Forums

Ahh, firmware (Subaru this time)

Started by Clifford Heath May 24, 2016
Timer race condition on the electronic parking brake?

<http://www.subaruoutback.org/forums/138-gen-5-2015-present/345297-new-recall-2015-outbacks.html>

Clifford Heath.
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? -- Rick C
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.
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. -- Rick C
On Tue, 24 May 2016 23:52:43 -0400, rickman <gnuarm@gmail.com> 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.
If the "electronic" brake is mechanically hydraulic, I'd expect similar temperature-related issues as seen on aircraft. If there's a large drop in the temperature of the trapped hydraulic fluid, a significant reduction in pressure is possible.
On 5/25/2016 2:01 AM, Robert Wessel wrote:
> On Tue, 24 May 2016 23:52:43 -0400, rickman <gnuarm@gmail.com> 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. > > > If the "electronic" brake is mechanically hydraulic, I'd expect > similar temperature-related issues as seen on aircraft. If there's a > large drop in the temperature of the trapped hydraulic fluid, a > significant reduction in pressure is possible.
Why would that happen in a car? -- Rick C
On Wed, 25 May 2016 02:15:14 -0400, rickman <gnuarm@gmail.com> wrote:

>On 5/25/2016 2:01 AM, Robert Wessel wrote: >> On Tue, 24 May 2016 23:52:43 -0400, rickman <gnuarm@gmail.com> 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. >> >> >> If the "electronic" brake is mechanically hydraulic, I'd expect >> similar temperature-related issues as seen on aircraft. If there's a >> large drop in the temperature of the trapped hydraulic fluid, a >> significant reduction in pressure is possible. > >Why would that happen in a car?
If the brakes are hot, presumably due to heavy use, just before the parking brake is set, they might significantly heat the hydraulic fluid near the brake.
On Wednesday, May 25, 2016 at 3:46:53 AM UTC-4, robert...@yahoo.com wrote:
> On Wed, 25 May 2016 02:15:14 -0400, rickman <gnuarm@gmail.com> wrote: > >On 5/25/2016 2:01 AM, Robert Wessel wrote: > >> If the "electronic" brake is mechanically hydraulic, I'd expect > >> similar temperature-related issues as seen on aircraft. If there's a > >> large drop in the temperature of the trapped hydraulic fluid, a > >> significant reduction in pressure is possible. > > > >Why would that happen in a car? > > > If the brakes are hot, presumably due to heavy use, just before the > parking brake is set, they might significantly heat the hydraulic > fluid near the brake.
There are a few nasty things that can happen with a hydraulic parking brake: (1) The caliper and fluid are hot. You set the brake, the fluid cools, and the car rolls away ;-) (1b) You set the brake at noon. In the evening, the fluid cools, and the car rolls away ;-) (2) The caliper is OK, but the brake disc is really hot. You set the brake, and the hydraulic fluid boils as the caliper overheats (this is aircraft panic-stop scenario). Hydraulics can be entertaining. In my Antares, running the charger generates enough heat in the engine bay to heat the hydraulic cylinders that open the engine bay doors, and the doors open an inch. Unintended but provides better cooling during charging ;-) See ya, Dave
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.
On 5/25/2016 10:32 AM, Dave Nadler wrote:
> On Wednesday, May 25, 2016 at 3:46:53 AM UTC-4, robert...@yahoo.com wrote: >> On Wed, 25 May 2016 02:15:14 -0400, rickman <gnuarm@gmail.com> wrote: >>> On 5/25/2016 2:01 AM, Robert Wessel wrote: >>>> If the "electronic" brake is mechanically hydraulic, I'd expect >>>> similar temperature-related issues as seen on aircraft. If there's a >>>> large drop in the temperature of the trapped hydraulic fluid, a >>>> significant reduction in pressure is possible. >>> >>> Why would that happen in a car? >> >> >> If the brakes are hot, presumably due to heavy use, just before the >> parking brake is set, they might significantly heat the hydraulic >> fluid near the brake. > > There are a few nasty things that can happen with a > hydraulic parking brake: > > (1) The caliper and fluid are hot. You set the brake, > the fluid cools, and the car rolls away ;-) > (1b) You set the brake at noon. In the evening, the fluid > cools, and the car rolls away ;-)
This is a bit overstated. 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.
> (2) The caliper is OK, but the brake disc is really hot. > You set the brake, and the hydraulic fluid boils as the > caliper overheats (this is aircraft panic-stop scenario).
See above. How do you think the manual parking brake works? Fluid is not the only thing that changes size with temperature. -- Rick C