Automatic VS Manual transmission architecture 1

[jp1726qc]

Hi,

I just learned that automatic and manual transmissions don't have the same mechanical architecture. The first thing that came in my mind is why. Why manual transmission use 2 parallels shafts and the automatic transmission planetary gear set. (There are probably some exceptions but lets keep talking about the general case) What are the avantages and incovenients of each one?

Jean-Philippe

 

[Pancholin]

Expensive planetary gearsets lend themselves to clutches and bands, which don't lend themselves to manual operation, while cheaper spur gearsets lend themselves better to synchronizers which are almost self engaging manually. My mind went blank trying to synchronize a planetary gearset

 

[BrianPetersen]

The above post is correct, but it's worth noting a couple of exceptions.

Although I don't know about their current models, Honda and Saturn automatic gearboxes in the past have used the same dual-shaft architecture as a manual transmission, with hydraulic multi-plate clutches engaging each gear in turn. So, it is possible to do it that way, it just hasn't been conventional. The VW/Audi DSG dual-clutch transmission uses the architecture of a manual transmission, including the synchromesh engagement.

The Ford Model T used a manually activated planetary gearset, but the way it was operated using foot pedals is hardly consistent with how automotive controls operate nowadays. A person who knows how to operate any manual transmission vehicle built in the last 50 years wouldn't have a clue what to do when sitting at the wheel of a Model T.

Planetary gearsets with the torque being transmitted through multiple paths (one path at each planet gear) lead to very high torque capacity for the size of the gearbox, too.

 

[patprimmer]

The Lenco style gear box and most external overdrive boxes are manually operated or at least externally controlled planetary gear boxes.



Regards
Pat
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[HybridEngr]

The difference in architectures are due to the gearing. In a manual transmission (including AMT and DCT), a set of helical gears are used. The coupling of a gear set is best performed using a synchronizer and dog clutch, which are relatively cheap to manufacture, and have low parasitic losses. In addition, a typical manual transmission will not have a hydraulic pump, so actuation of a multi-plate clutch would not be possible.
The exception here is the DCT, which will have a small hydraulic pump. In this case, the pump is used to actuate the synchronizers to select the ratio, and to actuate the servos on the dual clutch to perform the ratio change. The use of multi-plate clutches in this type of transmission would result in higher parasitic losses, which would defeat the purpose of using the DCT.
For the typical automatic transmission, a planetary gear set is used, which is a more power dense gear set, and allows the transmission (rear wheel drive) to be on a single axis. For these transmissions, you could use a dog clutch, however, a multi-plate clutch is easier to control and allows power-on shifting (no de-coupling of engine torque during the shift)

 

[evelrod]

Brian, one of the locals had a T coupe at the car show last month and made it available to anyone that wanted to sit in it. The spark advance and throttle were okay to most (very similar to my 30 Model A ). The starter button on the floor, too. However, the "three pedals" just had everyone stymied...totally. Not a single person, even guys my age that should have known, did not have a clue. Even after attempts at explanation...no clue. I'm not sure what that says about today's driver...........

Rod

 

[mfgenggear]

so one was brake, two clutches?

MfgEngGear

 

[evelrod]

Try this...

http://www.barefootsworld.net/ford-t-4-beginners.html

Rod

 

[mfgenggear]

my Pappi had one of these, when he was a youngster.

lol thanks for the link.

Mfgenggear