Hybrid Oil Pressure Question

Hybrid Oil Pressure
Been bothering me that when the 3G Tundra HV/Sequoia go into their idle or low speed hybrid mode that the oil pressure gauge goes to zero. I really don’t like looking down and seeing that condition! Yes, the actual 3.4L engine is ‘OFF’, but only in the sense of no fuel or ignition. The engine is still turning over - harmonic balancer spinning, alternator, AC, all spinning away while in hybrid mode. So if the reciprocating parts are being spun by the hybrid drive, wondering why would Toyota choose to show no oil pressure? The engine certainly still has oil pressure being made by the mechanical oil pump, and the engine certainly needs the circulation. I’d like to see the oil pressure continue to read. I think it’s enough that the tach goes to zero and things get quieter while the MAX gauge shows battery output, so drivers certainly know it’s in the hybrid mode. Any ideas of that logic?

 

I could be totally wrong since I don’t have a hybrid, but couldn’t the hybrid motor spin without turning the motor over, since it’s sandwiched between the motor and the transmission? If that’s not true, then yes, I’d imagine the oil pump is still pumpin, so it’d be weird for it to show as zero. I would imagine that there’s either clutches between the hybrid motor and output shaft of the ICE motor or that the hybrid motor isn’t directly attached to the output shaft of the ICE motor at all.

 

Yes the hybrid motor can spin without turning ICE over.

 

Maybe so, but not as I’ve seen. The hybrid electric drive is a supplemental, not an independent system. When you open the hood when running under hybrid mode, the engine reciprocating parts are turning. The hybrid drive is sandwiched between the engine block and transmission in what looks like an oversized bell housing, but the gasoline engine is not creating power ( not using fuel). If the engine spins it needs oil pressure. I’d just like the gauge to show it’s being protected.

 

The hybrid fully shuts down the gas engine when under low load and adequate levels of hybrid battery charge. The clutch that connects the electric motor to the crank disconnects, and the gas engine is stopped until the clutch engages. The electric motor can almost instantly (within milliseconds) get the engine rotating when it needs to restart, so the oil will be circulating before the engine actually fires.

There are also multiple systems that operate regardless of whether the gas engine is running. The AC compressor is electric, driven by the hybrid battery via a big orange cable coming out of the inverter. The inverter’s dedicated cooling system is also electric always running if the truck is on. The cooling loop for the turbos is also electric. There are two electric fans in the grille that keep running, even if the mechanical fan on the front of the engine isn’t.

 

That part of the statement needs corroboration IMO: oil pressure takes some time to build, and whether there is enough time available in an auto-stop-start situation is unknown at this point.

 

It's not like internal engine parts suddenly become dry as soon as the there is no oil pressure.

Thru the magic of oil technology, a film of oil remains on those parts. Otherwise, engines would fail in the first few start/stop cycles.

 

And yet it is known that the maximum rate of wear occurs at start up every time for that very reason: that it is not just the presence of oil, but enough of a film of oil under pressure that is needed to reduce wear for longevity.

 

My prior reading stated the transmission has an electric oil pump for the hybrid system, but the engine only has a mechanical oil pump (and p/n is same for iforce and iforce max). The max has an electric coolant pump for the turbos though.

When a warm engine is running it stays coated for a while, much more than a cold engine (which still will have film on startup). The Prius hybrid is the same and I know of many with very high miles.

 

There is a difference between an oil film between two bearing surfaces and an oil film under pressure between two bearing surfaces.

 

The torque of the electric motor gets the engine rotating at idle speed (800-ish rpm) in milliseconds. So, the oil pump is already operating as thought the engine is idling before the ignition kicks in. It has about as good oil pressure at startup as you can hope for, and certainly much better oiling than something using a traditional starter.

 

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I’m not denying what several of you have said in what you understand technically happens, but in every situation where I’ve opened the hood while parked and in HYBRID MODE, the mechanical fan and harmonic balancer are being spun by the hybrid drive system. At that point on the IP there is no tachometer reading and oil pressure gauge reads zero. When it switches back to engine internal combustion the tach comes alive and oil pressure comes back up. Could be environmental conditions in that it’s in Texas heat and after the vehicle has been previously driven. If the reciprocating parts of the engine are turning it’s making oil pressure from the mechanical oil pump, and I don’t understand the logic of not showing the oil pressure?

 

What you say is a reasonable hypothesis but there is nothing thus far to corroborate it. That is all.

One may hope that is true but at this point there is nothing to show it is indeed the case.

Even if we accept your hypothesis, just because the oil pump starts spinning instantly it cannot build oil pressure instantly. That takes much longer than milliseconds. The further away from the oil pump the longer it takes especially the heads.

 

What you fail to understand is the oil pump only delivers the oil to the bearings, it does not create the high localized pressure between the bearings and the crankshaft. It's the crankshaft's rotational motion that creates the high pressures at the bearings, which can reach hundreds of PSI.

So, while the pump might take a fraction of a second to build pressure, there is still pressurized oil at the bearings as soon as the crank starts spinning.

 

Incorrect. The oil pump creates the high pressure needed.

Please provide some corroboration for this claim, thanks.

Unless the oil pump is providing sufficient pressure, the spinning of the crankshaft will squeeze out the oil film and start wearing the bearing surfaces. Otherwise, an oil pump failure would not destroy bearings, since the crank is still spinning according to your claim and has pressurized oil. Try switching off an electric oil pump when the engine is spinning and see how long the bearings survive.

That is exactly why the maximum rate of wear is at start, since the oil pump takes a while to build up the pressure to maintain the oil film to bear the loads placed on it. The further away from the oil pump, the longer it takes, hence the heads and especially camshaft journals and lobes are particularly prone to this wear until the oil gets there with suitable pressure. There is also a delay with the length of the oil pickup tube, so much so that many manufacturers have moved to a belt driven oil pump at the side of the main block towards the rear to shorten the pickup length, instead of at the (usually) front end of the crankshaft.

That is also why oil pressure gauges (and their readings) are more credible than claims and hopes.

 

I believe the 3.4 liter motors use a chain and not a belt for timing? if so then is probably has enough lubrication built up that when it shuts off the Hybrid motor enough oil is in the passages that it doesn't lose circulation. Toyota Japan engineers are the smartest on the planet. I trust their knowledge over most others when it comes to this subject.

 

The method of driving the cams (belt, drive, chain, other) does not have any bearing on the delivery of pressurized oil whatsoever.

 

Wrong. It's well-known ICE physics. A mechanical oil pump typically only provides around 30-50 PSI. Oil pressure between the bearings and crank can reach hundreds of PSI. The pump is not creating those high pressures, its the rotational motion of the crank. Don't take my word for it, do some research.

Again, internal engine components don't suddenly become dry as soon as the pump shuts off. There is enough residual oil in the bearings to keep them lubricated for the split second it takes the pump to create pressure.

You are correct that conventional theory says startups create the most wear on an engine. Like you, that's what makes me leery about any auto stop/start features. But hybrids and auto stop/start have been around a long time, and I think the engineering has been proven to work.

 

LOL. Please provide the reference for the claims you have made below, thanks.

"It's well-known ICE physics. A mechanical oil pump typically only provides around 30-50 PSI. Oil pressure between the bearings and crank can reach hundreds of PSI. The pump is not creating those high pressures, its the rotational motion of the crank."

Without the oil pump, there is insufficient pressure to maintain the health of the bearings, regardless of what the peak pressures may be locally. After all, the pressure in the oil circuits is managed by the diameter of the galleys and orifices distributing and delivering and draining the oil to the bearings, and can vary according to the location in the circuit, including the bearing surface itself.

If it is "well known" then a reference source would be easy to find.

 

AI isn't always correct, but in this case it is. Feel free to verify it yourself.

What is the oil pressure at the main bearing of a typical ICE?

The oil pressure at the main bearing of a typical internal combustion engine (ICE) is a complex dynamic, influenced by several factors and varying depending on the specific location within the bearing and the operating conditions of the engine
.
Here's a breakdown:

• Overall Engine Oil Pressure:
  • Most engines operate within a range of 25 to 65 PSI.
  • At idle, typical pressure ranges from 20 to 35 PSI.
  • At higher RPMs, this can increase to 60 to 70 PSI.
  • A general rule of thumb is 10 PSI per 1,000 RPM, according to Summit Racing and King Engine Bearings.
• Local Pressure at the Bearing:
  • The local pressure at the crankshaft journal and bearing is significantly higher than the overall pump pressure, potentially reaching hundreds of PSI.
  • This higher pressure is generated by the hydrodynamic lubrication effect, where the relative speeds of the crankshaft journal and the bearing, coupled with oil viscosity and bearing clearance, create a pressurized oil film that separates the surfaces.

Factors Affecting Bearing Oil Pressure

• Engine Speed (RPM): Higher RPMs lead to faster rotation and increased oil flow from the pump, thus higher pressure.
• Oil Viscosity: Thicker oils (higher viscosity) create greater resistance to flow and thus higher pressure, especially at colder temperatures.
• Bearing Clearances: Excessive bearing clearances (due to wear) allow oil to leak out more quickly, reducing resistance and thus decreasing pressure at the bearing.
• Engine Load: Higher engine loads increase the forces on the bearings, requiring sufficient oil film pressure to prevent metal-to-metal contact.
• Oil Pump Performance: A worn or inefficient oil pump will not be able to deliver adequate oil flow and pressure.
• Oil Temperature: As oil heats up, its viscosity decreases, which can lead to lower pressure, according to Car From Japan and Wikipedia.

In essence, while the oil pressure gauge provides an overall system pressure reading, the actual pressure at the main bearings is much higher due to the dynamics of hydrodynamic lubrication. Maintaining proper oil viscosity and bearing clearances is crucial to ensure adequate pressure and prevent bearing wear.

 

Please keep in mind that without the oil pump, there is insufficient pressure to maintain the health of the bearings, regardless of what the peak pressures may be locally. After all, the pressure in the oil circuits is managed by the diameter of the galleys and orifices distributing and delivering and draining the oil to the bearings, and can vary according to the location in the circuit, including the bearing surface itself.

Besides, there is a difference between hydrodynamic and hydrostatic lubrication.

 

I never said oil pump pressure isn't necessary to maintain the health of bearings. I said there is enough residual oil on the bearings and crank to maintain lubrication for the split second it takes the pump to build pressure.

Maybe this simple exercise will make you understand. Soak a wrench in oil, then hang it up indoors, out of weather and sunlight. How many days, months, or years does it take for that wrench to no longer have a thin film of oil on it? I'll give you a hint, it's not measured in days or months.

That's why a ICE engine can sit for years without any oil pressure, and still fire up and run without eating itself to pieces. I have a 44 year old Jeep CJ that sat in my barn for 11 years without being started up. When I finally got around to restoring it, I put a new battery and fresh gas in it. It fired up after about 10 seconds of cranking. That engine still runs beautifully today without burning any oil or any other negative affects from sitting for that long.

 

My only issue here is with this "split second" for the pump to build pressure. How does one know that? I do know that it takes a "good while" to get the oil up to heads once the engine starts. Obviously, empirical observation shows that even engines with stop-start do not destroy themselves in short order. But they would logically have more wear at the bearings than engines not doing so many starts, since the maximum wear does happen at every start.

 

It's very simple. The lubrication system in a ICE engine is a closed system. If there are no leaks, the pump remains primed when the engine is off. A typical starter will crank the engine at around 300-500 RPMs. That's around 7 revolutions per second. It only takes a couple of revolutions of the crank to build oil pressure, so you do the math. I think the hybrid starting systems spin up even faster.

Think of it like the domestic water system in a house that's on a well. There's typically a water pump that maintains pressure in the system. That way, when you turn on a faucet 2 floors up there's still instant water. It's basically the same principle.

 

Well, there is a reason I went with the non-hybrid and disabled the auto stop-start from Day One. That is enough for me. Others will of course decide for themselves, with which I have no problem at all.

 

I went with the non-hybrid too, and I never use the auto stop/start either. But it's not because of concern over wear and tear to the engine. It's because I find the auto stop/start cycles to be distracting.

 

I am not distracted, and appreciated that I was able to set the stop duration to an extended interval reflecting certain long traffic signals but in the end, I don't like the idea of the starting and stopping oil flow to the turbos so I have abandoned using it. It doesn't seem to make any discernable difference to the fuel economy.

 

Why would the hybrid drive spin all that reciprocating mass with its pumping and mechanical losses? That would be an additional load on the battery for no reason. I think the oil pressure reads zero because the oil pump and the engine itself are not spinning when the electric motor only is deemed to be sufficient. That would at least be logical, but I really have no known source to confirm either possibility.

 

My well, and I would assume most other domestic household wells maintain system pressure with a pressure tank so that the pump doesn't dither on/off at the setpoint. (This could be different out in the field for irrigation or livestock tanks.) For the household, there are thus two setpoints; pump turns on at the low and off at the high. The pressurized tank maintains the system pressure whenever a faucet is opened so that the pump doesn't constantly turn on wearing itself out.