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Aviation History
1942
1942 - 1744.PDF
20Z FLIGHT AUGUST 20TH, 1942 THE B . M .W. 8 0 1 A DELIVERY Pump barrels are an easy push fit in the housing and are frictionally secured about mid way of their length by a channel-section spring ring. Radial adjustment of the barrel to align the ports for the datum setting is by a two pin spanner engaging holes in the top face. A spring-loaded non-return delivery valve drawn down by a sleeve-type nut against the top face finally secures the barrel in its ad justed position. From the common gallery, fuel is led to an annular space around the head of the barrel whence it reaches the iuterior by a drilled intake port. Diametrically opposite, but at a slightly different level, is the spill port. Injection is terminated on the delivery stroke when the uncover ing of this port by the plunger scroll relieves the pressure in the pump chamber and allows the fuel to escape back to the annular space. As shown in the sectioned perspective sketch, drillings in the wall of the barrel* allow fuel from the annular space to reach a groove in the bore of the barrel to ensure lubrication. As a further precaution against air in the fuel lines, the annular spaces around the two uppermost pump bar rels, numbers 1 and 14, are connected by small diameter drilled passages to the outlet from the de-aerator in order to bleed fuel and any entrained air continuously from the fuel gallery. Pump Control The pump plunger has a dual scroll to control the duration of injection. It will be seen that any variation of the quantity of fuel delivered affects both the commencement and the termina tion of the injection period, but leaves the timing, of the point of maximum delivery substantially constant. When, for example, the delivery' is increased, injection commences earlier and finishes later. Control of this function is effected in the usual manner with a slotted sleeve floating on the pump barrel and engaging the cross head on the stem oi the plunger. For simul taneous operation of the control, each sleeve is formed with a pinion and interconnected by a circular rack which floats in a recess in the main body of the unit and is retained by the overlapping edge's of the plunger spring seating washers. These seating washers also determine the longitud inal clearance of the sleeves against a washer placed over the channel- section spring ring positioning the pump barrels. Backlash is taken up by a torsion spring mounted on the outer diameter of each sleeve, with one end anchored in the body and the other in the pinion. The control spindle, servo operated One of the fourteen individual elements of the fuel injection pump unit. The plunger has a dual " scroll " and is furnished with a self-aligning pad at foot abutting the tappet. from the automatic control unit, carries a pinion in engagement with the sleeve pinion of No. 4 cylinder. The width of this control pinion is reduced over a sector of its diameter to accommodate a pin mounted in the body. This pin defines the permissible rotative movement of the pinion, and in turn of the control sleeves of all the pumps, and also prevents the torsional loading springs unwinding when the unit is detached from the engine and the control n.schanism is uncoupled. Actuation Gear The circular foot of the plunger carries a floating cup-shaped member which centres and retains the plunger spring. This cup also serves as a carrier for the. hardened steel self- aligning pad which is interposed between the end of the plunger and the head of the tappet. Tappets are furnished with a profiled roller run ning on a flanged bronze bush mounted on a steel pin. Pin, bush and roller are all assembled with running clear ances. The flange of the bronze bush, serving as a thrust member between, the face of the roller and the side of the tappet, is provided with radial oil grooves on each side. Registered and riveted to the flange of the splined drive shaft, the face-type actuation cam takes its bearing on a bronze bush pressed on the reduced end of the tap pet housing half of the body. The for ward face of the cam provides_one track for a full diameter ball-thrust race. The other track is, of course, registered on the mounting flange of the unit, which completes the body structure and carries an oil seal for the drive shaft. To avoid rotation of the tappet and consequent misalignment of the rollers in relation to the cam', each tappet is provided with a segmental extension, the ground edges of which loosely en gage a split ring positioned concentric ally around the cam and supported in the body casting. By way of drillings in the mounting flange and the body casting, oil from the engine lubrication system is delivered to the tappet en closure for lubricating the actuating gear. Injection Valve Also of new type is the open nozzle fuel injection valve, which is shown in section. The spray orifice in the end of the body is a parallel boring, and through this extends the reversed conical head of the stationary needle. Closely fit ting the bore of the body, the needle is positioned by a flange against a shoulder, and an in terposed washer is employed to adjust the critical height of the head relative to the sharp-edged spray orifice ^nd determine the characteristics of the spray cone. Incidentally, tb?e diameter of the conical head is 2.01 mm. From the axial boring of the needle three drillings lead to the base of the three-start thread on the end which promotes a whirling motion to the injected fuel. The open nozzle type fuel injection valve. It is positioned at an angle between the ports at the rear of the cylinder head. At the flange end the boring is screw- threaded for an extractor tool. The needle is held in position by the thimble-type housing of the ball non return valve, which is in turn secured by a screwed adaptor. In the adaptor is housed a small fuel filter. The plug forming the central element is screw- threaded 0.1 mm. deep and is a drive fit in the parallel bore of the adaptos*t Two diametrically - opposite longi tudinal slots from the upper end are alternated with a pair of similar slots from the lower end. The path of the fuel is down two slots, transversely around the screw threads and down the alternate slots to the ball valve. Injectors are mounted at an angle in the rear of the cylinder heads between the two valve ports, and the high-pressure fuel lines are all of con siderable length. To the extreme rear of the pump is strapped a float-and-pendulum type de-aerator. Fuel and air discharged from the pump feed into a pendulous casing swinging on a hollow shaft which serves as the air outlet. On the upper part of the pendulum a cork float slides on a ported sleeve. Whatever the attitude of the aircraft, flooding lifts the float to cut off the ports and prevents loss of fuel.
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