chassis

Does anyone have definitive Porsche/Audi/VAG references regarding lockup clutch strategy in the MLBevo with ZF8HP?

Looking for when clutch opens and closes, under what conditions, vehicle speeds, pedal status, etc.

There is a deep and broad well of knowledge on many topics for example engine and core transmission, but I haven’t seen similar technical depth addressing the lockup clutch.

Thanks for any pointers to definitive documentation.

Schnave

Here’s everything I have in my tech library on the ZF transmission.

Only one (Transmission Description) specifically addresses the transmission as installed in the Cayenne.

The document, ZF 8hp Manual, is a 122 page student handout for transmission school. Lots of details, schematics, pressures, etc.

The document, ZF_Workbook-transmission-6-8HP is a different 132 page student handout for a different transmission school. Lots of gory details in this one.

The document, zf8hp_introduction, is a 57 page PowerPoint presentation in pdf format.

chassis

Thanks @Schnave . I haven't worked through all the documents yet, but have found what I was looking for. In the white paper:

"The converter lockup clutch can be closed at even lower speeds and depending on the driveline, the transmission is coupled without loss to the engine directly after the starting process, as with a dualclutch transmission. The resulting reduction in consumption is about 0.8 %."

Car companies will do anything for lower fuel consumption which results in lower emissions. In this case, as usual and expected, the quest for lower emissions comes at a penalty to consumer/driver quality of driving experience.

Lurching/surging is the opening of the lockup clutch after the 3-->2 decelerating downshift with brakes applied. The lockup clutch opens just after 3-->2 gear change. Engine inertia is "let go" by opening the lockup clutch. The transmission, connected to the wheel brake rotors, is decelerating while the engine cranktrain is allowed to freely decelerate unbraked. This causes a sharp rise in torque converter pump-turbine speed differential, causing a sharp forward propulsive torque input due to converter torque multiplication. The lurch.

It takes careful observation to pin this down. You can watch rpms blip slightly, as expected, at the 3-->2 gearchange, then another slight blip when the lockup clutch opens and the engine is allowed to do its own thing momentarily. Then comes the lurch, or slight kick in the backside as felt in the seat because of the forward propulsive torque.

Porsche did a very poor job on drivetrain refinement. In .1 it lurches, clunks and is otherwise unrefined. Pedal programming, lockup clutch programming, transfer gear shudder and lash/freeplay are poor on this drivetrain.

chassis

Another phenomenon is detectable, and consistent with both the lurch and the quote above from the white paper.

In all cases below, "launch" means driving off from zero vehicle speed at a gradual, smooth, slowish pace. It does not mean mashing the pedal to the floor in a classic "launch mode" sense.

In comfort or normal mode, when gradually accelerating from a stop, the lockup clutch is closed, unless the software decides a more aggressive launch is needed. For a more aggressive launch, the lockup clutch is opened to allow turbine-pump speed differential, causing torque multiplication, delivering more aggressive launch.

Two observations can be made:
1. lockup clutch opening in Comfort/Normal mode can be felt when pedal velocity is increased due to driver perception of a sluggish launch. This is felt as nonlinear jerky/lurchy acceleration. It is not good. It is hard to reproduce this phenomenon because it is pedal velocity dependent which is hard to repeatably control with your foot.

2. Sport or Sport+ launches with open lockup clutch, thereby giving maximum available drivetrain torque multiplication at zero vehicle speed. The powertrain is far more responsive at launch in Sport or Sport+, most especially with slow launch. The powertrain feels connected in Sport/Sport+. In Comfort/Normal the powertrain feels like a wet noodle at gradual launch.

JGC

Awwwhhh man! I thought I would be getting away from this if I switched back to a Cayenne. The transmission in my 53 GLE is one of my biggest bug-bears.

Woofman

Hasn't it been established or at least suspected that much of the responsiveness difference between Normal and Sport/Sport+ - at least on the V6 engines - is due to the engine switching from Miller cycle to Otto cycle which comes with valve timing alternations? The "tone" and smoothness of the engine at idle changes immediately when Sport mode is selected. @Schnave , where are you?

I keep getting back to the Savage Geese review which notes that the Cayenne S V6 engine is slanted towards higher RPM performance which detracts from its low end performance. The Cayenne S 2.9 liter V6 achieves it's maximum torque at 1,800 RPM. The base 3.0 liter V6 achieves its max torque at 1,340 RPM which might be more practical for a "grocery getter". It's becoming a moot issue since the 2.9 liter V6 in the Cayenne S was discontinued beginning with the 2024 model year.

Relevant comments start at 20:12 if the video doesn't automatically start there:

chassis

Video says nothing. Opinions and gushing emotion.

Miller cycle at low throttle and low rpm gives lower compression ratio therefore lower bmep and lower torque. Not germane to idle vibration, lurching or 6th gear shudder.

Miller cycle has been connected to nothing as it relates to lurching, idle vibration or 6th gear shudder.

9Y0.1 V6 is a train wreck regarding drivetrain refinement. And it’s a fun car and I like it a lot.

Lurching is poor programming of when the lockup clutch opens and closes. We need a strip chart data recording of lockup clutch status vs current gear position, engine rpm and pedal status. On my MB I had XENTRY and this live data recording is possible. Probably also possible with PIWIS, but I don’t have it. I will see if my icarsoft has a strip chart or some kind of plotting feature for real time data.

chassis

Icarsoft cr max can display strip chart data for “value” parameters eg rpm. “Status” parameters eg brake pedal status can be viewed only in text display, not strip chart. So it will be a challenge to bring all of the relevant parameters together on one icarsoft screen.

Needsdecaf

Be glad you don't have a hybrid. Talk about bad (brake) pedal programming.

Tedster

I have a new 2024 eHybrid and traded our 2020 base. We have about 200 miles on it now. The base transmission had poor driveability characteristics including the pronounced lurch at slowing to a stop. Passengers thought I was an idiot at every stop sign. OTOH the new eHybrid is smooth as butter at stops with zero lurching and smooth shifts when accelerating. I have not detected any issue whatsoever while braking. Nothing like Needscafe is reporting at all. Am I missing something?

Woofman

None of which my 2022 base have except for a little idle vibration when the engine is cold which smooths out within a minute. It's about to hit 19,000 miles. The only lack of smoothness at low speeds is when I have auto stop/start on and that's due to engine shutting off while the vehicle is still rolling and sometimes a rather ragged re-start. That can be mitigated by feathering the throttle or just selecting Sport mode. I definitely don't have a 6th gear vibration. I've driven in 6th gear in Sport mode several times for the purpose of trying to sense a vibration. Maybe I have something to look forward to as the miles accumulate?

My experience with the "S" 2.9 liter V6 is limited but it sure seems much more "hyper" than a base V6. I was taken aback last summer when I rode in member @bearcat2000 's 2023 Cayenne S at how the idle was far "lumpier" than that of my base engine. It reminded me of an American muscle car. I thought the racket was from the sport exhaust option but he told me later that he had the standard exhaust.

If I remember, I'm going to see if I can get a Cayenne S (with a V6) as a loaner during the upcoming 20K service. That would be interesting.

chassis

Played with the iCarsoft CR Max, it's a good tool. Multiple "value" parameters can be strip chart graphed in the same chart, very useful. "Static" parameters e.g. gear position and lockup clutch status cannot be displayed on the strip chart but can be recorded and saved simultaneously with other selected parameters.

Lockup clutch status is a viewable parameter. I noticed it is closed nearly all of the time, not good from a driveability point of new. PCM drive mode was "Normal".

Sampling rate of the iCarsoft is not the best - the data is a bit jaggy/digitalized. To be expected, it is not $100k lab-grade oscilloscope.

I will do some recording and try to post here. Not a priority and my schedule is over the top busy at the moment. The data causes me to notice more clunks, thumps and bumps in the drivetrain because they are felt in the seat and seen in the data. Deceleration with closed throttle is the worst use case for this drivetrain - it doesn't know what to do when the driver does NOT have the pedal mashed to the floor.

p.s. AWD clutch actuator angle and electrical current parameters are visible and can be graphed and saved. This will help with the 6th gear shudder issue. It will only tell us what we already know - Porsche failed in the design and manufacturing.

95_993

chassis,

do you think it’s possible to alter/program the lock up differently to prevent early lockup? Are the lockup points different in sport vs comfort mode?

I am 100% with you on this. The odd lock/unlock causes a surge in rpm, which I believe gives a surge in boost from single turbo on base making it even more pronounced. This appears to be why a quick manual downshift ahead changes all of these dynamics. This is the one issue that my wife HATES about her 9y0 and will influence next purchase decision for sure.

TXSchnee

You aren't missing anything. My '20 E Hybrid had zero lurching issues when braking, my '24 S E Hybrid also has zero lurching. I have a feeling it is down to people trying to "rev match" when braking, instead of applying steady, even pressure to the brake pedal. Any 9Y0.1 or .2 Cayenne I have driven brakes smoothly (loaners or test drives). My '24 BMW XM was horrible when braking, especially on the first few stops, not a smooth transition from the regen to the friction brakes.

chassis

The lockup clutch opens after 3-->2 decelerating downshift with light brake application. Lockup clutch is open in 2nd gear below approx 15mph, and open in 1st gear. It remains open on initial gradual launch and closes nearly immediately. Torque converter turbine torque multiplication is used very sparingly, nearly not at all. The reason is that any time the lockup clutch is open, efficiency is lost (emissions, fuel economy).

The iCarsoft is good, but not great. The sample rate is pretty slow, around 1 second. This is OK for static measurements, for example at idle or constant vehicle speed. For dynamic phenomenon such as lurching, a low sample rate is not sufficient to precisely identify the issue. When the strip chart is displayed on the screen, the engine rpm and transmission input shaft rpm delta can be seen when the lockup clutch opens and causes the lurch. But the data capture rate to a saved file does not resolve the changes fast enough. The data sample rate needs to be maximum 100ms, better if it was 10ms.

In the end I am convinced lurching is related to poor management of powertrain mass, stiffness, damping and freeplay, combined with lockup clutch strategy.