T6.1 ABS (FtS & S&G) theory?

[solutionz]

I have a T6.1 with factory ACC, Front Assist, Emergency Brake and Hill Start Assist.. With handbrake, not EPB.

As we probably all know when using ACC following a vehicle to a stop the T6.1 will automatically hold the brakes for approx 3 seconds before warning then releasing the brakes.

If however you repeatedly push the RES button shortly after stopping it will keep cancelling the warning and keep the T6.1 held for much longer, at least 30sec or so, before it eventually again releases the brakes (this is how OpenPilot works around the limit to emulate S&G).

However if the vehicle is then permitted to roll for 1-2m (if enough room) and there is a vehicle still in front the process will start again.

So the ABS is obviously capable of holding the T6.1 for at least 30sec or so at a time for up to 1-2min so far I've tested.

The question is whether this upper timeout is also software controlled(able) or if there is some bleeding of pressure that needs to be re-established (but can eventually also be done solely by ABS) in which case there may also be a software and/or hardware workaround (such as forcing an ABS re-apply) which doesn't involve retrofit of an EPB.

I've read through related threads:

ACC & City Braking - How Its Done -

All DSG equipped T6 with factory ACC are "follow to stop" version. Is you ACC retrofit going to work: "follow to stop" or "stop and go"? I know that suppositiously electronic parking brake is required for "stop and go" functionality of ACC system but is it really necessary?

www.t6forum.com

EPB Retrofit ... the way to Stop & Go

So with ACC and DSG in the T6 we have the FollowToStop capability. But i wont more, i wont to have "Stop and Go" like it is available in the VW Sharan PQ35 which is very likely like the T6 which is PQ25. Needles to say we need Auto-Hold and EPB to get Stop & Go capability. T6 ABS is a complete...

www.t6forum.com

 

[Robert]

Let's make few things clear first of all.

FollowToStop and Stop&Go are types of ACC functionality embedded in the radar as a SWAP code(aka FEC).
Follow To Stop allows to keep ACC activate after performing full stop only for few seconds while Stop&Go supposedly keeps ACC active with no time limit.

To get Autohold functionality on a T6.1, EPB has to be introduced to vehicle CAN-BUS network.
This is quite popular exercise on a PQ35 platform with MK60EC1 ABS by adding 56D EPB controller(the only one as a stand alone unit on PQ platform).
I am not aware of any stand alone MQB EPB controllers (happy to be corrected) so it seems that the only way is to introduce the EPB emulator on the T6.1 CAN-BUS.
I am not even considering ABS retrofit from any other MQB vehicle as I can't see anything being suitable (from the safety perspective).

As an example NAR Golf MK7 is a MQB vehicle and it uses manual parking brake as opposed to the ROW Golf MK7 with EPB.
Some people in America do retrofit EPB by replacing ABS unit and using European version instead.

Summarising, to have the maximum "convenience" experience from OEM VW "AI systems" the following are required: EPB, ABS with AUTOHOLD and STOP&GO ACC.

 

[solutionz]

Can you elaborate on the "EPB emulator on the T6.1 CAN-BUS" ?

 

[Robert]

Daniel has made up his own EPB emulator (and therfore enabled "time unlimited" AUTOHOLD) on his PQ35 Touran.

A lot of CAN-BUS sniffing and I guess same thing could be done on MQB.

See below.

EPB Retrofit ... the way to Stop & Go

I understand what you mean now.

www.t6forum.com

 

[solutionz]

Ah yes, this is exactly what I'm talking about. Is the 3min limit he refers to hardware or software?

i.e. It seems that after nearly 3min he's manually re-primes his brakes (the EPB emulator just keeps the FtS engaged while he does so) suggesting the brake bleed theory above.

As I point out ABS is capable of "re-priming" itself if ACC is re-engaged through a brief reset or drive-off, so manual intervention should be unnecessary.

I wonder if there is something in VCDS which can output the brake pressure to see if it drops over time when FtS is active, I'll carry out some uphill/downhill tests.

In this case a more effective workaround could be to emulate a brief lead car movement every 2-3min to keep re-prime ABS (in addition to the short term RES spam).

@danman

 

[solutionz]

Okay so it seems the 3min timeout is entirely caused by the radar module.

When using joystick mode (yes you can control your T6.1 with an Xbox controller ) on OpenPilot with longitudinal control enabled to "manually" control ascel/descl it will happily come to a stop and hold for 5min+.

The ABS pump seems to only need to run for a few seconds initially, not continuously, so hopefully won't run into any duty cycle issues when used for short periods but shows S&G is fully possible without an EPB.