The automobile has been providing individual mobility for more than 100 years. This mobility is made possible first and foremost by combustion engines drawing their power from fossil energy carriers, which, even today, provide the foundation in generating mechanical drive power in the automobile. The primary objectives in developing drive systems are to curb fuel consumption and reduce CO2 emissions. In an effort to meet this challenge, the automotive industry is developing suitable new engines. The voluntary commitment assumed by the European Automobile Manufacturers Association (ACEA) is to reduce the fleet emission average of all newly introduced cars to 140g of CO2 per kilometer by 2008 . The first objective is to minimise emission components such as hydrocarbon, CO2 and nitrogen oxides (NOx) subject to specific limits. At the same time, manufacturers are seeking to minimise fuel consumption and, accordingly, CO2 emissions. All of this should be achieved with a maximum standard of comfort and safety on the road. In the homologation of motor vehicles, Europe, Japan and the US apply different driving cycles to determine emissions and fuel consumption. However, it is the individual customer who ultimately decides on his/her particular style of motoring and up to 30% of a car’s fuel consumption depends on how it is driven and the style of motoring that is preferred by the driver. Clearly, the development engineer is unable to influence these external parameters – all that he/she can do is change the basic functions and control factors in the car and its drivetrain. The amount of energy required for driving a vehicle also drops with decreasing driving resistance provided by, for example, a reduction in roll and air resistance. To make more efficient use of the energy in fuel, the actual process of using energy must reach a higher standard of efficiency. Despite modern engine technology, the process of on-going development has not yet come to an end. Looking at the overall concept of a vehicle, the development engineer must therefore optimize the efficiency chain formed by all of the car’s individual components. For example, a car with a state-of-the-art spark-ignition engine uses only about 20% of the energy consumed to actually generate driving power and mobility in the EU test cycle. This alone demonstrates the remaining potential 2. VALVETRONIC
2.1. Evolution of Valvetronic
The losses that are capable of being influenced are composed primarily of the following: • a combustion process not yet ideal;
• the charge cycle;
• friction; and
• thermal losses through the walls.
Optimisation in these areas in driving cycles with low loads and engine speeds provides the greatest improvements in fuel economy. Quite generally, steps taken to reduce the throttle effect have a greater potential for saving fuel than the reduction of friction in the drivetrain (see Figure 2.1). Precisely with this in mind, BMW has eveloped a fully variable valve drive referred to as Valvetronic, a system offering improvement in fuel consumption comparable in virtually all driving cycles to the latest spark-ignition engines with direct fuel injection (DFI) and leanburn operation.
A number of other important items were also included in the list of objectives: • achieving dynamic performance, fuel economy, noise management and quality typical of BMW; • having a flexible concept capable of fulfilling future emissions standards; • creating a benchmark product in terms of its package, weight and cost of ownership; • taking a modular approach in order to develop specific engine variants; • ensuring a significant potential for on-going development; and • providing the foundation for other engine variants, i.e. communality with future...