Two wheel drive vs 4 wheel drive (Torque, traction?) 1

[TrustButVerify]

Hello folks,

So, just imagen you have two commercial trucks, one with 2-wheel-drive and another with 4-wheel-drive, and their WEIGTH is the same.

Great, they are being manufactured to be able to be driven on a flat surface, both of them.. Like driving on the road.

Now, this is the question... Imagine you start scrapping both trucks the same way, I mean, you start to take weight off the truck, like reducing their self-weight...

Can you find the situation that the 4-wheel-drive truck will NOT go forward due to lack of weight on each axle (and thus less friction), but to start SLIDING due to much torque?

The 2-wheel drive truck will be able to go forward since the two wheels need to overcome their own resistance, plus the resistance of the other two wheels?

Where I can read about this?

Have a nice weekend.

 

[TrustButVerify]

To make it easier... you turn off the driven engines of two wheels, and then the truck is able to move in linear motion (no spinning of the wheels). How?

 

[3DDave]

The facts are clearly incomplete.

What were the trucks being used for when you observed this many times in several locations?

 

[TrustButVerify]

Ok. As I said previously, it is easier than that..

Just imagine that you have a truck with four driven wheels, and when you try to move it in linear motion, you cannot, the wheels just spin... then, you turn off the engines in two wheels, ending up in four wheels touching the ground, two with driven engine, and two in neutral (you turn off their driven engines), the truck start moving in linear motion.

How?

 

[TrustButVerify]

I mean... what is the science behind?

 

[TugboatEng]

I think I'm starting to understand your question. In 4wd your vehicle doesn't track straight, in 2wd it does. The answer to this is that steering and driving both require traction. If you have 100 units of traction available and you are using 90 units for driving then you have only 10 units left for steering. If it is not a driving wheel then all 100 units are available for steering. Available traction is the weigh on the wheel x coefficient of friction.

 

[3DDave]

Open differentials are not providing equal torque, and someone built a truck with a continuous rear axle.

Did I solve the riddle?

I'm going to make a one-wheel drive truck that will be twice as good as two wheel drive. And I'll make it with 1000 non-driven wheels. Sort of a homeopathic medicine approach to undercut the 4WD community offerings.

 

[TugboatEng]

I believe OP's case has 4 independently motor driven wheels. It sounds like a mining truck of some sort.

Your 1 wheel drive system sounds like a Detroit Locker. One wheel is directly connected to ring gear and opposite wheel is driven through a torque sensing clutch.

 

[TrustButVerify]

They are 4 independently motor driven wheels.

 

[3DDave]

Isn't a tuk-tuk a commercial truck? Sure, only 3 wheels, but then I'm back to:

What were the trucks being used for when you observed this many times in several locations?

 

[3DDave]

They are 4 independently motor driven wheels.

Hydraulic motors or electric motors?

 

[IRstuff]

If you start reducing the same weight in each truck, will you reach the situation when the 4 wheel driven wheel will start sliding due to lack of friction force to start moving,

This does not compute. The self-weight of the wheel, suspension, frame, and engine alone is sufficient; you have control of the torque being generated. The fact that mechanics roll wheels and tires around in a tire shop by hand says the premise is bogus.

TTFN (ta ta for now)
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[CWB1]

Your hypothetical is backwards. 4wd vehicles have higher driveline losses than 2wd vehicles so torque measured at the wheel will be lower than an identical 2wd. IOW, the 2wd will begin spinning before the 4wd in your hypothetical weight-reduction scenario.

 

[TugboatEng]

There is no drive line on OP's vehicle. It has independent drive for each wheel. I think OP is describing a mining truck. His descriptions are convoluted and misleading. It sounds like someone describing their perpetual motion machine but maybe there is a translation issue?

 

[CWB1]

Traction is still torque/wheel. If vehicle torque is equal between two and four-motor vehicles, two-motor has twice the torque/wheel and will spin before four motor. OTOH, if each motor's torque is equal then torque/wheel is the same between two and four-motor vehicles and they'll spin the tires simultaneously, even tho the four-motor vehicle will have twice the total torque.

 

[TugboatEng]

I think OP is complaining about difficulty steering while in 4wd operation. They are describing it in a very unusual way.

 

[3DDave]

There cannot be torque without resistance to motion and the OP has not said where that resistance comes from.

Q remaining 11: What were the trucks being used for when you observed this many times in several locations?
Q remaining 10: Hydraulic motors or electric motors? I missed the previous answer.
Q remaining 10: Show the hydraulic schematic of the two different trucks.
Q remaining 9: How many wheels spin when all are driven?
Q remaining 8: Was power to two wheels actually removed or is this a guess?
Q remaining 7: Was power to the slipping wheel(s) removed?

 

[TugboatEng]

OP's problem seems to be that the wheel is sliding sideways. Torque will not correct this problem.

 

[3DDave]

Not seeing sideways motion in the diagram. This leads me to believe the 4WD has all motors tied in parallel with no flow balancing, so if one spins there is insufficient backpressure to move the other motors. Whoever designed the 2WD did use a flow balancing circuit so it applies flow regardless of torque requirements. The advantage to not having flow balancing is to avoid Ackermann steering speed problems.

 

[TugboatEng]

Hydraulic motors in parallel behave exactly the same as an open differential. Equal torque to all wheels.

The line "not moving in linear motion" leads me to believe his is a steering problem, not a propulsion problem. Both are traction problems.

I have a new coworker with good knowledge but limited English. I'm starting to get use to mis-descriptions like this.

 

[gruntguru]

Nowhere near enough information. Question not clearly defined.

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