Idle Speed/Throttle Actuator - Electronic: Description and Operation
IDLE CONTROL SYSTEMSIdle Control Valve:
The idle control valve is a solenoid plunger type valve. Air bypasses the throttle valve through the idle control valve to increase or maintain the idle speed. The amount of bypass air depends on the amount of current through the valve. The current varies between 0 and 500 MA. The valve is open when the current is off.
The idle control unit controls the amount of current through the valve to regulate the idle speed.
The control unit receives as inputs: Engine Speed
Coolant Temperature(below/above 45°C)
Ambient Air Temperature
A/C on/off
Throttle Value Switch (idle contact)
Automatic Transmission Selector Position
IDLE CONTROL SPEEDS
Automatic Transmission
1) In drive, 1 or 2 700 rpm
2) Park or Neutral
a) engine cold <45°C 950 rpm
b) engine warm >45°C
i) ambient air temp. <0°C 850 rpm
ii) ambient air temp. >0°C
- A/C on 850 rpm
- A/C off 700 rpm
Manual Transmission
1) Engine cold <45°C 950 rpm
2) Engine warm >45°C
a) ambient air temp. <0°C 850 rpm
b) ambient air temp. >0°C
- A/C on 850 rpm
- A/C off 700 rpm
M30 ENGINES
The idle control valve for the M30 engine is a rotary slide type valve. A two-winding rotary actuator's used to open and close the valve. The idle control unit regulates the opening and closing of the valve. During each regulating period. The two actuator windings are energized alternately and exert opposing forces on the armature. The inertia on the armature causes the slide to be held at a given angle depending on the ratio of the signal voltages applied to the windings.
The idle control system has adaptive capabilities. The control unit continuously compares the programmed data, for idle control, with the input value. If a deviation occurs, the new input values are superimposed and stored in the programmed data map. As a result, new output signals are sent to the idle control valve. This allows the MCU to correct the idle speed for break-in wear or slight air leaks which might occur in the system. If power is interrupted to the control unit, new adaptation takes place within several minutes of engine operation.
The amount of bypass air through the idle control valve depends on the following inputs to the M.C.U.:
- Engine rpm
- Coolant Temperature
- Ambient Air Temperature
- A/C on/off
- Automatic Transmission Selector Position
1. Connector
2. Housing
3. Magnet/Windings
4. Armature
5. Air Passage
6. Rotary Slide
Deceleration Fuel Cut-off
To reduce fuel consumption during coasting, a temporary fuel cut-off to the injection valves is provided for under the following engine speed conditions:
Engine Cold - Above 1800 rpm
Engine at Operating Temp. - Above 1360 rpm
Fuel supply to the Injection Valves is resumed at an engine speed of 400 rpm less than the cut-off speed.
Engine Speed Limit
To limit the maximum engine speed, a fuel cut-off takes place:
- Above 6,600 for 3.3 litre engine
- Above 5,000 for ETA engine.
Closed Loop Control
An oxygen sensor is installed in the engine exhaust pipe, in front of the catalyst, so that it is fully immersed in the flow of exhaust gases leaving the engine. An opening connects the interior of the sensor with the ambient air
With varying partial oxygen pressure inside and outside the sensor, a voltage is generated at the terminals. This signal is fed into the MCU-lambda control.
As the passing exhaust gas stream changes from slightly rich to slightly lean, there is a big change in oxygen partial pressure. In response to this marked change in partial pressure, the electrical potential changes from about 625 millivolts on the rich side of the stoichiometric point to less than 175 millivolts under lean conditions. (Stoichiometric point means lambda = 1.) Mixture variations confined to either side of the stoichiometric point cause only slight changes in oxygen concentration and hence the sensor produces an essential on-off signal.