CONTROL FUNCTIONS (CONT’D)

General (Cont’d)

EGR valve output

The EGR valve output is a high-side output as shown in [Figure 10-40-13]

The EGR valve is driven by a stepping motor. This stepping motor adopts two-phase excitation and requires holding current to keep the valve stopped. "Two-phase excitation" means that the solenoid is supplied with two-phase current and "holding current" does that the solenoid is always energized. The motor of the EGR valve is consequently approx. 24 watt (12 watt x 2 phase) heated even while the engine is at rest be warned that touching it could burn you.

The E-ECU turns on or off the output transistors in the sequence shown in [Figure 10-40-13], thereby driving the solenoids for the stepping motor and opening/closing the EGR valve.

In the EGR valve, the full-close position is 0 step and the full-open position is 54 steps.

CONTROL FUNCTIONS (CONT’D)

Engine Control - General

Self-holding of the E-ECU power

The E-ECU saves engine logs including faults and running hours in the internal EEPROM. And it has a power selfholding feature that allows the power supply to be held until the engine logs are completely saved in EEPROM.

In the E-ECU, the EGR valve is moved to the full-close condition at engine stop to ensure starting the engine start sequence from the full-close condition. Therefore, the power self-holding feature holds the power supply until the EGR valve is cutoff completely after the key switch is turned off.

To implement the power self-holding feature, the main relay and the rack actuator relay must be connected as shown in [Figure 10-20-1]

This feature can also be activated through CAN communication. See “CAN communication specifications” for details.

Start control

The engine start sequence is shown in the figure below. The E-ECU performs rack self-diagnostics directly after power on. The rack self-diagnostics checks the rack motion alone without turning on the engine. So, the starter relay prevents the starter motor from starting until the rack self-diagnostics is completed.

Next, when ON-glow control is alive (default), the time of energization of the starting aid relay is adjusted according to the coolant temperature. The preheat lamp should illuminate while ON-glow control is in progress.

After ON-glow control is complete, the E-ECU waits until the key switch is moved to the START position.

When the key switch is moved to START or the engine speed reaches 240 min-1, rack position control on start takes place to move the rack to a predefined position.

Having detected that the engine speed reaches 600 min-1, the E-ECU goes to speed control mode. In this mode, the rack position is controlled so that the engine runs at a speed that matches the speed command from the accelerator.

When the engine speed is reduced to less than 240 min-1 or the key switch is turned off, the engine will stop.

Figure 10-40-14

Rack self-diagnostics

START ON glow control (optional)

Key at START position?

Rack position control on start

Engine started?

Speed control