Automobile relay control is widely used in auto start, preheating, air conditioning, lights, wiper, efi, oil pump, security, audio, navigation, electric fan, cooling fan, electric Windows, air bags, anti-lock braking and suspension control and automotive electronic instrument and fault diagnosis system, the second in size only to the sensor.

1. Structure and working principle of relay

The contact capacity of the control switch used on the car is generally small, and it is not possible to directly control the electrical equipment with a large working current. In this case, the relay is needed to control its on and off.As shown in the figure below, automotive relay is generally composed of iron core, coil and armature, contact reeds, etc, as long as the voltage on both ends of the coil with a certain, will flow through a certain amount of electric current in a coil to generate electromagnetic effect, the armature will be under the electromagnetic force attraction to overcome the return spring tension is attracted to the core, to drive the armature moving contact and the static contact (normally open contacts) and off.When the coil is powered off, the electromagnetic attraction will disappear, and the armature will return to its original position under the force of the spring, and the moving contact will attract the original static contact (normally closed contact).Through such a suction, release action, to achieve in the circuit, cut off the function.

Structure of relay

The relay is actually a switch in the circuit, but different from the traditional circuit switch, the core of the relay is to control the large current with a small current, in the circuit plays the role of automatic regulation, safety protection, conversion circuit, is an automatic switch of the automation circuit.As an automatic switch, the relay is not only controlled, but also plays a controlling role, with a control system (also known as the input loop) and a controlled system (also known as the output loop).

2.Application of relay in electrical maintenance

Automobile circuit can be divided into power circuit and control circuit.In most of the electricity system, the relay is the intersection of the power supply circuit and control circuit by controlling the on-off of the relay control circuit to control the power supply circuit, in the actual maintenance can through sub relay corresponding jacks, determine the stand or fall of control circuit work: if it is a power supply circuit, you need to check on a line of plug and wire, so as to rapidly determine vehicle electrical fault what happened in the control circuit and power circuit.

In practical application, the low-voltage power supply of the relay is controlled by an input quantity (such as current, voltage, temperature, etc.).When the input reaches the specified value, the relay turns on or off the controlled output circuit.

The following in the actual maintenance of the application of relay maintenance as an example.

Diagnosis example 1 - changan yuexiang car air conditioner not refrigeration

When the air conditioner is turned on, the compressor does not absorb normally. Press the bypass valve spool on the pipe road with a special tool, and it is found that white fog comes out. Confirm that there is refrigerant in the pipe.

After confirming that there is refrigerant in the pipe and that the compressor is not working, it is necessary to determine which part to start the inspection to confirm the cause of the failure.If the parts are checked one by one according to the suction condition of the compressor, the inspection and diagnosis process of the air conditioner will be too long, and the middle disassembly and assembly inspection may also cause damage to other parts.

Based on the above consideration, at the time of diagnosis is directly unplug compressor relay, with short cables connect the relay to control the socket (power supply side and load side), compressor suction chorus of "pa", which means the compressor normal electromagnetic clutch, power supply circuit is no problem (short after relay compressor normal off), so the judge fault in the control side, this means failure could in air conditioning controller, three states pressure switch, wiring harness plug parts and other components.In this way, the scope of fault diagnosis can be reduced directly, the fault problem can be simplified, the time of fault diagnosis can be shortened, and the unnecessary parts and components can be removed and damaged.

Similarly, a similar method can be used to short-circuit each connector terminal (it is recommended to short-circuit with a secured test light line), and quick diagnosis can be achieved by checking the sensors visible on the surface (such as three-state pressure switches or connectors).

Diagnosis example 2 - zhixiang hybrid car does not start

Oil, electricity and gas are the three essential elements for starting a car.Therefore, the car does not start the preliminary investigation is also from the three elements of the investigation, such as check whether the oil pump supply, high pressure fire, whether the intake and exhaust is unobssive, cylinder pressure is sufficient.

After a simple check on the hybrid electric car, it was found that the oil pump did not move when the car was just electrified.Further check the high-pressure fire and exhaust (blocked three-way catalytic converters will also cause failure to start), there is no problem, the fault is basically defined on the oil pump.

If the fault point is found according to the circuit diagram, the method from simple to complex is as follows:

(1) test insurance;

(2) check the gasoline pump relay is intact;

(3) one by one check circuit failure, if bad luck, may be the control circuit and power circuit all check once.

According to the method of short-circuit relay, the specific steps are as follows：

(1) the short connection relay is controlled end, listen to the electronic oil pump whether the work (or hand pinched fuel tube rubber part, feel whether there is pulse pressure).If working, the problem lies in the control circuit (main relay, ECU, etc.);If it doesn't work, the problem is the power supply.

(2) the real car inspection, the failure of the car electronic oil pump short connection relay is still not working, with the test lamp directly take the iron test relay power supply feet (30 feet), found 30 feet over electricity, that the problem is in the electric circuit after the relay (otherwise check the circuit in front of the relay), directly check the circuit after the relay can be.

(3) with the test lamp short check the electronic oil pump socket power pin and tie pin, found that the test lamp is on, unplug the socket, found that the electronic oil pump pin inserted crooked, not the oil pump caused by damage is not working.

Using the control principle of relay skillfully to diagnose electrical problems can make the purpose of diagnosis more clear, reduce a lot of unnecessary inspection, and achieve the purpose of rapid diagnosis.This method is not only applicable to air conditioning system, but also to fuel system, lighting system, starting system, etc.