The unit injector and unit pump fuel-injec-tion systems achieve the highest injecfuel-injec-tion pressures of all diesel fuel-injection systems currently available. They are capable of high-precision fuel injection that is infinitely variable in response to engine operating sta-tus. Diesel engines equipped with these sys-tems produce low emission levels, are eco-nomical and quiet to run, and offer high performance and torque characteristics.
Areas of application Unit injector system (UIS)
The unit injector system (UIS) went into volume production for commercial vehicles in 1994 and for cars in 1998. It is a fuel-in-jection system with timer-controlled discrete fuel-injection pumps for diesel engines with direct injection (DI). This system offers a significantly greater degree of adaptability to individual engine designs than conventional port-controlled systems. It can be used on a wide range of modern diesel engines for cars and commercial vehicles extending to
cars and light commercials with engines ranging from three-cylinder 1.2 l units producing 45 kW (61 bhp) of power and 195 Nm of torque to 10-cylinder, 5 l engines with power outputs of 230 kW (bhp) and torque levels of 750 Nm.
heavy-duty trucks developing up to 80 kW/cylinder.
As it requires no high-pressure fuel lines, the unit injector system has excellent hydraulic characteristics. That is the reason why this system is capable of producing the highest injection pressures (up to 2,050 bar). The unit injector system for cars also offers the option of pre-injection.
Unit pump system (UPS)
The unit pump system (UPS) is also referred to by the type designation PF..MV for large-scale engines.
Like the unit injector system, the unit pump system is a fuel-injection system with timer-controlled discrete fuel-injection pumps for direct injection (DI) diesel engines. There are three versions:
The UPS12 for commercial-vehicle en-gines with up to 8 cylinders and power outputs of up to 35 kW/cylinder
The UPS20 for heavy commercial-vehicle engines with up to 8 cylinders and power outputs of up to 80 kW/cylinder
UPS for engines in construction and agri-cultural machinery, railway locomotives and ships with power outputs of up to 500 kW/cylinder and up to 20 cylinders.
Design
System structure
The unit injector and unit pump systems are made up of four subsystems (Figure 1):
The fuel supply system (low-pressure sys-tem) provides suitably filtered fuel at the correct pressure.
The high-pressure system generates the necessary injection pressure and injects the fuel into the combustion chamber.
The EDC electronic control system consist-ing of the sensors, control unit and actua-tors performs all diesel engine manage-ment and control functions as well as providing all electrical and electronic interfaces.
The air-intake and exhaust-gas-systems handle the supply of air for combustion, exhaust-gas recirculation and exhaust-gas treatment.
The modular design of the individual sub-systems allows the entire fuel-injection sys-tem to be easily adapted to individual engine designs.
84 Overview of discrete cylinder systems Unit injector system (UIS) and unit pump system (UPS)
Differences
The essential difference between the unit injector system and the unit pump system lies in the way in which high pressure is generated (Figure 2).
In the unit injector system, the high-pres-sure pump and the nozzle form a single unit – the “unit injector”. There is a unit injector fitted in each cylinder of the engine. As there are no high-pressure fuel lines, extremely high injection pressures can be generated
and precisely controlled injection patterns can be produced.
With the unit pump system, the high pres-sure pump – the “unit pump” – and the noz-zle-and-holder assembly are separate units that are connected by a short length of high-pressure pipe. This arrangement has advan-tages in terms of use of space, pump-drive system, and servicing and maintenance.
Overview of discrete cylinder systems Unit injector system (UIS) and unit pump system (UPS) 85
Fig. 2
a Unit injector system for cars
b Unit injector system for commercial vehicles c Unit pump system
for commercial vehicles
1 Rocker arm 2 Camshaft 3 High-pressure
solenoid valve 4 Unit injector 5 Engine combustion
chamber 6 Nozzle-and-holder
assembly 7 Short high-pressure
line 8 Unit pump Signals
Diesel fuel
Engine
Electronic Diesel Control EDC: engine management, sensors, interfaces
Fuel supply
(low-pressure system) High-pressure system Air intake and exhaust-gas systems Structure of unit injector and unit pump systems
1
æ
NMK1724-1Ea
1
b c
2 3 4
5
6 7
3 5
2 8 1
2 3 4
5 High-pressure generation in unit injector and unit pump systems
2
æ
UMK1874YMethod of operation
UIS and UPS are both diesel fuel-injection systems that use timer-controlled integral solenoid valves. The point at which the sole-noid valve is actuated – and consequently at which the valve closes – determines the start of delivery. The length of time the valve re-mains closed is a measure of the injected-fuel quantity. The valve actuation point and closed period are determined by the elec-tronic control unit on the basis of the pro-grammed engine data maps. The calculation process also takes account of the current en-gine operating status and the ambient condi-tions. The input data includes the following:
accelerator pedal position
crankshaft angle of rotation
camshaft speed
charge-air pressure
temperature of intake air, engine coolant and fuel
vehicle road speed, etc.
These parameters are recorded by sensors and processed by the control unit. With this information, the control unit is able to con-trol the vehicle, and in particular the opera-tion of the engine, in such a way as to ensure optimum efficiency.
Generation of high pressure
The high-pressure pumps are driven directly by one of the engine’s camshafts or by rocker arms running off the camshaft. While the solenoid valve is closed, the piston in the high-pressure pump generates pressure and the nozzle opens. When the solenoid valve opens, the pressure is dissipated and the nozzle closes again.
Control Basic functions
The basic functions involve the precise con-trol of injection timing, quantity and pres-sure. In this way, they ensure that the diesel engine has low-emission, low-consumption and smooth-running characteristics.
Additional functions
Additional control functions perform the tasks of reducing exhaust-gas emissions and fuel consumption or providing added safety and convenience. Some examples are:
Exhaust-gas recirculation
Charge-air pressure control
Cruise control
Electronic immobilizer
A diagnosis interface enables analysis of stored system data when the vehicle is ser-viced.
Control unit configuration
The Type MSG engine control unit is fitted inside the engine compartment (partially engine-mounted). For some commercial-vehicle applications, the heat given off by the electronic components has to be dissipated through an integral heat sink to the fuel (control unit cooler). In addition to the in-put circuitry and the microcontroller, the control unit also incorporates all output stages for controlling the solenoid valves.
Master-and-slave configuration
Present-day control units contain six output stages for the injectors. For engines with more than six cylinders, two engine control units are used. They are linked via a dedi-cated high-speed CAN interface in a master-and-slave configuration. As a result, there is also a higher microcontroller processing ca-pacity available. Some functions are perma-nently allocated to a specific control unit (e.g. volume balancing). Other functions can be dynamically allocated to one or other of the control units as situations demand (e.g.
recording of sensor signals).
86 Overview of discrete cylinder systems Unit injector system (UIS) and unit pump system (UPS)
Air-intake and exhaust-gas systems Exhaust-gas recirculation for cars Exhaust-gas recirculation is an effective method of reducing NOXcomponents in the exhaust gas. It involves the use of a valve which returns some of the exhaust gas to the intake manifold. If the recirculated exhaust gas is also cooled, further advantages can be gained. This method has been the state of the art for diesel cars for a number of years. The exhaust gas is recirculated at low engine loads and speeds.
Exhaust-gas recirculation for commercial vehicles
The vast majority of modern diesel engines are fitted with exhaust-gas turbochargers.
Such engines do not generally have a nega-tive pressure differential between the ex-haust manifold upstream of the turbine and the inlet manifold downstream of the com-pressor at high engine loads.
Since exhaust-gas recircula-tion and cooling cannot be dispensed with even at the higher end of the load curve on commercial-vehicle en-gines, additional features such as turbochargers with variable turbine geometry (VTG), wastegates or flutter valves are necessary.
Exhaust-gas treatment
In order to be able to comply with stricter emission-control legislation, exhaust-gas treatment will become increasingly important for diesel engines in the future despite ad-vances in internal engine design.
This is particularly true for larger cars and commercial vehicles. There are many sys-tems currently in the process of develop-ment. Which of them will eventually be-come established remains an unanswered question. The possibilities include:
Diesel-oxidation catalytic converters
Various particulate filters (PF)
NOXaccumulator-type catalytic converters
SCR (selective catalytic reduction) cat-alytic converters.
In combination systems (also called four-way systems), several individual systems are combined. They can then reduce not only NOXbut also HC, CO and particulate
emis-sions. Such systems demand very powerful engine management systems.
The most important emission control systems are dealt with in a separate chapter.
Overview of discrete cylinder systems Unit injector system (UIS) and unit pump system (UPS) 87
Fig. 3 1 Nozzle 2 High-pressure
solenoid valve 3 Ball pin for driving
pump plunger 1
2
3 Example of a unit injector for cars
3