Press 4WD under HEAVY load, or not needed?

[maby]

I know it is not a phev, but it seems this guys does know which buttons to push ...

http://youtu.be/AI9lMky5lUU

That's something i'd really like you to clarify. Does this 4wd system work the same way of the one's on the PHEV. Does the PHEV have the same capability to get out of trouble as the diesel??

Well, the transmission is totally different, so the question is functionality, not design. I was looking at the brochure for the diesel Outlander yesterday to try to find out if it had locking diffs, but there is no mention of them.

 

[gwatpe]

It should be so easy with the PHEV to check the individual tyre rpm sensors and check the speed and use the ABS system to brake the spinning wheels and give traction back to the non spinning wheels.

I do believe MMC have deliberately not offered this system so as to make the PHEV a poor track performer.

 

[maby]

It should be so easy with the PHEV to check the individual tyre rpm sensors and check the speed and use the ABS system to brake the spinning wheels and give traction back to the non spinning wheels.

I do believe MMC have deliberately not offered this system so as to make the PHEV a poor track performer.

You may be right - to differentiate it from the Shogun?

But achieving it with the brakes is still a poor option in genuine off-road usage - the car regains traction and the braked wheel hits the ground stationary - the only way you can detect that traction has been regained is to momentarily release the brake. It will keep you moving - sort of... but it does not make for a good ride and will be imposing a lot of wear on the transmission and braking system. In real off-road use, this is happening on at least one wheel most of the time.

 

[ian4x4]

I am still not sure what happens to a stopped PHEV electric motor (wheel).
How much current (torque) will the electronics allow into the system if the car refuses to move.
The diesel will have kept running and have some inertial to kick start the wheel (via slipping clutch or torque converter)

Is it the electric motors that are being protected from overload, by not braking the wheels.

I am afraid that my electronics experience is getting older and perhaps irrelevant, but failures of 'stalled' electric motors used to mean auxiliary methods of helping them start, and limiting start up current were quite normal.

 

[maby]

I am still not sure what happens to a stopped PHEV electric motor (wheel).
How much current (torque) will the electronics allow into the system if the car refuses to move.
The diesel will have kept running and have some inertial to kick start the wheel (via slipping clutch or torque converter)

Is it the electric motors that are being protected from overload, by not braking the wheels.

I am afraid that my electronics experience is getting older and perhaps irrelevant, but failures of 'stalled' electric motors used to mean auxiliary methods of helping them start, and limiting start up current were quite normal.

I don't think the issue here is a stalled motor - rather the opposite really. When a wheel loses traction, the differential allows all the power from the electric motor to be directed to it and robs the other wheel of power. Even if the car applied the brakes to the spinning wheel, that would not stall the motor - it would result in all the power being directed to the other wheel. That much should be easy enough - the issue is how to detect and respond to traction being regained? With one wheel locked, the effective gear ratio between the motor and the other wheel will be doubled - the electronics would have to compensate for that in a 4WD vehicle in order to maintain the balance of drive between the front and rear axles. It also has to have a strategy for working out when contact has been re-established between the braked wheel and the ground - not easy to do without releasing the brake - at which point you will probably lose traction again - or alternatively lose traction on the other wheel if it's grip on the ground is now less than that of the previously braked wheel. It really is a difficult problem - Mitsubishi simply do not promote the PHEV as an off-roader which lets them off the hook...

 

[ian4x4]

Thanks Maby, after reading your explanation I looked again at the PHEV video.
It does seem that due to limited articulation of the front and rear 'axles', the PHEV has lost traction of one wheel of both axles.

When I looked initially, I thought that one axle still had both wheels on the ground, and it was the inability of this axle to start to move the car on its own that was the problem.

I see that I was wrong. It would seem the problem is not lack of power to get going on the incline on one motor/axle, which would be worrying.

 

[maby]

Thanks Maby, after reading your explanation I looked again at the PHEV video.
It does seem that due to limited articulation of the front and rear 'axles', the PHEV has lost traction of one wheel of both axles.

When I looked initially, I thought that one axle still had both wheels on the ground, and it was the inability of this axle to start to move the car on its own that was the problem.

I see that I was wrong. It would seem the problem is not lack of power to get going on the incline on one motor/axle, which would be worrying.

Exactly - it's a cross-articulation problem and very difficult to recover from without limited slip or lockable diffs on both axles and in the middle. The 4WD lock button on the PHEV simulates the lockable centre diff, but the diffs in each axle are just standard road units and not suitable for genuine off-road use.

It's always tempting to assume that you can play tricks with the ABS to achieve the same effect as a diff lock, but never forget that the two are designed for exactly opposite effects - the ABS is there to stop the car as quickly as possible - the diff lock is there to keep it moving!

 

[asterix550]

Thanks Maby, after reading your explanation I looked again at the PHEV video.
It does seem that due to limited articulation of the front and rear 'axles', the PHEV has lost traction of one wheel of both axles.

When I looked initially, I thought that one axle still had both wheels on the ground, and it was the inability of this axle to start to move the car on its own that was the problem.

I see that I was wrong. It would seem the problem is not lack of power to get going on the incline on one motor/axle, which would be worrying.

Exactly - it's a cross-articulation problem and very difficult to recover from without limited slip or lockable diffs on both axles and in the middle. The 4WD lock button on the PHEV simulates the lockable centre diff, but the diffs in each axle are just standard road units and not suitable for genuine off-road use.

It's always tempting to assume that you can play tricks with the ABS to achieve the same effect as a diff lock, but never forget that the two are designed for exactly opposite effects - the ABS is there to stop the car as quickly as possible - the diff lock is there to keep it moving!

What about the 4wd outlander diesel model. Does it have center diff and axles diffs?? How did it do it in the video without getting stuck like the PHEV?

 

[asterix550]

Here is some serious BMW SUV off road capabilities besides off course the limited ground clearance
http://youtu.be/1GbrR4YKM3Y

 

[ian4x4]

https://www.youtube.com/watch?v=fiQTs0Neo3U

Maby
Just after the BMW X5 video there is this Range Rover clip.

I notice that the airborne wheel does not spin helplessly or nor is it braked.
It continues to turn to match the road-speed revolutions, I take it that these are true locked differentials.

Luckily I have found this very professional test and explanation of 2016 Diesel Outlander's off road qualities.

It has an Electronically Controlled Clutch in the Front Differential, Part Time Coupling to Rear Axle, and an Open Rear Differential.
It also has the capability of braking individual wheels.

https://www.youtube.com/watch?v=-D2obMHziNQ

 

[maby]

Maby
Just after the BMW X5 video there is this Range Rover clip.

I notice that the airborne wheel does not spin helplessly or nor is it braked.
It continues to turn to match the road-speed revolutions, I take it that these are true locked differentials.


.....

I don't know the current generation of Range Rovers, but they have traditionally been sold with locking diffs.

 

[biosci]

...
What about the 4wd outlander diesel model. Does it have center diff and axles diffs?? How did it do it in the video without getting stuck like the PHEV?

If one looks at the PHEV video it is apparent that the driver is trying to put the car in a cross-axle position so that it becomes "stuck" - or just until the free wheels spins...

The video with the std model is much the same - first the wheels spin and then the car applies the brake to the spinning wheels and torque is applied to wheels with traction. This appears to take 1-2 seconds before the brake is applied to the free wheels. Perhaps if the the PHEV driver continued to apply power for longer than the initial tire spinning, the PHEV would also have applied the brake to the spinning wheels and applied useful torque to the other wheels?

I recall some Mitsubishi released videos of PHEVs in a cross-axle obstacle course where the wheels first spin for a short period before the brake is applied to provide torque to other wheels and allow the PHEV to continue.

The video with the BMW is much the same with limited free wheel spin and then braking of free wheel - although it is not clear if the car is actually ever cross-axle - it appears that maybe three wheels always have traction.

Of course a car with locked differentials will perform best under demanding 4x4 off-road conditions.

 

[gwatpe]

Once there is some rain and mud, like the real world situation all the help that the car can give to keep traction is what is needed.

 

[jainkjohn]

check out some video. it seems phev performs fine.

https://www.youtube.com/watch?v=XF1U5pDVpzo
https://www.youtube.com/watch?v=d1WO9x_laiU
https://www.youtube.com/watch?v=WSho8T_Sxlg

 

[Esparza]

In the second video the S-AWC seems to work much better than in other videos when is trying to stop wheels with no grip.

 

[jaapv]

Yes, but they never cross-axled it.

 

[markogts]

What about the 4wd outlander diesel model. Does it have center diff and axles diffs?? How did it do it in the video without getting stuck like the PHEV?

http://www.mitsubishi-motors.com/en/spirit/technology/library/s-awc.html

The diesel has some locking capability in the front differential, which the phev hasn't

 

[markogts]

Had little opportunities until now to test off road capabilities.

Once I got stuck after the car crept into thawing snow (16" winter pirelli scorpion). With ASC on, no wheel would spin, with ASC off, wheels would spin at dangerous speeds (tacho had a spike of 70 km/h in some tenths of second :shock: ) Got out thanks to the avalanche showel I always carry in winter...

4WD button: at low speed, I don't see any difference, will try anko's parallel situation.

I'm waiting for the 18" summer tires to wear out, I'd feel much better with 16" a bit off-road oriented.