ICE Runs in reverse..

seftonde · 06-19-2007, 09:30 PM

I live at the top of a very steep driveway. I am used to backing up it, and when I first got my Prius in March I did the same. I was amazed that I had to push the accellerator almost to the floor to go up! Then I read that in reverse it only uses the MG's, so it takes a lot of power.

Now, yesterday and today I did the same thing. When driving home I had almost depleted the battery. As I started up the driveway (in reverse) i heard the ICE running. I paused and hit the energy screen and sure enough there was a power line from the ICE to the MG only. I am sure it was kicking in to charge the battery, but I didn't realize it would run in reverse.

My understanding of the planetary gear system is not too good, and I'm trying to justify in my mind how it works in reverse - obviously the ICE only turns in one directoin....

Just thought it was interesting!

Daniel

john1701a · 06-19-2007, 09:57 PM

Yes, the engine running while in reverse is somewhat counter-productive. In fact, you can see that process in action at the bottom of this webpage.

Look at those animations closely. Though a little on choppy side, they do get the point across. The PSD is a very interesting device.

seftonde · 06-19-2007, 10:09 PM

<div class='quotetop'>QUOTE(john1701a @ Jun 19 2007, 09:57 PM) [snapback]464996[/snapback]</div>

Quote:

Yes, the engine running while in reverse is somewhat counter-productive. In fact, you can see that process in action at the bottom of this webpage.

Look at those animations closely. Though a little on choppy side, they do get the point across. The PSD is a very interesting device.
[/b]

Hi John,

Thanks! Yes, I saw your animations and your excellent page on the Prius before I bought it. I had not been to your site since I bought the car; thanks for reminding me - now the animations mean more to me since I have better understanding of how the beast operates. Yes, truly an interesting (wonderful) device.

Daniel

daniel · 06-20-2007, 12:06 PM

Amazing, indeed! The ICE runs (forward, of course), turning MG1, which generates electricity, which goes to MG2, which propels the car (backwards, in this case). I believe the geometry of the PSD limits how fast you can back up.

60% of the torque of the engine goes to MG2 and the wheels (forward) but force does work only in proportion to distance traveled, so that at slow speeds, where MG1 is turning very fast and MG2 is turning slowly, most of the power from the ICE goes through MG1 rather than directly to the wheels and MG2, so I believe there is little energy lost when going backwards at slow speeds. The counter-productive work done by the ICE on MG2 is small, while the work that follows the electrical path from MG1 to MG2 is large.

qbee42 · 06-20-2007, 01:51 PM

<div class='quotetop'>QUOTE(daniel @ Jun 20 2007, 12:06 PM) [snapback]465247[/snapback]</div>

Quote:

Amazing, indeed! The ICE runs (forward, of course), turning MG1, which generates electricity, which goes to MG2, which propels the car (backwards, in this case). I believe the geometry of the PSD limits how fast you can back up.

60% of the torque of the engine goes to MG2 and the wheels (forward) but force does work only in proportion to distance traveled, so that at slow speeds, where MG1 is turning very fast and MG2 is turning slowly, most of the power from the ICE goes through MG1 rather than directly to the wheels and MG2, so I believe there is little energy lost when going backwards at slow speeds. The counter-productive work done by the ICE on MG2 is small, while the work that follows the electrical path from MG1 to MG2 is large.
[/b]

This is correct. The HSD is a work of wonder. As an engineer, as soon as I understood how the HSD worked, I knew I had to have a Prius.

As for backing up, most cars are geared down in reverse. Most people don't need to drive fast in reverse, and car companies (and insurers) would just as soon you didn't.

Tom

Pinto Girl · 06-20-2007, 02:06 PM

<div class='quotetop'>QUOTE(qbee42 @ Jun 20 2007, 12:51 PM) [snapback]465323[/snapback]</div>

Quote:

This is correct. The HSD is a work of wonder. As an engineer, as soon as I understood how the HSD worked, I knew I had to have a Prius.

As for backing up, most cars are geared down in reverse. Most people don't need to drive fast in reverse, and car companies (and insurers) would just as soon you didn't.

Tom
[/b]

One cool little thing about the Prius is that the digital speedometer works in reverse (this is the first car I've owned without analogue gauges; those didn't)...I've seen it display 16mph, backing down my driveway in the morning, late to the transit station (but I always stop to look before pulling into the street!)

I'm fascinated by this for some strange reason.

subarutoo · 06-20-2007, 03:38 PM

<div class='quotetop'>QUOTE(Pinto Girl @ Jun 20 2007, 11:06 AM) [snapback]465332[/snapback]</div>

Quote:

One cool little thing about the Prius is that the digital speedometer works in reverse (this is the first car I've owned without analogue gauges; those didn't)...I've seen it display 16mph, backing down my driveway in the morning, late to the transit station (but I always stop to look before pulling into the street!)

I'm fascinated by this for some strange reason.
[/b]

What's your best 0-16 time, or is it 0 to minus 16?

usbseawolf2000 · 06-20-2007, 03:45 PM

You don't understand how PSD works until you "get" why the ICE can spin forward yet the Prius moves backward.

Planetary gear-set is amusing. I bought some to play/show around from a hobby store.

Tom6850 · 06-20-2007, 03:54 PM

<div class='quotetop'>QUOTE(Pinto Girl @ Jun 20 2007, 02:06 PM) [snapback]465332[/snapback]</div>

Quote:

One cool little thing about the Prius is that the digital speedometer works in reverse (this is the first car I've owned without analogue gauges; those didn't)...I've seen it display 16mph, backing down my driveway in the morning, late to the transit station (but I always stop to look before pulling into the street!)

I'm fascinated by this for some strange reason.

[/b]

If I was backing up at 16MPH I sure would not be looking at the speedometer!!!!!!

Pinto Girl · 06-20-2007, 04:28 PM

<div class='quotetop'>QUOTE(Tom 6850 @ Jun 20 2007, 02:54 PM) [snapback]465380[/snapback]</div>

Quote:

If I was backing up at 16MPH I sure would not be looking at the speedometer!!!!!!
[/b]

You know, I didn't have my head turned to look behind me (I normally back up using the mirrors and maybe the rear view camera)...and --darn--- the yard was sure going by fast that day (I had the pedal to the floor for a little bit); I simply *had* to see exactly *how* fast...

--------

I'm not sure if this has anything to do with what we're discussing or not, but I've always wanted to take the body off of a car and put it on facing the opposite direction, so you'd drive down the road looking through the rear window.

I guess you'd still be using the forward gears, though, normally...

Hmmmmmm....

This brings up the philosophical question: does a car with its body on backwards drive backwards...or not...?? I mean the chassis thinks it's still going forward, but the body doesn't.

Wondering, now, if I'm not overthinking this just a bit.

06-20-2007, 12:06 PM	#4
daniel Cat Lovers Against the Bomb Join Date: Feb 2004 Location: Spokane, WA Posts: 14,311 My Car: 2004 Prius Model: Package: #6 Thanks: 453 Thanked 1,326 Times in 928 Posts Friends: 0	Amazing, indeed! The ICE runs (forward, of course), turning MG1, which generates electricity, which goes to MG2, which propels the car (backwards, in this case). I believe the geometry of the PSD limits how fast you can back up. 60% of the torque of the engine goes to MG2 and the wheels (forward) but force does work only in proportion to distance traveled, so that at slow speeds, where MG1 is turning very fast and MG2 is turning slowly, most of the power from the ICE goes through MG1 rather than directly to the wheels and MG2, so I believe there is little energy lost when going backwards at slow speeds. The counter-productive work done by the ICE on MG2 is small, while the work that follows the electrical path from MG1 to MG2 is large. __________________ Daniel Primary car: 2010 Tesla Roadster. Range: 245 miles on a charge. Zero to sixty: 3.9 seconds. Torque: 273 foot-pounds. Horsepower: 288. 100% electric @ 2 cents per mile. Gas guzzler for road trips or when I park at the airport: 2004 Prius. "If voting changed anything, they'd make it illegal." -- Emma Goldman "Anyone who has ever looked into the glazed eyes of a soldier dying on the battlefield will think long and hard before starting a war." -- Otto von Bismarck

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06-19-2007, 09:30 PM	#1
seftonde Member Join Date: Mar 2007 Posts: 41 My Car: 2007 Prius Model: Two Package: Thanks: 0 Thanked 1 Time in 1 Post Friends: 0	I live at the top of a very steep driveway. I am used to backing up it, and when I first got my Prius in March I did the same. I was amazed that I had to push the accellerator almost to the floor to go up! Then I read that in reverse it only uses the MG's, so it takes a lot of power. Now, yesterday and today I did the same thing. When driving home I had almost depleted the battery. As I started up the driveway (in reverse) i heard the ICE running. I paused and hit the energy screen and sure enough there was a power line from the ICE to the MG only. I am sure it was kicking in to charge the battery, but I didn't realize it would run in reverse. My understanding of the planetary gear system is not too good, and I'm trying to justify in my mind how it works in reverse - obviously the ICE only turns in one directoin.... Just thought it was interesting! Daniel

06-19-2007, 09:57 PM	#2
john1701a Senior Member Join Date: Jan 2004 Location: Minnesota Posts: 5,488 My Car: 2012 Prius Plug-in Model: Plug-in Advanced Package: No Package Thanks: 137 Thanked 957 Times in 499 Posts Friends: 22	Yes, the engine running while in reverse is somewhat counter-productive. In fact, you can see that process in action at the bottom of this webpage. Look at those animations closely. Though a little on choppy side, they do get the point across. The PSD is a very interesting device.

06-20-2007, 03:45 PM	#8
usbseawolf2000 HSD PhD Join Date: Sep 2004 Location: Queens, NY Posts: 9,638 My Car: 2006 Prius Model: Package: #3 Thanks: 1,271 Thanked 1,266 Times in 848 Posts Friends: 81	You don't understand how PSD works until you "get" why the ICE can spin forward yet the Prius moves backward. Planetary gear-set is amusing. I bought some to play/show around from a hobby store.