In reverse they tend to make a whining noise. Isn’t it the same parts doing basically the same thing either way?
In: Engineering
Most transmission gears are straight cut. The interactive elements are parallel to the spin axis. This is less durable, provides more power loss, but is nearly silent while operating. In transmissions with a distinct reverse gear (almost certainly all of them for the last 30 years or so) the gear is a helically cut gear. The interactive elements are cut on a diagonal to the spin axis. These are stronger for their size, and substantially less prone to torque loss.
Helically-cut transmission gears have a distinct whine. This increased strength allows them to be smaller than the other components, and the time reverse is typically used makes the effect less annoying.
Reverse gears are straight cut gears, vs helical (angled) gears for forward. Straight cut gears make more noise but can give better torque, as you only have 1 reverse gear vs multiple forward.
There are different gears for forward and backwards; those gear ratios are different, so it sounds different.
As others said, by using a straight-cut gear. Why the spur when all the others are helical?
– Money. A simple spur gear is a bit cheaper to make than a helical, we’ve had that hobbing technique down for a very long time.
– No need to use a helical since you don’t spend much time in reverse anyway.
Most of your forward gears are what’s called helical cut, so if you look at it from the side the teeth are sort of diagonal. Your reverse gear is usually straight cut, so if you look from the side the teeth look to be all straight. Helical cut gears are more complicated to make, so they’re more expensive, but they’re worth it because they’re quieter. But since you’re rarely reversing for that long, they cheap out a little bit since the noise doesn’t matter there.
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