Scania : Perfect pitch at every speed

How should the perfect engine sound? Ask the operators at Scania's engine testing centre. Each day they listen to more than 300 assembled engines for discordant sounds. 'Although we very rarely discover deviations, we are committed to doing our utmost to avoid releasing less-than-perfect engines,' says Test Cell Technician Magnus Landin.

Each test staff member is fully trained in how fault-free engines sound and what the most common sounds are when, for example, a nut is insufficiently tightened. Before qualifying for this demanding assignment, they undergo hearing tests. 'The job requires a great deal of concentration and attentiveness. The more experience you gain, the more you are able to distinguish abnormal sounds such as barely audible clonking, scraping or knocking.'

Audio testing at the end of the production line is carried out in two steps. The first sequence to detect any unwanted sounds is when the engine in the test cell is started, idled and gradually speeded up. A second audio sequence takes place towards the end of the test cycle when the engine speed is reduced from full load to idling. These sound tests are recorded, and saved both for training purposes and as reference if faults are later discovered.

Among the 12 test cells, some are dedicated to testing gas, ethanol and marine engines. These engines clearly differ from diesel engines - technically and thereby also audibly - and require special hearing skills. While listening for abnormal sounds, operators also check oil pressure, coolant temperature, engine power and stability.

'This is only the start and we plan to further develop audio testing to ensure that our engines always perform as expected,' says Landin.