Redesigning the Dong Fang Hong locomotive speedometer system to suit diesel electric locomotives

Abstract

Thirty four out of forty (85%) TAZARA Diesel Electric (DE) locomotives were operating with either defective or no speedometer system at all. This compromised the safety of locomotives and peoples’ lives. As a result of financial challenges, TAZARA was unable buy new DE speedometer system costing over USD$3,800. Due to estimated travel speeds, it has been extremely difficult to adhere to scheduled train departure and arrival times resulting in the loss of customers and business at large. The aim of the research is to redesign the abundant DFH2 speedometer system components and apply them on DE locomotives. Failure to undertake a study would imply rendering all DFH2 system components in stock obsolete. Concepts and principles relating to the relationship between wheel diameter and worm gear teeth number, assembly requirements for the 1R (C) 2R (P) tachogenerator drive shaft and wheel axle to achieve reliability in the transmission axis were employed to redesign the DFH2 speedometer system to suit DE locomotives. Two designs involving use of circular and triangular plates to hold the transducer drive shaft were derived and gradually refined to achieve the desired goals. In both designs the fork assembly was removed, circular and triangular plates were introduced to hold the DFH2 drive shaft. The worm gear in the DFH2 mileage counter (odometer) with 34 teeth was replaced by another with 36 teeth to correspond to the DE wheel diameter of 900 mm. One transducer was used for two speedometer gauges on both locomotive ends as opposed to the original DE and DFH2 locomotive speedometer system installation designs. In the circular plate design, the plate thickness was increased from 3 mm to 7 mm until an optimum thickness of 6 mm was attained. However, deformations were observed on the peripherals of the plate. In the triangular plate design, no deformations observed and was adopted. The DE standard relationship of locomotive speed and DE locomotive sentry panel voltage (vsp) was used to verify the accuracy of the new system. The results conformed to the DE standards. In order to verify the performance of the mileage counter (odometer), predetermined distances between particular stations were compared with mileage counter distances. After replacement of worm gear and conducting line tests, the mileage counter readings corresponded to the actual predetermined distances between stations. In conclusion, therefore, regardless of the type of speedometer system available, it will work accurately on other automobile models if the above concepts and principles are applied accordingly. Keywords: Speedometer gauge, Mileage Counter, Transducer, Worm gear teeth number, drive shaft, plate.