[Automotive Relay] Working Principle of Automobile Relay Maintenance Method of Automobile Relay
Working Principle of Automobile Relay Maintenance methods of automotive relays
1. Working principle of automotive relays
When a certain voltage or current is applied to both ends of the electromagnetic relay coil, the coil generates The magnetic flux passes through the magnetic circuit composed of the iron core, the yoke, the armature, and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature is attracted to the pole face of the iron core, thereby pushing the normally closed contact to open and the normally open contact to close. ;When the voltage or current at both ends of the coil is less than a certain value, when the mechanical reaction force is greater than the electromagnetic suction force, the armature returns to the initial state, the normally open contact is disconnected, and the normally closed contact is connected.
Then, the automotive relay can be regarded as an aggregate composed of two parts, the control circuit for coil work and the main circuit for contact work. In the control circuit of the relay, there is only a small working current. This is because the contact capacity of the control switch is small and cannot be used to directly control the load with large power consumption. It can only be controlled by the contacts of the relay. on and off.
A relay is both a control switch and a control object (actuator). Taking the fuel pump relay as an example, it is the control switch of the fuel pump, but the coil of the fuel pump relay can only form a loop through the grounding point of the electronic control unit when the driving transistor in the electronic control unit is turned on.
Second, the components of the automotive relay
The automotive relay is composed of a magnetic circuit system, a contact system and a recovery mechanism. The magnetic circuit system consists of iron core, yoke, armature, coil and other parts. The contact system consists of static reeds, moving reeds, contact bases and other parts. The recovery mechanism consists of a recovery reed or a tension spring.
III. Installation method of automotive relays
1. Installation direction If the installation direction is the same as the direction of the shock resistance of the relay, the performance of the relay can be fully exerted. It is recommended to make the impact direction perpendicular to the movement direction of the contact and the armature, which can effectively improve the vibration resistance and impact resistance of the normally closed contact in the non-excited state. When installing, make the contact axis of the relay parallel to the ground, which can avoid contact splashes and carbides falling on the contact surface and improve the contact reliability. Multiple groups of relays should avoid that the small load contacts are located below the large load contacts.
2. When multiple relays are installed in close proximity, it will cause abnormal heat generation. Generally, a spacing of 2mm is recommended. Polarity or magnetic latching relays installed in close proximity will affect the operating voltage.
3. Install the relay on the casing, do not remove the casing and install it first. To prevent loosening, damage and deformation, please use a spring washer. The tightening torque should be within the range of 0.5 to 70N·m.
4. The insertion strength of the plug-in relay is recommended to be 40-70N.
5. Products that meet the same load requirements have different dimensions. According to the allowable installation space, products with low height or small installation area can be selected.
6. The installation methods of automotive relays include PCB board type, ISO socket installation type, ISO 280 socket installation type, shell fixing and card installation. For relays with small size and infrequent replacement, PCB board type is generally used, and for frequently replaced relays, socket installation method is used. For relays whose main circuit current exceeds 20A, the socket quick-connection type is generally used to prevent high current from passing through the circuit board and causing heat damage to the circuit board (except for short-term work relays). For bulky relays, the shell-mounted type can be selected to prevent damage to the mounting feet under shock and vibration conditions.
4. Maintenance of automotive relays
Welding process
1. Flux coating
PCB board type Non-plastic encapsulated relays are very susceptible to contamination by flux, it is recommended to use flux-resistant or plastic-encapsulated relays to prevent flux gas from invading from the terminal and the gap between the base and the shell. , the flux intrusion can be further prevented.
2. Soldering process
When using flux coating or automatic soldering, care should be taken not to damage the performance of the relay. Flux-resistant relays or plastic-encapsulated relays are suitable for dip soldering or wave crest soldering process, but the maximum soldering temperature and time should be controlled with the relay selected.
1. Wave soldering: The recommended soldering temperature is: 240℃～260℃, the time is about 5 seconds, and the best soldering temperature is 250℃. For other soldering temperature and soldering time (such as higher solder temperature, the soldering time will be shortened accordingly), please contact our technical service support or confirm the soldering quality.
2. Manual welding: The recommended welding temperature is 300℃-350℃, and the welding time is controlled within 2 seconds.
3. Cooling: The heating of the relay caused by the soldering process can be alleviated by cooling at the end of the process, so do not change the temperature suddenly, especially avoid cold shock to the thermal relay.
Cleaning Process
Soldering with no-clean flux should be used whenever possible, and overall cleaning of the relay should be avoided. Prevent cleaning agent from entering the relay and causing it to fail. Ultrasonic cleaning is prohibited to avoid contact cold welding, enameled wire breakage and other structural damage caused by ultrasonic energy. Immediately after cleaning and drying, ventilation should be performed to bring the relay to room temperature.
Preservative coating:
Sometimes in order to ensure the moisture resistance and high insulation of the circuit board, the circuit board must be coated with a preservative, and a softer glue that does not contain silicon should be used. The gluing process should prevent the relay from generating negative pressure and inhaling the preservative.
Maintenance method
(1) A simple method for judging the working performance of the relay
Turn on the ignition switch, and then listen to the control relay with ear or stethoscope to see if there is suction in the control relay. Harmony, or feel the vibration of the relay with your hand. If so, it means that the relay is working normally, and the electrical appliance is not working due to other reasons; otherwise, it means that the relay is not working properly.
You can also unplug the relay for testing, for example, if the air conditioner compressor does not work, you can start the engine, and then turn on the blower switch and the air conditioner switch. Then unplug the connector of the air conditioner compressor relay to judge. If the sound of the relay action can be heard, and the engine speed drops significantly when the relay is unplugged, and the engine speed rises when the relay is inserted, it means that the air conditioner compressor relay and its control circuit are normal.
Regarding the position of the relay, all relays and fuses marked with dotted lines on the circuit schematic diagram are generally arranged in the central distribution box.
(2) Common failure phenomena of relays The common fault phenomena of relays are: coil burnout, inter-turn short circuit (insulation aging), contact ablation, thermal decay, and inability to adjust the initial operating current.
①The relay coil is burnt out. In order to prevent this from happening, if the temperature may exceed 80°C during repair, maintenance and electric welding, the temperature-sensitive relays and electronic control units should be removed.
②Contact ablation. For example, the relay of the air conditioner condenser fan of the Jinbei Hiace car (using 491Q-ME engine) is just below the glass cleaning spray pipe. If the spray pipe breaks, the cleaning fluid will leak to the relay, making the relay normally open. The contacts are corroded and cannot be disconnected, which will lead to the failure of the air conditioner condenser fan to keep running. Therefore, water should be strictly prevented from entering the relay.
(3) Try to reduce the contact resistance of the relay contacts
The contact resistance between the contacts of the automotive relay is mainly composed of two parts: shrinkage resistance and surface film resistance. The contact resistance of the contact is related to the contact form, material properties and surface processing of the contact. It can be seen that to reduce the contact resistance of the relay contacts, under the condition of a certain contact pressure, it can be started by improving the contact state and improving the contact material.
(4) Poor grounding of the ECU may affect the normal operation of the relay A Shenlong Fukang 988 sedan, in normal driving, the engine automatically shuts off and starts again, and the car cannot be driven. Turn on the ignition switch, no sound of the fuel pump running, and no high pressure fire. Check the ignition coil and find that there is no power supply on the plug, but the resistances on the primary and secondary sides are normal. Measure the car’s jetted double-sealed relay, which has a 12V power supply at its plug. Replaced the spray double-sealed relay, but there is still no high-voltage fire, and there is no sound of the relay pulling in. Use a wire to directly ground the pin 10 of the jet double-sealed relay, you can hear the sound of the relay being pulled in, and the engine has started successfully. But the strange thing is that after disconnecting this ground wire, the engine does not turn off, and after turning off the ignition switch and restarting the engine, it is normal. Analysis of the reasons, this is due to the poor grounding of the engine ECU, resulting in a very low power supply voltage of the relay coil (sometimes only about 2V), it is impossible to make the relay pull in. After the wire is directly grounded, the relay has a voltage of 12V, so it is smoothly pulled in, so the engine starts successfully. After removing the temporary ground wire (the ignition switch is still on), the relay still has a low holding voltage (this is a common feature of relays), even if this holding voltage is only 2V, the relay will not be broken on, so the engine doesn’t turn off. Turn off the ignition switch, the self-inductive electromotive force generated by the circuit is much higher than the power supply voltage. Under the action of this strong electromotive force, the grounding place with poor contact may return to normal, so the engine is normal after starting. However, the above faults will recur, so the way to eradicate is to thoroughly deal with the bad grounding parts.
Storage environment
Avoid direct sunlight and keep normal temperature, humidity and pressure ; Temperature: 10℃～35℃ Humidity: 5～85%RH Air Pressure: 86～106kPa
Under high temperature and high humidity environment, when the ambient temperature changes rapidly, condensation may form inside the relay. Condensation is especially likely to occur when shipping by sea, so please pay attention to the transportation environment. Dew condensation is a phenomenon in which water vapor condenses into water droplets when the temperature changes from high temperature to low temperature or from low temperature to high temperature and high humidity in a high temperature and high humidity environment. Condensation can cause insulation degradation, coil corrosion and disconnection, rust, etc.
Low temperature freezing: In dew condensation and high humidity environments, in the state where moisture adheres to the relay, the moisture freezes when the temperature drops below the freezing point. Icing can cause sticking of moving parts, delayed action, or ice between the contacts, causing the contacts to fail.
In low temperature and low humidity environments, plastic may become brittle.
When stored in high temperature, high humidity and environment containing organic gas and sulfide gas for a long time, sulfide film and oxide film will be formed on the contact surface, resulting in unstable contact and contact failure. Please pay attention to the packaging form to minimize the influence of humidity, organic gas, sulfide gas, etc.
The relay should be stored and installed in a clean environment, please use a dust cover or plastic-enclosed relay in an environment with dust pollution.
Pay attention to monitoring the storage temperature and try to avoid the relay storage time for too long.
Storage and transportation stress During transportation, if a large drop shock is applied to the relay, it may cause malfunction. Please pay attention to whether the appearance of the packaging equipment is complete. The relay is packaged in a long tube. When the number of relays is small, if there is a lack of limit, it will slide down and affect the appearance and characteristics of the relay. Special attention should be paid to it.
