I'm off road by about 3.5 miles.  The last 250 yds or so is quite steep (more than 20º in places) and involves about 200yds forwards, a change of direction at a hairpin, and then 50yds reversing.  All downhill.  It only flattens out at the very end.

 

So I turn on the hill descent (I enjoy looking at the view while the car goes about its business) and a few minutes later I'm parked.  But at that point the hill descent hasn't released the pressure it has built up in the hydraulic system to do its job.

 

I can turn off the hill descent.  I can switch off the engine.  The handbrake is immaterial - it's a good old fashioned manual cable on my car.  So I'm guessing something triggers the hill descent system to open a relief valve somewhere so the pads are no longer pressed against the discs especially at the back it seems (but that might just be because the last stage is in reverse).  I know the pads are free enough - I've had them out recently, cleaned and coated the ends with copper grease.

 

It's as though there's a trigger to release the pressure which I haven't found.  It might be moving a certain distance on a flat surface.  Or just a sensor recognising it's on a flat surface - which literally doesn't happen until the last 3ft or so.  Or something else.  Anyone know please?

 

It's not an issue, I usually just turn off the hill descent before or during the final reversing bit, it's just a niggle.  If I knew what actually turns it off I might be able to trick it just at the right moment.  (Hate cars that think they are cleverer than I am!)

 

Edited 16 September, 20205 yr by aka_pseudonym

You havn't asked your question so if people know the info you are seeking they wont be able to answer.

4 minutes ago, J.R. said:

You havn't asked your question so if people know the info you are seeking they wont be able to answer.

 

Very true.  There you go!

 

It's as though there's a trigger to release the pressure which I haven't found.  It might be moving a certain distance on a flat surface.  Or just a sensor recognising it's on a flat surface - which literally doesn't happen until the last 3ft or so.  Or something else.  Anyone know please?

 

I suspect the reversing may have something to do with it, no suggestion as to the logic behind it, they may simply never have tested it under those circumstances.

 

Could you possibly try the last leg in forward motion to see if it has the same problem?

 

Does the braking system remain locked when you unlock the car after a few hours?

 

I'm pretty sure all the action is going on in the ABS block but commanded by the controller.

1 hour ago, J.R. said:

I suspect the reversing may have something to do with it, no suggestion as to the logic behind it, they may simply never have tested it under those circumstances.

 

Could you possibly try the last leg in forward motion to see if it has the same problem?

 

Does the braking system remain locked when you unlock the car after a few hours?

 

I'm pretty sure all the action is going on in the ABS block but commanded by the controller.

 

The fact it works in reverse is one of the best things about it I think.  I once went up the track in the snow in a Subaru Justy 4x4 and it lost traction almost at the top and started sliding down backwards.  No ABS on it so wheels just locked.  It was probably going at 25mph before I managed to stick it in a snow drift to stop it.  But it felt like 100mph.  One of the most frightening car things I've ever experienced!  Now I can go upwards in the Yeti with the hill descent switched on knowing that if traction is lost it'll work the ABS all by itself to get me down slowly again and it won't care what gear it's in.

 

I'll test it in forward motion next time.  I know it doesn't release the pressure over time - tried to push it a little a while ago a couple of days after it was parked and the wheels were still locked.  However when the ignition is turned on it seems to reset itself during its startup procedures even if the engine itself isn't running.

 

Edited 16 September, 20205 yr by aka_pseudonym

There is an electronic inclinometer fitted, that works a couple of systems, including the HDC.

It doesn't matter whether you are in forward or reverse gear.
And the regulation of the braking occurs in the central ABS unit not at the wheel cylinders. Sometimes you can hear the valves chattering as they move the braking around to different wheels.

And a bit of advice; never use the HDC in neutral. Although it does work then, it means that you don't have the ability to use a bit of power to get you out of a dodgy situation.

Thanks J.R. Thanks Llanigraham.  I've been testing.  I think I may have worked out what happens and how it's programmed to react!

 

I've decided the hill descent switches off after the car has gone a certain distance on the flat.  Likewise it switches on after it's gone a certain distance down a hill.  The distance seems to be about a car's length or a little more but it's probably a fixed number revolutions of the wheels.  And specifically the front wheels.

 

So if you go forwards down a hill and onto the flat the front wheels will go at least the length of the car while the back wheels are still dropping down.  If you go down in reverse it's the back wheels that'll run onto the flat while the front wheels will only reach the level area at the last moment - so not enough revolutions to trigger it to turn off.

 

I hope I've explained that coherently!  There's a sort of logic in that it waits until it has moved a fixed distance either down or along before it reacts.  There's a bit of video on the BBC website at the moment of the effects of the melting of the permafrost in Siberia.  If a Yeti drove across it (apt place for a Yeti after all) with the hill descent constantly turning on and off it'd be ridiculous.

 

https://www.bbc.co.uk/news/av/world-54195656

 

 

Edited 18 September, 20205 yr by aka_pseudonym

Erm, yes.
But didn't we all know that already?

5 hours ago, freedie said:

Erm, yes.
But didn't we all know that already?

 

Great.  Vacuous post then.  So how many wheel rotations are required to trigger the system?  Is it the same for on and off?  Is it front wheels only being monitored?  What angle does the inclinometer look for when descending and levelling?  I run 16" M+S's all year round due to my location so I'll need to do some calculations before I start re-landscaping my stopping spot.  Thanks, be great to know that.

 

Edited 19 September, 20205 yr by aka_pseudonym

3 hours ago, aka_pseudonym said:

 

Great.  Vacuous post then.  So how many wheel rotations are required to trigger the system?  Is it the same for on and off?  Is it front wheels only being monitored?  What angle does the inclinometer look for when descending and levelling?  I run 16" M+S's all year round due to my location so I'll need to do some calculations before I start re-landscaping my stopping spot.  Thanks, be great to know that.

 

It has nothing to do with wheel revolutions!!
As has been pointed out there is an in-built inclinometer that works with the system. And no-one knows what angle is needed.
Can I suggest that you read the Owners Handbook; the section about the Off Road Button is probably one of the best written pieces in there.

46 minutes ago, Llanigraham said:

It has nothing to do with wheel revolutions!!
As has been pointed out there is an in-built inclinometer that works with the system. And no-one knows what angle is needed.
Can I suggest that you read the Owners Handbook; the section about the Off Road Button is probably one of the best written pieces in there.

 

No.  You are totally wrong on that.  And I have read the handbook.

 

If you sit still on a slope that's great enough to trigger the hill descent and turn it on it does NOT become active.  The dash light is illuminated, yes, but not flashing.  To trigger it the car has to move.  In reverse it's something like 2-3 metres  or a bit more.  At that point the dash light will start flashing showing it's active.  It's the movement which starts it working - the wheel revolutions - not the inclinometer.  The angle on my car appears to be about 7.5º but it's hard to judge on rough surfaces.

 

As I appear to be considered a bit of an idiot asking such questions, I presumed somebody would actually have the technical answers to hand that they could give me.

 

 

Edited 19 September, 20205 yr by aka_pseudonym

I suggest you read what I wrote.
You can turn the ORR system on whenever you like.
However the HDC will not "become active" until the inclinometer senses that there is an incline, It doesn't matter whether you are in forward or reverse gear. 
It does not count revolutions to become "active", it just senses movement.

1 hour ago, Llanigraham said:

I suggest you read what I wrote.
You can turn the ORR system on whenever you like.
However the HDC will not "become active" until the inclinometer senses that there is an incline, It doesn't matter whether you are in forward or reverse gear. 
It does not count revolutions to become "active", it just senses movement.

 

I do read what you've written!

 

Yes - quite right - "... it just senses movement".  And to do that it must sense that a wheel(s) is revolving you'd therefore agree, as only such a sensor could tell it it's moving.  (I suppose its GPS could but hardly likely.)  In fact it has to travel a distance, if short, for those sensor(s) to register a suitable number of pulses to send to the CPU - so there will definitely be a minimum distance involved.  And even more to the point, it's highly likely using the speedometer's sensor, wherever that gets its signal from, because it says in the manual "The Downhill Drive Support is available in the speed range of 2 km/h up to 30 km/h."  So if knew which sensor the speedo used; how many pulses were supplied per wheel revolution, or prop shaft rev, or whatever that sensor is sensing; how many pulses the CPU was programmed to require before it calculated a speed; I could extrapolate from that, knowing the circumference of my M+S tyres, how far the car needed to to go for the hill descent to turn on or off.  Which would equate to wheel revolutions.  Yes?

 

Obviously the inclinometer (or possibly just a pair of tilt switches?) will need to register that it's over its pre-determined angle and the hill descent needs to be used.  Incidentally the manual says "... the downhill gradient is at least 10%", so, to correct you again when you said above "no-one knows what angle is needed", there is a published angle even though my car seems nearer 7.5º which converts to a 12.5% slope.

 

All of which actually answers my original question which was:  why, when I come to a halt, is the hill descent system still pressing the pads against the discs.  The answer being that it hasn't had enough distance to re-calculate that it's no longer (movement+inclinometer) on a slope and can switch itself off.  So I've answered my own question which I now wish I hadn't asked in the first place.  And I now know that the easiest way to reset the hill descent system when I've stopped is to switch off, switch back on, count to three, and switch off again.  Voilà.

 

 

 

Edited 19 September, 20205 yr by aka_pseudonym

Well I for one am glad that you asked the question and worked out and posted the plausible answer even though I dont have hill assist, its just a shame that you had to experience that there is sometimes a price to be paid from certain contributors whose contribution is often the same.