JPS6198990A - Scroll fluid machine for vacuum pump - Google Patents

Abstract

PURPOSE:To enable a machine to sufficiently hold its sealing in the axial direction over the range from the atmospheric pressure to a high vacuum, by providing a communication port which connects a space, connected with a delivery port, with a back pressure chamber at the moment a volute center space, connected with the delivery port, communicates with a minimum enclosed space. CONSTITUTION:A machine, providing a communication port 21 with a throttle mechanism connecting with a back pressure chamber 20 a space connected with a delivery port 17, provides this communication port 21 in a position that it connects the space with the chamber 20 at the moment the volute center space 22 connected with the delivery port 17 communicates with a minimum enclosed space 23. In this way, fluid in the volute center space 22 and the space connected with the delivery port 17 is not delivered being reexpanded in the minimum enclosed space 23 by the turning action of a turning scroll 11, and the machine delivers a part of the fluid being recompressed while repeats reexpansion of a part of the fluid. Here an outflow and an inflow of the fluid are provided by the communication port 21, but the machine, maintaining the back pressure chamber 20 to a mean pressure in the space connected with the delivery port 17 by the throttle mechanism and pressing the turning scroll 11 to a fixed scroll 12, is enabled to hold the sealing in the axial direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scroll fluid machine used as a vacuum pump, and particularly to a structure for sealing an orbiting scroll in the axial direction.

[Background of the invention]

Japanese Patent Laid-Open No. 55-875 discloses a device for maintaining axial sealing of an orbiting scroll in a scroll fluid machine.
There is a structure disclosed in Publication No. 20. This structure is the fourth
As shown in FIG. 6, the compressed fluid in the closed space formed between the orbiting scroll 1 and the fixed scroll 2 is connected to the housing 3 and the rear surface of the orbiting scroll 1 through a connecting port 6 with a throttle mechanism provided in the orbiting scroll l. The fluid pressure during compression is used to keep the orbiting scroll 1 sealed in the axial direction. The above structure is applied when the scroll fluid machine is used as a compressor, an expander, or a pump. It is characterized by being located at or near the same location.

However, when a scroll fluid machine having this structure is used as a vacuum pump, the following problems occur.

During high vacuum operation (in a state where the JE temperature is increased), there is insufficient fluid pressure (hereinafter referred to as back pressure) to keep the orbiting scroll 1 sealed in the axial direction, making it impossible to maintain sufficient sealing. That is, the back pressure is maintained approximately at the geometric mean pressure of the maximum sealed space and the minimum sealed space. In a normal scroll fluid machine, the ratio of the maximum sealed space to the minimum sealed space is selected to be 2 to 5/1.
When operating in such a way that s is approximately 9/d to 1 x 10-5, the maximum pressure in the closed space is 1 x 10'K.
q/d, and the pressure of the minimum sealed space Pc = Ps (2 to 5
) to (0,8-1)XIO' becomes 9/c-. However, is the specific heat ratio, and for dry fresh air, the can = 1.4°, so the back pressure maintained at the geometric mean pressure pbVc is approximately (
2-3) x 1o'Kq/CIA. This value cannot support the weight of an orbiting scroll made of ordinary materials, and it is not possible to maintain sufficient axial sealing.

[Purpose of the invention]

An object of the present invention is to provide a scroll fluid machine for a vacuum pump that can maintain sufficient axial sealing of an orbiting scroll over a range from atmospheric pressure to high vacuum.

[Summary of the invention]

Due to its operating principle, scroll fluid machines do not allow the fluid in the space connected to the discharge port (the size of the space changes depending on the relative position of the orbiting scroll and fixed scroll) to be compressed and expanded. return. The pressure in this space is the discharge pressure (usually atmospheric pressure in the case of a vacuum pump) when the volume between the walls connected to the discharge port is at its minimum.
In the case of a scroll fluid machine in which the discharge port is equipped with a valve, the fluid in the space re-expands to the width of the minimum sealed space formed by both scrolls, the discharge port, and the space connected to the discharge port. Even if the suction pressure becomes a high vacuum, the average pressure in the space connected to the discharge port will not drop below a certain value. Therefore, by appropriately selecting the shape of the wrap center of both scrolls and the volume of the discharge port portion, the average pressure in the space connected to the discharge port can be set to an appropriate value, and this space and the back pressure chamber can be adjusted to an appropriate value. By communicating through the communication port, the pressure in the back pressure chamber, that is, the back pressure, can be set to a value necessary for axially sealing the orbiting scroll.

Therefore, one aspect of the present invention is to provide a valve for opening and closing a discharge port, and a communication port with a throttle mechanism that communicates a back pressure chamber with a space formed by both scrolls and connected to the discharge port, and to connect the communication port to the discharge port. The structure is such that it is installed at a position that communicates with the minimum airtight space at the moment when the central space communicates with the minimum airtight space.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

FIG. 1 shows a longitudinal sectional view of a compression mechanism section of a scroll fluid machine for a vacuum pump according to the present invention, and FIG. 2 shows a cross sectional view thereof. In the figure, 11 indicates an orbiting scroll, and 12 indicates a fixed scroll. The orbiting scroll 11 has an end plate 11
a, and a wrap 111) standing upright thereon and formed of an impolinide curve or a curve close to an impolinide curve. The fixed scroll 12 also has an end plate 12a,
It consists of a wrap 12b that stands upright on this and is formed with a curve close to an impolinide curve or an involute curve. Both scrolls are combined with their wraps inside each other. Moreover, the orbiting scroll 11 is surrounded by a housing 13, and the housing 18+
-j is connected to the fixed scroll 12 by a bolt 14. The housing 18 also includes a bearing 15 that supports a crankshaft 16 that makes the orbiting scroll 11 orbit.

A discharge port 17 is provided at the center of the end plate 1'2a of the fixed scroll 12, and a valve 18 for opening and closing the discharge port 17 is attached by a screw 19. Further, a back pressure chamber 20 is formed between the back surface of the orbiting scroll 11 and the housing 18. This back pressure chamber 20 is
A communication port 21 provided in the end plate 11a of the orbiting scroll 11 and equipped with an FC throttle mechanism communicates with the space formed by both scrolls and the valve 18.

The communication 021 is provided at a position connected to the discharge port 17.

Next, the position connected to the discharge bow 17 will be explained with reference to FIG. FIG. 3 shows the positional relationship immediately before the center tooth tips of the orbiting scroll 11 and the fixed scroll 12, that is, the contact point A on the center side are separated. In this state, discharge port 1
The vortex center space 22 and the minimum enclosed space 23 directly trace back to 7.
However, when the contact point A separates due to the orbiting operation of the orbiting scroll 11, the thin center space 22 and the minimum sealed space 23 are no longer connected. Therefore, the position where the communication port 21 connects to the discharge port 17 refers to a position closer to the center than the minimum sealed space 23, that is, closer to the discharge port 17 side. In FIG. 1, reference numeral 24 indicates an Oldham mechanism that prevents the orbiting scroll 11 from rotating.

Next, the operation of this embodiment will be explained. The fully opened fluid connected to the thin center gap 22 and the discharge port 17 shown in FIG. is discharged, and some of the fluid repeats re-expansion.

The back pressure chamber 20 communicates with the space where this compression and re-expansion are repeated via the communication port 21, and although fluid flows in and out through the communication port 21, the back pressure chamber 20Vi The average pressure in the space connected to the discharge port 17YC is maintained. Then, the orbiting scroll 11 is pressed against the fixed scroll 12 by the pressure of the back pressure chamber 20,
An axial seal is provided.

Further, airtightness between the back pressure chamber 20 and the suction side is achieved at the contact surface between the L41 constant scroll 12 and the orbiting scroll 11 on the outer peripheral side.

Therefore, in this embodiment, the axial sealing of the orbiting scroll 11 can be maintained sufficiently from the atmospheric pressure to the high nitrogen range.

Similarly, in the above embodiment, the communication port 21 is connected to the orbiting scroll 1.
Although an example is shown in which the communication port 21 is provided in the plate 11a of the fixed scroll 12, the communication port 21 may be provided in the end plate 12a of the fixed scroll 12 and communicated with the back pressure chamber 20 via external piping.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to maintain sufficient axial sealing of the orbiting scroll from atmospheric pressure to a high nitrogen pressure region, and a high-performance vacuum pump can be provided.

[Brief explanation of drawings]

1 to 8 show an embodiment of the present invention, FIG. 1 is a longitudinal sectional view of a compression mechanism of a scroll fluid machine for a vacuum pump according to the present invention, and FIG. 2 is a transverse sectional view thereof. FIG. 8 is an explanatory diagram of the operation, FIG. 4 is a longitudinal cross-sectional view of the compression mechanism section of a conventional scroll fluid machine, and FIG. 5 is a cross-sectional view thereof. 11... Orbiting scroll 12... Fixed scroll 13... Housing 17..., 1') 4-Outlet 1Q, -, Valve 20... Back pressure chamber 21... Communication port
23...Minimum enclosed space I+"i"person#press-↓-s 1Ct bullet? ＠d-ni:-Nouhat second country type 3 box 1b rtb t

Claims (1)

[Claims] A scroll fluid machine for a vacuum pump that performs a vacuum pumping action by a compression operation of a fixed scroll and an orbiting scroll that rotates while being prevented from rotating, and a housing that surrounds the orbiting scroll and is coupled to the fixed scroll; A back pressure chamber formed between the housing and the back surface of the orbiting scroll, a valve that opens and closes a discharge port bored in the center of the fixed scroll, a space formed by both scrolls and connected to the discharge port, and the back pressure and a communication port that communicates with the chamber, the communication port having a throttle mechanism and provided at a position where it communicates with the minimum sealed space at the moment when the swirl center space directly connected to the discharge port communicates with the minimum sealed space. A scroll fluid machine for vacuum pumps characterized by: