Patent Publication Number: US-2016243943-A1

Title: Antilock brake control device

Description:
CROSS REFERENCE TO THE RELATED APPLICATION 
     This application is a continuation application, under 35 U.S.C. §111(a), of international application No. PCT/JP2014/079407, filed Nov. 6, 2014, which is based on and claims Convention priority to Japanese patent application No. 2013-237726, filed Nov. 18, 2013, the entire disclosure of which is herein incorporated by reference as a part of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antilock brake control device that prevents each wheel from locking during braking of a vehicle, and particularly relates to an antilock brake control device for an in-wheel motor driving type vehicle including a friction brake. 
     2. Description of Related Art 
     Hitherto, as an antilock brake control device that prevents each wheel from locking during braking of a vehicle, a control device has been proposed which includes fluid pressure adjustment mechanism in a hydraulic friction brake and adjusts a fluid pressure such that a slip ratio becomes a target slip ratio (e.g., Patent Document 1). 
     In addition, in recent years, as one form of electric vehicles, a so-called in-wheel motor type vehicle has been developed in which a motor is incorporated into a wheel and the wheel is driven directly by the motor. The in-wheel motor type vehicle has a characteristic of being able to individually control a driving torque or a braking torque which is provided to each wheel. A control device has been proposed which performs antilock brake control by causing a mechanical brake and an electrical brake for an in-wheel motor to cooperate with each other (e.g., Patent Document 2). 
     RELATED DOCUMENT  
     Patent Document 
     [Patent Document 1] JP Laid-open Patent Publication No. H09-328063 
     [Patent Document 2] JP Patent No. 3972535 
     The antilock brake control device including the fluid pressure adjustment mechanism as disclosed in Patent Document 1 needs an additional actuator, such as an ON/OFF operation solenoid valve or a linear solenoid, which is used for antilock brake control and serves to adjust a brake fluid pressure of the friction brake, resulting in higher cost of the antilock brake control device. 
     In the control device that performs antilock brake control by causing the mechanical brake and the electrical brake for the in-wheel motor to cooperate with each other as disclosed in Patent Document 2, an additional actuator is needed to control the mechanical brake, as antilock brake control, independently of a braking instruction (an brake pedal depressing force) from a driver, resulting in higher cost of the control device as with Patent Document 1. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an antilock brake control device that does not need an additional actuator for a friction brake which brakes each wheel driven by a motor in a vehicle and that is able to suppress locking of each wheel or reduce locking tendency of each wheel at low cost. 
     Hereinafter, in order to facilitate understanding of the present invention, the present invention will be described with reference to the reference numerals in embodiments for the sake of convenience. 
     An antilock brake control device  1  according to the present invention is an antilock brake control device in a vehicle including: a motor  3  configured to drive a wheel  2 ; a wheel bearing  5  configured to transmit a rotation of the motor  3  to the wheel  2  and to rotationally support the wheel  2 ; and a friction brake  7  configured to urge a press member  9  against a brake rotor  8  provided in each wheel  2 , thereby to generate a frictional force to brake the wheel  2 , the antilock brake control device including: 
         a slip ratio monitor  21  configured to monitor a slip ratio of the wheel  2 ; and   a driving torque addition section  22  configured to add a torque in a driving direction to a torque command value for the motor  3  when the slip ratio monitored by the slip ratio monitor  21  exceeds a preset target slip ratio, wherein   an operation of the friction brake  7  is suspended when the torque in the driving direction is added to the torque command value for the motor  3 .       

     As the “target slip ratio”, for example, a slip ratio at which a frictional coefficient with a road surface is maximum is used. The “motor  3  configured to drive a wheel  2 ” may be a motor connected to each wheel in a one-to-one relation, and a so-called one motor type with a plurality of wheels driven by one motor is not included. 
     According to this configuration, the friction brake  7  or urges presses the press member  9  against the brake rotor  8  provided in each wheel  2  thereby to generate a frictional force to brake the wheel  2 . The slip ratio of the wheel  2  changes moment by moment, and, for example, the slip ratio monitor  21  constantly monitors the calculated slip ratio of the wheel  2 . When the monitored slip ratio exceeds the target slip ratio, the driving torque addition section  22  adds a positive torque, that is, a torque in the driving direction, to the torque command value for the motor  3 , thereby suppressing locking of the wheel  2 . When adding the torque in the driving direction, for example, for antilock brake control, the antilock brake control device  1  adjusts the fluid pressure of the brake fluid by fluid pressure adjustment mechanism provided at a master cylinder, or the like, such that the friction brake  7  is not operated. Thus, in the vehicle in which each wheel  2  is driven by the motor  3 , an additional actuator or the like (such as the fluid pressure adjustment mechanism) is not needed for the friction brake  7  configured to brake each wheel  2 , and it is possible to suppress locking of the wheel  2  or reduce locking tendency of the wheel  2  at low cost, for example, by merely rewriting a control program or the like.  
     The driving torque addition section  22  may determine the torque to be added, through PID control based on a deviation between the monitored slip ratio and the target slip ratio. In this case, for example, the antilock brake control device  1  adds a PID calculation value to a torque command value from a primary control unit  11 , to calculate a motor torque. When the torque command value from the primary control unit  11  is negative, that is, when regenerative braking is performed, the regenerative braking is loosened. When the torque command value from the primary control unit  11  is zero, a driving torque is generated. Accordingly, locking of each wheel  2  can be suppressed or locking tendency of each wheel  2  can be reduced. The friction brake  7  is controlled in accordance with a depressing amount of a brake pedal  14 , or the like, independently of the antilock brake control device  1 . 
     An acceleration sensor  19  configured to detect an acceleration in a front-rear direction of the vehicle may be provided, and the driving torque addition section  22  may use the acceleration detected by the acceleration sensor  19  instead of a differential value of a vehicle speed, in the case that calculating a differential value to be used in the PID control based on the deviation is needed. Since the differential value of the deviation is calculated or obtained by using the acceleration detected by the acceleration sensor  19  as described above, when a noise of a vehicle speed signal is great, the influence of the noise can be reduced. 
     A road surface frictional coefficient estimation section  20  configured to estimate a road surface frictional coefficient may be provided, and when the road surface frictional coefficient estimated by the road surface frictional coefficient estimation section  20  is lower than a preset road surface frictional coefficient, the driving torque addition section  22  may make a proportional gain and an integral gain lower than respective predetermined gains. In addition, in the case where a road surface frictional coefficient estimation section  20  is provided, when the road surface frictional coefficient estimated by the road surface frictional coefficient estimation section  20  is higher than a preset road  surface frictional coefficient, the driving torque addition section  22  may make a proportional gain and an integral gain higher than the respective predetermined gains. The “preset road surface frictional coefficient” is determined by a test, simulation, or the like. 
     On a road surface having a high frictional coefficient, responsiveness can be enhanced by increasing the proportional gain and the integral gain, and on a road surface having a low frictional coefficient (a low μ road), stability of the control can be ensured by making the proportional gain and the integral gain lower than the respective predetermined gains. A braking/driving force generated by the torque of the in-wheel motor has, for example, better controllability and quicker responsiveness than a braking force generated by fluid pressure adjustment mechanism of a hydraulic friction brake. Thus, a control gain can be increased, so that the accuracy of control improves. On a low μ road, since instability may be caused when the gains are high, stability of the control can be ensured by decreasing the gains. 
     The slip ratio monitor  21  may monitor a slip ratio λ of the wheel  2  that is obtained on the basis of a formula, λ=(V−rω)/V, from an angular speed w of the wheel  2 , a vehicle speed V, and a radius r of the wheel  2 , and may obtain the angular speed ω of the wheel  2  by using a low-pass filter  25  that is different from a low-pass filter for control of the motor  3  and that has a cut-off frequency higher than a predetermined frequency. The “predetermined frequency” is set by a test, simulation, or the like. In this case, in measurement and calculation of the angular speed ω of the wheel  2 , by using the low-pass filter  25  that is different from the low-pass filter for control of the motor  3  and that has a high cut-off frequency, a response delay can be made smaller than in the case where the wheel speed ω is obtained without using the low-pass filter  25 . During antilock brake control, a response delay can be reduced to improve the accuracy of slip ratio control.  
     The torque in the driving direction may be added to the torque command value for the motor  3  by the driving torque addition section  22  in a state where the press member  9  is urged or pressed against the brake rotor  8  thereby to cause the friction brake  7  to perform a braking operation by an operation performed by a driver. Accordingly, in the operation state of the driver, locking of each wheel can be suppressed or locking tendency of each wheel can be reduced. 
     Any combination of at least two constructions, disclosed in the appended claims and/or the specification and/or the accompanying drawings should be construed as included within the scope of the present invention. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and: 
         FIG. 1  is a diagram schematically showing a system configuration of an antilock brake control device according to a first embodiment of the present invention; 
         FIG. 2  is a diagram showing, in combination, a front view of an in-wheel motor drive device and a block diagram of a control system in a vehicle equipped with the antilock brake control device; 
         FIG. 3  is a block diagram of a main part of a control system of the antilock brake control device;  
         FIG. 4  is a block diagram of a main part of a control system of an antilock brake control device according to another embodiment of the present invention; and 
         FIG. 5  is a diagram schematically showing a system configuration of an antilock brake control device according to still another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 to 3 .  FIG. 1  is a diagram schematically showing a system configuration of an antilock brake control device according to the first embodiment.  FIG. 1  shows an example in which the antilock brake control device  1  is mounted on a four-wheel drive vehicle. A vehicle that is the four-wheel drive vehicle includes left and right wheels  2 ,  2  at the front and rear sides of a vehicle body as drive wheels respectively, and the respective wheels  2 ,  2  are driven by corresponding independent traction motors  3 ,  3 . 
     As shown in  FIG. 2 , a rotation of each motor  3  is transmitted via a reducer  4  and a wheel bearing  5  to the corresponding wheel  2 . The motor  3 , the reducer  4 , and the wheel bearing  5  are integrally assembled with each other to form an in-wheel motor drive device  6 . The wheels  2  that are the front wheels are steered wheels. In each wheel  2 , an electrical or mechanical friction brake  7  is provided. The friction brake  7  presses a brake pad  9 , which is a press member, against a brake rotor  8  provided in the wheel  2 , respectively, thereby to generate a frictional force to brake the wheel  2 . The friction brake  7  is controlled in accordance with a depressing amount of a brake pedal  14 , or the like, independently of the antilock brake control device  1 . 
     A control system will be described. As shown in  FIG. 1 , a primary ECU  11 , the antilock brake control device  1 , and inverter devices  12  are mounted on a vehicle body  10 . The primary ECU  11  includes a computer, programs that are executed by the computer, and various electronic circuits. A light electrical  current system of the antilock brake control device  1  and inverter devices  12  also includes a computer, programs that are executed by the computer, and various electronic circuits. 
       FIG. 2  is a diagram showing, in combination, a front view of the in-wheel motor drive device  6  and a block diagram of the control system in the vehicle equipped with the antilock brake control device  1 . The primary ECU  11  is an electronic control unit that performs an integrated control and cooperative control of an entirety of the vehicle. The primary ECU  11  includes a torque allocation block  11   a , and the torque allocation block  11   a  generates an accelerating/decelerating command as a driving or braking torque command value, which is to be sent to each motor  3 , on the basis of an amount of stroke of an accelerator pedal  13 , a depressing force of the brake pedal  14 , and the like, and outputs the accelerating/decelerating command to a controller  15  of the antilock brake control device  1 . The braking torque has a negative value. 
     Each inverter device  12  includes: a power circuit section  16  that is a power conversion circuit provided for each motor  3 ; and a motor control section  17  that controls the power circuit section  16 . Then inverter device  12  includes: two power circuit sections  16  and two motor control sections  17 . The power circuit section  16  includes: an inverter  16   a  that converts DC power from a battery  26  into three-phase AC power to be used for driving the motor  3 ; and a PWM driver  16   b  that controls the inverter  16   a.    
     Each motor  3  is composed of a three-phase synchronous motor such as an interior permanent magnet (IPM) synchronous motor. The inverter  16   a  includes a plurality of semiconductor switching elements, and the PWM driver  16   b  performs a pulse width modulation of an inputted current command and sends ON/OFF commands to each of the semiconductor switching elements. 
     The antilock brake control devices  1  includes the controller  15 , a vehicle speed detector  18 , and an acceleration sensor  19 .  FIG. 3  is a block diagram of a main part of a control system of the antilock brake control device  1 .  The controller  15  includes a slip ratio monitor  21 , a driving torque addition section  22 , a road surface frictional coefficient estimation section  20 , and a motor output limiter  23 . The slip ratio monitor  21  monitors a slip ratio of the wheel, and calculates a slip ratio λ of the wheel on the basis of the following formula (1) from an angular speed (wheel speed) ω of the wheel, a vehicle speed V, and a radius r of the wheel. 
       λ=( V−r ω)/ V   (1)
 
     In each motor  3 , a wheel speed sensor  24  that detects a motor rotation speed is incorporated. The angular speed ω of the wheel is obtained through calculation from the motor rotation speed detected constantly by the wheel speed sensor  24 . The vehicle speed detector  18  detects the vehicle speed V. The slip ratio λ of the wheel is calculated from the wheel speed ω, the vehicle speed V, and the radius r. 
     When the slip ratio λ monitored by the slip ratio monitor  21  exceeds a preset target slip ratio λ, the driving torque addition section  22  adds a torque in a driving direction to a torque command value for the motor  3  (shown as “IWM TORQUE COMMAND VALUE” in  FIG. 3 ). Specifically, in a state where the brake pads are pressed against the brake rotors, respectively, thereby to cause the friction brake to perform a braking operation by an operation of the brake pedal by the driver, the torque in the driving direction is added to the torque command value for the motor  3  by the driving torque addition section  22 . At this time, for example, for antilock brake control, the antilock brake control device  1  adjusts the fluid pressure of a brake fluid by fluid pressure adjustment mechanism called an ABS actuator provided at a master cylinder, or the like, such that the friction brake  7  is not operated. Thus, the vehicle according to the present embodiment does not include, for example, the fluid pressure adjustment mechanism or the like. The addition of the torque in the driving direction may be performed periodically, for example, at a period of several milliseconds. The driving torque addition section  22  includes a controller (PID)  22   a , and the controller  22   a   performs a proportional-integral-derivative (PID) calculation based on a deviation Δλ between the target slip ratio λ t  and the slip ratio λ from the slip ratio monitor  21  according to the following formula, thereby to obtain a PID calculation value K PID . 
         K   PID   =K   P   Δλ+K   i   ΣΔλ+K   D (Δλ( n− 1)−Δλ( n ))  [Formula 1]
 
     Here, K P , K I , and K D  are gain constants of proportional calculation, integral calculation, and differential calculation, respectively. This PID calculation value is zero or a positive value (driving torque). The controller  15  adds the PID calculation value K PID  to an IWM torque command value from the primary ECU  11 , to calculate a motor torque (shown as “IWM TORQUE” in  FIG. 3 ). However, when the calculated IWM torque is greater than a torque determined with respect to the wheel speed ω, the motor output limiter  23  limits motor output. 
     By the addition of the PID calculation value K PID  in accordance with the result of the monitoring of the slip ratio λ, when the IWM torque command value from the primary ECU  11  is negative, that is, when a regenerative braking is performed, the regenerative braking is loosened. When the IWM torque command value from the primary ECU  11  is zero or positive, a driving torque is generated. Accordingly, during braking by a brake pedal operation, locking of each wheel can be suppressed or locking tendency of each wheel can be reduced. 
     In the PID calculation based on the deviation Δλ between the slip ratio and the target slip ratio, in the case that calculating a differential value of the deviation Δλ is needed as described below, the controller  22   a  uses an acceleration detected by the acceleration sensor  19 , not a differential value of the vehicle speed. The differential value of the deviation is represented by the following formula 
     
       
         
           
             
               
                 
                   
                     
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      For the term V(n−1)−V(n) corresponding to differentiation of the vehicle speed in the above formula, a value of the acceleration sensor  19  may be used instead of this difference V(n−1)−V(n) in vehicle speed value. Accordingly, when a noise of a vehicle speed signal is great, an influence of the noise can be reduced. In addition, when a road surface frictional coefficient estimated by the road surface frictional coefficient estimation section  20  is lower than a preset road surface frictional coefficient (this means low μ), the controller  22   a  makes the proportional gain K P  and the integral gain K I  lower than respective predetermined gains. Accordingly, a stability of the control can be ensured. On a low μ road surface, since instability may be caused when the gains are high, the stability of the control can be ensured by decreasing the proportional gain K P  and the integral gain K I  as described above. 
     A braking/driving force generated by the torque of the in-wheel motor drive device  6  has, for example, a better controllability and quicker responsiveness than a braking force generated by fluid pressure adjustment mechanism of a hydraulic friction brake. Thus, on a road surface for which the road surface frictional coefficient estimated by the road surface frictional coefficient estimation section  20  is greater than the preset road surface frictional coefficient, the controller  22   a  is able to enhance responsiveness by making the proportional gain K P  and the integral gain K I  higher than the respective predetermined gains. 
     According to the antilock brake control device  1  described above, each friction brake  7  presses the brake pad  9  against the brake rotor  8  provided in each wheel  2  thereby to generate a frictional force to brake the wheel  2 . The slip ratio of the wheel  2  changes moment by moment, and the slip ratio monitor  21  constantly calculates and monitors the slip ratio of the wheel  2 . When the monitored slip ratio exceeds the target slip ratio, the driving torque addition  section  22  adds a positive torque, that is, the torque in the driving direction, to the torque command value for the motor  3 , thereby suppressing locking of the wheel  2 . When adding the torque in the driving direction, for example, for antilock brake control, the antilock brake control device  1  adjusts the fluid pressure of the brake fluid by the fluid pressure adjustment mechanism provided at the master cylinder, or the like, such that the friction brake  7  is not operated. Thus, an additional actuator or the like for antilock brake control is not needed for the friction brake  7 , and it is possible to suppress locking of the wheel  2  or reduce locking tendency of the wheel  2  at low cost, for example, by merely rewriting a control program or the like. 
     Other embodiments will be described. In the following description of each embodiment, portions corresponding to the matters described in the preceding embodiment are designated by the same reference numerals, and the redundant description thereof is omitted. When only a part of a configuration is described, the remaining part of the configuration is the same as that of the previously described embodiment unless otherwise specified. The same advantageous effects are achieved by the same configuration. In addition to the combinations of portions described specifically in each embodiment, it is also possible to partially combine the embodiments unless any problem is particularly posed due to the combination. 
     As shown in  FIG. 4 , the slip ratio monitor  21  may obtain the wheel speed ω by using a low-pass filter  25  that is different from the low-pass filter for control of the motor  3  or is not for motor control and that has a cut-off frequency higher than a predetermined frequency, in measurement/calculation of the wheel speed ω. In comparison with the case of obtaining the wheel speed ω using the low-pass filter  25  that is not for control of the motor  3  and has a high cut-off frequency as described above, a response delay can be made smaller than the case where the wheel speed ω is obtained without using the low-pass filter  25 .  During antilock brake control, the response delay can be reduced to improve the accuracy of slip ratio control. 
     In the first embodiment, the example in which the antilock brake control device  1  is mounted on the four-wheel drive vehicle has been described, but it is not limited to this example. For example, as shown in  FIG. 5 , the antilock brake control device  1  may be mounted on a two-wheel drive vehicle that is driven with left and right rear wheels  2 . Alternatively, the antilock brake control device  1  may be mounted on a two-wheel drive vehicle that is driven with left and right front wheels  2  (not shown). 
     In the vehicle including the electrical friction brake that presses the brake pad against the brake rotor by the electric actuator, on the basis of the same idea as that of taking the PID calculation value K PID  into consideration in the driving torque control, when the slip ratio monitored by the slip ratio monitor exceeds the target slip ratio, for example, cooperative control of performing the above-described periodic loosening operation of the brake pad by the electric actuator which cooperative control corresponds to antilock brake control may be performed solely or together with addition of the torque in the driving direction to the IWM torque command value. In this case as well, an additional actuator is not needed for the friction brake, and locking of each wheel  2  can be suppressed or locking tendency of each wheel  2  can be reduced at low cost. 
     In each in-wheel motor drive device  6  of this embodiment, as the reducer, a cycloidal reducer, a planetary reducer, a reducer with two parallel shafts, or another reducer can be used. In addition, each in-wheel motor drive device  6  of this embodiment may be a so-called direct motor type in which a reducer is not used. It should be understood that although the described above is regarding the each in-wheel motor drive device  6 , the vehicle equipped with the antilock brake control device  1  may be a so-called on-board type in which each wheel, a drive shaft, and a motor are connected to each other in a one-by-one relation, and may also include a hybrid car in which each in-wheel  motor drive device  6  and an internal combustion engine are used in combination, and the like. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included within the scope. 
     REFERENCE NUMERALS 
       1  . . . antilock brake control device 
       2  . . . wheel 
       3  . . . motor 
       5  . . . wheel bearing 
       8  . . . brake rotor 
       9  . . . brake pad (press member) 
       7  . . . friction brake 
       19  . . . acceleration sensor 
       20  . . . road surface frictional coefficient estimation section 
       21  . . . slip ratio monitor 
       22  . . . driving torque addition section 
       25  . . . low-pass filter