1111 Spill Control

Figure 1.34 shows a cross-section of a rotary-type fuel injection pump. The high pressure pump chamber that produces the several hundred bars of pressure

Spill Control Valve Fuel Temp. Sensor

1st Gear Position Switch or

Neutral Start Switch

Intake Shuttter Intake Heater

Crankshaft Position Sensor

Accelerator Pedal Switch

Fig. 1.33 Computer controlled diesel engine system

1st Gear Position Switch or

Neutral Start Switch

Intake Shuttter Intake Heater

Crankshaft Position Sensor

Accelerator Pedal Switch

Fig. 1.33 Computer controlled diesel engine system

Engine ECU rDIJ

Engine ECU rDIJ

Rotary Type Injection Pump
Fig. 1.34 Rotary-type fuel injection pump

that operate the fuel injectors, has two outlet ports. One of these outlet ports connects to the solenoid-operated spill valve, and the other one connects to the port and pipe that supplies the injector. When the spill valve is opened by ECM signals to the solenoid, fuel from the feed pump enters the pressure chamber at a pressure of 15-20 bar, thus charging the high pressure pump element. When signals from the ECM to the solenoid cause the spill valve to close, the high pressure pump plungers will force the fuel through the outlet to operate the injector. When injection is completed, the ECM will again signal the solenoid to open the spill valve, ready for the next sequence. The electronic driving unit (EDU) contains a device that amplifies the 5 V computer pulse into a 150 V supply to operate the spill valve at high speed.

1.11.2 TIMING CONTROL

The timing control valve is a solenoid-operated hydraulic valve that directs a regulated supply of fuel to the plungers that rotate the high pressure pump cam ring, clockwise or anticlockwise, in order to advance or retard the injection point as required. The sensor inputs that are required for this operation are shown on Fig. 1.35.

1.11.3 IDLE SPEED CONTROL

The idling speed of a diesel engine is controlled by the amount of fuel that is injected into the cylinders. As the conditions under which the engine is required to idle vary, the computer program must be arranged to provide the correct fuelling to ensure a steady idling speed under all conditions. The inputs to the ECM that are shown in Fig. 1.36 give an indication of the sensor inputs that are

Fig. 1.35 Sensor inputs for the timing control valve
Fig. 1.36 Diesel engine idle speed control

required in order that the ECM can provide the correct signals to the spill control valve.

Another recent development in computer controlled diesel systems is the common rail system shown in Fig. 1.37. In this common rail system, the fuel in the common rail (gallery) is maintained at a constant high pressure. A solenoid-operated control valve that is incorporated into the head of each injector is operated by the ECM. The point of opening and closing of the injector control valve is determined by the ROM program and the sensor inputs. The injection timing is thus controlled by the injector control valve and the ECM. The quantity of fuel injected is determined by the length of time for which the injector remains open and this is also determined by the ECM.

1. Accelerator

2. Engine speed (crank)

3. Engine speed (cam)

4. Engine control module

5. Overflow valve

6. Fuel filter

7. High pressure pump

8. Pressure regulating valve

9. Plunger shut-off

10. Pressure limiting valve

11. Rail pressure sensor

12. Common rail

13. Flowlimiter

14. Injector

15. Sensor inputs

16. Actuator outputs

Fig. 1.37 The Rover 75 common rail diesel fuel system

1.12 Summary

As a result of this survey of computer controlled systems it is possible to see that electromagnetism, semiconductors, variable resistance, circuits and computers all figure prominently in the systems reviewed. This gives a lead to the types of background technology that is common to a range of systems. In the following chapters some of this background technology is examined in greater detail and in Chapter 7 there are examples of many tests that can be applied to aid fault diagnosis on computer controlled vehicle systems.

An important element in diagnostics on computer controlled systems is the self-diagnostic power of the computer and the fault codes that are created. This aspect is discussed in Chapters 2 and 3. However, fault codes are often just the beginning of a fault-finding task, and reading of the codes is often followed by a process of testing the performance of sensors and actuators and their interconnecting circuits. The range of systems reviewed in this chapter indicates that there is a body of knowledge about sensors and actuators that is applicable across a range of systems. The operating principles of sensors and actuators are examined in greater depth in Chapters 5 and 6 and once this basic knowledge has been acquired it can be used to advantage in the testing of many systems, as will be seen in Chapter 7.

1.13 Review questions (see Appendix 2 for answers)

1. The purpose of exhaust gas recirculation is:

(a) to reburn the exhaust gas?

(b) to reduce combustion temperature and reduce NOx emissions?

(c) to increase power output?

(d) to give better fuel economy?

2. A Hall effect sensor:

(a) generates electricity?

(b) shuts off current in the Hall element so that the signal voltage is zero when the magnetic field is blocked?

(c) gives an increase in signal current as the speed increases?

(d) is only used in ignition systems?

3. In an ABS system:

(a) the computer uses the peak-to-peak voltage from the wheel sensor to control braking?

(b) the computer compares frequencies from wheel sensors to help control braking?

(c) the warning light will go out when the vehicle speed reaches 50 km/h?

(d) the braking distance is greatly reduced in all conditions?

4. In sequential multi-point petrol injection systems there is one injection of fuel to each cylinder:

(a) on each stroke of the piston?

(b) each time a piston approaches TDC on the exhaust stroke?

(c) whenever hard acceleration takes place?

(d) when the knock sensor transmits a signal?

5. The manifold absolute pressure sensor is used in speed density fuel injection systems to:

(a) provide a signal that enables the ECM to calculate the amount of fuel entering the engine?

(b) provide a signal that enables the ECM to calculate the amount of air entering the engine?

(c) control the fuel pressure at the injectors?

(d) control the EGR valve?

6. An adaptive strategy:

(a) is a procedure that allows the ECM to set new values for certain operating variables as the system wears?

(b) is a limited operating strategy that allows the ECM to set values that will get a vehicle back to the workshop for repair?

(c) alters map values in the ROM?

(d) is a procedure for fault tracing?

7. In diesel engines:

(a) the fuel and air are mixed in the intake manifold?

(b) ignition is caused by glow plugs?

(c) the heat generated by compression causes combustion to take place?

(d) a mixture of fuel and air is forced into the cylinder by the injector?

8. In adaptive suspension systems:

(a) the ECM changes the damping rate to suit driving conditions?

(b) the steering angle sensor is fitted to the front wheel drive shafts?

(c) the system must not operate at speeds greater than 25 km/h?

(d) the ECM learns a new set of values if a suspension spring breaks?

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