petrol injection systems

8/14/2019 Petrol Injection Systems

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PETROL INJECTION SYSTEMSFuel injection principle is today being adopted more instead of the carburetor. The fuelpump, the injector pump and the injectors perform the functions of the carburetor. Fuel ismetered to the injectors which atomize it. This makes the fuel injected petrol similar to adiesel engine. However unlike the diesel engine it retains the usual electrical ignitionsystem.

The injection takes place before or during the induction stroke, not towards the end ofcompression stroke as on the diesel engine. Fuel injection systems can be controlledmechanically or electronically.

Fuel can be injected directly into the cylinder or into the intake manifold or port.

Advantages of the fuel injection

1 park ignition achieve better filling as result of improved layout of intake passages.

! The mi"ture proportions are more uniform and suitable for momentary operatingconditions throughout the engine speed range. This makes it possible to boost output perlitre, increase tor#ue at low speeds and achieve reduction in specific fuel consumption.

$. The engines pick up from idling speed and its fle"ibility also improves as does coldstarting.

%. fuel injection engines accelerate and slow down better, since fuel injection systemreacts more rapidly and smoothly to throttle movements &accelerating and decelerating '.

(. less fuel is needed to accelerate, since the injected fuel is available immediately, withno time lag in its flows compared to air flow.

). *n the overrun, e.g. + towns and when descending gradients, the fuel supply can be cutoff completely by the control unit to save fuel and reduce e"haust emissions.

T!es of !et"ol injection sste#s$

Mechanical injection sste#

%&jet"onicis a mechanical injection system. This drive less system injects the fuel in acontinuous process.

Co#'ined #echanical and elect"onic injection sste#$

-jetronic is an e"panded version of the basic jetronic system. +t monitors ane"tended range of operating data that provide a more precise fuel metering under varyingengine operating conditions.

Elect"onic injection sste#

-lectronically controlled injection system use electromagnetic injectors to inject the fuelintermittently.

-"amples.

/jetronic, /Hjetronic, and 0onojetronic or 0otronics petrol injection systems are furthercategorized as &a' inglepoint fuel injection system, and

&b' 0ultipoint fuel injection system.

Single&!oint fuel injection sste#$

various single point injection systems differ in design of the centralinline injection unit.

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ll systems are similar in an injector located above the throttle plate.

They differ from multipoint due to the fact that they operate at low pressures & 2.3 bar to1.2 bar'. This means that a single hydrodynamic electric fuel pump can be used, which isgenerally installed in the fuel tank.

Mono&jet"onic0onojetronic is an electronically controlled, low pressure single point injection system for% cylinder engines featuring a centrally located solenoid 4controlled fuel injector. at theheart of the system is a central injection unit, which uses the throttle valve to meter theintake air while injecting the fuel intermittently above the throttle valve. The intake manifoldthen distributes the fuel to the individual cylinders. 5arious sensors monitor all importantengine operating data6 these are used to calculate the control signals for injectors andother system actuators.

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Cent"al injection unit$

The injector is located above the throttle, in the intake air path, in order to ensurehomogenous mi"ture and consistent cylinder to cylinder distribution. The spray pattern isdirected into the sickle 4shaped orifice between the housing and the throttle plate, wherethe high pressure differential promotes optimum mi"ture formation to inhibit fuelaccumulation on the walls of the intake tract.

-fficient fuel atomisation ensures consistently good mi"ture distribution even in the criticalfull load range. +njector firing is synchronized with the ignition pulses.

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Sste# cont"ol$

+n addition to engine speed, other actuating variables for the injection system include6

&a' ir volume7air mass flow

&b' absolute manifold pressure

&c' throttle position 7throttle valve angle

&d' -ngine and intake air temperature

&e' 8esidual o"ygen content of the e"haust gas & depending on the engine condition '

&f' utomatic transmission, air condition setting and account compressor clutch status&engaged or disengaged '.

Thus the sensors maintain a precise operation throughout the lifetime of the system.

Ada!tation (unctions

9ertain operating states will cause the fuel re#uirements deviate considerably from there#uired by a stationary engine at normal operating temperatures.

Cold Sta"ts

:uring cold starts, the relative amount of fuel in the mi"ture decreases6 the mi"ture ;goeslean


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Post&sta"t !hase$

fter starts at low temperatures supplementary fuel must be provided to enrich the mi"tureuntil the combustion chamber heats up and the mi"ture formation within the cylinderimproves. The richer mi"ture also increases tor#ue to provide a smoother transition todesired idle speed.

-a"#&u! !hase$

The starting and poststart are followed by the engines warmup phase. +n this phase theengine re#uires a richer mi"ture as the cylinder walls are still cool and a portion of the fuelcontinues to condense on them. ince the #uality of mi"ture formation drops along withfailing temperatures &due to less effective mi"ing of air and fuel and large fuel droplets '.9ondensation forms in the intake manifold, where it remains until it is vaporized astemperature increase. These factors make it necessary to provide progressive mi"tureenrichment in response to decreasing temperatures.

Pa"t th"ottle o!e"ation

:uring part throttle operation priority is assigned to adjusting the mi"ture for minimum fuelconsumption.

(ull th"ottle o!e"ation$

=hen the throttle valve has opened to the ma"imum, the engine should respond byproviding its ma"imum tor#ue7output. This necessitates the enriching of the air fuelmi"ture.

Accele"ation$

=hen the throttle valve opens suddenly the air fuel mi"ture responds by leaning outbriefly. This is due to the fuels restricted vaporization potential at higher manifold vacuumlevels &increasing tendency to form fuel layers on intake tract walls.

To obtain good transition response, the mi"ture must be enriched by an amount whichvaries according to engine temperature. This enrichment provides good accelerationresponse.

T"ailing th"ottle .ove""un /o!e"ation

The fuel metering process can be interrupted on trailing throttle to reduce fuelconsumption during descents and under braking. nother advantage is the fact that noharmful e"haust emissions are generated in this operating mode.

0igh altitude adjust#ents

+ncrease in altitude & as e"perienced in alpine conditions ' are accompanied by a reductionin air density. This means that the intake being drawn into the engine at high altitudesdisplays a lower mass per unit volume. system which fails to adjust the mi"tureaccordingly will supply an e"cessively rich mi"ture and the ultimate result will be higherfuel consumption and increased e"haust emissions.

M*LTI&POINT (*EL&INJECTION SYSTEM$

%&JETRONIC

O!e"ating !"inci!le

9ontinuous injection.

:irect air flow measurement.

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jetronic is a mechanical system which does not re#uire an engine driven injection pump.+t meters a continuous supply of fuel proportional to the amount of air drawn into theengine. >ecause the jetronic system incorporates direct air flow measurement, it candetect changes caused by the engine allowing its use with emission control e#uipmentsre#uiring precise intake air monitoring

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O!e"ation

+ntake air flows through the air filter, the air flow sensor and the throttle valve beforeentering the intake manifold and continuing to the individual cylinders.

The fuel is delivered from the fuel tank by an electric &rollercell' fuel pump. +t then flowsthrough a fuel accumulater and the fuel filter to the fuel distributer, where the pressureregulator maintains a constant system pressure. The fuel flows from the distributer to the

injectors. -"cess fuel not re#uired by the engine is returned to the tank.Mi2tu"e cont"ol unit$

The mi"ture control unit consists of the air 4flow sensor and the fuel distributer.

Ai"flo3 senso"$

The flow sensor consists of an air funnel and a pivoting air flow sensor plate.9ounterweight compensates for the weight of the sensor plate and pivot assembly. Thesensor plate is displaced by the air flow while the control plunger in the fuel distributore"erts hydraulic counter pressure to maintain the system in a balanced state. The positionof the air flow sensor provides an inde" of intake air flow and is transmitted to the fuel

distributor?s control plunger by a lever.

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(uel dist"i'uto"$

The amount of fuel distributed to the individual cylinders, is regulated by varying theaperture of the metering slots in the fuel distributer barrel. The number of regulatorshaped metering slots in the barrel corresponds to the number of engine cylinders.

The specific size of the metering slot aperture depends on the control plunger?s position inorder to ensure constant pressure drop at the slots for various flow rates, a differentialpressure regulator is located downstream of each metering slot.

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Injecto"$

The injector opens automatically at a pressure of appro"imately $.@ bar and has nometering function.

-a"#& u! "egulato"$

=arm 4up regulator is controlled by an electrically 4heated bimetallic element6 it enrichesthe mi"ture in the warmup phase by reducing the counter pressure e"erted against thecontrol plunger. reduction in the control pressure means that the stroke of the air flowsensor plate for a given airflow increases &reflecting the larger metering slot aperture '.The result is a richer mi"ture during warm up

=here desired the warmup regulator can be e"panded to incorporate the followingfunctions6

Full throttle enrichment,

cceleration enrichment,

ltitude compensation

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Au2ilia" ai" valve$

+t controlled by either a bimetallic spring or an e"pansion element, supplies the enginewith additional air &which is monitored by the air flow sensor but bypasses the throttlevalve ' during warm up phase. This supplementary air compensates for the cold engine?shigher friction loses6 it either maintains the normal idle speed increases it in order to heatthe engine and e"haust more #uickly.

Elect"ic sta"t valve$

The thermotime switch activates the electric start valve according to engine temperatureand elapsed time. :uring low temperature starts, the start valve injects supplementary fuelinto the intake manifold &cold start enrichment '

La#'da #i2tu"e cont"ol$

*penloop control systems do not regulate the air 7 flow ratio with enough accuracy toallow compliance with stringent emission limits.

=hen lambda closed loop controls & re#uired for operation of the three way catalyticconverter ' is installed, the jetronic system must include an electronic control unit whichuses the lambda &*!' sensor?s signal as its main input variable.

s solenoid fre#uency valve regulates the mi"ture ratio by controlling the pressuredifferential at metering slots. However this principle cannot be applied to meet morestringent emission re#uirements scheduled for the future.

%E JETRONIC

-jetronic is an advanced version of the jetronic system. -jetronic includes an

-.9.A. for increased fle"ibility and supplementary functions. The additional componentsincludeB

a sensor for intake air flow,

a pressure actuator for mi"ture ratio adjustment, and

a pressure regulator which maintains system pressure at constant level as well as

providing a fuel cutoff function when the engine is switched off

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O!e"ation$

n electric fuel pump generates the system pressure. The fuel flows through the fueldistributor, while a diaphragm regulator maintains the system pressure at constant level.=ith jetronic, the control circuit performs mi"ture corrections via warm up regulator. +ncontrast, with the -jetronic the primary and the pressure e"erted upon the controlplunger are e#ual. The ratio is corrected by adjusting the pressure differential in all the fueldistributor chambers simultaneously.

The system pressure is present upstream from the metering slots and applies a counterpressure to the control plunger. s with the jetronic the control plunger is moved by anair flow sensor flap. damper unit prevents the oscillations that could be induced by theforces generated at the sensor flap. From the control plunger the fuels flow through the

pressure actuator, the lower chambers of the differential pressure valve, a fi"ed flowrestrictor and the pressure regulator before returning to the fuel tank. Together with theflow restrictor, the actuator forms a pressure divider in which the pressure can be adjustedelectrodynamically. This pressure is present in the lower chambers of the differentialpressure valve.

pressure drop corresponding to actuator current occurs between its two connections.This causes variations in the pressure differential at the metering slots and alters theamount of fuel injected. The current can be reversed to shut down the fuel supplycompletely. This feature can be employed for such function as overrun fuel cut off andengine speed limitations.

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Advantages of %E&Jet"onic$

+$ Lo3 fuel consu#!tion$

=ith conventional fuel management systems, the differences in the length of the intakepassages results in different airfuel mi"tures at individual cylinders.

=ith -jetronic injection system, each cylinder is allocated its own fuel injection valvewhich injects continually onto the intake valve. The injected fuel vapourises and mi"esintensively with the air drawn in by the piston. This means that in addition to precisemetering, the fuel is evenly distributed between the individual engine cylinders. ince theintake manifold serve only to carry intake air into the cylinders, the condensation of thefuel on the manifold walls, a phenomenon in conventional systems, which increases thefuel consumption is practically ruled out.

The -jetronic system ensures that considerably less fuel is used, particularly duringwarm up phase, during acceleration enrichment, at full load and during overrun when itswitches off the fuel supply.

,$ Ada!tation to o!e"ating conditions$

Fuel re#uirements differs greatly from the normal figures during the post start period,during warm up and during acceleration and fullload.

>y means of commands received from its -.9.A. &electronic control unit' the - jetronicintervenes in the preparation of air fuel mi"ture and increases or decreases the injectedfuel accordingly.

The -jetronic system incorporates additional sensors for detecting the enginetemperature, throttle valve position &load signal' and the sensor plate deflection&corresponding appro"imately to the change in engine power as a function of time'. =ith

the aid of these sensors, the -.9.A. commands the hydraulic pressure actuator to either;lean off< the mi"ture or ;enrich ; it as appropriate.

The -jetronic responds rapidly to the variations in the engine operating condition, andimproves the tor#ue characteristics as well as the engine fle"ibility. This results in distinctadvantages when driving at energy efficient low engine speeds and in as high gear aspossible and also improvement of drivability. 8eliable starting is another of the outstandingfeatures of the -jetronic system. The smooth overrun fuel cutoff responds to enginespeed and temperature and cut off the supply of fuel during deceleration. There are nounpleasant jerks when the fuel supply cuts back in again. This system results in areduction of the fuel consumption and, since ,combustion ceases during fuel cut off there

is no emission of to"ic gases.1$ Cleane" e2haust gases$

re#uirement for minimum pollutants in the e"haust gas is a complete combustion of thefuel as possible. The -jetronic supplies each cylinder with precisely the amount of fuelappropriate for the particular engine operating condition and for changes in loading. Forinstance the re#uired air fuel mi"ture is precisely maintained at the level necessary forminimum to"ic emissions by reducing the post start enrichment as soon as possible, or byrapid response of the acceleration enrichment function. Further improvement in thee"haust gas can be achieved by employing lambda closed loop control together withe"haust 4gas after treatment using catalyst converter.

6$ 0ighe" !o3e" out!ut$

The efficiently designed air intake system of the -jetronic permits increase in power dueto improved cylinder change. The fuel injection path are shorter, with the result that there

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P"inci!le of ai" flo3 senso"$

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& 1 s m a l l a m o u n t o f a i r i s

d r a w n i n Bs e n s o r p l a t e i s l i f t e d s l i g h t l y .

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& / a r g e a m o u n t o f a i r i s

d r a w n i n B s e n s o r p l a t e i sl i f t e d c o n s i d e r a b l y f u r t h e r

o!e"ation$

The air flow sensor is located upstream of the throttle valve so that it measures all the airwhich enters the engine cylinders.

The air flow sensor comprises of an air funnel in which the sensor flap &suspended body'is free to pivot. The air flowing through the funnel deflects the sensor plate by a given

amount out of its zero position.

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The movements of the sensor plate are transmitted by a lever system to a control plungerwhich determines the basic injection #uantity re#uired for the basic functions.

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9onsiderable pressure shocks can occur in the intake system if backfiring takes place inthe intake manifold. For this reason the air flow sensor is so designed that the sensorplate can swing back in the opposite direction in the event of misfiring and past its zeroposition to open a relief crosssection in the funnel.

rubber buffer limits the downward stroke &upward stroke on the down 4draft air flowsensor'

counter weight compensates for the weight of the sensor plate and lever system &thisis performed by means of an e"tension spring on the downdraft air flow sensor.'

n adjustable leaf spring is fitted to ensure the correct zero position in the switched offphase.

(uel dist"i'uto"$

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:epending upon the position of the plate in the air flow sensor, the fuel distributer metersthe basic injection #uantity to the individual engine cylinders. The position of the sensorplate is a measure of the amount of the air drawn in by the engine. The position of theplate is transmitted to the control plunger by a lever. :epending upon the position in thebarrel with metering slits to a greater or lesser e"tent. The fuel flows through the opensections of these slits to the differential pressure valves and then to the fuel injectionvalves &see Figure @'.

+f the sensor plate travel is only very small, the control plunger is lifted only slightly, and asa result only a very small section of the slit is opened for the passage of fuel.

*n the other hand, with a larger plunger travel, the plunger opens a larger section of theslits and more fuel can flow.

hydraulic force is applied to the control plunger and acts in opposition to the movementresulting from the sensor plate deflection. constant airpressure drop at the sensor plate

is the result and this ensures that the control plunger always follows the movement of thesensor plate lever.

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9iffe"ential !"essu"e

The differential pressure valve in the fuel distributer serve to generate given pressure dropat the metering slits. The air flow sensor has a linear characteristic. This means that ifdouble the #uantity of air is drawn in, the sensor plate travel is also doubled. +f this &linear'

travel is to result in a change of basic injection #uantity in the same relationship, then aconstant pressure drop must be guaranteed at the metering slits regardless of the amountof the fuel flowing through them.

The differential pressure valve maintain the drop in pressure between the upper and lowerchambers constant, regardless of the fuel passing through.

Mi2tu"e fo"#ation$

The formation of the air fuel mi"ture takes place in the intake ports and cylinders of theengine.

The continually injected fuel coming from the injection valves is ;stored< in front of theintake valves. =hen the intake valves is opened, the air drawn in by the engine carries thewaiting ;cloud ; of fuel with it into the cylinder. n ignitable air fuel mi"ture is formed duringthe induction stroke due to swirl effect.

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L& JETRONICS

O!e"ating !"inci!les

ir flow measurements

0ain actuating variablesB air flow and engine speed.

+ntermittent injection.

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/jetronic combines the advantages of direct air flow measurement with the uni#uepossibilities afforded by electronics. +t is similar to jetronic in that it recognizes allchanges in engine conditions &due to wear, combustion chamber deposits, changes in

valve clearances' to ensure consistently good e"haust gas composition.

O!e"ation

The fuel is injected through a solenoid operated injectors. solenoid valve assigned toeach cylinder is triggered once per crankshaft revolution. ll the injectors are wired inparallel to reduce the comple"ity of electrical circuit. The differential between fuel andmanifold and manifold pressures is maintained at a constant levels of !.(or $.2 bars, thusthe amount of discharged fuel is determined e"clusively by pulse duration specified by the-. 9. A. Dulse duration varies according to intake air flow, engine speed and otherparameters monitored by the sensors for processing in the -9A.

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Th"ottle S3itch$

This transmits a control signal to the -9A when the throttle valve is either completelyclosed &idle' or fully open &full throttle'.

Engine te#!e"atu"e senso"$

The engine temperature sensor is designed as temperaturesensitive resister &thermister'and controls the warmup enrichment.

Au2ilia"&ai" valve< Elect"ic sta"t valve< The"#o&ti#e s3itch$

The design and function are similar to those of the corresponding jetronic components.

Elect"onic Cont"ol *nit .EC*/$

This -9A converts the engine variables into electrical pulses. The transmission intervalsfor these pulses are correlated with ignition timing , while their duration is basically afunction of speed and intake air flow. ince all injected are activated simultaneously only asingle driver stage is re#uired. The temperature sensors respond to lower engine and air

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temperature by increasing the injection duration. The throttle switch signals allows mi"tureadaptation for idle and full throttle operation.

La#'da closed&loo! cont"ol$

The -9A compares the signal from the lambda &*!' sensor with a set point value before

activating a two state controller. The control adjustment is then performed as are allcorrections by modifying the injection duration.

L0&JETRONIC

(I)*RE$ ++/HEetronic is closely related to /Eetronic, the main difference being the method of intakeairflow measurement. =ith /HEetronic using a hotwire mass airflow sensor to measurethe mass of intake air. Thus the result no longer depend on the air density, which varieswith temperature and pressure. The other /HEetronic components and the basic systemconcept are to a large e"tent the same in /Eetronic.

O!e"ating data !"ocessing in the EC*$

/HEetronic is e#uipped with a digital -9A. rrangement for adjusting the mi"ture ratiovary from those used with /Eetronic in using a load7engine speed map programmed forminimum fuel consumption and e"haust emissions. The -9A processes the sensorsignals when calculating the injection durations that determines the injection #uantity. The-9A includes a microprocessor, program and data memories. The microprocessor isprovided with a suitable voltage supply and with a stable clock rate for data processing.

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0ot&3i"e ai"ass flo3 senso"

The steam of intake air to the engine is conducted past a heated wire &hot wire' formingpart of an electrical bridge circuit. The flow if current through the wire serves to maintain itat constant temperature above that of the intake air. This principle makes it possible toemploy current re#uirement as an inde" of the air mass being drawn into the engine. Theresistor converts the heating current into a voltage signal, which the -9A then processesalong with the engine speed as the main input variable. The temperature sensor ismounted in the hotwire airmass flow sensor to ensure that its output signal is notinfluenced by the temperature of the intake air. The idle mi"ture can be adjusted with apotentiometer. s contamination on the surface of the surface of the hot wire could affectthe output signal, each time the engine is shut down the wire is electrically heated for onesecond to burn off any contamination. The hotwire airmass flow sensor has no movingparts and its aerodynamic resistance with in the intake tract is negligible.

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petrol injection systems

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