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NAVISTAR RAISES THE PRESSURE

4th November 1993
Page 12
Page 12, 4th November 1993 — NAVISTAR RAISES THE PRESSURE
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by Steve Sturgess • Navistar has launched a 7.3-litre vee-eight diesel which could be sold in Europe by Perkins.

The T444Eis designed to meet 1994 US emissions regulations without exhaust filters or catalysts. It features hydraulically activated electronic unit injectors, using a novel system developed by Caterpillar. The heart of this is a three-loop, lubricating-oil and fuel pressure system.

Lubricating oil is raised to lube system pressure, then the supply is split. Part goes through a conventional kin circuit to the bearings; the rest goes to a high pressure swash-plate pump. From here it is fed at pressures between 35 and 207bar to a large gallery in each cylinder head that acts as a pressure accumulator.

Fuel is raised by a diaphragm pump, filtered and pumped to rail pressure by yet another gear pump.

The fuel is fed at rail pressure to the heads and, via its own in-head galleries, to the electronic unit injectors where electronically controlled solenoids allow the high-pressure lube oil to bear on the tops of the pressure pistons.

These can increase lube oil pressure up to sevenfold, giving injection pressures up to 1,450 bar.

Injection timing and duration are controlled electronically. Unlike systems that control the fuel flow directly, the Navistar/Caterpillar system controls injection by modulation of the pressure on the amplifier piston.

This also means the speed of injection can be altered, giving additional control of combustion characteristics at a wide range of engine speed and load conditions.

Perkins has a marketing agreement with Navistar so the fuel/hydraulic system could find its way on to Perkins Euro-3 engines by the late 1990s.

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Organisations: US Federal Reserve
People: Steve Sturgess

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