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Research work on the energy efficiency of vehicles is driven, among other things, by limits related to fuel consumption carbon dioxide emissions. This also applies to city buses, where fuel consumption averages between 25 and 30 dm3 per 100 km, which can be converted into approximately 87 kg CO2 per dm3. This article therefore presents the results of a study of the total efficiency of the power train of a city bus, taking into account the internal combustion engine, transmission, hydrokinetic clutch, and tyre friction on the rollers. The test object was a 12-metre city bus equipped with diesel engines and an automatic gearbox. The tests were carried out on a chassis dynamometer by implementing the World Harmonized Vehicle Cycle (WHVC). The WHVC driving test is a synthesis of the vehicle's on-road speeds and consists of three stages: Urban, Rural and Motorway. During the tests, the fuel consumption, vehicle speed and power generated at the wheels of the bus were recorded. From this, efficiency was calculated as the ratio of the power measured at the wheels of the bus to the power contained in the fuel supplied to the engine. Efficiency was shown to range from 5 to 22%.
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