Recently purchased a Prius and have a question on the braking system. When going down hill if you just take your foot off the gas do you get full regenerative braking or are you only using MG1? Do you actually have to slightly touch the brake pedal to engage MG2 and get the full reclaim of energy? If the latter how do you know when MG1 is generating versus when MG2 is doing it?

 

If you are going downhill and you do not have your foot on the brake, you should go into a regenerative braking mode. The Prius simulates auto tranny drag by engaging regenerative braking whenever you are not on the gas or brake. Just like the car simulates auto tranny creep when you take your foot off the brake.

Regen is less when you are just coasting dowhill than when you apply the brake. Now, if you have your foot lightly on the gas while going downhill, as if you were coaxing the vehicle to speed up slightly on a downhill, the vehicle will disengage the regenerative system and allow the vehicle to coast up to speed.

On a moderate downhill slope you can actually control your speed with light application of the throttle. The MFD's energy monitor demonstrates this pretty well. Keep in mind, anytime the green arrows from the drive train to the battery light up, you are regenerating or charging the battery.

I hope this answers your question.

 

I'm pretty sure the Prius uses variable force regenerative braking, meaning that it will "allow" more power to be generated depending on how hard you are pressing the brake pedal. This effectively simulates friction brakes, until your are going slow enough, then it is using 100% friction brakes to slow you down and bring you to a stop. It's controlled by the inverter, much the same as it controls your variable acceleration, it does it in regen mode too. If there were only two levels of regenerative braking then your car would be extremely herky-jerky to say the least, but that's not the case.

I would like to see the bar graph in the Prius display regenerative current, as a negative graph, or just changing the color of the fill of the graph to indicate the gain of power. This would get drivers using the regenerative braking more efficiently, just like the positive graph gets us using the ICE more efficiently.

Ideally something like this:

http://www.vassfamily.net/ToyotaPrius/CAN/cindex.html

Hopefully there will be some decent applications written for Win/Linux for interfacing with the Prius, then we can use them in Stealth Wardriver.

 

I have started using neutral - holding the lever there for 2 seconds disengages the gear - for predictable stretches - this should increase consumption as there is heat loss (tyre friction, coil heating) in acceleration and regeneration which is avoided by coasting in neutral. what I am not sure of is is the prius designed to coast in neutral. Any ideas?

 

No, Prius is not designed to coast in neutral.
Please take look the towing section on your Owner's manual.
The standard towing procedure is done by lifting front wheels.
In emergency case, you can tow by cable in neutral, but the manual states following caution.
"Towing in this manner may be done only on hard-surfaced roads for a short distance and at low speeds".

Ken@Japan

 

Thanks for response, but I am not sure why the towing issue is related to not being able to coast in Neutral. It seems to work fine and engages perfectly when you reengage.

 

The towed vehicle is coasting in neutral which is suggested to limit a short distance and at low speeds.
You're just lucky not to see any problems yet.

Ken@Japan

 

What is MG1 and MG2? I like the graphics, is that what the prius has?

 

Hi Livvie,

Just passing useful information when I was asking what certain acronyms meant. There is a "glossary" link in the upper left hand section that you can always reference when you see acronyms you dont know yet

MG1
Motor Generator 1 of the Toyota Hybrid Synergy Drive. It is driven by the ICE as a generator to power MG2 or charge the traction battery. It is also the ICE's starter motor.

MG2
Motor Generator 2 of the Toyota Hybrid Synergy Drive. Also referred to as the "traction motor" it is the motor that actually turns the wheels. It can also run as a generator for regenerative braking.

 

To add a point to the other comments, coasting in neutral is illegal in my state, California, and I'm told that's the case in most others.