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Reed sensor application in the automotive industry

- May 22, 2018 -

The automotive industry has a standard power level of 24 VDC or less, and the reed switch performs very well under such low load conditions, and therefore has a high usage value. Specially manufactured molded reed sensors can withstand shocks and extreme temperatures and humidity. The dry reed switch manufacturers Huajun electronic matching reed switch and reed sensor can be used in the following automotive industry applications:

Shock sensor triggers airbag

Anti-lock brake system (ABS)

Doors, windows, skylights, fuel tank cap end position sensing

Safety belt lock induction

Gear position sensing

Position sensing of hydraulic mobile terminals in heavy vehicles

Low level sensing fuel, brake fluid, wiper fluid, coolant tank

Two-wheeler application

Poor lamp detection

Electronic load switch in car

Radiator and engine temperature sensing

Accurate fuel tank level sensing

Coolant flow sensing

Air conditioning control

Tachometer, odometer, cruise control system

Inclination sensor to detect rollover

Car electronic key lock

Airbag accident prevention

Hood tilt switch

Suspension load balancing system


Trigger airbag crash sensor

        According to statistics, nearly 80% of cars use reed sensors to trigger airbag crash sensors. A ring magnet is mounted on a very precise tension spring that slides over the reed switch. The use of different tension springs depends on the required triggering of the reed switch. Two reed switches are used to replace a fail-safe mechanism. In the event of an accident, the mass of the magnet compresses the spring, moves closer to the reed switch, and closes it. This signal is used to trigger the compression of the inflated air cylinder.

Anti-lock brake system (ABS)

        In the ABS control, the vehicle-mounted electronic products require the use of differential hydraulic brakes to prevent slipping tails during driving. Four reed sensors were installed near the wheels, and the magnets were mounted on the wheels themselves. In this way, feedback from the rotational speed of each wheel to the on-board computer, as braking, if the target wheel rotates faster, more hydraulic oil pressure is fed into these brakes.

Door, window, cover position sensing

        The dashboard dashboard needs to display more and more information to ensure the safety of drivers and passengers. In particular, reed sensors, which can withstand shocks and vibrations, can be used to sense doors, power windows, skylights, trunks, hoods, radiators, and fuel tank caps. Reed sensors have the added benefit of being able to withstand temperatures up to 150°C.

Seat belt lock detection

        In some cars, the seat belt needs to be pressed or flashed to display a message. The dicing sensor is installed inside the seat belt locking concave side, and when the seat belt insertion is locked, the magnetic field diverting reed switch is opened. (NO) The normally open reed sensor can be designed to use a normally closed reed switch at a time. The magnet is mounted on the other side, strong enough to keep the (NC) normally closed reed switch open.

Hydraulic arm end position sensing in heavy vehicles

        Bulldozers, excavators, tractors, forklifts and garbage compactors are used to carry out various tasks with hydraulic cylinders and pistons. The hydraulic solenoid valve can detect the end position and middle position of the piston and cylinder through the reed sensor, and perform pressure control.

Low level monitoring

        The reed sensor can detect the level of brake oil, power steering oil, radiator coolant tank. The foam magnet float is mounted on the rod inside the lid. Reed sensor can be installed outside the tank to detect low level. The signal can be used to trigger the display of the driver's LED information panel. Because the reed sensor is installed outside the liquid container, the container can be easily repaired without removing any equipment. Some car manufacturers also install reed sensors to detect an empty slot, rather than a full tank, because it will be easier to find faults.

Two-wheeler application

        A piston switch for a two-wheeled vehicle such as a motorcycle is used to detect the restraint of the front and rear brake levers to turn on the brake lights. It can also be used to detect the position of side brackets. These piston switches are purely mechanical so they can be prematurely damaged in ambient conditions. The use of the reed sensor in this type of application is due to its inherent sealing properties and mobile mechanical components that are freely replaceable. Reed switch sensors can also be used to sense the throttle position to a signal processor to control the timing of the engine.

Poor lamp detection

        Taillights and stoplights are very important factors in driving. Their breakdown may lead to accidents. Reed relays play an important role in these applications due to their small size and long life. When the reed switch and a resistor cross the fuses of the lamp and the lamp, the reed switch relay is energized and the output can be used to trigger the alarm dashboard. Although bulbs can be used instead of reed relays, two bulbs may fail.

Radiator, engine and four-wheel drive transmission temperature sensing

        The thermo-magnetic reed switch sensor can be mounted on the engine block and the induction high temperature is displayed on the indicating instrument panel. The thermal reed sensor can switch loads up to 60W and can be directly connected to a radiator fan when used in a radiator. When the temperature reaches a predetermined temperature, the fan is turned on. When the temperature drops below 10°C, the thermal reed sensor cuts off the power supply fan. They can also be mounted on four-wheel drive transmission systems to check for overheating. The thermal reed sensor can be designed to have a temperature difference of 2°C to 10°C.

Accurate fuel level sensing

        A special reed sensor and an integrated resistor can be mounted on the printed circuit board to give potential feedback through two output foamed magnetic floats that move along their length. The PCB track can be designed in such a way that there is a full tank of high resistance and a low resistance tank, and vice versa. As a sealing device, the reed sensor is particularly suitable for an explosive environment such as a fuel tank.

Coolant flow sensing

        A simple, cost-effective flow sensor reed switch can be attached to the car's coolant tube. As long as the coolant flows, the reed sensor is not actuated. If it is accidental, the coolant tube is clogged or if the coolant valve fails, a signal is given on the indicator dashboard.

Climate control

        Miniature reed relays are capable of high load use of automotive climate control circuits that turn heaters and coolers on or off. It can also be used with a thermal reed sensor to trigger these relays to stay within 23°C of comfort inside at the required temperature.

Tachometer, odometer, cruise control system

        A multi-pole ring magnet is linked to the actuating shaft of the speedometer. The reed sensor can sense the pulse and generate a square wave. Vehicle electronics can use these square wave pulses to calculate speed and speed. In the car cruise control system, when the cruise setting is 80 kph, as the road inclination changes, the on-board computer can adjust the fuel supply to the engine to correct the cruising speed by monitoring these pulses.

Tilt sensor for detecting rollover

        The latest statistics on auto accidents show that the majority of deaths are due to sideways rollovers. Based on the reed switch tilt sensor detects the front and rear impact of the smart roller, which inspires the airbag. Movement of the magnets is like a rollover of a pendulum when sideways, activating multiple reed pipes mounted on strategic points and triggering the airbag. This tilt sensor is a standard vibration sensor.

Automotive electronic key sensor door

        In newer car electronic keys, comparisons are made through key codes and then sent to the central locking system and on-board computer. A reed sensor is also used on a manually opened door that can be opened using a remote control or opened manually. The sensor is mounted on the door and the magnet installs the lower door handle. If the handle is raised, the reed sensor detects and sends a signal to the computer and opens the door. An additional advantage is that the same reed sensor can be used as a safety protection device. In the unlocked state, the door is opened and an alarm is triggered.

Airbag accident prevention

        When a collision occurs, the airbag is protected against accidental deployment by sensing the presence of an airbag in which passengers are seated. A reed sensor is mounted under the seat, and a magnet assembles to the seat's foam to actuate the reed sensor. If there is a passenger on the seat, this signal activates airbag deployment.

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