Patent Publication Number: US-2023150461-A1

Title: Brake system for motorcycle, and motorcycle

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a brake system for a motorcycle, and a motorcycle including such a brake system, the brake system including a first operation element and a second operation element operated by a rider. 
     A brake system, which includes a first operation element and a second operation element operated by a rider, for a motorcycle has been known. The brake system includes: a front-wheel braking section that includes a first friction application device for braking a front wheel at least with a friction force corresponding to motion of the first operation element; and a rear-wheel braking section that includes a second friction application device for braking a rear wheel at least with a friction force corresponding to motion of the second operation element. The brake system also includes a controller that performs slip control operation to control slips of the front wheel and the rear wheel. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-2014-15077 
     SUMMARY OF THE INVENTION 
     The conventional brake system for the motorcycle is configured that each of the front-wheel braking section and the rear-wheel braking section includes: a master cylinder to which the motion of the operation element is transmitted; a wheel cylinder that communicates with the master cylinder via a fluid path filled with a brake fluid; and a hydraulic pressure adjustment mechanism that adjusts a hydraulic pressure of the brake fluid in the wheel cylinder. In such a configuration, a brake fluid pipe for constituting the fluid path has to be disposed from the front wheel to the rear wheel. The motorcycle has extremely small body size compared to other vehicles (for example, an automobile, a truck, and the like). Thus, in the configuration of the conventional brake system for the motorcycle, there may be a case where a space for disposing the brake fluid pipe and a work space therefor cannot be provided. 
     The present invention has been made with the above-described problem as the background and therefore has a purpose of improving mountability of the brake system capable of performing slip control operation of a front wheel and a rear wheel to a motorcycle. The present invention further has a purpose of obtaining a motorcycle that includes such a brake system. 
     Solution to Problem 
     A brake system according to the present invention is a brake system for a motorcycle, the brake system including a first operation element and a second operation element operated by a rider. The brake system includes: a front-wheel braking section that includes a first friction application device for braking a front wheel of the motorcycle at least with a friction force corresponding to motion of the first operation element; a rear-wheel braking section that includes a second friction application device for braking a rear wheel of the motorcycle at least with a friction force corresponding to motion of the second operation element; and a controller that performs slip control operation for controlling slips of the front wheel and the rear wheel. The front-wheel braking section further includes: a master cylinder, to which the motion of the first operation element is transmitted; a wheel cylinder that communicates with the master cylinder via a fluid path filled with a brake fluid: and a hydraulic pressure adjustment mechanism that adjusts a hydraulic pressure of the brake fluid in the wheel cylinder. In the front-wheel braking section, the friction force, which is applied to the front wheel by the first friction application device, varies according to the hydraulic pressure of the brake fluid in the master cylinder during service braking and varies by control of the hydraulic pressure adjustment mechanism by the controller during the slip control operation. The rear-wheel braking section further includes: a second operation element motion sensor that detects motion of the second operation element; and an actuator that is unitized with the second friction application device. In the rear-wheel braking section, the friction force, which is applied to the rear wheel by the second friction application device, varies according to control of the actuator by the controller corresponding to a detection result of the second operation element motion sensor during the service braking and varies by the control of the actuator by the controller during the slip control operation. 
     A motorcycle according to the present invention includes the above-described brake system. 
     Advantageous Effects of Invention 
     In the brake system according to the present invention, the front-wheel braking section is configured to include: the master cylinder, to which the motion of the first operation element is transmitted; the wheel cylinder that communicates with the master cylinder via the fluid path filled with the brake fluid; and the hydraulic pressure adjustment mechanism that adjusts the hydraulic pressure of the brake fluid in the wheel cylinder, and the rear-wheel braking section is configured to include: the second operation element motion sensor that detects the motion of the second operation element; and the actuator that is unitized with the second friction application device. In the front-wheel braking section, the friction force, which is applied to the front wheel by the first friction application device, varies according to the hydraulic pressure of the brake fluid in the master cylinder during the service braking and varies by the control of the hydraulic pressure adjustment mechanism by the controller during the slip control operation. Meanwhile, in the rear-wheel braking section, the friction force, which is applied to the rear wheel by the second friction application device, varies by the control of the actuator by the controller during the service braking and during the slip control operation. Thus, disposition of a brake fluid pipe for constituting the fluid path in a further narrow area suffices. In addition, the slip of the front wheel, which has a significant impact on behavior of the motorcycle, can be suppressed by controlling the hydraulic pressure, that is, by control with superior responsiveness. As a result, it is possible to simultaneously improve the mountability and secure safety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view illustrating a configuration of a motorcycle to which a brake system according to an embodiment of the present invention is mounted. 
         FIG.  2    is a view illustrating a configuration of the brake system according to the embodiment of the present invention. 
         FIG.  3    is a view illustrating a configuration of a hydraulic pressure adjustment unit in the brake system according to the embodiment of the present invention. 
         FIG.  4    is a view illustrating a configuration of main components of a rear-wheel braking section in the brake system according to the embodiment of the present invention. 
         FIG.  5    is a system configuration diagram of the brake system according to the embodiment of the present invention. 
         FIG.  6    is a view illustrating a modified example of the configuration of the brake system according to the embodiment of the present invention. 
         FIG.  7    is a view illustrating another modified example of the configuration of the brake system according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A description will hereinafter be made on the present invention with reference to the drawings. 
     The following description will be made on a case where a brake system according to the present invention is applied to a two-wheeled motor vehicle. However, the brake system according to the present invention may be applied to a motorcycle other than the two-wheeled motor vehicle. The motorcycle includes a three-wheeled motor vehicle. Examples of the two-wheeled motor vehicle and the three-wheeled motor vehicle are a motorbike, a scooter, and an electric scooter. In addition, the following description will be made on a case where a front-wheel braking section is only connected to a first operation element and a rear-wheel braking section is only connected to a second operation element. However, at least one of the front-wheel braking section and the rear-wheel braking section maybe connected to both of the first operation element and the second operation element. 
     A configuration, operation, and the like, which will be described below, constitute merely one example, and the brake system according to the present invention is not limited to a case with such a configuration, such operation, and the like. 
     In the drawings, the same or similar members or portions will be denoted by the same reference sign or will not be denoted by the reference sign. In addition, a detailed structure will appropriately be illustrated in a simplified manner or will not be illustrated. Furthermore, an overlapping description will appropriately be simplified or will not be made. 
     EMBODIMENT 
     A description will hereinafter be made on a brake system according to an embodiment. 
     &lt;Configuration and Operation of Brake System&gt; 
     A description will be made on a configuration and operation of the brake system according to the embodiment with reference to  FIG.  1    to  FIG.  7   . 
       FIG.  1    is a view illustrating a configuration of a motorcycle to which the brake system according to the embodiment of the present invention is mounted.  FIG.  2    is a view illustrating a configuration of the brake system according to the embodiment of the present invention.  FIG.  3    is a view illustrating a configuration of a hydraulic pressure adjustment unit in the brake system according to the embodiment of the present invention.  FIG.  4    is a view illustrating a configuration of main components of a rear-wheel braking section in the brake system according to the embodiment of the present invention.  FIG.  5    is a system configuration diagram of the brake system according to the embodiment of the present invention.  FIG.  6    and  FIG.  7    are views, each of which illustrates a modified example of the configuration of the brake system according to the embodiment of the present invention. 
     As particularly illustrated in  FIG.  1    and  FIG.  2   , a brake system  10  is mounted to a motorcycle  100 . The motorcycle  100  includes: a trunk  1 ; a handlebar  2  that is held in a freely turnable manner by the trunk  1 ; a front wheel  3  that is held in a freely turnable manner with the handlebar  2  by the trunk  1 ; and a rear wheel  4  that is held in a freely rotatable manner by the trunk  1 . 
     The brake system  10  includes a first operation element  11  and a second operation element  12  that are operated by a rider. The first operation element  11  is configured as a brake lever that is provided to the handlebar  2 , for example, and is operated by the rider&#39;s hand. The second operation element  12  is configured as a foot pedal that is provided to a lower portion of the trunk  1 , for example, and is operated by the rider&#39;s foot. 
     The brake system  10  includes: a front-wheel braking section  20  that is hydraulically connected to the first operation element  11 ; and a rear-wheel braking section  40  that is electrically connected to the second operation element  12 . The front-wheel braking section  20  brakes the front wheel  3  with a friction force corresponding to an operation amount of the first operation element  11  by pressing a friction member (not illustrated) of a first friction application device  21 , which is held by the trunk  1 , against a disc rotor  3   a  rotating with the front wheel  3 . The rear-wheel braking section  40  brakes the rear wheel  4  with a friction force corresponding to an operation amount of the second operation element  12  by pressing a friction member  51  of a second friction application device  50 , which is held by the trunk  1 , against a disc rotor  4   a  rotating with the rear wheel  4 . The first friction application device  21  and the second friction application device  50  may be structured differently. For example, the first friction application device  21  may generate the friction force corresponding to the operation amount of the first operation element  11  by pressing a friction member of a brake shoe, which is held by the trunk  1 , against a brake drum rotating with the front wheel  3 . In addition, the second friction application device  50  may generate the friction force corresponding to the operation amount of the second operation element  12  by pressing a friction member of a brake shoe, which is held by the trunk  1 , against a brake drum rotating with the rear wheel  4 . 
     The front-wheel braking section  20  includes: a master cylinder  22  to which motion of the first operation element  11  is transmitted; a reservoir  23  attached to the master cylinder  22 ; a wheel cylinder  25  that communicates with the master cylinder  22  via a fluid path  24  filled with a brake fluid and is installed in the first friction application device  21 ; a brake fluid pipe  24   a  that constitutes apart of the fluid path  24  and one end of which is connected to the master cylinder  22 ; a brake fluid pipe  24   b  that constitutes a part of the fluid path  24  and one end of which is connected to the wheel cylinder  25 ; and a hydraulic pressure adjustment unit  30  that is connected to the other end of the brake fluid pipe  24   a  and the other end of the brake fluid pipe  24   b.  The brake fluid pipe  24   a  may not be used, and the hydraulic pressure adjustment unit  30  may directly be connected to the master cylinder  22 . In addition, the brake fluid pipe  24   b  may not be used, and the hydraulic pressure adjustment unit  30  may directly be connected to the wheel cylinder  25 . Alternatively, the hydraulic pressure adjustment unit  30  may be unitized with the master cylinder  22  or the wheel cylinder  25 . 
     As particularly illustrated in  FIG.  2    and  FIG.  3   , the hydraulic pressure adjustment unit  30  includes a base body  31 . The base body  31  is formed with: a master cylinder port MP to which the brake fluid pipe  24   a  is connected; a wheel cylinder port WP to which the brake fluid pipe  24   b  is connected; a primary fluid path  24   c  that constitutes a part of the fluid path  24  and is an internal fluid path connecting the master cylinder port MP and the wheel cylinder port WP; and a secondary fluid path  24   d  that constitutes a part of the fluid path  24  and is an internal fluid path bypassing the primary fluid path  24   c.  The brake fluid in the wheel cylinder  25  is released to an intermediate portion of the primary fluid path  24   c  via the secondary fluid path  24   d.    
     An inlet valve  32  is provided to the primary fluid path  24   c.  The secondary fluid path  24   d  is sequentially provided with an outlet valve  33 , an accumulator  34  that stores the brake fluid, and a pump  35  from an upstream side. The pump  35  is driven by a motor  36 . The inlet valve  32 , the outlet valve  33 , the accumulator  34 , the pump  35 , and the motor  36  are assembled to the base body  31 . A housing  37  for accommodating at least a part of a controller (ECU)  60  is attached to the base body  31 . The inlet valve  32  is an electromagnetic valve that is switched from being opened to being closed and thereby blocks a flow of the brake fluid at a mounted position thereof when being brought from an unenergized state into an energized state by the controller  60 , for example. In addition, the outlet valve  33  is an electromagnetic valve that is switched from being opened to being closed and thereby blocks the flow of the brake fluid toward the pump  35  via the mounted position thereof when being brought from the unenergized state into the energized state by the controller  60 , for example. The inlet valve  32 , the outlet valve  33 , and the motor  36  correspond to the “hydraulic pressure adjustment mechanism” in the present invention. 
     As particularly illustrated in  FIG.  2    and  FIG.  4   , the rear-wheel braking section  40  includes an actuator  41  that is unitized with the second friction application device  50 . The actuator  41  may be attached to an outer side of the second friction application device  50  or may be provided in the second friction application device  50 . The second friction application device  50  is configured as a floating caliper. The second friction application device  50  may have a different structure. For example, the second friction application device  50  may be configured as an opposed caliper. The second friction application device  50  includes: the paired friction members  51  that hold the disc rotor  4   a  therebetween; and a spindle  52  that adjusts a distance of each of the friction members  51  from the disc rotor  4   a.  The actuator  41  is coupled to the spindle  52  and causes linear motion of the spindle  52  to adjust the distance thereof. The actuator  41  is a motor, for example. The linear motion of the spindle  52  may be transmitted to the friction members  51  via an elastic member or may be transmitted to the friction members  51  via a fluid such as a hydraulic fluid. 
     As particularly illustrated in  FIG.  2    and  FIG.  5   , the controller  60  includes: a first control section  61  that governs operation of the inlet valve  32 , the outlet valve  33 , and the motor  36 ; and a second control section  62  that governs operation of the actuator  41 . The first control section  61  and the second control section  62  maybe provided as one unit or may be divided into multiple units. Each of the first control section  61  and the second control section  62  may partially or entirely be constructed of a microcomputer, a microprocessor unit, or the like, may be constructed of a member in which firmware or the like can be updated, or may be a program module or the like that is executed by a command from a CPU or the like, for example. 
     For example, the controller  60  receives output signals wirelessly or by wire from a front-wheel rotational frequency sensor  81 , a brake hydraulic pressure sensor  82 , a rear-wheel rotational frequency sensor  91 , a second operation element motion sensor  92 , a friction member motion sensor  93 , and the like. The controller  60  may receive the output signal from another sensor. The controller  60  derives a target braking force to be generated on each of the front wheel  3  and the rear wheel  4  on the basis of those output signals. The first control section  61  sends a command signal, which corresponds to the target braking force to be generated on the front wheel  3 , to drivers in the inlet valve  32 , the outlet valve  33 , and the motor  36  wirelessly or by wire. The second control section  62  sends a command signal, which corresponds to the target braking force to be generated on the rear wheel  4 , to a driver in the actuator  41  wirelessly or by wire. 
     The front-wheel rotational frequency sensor  81  detects a rotational frequency of the front wheel  3 . The front-wheel rotational frequency sensor  81  is held by the trunk  1 , for example. The front-wheel rotational frequency sensor  81  may detect another physical quantity that can substantially be converted to the rotational frequency of the front wheel  3 . 
     The brake hydraulic pressure sensor  82  detects a hydraulic pressure of the brake fluid in the wheel cylinder  25 , for example. For example, the brake hydraulic pressure sensor  82  is provided in an area on the wheel cylinder  25  side from the inlet valve  32  in the primary fluid path  24   c.  The brake hydraulic pressure sensor  82  may detect another physical quantity that can substantially be converted to the hydraulic pressure of the brake fluid in the wheel cylinder  25 . 
     The rear-wheel rotational frequency sensor  91  detects a rotational frequency of the rear wheel  4 . The rear-wheel rotational frequency sensor  91  is held by the trunk  1 , for example. The rear-wheel rotational frequency sensor  91  may detect another physical quantity that can substantially be converted to the rotational frequency of the rear wheel  4 . 
     The second operation element motion sensor  92  detects motion of the second operation element  12 . Any type of sensor can be adopted as the second operation element motion sensor  92  as long as the second operation element motion sensor  92  detects a physical quantity to which a desired braking force by the rider is reflected. For example, the second operation element motion sensor  92  may detects the operation amount of the second operation element  12  by the rider or may detect a force that is applied to the second operation element  12  by the rider. The second operation element motion sensor  92  is held by the trunk  1 , for example. The second operation element motion sensor  92  may detect another physical quantity that can substantially be converted to the operation amount of the second operation element  12  or the force that is applied to the second operation element  12 . 
     The friction member motion sensor  93  detects motion of the friction members  51  in the second friction application device  50 . Any type of sensor can be adopted as the friction member motion sensor  93  as long as the friction member motion sensor  93  detects a physical quantity to which the braking force generated on the rear wheel  4  by the second friction application device  50  is reflected. For example, the friction member motion sensor  93  may detect a drive amount of the actuator  41  or may detect a reaction force that acts on the spindle  52 . The friction member motion sensor  93  is held by the second friction application device  50 , for example. The friction member motion sensor  93  may detect another physical quantity that can substantially be converted to the drive amount of the actuator  41  or the reaction force that acts on the spindle  52 . 
     The first control section  61  and the second control section  62  are accommodated in the housing  37  of the hydraulic pressure adjustment unit  30 . That is, the first control section  61  and the second control section  62  are unitized with the inlet valve  32 , the outlet valve  33 , and the motor  36 . The second control section  62  may be unitized with the second friction application device  50  and the actuator  41  or may be unitized with the second operation element motion sensor  92 . 
     When the rider operates the first operation element  11  in a state where the motorcycle  100  is stopped or where the motorcycle  100  travels while a slip exceeding a reference value is not generated on the front wheel  3  and the rear wheel  4 , that is, during service braking by the front-wheel braking section  20 , the first control section  61  controls the inlet valve  32  and the outlet valve  33  in the unenergized state and controls the motor  36  in an undriven state. When the rider operates the first operation element  11 , a piston (not illustrated) in the master cylinder  22  is pressed to increase the hydraulic pressure of the brake fluid in the wheel cylinder  25 , the friction member (not illustrated) of the first friction application device  21  is pressed against the disc rotor  3   a,  and the front wheel  3  is thereby braked. When the rider releases the first operation element  11 , the piston (not illustrated) in the master cylinder  22  returns to reduce the hydraulic pressure of the brake fluid in the wheel cylinder  25 , and the friction member (not illustrated) of the first friction application device  21  separates from the disc rotor  3   a.  That is, during the service braking, in the front-wheel braking section  20 , the friction force that is applied to the front wheel  3  by the first friction application device  21  varies according to the hydraulic pressure of the brake fluid in the master cylinder  22 . When the rider operates the first operation element  11 , in addition to the application of the friction force to the front wheel  3  by the first friction application device  21 , interlocking brake control operation may be performed to apply the friction force to the rear wheel  4  by the second friction application device  50 . 
     When the rider operates the second operation element  12  in the state where the motorcycle  100  is stopped or where the motorcycle  100  travels while the slip exceeding the reference value is not generated on the front wheel  3  and the rear wheel  4 , that is, during service braking by the rear-wheel braking section  40 , the second control section  62  drives the actuator  41  with the drive amount that corresponds to the output signal of the second operation element motion sensor  92 . When the rider operates the second operation element  12 , the spindle  52  is pushed out by driving of the actuator  41 , the friction members  51  of the second friction application device  50  are pressed against the disc rotor  4   a,  and the rear wheel  4  is thereby braked. When the rider releases the second operation element  12 , the spindle  52  returns by driving of the actuator  41 , and the friction members  51  of the second friction application device  50  separate from the disc rotor  4   a.  That is, during the service braking, in the rear-wheel braking section  40 , the friction force that is applied to the rear wheel  4  by the second friction application device  50  varies by the control of the actuator  41  by the controller  60  that corresponds to the detection result by the second operation element motion sensor  92 . When the rider operates the second operation element  12 , in addition to the application of the friction force to the rear wheel  4  by the second friction application device  50 , interlocking brake control operation may be performed to apply the friction force to the front wheel  3  by the first friction application device  21 . 
     The stop of the motorcycle  100  and the slip generated on the front wheel  3  and the rear wheel  4  can be determined by a well-known method using the output signals of the front-wheel rotational frequency sensor  81  and the rear-wheel rotational frequency sensor  91 . 
     In the case where the motorcycle  100  travels in a state where the slip exceeding the reference value is generated on the front wheel  3  or the rear wheel  4 , the controller  60  performs slip control operation to suppress the slip. Examples of the slip control operation are operation to execute anti-lock brake control for each of the wheels, operation to execute wheel slip suppression control for each of the wheels, and operation to execute sideslip suppression control for each of the wheels. When performing the slip control operation, the controller  60  may control, in addition to the brake system  10 , another system that is mounted to the motorcycle  100 . 
     During the slip control operation, when it is necessary to reduce the friction force applied to the front wheel  3 , the first control section  61  controls the inlet valve  32  and the outlet valve  33  in the energized state and drives the motor  36  with the drive amount that corresponds to the output signal of the brake hydraulic pressure sensor  82 . By such control, the hydraulic pressure of the brake fluid in the wheel cylinder  25  is reduced, and the friction member (not illustrated) of the first friction application device  21  separates from the disc rotor  3   a.  That is, during the slip control operation, in the front-wheel braking section  20 , the friction force that is applied to the front wheel  3  by the first friction application device  21  varies by the control of the inlet valve  32 , the outlet valve  33 , and the motor  36  by the controller  60 . Instead of the output signal of the brake hydraulic pressure sensor  82 , command signals to the drivers in the inlet valve  32 , the outlet valve  33 , and the motor  36 , which are sent by the first control section  61  immediately before sending of the output signal of the brake hydraulic pressure sensor  82 , may be used. 
     During the slip control operation, when it is necessary to reduce the friction force applied to the rear wheel  4 , the second control section  62  drives the actuator  41  with the drive amount that corresponds to the output signal of the friction member motion sensor  93 . By such control, the spindle  52  returns, and the friction members  51  of the second friction application device  50  separate from the disc rotor  4   a.  That is, during the slip control operation, in the rear-wheel braking section  40 , the friction force that is applied to the rear wheel  4  by the second friction application device  50  varies by the control of the actuator  41  by the controller  60 . Instead of the output signal of the friction member motion sensor  93 , a command signal to the driver in the actuator  41 , which is sent by the second control section  62  immediately before sending of the output signal of the friction member motion sensor  93 , may be used. 
     The brake system  10  may be configured to be able to reduce or increase the friction force applied to the front wheel  3  during the slip control operation. That is, as illustrated in  FIG.  6   , a pressure boosting fluid path  24   e  as an internal channel may be formed in the base body  31  of the hydraulic pressure adjustment unit  30 . One end of the pressure boosting fluid path  24   e  is connected to a portion of the primary fluid path  24   c  that is on the master cylinder  22  side from a merging portion with a downstream end of the secondary fluid path  24   d,  and the other end is connected to a portion of the secondary fluid path  24   d  between the accumulator  34  and the pump  35 . A switching valve  38  is provided between a merging portion of the primary fluid path  24   c  with the pressure boosting fluid path  24   e  and the merging portion of the primary fluid path  24   c  with the downstream end of the secondary fluid path  24   d,  and a booster regulator  39  is provided to the pressure boosting fluid path  24   e.  The switching valve  38  is an electromagnetic valve that is switched from being opened to being closed and thereby blocks the flow of the brake fluid at a mounted position thereof when being brought from the unenergized state into the energized state by the controller  60 , for example. The booster regulator  39  is an electromagnetic valve that is switched from being closed to being opened and thereby allows the flow of the brake fluid toward the pump  35  via a mounted position thereof when being brought from the unenergized state into the energized state by the controller  60 , for example. The switching valve  38  and the booster regulator  39  correspond to the “hydraulic pressure adjustment mechanism” in the present invention. 
     During the slip control operation, when it is necessary to increase the friction force applied to the front wheel  3 , the first control section  61  controls the inlet valve  32  and the outlet valve  33  in the unenergized state, controls the switching valve  38  and the booster regulator  39  in the energized state, and drives the motor  36  with the drive amount that corresponds to the output signal of the brake hydraulic pressure sensor  82 . By such control, the hydraulic pressure of the brake fluid in the wheel cylinder  25  is increased, and the friction member (not illustrated) of the first friction application device  21  is pressed against the disc rotor  3   a . That is, during the slip control operation, in the front-wheel braking section  20 , the friction force that is applied to the front wheel  3  by the first friction application device  21  varies by the control of the inlet valve  32 , the outlet valve  33 , the switching valve  38 , the booster regulator  39 , and the motor  36  by the controller  60 . Instead of the output signal of the brake hydraulic pressure sensor  82 , the command signals to the drivers in the inlet valve  32 , the outlet valve  33 , the switching valve  38 , the booster regulator  39 , and the motor  36 , which are sent by the first control section  61  immediately before sending of the output signal of the brake hydraulic pressure sensor  82 , may be used. 
     The brake system  10  may be configured to be able to reduce or increase the friction force applied to the rear wheel  4  during the slip control operation. During the slip control operation, when it is necessary to increase the friction force applied to the rear wheel  4 , the second control section  62  drives the actuator  41  with the drive amount that corresponds to the output signal of the friction member motion sensor  93 . By such control, the spindle  52  is pushed out, and the friction members  51  of the second friction application device  50  are pressed against the disc rotor  4   a.  That is, during the slip control operation, in the rear-wheel braking section  40 , the friction force that is applied to the rear wheel  4  by the second friction application device  50  varies by the control of the actuator  41  by the controller  60 . Instead of the output signal of the friction member motion sensor  93 , the command signal to the driver in the actuator  41 , which is sent by the second control section  62  immediately before sending of the output signal of the friction member motion sensor  93 , may be used. 
     The front-wheel braking section  20  of the brake system  10  may be of a pumpless type. That is, as illustrated in  FIG.  7   , the pump  35  is not provided to the secondary fluid path  24   d.  Even with such a configuration, during the slip control operation, when the first control section  61  executes PWM control on the inlet valve  32  and the outlet valve  33  with a pulse width according to the output signal of the brake hydraulic pressure sensor  82 , for example, the brake fluid in the wheel cylinder  25  can return to the master cylinder  22  via the secondary fluid path  24   d  by a reaction force of a spring mounted in the accumulator  34 , and the friction force applied to the front wheel  3  can thereby be reduced. That is, during the slip control operation, in the front-wheel braking section  20 , the friction force that is applied to the front wheel  3  by the first friction application device  21  varies by the control of the inlet valve  32  and the outlet valve  33  by the controller  60 . Instead of the output signal of the brake hydraulic pressure sensor  82 , the command signals to the drivers in the inlet valve  32  and the outlet valve  33 , which are sent by the first control section  61  immediately before sending of the output signal of the brake hydraulic pressure sensor  82 , may be used. 
     &lt;Effects of Brake System&gt; 
     A description will be made on effects of the brake system according to the embodiment. 
     In the brake system  10 , the front-wheel braking section  20  is configured to include: the master cylinder  22 , to which the motion of the first operation element  11  is transmitted; the wheel cylinder  25  that communicates with the master cylinder  22  via the fluid path  24  filled with the brake fluid; and the hydraulic pressure adjustment mechanism (for example, the inlet valve  32 , the outlet valve  33 , the motor  36 , the switching valve  38 , the booster regulator  39 , and the like) that adjusts the hydraulic pressure of the brake fluid in the wheel cylinder  25 , and the rear-wheel braking section  40  is configured to include: the second operation element motion sensor  92  that detects the motion of the second operation element  12 ; and the actuator  41  that is unitized with the second friction application device  50 . In the front-wheel braking section  20 , the friction force, which is applied to the front wheel  3  by the first friction application device  21 , varies according to the hydraulic pressure of the brake fluid in the master cylinder  22  during the service braking and varies by the control of the hydraulic pressure adjustment mechanism by the controller  60  during the slip control operation. Meanwhile, in the rear-wheel braking section  40 , the friction force, which is applied to the rear wheel  4  by the second friction application device  50 , varies by the control of the actuator  41  by the controller  60  during the service braking and during the slip control operation. Thus, the disposition of the brake fluid pipe for constituting the fluid path  24  in a further narrow area suffices. In addition, the slip of the front wheel  3 , which has the significant impact on behavior of the motorcycle  100 , can be suppressed by controlling the hydraulic pressure, that is, by the control with the superior responsiveness. As a result, it is possible to simultaneously improve the mountability and secure safety. 
     Preferably, the controller  60  includes the first control section  61  that governs the operation of the hydraulic pressure adjustment mechanism (for example, the inlet valve  32 , the outlet valve  33 , the motor  36 , the switching valve  38 , the booster regulator  39 , and the like) and the second control section  62  that governs the operation of the actuator  41 . The first control section  61  and the second control section  62  are unitized with the hydraulic pressure adjustment mechanism. With such a configuration, a sealing structure can be shared among the first control section  61  and the second control section  62 , which cuts down on cost of the brake system  10 . 
     Preferably, the controller  60  includes the first control section  61  that governs the operation of the hydraulic pressure adjustment mechanism (for example, the inlet valve  32 , the outlet valve  33 , the motor  36 , the switching valve  38 , the booster regulator  39 , and the like) and the second control section  62  that governs the operation of the actuator  41 . The first control section  61  is unitized with the hydraulic pressure adjustment mechanism, and the second control section  62  is unitized with the second friction application device  50  and the actuator  41  or with the second operation element motion sensor  92 . With such a configuration, the front-wheel braking section  20  and the rear-wheel braking section  40  can separately be managed, which improves maintainability, a retrofit property, and the like of the brake system  10 . 
     The description has been made so far on the brake system according to the embodiment. However, the brake system according to the present invention is not limited to that in the description of the embodiment. For example, the embodiment may only partially be implemented. 
     REFERENCE SIGNS LIST 
       1 : Trunk 
       2 : Handlebar 
       3 : Front wheel 
       4 : Rear wheel 
       10 : Brake system 
       11 : First operation element 
       12 : Second operation element 
       20 : Front-wheel braking section 
       21 : First friction application device 
       22 : Master cylinder 
       23 : Reservoir 
       24 : Fluid path 
       25 : Wheel cylinder 
       30 : Hydraulic pressure adjustment unit 
       31 : Base body 
       32 : Inlet valve 
       33 : Outlet valve 
       34 : Accumulator 
       35 : Pump 
       36 : Motor 
       37 : Housing 
       38 : Switching valve 
       39 : Booster regulator 
       40 : Rear-wheel braking section 
       41 : Actuator 
       50 : Second friction application device 
       51 : Friction member 
       52 : Spindle 
       60 : Controller 
       61 : First control section 
       62 : Second control section 
       81 : Front-wheel rotational frequency sensor 
       82 : Brake hydraulic pressure sensor 
       91 : Rear-wheel rotational frequency sensor 
       92 : Second operation element motion sensor 
       93 : Friction member motion sensor 
       100 : Motorcycle