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Cummins tests Apex for '98
Page 30
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by Steve Stu/gess III Cummins is selecting operators in the United States to field test an allnew 15-litre engine for the US 1998 emissions deadline, Code-named Apex, the engine is a double overhead camshaft in-line six with four valves per cylinder and a common-rail fuel system controlled by electronics.
Development engines are said to be producing 600hp (448kW) with 2,0501bft (2,780Nm) of torque and a 181kg weight saving over the N14 which it may replace. Industry sources say the N14 14-litre is at the end of its development while the Apex is believed to have a potential output of 1,000hp (746kW).
One of the Apex engine's two overhead camshafts drives the valve train; the other controls the fuel system. The common-rail fuel system is similar to that on Cummins' QSK19 industrial diesel with two rails, both pressurised from a sidemounted pump driven off the back of the timing case. One rail feeds the bottom of the in-head injector with "combustion" fuel; rail pressure against an injector spring determines the quantity of fuel to be injected into the cylinder. The second rail feeds the top of the injector and inserts a column of fuel that varies with pressure to change the timing of the injection stroke.
Electronic controls on the output of the fuel pump control these rail pressures to inject a precisely-timed and measured dose of fuel into the cylinder.
According to Cummins. one of the system's major advantages is its simplicity—there are no electronics in the head to complicate servicing and the cost of the injectors is significantly reduced. The electronics are encapsulated on the side of the engine and in the back of the pump mounted on the timiing case.
Also, all injectors receive the same common-rail pressures, so combustion pressures are equalized throughout the engine. overhead camshafts are becoming more common because the injection pressures needed for efficient combustion to meet US 1998 emissions levels are so high that conventional overhead-valve designs demand excessively heavy pushrod assemblies. By opting for direct actuation of the injectors by an overhead camshaft Cummins is following a trend set by Caterpillar, Detroit Diesel and Volvo.
At least five OHC Apex engines are due to start US service trials by early sturuner.
It is believed that Apex engines are already on trial in Canada and Australia. Cummins is interested in partnerships with truck manufacturers, and is thought to be talking to Iveco about the use of the Apex for its premium tractors. Cummins denies that the Apex or any of its other engines is yet capable of developing such torque.
However, at the urging of the engine manufacturers, transmission and clutch suppliers in the US are preparing products to handle that much torque.
This indicates the next round of US emissions regulation, with the higher injection pressures, new platform designs and higher cylinder pressures, will promote a new phase in the power and torque race.