New Providence, NJ--As cars get ever quieter, even the tiny click-click of intermittent windshield wipers can be bothersome to cranky drivers stuck in rush-hour traffic.
As a consequence, engineers have begun concentrating their efforts on reducing the noise output on devices as seemingly innocuous as electromechanical relays. That makes sense, given that more and more electronic control units are going into the operator compartment of cars.
Conventional auto relays actually produce noise in two ways: When the contacts open and close, and when the hinged armature makes contact with the iron core in the electromagnet area. Moreover, the latter will typically resonate, increasing noise levels further. These sounds can, frankly, be irritating.
Not so with Aromat Corp.'s new line of NAiS relays. Called the CQ and CR (a dual-power version), they deliver the same performance as equally-rated conventional relays, but with a noise reduction of 20 full decibels, according to engineers at Aromat. That decrease is all the more impressive when you consider the fact that decibels are logarithms of noise levels.
The relays are used in a variety of auto applications, from intermittent windshield wipers to cruise controllers, flashers, foglamps, stereo equipment, and air-conditioning units. Each relay provides a maximum switching current of 35A for 2 minutes at 20C and 30A for 2 minutes at 85C.
How did Aromat's engineers quiet down their relays? They used a combination of techniques to dampen vibrations and suppress the noise, specifically by:
- Adding a vibration-damping rubberized casing over the relay unit to form a doublecasing structure.
- Using springlike terminals that connect the relay to the circuit board to reduce vibrations transmitted to the board.
- Stretching a cushioning material (essentially a sponge) over the inside of the case.
- Applying an additional layer of vibration-damping rubberized material and a layer of resilient epoxy resin at the base of relay to damp down the vibration and better secure the terminals.
In tests conducted by automakers, the decibel level of the Aromat relays averaged less than 55 dB. Conventional relays tested between 65 and 75 dB. As a point of reference, normal conversation (not when screaming at other drivers) averages about 60 dB.
A major factor determining noise levels is the acoustical environment. If a relay is operating in the vicinity of a substantially noisier piece of equipment--say the V10 engine in the Dodge Viper or Mick Jagger blasting on the radio--it probably won't make any difference what its noise output is. But even small reductions in noise are likely to matter to the driver who's looking for a quiet, comfortable commute.
The relays have been approved as recommended parts for controlling the intermittent wipers and power windows in some luxury models. Down the road, Aromat expects the market to expand to lower-priced cars.