Pump unit and fluid supplying system

Abstract

A fuel supplying system includes a tank and a pump unit, which transfers fluid from the tank. The pump unit includes a first pump, a second pump, and a drive source. The first pump and the second pump are driven by the common drive source. The first pump, the second pump, and the drive source are structured as one unit. This reduces the size and simplifies the structure of the fuel supplying system.

1 . A pump unit comprising: 
 a first pump, which has no expansion phase, wherein the first pump draws in and discharges fluid;    a second pump, which has an expansion phase, wherein the second pump is connected to the first pump for drawing in and discharging fluid that is discharged from the first pump; and    a single drive source for driving the first pump and the second pump.    
     
     
         2 . The pump unit according to  claim 1 , wherein the discharge capacity of the first pump is equal to or greater than the discharge capacity of the second pump.  
     
     
         3 . The pump unit according to  claim 1 , wherein the first pump, the second pump, and the drive source are coupled with one another to form a single unit.  
     
     
         4 . The pump unit according to  claim 3 , wherein the drive source is an electric motor, and wherein a housing of the electric motor, a housing of the first pump, and a housing of the second pump are coupled to one another.  
     
     
         5 . The pump unit according to  claim 1 , wherein the first pump and the second pump are driven by a common single drive shaft.  
     
     
         6 . The pump unit according to  claim 5 , wherein the drive shaft extends to the drive source to serve also as an output shaft of the drive source.  
     
     
         7 . The pump unit according to  claim 1  further comprising: 
 a communication passage for introducing fluid that is discharged from the first pump into the second pump; and  
 a relief valve for releasing excessive pressure from the communication passage.  
 
     
     
         8 . The pump unit according to  claim 7 , wherein the relief valve releases excessive pressure from the communication passage toward a section where the fluid is stored before being introduced into the first pump.  
     
     
         9 . The pump unit according to  claim 1 , wherein the second pump is a piston pump, the piston pump comprising: 
 a drive shaft;    a piston;    a housing, which defines a crank chamber;    a cam arranged in the crank chamber, wherein the cam converts the rotation of the drive shaft into the reciprocation of the piston; and    a bleed passage, which communicates the crank chamber with the outside of the housing.    
     
     
         10 . The pump unit according to  claim 9 , wherein the bleed passage communicates the crank chamber with a section where the fluid is stored before being introduced into the first pump.  
     
     
         11 . The pump unit according to  claim 9 , wherein the bleed passage extends upward from the crank chamber.  
     
     
         12 . The pump unit according to  claim 1 , wherein the first pump is a gear pump or a centrifugal pump.  
     
     
         13 . The pump unit according to  claim 1  further comprising a suction passage for introducing fluid into the first pump, wherein the suction passage is structured such that gas that is generated in the suction passage can ascend toward the upstream of the suction passage.  
     
     
         14 . A fluid supplying system comprising: 
 a tank for reserving fluid; and    a pump unit for transferring fluid from the tank, wherein the pump unit includes: 
 a first pump, which has no expansion phase, wherein the first pump draws in fluid from the tank and discharges the fluid;  
 a second pump, which has an expansion phase, wherein the second pump is connected to the first pump for drawing in and discharging fluid that is discharged from the first pump; and  
 a single drive source for driving the first pump and the second pump.  
   
     
     
         15 . The fluid supplying system according to  claim 14 , wherein the pump unit is attached to the tank such that substantially almost the entire pump unit is exposed outside the tank.  
     
     
         16 . The fluid supplying system according to  claim 14 , wherein the pump unit is accommodated in the tank.  
     
     
         17 . A fluid supplying system comprising: 
 a main tank for reserving fluid;    a sub-tank arranged separately from the main tank, wherein the sub-tank receives fluid from the main tank; and    a pump unit attached to the sub-tank, wherein the pump unit transfers fluid from the sub-tank, wherein the pump unit includes: 
 a first pump, which has no expansion phase, wherein the first pump draws in fluid from the sub-tank and discharges the fluid;  
 a second pump, which has an expansion phase, wherein the second pump is connected to the first pump for drawing in and discharging fluid that is discharged from the first pump; and  
 a single drive source for driving the first pump and the second pump.  
   
     
     
         18 . The fluid supplying system according to  claim 17 , wherein the first pump is located below an inner bottom surface of the main tank.  
     
     
         19 . The fluid supplying system according to  claim 17  further comprising a return pipe for returning vaporized fluid in the sub-tank into the main tank.  
     
     
         20 . The fluid supplying system according to  claim 17 , wherein the fluid is fuel for an internal combustion engine, the system further comprising: 
 a fuel injection device for injecting the fuel into the internal combustion engine; and    a feedback pipe, which connects the fuel injection device to the main tank, wherein the feedback pipe returns excessive fuel that is generated in the fuel injection device to the main tank.    
     
     
         21 . The fluid supplying system according to  claim 17 , wherein the fluid is fuel for an internal combustion engine, the system further comprising: 
 a fuel injection device for injecting fuel into the internal combustion engine; and    a feedback pipe, which connects the fuel injection device to the sub-tank, wherein the feedback pipe returns the excessive fuel generated in the fuel injection device to the sub-tank.