Hello! I have enjoyed the many illuminating posts here, as well as driving my new Gen III Prius. I have followed the many discussions about driving techniques, the rpm v. torque plots for the Gen III engine, and more. One question I have that I have not been able to answer is what determines the position of the HSI display bar? For reference, lets say that the “chg†bar goes from -25% to 0%; the “pwr†bar goes from 100% to 125%; and the the middle section goes from 0% to 100% with the vertical line in the middle being 50%. I understand that when the bar is between 0% and -25%, regenerative braking is happening, so long as the battery can accept charge. At 0%, the vehicle is coasting just as though it was in a neutral coast, but with the ICE still engaged and able to protect MG1 from overspeed. Between 0% and 50%, the vehicle utilizes primarily electric propulsion, though the ICE may run to charge the battery, keep itself (and the cabin) warm, or other such needs. Between 50% and 100%, the vehicle utilizes the ICE for propulsion. It may also utilize battery power if needed, or it may charge the batteries if needed. Between 100% and 125%, the vehicle operates as between 50% and 100%, but less efficiently and with the ability to provide more power. My question is, what determines the position of the bar between 0% and 125%? My observation is that if I keep the accelerator pedal at a constant position, the bar also remains in the same place so I have tentatively concluded that the bar position is completely determined by the pedal position. If this is so, the next question is what does pedal position determine? My understanding from posts here, and from my own observations, is that the pedal position determines the amount of power delivered to the wheels. Thus, at a 75% HSI bar position, and the associated pedal position, the vehicle is delivering a generally fixed amount of power to the wheels, and likewise for all other positions above 0%. If this is the case, then the next question is what is the amount of power delivered to the wheels at any given HSI bar position? Looking at the rpm v. torque plots for the Gen III engine, it appears that the engine turns on at about 1000 rpm, and produces about 8 or 9 kW. This then suggests that the HSI bar goes from 0 kW at 0% to about 8.5 kW at 50%. But how many kW are being delivered at 100%? One possibility is 40 kW where there is a sharp bend in the rpm v. torque plot, but this is just speculation. My questions then are: 1. Is the HSI bar’s position between 0% and 125% determined solely by pedal position? 2. Does pedal position in fact determine a unique “power call†to the wheels? 3. If 1 and 2 are true, what is the power delivery at 50% and 100%? I think this can be determined by the rpm of the engine at these HSI positions. Unfortunately, I don’t have a ready way (Scanguage, etc.) to determine rpm at different pedal positions and HSI bar positions. 4. What changes in the operation of the HSD above 100% that makes Toyota tell us the vehicle is operating less efficiently (turns off “eco†light)? Does anyone have insights into any of the these questions? Thanks! Michael Morrison
Welcome aboard! Good questions. There are many factors that influence the "bar"... SOC being one of them. Typically the ICE will come on at 50% (half way mark) but no always. Depending on temp and the SOC. I have seen the ICE off (0 rpm) above 50%. Others will fill I am sure.
My ScanguageII RPM Xgauge indicates that Between 0% to 20% the ICE normally is off Between 25% to 55% the ICE will go on depending on the power(resistance) needs to turn the wheels. The higher the power needed to turn the wheels the sooner the ICE will rev up. When the Prius is going downhill the power needs can be 20% less and while going uphill the power needs can by 50% higher. The 2010 Prius ICE will automatically engage to protect MG1 at around 43 to 46 mph. When going over 50% the ICE is charging the traction batteries. The HSI State of Charge(SOC) battery bar actually displays only from 70% (top bar) to 40%(bottom bar) if you allow the SOC to go less than 45% the ECU runs the ICE to aggressively recharge the traction battery. When this happens there is normally a -3 mpg to -5 mpg loss in fuel efficiency. Therefore, most hypermilers work to keep the SOC display from dropping more than three bar. At about 50% HSI, the ICE is burning between .80 gallons per hour to 1.10 gallons per hour and the engine is working at about 1200 rpm to 1400 rpm. At about 100% HSI, the ICE is burning between about 1.80 gallons per hour to 2.30 gallons per hour and the engine is working at about 1800 rpm to 2400 rpm. The bar's position is reset every time you release the accelerator pedal. The HSI bar will change depending on the torque/power requirements that the ICE and MG1/MG2 senses. Initially as you press the accelerator pedal the Prius starts up the MG1 and MG2 electric motor and as the pedal is pressed further down the ICE is started up. Hence, by releasing the accelerator and then pressing it again very lightly you can turn off the ICE and switch to electric motors only ( this feature is used to do what hypermilers call steath highway mode). If the Prius is going downhill which requires less power, the bar location will be more to the left for the same speed than if the Prius was going uphill which requires more power. that is to say the pedal position and the HSI bar determine the aggragate power output of both the electric motors and the gasoline engine working in tandem to move the wheels. Essentially, when the Prius is burning more than 2.00 gallons per hour, the ECO light is turned off. The Prius gets its best fuel efficiency when its being driven for longer than 30 minutes/7 miles AND when it is driven between 20 mph to 40 mph AND when the tire pressure is set to the tires maximum sidewall pressure AND when the gasoline consumption per hour is less than 1.25 gallons per hour AND when acceleration is synchronized with flat or downhill grades AND when the outside temperature is greater than 60 degrees Farenheit. Walter Lee 2010 Toyota Prius III, Blue Ribbon/Dark Grey, Oem floormats Yokohama Avid S33 (psi 48 front psi 44 rear) Scangauge II ( MPG, AVG, SOC, GPH) odeometer +12000 miles, 58.6 mpg overall
I have a couple comments on some of your points... That is correct, and because the car tries to keep the batter no more than 60-80% charged there are very few cases where the battery cannot accept a charge. The length of this bar is based on the amount of power going to the battery... the more power going to the battery the longer the bar is. [/QUOTE] At 0%, the vehicle is coasting just as though it was in a neutral coast, but with the ICE still engaged and able to protect MG1 from overspeed.[/QUOTE] The ICE is only engaged when you're coasting above about 45MPH. When you're coasting under 45MPH the ICE isn't turning at all. My understanding is that you're correct and the pedal position is the only thing that influences the position of the bar above 0%.
Don't think that's -quite- right. At mid-low speeds try putting your foot at a certain place and keep an eye on HSI position. if you start to go up a hill, your speed will drop. as it drops, your HSI position will move down. Not entirely sure why it does this, but it does. You'll also notice that if SOC is very low that the HSI becomes very sensitive. So while the HSI position is determined by pedal position, it is not absolute.
In EV mode, you can max out the bar to 100% and that is about 20 kW, if it does indeed max out the battery. In non-EV mode, you can only drive in EV up to 50% of the bar. Based on that, my guess is 50% bar is about 10 kW and 100% bar is about 20 kW, *if* you assume a given HSI bar position provides the same power in EV and non-EV modes. I don't have a scanguage, but one can calculate power based on speed and mpg on level ground. If you could measure elevation using a GPS, you can do it on non-level terrain.
I've observed that in "out of gas" mode you can push well into the PWR area, and it definitely feels like more power is available than in EV mode. I doubt it exceeds the 25kw limit in "out of gas" mode, so i would say 100% HSI in EV mode represents less than 25kw.
