2010 Prius ICE power and efficiency Vs RPM charts

Hi everyone

In this thread Measuring GenIII Prius energy (power) flow with OBD | PriusChat I showed the way I measure the energy flow in the 2010 Prius.

Having recorded more than 1500 trips, I can display some interesting charts about the ICE power and efficiency from my records. However it was difficult to find high power data because I am a fuel efficiency minded driver (the reason I bought a Prius) and charts have only 130 points above 3000RPM which corresponds to an average of 30kW (40hp)

The first chart is the Power Vs RPM with colors indicating coolant temperature. Points are drawn by increasing coolant temperature order; that is blue dots (cool) are behind red dots (hot) and most of them cannot be seen:



My first comment is the big difference of the Prius chart using normal driving data compared with other cars. In any other vehicle with a manual or automatic transmission you may measure almost any power (from zero to more than 50% of the max power) at any RPM above idle. It only depends of how much you press the accelerator; so it will be almost impossible to see shapes in the chart other than those coming from the driving style of the driver. But in the Prius there is a defined relationship of the demanded power by the HSD and the commanded RPM to the ICE.

My second comment is about the warming stages, you may see blue dots (less than 60ºC - 140ºF) around 1300RPM that produce less than 5kW during S1a stage as reported in this post HSD behaviour during S1a & S1b warming stages | PriusChat

My third comment is about the influence of the coolant temperature in the RPM for a given power. If you look at the 20kW power line, it seems that the ICE revs to 1900RPM with coolant temperature between 60-70ºC (140-158ºF) but revs to 2200RPM with coolant over 88ºC (190ºF). This was noticed in this post from october 2011 with the following chart showing that below 70ºC (158ºF) coolant temperature, the Torque produced by the ICE in the range 1300-2100RPM is some 20% higher than with coolant temperatures over 70ºC (158ºF). Both curves fall into the 220g/kWh area:



The second chart for today is the ICE efficiency Vs RPM with colors indicating coolant temperature. Points are drawn by increasing coolant temperature order; that is blue dots (cool) are behind red dots (hot) and most of them cannot be seen:



The efficiency is almost flat in the 34%-38% region from 1100RPM up to 3000RPM (no available data above that) As in the power chart, blue dots corresponding to S1a (accumulated around 10% efficiency) & S1b warming stages can be clearly seen in the 1300RPM region.

The influence of coolant temperature is not very important. You may notice that red dots are in the upper part of the main body; below are orange, yellow and light blue strips of data in the 32%-34% efficiency band. A more detailed analysis tells me that below 1800RPM the coolant temperature above 60ºC (140ºF) has a maximum influence of 1 percentage point of efficiency (from 36% at 61-70ºC to 37% at >88ºC). Above 2000RPM, it seems that efficiency goes to 35% for lower coolant temperatures, probably related to the flame lower speed at lower temp.

Hope you enjoy the data.

Big hugs from Frank

 

Hi everyone

In the first post of the thread I showed the charts of power, efficiency and torque Vs RPM with more than 56087 scattered points just to show the main patterns, but it is possible to take the reading average for each RPM range and coolant temperature range to improve the analysis.
The average power Vs RPM for each coolant temperature range is:



From 1450RPM with coolant temperatures lower than 70ºC (158ºF) the ICE provides some 2kW more than with warmer coolant temperatures.

The average torque Vs RPM for each coolant temperature range is:



The 8 Nm increase of torque with lower than 70ºC coolant temperatures is noticeable above 1450 RPM. Another characteristic of the warm coolant temperatures curves is the positive slope above 1500RPM which suggests the engine could do better at higher RPM ¿or may be a penalty on efficiency at higher RPM and higher torque? Let’s see the average efficiency Vs RPM for each coolant temperature range:


Yes! There is a minute penalty on efficiency at higher than 1900RPM. The maximum efficiency obtained at these RPM are: 36.2% with coolant at 71-80ºC; 36.5% with coolant at 81-85ºC; 36.7% with coolant at 86-88ºC; 38.0% with coolant at 89-93ºC (at 2100RPM this one).

Also good news for Prius owners that stay away from cold; the higher the coolant temperature, the higher ICE efficiency at any RPM.

Hope you enjoy the charts.

Big hugs from Frank

 

Hi SageBrush
Interesting question this one. From my understanding, when the Prius is coasting the drag sources are:

* Aerodynamic drag. Well known; force is proportional to speed^2. Power proportional to speed^3
* Tyre drag. Force is constant with speed. Power is proportional to speed.
* Friction brakes. Assume that they are not applied in this example.
* PSD and transmission friction. I do not have a consistant math model of its behaviour yet.
* ICE friction (only over 67Km/h =41.6mph= OBD vehicle speed) force is constant with speed (you'll see that); power proportional to speed.
* MG1 and MG2 energy drained. A high percentage is converted to electricity and used to charge the hybrid battery. Force and power are regulated by HSD (and driver pressing pedals or changing gears)

Talking about ICE drag, the Prius is again a "rara avis" among cars. HSD keeps ICE at 1000 RPM when dragging and drag torque is therefore constant at any speed.

This is a 3D chart of the number of readings (out of a total of 3964 in this set) in the vertical scale within a torque/RPM grid. As you can see, almost all of the readings are located at 1000RPM and 12Nm (0.89 ft-lbf) of drag torque which gives 1.2kW (1.6hp) drag power. This is independant of the vehicle speed (over 67Km/h upto 103Km/h max registered in my data).

The 3D chart is:



The same chart viewed from above whre you can see that all points are accumulated at 12Nm and 1000RPM:



Hope this answers your question.

Big hugs from Frank