BRAKE CONTROL DEVICE FOR A VEHICLE

Abstract

A brake control device for a vehicle that generates a braking force at a wheel (WH) by supplying a brake fluid pressure to a wheel cylinder (WC) in accordance with an operation of a brake operating member (BP) of a vehicle, the brake control device comprising: a first fluid pressure unit (EAA) that transmits the brake fluid pressure through a first power source (PUA); a second fluid pressure unit (EAB) that transmits the brake fluid pressure through a second power source (PUB) that is different from the first power source (PUA); and a suitability determination device (HNA) that determines a suitability of an operating state of the first fluid pressure unit (EAA); wherein, when the suitability determining means (HNA) determines that the operating state of the first fluid pressure unit (EAA) is suitable, the first fluid pressure unit (EAA) outputs the brake fluid pressure based on a suitability characteristic (CHgo), which is a relationship between an operation amount (Bpa) of the brake operating member (BP), which is set in advance, and the brake fluid pressure; the second fluid pressure unit (EAB) an approach characteristic (CHgp) that is substantially the same as the suitability characteristic (CHgo) and a notification characteristic (CHbp, CHzg, CHkr) that is different from the suitability characteristic (CHgo); and transmits the brake fluid pressure based on at least one of the proximity characteristic (CHgp) and the notification characteristic (CHbp, CHzg, CHkr) when the suitability determination device (HNA) determines that the operating state of the first fluid pressure unit (EAA) is not suitable, wherein the second fluid pressure unit (EAB) the number (NKR) of repetitions of a sequence of operations of the brake operating element (BP) from a time when the suitability determining means (HNA) determines that the operating state of the first fluid pressure unit (EAA) is not suitable is counted on the basis of the operation amount (Bpa), transmits the brake fluid pressure based on the approximate characteristic (CHgp) when the number (NKR) of repetitions is less than a predetermined number of times (nkx), and communicates the brake fluid pressure based on the notification characteristic (CHkr) when the number (NKR) of repetitions is greater than or equal to the predetermined number of times (nkx).

Description

TECHNICAL FIELD

[0001] The present invention relates to a brake control device for a vehicle. BACKGROUND OF THE INVENTION

[0002] JP 2014-97687 A describes, with the intention of "suppressing the supply of fluid pressure to a wheel cylinder having both a fluid pressure control mechanism and a booster mechanism," that "a first ECU 26 controls an electric actuator 20 of an electric booster device 16. A second ECU 33 controls the operation of an ESC 31, which is a fluid pressure control device. The second ECU 33 operates the ESC 31 to perform backup control for supplying brake fluid to wheel cylinders 3L, 3R, 4L, 4R when it is determined that the first ECU 26 is malfunctioning. In contrast, the first ECU 26 does not control the electric actuator 20 when the second ECU 33 is performing backup control."

[0003] JP 2014-4879 A discloses, with the intention of "improving a practicality of a power source-dependent vehicle braking system", that "a power source device (for example, a high-pressure source device that supplies a high-pressure operating fluid) that generates a force different from a driver's braking operation force applied to a braking operation member is arranged, wherein, at a normal time, in a vehicle braking system configured such that a braking force generated by a braking device provided at a wheel becomes a braking force dependent on a power source force, which is a force generated by the power source device, a braking force GT that is a magnitude of a center of a braking force GN generated in the normal operation mode and a braking force GD generated in a fault operation mode,during a transition from the normal operating mode to the fault operating mode caused by any type of fault during brake application.",

[0004] JP 2014-97687 A describes backup control for operating the fluid pressure control device to supply brake fluid to a wheel cylinder when it is determined that the electric booster device is malfunctioning. Furthermore, JP 2014-4879 A describes operating characteristics in a case where the braking function is malfunctioning. Specifically, in the device described in JP 2014-4879 A, a sudden change in the braking force (brake application force) is suppressed or mitigated, a stable braking force is generated, and a satisfactory braking feeling is achieved. However, there are still differences between "normal characteristics" and "intermediate magnitude characteristics," and thus, it is desirable to reduce the difference.If there is no difference in operating characteristics, a driver is unlikely to notice the device malfunction. Therefore, a brake control device is desired that minimizes driver discomfort while providing appropriate notification to the driver.

[0005] The document DE 697 31 248 T2 describes a brake control device for a vehicle, comprising: a first booster device that boosts a depression force generated by a driver's brake pedal operation and generates an operating force; a master cylinder that generates a master cylinder pressure in response to the operating force of the first booster device; a wheel braking force generating device that generates a wheel braking force in response to the master cylinder pressure; a conduit connected between the master cylinder and the wheel braking force generating device; a second booster device that is provided separately from the first booster device and is operated to supply a brake fluid pressure higher than the master cylinder pressure to the wheel braking force generating device.The second booster device is coupled to a portion of the line between the master cylinder and the wheel braking force generating device. The brake control device includes a detection device for detecting a malfunction or functional impairment of the first booster device and a control device for actuating the second booster device to generate or increase the brake fluid pressure applied to the wheel braking force generating device when the malfunction or functional impairment of the first booster device is detected. SUMMARY OF THE INVENTION TECHNICAL PROBLEMS

[0006] It is an object of the present invention to provide a brake control device for a vehicle in which, when the device malfunctions, the driver's operating characteristics are appropriately adjusted, the driver's discomfort is suppressed, and this is reliably reported. SOLUTIONS TO THE PROBLEMS

[0007] This object is achieved by a brake control device according to claim 1. Advantageous further developments are specified in the dependent claims.

[0008] A brake control device for a vehicle according to the present invention generates a braking force at a wheel (WH) by supplying a brake fluid pressure (Pwc) to a wheel cylinder (WC) in accordance with an operation of a brake operating member (BP) of the vehicle. The brake control device for the vehicle includes a first fluid pressure unit (EAA) that supplies the brake fluid pressure (Pwc) through a first power source (PUA), a second fluid pressure unit (EAB) that supplies the brake fluid pressure (Pwc) through a second power source (PUB) different from the first power source (PUA), and suitability determination means (HNA, HNB) that determines the suitability of the operating state of the first fluid pressure unit (EAA).

[0009] In the brake control device for the vehicle according to the present invention, when the suitability determining means (HNA, HNB) determines that “the operating state of the first fluid pressure unit (EAA) is suitable,” the first fluid pressure unit (EAA) outputs the brake fluid pressure (Pwc) based on a suitability characteristic (CHgo) that is a relationship between an operation amount (Bpa) of the brake operating member, which is set in advance, and the brake fluid pressure (Pwc).The second fluid pressure unit (EAB) has an approximate characteristic (CHgp) substantially consistent with the suitability characteristic (CHgo) and a notification characteristic (CHbp, CHzg, CHkr) different from the suitability characteristic (CHgo); and it outputs the brake fluid pressure (Pwc) based on at least one of the approximate characteristic (CHgp) and the notification characteristic (CHbp, CHzg, CHkr) when the suitability determining means (HNA, HNB) determines that "the operating state of the first fluid pressure unit (EAA) is not suitable."

[0010] In the brake control device for the vehicle according to the present invention, the second fluid pressure unit (EAB) outputs the brake fluid pressure (Pwc) based on the approximate characteristic (CHgp) when an operation equivalent amount (Bpa, Gxa, Pwc) equivalent to the operation amount (Bpa) of the brake operating member (BP) is less than a predetermined value (bpx), and outputs the brake fluid pressure (Pwc) based on the notification characteristic (CHbp) when the operation equivalent amount (Bpa, Gxa, Pwc) is greater than or equal to the predetermined value (Bpx). Here, the second fluid pressure unit (EAB) sets the predetermined value (bpx) to a value equivalent to "0.3 to 0.4 G" of the deceleration (Gxa) of the vehicle.

[0011] In the brake control device for the vehicle according to the present invention, the second fluid pressure unit (EAB) outputs the brake fluid pressure (Pwc) based on the approach characteristic (CHgp) when the operation amount (Bpa) increases, and outputs the brake fluid pressure (Pwc) based on the notification characteristic (CHzg) when the operation amount (Bpa) decreases.

[0012] In the brake control device for the vehicle according to the present invention, the second fluid pressure unit (EAB) counts a number of repetitions (NKR) of a sequence of operations of the brake operating member (BP) from a time when the suitability determining means (HNA, HNB) determines that the operating state of the first fluid pressure unit (EAA) is not suitable based on the operation amount (Bpa), it outputs the brake fluid pressure (Pwc) based on the approximate characteristic (CHgp) when the number of repetitions (NKR) is less than a predetermined number of times (nkx), and it outputs the brake fluid pressure (Pwc) based on the notification characteristic (CHkr) when the number of repetitions (NKR) is equal to or greater than the predetermined number of times (nkx).Furthermore, the second fluid pressure unit (EAB) decreases the notification characteristic (CHkr) according to the increase in the number of repetitions (NKR) when the number of repetitions (NKR) is greater than or equal to the predetermined number (nkx).

[0013] According to the configuration described above, when the first fluid pressure unit EAA malfunctions, substitute control is performed by the second fluid pressure unit EAB, passing the brake fluid pressure Pwc corresponding to the operation amount Bpa. Two different characteristics (calculation maps) are provided in the second fluid pressure unit (EAB) as characteristics of the substitute control (referred to as substitute characteristics). The approximate characteristic CHgp (when the specific condition JSP is satisfied), which is one of the two characteristics, is a characteristic similar to the suitability characteristic CHgo when the first fluid pressure unit EAA is in the suitable state. Consequently, a feeling of discomfort in the driver at the time of a malfunction of the first fluid pressure unit EAA is suppressed.The notification characteristics CHbp, CHzg, CHkr (when the specific condition JSP is not met), which are the other characteristics of the two characteristics, are different from the suitability characteristic CHgo. As a result of applying the notification characteristics CHbp, CHzg, CHkr, the malfunction of the first fluid pressure unit EAA is notified to the driver through the relationship (operation characteristic) of the vehicle deceleration Gxa with respect to the brake application amount Bpa. The malfunction of the first fluid pressure unit EAA can be notified to the driver without discomfort through the two different substitute characteristics. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is an overall configuration diagram for describing a first embodiment of a brake control device for a vehicle according to the present invention. Fig. 2 shows a flowchart for explaining a setting processing of a substitute characteristic. Fig. 3 shows a characteristic diagram for explaining a first setting example of the equivalent characteristics. Fig. 4 shows a characteristic diagram for explaining a second setting example of the equivalent characteristics. Fig. 5 shows a characteristic diagram for explaining a third setting example of the equivalent characteristics. Fig. 6 is an overall configuration diagram for explaining a second embodiment of a brake control device of a vehicle according to the present invention. DESCRIPTION OF THE EMBODIMENTS<Erstes Ausführungsbeispiel einer Bremssteuerungsvorrichtung>

[0014] A first embodiment of a brake control device according to the present invention will be described with reference to an overall configuration diagram according to Fig. 1. In the following description, components denoted by the same symbols, calculation processing, signals, characteristics, and values have the same functions. Therefore, redundant explanations can be omitted.

[0015] The vehicle includes two different fluid pressure units EAA and EAB. In addition to the first and second fluid pressure units EAA, EAB, the vehicle includes a brake operating element BP, an operation amount sensor BPA (collectively, an operation displacement sensor SBP, an operation force sensor FBP, and a simulator fluid pressure sensor (PSM)), a master cylinder MC, a stroke simulator SSM, a simulator cut-off valve VSM, a master cylinder cut-off valve VMC, a fluid path (brake piping) HKA, HKB, HKW, and a notification device HC. Furthermore, each wheel WH of the vehicle is provided with a brake caliper CP, a wheel cylinder WC, a rotating element KT, and a friction element.

[0016] The brake operating member (e.g., a brake pedal) BP is a member operated by the driver to decelerate the vehicle. The braking torque of the wheel WH is adjusted, and the braking force at the wheel WH is generated by operating the brake operating member BP. Specifically, a rotating member (e.g., a brake disc) KT is fixed to the wheel WH of the vehicle. The brake caliper CP is arranged to clamp the rotating member KT. A wheel cylinder WC is provided in the brake caliper (also simply referred to as a caliper) CP. When the pressure Pwc of the brake fluid in the wheel cylinder WC increases, a friction member (e.g., a brake pad) is pressed against the rotating member KT. Since the rotating member KT and the wheel WH are fixed to rotate integrally, a braking torque (a braking force) is generated at the wheel WH by the friction force generated at that time.As the caliper CP, a caliper of a floating type or a caliper of an opposed type can be applied.

[0017] In the brake operating member BP, an operating displacement sensor SBP is provided to detect the operating displacement Sbp. A state variable related to a "displacement" of the brake operating member BP is detected as the operating displacement Sbp. In other words, the operating displacement sensor SBP detects the "state quantity related to an offset" as the operating displacement Sbp. For example, in the brake operating member BP that is rotatably fixed to a vehicle body, a rotation angle of the brake operating member BP with respect to the vehicle body is detected as the operating displacement Sbp. In this case, the operating displacement sensor SBP is a rotation angle sensor. Further, a displacement of a brake rod BRD that mechanically connects the brake operating member BP and a piston of the master cylinder MC with respect to the vehicle body can be detected as the operating displacement Sbp.In this case, the actuation displacement sensor SBP is a linear displacement sensor.

[0018] The brake operating member BP is provided with an operating force sensor FBP for detecting an operating force Fbp. A state variable related to a "force" of the brake operating member BP is detected as the operating force Fbp. In other words, the operating force sensor FBP detects the "state variable related to a force" as the operating force Fbp. For example, in a case where the brake operating member BP is a brake pedal operated by a foot, the pedal depression force is detected as the operating force Fbp by a pedal depression force sensor Fbp. Furthermore, the fluid pressure Psm in a simulator SSM (i.e., in a brake master cylinder MC) can be detected as the operating force Fbp. In this case, the operating force sensor FBP is a pressure sensor PSM.

[0019] The operation displacement sensor SBP and the operation force sensor FBP are collectively referred to as an operation amount sensor BPA. Furthermore, the operation displacement Sbp and the operation force Fbp are referred to as an operation amount Bpa. The detected brake operation amount Bpa is input to the first and second fluid pressure units EAA, EAB (specifically, to the first and second control devices ECA, ECB).

[0020] A tandem brake master cylinder (MC) (also simply referred to as a brake master cylinder) is connected to the brake operating element (BP) via a piston rod (BRD). The operating force (e.g., a brake pedal force) of the brake operating element (BP) is converted into brake fluid pressure by the master cylinder (MC). A fluid path (master cylinder piping) (HKA) is connected to the master cylinder (MC). When the brake operating element (BP) is operated, brake fluid is expelled (pressurized) from the master cylinder (MC) to the fluid path (HKA).

[0021] A stroke simulator (also simply referred to as a simulator) SSM is provided to cause the brake operating member BP to generate an operating force. A simulator cut-off valve VSM is provided between a fluid pressure chamber in the master cylinder MC and the simulator SSM. The simulator cut-off valve VSM is a two-position electromagnetic valve having an open position and a closed position. When the simulator cut-off valve VSM is at the open position, the master cylinder MC and the simulator SSM are in a communication state. Conversely, when the simulator cut-off valve VSM is in the closed position, the master cylinder MC and the simulator SSM are in a cut-off (non-communication) state. A normally closed electromagnetic valve, or normally closed (NC) valve, can be applied as the simulator cut-off valve VSM.

[0022] A piston and an elastic body (e.g., a compression spring) are provided within the simulator SSM. The brake fluid is moved from the master cylinder MC into the simulator SSM, and the piston is pushed out by the flowing brake fluid. A force is transmitted to the piston in a direction to prevent the brake fluid from flowing in by the elastic body. An operating force (e.g., a brake pedal depression force) Fbp in the case where the brake operating element BP is operated is formed by the elastic body.

[0023] A simulator fluid pressure sensor PSM is provided to detect the simulator fluid pressure Psm as the operation force Fbp. The simulator fluid pressure sensor PSM is one of the operation force sensors FBP and is an operation amount sensor BPA (collectively). The simulator fluid pressure Psm is input to the first control device ECA of the first fluid pressure unit EAA.

[0024] A master cylinder cut valve (VMC) is provided in a fluid path (master cylinder piping) (HKA) connecting the master cylinder (MC) and the wheel cylinder (WC). The master cylinder cut valve (VMC) is a two-position electromagnetic valve with an open position and a closed position. When the master cylinder cut valve (VMC) is in the open position, the master cylinder (MC) and the wheel cylinder (WC) are in communication. Conversely, when the master cylinder cut valve (VMC) is in the closed position, the master cylinder (MC) and the wheel cylinder (WC) are in a cut-off (non-communication) state.

[0025] A normally open electromagnetic valve or electromagnetic normally closed valve (NO valve) can be used as the brake master cylinder cut-off valve VMC. <<Erste Fluiddruckeinheit EAA> >

[0026] Instead of the master cylinder MC, the first fluid pressure unit EAA causes the wheel cylinder WC provided in the four wheels WH of the vehicle to generate the fluid pressure Pwc. When the first fluid pressure unit EAA is operated, the master cylinder cutoff valve VMC is arranged at the closed position, preventing movement of the brake fluid from the master cylinder MC to the wheel cylinder WC. In this case, the simulator cutoff valve VSM is at the open position, thus moving the brake fluid from the master cylinder MC to the simulator SSM. The first fluid pressure unit EAA is a brake control device having a so-called break-by-wire configuration. The first fluid pressure unit EAA is configured by a first power source PUA, a first pressure regulating mechanism CHA, a first fluid pressure sensor PWA, and a first controller (electronic control unit) ECA.

[0027] In the first power source PUA, the pressure of the brake fluid is generated using power other than the driver's muscle power as a power source. For example, the first power source PUA is a hydraulic pump driven by an electric motor. In this case, the fluid pressure generated by the hydraulic pump can be stored in the pressure storage device and used. Furthermore, a fluid cylinder (electric cylinder) driven by the electric motor can be applied as the first power source PUA. Specifically, the rotational power of the electric motor is converted into linear power by a power conversion mechanism (e.g., a worm mechanism), thereby pushing the piston in the electric cylinder, generating pressure in the brake fluid.

[0028] The fluid pressure generated by the first power source PUA is controlled to a desired fluid pressure by the first pressure regulating mechanism CHA. The pressure regulating mechanism CHA is controlled by the first control device ECA. For example, the first pressure regulating mechanism CHA is configured by a linear electromagnetic valve. Specifically, the high pressure stored in the pressure accumulating device is regulated by the linear electromagnetic valve, being output from the first pressure regulating mechanism CHA. In the case where the electric cylinder is applied as the first power source PUA, the first power source PUA functions as the first pressure regulating mechanism CHA. Specifically, fluid pressure control is performed by adjusting the output of the electric motor of the electric cylinder.Consequently, the electric cylinder functions as the first power source PUA and the first pressure regulating mechanism CHA. The first fluid pressure unit EAA (i.e., the first pressure regulating mechanism CHA) is fluidly connected to the second fluid pressure unit EAB via a fluid path HKB.

[0029] The pressure regulation result Pwa of the first pressure regulation mechanism CHA is detected by the first fluid pressure sensor PWA. That is, the first fluid pressure sensor PWA detects the output fluid pressure Pwa of the first fluid pressure unit EAA (specifically, the first pressure regulation mechanism CHA). The output fluid pressure Pwa is input to the first control device ECA.

[0030] The first power source PUA and the first pressure regulating mechanism CHA are controlled by the first control device (electronic control unit) ECA. In the first control device ECA, signals for controlling the electromagnetic valves VSM, VMC are calculated and output. The first control device ECA is configured by a control algorithm programmed into the microprocessor and an electrical circuit (drive circuit) that drives the electric motor and the electromagnetic valve according to the algorithm. Furthermore, the first control device ECA is connected to the second control device ECB of the second fluid pressure unit EAB through a communication bus or communication bus CMB (for example, a serial communication bus) in a state where signal transmission with the second control device ECB can be performed.For example, a CAN (controller area network) can be used as the communication bus CMB.

[0031] In the control algorithm programmed into the first control device ECA, a target fluid pressure Pwt is calculated based on the brake operation amount Bpa (that is, at least one of the operating offset Sbp and the operation force Fbp) and the suitability characteristic CHgo. The target fluid pressure Pwt is a target value of the output fluid pressure of the first fluid pressure unit EAA. The suitability characteristic CHgo is a preset calculation map for determining the target fluid pressure Pwt in a case where the device operates properly. In the suitability characteristic CHgo, the target fluid pressure Pwt is determined to be “0” when the operation amount Bpa is greater than or equal to “0” or less than a predetermined value bpo, and the target fluid pressure Pwt is calculated to monotonically increase (see Fig. 3) when the operation amount Bpa increases when the operation amount Bpa is greater than or equal to a predetermined value bpo. Here, the predetermined value bpo is a value equivalent to the play of the brake operating member BP.

[0032] When the actuation amount Bpa becomes greater than or equal to the predetermined value bpo, the first control device ECA outputs a drive signal to open the simulator cut-off valve VSM and a drive signal to close the master cylinder cut-off valve VMC. With these signals, the master cylinder MC is brought into communication with the simulator SSM, and the first fluid pressure unit EAA is brought into communication with the wheel cylinder WC.

[0033] The first power source PUA and the electric motor (for driving a hydraulic pump or for an electric cylinder) constituting the first pressure regulating mechanism CHA, and the linear electromagnetic valve are controlled based on the fluid pressure command value Pwt calculated by the first controller ECA. Specifically, the command value of the energization amount of the electric motor and the linear electromagnetic valve is determined based on the command fluid pressure Pwt. The energization state of the electric motor and the linear electromagnetic valve is adjusted by the drive circuit based on such command values. In addition, fluid pressure control is performed based on the actual fluid pressure value Pwa (detected value of the fluid pressure sensor PWA).Specifically, a deviation ePw between the target value Pwt of the brake fluid pressure and the actual value Pwa is calculated, and fine adjustment of the power supply condition (e.g., a current value) is performed based on the deviation ePw. High-precision fluid pressure control is performed by PID control based on the so-called fluid pressure deviation ePw so that the actual value Pwa matches the target value Pwt.

[0034] In the first control device ECA, a determination processing block HNA (equivalent to a determination means) for determining the suitability of the operating state of the first fluid pressure unit EAA is formed. In the first determination means HNA, it is determined whether or not the first fluid pressure unit EAA is in a suitable state. When the first fluid pressure unit EAA is in a suitable state, "0 (zero)" is output to the second fluid pressure unit EAB through the communication flow CMB as a first determination result (determination flag) Hna. On the other hand, when the first fluid pressure unit EAA is not in the suitable state (i.e., is in an unsuitable state), "1" is output to the second fluid pressure unit EAB through the communication flow CMB as the determination flag Hna.

[0035] The first determination means HNA is an arithmetic algorithm programmed into the microcomputer of the first control means ECA. The first determination means HNA determines the suitability of the operating state of the first power source PUA, the first pressure regulating mechanism CHA, and the first fluid pressure sensor PWA. For example, the power supply state to the electric motor, the electromagnetic valve, and the like is monitored by a current sensor or the like, and the suitability of the operating state of such configuring elements is determined.

[0036] The first determination means HNA performs an initial diagnosis of the first fluid pressure unit EAA when the powertrain (engine or electric motor for propulsion) of the vehicle is started by a start switch STR (i.e., at the time of starting). In the initial diagnosis, the state of power supply to the first fluid pressure unit EAA, the diagnosis of the first control means ECA itself (e.g., a memory diagnosis), and the confirmation of operation of the connection state via the electric motor, the electromagnetic valve, the drive circuit, various sensors (first fluid pressure sensor PWA, current sensors, etc.), and the communication bus CMB are performed. The first fluid pressure unit EAA has been described above. <<Zweite Fluiddruckeinheit EAB> >

[0037] In the vehicle, the second fluid pressure unit EAB is provided separately from the first fluid pressure unit EAA. That is, two fluid pressure units EAA, EAB are provided in the vehicle. The second fluid pressure unit EAB is provided in a fluid path between the first fluid pressure unit EAA and the wheel cylinder WC. A fluid path HKB between the first fluid pressure unit EAA and the second fluid pressure unit EAB is a pressure regulating piping, and a fluid path HKW between the second fluid pressure unit EAB and the wheel cylinder WC is a wheel cylinder piping. That is, the first fluid pressure unit EAA and the second fluid pressure unit EAB are arranged in series with respect to the wheel cylinder WC.

[0038] The second fluid pressure unit EAB regulates the fluid pressure Pwc of the wheel cylinder WC of each wheel WH independently of the driver's braking operation based on the vehicle's turning state. Accordingly, the fluid pressure (i.e., the output fluid pressure Pwa) generated by the first fluid pressure unit EAA is regulated by the second fluid pressure unit EAB, generating the final wheel cylinder fluid pressure Pwc. The second fluid pressure unit EAB is a fluid pressure unit for a so-called electronic stability control (ESC).

[0039] Similar to the first fluid pressure unit EAA, the second fluid pressure unit EAB is configured by a second power source PUB, a second pressure regulating mechanism CHB, a second fluid pressure sensor PWB, and a second control device (electronic control unit) ECB. The brake fluid pressure is generated by the second power source PUB, which is separate from the first power source PUA. For example, the second power source PUB is a hydraulic pump driven by an electric motor.

[0040] The fluid pressure generated by the second power source PUB is controlled to a desired fluid pressure by the second pressure regulating mechanism CHB. The second power source PUB and the second pressure regulating mechanism CHB are controlled by the second control device ECB. For example, the second pressure regulating mechanism CHB is configured by a linear electromagnetic valve. The fluid pressure is increased by the hydraulic pump driven by the electric motor, and the fluid pressure is regulated by a differential pressure valve (electromagnetic valve). Furthermore, the fluid pressure Pwc in the wheel cylinder WC of each wheel WH is independently regulated by a combination of an electromagnetic pressure increasing valve and an electromagnetic pressure decreasing valve.

[0041] Similar to the first control device ECA, the second control device ECB of the second fluid pressure unit EAB is configured by a control algorithm programmed into the microprocessor and an electric circuit (drive circuit) that drives the electric motor and the electromagnetic valve according to the algorithm.

[0042] The second control device ECB receives a yaw rate Yra from a yaw rate sensor YRA, a lateral acceleration Gya from a lateral acceleration sensor GYA, a steering angle Swa from an operation angle sensor SWA, and a wheel speed Vwa from a wheel speed sensor VWA. In order to execute vehicle stability control (control for suppressing excessive understeer and oversteer based on the yaw rate Yra, etc.), anti-skid control (control for suppressing wheel lock based on the wheel speed Vwa, etc.), and the like based on the signals (Yra, Vwa, etc.), the target value Pwt of the brake fluid pressure (the fluid pressure in the wheel cylinder WC) in each wheel WH is calculated. Then, the wheel cylinder fluid pressure Pwc is regulated so as to achieve the target value Pwt.

[0043] In the second fluid pressure unit EAB, in addition to executing vehicle stability control and the like, fluid pressure regulation of the wheel cylinder WC is performed according to the operation amount Bpa (at least one of the operation displacement Sbp and the operation force Fbp) of the brake operating member PB when the first fluid pressure unit EAA is in a malfunction state. The second fluid pressure unit EAB is provided with the second power source PUB and the second pressure regulating mechanism CHB, which are different from the first fluid pressure unit EAA.

[0044] At least one of the operation displacement Sbp and the operation force Fbp is input to the second control device ECB (that is, an operation amount Bpa is input). Further, the first control device ECA transmits the first determination result Hna to the second control device ECB via the communication bus CMB (for example, a serial communication bus). In a case where the first determination result Hna indicates an appropriate state (that is, "Hna = 0"), the second fluid pressure unit EAB does not execute the pressure regulation control corresponding to the operation amount Bpa. However, if the first determination result Hna indicates an inappropriate state (that is, "Hna = 1"), the second fluid pressure unit EAB increases the fluid pressure Pwc in the wheel cylinder WC instead of the first fluid pressure unit EAA based on the brake operation amount Bpa.The brake fluid pressure control by the second fluid pressure unit EAB in a malfunction state of the first fluid pressure unit EAA is referred to as "backup control." When the backup control is executed in the second fluid pressure unit EAB, the operation of the first fluid pressure unit EAA is stopped.

[0045] In the second control device ECB of the second fluid pressure unit EAB, a characteristic curve (calculation map) for executing the backup control is stored. This characteristic curve is the relationship between the wheel cylinder fluid pressure Pwc and the operation amount Bpa (result, a relationship of vehicle deceleration Gxa with respect to the operation amount Bpa), and is referred to as a "backup characteristic curve." The backup characteristic curve is set in advance in the second fluid pressure unit EAB (specifically, in the second control device ECB) to ensure that the driver notices the malfunction of the device while not causing discomfort to the driver.Specifically, the equivalent characteristic is set such that the characteristic changes based on at least one parameter from a value equivalent to the brake operation amount Bpa (equivalent to Bpa, Gxa, Pwc, collectively referred to as an operation equivalent value), a state of increase / decrease of the operation amount Bpa, and a number of repetitions NKR of a brake operation sequence. Details of the equivalent characteristic are described below.

[0046] Similar to the first determination means (first determination calculation unit) HNA of the first control means ECA, the second determination means (second determination calculation unit) HNB is formed in the second control means ECB. The suitability of the operating state of the second fluid pressure unit EAB is determined in the second determination means HNB (which is equivalent to a determination means) according to the method similar to the first determination means HNA. In addition, it is determined by the second determination means HNB whether the operating state of the first fluid pressure unit EAA is in a suitable state or not. The second determination means HNB acquires a signal related to the operating state of the first fluid pressure unit EAA through the communication bus CMB and determines the suitability of the first fluid pressure unit EAA based on the signal.The second fluid pressure unit EAB has been described above.

[0047] From the second fluid pressure unit EAB (specifically, the first pressure regulating mechanism CHA), the brake fluid regulated by each wheel cylinder WC is discharged and inflowed through the fluid path (wheel cylinder piping) HKW. The piston in the wheel cylinder WC moves (forward and backward) with respect to the rotating element KT, and the braking force of the wheel WH is regulated (increased or decreased) by regulating the fluid pressure Pwc in the wheel cylinder WC of the caliper CP.

[0048] The vehicle is equipped with a notification device HC. If the first fluid pressure unit EAA is in an unsuitable state, this is reported to the driver via the notification device HC. For example, the notification device HC notifies the driver of the unsuitable state of the device through a sound, a light, or the like. <Einstellungsverarbeitung der Ersatzkennlinie>

[0049] Setting processing of the operating characteristics (substitute characteristics) in the substitute control is carried out with reference to the flowchart according to Fig. 2. Here, in the backup control, when the first fluid pressure unit EAA (pressurizing device for normal braking) malfunctions, the operation of the first fluid pressure unit EAA is stopped, and the wheel cylinder fluid pressure Pwc is increased according to the operation amount Bpa by the second fluid pressure unit EAB (pressurizing device for vehicle stability control). The operation characteristics (brake fluid pressure Pwc with respect to the operation amount Bpa, corresponding to the vehicle deceleration Gxa) when the backup control is executed are the backup characteristics. The backup characteristics consist of two types of characteristics (approach characteristics CHgp and notification characteristics CHbp, CHzg, CHkr).

[0050] First, in step S110, the suitability determination result (Hna, etc.) of the first fluid pressure unit EAA is read. Processing proceeds to step S120, where, based on the determination result, it is determined whether or not the operation of the first fluid pressure unit EAA is in a suitable state. If the first fluid pressure unit EAA is in a suitable state and the result in step S120 is affirmative ("YES"), processing proceeds to step S210. Conversely, if the first fluid pressure unit EAA is in an unsuitable state and the result in step S120 is negative ("NO"), processing proceeds to step S130.

[0051] In step S130, the brake application amount Bpa (a collective expression of the application offset Sbp and the application force Fbp) is read. In step S140, the application amount Bpa is stored.

[0052] In step S150, the operation amount Bpa is calculated from the increase, maintenance, and decrease. Specifically, a time change amount dBp of the operation amount Bpa (i.e., a time differential value of the operation amount Bpa) is calculated based on the operation amount Bpa in the current calculation cycle and the stored operation amount Bpa. The operation amount Bpa is increasing when the operation change amount dBp is greater than "0" (i.e., the operation change amount dBp is a positive value), and the operation amount Bpa is maintained at a constant value when the operation change amount dBp is "0" (i.e., "dBp = 0"). Furthermore, the operation amount Bpa is decreasing when the operation change amount dBp is less than "0" (i.e., the operation change amount dBp is a negative value).

[0053] In step S160, the number of repetitions NKR of the operation of the brake operating member BP in a sequence of operations of the brake operating member BP is calculated based on the operation amount Bpa in the current calculation cycle and the stored operation amount Bpa. Here, the "sequence of operations" means from the start of the operation to the end of the operation. Therefore, when the operation amount Bpa increases from "0", decreases, and returns to "0", "one time" of the brake operation is counted at that time. The number of repetitions NKR is a value indicating "what number of brake operations" a current (present) calculation cycle is from the time when the malfunction state of the first fluid pressure unit EAA is first detected (that is, a calculation cycle that transitions from the appropriate state to the inappropriate state).

[0054] In step S170, it is determined whether or not the specific condition JSP exists based on at least one of the magnitude of the operation amount Bpa, the increase / decrease state of the operation amount Bpa, and the number of repetitions NKR. Here, the "specific condition JSP" is a condition for selecting one of two types of substitute characteristics. When the specific condition JSP is satisfied, the approximate characteristic CHgp (a characteristic that substantially matches a suitability characteristic CHgo), to be described below, is selected as the calculation map of the operation characteristic. On the other hand, when the specific condition JSP is not satisfied (that is, referred to as "notification condition JHC"), the notification characteristics CHbp, CHzg, and CHkr, which are different from the suitability characteristic CHgo, are selected as the calculation map of the operation characteristic.

[0055] In step S170, it is determined whether the specific condition JSP exists based on whether the operation amount Bpa is less than a predetermined amount bpx. If Bpa < bpx and the result in step S170 is affirmative ("YES"), the processing proceeds to step S220. On the other hand, if Bpa ≥ bpx and the result in step S170 is negative ("NO"), the processing proceeds to step S230. Here, the predetermined amount bpx is a threshold value for determination that is set in advance. For example, the predetermined amount bpx can be set as a value equivalent to a general braking state of "0.3 to 0.4 [G]" in the deceleration Gxa of the vehicle.

[0056] Further, in step S170, it is determined whether the specific condition JSP exists based on whether the operation amount Bpa is increasing or not. If "dBp > 0 (increasing)" and the result in step S170 is affirmative ("YES"), the processing proceeds to step S220. On the other hand, if "dBp ≤ 0 (maintaining or decreasing)" and the result in step S170 is negative ("NO"), the processing proceeds to step S230.

[0057] Further, in step S170, it is determined whether the specific condition JSP is satisfied based on whether the number of repetitions NKR is less than a predetermined number of times nkx. If "NKR < nkx" is satisfied and the result in step S170 is affirmative ("YES"), the processing proceeds to step S220. On the other hand, if "NKR ≥ nkx" and the result in step S170 is negative ("NO"), the processing proceeds to step S230. Here, the predetermined number of times nkx is a threshold value for determination that is set in advance.

[0058] In step S210, the suitability characteristic CHgo is set when the first fluid pressure unit EAA is in a suitable state. The suitability characteristic CHgo is a relationship between the brake operation amount Bpa and the brake fluid pressure Pwc when the device is operating properly (normal braking time). The suitability characteristic CHgo is set in advance in the first fluid pressure unit EAA. Then, the first fluid pressure unit EAA is controlled based on the suitability characteristic CHgo. At this time, the second fluid pressure unit EAB is stopped as long as the vehicle stability control or the like is not being executed.

[0059] In step S220, since the specific condition JSP is satisfied, the approximate characteristic CHgp is set as the substitute characteristic (a calculation characteristic in the substitute control). The approximate characteristic CHgp substantially coincides with the suitable characteristic CHgo so as not to cause discomfort to the driver. The approximate characteristic CHgp is set in advance in the second fluid pressure unit EAB.

[0060] In step S230, the first, second, and third notification characteristics CHbp, CHzg, CHkr are set as backup characteristics (in the case of the notification condition JHC). The notification characteristics CHbp, CHzg, CHkr are set differently from the suitability characteristic CHgo to inform the driver of the device malfunction. The notification characteristics CHbp, CHzg, CHkr are preset in the second fluid pressure unit EAB.

[0061] Here, the first notification characteristic CHbp is selected based on "whether the operation amount Bpa is less than the predetermined amount bpx or not." The second notification characteristic CHzg is selected based on "whether the operation amount Bpa is increasing or not." The third notification characteristic CHkr is selected based on "whether the number of repetitions NKR is less than the predetermined number nkx or not." In the determination of step S170, the three conditions described above may be combined. That is, in step S170, a determination is made as to "whether the specific condition JSP exists or not" based on at least one of the three conditions. Details of the notification characteristics CHbp, CHzg, CHkr will be described below.

[0062] In the brake control device, when the first fluid pressure unit EAA is in a malfunction state, one of the proximity characteristic curve CHgp and the notification characteristics (CHbp, etc.) is set as the backup characteristic (calculation map of backup control). Then, the second fluid pressure unit EAB is controlled based on the backup characteristic. At this time, the first fluid pressure unit EAA is stopped.

[0063] During normal braking, the brake fluid pressure Pwc is regulated by the first fluid pressure unit EAA according to the suitability characteristic CHgo (calculation map stored in the first control device ECA) corresponding to the operation of the brake operating element BP. However, when the first fluid pressure unit EAA malfunctions, the brake fluid pressure Pwc is not only increased by the master cylinder MC, but also increased by the second fluid pressure unit EAB according to the alternative characteristics CHgp, CHbp, CHzg, and CHkr (calculation map stored in the second control device ECB) corresponding to the operation of the brake operating element BP. The second fluid pressure unit EAB is not newly provided for fail-safe operation, but exists for braking control such as vehicle stability control.Consequently, it is possible to deal with the malfunction of the first fluid pressure unit EAA without providing an additional device.

[0064] Furthermore, the equivalent characteristic curve is composed of two types: the proximity characteristic curve CHgp, which does not cause discomfort to the driver, and the notification characteristics CHbp, CHzg, and CHkr, which notify the driver of the device malfunction through the operating characteristic curve. The device malfunction can be reliably reported without causing discomfort to the driver by appropriately selecting the above-mentioned characteristics.

[0065] In step S170, the determination of the specific condition JSP may be made based on a value (referred to as an operation equivalent value) equivalent to the operation amount Bpa, instead of the operation amount Bpa. The operation equivalent value is a value in the power transmission path from the operation amount Bpa to the vehicle deceleration Gxa. For example, the operation amount Bpa itself, the brake fluid pressure Pwc, and the vehicle deceleration Gxa correspond to the operation equivalent value. The case where the operation equivalent value is less than the predetermined amount bpx is the specific condition JSP, and the approximate characteristic CHgp is applied as the substitute characteristic. In contrast, the case where the operation equivalent value is greater than or equal to the predetermined amount bpx is the notification condition JHC, and the notification characteristic CHbp is applied as the substitute characteristic. <Erstes Einstellungsbeispiel der Ersatzkennlinien>

[0066] A first setting example of the equivalent characteristic curve is shown with reference to the characteristic diagram according to Fig. 3. In the first setting example, the specific condition JSP of the substitute control is determined based on the operation equivalent value (Bpa, etc.).

[0067] When the operation of the first fluid pressure unit EAA is in a suitable state, the suitability characteristic curve CHgo (see dashed line) is set as the calculation map for the first fluid pressure unit EAA. In the suitability characteristic curve CHgo, the brake fluid pressure Pwc (fluid pressure in the wheel cylinder WC) is set to maintain "0" from the brake operation amount Bpa from "0" to the predetermined value bpo, and the brake fluid pressure Pwc is set to monotonously increase from "0" (see characteristic curve PQR) as the operation amount Bpa increases from the predetermined value bpo. Here, the predetermined value bpo is a preset predetermined value equivalent to the play of the brake operation member BP.

[0068] When the operation of the first fluid pressure unit EAA is in an unsuitable state, the notification device HC notifies the driver that the first fluid pressure unit EAA is unsuitable. In addition, a substitute control is performed by the second fluid pressure unit EAB. In the substitute control, the brake fluid pressure Pwc is increased by the second fluid pressure unit EAB instead of the first fluid pressure unit EAA. In the substitute control, the operation characteristic (brake fluid pressure characteristic with respect to the operation amount Bpa) is changed from the suitability characteristic CHgo to the substitute characteristic CHgp, CHbp.

[0069] The equivalent characteristic is configured by two characteristics: the approximate characteristic CHgp, which corresponds to the specific condition JSP, and the first notification characteristic CHbp, which corresponds to the notification condition JHC (a condition when the specific condition JSP is negated). In the equivalent characteristic, the case where the brake application amount Bpa is applied is described as an example of the application equivalent value.

[0070] The case where the actuation amount Bpa is "0" to less than the predetermined amount bpx satisfies the specific condition JSP. In the specific condition JSP, the substitute characteristic is set to the approximate characteristic CHgp, which is close to the suitability characteristic CHgo. In Fig. 3, the approximate characteristic curve CHgp substantially coincides with and overlaps the suitability characteristic curve CHgo. Specifically, in the approximate characteristic curve CHgp, the brake fluid pressure Pwc (fluid pressure in the wheel cylinder WC) is set to maintain "0" from the operation amount Bpa from "0" to the predetermined value bpo, and the brake fluid pressure Pwc is set to monotonously increase from "0" (refer to characteristic curve PQ) as the operation amount Bpa increases from the predetermined value bpo.

[0071] The case where the actuation amount Bpa is greater than or equal to the predetermined amount bpx is the notification condition JHC (when the specific condition JSP is not met). In the notification condition JHC, the substitute characteristic is set to the first notification characteristic CHbp, which is completely different from the suitability characteristic CHgo. The device malfunction is notified to the driver through the change in the operation characteristic caused by the first notification characteristic Chbp.

[0072] Specifically, when the operation amount Bpa is greater than or equal to the predetermined amount bpx, the brake fluid pressure Pwc increases monotonously as the operation amount Bpa increases, but the increase amount (i.e., a fluid pressure increase gradient) of the brake fluid pressure Pwc with respect to the increase in the operation amount Bpa is made smaller than the suitability characteristic CHgo (refer to characteristic QS). Consequently, in the first notification characteristic CHbp, the brake fluid pressure Pwc is determined to be small compared with the suitability characteristic CHgo with respect to the same operation amount Bpa. As a result, at the time of a malfunction of the first fluid pressure unit EAA, even with the same operation amount Bpa, the vehicle deceleration Gxa is less likely to be generated compared with the time of normal braking.In addition to the notification by the notification device HC, the driver is able to notice the malfunction of the brake control device by such a difference.

[0073] The approach characteristic CHgp and the first notification characteristic CHbp are made continuous at a point Q (predetermined amount bpx, predetermined fluid pressure pwx). Therefore, even when transitioning from the approach characteristic CHgp to the first notification characteristic CHbp, the driver is not given a sense of discontinuity corresponding to the increase in the operation amount Bpa.

[0074] In the first notification characteristic CHbp, it is set as a characteristic smaller than the suitability characteristic CHgo (that is, a calculation map in which a small brake fluid pressure Pwc is determined with the same operation amount Bpa). In order to notify the driver of the malfunction of the first fluid pressure unit EAA, it is sufficient for the first notification characteristic CHbp to be different from the suitability characteristic CHgo. That is, the first notification characteristic CHbp may be a characteristic larger than the suitability characteristic CHgo (a characteristic in which the slope of the fluid pressure with respect to the operation amount Bpa is large). However, unlike the first fluid pressure unit EAA, the second fluid pressure unit EAB is applied for vehicle stability control and the like.Consequently, the first notification characteristic CHbp is desirably set to be a characteristic smaller than the suitability characteristic CHgo (a characteristic in which the gradient of the fluid pressure with respect to the operation amount Bpa is small) in order to suppress a sudden change in the brake fluid pressure Pwc.

[0075] Here, the characteristic curve CHmc (a characteristic curve in which the brake fluid pressure Pwc increases from the predetermined value bpm, which is greater than the predetermined value bpo, which is indicated by a dot-dash line) is the characteristic curve (“pressurization characteristic” of the master cylinder MC) of a time when the first fluid pressure unit EAA and the second fluid pressure unit EAB are both not operating. That is, in Fig. 1, the pressurization characteristic is when the master cylinder cut valve VMC is at the open position (connected state) and the simulator cut valve VSM is at the closed position (non-connected state). In this case, the brake fluid is supplied under pressure directly from the master cylinder MC to the wheel cylinders WC, increasing the pressure Pwc of the brake fluid. The first notification characteristic CHbp is a characteristic smaller than the suitability characteristic CHgo (a characteristic in which the gradient of the fluid pressure Pwc with respect to the operation amount Bpa is small), but is set as a characteristic larger than the pressurization characteristic CHmc. Consequently, a sufficient brake fluid pressure Pwc can be ensured at a small operation amount Bpa through the substitute control.

[0076] The setting and modification of the substitute characteristic based on the brake application amount Bpa has been described above. As described above, the vehicle deceleration Gxa or the brake fluid pressure Pwc may be applied instead of the brake application amount Bpa. The application amount Bpa, the vehicle deceleration Gxa, and the brake fluid pressure Pwc are collectively referred to as the application equivalent value. Therefore, the substitute characteristic is set based on the application equivalent value. When the brake fluid pressure Pwc is applied for a condition setting, "the case where the brake fluid pressure Pwc is less than the predetermined fluid pressure pwx" corresponds to the specific condition JSP, and "the case where the brake fluid pressure Pwc is greater than or equal to the predetermined fluid pressure pwx" corresponds to the notification condition JHC. <Zweites Einstellungsbeispiel der Ersatzkennlinien>

[0077] A second setting example of the equivalent characteristic is shown with reference to the characteristic diagram according to Fig. 4. In the second setting example, the case where the operation amount Bpa is increased corresponds to the specific condition JSP (applying the approach characteristic CHgp), and the case where the brake operating element BP is returned and the operation amount Bpa is decreased corresponds to the notification condition JHC (applying the second notification characteristic CHzg).

[0078] In the suitability characteristic CHgo in the suitable state of the first fluid pressure unit EAA, the brake fluid pressure Pwc is increased from "0" with an increase in the operation amount Bpa at "Bpa = bpo". When the operation amount Bpa is decreased, a hysteresis is provided in the suitability characteristic CHgo. Specifically, when the brake operation member BP is returned to the initial position (corresponding to "Bpa = 0"), the brake fluid pressure Pwc is not immediately decreased, but is maintained at the constant value pw1 once and decreased toward "0". That is, the brake fluid pressure Pwc changes in the order of "P → T → U → P" as indicated by the dashed line, according to the increase and decrease of the brake operation amount Bpa.

[0079] The approximate characteristic CHgp in the unsuitable state of the first fluid pressure unit EAA is applied in the case of “dBp > 0 (i.e., during an increase in the operation amount Bpa)”. Specifically, the approximate characteristic CHgp is a characteristic that is close to the suitability characteristic CHgo as described above, and is Fig. 4 is a section of “P → T” that overlaps the suitability curve CHgo.

[0080] In the case where the brake operating element BP is returned ("dBp ≥ 0 (that is, the operation amount Bpa is maintained or decreases)"), the second notification characteristic CHzg is applied. Different from the suitability characteristic CHgo, the second notification characteristic CHzg is the one in which the hysteresis is further increased. More specifically, as the operation amount Bpa decreases, the constant value pw1 is maintained at a smaller operation amount Bpa, and thereafter, the brake fluid pressure Pwc is returned to "0" in the order of "T → U → V → P" with a larger fluid pressure decrease gradient (slope of fluid pressure decrease with respect to the operation amount Bpa).

[0081] Similar to the first setting example, when the first fluid pressure unit EAA malfunctions, the device malfunction is notified by the notification device HC. As the operation amount Bpa increases, the brake fluid pressure Pwc (and accordingly, the vehicle deceleration Gxa) is maintained similar to that at the time of normal braking (when the first fluid pressure unit EAA is operating properly), even when the first fluid pressure unit EAA malfunctions, thus the driver does not feel discomfort. However, since the hysteresis of the brake fluid pressure Pwc with respect to the operation amount Bpa is increased when the brake operating element BP is returned, the decrease in the vehicle deceleration Gxa with respect to time lags slightly. Consequently, the driver can notice the malfunction of the brake control function. <Drittes Einstellungsbeispiel der Ersatzkennlinien>

[0082] A third setting example of the equivalent characteristic is shown with reference to the characteristic diagram according to Fig. 5. In the third setting example, the specific condition JSP (applying the proximity characteristic CHgp) or the notification condition JHC (applying the third notification characteristic CHkr) is determined based on the number of repetitions NKR of the brake operation after detection of the malfunction of the first fluid pressure unit EAA. The number of repetitions NKR represents the number of operations (from a start to an end, counted as one time) of the current brake operation by counting from a point in time after the malfunction is detected. Here, the number of repetitions NKR is calculated by storing the change thereof and monitoring it based on the operation amount Bpa.

[0083] Similar to the first setting example, the suitability characteristic CHgo (see dashed line) is set when the first fluid pressure unit EAA is suitable. When the first and second fluid pressure units EAA or EAB are not operating, the operating characteristic becomes the pressurization characteristic CHmc (see dot-dash line), which is determined by the specifications of the master cylinder MC and wheel cylinder WC (piston cross-sectional area, etc.).

[0084] The case where the number of repetitions NKR is less than the predetermined number of times nkx is equivalent to the specific condition JSP. In the specific condition JSP, a characteristic curve similar to the suitability characteristic CHgo is set as the approximate characteristic CHgp (see the dashed line overlapping the suitability characteristic CHgo). Here, the predetermined number of times nkx is a threshold value set in advance for determining the specific condition.

[0085] The case where the number of repetitions NKR is greater than or equal to the predetermined number of times nkx is equivalent to the notification condition JHC. In the notification condition JHC, the third notification characteristic CHkr is set as a characteristic that is different from the suitability characteristic CHgo (for example, a characteristic that is smaller than the suitability characteristic CHgo). Furthermore, the third notification characteristic CHkr may be set as a characteristic that sequentially decreases with an increase in the number of repetitions NKR (that is, a calculation map in which a smaller brake fluid pressure Pwc is determined with the same operation amount Bpa). Specifically, as the number of repetitions NKR increases, the slope (fluid pressure gradient) of the generated fluid pressure with respect to the operation amount Bpa is gradually reduced, so that the obtained brake fluid pressure Pwc gradually decreases.Furthermore, the operation amount Bpa (fluid pressure generation operation amount) in which the brake fluid pressure Pwc increases from "0" is gradually increased from the predetermined value bpo to the predetermined value bpm (>bpo) as the number of repetitions of NKR increases. That is, in the third notification characteristic CHkr, at least one of a decrease in the fluid pressure gradient and an increase in the fluid pressure generation operation amount can be applied according to the number of repetitions of NKR.

[0086] Similar to the first and second setting examples, when the first fluid pressure unit EAA malfunctions, the device malfunction is notified by the notification device HC. When the number of repetitions of NKR is small, the brake fluid pressure Pwc (and accordingly, the vehicle deceleration Gxa) is obtained similar to the time of normal braking (when the first fluid pressure unit EAA is operating properly) even when the first fluid pressure unit EAA malfunctions. For this reason, the driver does not feel discomfort. However, as the number of repetitions of NKR increases, the third notification characteristic CHkr is sequentially changed to a characteristic smaller than the suitability characteristic CHgo (a characteristic in which it is difficult to obtain the brake fluid pressure Pwc). Consequently, the driver can notice the malfunction of the brake control device. <Zweites Ausführungsbeispiel der Bremssteuerungsvorrichtung>

[0087] A second embodiment of a brake control device of a vehicle according to the present invention will be described with reference to an overall configuration diagram of Fig. 6. In the first embodiment, the wheel cylinder WC is selectively pressurized by one of the first fluid pressure unit EAA and the master cylinder MC (a so-called break-by-wire configuration). In the second embodiment, the first fluid pressure unit EAA is provided between the master cylinder MC and the brake operating member BP, and the pressurization of the wheel cylinder WC is always performed by the master cylinder MC. As described above, since elements having the same symbols, calculation processing, signals, characteristics, values, and the like are the same, the difference from the first embodiment will be mainly described.

[0088] The first fluid pressure unit EAA is provided between the master cylinder MC and the brake actuator BP. As shown in the cross-sectional view of the balloon portion, the master cylinder MC is of a tandem type, forming two master cylinder chambers Rmc partitioned by first and second master pistons PSN, PSM and the inner wall of the master cylinder MC. A compression spring SPR is provided between the first master piston PSN and the second master piston PSM. The master cylinder chamber Rmc is fluidly connected to the second fluid pressure unit EAB through a fluid path HKA. When the first and second master pistons PSN and PSM are moved in the forward direction (to the left in the figure), the volume of the master cylinder chamber RMC is reduced, and brake fluid is supplied under pressure from the master cylinder MC toward the wheel cylinder WC.The fluid pressure Pwc of the wheel cylinder WC thus increases. In contrast, when the master pistons PSN and PSM are moved in the reverse direction (to the right in the figure), the volume of the master cylinder chamber RMC increases, and the brake fluid is absorbed from the wheel cylinder WC into the master cylinder MC. The fluid pressure Pwc of the wheel cylinder WC thus decreases.

[0089] The first fluid pressure unit EAA is provided with a pressurizing piston PSH for pressing the first master piston PSN into the brake master cylinder MC. A pressurizing chamber Rka is formed by the inner wall of the first fluid pressure unit EAA and the pressurizing piston PSH. Furthermore, a reservoir chamber Rrs is formed by the inner wall of the first fluid pressure unit EAA, the master piston PSN, and the pressurizing piston PSH. The reservoir chamber Rrs is connected to the reservoir RSV, and the internal pressure is set to atmospheric pressure. The first pressure regulating mechanism CHA is fluidly connected to the pressurizing chamber Rka. The fluid pressure generated by the first power source PUA is regulated by the first pressure regulating mechanism CHA and supplied to the pressurizing chamber Rka.

[0090] When the fluid pressure in the pressurizing chamber Rka increases, the pressurizing piston PSH pushes the master piston PSN in the forward direction. As a result, the first and second master pistons PSN and PSM are moved in the forward direction, and the fluid pressure Pwc of the wheel cylinder WC is increased. Conversely, when the fluid pressure in the pressurizing chamber Rka decreases, the force for pushing the master piston PSN in the forward direction by the pressurizing piston PSH is reduced. As a result, the first and second master pistons PSN and PSM are moved in the reverse direction by the return spring SPR or the like, and the fluid pressure Pwc of the wheel cylinder WC is reduced.

[0091] Similar to the first embodiment, the simulator SSM may be provided. In this case, the brake control device is of a break-by-wire type, and the operating force Fbp of the brake operating element BP is generated by the simulator SSM.

[0092] Furthermore, a configuration can be used in which the SSM simulator is omitted. In the configuration without the SSM simulator, the actuating force Fbp of the brake actuating element BP is generated by the brake master cylinder MC. In this case, the first fluid pressure unit EAA functions as a booster device (brake booster).

[0093] Also in the second embodiment, similar to the first embodiment, the backup control is executed when the first fluid pressure unit EAA is in an unsuitable state. In the backup control, two different operation characteristics (Bpa-Pwc characteristic, Bpa-Gxa characteristic, respectively) are applied, whereby the second fluid pressure unit EAB is controlled. One characteristic is the approximate characteristic CHgp in the specific condition JSP. The approximate characteristic CHgp is a characteristic similar to the suitability characteristic CHgo when the first fluid pressure unit EAA is in a suitable state. The discomfort for the driver at the time of a malfunction of the first fluid pressure unit EAA is suppressed by the approximate characteristic CHgp. The other characteristic is the first, second, and third notification characteristics CHbp, CHzg, and CHkr in the notification condition JHC.The malfunction of the first fluid pressure unit EAA is appropriately reported to the driver according to the relationship between the vehicle deceleration Gxa and the brake application amount Bpa through these notification characteristics CHbp, CHzg, CHkr. The malfunction of the first fluid pressure unit EAA can be reported to the driver without discomfort through the two different replacement characteristics. <Andere Ausführungsbeispiele>

[0094] In the embodiments described above, the configuration of a disc-type brake device (disc brake) has been exemplified as a device for transmitting the braking torque to the wheel WH. In this case, the friction element is a brake pad, and the rotating element KT is a brake disc. Instead of the disc-type brake device, a drum-type brake device (drum brake) may be employed. In the case of the drum brake, a brake drum is employed instead of the caliper CP. Furthermore, the friction element is a brake shoe, and the rotating element KT is a brake drum.

[0095] A configuration in which the first determination means HNA is included in the first control means ECA to determine "whether the first fluid pressure unit EAA is in a proper state or a malfunction state" has been described by way of example. However, the present invention is not limited to this configuration; the proper determination of the first fluid pressure unit EAA may be performed based on information (a signal) obtained through the communication bus CMB by another control means connected to the first control means ECA through the communication bus CMB. Then, the result of the proper determination of the first fluid pressure unit EAA is transmitted to the second control means ECB through the communication bus CMB.For example, the suitability determination of the first fluid pressure unit EAA may also be carried out by the second control device ECB itself on the basis of a signal passing through the communication bus CMB.

[0096] If the start switch STR (also known as the ignition switch) is turned off once and then turned back on again, backup control may be configured not to execute. The operating characteristic in this case is the pressurization characteristic CHmc of the main combustion cylinder MC. Backup control is a measure to cope with an emergency situation involving a malfunction of the first fluid pressure unit EAA.

[0097] The first, second and third notification characteristics CHbp, CHzg and CHkr are individually defined with reference to Figures Fig. 3 to Fig.5. These notification characteristics can be combined with the corresponding specific condition JSP. That is, at least one of the "three notification characteristics CHbp, CHzg, CHkr and the three corresponding specific conditions JSP" can be applied (in other words, corresponding to one or more "set(s) of specific conditions and notification characteristics"), whereby the final notification characteristics and specific conditions can be determined.For example, in a case where the first and second notification characteristics CHbp and CHzg are combined, the notification characteristic (decrease in the fluid pressure increase gradient) is determined according to the first notification characteristic CHbp when the operation amount Bpa is increased, and the notification characteristic (increase in hysteresis) is determined according to the second notification characteristic CHzg when the operation amount Bpa is decreased. Furthermore, when the second and third notification characteristics CHzg, CHkr are combined, the fluid pressure gradient is sequentially decreased, and the hysteresis is increased with an increase in the number of repetitions NKR.

Claims

[1] A brake control device for a vehicle which generates a braking force at a wheel (WH) by supplying a brake fluid pressure to a wheel cylinder (WC) in accordance with an operation of a brake operating member (BP) of a vehicle, the brake control device comprising: a first fluid pressure unit (EAA) that transmits the brake fluid pressure through a first power source (PUA); a second fluid pressure unit (EAB) that transmits the brake fluid pressure through a second power source (PUB) that is different from the first power source (PUA); and a suitability determination device (HNA) that determines a suitability of an operating state of the first fluid pressure unit (EAA); wherein, when the suitability determining means (HNA) determines that the operating state of the first fluid pressure unit (EAA) is suitable, the first fluid pressure unit (EAA) outputs the brake fluid pressure based on a suitability characteristic (CHgo), which is a relationship between an operation amount (Bpa) of the brake operating member (BP), which is set in advance, and the brake fluid pressure; the second fluid pressure unit (EAB) an approach characteristic (CHgp) that is substantially the same as the suitability characteristic (CHgo) and a notification characteristic (CHbp, CHzg, CHkr) that is different from the suitability characteristic (CHgo); and transmits the brake fluid pressure based on at least one of the proximity characteristic (CHgp) and the notification characteristic (CHbp, CHzg, CHkr) when the suitability determination device (HNA) determines that the operating state of the first fluid pressure unit (EAA) is not suitable, wherein the second fluid pressure unit (EAB) the number (NKR) of repetitions of a sequence of operations of the brake operating element (BP) from a time when the suitability determining means (HNA) determines that the operating state of the first fluid pressure unit (EAA) is not suitable is counted on the basis of the operation amount (Bpa), transmits the brake fluid pressure based on the approximate characteristic (CHgp) when the number (NKR) of repetitions is less than a predetermined number of times (nkx), and communicates the brake fluid pressure based on the notification characteristic (CHkr) when the number (NKR) of repetitions is greater than or equal to the predetermined number of times (nkx). [2] A brake control device for a vehicle according to claim 1, wherein the second fluid pressure unit (EAB) transmits the brake fluid pressure based on the approximate characteristic (CHgp) when an operation equivalent amount equivalent to the operation amount (Bpa) of the brake operating element (BP) is less than a predetermined value (bpx), and communicates the brake fluid pressure based on the notification characteristic (CHbp) when the operation equivalent amount is greater than or equal to the predetermined value (bpx). [3] A brake control device for the vehicle according to claim 2, wherein the second fluid pressure unit (EAB) sets the predetermined value to a value equivalent to “0.3 - 0.4 G” of deceleration of the vehicle. [4] A brake control device for the vehicle according to claims 1 to 3, wherein the second fluid pressure unit (EAB) transmits the brake fluid pressure based on the approximate characteristic (CHgp) as the operation amount (Bpa) increases, and communicates the brake fluid pressure based on the notification characteristic (CHzg) when the operation amount (Bpa) decreases. [5] The brake control device for the vehicle according to claim 1, wherein the second fluid pressure unit (EAB) decreases the notification characteristic (CHkr) according to an increase in the number (NKR) of repetitions when the number (NKR) of repetitions is greater than or equal to the predetermined number of times.

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