We took some time with the 2006 Toyota Highlander LTD Hybrid 4WD-i V-6, driving it to and from the office, winding through mountain twisties, and impressing our friends with Toyota's latest high-tech ride. We have a kind of picture-in-picture approach to this article. We're going to talk about our experiences with the Highlander Hybrid while we concurrently run an explanation of what all this hybrid stuff is about.

If you know Highlanders, then you have a good idea of what the Hybrid version looks and feels like. It's a mid-sized SUV that exudes that competent, eager-to-please demeanor that has been the hallmark of Toyota design for some time. We liked the paint color; Bluestone Metallic they call it. This being the Limited model, the interior was well appointed, with tan leather seats and a pleasing layout. The Highlander squeezes in seven passengers, with two captain's chairs in the front, a 60/40 split in the second row, and a third row with its own heating system and cupholders. Both the second and third rows recline and fold flat to maximize the Highlander's cute-ute cargo capacity.

Sitting in the driver's seat wasn't so bad for those of us who are long of leg. In fact, we would even characterize the legroom as "adequate" for the vertically endowed. Larger riders may feel like they tower over the low-lying interior, but otherwise, it's about what you would expect. Dominating the center is the LCD touchscreen through which you can control the JBL Premium AM/FM/cassette/six-disc/eight-speaker audio system, use the navigation system, access a calendar, keep tabs on our trip and fuel consumption, and more. We'll touch on this again later.

Starting the Highlander's Hybrid Synergy Drive means unlearning a lifetime of every tactile experience you ever had with an automobile. The routine went something like this: We walked up to the Highlander Hybrid after a hard day at the office. Unlocked the door. Dropped into the seat. Slid the key into the ignition and turned it. Thought about dinner. Turned the ignition again. Considered getting some work done after dinner as a way to suck up to the boss. Turned the ignition...again? Reconsidered working at home, screw the boss. Turned the ignition...again! No vibration, no exhaust note. Is something wrong with this thing?!

Nothing was wrong. Looking at the power gauge to the left of the IP, we saw that the electric motor was ready and awaiting our command. A tentative touch of the accelerator allowed us to slip quietly down the road to 25 mph on electric power only. A confident mash on the pedal led to, well, let us tell you: Driving the Highlander Hybrid is like riding an electric rocket.

The Highlander Hybrid total system cranks out 268 effective horsepower. Horsepower from the 3.3L V-6 is 208 at 5600 rpm, while torque comes out to 212 at 4400 rpm. The breakdown for the electric motors is more interesting. Horses for the one that drives the front wheels is 167 at 4500 rpm, and the motor for the rear is 68 at 4610 to 5120 rpm. Torque gets better: Try 247 lb-ft at 0-1,500 rpm and 96 lb-ft at 0-610 rpm. Like the rpm numbers? You see, an electric motor has no torque "curve." It has a horizontal line. In other words, you get 100-percent torque from the second you push the accelerator.

Combine that instant torque with the electronically controlled continuously variable transmission coupled to the V-6, and you get seamless, inexorable acceleration that doesn't necessarily push you into your seat, but it does destroy any vestigial associations between "hybrid" and "golf cart." Weaving through traffic was a breeze, not the hurricane of a supercharger or gale of a high-displacement mill, but the torque was always available to zip around some 60-mph slowpoke. We did make the tires chirp by mashing the pedal while turning corners, and the Highlander Hybrid did beat our borrowed Honda Ridgeline off the line in an impromptu test of both vehicles' holeshot. Toyota claims a 0-60 of 7.3 seconds for this model.

The Highlander Hybrid's acceleration made scooting through the mountains kind of fun. The vehicle was stable going around the curves, although we wouldn't call the suspension performance-tuned. We noticed the hybrid system's battery got sucked almost dry very quickly during the uphill leg, necessitating an increased reliance on the gas engine. Driving downhill was facilitated by sliding the shifter to B, which provided the "engine braking" that you don't get anymore from the Hybrid version of the Highlander, and the gas engine hardly turned on at all. Fuel economy through our 105-mile trek through the mountains was 21.5 mpg, barely lower than the 22.85 mpg we got from combined street and highway driving.

3 Hybrid Systems
There are three different kinds of hybrid powertrains out there: series, parallel, and series/parallel.

Series Hybrid: What you have here are three motors running in series. An internal combustion engine drives an electrical generator, which, in turn, powers an electric motor that ultimately spins the vehicle's wheels. One of the hallmarks of this approach is that the internal combustion engine can run at a constant, optimal rpm while it turns the generator, allowing the engine to run efficiently and durably. Series hybrids don't necessarily require a mechanical transmission, either, since the electric motor doesn't need gears to stay in its optimal powerband. Diesel train engines use this sort of arrangement; the diesel motor powers the system, while the electric motors do the actual work.

Parallel Hybrid: Both the internal combustion engine and the electric motor drive the wheels of the vehicle. There is one electric motor. And since generators and motors are basically structured the same way, the motor does the double duty of driving the wheels and charging the batteries. The drawback is that the electric motor can't do both of these jobs at the same time, which is why a parallel hybrid can't power the wheels with electric power alone and charge the battery at the same time, but it can rely on just the internal combustion engine to propel the vehicle.

Series/Parallel Hybrid: This combines the attributes of both approaches. Comprised of an internal combustion engine and two electric motors, the system can propel the vehicle with the engine only, electric motor only, and with both, and charge the battery at the same time. Software decides what the most efficient propulsive mix is needed for the conditions at hand. The Ford Escape Hybrid (and its cousin, the Mercury Mariner Hybrid) and the Toyota Highlander Hybrid are examples of this.

Mild Hybrids
Ever wonder what a mild hybrid is? An expedient way to attach the word "hybrid" to an automaker's lineup in order to buy them some time to produce a full hybrid system? Not necessarily. What it does is shut off the internal combustion engine when you aren't actually using it. For example, the Chevrolet and GMC hybrid pickups are mild. Their gas powerplants propel them, burning fuel just like they always did and giving you all that power you are accustomed to. The hybrid part kicks in when you brake to a stop. At about 15 mph or so, the engines shut off. When you lift your foot from the brake pedal, the engines start again. What you get is a mild fuel savings and perhaps a mild reduction of emissions.

Back to the center console monitor. We were able to keep tabs on the goings-on of the hybrid system via two screen views on the touchscreen. One view tracks the amount of electrical power expended and regenerated by the hybrid system using, among other things, little car icons arrayed like a bar graph. Yawn.

Another view was more fun to watch. It's a representation of what the powertrain is doing at any particular time. As we were often stuck in traffic, we had plenty of opportunities to glance at the screen to see the wheels spin, the battery level go up and down, the two electric motors come on and off, the gas engine kick in. It looked chaotic at first until we started to see a pattern. What we were watching was the hybrid system trying to allocate power from the electric motors and gas engine to keep the batteries charged and the drivetrain turning as efficiently as possible. Sophisticated software makes this all happen, and without it today's hybrid systems wouldn't be very effective. Remember that recall from late last year of Toyota Priuses? That fancy software would sometimes hiccup and shut down the engines for no reason. Don't worry, they fixed that. Hey, nobody's perfect.

So what's the price of Toyota's Highlander Hybrid 4WD-i V-6? Without the destination, $42,146 as tested. That includes the options of the navigation, hitch receiver (tows 3,500 pounds), and the Preferred Accessory Package (carpet/cargo mat set, cargo net, first aid kit, VIP glass breakage sensor).

How The Highlander Hybrid Works
This is a summary of Toyota's explanation of how the Highlander's hybrid system works.

There are three electric motors employed in the 4WD-i models. Two of them (called MG2 and MGR) act as generators (charging the batteries through regenerative braking) and propel the front and rear wheels of the vehicle respectively. Meanwhile, another (MG1) simply acts as a starter for the gas engine and a generator (charging the batteries, which powers the other two motors as needed).

The electronically controlled continuously variable transmission distributes power from the gas engine and MG2 to the drive wheels (CVT-type trannys don't use specific gear ratios to accomplish this). A power split unit diverts some power to MG1 so it can act as a generator. A motor speed reduction unit reduces the speed of MG2 and increases its torque, boosting acceleration performance.

MG1 also controls the output speed of the transaxle through the CVT without clutches or viscous couplings. This is one of the reasons you don't feel the unit shifting.

The electric 4WD-i system uses a separate electric motor (MGR) at the rear to provide more torque as needed. The system electronically varies front and rear torque distribution depending on driving conditions. MG2 produces peak torque from 0-1,500 rpm, giving the Highlander Hybrid extra oomph at lower and middle speeds.

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