Patent ID: 8093913
Filing Date: 2012-01-10
Classification: G01N

Abstract:
1. A film thickness measurement device, which measures the film thickness of an oil film of lubricating oil formed in a gap between a piston ring and one or a plurality of electrodes provided flush with a piston ring sliding surface of a cylinder liner, by detecting the electrostatic capacitance across the gap, the device comprising: an electrostatic capacitance detection portion, which charges the electrostatic capacitance by supplying a constant current to the electrode, detects the electrostatic capacitance based on changes in the charging voltage accompanying the charging, and outputs a detection signal indicating the electrostatic capacitance; a film thickness computation portion, which calculates the film thickness of the oil film based on the electrostatic capacitance indicated by the detection signal input from the electrostatic capacitance detection portion; and a crank rotation angle detection portion which detects the crank rotation angle indicating the position of the piston ring with respect to the piston ring sliding surface, wherein the film thickness computation portion calculates the film thickness of the oil film in synchronization with the crank rotation angle detected by the crank rotation angle detection portion.