Unit Injector System (UIS)
The Unit Injector-System (UIS) is a system for diesel direct injection. This technology is also known as the pump-nozzle system. In 1994 Bosch supplied he world’s first UIS for commercial vehicles. 1998 saw the appearance of the UIS
for passenger cars. Its special feature is that it combines the injection pump and injection nozzle in one unit (Unit Injector).
With the UIS, a separate Unit Injector (UI) for each cylinder is installed directly in the cylinder head. The engine camshaft provides the mechanical build-up of pressure. Via tappets or rocker arms it activates a small piston inside the UI unit. The cam is shaped in such a way that the desired high fuel pressure is built up as quickly as possible in the so-called plunger chamber below the plunger. A fast-switching solenoid valve determines start and end of injection as well as the injected fuel quantity.
Fitting in the cylinder head obviates the need for the high-pressure lines required for traditional distributor injection pumps. The advantage: depending on the engine speed, the UIS can generate injection pressures of up to 2,200 bar in passenger cars. Diesel models with UIS were the first compression-ignition vehicles to achieve exhaust-gas values better than those prescribed by the EU5 regulations. Because of their high injection pressures, UI diesel engines also display an extremely good degree of efficiency and provide an extremely high torque with low fuel consumption even at low engine speeds.