Search Results

The main targets concerning development activities for diesel engines are defined by future exhaust gas legislations (EURO IV, V). Due to the conflict between particulate and NOx emissions, both components of the exhaust gas are limited: The combination of direct injection of diesel into the combustion bowl and limited adoption of air swirl causes locally fuel-rich regions which lead to soot and burn at high peak temperatures in stoichometric regions. Simultaneously, the transient drive-off torque and the maximum power output are limited due to the time which is necessary for the mixture formation process. By means of intensified flow energy and a demand-oriented regulation of the air mass flow using an impulse charging device for diesel engines, locally fuel rich regions inside the combustion bowl can be minimized which finally influences the NOx-Soot Trade-Off by inside-engine measures and improves low-end torque and power characteristics.

A variable valve actuation mechanism suitable to activate and deactivate the intake and exhaust valves of reciprocating engines will be presented within this paper. This system called the “CVD System” (Cylinder and Valve Deactivation) allows a reliable activation and deactivation of the valves of conventional cam-controlled valve trains within one engine cycle, independent of the oil feeding system. The system can be used for both the deactivation of single valves of multi-valve engines - e.g. to increase the in-cylinder charge motion - or the deactivation of complete cylinders of multi-cylinder engines. Different to the well known hydraulic valve shifting or switching devices the CVD system represents an electromechanical device with an unlocked (deactivated) position being mechanically offered to a solenoid operated coupling lever once per cam revolution. If valve deactivation is required the solenoid is switched on to cut the force line between cam and valve.

This paper describes the principles, effects and the potentials of impulse charging systems applied to SI and Diesel engines. In general, impulse charging is realized by closing the inlet port upstream of the inlet valve during the intake stroke with an additional switching device. The piston, moving towards bottom dead center, generates a vacuum inside the combustion chamber and inlet port. By opening the switching device abruptly, the sub-atmospheric pressure level induces an enhanced volumetric efficiency due to the significantly increased gas dynamic effects in the intake manifold. One major advantage of impulse charging in comparison to the well known supercharging techniques lies in the dynamic behavior. The charging effect can be realized within one engine cycle. Furthermore, impulse charging provides high low-end torque, a nearly constant torque over a wide engine speed range with charging rates from 20% to 30%.

The VVH System - Variabler (variable) Ventil (valve) Hub (lift) - is a variable valve timing system suitable for an unthrottled load control of spark ignition engines. This mechanical valve train system allows a continuously variable intake valve lift from zero to maximum with a corresponding variable intake closing. Based on a first introduction of the VVH system during the SAE '98 Annual Congress this paper gives a more detailed description of this technology and reports about the progress of development. In a first part of this paper a systematic design study showing application variants of the principle design proves that the VVH technology can be designed for all kinds of combustion engines with poppet valves including two and multi-valve cylinder heads, engines with over-head cam drive or pushrod valve train, inline or V-engines.