Introduction of  Hitachi ZAXIS70/70LC Excavator Engine Control System

A microcomputer built into the main controller (MC) monitors and controls all machine operations. The MC receives signals from the engine control knob and various other sensor switches. The MC then processes these signals and issues control signals to start the EC motor and various solenoid valves. The microcomputer control operation is as follows.
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1. Engine Control
The engine control system includes by combination: engine control knob control, E mode control, automatic idle speed control; optional ML (crane mode) engine speed limit control and engine learning control. The layout of the engine control system is shown in Figure 2-1.

2. Engine control knob control
Engine control knob control function: Control the engine speed according to the rotation angle of the engine control knob and reduce the engine speed by 100r/min when all joysticks are in the neutral position to reduce fuel consumption and noise. Operation: MC drives the governor lever according to the turning angle of the engine control knob to adjust the engine speed.
TIP: Even when the control knob is turned to the full speed position, the governor lever does not make contact with the full speed stop. With all joysticks in neutral (travel and nose attachment/swing sensors off)
After about 1 second, MC drives the EC engine to reduce the engine speed by 100r/min from the maximum speed.
The engine speed drops 100r/min from the maximum speed. Therefore, when the engine speed set by the engine control knob is already lower than the maximum speed of 100r/min, the engine speed remains unchanged. This engine speed deceleration control works regardless of whether the automatic idle speed control works. High and low idle speed control ranges are shown in Figure 2-2. The engine control knob controls are shown in Figure 2-3.

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The angle of rotation decreases proportionally.
The E-mode control diagram is shown in Figure 2-5.

4. Automatic idle speed control
engine control
knob position
Automatic idle speed control function: when all joysticks are in the neutral position
, reduce engine speed to reduce fuel consumption and noise levels.
Figure 2-4 Engine speed drops at a constant specified rate
Automatic idle speed control operation: about 3.5s after all joysticks return to the neutral position, MC drives the EC motor, as shown in Figure 2-6, to reduce the engine speed to the automatic idle speed. As long as the joystick is operated (travel and/or front attachment, swing pressure sensor on) the MC drives the EC motor to increase the engine speed to the original engine speed (set by the engine control knob). Conditions under which the automatic idle system does not work:
1) Joystick: When operating (travel, swing, or front attachment joystick when the pilot sensor is on).
2) Power mode switch: when E mode is converted into P mode or P mode is converted into E mode.
3) Engine Control Knob: When changing the engine speed.
The automatic idle speed control is shown in Figure 2-7.

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5. Idle acceleration control
Idling Acceleration Control Function: When the engine is running at a low speed, it prevents the engine from vibrating irregularly.
Idle speed acceleration control operation: as shown in Figure 2-8, when the engine is running at a speed between low idle speed and idle speed acceleration, when the travel or front-end accessory function is operated, MC drives the EC motor to make the engine speed idle speed acceleration control as shown in Figure 2 -9 shown.

6. Engine Learning Control
Engine Learn Function: Enter Governor Lever Stop in STOP
and FULL (full speed) side position as standard data to control the engine.
Engine learning operation: As shown in Figure 2-10, when the learning switch in the rear console is turned to the engine learning position, the EC motor is driven sequentially by signals from idle speed to full speed and to stop position. The EC sensor detects the position of the stoppers of the speed control lever on the FULL (full speed) and STOP (stop) sides and sends the stopper position signals to the MC, which stores these signals in its memory. Engine learning control is shown in Figure 2-11.
TIP: If repair work is done, be sure to perform an engine study. After performing the engine learning, use Dr.EX to check whether the engine learning has been carried out correctly.
When the battery is replaced, engine learning is not required.

7. Valve control
1. Travel motor swash plate angle control
Valve control function: select the walking speed in fast or slow mode.
2. Valve control operation
Slow mode: When the travel mode switch is in the SLOW (slow) position, MC will close the travel mode solenoid valve. The travel mode solenoid valve blocks the travel motor swash plate angle control oil pressure. Therefore, the travel motor swash plate angle increases, reducing the travel motor speed.
Fast mode: When the travel motor switch is set to the FAST (fast) position, MC will open the travel mode solenoid valve. The travel mode solenoid valve provides swash plate angle control oil pressure to the travel motor. Therefore, the angle of the travel motor swash plate is reduced, and the speed of the travel motor is increased.

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8. Walking alarm control
Walking alarm control works only when optional parts are installed. Walking alarm control function: the buzzer sounds when walking.
Walking alarm control operation: When performing a walking operation, the pressure sensor (walking) sends a signal to the MC. As soon as this signal is sent out, the MC outputs a signal to the walking alarm device to sound the buzzer.
Tips: After continuous walking for 13s or more, operating the buzzer release switch will disable the buzzer.
Walking alarm control is shown in Figure 2-13.
9. Slewing alarm control
The slewing alarm control works only when the option is installed.
Slewing alarm control function: During the slewing operation, the buzzer will sound while the indicator light is turning.
Swing alarm control operation: When performing a swing operation, the pressure sensor (swing) sends a signal to the MC. As soon as this signal is sent out, the MC outputs a signal to the slewing alarm device, sounds the buzzer and rotates the indicator light.
Note: Operating the buzzer release switch will disable the buzzer.
The rotation alarm control is shown in Figure 2-14.