Atkinson Cycle engine surmise (and question)

It is variable, but I am unaware that it is variable by altitude specifically. (my surmise is that since batteries work as well at 15,000 feet as sea level, you suffered less power loss than an all engine powered car)


This chart is for a Gen 2 Prius and a Gen 4 may vary from it. The black arc is the exhaust timing and duration, which is fixed. The white arc is the intake, which has a fixed duration but variable timing. Under heavy load, speed seems to be a factor in the valve timing, as does temperature.

 

The gen4 does make use of advances Toyota has made since the gen2, but the variable valve timing isn't the wide range VVT that can switch between Atkinson and Otto cycles, and it is still on the intake only.

Atkinsonized engines aren't regarded for their performance, and full hybrids have always relied on the traction motor to make up for the ICE's shortcomings in that area.

 

I agree with that. In fact, I'll add another supposition to it.

Since MG1 has to react the torque going from the engine to the wheels, it has to act as a generator, pumping its generated power to MG2 to propel the car. This limits how much power can flow from the batteries to MG2 to propel the car from that source.

If the engine loses power (because of lower barometric pressure, in this case), MG1 has to react less torque and thus provide less power to MG2, leaving a larger amount of MG2's total power for the battery to provide. This might mean that most of the power lost by the engine is made up for by the Prime's larger battery system through supplementing MG2.

 

Changing the valve timing with respect to altitude, implies that it is not using the full available valve adjustment range when down at sea level. I very much doubt that this is the case.

When climbing at high altitude, I would expect the Prius to simply increase engine RPM as needed to compensate for the reduced air pressure. If you don't compare engine RPM (reported by any of the aftermarket accessories, such as ScanGauge-II) on Pikes Pikes to a similar slope at much lower elevation, and you are not having to completely floor it, then there is nothing else to notice.

With fixed speed transmissions, the difference will be more obvious as the operator needs to downshift to get the higher RPM needed to compensate for the thinner air. I really noticed it when driving my manual transmission cars high up in Colorado. But with auto-CVT systems, this can easily be hidden from the driver.

 

But the Prius intake valve system can't close at BDC, or anywhere near that. The mechanical system can't adjust that far. See the chart back at post #2.

And my answer remains the same:

"Changing the valve timing with respect to altitude, implies that it is not using the full available valve adjustment range when down at sea level. I very much doubt that this is the case."