JP5452953B2 - Screw compressor - Google Patents

Description

  The present invention relates to a screw compressor.

  As shown in FIG. 4, the rotor shaft 101 of one screw rotor 103 is extended out of the screw rotors 103, 103 that are engaged with each other by the rotor shaft 101 supported by the bearing 102, and the screw rotor 103 is attached to the rotor shaft 101. Patent Document 1 discloses a screw compressor in which a rotor 104 of a motor to be driven is directly connected. In such a screw compressor, since the coupling for connecting the output shaft of the motor and the rotor shaft of the screw rotor is not required, the centering operation of the shaft is not required, and the structure can be simplified.

  However, such a structure is a cantilever structure in which the rotor 104 of the motor is supported on one side when the screw rotor 103 supported on both sides can be regarded as a rigid body. The cantilever structure has a lower natural frequency than the both-end support structure.

  As shown in FIG. 5, the rotor 104 of the cantilever structure in which the other end of the rotor shaft 101 that is directly connected to the rotor 104 of the motor is fixed to the screw rotor 103 is centered on the end surface 105 of the screw rotor. It can be considered that a transverse vibration of a one-degree-of-freedom system is generated. The natural frequency is determined by the distance L from the end surface 105 of the screw rotor 103 on the motor rotor 104 side to the center of gravity of the motor rotor 104 and the mass M of the motor rotor 104. The spring constant K of the rotor shaft 101 of the screw rotor 103 is expressed by the following equation (1), where E is Young's modulus and I is the secondary moment of section.

一方、固有振動数ωは、次式（２）で表される。

On the other hand, the natural frequency ω is expressed by the following equation (2).

（１）及び（２）式より、（３）式が表される。

From the expressions (1) and (2), the expression (3) is expressed.

  As long as the motor has a cantilever structure, it cannot be avoided that the natural frequency decreases. For example, even a screw compressor having a motor capable of operating at a higher speed than 7000 rpm cannot be operated at a rotational speed higher than 7000 rpm if the critical speed (natural frequency) is 7000 rpm. There is a problem.

JP 2004-343857 A

  An object of the present invention is to increase the critical speed (natural frequency) of a motor without lowering the output in a screw compressor, and to realize operation in a high rotation region.

As a means for solving the above-mentioned problems, the screw compressor of the present invention is driven by a motor, and includes a screw rotor that engages male and female, and the sum of the outputs is necessary to drive the screw rotor. A first motor and a second motor that have the same output as or more than a single motor, and each rotor of the first motor and the second motor is provided on the tip side of a rotor shaft that extends to both sides of the male rotor of the screw rotor. The first motor and the second motor are supplied with electric power having different phases from each other .

With this configuration, if the power of a single motor required to drive the screw rotor is supplied by the first motor and the second motor , each motor can be reduced in size, and the mass of each motor. Can be reduced. Thereby, the natural frequency of each motor directly connected to the rotor shaft of the screw rotor can be increased, and the motor can be operated at high speed rotation while obtaining an output equal to or higher than that of a single motor. Further, the screw compressor can be reduced in size.

In addition , since the first motor and the second motor are respectively provided on the tip side of the rotor shaft extending to both sides of the male rotor, the transmission power to the female rotor driven by the male rotor can be minimized. it can. Thereby, the loss of output can be minimized and the apparatus can be made difficult to break.

In addition , a waveform obtained by synthesizing a waveform of current or voltage serving as electric power input to each of the first motor and the second motor can be approximated to an ideal sine curve. As a result, the fluctuating torque that causes the deviation from the sine curve can be reduced, and the generation of noise and vibration can be reduced.

According to the present invention, if the power of a single motor necessary for driving the screw rotor is supplied by the first motor and the second motor , each motor can be reduced in size, and the mass of each motor. Can be reduced. Thereby, the critical speed (natural frequency) of each motor directly connected to the rotor shaft of the screw rotor can be increased, and the motor can be operated at high speed while obtaining an output equivalent to or higher than that of a single motor. Further, the screw compressor can be reduced in size.

Since one each of the first motor and the second motor is provided on the tip side of the rotor shaft extending to both sides of the male rotor, the transmission power to the female rotor driven by the male rotor can be minimized. Thereby, the loss of output can be minimized and the apparatus can be made difficult to break.

A waveform obtained by synthesizing waveforms of currents or voltages supplied to the first motor and the second motor can be brought close to an ideal sine curve. As a result, the fluctuating torque that causes the deviation from the sine curve can be reduced, and the generation of noise and vibration can be reduced.

The schematic diagram which shows the screw rotor of the screw compressor concerning this invention, and the rotor of a motor. 2A and 2B are views showing the arrangement of the rotor of the motor with respect to a pair of male and female screw rotors different from FIG. FIG. 3A is a diagram showing a composite pulse when the phases of the input pulses of the first motor and the second motor are the same, and FIG. 3B is a phase of the input pulses of the first motor and the second motor different The figure which shows the synthetic | combination pulse in a case. The schematic diagram which shows the screw rotor of the conventional screw compressor, and the rotor of a motor. The figure which shows the transverse vibration with respect to the rotor axial direction of the rotor of a motor.

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

  FIG. 1 is a schematic diagram of screw rotors 11a and 11b of a screw compressor (hereinafter simply referred to as a compressor) and rotors 12a and 19a of motors 12 and 19 according to the present invention.

  The compressor includes a male screw rotor 11a and a female screw rotor 11b that engage with each other. The rotor shafts extending to both ends of the male and female screw rotors 11a and 11b are supported by bearings 14, respectively. The rotor 12a of the first motor 12 and the rotor 19a of the second motor 19 are directly connected to the distal ends of the rotor shafts 15a and 15b extending to both sides of the male rotor 11a. The male rotor 11a is driven by the rotational force obtained by the interaction between the magnetic fields generated by the stators provided in the motor casings of the first motor 12 and the second motor 19 (not shown) and the rotors 12a and 19a, thereby driving the female rotor 11a. 11b is driven. The first motor 12 and the second motor 19 are controlled by the control device 17 via inverters 18a and 18b. The compressor sucks air from the outside into a compression space (not shown) of the screw rotors 11 a and 11 b through the suction portion 13. When the male and female screw rotors 11a and 11b are engaged, air is compressed in the compression space, and compressed air is discharged from the discharge portions 16 of the screw rotors 11a and 11b.

  In contrast to the conventional screw compressor, which uses a single motor to rotate the male and female screw rotors, the screw compressor according to the present embodiment divides the single motor into two motors 12 and 19, thereby providing a motor. The resonance frequency (dangerous speed) of 12 and 19 is increased, and operation at a higher speed is realized. Hereinafter, the reason why the resonance frequency is increased by dividing the single motor into the two motors 12 and 19 will be described in detail.

  When a single motor is divided into two motors 12, 19 having a power ratio F1: F2, the mass ratio of the rotors 12a, 19a of these motors 12, 19 can also be regarded as F1: F2. Therefore, when the mass of the rotor in the case of a single motor is M, the masses M1 and M2 of the rotors 12a and 19a of these motors 12 and 19 are expressed by the following equation (4).

  Here, as shown by the following equation (5), a power distribution coefficient to each motor 12, 19 is defined (α1 + α2 = 1).

  When the power distribution coefficients α1 and α2 are used, the masses M1 and M2 of the rotors 12a and 19a of the individual motors 12 and 19 are expressed by the following equation (6).

  Therefore, the natural frequencies ω1, ω2 of the two motors 12, 19 divided by the power ratio F1: F2 (power distribution ratio α1, α2) from the equations (3), (6) are expressed by the following equations, respectively.

  The relationship between the natural frequencies ω1 and ω2 of the two motors 12 and 19 and the natural frequency ω of a single motor is expressed by the following equation (8).

  For example, when a single motor is divided into two motors 12 and 19 with a power ratio of 1: 1 (power distribution coefficient α1, α2 = 1/2), the masses M1 and M2 are 1 / 2M, that is, a single motor. Half of the case. Therefore, if the natural frequency (critical speed) ω of a single motor is 7000 rpm, the natural frequencies ω1 and ω2 of the motors divided into two are about 9898 rpm from the equation (8). That is, the critical speed at which resonance occurs increases from 7000 rpm to about 9898 rpm.

  Next, when a single motor is divided into two motors with a power ratio of 3: 7 (power distribution coefficient α1 = 3/10, α2 = 7/10), the masses M1 and M2 are 3 / 10M and 7 / respectively. 10M. Therefore, when the natural frequency (critical speed) ω of a single motor is 7000 rpm, the natural frequencies ω1 and ω2 of the motor divided into two are about 12780 rpm and about 8367 rpm, respectively, from the equation (8). That is, the critical speed at which resonance occurs increases from 7000 rpm to about 8367 rpm.

  When a single motor is divided into two motors with a power ratio of 1: 9 (power distribution coefficient α1 = 1/10, α2 = 9/10), the masses M1 and M2 are 1 / 10M and 9 / 10M, respectively. It becomes. Therefore, if the natural frequency (critical speed) ω of a single motor is 7000 rpm, the natural frequencies ω1 and ω2 of the two motors are about 22136 rpm and about 7379 rpm, respectively, from the equation (8). That is, the critical speed at which resonance occurs increases from 7000 rpm to about 7379 rpm.

From the above, when the single motor necessary for driving the screw rotor is changed to the two motors 12 and 19 such that the sum of the outputs is the same, the two motors 12 and 12 having any power ratio are obtained. 19 also shows that the natural frequency of the whole compressor increases. In particular, it can be seen that when the single motor is made into two motors 12 and 19 each having a power ratio of 5: 5 (same power), the natural frequency of the compressor as a whole increases most. According to the present invention, if the power of a single motor necessary for driving the screw rotor is supplied by the first motor 12 and the second motor 12, 19, the motors 12 and 19 can be reduced in size. The mass of each motor 12, 19 can be reduced. As a result, the natural frequencies of the motors 12 and 19 directly connected to the rotor shafts 15a and 15b of the screw rotors 11a and 11b can be increased, and an output equivalent to or higher than that of a single motor can be obtained while rotating at high speed. I can drive. Further, the screw compressor can be reduced in size.

  Next, the arrangement of the first motor 12 and the second motor 19 will be described. The compressor has a male rotor 11a and a female rotor 11b. As the arrangement of two motors 12 and 19 for driving the screw rotors 11a and 11b, the first motor 12 is arranged on one side of the male rotor 11a shown in FIG. 2A, a combination in which the first motor 12 is disposed on the male rotor 11a and the second motor 19 is disposed on the female rotor 11b, as shown in FIG. 2A, and FIG. As shown in (b), there are a total of three combinations in which the first motor 12 is arranged on one side of the female rotor 11b and the second motor 19 is arranged on the other side.

  On the other hand, the work ratio of the male rotor 11a and the female rotor 11b is normally 9: 1. For example, when the male rotor 11a is driven and the female rotor 11b is driven, the female rotor 11b is driven and the male rotor 11a is driven. In this case, the transmission power between the male rotor 11a and the female rotor 11b is different. For example, when both the first motor 12 and the second motor 19 are attached to the male rotor 11a, the transmission power from the male rotor 11a to the female rotor 11b is about 10%. When both the first motor 12 and the second motor 19 are attached to the female rotor 11b, the transmission power from the female rotor 11b to the male rotor 11a is about 90%. When either the first motor 12 or the second motor 19 is attached to the male rotor 11a, and either the first motor 12 or the second motor 19 is attached to the female rotor 11b, the space between the male rotor 11a and the female rotor 11b Is about 40%.

  If the transmission power between the screw rotors 11a and 11b is large, it will cause damage to the screw rotors 11a and 11b, noise and vibration, so the transmission power should be as small as possible. Therefore, the arrangement in which both the first motor 12 and the second motor 19 are attached to the male rotor 11a is the best. Since the two motors 12 and 19 are provided one on each of the front ends of the rotor shafts 15a and 15b extending to both sides of the male rotor 11a, the transmission power to the female rotor 11b driven by the male rotor 11a is the lowest. Can be suppressed. Thereby, the loss of output can be minimized and the apparatus can be made difficult to break.

  As shown in the input pulses of the first motor 12 and the second motor 19 in FIGS. 3A and 3B, the control device 17 applies a rectangular voltage or current to the motor via the inverters 18a and 18b. 12 and 19. Ideally, the voltage or current waveform is input so as to draw a sine curve. Since the torque generated in the motors 12 and 19 approximates the waveform of the applied voltage or applied current, the deviation from the sine curve that causes the fluctuation torque is avoided as much as possible. In this way, the generation of fluctuating torque is suppressed as much as possible, and noise and vibration are reduced.

  As shown in FIG. 3A, a voltage or current having the same waveform (maximum pulse value A, period T) is applied to each of the first motor 12 and the second motor 19 directly connected to both sides of the male rotor 11a. Since the first motor 12 and the second motor 19 are coaxial, the torque generated by the two motors 12 and 19 is the sum of the torques. The pulse obtained by synthesizing the pulses input to the first motor 12 and the second motor 19 is a waveform in which only the pulse maximum value (absolute value) is doubled with respect to the waveforms of the first motor 12 and the second motor 19, respectively. It is. The deviation from the synthesized pulse is indicated by diagonal lines with respect to the sine curve of amplitude 2A and period T.

  In order to bring the synthesized pulse closer to the sine curve, the phase of the voltage or current applied to either the first motor 12 or the second motor 19 is shifted. As shown in FIG. 3B, when the phase of the second motor 19 is shifted (delayed) by T / 8 from the phase of the first motor 12, it is input to the first motor 12 and the second motor 19. The combined pulse is delayed by T / 16 with respect to the phase of the waveform of the first motor 12 and preceded by T / 16 with respect to the phase of the waveform of the second motor 19. The synthesized pulse shown in FIG. 3B is the same as the synthesized pulse shown in FIG. 3A in that the maximum value is 2A (absolute value), but the value is A (absolute value). It differs from the synthesized pulse shown in FIG. 3A in that the range is also included. The deviation of the synthesized pulse waveform from the sine curve of amplitude 2A and period T is indicated by diagonal lines. Rather than applying the same phase power (voltage or current) to the first motor 12 and the second motor 19, the phase is shifted (delayed) by T / 8 from the phase of the first motor 12. When the power (voltage or current) is applied to the second motor 19, the shift (shaded area in FIGS. 3A and 3B) can be reduced. In this way, the synthesized pulse waveform can be made closer to the shape of the sine curve, the harmonics can be reduced, and noise and vibration can be reduced.

11a Male screw rotor 11b Female screw rotor 12 First motor 12a Rotor 13 Suction part 14 Bearing 15a, 15b Rotor shaft 16 Discharge part 17 Controller 18a, 18b Inverter 19 Second motor 19a Rotor

Claims (1)

In a screw compressor provided with a screw rotor driven by a motor and meshing male and female,
A first motor and a second motor each having a sum of outputs equal to or greater than a single motor required to drive the screw rotor;
Each of the rotors of the first motor and the second motor is directly connected to the tip end side of the rotor shaft extending to both sides of the male rotor of the screw rotor, and is supported in a cantilever state .
A screw compressor characterized in that electric power having different phases is supplied to each of the first motor and the second motor .

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