A discussion of gliding and a comparison of methods: pedal control vs. neutral

Excellent report!

With the data recorded, could you report the average speed for each method? It would be great to compare the constant-speed MPG to either P&G method.

A minor variation, I used cruise control to handle P&G from 25-43 MPG.This allowed me to use cruise control "resume" to handle the pulse in a consistent fashion. Minor variation, it was my approach.

Thanks!

Bob Wilson

 

Just set up XGauge and observed the said current flow first hand. No doubt the Prius seems to glide forever, and long glides tend to drain the battery.

Also found the current flow into the battery isn't that much when ICE is running efficiently (about 1200 RPM and 14 IGN), even though there is the alarming yellow arrow. I think this probably means that the no arrow pulsing (ICE less efficient) may not be necessary or as advantageous as one may think.

 

Have been keeping an eye on the batter current since the XGauge set up. Sometimes at a gentle uphill I see the XGauge showing 1 or 2 A flowing out of the battery but the MFD showing yellow arrow into the battery. I suppose if the MFD lied about no arrows then it might as well lie about the directions of the arrows.

 

I wonder if the "acceleration" that some people are perceiving when going into a glide is the transition from a brief period of coasting (green arrows) which is a mild deceleration to no (or nearly none, friction and all that) deceleration of the glide. Net effect is a slight decrease in G's.

 

Maybe the slight flow out of the battery may have been feeding the A/C not the wheels, which may explain the discrepancy if the mfd is just showing propulsion draws.

I just installed a scanguage today and am looking forward to ign 14 glides for a bit of experiments, too.

 

I am a newbie... and have been reading about neutral and how the ICE and MG1 &MG2 keep spinning and how we should not use neutral over 42 mph. I am wondering what the difference is in GLIDING vs NEUTRAL. I have been reading about it, and I am still unclear if gliding with no arrows in D is causing the same spinning of the motors and engine as in Neutral. I have been enjoying using GLIDING but do not want to wear out the system but gliding around if that will put extra strain on the HSD. Thank you!

 

With normal gliding (in "D") the engine will not rotate if you stay at or below 42 MPH. Above 42 MPH the engine will be forced to rotate, however there won't necessarily be any fuel injection, so you may be able to remain in glide (or at least EV only) mode.

If you do an "N" glide then there are two possibilities. If you shift to "N" above 42 MPH then it will idle the engine, meaning there will be fuel injection happening. If however you shift to "N" on a downhill before your speed reaches 42 MPH, and then let gravity accelerate you to over 42 MPH, then the engine will stay off. This mode uses the least energy but may place a strain on the HSD as it causes MG1 to exceed 6500 RPM. Some people do regularly make use of this mode, but of course it's at your own risk. Personally I wont do it any faster than about 52 MPH.

 

I only use N-glide for bumper-to-bumper traffic. Coasting or PC-gliding to a stop, i monitor the amp in/out through the SGII so that just before the car reaches 6-7mph, i engage to neutral because the SGII is telling me that either there is no more regen happening or that PC-gliding to a halt still uses around 2.5 - 4.0 even if the speed is almost zero. so at around 6-7mph, i engage to N so that current draw will drop down to only 1.2 - 1.5 to conserve juice. it really helps in heavy traffic especially if you time it right. I'll also confirm as per JimboK's tests, is that N has more friction because there's no more of the unseen (as per MFD screen) minimum current draw to keep the car in a "gliding" state. This can be felt at really slow/creeping speeds when N is engaged. The car decelerates more than when PC-gliding. So take this into consideration if you decide to employ N-glides into stop-and-go traffic.

just my 2 amps worth..

 

I think I may be able to shed a little light on the N vs. PC glide differences. Some people have noticed an apparent difference when shifting from PC glide to N glide while others haven't. I've experimented a bit with warp-stealth mode driving after reading that sometimes using cruise control you can get a no arrows warp-stealth glide at over 42 MPH with cruise control but you can't by using your foot.

In my experiments, I've found that you can indeed get a no arrows warp-stealth glide at speeds over 42 MPH manually. I have yet to monitor my SGII for what pedal percent is required to go into this mode of operation, but I can reliably get into this mode at any speed (I've even done it at 80 MPH) and somewhat reliably remain in this mode as long as the road isn't very bumpy. I've found that as tricky as getting into stealth mode at 40 MPH or below is for new drivers, getting into and maintaining the no arrows warp-stealth glide is about 10-15 times harder. There is an absolutely razor thin margin in which you get this mode.

Recently after putting the xgauge for the HV battery current into my SGII and having been monitoring that, I think I've narrowed down that that same razor thin margin on the gas pedal is also available for a "neutral current" (~1 amp) no arrows PC glide at speeds below 40 MPH as well.

Separately, I've also noticed that the amount of residual current drawn from the HV battery during a PC glide varies depending on HV SOC. If my SOC is down around 54%, the residual current draw is usually closer to 3-4 amps, while if my SOC is around 58-60% then the residual current draw can climb as high as 8-9 amps under the same conditions. My thinking is that the residual current draw that seems to be going to MG2 may be something the Prius does quietly behind the scenes in order to try to maintain its preferred SOC.

Anyway, after playing with all of this and watching my HV current while playing with PC gliding and neutral gliding, I've noticed that if I shift into N while in that razor thin margin of neutral current, there is no perceptible difference between the two. However, if I'm doing a normal PC glide where it's got the residual current draw, then I can usually feel a very slight difference when I shift into N.

Maybe that will help shed some light on this whole thing for those interested. Or just provide some interesting information for those interested in their own experimentation.

Now I think I may have to test a tank or two on all N gliding vs. all PC gliding to see how that goes. It sort of looks from the graphs that if you don't care about increasing your SOC, that PC gliding may net you slightly higher MPG, but if you're trying to keep your SOC higher, you'll be better off with N gliding. I'll have to do my own playing around to see what I can figure out from that.