Patent Publication Number: US-2021179050-A1

Title: Brake Control Apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a brake control apparatus. 
     BACKGROUND ART 
     PTL 1 discloses a brake control apparatus including a plunger pump provided in a housing. A plunger of the plunger pump is contained in a cylinder containing hole of the housing, and extends into a cam chamber with the distal end portion thereof supported by a bearing. 
     CITATION LIST 
     Patent Literature 
     PTL 1: US Patent Application Public Disclosure No. 2005-0253451 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the brake control apparatus disclosed in the above-described patent literature, PTL 1, contamination staying in a gap between the inner peripheral surface of the cylinder containing hole and the outer peripheral surface of the plunger may scar the plunger by entering between the inner peripheral surface of the bearing and the outer peripheral surface of the plunger when the plunger is actuated, thereby resulting in a reduction in the durability of the plunger pump. 
     Solution to Problem 
     One of objects of the present invention is to provide a brake control apparatus capable of improving durability of a plunger pump. 
     According to one aspect of the present invention, a brake control apparatus includes a bearing through which a plunger is inserted. The bearing is fixed to a housing so as to protrude in an insertion hole or be arranged coplanarly with the insertion hole. 
     Advantageous Effects of Invention 
     Therefore, the brake control apparatus according to the one aspect of the present invention can improve the durability of the plunger pump. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a brake control apparatus  1  according to a first embodiment. 
         FIG. 2  is a cross-sectional view of a housing  8  of a second unit  1 B according to the first embodiment taken along a direction perpendicular to an axis. 
         FIG. 3  is an enlarged view of main portions of a pump portion  3 A according to the first embodiment. 
         FIG. 4  is a perspective view of a guide ring  34 A according to the first embodiment. 
         FIG. 5  is an axial cross-sectional view of the guide ring  34 A according to the first embodiment. 
         FIG. 6  is an enlarged view of main portions of the pump portion  3 A according to a second embodiment. 
         FIG. 7  is an axial cross-sectional view of the guide ring  34 A according to a third embodiment. 
         FIG. 8  is an axial cross-sectional view of the guide ring  34 A according to a fourth embodiment. 
         FIG. 9  is a cross-sectional view of the housing  8  of the second unit  1 B according to a fifth embodiment taken along the direction perpendicular to the axis. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     First, the configuration will be described. 
       FIG. 1  is a perspective view of a brake control apparatus  1  according to a first embodiment, and  FIG. 2  is a cross-sectional view of a housing  8  of a second unit  1 B according to the first embodiment taken along a direction perpendicular to an axis. 
     The brake control apparatus  1  is usable for a hybrid automobile including an electric motor (a generator) in addition to an internal combustion engine, an electric automobile including only an electric motor, and the like, besides a general vehicle including only an internal combustion engine (an engine) as a prime mover that drives wheels. The brake control apparatus  1  is a hydraulic braking apparatus that applies a frictional braking force based on a hydraulic pressure to each of the wheels of the vehicle. A brake actuation unit is provided on each of the wheels. The brake actuation unit is, for example, a disk-type brake, and includes a wheel cylinder and a caliper. The caliper includes a brake disk and brake pads. The brake disk is a brake rotor that rotates integrally with a tire. The brake pads are disposed with predetermined clearances generated from the brake disk, and contact the brake disk by being moved by the hydraulic pressure in the wheel cylinder. By this operation, the brake actuation unit generates the frictional braking force. The brake control apparatus  1  includes two brake pipe systems (a primary P system and a secondary S system). The brake pipe configuration is, for example, the X-split pipe configuration. The brake control apparatus  1  may employ another pipe configuration, such as the front/rear split pipe configuration. Hereinafter, when a member provided in correspondence with the P system and a member provided in correspondence with the S system are distinguished from each other, indexes P and S will be added at the ends of the respective reference numerals. The brake control apparatus  1  supplies brake fluid working as hydraulic fluid (hydraulic liquid) to each of the brake actuation units via the brake pipes, and generates the hydraulic pressure (a brake hydraulic pressure) in the wheel cylinder. By this operation, the brake control apparatus  1  applies a hydraulic braking force to each of the wheels. 
     The brake control apparatus  1  includes a first unit  1 A and a second unit  1 B. The wheel cylinder on each of the wheels and the second unit  1 B are connected to each other via a wheel cylinder pipe  10 W. The first unit  1 A and the second unit  1 B are set up in, for example, an engine room isolated from a driving compartment of the vehicle, and are connected to each other via a plurality of pipes. The plurality of pipes includes master cylinder pipes  10 M (a primary pipe  10 MP and a secondary pipe  10 MS), an intake pipe  10 R, and a back-pressure pipe  10 X. Except for the intake pipe  10 R, each of the pipes  10 M,  10 W, and  10 X is a metallic brake pipe (a metallic pipe), and, in particular, a steel tube such as a double-walled steel tube. The both end portions of each of the pipes  10 M,  10 W, and  10 X each include a male pipe joint processed by flaring processing. The intake pipe  10 R is a brake hose (a hose pipe) formed so as to become flexible from a material such as rubber. The end portions of the intake pipe  10 R are connected to a port  873  and the like via nipples  10 R 1  and  10 R 2 . The nipples  10 R 1  and  10 R 2  are each a resin connection member having a tubular portion. Hereinafter, a three-dimensional orthogonal coordinate system having an X axis, a Y axis, and a Z axis is set for convenience of the description. A Z-axis direction is defined to be the vertical direction and a Z-axis positive direction side is defined to be the upper side in the vertical direction with the first unit  1 A and the second unit  1 B mounted on the vehicle. An X-axis direction is defined to be the longitudinal direction of the vehicle and an X-axis positive direction side is defined to be the front side of the vehicle. A Y-axis direction is defined to be the lateral direction of the vehicle. 
     A push rod PR is rotatably connected to a brake pedal, which receives an input of a brake operation performed by a driver. The push rod PR extends from the end portion thereof on the X-axis negative direction side, which is connected to the brake pedal, toward the X-axis positive direction side. The first unit  1 A is a brake operation unit mechanically connected to the brake pedal, and is a master cylinder unit including a master cylinder  5 . The first unit  1 A includes a reservoir tank  4 , a housing  7 , the master cylinder  5 , a stroke sensor  94 , and a stroke simulator  6 . The reservoir tank  4  is a brake fluid source storing the brake fluid therein, and is a low-pressure portion opened to the atmospheric pressure. The housing  7  contains the master cylinder  5  and the stroke simulator  6  therein. A rectangular plate-like flange portion  78  is provided at the end portion of the housing  7  on the X-axis negative direction side. The four corners of the flange portion  78  are fixed to the dashboard on the vehicle body side with use of bolts B 1 . The reservoir tank  4  is set up on the Z-axis positive direction side of the housing  7 . The master cylinder  5  is a first hydraulic pressure source capable of supplying the hydraulic pressure to the wheel cylinders, and is connected to the brake pedal via the push rod PR and is actuated according to the operation performed by the driver on the brake pedal. The stroke sensor  94  detects the stroke amount of a primary piston of the master cylinder  5 . The stroke simulator  6  is actuated according to the brake operation performed by the driver, and provides a reaction force and a stroke to the brake pedal. 
     The second unit  1 B is a hydraulic pressure control apparatus provided between the first unit  1 A and the brake actuation unit of each of the wheels. The second unit  1 B includes a housing  8 , a motor  20 , a pump  3 , a plurality of electromagnetic valves and the like, a plurality of hydraulic pressure sensors and the like, and an electronic control unit (a control unit, hereinafter referred to as an ECU)  90 . The housing  8  contains the pump  3  and the valve bodies of electromagnetic valves  21  and the like therein. The circuits (the brake hydraulic circuits) of the above-described two systems (the P system and the S system), through which the brake fluid flows, are formed by a plurality of fluid passages inside the housing  8 . Further, a plurality of ports is formed inside the housing  8 , and these ports are opened to the outer surface of the housing  8 . The plurality of ports is connected to the fluid passages inside the housing  8 , and connects these internal fluid passages and fluid passages (the pipes  10 M and the like) outside the housing  8  to each other. 
     The motor  20  is a rotary electric motor, and includes a rotational shaft for driving the pump  3 . The motor  20  may be a brushed motor or may be a brushless motor including a resolver that detects the rotational angle or the number of rotations of the rotational shaft. The pump  3  is a second hydraulic pressure source capable of supplying the hydraulic pressure to the wheel cylinders, and includes five pump portions  3 A to  3 E configured to be driven by the single motor  20 . The pump  3  is used by the S system and the P system in common. The electromagnetic valves and the like are each an actuator that operates according to a control signal, and each include a solenoid and a valve body. The valve body is stroked according to electric power supply to the solenoid to switch the opening/closing of the fluid passage (establish or block the communication through the fluid passage). The electromagnetic valves and the like control the communication state of the above-described circuit to adjust the flow state of the brake fluid, thereby generating a control hydraulic pressure. The hydraulic pressure sensors and the like detect the discharge pressure of the pump  3  and the master cylinder hydraulic pressure. 
     The second unit  1 B supplies the brake fluid pressurized by the pump  3  to the brake actuation units via the wheel cylinder pipes  10 W, thereby generating the brake hydraulic pressures (the wheel cylinder hydraulic pressures). The second unit  1 B can supply the master cylinder hydraulic pressure to each of the wheel cylinders, and can also control the hydraulic pressure in each of the wheel cylinders individually with use of the hydraulic pressure generated by the pump  3  independently of the brake operation performed by the driver with the communication blocked between the master cylinder  5  and the wheel cylinders. The ECU  90  receives inputs of the values detected by the stroke sensor  94 , the hydraulic pressure sensors, and the like, and information regarding the running state from the vehicle side, and controls the opening/closing operations of the electromagnetic valves and the like and the number of rotations of the motor  20  (i.e., the discharge amount of the pump  3 ) based on a program installed therein, thereby controlling the wheel cylinder hydraulic pressure (the hydraulic braking force) at each of the wheels. By this control, the ECU  90  performs various kinds of brake control (anti-lock brake control for preventing a slip of a wheel due to braking, boosting control for reducing the brake operation force that the driver should input, brake control for controlling the motion of the vehicle, autonomous brake control such as preceding vehicle following control, regenerative cooperative brake control, and the like). The control of the motion of the vehicle includes vehicle behavior stabilization control such as electronic stability control. In the regenerative cooperative brake control, the ECU  90  controls the wheel cylinder hydraulic pressures so as to achieve a target deceleration (a target braking force) in cooperation with the regenerative brake. 
     Next, the housing  8  of the second unit  1 B will be described. 
     The housing  8  is a generally cuboidal block formed with use of an aluminum alloy as a material thereof. The outer surface of the housing  8  includes a front surface  801 , a back surface  802 , a bottom surface  803 , a top surface  804 , a left side surface  805 , and a right side surface  806 . The front surface  801  (a first surface) is a flat surface relatively large in area. The back surface  802  (a second surface) is a flat surface generally in parallel with the front surface  801 , and is located opposite (of the housing  8 ) from the front surface  801 . The bottom surface  803  (a third surface) is a flat surface connected to the front surface  801  and the back surface  802 . The top surface  804  (a fourth surface) is a flat surface generally in parallel with the bottom surface  803 , and is located opposite (of the housing  8 ) from the bottom surface  803 . The left side surface  805  (a fifth surface) is a flat surface connected to the front surface  801 , the back surface  802 , the bottom surface  803 , and the top surface  804 . The right side surface  806  (a sixth surface) is a flat surface generally in parallel with the left side surface  805 , and is located opposite (of the housing  8 ) from the left side surface  805 . The right side surface  806  is connected to the front surface  801 , the back surface  802 , the bottom surface  803 , and the top surface  804 . The front surface  801  is disposed on the Y-axis positive direction side and extends in parallel with the X axis and the Z axis with the housing  8  mounted on the vehicle. The back surface  802  is disposed on the Y-axis negative direction side, and extends in parallel with the X axis and the Z axis. The top surface  804  is disposed on the Z-axis positive direction side, and extends in parallel with the X axis and the Y axis. The bottom surface  803  is disposed on the Z-axis negative direction side, and extends in parallel with the X axis and the Y axis. The right side surface  806  is disposed on the X-axis positive direction side, and extends in parallel with the Y axis and the Z axis. The left side surface  805  is disposed on the X-axis negative direction side, and extends in parallel with the Y axis and the Z axis. In actual use, the layout of the housing  8  in the XY plane is not limited in any manner, and the housing  8  can be arranged in the XY plane at any position and in any orientation according to the vehicle layout and/or the like. 
     A recessed portion  80  is formed at each of the corner portions of the housing  8  on the front surface  801  side and the top surface  804  side. In other words, the vertex formed by the front surface  801 , the top surface  804 , and the right side surface  806 , and the vertex formed by the front surface  801 , the top surface  804 , and the left side surface  805  have truncated shapes, and include first and second recessed portions  80 A and  80 B, respectively. The first recessed portion  80 A is opened to the front surface  801 , the top surface  804 , and the left side surface  805 . The second recessed portion  80 B is opened to the front surface  801 , the top surface  804 , and the right side surface  806 . The first recessed portion  80 A includes a first flat surface portion  807 , a second flat surface portion  808 , and a third flat surface portion  809 . The first flat surface portion  807  extends perpendicularly to the Y axis and in parallel with the XZ plane. The second flat surface portion  808  extends perpendicularly to the X axis and generally in parallel with the YZ plane. The third flat surface portion  809  extends in the Y-axis direction, and forms an angle of approximately 50 degrees with respect to the right side surface  806  in the counterclockwise direction as viewed from the Y-axis positive direction side. The second flat surface portion  808  and the third flat surface portion  809  are connected to each other smoothly via a concaved curved surface extending in the Y-axis direction. The second recessed portion  80 B includes the first flat surface portion  807 , the second flat surface portion  808 , and the third flat surface portion  809 . The third flat surface portion  809  extends in the Y-axis direction, and forms an angle of approximately 50 degrees with respect to the left side surface  805  in the clockwise direction as viewed from the Y-axis positive direction side. The other configuration of the second recessed portion  80 B is similar to the first recessed portion  80 A. The first and second recessed portions  80 A and  80 B are generally symmetric with respect to the YZ plane at the center of the housing  8  in the X-axis direction. 
     The housing  8  includes a cam containing hole (insertion hole)  81 , a plurality of (five) cylinder containing holes  82 A to  82 E, a first fluid pool chamber  83 , a second fluid pool chamber  84 , a plurality of fixation holes  85 , a plurality of valve containing holes, a plurality of sensor containing holes, an electric power source hole  86 , a plurality of ports  87 , the plurality of fluid passages, and the like. These holes and ports are formed with use of a drill or the like. The cam containing hole  81  has a bottomed cylindrical shape extending in the Y-axis direction, and is opened to the front surface  801 . A central axis O of the cam containing hole  81  is disposed at a position of the front surface  801  that is approximately central in the X-axis direction and slightly offset from the center in the Z-axis direction toward the Z-axis negative direction side. The bottom surface  803  is positioned on the Z-axis negative direction side with respect to the central axis O, and the first recessed portion  80 A and the second recessed portion  80 B are positioned on the Z-axis positive direction side with respect to the central axis O. 
     Each of the cylinder containing holes  82  has a stepped cylindrical shape and has a central axis extending in the radial direction of the cam containing hole  81  (the radial direction around the central axis O). The hole  82  includes a small diameter portion  820  on one side closer to the cam containing hole  81 , a large diameter portion  821  on the other side farther away from the cam containing hole  81 , and an intermediate diameter portion  822  between the small diameter portion  820  and the large diameter portion  821 . A part  823  of the intermediate diameter portion  822  on the one side closer to the cam containing hole  81  functions as an intake port, and the large diameter portion  821  functions as a discharge port. The plurality of holes  82 A to  82 E is disposed approximately evenly (at approximately even intervals) in the circumferential direction around the central axis O. An angle formed by the central axes of the holes  82  adjacent to each other in the circumferential direction around the central axis O is approximately 72 degrees (falls within a predetermined range including 72 degrees). The plurality of holes  82 A to  82 E is a single row along the Y-axis direction, and is disposed on the Y-axis positive direction side of the housing  8 . In other words, the central axes of these holes  82 A to  82 E are located in the same plane a generally perpendicular to the central axis O. The plane a extends generally in parallel with the front surface  801  and the back surface  802  of the housing  8 , and is located on a closer side to the front surface  801  side than to the back surface  802 . The respective intake ports  823  of the holes  82 A to  82 E are connected to one another via a first communication fluid passage. The respective discharge ports  821  of the holes  82 A to  82 E are connected to one another via a second communication fluid passage. 
     Each of the holes  82 A to  82 E is disposed inside the housing  8  in the following manner. The hole  82 A extends from the bottom surface  803  toward the Z-axis positive direction side. The hole  82 B extends from a portion of the left side surface  805  that is positioned on the lower side in the Z-axis negative direction with respect to the central axis O to the X-axis positive direction side and the Z-axis positive direction side. The hole  82 C extends from the first recessed portion  80 A to the X-axis positive direction side and the Z-axis negative direction side. The hole  82 D extends from the second recessed portion  80 B to the X-axis negative direction side and the Z-axis negative direction side. The hole  82 E extends from a portion of the right side surface  806  that is positioned on the lower side in the Z-axis negative direction with respect to the central axis O to the X-axis negative direction side and the Z-axis positive direction side. On the Z-axis negative direction side with respect to the central axis O, the hole  82 A is positioned at approximately the same position in the X-axis direction as the central axis O, and the holes  82 B and  82 E are disposed on the both sides of the central axis O (the hole  82 A) in the X-axis direction. On the Z-axis positive direction side with respect to the central axis O, the holes  82 C and  82 D are disposed on the both sides of the central axis O in the X-axis direction. The small diameter portion  820  of each of the holes  82 A to  82 E is opened to the inner peripheral surface of the cam containing hole  81 . The end portion of the hole  82 A on the large diameter portion  821  side is opened to a portion of the bottom surface  803  that is approximately central in the X-axis direction and located on the Y-axis positive direction side. The end portion of the hole  82 B on the large diameter portion  821  side is opened to a portion of the left side surface  805  that is located on the Y-axis positive direction side and the Z-axis negative direction side. The end portion of the hole  82 E on the large diameter portion  821  side is opened to a portion of the right side surface  806  that is located on the Y-axis positive direction side and the Z-axis negative direction side. The end portions of the holes  82 C and  82 D on the large diameter portion  821  sides are opened to the first and second recessed portions  80 A and  80 B, respectively. More specifically, more than half of the end portion on the large diameter portion  821  side is opened to the third flat surface portion  809 , and the remaining portion thereof is opened to the second flat surface portion  808 . The third flat surface portion  809  extends generally perpendicularly to the central axes of the holes  82 C and  82 D. 
     The first fluid pool chamber  83  has a bottomed cylindrical shape with the central axis thereof extending in the Z-axis direction. The first fluid pool chamber  83  is opened to a portion of the top surface  804  that is approximately central in the X-axis direction and offset toward the Y-axis positive direction, and is disposed from the top surface  804  into the housing  8 . The first fluid pool chamber  83  (the bottom portion thereof on the Z-axis negative direction side) is disposed on the Z-axis positive direction side with respect to the intake port  823  of each of the cylinder containing holes  82 . The first fluid pool chamber  83  is formed in a region between the cylinder containing holes  82 C and  82 D adjacent to each other in the circumferential direction around the central axis O on the Z-axis positive direction side with respect to the central axis O. The first fluid pool chamber  83 , and the holes  82 C and  82 D partially overlap each other in the Y-axis direction (as viewed from the X-axis direction). The first fluid pool chamber  83  and the intake port  823  of each of the holes  82 A to  82 E are connected to each other via an intake fluid passage  12 . The second fluid pool chamber  84  has a bottomed cylindrical shape with the central axis thereof extending in the Z-axis direction. The second fluid pool chamber  84  is opened to a portion of the bottom surface  803  that is located on the X-axis negative direction side and offset toward the Y-axis positive direction, and is disposed from the bottom surface  803  into the housing  8 . The second fluid pool chamber  84  is formed in a region between the cylinder containing holes  82 A and  82 B adjacent to each other in the circumferential direction around the central axis O on the Z-axis negative direction side with respect to the central axis O. The cylinder containing hole  82 A and the second fluid pool chamber  84  partially overlap each other in the Y-axis direction (as viewed from the X-axis direction). The cam containing hole  81  and the second fluid pool chamber  84  are connected to each other via a drain fluid passage  19 . One end of the drain fluid passage  19  is opened to a portion on the inner peripheral surface of the cam containing hole  81  that is located on the Y-axis negative direction side and the Z-axis negative direction side, and the other end of the drain fluid passage  19  is opened to the outer peripheral edge of the bottom surface of the second fluid pool chamber  84  on the Z-axis positive direction side. 
     The plurality of valve containing holes each has a bottomed cylindrical shape, and extends in the Y-axis direction to be opened to the back surface  802 . The plurality of valve containing holes is a single row along the Y-axis direction, and is disposed on the Y-axis negative direction side of the housing  8 . The cylinder containing holes  82  and the valve containing holes are arranged along the Y-axis direction. The plurality of valve containing holes at least partially overlaps the cylinder containing holes  82  as viewed from the Y-axis direction. Most of the plurality of valve containing holes is contained in a circle connecting the ends of the plurality of cylinder containing holes  82  on the large diameter portion  821  sides (the other sides farther away from the central axis O). Alternatively, the outer periphery of this circle and the valve containing holes at least partially overlap each other. The valve portion of the electromagnetic valve is fitted and the valve body thereof is contained in each of the valve containing holes. The plurality of sensor containing holes each has a bottomed cylindrical shape with the central axis thereof extending in the Y-axis direction, and is opened to the back surface  802 . A pressure-sensitive portion, such as the hydraulic pressure sensor, is contained in each of the sensor containing portions. The electric power source hole  86  has a cylindrical shape and extends through the housing  8  (between the front surface  801  and the back surface  802 ) in the Y-axis direction. The hole  86  is disposed at a position of the housing  8  that is approximately central in the X-axis direction and located on the Z-axis positive direction side. The hole  86  is disposed in a region between the cylinder containing holes  82 C and  82 D adjacent to each other. 
     The intake port  873  is an opening portion of the first fluid pool chamber  83  on the top surface  804 , and is opened to the upper side in the vertical direction. The port  873  is opened to a portion of the top surface  804  that is located on the central side in the X-axis direction and offset to the Y-axis positive direction. The port  873  is disposed on the Z-axis positive direction side with respect to the intake port  823  of each of the cylinder containing holes  82 A to  82 E. The cylinder containing holes  82 C and  82 D sandwich the port  873  as viewed from the Y-axis direction. The openings of the cylinder containing holes  82 C and  82 D and the port  873  partially overlap each other in the Y-axis direction (as viewed from the X-axis direction). Master cylinder ports  871  each have a bottomed cylindrical shape having a central axis extending in the Y-axis direction, and are opened to a portion that is an end portion of the front surface  801  on the Z-axis positive direction side and is sandwiched between the recessed portions  80 A and  80 B. The primary port  871 P is disposed on the X-axis positive direction side, and the secondary port  871 S is disposed on the X-axis negative direction side. Both the ports  871 P and  871 S are arranged in the X-axis direction, and sandwich the first fluid pool chamber  83  in the X-axis direction (as viewed from the Y-axis direction). The ports  871 P and  871 S are sandwiched between the first fluid pool chamber  83  and the cylinder containing holes  82 D and  82 C, respectively, in the circumferential direction around the central axis O (as viewed from the Y-axis direction). Wheel cylinder ports  872  each have a bottomed cylindrical shape with the central axis thereof extending in the Z-axis direction, and are opened to the Y-axis negative direction side of the top surface  804  (a position closer to the back surface  802  than to the front surface  801 ). The ports  872  are arranged in one row in the X-axis direction. The two ports  872  of the P system are disposed on the X-axis positive direction side, and the two ports  872  of the S system are disposed on the X-axis negative direction side. The first fluid pool chamber  83  is disposed in a region surrounded by the master cylinder ports  871  and the wheel cylinder ports  872 . The plurality of fluid passages and the like connect the ports  87 , the fluid pool chambers  83  and  84 , the cylinder containing holes  82 , the valve containing holes, and the hydraulic pressure sensor containing holes to one another. 
     The plurality of fixation holes  85  includes bolt holes  851  to  853  for fixing the motor, bolt holes  854  to  857  for fixing the ECU, and a bolt hole  858  for fixing the housing. The bolt holes  851  to  853  each have a bottomed cylindrical shape with the central axis thereof extending in the Y-axis direction, and are opened to the front surface  801 . The holes  851  to  853  are located on the Y-axis positive direction side of the housing  8 , and partially overlap the cylinder containing holes  82  in the Y-axis direction. The holes  851  to  853  are provided at positions generally symmetric with respect to the central axis O of the cam containing hole  81 . The respective distances from the central axis O to the holes  851  to  853  are approximately equal to one another. The holes  852  and  853  are located on the both sides of the central axis O in the X-axis direction, and on the Z-axis positive direction side with respect to the central axis O. The holes  852  and  853  are located adjacent to the cylinder containing holes  82 C and  82 D (the large diameter portions  821  thereof) and are also located adjacent to the third flat surface portions  809  of the recessed portions  80 A and  80 B on the side surface  805  and  806  sides with respect to the cylinder containing holes  82 C and  82 D (on the opposite sides of the cylinder containing holes  82  from the first fluid pool chamber  83 ), respectively. The hole  851  is located on the X-axis positive direction side with respect to the cylinder containing hole  82 A, and on the Z-axis negative direction side with respect to the central axis O. The hole  851  is located adjacent to the cylinder containing hole  82 A (the large diameter portion  821  thereof) and is also located adjacent to the bottom surface  803  on the opposite side of the cylinder containing hole  82 A from the second fluid pool chamber  84 . The bolt holes  854  to  857  each have a cylindrical shape with the central axis thereof extending in the Y-axis direction, and extend through the housing  8 . The holes  854  and  855  are located on the bottom surface  803  side, and the holes  856  and  857  are located on the top surface  804  side. The holes  854  and  855  are positioned at the corner portions sandwiched between the bottom surface  803  and the side surfaces  806  and  805 , and are opened to the front surface  801  and the back surface  802 . The holes  856  and  857  are positioned at the corner portions sandwiched between the top surface  804  and the second flat surface portions  808  of the recessed portions  80  as viewed from the Y-axis direction, and are opened to the first flat surfaces  807  of the recessed portions  80  and the back surface  802 . The hole  856  is located adjacent to the wheel cylinder port  872   b  and is sandwiched between the ports  872   b  and  872   c  in the X-axis direction. The hole  857  is located adjacent to the wheel cylinder port  872   a  and is sandwiched between the ports  872   a  and  872   d . The bolt holes  858 A and  858 B are positioned on the Z-axis negative direction side with respect to the central axis O. The bolt holes  858 A and  858 B each have a bottomed cylindrical shape with the central axis thereof extending in the Y-axis direction, and are opened to the both ends of the front surface  801  in the X-axis direction. The holes  858 A and  858 B are located on the Y-axis positive direction side of the housing  8 , and partially overlap the cylinder containing holes  82  in the Y-axis direction. The holes  858 A and  858 B are located adjacent to the side surfaces  805  and  806 , and are sandwiched between the cylinder containing holes  82 B and  82 E and the bolt holes  855  and  854  in the Z-axis direction, respectively. The hole  858 A on the X-axis negative direction side is sandwiched between the left side surface  805  and the second fluid pool chamber  84 . The hole  858 A is positioned on the opposite side of the vicinity of the central axis O from the primary port  871 P. The hole  858 B on the X-axis positive direction side is positioned on the opposite side of the vicinity of the central axis O from the secondary port  871 S. The bolt hole  858 C is positioned on the Z-axis negative direction side with respect to the central axis O. The hole  858 C has a bottomed cylindrical shape with the central axis thereof extending in the X-axis direction, and is opened to an approximately central portion of the right side surface  806  in the Y-axis direction. The hole  858 C is opened while being located adjacent to the corner portion sandwiched between the first flat surface portion  807  and the third flat surface portion  809  of the second recessed portion  80 B as viewed from the X-axis direction. The hole  858 C is positioned on the opposite side of the vicinity of the central axis O from the hole  858 A. 
     The ECU  90  is disposed and attached on the back surface  802  of the housing  8 . In other words, the ECU  90  is provided integrally with the housing  8 . The ECU  90  includes a control board and a control unit housing  901 . The control board controls the states of electric power supply to the motor  20  and the solenoids of the electromagnetic valves and the like. Various kinds of sensors that detect the motion state of the vehicle, such as an acceleration sensor that detects the acceleration of the vehicle, and an angular speed sensor that detects the angular speed (the yaw rate) of the vehicle, may be mounted on the control board. Further, a combination sensor (a combined sensor) formed by unitizing these sensors may be mounted on the control board. The control board is contained in the case  901 . The case  901  is a cover member attached to the back surface  802  (the bolt holes  854  to  857 ) of the housing  8  with use of bolts b 2 . The back surface  802  functions as a case attachment surface. The bolt holes  854  to  857  function as a fixation portion for fixing the ECU  90  to the housing  8 . The head portions of the bolts b 2  are disposed on the front surface  801  side of the housing  8 . The shaft portions of the bolts b 2  extend through the bolt holes  854  to  857 , and the male screws on the distal end sides of the shaft portions are threadably engaged with the female screws on the case  901  side. The case  901  is fixedly fastened to the back surface  802  of the housing  8  with the aid of the axial forces of the bolts b 2 . The head portions b 21  of the bolts b 2  protrude in the first recessed portion  80 A and the second recessed portion  80 B, respectively. The head portions b 21  are contained inside the recessed portions  80  and do not protrude beyond the front surface  801  toward the Y-axis positive direction side. 
     The case  901  is a cover member made from a resin material, and includes a board containing portion  902  and a connector portion  903 . The board containing portion  902  contains the control board and parts of the solenoids of the electromagnetic valves and the like (hereinafter referred to as the control board and the like). The control board is mounted in the board containing portion  902  generally in parallel with the back surface  802 . The terminals of the solenoids of the electromagnetic valves and the like, the terminals of the hydraulic pressure sensors and the like, and the conductive member from the motor  20  protrude from the back surface  802 . The above-described terminals and conductive member extend toward the Y-axis negative direction side to be connected to the control board. The connector portion  903  is disposed on the X-axis negative direction side of the board containing portion  902  with respect to the above-described terminals and conductive member, and protrudes toward the Y-axis positive direction side of the board containing portion  902 . The connector portion  903  is disposed on the slightly outer side (the X-axis negative direction side) with respect to the left side surface  805  of the housing  8  as viewed from the Y-axis direction. Terminals of the connector portion  903  are exposed toward the Y-axis positive direction side, and also extend toward the Y-axis negative direction side to be connected to the control board. Each of the terminals of the connector portion  903  (which are exposed toward the Y-axis positive direction side) is connectable to an external apparatus or the stroke sensor  94  (hereinafter referred to as the external apparatus and the like). An electric connection is established between the external apparatus and the like and the control board (the ECU  90 ) by insertion of another connector connected to the external apparatus and the like into the connector portion  903  from the Y-axis positive direction side. Further, electric power is supplied from an external electric power source (a battery) to the control board via the connector portion  903 . The conductive member functions as a connection portion that electrically connects the control board and the motor  20  to each other, and electric power is supplied from the control board to the motor  20  via the conductive member. 
     The motor  20  is disposed and a motor housing  200  is attached on the front surface  801  of the housing  8 . The front surface  801  functions as a motor attachment surface. The bolt holes  851  to  853  function as a fixation portion for fixing the motor  20  to the housing  8 . The motor  20  includes the motor housing  200 . The motor housing  200  has a bottomed cylindrical shape, and contains a magnet as a stator, a rotor, and the like on the inner peripheral side thereof, assuming that the motor  20  is a brushed DC motor by way of example. The conductive member for electric power supply is connected to the rotor via a brush. The central axis (the rotational axis) of the rotational shaft of the motor  20  approximately coincides with the central axis O of the cam containing hole  81 . A rotational driving shaft  300 , which is the rotational shaft and the driving shaft of the pump  3 , and a cam unit  30  are contained in the cam containing hole  81  (inside the housing  8 ). The rotational driving shaft  300  is the driving shaft of the pump  3 . The rotational driving shaft  300  is fixedly coupled with the rotational shaft of the motor  20  in such a manner that the central axis thereof extends on an extension of the central axis of the rotational shaft of the motor  20 , and is rotationally driven by the motor  20 . The central axis of the rotational driving shaft  300  approximately coincides with the central axis O. The rotational driving shaft  300  rotates integrally with the rotational shaft of the motor  20  around the central axis O. The cam unit  30  is provided on the rotational driving shaft  300 . The cam unit  30  includes a cam  301 , a driving member  302 , and a plurality of rolling elements  303 . The cam  301  is a columnar eccentric cam, and has a central axis P eccentric with respect to the central axis O of the rotational driving shaft  300 . The central axis P extends generally in parallel with the central axis O. The cam  301  swings while rotating around the central axis O integrally with the rotational driving shaft  300 . The driving member  302  has a cylindrical shape, and is disposed on the outer peripheral side of the cam  301 . The central axis of the driving member  302  approximately coincides with the central axis P. The driving member  302  is rotatable around the central axis P relative to the cam  301 . The driving member  302  is configured similarly to an outer race of a rolling bearing. The plurality of rolling elements  303  is disposed between the outer peripheral surface of the cam  301  and the inner peripheral surface of the driving member  302 . The rolling elements  303  are needle rollers, and extend along the direction of the central axis of the rotational driving shaft  300 . 
     The pump  3  is a radial plunger pump in the form of a fixed cylinder, and includes the housing  8 , the rotational driving shaft  300 , the cam unit  30 , and the plurality of (five) pump portions  3 A to  3 E. The pump portions  3 A to  3 E are each a plunger pump (a piston pump) as a reciprocating pump, and are actuated by the rotation of the rotational driving shaft  300 . The brake fluid as the hydraulic fluid is sucked and discharged according to reciprocating movements of plungers  36 . The cam unit  30  has a function of converting the rotational movement of the rotational driving shaft  300  into the reciprocating movements of the plungers  36 . When the respective configurations of the pump portions  3 A to  3 E are distinguished from one another, indexes A to E are added to the reference numerals thereof. The respective plungers  36  are disposed around the cam unit  30 , and are each contained in the cylinder containing hole  82 . A central axis  360  of each of the plungers  36  approximately coincides with the central axis of the cylinder containing hole  82 , and extends in the radial direction of the rotational driving shaft  300 . In other words, the plungers  36  as many as the number of the cylinder containing holes  82  (five) are provided, and extend in the radial direction with respect to the central axis O. The plungers  36 A to  36 E are disposed approximately evenly in the circumferential direction around the rotational driving shaft  300 , i.e., at approximately even intervals in the rotational direction of the rotational driving shaft  300 . Central axes  360 A to  360 E of these plungers  36 A to  36 E are located in the same plane a. These plungers  36 A to  36 E are driven by the same rotational driving shaft  300  and the same cam unit  30 . 
     The pump portion  3 A includes a cylinder sleeve  31 , a filter member  32 , a plug member  33 , a guide ring (a bearing)  34 , a first seal ring  351 , a second seal ring  352 , the plunger  36 , a return spring  37 , an intake valve  38 , and a discharge valve  39 , and these components are set in the cylinder containing hole  82 . The cylinder sleeve  31  has a bottomed cylindrical shape, and a hole  311  extends through a bottom portion  310  thereof. The cylinder sleeve  31  is fixed in the cylinder containing hole  82 . The central axis of the cylinder sleeve  31  approximately coincides with the central axis  360  of the cylinder containing hole  82 . An end portion  312  of the cylinder sleeve  31  on the opening side is disposed in the intermediate diameter portion  822  (the intake port  823 ), and the bottom portion  310  is disposed in the large diameter portion (discharge port)  821 . The filter member  32  has a bottomed cylindrical shape, and a hole  321  extends through a bottom portion  320  thereof and a plurality of opening portions also extends through a side wall portion thereof. A filter is set on each of these opening portions. An end portion  323  of the filter member  32  on the opening side is fixed to the end portion  312  of the cylinder sleeve  31  on the opening side. The bottom portion  320  is disposed in the small diameter portion  820 . The central axis of the filter member  32  approximately coincides with the central axis  360  of the cylinder containing hole  82 . A gap is generated between the outer peripheral surface where the opening portion of the filter member  32  is opened and the inner peripheral surface of the cylinder containing hole  82  (the intake port  823 ). The first communication fluid passage is in communication with the intake port  823  and the above-described gap. The plug member  33  has a columnar shape, and includes a recessed portion  330  and a groove on one end side in the direction of the central axis thereof. This groove extends radially to connect the recessed portion  330  and the outer peripheral surface of the plug member  33  to each other, and is in communication with the discharge port  821 . The above-described one end side of the plug member  33  in the axial direction is fixed to the bottom portion  310  of the cylinder sleeve  31 . The central axis of the plug member  33  approximately coincides with the central axis  360  of the cylinder containing hole  82 . The plug member  33  is fixed to the large diameter portion  821 , and closes the opening of the cylinder containing hole  82  on the outer peripheral surface of the housing  8 . The second communication fluid passage is in communication with the discharge port  821  and the above-described groove of the plug member  33 . The guide ring  34  has a cylindrical shape, and is fixed on the cam containing hole  81  side (the small diameter portion  820 ) of the cylinder containing hole  82  with respect to the filter member  32 . The guide ring  34  is made from a resin material. The central axis of the guide ring  34  approximately coincides with the central axis  360  of the cylinder containing hole  82 . The first seal ring  351  is set between the guide ring  34  and the filter member  32  in the cylinder containing hole  82  (the small diameter portion  820 ). 
     The plunger  36  has a columnar shape, and includes an end surface (hereinafter referred to as a plunger end surface)  361  on one side in the direction of the central axis thereof and a flange portion  362  on the outer periphery on the other side in the direction of the central axis thereof. The plunger end surface  361  has a flat shape extending in a direction generally perpendicular to the central axis  360  of the plunger  36 , and has a generally circular shape centered at the central axis  360 . The plunger  36  includes an axial hole  363  and a radial hole  364  therein. The axial hole  363  extends on the central axis  360  to be opened to the end surface of the plunger  36  on the above-described other side in the direction of the central axis. The radial hole  364  extends in the radial direction of the plunger  36  to be opened to the outer peripheral surface on the above-described one side in the direction of the central axis with respect to the flange portion  362  and to be also connected to the above-described one side of the axial hole  363  in the direction of the central axis. A check valve case  365  is fixed at the end portion of the plunger  36  on the above-described other side in the direction of the central axis. The check valve case  365  has a bottomed cylindrical shape made of a thin plate, and includes a flange portion  366  on the outer periphery of the end portion thereof on the opening side and a plurality of holes  368  extending through a side wall portion and a bottom portion  367  thereof. The end portion of the check valve case  365  on the opening side is fitted to the end portion of the plunger  36  on the above-described other side in the direction of the central axis. The second seal ring  352  is set between the flange portion  366  of the check valve case  365  and the flange portion  362  of the plunger  36 . The above-described other side of the plunger  36  in the direction of the central axis is inserted in the inner peripheral side of the cylinder sleeve  31 , and the plunger portion  362  is guided and supported by the cylinder sleeve  31 . The above-described one side of the plunger  36  in the direction of the central axis with respect to the radial hole  364  is inserted in the inner peripheral side (the hole  321 ) of the bottom portion  320  of the filter member  32 , the inner peripheral side of the first seal ring  351 , and the inner peripheral side of the guide ring  34 , and is guided and supported by them. The central axis  360  of the plunger  36  approximately coincides with the central axis of the cylinder sleeve  31  and the like (the cylinder containing hole  82 ). The end portion of the plunger  36  on the above-describe one side in the direction of the central axis (the plunger end surface  361 ) protrudes inside the cam containing hole  81 . 
     The return spring  37  is a compression coil spring, and is set on the inner peripheral side of the cylinder sleeve  31 . One end and the other end of the return spring  37  are set on the bottom portion  310  of the cylinder sleeve  31  and the flange portion  366  of the check valve case  365 , respectively. The return spring  37  constantly biases the plunger  36  toward the cam containing hole  81  side relative to the cylinder sleeve  31  (the cylinder containing hole  82 ). The intake valve  38  includes a ball  380  as a valve body and a return spring  381 , and they are contained on the inner peripheral side of the check valve case  365 . A valve seat  369  is provided around the opening of the axial hole  363  on the end surface of the plunger  36  on the above-described other side in the direction of the central axis. The ball  380  is seated on the valve seat  369 , by which the axial hole  363  is closed. The return spring  381  is a compression coil spring, and one end and the other end thereof are set on the bottom portion  367  of the check valve case  365  and the ball  380 , respectively. The return spring  381  constantly biases the ball  380  toward the valve seat  369  side relative to the check valve case  365  (the plunger  36 ). The discharge valve  39  includes a ball  390  as a valve body and a return spring  391 , and they are contained in the recessed portion  330  of the plug member  33 . A valve seat  313  is provided around the opening portion of the through-hole  311  on the bottom portion  310  of the cylinder sleeve  31 . The ball  390  is seated on the valve seat  313 , by which the through-hole  311  is closed. The return spring  391  is a compression coil spring, and one end and the other end thereof are set on the bottom surface of the recessed portion  330  and the ball  390 , respectively. The return spring  391  constantly biases the ball  390  toward the valve seat  313  side. 
     Inside the cylinder containing hole  82 , a space R 1  on the cam containing hole  81  side with respect to the flange portion  362  of the plunger  36  is a space on the intake side in communication with the first communication fluid passage. More specifically, a space that functions as the intake-side space R 1  extends from the above-described gap between the outer peripheral surface of the filter member  32  and the inner peripheral surface (the intake port  823 ) of the cylinder containing hole  82  through the plurality of openings of the filter member  32  and a gap between the outer peripheral surface of the plunger  36  and the inner peripheral surface of the filter member  32 , and leads to the radial hole  364  and the axial hole  363  of the plunger  36 . The communication of this intake-side space R 1  with the cam containing hole  81  is blocked by the first seal ring  351 . Inside the cylinder containing hole  82 , a space R 3  between the cylinder sleeve  31  and the plug member  33  is a discharge-side space in communication with the second communication fluid passage. More specifically, a space extending from the above-described groove of the plug member  33  to the discharge port  821  functions as the discharge-side space R 3 . On the inner peripheral side of the cylinder sleeve  31 , the volume of a space R 2  between the flange portion  362  of the plunger  36  and the bottom portion  310  of the cylinder sleeve  31  changes due to a reciprocating movement (a stroke) of the plunger  36  relative to the cylinder sleeve  31 . This space R 2  is in communication with the intake-side space R 1  according to the opening of the intake valve  38 , and is in communication with the discharge-side space R 3  according to the opening of the discharge valve  39 . The plunger  36  of the pump portion  3 A exerts a pump function by reciprocating. More specifically, when the plunger  36  is stroked to one side approaching the cam containing hole  81  (the central axis O), the volume of the space R 2  increases and the pressure in R 2  reduces. According to the closing of the discharge valve  39  and the opening of the intake valve  38 , the brake fluid as the hydraulic fluid is introduced from the intake-side space R 1  to the space R 2 , and the brake fluid is supplied from the first communication fluid passage into the space R 2  via the intake port  823 . When the plunger  36  is stroked to the other side moving away from the cam containing hole  81 , the volume of the space R 2  reduces and the pressure in R 2  increases. Due to the closing of the intake valve  38  and the opening of the discharge valve  39 , the brake fluid is transmitted out of the space R 2  into the discharge-side space R 3 , and the brake fluid is supplied into the second communication fluid passage via the discharge port  821 . The other pump portions  3 B to  3 E are also configured in a similar manner. The brake fluid discharged to the second communication fluid passage by each of the pump portions  3 A to  3 E is collected into a single discharge fluid passage  13 , and is used in common by the two hydraulic circuit systems. 
       FIG. 3  is an enlarged view of main portions of the pump portion  3 A according to the first embodiment.  FIG. 4  is a perspective view of the guide ring  34 A according to the first embodiment.  FIG. 5  is an axial cross-sectional view of the guide ring  34 A according to the first embodiment. 
     The guide ring  34 A includes a cylindrical portion  341  and a flange portion  342 . The cylindrical portion  341  is cylindrically formed, and includes a first end portion  341   a  and a second end portion  341   b  at the both axial ends thereof. The guide ring  34 A is fixed to the housing  8  with the first end portion  341   a  protruding in the cam containing hole  81 . The flange portion  342  protrudes from the second end portion  341   b  of the cylindrical portion  341  radially outward. The outer periphery of the guide ring  34 A except for the flange portion  342  is a small outer-diameter portion  341   c . Further, the outer periphery of the flange portion  342  is a large outer-diameter portion  341   d  larger in outer diameter than the small outer-diameter portion  341   c . A smallest diameter portion  824  smaller in inner diameter than the small diameter portion  820  is provided at a position of the cylinder containing hole  82 A closer to the cam containing hole  81  than the small diameter portion  820  is. The cylindrical portion  341  of the guide ring  34 A is press-fitted in the smallest diameter portion  824 . The inner diameter of the small diameter portion  820  is larger than the outer diameter of the flange portion  342 . 
     The cylindrical portion  341  includes a small inner-diameter portion  341   e  and a large inner-diameter portion  341   f  on the inner periphery thereof. The small inner-diameter portion  341   e  is disposed on the first end portion  341   a  side, and the large inner-diameter portion  341   f  is disposed on the second end portion  341   b  side. The large inner-diameter portion  341   f  is larger in inner diameter than the small inner-diameter portion  341   e . Further, the axial length of the large inner-diameter portion  341   f  is set to longer than the stroke range of the plunger  36 A. The first end portion  341   a  includes a R-shaped portion  341   g  on the outer periphery of the distal end thereof. 
     The guide rings  34 B to  34 E of the pump portions  3 B to  3 E do not protrude in the cam insertion hole  81 . In other words, the distal ends of the guide rings  34 B to  34 E on the radially inner sides are located on the radially outer sides with respect to the inner peripheral surface of the cam containing hole  81 . 
     Next, the functions will be described. 
     When the pump  3  is actuated, contamination such as wear debris is generated according to the sliding contact between each of the plungers  36 A to  36 E and the driving member  302 . The contamination mixed with the brake fluid leaked from the cylinder containing holes  82 A to  82 E is deposited in the cam containing hole  81 . Now, the cylinder containing hole  82 A of the pump portion  3 A, among these cylinder containing holes  82 A to  82 E, is opened upward at the lowest end of the cam containing hole  81 . In other words, the pump portion  3 A is positioned on the lower side in the vertical direction with respect to the center of the cam containing hole  81  when the brake control apparatus  1  is mounted on the vehicle. Therefore, the contamination deposited in the cam containing hole  81  enters a gap between the outer peripheral surface of the plunger  36 A and the inner peripheral surface of the guide ring  34  according to the reciprocating sliding movement of the plunger  36 A, and scars the plunger  36 A. As a result, the scar (the unevenness) generated on the outer peripheral surface of the plunger  36 A may damage the first seal ring  351 , thereby resulting in a reduction in the durability of the pump portion  3 A. Especially, the above-described problem noticeably arises with recent vehicles equipped with the autonomous driving function or the brake-by-wire system because the pump  3  is highly frequently actuated and the contamination is generated by a large amount on these vehicles. 
     To address this problem, in the brake control apparatus  1  according to the first embodiment, the guide ring  34 A of the pump portion  3 A protrudes in the cam containing hole  81 . In other words, the guide ring  34 A is fixed in the cylinder containing hole  82 A in such a manner that the upper end thereof (the distal end of the first end portion  341   a ) is positioned in the cam containing hole  81  on the upper side with respect to the opening edge of the cylinder containing hole  82 A. The contamination generated due to the actuation of the pump  3  is deposited on the outer peripheral side of the guide ring  34 , but is isolated from the plunger  36 A by the guide ring  34  and therefore can be less attached to the plunger  36 A and less enter the inner peripheral side of the guide ring  34 . As a result, the brake control apparatus  1  can prevent or reduce the scar on the plunger  36 A by the contamination, thereby preventing or reducing the deterioration of the sealing performance of the first seal ring  351  and thus improving the durability of the pump portion  3 A. 
     The guide ring  34 A includes the small inner-diameter portion  341   e  and the large inner-diameter portion  341   f  on the inner periphery thereof. The small inner-diameter portion  341   e  and the large inner-diameter portion  341   f  are provided on the first end portion  341   a  side and the second end portion  341   b  side in the axial direction of the guide ring  34 A, respectively, and the large inner-diameter portion  341   f  is larger in inner diameter than the small inner-diameter portion  341   e . A gap between the large inner-diameter portion  341   f  and the plunger  36 A is large compared to the small inner-diameter portion  341   e , and therefore the outer peripheral surface of the plunger  36 A is less likely scarred even when the contamination enters between the inner peripheral surface of the large inner-diameter portion  341   f  and the outer peripheral surface of the plunger  36 A. More specifically, even when the plunger  36 A slidably reciprocates with the contamination stuck between the inner peripheral surface of the guide ring  34  and the outer peripheral surface of the plunger  36 A, the range where the plunger  36 A is scarred can be limited to the range where the plunger  36 A is in contact with the small inner-diameter portion  341   e.    
     The axial length of the large inner-diameter portion  34   f  of the guide ring  34 A is set to longer than the stroke range of the plunger  34 A. Due to this setting, even when the plunger  36 A slidably reciprocates with the contamination stuck in the gap between the small inner-diameter portion  341   e  and the plunger  36 A and the outer peripheral surface of the plunger  36 A is scarred, this scar does not reach the first seal ring  351  and therefore the first seal ring  351  can be prevented from being damaged. 
     The guide ring  34 A includes the flange portion  342  on the outer periphery thereof and on the radially outer side of the large inner-diameter portion  341   f . Due to this configuration, when the guide ring  34 A is installed in the cylinder containing hole  82 A, the flange portion  362  is brought into abutment with the stepped surface between the small diameter portion  820  and the smallest diameter portion  824 , and this abutment allows the guide ring  34 A to be positioned in the axial direction of the cylinder containing hole  82 A with improved accuracy. 
     The guide ring  34 A includes the small outer-diameter portion  341   c  on the outer periphery thereof. The small outer-diameter portion  341   c  is smaller in outer diameter than the flange portion  342 . The small outer-diameter portion  341   c  is fixed to the housing  8  by being press-fitted to the smallest diameter portion  824  of the cylinder containing hole  82 A. As a result, the guide ring  34 A can be easily fixed to the housing  8 . 
     The guide ring  34 A includes the first end portion  341   a  and the second end portion  341   b  as the both axial end portions thereof. Then, the first end portion  341   a , which is one of these end portions that is located on the cam containing hole  81  side, includes the R-shaped portion  341   g , and the first end portion  341   a  is reducing in diameter toward the distal end thereof. Due to this configuration, the brake control apparatus  1  can facilitate the positioning at the initial stage of the press-fitting when the guide ring  34 A is press-fitted into the cylinder containing hole  82 A, thereby preventing or reducing biting at the time of the press-fitting. Further, the brake control apparatus  1  can prevent or reduce the deposition of the contamination on the end surface of the first end portion  341   a.    
     Second Embodiment 
     A second embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing only on differences from the first embodiment. 
       FIG. 6  is an enlarged view of main portions of the pump portion  3 A according to the second embodiment. 
     The pump portion  3 A according to the second embodiment is different from the first embodiment in terms of the guide ring  34 A including a seal member  343 . The seal member  343  is annularly formed, and is fixed to the end surface of the first end portion  341   a  by adhesion in close contact with the outer peripheral surface of the plunger  36 A. The first end portion  341   a  has a constant outer diameter. 
     In the second embodiment, the amount of the contamination entering the inner peripheral side of the guide ring  34 A can be reduced by eliminating the gap between the inner peripheral surface of the guide ring  34 A and the outer peripheral surface of the plunger  36 A with use of the seal member  343 . 
     Third Embodiment 
     A third embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing on only differences from the first embodiment. 
       FIG. 7  is an axial cross-sectional view of the guide ring  34 A according to the third embodiment. 
     The guide ring  34 A according to the third embodiment is different from the first embodiment in terms of the flange portion  342  press-fitted in the small diameter portion  820  of the cylinder containing hole  82 A. The inner diameter of the smallest diameter portion  824  is larger than the outer diameter of the cylindrical portion  341 . The first end portion  341   a  of the guide ring  34 A includes a taper portion  341   h  on the outer periphery of the distal end thereof. The taper portion  341   h  is reducing in diameter toward the distal end thereof. 
     The guide ring  34 A is a resin molded product, and therefore the inner diameter dimension of the press-fitted portion largely changes when the guide ring  34 A is press-fitted in the cylinder containing hole  82 A, compared to a metallic product. Further, there is a large variation in the dimension of the resin molded product compared to the metallic product. Therefore, in the case where the radially outer side of the small inner-diameter portion  341   e  in sliding contact with the plunger  36 A is press-fitted in the cylinder containing hole  82 A, the dimension of the small inner-diameter portion  341   e  should be designed in consideration of deformation due to the press-fitting and variations in the dimensions of the cylinder containing hole  82 A and the small outer-diameter portion  341   c . To address this inconvenience, in the third embodiment, the guide ring  34 A is fixed to the housing  8  by press-fitting the radially outer side of the large inner-diameter portion  341   f  in the small diameter portion  820 . Due to this configuration, the dimension of the small inner-diameter portion  341   e  can be designed without consideration of the deformation due to the press-fitting and the dimensional variation in each portion. In other words, the third embodiment allows the dimension of the small inner-diameter portion  341   e  to be set with high accuracy, thereby being able to further reduce the gap between the small inner-diameter portion  341   e  and the plunger  36 A. As a result, the third embodiment can reduce the amount of the contamination entering the gap between the small inner-diameter portion  341   e  and the plunger  36 A, and can also reduce the tilt of the plunger  36 A, thereby achieving ideal actuation of the pump portion  3 A. 
     The guide ring  34 A includes the first end portion  341   a  and the second end portion  341   b  as the both axial end portions thereof. Then, the first end portion  341   a , which is one of these end portions that is located on the cam containing hole  81  side, includes the taper portion  341   h , and the first end portion  341   a  is reducing in diameter toward the distal end thereof. Due to this configuration, the third embodiment can facilitate the positioning at the initial stage of the press-fitting when the guide ring  34 A is press-fitted into the cylinder containing hole  82 A, thereby preventing or reducing biting at the time of the press-fitting. Further, the third embodiment can prevent or reduce the deposition of the contamination on the end surface of the first end portion  341   a.    
     Fourth Embodiment 
     A fourth embodiment has a basic configuration similar to the third embodiment, and therefore will be described focusing on only differences from the third embodiment. 
       FIG. 8  is an axial cross-sectional view of the guide ring  34 A according to the fourth embodiment. 
     The guide ring  34 A according to the fourth embodiment is different from the third embodiment in terms of omission of the flange portion. The outer diameter of the guide ring  34 A is constant except for the taper portion  341   h . The smallest diameter portion  824  of the cylinder containing hole  82 A is provided between the small diameter portion  820  and the intermediate diameter portion  822 . The guide ring  34 A is press-fitted in the smallest diameter portion  824 . The fourth embodiment can also bring about similar advantageous effects to the third embodiment. 
     Fifth Embodiment 
     A fifth embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing on only differences from the first embodiment. 
       FIG. 9  is a cross-sectional view of the housing  8  of the second unit  1 B according to the fifth embodiment taken along the direction perpendicular to the axis. 
     The fifth embodiment is different from the first embodiment in terms of employing the guide ring  34 A according to the first embodiment for all of the pump portions  3 A to  3 E. 
     Mounting one type of guide ring as the guide ring  34 A for all of the pump portions  3 A to  3 E allows the same mounting process to be employed therefor, thereby being able to prevent an error in the mounting and simplify the process. 
     Other Embodiments 
     Having described the embodiments for implementing the present invention, the specific configuration of the present invention is not limited to the configurations of the embodiments, and the present invention also includes even a design modification and the like thereof made within a range that does not depart from the spirit of the present invention, if any. 
     The guide ring  34  may be coplanar with the cam insertion hole  81 . 
     In the fifth embodiment, the guide ring  34 A according to the first embodiment may be employed for only the three pump portions  3 A,  3 B, and  3 E. 
     In the following description, technical ideas recognizable from the above-described embodiments will be described. 
     A brake control apparatus, in one configuration thereof, includes a motor and a housing. The housing includes a first surface on which the motor is disposed, a second surface spaced apart from the first surface by a predetermined distance in a direction of a rotational axis of the motor, and an insertion hole extending from the first surface toward the second surface in the direction of the rotational axis and configured to receive insertion of a shaft that is rotated by the motor. The brake control apparatus further includes a plunger pump. The plunger pump includes a plunger configured to be actuated by a rotation of the motor. The plunger pump includes a bearing through which a plunger is inserted. The bearing is fixed to the housing so as to protrude in the insertion hole or be arranged coplanarly with the insertion hole. 
     According to a further preferable configuration, in the above-described configuration, the bearing includes a small inner-diameter portion and a large inner-diameter portion on an inner periphery thereof. The large inner-diameter portion has a larger inner diameter than the small inner-diameter portion. 
     According to another preferable configuration, in any of the above-described configurations, an axial length of the large inner-diameter portion is equal to or longer than a stroke range of the plunger. 
     According to further another preferable configuration, in any of the above-described configurations, a radially outer side of the large inner-diameter portion of the bearing is fixed to the housing. 
     According to further another preferable configuration, in any of the above-described configurations, the bearing includes a flange portion on an outer periphery thereof and on the radially outer side of the large inner-diameter portion. 
     According to further another preferable configuration, in any of the above-described configurations, the bearing includes a flange portion on an outer periphery thereof. 
     According to further another preferable configuration, in any of the above-described configurations, the bearing includes a small outer-diameter portion on the outer periphery thereof. The small outer-diameter portion has a smaller outer diameter than the flange portion. The small outer-diameter portion is fixed to the housing. 
     According to further another preferable configuration, in any of the above-described configurations, the bearing includes a small inner-diameter portion and a large inner-diameter portion on an inner periphery thereof. The small inner-diameter portion is positioned on a radially inner side of the small outer-diameter portion. The large inner-diameter portion is positioned on a radially inner side of the flange portion. 
     According to further another preferable configuration, in any of the above-described configurations, at an end portion of both axial end portions of the bearing that is located on one side closer to the insertion hole, a diameter thereof is reducing toward a distal end. 
     According to further another preferable configuration, in any of the above-described configurations, the end portion has a R-shape. 
     According to further another preferable configuration, in any of the above-described configurations, the end portion has a tapering shape. 
     According to further another preferable configuration, in any of the above-described configurations, the bearing includes a seal member at an end portion of both axial end portions thereof that is located on one side closer to the insertion hole. 
     According to further another preferable configuration, in any of the above-described configurations, the plunger pump is located on a lower side in a vertical direction with respect to a center of the insertion hole when the brake control apparatus is mounted on a vehicle. 
     According to further another preferable configuration, in any of the above-described configurations, the plunger pump includes a plurality of plunger pumps arranged around the rotational axis. 
     The present invention shall not be limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to facilitate a better understanding of the present invention, and the present invention shall not necessarily be limited to the configuration including all of the described features. Further, a part of the configuration of some embodiment can be replaced with the configuration of another embodiment. Further, some embodiment can also be implemented with a configuration of another embodiment added to the configuration of this embodiment. Further, each of the embodiments can also be implemented with another configuration added, deleted, or replaced with respect to a part of the configuration of this embodiment. 
     The present application claims priority under the Paris Convention to Japanese Patent Application No. 2018-155195 filed on Aug. 22, 2018. The entire disclosure of Japanese Patent Application No. 2018-155195 filed on Aug. 22, 2018 including the specification, the claims, the drawings, and the abstract is incorporated herein by reference in its entirety. 
     REFERENCE SIGN LIST 
     
         
           3 A pump portion (plunger pump) 
           8  housing 
           20  motor 
           34 A guide ring (bearing) 
           36  plunger 
           81  cam containing hole (insertion hole) 
           300  rotational driving shaft (shaft) 
           801  front surface (first surface) 
           802  back surface (second surface)