A computer on wheels

Toyota’s Prius is a fantastic gadget-and it’s not a bad car, either. Gadgets hed: A computer on wheels dek: Toyota’s Prius is a fantastic gadget-and it’s not a bad car, either. by Ken Henningsen

Last fall, I finally started looking to replace my faithful 13-year-old Honda Accord, which was going on 200,000 miles. Being both cheap and a bit of a tree-hugger, I was very much interested in the introduction last year of the first two production gas/electric hybrid vehicles to hit these shores–the Honda Insight and the Toyota Prius. Both promised outstanding gas mileage and very low emissions, and I knew I had to have a look. I quickly discovered that the Insight was too small to meet my needs, so I zeroed in on the Prius (which, besides being a very practical sedan, is a great gadget). It was on the latter score that I proposed an article to my editor, who, to my surprise, agreed. What follows is, as far as I know, the first auto review in COMPUTERUSER’s history.

A more powerful version of a model sold in Japan since 1997, the U.S. Prius is a four-door sedan that’s shorter than a Corolla but actually roomier inside (except in the trunk, where the battery pack encroaches a bit on the space). Where Honda has a pretty narrow market for its tiny two-seater, Toyota is aiming squarely at the middle-class family. Both Insight and Prius come loaded at a little less than $21,000, but the Prius can carry four adults comfortably–five without serious discomfort. With a conventional steel body and more power, the Prius weighs in at nearly 1,000 pounds more than the Insight’s svelte 1,880 pounds.

The Prius’s EPA figures are predictably lower than the Insight’s first-place numbers of 61/70 miles per gallon: 52 city, 45 highway. (No, that’s not a misprint; its city figures beat its highway numbers in the EPA cycle because of engine shutdown and regenerative battery charging.) However, users are reporting more realistic averages from the high 30s to mid-40s, with city mileage lower than highway. Over about 300 miles of mixed driving in a borrowed Prius, I recorded an average of about 37 MPG in temperatures mostly in the single digits-cold hurts mileage on all cars.

The Prius is a fascinating car, both mechanically and electronically. It’s a combination series/parallel hybrid, depending on its operating mode at any given moment. (A pure series hybrid uses an engine to drive a generator, which charges the batteries and drives a motor that powers the wheels. In a parallel hybrid like the Insight, both engine and motor drive the wheels directly.) The Toyota Hybrid System (THS) consists of five major components.

First, a lightweight, 70-horsepower four-cylinder engine provides all power for the car, directly and indirectly. This engine is worthy of a treatise by itself, with many features optimized for the hybrid environment and low emissions. These include variable intake-valve timing (electronically controlled to adapt to varying loads), Atkinson-cycle design (which permits a high effective-compression ratio on regular gas), and electronic throttle control (to automatically provide engine output as needed by the THS).

Second, a generator/motor (which I’ll call the generator) allows the engine to charge the batteries and provide juice to the traction motor. It also acts as a motor to instantly start the engine when needed.

Third, a 44-horsepower motor/generator (which I’ll call the motor) is directly coupled to the front wheels through a transmission and differential. This motor is powerful enough to power the car at lower speeds by itself, and on deceleration, the wheels drive it as a generator to provide regenerative braking, recharging the batteries. Fourth, a 110-pound, 274-volt NiMH battery pack stores and releases electrical power as needed. Finally, a “power-split device” connects all the mechanical drive-train components together.

The way these components play together is an engineering tour de force. The engine, generator, and motor are connected to concentric shafts, occupying–with the power-split device–a space no more than that of the engine and transmission in a conventional transverse front-wheel-drive power plant. The power-split device is a planetary gearset, much like that of a standard automotive differential.

For the technically inclined, the engine is on the planetary carrier, the generator is on the sun gear, and the motor is on the ring gear. In operational terms, this setup lets each component operate both independently and cooperatively as the situation demands. It also acts as a continuously variable transmission (CVT), allowing the engine speed to be optimized for power or efficiency (and limited to 4,500 RPM, to reduce stresses and allow lighter components). This is all done efficiently enough to earn the Prius SULEV (Super ULEV) status under California emission rules.

Just as the pilot of a modern jet fighter can’t fly the plane at all without electronic help, the Prius drivetrain is too complex to be directly controlled by the driver. Virtually every major subsystem (and many minor ones) has its own Electronic Control Unit (ECU)–a computer, in other words. The major ECUs communicate with each other over high-bandwidth channels–a system bus, in PC terminology. Every orchestra needs a conductor, and in the Prius that’s the Hybrid ECU, the unit that directs the activities of the Engine Control Module, the Motor ECU, Battery ECU and Inverter ECU. (The inverter converts the three-phase AC of the generator and motor to and from the DC of the batteries.)

Other subsystems consist of “smart” components in the equivalent of a LAN, eliminating the equivalent of 40 circuits’ worth of point-to-point wiring. For example, instead of discrete wires from each of the power window switches to its corresponding motor, each switch sends a coded signal through a common network–a signal only its own window motor will act on. Components of this network include the Body ECU, Engine ECU, Air Conditioner ECU, and Display ECU, among others. As mentioned, the power windows are on this system, as are the remote power door locks.

Car/computer interface

In keeping with its other techno features, the Prius has an LCD touchscreen in the middle of the dash that displays a graphic of the power flow in the hybrid system, a histogram of the instant and 5-minute average mileage over 30 minutes, and even the outside temperature. Another use for this screen is control of the AM/FM/cassette (and CD player or changer, if installed–two of the few options). It’s also set up as the display and programming interface for an integrated GPS navigation system (an option not yet available here).

A separate pod–also in the center of the dash, but at the base of the windshield–contains the digital speedometer, odometer (switchable with two trip meters), gas gauge, and indicator/warning lights. There are no instruments directly in front of the driver; Toyota designers contend that this central/forward location (also used on the Echo) minimizes re-focusing from the road and eliminates viewing interference from the steering wheel. Some reviewers have carped about this location, but I found it very easy to adjust to.

Performance upsides

So how does all this high-tech stuff work? Perhaps the most remarkable thing about the Prius is how unremarkably it goes about its business. It’s no stoplight dragster, but it has adequate power, particularly with the kick from the electric motor in passing situations (at highway speeds, the engine provides most of the normal propulsion). Handling feels secure, and ride is firm but quiet and comfortable. Besides what the displays are telling you, there are only a few reminders (such as engine noise that doesn’t always match your speed) that this isn’t an ordinary car when you’re driving at speeds above 20 MPH or so. The real fun happens below that speed.

When the engine is cold, starting the car seems pretty normal (except there’s no perceptible cranking or “catching”), but when it’s warm, turning the key will only illuminate a “Ready” light in the speed pod, signifying that all systems are go. The engine only runs when it’s needed or needs to warm up. For instance, the air-conditioning compressor is engine-driven, so if the air conditioner is set to “Max” the engine will run continuously. Likewise, the engine may run if cabin heat is required, though this need is reduced with an electric coolant pump (to circulate warm coolant to the heater) and electric heating elements that provide some instant heat in a cold car.

(Incidentally, when the climate-control system is set to “Auto,” a variety of ECUs cooperate to maintain your preset temperature, using several temperature sensors and even a sunlight sensor.)

Both the power brake booster and power steering are electrically operated, so these can function with the engine off. Floor the “gas” pedal in Park or Neutral and nothing happens; it’s only an input device to the Hybrid ECU, and the latter concludes that nothing needs to be done. Shift into reverse, and you’ll silently glide backward. There’s no reverse gear; the electric motor handles this chore alone.

Shift into Drive and keep a light foot on the accelerator, and with a full battery you can drive for several miles at 20 MPH or even faster on electric power alone. A favorite pastime of Prius owners is to see how far and fast they can go in “stealth” mode, which is silent enough to startle pedestrians. Put your foot in it (or drain the battery a bit), and the engine will kick in to add its 70-horsepower to the mix. This happens very seamlessly, and around town–or decelerating on the highway–the engine will stop when it’s not needed; often the only way to tell what’s going on is to check the graphic display. Pull up to a stoplight and you’ll often sit in vibration-free silence–a bit alarming until you learn to trust the car to start up on command. To provide reassurance, the Prius will creep or hold on a hill (using the electric motor) when you take your foot off the brake in Drive, just like a standard automatic.

One thing everybody notices is the braking. Light pressure on the brake pedal engages the regenerative braking, which tends to be a bit more aggressive than pure friction braking with similar pressures, making the brakes feel touchy at first. Likewise, when you drop below about 10 MPH, regeneration slows the car faster than you expect. However, both effects are mild, and modulating the brakes to achieve the intended result soon becomes second nature. Four-channel antilock disk/drum brakes are standard, as is automatic traction control that uses the brake and hybrid drive systems to sense and control wheel spin. Both work very effectively.

Performance downsides

Alas, no car is perfect, and the Prius is no exception. For instance, the shift lever is an odd, nearly vertical handle sprouting from the dash. Many people dislike its appearance, but my complaints mainly have to do with ergonomics: It obscures several controls near the LCD display, and at night I’ve bumped the lever into Neutral while reaching for the radio controls. I’d much prefer a console shifter.

Also, the controls surrounding and residing on the touchscreen display could use some ergonomic re-thinking. Some equipment available elsewhere isn’t offered here yet, including the GPS mentioned earlier, side airbags, a fold-down rear seatback, and most unaccountably, cruise control (for which the car is pre-wired). The latter is the subject of much online gnashing of teeth, especially since it’s offered in Canada. After installation instructions were posted by one intrepid owner, others have spent $500 or so (twice the option price) at the Toyota parts counter for the bits and pieces-including a new steering wheel-and installed their own.

Another question about a car this new and complex is that of reliability. However, those concerns are allayed by the facts that the design is essentially four years old, Toyota provides an eight-year/100,000 mile warranty on the hybrid system (including the NiMH battery pack)–and that, of course, it is a Toyota.

Do I sound like there’s a Prius in my future? You bet; I’m saving my pennies for a 2002 model (which should get most or all of the options mentioned above). That is, unless my head gets turned by the HV-M4 minivan Toyota recently showed in prototype at the Tokyo Motorshow–a Prius-like drivetrain up front and a second electric motor in the rear for hybrid all-wheel drive. It even has a pop-out 120 VAC outlet in one fender, to tap some of that wealth of juice when it’s not needed for powering the car. Hmm, why not 240 VAC? With all that power available, one of these babies could electrify your whole house in an emergency, or not only get you to that remote cabin, but also power it up while you’re there. Welcome to the 21st century.

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