Patent ID: 7463995
Filing Date: 2008-12-09
Classification: F04B

Abstract:
1. A method of identifying suction valve closure in a reciprocating compressor, comprising the steps of: receiving pressure and volume values for a pre-determined number of samples taken during a compression cycle; locating a first sample with a pressure value greater than a pressure value of the sample taken closest to 180 degrees of a crankshaft rotation; locating a second sample with a pressure value greater than or equal to a pressure value defined as [(the pressure value of the sample taken closest to 180 degrees of the crankshaft rotation−a pressure value of a sample taken closest to 0 degrees of the crankshaft rotation)*a factor less than 1]+ the pressure value of the sample taken closest to 0 degrees of the crankshaft rotation; storing log scaled pressure values for at least some of the samples; storing log scaled volume values for at least some of the samples; determining a best-fit linear line running through a first location corresponding to the second sample and a second location corresponding to the first sample, where each location comprises an x-value equal to the log scaled volume value of the sample and a y-value equal to the log scaled pressure value of the sample; determining a second line with one-half a slope of the best-fit linear line, wherein the second line intersects the best-fit linear line at the first location; calculating a second line solution for at least some of the locations, wherein the second line solution is a solution to the second line determined using the x-value of the location; calculating first best-fit coefficients of a first best-fit 6th-order polynomial running through a third location, corresponding to the sample taken closest to 0 degrees of the crankshaft rotation, and the second location; calculating a first best-fit 6th-order polynomial solution for at least some of the locations, wherein the first best-fit 6th order polynomial solution is equal to Ax determining a first target location, the first target location having a maximum difference between the first best-fit 6th-order polynomial solution for the location and the corresponding second line solution for the location, the first target location being between the second location and the first location; defining a first target sample as the sample associated with the first target location; calculating second best-fit coefficients of a second best-fit 6th-order polynomial running through a fourth location, located a pre-determined number of locations prior to the first target location, and a fifth location, located a pre-determined number of locations after the first target location; calculating a second best-fit 6th-order polynomial solution for locations between the fourth location and the fifth location, wherein the second best-fit 6th-order polynomial solution is equal to Hx determining a second target location, the second target location having a maximum difference between the second best-fit 6th-order polynomial solution for the location and the corresponding second line solution for the location, the second target location being between the fourth location and the fifth location; defining a second target sample as the sample associated with the second target location; identifying the suction valve closure event as being located at the crankshaft rotation angle corresponding to the second target sample.