What makes the 8hp so much better then an ordinary 8spd?
Yes.
In regards to the 'first' A - AW / 'A' ....'TL'xxxxx and Hyundai's whatever they call it + an approximation for the HD A - AW / 'A' 'TR'xxxxx.
Over simplified......... the first two appear to be technically speaking, modified 6sp ATs and the TR still has at least a really big piece of that in it.
ZF on the otherhand, started with a strong Management commitment, a design staff, a highly motivated and 'helpful' ? 'first' customer ( BMW ), a big or big enough budget - and timeframe, some seriously kickass 'design' process software ( at the time ) and ....... a
clean sheet.
They
do say they evaluated
thousands of configurations.........
Hyundai and 'Aisin' /
Toyota were motivated to have 8 gears quite arbitrarily - so they could 'attempt' to lord over MB's 7G on gear count marketing wise.Or perhaps better said, that was what happened with Aisin / Toyota, and then in part because of that, Hyundai wanted to at least match Lexus while pulling out in front of MB on gear count.
Which unit btw, they miscalculated in terms of it's ZF inspired improvement program.
The second gen 7G is 'better' to have than either of those two - although down 1 gear for marketing purposes. It may be - key phrase "
may be " a different story with regard to the TRxxxxx in it's HD torque range and or in certain kinds of vehicles.
*****
So.....
the first 8 speed from A - AW for Toyota / Lexus ie the A -AW or 'A'
TL80SN comes as a modified 6 sp - still using a Lepelletier gear train
concept ( common on almost all 6 sp CATs ) ie a single basic planetary gear
set connected to a now augmented Ravigneaux gear
set but with a slight twist. And that is the terrible mistake of using a double planetary gearset in first position. The TR series corrects this error although that does not make it all right - just better than the failed TL series.
Which Ravigneaux assembly is as always, in this 'L' gear train concept - 'R' gear set - composed of two interconnected planetary gear sets via shared planet gears. So, a total of three planetary gear sets ie one double planetary connected to a paired Ravigneaux set.
What they did was to - the other thing was to - within one of the planetary sets in the Ravigneaux 'section' - was to pair up the existing shared planet gears - with an additional 'brother' - not shared.( And then fiddle with the control elements. )
Total gear spread is about 6.709x vs approximately 7.04x for the ZF 8HP.
I cannot remember the details of the second 8 speed under discussion ie from Hyundai although we have had big parts of it posted previously.
Since GM is not potentially buying '
that one', it will suffice to say that although it does vary from the TL80SN and also the details of how it falls short from the 8H P........ it does not matter.
Basically, it ends up the same sort of difference with a little plus and minus variation here and there.
Then we come to # 4 ( 8HP IS #3 ).
Which is the one of most interest in terms of the topic -
or so we can hope.
That would be the second A - AW / 'A' unit aka the
TR80SD - and formally in words as the "
High Torque Capacity Rwd 8 Speed Automatic Transmission ".
As suggested previously, this one is both an improved derivative of - and also separately a higher torque capacity unit derived from the earlier TL80SN ( aka @ Toyota / Lexus as the 'AA80E'. )
Also per previous , it's also appears to be 'better' than the Hyundai unit - in it's original form...... so this is the one to find out about.
It is in essence a redo with a significantly different gear train and function.
VAG..... may have helped....
*****
Anyway.....
ZF started with the number of gears as a variable to be solved for.
Could've been, one supposes based on the way they speak about it....... 'somewhere' between '1' - 10 +.
So....... ZF ends up with.........
1. ) A wider gear spread, better apportioned.
2. ) Critically, a
better type of gear train composed of one relatively simple Simpson gearset with it's two planetary elements, and then the mind blowing aspect ie two
simple planetary gearsets ( thought to be obsolete at this point ) for a total of four planetary sets -
Then mind blower #3 - controlled by only five shift elements of which only two are open in any given gear. The thing of it is...... it is that combination + the specifics
within that combination that are so different and so powerful - and so efficient.
In otherwords, the type of gear train, the arrangement of that gear train, and then how you use it - and control it - which is all very much - completely interdependent is different - and better - all around for everything or every consideration.
There is also with the HP8 some super clever eh, benefits from the exact details of the shift element designs........
It is a more balanced box in all ways possible and this plus all the other means it ends up, lighter, cheaper, stronger, more efficient, faster, and more adaptable.
And that is not the whole list.
Torque converter - pump etc ie all of it and again with even an extra dose because of the synergistic effects.
In comparison.......
The twenty / twenty plus year old WA580 / 5G that was at intro the cat's meow - gets 5 ( forward ) gears out out of 3 planetary sets - arranged as a less efficient Simpson plus a simple - which is pretty good except ..... it has 8 control elements of which 3 or 4 are always open - which means among other things more mass / dynamic 'spinning mass' / more fluid volume / pressure requirements / fluid drag ......although second gear may just be 2 - I always screw that one up for some reason.
The A -AW 'A' TL has
3 planetary sets but of of a more expensive yet less efficient/ higher friction type - with a lower gear spread less ideally split that requires 7 shift elements to control and eh, I cannot remember but does run with 3 or 4 open often....... maybe 2 or 5 once or both or something like that.
3. ) A bunch of other from the specifics of the torque converter to the mechtronics to the hydraulic pump etc etc etc. Much of these parts can be duplicated elsewhere to at least some extent - eventually. For example many have already incorporated much of the torque converter improvements although again because of other differences ( gear train / gear splits ) they cannot do that as strongly.
4. And then the other biggy. The integration factor ie all of this decided pretty much
simultaneously. So..... a unique amalgamation of many 'common or somewhat common elements - resulting in an extra dollop of synergy.
Think - like - a block of stone representing
all possible AT design space.
Then think of Michelangelo's '
David' - that kinda' catches the essence of it.
So if we crudely sum up just the most important main parts of it, it uses less power to run itself, reacts quicker and with a higher quality, has a better geartrain in all ways possible - with a wider and better apportioned set of gear splits, weighs less,
and cost's considerably less - and pound for pound can handle more torque while also generating less heat.
One has to wonder.... if GM is still sore about the ZF second gen 6HP / BMW.......dirty play...... which kinda' helped fund the somewhat simultaneous 8HP development program.......
Any idea what the new improved hemi will be and when it arrives
No, not really....... I've my list like everyone else but .....
I expect them for certain to bring 'more active tech' to it than GM is going to for the LT1.
You will notice that GM is kinda' strongly in the mode of doing as little as possible for the conventional stuff ala the last DM update - and the LT1.
Great - even superlative results for sure but ...... there was more to be had if the teams hadn't of been so constrained ( and yes, they should have their own flavor of something special in the pipeline - that flows like sludge on a really cold day - ) Others...... like Chrysler are not going to let that mid game space go by like GM is - to shift resources to the electrification efforts.
I hope it is clear that I am complaining as one who wishes and wants them to do well - and not as a 'nother brand spin doc.
Finally worth remembering, the 8HP program is so good, so strong that ZF is going to drop the world's best rwd 6speed CAT in or around mid 2014........Which, besides being quite quick - and therefore early, is mostly about their 8HP production capacity - and perhaps their customer's timing - it is not about technical merit in any aspect - or cost.
Notice also - although coming much much later than the all other 8sp CATs, the 8HP is fully dominating the volume space - which will increase even more as each day goes by. As far as speed of rollout, it's a bit like a man leading a small donkey all loaded up who had a big head start - vs an F14 for coast to coast travel.