Last Updated: Sat. 8/24/2002
Prius is unique. It differs from both traditional vehicles and the other hybrids currently available. The following information identifies & explains those differences.:
Prius offers the ability to drive using only electricity without the engine running under certain conditions. The maximum speed available is 42 MPH. And the maximum distance is typically about 2 miles. The total silence of this design is how the term was coined.
Once the engine is warmed up, you will experience "stealth" while driving through parking lots and on flat streets with 30 or 35 MPH limits.
Prius adjusts engine, motor, and battery-pack use automatically to insure operation is the most efficient possible. When accelerating on both the highway and on city streets, the hybrid system will use electricity as much as possible to provide thrust. The larger motor will draw all the electricity available from the smaller motor. If that's not enough, it will either draw electricity from the battery-pack or increase the RPM of the engine to spin the smaller motor faster depending on several factors.
All of the efficiency adjustments are automatic. If you didn't have the Multi-Display available, you probably wouldn't have any idea what was happening under the hood. All you need to do is press down on the accelerator pedal.
Prius can replenish electricity at the same time it consumes it. So when you reach the top of an elevation climb, the electricity reserve is usually not drained much. It can do this because the hybrid system has 2 motors. When power demands are high, the engine will rev at full-speed. This spins the smaller motor to generate electricity. The larger motor will consume a majority of that electricity to provide power to the wheels. The remaining electricity (if any) gets routed into the battery-pack to recharge it.
You will routinely see this happen on the "Energy Monitor" mode of the Multi-Display when you encounter a hill. Still having full-power available once you reach the top will provide a feeling of reassurance, knowing you can still accelerate rapidly afterward if needed.
Prius generates electricity while you drive. When cruising on the highway, the engine will spin at the most fuel-efficient RPM. The excess power is used to spin the smaller motor to create electricity for recharging. When accelerating on both the highway and on city streets, the hybrid system will sometimes increases the RPM of the engine to a faster efficient speed. If that results in more electricity than what was needed for thrust, the excess is used to recharge the battery-pack.
The functions under the hood are completely automatic. To fully understand all the adjustments happening for you, watch the Multi-Display. Many find it fascinating to see consumption one moment, then recharging the next.
Prius goes out of it's way to protect the battery-pack. Avoiding deep-discharges is the key to longer life. So when the SOC (State Of Charge) drops to about half, the engine will occasionally run to replenish the electricity. Doing that lowers MPG slightly and sometimes limits your stealth enjoyment, but it's a major benefit that will help prevent the need to ever have to replace the battery-pack.
Prius also goes out of it's way to insure your safety. If you run out of gas, the engine can't run to protect the battery-pack. But in that case, you'll still be allowed to drive using only electricity. Doing that will shorten the life of the battery-pack; however, being able to move the car out of harm's way is a benefit you'll truly appreciate. (To avoid this, please fill up the tank before getting close to empty or exceeding about 400 miles of driving.)
