Unit Injector System (UIS) : Installation and Drive
Unit Injector System (UIS) : Installation and Drive
Unit Injector System (UIS) : Installation and Drive
In the unit injector system (UIS), the fuel- using a clamping block at an angle of ap-
injection pump, high-pressure solenoid prox. 20° in the engine's cylinder head. In a
valve and injection nozzle form a single 4-valve engine, the smaller injector (UI-2)
unit. The compact construction – with is used on account of the smaller amount of
very short high-pressure lines integrated space available; this injector is secured ver-
in the component between pump and tically in the cylinder head with anti-fatigue
nozzle – makes it easier to deliver higher bolts.
injection pressures compared with other
fuel-injection systems because the com- The engine camshaft (2) has an actuating
1) The compression pression volume 1) and thus the compres- cam for each unit injector, the particular
volume is the fuel sion losses are lower. The peak pressure in cam lift being transferred to the pump
volume which is
the UIS currently varies, depending on the plunger (6) by a rocker arm (1). The injec-
compressed
type of pump, between 1,800 and 2,200 bar. tion curve is influenced by the shape of the
actuating cams. These are shaped so that
the pump plunger moves more slowly when
Installation and drive fuel is taken in (upward movement) than
during injection (downward movement) in
Each cylinder has its own unit injector (UI), order, on the one hand, to prevent air from
which is installed directly in the cylinder being accidentally drawn in and, on the
head (Fig. 1). For passenger cars, there are other hand, to achieve a high delivery rate.
two types of unit injector (UI-1, UI-2), which – Torsional vibration is induced in the cam-
while having an identical function – differ in shaft by the forces applied to it during
size. In a 2-valve engine, the UI‑1 is secured operation, and adversely affects injection
1 6
Fig. 1
1 Rocker arm
2 Engine camshaft
5
3 Plug
« UMK1736-2Y
4 Unit injector 7
5 Injection nozzle
6 Pump plunger
7 Engine combustion
chamber
1 Fig. 2
11 Return spring
9 12 Plug
2 13 High-pressure
chamber
3 10 (element chamber)
14 Solenoid coil
4
5 15 Solenoid-valve body
11 16 Solenoid-valve
needle
6 12
17 Injection nozzle
18 Rocker arm
19 Actuating cam
« UMK1743-2Y
10 Clamping element
13 11 Fuel return
7
14 12 Fuel inlet
13 Retaining nut
14 Gas-exchange valve