Background and Overview
In response to the need for continued operation of aging commuter diesel
multiple units (DMUs), Japanese National Railways (JNR) initiated a targeted
refurbishment programme. While approximately 1,000 Kiha47 series DMUs and
900 intercity DMUs underwent extensive refurbishment and remained in service,
an additional 500 commuter DMUs were deemed insufficient for continued
operation without significant upgrades.
To address this, JNR developed the class kiha38 commuter DMU, designed
to replace aging units with a modernized configuration. The kiha38 was
based on the structural and mechanical design of the class kiha37, but
featured a newly constructed carbody equipped with three passenger doors
per side to improve boarding efficiency during peak hours. In addition,
many components were repurposed from decommissioned kiha35 series vehicles,
ensuring cost-effective production and parts compatibility.
The class kiha38 was produced in two variants:
- Kiha38-0: Equipped with a toilet.
- Kiha38-1000: A simplified version without a toilet.
A total of seven units were manufactured and delivered between 1986 and
1987.
Car body
The class kiha38 commuter diesel multiple unit, developed by Japanese National
Railways (JNR), features a steel carbody measuring 20,000 mm in length
and 2,928 mm in width, with a bogie centre distance of 13,800 mm. The body
structure incorporates a 1.6 mm thick steel plate for the side panels,
a 1.2 mm thick plate for the roof, and a 2.0 mm thick floor plate laid
over the underframe. Both the body skin and roof panels utilize weather-resistant
steel sheet (Steel Plate Atmospheric), conforming to JNR's material standards
to ensure long-term durability under varying environmental conditions.
At the cab end, the vehicle is gangwayed and fitted with a gangway door to allow inter-vehicle passage. The driver's cab is mounted 300 mm above the floor level, a design measure introduced to enhance protection against obstacles at level crossings. Flat windscreens are employed to reduce manufacturing costs, and a classification and destination roll sign is installed above the co-driver's side windscreen. Below the windscreens, the vehicle is equipped with two sealed-beam headlights and taillights, along with a pneumatic horn positioned beneath the co-driver's side windscreen.
Passenger access is facilitated by three double-leaf, semi-automatic sliding doors on each side of the vehicle, each measuring 1,300 mm in width and incorporating steps for platform alignment. These doors can be manually opened and closed via push-button controls located adjacent to each doorway. The door operating mechanism, designated TK106A, is mounted on the door header. Unlike the kiha35 series, which employed externally hung doors to preserve underframe integrity by omitting door case space, the kiha38 adopts standard sliding doors. Structural evaluations confirmed that the inclusion of door case space does not compromise body strength, allowing for a more conventional and maintainable door design.
Between the doors and the ends of the carbody, the kiha38 is fitted with 830 mm wide double-hung windows originally developed for transit buses. These windows feature a vertically sliding mechanism, with the upper sash moving downward and the lower sash moving upward. The sashes are painted black, providing visual contrast and a modern appearance.
Roof-mounted forced-draught ventilators made of fibre-reinforced plastic ensure adequate airflow within the passenger compartment. For climate control, the vehicle is equipped with a self-powered AU34 air conditioning unit installed beneath the floor, rated at 26,000 kcal/h. The exhaust pipe of the prime mover is routed internally through the cab, a layout choice that balances space constraints with functional requirements.
Coupling between vehicles is achieved using tight-lock automatic couplers fitted with RD13 rubber draft gear, which provides improved shock absorption and operational reliability. The exterior livery of the kiha38 features an ivory base color accented by a vermilion waistline band located beneath the side windows.
Bogies
The Class kiha38 commuter DMU utilizes bogie components inherited from the earlier kiha35 series, ensuring compatibility and cost-efficiency in production and maintenance. The powered bogies are designated DT22C, while the trailer bogies are TR51B. Both types adopt a swing hanger suspension system.
Each bogie incorporates coil springs as bolster springs, providing vertical flexibility and damping, and employs a pedestal-type journal support system, a conventional yet reliable configuration widely used in Japanese DMUs of the era. The gear ratio of the powered bogies is set at 2.976, optimized for the acceleration and speed profile required in short-interval commuter operations.
In response to increased load demands typical of urban commuter service, the axle diameter was enlarged to 175 mm, enhancing structural strength and fatigue resistance. The bogies are equipped with single-tread brake rigging, a simplified and maintainable system suitable for the vehicle's operational context.
To accommodate the reduced overall body mass of the Kiha38 compared to its predecessors, the brake lever ratio was recalibrated, ensuring appropriate braking force distribution and responsiveness. This adjustment reflects a careful balance between braking performance and mechanical efficiency, tailored to the vehicle's lightweight construction and service profile.
Traction unit and ancillary equipments
The class Kiha38 is powered by a DMF13HS diesel engine, a horizontally mounted, four-cycle, straight-six prime mover installed beneath the vehicle floor. This engine delivers a rated output of 250 PS, and is equipped with a turbocharger driven by exhaust gas flow, enhancing combustion efficiency and power density. To further improve fuel economy and operational responsiveness, the engine incorporates a direct injection system along with a fuel injection control mechanism, enabling precise fuel delivery under varying load conditions.
Power from the prime mover is transmitted through a hydraulic transmission unit, either the TC2A or DF115A, both repurposed from decommissioned DMU stock. These transmissions underwent targeted modifications to accommodate the increased output of the DMF13HS engine. Specifically, enhancements were made to the torque converter and clutch assemblies, ensuring compatibility with the higher torque characteristics and improving overall transmission durability.
In the case of the TC2A unit, an additional modification was implemented to reposition the servo piston responsible for hydraulic/direct drive stage changeover. This adjustment was necessary to prevent mechanical interference with the gear case of the newly installed prime mover, reflecting careful integration of legacy components with updated powertrain architecture.
Auxiliary pneumatic systems are supported by a C600 air compressor, mechanically driven by the prime mover. This compressor supplies air for various onboard systems, including the braking apparatus. The vehicle employs a DA-type automatic air brake system, a standard configuration for Japanese DMUs, offering reliable and proportional braking performance.
Accommodation
The interior of the class kiha38 is designed to accommodate high-density commuter traffic while maintaining basic passenger comfort. The seating arrangement primarily consists of longitudinal bucket-style bench seats installed along both sides of the passenger saloon. Each bench is fitted with armrests at both ends, providing minimal personal space demarcation. An exception to the longitudinal layout is a single transverse seat positioned across the aisle from the toilet compartment.
Illumination within the saloon is provided by fluorescent lighting fixtures arranged in two parallel rows, ensuring uniform brightness throughout the cabin. For thermal comfort, the vehicles are equipped with a water-based heating system, suitable for maintaining cabin temperature during colder seasons. However, due to the limited cooling capacity of the underfloor-mounted air conditioning unit, seven ceiling-mounted fans are installed to assist in air circulation and supplement the cooling effect, particularly during peak summer conditions.
In the kiha38-0 variant, a Japanese-style toilet is installed at the rear end of the carbody. The compartment is constructed with provisions for the future installation of a chemical holding tank, allowing for potential upgrades in waste management depending on operational requirements.
Operations
These units were delivered to the Takasaki Depot in July 1986 to commence revenue service on the Hachiko Line, alongside the kiha35 and kiha45 series.
Following the electrification of the Hachiko Line between Hachioji and Komagawa, they were withdrawn from the line and subsequently reassigned to the Kisarazu Depot for operation on the Kururi Line.
After several years in service on the Kururi Line, they were replaced by the kihaE130-100 series DMUs and fully retired from operation in 2012.
Of the retired units, one was transferred to the Mizushima Seaside Railway in Kurashiki, Okayama Prefecture, while the remaining cars were scrapped. |
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