Abstract:
A cylinder device, which is provided with: a substrate having a cylinder hole and a reservoir union port; a piston which is inserted into the cylinder hole; a regulation member which regulates the rearward limit of the piston; a reservoir having a liquid supply part; and a seal member which is for the reservoir and which is externally fitted to the liquid supply part. Therein: the substrate comprises a mounting hole and a first communication hole which open to the reservoir union port and the cylinder hole; the regulation member is inserted into the mounting hole ( 11   h ); and the liquid supply part has a cut-out section and a tip section arranged so as to face the regulation member. This structure enables the number of components to be reduced, reduces the size of the substrate, and also prevents air from collecting inside the reservoir union port.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cylinder device which is used in a vehicle brake system. 
       BACKGROUND ART 
       [0002]    Some type of cylinder device which generates a brake pressure according to the amount of manipulation of a brake manipulator includes a base body, a piston, an elastic member, and a reservoir. A cylinder bore and a reservoir union port are formed in the base body, the piston is inserted in the cylinder bore, the elastic member is arranged between the bottom surface of the cylinder bore and the piston, and the reservoir has a fluid feeding portion inserted into the reservoir union port. In such a cylinder device, a rod-like limiting member is arranged to project into the cylinder bore such that the backward motion of the piston is limited by abutting of the piston on the limiting member. (See, for example, Patent Literature 1.) 
       CITATION LIST PATENT LITERATURE 
       [0003]    Patent Literature 1: Japanese Patent Laid-Open No. 2009-279966 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    In the aforementioned conventional cylinder device, a limiting member is inserted in an installation bore penetrating through a circumferential wall of the base body in such a manner that the limiting member projects into the cylinder bore. In this arrangement, it is necessary to arrange on the outer circumferential surface of the base body a means for preventing a fall of the limiting member, and seal the installation bore from the external space. Therefore, it is necessary to secure space for arranging parts for the fall prevention and the sealing, as the number of parts increases. 
         [0005]    The object of the present invention is to solve the above problems, and provide a cylinder device which can reduce the number of parts and the size of the base body by effectively using a space in the base body for arranging a limiting member for limiting the backward motion of the piston, and can further prevent accumulation of air in a reservoir union port. 
       Solution to Problem 
       [0006]    In order to accomplish the above object, according to the present invention, a cylinder device for generating a brake pressure according to an amount of manipulation of a brake manipulator is provided. The cylinder device includes: a base body in which a cylinder bore and a reservoir union port are formed, and the cylinder bore has a bottom, and the reservoir union port communicates with the cylinder bore, and a reservoir reserving brake fluid is connected to the reservoir union port; a piston inserted in the cylinder bore; an elastic member arranged between a bottom surface of the cylinder bore and the piston; a limiting member which projects into the cylinder bore and limits backward motion of the piston; the reservoir which has a fluid feeding portion having a tubular shape and being inserted in the reservoir union port; and a reservoir sealing member which has an annular shape and is externally fitted on the fluid feeding portion. In the cylinder device, a communication bore and an installation bore each of which has an end opened in the bottom surface of the reservoir union port and another end opened in an inner circumferential surface of the cylinder bore are formed in the base body, and the limiting member is inserted in the installation bore; and the fluid feeding portion includes a tip portion arranged opposed to the limiting member, and a cutout portion extended in an axial direction to the tip side of the fluid feeding portion. 
         [0007]    In the above structure, a means for preventing a fall of the limiting member is realized by the fluid feeding portion of the reservoir, and the installation bore is sealed from the external space by the reservoir sealing member which is externally fitted on the fluid feeding portion. That is, according to the present invention, the limiting member is arranged by effectively using the space in the base body. Therefore, it is possible to reduce the number of parts and the size of the base body. 
         [0008]    In addition, even when air intrudes into the gap between the inner circumferential surface of the reservoir union port and the outer circumferential surface of the fluid feeding portion, the air is exhausted into the reservoir through the cutout portion of the fluid feeding portion, so that accumulation of air in the reservoir union port can be prevented. Further, in the case where the cutout portion is formed to extend to the vicinity of the reservoir sealing member, air can be exhausted from the gap between the inner circumferential surface of the reservoir union port and the outer circumferential surface of the fluid feeding portion with high reliability. 
         [0009]    In the case where the communication bore is formed in a position opposed to the cutout portion, it is possible to cause the brake fluid to smoothly flow from the fluid feeding portion into the communication bore. In addition, since the cutout portion is formed in the fluid feeding portion, the communication bore can be formed close to the outer peripheral portion of the bottom surface of the reservoir union port, so that the degree of freedom in designing the cylinder device can be increased. 
         [0010]    In the case where the piston includes a shaft member and a flange portion formed on an outer circumferential surface of the shaft member, and a pressure chamber is formed between the bottom surface of the cylinder bore and the shaft member, it is possible to cause the brake fluid to smoothly flow into the communication bore through a feeding path by arranging, on the pressure chamber side of the flange portion, a piston sealing member externally fitted on the shaft member, and arranging the communication bore to be opened in the inner circumferential surface of the cylinder bore on the side, opposite to the pressure chamber, of the piston sealing member, and forming in the flange portion the feeding path which is open on the pressure chamber side and on the side opposite to the pressure chamber. This arrangement is particularly effective in the case where the amount of the brake fluid absorbed to the pressure chamber side is great. 
         [0011]    In the case where the piston sealing member is a cup seal, and an outer peripheral portion of the piston sealing member allows only the flow of the brake fluid from the side opposite to the pressure chamber to the pressure chamber side, it is possible to prevent flow of the brake fluid from the pressure chamber to the side, opposite to the pressure chamber, of the piston sealing member, and feed the brake fluid to the pressure chamber over the outer peripheral portion of the piston sealing member. 
       Effect of Invention 
       [0012]    In the cylinder device according to the present invention, a means for prevention of a fall of the limiting member is realized by the fluid feeding portion of the reservoir, and the installation bore is sealed from the external space by the reservoir sealing member. Therefore, it is possible to reduce the number of parts and the size of the base body. In addition, since the air which intrudes into the gap between the inner circumferential surface of the reservoir union port and the outer circumferential surface of the fluid feeding portion is exhausted through the cutout portion in the fluid feeding portion, it is possible to prevent accumulation of the air in the reservoir union port. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a construction diagram illustrating the entire construction of a vehicle brake system using a motor cylinder device according to an embodiment. 
           [0014]      FIG. 2  is a perspective diagram illustrating the motor cylinder device according to the embodiment. 
           [0015]      FIG. 3  is a side cross-sectional view of the motor cylinder device according to the embodiment. 
           [0016]      FIG. 4  is an exploded perspective view of a slave cylinder according to the embodiment. 
           [0017]      FIGS. 5A and 5B  include diagrams illustrating the slave cylinder according to the embodiment, where  FIG. 5A  is a cross-sectional view at the A-A cross section in  FIG. 3 , and  FIG. 5B  is a cross-sectional view at the B-B cross section in  FIG. 5A . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    An embodiment of the present invention is explained below with reference to the accompanying drawings. The present embodiment is an embodiment of the cylinder device according to the present invention, which is used in the vehicle brake system A illustrated in  FIG. 1 . 
         [0019]    The vehicle brake system A illustrated in  FIG. 1  includes both of a by-wire brake system which operates when a prime mover (an engine, an electric motor, or the like) is started, and a hydraulic brake system which operates at times of emergency or stop of the prime mover. The vehicle brake system A includes a master cylinder device A 1 , a motor cylinder device A 2 , and a hydraulic control device A 3 . The master cylinder device A 1  generates a hydraulic brake pressure according to the tread force with which the brake pedal P (as a brake manipulator) is depressed, the motor cylinder device A 2  generates a hydraulic brake pressure by use of the electric motor  20 , and the hydraulic control device A 3  assists in stabilization of the vehicle behavior. The master cylinder device A 1 , the motor cylinder device A 2 , and the hydraulic control device A 3  are respectively configured in the forms of separate units, and are connected through external piping. 
         [0020]    The vehicle brake system A can be mounted on vehicles including the automobiles driven by only an engine (internal-combustion-engine), hybrid electric vehicles using electric motors as well as an engine, and electric vehicles, fuel-cell vehicles, and the like which use only electric motors as power sources. 
         [0021]    The master cylinder device A 1  includes a tandem-type master cylinder  71 , a stroke simulator  72 , a reservoir  73 , normally-open shutoff valves  74  and  75 , a normally-close shutoff valve  76 , pressure sensors  77  and  78 , main hydraulic paths  79   a  and  79   b , hydraulic communication paths  79   c  and  79   d , and a hydraulic branch path  79   e . The above components are installed in a base body  60 , and the respective hydraulic paths are formed inside the base body  60 . 
         [0022]    The master cylinder  71  converts the tread force on the brake pedal P into the hydraulic brake pressure. The master cylinder  71  includes a first piston  71   a , a second piston  71   b , a first elastic member  71   c , and a second elastic member  71   d . The first piston  71   a  is arranged on the bottom surface side of a first cylinder bore  61   a , the second piston  71   b  is connected to a push rod P 1 , the first elastic member  71   c  is contained in a first pressure chamber  71   e  formed between the bottom surface of the first cylinder bore  61   a  and the first piston  71   a , and the second elastic member  71   d  is contained in a second pressure chamber  71   f  formed between the pistons  71   a  and  71   b.    
         [0023]    The second piston  71   b  is connected to the brake pedal P through the push rod P 1 . The pistons  71   a  and  71   b  receive the tread force from the brake pedal P, slide in the first cylinder bore  61   a , and pressurize the brake fluid in the pressure chambers  71   e  and  71   f . The main hydraulic paths  79   a  and  79   b  respectively communicate with the pressure chambers  71   e  and  71   f.    
         [0024]    The stroke simulator  72  generates a simulated reaction force in response to a manipulation of the brake pedal P, and includes a piston  72   a  and two elastic members  72   b  and  72   c . The piston  72   a  slides in a second cylinder bore  61   b , and the elastic members  72   b  and  72   c  bias the piston  72   a  toward the bottom surface side. The stroke simulator  72  communicates with the first pressure chamber  71   e  in the master cylinder  71  through the hydraulic branch path  79   e  and the main hydraulic path  79   a , so that the hydraulic brake pressure generated in the first pressure chamber  71   e  actuates the piston  72   a.    
         [0025]    The reservoir  73  is a container reserving the brake fluid, and includes the fluid feeding bores  73   a  and  73   b  connected to the master cylinder  71 . A hose extended from a main reservoir (not shown) is connected to the reservoir  73 . 
         [0026]    The main hydraulic paths  79   a  and  79   b  are hydraulic paths originated from the master cylinder  71 . Tubes Ha and Hb extending to the hydraulic control device A 3  are connected to the output ports  65   a  and  65   b , at which the main hydraulic paths  79   a  and  79   b  terminate. 
         [0027]    The hydraulic communication paths  79   c  and  79   d  are hydraulic paths extending from the input ports  65   c  and  65   d  to the main hydraulic paths  79   a  and  79   b . Tubes Hc and Hd extending to the motor cylinder device A 2  are connected to the input ports  65   c  and  65   d.    
         [0028]    The hydraulic branch path  79   e  is a hydraulic path which branches off from the main hydraulic path  79   a  extending to the first pressure chamber  71   e , and extends to the stroke simulator  72 . 
         [0029]    The normally-open shutoff valves  74  and  75  open and close the main hydraulic paths  79   a  and  79   b , and are realized by normally-open solenoid valves. 
         [0030]    The normally-open shutoff valve  74  opens and closes the main hydraulic path  79   a  in the section from the intersection point of the main hydraulic path  79   a  and the hydraulic branch path  79   e  to the intersection point of the main hydraulic path  79   a  and the hydraulic communication path  79   c . The normally-open shutoff valve  75  opens and closes the main hydraulic path  79   b  on the upstream side of the intersection point of the main hydraulic path  79   b  and the hydraulic communication path  79   d.    
         [0031]    The normally-close shutoff valve  76  opens and closes the hydraulic branch path  79   e , and is realized by a normally-closed solenoid valve. 
         [0032]    The pressure sensors  77  and  78  detect the magnitude of the hydraulic brake pressure, and are fitted to sensor installation bores (not shown) which communicate with the main hydraulic paths  79   a  and  79   b . The pressure sensor  77  is arranged on the downstream side of the normally-open shutoff valve  74 , and detects the hydraulic brake pressure generated in the motor cylinder device A 2  when the normally-open shutoff valve  74  is in a closed state (in the state in which the main hydraulic path  79   a  is shut off). The pressure sensor  78  is arranged on the upstream side of the normally-open shutoff valve  75 , and detects the hydraulic brake pressure generated in the master cylinder  71  when the normally-open shutoff valve  75  is in a closed state (in the state in which the main hydraulic path  79   b  is shut off). The information acquired by the pressure sensors  77  and  78  is outputted to an electronic control unit (not shown). 
         [0033]    The master cylinder device A 1  communicates with the hydraulic control device A 3  through the tubes Ha and Hb. The hydraulic brake pressure generated in the master cylinder  71  when the normally-open shutoff valves  74  and  75  are in an open state is inputted to the hydraulic control device A 3  through the main hydraulic paths  79   a  and  79   b  and the tubes Ha and Hb. 
         [0034]    The motor cylinder device A 2  includes a tandem-type slave cylinder  10 , an electric motor  20 , a drive transmission portion  30 , and a reservoir  40 . (See  FIG. 2 .) 
         [0035]    The slave cylinder  10  generates a hydraulic brake pressure corresponding to the hydraulic brake pressure generated in the master cylinder  71 . The slave cylinder  10  includes the base body  11 , a first slave piston  12 , a second slave piston  13 , a first elastic member  14 , and a second elastic member  15 . The first slave piston  12  is arranged on the bottom surface  11   d  side of a slave cylinder bore  11   a  formed in the base body  11 . The second slave piston  13  is arranged on the opening  11   e  side of the slave cylinder bore  11   a  formed in the base body  11 . The first elastic member  14  is contained in a first pressure chamber  11   b  formed between the bottom surface  11   d  of the slave cylinder bore  11   a  and the first slave piston  12 . The second elastic member  15  is contained in a second pressure chamber  11   c  formed between the slave pistons  12  and  13 . 
         [0036]    A rod  31  in the drive transmission portion  30  is in contact with the rear portion of the second slave piston  13 . In addition, the first slave piston  12  and the second slave piston  13  receive an input from the rod  31 , slide in the slave cylinder bore  11   a , and pressurize the brake fluid in the pressure chambers  11   b  and  11   c . Further, the pressure chambers  11   b  and  11   c  respectively communicate with the tubes Hc and Hd. 
         [0037]    The electric motor  20  is a servo motor which is under drive control based on a control signal from the electronic control unit (not shown), arranged on the upper side of a rear portion of the base body  11 , and fixed to the drive transmission portion  30 . (See  FIG. 2 .) An output shaft  21  protrudes from the central portion of the rear end face of the electric motor  20 . 
         [0038]    The drive transmission portion  30  converts the rotational drive force of the output shaft  21  into an axial force in the linear direction, and is attached to the rear portion of the base body  11 . (See  FIG. 2 .) 
         [0039]    The drive transmission portion  30  includes the rod  31 , a plurality of balls  32 , a tubular nut member  33 , and a gear mechanism  34 . The rod  31  is in contact with the second slave piston  13 . The balls  32  rollingly move along a thread groove spirally formed on the outer circumferential surface of the rod  31 , and the nut member  33  is in a screw engagement with the balls  32 . The gear mechanism  34  transmits the rotational drive force of the output shaft  21  to the nut member  33 . The above components are contained in a housing  35 . 
         [0040]    A cylinder fixing portion  35   a  fixed to the base body  11  is arranged in a front end portion in the housing  35 . An opening  35   b  and a flange portion  35   c  (as illustrated in  FIG. 2 ) are formed in the cylinder fixing portion  35   a . The rear portion of the base body  11  is inserted in the opening  35   b , and the flange portion  35   c  is formed on the outer surface of the housing  35 . A motor fixing portion  35   d  to which the electric motor  20  is fixed is formed on the upper side of the rear portion of the housing  35 , and an opening  35   e  in which the output shaft  21  is inserted is formed in the motor fixing portion  35   d.    
         [0041]    When the rotational driving force of the output shaft  21  is inputted into the nut member  33  through the gear mechanism  34 , the axial force in the linear direction is exerted on the rod  31  by a ball-screw mechanism arranged between the nut member  33  and the rod  31 , so that the rod  31  moves back and forth in the axial direction. 
         [0042]    The reservoir  40  is a container reserving the brake fluid, and arranged on the upper side of a front portion of the base body  11  of the slave cylinder  10 . (See  FIG. 2 .) The reservoir  40  includes fluid feed portions  41  and  42  connected to the base body  11 , and a hose extended from the main reservoir (not shown) is connected to the reservoir  40 . 
         [0043]    The motor cylinder device A 2  communicates with the master cylinder device A 1  through the tubes Hc and Hd. When the normally-open shutoff valves  74  and  75  are in the closed state, the hydraulic brake pressure generated in the motor cylinder device A 2  is inputted into the master cylinder device A 1  through the tubes Hc and Hd, and is further inputted into the hydraulic control device A 3  through the hydraulic communication paths  79   c  and  79   d  and the tubes Ha and Hb. 
         [0044]    The hydraulic control device A 3  has such a structure that antilock brake control (ABS control) for suppressing wheel slips, sideslip control and traction control for stabilizing the vehicle behavior, and the like can be performed. The hydraulic control device A 3  is connected to the wheel cylinders W through tubes. Although not shown, the hydraulic control device A 3  includes a hydraulic unit, electric motors, the electronic control unit (not shown), and the like, where solenoid valves, pumps, and the like are arranged in the hydraulic unit, the electric motors drive the pumps, and the electronic control unit controls the solenoid valves, the motors, and the like. 
         [0045]    Next, operations of the vehicle brake system A are briefly explained below. In the normal state, in which the vehicle brake system A normally operates, the normally-open shutoff valves  74  and  75  are closed, and the normally-close shutoff valve  76  is open. When the brake pedal P is manipulated in the above state, the hydraulic brake pressure generated in the master cylinder  71  is not transmitted to the wheel cylinders W, and is instead transmitted to the stroke simulator  72 , so that the piston  72   a  is displaced. Therefore, a stroke of the brake pedal P is allowed and simulated reaction force in response to a manipulation of the brake pedal P is imparted to the brake pedal P. 
         [0046]    In addition, when depressing of the brake pedal P is detected by a stroke sensor (not shown) or the like, the electric motor  20  in the motor cylinder device A 2  is driven, both of the slave pistons  12  and  13  are displaced, so that the brake fluid in both of the pressure chambers  11   b  and  11   c  is pressurized. The electronic control unit (not shown) compares the hydraulic brake pressure outputted from the slave cylinder  10  (the hydraulic brake pressure detected by the pressure sensor  77 ) with the hydraulic brake pressure outputted from the master cylinder  71  (the hydraulic brake pressure detected by the pressure sensor  78 ), and controls the number of rotations and the like of the electric motor  20  on the basis of the comparison result. 
         [0047]    The hydraulic brake pressure generated in the slave cylinder  10  is transmitted to the wheel cylinders W through the hydraulic control device A 3 , and the wheel cylinders W are actuated, so that braking forces are exerted on the respective wheels. 
         [0048]    Further, in the situation in which the motor cylinder device A 2  does not operate (e.g., in cases of emergency or loss of electric power), both of the normally-open shutoff valves  74  and  75  are brought into the open state and the normally-close shutoff valve  76  is brought into the closed state, so that the hydraulic brake pressure generated in the master cylinder  71  is transmitted to the wheel cylinders W. 
         [0049]    Next, a concrete structure of the motor cylinder device A 2  is explained below. 
         [0050]    The base body  11  is a casting of an aluminum alloy. As illustrated in  FIG. 3 , the slave cylinder bore  11   a  having a cylindrical shape with a bottom extends in the front-back direction in the base body  11 . The bottom surface  11   d  is formed on the front side (on the left side in  FIG. 3 ), and the opening  11   e  is formed on the rear side (on the right side in  FIG. 3 ). In addition, a housing attachment portion  16  is formed in the rear portion of the base body  11 , and a reservoir mounting portion  17  is formed in an upper portion of the base body  11 . 
         [0051]    As illustrated in  FIG. 2 , a flange portion  16   b  is formed on the outer surface of the housing attachment portion  16 . A drive transmission portion  30  is connected to the rear portion of the base body  11  by fixing the flange portion  16   b  of the housing attachment portion  16  to the flange portion  35   c  of the cylinder fixing portion  35   a  with bolts B 1 . 
         [0052]    As illustrated in  FIG. 3 , the first slave piston  12  and the second slave piston  13  are arranged in the slave cylinder bore  11   a , the first pressure chamber  11   b  is formed between the bottom surface  11   d  and the first slave piston  12 , and the second pressure chamber  11   c  is formed between the slave pistons  12  and  13 . As illustrated in  FIG. 1 , the first pressure chamber  11   b  communicates with the tube Hc through a connection port  11   f , and the second pressure chamber  11   c  communicates with the tube Hd through a connection port  11   g.    
         [0053]    As illustrated in  FIG. 4 , the first slave piston  12  is a metal part constituted by the shaft member  12   a , which has a round cross section. The first flange portion  12   b  is formed on the outer circumferential surface of the front portion of the shaft member  12   a , and the second flange portion  12   c  is formed on the outer circumferential surface of an approximately middle portion of the shaft member  12   a.    
         [0054]    As illustrated in  FIG. 5A , feeding paths  12   i  penetrate through the first flange portion  12   b  in the axial direction. The feeding paths  12   i  are through-bores having a cylindrical shape and opening on the first pressure chamber  11   b  side and the side opposite to the first pressure chamber  11   b . According to the present embodiment, six feeding paths  12   i  are arranged equally spaced along the circumferential direction in the first flange portion  12   b.    
         [0055]    As illustrated in  FIG. 3 , in the shaft member  12   a , a through-bore  12   h  penetrates in the vertical direction through a middle shaft portion of the shaft member  12   a  between the first flange portion  12   b  and the second flange portion  12   c . The through-bore  12   h  is an elongated bore, which is elongated in the axial direction of the shaft member  12   a  (as illustrated in  FIG. 4 ), and the limiting member  19  is inserted through the through-bore  12   h . The limiting member  19  is explained later. 
         [0056]    Further, an insertion bore  12   g  having a cylindrical shape with a bottom is open in a rear end face  12   f  of the shaft member  12   a  (as illustrated in  FIG. 4 ). 
         [0057]    A first piston sealing member  18   a  is in contact with the front face of the first flange portion  12   b . The first piston sealing member  18   a  is an annular rubber part, which is externally fitted on a protrusion  12   e . The protrusion  12   e  has a round cross section and protrudes forward from the first flange portion  12   b . The first piston sealing member  18   a  closes the openings on the front side (the first pressure chamber  11   b  side) of the feeding paths  12   i.    
         [0058]    The first piston sealing member  18   a  is a cup seal having a cylindrical portion  18   b  and a lip portion  18   c . The cylindrical portion  18   b  is externally fitted on a base portion  12   d  of the protrusion  12   e . The lip portion  18   c  radially extends from the rear-end edge portion of the cylindrical portion  18   b . The lip portion  18   c  is more inclined forward (toward the first pressure chamber  11   b  side) in relatively outside locations in the radial direction, and the outer circumferential surface of the lip portion  18   c  is in contact with the inner circumferential surface of the slave cylinder bore  11   a.    
         [0059]    A fall prevention member  12   j  is externally fitted on the protrusion  12   e . The fall prevention member  12   j  has an annular shape and constitutes a means for preventing a fall of the first piston sealing member  18   a . The fall prevention member  12   j  is in contact with the base portion  12   d  of the protrusion  12   e  and the cylindrical portion  18   b  of the first piston sealing member  18   a.    
         [0060]    A concave grove  12   k  is formed over the entire circumference of the shaft member  12   a  on the rear side of the second flange portion  12   c . A second piston sealing member  18   d  as a cup seal is externally fitted on the concave grove  12   k.    
         [0061]    The limiting member  19  protrudes into the slave cylinder bore  11   a . The limiting member  19  according to the present embodiment is a rod-like member which passes through the slave cylinder bore  11   a  in the vertical direction, and also passes through the through-bore  12   h  in the first slave piston  12 . The upper end portion of the limiting member  19  is inserted into an installation bore  11   h , and the lower end portion of the limiting member  19  is inserted into a recess  11   i . The installation bore  11   h  and the recess  11   i  are open in the inner circumferential surface of the slave cylinder bore  11   a.    
         [0062]    The backward motion of the first slave piston  12  is limited by abutting of the front end of the inner circumferential surface of the through-bore  12   h  on the limiting member  19 . In addition, the forward motion of the first slave piston  12  is limited by abutting of the rear end of the inner circumferential surface of the through-bore  12   h  on the limiting member  19 . 
         [0063]    The first elastic member  14  is contained in the first pressure chamber  11   b . The first elastic member  14  is a coil spring which is arranged between the bottom surface  11   d  of the slave cylinder bore  11   a  and the front end face  12   d  (the fall prevention member  12   j ) of the first slave piston  12 . The first elastic member  14  is compressed when the first slave piston  12  moves forward, and returns the first slave piston  12  to the backward limit (the initial position) by the elastic force of the first elastic member  14 . 
         [0064]    As illustrated in  FIG. 4 , the second slave piston  13  is a metal part constituted by a shaft member  13   a , which has a round cross section. A first flange portion  13   b  and a second flange portion  13   c  are formed on the outer circumferential surface of an approximately middle portion, in the axial direction, of the shaft member  13   a . A plurality of feeding paths  13   i  penetrate through the first flange portion  13   b  in the axial direction. 
         [0065]    As illustrated in  FIG. 3 , a third piston sealing member  18   e  is in contact with the front face of the first flange portion  13   b . The third piston sealing member  18   e  is a cup seal, which is externally fitted on the shaft member  13   a . A guide member  18   f , which is fitted into the opening  11   e  of the slave cylinder bore  11   a , is arranged on the rear side of the second flange portion  13   c . A through-bore is formed in the center of the guide member  18   f , and the shaft member  13   a  is slidably inserted in the guide member  18   f . The guide member  18   f  seals the gap between the inner circumferential surface of the slave cylinder bore  11   a  and the outer circumferential surface of the shaft member  13   a.    
         [0066]    A front portion of the shaft member  13   a  is inserted into the insertion bore  12   g  in the first slave piston  12 . A limiting member  13   e , which protrudes into the insertion bore  12   g , is inserted into a through-bore  13   d  formed in the front portion of the shaft member  13   a . Therefore, when the second slave piston  13  moves back and forth in the slave cylinder bore  11   a , the forward and backward motions of the second slave piston  13  are limited by abutting of the inner circumferential surface of the insertion bore  12   g  on the limiting member  13   e.    
         [0067]    A guide bore  13   g  having a cylindrical shape with a bottom is open in a rear end face  13   f  of the shaft member  13   a  (as illustrated in  FIG. 4 ). As illustrated in  FIG. 1 , the rod  31  in the drive transmission portion  30  is inserted into the guide bore  13   g , and the front end face of the rod  31  is in contact with a bottom surface  13   h  of the guide bore  13   g.    
         [0068]    As illustrated in  FIG. 3 , the second elastic member  15  is a coil spring which surrounds the shaft member  13   a  on the front side of the third piston sealing member  18   e . The second elastic member  15  is arranged between a rear end portion of the first slave piston  12  and the first flange portion  13   b  of the second slave piston  13 . The second elastic member  15  is compressed when the second slave piston  13  moves forward, and returns the second slave piston  13  to the backward limit (the initial position) by the elastic force of the second elastic member  15 . 
         [0069]    The reservoir mounting portion  17  is a portion which is arranged as a mounting seat for the reservoir  40 , and is formed in the upper portion of the base body  11 . The reservoir mounting portion  17  includes front and rear reservoir union ports  17   a  and  17   b , a first communication bore  17   c  (as illustrated in  FIG. 5A ), a second communication bore  17   d , and a connection portion  17   e.    
         [0070]    Each of the front and rear reservoir union ports  17   a  and  17   b  has a cylindrical shape, and is arranged on the upper portion of the base body  11  to protrude from the upper portion of the base body  11 . In addition, an increased-diameter portion  17   f  is formed in an upper portion of the inner circumferential surface of each of the front and rear reservoir union ports  17   a  and  17   b . In addition, the connection portion  17   e  is arranged between the front and rear reservoir union ports  17   a  and  17   b.    
         [0071]    As illustrated in  FIG. 5B , the installation bore  11   h  having a cylindrical shape is open in the bottom surface  17   g  of the front reservoir union port  17   a . The installation bore  11   h  penetrates through the bottom surface  17   g  and the inner circumferential surface of the slave cylinder bore  11   a . The upper portion of the limiting member  19  is inserted in the installation bore  11   h . The installation bore  11   h  is located on the rear side of the center of the bottom surface  17   g , and is open in a vicinity of the outer peripheral area of the bottom surface  17   g.    
         [0072]    Further, the first communication bore  17   c  is open in the bottom surface  17   g  of the front reservoir union port  17   a . As illustrated in  FIG. 5A , the first communication bore  17   c  is a through-bore having a cylindrical shape, an upper end opened in the bottom surface  17   g  of the front reservoir union port  17   a , and a lower end opened in the inner circumferential surface of the slave cylinder bore  11   a.    
         [0073]    As illustrated in  FIG. 5B , It is necessary that the first communication bore  17   c  be open in the inner circumferential surface of the slave cylinder bore  11   a  on the rear side of the first piston sealing member  18   a  (the side opposite to the first pressure chamber  11   b ) in order to prevent inflow of the brake fluid from the first pressure chamber  11   b  when the first pressure chamber  11   b  is pressurized. In the state (illustrated in  FIG. 5B ) in which the first slave piston  12  is located at the backward limit, the first piston sealing member  18   a  moves backward to the position in which the first piston sealing member  18   a  overlaps a front portion of the bottom surface  17   g , and the lower end portion of the first communication bore  17   c  is open in a position in which the lower end portion of the first communication bore  17   c  overlaps the outer circumferential surface of the first flange portion  12   b . Since the gap between the first piston sealing member  18   a  and the installation bore  11   h  in the front-back direction is reduced as above, it is difficult to open the first communication bore  17   c  in the central area of the bottom surface  17   g.    
         [0074]    Therefore, according to the present embodiment, the first communication bore  17   c  is formed to be open in the area on the right side (in  FIG. 5B ) of the center of the bottom surface  17   g . Since the first communication bore  17   c  is formed to be open in the position laterally shifted from the central area of the bottom surface  17   g  as above, i.e., in the vicinity of the outer peripheral portion of the bottom surface  17   g , it is possible to avoid interference of the first communication bore  17   c  and the installation bore  11   h  while arranging the first communication bore  17   c  on the rear side of the first piston sealing member  18   a.    
         [0075]    As illustrated in  FIG. 3 , one end of the second communication bore  17   d  is open in the inner circumferential surface of the rear reservoir union port  17   b , and the other end of the second communication bore  17   d  is open in the inner circumferential surface of the slave cylinder bore  11   a  on the rear side of the first flange portion  13   b  in the second slave piston  13 . 
         [0076]    The fluid feeding portions  41  and  42  having a cylindrical shape and being arranged to protrude from the lower face of the reservoir  40  are respectively inserted in the front and rear reservoir union ports  17   a  and  17   b , and the container body  43  of the reservoir  40  is placed on the upper ends of the front and rear reservoir union ports  17   a  and  17   b . A connection portion  45 , which is formed between the front-side and rear-side fluid feed portions  41  and  42  (as illustrated in  FIG. 2 ), is fixed to the connection portion  17   e  in the reservoir mounting portion  17  with a spring pin  45   a.    
         [0077]    Fluid feeding bores  41   a  and  42   a , which communicate with a reservation space  43   a  in the container body  43 , penetrate through the fluid feed portions  41  and  42  in the vertical direction. The reservation space  43   a  communicates with the slave cylinder bore  11   a  through the front-side fluid feeding bore  41   a  and the first communication bore  17   c  (illustrated in  FIG. 5A ). The brake fluid in the reservation space  43   a  flows into the rear side of the first flange portion  12   b  through the gap between the inner circumferential surface of the slave cylinder bore  11   a  and the outer circumferential surface of the first flange portion  12   b . In addition, the reservation space  43   a  communicates with the slave cylinder bore  11   a  through the rear-side fluid feeding bore  42   a  and the second communication bore  17   d.    
         [0078]    When the hydraulic brake pressure in the first pressure chamber  11   b  falls below the hydraulic brake pressure on the rear side of the first piston sealing member  18   a  because of the wearing of the brake pads or the absorption effect during the vehicle behavior control, the pressure difference causes the lip portion  18   c  of the first piston sealing member  18   a  to bend inward, so that the brake fluid passes over the outer peripheral portion of the first piston sealing member  18   a  from the rear side to the front side, and flows into the first pressure chamber  11   b.    
         [0079]    As explained above, the lip portion  18   c  formed in the outer peripheral portion of the first piston sealing member  18   a  realizes a check valve which allows only the inflow of the brake fluid from the rear side (the side opposite to the first pressure chamber  11   b ) to the front side (the first pressure chamber  11   b  side). Therefore, it is possible to prevent inflow of the brake fluid from the first pressure chamber  11   b  to the rear side of the first piston sealing member  18   a  (the first communication bore  17   c  side) when the first slave piston  12  moves forward, cause the brake fluid to pass over the outer peripheral portion of the first piston sealing member  18   a , and feed the brake fluid to the first pressure chamber  11   b  when the hydraulic brake pressure in the first pressure chamber  11   b  is lowered. 
         [0080]    In addition, the brake fluid flows from the rear side of the first flange portion  12   b  of the first slave piston  12  into the rear side of the first piston sealing member  18   a  (the front side of the first flange portion  12   b ) through the feeding paths  12   i . Therefore, it is possible to cause the brake fluid to smoothly flow into the first pressure chamber  11   b  through each of the feeding paths  12   i  even when the flow rate of the brake fluid absorbed by the first pressure chamber  11   b  is great, e.g., when the hydraulic brake pressure in the first pressure chamber  11   b  is greatly lowered by the absorption effect during the vehicle behavior control. 
         [0081]    Further, when the brake fluid is absorbed into the second pressure chamber  11   c , the brake fluid passes over the outer peripheral portion of the third piston sealing member  18   e  and flows into the second pressure chamber  11   c.    
         [0082]    Reservoir sealing members  44  having an annular shape and being externally fitted on the fluid feed portions  41  and  42  are fitted into the increased-diameter portions  17   f  of the front and rear reservoir union ports  17   a  and  17   b . The reservoir sealing members  44  are rubber parts which seal the gaps between the inner circumferential surfaces of the front and rear reservoir union ports  17   a  and  17   b  and the outer circumferential surfaces of the fluid feed portions  41  and  42 . Thus, in the above structure, the installation bore  11   h  and the first communication bore  17   c  which are formed in the bottom surface  17   g  of the front reservoir union port  17   a  are sealed with one of the reservoir sealing members  44  from the external space. 
         [0083]    As illustrated in  FIG. 5B , the front-side fluid feed portion  41  includes a fall prevention portion  41   c  and a cutout portion  41   d . The fall prevention portion  41   c  is arranged opposed to the installation bore  11   h , and the cutout portion  41   d  is arranged opposed to the first communication bore  17   c . (See  FIG. 5A .) That is, the upper half of the fluid feed portion  41  has a circumferentially continuous, completely cylindrical shape, and the lower half of the fluid feed portion  41  has an arc-shaped (C-shaped) axial cross section, in which an approximately half in the circumferential direction is lacking. 
         [0084]    As illustrated in  FIG. 3 , the fall prevention portion  41   c  is arranged in a vicinity of the bottom surface  17   g  of the front reservoir union port  17   a . Thus, a means for preventing a fall of the limiting member  19  from the installation bore  11   h  is realized by arranging the fall prevention portion  41   c  over the limiting member  19  as above. 
         [0085]    As illustrated in  FIG. 5B , the cutout portion  41   d  is a portion which is extended in the axial direction to the tip side of the fluid feed portion  41  and produced by removing an approximately half of a lower-end edge portion  41   b  (the right side illustrated in  FIG. 5B ) in the circumferential direction. In the cutout portion  41   d , the removed portion extends in the vertical direction to a vicinity of the one of the reservoir sealing members  44 , so that the space over the first communication bore  17   c  is enlarged by the cutout portion  41   d.    
         [0086]    In the motor cylinder device A 2  as explained above, the lower-end edge portion  41   b  realizes the means for preventing a fall of the limiting member  19  as illustrated in  FIG. 5A . In addition, the installation bore  11   h  for the limiting member  19  is sealed from the external space with the one of the reservoir sealing members  44  externally fitted on the fluid feed portion  41 . Since the limiting member  19  is arranged by effectively using the space in the base body  11  as above, it is possible to reduce the number of parts and the size of the base body  11 . 
         [0087]    In addition, even when air intrudes into the gap S between the inner circumferential surface of the front reservoir union port  17   a  and the outer circumferential surface of the fluid feed portion  41 , the air is exhausted into the reservoir  40  through the cutout portion  41   d  in the fluid feed portion  41 . Therefore, it is possible to prevent air accumulation in the front reservoir union port  17   a . Further, since the cutout portion  41   d  is formed to extend to the vicinity of the one of the reservoir sealing members  44 , it is possible to exhaust the air, with high reliability, through the gap S between the inner circumferential surface of the front reservoir union port  17   a  and the outer circumferential surface of the fluid feed portion  41 . 
         [0088]    Furthermore, since the first communication bore  17   c  is formed at the position opposed to the cutout portion  41   d  of the fluid feed portion  41 , it is possible to cause the brake fluid to smoothly flow from the fluid feed portion  41  into the first communication bore  17   c.    
         [0089]    Moreover, since the cutout portion  41   d  is formed in the fluid feed portion  41 , the first communication bore  17   c  can be located close to the outer peripheral portion of the bottom surface  17   g  in the front reservoir union port  17   a , so that the degree of freedom in designing the slave cylinder  10  can be increased. 
         [0090]    Although an embodiment of the present invention is explained above, the present invention is not limited to the explained embodiment, and the present invention can be modified as needed without departing from the gist of the present invention. Although, in the explained embodiment, the first communication bore  17   c  is formed in the position opposed to the cutout portion  41   d  as illustrated in  FIG. 5B , the first communication bore  17   c  may be formed in the center of the bottom surface  17   g  in the case where space can be secured in the center of the bottom surface  17   g.    
         [0091]    In addition, although the six feeding paths  12   i  are formed in the first flange portion  12   b  of the first slave piston  12  as illustrated in  FIG. 5A , the number of the feeding paths  12   i  is not limited to six. Further, the feeding paths may be constituted by one or more grooves formed on the outer peripheral portions of the first flange portion  12   b.    
       LIST OF REFERENCES 
       [0000]    
       
           10 : Slave Cylinder 
           11 : Base Body 
           11   a : Slave Cylinder Bore 
           11   c : First Pressure Chamber 
           11   b : Second Pressure Chamber 
           11   h : Installation Bore 
           12 : First Slave Piston 
           12   a : Shaft Member 
           12   b : First Flange Portion 
           12   c : Second Flange Portion 
           12   i : Feeding Paths 
           13 : Second Slave Piston 
           14 : First Elastic Member 
           15 : Second Elastic Member 
           17 : Reservoir Mounting Portion 
           17   a : Reservoir Union Port 
           17   b : Reservoir Union Port 
           17   c : First Communication Bore 
           17   d : Second Communication Bore 
           17   g : Bottom Surface 
           18   a : First Piston Sealing Member 
           18   d : Second Piston Sealing Member 
           18   e : Third Piston Sealing Member 
           19 : Limiting Member 
           20 : Electric Motor 
           21 : Output Shaft 
           30 : Drive Transmission Portion 
           31 : Rod 
           40 : Reservoir 
           41 : Fluid feeding portion 
           41   a : Fluid Feeding Bore 
           41   c : Fall Prevention Portion 
           41   d : Cutout Portion 
           42 : Fluid feeding portion 
           44 : Reservoir Sealing Member 
           71 : Master Cylinder 
           72 : Stroke Simulator 
           73 : Reservoir 
         A: Vehicle Brake System 
         A 1 : Master Cylinder Device 
         A 2 : Motor Cylinder Device (Cylinder Device) 
         A 3 : Hydraulic Control Device 
         P: Brake Pedal (Brake Manipulator) 
         W: Wheel Cylinders