Background and overview
To support the financial stability of JR Kyushu—whose business foundation
was relatively weak following the 1987 privatization and division of Japanese
National Railways (JNR)—JNR developed the class kiha31 as a cost-efficient
diesel railcar, designed with low construction and operating costs. The
class kiha31 is a double-ended vehicle, and a total of 12 units were manufactured.
Car body
The vehicles feature stainless steel car bodies measuring 17,750 mm in
length and 2,800 mm in width, with a bogie center distance of 12,250 mm
to achieve weight reduction. Exceptions include the bolster beams, the
end sections of the centre beam, and selected cross beams, which are constructed
from weather-resistant steel plate (Steel Plate Atmospheric).
The exterior skin consists of unpainted, bead-processed stainless-steel panels, accented by a blue waistline band located below the side windows. The gangway-equipped cab end incorporates a low-profile driver's cab, designed to accommodate future conductor-less operation. The cab corners are fitted with decorative FRP frames. Flat windscreens are used to reduce manufacturing costs.
Above the driver's windscreen is a destination roll sign, while a separate display window indicating "conductor-less operation" is positioned above the assistant driver's windscreen. Two sealed-beam headlights are mounted above the gangway door, and taillights are installed below the windscreens.
Each car is equipped with two 900 mm-wide automatic folding doors with
stepped access, utilizing bus-type door operating mechanisms. Between the
doors are 770 mm-wide single-hung side windows, which slide upward and
are assembled as modular units.
Climate control is provided by a self-powered AU34 air conditioner rated
at 26,000 kcal/h, mounted beneath the floor, along with three roof-mounted
ventilation fans originally developed for bus applications. The exhaust
pipe for the prime mover is located directly behind the front door.
The vehicles are fitted with tight-lock automatic couplers incorporating RD13-type rubber draft gears.
Bogies
The vehicles are equipped with DT22G powered bogies and TR51E trailer bogies, both inherited from the kiha35 series. These bogies feature swing hanger suspension, coil springs as bolster springs, and a pedestal-type journal support system. The gear ratio of the powered bogies is 2.976.
To accommodate the increased axle load associated with commuter service,
the axle diameter was enlarged to 175 mm. The bogies employ single-tread
brake rigging. To allow the brake cylinder to be positioned closer to the
vehicle centerline, modifications were made to both the bogie frame and
the brake rigging.
Powertrain and Ancillary Equipment
The vehicles are powered by a horizontally mounted DMF13HS diesel engine—a four-cycle, straight—six prime mover-installed beneath the floor. It delivers an output of 250 PS and features a turbocharger driven by exhaust gas flow, a direct injection system, and a fuel injection control system designed to improve fuel efficiency.
The hydraulic transmission, either TC2A or DF115A, was sourced from decommissioned diesel multiple units and upgraded with enhancements to the torque converter and clutch to accommodate the increased engine output. The TC2A model also underwent modification to reposition the hydraulic/direct drive stage changeover servo piston, preventing interference with the engine's gear case.
An air compressor (model C600), driven by the prime mover, is also installed. The braking system consists of an automatic Pair brake (DA1A), supplemented by a straight air reserve brake.
Accommodation
The seating arrangement consists of 1+2 abreast flip-over transverse seats (type W12), repurposed from decommissioned 0 Series Shinkansen cars. A seating pitch of 910 mm was adopted to widen the aisle, thereby reducing boarding and alighting times.
The passenger saloons are illuminated by two rows of fluorescent lights. Water heating units are installed beneath the seats. To enhance the interior layout, an air conditioning duct is fitted above the ceiling, and ceiling-mounted fans are provided to supplement the limited cooling capacity of the air conditioner.
The driver's cab is a compartment-type configuration located on the left side of the vehicle, designed to accommodate future conductor-less operation. No toilet facilities are provided.
Additional Delivery
In 1988, JR Kyushu added three vehicles equipped for conductor-less operation. These units featured ticket machines installed beside the doorways, a seven-segment fare chart display, and a fare box located behind the driver's cab.
Modifications
Modification for conductor less operation
Vehicles used on the Misumi line received modifications with installation of the ticket machine located beside doorways, and the fare chart seven segment display and the fare box located behind the driver's cab, over the period from November 1992 until March 1993 to introduce conductor less operations. Subsequently, the rest vehicles also received the same modifications.
Accommodation modifications
Between October 1997 and March 1999, five vehicles operating in the Oita
area underwent interior modifications. Except for four rows, the original
2-abreast flip-over transverse seats were removed and replaced with longitudinal
bench seating.
Operations
The class kiha31 was initially allocated to Kumamoto, Hita, and Takeshita
depots, entering revenue service in 1987 on the Chikuho, Sasaguri, Kashii,
Kyudai, Hohi, and Misumi lines. In 1988, three additional units were delivered
to Takeshita Depot, while three existing units there were transferred to
Nagasaki Depot.
Subsequently, six units from Hita Depot were reassigned to Nogata Depot.
In addition, four units each from Kumamoto and Kagoshima depots were transferred
to Nogata Depot to support rural operations on the Chikuho, Gotoji, Hita-Hikosan,
Misumi, and Hisatsu lines.
However, kiha31 units operating on the Chikuho Line between Wakamatsu and
Orio were replaced by BEC819 series battery electric multiple units in
2017. Those operating on the Hita-Hikosan Line were replaced by class kiha140
diesel multiple units and subsequently withdrawn from service. Vehicles
assigned to the Misumi Line were also replaced and fully scrapped by 2019. |
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