Home - AFV Events - Test Drives - Toyota Prius

RSS feed for altfuels Find us on Facebook Follow us on Twitter Google+ page for altfuels

Toyota Prius Hybrid-Electric Car from EV Rental

The Toyota Prius hybrid-electric car has been available in Japan since late 1997, and in the U.S. since the middle of 2000; EV Rental Cars had planned to add them to their fleet for months, and finally got their first ones in December (there has apparently been strong demand, keeping ahead of supply, as there has also been for the Honda Insight hybrid). I finally made time to rent one for a test-drive on 5 February 2001; the car is dangerously fun!

Toyota Prius and me

As you can see, the Prius is almost exactly the same size and proportions as the Toyota Echo; I still have trouble telling them apart at a distance, though there are of course distinctive features (the converging lines in the hood, a slightly longer wheelbase) that can be seen even if the lettering on the rear is not visible. The engine is the same size, a 1.5-liter 4-cylinder, but it is tuned more for economy than power; nonetheless, the Prius has more total power available than the Echo because, unlike the Honda Insight, the electric motor in the Prius' hybrid drivetrain can produce a large fraction of the power of the gasoline engine! As I discussed in my driving report on the Insight, its small electric motor cannot drive the car by itself, but instead contributes regenerative braking (it can run as a generator to feed energy of motion back into the battery pack as the car slows down, rather than letting all that energy be wasted as heat in the brakes) and the ability for the gasoline engine to restart almost instantly. The Prius, by contrast, can run on electricity from its batteries alone, if demand is relatively light; I was able to accelerate to over 25 MPH (gently, and on a flat road!) without the gasoline engine needing to start up to provide power, and while cruising at 40 MPH (also on a flat stretch of road) the engine was again able to shut off and let the electric motor sustain motion.

Prius Energy Monitor

Here's how you keep track of what's working and what's resting, since the shutdown and restart of the gasoline engine is very smooth and hard to notice unless you're stopped. This is a small (approximately 6" diagonal) touch-screen monitor built into the center of the dash; the arrows show where power is flowing. When this photo was taken, the car was stopped (of course, since I was both the driver and the photographer!) and the engine was turning the electric motor as a generator to "top off" the battery pack. Under light throttle, orange arrows showed power moving from the batteries to the wheels via the electric motor; under heavier acceleration, the engine would also feed power to the wheels. When the gasoline engine was driving the wheels, sometimes it would feed power to the electric motor to send to the wheels in addition to or instead of the power that was coming from the batteries, and sometimes it would send power back to the batteries by the route shown in the photo above. Then when the car slows down, the wheels feed a blue arrow of power to the electric motor, which recharges the batteries to provide regenerative braking. You can see why I said the car is "dangerously fun"--one could easily run off the road while watching the changing patterns on the monitor!

Prius Power Consumption Monitor

That's not the worst of it, though; in addition to controls for the audio system and (optionally) a GPS mapping system, the monitor also can display a history of fuel consumption for the last half hour, averaged over five-minute intervals. The "Current" MPG reading at the right is zero when the car is not moving, is off the top of the scale when the car is moving but the gasoline engine is off, and otherwise shows the fuel economy you're achieving moment by moment.Then it's averaged over five minutes, and displayed on the chart at the left; the little yellow "E" symbols show how much energy you've put back into the battery pack using regenerative braking. This chart analyzes my drive of 5.5 miles from work to my apartment, and adding up one whole and two half "E" symbols, each worth 50 watt-hours (Wh), it looks like I've saved 100 Wh (one tenth of a kilowatt-hour, or kWh) that would otherwise have been wasted to heat up the brakes. An efficient electric drivetrain can use 200 Wh, or even less, to go one mile; thus the amount of regenerated power shown here represents about half a mile out of my 5-mile trip, or about a 10% boost in fuel economy. This display is even more dangerous than the Energy Monitor screen above because of the video-game aspect: you want to keep an eye on it as you try to push those bars as high as you can, while collecting "Power-Ups" for using regenerative braking!

The EPA fuel economy rating of the Prius is 52 MPG city and 45 MPG highway; it has better city than highway fuel economy, unlike a conventional car, because its biggest power need is for shoving air out of the way, and this costs more fuel at higher speeds. In a conventional car, the inefficiency of the gasoline engine at low loads and while sitting at idle in city traffic wastes more than enough fuel to increase consumption in the city, even though air-resistance losses are smaller at low speeds. This is actually reflected in the graph above, in which I can trace out the pattern of my drive home. The first five minutes (from 25 minutes ago to 20 minutes ago) had low fuel economy because the gasoline engine stays on after a cold start, even when the car is stopped and the batteries don't need recharging, just so it can warm up. The second and third periods of five minutes were in stop-and-go traffic, exactly where this car is most efficient, so though the warm-up period of continuous engine-running extended into the second period, these two bars are much higher than the first. The fourth five-minute period was mostly steady cruising at 40 MPH, so fuel economy came down a bit as speed picked up (and I got little energy back from regenerative braking), and the last five-minute period saw me coasting down a couple of long hills to my apartment near the ocean, which pushed fuel consumption down and regenerative braking up (I earned a full "E" symbol in this period!). See what I mean about a video game? Don't let the low average fuel economy (35.2 MPG over 16 miles) put you off, by the way; this included three cold starts, plus my usual lunchtime demonstration of the vehicle to my co-workers, during which time I floored the accelerator a few times to demonstrate that, no, this is not an overgrown golf cart. During normal short-commuting use, with a cold start about every five miles, I got over 40 MPG; a longer commute in city traffic, with the vehicle warmed up, would probably result in figures closer to the EPA's 52 MPG.

Toyota Prius at gas station

So, is it worth it to get a $20,000 Prius with 52/45 MPG fuel economy instead of an Echo with 32/38 MPG economy for several thousand bucks less (with comparable options--of course, I don't know enough about the Echo to comment on ride, handling, fit and finish, etc.)? Well, gas prices have come down about ten cents a gallon since I shot a photo in March 2000 of the Insight under this same fuel-station sign, but they went up quite a bit before they came back down to what you see here, and the betting is that they will head up again when the "driving season" resumes this year. At this price for regular gasoline and with typical driving patterns, the EPA fuel economy website calculates that you'd save about $185 a year on gasoline by choosing the Prius--so it would take you over a couple of decades to pay off the MSRP difference with fuel savings. Of course, during that time you'd also be emitting about one and a half tons of carbon-dioxide less each year, contributing to U.S. energy security, and buying insurance against gasoline prices going up again; and over the next few years we can expect hybrid-electric vehicles to come down in price as production volumes rise (for example, Honda will begin offering the Insight drivetrain in their popular Civic line of cars in a year or so, and Ford will introduce the first hybrid-electric SUV in the 2003 model year), so the math will get better as time goes on. Those who (like me) are partial to pure battery-electric vehicles will also be grateful to you for the "trickle-down effect" as hybrid-electric vehicles bring volumes up and costs down for expensive, shared components like NiMH batteries and power-control electronics! So it's your choice; and hey, until a year ago you didn't even have the choice of a hybrid-electric car...

Back to AFV Events PageBack to AFV Events Page

Back to Fueling StationBack to Fueling Station

Site MapSite Map

Contact MeContact Me


RSS feed for altfuels Find us on Facebook Follow us on Twitter Google+ page for altfuels

Built With BBEdit Valid XHTML 1.0 Transitional

new 6 February 2001