Patent Publication Number: US-6987373-B2

Title: System and method for starting pump

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a system and a method for starting a pump, and in particular to a starting in an environment of a low temperature. 
   Japanese Unexamined Patent Publication No. 2003-178782 discloses a fuel cell system which generates electricity through reaction of hydrogen gas and air. A part of the hydrogen gas which is supplied to a hydrogen electrode of a fuel cell stack is often contained in hydrogen off-gas without being reacted and is exhausted from the fuel cell stack. To effectively utilize the unreacted hydrogen gas, such a system is proposed that a hydrogen pump circulates the hydrogen off-gas to the hydrogen electrode of the fuel cell stack. 
   However, since water is produced with generation of electricity in the fuel cell system and this water is exhausted from the fuel cell stack with the hydrogen off-gas, moisture is introduced into the hydrogen pump with the hydrogen off-gas. Therefore, if the operation of the fuel cell system is stopped in an environment of a low temperature, there is fear that the moisture in the hydrogen pump condenses and freezes therein. Even in an air pump for supplying air to an oxygen electrode of the fuel cell stack, there is also fear that moisture in introduced air or a backflow of humidification air from an exhaust-side causes freeze inside the air pump. 
   If a roots pump shown in  FIG. 4  is adapted for the hydrogen pump or the air pump, the moisture remains in a space between a pair of rotors  21 , or in a space between each rotor  21  and a casing  22 , and freezes therein due to surface tension of water. If the moisture freezes in the surface of each rotor  21 , there is fear that the roots pump is not capable of being started upon restarted. 
   SUMMARY OF THE INVENTION 
   In order to solve the above and other problems, according to a first aspect of the current invention, a starting system for a pump including a motor for driving the pump, an electric source connected to the driving motor for supplying the driving motor with electric power, a selector switch located between the driving motor and the electric source for reversing polarity of the electric power supplied from the electric source to the driving motor while selectively connecting the driving motor to the electric source and disconnecting the driving motor from the electric source, a starter sensor provided with the driving motor for sensing whether or not the driving motor has been started, a temperature sensor provided for sensing a temperature, and a control unit connected to the electric source, the selector switch, the starter sensor and the temperature sensor, wherein the control unit operates the selector switch so as to repeatedly give the driving motor indications of reverse rotation and normal rotation in a case where the starter sensor does not sense that the driving motor has been started even if the control unit operates the selector switch so as to give the driving motor the indication of normal rotation in a state where the temperature sensed by the temperature sensor is a preset temperature or below. 
   According to the second aspect of the current invention, a method of starting a pump including a motor for driving the pump, including the steps of sensing a temperature, giving the driving motor an indication of normal rotation, and starting the driving motor by giving the driving motor indications of reverse rotation and normal rotation repeatedly in a case where the driving motor is not started even if the indication of normal rotation is given to the driving motor in a state where the sensed temperature is a preset temperature or below. 
   According to the third aspect of the current invention, a starting system for a pump motor, including a starter sensor located near the pump motor for ultimately determining an operational status of the pump motor, the operational status being active and inactive, a temperature sensor for detecting a temperature, and a control unit connected to the starter sensor and the temperature sensor for generating a signal to the pump motor, in response to the inactive operational status from the starter sensor after a predetermined normal activation attempt of starting the pump motor, the control unit generating a reverse/forward rotation signal sequence indicative of alternately rotating the pump motor in a predetermined reverse direction and a predetermined forward direction if the detected temperature is equal to or below a predetermined temperature. 
   According to the fourth aspect of the current invention, a method of starting a pump motor, including the steps of rotating the pump motor in a predetermined forward direction, determining an operational status of the pump motor, the operational status being active and inactive, in response to the inactive operational status, detecting a temperature, and generating a reverse/forward rotation signal sequence indicative of alternately rotating the pump motor in a predetermined reverse direction and the predetermined forward direction if the detected temperature is equal to or below a predetermined temperature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments, together with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing a structure of a starting system for a roots pump according to a first preferred embodiment of the present invention; 
       FIG. 2  is a sectional view showing an inside of the roots pump; 
       FIG. 3  is a flow chart showing an operation of the first preferred embodiment of the present invention; 
       FIG. 4  is a sectional view showing an operation of a roots pump stepwise; and 
       FIG. 5  is a sectional view showing an inside of a screw pump according to a second preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A first preferred embodiment of the present invention will now be described with reference to  FIGS. 1 through 4 . A structure of a system for starting a roots pump  1  which is adapted for a hydrogen pump or an air pump in a fuel cell system is shown in FIG.  1 . The roots pump  1  is provided with a motor  2  for driving the roots pump  1 . The driving motor  2  is connected to a battery  4  that serves as an electric source through a selector switch  3 . The driving motor  2  is also provided with a starter sensor  5  for sensing whether or not the driving motor  2  has been started. In addition, a temperature sensor  6  is provided for measuring an outdoor air temperature T. The selector switch  3 , the battery  4 , the starter sensor  5  and the temperature sensor  6  are connected to a control unit  7 . 
   When the selector switch  3  is switched, the polarity of electric power supplied from the battery  4  to the driving motor  2  is reversed while the battery  4  is selectively connected to the driving motor  2  and disconnected from the driving motor  2 , thereby giving the driving motor  2  indications of normal rotation and reverse rotation selectively. 
     FIG. 2  shows an internal structure of the roots pump  1 . The roots pump  1  has a casing  8  in which a drive shaft  9  and a driven shaft  10  are rotatably arranged so as to be parallel with each other. One end of the drive shaft  9  is provided with a drive gear  11 , and one end of the driven shaft  10  is provided with a driven gear  12 . The drive gear  11  engages with the driven gear  12 . The drive shaft  9  and the driven shaft  10  have passed through a rotor chamber  13  defined in the casing  8 . The drive shaft  9  and the driven shaft  10  have fixed respectively a first rotor  14  and a second rotor  15  in the rotor chamber  13 . The other end of the drive shaft  9  protrudes from the casing  8 , and forms a rotary shaft of the driving motor  2  fixed to the casing  8 . 
   As the drive shaft  9  rotates by the driving motor  2 , the driven shaft  10  is rotated in an opposite direction to the drive shaft  9  through the drive gear  11  and the driven gear  12 . Thus, the first rotor  14  and the second rotor  15  are rotated in an opposite direction to each other (as shown by a pair of rotors  21  in FIG.  4 ), and intake and exhaust occur in the rotor chamber  13 , accordingly. 
   Operation of the present embodiment will now be explained with reference to a flow chart in FIG.  3 . When the control unit  7  operates the selector switch  3  so as to supply electric power from the battery  4  to the driving motor  2  thereby giving the driving motor  2  a starting indication in a direction of normal rotation, the control unit  7  judges whether or not the driving motor  2  has been started by a signal from the starter sensor  5  in a step S 1 . In a case where the control unit  7  judges that the driving motor  2  has not been started, the control unit  7  reads an outdoor air temperature T sensed by the temperature sensor  6  in a step S 2 . Subsequently, the control unit  7  contrasts the value of the outdoor temperature T and a preset temperature such as 4 degrees C. in a step S 3 . 
   If the outdoor air temperature T is 4 degrees C. or below, it is estimated that the driving motor  2  is not started due to a freeze of moisture inside the roots pump  1 , and the control unit  7  operates the selector switch  3  in a step S 4  so as to reverse the polarity of the electric power supplied from the battery  4  to the driving motor  2 , thereby giving the driving motor  2  a starting indication in a direction of reverse rotation. Subsequently, the control unit  7  judges whether or not the driving motor  2  has been started by the signature from the starter sensor  5  in a step S 5 . In a case where the control unit  7  judges that the driving motor  2  has not been started, the control unit  7  contrasts a charging capacity Ps of the battery  4  and a preset value Pm in a step S 6 . 
   If the charging capacity Ps exceeds in the preset value Pm, it is estimated that the control unit  7  is capable of proceeding with a starting process in this state, and the control unit  7  operates the selector switch  3  in a step S 7  so as to reverse the polarity of the electric power supplied from the battery  4  to the driving motor  2  once again, thereby giving the driving motor  2  the starting indication in the direction of normal rotation this time. Subsequently, the control unit  7  judges whether or not the driving motor  2  has been started by the signature from the starter sensor  5  in a step S 8 . In a case where the control unit  7  judges that the driving motor  2  has not been started, the control unit  7  contrasts the charging capacity Ps of the battery  4  and the preset value Pm in a step S 9 . If the charging capacity Ps exceeds in the preset value Pm, the control unit  7  returns the process from the step S 9  to the step S 4 , thereby giving the driving motor  2  the starting indication in the direction of reverse rotation. 
   Thus, the processes of the step S 4  through the step S 9  are repeated until the driving motor  2  is started, and the indications of the reverse rotation and the normal rotation are repeatedly given to the driving motor  2  by the control unit  7 . 
   In a case where the control unit  7  judges that the driving motor  2  has been started by the signature from the starter sensor  5  in the step S 1 , S 5  or S 8 , those steps proceed to a step S 10 . The control unit  7  gives the driving motor  2  the starting indication in the direction of normal rotation once more in a system starting loop, the fuel cell system as a whole is started while the operation of the roots pump  1  is started. It is noted that in a case where the driving motor  2  is started when the control unit  7  gives the driving motor  2  the instruction of starting in the direction of normal rotation, the driving motor  2  may continue the operation and be followed by the starting of the fuel cell system as a whole. 
   In a case where the control unit  7  judges that the charging capacity Ps of the battery  4  is the preset value Pm or below in the step S 6  or S 9 , it is estimated that the charging capacity Ps is insufficient to start the operation of the fuel cell system as a whole after the operation of the pump is started even if the starting process proceeds in this state. In this case, those steps proceed to a step S 11 , in which the starting process is ended for the reason that the fuel cell system is incapable of being started. 
   Further, if the outdoor air temperature T is above 4 degrees C. in the step S 3 , it is estimated that the driving motor  2  is incapable of being started for the causes other than the freeze of the moisture. In this case, the step S 3  proceeds to a step S 12 , in which the cause of impossibility of the starting is investigated in a failure-diagnosis loop. 
   In the first embodiment of the present invention, reverse rotation and normal rotation are repeated by the driving motor if the driving motor is not started after normal rotation is attempted by the driving motor of the roots pump in a low temperature environment. If the moisture freezes inside the roots pump, the frozen moisture is peeled off from the rotor or the casing of the roots pump by torque of reverse rotation and normal rotation. Thereby, the roots pump is enabled to start. 
   A second preferred embodiment will now be described with reference to FIG.  5 . In the second preferred embodiment, a screw pump  30  is used in the fuel cell system instead of the roots pump  1 . The same reference numerals of the first preferred embodiment are applied to substantially the same components in the second preferred embodiment.  FIG. 5  shows an internal structure of the screw pump  30 . 
   The screw pump  30  has a front housing  8   a , a rotor housing  8   b , a rear housing  8   c  and a gear housing  8   d . The front housing  8   a  is joined to the rotor housing  8   b . The rotor housing  8   b  is joined to the rear housing  8   c . The rear housing  8   c  is joined to the gear housing  8   d . These housings  8   a ,  8   b ,  8   c ,  8   d  form a screw pump housing in which the drive shaft  9  and the driven shaft  10  are rotatably arranged. One end of the drive shaft  9  is provided with the drive gear  11 , and one end of the driven shaft  10  is provided with the driven gear  12 . The drive gear  11  engages with the driven gear  12 . The rotor housing  8   b  has defined therein a main pump chamber  31  and an auxiliary pump chamber  32 . The main pump chamber  31  has accommodated therein first and second main screw rotors  33 ,  34 . The auxiliary pump chamber  32  has accommodated therein first and second auxiliary screw rotors  35 ,  36 . The first main screw rotor  33  and the first auxiliary screw rotor  35  are integrally rotated with the drive shaft  9 . The second main screw rotor  34  and the second auxiliary screw rotor  36  are integrally rotated with the driven shaft  10 . 
   The main pump chamber  31 , the first and second main screw rotors  33 ,  34  form a main pump  37 . The auxiliary pump chamber  32 , the first and second auxiliary screw rotors  35 ,  36  form an auxiliary pump  38 . A first screw pitch p 2  between the first and second auxiliary screw rotors  35 ,  36  is set to be smaller than a second screw pitch p 1  between the first and second main screw rotors  33 ,  34 . That is, since volume of the gas trapped in the auxiliary pump chamber  32  is smaller than that of the gas trapped in the main pump chamber  31 , displacement of the auxiliary pump  38  is smaller than that of the main pump  37 . 
   A part of the main pump chamber  31  is defined as a semi-exhaust chamber  311  communicating with a main exhaust port (not shown). The rotation of the first and second main screw rotors  33 ,  34  pumps the gas from a suction port side (not shown) to the main exhaust port side. The rotation of the first and second auxiliary screw rotors  35 ,  36  pumps a part of the gas in the semi-exhaust chamber  311  into the auxiliary pump chamber  32  through a passage  39  between the main pump chamber  31  and the auxiliary pump chamber  32  and then discharges the pumped gas outside the auxiliary pump chamber  32 . 
   As is the case with the operation of the first embodiment, operation of the second embodiment is explained with reference to the flow chart in FIG.  3 . 
   In the second embodiment of the present invention, reverse rotation and normal rotation are repeated by the driving motor if the driving motor is not started after normal rotation is attempted by the driving motor of the screw pump in low temperature environment. If the moisture freezes inside the roots pump, the frozen moisture is peeled off from the rotor or the casing of the screw pump by torque of reverse rotation and normal rotation. Thereby, the screw pump is enabled to start. 
   In the above first and second embodiments, alternative sensors may be used instead of the starter sensor  5  which senses whether or not the driving motor  2  has been started. These alternative sensors include a torque sensor which senses torque of the driving motor  2 , an electric current sensor which senses a value of an electric current flowing into the driving motor  2 , a sensor which senses number of rotation of the driving motor  2 , or a pressure sensor which senses a discharge pressure of the roots pump  1  (or the screw pump  30 ). 
   In the above first and second embodiments, as the temperature sensor  6 , a sensor which measures a temperature of the driving motor  2  instead of the outdoor air temperature T or a sensor which measures the temperature of the fuel cell stack may be used. However, since the temperature sensor  6  is intended to monitor the temperature at which the freeze of the moisture begins, it is efficiently estimated whether or not the driving motor  2  has been started if the outdoor air temperature T is measured. In addition, the preset temperature contrasted with the outdoor air temperature T in the step S 3  of  FIG. 3  is 4 degrees C., for the freeze of the moisture normally begins if temperature falls to about 4 degrees C. It is noted that the values other than 4 degrees C. may be adapted for the preset temperature. 
   In the above first embodiment, the roots pump  1  is transversely arranged such that the drive shaft  9  faces a horizontal direction, thereby locating a suction port which allows a working fluid to be introduced from the outside of the roots pump  1  to the rotor chamber  13  on the upside of the drive shaft  9  and a discharge port which allows the working fluid to be discharged from the rotor chamber  13  to the outside of the roots pump  1  on the downside of the drive shaft  9 . It is noted that the roots pump  1  may be arranged such that the drive shaft  9  faces a vertical direction. In addition, the roots pump  1  may be longitudinally arranged such that the drive shaft  9  faces a vertical direction. Further, the roots pump  1  may be arranged at any angle. 
   The present invention is adapted for the roots pump or the screw pump, which is used as a hydrogen pump or an air pump supplying a fuel gas to a fuel cell in a fuel cell powered vehicle equipped with a battery. In addition, the present invention is also adapted for a roots blower which is used as an air conditioning apparatus in a fuel cell powered vehicle equipped with a battery. 
   Further, the present invention is also adapted for one of a roots pump, a screw pump and a roots blower used in a fixed power plant whose power source is supplied from a commercial power source instead of a battery. In this case, there is no need for measuring the charging capacity Ps of the battery  4  in the steps S 6 , S 9  of FIG.  3 . 
   Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified.