Mechanical Mechanism of PDK Clutch Activation
1 - 11 of 11 Posts
Joined
·
606 Posts
Okay, so it's a wet clutch, and I don't know much about wet clutches other than motorcycles tend to use the motor oil. What I'm asking about is: in the PDK system, is there an equivalent to the little engine compartment reservoir full of brake fluid in a manual transmission car that the clutch pedal drives through master and slave cylinders to provide the mechanical force to disengage the clutch? Or, I believe another way of saying that is: what is the "hydraulic" in the "electro-hydraulic" actuation of our PDK's?
Joined
·
606 Posts
Without watching it a second time, it seems to imply, since it doesn't explicitly answer my question, that a single fluid inside the unit lubricates and has its flow controlled enough to engage and disengage the clutches.
The next question would be: how do the gear selector forks get moved? What's moving them?
Where I'm going with this, in case anybody cares, is service. I change clutch fluid - if it is brake fluid - every two years, max. I haven't found clutch or transmission service intervals yet.
If anyone actually knows the answer, I'd appreciate it.
The next question would be: how do the gear selector forks get moved? What's moving them?
Where I'm going with this, in case anybody cares, is service. I change clutch fluid - if it is brake fluid - every two years, max. I haven't found clutch or transmission service intervals yet.
If anyone actually knows the answer, I'd appreciate it.
Joined
·
2,229 Posts
Why? We change the brake fluid every two years because of the high temperature brake service. If it gets any water (and it will), the water may evaporate due to the high temperatures developed over braking and the steam bubbles will be compressible, making your brake pedal go to the floor.
I sincerely doubt that the clutch liquid will ever reach 100C. If the water remains liquid, it will be just as incompressible as the brake fluid and there is no loss of function.
Am I missing something here?
Joined
·
2,592 Posts
Interesting video with some good details (despite the time wasted on fluff conversation).
Two concentric clutches driving to coaxial input shafts, on inside the other which is hollow. So that's how they do it, a neat solution, probably the only one that makes sense.
Gear selection seems pretty conventional for a manual gearbox.
The really interesting feature is the use of two secondary shafts, each split into two coaxial sections, one section carrying odd numbered gears and the other carrying even numbered gears. The split of each is what allows the dual-clutch feature to pre-select a gear. A traditional 4-speed box would have only one secondary shaft, which of course is not split. It would carry all the gears, possibly using direct drive for 4th.
Using two secondary shafts would seem to be a way to squeeze more gears into a smaller space, and would accomplish the same thing even if it wasn't a dual-clutch transmission. They mentioned it only briefly in the video but both shafts seem to be directly connected to the equivalent of the differential ring gear. One shaft holds the lower gears, the other holds the higher, but would actually use different size drive gears to create different ratios for the two shafts.
They did not describe what sort of fluid makes it a wet clutch. The alternating drive and driven plates in the clutch are like the old New Departure coaster brake on bicycles, effective and robust.
Finally and predictably, gear selection management is handled by a computer control unit that anticipates the gear based on the driver's behavior. All straightforward. It uses electromagnetic pickups to keep track of what gear is selected. That's not necessarily the only way to do it but seems pretty simple and effective.
Takeaway number one - gearboxes are non-trivial!
Two concentric clutches driving to coaxial input shafts, on inside the other which is hollow. So that's how they do it, a neat solution, probably the only one that makes sense.
Gear selection seems pretty conventional for a manual gearbox.
The really interesting feature is the use of two secondary shafts, each split into two coaxial sections, one section carrying odd numbered gears and the other carrying even numbered gears. The split of each is what allows the dual-clutch feature to pre-select a gear. A traditional 4-speed box would have only one secondary shaft, which of course is not split. It would carry all the gears, possibly using direct drive for 4th.
Using two secondary shafts would seem to be a way to squeeze more gears into a smaller space, and would accomplish the same thing even if it wasn't a dual-clutch transmission. They mentioned it only briefly in the video but both shafts seem to be directly connected to the equivalent of the differential ring gear. One shaft holds the lower gears, the other holds the higher, but would actually use different size drive gears to create different ratios for the two shafts.
They did not describe what sort of fluid makes it a wet clutch. The alternating drive and driven plates in the clutch are like the old New Departure coaster brake on bicycles, effective and robust.
Finally and predictably, gear selection management is handled by a computer control unit that anticipates the gear based on the driver's behavior. All straightforward. It uses electromagnetic pickups to keep track of what gear is selected. That's not necessarily the only way to do it but seems pretty simple and effective.
Takeaway number one - gearboxes are non-trivial!
In the following link there is a nice simulation of the actual ZF/PDK 7-Speed Dual Clutch Transmission
1 - 11 of 11 Posts
