Engine lubrication before (auto)start?

Back in the day long ago with really big engines and weak oil pumps waiting 5-10 seconds or so for oil to be flowing at its best made sense. But in small modern engines, especially engines in hybrid cars that are designed to start and stop often, the lubrication system is close enough to instantaneous to not ever be an issue. However once you get more than 2 quarts low on oil in a Prius and slam on the brakes or driving around a corner, your oil pump will not have enough oil to pump and you'll get a red triangle flickering.

 

Yes, it does. Not for a few seconds, but for a little bit.

 

Near as I can tell it seems like engine is always spinning at freeway speeds, even when you're going down a long steep grade. Is that true? And if so what's the reasoning?

 

If you look at a nomograph for the engine, MG1, and MG2 speeds determined by the gear tooth counts in the PSD, you see that when the engine is stopped, high car speeds require MG1 to spin quite fast (in the − direction). (Lay a ruler from a given "car speed" on the right, through zero "ICE" (engine) speed, and see where it hits the MG1 speed on the left.)

MG1 has a maximum safe rev limit (in either direction). Above a certain car speed, the engine has to be allowed to spin; notice that when the ruler passes through the same car speed but a nonzero engine speed (say 1000 RPM), MG1 does not end up spinning as fast.

The magic number for the car speed differs between generations. That isn't because the tooth counts in the PSD have changed; whether surprisingly or unsurprisingly, Toyota has kept the same tooth counts there through all the generations I know about. But they keep improving the maximum safe MG1 revs, so they keep increasing the car speed you can hit before the engine has to turn. (Also, the final drive ratios have been changed between generations and models.) Back in gen 1 it was as low as 42 MPH.

 

I may be wrong, but I seem to recall learning in a hybrid class that the Gen3 transmission had a second "fixed" planetary gearset that reduced MG1 speeds.

I tried one time to see what happens to a Gen2 MG1 at 10,000 RPM but couldn't get there. The normal "software limit" is about 6500 RPM (about 40mph). Above that the ecu spins the ICE at around 1000 RPM (as you know).

IF you shift to neutral while the ICE is off (below 40) the accelerate (coast down a steep hill), then ICE will stay off and MG1 goes faster. I ran out of hill at 66mph, math says I need about 70.

Shift to neutral anytime the ICE is spinning, and it will (start and) stay running indefinitely - but not charge the HV battery.

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The second planetary in gen 3 lies between MG2 and the PSD ring, as a reduction gear. It allows a smaller lighter MG2 that makes its power at higher speed and lower torque.

The final drive is still connected to the PSD ring, and the PSD tooth counts are still the same, so the relationship between road speed and engine/MG1 speeds stays pretty much the same (except for the differences in final drive ratio.)

The biggest difference is that in gen 1 or gen 2, you could speak informally of either PSD ring RPM or of MG2 RPM because they were the same. In gen 3 and later, you have to be careful which one you mean.

I remember "about 40mph" being the magic road speed in gen 1, corresponding to gen 1's 6,500 RPM limit for MG1.

The gen 2 New Car Features manual, page TH-26 under "Main Changes from '03 Prius", mentions increasing MG1's safe rev limit from 6,500 to 10,000 RPM, which would correspond to a higher road speed than 40mph.

I'm not sure the engine will stay off forever. The New Car Features manual again, on page TH-46 under "Shut Down Control", explains that the ECU can veto your selection of "neutral" in three special circumstances, and picking up speed beyond the safe range is one of them. So it can then decide "neutral" wasn't quite what you meant, at least long enough to crank up the engine and keep the speeds under control. I'm betting later generations do the same.

If it hadn't done that by 66mph, my suspicion is that it would have shortly if you hadn't run out of hill. But it's not an experiment I've run myself.

 

An an engineer, I'm still fascinated at the hybrid vehicles and believe Toyota's are heads-and-shoulders better than anything else out there.

When I learned the F1 Race cars are hybrid, I went down a very fun rabbit hole learning about them....

The history of hybrid cars in Formula One (F1) includes the development of the first hybrid, the reintroduction of hybrid systems, and the evolution of hybrid technology:

• McLaren's KERS
  In 1998, McLaren developed the first F1 hybrid car with a largely secret KERS system. However, the technology was quickly banned and only permitted to return in 2009.
• Honda's RA109
  In 2008, Honda tested a hybrid system on a full track at Silverstone, the first time an F1 team had done so since McLaren a decade earlier. Honda's RA109 was designed to be fitted with a battery-electric hybrid system.
• The 2009 Hungarian GP
  The first hybrid victory in F1 was at the 2009 Hungarian GP. However, the reintroduction of hybrid systems was not a huge success, and most teams struggled to get the technology to work properly.
• Turbochargers return in 2014
  Hybrid engines that combine a turbocharged engine with energy recovery systems (ERS) were introduced in 2014. ERS includes kinetic recovery (ERS-K) and heat recovery (ERS-H).
• F1 technology advancements
  F1 technology advancements have continued to rise, with the use of 3D printing, augmented reality (AR), and artificial intelligence (AI).