Patent Publication Number: US-2022227341-A1

Title: Vehicle brake system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Japanese Patent Application No. 2021-004700, which was filed on Jan. 15, 2021, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     The following disclosure relates to a brake system for a vehicle configured to apply a braking force to the vehicle. 
     Description of Related Art 
     Patent Document 1 (Japanese Patent Application Publication No. 2018-111423) discloses a vehicle hydraulic brake system in which a hydraulic pressure in a hydraulic brake is controlled based on one of first target data and second target data. In the disclosed system, a determination time for the second target data is shortened when the first target data is not input for a first reference determination time as a determination time. The configuration enables early detection of an abnormal non-input state of the target data and early start of a backup control, thus preventing or reducing a shortage of a braking force that arises from the abnormality. 
     SUMMARY 
     An aspect of the present disclosure is directed to a vehicle brake system that prevents or reduces a shortage of a braking force in a time period from a time point of starting detection of the presence or absence of an abnormality of a first hydraulic-pressure control mechanism to a time point of determining the presence or absence of the abnormality, while preventing or reducing a decrease in an accuracy of detecting the abnormality of the first hydraulic-pressure control mechanism. 
     In the vehicle brake system, when a temperature is low, actuation of the first hydraulic-pressure control mechanism may be delayed. If a monitoring time is short in such a case, the first hydraulic-pressure control mechanism may be erroneously detected to be in an abnormal state even if the first hydraulic-pressure control mechanism is normal. For preventing such erroneous detection, the monitoring time is made longer in detecting whether the first hydraulic-pressure control mechanism is in the abnormal state. However, the increase in the monitoring time undesirably causes the braking force to remain insufficient for a long time till the time point of determining whether the first hydraulic-pressure control mechanism is in the abnormal state. 
     In the vehicle brake system according to the present disclosure, when the first hydraulic-pressure control mechanism is detected to be in a second abnormal state that the first hydraulic-pressure control mechanism reaches before reaching a first abnormal state, a second braking-force control mechanism is operated after a lapse of an assist wait time that is determined based on the temperature. This configuration prevents the shortage of the braking force while preventing a decrease in the accuracy of detection as to whether the first hydraulic-pressure control mechanism is in the first abnormal state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of an embodiment, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a conceptual view of a controller and components therearound in a vehicle brake system according to one embodiment of the present disclosure; 
         FIG. 2  is a circuit diagram of the brake system; 
         FIG. 3  is a conceptual view illustrating an assist-wait-time determination map stored in a memory of the controller in the brake system; 
         FIG. 4  is a conceptual view illustrating a brake-operation-timing determination map stored in the memory; 
         FIG. 5  is a flowchart representing a control-command-value generating program stored in the memory; 
         FIG. 6  is a flowchart representing a braking-force control program stored in the memory; 
         FIG. 7  is a flowchart representing a first-abnormal-state detecting program stored in the memory; 
         FIG. 8  is a conceptual view illustrating a state of a braking-force control when an upstream hydraulic-pressure control mechanism of the brake system is normal; 
         FIG. 9  is a conceptual view illustrating a state of the braking-force control when the upstream hydraulic-pressure mechanism is detected to in a first abnormal state after an assist control has been executed in the brake system; 
         FIG. 10  is a conceptual view illustrating a state of the braking-force control in a case where the assist control is executed in a low temperature condition in the brake system; 
         FIG. 11  is a conceptual view illustrating a state of the braking-force control in a case where the upstream hydraulic-pressure control mechanism is in the first abnormal state in a conventional vehicle brake system; and 
         FIG. 12  is a conceptual view illustrating one example of a detailed configuration of the controller. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Referring to the drawings, there will be hereinafter described in details a vehicle brake system according to one embodiment of the present disclosure. 
     As illustrated in  FIG. 2 , the vehicle brake system according to the present embodiment is a hydraulic brake system including hydraulic brakes  12 FL,  12 FR respectively provided for front left and right wheels  8 FL,  8 FR and hydraulic brakes  14 RL,  14 RR respectively provided for rear right and left wheels  10 RL,  10 RR. The present brake system includes an upstream hydraulic-pressure control mechanism  34  as a first braking-force control mechanism and a first hydraulic-pressure control mechanism, a downstream hydraulic-pressure control mechanism  33  as a second braking-force control mechanism and a second hydraulic-pressure control mechanism, and a controller  20  ( FIG. 1 ) constituted principally by a computer. 
     In the following description, components, such as the hydraulic brakes, will be referred to without suffixes such as FL, FR, RL, RR, F, R indicative of the corresponding wheel positions where it is not necessary to distinguish the components by their wheel positions. 
     As illustrated in  FIG. 2 , the upstream hydraulic-pressure control mechanism  34  includes (a) a master cylinder  43  including: an input piston  40  coupled to a brake pedal  39  as a brake operating member operable by a driver and two pressurizing pistons  41 ,  42  and (b) a rear-hydraulic-pressure control device  48  including a regulator  45  connected to a rear chamber  44  provided rearward of the pressurizing piston  41  of the master cylinder  43 . The rear-hydraulic-pressure control device  48  controls a hydraulic pressure in the rear chamber  44  to thereby control a hydraulic pressure in the pressurizing chambers  46 ,  47  respectively located frontward of the corresponding pressurizing pistons  41 ,  42 . 
     The pressurizing pistons  41 ,  42  and the input piston  40  are fluid-tightly and slidably disposed in a housing  50  of the master cylinder  43  so as to be arranged in series with one another. The wheel cylinders  36  of the hydraulic brakes  12  provided for the front left and right wheels  8  are connected to the pressurizing chamber  46  via a fluid passage  54  while the wheel cylinders  38  of the hydraulic brakes  14  provided for the rear left and right wheels  10  are connected to the pressurizing chamber  47  via a fluid passage  56 . The pressurizing pistons  41 ,  42  are urged in a backward direction by respective return springs. When the pressurizing pistons  41 ,  42  are located at respective back end positions, the pressurizing chambers  46 ,  47  are in communication with a master reservoir  60 . 
     The pressurizing piston  41  of the master cylinder  43  has a generally stepped shape. The pressurizing piston  41  includes (a) a front piston portion  62  located at a front portion of the pressurizing piston  41 , (b) an intermediate piston portion  64  located at an intermediate portion of the pressurizing piston  41  so as to radially protrude, and (c) a rear small-diameter portion  66  located at a rear portion of the pressurizing piston  41  and having a diameter smaller than a diameter of the intermediate piston portion  64 . The front piston portion  62 , the intermediate piston portion  64 , and the rear small-diameter portion  66  are fluid-tightly and slidably disposed in the housing  50 . A space in front of the front piston portion  62  is the pressurizing chamber  46 , and a space in front of the intermediate piston portion  64  is an annular chamber  70 . A chamber located at a rear of the intermediate piston portion  64  and defined by the housing  50 , the rear small-diameter portion  66 , and the intermediate piston portion  64  is the rear chamber  44 . 
     The input piston  40  is located rearward of the pressurizing piston  41 , and a separated chamber  72  is defined between the rear small-diameter portion  66  and the input piston  40 . The brake pedal  39  is linked to a rear portion of the input piston  40  via an operating rod (hereinafter simply referred to as “rod” where appropriate) and other components. 
     The annular chamber  70  and the separated chamber  72  are connected to each other via a connecting passage  74 . A communication control valve  76  is provided in the connecting passage  74 . The communication control valve  76  is a normally-closed electromagnetic open/close valve. The communication control valve  76  is placed in an open state when the brake pedal  39  is operated or when a main switch of the vehicle is turned to ON, for instance. Thus, the communication control valve  76  is basically in the open state. A portion of the connecting passage  74  located on one of opposite sides of the communication control valve  76  that is closer to the annular chamber  70  is connected to a stroke simulator  78  and is connected to the master reservoir  60  via a reservoir passage  80 . A reservoir cut-off valve  82 , which is a normally-open electromagnetic open/close valve, is provided in the reservoir passage  80 . 
     A hydraulic pressure sensor  84  is provided at the above-indicated portion of the connecting passage  74  located on the one of opposite sides of the communication control valve  76  that is closer to the annular chamber  70 . The hydraulic pressure sensor  84  detects a hydraulic pressure in the annular chamber  70  and the separated chamber  72  in a state in which the annular chamber  70  and the separated chamber  72  are in communication with each other and are isolated from the master reservoir  60 . The hydraulic pressure level in the annular chamber  70  and the separated chamber  72  corresponds to a magnitude of an operation force of the brake pedal  39 . In this sense, the hydraulic pressure sensor  84  will be hereinafter referred to as an “operation-related hydraulic pressure sensor”. 
     The rear-hydraulic-pressure control device  48  includes a high pressure source  93 , a hydraulic-pressure control valve device, etc., in addition to the regulator  45 . The high pressure source  93  includes: a pump device  90  including a pump  86  and a pump motor  88 ; and an accumulator  92 , for instance. The hydraulic-pressure control valve device controls a hydraulic pressure in a control chamber  122  that will be explained. The hydraulic-pressure control valve device includes a pressure-increase control valve  94 , a pressure-decrease control valve  96 , etc. 
     The accumulator  92  accumulates, in a pressurized state, a working fluid ejected from the pump device  90 . An accumulator pressure that is a hydraulic pressure of the working fluid accumulated in the accumulator  92  is detected by an accumulator pressure sensor  98 . The pump motor  88  is controlled such that the accumulator pressure detected by the accumulator pressure sensor  98  is kept within a predetermined range. 
     The regulator  45  includes (d) a housing  110  and (e) a pilot piston  112  and a control piston  114  disposed in the housing  110  so as to be arranged in series in a direction parallel to an axis h. A high-pressure chamber  116  is formed in the housing  110  at a position in front of the control piston  114 . The high-pressure chamber  116  is connected to the high pressure source  93 . A space between the pilot piston  112  and the housing  110  is a pilot pressure chamber  120 . A space at a rear of the control piston  114  is the control chamber  122 . A space in front of the control piston  114  is a servo chamber  124  as an output chamber. A high-pressure supply valve  126  is provided between the servo chamber  124  and the high-pressure chamber  116 . The high-pressure supply valve  126  is a normally-closed valve that isolates the servo chamber  124  and the high-pressure chamber  116  from each other in a non-operating state of the regulator  45 . The control piston  114  is urged in the backward direction by a return spring  130 . 
     A low-pressure passage  128  is formed in the control piston  114  so as to communicate with the master reservoir  60  all the time. The low-pressure passage  128  is open in a front end of the control piston  114 . The opening is opposed to the high-pressure supply valve  126 . Thus, when the control piston  114  is located at its back end position, the servo chamber  124  is isolated from the high-pressure chamber  116  and communicates with the master reservoir  60  via the low-pressure passage  128 . When the control piston  114  is moved forward and the opening of the low-pressure passage  128  is accordingly closed, the servo chamber  124  is isolated from the master reservoir  60 , and the high-pressure supply valve  126  is opened so that the servo chamber  124  is brought into communication with the high-pressure chamber  116 . 
     The pressurizing chamber  46  is connected to the pilot pressure chamber  120 . The pilot pressure chamber  120  and the pressurizing chamber  46  are held in communication with each other all the time. Thus, the hydraulic pressure in the pressurizing chamber  46  acts on the pilot piston  112  all the time. 
     The rear chamber  44  is connected to the servo chamber  124 . The servo chamber  124  and the rear chamber  44  are held in communication with each other all the time. Thus, a servo pressure Ps, which is a hydraulic pressure in the servo chamber  124 , is basically equal to the hydraulic pressure in the rear chamber  44 . The servo pressure Ps is detected by a servo pressure sensor  132 . 
     The pressure-increase control valve (SLA)  94  and the pressure-decrease control valve (SLR)  96  are connected to the control chamber  122 . The pressure-increase control valve  94  is provided between the control chamber  122  and the high pressure source  93 , and the pressure-decrease control valve  96  is provided between the control chamber  122  and the master reservoir  60 . An electric current supplied to coils of the pressure-increase control valve  94  and the pressure-decrease control valve  96  is controlled to control the hydraulic pressure in the control chamber  122 . (The electric current will be hereinafter referred to as a “supply current” where appropriate. The same applies to other electromagnetic valves.) A damper  134  is connected to the control chamber  122 , and the working fluid flows between the control chamber  122  and the damper  134 . 
     In the present embodiment, a relationship between the hydraulic pressure of the control chamber  122  and the servo pressure Ps of the servo chamber  124  in the regulator  45  and a relationship between the hydraulic pressure of the rear chamber  44  and the hydraulic pressure of the pressurizing chambers  46 ,  47  in the master cylinder  43  are determined based on the configurations of the regulator  45  and the master cylinder  43 . Accordingly, the hydraulic pressure of the control chamber  122  is controlled such that the hydraulic pressure of the pressurizing chambers  46 ,  47  becomes close to a target hydraulic pressure. 
     The downstream hydraulic-pressure control mechanism  33  includes, for instance, (a) a slip control valve device  150 , (b) a pump device  158  including: pumps  154 F,  154 R configured to pump up the working fluid in pressure-reduction reservoirs  152 F,  152 R to eject the working fluid toward an upstream side of the slip control valve device  150 ; and a pump motor  156 , and (c) normally-open hydraulic pressure control valves  160 F,  160 R disposed between the pumps  154 F,  154 R and the pressurizing chambers  46 ,  47  of the master cylinder  43 . The hydraulic pressure control valves  160 F,  160 R control a pressure difference between the hydraulic pressure in the pressurizing chambers  46 ,  47  of the master cylinder  43  and a hydraulic pressure in the wheel cylinders  36 FR,  36 FL,  38 RR,  38 RL of the hydraulic brakes  12 FL,  12 FR,  14 RL,  14 RR. 
     The downstream hydraulic-pressure control mechanism  33  has front and rear lines. In the front-wheel-side line, there are connected, to the fluid passage  54 , individual passages  146 FL,  146 FR that are connected respectively to the wheel cylinders  36 FL,  36 FR of the front left and right wheels  8 FL,  8 FR. Pressure-hold valves  170 FL,  170 FR are provided respectively in the individual passages  146 FR,  146 FL. The wheel cylinders  36 FL,  36 FR are connected to a fluid chamber  178 F of the pressure-reduction reservoir  152 F via corresponding pressure reduction passages in which pressure-reduction valves  172 FL,  172 FR are respectively provided. 
     In the rear-wheel-side line, there are connected, to the fluid passage  56 , individual passages  148 RL,  148 RR that are connected respectively to the wheel cylinders  38 RL,  38 RR of the rear left and right wheels  10 RL,  10 RR. Pressure-hold valves  170 RL,  170 RR are provided respectively in the individual passages  148 RL,  148 RR. A pressure-reduction valve  172 RL is provided between the wheel cylinder  38 RL and a fluid chamber  178 R of the pressure-reduction reservoir  152 R, and a pressure-reduction valve  172 RR is provided between the wheel cylinder  38 RR and the fluid chamber  178 R of the pressure-reduction reservoir  152 R. The pressure-hold valves  170 , the pressure-reduction valves  172 , the pressure-reduction reservoirs  152 , etc., constitute the slip control valve device  150 . 
     Hereinafter, the front-wheel-side line will be explained, and an explanation of the rear-wheel-side is dispensed with. 
     The pressure-reduction reservoir  152 F includes a housing, a partition member  174 F slidably disposed in the housing, and an elastic member  176 F provided on one of opposite sides of the partition member  174 F in the housing. A space in the housing located on the other of the opposite sides of the partition member  174 F that is remote from the elastic member  176 F is the fluid chamber  178 F in which the working fluid is stored. 
     A replenishment valve  179 F is provided in the fluid chamber  178 F. The replenishment valve  179 F includes a valve seat, a valve member, a spring for applying an elastic force in a direction in which the valve member is pushed onto the valve seat, and a valve opening member  175 F provided on the partition member  174 F. In a case where the amount of the working fluid stored in the fluid chamber  178 F of the pressure-reduction reservoir  152 F is not smaller than a set amount, the valve member is seated on the valve seat, and the replenishment valve  179 F is in a closed state. When the amount of the working fluid in the fluid chamber  178 F becomes smaller than the set amount, the partition member  174 F is moved by an elastic force of the elastic member  176 F and the valve opening member  175 F causes the valve member to be separated away from the valve seat, so that the replenishment valve  179 F is placed in an open state. 
     The fluid chamber  178 F of the pressure-reduction reservoir  152 F and a portion of the fluid passage  54  located upstream of positions at which the individual passages  146 FL,  146 FR are respectively connected (i.e., a portion of the fluid passage  54  located upstream of the pressure-hold valves  170 FL,  170 FR) are connected via a pump passage  180 F in which the pump  154 F is provided. In a portion of the pump passage  180 F located on the ejection side of the pump  154 F, a damper, a restrictor, etc., are provided for preventing or reducing pulsation of the working fluid ejected from the pump  154 F. The suction side of the pump  154 F is connected to the fluid chamber  178 F of the pressure-reduction reservoir  152 F via a suction valve. 
     The hydraulic pressure control valve  160 F is provided in a portion of the fluid passage  54  located upstream of a position at which the pump passage  180 F is connected. A portion of the fluid passage  54  located upstream of the hydraulic pressure control valve  160 F and the pressure-reduction reservoir  152 F are connected to each other by a replenishment passage  182 F via the replenishment valve  179 F. 
     The hydraulic pressure control valve  160 F is configured to control a difference dP in a hydraulic pressure between an upstream side and a downstream side of the hydraulic pressure control valve  160 F to a pressure level corresponding to a supply current to the hydraulic pressure control valve  160 F. The pressure difference dP increases with an increase in the supply current to the hydraulic pressure control valve  160 F, and the hydraulic pressure in the wheel cylinders  36  increases with respect to the hydraulic pressure in the pressurizing chamber  46  of the master cylinder  43 . 
     An electric parking brake  186  is provided for each of the rear left and right wheels  10 . The electric parking brakes  186  are operated by an actuator  188  (indicated as “EPBACT  188 ” in  FIG. 1 ). 
     In the present embodiment, a master cylinder pressure sensor  190  is provided in the fluid passage  54 , and wheel cylinder pressure sensors  192 F,  192 R are provided respectively in the individual passages  146 FL,  148 RR. The master cylinder pressure sensor  190  provided in the fluid passage  54  is configured to detect the hydraulic pressure in the pressurizing chamber  46 . The hydraulic pressure in the pressurizing chamber  46  and the hydraulic pressure in the pressurizing chamber  47  are estimated to be substantially the same. Thus, the hydraulic pressure in the pressurizing chamber  47  can be estimated based on the detection value of the master cylinder pressure sensor  190 . The wheel cylinder pressure sensors  192 F,  192 R detect the hydraulic pressures in the respective wheel cylinders  36 FL,  38 RR. When the hydraulic pressures in the wheel cylinders  36 FR,  36 FL on the front-wheel side are substantially the same and when the hydraulic pressures in the wheel cylinders  38 RL,  38 RR on the rear-wheel side are substantially the same, detection of the hydraulic pressure in one of the two wheel cylinders enables estimation of the hydraulic pressure in the other of the two wheel cylinders. 
     Wheel speed sensors  194  are provided respectively for the front left and right wheels  8  and the rear left and right wheels  10  for detecting rotational speeds of the corresponding wheels. A running speed of the vehicle is obtained based on detection values of the wheel speed sensors  194 . 
     As illustrated in  FIG. 1 , the controller  20  is constituted principally by a computer. The controller  20  includes, a control-command-value generating device  198 , a brake control device  200 , etc. The controller  20  further includes an executing device, a memory, an input/output device, etc. There are connected, to the input/output device, the operation-related hydraulic pressure sensor  84 , the accumulator pressure sensor  98 , the servo pressure sensor  132 , the master cylinder pressure sensor  190 , the wheel cylinder pressure sensors  192 , the wheel speed sensors  194 , digital cameras  212 , sonar  214 , and a temperature sensor  216 , for instance. To the input/output device, there are further connected, actuators included in the upstream hydraulic-pressure control mechanism  34  (such as the pump motor  88 , the pressure-increase control valve  94 , the pressure-decrease control valve  96 , the communication control valve  76 , and the reservoir cut-off valve  82 ), actuators included in the downstream hydraulic-pressure control mechanism  33  (such as the pump motor  156 , the hydraulic pressure control valves  160 , the pressure-hold valves  170 , and the pressure-reduction valves  172 ), the actuator  188  for the electric parking brakes  186 , etc., via respective drive circuits (not illustrated). 
     The digital cameras  212  and the sonar  214  are provided at a plurality of portions of the vehicle. The temperature sensor  216  may detect an outside air temperature or may detect a temperature in the brake system. In the present embodiment, a temperature of the working fluid in the brake system is obtained based on the temperature detected by the temperature sensor  216 . The outside air temperature or the temperature in the brake system may be estimated as the temperature of the working fluid. The temperature of the working fluid may be obtained based on the detection value of the temperature sensor  216  and an operating time of the hydraulic brakes  12 ,  14 , for instance. 
     A verification electric control unit (ECU)  218  is connected to the controller  20 . The verification ECU  218  is configured to transmit and receive information to and from an information communication terminal  220  present outside the vehicle. For instance, the verification ECU  218  performs verification of ID of the information communication terminal  220  and obtains remote information supplied from the information communication terminal  220 , for instance. The remote information is sent to the controller  20  via the verification ECU  218 . Here, an automated parking control executed based on the remote information will be referred to as “remote parking control”. The remote parking control is executed when a driver, etc., are not on the vehicle. 
     In the remote parking control, the control-command-value generating device  198  performs image recognition based on images taken by the plurality of digital cameras  212  and information supplied from the sonar  214  and creates a route and a running plan according to which the vehicle runs when the vehicle is moved to a target parking position. Further, the control-command-value generating device  198  generates, based on the running plan, a control command value such as a request for the operation of the hydraulic brakes  12 ,  14  (including a request for initiation of the operation) and a target deceleration and supplies the generated control command value to the brake control device  200 . Based on the recognized image, the control-command-value generating device  198  obtains a distance D between: a three-dimensional object or a human present in surroundings of an own vehicle (as the vehicle on which the present brake system is installed); and the own vehicle. A three-dimensional object, a human, etc., will be collectively referred to as an “object” where appropriate. Based on the obtained distance D, a speed at which the own vehicle and the object approach each other (hereinafter referred to as “approach speed” where appropriate), the temperature of the working fluid obtained based on the detection value of the temperature sensor  216 , etc., the control-command-value generating device  198  obtains an operation timing of the hydraulic brakes  12 ,  14  and creates or modifies the running plan. 
     The brake control device  200  controls the upstream hydraulic-pressure control mechanism  34 , the downstream hydraulic-pressure control mechanism  33 , the EPBACT  188 , etc., based on the control command value (such as the request for the operation of the hydraulic brakes  12 ,  14  and the target deceleration) supplied from the control-command-value generating device  198 . For instance, the brake control device  200  obtains a total target hydraulic pressure that is a target value of the hydraulic pressure of the hydraulic brakes  12 ,  14  and that corresponds to the target deceleration. The brake control device  200  controls the supply current to each of the pressure-increase control valve  94 , the pressure-decrease control valve  96 , and the hydraulic pressure control valves  160 , etc., such that an actual hydraulic pressure in the hydraulic brakes  12 ,  14  becomes close to the total target hydraulic pressure. Further, when the own vehicle reaches the target parking position, the brake control device  200  controls the EPBACT  188  to operate the parking brakes. 
     The controller  20  includes not only the brake control device  200  but also a hybrid vehicle/electronic fuel injection (HV/EFI) control device, an electronic controlled power steer (EPS) control device, a shift by wire (SBW) control device, etc., and controls an HV/EFI actuator, an EPS actuator, an SBW actuator, etc. However, a control of the HV/EFI actuator, the EPS actuator, the SBW actuator, etc., is not relevant to the present disclosure, and an explanation thereof is dispensed with. 
     There will be next explained operations of the thus configured brake system in a case where the remote parking control is executed. 
     In the remote parking control, the brake control device  200  obtains the total target hydraulic pressure corresponding to the target deceleration that is the control command value generated by the control-command-value generating device  198  and controls the upstream hydraulic-pressure control mechanism  34  such that the actual hydraulic pressure of the hydraulic brakes  12 ,  14  becomes close to the total target hydraulic pressure. That is, when the upstream hydraulic-pressure control mechanism  34  is not in an abnormal state, the hydraulic pressure is generated in the hydraulic brakes  12 ,  14  by the operation of the upstream hydraulic-pressure control mechanism  34 , so that the own vehicle is decelerated. 
     The regulator  45  in the upstream hydraulic-pressure control mechanism  34  is operated, the hydraulic pressure in the rear chamber  44  is controlled, and the hydraulic pressure in the pressurizing chambers  46 ,  47  is controlled. 
     In the rear-hydraulic-pressure control device  48 , the hydraulic pressure in the control chamber  122  is controlled by controlling the pressure-increase control valve  94  and the pressure-decrease control valve  96 . The control piston  114  is moved forward, and the servo pressure is generated in the servo chamber  124 . The generated servo pressure is supplied to the rear chamber  44 . The pressurizing piston  41  is moved forward by the hydraulic pressure in the rear chamber  44 , and the pressurizing piston  42  is moved forward. Thus, the hydraulic pressure is generated in the pressurizing chambers  46 ,  47 . When the pressurizing chambers  46 ,  47  and the wheel cylinders  36 ,  38  are held in communication with each other, the hydraulic pressure in the pressurizing chambers  46 ,  47  is supplied to the corresponding wheel cylinders  36 ,  38 , so that the hydraulic brakes  12 ,  14  are operated. The hydraulic pressure in the wheel cylinders  36 ,  38  is substantially the same as the hydraulic pressure in the pressurizing chambers  46 ,  47 . 
     In the present embodiment, as illustrated in  FIG. 8 , the pressure-increase control valve  94  and the pressure-decrease control valve  96  are controlled such that an actual hydraulic pressure, which is the hydraulic pressure in the pressurizing chamber  46  detected by the master cylinder pressure sensor  190 , becomes close to a target upstream hydraulic pressure that is the total target hydraulic pressure. The above-indicated actual hydraulic pressure may be referred to as a first actual hydraulic pressure or an actual upstream hydraulic pressure. 
     In the brake control device  200 , it is detected whether the upstream hydraulic-pressure control mechanism  34  is in the abnormal state. In the brake control device  200  of the present embodiment, the detection value of the master cylinder pressure sensor  190  is obtained at intervals of a cycle time, and the actual upstream hydraulic pressure is obtained. A difference between the actual upstream hydraulic pressure and the target upstream hydraulic pressure is obtained at intervals of the cycle time, and it is determined whether the difference is greater than an abnormality determination threshold. For accurately detecting whether the upstream hydraulic-pressure control mechanism  34  is in a first abnormal state (as the abnormal state), a monitoring time (i.e., a time during which monitoring for the actual upstream hydraulic pressure is performed) is increased. In particular, in a case where unattended driving is performed such as when the remote parking control is executed, it is highly needed to detect, with high accuracy, the presence or absence of the abnormality of the vehicle brake system. 
     In the meantime, when the temperature of the working fluid is low and the viscosity of the working fluid is high, actuation of the rear-hydraulic-pressure control device  48  may be delayed, causing a delay in an increase of the hydraulic pressure in the pressurizing chambers  46 ,  47 . In this case, the upstream hydraulic-pressure control mechanism  34  may be erroneously detected to be in the first abnormal state even if it is actually normal. For preventing such erroneous detection, the monitoring time is made longer when the temperature of the working fluid is lower than a first set temperature than when the temperature of the working fluid is not lower than the first set temperature (including a case in which the temperature of the working fluid is equal to the normal temperature). The first set temperature may be a temperature at which it is estimated that the viscosity of the working fluid is high and the delay in the actuation is caused. 
     In the present embodiment, the monitoring time is set to a first set time when the temperature of the working fluid is not lower than the first set temperature, and the monitoring time is set to a second set time when the temperature of the working fluid is lower than the first set temperature, the second set time being longer than the first set time. 
     When the temperature of the working fluid is not lower than the first set temperature, the detection value of the master cylinder pressure sensor  190  is obtained for the first set time at intervals of the cycle time, and it is determined whether the difference between the actual upstream hydraulic pressure and the target upstream hydraulic pressure is greater than the abnormality determination threshold. The upstream hydraulic-pressure control mechanism  34  may be detected to be in the first abnormal state when at least one of the following conditions is satisfied: (i) a condition that the number of times in which the difference has been determined to be greater than the abnormality determination threshold  6   s  is greater than or equal to a first abnormality-determination number; (ii) a condition that a representative value is greater than the abnormality determination threshold  6   s , the representative value being a value obtained by statistically processing a plurality of differences obtained for the first set time at intervals of the cycle time; and (iii) a condition that the difference is greater than the abnormality determination threshold  6   s  at a time point when the first set time elapses. The abnormality determination threshold  6   s  may be determined based on a certain magnitude of the difference that is less likely to be generated when the upstream hydraulic-pressure control mechanism  34  is normal. 
     When the temperature of the working fluid is lower than the first set temperature, the detection value of the master cylinder pressure sensor  190  is obtained for the second set time at intervals of the cycle time, and it is determined whether the difference is greater than the abnormality determination threshold  6   s . The upstream hydraulic-pressure control mechanism  34  may be determined to be in the first abnormal state when at least one of the following conditions is satisfied: (i) a condition that the number of times in which the difference has been determined to be greater than the abnormality determination threshold  6   s  is greater than or equal to a second abnormality-determination number that is greater than the first abnormality-determination number; (ii) a condition that the representative value is greater than the abnormality determination threshold  6   s , the representative value being a value obtained by statistically processing the plurality of differences obtained for the second set time at intervals of the cycle time; and (iii) a condition that the difference is greater than the abnormality determination threshold  6   s  at a time point when the second set time elapses. 
     A first-abnormal-state detecting program of  FIG. 7  is executed by the controller  20  (the brake control device  200 ) at intervals of the predetermined cycle time. 
     At Step  101 , the actual upstream hydraulic pressure, which is the detection value of the master cylinder pressure sensor  190 , is obtained. (Step  101  is abbreviated as S 101 . Other steps are similarly abbreviated.) At S 102 , the target upstream hydraulic pressure is obtained. The target upstream hydraulic pressure is the total target hydraulic pressure. At S 103 , the temperature of the working fluid is obtained based on the detection value of the temperature sensor  216 . At S 104 , it is determined whether the temperature of the working fluid is lower than a first set temperature Temth 1 . When the temperature of the working fluid is not lower than the first set temperature, the control flow proceeds to S 105  at which monitoring for the actual upstream hydraulic-pressure is performed for the first set time. When the temperature of the working fluid is lower than the first set temperature, the control flow proceeds to S 106  at which the monitoring is performed for the second set time. At S 107 , it is determined whether the upstream hydraulic-pressure control mechanism  34  has been detected to be in the first abnormal state. When an affirmative determination (YES) is made at S 107 , an abnormality flag is set to ON at S 108 . 
     When the abnormality flag is set to ON, the remote parking control is suspended, the upstream hydraulic-pressure control mechanism  34  stops operating, and the downstream hydraulic-pressure control mechanism  33  is operated, as illustrated in  FIG. 11 . 
     In the downstream hydraulic-pressure control mechanism  33 , the pump device  158  is operated, and the hydraulic pressure in the wheel cylinders  36 ,  38  is controlled by the hydraulic pressure control valves  160 . 
     The hydraulic pressure on the downstream side of the hydraulic pressure control valves  160  corresponds to the hydraulic pressure in the wheel cylinders  36 ,  38 , and the hydraulic pressure on the upstream side of the hydraulic pressure control valves  160  corresponds to the hydraulic pressure in the pressurizing chambers  46 ,  47 . By controlling the supply current to the hydraulic pressure control valves  160 , the pressure difference between the hydraulic pressure on the upstream side and the hydraulic pressure on the downstream side is controlled, so that the hydraulic pressure in the wheel cylinders  36 ,  38  is made higher than the hydraulic pressure in the pressurizing chambers  46 ,  47 . 
     The pressure difference, which is obtained by subtracting the detection values of the wheel cylinder pressure sensors  192  from the detection value of the master cylinder pressure sensor  190 , is determined to be an actual downstream hydraulic pressure. The supply current to the hydraulic pressure control valves  160  is controlled in the operating state of the pump device  158  such that the actual downstream hydraulic pressure becomes close to the target downstream hydraulic pressure obtained based on the total target hydraulic pressure. In a stopped state of the upstream hydraulic-pressure control mechanism  34 , the actual downstream hydraulic pressure that corresponds to the pressure difference is substantially the same as the hydraulic pressure in the wheel cylinders  36 ,  38 , and the total target hydraulic pressure is determined to be the target downstream hydraulic pressure. 
     It takes, however, a long time for detecting whether the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state. This may cause in some cases a shortage of the braking force till a time point when the upstream hydraulic-pressure control mechanism  34  is detected to be in the first abnormal state. 
     On the other hand, if the downstream hydraulic-pressure control mechanism  33  is excessively or unnecessarily operated before it is detected whether the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state, the working fluid ejected from the pump device  158  may be supplied to the fluid passage  54 , and the detection value of the master cylinder pressure sensor  190  may sometimes vary. In this case, it is difficult to detect, with high accuracy, whether the upstream hydraulic-pressure control mechanism  34  is abnormal. 
     In view of the above, in a period before it is detected whether the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state, the downstream hydraulic-pressure control mechanism  33  is operated later when the temperature of the working fluid is low than when the temperature of the working fluid is high, to assist the braking force. In other words, the downstream hydraulic-pressure control mechanism  33  is operated after a lapse of an assist wait time from a time point of detection that the upstream hydraulic-pressure control mechanism  34  has reached the second abnormal state, the second abnormal state being a state that the upstream hydraulic-pressure control mechanism  34  reaches before reaching the first abnormal state. Further, the assist wait time is made longer when the temperature of the working fluid is low than when the temperature of the working fluid is high. 
     In the present embodiment, the memory of the controller  20  stores an assist-wait-time determination map. As illustrated in  FIG. 3 , the assist wait time is shorter when the temperature of the working fluid is high than when the temperature of the working fluid is low. (The assist wait time is shorter when the temperature of the working fluid is not lower than a second set temperature as a predetermined temperature than when the temperature of the working fluid is lower than the second set temperature.) For instance, the assist wait time may be made shorter continuously or in steps with an increase in the temperature. The assist-wait-time determination map may be obtained in advance by simulations, experiments, etc., or may be theoretically obtained in advance. 
     Though the second set temperature is illustrated in  FIG. 3  as a temperature lower than the normal temperature, the second set temperature may be a temperature higher than or equal to the normal temperature. 
     The second abnormal state of the upstream hydraulic-pressure control mechanism  34  is a state prior to detection that the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state. For instance, the monitoring time when detecting whether the upstream hydraulic-pressure control mechanism  34  is in the second abnormal state may be set to a third set time that is shorter than the first set time. When it is detected that the difference is greater than the abnormality determination threshold  6   s  as a result of the monitoring performed for the third set time, the upstream hydraulic-pressure control mechanism  34  may be detected to be in the second abnormal state. The third set time may be set as a length of time that is considerably shorter than the first set time. 
     Even when the upstream hydraulic-pressure control mechanism  34  is detected to be in the second abnormal state, the downstream hydraulic-pressure control mechanism  33  is not immediately operated. Accordingly, the braking force is sometimes insufficient in the remote parking control. Here, a case is considered in which a relationship between: the distance D between the object (such as a wall) present in the surroundings of the own vehicle and the own vehicle; and the running speed V of the own vehicle is a relationship in which the distance D is shorter or the running speed V is higher than a map representing a brake operation timing. In this case, the request for the operation of the hydraulic brakes  12 ,  14  is made in the remote parking control. The map that represents the brake operation timing is set so as to have a relationship in which the distance D is longer and the running speed V is lower when the temperature of the working fluid is low than when the temperature of the working fluid is high. 
     In the present embodiment, a brake-operation-timing determination map illustrated in  FIG. 4  is stored. The brake-operation-timing determination map is set such that the operation timing is earlier when the temperature of the working fluid is lower than a third set temperature Temth 3  than when the temperature of the working fluid is not lower than the third set temperature Temth 3 . When the temperature of the working fluid is not lower than the third set temperature, a normal-temperature-condition map indicated by the long dashed short dashed line is selected as the brake-operation-timing determination map, and the request for the operation of the hydraulic brakes  12 ,  14  is made in a case where the running speed V and the distance D fall within a dotted region in  FIG. 4 . (In a case where the object is a human or a three-dimensional object, the speed at which the own vehicle and the object approach each other may be considered as being substantially equal to the running speed of the own vehicle.) When the temperature of the working fluid is lower than the third set temperature, the low-temperature-condition map indicated by the solid line is selected as the brake-operation-timing determination map, and the request for the operation of the hydraulic brakes  12 ,  14  is made in a case where the running speed V and the distance D fall within a shaded region in  FIG. 4 . 
     As apparent from the low-temperature-condition map indicated by the solid line and the normal-temperature-condition map indicated by the long dashed short dashed line, the request for the operation of the hydraulic brakes  12 ,  14  is made at earlier timing when the temperature of the working fluid is low, as compared with when the temperature of the working fluid is high, and the request for the operation of the hydraulic brakes  12 ,  14  is made even if the running speed V is low and the distance D is large. 
     The third set temperature may be substantially the same as or different from the first set temperature or the second set temperature. Further, the first set temperature and the second set temperature may be substantially the same or different from each other. 
     The controller  20  executes a control-command-value generating program represented by a flowchart of  FIG. 5  at intervals of the predetermined cycle time. 
     At S 1 , it is determined whether the abnormality flag is ON. When a negative determination (NO) is made at S 1 , S 2  is implemented to obtain the temperature of the working fluid based on the detection value of the temperature sensor  216 . At S 3 , it is determined whether the temperature Tem of the working fluid is lower than the third set temperature Temth 3 . 
     When a negative determination (NO) is made at S 3 , S 4  is implemented to select the normal-temperature-condition map indicated by the long dashed short dashed line in  FIG. 4 . When an affirmative determination (YES) is made at S 3 , S 5  is implemented to select the low-temperature-condition map indicated by the solid line in  FIG. 4 . 
     At S 6 , the distance D between the own vehicle and the object is obtained. At S 7 , the running speed V of the own vehicle is obtained based on the detection values of the wheel speed sensors  194 , etc. 
     At S 8 , it is determined whether the distance D and the running speed V fall within a region in which the distance D is smaller or the running speed V is higher than those represented by the selected brake-operation-timing determination map, namely, it is determined whether the request for the operation of the hydraulic brakes  12 ,  14  is made. When an affirmative determination (YES) is made at S 8 , the control flow proceeds to S 9  at which the target deceleration as the control command value is generated. When a negative determination (NO) is made at S 8 , S 9  is not implemented. 
     When an affirmative determination (YES) is made at S 1 , S 2  and subsequent steps are not implemented because the remote parking control is not executed. 
     The brake control device  200  of the controller  20  executes a braking-force control program represented by a flowchart of  FIG. 6 . 
     At S 21 , it is determined whether the abnormality flag is ON. When a negative determination (NO) is made at S 21 , S 22  is implemented to determine whether the target deceleration is greater than a set deceleration Gs. The set deceleration Gs has a magnitude at which it is considered that there is a risk of a shortage of the braking force. For instance, the set deceleration Gs may have a magnitude at which it is considered that the assist control should be executed in a case where the braking force generated by the upstream hydraulic-pressure control mechanism  34  is small. Further, the set deceleration Gs may have a magnitude that enables the presence of the request for the operation of the hydraulic brakes  12 ,  14  to be surely recognized. At S 23 , the target upstream hydraulic pressure is obtained based on the target deceleration. At S 24 , the actual upstream hydraulic pressure that is the detection value of the master cylinder pressure sensor  190  is obtained. At S 25 , it is determined whether the difference is greater than the abnormality determination threshold  6   s.    
     When a negative determination (NO) is made at S 22  or S 25 , the control flow proceeds to S 26  at which an ordinary control is executed. In a case where the upstream hydraulic-pressure control mechanism  34  is not detected to be in the first abnormal state and the second abnormal state or in a case where the target deceleration is less than the set deceleration Gs, the upstream hydraulic-pressure control mechanism  34  is controlled to attain the target deceleration in the remote parking control. 
     When an affirmative determination (YES) is made at S 25 , the upstream hydraulic-pressure control mechanism  34  is detected to be in the second abnormal state. In the present embodiment, the upstream hydraulic-pressure control mechanism  34  is detected to be in the second abnormal state when it is determined once or more than once that the abnormality flag is OFF and the difference is not less than the abnormality determination threshold  6   s . In other words, a length of time, during which the difference is obtained and it is determined once or more than once that the difference is not less than the abnormality determination threshold  6   s , is considered as the third set time. 
     At S 27 , the temperature of the working fluid is obtained based on the detection value of the temperature sensor  216 . At S 28 , the assist wait time TW is determined according to the map of  FIG. 3 . When the temperature of the working fluid is a temperature Tem 1  that is not lower than the second set temperature, the assist wait time TW is determined to be an assist wait time TW 1 . When the temperature of the working fluid is a temperature Tem 2  that is lower than the second set temperature, the assist wait time TW is determined to be an assist wait time TW 2 . At S 29 , it is determined whether an elapsed time t, which is a time elapsed after an affirmative determination (YES) is made at S 25  for the first time, reaches the assist wait time TW. When an affirmative determination (YES) is made at S 29 , the control flow proceeds to S 30  at which the assist control is executed. When a negative determination (NO) is made at S 29 , the control flow proceeds to S 26  at which the ordinary control is executed. It is noted that an abnormal-state control is executed at S 31  when an affirmative determination (YES) is made at S 21 . 
     The target upstream hydraulic pressure may be taken into consideration in determining the assist wait time TW at S 28 . For instance, the assist wait time TW may be determined to be shorter when the target upstream hydraulic pressure is high than when the target upstream hydraulic pressure is low in a case where the temperature of the working fluid is the same. 
     One example of the ordinary control at S 26  is illustrated in  FIG. 8 . In the ordinary control, the pressure-increase control valve  94  and the pressure-decrease control valve  96  are controlled such that the actual upstream hydraulic pressure, which is the detection value of the master cylinder pressure sensor  190 , becomes close to the target upstream hydraulic pressure (corresponding to the total target hydraulic pressure). The ordinary control is executed when the upstream hydraulic-pressure control mechanism  34  is detected to be in the second abnormal state and before the assist wait time elapses. In the present embodiment, however, because the operation timing of the hydraulic brakes  12 ,  14  is obtained based on the brake-operation-timing determination map ( FIG. 4 ) determined based on the temperature of the working fluid, the shortage of the braking force in the remote parking control is prevented or reduced. 
     In the assist control at S 30 , a cooperative control by the upstream hydraulic-pressure control mechanism  34  and the downstream hydraulic-pressure control mechanism  33  is executed. The target downstream hydraulic pressure is obtained based on a value obtained by subtracting the actual upstream hydraulic pressure from the total target hydraulic pressure. The pump motor  156  is operated and the hydraulic pressure control valves  160  are controlled such that the pressure difference between a wheel cylinder pressure detected by the wheel cylinder pressure sensors  192  and a master cylinder pressure detected by the master cylinder pressure sensor  190 , i.e., the actual downstream hydraulic pressure, becomes close to the target downstream hydraulic pressure. 
     In a case where the temperature of the working fluid is the temperature Tem 1  that is not lower than the first set temperature as illustrated in  FIG. 9 , an affirmative determination (YES) is made at S 29  after a lapse of the assist wait time TW 1  from a time point of detection that the upstream hydraulic-pressure control mechanism  34  is in the second abnormal state, and the assist control is executed at S 30 . It is determined whether the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state after a lapse of the first set time. In a case where the upstream hydraulic-pressure control mechanism  34  is detected to be in the first abnormal state, an affirmative determination (YES) is made at S 21 , and the abnormal-state control is executed at S 31 . In the abnormal-state control, the target downstream hydraulic pressure that is the total target hydraulic pressure is determined to be the abnormal-state target hydraulic pressure irrespective of the target deceleration for the remote parking control determined by the control-command-value generating device  198 , and the downstream hydraulic-pressure control mechanism  33  is controlled. The hydraulic pressure control valves  160  are controlled such that the actual downstream hydraulic pressure becomes close to the abnormal-state target hydraulic pressure that is the target downstream hydraulic pressure. Because the upstream hydraulic-pressure control mechanism  34  is in a stopped state, the detection value of the master cylinder pressure sensor  190  is small, and the actual downstream hydraulic pressure is considered as being substantially equal to the hydraulic pressure in the wheel cylinders  36 ,  38 . 
     The abnormal-state target hydraulic pressure is a pressure level at which the abnormal-state target braking force and the abnormal-state target deceleration are attained. In other words, the actual downstream hydraulic pressure is controlled so as to become close to the abnormal-state target hydraulic pressure, so that the abnormal-state target braking force is applied to the vehicle in principle, and the deceleration of the vehicle is brought close to the abnormal-state target deceleration. 
     In a case where the temperature of the working fluid is the temperature Tem 2  that is lower than the first set temperature as illustrated in  FIG. 10 , the assist wait time is determined to be the assist wait time TW 2 . After a lapse of the assist wait time TW 2  from a time point of detection that the upstream hydraulic-pressure control mechanism  34  is in the second abnormal state, the assist control is executed at S 30 . In a case where the actual upstream hydraulic pressure is increased and the difference between the actual upstream hydraulic pressure and the target upstream hydraulic pressure becomes less than the abnormality determination threshold  6   s , the ordinary control is executed even before the second set time elapses. 
     In the present embodiment, timing at which the downstream hydraulic-pressure control mechanism  33  starts assisting the braking force (i.e., assist timing) is later when the temperature of the working fluid is low than when the temperature of the working fluid is high. This configuration prevents or reduces a decrease in the accuracy of detecting whether the upstream hydraulic-pressure control mechanism  34  is in the first abnormal state even in a case where the temperature of the working fluid is low and the delay in actuation of the upstream hydraulic-pressure control mechanism  34  is caused. In the remote parking control, the hydraulic brakes  12 ,  14  are operated more readily when the temperature of the working fluid is low than when the temperature of the working fluid is high. This configuration obviates disadvantages in the remote parking control that arise from a delay in the assist timing, improving safety in the remote parking control. 
     In the present embodiment, the first-abnormal-state detecting device includes, for instance, portions of the controller  20  that store and execute the first-abnormal-state detecting program. The second-abnormal-state detecting device includes, for instance, portions of the controller  20  that store and execute S 23 -S 25  of the hydraulic pressure control program. The first-actual-hydraulic-pressure obtaining device includes, for instance, the master cylinder pressure sensor  190  and portions of the controller  20  that store and execute S 101 , S 24 . The assist-wait-time determining device incudes, for instance, a portion of the controller  20  that store the map of  FIG. 3  and portions of the controller  20  that store and execute S 27 , S 28 . The assist control device includes, for instance, portions of the controller that store and execute S 30 . The abnormal-state control device includes, for instance, portions of the controller that store and execute S 31 . The control-command-value generating device includes, for instance, portions of the controller that store and execute the control-command-value generating program. The brake control device includes, for instance, portions of the controller  20  that store and execute the braking-force control program. The first actual hydraulic pressure corresponds to the actual upstream hydraulic pressure, and the first target hydraulic pressure corresponds to the target upstream hydraulic pressure. 
     In the embodiment illustrated above, the control of the hydraulic pressure in the hydraulic brakes  12 ,  14  in the remote parking control has been explained. The control of the hydraulic pressure in the hydraulic brakes  12 ,  14  described above is widely applicable to a case in which automatic braking is performed, in addition to the case in which the remote parking control is executed. 
     The controller  20  may have any suitable configuration. The controller  20  may include a plurality of ECUs or may include a single ECU. One example of an arrangement in which the controller  20  includes a plurality of ECUs will be explained referring to  FIG. 12 . It is noted that the same reference signs as used in  FIG. 1  are used to identify the corresponding constituent elements in  FIG. 12 , and an explanation thereof is dispensed with. 
     As illustrated in  FIG. 12 , the controller  20  is constituted by a plurality of ECUs  230 ,  232 ,  236 ,  238 , etc., each of which is constituted principally by a computer. The plurality of ECUs  230 - 238  are communicably connected to one another via a central gate way (CGW)  246 , buses  248 - 252 , etc. The digital cameras  212 , the sonar  214 , the temperature sensor  216  are connected to the bus  248 . Image information obtained by the digital cameras  212 , information obtained by the sonar  214 , the temperature detected by the temperature sensor  216  are suppliable to the plurality of ECUs  230 ,  232 ,  236 ,  238  etc. 
     The ECU  230  is a panoramic view monitor (PVM) ECU  230 . The PVM ECU  230  includes an image recognizing device that recognizes a three-dimensional object, a human, a lane line etc., in the surroundings of the vehicle. The PVM ECU  230  forms a panoramic image based on images taken by the plurality of digital cameras  212 , for instance. 
     The ECU  232  is a clearance sonar (CSR) ECU  232 . The CSR ECU  232  includes a route and running-plan creating device, a vehicle control device, etc. The route and running-plan creating device performs image recognition based on information representative of the panoramic image supplied from the PVM ECU  230 , information from the sonar  214 , etc. The route and running-plan creating device creates an overhead view image and creates a route and a running plan according to which the vehicle is moved to the target parking position. Based on the route and the running plan created by the route and running-plan creating device, for instance, the vehicle control device generates a control command value for the brake system and outputs the generated control command value to a driving manager  242 . Based on the overhead view image, the route and running-plan generating device obtains the distance D between the own vehicle and the object present in the surroundings of the own vehicle such as a three-dimensional object or a human. The route and running-plan generating device may create the running plan by obtaining the operation timing of the hydraulic brakes  12 ,  14  based on the obtained distance D and the temperature of the working fluid obtained based on the detection value of the temperature sensor  216 , for instance. 
     The ECU  236  is an upstream brake ECU  236 . The upstream hydraulic-pressure control mechanism  34  is connected to the upstream brake ECU  236 . The upstream hydraulic-pressure control mechanism  34  supplies, to the upstream brake ECU  236 , the detection values of the sensors such as the servo pressure sensor  132  included in the upstream hydraulic-pressure control mechanism  34 . The upstream brake ECU  236  outputs, to the upstream hydraulic-pressure control mechanism  34 , the control command value for the pump motor  88  and the solenoids of the electromagnetic valves such as the pressure-increase control valve  94  and the pressure-decrease control valve  96 . 
     The ECU  238  is a downstream brake ECU  238 . The downstream hydraulic-pressure control mechanism  33  is connected to the downstream brake ECU  238 . The downstream hydraulic-pressure control mechanism  33  supplies, to the downstream brake ECU  238 , the detection values of the plurality of sensors such as the master cylinder pressure sensor  190  included in the downstream hydraulic-pressure control mechanism  33 . The downstream brake ECU  238  outputs, to the downstream hydraulic-pressure control mechanism  33 , the control command value for the pump motor  156 , the solenoids of the electromagnetic valves such as the hydraulic pressure control valves  160  and the pressure-hold valves  170 , and the parking brake actuator  188 . Though the driving manager  242  is included in the downstream brake ECU  238 , the driving manager  242  controls the downstream hydraulic-pressure control mechanism  33  based on the control command value supplied from the vehicle control device of the CSR ECU  232  and supplies the control command value to the upstream brake ECU  236 . The control command value is supplied also to the HV/EFI control device and the EPS control device. The upstream brake ECU  236  controls the upstream hydraulic-pressure control mechanism  34  based on the control command value. 
     The programs described above may be executed by any of the plurality of ECUs of the controller  20 . For instance, the first-abnormal-state detecting program of  FIG. 7  and the braking-force control program of  FIG. 6  may be executed by at least one of the upstream brake ECU  236  and the downstream brake ECU  238 . The control-command-value generating program of  FIG. 5  may be executed by at least one of the CSR ECU  232  and the downstream brake ECU  202 . 
     The temperature sensor  216  may include at least one of a temperature sensor used in the CSR ECU 232  and a temperature sensor used in the downstream brake ECU  238 . 
     The present disclosure is applicable to hybrid vehicles, battery electric vehicles, engine-driven vehicles, etc. A parking lock mechanism may be operated instead of operating parking brakes when the vehicle stops. In this case, the upstream brake ECU  236  supplies a parking lock command to an SBW ECU (SBW control device) not illustrated. 
     It is to be understood that the present disclosure is not limited to the details of the illustrated embodiment, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and the scope of the disclosure. For instance, the brake circuit may have any configuration. 
     Claimable Invention 
     (1) A brake system for a vehicle, comprising: 
     a first hydraulic-pressure control mechanism configured to control a hydraulic pressure in a plurality of hydraulic brakes respectively provided for a plurality of wheels of the vehicle to thereby control a braking force to be applied to the vehicle; 
     a second braking-force control mechanism configured to control the braking force, the second braking-force control mechanism being different from the first hydraulic-pressure control mechanism; and 
     a controller including a first-abnormal-state detecting device configured to detect whether the first hydraulic-pressure control mechanism is in a first abnormal state as an abnormal state, 
     wherein the controller is configured to: 
     control the first hydraulic-pressure control mechanism so as to control the braking force when the first-abnormal-state detecting device does not detect that the first hydraulic-pressure control mechanism is in the first abnormal state; and 
     control not the first hydraulic-pressure control mechanism but the second braking-force control mechanism so as to control the braking force when the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state, 
     wherein the brake system comprises a temperature obtaining device configured to obtain a temperature of a working fluid in the brake system, 
     wherein the controller includes: 
     a second-abnormal-state detecting device configured to detect whether the first hydraulic-pressure control mechanism is in a second abnormal state, the second abnormal state being a state that the first hydraulic-pressure control mechanism reaches before reaching the first abnormal state; and 
     an assist control device configured to control the second braking-force control mechanism so as to control the braking force when an assist wait time elapses after the second-abnormal-state detecting device has detected that the first hydraulic-pressure control mechanism is in the second abnormal state, the assist wait time being determined based on the temperature of the working fluid obtained by the temperature obtaining device. 
     Both the first hydraulic-pressure control mechanism and the second braking-force control mechanism are capable of controlling the braking force to the magnitude greater than or equal to 0. In other words, the first hydraulic-pressure control mechanism and the second braking-force control mechanism are capable of generating and controlling the braking force. 
     The first abnormal state of the first hydraulic-pressure control mechanism refers to a state in which the hydraulic pressure in the hydraulic brakes is difficult to be controlled in the first hydraulic-pressure control mechanism. The first abnormal state of the first hydraulic-pressure control mechanism is caused in most cases due to an abnormality of the drive source and/or the control system elements included in the first hydraulic-pressure control mechanism or an abnormality in which sufficient electric power is not supplied to the constituent elements of the first hydraulic-pressure control mechanism such as the drive source, for instance. 
     The second abnormal state of the first hydraulic-pressure control mechanism refers to a state that precedes a state in which the first hydraulic-pressure control mechanism is detected to be in the first abnormal state. For instance, the second abnormal state refers to a state in which it is highly probable that the first hydraulic-pressure control mechanism is detected to be in the first abnormal state. 
     The temperature obtaining device obtains the temperature of the working fluid in the brake system. The temperature obtaining device may obtain the outside air temperature as the temperature of the working fluid. The temperature obtaining device may estimate the temperature of the working fluid based on the outside air temperature and the operating time of the brake system, for instance. 
     The second braking-force control mechanism may be a second hydraulic-pressure control mechanism configured to control the hydraulic pressure in the hydraulic brakes, an electric braking-force control mechanism configured to control the braking force of electric brakes provided for the wheels, or a regenerative braking-force control mechanism configured to control a regenerative braking force applied to the vehicle. 
     The assist wait time may be a length of time that is shorter when the temperature of the working fluid is high than when the temperature of the working fluid is low. 
     When the first-abnormal-state detecting device does not detect that the first hydraulic-pressure control mechanism is in the first abnormal state, the controller controls not the second braking-force control mechanism but the first hydraulic-pressure control mechanism so as to control the braking force. When the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state, the controller controls not the first hydraulic-pressure control mechanism but the second braking-force control mechanism so as to control the braking force. 
     After a lapse of the assist wait time, the assist control device may control the second braking-force control mechanism without stopping controlling the first hydraulic-pressure control mechanism, so as to control the braking force. 
     (2) The brake system according to the form (1), comprising a first-actual-hydraulic-pressure obtaining device configured to obtain a first actual hydraulic pressure at intervals of a predetermined cycle time, the first actual hydraulic pressure being an actual hydraulic pressure in the plurality of hydraulic brakes generated by an operation of the first hydraulic-pressure control mechanism, 
     wherein, when the temperature of the working fluid obtained by the temperature obtaining device is not lower than a first set temperature, the first-abnormal-state detecting device monitors, for a first set time, the first actual hydraulic pressure obtained by the first-actual-hydraulic-pressure obtaining device, 
     wherein the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state when a difference between the first actual hydraulic pressure and a first target hydraulic pressure is greater than an abnormality determination threshold, 
     wherein, when the temperature of the working fluid is lower than the first set temperature, the first-abnormal-state detecting device monitors, for a second set time that is longer than the first set time, the first actual hydraulic pressure obtained by the first-actual-hydraulic-pressure obtaining device, 
     wherein the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state when the difference is greater than the abnormality determination threshold, 
     wherein the second-abnormal-state detecting device monitors, for a third set time that is shorter than the first set time, the first actual hydraulic pressure obtained by the first-actual-hydraulic-pressure obtaining device, and 
     wherein the second-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the second abnormal state when the difference is greater than the abnormality determination threshold. 
     The third set time may be a length of time in which the first actual hydraulic pressure is obtained by the first-actual-hydraulic-pressure obtaining device and whether the difference is greater than the abnormality determination threshold can be determined once or more than once. 
     (3) The brake system according to the form (1) or (2), wherein the controller includes an assist-wait-time determining device configured to determine the assist wait time such that the assist wait time is longer when the temperature of the working fluid obtained by the temperature obtaining device is lower than a second set temperature than when the temperature of the working fluid is not lower than the second set temperature. 
     The second set temperature may be the same as or different from the first set temperature. The assist wait time may be made shorter continuously or discontinuously with an increase in the temperature. 
     (4) The brake system according to any one of the forms (1)-(3), wherein the controller is configured to determine an operation timing of at least one of the first hydraulic-pressure control mechanism and the second braking-force control mechanism such that the operation timing is earlier when the temperature of the working fluid obtained by the temperature obtaining device is low than when the temperature of the working fluid is high. 
     The present system may execute an automatic brake control in which the braking force is automatically applied to the own vehicle that is the vehicle on which the present brake system is installed, based on the relative positional relationship between the own vehicle and the object or the like present in the surroundings of the own vehicle. For instance, the automatic brake control may be a control executed in ordinary running of the own vehicle or running for parking. Further, the automatic brake control may be a control executed when the driver is on the vehicle or a control executed when the driver is not on the vehicle (unattended control). 
     (5) The brake system according to the form (4), wherein, in a case where the temperature of the working fluid obtained by the temperature obtaining device is not lower than a third set temperature, the controller causes at least one of the first hydraulic-pressure control mechanism and the second braking-force control mechanism to be operated when a relative positional relationship between the vehicle and an object present in surroundings of the vehicle is a first set relationship, and 
     wherein, in a case where the temperature of the working fluid is lower than the third set temperature, the controller causes at least one of the first hydraulic-pressure control mechanism and the second braking-force control mechanism to be operated even when the relative positional relationship between the vehicle and object is a second set relationship in which the vehicle and the object are less likely to approach each other than in the first set relationship. 
     The second set relationship may be determined as a relative positional relationship in which the approach speed of the vehicle and the object present in the surroundings of the vehicle is lower and the distance between the vehicle and the object present in surroundings of the vehicle is greater than those in the first set relationship. 
     (6) The brake system according to any one of the forms (1)-(5), wherein the controller includes an abnormal-state control device configured to control the second braking-force control mechanism so as to control the braking force to be not less than a predetermined abnormal-state target braking force when the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state. 
     (7) The brake system according to any one of the forms (1)-(6), 
     wherein the controller includes: 
     a control-command-value generating device configured to generate a control command value based on a running state of the vehicle; and 
     a brake control device configured to control at least one of the first hydraulic-pressure control mechanism and the second braking-force control mechanism based on the control command value generated by the control-command-value generating device, so as to control the braking force. 
     The control-command-value generating device generates the control command value based on the running state of the vehicle. The running state of the vehicle may be represented by the running route of the vehicle, the running speed of the vehicle, etc. When a running direction of the vehicle is changed based on the running route of the vehicle, for instance, the vehicle needs to be stopped in some cases. In this instance, the control command value for stopping the vehicle is generated. In a case where an object such as a three-dimensional object or a human is present in the surroundings of the vehicle, the vehicle needs to be stopped for avoiding a collision with the object. In this instance, the control command value is generated based on the approach speed of the vehicle and the object (obtained based on the running speed of the vehicle) and the distance between the vehicle and the object, for instance. 
     (8) The brake system according to the form (7), 
     wherein the control-command-value generating device is configured to generate a target deceleration as the control command value, 
     wherein the brake control device controls the first hydraulic-pressure control mechanism based on the target deceleration when the first-abnormal-state detecting device does not detect that the first hydraulic-pressure control mechanism is in the first abnormal state, and 
     wherein the brake control device stops the first hydraulic-pressure control mechanism from operating and controls the second braking-force control mechanism based on an abnormal-state target deceleration that is greater than the target deceleration when the first-abnormal-state detecting device detects that the first hydraulic-pressure control mechanism is in the first abnormal state. 
     (9) The vehicle brake system according to any one of the forms (1)-(8), 
     wherein the first hydraulic-pressure control mechanism includes: a master cylinder including a pressurizing piston; and a rear-hydraulic-pressure control device configured to control a hydraulic pressure in a rear chamber provided rearward of the pressurizing piston, and 
     wherein the rear-hydraulic-pressure control device is configured to control a hydraulic pressure in the rear chamber to cause the pressurizing piston to move forward and to thereby control a hydraulic pressure in a pressurizing chamber provided forward of the pressurizing piston. 
     (10) The brake system according to any one of the forms (1)-(9), wherein the second braking-force control mechanism includes: a pump device disposed between the first hydraulic-pressure control mechanism and wheel cylinders of the plurality of hydraulic brakes and configured to pump up and pressurize a working fluid and to supply the pressurized working fluid to the wheel cylinders; and hydraulic pressure control valves configured to control a hydraulic pressure in the wheel cylinders utilizing a hydraulic pressure of the working fluid ejected from the pump device. 
     (11) The brake system according to any one of the forms (1)-(10), wherein the controller is configured to determine the assist wait time such that the assist time is shorter when a target hydraulic pressure for the first hydraulic-pressure control mechanism is high than when the target hydraulic pressure for the first hydraulic-pressure control mechanism is low. 
     (12) A brake system for a vehicle, comprising: 
     a first braking-force control mechanism configured to control a braking force to be applied to the vehicle; 
     a second braking-force control mechanism configured to control the braking force, the second braking-force control mechanism being different from the first braking-force control mechanism; 
     a first-abnormal-state detecting device configured to detect whether the first braking-force control mechanism is in a first abnormal state as an abnormal state; and 
     a controller configured to: 
     control the first braking-force control mechanism so as to control the braking force when the first-abnormal-state detecting device does not detect that the first braking-force control mechanism is in the first abnormal state; and 
     control not the first braking-force control mechanism but the second braking-force control mechanism so as to control the braking force when the first-abnormal-state detecting device detects that the first braking-force control mechanism is in the first abnormal state, 
     wherein the brake system includes: 
     a temperature obtaining device configured to obtain a temperature of the brake system; and 
     a second-abnormal-state detecting device configured to detect whether the first hydraulic-pressure control mechanism is in a second abnormal that the first hydraulic-pressure control mechanism reaches before reaching the first abnormal state, and 
     wherein the controller includes an assist control device configured to control the second braking-force control mechanism so as to control the braking force when an assist wait time elapses after the second-abnormal-state detecting device has detected that the first braking-force control mechanism is in the second abnormal state, the assist wait time being determined based on the temperature of the brake system obtained by the temperature obtaining device. 
     The brake system according to this form may employ the technical features described in any of the forms (1)-(11).