Cred ca un forum e un loc pt. dezbatere cu argumente pro si contra in ceea ce ne intereseaza.
Aducem fiecare cite ceva din propriile cunostinte sau experiente acumulate in timp. Putem chiar sa si glumim pt. a colora atmosfera.
Nu spun ca tot ce afirmam este 100% corect sau nu, dar parca ar fi mai placut pt. toti sa aducem totusi contraargumente cind facem o observatie si sa nu invocam lipsa timpului. Pt. fiecare este poate pretios acest timp, dar daca ne apucam de comentat atunci sa o facem macar pina la capat.
Nu cred ca se vor consuma orgolii in niste discutii unde toti avem de cistigat.
Acum o intrebare poate putin retorica: cind este mai solicitat un motor - cind urcam o panta cu treapta 4 si 50 Km/h , 2000 turatii/min sau cu treapta 2 tot 50 Km/h si 4000 turatii/min.
De curind am gasit si afirmatia: consumul minim este la cuplul maxim - aici nu stiu ce sa spun, astept dezbateri.
Pentru
mihaitza2007, nu prea am ce sa pun, sunt grafice care arata curbele, corelatia cuplu si putere.
1kW = aprox. 1,33 CP
Ceva legat si de motorul VVT, traduce fiecare cum poate mai bine...
5.1 VVT-I System
The VVT-i pulley used for the previously announced 2JZ-GE engine is also used for this application. Diagram 3 shows a drawing of the VVT-i system.
Main configuration
1. An ECU that optimizes the valve timing for the engine operating conditions.
2. An OCV (Oil Control Valve) that controls the oil pressure according to the instructions of the ECU
3. A VVT-i belt pulley with a simple structure that changes the intake valve timing according to the oil pressure used to drive it. It is driven by oil pressure supplied by the engine oil pump.
VVT-i continuously varies the valve timing within a range of 60 degrees crank angle to achieve the best intake valve timing for operating conditions.
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5.2 Operation of VVT-i
Idling and at light loads The VVT-i pulley angle is retarded, reducing valve overlap, thus stabilizing combustion and reducing vibration at idle.
(1) Operation at partial loads The VVT-i pulley angle is advanced, overlap is increased, increasing internal EGR volume, thus fuel consumption and exhaust emissions are improved.
(2) At high loads At low engine speeds, the VVT-i pulley angle is advanced, resulting in early intake valve closing. At high speeds, the retarding of the cam pulley increases the intake air volume due to the retarding of the intake valve closing.
In this manner, it is possible to provide continuously variable valve timing to satisfy operation requirements.
VVT-i: It's All a Matter of Timing
Just when you begin thinking that engineers have gotten everything out of the internal-combustion that they can get out of it, they come up with something new that gets more out of it.
Here’s a case in point: Variable Valve Timing-intelligent, or VVT-i.
VVT-i is a way to enhance performance, economy and emissions through control of the phasing, or timing, of an engine’s camshafts.
Stick with me, now, I’m going to get technical: The valves that admit air-fuel mixture into the engine’s combustion chambers, and that open to allow the burned gasses to be pushed out as exhaust, are controlled by egg-shaped lobes on these camshafts, as you see on the image to the left.
The shape of those lobes, and their positioning on the shaft, determine a cam’s timing. In most cases, cam timing is fixed, and that means that it’s a compromise that provides optimal performance only at the speed at which the engine is likely to do most of its work.
But engines operate over a wide range of speeds, from an idle speed of about 600 rpm to a peak speed of more than 6,000 rpm. What if cam timing could be optimized over the engine’s entire operating range?
That’s precisely what VVT-i does.
Using a combination of electronics and hydraulics, VVT-i allows the intake cam to change phase, or timing, over a range of about 30 degrees. Changing the cam timing improves engine breathing at all rpm because the combustion chambers get an optimized volume of air/fuel mixture over a broader range of conditions. The result is more power, more torque, reduced emissions and enhanced fuel economy.
But what if we were able to change the phase of not just the intake cam, but also the exhaust cam? That’s exactly what Dual VVT-i does. By varying the phasing of the exhaust cam by about 30 degrees, we can vary the phasing of the intake cam by a wider range – by about 45 degrees. That means there’s a broader range over which we can open and close the intake valves. And that means we can extract still more power, torque, economy and better emissions.
The way this all works is that a computer controls an oil pump, which controls an oil pressure valve. This valve controls oil pressure in two chambers of the cam-sprocket housing. Based on the oil pressure on both sides of a cam vane inside the sprocket housing, seen here in the below image, the cam’s timing will advance or retard. More oil pressure on one side of the vane rotates the cam in one direction, more oil pressure on the other side of the vane rotates it the other way. This of course is independent of its basic operational rotation, which is provided by the cam’s chain drive.
The oil pressure that controls cam position is, in its turn, based on rpm, load and throttle input. It’s all quite nicely and efficiently managed; the system’s operation is seamless, and works as quickly as a computer can think. Applied to any of our engines, dual VVT-i results in 10-12% more horsepower and torque, and in improved efficiency.