Figure: Electronics in modern vehicle

Vehicle design typically consists of ignition systems, generator and alternator systems, electric motors, actuators, as well as electronic devices for controlling, monitoring, communication, and displaying purposes. These components work together to ensure the efficient operation of the vehicle and enhance the driving experience. However, electrical disturbances, which are unwanted signals or electromagnetic noise, are typically generated during the normal operation of electrical and electronic devices (e.g., electric motors and other electronic devices). These disturbances can disturb or even permanently damage other electrical and electronic equipment/devices installed in the vehicle. This event is referred to as electromagnetic interference (EMI).  

In a vehicle system, the disturbance signals are generated/emitted from a device over a wide frequency range and can affect other onboard electronic devices and systems in two ways:

• by conduction (i.e., traveling through cables or wires) and/or 
• by coupling (radiation) mechanism (through the air via electromagnetic waves). 

ISO 7637 is an international automotive EMC immunity test standard that specifies test methods, procedures, and other relevant details for evaluating the immunity of devices under test (DUTs) to the conducted electrical transient disturbances. The purpose of this standard is to ensure that electrical and electronic devices installed in road vehicles can withstand electrical transients traveling along power supply lines and other connected lines, continuing to operate satisfactorily when exposed to such disturbances. ISO 7637 applies to all types of road vehicles, regardless of propulsion system (e.g., spark ignition, diesel engines, and electric vehicles). 

The ISO 7637 standard consists of the following five parts, under the general title "Road vehicles — Electrical disturbances from conduction and coupling”: published by the International Organization for Standardization (ISO).

Let’s discuss these sub parts. 

What is ISO 7637-1?

ISO 7637-1 is an automotive EMC immunity standard that contains definitions for basic terms relating to electrical disturbances from conduction and coupling (radiation) mechanisms in road vehicles. This first part defines key terms like electromagnetic disturbance, electromagnetic interference (EMI), coupling, coupling network, susceptibility, shielded enclosure, transient, etc.  This EMC standard is a part of the ISO 7637 series. 

The basic terms defined in ISO 7637-1 document are used in the other parts of ISO 7637. This first part also provides general information on the whole ISO 7637 series. Currently (Oct 2024), the fourth edition (published in 2023) of this standard is available that cancels and replaces the third edition (ISO 7637-1:2015). 

Note:  A general method for function performance status classification (FPSC) is specified in Annex A of ISO 7637-1 document.

What is ISO 7637-2?

ISO 7637-2 is an automotive EMC immunity test standard. It outlines the test methods and procedures to ensure that the equipment installed in commercial vehicles and passenger cars with 12 V or 24 V electrical systems can withstand conducted electrical transients (traveling along supply lines only) and continue to operate satisfactorily when exposed to such transients. This EMC standard is a part of the ISO 7637 series.

This second part of the ISO 7637 series applies to all kinds of road vehicles regardless of the propulsion system (e.g., electric motor, spark ignition, or diesel engine). As of October 2024, the third edition (published in 2011) of this standard is the current version, replacing the second edition (ISO 7637-2:2004).

Figure: Test setup for immunity testing

ISO 7637-2 outlines bench tests for both the injection and measurement of transients. The test methods and procedures described in this standard are used to assess the immunity of devices under test (DUTs) to electrical transients conducted along supply lines. During testing, test signals are applied to DUT to simulate electrical transient conducted along supply lines to DUT. If the DUT withstands the applied test signals and continues to function satisfactorily, the DUT passes the test. If the DUT does NOT withstand the test signals and malfunctions, the DUT fails the test. 

Note: Details on function performance status classification for immunity to transients are provided in Annex A of the ISO 7637-2 document. Also, for the purposes of this document, the terms and definitions defined in ISO 7637-1 apply.

What is ISO 7637-3?

ISO 7637-3 is an automotive EMC immunity test standard that outlines bench-testing methods and procedures to evaluate the immunity of DUTs (devices under test) to transient pulses that are coupled to lines other than supply lines through capacitive and inductive coupling. During testing, test pulses are applied to the DUT to simulate both fast and slow transient disturbances caused by the switching operation of inductive loads and relay contact bounce. This standard applies to electrical and electronic devices installed in road vehicles with nominal 12 V or 24 V electrical systems. This EMC standard is a part of the ISO 7637 series.

The ISO 7637-3 describes the following three test methods:

•            Capacitive coupling clamp (CCC) method;

•            Direct capacitive coupling (DCC) method;

•            Inductive coupling clamp (ICC) method.

Figure: ISO 7637-3 CCC test setup

The purpose of the ISO 7637-3 standard is to ensure that road vehicles equipped with nominal 12 V or 24 V electrical systems can withstand transient disturbances (coupled to lines other than supply lines through capacitive and inductive coupling) and continue to operate reliably when exposed to such disturbances. 

As of October 2024, the third edition (published in 2016) is the current version of this standard, replacing the second edition (ISO 7637-3:2007).

Note: For this document's purposes, the terms and definitions defined in ISO 7637-1 apply.

What is ISO 7637-4?

ISO 7637-4 is an automotive EMC immunity test standard that specifies test methods and procedures to ensure that equipment installed on passenger cars and commercial vehicles fitted with electrical systems can withstand conducted electrical transients (traveling along shielded high voltage supply lines of equipment) and continue to operate satisfactorily when exposed to such transients. This document focuses on equipment installed in road vehicles with electrical systems with D.C. voltage ratings between 60 V and 1 500 V and with a power supply isolated from the vehicle body. 

This EMC standard is a part of the ISO 7637 series and applies to all varieties of electrically independent road vehicles, such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

ISO 7637-4 outlines bench tests for both injection and measurement of transients. The testing methods and procedures specified in this standard are used to evaluate the immunity of devices under test (DUT) by applying test pulses that simulate electrical transients conducted along the shielded high-voltage supply lines of DUT. Immunity testing ensures that equipment installed in road vehicles has sufficient immunity against conducted electrical disturbance and can operate properly while exposed to these disturbances in real-world environments. As of October 2024, the first edition (published in 2020) is the current version.

Note: For this document's purposes, the terms and definitions defined in ISO 7637-1 apply.

What is ISO 7637-5?

In vehicles, electrical loads connected to the supply system generate pulses during various switching events. These pulses are coupled through the wiring harness to other components or wires. For test purposes, pulse generators are used to generate test pulses that simulate these pulse phenomena. The generated test pulses are coupled via coupling structures to the wiring of a device under test (DUT). The test pulses are not real pulses but serve as representations for the wide range of pulse shapes, amplitudes, source resistances, and pulse energy observed in vehicles. The definition of the test pulses and the coupling structures are given in ISO 7637-1, ISO 7637-2, and ISO 7637-3 documents. 

Test equipment has been developed and is commercially available based on the standard definition.   Experience with existing test equipment shows difficulties in achieving result reproducibility for the same DUT, depending on the generator used. This variation is due to different realizations of test generators coupling and decoupling networks. The purpose of the ISO 7637-5 document is to explain the reasons for these variations and to propose verification methods for harmonizing the behavior of different generators. This document is a part of the ISO 7637 series

ISO 7637-5 technical document provides extended definitions for pulse generators and verification methods required to harmonize the various generators used for pulse testing according to ISO 7637-2. The aim is to ensure that test results are comparable and reproducible, regardless of generator type. As of October 2024, the first edition (published in 2016) is the current version.

Note: This technical document/report is based on ISO 7637-1, ISO 7637-2, and ISO 7637-3.

Conclusion:

 ISO 7637 is the automotive EMC immunity standard that defines test methods and procedures to ensure that electrical and electronic components installed in road vehicles can withstand conducted electrical transient disturbances that travel via power supply lines and other connected lines of equipment and continue to operate satisfactorily when exposed to such disturbance in a real-world environment. This standard comprises five parts (ISO 7637-1, ISO 7637-2, ISO 7637-3, ISO 7637-4, and ISO 7637-5) and applies to all road vehicles, regardless of propulsion systems, including spark ignition, diesel engines, and electric vehicles.