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Vehicle description:
Mechanical part
The 709.4 locomotive is a cab-behind-engine unit with a single driver’s cab; the traction equipment is mounted in the front hood and in the rear hood. The underframe is of massive, welded construction with two longitudinal beams, two buffer beams and two cross members, covered by metal plate floor on its upper side. There are spacious platforms for shunting personnel on each buffer beam and flights of steps facilitating easy and safe access to the catwalks and the cab. The buffer beams are equipped with crumple zones behind the buffers, which are capable of absorbing large amounts of kinetic energy in the event of end-on collisions. Two interconnected fuel tanks and accumulator batteries are housed outside the longitudinal beams mid-way along the underframe. The locomotive’s bogie assembly comprises the underframe, to which two wheelsets with nose-suspended DC traction motors are attached by means of swinging arms. The traction motors are positioned mid-way along the locomotive, suspended from the underframe with flexible supports. The cab profile is compliant with the UIC 505 loading gauge. Cab heating is provided from engine exhaust using exchangers located within the cab floor, and also from an independent heating system.
Power pack
The main power pack is flexibly mounted in the longer part of the hood. The shunting locomotive is driven by a 4-stroke, compression-ignition, 6-cylinder in-line Caterpillar C15 diesel coupled to a traction alternator. The engine features direct fuel injection and electronically operated injection pump units. An electronic system controls motor functions and also provides operation monitoring and basic diagnostics. The engine is supercharged by a turbo blower driven by exhaust fumes and cooled by water flowing through a closed circuit and bypass arrangement. Power transmission is AC-DC, with the traction alternator feeding a pair of traction motors linked in series via a three-phase link, air-cooled traction rectifier. The electronic control system comprises a regulator together with sensors and converters. The on-board network has a 24 V DC nominal output and is powered by alkaline accumulator batteries.
Braking system
The locomotive is equipped with a DAKO-GP air brake. The air braking system consists of an automatic, single circuit brake with a distributor, a pressure relay and an electronically controlled brake valve. Additionally, the locomotive has a two-level parking brake, which is activated once the electrodynamic braking system shuts off, or if the locomotive slows to a halt. The mechanical brake acts separately on each wheel from both sides, while the brake cylinder has a built-in device which adjusts brake shoe positions. The stored-energy spring-actuated parking brake also acts always on both sides of one wheel of each wheelset. The locomotive’s electrical equipment enables electro-pneumatic control of the brake shoes of the automatic brakes. The basic 709.4 version is supplied with an 18 t axle weight. However, by ballasting it can be increased to an axle weight of 19 t. Use of heavier underframe plates can, if desired, result in a 22 t axle weight. The 709, on account of its design features, offers an efficient and economical shunting locomotive alternative.
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