Tuesday, September 15, 2009

KERS and the common Prius

Formula One racing this season has endorsed and allowed Kinetic Energy Recovery Systems (KERS for short) for the 2009 season. The systems have been used with some success by Ferrari, McLaren and Renault this season. I won't go into detail about the systems allowed in F1, but there is plenty of information available here. The main idea behind the systems is to capture energy while braking, store it in a battery or flywheel, and release it to aid the performance of the racing cars. F1 cars using the KERS system get an 80 HP boost from their electric motors, but can only use the extra power for about six seconds each lap. Drivers press a button in the cockpit to engage the system.
In the past, many advancements from motor racing have been used to add safety and performance to road-going vehicles. rear-view mirrors, active suspension and quick-changing manual/automatic transmissions are all examples of this. The idea of using a kinetic energy recovery system through regenerative braking, however, is not an idea created by racingteams. It has been used for several years now in production hybrid cars and trucks.
I had never driven any sort of hybrid, but had an opportunity recently when my mid-sized rental turned out to be the very popular Toyota Prius.
I must admit that I was excited to see the cars available for hire at the Hertz agent at the San Jose, CA airport. As I came onto the lot I spotted special Hertz-liveried Corvette ZHZ models, as well as new Camaros and Mercedes C-Class vehicles. Since I was going to be driving on Highway 1 along the scenic California coast, I was salivating at the thought of using a high-performance car for the duration of my trip. When I arrived at the counter, they gave me a high-performance car of a different type. After only three minutes or so of pressing buttons and looking for directions, I was able to get the car to turn on and move out of the lot. The start up procedure is not intuitive, but simple once you understand the steps.
Since the Pruis uses a sort of KERS system, I thought I would give the car a fair shake. The biggest thing I dislike about the Prius (before driving) is the self-righteous attitude of the drivers and of the manufacturer about how good their car is for the planet. The commercials show Priuses driving around emitting only flowers and rainbows, and the fact is that while it does use a bit less petrol, the manufacturing process for the batteries offsets any eco-karma generated by lowering emissions. But this does not seem to diminish owner enthusiasm for them and there are many on the road. On at least three occasions while in my Prius, I was in a "train" of at least three Priuses in a row.
After driving some friends from Los Gatos to Monterey, I was happy that for the most part, it drove like a normal car and achieved pretty impressive fuel economy. The car seated the three of us comfortably (though I wish the seat went back a bit further) with all of our luggage and some of the party favors for a medium-sized wedding.
I woke early the next morning to wring-out the Toyota and the explore the scenic California coastline.
Any motoring enthusiast would surely love to see a sign indicating 74 miles of twisty road and I was no exception. I was nearly the only vehicle on the road when I set off, and the speed limit was a very reasonable 55 mph for most of the 60 mile stretch of Hwy 1 I drove.
The technology of the Prius has been written about ad naseum, and I am not going to go into how it works, but will instead give my take on its utility and function. Suffice to say the Prius electric motor does not provide quite the performance benefit of F1's KERS.
I set out to drive the car hard. I sped past the sign pictured nearby indicating 74 miles of curvy road. When I saw the sign and decided to take a picture, I wasn't shy about jamming on the brakes, pulling onto the gravelly verge and flooring the car in reverse to get myself back in position to take a shot. The brakes on the car have a two-phase operation. At the first tough of the brakes, the power regeneration system activates, and if more stopping power is required, the conventional hydraulic brakes operate. There is a jerkiness to the two systems that requires some getting used to. The car skidded around a bit as I pulled it onto the shoulder of the road. Upon shifting into reverse, a back-up camera turns on and shows on the display on the dash. As I found in a parking lot, the camera is great for locating the lines of parking stalls, but bad at letting you know how close you actually are to objects behind. The fish-eye lens of the camera gives no sense of distance to the objects in the camera. Also, there is an annoying beep inside the cabin any time the car is in reverse. The beeping is not a radar-type parking assistance device with beeps that get more frequent as you get closer to what is behind you--it is just an annoyance letting you know you're in reverse.
After snapping the pictures, I sped off from the verge, spinning the inadequate tires as the traction-control icon lit on the far-away dashboard.
The display in the center of the dashboard can be switched to show information about performance/economy, climate systems and audio. I found the climate system to me non-intuitive, and it required a bit more distraction from the road to be able to accurately adjust the temperature and fan settings. The radio controls were even more frustrating. There were seemingly three ways to adjust the volume for the stereo. There buttons on the steering wheel, a knob on the dash, and buttons on the LCD touch screen. The knob on the dash never seemed to work to control volume, but the dash controls were the only way to scan the radio. I was never able to turn the radio off, only down.
I really tried to go just about as quickly as possible down the highway. I was braking late and jabbing the go-pedal to get maximum thrust out of the corners. Driving this way I was surprised that the battery stayed at near-maximum charge. It is apparently easier to charge the battery than drain it this way, as there were lots of short bursts of maximum acceleration and lots of heavy braking. For my taste, Toyota could have put a bigger electric motor in the car to provide more of a kick. The acceleration did not come quickly, but instead came on quite oddly, due to the continuously variable transmission (CVT). I'd never driven a car with a CVT, and I'll say I'm not anxious to do so again. The engine stayed at a near constant rev while speed increased, which is a bit of an odd sensation. But I'm sure the computers were doing their best to give me maximum power.
The information display on the Prius provides a bar-graph history of the last 30 minutes (in five-minute increments) detailing both fuel economy and power captured through regeneration. In normal driving the higher regeneration numbers would mostly correspond to higher MPG numbers. However, as I was trying to wring-out the Prius, regeneration numbers were quite high, but MPG numbers were pretty low (below 25 MPG). The one thing I think the display is missing is a figure to show how much electricity the motor is using, in addition to showing how much is generated. Again, with how slowly the battery seemed to discharge during spirited driving, I think a more powerful electric motor would definitely help the car's enjoyment factor, and it seems it would also be able to power the car to a cruising speed of 30 mph or so before the gasoline motor kicks in. (The gas motor seems to kick in at 10-15mph in normal operation.)
After 60 miles of driving south on Hwy 1 and passing through Big Sur, I turned onto Nacimiento Road. Nacimiento Road was barely more than a paved donkey path that wound its way up a steep mountain. The bottom part of the road was covered fog, and there were blind curves the enitre way up the mountain. The bottom three-to-four miles were paved, with steep gravel edges that plunged into a deep canyon and out to sea. Near the top of the ridge the road turned to dirt and grew steeper, and potholes were common. I shortly entertained ideas of rallying the Pruis, but the car's small wheels and tires, combined with the deteriorating road conditions led me to turn around.

By the time I reached the top of my climb, the battery was nearly depleted, and the engine was running non-stop to recharge the battery, even when the car was not in motion. Indicated mileage for the duration of the climb was in the 10-12 mpg range. Indicated mileage on the descent was much better. Almost all acceleration I used on the trip back down the mountain was taken care of by the electric motor. By the bottom of the hill, however, I had pretty substantial brake fade, and the smell of hot brakes permeated the car.
Overall, the Prius drove about as I expected. On hard, skinny tires the car would plow through corners if I tried to carry too much speed. Needless to say, I did not have to deal with any wheelspin on corner exits. I was craving the ability to press a button on the steering wheel and gain another 80 HP, if even just for a few seconds. The car seemed rather well-balanced, and I think that if the car had better tires and about twice the power, it could be useful and entertaining to drive.