Micro APU Micro Hybrid Car

Let's compare what happens when three types of cars pull up to an intersection, stop for a light, sit around, and drive away.

For simplicity, let's assume they all have automatic transmissions. Thus, in all three cases, the driver brings the car to a halt with the brake, keeps his foot on the brake for a minute or two, then puts his foot on the gas to drive away.

In the case of a conventional car, the efficiency of the engine drops off sharply as demand on the engine decreases. When slowing down or idling, the only load on the engine is from the accessories, which are a few hundred watts at most. Thus, the efficiency as the driver slows to a halt and idles is very low. As long as the car sits still, it consumes fuel and spews out exhaust. The only positive thing is that when the driver accelerates away, no external energy is needed to get the engine going, since it was idling the whole time.

Next, consider a Micro Hybrid Car, also known as a Stop/Star Car. When the car is moving, the accessories are powered electrically, from the engine's alternator. When the driver is slowing down the car, or when the car is off, the engine is automatically turned off. When the driver puts his foot on the accelerator, the engine is automatically restarted. In between stopping and starting the engine, all power for the accessories comes from the batteries.

While Micro Hybrids obviously use less gas and produce less emissions, they are very hard on their batteries. In part, this is because in the time between an automatic engine stop and the following restart, the car's accessories consume about ten times as much energy as what's needed for engine restart alone.

Overall, they are approximately one hundred times harder on their batteries than conventional vehicles. Next generation car batteries, such as Axion's Lead- Carbon cells, can merely withstand about ten times as many charge/discharge cycles as a conventional battery.

So even though Micro Hybrids are the least expensive of all hybrid technologies, they will, apparently, be really bad for their batteries.

Now we consider a Micro Hybrid Car, with a very tiny Auxiliary Power Unit. At the same time as the car is being brought to a halt, the APU automatically starts. As soon as the APU reaches its operating speed, it takes over powering the vehicle accessories, after which the main engine shuts off.

When the traffic light turns green, and the driver hits the gas, the APU's throttle is fully opened, and power from either the APU alone, or the APU and battery together are used to start the main engine.

When the main engine's rpms are above some threshold, the APU shuts off.

Since size of the APU is carefully matched to the amount of power needed for running the accessories, it does it's primary task fuel efficiently.

And while the APU might not be able to completely cover the energy needs of the main engine's starter, it will reduce it significantly.

By eliminating drain on the battery from the accessories, and reducing drain during engine restarting, the battery life should very much extended... at least compared to a conventional Micro Hybrid Car's battery.

PS: I almost forgot to state the size! I expect that one or two horsepower ought to suffice to run all of the typical accessories, except perhaps the A/C.