Patent Publication Number: US-2015086402-A1

Title: Pump device

Description:
TECHNICAL FIELD 
     The present invention relates to a pump device including a vacuum pump and a pressurizing pump. 
     BACKGROUND ART 
     An oscillating-piston-type pump as a type of vacuum pump is known as a reciprocating-type pump that alternately performs suction and discharge of air inside a pump chamber by a piston reciprocating within a cylinder, and is widely used as a vacuum pump or a pressurizing pump, for example. 
     Meanwhile, a complex type of pump device including two pistons for evacuation and for pressurization, which are simultaneously driven by a common motor, is also known. As a method of driving this type of pump device, there are known a method of causing the two pistons to reciprocate in opposite phases and a method of causing the two pistons to reciprocate in the same phase (see, for example, Patent Document 1 below). 
     The former method, that is, a drive method of causing both the pistons to reciprocate with rotation phases thereof being made different by 180° has an advantage that a dynamic balance of each pump can be successfully maintained and vibrations of the whole of the pump device can be reduced. On the other hand, the latter method, that is, a drive method of simultaneously moving both the pistons to a top dead center or a bottom dead center can reduce a load fluctuation of a drive source and achieve a stable operation of the pump device. 
     Patent Document 1: Japanese Patent Application Laid-open No. Hei 7-310651 
     DISCLOSURE OF THE INVENTION 
     Problem to be solved by the Invention 
     In recent years, there has been a demand for a reduction in power consumption of the pump device, and it is desirable to further reduce power consumption also in the complex-type pump device described above. 
     In view of the circumstances as described above, it is an object of the present invention to provide a pump device capable of achieving a further reduction in power consumption. 
     Means for solving the Problem 
     In order to achieve the object described above, according to an embodiment of the present invention, there is provided a pump device including a drive motor, a first pump unit for evacuation, and a second pump unit for pressurization. 
     The drive motor includes a first drive shaft and a second drive shaft. The drive motor is configured to be capable of rotating the first drive shaft and the second drive shaft in synchronization about a first axis. 
     The first pump unit includes a first piston that reciprocates in a direction of a second axis orthogonal to the first axis by a rotation of the first drive shaft, and a first pump chamber that has an internal pressure changing in accordance with a reciprocating movement of the first piston. 
     The second pump unit includes a second piston that reciprocates in the direction of the second axis by a rotation of the second drive shaft, and a second pump chamber that has an internal pressure changing in accordance with a reciprocating movement of the second piston. The second piston has a phase advanced with a rotational phase difference of more than 0° and less than 80° with respect to the first piston. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ]  FIG. 1  is a perspective view of a pump device seen from the front side according to an embodiment of the present invention. 
       [ FIG. 2 ]  FIG. 2  is a perspective view of the pump device seen from the back side. 
       [ FIG. 3 ]  FIG. 3  is a right side view of the pump device. 
       [ FIG. 4 ]  FIG. 4  is a left side view of the pump device. 
       [ FIG. 5 ]  FIG. 5  is a vertical cross-sectional view showing a part of a configuration of a vacuum pump unit and a drive unit of the pump device. 
       [ FIG. 6 ]  FIG. 6  is a schematic view for describing a relationship between an eccentric shaft on the vacuum pump unit side and an eccentric shaft on the pressurizing pump unit side of the pump device, in which (A) is a front view and (B) is a side view seen from the vacuum pump unit side. 
       [ FIG. 7 ]  FIG. 7  shows results of an experiment when the pump device is driven such that the internal pressure of a pump chamber in a vacuum stage and the internal pressure of a pump chamber in a pressurizing stage have the same phase, in which (A) shows time changes in internal pressure of the pump chamber and in piston position in the vacuum stage, (B) shows time changes in internal pressure of the pump chamber and in piston position in the pressurizing stage, and (C) shows a composite waveform of a pressure waveform of the pump chamber in the vacuum stage and a pressure waveform of the pump chamber in the pressurizing stage. 
       [ FIG. 8 ]  FIG. 8  shows results of an experiment when the pump device is driven such that the internal pressure of the pump chamber in the vacuum stage and the internal pressure of the pump chamber in the pressurizing stage have opposite phases, in which (A) shows time changes in internal pressure of the pump chamber and in piston position in the vacuum stage, (B) shows time changes in internal pressure of the pump chamber and in piston position in the pressurizing stage, and (C) shows a composite waveform of a pressure waveform of the pump chamber in the vacuum stage and a pressure waveform of the pump chamber in the pressurizing stage. 
       [ FIG. 9 ]  FIG. 9  shows results of an experiment showing a relationship between a rotational phase difference of a piston of the pressurizing stage with respect to a piston of the vacuum stage and a consumption current of a motor. 
     
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     The internal pressure of a pump chamber in an oscillating-type piston pump periodically changes by a reciprocating movement of a piston. For example, when the piston moves from a bottom dead center to a top dead center, the volume of the pump chamber decreases and thus the internal pressure transfers to an increasing direction, and when the piston moves from the top dead center to the bottom dead center, the volume of the pump chamber increases and thus the internal pressure transfers to a decreasing direction. At that time, in the case of a vacuum pump, the internal pressure of the pump chamber changes within a pressure range (negative pressure) equal to or lower than an atmospheric pressure, and in the case of a pressurizing pump, the internal pressure of the pump chamber changes within a pressure range (positive pressure) equal to or higher than the atmospheric pressure. 
     However, according to an experiment by the inventors of the present invention, it was found that even in the case where the piston for a vacuum pump and the piston for a pressurizing pump are caused to reciprocate in the same phase as described above, the internal pressures of both the pump chambers are synchronized with each other and do not change, and a phase difference in pressure change is caused between both of the pump chambers. Further, it was found that even when the rotation phases of both the pistons are controlled such that changes in internal pressure of both the pump chambers in the vacuum pump and the pressurizing pump have the same phase, the load of a motor is not reduced to a minimum value. 
     In this regard, in order to achieve a further reduction in power consumption of a pump device, according to the present invention, the following pump device is configured. 
     Specifically, according to an embodiment of the present invention, there is provided a pump device including a drive motor, a first pump unit for evacuation, and a second pump unit for pressurization. 
     The drive motor includes a first drive shaft and a second drive shaft. The drive motor is configured to be capable of rotating the first drive shaft and the second drive shaft in synchronization about a first axis. 
     The first pump unit includes a first piston that reciprocates in a direction of a second axis orthogonal to the first axis by a rotation of the first drive shaft, and a first pump chamber that has an internal pressure changing in accordance with a reciprocating movement of the first piston. 
     The second pump unit includes a second piston that reciprocates in the direction of the second axis by a rotation of the second drive shaft, and a second pump chamber that has an internal pressure changing in accordance with a reciprocating movement of the second piston. The second piston has a phase advanced with a rotational phase difference of more than 0° and less than 80° with respect to the first piston. 
     According to an experiment by the inventors of the present invention, in the first pump unit for evacuation, a top dead center of the piston and a pressure peak position of the pump chamber almost coincided with each other, while in the second pump unit for pressurization, a top dead center of the piston and a pressure peak position of the pump chamber did not coincide with each other. In particular, in the second pump unit, it was found that the pump chamber reaches a pressure peak before the piston arrives at the top dead center. 
     The rotational phase difference can be appropriately set in the range of more than 0° and less than 80°. For example, a stable reduction effect of power consumption is obtained in the range of 40°±30°, and a further reduction effect of power consumption is obtained in the range of 40°±15°. In such a manner, the rotational phase difference is optimized and thus the pump device can be stably operated at low power consumption. 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
       FIGS. 1 to 4  are outer appearance views each showing a pump device according to an embodiment of the present invention.  FIG. 1  is a perspective view seen from the front side,  FIG. 2  is a perspective view seen from the back side,  FIG. 3  is a right side view, and  FIG. 4  is a left side view. 
     A pump device  1  of this embodiment includes a vacuum pump unit  11  (first pump unit) as a vacuum stage, a pressurizing pump unit  12  (second pump unit) as a pressurizing stage, and a drive unit  13  that drives in common the vacuum pump unit  11  and the pressurizing pump unit  12 . For example, the pump device  1  is used as a booster blower of gas used in a fuel cell system or as a vacuum and pressurizing pump used in a medical analyzer. 
     The vacuum pump unit  11  and the pressurizing pump unit  12  typically have a common configuration and are each configured as an oscillating piston pump in this embodiment. 
     The pump device  1  includes a pump case  100  including a first casing  101  that constitutes a part of the vacuum pump unit  11 , a second casing  102  that constitutes a part of the pressurizing pump unit  12 , and a third casing  103  that constitutes a part of the drive unit  13 . 
       FIG. 5  is a vertical cross-sectional view showing a part of a configuration of the vacuum pump unit  11  and the drive unit  13 . In  FIG. 5 , an X axis, a Y axis, and a Z axis represent three axis directions that are orthogonal to one another. It should be noted that the pressurizing pump unit  12  has the same configuration as that of the vacuum pump unit  11 , and thus the vacuum pump unit  11  will be mainly described here. 
     The vacuum pump unit  11  includes the first casing  101 , a piston  21 , a connecting rod  22  (rod member), and an eccentric member  23 . 
     The first casing  101  includes a case body  110 , a cylinder  111 , a pump head  112 , and a pump head cover  113 . The case body  110 , the cylinder  111 , the pump head  112 , and the pump head cover  113  are mutually integrated so as to be stacked in a Z-axis direction. 
     The case body  110  is connected to the third casing  103  that contains a motor M, and includes a through-hole  110   h  through which the connecting rod  22  passes. The case body  110  includes a fixing portion  110   a  that fixes a bearing  32 , the bearing  32  rotatably supporting a drive shaft  131  of the motor M, and a cylindrical portion  110   b  that contains a coil  132  of the motor M. The drive shaft  131  is disposed parallel to a Y-axis direction (first axis direction) and rotates about the Y axis by the drive of the motor M. The bearing  32  is disposed between the main body of the motor M and the eccentric member  23 . 
     The cylinder  111  is disposed between the case body  110  and the pump head  112  and contains the piston  21  so as to be slidable in the Z-axis direction. The pump head  112  is disposed between the cylinder  111  and the pump head cover  113  and includes a suction valve  112   a  and a discharge valve  112   b.  The pump head cover  113  is disposed on the pump head  112  and includes a suction chamber  113   a  that communicates with a suction port  114   a  and a discharge chamber  113   b  that communicates with a discharge port  114   b.  The suction port  114   a  and the discharge port  114   b  are provided to a side surface of each of the pump units  11  and  12 , the side surfaces of the pump units  11  and  12  being opposed to each other as shown in  FIGS. 1 and 2 . 
     The piston  21  has a circular disk shape and is fixed to a first end  221  of the connecting rod  22  via a screw member  25 . The piston  21  forms a pump chamber  26  between the piston  21  and the pump head  112 . The piston  21  changes the internal pressure of the pump chamber  26  by a reciprocating movement to a direction parallel to the Z-axis direction (second axis direction) within the cylinder  111 . The piston  21  alternately performs suction and discharge of air in the pump chamber  26  via the suction valve  112   a  and the discharge valve  112   b,  thus performing a predetermined pump action. 
     The connecting rod  22  couples the piston  21  and the eccentric member  23  to each other. The connecting rod  22  includes the first end  221  connected to the piston  21  and a second end  222  connected to the eccentric member  23 . The first end  221  is formed into a circular form having substantially the same diameter as the piston  21 . A circular disk-shaped seal member  24  is attached between the piston  21  and the first end  221 . The outer edge of the seal member  24  is folded back to the pump chamber  26  side so as to be capable of sliding on an inner peripheral surface of the cylinder  111 . 
     It should be noted that in the pressurizing pump unit  12 , the outer edge of the seal member is folded back to the pump chamber side, contrary to the example described above. 
     A fitting hole  222   a  into which an eccentric shaft  232  of the eccentric member  23  is fitted is formed in the second end  222  of the connecting rod  22 . A bearing  31  that rotatably supports the eccentric shaft  232  is fitted to the fitting hole  222   a.    
     The eccentric member  23  couples the drive shaft  131  of the motor M contained in the third casing  103  and the connecting rod  22  to each other. The eccentric member  23  includes a base block  230  having a substantially columnar shape. The base block  230  has a surface on the motor M side, to which the drive shaft  131  is coupled, and a surface on the connecting rod  22  side, on which the eccentric shaft  232  is formed. The shaft center of the eccentric shaft  232  is eccentric relative to the drive shaft  131  so as to be biased along with the rotation of the drive shaft  131 . The drive shaft  131  is coupled to the base block  230  with a screw  41  fastened to a side peripheral surface of the base block  230 . 
     A counterweight  51  is attached to the eccentric member  23 . The counterweight  51  is fixed to a side peripheral portion of the eccentric member  23  with a fixing screw  42  fastened to the side peripheral surface of the base block  230 . The counterweight  51  rotates together with the piston  21  and has an action of cancelling a vibration that is generated when the connecting rod  22  rotates about the eccentric shaft  232  along with the rotation of the drive shaft  131 . The counterweight  51  is disposed at a position biased in a direction opposite to the bias direction of the eccentric shaft  232  with respect to the drive shaft  131 . 
     In the vacuum pump unit  11  configured as described above, the eccentric member  23  rotates about the drive shaft  131  by the drive of the motor M, and thus the eccentric shaft  232  revolves around the drive shaft  131  along a circumference having a radius corresponding to an eccentricity amount from the drive shaft  131 . The connecting rod  22  coupled to the eccentric shaft  232  converts the rotation of the drive shaft  131  into a reciprocating movement of the piston  21  within the cylinder  111 . Specifically, the piston  21  reciprocates in the Z-axis direction while oscillating in the X-axis direction in  FIG. 5  within the cylinder  111 . With this, the suction and discharge of air in the pump chamber  26  are alternately performed, and a predetermined evacuation action by the vacuum pump unit  11  is obtained. 
     On the other hand, the pressurizing pump unit  12  is configured in the same manner as the vacuum pump unit  11 , and the drive shaft  131  also protrudes to the pressurizing pump unit  12  side and is coupled to an eccentric shaft (not shown) of the pressurizing pump unit  12 . With this, the pressurizing pump unit  12  is driven by the common motor M simultaneously with the vacuum pump unit  11 , and a predetermined pressurizing (boosting) action is performed. 
     Here, the vacuum pump unit  11  and the pressurizing pump unit  12  are driven in phases that are different from each other. Specifically, in this embodiment, the piston  21  (second piston) of the pressurizing pump unit  12  is configured such that its phase is advanced with a rotational phase difference of more than 0° and less than 80° with respect to the piston  21  (first piston) of the vacuum pump unit  11 . 
     In order to provide the rotational phase difference as described above to each piston, in this embodiment, the positions of the eccentric shafts  232  of the respective pumps  11  and  12  are made different. According to this embodiment, since the eccentric members  23  are fixed to the drive shaft  131  by only fastening of the screws  41 , it is easy to adjust relative positions of the eccentric shafts  232  of both the pumps  11  and  12 . 
     Further, since the position of the counterweight fixed to the eccentric member  23  correlates with the bias direction of the eccentric shaft  232 , it is also possible to easily determine a rotational phase difference of both the pistons  21  from the outside of the pump device  1 . 
     Specifically, as shown in  FIGS. 1 to 4 , a counterweight  52  of the pressurizing pump unit  12  is fixed to a position at which a phase is advanced by the predetermined rotational phase difference (more than 0° and less than 80°) in a rotation direction of the drive shaft  131  (in a clockwise direction about the Y axis in  FIG. 3  and in a counterclockwise direction about the Y axis in  FIG. 4 ) with respect to the counterweight  51  of the vacuum pump unit  11 . 
       FIGS. 6(A)  and (B) is a schematic view for describing a relationship between an eccentric shaft  232   v  on the vacuum pump unit  11  side and an eccentric shaft  232   c  on the pressurizing pump unit  12  side, in which (A) is a front view and (B) is a side view seen from the vacuum pump unit  11  side. As shown in  FIG. 6(B) , the eccentric shaft  232   c  on the pressurizing pump side is provided at a position at which a phase is more advanced with a predetermined rotational phase difference cp than the eccentric shaft  232   v  on the vacuum pump unit  11  side. So, a piston  21   v  on the vacuum pump unit  11  side and a piston  21   c  on the pressurizing pump unit  12  side are driven with a shift of a phase difference φ, and the piston  21  c arrives at a top dead center earlier than the piston  21   v  by a time corresponding to the phase difference φp. 
     The rotational phase difference φp is set to an appropriate range of more than 0° and less than 80°. With this, as compared to a case where both the pistons  21   v  and  21   c  are driven in the same phase (φ=0), the power consumption of the motor M can be reduced. Further, the rotational phase difference φ is set to 40°±15°, and thus the above-mentioned operation of the motor M at low power consumption can be stably maintained. 
       FIG. 7(A)  shows results of an experiment showing time changes in internal pressure of the pump chamber and in piston position in the vacuum pump, and  FIG. 7(B)  shows results of an experiment showing time changes in internal pressure of the pump chamber and in piston position in the pressurizing pump. In the figure, solid lines indicate experimental results of the operation in 50 Hz, and broken lines indicate experimental results of the operation in 60 Hz. 
     It should be noted that a lifting height of the pump device used in the experiments was set to 40 [kPa (absolute pressure)] in the vacuum stage (vacuum pump) and set to 220 [kPaG (gauge pressure)] in the pressurizing stage (pressurizing pump). The internal pressure of the pump chamber was measured via a tube hermetically inserted into the pump chamber. For the piston position, an output of an accelerometer attached to the lower portion of the connecting rod was used. A cylinder diameter of the pump in each stage was set to φ37 mm, the eccentricity amount of the eccentric shaft to 3.3 mm, and the rotation speed of the motor to about 1400 rpm/1700 rpm-range (50 Hz/60 Hz). The same holds true for the conditions of experimental results shown in  FIGS. 8 and 9 . 
     In the vacuum stage, the internal pressure of the pump chamber is synchronized with the piston position and the internal pressure of the pump chamber and the piston position change in the same phase (FIG.  7 (A)), while in the pressurizing stage, the internal pressure of the pump chamber is not synchronized with the piston position and a phase difference is caused therebetween ( FIG. 7(B) ). More specifically, before the piston of the pressurizing stage arrives at the top dead center, a pressure peak appears in the pump chamber. 
     From the experimental results described above, it was found that even when the pistons in the vacuum stage and the pressurizing stage are driven in the same phase, the internal pressures of the pump chambers in the vacuum stage and the pressurizing stage do not change in the same phase and the pump chamber in the pressurizing stage reaches a maximum pressure value earlier than the pump chamber in the vacuum stage. 
     Further, since the pump device is configured such that changes in internal pressure of both the pump chambers have opposite phases in the first pump unit and the second pump unit, it was found by the experiments that power consumption of the drive motor can be reduced as compared to a case where the pistons of the respective pumps are driven in the same phase. 
     Here, the fact that time changes in internal pressure have opposite phases typically means that pressure waveforms of the both pump chambers have a phase of 180°, but the present invention is not limited thereto and only needs to have such a phase relationship that can be interpreted to be an opposite phase relationship in a practical sense. Here, the opposite phase relationship in the practical sense can be defined as, for example, a phase relationship in which power consumption becomes smaller than in a case where both the pistons are driven in the same phase. 
     In the case where the pump device is constituted with a predetermined phase difference between the piston of the pressurizing stage and the piston of the vacuum stage such that the pressure waveform of the internal pressure of the pump chamber in the vacuum stage and the pressure waveform of the internal pressure of the pump chamber in the pressurizing stage have the same phase, the piston of the pressurizing stage is set to have a rotational phase difference that is advanced by more than 180° and less than 260° with respect to the piston of the vacuum stage. The results of an experiment when the rotational phase difference is 220° are shown in  FIGS. 7(A)  to (C).  FIG. 7(C)  shows a composite waveform of the pressure waveform of the pump chamber in the vacuum stage and the pressure waveform of the pump chamber in the pressurizing stage. 
     On the other hand, in the case where the pump device is constituted with a predetermined phase difference between the piston of the pressurizing stage and the piston of the vacuum stage such that the pressure waveform of the internal pressure of the pump chamber in the vacuum stage and the pressure waveform of the internal pressure of the pump chamber in the pressurizing stage have opposite phases, the piston of the pressurizing stage is set to have a rotational phase difference that is advanced by more than 0° and less than 80° with respect to the piston of the vacuum stage. The results of an experiment when the rotational phase difference is 40° are shown in  FIGS. 8(A)  to (C).  FIG. 8(A)  shows time changes in internal pressure of the pump chamber and in piston position in the vacuum stage.  FIG. 8(B)  shows time changes in internal pressure of the pump chamber and in piston position in the pressurizing stage. Further, FIG.  8 (C) shows a composite waveform of the pressure waveform of the pump chamber in the vacuum stage and the pressure waveform of the pump chamber in the pressurizing stage. 
     Subsequently,  FIG. 9  shows results of an experiment showing a relationship between a rotational phase difference of the piston of the pressurizing stage with respect to the piston of the vacuum stage and a consumption current of the motor. The rotational phase difference in the horizontal axis indicates a phase advance angle of the piston of the pressurizing stage with respect to the piston of the vacuum stage (phase angle by which the piston on the pressurizing side is advanced more than the piston on the vacuum side in the rotation direction of the drive shaft). 
     As shown in  FIG. 9 , it is found that a current value of the motor changes in accordance with the rotational phase difference φ of the piston of the pressurizing stage with respect to the piston of the vacuum stage. This is thought to be related to a balance of a pressure change between the pump chambers in the respective stages. 
     In this experimental example, the rotational phase difference φ at the lowest current value is 40°, and the pressure waveforms of the pump chambers in the respective stages at that time have an opposite phase relationship as shown in  FIGS. 8(A)  and (B). In this case, a composite waveform of the internal pressures of the pump chambers in the respective stages is as shown in  FIG. 8(C) , and the internal pressures of the pump chambers in the respective stages are canceled by each other. As a result, it is thought that the consumption current of the motor becomes the minimum. 
     In contrast to this, in drive conditions in which the internal pressures of the pump chambers in the respective stages have the same phase (the rotational phase difference of the piston in the pressurizing stage with respect to the piston in the vacuum stage is +220°, the internal pressures of the pump chambers in the respective stages are superimposed on each other as shown in  FIG. 7(C) , and thus a periodic load fluctuation is caused in the motor. It is thought that this leads to an increase in consumption current value. 
     Further, as shown in  FIG. 9 , in the range of more than 0° and less than 80° of the rotational phase difference φ, it was found that the drive current of the motor can be reduced as compared with a case where the rotational phase difference φ is 0° (360°), in the power supply frequency of 50 Hz or 60 Hz. In particular, in the range of 40°±30° of the rotational phase difference φ, the current value can be constantly reduced more than the case where φ=0° irrespective of a difference in power supply frequency. Further, in the range of 40°35 15 of the rotational phase difference φ, the power consumption could be effectively reduced more, and the current value could be reduced by about 4.1% in the case of 50 Hz and by about 2.2% in the case of 60 Hz. 
     Furthermore, the phase difference φ is set to 40°±15°, and thus it is possible to reduce not only the amount of current consumption but also vibrations generated when the pump device  1  is driven. According to the experiments of the inventors of the present invention, for example, when φ=40°, it was found that a vibration acceleration in each of the X-, Y- and Z-axis directions (see  FIG. 1 ) can be reduced as compared with the case where the pistons of the vacuum stage and the pressurizing stage have the same phase (φ=0°). This vibration reducing effect was found in each of the power supply frequencies of 50 Hz and 60 Hz. 
     Hereinabove, the embodiment of the present invention has been described, but the present invention is not limited to the embodiment described above and can be variously modified without departing from the gist of the present invention. 
     For example, in the embodiment described above, the vacuum pump unit  11  and the pressurizing pump unit  12  that constitute the pump device are each constituted of an oscillating-type piston pump. However, the present invention is not limited to this and each pump may be constituted of another reciprocating-type piston pump such as a diaphragm pump. 
     Further, in the embodiment described above, the pump device including a single drive motor and two pump units has been described as an example, but the present invention is also applicable to a pump device including a plurality of sets (for example, two sets) of pump units each constituted of the drive motor and the two pump units. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       1  pump device 
       11  vacuum pump 
       12  pressurizing pump 
       21 ,  21   v,    21   c  piston 
       26  pump chamber 
       51 ,  52  counterweight 
       131  drive shaft 
       232 ,  232   v,    232   c  eccentric shaft 
     M motor