this is very odd for me to understand. The exact opposite happens to me. during stop and go times my mpg drops or stays the same. For example, I cannot (due to flow of traffic) accelerate from, say, 0 to 25 mph using battery power alone. I, technically, could - believe me. I tried when I first bought the car, but I got cigarette butts thrown at me, people honked at me and sprayed windshield washer fluids at me, and worst of all, cut me off only to stab on their brakes for a second in front of me just to tick me off.

Some places in the world (where I've been) where mpg may actually go up in stop and go city traffic (I think), are Honolulu - you can take all day to accelerate. People aren't in a hurry. Tokyo and some other large cities in Asia - for some reason, these drivers do not accelerate quick yet the traffic is horrendous...

 

Stop and go traffic can vary quite a bit in how extreme are the "go" periods and acceleration rates. I've been in stop and go on the interstate where you stop, and then go all the way up to 30-40 mph for 30 seconds, and then stop again, only to continue repeating the pattern for an hour. Conversely, I've been in stop and go on city streets where the "go" periods are characterized by max of 10 mph for short periods, and the stop sessions are quite short as well. I believe the former will capture a lot of harder acceleration rates and give lower mpg than the latter.

 

In any case whether mpg goes up, holds steady, or dips, just imagine how bad it is for all the regular gas powered cars in stop-and-go. Their numbers drop so deep it's like a black hole, decent mpg numbers can never escape for the current tank. The gravity of the situation is also sucking up brake linings.

Driving in stop-and-go efficiently can be a social chess game. How to take advantage of space, predict emerging patterns, and block attacks before the guy behind goes insane because there's a momentary 3 car gap in front of you. The best (or worst) I've ever seen, on a two lane road which was creeping along one way, and the oncoming lane was fairly busy but allowed the occasional pass, this one driver literally was staying back 30 car lengths (no exaggeration) from the car in front, at 5mph. It's Canada though, so as cars passed he got the stern look instead of the death penalty.

 

very well put. I think you describe the different situations in various places much more elegantly than how I described it.

 

I think Toyota did just about right with the RX450h hybrid design. It essentially increased the mileage of this big car from roughly 18 to roughly 28 overall, or at least it did for my driving location and style.

To go from 28 to 38 would be a far less-significant drop in operating cost

 

I wish they would make some improvements to the battery, they've used the same setup for almost 3 generations. The battery didn't change much from the 400h.

The MG2 motors in our 450h is rated at 123kW, but never sees more than 37kW. that's around 30% of it's rated power. If the battery was capable of outputting slightly more power, acceleration from the Electric motors would likely improve as well.

They left the system basically unchanged for the 4th gens, so they seem to have no desire to improve it. Pitty, it would put that even more ahead of the competition.

 

Toyota can always make friends with Elon Musk and buy some batteries from the Gigafactory. Lithium Ion and/or polymer should save space needed thus increasing total capacity.

 

It might not even be the battery itself, 37kW output is pretty low, maybe upgraded electronics would allow the NiMH pack to output more power.
Telsa's pack can output over 500+kW of power to it's motors, I remember it was upgraded electronics that improved in new telsa's that allow it to output more power when they came out with Ludicrous mode, that battery packs were the same.

 

Are you overlooking that the electric energy to MG2 (and MGR, if an AWD) gets augmented electrical energy from that which is generated by MG1 by the ICE?

The 37 kW to which you're referring is only that which is instantaneously available from the battery (ICE off); however once the ICE is running, the source and intensity of the electrical share of total torque/horsepower is dependent upon vehicle speed and driver inputs - and is then managed/apportioned by the computer.

At WOT, you'll see the full 295 HP (which includes the 37 kW you've referenced) up until the traction battery becomes depleted -- at which point you'll have somewhere around the ICE's 245 HP until you let up on the throttle (or run out of gas).

 

From what I read, I don't think that factors into the equation, if it did, I would think that peak output would be greater than 295HP (245hp (ICE) + 50hp (37kW)). It does not seem under any circumstances that the electric motors can output more then 37kW of power no matter what combination is used.

If that is the case, the 123kW motor is severely under utilized, but that probably also gives it great reliability which we all know Toyota prefers over performance.

 

Nate is correct, there is far more power sent to MG2 than just the 37KW from the battery. While the ICE can produce 245HP, this is not all sent to the wheels mechanically. Much of the power is used to produce electricity at MG1 to power MG2. This is necessary because the atkinson cycle ICE is quite low on torque, and relies on the electric motor to provide extra torque at power levels far greater than the 37KW the battery would provide. This is not unlike how a train locomotive works, using a diesel engine to produce electricity and then using electric motors to produce high torque.

 

Don't forget that the primary purpose of this application (the RXh) of electrics is to maintain the primary source of locomotion (the ICE) at it's most efficient operating range as much as possible; while the secondary goal is to recover kinetic energy to augment the ICE during acceleration -- and to allow the ICE to shut down during load demands that would normally cause the ICE to locomote at woefully-inefficient levels.

That both performance and net fuel efficiency are improved despite the inefficiency of the conversion process (90~95% at each of the conversions: MG1 to battery, battery 288 to 650, 650 to three phase, 288 to A/C compressor, MG1 to MG2, MGR to batt, etc) speaks to how much time a normal ICE spends in an inefficient mode.