What happens to the electronic expansion valve? How to measure the electronic expansion valve

Electronic expansion valve has two types of structure: stepper motor type and electromagnetic coil type. The electromagnetic coil type is strictly speaking an electromagnetic expansion valve. At present, electronic expansion valves commonly used in refrigeration equipment such as home air conditioners and refrigerators often refer to stepper motors. The electromagnetic valve consists of a valve body, a valve core, a bellows, a transmission mechanism and a pulse stepping motor, as shown in FIG. 2 .

The valve body is the expansion valve itself, which consists of a needle valve, a magnet, and upper and lower covers, as shown in Figure 3. The degree of opening of the needle valve is controlled by the superheat degree of return gas (detected by return air temperature and pressure). The greater the degree of superheat is, the larger the degree of opening is, and the smaller the degree of superheat is, the smaller the degree of opening is.

The bellows separates the refrigerant passage from the moving parts to prevent refrigerant leakage. The pulse stepper motor is a drive mechanism and mainly consists of a coil, a bracket, and a connector, as shown in FIG. 4 .

The role of the transmission mechanism is to convert the rotation of the motor into a reciprocating movement of the valve core. There are two kinds of transmission mechanism, and the deceleration type transmission mechanism includes a gear pair (a basic structure composed of two meshing gears), a rib pair (a mechanical combination that uses a screw thread to realize the connection function), a transmission rod, and the like. Direct-acting gears do not have gear pairs.

Tip: The expansion valve, also called throttling valve, is the main component of the refrigeration system. It is installed at the entrance of the evaporator and is the demarcation point between high pressure and low pressure of the refrigeration system. Its function is: throttling the high-pressure liquid refrigerant from the receiver drier to reduce the pressure, adjust and control the amount of liquid refrigerant entering the evaporator, so that it can adapt to changes in the refrigeration load, and at the same time prevent the liquid hammer from occurring in the compressor (ie, The unevaporated liquid refrigerant is compressed after entering the compressor, which can easily cause the damage of the compressor valve and abnormal vapor overheating at the outlet of the evaporator.

From the structural analysis we can see that the working principle of the commonly used electronic expansion valve is actually the working principle of the stepping motor.

The rotor of a conventional stepper motor is a permanent magnet. When a current flows through the stator winding, a vector magnetic field is generated by the stator winding. The magnetic field will drive the rotor to rotate an angle so that the direction of a pair of magnetic fields of the rotor coincides with the direction of the magnetic field of the stator. When the vector magnetic field of the stator is rotated by an angle, the rotor also rotates by an angle with the magnetic field. That is, each time an electric pulse is applied to the stepper motor, the motor rotates by one angle. The angular displacement of the motor rotation is proportional to the number of input pulses. The rotation speed is proportional to the pulse frequency. By changing the order in which the windings are energized, the motor will reverse.

1. Current and magnetic field

When the current flows through the conductor, according to the right-handed screw rule, a rightward rotating magnetic flux line perpendicular to the current direction will be generated. If it is a spiral conductor, it will generate a magnetic field as shown below.

2. Coil excitation

The pulse stepper motor coil is divided into two phases. As shown in the following figure, the upper coil performs A and excitation (provides a working magnetic field for the electromagnetic induction equipment). The winding direction of the coil is in the same direction, and the COM line is drawn in the middle of the coil. The ports are A and A, and the excitation can be changed by changing the direction of the current at the COM terminal to realize unipolar driving.

In 1-2 phase excitation, the exciting state of the claws of the coil holder and the stator is as shown in the figure below. The valve opening sequence is A→AB→B→BA→A→AB→B→BA. The valve closing sequence is the opposite of opening the valve. The claws of the pulse stepper motor stator consist of 4 groups of 1 group and a total of 12 groups. Apply 96 pulses and the magnet rotates 1 turn.

In the actual maintenance, pay attention to the following characteristics of the stepper motor:

Excitation mode: 1-2 phase excitation. Excitation speed (usually the number of pulses per second, in pps):

31.25pps/83.4pps (CPF, YPF: 30~35pps).

Coil working voltage: DC12V + 10 ‰. In order to prevent the temperature of the coil from rising, the solenoid can no longer be energized when the solenoid valve stops operating. Current direction: Use COM side as positive (+). The initial valve base point is 0 pulse in phase A excitation state. When the expansion valve is operated in reverse, an excitation of about 0.5s should be added to stabilize the motor. Otherwise, it will cause a loss of pace.

3. Flow control method

The rotation of the stepper motor is converted into a linear motion through the transmission mechanism to control the gap between the needle valve and the valve hole to achieve flow regulation.

Electronic expansion valve is characterized by a large range of adjustment, rapid and sensitive action, precise adjustment, stable and reliable. The refrigerant can flow in both the forward and reverse directions in the electronic expansion valve, avoiding the disadvantage of only one direction of the thermal expansion valve. When used in a heat pump, the refrigeration system can be greatly simplified. When the refrigeration system is shut down, the electronic expansion valve can be completely closed so that there is no need to install a solenoid valve at the refrigerant inlet.

1: The valve of the electronic expansion valve is fully closed.

2: After starting up, there is noise in the electronic expansion valve.

3: The electronic expansion valve does not operate.

4: Electronic expansion valve stuck.

5: The supplied refrigerant flow rate is small and the supply liquid is small.

6: The liquid supply causes liquid return.

7: Incorrect selection of the expansion valve causes the fluid to fluctuate.

8: Damaged temperature package.

9: Ice blocking or dirty plugging in the electronic expansion valve.

10: Electronic expansion valve coil burned.

Failure phenomenon 1: The valve of the electronic expansion valve is fully closed

Analysis and Maintenance: Normally, before the electronic expansion valve is energized, the needle valve is in the open position. The valve opening of the valve body is 480 pulses, but since the rotor is fixed by the thread structure, the position of the rotor may be changed due to vibration in the transportation process, and finally the valve is fully closed.

In case of failure, the reset operation can be performed after power-on to ensure that the valve body is in an open state, so that the size of the needle valve opening can be controlled by the stepping motor, thereby regulating the flow of the expansion valve.

Symptom 2: After starting up, there is noise in the electronic expansion valve

Analysis and maintenance: If the noise is too loud, it indicates that the internal devices are stuck and need to be replaced as a whole.

It is worth mentioning that if there is a "click" sound in the valve body when the power is turned on, this is normal. After the air conditioner is energized, the electronic control board will send a fully open or fully closed pulse to the electronic expansion valve. At this time, when the rotor of the electronic expansion valve reaches the maximum opening degree, it will collide with the limit device and issue a “click” friction sound. When the air-conditioning system is filled with refrigerant, the rotation resistance of the rotor is increased, and the sound propagation mode is changed, the operating sound of the electronic expansion valve becomes very small.

Symptom 3: Electronic expansion valve does not move

Analyze and repair: When the power is turned on, first listen to the body whether there is "click" sound, if not, then check whether the valve body is completely set into the coil, the coil and the circuit board connection is normal, the coil power supply voltage meets the requirements (12V ± 1.2V).

If the above checks are all normal, check whether the valve body can be fully opened. If not, it means that the valve body is bad and needs to be replaced. If the valve body is fully open, check if the number of fully closed valves is greater than 480 pps. If it is less than 480 pps, check the drive mechanism.

Symptom 4: Electronic expansion valve stuck

Analysis and maintenance: The fault is due to debris in the refrigerant flow into the electronic expansion valve and accumulate, debris embedded in the valve body, it will make the rotor rotation friction increases, causing the phenomenon of stuck, usually only the overall replacement to solve .

Common impurities include pipe foreign bodies, welding oxides, etc., that is, the fault is mostly caused by humans. In order to prevent the occurrence of such failures, one is to strengthen the pipeline cleanliness during inspection and repair, the other is to adopt welding protection, and the method of charging chlorine is generally adopted to reduce oxides, and the third is to install a filter over 100 meshes at both ends of the valve body. .

The normal electronic expansion valve has a clicking sound after it is plugged in. If there is no sound, or if the expansion valve starts to frost after the compressor is operating during cooling, the coil and power supply should be checked for normal (12V pulse). If the voltage is normal, it means that the computer board is normal. If there is no sound in the expansion valve at this time, it is an expansion valve failure. At this time, the DC resistance of the coil of the electronic expansion valve is measured first. If it is normal, the internal blockage of the valve body may be dirty, and the high pressure gas may be used. Purge.

In addition, the electronic expansion valve should be reset when the power is turned off. At this time, it can be determined whether there is a problem with the valve needle by listening to sound or feeling vibration. In the off state, the valve is generally at the maximum opening, then disconnect the coil lead, and then start running, if the refrigerant can not pass at this time, you can determine the valve pin stuck. Under normal circumstances, touch the ends of the electronic expansion valve by hand, the inlet is warm and the outlet is cool.

The coil detection method is illustrated by taking the example of three-wire and five-wire Q12-GL-01 and shield-wire six-wire DPF1.65C-002 electronic expansion valve as an example.

1. Three-wire five-wire Q12-GL-01 coil

The equivalent circuit diagram of this coil is shown in the figure below. Normally, the resistances of the 1 and 2, 3, 4, and 5 sides measured with a multimeter were 47.1Ω, 47.0Ω, 47.0Ω, and 46.3Ω, respectively; the resistances at the 2 and 3 and 4 ends were 94.4Ω and 93.4Ω, respectively. It can be seen that the resistance values ​​of Line 1 and other coil ends are all around 47Ω, which means that Line 1 is the common terminal, and the other 4 lines are coil terminals, that is, share a common terminal.

If the measured resistance between the leads is infinite, it indicates that the coil is open; if the resistance is too small, it indicates that the coil is short-circuited and all of them need to be replaced.

2. Six-wire shield type DPF1.65C-002 coil

The equivalent circuit diagram of this coil is shown in the figure below.

Normally, the resistances of the 1 and 3 and 5 terminals were measured to be 47.3Ω and 47.5Ω, respectively, with a multimeter. The resistances of the 1 and 2 terminals were infinite; the resistances of the 2 and 4 and 6 terminals were both 47.5Ω. It can be seen that this type of coil is divided into two groups, in which the 1, 3, and 5 ends are a group, the 1st line is the common end, 3, 5 is the coil end; the 2nd, 4th, and 6th ends are another group, and its The common ends are 2, 4 and 6 coil ends.

Silicon TVS / TSS

Silicon TVS / TSS:

Diode TVS (Transient Voltage Suppressor), also known as Transient suppression diodes, is widely used a new type of high efficient circuit protection device, it has a fast response time (the nanosecond) and high surge absorbing ability.When it ends of stand moments of high energy shock, TVS can bring the two ends at high rate from high impedance to a low impedance between impedance values, to absorb a large current moment, put it at both ends of the voltage restraint on a predetermined value, thus protecting the back of the circuit components are not affected by the impact of the transient high pressure spikes.

Silicon TVS Transient Voltage Suppresso,Silicon TSS Transient Voltage Suppresso

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