VVT-i Operation at Idle?

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Old 27 Jul 2003, 11:33 am   #1 (permalink)
Platil
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Default VVT-i Operation at Idle?

Hello,

Since I posted about a valve clatter like noise with my 03 Camry/ 4cyl
(2AZ-FE), I think it must be related to the VVT mechanism. Reasoning to
follow.

While at work, I recently examined, and disassembled a VVT unit form a
Celica GT. First off, I was struck by its weight. It's all steel, and I
would say about 1.5-2 pounds in weight. Interesting to note the bolts
holding it together were 5 sided.

Secondly I was struck by its simplicity. Basically it was a finely machined
cylinder sprocket, with a vaned rotor inside making variable chambers. It
operates by a solenoid allowing oil enter the cylinder through holes at
varying rates/volume, enlarging the chambers, thus making the camshaft
advance a certain degree.

I am wondering if these chambers are totally empty at idle (no VVT action),
allowing some metal-to-metal contact inside the VVT to happen, producing the
clatter/tapping I am hearing. I also noticed if I hold a sustained 2500
rpm's in park with a fully warmed engine for 30 seconds or so, the clatter
will many times disappear. Maybe some residual oil/mild VVT action at idle
stops the noise?

I know Toyota says the VVT-i is continuously variable, but wonder if this
means at idle? I would be interested to know what variables/parameters must
be set to activate the VVT system.

Your thoughts and insights on this matter would be appreciated.




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Old 27 Jul 2003, 07:10 pm   #2 (permalink)
Philip«
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Default Re: VVT-i Operation at Idle?

The following information is for the Corolla VVT-i but should help you.

The intake valve opening timing can vary from 2║~42║ BTDC, and close
50║~10║ ABDC. The exhaust timing is fixed with VVT-i. VVT-i at
low-medium RPM / light-medium throttle increases valve over lap
excessively which accomplishes the function of an EGR valve. High degrees
of overlap at lower rpm permits exhaust gases to contaminate the incoming
fresh Air/Fuel charge just like an EGR valve would. At full
throttle-high RPM, the intake cam is fully retarded (minimum valve
overlap) for maximum volumetric efficiency. The ECM reads and compares
camshaft to crankshaft postion (sensors on both) and modulates cam
relative cam position with oil pressure metered by the VVT-i controller
solenoid.

Idle, Light throttle, Full throttle, Low temperature, Starting: Intake
cam fully retarded.

Medium load, Low-Medium RPM, Heavy load: Intake cam fully advanced.
--

Philip

"If a long train of abuses, prevarications, and artifices, all tending
the same way, make the design visible to the people . tis not to
be wondered that they should then rouse themselves."
- John Locke (1632-1704)


Platil wrote:
> Hello,
>
> Since I posted about a valve clatter like noise with my 03 Camry/ 4cyl
> (2AZ-FE), I think it must be related to the VVT mechanism. Reasoning
> to follow.
>
> While at work, I recently examined, and disassembled a VVT unit form a
> Celica GT. First off, I was struck by its weight. It's all steel,
> and I would say about 1.5-2 pounds in weight. Interesting to note
> the bolts holding it together were 5 sided.
>
> Secondly I was struck by its simplicity. Basically it was a finely
> machined cylinder sprocket, with a vaned rotor inside making variable
> chambers. It operates by a solenoid allowing oil enter the cylinder
> through holes at varying rates/volume, enlarging the chambers, thus
> making the camshaft advance a certain degree.
>
> I am wondering if these chambers are totally empty at idle (no VVT
> action), allowing some metal-to-metal contact inside the VVT to
> happen, producing the clatter/tapping I am hearing. I also noticed
> if I hold a sustained 2500 rpm's in park with a fully warmed engine
> for 30 seconds or so, the clatter will many times disappear. Maybe
> some residual oil/mild VVT action at idle stops the noise?
>
> I know Toyota says the VVT-i is continuously variable, but wonder if
> this means at idle? I would be interested to know what
> variables/parameters must be set to activate the VVT system.
>
> Your thoughts and insights on this matter would be appreciated.




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