Honda real time AWD

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Originally Posted By: supton
I gave serious thought to RAV4 a while ago, and one of its allures was the "lock" button. Instead of waiting until the rear slips to engage the rear (or to deliver more than 10% torque, whatever) you could "command" it to "lock" the rear in at 50%. And above a certain speed (35mph?) it would revert back to its FWD bias.


Honda's VTM-4 is similar. Our MDX has that system, and it has a "VTM Lock" button on the dash. That locks the rear differential clutches so you actually have true 3-wheel drive. The rears are locked together (like a locker) and it's locked to the propeller shaft, which spins at transmission output speed. So it's impossible to get a front wheel to spin without the two rear wheels spinning at the same time.

It defaults back to "automatic" operation above 18 mph, but even its automatic operation is somewhat proactive, and it works very well. I certainly favor their VTM-4 system over the Real Time AWD. That said, we own one of each and both get the job done.
 
All of these AWD systems handle better in the snow than my NP231 part time 4x4 does!

I wish they could be run with different size tires, though. If needed,I can run a worn out tire on my Cherokee along with a brand new one.

They come with a donut spare but tell you don't run with it because it'll overheat [they don't say but will likely explode too] the PDU on it.

On my parents' Focuscape you can't even fit a full size tire in the compartment for it. Thinking of buying a bigger donut tire and having it mounted so if they do need to use it, they don't overheat the AWD system.
 
Originally Posted By: Miller88
If needed,I can run a worn out tire on my Cherokee along with a brand new one.

If needed? When is this ever a good idea to run a worn out tire on a vehicle?
 
Originally Posted By: Quattro Pete
Originally Posted By: Miller88
If needed,I can run a worn out tire on my Cherokee along with a brand new one.

If needed? When is this ever a good idea to run a worn out tire on a vehicle?


It's never a good idea, but it isn't going to cause anything to explode as a temporary means.

Or, where i live, two tires on every vehicle got slashed. Luckily I was out of town with the Cherokee. But if I had to, I could have replaced the two rear tires. A few people with AWD vehicles had to buy 4 new tires.
 
I can't speak for ALL of the "fake AWD systems", but I can say that Honda's systems are apparently less sensitive when it comes to tire size deltas. There are no such warnings in the owner's manual to not use the spare tire as the Escape's manual apparently has.
 
My Tundra has part time four wheel drive. I can get binding easily in my yard. Zero warning in the manual about not using 4hi on bare pavement though.
 
Originally Posted By: Hokiefyd
I can't speak for ALL of the "fake AWD systems", but I can say that Honda's systems are apparently less sensitive when it comes to tire size deltas. There are no such warnings in the owner's manual to not use the spare tire as the Escape's manual apparently has.


On the escape it says it'll overheat and disable the 4WD. On some subarus, you have to pull a fuse.
 
Originally Posted By: Hokiefyd
I can't speak for ALL of the "fake AWD systems", but I can say that Honda's systems are apparently less sensitive when it comes to tire size deltas. There are no such warnings in the owner's manual to not use the spare tire as the Escape's manual apparently has.


I think the more sensitive AWD systems are Subaru(most) and Audi. The rest of them seem to be a computer based approach to AWD and they can shut themselves down mostly. For example the SH AWD has a distinct disadvantage if the Check Engine Light turns on while driving the SH AWD and vehicle stability is shut down. If you restart it works again even with CEL illuminated solid. I went thru this when my Acura MDX was a nightmare to own for its first months due to a bad battery causing electrical faults all over the place.
 
Originally Posted By: Miller88
On some subarus, you have to pull a fuse.


Wait...I thought that Subaru's systems' claim to fame is that they're a mechanical system with a 50/50 torque split, and that's why they're supposed to be better than others?
 
Originally Posted By: Hokiefyd
Originally Posted By: Miller88
On some subarus, you have to pull a fuse.


Wait...I thought that Subaru's systems' claim to fame is that they're a mechanical system with a 50/50 torque split, and that's why they're supposed to be better than others?


You are correct. If you want to tow with two wheels down you have to disconnect the drive shaft.
 
Originally Posted By: Hokiefyd
Originally Posted By: Miller88
On some subarus, you have to pull a fuse.


Wait...I thought that Subaru's systems' claim to fame is that they're a mechanical system with a 50/50 torque split, and that's why they're supposed to be better than others?


Subaru has many AWD systems. The pure mechanical(bliss) system is for manual transmission vehicles only. This describes all the current ones>>> http://www.cnet.com/news/not-every-subaru-all-wheel-drive-system-is-created-equal/

They all carry the same idea, pro-active vs reactive systems. Subaru also designed the cars like Audi to be AWD to start. They did not back engineer an AWD system into a FWD or RWD platform like the rest of carmakers.
 
Originally Posted By: rjundi
Originally Posted By: Hokiefyd
Originally Posted By: Miller88
On some subarus, you have to pull a fuse.


Wait...I thought that Subaru's systems' claim to fame is that they're a mechanical system with a 50/50 torque split, and that's why they're supposed to be better than others?


Subaru has many AWD systems. The pure mechanical(bliss) system is for manual transmission vehicles only. This describes all the current ones>>> http://www.cnet.com/news/not-every-subaru-all-wheel-drive-system-is-created-equal/

They all carry the same idea, pro-active vs reactive systems. Subaru also designed the cars like Audi to be AWD to start. They did not back engineer an AWD system into a FWD or RWD platform like the rest of carmakers.


That is one thing I'll give Subaru! I believe the AWD LX platform uses the same type of setup.

Unlike these FWD vehicles we see today with a transfer-case-type-thing attached to the transaxle.
 
Originally Posted By: supton
I gave serious thought to RAV4 a while ago, and one of its allures was the "lock" button.


That was one of the odd things about the CRV when we test-drove it this year. Most of the competition have some kind of 'AWD Lock' button that tells it to get serious about using all four wheels, but the CRV doesn't.

That said, it ended up our second choice behind the Forester; I'm sure it would be fine on the kind of roads we drive in the winters, where our Civic does OK but could really do with power to the rear wheels at times when the front wheels are on ice when trying to pull out at a junction, and the back ones aren't.
 
Now that the current CR-V uses electronics in its AWD system, I think Honda doesn't have much of a good reason anymore to not have a "lock" button in it. It doesn't take anything away from the user who wants to be completely hands-off, but it adds functionality to those who want it.

The generation I have doesn't have any electronics at all in the AWD system. It's 100% mechanical.
 
Originally Posted By: rjundi
They did not back engineer an AWD system into a FWD or RWD platform like the rest of carmakers.
Yes, but despite that forethought the "VTD" system found on Subaru automatics for example simply places the multi-plate clutch at the front of the drive shaft rather than at the rear like all the common FWD-based add-on AWD systems. It's still functionally the same and any difference in performance is all up to the electronics, which certainly the evidence suggests that Subaru has done a good job at that. The "symmetric" thing is equally of little practical advantage other than giving the marketing department something to do. In the end, the number of 90-degree changes in drivetrain re-direction are the same, no matter how they spin it.

***

Overall, not to make another bad pun but the differentiation of AWD (or full-time 4WD) systems all boils down to whether you have a center diff giving equal push at each wheel all of the time, or a reactive system that not only must detect slip at the primary axle, but also in most cases utilise the speed difference to actually power the compression of the clutch itself.

But the Cherokee moving to the latter system has legitimised the system now and both themselves and Honda/Acura have extended the same idea to provide active rear diff LSD action as well.
 
Originally Posted By: emg
Originally Posted By: supton
I gave serious thought to RAV4 a while ago, and one of its allures was the "lock" button.


That was one of the odd things about the CRV when we test-drove it this year. Most of the competition have some kind of 'AWD Lock' button that tells it to get serious about using all four wheels, but the CRV doesn't.

In the electronic AWD systems I've looked at the "lock" button does not lock anything.

These electronic on-demand systems almost without exception use a computer-provided control current to engage a small magnetic pilot clutch which turns a ball-cam ramp providing a high axial force to engage the main multi-plate clutch. The "lock" button simply puts the current at 100% (overriding the computer) but the system still depends on a slight difference in speed between axles to transfer torque. Subsequently these clutches always slip slightly and can get hot with extended use. They also often run in their own specialised lifetime non-replaceable fluid.

Since most of these systems are from only a few suppliers the vehicle manufacturers have to use their own firmware and marketing spin to differentiate themselves. This makes it harder for consumers to figure out exactly how they work and judge the merits for themselves.
 
Originally Posted By: Kiwi_ME
They also often run in their own specialised lifetime non-replaceable fluid.


Since the topic of the tread is Honda's AWD in particular, I'll say that Honda's systems have real drain and fill plugs. Fluid change intervals are specified in the owner's manual as well. The current CR-V uses two quarts of Honda Dual Pump Fluid II. Honda's "lockable" VTM-4 uses VTM-4 Fluid. The fluid is proprietary, but it is servicable.
 
Originally Posted By: Kiwi_ME
In the electronic AWD systems I've looked at the "lock" button does not lock anything.


Yes, definitely. It's a hint to the computer that you're driving in really bad conditions, not a physical lock like a mechanical 4WD system... the computer then does whatever it's been programmed to do in those circumstanced.

Subaru's 'X-Mode' button sets the clutch to 100%, changes throttle response, uses the brakes to limit wheel spin, and enables hill descent mode, for example.
 
Originally Posted By: Kiwi_ME
The "symmetric" thing is equally of little practical advantage other than giving the marketing department something to do. In the end, the number of 90-degree changes in drivetrain re-direction are the same, no matter how they spin it.


Actually if you ever drove a FWD car with a bit of power you'd realize that equal length driveshafts do help a lot with trq steer. That is what symmetrical is referring too. Equal length shafts at the back & front(or close to it).

In the above video you can see the Audi Q7 fighting trq steer.

This pic you can see why.
header217.jpg
 
I can't see why having different length drive shafts on the front and back axle would matter at all for torque steer? Both sides of each end are effected the same, by their drive shafts?
I think almost all higher hp cars with streetable bushings in the suspension will do some odd things under power, especially a luxury type car like an Audi. I've watched a WRX sti with all sorts of mods on sticky autocross rubber, start to get almost wheel hop torqueing itself around in a tight section. Symmetrical drive shafts or not, the driver was getting all sorts of "torque steer" through the steering wheel.
 
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