Warm Curb Idle

When the STA signal to the ECU is on, theECU cycles the VSV at a 100% duty cycle toimprove startability. The ACV does not haveany effect on cold fast idle or warm-up fastidle speed.




9/14

When the engine has reached normaloperating temperature, and the IDL contact isclosed, the ECU uses a feedback idle speedcontrol strategy to control warm curb idlespeed. When loads are applied to the engine

from the automatic transmission or electricaldevices, the ECU adjusts target idle speedsaccordingly. When the IDL contact is open orany time the Air Conditioning (A/C) signal tothe ECU is on, the ECU maintains a constantduty cycle ratio to the ACV, allowing a fixedamount of by-pass air to flow.

Diagnostic Mode

When the TCCS system enters diagnosticmode (TE1 shorted to E1), the ECU will drivethe ACV to a fixed duty cycle ratio regardlessof engine operating conditions. Curb idleadjustment on engines equipped with thisISC system is performed in diagnosticmode. For more information on curb idleadjustment procedures, refer to Appendix C.

On-Off Control Vacuum SwitchingValve (V-ISC System)

The simple On-Off Vacuum Switching Valve(VSV) ISC system is controlled by signalsfrom the ECU or directly by tail lamp and rear

window defogger circuits. The VacuumSwitching Valve (VSV) is typically located onthe engine (often under the intake manifold)or in the engine compartment, controlling afixed air bleed into the intake manifold.

The valve is a normally closed (N/Q designwhich is opened when current is passedthrough the solenoid windings. Unlike mostECU controlled circuits which are groundcircuit driven, the ECU controls this VSV bysupplying current to the solenoid coil whenpre-programmed conditions are met.

Additionally, current can be supplied to thesolenoid from the rear window defogger ortaillight circuits by passing through isolationdiodes.




10/14

The VSV allows only a small amount of air toby-pass the closed throttle valve when it isopen, increasing engine speed by about 100rpm when energized. This ISC system doesnot control cold fast idle, and engines

equipped with the system use a mechanicalair valve for cold engine fast idle.

On-Off Control VSV Controlled Parameters

Engine Starting and Warm Curb Idle Control

The solenoid is energized by the ECUwhenever the STA signal is on and for a short

period of time thereafter to improvestartability. Additionally, when the IDL contactis closed, the ECU will energize the solenoidwhenever engine speed drops below a pre-determined rpm.

Automatic Transmission Idle-up Control

The ECU will energize the VSV for severalseconds after shifting the transmission fromPark or Neutral to any other gear to stabilizeengine speed during the transition fromunloaded to loaded conditions.

Electrical Load Idle-up

Referring to the electrical schematic, the VSVreceives current directly from the tail lampand rear window defogger circuits throughisolation diodes whenever these circuits areoperating.

Diagnostic Mode

Whenever the TE1 circuit is grounded, theECU is prevented from actuating the V-ISCVacuum Switching Valve. This inhibit featureis useful during diagnostic and other serviceprocedures. It is important to note that thiswill not prevent the VSV from energizing whenthe defogger or tail lamp relays areenergized.




11/14

Input Sensors Affecting IdleSpeed Control Output

Major Impact Sensors

The following input signals to the ECU havea major impact on the output commandssent to the Idle Speed Control Valve.

Engine RPM (Ne)

The Ne signal is one of the most criticalinputs for proper operation of the ISCsystem. This sensor supplies the enginerpm feedback used to determine whetheractual rpm equals target rpm.

Throttle Position (IDL)

The Idle Speed Control System is functionalonly when the throttle is closed and thevehicle is not moving. The ECU monitors theIDL signal to determine when to outputcommands to the ISC actuator. When the IDLcontact is closed and the vehicle is notmoving, the ECU outputs signals to the ISCV.When the IDL contact is open, the ISCsystem is not functional. Without an accurate

signal from the IDL contact, the ISC systemcannot function normally.

Engine Coolant Temperature (THW)

The idle speed control program look uptables list different engine rpm targetsdepending on coolant temperature for theStep and Rotary ISC systems which controlcold fast idle. The ECU uses the THW signalto determine engine coolant temperature foraccurate control of idle speed under all

engine temperature conditions.

Vehicle Speed (SPD)

The ISC system is not functional when thevehicle is moving. The ECU monitors theSPD signal from the vehicle speed sensor todetermine when to operate the ISCV. If theIDL contact is closed and no SPD signal isdetected, the ECU will output a signal to theISCV.

Vehicle Speed Sensor Operation

The ECU expects to see a digital signal offour pulses for each speedometer cablerevolution when the vehicle is moving. Thevehicle speed sensor (VSS) provides this

signal.

There are two different types of vehicle speedsensors used to supply information to theengine ECU. Although these sensors differ indesign, the final output signal to the ECU isthe same for both, four digital pulses percable revolution.

Reed Switch Type:The Reed Switch vehiclespeed sensor is located in the combinationmeter assembly and is operated by thespeedometer cable. The sensor consists ofan electrical reed switch and a multiple polepermanent magnet. As the the speedometercable turns, the permanent magnet rotatespast the reed switch. The magnetic flux linescause the contacts to open and close as theypass. The magnet is arranged so that thesensor contacts open and close four times

for each revolution of the sensor.




12/14

Photocoupler Type: The Photocouplervehicle speed sensor is also located in thecombination meter and operated by thespeedometer cable. The sensor consists ofa photocoupler circuit and a 20-slot trigger

wheel.

The photocoupler circuit is a simpleelectronic device which uses a photo-transistor and a light emitting diode (LED) togenerate a digital electrical signal (seearticle on Karman vortex air flow meter inChapter 5 for operation theory ofphotocoupler circuit). As the slotted trigger

wheel moves between the LED andphototransistor, it intermittently blocks andpasses light at the photo-transistor. Whenthe wheel blocks the LED, the transistorturns off and when the wheel passes thelight, the transistor turns on.

With 20 slots, this sensor generates 20digital pulses per speedometer revolution. Anelectronic circuit in the combination meterconditions this signal into four pulses whichare sensed by the SPD circuit in the ECU.

Electrically, both the Reed type andPhotocoupler type speed sensors work thesame. The sensor is, in fact, a switch. Byswitching on and off, the sensor pulls areference voltage from the ECU to ground.The resulting voltage drop is monitored bythe ECU as the SPD signal.




13/14

Minor Impact Sensors

Neutral Start Switch (NSW)

The Neutral Start Switch input to the ECU isused for ISC control as well as having an

influence, although minor, on the fuel deliveryprogram. As it relates to the ISC system, thisinput is used to determine when to increaseidle speed for Engine Load/Speed ChangeEstimate strategy.

The NSW signal at the ECU will be low (lessthan 1 volt) as long as the neutral start switchis closed, as it will be with the gear selectorin Park or Neutral. This low signal is causedby the voltage drop across R1 which has arelatively high resistance compared to thestarter and circuit opening relay coils. Whenthe transmission is shifted into any gear, theneutral start switch opens, causing a halt incurrent flow through the NSW circuit. Thiscauses an increase in signal voltage at theNSW terminal of the ECU.

In the event this signal malfunctions, the ECUwill use the wrong target idle speed for ingear operation and a distinct drop in idle rpmwill be noticed as the transmission is shiftedfrom Park or Neutral to any drive gear.

Engine Cranking Signal (STA)

The STA signal is used by the ECU to allowadditional air to enter the intake manifoldwhile cranking the engine. Additionally, it isused to determine when to enrich injectionfor starting and when to operate the FuelPressure-Up (FPU) system. In the event thatthe STA signal malfunctions, the engine maybe difficult to start.

The STA signal at the ECU will be low at alltimes except while the engine is cranking.While cranking, the STA signal goes high(cranking voltage) as current flows throughthe closed ignition switch and neutral startswitch contacts.




14/14

Air Conditioning Compressor Signal (A/C)

The A/C signal to the ECU is used todetermine when the air conditioningcompressor is loading the engine. Thesignal is used primarily as an indication to

increase ISC air flow to stabilize idle speed.The A/C input is also used by the ECU tomodify ignition timing and deceleration fuelcut parameters during compressor operationperiods. When the A/C signal is high and theIDL contact is closed, the ECU limitsminimum ignition spark advance angle.

Additionally, decel fuel cut rpm is increased.In the event that this signal malfunctions, idlequality may suffer and driveability duringdeceleration could be affected.

The A/C signal at the ECU will be high anytime the compressor clutch is energized.When power is removed from the clutchcircuit, it is simultaneously removed from the

A/C input at the ECU.

Electrical Load Sensor (ELS)

The ELS circuit signals the ECU whensignificant electrical load has been placed onthe charging system from the vehicle lightingor rear window defogger systems. The ECU

uses this information to increase the dutycycle ratio on the Rotary ISC Valve, therebymaintaining a stable idle speed.

The ELS signal at the ECU will be low aslong as the tail lamps and rear windowdefogger are off. When either of theseaccessories are turned on, current flows tothe accessory and through an isolation diodeto the ECU. When either accessory is on, thesignal at the ECU will go to battery voltage.



Date post:	04-Jun-2018
Category:	Documents
Upload:	aniket-sankpal
View:	220 times
Download:	0 times

M Idle Speed Control

Documents