Electronic Throttle Control System (Montero): Notes
An electronically controlled throttle valve system, which electronically regulates throttle valve opening, is used. Engine control unit in Powertrain Control Module (PCM) monitors amount of accelerator pedal travel through accelerator pedal position sensor and issues premapped target throttle valve opening values to throttle actuator control unit in PCM in accordance with operating conditions. See Fig 1. Thus, throttle actuator control unit achieves target throttle valve opening by controlling current supplied to throttle actuator motor, which is attached to throttle body.
This system also controls idle speed in addition to controlling throttle valve opening. Thus, previously used Idle Air Control (IAC) motor has been discontinued.
This system can also effect auto-cruise control as an extension of throttle valve opening control. Therefore, an auto-cruise control function has been integrated in PCM.
The operation of throttle valve is controlled to target throttle opening, which is determined by amount of accelerator pedal travel and driving conditions.
The PCM continuously calculates actual idle speed in order to effect idle speed control. If there is a difference from target idle speed, two types of controls are effected: engine speed feedback control that actuates throttle valve in order to correct actual idle speed to target idle speed; and throttle position control that actuates throttle valve in order to accommodate load fluctuations that are caused by A/C or other loads.
The engine speed feedback control regulates volume of air that flows through throttle valve by actuating throttle valve, in order to maintain engine at a prescribed target idle speed. An optimal target idle speed is set to suit every operating condition (such as whether A/C switch is ON or OFF). Engine speed feedback control is effected only when prescribed operating conditions are met, and throttle valve position control is effected at all other times.
While engine is operating at idle, idle speed could change suddenly when load that is applied to engine changes, such as when steering wheel is turned, air conditioning switch is turned ON/OFF, or shift lever is operated. Immediately after any of these signals are detected, this control actuates throttle valve until target position is attained, in order to regulate volume of air that flows through throttle valve. Thus, fluctuation of engine speed is restrained.
If engine control unit or throttle actuator control unit in PCM detects a malfunction in system, it illuminates Malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp). At same time, PCM reduces engine output by restricting throttle valve opening or by cutting off fuel supply, or, it disables throttle actuator control motor by cutting off power to throttle actuator control motor relay. When power to throttle actuator control motor relay is cut off, throttle valve assumes a prescribed opening (to supply a volume of air that enables a minimum operation of vehicle). Thus, this control enables vehicle to be driven at a minimum level even if a malfunction occurs in throttle control system.