64 % of Prius Power gets to wheels during max acceleration?

The Prius isn't really a CVT (Continuously Variable [RATIO] Transmission) - they just didn't know what else to call it. The Power Split Device has only one "speed" (ratio). The ICE torque transmitted to the ground is approx. 74% of total, if memory serves, and has an effective ratio in the neighborhood of 3.7 - 3.9:1. The remaining ICE torque is available to spin MG1. The Prius ICE can't put enough torque on the ground to accelerate at an acceptable rate from a standing stop and requires assistance from the battery and MG2 to get up to speed. MG1 can send surplus electron's to the battery or to MG2 depending on how much of a hurry you're in. Your foot's "suggestion" helps the computer decide how much extra "oomph" is required, and it seamlessly orchestrates the magic going on behind the scenes.

 

Does that take into account electrical losses too, not just mechanical? A jackrabbit start will put a much larger than normal power fraction through the electrical path, which has many more conversion losses than the mechanical path. Even if each electrical stage is reasonable efficient, the total losses through the whole chain really add up.

 

A much larger loss is normally considered for the differential, typically in the 30% range. The Prius does have a differential. Consider the electrical parts (MG1 and MG2 as well as the inverter) to have in the area of 95% efficiency. So the DC comes out of the inverter as AC at 95% of input power, and is converted to torque at 95% of the input to MG2. I suspect the quoted power values are input not output torque.

Yes, all that power being lost in a differential is converted to heat. We don't see this as a problem because the car can't produce that much power continuously. But if it could it would need a cooler, like a NASCAR racing car has.

 

is from World's first 2010 Prius Dyno | PriusChat

 

I don't think 0-60 time is a deal breaker on economy cars. My previous Corolla also had almost exactly 10 sec or so and sold in millions. I felt it was acceptable and I vividly remember European cars in 1970s/80s somewhere in 15 sec range, or closer to 20 if fuel efficient. BTW, the corolla's engine had 130 HP max power, and you cannot reasonably expect max power all the time during acceleration.

 

Hi briank101

You may enjoy taking a look at this thread Measuring GenIII Prius energy (power) flow with OBD | PriusChat

Over there you may find the following diagram of energy flow while my 2010 Prius is going up a ramp of 4% with the HSD indicator still in the ECO but close to the POWER zone.



In this case, 13228/19651 = 67% of the ICE mechanical power reach the road. The ratio is very close to the 64% you calculated

Big hugs from Frank

 

Power loss in an automotive differential is 5% or less, not 30%.

 

Close but the maximum is actually 72%. That's how PSD is set up so that 72% of the torque goes out to the wheels. As ICE revs, so will the power peak at 72%. The remaining 28% goes to the generator (normally MG1) and the motor (MG2) will reroute the power back into the wheels.

Therefore, 100% of the gas engine 84 hp will get to the wheels, minus the conversion loss through the electrical path.

 

Don't confuse power and torque. Revving the ICE per se does not increase the power through the mechanical PSD path to the wheels, if the wheel RPM and ICE torque remain the same. Instead, revving the ICE will also rev MG1, pushing all the increased power through the electrical path from MG1 to MG2.

Depending on component RPMs, that 72-28 torque split can still produce just about any arbitrary power split.

 

You are right. Come to think of it, when Prius is at near top speed, all of ICE power would go out the wheels because MG1 rpm is near zero. 28% of the torque would be at MG1 but since it is barely spinning, no power would go out.

Another example of this condition is at 60 mph with ICE at 2,500 rpm. I used to monitor MG1 rpm (with Torque app) when accelerating and I try to get it as close to zero as possible... because I knew at that point, there are no power going out the electric path, meaning the most efficient state to accelerate.

 

I tried the same thing with torque app and couldn't find anything conclusive. As far I could determine, MG1 would always spin at various speeds and I tried MG1 torque readings too and could not catch the system at 0 MG1 torque.

 

Most people are shocked the first time they see the real-world energy losses of vehicles. Conventional vehicles are lucky to reach 35% energy efficiency. The 74% figure for the Prius is quite high. Tesla claims 88% efficiency. See the following links:

Fuel Economy: Where the Energy Goes

Energy Losses in a Vehicle

Energy Efficiency of Tesla Electric Vehicles | Tesla Motors

 

-100 to +100 rpm is good enough for me. I couldn't get any conclusive result (MPG) as well.

 

According to this, Prius ICE is 38% thermal efficient.

 

A problem with that is that high efficiency CVTs for automotive applications don't exist, and it's been over 100 years since the first CVT car (1908 Carter). Another problem is that the total range of ratios in a CVT is limited by materials science, lubricants and other ugly bits of reality. The present state of the art is stretched more than enough just generating the ratios that are needed to match an ICE engine to the road.

Many people are under the mistaken impression that CVT transmission are efficient when the real overall automotive system efficiency gain is because they are able to keep the ICE engine at it's most efficient operating RPM for the power required at the moment. That's kind of like an overdrive gear ratio in a manual transmission is less efficient than the direct drive gear ration, but overall automotive efficiency is higher because overdrive puts the engine at a more efficient rpm for the load.