Vehicle braking system

Abstract

To provide a braking device for a vehicle, capable of adjusting a balance between a current reduction effect while holding braking force and responsiveness when switching from holding operation to braking force increasing operation.SOLUTION: The relationship between the torque of a motor and braking force generated in an electric brake has hysteresis characteristics. When the torque increases, the braking force increases along a positive efficiency line. When the torque decreases, the braking force decreases along an inverse efficiency line. A prediction unit 45 in a torque command calculation unit 40 predicts a change in required braking force at and after the present time. An operation point adjuster 46 stores maximum torque on the positive efficiency line and minimum torque on the inverse efficiency line which correspond to held braking force. The operation point adjuster 46 adjusts an operation point at which braking force is held in an adjustment zone between the minimum torque and the maximum torque, on the basis of prediction information from the prediction unit 45. The torque command calculation unit 40 calculates a torque command value Trq* for the motor at the operation point adjusted by the operation point adjuster 46.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, in an electric brake device for a vehicle in which the relationship between the torque of the motor and the pressing force applied to the brake disc from the motion conversion mechanism has a hysteresis characteristic, a technique is known for controlling the drive of the motor so that the magnitude of the pressing force reaches a target value.

[0003] For example, in the electric brake device disclosed in Patent Document 1, the motor control device controls the motor drive current based on the magnitude of the pressing force detected by a load sensor. The relationship between motor torque and pressing force has a hysteresis characteristic. When a pressing force is applied to the brake disc and maintained, this motor control device increases the motor torque along the positive efficiency line until the pressing force rises to a predetermined value greater than the target value, and then decreases the motor torque along the inverse efficiency line until the pressing force decreases to the target value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6080682 Summary of the Invention [Problem to be solved by the invention]

[0005] In this specification, the vertical axis of the hysteresis diagram is described as the "braking force correlation amount." In Patent Document 1, the pressing force detected by the load sensor corresponds to the actual braking force, which is the braking force actually output by the electric brake. Also, in Patent Document 1, the load command value corresponds to the required braking force. In the conventional technology of Patent Document 1, the operating point is shifted from the positive efficiency line to the inverse efficiency line to maintain the braking force, thereby making it possible to reduce the current that drives the motor while the braking force is maintained.

[0006] Patent Document 1 describes an operation of increasing the braking force and then maintaining it, but does not describe an operation of decreasing the braking force and then maintaining it, or an operation of switching from a decrease to an increase in braking force. When decreasing the braking force and then maintaining it, it is assumed that the braking force will be maintained at an operating point on the inverse efficiency line as a matter of course. When switching from a maintaining operation at an operating point on the inverse efficiency line to a braking force increasing operation, a torque change equivalent to the width between the normal efficiency line and the inverse efficiency line is required, which poses a problem of response delay.

[0007] The present invention was created in consideration of the above points, and its purpose is to provide a vehicle braking device that is capable of adjusting the balance between the current reduction effect while maintaining braking force and the responsiveness when switching from maintaining operation to increasing braking force operation. [Means for solving the problem]

[0008] The vehicle braking device of the present invention is mounted on a vehicle (900) having a plurality of electric brakes (81-84) provided on each wheel, which convert the torque output by a motor (60) into linear force by a linear motion mechanism (85) and press the electric brakes against the corresponding wheels (91-94) to generate braking force.

[0009] The vehicle braking system includes a braking force control unit (400) that includes a torque command calculation unit (40) and a current command calculation unit (50) and controls the braking force generated by each electric brake. The torque command calculation unit calculates a torque command value for the motor based on a required braking force commanded from an external source. The current command calculation unit calculates a current command value for supplying current to the motor based on the torque command value.

[0010] The relationship between the motor torque and the braking force generated by the electric brake has a hysteresis characteristic in which, as the torque increases, the braking force increases along the positive efficiency line, as the torque decreases from the turning value where the torque changes from increasing to decreasing to the holding critical value, the braking force is maintained constant, and as the torque decreases from the holding critical value, the braking force decreases along the inverse efficiency line.

[0011] The torque command calculation unit has a prediction unit 45 and an operating point adjuster 46. The prediction unit predicts a change in the required braking force from now on.

[0012] The operating point adjuster stores the maximum torque on the positive efficiency line and the minimum torque on the inverse efficiency line corresponding to the maintained braking force, and adjusts the operating point that maintains the braking force in an adjustment zone (Za) between the minimum and maximum torque based on the prediction information from the prediction unit. The torque command calculation unit calculates a torque command value for the motor at the operating point adjusted by the operating point adjuster.

[0013] Depending on the vehicle state, improving responsiveness when switching from maintaining braking force to increasing braking force may take priority over reducing the current while maintaining braking force. In this case, when the prediction unit predicts that the required braking force will increase within the prediction time from the present, the operating point adjuster maintains the braking force at an operating point on the positive efficiency line side of the operating point boundary when the increase is predicted in the adjustment zone. This reduces the response delay when switching from maintaining braking force to increasing braking force. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram of a vehicle equipped with a vehicle braking device according to an embodiment; [Figure 2] FIG. 2 is a block diagram illustrating braking force control of electric brakes corresponding to each wheel. [Figure 3] (a) Schematic diagram of an electric brake pad, (b) Characteristics diagram of pad load and pad position. [Figure 4] FIG. 4 is a diagram showing the hysteresis characteristics of the motor torque and braking force. [Figure 5] FIG. 3 is a block diagram of a torque command calculation unit according to an embodiment. [Figure 6] FIG. 4 is a diagram illustrating calculation of maximum torque and minimum torque. [Figure 7] 10A and 10B are diagrams illustrating setting of operating point boundaries and adjustment of operating points when a required braking force is predicted to increase, be maintained, or decrease. [Figure 8] 10A and 10B are diagrams showing examples of changes in boundary coefficients depending on electric brake temperature and vehicle speed. [Figure 9] 10 is a flowchart of a process for adjusting an operating point. DETAILED DESCRIPTION OF THE INVENTION

[0015] A vehicle braking system according to one embodiment of the present invention will be described with reference to the drawings. The vehicle braking system of this embodiment is mounted on a vehicle in which a plurality of electric brakes are provided on each wheel, and each electric brake converts torque output by a motor into linear force using a linear motion mechanism, and applies braking force to the corresponding wheel. The vehicle braking system includes a braking force control unit that controls the braking force generated by each electric brake.

[0016] [Vehicle configuration] 1 to 3(b), the configuration of a vehicle 900 and electric brakes 81-84 equipped with a vehicle braking device 30 of this embodiment will be described. As shown in Fig. 1, the vehicle 900 is a four-wheel vehicle having two rows of left and right pairs of wheels 91, 92, 93, 94 in the front-rear direction. The front left and right wheels 91, 92 are marked "FL, FR", and the rear left and right wheels 93, 94 are marked "RL, RR".

[0017] A plurality of electric brakes 81, 82, 83, 84 (four in this example) are provided corresponding to the wheels 91, 92, 93, 94. Hereinafter, four consecutive reference numerals will be abbreviated as "wheels 91-94" and "electric brakes 81-84." The same applies to the reference numerals "electric brake temperatures Temp1-Temp4."

[0018] The vehicle braking system 30 includes a braking force control unit 400. The braking force control unit 400 controls the braking force generated by each of the electric brakes 81-84 based on a required braking force commanded from an external device. The required braking force is commanded by the driver's brake operation, a braking signal from a driving assistance device, or the like.

[0019] The braking force control unit 400 of this embodiment obtains the vehicle speed V from the vehicle speed sensor 97 and obtains the electric brake temperatures Temp1-Temp4 from each of the electric brakes 81-84. The electric brake temperatures Temp1-Temp4 are detected by, for example, a temperature sensor. Alternatively, if the electric brakes 81-84 are all equally affected by the outside air temperature, the exhaust heat of the vehicle, and the like, the electric brake temperatures Temp1-Temp4 may be calculated based on the integrated power values ​​of each of the electric brakes 81-84.

[0020] Furthermore, the braking force control unit 400 of this embodiment acquires information related to autonomous driving from the autonomous driving controller 200. For example, while driving while braking downhill, the autonomous driving controller 200 notifies the vehicle of information that the gradient of the downhill slope ahead will become steeper, gentler, or transition to an uphill slope, or that the vehicle is stopped at a traffic light. As will be described later, the braking force control unit 400 predicts future changes in the required braking force based on the autonomous driving information from the autonomous driving controller 200, other camera and map information, and the like.

[0021] In this embodiment, the control configuration of each of the electric brakes 81 to 84 is the same. Fig. 2 shows the control configuration of the electric brakes by the braking force control unit 400, taking one of the electric brakes 81 to 84 as an example.

[0022] Each of the electric brakes 81-84 includes a motor 60, a linear motion mechanism 85, and a caliper 86. The motor 60 is configured, for example, as a permanent magnet three-phase brushless motor, and outputs torque in response to a drive current supplied from a braking force control unit 400. The linear motion mechanism 85 is an actuator that converts the output rotation of the motor 60 into linear motion while decelerating. The rotation angle θ of the motor 60 is proportional to the stroke X of the linear motion mechanism 85. In this way, each of the electric brakes 81-84 converts the torque output by the motor 60 into linear force by the linear motion mechanism 85, and presses the torque against the corresponding wheel 91-94 to generate a braking force.

[0023] The output torque of the motor 60 operates the pads 87 of the caliper 86 via the linear motion mechanism 85. The pads 87 move and are pressed against the disks 88 of the wheels 91-94, generating a braking force due to friction. When the pads 87 move away from the disks 88, the braking force is released.

[0024] With reference to Figures 3(a) and (b), the characteristics of the pad 87 of the electric brake 81-81 shown in part IIIa of Figure 2 will be explained in more detail. As shown in Figure 3(a), the pad 87 has spring-like characteristics, and a pressing force Fd by the linear motion mechanism 85 and a reaction force Fr corresponding to the amount of strain act in opposite directions. As shown in Figure 3(b), the pad position X based on the stroke of the linear motion mechanism 85 is approximately proportional to the pad load F. If the pad position changes by ΔX due to a change Δθ in the rotation angle of the motor 60, the pad load changes by ΔF. Note that only in Figure 3(b) is the symbol "ΔF" used to indicate the change in load. This symbol has a different meaning from "ΔF," which indicates the load deviation between the load command value and the actual load and is used in Figure 5 and subsequent figures.

[0025] 2, the braking force control unit 400 includes a torque command calculation unit 40, a current command calculation unit 50, and an inverter 55. The torque command calculation unit 40 calculates a torque command value Trq of the motor 60 based on a required braking force commanded from the outside. * The current command calculation unit 50 calculates a current command value I to be supplied to the motor 60 based on the torque command value. * Calculate the following.

[0026] The inverter 55 converts the DC power of the battery 15 into AC power and outputs a current command value I * The motor 60 is supplied with AC power according to the current command calculation unit 50. Note that detailed configurations such as current feedback from the current command calculation unit 50 to the inverter 55 are omitted. Using general motor control technology, the inverter 55 performs switching operations in accordance with switching signals generated by PWM control or the like.

[0027] In the basic embodiment, the electric brakes 81-84 are equipped with a load sensor 71 that detects an actual load F, which is a braking load that is actually applied to the wheels 91-94. The actual load F detected by the load sensor 71 is input to the torque command calculation unit 40. The torque command calculation unit 40 performs load control so that the actual load F approaches a load command value calculated based on the required braking force, and the torque command value Trq * In the description of the embodiment, it is assumed that the torque command calculation unit 40 performs load control.

[0028] However, electric brakes 81-84 in other embodiments may be equipped with an angle sensor 72 indicated by a dashed line or a stroke sensor 73 indicated by a dashed double-dashed line. The angle sensor 72 detects an actual angle θ, which is the actual rotation angle of the motor 60. The stroke sensor 73 detects an actual stroke X, which is the actual stroke of the linear motion mechanism 85.

[0029] The angle sensor 72 and stroke sensor 73 are collectively referred to as the "position sensor," and the actual angle θ and actual stroke X are collectively referred to as the "actual position." The actual positions θ and X detected by the position sensors 72 and 73 are input to the torque command calculation unit 40. Instead of or in addition to load control, the torque command calculation unit 40 performs position control so that the actual positions θ and X approach position command values ​​calculated based on the required braking force, and calculates the torque command value Trq * may be calculated.

[0030] Next, the relationship between motor torque and braking force in an electric brake with this configuration will be explained with reference to FIG. 4. Braking force correlates with brake pad load. Hereinafter, "torque" simply refers to the torque output by motor 60, and "load" simply refers to the pressing load by pad 87. FIG. 4 corresponds to FIG. 10 in Patent Document 1 (Japanese Patent No. 6080682).

[0031] The relationship between the torque of the motor 60 and the braking force generated by the electric brakes 81-84 has a hysteresis characteristic. When the torque increases, the braking force increases along the positive efficiency line. When the torque decreases from the turning value Tconv, where the torque starts to decrease, to the holding critical value Tcr, the braking force is maintained constant. When the torque decreases from the holding critical value Tcr, the braking force decreases along the inverse efficiency line.

[0032] In the prior art of Patent Document 1, the magnitude of the load detected by the load sensor is set to the "target value F * The motor torque is increased until it reaches a value greater than the predetermined offset value dF. After that, the magnitude of the load detected by the load sensor reaches the target value F. * The motor drive current is controlled so that the motor torque is reduced until it reaches F. In the process of reducing the motor torque, the load F, i.e., the braking force, is maintained.

[0033] An operation that increases the torque and braking force along the positive efficiency line is defined as an "increase operation," an operation that maintains the braking force at any operating point between the positive efficiency line and the inverse efficiency line is defined as a "maintain operation," and an operation that decreases the torque and braking force along the inverse efficiency line is defined as a "decrease operation."

[0034] In the conventional technology of Patent Document 1, when switching from a holding operation to a braking force increasing operation at an operating point on the inverse efficiency line, a torque change corresponding to the width between the positive efficiency line and the inverse efficiency line is required, resulting in a response delay. Therefore, an object of the vehicle brake device 30 of this embodiment is to make it possible to adjust the balance between the current reduction effect while the braking force is being held and the responsiveness when switching from a holding operation to a braking force increasing operation, depending on the vehicle state, etc.

[0035] (One embodiment) 5 shows a block diagram of the torque command calculation unit 40 according to one embodiment. The torque command calculation unit 40 includes a load command calculation unit 41, a load deviation calculator 42, a prediction unit 45, an operating point adjuster 46, and a load controller 48.

[0036] The load command calculation unit 41 calculates a load command value F based on the required braking force.* The load deviation calculator 42 calculates the actual load F detected by the load sensor 71 and the load command value F * Load deviation ΔF (=F * −F) and output it to the load controller 48.

[0037] The prediction unit 45 acquires the current required braking force, as well as autonomous driving information from the autonomous driving controller 200 and other camera and map information, and predicts future changes in the required braking force based on this information. The prediction unit 45 notifies the operating point adjuster 46 of prediction information regarding future changes in the required braking force.

[0038] For example, suppose that while the vehicle is traveling downhill in autonomous driving mode while maintaining a constant deceleration and braking force, it receives information based on camera images and map information that the road ahead is a steeper downhill slope than the one it is currently traveling on. In this case, the braking force needs to be increased to maintain a constant deceleration. Therefore, the prediction unit 45 predicts that the required braking force will increase from now on.

[0039] Conversely, when autonomous driving is running downhill while maintaining braking force at a constant deceleration, if information is notified that the road ahead is a downhill or uphill road with a gentler gradient than the current driving point, the prediction unit 45 predicts that the required braking force will decrease from now on. Also, if the vehicle ahead decelerates in a vehicle equipped with ACC (adaptive cruise control), the prediction unit 45 predicts that the required braking force will increase from now on. When the brakes are released just before stopping and the vehicle moves slightly, the prediction unit 45 predicts that the required braking force will decrease from now on.

[0040] In this way, the prediction unit 45 is not limited to the example of predicting a change in the required braking force based on vehicle behavior information acquired from the outside, but may also be configured to accept the result of a prediction of a change in the required braking force by the automatic driving controller 200 or the like, and issue a command to the operating point adjuster 46.

[0041] The operating point adjuster 46 acquires the actual load F, load deviation ΔF, electric brake temperatures Temp1-Temp4, and vehicle speed V. Based on the actual load F and load deviation ΔF, the current operating point on the map and the direction of increase / decrease in braking force are estimated. The operating point adjuster 46 also acquires autonomous driving information from the autonomous driving controller 200, as well as other camera and map information, etc.

[0042] The operating point adjuster 46 stores the torque-braking force relationship shown in FIG. 4 as a map. When the braking force is held, the operating point adjuster 46 stores the maximum torque on the positive efficiency line and the minimum torque on the inverse efficiency line corresponding to the held braking force based on the map. The operating point adjuster 46 also adjusts the operating point that holds the braking force in the adjustment zone between the minimum torque and the maximum torque based on prediction information from the prediction unit 45. For example, when the prediction unit 45 predicts that the required braking force will increase from now on, the operating point adjuster 46 shifts the operating point toward the positive efficiency line. The operation of the operating point adjuster 46 will be described in detail below with reference to FIGS. 6 to 9.

[0043] The load controller 48 basically adjusts the load deviation ΔF to approach zero, that is, adjusts the actual load F to the load command value F * Torque command value Trq * Furthermore, the load controller 48 calculates the torque command value Trq at the operating point adjusted by the operating point adjuster 46 while the braking force is being maintained. * Calculate the following.

[0044] 6, the storage of the maximum torque Trq_max and the minimum torque Trq_min by the operating point adjuster 46 and the calculation of the hysteresis width W_hys will be described. In the torque-braking force map of FIG. 6, the white circle on the positive efficiency line indicates the maximum torque Trq_max, and the hatched circle on the inverse efficiency line indicates the minimum torque Trq_min. The operating point adjuster 46 stores the maximum torque Trq_max and the minimum torque Trq_min in the torque-braking force map. * The maximum torque Trq_max and the minimum torque Trq_min corresponding to the torque Trq_max and the torque Trq_min are stored.

[0045] For example, during the manufacturing process or the initial operation, the operating point adjuster 46 adjusts the load command value F* The torque is changed from "0 → maximum torque → 0" for the load command value F and the maximum torque Trq_max and minimum torque Trq_min are stored. The map may be updated as needed each time the power is turned on or for each operation. * When performing a holding operation in which the torque is exceeded and then returned to its original value, the operating point adjuster 46 may store the torque values ​​at the start of the exceeding operation and the end of the returning operation. In this case, there is no need to store the entire map, which is efficient.

[0046] The torque width from the minimum torque Trq_min to the maximum torque Trq_max is defined as the "hysteresis width W_hys." The thick line between the minimum torque Trq_min and the maximum torque Trq_max represents the adjustment zone Za of the operating point where the braking force is maintained. The operating point adjuster 46 adjusts the operating point where the braking force is maintained in the adjustment zone Za based on the prediction information from the prediction unit 45.

[0047] Next, adjustment of the operating point during braking force maintenance operation will be described with reference to Figures 7 and 8. In the following description, "operating points close to the positive efficiency line" includes "operating points on the positive efficiency line," and "operating points close to the inverse efficiency line" includes "operating points on the inverse efficiency line." "Reducing response delay" includes "reducing response delay to zero." Based on prediction information from prediction unit 45, operating point adjuster 46 recognizes changes in the required braking force at a predetermined prediction time from the present.

[0048] The case where the required braking force is predicted to increase within a predicted time from the present time and to switch from maintaining operation to increasing operation is called the "time of predicted increase." When an increase is predicted, the operating point adjuster 46 maintains the braking force at an operating point close to the positive efficiency line, which reduces the current reduction effect while maintaining the braking force, but makes it possible to reduce the response delay when switching to increasing operation.

[0049] On the other hand, when it is predicted that the required braking force will decrease within a predicted time from the present time and that the operation will switch from maintaining the braking force to reducing the braking force, this is referred to as a "predicted decrease." During a predicted decrease, the operating point adjuster 46 maintains the braking force at an operating point close to the inverse efficiency line, thereby ensuring an appropriate current reduction effect while maintaining the braking force and reducing the response delay when switching to reducing the braking force.

[0050] A case where the required braking force is predicted to be maintained for at least the predicted time from the present is called a “hold prediction time.” Even during a hold prediction time, the operating point adjuster 46 maintains the braking force at an operating point close to the inverse efficiency line, thereby ensuring an appropriate current reduction effect during the hold time.

[0051] For example, the operating point adjuster 46 specifically adjusts the operating point using the configuration shown in Fig. 7. The operating point adjuster 46 sets an operating point boundary OBi when an increase is predicted, an operating point boundary OBh when a hold is predicted, and an operating point boundary OBd when a decrease is predicted in the adjustment zone Za. The operating point boundaries OBi, OBh, and OBd are determined based on the load command value F * It is expressed as follows using the minimum torque Trq_min, hysteresis width W_hys, and boundary coefficients α, β, γ (0≦α≦1, 0≦β≦1, 0≦γ≦1) corresponding to the above. When the boundary coefficients α, β, and γ are 0, the operating point is set on the inverse efficiency line, and when the boundary coefficients α, β, and γ are 1, the operating point is set on the normal efficiency line.

[0052] OBi=Trq_min+α×W_hys OBh=Trq_min+β×W_hys OBd=Trq_min+γ×W_hys

[0053] 7 shows the operating point boundaries OBi, OBh, and OBd with α>0.5, β≈0.5, and γ<0.5. When predicting an increase, the operating point adjuster 46 maintains the braking force at an operating point closer to the positive efficiency line than the operating point boundary OBi, thereby reducing the response delay when switching to increasing operation. Furthermore, when predicting a hold or decrease, the operating point adjuster 46 maintains the braking force at an operating point closer to the inverse efficiency line than the operating point boundary OBh or the operating point boundary OBd, respectively, thereby ensuring an optimal current reduction effect.

[0054] As shown in Fig. 8, the operating point adjuster 46 may change the boundary coefficients α, β, and γ in accordance with at least one of the electric brake temperature Temp and the vehicle speed V, thereby changing the operating point boundaries OBi, OBh, and OBd. Here, the electric brake temperature Temp is a representative value calculated as the maximum or average value of each electric brake temperature Temp1-Temp4. While Fig. 8 shows an example of a simple broken line characteristic, a multi-step or curved characteristic may also be used. Furthermore, logic may be added to determine the boundary coefficients α, β, and γ by arbitrating the degree of dependency on the electric brake temperature Temp and the degree of dependency on the vehicle speed V.

[0055] In a high temperature range where the electric brake temperature Temp is equal to or higher than the critical value TempX, the need to avoid breakdown of elements by reducing heat generated by energizing the windings of the inverter 55 and the motor 60 becomes greater than the need for responsiveness in switching to braking force increasing operation. Therefore, it is preferable to reduce the boundary coefficients α, β, and γ to near 0.

[0056] On the other hand, in the high-speed range where the vehicle speed V is equal to or greater than the critical value VX, the delay in switching to the braking force increasing operation has a large impact, so it is necessary to prioritize improving responsiveness over reducing the current while the vehicle is being held. In particular, when predicting an increase, it is preferable to increase the boundary coefficient α to close to 1 to minimize the response delay. If the prediction reliability is high during the holding prediction and the decrease prediction, the boundary coefficients β and γ may be constant regardless of the vehicle speed V, as shown by the dashed line. However, in preparation for sudden braking contrary to the prediction, the boundary coefficients β and γ may be changed significantly when the vehicle speed V is equal to or greater than the critical value VX.

[0057] The processing executed by the operating point adjuster 46 will be described with reference to the flowchart in Fig. 9. In the description of the flowchart, the symbol "S" denotes a step. In S1, the operating point adjuster 46 changes the operating point boundaries OBi, OBh, and OBD of the increasing operation, maintaining operation, and decreasing operation, in accordance with the vehicle speed V or the electric brake temperature Temp. For example, the operating point adjuster 46 changes the boundary coefficients α, β, and γ in accordance with the electric brake temperature Temp or the vehicle speed V, as shown in Fig. 8. Note that the operating point boundaries may be fixed values ​​regardless of the electric brake temperature Temp or the vehicle speed V.

[0058] In S2, the operating point adjuster 46 obtains predicted information on the required braking force from the prediction unit 45. When the prediction unit 45 predicts that the required braking force will increase within the predicted time from the present, a determination of YES is made in S3. At this time, in S4, the operating point adjuster 46 maintains the braking force at an operating point on the positive efficiency line side of the operating point boundary OBi at the time of the predicted increase in the adjustment zone Za.

[0059] When the prediction unit 45 predicts that the required braking force will be maintained for at least the predicted time from the present, a determination of YES is made in S5. At this time, in S6, the operating point adjuster 46 maintains the braking force at an operating point on the inverse efficiency line side of the operating point boundary OBh at the time of the maintenance prediction in the adjustment zone Za.

[0060] When the prediction unit 45 predicts that the required braking force will decrease within the predicted time from the present, a YES determination is made in S7. At this time, in S8, the operating point adjuster 46 maintains the braking force at an operating point on the inverse efficiency line side of the operating point boundary OBd at the time of the predicted decrease in the adjustment zone Za.

[0061] As described above, the operating point adjuster 46 adjusts the operating point at which the braking force is maintained based on the prediction information from the prediction unit 45. This makes it possible to appropriately adjust the balance between the current reduction effect while the braking force is maintained and the responsiveness when switching from the maintaining operation to the braking force increasing operation.

[0062] (Other embodiments) (a) The vehicle on which the vehicle braking device of the present invention is mounted is not limited to a four-wheel vehicle having two rows of left and right pairs of wheels in the longitudinal direction of the vehicle, but may also be a vehicle with six or more wheels having three or more rows of wheels in the longitudinal direction of the vehicle. Furthermore, the vehicle braking device of the present invention may be mounted on a vehicle that does not have an automatic driving controller 200.

[0063] (b) In the above embodiment, the torque command calculation unit 40 calculates the torque command value Trq by load control. * However, in another embodiment, the torque command calculation unit 40 calculates the torque command value Trq by position control. * In this case, the braking force correlates with the positions θ and X, and the positions θ and X are used as the vertical axes of the hysteresis diagrams corresponding to Figs. 4 and 6.

[0064] (c) When adjusting the operating point, information on the electric brake temperature Temp or the vehicle speed V does not need to be used. Furthermore, for example, in areas where the influence of air temperature is greater than the heat generated by current flow, the air temperature may be regarded as the electric brake temperature Temp and processed accordingly.

[0065] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention.

[0066] The braking force control unit and the method thereof described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the braking force control unit and the method thereof described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the braking force control unit and the method thereof described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium. [Explanation of symbols]

[0067] 30. Vehicle braking device, 400 Braking force control section, 40: Torque command calculation unit; 45: Prediction unit; 46: Operating point adjuster; 50...Current command calculation section, 60···motor, 81-84 Electric brake, 85 Linear motion mechanism, 900···Vehicles, 91-94···Wheels.

Claims

1. A vehicle braking device mounted on a vehicle (900) in which a plurality of electric brakes (81-84) are provided on each wheel, and the electric brakes (81-84) convert torque output by a motor (60) into linear force by a linear motion mechanism (85), and press the torque against the corresponding wheel (91-94) to generate a braking force, a braking force control unit (400) including a torque command calculation unit (40) that calculates a torque command value for the motor based on a required braking force commanded from an external source, and a current command calculation unit (50) that calculates a current command value to be supplied to the motor based on the torque command value, and that controls the braking force generated by each of the electric brakes; The relationship between the torque of the motor and the braking force generated in the electric brake has a hysteresis characteristic in which, when the torque increases, the braking force increases along a positive efficiency line, when the torque decreases from a turning value where the torque changes from increasing to decreasing to a holding critical value, the braking force is maintained constant, and when the torque decreases from the holding critical value, the braking force decreases along an inverse efficiency line; The torque command calculation unit a prediction unit (45) for predicting a change in the required braking force from now on; an operating point adjuster (46) that stores a maximum torque on the positive efficiency line and a minimum torque on the inverse efficiency line corresponding to the maintained braking force, and adjusts an operating point that maintains the braking force in an adjustment zone (Za) between the minimum torque and the maximum torque based on prediction information from the prediction unit; and calculating a torque command value for the motor at an operating point adjusted by the operating point adjuster.

2. When the prediction unit predicts that the required braking force will increase within a prediction time from the present, 2. The vehicle brake system according to claim 1, wherein the operating point adjuster maintains the braking force at an operating point on the positive efficiency line side of an operating point boundary (OBi) when an increase is predicted in the adjustment zone.

3. When the prediction unit predicts that the required braking force will be maintained for a predicted time or longer from the present, 2. The vehicle brake device according to claim 1, wherein the operating point adjuster maintains the braking force at an operating point on the inverse efficiency line side of an operating point boundary (OBh) during the maintenance prediction in the adjustment zone.

4. When the prediction unit predicts that the required braking force will decrease within a prediction time from the present, 2. The vehicle brake device according to claim 1, wherein the operating point adjuster maintains the braking force at an operating point on the inverse efficiency line side of an operating point boundary (OBd) when a decrease is predicted in the adjustment zone.

5. 5. The vehicle braking system according to claim 2, wherein the operating point adjuster changes the operating point boundary in accordance with at least one of a temperature of the electric brake and a vehicle speed.

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