Modern commercial vehicles are cleaner and more economical than ever before, and Bosch says its diesel direct-injection systems have contributed significantly to this progress. The high-injection pressures and the accurately
measured quantities of injected fuel they provide permit highly efficient combustion with low levels of harmful emissions and consumption.
In contrast to other injection systems, the common-rail system separates the pressure-generation and injection processes. Each cylinder is supplied with fuel under high pressure from a common feed line (hence "common-rail"). This permits the moment of injection to be controlled very accurately, and the quantity of fuel to be metered very precisely. It is also possible for pre-injection and post-injection to be provided flexibly, and one of the benefits of this is smooth, and therefore comfortable, engine running. The Bosch common-rail system is therefore being fitted to more and more modern commercial vehicles for use both on and off the highway.
The greater the injection pressure, the more finely the injection system atomizes the fuel, thus permitting even more efficient combustion. Bosch launched the third-generation common-rail system, which provides 1,800 bar of injection pressure, for lightweight and medium-sized commercial vehicles in 2005. For heavy commercial vehicles, the common-rail system supplies 1,600 bar injection pressure, and 1,800 bar is already planned for next year.
Bosch introduced the common-rail injection system for cars in 1997, a world first. The first Bosch common-rail generation for commercial vehicles went into series production in 1999, employing 1,400 bar injection pressure. The second generation, with 1,600-bar pressure, followed in 2001.
With exhaust limits becoming increasingly strict in all parts of the world, Bosch is continuously developing its injection systems even further. A further development of the third common-rail generation, for instance, employing up to 2,200-bar injection pressure, is planned for light commercial vehicles in 2009, and for heavy commercial vehicles one year later.
In addition, Bosch is developing a pressure-converter common-rail system, with 2,100 bar injection pressure, for heavy commercial vehicles, which will go into series production at the end of 2006. The special feature of this system is that it uses two solenoid valves for each injector, which allows pre-injection, main injection, and post-injection to be matched accurately to the requirements of every engine operating state, in order to reduce both harmful emissions and consumption even further.
The unit-injector system (UIS) integrates the injection pump and nozzle for each cylinder into a single assembly (the "unit injector"). The pump pistons are driven by the engine's camshaft, and generate an injection pressure of up to 2,200 bar for each cylinder separately. In the unit-pump system (UPS), a high-pressure pump with an integrated solenoid valve, a short injection line, and an injector is assigned to each individual cylinder. The camshaft is again used to drive the fuel pumps. Bosch has also achieved injection pressures of up to 2,200 bar with this system.
Bosch has developed the new EDC 17 control unit as a universal "brain" for all diesel-injection systems. Among other things, the Electronic Diesel Control (EDC) controls all the parameters that are significant for economical, low-emission combustion. Because the computing power and functional scope of the control unit can be adapted to a variety of requirements, it can be used very flexibly for all segments in any of the world's markets.
Bosch has pioneered diesel-injection technology from the very beginning: in 1927 the company was the first in the world to begin series production of diesel-injection pumps and nozzles for trucks, and thus paved the way for fast-running diesels in commercial vehicles, buses, and later even in automobiles. Today, Bosch offers injection systems for a wide spectrum of on-highway and off-highway engines around the world – from small, single-cylinder units for mobile construction machines to large marine diesel engines – and has achieved a market coverage that is almost unrivaled.