# mechatronics in cars petrol engine



## ahmed moawia (3 أبريل 2011)

_Electronic Control Unit ECU_



The Electronic Control Unit (ECU) or Electronic Control Module
(ECM) and sometimes also know as the automobile's ‘Fuel Computer’
or ‘Brain Box’, is an electronic computer that regulates the amount of
fuel that your vehicle's injectors release into the intake manifold.
Car engine tuning, once the domain
of the mechanical engineer, has
developed with the introduction of
high speed, low cost electronics and
can now be manage quicker and
more efficiently by electronic means.
Cars are increasing controlled by a
multitude of Electronic Control
Units (ECU). These units are now
being linked or interfaced to control functions such as the immobiliser
system, climate control, traction control, fly-by-wire throttle, anti-lock
braking, stability control, active suspension and differential. In fact
there is virtually no part of the car now, in which at least one ECU
does not have influence.
Until recently, ECU manufacturers created stand alone units for the
control of individual areas, such as engine, ABS systems etc. These
units had data storage devices inside them and the storage "chips"
could be removed and read, then
the data could be analysed. The
data was not encoded, however
when downloaded it was in a
hexadecimal format which made
very little sense to most people.
Some companies sprang up and
then specialised in making sense of
this data. Functions of small
sections of this data was guessed at
and then altered to see what the
effect would be on the tuning of the car. This was not a particularly
satisfactory way to proceed but sometimes there was an improvement
in some aspect of the vehicle’s functionality. In those early stages,
there were very few cases where there was any real knowledge of what
was happening within this ECU.
ECU: Ready to be packaged.
Quality control testing of the ECU
before packing and shipping.
3
The situation now is actually worse than it was in the early days due to
the complexity of the ECU and the advances made in microprocessor
design. These ECU have many times more data and code than they
used to. Analysis of this information is now very time-consuming, but
with the European ECU technology, the situation is now much more
straightforward.
All our ECU meets the EU III standard. Most of the world’s major car
manufacturers use standard technology bought in from a specialist
company. This means that the information on how to program the units
is far more accessible to aftermarket tuners.
Testing process; at our R & D centre
in China.
ECU;: testing process.
4
Definition:
The Electronic Control Unit (ECU) controls the fuel injection system
of an internal combustion engine. It
also controls the ignition timing, and
the idle speed of the engine.
The ECU looks after many other
important functions that contribute to
the efficient and optimum
performance of an engine. These
monitoring points use sensors,
sometimes called transmitters, to
send information back to the ECU.
The ECU consists of: -
• A microprocessor.
• Random access memory (RAM).
• Read only memory (ROM).
• An input and output port or interface.
• Plus the usual electronic parts that make up a small computer.
As information such as engine
temperature, airflow, crankshaft
position etc., are monitored and sent
to the ECU (input), the data is
processed by the software within the
ECU and then instructions that
determine the optimum settings are
sent (output) to the various actuators
such as; injection, ignition timing,
idle speed and so on.
No vehicle should be ‘on the road’ without the fuel-saving and
performance boosting characteristics of this wonderfully exciting
ECU. It’s a must have for every motoring enthusiast.
An engine with ECU fitted, under test
conditions.
Our ECU is a very compact and
efficient technological advancement.
5
Monitoring
The monitoring process of the ECU is a complex and exacting science.
Following is a general outline of where the sensors monitor, in order to
input information to the ECU, so that the output is fully optimized.
• Mass Air flow (MAS). This is the control for the volume
stream of intake air.
• Intake Air Temperature (IAT). Air temperature of the intake
air stream is measured.
• Camshaft or Crankshaft Position. (CPS) Here the engine speed
and piston position is checked to determine, ignition, injection
etc.
• Coolant Temperature Sensor (CTS). Engine cooling control
for fan speeds etc.
• Knock Sensor (KS). Vibrations from the cylinder block are
sent to the ECU.
• Heated Oxygen Sensor (HO2S). This detects the amount of
oxygen in the exhaust gas compared to the air outside.
• Throttle Position Sensor (TPS). The movement and position of
the accelerator peddle is monitored.
• Vehicle Speed Sensor (VSS). Here the speed is transmitted to
the speedometer.
• Power Steering Pressure Switch (PSPS). As the power steering
is turned, the signal from the sensor sends an instruction to
increase the engine idle speed to compensate for the increased
load.
• Manifold Absolute Pressure (MAP). Fuel input is altered
depending upon the MAP.
• Crank Signal (CS). Preparation in starting mode for engine
start-up.
With all these sensors monitoring changes in the engine, with the
information being quickly analysed and the necessary adaptations
being made, an engine will have every opportunity to enjoy extreme
longevity with a lifetime of smooth and powerful operation.
6
An Economic Alternative
We were the first ECU R&D commercial manufacturer in
China, where we now have first class engineers and facilities.
Our developing ‘industrial age’ and large population gives us
many fine minds and skilled hands to produce products at very
reasonable prices.
There are currently only a handful of ECU manufactures in the
world and they understandable protect the designs of their
products very well.
These manufactures are:
• Delphi, USA - our main competitor.
• BOSCH Corporation, German.
• Denso, Japan.
Delphi is the world biggest automobile spare part supplier.
In the gasoline/petrol fuel injection domain, BOSCH and
Delphi have about equal market share.
If the new owner takes over our Intellectual Property and
facility, they could easily become the world biggest ECU
manufacturer as we own 100% of the Intellectual Property
rights in our product, and our R&D costs may only be about
20% of those of our competitors.
Our company's ECU product is of an extremely high technical
standard, with the product selling price being much lower than
that of our competitors. In the present market our unit sells at
70% - 82% below that of our competitors, and so has a large
market advantage with respect to price.
7
The Business Offers:
• A fully developed product already available in the market
place.
• Fully equipped and established laboratories.
• Training facilities for all involved parties.
• All source code, that has already been debugged and tested
• On-going support (if required) under the purchase agreement.
• A manufacturing wing, which may be located in China or
elsewhere.
Option 1
• Send your engine to China with your requirements.
• We manufacture the ECU and program it.
• You sell it with your engine, but we do not supply source
code.
Option 2
• Send your engine to China with your requirements.
• We manufacture the ECU and program it.
• We supply the source code, but retain the copyright.
Option 3
• Send your engine to China with your requirements.
• We assist you to establish your own laboratory and
manufacturing facility at your chosen location.
• We supply all source code but retain the copyright.
Option 4
• Send your engine to China with your requirements.
• We assist you to establish your own laboratory and
manufacturing facility at your chosen location.
• We supply you with all source code and the associated
exclusive rights to it.
Option 5
• You may have an option that could be of benefit to your
particular needs. Should this be the case, we are always
ready to negotiate with you regarding price and options.
END




The Computer ECM

Whilst vehicle computers (ECMs) are not made to be repaired in garage workshops,
there are certain factors that require technicians to have an appreciation of
computer technology. For example, diagnostic trouble codes (DTCs) are an
important part of fault finding and DTCs are stored in the computer memory. The
means by which these codes are read out varies from vehicle to vehicle and it is
helpful for technicians to understand why a procedure for reading DTCs on one
vehicle may not work on another vehicle. It is also the case that technicians in
some main dealer workshops are required to use special equipment to amend the
computer operating program. Increasingly, use is being made of ‘freeze frame’
data. This is ‘live’ data that is captured whilst the system is in operation and it is
useful in helping to determine the causes of a system fault. Whilst these operations
are normally performed through the use of ‘user friendly’ diagnostic equipment,
it is still the case that an understanding of what can and what cannot be done via
the ECM is useful.
2.1 The fundamental parts of a computer
Figure 2.1 shows the general form of a computer that consists of the following
parts:
ž a central processing unit (CPU)
ž input and output devices (I/O)
ž memory
ž a program
ž a clock for timing purposes.
Data processing is one of the main functions that computers perform. Data, in
computer terms, is the representation of facts or ideas in a special way that allows
it to be used by the computer. In the case of digital computers this usually means
binary data where numbers and letters are represented by codes made up from 0s
and 1s. The input and output interfaces enable the computer to read inputs and to
make the required outputs. Processing is the manipulation and movement of data
A practical automotive computer system 41
Memory
Central
processing
unit
(CPU)
Clock
Crystal
Fuel injection
Inputs Outputs
EGR
valve
Speed sensor
Air flow sensor
Temperature
sensor
Program
Fig. 2.1 The basic components of a computer system
and this is controlled by the clock. Memory is required to hold the main operating
program and to hold data temporarily while it is being worked on.
2.1.1 COMPUTER MEMORY
Read only memory (ROM) is where the operating program for the computer
is placed. It consists of an electronic circuit which gives certain outputs for
predetermined input values. ROMs have large storage capacity.
Read and write, or random access memory (RAM), is where data is held
temporarily while it is being worked on by the processing unit. Placing data in
memory is referred to as ‘writing’ and the process of using this data is called
‘reading’.
2.1.2 THE CLOCK
The clock is an electronic circuit that utilizes the piezoelectric effect of a quartz
crystal to produce accurately timed electrical pulses that are used to control the
actions of the computer. Clock speeds are measured in the number of electrical
pulses generated in one second. One pulse per second is 1 Hertz and most
computer clocks operate in millions of pulses per second. One million pulses per
second is 1 megahertz (1 MHz).
2.2 A practical automotive computer system
Figure 2.2 shows a computer controlled transmission system. At the heart of
the system is an electronic module. This particular module is a self-contained
42 The Computer ECM
Fig. 2.2 A computer controlled transmission system
computer which is also known as a microcontroller. Microcontrollers are available
in many sizes, e.g. 4, 8, 16 and 32 bit, which refers to the length of the binary
code words that they work on. In this system it is an 8-bit microcontroller.
Figure 2.3 shows some of the internal details of the computer and the following
description gives an insight into the way that it operates.
The microcomputer (1)
This is an 8-bit microcontroller. In computer language a bit is a 0 or a 1. The 0
normally represents zero, or low voltage, and the 1 normally represents a higher
voltage, probably 1.8 V.
The microcontroller integrated circuit (chip) has a ROM capacity of 2048 bytes
(there are 8 bits to one byte) and a RAM that holds 64 bytes. The microcontroller
also has an on-chip capacity to convert four analogue inputs into 8-bit digital codes.
The power supply (2)
The power supply is a circuit that takes its supply from the vehicle battery then
provides a regulated d.c. supply of 5 V to the microcontroller, and this is its
A practical automotive computer system 43
Fig. 2.3 Internal details of the computer
working voltage. The power supply also includes protection against over voltage
and low voltage. The low voltage protection is required if battery voltage is low
and it often takes the form of a capacitor.
The clock circuit (3)
In this particular application the clock operates at 4 MHz. The clock controls
the actions of the computer, such as counting sensor pulses to determine speed
and timing the output pulses to the electrovalves so that gear changes take place
smoothly and at the required time.
The input interface (4)
The input interface contains the electronic circuits that provide the electrical
power for the sensors and switches that are connected to it. Some of these inputs
44 The Computer ECM
are in an electrical form (analogue) that cannot be read directly into the computer
and these inputs must be converted into computer (digital) form at the interface.
The output (power) interface (5)
The power driver consists of power transistors that are switched electronically to
operate electrovalves that operate the gear change hydraulics.
Feedback (6)
At (6) on the diagram the inscription reads ‘ Reading electrical state’. This means
that the computer is being made aware of the positions (on or off) of the
electrovalves.
The watchdog (7)
The watchdog circuit is a timer circuit that prevents the computer from going
into an endless loop that can sometimes happen if false readings occur.
The diagnostic interface (8)
The diagnostic interface is a circuit that causes a warning lamp to be illuminated in
case of a system malfunction. It can also be used to connect to the diagnostic kit.
2.3 Principles of operation
As with all automotive computer controlled systems, this one relies on inputs from
sensors. The computer compares these input values with values that are held in
the program memory (ROM) and then determines what signals are to be delivered
to the actuators (electrovalves) in order to cause gear changes.
In this particular application the computer program makes use of a concept
known as the vehicle operating point. The operating point is dependent on two
sensor inputs, vehicle speed and load. Speed is determined by an electromagnetic
sensor and the load is determined from the throttle position sensor. (Details of
both types of sensor are given in Chapter 5.)
A set of vehicle operating points is stored in the ROM and these are used, whilst
the vehicle is operating, as references for making gear changes. When the vehicle
speed, as measured by the speed sensor, is greater than the speed held in the ROM
for a given operating point the computer will call for a change to a higher gear. A
lower gear (change down) will be called for when the vehicle speed falls below
that held in the ROM.
Should the microcomputer detect a sensor reading that is out of limits for a
sequence of readings (probably three readings) then the fault detection system
comes into operation. In the case of this transmission control the types of failure
that may be detected are:
ž electrohydraulic valve failure
ž throttle position (load) sensor failure
Computer data 45
ž speed sensor failure
ž power source (battery) voltage failure.
In the event of a failure being detected, the warning lamp(s) are illuminated and
the ‘limp home’ facility is activated and, in all probability, a code will be entered
in a section of RAM for later use in diagnosing cause and effect. In this case the
‘limp home’ mode consists of a computer subroutine that causes the system to
operate in high gear. This is intended to permit the driver to drive to a service
garage where the required rectification work can be performed.
2.4 Computer data
At the base level inside the computer, the values that the computer processor
works on are all expressed in digital form. That is to say that sensor readings, such
as engine speed, coolant temperature etc., will be presented in the computer as
binary codes made up of 0s and 1s. The 0s and 1s are electrical signals and values
often used are binary 0 = 0.0–0.8 V and binary 1 = 2–5 V. The computer thus
operates on electrical signals.
2.4.1 DATA TRANSFERS
Coded data is transmitted as electrical pulses, both inside the computer and
between the computer and other computers connected to it. Inside the computer
a coded number such as 20, which is 0001 0100 in 8-bit binary, is transmitted on
a parallel bus which comprises eight wires, side by side. This is known as parallel
data transmission and the concept is shown in Fig. 2.4(a).
(a)
(b)
Data
1 Wire
Serial
0 0 0 1 0 1 0 0
1 Bit at a time
Data
8 Wires side by side
Parallel
00010100
Whole word in one go
Fig. 2.4 Data transmission
46 The Computer ECM
When data is transmitted along a single wire, as happens in networked systems,
each bit (0 or 1) is transmitted so that one bit follows another until the whole
set of 0s and 1s has been transmitted. This method is known as serial data
transmission. The speed of transmission is measured in the number of 0s and
1s that are sent in 1 s. Each 0 or 1 is a ‘bit’ and the number of bits per
second is known as the ‘Baud’ rate, named after the person who first thought of
measuring bits per second. The principle of serial data transmission is shown in
Fig. 2.4(b).
2.4.2 DATA TRANSFER REQUIREMENTS
In order for the computer controlled systems to function correctly certain requirements
must be met.
1. There must be a method that enables the computer processor to identify a
specific device’s interface from all other interfaces and memory devices that
are attached to the internal buses of the computer.
2. There must be a temporary storage space (buffer) where data can be held (if
necessary) when it is being transferred between the computer processor and a
peripheral, such as a sensor or an actuator.
3. The peripherals, such as speed sensors and fuel injectors, must supply status
information to the computer processor, via the interfaces, to inform the
computer processor that they are ready to send data to it, or receive data
from it.
4. The computer must generate and receive timing and control signals that are
compatible with the computer’s processor. These timings and signals must
also be compatible with the sending or receiving device, i.e. the sensor or
actuator.
5. There must be a means to convert the sensor signals into digital data that the
computer can use and also a means to convert digital data into a form that the
actuators can use.
2.5 Computer interfaces
Often the interface between the computer and peripherals, such as sensors
and actuators, is based on a single chip integrated circuit. Figure 2.5 shows
such an interface which is based on the Motorola MC6805 ACIA (asynchronous
communications interface adaptor).
The blocks marked R1 and R2 are shift registers. R1 receives a data word as
8 parallel bits and then sends it out as a stream of serial bits. R2 receives a
stream of data as serial bits and transfers it to the bus as an 8-bit parallel word.
The control logic circuit is operated from the computer and the 8-bit bus at the
top left communicates with the control unit and other internal circuits of the
microcontroller.
Control of output devices 47
Control
logic
circuit
Send
data
register
Receive
data
register
Status
register
Control
register
R1
R2
Transmit
control
Receive
control
Bus
8
Bus
8
Serial data out
Serial data in D
A
Sensor signal
Microcontroller
8 bit parallel bus
Other
signals
Read / write
Fig. 2.5 A communications interface
2.6 Control of output devices
In many cases the commands from the computer are used to connect a circuit
to earth, via a transistor. Two methods are used; one method is known as
‘duty cycle’ and the other is known as pulse width modulation. Each of
these methods produces a different voltage pattern when the operation of
the device is checked with an oscilloscope. The two patterns are shown in
Fig. 2.6.
With duty cycle control the transistor that drives the device may be switched
on for 100% of the time available, or for a small amount of the time available, for
example 30%. The control of the device being operated is thus achieved by the
length of the ‘on time’. So a duty cycle reading of 50% means that the device,
such as a petrol injector or mixture control valve, is switched on for 50% of the
available time.
With pulse width control the transistor is switched on and off at fairly high
frequency. The use of pulse width modulation (PWM) can reduce the heating
effect in the solenoid of the device (injector) that is being operated.
Fig. 2.6(a) Duty cycle control of a mixture control solenoid
48 The Computer ECM
Fig. 2.6(b) Pulse width modulation applied to a fuel injector
2.7 Computer memories
The term ‘memory chip’ derives from the fact that most computer memories are
circuits that are made on a silicon chip. Automotive computers use memory chips
that are very similar to those used in personal computers. The correct name for
a ‘chip’ is integrated circuit or I/C. A large part of electronic memory is made of
transistors and the number of transistors that can be made on a very small piece
of silicon runs into millions.
Figure 2.7 shows a memory element known as a D type flip-flop. The D type
flip-flop is called a memory device because it has the property that, whatever
appears at D, either 0 or 1, will appear at Q when the clock pulse (C) is 1. When
Fig. 2.7 A computer memory element
Computer memories 49
C goes to 0, Q stops following the D value and holds the value it has when C
changed to 0. Q will follow D again when C goes back to 1.
The logic gates shown in this diagram are made up from electronic components
such as transistors, and large numbers of them can be made on a single integrated
circuit.
2.7.1 READ ONLY MEMORIES
The program that controls the system is stored in the ROM, or read only memory.
Various types of ROM are used in automotive computers and it is important to
understand the differences between them because a service procedure that is used
on one make of vehicle may not necessarily work on a similar type of vehicle.
Part of the reason for this is to be found in the different types of ROM that
are used.
Figure 2.8 shows a block diagram of a small ROM circuit. The truth table shows
the data that appears on the output lines (F0 to F3). It is read as follows: when
the electrical inputs at A, B and C represent logic 0, the output values F0 to F3 are
1010, and so on.
Fig. 2.8 A ROM circuit and truth table
ROMs are available in various forms. Normally themain programmemory cannot
be changed once it has been configured, unless the integrated circuit is changed.
However, there are other types of ROM and some of these are used in vehicle
computers. Some vehicles are equipped with the type of program memory that
can be changed in service, but only by approved agents. The ROM is the part of
the ECM where the program that controls the working of the system is stored and
any attempt to tamper with it could have disastrous consequences.
Mask programmable ROMS
This type of ROM is widely used in large scale manufacture. The term ‘mask’
refers to the mask that is used during the stage when the ROM’s electronic circuit
is being constructed. Once a mask programmable ROM has been configured it
cannot be altered.
50 The Computer ECM
PROM
Programmable ROMs are sometimes referred to as field programmable ROMs
because the circuits can be changed ‘in the field’, that is to say away from the
factory. The memory circuits contain fusible links that can be ‘blown’ selectively
by the use of special equipment called a PROM programmer. Once the fusible
links are blown (broken) they cannot be ‘unblown’.
EPROM
Electrically programmable read only memories (EPROM) are memory circuits that
use an electrical charge storage mechanism (like a capacitor) that keeps the
memory alive, even when the main source of electrical power is removed. The
memory can be erased by exposing the I/C to ultraviolet light. This type of memory
chip may be identified by a small window (usually taped over) in the chip housing.
After erasure of the memory it can be reset electrically.
EEPROM
An electrically erasable PROM works in a similar way to the EPROM, the main
difference is that the memory can be erased and reset by a special charge pump
circuit that is controlled by the microcontroller according to the working program
of the ECM.
2.7.2 RANDOM ACCESS MEMORY
The RAM, or random access memory, is the section of memory that is used for
temporary storage of data while it is being worked on. It must be the type of
memory that can be written to (i.e. data is placed in it) and read from (i.e. data
is taken from it). This means that the memory *******s are constantly changing
whenever the computer is operating. It is also known as a read-and-write memory.
The *******s of RAM are sustained by electricity and when the source of electrical
power is removed, the *******s of the RAM are lost. This is why the RAM is called
volatile memory.
2.7.3 OTHER TYPES OF COMPUTER MEMORY
Hard discs are made of material that can be magnetized in very small localized
areas arranged in circular tracks. A magnetized area probably represents a ‘1’ in
computer language, and a non-magnetized area represents a ‘0’. When the disc
is rotated through a read-and-write head, the magnetism is converted into an
electrical signal and it is these electrical signals that produce the data that operates
the computer. Hard discs can hold many millions of bits of data. Floppy discs
operate on similar principles, but they have a smaller storage capacity.
Compact discs (CDROMs) also have a large storage capacity. They are similar to
an old fashioned gramophone record in that they have grooves which are deeper
in some places than they are in others. The depth of the groove is read by a laser
Adaptive operating strategy of the ECM 51
beam that is connected to an electronic circuit and this circuit converts the laser
readings into voltages that represent the 0s and 1s used by the computer.
2.8 Fault codes
When a microcontroller (computer) is controlling the operation of an automotive
system, such as enginemanagement, it is constantly taking readings from a range of
sensors. These sensor readings are compared with readings held in the operating
program and if the sensor reading agrees with the program value in the ROM, the
microcontroller will make decisions about the required output to the actuators,
such as injectors.
If the sensor reading is not within the required limits it will be read again and
if it continues to be ‘out of limits’ a fault code will be stored in a section of RAM.
It is also likely that the designer will have written the main program so that the
microcontroller will cause the system to operate on different criteria until a repair
can be made, or until the fault has cleared. The fault codes, or diagnostic trouble
codes (DTCs), are of great importance to service technicians and the procedures
for gaining access to them need to be understood. It should be clear that if they
are held in ordinary RAM, they will be erased when the ECM power is removed.
This is why various methods of preserving them are deployed.
The term keep alive memory (KAM) refers to the systems where the ECM has
a permanent, fused, supply of electricity. Here the fault codes are preserved, but
only while there is battery power. Figure 2.9 shows a circuit for a KAM system.
Fig. 2.9 A KAM system
EEPROMs are sometimes used for the storage of fault codes and other data
relating to events relating to the vehicle system. This type of memory is sustained
even when power is removed. The use of fault codes is discussed in Chapter 3.
2.9 Adaptive operating strategy of the ECM
During the normal lifetime of a vehicle it often happens that compression pressures
and other operating factors change. To minimize the effect of these changes, many
52 The Computer ECM
computer controlled systems are programmed to generate new settings that are
used as references, by the computer, when it is controlling the system. These new
(learned) settings are stored in a section of memory, normally RAM. This means
that such ‘temporary’ operating settings can be lost if electrical power is removed
from the ECM. In general, when a part is replaced or the electrical power is
removed for some reason, the vehicle must be test driven for a specified period in
order to permit the ECM to ‘learn’ the new settings. It is always necessary to refer
to the repair instructions for the vehicle in question, because the procedures do
vary from vehicle to vehicle.
2.9.1 LIMITED OPERATING STRATEGY (LOS)
When a defect occurs that affects the engine, but is not serious enough to
prevent the vehicle from being driven, the ROM program will normally contain an
alternative loop in the program that will allow the vehicle to be driven to a service
point. This mode of operation is often referred to as the ‘limp home mode’. It
should be noted that any attempt to cure a defect must take account of the fact
that the system may be in its limited operating mode.
2.10 Networking of computers
As the use of separate computer controlled systems has increased, the desirability
of linking the systems together has become evident and it is now quite common
to find systems, such as engine management, traction control, anti-lock braking
etc., working together to produce improved vehicle control. When computer
controlled systems are linked together they are said to be ‘networked’. The
networking of computers on vehicles is often referred to as ‘multiplexing’, but as
an introduction to the topic it is helpful to consider some general principles of
computer networking as this provides a good insight into the networking that is
used on vehicles.
2.10.1 A BUS-BASED SYSTEM
Figure 2.10 shows the basic principle of a number of computers which are linked
together by a common wire along which are sent the messages that the computers
use to share data.
A principal advantage of this system is that it reduces the number of wires that
are needed but, as you will appreciate, there are likely to be problems if more than
one message is ‘on the data bus’ at any one time. The problem is overcome by
having strict rules about the way in which data is moved between the computers
connected to the bus. These sets of rules are known as ‘protocols’.
2.10.2 STAR CONNECTED COMPUTERS
An alternative to the bus system of connecting computers together is the star
system shown in Fig. 2.11. An advantage of this system is that a break in the
Networking of computers 53
C1
C4 C5
C2 C3
Bus
Fig. 2.10 A simple bus-based network of computers
C1
C2
C3
C4
C5
C6
Hub
Fig. 2.11 A star-connected computer network
connection between one computer and the hub will not cause a failure of the
entire network. The central hub can also be an electronic switch that receives
messages from any of the computers. It then determines which of the computers
(ECMs) on the network is the intended destination and then sends the message to
that computer (ECM) only.
Networked computer systems of both types are often found on the same vehicle.
Controller area network (CAN) is a networking system devised by Bosch that is
widely used for high speed automotive networks. (Note, the term ‘high speed’
refers to the speed at which data is moved around the network and not the
speed of the vehicle.) When a vehicle is equipped with networks that operate
at different speeds (baud rates, or data bits per second), the normal practice is
to permit them to communicate with each other via an interface known as a
‘gateway’.
2.10.3 MESSAGES
Message is the term used to describe a data item that is sent from one computer
(ECM) to another across a network. A message can be long, e.g. the *******s of a
file made up from many megabytes, or short comprising only a few bytes.
54 The Computer ECM
For a given speed of data transmission (baud rate) a long message will take
a long time to be transmitted and this can cause problems if another computer
needs to send a more urgent message. To prevent this from happening, messages
are divided up into smaller parts called packets. Each packet is transmitted on the
bus as a separate entity, the receiving computer then reassembles the packets to
reconstruct the full message.
(Note, 1 baud D 1 bit, binary 0 or 1, per second.)
The packet is formed into a frame before it is transmitted. The frame consists of:
ž the packet itself;
ž extra data bits (0s and 1s) to enable errors to be detected;
ž data bits to enable the sending computer to be identified;
ž data bits which enable the destination computer to be recognized;
ž a sequence of data bits to signify the start of the frame;
ž a number of data bits to signify the length of the frame and/or the end of the
frame.
Each computer on the network has a unique network address.
2.10.4 PROTOCOLS
In order for networks to function there must be rules (protocols) governing
the transfer of data. A commonly used protocol for communication between
networked computers is that known as carrier-sense multiple access with collision
avoidance (CSMA-CD). CSMA-CD works as follows.
A computer on the network must wait for the network to be idle before it
can transmit a frame. When the frame has been transmitted all computers on
the network check the destination address and, when the checks are completed,
the destination computer accepts (reads in) the whole frame. The destination
computer then carries out an error check and if an error is detected it will transmit
an error message to the transmitting computer. On receipt of an error message,
the transmitting computer will re-transmit the entire frame.
If two computers try to transmit a frame simultaneously there will be problems
on the bus. This is known as a collision and it causes the frames to be corrupted. If
this happens the protocol requires the transmitting computers to stop transmitting
their frames immediately and to transmit a ‘jamming signal’. The jamming signal
warns other computers on the network and they then ignore the parts of frames
that have been transmitted. Each computer must then wait a short period of time
before attempting to re-transmit.
Each computer, or other device, that is connected to the network must be
equipped with a suitable interface. The interface circuit card is equipped with a
microprocessor that permits it to receive and check frames without interfering
with the tasks that the computer’s main processor is dealing with.
To summarize, in order for a local area network (LAN) to function the following
must happen:
Vehicle network systems 55
ž the data must be divided into packets;
ž error detection bits must be added;
ž each packet must be formed into a frame;
ž the frame must be transmitted onto the network;
ž collision detection must take place, transmission must stop and a jamming signal
must be sent out;
ž computers must wait for a random period of time before transmitting again.
It should be noted that this all takes place in microseconds under the control of
the computer clock.
2.11 Vehicle network systems
A primary purpose of automotive networked systems is to reduce the amount of
wire that is used. Some estimates suggest that as much as 15 kg of wire can be
eliminated by the use of networking on a single vehicle. Other savings are made
in the use of sensors. For example, systems such as traction control and engine
management that make use of the engine speed sensor can make use of a single
engine speed sensor by placing the reading on the data bus as required (i.e. the
sensor is multiplexed), instead of having a separate sensor for each system. Similar
economies are possible with a range of systems and this can result in a reduction
in the total number of sensors on a vehicle.
There are several areas of vehicle control where data buses can be used
to advantage. Some of these, such as lighting and instrumentation systems,
can operate at fairly low speeds of data transfer, e.g. 1000 bits per second.
Others such as engine and transmission control require much higher speeds,
probably 250 000 bits per second, and these are said to operate in ‘real time’. To
cater for these differing requirements the Society of Automotive Engineers (SAE)
recommends three classes known as Class A, Class B and Class C.
ž Class A. Low speed data transmission, up to 10 000 bits/s, used for body wiring
such as exterior lamps etc.
ž Class B. Medium speed data transmission, 10 000 bits/s up to 125 000 bits/s,
used for vehicle speed controls, instrumentation, emission control etc.
ž Class C. High speed (real time) data transmission, 125 000 bits/s up to 1 000 000
bits/s (or more), used for brake by wire, traction and stability control etc.
2.11.1 THE PRINCIPLE OF A BUS-BASED VEHICLE SYSTEM
The controls (switches) for almost every system on a vehicle must be near the
driver’s seat.With ordinary wiring this means that there is a cable taking electrical
power to the switch and another taking the electricity from the switch to the unit
being operated.
As the amount of electrically-operated equipment on vehicles has increased a
very large number of electrical cables have become concentrated near the driving
56 The Computer ECM
position. This causes problems such as finding sufficient space for the wires,
extra cable connectors that can cause defects etc. Multiplexed, or data bus-based
systems overcome some of these problems.
Figure 2.12 shows the basic concept of multiplexed vehicle wiring. In order to
keep it as simple as possible fuses etc. have been omitted because at this stage, it
is the ‘idea’ that is the focus of attention.
−
3
4
1 2
Diagnostics
ECU
MUX
ABCD
Side
Head
HRW
Tail
Databus
Powerbus
1 & 2. Electronic switches for side and tail lights.
3. Electronic switch for head lights.
4. Electronic switch for rear window demister.
A, B, C & D. Dash panel switches for lights etc.
Fig. 2.12 The multiplexed wiring concept
As the legend for the diagram states, the broken line represents the data bus.
This is the electrical conductor (wire) which conveys messages along the data bus
to the respective remote control units. These messages are composed of digital
data (0s and 1s) as described earlier.
The rectangles numbered 1, 2, 3 and 4 represent the electronic interface
that permits two-way communication between the ECU and the lamps, or the
heated rear window. The dash panel switches are connected to a multiplexer
(MUX) which permits binary codes to represent different combinations of switch
positions to be transmitted via the ECU onto the data bus. For example, switches
for the side and tail lamps on and the other switches off could result in a binary
code of 1000, plus the other bits (0s and 1s) required by the protocol, which
are placed on the data bus so that the side lamps are energized. Operating other
switches, e.g. switching on the heated rear window would result in a different
code and this would be transmitted by the ECU to the data bus, in a similar way.
As the processor is moving the data bits at a rate of around 10 000 per second it is
evident that, to the human eye, any changes appear to occur instantaneously.
Vehicle network systems 57
2.11.2 DATA BUSES FOR DIFFERENT APPLICATIONS
The traction control system described in Chapter 1 operates in ‘real-time’ and
this means that data must move between elements of the system at high speed.
Increasing use is being made of the high data speed network system, CAN, for
systems such as traction control. CAN originate from Bosch and falls into SAE
Class C. It utilizes a two-wire twisted pair for the transmission of data.
The Rover 75 is a modern vehicle that uses several different data buses, as
described below.
1. A two-wire CAN bus that can operate at high data transmission speeds of up to
500 kbaud (500 000 bits/s) (Fig. 2.13).
2 3
1
4
1. Automatic transmission control unit
2. Engine control module
3. ABS/ traction control ECU
4. Instrument pack
Fig. 2.13 The CAN bus system
2. A single-wire bus for doors, lights, sun roof etc. This bus operates at a data
speed of 9.6 kbaud (Fig. 2.14).
3. A single-wire bus for diagnostic purposes. This bus operates at 10.4 kbaud
(Fig. 2.15).
The twisted pair of the CAN bus system minimizes electrically-initiated interference
and virtually eliminates the possibility of messages becoming corrupted.
2.11.3 ENCODING SERIAL DATA
Apart from the details about protocols that are given in section 2.10.4, consideration
has to be given to practical methods of transmitting the ‘messages’ around the
data buses. Factors such as speed of transmission (bit rate), electrical interference
and preservation of the integrity of messages has to be considered. Two of the
methods currently in use are:
ž non-return to zero (NRZ) (Fig. 2.16);
ž controller area network (CAN) (Fig. 2.17).
The differences between them are largely to do with the ways of representing
the logic levels ( 0 and 1, or high and low) that are used in computing. In the NRZ
method a binary code of 0,1,1,1,0,0,1 would be transmitted as shown in Fig. 2.16.
58 The Computer ECM
Parking
aid
Sunroof Rain
sensor
Instrument
pack
Climate
control
CD
player
Driver
seat
Low line
navigation
Bord monitor
radio
High line
bord monitor
switch interface
Telephone
K BUS
Low line
navigation
switches
GM6 LSM EWS 3
Low line
audio
High line
audio
Bord
monitor
Trim level dependant
Option
Base vehicles
Fig. 2.14 The single wire BMW K bus
Diagnostic
tester
DDE
M.E.M.S.
V6
Traction
control
A.B.S.
Jatco
gearbox
control
Instrument
pack
SRS
DCU
Diagnostic bus
Base vehicles
Option
Fig. 2.15 The single wire diagnostic bus
The point to note is that each bit is transmitted for one bit time without any
change.
In CAN, two wires are used for data transmission. One wire is known as CANhigh
(CAN-H) and the other as CAN-low (CAN-L). A CAN bit sequence is shown in
Fig. 2.17.
Prototype network systems 59
1.Bit
time
Bit
sequence
(Data)
NRZ
logic
levels
Clock
pulses
0
0 1
1
1 1 0 0
Fig. 2.16 NRZ transmission of a binary bit sequence
3.5 V
1.5 V
2.5 V
CAN-H
CAN-L
Fig. 2.17 A CAN bit sequence
The CAN-H wire switches between 2.5 and 3.5 V and the CAN-L wire switches
between 2.5 and 1.5 V. When CAN-H and CAN-L are at 2.5 V, there is no voltage
difference between them and this represents computer logic 0. Computer logic 1
is created when there is a 2 V difference between the two wires as happens when
CAN-H is at 3.5 V and CAN-L is at 1.5 V.
2.12 Prototype network systems
In order to provide further insight into the way in which vehicle systems are
networked it will be helpful to consider the following details of a concept vehicle
that was developed by LucasVarity. Figure 2.18 gives an impression of the system.
Several references to networked systems, e.g. traction control, stability control
etc., have already been made. The system shown in Fig. 2.18 is suitable for virtually
any vehicle, including trucks and buses. The system comprises four subsystems.
1. The Lucas EPIC electronically-programmed injection control system, which is
a computer controlled engine management system for diesel engines, similar
to the one described in section 1.11.
2. The Lucas flow valve anti-lock braking system. On this advanced prototype
vehicle, the ABS system is provided with a second solenoid valve at each front
wheel that permits independent application of the brakes by using the ABS
pump to supply pressure.
3. A clutch management system (CMS). This replaces the normal clutch pedal
linkage with a computer controlled, hydraulically actuated system. The manual
60 The Computer ECM
Fig. 2.18 The LucasVarity advanced prototype vehicle
gearshift is retained, but there is no clutch pedal. The driver still lifts the foot
from the accelerator pedal when changing gear. The advantage of this is that
the driver gains two-pedal control without the fuel consumption penalty that
is associated with automatic transmission. The driver also retains full control
over gear change operations.
4. Adjustable rate dampers are fitted. The damping rate is adjusted by the computer
(ECM) to provide optimum damping during rapid steering input, braking and
acceleration.
Master controller
Each of the above systems has a CAN interfacewhich permits them to be connected
to the master controller. A network of twisted pair cables connects each of the
above subsystems to the master controller and this allows the transfer of sensor
information and control signals with reliable safety checking and minimal wiring.
The master controller thus receives information from the subsystems via the CAN
bus (cables).
The master controller is directly connected to a switch pack (for cruise and
damper control), two accelerometers and an inclinometer (for hill detection).
This means that the master controller ‘knows’ the complete status of the vehicle
and the driver’s requirements. The vehicle status information is processed by the
master controller to generate control signals which are sent to the subsystems.
These ‘master’ signals over-ride the normal operation of the subsystems to operate
Prototype network systems 61
another tier of systems known as the integrated systems. In the event of CAN
failure, each subsystem defaults to stand-alone operation.
The integrated systems
The four subsystems, i.e. EPIC, ABS, damper control and clutch management,
are integrated (made to work together) to provide seven additional functions
of vehicle management. The computer programs that do this controlling are
executed by the master controller. These seven integrated systems are:
ž traction and stability control
ž cruise control
ž power shift
ž engine drag control
ž hill hold
ž damper control
ž centralized diagnostics.
Traction and stability control
The ABS wheel speed sensor signals inform the ABS computer of wheel to
surface conditions. At low speeds, or when only one wheel spins (such as pulling
away with one driving wheel on ice and the other on dry tarmac), the brake
is automatically applied to the spinning wheel. At higher speeds, or when both
wheels spin, engine power is reduced to eliminate wheel spin. These two strategies
combine to give improved traction and acceleration, and safer cornering at higher
speeds.
Cruise control
The vehicle speed sensor information is used by the engine control (EPIC) to
maintain a constant vehicle speed that is selected by the driver. The cruise control
switch pack provides commands for setting the desired cruise speed and for
switching on and off as required.
Power shift
The power shift function automatically reduces engine power during gear changes.
This means that the driver no longer has to lift the foot from the accelerator pedal
and need only move the gear lever to effect a gear change. This reduction of
engine power, via the controller, overcomes the difficulty of synchronizing the
accelerator and gear lever movements. It is also possible to provide for ‘blipping’
of the throttle to give smooth downward gear changes.
Engine drag control
This eliminates wheel locking due to engine braking on very slippery surfaces,
and improves anti-lock braking performance. The reduced engine drag is achieved
62 The Computer ECM
by increasing engine power slightly to maintain the correct level of wheel slip for
maximum retardation and stability. In extreme cases, the clutch can be disengaged
to remove the inertia from the engine driveline. This allows the wheels to respond
more quickly to the anti-lock brake control and gives improved steering capability
and reduced stopping distances.
Hill hold
Hill hold uses brake actuation to apply the rear brakes automatically when coming
to a halt on a hill. When re-starting on the hill, information from the inclinometer
sensor, the EPIC system, the ABS controller and the clutch management controller
is used to determine the point at which the brakes should be released to give a
smooth pull away, with no roll back.
Damper control
The damper control system uses data from the CAN data bus to control the damping
rate settings. The dampers are switched to ‘firm’ setting for optimum response to
rapid steering input, braking and acceleration. On returning to ‘normal’ cruising,
the ‘soft’ damper setting is selected for improved ride comfort.
Centralized diagnostics
The centralized diagnostics uses the master controller to monitor all of the
networked systems. Data bus information is interpreted in order to detect and
respond to faults in the subsystems and the network communications. By this
means, fail safe operation is achieved and correct fault recognition is made. The
diagnostic section is provided with an interface which permits an interrogation
tool, the Lucas Laser 2000, to access diagnostic information. Future developments
of this system are anticipated and these will include electronic power assisted
steering, electronic braking, and active anti-roll bars.
2.13 Summary
The details of data bus communication that are outlined in this chapter are highly
specialized and it is work that is normally of most concern to designers. However,
vehicle repair technicians do encounter the terminology and it is helpful to have an
insight into some of the details. Fortunately, diagnostic equipment manufacturers
need to take care of the aspects that affect the suitability of their equipment for
diagnostic tests on the vehicles that it is made for. It is probably in the area of
equipment selection that a vehicle repair technician is most likely to feel the need
for familiarity with serial data terminology. Equipment specifications sometimes
contain references to some of the material contained in this chapter and it should
help when arranging for a demonstration of an instrument’s capabilities, which
should always be a step in the process of making a decision about purchasing an
item of equipment.
Review questions 63

Automotive Computer
Controlled Systems


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## GOSEF (14 أبريل 2013)

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