14-07-2012, 03:24 PM
VALVETRONIC SYSTEM
VALVETRONIC SYSTEM.ppt (Size: 393.5 KB / Downloads: 76)
Introduction
When you floor down throttle pedal, you do not control the amount of fuel injection but the amount of air running into the cylinders.
Fuel injection system monitor the amount of air passing the throttle butterfly and then determine the corresponding amount of fuel needed.
The more the throttle butterfly opens, the more air runs into the combustion chamber.
Major Drawback
During low revs the creation of partial vacuum in the combustion chamber leads to energy loss known as "Pumping Loss".
The slower the engine runs, the more the throttle butterfly closes, thus the more energy loss.
VALVETRONIC SYSTEM:
The Valvetronic system is a variable valve timing system to offer continuously variable timing along with continuously variable intake valve lift, from ~0 to 10 mm.
Valvetronic-equipped engines are unique in that they rely on the amount of valve lift to throttle the engine rather than a butterfly valve in the intake tract.
Origin:
Engines are equivalent to the human respiratory system. "Whenever we are required to make a greater effort we breathe with a deep and long process of ventilation. Whenever we need less air, we do not throttle the supply of air by closing our nose or our mouth"
The Valvetronic system is based on BMW's established double VANOS system, which steplessly varies the timing of both the inlet and exhaust cams.
Constructional Features
It employs an additional eccentric shaft, an electric motor and several (one per valve) intermediate rocker arms.
The motor control the angle of eccentric shaft, which rotate the shaft hence depth of the intermediate rocker arms acting on finger followers, which in turn activate opening and closing of valves.
Features:
The accelerator pedals are no longer attached with a cable; they are now just sensors that will send the information to the computer.
The Valvetronic engine does not require a timing belt or chain. Valvetronic has its own computer housed in a separate unit away from the engine management system, networked with the digital engine management system incorporating a 40-megahertz, 32-bit computer.
Technical Specifications:
Valve lift is variable between 0 and 9.7 mm.
Adjustment of the worm gear from one extreme to the other takes 300 milliseconds.
Combined with double-Vanos valve timing technology, the camshaft angle relative to the crankshaft can be adjusted by up to 60°.
The intermediate arm is finished to a tolerance of 0.008 mm.
The cams controlling the eccentric shaft are machined to tolerances of a few hundredths of a millimeter.
Future Implementations:
Toyota will be launching its newest variable valve timing innovation dubbed Valvematic.
This new mechanism will manipulate the intake valve lift volume, adjusting the level of sacrificial oxygen molecules to increase both performance and fuel efficiency.
According to Toyota, Valvematic will increase power output by ten-percent, while at the same time increasing fuel efficiency anywhere between five- and ten-percent.
Advantages:
The engine delivers spontaneous response to the accelerator pedal.
Gives high power output.
More refined operation.
Higher fuel efficiency.
Limitations:
The downside is that at above 6,000 RPM valvetronics efficiency drops quickly.
The stronger springs create higher friction losses.
Overall size of the engine increases.
Conclusion:
Valvetronic mechanism get rid of throttle butterfly thus saves fuel, especially at lower revolutions.
According to the EU combined test cycle consist of high speed and low speed running, the 1.8-litre Valvetronic engine used by 316ti Compact saves 10% fuel (at 53.3 mpg or 5.3 litre / 100 km).
For those who regularly drive in city, the saving could be bigger. Moreover, unlike direct-injection it need not to drink low-sulphur gasoline.