Pulse and Glide - Battery or ICE

[mini 1l]

I'm recently new to forum. I just purchased a 2009 and learned a tremendous amount of fuel economy information from this forum.

With respect to Pulse and Glide, should I be extending my glide by using the battery or should I not extent the glide and simple come back up to speed with the ICE? It seem that running off the battery would improve fuel mileage, but I'm not convinced.

Thanks for your time.

[Shawn Clark]

Here is my take:

Extending glides with EV rarely makes sense since it is the same as using the ICE, but with an efficiency hit for the path through the battery and back to the electric motor. Using electric propulsion in lieu of the ICE actually reduces mileage.

Pulsing with the ICE is the proper course.

There are some exceptions but these are short transient events where the EV use is small and smooth and the ICE would turn on and run very inefficiently for a short time and/or stay one when it really should be off.

[JimboK]

In general, though it seems counterintuitive, it is less efficient to use battery power for propulsion due to energy conversion losses that Shawn suggests. However, I use EV mode for short, low-demand situations, including short extensions of glides, where I think using the ICE would be less efficient.

By less efficient, I mean two primary situations: low-load or very short duration. When so little propulsion is needed that lighting the ICE would put it in an inefficient low-load situation, I'll use battery power. I have the benefit of added instrumentation, so I can quantify how much load the engine is under or how much battery power I'm using. I generally try to keep current flow under 10 amps, allowing occasional spikes up to 20 amps over short distances. For those who can't monitor current flow (i.e., most Prius pilots), aim for just barely enough go-pedal pressure to light the yellow arrows on the Energy monitor (Gen II Prius).

For short duration pulsing, there are presumably inefficiencies in rapid cycling of the ICE, though no one has quantified them, AFAIK. So if I need a very short burst of propulsion -- say, 2 seconds or less -- I might use EV even if it pushes current above 20 amps. As an example, there is a particular spot on my morning commute with a short but rather steep downhill to cross a creek, with an equally short and steep uphill on the other side. After the road crests on the backside of the hill it turns slightly downhill for perhaps 200 yards until an intersection with a traffic light, usually red. I glide down to the bridge, gaining as much momentum as possible to carry me up the other side. But it's generally not enough to get me to the top without a short burst of power. Only a couple of seconds of ICE power is needed, so instead I use the battery just to get me to the crest, where I can then glide to the light. Current flow might be 30-40 amps and it's a slightly longer power cycle than with the ICE, but it's still brief and drops state of charge by no more than 1%.

Much of what I do here is intuitive, not data-driven, and even a bit arbitrary, so don't take it as gospel. But I am getting fair-to-middlin' results these days.

[TonyPSchaefer]

It really is a matter of current situation. As with so many things, there is no single correct answer. As Shawn hit on, engaging the ICE just to make that last 50 feet to the stop sign doesn't make a lot of sense. Also, stealthing just over the crest of a hill to pick up regen down the other side makes sense.

Personally, I pulse-n-glide, stealth-n-glide, pulse-n-steath whatever it takes given the situation at hand. Just keep in mind that it's always a good idea to "protect the pack." In my opinion, you're stealthing too much if you find that you are often running on a pack that's only three or four bars.

[qbee42]

I agree with the posts above, but want to emphasize one of the points: using the battery always wastes energy. Always - no exceptions. So why do we have a battery? Sometimes using it wastes less energy than the other options. This is Tony's point. You have to ask yourself which is the lesser of the evils. Do I kick on the ICE and short cycle it, or do I pay for the conversion losses of using the battery? Keep this in mind and you can make intelligent decisions about the trade offs on a case by case basis.

Tom