Why my car switches to EV mode at 40-45 mph? Seems inefficient.

If this is news to you, it helps explain why you achieved only 40 mpg in LA city traffic.

When this operation is sustained for a few miles, it means the needed propulsion power is quite low (likely including some minor downhill slope, not necessary preceptible to the driver), so the car can almost glide.

Yes, some energy is lost in the extra energy conversions of EV. But the ICE consumes some minimum overhead power just to run at all, so it cannot operate near to its optimum efficiency when traction power is under about 10 HP. When the needed traction power is much less than that, the ICE overhead loss exceeds the extra overhead loss of EV. If the traction battery has enough charge to support EV, then it becomes worthwhile to shut off the ICE.

At these lower speeds, best efficiency comes from alternating between ICE and glide/EV, not sticking to ICE-only or EV-only. The car does very well when making its own choice on its own schedule. Drivers using Pulse & Glide or similar strategies can do significantly better by incorporating knowledge about conditions ahead (traffic, required stops, slope, etc.) that the car alone cannot know.

At higher speeds, where the air drag and traction power are high enough to keep the ICE operating in or near its peak efficiency zone, then ICE-only operation becomes efficient. Geeks can derive this minimum power from the engine's BSFC chart (frequently linked in other postings), and monitor actual power output with many OBDII-type scanners (ScanGauge, Torque, etc.)

 

Too much power? As the most gutless car I've ever owned I'd have to disagree with that.

 

Rapidly compared to what? It's certainly adequate, but I've never had the pleasure of driving a car with slower acceleration than this thing. Which is fine because I don't think any of us bought them looking for outstanding performance.

I like my car a lot, but it definitely sacrifices some things to get the spectacular fuel economy that it does. It moves in and out of traffic just fine, but I wouldn't want it to make any less power than it already does.

 

I've got an '06 with a 1.5, I guess I'd be willing to trade cars with you, mines paid for and it would have to be an even steven trade.
As I'm in NH and am willing to travel to the other coast, I'd want to pay for gas one way.

Or, you could unbolt the traction battery and leave it in the garage, no more nasty traction battery upsetting the ice.

 

Have you driven a typical car from the 1980s? My Prius easily beats my 1984 2.3L, 88 hp Mustang.

Since then, American's car horsepower has bloated faster than their waists and butts.

 

Because they're not trying. Like I said before, I think this thing handles and drives perfectly adequately, but I have never been in a car with less acceleration than "Polly" the Prius. Which is great because it vindicates itself with outstanding efficiency.

I think there's more to efficiency than engine size. A quick survey of Fuel Economy and Fuelly - Track and Compare Your MPG suggests that the Gen 2 Prius gets worse fuel economy than the Gen 3. I have no doubt a new generation 1.5L engine should be capable of better efficiency than the 1.8 currently in use, but that would likely come at the expense of power output.

Just today on the way home I noticed that the engine was turning 3,870 RPMs climbing a hill on I-84 while maintaining 68 MPH on cruise control. It's certainly not overwhelmed climbing the hill, but it's working hard to maintain speed. I wouldn't want a smaller engine, I like Polly just the way she is!

 

Nope, I was born in '85, and the oldest thing I've spent any time in was my first car which was an '89 Jeep Cherokee. I take it back, after thinking about it I've driven some HMMWVs at work that were more gutless than the Prius. So were the tractor-trailers I used to drive. I guess I was mainly comparing it with other passenger cars.

 

Yep, I agree with you there, the performance is perfectly adequate.

And a Rav4 gets significantly better fuel economy than my wife's Sienna with the exact same V6. So what? It's a smaller car, so all things being equal it will be more efficient.

 

Of course there's lots more to it, that's all I was trying to illustrate with my comparison. You compared a smaller car with a smaller engine trying to make the point that said smaller engine would yield better efficiency in a larger car. I think you're probably right, but you can't compare the efficiency of a smaller car and make that point. Thats all.

 

I believe IMA can run with the hybrid system shut down, and use a purely mechanical path between ICE and wheels. In this sense, the electric part of the hybrid system can be portrayed as an assist.

HSD is very different. A considerable portion of the traction power is transmitted mechanically. But the electric part is not an assist at all, rather is an integral and essential part of HSD operation. If it stops, the ICE just causes MG1 to spin with no power reaching the wheels, just like an old fashioned open differential with one wheel jacked up into the air (or spinning on glare ice). The wheel on the ground can't get torque to move the car.

 

I like to think of HSD when the engine is powering the wheels as the electric portion is providing resistance to the elements of the planetary gear set that need it in order to allow the torque to hit the wheels. The relationship of MG1/MG2 float back and forth, while not consuming any energy from the battery, to get the right ratio for the ICE.