The common consensus on the Prius groups is the intermittent duty cycle of the hybrid's engine only reduces wear and tear.
A non-rotating engine is subject to infinitely less wear and tear than one that is rotating. Also the startup process of the hybrids ICE is a gentle process compared to the normal automobile's engine.
The MG1 rotates the engine through multiple revolutions before the injectors and plugs fire. That's one reason it's hard to tell exactly when the engine actualy starts while driving.
Also above approx 42 mph there is a large amount of time where the engine may be rotating but doing no work. It's called "air pump mode" and is required because of the geometry of the PSD. In "air pump mode" the stress on the engine is very low which also contributes to engine longevity.

 

I'm not concerned about the ICE in the least. Cold start is the only time that an engine is truly subjected to additional wear, and that only happens once per trip. The rest of those starts and stops are after the engine is well lubricated.

 

AND during the cold engine stages the TCH favors (even more than usual) using battery power just to reduce the stress on the ICE during it's early warmup period.
This (I think) contributes to the TCH's unusual quietness during the initial warmup. The ICE tends to NOT come out of idle unless you really tromp on the accelerator when the ICE is cold.

 

The Toyota hybrids start with the valves open and fuel off. That is, it is very low resistance run up well past the point that the oil is fully pressurized in the bearings, which is why they start so easily and virtually unnoticeably. The engine is already at full idle speed with full oil pressure before the valves are allowed to operate, allowing cylinder compression, fuel and spark, resulting in nearly "shock-free" starting.

Also, the oil pressure stays high during the shut down so the start/stop theory of engine wear is mostly about the starting, and little about the stopping. That is, just as there is a small delay for oil pressure to build when an engine starts up, there is also a small delay as the oil pressure drops off after the engine stops.

With the PSD, the engine is hardly ever exposed to external jerking loads, as is seen with normal transmissions and clutches. Try shifting from drive to reverse while moving forward slowly, or from reverse to drive while still going backwards. You can feels the drive force change directions, but there is no "thunk" or other hard jerk as would be expected in a normal drive train. While such poor gear shifting is really hard on most transmissions, it is also hard on the engine bearings for non-HSD's, but is not particularly hard at all on any part of the Toyota Synergy Drive system. The comparably low inertia MG1 motor easily absorbs most of the shocks of this sort that would normally add hard wear and tear to a normal transmission and engine bearings. Also, the MG1 is radially balanced by inertia and torque within the planetary gears so nearly all of it's shock is always on axis and not against it's bearings.

My guess is that the frequent starting/stopping of the HSD system is of little consequence to the ICE durability or reliability, and the somewhat lower total run time as a function of total miles driven may add more to the life of the engine than the frequent start/stops reduce life (not that engine idling that other cars do so much more of is particularly hard on an engine!).

-- Alan

 

Alan - I read your response earlier today and thought it was a pretty cool way to handle starting the engine. I decided to watch my engine start in the driveway. Powered the car up and had my wife sit in the car while I opened the hood. She set the heat to full hot and I watched / listened to the engine crank not even a full revolution as it shook to life. I had started it and then remembered your post and shut it down again before I ran this test. Since it wasn't fully warmed up yet - maybe it has a different programming profile in the ECU. I'm going to observe it again tomorrow when fully cold and again when fully warmed up.
Unlike my friend's Prius, I can feel the ICE (in my TCH) start every time. The Prius' engine must be isolated better than that of the TCH. I've also driven (and plan to purchase next year) a Ford Escape Hybrid. The FEH uses the HSD system under license from Toyota. The FEH engine is isolated extremely well and is actually more quiet than the TCH and Prius.

Then too - there may be something awry with my TCH. Although there are no SES lights on. I do have an OBD-II scanner I should check to see if there are any codes set.

 

Big-Foot, all I can say is my experience is different. I have an 05 FEH, and my dad has an 05 Prius. Both of them have a noiser ICE, and more noticable ICE start than my TCH. Maybe the newer Prius and FEH are better now?

 

How can it do this? It is cam driven isn't it? It is capable of varying the valve timing by advancing/retarding the cam shaft but to open ALL the valves seems impossible. Unless the cylinders are machined for clearance opening all the valves would damage them.
Is this documented anywhere?
Curious.

 

Very old tecnolodgy, Caddillac was doing this in the late 70' early 80's and called a 4-6-8, the computer (on a straight no load road) would cancel out first 2 cylinders and run on 6, then if everything went ok cancel out 2 more and run on 4. An electronic commpression release device along with canceling the fuel at the injector.

 

Many engines have TDC piston clearance with an open valve that would allow this, and it is very easy to hold a valve open without interfering with the cam; keeping it closed would be the problem for the cam. Also, only one valve per cylinder - not "ALL" - need be held open, and even a small opening possible in all engines would significantly reduce compression forces.

However, I am not able to find the source of this information, nor can I recall where I read that there was non-compression starts for the TCH. I thought I saw it on a Toyota technical web page, but can not find it now. Unless I find it later, or someone else can help me, I retract, and apologize for making this claim.

-- Alan

 

I read that somewhere also, cant remember where,,,but I will think about it.......