Two New Diesel Engines For The Toyota Avensis | Part Three (2005)

New Injection And Induction Technologies

Most current common rail systems use solenoid injectors, actuated by a magnetic field generated by an electric current. By contrast, the new 2.2 D-4D Clean Power engine uses piezoelectric technology, a first in its displacement class.

The principle behind this technology is the capacity of certain materials to deform when an electrical charge is applied and return to their original state when the current is removed. This concept is applied to the new engine, with each injector composed of a stack of piezoelectric ceramic elements. When an electric current is applied to the stack, the elements instantly expand, allowing the fuel from the common rail to be injected into the cylinder. This means more fuel can be injected in a shorter time than is possible with conventional injectors. This in turn leads to greater fuel atomisation and more precise injection timing.

There are many advantages to this system. For instance, the new piezoelectric injectors operate 10 times quicker than solenoids when producing an injection and can perform up to five injections per cycle, with a single pilot injection at hot idle and multiple injection at partial load. With piezoelectric technology, pilot injection can be optimised, substantially reducing combustion noise.

Toyota’s piezoelectric common rail system produces the highest injection pressure (1800 bar) and the highest number if injections per cycle of any system of its type. Toyota is the first manufacturer to bring this diesel technology to the mainstream car market, first in the Avensis and with other models to follow.

The 2.2 D-4D Clean Power engine uses an electrically activated Variable Nozzle Turbocharger (VNT). The vanes of the VNT are installed in turbine housing and change position according to the speed of the gas flow. Rather than being activated by a step motor, they are triggered directly by a direct-current electric motor. This lets the engine ECU perform more precise and progressive activation of the vanes, helping increase turbocharger efficiency. Vane activation can also take place at lower engine speeds, if necessary. Compared with the 2.0 D-4D engine, the turbine wheel intertia has been lowered by 30 per cent, by reducing the number of blades and their thickness. This contributes to much quicker response at low speeds.

World-Beating Emissions Control System

The new 2.2 D-4D Clean Power engine uses the revolutionary Toyota D-CAT system, which renders the high-performance engine the cleanest diesel power unit in the world in terms of combined nitrogen oxides (NOx) and particulate matter (PM) emissions.

D-CAT features a Diesel Particulate NOx Reduction (DPNR) four-way catalyst, the only system in the world which simultaneously reduces NOx and PM via the combination of a NOx-reduction catalyst and a particulate filter.

Effective operation of the DPNR is controlled by the engine management system varying the air-fuel ratio in the exhaust gases. To do this a fifth injector, the Exhaust Port Injector (EPI), injects fuel into the exhaust gas flow at a critical moment, creating the right stoichiometric conditions for the DPNR catalyst to reduce harmful emissions.

continues... | Part Four
Published 2 March 2005 Melanie Carter

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