Sulzer RT-flex. Supply unit
Fuel and servo oil are supplied to the common-rail system from the supply unit which is driven through gearing from the engine crankshaft.
In the first few RT-flex engines, the supply unit is on the exhaust side of the engine so that it could be lower down without interfering with access to the crankcase. However, for all subsequent engines, the location of the supply unit has been standardised on the front of the engine (on the same side as the rail unit) and at about mid height. This keeps the engine “footprint” small so that the engines can be located far aft in ships with fine afterbodies.
The supply unit is naturally at the location of the geardrive: at the driving end for five- to seven-cylinder engines, and at the mid gear drive for greater cylinder numbers.
The supply unit has a rigid housing of GGG-grade nodular cast iron. The fuel supply pumps are arranged on one side of the drive gear and the hydraulic servo-oil pumps are on the other side. This pump arrangement allows a very short, compact supply unit with reasonable service access. The numbers, size and arrangement of pumps are adapted to the engine type and the number of engine cylinders.
For RT-flex Sizes I and IV, the supply unit is equipped with between four and eight fuel supply pumps arranged in Vee-form. The Size 0 supply unit, however, has just two or three supply pumps in-line.
Two sizes of fuel pumps are employed for all RT-flex engines, both based on the well-proven injection pumps used in Sulzer Z-type medium-speed four-stroke engines though with some adaptations to suit their function as supply pumps and to raise their volumetric efficiency up to a very high degree. For Sizes 0 and I, the fuel pump elements are based on the injection pumps of Sulzer ZA40S engines, while the Sixe IV pumps based on the injection pumps of the Sulzer ZA50S engine type.
Fig 3. Supply unit for a Sulzer 12RT-flex96C engine with the fuel pumps in a Vee-form arrangement on the left and servo oil pumps on the right-hand face of the central gear drive. The fuel pumps all deliver into the collector seen above the fuel pumps
The fuel supply pumps are driven through a camshaft with three-lobe cams. This camshaft cannot be compared with the traditional engine camshaft. It is very short and of much smaller diameter, and is quite differently loaded. There is no sudden, jerk action as in fuel injection pumps but rather the pump plungers have a stedy reciprocating motion. With tri-lobe cams and the speed-increasing gear drive, each fuel supply pump makes several strokes during each crankshaft revolution. The result is a compact supply unit.
Two designs of camshaft are employed. For Size I it is manufactured in one piece. For Size IV, the camshaft is assembled from a straight shaft on to which the tri-lobe cams are hydraulically press fitted. This latter form of construction has been used for decades in Sulzer Z-type engines. It is extremely service friendly and minimises maintenance cost. The camshaft bearings have an aluminium running layer.
The fuel delivery volume and rail pressure are regulated according to engine requirements through suction control with helix-controlled filling volume regulation of the fuel supply pumps. Suction control was selected for its power consumption as no excess fuel is pressurised.
The roller guide pistons contain the floating-bush bearings for the rollers as they are used on all Sulzer RTA- and Z-type engines. Owing to the moderate accelerations given by the tri-lobe cam shape, the specific loads of roller bearings and pins as well as the Herzian pressure between cam and roller are less than for the original pumps in ZA40S and ZA50S engines.
For every individual fuel pump element of the supply unit, the roller can be lifted off the cam, blocked and manually taken out of service in case of difficulties.
The fuel pumps deliver the pressurised fuel to an adjacent collector from which two independent, double-walled delivery pipe is dimensioned for full fuel flow. The collector is equipped with a safety relief valve set to 1250 bar.
An equivalent arrangement of a collector and duplicated independent, double-walled delivery pipes is employed for the servo oil supply.