[DRAFT] How I did it

A work in progress, this is how I'm doing a 'stunt' drive in our NHW11, 2003 Prius:

These are the rules I'm following in my latest driving stunt . . . to achieve maximum range in our 2003 Prius . . . and keep my job. Traditional stunts in North America have been done as single, butt-busting efforts often requiring more than one driver over multiple days. But by managing warm-up costs, one can spread such efforts over several weeks and in the end, achieve 90% of the non-stop, endurance drives.

The goals:

• minimize warm-up cost - this is the least efficient Prius mode so burn as little gas as possible as there will be at least two per day
• dilute warm-up cost by a 5x efficient, trip extension - for every trip during the stunt
• minimize drag - run the car at the lowest, practical Prius speed on cruise control and found on North American, urban roads, 25 mph
• minimize traction battery charging from kinetic energy - transfer efficiency between kinetic-potential energy is 100% but round-trip traction battery transfer is less efficient

Objectives:

1. Have a loop near destinations where you can do the 5x trip extension. It should be mostly free from stops and traffic.
2. Choose routes with two lanes in direction of travel so following traffic can easily pass.
3. Choose routes less traveled to avoid other traffic.
4. Shift travel times between midnight and dawn or other non-busy periods.
5. It is terribly boring!
6. Obey traffic rules as they are 'noise' in achieving the driving stunt objective, maximum duration.

Instrumentation (optional):

1. Engine coolant reader
2. Engine rpm reader

Example:

140827


140828


140829
​

2010 Prius example

130721:

I did this driving stunt last year following the guidelines.​

Questions?

Bob Wilson

 

With the engine off, the legacy, highest velocity is 42 mph. However, I've 'tickled the dragon' up to 48-49 mph. What happens is with the engine off, the geometry spins MG1 faster than 6,000 rpm. For a driving stunt like this, simply use "B" to slow down or moderate the speed as slow as practical, often 30-35 mph.

One of my experiments was to start at the top of an 8%, 525 ft hill in "N" with engine in idle, ~1,000 rpm. I then monitored the engine idle speed as the car picked up speed going down the hill. Around 55 mph, the engine idle speed started increasing on its own to keep MG1 spinning around 6,000 rpm. But the real risk is overheating the traction battery.

Charging the traction battery is exothermic and the traction battery can be 'heat pumped' to excessive temperatures in hilly trips. What happens is the descent charging warms the battery and then going up the next hill, especially with a heavy foot, engages ohmic-heating so the battery never has a chance to dump the heat. Then the next descent . . . heats it again. This is why I recommend using "B" to descend as it dumps the excess energy to the engine drag.

The other problem is aerodynamic drag increases by the square of the velocity even coasting down a hill. Once your speed increases much above 35 mph, you're just using the Prius as a parachute, wasting energy. Descending tall, steep hills makes an endurance stunt drive impractical. Let me think about it and I'll add something to the first posting.

Bob Wilson