Looking at a 2012 RZR 800 and would like to know how the system works? When in 2x4 does only the rear wheels pull or rear wheels plus one front? When in AWD does all 4 wheels have traction to pull?



Thanks ATV rookie!

When in 2 wheel drive power is supplied to the rear wheels only, when AWD drive is engaged power is supplied to all 4 wheels


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To explain a little further. When the AWD switch is set to AWD and the rear wheels (which are locked) must lose traction (rpm must be less than about 3100) then within about 1/5th of the rear wheels turn the front wheels begin to turn - both front wheels are locked and turn at the same speed any time the AWD system is actively working. Shortly after the rear wheels again gain traction the front wheels stop driving and begin coasting allowing the driver to more easily steer the vehicle.

Mike

 

When the AWD button is pushed the rpm has to drop below 3100 for the computer to power up the electromagnet. Once it is powered the AWD will kick in at any rpm.

 

AWD is a electric and mechanical system once the AWD switch is on, you are still in 2wd until the rear wheels spin then the front engage. Once rear gets traction the front disengages again. The AWD switch "allows" it to go into 4wd once the rear tires slip

Also, the front is not a positive locking either, it is open type diff.

So there is no such thing as full time 4 wheel drive lock in a RZR

Todd

 

I have never seen a rzr spin one front tire like a can am or cf moto. I don't know it does this without some sort of locker.

 

Todd,

I believe you are mistaken. On a properly working RZR when the front wheels engage it is through a locked differential. Both front wheels will turn and at the same speed and because of this steering will be much heavier than with the front disengaged. If you have a RZR available to experiment with raise both rear wheels and one front. (Use rolling jacks to do this) put it in AWD and start the rears spinning, if the system is working correctly both front wheels will turn and the RZR will attempt to move or will move if on rolling jacks.

If Pirate still hangs out here in the 800 section, he can explain it much better than I can. He is the "Einstein" of the Hilliard differential system. If I'm wrong my sincerest apologies.

Mike

 

Can I engage the awd while driving or have to completely stop? 13 jagged x

 

Yes, you can hit the awd switch at any time you like, however, the front wheels/diff won't engage until you are below 3100 rpm (and the rear wheels slip).

 

Correct. Low to high and vice verse stopped and at idle.

 

thank you

 

When the front differential locks in it definitely for sure locks both wheels and pulls in the direction you are traveling. If you stop and go in reverse it will definitely lock and pull both wheels in the reverse direction.

It uses an over running sprag (Hilliard) clutch for each axle. These let the axle over run (go faster) than the differential carrier but will not let it go slower (lock).

It is NOT a limited slip, or open, differential.

 

Acts like a locking differential when engaged, but like an open differential
when cornering.

So it locks until you corner the different tire speeds unlock it.

 

I was comparing to what others use such as CFMoto which has a choice to engage front and then also lock front solid. But from the posts it looks like Polaris does the same with combining both features into the front and not being concerned about if front diff is locked or open for turns.

 

Look at it like this. If you are spinning and it needs to be locked it will lock.
If you are not spinning it will unlock.
You don't need to stop to lock or unlock. Just push the button and leave it.
You don't have to worry about it being hard to steer or not turning at all because it is locked. It unlocks for you automatically. If you want to run fast and need 4WD just leave it locked in. When you let off the gas to turn it will unlock so you can turn. If you need the front to kick in and help power you around the turn just gas it and go.

Now the flip side of this amazing device. You need to learn the trick of going down steep slick hills because the front doesn't help hold you back like the full geared differentials that some of the other makes use. But that is usually just a minor annoyance after you learn how it works.

 

Now the flip side of this amazing device. You need to learn the trick of going down steep slick hills because the front doesn't help hold you back like the full geared differentials that some of the other makes use. But that is usually just a minor annoyance after you learn how it works.

What is this trick? Is it to accelerate slightly to keep the belt engaged? (Which I do with my left foot on the brake as well).

 

Does everyone usually run in 2WD? When do you guys use AWD?

 

When I leave the pavement, I activate AWD.

 

Same here. Because nothing really happens anyway until you need AWD and then you have it. Lots of guys leave it on all the time.

Mike

 

There is virtually no comparing Polaris AWD system to another 4WD system. I have taken apart the hubs and learned how they work. Pretty cool the only drawback is no engine braking on the front, once they unload they freewheel. It had a locked front diff, the second part of the system is in each hub, when engaged in AWD the front shaft and diff are spinning at the same speed the rear wheels are but the only way it will engage a front wheel is if the rear wheels spin, if that happened this causes the front axle shaft to spin faster than the wheel is turning, when that happens there is a mechanism inside the hub that turns and throws the outside of the mechanism out and grabs the hub which then causes the wheels to turn. Once there is no more spinning the load comes off the front hub and the mechanism relaxes and releases its hold on the hub. It is an amazing system and works great. Until wear and water gets inside and its starts to lose it's magnetism, I had issues on an old Polaris quad I had to shaft down the hub a little to get the magnetized plate to grab better.

 

The older models had the sprag units in the hubs.
The central Hilliard differential unit superceded the hub units many years ago. But the operation is basically the same.

 

Maybe I'll be taking one apart on a newer model some day and get to see how that works exactly too.

 

At it's core the Hilliard mechanism is a pair of sprag clutches (one way bearings) that give each front wheel the ability to spin faster (overrun) the front ring gear but not slower. (if 12 volts is supplied to the armature- dash 4wd switch is on AND the ECU allows). With steering input the faster spinning front wheel overruns while the other receives power. The front ring and pinion ratio is slightly lower (higher numerically) than the rear so driving straight on level ground and with all of 4wd requirements met from above, the front wheels are slightly overrunning the front ring gear. Same thing happens in reverse, buts it's reversed lol.

"If" the front diff is operating correctly this all happens seamlessly with virtually no steering wheel pull. With car weights, engine HP and tire sizes all going up the front diff has increasing become less reliable.