Unit Injector & Unit Pump Systems

Unit Injector & Unit Pump Systems

1.Introduction for Unit Pump System

The Unit Pump System is a high-pressure fuel-injection system specially designed for commercial vehicles.

As with the Unit Injector System, each engine cylinder has a single-cylinder pump with integrated solenoid valve. This is connected to a conventional nozzle-holder combination via a short high-pressure line. This construction allows fuel-injection pressures of up to 2,200 bar.

The high-pressure pump is driven directly by the engine camshaft. The pump’s high delivery rate ensures a continuous rise in pressure during the entire duration of the injection.

The injection valves meter the fuel with the help of high-speed solenoid valves. These are triggered by the electronic engine control unit. With variable injection start, variable injection duration, great latitude in adapting to the engine’s operating conditions as well as cylinder-specific correction capabilities, UPS contributes toward environmentally-friendly and fuel-saving engine operation.

The Unit Pump System is used for commercial-vehicle engines with performances of up to 80 kW per cylinder and up to eight cylinders. The electronic control unit can trigger a system comprising a maximum of eight cylinders. A second control unit allows the system to be extended to 16 cylinders.

Benefits

Low emissions
Favorable fuel consumption
Easy conversion from fuel-injection systems with in-line or distributor pumps (no need to redesign the cylinder head)
Simple and fast customer service as the pumps can be exchanged easily

2.Unit Injector & Unit Pump Systems

In unit injector (UI) and unit pump (UP) systems, each engine cylinder is served by a separate injection pumping element or injection pump in close proximity to the cylinder. Unit pump (UP) systems enable short high pressure fuel lines by locating the pump close to the injector. Combining the pumping element and the injector into one assembly as in unit injector (UI) systems, allows these lines to be eliminated altogether. The elimination—or length reduction—of high pressure fuel lines in the UI/UP injection systems results in two benefits:

Reduction of line dynamics problems: line dynamics difficulties in unit injectors/unit pump systems are less troublesome than in their pump-line-nozzle (P-L-N) counterparts. The possibility of wave superposition—which troubled the P-L-N systems by causing after-injections and contributing to injection delays—is greatly reduced. However, it should be mentioned that line dynamics problems generated within the narrow passages of unit injectors may still modulate the rate of injection [Challen 1999].

Higher injection pressure: the UI system has traditionally had the highest injection pressure capability among all types of injection system. In the early 2000s, UI systems had pressure capabilities of 200 MPa, compared to 160 MPa in common rail systems. Since then, UI/UP system peak injection pressures have risen to as high 250 MPa for some 2007 model year applications.

With regards to fuel pressure, it should be noted that common rail fuel injection system pressures have risen as well and in some systems have reached or exceeded the pressures available from UI/UP systems. While there is no technical reason keeping UI/UP pressures from rising even further, engine manufacturers are increasingly using common rail systems in applications traditionally dominated by UI/UP systems. For this reason, UI/UP systems will likely see little evolution beyond their current peak pressures of about 250 MPa.

Both the UI and UP systems are driven from the engine camshaft. In one common mechanical system design, fuel control was typically achieved by rotation of the pumping element (plunger) in the same way as is done in P-L-N systems. With the introduction of electronics to diesel engines, electronic unit injector (EUI) and electronic unit pump (EUP) systems were developed. These employ an electromagnetically operated spill valve for fuel control.