Abstract:
A vehicle motion control device which includes a wheel cylinder equipped on a vehicle wheel; an automatic hydraulic pressure generator generating a brake hydraulic pressure irrespective of the operation of a brake pedal by using an intake vacuum pressure of an engine of a vehicle; a hydraulic pressure control valve disposed between the wheel cylinder and the automatic hydraulic pressure generator; a throttle opening amount automatic adjusting device for adjusting automatically the opening amount of a throttle valve of the engine irrespective of the operation of an accelerator pedal of the vehicle; control, device for controlling the automatic hydraulic pressure generator and the hydraulic pressure control valve in accordance with a running condition of the vehicle and for performing an automatic pressure increase control to the wheel cylinder at least non-operating condition of the brake pedal, the control means for controlling the throttle opening amount automatic adjusting device in accordance with the running condition of the vehicle and for performing an opening amount automatic adjust control to the wheel cylinder; intake vacuum pressure decrease condition detecting device for detecting a decrease condition of the intake vacuum pressure; and counter device for counting the number of performance of the automatic pressure increase control performed under the intake vacuum pressure decrease condition detected by the intake vacuum pressure decrease condition detecting device. The control device corrects the throttle opening amount requested to the throttle opening amount automatic adjusting device at the automatic pressure increase control so as to decrease in accordance with the number of performance of the automatic pressure increase control counted by the counter device.

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 2001-160470, filed on May 29, 2001, the entire content of which is incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    This invention relates to a vehicle motion control device which is applicable to a brake steering control device, a traction control device and so on.  
         BACKGROUND OF THE INVENTION  
         [0003]    A Japanese Patent Laid-Open Publication No. 7-304436 discloses a vehicle motion control device of this kind. This known device includes a wheel cylinder equipped on a vehicle wheel, an automatic hydraulic pressure generator generating a brake hydraulic pressure irrespective of the operation of a brake pedal by using an intake vacuum pressure of an engine of a vehicle, a hydraulic pressure control valve disposed between the wheel cylinder and the automatic hydraulic pressure generator, a throttle opening amount automatic adjusting means for adjusting automatically the opening amount of a throttle valve of the engine irrespective of the operation of an accelerator pedal of the vehicle and control means for controlling the automatic hydraulic pressure generator and the hydraulic pressure control valve in accordance with a running condition of the vehicle and for performing an automatic pressure increase control to the wheel cylinder at least when the brake pedal is not operated. Further, the control means controls the throttle opening amount automatic adjusting means in accordance with the running condition of the vehicle and performs an opening amount automatic adjust control to the wheel cylinder.  
           [0004]    In the vehicle motion control device of this kind, when the automatic pressure Increase control is performed intermittently at relative shorter intervals, the vacuum pressure in the automatic hydraulic pressure generator is dissipated excessively and is decreased. As a result, the brake hydraulic pressure which the automatic hydraulic pressure generator can generate is decreased and the performance of the vehicle motion control device decreases. Further, a brake operational force which is required for normal braking is increased.  
           [0005]    A need thus exists for a vehicle motion control device which lessens the decrease of the vacuum pressure in the automatic hydraulic pressure generator when the automatic pressure increase control is performed intermittently at relative shorter intervals.  
         SUMMARY OF THE INVENTION  
         [0006]    In light of the foregoing, the present invention provides a vehicle motion control device which includes a wheel cylinder equipped on a vehicle wheel; an automatic hydraulic pressure generator generating a brake hydraulic pressure irrespective of the operation of a brake pedal by using an intake vacuum pressure of an engine of a vehicle; a hydraulic pressure control valve disposed between the wheel cylinder and the automatic hydraulic pressure generator; a throttle opening amount automatic adjusting means for adjusting automatically the opening amount of a throttle valve of the engine irrespective of the operation of an accelerator pedal of the vehicle; control means for controlling the automatic hydraulic pressure generator and the hydraulic pressure control valve in accordance with a running condition of the vehicle and for performing an automatic pressure increase control to the wheel cylinder at least non-operating condition of the brake pedal, the control means for controlling the throttle opening amount automatic adjusting means in accordance with the running condition of the vehicle and for performing an opening amount automatic adjust control to the wheel cylinder; intake vacuum pressure decrease condition detecting means for detecting a decrease condition of the intake vacuum pressure; and counter means for counting the number of performance of the automatic pressure increase control performed under the intake vacuum pressure decrease condition detected by the intake vacuum pressure decrease condition detecting means, wherein the control means corrects the throttle opening amount requested to the throttle opening amount automatic adjusting means at the automatic pressure increase control so as to decrease in accordance with the number of performance of the automatic pressure increase control counted by the counter means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0007]    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:  
         [0008]    [0008]FIG. 1 is an overview of a vehicle motion control device according to an embodiment of the present invention;  
         [0009]    [0009]FIG. 2 is a schematic illustration of a brake system according to the embodiment of the present invention;  
         [0010]    [0010]FIG. 3 is a partial cross-sectional view of a vacuum booster according to the embodiment of the present invention;  
         [0011]    [0011]FIG. 4 is a flowchart showing a flow of a motion control according to the embodiment of the present invention;  
         [0012]    [0012]FIG. 5 is a flowchart showing a flow of the motion control according to the present invention;  
         [0013]    [0013]FIG. 6 is a flowchart showing details of a step S 113  of FIG. 5;  
         [0014]    [0014]FIG. 7 is a flowchart showing details of a step S 201  of FIG. 6;  
         [0015]    [0015]FIG. 8 is a flowchart showing details of a step S 202  of FIG. 6; and  
         [0016]    [0016]FIG. 9 is a timing chart showing an operation of the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    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  9  in accompanying drawings.  
         [0018]    Referring to FIG. 1, an engine EG of a vehicle includes a throttle control device TH and a fuel injection device FI. In the throttle control device TH, a main throttle opening amount of a main throttle valve MT is controlled in response to the operation of an accelerator pedal AP. Further, in response to an output of an electronic control unit ECU, a sub throttle valve ST is moved and a sub throttle opening amount is controlled, and further an amount of fuel injection is controlled by the fuel injection device FI. In this embodiment, the engine EG is connected to front wheels FL, FR through a transmission device GS.  
         [0019]    Wheel cylinders Wfl, Wfr, Wrl and Wrr are equipped on wheels FL, FR, RL and RR and are connected to a brake hydraulic pressure control device BC. The wheel FL corresponds to a wheel which is located at front left side of the vehicle. Likewise, the wheel FR corresponds to a wheel on front right side, the wheel RL corresponds to a wheel on rear left side, and the wheel RR corresponds to a wheel on rear right side.  
         [0020]    Wheel speed sensors WS 1 , WS 2 , WS 3  and WS 4  are provided on the wheels FL, FR, RL and RR and are connected to the electronic control unit ECU. Rotational speed of each wheel, that is a pulse signal with pulse number proportional to a wheel speed is inputted into the electronic control unit ECU. Further, sensors such as a brake switch BS for detecting the operation of a brake pedal BP, a front wheel steering sensor SSf for detecting a steering angle δ f of the front wheels FL, FR, a lateral G sensor YG for detecting a lateral acceleration of the vehicle, a yaw rate sensor YS for detecting a yaw rate and a throttle sensor SS for detecting the opening amounts of the main throttle valve MT and the sub throttle valve ST are connected to the electronic control unit ECU. According to the yaw rate sensor YS, a change speed of vehicle yaw angle about the vehicle axis on the vehicle center of gravity, that is yaw angular velocity (i.e., yaw rate) is detected to be outputted as an actual yaw rate γ to the electronic control unit ECU.  
         [0021]    As shown in FIG. 1, the electronic control unit ECU includes a microcomputer CMP which includes a processing unit CPU, memories ROM, RAM, and input ports IPT and output ports OPT all of which are interconnected via a bus. Output signals from the wheel speed sensors WS 1 -WS 4 , the brake switch BS, the front wheel steering angle sensor SSf, the yaw rate sensor YS, the lateral G sensor YG and the throttle sensor SS are inputted from the Input ports IPT to the processing unit CPU via an amplifier circuit AMP. The control signals are outputted from the output ports OPT to the throttle control device TH and the brake hydraulic pressure control device BC.  
         [0022]    In the microcomputer CMP, the memory ROM memorizes programs regading various transactions including flowcharts shown in FIGS.  4  to  8 , the processing unit CPU carries out the program while an ignition switch (not shown) is closed, and the memory RAM tentatively memorizes a parameter data which is required for carrying out the program.  
         [0023]    Next, a brake system including the brake hydraulic pressure control device BC will be explained as follows. As shown in FIG. 2, a master cylinder MC is boosted via a vacuum booster VB in accordance with the operation of the brake pedal BP. A pressure of a brake fluid which is supplied from a master cylinder reservoir LRS into the master cylinder MC is increased to output a master cylinder hydraulic pressure to two brake hydraulic pressure systems of the wheels FR, RL side and the wheels FL, RR side respectively. As it called X type dual circuit is provided in the vehicle motion control device of this embodiment. The master cylinder MC is a tandem type master cylinder having two pressure chambers. A first pressure chamber is in communication with the brake hydraulic pressure system on the wheels FR, RL side, and a second pressure chamber is in communication with the brake hydraulic pressure system on the wheels FL, RR.  
         [0024]    Regarding the brake hydraulic pressure system on the wheels FR, RL side, the first pressure chamber of the master cylinder MC is connected to the wheel cylinders Wfr, Wrl via a main hydraulic pressure conduit MF and branch hydraulic pressure conduits MFr, MFl respectively. The branch hydraulic pressure conduits MFr, MFl are provided with normal-open type two-port two-position solenoid valves PC 1  and PC 2  (hereinafter referred as the solenoid valves PC 1  and PC 2 ) respectively. Check valves CV 1  and CV 2  are provided in parallel with the solenoid valves PC 1  and PC 2  respectively. The check valves CV 1  and CV 2  allow the flow of the brake fluid in the direction only toward the master cylinder MC. The brake fluid in the wheel cylinders Wfr, Wrl is returned to the master cylinder MC and eventually to the master cylinder reservoir LRS via the check valves CV 1  and CV 2 . Accordingly, when the brake pedal BP is released, the hydraulic pressure in the wheel cylinders Wfr, Wrl promptly follows the decrease of the hydraulic pressure of the master cylinder MC side. Normal closed type two-port two-position solenoid valves PC 5  and PC 6  (hereinafter referred as the solenoid valves PC 5  and PC 6 ) are provided on output side branch pressure conduits RFr, RFl which are in communication with the wheel cylinders Wfr, Wrl. An output hydraulic pressure conduit RF confluent with the branch hydraulic pressure conduits RFr, RFl is connected with an auxiliary reservoir RS 1 .  
         [0025]    A hydraulic pressure pump HP 1  is interposed in a hydraulic pressure conduit MFp which is in communication with the branch hydraulic pressure conduits MFr, MFl at upper stream side of the solenoid valves PC 1  and PC 2 . The auxiliary reservoir RS 1  is connected with an inlet side of the hydraulic pressure pump HP 1  via a check valve CV 5 . An outlet side of the hydraulic pressure pump HP 1  is connected to the upper stream side of the solenoid valves PC 1  and PC 2  via a check valve CV 6 . The hydraulic pressure pump HP 1  is actuated by a single electric motor M along with a hydraulic pressure pump HP 2  for sucking the brake fluid from the auxiliary reservoir RS 1  to return to the outlet side. The auxiliary reservoir RS 1  is provided independently from the master cylinder reservoir LRS. The auxiliary reservoir RS 1  may also be called an accumulator which includes a piston and a spring for preserving a predetermined volume of the brake fluid. The check valves CV 5  and CV 6  function as an inlet valve and an outlet valve for restricting the flow of the brake fluid outputted via the hydraulic pressure pump HP 1  in a fixed direction. The check valves CV 5  and CV 6  are unitary structured in the hydraulic pressure pump HP 1 . A damper DP 1  is provided on the outlet side of the hydraulic pressure pump HP 1 . A proportioning valve PV 1  is disposed in a hydraulic pressure conduit which is connected to the wheel cylinder Wrl on the rear wheel side. Likewise, normal open type two-port two-position solenoid valves PC 3  and PC 4 , normal closed type two-port two-position solenoid valves PC 7  and PC 8 , check valves CV 3 , CV 4 , CV 7  and CV 8 , an auxiliary reservoir RS 2 , a damper DP 2 , and a proportioning PV 2  are provided in the brake hydraulic pressure system on the wheels FL, RR side. As mentioned above, the hydraulic pressure pump HP 2  is actuated by the electric motor M along with the hydraulic pressure pump HP 1 . The solenoid valves PC 1 -PC 8  for changing the brake hydraulic pressure of the wheel cylinders of the respective wheels correspond to the hydraulic pressure control valves of the present invention.  
         [0026]    As shown in FIG. 3, the vacuum booster VB includes a booster actuator BD for automatically actuating the vacuum booster VB irrespective of the operation of the brake pedal (i.e., at least when the brake pedal BP is not operated). Known structure of the vacuum booster VB is employed in the vehicle motion control device according to this embodiment. A constant pressure chamber B 2  and a variable pressure chamber B 3  are formed by a movable wall B 1 . The movable wall B 1  is unitary connected to a power piston B 4 . The constant pressure chamber B 2  is always in communication with an intake manifold (not shown) of the engine EG to be introduced with the vacuum pressure. The power piston B 4  is operatively connected to an output rod B 10  for transmitting the power via a fixed core D 2  and a reaction disc B 9 . The output rod B 10  is connected to the master cylinder MC.  
         [0027]    A valve mechanism B 5  including a vacuum valve V 1  for establishing and interrupting the fluid communication between the constant pressure chamber B 2  and the variable pressure chamber B 3  and an air valve V 2  for establishing and interrupting the fluid communication between the variable pressure chamber B 3  and the atmosphere is provided in the power piston B 4 . The vacuum valve V 1  includes an annular valve seat V 11  formed on the power piston B 4  and an elastic valve body V 12  which is detachable to the valve seat V 11 . The air valve V 2  includes an elastic valve seat V 21  equipped to the elastic valve body V 12  and a valve body V 22  which is detachable to the elastic valve seat V 21 . The valve body V 22  is connected to an input rod B 6  which is operatively connected to the brake pedal BP. The valve body V 22  is biased in the direction to be seated on the elastic valve seat  21  by the biasing force of a spring B 7 . The elastic valve body V 12  of the vacuum valve V 1  is biased in the direction to be seated on the annular valve seat V 11  by the biasing force of a spring B 8 . The biasing force of the spring B 8  also biases the elastic valve seat V 21  of the air valve V 2  in the direction to be seated on the Valve body V 22 .  
         [0028]    Accordingly, the vacuum valve V 1  and the air valve V 2  of the valve mechanism B 5  are opened and closed in accordance with the operational force of the brake pedal BP to generate the pressure difference between the constant pressure chamber B 2  and the variable pressure chamber B 3 . Thus, the output force amplified by the operation of the brake pedal BP is transmitted to the master cylinder MC.  
         [0029]    The booster actuator BD includes a linear solenoid D 1 , the fixed core D 2 , and a movable core D 3 . The linear solenoid D 1  which is connected to the electronic control unit ECU attracts the movable core D 3  towards the fixed core D 2  when energized, The attraction force of the linear solenoid D 1  is varied in accordance with the actuating electric current. The fixed core D 2  is disposed between the power piston B 4  and the reaction disc B 9  for transmitting the force from the power piston B 4  to the reaction disc B 9 . The movable core D 3  is positioned opposing to the fixed core D 2  in the linear solenoid D 1  and thus a magnetic gap D 4  is formed between the movable core D 3  and the fixed core D 2 . The movable core D 3  is engaged with the valve body V 22  of the air valve V 2 . By attracting the movable core D 3  relative to the fixed core D 2  in the direction to reduce the magnetic gap D 4 , the valve body V 22  of the air valve V 2  can be unitary moved.  
         [0030]    The input rod B 6  includes a first input rod B 61  and a second input rod B 62 . The first input rod B 61  is unitary connected to the brake pedal BP. The second input rod B 62  is movable relative to the first input rod B 61  for transmitting the force to the output rod B 10  via the key member B 11  by the power piston B 4 . Accordingly, when only the second input rod B 62  is actuated to forward, the first input rod B 61  is left behind. The first and the second input rods B 61 , B 62  structure a mechanism for leaving a pedal behind.  
         [0031]    The master cylinder MC, the vacuum booster VB, and the booster actuator BD correspond to an automatic hydraulic pressure generator of the present invention. The operation of the booster actuator BD and the vacuum booster VB when performing the automatic pressure increase control (e.g., brake steering control and traction control) for automatically pressurizing the wheel cylinders of the wheels to be controlled at least when the brake pedal is not operated will be explained as follows.  
         [0032]    When it is determined that the automatic pressure increase control is required by the electronic control unit ECU, the linear solenoid D 1  is energized, the movable core D 3  is moved towards the magnetic gap D 4  side, and the valve body V 22  of the air valve V 2  is unitary moved with the movable core B 3  against the biasing force of the spring B 7 . Accordingly, the elastic valve body V 12  of the vacuum valve V 1  is seated on the annular valve seat V 11  for interrupting the fluid communication between the variable pressure chamber B 3  and the constant pressure chamber B 1 . then because the valve body V 22  of the air valve V 2  is further moved, the valve body V 22  is separated from the elastic valve seat V 21  and the atmosphere is introduced into the variable pressure chamber B 3 . Accordingly, the pressure difference is generated between the variable pressure chamber B 3  and the constant pressure chamber B 1  to move the power piston B 4 , the fixed core D 1 , the reaction disc B 9 , and the output rod B 10  towards the master cylinder side. Thus, the master cylinder MC automatically generates the hydraulic pressure.  
         [0033]    After the power piston B 4  is engaged with the key member B 11 , the second input rod B 62  engaged with the key member B 11  is unitary moved forwardly with the power piston B 4 . On the other hand, since the forwarding force of the power piston B 4  is not transmitted to the first input rod B 61 , the first input rod B 61  is maintained at an initial position. That is, when the booster actuator BD automatically actuates the vacuum booster VB, the brake pedal BP is maintained at the initial position.  
         [0034]    The booster actuator BD, the solenoid valves PC 1 -PC 8 , and the electric motor M are actuated by the electronic control unit ECU for performing the brake steering control (i.e., over steer control or under steer control). When the ignition switch (not shown) is closed, a program for vehicle motion control according to the flowcharts of FIGS. 4 and 5 is carried out with calculation period of 6 ms.  
         [0035]    In Step S 101 , the microcomputer CMP is initialized to clear various calculated value. In Step S 102 , detection signals of the wheel speed sensors WS 1 -WS 4 , a detection signal (i.e., the steering angle δ f) of the front wheel steering angle sensor SSf, a detection signal (i.e., the actual yaw rate γ a) of the yaw rate sensor YS, a detection signal (i.e., actual lateral acceleration Gya) of the lateral acceleration sensor YG, and a detection signal of the throttle sensor SS are read in.  
         [0036]    Next, in Step S 103 , a wheel speed Vw** of each wheel is calculated and a wheel acceleration DVw** of each wheel is calculated by differentiating wheel speed V** of each wheel. In Step S 104 , a maximum value of wheel speed Vw** of each wheel is calculated as an estimated vehicle body speed Vso at the gravitational center position of the vehicle (Vso=MAX(Vw**)). Then, an estimated vehicle body speed Vso** at each wheel is obtained on the basis of the wheel speed Vw** of each wheel. If necessary, the normalization of each estimated vehicle body speed Vso** is performed in order to reduce the error due to wheel speed difference between inner wheels and outer wheels when the vehicle is turning. Further, the estimated vehicle body speed Vso is differentiated and an estimated vehicle acceleration (including an estimated vehicle body deceleration) Dvso at the gravitational center position of the vehicle is obtained.  
         [0037]    In Step S 105 , an actual slip ratio Sa** of each wheel is calculated as follows based on the wheel speed Vw** and the estimated vehicle body speed Vso** of each wheel obtained in Step S 103  and Step S 104 . 
           Sa**= ( Vso**−Vw** )/ Vso**   
         [0038]    In Step S 106 , an approximate road surface frictional coefficient μ is estimated based on the estimated vehicle body acceleration Dvso and the detection signal Gya of the lateral acceleration sensor YG as follows. 
         μ=( Dvso   2   +Gya   2 ) ½   
         [0039]    In Step S 107 , a vehicle body skidding angular velocity D β is obtained based on the actual lateral acceleration Gya, the actual yaw rate γ a, and estimated vehicle body speed Vso as follows. 
         
       Dβ=Gy/Vso−γa 
     
         [0040]    In Step S 108 , a vehicle body skidding angle β is obtained as follows. 
         β=∫( Gy/Vso−γa ) dt   
         [0041]    In this case, the vehicle body skidding angle β corresponds to a directional angle of the vehicle relative to the running direction of the vehicle. The vehicle body slidding angular velocity D β corresponds to a differentiated value of the vehicle body skidding angle β (i.e., d β/dt).  
         [0042]    In Step S 109 , a brake steering control calculation transaction is carried out to determine a target slip ratio for wheels to be brake steering controlled. In Step S 110 , an anti-skid control is carried out and a front-rear braking force division control is carried out in Step S 111 . In Step S 112 , a traction control is carried out. In each of the Steps S 109 -S 112 , it is judged whether conditions for starting each control are satisfied or whether conditions for ending each control is satisfied. Further, a target slip, ratio for each control is set.  
         [0043]    In Step S 113 , a sub throttle opening amount is determined and an automatic pressure increase is determined in Step S 114 . Namely, in Step S 114 , an operation or non operation of the booster actuator BD is determined. In Step S 115 , a brake hydraulic pressure of the wheel to be controlled is determined. Namely, pressure decrease, pressure increase, or pressure hold is determined. In Step S 116 , an operation or non operation of the electric motor M is determined. After these determinations are outputted in Step S 117 , the Step S 102  is performed.  
         [0044]    [0044]FIG. 6 shows a process of the determination of the sub throttle opening amount in Step S 113  of FIG. 5. In Step S 201 , a correcting amount θ d for moving the sub throttle valve so as to decrease the opening amount is calculated. Next, in Step S 202 , the opening amount θ of the sub throttle valve ST is calculated and the Step S 114  in FIG. 6 is performed.  
         [0045]    [0045]FIG. 7 shows a process of the calculation of the correcting amount θ d in Step S 201  of FIG. 6. In Step S 301 , it is judged whether the condition of vacuum is in decrease condition. Namely, a main throttle opening amount detected by the throttle sensor SS is compared with a first predetermined value and a second predetermined value which is larger than the first predetermined value. When the main throttle valve opening amount is larger than the second predetermined value, it is judged that the vacuum condition is in decrease condition. When the main throttle valve opening amount is smaller than the first predetermined value, it is judged that the vacuum condition is not in decrease condition.  
         [0046]    When the result of the judgment of the Step S 301  is Yes, the Step S 302  is performed and it is judged whether the state of traction control is changed from ending state to starting state. When the state of the traction control is changed, “1” is added to a discrete value of a control counter in Step S 303 . Then, in Step S 306 , the correcting amount θd is calculated and the Step S 202  in FIG. 6 is performed. When the state of the traction control is not changed, it is judged whether the state of the brake steering control is changed from the ending state to starting state. When the state of the brake steering control is changed, “1” is added to a discrete value of the control counter in Step S 303 . When the state of the brake steering control is not changed, the correcting amount θ d is calculated in Step S 306 . When the result of the judgment of the Step S 301  is No, a discrete value of the control counter becomes “0” in Step S 305  and then the correcting amount θ d is calculated in Step S 306 . In Step S 306 , the correcting amount θ d is calculated by multiplying a predetermined value by the discrete value of the control counter.  
         [0047]    [0047]FIG. 8 shows a process the calculation of the opening amount θ of the sub throttle valve ST in FIG. 6. In Step S 401 , it is judged whether the traction control or brake steering control is under control. When the traction control or the brake steering control is not under control, the opening amount of the sub throttle valve θ (n) is set to max value in Step S 402  and the Step S 114  in FIG. 5 is performed. When the traction, control or the brake steering control is under control, it is judged whether the calculation is a first calculation in Step S 403 . When the calculation is a first calculation, an initial opening amount θ l of the sub throttle valve is obtained at a function of the main throttle opening amount θ m and the rotational number of the engine Ne in Step S 404 . Then, in Step S 405 , the opening amount of the sub throttle valve is obtained as follows. 
         θ( n )=θ i−θd   
         [0048]    Then, the Step S 114  in FIG. 5 is performed, in the above description, (n) means the times of calculation and θ (n) means a present calculated value.  
         [0049]    When the calculation is not a first calculation, in the Step S 406 , the opening amount θ (n) is renewed to a value which is obtained by adding an increase or decrease amount obtained as a function of the actual slip ration Sa** of the wheel to be controlled to the previous calculation valve θ (n−1). Then, the Step S 114  in FIG. 5 is performed.  
         [0050]    [0050]FIG. 9 is a time chart showing the operation of this embodiment. In FIG. 9, dotted line of the opening amount θ shows a case in which the opening amount of the sub throttle valve ST is not corrected with the correcting amount θ d. As shown in FIG. 9, in the condition that the intake vacuum pressure of the engine EG is decreased, the sub throttle opening amount is corrected so as to decrease the opening amount in accordance with the number of performance of the automatic pressure increase control. Therefore, even if the automatic pressure increase control is performed intermittently at relative shorter intervals, the vacuum pressure in the constant pressure chamber B 2  of the vacuum booster VB is prevented from decreasing. Further, it is prevented that the brake hydraulic pressure which the automatic hydraulic pressure generator can generate is decreased and that the performance of the vehicle motion control device decreases. Further, the increase of a brake operational force which is required for normal braking is avoided.  
         [0051]    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.