"Cé hé sin" (michael-m-mouse)
05/03/2015 at 15:25 • Filed to: Automatic transmissions
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"Cé hé sin" (michael-m-mouse)
05/03/2015 at 15:25 • Filed to: Automatic transmissions | 4
| 6 |
Even for those of us who live in places which are essentially manual-only, city buses have conventional torque converter automatic transmissions.
We get them from ZF:
!!! UNKNOWN CONTENT TYPE !!!
and Voith (pronounced Foyt, it’s the origin of the racing family’s name)
!!! UNKNOWN CONTENT TYPE !!!
Americans tend to get them from Allison:
!!! UNKNOWN CONTENT TYPE !!!
All these have something in common. No Park position. Why?
Weight. Park works by using a pawl to lock a toothed wheel thus providing a mechanical lock. If you tried this on a heavy truck or bus you’d find that if the park pawl was actually holding the vehicle the pressure exerted would be such that getting out of park could be impossible.
So there you have it. Every day we learn something new.
lonestranger
> Cé hé sin
05/03/2015 at 15:43 |
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Well that and the fact that buses use air brakes. Air parking brakes are extraordinarily strong and fail-safe, so adding a park pawl wouldn’t provide any benefit.
European style:
North American style:
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Cé hé sin
> lonestranger
05/03/2015 at 15:55 |
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Oddly, American trucks have two pull out knobs, red and yellow, for parking purposes while the rest of us need just the one.
tromoly
> Cé hé sin
05/03/2015 at 15:56 |
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Air brakes FTW.
Slant6
> Cé hé sin
05/03/2015 at 16:50 |
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Red is for Trailers. And most trucks I’ve driven in NA have EatonFuller transmissions.
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lonestranger
> Cé hé sin
05/03/2015 at 17:01 |
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The red octagonal knob is the trailer supply valve. It allows the trailer’s reservoir to be filled by the tractor’s compressor, but it’s not used for parking the combined vehicle.
But yeah, the differences between the systems is weird.
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Cé hé sin
> Slant6
05/03/2015 at 17:54 |
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I was writing more about city buses though. Interestingly, Eaton used to be able to sell gearboxes to the various smaller makers that existed at one time particularly in the UK but with their demise they disappeared from Europe. Eaton’s last gasp was the Twin Splitter, loved by some and loathed by more and so a commercial failure. Nowadays makers here either make their own manual and AMT boxes or buy from ZF.
I wonder how trucks in Europe manage without those truck air knobs?