Violent Shudder

Normally the shudder is from the engine shutting down. Are you absolutely positive that the engine is already off? I'm betting it's not.

Tom

 

Just because the little engine diagram doesn't show the engine on doesn't mean it's not on. My Prius does the same thing, but I've noticed that it has gotten better as the car has broken in (mine is 5 months old now). It's a little disconcerting to feel the car "shut off" at a traffic light but I don't think it's anything unusual.

 

The shut down shudder is most common with new engines, and cold engines. It's completely normal. The control system on the Prius parks the engine in a way to make restarting easy and clean. If it misses the correct spot, it will cycle the engine around again until it gets it right. This causes the shuddering that you feel.

As others have stated, the MFD screen shows energy flow, not engine state. The engine can be idling away warming up and not show on the screen. It's very quiet in this mode, so it's easy to think it is off.

Tom

 

Mine has the same shudder when cold.

 

Makes me shutter when I think about it.

 

Probably just a sideband from one of your radios.

Tom

 

Hi Tom,

I'm wondering if anyone can provide a Toyota technical citation for this, as I've not come across this concept before.
Thanks!

 

It came up in discussions with Toyota engineering, as I recall, but I don't have any documentation. My only reference is word of mouth on this forum, so it seems likely but is not proven. Supposedly the system burns off any fuel and then uses MG1 to power the engine around to a good position for easy restarting.

Tom

 

The only way to know for certain that the ICE is off is to use a scan gauge. or have the hood open and shove your head under it. Far easier to get a scan gauge than to run around in traffic opening and closing your hood just to find out if the engine is running.

Wait for a group buy and get a scan gauge, this will also allow you to find out if there are any codes being generated. No codes + tachometer = knowledge.

 

Hi Bobwho,

Some of us have engine tachometers hooked through the OBDII port.

 

Hi Tony & Tom:

I'm bumping this to see whether there are other replies to my query about a Toyota technical citation supporting the premise that the ICE is intended to stop only at a particular crankshaft position.

We know that MG1 spins the ICE up to idle speed before the ICE is started. Consider that ICE idle speed is ~1,000 rpm, hence 17 revolutions per second or 0.06 seconds per revolution. The ICE is a traditional four cylinder, four-stroke engine, so two cylinders will fire per crankshaft revolution.

If there was an ideal crankshaft position for the ICE to park itself while waiting for the next hybrid vehicle command to start up, the difference between the ideal position vs. any other position would at most be half (since two cylinders can fire per crankshaft revolution) of 0.06 seconds, or 0.03 seconds. I do not think that an ICE startup difference of 0.03 seconds would be noticeable to the driver or passengers; hence I question the premise that it matters where the ICE crankshaft position stops.

I've reviewed the Toyota hybrid tech training documents, the 2001/2004 New Car Features Manual, and the Toyota repair manual; and have not noticed any reference to this premise.

 

Hmmm, if the ICE is always spun up before ignition (my assumption), why would it matter the current crank shaft position at the moment when MG1 starts it spinning? Aren't the valves all open at this point in time as well to allow the ICE to spin freely?

Curious,

-- Ian

 

The usual reason for parking an engine at a particular point is to control what happens when it is sitting. It's not a issue of having it in the proper launch position. Some positions are more prone to the accumulation of unburned fuel and lubricating oil, which will result in smoke during the starting cycle.

On a single cylinder engine, the easiest way to prevent this is to run the piston up and build a little pressure against the closed valves. With a four cylinder engine you can't do it to all of the cylinders at the same time, so that would be a problem.

As this discussion progresses, it seems more likely that the shutdown maneuver is strictly an exercise in removing unburned fuel.

Tom

 

Hi Ian,

The Prius valvetrain is relatively simple:

• the exhaust valve side is controlled by a traditional camshaft, nothing tricky.
• the intake valve side is controlled by a camshaft that has a sprocket whose position relative to the camshaft can be controlled by engine oil pressure, to allow variable intake valve timing.

However, there is no provision to allow all valves to be simultaneously opened or closed.

Hi Tom,

OK - if this is a concern, then the solution could be for the engine ECU to cut power to the four fuel injectors so that no new fuel is entering the intake manifold; then have the hybrid vehicle ECU direct MG1 to spin the engine for a few revolutions while the engine ECU continues to energize the spark igniters in firing order sequence, so that the spark plugs can ignite whatever residual fuel/air mixture remains.

However, I have not seen this documented as a feature...

 

Patrick,

This is the closest I've seen to documentation supporting the premise of seeking the optimal valve position upon shutdown. I knew I had read this somewhere but couldn't remember where. This is a link to hobbit's techie site:

http://techno-fandom.org/~hobbit/cars/valvetmg.png

* Take note of the last frame.