Starting: hardest thing on an engine

No concerns because it is spooled up to 1,000 rpm, establishing some oil pressure, prior to fuel and spark.

 

<div class='quotetop'>QUOTE(kente777 @ Apr 25 2006, 08:21 AM) [snapback]244802[/snapback]</div>

You are right to a point. On a regular car the small starter spins the engine fast enough to start but not to get the oil flowing.

MG1 on the Prius is larger enough to spin the engine to idle speed (about 1000 RPM) and establish oil pressure. Meanwhile valves are held open so there is no compresstion stress. Once speed and oil pressure is estblished, the engine is started.

 

<div class='quotetop'>QUOTE(kente777 @ Apr 25 2006, 08:21 AM) [snapback]244802[/snapback]</div>

The Prius's engine avoids a lot of startup wear and tear because of the 10kw motor - which acts almost like a starter motor. Being much bigger, it actually spins up with ICE to operation speed without actually starting the combustion process. This allows the engine to be nice and lubed up by the time there's any spark or fuel in the cylendars.

I'm really curious too about what this means in the long run - will my prius's engine last longer than most cars because of this or does it only partially mitigate constant startups?

Dave

 

Folks-
I really had to respond to this one.
Whether the engine is firing & combusting or not is not related to engine wear in this respect.
If I took an engine and motored it on a dyno with no lube, it would wear the sliding parts at a much accelerated rate. Ultimately, I could sieze the engine if I ran it at fast speeds and/or high temps.
The pistons sliding up & down in dry cylinders, the crank spinning on dry bearings, dry gears meshing with dry gears, etc. are what promotes accelerated wear. When a cold engine starts, for example, the oil has drained away into the crankcase, and takes a bit of time for it to make its way to all the critical bearings within the engine. The cylinders are (relatively) dry, the bearings are dry, etc. Compound that with cold, thick oil, and you make the problem worse. This is where these 0W20 oils and the like are coming from - they are extremely thin, and do not thicken at cold temps as the older oils did. They get to critical areas much more quickly at cold start-up. Also, Mobil-1 and other synthetics excel in this area, and can help at cold start-up.
Now, having said that, the way the Prius engine starts/stops the way it does will not lead to premature wear, because the oil is there from running just before shutting down, and it is warmed up. It takes a long time for that oil to drain away. Main crank bearings, cam bearings, and the like will retain oil for quite a long time. The wear you speak of will occur at initial engine start-up just as with any other car. Plus the oil is warmer, will flow quicker, and those main bearings will have that pressure-maintained oil film created just that much quicker when the Prius ICE starts/stops/starts.
You see, the crank really rides on a thin film of oil, and not the bearings. That is why getting the oil pressure there quickly is of such import.
No, the start/stop of the Prius ICE should not affect its longevity IMHO.

 

hmmm, three posts saying the same thing, but I am not sure I follow.

Just thinking about the cylinder now, why is there less friction when MG1 does the work, rather than fuel combustion during the phase that the cylinder wall is inadequately lubricated ?

 

The forces required merely to spin the engine without compression are much smaller than the forces generated by detonation; less force -> less pressure on the bearing and mating surfaces -> less friction and less wear. Also, since the engine is on and off frequently, there is not enough time for much of the oil to drain off the bearing and mating surfaces. The Prius engine ought to last a very long time.