BMW’s Valvetronic System
A new generation of 4-cylinder petrol engines powers the latest 3-Series and the most outstanding feature of the new powerplant family – which is claimed to be absolutely new in every respect – is the Valvetronic system which makes this the first production petrol engine in the world no longer requiring a throttle butterfly.
The function of the throttle butterfly, the component that has obstructed the free ventilation of the petrol engine throughout a wide range of operation ever since its invention, is replaced by infinitely variable intake valve lift – a quantum leap in the history of the combustion engine comparable in significance to the transition from the carburettor to fuel injection, from the distributor-type injection pump to common rail technology, from mechanical to electronic engine management.
The decisive advantage for the driver is a significant decrease in fuel consumption combined with much lower exhaust emissions, as well as a much better engine response and superior refinement. A further point is that the system does not require specific fuel grades or qualities in order to achieve maximum fuel economy, just as there is no need for oil grades not readily available in the market.
In the operating range relevant to the customer, the Valvetronic system is claimed to reduce fuel consumption by at least 10%. It is also the most significant and outstanding technology used by BMW for achieving the demanding EU fuel economy targets specified for the future, requiring a reduction of fleet consumption to 140 grams of CO2 per kilometre by the year 2008.
To give as many BMW owners as possible the advantages of the Valvetronic system, BMW’s 8 and 12-cylinder powerplants will also be converted to this technology this year. This is in line with BMW’s philosophy to offer the most advanced and advantageous technology not only in individual models built in small numbers for specific markets, but rather in all models, thus introducing such new technology as quickly as possible in all markets the world over. It is this change in engine generations that is deemed the largest engine project ever throughout the entire history of BMW.
A deeper look
So far, the process of controlling the gas charge cycle in a petrol engine has always been a compromise between output and torque, on the one hand, and fuel consumption, emissions and comfort, on the other. Partly variable valve control currently culminating in BMW double-VANOS (with the abbreviation VANOS standing for ‘variable camshaft angle control’) as the most sophisticated technology of this kind already reduces this compromise to a minimum, but cannot provide a complete, all-round solution.
This is because the throttle butterfly makes it impossible to reduce fuel consumption any further, since the throttle butterfly has obstructed free ventilation of the petrol engine throughout a wide range of operation ever since its invention. To briefly recap, the throttle butterfly serves to control engine output. Without the throttle butterfly, the engine would constantly run at full throttle. Whenever it is not fully open, however, the throttle butterfly causes a loss in power and therefore wastes fuel. And while the BMW double-VANOS is able to adjust both the beginning and the end of the valve opening period, even this option for controlling engine output has certain limits.
Controlling output by adjusting valve lift
BMW’s engineers have now succeeded in achieving the indispensable throttle butterfly effect without the fundamental disadvantages of the throttle butterfly, ie a substantial loss in power whenever the butterfly is not fully open. They have replaced the throttle butterfly by variable intake valve lift, thus creating the first fully variable valve drive for large-scale production.
This system is based consistently on BMW’s proven, infinitely variable double-VANOS already so successful in the market. Now the additional, variable valve lift adjusts the effective cam action and, accordingly, the valve opening cross-section and period according to the specific requirements involved.
Same Fuel Economy as only a Diesel in the Past
The reduction in fuel consumption provided by this concept of throttle-free load management is roughly 10% in the EU cycle and at least 10% under practical driving conditions relevant to the customer. The basic calculation is that the savings effect increases versus other engine concepts the more often the driver runs the engine at low loads and engine speeds. The potential offered by the Valvetronic system for saving fuel is therefore far greater than that of partly variable concepts such as double-VANOS or switchable valve levers. Indeed, the fuel economy achieved in this way is comparable to the standard of economy only the diesel engine was able to offer until recently.
Taking Nature as a Role Model
A comparison with the human being makes the effect and efficiency of the Valvetronic system easy to understand: When making a great physical effort, the human being breathes in a deep and long pro-cess of ventilation. Whenever he needs less air, on the other hand, he does not ‘throttle’ the intake of air by, say, holding his nose or mouth, but rather simply breathes in a shorter and “flatter” process.
On a conventional combustion engine, the throttle butterfly is basically comparable to a human being holding his hand over his nose or mouth. Valvetronic, in turn, with its valve lift sometimes larger (= deep, long ventilation) and sometimes smaller (= flat, short ventilation) allows the engine to breathe like a human being in nature, always taking up air in accordance with current requirements, without any throttle effect and therefore with maximum efficiency.
Decisive Advantages
Another advantage of Valvetronic highly relevant to the customer is that it offers at least the same fuel economy as a modern direct-injection (DI) petrol engine, but without the same compromises in terms of emissions. And it therefore does not require the elaborate and currently not very robust emission management technology still absolutely essential with a direct-injection petrol engine.
Yet a further advantage is that the Valvetronic engine does not require sulphur-free fuel and achieves its superior standard of fuel economy with proven technology, running in the process on all usual fuel grades. The customer therefore benefits from the full economic potential offered by Valvetronic even when driving in countries without a nationwide supply of sulphur-free fuel, which is not the case, of course, with a direct-injection petrol engine.
Many Other Intelligent Features
Not only the cylinder head with Valvetronic, but rather the entire 4-cylinder power unit is an all-new design with a whole range of special features serving to further reduce fuel consumption and increase both running smoothness and practical reliability. The engine block itself is made of aluminium in open deck design featured for the first time ever by BMW. With the “top deck” being dropped in this case, the engine can be manufactured through pressure die-casting with reduced wall thickness and, as a result, a corresponding reduction in weight.
A further advantage is that this process allows direct casting of the grey-cast cylinder liners subject to less deformation than with a closed deck engine block. With cylinder roundness being enhanced in this way, the engine offers further advantages in terms of oil consumption and friction, which ultimately again means greater fuel economy.
As on all BMW engines, the crankshafts are driven by a chain not requiring any maintenance at all throughout the entire service life of the engine. This relieves the customer of any annoying and time-consuming visits to the workshop as well as the high cost of maintenance and unnecessary operating risks inevitably resulting from the use of a toothed belt running the crankshafts.
The locally-assembled 318i
The latest BMW 318i assembled in Malaysia is powered by a 2.0-litre four-cylinder petrol engine with Valvetronic. Compared to the previous model with a 1.9-litre powerplant, the new 318i produces 21% more power, 11% more torque and up to 20% improvement in fuel economy. Top speed is now claimed to be 218 km/h while the 0-100 km/h sprint takes just 9.3 seconds. Fuel consumption, as declared by BMW, is a frugal 13.8 kms/litre(39 mpg).
The model comes with a new 5-speed automatic adaptive transmission with Steptronic that allows driving with either automatic shifting or manual selection in a sequential manner. It retails at RM218,091.63 (personal registration, excluding insurance).
