1. Abstract

For electric vehicles, which are expected to prevalent in the future, improving the quietness of electric compressors in the automotive air conditioners is crucial for satisfying consumer preferences. Based on the “SHIN–HAGATA theory” concerning gear design technology, we established a new scroll wrap design technology to replace a traditional involute curve, which has remained unchanged for a long time, and simultaneously improved multiple performance characteristics (e.g., compression performance, quietness, strength, and durability) by expanding the design freedom (Fig. 1). Using the newly developed design technology, we derived a shape that reduces the compression forces acting on the scroll wrap and developed electric scroll compressors that achieve significant noise reduction.

Fig. 1 New scroll compressor and scroll wrap profile

2. Technical Details

2.1 Scroll Compressor

In scroll compressors, a pair of scroll wraps forms multiple crescent-shaped compression chambers with different phases during the compression process. As the orbiting scroll revolves around the fixed scroll, the compression chambers move from the outside to the inside while reducing the volume and compressing the refrigerant (Fig. 2).

Fig. 2 Compression chamber formed by a pair of scroll wraps

2.2 Scroll Curve Design Technology

The conventional scroll wrap profile is created with a traditional involute curve, defined by the function of involute angle 𝜙 as

x=a cos⁡(ϕ)+aϕ sin⁡(ϕ)　　　　　（1）
y=a sin⁡(ϕ)-aϕ cos⁡(ϕ)　　　　　（2）

where a represents the radius of the base circle.

In the conventional design method, because the compression force acting on the compression chamber is determined by the involute curve, the summation of the radial compression force and its fluctuation, which affects noise but is unrelated to the compression work, cannot be controlled. Therefore, it is difficult to control the compression force; this has been a fundamental obstacle to noise and vibration reduction for several years. To address this problem, we constructed a new scroll wrap design technology that can set the compressive force and scroll wrap thickness to the desired values by creating a base circle radius of the involute curve variable (SHIN–HAGATA theory) and making the conventionally symmetrical shape asymmetrical. Using this technology, we designed a scroll wrap profile shape with a small radial compression force fluctuation at a specific phase by increasing the number of turns of the scroll wrap and adjusting the contact positions of the spiral bodies (Fig. 3).

Fig. 3　Scroll wrap design based on the SHIN–HAGATA theory

2.3　Application to Product

The new scroll wrap (SHIN–HAGATA scroll ®, Fig. 3) designed based on the SHIN–HAGATA theory, achieved a noise reduction of approximately 2 dB (compared to the conventional product) under standard operating conditions. Combined with other improvements, we achieved further quietness in the new product while maintaining its weight and improving the compression efficiency.

3. Summary

By applying the innovative scroll curve design technology based on the SHIN–HAGATA theory, we improved the noise characteristics, and achieved a multi-performance parallel design that simultaneously satisfy compression performance, strength, durability, and sealing performance requirements. In the future, we plan to create various scroll wrap profiles based on the expansion of compressor applications.

山下　拓郎*1
Member, Toyota Industries Corporation (2-1, Toyoda-cho, Kariya-shi, Aichi, 448-8641, Japan)

前田　拓巳*2
Toyota Industries Corporation (2-1, Toyoda-cho, Kariya-shi, Aichi, 448-8641, Japan)

友田　達規*3
Member, Toyota Central R&D Labs., Inc. (41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan)

近藤　靖裕*3
Member, Toyota Central R&D Labs., Inc. (41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan)

堀　英津子*3
Member, Toyota Central R&D Labs., Inc. (41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan)