Auto box question

[Bren]

Can anybody tell me (in layman's terms) what the brake bands do in an auto box?

 

Many years ago the guy that used to take our granada for it's MOT told us it felt like the bands needed adjustment - there is even a how to in the haynes BOL but it does'nt say what they do.

 

Anybody tell me?

[Eddie Honda]

They wrap round the annular ring gear and either let them turn or not

 

 

Edit, well they wrap round other bits too, as some bits you want to lock to change ratios.

[colnerov]

 Hi, Referring to the animation kindly supplied by EH the drive from the engine comes through the centre orange SUN gear to the grey PLANETARY gears and to the outer blue gear or the ANNULUS. The planetary gears are splined to the output shaft through a clutch and the annulus has a brake band round it. Now depending on whether the clutch or the brake band is applied gives one of two gears. In a three speed g/box there are two of those clusters interconnected and again depending on which combination of clutches and bands gives the three speeds and reverse.

 

Now to answer the question if the sun gear rotates and the annulus is held still the the planetary gears rotate the the carrier they are fixed to. If the brake band on the annulus slips and the annulus rotates as well, drive to the planetary carrier is reduced or lost.

 

 Colin

[Tamworthbay]

Are you seriously trying to make us all believe that auto boxes don't work by magic?

[Rocket88]

auto boxes and electricity are the work of Satan, along with electric hand brakes, and Donald Trump

[scdan4]

any more animations?

 

I don't really understand how autos work, and would love to.....

[ray]

[dollywobbler]

If you want a real giggle, it's worth looking at how a Ford Model T gearbox works. I still don't understand it, and I drove one last week.

[Tamworthbay]

I have stripped a few end of life auto boxes now and still have no real concept of exactly how they work. I have the guts of one from a Volvo bus as a desk ornament at work.

[RayMK]

Strip a Sturmey Archer 3 speed hub. The basic principle of operation of an epicyclic gearbox is clearer when bike sized, though being manually controlled like the box in a Model T or Trojan Utility, there are detail differences.  It's the fluidic control unit on autoboxes that I just gaze at in wonder - millions* of tiny galleries and ports (maybe dinky valves as well), the flow through which responds to oil pressure and thus selects the gears (possibly).  

[Tamworthbay]

Yup, magic

[Eddie Honda]

Are you seriously trying to make us all believe that auto boxes don't work by magic?

Well here's how DAF Variomatics work. It's all down to the belt toilers beating the wicked spoilers...

 

How the belt toilers 01 by E Honda, on Flickr

How the belt toilers 02 by E Honda, on Flickr

How the belt toilers 03 by E Honda, on Flickr

[Tamworthbay]

Well here's how DAF Variomatics work. It's all down to the belt toilers beating the wicked spoilers...How the belt toilers 01 by E Honda, on FlickrHow the belt toilers 02 by E Honda, on FlickrHow the belt toilers 03 by E Honda, on Flickr

The variomatic is a thing of true engineering beauty and I will own a daf with it one day.

[Stanky]

On a similar note, this video from the 30s about differentials is fascinating and explains the concept extremely well - even including a motorcycle display team.

 

[media]https://www.youtube.com/watch?v=K4JhruinbWc[/media]

[scdan4]

 

good link.

 

thanks.

 

That, the linked videos and the variomatic stuff above, I am considerably more knowledgeable than I was before.

 

[JohnDeere]

I also found this video which I think is even more specific about how a multi-speed gearbbox with lock-up works.  I've been trying to better understand the Prelude 'box and what the 1:1 direct drive ratio is supposed to do if it was working properly.  And still mystified - because 4th gear is a .750 ratio, so "top" must be lower still than that... and the tech book says the lock-up applies across multiple gears.  It's all magic.

 

[colnerov]

 Hi, The lock up is the torque converter locking up so there is no slip. It unlikely to be across all gears at all speeds, it's usually in top above a set speed to improve economy.

 

 Colin

 

 Edit: Thinking about it, with the use of ECU,s it could lock up above set speeds in some gears taking in to account throttle position. It certainly wouldn't do it stationary in first gear.

[Junkman]

auto boxes and electricity are the work of Satan, along with electric hand brakes, and the EU

 

EFA

[SiC]

Hi, The lock up is the torque converter locking up so there is no slip. It unlikely to be across all gears at all speeds, it's usually in top above a set speed to improve economy.

 

Colin

 

Edit: Thinking about it, with the use of ECU,s it could lock up above set speeds in some gears taking in to account throttle position. It certainly wouldn't do it stationary in first gear.

My Laguna box does lockup in 4th and 5th for sure, also pretty sure it can do it in 3rd too.

 

My mates a6 does it in all gears from 2nd to 6th. Before his box had a flush, it actually stuck a bit when shifting - which gave a juddering sound as it wasn't quite disengaged quick enough.

 

I guess it's easier to do when an ECU is deciding and controlling it. Also helps a lot with fuel efficiency.

[colnerov]

 Hi, Having the wrong spec fluid in can alter shift quality.

 

 Colin

[Stanky]

Possibly SQA fodder, but how does one know when a torque converter locks up? From behind the wheel I mean.

[Noel Tidybeard]

Possibly SQA fodder, but how does one know when a torque converter locks up? From behind the wheel I mean.

 

the revs drop

[JohnDeere]

Prelude apparently locks up in 2nd, 3rd and 4th when in normal Drive (D4) - only in 3rd in D3 - but you only really notice it in top when the revs drop. The other noticeable thing is that engine revs become directly proportional to speed - though hard to notice in other than 1st where you can blip the thottle without the car leaping forward.

 

There seem to be various complicated rules about when it unlocks - during acceleration, kick-down, certain deceleration (for engine braking). As the shop manual states "The lockup valves control the range of lockup according to the lockup control solenoid valves A and B and throttle valve B. This is all controlled by the ECU, meaning faults can be any combination of electrical or hydraulic gremlins, in the ECU, fluid, servo valves, solenoids, clutches,

 

Having said all of that, I've now decided the Prelude box is fine after all (see Prelude thread). At least I've learned about auto boxes in the process.