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Delphi Technologies’ new ultra-high-precision fuel injector, with a valve just 1.0mm in diameter, is now in pilot production in response to major orders from Europe and the US. The ground-breaking DFI 21 injector, for medium- and heavy-duty diesel applications, is produced using new manufacturing techniques that enable better than aerospace tolerances to be delivered in conjunction with automotive volumes and pricing.

Achieving robust quality levels with such high precision components, involving sub-micron clearances, required significant innovations in manufacturing technology, according to Delphi Technologies product engineering director James Kewley.

“Our product designers needed levels of accuacy and consistency that could not be achieved using existing techniques,” he explains. “Our challenge was to work with our manufacturing specialists to deliver not just a radically-miniaturised technology with world-leading performance, but also a robust, completely consistent process that allows it to be manufactured with automotive industry pricing.”

The DFI 21 injector is at the heart of Delphi’s new F3 common-rail system, which builds on the proven technology of the F2 Euro 6 system to provide a substantial improvement in emissions, fuel economy and refinement while maintaining exceptional reliability. It was announced as a development concept in 2016 and, following business wins in Europe and the US, will enter volume production in 2021.

The ultra-light weight of the new 1.0mm valve helps the DFI 21 injector deliver up to nine injection events per cycle compared with just two or three for a typical Euro VI system, providing substantially greater opportunities to profile the entire combustion event. The improved control means peak temperatures, and hence NOx, can be reduced; allows multiple pilot injection, which enhances refinement by slowing the rate of pressure rise; and enables multiple post-injection events, reducing soot formation.

“Reducing engine-out emissions gives engine designers much greater flexibility in their aftertreatment strategy, with some significant potential cost savings for the vehicle manufacturer and the vehicle operator,” adds Kewley. “For example, DFI 21 could allow simplification of exhaust aftertreatment and a reduction in SCR fluid consumption, which can be of significant value to long distance truck fleets.”
Closed loop control with no additional wiring
Closed-loop control of combustion is long established but Delphi’s F3 system adds closed-loop compensation for any minute variation between the characteristics of individual injectors. This enables the use of more and smaller injection events because the closed-loop system ensures they will remain accurate throughout the engine’s design life of typically 1.6 million km (1.0 million miles).

The unique performance signature of each individual DFI 21 injector is coded onto a chip within the injector which communicates with the ECU, enabling it to adjust (trim) each pulse. Any change in characteristics over time is compensated, in real time, avoiding the compromises in injector calibration previously required to accommodate drift during the injectors’ considerable service life. If an injector is replaced, the new one is automatically interrogated by the ECU which adjusts to suit.

Kewley says that one of the major benefits of the Delphi Technologies approach to closed loop control is that their system requires no additional wiring. “This will significantly reduce the system cost and the manufacturing and packaging penalties usually associated with the introduction of closed loop sensing,” he explains. “It’s a great example of our ‘clever not complex’ design philosophy.

Applications extended to medium duty diesels
F3 is the first Delphi common-rail system family to cover both heavy duty and medium duty engines, using a range of proven, modular sub-systems that allow applications from 0.7 litres per cylinder up to 3.0 litres per cylinder and beyond. It is compatible with existing packaging dimensions to allow cost-effective integration with existing engine designs.

As with the Delphi F2 systems for Euro 6, three common-rail architectures are available: traditional common-rail with a remote pump, EUI-style with a cam-driven pump in selected injectors, and EUP-style with separate pumps driven by a cam in the engine block. Injector fitment dimensions are also unchanged, allowing integration with engines originally designed for EUI or EUP without costly changes to major engine components.

Manufacturing innovation

Advanced grinding processes using cubic boron nitride (CBN) were necessary to achieve the required quality and throughput, but these had to be developed beyond anything that had previous been achieved. New automation technologies were applied to handle the tiny parts safely and repeatedly and special surface finishing techniques were applied to eliminate burrs at the sub-micron scale.

Delphi Technologies is currently manufacturing beta-level samples of the DFI 21 in batches of several hundred using production-representative processes that are readily scalable. “One of the proven strengths of our team is that we have very robust Start Of Production (SOP) processes, leading to efficient product introductions with consistently high quality from delivery one,” concludes Kewley. “DFI 21 pushes high-precision, high volume manufacturing technology to the limit. Our goal is to make this remarkable achievement seem simple.”

Delphi Technologies says it can provide the entire engine management system including control electronics, software, sensors, smart remote actuator for the wastegate, SCR dosing control, variable cam timing, electric lift pump and compact, high-efficiency power electronics for electrification.