Gen4 Prius ICE Details: 40% Efficiency

no one can without the legend.

 

There is only one paragraph with three sentences for these graphs:

Figure 1 shows the operation area of a HV engine and of a conventional engine. - This refers to the upper graph, an engine efficiency chart.

It can be shown that the HV engine uses higher brake mean effective pressure (BMEP) area and higher engine thermal efficiency area compared to conventional engines. - Good hybrid runs the engine in the fuel-efficient power range and banks the excess power in some form of energy storage, a traction battery. Then when the battery is charged enough, the engine is turned off.

Therefore improving the maximum engine thermal efficiency leads to better fuel economy of the hybrid vehicles. - It follows that a more efficient engine will have greater, total efficiency in a hybrid . . . assuming the control laws are aggressive.​

I see nothing in the paper that tells us how to interpret the lower chart. So this is my thinking:

• "HV" line - if the car has a 'x' MPG at any given power setting, the y-axis percentage calculates the expected improvement. For example, at 15 hp (~12 kW) there should be just under 40% MPG improvement. I would expect at 55 mph (~15 hp load) and ~60 MPG, the car should get 60 + (40% * 60) ~= 84 MPG. This would be awesome and put the EPA numbers on their heels. Even at CR's 65 mph highway test, 52 + (30% * 52) ~= 67 MPG. We are talking efficiencies in the low-range of EVs!
• "MT" and "CVT" are relative transmission efficiencies but not well explained.

Occam's razor: the bottom scale is off by a decimal point.

"20" -> "2.0"
"40" -> "4.0"
"60" -> "6.0"​

Now everything makes sense. Otherwise, we'd be talking 'cold fusion' level of efficiency improvement. <GRINS>

FYI, I am trying to ask the authors for more details about the lower chart.

Bob Wilson

 

The correlation is OK but the % units on the Y-axis do not make sense. But my interest is in projected vehicle MPG as a function of ICE thermal dynamic improvement.

Here is another approach:

• 38% - base performance of ICE becomes 100% performance of base vehicle
  • 100%/38% scaling factor, ~2.63 (nondimensonal)
• 2% ICE efficiency * 2.63 ~= 5.26% vehicle MPG improvement

Now this makes more sense than trying to use the unknown Y-axis values of the second chart. More importantly it can lead to credible MPG projections over my 2010 benchmark:

A few projected data points:

• ~100 MPG (true) @25 mph
• ~92 MPG @30 mph
• ~80 MPG @40 mph
• ~66 MPG @50 mph
• ~60 MPG @60 mph
• ~55 MPG @65 mph
• ~44 MPG @75 mph

This is outside of any vehicle drivetrain, rolling drag, and aerodynamic tricks. Add advanced power electronics and control law optimizations . . . it has a good chance of achieving current PIP-like performance in the base car.

Bob Wilson

 

Don't forget weight savings. Promised 20% should be good for 8.3% alone improvement