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Issue: Jun 2004


Supplier Tech



Pressure Is On SI Injection

by Roberto Chellini

Siemens views future for direct injection systems for gasoline engines.

Through various companies that now are a part of Siemens VDO Automotive, based in Regensburg, Germany, Siemens has been involved in the production of fuel components for gasoline and diesel engines since 1971 when the Newport News, Va., facility began operation doing primarily diesel oriented work.







 
 The new DEKA VII injector generation comes in five variants.
A further boost to this activity in the U.S. took place in 1988 with the acquisition of Bendix Electronics. One year later, in Europe, the San Piero a Grado engineering and production center began operation a few miles from Pisa, Italy.

The Italian operation was initially comprised of specialists from Spica of Leghorn, a company owned by Alfa Romeo. It was spun off when Alfa Romeo was purchased by Fiat. Under Siemens the San Piero activities developed to the point where a new production unit was added in 1996 a few miles away in Fauglia, is also in the Pisa area.

The two groups are working in close cooperation, with the R&D concentrated in San Piero, and also some productionsuch as the Deka II injectors. Mass production, however, is based in Fauglia where the Deka VII injector is produced at a rate of 60,000 pieces per day (for 15,000 4- cylinder engines/day) giving to the company a close to 30 percent European market share. Production of the Deka VII began in November, 2003.

To serve the American market, the Deka VII injector went into production just this year at Newport News. By 2006, Siemens VDO Automotive hopes to increase worldwide manufacturing to 16 million injectors per year, more than half of which will be produced in Italy. The Deka VII injector for is used for multipoint port injection systems, which seem to be the state-of-the-art for todays automotive gasoline engines.







 
For the first time Siemens VDO offers piezo injection systems for gasoline engines. Siemens anticipates fuel consumption savings of up to 20 percent.
Thanks to its flexibility, the Deka VII can be located on an engine in the position desired by the engine designer. No need to build the engine around the injector.

This injector family is available with different overall lengths (long, standard and short) and several valve body tip lengths, standard, extended (10 mm) and extra-extended (15 mm). The configuration of the electrical connector is also tailored to the specific application. The design of this injector combines enhanced performance and reliability with best price. Such a combination was achieved by streamlining the manufacturing process.

The number of components has been reduced from 28 to 19 (a 30 percent savings) and assembly operations from 120 to 50 (a savings of 60 percent). The manufacturing process has been simplified by reducing the machined components by half, eliminating internal O-rings, increasing the use of laser welding and standardizing the coil sub-assembly regardless of injector length or electrical connector type.

The entire assembly process takes place in clean rooms to minimize dust contamination of metal-to-metal seals.

The Deka VII injector operates at a pressure of 3 to 5 bar (1 bar = 14.5 psi) and ensures an average droplet size of less than 70 microns. When combined with the right engine control unit (ECU) they are suited to meet the next generation of emission standards (Euro V). Siemens VDO reported that in fiscal year 2003 they had a market share of nearly 17 percent worldwide. With the introduction of the Deka VII, it expects to become the market leader by 2008 with over 25 percent market share worldwide forecast at 190 million injectors.

Multipoint port injection is in its infancy
 
The R&D department of Regensburg and the Pisa team are developing injectors with medium (20 bar) and high pressure (200 bar) fuel pumps as well as more advanced electronic control units (ECU) for the gasoline fuel systems. Back in 1999 Siemens VDO became the first European supplier of DI injectors for the homogeneous charged engines for the Renault Megane and Laguna. In 2001, PSA purchased DI injectors for the stratified operating engines of the C5 and 406. Then in 2003, DaimlerChrysler went to DI injectors on the Mercedes DC C-Class turbocharged stratified charge engine and Opel on the Signum homogeneous charged engine, both responding to Euro IV emission limits. Looking into the near future, Siemens says 2006 will see the first application of high pressure pumps and spray-guided stratified engines. In 2007, homogeneous charged naturally aspirated and turbo engines will follow.

American, European and Asian emission legislation are imposing reduction in NOx, CO, HC and particulate emissions. Primary automobile associations (ACEA, JAMA, KAMA) are also committed to reducing fuel consumption thus lowering the CO2 emissions from 170 g/km in 2003 to 140 g/km in 2008. According to Siemens VDO, the high pressure piezo direct fuel injection will provide engines with ratings of over 80 hp/liter fuel savings on the order of 20 percent compared to conventional fuel systems. At the same time, engine performance and torque characteristics will improve. That translates into more fun to drive.

The two main applications for future gasoline DI are for stratified combustion engines with spray guided combustion systems and homogeneous combustion engines in both the naturally aspirated and turbocharged versions. Solenoid direct injection (SDI) is used for homogeneous combustion engines while piezo direct injection (PDI) satisfies the needs of stratified combustion.

The piezo-based direct injection system is designed for the spray-guided combustion processes. The fuel is injected directly in front of the spark plug during various stratified operations. As was the case with diesel engines, piezo technology enabled the breakthrough for the PDI system in SI engines.







 
The key components of the injection system include the piezo injector, gasoline high-pressure pump and engine control unit.
A piezo actuator acting directly on the nozzle needle makes the injector highly dynamic. The nozzle needle completes its full stoke in only 0.2 milliseconds. At the same time, the maximum deviation between individual injected quantities of fuel is 2 percent, even with the very short injection pulses. Piezo injectors also allow a very late moment of injection in stratified charge operation without misfiring.

In particular, piezo injectors allow precisely- timed, precisely-dosed multiple injection in the light and medium load range to enable stable combustion with low cyclical fluctuations. Thanks to the 200 bar injection pressure the flame will not be in contact with the injector tip avoiding carbon formation. The engine management system can adapt the actual moment of fuel injection to the needs of the combustion process or exhaust aftertreatment. In stratified operation, the quality of the fuel feed is also enhanced by the piezo elements ability to partially and completely open and close the injector.

In order to fully exploit the characteristics of these injectors Siemens VDO has developed an axial piston pump with extremely efficient dose control. This pump, provided with a separate lubrication system, provides in 15 micron droplets, the amount of fuel precisely required by the engine with a minimum of power consumption.

A newly developed 32-bit processorbased (EMS 2) engine management system offers a common architecture for both SI and diesel engines.

All EMS 2 software is organized into modules that can be retrieved from a database as needed by the development project. In general, electronic components have dramatically grown in complexity over the last decade. The Siemens VDO development philosophy for the new EMS 2 was to keep it simple to increase reliability.

Sixty percent of the software is constituted by modules containing generic functions common to SI and diesel engines. Some 30 percent are generic functions customized according to the project configuration and only 10 percent specifically defined to the customer function. Such system architecture significantly reduces time to market, yet another primary concern for todays OEMs.

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