Since I acquired an electric vehicle (EV), I have thought about the future of these things. They are too expensive now, and too heavy, because of the huge and costly lithium-ion battery that provides limited range, making the car useful only for commuting and local errands. Even so, my car is a joy to drive, quick and silent with virtually no maintenance other than checking the tires. Even the disk brake pads will probably never need replacement because it employs regenerative braking, converting the electric drive motor to a generator, reclaiming the kinetic energy of the vehicle to recharge the battery when stopping.
But EV’s will not replace cars powered by internal combustion engines (ICE’s) until better batteries are developed…smaller, lighter and lower in cost. Also the current EV designs are derivatives of their ICE forbears. The motor is still under the hood, driving a transmission with drive shafts connected to the front wheels. Much of this mechanical stuff is unnecessary and will be eliminated when future EV’s are designed starting with a clean sheet of paper.
Even so, current EV’s are far simpler than an ICE-powered car. The electric motor has one moving part. Compare that to the valves and rocker arms, pumps and pistons, belts and gears in an ICE. Electric motors are ideally suited to vehicle propulsion. Maximum torque occurs at start, so no multi-speed transmission is needed to multiply the puny low-speed torque of an ICE. All of that mechanical complexity is gone, replaced by a spinning rotor containing magnets, driven by a magnetic field. Let me say that again; one moving part.
Well, not quite, in the current generation of EV’s. They have a single–speed transmission to reduce the motor speed and multiply the torque applied at the wheels. But that is part of the legacy from their ICE-powered ancestors. There is a better way.
It’s called hub-drive motors. Instead of putting a large electric motor under the hood, with transmission and drive shafts connecting to the wheels, smaller motors can be located at each wheel, integrated with a smaller, lighter hydraulic brake assembly.
The challenge with this design approach is to limit “unsprung weight.” Handling and ride of a vehicle are adversely affected by unsprung weight, so it is essential that the motor is small and lightweight. It must also be able to withstand a challenging environment. It will be subjected to a wide range of operating temperature, shock, vibration, water, ice, even mud. And, of course, it can’t cost a fortune because every car will have four of them.
The advantages of 4-wheel hub drive include stronger and more efficient regenerative braking and full-time 4-wheel drive. Antilock braking and traction control come almost free with this setup. Each motor will require a separate electronic controller, resulting in a fault-tolerant design. If a controller or a motor fails, the vehicle can continue, although with somewhat reduced performance.
Hub drive motors are currently available, although still a bit on the heavy side. But the motors are not the main problem confronting EV designers. That problem is, of course, the battery. There is a lot of research going forward on battery design. IBM has a long-term project called Battery 500. Its goal is to develop a lithium-air battery that will provide a 500-mile range in an EV, but that is not expected to be available for at least ten years. Air batteries offer significant advantages in energy density (pounds per kilowatt-hour) but the current versions tend to degrade quickly after a few charges. Many chemically active metals could be used in an air battery. Sodium, calcium, magnesium and aluminum are all candidates, but lithium is the lightest, so it has the highest potential energy density. An air battery using any of the aforementioned metals would result in a big improvement in energy density over the lithium-ion batteries in EV’s today, but recharge cycle life must be vastly improved, and cost is still a problem.
Meanwhile, progress continues on lithium-ion batteries, and some modest improvements in energy density and service life are expected in the next three to five years. Those evolutionary improvements will probably not result in an EV design that can compete with ICE-powered cars, even in short-haul urban/suburban environments unless the cost of the battery can be reduced substantially.
What is needed, obviously, is a breakthrough in energy storage. One possibility is ultra-capacitors which store energy in an electric field instead of electrochemically, as a battery does. Capacitors have significant advantages over batteries as energy storage devices, with high charge and discharge current capability and almost unlimited recharge cycle life, all limiting factors in battery design, but the storage capability is far below even current batteries. Research continues on ultra-capacitors, and we can only hope for a breakthrough.
Having worked in the microelectronics industry for many years, I find myself impatient with the slow progress in the development of EV’s. Microcomputers literally exploded into the world of high technology thirty or forty years ago, and progress has continued at a breathtaking pace ever since. Compared to that, progress in energy storage is glacial. To some extent, my expectations are probably unrealistic. Historically, technological progress has been uneven, sometimes slowing almost to a halt, and then suddenly leaping ahead when a critical obstacle is overcome. Hopefully, the same will happen here, and we will soon have a small, inexpensive box under the hood or in the trunk of our car that will store enough energy to travel several hundred miles.
When that happens, ICE-powered cars will follow whale oil lamps and buggy whips into the museums as charming antiques from an earlier time.
But until that happens, EV’s will remain merely an interesting curiosity.