Modern family car is a complicated machine. It introduces technologies originally used in jet fighters, including head up display and fly by wire flight control system. On the whole, there are great differences between modern cars and the previous generation of cars.

However, the expectation of consumers is increasing day by day. People are eager to regard the car as a safe harbor far away from the world and a comfortable home. In the car, we can enjoy advanced technology, listen to high-quality music at the same time, or chat happily with friends on the other side of the earth – and free our hands.

Car manufacturers are developing new and innovative technologies to reduce or even eliminate unnecessary noise in cars. Therefore, more and more active noise reduction methods are used in vehicle design to reduce unnecessary noise, vibration and NVH.

Molex has rich experience in the design, manufacture and supply of automotive connectors, and can provide high-quality application solutions. This expertise has been applied to Molex road noise cancellation technology (RNC) sensors.

voice

Sound is a kind of pressure wave caused by mechanical vibration that can be received and processed by human ear. The human ear can usually sense the vibration frequency fluctuation between 20-20000 Hz. NVH (vibration noise) is an unwelcome sound, which can cause discomfort and even physical injury. Many industries began to reduce nhv in order to protect users and prevent noise pollution.

The traditional method of noise reduction is passive noise reduction. Different methods are adopted for different applications, such as energy absorbing materials, such as foam plastic or rubber, or using air gap to attenuate sound energy. The purpose is to dissipate energy vibrations before they reach the human ear. At present, no technology can effectively eliminate the noise of different frequencies.

Active noise reduction technology

Compared with passive technology, the working principle of active noise cancellation (ANC) is to detect unwanted sound waveform and generate equivalent reverse signal. This signal is transmitted with the original signal. These two kinds of waveforms are opposite to each other. After merging, they cancel each other, so as to weaken the amplitude of the original signal and reduce the volume of noise.

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Noise source waveform

Control sound wave form

Controlling sound source speaker

Superposed waveform

Opposite sound source wave form cancels noise

The field of electronic technology is developing rapidly. Sensors and signal processors become faster, more accurate, and easier to analyze unnecessary noise and generate corresponding noise reduction signals. With the popularity of technology, designers are looking for innovative ways to solve problems.

Road noise

Road noise is a topic of particular interest to automotive designers. The car adopts advanced internal combustion engine design and is equipped with silent electric motor to keep the cabin environment quiet. However, the problem of road noise still exists, with the improvement of vehicle performance, this problem becomes more prominent.

With the acceleration of vehicle speed, the interaction between vehicle and environment will produce noise, such as wind and road noise. NVH can make drivers feel tired, so solving the noise problem is not only related to convenience and comfort, but also plays a great role in improving road safety.

Passive technology can effectively reduce the wind noise, but it has limited effect on the noise caused by road contact. The direct contact between road and tire surface will produce continuous vibration. With the increase of speed, the vibration will become more significant. When the road surface is uneven, the suspension machinery in the car will also produce noise.

Installation position and vehicle environment

The key to the effective application of noise elimination technology is to place the sensor near the noise source. The denoised signal is as close as possible to the original signal. It provides time for signal processor to analyze and generate new waveform.

In automotive applications, this means that the location of the sensor needs to be as close to the road as possible, that is, the sensor needs to be installed at the bottom of the car. This is a challenge for product design

The driving environment of automobile is one of the most complex environments in the world. Cars and other vehicles are required to be designed to work in a variety of environments. From the icy Arctic Circle to the hot equatorial desert, cars need to be able to withstand ambient temperatures from minus 40 degrees Celsius to near the boiling point of water.

Auto parts must also withstand chemical attack. In some countries, salt is often used to help keep roads open and reduce ice in cold and snowy weather. The equipment installed on the bottom of the car will be exposed to the road surface containing salt water. In addition, it may be exposed to other chemicals, including fuel and lubricants on the road surface.

At the same time, the physical risk of the equipment must be considered. In general, cars designed by automobile manufacturers are sold all over the world. Designers must consider the possible damage to the bottom of vehicles caused by special roads, tracks and mountain roads in daily driving. Even if the ordinary family car is just driving on the ordinary urban road, it will be affected by gravel, stones and other debris in the process of driving.

These extreme conditions should be taken into account in the early design of RNC sensors and components. Material selection is also particularly important, which needs to meet the requirements of both extreme temperature resistance and chemical erosion resistance. Must be designed to be physically strong while maintaining lightweight quality. In addition, it is easy to install, safe and able to withstand vehicle vibration and impact.

Molex RNC sensor

Molex has designed a variety of RNC sensors, which are installed on the chassis of cars and other vehicles. The housing design of these sensors can withstand the harsh driving environment of the car, and provide ip6k9k level protection, waterproof, ash proof and other pollutants.

The sensor can be used in a variety of different enclosures to accommodate different vehicle mounting positions, including longitudinal mounting and vertical positioning.

The sensor includes an integrated connector for easy connection to the vehicle’s cable system. The connector is Molex’s own mini50 series, which saves a lot of space compared with the traditional uscar0.64mm connector. This also makes the sensor design as small as possible, easy to install as close as possible to the noise producing place. As we can see, this installation position is the most effective for eliminating noise.

Daisy chain concatenation

Weight has always been a key issue for automotive designers, especially suspension components. We expect to keep the light components suspended so that we can react quickly to the road conditions. In addition to keeping the sensor as light as possible, MOLEX also uses daisy chain wiring.

Functionally, each sensor will be directly connected to the signal processor through a separate cable, which is called “autonomous management”. Molex’s solution is to use daisy chains to connect sensors. Each sensor is connected to the next sequence of up to nine units. This reduces the length of the cable required to provide the necessary connections and reduces the weight of the cable by 30%.

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Passive noise reduction materials can weigh up to 60 pounds in ordinary cars, and more than 100 pounds in luxury cars. This is not conducive to the performance of the vehicle, and the cost of materials and installation is high. RNC system not only saves material cost, but also reduces weight and installation cost.

Sensor with superior performance

Molex’s sensors perform well in automotive environments. One of the key standards of sensor is delay time. This is defined as the time delay between the signal received by the sensor (excitation) and the signal received by the signal processor. It is very important to keep the delay time to a minimum when actively eliminating noise.

The noise cancellation system needs to receive and analyze the signal in a very short time to generate the reverse signal. Low delay sensor can respond quickly and effectively.

The delay of Molex RNC sensor is less than 150 μ s, which is superior to other similar products in the current market. This low delay improves the effectiveness of the noise cancellation system, which can make a rapid response to the road noise situation.

Another key index of sensor effectiveness is noise density. Although the goal is to let the sensor detect all the signals, there is a threshold or lower noise limit. The sensor cannot detect a signal below this threshold. As far as road noise is concerned, driving at a lower speed will reduce the noise. Sensors with high noise limits will not be able to detect the low noise generated by low speed, resulting in ineffective noise reduction.

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Molex rncsensor Molex RNC sensor

NDRNC<>

Allowsvehicletomeasureroadnoiseatslowerspeeds

Enablessensoplacementfartherfromenergysource

Allow the vehicle to measure road noise at a slower speed,

The position of the sensor can be placed far away from the sound source

Capturedwaveform capture waveform

HowlowofanexcitaTIonsensorcanmeasure

How low noise can be measured

Competingsensor reverse sensor

NDComp>>100μg/√Hz

The design of Molex sensor has a lower noise limit, so it can detect a larger proportion of the original waveform, allowing noise elimination at low speed. The advantage of this extreme sensitivity is that it allows the sensor to be located further away from the noise source. This allows the designer to say that the sensor is installed in a more advantageous position, which can protect the sensor or shorten the length of the short cable.

conclusion

Although road noise abatement technology may be the selling point of high-end car brands, RNC technology is becoming more and more perfect and cost-effective. Like other high-end technologies in the past, this technology will also enter the mainstream automotive market. MOLEX, with its superior sensor technology, mechanical design and innovative connectivity solutions, can provide a complete RNC sensor suite to meet the most stringent driving requirements at any time.

Editor: hfy

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