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首页Understanding Automotive Electronics 8th - Chapter 4
Understanding Automotive Electronics 8th - Chapter 4
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Engine control in the vast majority of engines means regulating fuel and air intake and spark timing to achieve desired performance in the form of power output. Until the 1960s, control of the engine output torque and RPM was accomplished through some combination of mechanical, pneumatic, or hydraulic systems. Then, in the 1970s, electronic control systems were introduced.
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CHAPTER
THE BASICS OF ELECTRONIC
ENGINE CONTROL
4
CHAPTER OUTLINE
Motivation for Electronic Engine Control .............................................................................................. 136
Exhaust Emissions ............................................................................................................................. 136
Fuel Economy .................................................................................................................................... 137
Federal Government Test Procedures .................................................................................................. 137
Fuel Economy Requirements ................................................................................................ 140
Meeting the Requirements ................................................................................................... 141
The Role of Electronics ........................................................................................................ 141
Concept of an Electronic Engine Control System .................................................................................. 142
Inputs to Controller .............................................................................................................. 144
Output from Controller ......................................................................................................... 145
Basic Principle of Four-Stroke Engine Operation .................................................................... 146
Definition of Engine Performance Terms .............................................................................................. 150
Torque ................................................................................................................................ 150
Power ................................................................................................................................. 153
Fuel Consumption ............................................................................................................... 154
Engine Overall Efficiency ..................................................................................................... 156
Calibration .......................................................................................................................... 156
Engine Mapping .................................................................................................................. 157
Effect of Air/Fuel Ratio on Performance ................................................................................. 157
Effect of Spark Timing on Performance ................................................................................. 158
Effect of EGR on Performance .............................................................................................. 159
Exhaust Catalytic Converters .............................................................................................................. 161
Oxidizing Catalytic Converter ................................................................................................ 161
The Three-Way Catalyst ........................................................................................................ 162
Electronic Fuel Control System ........................................................................................................... 164
Engine Control Sequence ..................................................................................................... 166
OL Control .......................................................................................................................... 167
CL Control .......................................................................................................................... 167
CL Operation ....................................................................................................................... 169
Understanding Automotive Electronics. http://dx.doi.org/10.1016/B978-0-12-810434-7.00004-1
Copyright # 2017 Elsevier Inc. All rights reserved.
135
Analysis of Intake Manifold Pressure .................................................................................................. 172
Measuring Air Mass ............................................................................................................. 173
Influence of Valve System on Volumetric Efficiency ................................................................ 175
Idle Speed Control ............................................................................................................................. 176
Electronic Ignition ............................................................................................................................. 181
Engine control in the vast majority of engines means regulating fuel and air intake and spark timing to
achieve desired performance in the form of power output. Until the 1960s, control of the engine output
torque and RPM was accomplished through some combination of mechanical, pneumatic, or hydraulic
systems. Then, in the 1970s, electronic control systems were introduced.
This chapter is intended to explain, in general terms, the theory of electronic control of a gasoline-
fueled, spark-ignited automotive engine. Cha pter 6 explain s practical digital control methods and sys-
tems. The examples used to explain the major developments and principles of electronic control have
been culled from the techniqu es of various manufacturers and do not necessarily represent any single
automobile manufacturer at the highest level of detail. Moreover, Chapter 6 presents major improve-
ment in electronic control of the entire power train. However, the most basic aspects of engine control
are presented in this chapter in preparation for the detailed explanation of contemporary engines.
MOTIVATION FOR ELECTRONIC ENGINE CONTROL
The initial motivation for electronic engine control came, in part, from two government requirements.
The first came about as a result of legislation to regulate automobile exhaust emissions under the
authority of the Environmental Protection Agency (EPA). The second was a thrust to improve the
national average fuel economy by government regulation. The issues involved in these regulations
along with normal market forces continue to motivate improvements in reduction of regulated gases
and fuel economy. Electronic engine control is only one of the automotive design factors involved in
fuel economy improvements. However, this book is only concerned with the electronic systems.
EXHAUST EMISSIONS
Although dies el engines are in common use in heavy trucks, railroads, and some pickup trucks, the
gasoline-fueled engine is the most commonly used engine for passenger cars and light trucks in the
United States. This engine is more precisely termed the gasoline-fueled, spar k-ignited, four-stroke/
cycle, normally aspirated, liquid-cooled internal combustion engine. It is this engine, which is denoted
the SI engine, that is discussed in this book. The following discussion of exhaust emission regulations
applies to the SI engine.
The engine exhaust consists of the products of combustion of air and gasoline mixture. Gasoline is a
mixture of chemical compounds that are called hydrocarbons. This name is derived from the chemical
formation of the various gasoline compounds, each of which is a chemical union of hydrogen (H) and
carbon (C) in various proportions. Gasoline also contains natural impurities and chemicals added by the
refiner. All of these can produce undesirable exhaust elements. The combustion of gasoline in an en-
gine results in exhaust gases, including CO
2
,H
2
O, CO, oxides of nitrogen, and various hydrocarbons.
136 CHAPTER 4 THE BASICS OF ELECTRONIC ENGINE CONTROL
During the combustion process, the carbon and hydrogen combine with oxygen from the air, releas-
ing heat energy and forming various chemical compounds. If the combustion were perfect, the exhaust
gases would consist only of carbon dioxide (CO
2
) and water (H
2
O), neither of which is considered
harmful to human health in the atmosphere. In fact, both are present in an animal’s breath.
Unfortunately, the combustion of the SI engine is not perfect. In addition to the CO
2
and H
2
O, the
exhaust contains amounts of carbon monoxide (CO), oxides of nitrogen (chemical unions of nitrogen
and oxygen that are denoted NOx), unburned hydrocarbons (HC), oxides of sulfur, and other compounds.
Some of the exhaust constituents are considered harmful and are now under the control of the federal
government. The exhaust emissions controlled by government standards are CO, HC, and NOx.
Automotive exhaust emission control requirements began in the United States in 1966 when the
California state regulations became effective. Since then, the federal government has imposed emission
control limits for all states, and the standards became progressively tighter throughout the remainder of
the twentieth century and will continue to tighten in the 21st century. Auto manufacturers found that the
traditional engine controls coul d not control the engine sufficiently to meet these emission limits and
maintain adequate engine performance at the same time, so they turned to electronic controls.
FUEL ECONOMY
Everyone has some idea of what fuel economy means. It is related to the number of miles that can be
driven for each gallon of gasoline consumed. It is referred to as miles per gallon (MPG) or simply
mileage. In addition to improving emission control, another important feature of electroni c engine
control is its ability to improve fuel economy.
It is well recognized by layman and experts alike that the mileage of a vehicle is not unique. Mileage
depends on the size, shape, and weight of the car and how the car is driven. The best mileage is achieved
under steady cruise conditions. City driving, with many starts and stops, yields worse mileage than
steady highway driving. In order to establish a regulatory framework for fuel economy standards,
the federal government has established hypothetical driving cycles that are intended to represent
how cars are operated on a sort of average basis.
The government fuel economy standards are not based on one car but are stated in terms of the
average rated MPG fuel mileage for the production of all models by a manufacturer for any year. This
latter requirement is known in the automotive industry by the acronym CAFE or corporate average fuel
economy. It is a somewhat complex requirement and is based on measurements of the fuel used during
a prescribed simulated standard driving cycle.
FEDERAL GOVERNMENT TEST PROCEDURES
For an understanding of both emission and CAFE requirements, it is helpful to review the standar d
cycle and how the emission and fuel economy measurements were made in the earliest days of emission
control. The US federal government published test procedures that included several steps. The first step
was to place the automobile on a chassis dynamometer, like the one shown in Fig. 4.1.
In many states, the government requires a year ly measurement of exhaust emissions with the ve-
hicle placed on a chassis dynamometer and operated with a specific set of load and speed conditions
137FEDERAL GOVERNMENT TEST PROCEDURES
simulating normal vehicle operation. A chassis dynamometer is a test stand that holds a vehicle such as
a car or truck. It is equipped with instruments capab le of measuring the power that is delivered at the
drive wheels of the vehicle under various conditions. The vehicle is held on the dynamometer so that it
cannot move when power is applied to the drive wheels. The drive wheels are in contact with two large
rollers. One roller is mechanically coupled to an electric generator that can vary the load on its elect ric
output. The other roller has instruments to measure and record the vehicle speed. The generator absorbs
and provides a measurement of all mechanical power that is delivered at the drive wheels to the
dynamometer. The power is calculated from the electric output in the correct units of kW or hp (horse-
power where 1 hp ¼0.746 kW). The controls of the dynamometer can be set to simulate the correct load
(including the effects of tire rolling resistance and aerodynamic drag) and inertia of the vehicle moving
along a road under various conditions. The conditions are the same as if the vehicle actually was being
driven except for wind loads.
The vehicle is operated according to a prescribed schedule of speed and load to simulate the spec-
ified trip. One driving cycle simulates an urban trip, and another simulates a highway trip. Over the
years, the hypothetical driving cycles for urban and rural trips have evolved. Fig. 4.2 illustrates sample
FIG. 4.1 Chassis dynamometer.
138 CHAPTER 4 THE BASICS OF ELECTRONIC ENGINE CONTROL
60
50
40
30
20
10
0
60
50
40
30
20
10
0
0 200
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Time (s)
(A)
(
B
)
Car speed (min/h)
Car speed (min/h)
Time (s)
400 600
0 200 400 600 765
800 1000 1200 1372
FIG. 4.2 Federal driving schedules (Title 40 US Code of Federal Regulations). (A) Urban and (B) Highway.
139FEDERAL GOVERNMENT TEST PROCEDURES
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