Pump Start Control

Abstract

A rotary vane vacuum pump and method for evacuating gas from a vacuum chamber is disclosed. The rotary vane vacuum pump includes an inlet for connecting to the vacuum chamber, an outlet for evacuating fluid pumped by the vacuum pump, a rotor, and a stator for operating the rotor. The pump has a vent passage for venting one of the pumping chambers in the vacuum pump. The vent passage has a flow control device for controlling flow through the vent passage. The flow control device is configured to permit flow through the vent passage upon start-up of the pump and to prevent flow through the vent passage in response to at least one of a predetermined time elapsed, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from at least one sensor indicative of operation of the vacuum pump.

Description

[Technical field]

[0001] The field of the invention relates to starting up vacuum pumps, and in certain preferred embodiments, to reducing the torque required during pump start-up. [Background technology]

[0002] When a vacuum pump starts up, it may initially pump gas at a high pressure, e.g. atmospheric pressure, which may require much more torque than is required during steady-state operation where the pressure is much lower. This is because, in addition to the resistance due to rotor inertia and static friction, there is a large resistance offered by the additional fluid being transported within the pump.

[0003] This is particularly problematic for some types of pumps, such as sliding vane rotary vacuum pumps, which in addition to transporting gas also transport oil used to seal the vanes during start-up. The torque required to overcome these forces at start-up causes initial loads on the pump motor that can be several times higher than the loads during normal steady-state operation. This can be a limiting factor in sizing the motor needed to drive the pump. It can also result in starting problems over the life of the pump. Summary of the Invention [Problem to be solved by the invention]

[0004] It would be desirable to be able to reduce the torque during startup. [Means for solving the problem]

[0005] 1. A rotary vane vacuum pump of a first aspect for evacuating a vacuum chamber, the rotary vane vacuum pump comprising: an inlet for connecting to the vacuum chamber; an outlet for evacuating a fluid pumped by the vacuum pump; a rotor and a stator having a plurality of vanes, the rotor configured to rotate within the stator, the rotor and the stator defining a plurality of pumping chambers for pumping fluid from the inlet to the exhaust upon rotation of the rotor; a motor for driving the rotor; and an airflow passage for providing fluid communication between an exterior of the vacuum pump and the pumping chambers within the vacuum pump, the airflow passage comprising a flow control device for controlling flow through the airflow passage, the flow control device configured to permit flow through the airflow passage upon start-up of the pump and to prevent flow through the airflow passage in response to at least one of a predetermined time elapsed, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from at least one sensor indicative of operation of the vacuum pump.

[0006] The inventors have recognized that the torque required to rotate the rotor during start-up of a vacuum pump, particularly one pumping down from atmospheric pressure, is very high and is often a limiting factor when selecting a motor to drive the pump. The inventors have also recognized that much of the torque required is due to the pressure differential across the vanes during initial rotation, and that this can be mitigated by providing a controlled venting of the pump during start-up so that fluid enters the suction pump chamber. After a certain point, flow through the vent passages can be impeded or stopped and the vacuum pump can function in a normal manner. By reducing the pressure differential across the vanes using a vent passage that provides a fluid passage to an unreduced pressure area, the maximum torque required during start-up is reduced. The vent passages can be vented to atmosphere or possibly to an area of ​​increased pressure such as an oil casing.

[0007] Selecting the most preferred time to stop venting can be based on one or more of a number of different factors indicative of pump operation. This can simply be a certain time after start-up. Alternatively, the decision to stop venting can be based on the operation of the pump itself, so that this can be based on one or more of the rotor rotational speed reaching a predefined threshold, the motor current reaching a predefined value, or an output from a sensor indicative of some operating parameter of the vacuum pump. The decision based on the detected pump operation can stop venting at a preferred or optimal point. The sensor can be a sensor associated with the vacuum pump or a sensor associated with the system that the pump is pumping.

[0008] In some embodiments, the vacuum pump comprises the at least one sensor, which in some embodiments includes at least one of a temperature sensor, a pressure sensor, a humidity sensor, and a sensor for detecting a rotation speed of the rotor.

[0009] Pressure, temperature, humidity, and rotor RPM since start-up are all related to the current state of the vacuum pump, and one or more of these measurements can be used in the decision to stop venting the pump.

[0010] In some embodiments, the intake port includes a movable closure element for opening and closing the intake port, the movable closure element configured to move between an open position and a closed position in response to pressure on a vacuum pump side of the movable closure element increasing above pressure on a vacuum chamber side of the movable closure element, the vent flow passage being in fluid communication with the vacuum chamber side of the movable element, and the fluid control device allowing flow through the vent flow passage causes the movable element to move to the closed position.

[0011] Vacuum pumps may have movable closure elements for sealing their intakes so that, when the pump is stopped, the vacuum chamber to which they are attached can be sealed under vacuum. In some cases, these movable closure elements are moved to a closed position under the control of a flow control device, which can be opened to allow flow through the flow path, and the flow changes the pressure on one side of the movable closure element so that opening the flow path changes the pressure difference across the closure element, forcing it to the closed position. The flow control device is conventionally a solenoid valve controlled by the power supplied to the motor, such that the valve opens and the closure element closes when the motor is stopped, and the valve closes when the motor is started. In an embodiment, the system for controlling the movable closure element can be combined with a system for venting the pump at start-up. In this case, the number of flow control elements required can be reduced, and one flow control element, which is sometimes a valve, is used both to control the movable closure element and to vent the pump at start-up. In this case, rather than immediately closing the valve at motor start-up, the closing of the valve is delayed so that the pump chamber is vented during the initial phase of the pump's rotation and the movable closure element remains closed.

[0012] In some embodiments, the vent passage is configured to open into the rotary vane pump closer to the inlet of the vacuum pump than the exhaust.

[0013] The vent passage can open into the pump near the pump inlet where gas is drawn in. In some embodiments, the vent passage can open into the vacuum pump downstream in the direction of pump rotation from the inlet, such that the vent passage opens into the intake pump chamber.

[0014] In some embodiments, the vent passage vents to the exterior of the vacuum pump at atmospheric pressure.

[0015] In other embodiments, the vent channel vents to pressures above atmospheric pressure.

[0016] In some embodiments, the rotary vane vacuum pump comprises a lubricated sliding vane vacuum pump and the vent passage vents air to a lubricated casing of the pump.

[0017] If the vacuum pump is an oil-filled vacuum pump, it may be advantageous to vent to the oil casing to avoid lubricant contamination from the vent passages, which can be a problem when the pump is stopped, such as during transport.

[0018] The venting chamber accomplishes this by providing fluid communication between the interior of the pump and the exterior of the pump or lubricant casing. The vent passage may open at one end to the pump chamber and at the other end to the exterior of the vacuum pump or somewhere within the lubricant casing of the vacuum pump.

[0019] In some embodiments, the flow control device may be configured to either open the ventilation flow path or close the ventilation flow path.

[0020] In other embodiments, the flow control device may be configured to control the opening of the ventilation passageway and therefore the flow rate through the ventilation passageway.

[0021] Flow control can be accomplished in many ways, but in some embodiments, the flow control device comprises a valve.

[0022] In some embodiments, the valve includes a mechanical valve including a resilient member for biasing the closure element toward the closed position.

[0023] In other embodiments, the valve includes an electrically controlled valve configured to operate in response to a control signal sent from a control circuit.

[0024] If the valve is an electrically controlled valve, there may be a control circuit for controlling the valve. Such a control circuit may slightly increase the complexity of the vacuum pump, but it allows the starting phase to be more carefully controlled and can result in a very effective reduction in the maximum torque required.

[0025] In some embodiments, the rotary vane pump further comprises a control circuit configured to control the motor to drive the pump; and to control the flow control device, the control circuit configured to control the flow control device to allow flow through the ventilation flow path when the pump is started, control the motor to begin driving the pump, and then control the flow control device to prevent flow through the ventilation flow path.

[0026] The control circuitry may simply control the valve to open after a predetermined time, or in some cases may be very sophisticated and may respond to signals from one or more sensors in determining the preferred or optimal time to prevent flow through the vent flow path. In some cases, the control circuitry may include an algorithm for determining when to stop venting based on multiple inputs.

[0027] A second aspect provides a method of starting a rotary vane vacuum pump according to the first aspect, the method comprising the steps of controlling a flow control device to allow flow through an airflow passage, commencing rotation of a rotor of the pump, and preventing flow through the airflow passage in response to at least one of a predetermined time elapsed, the rotational speed of the rotor reaching a predetermined threshold, the motor current reaching a predetermined value, and an output from a sensor indicative of operation of the vacuum pump.

[0028] In some embodiments, the method further includes moving a movable element from obscuring an inlet to the vacuum pump to opening the inlet to the vacuum pump by obstructing flow through the ventilation passage.

[0029] In some embodiments, impeding flow through the ventilation channel comprises closing a valve.

[0030] Further particular and preferred aspects are set out in the independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate or in combinations other than those explicitly set out in the claims.

[0031] Where features of an apparatus are described as operable to provide a certain functionality, this should be understood to include features of the apparatus that provide that functionality or that are adapted or configured to provide that functionality.

[0032] Embodiments of the invention are further described below with reference to the accompanying drawings. [Brief description of the drawings]

[0033] [Figure 1] The cross section of an oil-sealed vane pump and the required starting torque are shown. [Diagram 2] 1 illustrates a schematic of a rotary vane pump according to one embodiment. [Diagram 3] 1 illustrates diagrammatically a rotary vane pump according to a further embodiment; [Figure 4A-C] 1 shows a schematic diagram of the phases during start-up. [Diagram 5] 4 shows the change in torque required for a pump according to the prior art and a pump according to an embodiment. [Figure 6] 4 illustrates steps of a method according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Before describing the embodiments in more detail, an overview will first be provided.

[0035] Starting up a vacuum pump, particularly a sliding vane oil sealed vacuum pump, places high loads on the motor due to inertia, pressure differential across the vanes of the pump, and oil transfer. Embodiments seek to reduce the loads caused during start-up by venting the pump, where the pressure differential across the vanes of the pump is reduced by fluid flowing through a vent passageway into the inlet of the pump chamber. This venting can be achieved by opening a valve in the passageway between the pump chamber and the exterior of the stator.

[0036] The valves can be mechanical valves that operate in response to a pressure differential, or they can be electric valves driven by an electronic control circuit. The valves can be modulating valves or binary valves with an ON / OFF state.

[0037] The control of the valves can be synchronized with the operation of the pump at start-up, for example the pump rotation speed and / or time.

[0038] In the case of oil-sealed pumps, venting the intake pump chamber when the pump is stopped and when it is started limits the suction due to the pressure drop in the pump and thus the amount of oil sucked into the pump from the oil casing. This reduces the amount of oil in the pump at start-up and accordingly reduces the torque required at start-up. The ducts or channels used for venting can open to the outside or lead to the oil casing of the pump at high pressure (atmospheric pressure + overpressure due to gas extraction).

[0039] The valve can be controlled by an ON / OFF switching valve or a proportional valve.

[0040] Venting reduces the motor power required at start-up, which can allow for smaller motor sizes without compromising pump performance.

[0041] Some pumps are configured with a solenoid valve that is used to control a movable closure element or shutter to seal the pump from the vacuum chamber before the pump is shut down. Such a valve controls the flow through a passage that is used to increase the pressure on one side of the movable closure element, which is adapted to move to seal the pump from the vacuum chamber. This valve can be a solenoid valve controlled by the power supply of the pump, such that the valve closes when the pump is powered on. An embodiment connects this vent passage and the valve to an additional vent flow path to the pump chamber, such that the valve can be used to control the closure of the movable closure element and to vent the pump chamber to make it easier to start the pump. In this case, rather than closing the valve when the pump is started, the valve can be closed at a certain point during the start of the pump, for example after a predetermined time or at a predetermined speed, so that the valve closes such that the pump chamber is no longer vented and the pressure in the pump drops to open the movable closure element.

[0042] In summary, the integrated control and management of the solenoid valves allows the vent to remain open during the start-up phase, independent of the pump power supply, until a specified time, rotor speed, pressure, temperature, rotor speed or humidity is reached.

[0043] FIG. 1 shows a conventional sliding vane oil vacuum pump comprising a rotor 6 arranged to rotate about an axis, sliding vanes 12 defining a pump chamber, and a stator 5 within which the rotor 6 rotates, as well as a graph showing the torque 50 required to drive the pump and the number of revolutions 40 of the pump as a function of time. At start-up, the pressure in the pump is atmospheric pressure, and as the pump begins to rotate, there is a significant gas transfer, as well as the inertia of the rotor itself. This requires a large initial torque to initiate the rotation of the rotor and reduce the pressure in the pump. Initially, the vanes 12 cause compression and suction of gas and transfer of oil in the pump, and the torque increases sharply. Arrow 42 indicates the phase in which the vanes 12 cause significant gas transfer and the torque required to drive the motor is greater than three times that required during steady-state operation. This initial high torque demand can lead to pump failure and, as can be seen from the torque graph, requires a larger sized motor than would be required to drive the pump under normal operating conditions.

[0044] FIG. 2 shows a schematic of a sliding vane pump according to an embodiment. The pump has a movable closure element or shutter 9 connected to a vacuum chamber 2 and biased to a closed position by a spring 24. The pump 1 comprises an exhaust port 4 and an inlet port 3 leading to the vacuum chamber 2. There is also a vent passage 7 and a controllable valve 29. The valve can be opened to vent the inlet pump chamber, and when opened at start-up, the pressure difference across the vanes during the initial rotation of the rotor is reduced, which in turn reduces the torque required for rotation. Once the pump has been running for a certain time, or has reached a certain rotor speed, pressure, temperature, or a certain rotor speed, the valve 29 can be closed, so that the pressure in the pump chamber starts to decrease and the closure element 9 opens to connect the vacuum chamber to the pump, allowing the pump to evacuate the vacuum chamber 2.

[0045] In this embodiment there is an oil casing 32 which supplies oil to the oil sealed pump, and the vent passage 7 in this embodiment opens into this oil casing 32. This is at an increased pressure compared to atmospheric pressure. Venting into the oil casing has the advantage that contamination of the vent gas leaking outside the pump with oil is avoided or at least prevented.

[0046] Figure 3 shows a schematic diagram of a pump according to one embodiment, with a vent channel 7 adjacent the pump inlet, which when open serves both to evacuate the inlet pump chamber and to close a shutter 9. The vacuum pump 1 has an inlet 3 connected to the vacuum chamber 2 to be evacuated. The vacuum pump 1 has an outlet 4 for evacuating the pumped gas. The vacuum pump 1 has a stator 5 and a rotor 6 rotatably mounted within the stator 5, with an inlet or pumping region 8. There is a sensor 11 for measuring a parameter indicative of the operating state of the pump, and a control circuit 15 which receives a signal from the sensor 11. There is also a motor 13 for driving the pump.

[0047] A control circuit 15 controls the motor and valve 7 to vent the pump, and at start-up the control circuit controls the motor to begin driving the rotor and the valve to an open state. After a predetermined time and / or upon receiving a signal from sensor 11 indicating a predetermined condition, such as exceeding a threshold temperature, the control circuit 15 controls the valve 7 to close, after which the shutter 9 opens and the pump 1 begins evacuating the vacuum chamber 2.

[0048] Figures 4A to 4C show the start-up procedure according to one embodiment. Figure 4A shows the pump stopped, valve 29 open, and atmospheric pressure inside the pump. The vacuum chamber 2 is at low pressure and the inlet closure element 9 is closed. Figure 4B shows the pump started, valve 29 remains open, allowing air in the pump to vent as the rotor rotates, reducing the pressure difference across the vanes and the load on the motor. Figure 4C shows the situation when the pump reaches a predetermined start-up condition, which may mean that a predetermined time has elapsed or other operating threshold has been exceeded, at which point valve 29 closes and the pressure in the pump drops above the low pressure in the vacuum chamber 2, so that the closure element 9 opens and the pump operates to evacuate the vacuum chamber 2.

[0049] 5 shows the speed reached by the pump and the torque required to drive the pump as a function of time during start-up, with and without a vent valve. The left Y-axis shows torque, the right Y-axis shows speed, and time is shown on the X-axis. Line 40 shows the rotor speed steadily increasing up to operating speed, line 50 shows the torque required for this initial acceleration and therefore the torque required to maintain speed in a conventional pump with no venting, and dotted line 60 shows the torque required for an initially vented pump according to one embodiment. As can be seen from both torque graphs, a large torque is required initially, which starts to decrease as the rotor reaches a certain speed and the pressure in the pump and vacuum chamber drops.

[0050] If there is a valve to vent the pump (dotted line 60), less torque is required at start-up. Note that as shown by dotted line 60, when the pump is first vented, it takes time to evacuate the chamber and reach a stable low pressure condition, so the torque required initially at start-up is significantly reduced, but remains high for a longer period of time.

[0051] 6 is a flow diagram showing steps of a method according to one embodiment. In a first step S10, the vent is controlled to open and the pump is stopped. In step S20, a start instruction is received and in response the motor starts driving the pump, the pump starts to rotate and the vent remains open. In step D5, it is determined whether a predetermined start condition has been achieved. This condition may be one or more of: a predetermined time has elapsed, a pressure, temperature or humidity threshold has been exceeded, or a rotational speed or rotational speed threshold has been exceeded.

[0052] If this condition is met, then in step S30 the vent is closed. The pump then continues pumping and evacuates the pump chamber. If there is a shutter between the vacuum chamber and the vacuum pump, this will open when the pressure in the pump drops below the pressure in the vacuum chamber. In step S40, a stop command is received and pumping is stopped. At this point the method returns to step S10 where the pump is stopped and the vent is opened. In some embodiments where the pump has a shutter to the pump chamber, this will be closed.

[0053] Although exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, it should be understood that the present invention is not limited to the precise embodiments, and various changes and modifications may result by those skilled in the art without departing from the scope of the present invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0054] 1. Vacuum pump 2 Vacuum chamber 3 Pump Inlet 4 Pump exhaust port 5 Stator 6 Rotor 7 Ventilation channel 8 Intake or pump area 9 Closing elements or shutters 11 Sensors 12 Slide vane 13 Motor 15 Control circuit 24 Actuation means 29 Flow Control Device 32 Oil casing 40 Pump Speed 50 Standard pump torque 60 Torque of pump according to embodiment

Claims

1. 1. A rotary vane vacuum pump for evacuating gas from a vacuum chamber, comprising: an inlet for connecting to the vacuum chamber; and an outlet for exhausting fluid pumped by the vacuum pump; a rotor and stator including a plurality of vanes, the rotor configured to rotate within the stator, the rotor and the stator defining a plurality of pumping chambers for pumping fluid from the inlet to the exhaust upon rotation of the rotor; A motor that drives the rotor; a vent passage for venting one of the plurality of pumping chambers within the vacuum pump; Equipped with the ventilation flow path includes a flow control device for controlling flow through the ventilation flow path; 1. A rotary vane vacuum pump, comprising: a rotor that is adapted to rotate about a rotor axis and a rotor shaft that is adapted to receive a flow path through the flow path; a rotor that is adapted to receive a flow path through the flow path; a motor current that is adapted to receive a flow path through the flow path;

2. 2. The vacuum pump of claim 1, wherein the rotary vane vacuum pump further comprises the at least one sensor, the at least one sensor including at least one of a temperature sensor, a pressure sensor, a humidity sensor, and a sensor for detecting a rotation speed of the rotor.

3. the intake port includes a movable closure element for opening and closing the intake port, the movable closure element being configured to move between an open position and a closed position in response to a pressure on a vacuum pump side of the movable closure element increasing above a pressure on a vacuum chamber side of the movable closure element; 3. A rotary vane vacuum pump as claimed in claim 1 or 2, wherein the vent passage is in fluid communication with the vacuum chamber side of the movable closing element, and the fluid control device allowing flow through the vent passage causes the movable closing element to move to the closed position.

4. 4. A rotary vane vacuum pump as claimed in claim 1, wherein the vent passage is arranged to open into the rotary vane pump closer to the inlet to the vacuum pump than the exhaust port.

5. 5. A rotary vane vacuum pump as claimed in any preceding claim, wherein the vent passage vents to a pressure above atmospheric pressure.

6. 6. A rotary vane vacuum pump as claimed in any preceding claim, wherein the rotary vane vacuum pump comprises a lubricated sliding vane vacuum pump and the vent passage vents to a lubricated oil casing of the pump.

7. 7. A rotary vane vacuum pump according to claim 1, wherein the flow control device is configured to either open the vent passage or close the vent passage.

8. 7. A rotary vane vacuum pump as claimed in any preceding claim, wherein the flow control device is arranged to control the opening of the vent passage and therefore the flow rate through the vent passage.

9. 7. A rotary vane vacuum pump as claimed in any preceding claim, wherein the flow control device comprises a valve.

10. 10. The rotary vane vacuum pump of claim 9, wherein the valve comprises a mechanical valve including a resilient member for biasing the closure element towards the closed position.

11. 10. The rotary vane vacuum pump of claim 9, wherein the valve comprises an electrically controlled valve configured to operate in response to a control signal provided by a control circuit.

12. The rotary vane pump further comprises: Controlling the motor for driving the vacuum pump; Controlling the flow control device. A control circuit configured to:

12. A rotary vane vacuum pump as claimed in any one of claims 1 to 9 or 11, wherein the control circuit is configured to control the flow controller to permit flow through the ventilation passage when the pump is started, to control the motor to commence driving the pump, and then to control the flow controller to prevent flow through the ventilation passage, the preventing of flow through the ventilation passage being in response to at least one of a predetermined time elapsed, the rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from the at least one sensor indicative of operation of the vacuum pump.

13. 13. A method for starting a rotary vane vacuum pump according to any one of claims 1 to 12, comprising the steps of: controlling the flow control device to permit flow through the ventilation flow path; commencing rotation of the rotor of the pump; impeding flow through the vent passage in response to at least one of a predetermined time lapse, a rotational speed of the rotor reaching a predetermined threshold, a motor current reaching a predetermined value, and an output from a sensor indicative of operation of the vacuum pump; The method includes:

14. 14. The method of claim 13, further comprising: obstructing flow through the vent passage causes a movable element to move from a state that covers an inlet to the vacuum pump to a state that opens the inlet to the vacuum pump.

15. 15. The method of claim 13 or 14, wherein the step of impeding flow through the ventilation channel comprises closing a valve.

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