Systems and methods of using a fuel injector as a pressure sensor to detect top-dead-center for a cylinder

A method of using a fuel injector to determine a top-dead-center (“TDC”) position of a piston configured to reciprocate in an engine cylinder, comprising:

• receiving signals from a pressure sensor indicating a sensed pressure of fuel in a fuel accumulator fluidically coupled to the fuel injector;
• responding to the sensed pressure of fuel corresponding to a desired fuel pressure, preventing fuel flow into the fuel accumulator;
• after preventing fuel flow into the fuel accumulator, causing the fuel injector to provide a plurality of fuel injections into the engine cylinder when the piston is in a corresponding plurality of positions in the engine cylinder;
• estimating a corresponding plurality of cylinder pressures in response to the plurality of fuel injections;
• estimating a plurality of accumulator fuel pressure drop measurements for injections corresponding to the corresponding plurality of cylinder pressures;
• fitting a curve to the plurality of accumulator fuel pressure drop measurements that have been estimated;
• determining a maximum pressure drop value on the curve;
• and
• correlating the maximum pressure drop value to a true TDC position of the piston.

A pressure-based piston top-dead-center (“TDC”) position measurement system, comprising:

• a fuel injector configured to inject fuel into a combustion chamber bounded in part by a piston;
• and
• a controller configured to control the fuel injector to cause a fuel injection when the piston is at each of a plurality of different positions relative to TDC while ensuring fuel is provided to the fuel injector at a substantially constant pressure;
• wherein the controller is further configured to estimate a pressure in the combustion chamber in response to each fuel injection, fit a curve to the pressures in the combustion chamber that have been estimated, and determine a TDC position of the piston as correlating with a maximum pressure on the curve.