Eng/Sci/TechLifeOpinions

Future of Green Cars

Last semester, I made a presentation in my Intro to Systems Engineering class about the design of the Chevrolet Volt. While I conceded it was a remarkable piece of engineering because my group members were all gung ho about it, deep down inside I thought the Volt was a dismal failure. And in fact, the sales numbers did back me up on that. But after ruminating on the concept of of the Volt, and yet another “Green” marketing acronym “EREV” (extended-range electric vehicle), I’ve realized that the idea deserves far more consideration from frugal greenies and power-mongers alike. Yes, the Volt sucks, but the ideas and technology behind it are probably the best way forward for cars of the future.

To the uninitiated, the Chevrolet Volt is just another hybrid. It has a gasoline engine and batteries, which it drives off of. The gasoline engine will top off the batteries as you drive. Pretty similar to the Toyota Prius. The biggest difference comes from the intent of the drivetrain system. The Prius is a series-parallel hybrid, which means the car can use any combination of electric and mechanical force to drive. The Volt, under certain circumstances, can technically operate the same way. It is capable of passing some energy from it’s engines to the wheels to supplement electrical power. But what it does under normal circumstances (read: when the accelerator is not flat on the floor) is operate as a series hybrid.

Series-Parallel:

Series:

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Series hybrid drivetrains are not new ideas. There are plenty in use today, largely in diesel-electric locomotives. Some have even been used in cars to varying degrees of success… or failure. The concept can basically be explained with water. Imagine that a car is actually a town, and its battery is a water tower. The gasoline engine is a water pump. In a series hybrid setup, people in the town get their water directly from the water tower. The water pump is only used to top off the tower’s reserves. If the town were a series-parallel hybrid, then people could sometimes get water from the pump, or sometimes from the tower. The series-hybrid setup is inherently simpler (less plumbing, so to speak), but in cars, the idea just hasn’t gathered momentum.

The problem with the Volt is its price $40,000+. Part of the reason for that cost is the enormous and enormously expensive battery pack it hauls around. Chevrolet wanted to make a predominantly electric car with a gasoline generator. To do that, they needed a reaaaally large “water tower”. If you watched the youtube video I posted at the top (if it didn’t load, just hit refresh), you’ll realize that it’s a very expensive solution for not very much gain. Relying on modern batteries as a primary power source is impractical to say the least.

What I think will emerge as the way forward will be a car that’s primarily gasoline (or fuel cell, or whatever) powered but still has a battery and an all-electric drivetrain. Instead of trying to build a battery with enough capacity to get you anywhere awesome enough to do it all, car manufacturers will instead look to highlight the benefits of electricity instead of trying to tackle the challenges of harnessing and storing it.

So what is electricity good for? Instant power, for starters. A car with an electric motor can instantaneously put full power to the asphalt when it is commanded. There is no turbo lag, no waiting for RPMs to reach their butter zone, nothing. Coupled with great torque and efficiency bands that negate the need for aggressive gear-shifting, a sufficiently well-endowed electric car will always beat a petrol powered drag racer.

What else is it good for? Power transmission. You can put a motor in the front of a car, and a motor in the back, and have four wheel drive without any sort of complex mechanical linkages. You don’t have to sacrifice engine placement to fit drive shafts, and you can dynamically manage power splitting between the front and the back. All the fancy engineering Ferrari and Lamborghini do, or all that chunky stuff that goes on in a Jeep, it’s all obsolote. You can control what power goes to what wheel with a chip.

A vehicle that’s propelled with electric motors is the ultimate performance machine. What car manufacturers have been trying to do instead is to put underpowered electric motors in cars in an effort to extend the range of anemic battery technology. But gasoline engines can still be reasonably efficient when they’re not racing all over various RPMs. So can gas turbines. And chemical fuel is an extremely dense energy storage medium. Using an internal combustion engine (ICE) as a constant power source rates about an 11 on a scale of 1 to 10 in terms of practicality. Battery swap stations will *never* gain traction unless batteries are small and you can guarantee that every pack works (imagine going to such a station in the future and getting a lemon that some jerk dropped off earlier). And “quick” charge stations? Well… they’re not so quick for a family on a road trip. Using an ICE as an emergency backup device is okay but is a waste of space then, and a waste of weight.

A series hybrid really only needs a battery large enough to provide power for transient activities, like acceleration. Under conditions like highway driving, the ICE would nominally be providing just enough power for the car to break even, maybe recharge some of its depleted battery as well. Regardless of its actual size, the battery would be smaller than it is in hybrids today. Its purpose is to really be an energy buffer, not what you’re counting on you reach your final destination. Heck, at this point/capacity-need, you could even use super-capacitors. And that translates to reduced cost, size, and weight.

Basically, my thoughts on the whole eco-car movement is that it’s noble, but fundamentally flawed. Plug-in cars are a complete waste of money, and valuable mineral resources. Manufacturers are trying to fight a losing fight. Engineering energy storage solutions is a difficult battle, fraught with miniaturization problems, yield problems, environment/toxicity problems, etc. Nature has already provided us with energy packs that are abundant. They’re called gasoline, diesel, and natural gas. Even hydrogen can work. No matter what kind of battery you build, you can’t beat a molecule for storing energy. Instead, what car-makers should be doing is rethinking power trains to take advantage of the benefits of each system at their disposal. Electrical energy is a wonderfully fluid power medium, and chemical energy storage is convenient, and relatively clean under the controlled circumstances. Combine them properly, and you have the ultimate driving machine. Efficient and powerful. Imagine a Tesla Roadster for a third the price, all the performance, and the gas-consumption of a Prius. That is a future I can get behind.

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