During recent years there has been a continuing increase in the demands for higher braking performance of commercial vehicle engines.
Mercedes-Benz had introduced the engine brake with continuously open decompression valve (‘Konstantdrossel’) into series production in 1989 as an option (1).
A further increase of braking power was to be achieved while retaining the additional decompression valve in the cylinder head. For this, the decompression valve was no longer kept open during the whole working cycle (continuously open decompression valve), but only for a short period from just before compression TDC to about 90...120° crank angle after compression TDC (pulsed decompression valve).
The hydraulic actuating system which opens and closes the decompression valves was developed in cooperation with Mannesmann-Rexroth GmbH, Lohr, Germany.
The engine braking performance attainable with this system is shown in comparison to other known engine braking systems. The effects of the engine braking system on the downhill performance of commercial vehicles compared to other continuous braking systems are presented.