Lubricating oil seal type vacuum pump, lubricating oil filter and method

Abstract

A lubricated oil sealed vacuum pump, method, and filter configured to deliver fluid from an inlet to an outlet is disclosed, the lubricated oil sealed vacuum pump including a rotor, a filter for filtering lubricating oil from the fluid output by the pump, and a control circuit configured to control the rotational speed of the rotor such that the rotor rotates initially at a slow speed when the inlet pressure is high and rotates at a higher operating speed when the inlet pressure decreases.

Description

Technical Field

[0001] The field of the present invention relates to a lubricating oil sealed or oil sealed vacuum pump.

Background Art

[0002] The size of a lubricating oil sealed vacuum pump greatly depends on the size of a lubricating oil filter for filtering lubricating oil from the fluid exhausted from the pump. The lubricating oil mist filter is an important component of the pump as it purifies the lubricating oil from the exhausted fluid. The filter needs to be large enough to allow the required air flow without generating a large pressure loss, and further, it needs to provide the desired filtering effect. This means that a large exchange surface and filter size are required.

Summary of the Invention

Problems to be Solved by the Invention

[0003] It is desirable to provide a pump and a pump feeding method in which a miniaturized filter can effectively filter exhaust gas, and to provide a miniaturized filter for such a pump.

Means for Solving the Problems

[0004] A first aspect provides a lubricating oil sealed vacuum pump configured to send fluid from an intake port to an exhaust port, the lubricating oil sealed vacuum pump including a rotor, a motor for rotating the rotor, a filter for filtering lubricating oil from the fluid output by the pump, and a control circuit for controlling the rotational speed of the rotor, the control circuit being configured to control the rotation of the rotor such that the rotor rotates at a first selected low speed when the pressure at the intake port is high and rotates at a high operating speed when the pressure at the intake port decreases.

[0005] The inventor of the present invention recognized that the filter size required for a particular pump depends on the maximum fluid flow rate through the filter. The inventor also recognized that this occurs when the pump is pumping the maximum amount of air from the custom chamber, and further, that this occurs at the start of chamber evacuation when the pressure in the chamber is generally at atmospheric pressure and is highest. Further, this occurs for only a small part of the pump operation time, and the pump generally operates to maintain the chamber at the desired operating vacuum or near thereto for most of that time. Therefore, the inventor recognized that determining the filter size based on the flow rate at the first pump-down would lead to a filter that is too large for most of the pump operation.

[0006] The inventor recognized that by providing a control circuit for controlling the rotational speed of the rotor of the pump, particularly by reducing the initial rotational speed, a smaller sized filter can be used. Thereby, when the high pressure in the chamber is exhausted at the start of pumping, the rotational speed is set to the selected low speed, and the corresponding maximum flow rate expected for the filter is also reduced accordingly. Thereby, a filter smaller than before can be selected. In this case, there is a disadvantage that the time required to lower the chamber to the operating pressure becomes longer. However, as described above, this is only a small part of the total pump operation time, and thus this is generally a completely acceptable compromise.

[0007] The rotational speed of the rotor can be controlled in many ways, for example, by using a gear mechanism or a brake mechanism in some cases. In some embodiments, the motor is composed of a variable speed motor for driving the rotor, and the control circuit is configured to control the rotational speed of the rotor by controlling the rotational speed of the motor.

[0008] The pump can be provided with a variable speed motor for driving the rotor, and by using this, it is possible to provide an initially low controlled speed of the rotor. As an example of such an arrangement, the pump is provided with a frequency converter that converts a single-phase power supply into a three-phase power supply for powering the motor. Such a frequency converter can also be used to change the speed of the motor, and if such a converter is present within the pump, this can be done without adding components other than the control circuit. Changing the speed of the motor driving the rotor is a convenient and effective way to control the rotor speed.

[0009] In some embodiments, the lubricating oil sealed vacuum pump is provided with a sensor for sensing the characteristics of the fluid being pumped, where this characteristic indicates the pressure at the intake port, and the control circuit is provided with a feedback control system for controlling the speed of the rotor in response to the sensed characteristic.

[0010] The sensor can be at least one of a pressure sensor configured to sense the pressure of the fluid being pumped and a flow rate sensor configured to sense the flow rate of the fluid being pumped, and the control circuit is configured to control the rotational speed of the rotor in response to a signal from at least one of the pressure sensor and the flow rate sensor.

[0011] When the rotational speed of the rotor is controlled according to the sensed characteristics of the fluid being pumped, a sensor for sensing the characteristics of the fluid is required. This sensor can sense the pump speed or the fluid flow rate (either mass flow rate or volume flow rate) or can also sense the pressure of the fluid being pumped. This pressure can in some cases be measured directly at the inlet or outlet, or can also be measured indirectly, for example, using a current sensor that senses the current supplied to the motor, where the current indicates the required torque and thus the pressure of the fluid being pumped. One skilled in the art should understand that the flow rate can be derived using a sensor configured to directly measure the pressure, and similarly, the pressure can be derived using a flow rate sensor configured to directly measure the flow rate.

[0012] Assuming that the purpose of the initial low speed of the rotor is to limit the maximum fluid flow rate and thus limit the required size of the lubricating oil filter, control can be provided that gives a rotational speed that is precisely tied to a specific flow rate by controlling the rotational speed according to factors related to the flow rate such as the flow rate itself or the fluid pressure. This allows the flow rate to be maintained below a desired value, and in some embodiments, maintained at or near the maximum allowable flow rate, thereby preventing the initial pump-down time from increasing excessively while keeping the flow rate within the limits required by the filter.

[0013] In some embodiments, the low speed is a constant low speed and the control circuit is configured to control the rotor to rotate at the constant low speed for a predetermined period and then increase the speed to a higher operating speed after the predetermined period.

[0014] One simple control mechanism could be to control the rotor to rotate at a low constant fixed speed during an initial predetermined period and then increase the speed to a higher operating speed, a steady state speed, of the pump after this period. In this way, the pump operates at substantially two different speeds, and the point at which the rotor accelerates to the higher speed determines the maximum fluid flow rate that the pump will deliver.

[0015] In some embodiments, the predetermined period consists of a predetermined time zone. The control circuit can be configured to control the pump for evacuation of a particular chamber or chamber type and / or for a particular application, in which case the pump can simply be configured to pump at a low speed during a predetermined time zone, which is selected according to the desired maximum fluid flow rate and determined from the characteristics of the pump and the chamber. Thus, no additional sensors are required and the control circuit simply controls the pump according to the elapsed time.

[0016] In other embodiments, the predetermined period consists of the period while the pressure is above a predetermined value. Alternatively, the pump can pump at a low speed while the pressure of the pumped fluid is above a predetermined value. This pressure can be the inlet pressure, the outlet pressure, or the pressure within the pump chamber, depending on the location of the pressure sensor, and the predetermined value is selected accordingly.

[0017] In other embodiments, the predetermined period consists of the period while the flow rate of the pumped fluid is greater than a predetermined amount.

[0018] Alternatively, the pump can vary its pumping speed according to the flow rate of the pumped fluid. This is a convenient way to limit the flow rate of the pumped fluid but requires a certain type of flow sensor.

[0019] Optionally, the selected initial low speed can be held at a constant value during the predetermined period, but in other embodiments, the low speed is a variable low speed.

[0020] Using a constant low rotational speed is simple to control, but a variable low speed may be more effective and the speed can be gradually increased in response to a pressure drop. Thereby, the flow rate can be maintained near the desired value during pump-down and the time taken to achieve pump-down can be shortened.

[0021] In some embodiments, the control circuit is configured to set a variable low speed in response to a signal received from at least one sensor.

[0022] The variation of the low speed can be controlled in response to the measured changes in flow rate and / or pressure. In this way, when the pressure and flow rate decrease, the speed can be increased without exceeding the maximum flow rate.

[0023] In some embodiments, the at least one sensor is a flow sensor, and the control circuit is configured to set a variable low speed to provide a predetermined fluid flow rate.

[0024] As described above, the idea of the initial low speed is to limit the maximum flow rate. Therefore, one effective way to control the low speed is to control the speed according to the flow rate, which in some embodiments makes it possible to maintain the speed lower but close to the maximum level supported by the filter.

[0025] In some embodiments, the at least one sensor is a pressure sensor, and the control circuit is configured to set a variable low speed in response to a signal from the pressure sensor, and the speed increases in response to a decrease in pressure.

[0026] Alternatively, the speed can be set according to the pressure, and the flow rate depends on the pressure and the rotational speed. Therefore, it can be controlled by controlling the speed according to the pressure.

[0027] In some embodiments, the control circuit is configured to maintain the rotor speed at a high operating speed when the rotational speed of the rotor increases to the high operating speed.

[0028] If the selected initial low rotational speed is variable, it will be controlled to gradually increase as the chamber is evacuated. At some point, the gradually increasing speed reaches the operating speed of the pump, at which point the increase in speed stops and the pump will operate continuously at this high operating speed.

[0029] In some embodiments, the filter is a miniaturized filter, the filter is sized to filter a predetermined maximum flow rate of the fluid pumped by the lubricating oil sealed vacuum pump, and the control circuit is configured to maintain the flow rate of the fluid pumped by the pump below the maximum flow rate by controlling the rotor to initially rotate at a low speed.

[0030] In some embodiments, the selected initial low speed is less than half of the high operating speed. In some embodiments, the selected initial low speed is less than one-third of the high operating speed, and in some cases, less than one-fourth of the high operating speed.

[0031] A second aspect provides a method of evacuating a chamber using a lubricating oil sealed pump according to the first aspect, the method including rotating the rotor of the pump at a selected initial low speed for a predetermined period of time and increasing the rotational speed of the rotor to a high operating speed after the predetermined period of time.

[0032] In some embodiments, the method further includes sensing at least one of the pressure and flow rate of the fluid being pumped and controlling the rotational speed of the rotor in response to at least one of the sensed fluid pressure and the sensed flow rate.

[0033] A third aspect provides a miniaturized filter for a lubricating oil sealed vacuum pump according to the first aspect, the miniaturized filter having a filtration surface area that is less than or equal to a value obtained by dividing the volumetric flow rate of the pump at a selected initial low speed configured to be provided by the pump by the permeability and the pressure loss across the filter.

[0034] The transmittance and the pressure loss across the filter are characteristics of the filter, and thus, the reduction in surface area will depend on the reduction in the maximum flow rate. Thus, if the selected initial low speed is a fraction of the operating speed, the filtration surface will decrease accordingly.

[0035] Further specific preferred embodiments are set forth in the independent and dependent claims. The features of the dependent claims can, where appropriate, be combined with the features of the independent claims and can be combined in combinations other than those explicitly defined in the claims.

[0036] When a feature of an apparatus is described as being operable to provide a certain function, it is to be understood that this includes features of the apparatus that provide or are adapted or configured to provide that function. Embodiments of the present invention are described in detail below with reference to the accompanying drawings.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] Before explaining the embodiments in detail, an overview will first be presented. In order to reduce the flow rate passing through the lubricating oil seal type pump and the filter, when starting the pump, since the flow rate is generally maximum at this time, the pump speed is reduced. This is done by changing the rotational speed of the rotor. As an example, this can be done in two ways. That is, 1. A constant limited speed at startup, 2. A variable rise speed at startup, 3. A variable speed at startup adjusted according to the characteristics of the fluid being pumped by the pump so that the flow rate becomes constant at the exhaust port, are available.

[0039] By changing the starting speed of the pump in this way, the size of the filter can be substantially reduced, and in this way, the maximum flow rate passing through the pump and the filter becomes possible.

[0040] FIG. 1 shows an oil seal type pump according to an embodiment. The oil seal type pump includes a motor 20 for driving a rotor 10 in a pump chamber (not shown). The rotor 10 pumps the fluid arriving at the intake port indicated by the arrow 12 through the pump chamber to the filter 30, and the filter 30 functions to remove the oil mist from the pumped fluid, and the fluid is exhausted from the exhaust port 14.

[0041] The motor 20 is a variable speed motor, and the speed of the motor, and thus the rotational speed of the rotor, is controlled by the control circuit 22. In this embodiment, the control circuit 22 is configured to control the motor to rotate at an initially low speed for a predetermined time and then accelerate to the maximum operating speed. In this embodiment, the initial speed is about one-fourth of the maximum operating speed, and the pump is configured to operate at this low speed for about 20 seconds at startup. As a result, if the pressure in the chamber to be evacuated is initially high, the rotational speed is low, and thus the flow rate of the fluid through the pump is reduced compared to a conventional pump. As the pressure in the chamber decreases, the rotational speed of the rotor increases to the normal operating speed. At this point, since the pressure in the chamber is decreasing, the rotor begins to rotate at a high speed, but the flow rate of the fluid passing through the pump is not as high as when the rotor was initially rotating at this high speed. In this way, the maximum flow rate passing through the filter 30 is reduced, and accordingly the size of the filter can also be made smaller.

[0042] Since the initial rotational speed is low, the time required to pump down the chamber to the operating pressure increases, but this is generally acceptable because it is only a very small part of the pump's operating time.

[0043] In the embodiment of FIG. 1, the control circuit 22 is configured to control the rotor to operate at a constant slow speed for a predetermined time. In other embodiments, the control circuit can be configured to operate at a slow initial speed and gradually rise over time to a high operating speed. If the pump is configured to evacuate a chamber having known dimensions or dimensions within certain known limits, the pressure drop occurring during this time can be estimated based on the known dimensions and pump speed, so it is permissible to limit the rotational speed based on the operating time, and to select the time such that the operating speed increases when the pressure in the chamber has dropped sufficiently to enable the flow rate not to exceed a predetermined maximum value that the filter 30 is configured to support.

[0044] Figure 2 shows another embodiment where the control circuit is not configured to pump at a low speed for a predetermined time, but is configured to receive a signal from a flow sensor 26. The flow sensor 26 measures the flow rate at the pump outlet and sends a signal indicating this flow rate to the control circuit 22. The control circuit 22 controls the rotation of the motor such that the flow rate measured by the sensor 26 remains substantially constant during an initial period at or near the maximum flow rate that the filter 30 is designed to support. In this way, the size of the filter can be reduced, and the pump-down time will not increase excessively.

[0045] The flow sensor can be a volumetric flow sensor or a mass flow sensor. The flow sensor 26 is shown at the pump outlet in this embodiment, but in other embodiments, it can be placed at other locations within the system.

[0046] Figure 3 shows another embodiment where the control circuit 22 receives a signal from a pressure sensor 24. In this embodiment, the pressure sensor directly measures the gas pressure at the pump inlet. In other embodiments, the pressure can be sensed directly at another part of the pump or indirectly, for example, by sensing the torque exerted on the rotor by the motor. The control circuit 22 controls the speed of the motor, and thus the speed of the rotor, according to the pressure of the fluid being pumped. As described above, the filter 30 is configured for a specific maximum flow rate, and the gas flow rate being pumped depends on the pressure and the rotational speed of the rotor. Therefore, depending on the pressure, the rotational speed of the rotor can be controlled to maintain the fluid flow rate below this maximum flow rate. Again, this control of the motor enables effective and accurate control of the flow rate to protect the filter from overload without unduly reducing the initial pump-down time.

[0047] Figure 4 shows examples of different ways in which the rotational speed of the pump rotor can be controlled to vary over time. Curve 40 shows a constant rotational speed of 1800 rpm, which represents a conventional pump operating at an operating speed of 1800 rpm from start-up to the end of the pump cycle.

[0048] Curve 42 shows the variation of the rotor speed according to one embodiment, where an initial low speed of 400 rpm increases with start-up time using a feedback loop to provide a substantially constant mass flow rate through the pump during an initial start-up period until the maximum operating speed of the pump is reached in response to measurements from the sensor.

[0049] Curve 44 shows another embodiment where an initial low speed of 400 rpm is provided for a set period and then increased to the operating speed of the pump.

[0050] Figure 5 shows the effect of the different pump speeds of Figure 4 on the flow rate through the pump and the pump-down time. In addition to curves 40, 42, 44 corresponding to Figure 4, curve 41, which is the theoretical curve of a constant flow rate for a conventional pump, is shown, which corresponds to curve 40 showing the measured curve of such a conventional pump. As can be seen from this figure, the control of the speed by curve 42 results in a constant maximum flow rate during an initial start-up period, and that flow rate decreases when the maximum operating speed is reached.

[0051] Curve 44 shows how a constant low speed during the start-up period results in a flow rate that gradually decreases as the pressure decreases. When the point is reached where the pump speed increases to the maximum operating speed, the flow rate surges. The point at which this speed increases is set so that this peak does not exceed the maximum flow rate that the pump filter can tolerate.

[0052] As can be understood, the pump-down times for examples with different pump speeds vary, and are shortest for conventional pumps. The pump-down time shown by curve 42 having a variable low speed is lower than the pump-down time required for curve 44 where the low speed is constant. However, the variable pump speed provided by curve 42 may require a sensor that enables feedback in order to maintain a flow rate close to the maximum value that the miniaturized filter can support.

[0053] In the examples of FIGS. 4 and 5, the initial rotor speed is 400 rpm for both exemplary embodiments (42, 44), and this initial speed will set the maximum flow rate and determine the required filter size. In this example, it is less than 1 / 4 of the operating speed, and as a result, the filter size can be correspondingly reduced.

[0054] FIG. 6 shows how both the required filter size and the pump-down time, shown by curve 35, increase when the maximum flow rate at which the pump is set is reduced for both the mass flow rate limit and the volume flow rate limit. These reduced maximum flow rates are brought about by providing a low initial rotational speed of the pump. Curve 46 shows how the time increases when the maximum flow rate is limited by the volume flow rate, while curve 48 shows how the time increases when the flow rate is limited by the mass flow rate.

[0055] Table 1 presents this information in tabular form.

Table 1

[0056] As can be seen from the graph of FIG. 6 and Table 1, when the maximum flow rate is set to 120, which corresponds to the flow rate of a conventional pump, the required filter is the same as that of the conventional pump, and this is taken as 100%. The pump-down time is the pump-down time of the conventional pump, which is 17.8 seconds in this case. When the maximum flow rate decreases from 120 to 110, the size of the filter decreases by only 8%, and the pump-down time increases by only 1% for both the volumetric flow rate and the mass flow rate. As the decrease in the maximum flow rate continues, the pump-down time increases and the size of the filter decreases. As can be seen from FIG. 6, there is an optimal point where even if the size of the filter decreases significantly, the pump-down time does not increase significantly. This occurs at a flow rate of approximately 30, which is one-fourth of the maximum flow rate, and beyond this, the pump-down time increases significantly. This reduced flow rate requires a filter that is approximately one-fourth the size of the standard filter for a conventional pump.

[0057] FIG. 7 shows a filter 30 according to one embodiment. FIG. 8 is a flowchart showing the steps of a method for evacuating a chamber according to one embodiment. In an initial step S10, the rotor is rotated at an initial speed. The initial speed is set such that the maximum air flow rate is less than a predetermined value. This maximum air flow rate determines the size of the filter. This method has a feedback loop by which the flow rate is monitored and the rotor speed increases in response to detecting that the flow rate is decreasing. This feedback loop includes determining at S15 whether the flow rate has dropped below a certain value, and if so, increasing the rotor speed by a certain amount Δ at step S20. In this way, the rotor speed is maintained substantially constant. When it is determined at step S25 that the rotor speed has reached the maximum operating speed of the pump, i.e., the operating speed during a normal pumping process, the control process for adjusting the speed is stopped, and at step S30, the rotational speed of the rotor is maintained at this maximum operating speed for the remainder of the pumping process.

[0058] In summary, the initial rotational speed of the rotor is restricted to reduce the maximum air flow, which, as a result, reduces the size of the lubricating oil filter required to purify the lubricating oil from the fluid output by the pump.

[0059] In this regard, the size of the required filter is related to the maximum flow rate of the fluid pumped by the pump and the formula S = Q / (Permeability x P) where S: Filter area (m 2 )(in the case of a cylindrical filter S = πr2L), L: (m) Length of the filter, r: (m) Radius of the filter, P: Allowable pressure loss across the filter, Q: Air flow rate (m 3 / s), (Permeability: A parameter of the filter m 3 / (m 2 x Pa x s) is.

[0060] Since the pressure loss across the filter and the permeability of the filter are characteristics of the filter, the maximum flow rate of the pump is set to the size of the filter. By reducing the rotational speed of the rotor to make the maximum flow rate, which is the initial flow rate, less than half of the conventional value, the size of the filter can be correspondingly reduced to less than half.

[0061] Different speed control modes can be used to control the initial rotational speed of the rotor and thereby control the initial flow rate of the fluid. This is 1. Mode where the initial speed is restricted, 2. Mode where the initial speed is a rise from an initially low value, and the slope of the rise depends on the size of the container to be evacuated, 3. Mode where the speed may have an initially low value at a predetermined time depending on the size of the container to be evacuated, 4. Mode where the initial speed may be adjusted by feedback loop control depending on the air flow measured at the exhaust port in some embodiments, 5. A mode in which the initial velocity may be adjusted by feedback loop control that depends on the pressure measured at the pump inlet in some embodiments. including.

[0062] Exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, but the present invention is not limited to the exact embodiments, and it should be understood that various changes and modifications can be made thereto by those skilled in the art without departing from the scope of the present invention defined by the appended claims and their equivalents.

Explanation of Signs

[0063] 10 Rotor 12 Pump inlet 14 Pump exhaust port 20 Motor 22 Control circuit 24 Pressure sensor 26 Flow rate sensor 30 Filter 35 Change in required filter size with change in initial flow rate 40 Curve of conventional pump 41 Curve of theoretical flow rate of conventional pump 42 Curve of variable initial velocity pump 44 Curve of constant initial velocity pump 46 Change in pump down speed with change in initial volumetric flow rate 48 Change in pump down speed with change in initial mass flow rate

Claims

1. A lubricating oil seal type vacuum pump configured to send fluid from an intake port to an exhaust port, a rotor, a motor for rotating the rotor, a filter for filtering lubricating oil from the fluid output by the pump, and a control circuit for controlling the rotational speed of the rotor, wherein the control circuit is configured to control the rotation of the rotor such that the rotor rotates at a fixed low speed during a predetermined period in which the pressure at the intake port decreases, and rotates at a high operating speed after the predetermined period, wherein the predetermined period is selected such that the flow rate of the fluid passing through the filter does not exceed the maximum flow rate supported by the filter both during and after the predetermined period, a lubricating oil seal type vacuum pump characterized by the above.

2. The motor is composed of a variable speed motor for driving the rotor, and the control circuit is configured to control the rotational speed of the rotor by controlling the rotational speed of the motor. The lubricating oil seal type vacuum pump according to Claim 1.

3. The lubricating oil seal type vacuum pump includes at least one sensor for sensing the characteristics of the fluid fed by the pump, the characteristics indicating the pressure at the intake port, and the control circuit includes a feedback control system for controlling the speed of the rotor according to the sensed characteristics. The lubricating oil seal type vacuum pump according to Claim 1 or 2.

4. The fixed low speed is less than half of the high operating speed. The lubricating oil seal type vacuum pump according to any one of Claims 1 to 3.

5. A method of evacuating a chamber using the lubricating oil seal type pump according to any one of Claims 1 to 4, including rotating the rotor of the pump at a selected fixed low speed during a predetermined period in which the pressure at the intake port decreases, and increasing the rotational speed of the rotor to a high operating speed after the predetermined period, wherein the predetermined period is selected such that the flow rate of the fluid passing through the filter does not exceed the maximum flow rate supported by the filter both during and after the predetermined period, a method characterized by the above.

6. A miniaturized filter for a lubricating oil sealed vacuum pump according to any one of claims 1 to 4, wherein the miniaturized filter has a filtration surface area that is smaller than or equal to a value obtained by dividing the volumetric flow rate of the pump at an initial low speed configured to be provided by the pump by the transmittance and the pressure loss across the filter.

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