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Vehicle description:
The new 797.5 class – designed for light shunting on sidings and transportation of light trains at speeds of up to 40 km/h (e.g. service trains) – was the product of a comprehensive upgrade of the original 700, 701 or 702 class at ČMKS - JLS. The following parts from the original locomotive have been used: the underframe with buffer and draw gear, axles (including axle gearboxes) and mechanical brake part. All other parts have been newly designed and made. The 797.5 class was equipped with a Liaz engine, but this was replaced in 2002 with a Caterpillar 3306 to produce a locomotive with a new class ID of 797.7. The 797.7 locomotive is equipped with a Caterpillar 3306 engine, flange-coupled to a Siemens Drásov 1FC2 284-04 double-bearing traction alternator, which powers a TE 005 traction motor via a rectifier. From the traction motor a new TK 140 mechanical downward gearbox is driven via a cardan shaft. The other parts of the drive (cardan shafts and axle gearboxes) are original. The Caterpillar engine (including cooling block) is mounted in the front hood, while the traction motor with air reservoirs is located in the shorter rear hood.
The redesigned driver’s cab with large windows, diagonal side doors and a pair of diagonally located control desks is constructed across the full standard track gauge. To reduce the temperature in the cab in the summer months, a “tropical” (double) roof has been fitted. New low hoods give much better visibility than the original hood on the 700–702 class locomotives.
The mechanical brake in the frame of the locomotive is the original. The wheels are braked unilaterally by means of brake shoes. The hand brake is operated by a hand lever from the driver’s cab and acts on the brake shoes of both wheelsets. The DAKO-GP automatic pressure brake consists of a DAKO-L 8" distributor and an electronically controlled DAKO-BSE brake valve operated by DAKO OBE-1 controllers from both driver’s posts. The direct-acting pressure brake is operated by DAKO BP brake valves, again from both driver’s posts. The compressed air source is a 3 DSK 75 compressor. Four units are to be upgraded this year.
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