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Confused about PHEV, Hybrids, etc...

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edy:
One of my colleagues recently leased an Acura 350h NX 2023. She was told by the sales rep that it will use all electric up to 60 km per hour. I said, "do you mean up to 60 km distance", and she said "no until driving 60 km per hour". I asked "what is the range, does it do all electric, is it a plug-in" and got a blank stare.

My point is, I'm getting very confused about the mix of technologies now available in hybrid vehicles. It seems that we have a huge mix of modes and much of it seems to be minimally controlled by the user (which I guess is a good thing?).

On the one extreme, you have your typical internal combustion engine (ICE), and on the other is EV all-battery vehicle. In between I thought there were essentially only 2 different hybrids... "HEV" and "PHEV". The HEV doesn't plug-in and essentially just figures out the best mix of power from the ICE and Battery and charges itself, and the PHEV actually lets you drive for a certain distance using all-battery and when it depletes it switches on the ICE to charge it and falls back to more of an HEV mode.

What confuses me about the Acura 350h is that it does not seem to be a PHEV, but up to a certain speed it will operate only from the battery and if you drive slowly and not accelerate too much it will stay on battery only? I guess they didn't bother giving a range spec as it doesn't apply in this case, as it is not truly a PHEV. I don't know what kind of algorithms they are using so I was hoping someone in here can shed some more light on this.

The PHEV is simpler to understand. It seems that if a user wants to travel under a certain range per day they could simply use their car almost like a full EV, and never rely on the ICE. However if they decide to go beyond the range and battery depletes, they can rely on the ICE to get them around (eliminating range anxiety).

HEV mode is more confusing as there seems to be more going on regarding how the car actually balances between the two. Does it use the EV motors to accelerate only, to assist torque during acceleration, to keep it rolling at a constant speed? When are those motors active and do you really have any control over it? Can you actually drive the car so that you never use the ICE, or is going to be running no matter what as it needs to recharge the battery?

sokoloff:
I'm not familiar with that specific car (I wonder if it's actually a Lexus rather than an Acura), but I am shopping for and have done a lot of research on a different brand's PHEV.

There's a limit of both capacity and power that would limit the distance you could go on battery (capacity) as well as the maximum speed (where power matches aerodynamic drag), so having a maximum speed limit spec makes sense.

Integration between the ICE and electric motors is automated and relatively seamless in the current hybrids (and has been for years).

The Lexus 350h is not a plug-in hybrid, but uses the ICE to charge the electric battery. Where the electric battery gets its charge is somewhat irrelevant to the hybrid driving experience. You have to run the ICE engine at some point to charge the battery, but while the battery is charged, you can drive it in electric-only mode. Some amount of people buy a PHEV and then rarely plug it in. This car works the same way as those cars, just with a smaller battery and no capability to plug it in.

https://www.drivingelectric.com/lexus/nx-350h has more info on this specific car.

ejeffrey:
The NX 350h is a Lexus, not an Acura, and it is a regular hybrid.  The NX 450h is a PHEV.

I'm not familiar with the newer hybrid systems, but if it is like the older Prius models it can can travel at low speeds (like in a parking lot) on battery alone but with no significant battery only range.  Also, sometimes the sales staff will quote a number that doesn't mean much of anything: the maximum vehicle speed at which the ICE engine can be at zero RPM.  This is given by the gear ratios and the maximum RPM of the electric motor.  On the Prius this is in the 40 mph / 60 kph range.  Again, this number is not terribly relevant -- the electric motor doesn't have enough power to maintain this speed on level ground.  When coasting or going downhill at above 40 mph, the engine still must rotate but will do complete cylinder deactivation.  The exhaust and intake valves are closed and fuel delivery is shut off.  This eliminates pumping losses and overall the drag is pretty low.

tom66:
Toyota only makes a few PHEVs;  the majority of their hybrid line up is the so-called "self-charging hybrid" which is a stupid, loaded marketing term that makes people think the car is better than one which needs to charge, but I suppose that's the awful genius of marketing terms.

The Toyota hybrid architecture has changed over the years but the majority of these are based on some kind of power-split device.  This allows the electric motors and engine to run simultaneously with the pairing of motors and planetary gearset acting as a variable-ratio transmission, and it gives these cars the "e-CVT" gearbox marketing name, but crucially these cars do not really have a CVT with all of its associated problems.  The hybrid synergy drive is actually a rather clever architecture and it deserves praise for its simplicity and performance (as much as I think hybrids are becoming obsoleted by pure electric vehicles for most users.)


--- Quote ---What confuses me about the Acura 350h is that it does not seem to be a PHEV, but up to a certain speed it will operate only from the battery and if you drive slowly and not accelerate too much it will stay on battery only? I guess they didn't bother giving a range spec as it doesn't apply in this case, as it is not truly a PHEV. I don't know what kind of algorithms they are using so I was hoping someone in here can shed some more light on this.
--- End quote ---

When Toyota (not Acura/Honda) say the vehicle can run up to 60km/h on electric power alone they are in the technically correct but not really useful category of facts.  Yes, the e-CVT/HSD architecture can *probably* get the vehicle up to 60km/h without engaging the engine, but since achieving that will likely (a) exceed the nominal acceleration limit for pure-electric mode (typically more than 20-30kW) and (b) likely deplete the battery sufficiently such that the engine must run to recover charge, that fact is really not that useful.   

The battery in these vehicles is typically of the order of 1-2kWh, with peak charge/discharge of around 25-40kW.  Even in the most optimistic driving pattern you are not going more than 1-2 miles on a full charge, and the full battery cannot be utilised anyway (merely around 50% to protect its lifespan).  And, even so, that battery must be topped up by the ICE, as you note, there is no way to plug the vehicle in.  So even if it did offer pure EV mode, what would be the point?  You are still burning petrol, just a few miles earlier.  They do often offer an 'EV Mode' button in the car.   I would not recommend using this, because you are just going to get 1 mile of pure electric mode, followed by a few miles more of the engine running under higher load to recuperate that charge.  You would be better off just using the petrol-electric motor hybrid as normal, with the computer selecting the most appropriate mode given the acceleration, grade, temperature etc.

Non-plugin hybrids offer pretty good economy when you use them as they are really intended for:  stop-and-go traffic or city traffic.  There is a lot of opportunity to recuperate charge there, which can allow the pure EV modes to work longer.  However, many times they seem to be sold to people who do a lot of driving on the highway, and this might be where the 60km/h claim also comes into it.  These people would be better with diesel or pure EV, but Toyota doesn't like marketing either.

edy:

--- Quote from: ejeffrey on July 26, 2022, 04:17:18 pm ---The NX 350h is a Lexus, not an Acura, and it is a regular hybrid.  The NX 450h is a PHEV.

--- End quote ---

Thanks! Yes it's the Lexus she was talking about.


--- Quote from: ejeffrey on July 26, 2022, 04:17:18 pm ---When coasting or going downhill at above 40 mph, the engine still must rotate but will do complete cylinder deactivation.  The exhaust and intake valves are closed and fuel delivery is shut off.  This eliminates pumping losses and overall the drag is pretty low.

--- End quote ---

So the ICE is still mechanically coupled to the wheels via the transmission via some gear ratio, so it is actually still rotating the crank shaft and cylinders are pumping but empty (no fuel/spark), or does the ICE get disconnected from the wheels completely (like when the transmission is put into "Neutral" or like when a clutch is pressed down?).

I wonder if some kind of "phase diagram" exists which shows the blend of ICE/electric contributing in different scenarios. Like a chart with one axis being speed/RPM, the other being torque or something like that, with areas shaded based on whether they are mostly ICE, mostly electric motor or both.

There is also "parallel" and "series" hybrid configurations, where in parallel mode both ICE and electric motor can drive the wheels (coupled to transmission).... i.e. "electric motor assist", whereas in the series mode the ICE is used to primarily produce electricity for the electric motor system and not coupled directly to the drivetrain (essentially it is an EV with a small efficient ICE that runs only to charge the battery when needed). I'm assuming the second type (series) would be more likely to be in the PHEV type of vehicle.

I'm sure at the end of the day the consumer doesn't really care what is going on under the hood as long as they see a fuel savings. Driving pattern will likely also affect efficiency. If I'm interested in purchasing a hybrid one day in the future I would also want to understand at least a bit about what is going on, but it seems there quite a number of variations now and algorithms that the vehicle uses to figure out what to use when.


--- Quote from: tom66 on July 26, 2022, 04:47:17 pm ---The Toyota hybrid architecture has changed over the years but the majority of these are based on some kind of power-split device.  This allows the electric motors and engine to run simultaneously with the pairing of motors and planetary gearset acting as a variable-ratio transmission, and it gives these cars the "e-CVT" gearbox marketing name, but crucially these cars do not really have a CVT with all of its associated problems.  The hybrid synergy drive is actually a rather clever architecture and it deserves praise for its simplicity and performance (as much as I think hybrids are becoming obsoleted by pure electric vehicles for most users.)

--- End quote ---

Thank you for the explanation, as well about the EV mode button and the way the battery is used. Then I am to assume this is a "parallel" type configuration and that the ICE/electric motors are both coupled into the drive-train and a computer can figure out the best times to use either and even do some fancy engine shut-off or cut fuel to cylinders (cylinder deactivation/CDA) when needed?

My wife's Acura MDX is not a hybrid, but when we come to a full stop the engine will shut off completely. When you press the gas, it starts up again quickly and let's you move. it's a bit scary because there is a delay and I worry sometimes doing a left turn, if it shuts off how much lag will there be to start up again. Feels like those diesel golf carts.

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