Eco Bar

I think you are talking about the Hybrid System Indicator:

• ECO - means the car in 'economical' mode and goes out when the engine provides a high level of power
• PWR - means the engine is in a higher power mode, about 23.4 hp or more from the hybrid system
• CHG - is charging the battery from regenerative braking
• 75% - appears to be about 15.3 hp, where I have the small, yellow plastic tape marker

Check the archives under HSI and you'll find the earlier reports. Hobbit was curious and I used GPS measurements to calculate the wheel power levels:



Bob Wilson

 

The big bar is a non-linear, power scale and the center divider is just 'nice' but otherwise of little good. Ken@Japan posts that the Japanese drivers like to use the lower 25% for 'glide' and upper 25% for 'pulse.'

I was only interested in understanding the relative amount of power being requested. Hobbit was curious too so I used two metrics:

• acceleration as a function of power bar setting
• hill climb speed as a function of power bar setting

What I haven't tried to do is figure the Brake Specific Fuel Consumption at these different power settings. It is easy enough to do with a GPS and the now calibrated trip meter. However, these power regions don't really interest me.

I'm more interested in BSFC in the "PWR" region using "P" "W" and "R" as the scales. If there is a BSFC 'knee in the curve,' it could be very useful to understand how much we can apply without having to worry about excessive fuel consumption.

One tricky aspect is the traction battery SOC needs to be monitored during these tests. It turns out that traction battery starting SOC can have a major impact on the results. A cleaner method will be to monitor MG1 current and map the torque. This in turn allows a more accurate measurement of ICE power and with injector timing and pulses, actual BSFC without having to worry about traction batter SOC.

Bob Wilson

 

Doesn't there have to be a "knee" in the curve? If you designed it wouldn't you put the knee right at the point at which the display turns red? I don't want to sound stupid, but doesn't it turning red mean something? Why red? Isn't red normally used to designate an undesirable range of operation? Maybe I'm giving Toyota too much credit, but I think they picked red to indicate you are in a range you don't want to be in. The ECO light extinguishing was my second clue

 

Oh and maybe I'm imagining this, but the non linearity of the HSI seems to be speed related. Butt Dyno indicates that there is more power being applied at higher speeds in the same region of the HSI. Butt Dyno's are terribly unreliable though. It could be simply that the ICE is at higher RPM's, but power output could be the same?
We need a fuel flow meter don't we?

 

What we need is a dang chart in the Owner's manual showing fuel consumption as a function of HSI bar setting. <grumble grumble>

Fortunately, there are enough engineering type Prius owners that it become more of a "what will I do today" versus cursing the darkness.

Bob Wilson