optimal speed for economy, Gen 1?

This may help:
2003 Prius

Executive summary:

• 17-19 mph - maximum range speed
• 23 mph - lowest cruise control set speed but it too easily drops out
• 24-25 mph - lowest practical cruise control set speed
  
• 0-38 mph (indicated) - best speed range for hybrid operation
• 39-44 mph (indicated) - avoid because it brackets the hybrid threshold speed, 42 mph, can can lead to inefficiencies
  
• 45-65 mph (indicated) - best higher speed range for ~52 MPG depending upon air density
• 70 mph - Ugh, 49 MPG and car starts running a little warmer than good for long life
  
• 75+ mph - 39 MPG or less so the car will wear out sooner by stressing the systems
  
• 100 mph - ~22-23 MPG
• oversized front tires - provide a constant 'over-drive' gear allowing faster true speeds in hybrid mode, 38 mph -> 40 mph true
• no power arrows - optimum speed climbing any grade

GOOD LUCK!
Bob Wilson

 

Uhh, what? I did a cruise control test latev at night in my Prius c. There was no wind, and was on flat ground, and 40-44 mph seemed to be the most efficient, netting me around 68mpg. To be honest though, anything between 40-49 mph was hard to discern any reasonable difference

 

This is specific to the 2001-03 Prius that has an earlier generation engine, transmission, and control laws. The 2010 Prius control laws have some form of hysteresis so it doesn't 'flip' between engine OFF and ON at 42 mph. I would expect the same to be true with a 'prius c.' It may have been implemented in the 2004-09 model BUT I don't have one to test.

In the 2010, it can reach ~46 mph with the engine off and 42 mph is no longer a hard limit. The control law acts as if the hybrid threshold is in the 42-46 mph speed range but also a function possibly of engine temperature and battery state. In contrast, the 2001-03 has a hard threshold at 42 mph after reaching 70C and stage 4.

The 2001-03 cruise control has a +/- 1 mph at any set speed. So we can set it to 42 mph and see the engine come on 42 mph and higher and then go off at 41 mph or slower . . . unless there is a significant load that turns the engine on again. So on a road with a small height rises, say 2-5 meters, the engine will cycle on-off-on. On the downgrades, the speed exceeds 42 mph and the engine runs due to the speed. Then on the upgrades, the speed falls off, the engine stops when the speed creeps under 42 mph and and then as the load increases and the engine starts again. The terrain and 'slop' in the cruise control leads the engine to cycling with attendant loss of energy.

We don't find this on the 2010 Prius and I suspect the 'Prius c' works like the 2010 Prius.

Bob Wilson

 

My understanding is the 2004-05 had a latent, manufacturing defect with weak solder joints that could cause the MDF to fail. Good Prius Friend, Hobbit, fully documented the fixes. But as a general rule, the last model year, a 2009, would be an ideal, used Prius as everything known would be in that one. Still 2006-09 would be a good base to start from.

There is another source, AutoBeYours, Steve who rebuilds crashed Prius and offers years of NHW20 Prius experience. I would trust his work. But there are others our collaborators may recommend.

Bob Wilson

ps. My favorite list of add-ons:

1) 12V-to-110VAC inverter in the sustained 1.2-1.5kW range but used to provide 1kW emergency and remote power. Sine wave desirable but modified sine wave is what we have in the 2003. We've used it EVERY year and once for 4.25 days.

2) Tow receiver and folding or light weight trailer - makes the Prius a light-duty, Chevy LUV, transporter.

 

The (full-sized Prius) P410 and (c-sized Prius) P510 (Gen 3) transaxles are the current generation, and both have a "motor speed reduction" planetary gearset in the MG2's path, about a 2.5:1 reduction ratio to the carrier, which allows the MG2 to achieve its maximum rated power at over 10K rpm, while the MG1 stays in its safe range at higher road speeds.

The prior P110, P111 (Gen 1) and P210 (Gen 2) transaxles had just a single planetary gearset, with the MG2 always 1:1 with the carrier, so this motor-generator had to be extra large to achieve maximum rated power. Also, the MG1 tended to overspeed, so the ICE was expected and required to turn on in order to reduce the MG1's speed.