CN118176362A

CN118176362A - Vacuum pump, control method for vacuum pump, power conversion device for compressor, and compressor

Info

Publication number: CN118176362A
Application number: CN202180103879.0A
Authority: CN
Inventors: 木村康宏; 横泽荣秀; 町家贤二; 井上英晃; 后藤彬德
Original assignee: Ulvac Inc
Current assignee: Ulvac Inc
Priority date: 2021-11-04
Filing date: 2021-11-04
Publication date: 2024-06-11
Also published as: JPWO2023079621A1; JP7189394B1; WO2023079621A1

Abstract

The invention provides a vacuum pump capable of protecting a motor from overheating and improving vacuum exhaust performance, and a control method thereof. The vacuum pump according to one embodiment of the present invention includes: a positive displacement pump body, an electric motor, and a control unit. The pump body has a pump rotor. The motor rotates the pump rotor. The control unit executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when the load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and a torque equal to or less than a second predetermined torque higher than the first predetermined torque when the load torque is greater than the first predetermined torque, with the first predetermined power as an upper limit.

Description

Vacuum pump, control method for vacuum pump, power conversion device for compressor, and compressor

Technical Field

The present invention relates to a positive displacement vacuum pump and a control method thereof.

Background

In the positive displacement vacuum pump, the volume of the positive displacement vacuum pump is transferred by the motor, so that the gas in the chamber, which is the space to be evacuated, is evacuated. The motor is controlled by determining the rotational speed (also referred to as slip rotational speed) of the motor based on the input power frequency, as represented by a squirrel-cage induction motor, and setting the rotational speed to a fixed range. However, the displacement of the volume is an event in which the displacement of the gas, the accompanying compression load, and the load for maintaining the differential pressure between the gas suction port and the gas discharge port are combined, and depending on the design concept of the displacement of the pump, depending on the object, the overload operation may be forced so that the rated rotation speed cannot be maintained for the load to be handled per unit time as the work of the motor.

If overload operation is maintained, the motor or the pump unit is overheated and the vacuum pump is failed, and therefore, a mechanical structure (relief valve (compression load limitation) and magnetic coupling (torque transmission limitation)) for limiting the load to a certain level or less is added to cope with the overload operation. In addition, with the recent progress of the control device, a torque limit (current limit) which is a function attached to the control device may be used instead of the magnetic coupling (for example, refer to patent document 1).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 8-254193.

Disclosure of Invention

Problems to be solved by the invention

Such a vacuum pump is designed on the premise that overload operation equal to or higher than the rated value is periodically forced. The reason for this is that there is typically a situation where a falling load is connected, which is the load that initially is the largest and then exponentially falls. In addition, there are cases where only the work of maintaining the differential pressure is a load (the differential pressure is small depending on the system configuration of the vacuum pump) when maintaining the vacuum, and the ratio of the vacuum maintaining time is large compared with the time of the maximum load. That is, if the load is considered, it is reasonable that the motor and the pump section have a structure capable of separating the load of the continuous rating or more and the vacuum pump is designed on the basis of this, and the pump system thus designed has been configured or employed.

Although the vacuum pump used in this way is used, the operation process at the time of overload as described above adversely affects the vacuum exhaust performance. Specifically, when the load of the vacuum pump is increased or when the displacement amount of the volume, particularly the displacement amount per unit time, is increased during operation, the capacity of the motor is limited to the maximum, that is, the capacity of the motor to be at least continuous rated, and the capacity of the motor to be at least continuous rated cannot be exhibited.

In view of the above, an object of the present invention is to provide a vacuum pump capable of protecting a motor from overheating and improving vacuum exhaust performance, and a control method thereof.

Solution for solving the problem

The vacuum pump according to one embodiment of the present invention includes: a positive displacement pump body, a motor, and a control unit.

The pump body has a pump rotor.

The motor rotates the pump rotor.

The control unit executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when the load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and a torque equal to or less than a second predetermined torque higher than the first predetermined torque when the load torque is greater than the first predetermined torque, with the first predetermined power as an upper limit.

Accordingly, even in the overload operation, the reduction in the rotation speed of the motor is suppressed, and therefore, the displacement amount of the pump rotor per unit time can be maintained, and the time for exhausting gas to the target pressure can be shortened. Further, since the rotation speed of the motor is limited to a predetermined rotation speed or less, the vacuum pump can be protected from overheating.

Typically, the first prescribed torque is a rated torque of the motor.

Typically, the first prescribed power is a rated power of the motor.

Typically, the prescribed rotational speed is a rated rotational speed of the motor. The predetermined rotational speed may be a rotational speed higher than the rated rotational speed when the load torque is equal to or less than the first predetermined torque and the power of the motor is equal to or less than the first predetermined power.

In the second control mode, the control unit may be configured to drive the motor at a second predetermined power higher than the first predetermined power for only a predetermined time when the rotation state of the motor satisfies a predetermined condition.

The control unit may be configured to calculate an estimated value of the temperature of the entire vacuum pump in the second control mode, and to drive the motor in the first control mode when the estimated value is equal to or higher than a predetermined temperature.

In the method for controlling a vacuum pump according to an aspect of the present invention, the vacuum pump is a positive displacement vacuum pump, and includes: a pump rotor, and a motor for rotating the pump rotor, wherein in the control method of the vacuum pump,

The electric motor is started up and the motor is started,

Executing a first control mode for driving the motor at a rotation speed equal to or less than a predetermined rotation speed when the load torque is equal to or less than a first predetermined torque,

And executing a second control mode in which the motor is driven at a rotational speed equal to or less than the predetermined rotational speed and at a torque equal to or less than a second predetermined torque higher than the first predetermined torque, with the first predetermined power as an upper limit, when the load torque is greater than the first predetermined torque.

In one embodiment of the present invention, a power conversion device for a vacuum pump supplies power to a motor that rotates a pump rotor of a positive displacement pump, wherein,

The vacuum pump power conversion device includes a control unit that executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when a load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and a second predetermined torque higher than the first predetermined torque when the load torque is greater than the first predetermined torque, with a first predetermined power as an upper limit.

Effects of the invention

According to the present invention, the motor can be protected from overheating, and the vacuum exhaust performance can be improved.

Drawings

Fig. 1 is a schematic cross-sectional view showing an internal structure of a vacuum pump according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view taken along line A-A of fig. 1.

Fig. 3 is a block diagram schematically showing the result of the vacuum pump.

Fig. 4 is a functional block diagram of the control unit of the vacuum pump.

Fig. 5 is a flowchart showing an example of steps of the process performed by the control unit.

Fig. 6 is a graph showing experimental results of an example of the operation of the vacuum pump, and a relationship between load torque and pressure.

Fig. 7 is a graph showing experimental results of one example of the operation of the vacuum pump described above, and a relationship between power and pressure.

Fig. 8 is a graph showing experimental results of an example of the operation of the vacuum pump, and a relationship between the rotational speed and the pressure.

Fig. 9 is a graph showing experimental results of an example of the operation of the vacuum pump, and shows a relationship between the exhaust speed and the pressure.

Fig. 10 is a graph showing experimental results of one example of the operation of the vacuum pump, and a relationship between pressure and time.

Fig. 11 is an experimental result showing an example of the operation of the vacuum pump according to another embodiment of the present invention.

Fig. 12 is a diagram showing a typical refrigeration circuit.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1is a schematic cross-sectional view showing an internal structure of a vacuum pump 100 according to an embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line A-A of fig. 1. In each figure, the X-axis, Y-axis, and Z-axis show three mutually orthogonal axis directions.

The vacuum pump 100 of the present embodiment includes: pump body 10, motor 20, and control unit 30. In the present embodiment, the single-stage mechanical booster pump is exemplified as the vacuum pump 100, but other positive displacement pumps such as a screw pump, a vane pump, and a roots pump may be used.

(Pump body)

The pump body 10 has: a first pump rotor 11, a second pump rotor 12, and a housing 13 accommodating the first and second pump rotors 11, 12.

The housing 13 has: the first housing portion 131, the separators 132, 133 disposed at both ends of the first housing portion 131 in the Y-axis direction, and the second housing portion 134 fixed to the separator 133. The first housing portion 131 and the diaphragms 132, 133 form a pump chamber P that accommodates the first and second pump rotors 11, 12.

The first housing portion 131 and the separators 132, 133 are made of an iron-based metal material such as cast iron or stainless steel, for example, and are coupled to each other via a seal ring, not shown. The second housing 134 is made of a nonferrous metal material such as an aluminum alloy.

An intake port E1 communicating with the pump chamber P is formed on one main surface (upper surface in fig. 2) of the first housing portion 131, and an exhaust port E2 communicating with the pump chamber P is formed on the other main surface (lower surface in fig. 2). An intake pipe communicating with the interior of a vacuum chamber, not shown, is connected to the intake port E1, and an intake port of an exhaust pipe or auxiliary pump, not shown, is connected to the exhaust port E2.

The first and second pump rotors 11 and 12 are composed of a cocoon-shaped rotor (japanese-style horsetail rotor) made of an iron-based metal material such as cast iron, and are disposed so as to face each other in the X-axis direction. The first and second pump rotors 11, 12 have rotation axes 11s, 12s, respectively, parallel to the Y-axis direction. The bearings B1 fixed to the partition 132 are rotatably supported by one end portions 11s1 and 12s1 of the rotation shafts 11s and 12s, and the bearings B2 fixed to the partition 133 are rotatably supported by the other end portions 11s2 and 12s2 of the rotation shafts 11s and 12s. A predetermined gap is formed between the first pump rotor 11 and the second pump rotor 12 and between each of the pump rotors 11, 12 and the inner wall surface of the pump chamber P, and each of the pump rotors 11, 12 is configured to rotate so as not to contact each other and the inner wall surface of the pump chamber P.

A rotor core 21 constituting the motor 20 is fixed to one end 11s1 of the rotary shaft 11s of the first pump rotor 11, and a first synchronizing gear 141 is fixed between the rotor core 21 and the bearing B1. A second synchronizing gear 142 that meshes with the first synchronizing gear 141 is fixed to one end 12s1 of the rotary shaft 12s of the second pump rotor 12. By driving the motor 20, the first and second pump rotors 11, 12 rotate in opposite directions to each other via the synchronizing gears 141, 142, whereby the volume of the pump chamber P changes, and the gas is transferred from the intake port E1 to the exhaust port E2.

(Electric Motor)

In the present embodiment, the motor 20 is constituted by a closed motor of a permanent magnet synchronous type. In addition to this, the motor 20 may be an induction motor such as a squirrel cage motor. The vacuum pump 100 in which the pump body 10 and the motor 20 are integrated as shown in fig. 1 is not limited to the one in which the pump body 10 and the motor 20 are integrated, and may be a vacuum pump 100 in which the pump body 10 and the motor 20 are separated. Specifically, the pump body 10 and the motor 20 may be independent as a thermal circuit.

The motor 20 includes: a rotor core 21, a stator core 22, a closing cover 23, and a motor housing 24.

The rotor core 21 is fixed to one end 11s1 of the rotary shaft 11s of the first pump rotor 11. The rotor core 21 has: a laminated body of electromagnetic steel plates, and a plurality of permanent magnets M attached to the peripheral surface thereof. The permanent magnets M are alternately arranged with different polarities (N-pole and S-pole) along the periphery of the rotor core 21.

In the present embodiment, as the permanent magnet material, an iron-based material such as neodymium magnet or ferrite is used. The arrangement of the permanent magnets is not particularly limited, and may be a surface magnet type (SPM) in which permanent magnets are arranged on the surface of the rotor core 21, or an embedded magnet type (IPM) in which permanent magnets are embedded in the rotor core 21.

The stator core 22 is disposed around the rotor core 21 and fixed to the inner wall surface of the motor case 24. The stator core 22 has: a laminated body of electromagnetic steel plates, and a plurality of coils C wound around the laminated body. The coil C is formed of three-phase windings including a U-phase winding, a V-phase winding, and a W-phase winding, and is electrically connected to the control unit 30.

The closing cover 23 is disposed between the rotor core 21 and the stator core 22, and accommodates the rotor core 21 therein. The closing cover 23 is a bottomed cylindrical member having one end open on the gear chamber G side, and is made of a synthetic resin material such as PPS (polyphenylene sulfide) or PEEK (polyether ether ketone). The closing cover 23 is fixed to the motor case 24 via a seal ring S disposed around the opening end side thereof, and seals the rotor core 21 from the atmosphere (outside air).

The motor case 24 is made of, for example, an aluminum alloy, and accommodates the rotor core 21, the stator core 22, the closing cover 23, and the synchronizing gears 141 and 142. The motor case 24 is fixed to the partition 132 via a seal ring, not shown, to thereby form a gear chamber G. The gear chamber G accommodates lubricating oil for lubricating the synchronizing gears 141, 142 and the bearing B1. Typically, a plurality of cooling fins are provided on the outer surface of the motor housing 24.

The top end of the motor housing 24 is covered with a cover 25. The cover 25 is provided with a through hole that can communicate with the outside air, and can be configured to cool the rotor core 21 and the stator core 22 via a cooling fan 50 disposed adjacent to the motor 20. Instead of the cooling fan 50, or in addition to this, a structure capable of cooling the motor case 24 with water may be employed. The same applies to the pump body 10, and a structure capable of water-cooling the casing 13 may be employed. The structure of the cooling fan 50, the water-cooling structure, and the like is not limited as long as the structure can ensure the heat discharge amount capable of maintaining the continuous rated operation.

(Control Unit)

Next, details of the control unit 30 will be described. Fig. 3 is a block diagram schematically showing the structure of the control unit 30.

As shown in fig. 3, the control unit 30 has: a drive circuit 31, a position detecting unit 32, a control unit 33, and a current detector 34. The control unit 30 is used to control the driving of the motor 20. The control unit 30 is composed of a circuit board housed in a metal casing or the like provided in the motor casing 24, and various electronic components mounted thereon, and functions thereof are realized by a power conversion device (inverter) that controls the motor 20.

The drive circuit 31 is constituted by an inverter circuit having a plurality of semiconductor switching elements (transistors) for generating a drive signal for rotating the motor 20 at a predetermined rotational speed, a predetermined power, or the like. The switching timings are controlled by the control unit 33, so that the semiconductor switching elements supply outputs (power) to the coils C (U-phase winding, V-phase winding, and W-phase winding) of the stator core 22.

The current detector 34 detects a current (output current) flowing between the drive circuit 31 and the coil C of the stator core 22. For example, the current detector 34 may be configured to detect the current of all phases (U-phase, V-phase, and W-phase) of the three-phase ac, or may be configured to detect the current of any two phases of the three-phase ac. As long as the zero-phase current is not generated, the sum of the currents of the U-phase, V-phase, and W-phase is zero, and thus information on the currents of all phases can be obtained even when the currents of both phases are detected. The current detector 34 may be configured to detect a voltage. This can be achieved by detecting the current or the like by using a resistor present in a circuit such as a shunt, a motor, a driving circuit, or the like.

The position detecting unit 32 recognizes the current value of each layer detected by the current detector 34, thereby indirectly detecting the magnetic pole position of the rotor core 21 from the waveform of the counter electromotive force generated in the coil C due to the time-dependent change in the magnetic flux intersecting the coil C, and outputs the detected magnetic pole position to the control unit 33 as a position detection signal for controlling the timing of energization to the coil C. In the case where the motor 20 is not a synchronous machine but an induction machine, for example, the position detecting unit 32 may be read as the magnetic flux estimating unit 32, and a vector control using well-known d-axis magnetic fluxes and q-axis magnetic fluxes may be performed on the control unit 33 described later, so that a drive signal may be supplied to the drive circuit 31.

The control unit 33 generates a control signal for exciting the coil C of the stator core 21 based on the magnetic pole position of the rotor core 21 detected by the position detection unit 32, and outputs the control signal to the drive circuit 31. Typically, the control unit 33 is constituted by an information processing device (computer) having a CPU (Central Processing Unit ) and a memory. The memory stores a program for executing a processing procedure described later in the control unit 33 and various parameters for calculation.

Fig. 4 is a functional block diagram showing the configuration of the control section 33. The control unit 33 includes: a speed calculating unit 331, a power calculating unit 332, a temperature calculating unit 333, a determining unit 334, and a signal generating unit 335.

The speed calculating unit 331 calculates the rotational speed of the motor 20 based on the change in the magnetic pole position of the rotor core 21 detected by the position detecting unit 32. The power calculation unit 332 detects the load torque of the motor 20 from the magnetic pole position of the rotor core 21 or the current value flowing through the coil C obtained by the position detection unit 32, and calculates the output (power) to be supplied to the motor 20 based on the detected load torque and the rotational speed of the motor. Further, a detector such as a strain gauge may be provided on the rotation shaft of the motor 20 and the rotation shafts 11s, 12s of the pump rotors 11, 12 to determine the load torque.

The temperature calculation unit 333 calculates an estimated value of the heat generation amount (temperature) of the entire vacuum pump 100 including the pump main body 10 and the motor 20. For example, an arithmetic algorithm based on a parameter simulating the heat capacity of the entire vacuum pump 100 and the operation time of the vacuum pump 100 is used for calculating the estimated value. In addition, the estimated value may be calculated based on the output of a temperature sensor that directly or indirectly detects the temperatures of the pump body 10 and the motor 20.

The determination unit 334 determines the magnitude relation between the load torque and the rotational speed of the motor 20 calculated by the speed calculation unit 331 and predetermined torques (T1, T2) and predetermined rotational speeds (Rth) described later, respectively, at the time of driving the motor 20. The determination unit 334 determines whether or not the estimated value of the heat generation amount calculated by the temperature calculation unit 333 is equal to or higher than a predetermined temperature (Tm) described later, at the time of driving the motor 20.

The signal generating unit 335 generates a drive signal corresponding to a control mode described later to the drive circuit 31. In the present embodiment, the control unit 33 has a first control mode and a second control mode as control modes of the motor 20, and switches the control mode of the motor 20 between the first control mode and the second control mode based on the determination result of the determination unit 334 regarding the load torque, the output (power), and the rotation speed of the motor 20.

When the load torque is equal to or less than the first predetermined torque T1, the first control mode is executed to drive the motor 20 at a rotation speed equal to or less than the predetermined rotation speed (Rth). On the other hand, when the load torque is larger than the first predetermined torque T1, the second control mode is executed, and the motor 20 is driven at a rotation speed equal to or smaller than the predetermined rotation speed (Rth) and at a torque equal to or smaller than a second predetermined torque T2 higher than the first predetermined torque T1, with the first predetermined power P1 as an upper limit. Typically, the predetermined rotational speed Rth is a rated rotational speed, the first predetermined torque T1 is a rated torque, and the first predetermined power P1 is a rated output, but the present invention is not limited thereto.

In general, as shown in the following expression (1), the output (power) P [ kW ] of the motor is proportional to the product of the load torque T [ N.m ] and the rotation speed N [ rpm ] of the motor.

P∝T·n…(1)

When the displacement amount of the pump body is represented by the rotation speed n of the motor, the displacement amount is determined by the load torque of the motor. Typically, the displacement amount is derived from the rotational speed in a state where the load (hereinafter, also referred to as a total load) obtained by adding the displacement load and the differential pressure load and the torque (load torque) exerted by the motor are balanced. Thus, for example, the vacuum pump can be designed in consideration of the condition that the motor is continuously driven at the rated rotation speed to ensure the exhaust performance for the purpose of the vacuum pump.

On the other hand, when the chamber is exhausted from the atmospheric pressure, for example, the capacity transfer load of the vacuum pump immediately after start or the compression load accompanying the capacity transfer load is large, and therefore, the load torque of the motor is high, and the operation of the vacuum pump is in a high load state or an overload state. In the overload state, the motor sometimes exceeds the rated torque, and if the state is continued for a long time, the motor cannot be protected from overheating. Therefore, in the case of driving the motor, in general, the load torque (torque limit) is limited so that the motor is not greater than its rated torque. If the load torque of the motor is limited to the rated torque, the rotational speed of the motor is reduced to be balanced with the total load, and as a result, the displacement amount is reduced, and the exhaust performance of the vacuum pump is also reduced. At this time, the values of the load torque T, the rotation speed n, and the output P in the above expression (1) are as follows.

T=torque limit value (rated torque)

N is less than rated rotation speed

P < rated power

That is, when considering the output, it can be said that the vacuum pump is operated at an output lower than the rated power, and the original exhaust capability is not fully exhibited.

Therefore, in the present embodiment, when the load torque of the motor 20 is greater than the first predetermined torque T1 (rated torque), the control method of the motor 20 is switched from the first control mode to the second control mode, and the motor 20 is allowed to be driven at a torque equal to or less than the second predetermined torque T2 higher than the first predetermined torque T1. The second predetermined torque T2 is not particularly limited as long as the output of the motor 20 is not greater than the first predetermined power P1 (rated power), and may vary according to the rotation speed n.

The method of driving the motor 20 in the first control mode is not particularly limited as long as the rotational speed and the load torque are equal to or less than a predetermined value, and rotational speed control is typically performed using the rated rotational speed as an instruction value. For example, torque control using the first predetermined torque T1 (rated torque) as an instruction value or power control using the first predetermined power P1 (rated power) as an instruction value may be used.

On the other hand, a typical driving method of the motor 20 in the second control mode is power control for driving with the first predetermined power P1 (rated power) as an upper limit. Therefore, even if the load torque is larger than the first prescribed torque T1 (rated torque), the torque designated value for the motor 20 can be increased by (N/N) times as long as the current rotational speed (N) of the motor 20 is lower than the rated rotational speed (N). This increases the volume transfer amount, and shortens the exhaust time. Further, even if the load torque of the motor is increased by (N/N), the output of the motor 20 is equal to or less than the rated power, so that overheating of the vacuum pump 100 can be suppressed.

The driving method of the motor 20 in the second control mode is not limited to the above-described power control as long as the driving method is performed with the predetermined power as the upper limit, and for example, torque control may be employed in which the torque value as the target value is gradually increased or gradually decreased while monitoring the output power value, and speed control may be employed in which the speed command value as the target value is gradually increased or gradually decreased while monitoring the power value.

Further, when the motor 20 is caused to generate a torque equal to or higher than the rated torque, a current equal to or higher than the rated torque is caused to flow in the motor 20, and the amount of heat generated does not match the amount of heat discharged, so that it is impossible to avoid a overheat state of the motor 20, and thermal destruction of the coil C or the like is caused. In addition, similarly, the pump body 10 is overheated due to an excessive compression load of the pump body 10 compared to the rated load, and there is a risk of occurrence of a seizure phenomenon due to insufficient clearance between the pump rotors 11, 12 or insufficient clearance between the pump rotors 11, 12 and the housing 13. That is, if the rated torque is understood to mean that the balance between the heat generation amount and the heat release amount is maintained so that the respective constituent members are maintained in a safe temperature range during operation, a temperature range in which safety cannot be ensured occurs when the rated torque or more is exerted. Therefore, it is necessary to estimate or monitor the temperature or a physical quantity corresponding to the temperature to protect the vacuum pump 100 from an overheat state.

Therefore, in the present embodiment, the temperature calculating unit 333 that calculates the estimated value of the amount of heat generated by the entire vacuum pump 100 is configured to switch to the first control mode in which the motor 20 is driven at the torque equal to or less than the rated torque when the estimated value of the amount of heat generated is equal to or greater than the predetermined temperature (Tm), for example. This can protect the vacuum pump 100 from an overheat state.

Further, when the load torque is low, the volume displacement amount can be increased by increasing the rotational speed until the rated power is reached, but when the load torque is too low, there is a risk that the rotational speed of the motor 20 exceeds the limit speed of the mechanical components constituting the vacuum pump 100. In order to avoid such a problem, in the second control mode, the upper limit of the rotation speed is set to the rated rotation speed (Rth). Thereby, the vacuum pump 100 can be operated in a safe speed range. In addition, not limited to this, when the load torque and the power are set to be equal to or less than the rated rotational speed, as will be described later, the upper limit value of the rotational speed may be set to be equal to or less than the limit speed of the mechanical component and higher than the rated rotational speed.

Further, since continuous driving of the motor 20 at a rated power or higher causes overload, the rated power or higher is not normally set to a command value in power control. That is, it is reasonable to use a fixed value as the rated power for the command value of the power control. However, it cannot be said that the vacuum pump can be made to exert its original maximum capacity at the fixed value. That is, although the power higher than the rated power can be exerted on the load in a short time in a range where the overheat is not reached, the command value is a fixed power, and therefore, it can be said that the exhaust capacity of the pump is limited.

Here, in the positive displacement vacuum pump, as its capacity, there is an exhaust time, and the exhaust time is shorter as the cumulative transfer amount of the volume at a certain time is larger. That is, when it is determined that there is a tendency for the load to decrease (or the rotational speed to increase) as the rotational state of the motor, the power, which is the torque equal to or greater than the rated torque, can be input, and the function as the vacuum pump can be improved. In contrast, for example, when the pressure in the chamber is released during the pump operation, and the load is determined to be liable to increase (or the rotation speed is reduced), it is not necessary to improve the exhaust performance of the vacuum pump except for the special case.

That is, when it is determined that the rotational state of the motor is a state in which the rated torque or power or more can be input, the motor 20 may be driven with a torque or power (for example, 120% to 200% of the rated torque or rated power) that is larger than the rated torque or rated power. By executing such control, the volume transfer amount (or transfer number) per unit time can be increased, and as a result, the exhaust time becomes shorter. Further, if the above-described temperature estimation function is provided, the problem of overheat due to overload can be avoided, and safe operation of the vacuum pump can be ensured.

In addition, instead of the above-described temperature estimation function, the operation exceeding the rated value may be limited to a predetermined time, and a time (prohibition period) or the like may be set to a predetermined time or more as an interval of the operation exceeding the rated value, and after the operation exceeding the rated value, the vacuum pump may be quickly returned to the temperature at the time of the rated operation. This makes it possible to suppress overheating of the vacuum pump due to overload with a simple configuration without using the temperature estimation function.

In the case where the vacuum pump 100 in which the pump body 10 and the motor 20 are independent is used as the heat circuit, the temperature calculating unit 333 that calculates the estimated value of the heat generation amount estimates the heat generation amount for each of the pump body 10 and the motor 20. In this case, since the heat balance between the pump body 10 and the motor 20 is different, for example, when any estimated value is equal to or higher than a predetermined temperature (Tm), the control mode is switched to the first control mode in which the motor 20 is driven at the first predetermined torque T1, and the motor 20 is driven at a torque equal to or lower than the rated torque. The predetermined temperature may be set independently according to the pump body 10 and the motor 20. This is preferable because overheating of the vacuum pump is suppressed for a longer period of time when the heat resistances are different from each other.

[ Control method of vacuum Pump ]

Next, the details of the control unit 33 will be described in connection with the operation of the vacuum pump. Fig. 5 is a flowchart showing an example of steps of the process performed in the control section 33.

Fig. 6 to 10 are experimental results showing an example of an operation of the vacuum pump 100 according to the present embodiment to reach the target pressure after a fixed time has elapsed since the start of the operation, in which fig. 6 shows a relationship between load torque and pressure, fig. 7 shows a relationship between power and pressure, fig. 8 shows a relationship between rotational speed and pressure, fig. 9 shows a relationship between exhaust speed and pressure, and fig. 10 shows a relationship between pressure and time. In fig. 6 to 8, the load torque, power, and rotational speed on the vertical axis of the table are represented on an arbitrary scale, and are shown in relative ratios when the respective rated values are 1. In fig. 6 to 10, the "power control" corresponds to the control method executed in the present embodiment, and the control method of the "rotation speed control" is also shown in comparison. The terms "power control" and "rotational speed control" mean that the control target of the control loop is power or rotational speed, and for example, the power or rotational speed is controlled so as to be maintained at a certain target value.

When the operation of the vacuum pump 100 is started, the control unit 33 drives the motor 20 in the first control mode (step 101). In the first control mode, the motor 20 is driven by rotational speed control using the rated rotational speed Rth as an instruction value. The control loop may be any type as long as it can determine the load torque described later.

In the case where the pressure in the vacuum chamber is atmospheric pressure, the vacuum pump 100 is driven in a high load state immediately after the start of operation. The control unit 33 monitors the load torque obtained as a result of the operation of the motor 20, and determines whether or not the load torque is equal to or less than the first predetermined torque T1 (step 102).

When the load torque is equal to or less than the first predetermined torque T1 (yes in step 102), the control unit 33 continues to drive the motor 20 in the first control mode. On the other hand, when the load torque is greater than the first predetermined torque T1 (no in step 102), the control unit 33 determines whether or not the rotational speed of the motor 20 is less than the predetermined rotational speed Rth (step 103). When the rotation speed is smaller than the predetermined rotation speed Rth (yes in step 103), the control unit 33 switches from the first control mode to the second control mode (step 104). That is, the second control mode is executed when the load torque is greater than the first prescribed torque T1 and the rotation speed of the motor 20 is less than the prescribed rotation speed Rth.

In the second control mode, the motor 20 is driven at a rotational speed equal to or less than the rated rotational speed Rth and at a torque equal to or less than a second predetermined torque T2 higher than the first predetermined torque T1, with the first predetermined power P1 (rated power) as the power upper limit value. The second predetermined torque T2 is set to a torque value corresponding to 120% to 200% of the rated torque, for example.

As described above, in the present embodiment, since the load torque can be increased within a range not greater than the rated power during high operation of the vacuum pump 100, the motor 20 can be driven with high torque (see fig. 6). This increases the volume transfer amount (rotational speed), thereby shortening the exhaust time (see fig. 8 to 10). Further, since the upper limit of the rotation speed is limited to the rated rotation speed Rth, breakage of the vacuum pump 100 due to over rotation of the motor 20 can be prevented.

In particular, the second control mode is preferably configured to be set to the first predetermined power P1 by adjusting (gradually increasing or gradually decreasing) the second predetermined torque T2. This configuration is typical power control, and uses the control target of the control loop as power and the target power as the first predetermined power P1. Further, if the second predetermined torque T2 is a set value for achieving the first predetermined power P1 or less, it is preferable in terms of suppressing the amount of heat generation described later.

The control unit 33 determines whether or not the temperature of the entire vacuum pump 100 (the estimated value of the heat generation amount calculated by the temperature calculating unit 333) is equal to or higher than a predetermined temperature Tm during execution of the second control mode (step 105). When determining that the temperature of the vacuum pump 100 is equal to or higher than the predetermined temperature Tm (yes in step 105), the control unit 33 switches from the second control mode to the first control mode. This can protect the vacuum pump 100 from an overheat state. On the other hand, when it is determined that the temperature of the vacuum pump 100 is less than the predetermined temperature Tm (no in step 105), the control unit 33 continues to drive the motor 20 in the second control mode.

Further, the control unit 33 determines whether or not the load torque tends to decrease during execution of the second control mode (step 106). The determination of whether the load torque tends to decrease is performed based on, for example, whether the detected value of the load torque detected at a predetermined period is fixed or the load torque tends to decrease in the speed calculation unit 331. In the power control, if the load torque tends to decrease, the rotational speed tends to increase, and therefore it can be determined that the chamber is inclined to the vacuum.

Therefore, when the load torque tends to decrease (yes in step 106), the control unit 33 executes torque up control to increase the power upper limit value (power target value) from the first predetermined power P1 (rated power) to the second predetermined power P2 only for a predetermined time (step 107). Accordingly, the rotational speed of the motor 20 temporarily increases, and therefore, the volume transfer amount further increases, and accordingly, the exhaust time can be shortened (see fig. 10). The second predetermined power P2 is not particularly limited as long as it is higher than the first predetermined power P1, and is set to a power value corresponding to 120% to 200% of the rated power, for example. In this way, the ability to rating for a short time is exhibited to the maximum extent in the region of vacuum degree (medium vacuum region) shown in fig. 10, and as a result, shortening of the exhaust time can be confirmed.

On the other hand, the heating value of the vacuum pump 100 increases by execution of the torque lifting control, but since the torque lifting control is limited to a predetermined time, the vacuum pump 100 can be prevented from reaching an overheated state (refer to fig. 7). The predetermined time can be determined experimentally in advance based on the rate of thermal rise of the vacuum pump 100 due to torque up control, and the like. After the torque boosting process for the predetermined time is performed, and when the load torque is not in a tendency to decrease (no in step 105), the control unit 33 continues to perform power control with the power upper limit value as the first predetermined power P1 (rated power).

By repeating the above operations, the drive control of the motor 20 mainly including the power control is performed. As a result, the exhaust performance inherent in the vacuum pump 100 can be maximally exerted, and thus the time to reach the target vacuum pressure (exhaust time) can be shortened, as compared with the case where the motor 20 is driven only by the rotation speed control.

Further, at the time of starting from the atmospheric pressure condition, the start torque can be increased as compared with the rotational speed control in which the torque limit is applied by quickly switching to the second control mode in which the power control is mainly used, and therefore, not only the exhaust time can be shortened, but also the possibility of coming off from the stuck state can be improved, and further, even under the condition of low oil temperature, that is, under the condition of low pump temperature, high mechanical loss, or other severe environments, the effect of shortening the exhaust time can be achieved, and by mainly using the power control, the operation in which the heat generation is suppressed can be achieved as compared with the operation in which the torque value is only increased.

When the pressure in the vacuum chamber is reduced to a predetermined value or less and the compression load of the gas in the pump body 10 is reduced, the load of the vacuum pump 100 is only work for maintaining the differential pressure between the suction port E1 and the discharge port E2. Therefore, the control unit 33 determines whether or not the load torque is equal to or less than the first torque T1 (rated torque) during execution of the second control mode (step 102), and switches from the second control mode to the first control mode when the load torque is equal to or less than the first torque T1 (yes in step 102). In the first control mode, since the rated rotational speed (predetermined rotational speed Rth) is the upper limit value of the rotational speed, the motor 20 is driven at a fixed rotational speed (rated rotational speed) from the low vacuum to the medium vacuum (about 2kPa to 0.1Pa in fig. 8). Here, the definition of medium vacuum/high vacuum is based on JIS Z8126-1 vacuum technology-term-part 1: general terms.

< Other embodiment 1 >

In the above embodiment, the motor 20 is driven at the rotation speed equal to or less than the predetermined rotation speed Rth in the first control mode, and the predetermined rotation speed Rth is set to the rated rotation speed, but the present invention is not limited thereto, and the predetermined rotation speed Rth may be set to a variable value corresponding to the operation state of the motor 20 at this time.

For example, in the first control mode, when the load torque is equal to or less than the first predetermined torque T1 and the power is equal to or less than the first predetermined power P1, the predetermined rotation speed Rth may be set to a rotation speed higher than the rated rotation speed. That is, a control loop of power control is employed in the first control mode, and an increase in the rotational speed is permitted within a range where the power of the motor 20 is not greater than a first predetermined power P1 (typically, rated power) (hereinafter, also referred to as high rotational speed control). The rotational speed upper limit value under the high rotational speed control can be arbitrarily set, for example, to 120% of the rated rotational speed, depending on the rotational speed upper limit value of the pump main body or the motor. As indicated by a broken line Ep in fig. 11, the rate of increase in the rotational speed from the high rated rotational speed to the rotational speed upper limit value is a value lower than the rate of increase in the rotational speed of the power control.

As shown in fig. 11, such high rotation speed control can be performed in the vicinity of the medium vacuum at a predetermined time after switching from the second control mode to the first control mode. The operating time of the high-speed control may be fixed in advance or may be a time until the power reaches the first prescribed power P1. After the high rotation speed control is performed for a prescribed time, a first control mode is performed in which the rated rotation speed is set as the rotation speed upper limit value. This further leads to the evacuation capability of the vacuum pump 100, and therefore, the evacuation time up to the maximum vacuum level can be further shortened, and the displacement volume can be increased when the pressure zone is continuously operated under high rotation speed control.

< Other embodiments 2 >

Although the vacuum pump is exemplified in the above embodiments, the present invention is also applicable to pumps other than the vacuum pump, for example, a compressor in a compression system or a driving motor thereof.

Fig. 12 shows a typical refrigeration circuit. The high-pressure superheated gas refrigerant discharged from the compressor 201 is condensed in the condenser 202. The high-pressure supercooled liquid refrigerant flowing out of the condenser 202 passes through the expansion valve 203, and is decompressed. The low-pressure liquid refrigerant passing through the expansion valve 203 is evaporated in the evaporator 204. The low-pressure superheated gas refrigerant flowing out of the evaporator 204 is sucked into the compressor 201.

As the compressor 201, a positive displacement pump such as a rotary pump or a scroll pump can be used. The compressor 201 is easily subjected to a thermal load due to the condensing temperature, evaporating temperature, and superheat degree of the suction vapor of the refrigerant. On the other hand, in the compressor, under the same operation conditions, the following capacity is required, which is capable of sucking a larger amount of vapor and exerting a strong refrigerating capacity. Therefore, in the compressor 201, as in the vacuum pump described above, a technique is required to improve the pump performance while preventing overheating of the motor as a driving source of the compressor 201. The above-described operation control of the vacuum pump is also effective against such problems.

If the evaporator 204 is regarded as a vacuum chamber of the vacuum exhaust system described above, the refrigerant flowing into the evaporator 204 from the expansion valve 203 can be regarded as a gas introduced into the vacuum chamber. If the pressures of the condenser 202 and the evaporator 204 are stabilized, the load torque of the compressor 201 is also stabilized. For example, if the condensing pressure is regarded as the atmospheric pressure in the vacuum exhaust system, the operation state of the compressor 201 can be set to the same state as the medium vacuum region of the vacuum exhaust system as long as the evaporating pressure is stable and the thermal flow rate of the evaporator 204 is also a certain condition.

Description of the reference numerals

10: A pump body;

11. 12: a pump rotor;

20: a motor;

30: a control unit;

31: a driving circuit;

32: a position detection unit;

33: a control unit;

100: a vacuum pump;

201: a compressor.

Claims

1. A vacuum pump, comprising:

A positive displacement pump body having a pump rotor;

A motor that rotates the pump rotor; and

And a control unit that executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when the load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and a torque equal to or less than a second predetermined torque higher than the first predetermined torque when the load torque is greater than the first predetermined torque, with the first predetermined power as an upper limit.

2. The vacuum pump according to claim 1, wherein,

The predetermined rotational speed is a rated rotational speed of the motor.

3. The vacuum pump according to claim 1, wherein,

When the load torque is equal to or less than the first predetermined torque and the power of the motor is equal to or less than the first predetermined power, the predetermined rotational speed is a rotational speed higher than a rated rotational speed of the motor.

4. A vacuum pump according to any one of claims 1 to 3, wherein,

The first prescribed power is a rated power of the motor.

5. The vacuum pump according to any one of claims 1 to 4, wherein,

The first predetermined torque is a rated torque of the motor.

6. The vacuum pump according to any one of claims 1 to 5, wherein,

In the second control mode, the control unit drives the motor at a power equal to or lower than a second predetermined power higher than the first predetermined power for only a predetermined time when a rotation state of the motor satisfies a predetermined condition.

7. The vacuum pump according to any one of claims 1 to 6, wherein,

The control unit calculates an estimated value of the temperature of the entire vacuum pump in the second control mode, and drives the motor in the first control mode when the estimated value is equal to or higher than a predetermined temperature.

8. A method of controlling a vacuum pump, the vacuum pump being a positive displacement vacuum pump, comprising: a pump rotor, and a motor for rotating the pump rotor, wherein in the control method of the vacuum pump,

The electric motor is started up and the motor is started,

9. A power conversion device for a vacuum pump supplies power to a motor that rotates a pump rotor of a positive displacement pump, wherein,

The power conversion device for a vacuum pump comprises: and a control unit that executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when the load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and a torque equal to or less than a second predetermined torque higher than the first predetermined torque when the load torque is greater than the first predetermined torque, with the first predetermined power as an upper limit.

10. A power conversion device for a compressor supplies power to a compressor motor of a compression system, wherein,

The compressor power conversion device includes: and a control unit that executes a first control mode for driving the motor at a rotational speed equal to or less than a predetermined rotational speed when the load torque is equal to or less than a first predetermined torque, and executes a second control mode for driving the motor at a rotational speed equal to or less than the predetermined rotational speed and at a second predetermined torque higher than the first predetermined torque, with the first predetermined power as an upper limit, when the load torque is greater than the first predetermined torque.

11. A compressor, comprising:

A positive displacement pump body having a pump rotor;

A motor that rotates the pump rotor; and