Application of Variane in Compressor

ANALYSIS OF VARIANCE FOR COMPRESSOR SWASH-PLATE DESIGN WITH 3 DIFFERENT COATING MATERIALS

1. INTRODUCTION

In this project I am going to present the 3 sample data on the strength of the swash-plate with different 3 different types of advanced material coatings that a compressor supplier uses to achieve higher durability and lower warranty returns.

1.1 Compressor Swash-Plate Function

A swash plate is used in a rotary valve AC compressor [used for automotive application] wherein pistons are fitted into a cylinder bores having their centers on a circle are reciprocated by swash-plate secured to a rotary shaft at a tilt-angle. A swash-plate chamber accommodating the swash-plate functions as a passage for the refrigerant gas. The refrigerant gas enters into the system through an annular passage and the refrigerant gas sucked functions as a by-pass therefor, diminishes the flow resistance of the refrigerant gas, and facilitates the cooling of the pistons with a result of reducing the operation noise produced from the engaging portion of the pistons and the swash-plate. Please see figure 1 and 2 for the cross-sction of the compressor and the location of swash-plate inside the compressor.

Figure 1: Cross-section of AC Compressor showing the Oil Flow

Figure 2: AC Compressor showing Swash-Plate and Pistons

1.2 Swash-Plate Issues On Low Oil

Seizing of the swash-plate occurs when the refrigerant oil is low, which result in seizing of the compressor thereby creating a customer complaint. Around 10 % of the compressor warranty returns are due to seizing of the compressor. Improving the durability of the swash-plate results in less seizures of the AC compressor and there by increasing the customer satisfaction. In order to increase the durability of the swash-plate, compressor suppliers use several kinds of advanced material coatings that help keep the compressor running even under low oil condition. The coatings act as a lubricant and high temperatures at pressures.

1.3 Durability Testing of Coatings on Swash-Plate

In order to determine how long a swash-plate can perform under low-oil conditions, the supplier has developed a standard test called “Component Dry-Lock test”. This test uses adds a constant load [400 lbf] at a rotational speed of 10.4 m/s under low-oil condition and measures the time [in seconds] it takes for the swash-plate to seize. For each surface coating of the swash-plate the test is carried out at least 30 times to get a good estimate of seizure data. Please see figure 3 for test set-up.

Testing is carried out, by applying a constant load of 440 lbf on swash-plate that rotates at 10.4 m/s on its axis. Time is recorded as long as the swash-plate keeps rotating. The longer the swash-plate rotates the better. The coating on the swash-plate which acts as a solid lubricant helps the swash-plate to rotate easily. Different coatings have different lubricant properties.

Test Conditions:

Load: 440 lbf

Speed: 10.4 m/s

Environment: R134a [refrigerant oil]

Figure 3: Test setup to measure the durability of the Swash-Plate

The three different types of coatings used for this design study are shown in the Table 1 below:

Table 1: Swash-Plate Coatings used for this Design Study

Swash-Plate Coating Material Used

Coating 1 MoS2*

Coating 2 MoS2*+ PTFE **

Coating 3 MoS2*+ PTFE ** + Patented Binder***

* Molybdenum Disulfide

** Polytetrafluoroethylene or Teflon

*** Patented Binder [Includes nano-particles that show exceptional lubricant properties at high temperatures and pressures]

2. APPLICATION OF ANOVA FOR ONE-FACTOR DESIGN STUDY

Here I will present the test of hypothesis and use the ANOVA [with the help of Minitab] to make my recommendations and conclusions on the 3 coatings.

2.1 Test of Hypothesis

I