More Pwr Egor

November 1, 2010

I've been wondering...

Does anyone know EXACTLY what happens inside the engineering of the Gen3 Prius when PWR mode is activated?

Subjectively the car feels much quicker and certainly accelerates more promptly when lightly pressing the accelerator.

I know the throttle response gets sharpened up.

But I saw the instantaneous MPG meter drop one time as soon as I touched PWR, so I am guessing the engine is also encouraged to rev more, presumably to get it more firmly into the optimum power band.

I'd love to know more detail about exactly what happens and I have enough engineering background not to be put off my some informed discussion!

Just curious... :rolleyes:

November 1, 2010

Everywhere I've read about this the consensus has been that PWR mode just changes the mapping of the accelerator pedal to engine response.

Priuschat would normally be a place where this sort of thing is discussed in detail; I had quick look but only found this thread - the link takes you to a post where one member quotes the "Prius Chief Engineer" as pretty much stating the above.

Compared with ECO mode, the aircon/heater might be used more heavily, but my understanding is that there is no difference between PWR and normal mode in this respect.

The only other difference is that the "ECO" indicator in the HSI doesn't light up at all in PWR mode - maybe saving fuel as there are less pixels to light up on the display? :wacko:

If your instantaneous mpg dropped while you had the accelerator pedal depressed to some degree, the PWR mapping could explain the difference (same pedal position = more engine power). Presumably you would have felt the car accelerate a little more if this was the case?

It's possible that something more sophisticated is going on but I haven't found a description of this yet if so (maybe someone with a Scangauge or something similar would care to comment?)

November 1, 2010

I've been wondering...
Does anyone know EXACTLY what happens inside the engineering of the Gen3 Prius when PWR mode is activated?
...
I'd love to know more detail about exactly what happens and I have enough engineering background not to be put off my some informed discussion!
Just curious...

The 3 modes (PWR,Normal,ECO) largly affect the accelerator pedal mapping. ECO mode also does affect aircon and engine running. You can find all you need to know over on Prius Chat. There are many many threads, like

http://priuschat.com/forums/gen-iii-2010-prius-main-forum/79385-0-60mph-eco-vs-pwr.html

November 1, 2010

Priuschat would normally be a place where this sort of thing is discussed in detail; I had quick look but only found this thread - the link takes you to a post where one member quotes the "Prius Chief Engineer" as pretty much stating the above.

Great thread, thanks!

The only other difference is that the "ECO" indicator in the HSI doesn't light up at all in PWR mode - maybe saving fuel as there are less pixels to light up on the display?

LOL. I think it's a psychology thing. If you want PWR mode then the car will treat you as if you don't care about Economy. It won't tell you when you are driving economically. Since most people do care about economy, they end up switching back to NORMAL or ECO so that they can see the ECO gauge. Job done! ;)

If your instantaneous mpg dropped while you had the accelerator pedal depressed to some degree, the PWR mapping could explain the difference (same pedal position = more engine power). Presumably you would have felt the car accelerate a little more if this was the case?

No, I didn't notice any extra acceleration at that instant. I pressed the PWR button because I knew that in 2 seconds I would be accelerating hard (exiting a 30 MPH limit zone into an open single carriageway road at the 60 MPH limit, with traffic already breathing down my exhaust pipe). It felt like the car was preparing to accelerate i.e. was revving harder, with the ICE (Internal Combustion Engine) revs being raised to a point on the power band which would give better acceleration. The transmission would have decreased the gearing so net result would be:

1) Speed the same

2) acceleration the same - still zero

3) engine revving more leading to

4) more fuel being consumed and

5) engine being at a better point on the power band to respond more quickly to a prod on the accelerator pedal

I guess what I am trying to fathom out is if PWR mode has any effect on the CVT, not just the throttle sensitivity. (Or indeed on any other areas.)

Otherwise, my anecdotal observation could simply be a coincidence.

R04drunner1

November 2, 2010

The transmission would have decreased the gearing so net result would be

The Prius doesn't have a traditional CVT. It has a single fixed gear so there is no gearing up or down to do.

Have a look at

http://eahart.com/prius/psd/

and

http://prius.ecrostech.com/original/Understanding/ContinuouslyVariableTransmission.htm

However, in PWR mode it does seem that as well as most of the power being mapped to the first few % of movement, the pedal is more responsive.

If I floor the accelerator in PWR mode, the car takes off instantly.

If I do the same in ECO, there is a delay (half sec?) before the car takes off.

November 2, 2010

The transmission would have decreased the gearing so net result would be
The Prius doesn't have a traditional CVT. It has a single fixed gear so there is no gearing up or down to do.
Have a look at
http://eahart.com/prius/psd/
...

True but if you play with the simulator at eahart.com you can see that the ICE can spin at different rates while the car maintains the same speed, which is sort of what gearing in a conventional gearbox would achieve. For example at 30 mph the ICE can be made to run at anywhere between 1000-3000 rpm by varying the speed (and even direction of rotation) of MG1.

PWR mode could therefore conceivably allow the engine to rev faster so that more torque is available at a given speed, but I'm just speculating.

r04drunner1, if you haven't seen this you might also be interested in The Tao of HSI (also linked to from PriusChat) which is an in depth discussion of how the HSI relates to things like ICE speed and where the most efficient "sweet spots" lie, including a link to the diagram of torque vs. engine speed shown below for the Gen 2 (1NZ-FXE) and Gen 3 (2ZR FXE) ICE's (I think the contour lines relate to efficiency with the shaded areas being most efficient).

November 2, 2010

Wow, mega-thanks guys!

As Spock would have said, "Fascinating". Lots of interesting :bookworm: reading in those articles and in the associated links.

They pretty much confirm what people have been saying: apart from sharpening the throttle response the PWR button does not do anything.

The ECO button makes the throttle response more sluggish, which in turn can make it easier to maintain a given throttle position for hypermiling. Also the ECO reduces the fan / a/c limit. And it automatically brings in the HSI display. Now, up until now, I did not want the HSI display. I already have it configured on the HUD and, besides, I wanted to see the energy display so that I could try and get the engine to turn off - glide mode. But every time I pressed the ECO button (the one with the blob! in my car anyway) I got the HSI. Grrr... also I was forced to display the HSI to see the CONS figure. I know, you can see CONS figures on the bar graphs... but for safety's sake I did not want to drive along staring at bar graph readings, the results could be painful! :crutchy:

However... now that I've read the most informative article on what information can be gleaned from the HSI and how it can be used to achieve hypermiling techniques, I am a happy bunny again. :wub: