Symbols
Many of the symbols used in vehicle wiring diagrams conform closely to those laid down by the IEC
(International Electrotechnical Committee). They form the smallest element of any wiring diagram and are the simplest way to represent a device or component. They can illustrate clearly how a device operates or how technical sequences are executed. They do not necessarily replicate the design or form of the device they represent. Typical examples of symbols used in automotive wiring diagrams are shown in Tables 6.6 and 6.7.
Block diagrams
These are commonly used to give an uncomplicated overview of a system or sub-system and its function. Usually they do not give details of internal component circuitry and just show the most significant elements. Wiring is usually represented in single pole form. The block diagram can be used as an initial reference point for understanding more detailed wiring diagrams. An example of a Motronic system in block diagram form is shown in Figure 6.19.
Schematic diagrams
Schematic diagrams show the circuit and its components in detail. In addition, they show the current paths and detail of how the circuit operates, often including detail of internal circuitry in component parts. Schematics can be shown in assembled representation, and in this way the mechanical interconnection of parts (switches, relays etc.) is shown by broken or dotted lines. Alternatively, detached representation shows the current paths with
Table 6.6
Three-position switch with three contact modes (e.g. turn signal)
Actuators with one windng Resistor
Connections Mechanical functions
Make-and-break contact Actuator with two windings acting in same direction
Potentiometer
(with three connections)
Double-make contact Actuator with two opposed windings Resistor heater element, glow plug, flame plug, screen defroster
Multiple-position switch 0 1 2 Electrothermal actuator (thermal relay) Antenna Cam-lobe switch (e.g. ignition points)
Electrothermal actuator, tractive solenoid
Fuse
Thermal switch Solenoid valve (closed) Permanent magnets
Trigger Relay (actuator and switch), example: NC contact operates without delay, NO contact operates with delay
Winding, inductive
130 Power distribution Fundamentals of Motor Vehicle Technology: Book 3
Table 6.7
Push-button switch Spark plug Motor with blower fan
Relay, general Ignition coil Starter motor with solenoid switch (with/without internal circuitry)
Solenoid valve, injection valve (injector), cold-start valve
Ignition distributor, general
Thermo-time switch Voltage regulator Wiper motor (one/two wiper speeds)
Throttle-valve switch Alternator with voltage
regulator (with/without internal circuitry)
Rotary actuator Intermittent-wiper relay
Auxiliary air valve with electrothermal drive
Electric fuel pump, hydraulic pump motor
Car radio
priority given to clarity, and hence the component parts are not shown with their relative orientation or interconnection. The main purpose is to show clearly the function and operation of a circuit or component. An example of detached and assembled representation is shown in Figure 6.20.
Terminal diagrams
Terminal diagrams focus on the terminal designations of components and illustrate this at the connection points. Normally devices are represented by simple shapes with symbolic or pictorial representation of components. At each component the connections are marked with terminal codes which designate the function of the connection (not the wire designation!). This system has been designed to facilitate correct connection of devices and their wiring with an emphasis on repair and installation work. Typical terminal designations are shown in Figure 6.3 on page 121 and conform to a DIN specification (DIN 72 552). Figure 6.21 shows a typical diagram.
Current flow diagrams
Current flow diagrams are widely used by manufacturers and provide a clear overview of the most complex automotive electrical systems, including their numerous interfaces, in a concise, easy-to-understand way. Generally they show supply lines across the top of the page (battery and ignition) and an earth line across the bottom. The
‘current flow’ for the system or sub-system is depicted using tracks between the supply and earth lines, through the component internal and external circuitry, which is clearly shown on the diagram. Often the position of the track is numbered (similar to line numbers in a page of text) and this allows cross-reference to be made to other positions on the diagram, allowing connections between sub-systems to be highlighted. A typical example for an ABS system is shown in Figure 6.22.
Wiring diagrams are extremely helpful in understanding faults. However, it is important that the correct information is available and used. Also, that the type of diagram methodology must be fully understood by the user, as this can vary considerably between manufacturers
Current-flow diagrams are very popular and easy to understand. Block diagrams give a simplistic overview which promotes understanding of a complex system
Schematics show the system, including internal detail of components, in a concise way so that function and operation can be seen clearly. Terminal diagrams focus on the function of the circuit using codes as identifiers
K ey P oints K ey P oints A1 ECI B1 Engine-speed sensor B2 Reference-mark sensor B3 Air-flow sensor B4 Intake air B5 Engine-temperature sensor B6 Throttle-valve switch D1 Microprocessor (CPU) D2 Address bus D3 Working memory (RAM) D4 Program data memory (ROM) D5 I/O D6 Data bus D7 Microcomputer G1 Battery K1 Pump relay M1 Electric fuel pump N1... N3 Power-output stages S1 Ignition switch S2 Program map
selector T1 Ignition coil U1 and U2 Pulse generators U3 … U6 A/D convertors Y1 Injector
Figure 6.19 Motronic system in block diagram form
132 Power distribution Fundamentals of Motor Vehicle Technology: Book 3 a Assembled representation b Detached representation K1 Control relay K2 Solenoid switch,
hold-in winding, pull-in winding
M1 Starter motor with series and shunt windings
Figure 6.20 Schematic of a starter motor (assembled and detached representation)
Figure 6.22 Current flow diagram
6.4.1 Introduction
Vehicle networks have become commonplace in modern automotive electrical and electronic systems for a number of reasons:
● increased requirement for interaction of electronic
control systems, to allow sharing of information between intelligent controllers
● to implement the above functionality with cable
interfaces and point-to-point connections would mean extra cable and hence extra weight
● increasing requirement for cross-diagnostic and plausibility checking for complex, interacting systems or safety-critical systems (e.g. ABS, ESP)
● system expansion is easier to implement.
As the cost of electronic systems has reduced, this technology has become the most cost effective method for handling the large amount of data required and shared by modern vehicle control systems. The introduction of automotive-compatible serial data networks has expanded the capabilities for intelligent data transfer and sharing and is a logical development for modern vehicles.
Figure 6.23 shows the advantages of implementing a bus communication system in-vehicle. The reduced number of connections is clear.
Bus systems for different applications require different data transmission rate capability (also known as bandwidth). It is very common to see several networks on the same vehicle running at different speeds appropriate for the application. A number of typical groups are implemented with different performance requirements:
6.4
VEHICLE NETWORKS AND COMMUNICATION BUSES
Car with 3 control units
Car with 3 control units and bus system
Figure 6.23 Comparison showing increased complexity with point-to-point connection compared to a bus-based system for sharing data
Vehicle networks and communication buses 133
● Entertainment/multimedia: mobile communications, radio, navigation.
● Body and convenience: lighting, HVAC, door locks,
● Powertrain: powertrain control, vehicle dynamic control, driver safety systems.
Figure 6.24 shows the typical speeds available at the time of publishing.
Figure 6.24 Data transmission rates on the CAN bus system
1 = 500 kbps Drive train CAN bus 2 = 100 kbps Convenience CAN bus 3 = 100 kbps Infotainment CAN bus 4 = 1000 kbps Maximum data transmission rate