Silent traffic is coming. Okay, EVs hum a bit and there are electric cars that hum through a speaker, but a petrol engine that climbs in revs and shifts, you will hear that less and less. Except for the Porsche Taycan or the Hyundai Ioniq 5 N. For even more shifting noise, you can go to a train platform. A train of the NS also has no gearbox, but you can apparently hear it shifting. How does that work?
You may recognize the sound we mean, often accompanied by the slightly too loud earphones of a fellow passenger. If not: listen to the sound in the video below. Do you hear it? The tone the train makes rises, drops, and climbs steadily upwards – roughly the sound of a car approaching the limiter and then changing gear.
For this issue, we call in Ricardo’s help. He is not a model train collector or the janitor of TopGear HQ, but an innovative company that provides technical services for the NS, among other things. An employee of the company explains where the switching noise comes from.
The sound really comes through switching
The overhead line carries direct current, but the electric motors of the train need alternating current. The direct current must therefore be converted to alternating current. This is done by a converter. This device switches the direct current on and off 16,000 times per second. By quickly switching the direct current on and off, the current changes to alternating current.
The act of switching on and off is called pulsing and the series of pulses is called a pulse pattern. A certain speed of the train corresponds to a certain pulse pattern. This differs per manufacturer. It is therefore possible that one train does not need to switch between 0 and 5 km/h and another only after 10 km/h. When a train accelerates, it switches between these different pulse patterns. If the pulse pattern is too fast or too slow, components become warm and energy is lost. In addition, an electrical disturbance can occur if the pattern does not match the speed.
‘When the pulse pattern is changed, you can hear it through a different sound from the drive: it sounds like a car shifting up’, an expert from Ricardo Rail tells TopGear Nederland. The converter works as a kind of automatic gearbox. Unfortunately, the driver cannot shift or go towards the limiter himself.
Why don’t you hear most EVs shifting?
According to Ricardo Rail, this same system is also in electric cars, but you don’t hear it there. ‘The fact that an electric car doesn’t make the same sound as a train is partly due to the power of the drive. The converter of the car can switch at a higher frequency due to the lower power, which makes the sound of the drive less audible. This also means that the pulse pattern doesn’t have to be changed’, according to Ricardo Rail. In other words, all electric cars make a switching sound, but it happens much less often and much less loudly.
The sound of a train changing gears
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