Product category:
Electromechanical Components
News Release from: Panasonic Electric Works UK | Subject: Relays for automotive applications
Edited by the Electronicstalk Editorial
Team on 16 September 2004
Relays evolve for automotive
applications
The electromechanical relay is constantly changing and updating to meet the needs of the customer, making it a cost effective solution to many switching needs in automotive applications.
In line with most consumer items the expectations of the modern car buyer continue to rise in terms of cost, specification and an expectation of technical advancement However there are other more specific factors that also affect car buyers' decisions - such as comfort and safety devices
This article was originally published on Electronicstalk on 23 Feb 2000 at 8.00am (UK)
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In turn this has led to a large increase in the electrical and electronic functions required to control the new features.
One obvious problem with the nature of automotive applications is the necessity to control large currents with typically small control signals.
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This has lead to the increasing requirement for electromechanical and solid state relays in automotive circuits - not just in the traditional alternator or wiper motor applications - but also in the window, seat and environmental control areas.
To avoid duplication and complexity of wiring the development of control protocol, such as the CANbus network control system, are now being incorporated in the modern car.
As an example this two-wire serial bus system, which reduces the amount of wiring in the vehicle by a significant amount, is ideally suited to interconnecting devices, to build smart systems or subsystems.
The CANbus enables closed loop or open loop control of outputs thus allowing relays to be remotely controlled in steering-by-wire, driving-by-wire and intelligent braking systems.
Even though applications within a car become more sophisticated the electromechanical relay is still often used as the final control device.
With the advent of less audible engine operation due to electronic engine management, braking and climate control systems, the ambient noise in the cab has significantly lowered on modern cars.
This means that even a small sound such as relay contacts coming together as a function is activated might disturb the end user - especially when it manifests itself from an area within the cab.
To overcome this a range of both SPDT and H-bridge quiet relays have been introduced to the market.
To produce a relay with a lower operating noise, a compact 20A/14V DC device was taken as the starting point for development.
Vibration and impact is absorbed by mounting the relay on to a terminal with a spring, the characteristics of which have been shaped by compound bends.
This has the effect of reducing vibration transmitted to the circuit board.
An upgraded casing material covered with a vibration-damping material containing rubber is used to form a double casing structure to suppress transmitted sound and a cushioning sponge material is stretched over the inside of the external case to bring down the vibration and transmitted sound to a minimum.
Furthermore, a vibration-damping material containing rubber is used on the base of the relay.
Finally a resilient epoxy resin is used for the adhesive material to achieve a dual purpose, namely, to damp down the vibration and secure the terminals.
These sound damping levels effectively reduce the noise levels caused by the relay operation by about 20dB.
Typically this can reduce the sound level from 65dB to 45dB - a level that would not be audible to the human ear.
With all the extra demands on the battery made by the modern vehicle the need for a larger power supply becomes more apparent and so the future uptake of 42V systems will become a necessity rather than a desirable outcome.
For some time there will be the need to switch between both 14 and 42V systems.
Protocols such as CANbus will allow the change from passive load switching to active power and load management and enable communication between the modules of both systems.
Therefore a range of relays has been developed to meet these requirements of a 42V system.
Some problems do have to be surmounted in 42V systems.
For example one consideration is the difficulties that an electromechanical relay has in switching a higher voltage due to arcing on contact break.
This reduces the effectiveness of the contact and shortens the contact life and, in the worst case, can cause contacts to weld.
Therefore methods of reducing the arc life and minimising contact damage must be used.
One way of solving this is to have a wider contact gap.
However this would mean that the relay would have to become larger to accommodate this feature, which is not always the best option.
To overcome this relay designers have used a magnetic arc blowout method in the 100A/42V and 30A/42V relays.
This incorporates the use of silver cupric contact materials, alteration in the shape of the contact pads and a permanent magnet.
In principle the arc is stretched as it is pulled out of the magnetic force, thus weakening it.
The arc striking points are diverted away from the softer zone of the contacts into a harder zone.
This will increase the contact resistance and consequently raise the arc voltage, which makes arc extinction easier to achieve.
Using a micro ISO package the 10A/42VDC relay has been designed with a different contact configuration.
As mentioned, one of the ways of reducing arcing life or arc prevention is to widen the contact, therefore for lighter applications this relay uses double contacts and as the contacts are connected in series this effectively doubles the contact gap so reducing possible contact damage.
The electromechanical relay is constantly changing and updating to meet the needs of the customer, which together with its proven reliability in the field, is a cost effective solution to many switching needs in automotive applications.
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