Mitsubishi Heavy Industries Technical Review Vol. 47 No. 2 (June 2010)
9Oilless Scroll-Type Air Compressor for
Railway Locomotives

Tr a n s p o r ta t i o n S y s t e m s a n dAd va n c e d Te c h n o l o g y D i vi s i o n

Mitsubishi Heavy Industries, Ltd. (MHI) works together with Mitsubishi Electric
Corporation (MEC) to provide brake systems for railway locomotives. MHI supplies themechanical portion, including air compressors, brake control units, and bogie-mounted brakes
while MEC produces the electrical components.
Until recently, MHI has used oil-cooled scroll-type compressors in its rotary air compressor
products to achieve low noise and low vibration. This type of compressor compresses oil and air
simultaneously to maintain air tightness and to cool down the compressed air. It separates the oilfrom the compressed air and is the most common type of air compressor used in railway
locomotives. However, this compressor has several drawbacks related to oil leaks and waste oil
disposal.
MHI has devoted considerable effort to developing completely oilless scroll-type aircompressors to address these oil-related problems and society’s environmental concerns. This new
type of compressor has other major advantages, such as a simplified structure, with direct benefits
for railway companies, a safer and healthier work environment, reduced workload by permitting
maintenance without refills with oil, and elimination of oil-related problems. MHI’s achievements
to date and plans for the future are described below.

|1. Application to automated people movers and other new vehicles
Automated People Mover (APM) vehicles (see “Land Transportation System,” Mitsubishi
Heavy Industries Technical Review, Vol. 40, No. 3) rely on low-vibration, low-noise operation tofunction in densely-populated areas or airport facilities. Due to recent increased environmental
considerations, we decided to use oilless scroll-type air compressors in our Crystal Mover vehicles.
Development started in 1999 and progress has been favorable to date.
The Singapore Sengkang Light Rapid Transit APM started operation about eight years ago.
The oilless scroll-type air compressor has been operating during that entire period without
problems. This success proves that the compressor is sufficiently durable for practical use, evenunder the extreme hot, humid conditions of Singapore.

Figure 1
Oilless scroll-type aircompressor installed inan APM, shown withthe side panels open
Figure 2

Applications of oilless scroll-type air compressors

Mitsubishi Heavy Industries Technical Review Vol. 47 No.2 (June 2010)10

Table 1Country

Number of oilless scroll-type
air compressors installed

Name of facility
Sengkang / Punggol
Light Rapid Transit APM
Changi International Airport APM
Inchoen International Airport APM
Dubai International Airport
Total

Singapore
Singapore
Korea
United Arab Emirates

Table 2

Details of oilless scroll-type air compressor applications

411691884

Specifications of the RC400 oilless scroll-type air compressor

Model
Compression system

RC400

Discharge pressure

scroll, one-stage

WeightAllowable volumetricefficiency
Cooling type

Drive systembelt-driven

Actual discharge volume318 L/min.

Figure 3

RC400 top and side views

Figure 4

RC400 bottom and other side views

Max working pressure
0.88 MPa
215 kgcontinuous
air|2. Application to railway vehicles
Extending the use of oilless scroll-type air compressors to railway vehicles required
addressing the following issues:(1) Increasing the discharge volume because railway vehicles consume more air than APMvehicles. The initial discharge volume was too low for railway use.
(2) Changing the belt drive system to a direct motor drive. This eliminated the need for belttension control.
(3) Including a cooling unit and a dryer along with the other components in a single enclosed
all-in-one unit.

Mitsubishi Heavy Industries Technical Review Vol. 47 No.2 (June 2010)
11

Taking advantage of their small size, multiple oilless scroll-type compressors were integrated
into a single unit to increase the discharge volume. Durability testing was conducted of multiple
prototypes with direct motor drives, cooling units, and dryers in a single enclosure, the same size asexisting compressor units.
Figure 6 shows the internal details of an all-in-one oilless scroll-type air compressor withfour internal compressor units. The number of the compressors in any single unit varies from one tofour, depending on the required discharge volume.

Figure 5
Main structure of a direct motor drive oilless
scroll-type air compressor

Figure 6

Internal details of an all-in-one oilless scroll-type air compressor

Table 3Specifications of a four-unit all-in-one oilless scroll-type
air compressor

Model
Number of internal compressors
Actual discharge volume
Discharge pressure

URC 1,600
4 direct-drive oilless air compressors
Greater than 1,280 NL/min(320 NL/min × 4 internal compressors)
880 kPa