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Port-Helix Metering Injection Pumps Chapter 22. DSL 131. OBJECTIVES. Identify the major components in a typical port-helix metering injection pump. Explain the principles of operation of an inline, port-helix metering injection pump.
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OBJECTIVES • Identify the major components in a typical port-helix metering injection pump. • Explain the principles of operation of an inline, port-helix metering injection pump. • Define the terms effective stroke, port closure, port opening, NOP, residual line pressure, and peak pressure. • Explain how the pump element components create injection pressures. • Define metering and the factors that control it. • Identify the differences between hydromechanical and electronically-controlled versions of port-helix metering injection pumps. • Explain the operation of aneroid devices, altitude compensators, and variable timing/timing advance mechanisms. Time an injection pump to an engine using spill timing, pin timing, or electronic timing devices. • Outline the operating principles of electronically-controlled versions of inline port-helix metering injection pumps.
OBJECTIVES (Cont.) • Describe the functions of a Bosch rack actuator housing in electronically-controlled versions of port-helix metering injection pumps. • Time a Bosch electronic PE pump to an engine using the appropriate timing tool. • The first high-pressure liquid fuel injection to a high-speed diesel combustion chamber was developed in 1927 by Robert Bosch. • This evolved into the pump-line-nozzle (PLN) fuel pumps used by Caterpillar, Mack, Navistar, Deere, and other diesel engine manufacturers.
Inline, Port-Helix Metering Injection Pump • First high pressure liquid fuel injection to a high speed diesel combustion chamber developed in 1927 by Robert Bosch. • Developed into PLN (Pump-Line-Nozzel used by my many OEMs into the 1990’s for highway trucks. • Last generation operated until 1997, but were electronically controlled. • After 2011, used only in off highway applications of 70 hp or less. • Electronic versions could not keep up with fuel economy and emissions standards. • Shown is a Bosch port-helix injection pump.
Interpreting a Bosch Injection PumpSerial Number • Chart used to decipher the serial numbers of a Bosch injection pump.
INJECTION PUMP COMPONENTS • Pump Housing • Flange mounted to the engine accessory drive. • Cam Box • Lower portion of the pump housing • Houses the camshaft • Houses the tappets • Provides an oil sump • Note: Older systems had a separate oil supply that needed to be serviced separately from the engine. • Newer units use engine lubricating oil, and have a drain port to return excess oil to the engine sump. • Camshaft • Turns 360 deg for each 720 deg of engine rotation. • May be of symmetrical, asymmetrical or anti-back kick design.
Actuating a Port-Helix Type Pump Element • Each injector is actuated by a dedicated cam profile on the camshaft. • Riding each profile is a tappet assembly consisting of a plunger and a barrel. • Barrel • Stationary • Ports in upper portion, exposed to fuel charging gallery
Actuating Cam Geometry • The three cam profiles normally used on a port helix pump.
Port Closure As the plunger is pushed upward, it closes the ports and traps fuel in the barrel.
Effective Stroke As the plunger continues upward the inlet and spill ports are closed, and the fuel in the barrel forces the delivery valve open.
Port Opening The plunger continues upward with the helix now opening the spill port and the inlet port, causing the pressure in the barrel to drop. The delivery valve now closes by spring pressure.
Plunger Travel Throughthe Effective Stroke The effective stroke is defined as the distance the plunger moves from the time the port is closed (starting fuel delivery) until the port is opened (ending fuel delivery).
Rack Position and Relationshipto Fuel Delivery Quantity • The closing point of the ports is fixed by the flat crown of the plunger, but rotating the plunger changes the point at which the helix opens the ports, which effectively varies the effective stroke. • The vertical slots in the plunger can be aligned with the ports so that no fuel delivery occurs.
Control Rack and Sleeve Gear A control rack and a geared sleeve rotate the plunger to change the point at which the helix ends the effective stroke of the plunger.
Typical Delivery Valve Assemblies inClosed and Open Positions • Delivery valves reduce the work required of pump elements by keeping fluid from returning from the injection lines. • They are simply one-way check valves. • Fuel held in the pressure lines by the delivery valve between injection pulses is called dead volume fuel.
Mechanical Timing Advance Mechanism Older port-helix pumps were driven directly by engine gearing (camshaft) and were static timed so that the port closing occurred at the same time regardless of engine speed or load. This resulted in poor emission and economy results. Most later-generation port-helix metering injection pumps have a variable-timing mechanism that acts as an intermediary between the pump drive gear (on the engine) and the pump camshaft coupling. Advance values could range from 3 to 10 degrees of crankshaft angle.
ANEROIDS • An aneroid is a low-pressure sensing device. • Limits fueling until boost pressure reaches a pre-determined value. • Used on hydromechanical injection pumps as an altitude compensator to prevent more fuel from being injected into an engine cylinder than there is oxygen to burn it. • Also known as a puff limiter, turbo-boost sensor, air-fuel control valves (AFC) and smoke limiters.
TIMING INJECTION PUMPS TO AN ENGINE • Port-helix metering injection pumps are timed to the engine they manage by phasing port closure on the #1 cylinder. • All injection pumps must be accurately timed to the engine they will fuel.
TECH TIP • Most injection pumps on North American engines are timed to the #1 engine cylinder but not all, so watch for those that are not. • The #6 cylinder (on an inline 6) is the next most common, but assume nothing. • Always check the specifications in the service literature.
SPILL TIMING PROCEDURE • Spill timing is a procedure to set the timing of the injection pump by watching the fuel exiting the spill port of the injector. • When the flow is reduced to 6 to 10 drops over a ten second period, the injector is considered timed. • This procedure is only used on older engines now.
TECH TIP • Although approved by manufacturers of older automotive diesel engines, using a timing light is not considered to be a sufficiently accurate method of testing commercial diesel engine timing. • Limit the use of a timing light to verify the operation of timing advance mechanisms.
CAUTION • If resistance is encountered while installing a fuel injection pump, remove and check the cause. • Forcing a pump home on its mounting flange using the fasteners can damage the pump drive, and it will almost certainly result in an out-of-time pump.
PHASING • Phasing the injection pump sets the phase angle between the individual pump elements, and essentially ensures that PC (port closing) on each occurs at a precise spacing. • On a six-cylinder engine, this would be exactly 60 degrees. • This procedure is something that will not be done by a line mechanic, but rather a specially trained technician in a specialty shop.
CALIBRATION • Calibrating the injection pump dynamically balances fuel delivery quantity output from the individual pumping elements. • The output from each pump element is measured in calibrated vials and displayed on a monitor.
BENCH TESTING • The following are some of the tests/adjustments that are done on a test bench. • Phasing • Full-fuel quantity calibration • Peak torque rpm fuel quantity calibration • Droop calibration • High-idle rpm calibration • Idle speed calibration • Cranking fuel calibration • Start retard fueling • Aneroid operation and adjustment • Supply pump charging pressure
TECH TIP • Never be tempted to perform any adjustment on an inline port-helix metering pump that should be performed on a comparator bench. • Both specialized training and equipment are required to perform internal pump adjustments. • The cost of attempting to adjust fuel pumps outside of the manufacturer specifications can be the price of a replacement engine.
CRITICAL SYSTEM PRESSURE VALUES • Charging Pressure • Pressure produced by the delivery pump, normally between 15 and 75 psi. • Delivery Valve Crack Pressure • Normally about 300 psi when there is no residual line pressure. • Residual Line Pressure • The pressure of the dead volume fuel in the pressure pipe. • Usually about 2/3 NOP (nozzle opening pressure). • Nozzle Opening Pressure • Pressure required to open the nozzle valve in a hydraulic injector. • Normally ranges from 2,200 and 5,000 psi. • Peak Pressure • The highest pressure the system can produce. • Normally 2 to 10 times NOP.
SUMMARY • The hydromechanical pumping devices using inline port-helix metering injection pumps changed little from the time of their introduction in 1927 until emissions standards legislated them off highway-compliant, commercial diesel engines a few years ago. • Management of the port-helix metering injection pump evolved from hydromechanical governing to the electronic governing devices introduced in the late 1980s. • Most inline port-helix metering injection pumps are flange mounted to the engine cylinder block or timing cover and gear driven at camshaft speed. • The port-helix metering pump is driven through one full rotation (360 degrees) per full-effective cycle of the engine (720 degrees in a four-stroke cycle). • The pump camshaft is supported by main bearings and driven in the cambox, which also acts as a lubrication sump. • Pump element actuating tappets are spring-loaded to ride the cam profiles.
SUMMARY (Cont.) • Cam geometry dictates the pump element activity. • There is a pump element dedicated to each engine cylinder. • A pump element consists of a stationary barrel and a reciprocating plunger. • The plunger is milled during manufacture with a metering recess known as a helix or scroll. • Plunger rotational position determines the point of register of the barrel spill port and the helix. • The plungers are rotated in unison by a toothed rack meshed to slotted control sleeves, themselves lugged to the plungers. • Plunger effective stroke begins at port closure and ends at port opening. • Delivery valves separate the pump elements from each high-pressure pipe and act to retain dead volume fuel at pressure values approximating two thirds NOP. • Delivery valves are designed to seal before they seat.
SUMMARY (Cont.) • Delivery valves increase the volume available for dead volume fuel storage in the high-pressure pipe by the swept volume of the retraction collar. • Most later-generation port-helix metering injection pumps have a variable-timing mechanism that acts as an intermediary between the pump drive gear (on the engine) and the pump camshaft coupling. • Hydromechanically managed injection pumps often incorporate an aneroid device and an altitude compensator to prevent more fuel from being injected into an engine cylinder than there is oxygen to burn it. • Inline port-helix metering injection pumps must be accurately timed to the engine. • Caterpillar and Bosch electronically-controlled port-helix metering fuel injection pumps used similar operating principles. • Bosch P7100 and P8500 injection pumps were port-helix metering injection pumps adapted for electronic control.
SUMMARY (Cont.) • The primary ECM outputs used to manage Bosch P7100 and P8500 injection pumps are the rack actuator and Econovance. • Timing of Bosch P7100 and P8500 injection pumps to the engine requires the use of a Mack electronic timing device.
Any Questions ? • Thank You !