JP2007270648A - Compressor for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compressor for fuel cells capable of eliminating degradation of supply capacity of compressed air when an input voltage fluctuates without increase in size and cost. <P>SOLUTION: A driving device 15 to drive a motor 20 comprises a motor driver 16 to control the motor 20 by the PWM control, a battery 17 to supply power to the motor driver 16, and a voltage detecting means 18 to detect the voltage which is input into the motor driver 16. The motor driver 16 has a pulse-width modulation means which extends the pulse-width of the PWM when the input voltage descends. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a compressor for a fuel cell that is installed on an oxygen supply side of a fuel cell device that generates energy from hydrogen and oxygen and supplies compressed air to the fuel cell, and more particularly, a fuel suitable for mounting in a fuel cell vehicle. The present invention relates to a battery compressor.

  A prototype of a fuel cell vehicle that travels with a fuel cell has already been manufactured. Patent Document 1 discloses a scroll that is suitable for a compressor for supplying compressed air to a fuel cell of a fuel cell vehicle. One with a mold compressor has been proposed.

In addition to the scroll type, the compressor is referred to as a turbine compressor having an impeller at one end and a rotating shaft that rotates inside the casing, and compresses air in the space in the gas circulation portion of the casing by the rotation of the impeller. A centrifugal compressor is also known (Patent Document 2).
JP 2002-70762 A Japanese Patent Application Laid-Open No. 7-91760

  In a fuel cell device used in a fuel cell vehicle, downsizing, cost reduction, and weight reduction are important issues, and further downsizing of the compressor is required. Therefore, it is desired to use a non-displacement centrifugal compressor that is free from compression fluctuations and can be reduced in size, instead of the scroll compressor of Patent Document 1, which is a type of positive displacement compressor. .

  In a centrifugal compressor, it is common to perform PWM control of a motor by a motor driver. In this case, if the input voltage (usually battery voltage) of the motor driver fluctuates, the motor driver that performs PWM control Since the output fluctuates accordingly, there arises a problem that the compressed air supply capability of the compressor cannot be kept constant. In order to solve this problem, for example, a converter that supplies a constant voltage to the power supply input may be provided. However, this configuration has a problem of increasing the size and cost.

  An object of the present invention is to provide a compressor for a fuel cell that eliminates a decrease in compressed air supply capability when an input voltage fluctuates without increasing the size and cost.

  A compressor for a fuel cell according to the present invention includes a rotating shaft that has an impeller at one end and rotates inside the casing, a bearing device that supports the rotating shaft, a motor that rotates the rotating shaft, and a drive device that drives the motor. A compressor for a fuel cell that supplies air to a fuel cell by compressing air in a space in a gas circulation portion of the casing by rotation of an impeller, and a driving device includes a motor driver that controls the motor by PWM control, and a motor driver A power supply for supplying power; and a voltage detection means for detecting a voltage input to the motor driver. The motor driver includes a pulse width changing means for increasing the PWM pulse width when the input voltage decreases. It is characterized by having.

  The bearing device includes a pair of radial foil bearings that are concentrically provided on the rotating shaft and support the rotating shaft from the radial direction, and a control type axial that is opposed to the rotating shaft from the axial direction and supports the rotating shaft from the axial direction. It is preferable to provide a magnetic bearing.

  The radial foil bearing is, for example, a flexible bearing foil having a bearing surface that is radially opposed to the rotating shaft, an elastic body that supports the bearing foil, and the bearing foil and the elastic body are held between the rotating shaft. And a bearing housing.

  As the control type axial magnetic bearing, various types used in the 5-axis control type magnetic bearing device can be used. For example, the control type axial magnetic bearing may be composed of a permanent magnet and an axial electromagnet. It may be composed of a pair of axial electromagnets.

  According to the bearing device described above, the radial foil bearing is supported by the radial foil bearing, and the surrounding air is drawn between the bearing foil and the rotating shaft during the rotation of the rotating shaft to generate pressure (dynamic pressure). The rotating shaft is held by contact. Further, the axial magnetic bearing is responsible for supporting in the axial direction, and the current flowing through 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.

  The control type axial magnetic bearing is composed of, for example, an impeller-side permanent magnet and an anti-impeller-side axial electromagnet that are opposed to each other via a flange portion of a rotating shaft. Thereby, the axial electromagnet is arranged so that its attractive force is opposite to the direction of the axial force generated by the rotation. In this way, the axial length can be shortened compared to an axial magnetic bearing that normally has a pair of axial electromagnets, thereby increasing the natural frequency of the rotating shaft and rotating at high speed. As well as being smaller and lighter. Then, by passing a control current through the electromagnet coil of the axial electromagnet, the rotating shaft is attracted to the anti-impeller side.

  When the axial magnetic bearing is composed of a permanent magnet and an axial electromagnet, the axial electromagnet paired with the permanent magnet is composed of an electromagnet yoke and an electromagnet coil, and of course it may be separated from the radial foil bearing. It may be integrated into one of the radial foil bearings.

  According to the fuel cell compressor of the present invention, the PWM pulse width is lengthened when the input voltage is lowered by the pulse width changing means of the motor driver, so that the average current is prevented from being lowered. The flow rate and discharge pressure of the compressed air can be kept constant. Further, since the pulse width can be changed by providing a simple control circuit, the compressor can be made cheaper and more compact than when a converter that supplies a constant voltage to the power input is provided. .

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the compressor (1) has an impeller (12) at one end and a rotating shaft (13) that rotates inside the casing (11), and a bearing device that supports the rotating shaft (13). 14), a motor (20) that rotates the rotating shaft (13), and a drive device (15) that drives the motor (20), and supplies compressed air to the fuel cell stack (19).

  The drive device (15) includes a motor driver (16) for controlling the motor by PWM control, a battery (17) as a power source for supplying power to the motor driver (16), and a voltage input to the motor driver (16). Voltage detecting means (18) for detecting.

  The motor driver (16) is designed to control the output of the PWM wave according to the fluctuation of the input voltage, and when the voltage input from the battery (17) decreases, the pulse width is changed to increase the PWM pulse width. Means (16a) are provided.

  In FIG. 2, (a) shows the conventional PWM control, and when the input voltage is lowered due to the control with a constant pulse width, it is output to the motor driver in proportion thereto. The average current is also decreasing. FIG. 2 (b) shows the PWM control by the motor driver (16) having the pulse width changing means (16a). When the input voltage is lowered, the pulse width becomes black in the figure. By increasing the amount by filling, the output current for each pulse obtained by the pulse width × current is kept constant and output to the motor (20). As a result, the flow rate and discharge pressure of the compressed air supplied by the compressor (1) are kept constant.

  In the above, the type of the compressor (1) and the configuration of the bearing device (14) are arbitrary, but an example of a preferred embodiment is shown below. In the following description, the right in FIG. 3 is the front and the left is the rear.

  FIG. 3 shows a schematic configuration of a preferred embodiment of a fuel cell compressor. The fuel cell compressor (1) is a non-displacement centrifugal compressor and is disposed on a horizontal axis in the front-rear direction. A substantially cylindrical sealed casing (11), an impeller (12) at the rear end, a horizontal shaft-shaped rotating shaft (13) that rotates inside the casing (11), and a rotating shaft (13) And a bearing device (14).

  The casing (11) is composed of a front rotary shaft support portion (11a) that supports the rotary shaft (13) and a rear gas flow portion (11b) on which the impeller (12) is disposed.

  The rotating shaft (13) has a stepped shaft shape and is disposed in a space in the rotating shaft support (11a).

  A built-in motor (20) that rotates the rotating shaft (13) at a high speed on the inner periphery of the rotating shaft support (11a), and a pair of front and rear radial foil bearings (21) that support the rotating shaft (13) from the radial direction. 22) and a set of control type axial magnetic bearings (23) for supporting the rotating shaft (13) from the axial direction (front-rear direction).

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

  The bearing 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 gas circulation part (11b). When the rotating shaft (13) rotates, the impeller (12) rotates.By the rotation of the impeller (12), air is transferred from the gas inflow path (11c) to the space (11d) in the gas circulation 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). A gap of a predetermined size is formed between the inner surface of the gas flow part (11b) and the impeller (12) to ensure compression performance.

  The stepped rotary shaft (13) is connected to the large-diameter portion (31) where the rotor (20b) of the motor (20) is provided at the intermediate portion in the axial direction and to the outside in the front-back direction of the large-diameter portion (31) It consists of front and rear small diameter portions (32), (33) and a flange portion (34) provided in the axially intermediate portion of the front small diameter portion (32). The impeller (12) is attached to the rear end portion of the rear small diameter portion (33), and the radial foil bearings (21) and (22) are provided at both end portions of the large diameter portion (31).

  As shown in FIG. 4, each radial foil bearing (21) (22) is a flexible top foil having a bearing gap (44) arranged radially outside the rotary shaft large diameter portion (31). (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) ( Bearing housing) (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. It is formed by cutting both ends in the axial direction of one end of the steel plate in the radial direction and bending the tip. 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 engagement groove (43a) extending in a substantially radial direction is formed. Then, the cylindrical portion (42a) of the bump foil (42) is arranged along the inner peripheral surface of the outer ring (43), and the engaging portion (42b) is formed in the engaging groove (43a) 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 (43a) of the outer ring (43), so that the top foil (41) is attached to the outer ring (43).

  The axial magnetic bearing (23) includes an axial electromagnet (24) and a permanent magnet provided on the rotating shaft support (11a) of the casing (11) so as to face each other via the flange (34) of the rotating shaft (13). (25). The axial electromagnet (24) includes a yoke (24a) and a coil (24b). The direction of the force acting on the impeller (12) by the rotation is backward (leftward in FIG. 3). Correspondingly, the permanent magnet (25) is arranged on the rear side of the flange portion (34) and is axial. The electromagnet (24) is disposed on the front side of the flange portion (34) so that its attractive force is opposite to the direction of the axial force generated by the rotation.

  On the rear surface of the front wall of the rotating shaft support portion (11a) of the casing (11), a target portion made of soft magnetic stainless steel (35) concentrically provided at the front end of the small diameter portion (32) of the rotating shaft (13). An axial position sensor (26) is provided to detect the position of the rotary shaft (13) in the axial direction facing the center of the rear end surface. On the rear surface of the front wall of the rotating shaft support portion (11a) of the casing (11), further facing the recess (37) provided on the outer periphery of the rear end surface of the target portion (35), the rotational speed of the rotating shaft (13) A rotation sensor (36) is provided for detecting.

  Based on the position of the rotating shaft (13) detected by the position sensor (26) and the rotational speed detected by the rotation sensor (36), the current flowing in the electromagnetic coil (24b) of the axial magnetic bearing (23) Is controlled. The current flowing in the coil (24b) is controlled so that an attractive force that is balanced with the force acting on the impeller (12) and the attractive force of the permanent magnet (25) by the rotation is generated in the axial electromagnet (24). The rotation shaft (13) is supported in a non-contact manner at a predetermined position in the axial direction.

  According to the fuel cell compressor (1) of this embodiment, the radial support of the rotary shaft (13) is handled by the radial foil bearings (21) and (22), and the rotary shaft (13) is rotated during rotation. These are supported in the radial direction in a non-contact manner by the dynamic pressure generated in each of the foil bearings (21) and (22). Also, the axial support of the rotary shaft (13) is handled by the axial magnetic bearing (23) .If the axial force acting on the impeller (12) 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.

FIG. 1 is a view schematically showing one embodiment of a compressor for a fuel cell according to the present invention. FIG. 2 is a diagram showing the characteristics of the control portion according to the present invention in comparison with the conventional one. FIG. 3 is a longitudinal sectional view schematically showing a detailed embodiment of a fuel cell compressor. FIG. 4 is a cross-sectional view showing a radial foil bearing used in the fuel cell compressor.

Explanation of symbols

(1) Fuel cell compressor
(11) Casing
(12) Impeller
(13) Rotating shaft
(14) Bearing device
(15) Drive unit
(16) Motor driver
(17) Battery (power supply)
(18) Voltage detection means
(20) Motor

Claims (1)

A rotating shaft that has an impeller at one end and rotates inside the casing, a bearing device that supports the rotating shaft, a motor that rotates the rotating shaft, and a drive device that drives the motor, and casing the air by rotating the impeller In the compressor for a fuel cell, which is compressed in the space in the gas flow part and supplied to the fuel cell,
The drive device includes a motor driver that controls the motor by PWM control, a power source that supplies power to the motor driver, and voltage detection means that detects a voltage input to the motor driver. A fuel cell compressor comprising pulse width changing means for increasing a PWM pulse width when the voltage drops.

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