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4WD: Differential description

44K views 40 replies 24 participants last post by  lizzurd 
#1 · (Edited)
Thought I would post this as an FYI.....it is quite extensive but it's a good resource for this information and deserves it's own post......maybe even a sticky??
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REAR DIFFERENTIAL SYSTEM DESCRIPTION

Outline
The real-time 4WD Dual Pump System model has a hydraulic clutch and a differential mechanism in the rear differential assembly. Under normal conditions, the vehicle is driven by the front wheels. However, depending on to the driving force of the front wheels and the road conditions, the system instantly transmits appropriate driving force to the rear wheels without requiring the driver to switch between 2WD and 4WD. The switching mechanism between 2WD & 4WD is intergrated into the rear differential assembly to make the system light and compact.
In addition, the dual-pump system switches off the rear-wheel-drive force when braking in a forward gear. This allows the braking system to work properly on models equipped with ABS.
Construction
The rear diff. assembly consists of the torque control diff. case assembly and the rear diff. carrier assembly. The torque control diff. case assembly consists of the diff. clutch assembly, the companion flange, and the oil pump body assembly. The rear diff. carrier assembly consists of the diff. mechanism.
The diff. drive and driven gears are hypoid gears.
The oil pump body assembly consists of the front oil pump, the rear oil pump, the hydraulic control mechanism, and the clutch piston. The clutch piston has a disc spring that constantly provides the diff. clutch assembly with a preset torque to prevent abnormal sound.
The clutch guide in the diff. clutch assembly is connected to the propeller shaft via the companion flange, and it receives the driving force from the transfer assembly. The clutch guide rotates the clutch plate and the front oil pump in the oil pump body.
The clutch hub in the diff. clutch assembly has a clutch disc that is splined with the hypoid drive pinion gear.
The hypoid drive gear drives the rear oil pump.
The front and rear oil pumps are trochoidal pumps. The rear oil pump capacity is 2.5 % larger than the front oil pump to handle the rotation difference between the front and rear wheels caused by worn front tires and tight corner braking. The oil pumps are designed so the fluid intake works as a fluid discharge when the oil pumps rotate in reverse.
Honda dual pump fluid is used instead of diff. fluid.
Operation
When there is a difference in rotation speed between the front wheels (clutch guide) and rear wheels (hypoid driven gear), hydraulic pressure from the front and rear oil pumps engages the differential clutch, and drive force from the transfer assembly is applied to the rear wheels.
The hydraulic pressure control mechanism in the oil pump body selects 4WD mode when the vehicle is started abruptly, or when accelerating in a forward or reverse gear (causing rotation difference between the front and rear wheels), or when braking in reverse gear (when decelerating). It switches to 2WD mode when the vehicle is driven at a constant speed in forward or reverse gear (when there is no rotation difference between the front and rear wheels), or when braking in a forward gear (when decelerating).
To protect the system, the diff. clutch assembly is lubricated by hydraulic pressure generated by the oil pumps in both 4WD and 2WD modes. Also, the thermal switch relieves the hydraulic pressure on the clutch piston and cancels 4WD mode if the temperature of the diff. fluid rises above normal.
 
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#2 · (Edited)
Also here are some illustrations on how to test your System. (Taken from 2003/04 Service Manual)

First pic is a DUAL PUMP SYSTEM FUNCTION TEST FOR Auto Trans. (sorry if the pic is blurred)

Starting and Accelerating in forward gears (4WD mode)
Note: Do not test repeatedly or the fluid will overheat.

1. Lift up the vehicle so all four wheels are off the ground.
2. Make a mark on either #1 or #2 propeller shaft.
3. Start the engine, and let it run until it warms up (the radiator fan comes on at least twice)
4. With the engine at idle, shift to the 1 position.
5. Apply the parking brake firmly to lock the rear wheels, and measure the time it takes to propeller shaft to rotate 10 times.
-If the measured time is more than 10 seconds, the 4WD system is normal.
-If the time is less than 10 seconds, there is a problem in the 4WD system. Check the diff. fuid. If the diff. fluid is normal, replace the torque control diff. case kit. (front pump portion)

***You can do the exact same test using the "Reverse" gear as well.
 
#3 · (Edited)
This next test is for DECELERATING IN A FORWARD GEARS (2WD Mode)

1. Block the front wheels, raise the left rear wheel and support it with a safety stand.
2. Hold the tire, and turn it counterclockwise continuously for more than one rotation.
-If the rotation of the wheel does not gradually feel heavy while rotating, the 2WD system when decelerating in a forward gear is normal.
-If the rotation of the wheels gradually feels heavy, there is a problem in the system. Check the diff. fluid. If the fluid is normal, replace the torque control diff. case kit.

DECELERATING IN REVERSE GEARS (4WD Mode)
1. Block the front wheels, raise the left rear wheel and support it with a safety stand.
2. Hold the tire, and turn it clockwise continuously for more than one rotation.
-If the rotation of the wheel gradually feels heavy, the 4WD system when decelerating in reverse gear is normal.
-If the rotation of the wheel does not gradually feel heavy, there is a problem in the system. Check the diff. fluid. If the fluid is normal, replace the torque control diff. case kit.
 
#6 ·
Thanks for the great write up

The real-time 4WD Dual Pump System model has a hydraulic clutch and a differential mechanism in the rear differential assembly ...
This system sounds amazing similar to the Haldex Limited Slip Coupling. The only difference I can see is that the Honda system is completely enclosed in the rear differential housing while the Haldex is a separate unit between the front and read diff's

For all you mechanical types, check out some of the other links off of this page
 
#7 ·
theoldwizard said:
This system sounds amazing similar to the Haldex Limited Slip Coupling. The only difference I can see is that the Honda system is completely enclosed in the rear differential housing while the Haldex is a separate unit between the front and read diff's

For all you mechanical types, check out some of the other links off of this page
Unfortuntaley the Honda Real Time 4WD system doesn't work anywhere nea as well as the Haldex system works. I owned an Audi TT Quattro which has the Haldex system and my TT could do things that my Element only dreamed of being able to do as far as traction in snow, ice and rain. It wasn't the tires because I used the same Nokian's on both vehicles. It is the systems and how they work that is the difference. Noticed this from the very beginning, it's one of the few disappointments that I have with the Element.

One of the biggest reasons the Haldex is a better system is the speed in which it reacts to wheel slippage and the amount of slip that it takes before power is transferred. Haldex reacts faster and it takes far less wheel slip to transfer that power.



 
#13 ·
Will - I think spdrcr added this to another thread....the FAQ/How To section...so that's a good place to find it too.

But I'd be glad to see it a sticky too...maybe when I get better pictures posted :|
 
#14 ·
ApriliaGuy said:
somebody should wip out their magic wand and make this thread a stickie. :)


Will
Will we can only make so many threads "stickies" before it gets too busy at the top of each forum. We try to keep it under 5 stickies. We know we need to clean things up, it just comes down to finding the time to do it.

As Dance said, it can be found in the FAQ section.



 
#16 ·
paulj said:
A couple of years ago, the CRV got a variation on the RT4WD that added a cam activated mechanism, that reacted sooner and transferred smaller amounts of torque. I don't know if the 2007 Element got this version or not.
Unfortunately the link you listed showed an older version (2003) of the RT4WD without the cam.

Still, overall, excellent drawings and explanation !
 
#17 ·
Element 4WD system limitations

Unfortuntaley the Honda Real Time 4WD system doesn't work anywhere nea as well as the Haldex system works. I owned an Audi TT Quattro which has the Haldex system and my TT could do things that my Element only dreamed of being able to do as far as traction in snow, ice and rain.
Larry, could you explain in more detail the limitations you find in the Element 4WD system compared to the more sophisticated Audi and Subaru AWD systems? In what circumstances will the Element's system prove inferior, and how?

I'm strongly considering an Element and my current car is a '98 Audi A4 Quattro Avant ("Old Unreliable," as I call her). I do love the Audi's handling, safety, and comfort, but the cost in time and money to keep her on the road is ridiculous. I'm curious how you, as a former Audi TT owner, feel the Element's 4WD system will compare.

I also wonder to what degree the '07 Element's traction control (4 wheel, I believe) will improve its low traction performance, especially since I don't believe any Element has a limited slip rear differential.

Though almost everything else on the A4 has let me down, at one time or another, Quattro plus winter tires never has. I once had to drive my dog to the emergency hospital in a raging blizzard on unplowed highways; I had to maneuver around stuck cars, trucks, and SUV's everywhere, but the A4 got me through no problem. I'm also considering a Subaru Outback, but I am highly tempted by the Element's incredible practicality.

Thanks for any thoughts.
 
#18 ·
was said:
I'm strongly considering an Element and my current car is a '98 Audi A4 Quattro Avant ("Old Unreliable," as I call her). I do love the Audi's handling, safety, and comfort, but the cost in time and money to keep her on the road is ridiculous. I'm curious how you, as a former Audi TT owner, feel the Element's 4WD system will compare.
I too am a former TT owner. I really love my AWD Element (in fact, I prefer it over the TT - the TT was posh and fun, but the element is more practical and better designed). That said, I agree with the comments on the AWD having a noticeably larger delay before kicking in on the Element. The TT always felt like it was friggen glued to the road. However, in the element I do notice sometimes when the front wheels will briefly spin before the rearwheels are making power.

That said, I do a fair amount of driving on bad dirt roads (and Tahoe snowboard outings) and the Element handles them fine.
 
#19 ·
punkgeek said:
...That said, I agree with the comments on the AWD having a noticeably larger delay before kicking in on the Element. The TT always felt like it was friggen glued to the road. However, in the element I do notice sometimes when the front wheels will briefly spin before the rearwheels are making power.
Yeah....same here but replace Audi TT w/ 2003 Subaru Forester XS. The Subaru has a rear limited slip diff besides (not all models have the LSD) so that little wagon is great in all weather conditions. The E does just fine, just slips more noticably before kickin in....then kicks out... and back in again.

Will
 
#20 ·
question about Element 4WD

I appreciated the description of the Element's 4WD system but have an even more basic question. I'm thinking of buying an Element advertised as having the 4WD system but there is only one axle between the front wheels, no axle between the real wheels. Does the Element 4WD system have no axle for the rear wheels?
 
#23 ·
Easy way is check for the sunroof. Prior to 2009's, all E's with a sunroof are 4WD.



 
#26 ·
How AWD works

New owner of 2010 Silver EX AWD.

From the Honda site: The Real Time™ 4WD system engages when slippage is detected.

Can the AWD be turned on manually, switch, button, etc?
Is it ok to drive this car on the beach on loose sands?

I couldn't find any information about this in the owner manual.

Thanks,
 
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