“Rds_on” Based OBD for Pre-Supply Fuel Pump Driver Modules

In automotive electronics on-board diagnostics does the fault diagnosis and reporting. It provides the level of robustness required for the control electronics against various faults. The amount of diagnostic information available via on board diagnostics are depends on the type of vehicle. Pre-supply fuel pump is the component in the common rail hydraulic system. It pumps the fuel from the fuel tank to the inlet valve of the high pressure fuel pump. Electronic control unit synchronizes its operation with high pressure fuel pump. A dedicated driver module in the ECU controls the operation of pre-supply fuel pump. The driver module consist of an ASIC with internal voltage, current monitoring modules for the fault diagnosis and the pre-drivers to control external HS and LS power stages. The software part of the OBD programmed in the internal memory of the ASIC. The “Rds_on” of the power MOSFETs are used for the fault detection purpose. The module designed to operate in dual frequencies and variable duty cycles. It ensures the optimum hydraulic performance of the pump and provides maximum possible diagnostic coverage against various faults. The on-board diagnosis against the faults such as motor inrush current, rotor Lock, short circuit to ground, short circuit to battery, line to line fault (short circuit between high side and low side pins) and open load are discussed in this paper. The wiring harness impedance has significant influence on the fault detection duration. The wiring harness length depends on the position of ECU and pump in the vehicle. Pre-supply fuel pump normally immersed in the fuel tank and ECU normally kept either in the dash board or mounted on the body of engine. The resistance and inductance of the wiring harness are the functions of wire diameter and length. The below are the parameters influences the fault diagnostics of the driver module discussed in this paper.

• Fault detection threshold (Vth),
• The “Rds_on” of the MOSFET,
• Fault current magnitude,
• Frequency at which power stage operates,
• Duty cycle,
• Thermal response of the MOSFET,
• Safe operating conditions,
• Blind bands and MOSFET turn on/off delays.

These parameters possesses typical relationships each another depending on the operating modes of engine and ambient conditions.