Pulse and Glide in EV mode? Also are there best speeds to do P&G?

EV mode = glide

 

It sounds like a good technique, but there isn't any way to disengage the gasoline engine from the wheels. Putting the Prius in neutral, only runs one of the electric motors in reverse to compensate for the lack of rotation by the engine. The car rolls like it's in neutral, but it's actually matching the speed of the electric motor to the speed of the wheels to prevent any power being transmitted to the wheels.

 

100 MPG (instantaneous) is not in the range of efficient ICE use.
Best practice for the ICE starts at about 15 kW or about 41 kWh/hour of fuel. That is 1.23 GPH

 

Pulse & Glide was created to get around some of the lossy mechanisms of gasoline engines, particularly Otto cycle engines under light load, operating well below their best efficiency. P&G pulses the gas engine at or near it best efficiency, then glides with the gas engine shut down or idling. Done right, this can get average out to a better overall efficiency than is available at constant speed light load.

Electric motors operate completely differently, without the specific loss mechanisms that lead to the creation of P & G in gassers. So don't expect it to be of any benefit in pure EV mode.

 

I agree with fuzzy1, P&G isn't any better than steady speed when using electric power. In hybrid mode/non-PiP, P&G can greatly increase mileage. The glide should be a true coast, no power in or out of the battery (no arrows on MFD, right on the zero line of the HSI). Gliding with regen is probably no more efficient than steady speed (possibly worse), gliding with a little electric power to extend the glide and keep traffic happy is also good (whether or not its more efficient than coasting would depend on the conditions).

 

How does P&G help in HV mode? The control software is going to try keep the ICE either off or running at an efficient speed, dumping excess energy into the battery. I can see that there would an issue with the standard Prius, since it quite possible that the (smaller) battery will be full, and there will be no place to dump the excess energy. I would expect this situation to be a lot less likely with the PiP.

 

you can do better with p&g than the control software.

 

That is a common misconception. The rules, in decreasing priority, are:

1. Protect the SOC
2. Support the weak, small ICE when high demand is called for
3. Allow EV if SOC is adequate, speed and demand VERY low

Coasting turns into gliding in a Prius if speeds are low enough, and that saves about 1.5 - 2.0 kW by not turning the ICE. If P/G are equal in time, not spinning the ICE during glide saves 0.75 - 1.0 kW on average.

 

I think that we are talking about different things here. The rules you mention are the priorities for turning on the ICE when in HV mode, right? No argument there. That does not change the point that the control software really wants the ICE, when it is running (per the above rules), to operate in its efficient range. That is why it will sometimes divert power from the ICE, through electricity from MG1, to drive MG2 and thence the wheels, rather than just drive the wheels mechanically. Or dump excess power to the battery. Or supplement the ICE with electric power (subject to above rules). Always trying very hard to keep the ICE running in its efficient range, or not at all. (Is a "glide" running in HV mode with the ICE off and no regeneration? ) Why is the power output of the ICE considered wasted (is that the 1.5-2.0kW mentioned)? Either it moves the car, or it goes into the battery (minus conversion losses). I still feel that things are a bit different for the PiP in HV mode than for the straight Prius, due to the larger battery and faster charge/discharge rate.

 

Those are the rules for using the battery.
The 1.5 - 2.0 kW power drain is to spin the ICE -- regardless whether fuel is combusted. Think of it as the cumulative friction of all the engine's moving parts.

Glide is so misunderstood. The important feature of glide is NO ICE SPIN.

 

Thanks for the clarification. But I don't think that that whether these are the rules for using the ICE or are those for using the battery really changes my argument that the control software really wants the ICE, when it is running (due to whatever rules), to be running efficiently, and it will use the electric side of things to achieve this if feasible (such as having sufficient SOC). That is why this is so non-trivial; they are trying to optimize two power systems at the same time and what happens with one effects the other.

 

I was trying to explain why P&G is advantageous.
The design strategy (stated no doubt over simply) of the Prius is to run an efficient, small Atkinson ICE. The traction battery is present to cover transient high loads that the engine cannot. While it is true that the control laws allow EV at low speed/low demand, it is a minor part of overall fuel economy and it tends to confuse those of us new to Prius trying to understand how best to drive the car.

Example: If you drive a level road at a speed that requires 10 kW constantly, the ICE will run most of the time and will do so inefficiently.
On the other hand, if you P&G so that ~ half the time the engine is loaded with 20 kW and half the time the engine is stopped, not only will the engine use be more efficient for equivalent average power output, the work to simply spin the engine will be halved.

 

OK, you are saying that it takes 1.5-2.0 kW of wasted power to just have the ICE turning, and that is where the savings come from with P&G? I think that is high, but I am not an engineer and I am not in any position to dispute that. I am not trying to be difficult; just trying to understand. But I don't understand the 20kW for half the time argument. As I understand the Prius control laws, if your power requirement to move the car would put the ICE into an inefficient range, then if there is available battery capacity, it will increase the power output from the ICE to put it into an efficient operating state, and dump the excess power into the battery. This is more useful on the PiP with its bigger battery which can take a charge faster than the battery on the standard Prius. So the gain from P&G beyond the 1.5-2.0 kW friction loss would depend on how efficiently the power was dumped into the battery and recovered; the more efficient it is, the less is to be gained from P&G.

Has the efficacy of P&G been tested specifically with the PiP in HV mode and compared with the Gen III liftback? I don't think that it can just blindly be assumed to be the same.

 

Right, and some benefit from improved ICE efficiency

Instead of 10 kW continuous, pulse at 20 kW and glide at 0 kW for the same average power output.

Nope -- this is the common misconception.

Not to my knowledge. BobWilson did compare P&G to CC and found a modest improvement in his G2 Prius with P&G -- up to 12%. That is about what I expect from my envelope calculations.

Back to this thread, OP wondered about 'P&G' in EV. That is an (unintentional) oxymoron because the PULSE in P&G is ICE use.

 

I think I've sorted it out. Firstly, for the OP, P&G is irrelevant to EV mode, since the PULSE phase uses the ICE. And you are saying that the power output of the ICE is NOT adjusted to put it into an efficient range. I am not questioning you, but I would like to find out more about this. Particularly if it is an artifact of the small battery in the standard Prius really not having the capacity to accept the excess charge for any meaningful period of time, but with this factor being different with the PiP. Or is it just a flat-out control rule to not even try to adjust the power output of the ICE to an efficient range.

Thank you for your explanations of P&G.

 

there really is no excess charge in normal driving.

 

I can tell you with a high level of certainty, based on many miles of P&G in both a PiP and regular Gen3, that they are virtually identical with the PiP being able to do slightly better (all other variables the same) than the Gen3. P&G definitely gets you much better fuel economy in either model.

 

Sorry to hijack thread.
Occasionally I see a post suggesting its a bad thing for the traction battery charge level to drop to two bars.
I guess I am looking for some guidance on when to avoid letting the car run on EV mode ?

For instance what should one do in a situation where the car is idling in P with AC on full blast in direct sunlight in Alabama today with a Heat Advisory out...no way the battery will ever get above three bars I dont think. It will cycle back and forth between ICE and traction battery with the SOC at 3 then 2 bars(I think)

Thanks for the input. I am still trying to figure out how to take care of the car properly and looking for tips.

 

This is a discussion about the Plug In version. Looks like you have a regular Gen3. But no, it's not a bad thing for it to occasionally get to 2 bars. It's made to do that. The computer will protect the battery.