PT Fuel System Cummins

a gear pump is located at the rear of the fuel pump assembly it is driven by the fuel pump main shaft at engine speed fuel from the tank enters the inlet or suction side of the gear pump and is carried around the outside of the two mission gears to the outlet or pressure side of the gear the pulsation damper is connected to the pressure side of the gears up to smooth the pressure pulsations created in the fuel by the rotating gear teeth you from the gear pump fuel flows to the wire mesh magnetic filter you from the filter we will flows to the inlet or supply passage of the automotive governor caverna is a speed sensitive device that automatically controls or limits the engine speed it does this by varying the fuel delivered to the engine under changing operating conditions the governor assembly performs three functions pressure regulation idle speed governing maximum speed governing let’s look at the makeup of the governor assembly wait assist spring wait assist spring shims wait assist plunger governor wait carrier govenor flyweight Governor plunger dock control spring idle passage main passage supply passage by pass passage idle spring plunger or button idle plunger guide idle spring govenor spring idle spring seat washer idle screw retention spring idle speed adjusting screw governor shims you in the governor the fly weights are driven through gears by the fuel pump main shaft you the governor plunger is held between the flyweight feet and rotate with the flyweight you any rotation creates a tendency for the fly weights to move away from their axis of rotation which is the centerline of the weight carrier shaft this outward push is known as centrifugal force the rotating fly weights pivot on the fly weight pins through this pivoting action an axial force is exerted on the governor plunger through the flyweight feet at any given speed the position of the governor plunger is determined by the balance between the fly weight force exerted on one end of the governor plunger and the spring force applied to the opposite end of the plunger the position of the governor plunger is determined by the balance between the flyweight force exerted on one end of the governor plunger and the spring force applied to the

opposite end of the plunger you torque is dependent upon the quantity of fuel that is metered and injected perm cycle in the PT fuel system at any given speed torque is dependent on rail pressure the control of rain pressure in the PT fuel system begins by regulating the fuel pressure supplied to the governor assembly appropriately called supply pressure the control of this supply pressure is accomplished through the use of a bypass type pressure regulator this type of pressure regulator is designed to unseat when a designated supply pressure is reached for this type of regulator to function and exist supply of fuel must be delivered to the governor assembly this ensures that during fuel pump operation some fuel is always being bypassed enabling the regulator to maintain control of the supply pressure when the fuel pressure exerted on the button exceeds the force holding the button and plunger together the button is unseated and fume is bypassed to the suction side of the gear pump the pressure at which the button separates from the governor plunger is determined by dividing the spring force acting on the button by the recessed area of the button the recessed area or counterbore is the specific area the fuel is pushing against you for a given spring force acting on the button increasing the recessed area reduces the pressure at which the fuel begins bypassing thereby lowering the supply pressure decreasing the recessed area will have the opposite effect that is fuel we’ll begin by passing at a higher pressure raising the supply pressure changing the resist area of the button will change the height of the supply pressure curve you a button of a smaller recessed area will raise the supply pressure curve while a button with a larger recessed area will lower the supply pressure cup also with a given recessed area any change in plunger position will change the force on the button and change the supply pressure increasing speed changes the plungers position increasing the force on the button which raises the supply pressure it is important to understand that there is a unique supply pressure for each speed you the supply pressure is independent of the flow out of the pump the regulation of the supply pressure is the first step in controlling the real pressure the automotive governor controls idle govern speed and maximum speed by positioning the governor plunger cutoff shoulder over the appropriate fuel passage around idle speed flyweight force is opposed by the idle spring at speeds close to but below torque peak speed the flyweight force is opposed by the governor spring during engine operation between torque peak ed and rated speed the flyweight force is balanced by the combined spring force of the governor spring and the torque spring once the talk spring is engaged it opposes the flyweight force exerted on the governor plunger this results in a reduction of the flyweight force which affects the governor plunger position

the automotive governor controls idle governed speed and maximum speed by positioning the governor plunger cutoff shoulder over the appropriate fuel passage in governing maximum engine speed the forces acting to position the governor plunger include the flyweight force working against a combination of the talk spring and the governor spring the flyweight force acts to close the main fuel passage while the spring force acts to keep the main fuel passage open several items should be noted at this time the weight assist spring no longer affects the governor plunger position the idle passage has been closed by the governor plunger the idle spring no longer affects the governor plunger position as the button has bottomed in the idle plunger guide when the engine exceeds its rated speed the governor reduces the fuel supplied to the injectors the speed at which the governor begins to decrease fuel pressure is called governor brake governor brake occurs when the governor plunger cutoff shoulder begins to restrict the main passage to other terms often involved in a discussion of maximum engine speed include high idle and governor cutoff the maximum no load engine speed is known as high idle anytime engine speed exceeds high idle the main fuel passage is closed by the governor plunger governor cutoff occurs at the point at which the main passage is completely closed the difference in engine speed between rated speed and high idle speed is known as governor droop it is usually expressed as a percentage of rated speed up to this point we have established some limits for the engine operating range a supply pressure which is controlled by the pressure regulator incorporated within the governor assembly a rail pressure which at any given engine speed is the supply pressure minus the total pressure drop across the remaining fuel pump components maximum speed which is limited by controlling the engine power output this is done by the governor which controls the rail pressure to the injectors within these established limits the power output can be controlled by the operator through the throttle the throttle shaft is located between the governor and the fuel pump discharge it allows the operator to reduce the rain pressure and therefore the par to the level needed the total travel of the throttle shaft is limited by 2stop screws located in the throttle shaft housing located within the throttle shaft is the fuel adjusting screw which determines the maximum flow area of the throttle shaft passage when it is wide open you it is used to adjust the rain pressure during calibration while the throttle shaft is in the closed position there is always a small amount of fuel flowing through the throttle shaft this is defined as throttle linkage and is required to keep the fuel lines filled with fuel to cool and lubricate the injectors when the throttle is closed throttle leakage is an important setting on the fuel pump if set too high it can result in slow deceleration and excessive carbon ofthe uh injectors if set too low it causes a hesitation in engine response when the throttle is reopened after a downhill run and leads to inject a plunger damaged in the lowest speed range the small amount of fuel flowing to the injectors is insufficient to maintain engine idle speed the necessary additional fuel

flows from the governor through the idle passage around the throttle shaft the amount of fuel needed for idling is a total of the fuel flowing through the idle passage plus some throttle leakage flowing through the throttle shaft with a given throttle leakage setting closed throttle idle speed is maintained by controlling rail pressure this pressure is determined by the position of the governor plunger cut off shoulder over the idle passage the closed throttle fuel pressure curve is very similar to the open throttle fuel pressure curve the no load idle speed on the closed throttle fuel pressure curve corresponds to the high idle or maximum no load speed on the open throttle fuel pressure curve decreasing engine speed will increase the rail pressure this increase in range pressure along with the increase in metering time maintains a satisfactory idle speed the change in speed between the non-load idle speed and the speed at which the maximum closed throttle fuel pressure occurs is referred to as the idle droop curve you from the throttle shaft fuel flows to the AFC or air fuel control section of the pump the AFC assembly is needed on turbocharged engines to provide the proper fuel pressure to the engine during acceleration it does this by controlling the fuel to the injectors to an amount compatible with the air supplied by the turbocharger this effectively controls acceleration black smoke the main components of the AFC assembly include cover piston assembly which includes diaphragm piston plunger spring retainer barrel spring let’s review some basic terminology which will be used in our explanation of the AFC operation air pressure from intake manifold AFC drain or vent fuel to injectors no air adjusting screw fell from throttle shaft internal drain plunger spring air diaphragm check valve you air pressure is applied to the diaphragm and piston through the inlet fitting of the cover increasing any pressure overcomes the AFC spring force causing the plunger to move in the battle as the plunger moves the passage is uncovered and fuel flows through the AFC as the air pressure continues to increase the plunger is pushed in even further uncovering more area until the fuel restriction is eliminated when there is little or no air pressure applied to the AFC diaphragm maximum fuel pressure and flow is controlled by the no air adjusting screw under these conditions on the fuel flow is around the no air adjusting screw new PT fuel pumps are currently fitted with dual spring AFC assembly dual spring AFC is a class fit assembly a class fit assembly has a tightly controlled clearance between barrel and plunger ranging from 100 to 160 millionths of an inch dual spring AFC incorporates two hex screws on the AFC

cover the no air setting is made with a lower internal hex screw this screw also acts as a positive stop the AFC plunger setting is made with the top internal hex screw advantages of dual spring AFC are easier to calibrate cannot be easily tampered with settings not sensitive to inject a drain line restriction more repeatable AFC setting no boost pressure on AFC dual spring AFC assemblies are available in two standard types standard assembly and shaped port assembly the standard AFC contains cross drilling in the barrel connecting the AFC Inlet and outlet ports let’s take a look at the working of the standard dual spring AFC in the no air condition the AFC in passage is blocked by the AFC plunger all the fuel will flow through the cross drilling in the barrel when air pressure is applied the plunger is pushed forward in the barrel opening the AFC in passage and allowing fuel to flow through the AFC on increase of air pressure the plunger moves even further eliminating the fuel restriction the shaped port AFC assembly contains a shaped passage instead of the cross drilling in the barrel the shape of the AFC in Port ensures that there is always some fuel flowing through the AFC advantages of shaped port dual spring AFC are better torque control below torque speed insensitivity to viscosity during cold engine start idle and response better transition curve the AFC assembly or no air adjusting screw fuel flows to the shutdown valve you most Chandon valves are controlled by an trickily operated solenoid in the shutdown mode a spring washer seats a disk preventing fuel flow out of the pump when the solenoid is energized the electromagnetic force that is created overcomes the force of the spring washer unseating the disk and permitting fuel to flow from the pump to the injectors you the main components of the PGD top stop injector include cup retainer filter screen adjustable orifice adapte Oh rings you injector Cup injector returned spring injector plunger washer don’t stop adjusting screw stopstop locknut injector link you check ball fuel Inlet bottle plunger metering edge metering orifice drain port

you’ll return the injector plunger is actuated by rotation of the camshaft injector lobe when the cam follower Ramallah is on the inner bass circle the injector returned spring has lifted the injector plunger uncovering the metering orifice you the period of time the metering orifice is uncovered is referred to as metering time you when the cam follower roller is on the outer base circle the downward movement of the injector plunger has overcome the injector return spring closed the metering orifice and injected the meter view into the combustion chamber the injector plunger is now seated in the injector Cup Phil entering the injector flows through a wire mesh filter screen and an adjustable orifice located beneath the filter screen the size of the adjustable orifice determines the flow rate through the injector and therefore the pressure at the metering orifice from the adjustable orifice fuel flows down an internally drilled passage on seating a check ball the purpose of the check bond is to prevent the reversal of fuel flow as the plunger moves downward across the metering orifice during deceleration and shutdown the time during which the metering edge uncovers the metering orifice is the time available for fuel to flow into the cup this begins as the cam-follower roller travels down the retraction ramp toward the inner base circle of the camshaft injector lobe as this occurs the injector returns spring lifts the injector plunger uncovering the metering orifice during this time flow through the drain port is blocked by the injector plunger metering of fuel occurs during the entire time the cam roller is on the inner base circle with continued camshaft rotation the cam roller travels up the injector ramp and the upward movement of the push rod pushes the injector plunger downward as the injector plunger moves downward it closes off the metering orifice completing the metering cycle shortly after the metering orifice is closed the drain port is uncovered the point at which the plunger makes contact with the fuel is determined by the volume of fuel in the cup with an increased fuel level the injector plunger contacts the fuel onlya thus advancing the beginning of injection finn’ll will be injected when the pressure exerted on the fuel by the downward movement of the injector plunger exceeds combustion chamber pressures injection ends when the plunger bottoms in the cup shortly before reaching the outer base circle of the injector lobe the roller travels over the cam nose which affects a positive ending of injection you with injunction completed and the injector plunger bottom in the cup the

cam roller is now on the unter base circle of the camshaft injector lobe while this is happening the drain groove on the injector plunger has aligned the drain passages in the injector barrel permitting fuel to flow out of the drain groove and return to the tank