Continental presents a new generation of piezo injectors for common-rail diesel

Piezo technology makes diesel engines efficient, clean and quiet. And Continental now has the answer to the increasing environmental demands being imposed on the diesel engine. At the 29th Vienna International Engine Symposium, the Powertrain Division presented a new piezo injector with direct drive and closed-loop needle control, opening the way for engine developers to further reduce consumption and emissions. As Wendelin Klügl, Senior Vice President, Powertrain System & Technology points out, "when considering the overall cost of engine production, the new injector offers further potential savings by simplifying other emissions-related components such as sensors and control algorithms". He added: "even vehicles in higher weight categories will now meet the Euro 6 emissions standard without nitrogen oxide aftertreatment."

Piezo injectors have been installed as standard components in vehicles since the beginning of the millennium. Instead of an electromagnet, a piezo actuator, consisting of a stack of over 300 wafer-thin ceramic platelets, controls the nozzle needle in the injector. When a switching voltage is applied, the piezo actuator expands, opening the injection nozzle within milliseconds. These extremely rapid response times allow the fuel to be apportioned precisely and reproducibly between up to seven injections per combustion cycle. This permits optimized combustion of the fuel-air mixture, so that consumption is lowered, pollutant emissions are reduced and more effective regeneration of the particulate filter is achieved through selective temperature control.

Closed-loop needle control for stable combustion processes

While continuing to develop the current generation of injectors, Continental is relying on a new design which, from the engine manufacturer's perspective, offers numerous advantages for particularly demanding diesel applications. The direct drive allows the nozzle needle to be actuated even more rapidly and accurately without hydraulic transmission. In addition, for the first time, this can give flexibility to the injection rate pattern for individual injections, thus ideally complementing the already well-established multiple injection systems in today's common-rail diesel engines. With this design, the piezo actuator simultaneously acts as a sensor by reporting the precise position of the nozzle needle to the electronic control unit, producing the first self-contained fuel mass control system. The smallest instances of variations or drift in the course of a vehicle's life can be detected and automatically corrected within the system. It is also possible, with the new injector, to increase the injection pressure to over 2000 bar.

"Our new injector has enormous potential", says Dr. Andreas Pfeifer, head of System Design, Diesel Systems, adding that "our trials with an engine optimized to comply with Euro 6 are already achieving an almost 3 percent reduction in consumption. And we have been able to reduce particulate and nitrogen oxide emissions by some 35 percent." The direct drive injector is, therefore, the key technology which will allow engine manufacturers to meet the Euro 6 exhaust gas directive limits which will apply to passenger cars from 2014. The first series production application of the new technology will be in a light commercial vehicle in 2009.