Abstract:
An electronic controlled brake device comprises a ball screw for converting a rotational torque of an electric motor to an axial impulsive force of a spindle, a brake pad pressed against a disc rotor by the axial impulsive force of the spindle for generating a braking force, electronic control unit for controlling a drive of the electric motor and braking operation judging device for judging a braking operational condition. The spindle is moved from an initial position in a predetermined distance by the electric motor so as to back away from the disc rotor when the non braking operational condition is judged by braking operation judging device and thereafter is returned to the initial position by the electric motor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based on and claims priority under 35 U.S.C. §  119  with respect to a Japanese Patent Application 2001-173052, filed on Jun. 7, 2001, the entire content of which is incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    This invention relates to an electronic controlled brake device. More particularly, the present Invention pertains to an electronic controlled brake device in which a brake pad is pressed against the disc rotor by an electric motor for obtaining a braking force.  
         BACKGROUND OF THE INVENTION  
         [0003]    A conventional electronic controlled brake device of this kind is disclosed In, for example, Japanese Patent Laid-Open Publication No. 63-266228. In this device, a rotational torque of an electric motor is converted to an impulsive force of a spindle by a planetary gear unit and a ball screw. Thereby, a brake pad Is pressed against a disc rotor by the spindle and a braking force Is obtained.  
           [0004]    In this prior device, an axial moving distance of the spindle corresponding to a piston of a hydraulic brake device for pressing the brake pad against the disc rotor is around 1 mm and is small. Further, as shown in FIG. 3, an axial moving distance of a male screw  147  of the ball screw formed on the spindle Is also around 1 mm and is also small. A lead L of the ball screw is around 2 to 4 mm. Accordingly, la female screw  145  of the ball screw does not go Into a 360-degree roll until the brake pad Is pressed against the disc rotor for obtaining the braking force after the spindle is moved from its initial position.  
           [0005]    This means that a ball  148  which rolls in a screw groove formed between a screw groove  147   a  of the male screw  147  and a screw groove  145   a  of the female screw  145  while rotating on Its axis being at right angle to the screw groove exits. A portion of such ball  148  contacting with the screw groove while rolling In the screw groove wears partially and the durability of the ball screw is decreased.  
           [0006]    In the ball screw, circulators (ball circulating means)  149 ,  150  for circulating balls  148  are provided. If the ball proceeds in the circulators  149 ,  150 , the direction of the rotational axis thereof Is changed and the portion contacting with the screw groove is changed. In such ball, a partial wear hard to generate. However, in the circumstance which the female screw  145  does not go into a 360-degree roll, most of the ball can not proceed in the circulators  149 ,  150  and therefore the portion of such ball  148  contacting with the screw groove while rolling In the screw groove wears partially. As a result, the durability of the ball screw is decreased.  
           [0007]    If the moving distance of the ball screw is increase by a lever mechanism and as many balls as possible are proceeded in the circulators, the balls is prevented from wearing partially and the durability of the ball screw Is prevented from decreasing. According to these measures, however, a size of the brake device is increased.  
           [0008]    A need exists for an electronic brake device which can improve the durability of the ball screw without increasing in size.  
         SUMMARY OF THE INVENTION  
         [0009]    According to an aspect of the present Invention, an electronic controlled brake device comprises a ball screw- for converting a rotational torque of an electric motor to an axial impulsive force of a spindle, a brake pad pressed against a disc rotor by.the axial impulsive force of the spindle for generating a braking force, electronic control means for controlling a drive of the electric motor and braking operation judging means for judging a braking operational condition, wherein the spindle Is moved from an initial position in a predetermined distance by the electric motor so as to back away from the disc rotor when the non braking operational condition is judged by braking operation judging means and thereafter is returned to the initial position by the electric motor. According to the other aspect of the present invention, an electronic controlled brake device comprises a ball screw for converting a rotational torque of an electric motor to an axial Impulsive force of a spindle, a brake pad pressed against a disc rotor by the axial, impulsive force of the spindle for generating a braking force, electronic control means for controlling a drive of the electric motor and braking operation judging means for judging a braking operational condition, wherein the spindle is moved from an initial position in a predetermined time by the electric motor so as to back away from the disc rotor when the non braking operational condition Is judged by braking operation judging means and thereafter is returned to the initial position by the electric motor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0010]    A more complete appreciation of the invention and other advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered In connection with the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is a schematic illustration of an electronic controlled brake device of an embodiment in accordance with the present Invention;  
         [0012]    [0012]FIG. 2 is a cross sectional view of an electronic controlled brake of an embodiment In accordance with the present invention; and  
         [0013]    [0013]FIG. 3 is a cross sectional view of a conventional ball screw. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Having generally described the present invention, a further understanding of the invention can be obtained now according to an embodiment of the present invention with reference to FIGS.  1  to  2  in accompanying drawings.  
         [0015]    [0015]FIG. 1 is a schematic illustration of an electronic controlled brake device of the embodiment. In FIG. 1, an electric control unit  81  is provided with a micro computer  82  which includes a CPU  85 , a ROM  86 , RAM  87 , a timer (TMR)  88 , an input port  83  and an output port  84 . The CPU  85 , the ROM  86 , the RAM  87 , the timer  88 , the input port  83  and the output port  84  are mutually connected via bus.  
         [0016]    The input port  83  is connected to a pedal depressing force sensor  71  for detecting a pedal depressing force applied to a brake pedal BP, a pedal stroke sensor  72  for detecting a stroke of the brake pedal BP, a stop lump switch  73  for lighting on a stop lump when the brake pedal is depressed In a predetermined stroke, a shift lever position sensor  74  for detecting a position of a shift lever AL of an automatic transmission, a parking brake sensor  75  for detecting a parking brake operational condition, a pressure sensor  76  for detecting a pressing force of a male screw (spindle)  47  against a disc rotor  5 , an ignition switch  77 , a throttle sensor  78  for detecting a throttle opening amount and wheel speed sensors  79  provided on each wheels FL, FR, RL, RR via an amplification circuit  89 . On the other hand, the output port  84  Is connected to electric motors  31  provided on each electronic controlled brake  1 ,  2 ,  3 ,  4  via a driving circuit  90 .  
         [0017]    The ROM  86  memorizes control programs for a normal brake control, an anti lock brake control (ABS control) and so on. The CPU  85  performs the control programs when the ignition switch  77  is turned on. The RAM  87  memorizes temporary parameter data which are necessary for performing the control programs. The CPU  85  corresponds to a judge circuit for judging whether the brake operation is carried out on the basis of the signals from the above mentioned sensors and switches.  
         [0018]    As shown In FIG. 2, the electronic controlled brake  1  includes a disc rotor  5  which is rotated with the wheel (not shown), an inner pad  7  and an outer pad  8  which are disposed at inside and outside of the disc rotor  5 , a mounting member  6  which Is fixed to the non rotational portion (not shown) of a vehicle and which receives a brake torque applied to the pads  7 ,  8  and a caliper member  9  which is supported on the mounting member  6  so as to be able to move in the axial direction of the disc rotor  5 . The inner pad  7  and the outer pad  8  includes pad linings  7   a,    8   a  and backing plates  7   b,    8   b  on which the pad linings  7   a,    8   a  are integrally connected, respectively.  
         [0019]    The caliper member  9  includes a caliper outer side portion  10 , a pad pressing mechanism  11  and a cover  13 . The pad preasing mechanism  11  is fixed to the caliper outer side portion  10  by bolts (not shown) and the cover  13  is fixed to the pad pressing mechanism  11  by bolts (not shown).  
         [0020]    The pad pressing mechanism  11 l includes a housing  12 , an electric motor  21 , a planetary gear mechanism  40  which amplifiers the rotational torque of the electric motor  31  and a ball screw  45 . The ball screw  45  includes a female screw  46  having a flange portion  46   b  which functions as a carrier of the planetary gear mechanism  40 , the male screw  47  which the pressure sensor  76  is fixed to an one end thereof and balls  48 , The numeral  61  is a boot which is interposed between the pressure sensor  76  and the caliper  9 .  
         [0021]    The electric motor  31  is a direct current brush less motor and includes a stator core  32   a,  stator coils  32   b,  a rotational shaft  33 , magnets  34  fixed on the rotational shaft  33  and an angular sensor which is constituted by a detecting magnet  35  and a hole lC  37 . The stator core  32   a  and the stator coils  32   b  are fixed on the inner surface of the housing  12 . The rotational shaft  33  is rotatably supported on a cylindrical portion  46   c  of the female screw  46  via a bearing bush  53 . The female screw  46  is rotatably supported in the housing  12  by bearings  51 ,  52 . A gear is integrally formed as a sun gear  33   a  of the planetary gear unit  40  on the outer surface of the left end portion of the rotational shaft  33 . When a plurality phases of stator coils  32   b  are selectively energized on the basis of the signal from the angular sensor, the electric motor  31  is rotated.  
         [0022]    The planetary gear unit  40  includes the sun gear  33   a,  a ring gear  44  which Is fixed to the inner circumferential surface of the caliper outer side portion  10  and pinions  41  which are engaged with the ring gear  44  and the sun gear  33   a  and which are rotatably supported on a flange portion  46   b  of the female screw  46  via pins  42  and bushes  43 . The female screw  46  functions as an output shaft of the planetary gear unit  40 . the balls  48  are disposed between a screw groove  46   a  of the female screw  46  and a screw groove  47   a  of the male screw  47  and the ball screw  45  is formed. When the female screw  46  is rotated, the balls  48  are circulated by the circulator shown in FIG. 3 and the rotational movement of the female screw  46  is converted to the linear motion of the male screw  46 . As a result, the ball screw  45  converts the rotational torque of the electric motor  31  amplified by the planetary gear unit  40  to the axial impulsive force of the male screw  47 .  
         [0023]    When the inner pad  7  Is pressed toward the disc rotor  5  by the male screw  47  due to the impulsive force of the male screw  47  (left ward) via the pressure sensor  76 , simultaneously the caliper member  9  is pressed rightward by the reaction force. Thereby, the outer pad  8  is pressed against the disc rotor  5  by a nail portion  10   a  of the caliper outer side portion  10 . Namely, the caliper member  9  and the male screw  47  are pressed in the counter direction each other and the inner pad  7  and the outer pad  8  are pressed against the disc rotor  5  by the male screw  47  and the nail portion  10   a,  respectively.  
         [0024]    In the above mentioned electronic controlled brake device, at the initial condition shown In FIG. 2 in which the brake operation is not carried out, a clearance B is formed between the right end surface of the male screw  47  and a switch  80  of the cover  13 . The distance of the clearance B is a length which has several times the lead of the ball screw  45 . The switch  80  Is provided for preventing the male screw  47  from excessively moving rightward.  
         [0025]    When the pedal depressing force detected by the pedal depressing force sensor  71  is less than a predetermined value, the CPU  85  judges that the brake operation is not carried out and an first idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times. In the first idle operation, the male screw  47  is moved from the initial position rightward in a predetermined distance (B−α(&lt;B)) and thereafter is returned to the initial position.  
         [0026]    Alternatively, when the pedal depressing force detected by the pedal depressing force sensor  71  is less than a predetermined value, the CPU  85  judges that the brake operation is not carried out and an second idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times. In the second idle operation, the male screw  47  is moved from the initial position rightward in a predetermined time and thereafter is returned to the initial position. The predetermined time is set to a time in which the right end surface of the male screw  47  does not contact with the switch  80  of the cover  13 .  
         [0027]    Further, when the pedal stroke detected by the pedal stroke sensor  72  is less than a predetermined value, the CPU  85  judges that the brake operation Is not carried out and the first idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0028]    Alternatively, when the pedal stroke detected by the pedal stroke sensor  72  is less than a predetermined value, the CPU  85  judges that the brake operation is not carried out and the second idle operation of the electric motor  31  Is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0029]    Further, when the signal from the stop lump switch  73  is OFF, the CPU  85  judges that the brake operation Is not carried out and the first idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0030]    Alternatively, when the signal from the stop lump switch  73  is OFF, the CPU  85  judges that the brake operation is not carried out and the second idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment Is done one or more times  
         [0031]    Further, when it is detected by the shift lever position sensor  74  that the shift lever is in a P range position, the CPU  85  judges that the brake operation is not carried out and the first idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0032]    Alternatively, When It Is detected by the shift lever position sensor  74  that the shift lever is in a P range position, the CPU  85  judges that the brake operation is not carried out and the second Idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is, done one or more times.  
         [0033]    Further, when, it is detected by the parking brake sensor  76  that the parking brake is operated, the CPU  85  judges that the brake operation is not carried out and the first Idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0034]    Alternatively, when it is detected by the parking brake sensor  75  that the parking brake is operated, the CPU  85  judges that the brake operation is not carried out and the second idle operation of the electric motor  31  Is carried out one or more times by the ECU  21  after the above judgment is done one or more times.  
         [0035]    Further, when the ECU  81  carries out an initial check lust after the ignition switch  77  is turned on, the CPU  85  judges that the brake operation Is not carried out and the first idle operation of the electric motor  31  is carried out one or more times by the ECU  51  after the above judgment is done one or more times.  
         [0036]    Alternatively, when the ECU  81  carries out an initial check just after the ignition switch  77  is turned an, the CPU  85  judges that the brake operation is not carried out and the second idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0037]    Further, when the throttle opening amount detected by the throttle sensor  78  is more than a predetermined value, the CPU  85  judges that the brake operation is not carried out and the first idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0038]    Alternatively, when the throttle, opening amount detected by the throttle sensor  78  Is more than a predetermined value, the CPU  85  judges that the brake operation is not carried out and the second idle operation of the electric motor  31  is carried out one or more times by the ECU  81  after the above judgment is done one or more times.  
         [0039]    According to this embodiment, when the male screw  47  carries out the above idle operation, the balls which can not proceed in the circulator at the brake operation are able to proceed In the circulator from the screw groove. Further, when the balls proceed in the circulator, the direction of the rotational axis thereof are changed and the portion contacting with the screw groove are changed. As a result, it is prevented that the balls wear partially and the durability of the ball screw  45  is improved.  
         [0040]    According to the present invention, it is able to obtain an electronic controlled brake device which can improve the durability of the ball screw without increasing in size.  
         [0041]    The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein is to be regarded as Illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.