Patent Publication Number: US-2023140171-A1

Title: Brake state estimation device and vehicle equipped therewith, brake state estimating method, and recording medium storing program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-176664 filed on Oct. 28, 2021, the disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a brake state estimation device and a vehicle equipped therewith, and to a brake state estimating method and a program. 
     Related Art 
     Japanese Patent Application Laid-Open (JP-A) No. 2019-119401 discloses a brake device monitoring system having a sensor that is built into a banjo bolt used at the time of connecting the brake hose to the brake caliper, and notifying means for notifying the driver of a parameter expressing the state of the brake fluid which parameter is generated on the basis of a sensor signal sensed by the sensor. 
     In the technique disclosed in JP-A No. 2019-119401, the sensor must be mounted separately in order to detect the state of the brake fluid. 
     SUMMARY 
     In view of the above-described circumstances, an object of the present disclosure is to estimate the state of deterioration of brake fluid by a simple structure. 
     A first aspect is a brake state estimation device including: a position acquisition section that acquires a position of a subject vehicle; and a state estimation section that estimates a state of deterioration of brake fluid for operating a hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to a position of the subject vehicle, and of duration information expressing a duration of stay in an area that includes the position of the subject vehicle. 
     In the brake state estimation device of the first aspect, the position acquisition section acquires the position of the subject vehicle. Further, the state estimation section estimates the state of deterioration of brake fluid for operating the hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to the position of the subject vehicle, and duration information expressing the duration of staying in an area that includes the position of the subject vehicle. Here, “humidity information” is information relating to the humidity at the position of the subject vehicle, and means information relating to the amount of moisture contained in the brake fluid of the subject vehicle. Further, “state of deterioration of the brake fluid” means the state relating to the occurrence of vapor lock of the brake fluid. In accordance with this brake state estimation device, the state of deterioration of the brake fluid can be estimated by a simple structure. 
     A brake state estimation device of a second aspect further includes, in the brake state estimation device of the first aspect, a temperature acquisition section that acquires a temperature of the brake device, wherein the state estimation section estimates the state of deterioration of the brake fluid on the basis of the temperature of the brake device, the humidity information, and the duration information. 
     The brake state estimation device of the second aspect further acquires the temperature of the brake device, and estimates the state of deterioration of the brake fluid on the basis of the temperature of the brake device, the humidity information, and the duration information. In accordance with this brake state estimation device, the state of deterioration of the brake fluid can be estimated accurately. 
     In a brake state estimation device of a third aspect, in the brake state estimation device of the second aspect, the state estimation section estimates a state of moisture contained in the brake fluid on the basis of the humidity information and the duration information, estimates a heat state of the brake fluid on the basis of the temperature of the brake device, and estimates the state of deterioration of the brake fluid on the basis of the moisture state and the heat state. 
     The brake state estimation device of the third aspect estimates the state of moisture contained in the brake fluid on the basis of the humidity information and the duration information, and estimates the heat state of the brake fluid on the basis of the temperature of the brake device, and estimates the state of deterioration of the brake fluid on the basis of the moisture state and the heat state. In accordance with this brake state estimation device, the state of deterioration of the brake fluid can be estimated accurately while taking the moisture state and the heat state of the brake fluid into consideration. 
     In a brake state estimation device of a fourth aspect, in the brake state estimation device of the second aspect, the state estimation section estimates the state of deterioration by using a learned model for estimating the state of deterioration of the brake fluid on the basis of the temperature of the brake device, the humidity information and the duration information. 
     In the brake state estimation device of the fourth aspect, the state of deterioration is estimated by using a learned model for estimating the state of deterioration of the brake fluid on the basis of the temperature of the brake device, the humidity information and the duration information. In accordance with this brake state estimation device, the state of deterioration of the brake fluid can be estimated accurately. 
     A vehicle of a fifth aspect includes: the brake state estimation device of any of the first through fourth aspects; and a hydraulic brake device. 
     The vehicle of the fifth aspect has the hydraulic brake device, and estimates the state of deterioration of the brake fluid of the hydraulic brake device. In accordance with this vehicle, the state of deterioration of the brake fluid can be estimated by a simple structure. 
     A brake state estimation method of a sixth aspect includes: acquiring, by a position acquisition section, a position of a subject vehicle; and estimating, by a state estimation section, a state of deterioration of brake fluid for operating a hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to a position of the subject vehicle, and of duration information expressing a duration of stay in an area that includes the position of the subject vehicle. 
     The sixth aspect is a brake state estimating method in which the position acquisition section acquires the position of a subject vehicle, and the state estimation section estimates the state of deterioration of brake fluid for operating the hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to the position of the subject vehicle, and duration information expressing the duration of staying in an area that includes the position of the subject vehicle. In accordance with this brake state estimating method, the state of deterioration of the brake fluid can be estimated by a simple structure. 
     A seventh aspect is a non-transitory recording medium storing a program for causing a computer to execute: acquiring a position of a subject vehicle; and estimating a state of deterioration of brake fluid for operating a hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to a position of the subject vehicle, and of duration information expressing a duration of stay in an area that includes the position of the subject vehicle. 
     In the program that is recorded on a non-transitory recording medium of the seventh aspect, the computer acquires the position of a subject vehicle. Further, the computer estimates the state of deterioration of brake fluid for operating the hydraulic brake device of the subject vehicle, on the basis of humidity information corresponding to the position of the subject vehicle, and duration information expressing the duration of staying in an area that includes the position of the subject vehicle. In accordance with this program, the state of deterioration of the brake fluid can be estimated by a simple structure. 
     In accordance with the present disclosure, the state of deterioration of brake fluid can be estimated by a simple structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG.  1    is a drawing illustrating the schematic structure of a vehicle system relating to first, second and third embodiments; 
         FIG.  2    is a schematic drawing illustrating the structure of a brake device of a vehicle relating to the first, second and third embodiments; 
         FIG.  3    is a block drawing illustrating hardware structures of the vehicle relating to the first, second and third embodiments; 
         FIG.  4    is a block drawing illustrating an example of functional structures of a CPU of a control ECU at onboard devices of the first and second embodiments; 
         FIG.  5    is a graph showing the relationship between moisture amount and duration, per area; 
         FIG.  6    is a graph illustrating the relationship between moisture amount and duration in a case of staying in plural areas; 
         FIG.  7    is a drawing illustrating an example of display of results of estimating the state of deterioration of brake fluid; 
         FIG.  8    is a flowchart illustrating an example of the flow of brake state estimating processing that is executed at the CPU of the control ECU at the onboard devices of the first embodiment; 
         FIG.  9    is a flowchart illustrating an example of the flow of brake state estimating processing that is executed at the CPU of the control ECU at the onboard devices of the second embodiment; 
         FIG.  10    is a block drawing illustrating hardware structures of a managing server of the third embodiment; and 
         FIG.  11    is a block drawing illustrating an example of functional structures of a CPU of a control device at the managing server of the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A vehicle system relating to embodiments of the present disclosure is described by using  FIG.  1    through  FIG.  11   . 
     First Embodiment 
       FIG.  1    is a block drawing illustrating the schematic structure of a vehicle system  10  relating to a first embodiment. 
     (Overall Structure) 
     As illustrated in  FIG.  1   , the vehicle system  10  relating to the present embodiment includes a vehicle  12  and a managing server  16 . 
     The vehicle  12  and the managing server  16  are respectively structured so as to be able to communicate via network N. Here, the vehicle  12  has a communication section  14  that is connected to the network N. The network N includes a mobile communications service such as 3G, LTE or the like, or an internet line. 
     (Vehicle) 
     The vehicle  12  has a hydraulic brake device  18 . As illustrated in  FIG.  2   , the brake device  18  is structured to include a brake pedal  40  that is provided at the driver&#39;s seat and is operated by being depressed by the driver, a brake booster  42  that increases the depressing force applied to the brake pedal  40 , a master cylinder  44  provided integrally with the brake booster  42  and generating hydraulic pressure of brake fluid  48  corresponding to the stepping force applied to the brake pedal  40 , a brake pipe  46  connecting the master cylinder  44  and brake mechanisms (e.g., brake discs) of the respective wheels, a reservoir tank  50  that is provided at the upper portion of the master cylinder  44  and in which the brake fluid  48  is stored such that the brake fluid  48  is injected into and always filled into the brake pipe  46 , and a hydraulic pressure sensor  52  that detects the hydraulic pressure of the brake fluid  48  within the brake pipe  46 . Note that the hydraulic pressure sensor  52  may be provided at a brake actuator (not illustrated) for controlling the brakes of an ABS (Antilock Brake System) or the like. 
     As illustrated in  FIG.  3   , onboard devices  11  that are installed in the vehicle  12  include a control ECU (Electronic Control Unit)  20 , a temperature sensor  22 , a vehicle speed sensor  24 , a hybrid ECU  26  and the communication section  14 . 
     The temperature sensor  22  detects the air temperature at the periphery of the vehicle  12 . The vehicle speed sensor  24  detects the vehicle speed of the vehicle  12 . On the basis of signals from various sensors including an accelerator opening sensor (not illustrated), the vehicle speed sensor  24  and the like, the hybrid ECU  26  sets the operation mode (engine running mode, motor running mode, or the like), and sets the engine torque and the motor torque, and commands an engine ECU (not illustrated) and a motor ECU (not illustrated). Further, the hybrid ECU  26  detects the regeneration amount of the motor. 
     The control ECU  20  is structured to include a CPU (Central Processing Unit)  20 A, a ROM (Read Only Memory)  20 B, a RAM (Random Access Memory)  20 C, a storage  20 D and an input/output I/F (Inter Face)  20 E. The CPU  20 A, the ROM  20 B, the RAM  20 C and the input/output I/F  20 E are connected so as to be able to communicate with one another via an unillustrated internal bus. The CPU  20 A is an example of the processor, and the RAM  20 C is an example of the memory. 
     The CPU  20 A is a central computing processing unit, and executes various programs and controls the respective sections. Namely, the CPU  20 A reads-out programs from the ROM  20 B, and executes the programs by using the RAM  20 C as a workspace. 
     The ROM  20 B stores various programs and various data. The RAM  20 C temporarily stores programs and data as a workspace. 
     A brake state estimating program  100  is stored in the storage  20 D. The storage  20 D is structured by, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive). 
     The input/output I/F  20 E is an interface for communicating with the brake device  18 , the temperature sensor  22 , the vehicle speed sensor  24 , the hybrid ECU  26  and the communication section  14 , respectively. 
     With braking fluid, there is the problem that the stopping distance increases due to a phenomenon called vapor lock. Vapor lock affects the boiling point of brake fluid. The amount of moisture, which is a cause of a decrease in the boiling point, is determined by the total heat load, the duration and the humidity. 
     Current systems are setups in which leaking of brake fluid is detected by a sensor at the reservoir tank. The total amount of the brake fluid is detected by the sensor, but how much moisture is contained in the brake fluid itself and the state of deterioration of the brake fluid cannot be judged objectively or quantitatively. 
     Even if automobile manufacturers set the time for replacement to be at the time of the mandatory vehicle inspection which is every two years, the state of the brake fluid also depends on the traveling situation of the vehicle, and therefore, the brake fluid replacement time is not always uniform. For example, the replacement time may be earlier or may be later, depending on the dirtying of and the deteriorated state of the brake fluid. Ultimately, Japanese automobile manufacturers basically uniformly recommend that the replacement time of the brake fluid be replacement at the time of each mandatory vehicle inspection. 
     The psychology of a user who is having their vehicle inspected may include the point that, if dirtying of the brake fluid cannot be visually recognized, it would be better to reduce the costs of the mandatory vehicle inspection. Actual circumstances are that there are vehicles in which, in cases in which the vehicle undergoes an owner-performed inspection or an inspection at a privately-owned business, the brake fluid of the vehicle may not be replaced. 
     In this way, a method of judging the actual deteriorated state of the brake fluid because the brake pipe into which the brake fluid is injected is closed-off, is a method using the amount in the reservoir tank and the color of the brake fluid. Immediately after replacing brake fluid, the brake fluid is substantially transparent, but, as the brake fluid deteriorates, it changes from transparent to yellow to brown and then to black. In many vehicles, the color of the brake fluid is yellow, and the deteriorated state cannot be judged from the color of the brake fluid. 
     Thus, in the present embodiment, the onboard devices  11  estimate the state of deterioration of the brake fluid by using traveling data of the vehicle. 
     Specifically, as illustrated in  FIG.  4   , at the control ECU  20  of the present embodiment, due to the CPU  20 A executing the brake state estimating program  100 , the CPU  20 A functions as a position acquiring section  30 , an information acquiring section  32 , a temperature acquiring section  34 , and a state estimating section  36 . 
     The position acquiring section  30  acquires the position of the vehicle  12 . The position acquiring section  30  acquires the longitude and latitude of the position of the vehicle  12  from, for example, a navigation system installed in the vehicle  12 . 
     On the basis of the position of the vehicle  12  acquired by the position acquiring section  30 , the information acquiring section  32  acquires duration information that expresses the duration of staying in an area that includes the position of the vehicle. Further, on the basis of the position of the vehicle  12  acquired by the position acquiring section  30 , the information acquiring section  32  acquires humidity information. For example, the information acquiring section  32  transmits the position of the vehicle  12 , which was acquired by the position acquiring section  30 , to the managing server  16  by the communication section  14 , and acquires, from the managing server and as humidity information corresponding to the position of the vehicle  12 , a factor expressing the relationship between the duration and the amount of moisture contained in the brake fluid, which relationship is determined in advance for the area that includes the position of the vehicle  12 . 
     The temperature acquiring section  34  acquires the temperature of the brake device  18 . Specifically, the temperature acquiring section  34  computes the temperature of the brake device  18  on the basis of the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 . 
     For example, each predetermined time period, the temperature acquiring section  34  acquires the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 . The temperature acquiring section  34  computes temperature TR of the brake disc by cumulatively estimating a change amount ΔT of the temperature of the brake disc during Δt seconds, in accordance with following formula (1) and formula (2). 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     T 
                   
                   = 
                   
                     
                       
                         Q 
                         in 
                       
                       - 
                       
                         Q 
                         out 
                       
                     
                     
                       
                         W 
                         b 
                       
                       * 
                       C 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   
                     T 
                     R 
                   
                   = 
                   
                     
                       T 
                       before 
                     
                     + 
                     
                       Δ 
                       ⁢ 
                       T 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Here, Q in  is the brake absorption energy, Q out  is the brake heat dissipation energy, W b  is the weight of the sliding portion of the brake disc, C is the specific heat, and T before  is the temperature of the brake disc before Δt seconds. Further, Δt is the sampling period. 
     The brake absorption energy Q in  at the time of braking is expressed by the following formula. 
     
       
         
           
             
               Q 
               in 
             
             = 
             
               P 
               * 
               
                 A 
                 b 
               
               * 
               2 
               * 
               μ 
               * 
               
                 V 
                 
                   2 
                   ⁢ 
                   π 
                   ⁢ 
                   R 
                 
               
               * 
               2 
               ⁢ 
               π 
               ⁢ 
               R 
               * 
               Δ 
               ⁢ 
               t 
             
           
         
       
     
     Here, P is the hydraulic pressure of the brake fluid  48 , A b  is the surface area of the sliding portion of the brake disc, ρ is the coefficient of friction of the pad, and R is the braking effective radius (the distance between the tire center and the caliper piston center). 
     Further, at times other than the time of braking, in cases in which regenerative braking is not considered, the brake absorption energy Q in  is expressed by the following formula. 
     
       
         
           
             
               Q 
               in 
             
             = 
             
               
                 
                   1 
                   2 
                 
                 ⁢ 
                 
                   M 
                   ⁡ 
                   ( 
                   
                     
                       V 
                       2 
                     
                     - 
                     
                       V 
                       before 
                       2 
                     
                   
                   ) 
                 
                 * 
                 α 
               
               ⋆ 
               
                 
                   C 
                   1 
                 
                 * 
                 
                   C 
                   2 
                 
                 * 
                 
                   1 
                   2 
                 
               
             
           
         
       
     
     Here, M is the weight of the vehicle  12 , V is the vehicle speed, V before  is the vehicle speed Δt seconds before, α is the braking force distribution, C 1  is the traveling resistance loss factor, and C 2  is the heat loss factor at other than the sliding portion of the disc brake. 
     Further, at times other than the time of braking, in cases in which regenerative braking is taken into consideration, the brake absorption energy Q in  is expressed by the following formula. 
     
       
         
           
             
               Q 
               in 
             
             = 
             
               
                 
                   
                     1 
                     2 
                   
                   ⁢ 
                   
                     M 
                     ⁡ 
                     ( 
                     
                       
                         V 
                         2 
                       
                       - 
                       
                         V 
                         before 
                         2 
                       
                     
                     ) 
                   
                   * 
                   α 
                 
                 ⋆ 
                 
                   
                     C 
                     1 
                   
                   * 
                   
                     C 
                     2 
                   
                   * 
                   
                     1 
                     2 
                   
                 
               
               - 
               
                 
                   W 
                   in 
                 
                 * 
                 Δ 
                 ⁢ 
                 t 
               
             
           
         
       
     
     Here, Win is the regeneration amount. 
     Further, the braking heat dissipating energy Q out  is expressed by the following formula. 
         Q   out   =h   V   *A   b *( T   before   −T   atm )*Δ T  
 
     Here, by is the heat transfer coefficient, and Tam, is the air temperature detected by the temperature sensor  22 . 
     The state estimating section  36  estimates the state of deterioration of the brake fluid  48  on the basis of humidity information, duration information expressing the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 . 
     Specifically, the state estimating section  36  estimates the state of the moisture contained in the brake fluid  48  on the basis of the humidity information and the duration information, and estimates the heat state of the brake fluid on the basis of the temperature of the brake device  18 , and estimates the state of deterioration of the brake fluid  48  on the basis of the moisture state and the heat state. 
     For example, each time the temperature of the brake disc exceeds a threshold temperature, the value of the heat state, which expresses the deteriorated state of the brake fluid  48  due to heat, is incremented by 1, and the possibility that vapor lock has occurred is inferred. It suffices for the threshold temperature to be a temperature at which the efficacy of the brake deteriorates. 
     Further, a factor, which expresses the relationship between the duration and the amount of moisture contained in the brake fluid, per area that is readied in advance by utilizing big data is stored in the managing server  16  as humidity information. In particular, it is known that there is a difference in the relationship between the duration and the amount of moisture contained in the brake fluid, between areas of high humidity and areas of low humidity. 
     Thus, on the basis of the duration information and factor B of the area that is obtained as humidity information from the managing server  16 , moisture amount Y is computed (see  FIG.  5   ) in accordance with the following formula. Each time that the moisture amount Y exceeds the threshold value, the value of the moisture state, which expresses the deteriorated state of the brake fluid  48  due to a decrease in the boiling point, is incremented by one. 
     
       
      
       Y=B×T  
      
     
     Here, T is the duration from the point in time when the value of moisture state was incremented by one the previous time. 
       FIG.  5    illustrates an example in which the moisture amount exceeds the threshold value in area  1  in which the humidity is high, and, on the other hand, the moisture amount does not exceed the threshold value in area  2  in which the humidity is low. 
     Note that, in a case of staying in plural areas during the duration from the point in time when the value of moisture state was incremented by one the previous time, it suffices to compute the moisture amount Y in accordance with the above formula and on the basis of the factors B of the areas and the duration information for each of the areas, and to add the moisture amounts (see  FIG.  6   ). 
       FIG.  6    illustrates an example of the relationship between the moisture amount and the duration in a case of staying in area  1  in which the humidity is high and in area  2  in which the humidity is low. 
     The state estimating section  36  estimates the value, which is the sum of the value of the heat state and the value of the moisture state, as the deteriorated state of the brake fluid  48 . As illustrated in  FIG.  7   , the state estimating section  36  displays the deteriorated state of the brake fluid  48  on a display (not illustrated) of the onboard devices  11 .  FIG.  7    illustrates an example in which the deteriorated state of the brake fluid  48  is displayed in levels of four stages. Note that the deteriorated state of the brake fluid  48  may be displayed on a terminal (e.g., a diagnostic device) at a dealer that is connected to the onboard devices  11 . 
     (Managing Server) 
     The managing server  16  stores, as the humidity information and per area, the factor that expresses the relationship between the duration and the amount of moisture contained in the brake fluid, which factor has been prepared in advance. When the managing server  16  receives, from the onboard devices  11 , the position of the vehicle  12  that has been acquired by the position acquiring section  30 , the managing server  16  stores that position as humidity information corresponding to the area that includes the position of the vehicle  12 . The factor that expresses the relationship between the duration and the amount of moisture contained in the brake fluid is transmitted to the onboard devices  11  via the network N. 
     (Flow of Processing) The flow of processing at the vehicle system  10  of the first embodiment is described next by using the flowchart of  FIG.  8   . 
     First, while the vehicle  12  is traveling, each predetermined time period, the control ECU  20  of the onboard devices  11  acquires the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 . 
     Then, when the ignition switch (not illustrated) of the vehicle  12  is turned off, the CPU  20 A of the control ECU  20  of the onboard devices  11  executes the brake state estimating program  100 , and thereby carries out the brake state estimating processing illustrated in  FIG.  8   . 
     First, in step S 100 , on the basis of the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , which are acquired each predetermined time period, the CPU  20 A as the temperature acquiring section  34  cumulatively estimates the change amount ΔT of the temperature of the brake disc during Δt seconds, and thereby computes the temperature TR of the brake disc for each predetermined time period. 
     In step S 102 , the CPU  20 A as the state estimating section  36  judges whether or not the temperature of the brake disc that was computed in above step S 100  is less than or equal to a threshold temperature. If the temperature of the brake disc exceeds the threshold temperature, the CPU  20 A moves on to step S 104 . On the other hand, if the temperature of the brake disc is less than or equal to the threshold temperature, the CPU  20 A moves on to step S 106 . Note that the threshold temperature differs depending on the type of the brake fluid, i.e., the different standards such as DOT3, DOT4, DOT5.1 and the like of FMVS standards (Federal Motor Vehicle Safety Standards) of the U.S. 
     In step S 104 , the CPU  20 A as the state estimating section  36  increments by one the value of the heat state, which expresses the state of deterioration of the brake fluid  48  due to heat, and moves on to step S 116 . 
     In step S 106 , the CPU  20 A as the position acquiring section  30  acquires the position of the vehicle  12 . 
     In step S 108 , on the basis of the position of the vehicle  12  acquired in above step S 106 , the CPU  20 A as the information acquiring section  32  acquires the duration information that expresses the duration of staying in the area that includes the position of the vehicle. Further, on the basis of the position of the vehicle  12  acquired in above step S 106 , the CPU  20 A as the information acquiring section  32  acquires humidity information. 
     In step S 110 , the CPU  20 A as the state estimating section  36  computes the moisture amount on the basis of the duration information and the factor B of the area including the position of the vehicle  12  that was obtained as the humidity information in above step S 108 . 
     In step S 112 , the CPU  20 A as the state estimating section  36  judges whether or not the moisture amount computed in above step S 110  is less than or equal to a threshold value. If the moisture amount exceeds the threshold value, the CPU  20 A moves on to step S 114 . 
     On the other hand, if the moisture amount is less than or equal to the threshold value, the CPU  20 A ends the brake state estimating processing. Note that the threshold value relating to the moisture amount differs in accordance with the type of brake fluid. 
     In step S 114 , the CPU  20 A as the state estimating section  36  increments by 1 the value of the moisture state that expresses the state of deterioration of the brake fluid  48  due to a decrease in the boiling point. 
     In step S 116 , the CPU  20 A as the state estimating section  36  estimates the value, which is the sum of the value of the heat state and the value of the moisture state, as the state of deterioration of the brake fluid  48 . 
     In step S 118 , the CPU  20 A displays the state of deterioration of the brake fluid  48  on a display (not illustrated) of the onboard devices  11 , and ends the brake state estimating processing. 
     Overview of First Embodiment 
     At the vehicle  12  of the present embodiment, the control ECU  20  is structured so as to estimate the state of the moisture contained in the brake fluid on the basis of the humidity information and the duration information, and estimate the heat state of the brake fluid on the basis of the temperature of the brake device, and estimate the state of deterioration of the brake fluid on the basis of the moisture state and the heat state. In this way, the control ECU  20  estimates the state of deterioration of the brake fluid by taking the moisture state and the heat state of the brake fluid into consideration. Due thereto, the state of deterioration of the brake fluid can be estimated accurately by a simple structure. 
     Further, the managing server  16  is structured so as to store a factor, which expresses the relationship between the duration and the amount of moisture contained in the brake fluid, per area as humidity information. Due thereto, at the managing server  16  side, changing of the factor, which expresses the relationship between the duration and the amount of moisture contained in the brake fluid, per area can be carried out easily. 
     Further, at the time when the ignition switch of the vehicle  12  is turned off, various information are transmitted from the onboard devices  11  to the managing server  16 , and therefore, the communication load can be reduced. 
     Second Embodiment 
     In the first embodiment, the state of the moisture contained in the brake fluid is estimated on the basis of the humidity information and the duration information, and the heat state of the brake fluid is estimated on the basis of the temperature of the brake device, and the state of deterioration of the brake fluid is estimated on the basis of the moisture state and the heat state. In contrast, the second embodiment differs from the first embodiment with regard to the point that the deteriorated state is estimated by using a learned model for estimating the deteriorated state of the brake fluid on the basis of the temperature of the brake device, humidity information, and duration information. The points that differ from the first embodiment are described hereinafter. Note that the same structures are denoted by the same reference numerals, and description thereof is omitted. 
     (Vehicle) 
     The state estimating section  36  of the onboard devices  11  of the present embodiment estimates the deteriorated state of the brake fluid  48  by using a learned model for estimating the deteriorated state of the brake fluid  48  on the basis of humidity information, duration information expressing the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 . 
     Specifically, a learned model is prepared in advance whose inputs are the factor of the area obtained as the humidity information, the duration information expressing the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 , and that outputs a level expressing the state of deterioration of the brake fluid  48 . Note that the learned model differs in accordance with the type of the brake fluid  48 . 
     Then, the state estimating section  36  inputs, to the learned model, the factor of the area that is obtained as humidity information, and the duration information expressing the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 , and the state estimating section  36  uses the output of the learned model as the results of estimating the deteriorated state of the brake fluid  48 . 
     (Flow of Processing) 
     The flow of processing at the vehicle system  10  of the second embodiment is described next by using the flowchart of  FIG.  9   . 
     First, while the vehicle  12  is traveling, the control ECU  20  of the onboard devices  11  acquires the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 . 
     Then, when the ignition switch (not illustrated) of the vehicle  12  is turned off, the CPU  20 A of the control ECU  20  of the onboard devices  11  executes the brake state estimating program  100 , and thereby carries out the brake state estimating processing illustrated in  FIG.  9   . Note that processings that are similar to those of the first embodiment are denoted by the same step numbers, and detailed description thereof is omitted. 
     First, in step S 100 , on the basis of the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , which are acquired each predetermined time period, the CPU  20 A as the temperature acquiring section  34  cumulatively estimates the change amount ΔT of the temperature of the brake disc during Δt seconds, and thereby computes the temperature TR of the brake disc for each predetermined time period. 
     In step S 106 , the CPU  20 A as the position acquiring section  30  acquires the position of the vehicle  12 . 
     In step S 108 , on the basis of the position of the vehicle  12  acquired in above step S 106 , the CPU  20 A as the information acquiring section  32  acquires the duration information that expresses the duration of staying in the area that includes the position of the vehicle. Further, on the basis of the position of the vehicle  12  acquired in above step S 106 , the CPU  20 A as the information acquiring section  32  acquires humidity information. 
     In step S 200 , the CPU  20 A as the state estimating section  36  inputs, to the learned model, the maximum temperature of the brake disc temperatures computed in above step S 100 , and the factor of the area that includes the position of the vehicle  12  which factor was obtained as the humidity information in above step S 108 , and the duration information, and estimates the state of deterioration of the brake fluid  48 . 
     In step S 118 , the CPU  20 A displays the state of deterioration of the brake fluid  48  on a display (not illustrated) of the onboard devices  11 , and ends the brake state estimating processing. 
     Overview of Second Embodiment 
     The vehicle  12  of the present embodiment is structured such that the control ECU  20  estimates the deteriorated state of the brake fluid by using a learned model for estimating the deteriorated state of the brake fluid on the basis of the temperature of the brake device, humidity information, and duration information. Due thereto, the state of deterioration of the brake fluid can be estimated accurately by a simple structure. 
     Third Embodiment 
     In the first and second embodiments, the state of deterioration of the brake fluid is estimated at the onboard devices. In contrast, the third embodiment differs from the first and second embodiments with regard to the point that the deteriorated state of the brake fluid of the vehicle is estimated at the managing server side. The points that differ from the first embodiment are described hereinafter. Note that the same structures are denoted by the same reference numerals, and description thereof is omitted. 
     (Overall Structure) As illustrated in above-described  FIG.  1   , a vehicle system  310  relating to the present embodiment includes the vehicle  12  and a managing server  316 . 
     (Vehicle) The onboard devices  11  installed in the vehicle  12  periodically acquire the longitude and latitude of the position of the vehicle  12  from a navigation system installed in the vehicle  12 , and transmit the longitude and latitude from the communication section  14  to the managing server  316 . 
     The onboard devices  11  acquire the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , and transmit these information from the communication section  14  to the managing server  316  each predetermined time period. 
     Further, the onboard devices  11  acquire results of estimation of the deteriorated state of the brake fluid from the managing server  316 , and display the results of estimation on a display (not illustrated) of the onboard devices  11 . 
     (Managing Server) As illustrated in  FIG.  10   , the managing server  316  is structured to include a control device  380  and a communication section  316 B. 
     The control device  380  has a CPU  382 , a ROM  383 , a RAM  384 , a storage  385 , and an input/output I/F  386 . The CPU  382 , the ROM  383 , the RAM  384 , the storage  385  and the input/output I/F  386  are connected to one another via a bus  388 . The CPU  382  is an example of the processor, and the RAM  384  is an example of the memory. 
     The respective functions of the CPU  382 , the ROM  383 , the RAM  384 , the storage  385  and the input/output I/F  386  are the same as those of the above-described CPU  20 A, ROM  20 B, RAM  20 C, storage  20 D and input/output I/F  20 E. 
     The CPU  382  reads-out a brake state estimating program  300  from the storage  385 , and executes the program by using the RAM  384  as a workspace. In the present embodiment, the brake state estimating program  300  is stored in the storage  385 . 
     The communication section  316 B is connected to the control device  380  of the present embodiment via the input/output I/F  386 . Note that the communication section  316 B may be directly connected to the bus  388 . 
     As illustrated in  FIG.  11   , at the control device  380  of the present embodiment, due to the CPU  382  executing the brake state estimating program  300 , the CPU  382  functions as a position acquiring section  330 , an information acquiring section  332 , a temperature acquiring section  334 , and a state estimating section  336 . 
     The position acquiring section  330  acquires the longitude and the latitude of the position of the vehicle  12  that are received from the onboard devices  11  of the vehicle  12 . 
     On the basis of the position of the vehicle  12  acquired by the position acquiring section  330 , the information acquiring section  332  acquires duration information that expresses the duration of staying in the area that includes the position of the vehicle. Further, on the basis of the position of the vehicle  12  acquired by the position acquiring section  330 , the information acquiring section  332  acquires humidity information. For example, the information acquiring section  332  retains, as humidity information, a factor that expresses the relationship between the duration and the amount of moisture contained in the brake fluid, per area that has been readied in advance. The information acquiring section  332  acquires the factor that expresses the relationship between the duration and the amount of moisture contained in the brake fluid, and that serves as the humidity information corresponding to the area that includes the position of the vehicle  12  acquired by the position acquiring section  330 . 
     The temperature acquiring section  334  acquires the temperature of the brake device  18  that was received from the onboard devices  11  of the vehicle  12 . Specifically, in the same way as the temperature acquiring section  34  of the above-described first embodiment, the temperature acquiring section  334  computes the temperature of the brake device  18  on the basis of the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , which were received from the onboard devices  11  of the vehicle  12 . 
     The state estimating section  336  estimates the state of deterioration of the brake fluid  48  on the basis of the humidity information, the duration information that expresses the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 . 
     Specifically, in the same way as the state estimating section  36  in the above-described first embodiment, the state estimating section  336  estimates the state of the moisture continued in the brake fluid  48  on the basis of the humidity information and the duration information, and estimates the heat state of the brake fluid  48  on the basis of the temperature of the brake device  18 , and estimates the state of deterioration of the brake fluid  48  on the basis of the moisture state and the heat state. 
     The state estimating section  336  transmits the results of estimation of the deteriorated state of the brake fluid  48  from the communication section  316 B via the network N to the onboard devices  11 . 
     (Flow of Processing) 
     First, while the vehicle  12  is traveling, the control ECU  20  of the onboard devices  11  acquires, each predetermined time period, the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , and transmits these information from the communication section  14  to the managing server  316 . 
     Further, the onboard devices  11  periodically acquire the longitude and latitude of the position of the vehicle  12  from the navigation system installed in the vehicle  12 , and transmit the longitude and latitude from the communication section  14  to the managing server  316 . 
     Then, when the ignition switch (not illustrated) of the vehicle  12  is turned off, the onboard devices  11  transmit a request to estimate the deteriorated state of the brake fluid  48 , from the communication section  14  to the managing server  316 . 
     Then, when the managing server  316  receives the request to estimate the deteriorated state of the brake fluid  48  from the onboard devices  11 , the CPU  382  of the control device  380  of the managing server  316  executes the brake state estimating program  300 , and thereby carries out processing that is similar to the brake state estimating processing illustrated in above-described  FIG.  8   . 
     Overview of Third Embodiment 
     The managing server  316  of the present embodiment is structured such that the control device  380  estimates the state of the moisture contained in the brake fluid on the basis of the humidity information and the duration information, and estimates the heat state of the brake fluid on the basis of the temperature of the brake device, and estimates the state of deterioration of the brake fluid on the basis of the moisture state and the heat state. In this way, the control device  380  estimates the state of deterioration of the brake fluid by taking the moisture state and the heat state of the brake fluid into consideration. Due thereto, the state of deterioration of the brake fluid can be estimated accurately by a simple structure. 
     Further, the managing server  316  is structured so as to estimate the state of the moisture contained in the brake fluid on the basis of the humidity information and the duration information, and estimate the heat state of the brake fluid on the basis of the temperature of the brake device. Due thereto, at the managing server  316  side, the threshold values relating to the moisture state and the heat state can be changed easily. 
     Modified Example of Third Embodiment 
     The third embodiment describes, as an example, a case in which the managing server  316  estimates the state of the moisture contained in the brake fluid on the basis of the humidity information and the duration information, and estimates the heat state of the brake fluid on the basis of the temperature of the brake device, and estimates the deteriorated state of the brake fluid on the basis of the moisture state and the heat state. However, the present disclosure is not limited to this. In the same way as in the above-described second embodiment, the state estimating section  336  of the managing server  316  may input the factor of the area obtained as the humidity information, and the duration information expressing the duration of staying in the area that includes the position of the vehicle, and the temperature of the brake device  18 , to a learned model, and may use the output of the learned model as the results of estimating the deteriorated state of the brake fluid  48 . In this case, by executing the brake state estimating program  300 , the CPU  382  of the control device  380  of the managing server  16  carries out processing that is similar to the brake state estimating processing illustrated in above-described  FIG.  9   . 
     Further, the above describes, as an example, a case in which the control ECU  20  of the onboard devices  11  acquires, each predetermined time period, the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , and transmits these information to the managing server  16  from the communication section  14 . However, the present disclosure is not limited to this. The control ECU  20  of the onboard devices  11  may, on the basis of the air temperature detected by the temperature sensor  22 , the vehicle speed detected by the vehicle speed sensor  24 , the hydraulic pressure of the brake fluid  48  detected by the hydraulic pressure sensor  52  of the brake device  18 , and the regeneration amount detected by the hybrid ECU  26 , which were acquired each predetermined time period, compute the temperature of the brake disc, and transmit the results of computation from the communication section  14  to the managing server  16 . 
     [Notes] 
     Although the above embodiments describe, as examples, cases of detecting the air temperature from the temperature sensor  22 , the present disclosure is not limited to this. The air temperature of the area that includes the position of the vehicle  12  may be acquired from an external server. 
     Further, any of various types of processors other than a CPU may execute the various processings that are executed due to the CPU  20 A,  382  reading software (a program) in the above-described embodiments. Examples of processors in this case include PLDs 
     (Programmable Logic Devices) whose circuit structure can be changed after production such as FPGAs (Field-Programmable Gate Arrays) and the like, and dedicated electrical circuits that are processors having circuit structures that are designed for the sole purpose of executing specific processings such as ASICs (Application Specific Integrated Circuits) and the like, and the like. Further, the various processings may be executed by one of these various types of processors, or may be executed by a combination of two or more of the same type or different types of processors (e.g., plural FPGAs, or a combination of a CPU and an FPGA, or the like). Further, the hardware structures of these various types of processors are, more specifically, electrical circuits that combine circuit elements such as semiconductor elements and the like. 
     Further, the above-described respective embodiments describe forms in which the respective programs are stored in advance (are installed) on a computer-readable, non-transitory recording medium. For example, at the onboard devices  11 , the brake state estimating program  100  is stored in advance in the storage  20 D. Further, for example, at the managing server  316 , the brake state estimating program  300  is stored in advance in the storage  385 . However, the present disclosure is not limited to this, and the respective programs may be provided in a form of being recorded on a non-transitory recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), a USB (Universal Serial Bus) memory, or the like. Further, the respective programs may in a form of being downloaded from an external device over a network. 
     The flows of the processings described in the above embodiments also are examples, and unnecessary steps may be deleted therefrom, new steps may be added thereto, or the order of processings may be rearranged, within a scope that does not depart from the gist of the present disclosure. 
     In addition, the respective structures of the onboard devices and the managing server described in the above embodiments are examples, and may be changed in accordance with the situation within a scope that does not depart from the gist of the present disclosure.