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Polo / VW Group Electric Rear Calipers - retrofitted???
woodsy144 - 15/7/24 at 11:51 PM

Hello,

Been doing some research and fumbling around, and came across the electric park brake caliper for the polo.
the interesting thing, is the motor for the EPS is only 2 pin.

https://www.trwaftermarket.com/en/news/electric-parking-brake/?VehicleType=News

Now, i would make the super high level inference that the motor is a 'dumb' setup, with only power and group.
Which would lean me to think that this maybe a good candidate for kit vehicles.

Question - has anyone played around with such calipers??? Anyone have any experience with them?

car man - 16/7/24 at 08:52 AM

I have the vw passat ones on my car with a small microcontroller and two buttons. It passed the IVA no problem still working.

gremlin1234 - 16/7/24 at 09:49 AM

I have not played with them myself,
but the wiring would be fairy simple, you just power it until the motor stalls, (detected by the current drawn)
I did see some of the most advanced systems actually check the temperature of the disk, and compensate as the disk cools down, (ie reapply the force after a few minutes)

gremlin1234 - 16/7/24 at 09:50 AM

quote:
Originally posted by car man
I have the vw passat ones on my car with a small microcontroller and two buttons. It passed the IVA no problem still working.


that's interesting, do you please have a link for the microcontroller

car man - 16/7/24 at 10:28 AM

The microcontroller was a pic16f886.

JAG - 16/7/24 at 11:29 AM

You're correct about the motor on the EPB calipers - it is a dumb motor with a gearbox.

12v polarity is switched around to apply & release. It uses a current cut off device to reach the desired clamp force.

On a production car it can perform "drive-away-release" "hot-disc-reclamp" "service-brake-support" plus a bunch of other clever stuff. However you'd need a whole host of other 'stuff' to achieve that and it's not really practical or necessary on a kit car.

For our cars you just need an on/off switch and a controller that can sense and cut-off when a current is reached. It would be useful to be able to adjust the cut-off value.

On a large saloon or SUV the cut-off is approx' 15 amps to achieve 20-25 kN clamp load.

You wouldn't need anything like that for a Se7en-esque kit car.

Has anyone designed a suitable controller?

Could you share the details?

[Edited on 16/7/24 by JAG]

coyoteboy - 16/7/24 at 11:59 AM

Super cheap and simple, I considered it for a while but I was under the impression the IVA required mechanical latching - I know the worm drives are anti-backdrive but they're not normally that pragmatic If it were a thing people wanted, I could fairly quickly lob a cheap kit or product together for funsees.

woodsy144 - 16/7/24 at 12:31 PM

quote:
Originally posted by coyoteboy
Super cheap and simple, I considered it for a while but I was under the impression the IVA required mechanical latching - I know the worm drives are anti-backdrive but they're not normally that pragmatic If it were a thing people wanted, I could fairly quickly lob a cheap kit or product together for funsees.


Definitely keen to know more.
A bit of a brain dump, but would like an over ride on and off and an current adjuster.

Anything else??

Secondly, I am assuming that when battery power is off, is it locked on??

[Edited on 16/7/24 by woodsy144]

JAG - 16/7/24 at 12:43 PM

quote:

I considered it for a while but I was under the impression the IVA required mechanical latching


quote:

when battery power is off, is it locked on??


The mechanical latching is the same for production cars and they're OK with the EPB calipers. Basically the gearbox prevents the parkbrake from releasing once it's been applied, even without the 12v power. It works for production type approval so it works for IVA.

There are two basic types. The worm & wheel gearbox (from Continental and a few others) and the beltdrive with an epicyclic gearbox (from TRW/ZF).


[Edited on 16/7/24 by JAG]

[Edited on 16/7/24 by JAG]

Half Finished - 16/7/24 at 01:07 PM

For a controller, this would work well out of the box. I've used one before in a similar application. The current and speed can be set with a potentiometer and the motor direction is then set by two buttons. There is also a 50amp version and an external programmer available.


https://uk.rs-online.com/web/p/motor-controllers/7736841?gb=s

gremlin1234 - 16/7/24 at 01:16 PM

quote:
Originally posted by Half Finished
For a controller, this would work well out of the box. I've used one before in a similar application. The current and speed can be set with a potentiometer and the motor direction is then set by two buttons. There is also a 50amp version and an external programmer available.


https://uk.rs-online.com/web/p/motor-controllers/7736841?gb=s

I guess you would require a controller like this, for each caliper

gremlin1234 - 16/7/24 at 01:19 PM

quote:
Originally posted by car man
The microcontroller was a pic16f886.


Thank You
could you also please share the circuit used, and the programming? or where to get a unit commercially

Half Finished - 16/7/24 at 01:30 PM

quote:
Originally posted by gremlin1234
quote:
Originally posted by Half Finished
For a controller, this would work well out of the box. I've used one before in a similar application. The current and speed can be set with a potentiometer and the motor direction is then set by two buttons. There is also a 50amp version and an external programmer available.


https://uk.rs-online.com/web/p/motor-controllers/7736841?gb=s

I guess you would require a controller like this, for each caliper


Im not sure if they would get out of phase if you drive them in parallel? They are hitting end stops each cycle. As long as the wire lengths are identical.

JAG - 16/7/24 at 01:45 PM

quote:

For a controller, this would work well out of the box


That looks like it would work. It's 15 amps per caliper on a large saloon or SUV that weighs over 1.5 tons.

I suspect our cars would be very capable at 5-8 amps per caliper. So I think one of these units, connected to both calipers, would be sufficient.

Can someone show me how the switch and calipers would be connected?

Draw a diagram perhaps?

Mr Whippy - 16/7/24 at 02:50 PM

I have this on the golf, as the car has hill hold it's fine but without that I can imagine it would be crap as there's zero 'feel" when it's about to let go. It's really all or nothing as far as braking is concerned.

Try it in your tin top, ram on the handbrake fully on in your car next time your on a hill and then let it go all at once, see how you get on with hill starts

Half Finished - 16/7/24 at 04:44 PM

I linked to the older version before, there is a newer version with some additional features. They also support up to 30A for 5 seconds so should cover 2 calipers. I'm not affiliated with them, I just used one in a university project.
I think it would be pragmatic to implement some kind of technical interlock so it's not easy to accidentally trigger the handbrake whilst moving. Normally you would need to press and hold the EPB button for activation whilst moving.

What hubs would the polo calipers fit too? I'm tempted to go this route myself with mx5 hubs.

https://uk.rs-online.com/web/p/motor-controllers/1837330

adithorp - 16/7/24 at 09:53 PM

Controlling when the motor stops when applying is one thing but how fo you control how far it goes when disengaging and adjusts that for wear?
If it goes fully back it'll take several seconds to reapply. A timer circuit maybe but it'd have to have a lockout to stop it releasing/backing off unless the brake was applied.

coyoteboy - 16/7/24 at 10:26 PM

quote:
Originally posted by Mr Whippy
I have this on the golf, as the car has hill hold it's fine but without that I can imagine it would be crap as there's zero 'feel" when it's about to let go. It's really all or nothing as far as braking is concerned.

Try it in your tin top, ram on the handbrake fully on in your car next time your on a hill and then let it go all at once, see how you get on with hill starts


Does anyone use the handbrake for hill stats after their driving test? Don't think i have in 25 years of driving up hill and down dale, i can balance the footbrake and clutch bite just fine

coyoteboy - 16/7/24 at 10:27 PM

quote:
Originally posted by adithorp
Controlling when the motor stops when applying is one thing but how fo you control how far it goes when disengaging and adjusts that for wear?
If it goes fully back it'll take several seconds to reapply. A timer circuit maybe but it'd have to have a lockout to stop it releasing/backing off unless the brake was applied.


I think by default they go all the way back, whenever i hear them in the car park thru go a good second or so, and thats a fair old travel. The piston usually do the auto adjustment and the motor takes up the last slack

[Edited on 16/7/2024 by coyoteboy]

adithorp - 16/7/24 at 11:04 PM

There's a big difference between how long the take to disengage and how long it takes to do a full wind back in service mode when changing pads and again switching out of service setting (done 2 today).
Keep holding on the clutch though; keeps garages in work replacing them.

car man - 17/7/24 at 08:59 AM

This is a good motor control unit https://thepihut.com/products/15a-single-dc-motor-driver?variant=27740754833&currency=GBP&utm_medium=product_sync&utm_source=google&ut m_content=sag_organic&utm_campaign=sag_organic&gad_source=1&gclid=CjwKCAjw1920BhA3EiwAJT3lSdvk5lviku0UTqq_QnGjZbcF4UWLOLh9HYQe0n-vH1Y1movV 4Tj61xoCTZAQAvD_BwE
I back my motor off for just 1 second.

JAG - 17/7/24 at 11:56 AM

Thinking more...

Adjustment for pad wear is automatic and built into the mechanism behind the caliper piston. Apply/release times are not affected by pad wear.

The motor controller is a great start BUT we also need something with software (that we can program/modify) to sit between the EPB Switch (in the cockpit) and the Motor Controller. Could we use a Raspberry Pi or Arduino device?

This would control the apply/release current and timing.

Plus a suitable EPB switch - it should have an ON/OFF/ON configuration to enable apply and release.

I think the final system would look like this;

[EPB Switch] - [Raspberry Pi or Arduino] - [Motor Controller] - [2 x EPB Calipers]

coyoteboy - 17/7/24 at 01:35 PM

quote:
Originally posted by adithorp
Keep holding on the clutch though; keeps garages in work replacing them.


Owned 4 manual cars since 1998, I still own 3 of them. I've replaced 1 clutch in 300K miles.

A Peugeot 205 that managed 85K to 145K miles in my name, still on original clutch when written off.
A Celica GT4 which managed 84K to 115K miles, clutch gone at 110K miles due to a 4WD launch that shattered the friction plate - plenty of meat left on both the plate and the fly.
A Peugeot 306 HDI which I had from 75K miles to 250K miles and just started to slip at 250K (just had new clutch but sits unused).
A 370Z which I've taken from 86K miles to 125K miles still on stock clutch (but this has hill-hold that works above about a 10 degree slope to be fair).

Can't be that worrying eh
Not like you hold it on the clutch the whole time eh, you hold it on the foot brake and then at the last second drop to bite and move off, if you can't do that without rolling less than an inch you shouldn't be driving.

[Edited on 17/7/2024 by coyoteboy]

coyoteboy - 17/7/24 at 03:06 PM

quote:
Originally posted by JAG
Thinking more...

Adjustment for pad wear is automatic and built into the mechanism behind the caliper piston. Apply/release times are not affected by pad wear.

The motor controller is a great start BUT we also need something with software (that we can program/modify) to sit between the EPB Switch (in the cockpit) and the Motor Controller. Could we use a Raspberry Pi or Arduino device?

This would control the apply/release current and timing.

Plus a suitable EPB switch - it should have an ON/OFF/ON configuration to enable apply and release.

I think the final system would look like this;

[EPB Switch] - [Raspberry Pi or Arduino] - [Motor Controller] - [2 x EPB Calipers]


Arduino is more than enough to do this, a pi would be a mistake. Your biggest issue is how long to back-drive to release, nothing 5 mins of testing won't solve.

scudderfish - 17/7/24 at 04:15 PM

quote:
Originally posted by coyoteboy

I think the final system would look like this;

[EPB Switch] - [Raspberry Pi or Arduino] - [Motor Controller] - [2 x EPB Calipers]


Arduino is more than enough to do this, a pi would be a mistake. Your biggest issue is how long to back-drive to release, nothing 5 mins of testing won't solve.


ESP32 and Wifi enable your handbrake!

woodsy144 - 17/7/24 at 10:12 PM

I might be mistaken,
I thought there were Polo EPB units out there, but subsequent searches I couldn't find them.
The Polo rear calipers I am using appears to be from a 2009 to 2014 unit.
I wonder if the Passet unit could be placed within the Polo slide unit (I might be asking too much).

Does anyone have the dimensions of the VW EPB unit??

JAG - 18/7/24 at 06:44 AM

Most of the integrated EPB calipers, from TRW say, use the same motor-gearbox unit. There is a more powerful version for heavier cars but the external dimensions and wiring are the same - they only change the internal gear ratio.

It's a similar story for the other big player - Continental. The motor-gearbox-unit is common.

Different vehicles will have different hydraulic piston sizes - so you should select your caliper based on the hydraulic sizing and the front:rear hydraulic brake balance.

Common piston sizes are 34mm, 38mm and 43mm.

woodsy144 - 19/7/24 at 01:21 PM

quote:
Originally posted by JAG
Most of the integrated EPB calipers, from TRW say, use the same motor-gearbox unit. There is a more powerful version for heavier cars but the external dimensions and wiring are the same - they only change the internal gear ratio.

It's a similar story for the other big player - Continental. The motor-gearbox-unit is common.

Different vehicles will have different hydraulic piston sizes - so you should select your caliper based on the hydraulic sizing and the front:rear hydraulic brake balance.

Common piston sizes are 34mm, 38mm and 43mm.


The vw caliper I am using is 38 diameter piston, the rod diameter is 6mm and the distance between them is approx 118mm. How does that compare to the epb unit??

car man - 20/7/24 at 05:57 PM

Epb units a passat are 38mm.

coyoteboy - 21/7/24 at 09:32 AM

Dont forget theres a few safety features youre going to want to have. you dont want it commandable while moving, you dont want it commandable while ign off, you might want self diag and retract for pad change etc.

car man - 21/7/24 at 10:08 AM

Wilwood do a kit https://www.wilwood.com/brakekits/BrakeKitListRear?mincatdesc=Electronic%20Parking%20Brake%20Rear%20Retrofit%20Brake%20Kit.
No speed input so you could operate at any time.

scudderfish - 21/7/24 at 11:40 AM

quote:
Originally posted by coyoteboy
you dont want it commandable while moving


You absolutely do! It's the emergency brake for when your hydraulic brakes fail.

woodsy144 - 21/7/24 at 12:45 PM

quote:
Originally posted by car man
Epb units a passat are 38mm.


Any idea on what the pin slide diameter and distance is??

coyoteboy - 21/7/24 at 03:24 PM

quote:
Originally posted by scudderfish
quote:
Originally posted by coyoteboy
you dont want it commandable while moving


You absolutely do! It's the emergency brake for when your hydraulic brakes fail.


That just isnt a good idea with an epb which just rams itself on full, with a hand operated brake that you can modulate you can prevent yourself being an uncontrolled missile. It would have to be hooked onto your ABS sensors to prevent lockup.

[Edited on 21/7/2024 by coyoteboy]

obfripper - 21/7/24 at 04:28 PM

The OE systems use an inbuilt accelerometer to stop the brakes locking when applied while moving, this amount of deceleration will be vehicle specific to stop wheel locking when used in an emergency. The epb controller can also use any available can bus data to augment the acceleration data, this may not be available in the event of an abs control unit failure. Later cars have the epb control integrated into the abs control unit, a failure here leaves no secondary brake available.

The OE systems also apply the hydraulic brake in preference to the electromechanical brake when moving, which means the hydraulic brakes are still applied in the case of a master cylinder failure. This is why for a dynamic test the EPB needs to be put into a test/bedding mode, otherwise you would be testing the hydraulic brakes in lieu of the electromechanical brake.

I'm pretty sure all the vw group cars based on pq and mqb platforms (last ~20 years with 5 stud wheels) use a rear caliper with a 118mm slider spacing(whether epb or not), the older platform cars used a 110mm slider spacing. There are lucas(trw) and ate(continental) variants, and both use their own caliper brackets and pad shapes.

The oe systems also use the brake pedal operation as an interlock for the manual release of the epb, this would be easily done by needing the brake light output to be on to activate the release switch.


Dave

coyoteboy - 22/7/24 at 11:45 AM

Interesting info on the OE, thanks!

You could indeed use an accel here, but I'd be concerned it was too variable, or at least too conservative - if I brake on a wet slick road my slip would occur an order of magnitude lower G than on a dry grippy road. Seems you'd be leaving a lot of brake unused. A combo of both would be nice but then you get into authority issues, but I realise not everyone has wheel speed feedback either.

JAG - 24/7/24 at 01:12 PM

All of that is true but the same is/was true of the original 'emergency brake' the park brake lever. The only real difference is/was that the driver could modulate the brake output to provide the most braking while avoiding rear wheel lock.

For reference the legal requirement, for the emergency brake, is to provide 0.3g of deceleration. There is no requirement to avoid rear wheel lock, because this is an emergency.

Early EPB systems used to provide an 'emergency brake' output without needing an accel' signal - they did it with a gradual ramp up of brake output. So when the car was above a threshold speed (say 5mph from a speed sensor signal somewhere on the car) and the driver commanded an EPB apply the EPB unit would provide a stepped apply....

5 amp apply -> 5 seconds -> check EPB switch state -> 10 amp apply -> 5 seconds -> check EPB switch state -> 15 amp apply (until max' current)

If the driver released the EPB switch at any point in that cycle the EPB released all clamp.

For a kitcar you'd need to have a speed signal input, probably a slotted disc on the propshaft. Then the same strategy could be implemented and would meet the legal requirement.

[Edited on 24/7/24 by JAG]