The First Law of Thermodynamics is an immutable law of nature. Commonly referred to as The Principe of the Conservation of Energy, it states that energy can’t be created nor can it be destroyed; energy can only be converted from one form to another. Energy may appear in several different forms–electrical, chemical, thermal, mechanical, thermal, etc. Batteries convert chemical energy into electrical energy. Generators convert mechanical energy into electrical energy. Motors convert electrical energy into mechanical energy. Incandescent light converts electrical energy into light energy and thermal energy. Solar cells convert light energy into electrical energy. Internal combustion engines convert the chemical energy found in gasoline into thermal energy and then converts that thermal energy into mechanical energy. The examples of energy conversions are numerous; unfortunately, many of these conversions become wasted energy.
One of the chief sources of wasted energy where cars, trucks, and buses are concerned comes from the heat generated during the braking process. At least that was the case until the advent of electric and hybrid vehicles. Most electric and hybrid vehicles employ a system called regenerative braking where the electric motor becomes a generator during braking and provides electricity to recharge the batteries. Regenerative braking works because a generator produces two forces, an EMF (Electromotive Force) which is the voltage that charges the batteries, and an CEMF (Counter Electromotive Force) which is actually a voltage 180 degrees out of phase with the EMF. The CEMF acts as a brake, causing the vehicle to slow and come to a halt. That’s a very simplified description of how dynamic braking works, because a full explanation is beyond the scope of this article.
Another source of wasted energy with motor vehicles have been their mechanical shock absorber systems. Shock absorbers converted mechanical energy into heat energy that served no useful purpose; at least that was the case until recently. Engineers at the Massachusetts Institute of Technology have designed a new type of shock absorber that converts the mechanical motion into electrical energy, enough energy in fact to charge the vehicle’s battery and to operate lights and onboard electronics. This new shock absorber system, called the GenShock, uses hydraulic fluid to power a turbine that in turn powers small alternators which generate the actual electrical energy. According to the engineers at MIT, the GenShock would not be cost effective for small vehicles at their current stage of development but would be a viable source of electrical energy for larger vehicles like buses and tractor trailers.
This article was based on an article appearing in the Wednesday, February 11, 2009 edition of TechTalk, a paper serving the MIT Community.
