Are VVT and VCT similar, the same or totally different and what part does motor oil play in their operation? Is one better than the other? Thank you.
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VVT vs VCT
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I think they are essentially similar until you add variable lift (vvel, etc)
In some cases oil is used to actuate whatever the system is, in some cases an electric solenoid will control that oil pressure. In other cases it is mostly electromechanical with oil only providing lubrication duties.
In some cases oil is used to actuate whatever the system is, in some cases an electric solenoid will control that oil pressure. In other cases it is mostly electromechanical with oil only providing lubrication duties.
VCT = Variable Cam Timing. A system that makes the valves open and close earlier or later in the piston cycle by changing the "phase" of the camshaft.
VVT = Variable Valve Timing. A general term for any system that can make the valves open and close earlier or later in the piston cycle, whether through cam phasing or some other method.
In other words, VVT is a blanket term; VCT is a type of VVT.
Usually those kinds of systems work with oil pressure; the ECU activates a valve electronically, the valve lets oil into a chamber or something, and the resulting pressure causes something to move which alters the valve timing. This makes it a little more important for the oil to be the right viscosity, because viscosity affects oil pressure.
VVT = Variable Valve Timing. A general term for any system that can make the valves open and close earlier or later in the piston cycle, whether through cam phasing or some other method.
In other words, VVT is a blanket term; VCT is a type of VVT.
Usually those kinds of systems work with oil pressure; the ECU activates a valve electronically, the valve lets oil into a chamber or something, and the resulting pressure causes something to move which alters the valve timing. This makes it a little more important for the oil to be the right viscosity, because viscosity affects oil pressure.
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General Motors has advertised VVT in their OHC engines which would be of the camshaft 'phasing' type (changing cam to crankshaft timing). When one camshaft controls both the intake valves and the exhaust valves, you're very limited in variability.
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
So there is definitely a difference between variable valve timing and variable camshaft phasing. It's all in the application that it's applied.
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
So there is definitely a difference between variable valve timing and variable camshaft phasing. It's all in the application that it's applied.
So according to the wiki article Gm was the first to patent a vvt system in 1975. Just found that a bit interesting. Any was the vvt wiki entry seems pretty informative to me.
http://en.wikipedia.org/wiki/Variable_valve_timing
http://en.wikipedia.org/wiki/Variable_valve_timing
VVT was old in 1975.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam are advanced /retarded, the lift of the valves is regulated, or both together.
Each Mfr. does it differently.
BTW, I have a Ford Zetec 2.0 in a ZX2 and the VCT is on the EXHAUST CAM! It retards under cruise conditions to simulate an EGR valve - maybe get a longer burn time to tweak a bit more gas mileage.. I would love to have it on the intake - to do some good.
When they work right, they generally provide very real benefits.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam
Each Mfr. does it differently.
BTW, I have a Ford Zetec 2.0 in a ZX2 and the VCT is on the EXHAUST CAM! It retards under cruise conditions to simulate an EGR valve - maybe get a longer burn time to tweak a bit more gas mileage.. I would love to have it on the intake - to do some good.
When they work right, they generally provide very real benefits.
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Originally Posted By: FowVay
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
This is very misleading. Very few models can move their cams very much at all.
It's waaaaaay different than infinite!
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
This is very misleading. Very few models can move their cams very much at all.
It's waaaaaay different than infinite!
Originally Posted By: d00df00d
VTEC can actually completely change the cam profile, not just the timing.
Actually they just switch to a different lobe ground right on the same cam.
VTEC can actually completely change the cam profile, not just the timing.
Actually they just switch to a different lobe ground right on the same cam.
Originally Posted By: SteveSRT8
Originally Posted By: d00df00d
VTEC can actually completely change the cam profile, not just the timing.
Actually they just switch to a different lobe ground right on the same cam.
Exactly. The point is that the VTEC lobe can be different in terms of lift and duration as well as timing, so VTEC can change more than a VVT system can.
Originally Posted By: d00df00d
VTEC can actually completely change the cam profile, not just the timing.
Actually they just switch to a different lobe ground right on the same cam.
Exactly. The point is that the VTEC lobe can be different in terms of lift and duration as well as timing, so VTEC can change more than a VVT system can.
Originally Posted By: SteveSRT8
Originally Posted By: FowVay
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
This is very misleading. Very few models can move their cams very much at all.
It's waaaaaay different than infinite!
My cam gears are infinitely adjustable -[ no keys, pins, dowels]. But any cam can be adjusted anywhwere.
You may hit pistons with valves, or have some ridiculous settings, but why not?
What cams can't be adjusted one way or another?
Originally Posted By: FowVay
When you have a dual cam engine, you can vary the intake timing or exhaust timing in relation to the crankshaft position OR in relation to the intake/exhaust cam almost infinitely.
This is very misleading. Very few models can move their cams very much at all.
It's waaaaaay different than infinite!
My cam gears are infinitely adjustable -[ no keys, pins, dowels]. But any cam can be adjusted anywhwere.
You may hit pistons with valves, or have some ridiculous settings, but why not?
What cams can't be adjusted one way or another?
I'm talking about while the engine is in operation.
And I also have a drawer full of adjustable timing sets for American V-8's, and they almost never allow more than 6 degrees of advance/retard.
I'm pretty sure about 35 degrees is the largest number I've heard quoted for a VVT setup, and that was a large one.
And I also have a drawer full of adjustable timing sets for American V-8's, and they almost never allow more than 6 degrees of advance/retard.
I'm pretty sure about 35 degrees is the largest number I've heard quoted for a VVT setup, and that was a large one.
I may be wrong, but I think that the xMZ Toyota V-6 engines with VVT-i allowed about 60 degrees of adjustment of the timing of the intake camshaft. In this context, that would be about 300 degrees short of "infinite", but would still seem to me to be pretty substantial.
I've searched internally and externally, and can't find my source for that (but I'll keep trying). Anyone out there have anything on this?
I've searched internally and externally, and can't find my source for that (but I'll keep trying). Anyone out there have anything on this?
Originally Posted By: mechtech2
VVT was old in 1975.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam are advanced /retarded, the lift of the valves is regulated, or both together.
Each Mfr. does it differently.
+1
VVT was old in 1975.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam
Each Mfr. does it differently.
+1
Originally Posted By: mechtech2
VVT was old in 1975.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam are advanced /retarded, the lift of the valves is regulated, or both together.
Each Mfr. does it differently.
BTW, I have a Ford Zetec 2.0 in a ZX2 and the VCT is on the EXHAUST CAM! It retards under cruise conditions to simulate an EGR valve - maybe get a longer burn time to tweak a bit more gas mileage.. I would love to have it on the intake - to do some good.
When they work right, they generally provide very real benefits.
Well, thankfully, I was not "old" in 1975 (in fact, I started high school that year). That said, I think this statement is a little misleading (I'm not claiming that's intentional). The concept of vvt was known by then, but because of the primitive computer systems available to control engines, it simply was not feasible to implement until about ten years ago (when, surprise surprise, it started appearing on production cars). In the near future, vvt, controlled by powerful computers, will be the order of the day for ALL vehicles.
VVT was old in 1975.
There were heavily sprung centrifigally activated cam gears available for V8s that were around way before this.
They retarded the cam for high end power.
Unfortunately, they retarded the ignition timing, because the distributor ran off of the cam.
VVT, VCT? Just names. Variable valve and variable cam timing. the cam
Each Mfr. does it differently.
BTW, I have a Ford Zetec 2.0 in a ZX2 and the VCT is on the EXHAUST CAM! It retards under cruise conditions to simulate an EGR valve - maybe get a longer burn time to tweak a bit more gas mileage.. I would love to have it on the intake - to do some good.
When they work right, they generally provide very real benefits.
Well, thankfully, I was not "old" in 1975 (in fact, I started high school that year). That said, I think this statement is a little misleading (I'm not claiming that's intentional). The concept of vvt was known by then, but because of the primitive computer systems available to control engines, it simply was not feasible to implement until about ten years ago (when, surprise surprise, it started appearing on production cars). In the near future, vvt, controlled by powerful computers, will be the order of the day for ALL vehicles.
Well as they say: necessity is the mother of invention- or at least the auntie of continued R&D. Stricter emissions and efficiency requirements have really driven modern valve control dynamics it seems, and they're not done yet with the development and introduction of continuously variable phasing and lift!
I've often thought it would be cool to do away with camshafts entirely and use oil pressure or solenoids to directly actuate the valves. From what I've read, this is difficult because of amount of force needed in a short amount of time. Still, a cool idea.
Originally Posted By: NateDN10
I've often thought it would be cool to do away with camshafts entirely and use oil pressure or solenoids to directly actuate the valves. From what I've read, this is difficult because of amount of force needed in a short amount of time. Still, a cool idea.
BMW have that in some of their production engines for many years now... Valvetronic?
I've often thought it would be cool to do away with camshafts entirely and use oil pressure or solenoids to directly actuate the valves. From what I've read, this is difficult because of amount of force needed in a short amount of time. Still, a cool idea.
BMW have that in some of their production engines for many years now... Valvetronic?
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