Abstract:
In a brake system for a vehicle, a first control mode and a second control mode are provided by which it is possible to cope with variations in the running environments such as changes between traveling on a public road and traveling on a circuit racecourse and variations in road conditions such as changes between a dry road surface and a wet road surface. A mode change-over switch is disposed between a kill switch on the upper side and a starter switch on the lower side, on the vehicle body center side relative to a right grip. Switching between the first control mode and the second control mode is carried out by use of the mode change-over switch.

Description:
BACKGROUND 
     1. Field 
     The present invention relates to a brake system for a motorcycle. 
     2. Description of the Related Art 
     By-wire type brake devices (BBW: brake-by-wire) have been put to practical use. In this type of brake device, an amount of operation on the brake (brake operation amount) is detected, then a hydraulic pressure is generated in a hydraulic modulator on the basis of the detected value, and a braking force is generated by the hydraulic pressure. 
     By the above-mentioned brake device (BBW), an ABS (antilock brake system) function can be exhibited. 
     Furthermore, there has been known a system in which not only the ABS function is exhibited by the brake device as above-mentioned but also front and rear brake devices are operated in an interlocked manner by operating one of front and rear brake operating members (see, for example, FIGS. 1 and 3 of Patent Document 1 (Japanese Patent Laid-Open No. 2006-175993)). 
     The system in which front-wheel and rear-wheel brake devices are operated in an interlocked manner is called a CBS (combined brake system). When a mode change-over switch  32  shown in FIG. 1 of Patent Document 1 is switched over, a CBS function is selected, whereby a front wheel braking force and a rear wheel braking force are controlled based on a predetermined correlation, as shown in FIG. 3 of Patent Document 1. 
     In this way, in the CBS function according to the related art, the front-rear distribution of braking force is unequivocally determined. From the driver&#39;s point of view, however, there is a demand for changing the front-rear distribution correspondingly to variations in the running environments such as changes between traveling on a public road and traveling on a circuit racecourse, or variations in road conditions such as changes between a dry road surface and a wet road surface. For instance, a desirable front-rear distribution at the time of straight forward traveling or that at the time of putting priority on vehicle body control during turning, in the case where the coefficient of friction (μ) on a road is high and a high braking force at the tire can be expected, are different from the front-rear distributions favored in the case where the coefficient of friction on a road is low. Thus, there is a demand for changing the front-rear distribution of braking force according to the running environments. Accordingly, there is room for further improvement in order to make it possible to cope with variations in the front-rear distribution of braking force according to various parameters or environmental conditions. 
     SUMMARY 
     It is an object of the present invention to provide a brake system capable of realizing a front-rear distribution of braking force according to variations in the running environments. 
     According to one embodiment of the invention, there is provided a brake control system for a motorcycle, which is a by-wire type brake control system for a motorcycle and in which amounts of operation on front-wheel and rear-wheel brake operating units are detected. Hydraulic pressures are generated in front-wheel and rear-wheel hydraulic modulators on the basis of the detected values, and front-wheel and rear-wheel brake devices generate braking forces by the hydraulic pressures. The brake control system can be provided with a mode change-over unit configured to changing over a plurality of braking force control modes according to a driver&#39;s operation. A control mode can include a first section in which the braking force generated on a front wheel and the braking force generated on a rear wheel are both increased when the amount of operation on the front-wheel brake operating unit increases. A third section can be provided, in which the braking force generated on the front wheel is further increased whereas the braking force generated on the rear wheel is decreased when the amount of operation on the front-wheel brake operating unit further increases. The plurality of control modes can be a plurality of modes which differ from each other in the magnitude of the braking force generated on the rear wheel in the first section. 
     According to another embodiment of the invention, the plurality of control modes can include a first control mode and a second control mode, each of which has a second section between the first section and the third section. In the first control mode, when the front-wheel brake operating means is operated, a braking force is generated by the front-wheel brake device according to the operation amount of the front-wheel brake operating unit. A braking force interlocked with the operation amount of the front-wheel brake operating unit is generated on the rear wheel by the rear-wheel brake device for which no operation is made. 
     In a first mode first section in which the operation amount of the front-wheel brake operating unit ranges from zero to a first mode first predetermined value, the braking force generated on the rear wheel gradually increases correspondingly to an increase in the operation amount. 
     In a first mode second section in which the operation amount of the front-wheel brake operating unit ranges from the first mode first predetermined value to a first mode second predetermined value greater than the first mode first predetermined value, the braking force generated on the rear wheel is maintained at a maximum value in the first mode first section, irrespective of an increase in the operation amount. 
     In a first mode third section in which the operation amount of the front-wheel brake operating unit is in excess of the first mode second predetermined value, the braking force generated on the rear wheel gradually decreases to zero correspondingly to an increase in the operation amount. 
     In the second control mode, like in the first control mode, when the front-wheel brake operating unit is operated, a braking force is generated by the front-wheel brake device according to the operation amount of the front-wheel brake operating unit. A braking force interlocked with the operation amount of the front-wheel brake operating unit is generated on the rear wheel by the rear-wheel brake device for which no operation is made. 
     In a second mode first section in which the operation amount of the front-wheel brake operating unit ranges from zero to a second mode first predetermined value, the braking force generated on the rear wheel gradually increases correspondingly to an increase in the operation amount, and this braking force is set to be smaller than the corresponding braking force generated on the rear wheel in the first mode first section. 
     The electronic control unit can cause the front-wheel and rear-wheel brake devices to generate braking forces according to the control mode selected. 
     According to another embodiment of the invention, in the second control mode, like in the first control mode, in a second mode second section in which the operation amount of the front-wheel brake operating unit ranges from the second mode first predetermined value to a second mode second predetermined value greater than the second mode first predetermined value, the braking force generated on the rear wheel is maintained at a maximum value in the second mode first section irrespectively of an increase in the operation amount. This braking force is controlled to be smaller than the corresponding braking force generated on the rear wheel in the first mode second section. 
     According to another embodiment of the invention, in the second control mode, like in the first control mode, in a second mode third section in which the operation amount of the front-wheel brake operating unit is in excess of the second mode second predetermined value, the braking force generated on the rear wheel gradually decreases correspondingly to an increase in the operation amount. The operation amount at a point where the braking force is minimized is set to be greater than the corresponding operation amount in the first control mode. 
     According to another embodiment of the invention, the mode change-over unit is a switch provided on a handle bar. 
     According to another embodiment of the invention, the first control mode and the second control mode are so configured that when the rear-wheel brake operating unit is operated, a braking force is generated by the rear-wheel brake device according to the operation amount of the rear-wheel brake operating unit. A braking force interlocked with the operation amount of the rear-wheel brake operating unit is generated by the front-wheel brake device for which no operation is made. 
     The braking force generated on the rear wheel is set to be greater than the braking force generated on the front wheel. 
     The operation amount of the rear-wheel brake operating unit at which braking of the front wheel is started is set to be greater in the second control mode than in the first control mode. 
     According to embodiment of the invention, the plurality of modes are provided so that the degree of increase in the braking force generated on the rear wheel can be set differently in relation to the braking force generated on the front wheel. 
     When the degree of increase in the braking force generated on the rear wheel is set to be comparatively high, the front-wheel and rear-wheel braking forces are given priority, so that the driver can focus on deceleration of the vehicle. 
     When the degree of increase in the braking force generated on the rear wheel is set to be moderate, the operation amount on the rear wheel side, particularly at the time of turning, is rather enlarged, so that the range of control is widened. 
     According to other embodiments of the invention, in the first section (in a beginning section of braking), the braking force generated on the rear wheel by the front-wheel brake operating unit is suppressed in the second control mode as compared with that in the first control mode. The second control mode can be used, for example, as a mode effective in the case of a driver&#39;s desire to put priority on attitude control for turning performance over braking during cornering. 
     According to other embodiments of the invention, it is possible to control the attitude by the braking force generated on the front wheel, more favorably in the second control mode than in the first control mode. 
     According to other embodiments of the invention, for example in the case where it is desired to accomplish deceleration in as short a time as possible, both a braking force on the front wheel and a braking force on the rear wheel can be generated effectively. 
     As compared with the first control mode, the second control mode makes it possible to easily generate both the braking forces in a maximal manner at the time of, for example, full-braking or the like. Besides, in the second control mode, the driver is not required to operate both the front-wheel brake operating unit and the rear-wheel brake operating unit, and an operation of only the front-wheel brake operating unit suffices. In other words, at the time of full-braking, rather the second control mode than the first control mode ensures that an ideal front-rear distribution of braking can be automatically carried out, and that the driver can focus on a front-wheel braking operation. 
     According to other embodiments of the invention, the mode change-over unit is provided on the handle bar. The mode change-over unit permits the driver to perform change-over operations while gripping the grip, and is therefore easier to use. 
     According to other embodiments of the invention, the braking force generated on the rear wheel is set to be greater than the braking force generated on the front wheel, and the operation amount of the rear-wheel brake operating unit until the braking of the front wheel is started is set to be greater in the second control mode than in the first control mode. 
     Where the front-wheel brake operating unit is a brake lever whereas the rear-wheel brake operating unit is a brake pedal, it is said that the brake pedal operated by foot needs a more delicate operation as compared with the brake lever operated by hand. According to the present invention, the deceleration by the foot operation which is said to need a delicate operation can be carried out assuredly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side view (conceptual diagram) of a motorcycle according to an embodiment of the present invention. 
         FIG. 2  is a plan view (conceptual diagram) of the motorcycle. 
         FIG. 3  is an illustration of the layout of a mode change-over means. 
         FIG. 4  is a perspective view of a hydraulic modulator. 
         FIG. 5  is a circuit diagram of a brake control system in the motorcycle according to an embodiment of the present invention. 
         FIG. 6  is a map diagram concerning a first control mode. 
         FIG. 7  is a map diagram concerning a second control mode. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention will be described below, based on the accompanying drawings. Incidentally, the drawings are to be viewed according to the orientation of reference symbols. 
     An embodiment of the present invention will be described, based on the drawings. 
     As shown in the example of  FIG. 1 , a motorcycle has a front wheel  11   f  (f is a suffix indicative of front, here and below) accompanied by a pulser ring  13   f , and has a front wheel speed sensor  14   f  provided on a vehicle body  15  so as to detect the rotational speed of the front wheel  11   f  by counting pulses relevant to the pulser ring  13   f , whereby the front wheel speed can always be detected. 
     Further, the motorcycle  10  has a rear wheel  11   r  (r is a suffix indicative of rear, here and below) accompanied by a brake disk  12   r  and a pulser ring  13   r , and has a rear wheel speed sensor  14   r  provided on the vehicle body  15  so as to detect the rotational speed of the rear wheel  11   r  by counting pulses relevant to the pulser ring  13   r , whereby the rear wheel speed can always be detected. 
     The motorcycle  10  can have a front-wheel hydraulic modulator  21   f  and a front-wheel valve unit  22   f  provided on the vehicle body  15  at positions under a fuel tank  16  provided on the vehicle body  15 . In addition, the motorcycle  10  can have a rear-wheel hydraulic modulator  21   r  and a rear-wheel valve unit  22   r  provided at positions under a seat  17  provided on the vehicle body  15 . An electronic control unit  47  can be disposed rearwardly of the seat  17 . 
     As shown in  FIG. 2 , the front wheel  11   f  is braked by a front-wheel brake device  20   f , and the rear wheel  11   r  by a rear brake device  20   r . Each of the brake devices operates according to an operation amount of a front-wheel brake operating unit or means  19   f  represented by a brake lever or an operation amount of a rear-wheel brake operating unit or means  19   r  represented by a brake pedal. 
     The front-wheel brake device  20   f  can include, for example, the front-wheel hydraulic modulator  21   f  (the structure of which will be described later), the front-wheel valve unit  22   f , a brake caliper  23   f  and a brake disc  24   f.    
     The rear brake device  20   r  can include, for example, the rear-wheel hydraulic modulator  21   r , the rear-wheel valve unit  22   r , a brake caliper  23   r  and a brake disc  24   r.    
     In the vicinity of the front-wheel brake operating means  19   f , a mode change-over unit or means  26  is provided on a handle bar  25 . 
     As shown in  FIG. 3 , the mode change-over means  26  is disposed between a kill switch  28  on an upper side and a starter switch  29  on a lower side, on the vehicle body center side relative to a right grip  27 . The mode change-over means  26  is preferably a change-over switch which makes change-over (selection) between a first control mode and a second control mode when moved to the left or the right. The change-over switch may be a push-push switch which, when depressed repeatedly, effects selection of the first control mode and selection of the second control mode in an alternating manner. 
     The mode change-over switch  26  may be provided not only on the handle bar  25  but also in the periphery of meters or in the periphery of a combination switch. It is recommendable, however, to provide the mode change-over means  26  on the handle bar  25 , like in the present embodiment, since this configuration permits the driver to perform change-over operations while gripping the right grip  27 . 
     A preferred embodiment of the front-wheel hydraulic modulator  21   f  will be described based on  FIG. 4 . 
     As shown in  FIG. 4 , the front-wheel hydraulic modulator  21   f  can include a control motor  31 , a drive gear  33  is driven by a motor shaft  32  of the control motor  31 . A driven gear  33  greater than the drive gear  33  in diameter is driven by the drive gear  33 . A ball screw  35  is screw-connected to the driven gear  34  and is configured to be moved in an axial direction though not rotated. A modulator piston  36  is configured to be pushed by the ball screw  35 , and a return spring  37  biases the modulator piston  36 . A case  38  houses the drive gear  33 , the driven gear  34  and the modulator piston  36  collectively. 
     When the modulator piston  36  is advanced or moved forward with the control motor  31  as a drive source, a brake fluid is put under pressure or compressed, to generate a hydraulic pressure. The hydraulic pressure is sent through a port  39  to the front-wheel valve unit (reference symbol  22   f  in  FIG. 2 ). When the control motor  31  is rotated in a reverse direction so that the modulator piston  36  is retracted (moved backward), the brake fluid is unpressurized or decompressed. 
     The rear-wheel hydraulic modulator (reference symbol  21   r  in  FIG. 2 ) is the same as the front-wheel hydraulic modulator  21   f  in structure, and, therefore, description thereof is omitted. 
     The configuration of the front-wheel valve unit  22   f  and the rear-wheel valve unit  22   r  will now be described, based on  FIG. 5 . 
       FIG. 5  is a combined ABS control diagram illustrating an example of a brake control system  40  of the motorcycle. The front-wheel valve unit  22   f  as a major part of the brake control system  40  includes a normally closed type first solenoid valve  41   f , a normally open type second solenoid valve  42   f , a normally closed type third solenoid valve  43   f , a first pressure sensor  44   f , a second pressure sensor  45   f , and a third pressure sensor  46   f  as main components. 
     The rear-wheel valve unit  22   r  is the same as mentioned above; therefore, the components thereof are denoted by numerals accompanied by suffix r, and description thereof will be omitted. 
     Operation of a CBS (combined brake system) for interlocking the front-wheel and rear-wheel brake devices  20   f  and  20   r  will be described. 
     The CBS is a system for causing the front-wheel and rear-wheel brake devices  20   f ,  20   r  to exhibit braking actions when the front-wheel one of the front-wheel and rear-wheel brake operating units or means  19   f ,  19   r  is operated. 
     An example in which the front-wheel brake operating means  19   f  is operated will now be described. 
     In this case, the first solenoid valve  41   f  and the second solenoid valve  42   f  for the front wheel are opened, whereas the third solenoid valve  43   f  for the front wheel is closed. On the other hand, the second solenoid valve  42   r  for the rear is opened, whereas the third solenoid valve  43   r  for the rear is closed. 
     When the front-wheel brake operating means  19   f  is operated, a hydraulic pressure is generated, and the hydraulic pressure is detected by the second pressure sensor  45   f . Based on the detected pressure value, the electronic control unit  47  determines a target value (pressure value) for the front-wheel third pressure sensor  46   f  and a target value (pressure value) for the rear third pressure sensor  46   r . In addition, the electronic control unit  47  operates the front-wheel hydraulic modulator  21   f  and the rear-wheel hydraulic modulator  21   r  so that the front-wheel and rear-wheel hydraulic modulators  21   f ,  21   r  generate hydraulic pressures at the target values (pressure values), whereby the front wheel  11   f  and the rear wheel  11   r  are braked by the front-wheel and rear-wheel brake devices  20   f ,  20   r.    
     When the rear-wheel brake operating means  19   r  is operated, also, the electronic control unit  47  determines a target value (pressure value) for the front-wheel third pressure sensor  46   f  and a target value (pressure value) for the rear third pressure sensor  46   r . Besides, the electronic control unit  47  operates the front-wheel hydraulic modulator  21   f  and the rear-wheel hydraulic modulator  21   r  so that the front-wheel and rear-wheel hydraulic modulators  21   f ,  21   r  generate hydraulic pressures at the target values (pressure values), whereby the front wheel  11   f  and the rear wheel  11   r  are braked by the front-wheel and rear-wheel brake devices  20   f ,  20   r.    
     In addition, by switching over the mode change-over means  26  by hand, it is possible in embodiments of the invention to set a diversity of target values (control modes) and to create a variety of braking modes. 
     As the control mode, a plurality (in this example, two) of modes are provided. A first control mode and a second control mode are each configured (as a presumption) so that when the front-wheel brake operating means  19   f  is operated, a braking force for the front wheel is generated by the front-wheel brake device  20   f  according to an operation amount of the front-wheel brake operating means  19   f . A braking force for the rear wheel interlocked with the operation amount of the front-wheel brake operating means  19   f  is generated by the rear-wheel brake device  20   r  for which no operation is made. In the alternative, when the rear-wheel brake operating means  19   r  is operated, a braking force for the rear wheel is generated by the rear-wheel brake device  20   r  according to an operation amount of the rear-wheel brake operating means  19   r . A braking force for the front wheel interlocked with the operation amount of the rear-wheel brake operating means  19   r  is generated by the front-wheel brake device  20   f  for which no operation is made. 
     When the first control mode is selected by the mode change-over means  26 , Map  1  shown in  FIG. 6  can be selected in the electronic control unit  47 , whereas when the second control mode is selected by the mode change-over means  26 , Map  2  shown in  FIG. 7  is selected in the electronic control unit  47 . 
     As shown in  FIG. 6 , Map  1  includes Map  1   a  and Map  1   b.    
     In Map  1   a , the axis of abscissas (x-axis) represents the operation amount of the front-wheel brake operating means, and the axis of ordinates (y-axis) represents the braking force of each of the front-wheel and rear-wheel brake devices. In the figure, the substantially linear-functional curve (with an expression “BRAKING FORCE GENERATED ON FRONT WHEEL”) is a curve of a braking force provided for the front-wheel brake device, and a substantially trapezoidal curve (with an expression “BRAKING FORCE GENERATED ON REAR WHEEL”) is a curve of a braking force provided for the rear-wheel brake device. 
     In other words, when the front-wheel brake operating means is operated under the condition where the first control mode is selected by the mode change-over means  26 , Map  1   a  is selected. 
     The operation amount of the front-wheel brake operating means taken on the axis of abscissas can be determined from the value detected by the second pressure sensor, illustrated in this example as  45   f  or  45   r  in  FIG. 5 . Besides, the braking forces of the front-wheel and rear-wheel brake devices taken on the axis of ordinates are obtained by conversion from the target values of hydraulic pressure which are given to the third pressure sensor, shown as  46   f  or  46   r  in  FIG. 5  and the hydraulic modulator  21   f  or  21   r  in  FIG. 5  by the electronic control unit  47 . 
     Referring to the substantially trapezoidal curve in Map  1   a , in a first-mode first section where the operation amount of the front-wheel brake operating means ranges from zero to a first-mode first predetermined value, the braking force generated on the rear wheel gradually increases correspondingly to an increase in the operation amount. 
     In a first-mode second section where the operation amount of the front-wheel brake operating means ranges from the first-mode first predetermined value to a first-mode second predetermined value greater than the first-mode first predetermined value, the braking force generated on the rear wheel is maintained at a maximum value F 1  in the first-mode first section, irrespective of an increase in the operation amount. 
     In a first-mode third section where the operation amount of the front-wheel brake operating means is in excess of the first-mode second predetermined value, the braking force generated on the rear wheel gradually decreases, for example to zero in the case shown in the drawing, correspondingly to an increase in the operation amount. 
     In Map  1   b , the axis of abscissas represents the operation amount of the rear-wheel brake operating means, and the axis of ordinates represents the braking force of each of the front-wheel and rear-wheel brake devices. The substantially linear-functional curve (with an expression “BRAKING FORCE GENERATED ON REAR WHEEL”) is a curve of a braking force provided for the rear-wheel brake device, and a substantially bent-line-like curve (with an expression “BRAKING FORCE GENERATED ON FRONT WHEEL”) is a curve of a braking force provided for the front-wheel brake device. 
     In other words, when the rear-wheel brake operating means is operated under the condition where the first control mode is selected by the mode change-over means  26 , Map  1   b  is selected. 
     In addition, as shown in  FIG. 7 , Map  2  includes Map  2   a  and Map  2   b.    
     In Map  2   a , the axis of abscissas represents the operation amount of the front-wheel brake operating means, and the axis of ordinates represents the braking force of each of the front-wheel and rear-wheel brake devices. The substantially linear-functional curve (with an expression “BRAKING FORCE GENERATED ON FRONT WHEEL”) is a curve of a braking force provided for the front-wheel brake device, and the substantially trapezoidal curve (with an expression “BRAKING FORCE GENERATED ON REAR WHEEL”) is a curve of a braking force provided for the rear-wheel brake device. 
     In other words, when the front-wheel brake operating means is operated under the condition where the second control mode is selected by the mode change-over means  26 , Map  2   a  is selected. 
     Paying attention to the substantially trapezoidal curve in Map  2   a , in a second-mode first section where the operation amount of the front-wheel brake operating means ranges from zero to a second-mode first predetermined value, the braking force generated on the rear wheel gradually increases correspondingly to an increase in the operation amount. 
     In a second-mode second section where the operation amount of the front-wheel brake operating means ranges from the second-mode first predetermined value to a second-mode second predetermined value greater than the second-mode first predetermined value, the braking force generated on the rear wheel is maintained at a maximum value F 2  in the second-mode first section, irrespectively of an increase in the operation amount. 
     In a second-mode third section where the operation amount of the front-wheel brake operating means is in excess of the second-mode second predetermined value, the braking force generated on the rear wheel gradually decreases, for example to zero in the case shown in the drawing, correspondingly to an increase in the operation amount. 
     In Map  2   b , the axis of abscissas represents the operation amount of the rear-wheel brake operating means, and the axis of ordinates represents the braking force of each of the front-wheel and rear-wheel brake devices. The substantially linear-functional curve (with an expression “BRAKING FORCE GENERATED ON REAR WHEEL”) is a curve of a braking force provided for the rear-wheel brake device, and the substantially bent-line-like curve (with an expression “BRAKING FORCE GENERATED ON FRONT WHEEL”) is a curve of a braking force provided for the front-wheel brake device. 
     In other words, when the rear-wheel brake operating means is operated under the condition where the second control mode is selected by the mode change-over means  26 , Map  2   b  is selected. 
     Map  2   a  differs from Map  1   a  in the following points. 
     The braking force F 2  is smaller than the braking force F 1 . In other words, the braking force generated on the rear wheel in the second-mode first section is set to be smaller than the braking force generated on the rear wheel in the first-mode first section. 
     In addition, the second-mode first section is set longer than the first-mode first section, the second-mode second section is set longer than the first-mode second section, and the second-mode third section is set longer than the first-mode third section. 
     In the first section (a beginning section of braking), the braking force generated on the rear wheel by the front-wheel brake operating means is suppressed in the second control mode, as compared with that in the first control mode. The second control mode can be used, for example, as a mode effective in the case of a driver&#39;s wish to put priority on attitude control for turning performance over braking during cornering. 
     In the second section, the braking force generated on the rear wheel is kept constant. In addition, the braking force F 2  generated on the rear wheel in the second-mode second section shown in Map  2   a  is set to be smaller than the braking force F 1  generated on the rear wheel in the first-mode second section shown in Map  1   a.    
     As compared with the first control mode, the second control mode is a mode effective in the case where the attitude of the vehicle is controlled by the braking force generated on the rear wheel. 
     In the first-mode third section in Map  1   a , the braking force generated on the rear wheel is gradually decreased, for example, to zero. The value on the axis of abscissas (the operation amount of the front-wheel brake operating means) at the time when the braking force on the rear wheel reaches zero is denoted by M 1 . 
     Similarly, in the second-mode third section in Map  2   a , the braking force generated on the rear wheel is gradually decreased, for example, to zero. The value on the axis of abscissas (the operation amount of the front-wheel brake operating means) at the time when the braking force on the rear wheel reaches zero is denoted by M 2 . 
     For reference, M 1  in Map  1   a  is transcribed into Map  2   a.    
     In the present invention, a setting of M 1 &lt;M 2  is adopted. Specifically, a case is illustrated in the drawings wherein like the first control mode (Map  1   a ) the second control mode (Map  2   a ) is so configured that in the second-mode third section where the operation amount of the front-wheel brake operating means is in excess of the second-mode second predetermined value, the braking force generated on the rear wheel decreases, for example to zero, correspondingly to an increase in the operation amount. Besides, in this case, the operation amount M 2  when the braking force reaches zero in the second control mode is set to be greater than the corresponding operation amount M 1  in the first control mode. 
     For instance in the case where deceleration is to be accomplished in as short a time as possible, it is desirable to effectively generate both a braking force on the front wheel and a braking force on the rear wheel. 
     As compared with the first control mode, the second control mode makes it possible to easily generate both the braking forces in a maximal manner at the time of, for example, full-braking or the like. Besides, in the second control mode, the driver is not required to operate both the front-wheel brake operating means and the rear-wheel brake operating means, and an operation of only the front-wheel brake operating means suffices. In other words, at the time of full-braking, rather the second control mode than the first control mode ensures that an ideal front-rear distribution of braking can be automatically carried out, and that the driver can focus on a front-wheel braking operation. 
     The front-wheel brake operating means is preferably a front brake provided in the motorcycle, whereas the rear-wheel brake operating means is preferably a brake pedal. 
     In Map  1   a  shown in  FIG. 6 , when the front-wheel brake operating means is operated, particularly, the braking force generated on the front wheel in the first-mode third section is increased. The same applies in Map  2   a  in  FIG. 7 . 
     A control suited to the characteristics peculiar to a motorcycle is performed in which the vertical load (grip force) on the front wheel increases whereas the vertical load on the rear wheel decreases, as the braking force becomes stronger. 
     Now, attention is paid to Map  1   b  in  FIG. 6  and Map  2   b  in  FIG. 7 . 
     Map  1   b  in  FIG. 6  relates to the first control mode. In this mode, as shown in Map  1   b , when the rear-wheel brake operating means is operated, a control is performed such that a braking force is generated by the rear brake device according to the operation amount of the rear-wheel brake operating means and that a braking force interlocked with the operation amount of the rear-wheel brake operating means is generated by the front-wheel brake device for which no operation is made. In addition, the braking force generated on the rear wheel is set greater than the braking force generated on the front wheel. 
     Map  2   b  in  FIG. 7  relates to the second control mode. In this mode, as shown in Map  2   b , when the rear-wheel brake operating means is operated, a control is performed such that a braking force is generated by the rear brake device according to the operation amount of the rear-wheel brake operating means and that a braking force interlocked with the operation amount of the rear-wheel brake operating means is generated by the front-wheel brake device for which no operation is made. Besides, the braking force generated on the rear wheel is set greater than the braking force generated on the front wheel. 
     The braking force generated on the front wheel is so set as to be generated starting from a point remote from the origin by M 4 . 
     For reference, M 3  in Map  1   b  is transcribed into Map  2   b.    
     In the present invention, a setting of M 3 &lt;M 4  is adopted. 
     Specifically, the operation amounts M 3 , M 4  of the rear-wheel brake operating means until braking of the front wheel is started are so set that the operation amount M 4  in the second control mode is greater than the operation amount M 3  in the first control mode. 
     In the first control mode shown in Map  1   b , the braking force generated on the front wheel is generated earlier than in the second control mode; therefore, the interlocked brake operates even from an early stage of the braking operation, whereby assured deceleration can be accomplished. 
     Where the front-wheel brake operating means is a brake lever whereas the rear-wheel brake operating means is a brake pedal, it is said that the brake pedal operated by foot needs a more delicate operation as compared with the brake lever operated by hand. According to Map  1   b , the deceleration by the foot operation which is said to need a delicate operation can be carried out assuredly. 
     On the contrary, in the second control mode, as shown in Map  2   b , the braking force to be generated on the front wheel is not yet generated in an early stage of the braking operation; in this stage, therefore, a control in which attitude control is given priority over braking is carried out. 
     As above described, according to embodiments of the present invention, by arbitrary change-over between the first control mode (Map  1 ) and the second control mode (Map  2 ) it is possible to perform braking control for a motorcycle according to variations in running environments and operating parameters. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       10  . . . Motorcycle,  19   f  . . . Front-wheel brake operating means,  19   r  . . . Rear-wheel brake operating means,  20   f  . . . Front-wheel brake device,  20   r  . . . Rear brake device,  21   f  . . . Front-wheel hydraulic modulator,  21   r  . . . Rear-wheel hydraulic modulator,  25  . . . Handle bar,  26  . . . Mode change-over means,  40  . . . Brake control system,  47  . . . Electronic control unit.