Q: Best way to approach a red light or stop sign

For both fuel economy and brake wear: Since you know you must stop, go to full regen (no throttle) as soon as you realize the need to stop. This will maximize regen and minimize brake use. Then, if that is not enough, brake within the regen region of HSI to come to a smooth stop. Avoid braking harder later, since that will involve more friction braking.

 

I think that's two separate cases.

For the STOP sign, where you will definitely have to stop, I recommend gentle braking for the entire slow-down period. The more time you spend at high speed, the more energy gets dissipated in atmospheric friction and the less you can dump into your batteries. A second order effect: Battery charging is somewhat more efficient when done for a longer period at a lower current. Thus long, gentle braking also benefits you that way. Electrodynamic braking shouldn't cause significant "wear and tear" as mechanical braking does, so again this suggests gentle braking at the beginning of the period rather than heavier braking nearer the end.

With the traffic light scenario, if you're certain that it will remain red long enough, then it's the same as the STOP sign. But if you can time the light (experience, GPS, etc.), then you should try to arrive at the light with maximum kinetic energy, i.e., going as fast as possible. Given the uncertainty of the time the light will change and how long it will take cars in front of you to accelerate, this can be something of a gamble. In general, if I don't know when the light will go green, I try to maintain maximum speed consistent with being able to stop without scaring anyone in front of or behind me.

Ask a simple question, you get a pageant.

Richard

 

"regen region" is the area to the left of the ECO area. You know, when the bar goes to the left instead of the right when you lift fully off the throttle.

 

sorry, I didn't notice you were in a gen2. I'm in a gen3. For your car, you want the mfd to show NO ARROWS for a glide.

You can see the process detailed in various threads here, or see xcel's article on hypermiling the gen2 over at cleanmpg.com

 

While generally correct, at light regen levels the Prius recovers less energy. The charging system is non-linear, and seems to require a certain amount of overhead before charge goes into the battery. Very light braking causes a larger percentage of the recovered energy to be wasted as overhead. In addition, regeneration is always less efficient than coasting. Because of this, generally the most efficient way to approach a stop is the following:

1) Glide (no regen or thrust). Gliding directly uses the car's kinetic energy, avoiding conversion losses.

2) If you have to brake, brake a bit more aggressively at the end instead of very light regeneration for a prolonged period. This is a bit tricky because you want to avoid friction braking and high battery temperatures, both of which waste energy. Finding the sweet spot in between is the trick.

Tom

 

The grab before the full stop is the transition to friction braking. At higher speeds it is very hard to tell when a combination of regeneration and friction braking is occurring. I'm not a hypermiler, so I use a simple "middle of the road" approach and brake just a bit, as opposed to only simulated engine drag.

As for instrumentation, I know of one PC member who wired his brake control system to collect hard information about friction braking. As for what you can do with ScanGauge, I'll leave that for one of the ScanGauge users.

Tom

 

At very low speed (< 7 MPH IIRC) the car uses pure friction brake.

ScanGauge can show the regen current and IIRC 60 Amp is the max optimal regen current.

As others already said safety first. If we get into an accident then all the hypermile effort just goes down the drain.

Good luck!

 

For the benefit of newcomers who are not afraid of information overload: "No arrow glide" actually consumes some small amount of energy from the HV battery (a few amperes depending on speed) so there is still some small conversion losses. This may be the reason why some hypermilers use "neutral glide" in some occasions.

 

In China, everybody seems to put the car into neutral or even turn the car off when going downhill or coming to a stop. It seems silly but one guy told me it saves him a lot of gas. I suppose if you did it with the Prius...