Mild HybridsEver 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 WorksThis 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.