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Variable valve timing represents one of the key technologies in further development of automotive engines. Different valve lift profiles and variable valve timing in the engine operation map offer the flexibility to better meet the load specific engine requirements regarding the intake flow conditions, the exhaust gas control and the efficiency of load exchange, mixture preparation and combustion.

Variable valve timing is one of the key technologies in the further development of automotive engines. A variation of valve lift profiles and variable valve timing in the engine operation map offer the flexibility to better meet the load specific engine requirements regarding the intake flow conditions, the exhaust gas control and the efficiency of load exchange, mixture preparation and combustion. This paper describes solutions of variable valve lift systems for both a two or three-step switchable system as well as the actual design of the continuously variable valve lift system VVH. The system properties will be described and analyzed regarding their specific benefits in fuel economy, emission behavior and performance as well as regarding the systems trade-off. Optimization strategies regarding a two or three-step variable maximum valve lift are pointed out and will be compared to the continuously variable intake valve timing.

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%.

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.

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.

A continuously variable valve timing system called the “Meta VVH System” is presented. It allows the unthrottled load control of spark ignition engines. Two camshafts rotating at the same speed are acting on the intake valve(s) via a follower and a transmission element in such a way, that the output displacement is the sum of the effective displacements of the two cams. The first camshaft which operates as an opening cam is driven directly by the crankshaft. The second camshaft operating as the closing cam is driven by the opening cam via a four wheel gear drive. This gear drive allows a phasing between both camshafts in a range necessary to vary lift and duration of the valve(s) from zero to maximum. This system not only offers the flexibility and range required for an unthrottled load control but also shows benefits concerning its friction losses even in comparison to modern state of the art valve trains like the roller finger follower.

This paper reports the results of theoretical and experimental investigations in the field of variable intake - valve control of spark-ignition engines. Different degrees of freedom for a variable intake profile such as variable intake opening and closing events, variable valve lift, as well as the deactivation of one of the intake valves per cylinder of a multi-valve engine are considered and evaluated concerning their potential to reduce pumping losses, to support mixture formation, and to improve combustion. The investigations show that additional efforts are necessary to convert the potential of minimized pumping losses due to unthrottled SI-engine load control into reduced fuel consumption and good driveability. Increased gas velocities during intake for low engine speed and load and adjusted residual-gas fractions according to the different operating conditions prove to be very efficient parameters to improve engine performance under unthrottled conditions.