Computers and Control Systems: Description and Operation

The engine control system utilizes a microcomputer and maintain overall control of the engine etc. An outline of engine control is given here.

1. INPUT SIGNALS
1. Engine coolant temp. sensor signal system
The engine coolant temp. sensor detects the engine coolant temp. and has a built-in thermistor with a resistance which varies according to the engine coolant temp. Thus the engine coolant temp. is input as a control signal to TERMINAL THW of the engine control module.

2. Intake air temp. signal system
The intake air temp. sensor detects the intake air temp., which is input as a control signal to TERMINAL THA of the engine control module.

3. Oxygen sensor signal system
The oxygen sensor detects the oxygen density in the exhaust emission, which is input as a control signal to TERMINALS OX1 (except California) and OX2 of the engine control module.

4. RPM signal system
Camshaft position is detected by the camshaft position sensor and input as a control signal to TERMINAL G+ of the engine control module. Crankshaft position and engine RPM are detected by the crankshaft position sensor. Crankshaft position and engine RPM are input as a control signal to TERMINAL NE of the engine control module.

5. Throttle signal system
The throttle position sensor detects the throttle valve opening angle, which is input as a control signal to TERMINAL VTA of the engine control module.

6. Vehicle speed circuit
The vehicle speed is detected by the vehicle speed sensor installed in the transmission and the signal is input to TERMINAL SPD of the engine control module via the combination meter.

7. Park/Neutral position SW signal system
The Park/Neutral position SW detects whether the shift position is in neutral or not, and inputs a control signal to TERMINAL NSW of the engine control module.

8. A/C SW signal system
The operating voltage of the A/C magnetic clutch is detected and input as a control signal to TERMINAL AC1 of the engine control module.

9. Battery signal system
Voltage is constantly applied to TERMINAL BATT of the engine control module. When the ignition SW is turned ON, voltage for the engine control module operation is applied via the EFI relay to TERMINAL +B of the engine control module.

10. Intake air volume signal system
Intake air volume is detected by the manifold absolute pressure sensor and is input as a control signal to TERMINAL PIM of the engine control module.

11. Starter signal system
To confirm that the engine is cranking, the voltage applied to the starter motor during cranking is detected and is input as a control signal to TERMINAL STA of the engine control module.

12. E1ectrical load signal system
The signal when systems such as the rear window defogger which causes a high electrical burden to be on is input to TERMINAL ELS as a control signal.

13. Air fuel ratio signal system (California)
The air fuel ratio is detected and input as a control signal into TERMINAL AF+ of the engine control module.

2. CONTROL SYSTEM

* SFI (Sequential multiport Fuel Injection) system
The SFI system monitors the engine condition through the signals which are input from each sensor (Input signals (1) to (13)). The best fuel injection volume is decided based on this data and the program memorized by the engine control module, and the control signal is output to TERMINALS # 10, # 20, # 30, and # 40 of the engine control module to operate the injector (Inject the fuel). The SFI system produces control of fuel injection operation by the engine control module in response to the driving conditions.

* Idle speed control system
The idle speed control system increases the RPM and provides idling stability for fast idle-up when the engine is cold and when the idle speed has dropped due to electrical load, etc. The engine control module evaluates the signals from each sensor (Input signals (1 to 6, 12)), outputs current to TERMINALS ISCO and ISCC, and controls the idle air control valve.

* A/C cut control system
When the vehicle suddenly accelerates from low engine speed, this system cuts off air conditioner operation for a fixed period of time in response to the speed sensor, throttle valve opening angle and intake manifold pressure in order to maintain acceleration performance.
The engine control module receives input signals (5, 6 and 10), and outputs signals to TERMINAL ACT.

3. DIAGNOSIS SYSTEM
With the diagnosis system, when there is a malfunction in the engine control module signal system, the malfunctioning system is recorded in the memory. The malfunctioning system can then be found by reading the display (Code) of the malfunction indicator lamp.

4. FAIL-SAFE SYSTEM
When a malfunction occurs in any system, if there is a possibility of engine trouble being caused by continued control based on the signals from that system, the fail-safe system either controls the system by using data (Standard values) recorded in the engine control module memory or else stops the engine.