ABS control device and air brake system

Abstract

To perform ABS control properly when a value of a wheel speed is not acquired from a wheel speed sensor.SOLUTION: A solenoid valve control part 900 includes: an acquisition part 901 which acquires a rotation number of a propeller shaft which transmits power from a transmission of a vehicle to a differential gear; an estimation part 902 which estimates a wheel speed of the vehicle based on the rotation number of the propeller shaft; a calculation part 903 which calculates a brake slip ratio of the vehicle based on the vehicle speed estimated by the estimation part 902; and a control unit 904 which performs ABS control of the vehicle based on the brake slip ratio calculated by the calculation part 903.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] One aspect of the present invention relates to an ABS control device for a vehicle and an air brake system.

Background Art

[0002] As an ABS (Anti-lock Brake System) control device, an ABS control device that calculates a brake slip ratio based on the wheel speed acquired from a wheel speed sensor and performs ABS control based on the brake slip ratio is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, for example, when a failure occurs in the electronic control brake system itself, a failure of the wheel speed sensor, or a disconnection of the harness, etc., it becomes impossible to acquire the wheel speed value from the wheel speed sensor, and it may be impossible to calculate the brake slip ratio and appropriately perform ABS control.

[0005] One aspect of the present invention has been made in view of the above circumstances, and an object thereof is to provide an ABS control device and an air brake system that can appropriately perform ABS control even when the wheel speed value cannot be acquired from the wheel speed sensor.

Means for Solving the Problems

[0006] An ABS control device according to one aspect of the present invention includes: an acquisition unit that acquires the rotational speed of a drive shaft that transmits power from the vehicle's transmission to the differential gear; an estimation unit that estimates the vehicle's wheel speed based on the rotational speed of the drive shaft; a calculation unit that calculates the vehicle's brake slip ratio based on the wheel speed estimated by the estimation unit; and a control unit that performs ABS control of the vehicle based on the brake slip ratio calculated by the calculation unit.

[0007] In an ABS control device according to one aspect of the present invention, the wheel speed is estimated from the rotational speed of the drive shaft, the brake slip ratio is calculated based on the estimated wheel speed, and ABS control is performed. Since there is a correlation between the rotational speed of the drive shaft and the wheel speed, with this configuration, even if the wheel speed cannot be obtained from the wheel speed sensor due to, for example, a failure of the electronic brake system (EBS) itself, the wheel speed can be estimated based on the rotational speed of the drive shaft, and ABS control can be performed based on the estimated value. As described above, according to an ABS control device according to one aspect of the present invention, ABS control can be performed appropriately even when the wheel speed value cannot be obtained from the wheel speed sensor.

[0008] The acquisition unit further acquires information indicating the vehicle's weight, and the control unit may perform ABS control only if the vehicle's weight is below a predetermined value. It is thought that the heavier the vehicle, the greater the braking distance due to the activation of the ABS function (release of the brakes), and the less likely wheel slip is to occur due to the heavy wheel load, thus reducing the need for ABS control. Therefore, by limiting the implementation of ABS control to when the vehicle's weight is below a predetermined value, it is possible to avoid the braking distance becoming unnecessarily large.

[0009] If the acquisition unit cannot acquire the wheel speed detected by the wheel speed sensor in real time, it further acquires the last updated value of the available wheel speed and further acquires the actual deceleration of the vehicle from the inertial measuring device installed on the vehicle. The control unit then estimates the current vehicle speed by integrating the actual deceleration over time, using the last updated value of the wheel speed as the initial value, and may perform ABS control of the vehicle only if the estimated vehicle speed is equal to or greater than a predetermined value. With this configuration, the current vehicle speed can be appropriately estimated even when the wheel speed cannot be acquired in real time from the wheel speed sensor. Furthermore, by not performing ABS control when the estimated vehicle speed is too low, the vehicle can be stopped early and reliably.

[0010] The calculation unit calculates the brake slip ratio λ from the following formula based on the estimated wheel speed Vp and the estimated vehicle speed V: λ = (V - Vp) / V. The control unit may determine that the vehicle's wheels are locked if the brake slip ratio exceeds a predetermined value. With this configuration, the brake slip ratio can be appropriately calculated from the estimated wheel speed, and it can be determined that the wheels are locked if the calculated brake slip ratio is large, thereby appropriately determining the wheel lock state in ABS control. This enables appropriate ABS control according to the state of the wheels.

[0011] The control unit may derive the estimated wheel acceleration by differentiating the estimated wheel speed with respect to time, and determine that the vehicle's wheels have been unlocked when the estimated wheel acceleration becomes a positive value. In this way, by determining that the wheels have been unlocked when the estimated wheel acceleration becomes a positive value, i.e., when the wheel speed is increasing, the wheel unlock state can be appropriately determined. This enables appropriate ABS control according to the state of the wheels.

[0012] An air brake system according to one aspect of the present invention is an air brake system having a backup system, comprising: a double check valve provided in a first air passage connecting a brake valve and an axle modulator in the backup system; a second air passage connecting the double check valve and an air tank; a solenoid valve provided in the second air passage; and an ABS control device, wherein the ABS control device has an acquisition unit that acquires the rotational speed of a drive shaft that transmits power from the vehicle's transmission to the differential gear; an estimation unit that estimates the vehicle's wheel speed based on the rotational speed of the drive shaft; a calculation unit that calculates the vehicle's brake slip ratio based on the wheel speed estimated by the estimation unit; and a control unit that performs ABS control of the vehicle based on the brake slip ratio calculated by the calculation unit, wherein the control unit performs ABS control of the vehicle by activating the solenoid valve.

[0013] In an air brake system according to one aspect of the present invention, a first air passage and a second air passage are connected to a double check valve, so that the air with higher pressure flows to the axle modulator side. A solenoid valve is provided in the second air passage, and when this solenoid valve is activated, the air flowing out of the air tank flows through the second passage, passes through the double check valve, and flows to the axle modulator side. In this way, the operation of the solenoid valve supplies air from the air tank to the axle modulator, and brake control in the backup system is realized. Since the operation of this solenoid valve is performed by the control unit, it can also be implemented in unmanned autonomous vehicles that do not have a driver. As described above, according to an air brake system according to one aspect of the present invention, a redundant brake system can be provided even in unmanned autonomous vehicles. The control unit estimates the wheel speed from the rotation speed of the drive shaft, calculates the brake slip ratio based on the estimated wheel speed, and performs ABS control. Since there is a correlation between the rotational speed of the drive shaft and the wheel speed, with this configuration, even if the wheel speed cannot be obtained from the wheel speed sensor due to, for example, a failure of the electronically controlled brake system itself, the wheel speed can be estimated based on the rotational speed of the drive shaft, and ABS control can be performed based on the estimated value. As described above, according to one aspect of the present invention, ABS control can be appropriately performed even when the wheel speed value cannot be obtained from the wheel speed sensor. [Effects of the Invention]

[0014] According to one aspect of the present invention, ABS control can be appropriately performed even when the wheel speed value cannot be obtained from the wheel speed sensor. [Brief explanation of the drawing]

[0015] [Figure 1] This block diagram shows an example configuration of an autonomous vehicle according to this embodiment. [Figure 2]It is a schematic configuration diagram of an air brake system included in an autonomous vehicle shown in FIG. 1. [Figure 3] It is a functional block diagram of a solenoid valve control unit. [Figure 4] It is a flowchart showing a procedure for determining the establishment of ABS conditions executed in the solenoid valve control unit. [Figure 5] It is a flowchart showing a wheel lock determination and ABS operation procedure executed in the solenoid valve control unit.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] FIG. 1 is a block diagram showing a configuration example of an autonomous vehicle 1. In the present embodiment, the vehicle will be described as an unmanned autonomous vehicle that travels without a driver. Further, in the autonomous vehicle 1, a redundant brake system is provided even in the unmanned autonomous vehicle by an air brake system described later (details will be described later). Further, in the autonomous vehicle 1, ABS control is implemented by a solenoid valve control unit (ABS control device) described later. The autonomous vehicle 1 includes, for example, a GPS (Global Positioning System) receiver 20, a map database 30, a surrounding situation sensor 40, a vehicle state sensor 50, a communication device 60, a traveling device 70, and a control device 10.

[0018] The GPS receiver 20 receives signals transmitted from a plurality of GPS satellites and calculates the position and orientation of the vehicle based on the received signals. The GPS receiver 20 transmits the calculated information to the control device 10.

[0019] The map database 30 is a database that stores in advance information indicating the boundary positions of each lane on a road. The map database 30 is stored, for example, in a predetermined storage device.

[0020] The surrounding situation sensor 40 detects the situation around the vehicle. As the surrounding situation sensor 40, for example, a lidar, a radar, a camera, etc. are used. The lidar detects targets around the vehicle using light. The radar detects targets around the vehicle using radio waves. The camera images the situation around the vehicle. The surrounding situation sensor 40 transmits the detected information to the control device 10.

[0021] The vehicle state sensor 50 detects the driving state of the vehicle. As the vehicle state sensor 50, for example, a vehicle speed sensor, a steering angle sensor, a yaw rate sensor, an acceleration sensor, a steering torque sensor, a motor output torque sensor, a wheel speed sensor, a sensor for detecting the rotational speed of the propeller shaft (for example, a sensor provided on the clutch), etc. are exemplified. The propeller shaft is a propeller shaft that transmits power from the transmission of the vehicle to the differential gear. The vehicle speed sensor detects the speed of the vehicle. The steering angle sensor detects the steering angle of the vehicle. The yaw rate sensor detects the yaw rate of the vehicle. The acceleration sensor detects the acceleration acting on the vehicle. The vehicle state sensor 50 transmits the detected information to the control device 10.

[0022] The vehicle state sensor 50 includes an IMU (Inertial Measurement Unit) 801 provided on the chassis. The IMU 801 continuously detects the longitudinal acceleration of the vehicle (deceleration when the value is negative) during the running of the vehicle.

[0023] The communication device 60 performs, for example, V2X communication (vehicle-to-vehicle communication and vehicle-to-infrastructure communication). Specifically, the communication device 60 performs V2V communication (vehicle-to-vehicle communication) with other vehicles. Also, the communication device 60 performs V2I communication (vehicle-to-infrastructure communication) with the surrounding infrastructure. Through V2X communication, the communication device 60 can acquire information on the environment around the vehicle. The communication device 60 transmits the acquired information to the control device 10. Note that the communication device 60 may receive information indicating a driving route instruction or the road surface condition of the road from the outside, for example, by V2X communication.

[0024] The running gear 70 includes a steering system, a drive system, a braking system, a transmission, etc. The steering system steers the wheels. The drive system is a power source that generates driving force. Examples of drive systems include engines and electric motors. The braking system generates braking force. The running gear 70 may also include a microcomputer equipped with a processor, memory, and input / output interfaces so that the steering system, drive system, braking system, transmission, etc. can be operated by electrical commands. These microcomputers are also called ECUs (Electronic Control Units). More specifically, the braking system may include the ECU of an EBS (Electronic Braking System).

[0025] The control device 10 performs automatic driving control to manage the vehicle's autonomous driving. The control device 10 is a microcomputer equipped with a processor, memory, and input / output interface. The control device 10 is also called an ECU (Electronic Control Unit). The control device 10 receives various information through the input / output interface. Based on the received information, the control device 10 performs automatic driving control.

[0026] The control device 10 includes an acquisition unit 101 and an automatic driving control unit 102 as functional blocks related to automatic driving control. These functional blocks are realized when the processor of the control device 10 executes a control program stored in a storage device. The control program may be stored in a computer-readable recording medium.

[0027] The acquisition unit 101 acquires information necessary for automatic driving control. The information acquisition process by the acquisition unit 101 is repeatedly executed in predetermined or arbitrary cycles. The acquisition unit 101 acquires the vehicle's position and direction from the GPS receiver 20. The acquisition unit 101 acquires information about road lanes, etc., from the map database 30. The acquisition unit 101 acquires information about the area around the vehicle detected by the surrounding conditions sensor 40. The acquisition unit 101 acquires information indicating the vehicle's status detected by the vehicle status sensor 50. The acquisition unit 101 acquires information such as driving route instructions and road surface conditions from the communication device 60.

[0028] The automatic driving control unit 102 generates the overall route (the entire route the vehicle will travel) based on the information acquired by the acquisition unit 101. In addition to the driving route instruction, the automatic driving control unit 102 may generate the overall route by considering information such as the vehicle's position and orientation, road lane, information about the vehicle's surroundings, and information indicating the vehicle's status. Based on the generated overall route, the automatic driving control unit 102 generates the target route that the vehicle will actually travel in real time. Target route generation is performed repeatedly at predetermined or arbitrary cycles while the vehicle is traveling. Based on the generated target route, the automatic driving control unit 102 performs route-following control of the vehicle. The automatic driving control unit 102 uses conventionally known follow-up control techniques to control each device included in the driving device 70 so that the vehicle travels following the target route.

[0029] Figure 2 is a schematic diagram of the air brake system 200 included in the autonomous vehicle 1 shown in Figure 1. The air brake system 200 may also be included in the running gear 70. The autonomous vehicle 1 has at least a function to control the solenoid valve of the air brake system 200 (solenoid valve control function) in order to operate the air brake system 200. Solenoid valve control is a control that controls the power output supplied to the solenoid valve or the electrical signal to the solenoid valve, and by operating the solenoid valve, supplies air whose pressure has been adjusted by the pressure reducing valve to the axle modulator, thereby achieving braking with a predetermined braking force. Such solenoid valve control is a control that is equivalent to (replaces) air supply by brake pedal operation by the driver, and is a control that enables backup air supply even in an unmanned autonomous vehicle. Solenoid valve control is also performed when brake control by electrical commands cannot be performed, for example, in the event of failure of the electronically controlled brake.

[0030] As shown in Figure 2, the air brake system 200 includes a brake signal transmitter 210, a multi-protection valve 220, air tanks 230 and 250, a front axle modulator 240, brake chambers 241 and 242, a rear axle modulator 260, brake chambers 261 and 262, and a trailer control valve 265.

[0031] The front axle modulator 240 incorporates an ECU, solenoid valve, pressure sensor, etc., and controls the air pressure to the front brake chambers 241 and 242 based on electrical signals from the EBS ECU. In the event of an EBS failure, the front axle modulator 240 uses a relay valve, which uses the air pressure from the brake valve 212 of the brake signal transmitter 210 as the signal pressure, to send air from the air tank 230 to the brake chambers 241 and 242. The air from the air tank 230 flows through the air passage 307 into the front axle modulator 240, and then flows through the air passage 310 into the brake chamber 241, and through the air passage 311 into the brake chamber 242. The brake chamber 241 activates the brake of the right front wheel RF according to the air pressure. The brake chamber 242 activates the brake of the left front wheel LF according to the air pressure. In this embodiment, when the EBS fails, air corresponding to the solenoid valve control flows into the front axle modulator 240, and the brakes are activated (details will be described later).

[0032] The rear axle modulator 260 incorporates an ECU, solenoid valve, pressure sensor, etc., and controls the air pressure to the rear brake chambers 261 and 262 based on electrical signals from the EBS ECU. In the event of an EBS failure, the rear axle modulator 260 uses a relay valve, which uses the air pressure from the brake valve 212 of the brake signal transmitter 210 as the signal pressure, to send air from the air tank 250 to the brake chambers 261 and 262. The air from the air tank 250 flows through the air passage 308 into the rear axle modulator 260, then flows through the air passage 313 into the brake chamber 261, and then flows through the air passage 314 into the brake chamber 262. The brake chamber 261 activates the brake of the right rear wheel RR according to the air pressure. The brake chamber 262 activates the brake of the left rear wheel LR according to the air pressure. In this embodiment, when the EBS fails, air corresponding to the solenoid valve control flows into the rear axle modulator 260, and the brakes are activated (details will be described later).

[0033] The trailer control valve 265, acting as a relay valve that uses the air pressure from the brake valve 212 of the brake signal transmitter 210 as a signal pressure, sends air from the trailer system's air tank (not shown) to the trailer, thereby activating the brakes on each wheel of the trailer.

[0034] The brake signal transmitter 210 incorporates a brake pedal switch 211 and a stroke sensor (not shown), and transmits the amount of brake pedal depression as a pedal stroke signal to the EBS ECU to control the braking force. When the EBS fails, the brake signal transmitter 210 functions as a brake valve 212, outputting air pressure as a signal pressure to the front axle modulator 240 and the rear axle modulator 260. Air from the brake valve 212 flows into the front axle modulator 240 via air passages 301 and 309, and into the rear axle modulator 260 via air passages 302 and 312.

[0035] The multi-protection valve 220 supplies the minimum necessary air pressure to the remaining functioning circuits in the event of damage (loss) to one or more circuits in the vehicle's air system circuitry. This ensures minimum braking force, allowing the vehicle to be driven to a repair shop for emergency repairs. The multi-protection valve 220 is connected to the air tanks 230, 250, and 270, respectively, via air passages.

[0036] From here, we will mainly explain the configuration related to solenoid valve control. Solenoid valve control is performed when the EBS fails and replaces the air supply via brake pedal operation as described above. Unlike air supply via brake pedal operation, solenoid valve control provides backup air supply even in unmanned autonomous vehicles where there is no driver.

[0037] As shown in Figure 2, the air brake system 200 includes, as a configuration related to solenoid valve control, an air tank 270, a single protection valve 280, a double check valve 500, a front solenoid valve 510, a double check valve 600, a rear solenoid valve 610, a pressure reducing valve 700, and a solenoid valve control unit 900 (ABS control device).

[0038] The double check valve 500 is located in the air passage 301 (first air passage) in the backup system, which connects the brake valve 212 and the front axle modulator 240. The double check valve 500 is connected to air passages 301 and 303, and the air with higher pressure flows into air passage 309 and then to the front axle modulator 240. One end of air passage 303 is connected to the double check valve 500, and the other end is connected to a branching point 305. Air passage 306 extends from the branching point 305 to the air tank 270. In other words, air passages 303 and 306 are continuous with each other via the branching point 305 and constitute a second air passage connecting the double check valve 500 and the air tank 270. Air passage 306 is provided with a single protection valve 280 to prevent backflow of air.

[0039] The front solenoid valve 510 is located in the air passage 303, which constitutes the second air passage. That is, the front solenoid valve 510 is arranged in parallel with the brake valve 212 as part of the air circuit. Because the solenoid valve and the brake valve are arranged in parallel, even when the vehicle is operated by a human driver, the driver's operation of the brake valve is effective, thus ensuring the same level of safety for the vehicle whether it is in automatic or manual operation. The front solenoid valve 510 is a normally closed solenoid valve that controls the emergency brake in the event of an EBS failure by opening and closing the air circuit. The front solenoid valve 510 operates based on the control of the solenoid valve control unit 900, directing the air flowing through the air passage 303 (i.e., air from the air tank 270) towards the double check valve 500 (i.e., towards the front axle modulator 240).

[0040] The double check valve 600 is located in the air passage 302 (first air passage) in the backup system, which connects the brake valve 212 and the rear axle modulator 260. The double check valve 600 is connected to air passages 302 and 304, and the air with higher pressure flows into air passage 312 and then to the rear axle modulator 260. One end of air passage 304 is connected to the double check valve 600, and the other end is connected to a branching point 305. Air passage 306 extends from the branching point 305 to the air tank 270. In other words, air passages 304 and 306 are continuous with each other via the branching point 305, and constitute a second air passage connecting the double check valve 600 and the air tank 270.

[0041] The rear solenoid valve 610 is located in the air passage 304, which constitutes the second air passage. The rear solenoid valve 610 is arranged in parallel with the brake valve 212 as part of the air circuit. Because the solenoid valve and brake valve are arranged in parallel, even when the vehicle is operated by a human driver, the driver's operation of the brake valve is effective, thus ensuring the same level of safety for the vehicle whether it is in automatic or manual operation. The rear solenoid valve 610 is a normally closed solenoid valve that controls the emergency brake in the event of an EBS failure by opening and closing the air circuit. The rear solenoid valve 610 operates based on the control of the solenoid valve control unit 900, directing the air flowing through the air passage 304 (i.e., air from the air tank 270) towards the double check valve 600 (i.e., towards the front axle modulator 240).

[0042] The pressure reducing valve 700 is a pressure regulating valve located upstream of the front solenoid valve 510 and the rear solenoid valve 610 in the second air passage (on the air tank 270 side), specifically in the air passage 306. The pressure reducing valve 700 reduces the air pressure in the air tank 270 to a predetermined pressure. The pressure reducing valve 700 may have a certain pressure regulation range to achieve a predetermined braking force, for example, as an emergency brake. Furthermore, the pressure reducing valve 700 is required to have good time response in order to realize the ABS control function.

[0043] The solenoid valve control unit 900 is a microcomputer equipped with a processor, a memory device, and an input / output interface. In this embodiment, the solenoid valve control unit 900 is included in the air brake system 200, but the solenoid valve control unit 900 may be included in at least one of either the air brake system 200 or the control device 10. The solenoid valve control unit 900 is configured to activate at least one of the front solenoid valve 510 and the rear solenoid valve 610 in the event of an EBS failure. By activating at least one of the front solenoid valve 510 and the rear solenoid valve 610, the solenoid valve control unit 900 realizes brake control by supplying backup air and also realizes the ABS function. The details of the ABS function of the solenoid valve control unit 900 will be described below with reference to Figures 3 to 5.

[0044] Figure 3 is a functional block diagram of the solenoid valve control unit 900 related to the ABS function. Here, we will explain the part of the solenoid valve control unit 900 related to the ABS function. As shown in Figure 3, the solenoid valve control unit 900 includes an acquisition unit 901, an estimation unit 902, a calculation unit 903, and a control unit 904. In this embodiment, the control of the solenoid valve control unit 900 is performed in situations such as when the ABS fails, as described above.

[0045] The acquisition unit 901 acquires various information related to ABS control. The acquisition unit 901 acquires the rotational speed of the drive shaft from the drive shaft rotational speed sensor 803. The rotational speed of the drive shaft acquired from the drive shaft rotational speed sensor 803 is, for example, detected by a sensor that detects the rotational speed of the drive shaft, which is provided on the clutch. The acquisition unit 901 acquires the rotational speed of the drive shaft from the drive shaft rotational speed sensor 803, for example, at predetermined time intervals or at any arbitrary timing.

[0046] The acquisition unit 901 acquires the estimated vehicle weight result (information indicating the vehicle's weight) from the ECU of the EBS802. The estimated vehicle weight result here is estimated by the EBS802 based on, for example, braking force information and vehicle acceleration. In this scenario, we are assuming that the EBS802 has failed, so the estimated vehicle weight result here is the last updated value before the EBS802 failed (the value of the vehicle weight that was last correctly estimated by the EBS802 before it failed).

[0047] The acquisition unit 901 obtains the last updated value of the obtainable wheel speed from the ECU of the EBS802. As mentioned above, we are currently assuming a scenario where the EBS802 has failed, so it is not possible to obtain the wheel speed detected by the wheel speed sensor from the EBS802 in real time. The last updated value of the wheel speed here refers to the last updated value of the wheel speed before the EBS802 failed (the last wheel speed value correctly obtained from the wheel speed sensor before the EBS802 failed).

[0048] The acquisition unit 901 acquires the vehicle's longitudinal acceleration (or the actual deceleration of the vehicle if it is a negative value) from the IMU 801. The acquisition unit 901 acquires the actual deceleration of the vehicle from the IMU 801, for example, at predetermined time intervals or at any arbitrary timing.

[0049] The estimation unit 902 estimates the vehicle's wheel speed based on the rotational speed of the drive shaft acquired by the acquisition unit 901. Vehicle information such as the final reduction ratio and the tire diameter of the drive wheels may also be used to estimate the wheel speed.

[0050] The calculation unit 903 calculates the vehicle's brake slip ratio based on the wheel speed estimated by the estimation unit 902. More specifically, the calculation unit 903 calculates the brake slip ratio based on the wheel speed estimated by the estimation unit 902 and the vehicle's current speed estimated by the control unit 904 (details will be described later). If the estimated wheel speed is Vp, the estimated vehicle speed is V, and the brake slip ratio is λ, then the brake slip ratio λ is calculated by the following equation (1). λ = (V - Vp) / V ... (1)

[0051] The control unit 904 performs ABS control of the vehicle based on the brake slip ratio calculated by the calculation unit 903. Here, the control unit 904 performs two main processes: a process to determine whether or not the vehicle is in a state to perform ABS control (ABS condition fulfillment determination process), and a process related to ABS control that is performed when it is determined that the ABS condition is fulfilled (ABS process).

[0052] In the ABS condition fulfillment determination process, the control unit 904 determines whether or not the rotational speed of the drive shaft has been acquired by the acquisition unit 901. If the rotational speed of the drive shaft has not been acquired, the control unit 904 determines that the ABS condition is not met, as it is not in a state to perform ABS control.

[0053] Furthermore, the control unit 904 determines whether the estimated vehicle weight obtained by the acquisition unit 901 is below a predetermined value. If the estimated vehicle weight is not below the predetermined value, the control unit 904 determines that the ABS condition is not met, as it is not in a state to perform ABS control.

[0054] Furthermore, the control unit 904 estimates the current vehicle speed by integrating the actual deceleration of the vehicle acquired by the acquisition unit 901 over time, using the last updated value of the wheel speed acquired by the acquisition unit 901 as the initial value. The control unit 904 then determines whether the estimated current vehicle speed is equal to or greater than a predetermined value. If the estimated current vehicle speed is not equal to or greater than the predetermined value, the control unit 904 determines that the ABS condition is not met.

[0055] The control unit 904 determines that the ABS conditions are met if the rotational speed of the drive shaft has been acquired, the estimated vehicle weight is less than or equal to a predetermined value, and the estimated current vehicle speed is greater than or equal to a predetermined value. The control unit 904 then performs the ABS process described below only if the ABS conditions are met.

[0056] In ABS processing, the control unit 904 performs ABS control of the vehicle based on the brake slip ratio λ calculated by the calculation unit 903. Specifically, the control unit 904 determines that the vehicle's wheels (for example, the rear wheels, which are drive wheels) are locked when the brake slip ratio λ exceeds a predetermined value. When the control unit 904 determines that the wheels are locked, it activates the ABS for the rear wheels by, for example, activating the rear solenoid valve 610. The control unit 904 operates the rear solenoid valve 610 so that the brakes are weakened and strengthened as appropriate, and ABS control is performed appropriately.

[0057] After determining that the wheels are locked as described above, the control unit 904 may derive the estimated wheel acceleration by differentiating the estimated wheel speed with respect to time, and if the estimated wheel acceleration becomes a positive value, it may determine that the lock on the vehicle's wheels (for example, the rear wheels, which are the drive wheels) has been released. A state in which the estimated wheel acceleration becomes a positive value means that the wheel speed is increasing and it is estimated that the wheels are not locked. In this case, the control unit 904 stops the ABS control. In this way, by determining whether or not the wheels are locked and switching the ABS control according to the determination result, appropriate ABS control can be performed according to the condition of the wheels.

[0058] Next, the procedure for determining whether the ABS condition is met will be explained with reference to Figure 4. Figure 4 is a flowchart showing the procedure for determining whether the ABS condition is met, which is performed in the solenoid valve control unit 900.

[0059] As shown in Figure 4, the solenoid valve control unit 900 first attempts to acquire the rotational speed of the drive shaft (step S1), and determines whether or not the rotational speed of the drive shaft could be acquired (step S2). If it is determined in step S2 that the rotational speed of the drive shaft could not be acquired, it is determined that the ABS condition is not met (step S10).

[0060] On the other hand, if it is determined in step S2 that the rotational speed of the drive shaft can be obtained, the estimated vehicle weight (final updated value) is obtained (step S3), and it is determined whether or not the estimated vehicle weight is below a predetermined value (step S4). If it is determined in step S4 that the estimated vehicle weight is not below a predetermined value, it is determined that the ABS condition is not met (step S10).

[0061] On the other hand, if the estimated vehicle weight in step S4 is determined to be below a predetermined value, the final updated value of the wheel speed is obtained (step S5), and further, the actual deceleration of the vehicle is obtained (step S6). Then, using the final updated value of the wheel speed as the initial value, the current vehicle speed is estimated by integrating the actual deceleration of the vehicle over time (step S7).

[0062] Then, it is determined whether the estimated current vehicle speed is equal to or greater than a predetermined value (step S8). If it is determined in step S8 that the current vehicle speed is not equal to or greater than a predetermined value, it is determined that the ABS condition is not met (step S10).

[0063] On the other hand, if it is determined in step S8 that the current vehicle speed is above a predetermined value, it is determined that the ABS condition is met (step S9). If the ABS condition is met, the ABS process is performed.

[0064] Next, the ABS procedure will be described with reference to Figure 5. Figure 5 is a flowchart showing the wheel lock determination and ABS activation procedure performed in the solenoid valve control unit 900. Note that this wheel lock determination and ABS activation procedure flowchart may be repeated while the ABS condition in step S9 of Figure 4 is met.

[0065] As shown in Figure 5, the solenoid valve control unit 900 calculates the brake slip ratio λ from the estimated wheel speed and vehicle speed (step S11). Specifically, the brake slip ratio λ is calculated using equation (1) described above.

[0066] Next, it is determined whether the brake slip ratio λ exceeds a predetermined value (step S12). If it is determined in step S12 that it does not exceed the value, the process in step S11 is performed again after a predetermined time has elapsed.

[0067] On the other hand, in step S12, if it is determined that the brake slip ratio λ exceeds a predetermined value, it is determined that the vehicle's wheels (for example, the rear wheels which are drive wheels) are locked, and the ABS is activated (step S13). The solenoid valve control unit 900 operates the rear solenoid valve 610 so that the brakes are weakened and strengthened as appropriate, and ABS control is performed appropriately.

[0068] Next, the estimated wheel acceleration is derived by differentiating the estimated wheel speed with respect to time, and it is determined whether the estimated wheel acceleration is a positive value or not (step S14). If it is determined in step S14 that the value is not positive, the process in step S13 is repeated.

[0069] On the other hand, if it is determined in step S14 that the estimated wheel acceleration is a positive value, it is determined that the lock on the vehicle's wheels (for example, the rear wheels which are the drive wheels) has been released, and the ABS control is stopped (step S15).

[0070] Finally, the effects and advantages of the solenoid valve control unit 900 (ABS control device) according to this embodiment will be explained.

[0071] The solenoid valve control unit 900 according to this embodiment includes an acquisition unit 901 that acquires the rotational speed of the drive shaft that transmits power from the vehicle's transmission to the differential gear, an estimation unit 902 that estimates the vehicle's wheel speed based on the rotational speed of the drive shaft, a calculation unit 903 that calculates the vehicle's brake slip ratio based on the wheel speed estimated by the estimation unit 902, and a control unit 904 that performs ABS control of the vehicle based on the brake slip ratio calculated by the calculation unit 903.

[0072] In the solenoid valve control unit 900 according to this embodiment, the wheel speed is estimated from the rotational speed of the drive shaft, and the brake slip ratio is calculated based on the estimated wheel speed, and ABS control is performed. Since there is a correlation between the rotational speed of the drive shaft and the wheel speed, with this configuration, even if the wheel speed cannot be obtained in real time from the wheel speed sensor due to, for example, a failure of the electronically controlled brake system itself, the wheel speed can be estimated based on the rotational speed of the drive shaft, and ABS control can be performed based on the estimated value. As described above, the solenoid valve control unit 900 according to this embodiment can perform ABS control appropriately even when the wheel speed value cannot be obtained from the wheel speed sensor.

[0073] The acquisition unit 901 further acquires information indicating the vehicle's weight, and the control unit 904 may perform ABS control only if the vehicle's weight is below a predetermined value. It is thought that the heavier the vehicle, the greater the braking distance due to the activation of the ABS function (release of the brakes), and the less likely wheel slip is to occur due to the large wheel load, thus reducing the need for ABS control. Therefore, by limiting the implementation of ABS control to when the vehicle's weight is below a predetermined value, it is possible to avoid the braking distance becoming unnecessarily large.

[0074] If the acquisition unit 901 cannot acquire the wheel speed detected by the wheel speed sensor in real time, it further acquires the last updated value of the available wheel speed and further acquires the actual deceleration of the vehicle from the IMU 801 installed in the vehicle. The control unit 904 uses the last updated value of the wheel speed as an initial value and estimates the current vehicle speed by integrating the actual deceleration over time. If the estimated vehicle speed is greater than or equal to a predetermined value, it may perform ABS control of the vehicle. With this configuration, even if the wheel speed cannot be acquired in real time from the wheel speed sensor, the current vehicle speed can be appropriately estimated. Furthermore, by not performing ABS control when the estimated vehicle speed is too low, the vehicle can be stopped early and reliably.

[0075] The calculation unit 903 calculates the brake slip ratio λ based on the estimated wheel speed Vp and the estimated vehicle speed V, using equation (1) described above. The control unit 904 may determine that the vehicle's wheels are locked if the brake slip ratio exceeds a predetermined value. With this configuration, the brake slip ratio can be appropriately calculated from the estimated wheel speed, and it can be determined that the wheels are locked if the calculated brake slip ratio is large, thereby appropriately determining the wheel lock state in ABS control. This enables appropriate ABS control according to the state of the wheels.

[0076] The control unit 904 may derive the estimated wheel acceleration by differentiating the estimated wheel speed with respect to time, and may determine that the vehicle's wheels have been unlocked when the estimated wheel acceleration becomes a positive value. In this way, by determining that the wheels have been unlocked when the estimated wheel acceleration becomes a positive value, i.e., when the wheel speed is increasing, the wheel unlock state can be appropriately determined. This enables appropriate ABS control according to the state of the wheels. [Explanation of symbols]

[0077] 200...Air brake system, 900...Solenoid valve control unit, 901...Acquisition unit, 902...Estimation unit, 903...Calculation unit, 904...Control unit.

Claims

1. An acquisition unit that acquires the rotational speed of the drive shaft that transmits power from the vehicle's transmission to the differential gear, An estimation unit that estimates the wheel speed of the vehicle based on the rotational speed of the propulsion shaft, A calculation unit calculates the brake slip ratio of the vehicle based on the wheel speed estimated by the estimation unit, The system includes a control unit that performs ABS control on the vehicle based on the brake slip ratio calculated by the calculation unit, When the acquisition unit is unable to acquire the wheel speed detected by the wheel speed sensor in real time, it further acquires the last updated value of the wheel speed last detected by the wheel speed sensor that is unable to acquire the wheel speed in real time, and further acquires the actual deceleration of the vehicle from the inertial measuring device installed on the vehicle. The control unit estimates the current vehicle speed by integrating the actual deceleration over time, using the last updated value of the wheel speed as the initial value, and performs ABS control of the vehicle only if the estimated vehicle speed is equal to or greater than a predetermined value.

2. The acquisition unit further acquires information indicating the weight of the vehicle, The control unit performs ABS control of the vehicle only when the weight of the vehicle is less than or equal to a predetermined value, as described in claim 1.

3. The calculation unit calculates the brake slip ratio λ from the following formula based on the estimated wheel speed Vp and the estimated vehicle speed V, λ = (V - Vp) / V The ABS control device according to claim 1, wherein the control unit determines that the wheels of the vehicle are locked when the brake slip ratio exceeds a predetermined value.

4. The control unit derives an estimated wheel acceleration by differentiating the estimated wheel speed with respect to time, and determines that the wheel lock of the vehicle has been released when the estimated wheel acceleration becomes a positive value, according to claim 3.

5. An air brake system having a backup system, In the aforementioned backup system, a double check valve is provided in the first air passage connecting the brake valve and the axle modulator, A second air passage connecting the double check valve and the air tank, A solenoid valve provided in the second air passage, Equipped with an ABS control device, The ABS control device is An acquisition unit that acquires the rotational speed of the drive shaft that transmits power from the vehicle's transmission to the differential gear, An estimation unit that estimates the wheel speed of the vehicle based on the rotational speed of the propulsion shaft, A calculation unit calculates the brake slip ratio of the vehicle based on the wheel speed estimated by the estimation unit, The system includes a control unit that performs ABS control on the vehicle based on the brake slip ratio calculated by the calculation unit, The control unit, An air brake system that controls the ABS of the vehicle by activating the solenoid valve.

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