[BanziBarn]

I might be the only person to ever think this, but I'd really like some kind of indication to when the torque converter locks up.

When I'm driving I tend to alter my acceleration to make most use of the direct connection. Normally I can just about tell when the lock up happens, but it would be nice to not have to concentrate on the revs so much.

I know some of you will say "why didn't you get a manual?. Well, the answer to that was that I couldn't find one!

I like the Auto though, it's a good box, but it's nice to keep the slush to a minimum!

Anyone else ever thought about this?

[HighlandPete]

Not sure it is that simple any more. The older 5HP series boxes had a on/off lock up clutch, you could see it clearly engaging and the rev drop, almost like a 6th gear. But the 6HP series boxes have a stepped lock up and don't totally engage as such. Designed to slip to a degree and help damp out torque pulses, for one thing. So we run a much tighter torque converter even in the low gears, but harder to define how much lock up we have at any given time.

This is observable as well, my old E39 540i would lock up and break lock up with a clearly discernable effect. But the 330d is very different, just try adding a bit of throttle at say 60mph, and you will see the revs rise but not in a direct ratio to speed, there is still a bit of flexing going on, even at 60mph in 6th gear. The old 540i would be locked in, 100% at just over 50 mph.

Division Car Driveline Technology, ZF Friedrichshafen AG

Both converters (two output capacities) use the same design concept and are equipped with a 2-surface lock-up clutch. These clutches can be run in a continuous slip mode and are able to handle friction power up to 2 kW. Herewith, the operation range of the slip mode can be extended which helps to save fuel by further reducing speed ranges with open converter.

ZF 6HP26 Design Pointers

Hydrodynamic Torque Converter
Engine torque passes through the hydrodynamic torque converter equipped with a lockup clutch that can apply from first gear depending on software and user mode. Lockup never occurs completely, and the clutch when applied is designed to have a constant slip, preventing engine vibrations from entering the car. This also improves the acoustics coming from the transmission. This has been made possible through the use of newly designed oil and clutch materials.

So I'd suggest it's difficult to have an indicator.

highlandPete

[BanziBarn]

That's very interesting, thanks Pete.

I have to say, I've not noticed any constant slip. Above 2k rpm, if I'm not accelerating it appears to lock up and I've never noticed any slip when I subsequently give it more pedal. Even in 6th gear at low speeds where there would be a lot of torque going through the box it seems to pull without slip.

I even get engine breaking in manaul mode.

But, I suppose it's all a matter of how much slip there is. So, I guess it's enough to stop vibrations etc, but not enough so the driver notices.

[HighlandPete]

Yes, we are only talking a very small amount of slip. In the older designs was not uncommon to see 400 - 500 rpm drop or gain, when the lockup clutch engaged/disengaged.

Our boxes are closing the clutch as much as possible. When I say I notice the flexing it is only a few rpm, say 50 -100 according to engine rpm, can just sense it is not a solid coupling. High speed cruising does appear more direct a drive.

The benefits to the way it works, the efficiency of the slush boxes are much more in line with a manual transmission. The latest 8-speed boxes are showing they can match, or even better a 6-speed manual for economy.

HighlandPete

[BanziBarn]

I've been playing around with techniques to make the box lock-up (or as it turns out, nearly lock up) and have been using the manual shift and easing off the gas during chnages like in a manual.

I'm still trying to work out if there is a benefit. Between first and second I think there may be an effect becuase I've seen the TC light flash on engagement of second which I've never seen when the box takes care of the changes.

I'd guess that, if you are gunning it during the chnage to second, it's going to have to slip a lot more than if there is no strain on it?

[HighlandPete]

Originally Posted by BanziBarn

I'd guess that, if you are gunning it during the change to second, it's going to have to slip a lot more than if there is no strain on it?

Basically yes. The lock up clutch is only designed to take a fraction of the torque the converter can cope with.

I was out in my car this morning, thought I'd pay a bit more attention to the engagement, as we are discussing this subject. My drive included some steep hills, there is some rev flexing, but it is pretty tight most of the time. Just cruising behind some traffic, at about 55 mph, and a light blip on the throttle shows an instant rev rise, about 100 rpm (no increase in road speed), indicating it's not too tightly coupled, then there is not any real slip or losses anyway, at such low loads, at that speed.

HighlandPete