Mazda Motor Corp exhibited its own continuously variable valve lift system for the first time at the 40th Tokyo Motor Show, which opened to the public from Oct 27 to Nov 11, 2007.
The company plans to begin its commercial production at the beginning of the 2010s, aiming to reduce fuel consumption by 20% in combination with the improvement of combustion mechanism.
The prototype engine exhibited at the show is an advanced version of the MZR 2.0-liter gasoline direct injection engine. And it has a variable valve timing system for admission and emission, a variable valve lift system for admission and an ignition system with two spark plugs.
The injector was improved and a spark plug was added to make finer particles of fuel and burn them efficiently. To realize ideal combustion, the spark plug was added on the verge of the combustion chamber, and the two plugs are ignited at the same time or independently.
In addition, to reduce the pumping loss, the engine is mounted with a variable valve lift mechanism. Of the variable valve lift mechanisms developed by other companies, Mazda's is closest to Nissan's "VVEL" rather than BMW's "Valvetronic" or Toyota's "Valvematic."
Cranks were attached to the camshaft to convert the movement of the camshaft to the revolving movement of the cranks. And this revolving movement is converted to the oscillatory movement of the cams by several links.
To change the amount of valve lift, the supporting point that decides the positional relationship of those links is moved by moving a control axis with a motor. The company said that the amount of valve lift can be changed as much as that of other companies' engines but the amount has not been decided yet.
A camshaft is usually a cylinder. But the camshaft of this engine is four-cylinder type and has crank parts at four points, so it is a knocked-down camshaft. The cams in contact with the valve lifter are positioned so that they cover the camshaft; therefore, they have a double structure.
Commenting on the "Valvetronic" of BMW, Mazda said that it enables to reduce friction because it has only link mechanics and no return spring. Also, it possibly enhances the responsiveness of accelerator because it can change the amount of lift without changing the timing of opening the valves by changing the setting of the link mechanics.
When the valve lifts in normal variable valve lift mechanisms are changed, the timing of opening the valves is also changed; therefore, to change the amount of lift without changing the timing of opening the valves, it is necessary to wait till a hydraulic-vane type variable valve timing mechanism starts up.