An Environmentally Friendly,
Highly Efficient, Lightweight
Scroll Compressor (QS90) for
Car Air Conditioners
MAKOTO TAKEUCHI*1

TETSUZO UKAI*2

HIROSHI YAMAZAKI*1

KAZUHIDE WATANABE*2

TOMOHISA MORO*2

SHINTA MISHIMA*1

In recent years, global efforts towards conserving energy have accelerated in various ﬁelds, pushed by rising concern about
global environment protection. Mitsubishi Heavy Industries, Ltd. (MHI) has featured high-efficiency scroll compressors in a
number of its refrigerating and air-conditioning products, contributing to energy conservation. For car air conditioners, weightis an important factor in addition to efﬁciency. Therefore, with the introduction of the original new technology (3D scroll, direct
oil return system), MHI developed a compressor with reduced energy loss, which was realized through both improved efﬁciency andweight reduction.
The crankshaft, which is rotated by the engine, moves theorbiting scroll via a belt in an orbital motion using a rotationmotion-prevention mechanism, to compress the refrigerant.
T he QS 9 0 compressor adopt s a sc rol l ( 3D sc rol l )compressor that was recently developed for the purpose ofefficiency improvement. Figure 2 shows cross-sectionalviews of conventional and 3D scroll compressors.1 In theconventional scroll compressor, the wrap height is constantthroughout the compression process. T herefore, therefrigerant is compressed in two dimensions from the outer
to the inner sides. In the 3D scroll compressor, the outerwrap is higher than the inner one because of the steps in thescroll tips and end plates. Consequently, the 3D scroll can

1. Introduction
In recent years, public awareness of env ironment alprotection on a global scale has increased and efforts tocombat global warming have accelerated in both the publicand private sectors. In addition, the rising prices of crude oiland materials have prompted further energy and resource
conservation.
Most c u r rent c a r a i r c ond it ioner s op er at e on t he
refrigeration cycle, which requires the combination of acompressor, heat exchanger, and expansion valve. The
compressor is driven by the car engine through a belt andpulley and compresses the refrigerant. In this type of air
conditioner, the compressor consumes the majority of thepower used.
Therefore, to reduce the energy consumption of car airconditioners, it is essential to improve compressor efﬁciency
and thereby contribute directly to a reduction in engine
load. In addition, since much energy is required in the
production of aluminum, which is the primary raw material
for compressors, reducing the weight of compressors isimportant for both resource and energy conservation.
This paper introduces efﬁciency improvement and weight
reduction technologies for compressors that are essential
to the development of environmentally friendly car air
conditioners.

Electromagnetic clutch

Discharge
port2. Efﬁciency improvement of QS90
2.1 Structure of new scroll (3D scrollnote)
Figure 1 shows a cross-sectional view of the new QS90
scroll compressor for car air conditioners. T he scroll
compressor consists of a compression unit comprised of apair of scrolls (a fixed scroll and an orbiting scroll), eachcomposed of end plates and wrapped scroll blades, and aunit that drives the orbiting scroll through the crankshaft.

Crankshaft
Orbiting scroll

Fixed scroll

Fig. 1 The newly developed scroll compressor for a carair-conditioner (QS90)*1 Nagoya Research & Development Center, Technical Headquarters*2 Air-Conditioning & Refrigeration Systems Headquarters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)24

Conventional scroll
Constant
wrap height

Fixed scroll

results of a bench test of the overall adiabatic compression
r at io u nder t wo cond it ions − equ iva lent to id l i ng a ndequivalent to running at 40 km/h−for a QS90 compressor
and a conventional compressor (MSC90CAS).
When mounted in the same model of vehicle, the QS90
compressor was 7% more efficient than the conventional
compressor under conditions equivalent to idling and 13%
more efﬁcient under conditions equivalent to running at 40km/h.

3D scrollFixed scroll

Orbiting scroll

Outer wrap
height: large

Orbiting scroll

2D compression

Inner wrap
height:small

3. Weight reduction of the QS90
T he sl iding sect ions of t he compressors in ca r a ir
conditioners are lubricated by mixing oil with refrigerant
and circulating it in the air conditioner. The reliabilityof lubrication is improved by increasing the ratio of oil.
However, if there is too much oil, oil adhesion to the heatexchanger increases, decreasing the efﬁciency of the heatexchanger and reducing the refrigeration capacity.
To cope w it h t h is problem a nd to save energ y, we
included an oil separator; this reduces oil circulation in thesystem and supplies oil separately to prevent a reduction
in refrigerating capacity while supplying enough lubricant
to the sliding sections. This requires additional parts toseparate the refrigerant and oil (centrifugal separation
cylinder) and store the oil (oil sump).
In the course of developing the QS90 compressor, a direct
oil return (DOR) system that is lighter and smaller than aconventional oil separator was developed to facilitate weight
reduction. The DOR system was developed from original
new MHI technology for the lubrication of compressors in
car air conditioners, and enables the positive lubrication ofsliding sections using a simple structure. Figure 5 shows
the structures of a conventional oil separator and the DOR
system. In the conventional oil separator, oil mixed withrefrigerant is centrifuged in the cylinder section. Then,the separated oil is kept in the oil sump and supplied tothe sliding sections through the orifice. By contrast, in

3D compression

Fig. 2 Cross-sectional view of conventional and 3D scrolls
Introduction of the 3D scroll enables 3D compression.

compress the refrigerant in three dimensions, in the axial
dimension as well as the radial directions. The 3D scroll
compressor has the following features:• A high compression ratio is obtained by compressing therefrigerant both radially and axially.
• The strength of the scroll is improved by reducing theheight of the inner wrap, which receives a heavy load.
• A large capacity is obtained by increasing the height of theouter wrap without extending the outer diameter of thescroll. Therefore, the 3D scroll is smaller and lighter.
Note: The 3D scroll is a registered trademark of MHI.

Improved ratio of overall adiabatic
compression efficiency (%)(In comparison withthat of the MSC90CAS)

2.2 Efﬁciency improvement with the 3D Scroll
To improve the efficiency of the scroll compressor, thespecif ic parts where power loss occurs were analyzed.
Fig ure 3 shows t he result s of t he loss a na lysis of aconventional scroll compressor. 2 It was found that the largestloss was caused by recompression.
One of the features of the 3D scroll compressor is that it
can produce a high compression ratio by compressing therefrigerant both radially and axially. This feature reduces thepower loss caused by recompression. Figure 4 shows theEach loss/total loss

1.0
: Mechanical loss
: Recompression loss
: Leakage and heat loss
: Over compression loss

0.8
0.60.4Largest loss

0.20.0Scroll compressor

120110100

Equivalent toidling

Equivalent torunning at 40 km/hFig. 4 Efﬁciency comparison between conventional and QS90
scroll compressors
Energy saving (high efficiency) was achieved by adopting the 3D
scroll to reduce recompression loss.

Fig. 3 Power loss analysis of a conventional scroll
Recompression causes the greatest loss.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)25

33% weight reduction

Conventional oil separator (centrifugal separator)
Refrigerant + Oil

13% size reduction
Centrifugalcylinder

Oil
Orifice

Sliding section

Oil sump

224 mm

194 mmConventional compressor(MSC90CAS)

QS90 compressor

Fig. 6 External appearance of the compressor
In comparison with the conventional compressor, substantial weightand size reductions have been achieved.

Direct oil return system
Refrigerant + OilOrifice

usi ng a vehicle -mounted ca r a i r- condit ioni ng systemequipped with the QS90 compressor. 3 The results led to
the 2007 EPA Climate Protection Award.
While working continuously on protection of the global
environment and resource conservation, MHI is determined
to expand the QS compressor series from the perspectiveof the “environmentally friendly car air conditioner” and to
supply customers with small, lightweight, highly efficient
products, such as an electric air-conditioning system forhybrid or fuel-cell hybrid electric vehicles.

Refrigerant

Sliding section
OilFig. 5 Structure of a direct oil return system
The structure was simpliﬁed by supplying oil from the compression
chamber to the sliding sections directly.

References
1. Sato, H., et. al., Miniaturization and Efficiency Improvement ofRefrigerating and A ir Conditioning Systems Using 3D ScrollCompressor, Mitsubishi Heav y Industries Technical Review
Vol.45 No.2 (2008)
2. Noyama, H., et. al., Contribution of Automotive Air-Conditioning
Systems to Global Environmental Protection, Mitsubishi JukoGiho Vol.41 No.2 (2004)
3. H i d e t o N o y a m a , K a z u m i O k i n a k a ; " E n e r g y E f f i c i e n c y
Improvement of the MAC System with the New Development
Scroll Compressor", SA E Automotive A lternate Refrigerant
Systems Symposium (2006), Presentation material

the DOR system, some of the oil adhering to the insideof the compression chamber is collected by the tip of thescroll and returned from the scroll directly into the sliding
sections through the oriﬁce using the pressure inside thecompression chamber. The simple construction of the DOR
system does not require a cylinder to centrifuge the oil andan oil sump, both of which are necessary for a conventionaloil separator.
As shown in Fig. 6, by adopting the DOR system and 3D
scroll to reduce weight, the QS90 compressor has achieveda weight reduction of 33 % and a size reduction of 13 %compared to the conventional model (MSC90CAS).

5. Conclusion
MHI’s original new scroll compressor (3D scroll) in
combination with the new DOR oil-supply mechanism( DOR system) subst a nt ia lly improves ef f icienc y a ndreduces weight in comparison with a conventional scroll
compressor.
A joi nt st udy w it h Mitsubishi Motors Cor porat ion
veriﬁed the energy saving by measuring fuel consumption,

Makoto Takeuchi

Tetsuzo Ukai

Hiroshi Yamazaki

Kazuhide Watanabe

Tomohisa Moro

Shinta Mishima

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)26