Hi all.

I just read something on Edmunds.com that got me wondering about the AWD system of the 08 Highlander. I was hoping that you could comment on your experience driving in the snow/ice, specifically driving up/down hills. I'm especially interested in this statement: "There's no center differential and the V6 engine never provides power to the rear wheels".

If possible, it would really put it in perspective for me if you could compare it to other AWD systems you may have tried before, such Audi's Quattro, Volvo's Aldex (SP?) or Subaru's.

This is part of the articlle I found on Edmunds:
"Given the presence of the rear-mounted electric motor, the Toyota Highlander Hybrid is technically a four-wheel-drive vehicle. Most of the time, though, it functions in front-drive mode; the electric motor engages the rear wheels only when extra traction or torque is needed. Bear in mind that this setup differs significantly from the 4WD/all-wheel-drive system on the regular Highlander: There's no center differential and the V6 engine never provides power to the rear wheels. The upshot is that buyers shopping for a serious snow vehicle may not find the hybrid Highlander robust enough to meet their needs.".

This is the link to the article: http://www.edmunds.com/toyota/highla...08/review.html

Thanks!

The rear electric motor develops 67 hp and 96 foot-lbs of torque. That 96 ft-lbs is available all the way down to 0 rpms because electric motors develop full torque at stall unlike a gas engine. This is enough torque to wildly spin the rear tires in a deep snow condition if not moderated by the traction control.

You don't need a lot of torque in snow conditions. You need traction and ground clearance for deep snow. Get some good chains and store them in the vehicle just in case and you will be fine unless you slide off-road into a ditch or unless the drifts are so high your front bumper becomes a snow plow.

Some argue that the traction control system on the Highlander Hybrid may be a bit overzealous in preventing wheel spin in low traction situations. This applies equally to the rear drive and the front drive (which has an over abundance of torque and power from both the engine and electric motor on call.

The Highlander will not let you madly spin the tires when stuck in a snow drift or on glare ice for that mater. You can press the gas pedal all the way to the floor under these conditions and the engine will ignore your input and remain idling while the wheels may very slowly rotate trying to gently capture traction. This is very disconcerting to some who like to power themselves out of being stuck by smoking all the tires while rocks snow and mud go flying everywhere.

The rear electric motor develops 67 hp and 96 foot-lbs of torque. That 96 ft-lbs is available all the way down to 0 rpms because electric motors develop full torque at stall unlike a gas engine. This is enough torque to wildly spin the rear tires in a deep snow condition if not moderated by the traction control.

You don't need a lot of torque in snow conditions. You need traction and ground clearance for deep snow. Get some good chains and store them in the vehicle just in case and you will be fine unless you slide off-road into a ditch or unless the drifts are so high your front bumper becomes a snow plow.

Some argue that the traction control system on the Highlander Hybrid may be a bit overzealous in preventing wheel spin in low traction situations. This applies equally to the rear drive and the front drive (which has an over abundance of torque and power from both the engine and electric motor on call.

The Highlander will not let you madly spin the tires when stuck in a snow drift or on glare ice for that mater. You can press the gas pedal all the way to the floor under these conditions and the engine will ignore your input and remain idling while the wheels may very slowly rotate trying to gently capture traction. This is very disconcerting to some who like to power themselves out of being stuck by smoking all the tires while rocks snow and mud go flying everywhere.

So about 25 to 30%. Probably sufficient for most situations.

Now a stupid question from a beginner in hybrid technology. Is max power from the electric motor only reached when the battery at 100% of charge? In other words, if the battery is at 50% of charge, am I only getting 50% hp/torque from it?

Thanks!

Voltage, mostly, stays at a constant level as a battery discharges. It is that voltage which determines how much power is available, so the system should be capable of delivering close to %100 at all times. The battery is never allowed to fully discharge anyway. The system imposes artificial limits to maximize battery life.

Also, don't forget that the power doesn't have to come from the batteries, but can come from the generator as welll (in fact that is more efficient if the motor is already running and producing power).

Thanks guys, that's good information.

By the way, I tried the GMC Acadia yesterday. I heard they are going have a hybrid version based on what they are doing with the Yukon. The Acadia is quite a bit bigger than the HH and unfortunately the driving dynamics feel like it. Interior finish isn't as nice as the HH but let me tell you that GM came a long way in the last few years. I like the 60/40 split 3rd row seats and bigger cargo area with the 3rd row up. Of course, power is nowhere near what the HH feels like. Hopefully the hybrid powertrain will really improve that.

[quote=Don R;156435]The rear electric motor develops 67 hp and 96 foot-lbs of torque. That 96 ft-lbs is available all the way down to 0 rpms because electric motors develop full torque at stall unlike a gas engine. This is enough torque to wildly spin the rear tires in a deep snow condition if not moderated by the traction control.



Although the rear motor is theoretically capable of developing 67 HP and 96 ft-lbs torque, the HiHy's traction battery is a 45 KW/60 HP max sustained output unit, and this is the maximum electric assist possible between the two motors. Thus the total HP rating of 268, with 208 delivered by the engine.

I suspect the reason the front motor's capacity is so large (123 KW/165 HP) is for reliability as it is used so frequently. And maybe this makes its ability to start and spin the ICE up to speed quicker when demanded, with a transient battery draw of more than 45 KW.

Pete

[quote=PineywoodsPete;156788]

[quote=wwest;156839]
Although the rear motor is theoretically capable of developing 67 HP and 96 ft-lbs torque, the HiHy's traction battery is a 45 KW/60 HP max sustained output unit, and this is the maximum electric assist possible between the two motors. Thus the total HP rating of 268, with 208 delivered by the engine.

You're forgetting that the front generating capacity can be "diverted" (battery charge mode) to help power up the rear drive motor.

I suspect the reason the front motor's capacity is so large (123 KW/165 HP) is for reliability as it is used so frequently.

No, it's so that when that "motor" is acting as a generator it can more rapidly recharge the hybrid battery while simultaneously providing FULL power to the rear 67HP motor and whatever HP is needed for the other "front" motor.


Your point about oversized front motor being more related to regen capacity is well taken.

But the total sustained combined power of the two motors cannot exceed 45KW/60HP, as that is the maximum sustained electrical energy flow the battery will supply - analogous to the maximum total air/fuel mixture flow possible in an ICE, which is the limiting factor in power output regardless of engine displacement.

And that's why the 4WDi version has no more total combined HP at 268 than the FWD, in spite of the additional 67 HP motor.

Pete