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jalalski Profile
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


John,

What do you mean by "occasional tap of the brakes" to keep under the limit? I thought doing so will disengage the cruise control all together and you'd have to press the resume button again.

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17/Aug/2011, 7:13 pm Link to this post Send Private Message MSN Blog
 
Johngqld Profile
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Date Registered: 02-2011
Location: Caboolture, QLD
TOTAL POSTS: 297
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Re: Cruise Control Issues


Hi Jalal,
           Yes , that is correct, but what I probably didn't make all that clear, this was on some fairly steep downhill grades. There isn't a single vehicle I know of except for the Mercedes S Class that activates it's own brakes to maintain speed on a reasonable decent under cruise control. In fact the Xtrail's cruise control works far better than my Falcon use to, also better than the Commodore ute and the Rodeo which we have at work.

Did your overspeed occur on the crest of a hill or the ride down the otherside?

Also, do you know if it is a separate module?

Regards
John

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X-1834 (c)
2010 Series 3 CVT Diamond Black. Tow pak, Nissan Nudge Bar, Bonnet and headlight Protectors, Fog Lamps, Radiator Protection, L/H Cargo Drawer,Rear Spoiler, Koason DVD/GPS, Pwr Window Delay.

17/Aug/2011, 8:11 pm Link to this post Send Email PM   Send Private Message Blog
 
jalalski Profile
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


The over-speed happened at the run down the hill. I kept watching the speed and it just kept rising as the hill got steeper, so I had to disengage the cruise by pressing on the brake pedal.

Not sure if it is a separate module or not.

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17/Aug/2011, 8:25 pm Link to this post Send Private Message MSN Blog
 
Translucidus Profile
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Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: Re:


quote:

jalalski wrote:

The over-speed happened at the run down the hill. I kept watching the speed and it just kept rising as the hill got steeper, so I had to disengage the cruise by pressing on the brake pedal..



Hey Jalal - that's absolutely normal behaviour!!!

The cruise can't decelerate the car as it doesn't access the brakes!!!

The CVT would have lowered it's ratios for a little engine braking - you probably saw the engine revs increase as you gathered speed downhill; but that's the CVT lowering ratio to invoke engine braking. NOTHING to do with cruise control (which would at the time, have been requesting zero throttle.)

You car was just overunning normally with some engine braking (invoked by the ECM and a tilt sensor which detects down/up-hill)

We are actually lucky the X-Trail can automatically engine brake a little (it's not agressive braking) - most cars don't do this. There have been a few posts here about revs increasing with zero throttle and on a downhill slope - that's engine braking, NOT power to the wheels from throttle opening.

Let's relax now Image

Last edited by Translucidus, 17/Aug/2011, 8:45 pm


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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

17/Aug/2011, 8:36 pm Link to this post Send Email PM   Send Private Message
 
BarneyB Profile
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Date Registered: 11-2008
Location: Blakeview, Adelaide SA
TOTAL POSTS: 183
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Re:


During my recent 7500k 3 week trip I used the cruise control quite a bit, generally very good on level or climbing grades but was over running downhill. I found that disengaging cruise at the crest gave much better results except on the steepest grades when engine or CVT braking was required. Given these results I believe there is a fault with the programming of the cruise control part of the ECU.

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Regards,
Barney X1047 (c)

2008 ST31, CVT, Flint, Towbar, Cargo mat, Headlight protectors, Dashmat, LED kick steps. Bonnet protector
17/Aug/2011, 9:07 pm Link to this post Send Email PM   Send Private Message
 
jalalski Profile
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


Well, that is obviously VERY different to the after-market cruise control I had in my T30 which would maintain the speed at the same section of the road. The T31 didn't feel like it was engine braking at all, it was just gliding down that hill and picking-up speed. I reckon I would have gotten to 130kms/hour (from the set 110kms/hour) at the bottom of that hill.

Maybe it's normal for the T31 cruise behavior, but I am not used to it based on the way it used to work in the T30. This means am gonna have to disengage the T31 cruise at every steep downhill run.

At least it is working perfectly uphill, which wasn't that perfect in the T30 in terms of gear hunting.

Can't get everything emoticon

Last edited by jalalski, 17/Aug/2011, 9:31 pm


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17/Aug/2011, 9:30 pm Link to this post Send Private Message MSN Blog
 
Translucidus Profile
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Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: T31 Cruise control issues


Hey BarneyB, I notice you have a 2008 model. Mine is also an early T31 CVT and on request the dealer can apply a firmware patch to correct some cruise control issues such as you have described. I had the patch applied and cruise was much better. When speed increases downhill I just use the speed slowing device (brakes).

I must admit though, the Xy cruise control is not as precise as other cars I have driven. Possibly an artifact of Drive-by-Wire system used which has other issues too such as a halting acceleration on partial throttle or cornering sometimes. Other cars with DBWire also have same issues from what I have heard.

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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

17/Aug/2011, 9:30 pm Link to this post Send Email PM   Send Private Message
 
Translucidus Profile
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Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: T31 Cruise control issues


Jalal the engine braking via CVT is gentle and retards only a little. You'll get used to it. Brake to slow as necessary downhill (which disengages cruise) and re-engage cruise when appropriate.

The cruise is NOT increasing your speed downhill - the CVT is retarding a little within it's design parameters (as shown by rev increase). The T31 CVT is entirely different from an auto T30 and your experiencing change; not error.

No dealer will try and correct this normal behaviour.

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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

17/Aug/2011, 9:37 pm Link to this post Send Email PM   Send Private Message
 
jalalski Profile
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


I know the T31 cruise is NOT increasing the speed of the car, but it is doing nothing to try and maintain the set speed downhill.

Last edited by jalalski, 17/Aug/2011, 9:42 pm


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17/Aug/2011, 9:41 pm Link to this post Send Private Message MSN Blog
 
Translucidus Profile
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Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: T31 Cruise control issues


I would say your aftermarket cruise on your T30 was also doing nothing to reduce downhill speed - apart from having a closed throttle when speed over the set speed (which one would hope the T31 would also be doing).

Cruise controls can do NOTHING to reduce overun speed downhill because they only control throttle opening - unless you have a very sophisticated car in which the cruise can also brake (not T31 that's for sure)

The better T30 downhill retarding would have been an artifact of the gearing, over-run system and torque converter characteristics of the transmission fitted - and/or greater aero and mechanical drag.

The T31 appears much slipperier aerodynamically than the T30 and is also a low friction (mechanically) design.

A good way to test aero and general drag characteristics is to freewheel downhill and compare speeds/times when you change something eg add roof racks, add nudge-bar, change cars. The T31 is obviously better than your T30 in this regard as when going downhill, any cruise control is inactive whilst car is over set speed.

I also suspect the CVT only allows a little retarding force to preserve durability of the belt drive acting opposite to drive.

Last edited by Translucidus, 19/Aug/2011, 2:08 pm


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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

17/Aug/2011, 9:45 pm Link to this post Send Email PM   Send Private Message
 


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