Vehicle braking system

Abstract

To provide a brake apparatus for a vehicle, capable of generating a brake fluid pressure in the event of a failure in a switching valve, while simplifying the configuration of the apparatus.SOLUTION: A brake apparatus 1 comprises switching valves 24a and 24b. The switching valves 24a and 24b are switched between: a first state in which a first fluid pressure generating device (15) and a vehicle behavior stabilizing device (26) are made to communicate with each other; and a second state in which a second fluid pressure generating device (13) and the vehicle behavior stabilizing device are made to communicate with each other. When at least one of the switching valves 24a and 24b is put, due to a failure, into a third state in which each of the first fluid pressure generating device and the second fluid pressure generating device is made to communicate with a frictional brake (7) (ST5: Yes, see Fig. 5), a control device 11 controls the second fluid pressure generating device so that atmosphere opening ports 23c and 23d are closed by pistons (21a and 21b) (ST6, see Fig. 4).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a braking system for a vehicle. [Background technology]

[0002] A known automotive brake system includes a master cylinder and a slave cylinder, and functions as both a by-wire brake system and a hydraulic brake system (see Patent Document 1). This brake system includes a switching valve that switches the connection state of an oil passage to switch the source of hydraulic oil supplied to the wheel brakes between the master cylinder and the slave cylinder. A three-way valve is used for the switching valve, which shortens the oil passage of the brake system and reduces the overall size of the brake system. This brake system also includes a hydraulic pressure control device (vehicle behavior stabilization device) that controls the hydraulic pressure acting on the wheel brakes (friction brakes) and helps stabilize vehicle behavior. The vehicle behavior stabilization device is located between the switching valve and the wheel brakes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-147644 Summary of the Invention [Problem to be solved by the invention]

[0004] The slave cylinder has an oil supply port (open-to-air port) connected to the oil chamber so that hydraulic oil can be supplied from the reservoir tank when the slave cylinder is not in operation, i.e., when the piston is in a desired position where it does not generate hydraulic pressure. However, a malfunction of the switching valve can cause the master cylinder and slave cylinder to become inoperable while communicating with the wheel brakes (open to both oil passages). When the slave cylinder is not in operation, the slave cylinder's open-to-air port communicates with the switching valve. In the event of such a malfunction, even if the master cylinder generates hydraulic pressure, oil will flow from the open-to-air port to the reservoir tank. This prevents hydraulic pressure from increasing. Furthermore, if the switching valve malfunctions while the master cylinder is generating hydraulic pressure, hydraulic pressure will decrease. This causes the brake system to be unable to supply hydraulic pressure to the wheel cylinders, resulting in an inability to generate braking force.

[0005] The brake device of Patent Document 1 includes a shutoff valve installed in the oil line between the switching valve and the slave cylinder, so that if the switching valve fails, the shutoff valve can be closed to prevent hydraulic leakage from the slave cylinder. However, the configuration of the brake device of Patent Document 1 requires a large number of parts, which increases costs. An object of the present invention is to simplify the configuration of a vehicle brake device while still being able to generate brake fluid pressure in the event of a switching valve failure.

[0006] The present invention aims to improve vehicle safety in order to solve the above problems, and ultimately to further improve traffic safety and contribute to the development of a sustainable transportation system. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, one aspect of the present invention is a brake device (1) for a vehicle, comprising: a first hydraulic pressure generating device (15) that generates hydraulic pressure according to a brake operation amount (PS) applied to a brake operator (10) by a driver; a second hydraulic pressure generating device (13) that generates hydraulic pressure by moving pistons (21 a, 21 b) using an electric actuator (12); friction brakes (7) that are provided on each wheel (2) and are driven by hydraulic pressure; switching valves (24 a, 24 b) that switch a hydraulic path (16) so that the friction brakes are functionally connected to one of the first hydraulic pressure generating device and the second hydraulic pressure generating device; and a control device (11) that controls the second hydraulic pressure generating device and the switching valve, wherein the switching valves communicate the first hydraulic pressure generating device with the friction brakes. Both are configured to switch between a first state in which the second hydraulic pressure generating device and the friction brake are disconnected, and a second state in which the first hydraulic pressure generating device and the friction brake are disconnected and the second hydraulic pressure generating device and the friction brake are connected, and the second hydraulic pressure generating device has hydraulic pressure supply ports (23e, 23f) connected to the switching valve and atmosphere open ports (23c, 23d) connected to a reservoir tank (20), and when the switching valve has failed and is in a third state in which the first hydraulic pressure generating device and the second hydraulic pressure generating device are connected to the friction brake (ST5: Yes, ST13: Yes), the control device controls the second hydraulic pressure generating device to close the atmosphere open port by the piston (ST6, ST14).

[0008] According to this aspect, when the switching valve fails and enters the third state in which the first hydraulic pressure generating device and the second hydraulic pressure generating device are connected to the friction brake, the piston closes the air-release port connected to the reservoir tank of the second hydraulic pressure generating device. This prevents the fluid chamber of the second hydraulic pressure generating device from being open to the atmosphere. Therefore, it is possible to generate brake fluid pressure to be supplied to the friction brake when the switching valve fails, while simplifying the configuration of the vehicle brake device without requiring a conventional shut-off valve.

[0009] In the above aspect, the brake device may further include a pressure sensor (25b) arranged in the hydraulic path between the switching valve and the first hydraulic pressure generating device or the second hydraulic pressure generating device, and the control device may determine whether the switching valve has entered the third state based on the stroke amount of the piston and the detection value of the pressure sensor, and when it is determined that the switching valve has entered the third state (ST5: Yes), the control device may close the atmosphere release port with the piston (ST6).

[0010] According to this aspect, it is possible to determine that the switching valve has failed and entered the third state based on the stroke amount of the piston and the detection value of the pressure sensor, and a fail-safe can be quickly implemented when the switching valve fails.

[0011] In the above aspect, when the control device determines that the switching valve has entered the third state (ST5: Yes), it is preferable that the control device stops the piston at the position at which it determined that the switching valve had entered the third state (ST6).

[0012] According to this aspect, by stopping the piston at the position at which it is determined that the switching valve has entered the third state, the second hydraulic pressure generating device is maintained in a state in which hydraulic fluid does not flow from the atmosphere release port to the reservoir tank (a state in which the atmosphere release port is closed), thereby making it possible to prevent the second hydraulic pressure generating device from entering an atmosphere release state.

[0013] In the above aspect, when the switching valve is in the third state (ST13: Yes), the control device may control the second hydraulic pressure generating device to displace the piston to a position that closes the atmosphere open port (ST14).

[0014] According to this aspect, even if the atmosphere release port of the second hydraulic pressure generating device is opened due to a failure of the switching valve, the piston is displaced to a position that closes the atmosphere release port. Therefore, the second hydraulic pressure generating device can be prevented from being opened to the atmosphere without requiring a conventional shutoff valve, and the vehicle brake device can be simplified.

[0015] In the above aspect, the brake device further includes a vehicle behavior stabilization device (26) that is provided in the fluid path between the switching valve and the friction brake, adjusts the hydraulic pressure of the working fluid supplied from the first hydraulic pressure generating device or the second hydraulic pressure generating device, and applies the adjusted hydraulic pressure to the friction brake, and when the switching valve is in the third state (ST13: Yes), the control device drives the vehicle behavior stabilization device (ST16) to apply hydraulic pressure corresponding to the brake operation amount to the friction brake.

[0016] According to this aspect, even if the switching valve is in the third state due to a failure, the second hydraulic pressure generating device and the vehicle behavior stabilization device can be prevented from generating braking forces individually (double boost), and the vehicle behavior stabilization device can generate braking forces for each wheel. Therefore, it is possible to ensure the safety of the vehicle through braking control. [Effects of the Invention]

[0017] According to the above aspects, the configuration is simplified while brake fluid pressure can be generated when the switching valve fails, improving vehicle safety, and ultimately further improving traffic safety and contributing to the development of a sustainable transportation system. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a brake system of a vehicle according to a first embodiment; [Figure 2] Hydraulic circuit diagram of the brake system in a certain state [Figure 3] Hydraulic circuit diagram of the brake system in other states [Figure 4] Hydraulic circuit diagram of the brake system in other states [Figure 5] Hydraulic circuit diagram of the brake system in other states [Figure 6] FIG. 1 is a flow diagram of braking control by a control device according to a first embodiment; [Figure 7]FIG. 10 is a flow diagram of braking control by a control device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, several embodiments of the present invention will be described in detail with reference to the drawings.

[0020] First Embodiment A first embodiment of the present invention will be described with reference to Figures 1 to 6. Figure 1 is a schematic diagram of a brake system of an electric vehicle or hybrid vehicle (hereinafter simply referred to as vehicle V) to which a brake device 1 according to the present invention is applied. The vehicle V has a pair of left and right front wheels 2F disposed at the front of the vehicle and a pair of left and right rear wheels 2R disposed at the rear of the vehicle. A motor-generator 4 is mechanically connected to a front axle 3 connected to the left and right front wheels 2F. Note that a differential mechanism is not shown. In the illustrated example, the vehicle V is front-wheel drive, but in other embodiments, a motor-generator 4 that drives the rear wheels 2R may be provided to make the vehicle rear-wheel drive or four-wheel drive.

[0021] The motor generator 4 serves both as an electric motor for driving the vehicle and as a generator for regeneration. The motor generator 4 is powered by a secondary battery 5, and a control device 11 (described later) controls the power supply from the battery 5 via an inverter 6 and the power supply (charging) to the battery 5. The motor generator 4 serves as regenerative braking means that converts deceleration energy into electric power during deceleration, generating regenerative braking force.

[0022] Each of the front wheels 2F and rear wheels 2R is provided with a known disc brake 7, which serves as a friction brake for performing friction braking and is made up of a caliper with a disc 7a and a wheel cylinder 7b that are integral with the wheel 2 (front wheels 2F, rear wheels 2R). A brake fluid pressure generator 8 is connected to the wheel cylinder 7b via a known brake piping. As will be described in detail later, the brake fluid pressure generator 8 is made up of a hydraulic circuit that can increase or decrease the brake pressure and distribute it to each wheel.

[0023] Each of the front wheels 2F and rear wheels 2R is provided with a wheel speed sensor 9 as a wheel speed detection means for detecting the corresponding wheel speed. The automobile V is provided with a brake pedal 10 as a brake operator used for braking by the driver, and the brake pedal 10 is provided with a pedal stroke sensor 10a for detecting the amount of operation (amount of depression) of the brake pedal.

[0024] The automobile V is provided with a control device 11 that performs various vehicle controls and functions as a braking force control means. The control device 11 is an electronic control unit (ECU) that includes an arithmetic processing unit (a processor such as a CPU or MPU) and a storage device (memory such as a ROM or RAM) and is composed of a computer configured to execute various processes. The control device 11 being configured to execute various processes means that the arithmetic processing unit (processor) that constitutes the control device 11 is programmed to read necessary data and application software from the storage device (memory) and execute the specified arithmetic processing in accordance with the software. The control device 11 may be configured as a single piece of hardware, or may be configured as a unit consisting of multiple pieces of hardware.

[0025] The inverter 6 is electrically connected to the control device 11. Detection signals from the wheel speed sensor 9 and the pedal stroke sensor 10a are input to the control device 11. In the case of an electric vehicle, this configuration may be left as is, but in the case of a hybrid vehicle, the output shaft of an engine E (internal combustion engine), indicated by the two-dot chain line in the figure, is connected to the front axle 3.

[0026] The control device 11 determines that a braking command has been issued when the output signal from the pedal stroke sensor 10a of the brake pedal 10 increases from its initial value (=0), and performs control during braking using the brake fluid pressure generator 8. In this way, since regenerative cooperative control is performed, which performs both regenerative braking and hydraulic braking, the brake device 1 employs a brake-by-wire system.

[0027] Next, a brake device 1 to which the present invention is applied will be described with reference to FIG. 2. The brake device 1 of this embodiment is configured as a so-called brake-by-wire system that can control braking force independently of the driver's operation. That is, the brake device 1 does not use, as brake fluid pressure, the fluid pressure generated by a master cylinder 15 (first fluid pressure generating device) to which the operation of a brake pedal 10 is mechanically transmitted. A control device 11 detects the operation amount of the brake pedal 10 (brake pedal operation amount PS) using a pedal stroke sensor 10a and switches oil passages 16 (16c, 16d) based on this detected operation amount value. The control device 11 also drives an electric servo motor 12 (electric actuator) based on the fluid pressure generated by the master cylinder 15 to control the operation of a motor drive cylinder 13 (second fluid pressure generating device, slave cylinder), thereby generating brake fluid pressure.

[0028] Brake pedal 10 is rotatably supported on the vehicle body and moves in an arc in response to the driver's braking operation. One end of rod 14, which converts the arc motion into approximately linear motion, is connected to brake pedal 10, and the other end of rod 14 engages with a first piston 15a of a master cylinder 15 arranged in series so as to push against it in response to the driver's braking operation. A second piston 15b is arranged in series on the side of first piston 15a opposite rod 14 in master cylinder 15, and first piston 15a and second piston 15b are each spring-biased toward rod 14. Brake pedal 10 is spring-biased and stopped by a stopper (not shown) to be in the standby position shown in FIG. 2.

[0029] The brake device 1 includes a reservoir tank 20 connected to the motor drive cylinder 13 and the master cylinder 15 via oil passages 16a, 16b to replenish the motor drive cylinder 13 and the master cylinder 15 with brake fluid. Within the master cylinder 15, a first fluid chamber 17a is formed between the first piston 15a and the second piston 15b, and a second fluid chamber 17b is formed on the side of the second piston 15b opposite the first piston 15a. The first fluid chamber 17a and the second fluid chamber 17b of the master cylinder 15 are provided with two atmosphere-opening ports 17c, 17d, which are respectively connected to the reservoir tank 20 via the oil passage 16b. The first piston 15a and the second piston 15b of the master cylinder 15 are provided with seal members of known structure in appropriate positions to seal the first fluid chamber 17a and the second fluid chamber 17b.

[0030] The first fluid chamber 17a and the second fluid chamber 17b are provided with two hydraulic supply ports 17e and 17f, which are respectively connected to the disc brake 7 via an oil passage 16c. The two hydraulic supply ports 17e and 17f are not blocked by seal members regardless of the positions of the first piston 15a and the second piston 15b, and are always in communication with the corresponding first fluid chamber 17a and second fluid chamber 17b. On the other hand, when the first piston 15a and the second piston 15b move from the initial positions shown in FIG. 2, the atmosphere release ports 17c and 17d are blocked by the corresponding first piston 15a and second piston 15b as the seal members pass through.

[0031] Meanwhile, the motor-driven cylinder 13 is provided with the electric servo motor 12, a gear box 18 connected to the electric servo motor 12, a threaded rod 19, a first piston 21a, and a second piston 21b. The threaded rod 19 is displaced in the axial direction by torque transmitted to the gear box 18 via a ball screw mechanism. The first piston 21a and the second piston 21b are arranged coaxially with the threaded rod 19 and in series with each other. The first piston 21a and the second piston 21b are each spring-biased toward the threaded rod 19 by a return spring. Note that when the first piston 21a advances (displaces toward the second piston 21b), it can be displaced independently of the second piston 21b. When the first piston 21a retreats from the advanced state to the initial state shown in FIG. 2, the second piston 21b also returns to its initial position.

[0032] A first hydraulic pressure generating chamber 23a is formed between the first piston 21a and the second piston 21b within the motor drive cylinder 13, and a second hydraulic pressure generating chamber 23b is formed on the side of the second piston 21b opposite to the first piston 21a. Two open-to-atmosphere ports 23c, 23d are provided in the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b of the motor drive cylinder 13, and these ports are connected to the reservoir tank 20 via an oil passage 16a. Seal members of known construction are provided in appropriate positions in the first piston 21a and the second piston 21b of the motor drive cylinder 13, respectively, to seal the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b.

[0033] Furthermore, the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b are provided with two hydraulic pressure supply ports 23e, 23f, each connected to the disc brake 7 via an oil passage 16d. The two hydraulic pressure supply ports 23e, 23f are not blocked by seal members regardless of the positions of the first piston 21a and the second piston 21b, and are always in communication with the corresponding first hydraulic pressure generating chamber 23a and second hydraulic pressure generating chamber 23b. On the other hand, when the first piston 21a and the second piston 21b move from the initial positions shown in FIG. 2, the seal members pass through and the corresponding atmosphere release ports 23c, 23d are blocked by the first piston 21a and the second piston 21b.

[0034] The first fluid chamber 17a of the master cylinder 15 and the first fluid pressure generating chamber 23a of the motor drive cylinder 13 are connected to the disc brakes 7 of the rear wheel 2R via electromagnetic switching valves 24a, which are three-way valves. The second fluid chamber 17b of the master cylinder 15 and the second fluid pressure generating chamber 23b of the motor drive cylinder 13 are connected to the disc brakes 7 of the front wheel 2F via electromagnetic switching valves 24b, which are three-way valves.

[0035] Orifices are provided in each of the connection portions of the switching valves 24a, 24b with oil passage 16c communicating with the first fluid chamber 17a and the second fluid chamber 17b of the master cylinder 15, and with oil passage 16d communicating with the first fluid pressure generating chamber 23a and the second fluid pressure generating chamber 23b of the motor drive cylinder 13. The orifice provided in oil passage 16c connected to the master cylinder 15 is smaller than the orifices provided in oil passage 16d connected to the motor drive cylinder 13.

[0036] The switching valves 24a, 24b switch the oil passages 16c, 16d so that the disc brake 7 is functionally connected to one of the master cylinder 15 and the motor drive cylinder 13. Specifically, the switching valves 24a, 24b are configured to selectively take a first state shown in Figure 2 in which the disc brake 7 of the corresponding wheel 2 is connected to the master cylinder 15 via the oil passage 16c, and a second state shown in Figure 3 in which the disc brake 7 is connected to the motor drive cylinder 13 via the oil passage 16d. Note that the switching valves 24a, 24b are each in the first state when not energized.

[0037] In the first state, the switching valves 24a, 24b connect the wheel cylinder 7b of the disc brake 7 to the corresponding first fluid chamber 17a or second fluid chamber 17b of the master cylinder 15. In the first state, the switching valves 24a, 24b also function as check valves that allow fluid to flow from the corresponding first fluid pressure generating chamber 23a or second fluid pressure generating chamber 23b of the motor drive cylinder 13 to the wheel cylinder 7b, and prevent fluid from flowing in the opposite direction.

[0038] In the second state, the switching valves 24a, 24b connect the wheel cylinder 7b of the disc brake 7 to the corresponding first fluid pressure generating chamber 23a or second fluid pressure generating chamber 23b of the motor drive cylinder 13. In the second state, the switching valves 24a, 24b also function as check valves that allow fluid to flow from the corresponding first fluid chamber 17a or second fluid chamber 17b of the master cylinder 15 to the wheel cylinder 7b, and prevent fluid from flowing in the opposite direction.

[0039] 2, when the driver operates the brake pedal 10 and the master cylinder 15 generates hydraulic pressure, the generated hydraulic pressure is transmitted to the wheel cylinder 7b, causing the disc brake 7 to generate braking force. When the motor-driven cylinder 13 generates hydraulic pressure that exceeds the hydraulic pressure generated by the master cylinder 15, the hydraulic pressure is transmitted to the wheel cylinder 7b via the switch valves 24a, 24b, causing the disc brake 7 to generate greater braking force.

[0040] 3, when the motor drive cylinder 13 generates hydraulic pressure, the generated hydraulic pressure is transmitted to the wheel cylinder 7b, causing the disc brake 7 to generate braking force. When the driver operates the brake pedal 10, causing the master cylinder 15 to generate hydraulic pressure that exceeds the hydraulic pressure generated by the motor drive cylinder 13, the hydraulic pressure is transmitted to the wheel cylinder 7b via the switch valves 24a, 24b. This causes the disc brake 7 to generate a greater braking force.

[0041] A brake pressure sensor 25a, which is a pressure sensor on the master cylinder 15 side that detects the master cylinder side hydraulic pressure generated by the master cylinder 15, is connected between the second fluid chamber 17b and the switching valve 24b. A brake pressure sensor 25b, which is a pressure sensor on the motor drive cylinder 13 side that detects the actual brake hydraulic pressure generated by the motor drive cylinder 13, is connected between the switching valve 24a and the first hydraulic pressure generating chamber 23a.

[0042] Furthermore, both switching valves 24a, 24b are each connected to a plurality of (four in the illustrated example) wheel cylinders 7b via a VSA device 26. The VSA device 26 may be a known vehicle behavior stabilization device equipped with an ABS to prevent wheel lock during braking, a TCS (traction control system) to prevent wheel spin during acceleration, yaw moment control during cornering, a brake assist function, an automatic braking function to avoid collisions, and the like. A detailed description thereof will be omitted here. The VSA device 26 is provided with a first hydraulic circuit system corresponding to each wheel cylinder 7b of the front wheels 2F and a second hydraulic circuit system corresponding to each wheel cylinder 7b of the rear wheels 2R. The VSA device 26 is equipped with a hydraulic motor 26a as a hydraulic pressure generating device that generates hydraulic pressure to be supplied to each hydraulic circuit, and its operation is controlled by the control device 11.

[0043] A cylinder-type simulator 28 is connected between the first fluid chamber 17a and the switching valve 24a via an electromagnetic shutoff valve 27a and a one-way valve 27b arranged in parallel. The simulator 28 is provided with a piston 28a that divides the inside of the cylinder, and a fluid storage chamber 28b is formed on the shutoff valve 27a side of the piston 28a. A compression coil spring 28c is accommodated on the side of the piston 28a opposite to the fluid storage chamber 28b side. The chamber where the compression coil spring 28c is provided is connected to the reservoir tank 20 via the master cylinder 15 and oil passage 16b.

[0044] The shutoff valve 27a is configured to be able to selectively assume a first state shown in FIG. 2 in which it shuts off the first liquid chamber 17a from the liquid storage chamber 28b, and a second state shown in FIG. 3 in which it functions as a check valve. In the second state, the shutoff valve 27a allows liquid to flow from the first liquid chamber 17a to the liquid storage chamber 28b and prevents the reverse flow. The shutoff valve 27a is in the first state when not energized. The one-way valve 27b is a check valve that allows liquid to flow from the liquid storage chamber 28b to the first liquid chamber 17a and prevents the reverse flow.

[0045] 3, when the driver depresses the brake pedal 10, the brake fluid in the first fluid chamber 17a flows into the fluid storage chamber 28b, and the biasing force of the compression coil spring 28c is transmitted to the brake pedal 10. This provides a reaction force against depression similar to that of a known brake system in which the master cylinder 15 and the wheel cylinder 7b are directly connected.

[0046] The brake fluid pressure generating device 8 configured as described above is comprehensively controlled by the control device 11. The control device 11 receives detection signals from the pedal stroke sensor 10a and the brake pressure sensors 25a, 25b, as well as detection signals from various sensors (not shown) for detecting vehicle behavior. Based on the detection signal from the pedal stroke sensor 10a and the detection signals from the various sensors, the control device 11 controls the drive of the motor drive cylinder 13 to control the friction braking force generated in the disc brake 7. Furthermore, when the target vehicle is a hybrid vehicle (or an electric vehicle) as in this embodiment, regenerative control is performed by the motor-generator 4. The control device 11 also controls the distribution of the magnitude of the friction braking force generated by the motor drive cylinder 13 relative to the magnitude of the regenerative braking force when regenerative control is performed.

[0047] Furthermore, the control device 11 is configured to perform automatic driving control of Level 2 or higher. Specifically, the control device 11 performs longitudinal vehicle control (driving and braking control) and lateral vehicle control (steering control) under specific conditions based on input from the driver. During automatic driving control, the control device 11 performs automatic brake control that supplies hydraulic pressure to the disc brakes 7 regardless of the driver's brake operation. During automatic brake control, the control device 11 generates braking force by driving the motor drive cylinder 13 with both switching valves 24a and 24b in the second state shown in FIG. 3.

[0048] Specifically, as shown in Fig. 4, the control device 11 drives the electric servo motor 12 to move the first piston 21a and the second piston 21b of the motor drive cylinder 13 in a pushing direction. When the seal members pass through the atmosphere vent ports 23c and 23d and the atmosphere vent ports 23c and 23d are closed by the first piston 21a and the second piston 21b, hydraulic pressure is generated in the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b. The hydraulic pressure generated by the motor drive cylinder 13 is supplied to the wheel cylinder 7b of the disc brake 7 from hydraulic pressure supply ports 23e and 23f (hydraulic pressure supply ports) via the oil passage 16d. This causes each wheel 2 to generate a braking force.

[0049] However, a malfunction that interferes with the execution of automatic driving control may occur in the vehicle V. If such an abnormality occurs during manual driving of the vehicle V, the control device 11 terminates brake-by-wire control using the motor-driven cylinder 13 and prohibits subsequent automatic driving at level 2 or higher. Specifically, the control device 11, as a rule, sets both directional control valves 24a and 24b to the first state and also sets the shutoff valve 27a to the first state. On the other hand, if such an abnormality occurs during automatic driving of the vehicle V, the control device 11 notifies the driver of the occurrence of the abnormality and requests intervention in driving (handover request). When the driver begins to intervene in driving, the control device 11, as a rule, sets both directional control valves 24a and 24b to the first state and also sets the shutoff valve 27a to the first state. With both directional control valves 24a and 24b in the first state, hydraulic pressure generated by the master cylinder 15 is directly supplied to the disc brakes 7, generating braking force according to the amount of braking operation by the driver.

[0050] On the other hand, even if such an abnormality occurs, the control device 11 continues the vehicle behavior stabilization control by the VSA device 26, such as the ABS, TCS, yaw moment control, brake assist function, and automatic braking function. In other words, the control device 11 continues to permit some automatic driving, including the vehicle behavior stabilization control.

[0051] Among the failures that could impede the continuation of automatic driving is a failure in which the switching valves 24a and 24b become inoperable in the third state (open to both oil passages 16c and 16d), which connects the master cylinder 15 and the motor drive cylinder 13 to the disc brake 7, respectively. Figure 5 shows the hydraulic circuit of the brake device 1 with the switching valve 24a in the third state. As shown in Figure 5, when the motor drive cylinder 13 is not in operation, the air-open ports 23c and 23d of the motor drive cylinder 13 are in communication with the switching valves 24a and 24b. Therefore, if such a failure occurs, even if the driver applies the brakes and the master cylinder 15 generates hydraulic pressure, oil will flow from the air-open port 23c to the reservoir tank 20. Therefore, the hydraulic pressure in the oil passage 16, where the switching valve 24a is installed, will not rise to the level expected by the driver. Furthermore, if the switching valve 24a malfunctions and enters the third state while the master cylinder 15 is generating hydraulic pressure, the hydraulic pressure in the oil passage 16 in which the switching valve 24a is provided drops. As a result, the brake device 1 is unable to supply the desired hydraulic pressure to the wheel cylinder 7b, and is therefore unable to generate the desired braking force on the corresponding rear wheel 2R.

[0052] Therefore, the control device 11 controls the motor drive cylinder 13 so that the first piston 21a and second piston 21b of the motor drive cylinder 13 close the atmosphere release ports 23c and 23d. Details will be explained later. In other words, when the switching valve 24a fails and enters the third state, the atmosphere release ports 23c and 23d connected to the reservoir tank 20 of the motor drive cylinder 13 are closed by the first piston 21a and second piston 21b. This prevents the first hydraulic pressure generating chamber 23a of the motor drive cylinder 13 from being open to the atmosphere. Therefore, it is possible to generate brake hydraulic pressure to be supplied to the disc brake 7 when the switching valve 24a fails, while simplifying the configuration of the brake device 1 without requiring a shutoff valve as in the past.

[0053] Next, the braking control procedure under normal circumstances will be described. Fig. 2 shows a case where both change-over valves 24a, 24b are in the first state and shut-off valve 27a is in the first state (when the driver is not operating the brake pedal 10 during manual driving). When the driver operates the brake pedal 10 during manual driving, or when automatic driving control is being executed, both change-over valves 24a, 24b are in the second state and shut-off valve 27a is in the second state, as shown in Fig. 3. When the driver is not operating the brake pedal 10, the detection value of pedal stroke sensor 10a is the initial value (=0), and basically, no brake fluid pressure generation signal is output from control device 11.

[0054] When the brake pedal 10 is depressed and the detection value of the pedal stroke sensor 10a becomes greater than 0, the control device 11 performs brake-by-wire control. Specifically, the control device 11 places both directional control valves 24a and 24b in the second state shown in FIG. 3 to block the transmission of hydraulic pressure generated in the master cylinder 15 to the motor-driven cylinder 13. The control device 11 also places the shutoff valve 27a in the second state shown in FIG. 3 to allow the hydraulic pressure generated in the master cylinder 15 to be transmitted to the simulator 28. The control device 11 then sets a target brake hydraulic pressure based on the hydraulic pressure detected by the brake pressure sensor 25a on the master cylinder 15 side, taking regenerative braking force into consideration, and outputs a target current corresponding to this target brake hydraulic pressure to the electric servo motor 12. This drives the threaded rod 19 and the first piston 21a in the pushing direction, generating brake hydraulic pressure in the first hydraulic pressure generating chamber 23a according to the brake pedal depression amount PS. At the same time, the second piston 21b is pushed by the hydraulic pressure in the first hydraulic pressure generating chamber 23a and displaced against the biasing force of the return spring, and the same magnitude of brake hydraulic pressure is generated in the second hydraulic pressure generating chamber 23b.

[0055] When the driver displaces the brake pedal 10 in the return direction, the control device 11 causes the electric servo motor 12 to return the threaded rod 19 to the initial position in accordance with the hydraulic pressure detected by the brake pressure sensor 25a on the master cylinder 15 side. This reduces the brake hydraulic pressure in accordance with the amount of operation of the brake pedal 10. Furthermore, when the brake pedal 10 is returned to the initial position by a return spring (not shown), the control device 11 sets both changeover valves 24a, 24b to the first state shown in FIG. 2.

[0056] When the VSA device 26 is not operating, the brake fluid pressure generated by the motor-driven cylinder 13 is supplied equally to each of the front and rear wheel cylinders 7b. On the other hand, when the VSA device 26 controls the braking force distribution to each wheel, the brake fluid pressure supplied to the wheel cylinders 7b of each wheel is adjusted in accordance with that control.

[0057] Even during execution of automatic operation control, the control device 11 sets both switching valves 24a, 24b and shutoff valve 27a to the second state shown in Fig. 3 and generates the friction braking force required for automatic operation by driving the motor-driven cylinder 13. When the automatic operation control ends, the control device 11 sets both switching valves 24a, 24b and shutoff valve 27a to the first state.

[0058] Next, a braking control procedure when an abnormality occurs will be described. Fig. 6 is a flowchart of braking control by the control device 11 in the first embodiment. The control device 11 repeatedly executes the control routine shown in Fig. 6 at predetermined control intervals.

[0059] The control device 11 determines whether a predetermined abnormality that interferes with the execution of automatic driving control has occurred in the vehicle V (step ST1). If the predetermined abnormality has occurred in the vehicle V (ST1: Yes), the control device 11 sets both switching valves 24a, 24b to the first state (step ST2) and ends this routine. As a result, the hydraulic pressure generated by the master cylinder 15 is directly supplied to the disc brake 7, generating a braking force according to the amount of brake operation by the driver.

[0060] If a predetermined abnormality has not occurred in the vehicle V in step ST1 (No), the control device 11 determines whether the driver is braking, i.e., whether the detection value of the pedal stroke sensor 10a is greater than 0 (step ST3). If the driver is not braking (ST3: No), the control device 11 performs the processing of step ST2 and then ends this routine. On the other hand, if the driver is braking (ST3: Yes), the control device 11 sets both switching valves 24a and 24b to the second state shown in FIG. 3 and drives the motor drive cylinder 13 in accordance with the amount of braking operation by the driver (step ST4). As a result, the hydraulic pressure generated by the motor drive cylinder 13 is supplied to the disc brake 7, and the desired braking force is generated at each wheel 2 in accordance with the amount of braking operation by the driver.

[0061] Thereafter, the control device 11 determines whether both the switching valves 24a, 24b are in the third state (a failure state in which the master cylinder 15 and the motor drive cylinder 13 are connected to the disc brake 7) (step ST5). Specifically, the control device 11 compares the stroke amounts of the first piston 21a and the second piston 21b of the motor drive cylinder 13 with the detection values ​​of the brake pressure sensors 25a, 25b. If the stroke amount of the first piston 21a and the detection value of the brake pressure sensor 25b on the motor drive cylinder 13 side are in a predetermined relationship, the control device 11 determines that the switching valve 24a is in the second state. On the other hand, if the two values ​​are not in the predetermined relationship (if the predetermined relationship is not established), the control device 11 determines that the switching valve 24a is in the third state. Furthermore, if the stroke amount of the second piston 21b and the detection value of the brake pressure sensor 25a on the master cylinder 15 side are in a predetermined relationship, the control device 11 determines that the switching valve 24b is in the second state. On the other hand, if the two values ​​do not have the predetermined relationship (if the predetermined relationship is not met), the control device 11 determines that the switching valve 24b is in the third state.

[0062] In this way, the control device 11 determines that the corresponding switching valve 24a, 24b has failed and entered the third state based on the stroke amount of the first piston 21a or the second piston 21b of the motor-driven cylinder 13 and the detection values ​​of the corresponding brake pressure sensors 25a, 25b. This allows the control device 11 to quickly implement a fail-safe, which will be described later, when the switching valve 24a, 24b fails.

[0063] If neither of the switching valves 24a, 24b is in the third state in step ST5 (No), the control device 11 ends this routine without doing anything. On the other hand, if at least one of the switching valves 24a, 24b is in the third state in step ST5 (Yes), the control device 11 immediately stops driving the electric servo motor 12 (step ST6) and ends this routine.

[0064] That is, in step ST5, the control device 11 stops the first piston 21a and the second piston 21b of the motor drive cylinder 13 at the position at which it is determined that at least one of the switching valves 24a, 24b has entered the third state. The first piston 21a and the second piston 21b of the motor drive cylinder 13 are positioned to close the atmosphere release ports 23c, 23d (hereinafter referred to as the closed position). Therefore, the motor drive cylinder 13 is maintained in a state in which hydraulic oil does not flow from the atmosphere release ports 23c, 23d to the reservoir tank 20 (a state in which the atmosphere release ports 23c, 23d are closed). This provides a fail-safe that prevents the motor drive cylinder 13 from entering an atmosphere-open state.

[0065] Thus, if the switching valves 24a, 24b have entered the third state due to a failure in step ST5 (Yes), the control device 11 controls the motor drive cylinder 13 in step ST6 so that the first piston 21a and the second piston 21b close the atmosphere release ports 23c, 23d. This prevents the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b of the motor drive cylinder 13 from being open to the atmosphere. Therefore, the configuration of the brake device 1 is simplified without requiring a conventional shutoff valve, while still being able to generate brake hydraulic pressure to be supplied to the disc brakes 7 when the switching valves 24a, 24b fail.

[0066] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 7. In this embodiment, the procedure for braking control performed by the control device 11 when an abnormality occurs is different from that in the first embodiment, but the configuration of the brake device 1 is the same as that in the first embodiment. Elements that are the same as or similar to those in the first embodiment are given the same reference numerals, and duplicated explanations will be omitted as appropriate.

[0067] Fig. 7 is a flowchart of braking control by the control device 11 in the second embodiment. The control device 11 repeatedly executes the control routine shown in Fig. 6 at predetermined control intervals. The processing of steps ST11 and ST12 shown in Fig. 7 is the same as the processing of steps ST1 and ST2 in the first embodiment.

[0068] After both the switching valves 24a, 24b are set to the first state in step ST12, the control device 11 determines whether both the switching valves 24a, 24b are in the third state (step ST13). The determination of whether the switching valves 24a, 24b are in the third state may be performed by any method. If both the switching valves 24a, 24b are not in the third state (No) in step ST5, the control device 11 ends this routine without doing anything.

[0069] On the other hand, if at least one of the two switching valves 24a, 24b is in the third state in step ST13 (Yes), the control device 11 drives the electric servo motor 12 to move the first piston 21a and the second piston 21b of the motor drive cylinder 13 to a closing position that closes the atmosphere release ports 23c, 23d (step ST14). By closing the atmosphere release ports 23c, 23d by the first piston 21a and the second piston 21b, the motor drive cylinder 13 enters a state in which it can maintain the hydraulic pressure generated or transmitted to the first hydraulic pressure generating chamber 23a and the second hydraulic pressure generating chamber 23b.

[0070] In this way, when the switching valves 24a, 24b are in the third state in step ST13 (Yes), the control device 11 controls the motor drive cylinder 13 in step ST14 to displace the first piston 21a and the second piston 21b to positions that close the atmosphere release ports 23c, 23d. In other words, even if the atmosphere release ports 23c, 23d of the motor drive cylinder 13 are opened due to a failure of the switching valves 24a, 24b, the first piston 21a and the second piston 21b are displaced to positions that close the atmosphere release ports 23c, 23d. Therefore, the motor drive cylinder 13 is prevented from being opened to the atmosphere without requiring a conventional shutoff valve, and the brake device 1 can be simplified.

[0071] Thereafter, the control device 11 determines whether or not the driver is applying the brakes, i.e., whether or not the detection value of the pedal stroke sensor 10a is greater than 0 (step ST15). If the driver is not applying the brakes (ST15: No), the control device 11 terminates this routine without doing anything. On the other hand, if the driver is applying the brakes (ST15: Yes), the control device 11 drives the VSA device 26 instead of the motor drive cylinder 13 in accordance with the amount of brake operation by the driver (step ST16). As a result, the hydraulic pressure generated by the VSA device 26 is supplied to the disc brakes 7, and the desired braking force is generated on each wheel 2 in accordance with the amount of brake operation by the driver.

[0072] The hydraulic oil required by the VSA device 26 to generate hydraulic pressure is supplied from the master cylinder 15 by being pushed out from the first fluid chamber 17a and the second fluid chamber 17b when the brake pedal 10 is depressed.

[0073] In this way, if the switching valves 24a, 24b are in the third state in step ST13 (Yes), the control device 11 drives the VSA device 26 in step ST16 to apply hydraulic pressure corresponding to the amount of brake operation to the disc brakes 7. This prevents the motor-driven cylinder 13 and the VSA device 26 from each generating a braking force (double boost) even if the switching valves 24a, 24b are in the third state due to a malfunction. Specifically, the VSA device 26 can generate a braking force for each wheel 2. Therefore, the safety of the vehicle V can be ensured by braking control.

[0074] If a predetermined abnormality has not occurred in the vehicle V in step ST11 (No), the control device 11 determines whether or not the driver is braking (step ST17). If the driver is not braking (ST17: No), the control device 11 proceeds to step ST12. On the other hand, if the driver is braking (ST17: Yes), the control device 11 sets both switching valves 24a, 24b to the second state shown in FIG. 3 and drives the motor drive cylinder 13 in accordance with the amount of braking operation by the driver (step ST18). As a result, the hydraulic pressure generated by the motor drive cylinder 13 is supplied to the disc brake 7, and the desired braking force is generated at each wheel 2 in accordance with the amount of braking operation by the driver.

[0075] As in the first embodiment, when the switching valves 24a, 24b fail and enter the third state (step ST13: Yes), the control device 11 controls the motor-driven cylinder 13 so that the first piston 21a and the second piston 21b close the atmospheric open ports 23c, 23d (step ST6).

[0076] Although the description of the specific embodiment has been completed, the present invention is not limited to the above embodiment and can be widely modified and implemented. For example, in the above embodiment, the present invention is applied to an electric vehicle or a hybrid vehicle as an example. However, the present invention may also be applied to a vehicle V driven only by an engine E. Furthermore, in the above embodiment, two hydraulic circuits corresponding to the front wheels 2F and the rear wheels 2R are provided, and therefore the brake device 1 is equipped with two switching valves 24a and 24b. However, a single hydraulic circuit may be provided and the brake device 1 may be equipped with only one switching valve 24a. In the above embodiment, the control device 11 performs regenerative cooperative control, which performs not only hydraulic braking but also regenerative braking. However, the control device 11 may perform control that performs only hydraulic braking without regenerative braking. Furthermore, the specific configuration, arrangement, quantity, numerical values, and specific control mode of each member and part may be changed as appropriate without departing from the spirit of the present invention. Meanwhile, not all of the components of the brake device 1 shown in the above embodiment are necessarily required and may be selected as appropriate. [Explanation of symbols]

[0077] 1: Brake device 2: Wheels 2F: Front wheel 2R: Rear wheel 7: Disc brake (friction brake) 10: Brake pedal (brake operator) 11: Control device 12: Electric servo motor (electric actuator) 13: Motor-driven cylinder (second hydraulic pressure generating device) 15: Master cylinder (first hydraulic pressure generating unit) 16(16a~16d): Oil path (liquid path) 20: Reservoir tank 21a: First piston 21b: Second piston 23c: Atmospheric release port 23d: Atmospheric release port 23e: Hydraulic pressure supply port (fluid pressure supply port) 23f: Hydraulic pressure supply port (fluid pressure supply port) 24a: Switching valve 24b: Switching valve 25a: Brake pressure sensor (pressure sensor) 25b: Brake pressure sensor (pressure sensor) 26: VSA device (Vehicle Stabilization Device) PS: Brake pedal operation amount V: Automobile

Claims

1. A braking device for a vehicle, a first hydraulic pressure generating device that generates a hydraulic pressure according to an amount of brake operation by a driver on a brake operator; a second hydraulic pressure generating device that generates hydraulic pressure by moving a piston using an electric actuator; a hydraulically actuated friction brake provided on each wheel; a switching valve that switches a fluid path so that the friction brake is functionally connected to one of the first fluid pressure generating device and the second fluid pressure generating device; a control device that controls the second hydraulic pressure generating device and the switching valve, the switching valve is configured to switch between a first state in which the first hydraulic pressure generating device communicates with the friction brake and the second hydraulic pressure generating device is disconnected from the friction brake, and a second state in which the first hydraulic pressure generating device is disconnected from the friction brake and the second hydraulic pressure generating device is connected to the friction brake, the second hydraulic pressure generating device has a hydraulic pressure supply port connected to the switching valve and an atmosphere release port connected to a reservoir tank, When the switching valve fails and enters a third state in which the first hydraulic pressure generating device and the second hydraulic pressure generating device are connected to the friction brake, the control device controls the second hydraulic pressure generating device so that the piston closes the atmosphere release port.

2. a pressure sensor disposed in the fluid path between the switching valve and the first fluid pressure generating device or the second fluid pressure generating device; 2. The vehicle brake device according to claim 1, wherein the control device determines whether the switching valve has entered the third state based on a stroke amount of the piston and a detection value of the pressure sensor, and when it determines that the switching valve has entered the third state, closes the atmosphere release port with the piston.

3. 3. The vehicle brake device according to claim 2, wherein, when the control device determines that the switching valve has entered the third state, the control device stops the piston at a position at which the switching valve has entered the third state.

4. 2. The vehicle brake device according to claim 1, wherein the control device controls the second hydraulic pressure generating device to displace the piston to a position that closes the atmosphere release port when the switching valve is in the third state.

5. a vehicle behavior stabilization device that is provided in the fluid path between the switching valve and the friction brake, that adjusts the hydraulic pressure of the hydraulic fluid supplied from the first hydraulic pressure generating device or the second hydraulic pressure generating device, and causes the adjusted hydraulic pressure to act on the friction brake; 5. The vehicle brake device according to claim 4, wherein when the switching valve is in the third state, the control device drives the vehicle behavior stabilization device to apply a hydraulic pressure corresponding to the brake operation amount to the friction brake.

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