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Brushless Motors for In-Tank Fuel Pumps

The use of a brushless motor provides improvement in power usage and reduction of carbon dioxide emissions.

Most automotive fuel systems use a Fuel Delivery Module (FDM) with components to filter and pump gasoline at a specified pressure and flow rate from the fuel tank to the engine. The FDM uses a reservoir assembly to maintain a fuel supply at the pump inlet and support components such as pressure regulators and/or limiters, filters, level sensor, and the electrical and hydraulic connections that pass through the tank. Current systems predominantly use passive electrical components such as brush pumps and resistive fuel level sensors that are independently connected to a voltage supply and body control module, respectively. The high flow levels of these systems require high-power pumps that may operate continuously at maximum speed conditions. Some newer systems may employ a voltage controller to modulate the pump supply voltage to discrete speeds depending on projected engine demand, and provide some improvement in power consumption.

A new FDM employs a brushless (BL) motor in the pump assembly, and includes an integrated controller to provide electrical commutation for the motor. Since the BL pump is more efficient than the brush pump, and since the controller provides closed-loop speed control, this solution offers significant improvements in power consumption and consequently carbon dioxide (CO2) emissions. Another benefit of the BL pump is produced with the magnetic coupling between the motor's stator and rotor, and elimination of the contacts that may wear and/or film in aggressive fuels. This improves the durability and reliability of the FDM.

Additionally, the integrated controller provides pump diagnostics and may include sensor signal processing circuitry within the tank assembly to enable additional state-of-health information and/or provide further system performance improvements by interfacing with improved sensing technologies such as a non-contacting fuel level sensor. The BL controller benefits from close proximity to the pump in addition to the reduction in noise coupled to the back EMF (ElectroMotive Force) sensing phase for sensorless motor speed measurements.

The figure shows a vehicle architecture with the integrated module that includes the BL controller within the FDM. Using a similar technique as the voltage controller for brush pumps, the BL pump controller modulates the current that flows through each of the three phases by shutting off the supply voltage at high frequency. The shutoff time is adjusted to achieve the drive current level that is required to maintain the pump speed at the level commanded by the Engine Control Module (ECM). This pulse-width-modulated (PWM) voltage signal enables closed-loop speed control to ensure fuel flow independent of environmental factors such as pressure, supply voltage, fuel properties, and temperature.

In addition, the BL controller compensates for variations in pump parameters and time-induced drift. The integrated FDM assembly optimizes system performance by minimizing distance to the BL pump, and by providing a control algorithm tuned to the pump design and application requirements. In addition, the BL controller includes pump diagnostics for monitoring supply voltage, drive currents, controller temperature, and motor speed. Variations in these parameters outside predictable and/or acceptable limits may prompt system shutdown to prevent damage or simply communicate an abnormal condition to the ECM.

Robust engineering techniques and other statistical tools were used to derive the optimal solution to meet stringent torque, speed, pressure, and flow requirements. Full factorial design of experiments were executed using analytical tools to simulate the motor performance and derive the combination of parameters that meet the application torque and efficiency requirements while minimizing the cogging torque, torque ripple, and unbalanced magnetic pull that results in excess vibration and noise. The optimal combination and analytical results were confirmed with laboratory testing using motor assemblies. The experiments led to a motor design with 9 poles in the stator and 10 poles in the rotor. The winding configuration was tuned to meet a torque greater than 0.10 Nm at 12 Volts and 5000 rpm, with 68% efficiency with the design tolerance levels of the assembly.

This work was done by Duane Collins, Philip Anderson, Sharon Beyer, and Daniel Moreno of Delphi Powertrain Systems. The full technical paper on this technology is available for purchase through SAE International at http://papers.sae.org/2012-01-0426.