Patent Publication Number: US-7905711-B2

Title: Multiple pump unit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiple pump unit in which a plurality of pumps is arranged in series. 
     2. Background Art 
     A multiple pump unit in which a plurality of pumps is arranged in series is widely used as a hydraulic source for operating various actuators in a construction machine and the like. 
     Japanese Patent No. 3781899, for instance, proposes a multiple pump unit in which a piston pump, a trochoid pump, and a gear pump are coaxially arranged in series. 
     Specifically, the conventional multiple pump unit includes a pump shaft, a piston pump rotated about an axis line by the pump shaft, a housing main body having an opening that is sized to allow the piston pump to pass therethrough, a port block connected to the housing main body so as to close the opening with the piston pump accommodated in the housing main body, an auxiliary pump shaft connected to the pump shaft in a non-rotatable manner about an axis line, a trochoid pump accommodated in a concave portion formed in the port block and rotated by the auxiliary pump shaft, a gear pump rotated by the auxiliary pump shaft, and a gear pump case connected to the port block so as to surround the gear pump. 
     Such a multiple pump unit has an advantage that discharged fluids from the piston pump, the trochoid pump, and the gear pump can be independently used in various applications, but has several drawbacks. 
     For example, the number of pumps to be provided in the multiple pump unit and the number of discharge ports fluidly connected to the pumps functioning as the hydraulic source differ depending on the application to which the multiple pump unit is applied. 
     That is, in some cases, the piston pump, the trochoid pump and the gear pump all need to be provided, while in other cases, only the piston pump and the gear pump are sufficient to be provided depending on the application. 
     The number of actuators operated by hydraulic pressure from the trochoid pump also differs depending on the application. 
     Thus, the number of pumps to be provided and the preferred number of discharge ports for discharging hydraulic pressure from one pump to outside differ according to necessity and/or a specification, but the multiple pump unit described in the above patent document cannot correspond to such various specifications unless the port block itself is replaced. 
     Furthermore, there is no multiple pump unit, which includes the plurality of pumps, capable of enhancing piping workability of connecting conduits to suction fluid passages and discharge fluid passages of the plurality of pumps. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the conventional art, it is one object of the present invention to provide a multiple pump unit in which a first and a second pump are arranged in series along an axis line direction of a pump shaft, the multiple pump unit capable of easily changing specification to a mode in which the second pump is not provided and to a mode in which the number of discharge ports having the second pump as a hydraulic source is differed, while using a pump housing accommodating the first pump as it is. 
     It is another object of the present invention to provide a multiple pump unit, which includes the plurality of pumps, capable of enhancing piping workability of connecting conduits to suction fluid passages and discharge fluid passages of the plurality of pumps. 
     The present invention provides, in order to achieve the first object, a multiple pump unit including a pump shaft operatively connected to a driving power source, a first pump driven by the pump shaft, a pump housing for accommodating the first pump, and a second pump operatively driven by the pump shaft, the multiple pump unit further including a fluid passage block connected to one end surface in an axis line direction of the pump housing. One or both contacting surfaces of the pump housing and the fluid passage block is formed with a concave portion for accommodating the second pump. The pump housing is provided with a suction fluid passage having a first end opened to an outer surface to form a suction port, the suction fluid passage guiding hydraulic fluid, which has been introduced through the suction port, to a suction opening of the first pump, and a first pump discharge fluid passage having a proximal end fluidly connected to a discharge opening of the first pump and a distal end opened to an outer surface to faun a first pump discharge port. The fluid passage block is provided with a second pump discharge port having the second pump as a hydraulic source. 
     In the multiple pump unit according to the present invention, it is possible to easily change specification between one mode where the second pump  40  is provided and the other mode where the second pump is omitted. 
     Preferably, the fluid passage block may be provided with a plurality of the second pump discharge ports, and valves for controlling discharge states of the plurality of second pump discharge ports may be mounted to the fluid passage block. 
     More preferably, the plurality of second pump discharge ports may be provided on the same surface of the fluid passage block. 
     In one embodiment, the fluid passage block integrally includes a contacting portion contacting the pump housing and an extending portion extending radially outward from the contacting portion with the axis line of the pump shaft as the reference, and the valves are mounted to the extending portion. 
     In one embodiment, the fluid passage block preferably includes a valve block detachably connected to an end surface facing a direction parallel to the axis line of the pump shaft of the extending portion, and the valves are mounted to the valve block. 
     In another embodiment, the fluid passage block includes a fluid passage plate contacting the pump housing, and a valve block which is detachably connected to an end surface facing a direction orthogonal to the axis line of the pump shaft of the fluid passage plate and to which the valves are mounted. 
     In the above various configurations, the suction fluid passage is preferably configured to guide operation fluid, which has been sucked through the suction port, to a first suction opening on a side close to the first pump of the second pump as well as to the suction opening of the first pump. 
     Preferably, the multiple pump unit further includes a third pump arranged on a side opposite to the first pump in the axis line of the pump shaft with the second pump as a reference, the third pump being operatively driven by the pump shaft, and a third pump housing connected to an outer surface of the fluid passage block so as to surround the third pump. The suction fluid passage includes a third pump branched fluid passage for guiding hydraulic fluid, which has been introduced through the suction port, to a contacting surface with the fluid passage block. The third pump housing is provided with a third pump suction fluid passage having a first end opened to a contacting surface with the fluid passage block and a second end fluidly connected to a suction opening of the third pump, and a third pump discharge fluid passage having a first end fluidly connected to a discharge opening of the third pump and a second end opened to an outer surface to form a third pump discharge port. The fluid passage block is formed with a communication passage for fluidly connecting the third pump branched fluid passage to a second suction opening on a side opposite to the first suction opening in the axis line of the pump shaft of the second pump and the third pump suction fluid passage. 
     More preferably, the first pump discharge port, the second pump discharge port and the third pump discharge port are arranged on a same surface side of the multiple pump unit. 
     More preferably, at least a part of the concave portion is formed in the pump housing, and the first end of the third pump suction fluid passage is arranged so as to overlap at least one of the concave portion and the second end of the third pump branched fluid passage when seen along the axis line direction of the pump shaft. 
     Preferably, the first pump may include a cylinder block supported by the pump shaft in a relatively non-rotatable manner about the axis line, a plurality of pistons accommodated in the cylinder block in a slidable manner along the axis line, a movable swash plate capable of swinging about a swing axis orthogonal to the pump shaft so as to change sliding ranges of the plurality of pistons according to its tilted position about the swing axis, and a biasing member for biasing the movable swash plate towards a maximum tilted direction about the swing axis. The biasing member is accommodated in the pump housing so as to be substantially in parallel to the pump shaft with its distal end operatively engaged to the movable swash plate. The fluid passage block is provided with a manual operation member for changing a position of a proximal end of the biasing member. 
     More preferably, discharge pressure of the third pump acts on the movable swash plate so as to tilt the movable swash plate towards a neutral side about the swing axis against the biasing force of the biasing member. 
     Further, the present invention provides, in order to achieve another object, a multiple pump unit including a plurality of pumps directly or indirectly driven by a pump shaft that is operatively connected to a driving power source, the multiple pump unit further including a suction fluid passage having a first end opened to an outer surface to form a single suction port and second ends branched so as to be fluidly connected to suction openings of the plurality of pumps, respectively, and a plurality of discharge fluid passage having first ends respectively fluidly connected to discharge openings of the plurality of pumps and second ends opened to an outer surface to respectively form a plurality of discharge ports. The plurality of discharge ports face the same direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is an outline view of a multiple pump unit according to a first embodiment of the present invention. 
         FIG. 2  is a cross sectional view of the multiple pump unit shown in  FIG. 1 . 
         FIG. 3  is a cross sectional view taken along line of  FIG. 2 . 
         FIG. 4  is a hydraulic circuit view of the multiple pump unit shown in  FIGS. 1-3 . 
         FIG. 5  is an end view taken along line V-V of  FIG. 2 . 
         FIG. 6  is a cross sectional view taken along line VI-VI of  FIG. 2 . 
         FIG. 7  is a cross sectional view taken along line VII-VII of  FIG. 2 . 
         FIG. 8  is an end view taken along line VIII-VIII of  FIG. 2 . 
         FIG. 9  is an end view taken along line IX-IX of  FIG. 2 . 
         FIG. 10  is a cross sectional view of a multiple pump unit modified from the multiple pump unit according to the first embodiment. 
         FIG. 11  is a cross sectional view of a multiple pump unit according to a second embodiment of the present invention. 
         FIG. 12  is a cross sectional view of a multiple pump unit according to a third embodiment of the present invention. 
         FIG. 13  is a cross sectional view of a multiple pump unit according to a fourth embodiment of the present invention. 
         FIG. 14  is a cross sectional view of a multiple pump unit modified from the multiple pump unit according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     One embodiment of a multiple pump unit according to the present invention will now be described with reference to the accompanying drawings. 
     The multiple pump unit includes a plurality of pumps driven by a single drive shaft or a plurality of drive shafts arranged coaxially to each other, and is configured so as to independently supply hydraulic pressure from the plurality of pumps to hydraulic actuators. 
       FIG. 1  shows an outline view of a multiple pump unit  1  according to the present embodiment. 
       FIGS. 2 and 3  show cross sectional views of the multiple pump unit  1 ,  FIG. 3  showing the cross section taken along line of  FIG. 2 . 
       FIG. 4  shows a hydraulic circuit view of the multiple pump unit  1 . 
     In the present embodiment, the multiple pump unit includes a first to a third pumps. 
     Specifically, as shown in  FIGS. 1 to 4 , the multiple pump unit  1  includes a pump shaft  10  operatively connected to a driving power source  2  (see  FIG. 4 ), a piston pump  20  rotatably driven by the pump shaft  10 , the piston pump  20  serving as the first pump, a pump housing  30  for accommodating the piston pump  20 , a trochoid pump  40  serving as the second pump, a fluid passage block  50  connected to the pump housing  30 , a gear pump  60  serving as the third pump, and a gear pump case  70  connected to the fluid passage block  50  so as to surround the gear pump  60 . 
     As shown in  FIGS. 1 to 3 , the pump shaft  10  is supported by the pump housing  30  in a rotatable manner about the axis line with a first end  11  that forms an input end extending outward from the pump housing  30 . 
     In the present embodiment, the first end  11  of the pump shaft  10  is connected to an output shaft  2   a  of the driving power source  2  by way of a flywheel  3  and a damper  4  (see  FIG. 1 ). 
     Further, in the present embodiment, the pump shaft  10  has a second end  12  on a side opposite to the first end  11 , the second end  12  also extending outward from the pump housing  30  (see  FIGS. 2 and 3 ). 
     The pump housing  30  includes a housing main body  31  provided with an opening  31   c , which is sized to allow the piston pump  20  to pass therethrough, at one end side in the axis line direction, and a port block  35  connected to the housing main body  31  so as to close the opening  31   c.    
     The housing main body  31  has a first end wall  31   a  extending in a direction orthogonal to the pump shaft  10  and configured to allow the first end  11  of the pump shaft  10  to pass therethrough, and a peripheral wall  31   b  extending from a peripheral edge of the first end wall  31   a  to the one end side in the axis line direction, the peripheral wall  31   b  having the opening  31   c  on the one end side in the axis line direction. 
     In the present embodiment, as shown in  FIG. 1 , the first end wall  31   a  of the housing main body  31  is connected to a flywheel housing  5  supported by the driving power source  2  so as to surround the flywheel  3 , and thus the multiple pump unit  1  is supported by the driving power source  2 . 
     The port block  35  is removably connected to the housing main body  31  so as to close the opening  31   c  to form a piston pump accommodating space for accommodating the piston pump  20  in cooperation with the housing main body  31 . 
     The pump housing  30 A is formed with fluid passages including supply/discharge fluid passages of the piston pump  20 . Details of the fluid passages will be described later. 
     As shown in  FIGS. 2 and 3 , the piston pump  20  includes a pump main body  210  rotatably driven by the pump shaft  10 , and a plate  220  formed with a suction opening and a discharge opening of the pump main body  210 . 
     The pump main body  210  includes a cylinder block  211  supported in a relatively non-rotatable manner by the pump shaft  10 , and a plurality of pistons  215  accommodated in the cylinder block  211  in a slidable manner along the axis line direction. 
     The cylinder block  211  has a plurality of cylinder chambers opened to an end surface on a side opposite to the port block  35 , and the plurality of pistons  215  is respectively accommodated in the plurality of cylinder chambers in a slidable manner along the axis line direction. 
     Furthermore, the cylinder block  211  is formed with a plurality of communication ports, which are respectively fluidly connected to the plurality of cylinder chambers, at an end surface facing to the port block  35 . 
       FIG. 5  shows an end view of the plate  220  taken along line V-V of  FIG. 2 . 
     As shown in  FIG. 5 , the plate  220  has a single suction opening  221 , and a plurality of a first and a second discharge openings  225   a ,  225   b  in the present embodiment. 
     In the present embodiment, the piston pump  20  can discharge fluid, which has been sucked in through the single suction opening  221 , to two systems through the first and second discharge openings  225   a ,  225   b  by including the plate  220 . 
     As shown in  FIGS. 2 and 5 , the plate  220  is formed with a concave portion  229  opened radially outward, and the plate  220  is fixed to the port block  35  in a non-rotatable manner about the axis line by engaging a pin  228  into the concave portion  229 . 
     In the present embodiment, the piston pump  20  is a variable displacement type in which supply and discharge fluid amounts of the pump main body  210  can be changed. 
     Specifically, the piston pump  20  has a movable swash plate  230  defining sliding ranges of the plurality of pistons  215 , as shown in  FIGS. 2 to 4 . 
     The movable swash plate  230  can swing about a swing axis line orthogonal to the pump shaft  10  while directly or indirectly contacting free ends of the plurality of pistons  215 , so that the sliding ranges of the plurality of pistons  215  can be changed according to a tilted position about the swing axis line. 
     In the present embodiment, the movable swash plate  230  engages the free ends of the plurality of pistons  215  by way of shoes. 
     Furthermore, the piston pump  20  includes a biasing member  240  for biasing the movable swash plate  230  towards a maximum tilted direction about the swing axis line in the present embodiment, as shown in  FIGS. 2 ,  4 , and  5 . 
     Specifically, as shown in  FIG. 2 , the movable swash plate  230  has an opening  231  through which the pump shaft  10  is inserted, a piston contacting region  232  extending radially outward from the opening  231  and engaged directly or indirectly to the plurality of pistons  215 , and a first extending region  233  extending radially outward from the piston contacting region  232 . 
     The biasing member  240  is accommodated in the pump housing  30  so as to be substantially in parallel to the pump shaft  10  with its distal end directly or indirectly engaged to the first extending region  233 . 
     In the present embodiment, the piston pump  20  is configured such that an initial biasing force of the biasing member  240  can be adjusted by manual operation. 
     Specifically, a coil spring is used as the biasing member  240  in the present embodiment, as shown in  FIG. 2 . 
     The coil spring has a distal end engaged to the first extending region  233  of the movable swash plate  230  by way of a first spring receiving member  241 , and a proximal end engaged to a second spring receiving member  242  that is accommodated liquid tightly and slidably in the axis line direction within a pass-through hole formed in the port block  35 . 
     The fluid passage block  50  connected to the port block  35  is provided with a manual operation member  245 , which has a distal end engaged to the second spring receiving member  242  and a proximal end extending outward, at a region corresponding to the pass-through hole. 
     The manual operation member  245  is capable of changing an axial position thereof, and an axial position of the second spring receiving member  242  can be changed by changing the axial position of the manual operation member  245 , whereby the initial biasing force of the coil spring could be adjusted. 
     A bolt and a nut are used as the manual operation member  245  in the present embodiment. 
     The swing axis line of the movable swash plate  230  is displaced towards a side closer to the biasing member  240  with the axis line of the pump shaft  10  as a reference. 
     According to such a configuration, when discharge pressure of the pump main body  210  rises as rotation number of the pump shaft  10  increases, the movable swash plate  230  accordingly is tilted towards a neutral side against the biasing force of the biasing member  240  by way of the plurality of pistons  215 . 
     Therefore, the discharge pressure of the pump main body  210  can be effectively prevented from rising to an unnecessary pressure due to increase in rotation number of the pump shaft  10 . 
     The trochoid pump  40  is arranged coaxially with piston pump  20  so as to be operatively driven by the pump shaft  10 . 
     Specifically, the trochoid pump  40  is operatively driven by the pump shaft  10  in a state of being accommodated in a concave portion  45  formed in one or both contacting surfaces of the pump housing  30  and the fluid passage block  50 . 
     In the present embodiment, the fluid passage block  50  is connected to the port block  35  as described above. In this embodiment, the concave portion  45  is formed in one or both contacting surfaces of the port block  35  and the fluid passage block  50 . 
     As shown in  FIGS. 2 and 3 , the concave portion  45  is formed in the port block  35  in the present embodiment, and the trochoid pump  40  is driven by the pump shaft  10  in a state of being accommodated in the concave portion  45  formed in the port block  35 . 
     The fluid passage block  50  is removably connected to the port block  35  so as to close in a liquid-tight manner the concave portion  45 , as shown in  FIGS. 2 and 3 . 
     A detailed configuration of the fluid passage block  50  will be described later. 
     The gear pump  60  is arranged coaxially with the piston pump  20  and the trochoid pump  40  so as to be operatively driven by the pump shaft  10 . 
     As shown in  FIGS. 2 and 3 , in the present embodiment, a rotation shaft  65  is connected to the second end  12  of the pump shaft  10  in a relatively non-rotatable manner about the axis line by way of a coupling  66 . 
     The gear pump  60  is driven by the rotation shaft  65 . 
     The gear pump case  70  is removably connected to an end surface on a side opposite to the port block  35  of the fluid passage block  50  so as to surround the gear pump  60 . 
     The fluid passage formed in the pump housing  30  will now be described below. 
     The pump housing  30  is provided with a suction fluid passage  400  having a first end opened to an outer surface to form a suction port  400 P, and a piston pump discharge fluid passage  410  having a proximal end fluidly connected to the discharge opening of the piston pump  20  and a distal end opened to the outer surface to form a piston pump discharge port  410 P. 
     As shown in  FIGS. 3 and 5 , the suction fluid passage  400  and the piston pump discharge fluid passage  410  are formed in the port block  35  in the present embodiment. 
     As shown in  FIG. 3 , the suction fluid passage  400  is configured to guide hydraulic fluid, which has been introduced through the suction port  400 P, to the suction opening  221  of the piston pump  20 , and also guides the hydraulic fluid to a suction opening  41  of the trochoid pump  40  and a suction opening  61  of the gear pump  60 . 
     Specifically, the suction fluid passage  400  has a second end branched into three fluid passages of a piston pump suction fluid passage  402 , a trochoid pump suction fluid passage  403 , and a gear pump branched fluid passage  404 , as shown in  FIG. 3 . 
     That is, the suction fluid passage  400  includes a main fluid passage  401  having a first end opened to the outer surface of the port block  35  to form the suction port  400 P, and the piston pump suction fluid passage  402 , the trochoid pump suction fluid passage  403  and the gear pump branched fluid passage  404  each having a proximal end fluidly connected to the main fluid passage  401 . 
     The main fluid passage  401  extends in a direction substantially orthogonal to the pump shaft  10 . 
     The piston pump suction fluid passage  402  extends in a direction substantially orthogonal to the main fluid passage  401  in a state of having the proximal end fluidly connected to the main fluid passage  401  and a distal end fluidly connected to the suction opening  221  of the plate  220 . 
     The trochoid pump suction fluid passage  403  extends in a direction identical to the main fluid passage  401  in a state of having the proximal end fluidly connected to the main fluid passage  401  and a distal end fluidly connected to the first suction opening  41  that is provided in an end surface on a side close to the piston pump  20  of the trochoid pump  40 . 
     The gear pump branched fluid passage  404  extends in a direction substantially orthogonal to the main fluid passage  401  in a state of having the proximal end fluidly connected to the main fluid passage  401  and a distal end opened to a contacting surface with the fluid passage block  50 . 
     As described above, the piston pump  20  has first and second discharge openings  225   a ,  225   b.    
     Therefore, the piston discharge fluid passage  410  includes a piston pump first discharge fluid passage  411  having a proximal end fluidly connected to the first discharge opening  225   a  and a distal end opened to an outer surface to form a piston pump first discharge port  411 P, and a piston pump second discharge fluid passage  412  having a proximal end fluidly connected to the second discharge opening  225   b  and a distal end opened to an outer surface to form a piston pump second discharge port  412 P, as shown in  FIGS. 4 and 5 . 
     The detailed configuration of the fluid passage block  50  will now be described. 
       FIGS. 6 and 7  show cross sectional views of the fluid passage block  50  taken respectively along line VI-VI and line VII-VII of  FIG. 2 . 
     As shown in  FIGS. 3 and 6 , the fluid passage block  50  is formed with a trochoid pump discharge fluid passage  420  having a proximal end fluidly connected to a discharge opening  43  of the trochoid pump  40  and a distal end opened to an outer surface to form a trochoid pump discharge port  420 P (see  FIGS. 2 and 4 ). 
     As described above, in the present embodiment, the trochoid pump  40  is accommodated in the concave portion  45  formed in one or both contacting surfaces (the contacting surface with the fluid passage block  50  of the port block  35  in the illustrated embodiment) of the pump housing  30  (the port block  35  in the illustrated embodiment) and the fluid passage block  50 , the fluid passage block  50  is connected to the pump housing  30  so as to close in a liquid-tight manner the concave portion  45 , and the fluid passage block  50  is formed with the trochoid pump discharge port  420 P fluidly connected to the trochoid pump  40  functioning as the hydraulic source. 
     According to such a configuration, it is possible to change specification from one mode where the trochoid pump  40  is provided to the other mode where the trochoid pump  40  is omitted by simply replacing the fluid passage block  50  with a blocking plate (not shown) for closing in a liquid-tight manner the concave portion  45  while using the pump housing  30  as it is. 
     Therefore, pump units corresponding to various specifications could be easily obtained while using common components as much as possible. 
     Furthermore, in the present embodiment, as described above, the trochoid pump suction fluid passage  403  is branched from the main fluid passage  401  formed in the pump housing  30  (the port block  35  in the illustrated embodiment) along with the piston pump suction fluid passage  402 . 
     Therefore, it is possible to change specification from the one mode where the trochoid pump  40  is provided to the other mode where the trochoid pump  40  is not provided by simply replacing the fluid passage block  50  with the blocking plate without changing suction-side conduits fluidly connected to the suction port  400 P. 
     Moreover, in the present embodiment, valves  431 ,  432  for controlling a discharge state of the trochoid pump discharge port  420 P are mounted to the fluid passage block  50 , as shown in  FIGS. 1 ,  2 , and  4 . 
     Specifically, in the present embodiment, the fluid passage block  50  includes a fluid passage plate  51  removably connected to the pump housing  30 , and a valve block  55  removably connected to the fluid passage plate  51 , as shown in  FIGS. 1 and 2 . 
       FIGS. 8 and 9  show end views taken respectively along line VIII-VIII and line IX-IX of  FIG. 2 . 
     As shown in  FIGS. 1 ,  2 , and  6  to  8 , the fluid passage plate  51  has a contacting portion  52  contacting the pump housing  30 , and an extending portion  53  extending radially outward from the contacting portion  52  with the axis line of the pump shaft  10  as the reference. 
     The valve block  55  is connected to the extending portion  53 , as shown in  FIGS. 1 and 2 . 
     Preferably, the valve block  55  is connected to an end surface identical to an end surface contacting the pump housing  30 , out of end surfaces of the fluid passage plate  51 . 
     According to such a configuration, the valve block  55  can be arranged in a dead space defined by the flywheel housing  5 , the pump housing  30 , and the fluid passage plate  51  (see  FIG. 1 ). 
     The fluid passage plate  51 A is formed with a fluid passage plate-side discharge fluid passage  420   a  forming a part of the trochoid pump discharge fluid passage  420 . 
     The fluid passage plate-side discharge fluid passage  420   a  has a proximal end fluidly connected to the discharge opening  43  of the trochoid pump  40  and a distal end opened to a contacting surface with the valve block  55 , as shown in  FIG. 6 . 
     As shown in  FIGS. 1 and 2 , in the present embodiment, the valve block  55  is provided with trochoid first to third discharge ports  421 P to  423 P as the trochoid pump discharge port  420 P. 
     Specifically, as shown in  FIG. 4 , the valve block  55  is provided with a first branched fluid passage  421   a  having a first end opened to a contacting surface with the fluid passage plate  51  to fluidly connect to the fluid passage plate-side discharge fluid passage  420   a , a first discharge fluid passage  421   b  having a first end opened to an outer surface to form the first discharge port  421 P, a first switching valve  431  for selectively communicating or shutting off between the first branched fluid passage  421   a  and the first discharge fluid passage  421   b , a second branched fluid passage  422   a  having a first end fluidly connected to the first branched fluid passage  421   a  by way of a check valve  435 , a second discharge fluid passage  422   b  having a first end opened to the outer surface to form the second discharge port  422 P, a second switching valve  432  for selectively communicating or shutting off between the second branched fluid passage  422   a  and the second discharge fluid passage  422   b , and a third branched fluid passage  423   a  having a first end fluidly connected to the second branched fluid passage  422   a  and a second end opened to the outer surface to form the third discharge port  423 P. 
     In such a configuration, the first branched fluid passage  421   a , the first discharge fluid passage  421   b , the second branched fluid passage  422   a , the second discharge fluid passage  422   b  and the third branched fluid passage  423   a  faun the trochoid pump discharge fluid passage  420  together with the fluid passage plate-side discharge fluid passage  420   a.    
     The first to third discharge ports  421 P,  422 P and  423 P are preferably provided on a same surface (see  FIG. 1 ). 
     According to such a configuration, piping workability of connecting conduits to the first to third discharge ports  421 P,  422 P, and  423 P can be improved. 
     Furthermore, a relief valve  438  for setting hydraulic pressure of the trochoid pump discharge fluid passage  420  is mounted to the valve block  55  in the present embodiment. 
     Specifically, as shown in  FIG. 4 , the valve block  55  is formed with a hydraulic pressure setting fluid passage  425  having a first end fluidly connected to the first branched fluid passage  421   a , and the relief valve  438  is interposed in the hydraulic pressure setting fluid passage  425 . 
     A second end of the hydraulic pressure setting fluid passage  425  is fluidly connected to a valve block-side return fluid passage  440  formed in the valve block  55  so as to open to a contacting surface with the fluid passage plate  51 . 
     The valve block-side return fluid passage  440  is fluidly connected to the suction openings of the trochoid pump  40  and the gear pump  60  by way of a fluid passage plate-side return fluid passage  445  and a communication fluid passage  450  (see  FIGS. 6 and 7 ) formed in the fluid passage plate  51 . 
     A detailed configuration of the communication fluid passage  450  will be described later. 
     In the present embodiment, the first switching valve  431  is configured so as to take a hydraulic fluid discharging state of fluidly connecting the first branched fluid passage  421   a  to the first discharge fluid passage  421   b  to discharge hydraulic fluid through the first discharge port  421 P, and a hydraulic fluid returning state of returning return fluid, which has been brought in through the first discharge port  421 P, to the valve block-side return fluid passage  440 . 
     Similarly, the second switching valve  432  is configured to take a hydraulic fluid discharging state of fluidly connecting the second branched fluid passage  422   a  to the second discharge fluid passage  421   b  to discharge hydraulic fluid through the second discharge port  422 P, and a hydraulic fluid returning state of returning return fluid, which has been brought in through the second discharge port  422 P, to the valve block-side return fluid passage  440 . 
     Specifically, the valve block  55  is further formed with a first return fluid passage  441  having a first end fluidly connected to a primary side of the first switching valve  431  and a second end fluidly connected to the valve block-side return fluid passage  440 , and a second return fluid passage  442  having a first end fluidly connected to a primary side of the second switching valve  432  and a second end fluidly connected to the valve block-side return fluid passage  440 . 
     The first switching valve  431  is configured so as to selectively take a discharging position of fluidly connecting the first branched fluid passage  421   a  to the first discharge fluid passage  421   b  and blocking the first end of the first return fluid passage  441 , and a returning position of blocking a second end of the first branched fluid passage  421   a  and fluidly connecting the first discharge fluid passage  441  to the first return fluid passage  421   b.    
     Similarly, the second switching valve  432  is configured so as to selectively take a discharging position of fluidly connecting the second branched fluid passage  422   a  to the second discharge fluid passage  422   b  and blocking the first end of the second return fluid passage  442 , and a returning position of blocking a second end of the second branched fluid passage  422   a  and fluidly connecting the second discharge fluid passage  442   b  to the second return fluid passage  442 . 
     In the present embodiment, the valve block  55  is further formed with a fourth branched fluid passage  429  having a first end fluidly connected to the first branched fluid passage  421   a  and a second end opened to an outer surface to form a gauge port  429 P, as shown in  FIGS. 4 and 9 . 
     The gauge port  429 P may be used to measure discharge pressure of the trochoid pump  40 . 
     In the present embodiment, the fluid passage block  50  is formed by the fluid passage plate  51  and the valve block  55  that are separate bodies from each other, and the valves  431 ,  432  are attached to the valve block  55 , as described above. Alternatively, a fluid passage block  50 ′ integrally including the fluid passage plate  51  and the valve block  55  may be provide, and the valves  431 ,  432  may be attached to the single fluid passage block  50 ′, as shown in  FIG. 10 . 
     The communication fluid passage  450  formed in the fluid passage plate  51  will now be described. 
     As shown in  FIG. 3 , the communication fluid passage  450  has a first end opened to a contacting surface with the port block  35  so as to be fluidly connected to a distal end of the gear pump branched fluid passage  404 . 
     A second end of the communication fluid passage  450  is opened to a contacting surface with the gear pump case  70  while being fluidly connected to a second suction opening  42  provided on a side opposite to the first suction opening  41  in the trochoid pump  40 . 
     That is, the communication fluid passage  450  is configured so as to guide fluid, which has been sent from the gear pump branched fluid passage  404 , to the second suction opening  42  of the trochoid pump  40  and the suction opening  61  of the gear pump  60 . 
     The fluid passage plate-side return fluid passage  445  has a first end opened to a contacting surface with the valve block  55  so as to be fluidly connected to the valve block-side return fluid passage  440 , and a second end fluidly connected to the communication fluid passage  450  (see  FIGS. 6 and 7 ). 
     The fluid passages formed in the gear pump case  70  will now be described. 
     As shown in  FIGS. 3 and 4 , the gear pump case  70  is formed with a gear pump suction fluid passage  461  having a first end opened to a contacting surface with the fluid passage block  50  so as to be fluidly connected to the communication fluid passage  450  and a second end fluidly connected to the suction opening  61  of the gear pump  60 , and a gear pump discharge fluid passage  462  having a first end opened to an outer surface to form a gear pump discharge port  460 P. 
     In the present embodiment, at least a part of the concave portion  45  for accommodating the trochoid pump  40  is formed in the pump housing  30 , as described above. 
     In such an embodiment, the first end of the third pump suction fluid passage  461  is preferably arranged so as to overlap at least one of the concave portion  45  and the second end of the third pump branched fluid passage  404  when seen along the axis line direction of the pump shaft  10 . 
     According to such a configuration, in a case where the trochoid pump  40  is not necessary, it is possible to easily change specification to a mode where only the piston pump  20  and the gear pump  60  are provided by simply removing the trochoid pump  40  and the fluid passage block  50  and then connecting the gear pump case  70  to the pump housing  30 . 
     All the discharge ports including the piston pump first and second discharge ports  411 P,  412 P, the trochoid pump first to third discharge ports  421 P,  422 P,  423 P and the gear pump discharge port  460 P are preferably provided on a same side surface of the multiple pump unit  1  (see  FIG. 1 ). 
     According to such a configuration, piping workability in connecting external conduits to the discharge ports can be enhanced and an efficient layout of the external conduits can be obtained. 
     Furthermore, the movable swash plate  230  biased towards a maximum tilted direction by the biasing member  240  is configured so as to be tilted towards a neutral side according to rise in discharge pressure of the gear pump  60  as well as rise in discharge pressure of the piston pump  20  in the present embodiment. 
     That is, the multiple pump unit  1  has a neutral-side return line  470  for causing discharge pressure of the gear pump  60  to act on the movable swash plate  230  in addition to the above configurations as shown in  FIG. 4 . 
     Specifically, the movable swash plate  230  has a second extending region  234  on a side opposite to the first extending region  233  with the pump shaft  10  as the reference, as shown in  FIG. 2 . 
     As shown in  FIGS. 2 and 3 , the neutral-side return line  470  includes a gear pump case-side neutral return fluid passage  471  formed in the gear pump case  70  so as to have a proximal end fluidly connected to the gear pump discharge fluid passage  462  and a distal end opened to a contacting surface with the fluid passage block  50 , a fluid passage block-side neutral return fluid passage  472  formed in the fluid passage block  50  so as to have a proximal end opened to a contacting surface with the gear pump case  70  to be fluidly connected to the pump case-side neutral return fluid passage  471  and a distal end opened to a contacting surface with the port block  35 , a port block-side neutral return fluid passage  473  formed in the port block  35  so as to have a proximal end opened to a contacting surface with the fluid passage block  50  to be fluidly connected to the fluid passage block-side neutral return fluid passage  472  and a distal end opened into an internal space of the pump housing  30 , a conduit member  474  including a fluid passage that has an proximal end fluidly connected to the port block-side neutral return fluid passage  473  and a distal end opened towards the second extending region  234 , and a pushing member  475  accommodated in the fluid passage of the conduit member  474  in a slidable manner along the axis line direction with its distal end engaged to the second extending region  234  of the movable swash plate  230 . 
     A plug with throttle hole  476  is interposed in the fluid passage of the piping member  474 . 
     Second Embodiment 
     Another embodiment of the multiple pump unit according to the present invention will now be described with reference to the attached drawings. 
       FIG. 11  is a cross sectional view, which corresponds to  FIG. 2 , of a multiple pump unit  1 B according to the present embodiment. 
     In the drawing, the same reference characters are denoted for the same members as in the first embodiment, and the detailed explanations thereof are omitted. 
     The multiple pump unit  1 B according to the present embodiment includes a fluid passage block  50 B in place of the fluid passage block  50  with respect to the multiple pump unit  1  according to the first embodiment, as shown in  FIG. 11 . 
     The fluid passage block  50 B includes a fluid passage plate  51 B having a substantially same configuration as the contacting portion  52  of the fluid passage plate  51 , and a valve block  55 B having a substantially same configuration as the valve block  55 , the valve block  55 B being detachably connected to an end surface, which faces in a direction orthogonal to the axial line direction of the pump shaft  10 , of the fluid passage plate  51 B. 
     In the thus configured multiple pump unit  1 B, it is also possible to change specification from one mode where the trochoid pump  40  is provided to the other mode where the trochoid pump  40  is omitted by simply replacing the fluid passage block  50 B with the blocking plate (not shown) for liquid-tightly closing the concave portion  45  while using the pump housing  30  as it is. 
     Therefore, pump units corresponding to various specifications could be easily obtained while using common components as much as possible. 
     Further, as similarly to the first embodiment, the multiple pump unit  1 B may be configured so that the piston pump  20 , the trochoid pump  40  and the gear pump  60  suck the operation fluid through the common suction fluid passage  400 , and furthermore all the discharge ports including the piston pump first and second discharge ports  411 P,  412 P, the trochoid pump first to third discharge ports  421 P,  422 P,  423 P and the gear pump discharge port  460 P face towards the same direction as shown in  FIG. 11 . 
     According to such a configuration, efficiency of piping workability in connecting external conduits to the suction fluid passage and the discharge ports can be improved, and an efficient layout of the external conduits can be obtained. 
     Furthermore, as similarly to the first embodiment, the multiple pump unit  1 B is configured so that the valve block  55 B in which the trochoid pump first to third discharge ports  421 P,  422 P,  423 P are provided and to which the valves  431 ,  432  are mounted is detachably connected to the fluid passage plate  51 B. 
     Therefore, it is possible to easily change the number of the second pump discharge port by replacing the fluid passage block without changing the other components. 
     Third Embodiment 
     Still another embodiment of the multiple pump unit according to the present invention will now be described with reference to the attached drawings. 
       FIG. 12  is a cross sectional view, which corresponds to  FIG. 2 , of a multiple pump unit  1 C according to the present embodiment. 
     In the drawing, the same reference characters are denoted for the same members as in the first and second embodiments, and the detailed explanations thereof are omitted. 
     The multiple pump unit  1 C according to the present embodiment includes a fluid passage block  50 C in place of the fluid passage block  50  with respect to the multiple pump unit  1  according to the first embodiment, as shown in  FIG. 12 . 
     The fluid passage block  50 C includes a fluid passage plate  51 C detachably connected to the pump housing  30 , and a valve block  55 C in which the trochoid pump first to third discharge ports  421 P,  422 P,  423 P are provided and to which the valves  431 ,  432  are mounted. 
     The fluid passage plate  51 C is detachably connected to the pump housing  30  so as to accommodate the trochoid pump  40  between the fluid passage plate  51 C and the pump housing  30 , as similarly to the above embodiments. 
     In the present embodiment, the fluid passage plate  51 C has a shape corresponding to the pump housing  30  when seen along the axis line direction of the pump shaft  10 . 
     The valve block  55 C is detachably connected to an end surface on a side opposite to the fluid passage plate  51 C of the gear pump case  70 . 
     In the present embodiment, the trochoid pump discharge fluid passage  420  is foamed so as to extend over the fluid passage plate  51 C, the gear pump case  70  and the valve block  55 C. 
     In the thus configured multiple pump unit  1 C, it is also possible to change specification from one mode where the trochoid pump  40  is provided to the other mode where the trochoid pump  40  is omitted by simply replacing the fluid passage plate  51 C with the blocking plate (not shown) for liquid-tightly closing the concave portion  45  while using the pump housing  30  as it is. 
     Therefore, pump units corresponding to various specifications could be easily obtained while using common components as much as possible. 
     Further, as similarly to the first and second embodiments, the multiple pump unit  1 C may be configured so that the piston pump  20 , the trochoid pump  40  and the gear pump  60  suck the operation fluid through the common suction fluid passage  400 , and furthermore all the discharge ports including the piston pump first and second discharge ports  411 P,  412 P, the trochoid pump first to third discharge ports  421 P,  422 P,  423 P and the gear pump discharge port  460 P face towards the same direction as shown in  FIG. 12 . 
     According to such a configuration, efficiency of piping workability in connecting external conduits to the suction fluid passage and the discharge ports can be improved, and an efficient layout of the external conduits can be obtained. 
     Furthermore, the multiple pump unit  1 C is configured so that the valve block  55 C in which the trochoid pump first to third discharge ports  421 P,  422 P,  423 P are provided and to which the valves  431 ,  432  are mounted is detachably connected to the gear pump case  70 . 
     Therefore, it is possible to easily change the number of the trochoid pump discharge ports only by replacing the valve block  55 C. 
     Fourth Embodiment 
     Still another embodiment of the multiple pump unit according to the present invention will now be described with reference to the attached drawings. 
       FIG. 13  is a cross sectional view, which corresponds to  FIG. 2 , of a multiple pump unit  1 D according to the present embodiment. 
     In the drawing, the same reference characters are denoted for the same members as in the first to third embodiments, and the detailed explanations thereof are omitted. 
     The multiple pump unit  1 D is different from the multiple pump units  1 - 1 C according to the first to third embodiments in that the trochoid pump first to third discharge ports  421 P,  422 P,  423 P are provided in a pump housing  30 D for accommodating the piston pump  20 . 
     Specifically, the multiple pump unit  1 D includes the pump housing  30 D in place of the pump housing  30  and a fluid passage block  50 D in place of the fluid passage block  50  with respect to the multiple pump unit  1  according to the first embodiment. 
     As shown in  FIG. 13 , the pump housing  30 D includes the housing main body  31 , and a port block  35 D detachably connected to the housing main body  31  so as to close the opening  31   c  of the housing main body  31 . 
     The port block  35 D includes a contacting portion  36 D contacting the housing main body  31  while closing the opening  31   c , and an extending portion  37 D extending radially outward from the contacting portion  36 D with the axis line of the pump shaft  10  as the reference. 
     The port block  35 D is formed with the trochoid pump discharge fluid passage  420  in addition to the suction fluid passage  400  and the piston pump discharge fluid passage  410 . 
     The trochoid pump discharge fluid passage  420  has a proximal end fluidly connected to the discharge opening of the trochoid pump  40  that is accommodated between the contacting portion  36 D and the fluid passage block  50 D, and a distal end opened to an outer surface of the extending portion  37 D to form the trochoid pump discharge port  420 P. 
     Further, in the present embodiment, the valves  431 ,  432  are mounted on the extending portion  37 D as shown in  FIG. 13 . 
     The fluid passage block  50 D includes a fluid passage plate  51 D detachably connected to the pump housing  30 D. 
     The fluid passage plate  51 D is detachably connected to the port block  35 D while accommodating the trochoid pump  40  between the fluid passage plate  51 D and the port block  35 D. 
     As similarly to the first and second embodiments, the multiple pump unit  1 D is configured so that the piston pump  20 , the trochoid pump  40  and the gear pump  60  suck the operation fluid through the common suction fluid passage  400 , and all the discharge ports including the piston pump first and second discharge ports  411 P,  412 P, the trochoid pump first to third discharge ports  421 P,  422 P,  423 P and the gear pump discharge port  460 P face towards the same direction. 
     Therefore, efficiency of piping workability in connecting external conduits to the suction fluid passage and the discharge ports can be improved, and an efficient layout of the external conduits can be obtained. 
     In the present embodiment, the trochoid pump first to third discharge ports  421 P,  422 P,  423 P are provided in the port block  35 D. Alternatively, the trochoid pump first to third discharge ports  421 P,  422 P, and  423 P may be provided in the housing main body  31 D, as shown in  FIG. 14 . 
     This specification is by no means intended to restrict the present invention to the preferred embodiments or modified embodiments set forth therein. Various modifications to the multiple pump unit may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.