What disconnects the transmission when you are in park?

[television]

I have already found this to be true with my E320CDi, and was wondering if you could explain why Mercedes gearboxes don't lockup? I was under the impression that lockup improves fuel efficiency.

I understand that the Mercedes torque converters do have a lockup clutch, so when is it used?

Thanks for your help

Maybe I was not 100% correct,,many have tried just touching the throttle at 70, and the RPM will change. I have not tried it at 2500RPM as Rich Williams say as that equates to 80mph on my car

 

[rich.g.williams]

Thanks for the images and such a comprehensive pdf, here is something for you in case you did not yet see it.

http://i572.photobucket.com/albums/ss167/richgwilliams/722_6TransmissionSchematic2ndGea-1.jpg

 

[television]

Thanks for the images and such a comprehensive pdf, here is something for you in case you did not yet see it.

http://i572.photobucket.com/albums/ss167/richgwilliams/722_6TransmissionSchematic2ndGear.jpg

Thank you very much for that,, and for your input here.

As you love the High tech stuff this is all of them.


http://www.mercedestechstore.com/pdfs/index.htm

 

[rich.g.williams]

Thanks.

I just edited the post to give a better resolution picture.

Will need some time to read through all this.

Thanks.

 

[television]

Thanks.

I just edited the post to give a better resolution picture.

Will need some time to read through all this.

Thanks.

Thank you for everything and the change,,much easier to see.

I am off to bed, too many post again today

 

[rich.g.williams]

Maybe I was not 100% correct,,many have tried just touching the throttle at 70, and the RPM will change. I have not tried it at 2500RPM as Rich Williams say as that equates to 80mph on my car

Think of it this way, at 70 mph the hydraulic coupling is supplying much of the power to drive, the lock up clutch is "slipping" but still able to provide enough extra coupling so adding the two together you have what amounts to lock up or virtually no differential slip between torque converter input and output.

Once you blip the throttle there is slip, so no jerky feelings, typical MB engineering excellence.

At least that's what I think is going on, will read further.

 

[television]

Think of it this way, at 70 mph the hydraulic coupling is supplying much of the power to drive, the lock up clutch is "slipping" but still able to provide enough extra coupling so adding the two together you have what amounts to lock up or virtually no differential slip between torque converter input and output.

Once you blip the throttle there is slip, so no jerky feelings, typical MB engineering excellence.

At least that's what I think is going on, will read further.

That would fit the bill perfectly, and answers a few points.

It is always nice to know why on these things, and I understand things a little better now

 

[rich.g.williams]

Good morning.

Here is the link for the pdf of that drawing, much better resolution.

http://www.yuanfengat.com/bbs/images/upload/2007/12/05/220657.pdf

I have other stuff that I can PM across to you at a later date.

Thanks

 

[television]

Thank you and always nice to have

 

[Wirral_guy]

Can I just add my thanks to all of you. A very informative and interesting thread about somehting I've never really thought much about.

It also explains a lot about what happens when you press the loud pedal, which is very different to a manual. I'll be testing the lockup theory next time I'm on a motorway too but, certainly at lower revs, the rev/speed slippage is exactly what I experience (...and thought might be a problem :Oops

Dave
(still trying to get my head around the fact that merely oil friction between 2 impellers is powerful enough to provide so much drive at the wheels )

 

[television]

Can I just add my thanks to all of you. A very informative and interesting thread about somehting I've never really thought much about.

It also explains a lot about what happens when you press the loud pedal, which is very different to a manual. I'll be testing the lockup theory next time I'm on a motorway too but, certainly at lower revs, the rev/speed slippage is exactly what I experience (...and thought might be a problem :Oops

Dave
)

I do agree that this has been a good thread,, though I knew the rough workings, I was a long way out on many points till Rich came on the scene and joined in. His post has answered all of the bits that explain some faults that we get.

Re the (still trying to get my head around the fact that merely oil friction between 2 impellers is powerful enough to provide so much drive at the wheels that is all that drives a huge liner through the water, just a few large propellers .

Time is always the problem on these things,,one minute my head is full of CAN buses and EIS then over to this type of thing. At least in the factories they have specialist in their own field,, they guys that work on them need to know so much more

 

[Wirral_guy]

Re the (still trying to get my head around the fact that merely oil friction between 2 impellers is powerful enough to provide so much drive at the wheels that is all that drives a huge liner through the water, just a few large propellers .

OK, thanks Malcolm - put like that it makes perfect sense! Funny how your mind needs an example before it becomes clear.

Dave

 

[Number_Cruncher]

I've only one thing to add, which is that the torque convertor doesn't empty - this can be seen by looking at the the way both inlet and outlet are connected to valves which are always supplied with fluid.

All that happens to disconnect the engine from the gearbox is that at tick over, there isn't enough kinetic energy in the oil to transmit any meaningful torque* - as soon as you rev the engine, the fluid begins to circulate more quickly round the three sets of turbine blades, transmitting torque.

* On older transmissions, pre 722.6, just enough torque is transmitted to allow the car to creep forwards, or to hold it on slight hills.

The third set of blades, the stator is the part which makes a torque convertor different from a simple fluid flywheel. At low gearbox input shaft speeds, the stator realigns the flow of fluid so that it enters the engine side turbine blades at the best angle, giving more output torque - at higher gearbox inout shaft speeds, the fluid begins to hit the *back* of the stator blades, and the one way clutch allows the stator to simply spin, and do nothing - i.e., at higher gearbox input shaft speeds, the torque convertor functions just like a fluid flywheel.

 

[wireman]

Further to yesterdays input,

The torque convertor is always active, there is no control input to it so if you rev the engine the torque convertors output shaft will follow and raise the speed of its output shaft and of course the input shaft of the gear box.

In neutral/park there is no oil pressure to the gear selection mechanisms but to get oil pressure for the purpose of gear selection/engagement the oil pump needs to be turning, if there was no rotary input from the convertor when in neutral/park it would not be possible to engage any gear.

Inside the convertor there are three turbine bladed rotary components, an engine driven impeller which forces oil through a second freewheeling divertor to the output turbine, it does not rely on friction in any way, rather the oil is forced from a pump onto a turbine which will turn or at least attempt to turn if there is pressure from the impeller, this behaviour is modified by the presence of a divertor which depending on the speed difference between input and output shafts controls where the oil is delivered (radialy) to the output tubine i.e. at the outer or inner edge of its blades, it is this behaviour which makes it a torque convertor. In the condition of output shaft stalled the oil is delivered to its outer edge raising the output torque above the input torque, as the output gathers speed the oil is diverted to the centre of the tubine providing more speed and less torque, the oil is delivered in effect via a lever of varible length. The blade shapes of the divertor are selected by design to set the torque ratio and speed range of the convertor.

Due to the nature of any system with gaps and liquids there will always be some leakage around the system, which in a torque convertor gives rise to slip in input/output speed.

The slip at high speeds under normal loads can be typicaly around 5%, this represents a loss of power delivered into the gearbox (hence a gearbox oil cooler being almost mandatory), this can be combated by an additional clutch to lock/bypass the convertor at higher engine speeds. The lock up can be simple and controled entirly within the convertor or by external means in more sophistcated units, it is actuated by hydraulic means in most units.

A torque convertor is specificaly setup for the vehicles expected duty, vans and cars will require different speed/torque characteristics, trucks even more so.

Typicaly the torque ratio is around 2 or less for cars with carefull selection of the tranfer characteristics being made by the car builder with regard to trading performance for comfort. These characteristics cannot be changed once the convertor is built.

It is possible to get high torque ratios of around 4, but such a convertor would be unsuitable for most vehicles due to some sharp knees in its speed torque curves and somewhat more than acceptable slip. High ratio convertors see use in tractors used for heavy moving jobs i.e. aircraft tugs etc, they also saw duty in some very early cars with two speed auto gearboxes.

Wikipedia gives a good account and the Bosch automotive handbooks give lots of technical details, performance graphs and drawings of real units, other books are available.

 

[television]

Thank you NC and wireman for writing that all out

 

[rich.g.williams]

I also found a lot of good information from this thread.

What seems to be less well documented is how the ETC accomplishes gearbox control. There is some information about its inputs and outputs and so on but not much about the "algorithms" it relies upon.

For anybody interested here is some initial crystal ball gazing:-

1. The ETC has two primary purposes, to protect the gearbox and to accomplish appropriate gear changes.

(It does successfully play its part to protect the gearbox when you consider that one bad mistake can potentially chew the entire gearbox up in seconds)

2. The ETC compares four speed signals to accomplish specified gear changes and detect gearbox faults. The speed signals are Road Speed, Engine Speed and the two Speed Sensor signals from inside the Gearbox.

3. It uses feedback to control the Lock Up clutch solenoid and some of the other solenoids.

4. It can adapt to (or compensate for) wear inside the gearbox such that gear changes remain smooth (within spec).

5. It is adaptive and has logic that learns.

 

[television]

Thanks Rich,, interesting that when the engine power is down the box does not know what to do in many cases and locks up in 2nd

 

[rich.g.williams]

It may well be difficult to write firmware that can differentiate fully (safely) between a engine low power (torque) situation and faulty gearbox situation. The ETC therefore puts transmission into 2nd gear (turns all solenoids off and does nothing) it seems to be the safest option for the gearbox.

The newer 722.9 box has an extra speed sensor on gearbox output shaft therefore it gets output speed directly rather than from the ABS via the CAN bus as the 722.6 does. As a complete guess I would guess that the 722.9 box is less ready to go into second when the engine power is down.

 

[Number_Cruncher]

>>the oil pump needs to be turning, if there was no rotary input from the convertor when in neutral/park it would not be possible to engage any gear.

There are two output shafts from the torque convertor.

The fist shaft, the outer one, is solidly connected to the torque converter outer shell, and it is this shaft which drives the front oil pump.

The output turbine is connected to the inner shaft, and it is this inner shaft which drives the gear train.

So, as long as the engine is running, the gearbox front pump runs, and the gearox has oil pressure.

 

[reuben]

So many great replies - I think everyone is learning!

I have some more questions - specifically about the lockup clutch. I want to know a bit more about the lockup solenoid and what state it is in when the car is switched off (is it open or closed)?

Am I right in thinking that in P or N the clutches and brakes in the gearbox are all not selected and hence the output side of the gearbox would not turn, even if the input side turned? Also when you first engage D or R, do the clutches and brakes in the gearbox then apply themselves to the correct planetary configuration to then transmit the power to the output of the gearbox?