Page 384 - Understanding Automotive Electronics
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2735 | CH 11  Page 371  Tuesday, March 10, 1998  1:30 PM



                                         FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS                            11




                                              Figure 11.2 is a block diagram of an engine control system that obtains
                                         the required feedback signal from a cylinder pressure sensor. An example of fuel
                                         control strategy using cylinder pressure is based on the relationship between air/
                                         fuel ratio and the cyclic fluctuation in cylinder pressure. Figure 11.3 is a graph
                                         of the fluctuation in peak cylinder pressure (θ pmax ) as a function of air/fuel
                                         ratio. This fluctuation remains relatively low for air/fuel ratios of approximately
                                         13 to 20. For leaner mixtures, the random fluctuations in cylinder pressure
                                         increase. Such fluctuations are equivalent to rough engine operation and are
                                         undesirable. In the example fuel control strategy, the air/fuel ratio is maintained
                                         near 20 and is reduced whenever the measured cycle fluctuation in cylinder
                                         pressure exceeds a threshold value.




                    Figure 11.2
                    Engine Control
                    System Based on
                    Cylinder Pressure
                    Measurements















                                                         FPO























                                         UNDERSTANDING AUTOMOTIVE ELECTRONICS                            371
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