High RPM OK?
 

My normal driving habit is to accelerate fairly gently -- much more than the average person does I guess. However I finally got to a traffic situation where I had to boogie out at near max accel -- and that little engine wound itself up to 5500 RPM!

That's kinda hard on a four-stroke engine, but is the FEH engine different where that is considered "normal" operation?

Also kind of interesting is that I didn't seem to pay the price for it on the MPG meter.

Re: High RPM OK?
 

The electric motors were suppling most of the torque allowing the engine to increase in a fast RPM. If you had stayed at that RPM as the electric motors gave up that torque, you would be taking a larger hit on MPG. Instead, it may look like you robbed the bank on MPG, but your ICE must slowly replace that energy back to the battery at a cost to MPG. I do the same thing if I have a choice of making a stoplight verses stopping and taking a bigger overall hit on MPG.

That high of RPM's does not damage the engine, but clearly the torque curve is on the down hill side after 4,000 RPM's, so get back to your low RPM's ASAP. If your speed is over the limit, use "L" for regen to the speed limit to put some charge back in the battery.

GaryG

Re: High RPM OK?
 

These engine could easily hit 7000 rpm without worry. they are based on the Mazda 2.3 DOHC high performance engine. If you google miller cycle engine you will understand what they did to the engine, though they did not use the supercharger.

http://en.wikipedia.org/wiki/Miller_cycle

Re: High RPM OK?
 

Is the only difference between the Atkinson cycle and the Miler cycle the use of a supercharger?

It is easy to see how this makes sense in a hybrid, since you give up low end torque in the ICE in exchange for efficiency. You have the electric motors for low end torque so it isn't missed.

Is the low end torque in an Otto cycle engine the reason it gets high wear at high RPMs? The wikipedia articles don't address this.

Re: High RPM OK?
 

Is there a difference between stepping on the brakes (or just coasting) as opposed to shifting to "L"?

Re: High RPM OK?
 

When you press the brake pedal, a computer determines when to tranfer from regen brake to actual brake pads.

If the car is warm, and the weather is warm, and the battery SOC is low, about the first 50% of pedal travel will be regen brake. Pushing farther than this will start to put the brake pads on the disc with increasing force.

If the car is cold, the battery is cold, or the battery SOC is high, the brake pads hit the disc rotor sooner. On a 40'F day, maybe this happens after 25% of pedal travel. On a 0'F day, you might not get any regen brake until the car and battery warms up a bit.

So with the brake pedal, you never know exactly when the car will switch to brake pads... but with a Nav and energy flow screen ( or SG ) you can infer pretty close how this works.

On a warm day, using L setting, you can be positive you are getting 100% regen, and 0% brake pads.... ALWAYS. If it is cold, and the battery won't take regen, then you get Engine Compresson brake, with a high run-up in RPM, but all fuel is cut.

So for best FE, Regen is first choice, Engine Run-up is second best, and last resort should be brake pads against the disc rotor.

Coasting in N regen is shut off.
Coasting in D with foot off the gas, a small amount of regen happens.
Coasting in L with foot off the gas, a large amount of regen happens.

However, coasting in ANY gear, you can cut off all regen with a ~2mm press on the gas pedal while coasting.

You ( and I ) can coast down a 2% hill in L gear setting and GAIN speed without using gas, if you have a ~2mm press on the gas pedal.
This gentle press is enough to trigger a sensor to stop regen, but not far enough to trigger the gas or electric motor.

So this car has lots of options!
Does that make sense?

-John

Re: High RPM OK?
 

It does, actually. It makes perfect sense but I just wish the manufacturers wouldn't go to such lengths to hide these details. A friction-brake usage display/meter would have been nice.

Of course, the typical American consumer is easily confused and terrified so I understand that as well.

Thanks again for the detailed response.

Re: High RPM OK?
 

The original Atkinson cycle engine used a rather complex crankshaft to actually change the stroke of the engine between the intake/compression stroke and the power/exhaust stroke. Miller merely held the exhaust valve open longer which let some of the intake charge to return to the intake manifold which reduces the compression of the engine allowing a higher compression ratio. This give a larger delta between compressed and expanded gasses, similar to a diesel. The reversion back to the intake lowers the volumetric efficiency of the engine at lower rpms. Miller solved this by using a supercharger. So a real Atkinson engine is very different from a miller but the theory and principal is the same, high compression RATIO but controlled COMPRESSION

Not really. Friction is somewhat constant with respect to rpm, higher rpm higher friction so you wear an engine faster at high rpms. BUT most high rpm failures are not from wear. They tend to be catastrophic, IE a piston shattering, bearings spinning etc