An Electronic Control Throttle for Torque and Stability Optimization

The design and performance of an inlet throttle mechanism composed of a spool and a direct acting solenoid is demonstrated to yield similar fuel injection characteristics, described by injection traces, as a pressure regulator placed in the output of a HEUI (hydraulic electronic fuel injector) pump with the added advantage of yielding torque savings of approximately 50% through the speed and load operation map in a typical automotive application. The paper details: the throttle mechanism, a variable gain area with a linear schedule designed for fine flow control followed by a high-gain to remedy cold start; the solenoid design, optimized to yield a constant force over the entire stroke for a given current level; and the close-loop feedback algorithm, characterized by a feed-forward term determined from bench testing at discrete pump speeds and loads. Testing shows the flow desired to collapse onto a single band correlating with duty cycle to the solenoid, a robust feature that enables the feed-forward term of the control system to be effective in adjusting to transient conditions. The paper includes comparisons at 1200, 2000 and 3000 pump rpm of the inlet throttle mechanism and of a pressure regulator applied to a HEUI pump in a system that comprises the pump, high-pressure accumulator and 8 fuel injectors. Time traces of pressure in the accumulator and rates of injected fuel at the cylinders indicate the inlet throttle device is slower to recover pressure following an injection event as expected, but only at lower operating speeds, which is due to the limited response of the pressure regulator at the higher speeds. The rates of injection traces show that there is no deterioration of the fuel injection characteristics.