Can we bring up Power Mode again?

Don't see that I mentioned any compression ratios, just that the Prius engine is a regular engine not built as an Atkinson Cycle engine (you might want to look that up to see what an Atkinson Cycle engine is). Toyota notes they achieve the "Atkinson Cycle" effect via electronic controls, not engine construction. They could run a Corolla engine in "Atkinson" mode but at such a low torque setting, without the electric motor boost, it would be reeeeely slow acceleration.

Relating to the PWR mode (and ECO and REG modes) that the normal construction engine in the Prius is run on a spectrum via the electronic controls from the low torque "Atkinson" mode to higher torque "Otto" mode via those controls.

 

I can't visualize this, can you explain?

 

InsightCentral.net - Encyclopedia - Honda Insight Offset Cylinder


You can work out the geometry from the diagram. I don't know the offset in the prius engine, but given that and the valve timing you can work out where in the cycle the valves open and close.

The actual compression varies with rpm as this affects the way the cylinder breaths.

Its a traditional engine design with atkinson valve timing

The engine can not work in otto, both because of the valve timing and detonation problems. Otherwise they could just increase valve timing and run both. Mazda skyactiv allows for 13:1 compression in otto mode with regular gasoline, but it has a number of modifications (piston design, di, manifold) to allow it to do this. Skyactiv can also do the attikson valve timing, but part of it is implemented with variable lift as well as phase. That is off direct topic, but toyota could be doing something similar in gen IV.

 

You don't understand the simple fact, if Prius engine was allowed to run in Otto cycle, compression would be 13:1. Why don't you look it up yourself, please, and report back when you get it?

 

I did a simple experiment this AM while driving flat road at 40 MPG coasting at zero net charge (ICE off). I punched gas fully in quickly and let it go under a second 3 times each in different mode (normal, eco, power). Each time the ICE turned on, but didn't have time to accelerate the car noticeably before it was off again. I see no difference in response time in such quick gas on/off maneuver.

LOL, I meant 40MPH.

 

Your butt dyno may be off

Theory 1) Power has the ice on more often, so it is prepared to quickly accelerate. It would be nice if someone confirmed. Your test didn't test this as you put it in a situation where the engine would be off in power mode

Theory 2) ECO mode dampens response to acceleration inputs. To test this you would need to time acceleration to a new point, say 40-50 mph, and tell if ECO mode got there as fast as power. You can't tell response if you simply slow back down again. You would start the stop watch when you pressed the pedal, then hit stop as you climbed through 50 mph.

 

The Prius didn't have Power Mode until MY 2010, so anyone complaining in 2006 must have been prescient.

Secondly, all modes have exactly the same amount of available power. If you almost get hit in normal mode, you won't do any better in power mode. Perhaps you need to leave more room pulling into traffic. If that's not possible, you may need a higher performance car.

Tom

 

There are many of them on this site and a lot of them on this thread

 

"How many engineers does it take to explain Power Mode?" The answer is 15: one to hold down the OP, 14 to beat him senseless with the technical details.

Tom

 

I prefer to take Toyota's word for it. According to Toyota it is not built as Atkinson cycle engine but achieves the effect via electronic controls. It seems to be a religious issue to some here that the Prius engine is "Atkinson cycle engine" (angel) and not an "Otto cycle engine" (devil).

 

And that 1 isn't doing their job... [Catman hasn't been on since the day he posted.]

 

A true Atkinson cycle engine uses an unusual crankshaft design that achieves the four stroke cycle in a single turn of the crankshaft. This was done as patent beater to work around Otto's engine patents. A useful side effect of this unusual linkage is that the expansion stroke can be longer than the compression stroke, allowing for greater efficiency at the expense of lower torque.

Modern 'Atkinson' engines are really Otto cycle engines with altered valve timing. The intake valve is left open during the first part of the compression stroke, effectively shortening the stroke. This accomplishes the same thing as the true Atkinson engine without all of the extra mechanical complexity of the Atkinson crankshaft.

Tom

 

Atkinson and otto cycle is activated by vvti on the intake side. The atkinson cycle has less compression, air and fuel = more efficiency. Power mode is just otto cycle, more compression, air and fuel = more power.

 

That happens not to be the case. ECO and PWR mode only change the throttle pedal User Interface. (ECO also alters the A/C cycle)

The Prius has a 13.5:1 expansion ratio, if it was also the compression ratio, you would need a LOT more Octane rating.

 

Weird how a thread can fill 53 posts with competing misinformation, go dormant for six years, and get revived with more of it, everybody trying to guess at a topic that's explained and diagrammed in the manual.

-Chap

 

Chap, In their dreams, PWR mode means more power. Sadly, it just means more power for smaller changes in the accelerator pedal early in its travel.

The intake timing DOES change, but not due to any push button. (gen 2 shown)

 

I guess i got this confused with the way the atkinson cycle works on the tacoma, how it can cycle from otto to atkinson cycle. I always thought the prius did the same due to having vvti on the intake side.

 

Maybe you should not endanger others by recklessly pulling out in front of others and then blaming the car? My last car was heavier and had 90hp and still had no problems, and the car before that had 65hp and still no problems. Maybe different driving would help?