Drive by wire, gas and electricity--the technology of a Prius

Here's how they work

The Toyota hybrid cars are unique for two reasons. Most obviously: the gas-electric hybrid technology. But the cars also are the first mass-produced fly-by-wire vehicles in the world.

Hybrid Technology—The car has a very small Atkinson-Miller cycle gas engine up front, not your standard auto [Otto cycle] engine, but something much smaller and more efficient. It has a large rechargeable NiMH battery under the back seat connected to a 50kw power electric traction motor. Essentially, computers in the car choose between gas and electricity, depending on which is more efficient. If you are pulling out of a parking spot, the battery sends power to a traction engine, which moves the car forward. It runs silently (owners call it “stealth mode”) until about 8-12 mph, when the gas engine kicks in. Then, depending on what you want the car to do, either you are using gas, electricity or both. The computers decide. An LCD display on the center screen tells you what is happening. When you pull up to a traffic light, the gas engine dies, which can really be disconcerting because suddenly everything is totally silent. The gas engine starts again when you pick up speed. On the freeway, you are usually running on both the gas and the electric engines. In the city, it is rated at 60 mpg because most of the forward motion is on electricity. It all operates smoothly and you stop paying attention after a while.

The computers watch the battery and when power levels get below a certain point, power from the gas engine is diverted to recharge it so you never run out of battery power and you never have to plug it in. (You actually can’t plug it in; there is no way to do it.) The battery also is recharged when you coast and heat from the brakes is transferred into energy and diverted to the battery.

There is no starter; the little gas engine doesn’t require one. Because the heat is bled off the brake lining it is likely you never have to replace the brakes—or at least not nearly as much as you would with a normal car. There is no alternator. The transmission is a continuous belted system without gears that only have one direction: forward. It’s called a Planetary-Continuously Variable transmission (power-split device). Don’t ask. To go in reverse, you need the electric motor. And, because the torque on electric motors is so good, acceleration is not shabby.

Because you can get a readout of gas mileage on the display continuously, drivers learn to “drive to the display,” meaning your mileage improves the more you drive the car. The highest achievement among owners is to get the car up to 40 mph in stealth mode. I’ve done it once--down hill.

The most dangerous part of driving a Prius is that in electric mode it is totally silent, meaning people walking around in the parking lot can’t hear you coming. The decision is whether to honk the horn and scare the hell out of them, open the window and say hello or put the radio on loud.

Fly-by-wire—The hardest thing to get used to is starting up the Prius. You do not start it the way you do a normal car; you boot up the computers, turning the key to the right and back while the LED display says “ready.” (The new Prius uses a button, not a key). Parking lot attendants were often stumped by it, although they seem to know better now.

Say you are sitting at a stoplight. You put the car in neutral and stomp on the gas pedal. If you are in a normal car, the engine roars and maybe black smoke comes out of the exhaust. Do it in a Prius and absolutely nothing happens. The car’s bank of five computers takes a vote and decide that revving the engine is a stupid thing to do, wasteful if nothing else, and ignores your command.

Everything in the car goes through computers, just as if you were piloting an Airbus. The five computers monitor everything constantly and vote on what to do. They decide when to kick in the gas engine, when to rely on the battery, when to recharge, when to shut down the gas engine. Presumably, all votes have to be unanimous. The steering goes through computer-controlled hydraulics, as do the brakes. Everything you do goes to computers first, then to the driving part of the vehicle. Every moment, the computers (we named ours Totoro) decide the most efficient thing for you to be going and do it.

The hybrid technology, particularly the very expensive battery, is warranted until 100,000 miles. A taxi driver in Vancouver got his taxi Prius to more than 250,000 miles before Toyota bought it back from him to inspect. His battery was still going.

[Honda has a hybrid technology as well but it is not advanced as Toyota’s, using the battery only as a supplement to the gas engine.]

Prius owners include some of the strangest people I know, folks who have relationships with their car right out of a J.G. Ballard novel. Fortunately, that means some of them maintain resources that are invaluable. The best, if not the weirdest, is the website run by a man named John in Minnesota [his last name is a mystery], who is a combination computer programmer, Prius fanatic and Trekie, which should surprise no one. His site, if you want to know anything about the Prius or its technology, is amazing, far better than anything Toyota maintains. He has owned several of the cars, has monitored them every minute of their lives and has recorded same. The word “perverse” comes to mind, but whatever. If you have questions, see John.