Tag Archives: Motor

Motoring…

A discussion on the My Ford Mobile website linked to an Engadget article with cutaway pictures of the FFE’s motor. Some things you can figure out from the pictures and the article: like the long half-shaft for one of the wheels goes through the middle of the motor.

More details can also be found in this article.

Technology/Efficiency

Taking a break from the story for a bit.

Here I am going to go into a general discussion of the differences between various vehicle propulsion methods: Gas engine, hybrid, and electric motor.

Your normal gas engine operates at about 18%-20% efficiency. Much the losses associated with gas engines are attributed to heat loss through the exhaust and friction in the drive train. This can be increased slightly by adding turbo or super chargers but they only bring the engine closer to its theoretical maximum efficiency (37%).
Electric motors, on the other hand, have an efficiency in the range of 85%-90% thus more of the “fuel” will go to moving the car. This also poses a problem as there isn’t enough waste heat to be used for other purposes (heating the cabin, warming the batteries, etc.). This large difference gives the electric car an advantage in “fuel” economy.

Now lets look at other aspects of the vehicle: What is the one thing that a car does that wastes the most energy? Its not acceleration; its stopping. Think about it: What do brakes do? Brakes turn the forward momentum of the vehicle into heat at the braking mechanism. All of this heat is dissipated into the air–just thrown away.

How can we recover that lost heat? There is no way to feed that back into a gas engine and re-create gasoline. What you can do is spin up a generator and store the electricity. This is the exact principle used by hybrid vehicles: There is a motor/generator that recovers the stopping momentum and puts it back into a battery for use during acceleration (this is what regenerative braking does). Hybrids aren’t designed to run on electricity alone–the battery isn’t large enough–they are only designed to capture and re-use the deceleration energy (for the most part).

Now adding all the equipment for a hybrid increases the vehicles weight by a significant amount (we now have two “engines” and two “fuel” tanks). Manufacturers make a tradeoff between the sizes of the engine, motor, fuel tank, and battery when designing the hybrid car.

An electric car does not suffer from that limitation–only one motor is present and one “fuel” tank. In addition the electric car can make full use of regenerative braking.

Given all these advantages an electric car has one huge drawback to it (as you are probably screaming at your screen about now LOL): The energy density in today’s batteries is nowhere even close to the energy in a tank of gas. There is a ton of electricity storage research (battery, super capacitor, air-battery, etc.) going on with the goal of giving today’s electric vehicles more range. I’ve read of a few people posting their opinions for the battery criteria required for BEV’s to go mainstream. Jumping into the fray here is my guess as what is required for mass adoption of BEVs:

  • BEVs must have a range of 250+ miles (Not saying 300+ miles because one of my ICE vehicles (a rather large truck) only has a range of 250 miles on a tank)
  • The battery in said BEV of range 250+ miles must be not much larger than the average tank of gas (note that the battery doesn’t have to have the same energy density of gas due to the electric motors higher efficiency)
  • There must be available charging stations to allow the 250+ miles to be replaced in approx 10 minutes or so

Easy as pie right? The Tesla Model S comes really close to all of those above with a luxury price tag. The sub $30k planned Tesla model should take the market by storm..