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Just wondering about something: Does the prius use an electric oil-pump, so that the engine maintains oil pressure while the ICE isn't running, or does it use a mechanical pump (like most/all vehicles I know of)? My guess is that Toyota did this right and that the Prius has an electric oil pump or some other method to ensure proper lubrication while the ICE is off, such as when stopped in traffic. Otherwise we're going to see some significant engine wear... Anyone know?
 

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richard schumacher said:
Uhh, why would there be engine wear when the engine isn't turning (notice that I didn't write "running")? I'll bet it uses a mechanical oil pump.
Because the most stress an engine undergoes is in startup and there's no oil in the engine since it's all dripped out into the pan. With the Prius, it'd be easy to see this happening frequently when you're in heavy traffic. Ideally you want an electric pump, and that's what I'm hoping the prius has, but I don't know for sure.
 

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The oil doesn't all drip down into a pan when engine isn't running. All surfaces are covered with the film necessary to protect engine when starting. Do you remember the ads advertising different brands of oil when pan is drained and car run for several hours safely. And this even though oil in the standard engine is also used as a coolant. When an engine is torn down one of the practises is to use a solvent to remove oil from the parts.
 

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zinzindorff9 said:
The oil doesn't all drip down into a pan when engine isn't running. All surfaces are covered with the film necessary to protect engine when starting. Do you remember the ads advertising different brands of oil when pan is drained and car run for several hours safely. And this even though oil in the standard engine is also used as a coolant. When an engine is torn down one of the practises is to use a solvent to remove oil from the parts.
Having a film of oil on the engine isn't the same thing as having the oil pump running and delivering oil to the engine.
 

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Oil pressure question

Toyota has thought this issue throught. The oil pump is a mechanical design. To start the ICE, the crankshaft is spun up to a few hundred rpms without spark or gas. This allows the oil pressure to build and lubricate the moving parts. Then the gas and spark are turned on. Pretty cool.
 

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Starts are hard on traditional engines because raw fuel washes the oil film off the cylinder walls before the mechanical pump has a chance to get oil pressure up. In the Prius, no fuel enters the cylinders until the engine is spinning at 1000 RPM and the oil pressure is up.

The exhaust valves close at 2 deg past top dead center. The intake valves close at between 72 deg and 105 deg past bottom dead center. Exhaust valves are not adjustable. During start, the intake valves are set to reduce (but not eliminate) pumping loss.

The Prius can, and does frequently, run solely on one of its electric motors powered by the battery (with the engine off).
 

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zinzindorff9 said:
Exhaust valves do not close until pistons are 1/4 way up on compression stroke.
Intake valves. If you opened the exhaust valves on compression you would be pushing raw fuel out through the catalytic converter.

By keeping the intake valves open for a portion of the compression cycle you are effectively making the intake stroke shorter than the power stroke. This means that more of the power of the burning fuel is wrung out at then end of each power stroke. Reduces torque, improves efficency. Probably also improves emissions by performing a more complete combustion in the cylinder.

Really cool technology.

Of course I am trusting toyota on this, I have not had the engine apart, it could be powered by teams of mutant gasoline drinking japanese rat-weasels for all I really know.
 

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SkipHuffman said:
zinzindorff9 said:
Exhaust valves do not close until pistons are 1/4 way up on compression stroke.
Intake valves. If you opened the exhaust valves on compression you would be pushing raw fuel out through the catalytic converter.

By keeping the intake valves open for a portion of the compression cycle you are effectively making the intake stroke shorter than the power stroke. This means that more of the power of the burning fuel is wrung out at then end of each power stroke. Reduces torque, improves efficency. Probably also improves emissions by performing a more complete combustion in the cylinder.

Really cool technology.

Of course I am trusting toyota on this, I have not had the engine apart, it could be powered by teams of mutant gasoline drinking japanese rat-weasels for all I really know.
You are correct, it is the intake valves that vary in timing, to allow an effectivly shorter compression stroke, by allowing air to escape back into the intake port.
Remember, this is fuel injection, so the fuel would be injected once the valves are closed during the actual compression.You could just as well shorten the compression by opening the exhaust valve, as you are pushing only air (we haven't injected fuel yet). However, this means the exhaust valve would have to open twice during the whole cycle, rather than once, which unneccesarily to the complexity.
Also, by pushing air back into the exhaust would confuse the O2 sensors, since their job is to check how well the fuel/air mixture burned so the computer can adjust accordingly to minimize emissions.
 

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DanMan32 said:
Remember, this is fuel injection, so the fuel would be injected once the valves are closed during the actual compression.
You are right, I had forgotten about fuel injection. Just air gets pushed back into the intake manifold.
 
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