PDK at the traffic stop
07-22-2010, 02:05 PM
#1
Three Wheelin'
Thread Starter
PDK at the traffic stop
Question for anyone who has an understanding of the PDK design and operation.
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
07-22-2010, 03:05 PM
#2
Nordschleife Master
Question for anyone who has an understanding of the PDK design and operation.
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
07-22-2010, 07:26 PM
#3
Race Director
Question for anyone who has an understanding of the PDK design and operation.
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
As the device is somewhat of an automatically operated manual what happens when you are in gear at a stop with your foot on the brake? That is, is there a release bearing being utilized with the wear that would go with that scenerio? A traditional auto would not experience any real wear from this situation but a manual transmission should be in neutral with the clutch pedal out ( not depressed).
Any idea?
I had thought I knew but the more I think about it...I'm not sure it is possible to disengage both clutches at the same time (which could be a safety feature cause if it possible to disengage both clutches at the same time it could be possible -- though granted it may take a hardware or firmware failure -- to enage both clutches at the same time, with of course disasterous results.
Anyhow, both clutches would have to be disengaged at the same time -- one is already disengaged while the other clutch would also be disengaged -- when the car is driven up to a stop and stopped with the brake pedal applied. Of course, this means both clutch throwout bearings are under full load.
However, I note this is always the case when the car is moving. One clutch is enaged with its throwout bearing under no load while the other clutch being disengaged has its throwout bearing under full load.
Now bear in mind the designers of the PDK knew of this and no doubt the bearings adequately spec'd and the PDK lubrication system ensures they are properly lubricated and with cool and *clean* oil. (Now I might add there's already good reasons to adhere to a reasonable PDK fluid transmission service and this is just one more.)
Either the PDK works as I stated above or the PDK shifts to neutral and both clutches are released (or allowed to enage though of course with no gear selected this is ok) which cuts way down on clutch throwout bearing wear/tear and heat generated as well.
Then what would have to happen is when the driver lifts his foot from the brake pedal the PDK disengages both clutches then selects 1st and engages or releases the 1st gear clutch at a rate to move the car off at an acceptable fashion.
Maybe this is why launch control is offered? It does away with the temporary shifting into neutral and keeps 1st gear selected and of course both clutches disengaged (wihch does imply I guess both clutches can be disengaged at the same time) to avoid the lag in having to enage 1st gear and then release the clutch which is connected to the shaft upon which 1st gear resides as the driver releases the brake.
I don't know for sure. But it is an interesting question. I like to think the PDK enages neutral but I suspect it doesn't.
I always upon stopping shift a manual transmission into neutral unless I sense I can resume moving the car in just a moment or two. I can't stand to sit with the car stationary, the engine running, and holding the clutch pedal down.
Which begs the question is it possible or even appropriate to if one comes to a stop for which the driver knows the stop's going to take some time to shift the PDK into neutral?
Sincerely,
Macster.
07-22-2010, 08:21 PM
#4
Nordschleife Master
^ Interesting observation. I think that in D or M modes one clutch is always engaged. When stopped (brake on) the odd gear shifting clutch is open, with 1st engaged and it may have minimal slippage. In Neutral I am pretty sure both clutches are disengaged. I read somewhere (PAG doc perhaps) that when stopped it was OK to keep the PDK in D or M modes, unless the stop was a long one and N was recommended. I inferred from that that some minimal slippage occurs, developing heat - bear in mind that these are wet clutches.
As you point out, PDK in operation has always one clutch open - therefore the clutch thrust bearing is not an issue there.
As far as shifting to Neutral... if in D, it's just a flick of the wrist away. If in M, 2 flicks.
As you point out, PDK in operation has always one clutch open - therefore the clutch thrust bearing is not an issue there.
As far as shifting to Neutral... if in D, it's just a flick of the wrist away. If in M, 2 flicks.
07-23-2010, 03:24 PM
#5
Race Director
^ Interesting observation. I think that in D or M modes one clutch is always engaged. When stopped (brake on) the odd gear shifting clutch is open, with 1st engaged and it may have minimal slippage. In Neutral I am pretty sure both clutches are disengaged. I read somewhere (PAG doc perhaps) that when stopped it was OK to keep the PDK in D or M modes, unless the stop was a long one and N was recommended. I inferred from that that some minimal slippage occurs, developing heat - bear in mind that these are wet clutches.
As you point out, PDK in operation has always one clutch open - therefore the clutch thrust bearing is not an issue there.
As far as shifting to Neutral... if in D, it's just a flick of the wrist away. If in M, 2 flicks.
As you point out, PDK in operation has always one clutch open - therefore the clutch thrust bearing is not an issue there.
As far as shifting to Neutral... if in D, it's just a flick of the wrist away. If in M, 2 flicks.
At the stop 1st gear is enaged, obviously both clutches are disengaged. There is no partial engagement of the clutch to hold the car. Hill holding is AFAIK always done by the car's braking system, which delays releasing the brakes until it is sensed the car has sufficient engagement of the clutch to prevent the car from rolling backwards.
I'm seeking to find independent confirmation of this info. More when (if) I know more. Since I am thinking of buying a PDK equipped Porsche I want to know.
Sincerely,
Macster.
07-23-2010, 06:10 PM
#6
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Have only used since last fall, but usually put in neutral when stopped for any length of time....only hastle is to remember to put your foot on the brake, or you can't move into gear! Regardless, I have now tracked the car on 3 different tracks (Mid Ohio, VIR & Putnam Park) for 6 days and absolutely am sold on the PDK.....if the GT3 ever gets it, I'm all over it!
07-23-2010, 09:07 PM
#7
Race Director
Probably not the best place to hang this bit of info, but FWIW I asked a tech today and he told me the clutches are kept inactive (disengaged) by hydraulic pressure and hydrodynamic bearings. Ball/roller bearings are not used in this implementation in a similar fashion to the old dry clutch of a manual transmission.
At the stop 1st gear is enaged, obviously both clutches are disengaged. There is no partial engagement of the clutch to hold the car. Hill holding is AFAIK always done by the car's braking system, which delays releasing the brakes until it is sensed the car has sufficient engagement of the clutch to prevent the car from rolling backwards.
Macster.
At the stop 1st gear is enaged, obviously both clutches are disengaged. There is no partial engagement of the clutch to hold the car. Hill holding is AFAIK always done by the car's braking system, which delays releasing the brakes until it is sensed the car has sufficient engagement of the clutch to prevent the car from rolling backwards.
Macster.
Crawling
To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher driveoff power.
Stationary decoupling
When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.
Drive-Off Assistant
If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2seconds.
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07-23-2010, 09:53 PM
#8
Nordschleife Master
That part about no partial engagement seems somewhat at odds with this info from the Porsche 2009 Technik Introduction for the Carrera models. The info on hill holding is consistent with the Porsche documentation.
Crawling
To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher driveoff power.
Stationary decoupling
When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.
Drive-Off Assistant
If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2seconds.
Crawling
To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher driveoff power.
Stationary decoupling
When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.
Drive-Off Assistant
If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2seconds.
Last edited by ADias; 07-24-2010 at 12:15 AM. Reason: typo.
07-23-2010, 10:39 PM
#9
Race Director
That part about no partial engagement seems somewhat at odds with this info from the Porsche 2009 Technik Introduction for the Carrera models. The info on hill holding is consistent with the Porsche documentation.
Crawling
To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher driveoff power.
Stationary decoupling
When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.
Drive-Off Assistant
If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2seconds.
Crawling
To ensure that the PDK transmission behaves in the same way as a Tiptronic transmission when driving off, clutch 1 is already slightly engaged so that the transmission becomes positively engaged and must be held by the brake. Another advantage of this measure is that the vehicle drives off very comfortably and generally smoothly when only a light load is applied. Driving off at a higher load results in higher driveoff power.
Stationary decoupling
When the vehicle comes to a stop, the clutch is generally opened as long as the brake is applied. However, the clutch remains slightly engaged in order to take full advantage of crawling. The reason for this measure is reduced fuel consumption.
Drive-Off Assistant
If the vehicle is stopped on an incline, the driver will apply the brake and set a certain brake pressure. When the driver now switches from the brake pedal to the accelerator pedal in order to drive off, the set brake pressure is maintained for as long as it takes for the vehicle to drive off. This prevents the vehicle from rolling back while the driver is switching pedals. Rollback prevention is enabled for max. 2seconds.
Sincerely,
Macster.
07-24-2010, 12:25 AM
#11
Nordschleife Master
Everything wears. A regular clutch wears too (clutch disk, throw bearing, flywheel). The PDK wet clutches are expected to last 100k miles, may be longer - they say life of the car, which the industry normally understands to be 200k miles.
07-24-2010, 07:45 AM
#12
Three Wheelin'
Thread Starter
Yes, but there is wear and there is WEAR. With a standard trans, always holding the clutch pedal depressed at a traffic light is excessive wear and you will be replacing your release bearing early. The question is whether the PDK is experiencing this level or type of wear at such a stop.
07-24-2010, 02:24 PM
#13
Nordschleife Master
Yes, but there is wear and there is WEAR. With a standard trans, always holding the clutch pedal depressed at a traffic light is excessive wear and you will be replacing your release bearing early. The question is whether the PDK is experiencing this level or type of wear at such a stop.
