JP2007315317A - Pump and pump system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pump capable of being quickly started even when an impeller is frozen and locked. <P>SOLUTION: The pump comprises a motor consisting of a driving coil 3 and a rotor 4, and the impeller 5 for sucking/discharging fluid by rotating the motor. The impeller 5 is so arranged that part of itself exists in a space S defined by extending a plane region A encircled by the winding of the driving coil 3 toward the axial center of the driving coil 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pump that sucks and discharges fluid by rotating an impeller by a motor, and a pump system including the pump, and more particularly, to a method for thawing an impeller that is fixed by freezing of a liquid.

  Currently, fuel cells are attracting attention as an environmentally friendly energy source. A fuel cell is a device that generates electric power by electrochemically reacting a fuel gas such as hydrogen and an oxidant gas such as air, and one of them is a solid high membrane using a solid polymer membrane as an electrolyte membrane. Molecular fuel cells are known.

  In this type of fuel cell, the amount of hydrogen supplied to the fuel electrode is larger than the amount required for power generation from the viewpoint of not deficient in the amount of hydrogen necessary for the reaction. Excess hydrogen not consumed in the reaction is discharged. Therefore, in order to improve the utilization efficiency of hydrogen, many fuel cells employ a technique of circulating the discharged hydrogen again to the supply side by a circulation device such as a pump.

  By the way, in a fuel cell that generates electricity by reacting hydrogen and air, water is generated along with the power generation. Therefore, when this water circulates, water is supplied to the impeller (impeller) of the pump that is a circulation device. It will stick. Therefore, driving of the pump is stopped as in the case where the vehicle is stopped, and in a low temperature environment, the water is frozen, the impeller is locked, and the pump cannot be started.

For example, in Patent Document 1, from the viewpoint of suppressing the lock of a pump (impeller), a groove is provided on the end surface of the impeller or the inner surface of the casing facing the impeller, thereby freezing between the impeller and the inner surface of the casing. A pump with a reduced possible area is disclosed.
JP 2004-150298 A

  However, in the method disclosed in Patent Document 1, when the amount of water inside the pump is large, this water cannot be drained completely, and the impeller is locked by freezing when starting below freezing, and the pump is started. It may not be possible.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a pump that can be started quickly even when the impeller is locked by freezing.

  In order to solve such a problem, the present invention provides a pump having a motor including a driving coil and a rotor, and an impeller that sucks and discharges fluid by being rotated by the motor. In this pump, the impeller includes a part of itself in a space defined by extending a planar region surrounded by the winding of the driving coil in the axial direction of the driving coil. Is arranged.

  According to the present invention, the freeze-fixed impeller is heated by induction heating accompanying a magnetic field change generated from the driving coil. As a result, the solidified substance (ice) causing the sticking can be thawed. Therefore, even when the impeller is locked due to freezing, the pump can be started quickly.

  Hereinafter, a pump according to an embodiment of the present invention and a pump system including the pump will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram of a pump system according to a first embodiment of the present invention. This pump system can be used, for example, as a fuel gas circulation pump of a fuel cell system that generates electric power by electrochemically reacting a fuel gas and an oxidant gas. The pump system is mainly composed of a pump 1 and a control unit (control means) 10. In the figure, the cross-sectional state of the pump 1 is schematically shown.

  The pump 1 is mainly composed of a metal housing 2, a drive coil 3, a rotor 4, and an impeller 5, and the drive coil 3, the rotor 4 and the impeller 5 are accommodated in the housing 2. . A plurality of drive coils 3 are arranged in a circumferential shape, and constitute a motor together with the rotor 4 located in the center thereof, generate a magnetic field by an alternating current supplied to itself, and thereby rotate the rotor 4. .

  The rotor 4 is arranged vertically so as to sandwich the impeller 5. The pair of rotors 4 and the impeller 5 are connected by a rotating shaft 6. Therefore, the rotation of the rotor 4 is transmitted to the impeller 5 by the rotating shaft 6. When the impeller 5 rotates together with the rotation of the rotor 4, the pressure in the pump chamber is increased, whereby fluid (for example, hydrogen gas) is sucked and discharged.

  As one of the features of the present embodiment, the impeller 5 is arranged in a space surrounded by a plurality of driving coils 3 arranged circumferentially. FIG. 2 is an explanatory diagram of the space S in which the impeller 5 is arranged, (a) schematically shows a cross-sectional state when the pump 1 is viewed from above, and (b) is ( It is AA sectional drawing of the pump 1 shown to a). 3 is an explanatory diagram of the drive coil 3, (a) is a schematic perspective view of the drive coil 3, and (b) is a plane region A surrounded by the windings of the drive coil 3. FIG. It is explanatory drawing of.

  Specifically, as shown in FIGS. 2 and 3, the impeller 5 extends in a plane area A (see FIG. 3) surrounded by the windings of the driving coil 3 in the axial direction of the driving coil 3. It is arranged so that a part thereof is included in the space S (see FIG. 2) defined by the above. In other words, the impeller 5 is arranged so that a part thereof is included in the magnetic field space generated by the driving coil 3.

  In the example illustrated in FIG. 2, the space S is described for a single drive coil 3. However, the arrangement of the impeller 5 is only required to satisfy the above-described conditions in at least one of the circumferentially arranged drive coils 3. It is preferable that the above conditions are satisfied for the driving coil 3, and as a result, it is only necessary that a part of the impeller 5 is included in the space surrounded by the driving coil 3. In the present embodiment, the impeller 5 is a space defined by extending a planar region A (see FIG. 3) surrounded by the windings of each driving coil 3 in the axial direction of the driving coil 3. S is arranged in the center of the magnetic field space generated by each driving coil 3, and thus the impeller 5 is generally arranged at the center of each driving coil 3.

  The control unit 10 has a function of controlling the rotational speed of the pump 1 by controlling the energization state of the driving coil 3. As the control unit 10, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an input / output interface can be used. In order to control the energization state of the driving coil 3, an actual rotational speed signal indicating the actual rotational speed of the pump 1 is input to the controller 10 from a rotational speed sensor (rotational speed detection means) (not shown). ing.

  Here, the thawing principle of the pump 1 will be described assuming a case where the impeller 5 is fixed by freezing of the liquid adhering to the impeller 5. In the present embodiment, the pump 1 uses the magnetic field change generated by the driving coil 3 to defrost the frozen portion.

  As described above, the impeller 5 is arranged so that a part thereof is included in the magnetic field space generated by the driving coil 3. Therefore, when a high frequency current similar to that during normal operation is passed through the driving coil 3, a periodic magnetic field change occurs in the impeller 5 that is frozen and fixed. Due to this magnetic field change, an induced current (eddy current) is generated inside the impeller 5. At this time, most of the induced periodic current is concentrated in the range of the depth δ from the surface of the impeller 5 by the skin effect. Due to the Joule heat generated by the induced current, the temperature of the surface of the impeller 5 rises, and heat is transferred to the interface between the impeller 5 and the solidified substance (ice), which is a cause of sticking. Thereby, fixation of the impeller 5 by freezing can be eliminated.

(Formula 1)
δ = √ (2 / (fσμ))
This formula is a general formula indicating the skin depth δ. Here, f is the current frequency, σ is the conductivity of the object to be heated (impeller 5 in this embodiment), and μ is the magnetic permeability of the object to be heated (impeller 5 in this embodiment).

  FIG. 4 is an explanatory diagram showing the relationship between the current density flowing in the conductor and the depth from the conductor surface. As shown in the figure, the current density tends to decrease as it goes from the conductor surface to the inside of the conductor. The current density of the high-frequency current is maximum on the conductor surface due to the skin effect, and is about 37% of the current density on the conductor surface at the skin depth δ.

  FIG. 5 is a flowchart illustrating the procedure of the startup process of the pump system according to the first embodiment. For example, when a start command is input to a host system equipped with a pump system such as a fuel cell system, a rotation command signal is input from the host system to the control unit 10. Accordingly, in step 1 (S1), the control unit 10 outputs a rotation command to the pump 1 by supplying an alternating current to the driving coil 3 based on the rotation command signal from the host system. .

  In step 2 (S2), the control unit 10 determines whether or not the pump 1 is rotating based on the actual rotational speed signal. When the impeller 5 is fixed by freezing, the impeller 5 does not rotate even if a rotation command is output from the control unit 10 to the pump 1. Therefore, based on the rotation speed of the pump 1, it can be determined whether the impeller 5 is fixed by freezing. If a negative determination is made in step 2, that is, if the pump 1 is not rotating (freezing and fixing of the impeller 5), the process proceeds to step 3. On the other hand, if an affirmative determination is made in step 2, that is, if the pump 1 is rotating, the processing from step 3 to step 7 is skipped and the process proceeds to step 8 described later.

  In step 3, the control unit 10 starts the freeze activation mode. In step 4, the control unit 10 supplies current to the drive coil 3. Here, in order to maximize the induction heating effect, the control unit 10 performs control so as to flow an allowable maximum current that the coil can withstand. As a result, the impeller 5 undergoes a periodic magnetic field change in the impeller 5 fixed by freezing and fixing, and thereby the impeller 5 is induction-heated.

  In step 5, the control unit 10 determines whether or not the pump 1 is rotating based on the actual rotational speed signal. If a negative determination is made in this step 5, that is, if the pump 1 is not rotating, the energization of the driving coil 3 is continued and the process returns to step 4 and is the pump 1 rotating after a predetermined time? It is determined again whether or not. On the other hand, if an affirmative determination is made in step 5, that is, if the pump 1 is rotating, the process proceeds to step 6.

  In step 6, the control unit 10 reduces the value of the current supplied to the driving coil 3. In step 7, the control unit 10 ends the series of freeze activation modes started from step 3. In step 8, the control unit 10 performs a normal operation process for controlling the alternating current supplied to the drive coil 3 based on the rotation command signal from the host system.

  As described above, according to this embodiment, the pump 1 includes the motor including the driving coil 3 and the rotor 4 and the impeller 5 that sucks and discharges fluid by being rotated by the motor. Here, the impeller 5 is a part of itself in a space S defined by extending the planar region A surrounded by the windings of the driving coil 3 in the axial direction of the driving coil 3. Are arranged to be included. In other words, the impeller 5 is disposed so that a part of itself is included in the magnetic field space generated by the driving coil 3.

  According to such a configuration, the freeze-fixed impeller 5 is directly heated by induction heating accompanying a magnetic field change generated from the driving coil. Thereby, it is possible to thaw from the interface between the impeller 5 and the solidified substance (ice), which is a cause of sticking. Therefore, even when the impeller 5 is locked by freezing, the pump 1 can be started quickly.

  Further, according to the present embodiment, the impeller 5 is disposed at the center of the driving coil 3. Therefore, the magnetic field lines generated from the drive coil 3 do not diverge, and the impeller 5 is disposed in a region where the magnetic flux density is high. Thereby, the freeze-fixed site can be effectively induction-heated.

  Furthermore, according to the present embodiment, the pump system is mainly configured by the pump 1 described above, a rotation speed sensor that detects the rotation speed of the pump, and a control unit 10 that controls the energization state of the drive coil 3. Has been. Here, when the controller 10 determines that the pump 1 is frozen and fixed based on the actual rotational speed signal, that is, the rotational speed of the pump detected by the rotational speed sensor, A freeze-thaw process is performed to pass the maximum allowable current of the coil. Then, after executing the freeze-thaw process, the control unit 10 determines whether the pump 1 is frozen and fixed based on the actual rotational speed signal. The freeze-thaw process is continued, and when the pump 1 is not frozen and fixed, the current passed through the drive coil 3 is reduced and the freeze-thaw process is terminated.

  According to such a configuration, the rotating magnetic field of the rotor 4 is generated while suppressing the excessive current, and the thawing heating of the impeller 5 and the thawing determination can be performed in parallel. Therefore, induction heating is promoted and the thawing time can be shortened.

  In the present embodiment, the rotor 4 is provided above and below the impeller 5, but the present invention is not limited to this, and a configuration in which only one of them is provided may be employed.

(Second Embodiment)
FIG. 6 is a configuration diagram showing a pump 1 according to the second embodiment of the present invention. The pump 1 a according to the second embodiment is different from the pump 1 of the first embodiment in that an impeller 5 is provided on a part of the outer periphery of the rotor 4. The pump 1a according to the present embodiment is the same as the pump 1 of the first embodiment in the basic configuration, and the same reference numerals are used for the same configuration, and redundant description is omitted. .

  In the second embodiment, the rotor 4 has a single configuration extending in the direction of the rotation axis of the impeller 5. An impeller 5 (particularly a wing) is integrally provided on the rotor 4 so as to circumscribe the circumferential direction thereof, whereby the rotor 4 and the impeller 5 rotate integrally. It has become. The pump 1a having such a configuration constitutes a pump system together with the control unit 10 shown in the first embodiment. And as demonstrated with reference to FIG. 5, the starting process of a pump system can be performed by the control part 10. FIG.

  Thus, according to the present embodiment, the impeller 5 has a configuration in which a magnetic body is provided between the blade portion of the impeller 5 and the rotating shaft that connects the rotor 4 and the impeller 5. In particular, in this embodiment, the rotation shaft and the magnetic body are combined with the rotor 4. According to such a configuration, since a magnetic field is generated with the impeller 5 interposed therebetween, the magnetic flux density generated in the blade portion of the impeller 5 is increased, or the change in the magnetic field becomes steep. Therefore, when the impeller 5 is frozen, the magnetic material promotes a change in magnetic flux, so that induction heating is promoted and the thawing time can be shortened. Further, when the impeller 5 rotates, the magnetic body and the rotating shaft act as an impeller / rotor, so that the change in the magnetic field generated from the driving coil 3 can be utilized without undue loss. Thereby, the improvement of rotation efficiency can be aimed at.

  Note that the pump 1a shown in FIG. 6 is configured to include the impeller 5 on a part of the outer periphery of the rotor 4 as an example, but the present invention can be applied to any configuration that generates a magnetic field with the impeller 5 interposed therebetween. It is not limited to this. For example, in the pump 1 as shown in FIG. 1, a magnetic body may be provided in the central portion of the impeller 5 or the rotation shaft 6 in a position corresponding to the impeller 5 in a position.

(Third embodiment)
FIG. 7 is a block diagram showing a pump 1b according to the third embodiment of the present invention. The pump 1 b is mainly configured by a metal housing 2, a drive coil 3, a rotor 4, and an impeller 5, and the drive coil 3, the rotor 4 and the impeller 5 are housed in the metal housing 2. Has been. A plurality of drive coils 3 are arranged in a circumferential shape, and constitute a motor together with the rotor 4 located in the center thereof, generate a magnetic field by an alternating current supplied to itself, and thereby rotate the rotor 4. . The rotor 4 and the impeller 5 are connected by a rotating shaft 6. Therefore, the rotation of the rotor 4 is transmitted to the impeller 5 by the rotating shaft 6. When the impeller 5 rotates together with the rotation of the rotor 4, the pressure in the pump chamber is increased, whereby a fluid (for example, hydrogen gas) is sucked and discharged.

  As one of the features of the present embodiment, the driving coil 3 is such that a part of the iron core sandwiches the coil, that is, a U-shaped branch, and a protruding portion protruding in the normal direction of the coil 7. The impeller 5 is disposed such that the wing portion of the impeller 5 faces the end portion of the protruding portion 7. A slight clearance is formed between the end of the projecting portion 7 and the impeller 5 so that they do not mechanically interfere with each other. When the temperature is low, the liquid adhering to the impeller 5 freezes at this clearance, and the impeller 5 may be fixed to the iron core.

(Formula 2)
B = μ ₀ (1 + X) H
Here, B is the magnetic flux density reaching the impeller 5, μ ₀ is the vacuum magnetic permeability, Χ is the magnetic permeability (magnetism) of the substance through which the magnetic field lines pass, and H is the magnetic field strength. As shown in the equation, the magnetic flux density B depends on the magnetic permeability (susceptibility) of the space (material) through which the magnetic field lines pass.

  As described above, according to the present embodiment, the magnetic field generated in the drive coil 3 is guided to the end of the protruding portion 7 by the iron core having a high magnetic permeability, and then is a minimal space (clearance) that is a freezing generation site. Is reached and the impeller 5 is reached. For this reason, the part where the magnetic permeability becomes the lowest is only a minimal space, and the passage through the atmosphere which becomes the most resistance when transmitting the magnetic force is suppressed. For this reason, the magnetic flux density reaching the fixed frozen portion of the impeller 5 is increased. This makes it possible to intensively inductively heat a portion of the impeller 5 due to freezing and sticking, so that the freezing time can be further shortened.

  In addition, the pump 1b which has such a structure comprises a pump system with the control part 10 shown in 1st Embodiment. And as demonstrated with reference to FIG. 5, the starting process of a pump system can be performed by the control part 10. FIG.

(Fourth embodiment)
FIG. 8 is a configuration diagram of a pump 1c according to the fourth embodiment of the present invention. The pump 1c according to the fourth embodiment is different from the pumps 1 and 1b according to the first or third embodiment in that the impeller 5 has characteristics of high permeability and high conductivity. . The pump 1c according to the present embodiment is the same as the pump 1 of the first embodiment in the basic configuration, and the same reference numerals are used for the same configuration, and redundant description is omitted. .

  Examples of the material having high magnetic permeability and high conductivity include silicon steel plate, permalloy, and soft magnetic ferrite represented by the iron core of the driving coil 3. Here, the reason why the impeller 5 has the characteristics of high permeability and high conductivity is as follows. In order to enhance the induction heating effect of the impeller 5, it is necessary to consider the skin effect and hysteresis loss.

  First, in order to enhance the skin effect, it is important to reduce the depth from the conductor surface (skin depth) as shown in FIG. Since the skin depth becomes shallower as the magnetic permeability is higher and the electric conductivity is higher, the surface of the impeller 5 can be intensively heated by such a material.

  Next, the hysteresis loss is a loss generated in the impeller 5 to resist a steep change in the magnetic field with a material having high permeability, so-called ferromagnetic material. In the case of induction heating, this loss becomes heat and promotes heating. Used. For this reason, the impeller 5 has characteristics of high magnetic permeability and high conductivity, so that it is possible to shorten the thawing time.

  By the way, when the impeller 5 has the characteristics of high magnetic permeability and high conductivity, it is conceivable that the entire impeller 5 is formed of a material with high magnetic permeability and high conductivity. This is also not preferable. This is because the location that is desired to be heated is sufficient only when the impeller 5 is frozen and fixed. Therefore, it is sufficient for the impeller 5 to have a higher permeability and conductivity at a site where freezing occurs than at other sites. Such an impeller 5 may be configured by different materials so that the permeability and conductivity of a portion where the impeller 5 is frozen are higher than those of other portions. Further, as shown in FIG. 8, a thin plate 8 made of a material having high magnetic permeability and high conductivity is fixed to the impeller 5 in a position corresponding to a portion where freezing occurs (see FIG. 8B). A set of the impeller 5 and the thin plate 8 may be disposed in the impeller case (see FIG. 8A).

  Here, the thickness of the thin plate 8 having high magnetic permeability and high conductivity can be determined in advance through experiments and simulations from the viewpoint of skin depth. Moreover, it is preferable to form the lower part of the thin plate 8 made of a high magnetic permeability / high conductivity material with a material having a low thermal conductivity. Thus, it is possible to prevent the occurrence of a situation in which the heat generated by induction heating is used to heat the impeller 5 that is not related to freezing and fixing. Thereby, shortening of thawing | decompression time can be aimed at. In addition, since the induced current does not flow on the surface of the impeller 5 as described above, the thin plate 8 having high magnetic permeability and high conductivity does not have a possibility of reducing the heating efficiency.

  As described above, according to the present embodiment, the magnetic flux density transmitted through the impeller 5 can be increased, so that the induced current increases, and the skin depth is shallow, so that the induced current is concentrated on the impeller skin portion. The current density increases. Thereby, since heating is accelerated | stimulated, shortening of the thawing | decompression time can be aimed at.

(Fifth embodiment)
FIG. 9 is a configuration diagram of a pump 1d according to the fifth embodiment of the present invention. The pump 1d according to the fifth embodiment is different from the pumps 1 and 1c according to the first or third embodiment in that a portion of the iron core of the drive coil 3a that corresponds to the impeller 5 is positioned. The magnetic permeability is higher than that of other parts. The pump 1d according to the present embodiment is the same as the pump 1 of the first embodiment in the basic configuration, and the same reference numerals are used for the same configuration, and redundant description is omitted. .

  As shown in FIG. 9B, which is a BB cross section of the pump 1d shown in FIG. 9A, the iron core of the driving coil 3 has a location corresponding to the impeller 5 in a position that is more transparent than the other locations. It is made of a material having high magnetic permeability and high magnetic permeability. In the present embodiment, because the impeller 5 is located at the central portion of the driving coil 3, the central portion of the driving coil 3 is also made of a material having a higher magnetic permeability than the upper and lower portions.

  According to this configuration, the magnetic resistance of the iron core of the driving coil 3a is reduced, so that the magnetic permeability in the magnetic field line path is increased, and the magnetic flux density reaching the impeller 5 is increased. Thereby, induction heating is promoted and the thawing time can be shortened.

  In the present embodiment, the magnetic permeability of the iron core of the driving coil 3 is made different according to the position of the impeller 5, but the present invention is not limited to this configuration as long as the magnetic permeability in the magnetic field line path is increased. It is not limited to. For example, the impeller case that houses the impeller 5 may have a higher magnetic permeability than parts other than the impeller case. According to this configuration, the magnetic flux density reaching the impeller 5 is increased by reducing the magnetic resistance of the impeller case. Therefore, since induction heating is promoted, the thawing time can be shortened.

Configuration diagram of a pump system according to the first embodiment Explanatory drawing of space S where impeller 5 is arranged Explanatory drawing of the drive coil 3 Theory showing the relationship between the density of current flowing in the conductor and the depth from the conductor surface Flow chart showing the procedure for starting the pump system The block diagram which shows the pump 1a concerning 2nd Embodiment. The block diagram which shows the pump 1b concerning 3rd Embodiment. The block diagram of the pump 1c concerning 4th Embodiment Configuration diagram of pump 1d according to the fifth embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump 1a Pump 1b Pump 1c Pump 1d Pump 2 Housing 3 Drive coil 3a Drive coil 4 Rotor 5 Impeller 6 Rotating shaft 7 Protruding part 8 Thin plate 10 Control part

Claims (9)

In the pump,
A motor comprising a driving coil and a rotor;
An impeller that sucks and discharges fluid by being rotated by the motor;
The impeller is arranged such that a part of itself is included in a space defined by extending a planar region surrounded by the winding of the driving coil in the axial direction of the driving coil. Pump characterized by being made. In the pump,
A motor comprising a driving coil and a rotor;
An impeller that sucks and projects fluid by being rotated by the motor;
The impeller is arranged so that a part of itself is included in a magnetic field space generated by the driving coil.   The pump according to claim 1 or 2, wherein the impeller is disposed at a center of the driving coil.   The pump according to any one of claims 1 to 3, wherein the impeller includes a magnetic body between a blade portion of the impeller and a rotation shaft that connects the rotor and the impeller. . In the pump,
A motor comprising a driving coil and a rotor;
An impeller that sucks and projects fluid by being rotated by the motor;
The drive coil has a protruding portion that protrudes in the normal direction of the coil such that a part of the iron core sandwiches the coil,
The pump, wherein the impeller is arranged so that a blade portion of the impeller faces an end of the protruding portion.   6. The impeller according to claim 1, wherein the permeability and conductivity of a portion where freezing may occur is higher than the permeability and conductivity of other portions. Pump. An impeller case for storing the impeller;
The pump according to any one of claims 1 to 5, wherein the impeller case has a higher magnetic permeability than portions other than the impeller case.   6. The drive coil according to claim 1, wherein the iron core at a position corresponding to the impeller has a higher magnetic permeability than other portions of the iron core. Pump. In the pump system,
The pump according to any one of claims 1 to 8,
A rotational speed detection means for detecting the rotational speed of the pump;
Control means for controlling the energization state to the drive coil,
When the control means determines that the pump is frozen and fixed based on the rotation speed of the pump detected by the rotation speed detection means, the control means sets an allowable maximum current of the coil to the driving coil. Performing the freezing and thawing process to be performed, and determining whether or not the pump is frozen and fixed based on the number of revolutions of the pump detected by the number of revolutions detecting means after performing the freeze and thawing process, If it is determined that the pump is frozen and fixed, the freeze-thaw process is continued. If the pump is not frozen and fixed, the current passed through the drive coil is reduced to end the freeze-thaw process. A pump system characterized by that.

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