The Valvetronic engine is the world's first engine without a throttle butterfly. Valvetronic allows the engine to run without a throttle butterfly, the cylinder charge being determined under part load as a function of the valve-opening period. The intake and outlet camshafts are driven by variable cam adjustment, BMW’s Vanos technology. A further advantage of this concept is that it allows worldwide use of the proven three-way catalyst for emissions management, thus meeting even the strictest emissions standards in the US.
Innovative technology was essential in order to reach the demanding objectives and functional requirements desired. However, at the same time, this concept demanded the utmost of the electronic control and management systems in the engine.
Taking nature as the role model: human beings also apply the Valvetronic principle
A comparison with the human being clearly explains how Valvetronic works: Whenever we are required to make a great effort, we human beings breathe in a deep and long process of ventilation. Whenever we need less air, we do not throttle the supply of air by, say, closing our nose or our mouth, but simply breathe in a shorter, flatter process of ventilation. In a conventional combustion engine the throttle butterfly is basically comparable to a human being keeping his nose or mouth at least partially closed. With its large valve lift (= deep, long ventilation) and short valve lift (= flat, short process of ventilation), Valvetronic, on the other hand, is able to breathe in the same way as nature – always in line with current requirements, without any kind of throttling effect and therefore with maximum efficiency.
Accordingly, the Valvetronic engine no longer requires a throttle butterfly, which has quite literally restricted the free ventilation of the internal combustion engine ever since its invention. Now Valvetronic replaces this conventional function by infinitely variable intake valve lift, offering a quantum leap in technology quite comparable to the changeover from the carburetor to fuel injection.
Its most important feature is that it is able to save at least 10 per cent fuel throughout the entire operating range relevant to the customer, with a corresponding reduction in exhaust emissions, regardless of fuel quality. And a further important point is that the efficient operation of Valvetronic does not require any unusual types and grades of oil possibly difficult to obtain.
As a result of these particular features the 85 kW/115bhp BMW 316ti compact with its top speed of 210 km/h or 125 mph consumes a mere 6.9 liters of premium fuel on 100 kilometers in the European test cycle, equivalent to 40.9 mpg Imp. This is a significant 0.7 liters less than the former 77 kW/105 bhp compact and well over a liter less than all competitors in this class.
The Valvetronic system is based consistently on BMW’s proven double-VANOS (VANOS = variable adjustment of the camshafts), with infinite camshaft adjustment to meet specific requirements. The additional, variable valve lift adjusts the effective cam action and, accordingly, the opening cross-section of the valves.