Looking at the TCH's repair manual it looks like the valve stem connects directly to the mechanical lifter which rides the cam lobe. I see no mechanical or electrical mechanism to hold a valve open.

 

After examining the New Features Manual, I also don't believe that there's any mechanism to hold any valves open. According to page EG-3 of the New Features (Functions?) Manual posted to this thread recently) the TCH's 2AZ-FXE ICE's exhaust valves' timing is fixed, opening at 45 degrees BBDC and closing at 3 degrees ATDC (open for a total of 228 degrees); and the intake valves' range is: opening at 0 -> 30 degrees BTDC and closing at 100 -> 70 degrees ABDC. This shows the 30-degree range over which the VVTi can shift the intake valves. Notice that the intake valves stay open for 280 degrees — this is because of the Atkinson/Miller delayed closing of the intake valves. [The comparable figures for the non-hybrid's 2.4 L 2AZ-FE ICE are respectively (page EG-3 again): exhaust valves: same; intake valves: 3 -> 43 degrees BTDC and 65 -> 25 degrees ABDC. Notice that the intake valves stay open for only 248 degrees in this normal Otto-cycle ICE.]

In 'B' mode, I believe that the ICE is being turned over without gas or spark, but without changing the valve timing at all — certainly, no valves are being held open. If you think about it, at the ICE revolution rates that we're talking about (~1000 rpm or more), there will be no significant losses overall because of the approximately adiabatic compression/expansion of the air in the cylinders — for each piston compression there's a corresponding expansion which returns most of the energy. Only pumping losses will cause the engine drag which is what the TCH uses in this mode to simulate engine braking.

Continuing this argument, it actually needs relatively little power to turn the ICE over to start it up each time. Initially, the cranking of the ICE by MG1 is similar to what happens to it in 'B' mode. Once it's up to speed (~1000 rpm say), then according to Toyota, first two cylinders are given gas and spark, and then all four. This leads to a smooth startup.

By the way, the New Features Manual (page CH-10) shows that there's a "Transaxle Damper" single-dry-plate-type vibration absorber built into the coupling between the ICE and MG1 — presumably to provide a cushion between any ICE rotational torque fluctuations and the transmission. It would also help to reduce transmitted vibrations when the ICE shuts down. This seems to be the only friction-type component in the whole power train! I wonder — does it outlast the rest of the power train?

Stan

 

Interesting stuff SPL. I keep hearing different things. This is the first time I have heard about spark and gas being applied to the first 2 cylinders then the last 2. It woould seam this would make it more rough, unless the starter stays engaged during the whole process.

 

FL07THC — You may well be right about that. It would seem to make sense. Offhand, I don't know where I saw that information. I'll see if I can find my source.

Stan

 

Seems odd to me as well.
Understanding that these are 4 cycle engines, it takes 2 full revolutions of the crankshaft for all 4 cylinders to fire.

I do recall reading about the Honda Civic or Insight Hybrid having an event where the valves were held open with fuel injection turned off as the car was decelerating. This would cause far less drag on the driveline and allow more regeneration to occur. I would think that this would be most beneficial with the Insight with the Manual Transmission or if a normal automatic transmission were employed.

Also - if the VVT would allow a greater overlap between the closing of the exhaust valve to the opening of the intake valve - a substantial amount of cylinder pressure would be lost to that cycle.

 

I've just realized something that makes me modify some of what I said in my post #22. In the TCH's Atkinson/Miller-cycle ICE, the compression (intake) and expansion (power) strokes are the same physical length, but the intake valves are held open for 30 degrees longer than in the Otto-cycle (non-hybrid) engine of the same design. This means that the are indeed thermodynamic losses that occur when rotating the engine without gas or spark. The effective compression stroke is much shorter than the expansion stroke in the TCH engine, and there will thus be substantially greater thermodynamic losses when turning this engine over than would be the case for the regular non-hybrid version of this engine. This presumably accounts for the (quite considerable) braking effect felt in 'B' mode, which I had ascribed solely to "pumping losses" in my earlier post. I now believe that this braking effect is largely due to the delayed intake valve closing.

Stan

 

FL07TCH - I've located one of my sources for the information about the staged starting of the TCH's ICE. It's in the Prius pages on:
www.ecrostech.com/prius/original/PriusFrames.htm
at the page:
"What's Going On as I Drive my Toyota Prius?"

I'm assuming that something similar is being done with the TCH as is the case with the Prius. Note that the Web site given above is about the original Prius, but it's really excellent, with animated diagrams of the operation of the Power-Split device and discussion of the different modes of operation of the vehicle.

Please also note that I have corrected some valve opening angle calculations that I gave in post #22 above.

Stan