Volkswagen to introduce new range of diesels using pump-injection

Citation

(1999), "Volkswagen to introduce new range of diesels using pump-injection", Industrial Lubrication and Tribology, Vol. 51 No. 1. https://doi.org/10.1108/ilt.1999.01851aab.007

Volkswagen to introduce new range of diesels using pump-injection

Volkswagen to introduce new range of diesels using pump-injection

Keywords Diesel fuel, Volkswagen

Fuel lubricity problems associated with low-sulphur diesel fuels have been well publicised, but it remains to be seen whether the drive towards the adoption of higher and higher injection pressures will in time introduce further fuel lubricity problems in such engines. Although the introduction of high-pressure "common rail" injection systems has resulted in significant gains in terms of combustion control, Volkswagen are now developing a new pump injection system in conjunction with Bosch which will be fully introduced in some three years' time. This system will operate at pressures of 2,050 bar as opposed to the limit of 1,350 bar achieved with common rail systems, and meets Euro 3 emission quality levels as well as providing even higher specific power output.

In the new system, the pump-injectors are integrated into the cylinder head along with the valve gear and are driven by the camshaft. After the solenoid valve is fed with current and closes, the build-up of pressure begins during the downward movement of the pump plunger. When the nozzle operating pressure is reached, the injector needle rises and pre-injection commences. At this point, the injector needle lift is limited by a hydraulic stop on the needle damping, and the reservoir valve then opens. The pressure then falls momentarily and the injection needle closes again. Following this point, the injector spring is further compressed and when the now-increased opening pressure is reached, the main injection begins. Injection is ended by switching off the current to the solenoid valve.

This system avoids the difficulties with leakages and excessive power consumption experienced when endeavouring to achieve higher pressures from common rail and other systems.

Volkswagen claim that the mechanical-hydraulic retraction system offers several advantages over electrical control systems in that not only is it highly accurate, but it also uses cheaper and more robust injectors.