Ahh, firmware (Subaru this time)

On 5/25/2016 4:38 PM, Hans-Bernhard Br�ker wrote:
> Am 25.05.2016 um 05:52 schrieb rickman:
>
>> I've never needed to put my parking brake on twice.  Where's the
>> difference?
>
> Probably in that you've never had a hydraulic or electro-mechanic
> parking brake.
>
>> The electronic brake would be hydraulic I expect
>
> I guess that expectation is formed a bit prematurely.  AFAIK the
> currently available automatic / "electronic" parking brakes are actually
> electro-mechanical, i.e. there's a servo motor that opens/closes the brake.
>
> This is often accompanied by a hydraulic pressure store that holds the
> normal brake closed while the vehicle is stopped, so you can take your
> foot off the pedal --- even if the engine is stopped, too.  The car will
> then only (start the engine and) begin to move again once the pedals are
> pressed to indicate "go" (clutch for manual gear shifts, gas for
> automatic).
>
> In this combined system, pressure in the "auto hold" system is
> monitored, and if it drops far enough, either the engine is restarted,
> or the electric brake is activated automatically.  If you park (key
> leaves the car), the parking brake takes over right away
>
>> so no stretch.
>
> See the other replies on why a hydraulic system may move on its own,
> particularly without an active compressor feeding it.
>
>> But the actuator could easily be designed with some compliance to
>> compensate for a few thousandths of an inch as the parts cool down.
>
> Note that disk brake pads only move about 10 mils on actuation, anyway.
> I.e. one mil may already be all the difference it takes for the car to
> get moving.

Which is very, very easy to deal with in a parking brake.

-- 

Rick C

On Tue, 24 May 2016 23:52:43 -0400, rickman wrote:

> On 5/24/2016 11:12 PM, Robert Wessel wrote:
>> On Tue, 24 May 2016 22:49:35 -0400, rickman <gnuarm@gmail.com> wrote:
>>
>>> On 5/24/2016 12:36 PM, Clifford Heath wrote:
>>>> Timer race condition on the electronic parking brake?
>>>>
>>>> <http://www.subaruoutback.org/forums/138-gen-5-2015-present/345297-
new-recall-2015-outbacks.html>
>>>
>>> "9. Substantially similar U.S. vehicles:  2015MY Subaru Legacy/Outback
>>> and 2015MY Subaru WRX are substantially similar to their counterparts
>>> for sale in the United States.  Subaru determined that this is not a
>>> safety issue since there is no comparable US safety regulation to UN
>>> No.
>>> 13-H.  However, Subaru will initiate a service program to remedy
>>> affected vehicles in the US market"
>>>
>>> I think that is what is known as a "silent recall".  They'll fix your
>>> car if you know to ask them.
>>>
>>> What I'm wondering is why they feel the need to activate the parking
>>> break twice?
>>
>>
>> Perhaps to compensate for expansion and/or contraction of various bits
>> of the mechanism after a (potentially very hot) brake cools down.
>>
>> On aircraft, it's common to avoid setting parking brakes if the brakes
>> are hot, or if a significant temperature changes is expected. Although
>> the mechanism there is usually rather different (most aircraft parking
>> brakes usually just trap pressurized hydraulic fluid at the brake end
>> of the system, and expansion/contraction of that trapped fluid can do
>> interesting things).  So it's not strictly comparable.
> 
> I've never needed to put my parking brake on twice.  Where's the
> difference?  I think the expansion/contraction would be small compared
> to the amount of stretch in the cable pulling the brake in a manual
> brake.  The electronic brake would be hydraulic I expect so no stretch.
> But the actuator could easily be designed with some compliance to
> compensate for a few thousandths of an inch as the parts cool down.

But (A), they didn't do that, and (B) they proceeded to screw up the 
software.  At least it's not in something safety-related, so it's not an 
inexcusable screwup -- but give them time.

-- 
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work!  See my website if you're interested
http://www.wescottdesign.com

On 5/25/2016 10:35 PM, Tim Wescott wrote:
> On Tue, 24 May 2016 23:52:43 -0400, rickman wrote:
>
>> On 5/24/2016 11:12 PM, Robert Wessel wrote:
>>> On Tue, 24 May 2016 22:49:35 -0400, rickman <gnuarm@gmail.com> wrote:
>>>
>>>> On 5/24/2016 12:36 PM, Clifford Heath wrote:
>>>>> Timer race condition on the electronic parking brake?
>>>>>
>>>>> <http://www.subaruoutback.org/forums/138-gen-5-2015-present/345297-
> new-recall-2015-outbacks.html>
>>>>
>>>> "9. Substantially similar U.S. vehicles:  2015MY Subaru Legacy/Outback
>>>> and 2015MY Subaru WRX are substantially similar to their counterparts
>>>> for sale in the United States.  Subaru determined that this is not a
>>>> safety issue since there is no comparable US safety regulation to UN
>>>> No.
>>>> 13-H.  However, Subaru will initiate a service program to remedy
>>>> affected vehicles in the US market"
>>>>
>>>> I think that is what is known as a "silent recall".  They'll fix your
>>>> car if you know to ask them.
>>>>
>>>> What I'm wondering is why they feel the need to activate the parking
>>>> break twice?
>>>
>>>
>>> Perhaps to compensate for expansion and/or contraction of various bits
>>> of the mechanism after a (potentially very hot) brake cools down.
>>>
>>> On aircraft, it's common to avoid setting parking brakes if the brakes
>>> are hot, or if a significant temperature changes is expected. Although
>>> the mechanism there is usually rather different (most aircraft parking
>>> brakes usually just trap pressurized hydraulic fluid at the brake end
>>> of the system, and expansion/contraction of that trapped fluid can do
>>> interesting things).  So it's not strictly comparable.
>>
>> I've never needed to put my parking brake on twice.  Where's the
>> difference?  I think the expansion/contraction would be small compared
>> to the amount of stretch in the cable pulling the brake in a manual
>> brake.  The electronic brake would be hydraulic I expect so no stretch.
>> But the actuator could easily be designed with some compliance to
>> compensate for a few thousandths of an inch as the parts cool down.
>
> But (A), they didn't do that, and (B) they proceeded to screw up the
> software.  At least it's not in something safety-related, so it's not an
> inexcusable screwup -- but give them time.

If I am not mistaken, the idea that they are applying the brake twice to 
deal with thermal issues is speculation.  So you don't really know what 
they did or didn't do.

I don't think it was a screw up in the software really, but maybe I 
missed that.  I thought it was a systems design issue where they didn't 
catch that applying the brake at the same time the ignition was turned 
on would cause a problem.

-- 

Rick C

On Wednesday, May 25, 2016 at 7:32:18 PM UTC-4, rickman wrote:
> This is a bit overstated. 

Nope.

> The actuator simply needs some compliance. 
> Whatever is pressing on the brake needs to have a spring to take up the 
> slack when the fluid volume changes.

Sure, except a spring-loaded accumulator can cause brake response issues...

> How do you think the manual parking brake works?  Fluid is not the only 
> thing that changes size with temperature.

As you already posted, the Bowden cable is elastic (though because
the housing compresses; the tension cable doesn't stretch much).

From wasting far too much time debugging brake and hydraulic issues...
Best Regards, Dave

On 5/26/2016 8:49 AM, Dave Nadler wrote:
> On Wednesday, May 25, 2016 at 7:32:18 PM UTC-4, rickman wrote:
>> This is a bit overstated.
>
> Nope.
>
>> The actuator simply needs some compliance.
>> Whatever is pressing on the brake needs to have a spring to take up the
>> slack when the fluid volume changes.
>
> Sure, except a spring-loaded accumulator can cause brake response issues...

"Brake response issues"?  This is the emergency brake.  It doesn't need 
to "respond" in ms times.


>> How do you think the manual parking brake works?  Fluid is not the only
>> thing that changes size with temperature.
>
> As you already posted, the Bowden cable is elastic (though because
> the housing compresses; the tension cable doesn't stretch much).

What housing?  The ones I've seen are just a cable.  It might not 
stretch "much", but we seem to be talking about very small amounts.


> From wasting far too much time debugging brake and hydraulic issues...
> Best Regards, Dave
>


-- 

Rick C

On Wed, 25 May 2016 23:33:22 -0400, rickman wrote:

> On 5/25/2016 10:35 PM, Tim Wescott wrote:
>> On Tue, 24 May 2016 23:52:43 -0400, rickman wrote:
>>
>>> On 5/24/2016 11:12 PM, Robert Wessel wrote:
>>>> On Tue, 24 May 2016 22:49:35 -0400, rickman <gnuarm@gmail.com> wrote:
>>>>
>>>>> On 5/24/2016 12:36 PM, Clifford Heath wrote:
>>>>>> Timer race condition on the electronic parking brake?
>>>>>>
>>>>>> <http://www.subaruoutback.org/forums/138-gen-5-2015-present/345297-
>> new-recall-2015-outbacks.html>
>>>>>
>>>>> "9. Substantially similar U.S. vehicles:  2015MY Subaru
>>>>> Legacy/Outback and 2015MY Subaru WRX are substantially similar to
>>>>> their counterparts for sale in the United States.  Subaru determined
>>>>> that this is not a safety issue since there is no comparable US
>>>>> safety regulation to UN No.
>>>>> 13-H.  However, Subaru will initiate a service program to remedy
>>>>> affected vehicles in the US market"
>>>>>
>>>>> I think that is what is known as a "silent recall".  They'll fix
>>>>> your car if you know to ask them.
>>>>>
>>>>> What I'm wondering is why they feel the need to activate the parking
>>>>> break twice?
>>>>
>>>>
>>>> Perhaps to compensate for expansion and/or contraction of various
>>>> bits of the mechanism after a (potentially very hot) brake cools
>>>> down.
>>>>
>>>> On aircraft, it's common to avoid setting parking brakes if the
>>>> brakes are hot, or if a significant temperature changes is expected.
>>>> Although the mechanism there is usually rather different (most
>>>> aircraft parking brakes usually just trap pressurized hydraulic fluid
>>>> at the brake end of the system, and expansion/contraction of that
>>>> trapped fluid can do interesting things).  So it's not strictly
>>>> comparable.
>>>
>>> I've never needed to put my parking brake on twice.  Where's the
>>> difference?  I think the expansion/contraction would be small compared
>>> to the amount of stretch in the cable pulling the brake in a manual
>>> brake.  The electronic brake would be hydraulic I expect so no
>>> stretch.
>>> But the actuator could easily be designed with some compliance to
>>> compensate for a few thousandths of an inch as the parts cool down.
>>
>> But (A), they didn't do that, and (B) they proceeded to screw up the
>> software.  At least it's not in something safety-related, so it's not
>> an inexcusable screwup -- but give them time.
> 
> If I am not mistaken, the idea that they are applying the brake twice to
> deal with thermal issues is speculation.  So you don't really know what
> they did or didn't do.
> 
> I don't think it was a screw up in the software really, but maybe I
> missed that.  I thought it was a systems design issue where they didn't
> catch that applying the brake at the same time the ignition was turned
> on would cause a problem.

Why I think it's "software" rather than "systems" (even though there's 
significant overlap in most companies):

1: Software engineers are the systems engineers of last resort.  This 
shouldn't be -- but it is.

2: The service bulletin says it's a software problem.  This is about 1% 
of the necessary proof -- but still, it's there.

3: Only the left rear wheel is affected.  If it were a system problem, 
you'd expect the entire emergency brake system to be affected.

4: The effect is to damage hardware.  Excluding software in bombs and 
emergency fail-safe systems, software should never, ever, damage 
hardware.  That points to a bug severity known as "crazy way bad" in the 
industry.  Even if this were a job that was assigned to the system's 
people, and that assignment was enforced by goons with baseball bats, the 
software people should still make it not happen (see item 1, above).

So -- it's software.  It is, almost certainly, a dumb-ass race condition, 
and very possibly one that is very similar to the one that Toyota was 
using to kill people with their cruise control software a few years ago.  
Perhaps Toyota and Subaru buy their software from the same super-very-
good consulting company, and the critical code was written by the same 
engineer.

-- 
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work!  See my website if you're interested
http://www.wescottdesign.com

Den torsdag den 26. maj 2016 kl. 17.14.34 UTC+2 skrev rickman:
> On 5/26/2016 8:49 AM, Dave Nadler wrote:
> > On Wednesday, May 25, 2016 at 7:32:18 PM UTC-4, rickman wrote:
> >> This is a bit overstated.
> >
> > Nope.
> >
> >> The actuator simply needs some compliance.
> >> Whatever is pressing on the brake needs to have a spring to take up the
> >> slack when the fluid volume changes.
> >
> > Sure, except a spring-loaded accumulator can cause brake response issues...
> 
> "Brake response issues"?  This is the emergency brake.  It doesn't need 
> to "respond" in ms times.

parking brake, since dual circuit brake systems was mandated eons ago
cars haven't had emergency brakes

if the parking brake uses the same hydraulic system as the regular 
brakes you can't just add a spring some where it be like having air in 
the system 

-Lasse

On 27/05/16 01:59, Tim Wescott wrote:
> Perhaps Toyota and Subaru buy their software from the same super-very-
> good consulting company, and the critical code was written by the same
> engineer.

They share a lot of technology now there's joint ownership (BRZ/GT).
It could be the same in-house team.

On Thursday, May 26, 2016 at 11:14:34 AM UTC-4, rickman wrote:
> "Brake response issues"?  This is the emergency brake. 
> It doesn't need to "respond" in ms times.

If the primary brake system is shared with parking, you can't
introduce compliance without causing a spongy primary brake response.

> >> How do you think the manual parking brake works?  Fluid is not the only
> >> thing that changes size with temperature.
> >
> > As you already posted, the Bowden cable is elastic (though because
> > the housing compresses; the tension cable doesn't stretch much).
> 
> What housing?  The ones I've seen are just a cable.  It might not 
> stretch "much", but we seem to be talking about very small amounts.

A Bowden cable has a center tension cable, and (typically) a wound
outer compression housing (which looks suspiciously like a spring).
The outer housing compresses much more than the inner cable stretches.
A 6 foot light-weight Bowden cable can easily compress 1/2 inch.

Try it on your bicycle: Wedge the brake caliper so it cannot move
(using something really hard). Squeeze the brake handle hard and
watch what happens.

I've had to rework a number of applications where the mechanical
engineer forgot to allow for the compression, and so much travel
was wasted compressing the cable that the actuator ran out of
travel before the desired results were obtained.
(Some of you know a few of these: think Tost).
Sometimes the fix is as simple as a stiffer housing.

In the case of the parking brake, the springy Bowden cable is a
feature and not a bug.

Hope that explains OK!
Best Regards, Dave

On 5/26/2016 12:35 PM, lasselangwadtchristensen@gmail.com wrote:
> Den torsdag den 26. maj 2016 kl. 17.14.34 UTC+2 skrev rickman:
>> On 5/26/2016 8:49 AM, Dave Nadler wrote:
>>> On Wednesday, May 25, 2016 at 7:32:18 PM UTC-4, rickman wrote:
>>>> This is a bit overstated.
>>>
>>> Nope.
>>>
>>>> The actuator simply needs some compliance.
>>>> Whatever is pressing on the brake needs to have a spring to take up the
>>>> slack when the fluid volume changes.
>>>
>>> Sure, except a spring-loaded accumulator can cause brake response issues...
>>
>> "Brake response issues"?  This is the emergency brake.  It doesn't need
>> to "respond" in ms times.
>
> parking brake, since dual circuit brake systems was mandated eons ago
> cars haven't had emergency brakes

I think you are mistaken.  The parking brake and emergency brake are one 
and the same, always have been on typical passenger cars.


> if the parking brake uses the same hydraulic system as the regular
> brakes you can't just add a spring some where it be like having air in
> the system

It is easy.  The *actuator* has a spring involved, but not when it is 
inactive.  Then the actuator has a hard stop.

-- 

Rick C