Fuel Pump
The PSB model
fuel pump is similar to other distributor fuel system, in that a pump sends a measured
amount of fuel to each injector at a properly timed interval. The difference in the PSB
system is that the amount of fuel sent directly from the pump at high enough pressure
needed for injection. This eliminates the need for unit-type injectors and the associated
linkage and camshaft, making the system less cumbersome.
The purpose of
the fuel pump (fig. 5-31) is to deliver
measured quantities of fuel accurately under high pressure to the spray nozzle for
injection. The positive displacement fuel supply pump (fig. 5-32) is gear-driven by the pump camshaft
through an engine camshaft gear and provides fuel to the hydraulic head for injection and
cooling.
Figure 5-33 shows fuel intake at the hydraulic head.
Injection (fig. 5-34) begins when fuel
flows around the fuel plunger annulus (fig. 5-35) through the open distributing slot to
the injection nozzle. A continued upward movement of the fuel plunger causes the spill
passage to pass through the plunger sleeve (fig. 5-36). This reduces pressure, allowing the
fuel delivery valve to close, ending injection. This is accomplished through a single
plunger, multi-outlet hydraulic head assembly (fig. 5-31).
The
plunger is designed to operate at crankshaft speed on four-cycle engines. It is actuated
by a camshaft and tappet arrangement. The pump camshaft, which also includes the gearing
for fuel distribution, is supported on the governor end by a bushing-type bearing and by a
ball roller bearing on the driven end. An integral mechanical centrifugal governor (fig. 5-37),
that is driven directly from the pump camshaft without gearing, controls fuel delivery in
relation to engine speed. This pump has a smoke limit cam within the governor housing to
assist in controlling exhaust smoke of various fuels. The mechanical centrifugal advance
unit of this pump provides up to g-degrees advance timing and is driven clockwise at
crankshaft speed. |
Figure
5-31.—Metering and distributing fuel pump assembly-left sectional view.
Figure
5-32.—Fuel supply pump assembly—sectional view.
Figure 5-33.—Fuel intake flow diagram.
Figure
5-34.—Beginning of fuel delivery flow diagram.
Figure
5-35.—Fuel delivery flow diagram.
Figure
5-36.—End of fuel delivery flow diagram.
Figure
5-37.—Governor—sectional view. |
