2017 Prius Prime First Drive: Best Prius Ever

Doing an eye-ball integration, the red curve would result in a 0-60 time of under 7.5 seconds, the blue about 10.5 seconds.

 

There is no way that will happen. The Prime is limited to 68 kW of battery power whereas the Volt battery can output 120 kW. The Prime is helped a bit by a higher ~10:1 gearing ratio on MG2 to the wheels vs. the Volt's ~8:1 but the Volt is still going to have a big advantage.

 

Maybe @Danny would like to give his impression, but in my extremely limited driving experience, flooring the Prime at low speed in ev mode yielded a modest result. It didn't feel like sub 8 second territory to me.

 

Well, the axes on that graph are unlabled. I was assuming 1m/s^2 per division, but if it's not that, then the math could be very wrong. However, 10.5 seconds for HV mode, using the same assumption, sounds perfectly reasonable.

 

I rather expect the Prime to do the 0-60 in EV mode about as fast as the Leaf. But is that so important? If you do that often, the EV range will be much less then 22 miles.

Jan

 

The motors are officially rated as 111 kW combined (149 HP) output. Presumably, some power is lost as heat in the inverter and motor at maximum output and that accounts for the difference. I don't know in detail. The same effect may be an issue in the Prime ratings. Just what is that 68 kW rating? Is it battery output (I think) or is it power output at the motor after inverter and motor losses. I'm not certain.

 

I'm just going by the plot posted. Doing a more careful integration resulted in this plot:



By the way, moving a 1600kg car to 60mph in 7.5 seconds takes an average of 76.6kW.

 

MG1 is 23 kW in gen 4.

 

It would have to be what comes out of the inverters, because the battery is a DC source and both MG1 and MG2 are AC PM motors.


Unsupervised!

 

It originally had no cooling, but they then got hit with a class-action suit, which was sufficient for them to add a cooling system. I believe I heard that it was a liquid-cooling system, but I'm sure of that.

 

It still doesn't have a cooling system beyond passive convection airflow, and maybe some more while in motion. Nissan only switched battery chemistries in the Leaf. Their little BEV work van that uses the same battery and drive train as the Leaf has a fan, but that's because Nissan expects it to see more quick charging and constant use.

 

Does the new clutch added to the drive system disconnect the engine while driving purely on electric?

One thing that I've liked about the Volt is that the engine is off and completely stationary while it's driving on electric. That, since it gets no wear at all except when it's actually being used.

 

As Tideland Prius mentioned, the Prius has always had a mechanism for allowing the engine to be at zero rpm while driving electric. The engine, the smaller motor, and the output axle that is eventually connected to the wheels are each attached to one of the three gears in the planetary gear set known as the Power-Split Device. You should go and read the Wikipedia article on the PSD but basically the engine can be at zero rpm because the small motor free-spins instead.

The new clutch does not connect or disconnect anything. It is a special kind of clutch known as a one-way clutch -- it allows things to spin in one direct but locks up and prevents it from spinning backwards. It is effectively attached to the engine so it prevents the engine from spinning backwards which would happen if the car's wheels were turning and instead of the smaller motor free-spinning it instead tried to help push the car forward together with the bigger motor.

That scenario is sort of the opposite of how the smaller motor normally helps to start the engine when it is needed. It starts the engine by resisting against spinning and thus slowing down which forces the engine to spin forward instead and then gasoline and spark can be applied to start it running.

Having the new clutch means that if the smaller motor tries to spin faster (help push the car) when the engine is off that tries to push the engine backwards and the clutch locks up the engine to prevent that and that allows the smaller motor's efforts to help push the car. Without the clutch, the engine would just spin backwards without helping to push the car.

I hope that made sense....

Here's an article that I wrote about it:

Toyota’s Prius Prime Shows One Way for a Better Plug-in Hybrid

 

I like to see the planetary gear set as having "two degrees of freedom" as opposed to 'regular' helical set having only one.
In helical set you can only force change one element, the rest will follow. In a planetary set you can simultaneously force change two elements and the third will follow.

 

You can't effectively describe what is happening; it's something that needs to be seen, and even then it takes some head scratching to really understand it.

In context of the question, yes, the engine can be thought of as disconnected from the drive-train when driving in EV mode because the crankshaft doesn't rotate.

 

Might be time to hit the salvage yard with a tape measure ... see what might fit in place of the 2 rear buckets - once the PiP II inner dimensions are obtained. Might be faster than waiting 5 more years for PiP III.

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