Displacement Detection Device for Variable Displacement Compressor, and Variable Displacement Compressor Provided with Same

Abstract

Provided is a displacement detection device for a variable displacement compressor which has a configuration such that the displacement detection device can estimate the displacement with little effect from external disturbances, and can be used with pistons that do not require a high degree of machining precision, thus allowing for a greater degree of freedom in the shape of the surface to be detected. Also provided is a variable displacement compressor provided with the displacement detection device. The displacement detection device for a variable displacement compressor is equipped with: a position detection sensor, which is disposed laterally to the piston and outputs a surface displacement signal for the surface to be detected when the piston moves in a reciprocating manner; and an estimation means that measures and stores the waveform pattern (A) of the displacement signal for a stroke of the piston during operation at maximum displacement, detects the waveform pattern (B) of the displacement signal for one stroke of the piston in the current operating state, and estimates the displacement of one stroke of the piston in the current operating state from a comparison of waveform pattern (A) and waveform pattern (B).

1 . A displacement detection device for a variable displacement compressor, wherein a piston reciprocates to compress gas and a stroke of said piston is changed to vary a displacement, comprising
 a position detection sensor, which is disposed laterally to said piston and which outputs a displacement signal indicating that a detection point, which is a part of a surface to be detected facing said position detection sensor as a shape of said piston which moves in a traverse direction in front of said position detection sensor by a reciprocation motion of said piston, approaches and leaves said position detection sensor at a time of said reciprocation motion of said piston, and   an estimation means for estimating a current operational displacement corresponding to a current operational piston stroke by comparing waveform pattern (A) to waveform pattern (B), wherein said waveform pattern (A) of said displacement signal corresponding to one piston stroke in operation with a maximum displacement is measured and stored and said waveform pattern (B) of a current operational displacement signal corresponding to one current operational piston stroke is detected.   
     
     
         2 . The displacement detection device according to  claim 1 , wherein said estimation means estimates said current operational displacement by comparing said waveform pattern (A) and said waveform pattern (B) based on a comparative standard consisting of an one turn cycle signal of said compressor, a top dead center signal of said piston or both of said signals. 
     
     
         3 . The displacement detection device according to  claim 1 , wherein said estimation means estimates said current operational displacement at a displacement value corresponding to a maximum cross-correlation coefficient which is calculated by comparing a plurality of waveform patterns carved out from said waveform pattern (A) by a predetermined step with said waveform pattern (B). 
     
     
         4 . The displacement detection device according to  claim 1 , wherein said estimation means estimates said current operational displacement at a displacement value corresponding to a minimum cumulative residual sum calculated by comparing a plurality of waveform patterns carved out from said waveform pattern (A) by a predetermined step with said waveform pattern (B). 
     
     
         5 . The displacement detection device according to  claim 1 , wherein said estimation means estimates said current operational displacement at a displacement value corresponding to a minimum cumulative sum of differences between deviations of said waveform pattern (A) from its average and deviations of said waveform pattern (B) from its average. 
     
     
         6 . The displacement detection device according to  claim 4 , wherein said estimation means stops calculating said cumulative sum when a calculated result exceeds a minimum value during a calculation, and said minimum value is updated if a calculated result is less than said minimum value at an end of said calculation. 
     
     
         7 . The displacement detection device according to  claim 3 , wherein said estimation means interpolates a displacement region of between either said maximum cross-correlation coefficient or an estimated displacement value exhibiting said minimum cumulative sum and an adjacent calculated displacement value, and if a value, which is greater than said maximum cross-correlation coefficient or which is smaller than an already calculated cumulative sum, exists in said displacement region interpolated, said value is regarded as an estimated current operational displacement. 
     
     
         8 . The displacement detection device according to  claim 2 , wherein said one turn cycle signal of said compressor is obtained from a rotation signal of a compressor drive source. 
     
     
         9 . The displacement detection device according to  claim 2 , wherein said top dead center signal of said piston is obtained with a body to be detected which is provided at a part corresponding to a top dead center of said piston of a pulley for driving said compressor, and with a detection means which is provided at a position facing said body to be detected. 
     
     
         10 . The displacement detection device according to  claim 1 , wherein a waveform pattern of said displacement signal for said one piston stroke is obtained from a waveform pattern at said time of said reciprocation motion of said piston. 
     
     
         11 . The displacement detection device according to  claim 1 , wherein said position detection sensor detects at least any of distributions, among a distribution of an unevenness on said surface to be detected of said piston, a distribution of electromagnetic characteristics and a distribution of light reflection characteristics. 
     
     
         12 . The displacement detection device according to  claim 11 , wherein said position detection sensor is any of sensors including an eddy current type sensor, an electromagnetic induction type sensor, a capacitance type sensor and a photoelectric reflection type sensor. 
     
     
         13 . The displacement detection device according to  claim 12 , wherein a magnetic coating material is applied to said surface to be detected of said piston or a magnet is buried therein. 
     
     
         14 . The displacement detection device according to  claim 12 , wherein an optical coating material is applied to said surface to be detected of said piston or a light reflective body is buried therein. 
     
     
         15 . The displacement detection device according to  claim 1 , wherein said estimation means estimates said current operational displacement as removing an influence which has fluctuated a detected signal of said position detection sensor from an initial value, through a crack or an abrasion of said surface to be detected of said piston, by recording said waveform pattern (A) again in its state. 
     
     
         16 . A variable displacement compressor provided with said displacement detection device according to  claim 1 . 
     
     
         17 . The variable displacement compressor according to  claim 16 , wherein a torque of said compressor is estimated from said estimated displacement and at least a discharge pressure and a suction pressure of said compressor. 
     
     
         18 . The variable displacement compressor according to  claim 16 , wherein a valve opening of a displacement control valve for varying a displacement of said compressor is controlled with an estimated displacement as an input information.