The MI-04 system also performs minimum (min) and maximum (max) governing through the SECM and DBW throttle. For min governing, or idle speed control, the idle speed is fixed by the SECM. Unlike a mechanical system, the idle speed is not adjustable by the end user. The idle speed is adjusted by the SECM based on engine coolant temperature. At these low engine speeds, the SECM uses spark and throttle to maintain a constant speed regardless of load. The MI-04 system eliminates the need for air velocity governors. This substantially increases the peak torque and power available for a given system as shown in (Figure 29).
When the engine speed reaches the max governing point the speed is controlled by closing the DBW throttle. Using the DBW throttle as the primary engine speed control allows for a smooth transition into and out of the governor. If speed exceeds this max governing point, spark is interrupted to attempt to bring the speed back to a point that can be controlled by throttle alone. If over speed is detected multiple times, the engine is shutdown. (Figure 30) describes the signal flow process of the MI-04 DBW section. The Acceleration Pedal assembly uses two potentiometers to detect pedal position.
These two signals, accelerator pedal position 1 (APP1) and accelerator pedal position 2 (APP2) are sent directly to the SECM. The SECM uses a series of algorithms to self calibrate and cross check the signals from the pedal assembly. A demand position for the throttle will then be derived and sent to the throttle as a throttle position sensor demand (TPSd). The signal will be processed through a PID (Proportional, Integral, Derivative) controller in the SECM to achieve the appropriate motor-current response then passed to the throttle. The throttle moves to the commanded position and provides a feedback signal from the throttle position sensor (TPS) to the SECM.
Acceleration Pedal APP2 APP1 APP 0-100% •Self Calibration • Cross Check of APP1 & APP2 SECM 5msec Update Rate System Power Comparison 60.0 TPS TPSd (Demand) Power, hp (corrected) 40.0 DBW Throttle 20.0 PID 0.0 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 RPM Figure 30 System Torque Comparison Torque, ft-lb (corrected) 120.0 140.0 100.0 80.0 40.0 60.0 20.0 0.0 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 RPM G420E/G424E Tier LP Engine System Operational Overview 28 m MI-4 Base System line syste m MI -4 System Ba seline syst em