Thursday, August 24, 2006

Driving a Hybrid

So I have a week of driving this Civic Hybrid under my [seat] belt. I want to talk about the Navi system, but I need to grok it more before talking about it - just yesterday I poked around and learned about a cool feature.

There's the dynamic driving part, too, like how well it rides and corners. My first impressions still hold, that its steering is very direct and with good feel, and that it is surprisingly well-balanced for a front-engined car.

It does push (understeer) a bit when it gets near the limit, as expected, but it's not nearly as much as I would expect for a mass-market car. I still want to find a stiffer rear anti-roll bar so that I feel more comfortable in turns.

And why should you care about cornering well? Excellent question, glad you asked!

Hybrids are all about efficiency and recovering energy. People have such misconceptions about what wastes energy while driving. The proverbial jack-rabbit start does not inherently waste energy. Think about it - it takes the same amount of energy to reach 40 MPH whether you accelerate quickly or not.

The energy considerations of the jack-rabbit start have to do with 1) enrichment of fuel mixture under heavy throttle, 2) the thermodynamic efficiency of engines at various throttle settings, and 3) energy loss through an automatic transmission.

Roughly speaking, 1) enrichment takes more fuel, though not as much as in the days of carburetors and "accelerator pumps", 2) Carnot-cycle engines are typically most efficient at 60% speed and 60% throttle, and 3) slip is bad - think of holding still on an upgrade, wasting energy going 0 MPH.

I've spent way too much time on acceleration. The biggest expenditures of energy are 1) drag and 2) throwing heat away through the brakes.

Hybrids have tiny engines and are very aerodynamic. This is so they can be working harder (and more efficiently) at speed, and to reduce the drag at speed. No matter what your aerodynamics, drag still goes up as the square of speed, power required goes up as the cube, and mileage goes down as the square. So, if you get 40 MPG at 60 MPH, at 80 MPH you'll get (3/4)^2 of that, or 22.5 MPH!

This does not bode well for hybrid economy in Si Valley, where CA-85 seems to be a nickname for the speed you have to go on it to avoid being run over.

Now, finally to braking, and my original mention of cornering. Hybrids attempt to recover energy during braking by using the electric motor as a generator instead of just the brakes. It has a maximum generation capacity, however, so if you need to slow down faster, it's going to require the brakes.

The Civic Hybrid has a smaller battery and generator than the Prius, and you have to brake very gently indeed to avoid actually invoking the brakes.

Better not to have to slow down at all, I say! This is where racetrack and car control training come into play. The fastest way around a corner is also the smoothest, and it's important to take the right line through it. It sounds simple - and it is - but you'd be surprised how many people do this completely wrong. Like most of you. Yes, I'm talking to you .. next time you're on the road, try looking ahead more and driving smoothly.

As three-time world driving champion Jackie Stewart says, a good race driver is also a good chauffeur - the passenger shouldn't be able to tell exactly when she starts braking, turning, or accelerating. To go fast on the racetrack (and on the freeway on-ramp), you go slow in the cockpit.

And when you're driving a hybrid, go easy - very easy - on the brakes, and give the car the best chance possible to do its magic.

Click here for more advice on how to maximize Civic Hybrid fuel economy.


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