Toyota Prius Plug-in Hybrid - First Drive Review


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DRIVING DOWN THE ROAD
WITH CAREY RUSS

Toyota Prius Plug-in Hybrid - First Drive

I've just spent an unusual week with a Toyota Prius PHV (Plug-in Hybrid Vehicle). It may be the future of the Prius, but you can't go out and buy one. Yet… It's one of 160 factory plug-in conversions that have been in use by universities, government agencies, car-sharing programs, and corporate fleets for the past year as a beta-test program for Prius development.

Inputs from driver experiences will be used in design and construction of future Toyota hybrids. While there have been aftermarket plug-in Prius conversions, this is the official factory PHV program. I'll tell of my experience in a moment, but first some background.

If you're not familiar with the term "plug-in hybrid", it means an internal combustion-electric hybrid that can be also recharged by connection to the power grid, so it can operate as an electric vehicle (EV) to a greater extent. This may require an extra battery pack dedicated to electric propulsion. If that sounds more than a little counterintuitive since the rationale for a hybrid its independence from an external electrical supply, a plug-in hybrid has one major advantage over a purely electric vehicle -- when the electric-power battery runs down, the plug-in still runs as a regular hybrid. As long as there's fuel in the tank, no problem. No fuel? Call a tow truck, like anyone else in that situation. Compared to a regular hybrid, the PHV can operate under electric power for a greater range or at higher speeds.

The Prius's nickel existing metal-hydride battery pack was not designed to be recharged by a connection to the power grid. It's recharged by the traction motor-generator during operation of the car. So a plug-in Prius needs extra battery capacity for plug-in electric-mode power, and modification of the car's electronics to allow use of that power. In this case, three additional lithium-ion (Li-ion) battery packs are added, one primary and two secondary, with the primary and one of the secondaries giving power for EV mode. When the first secondary discharges, the second is brought online. When it and the primary discharge, it's back to regular hybrid mode until recharging.

There are advantages and disadvantages to the plug-in conversion. On the plus side, an EV or plug-in hybrid can be charged from the power grid. Its charging circuitry can be designed and built to allow charging from regular 110 or 220VAC house power, without need for an expensive special charging station. Electricity is less expensive per mile traveled than fossil fuel.

Negatives? The additional battery and control circuitry, plus physical and cooling system modifications add weight and cost. Weight is the enemy of efficiency, so too much extra weight and more power will be needed, which will require more power storage (battery) which will mean more weight… and the greater the battery capacity, the longer the charging time for any given voltage.

Meaning that there will be a practical upper limit on battery size, and hence range. Note that the same constraints also apply to larger fuel tanks.

The necessary compromises are not fatal to the plug-in concept. For many people, most driving is relatively short trips. The worst thing you can do to an internal combustion engine is drive so short a distance that it never reached optimum operating temperature. If you make a lot of short trips, an EV is a good choice of vehicle -- but battery range can vary wildly with driving style, terrain, and temperature. There is currently little recharging infrastructure, and current batteries take time to charge, even for short distances. So if you miscalculate the range of your EV, it's tow truck time.

The plug-in obviates that, as long as there's also fuel in the tank. And it can work as well as any regular internal-combustion car for long-distance transportation, as it reverts to regular hybrid mode when the EV battery is discharged. So think of it as two cars in one - an EV for short-distance, around-town driving, and a standard hybrid for that and longer distances. That takes up less space in your garage, and takes less from your budget.

How does it work and how well does it work?

Fine and just like any other Prius, if you want the short answer. While it's possible to never charge the Li-ion batteries and just use it as any other Prius, that would be missing the point. The only way to tell Toyota's plug-in from a regular Prius is an extra fuel door-sized flap on the left front fender. (The regular fuel door is on the left rear.) That's the charging port. The charging process is simple - plug the included charger and cable into a grounded wall socket, 110VAC for a three-hour full-charge time or 220 for 1.5 hours. I unplugged my dryer, ran the cable out the window into the driveway, connected it to the car, and in the advertised three hours the charge light on the dash went out, indicating a full charge.

Toyota says that the EV-mode range is 13 miles. While this doesn't sound like much, it's enough for many daily tasks, or even a short commute -- especially if the car can be recharged during work. And in reality, "EV mode" range can be considerably longer than 13 miles. This is because the engine may come on during "EV" mode, and provide some motive power. Under more than three-quarters throttle acceleration, when climbing a steep hill, over 60 to 70 mph, when the air is unusually hot or below freezing, or when the air conditioner is in use on a hot day, expect the engine to come on at least occasionally. As with a regular Prius, that's usually so subtle that you'll have to look at the power display to tell.

EV purists may complain, but that also means the "EV" range can be more than 13 miles. I found it to be closer to 25, on trips that included both city and 70mph highway driving. Yes, the engine came on at times. But a look at the bar-graph fuel consumption display, divided into one-minute intervals, showed plenty of "100" mpg -- the maximum displayed and meaning essentially no gasoline consumption -- with the balance ranging from 75 mpg to a low of 25 during full-throttle acceleration up a steep onramp. EV mode regularly returned over 75mpg average, a good boost above the standard 50. Think of it less as an electric vehicle than as a hybrid that operates electrically more than, and at higher speeds than, previous hybrids.

On the road, the PHV feels and works like any other Prius. The suspension is soft, but well-damped, steering doesn't have much road feel but works well, and the interior is quiet. There are some unusual sounds related to system cooling, but this is an experimental test vehicle -- which from Toyota means that's its made as well as any standard production vehicle. The PHV does feel heavy, but only because it is. Official weight has not been disclosed, but the Li-ion batteries add 330 pounds, and their cooling system adds even more. It's noticeable when cornering, but the suspension seems to have been modified to deal with it well. There is no negative impact on fuel economy. No negative at all, really, except that you can't buy one. Yet.

You'll have to wait until early 2012 for an official Prius PHV, which will be introduced first in the parts of the country where the Prius has proven to be most popular -- California and the Northeast. As availability increases, it will spread across the country.

Will the production version be like the experimental model I drove? I expect it to be similar in concept but somewhat different in detail. Toyota is not known for resting on its laurels. The current implementation runs in EV mode as soon as the Li-ion battery is charged. Perhaps it could be user-programmable to hold off on that - no point in using up the battery on the highway when your destination is city traffic, where EV mode would be more beneficial.

Also note that because of the space needed for the Li-ion battery pack my test car was missing a large chunk of luggage space and any sort of spare tire. The tires were not run-flats; the "tire repair kit" was a Toyota PR person's cell phone number. Gotta love experimental cars… You know the production model will have those issues ironed out.

Is a plug-in hybrid for everyone? No. And if you don't have ready access to power where you park, there is little point. But the PHV is one next step in fuel efficiency.

SPECIFICATIONS
Toyota Prius Plug-In Hybrid

Base Price			$ n/a
Price As Tested 		$ n/a
Engine Type			DOHC Atkinson cycle 16-valve aluminum
				 alloy 4-cylinder
Engine Size			1.8 liters / 110 cu. in.
Horsepower			98 @ 5200 rpm
Torque (lb-ft)			142 @ 4000 rpm
Electric Motor			Permanent magnet synchronous
Horsepower			80
Torque				153
Transmission			electronically-controlled CVT
Wheelbase / Length		106.3 in. / 175.6 in.
Curb Weight			n/a lbs.
Pounds Per Horsepower		n/a
Fuel Capacity			n/a gal.
Fuel Requirement		87 octane unleaded regular gasoline
				110 or 220VAC grounded wall socket
Tires				P195/65R15 89S Yokohama Avid S33D m+s
Brakes, front/rear		vented disc / solid disc,
				 ABS and regenerative braking standard
Suspension, front/rear		independent MacPherson strut/
				  semi-independent torsion beam axle
Drivetrain			transverse front engine and motor,
				  front-wheel drive

(1) An electric motor can also be used as a generator. This not only provides power, but the magnetic drag occurring helps slow the vehicle, whether power is generated or not. That's regenerative braking. The same principle, minus generation, is used to help stop railroad trains.

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