1 electromagnetic clutch structure principle

Compressors use two types of electromagnetic clutches: 4-pole and 6-pole. The structure is similar except for the number of poles. They are composed of coils, pulleys, and drive plates. The coil is press-fitted onto the shaft of the front cover. The pulley is seated on the front cover through double-row angular contact ball bearings and the drive plate is pressed onto the main shaft. After the coil is energized, an electromagnetic force is generated to suck the drive plate and the pulley to drive the rotation of the main shaft, and the compressor works. After the coil is de-energized, the drive plate and the pulley are disengaged, the belt pulley idles, and the compressor does not work.

1.1 Magnetic pole

The electromagnet has two poles: south (S) and north (N). The same pole repels and attracts different poles. The two attracting poles generate a suction, which is called a pair of magnetic poles. The compressor uses two types of clutches: 4-pole, 6-pole clutch, 4-pole 4-pole, and 6-pole 6-pole. According to the electromagnetic theory, a magnetic flux is generated after a coil is energized, and we use a magnetic flux line to form a closed loop along the minimum reluctance line in the magnetic circuit material. There are ring-shaped magnetic isolation rings on the end face of the pulley and the end face of the drive plate, so the 6-pole pulley magnetic field line enters the drive plate 6 times and the drive plate enters the pulley 6 times. The 4-pole pulley magnetic field line enters the drive plate 4 times and the drive plate enters the pulley 4 times. .

1.2 Air gap

There are three types of air gaps in the clutch: the air gap Δ0, which is the air gap between the pulley and the end face of the drive plate, Δ0=0.3-0.7. Its function is to prevent the pulley from rubbing against the drive plate. Larger force, lower drive torque, small value, it is necessary to improve the processing accuracy. Outer annulus Δ1—The radial (unilateral) clearance between the outer diameter of the coil and the inner wall of the pulley. The inner ring gap Δ2 is the clearance between the pulley hole seat and the coil shell. Theoretical analysis and calculation results show that 80% of the magnetic pressure drop is consumed in the internal and external annulus, so to reduce the internal and external annulus, usually take Δ1, Δ2 ≤ 0.5.

2 The key factors affecting the clutch loading capacity - the flatness of the pulley, the end face of the drive plate

Electromagnetic clutch is the friction force transmission torque, so the end face of the pulley and the end face of the drive plate is good, a significant impact on the clutch load capacity. The author made four groups of different combinations of plane comparison test, although the test conditions are simple, but the impact of the plane condition is clear, a set of pulley end surface convex 0.04 and drive plate concave surface 0.045, the highest load capacity. Because the end face of the pulley and the face of the drive plate constitute a good fitting surface, the two groups are just the opposite. It is the convex convex pair, forming a small area of ​​contact, the minimum load capacity, three and four groups for the convex convex 0.01 concave convex 0.02 General loading capacity. In terms of design, it is required that the flatness of the working end face of the pulley and the drive plate is less than 0.05, and the concave wheel is generally 0.01-0.03. The problem is that the drive plate has poor rigidity, riveting stress, deformation after riveting, and rivets Low, two rivets protruding from the midpoint of the connection, the entire plane forming a three-convex complex surface, which is very unfavorable for the transmission of torque.

To improve the flatness, take the following measures:

1) Increase the thickness of the drive plate: if the thickness is increased to 4.9±0.1, the stiffness of the drive plate can be increased by 60% for 40% and 4 for 17%.

2) Control the hole pitch and aperture accuracy of the yellow plate, drive plate and drive plate to reduce the riveting deformation.

3) Reduce the deformation of the drive plate caused by external forces during assembly, handling, installation and maintenance. Deformation has a significant impact on the load capacity. There are two common types of deformation: (1) The drive plate is twisted, and the drive plate and the pulley end surface have only a single point or Small area contact, unable to transmit torque.

(2) yaw or retraction, the contact between the drive plate and the end surface of the pulley is idling, the drive plate is worn off, and the drive plate and the pulley contact with each other after power-on.

3 Effect of Ampoule Number

The product of the number of turns of the coil n and the current A is called the ampere-turn number. Under the same conditions, the clutch load capacity is proportional to the square of the number of ampere turns, and the voltage is usually given. To increase the number of ampere turns, only the diameter of the enamel wire can be increased. If the diameter of the enameled wire does not increase, increasing the number of turns does not increase the number of ampere turns. Since the number of turns increases, the resistance of the coil increases in the same proportion, and the number of ampere turns does not change.

4 Influence of Drive Disk Size

If the drive disk is large, the magnetic pole area is large and the arm is also large, so that a large torque can be transmitted.

5 Effect of air gap size

The qualitative analysis of the influence of the air gap size on the bearing capacity and the calculation of this effect are given below. Known magnetic flux φ = 3 × 10-3Wb, iron core material D21, armature material cast iron, the number of ampere turns and suction. This is the known magnetic flux enthalpy and suction. It is a solution and a solution. Suction: F=0.5B2S/μ0 N where: B is the magnetic induction (Wb/m2); S is the magnetic pole area (m2); μ0 is the air permeability μ0=4π×10-7.

The test data is substituted into 2F=0.8B2S×106=0.8×12×3×10-3×106=2 400 N. Above, the clutch load capacity formula can be written; M=0.4B2SnfR×106 Nm where:n The number of pairs of clutches, 4 poles n=4, 6 poles n=6; f is the coefficient of friction, f=0.3 See Mechanical Design Handbook, Volume One Chemical Industry Press; R is the average radius of the driving disk (m) . The magnetic pressure drop in the air gap is very large, and the magnetic induction intensity is reduced, so the load capacity drops rapidly. The calculation result proves this point: when the air gap is 0.45 mm both inside and outside, the torque is 44 Nm, and the air gap inside and outside is 0.55 mm When the torque is 32N.m, a drop of 27%, both the internal and external air gap are 0.65mm, torque is 25N.m, a drop of 43%.

6 Low voltage, high temperature effects

Under normal conditions, the clutch design capability can meet the requirements, but the following circumstances may be exceptional.

1) Undervoltage, assuming the coil rated voltage is 12V, the actual voltage is 10V, according to Ohm's law, the coil current decreases to 10/12=0.83, the magnetic induction intensity drops to 0.832=0.69, set rated torque distance M0=40N.m, voltage 10V When M=0.69M 0 =27.6N.

m; 2) high temperature, if the room temperature resistance 3.06Ω, 1.14Ω when 1150C, assuming the actual operating temperature of the coil 1000 C, the resistance is 3.06 + (4.24 - 3.06) × 100/115 = 4.09Ω, due to increased resistance, the current decreases To 3.06/4.09 = 75%, it can be approximately considered that the torque is reduced to 0.752M0 = 22.4Nm

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