As a new generation of positive displacement compressor, scroll compressor is widely used in air conditioner refrigeration, gas booster, vacuum pump and other fields because it has the irreplaceable superiority of the same type of compressor. The scroll compressor mainly consists of five parts: an orbiting scroll, a fixed scroll, an anti-rotation mechanism, a crankshaft and a bracket body. When the compressor is in operation, the orbiting scroll is driven by the crankshaft between the fixed scroll and the bracket body, and is subjected to a large axial gas force that varies with the spindle angle. The presence of axial gas force not only increases the wear of the orbiting scroll and the bracket body, but also increases the power consumption. Moreover, the axial gas force has a tendency to separate the moving and stationary scrolls, which may result in the friction of the scroll top seal. The gap increases. The increase of axial clearance will increase leakage, reduce efficiency and displacement, increase power consumption, and cause scroll compressor failure in severe cases. Therefore, the application of axial change technology is the key to balance axial gas force and reduce gas leakage. . In the past, the balance method was to open the back pressure hole on the movable scroll to make the movable scroll float in the axial direction. This paper will open the back pressure hole on the fixed scroll, and analyze its feasibility and advantages.

1 design of the static scroll back pressure structure The scroll compressor designed in the past has fixed the fixed scroll on the bracket body, so the fixed scroll is inactive in the axial direction, and the movable scroll is in the bracket body and Floating between the fixed scrolls, the axial gas force balance mainly depends on the movable scroll to open a back pressure hole, so that part of the gas enters the back pressure chamber, thereby forming a gas force in the back pressure chamber to push the vortex The back of the disc, the principle is as shown. A certain pressure of gas in the compression chamber enters the back pressure chamber through the back pressure hole, so that an axial gas force is formed in the back pressure chamber, thereby ensuring the axial gap seal.

The technique of opening the back pressure hole in the movable scroll has been relatively mature, but there are still limitations. For example, the back pressure chamber should occupy a certain volume, the size of the back pressure chamber and the specific position of the back pressure hole can be accurately calculated in theory, but the moving disc back pressure structure cannot be actually processed, installed or operated. Played a very good result.

Based on the balance structure of the movable scroll, a static scroll balance structure is designed, that is, a back pressure hole is opened on the fixed scroll. Firstly, a card slot is opened on the bracket body, and a certain gap is left in the axial direction of the card slot, and the chuck on the fixed scroll is installed in the card slot. Since the card slot has a certain gap, the working condition changes. When the fixed scroll can be moved according to the slot limit, it can compensate and protect the wrap. The processing of the bracket body and the fixed scroll inlay is as shown. In order to ensure the installation, the card slot and the chuck of the fixed scroll cannot be completely closed.

The mosaic structure of the bracket body and the fixed scroll can satisfy the positioning of the fixed scroll and the axial change function, and provides conditions for opening the back pressure hole of the fixed scroll. A schematic diagram of the structure of the back pressure hole of the fixed scroll is shown.

A back pressure balance hole is opened on the fixed scroll, and the gas in the compression chamber is introduced into the sealing assembly nested on the fixed scroll. At this time, the inside of the sealing assembly will be filled with high-pressure gas, and this part of the gas will generate pressure. The radial pressure will cause the rubber pad of the sealing assembly to expand outward, causing elastic deformation, blocking the gap between the end cap and the fixed scroll in the sealing assembly, achieving gas sealing, and the axial pressure can be balanced. The axial gas force received by the scroll drives the fixed scroll to axially contact the orbiting scroll to ensure axial seal sealing. When the scroll compressor is in operation, since the orbiting scroll cannot move axially, the axial force will push the fixed scroll to move axially, and the seal assembly embedded in the fixed scroll will follow the fixed scroll. The disc moves together in the axial direction, and the positioning end cover mounted on the sealing assembly is connected to the outer casing to restrict the movement of the fixed scroll. At this time, the high pressure gas in the sealing assembly will generate a pressure to push the fixed scroll to achieve the axial direction. The role of compensation.

2 The opening of the back pressure hole of the fixed scroll 2. The principle of opening the back pressure hole of the fixed scroll According to the realization structure and working principle of the back scroll of the fixed scroll described above, the opening of the static vortex back hole should be provided. The following principles: 1) The range of the center angle of the back pressure hole is selected according to the magnitude of the axial gas force received by the fixed scroll and the effective sectional area of ​​the compression chamber.

2) The back pressure hole should be opened in the compression chamber, and should not interfere with the tooth head of the scroll body, so that not only the damage of the wrap tooth strength but also the gas flow of the back pressure hole can be avoided.

3) Select the appropriate back pressure hole size, according to experience, usually the back pressure hole diameter d = 1 ~ 2 mm.

4) The position of the back pressure hole should be as close as possible to the wrap. The back pressure hole is opened on the fixed scroll, and the movement track at any point on the orbiting scroll is centered on the center of the fixed scroll, and the circular motion is performed with the radius of the base circle. Under the same rotation speed, the back pressure hole The position should be closer to the inside of the wrap, and the time for the back pressure hole to be covered by the static wrap is shorter.

2. 2 method of opening the static scroll of the fixed scroll The force analysis of the fixed scroll is as shown, the axial scroll is mainly subjected to the gas axial force F a , the back pressure F b and the dynamic and fixed scroll in the axial direction. Section contact force N.

According to the static equilibrium principle, F b = N + F a (1) where: N is the contact force when the edge of the dynamic and fixed scroll just touches all. That is, N = M t / D (2) where: M t is the overturning moment of the fixed scroll, N ? m ; D is the effective diameter of the fixed scroll, m. back pressure F b is F b = S bpb (3) where: S b is the effective cross section of the pressure chamber formed in the bottom seal assembly of the fixed scroll, m 2 ;pb is back pressure, Pa.

Since the pressure chamber formed in the bottom scroll seal assembly of the fixed scroll is actually a hollow cylinder, its effective sectional area is the actual area of ​​the ring. That is, S b = π( D 2 0 - D 2 1) / 4(4) where: D 0 is the outer diameter of the effective section forming the pressure chamber in the bottom seal assembly of the fixed scroll, m; D 1 is the static vortex The inner diameter of the effective section forming the pressure chamber in the bottom surface seal assembly, m.

Therefore, the minimum pressure in the pressure chamber of the seal assembly can be obtained as pb, min = 4 < F a(4πna + 2πa - t) + 3 M t > π( D 2 0 - D 2 1) (4πna + 2πa - t) (5) where: t is the wall thickness of the wrap, m; r is the radius of the crank, m.

In the actual operation of the scroll compressor, the fixed scroll is not moving, and the orbiting scroll rotates around the center of the fixed scroll with a certain radius of revolution. Now suppose that the orbiting scroll does not move, the static scroll will rotate around the orbiting scroll. At this time, the trajectory of any point on the fixed scroll is a circle with the moving disk as the center and R or as the radius, so the trajectory of the back pressure hole is (x - a) 2 + ( y - b) 2 = R 2 or (6) The equation of motion at the edge of the back pressure hole is (X - x) 2 + ( Y - y) 2 = r 2 (7) When the crankshaft is at any angle θ, the center coordinates of the back pressure hole are satisfied. x = a + R or cos θy = b + R or sin θ (8) The circular involute equation outside the vortex wall is X o = a< cos( t -α) + t sin( t -α) > Y o = a< sin( t -α) - t cos( t -α) >(9) because when the back pressure hole is covered by the passive scroll, the outer wall of the orbiting scroll intersects the back pressure hole and has The common common normal, so the simultaneous solution: ( X o - x) 2 + ( Y o - y) 2 = r 2 ( Y o - y) 2 / ( X o - x) = tan β (10) The center roll angle of the fixed scroll is (t - α), and different values ​​of θ can be obtained for different β, thereby determining the center position of the back pressure hole.

For the determined back pressure hole, the pressure of the back pressure hole corresponding to the compression chamber can be correspondingly obtained, thereby obtaining the back pressure pb in the sealing assembly. In order to ensure the sealing of the vortex section, the back pressure in the seal assembly must satisfy: | pb - pb , min | ≤ δ where: δ is the calculation accuracy.

3 Application examples According to the above-mentioned description of the axial scrolling mechanism of the fixed scroll, a prototype is produced. The schematic diagram of the prototype is as shown. In the prototype, a static scroll back pressure structure is adopted, that is, a back pressure hole is started on the fixed scroll, so that a high pressure chamber is formed in the seal assembly, and the gas of the high pressure chamber is used to seal the end cover and the fixed scroll on the one hand. The gap, on the other hand, balances the circumferential gas force. The scroll compressor adopting the structure has the following advantages: 1) the air inlet, the moving plate and the cross slip ring are all operated in a low pressure environment; 2) the high pressure gas of the exhaust port is directly connected to the gas storage tank, thereby reducing unnecessary Leakage; 3) The fixed scroll rotates along the main axis, making the scroll compressor compact.

4 Conclusions A new type of static scroll with variable structure is proposed on the basis of the axially variable structure of the movable scroll, that is, the back pressure hole is opened on the fixed scroll. The feasibility of this structure is in the new generation. The closed air scroll compressor was verified. This mechanism makes the overall structure of the scroll compressor more compact, can effectively achieve axial compensation and balance the axial gas force of the fixed scroll, reduce friction loss, automatically compensate for wear and prevent overload, and vortex for the future. The design and development of the rotary compressor provides a new idea.

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