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View Full Version : How quickly does Prius ICE shut off?


Karkus
02-06-2008, 10:58 AM
If you're accelerating the Prius using the ICE, while under 40 mph and in full hybrid mode (stage 4), and you let off the accelerator, how quickly does the ICE shut off?
Sometimes I like to shift into N (at <40mph) so I can coast without the effort of slightly pressing the accelerator, but I want to be sure the ICE is off before I do that (and I don't have a scan gauge, BTW)
How quickly does that happen?

(and yes, I realize the issues some people have with driving in N, and I also know that engaging N while over 40 mph is no good since the Prius ICE will just keep running and require fuel).

JimboK
02-06-2008, 11:13 AM
Usually it shuts off immediately. I often do the same thing, and when I let off the gas I promptly shift into N.

An exception is when ICE temp drops back below the 157F S4 threshold, as can happen during winter driving with the cabin heater running.

pdk
02-06-2008, 11:14 AM
If you're accelerating the Prius using the ICE, while under 40 mph and in full hybrid mode (stage 4), and you let off the accelerator, how quickly does the ICE shut off?
Sometimes I like to shift into N (at <40mph) so I can coast without the effort of slightly pressing the accelerator, but I want to be sure the ICE is off before I do that (and I don't have a scan gauge, BTW)
How quickly does that happen?

Without a scan gauge or other OBDII device, it's difficult to know if conditions are exactly right (engine temp, for instance) or if the ICE has, in fact, shut down (scangauge would show 0 RPM ad the Prius unfortunately has no tach).

To answer your question, ICE usually shuts off within a second or two provided you are in stage 4 and you either regen or glide.

(and yes, I realize the issues some people have with driving in N, and I also know that engaging N while over 40 mph is no good since the Prius ICE will just keep running and require fuel).

You're half right on that. If you start below 40, pop into N, and coast above 40, ICE will remain off (we call it "warp neutral"). If you're above 40, not in N, and you do the equivalent of a glide (foot off the gas or feather the gas), the ICE will spin, but fuel-flow will be cut. It's called "warp stealth", and there are a few caveats to using it (it will drain your battery if you're not careful).

Hope this helps.

mparrish
02-06-2008, 02:06 PM
If you start below 40, pop into N, and coast above 40, ICE will remain off (we call it "warp neutral").

If you are on a 45-50mph road doing 45-50mph, and you climb a hill with a long descent on the other side, and you let your speed drop to 40mph, and traffic piles up behind you, and you crest the hill at 40mph, and you back off/glide/check for 0 RPM/shift to N in 0.4 seconds, we call that "super warp neutral." :D:D:D

xcel
02-06-2008, 02:56 PM
Hi Marc:

___I have this picture that keeps popping into my head … There is a particular Prius heading down the Interstate at 60 + mph (below 63 mph and MG1’s 10,000 R limits of course ;)) near the bottom of a long downhill with its engine at 0 RPM. The funny thing is the driver has a huge smile on his face and for some reason I cannot figure out why? Weird :D

___Karkus, once SG-II equipped, the Prius is completely different vehicle :)

___Good Luck

___Wayne

Tochatihu
02-06-2008, 11:53 PM
Wayne, my Prius-picture is a little different. The bluetooth-enabled cars chat with each other on the road, and exchange software that might me helpful with each other, based upon their histories. These exchanges must all be gratis, unless they are parked adjacently and can pass electricity via inductive paddles (there is no other 'money'). Weird huh?

DAS

Karkus
02-07-2008, 12:24 PM
Thanks for the answers, and yes, I also have used warp neutral and warp stealth.

However, the answers on ICE cutting off range from "immediately" to 0.4s to 1-2s.

So, what's the consensus? Under idea conditions, can I select N right after letting off the accelerator, or should I wait a second or two (like I usually do)?

(I guess I might need to just buy a SGII)

locutus
02-07-2008, 03:05 PM
Thanks for the answers, and yes, I also have used warp neutral and warp stealth.

However, the answers on ICE cutting off range from "immediately" to 0.4s to 1-2s.

So, what's the consensus? Under idea conditions, can I select N right after letting off the accelerator, or should I wait a second or two (like I usually do)?

(I guess I might need to just buy a SGII)

If I'm going to use N rather than feathered-pedal glide for some reason (a potential warp neutral being a good reason), I find myself doing the <0.5s let-off-completely-and-feather pattern anyway. Once I've established glide I'll flick it into N. It's definitely less than a second for the ICE to shut down after backing off of the pedal, provided conditions are otherwise right to do so. Can you feel when the ICE shuts off? There's a small shudder that happens that I have tuned into as confirmation. Also if you happen to glance at the MFD there might be a momentary flick to yellow-only arrows when it shuts down (before going to black).

But yes, a SGII monitoring RPM is even better. :)

mparrish
02-07-2008, 03:31 PM
ScanGauge does not immediately go from XXXX rpms to 0 rpms. There is a delay of a second or so. This may just be an instrumentation delay though. In fact, before dropping from XXXX to 0, ScanGauge often briefly shows an extremely low number like "96 rpms" before heading to 0. I'm sure other drivers find the "96 rpms" a nice soothing "engine about to cut out" tonic. ;)

You know you are a Prius driver when:

(1) You feather-pedal glide even in Neutral anyway, because heck.......that's what you've been doing for years and you know no other way. :)

(2) You continue to use the EV switch in winter at speeds below 34mph even in stage 4 because you've been in stages 1-3a for the first doggone 6 miles and you've forgotten you finally now have that luxury. :)

(3) You force stage 4 at 157F, the engine sputters for only a second, ScanGauge immediately drops to 154F, and you mutter an expletive. :)

JimboK
02-07-2008, 04:40 PM
(2) You continue to use the EV switch in winter at speeds below 34mph even in stage 4 because you've been in stages 1-3a for the first doggone 6 miles and you've forgotten you finally now have that luxury. :)
Or you've become so accustomed to using the EV switch in cold weather that you completely forget to trigger the S4 idle routine when given the chance. ;) I've done that a lot recently.

Back to the question: CAN-View shows RPM continuously and promptly dropping to zero as soon as the pedal is released, just like you'd expect when any ICE shuts down. I haven't set up CV to look at injector timing or something else to indicate exactly when fuel cut occurs, but I suspect it's nearly instantaneous. I'll take a look at that this evening on my ride home.

I think Dan has looked at this pretty closely. Where's he been?? :confused:

Marc, I'm pretty confident that the delay you're seeing is from a slightly slower refresh rate with SG.

locutus
02-07-2008, 11:28 PM
You know you are a Prius driver when:

(1) You feather-pedal glide even in Neutral anyway, because heck.......that's what you've been doing for years and you know no other way. :)

(2) You continue to use the EV switch in winter at speeds below 34mph even in stage 4 because you've been in stages 1-3a for the first doggone 6 miles and you've forgotten you finally now have that luxury. :)

(3) You force stage 4 at 157F, the engine sputters for only a second, ScanGauge immediately drops to 154F, and you mutter an expletive. :)

Been guilty of all three. I'm a lost cause. :D

hobbit
02-08-2008, 07:35 AM
Every so often, you can feel a little lurch on a shutdown. Try
to remember the timing of one of those events, get a feel for
the beat of it, and give it that long before moving to N.
.
_H*

JimboK
02-08-2008, 07:59 AM
I haven't set up CV to look at injector timing or something else to indicate exactly when fuel cut occurs, but I suspect it's nearly instantaneous. I'll take a look at that this evening on my ride home.
Well, that wasn't much help. Injector timing takes a second or two to refresh in CV, for some reason, whereas RPM is immediate.

But I did verify that the ICE stays off when immediately shifting into neutral after pedal release.

locutus
02-08-2008, 09:56 AM
Well, that wasn't much help. Injector timing takes a second or two to refresh in CV, for some reason, whereas RPM is immediate.

But I did verify that the ICE stays off when immediately shifting into neutral after pedal release.

It just occurred to me that shifting into N doesn't happen immediately. You have to hold it in N for about a second then the drive will release. This is probably enough time so that if you start holding N right when you release the pedal, the ICE should have enough time to shut down.

Karkus
02-08-2008, 10:26 AM
Thanks for the extra answers everyone

Dan
03-07-2008, 04:21 PM
Every so often, you can feel a little lurch on a shutdown. Try
to remember the timing of one of those events, get a feel for
the beat of it, and give it that long before moving to N.
.
_H*

Yep it takes that long exactly! Easiest thing is to get on a glass smooth road, pump the tires up to 70-80 psi so you feel everything, then hit the EV button while cruising at about 20 MPH. Don't change your position on the gas pedal at all, don't look at the gauge, speed or MFD, just tune into your butt sensors ;). Here's what you will feel.

0000-0100 ms) A sharp drop off of vibration and force as the injectors cut out.
0100-0400 ms) A lurch like someone holding a chain tugged on your back bumper.
0400-0600 ms) A release like the guy holding the chain let go.
0600-0800 ms) A jolt of power as the EV drive tries to "catch up".
0800-1200 ms) An evening out of the acceleration, now just an EV acceleration.

My best guess is that at 0000 the injectors cut and the you loose the power the ICE is providing. At 0100, I think the PSD is transferring power inversely to the ICE to force a quick spin down. You'll see this happening as the blue regen on ocasion flashing across the MFD. At around 400 ms I think the the spin down is in its final phases and less power is being drawn to spin down the engine. At this time I also think the "parking" of the heads takes place. As I understand it, the Prius Software likes to leave the cylinders at a very specific position so it's easy to spark and start again. At around 800 I think the focus of the ICE shutdown is complete and focus is returned to moving the car forward. Coming out of the shudder of the ICE shut off, this feels a bit like a kick in the pants. It's all comparative. Sometime after this "evening out" I drop into an N-Glide.

Now keep in mind my butt sensors have gotten very good, but this is all pure speculation and WAG. The only instrumentation feedback I get is a (very) occasional flash of blue on the MFD. I'll also note a skipped KPH on my accel curve when the guy tugs the chain at 200 ms. I usually accelerate at about 1 kph per second, so what I see, second by second is {49, 50, 51, 52, 52, 53, 54}, and between 53 kph and 54 kph I drop into neutral.

This generally is more observable if you keep your pedal position constant when you mash on the EV button. Now if you want to have fun with this you can play around with the timing and do some neat stuff. If you shift into neutral 7000-7100ms after starting your car you will feel the engine start then stall ;). If you mash the EV button at 54kph or 55kph then shift to N within 100 ms you will be denied EV, get the double beep, and the RPMs will go to zero ;).

I noticed slightly better FE with a hard shift into N-EV ( 100 ms shift ) than I do with a soft shift into N-EV ( 1200 ms shift ). I'd say the difference is about 1-2% It's a trade off I'm happy with since I think the soft shift into N-EV is kinder to the car.

11011011

JimboK
03-07-2008, 06:58 PM
I think Dan has looked at this pretty closely. Where's he been?? :confused:
What did I tell you?! :p

diamondlarry
03-07-2008, 08:16 PM
ScanGauge does not immediately go from XXXX rpms to 0 rpms. There is a delay of a second or so. This may just be an instrumentation delay though. In fact, before dropping from XXXX to 0, ScanGauge often briefly shows an extremely low number like "96 rpms" before heading to 0. I'm sure other drivers find the "96 rpms" a nice soothing "engine about to cut out" tonic. ;)

You know you are a Prius driver when:

(1) You feather-pedal glide even in Neutral anyway, because heck.......that's what you've been doing for years and you know no other way. :)

(2) You continue to use the EV switch in winter at speeds below 34mph even in stage 4 because you've been in stages 1-3a for the first doggone 6 miles and you've forgotten you finally now have that luxury. :)

(3) You force stage 4 at 157F, the engine sputters for only a second, ScanGauge immediately drops to 154F, and you mutter an expletive. :)

I have seen "96 rpms" numerous times. What I look for is any rpm value below 960.

1) I used to be very guilty of this but I quickly got used to letting off the pedal as soon as the car goes into N. It's so much easier on the right foot and calf.
2) This is also something I used to do. Now, I keep a very watchful eye out for 155F coolant temps and try to be at or above 35 mph when I hit that temp. If you aren't in S4 the ICE will not shut off until you reach 35 mph or above.
3) I tried this once and did utter the customary expletive.:p I now wait until the coolant hits 159F before I even try to force S4. This is a much safer practice especially when the kids or the significant other is in the car with me.:D

xcel
03-15-2008, 10:36 PM
Hi Karkus:

___I am probably the least experienced Prius driver amongst the group but once in a stable S4 and when temps are great for pushing a Prius-I or II into la la land territory (ambient above 65 degrees F), I will shift to N within 200 ms of letting off (if I choose to use N). I have not seen a failure of ICE-Off with an SG-II equipped Prius-II under those conditions in a very very long time.

___Good Luck

___Wayne

cuchulain
03-15-2008, 10:54 PM
As the NHW10 is a bit clonky, the engine shutoff is easy to spot through the seat of your pants or by the difference in vibration about 1s. Although it tends to miss 1/3rd of the time(need to accel and try again).
Probably only works on the NHW10 or 11 but at a stop light, toggle the A/C switch full mode on/off will usually knock the ICE off or begin to recharge the battery depending what stage your at.

Good Luck
Andrew



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