Patent Application
20080145258
1. Field of the Invention
The present invention relates to a vacuum pump for producing low or high vacuum and including a housing having an inlet and an outlet, a pumping system for compressing gas, a motor for driving the pumping system, and a fan for cooling the pump. The present invention also relates to a method of operating such a vacuum pump.
2. Description of the Prior Art
In vacuum pump, there exist several heat sources one of which is the pumping system in which the gas is compressed. The heat, which is generated in the pump, should not cause any operational disturbances resulting from overheating of pump components. Therefore, the important components need to be adequately cooled in order to offset their heating. A contemporary state of the art of cooling vacuum pump components is disclosed in a European Publication EP-A 1 242 744. The European Publication discloses an electromotor that drives a shaft that drives pump active components of the pumping system. A fan wheel having several blades is arranged on at least one end of the shaft. The fan wheel produces, upon rotation of the shaft, a gas flow directed to the pump components.
The amount of the produced cooling gas and, thereby, the cooling effect depends, among others, on the rotational speed of the shaft. Therefore, the heat balance of the vacuum pump strongly depends on the operation of the motor. This is often undesirable and requires a compromise, among others, with respect to selection of the rotational speed, which can be necessary from the point of view of the vacuum technology, e.g., to insure an adequate control a vacuum process.
Accordingly, an object of the present invention is to provide a vacuum pump with cooling that overcomes the drawbacks of the state of the art.
This and other objects of the present invention which will become apparent hereinafter, are achieved by providing a vacuum pump in which the fan has its own motor.
Because the fan has its own motor, it is possible to produce a cooling gas flow independent on the speed of the vacuum pump motor. With the fan having its own motor, it is possible to place the fan at a location most favorable for the pump heat balance. Thus, the cooling can be designed completely based on the needs and does not require any compromise between the vacuum and cooling requirements.
According to the inventive method, the pump motor is operated with a first rotational speed, and the fan motor is operated with a second rotational speed, with the first and second rotational speeds being at least temporarily different. This permits, e.g., to reduce the rotational speed of the vacuum pump and, simultaneously, increase the flow of the cooling air produced by the fan. This can prove advantageous during turning of the pump off.
The cooling of the vacuum pump is improved when the housing has cooling ribs, and the fan is arranged for feeding cooling air in space between the cooling ribs. This can be achieved when the fan is so arranged that the cooling gas flow, which is produced by the fan, is blown into the space between the cooling ribs. The cooling can further be improved when the vacuum pump includes a hood that at least partially surrounds the housing and the hood is so formed in a region of the cooling ribs that the cooling air from the fan is deflected in the space between the cooling ribs.
Further advantages in cooling the vacuum pump are achieved when the fan is located in a separate section of the pump housing. This permits to arrange the fan or fans in the regions of the housing where cooling is needed.
For an adequate heat balance of the vacuum pump and, thus, for the necessary cooling, it is advantageous when the control electronics that contains electronic components that require cooling, and the pump system in which a lot of heat is generated due to compression of the gases, are arranged in respective separate housing sections. This permits to thermally separate the respective cooling regions.
A vacuum pump can be so formed that the cooling air, which is generated by the fan, flows to the housing section in which the pumping system is located. This permits to use the cooling air entirely for cooling.
A vacuum pump with a sectional construction of the housing can be so formed that the housing section, which contains control electronics, is cooled by free convection. Thus, the cooling air flow, which is generated by the fan, can be used for cooling the hot sections of the vacuum pump.
Cooling, which is independent of the pump drive, is particularly advantageous in vane rotary vacuum pumps in which the pumping system contains lubricant for sealing and lubricating the vane. Inadequate cooling of the pumping system can lead to destruction of the lubricant.
The novel features of the present invention which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.
The drawings show:
a a side view of a vacuum pump equipped with a hood according to the present invention in a disassembled condition;
b a side view of the vacuum pump with a hood shown in
The sections of the vacuum pump include different functional units. The control section 2 includes the control electronics that controls feeding of current from a network to the coils of the pump drive. In the intermediate section 3, a fan 6 is arranged. The fan 6 aspirates air and delivers it in the space between cooling ribs 8 provided on the housing, whereby cooling of the pump takes place. The suction and the delivery of air by the fan 6 is shown with the arrows. The peripheral section 4 includes gas connections, i.e., gas inlet 9 and gas outlet. The stand 10 also is arranged at the peripheral section 10. The stand 10 includes means, e.g., an elastomeric body which reduces transmission of vibrations between the vacuum pump and the floor. In the pumping section 5, those components of the pump are located with which the gas is compressed to such an extent that it can be discharged against the atmosphere. These four sections are arranged axially one after another, with the intermediate section being located between the peripheral and control sections. The pumping section 5 is provided on a side of the peripheral section 4 remote from the intermediate section 3.
The sections of the vacuum pump are at least partially surrounded by the hood 1. In the embodiment shown in the drawings, the hood 1 is so formed that it covers the lower portion of the vacuum pump. Lower portion means a portion of the vacuum pump adjacent to the stand 10, i.e., in the direction of the floor. The shape of the hood 1 is such that the control and intermediate sections 2 and 3 are completely covered by the hood 1. The hood is somewhat short in the region of the pumping section, covering only the lower part of the pumping section. The cooling ribs 8 are provided in the lower part of the pumping section 5. However, the cooling ribs can also be formed in the upper part of the pumping section 5. The hood 1 covers at least a portion of the cooling ribs 8, forming channels that are limited by the hood 1, the pump housing, and the cooling ribs 8. For the purpose of protection, it can be sufficient to cover only the lower portion of the pump because it is in the lower portions of the pumping and peripheral sections 4 and 5 that the heat-carrying elements such as lubricant and coils are provided. When shaping a hood, design consideration can naturally play a certain role. The hood 1 also covers the fan 6.
In order for the fan to be able to aspirate the air and to deliver it into the channels, the hood has an opening. In the shown embodiment, the opening is formed as a plurality of aeration slots 7. The number and the shape of the slots 7 can vary for different pumps and are dependent on the requirements to the cooling gas flow.
The intermediate section 3 contains several components in its housing. A switch 15 serves for turning the vacuum pump on and off. Further switches can be also arranged in the intermediate section housing. The further switches can include, e.g., a standby switch or a speed selection switch. Here, likewise, a socket 16, to which the power supply is connected, is arranged. This power is transmitted to the control electronics, on one hand, and on the other hand, it is transmitted to a small panel that is connected by suitable conductors with an auxiliary electronics 18, supplying it with power. The auxiliary electronics serves for converting the switching condition of the switch 15 in a control signal that is transmitted over suitable conductors to the control electronics. The auxiliary electronics has also means that insures feeding voltage to the fan motor 6a and that controls switching the fan motor 6a on and off. According to further development of the present invention, further communication means can be arranged in the intermediate section 3, including the necessary switches, plugs, and bushings which are arranged on the housing wall similar to switch 15. These components are connected by electrical conductors or the like with the expanded auxiliary electronics that includes, e.g., means for controlling a field bus or serial interfaces and the like. These interfaces can be used for obtaining information from external control means and related to the operational state of the pump such as, e.g., “pump is operated,” actual rotational speed of the pump, or active standby.
A seal 14 provided between the housings of the intermediate section 3 and the control section 2. The seal 14 serves, on one hand, for sealing the inner space against the moisture and dust. On the other hand, the seal 14 functions as a thermal barrier, making the transmission of heat from the intermediate section to the control section more difficult. A similar seal is also provided between the intermediate section 3 and the peripheral section 4, making the transmission of heat therebetween also more difficult. In a portion of the intermediate section 3, a support 19 supports the fan 6 that includes the motor 6a and a fan blade 6b. The dash arrows show the cooling gas flow that is aspirated by the fan 6. The air is aspirated and flows between the cooling ribs 8.
The control electronics 12 provides for feeding power to the coils 26. A rotationally symmetrical separation member 23 is arranged between the coils 26 hermetically separating them from the inner space of the separation member 23. An end of a shaft 24, on which permanent magnets 25 are secured, projects into the inner space of the separation member 23. The cooling gas flow, which is generated by the fan 6, is again shown with dash arrows. The suction is effected through the aeration slots 7, and the air is delivered in the direction of the peripheral section 4. According to a further modification of the vacuum pump, such aeration slots are formed in the pump bottom. The stand then needs to be sufficiently spaced from the pump bottom in order to provide a clearance through which the air can be aspirated.
From
The housing of the pumping section 5 has good heat-conducting characteristics, so that the heat of the peripheral section 4 is transmitted to a large-surface body. The shaft 24 eccentrically extends through a cylindrical bore formed in the pumping section 5. The shaft 24 can be formed of one or several pieces and is supported by first and second slide bearings 31 and 32 which are lubricated by a lubricant. The lubricant is supplied from a lubricant reservoir 35 that surrounds the pumping system 30. A vane 33 is rotatably supported in the cylindrical bore of the pumping section 5, with a compression chamber 34 being formed between the wall of the cylindrical bore and the vane 33. The permanent magnets 25 are secured, as it has already been discussed above, on the end of the shaft 24 that projects into the peripheral section 4 in which the coils 26 are located. Cooperation of the magnets 25 with coils 26 provides for ration of the shaft 24, with the coils 26 and permanent magnets 26 forming an electric motor. Here, there is provided a brushless D.C. motor. Though the advantages of the present invention are particularly apparent with this type of an electric motor, the invention is not limited to this type of a drive motor. The lubricant, primarily oil, serves, in addition to lubrication of the bearings, also for lubrication and sealing of the vane 33.
Preferably, the hood 1 is so shaped that the channels are open at their ends. This can be managed very easily as the hood 1 does not cover the pumping section-side, end side of the inventive vacuum pump. Between the hood 1 and the housing, there is provided an intermediate element 40 that, e.g., has highly elastomeric components. The intermediate element 40 serves as a thermal barrier and also for reduction of transmission of vibrations from the pump housing to the hood 1. The hood 1 is fixed with attachment means, e.g., with screws 41.
The embodiment of the vacuum pump shown in the drawings has a favorable heat balance. A first source of an extensive heat is the heat of compression in the pumping section 5. A further source of an extensive heat is the peripheral section 4 because it is there that the drive coils, in which the power dissipation is converted into heat, are located. In addition, the heat to the peripheral section 4 is transmitted by the end side of the pumping system 30 which contact the peripheral section 4 along a large surface. These heat sources are isolated from the control section by the intermediate section. In view of the serial connection of the pump sections, this distance is maximized. Also, the thermal resistance of the seals, which are provided between the intermediate section and the adjacent sections, contributes to isolation of the heat sources from the control section 2. These passive measures provide for a very favorable heat balance. The active cooling with a fan also contributes to the favorable heat balance. By locating the fan in the intermediate section, the sections, which generate most of the heat, are subjected to the action of the cooling air. The hood serves, on one hand, as a convection protector and, on the other hand, guides the cooling air flow, which is generated by the fan, in optimal manner to the heat sources of the pumping and peripheral sections. In those regions, where no air movement takes place, under the hood, the air acts as an air cushion and isolates the environmental heat from the bottom parts, e.g., of the control section. In sum, the cooling of the inventive vacuum pump is noticeably improved in comparison with the state of the art.
The embodiment shown in the drawings represents an oil-tight vane rotary vacuum pump. However, the present invention can be adapted to other vacuum pumps for producing low and high vacuum by replacing the pumping section. In the replaced pumping section other pumping principles can be used. Examples of the applicable principles can be found in, e.g., dry piston compressor, dry van rotary or rotary piston pump.
Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 058 842.8 | Dec 2006 | DE | national |
