Tech Question: Highway Stealth Mode

8AA · 10-23-2004, 09:59 AM

What is actually happening when the car appears to be in "stealth mode" at highway speeds? If you're going down a grade at highway speeds, it is possible to let off on the accelerator to go into "engine braking regeneration," then lightly press on the accelerator to go into electric only "stealth mode." However, my understanding is that above 40-some MPH, the ICE needs to rotate to keep MG1 from over revving. Is the ICE actually running, but the MFD shows electric only? I know this happens when the ICE is first warming up, the MFD shows braking regeneration, but the ICE is actually running.

The other possibility is that the ICE is only rotating and not consuming any fuel. If this is true, what about compression losses? While the Atkinson engine has reduced compression losses, they still exist. Is it possible that the intake valves can be left open even longer than normal, or are the compression losses low enough to be insignificant?

Granted, these aren't critical questions, but the more I understand about the THSII system, the more I love the car.

DaveinOlyWA · 10-23-2004, 10:39 AM

me thinks the ICE is still on but not using any gas. it is the same as coasting on a hill. in a regular ICE, the car will still idle.

in the case of the Prius, the ICE may shutdown, but it still continues to turn.

the other day for the first time ever (i wonder if it has to do with the colder weather we have had) i felt the ICE start up when traveling near 50 mph. this was verified by the mileage indicator going from 99.9 to 30 something.

Frank Hudon · 10-23-2004, 12:19 PM

on the 2k3 the mini scanner say's the engine is turning over but the fuel flow to the injectors is cut off and the rate of air flow into the engine is really low according to the scanner. The valves are never left "open" at any time, at the time when the speed is high enough that the ICE spins to protect MG1 from an over speed condition the VVT-i retards the cam timing to lower the compression pumping effect.

hdrygas · 10-24-2004, 04:29 PM

I wish we had the scanner for the 04s and 05s. I would like to learn more as well. The display shows electric only operation down hill at 65 mph or at least it did when I was coming down off Lookout pass on I90 coming home. I saw it at 58 on the freeway yesterday in cruse control. I had a question about backing up that may or may not be related. When you feel the ICE cut in during back up is it consuming gas or just spinning up?
PS anyone know when the scanner will be ready??

Frank Hudon · 10-24-2004, 06:49 PM

any time at low speed if you feel the ICE start up it's using gas. In Reverse it runs MG1 to provide power to MG2 to provide full power for reverse.

10-23-2004, 09:59 AM	#1
8AA Senior Member Join Date: Feb 2004 Location: Maryland Posts: 492 My Car: 2004 Prius Model: Package: #9 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Tech Question: Highway Stealth Mode What is actually happening when the car appears to be in "stealth mode" at highway speeds? If you're going down a grade at highway speeds, it is possible to let off on the accelerator to go into "engine braking regeneration," then lightly press on the accelerator to go into electric only "stealth mode." However, my understanding is that above 40-some MPH, the ICE needs to rotate to keep MG1 from over revving. Is the ICE actually running, but the MFD shows electric only? I know this happens when the ICE is first warming up, the MFD shows braking regeneration, but the ICE is actually running. The other possibility is that the ICE is only rotating and not consuming any fuel. If this is true, what about compression losses? While the Atkinson engine has reduced compression losses, they still exist. Is it possible that the intake valves can be left open even longer than normal, or are the compression losses low enough to be insignificant? Granted, these aren't critical questions, but the more I understand about the THSII system, the more I love the car. __________________ '04 Salsa Red BC9 CN mudflaps (front only) • Back window fresnel lens • Inverted Homelink mirror • F37/R35 Lifetime MPG 51.6

10-24-2004, 04:29 PM	#4
hdrygas Senior Member Join Date: May 2004 Location: Olympia Wa Posts: 3,650 My Car: 2004 Prius Model: Package: #9 Thanks: 0 Thanked 2 Times in 2 Posts Friends: 0	Re: Tech Question: Highway Stealth Mode I wish we had the scanner for the 04s and 05s. I would like to learn more as well. The display shows electric only operation down hill at 65 mph or at least it did when I was coming down off Lookout pass on I90 coming home. I saw it at 58 on the freeway yesterday in cruse control. I had a question about backing up that may or may not be related. When you feel the ICE cut in during back up is it consuming gas or just spinning up? PS anyone know when the scanner will be ready?? __________________ Belle, a Millennium Silver '04 BC #9 "Becoming one with my Prius, ICE on ICE off" Belle has been passed on to my daughter. I have a new silver Prius 08. No name yet we have just met but not been introduced.

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10-23-2004, 10:39 AM	#2
DaveinOlyWA 3rd Time was Solariffic!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 12,378 My Car: 2010 Prius Model: IV Package: Solar Roof Thanks: 24 Thanked 121 Times in 103 Posts Friends: 10	me thinks the ICE is still on but not using any gas. it is the same as coasting on a hill. in a regular ICE, the car will still idle. in the case of the Prius, the ICE may shutdown, but it still continues to turn. the other day for the first time ever (i wonder if it has to do with the colder weather we have had) i felt the ICE start up when traveling near 50 mph. this was verified by the mileage indicator going from 99.9 to 30 something.

10-23-2004, 12:19 PM	#3
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	on the 2k3 the mini scanner say's the engine is turning over but the fuel flow to the injectors is cut off and the rate of air flow into the engine is really low according to the scanner. The valves are never left "open" at any time, at the time when the speed is high enough that the ICE spins to protect MG1 from an over speed condition the VVT-i retards the cam timing to lower the compression pumping effect.

10-24-2004, 06:49 PM	#5
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	any time at low speed if you feel the ICE start up it's using gas. In Reverse it runs MG1 to provide power to MG2 to provide full power for reverse.