Abstract:
An electric brake device, in which the rotational drive force of an electric motor ( 72 ) drives a first slave piston and a second slave piston housed in a cylinder body and thereby generates brake fluid pressure, an actuator housing ( 172 ) is coupled to the cylinder body, and the mechanism housing part ( 173   a ) and a brake fluid encapsulating part in the cylinder body are partitioned by a sealing member, the actuator housing having a mechanism housing part ( 173   a ) for housing an actuator mechanism ( 74 ) for converting the rotational drive force of the electric motor ( 72 ) into the linear drive force for the first slave piston and the second slave piston; wherein the electric brake device is characterized in being provided with an interconnecting hole ( 179 ) for interconnecting the mechanism housing part ( 173   a ) and the atmosphere.

Description:
TECHNICAL FIELD 
     The present invention relates to an electric brake device which generates hydraulic brake pressure by rotational driving force generated by an electric motor when a brake manipulation unit is manipulated. 
     BACKGROUND ART 
     The vehicle brake system for use in a vehicle having a brake booster for enhancing the brake force when a brake pedal is depressed is widely known. For example, Patent Literature 1 discloses an electric brake actuator (electric booster device) using an electric motor as a boosting power source. In the electric brake actuator disclosed in Patent Literature 1, a shaft member moving back and forth in response to manipulation of a brake pedal is used as a main piston, and a cylindrical member sheathing the shaft member (the main piston) is used as a booster piston, and a hydraulic brake pressure is generated on the basis of a driving force inputted from the brake pedal to the shaft member (the main piston) and a driving force given by the electric motor to the cylindrical member (booster piston) for enhancing the tread force. 
     CITATION LIST PATENT LITERATURE 
     Patent Literature 1: Japanese Patent Laid-Open No. 2010-23594 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the electric brake actuator disclosed in Patent Literature 1, a pressure chamber in a master cylinder filled with brake fluid and a housing (actuator housing) including an enclosing portion for a ball-screw mechanism have sealed structures. Therefore, when the booster piston and the main piston move in the direction away from the enclosing portion for the ball-screw mechanism, a portion of the ball-screw mechanism is pushed out of the enclosing portion, so that the volume inside the enclosing portion increases and the pressure inside the enclosing portion decreases. When the pressure inside the enclosing portion for the ball-screw mechanism decreases, it is necessary to take external air into the enclosing portion. 
     In addition, for example, when the internal temperature of the actuator housing varies with the ambient temperature of the electric brake actuator, the temperature of the enclosing portion for the ball screw mechanism also varies, so that the pressure inside the enclosing portion varies. Specifically, when the temperature of the enclosing portion falls, the internal pressure decreases. Therefore, when the temperature of the enclosing portion for the ball-screw mechanism falls, it is also necessary to take external air into the enclosing portion. However, Patent Literature 1 discloses no arrangement for taking in external air when the pressure inside the enclosing portion for the ball-screw mechanism decreases. 
     If the external air cannot be preferably taken in even in the case where the internal pressure of the enclosing portion for the ball-screw mechanism decreases, the decreased internal pressure of the enclosing portion is maintained, so that, in particular, when the pressure chamber in the master cylinder is pressurized, the pressure difference between the pressure chamber in the master cylinder and the enclosing portion for the ball-screw mechanism causes problems such as waterdrop intake or sealing imperfection of a sealing member with which the pressure chamber and the enclosing portion are partitioned. 
     In view of above, the object of the present invention is to provide an electric brake device for a vehicle which can preferably take in external air according to decrease in the internal pressure and can suppress occurrence of fluid leakage and the like. 
     Solution to Problem 
     In order to accomplish the above object, an electric brake device according to the present invention is provided. In the electric brake device, a brake pressure is generated by actuating, by a rotational driving force of an electric motor, a hydraulic control piston enclosed in a cylinder body, and an actuator housing including a mechanism-enclosing portion which encloses an actuator mechanism converting the rotational driving force around an output shaft of the electric motor into a linear driving force of the hydraulic control piston is connected to the cylinder body, and a brake-fluid enclosing portion in the cylinder body is partitioned off from the mechanism-enclosing portion with a sealing member. The electric brake device according to the present invention comprises a communication hole which realizes communication between the mechanism-enclosing portion and the atmosphere. 
     According to the present invention, it is possible to enable the cylinder body and the mechanism-enclosing portion to communicate with the atmosphere, where the cylinder body is filled with the brake fluid and the mechanism-enclosing portion is partitioned off with the sealing member. Therefore, when the pressure in the mechanism-enclosing portion decreases, the external air can be preferably taken into the mechanism-enclosing portion. 
     An additional characteristic feature of the present invention is that the flow of condensed water in the communication hole is blocked with the film of a material which has a water proofing property and a moisture permeability property and through which air can pass. 
     According to the above additional characteristic feature, it is possible to block the flow of condensed water in the communication hole, and make the communication hole block pass only the air. Therefore, it is possible to prevent intrusion of condensed water such as rain water through the communication hole. 
     Another additional characteristic feature of the present invention is that the communication hole is formed to realize communication between the mechanism-enclosing portion and an insertion hole into which an attachment fastening member for fixing the actuator housing to a vehicle is inserted. 
     According to the above additional characteristic feature, the mechanism-enclosing portion can communicate with the atmosphere through the insertion hole, into which the attachment fastening member for fixing the electric brake actuator to the vehicle is inserted. Therefore, when the pressure in the mechanism-enclosing portion decreases, the external air can be preferably taken into the mechanism-enclosing portion. 
     A further additional characteristic feature of the present invention is that an opening of the communication hole on the mechanism-enclosing portion side is formed vertically above the sealing member. 
     According to the above additional characteristic feature, since the opening of the communication hole on the mechanism-enclosing portion side is formed vertically above the sealing member, it is possible to prevent the communication hole from being closed on the mechanism-enclosing portion side by the brake fluid which flows beyond the sealing member. 
     Effect of Invention 
     According to the present invention, it is possible to provide an electric brake device which can preferably take in external air according to decrease in the internal pressure and can suppress occurrence of fluid leakage and the like. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a structural diagram of a vehicle brake system in which an electric brake device according to the present embodiment is provided. 
         FIG. 2  is a perspective diagram illustrating an arrangement in which the electric brake device is disposed in a power-plant containment room. 
         FIG. 3  is an exploded perspective view of the electric brake device. 
         FIG. 4  is an exploded perspective view of an actuator housing. 
         FIG. 5  is a diagram illustrating an example of a structure in which the electric brake device is attached to a bracket. 
         FIG. 6  is a cross-sectional view of the actuator housing from the lower side. 
         FIG. 7  is a cross-sectional view of an intake/exhaust hole which realizes communication between an insertion hole and a mechanism-enclosing portion. 
         FIG. 8A  is a diagram illustrating a manner of fixing a water-proof moisture-permeable film with a mount rubber, and 
         FIG. 8B  is a diagram in which a holding member for fixing the water-proof moisture-permeable film is illustrated by a partial cross-sectional view. 
         FIG. 9  is a cross-sectional view of an intake/exhaust hole which realizes communication between an engagement hole and the mechanism-enclosing portion. 
         FIG. 10  is a cross-sectional view of an intake/exhaust hole formed in the motor-enclosing portion. 
         FIG. 11A  is a magnified view of the Y1 portion in  FIG. 10 , and 
         FIG. 11B  is a diagram illustrating a structure of a cover member. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention is explained below with reference to the accompanying drawings as needed.  FIG. 1  schematically illustrates the arrangement of a vehicle brake system containing an electric brake device according to the embodiment of the present invention. 
     The vehicle brake system  10  illustrated in  FIG. 1  includes both of a brake-by-wire system for normal use and a conventional hydraulic brake system for fail-safe. The brake is operated by transmission of an electric signal in the brake-by-wire system, and by transmission of hydraulic pressure in the conventional hydraulic brake system. 
     Specifically, as illustrated in  FIG. 1 , the vehicle brake system  10  is basically constituted by a hydraulic-pressure generator (input apparatus)  14 , a pedal-stroke sensor St, an electric brake actuator (electric brake device)  16 , and a vehicle-behavior stabilizing apparatus  18 , which are separately arranged. When a brake manipulation unit such as a brake pedal  12  is manipulated by an operator, the manipulation is inputted into the input apparatus  14 . The pedal-stroke sensor St detects the amount of manipulation (stroke) of the brake pedal  12  when the brake pedal  12  is depressed. The electric brake actuator  16  controls (generates) hydraulic brake pressure. The vehicle-behavior stabilizing apparatus  18  assists in stabilization of the vehicle behavior. Hereinafter, the vehicle-behavior stabilizing apparatus  18  is referred to as the VSA (vehicle stability assist) apparatus. (VSA is a registered trademark.) 
     The input apparatus  14 , the electric brake device  16 , and the VSA apparatus  18  are connected through hydraulic paths formed with tubular members such as hoses or tubes, and the input apparatus  14  and the electric brake device  16  are electrically connected through wiring harness (not shown) so as to constitute the brake-by-wire system. 
     In the hydraulic paths, a connection port  20   a  of the input apparatus  14  is connected to a connection point A 1  (which is indicated on the slightly below the center of  FIG. 1  and regarded as a reference point) through a first piping tube  22   a , an outlet port  24   a  of the electric brake device  16  is also connected to the connection point A 1  through a second piping tube  22   b , and an inlet port  26   a  of the VSA apparatus  18  is connected to the connection point A 1  through a third piping tube  22   c.    
     In addition, another connection port  20   b  of the input apparatus  14  is connected to another connection point A 2  (which is regarded as another reference point) through a fourth piping tube  22   d , another outlet port  24   b  of the electric brake device  16  is also connected to the connection point A 2  through a fifth piping tube  22   e , and another inlet port  26   b  of the VSA apparatus  18  is connected to the connection point A 2  through a sixth piping tube  22   f.    
     The VSA apparatus  18  has a plurality of outlet ports  28   a  to  28   d . The first outlet port  28   a  is connected through a seventh piping tube  22   g  to a wheel cylinder  32 FR in a disk brake mechanism  30   a  arranged in the right front wheel, the second outlet port  28   b  is connected through an eighth piping tube  22   h  to a wheel cylinder  32 RL in a disk brake mechanism  30   b  arranged in the left rear wheel, the third outlet port  28   c  is connected through a ninth piping tube  22   i  to a wheel cylinder  32 RR in a disk brake mechanism  30   c  arranged in the right rear wheel, and the fourth outlet port  28   d  is connected through a tenth piping tube  22   j  to a wheel cylinder  32 FL in a disk brake mechanism  30   d  arranged in the left front wheel. 
     In the above arrangement, the brake fluid is supplied to the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL in the disk brake mechanisms  30   a  to  30   d  through the piping tubes  22   g  to  22   j  connected to the outlet ports  28   a  to  28   d , respectively. Therefore, when the hydraulic pressure in the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL rises, the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL operate, and exert braking force on the respectively corresponding wheels (i.e., the right front wheel, the left rear wheel, the right rear wheel, and the left front wheel). 
     The vehicle brake system  10  can be mounted on each type of vehicles including the automobiles driven by only an engine (internal-combustion-engine), hybrid electric vehicles, electric vehicles, and fuel-cell vehicles. In addition, the vehicle brake system  10  is not limited by the type of driving of the vehicle, and can be mounted on vehicles of any driving type, for example, the front-wheel drive, the rear-wheel drive, or the four-wheel drive. 
     The input apparatus  14  includes a master cylinder  34  and a first reservoir  36  which is attached to the master cylinder  34 . The master cylinder  34  is a tandem type, and can generate hydraulic pressure in response to manipulation of the brake pedal  12  by the operator. The master cylinder  34  has a cylinder tube  38 , in which two pistons  40   a  and  40   b  are arranged in such a manner that the two pistons  40   a  and  40   b  are a predetermined distance apart from each other and slidable along the axial direction of the cylinder tube  38 . The one  40   a  of the two pistons is arranged nearer to the brake pedal  12 , and connected to the brake pedal  12  through a pushrod  42 . The other  40   b  of the two pistons is arranged farther from the brake pedal  12  than the one  40   a  of the two pistons. 
     A pair of cup seals  44   a  and  44   b  are attached to the outer wall of each of the two pistons  40   a  and  40   b  by annular step portions. In addition, back chambers  48   a  and  48   b  are respectively formed in the gaps between the cup seals  44   a  and  44   b  on the two pistons  40   a  and  40   b , and respectively communicate with supply ports  46   a  and  46   b , which are explained later. Further, a spring member  50   a  is arranged between the pistons  40   a  and  40   b , and another spring member  50   b  is arranged between the piston  40   b  and a side edge portion of the cylinder tube  38 . Alternatively, the cup seals  44   a  and  44   b  may be attached on the inner wall of the cylinder tube  38 . 
     Moreover, the two supply ports  46   a  and  46   b , two relief ports  52   a  and  52   b , and two output ports  54   a  and  54   b  are arranged in the cylinder tube  38  in the master cylinder  34 . In this case, the supply port  46   a  and  46   b  and the relief ports  52   a  and  52   b  are arranged such that each of the supply ports  46   a  and  46   b  and one of the relief ports  52   a  and  52   b  join and communicate with a reservoir chamber (not shown) in the first reservoir  36 . 
     Further, a second pressure chamber  56   a  and a first pressure chamber  56   b  are realized in the cylinder tube  38  in the master cylinder  34 . Hydraulic pressure corresponding to the tread force with which the brake pedal  12  is depressed by the operator is generated in the first and second pressure chambers  56   b  and  56   a . The second pressure chamber  56   a  communicates with the connection port  20   a  through a second hydraulic path  58   a , and the first pressure chamber  56   b  communicates with the other connection port  20   b  through a first hydraulic path  58   b.    
     In addition, a pressure sensor Pm is arranged on the upstream side of the second hydraulic path  58   a  between the master cylinder  34  and the connection port  20   a , and a second shutoff valve  60   a  realized by a normally-open solenoid valve is arranged on the downstream side of the second hydraulic path  58   a . The pressure sensor Pm measures the hydraulic pressure on the upstream side of the second hydraulic path  58   a  (i.e., on the master cylinder  34  side of the second shutoff valve  60   a  in the second hydraulic path  58   a ). 
     Further, a first shutoff valve  60   b  realized by a normally-open solenoid valve is arranged on the upstream side of the first hydraulic path  58   b  between the master cylinder  34  and the connection port  20   b , and a pressure sensor Pp is arranged on the downstream side of the first hydraulic path  58   b . The pressure sensor Pp detects the hydraulic pressure on the downstream side of the first shutoff valve  60   b  (i.e., on the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL side of the first shutoff valve  60   b  in the first hydraulic path  58   b ). 
     The normally-open solenoid valves realizing the first and second shutoff valves  60   b  and  60   a  are valves in which the normal position of the valve element (i.e., the position of the valve element when the valves are unenergized) is open.  FIG. 1  shows the closed states of the first and second shutoff valves  60   b  and  60   a , in which the solenoids in the first and second shutoff valves  60   b  and  60   a  are energized so that the valve elements (not shown) are activated. 
     Further, a hydraulic branch path  58   c , which branches off from the first hydraulic path  58   b , is arranged in the first hydraulic path  58   b  between the master cylinder  34  and the first shutoff valve  60   b , and a third shutoff valve  62  and a stroke simulator  64  are connected in series to the hydraulic branch path  58   c . The third shutoff valve  62  is realized by a normally-closed solenoid valve. The normally-closed solenoid valve realizing the third shutoff valve  62  is a valve in which the normal position of the valve element (i.e., the position of the valve element when the valve is unenergized) is closed.  FIG. 1  shows the open state of the third shutoff valve  62  in which the solenoid in the third shutoff valve  62  is energized so that the valve element (not shown) is activated. 
     This stroke simulator  64  is a device which generates a brake stroke and reaction force in response to a manipulation of the brake pedal  12  during the break-by-wire control for making the operator feel as if braking force were directly generated by the tread force. The stroke simulator  64  is arranged on the master cylinder  34  side of the first shutoff valve  60   b  in the first hydraulic path  58   b . A hydraulic chamber  65 , which communicates with the hydraulic branch path  58   c , is arranged in the stroke simulator  64  such that the stroke simulator  64  can absorb, through the hydraulic chamber  65 , the brake fluid delivered from the second pressure chamber  56   b  in the master cylinder  34 . 
     In addition, the stroke simulator  64  includes first and second return springs  66   a  and  66   b  and a simulator piston  68 . The first and second return springs  66   a  and  66   b  are arranged in series, and the simulator piston  68  is energized by the first and second return springs  66   a  and  66   b . The spring constant of the first return spring  66   a  is great, and the spring constant of the second return spring  66   b  is small. The first and second return springs  66   a  and  66   b  and the simulator piston  68  are arranged in such a manner that the increase rate of the pedal reaction force is low in the beginning stage of depression of the brake pedal  12 , and the pedal reaction force becomes strong in the later stage of the depression of the brake pedal  12  and the operator feels a pedal feeling equivalent to the pedal feeling with the conventional master cylinder. 
     The hydraulic paths can be roughly divided into first and second hydraulic routes  70   b  and  70   a . The second hydraulic route  70   a  connects the second pressure chamber  56   a  in the master cylinder  34  to the wheel cylinders  32 FR and  32 RL, and the first hydraulic route  70   b  connects the first pressure chamber  56   b  in the master cylinder  34  to the wheel cylinders  32 RR and  32 FL. 
     The second hydraulic route  70   a  is constituted by the second hydraulic path  58   a  connecting the outlet port  54   a  of the master cylinder  34  (i.e., the outlet port  54   a  of the cylinder tube  38 ) to the connection port  20   a  in the input apparatus  14 , the piping tubes  22   a  and  22   b  connecting the connection port  20   a  of the input apparatus  14  to the outlet port  24   a  of the electric brake device  16 , the piping tubes  22   b  and  22   c  connecting the outlet port  24   a  of the electric brake device  16  to the inlet port  26   a  of the VSA apparatus  18 , and the piping tubes  22   g  and  22   h  respectively connecting the outlet ports  28   a  and  28   b  of the VSA apparatus  18  to the wheel cylinders  32 FR and  32 RL. 
     The first hydraulic route  70   b  is constituted by the first hydraulic path  58   b  connecting the outlet port  54   b  of the master cylinder  34  (i.e., the outlet port  54   b  of the cylinder tube  38 ) to the connection port  20   b  in the input apparatus  14 , the piping tubes  22   d  and  22   e  connecting the connection port  20   b  of the input apparatus  14  to the outlet port  24   b  of the electric brake device  16 , the piping tubes  22   e  and  22   f  connecting the outlet port  24   b  of the electric brake device  16  to the inlet port  26   b  of the VSA apparatus  18 , and the piping tubes  22   i  and  22   j  respectively connecting the outlet ports  28   c  and  28   d  of the VSA apparatus  18  to the wheel cylinders  32 RR and  32 FL. 
     The electric brake device  16  includes an actuator mechanism  74  including an electric motor  72 , and a cylinder mechanism  76  which is actuated by the actuator mechanism  74 . 
     The actuator mechanism  74  contains a gear mechanism (deceleration mechanism)  78  and a ball-screw structure  80 . The gear mechanism  78  is arranged on the output shaft  72   b  side of the electric motor  72 , has multiple gears, and transmits the rotational driving force of the electric motor  72  by engagement of the multiple gears. The ball-screw structure  80  is constituted by a ball-screw shaft  80   a  and balls  80   b . The rotational driving force is transmitted to the ball-screw structure  80  through the gear mechanism  78 , and the ball-screw shaft  80   a  moves back and forth along the axial direction by the transmitted rotational driving force. 
     In the present embodiment, the ball-screw structure  80 , together with the gear mechanism  78 , is enclosed in a mechanism-enclosing portion  173   a  of an actuator housing  172 . 
     The cylinder mechanism  76  includes a cylinder body  82  and a second reservoir  84 . The cylinder body  82  has an approximately cylindrical shape, and the second reservoir  84  is directly attached to the cylinder body  82 . The second reservoir  84  is arranged to be connected through a piping tube  86  to the first reservoir  36  (which is attached to the master cylinder  34  in the input apparatus  14 ) such that the brake fluid reserved in the first reservoir  36  is supplied to the second reservoir  84  through the piping tube  86 . A reservoir for reserving the brake fluid may be arranged in the piping tube  86 . The actuator housing  172  is constituted by a housing body  172 F and a housing cover  172 R. The electric brake device  16  is constructed by coupling the cylinder body  82  to the actuator housing  172 , where the cylinder body  82  has a cylindrical shape. The cylinder body  82  is coupled to the actuator housing  172  by fitting an open edge portion (open end portion) of the cylinder body  82  into the actuator housing  172 . The construction of the actuator housing  172  and the portion in which the cylinder body  82  and the actuator housing  172  are coupled will be explained in detail later. 
     In the cylinder body  82 , a second slave piston  88   a  and a first slave piston  88   b  are slidably arranged in such a manner that the first and second slave pistons  88   b  and  88   a  are a predetermined distance apart from each other along the direction of the axis of the cylinder body  82 . The second slave piston  88   a  is arranged close to the ball-screw structure  80  in contact with an end portion of the ball-screw shaft  80   a  such that the second slave piston  88   a  is displaced integrally with the ball-screw shaft  80   a  in the direction indicated by the arrow X 1  or X 2 . The first slave piston  88   b  is arranged more apart from the ball-screw structure  80  than the second slave piston  88   a . In the present embodiment, the second slave pistons  88   a  and first slave piston  88   b  realize the hydraulic control piston described in the appended claims. 
     In addition, the electric motor  72  in the present embodiment is arranged to be covered by a motor casing  72   a  which is formed separately from the cylinder body  82  in such a manner that the output shaft  72   b  is approximately parallel to the slide direction (axial direction) of the first and second slave pistons  88   b  and  88   a . That is, the electric motor  72  is arranged in such a manner that the axial direction of the output shaft  72   b  is approximately parallel to the axial direction of the hydraulic control pistons. Further, the electric motor  72  is formed such that the drive rotation of the output shaft  72   b  is transmitted to the ball-screw structure  80  through the gear mechanism  78 . 
     The gear mechanism  78  is constituted by three gears, first, second, and third gears  78   a ,  78   b , and  78   c . The first gear  78   a  is attached to the output shaft  72   b  of the electric motor  72 , the second gear  78   b  transmits the rotation of the third gear  78   c , and the third gear  78   c  causes the balls  80   b  to rotate around the axis of the ball-screw shaft  80   a , where the balls  80   b  moves back and forth the ball-screw shaft  80   a  along the direction of the axis of the ball-screw shaft  80   a . Therefore, the axis of rotation of the third gear  78   c  is the axis of rotation of the ball-screw shaft  80   a , and becomes approximately parallel to the slide direction (axial direction) of the hydraulic control pistons (the second and first slave pistons  88   a  and  88   b ). As explained above, the output shaft  72   b  of the electric motor  72  is approximately parallel to the axial direction of the hydraulic control pistons. Therefore, the output shaft  72   b  of the electric motor  72  is approximately parallel to the axis of rotation of the third gear  78   c.    
     Thus, in the case where the axis of rotation of the second gear  78   b  is arranged to be approximately parallel to the output shaft  72   b  of the electric motor  72 , the output shaft  72   b  of the electric motor  72 , the axis of rotation of the second gear  78   b , and the axis of rotation of the third gear  78   c  are arranged approximately parallel. According to the above arrangement, the actuator mechanism  74  in the present embodiment converts the rotational drive force of the output shaft  72   b  of the electric motor  72  to back-and-forth drive force (linear drive force) of the ball-screw shaft  80   a . Since the second slave piston  88   a  and the first slave piston  88   b  are driven by the ball-screw shaft  80   a , the actuator mechanism  74  converts the rotational drive force of the output shaft  72   b  of the electric motor  72  to back-and-forth drive force (linear drive force) of the hydraulic control pistons (the second slave piston  88   a  and the first slave piston  88   b ). In addition, the mechanism-enclosing portion, which encloses the ball-screw structure  80 , is indicated by the reference  173   a.    
     A pair of slave cup seals  90   a  and  90   b  are respectively attached to the outer peripheral surfaces of the annular step portions of the first slave piston  88   b . In addition, a first back chamber  94   b , which communicates with a reservoir port  92   b , is formed between the slave cup seals  90   a  and  90   b . The first back chamber  94   b  and the reservoir port  92   b  are described later. Further, a second return spring  96   a  is arranged between the first and second slave pistons  88   b  and  88   a , and a first return spring  96   b  is arranged between the first slave piston  88   b  and the side edge portion of the cylinder body  82 . 
     Furthermore, an annular guide piston  90   c  is arranged on the rear side of the second slave piston  88   a  as a sealing member which closes the cylinder body  82 . The guide piston  90   c  forms a fluid-tight seal between the outer peripheral surface of the second slave piston  88   a  and the mechanism-enclosing portion  173   a , and guides the second slave piston  88   a  such that the second slave piston  88   a  can move along the direction of the axis of the second slave piston  88   a . In addition, it is preferable that a slave cup seal (not shown) be attached to the inner peripheral surface of the guide piston  90   c  (through which the second slave piston  88   a  is inserted) such that a fluid-tight seal is formed between the second slave piston  88   a  and the guide piston  90   c . Further, a slave cup seal  90   b  is arranged by an annular step portion on the forward side of the outer peripheral surface of the second slave piston  88   a . According to the above arrangement, the brake fluid with which the inside of the cylinder body  82  is filled is sealed in the cylinder body  82  by the guide piston  90   c , and does not flow to the actuator housing  172  side. In addition, a second back chamber  94   a  communicating with a reservoir port  92   a  is formed between the guide piston  90   c  and the slave cup seal  90   b  on the second slave piston  88   a . The second back chamber  94   a  and the reservoir port  92   a  will be described later. 
     The two reservoir ports  92   a  and  92   b  and the two outlet ports  24   a  and  24   b  are arranged in the cylinder body  82  in the cylinder mechanism  76 . In this case, the reservoir ports  92   a  and  92   b  are arranged to communicate with a reservoir chamber (not shown) in the second reservoir  84 . 
     In addition, first and second hydraulic chambers  98   b  and  98   a  are arranged in the cylinder body  82 . The second hydraulic chamber  98   a  controls the hydraulic brake pressure outputted from the outlet port  24   a  to the wheel cylinders  32 FR and  32 RL, and the first hydraulic chamber  98   b  controls the hydraulic brake pressure outputted from the outlet port  24   b  to the wheel cylinders  32 RR and  32 FL. 
     In the above arrangement, the first and second back chambers  94   b  and  94   a  and the first and second hydraulic chambers  98   b  and  98   a  in the cylinder body  82  are spaces which are filled with the brake fluid, and the back chambers  94   b  and  94   a  and the hydraulic chambers  98   b  and  98   a  are fluid tightly (and air tightly) separated from the mechanism-enclosing portion  173   a  in the actuator housing  172  by the guide piston  90   c  (which functions as the sealing member). The manner of attaching the guide piston  90   c  to the cylinder body  82  is not specifically limited. For example, the guide piston  90   c  may be attached with a circlip (not shown). 
     A restriction means  100  which restricts the maximum strokes (the maximum displacement) and the minimum strokes (the minimum displacement) of the first and second slave pistons  88   b  and  88   a  is arranged between the first and second slave pistons  88   b  and  88   a . In addition, a stopper pin  102  is arranged in the first slave piston  88   b . The stopper pin  102  restricts the slidable range of the first slave piston  88   b , and prevents overreturn of the first slave piston  88   b  toward the second slave piston  88   a . Therefore, when the braking operation is backed up with the hydraulic brake pressure generated by the master cylinder  34 , it is possible to prevent occurrence of a failure in one of the hydraulic routes even when the other of the hydraulic routes fails. 
     The VSA apparatus  18  has a known configuration and includes first and second brake systems  110   b  and  110   a . The second brake system  110   a  controls the second hydraulic route  70   a  connected to (the wheel cylinders  32 FR and  32 RL in) the disk brake mechanisms  30   a  and  30   b  in the right front wheel and the left rear wheel, and the first brake system  110   b  controls the first hydraulic route  70   b  connected to (the wheel cylinders  32 RR and  32 FL in) the disk brake mechanisms  30   c  and  30   d  in the right rear wheel and the left front wheel. Alternatively, the second brake system  110   a  may be constituted by hydraulic routes connected to the disk brake mechanisms arranged for the right front wheel and the left front wheel, and the first brake system  110   b  may be constituted by hydraulic routes connected to the disk brake mechanisms arranged for the right rear wheel and the left rear wheel. Further alternatively, the second brake system  110   a  may be constituted by hydraulic routes connected to the disk brake mechanisms arranged for the right front wheel and the right rear wheel, and the first brake system  110   b  may be constituted by hydraulic routes connected to the disk brake mechanisms arranged for the left front wheel and the left rear wheel. 
     Since the first and second braking systems  110   b  and  110   a  have identical structures, identical reference numbers are assigned to equivalent elements in the first and second braking systems  110   b  and  110   a  in  FIG. 1 . The following explanations are focused on the second braking system  110   a , and the explanations on the first braking system  110   b  are indicated in parentheses. 
     The second braking system  110   a  (or the first braking system  110   b ) includes the first and second common hydraulic paths  112  and  114 , which are common to the wheel cylinders  32 FR and  32 RL (or common to the wheel cylinders  32 RR and  32 FL). The VSA apparatus  18  includes a regulator valve  16 , first, second, and third check valves  118 ,  122 , and  126 , and first and second in-valves  120  and  124 . The regulator valve  116  is realized by a normally-open solenoid valve, and arranged between the inlet port  26   a  and the first common hydraulic path  112 . The first check valve  118  is arranged parallel with the above regulator valve  116 , and allows passage of the brake fluid from the inlet port  26   a  side to the first common hydraulic path  112  side (and stops passage of the brake fluid from the first common hydraulic path  112  side to the inlet port  26   a  side). The first in-valve  120  is realized by a normally-open solenoid valve, and arranged between the first common hydraulic path  112  and the first outlet port  28   a . The second check valve  122  is arranged parallel with the above first in-valve  120 , and allows passage of the brake fluid from the first outlet port  28   a  side to the first common hydraulic path  112  side (and stops passage of the brake fluid from the first common hydraulic path  112  side to the first outlet port  28   a  side). The second in-valve  124  is realized by a normally-open solenoid valve, and arranged between the first common hydraulic path  112  and the second outlet port  28   b . The third check valve  126  is arranged parallel with the above second in-valve  124 , and allows passage of the brake fluid from the second outlet port  28   b  side to the first common hydraulic path  112  side (and stops passage of the brake fluid from the first common hydraulic path  112  side to the second outlet port  28   b  side). 
     Further, the VSA apparatus  18  includes first and second out-valves  128  and  130 , a reservoir  132 , a fourth check valve  134 , a pump  136 , suction valves  138  and  142 , a discharge valve  140 , and a motor M. The first out-valve  128  is realized by a normally-closed solenoid valve, and arranged between the first outlet port  28   a  and the second common hydraulic path  114 . The second out-valve  130  is realized by a normally-closed solenoid valve, and arranged between the second outlet port  28   b  and the second common hydraulic path  114 . The reservoir  132  is connected to the second common hydraulic path  114 . The fourth check valve  134  is arranged between the first common hydraulic path  112  and the second common hydraulic path  114 , and allows passage of the brake fluid from the second common hydraulic path  114  side to the first common hydraulic path  112  side (and stops passage of the brake fluid from the first common hydraulic path  112  side to the second common hydraulic path  114  side). The pump  136  is arranged between the fourth check valve  134  and the first common hydraulic path  112 , and supplies the brake fluid from the second common hydraulic path  114  side to the first common hydraulic path  112  side. The suction valve  138  and the discharge valve  140  are respectively arranged on the front and rear sides of the pump  136 . The motor M drives the pump  136 . The suction valve  142  is realized by a normally-closed solenoid valve, and arranged between the second common hydraulic path  114  and the inlet port  26   a.    
     Furthermore, a pressure sensor Ph is arranged on the hydraulic path close to the inlet port  26   a  in the second braking system  110   a , and detects the pressure of the brake fluid which is delivered from the outlet port  24   a  of the electric brake device  16  and controlled in the second hydraulic pressure chamber  98   a  in the electric brake device  16 . The detection signal from each of the pressure sensors Pm, Pp, and Ph is supplied to the detection signal to a controller (not shown). The VSA apparatus  18  can also perform ABS (antilock brake system) control as well as the VSA (vehicle stability assist) control, although an ABS apparatus having only the ABS function, instead of the VSA apparatus  18 , may be connected. The vehicle brake system  10  according to the present embodiment is basically constructed as above. The operations and advantages of the vehicle brake system  10  are explained below. 
     During normal operation of the vehicle brake system  10 , the first and second shutoff valves  60   b  and  60   a  (respectively realized by normally-open solenoid valves) are energized to be closed, and the third shutoff valve  62  (realized by a normally-closed solenoid valve) is energized to be opened. Since the first and second hydraulic routes  70   b  and  70   a  are closed by the first and second shutoff valves  60   b  and  60   a , the hydraulic brake pressure generated in the master cylinder  34  in the input apparatus  14  is not transmitted to the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL in the disk brake mechanisms  30   a  to  30   d.    
     At this time, the hydraulic brake pressure generated in the second pressure chamber  56   b  in the master cylinder  34  is transmitted to the hydraulic pressure chamber  65  in the stroke simulator  64  through the hydraulic branch path  58   c  and the third shutoff valve  62  (which is open). The hydraulic brake pressure transmitted to the hydraulic pressure chamber  65  causes the simulator piston  68  to move against the spring force produced by the first and second return springs  66   a  and  66   b . Therefore, a stroke of the brake pedal  12  is allowed, and the hydraulic brake pressure in the hydraulic pressure chamber  65  generates dummy pedal reaction force, and imparts the dummy pedal reaction force to the brake pedal  12 , so that a normal brake feel is provided to the operator without causing a sense of incongruity. 
     In the case where the vehicle brake system  10  is arranged as above, when the controller (not shown) detects depression of the brake pedal  12  by the operator, the controller activates the electric motor  72  in the electric brake device  16  so as to energize the actuator mechanism  74 , and causes displacement of the first and second slave pistons  88   b  and  88   a  toward the direction indicated by the arrow X 1  in  FIG. 1 , against the spring force generated by the first and second return springs  96   b  and  96   a . The displacement of the first and second slave pistons  88   b  and  88   a  presses the brake fluid in the first and second hydraulic pressure chambers  98   b  and  98   a  in such a manner that the brake fluid in the first and second hydraulic pressure chambers  98   b  and  98   a  balances and a desired hydraulic brake pressure is generated in the first and second hydraulic chambers  98   b  and  98   a.    
     Specifically, the control means (not shown) calculates the amount of depression of the brake pedal  12  (i.e., the brake depression amount) on the basis of a value obtained by detection by the pedal-stroke sensor St, and sets a target value of the hydraulic brake pressure (i.e., the target hydraulic pressure) on the basis of the amount of depression (brake manipulation amount) in consideration of the regenerative braking force, and causes the electric brake device  16  to generate the hydraulic pressure which is set as above. Then, the hydraulic brake pressure generated by the electric brake device  16  is applied through the inlet ports  26   a  and  26   b  to the VSA apparatus  18 . That is, when the brake pedal  12  is manipulated, the electric motor  72  is rotationally driven in response to an electric signal, the first and second slave pistons  88   b  and  88   a  are actuated by the rotational drive force of the electric motor  72 , so that the hydraulic brake pressure corresponding to the amount of manipulation of the brake pedal  12  is generated and applied to the VSA apparatus  18 . The electric signals in the present embodiment are, for example, a signal for supplying electric power to the electric motor  72  and control signals for controlling the electric motor  72 . 
     The manipulation-amount detection means, which detects the amount of depression of the brake pedal  12 , is not limited to the pedal-stroke sensor St, and may be realized by any sensor which can detect the amount of depression of the brake pedal  12 . For example, the manipulation-amount detection means may have an arrangement which converts the hydraulic pressure detected by the pressure sensor Pm, into the amount of depression of the brake pedal  12 , or an arrangement which detects the amount of depression of the brake pedal  12  by a tread-force sensor (not shown). 
     The hydraulic brake pressure in the first and second hydraulic chambers  98   b  and  98   a  in the electric brake device  16  is transmitted to the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL in the disc brake mechanisms  30   a  to  30   d  through the first and second in-valves  120  and  124  in the VSA apparatus  18 , which are in the valve-open state, so that the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL are actuated and desired braking force is exerted on the respective wheels. 
     In other words, during normal operation of the vehicle brake system  10  according to the present embodiment in which the electric brake device  16  (which functions as a hydraulic power source), the control means (which performs the brake-by-wire control), and other functions of the vehicle brake system  10  can operate, the aforementioned brake-by-wire system becomes active. In the brake-by-wire system, when the operator depresses the brake pedal  12 , the first and second shutoff valves  60   a  and  60   b  shut off the communication between the disc brake mechanisms  30   a  to  30   d  and the master cylinder  34  (which generates hydraulic pressure), and the disc brake mechanisms  30   a  to  30   d  (which have the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL and brake the respective wheels) are activated by the hydraulic brake pressure generated by the electric brake device  16 . Therefore, the present embodiment can be preferably applied to the vehicles (e.g., electric vehicles) in which the negative pressure produced by the internal combustion engine does not exist (although such negative pressure has been conventionally used). 
     On the other hand, under abnormal conditions in which the electric brake device  16  or the like cannot operate, the first and second shutoff valves  60   a  and  60   b  are opened and the third shutoff valve  62  is closed, so that the hydraulic brake pressure generated in the master cylinder  34  is transmitted to (the wheel cylinders  32 FR,  32 RL,  32 RR, and  32 FL in) the disc brake mechanisms  30   a  to  30   d , and the disc brake mechanisms  30   a  to  30   d  are activated by the hydraulic brake pressure transmitted from the master cylinder  34 . That is, the so-called traditional hydraulic brake system operates. 
     For example, the hybrid vehicles and the electric vehicles having one or more electric drive motors can be provided with a regenerative brake which generates braking force by regenerative power generation by the electric drive motor. In the case where the regenerative brake is used in such vehicles, the control means (not shown) causes one or more motors coupled to at least one of the front and rear shafts to operate as an electric generator and generate regenerative braking force corresponding to the amount of depression of the brake pedal  12  or the like. When the regenerative braking force is insufficient for the amount of depression of the brake pedal  12  (i.e., the braking force required by the operator), the control means drives the electric motor  72  and causes the electric brake device  16  to generate braking force. Thus, the control means performs cooperative control of the regenerative brake and the hydraulic brake (which is realized by the electric brake device  16 ). The control means can be configured to determine the amount of operation in the electric brake device  16  in a known manner. For example, the control means can be configured to determine the amount of operation in the electric brake device  16  by setting as the target hydraulic pressure a hydraulic brake pressure for causing the electric brake device  16  to generate the braking force equal to the difference between the regenerative braking force and the (total) braking force determined in correspondence with the amount of depression of the brake pedal  12 , or setting as the target hydraulic pressure a hydraulic brake pressure for causing the electric brake device  16  to generate the braking force at a predetermined ratio to the total braking force. 
     In the case where the vehicle brake system  10  arranged as above is installed in the vehicle, for example, as illustrated in  FIG. 2 , the input apparatus  14 , the electric brake device  16 , and the VSA apparatus  18  are separately formed and attached to the containment room (the power-plant containment room  2   a ) containing a power plant  2  of the vehicle  1 , so as to be dispersedly arranged as appropriate. The power plant  2  is a vehicle power unit which generates power for driving the vehicle  1 , and is, for example, an internal combustion engine, one or more electric motors installed in an electric vehicle for driving the electric vehicle, an integral unit of an internal combustion engine and one or more electric motors installed in a hybrid vehicle. 
     The power-plant containment room  2   a  is formed in a front portion of the vehicle  1  by partitioning off with a dashboard  3   a  from the room for the operator and one or more occupants (i.e., the cabin  3 ). The power plant  2 , the vehicle brake system  10  (including the input apparatus  14 , the electric brake device  16 , and the VSA apparatus  18 ), and auxiliary parts (not shown) are installed in the power-plant containment room  2   a . In addition, a containment-room cover  2   b  is arranged at an upper portion of the power-plant containment room  2   a  in such a manner that the containment-room cover  2   b  can be opened and closed. Further, front-side members  7  which are to extend in the front-back direction on the right and left sides of the vehicle  1  are arranged on the right and left sides of the power-plant containment room  2   a.    
     The front, back, up, down, right, and left directions are directions with respect to the vehicle  1 . For example, the up and down directions (vehicle up and down directions) are vertical directions of the vehicle  1  when the vehicle  1  is in a horizontal position, and the right and left directions are right and left directions in forward view of the vehicle  1 . 
     The power plant  2  is arranged in the power-plant containment room  2   a  between the front-side members  7  on the right and left sides, and supported by vibration-reduction supporting devices  8 , which are fixed to a subframe (not shown). In addition, spaces are formed between the power plant  2  and the front-side members  7  on the right and left sides. Further, a space is formed on the upper side of the power plant  2  between the containment-room cover  2   b  and the power plant  2 . 
     Therefore, according to the present embodiment, the input unit  14 , the electric brake device  16 , and the VSA apparatus  18  are installed in the power-plant containment room  2   a , and, for example, the electric brake device  16  is installed in such a manner that a portion of the cylinder body  82  is located in the space formed between the power plant  2  and the containment-room cover  2   b.    
     In addition, in the present embodiment, the state in which the electric motor  72  is arranged above the cylinder body  82  means the state in which the electric motor  72  is arranged in such a manner that the axis of the output shaft  72   b  which is arranged approximately parallel to the axial direction of the second and first slave pistons  88   a  and  88   b  (the hydraulic control pistons) illustrated in  FIG. 1  is located above the axes of the second and first slave pistons  88   a  and  88   b  in the vertical direction of the vehicle with respect to the right-left direction of the vehicle  1  (illustrated in  FIG. 2 ). 
     The electric brake device  16  according to the present embodiment is constructed in such a manner that the cylinder body  82  and the actuator housing  172 , which houses the gear mechanism  78  and the ball-screw structure  80  (which are illustrated in  FIG. 1 ), can be separated at a separation plane approximately perpendicular to the axis of the cylinder body  82 . The electric brake device  16  is constructed by coupling the cylinder body  82  to the actuator housing  172  and further attaching the electric motor  72  to the actuator housing  172 . 
     The cylinder body  82  is connected to the front side of the actuator housing  172 . Specifically, an opening  172   a , through which the ball-screw shaft  80   a  protrudes forward, is opened to the front side of the actuator housing  172 , and the cylinder body  82  is connected to the front side of the actuator housing  172  in such a manner that a hollow portion (not shown) in which the first and second slave pistons  88   b  and  88   a  (illustrated in  FIG. 1 ) slide communicates with the opening  172   a.    
     For example, a flange  175  extending in the right and left directions is formed around the opening  172   a  in the actuator housing  172 , and for example, two screw holes  176  are opened in the flange  175 . On the other hand, a flange  820  extending in the right and left directions is formed at the end of the cylinder body  82  on the actuator housing  172  side, and cylinder-attachment holes  821  are opened at the positions of the flange  820  corresponding to the screw holes  176  in the actuator housing  172 . In addition, a fitting portion  820   a  to be fitted into the opening  172   a  in the actuator housing  172  is formed by extending rearward (toward the actuator housing  172  side) a peripheral portion of the hollow portion (not shown) in the cylinder body  82 . Further, the cylinder body  82  and the actuator housing  172  are positioned such that the flange  820  in the cylinder body  82  faces the flange  175  in the actuator housing  172 , and fastening members  822  such as bolts are screwed from the cylinder body  82  side through the cylinder body  82  into the screw holes  176 , so that the cylinder body  82  is fastened to the actuator housing  172 . 
     At this time, it is preferable that the fitting portion  820   a  in the cylinder body  82  be fitted into the opening  172   a  in the actuator housing  172  through an O-ring  820   b  having a sealing function so as to realize a liquid-tight connection of the cylinder body  82  and the actuator housing  172 . In the case where the fitting portion  820   a  is fitted as above, it is possible to prevent external leakage of the brake fluid with which the cylinder body  82  is filled, from the connection of the cylinder body  82  and the actuator housing  172 . 
     As described above, the cylinder body  82  is connected to the front side of the actuator housing  172 , and the ball-screw shaft  80   a  comes into contact with the second slave piston  88   a.    
     In addition, the electric motor  72  is attached to the actuator housing  172  in a position above the cylinder body  82  in such a manner that the axial direction of the output shaft  72   b  (illustrated in  FIG. 1 ) is approximately parallel to the axial direction of the first and second slave pistons  88   b  and  88   a  (illustrated in  FIG. 1 ), i.e., parallel to the axial direction of the cylinder body  82 . 
     For example, the second gear  78   b  (illustrated in  FIG. 1 ) is placed above the third gear  78   c  (illustrated in  FIG. 1 ) and the actuator housing  172  is extended upward so as to enclose the second and third gears  78   b  and  78   c . In addition, the actuator housing  172  includes a first gear room  172   b  which encloses the first gear  78   a  such that the first gear  78   a  can be engaged with the second gear  78   b . The first gear room  172   b  is opened to the front side, and arranged above the second gear  78   b . Further, the electric motor  72  is attached to the front side of the actuator housing  172  in such a manner that the first gear  78   a  (illustrated in  FIG. 1 ), which is attached to the output shaft  72   b  (illustrated in  FIG. 1 ), is enclosed in the first gear room  172   b  and engaged with the second gear  78   b.    
     As illustrated in  FIG. 4 , the actuator housing  172  according to the present embodiment, which is constituted by a housing body  172 F and a housing cover  172 R, is constructed in such a manner that the housing body  172 F and the housing cover  172 R can be separated. Multiple through-holes  177   a , through which bolts  177  are to be inserted, are formed in the housing body  172 F so as to be located around the center axis of the first and second slave pistons  88   b  and  88   a  (illustrated in  FIG. 1 ), and multiple attachment screw holes  177   b  are formed in the positions of the housing cover  172 R corresponding to the through-holes  177   a . The housing body  172 F and the housing cover  172 R are coupled by inserting the bolts  177  through the through-holes  177   a  and screwing the bolts  177  into the attachment screw holes  177   b.    
     A space having an approximately cylindrical shape, centering at the center axis of the ball-screw shaft  80   a , and opening to the front side is formed in the housing cover  172 R to realize a mechanism-enclosing portion  173   a . In addition, the front side of the housing cover  172 R is extended upward to form a backside portion  173   b . The backside portion  173   b  constitutes the backside of the first gear room  172   b , which is formed in the housing body  172 F for enclosing the first gear  78   a  (illustrated in  FIG. 1 ) attached to the electric motor  72 . A space (realizing a bearing portion  173   c ) opening forward and containing a bearing member  173   d , which rotatably supports the output shaft  72   b , is formed at a position on the axis of the output shaft  72   b  of the electric motor  72  (illustrated in  FIG. 1 ). 
     The housing body  172 F and the housing cover  172 R are mated in the front-back direction and connected with the bolts  177  as described before in such a manner that the third gear  78   c  and the ball-screw structure  80  are enclosed in the mechanism-enclosing portion  173   a  and the bearing member  173   d  is enclosed in the bearing portion  173   c . Thus, the actuator housing  172  is constructed. 
     The second gear  78   b  is formed such that the second gear  78   b  can be rotatably enclosed in an enclosing portion (not shown) which is formed in the housing body  172 F, and the backside portion  173   b  becomes a back surface of the enclosing portion of the second gear  78   b . In addition, the reference  80   c  denotes a bearing member (e.g., a ball bearing) rotatably supports the third gear  78   c  in the mechanism-enclosing portion  173   a , and the mechanism-enclosing portion  173   a  is formed to enclose the third gear  78   c  through the bearing member  80   c.    
       FIG. 3  is referred to again. The structure for attaching the electric motor  72  to the actuator housing  172  is not specifically limited. For example, as illustrated in  FIG. 3 , in the motor casing  72   a , edge portions of the motor casing  72   a  on the actuator housing  172  side extend to the peripheral directions to form a flange  161 , and motor-attachment holes  162 , through which fastening members such as bolts are to be inserted, are opened in the flange  161 . In addition, screw holes  174  are opened at the positions of the actuator housing  172  corresponding to the motor-attachment holes  162 . The electric motor  72  is attached to the front side (the same side as the side to which the cylinder body  82  is connected) of the actuator housing  172  in such a manner that the output shaft  72   b  (illustrated in  FIG. 1 ) to which the first gear  78   a  (illustrated in  FIG. 1 ) is attached is approximately parallel to the axial direction of the cylinder body  82 , and the first gear  78   a  is enclosed in the first gear room  172   b  and engaged with the second gear  78   b  (illustrated in  FIG. 1 ). At this time, an end of the output shaft  72   b  of the electric motor  72  is rotatably supported by the bearing member  173   d  (illustrated in  FIG. 4 ). In addition, fastening members  162   a  are screwed from the electric motor  72  side into the screw holes  174  through the motor-attachment holes  162 , so that the motor casing  72   a  is fastened to the actuator housing  172 . 
     In the above construction, the cylinder body  82  and the electric motor  72  are arranged on the same side of the actuator housing  172 . That is, in the electric brake device  16  according to the present embodiment, the cylinder body  82  is connected to the actuator housing  172 , and the electric motor  72  is attached to the actuator housing  172  such that the electric motor  72  is located above the cylinder body  82 . 
     In addition, a mount portion for attaching the electric brake device  16  to the vehicle  1  (illustrated in  FIG. 2 ) through a bracket  2   a   1  (illustrated in  FIG. 2 ) is arranged in the actuator housing  172 . The bracket  2   a   1  has approximately a U-shape which opens upward in front view as illustrated in  FIG. 5 , and is formed to hold the actuator housing  172  of the electric brake device  16  in the bracket  2   a   1  from the right and left sides. Further, as illustrated in  FIGS. 4 and 5 , the mount portion is realized by forming in the actuator housing  172  fastening bosses  82   a  which are arranged for the bracket  2   a   1  to hold the actuator housing  172 . The fastening bosses are formed below the ball-screw shaft  80   a  to protrude to the right and left directions. 
     Furthermore, a through-hole is formed through the fastening bosses  82   a , which protrude to the right and left directions. The through-hole realizes insertion holes into which attachment fastening members (bolt members  206 ) are inserted, and is referred to as the attachment hole  82   a   1 . The actuator housing  172  in the electric brake device  16  is fixed to the bracket  2   a   1  with the attachment fastening members as explained later. Moreover, the diameters of both ends of the attachment hole  82   a   1  are increased to form diameter-increased portions  82   a   2 . The electric brake device  16  being constructed as above and having the mount portion is attached, for example, to the dashboard  3   a  of the power-plant containment room  2   a  through the bracket  2   a   1  as illustrated in  FIG. 2 . The structure for fixing the electric brake device  16  in the power-plant containment room  2   a  is not limited, and the electric brake device  16  may be fixed to a subframe (not shown) or the like. 
     As illustrated in  FIG. 5 , the bracket  2   a   1  has a structure in which a left wall portion  2   a   3  and a right wall portion  2   a   4  are erected from the right and left edges of a bottom portion  2   a   2 . The bracket  2   a   1  is formed such that the fastening bosses  82   a  formed in the actuator housing  172  are held by the left wall portion  2   a   3  and the right wall portion  2   a   4  from the left and right sides. For example, upward opening notches  200  are formed in the left wall portion  2   a   3  and the right wall portion  2   a   4  at the positions corresponding to the attachment hole  82   a   1  in the electric brake device  16  in such a manner that the notch  200  in the left wall portion  2   a   3 , the attachment hole  82   a   1 , and the notch  200  in the right wall portion  2   a   4  align on a straight line when the fastening bosses  82   a  are held by the left wall portion  2   a   3  and the right wall portion  2   a   4 . 
     In addition, mount rubbers  205 , which have an annular shape and a function of a buffer member, are fitted into the diameter-increased portions  82   a   2 , and the bolt members  206  are inserted into the central portions of the mount rubbers  205 . For example, in each of the bolt members  206  according to the present embodiment, a screw portion  206   a  and a shaft portion  206   c , which is inserted into the central portion of one of the mount rubber  205 , are formed along a straight line, and a flange  206   b  extending to the periphery is formed between the shaft portion  206   c  and the screw portion  206   a.    
     Further, as illustrated in  FIG. 5 , the shaft portion  206   c  of each bolt member  206  is inserted into the central portion of one of the mount rubbers  205 , which is fitted into one of the diameter-increased portions  82   a   2  of the attachment holes  82   a   1  in such a manner that each flange  206   b  is located between one of the mount rubbers  205  and one of the left and right wall portions  2   a   3  and  2   a   4 , and nuts  202  are fastened onto the screw portions  206   a  which externally protrude from the notches  200  of the bracket  2   a   1 . According to the above arrangement, the electric brake device  16  is attached to the bracket  2   a   1  by the insertion of the shaft portions  206   c  of the bolt members  206  into the central portions of the mount rubbers  205 , where the bolt members  206  are fixed to the left and right wall portions  2   a   3  and  2   a   4  with the nuts  202 , and the mount rubbers  205  are fitted into the attachment holes  82   a   1 . 
     In addition, the reference  203  denotes a protrusion for positioning the electric brake device  16  and is arranged to engage with an engagement hole  82   b  through an annular mount rubber  204 , where the engagement hole  82   b  is formed on the bottom side of the actuator housing  172  as a buffering member. Specifically, the protrusion  203  is fitted into a through-hole at the center of the mount rubber  204 , and the protrusion  203  and the mount rubber  204  are engaged with the engagement hole  82   b.    
     When the bracket  2   a   1  arranged as above is fixed to, for example, the dashboard  3   a  (illustrated in  FIG. 2 ) of the power-plant containment room  2   a  (illustrated in  FIG. 2 ), the electric brake device  16  is disposed in the power-plant containment room  2   a . The attachment holes  82   a   1  are not limited to the type realized by the through-hole formed through the fastening bosses  82   a . For example, bottomed holes, instead of the attachment holes  82   a   1 , may be formed at the right and left ends of the fastening bosses  82   a  which are formed in the right and left sides. 
     In the electric brake device  16  (illustrated in  FIG. 5 ) which is constructed and disposed in the power-plant containment room  2   a  (illustrated in  FIG. 2 ) as described above, the inside of the cylinder body  82  (illustrated in  FIG. 1 ) is filled with the brake fluid, and the brake fluid is sealed within the inside of the cylinder body  82  with the slave cup seals  90   a  and  90   b  (illustrated in  FIG. 1 ) and the guide piston  90   c  (illustrated in  FIG. 1 ) as explained before. 
     Further, the second slave piston  88   a  (illustrated in  FIG. 1 ) and the first slave piston  88   b  (illustrated in  FIG. 1 ) move along the axis of the cylinder body  82  and generate predetermined hydraulic pressure according to the brake manipulation force inputted into the input apparatus  14  (illustrated in  FIG. 1 ). At this time, the ball-screw shaft  80   a  moves forward for moving forward the first and second slave pistons  88   b  and  88   a , and a portion of the ball-screw shaft  80   a  enclosed in the mechanism-enclosing portion  173   a  is pushed out of the mechanism-enclosing portion  173   a , so that the volume inside the mechanism-enclosing portion  173   a  increases and the pressure inside the mechanism-enclosing portion  173   a  decreases. 
     The seals arranged around the guide piston  90   c  are formed to deliver preferable sealing performance when the pressures on the first and second slave pistons  88   b  and  88   a  side rise. Therefore, when the portion of the ball-screw shaft  80   a  returns to the mechanism-enclosing portion  173   a  and therefore the volume inside the mechanism-enclosing portion  173   a  decreases and the pressure inside the mechanism-enclosing portion  173   a  increases, in some cases, the sealing performance of the guide piston  90   c  is lowered and seal imperfection occurs in the guide piston  90   c.    
     Therefore, an intake/exhaust mechanism is provided in the electric brake device  16  (illustrated in  FIG. 3 ) according to the present embodiment. When the pressure of the mechanism-enclosing portion  173   a  decreases, for example, when the ball-screw shaft  80   a  moves forward, the intake/exhaust mechanism takes in external air so as to maintain the mechanism-enclosing portion  173   a  at the atmospheric pressure. When the pressure of the mechanism-enclosing portion  173   a  increases, for example, when the ball-screw shaft  80   a  moves backward, the intake/exhaust mechanism exhausts the air from the mechanism-enclosing portion  173   a  so as to suppress the pressure in the mechanism-enclosing portion  173   a  and maintain the mechanism-enclosing portion  173   a  at the atmospheric pressure. 
     For example, as illustrated in  FIG. 6 , a communication hole (intake/exhaust hole  179 ) which communicates with the outside of the actuator housing  172  is formed in a passage portion  172   d  of the actuator housing  172  in the direction perpendicular to the axis of the ball-screw shaft  80   a  in order to realize the intake/exhaust mechanism. The passage portion  172   d  is formed in the actuator housing  172  for allowing forward and backward movement of the tip portion of the ball-screw shaft  80   a . Since the passage portion  172   d  is formed to communicate with the mechanism-enclosing portion  173   a , the intake/exhaust hole  179  formed in the passage portion  172   d  can form a structure realizing communication between the mechanism-enclosing portion  173   a  and the outside of the actuator housing  172 . That is, the intake/exhaust hole  179  can realize communication between the mechanism-enclosing portion  173   a  and the atmosphere. 
     According to the above arrangement, when the pressure inside the mechanism-enclosing portion  173   a  decreases, for example, by forward movement of the ball-screw shaft  80   a , the external air is taken into the mechanism-enclosing portion  173   a  through the intake/exhaust hole  179 , so that the inside of the mechanism-enclosing portion  173   a  is maintained at the atmospheric pressure. Therefore, it is possible to avoid pressure reduction of the inside of the mechanism-enclosing portion  173   a  and prevent seal imperfection in the guide piston  90   c  (illustrated in  FIG. 1 ). 
     In addition, it is preferable that the intake/exhaust hole  179  is formed rightward, leftward, or downward (not shown) from the passage portion  172   d  as illustrated in  FIG. 6 . According to this arrangement, it is possible to prevent intrusion, from the intake/exhaust hole  179  into the mechanism-enclosing portion  173   a , of condensed water such as rain which falls from upside of the electric brake device  16 . 
     Further, it is preferable that the intake/exhaust hole  179  be provided with a water-proof moisture-permeable film  179   a  being formed of a material with a water proofing property and a moisture permeability property and covering an opening of the intake/exhaust hole  179 . This provision can preferably prevent flow of condensed water in the intake/exhaust hole  179 , and can prevent intrusion of condensed water such as rain water from the intake/exhaust hole  179  into the mechanism-enclosing portion  173   a  with high reliability. It is preferable that the water-proof moisture-permeable film  179   a  be a gas-permeable film which allows permeation of air (including water vapor) and does not allow permeation of condensed water. For example, the water-proof moisture-permeable film  179   a  is preferably a film of Gore-Tex (which is a registered trademark). For example, the water-proof moisture-permeable film  179   a  can be attached by adhesion or the like so as to cover the opening on the outer side of the intake/exhaust hole  179 . 
     The intake/exhaust mechanism according to the present embodiment is not limited to the intake/exhaust hole  179 , which realizes communication between the passage portion  172   d  and the outside of the electric brake device  16 . For example, the intake/exhaust mechanism may be realized by providing as an intake/exhaust hole  181   a  communication hole which realizes communication between the mechanism-enclosing portion  173   a  and the attachment hole  82   a   1  (which is formed in the actuator housing  172 ). In this case, the mechanism-enclosing portion  173   a  communicates with the atmosphere (the outside of the electric brake device  16 ) through the attachment hole  82   a   1  and the intake/exhaust hole  181 . Further, attachment of water-proof moisture-permeable films  181   a  to the intake/exhaust hole  181  can be easily realized by fixing the water-proof moisture-permeable films  181   a  with the mount rubbers  205 , which are fitted into the diameter-increased portions  82   a   2  of the attachment holes  82   a   1  as illustrated in  FIG. 8A  when the electric brake device  16  is attached to the bracket  2   a   1  (illustrated in  FIG. 5 ). 
     Specifically, when the electric brake device  16  (illustrated in  FIG. 5 ) is attached to the bracket  2   a   1  (illustrated in  FIG. 1 ), the water-proof moisture-permeable films  181   a  are fitted into the diameter-increased portions  82   a   2  so as to cover the attachment holes  82   a   1 , and the mount rubbers  205  are fitted into the diameter-increased portions  82   a   2  so as to hold the water-proof moisture-permeable films  181   a , as illustrated in  FIG. 8A . In addition, for example, in the case where a through-hole  206   d  is formed in each of the bolt members  206  through approximately the centers of the shaft portion  206   c  and the screw portion  206   a , the mechanism-enclosing portion  173   a  (illustrated in  FIG. 7 ) can be constructed such that the mechanism-enclosing portion  173   a  communicates with the atmosphere through the intake/exhaust hole  181 , the attachment holes  82   a   1 , and the through-holes  206   d  in the bolt members  206  even in the state in which the electric brake device  16  is attached the bracket  2   a   1 . Further, the water-proof moisture-permeable films  181   a  can prevent intrusion of condensed water such as rain water into the mechanism-enclosing portion  173   a . Furthermore, in order to prevent interference of the bolt members  206  with the water-proof moisture-permeable films  181   a  in the above construction, it is preferable that the length of the shaft portion  206   c  be smaller than the thickness of each of the mount rubbers  205 . 
     In addition, as illustrated in  FIG. 8B , each of the water-proof moisture-permeable films  181   a  may be supported (fixed) by a holding member  181   b . For example, the structure as illustrated in  FIG. 8B  may be used. That is, each holding member  181   b  may have a cuplike shape having a bottom, where approximately the central portion of the bottom opens. In addition, the holding members  181   b , by which the water-proof moisture-permeable films  181   a  are fixed, are press fitted into the diameter-increased portions  82   a   2 . Further, the mount rubbers  205  are inserted inside the holding members  181   b . According to the above construction, since the water-proof moisture-permeable films  181   a  are fixed by the holding members  181   b , it is possible to prevent intrusion of condensed water such as rain water into the attachment hole  82   a   1 , with high reliability. However, each holding member  181   b  is not limited to the cuplike bottomed member. For example, each holding member  181   b  may have an approximately cylindrical shape without a bottom. Further, a cut may be formed in the approximately cylindrical shape and have an approximately C-shape in front view. 
     Alternatively, as illustrated in  FIG. 9 , the intake/exhaust mechanism may include as an intake/exhaust hole  183  a communication hole which realizes communication between the mechanism-enclosing portion  173   a  and the engagement hole  82   b  in the actuator housing  172 , where the protrusion  203  formed in the bottom portion  2   a   2  of the bracket  2   a   1  is fitted into the engagement hole  82   b . In this case, the mechanism-enclosing portion  173   a  communicates with the atmosphere (the outside of the electric brake device  16 ) through the engagement hole  82   b  and the intake/exhaust hole  183 . In addition, a water-proof moisture-permeable film  183   a  can be easily attached to the intake/exhaust hole  183  by forming a structure in which the water-proof moisture-permeable film  183   a  is fixed with the mount rubber  204 , which is fitted into the engagement hole  82   b  when the electric brake device  16  is attached to the bracket  2   a   1 . 
     Further, in the case where a through-hole  203   a  is formed in the central portion of the protrusion  203  of the bracket  2   a   1 , the mechanism-enclosing portion  173   a  communicates with the atmosphere through the intake/exhaust hole  183 , the engagement hole  82   b , and the through-hole  203   a  in the protrusion  203 , and the water-proof moisture-permeable film  183   a  prevents intrusion of condensed water such as rain water into the mechanism-enclosing portion  173   a , even in the state in which the electric brake device  16  is attached to the bracket  2   a   1 . 
     Further alternatively, as illustrated in  FIG. 10 , the intake/exhaust mechanism may include as an intake/exhaust hole  185  a communication hole which realizes communication between the atmosphere and a motor-enclosing portion  172   m , which is formed in the housing body  172 F of the actuator housing  172  for enclosing an end portion of the main body  72   c  of the electric motor  72 . For example, in the case where the forward side of the first gear room  172   b  is formed to have an increased diameter and the motor-enclosing portion  172   m  communicates with the mechanism-enclosing portion  173   a  through the first gear room  172   b , the mechanism-enclosing portion  173   a  communicates with the atmosphere through the first gear room  172   b , the motor-enclosing portion  172   m , and the intake/exhaust hole  185 . 
     Preferably, the intake/exhaust hole  185  is formed in a position corresponding to the motor-enclosing portion  172   m  through the housing body  172 F in the axial direction of the output shaft  72   b  (illustrated in  FIG. 1 ) of the electric motor  72 , and a cylindrical protrusion is formed as a protruded portion  185   a  to protrude outward from the housing body  172 F at the position of the intake/exhaust hole  185 , as illustrated in  FIG. 11A . In addition, in a preferable construction, a cover member  187  constituted by an inner cylinder  187   a , a water-proof moisture-permeable film  187   b , and an outer cylinder  187   c  is attached to the protruded portion  185   a  for preventing intrusion of condensed water such as rain water into the motor-enclosing portion  172   m . Further, in a preferable construction, a guard portion  173   e , which is an upward extension of the backside portion  173   b  of the housing cover  172 R, limits movement of the cover member  187  along the protruded portion  185   a , so that the cover member  187  does not fall off. 
     As illustrated in  FIGS. 11A and 11B , the inner cylinder  187   a  in the cover member  187  according to the present embodiment has an approximately cylindrical shape and is engaged with the protruded portion  185   a  formed in the housing body  172 F, the water-proof moisture-permeable film  187   b  in the cover member  187  is arranged to close one of openings of the inner cylinder  187   a , and the outer cylinder  187   c  in the cover member  187  has a bottomed cylindrical shape and is fitted onto the inner cylinder  187   a . The outer cylinder  187   c  is formed to have an inner diameter greater than the outer diameter of the inner cylinder  187   a  in such a manner that air can flow through the gap between the inner cylinder  187   a  and the outer cylinder  187   c  when the outer cylinder  187   c  is fitted onto the inner cylinder  187   a . In addition, the water-proof moisture-permeable film  187   b  is attached by adhesion or the like so as to cover the opening of the inner cylinder  187   a  on the outer cylinder  187   c  side. 
     Further, at least one engagement protrusion  187   a   1  is formed around the inner cylinder  187   a . Each engagement protrusion  187   a   1  is a protrusion formed on a portion of the outer peripheral surface of the inner cylinder  187   a , and the outer diameter of the inner cylinder  187   a  including the at least one protrusion becomes approximately equivalent to the inner diameter of the outer cylinder  187   c . Preferably, the engagement protrusion  187   a   1  is formed in plurality (two or more) and arranged at appropriate intervals along the outer peripheral surface of the inner cylinder  187   a.    
     Furthermore, an engagement portion  187   c   1  is formed on the periphery of the outer cylinder  187   c  on the opening side of the outer cylinder  187   c , where the outer cylinder  187   c  has the bottomed cylindrical shape. Specifically, the engagement portion  187   c   1  is formed by making the inner circumference of the opening side of the outer cylinder  187   c  slightly jut inward, so that when the outer cylinder  187   c  is fitted onto the inner cylinder  187   a  the engagement portion  187   c   1  engages with the engagement protrusions  187   a   1  on the inner cylinder  187   a  and functions as a stopper which prevents fall-off. Moreover, in the case where the opening side of the engagement portion  187   c   1  is formed to incline toward the closed side of the engagement portion  187   c   1 , the outer cylinder  187   c  can be easily fitted onto the inner cylinder  187   a.    
     As described above, the cover member  187  is constructed by fitting the outer cylinder  187   c  onto the inner cylinder  187   a  from the side of the of the inner cylinder  187   a  covered by the water-proof moisture-permeable film  187   b  in such a manner that the engagement portion  187   c   1  is engaged with the engagement protrusion(s)  187   a   1 . Then, as illustrated in  FIG. 10  and  FIG. 11A , the cover member  187  is attached to the protruded portion  185   a  of the housing body  172 F in such a manner that the protruded portion  185   a  is inserted into the opening of the inner cylinder  187   a  which is not covered by the water-proof moisture-permeable film  187   b . In addition, the guard portion  173   e  formed in the housing cover  172 R as explained before prevents fall-off of the cover member  187  from the protruded portion  185   a.    
     At this time, the intake/exhaust hole  185  communicates with the atmosphere through the water-proof moisture-permeable film  187   b , the gap between the inner cylinder  187   a  and the outer cylinder  187   c , and the gaps between the plurality of engagement protrusions  187   a   1 . Thus, the mechanism-enclosing portion  173   a  communicates with the atmosphere. Further, for example, in the arrangement in which the outer cylinder  187   c  is tightly fitted onto the engagement protrusion  187   a   1 , the movement of the outer cylinder  187   c  fitted onto the inner cylinder  187   a  is limited, so that it is possible to prevent the opening of the inner cylinder  187   a  from being closed by the outer cylinder  187   c.    
     As explained above, the arrangement in which the intake/exhaust hole  185  is formed through the protruded portion  185   a , and the cover member  187  is attached to the protruded portion  185   a  prevents intrusion of condensed water such as rain water through the intake/exhaust hole  185  and the motor-enclosing portion  172   m  into the mechanism-enclosing portion  173   a . Further, the arrangement in which the opening of the inner cylinder  187   a  constituting the cover member  187  is covered by the water-proof moisture-permeable film  187   b  prevents intrusion of condensed water with higher reliability. 
     In addition, since the part in which the protruded portion  185   a  is formed opens upward as illustrated in  FIG. 10 , condensed water such as rain water which falls from upside can gather in the part. Therefore, it is possible to use, for example, a structure in which a drain hole  173   f  is formed in the guard portion  173   e  (which is formed in the housing cover  172 R) as illustrated in  FIG. 11A  for preventing the gathering of the condensed water. 
     Further, since the electric motor  72  is arranged above the cylinder body  82 , the motor-enclosing portion  172   m  (in which the electric motor  72  is enclosed) is formed above the cylinder body  82  as illustrated in  FIG. 10 . Therefore, the intake/exhaust hole  185 , which is formed in the motor-enclosing portion  172   m , comes to be formed above the cylinder body  82 , and therefore the intake/exhaust hole  185  is formed above the guide piston  90   c  (illustrated in  FIG. 1 ). In other words, the opening of the intake/exhaust hole  185  on the mechanism-enclosing portion  173   a  side is formed above the guide piston  90   c . According to the above arrangement, even when the brake fluid with which the cylinder body  82  is filled flows beyond the guide piston  90   c  to the actuator housing  172  side, the intake/exhaust hole  185  is not closed by the brake fluid, so that air can be taken into and exhausted from the mechanism-enclosing portion  173   a , and maintain the inside of the mechanism-enclosing portion  173   a  at the atmospheric pressure. 
     Alternatively, it is possible to attach a water-proof moisture-permeable film so as to cover the opening of the intake/exhaust hole  185  without attaching the cover member  187  as illustrated in  FIG. 11A . According to the above arrangement, it is possible to form, with a simpler construction, an intake/exhaust hole which can prevent intrusion of condensed water. 
     As explained above, the electric brake device  16  (illustrated in  FIG. 1 ) according to the present embodiment is provided with an intake/exhaust mechanism including the intake/exhaust hole  179  which realizes communication between the mechanism-enclosing portion  173   a  and the atmosphere. Therefore, when the pressure in the mechanism-enclosing portion  173   a  decreases, external air is taken into the mechanism-enclosing portion  173   a  through the intake/exhaust hole  179 , so that the pressure inside the mechanism-enclosing portion  173   a  can be maintained at the atmospheric pressure. In addition, it is possible to prevent occurrence of seal imperfection in the guide piston  90   c  (illustrated in  FIG. 1 ) and the like. 
     Incidentally, in some cases, the pressure in the mechanism-enclosing portion  173   a  illustrated in  FIG. 1  can vary with movement of the ball-screw structure  80  and temperature change inside the mechanism-enclosing portion  173   a . Specifically, when the temperature inside the mechanism-enclosing portion  173   a  falls, for example, because of a fall in the ambient temperature of the electric brake device  16 , the pressure in the mechanism-enclosing portion  173   a  decreases. On the other hand, when the temperature inside the mechanism-enclosing portion  173   a  rises, for example, because of a rise in the ambient temperature of the electric brake device  16 , the pressure in the mechanism-enclosing portion  173   a  increases. 
     Since the electric brake device  16  (illustrated in  FIG. 1 ) according to the present embodiment is provided with the intake/exhaust mechanism including the intake/exhaust hole  179  illustrated in  FIG. 6 , even when the temperature inside the mechanism-enclosing portion  173   a  changes, air can be taken into and exhausted from the mechanism-enclosing portion  173   a , so that the pressure inside the mechanism-enclosing portion  173   a  can be maintained at the atmospheric pressure. In addition, it is possible to prevent occurrence of seal imperfection in the guide piston  90   c  (illustrated in  FIG. 1 ) and the like. 
     Further, the position of the intake/exhaust hole for realizing communication between the mechanism-enclosing portion  173   a  and the atmosphere is not limited to the position of the intake/exhaust hole  179  illustrated in  FIG. 6 , the position of the intake/exhaust hole  181  illustrated in  FIG. 7 , the position of the intake/exhaust hole  183  illustrated in  FIG. 9 , and the position of the intake/exhaust hole  185  illustrated in  FIG. 10 . However, for example, in the case where the atmosphere-side opening of the intake/exhaust hole opens upward, the opening can be closed by condensed water such as rain water which falls from upside and air flow can be obstructed. Therefore, it is preferable that the intake/exhaust hole be formed at a position at which the intake/exhaust hole is unlikely to be closed by the rain water and the like which falls from upside. 
     On the other hand, for example, in the case where one or more openings of one or more intake/exhaust holes on the mechanism-enclosing portion  173   a  side open below the actuator mechanism  74  (illustrated in  FIG. 1 ), the one or more openings can be closed by lubricant which falls from the gear mechanism  78  or the like. Therefore, it is preferable that one or more intake/exhaust holes be formed at one or more positions at which the one or more openings are unlikely to be closed by the lubricant which falls from the gear mechanism  78  or the like. 
     LIST OF REFERENCES 
     
         
         
           
               1  Vehicle 
               10  Vehicle Brake System 
               12  Brake Pedal (Brake Manipulation Unit) 
               14  Input Unit 
               16  Electric Brake Device 
               72  Electric Motor 
               72   b  Output Shaft 
               74  Actuator Mechanism 
               82  Cylinder Body 
               82   a   1  Attachment Hole (Insertion Hole) 
               88   a  Second Slave Piston (Hydraulic Control Piston) 
               88   b  First Slave Piston (Hydraulic Control Piston) 
               90   c  Guide Piston (Sealing Member) 
               94   a  Second Back Chamber (Portion Filled with Brake Fluid) 
               94   b  First Back Chamber (Portion Filled with Brake Fluid) 
               98   a  Second Hydraulic Chamber (Portion Filled with Brake Fluid) 
               98   b  First Hydraulic Chamber (Portion Filled with Brake Fluid) 
               172  Actuator Housing 
               173   a  Mechanism-enclosing Portion 
               179 ,  181 ,  183 ,  185  Intake/Exhaust Hole (Communication Hole) 
               179   a ,  181   a ,  183   a ,  187   b  Water-proof Moisture-permeable Films (Films of Material with Water Proofing Property and Moisture Permeability Property) 
               206  Bolt Members (Attachment Fastening Members)