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Most of the auto shifting big truck transmissions are either 10 or 12 forward ratios. The Allison DC10 is a 10 speed, which is a conventional torque converter automatic suitable for truck tractors and large coaches. Volvo's I-shift, which is an automated manual (and very good) is a 12 speed.
Fleets love getting rid of the clutch pedal because they save fuel and wear and tear from bozo driving habits. A good driver will do nearly as well with a manual and owner operators tend to prefer the 13 or 18 speed Eaton Fuller over the more typical 10 speeds for the higher torque capacities and closer ratios.
There are a wide range of auto shifting transmissions for heavy duty trucks that cover a wide range of technologies but passenger and luxury coaches are generally not as cost or weight sensitive as truck tractors are. Plus it would be difficult if not impossible to put a manual gearbox into a coach that has the powertrain sitting in the back far away from the driver's seat. In a truck tractor the shift lever comes straight out of the top of the transmission through the floor of the cab. Manual gearboxes are simpler and cheaper and considered more reliable than auto shifting units, although that is changing.
I've been on quite a few European buses with manual transmissions. It seems it is not impossible.
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Quote:
Originally Posted by Bitey
Were they pushers?
yes, many buses I have driven were manual tranny pushers. Often a real wobbly shifter, but if maintained and adjusted correctly it works fine. I was counting on that this yr in NZ National Park / narrow STEEP gravel road w/ 60 passenger Pusher Bus + manual tranny and an 18 yo US 'wrong way' driver.
A typical semi transmission has 10 gears, new ones have 18 gears and even higher.
You mean the driver shifts 18 times, with a clutch in between, before reaching top gear? That's crazy. What about downshifts? Do I have to shift down to 16th or 12th gear and how do you know?
You mean the driver shifts 18 times, with a clutch in between, before reaching top gear? That's crazy. What about downshifts? Do I have to shift down to 16th or 12th gear and how do you know?
Experience.
Back when I learned to drive a truck, some trucks actually had TWO gearshift levers, though the ones I drove most had a single lever with an electric split-shift knob on the main shifter (dual-speed transaxle).
What gears you used when would depend on how much weight you had on.
The last TT I drove a couple of years ago (Freightliner) still had the split-shifter on the main lever.
The maximum weight of a fully loaded passenger bus is about 30,000 lbs. A semi with a fully loaded 40' trailer can be up to 80,000 lbs, almost 3 times the weight. As such, the gearing needs to be very short to get that weight moving. A typical semi transmission has 10 gears, new ones have 18 gears and even higher. I don't think any automatics even exist with that many gears.
I believe Coach buses are a bit heavier than 30,000lbs. Buses used to have standard transmissions generally 5 spd as the torque requirements aren't as great as a heavy truck. Between today's diesel engines with greater torque curves and the torque multiplication of a torque converter and ease of manufacture they're all automatics. Torque converters and automatic type transmissions have been used for years in heavy equipment. Very few bulldozers have a clutch, yet they have tremendous torque, in part because of the torque multiplication of the torque converter.
A vast majority of semi tractors used in larger fleets have 10 spd transmissions with or with out a clutch, the ones without the clutch are the "auto-shift" transmission. More trucks will have these because there are govt fuel economy goals and the auto-shift helps them meet those goals.
About the only 13-18 spd transmissions today are found in real heavy hauling operations. For the most part the closer gear spacing is unnecessary with today's diesel engines wider torque curves. The 18 spd transmission may have an extra 1 or 2 lower gears for off highway work that aren't used when on highway.
Automated manuals get better fuel economy than a manual transmission because they're programmed for optimal fuel economy. When you're only getting 6 or 7 MPG on expensive diesel fuel, fuel dwarfs all your other costs and picking up that 1/2 MPG really matters. You can still override it for engine braking. This is a money thing. A dual clutch automated manual makes more money for the trucking company than a manual transmission.
The name of the game in urban transit buses is to NOT throw the passengers on the floor when starting from a stop. Often passengers are walking to seats as the bus pulls off.
Around here, city buses were all automatics with first gear locked out. The bus took off in second gear which was very sluggish...which was the whole idea when you had 40 or 50 potential lawsuits on board.
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