332 Automobile electrical and electronic systems

Figure 9.65 Injector(Source:Bosch Media)

The quantity of fuel that is metered for injection at any time is computed bythe engine ECU, which sends signals to the injection-pump ECU for controlof the high-pressure solenoid valve. The electrical current for operating thisvalve is high and the two electronic control units are separated, in order toavoid high current interference, in the more electronically vulnerable engineECU.

The electronic diesel control units are provided with data signals from sensorsand switches attached to the engine, the pump and other vehicle systems. Thesensors are used for comparisons to programmed operating parameters andfor calculations for metering the amount of fuel delivered and for controlling theinjection advance.

Injection advance is obtained by rotation of the cam ring by pump body pressurein the injection advance mechanism. The injection advance mechanism consistsof a transverse timing device piston and control components and an electricalsolenoid valve. Maximum advance is 40° of crankshaft rotation.

A needle motion sensor in the injector sends a signal to the engine ECU atthe instant of opening of the injector (Figure 9.65). This point, relative to thecrankshaft rotational angle before top dead centre, is used for load and speedinjection timing calculations and for control of the exhaust gas recirculation valve.

The Bosch, VR electronic diesel control system, uses a number of sensors andcontrol actuators. This allows it to achieve optimum performance. However, eventhis sophisticated system has virtually been superseded by the common railinjection.

9.6.6 Common rail systemThe development of diesel fuel systems is continuing, with many new electronicchanges to the control and injection processes. One of the most significant is theCR 'common rail' system, which operates at very high injection pressures. It alsohas piloted and phased injection to reduce noise and vibration.

The common rail system has made it easier for small high speed diesel enginesto have all the advantages of direct injection. These developments have resultedin significant improvements in fuel consumption and performance.

Fuel control 315

Injector

Fuel filter

Bectricfuel pump

Electroniccontrol unit

Figure 9.40 LH-Jetronic

LU-Jetronic

This system is a further refinement of the LE systems but also utilizes closed looplambda control.

L3-Jetronic

The ECU for the L3-Jetronic forms part of the air flow meter installation. TheECU now includes a 'limp home' facility. The system can be operated with orwithout lambda closed loop control. The air-fuel ratio can be adjusted by ascrew-operated potentiometer on the side of the ECU.

LH-Jetronic

The LH system incorporates most of the improvements noted above. The maindifference is that a hot-wire type of air flow meter is used. The component layoutis shown in Figure 9.40. Further developments are continuing but, in general,most systems have now developed into combined fuel and ignition controlsystems as discussed in the next chapter.

9.5.5 Bosch Mono Jetronic - single point injectionThe Mono Jetronic is an electronically controlled system utilizing just one injectorpositioned above the throttle butterfly valve. The throttle body assembly is similar

314 Automobile electrical and electronic systems

9.5.4 Bosch 'L' Jetronic - VariationsOwing to continued demands for improvements, the 'L' Jetronic system, alongwith all other injection systems, developed and changed over the years. Thissection will highlight the main changes that have taken place.

L2-Jetronic

This system is changed little except for the removal of the injector series resistorsas the ECU now limits the output current to the injectors. The injector resistanceis 16 Q.

I I

LE1-Jetronic

No current resistors are used and the throttle switch is adjustable. The fuel pumpdoes not have safety contacts in the air flow sensor. The safety circuit is incor-porated in the electronic relay. This will only allow the fuel pump to operate whenan ignition signal is present; that is, when the engine is running or being cranked.

LE2-Jetronic

This is very similar to the LE1 systems except the thermo-time switch and coldstart injector are not used. The ECU determines cold starting enrichment andadjusts the injector open period accordingly.

Injector

a\Throttlepositionswitch

Fuel filter

Electroniccontrol unit

Electric fuel pump

Figure 9.39 L-Jetronic

Fuel control

Manifoldpressure

~Fuelinletf---=:=-l

o Fuel outlet

Figure 9.35 Pressure regulator

Battery supplywhen engine isbeing cranked

Cold startinjector

Earthcontacts --

Figure 9.36 Typical cold start arrangement

Combination relay (Figure 9.37)

This takes many forms on different systems but is basically two relays, one tocontrol the fuel pump and one to power the rest of the injection system. Therelay is often controlled by the ECU or will only operate when ignition pulsesare sensed as a safety feature. This will only allow the fuel pump to operate whenthe engine is being cranked or is running.

Electronic control unit (Figure 9.38)

Earlier ECUs were analogue in operation. All ECUs now in use employ digitalprocessing.

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Figure 9.37 Combination relay

Figure 9.38 Electronic control unit

III I II

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312 Automobile electrical and electronic systems

Key factThe pump ensures a constantsupply of fuel to the fuel rail.

In Itt-'1l1.JI.L Magneticcircuit

Pintle

Figure 9.33 Fuel Injector

Pressure relief valve

IArmature

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,Roller-cell pump

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Check valve

Figure 9.34 Fuel pump (high pressure)

Fuel pump (Figure 9.34)

The pump ensures a constant supply of fuel to the fuel rail. The volume in therail acts as a swamp to prevent pressure fluctuations as the injectors operateThe pump must be able to maintain a pressure of about 3 bar.

Fuel pressure regulator (Figure 9.35)

This device ensures a constant differential pressure across the injectors. It ismechanical device and has a connection to the inlet manifold.

Cold start injector and thermo-time switch (Figure 9.36)

An extra injector was used on earlier systems as a form of choke. This workin conjunction with the thermo-time switch to control the amount of coldenrichment. Both engine temperature and a heating winding heat it. Thistechnique has been replaced on newer systems, which enrich the mixture byincreasing the number of injector pulses or the pulse length.

Figure 9.28 Crank sensor in position

Figure 9.30 Throttle position sensors

Fuel control

Figure 9.29 Coolant temperature sensor

Lambda sensor (Figure 9.31)

This device provides information to the ECU on exhaust gas oxygen content.From this information, corrections can be applied to ensure the engine is kept ator very near to stoichiometry. Also shown in this figure is a combustion chamberpressure sensor.

Idle or fast idle control actuator (Figure 9.32)

Bimetal or stepper motor actuators are used but the one shown is a pulsedactuator. The air that it allows through is set by its open/close ratio.

Fuel injector(s) (Figure 9.33)

Two types are shown - the pintle and disc injectors. They are simple solenoid-operated valves designed to operate very quickly and produce a finely atomizedspray pattern.

Injector resistors

These resistors were used on some systems when the injector coil resistancewas very low. A lower inductive reactance in the circuit allows faster operationof the injectors. Most systems now limit injector maximum current in the ECUin much the same way as for low resistance ignition on coils.

311

Figure 9.31 Lambda sensor in theexhaust down pipe

Figure 9.32 Rotary idle actuator