More and more sensors are now installed in cars to increase active and passive safety. A sensor with high market penetration is a rain sensor for added comfort and safety. If the car has a rain sensor, the driver does not need to adjust the wiper settings to quickly stop the blade motion or get a better viewing angle. When driving on a wet road, the driver does not need to open the wiper, so the driver can concentrate on driving. If an additional "auxiliary light switch" is installed, the light will turn on under dim timeout conditions and will not waste fuel because the lights are always on. Most models currently use a single motor driven wiper system. The advantages of this system are self-evident, using a linkage mechanism to drive two wipers, the cost is relatively low. However, the noise of the wiper and the uncleanness of the rain and snow weather still occur from time to time.
First, the rain sensor works
Most rain sensors use an optical system consisting of a light emitting diode (LED), a light receiving diode (LRD), a surrounding environment sensor, an electrical control unit (ECU), and several lenses.
The light emitted by the LED is reflected at the total reflection angle on the outer surface of the windshield at an angle between 420 (glass-air) and 630 (glass-water). If it is said upstream of the windshield, some of the light will be doubled, and this will cause a decrease in the current from the LRD. The current is measured by electrons. The light from the LED is reflected to the area of ​​the windshield of the LRD. "sensitive area". It can only be detected when rain drops into this area. In order to have a sensitive and reliable system, there must be a good ratio between the windshield area and the sensitive area.
Second, the car wiper system
The windshield wiper system consists of a rain sensor, a wiper motor, a lever switch, a relay, and an ECU. The rain sensor is mounted on the windshield. When the rain is detected in the sweeping area, the wiper moves in such a way that the driver always has a good viewing angle. There are two different systems.
1. Independent rainwater system: In this system, the rain sensor is directly connected to the wiper lever switch, wiper motor relay and wiper motor stop signal.
2. Network Rainwater Sensor: In this system, the rainwater sensor is connected to the bus, which receives all information over the network and sends all commands.
After the driver turns on the system, the rain sensor controls all sweeping behavior, which will command a single wiper to sweep at low speed or at high speed. Because each driver's response to the wiper system is reflected by different expectations, the sensitivity setting allows the system to meet the different needs of the driver. Bosch's new wiper motor can continuously sweep at varying speeds.
Third, the signal evaluation
1, the transmitter
The transmitter consists of an analog-to-digital converter (DAC) and a power supply. The analog voltage control of the DAC determines the intensity of the light emitted by the LED. In general, 2 to 4 LEDs are used. The current regulation of the transmitter is very important because the effectiveness of the light conversion is very variable and has a temperature gradient. Generally, in LEDs, light is transmitted in a pulsating manner to reduce losses and increase current. Another reason for using a wide range of emitter currents is that the emission of light through the windshield is not well regulated and has a wide tolerance range. A typical windshield has a thickness of 4 to 6 mm and a specific emission level for the IR perpendicular to the surface. The upper and lower limits of different suppliers are different.
2, the receiver
The receiver consists of several LRDs, current-to-voltage converters, clear or low frequency offset filters, amplifiers and ADCs, which typically also include a microcontroller. The LRD has a microcontroller that is controlled by the microcontroller to turn it on and off. If there is interference light, the LRD will be turned off. The wide range of emissions is the reason for using variable current-to-voltage conversion to ensure good conditions for the rest of the receiver system. Fortunately, after the conversion, it was filtered. All DC or low frequency interference will be removed to obtain a pure signal. Interference is typically caused by ambient light, and the amount of interference is measured by a microcontroller to determine whether the optical path is satisfactory or saturated with sunlight and gives an indication of signal accuracy. The filtered signal is amplified and converted by the ADC.
3, the microcontroller
The microcontroller controls the entire system and evaluates the signal. The best working point is evaluated before the measurement is performed. Have the same test to carry out the assessment work. The conversion ratio in the receiver is least desirable to have a saturated signal in the ADC with the largest transmit current. After the emission current is evaluated, it generates a signal in the receiver. It is between the upper and lower limits. The upper limit is determined by the saturation effect and not by the accuracy of the ADC. The sensor starts working at the operating point. Interference and signals are constantly being measured and evaluated. The gradient of the received signal versus time is used by the rule system to measure the correct sweep strategy, and the ambient light is measured by an additional sensor to detect day or night conditions. In the evening, the sensitivity of the water droplets is greatly affected by the fact that the water droplets have a large influence on the visibility, especially if the bright headlights of other vehicles are illuminated.
Fourth, the sweep mode
Different sweep modes are used to optimize performance for all storm conditions, as shown in the rain density wiper speed mode.
1, direct mode
In direct mode, there is a single wiping action with a low wiper speed. This is the most basic working condition when the automatic mode is on and when the system detects a dry windshield. From this state, each rain event directly triggers a single wiping motion. During the wiping process, the system decides to stop at a low speed, continue to wipe or switch to a high speed wipe.
2, intermittent mode
This mode is for raining situations and runs a single wipe at low speed. Every few seconds, the sensor detects raindrops, and the time between two rains determines the interval between two single wipes. At the end of each interval, the time is recalculated, the more the rain, the shorter the interval, and vice versa. In the calculation, the previous interval will be taken into consideration to achieve a harmonious state. Otherwise "neural behavior" will annoy the driver. If the calculated interval is longer than the maximum interval, the system will go to direct mode. In each wipe cycle, the sensor checks to see if it is converting or continuing to wipe.
3, continuous wipe
In the wiping cycle, the number of rains will be calculated and the size of the raindrops will be evaluated and used to obtain information on the intensity of the rain. Based on this intensity, the rain sensor produces low speed, high speed or specific wiping speed (eg 50r/min). Dynamic hysteresis, which relies on this event in the final loop, prevents the system from quickly transitioning from one speed to another. The time base using the wiper motor stop signal ensures proper operation of all wiper motors under all conditions. If the motor is wiped at a low speed, the detection time is reduced and the critical value between low speed and high speed is automatically increased. The rain sensor mode always reduces the speed from high speed to low speed before stopping to prevent mechanical stress on the wiper.
Concerned about surprises
Tag: Rain sensor Sensor measurement Wiper headlight switch Analog-to-digital converter
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