Hasil (
Bahasa Indonesia) 1:
[Salinan]Disalin!
Construction. The Stanadyne pump, shown in Figure 5-62 incorporates four pumpingplungers. The driveshaft engages the distributor rotor in the hydraulic head. The rotorholds the four pumping plungers. The plungers are actuated simultaneously towardeach other by an internal cam ring through rollers and shoes located in slots at the endof the rotor. The number of lobes normally equals the number of engine cylinders.Figure5-62 -TheStanadyne DB4injectionpumpuses fouropposedplungers.The transfer pump is also a positive displacement vane type. It is enclosed in the endcap, which also houses the fuel inlet strainer and transfer pump pressure regulator. Thedistributor rotor incorporates two charging ports and a single axial bore. One dischargeport serves all the outlet ports to the injection lines. The hydraulic head contains thebore in which the rotor revolves, the metering valve bore, the charging ports, and thehead discharge fittings. The high pressure injection lines to the nozzles are fastened tothese discharge fittings.Stanadyne pumps have their own mechanical governor. The centrifugal force of theweights in their retainer is transmitted through a sleeve to the governor arm and to themetering valve. The metering valve can be closed to shut off fuel by an independentlyoperated shut-off lever. The automatic speed advance is a hydraulic mechanism thatadvances or retards the beginning of fuel delivery. This can respond to speed alone orto a combination of speed and load changes.Components. The aluminum alloy pump housing of an opposed plunger distributorinjection pump contains the driveshaft, distributor rotor, transfer pump blades, pumpingNAVEDTRA 14050A 5-65plungers, internal cam ring,hydraulic head, end plate,adjusting plates, transfer pump,pressure regulator assembly,governor, automatic advance,and metering valve.Driveshaft. The driveshaftconnects to the engine drivegear and is supported by abushing or ball bearing. Itsupports the governor assemblyand drives the distributor rotorand transfer pump. The transferpump consists of four linearblades. It delivers fuel to themetering valve located in thehydraulic head at low pressure.It also provides a fuel inlet to thepump and contains a pressureregulating valve that controls thetransfer pump pressurethroughout the speed range.Hydraulic Head. The hydraulichead is machined with boresFigure5-63-Explodedviewofarotorassemblyshowingthecamrollersandshoes.and passages that allow fuel to flow from the transfer pump to the metering valve, fromthe metering valve to the charging ports, and from the discharging ports to thedischarging fittings. On the latest designs, hydraulic heads have been fitted withindividual delivery valves to maintain residual line pressure and eliminate secondaryinjection.Distributor Rotor. The distributor rotor is lapped fitted to the hydraulic head and thegovernor weight retainer assembly is fastened to its drive end. The plungers are fitted tothe rotor and are pushed inward by the rollers and shoes to pump the diesel fuel. Therollers fit into the shoes and contact the cam in a way similar to a cam follower, asshown in Figure 5-63. Adjusting plates are mounted on the rotor and limit the outwardtravel of the rollers and shoes to control the fuel delivery.Cam Ring and Metering Valve. A circular cam ring surrounds the rotor base and islocated over the shoes and rollers. The number of internal cam lobes equals thenumber of cylinders. The cam ring forces the plungers toward each other, which causesthe fuel to be pumped. It can also be rotated back and forth about the rotor to vary thestart of injection.The metering valve contained in the hydraulic head regulates the volume of fuelentering the rotor. A piston valve is used with hydraulic governors. This valve is springloadedand controls the fuel according to the valve's axial position. When a mechanicalgovernor is used, the valve is a rotary type, with a slot cut in the periphery. The valve isrotated by the governor arm to regulate fuel injection.Automatic Advance and Governor. An automatic advance device is located I thebottom of the pump. A hydraulic piston rotates the cam ring against the direction ofpump rotation via the cam advance stud. The cam advance stud threads into the camand connects it to the cam advance mechanism.NAVEDTRA 14050A 5-66The governor weight retainer may be permanently fixed, splined, or bolted to the rotordrive end. Because the fuel metering mechanism can be affected by vibrations andshocks, the retainer often uses a cushioning device to isolate engine vibration andpulsation from the driveshaft. One end of the governor control arm rests against thethrust sleeve, and the other end connects to the governor spring and to the meteringvalve via a linkage hook. The control lever is connected to the shut-off lever and thefulcrum lever is connected to the governor spring.Pump Operation and Fuel Flow. The operating principles of an opposed plunger pumpcan be understood more readily by following the fuel circuit during a complete pumpcycle. Figure 5-64 illustrates the fuel flow for a Stanadyne DB2 two-plunger distributorpump. The fuel flow for the DB4 four-plunger pump is the same with the exception of thecharging of two additional plungers. As shown in the diagram, the transfer pump pullsfuel from the fuel tank. The fuel passes through a water separator and secondary fuelfilter before reaching the transfer pump. Once through the transfer pump, some of thefuel is bypassed to the transfer pump's suction side through the pressure regulatorassembly.Figure5-64-FuelflowduringthepumpingcycleinaStanadyneDB2distributor injection pump.Fuel under pressure flows past the rotor retainers and into an annulus on the distributorpump rotor. Some fuel flows through a connecting passage in the head to the automaticadvance mechanism. The remaining fuel moves into the charging passage. This fuelflows around the annulus, through a connecting passage, and to the metering valve.NAVEDTRA 14050A 5-67The radial position of the metering valve regulates the fuel flow into the chargingannulus, which holds the charging ports.Pressure Regulating Valve Operation. The pressure regulating valve is located in theend plate and performs two important functions. When the injection pump is beingprimed, fuel is forced into the inlet connection through the mesh filter. Fuel enters theregulating sleeve located at the upper port, forcing the regulating piston downward andcompressing the priming spring. When the piston has moved down far enough touncover the lower port in the sleeve, the fuel flows directly into the hydraulic head. Thepump is now primed and ready for start-up.When the engine is running, the pump rotates and fuel is pulled into the end plate by thetransfer pump. It passes through the mesh filter and is forced into the hydraulic headand end plate. When the transfer pump builds pressure, it forces the piston upwardagainst the regulating spring (Figure 5-65, View A). When the correct pressure isreached, the piston uncovers the regulating port. This bypasses a small amount of fuelback to the inlet side of the transfer pump to maintain fuel pressure at the desired level,(Figure 5-65, View B).
Transfer pump pressure can be adjusted in one of two ways. On some pumps, the
spring guide is replaced with one of a different size. This changes the fuel pressure by
altering the amount the regulating spring can be compressed. Other models are
equipped with an adjustment device that can be set using a special tool when the pump
is running on a test bench.
Charging Cycle. As the rotor revolves, the two inlet passages align with the charging
ports in the annulus. Fuel under pressure from the transfer pump and controlled by the
metering valve flows into the pumping chamber, forcing the plungers apart.
The plungers move outward a distance proportional to the amount of fuel required for
injection on the following stroke. If a small quantity of fuel is admitted into the pumping
chamber, the plungers move out a short distance. Maximum fuel delivery is limited by a
leaf spring or springs that contact the edge of the roller shoes.
During the charging phase of injection, the angled inlet passages in the rotor are in
alignment with the ports in the charging annulus. The rotor discharge port is not in
alignment with a head outlet, as shown in Figure 5-66. The rollers are also off of the
cam ring lobes.
Figure 5-65 - Pressure regulating valve operation.
NAVEDTRA 14050A 5-68
Discharging Cycle. As the rotor
continues to revolve, as shown
in Figure 5-67, the inlet
passages move out of alignment
with the charging ports. The
rotor discharge port opens to
one of the head outlets. The
rollers then contact the cam
lobes, and injection begins.
Further rotation of the motor
moves the rollers up the ramps,
pushing the plungers inward.
During this stroke, the fuel
trapped between the plungers
flows through the rotor's axial
passage and discharge port to
the injection line. Delivery to the
injection line continues until the
rollers move past the innermost
point on the cam lobe and begin
to move outward. The pressure
in the axial passage is then
reduced, allowing the nozzle to
close and ending injection.
Delivery Valve Operation. On
some distributor pumps,
individual delivery valves
(sometimes called pressure
valves) are installed in the
hydraulic head outlets for each
cylinder. In other pump models,
such as Stanadyne's, a single
delivery valve mounted in a bore
in the center of the distributor
rotor serves all injection lines.
The delivery valve or valves
keep the lines full of fuel so that
a full charge of fuel can be
injected at the next cycle for that
cylinder.
In addition, the delivery valve
rapidly decreases injection line
pressure to lower than nozzle
closing pressure. This allows the
nozzle to snap shut quickly
without nozzle dripping or
dribbl
Sedang diterjemahkan, harap tunggu..