New technologies Development of Measuring Technique for ... · tics in terms of resistance to heat, pressure and shock, and transparency considering refrigerant state in the cylinder

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New technologies

Development of Measuring Technique for Compressor Vane Behavior Analysis

Katsumi Endo* Makoto Kawamura** Keisuke Nakazawa**

Abstract Rotary compressors may emit noise caused by collision between vanes and the cylinder wall. To minimize the noise, it is crucial to examine the details of the mechanism of such vane-operating noise by tracing the behavior of the vanes in time series. This report describes a developed visualization technique to monitor the motion of the vane under operating conditions. Also a method of measuring pressure affecting the movement of the vanes is explained.

Key Words : Compressor, Vane, Noise, / Car Air Conditioning

1. Purpose For understanding compressor vane noise mechanism, relation among compressor rotation speed, ambient temperature, discharge pressure and intake pressure has been previously studied.(1)～(4) However, it has not fully been clarified in detail what vane behavior causes the noise. Since vane movement is influenced by the balance between vane pressure at vane tip (pressure in compression chamber) and vane back pressure (pres-sure in vane rear chamber space), we have developed a new technique to measure the pressure in the compres-sion chamber and in the vane rear chamber space, and simultaneously to visualize the vane movement in order to directly observe the mechanism.

2. Rotary compressor structure and principle of operation

Fig. 1 and Fig. 2 show a typical rotary compressor structure and compression process respectively. Cylinder and rotor are sandwiched between front side block and rear side block. Five vanes are placed at respective vane slots in the rotor body. Each vane is pushed by vane rear chamber pressure and rotates keeping in contact with cylinder inner wall. Refrigerant is sucked from a suction port into a compression chamber, compressed by volume change in the chamber, and discharged into the compressor rear chamber space. Lubricating oil mixed in the refrigerant is separated in the rear space by the oil separator to discharge only refrigerant. The oil is fed to the vane rear chamber and the pressure is raised to proper level, resulting in the vane collision force.

Fig. 1 Compressor structure

Fig. 2 Compressing process

3. Consideration for vane behavior visualization Since compressor vane operation noise varies with thermal environment, measurements have to be con-ducted under a wide range of temperature. For example high temperature durability and thermal shrinkage of parts must be considered. Since the parts must endure rather extreme conditions including high pressure and high speed rotation, careful selection of material and sensor setting method are needed. Also the sensors must be embedded inside the small compressor parts. In addition, acoustic resonance that prevents pressure measurement in the closed space should be avoided.

* Test Engineering Group, Global Technology Division** Compressor Development Group, Compressor Business Unit

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Development of Measuring Technique for Compressor Vane Behavior Analysis

4. Method for visualizing vane behavior4.1. Requirements for visualization

The following are needed for visualization equipment.(1) Materials can endure high temperature and

pressure.(2) View can be secured even in the operational

condition. Considering the above, we selected materials for vis-ibility and designed the measuring equipment structure.

4.2. Selection of part materials for visualization

To visualize the vane behavior, we studied whether we can apply a transparent structure in the rear side block. We compared the candidate material characteris-tics in terms of resistance to heat, pressure and shock, and transparency considering refrigerant state in the cylinder and the load by rotation parts. As a result of the study in this perspective, we adopted the polycar-bonate resin (Table 1).

Table 1 Candidate materials for visualization

○：Suitable　×：Inappropriate

4.3. Compressor structure for visualization

To observe the vane behavior, all we have to do is to use transparent materials for compressor rear side. However, the refrigerant is liquid at the start time, thus mist of the refrigerant and oil in the rear space occlude the view and the vane behavior cannot be visualized (Fig. 3, Fig. 4). We redesigned the rear side block with the integrated transparent parts to eliminate empty space in the rear part of the compressor (Fig. 5, Fig. 6). Instead, by an external oil separator, the refrigerant and oil pass through the outside of the compressor body.

Fig. 3 Conventional structure

Fig. 4 Visualized inside with the conventional structure

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CALSONIC KANSEI TECHNICAL REVIEW vol.11 2014

Fig. 5 Modified structure for visualization

Fig. 6 Modified parts for visualization

5. Method for pressure measurement 5.1. Consideration for pressure measurement

The following should be considered for the pressure measurement.(1) Parts can endure a wide range of temperature

from low to high.(2) Parts can endure high pressure. (3) Parts can endure centrifugal force due to high

speed rotation. (4) Sensor can be embedded in the internal parts.(5) Weight balance in the compressor mechanism

should not be affected.(6) Parts can endure thermal shrinkage.(7) Acoustic resonance that interferes with the evalu-

ation shall not occur.On the basis of the above consideration, we selected pressure sensor and designed the setting structure and fixing method.

5.2. Selection of pressure sensor

In order to measure pressure in compression chamber and vane rear chamber, we selected a pressure sensor to be mounted on the rotor perimeter portion and the vane slot. Table 2 compares the characteristics of the candidate sensors in consideration of body dimension, lead wire dimension, weight, pressure measurement range and heat resistance. We selected sensor-A in the table that can endure high temperature and pressure.

Table 2 Pressure sensor comparison

○：Suitable　×：Inappropriate

5.3. Placement of pressure sensor

The sensor is provided at the rotor perimeter and the vane slot respectively to measure pressure in the com-pression chamber and the rear chamber (Fig. 7). For the rotor perimeter part, since it is considerably larger than the size of the pressure receiving area of the sensor, it is thus suitable for the sensor to be placed. On the other hand, the vane slot width is narrower than the sensor pressure receiving area, thus the sen-sor cannot be directly mounted on the slot. Instead, a sensor storage room, connected with vane slot through communicating tube, is separately provided (Fig. 8). Resonance frequency of this communicating tube is designed outside the audible zone (＜20kHz) to avoid an influence on the evaluation. The following formula shows resonance frequency f(Hz) and speed of sound c (m/s).

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Development of Measuring Technique for Compressor Vane Behavior Analysis

=4

(1)

= (2)

L : communicating tube length，k : specific heat ratio，R : gas constant，T : gas temperature，M : molecular weight

Fig. 7 Pressure sensor installation

Fig. 8 Cross section of communicating tube

5.4. Fixing of pressure sensor

The selected pressure sensor is fixed to rotor with adhesive. The adhesive must bear severe operation state where thermal shrinkage, high centrifugal force and vibration shock occur. We selected acrylic adhesive-C, considering tensile shear adhesive strength, peeling adhesive strength, heat resistance and hardness (Table 3).

Table 3 Adhesives comparison

○：Suitable　×：Inappropriate

6. Results Fig. 9 and Fig. 10 show an example of the visualized vane and the results of the measured pressure respec-tively. The development of this measurement method has enabled us to visualize the vane behavior and to observe the pressure at each portion throughout the operation process.

Rotation speed = 800 rpmFig. 9 Visualized inside of the modified structure under

operating conditions

Fig. 10 Pressure measurement result

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CALSONIC KANSEI TECHNICAL REVIEW vol.11 2014

7. Conclusion(1) A new visualization method for directly understand-

ing the vane behavior has been developed.(2) Measuring the pressure profile along the compres-

sion process has also been made possible to analyze the pressure balance that controls the vane move-ment.

(3) Establishment of the method to simultaneously observe the pressure and the vane behavior will enable further detailed study on compressor noise generation mechanism.

Reference(1) Hiroshi Iijima, Mitsuhiro Fukuda：A model

to analyze the start characteristics of vane compressor，CKTR，６，p.88-93(2009)

(2) Mitsuhiro Fukuda, Tadashi Yanagisawa, Makoto Ijiri, Seichiro Yoda: Vane back pressure and its calculation model in vane compressor. Transactions of the JSRAE，20(3)，p.357(2003)

(3) Mitsuhiro Fukuda： Vane Behavior in Vane Compres-sors under Start-Up Operation (1st Report)，Transac-tions of the JSME B，59(567)，p.3487(1993)

(4) Mitsuhiro Fukuda: Vane Behavior in Vane Compres-sors under Start-Up Operation (2nd Repot) Transac-tions of the JSME B，60(571)，p.879(1994)

Katsumi Endo Makoto Kawamura

Keisuke Nakazawa