Abstract:
A plunger pump, includes: a plunger pump unit including a pump chamber and a plunger for pressing a hydraulic fluid in the pump chamber to perform a discharging operation of the hydraulic fluid; a motor; and a cam portion driven by the motor to rotate and press the plunger. The cam portion has at least two discharge regions for pressing the plunger and a suction region formed between the discharge region. The plunger performs the discharging operation two times or more by one rotation of the cam portion.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a plunger pump activated by a motor. 
   2. Background Art 
   Hitherto, as an automobile brake mechanism, an antilock brake mechanism (so-called ABS) is known. The antilock brake mechanism realizes stable braking by, for example, controlling a fluid pressure of a hydraulic fluid supplied to a brake at the time of braking on a slippery road surface. The antilock brake mechanism drives, in order to control the fluid pressure of a hydraulic fluid, a plunger pump by rotation of an electric motor (see JP-A-2000-179449, for example). 
   Such an antilock brake mechanism includes an electronic control unit and a fluid-pressure control unit. The electronic control unit controls operation of various solenoid valves of the fluid-pressure control unit and the electric motor based on information from various sensor systems, for example, a wheel speed sensor. An eccentric shaft portion is provided in a rotating shaft of the electric motor, and on the outer circumference of the eccentric shaft portion, a ball bearing is fitted as a drive member. By urging a plunger by a spring member so as to be always brought in contact with this ball bearing and turning the rotating shaft, the plunger is reciprocated to discharge a hydraulic fluid so as to generate a fluid pressure. 
   However, in such a plunger pump, a further improvement has been demanded in electric motor vibration due to the eccentric shaft portion and operation noise due to a pulsation of the hydraulic fluid discharged from the plunger pump. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a plunger pump wherein vibration of the electric motor is reduced and operation noise due to a pulsation of a hydraulic fluid discharged from the plunger pump is reduced. 
   The invention provides a plunger pump, including: a plunger pump unit including a pump chamber and a plunger for pressing a hydraulic fluid in the pump chamber to perform a discharging operation of the hydraulic fluid; a motor; and a cam portion driven by the motor to rotate and press the plunger; wherein the cam portion has at least two discharge regions for pressing the plunger and a suction region formed between the discharge region; and the plunger performs the discharging operation two times or more within one revolution of the cam portion. 
   According to the invention, a rotating cam portion is provided in place of an eccentric shaft portion having a discharge region at one position as in the related art, and the cam portion has two or more discharge regions. Therefore, vibration due to a motor rotation can be reduced, and pulsation due to a discharge can be dispersed. In addition, since two or more hydraulic fluid discharges can be carried out by one rotation of the cam portion, the discharging amount per each discharge can be reduced, and as a result, the motor vibration and pulsation due to a discharge of the hydraulic fluid can be reduced. Furthermore, if the discharging amount per each discharge is set equal, a discharging amount equivalent to that of the prior art can be achieved even when the rotation speed of the cam portion is reduced, therefore, reduction in the vibration and reduction in the noise thereby can be realized by a reduction in the rotation speed of the motor. 
   Preferably, the cam portion has an approximately triangular cross section in which the discharge regions are formed at three positions. 
   According to the invention, vibration due to a motor rotation can be reduced. In addition, compared to a case where discharging regions are formed at four or more positions, the discharging amount can be easily attained and space efficiency is also excellent. 
   Preferably, the plunger pump further includes: a rolling element; wherein the motor includes an output shaft having an outer circumferential surface on which a cam face including the discharging region of the cam portion is formed; the rolling element is disposed between the cam face and the plunger; the plunger is constantly urged toward the rolling element being in contact therewith to bring the rolling element into contact with the cam face; and the output shaft is rotated by the motor so that the discharge regions press and move the plunger via the rolling element to perform the discharging operation. 
   According to the invention, the rolling element has a small coefficient of friction in operation, whereby operation noise can be reduced and high temperature due to frictional heat can be prevented. 
   Preferably, the plunger includes a first plunger and a second plunger; the first plunger is brought in contact with the discharge region; and the second plunger is brought in contact with the suction region when the first plunger is brought in contact with the discharge region. 
   According to the invention, by bringing the first plunger and second plunger in contact with the discharge region and suction region of the cam portion, respectively, discharges of each plunger are alternately carried out, and the discharging timing slips, therefore, pulsation can be suppressed and operation noise can be reduced. 
   The invention may provide a plunger pump, including: a pair of plunger pump units each including a pump chamber and a plunger for pressing a hydraulic fluid in the pump chamber to perform a discharging operation of the hydraulic fluid; a cam portion for pressing the plungers of the pair of plunger pump units to perform the discharging operations while rotating; and a motor that drives the cam portion to rotate; wherein the cam portion alternately presses the plungers within one revolution. 
   Preferably, the plunger pump units are disposed at both sides of the cam portion. 
   The invention may provide a plunger pump drive unit, include: a motor; a cam portion driven by the motor to rotate and press a plunger to perform a discharging operation of a hydraulic fluid; wherein the cam portion has at least two discharge regions for pressing the plunger and a suction region formed between the discharge region; and the plunger performs the discharging operation two times or more by one rotation of the cam portion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more readily described with reference to the accompanying drawings: 
       FIG. 1  is a front view showing an antilock brake controller according to an embodiment of the present invention partially by a sectional view. 
       FIG. 2  is an enlarged longitudinal sectional view of a plunger pump and a plunger pump drive unit. 
       FIG. 3  is a cross sectional view of a plunger pump and a plunger pump drive unit. 
       FIG. 4  is a cross sectional view of a plunger pump and a plunger pump drive unit. 
       FIG. 5  is an enlarged cross sectional view of a cam portion and a roller. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 
     FIG. 1  is a front view showing an antilock brake mechanism according to an embodiment of the present invention.  FIG. 2  is an enlarged view of a longitudinal sectional view of the plunger pump drive unit of  FIG. 1 .  FIG. 3  is a sectional view along III—III of  FIG. 2  showing a discharge operation.  FIG. 4  is a sectional view along III—III showing a suction operation.  FIG. 5  is an enlarged sectional view for explaining the cam portion and roller of  FIG. 3 . 
   A plunger pump drive unit  5  according to an embodiment of the present invention as shown in  FIG. 1  and  FIG. 2  is used for generating a fluid pressure of a hydraulic fluid of an automobile antilock brake system (ABS), for example. An antilock brake controller  1  is, when a vehicle driver brakes by stepping onto a brake pedal, for controlling the brake fluid pressure working on respective wheel brakes. In particular, the antilock brake controller  1  can control, by reducing the brake fluid pressure to a wheel which was nearly locked during the braking, the wheels without locking. 
   The antilock brake controller  1  includes a fluid pressure control unit and an electronic control unit for electrically controlling this fluid pressure control unit. The fluid pressure control unit comprises the plunger pump drive unit  5  incorporated in a housing  4  and hydraulic components such as unillustrated solenoid valves and plunger pumps  41   a  and  41   b . The electronic control unit comprises an unillustrated substrate disposed in a cover  3  and electronic components disposed on the substrate, and this is electrically connected to an electric motor  2  of the fluid pressure control unit and unillustrated solenoid valves, etc. 
   The plunger pump drive unit  5  according to an embodiment of the present invention presses and moves plungers  71  and  71  of the two plunger pumps  41   a  and  41   b  to discharge a hydraulic fluid. The plunger pump  41   b  is provided at a position across the plunger pump drive unit  5  from the plunger pump  41   a . In addition, the plunger pump drive unit  5  can, by employing a mode of the present invention which will be described in detail in the following, reduce vibration of the electric motor, and thereby reduce operation noise due to a pulsation of the hydraulic fluid discharged from the pump. 
     FIG. 3  and  FIG. 4  are sections along III—III of  FIG. 2 , which are views for explaining a discharge operation and a suction operation by the plunger pump drive unit  5 . In the housing  4 , a plurality of operating passages  43  where a hydraulic fluid circulates are formed, unillustrated solenoid valves to open and close the operating passages  43  and plunger pumps  41   a  and  41   b  are fixedly disposed. Since the plunger pumps  41   a  and  41   b  have basically the same structure, description will be given of the plunger pump  41   a  in the following. The plunger pump  41   a  has a cover-like exit chamber body  52  inserted in an attaching hole  48  formed in the housing  4 , a pump chamber plunger  62 , and a plunger  71  inserted so as to be slidable on the inner wall of the pump chamber plunger  62 . The exit chamber body  52 , pump chamber plunger  62 , and plunger  71  are, by fitting annular seal members C 1 , C 2 , C 3 , C 4 , and CS made of a rubber composition to annular grooves formed on their outer wall surfaces, fluid-tightly sealed. 
   The plunger  71  is formed in a bottomed cylindrical shape whose one end is opened, and an interior space thereof is formed as an entrance chamber  70 . In addition, an exit chamber  50  is formed in a space between the exit chamber body  52  and pump chamber plunger  62 , and in a space between the pump chamber plunger  62  and plunger  71 , a pump chamber  60  is formed. 
   The entrance chamber  70  is formed by a hole which communicates a plurality of second suction opening portions  72 ,  72  . . . opened through a cylindrical outer circumferential wall of the plunger  71  with a first discharge opening portion  74  formed on one end of the plunger  71 . At the first discharge opening portion  74 , a funnel-like first valve seat  73  whose diameter increases toward the pump chamber  60  is formed, and a suction valve  69  of a spherical valve is disposed so as to be seatable. The suction valve  69  is always urged to the first valve seat  73  side by a first valve spring member  68  disposed between the same and inner wall surface of the pump chamber plunger  62 , and closes the first discharge opening portion  74 . In addition, the plunger  71  is urged to the plunger pump drive unit  5  by a first spring member  67  disposed between the same and the inner wall surface of the pump chamber plunger  62 . 
   The pump chamber  60  is formed in a space between the inner wall of the pump chamber plunger  62  formed in an approximately cylindrical shape and plunger  71 . At an opening end portion of the pump chamber plunger  62 , a second discharge opening portion  66  having a pinched-in narrow inside diameter and a funnel-like second valve seat  65  whose diameter increases from the second discharge opening portion  66  to the exit chamber  50  side are formed. A spherical discharge valve  59  to be seated on the second valve seat  65  closes the second discharge opening portion  66  by use of a second valve spring member  57  whose one end is restricted at a second spring receiving member  58  fixed by caulking to the opening end portion of the pump chamber plunger  62 . 
   The exit chamber  50  is formed in a space between the exit chamber body  52  and pump chamber plunger  62 . The exit chamber body  52  is disposed at the opening end of an attaching hole  48  while being restricted from shifting outside the housing  4 , and this is also restricted from shifting inside the housing  4  by a second spring member  54  disposed between the exit chamber body  52  and pump chamber plunger  62 . Accordingly, the pump chamber plunger  62  is urged inside the housing  4  by the exit chamber body  52  and second spring member  54 , and is fixedly disposed substantially inside the housing  4 . 
   The plunger pump drive unit  5  for driving the plunger  41   a  and  41   b  has an output shaft  22  of an electric motor  2  extended from the electric motor  2  to the inside of the housing  4  and rollers  26   a  and  26   b , which are rolling elements brought in contact with a part of the output shaft  22 . The output shaft  22  is, while using its both end portions as support portions  23   a  and  23   b , rotatably supported on the housing  4  via ball bearings  24   a  and  24   b . A cam portion  220  is formed between the support portions  23   a  and  23   b , and at both sides of the cam portion  220 , cylindrical rollers  26   a  and  26   b  are disposed in contact. The upper and lower end portions of the rollers  26   a  and  26   b  are formed in a spherical shape and are guided to slide by a first guide member  42   a  and a second guide member  42   b . In addition, the sidewalls of the rollers  26   a  and  26   b  are, as shown in  FIG. 3  and  FIG. 4 , guided to slide by a guide groove  47  formed on the first guide member  42  so as to advance and retract with respect to the plungers  71  and  71 . 
   As a result of a rotation of the cam portion, the plunger  71  repeats a discharge and suction of the hydraulic fluid. 
   In the present embodiment, two plungers  71  are disposed so as to alternately repeat a discharge and suction of the hydraulic fluid, respectively. Namely, in a case where one plunger  71  has been brought in contact with the discharge region of the cam portion, the other plunger is in contact with the suction region of the cam portion. Accordingly, discharge operations of the respective plungers  71  do not overlap, thus pulsation due to the discharges can be dispersed. 
   As shown in  FIG. 5 , the cam portion  220  has an approximately triangular prism shape whose cross section is an approximately equilateral triangle where a discharge region and a suction region are alternately formed. On the outer circumferential surface of the cam portion  220 , cam faces to be brought in contact with the roller  26   a  and  26   b  are formed. The cam portion  220  is rotated clockwise when the support portion  23   b  side is viewed from the support portion  23   a  side in  FIG. 5 . Of the cam faces, from the respective vertexes of the approximately triangular form, clockwise, to parts of the respective sides of the approximately triangular form closest to the central rotation axis are formed as suction cam faces  222  of suction regions. And, of the cam faces, from the parts of the respective sides of the approximately triangular form closest to the central rotation axis, counterclockwise, to the respective vertexes of the approximately triangular form are formed as discharge cam faces  224  of discharging cam regions. 
   Next, operations of the plunger pump drive unit  5  and plunger pump  41  will be described by use of  FIG. 3  and  FIG. 4 . 
   First, a suction operation will be described. In  FIG. 3 , when the output shaft  22  is rotated in the arrow direction by activating the electric motor  2 , the cam portion  220  formed on the output shaft  22  is rotated. Then, the roller  26   a  retracts while rolling along suction cam face  222  formed on the outer circumferential surface and reaches a condition of  FIG. 4 . During this suction operation, with the roller  26   a , an end portion  76  of the plunger  71  is always brought in contact by the first spring member  67  and is slidably in contact by rolling. Accordingly, with the retracting of the roller  26   a  in the center direction of the output shaft  22 , the plunger  71  also retracts. As shown in  FIG. 4 , as a result of the retraction of the plunger  71 , since the pump chamber  60  expands, the pressure is reduced, and the suction valve  69  is opened due to a differential pressure from the fluid pressure of the hydraulic fluid of the entrance chamber  70 . When the suction valve  69  is opened, the hydraulic fluid passes through a first suction opening portion  64  of the pump chamber plunger  62  from the suction port  44  of the operating passage  43  and is suctioned into the pump chamber  60  via the second suction opening portion  72  of the plunger  71 . 
   Next, a discharge operation will be described. When the output shaft  22  and cam portion  220  are further rotated, the pump chamber  60  finishes expanding, and the suction valve  69  is seated on the first valve seat  73  of the first discharge opening portion  74  to be closed. The roller  26   a  advances while rolling along the discharge cam face  224  and reaches a condition shown in  FIG. 3 . During this discharge operation, the plunger  71  is pressed and moved while being slidably in contact by rolling of the roller  26   a  and advances while compressing the first spring member  67  and the hydraulic fluid inside the pump chamber  60 . The hydraulic fluid suctioned into the pump chamber  60  is, while the discharge valve  59  compresses the second valve spring member  57  and is opened by a compressing operation of the plunger  71 , discharged into the exit chamber  50  via the second discharge opening portion  66 . The hydraulic fluid discharged from the plunger pump  41   a  passes through an opening portion of the spring receiving portion  58  and flows into the operating passage  43  via a discharge port  46 . 
   Since, in the cam portion  220 , the suction cam surfaces  222  and discharge cam surfaces  224  are provided at three positions, respectively, by one rotation of the output shaft  22  of the plunger pump drive unit  5 , the plunger pump  71  can repeat three suctions and discharges. Vibration of the electric motor  2  as in the conventional eccentric shaft is reduced. In addition, since the plunger pump  71  carries out three-time discharge operations by one rotation of the output shaft  22 , it also becomes possible to reduce the rotation speed of the electric motor  2 , thus vibration and operation noise of the electric motor  2  can be reduced. 
   In addition, in the present embodiment, since the cross sectional shape of the cam portion is formed in an approximately triangular form, when the plunger pump  41   a  carries out a suction operation, the plunger pump  41   b  carries out a discharge operation, thus the discharge and suction operations do not overlap, and pulsation can also be suppressed. Although the approximately triangular shape in the present embodiment has the respective vertexes as arcs, the respective sides are not limited to straight lines but can be in large arc forms as long as three discharge cam faces and three suction cam faces are arranged at even intervals. In addition, with regard to an arrangement of the plunger pump drive unit  5  and respective plunger pumps, if the discharge operations of the respective plunger pumps do not overlap, these can be appropriately arranged while taking an arrangement of other hydraulic components into consideration. 
   Here, the present invention is not limited to the present embodiment but can be modified into various modes within the spirit of the present invention. 
   For example, in the above-described embodiment, although cylindrical rollers have been used as rolling elements, without being limited thereto, rolling elements such as spherical ball bearings can be appropriately employed. 
   In the above-described embodiment, although the cam portion  220  has been formed as a part of the output shaft  22  of the electric motor  2 , without being limited thereto, the cam portion may be formed on another rotation axis portion which is driven to rotate by a rotation of the output shaft  22  and is engaged with, for example, a gear wheel or the like. 
   In addition, in the above-described embodiment, for the cam portion  220 , although the cam faces have been formed on the wall surface of an approximately triangular prism shape, these are not limited to faces as long as the cam portion has a suction region and a discharge region alternately. 
   Furthermore, in the above-described embodiment, although the cam portion  220  has had an approximately triangular cross section, an equilateral triangle is desirable, and it is also possible to employ another polygon while considering the discharging amount and arrangement space.