Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

Inline Fuel Injection Pumps by mikesanye

VIEWS: 1,064 PAGES: 16

									Inline Fuel Injection Pumps
In 1927 Robert Bosch produced the first practical diesel pump.
This design enabled the newly developed diesel engine to
become a viable engine for many applications. The method of
fuel metering on this initial pump was port and helix, (high-
pressure metering). This method of metering was still being
used on most modern injection pumps into l990's. Bosch has
licensed many companies to build these pumps but they all
retain the basic Bosch design principles. Bosch designed
pumps are used on many manufacturers’ engines. One of the
larger pumps in the Bosch line, the PE/S series has many
heavy-duty features, making it suitable for high-output engines
These pumps have been used on Mack, Navistar and Cummins
and countless others throughout the world. Larger camshafts,
plungers, and non-adjustable roller tappets enable this pump to be used with nozzle opening
pressures of 1,350 Bar, (10,000 to 20,000 psi). The hydro-mechanical versions of these pumps had
many add on features and controls such as a fuel lift pump, smoke limiter, (aneroid), injection
advance unit, and several different governors. The P size pump is generally used on engines having
more than 200 hp (149 Kwh). To meet increasingly stringent emissions requirements, manufacturers
of injection equipment are using much higher nozzle opening pressures than previously. Important
information about the pump is stamped on a plate mounted to the side of the pump. This plate will list
among other items, pump serial
number, pump model, and part
number.
Component Parts and their Function
The pump shown at right is typical of
most inline pumps. The pump housing
has a low-pressure fuel gallery
surrounding the pumping elements.
This gallery is sealed from the rest of
the pump housing so fuel is available
only to the inlet/spill ports of the pump
barrels. An excess supply of fuel is
supplied to the gallery by the transfer
pump in most applications and a return
line returns unused fuel to the tank.
This excess flow removes any bubbles
that form in the fuel caused by
vibration or aeration and also keeps
the pump cool. The camshaft, (14), is
coupled to the engine drive train
through various methods but most
commonly a gear train arrangement is
used. The camshaft causes
reciprocating movement of the pumping plungers. The pumping
plunger and barrel assembly, (8+4) performs two functions. It forces
fuel past the delivery valve, into the injection line, and to the nozzle
by way of its reciprocating action, it also controls the quantity of fuel
by rotating action. The roller tappets, (13), ride directly on the
camshaft and transmit its motion to the pumping plungers. The plunger springs, (11), keep the roller
tappets in contact with the camshaft. The control rack or rod, (15), transmits the action of the
governor to the pumping plunger through the control sleeves, (9).
The delivery valve, (5), seals off the high pressure line from the barrel during the plunger’s downward
stroke and also reduces pressure in the line to a predetermined level to prevent secondary injections
in the combustion chamber.

                                           Pump Operation
                                           The heart of the inline injection pump is the plunger and barrel
                                           assembly, (at left). This is where fuel at supply pump pressure
                                           is pressurized to injection levels ranging from 140 to 1,350 Bar,
                                           (2,000 to 20,000 PSI) and the precise control of fuel delivery is
                                           accomplished by changing the point of register of the helical
                                           control edge of the plunger, (the helix), with the spill/fill port.
                                           Because the plunger fits so precisely in the barrel (approximate
                                           clearance is only 2 to 4 microns), there are no sealing rings to
                                           retain the injection pressure as the plunger pumps fuel they
                                           seal by the viscosity of the fuel only. Pumping plungers and
                                           barrels are lapped together to provide this seal. Never
interchange a plunger from one barrel to another. Even the warmth caused by holding a plunger in
your hand can cause it not to fit in its barrel. Plunger and barrels
are sold as a matched set. The pump camshaft lobe provides a
constant mechanical stroke length of the pumping plunger. The
plunger is rotated indirectly by the governor to provide changes
in fuel delivery. The upper edge of the pumping plunger has a
vertical groove which connects the hydraulic pressure above the
plunger to the milled recesses below. Near the top is a helix (or
control edge) this edge provides precise control of fuel delivery
by covering and uncovering the fill/spill ports as the plunger is
driven upwards in the barrel. The barrel may have either one or
two control ports, also called fill/spill ports. Any fuel that does
leak by the plunger is usually collected in an annular groove cut
into the barrel or the plunger and a corresponding duct in the
barrel provides a means of returning this leakage fuel to the
charging gallery. Without this method of returning to the charging
gallery, any fuel that leaks by the plunger would end up in the
engines oil supply and cause it to dilute and lead to engine
                                                                   damage. The design of these pumps is
                                                                   so precise that fuel leakage by the
                                                                   plungers is very rarely the cause of
                                                                   diluted engine oil and if this occurs all
                                                                   other leakage possibilities should be
                                                                   eliminated before suspecting the pump
                                                                   as the cause.
                                                                   When the pumping plunger is at its
                                                                   bottom position, fuel from the pump
                                                                   gallery enters through the fill/spill port/s
                                                                   and floods the area above the plunger
                                                                   and down the vertical groove to the
                                                                   milled recesses. The plunger is now
                                                                   forced upward by the camshaft. Initially
                                                                   this upward motion merely displaces
                                                                   fuel back to the charging gallery
                                                                   because the fill/spill ports/s is/are still
                                                                   uncovered.
After a short period of upward travel, the plunger
leading edge covers the inlet or fill/spill port/s. This is
known as port closure and is critical to the timing of
the injection event. Continued upward movement will
raise the pressure and then force fuel past the
delivery valve into the high pressure line, open the
injection nozzle, and inject fuel into the combustion
chamber. Injection will continue until the plunger has
risen far enough to enable the lower control edge of
the helix to uncover the inlet or fill/spill port/s. At this
time, pressurized fuel will rush down the vertical
groove on the plunger and exit through the now open
port/s. This is known as spill and is the end of
pressurization; the pressure will collapse back from
the nozzle through the open port in the barrel and will
continue to drop until the delivery valve closing
pressure is reached, typically 2/3 of nozzle opening
pressure, (NOP). The delivery valve will then close
sealing the barrel chamber from the high pressure
line. This closing maintains a residual pressure in the
high pressure line so the system is ready for the next
injection to that cylinder. After the end of fuel
delivery, the plunger will continue to be forced
upward by the camshaft, but this movement will not
cause any further injection it merely displaces fuel
through the open fill/spill port/s back to the charging
gallery.

                                                                             The plunger stroke can be
                                                                             divided into four stages.
                                                                             Pre-stroke; this is the
                                                                             movement of the plunger
                                                                             from its bottom dead centre
                                                                             position to the point of port
                                                                             closure fuel is merely
                                                                             displaced back to the
                                                                             charging gallery during this
                                                                             portion of the stroke.
                                                                             Retraction stroke; this is
                                                                             the small portion of the
                                                                             stroke required to raise the
                                                                             fuel pressure to nozzle
                                                                             opening pressure or NOP.
                                                                             Effective stroke; this is the
                                                                             plunger stroke while fuel is
                                                                             actually being delivered to
                                                                             the injector nozzle.
Residual stroke; this is the remaining upward travel of the plunger after the spill port has been
uncovered by the helix until the plunger reaches its top dead centre position.
                                                               The effective stroke of the pumping plunger
                                                               is the time when fuel is being sent to the
                                                               injector. The plungers are milled with a
                                                               vertical groove, or it may have cross and
                                                               centre drillings, and helical recesses. The
                                                               function of the vertical groove or cross and
                                                               centre drillings is to maintain a constant
                                                               connection between the pumping chamber
                                                               above the plunger and the helical recesses
                                                               so that when the helix uncovers the spill port
                                                               pressure above the plunger can escape
                                                               through the drillings or the vertical groove.
                                                               The length of plunger effective stroke will
                                                               depend on where the plunger helix registers
                                                               (vertically aligns) with the spill port. Control
                                                               sleeves lugged to the plunger permit the
plunger to be rotated while reciprocating. Rotating the plunger in the bore of the barrel will change the
point of register of the spill port with the helix. Therefore, plunger effective stroke and injected fuel
quantity depends entirely on the rotational position of the plunger. This rotation is controlled by the
requirement of more or less fuel and has no connection to engine speed or plunger reciprocation. The
plungers rotational position when an engine is in a steady load condition will not change it will only
adjust by operator demand or load change.
                             In multiple cylinder engines, the plungers must be synchronised to move
                             in unison to ensure balanced fuelling at any given engine load. The
                             control sleeves are tooth meshed or mechanically connected to a
                             governor control rod or rack, which when moved linearly, rotates the
                             plungers in unison. This is important. It means that in any position of the
                             rack, all of the plungers will have identical points of register with their spill
                             ports, resulting in identical pump effective strokes. The consequence of
                             not doing this would be to unbalance the fuelling of the engine that is,
                             deliver different quantities of fuel to each cylinder causing rough running
                             or even engine damage.
                             Engine shutdown is achieved by moving the control rack to the no-fuel
                             position. The plungers are rotated to a point where the vertical groove will
                             be in register with the spill port for the entire plunger stroke. The plunger
                             will merely displace fuel as it travels upward, with no pressurization
                             possible. In other words as the plunger is driven into the pump chamber,
                             the fuel in the chamber will be squeezed back down the vertical groove to
                             exit through the spill port and return to the charging gallery.
Most port helix metering injection pumps use delivery valves to reduce the amount of work required of
each pump element per cycle. Most delivery valves will have a conical seat, a retraction piston or
                                     collar and flutes to guide it in its bore while allowing unrestricted
                                     fuel flow, without the flutes the delivery valve could stick open.
                                     Delivery valves reduce the amount of work the pump has to do on
                                     the next fuel injection cycle by isolating the high pressure circuit
                                     that extends from the injection pump chamber to the seat of the
                                     nozzle valve and holding it a pressure somewhat below NOP. Fuel
                                     retained in the high pressure pipes to the injectors between
                                     pumping pulses is known as dead volume fuel. Dead volume fuel is
                                     held at a residual pressure below NOP usually 2/3 of NOP.
                                     Delivery valves also help to stop secondary injections. When the
                                     spill port opens in the pumping chamber the pressure collapses
                                     very quickly, the injector nozzle will close first when its differential
                                     pressure is reached, usually 65 to 75% of NOP. Immediately
                                             following nozzle closure the delivery valve retracts into its
                                             holder. As soon as the retraction piston enters the delivery
                                             valve holder the high pressure fuel in the line is cut off from
                                             the open spill port.

                                      The delivery valve continues to retract however until the conical
                                      seat contacts the matching cup in the holder this extra movement
                                      allows a minute amount of extra space for the fuel to occupy
                                      thereby lowering its pressure to residual line pressure. This extra
                                      space is known as the swept volume of the delivery valves
                                      retraction piston or collar. Retraction collar swept volume is
                                      matched to the length of the high pressure pipe to achieve a
                                      precise residual line pressure. If the pressure was retained at
                                      close to NOP the rushing fuel slamming into the closed delivery
                                      valve would cause a reflected pressure wave or surge back
                                      toward the nozzle and in certain conditions this could cause the
                                      nozzle to reopen and dribble some fuel into the combustion
                                      chamber which in turn would cause poor fuel economy and HC
                                      emissions. Some delivery valves will have a return flow restriction
                                      valve to further reduce pressure wave reflections or oscillations in
                                      systems where cavitation is an issue.
The delivery valve is held in its closed position on its seat by a spring
and by the residual line pressure. If, for whatever reason, the residual
line pressure value was zero, hydraulic pressure of around 20 atms,
(300 psi), would have to be developed in the pump element to overcome
the mechanical force of the spring. This mechanical force is
compounded when the residual line pressure is pushing on the delivery
valve and establishes the pressure that must be developed in the pump
chamber before it is unseated.




                                                                       When the delivery valve is first
                                                                       unseated, it is driven upward
                                                                       in its bore by rising pressure
                                                                       in the pump chamber and it
                                                                       acts as a plunger being driven
                                                                       upward into the dead volume
                                                                       fuel retained in the high
                                                                       pressure pipe. By the time the
                                                                       fuel in the chamber and the
                                                                       pipe unite the pressure will be
                                                                       close to NOP then the injector
                                                                       nozzle valve (NOP) opens
                                                                       and forces atomised fuel into
                                                                       the engine cylinder.


                                                            Pump Housing
                                                            The pump housing is the frame that
                                                            encases all the injection pump
                                                            components and is a cast aluminium,
                                                            cast iron, or forged steel enclosure The
                                                            pump housing is usually flange mounted
                                                            by bolts to the engine cylinder block to be
                                                            driven by an accessory drive on the
                                                            engine gear train. In some offshore
                                                            applications of inline, port helix metering
                                                            injection pumps, the pump assembly is
                                                            cradle mounted on its base, in which
                                                            case, it is driven by means of an external
                                                            shaft from the timing gear train.
Cam Box
The cam box is the lower
portion of the pump housing
incorporating the lubricating oil
sump and main mounting
bores for the pump camshaft.
Camshaft main bearings are
usually pressure lubricated by
engine oil supplied from the
engine crankcase and the
cam-box sump level is
determined by the positioning
of a return port. In older
injection pumps, the pump oil
was isolated from the main
engine lubricant and the oil
was subject to periodic checks
and servicing.
Camshaft
 The camshaft is designed
with a cam profile for each
engine cylinder and supported
by main bearings at the base
of the pump housing. It is
driven at 1/2 engine rotational
speed in a four-stroke cycle engine by the pump drive plate, which is itself, either coupled directly to
the pump drive gear or to a variable timing device. Camshaft actuating profiles are usually
                                                    symmetrical, that is, geometrically similar on both
                                                    sides of the toe, and mostly inner base circle (IBC
                                                    the smallest radial dimension of an eccentric).
                                                    However asymmetrical (the geometry of each cam
                                                    ramp or flank differs) and mostly outer base circle
                                                    (OBC: the largest radial dimension of an
                                                    eccentric) designs are used.
                                                    Tappets
                                                    Tappets are arranged to ride the cam profile and
                                                    convert the rotary motion of the camshaft to the
                                                    reciprocating action required of the plunger.
                                                      A retraction spring is integral with the tappet
                                                    assembly. This is required to load the tappet and
                                                    plunger bases to ride the cam profile and it is
                                                    necessarily large enough to overcome the low
                                                     pressure (vacuum) established in the pump
                                                     chamber on the plunger return stroke. This low
                                                     pressure can be considerable when plunger
                                                     effective strokes are long but it does enable a
                                                     rapid recharge of the pump chamber with fuel
                                                     from the charging gallery. The time dimension
                                                     within which the pump element must be
                                                     recharged decreases proportionately with pump
                                                     rpm increase.
The Barrel
The barrel is the stationary member of the
pumping element; it is located in the pump
housing so its upper portion is exposed to
the charging gallery. This upper portion of
the barrel is usually drilled with diametrically
opposed ports known as fill and spill ports
that permit through flow of fuel to the barrel
chamber to be charged. Some older
systems had only one port this was changed
as pump pressures became higher in order
to provide a hydraulic balance at the spill
point to prevent the plunger from being
hammered against on side of the barrel as
pressure collapse occurs. Because it
contains the spill ports, both its height and
rotational position in relation to the plunger
is critical. Barrels are often manufactured
with upper flanges so that their relative heights
can be adjusted by means of shims and fastener
slots permit radial movement for purposes of
calibration and phasing.
Plunger
Plungers are the reciprocating (something that
reciprocates, moves backward and forward such
as in the action of a piston in an engine cylinder)
members of the pump elements and they are
spring loaded to ride their actuating cam's
profile. Plungers are lapped to the barrel in
manufacture, to a clearance close to 2µ,
ensuring controlled back leakage directed
toward a viscous seal consisting of an annular
groove and return duct in the barrel. Each
plunger is milled with a vertical slot, helical
recess/es, and an annular groove. In current
truck engine applications, a lower helix design is
generally used but both upper helix and dual
helix designs are sometimes observed. The
positioning and shape of the helices (plural of
helix) on a plunger are often described as the
plunger geometry.
Plunger geometry describes the physical shape
of the metering recesses machined into the
plunger and this defines the injection timing
characteristics. The function of the vertical slot is
to ensure a constant hydraulic connection
between the pump chamber above the plunger
and the plunger helical recess/es. A plunger with
a lower helix will have a constant beginning,
variable ending of delivery timing characteristic
because the fill/spill port will always close at the
same amount of plunger upward travel and will
open depending on its rotational position.
Upper helix designs will be of the variable beginning, constant ending type. Double helix designs are
designed with both an upper and a lower helix. Double helix designs will have a variable beginning
and variable ending of delivery; this geometric design tends not to be often used in highway diesel
engines.

In the most common helix designs, plungers have identical
helices milled on both sides of the plunger. These are used
in many modern high pressure injection pumps to provide
hydraulic balance to the pump element at the spill point.
This design prevents the side loading of the plunger into the
barrel wall from the high pressure fuel being suddenly
released. A further feature of some plungers is a start retard
notch, or starting groove. Start retard notches are milled
recesses in the leading edge of plungers with lower helix
geometry. The start retard notch is usually on the opposite
side of the vertical slot from the helix and in a position that
would correlate close to a full-fuel effective stroke. The
governor of the injection pump is designed to permit the
start retard notch to register with the spill port only at
cranking speeds (under 300 rpm) and usually with the
accelerator fully depressed. The objective of the start retard
notch on a lower helix design plunger is to retard the
injection pulse until there is a maximum amount of heat in
the engine cylinder, usually when the piston is close to TDC. The instant the engine exceeds 300
rpm; it becomes no longer possible for the start retard notch to register with the spill port.
                               Rack and Control Sleeves
                               The rack and control sleeves allow the plungers in a multi-cylinder engine
                               to be rotated in unison to ensure balanced fuel delivery to each cylinder.
                               Plungers must therefore be timed either directly or indirectly to the control
                               rack. The rack is a toothed rod or a notched bar that extends into the
                               governor or rack actuator housing. The rack teeth or notches mesh with
                              teeth or levers on plunger control sleeves, which are either lugged or
                              clamped to the plunger. It must be possible to rotate the plungers while
                              they reciprocate to permit changes in fuel requirements while the engine
                              is running. Linear movement of the rack will rotate the plungers in unison,
                              alter the point of register of the helices with their respective spill ports, and
                              thereby control engine fuelling.

                               Comparator bench testing
Pump Calibration
Because the plunger and barrel assemblies are matched lapped sets
small differences in delivery volumes occur. Pump calibration is a test
stand procedure in which the plunger helix point of register with the
spill port is incrementally adjusted either by rotating the barrels
slightly or rotating the individual plungers to alter there position
relative to the rack. This ensures the delivery from each pump
element is exactly equal.
Pump Phasing
Pump phasing involves setting the port closure dimension of each
pump element so it occurs exactly 120 crankshaft degrees apart, (for
a six cylinder engine). It is performed only on the comparator bench
and can be adjusted by shimming the pump barrels or the plunger
tappets.
                                             Charging Pumps
                                             The terms charging pump, transfer pump and supply
                                             pump tend to be used interchangeably, depending on the
                                             OEM. The charging pump is responsible for all fuel
                                             movement in the fuel subsystem. In truck applications
                                             using port helix metering injection, the charging pump is
                                             normally a single or double acting plunger pump, flange
                                             mounted to the fuel injection pump and actuated by a
                                             dedicated eccentric on the injection pump camshaft.




Fuel is pulled under suction from the fuel tank through hydraulic
hose by the transfer pump. A primary fuel filter and or water
separator may also be in series with the pump and tank; or a
more rudimentary pre-cleaner can be integral with the charging
pump. The charging or transfer pump is responsible for
producing charging pressure. It discharges to a secondary
filter(s) and then to the charging gallery in the upper housing of
the injection pump. Charging pressures range from 1 to 5 atms
(15-75 psi) depending on the system. In some cases, a hand
primer is fitted to the transfer pump assembly. Its only function
is to prime the system manually after it has been opened or run
dry. Transfer pumps are capable of delivering far more fuel the
engine requires so there is usually a return line from the
charging gallery to return excess fuel to the tank. This helps to
remove any bubbles that form due to aeration and to keep the
fuel cool.
Governor or Rack Actuator Housing
                                                                      Either a governor or rack actuator
                                                                      housing must be incorporated to a
                                                                      port helix metering injection pump.
                                                                      This acts as the control mechanism
                                                                      for managing fuelling. A Diesel
                                                                      engine must use a governor to
                                                                      control the amount of fuel injected
                                                                      because unlike a gasoline engine
                                                                      there is no throttle to control the
                                                                      amount of air ingested. Gasoline
                                                                      engines are managed to run on a
                                                                      stoichiometric fuel ratio of 14.7: 1,
                                                                      but diesels run with an excess of
                                                                      air at all times. A diesel can have
                                                                      as much as 1000 times the air
                                                                      required to burn the fuel inside the
                                                                      cylinder under certain operating
                                                                      conditions. Therefore we must
                                                                      precisely control the fuel quantity or
                                                                      the engine would quickly
                                                                      accelerate to self destruction,
                                                                      (1000 RPM per sec). Consider an
engine fuel system that is designed to deliver 185 mm3. of fuel for each injection pulse at peak
torque. While this engine is idling, (no load), it may need only 18.5 mm3. per pulse, just to keep the
engine running while it is cold (enough to overcome the friction and inertia of the pistons and
crankshaft etc.). As the engine warms these factors will reduce (less friction etc.), if we supply the
same amount of fuel the engine will run faster and faster until it disintegrates. A governor’s job is to
sense engine speed and limit it by cutting the fuel delivery to the amount necessary to maintain its
speed. To run the above engine at 1200 RPM under no load may require only 20 mm3 of fuel but as
load is applied the requirement will increase perhaps as high as full fuel or 185 mm3. per cycle. The
governor can precisely control fuelling to accommodate this. The governor will control low idle, (the
slowest speed that the engine will run), high idle, (the maximum engine speed), and will manage
fuelling in between these points based on driver input and load conditions.
Mechanical governors were originally designed by James Watt in 1788 to control the steam engine of
his day. Mechanical governors use a set of flyweights that spin in relation to engine RPM. The
flyweights always try to reduce engine fuelling and by that engine speed. Governors match adjustable
spring tension against the centrifugal force generated by the governor weights. The governor will
have a main spring and an idle spring and in most cases a torque control spring it may also have a
starting spring. The combined effort of these springs is to push the engine fuel control rack towards
full fuel. The main governor spring tension is affected by the throttle position under all operating
conditions the governor will find a balance between spring force and weight force to control engine
fuelling and therefore engine speed. Mechanical Governors are set so that at maximum engine speed
the governor weights can overcome the combined tension of all the spring and hold fuelling to a level
that the engine will not exceed its maximum speed. Mechanical Governors such as the one above
have not been used on highway applications since the 1990s.
Crude attempts were made to control engine emissions on turbocharged versions of these
mechanically controlled inline pump engines, their prime purpose was to reduce visible smoke
emissions. When a turbocharged engine is accelerated there is always a period of “lag” before the
exhausted heat energy can spin up the turbo to increase engine breathing, however on acceleration
the rack would move to full fuel and the available air could not combust the entire fuel load this would
result in a puff of black smoke on acceleration.
                                         These systems were variably called a puff limiter or smoke
                                         limiter or an aneroid. These devices functioned to delay
                                         the fuel racks travel to full fuel until there was sufficient air
                                         to combust the large fuel load. They consisted of a simple
                                         device that physically limited the racks travel until boost
                                         pressure acting on a diaphragm could overcome spring
                                         pressure holding the device restricting the racks travel.
                                         Most of these were on off devices if boost was below a
                                         certain level say 5PSI they held the rack at a proportion of
                                         full travel approximately 60 to 80%. Once boost pressure
                                         exceeded the 5PSI the rack would be allowed full travel.
                                         These aneroids were commonly tampered with by drivers
                                         thinking they could get better fuel economy and
                                         performance but remember that any fuel that exits an
                                         engine as black smoke is wasted fuel so the tell tale signs
                                         that an aneroid has been tampered with, that is a puff of
                                         black smoke on acceleration indicates a loss of efficiency
                                         rather than a gain.




A second device was introduced to control rack maximum
travel based on barometric pressure. At higher altitudes
the available air contains less oxygen and therefore
cannot oxidize the same amount of fuel so a barometric
capsule limits rack travel in much the same way as an
aneroid however based only on barometric pressure.




                                                   .
                                                   .




                                                   Hydro mechanical inline pumps could also be
                                                   fitted with crude mechanical timing advance
                                                   systems that were capable of advancing or
                                                   retarding engine timing, (depending on the
                                                   engine), by 8 to ten degrees but stricter emission
                                                   controls spelled the end for these systems.
The only way that manufacturers could meet the ever stricter emission control legislation was to
devise methods to get greater control over fuelling and injection timing throughout the operating
                                                                    range of the engine this was not
                                                                    achievable with mechanical
                                                                    controls.
                                                                    Inline pump systems were adapted
                                                                    so that they could be controlled by
                                                                    computer this makes them partial
                                                                    authority managed engines. The
                                                                    amount of control varied by
                                                                    manufacturer but most inline
                                                                    pumps were fitted with electronic
                                                                    timing control and electronic fuel
                                                                    rack position control these changes
                                                                    allowed these pumps to be used
                                                                    well into the 1990s.
                                                                    One of the most popular adapted
                                                                    systems was designed by Bosch
                                                                    using PE-7100 and PE-8500
                                                                    pumps.

                                                               These pumps featured electronic rack
                                                               actuators in place of mechanical
                                                               governors and timing control devices
                                                               capable of 20 degrees of timing
                                                               change also controlled by computer.



                                                               In order for the computer to
                                                               successfully manage these pumps a
                                                               variety of sensors were required to
                                                               relay to the computer details about
                                                               engine speed and position, temp, air
                                                               intake temperature and boost, throttle
                                                               position, road speed etc.
                                                               These signals and more were input to
                                                               a computer which then processed the
                                                               information and made changes to
                                                               fuelling amount and injection timing
                                                               based on internal fuel and timing
                                                               algorithms or “maps”. These “maps”
                                                               are basically a set of pre-programmed
                                                               instructions in the computers memory
                                                               that drive its decision making
                                                               processes.
The control over fuelling and timing had to be extremely accurate in order to maintain minimum
emissions while not sacrificing maximum engine performance.
                                                                    The rack actuators that Bosch
                                                                    used the RE-24 and RE-30 were
                                                                    quite sophisticated they were
                                                                    equipped with a linear
                                                                    proportional solenoid that was
                                                                    computer controlled with a pulse
                                                                    width modulated signal that
                                                                    precisely controlled the current
                                                                    flow to the solenoids magnet. By
                                                                    increasing the magnetic field the
                                                                    solenoid could overcome return
                                                                    spring tension and drive the
                                                                    control rack towards a full fuel
                                                                    position. The stronger the current
                                                                    flow through the solenoids coil the
                                                                    stronger the magnetic force would
                                                                    become.
                                                                    It’s all very fine to be able to
                                                                    control the racks position by this
linear proportional solenoid however the computer needs verification the desired position is obtained
this was accomplished with a rack position sensor.




                                                    The sensor consisted of a measuring coil as seen
                                                    above and left in the low idle fuel position. The coil
                                                    is energized by the ECM at 5 volts. The coil
                                                    surrounds a laminate iron core that has a moveable
                                                    short circuit ring that travels along the core but
                                                    does not contact it. This short circuit ring is
attached to the rack so as the rack is moved by the proportional solenoid the ring moves along the
iron core of the sensor. This varies the strength of the magnetic field produced by the coil and
therefore the induced signal returned to the ECM. This signal is very precise and is referenced by the
computer control up to 60 times per second so the exact position of the rack is known at all times.
The rack actuator is by necessity mounted at the rear of the pump which in turn is attached to the
engine and therefore is subject to large amounts of temperature change. These temperature swings
cause changes in resistance in the position sensor coils winding and could lead to inaccurate position
information.
                                             To combat this problem a reference coil is used that has
                                             the identical sensing coil as the position sensor and a
                                             fixed position short circuit ring. This sends a signal back
                                             to the ECM that only changes with temperature change.
                                             This allows the ECM to correct position data from the
                                             position sensor as temperature changes.




The second control item needed to control
emissions is timing with mechanical control of timing
very little adjustment could be made and it was
usually up to 8 degrees advance based on speed or
6 to 8 degrees retard based on load depending on
engine vocation. Some systems were slightly more
sophisticated but computer control was needed to
ensure compliance.
                                                        The first thing that was needed was precise
                                                        engine speed and position data. Inside the
                                                        rack actuator housing a tone or pulse wheel
                                                        was attached to the back of the pump
                                                        camshaft. This is a toothed wheel that turns at
                                                        camshaft speed. A speed sensor, (an
                                                        induction pulse generator), sensor was
                                                        installed referencing these teeth and its output
                                                        frequency would vary with changing camshaft
                                                        speed. A second induction pulse generator
                                                        sensor called a timing event marker was
                                                        installed and this sensor referenced a single
                                                        notch on the tone wheel marking top dead
                                                        centre number 1 cylinder.
                                                        The second requirement is a physical way to
                                                        change timing different methods were used
                                                        but one popular method used by MACK was
                                                        called Econovance. This system allowed
                                                        computer controlled changes to engine timing
                                                        of up to 20 crankshaft degrees. An initial or
                                                        static timing set at 4 degrees BTDC could be
                                                        limitlessly varied between 4 and 24 degrees
                                                        BTDC this gave the ECM great control in
                                                        terms of managing cylinder pressure and
                                                        temperature and therefore emissions.
The Econovance operated as an intermediary device between the engines pump drive gear and the
                                                                               pump camshaft. It
                                                                               consisted of high lead
                                                                               screw assembly; this
                                                                               is basically a helically
                                                                               splined sleeve that
                                                                               was forced along a
                                                                               helical spline that
                                                                               actually drove the
                                                                               pump camshaft. The
                                                                               sleeve was moved by
                                                                               hydraulic pressure.
                                                                               The ECM controls a
                                                                               proportional solenoid
                                                                               that in turn controls a
                                                                               hydraulic spool valve.
                                                                               By precisely
                                                                               controlling the spool
                                                                               through a pulse width
                                                                               modulated signal the
                                                                               timing could be
                                                                               manipulated by the
                                                                               ECM to any position
                                                                               within the operating
                                                                               range limits.
                                                                               Eventually even these
                                                                               advances were not
                                                                               enough to meet the
                                                                               emission standards
                                                                               and in the mid to late
                                                                               1990s inline pumps
                                                                               were dropped from the
                                                                               on highway market.
                                                                               Two main problems
                                                                               associated with these
                                                                               pumps led to their
                                                                               demise. They could
                                                                               not develop the
                                                                               pressures required
typical pressures developed ranged from 16,000 to 20,000 PSI or 1,100 to 1,400 Bar whereas EUI
systems develop up to 30,000 PSI or 2,000 Bar. The second shortcoming stems from the fact that as
pump line nozzle systems the are subject to injection lag and nozzle closure lag to a much greater
extent than an EUI system leading to fuel droplet sizing and other issues.

								
To top