4wd-i does not deliver what I expected
#2
03-08-2008, 10:57 AM
Re: 4wd-i does not deliver what I expected
4wd-i does not deliver what I expected.
At least a few people in this forum maintain that the 4wd-i Highlander Hybrid (HH) is poor in the snow and other adverse traction conditions because of ground clearance or other physical size constraints. Excuses, excuses. I don’t hear any Jeep owners talking like this. In reality, Toyota's 4wd-i system "hangs up the keys" when traction is poor. I was fooled too. I bought one. Toyota’s system may prevent you from getting into trouble under poor traction conditions but the same system may keep you from getting out of trouble also.
The 4wd-i system combines an inherently flawed mechanical torque-splitting device on the rear wheels with a traction control system that manages wheel slippage by simply removing or restraining power. The end result is that power is inconsistently available especially from the rear wheels when it is needed the most - when traction is poor!
When a driven wheel loses traction due to ice, gravel, sand, standing water, snow, etc. the ancient "differential" torque-splitting design has a nasty habit of making things worse. The wheel with lowering resistance is given increasing amounts of torque by the differential. There is no hope of regaining control without lifting off the gas and "steering" through the poor conditions. Power can only be applied safely again when normal traction is available. An experienced driver will perform these maneuvers instinctively but all drivers are at risk to end up dangerously out of control. To be completely objective, most automobiles still have at least one “differential.” How other safety systems interact with it’s foibles, though, is still being ironed out and can be very frustrating to the owner.
Enter "vehicle stability control" or VSC. In order to compensate for the vagaries of central power distribution and wacky differential output, yet another complex control layer is superimposed to monitor the speed of each wheel and selectively apply the brakes to regain a 1:1 connection between the road surface speed and tire speed. But if the road speed is zero (stuck in the snow) and the wheel speed is traction matched, forward movement may be impossible. Unfortunately, VSC is the primary safety improvement that we have at this time. Take it or leave it.
So what about the HH 4wd-i? The HH interposes a rear differential to split the power from one electric motor to two rear wheels. As we just discovered, a differential sends torque to the wheel with the least resistance. Now, superimpose a vehicle stability control system that compensates by removing power from the single electric motor. Ironically, BOTH wheels will be deprived of power if either one loses traction. The end result is that POWER IS NOT CONSISTENTLY AVAILABLE FROM THE REAR WHEELS UNDER POOR TRACTION CONDITIONS. This is really, really lame. The HH 4wd-i system is therefore mostly useless for its perceived purpose. How the heck did I ever get duped into paying extra for this?
On the other hand, when all 4 wheels have good traction the HH will slingshot forward like a rocket. This was an unexpected benefit that makes it rather fun to drive in city traffic. So 4wd-I gave me something I didn’t expect and didn’t deliver on something that I did expect. On average I’m still wishing it would act more like a real 4wd.
M, Denver, CO.
At least a few people in this forum maintain that the 4wd-i Highlander Hybrid (HH) is poor in the snow and other adverse traction conditions because of ground clearance or other physical size constraints. Excuses, excuses. I don’t hear any Jeep owners talking like this. In reality, Toyota's 4wd-i system "hangs up the keys" when traction is poor. I was fooled too. I bought one. Toyota’s system may prevent you from getting into trouble under poor traction conditions but the same system may keep you from getting out of trouble also.
The 4wd-i system combines an inherently flawed mechanical torque-splitting device on the rear wheels with a traction control system that manages wheel slippage by simply removing or restraining power. The end result is that power is inconsistently available especially from the rear wheels when it is needed the most - when traction is poor!
When a driven wheel loses traction due to ice, gravel, sand, standing water, snow, etc. the ancient "differential" torque-splitting design has a nasty habit of making things worse. The wheel with lowering resistance is given increasing amounts of torque by the differential. There is no hope of regaining control without lifting off the gas and "steering" through the poor conditions. Power can only be applied safely again when normal traction is available. An experienced driver will perform these maneuvers instinctively but all drivers are at risk to end up dangerously out of control. To be completely objective, most automobiles still have at least one “differential.” How other safety systems interact with it’s foibles, though, is still being ironed out and can be very frustrating to the owner.
Enter "vehicle stability control" or VSC. In order to compensate for the vagaries of central power distribution and wacky differential output, yet another complex control layer is superimposed to monitor the speed of each wheel and selectively apply the brakes to regain a 1:1 connection between the road surface speed and tire speed. But if the road speed is zero (stuck in the snow) and the wheel speed is traction matched, forward movement may be impossible. Unfortunately, VSC is the primary safety improvement that we have at this time. Take it or leave it.
So what about the HH 4wd-i? The HH interposes a rear differential to split the power from one electric motor to two rear wheels. As we just discovered, a differential sends torque to the wheel with the least resistance. Now, superimpose a vehicle stability control system that compensates by removing power from the single electric motor. Ironically, BOTH wheels will be deprived of power if either one loses traction. The end result is that POWER IS NOT CONSISTENTLY AVAILABLE FROM THE REAR WHEELS UNDER POOR TRACTION CONDITIONS. This is really, really lame. The HH 4wd-i system is therefore mostly useless for its perceived purpose. How the heck did I ever get duped into paying extra for this?
On the other hand, when all 4 wheels have good traction the HH will slingshot forward like a rocket. This was an unexpected benefit that makes it rather fun to drive in city traffic. So 4wd-I gave me something I didn’t expect and didn’t deliver on something that I did expect. On average I’m still wishing it would act more like a real 4wd.
M, Denver, CO.
M, you really seem hung up on your concept of the HiHy's rear differential, which is 180 degrees from the facts! First of all, limited slip differentials have been around for many years, and even with the primative "disc clutch" version, the rear axels are effectively locked together for equal traction. In the more advanced "helical" version, up to 80% of available torque can be biased to the wheel with the most traction. And you think Toyota's is less advanced than this!!
You seem in denial that the 3" more ground clearance of your Tahoe (or a Jeep) has any bearing on its deep snow capabilities. Believe it or not, it they can hang up too!
And you haven't mentioned snow tires, so I assume you don't have them. The HiHy's tires, although rated as "all season" have a very tame tread designed for mimimal rolling resistance rather than for mud/snow performance. Most full sized SUV's and Jeeps have a much more aggressive tread, which makes a huge difference.
The i4WD works great up to the point where no progress can be made with approprite power to each wheel to the point of spinning, but not beyond, and is overall a much safer design that less intelligent systems, that will merrily allow you to spin out, and /or roll over if pushed too far. It will deliver maximum traction and braking performance up to this limit.
See this thread, where you will find a kindred spirit - "Still Steamn" -shouting about how he was duped like you feel you were were - his HiHy just ain't no Silverado!
https://www.greenhybrid.com/discuss/...or-snow-12464/
But read the input of the 8-10 others who praise the deep snow performance, given adequate snow tires, in much more challenging climates than yours. I found #13 particularly interesting, comparing his HiHy to his Honda Passport 4WD which has no effective VSC system.
I take a pair of cable chains when we venture into the Sierras or to Tahoe, but so far have never had to use them.
Pete
#3
03-08-2008, 12:38 PM
Re: 4wd-i does not deliver what I expected
Great explanation. This helps me. I have a Honda Civic Hybrid which I love, but I was thinking about getting a Highlander Hybrid to be able to handle more of the winter weather. I've been watching these forums for a while and have been a little worried about what I have read about the Highlander's traction in adverse conditions. This is the best explanation that I have seen which shows how the quirky behavior is an unintended consequence of the safety controls. I hope Toyota will fix this. I may still get one anyway soon because I don't really expect to ever be in really deep snow. I do appreciate this honesty. Thanks, and I hope you keep posting.
BTW, for the other guy who gets crazy with people who share honestly he needs to realize how this discredits him. I read his response and it appears he didn't even read super10s posts carefully enough. Super10s already stated how his Highlander has snow tires. Colorado is not Beverly Hills either, it has more challenging high-altitude mountainous roads than another state in the lower 48. Maybe he knows what he's taking about?
BTW, for the other guy who gets crazy with people who share honestly he needs to realize how this discredits him. I read his response and it appears he didn't even read super10s posts carefully enough. Super10s already stated how his Highlander has snow tires. Colorado is not Beverly Hills either, it has more challenging high-altitude mountainous roads than another state in the lower 48. Maybe he knows what he's taking about?
#4
03-08-2008, 04:54 PM
Re: 4wd-i does not deliver what I expected
BTW, for the other guy who gets crazy with people who share honestly he needs to realize how this discredits him. I read his response and it appears he didn't even read super10s posts carefully enough. Super10s already stated how his Highlander has snow tires. Colorado is not Beverly Hills either, it has more challenging high-altitude mountainous roads than another state in the lower 48. Maybe he knows what he's taking about?[/quote]
You are right, I did miss the fact that he has winter tires in his post on the previous thread.
But this doesn't change the fact that the HiHy's system, functioning normally, gives as much power to each wheel as it can handle without uncontrolled wheel spinning. As soon as power exceeds traction in each wheel, independently, power is reduced to that wheel. That's the "intelligent" part. If it cannot make progress with the traction available, it shuts down - not for lacking adequate power to a wheel with more traction due to some sort of archaic differential design, which is his assumption.
If super10s is having uncontrolled wheelspin and scary operation on slick surfaces, then his system is not operating properly, as I said before. I refer you to comment #13 in the link I referenced in my previous post that demonstrates normal operation - the poster couldn't make his vehicle slide or spin out on snow/ice, whereas his Honda Passport would do just that.
All I can say is that if you are considering a HiHy, you should read the links and see that many more posters are satisfied with deeper snow performance than those not, and have found techniques that help.
And a lot of places have a lot more snow than the Denver area.
The reason the Highlander shuts down is to avoid overheating of the air-cooled rear motor with trying to "grind it out" - more likely with sand in summer than snow. Is it disconcerting? Of course, and deep snow with limited ground clearance is not a good combination regardless of your 4WD configuration.
Pete
You are right, I did miss the fact that he has winter tires in his post on the previous thread.
But this doesn't change the fact that the HiHy's system, functioning normally, gives as much power to each wheel as it can handle without uncontrolled wheel spinning. As soon as power exceeds traction in each wheel, independently, power is reduced to that wheel. That's the "intelligent" part. If it cannot make progress with the traction available, it shuts down - not for lacking adequate power to a wheel with more traction due to some sort of archaic differential design, which is his assumption.
If super10s is having uncontrolled wheelspin and scary operation on slick surfaces, then his system is not operating properly, as I said before. I refer you to comment #13 in the link I referenced in my previous post that demonstrates normal operation - the poster couldn't make his vehicle slide or spin out on snow/ice, whereas his Honda Passport would do just that.
All I can say is that if you are considering a HiHy, you should read the links and see that many more posters are satisfied with deeper snow performance than those not, and have found techniques that help.
And a lot of places have a lot more snow than the Denver area.
The reason the Highlander shuts down is to avoid overheating of the air-cooled rear motor with trying to "grind it out" - more likely with sand in summer than snow. Is it disconcerting? Of course, and deep snow with limited ground clearance is not a good combination regardless of your 4WD configuration.
Pete
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