Background and overview
To replace aging general-purpose diesel multiple unit (DMU) trains operating
on trunk lines, the Kiha47 series was developed. However, these units proved
to be excessively large and robust, resulting in high manufacturing and
operational costs. Consequently, there was a growing need for DMUs suitable
for branch line service that could reduce production, fuel, and maintenance
costs while also improving energy efficiency.
In response, Japanese National Railways introduced the Kiha37 pre-production series in 1983. These units featured a more compact carbody and were equipped with the lightweight DMF13S prime mover—an engine derived from Niigata Engineering's inboard motor design. This configuration was specifically chosen to reduce fuel consumption and optimize performance for branch line operations.
Car body
The vehicles feature steel bodies measuring 20,000 mm in length and 2,928
mm in width, with a bogie centre distance of 13,800 mm. The body skin is
constructed using 1.6 mm thick steel plate, the roof with 1.2 mm plate,
and the floor with 2 mm plate laid over the underframe.
The cab end is gangwayed, incorporating a gangway door and a driver's cab
elevated 300 mm above the floor level. This raised position enhances visibility
and provides additional protection against obstacles at level crossings.
Flat windscreens are used to reduce manufacturing costs. Above the co-driver's
side windscreen, a roll sign displays classification and destination information.
Lighting equipment includes two sealed-beam headlights mounted above the gangway door, and two taillights along with a pneumatic horn positioned below the windscreens.
Each car is equipped with two 1,000 mm wide single-leaf, stepped, semi-automatic
sliding doors. The front door is located directly behind the cab, while
the rear door is positioned 4,470 mm from the rear end of the carbody.
This layout ensures symmetrical door spacing when operating as a two-car
set.
Between the doors, the cars feature 930 mm wide double-hung unit windows.
Additional windows include a 930 mm wide unit immediately behind the rear
door, and a 625 mm wide unit located just behind the front door and at
the rear end of the carbody. The upper sash of each window slides downward,
while the lower sash moves upward.
Door operation is handled by TK105 equipment mounted on the door headers. Roof-mounted forced-draught ventilators made of fiber-reinforced plastic provide airflow. The exhaust pipe for the prime mover is routed through the cab interior.
The cars are fitted with tight-lock automatic couplers featuring RD13 rubber draft gear. Their exterior livery is finished in vermilion.
Bogies
The powered bogies are designated DT22A, while the trailer bogies are TR51A. Both types utilize a swing hanger suspension system, with coil springs serving as bolster springs and a pedestal-type journal support configuration. To accommodate the lighter carbody mass, swing bolsters and appropriately tuned shock absorbers are employed.
The gear ratio of the powered bogies is set at 2.976. Reflecting the load
conditions typical of commuter service, the axle diameter has been increased
to 175 mm for enhanced durability.
Braking equipment consists of single-tread brake rigging, incorporating an automatic slack adjuster to maintain optimal brake shoe clearance and reduce maintenance requirements.
Traction unit and ancillary equipments
The units are powered by a DMF13S prime mover—a four-cycle, straight-six
diesel engine mounted vertically beneath the floor. This engine delivers
an output of 210 PS and features a turbocharger driven by exhaust gas flow,
along with a direct fuel injection system for improved combustion efficiency.
Power is transmitted via a hydraulic transmission, either the TC2A or DF115A type, repurposed from decommissioned diesel multiple units. An air compressor (model C600), mechanically driven by the prime mover, supplies compressed air for onboard systems.
The braking system employed is the DA-type automatic air brake.
Accommodation
The interior layout consists primarily of longitudinal bench seating throughout the passenger saloon, with the exception of a single transverse seat positioned across the aisle from the toilet. All seats are upholstered with pile fabric.
Lighting is provided by two rows of fluorescent fixtures installed along the ceiling. The vehicles are equipped with a water-based heating system for passenger comfort.
Class Kiha37-0 units also include a Japanese-style toilet located at the
rear of the carbody. This toilet is designed with a provision for the future
installation of a chemical holding tank.
Modifications
JR East
Prime Mover Replacement
In January 1988, JR East began evaluation testing of a next-generation
prime mover to replace the aging DMH17 engine. However, following a fire
incident involving a Kiha58 series train, the replacement programme was
postponed and officially commenced in September 1989. The selected engine
was the DMF14HZ manufactured by Cummins Inc., with a rated output of 300
PS. To accommodate the reuse of existing hydraulic transmission and propeller
shaft components, the engine output was limited to 250 PS.
Air Conditioning Modification
Between 1998 and 1999, the vehicles were retrofitted with two roof-mounted AU26 air conditioning units, each driven by a prime mover and rated at 15,500?kcal/h.
JR West
Prime mover and hydraulic transmission replacement
JR West replaced both the prime mover and hydraulic transmission with the SA6D125H-1A engine and KTF3335A-1A transmission, both manufactured by Komatsu Ltd. This upgrade aimed to reduce maintenance costs and enhance operational performance.
The air conditioning modification
The vehicles were also fitted with a self-powered AU34 air conditioning
unit, roof-mounted and rated at 26,000 kcal/h.
Operations
In 1983, three class Kiha37 pre-production units were delivered to Kisarazu
Depot and two to Himeji Depot for deployment on rural services across the
Kururi, Kihara, Kakogawa, Takasago, Miki, Hojo, and Kajiya lines.
Following the privatization and division of Japanese National Railways in 1987, JR East inherited three vehicles and JR West received two.
JR East Operations
The Kiha37 units assigned to JR East were initially operated on the Kihara
and Kururi lines. After the Kihara Line was transferred to a newly established
third-sector railway operator, the Kiha37 fleet continued service exclusively
on the Kururi Line, alongside the Kiha35 and Kiha38 series. Eventually,
they were replaced by the KihaE130-100 series DMUs and subsequently retired.
The withdrawn units were later transferred to the Mizushima Seaside Railway
in Kurashiki, Okayama Prefecture.
JR West Operations
The Kiha37 units under JR West were first deployed on the Kakogawa Line. In 1999, they were reassigned to the Sakai Line, and later operated on local services along the San-in Line between Yonago and Izumo-shi. These units were replaced by the Kiha126 series DMUs in 2003 and were fully decommissioned by 2009. |
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