JP2009281213A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized centrifugal compressor with increased compression efficiency. <P>SOLUTION: The centrifugal compressor includes a radial foil bearing, an axial magnetic bearing and a magnetic bearing control device, and is provided with a rotary shaft support device supporting the rotary shaft 13. The magnetic bearing control device is provided with a low speed zone control means shifting an axial direction floating position of the rotary shaft 13 in a direction making a gap G between an impeller 13a and a scroll housing part 11b greater than reference value (position indicated by two-dot chain line) by shift quantity S when rotation speed of the rotary shaft 13 is not less than a prescribed value, and a normal speed zone control means returning the gap G in a direction to be the reference value (position indicated by continuous line) when rotation speed of the rotary shaft 13 exceeds the prescribed value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor, and for example, relates to a centrifugal compressor that is installed on the oxygen supply side of a fuel cell device and is suitable for use in supplying compressed air to a fuel cell.

In Patent Document 1, a centrifugal compressor is used to supply compressed air to a fuel cell of a fuel cell vehicle, and a radial foil bearing and an axial magnetic bearing, which are dynamic pressure bearings, are used as the rotating shaft support device. Proposed to use in combination.
JP 2007-192116 A

  According to the above centrifugal compressor, the fuel cell device used in the fuel cell vehicle has an advantage that the compressor can be downsized. However, in order to further improve the performance, it is necessary to increase the compression efficiency. It has become.

  In view of the above circumstances, an object of the present invention is to provide a centrifugal compressor that is reduced in size and improved in compression efficiency.

  A centrifugal compressor according to the present invention includes a housing having a bearing housing portion supporting a rotating shaft and a scroll housing portion in which the impeller is disposed, a rotating shaft having an impeller at one end and rotating inside the bearing housing portion, In a centrifugal compressor having a radial dynamic pressure bearing, a control-type axial magnetic bearing, and a magnetic bearing control device, and including a rotary shaft support device that supports the rotary shaft, the magnetic bearing control device has a rotational speed of the rotary shaft. Low-speed range control means for shifting the axial position of the rotary shaft in the direction in which the gap between the impeller and the scroll housing portion is larger than the reference value, and the rotational speed of the rotary shaft is a predetermined value. If the gap exceeds the upper limit, the position where the gap between the impeller and the scroll housing part becomes the reference value And it is characterized in that it comprises a normal speed range control means for returning to.

  A control device for a normal axial magnetic bearing is controlled so that the rotating shaft is positioned at a constant axial flying position regardless of the rotational speed (number of rotations). On the other hand, the control device for the axial magnetic bearing in the centrifugal compressor according to the present invention can switch between the low speed range control means and the normal speed range control means, and the axial direction of the rotary shaft is changed between the low speed range and the normal speed range. Control is performed to change the target flying position. The predetermined value of the rotational speed is a rotational speed (number of rotations) at which the support rigidity of the hydrodynamic bearing is sufficient. The shift amount is set in a range that can be controlled by the magnetic bearing device. For example, the shift amount in the axial direction is about 0.1 to 0.2 mm.

  The radial dynamic pressure bearing may be, for example, a radial foil bearing. The radial foil bearing may be, for example, a flexible bearing foil having a bearing surface that faces the rotating shaft in the radial direction, and an elastic body that supports the bearing foil. And an outer ring that holds the bearing foil and the elastic body between the rotary shaft and the bearing foil.

  The axial magnetic bearing controls the force acting between a pair of axial electromagnets consisting of an electromagnet yoke and an electromagnet coil (control type). Preferably, the outer ring of the radial foil bearing also serves as the electromagnet yoke. By inserting the electromagnet coil into the recess provided in the outer ring of the foil bearing, each axial electromagnet of the axial magnetic bearing is integrated with the radial foil bearing. And one axial electromagnet is made to oppose the flange part provided in the end of the rotating shaft, and the other axial electromagnet is made to oppose the flange part provided in the other end of the rotating shaft. The electromagnet yoke may be a member different from the outer ring of the radial foil bearing.

  According to the above rotary shaft support device, the radial foil bearing supports the radial direction, and when the rotary shaft rotates, ambient air is drawn between the bearing foil and the rotary shaft to generate pressure (dynamic pressure). The rotating shaft is held in a non-contact manner. Further, the axial magnetic bearing is responsible for supporting in the axial direction, and the current flowing through the electromagnetic coil of the axial electromagnet is controlled to hold the rotating shaft in a non-contact manner.

  Since the centrifugal compressor rotates the rotating shaft at a high speed with a motor, air is introduced into the impeller provided at one end of the rotating shaft from the axial direction, and compressed air is discharged in the radial direction. A large force in the axial direction acts on. Therefore, when the axial direction support is performed by the axial foil bearing, the rigidity of the bearing may be insufficient. On the other hand, by supporting the axial direction with the axial magnetic bearing, the load capacity is increased, and the control current is changed according to the fluctuation of the axial force, so that the axial direction is also applied to the rotational load fluctuation. Non-contact support is ensured.

  When controlling the floating position of the rotating shaft in the axial direction, the reference value of the gap between the impeller and the scroll housing portion is set as small as possible in order to increase the compression efficiency. In this case, when the rotational speed of the rotating shaft is equal to or less than a predetermined value, there is a possibility that the impeller and the scroll housing portion come into contact with each other due to insufficient support rigidity of each radial dynamic pressure bearing. In order to solve this problem, the axial magnetic bearing control device performs control by shifting the gap in a direction larger than the reference value by the low speed region control means when the rotational speed of the rotating shaft is equal to or lower than a predetermined value. When the rotational speed of the rotating shaft exceeds a predetermined value, the normal speed range control means returns the gap to the reference value and performs control. As a result, the impeller and the scroll housing portion are prevented from coming into contact with each other, and the floating position of the rotating shaft is controlled in the normal speed range with the gap optimized in order to increase the compression efficiency.

  Also, by integrating the axial magnetic bearing with the radial foil bearing, the axial length can be shortened, which increases the natural frequency of the rotating shaft and enables high-speed rotation, as well as compactness. And weight reduction.

  According to the centrifugal compressor of the present invention, the rotating shaft is supported by the radial dynamic pressure bearing from the radial direction and is also supported by the control type axial magnetic bearing from the axial direction. The reduction is suppressed, and the function for circulating the oil for lubrication becomes unnecessary, so that the compressor can be downsized. Furthermore, the control device for the axial magnetic bearing changes the axial target lift position of the rotating shaft between the low speed range and the normal speed range to prevent contact between the impeller and the scroll housing. In addition, in the normal speed range, the gap between the impeller and the scroll housing part can be optimized, and the compression efficiency can be increased.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the right in FIG. 1 is the front and the left is the back.

  FIG. 1 shows a schematic configuration of a centrifugal compressor according to the present invention. A compressor (1) is arranged in a substantially cylindrical hermetic housing (11) arranged on a horizontal axis in the front-rear direction. A horizontal shaft-like rotary shaft (13), an impeller (13a) provided at the end of the rotary shaft (13), and a rotary shaft support device (14) for supporting the rotary shaft (13) are provided.

  The housing (11) is composed of a bearing housing part (11a) which is a front side and serves as a bearing support part, and a scroll housing part (11b) which is a rear side and serves as a scroll housing part.

  The rotating shaft (13) has a stepped shaft shape and is arranged in a space in the bearing housing portion (11a). The impeller (13a) is fixed to the rear end of the rotary shaft (13) and is disposed in the scroll housing part (11b).

  A built-in motor (20) that rotates the rotating shaft (13) at high speed on the inner periphery of the bearing housing (11a), and a pair of front and rear radial foil bearings (radial dynamic pressure bearings) that support the rotating shaft (13) from the radial direction ) (21) (22) and a set of control type axial magnetic bearings (23) integrated with the front and rear radial foil bearings (21) and (22) to support the rotating shaft (13) from the axial direction (front and rear direction) Is provided.

  The motor (20) includes a stator (20a) provided on the bearing housing portion (11a) side and a rotor (20b) provided on the rotating shaft (13) side.

  The rotating shaft support device (14) includes front and rear radial foil bearings (21) and (22) and an axial magnetic bearing (23).

  A gas inflow passage (11c) is provided at the rear end of the space in the scroll housing portion (11b). As the rotating shaft (13) rotates, the impeller (13a) rotates.By the rotation of the impeller (13a), air flows from the gas inflow path (11c) to the space (11d) in the scroll housing part (11b). It flows in, is compressed in the space (11d), and is discharged through a gas outflow path (not shown) that leads to the space (11d).

  The stepped rotary shaft (13) includes a large-diameter portion (31) in which the rotor (20b) of the motor (20) is provided in the intermediate portion in the axial direction, and a small-diameter continuous to the rear side of the large-diameter portion (31). Part (32), a front flange part (34) provided at the front end part of the large diameter part (31), and a rear flange part (35) provided at the rear end part of the large diameter part (31). Become. The impeller (13a) is attached to the rear end of the small diameter portion (32) (boundary portion with the small diameter portion (32)), and each radial foil bearing (21) (22) is connected to each flange portion (34). It is provided in the vicinity of both end portions of the large-diameter portion (31) so that a slight gap is formed between (35).

  As shown in FIG. 2, each radial foil bearing (21) (22) has a flexible top foil that is arranged on the radially outer side of the rotary shaft large diameter portion (31) with a bearing gap (44) therebetween. (Bearing foil) (41), a bump foil (elastic body) (42) disposed on the radially outer side of the top foil (41), and an outer ring disposed on the radially outer side of the bump foil (42) ( 43).

  The top foil (41) is made of a strip-shaped stainless steel plate, and the strip-shaped stainless steel plate is formed into a cylindrical shape without overlapping in the circumferential direction by roll processing so that both ends in the longitudinal direction are adjacent to each other. The both ends of the steel plate in the axial direction are cut and raised in the radial direction, and the tip is bent. The cylindrical portion (41a) other than the cut and raised portion is a main portion of the top foil, and the cut and raised portion (41b) is an engaging portion of the top foil (41).

  The bump foil (42) includes a cylindrical portion (42a) formed of a corrugated plate made of stainless steel into a cylindrical shape, and an engaging portion that is connected to one end of the cylindrical portion (42a) and located on the radially outer side of the cylindrical portion (42a). (42b).

  On the inner peripheral surface of the outer ring (43), an engaging groove (43c) extending in a substantially radial direction is formed. Then, the cylindrical portion (42a) of the bump foil (42) is disposed along the inner peripheral surface of the outer ring (43), and the engaging portion (42b) is formed in the engaging groove (43c) of the outer ring (43). By being engaged, the bump foil (42) is attached to the outer ring (43), and the cylindrical portion (41a) of the top foil (41) is provided between the bump foil (42) and the rotary shaft large diameter portion (31). ) And the engaging portion (41b) is engaged with the engaging groove (43c) of the outer ring (43), so that the top foil (41) is attached to the outer ring (43).

  Radial foil bearings (21) and (22) have a top foil (41) that is formed into a cylindrical shape that does not overlap in the circumferential direction by roll processing so that both ends in the longitudinal direction are adjacent to each other in the longitudinal direction. Since the radius is constant and the roundness is high, the support performance of the rotary shaft (13) is high and the floating characteristics of the rotary shaft (13) are also good.

  The outer ring (43) of each radial foil bearing (21) (22) is made of a magnetic material, and is annularly formed on the outer end face (front end face) in the axial direction of the outer ring (43) of the radial foil bearing (21) on the front side. A recess (43a) is provided so as to face the front flange portion (34), and an annular recess is formed on the axially outer end surface (rear end surface) of the outer ring (43) of the rear radial foil bearing (22). The portion (43b) is provided so as to face the rear flange portion (35).

  An electromagnetic coil (24a) is fitted in the annular recess (43a) of the outer ring (43) of the front radial foil bearing (21), and the outer ring (43) of the rear radial foil bearing (22) An electromagnetic coil (25a) is fitted in the annular recess (43b). As a result, the outer ring (43) made of a magnetic material also serves as the yoke (24b) (25b) of the axial electromagnet (24) (25), and the outer ring (43) of the front radial foil bearing (21) = electromagnet yoke (24b) and the electromagnet coil (24a) form the front axial electromagnet (24) facing the front flange portion (34), and the outer ring (43) of the rear radial foil bearing (22) = electromagnet yoke A rear axial electromagnet (25) facing the rear flange portion (35) is formed by (25b) and the electromagnet coil (25a).

  The axial magnetic bearing (23) includes a front-side axial electromagnet (24) and a rear-side axial electromagnet (25) formed as described above.

  The rear surface of the front wall of the bearing housing portion (11a) of the housing (11) is faced to the center of the front flange portion (34) of the rotating shaft (13) and detects the position of the rotating shaft (13) in the axial direction. An axial position sensor (26) is provided. The rear surface of the front wall of the bearing housing part (11a) of the housing (11) is further faced by a recess (28) provided on the outer periphery of the front flange part (34) to reduce the rotational speed of the rotary shaft (13). A rotation sensor (27) for detection is provided.

  The axial magnetic bearing (23) is controlled by the controller (61) shown in FIG. 3 based on the position of the rotary shaft (13) detected by the position sensor (26) and the rotational speed detected by the rotation sensor (27). The current flowing through the electromagnetic coils (24a) and (25a) is controlled. The current flowing through the electromagnet coils (24a) and (25a) is controlled so that an attractive force that is balanced with the force acting on the impeller (13a) is generated in the axial electromagnets (24) and (25). The shaft (13) is supported in a non-contact manner at a predetermined position in the axial direction.

  As shown in FIG. 3, the controller (61) can be a motor drive circuit (62), a magnetic bearing drive circuit (63), a position sensor drive circuit (64), a rotation sensor drive circuit (65), and a software program. A DSP (66), an AD converter (67), and a DA converter (68) are provided as digital processing means.

  The DSP is an abbreviation for a digital signal processor. The digital signal processor refers to dedicated hardware that can input a digital signal and output the digital signal, can be software-programmed, and can perform high-speed real-time processing. The DSP (66) has a low speed range control means (69) in addition to various control means used in the conventional magnetic bearing control device. The low speed range control means (69) is a normal speed control. The means (normal speed range control means) (70) can be switched. When the rotational speed (rotational speed) of the rotary shaft (13) exceeds a predetermined value, the normal speed range control means (70) determines the axial position of the rotary shaft (13) in the axial direction and the scroll housing. The control is performed so that the gap (G) (see FIG. 4) with the part (11b) becomes the reference value, and the low speed region control means (69) is used when the rotational speed of the rotating shaft (13) is a predetermined value or less. In addition, the gap (G) is controlled to be shifted in the direction in which the gap (G) becomes larger than the reference value.

  The position sensor drive circuit (64) calculates the position of the rotary shaft (13) in the axial direction based on the distance signal that is the output of the position sensor (26), and converts the position signal that is the result of the calculation into an AD converter ( 67) to the DSP (66).

  If the size of the gap (gap) with the front flange (34) corresponding to the target changes with an alternating current flowing through the coil of the axial position sensor (26), an inductance change occurs, and the axial position sensor (26) Outputs a distance signal proportional to the size of the gap with the front flange portion (34). The position sensor drive circuit (64) sets the displacement when the rotating shaft (13) is at a target flying position corresponding to a predetermined number of rotations in the axial direction to 0, and the axial direction of the rotating shaft (13) relative to this target flying position is zero. A signal proportional to the displacement is output as a position signal.

  The output of the rotation sensor (27) also changes in proportion to the size of the gap with the front flange portion (34), and the portion other than the recess (28) of the front flange portion (34) is the rotation sensor (27). The gap between the rotation sensor (27) and the front flange (34) is different between when the recess (28) faces the rotation sensor (27) and when the recess (28) faces the rotation sensor (27). The output of the sensor (27) changes every time the recess (28) comes to the opposite position. Therefore, the rotation sensor (27) generates the same number of pulses as the number of recesses (28) during one rotation of the rotation shaft (13), and the output of the rotation sensor (27) rotates as a speed detection signal. The signal is output from the sensor drive circuit (65) to the DSP (66).

  The DSP (66) is an axial magnetic bearing (23) based on a digital position signal representing the rotational speed input from the rotation sensor drive circuit (65) and the position of the rotary shaft (13) input from the AD converter (67). The excitation current signal for the electromagnet (24) is output to the magnetic bearing drive circuit (63) via the DA converter (68). Then, the drive circuit (63) supplies an excitation current based on the excitation current signal from the DSP (66) to the electromagnet (24) of the corresponding axial magnetic bearing (23), whereby the rotating shaft (13) is targeted. Non-contact support at the floating position.

  The DSP (66) also calculates the rotation speed of the rotation shaft (13) from the rotation speed detection signal of the rotation sensor drive circuit (65), and controls the rotation speed of the motor (20) based on this. The command signal is output to the motor drive circuit (62). The motor drive circuit (62) includes an inverter and controls the rotation speed of the motor (20) based on the rotation speed command signal. As a result, the rotating shaft (13) is rotated at high speed by the motor (20) while being supported in a non-contact manner at the target floating position by the radial foil bearings (21), (22) and the axial magnetic bearing (23). .

  According to the above centrifugal compressor (1), the radial shaft bearing (dynamic bearing) (21) (22) is responsible for supporting the rotating shaft (13) in the radial direction, and the rotating shaft (13) is During rotation, the foil bearings (21) and (22) are supported in the radial direction in a non-contact manner by the dynamic pressure generated by the foil bearings (21) and (22). The axial support of the rotary shaft (13) is handled by the axial magnetic bearing (23), and if the axial force acting on the impeller (13a) fluctuates, the corresponding attractive force will be applied. Generated in the axial electromagnet (24). As a result, the rotary shaft (13) is stably supported in a non-contact manner without being affected by fluctuations in the rotational load, and its smooth rotation is guaranteed and durability (life) is excellent.

  When controlling the floating position of the rotary shaft (13) in the axial direction, the reference value of the gap (G) between the impeller (13a) and the scroll housing part (11b) is set as small as possible to increase the compression efficiency. The When the rotational speed of the rotary shaft (13) is less than a predetermined value (about 10,000 to 20,000 rpm), the radial foil bearings (21) and (22) have insufficient support rigidity, and the rotation of the rotary shaft (13) Since vibration is likely to occur, if the gap (G) between the impeller (13a) and the scroll housing part (11b) is small, there may be a problem that they come into contact with each other. Therefore, when the rotational speed of the rotating shaft (13) is below a predetermined value (when the rotational speed decreases during start-up and in the middle), this gap (G) is set to be lower than the reference value by the low speed region control means (69). Shifted in the direction of increasing.

  That is, when the rotational speed of the rotating shaft (13) is less than or equal to a predetermined value, the positional relationship between the impeller (13a) and the scroll housing portion (11b) is such that the gap (G) is determined by the low speed region control means (69). The floating position of the rotary shaft (13) is controlled so that it is shifted by the shift amount S in the direction larger than the reference value (forward = right side in FIG. 1) and is in the state indicated by the two-dot chain line in FIG. This prevents contact between the impeller (13a) and the scroll housing part (11b). When the rotational speed of the rotating shaft (13) exceeds a predetermined value (the rotational speed at which the radial foil bearings (21) and (22) have sufficient support rigidity), the impeller (13a) and the scroll housing portion (11b ) Is controlled by the normal speed range control means (70) so that the gap (G) is returned to the reference value, thereby increasing the compression efficiency indicated by the solid line in FIG. In a state where is optimized, the floating position of the rotating shaft (13) is controlled.

FIG. 1 is a longitudinal sectional view schematically showing one embodiment of a centrifugal compressor according to the present invention. FIG. 2 is a transverse sectional view showing a radial foil bearing used in the centrifugal compressor according to the present invention. FIG. 3 is a block diagram showing an axial magnetic bearing controller used in the centrifugal compressor according to the present invention. FIG. 4 is an enlarged vertical sectional view of a main part for explaining the control performed by the control device for the axial magnetic bearing.

Explanation of symbols

(1) Centrifugal compressor
(11) Housing
(11a) Bearing housing
(11b) Scroll housing
(13) Rotating shaft
(13a) Impeller
(14) Rotating shaft support device
(21) (22) Radial foil bearing
(23) Control type axial magnetic bearing
(61) Axial magnetic bearing controller
(69) Low speed control means
(70) Normal speed control means
(G) Gap

Claims (1)

A housing having a bearing housing portion supporting a rotating shaft and a scroll housing portion in which the impeller is disposed, a rotating shaft having an impeller at one end and rotating inside the bearing housing portion, a radial dynamic pressure bearing, and a control type axial magnetic In a centrifugal compressor having a bearing and a magnetic bearing control device, and having a rotating shaft support device for supporting a rotating shaft,
The magnetic bearing control device is a low-speed control that shifts the floating position in the axial direction of the rotating shaft in a direction in which the gap between the impeller and the scroll housing portion is larger than the reference value when the rotating speed of the rotating shaft is a predetermined value or less. And normal speed range control means for returning the axial position of the rotary shaft in the axial direction to a direction in which the gap between the impeller and the scroll housing portion becomes a reference value when the rotational speed of the rotary shaft exceeds a predetermined value. A centrifugal compressor characterized by that.

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