Autolexikon » Ignition » Ignition wires (ignition cables)

Ignition wires (ignition cables)

Function
Ignition wires must conduct the necessary voltage (U) to the spark plug with minimum possible losses.
Depending on how the vehicle is designed, this is achieved using:

A mechanical spark distributor and distributor cap

Since the ignition voltage (U) of up to 36,000 volts is in the high-voltage range, the ignition cables have
to be protected accordingly against overvoltage. The ignition voltage must never permeate the
insulation and flow to ground, since this could cause misfiring.

Although the fundamental aim is low-loss conduction, resistors are used in all ignition wire systems.
Looking into the electrical technology, it is clear that this is not necessarily a contradiction. All
electrically-operated devices create electromagnetic fields of greater or lesser strength. In most cases

1/5
they are only negligible, but under some circumstances they are undesired (e.g. interference with radio
reception). The ignition system requires optimal low-pass interference attenuation in order to ensure
interference-free operation of radios, communications equipment and control units for engines or
gearboxes. The assumption that resistors reduce ignition energy and thus engine performance has
been proved to be mistaken.

The resistors which are used are dimensioned so that they are hardly noticeable. The ignition cable
systems offered by brand manufacturers combine the best interference suppression with optimum
ignition performance. The unit of measurement for resistance (R) is the ohm. For ignition cables this
value lies in the range of a few thousand ohm or "kiloohm". The purpose of this resistance, as already
described, is to reduce electromagnetic radiation. This is achieved by limiting the current (I) through the
ignition wire and simultaneously ensuring that the spark plug also receives the necessary voltage (U).
The mathematical formula for this is U = R * I.

Electromagnetic compatibility of ignition wires

In simple terms, low-pass interference attenuation can be presented as follows: The ignition system
consists of a coil and capacitors, referred to in electrical engineering terms as an "oscillating circuit".
Interference suppressors (at least 1-5 kOhm) integrated into the ignition circuit reduce these
electromagnetic fluctuations and safeguard the fault-free interplay of the various items of equipment.
This is called "electromagnetic compatibility" (EMC).

Ignition wires with inductive resistor have a special feature: with this design the resistance changes
considerably depending on the ignition frequency (engine speed). In this case, a greater (inductive)
resistance is built up due to the coil.

2/5
Function of elecrical resistors

Wherever electric current flows, electromagnetic fields are formed, such as with mobile phones and
radio waves. Such electromagnetic fields also occur during ignition. They increase considerably in
intensity at the time of each "spark breakaway" on the centre electrodes of the spark plug – resulting in
strong voltage peaks along the cable. However, since strong electromagnetic fields can cause
malfunctions in electronic equipment - e.g. radios, the ABS, they must be kept within a harmless range.
For this purpose, ignition cables are equipped with electrical resistors. These limit the voltage peaks
during the spark breakaway and during the discharge of the ignition coil. In the process, the energy
from existing voltage and current strength is applied in a different energy-time relationship.

Requirements of ignition wires

Ignition wires must meet the following requirements:

High dielectric strength

When new cables are installed, they must not be bent or tangled. Above all, due to the risk of fire,
cables must not be allowed to come into contact with hot parts.

Safety
The location in which ignition wires are installed exposes them to high levels of stress and strain.

At first glance, the external appearance of ignition wires and ignition cable harnesses belies the
complexity within. They must rise to the toughest of technical challenges inside the engine
compartment, where temperatures induced by catalytic converters and more powerful and more
compact engines can reach up to 200 degrees Celsius and electronic ignition systems are producing
high voltages of up to 40,000 V. Brass and stainless steel contacts oxidise as they age. The electrical
resistance of the cable rises, along with the risk of the ignition coils failing.

PVC Hypalon ignition wires, which just a few years ago were more than able to rise to this challenge,
have long since fell by the wayside. Today's cars have even seen the use of class F silicone, which can
withstand temperatures of up to 220 degrees Celsius and exhibits a dielectric strength of up to 40,000
V. They protect against energy loss and provide optimum protection against vibrations, water, acids, oil
and petrol. With corresponding connectors they are able to meet the most stringent of requirements
where interference suppression and electromagnetic compatibility (EMC) are concerned.

Environmental protection
Because plasticisers escape from the plastics from which sheaths are made, the sheaths become brittle
over time. High temperatures as well as contact with oil or fuel vapours can accelerate this process or

3/5
even dissolve the plastic completely. Damage to the insulation results in ignition voltage being
conducted to earth. The consequences are misfiring and the engine running erratically, with unburned
fuel getting into the catalytic converter.

Every time a spark plug misfires, valuable petrol is injected but not combusted. As a result, there is a
significant increase in environmental pollution due to the increased in consumption per kilometre alone.
Furthermore, the unburned fuel in the catalytic converter can ignite explosively, causing damage that
will prevent the catalytic converter from rendering hazardous substances like carbon monoxide,
nitrogen oxide and hydrocarbons harmless and requiring it to be replaced.

Depreciation
As ignition wires are exposed to high levels of stress and strain, the wires must be checked regularly
and replaced at the first sign of ageing. Faults affecting the ignition system and the catalytic converter
usually only come to light during the statutory exhaust gas test. This regular test is an important
precautionary measure which can save you hard cash. After all, identifying and rectifying damage at an
early stage does not cost a lot. Purchasing ignition cables complete with connectors will cost much less
than having to replace a catalytic converter on account of consequential damage.

Damage detection of ignition wires

External damage to an ignition line can provide information about the cause of the fault. A thorough
visual inspection is the first step in diagnosing damage. For example, if a plastic sleeve is out of shape,
the ignition wire has most probably not been laid correctly inside the engine compartment.

Ignition wires that show no signs of external damage can be checked with what is known as a
multimeter. This important diagnostic device is able to read off the resistance of the ignition wire and
compare it with the permissible resistance values.

Change of ignition wires

Ignition wires in the engine compartment are wear parts which in most cases reach the end of their
service lives in quick succession. Garage mechanics know, therefore, that if a vehicle is of a
corresponding age or has clocked up high mileage, it is advisable to replace the entire set of ignition
wires. Another important consideration is that the components of an ignition system are complex and
must therefore be perfectly matched. Therefore, retrofitting an ignition wire in a different technology (a
carbon ignition wire instead of a copper ignition wire, for example) can lead to huge damage affecting
engine management, EMC and even electronic components that are relevant to safety.

Bilder

4/5
 Ignition cable

Hersteller

Bosch Hitachi Niterra UK Ltd. Valeo_EN

Herth+Buss Magneti Marelli_EN

Quelle:
http://www.my-cardictionary.comhttps://www.my-cardictionary.com/cardictionary/products/ignition-wires-
ignition-cables.html

5/5

Powered by TCPDF (www.tcpdf.org)