Vehicle braking system

Abstract

To provide a braking device for a vehicle, capable of appropriately achieving both the braking performance of the vehicle and a current reduction effect.SOLUTION: The relationship between a current and braking force in an electric brake has hysteresis characteristics. When the current increases, the braking force increases along a positive efficiency line. When the current decreases, from a turning value at which the current stops increasing and starts to decrease, to a holding critical value, the braking force is held constant. When the current decreases from the holding critical value, the braking force decreases along an inverse efficiency line. When required braking force is constant, a holding operation execution determiner determines whether to execute "current reduction holding operation" for holding braking force while reducing a current at an operation point on a side closer to the inverse efficiency line than the positive efficiency line, or to execute "fixed current application operation" for applying a constant current at an operation point on the positive efficiency line. The holding operation execution determiner determines the execution of the current reduction holding operation on the basis of a condition including at least one parameter out of the required braking force or its correlation amount, actual braking force or its correlation amount, the temperature of the electric brake, and a vehicle speed.SELECTED DRAWING: Figure 13

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 motor torque 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] When the required braking force is constant, the operation of maintaining braking force while reducing the current supplied to the electric brake at an operating point closer to the inverse efficiency line than the positive efficiency line is called "current reduction and maintenance operation." On the other hand, the operation of supplying a constant current to the electric brake at an operating point on the positive efficiency line is called "fixed current operation." When current reduction and maintenance operation is not performed, the fixed current operation is performed.

[0007] If the required braking force increases during the current reduction and maintenance operation, a response delay occurs in returning the operating point to the positive efficiency line, which may impair the vehicle's braking performance. In other words, it is not necessarily best to always perform the current reduction and maintenance operation. The challenge is to switch between the current reduction and maintenance operation and the fixed current operation depending on the vehicle condition, etc., and to appropriately achieve both the vehicle's braking performance and the current reduction effect. Patent Document 1 does not mention at all when to perform the current reduction and maintenance operation.

[0008] The present invention has been made in view of the above points, and an object of the present invention is to provide a vehicle braking device that appropriately achieves both the braking performance of the vehicle and the current reduction effect. [Means for solving the problem]

[0009] The vehicle braking system of the present invention is mounted on a vehicle (900) having a plurality of electric brakes (81-84) provided on each wheel to generate braking forces on the corresponding wheels (91-94). The vehicle braking system includes a braking force control unit (400) that controls the braking forces generated by each electric brake based on a required braking force commanded from an external source.

[0010] The relationship between current and braking force in an electric brake has a hysteresis characteristic. When the current increases, the braking force increases along the positive efficiency line. When the current decreases from the turning value where it changes from increasing to decreasing to the holding critical value, the braking force is maintained constant. When the current decreases from the holding critical value, the braking force decreases along the inverse efficiency line.

[0011] The braking force control unit has a holding operation execution determiner (44). When the required braking force is constant, the holding operation execution determiner determines whether to execute a "current reduction and holding operation" in which the braking force is maintained while reducing the current at an operating point closer to the inverse efficiency line than the positive efficiency line, or whether to execute a "fixed current supply operation" in which a constant current is supplied at an operating point on the positive efficiency line.

[0012] In one aspect of the present invention, The holding operation execution determiner is When at least one of the following is confirmed to have continued for more than the judgment time in the current results or future predictions: Current reduction and maintenance operation of implementation Then Make a judgment. (a) Required braking force (F * ), or the time rate of change of the correlation amount of the required braking force (dF * / dt) is less than the rate of change threshold, (b) The difference between the maximum and minimum values ​​of the required braking force or the correlation amount of the required braking force in a predetermined period (RF * ) is less than the range threshold, (c) A state in which the absolute value of the deviation between the required braking force and the actual braking force (F), which is the braking force actually output by the electric brake, or the absolute value of the deviation between the correlation amount of the required braking force and the correlation amount of the actual braking force (|ΔF|) is smaller than the deviation threshold value; (d) A state in which the required braking force or the correlation amount of the required braking force is greater than the required amount threshold value.

[0013] The holding operation execution determiner of the present invention determines whether to execute the current reduction holding operation or the fixed current application operation depending on the above conditions, and therefore can appropriately achieve both the vehicle's braking performance and the current reduction effect. [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 hysteresis characteristics between current and braking force. [Figure 5] FIG. 10 is a diagram illustrating a current reduction and maintenance operation. [Figure 6] FIG. [Figure 7] FIG. 3 is a block diagram of a torque command calculation unit according to an embodiment. [Figure 8] 10A is a graph showing the time rate of change of the required braking force, and FIG. 10B is a graph showing whether or not to perform the current reduction and maintaining operation based on the range of the required braking force. [Figure 9] 10A is a diagram showing a braking force deviation and FIG. 10B is a diagram showing a determination of whether to perform a current reduction and maintaining operation based on a required braking force. [Figure 10] 10A and 10B are diagrams showing examples of changing threshold values ​​according to electric brake temperature and vehicle speed. [Figure 11] 10A and 10B are diagrams showing a determination of whether to perform a current reduction and maintenance operation based on the electric brake temperature and vehicle speed, respectively. [Figure 12] 10A and 10B are diagrams showing switching of thresholds at the start and end of a current reduction and maintenance operation. [Figure 13] 10 is a flowchart of a process for determining whether to perform a current reduction and maintenance operation. 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 driver 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 acquires autonomous driving information from the autonomous driving controller 200 and other prediction information from cameras, map information, etc.

[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 7 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, referring to Figure 4, the relationship between the current flowing through the electric brakes 81-84 and the braking force will be explained. The braking force on the vertical axis correlates with the brake pad load. The braking force actually output by the electric brakes 81-84 is called the "actual braking force." Figure 4 corresponds to Figure 10 in Patent Document 1 (Japanese Patent No. 6080682). However, while Patent Document 1 assumes that the electric brake actuator is a motor and describes the horizontal axis as torque, Figure 4 does not limit the electric brake actuator to a motor and generally describes it as "current." For example, an electric linear actuator may be used.

[0031] The relationship between current and braking force in the electric brakes 81-84 has a hysteresis characteristic. When the current increases, the braking force increases along the positive efficiency line. When the current decreases from the turning value Iconv, where the current changes from increasing to decreasing, to the holding critical value Icr, the braking force is maintained constant. When the current decreases from the holding critical value Icr, 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 current 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 current is reduced until it reaches F. During the process of reducing the current, the load F, i.e., the braking force, is maintained.

[0033] An operation to increase the current and braking force along the positive efficiency line is called an "increase operation," and an operation to decrease the current and braking force along the inverse efficiency line is called a "decrease operation." Furthermore, when the required braking force is constant, an operation to maintain braking force while reducing the current supplied to the electric brakes 81-84 at an operating point closer to the inverse efficiency line than the positive efficiency line is called a "current reduction and maintenance operation." On the other hand, an operation to supply a constant current to the electric brakes 81-84 at an operating point on the positive efficiency line is called a "fixed current supply operation." If a current reduction and maintenance operation is not performed, a fixed current supply operation is performed.

[0034] Referring to FIGS. 5 and 6, the current reduction holding operation and the fixed energization operation will be specifically described. In the current - braking force map shown at the upper part of the figure, the current corresponding to point P1 of braking force Br1 on the positive efficiency line is denoted as I1, and the current corresponding to point P3 (>Br1) of braking force Br3 is denoted as I3 (>I1). Also, the current corresponding to point P2 of braking force Br1 on the reverse efficiency line is denoted as I2 (<I1).

[0035] In the middle and lower parts of the figure, the time variations of the braking force and the current are shown. In common for both the current reduction holding operation and the fixed energization operation, in period I, the current and the braking force increase along the positive efficiency line to I1 and Br1. In the solid - line operation of period III, the current and the braking force increase along the positive efficiency line to I3 and Br3. In the dashed - line operation of period III, the braking force decreases from Br1 along the reverse efficiency line.

[0036] The braking force in period II is constant at Br1. In the current reduction holding operation shown in FIG. 5, after the current decreases from I1, it is maintained at I2 (or an operating point between I2 and I1). Then, when the braking force increases and moves from period II to the solid line in period III, the current increases from a maximum of I2 to I1, that is, by the current difference between the reverse efficiency line and the positive efficiency line, and then further increases to I3 along the positive efficiency line. Therefore, a response delay occurs for the increase requirement of the braking force. On the other hand, in the fixed energization operation shown in FIG. 6, the current in period II remains constant at I1, and when moving from period II to the solid line in period III, the current increases from I1 to I3 without response delay. [[ID=,10]]

[0037] Conversely, when the braking force decreases from period II and moves to the dashed line in period III, in the current reduction holding operation, the current decreases from I2 (or from an operating point between I2 and I1 through I2) along the reverse efficiency line without response delay. On the other hand, in the fixed energization operation, the current decreases from I1 to I2 and then further decreases along the reverse efficiency line. Therefore, a response delay occurs for the decrease requirement of the braking force. However, the influence is smaller compared to when the braking force increases.

[0038] Thus, if the required braking force increases during current reduction and maintenance at an operating point close to the inverse efficiency line, a delay in response occurs before the required braking force shifts to increasing operation along the positive efficiency line, which may impair the vehicle's braking performance. In other words, always performing current reduction and maintenance is not necessarily the best option. Therefore, the vehicle brake device 30 of this embodiment switches between current reduction and maintenance and fixed current application depending on the vehicle state, etc., with the aim of reducing the current as much as possible when the vehicle's braking performance is not impaired. This aims to achieve both vehicle braking performance and current reduction effects.

[0039] (One embodiment) 7 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 holding operation execution determiner 44, and a load controller 48.

[0040] 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. In this embodiment, the load command value F * is the "correlation amount of the required braking force", and the actual load F is the "correlation amount of the actual braking force".

[0041] The holding operation execution determiner 44 determines the load command value F * , actual load F, electric brake temperatures Temp1-Temp4, and vehicle speed V are acquired. At this time, values ​​after processing with a low-pass filter may be acquired. The holding operation execution determiner 44 also acquires autonomous driving information from the autonomous driving controller 200, as well as other camera and map information, etc. When the required braking force is constant, the holding operation execution determiner 44 determines whether to perform a "current reduction holding operation" or a "fixed current supply operation."

[0042] In the current reduction and maintenance operation, the braking force control unit 400 maintains the braking force while reducing the current supplied to the electric brakes 81-84 at an operating point on the inverse efficiency line rather than the positive efficiency line. In the fixed current supply operation, the braking force control unit 400 supplies a constant current to the electric brakes 81-84 at an operating point on the positive efficiency line.

[0043] The holding operation execution determiner 44 determines the load command value F * The determination as to whether to perform the current reduction and maintenance operation is based on conditions including at least one parameter from among the actual load F, electric brake temperatures Temp1-Temp4, and vehicle speed V. For the electric brake temperature, for example, the electric brake temperature Temp calculated as the maximum or average value of each electric brake temperature Temp1-Temp4 is used as a representative value.

[0044] On the time axis, the holding operation execution determiner 44 may use the current result of each parameter as a condition, or may use a prediction for the future (for example, several tens of milliseconds to several seconds in the future) as a condition. The holding operation execution determiner 44 of this embodiment acquires at least a portion of the prediction information used to determine whether to perform the current reduction holding operation from the autonomous driving controller 200. In addition, the holding operation execution determiner 44 may acquire camera or map information other than autonomous driving information as future prediction information.

[0045] As an example of future prediction information, consider a situation where, while driving autonomously downhill while maintaining a constant deceleration and braking force, the vehicle receives information based on camera footage and map information that the road ahead is on a steeper downhill slope than the one it is currently traveling on. In this case, since it is necessary to increase braking force to maintain a constant deceleration, it is predicted that the required braking force will increase from now on. If the vehicle ahead decelerates in a vehicle equipped with ACC (adaptive cruise control), the required braking force is also predicted to increase from now on.

[0046] Furthermore, while the vehicle is stopped at a traffic light with a constant braking force being applied, it is predicted that the required braking force will be maintained at a constant level for some time from now.

[0047] 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 * When the required braking force is constant, the load controller 48 calculates the torque command value Trq in the current reduction holding operation or the fixed current supply operation in accordance with the determination of the holding operation execution determiner 44. * Calculate the following.

[0048] 8 to 12, the determination of whether to perform the current reduction and maintenance operation based on conditions including each parameter will be described. Regarding the symbols for the thresholds for each determination, "thU" indicates an upper threshold and "thL" indicates a lower threshold. When it is determined that the evaluation value is smaller (or lower) than the upper threshold or larger (or higher) than the lower threshold for a determination time Tj or longer, the maintenance operation execution determiner 44 determines that the current reduction and maintenance operation should be performed. In order to prevent erroneous determinations due to temporary fluctuations in the evaluation value or noise, the condition that the current reduction and maintenance operation should be performed for a determination time Tj or longer is required. The determination time Tj for each determination may be the same or different. Furthermore, the thresholds may be set so that the current reduction and maintenance operation is essentially performed 100% or not performed 100%.

[0049] In terms of tense, in the case of a judgment based on a current result, the condition is "when the evaluation value remains smaller (or lower) than the upper threshold value, or remains larger (or higher) than the lower threshold value for a judgment time Tj or more." In the case of a judgment based on a future prediction, the condition is "when the state is predicted to continue for a judgment time Tj or more." Both of these are encompassed, and from the standpoint of the holding operation execution determiner 44 making a judgment based on information, it is expressed as "when it is recognized that the state continues for a judgment time Tj or more."

[0050] 8(a) to 9(b) show the load command value F *An example of an implementation determination based on four types of parameters including the above is shown. In this determination, the required braking force itself may be evaluated, or a correlation amount of the required braking force may be evaluated. For example, in a configuration in which the required braking force from a higher-level vehicle control circuit is converted to generate a command value for current reduction and maintenance operation, adding the current reduction and maintenance function to an existing braking force control unit requires modification of the higher-level vehicle control circuit. In contrast, by configuring the system to be able to use the required braking force input from the higher-level vehicle control circuit, compatibility with existing braking force control units can be easily ensured.

[0051] Figure 8(a) shows the time change rate of the load command value (dF * The holding operation execution determiner 44 determines the execution of the holding operation based on the time rate of change (dF * / dt) is the rate of change threshold (dF * When it is determined that the state where the current is less than 1 / dt)thU continues for a determination time Tj or longer, it is determined that the current reduction and maintenance operation should be performed. At this time, since there is little possibility that the operation will immediately switch to an increase operation, the current reduction effect can be obtained without impairing the braking performance of the vehicle.

[0052] In Fig. 8(b), the load command value F * The difference RF between the maximum and minimum values ​​in a given period Tr * For example, if the difference between the maximum and minimum values ​​in a predetermined period Tr going back from the monitoring time to is within the "load command value range RF * The holding operation execution determiner 44 calculates the load command value range RF * is the range threshold RF * When it is determined that the state where the load command value is smaller than thU continues for a determination time Tj or longer, it is determined that the current reduction and maintenance operation should be performed. As with the determination based on the time rate of change of the load command value, at this time, there is little possibility that the operation will immediately switch to increasing operation, so the current reduction effect can be obtained without impairing the braking performance of the vehicle.

[0053] Figure 9(a) shows the load command value F *The following shows an example of an implementation decision based on the absolute value |ΔF| of the load deviation between the actual load F and the load command value F. The holding operation implementation decision unit 44 decides to implement the current reduction holding operation when it is confirmed that the absolute value |ΔF| of the load deviation is smaller than the deviation threshold value ΔFthU for a period of time equal to or longer than the decision time Tj. * When the braking force is following the current, there is a low possibility that the operation will immediately switch to an increasing operation, so that the current reduction effect can be obtained without impairing the braking performance of the vehicle.

[0054] Figure 9(b) shows the load command value F * The holding operation execution determiner 44 determines whether to execute the holding operation based on the load command value F * is the demand threshold F * When it is determined that the state where the load is greater than thL continues for a determination time Tj or more, it is determined that the current reduction and maintenance operation is to be performed. * is the demand threshold F * When it is smaller than thL, the current reduction effect is small, so there is no need to perform the current reduction and maintenance operation.

[0055] As shown in FIG. 10, the holding operation execution determiner 44 determines the change rate threshold (dF * / dt)thU, range threshold RF * thU, deviation threshold ΔFthU and demand threshold F * One or more of the thresholds thL may be changed. While a simple broken line characteristic is illustrated in Fig. 10, a multi-step or curved characteristic may also be used. Also, logic may be added to arbitrate the dependency on the electric brake temperature Temp and the dependency on the vehicle speed V to determine each threshold.

[0056] When the electric brake temperature Temp is in a high temperature range above the critical value TempX, it is highly necessary to reduce the heat generated by the current supplied to the inverter 55 and the motor 60 by the current reduction and maintenance operation, thereby avoiding breakdown of the elements. Therefore, the upper limit thresholds (dF * / dt)thU, RF * Increase thU and ΔFthU, and increase the demand threshold F *It is preferable to change it to lower thL.

[0057] On the other hand, in the high-speed range where the vehicle speed V is equal to or greater than the critical value VX, priority is given to improving the response of switching to the braking force increasing operation by the fixed current supply operation rather than the effect of the current reduction and maintenance operation. Therefore, the upper limit thresholds (dF * / dt)thU, RF * Lower thU and ΔFthU, and increase the demand threshold F * It is preferable to change the thL to increase it.

[0058] 11(a) shows an example of an implementation determination based on the electric brake temperature Temp. The holding operation implementation determiner 44 determines to implement the current reduction holding operation when it is determined that the electric brake temperature Temp remains higher than the temperature threshold value Temp_thL for a period of time equal to or longer than the determination time Tj. This is advantageous for reducing heat generation in the inverter 55 and the motor 60. On the other hand, when the electric brake temperature Temp is lower than the temperature threshold value Temp_thL, there is little need to reduce the current, and therefore the current reduction holding operation does not need to be implemented.

[0059] 11(b) shows an example of an implementation determination based on vehicle speed V. When it is determined that the state in which vehicle speed V is lower than vehicle speed threshold VthU continues for determination time Tj or longer, the holding operation execution determiner 44 determines to implement current reduction holding operation. On the other hand, when vehicle speed V is higher than vehicle speed threshold VthU, a delay in switching from braking force holding operation to braking force increasing operation has a large impact on vehicle behavior, so a fixed current supply operation is implemented with priority given to responsiveness.

[0060] The switching of the threshold when the reduced current holding operation is started and released will be described with reference to Fig. 12. "Start" refers to switching from the fixed current holding operation to the reduced current holding operation, and "release" refers to switching from the reduced current holding operation to the fixed current holding operation.

[0061] Each upper threshold (dF * / dt)thU, RF *It is preferable that the values ​​of thU, ΔFthU, and VthU at the time of release are set to be larger than the values ​​at the time of start. * It is preferable that the values ​​of thL and Temp_thL at the time of release are set smaller than the values ​​at the time of start, thereby preventing control hunting near the threshold, i.e., preventing frequent switching between fixed current operation and current reduction and maintenance operation.

[0062] The process executed by the holding operation execution determiner 44 will be described with reference to the flowchart in FIG. 13. In the description of the flowchart, the symbol "S" means step. In S1 to S3, the holding operation execution determiner 44 determines whether each determination condition for the current result or future prediction is met. Here, it is not necessary to perform all of the determinations in S1 to S3, and it is sufficient if at least one of the determinations in S1 to S3 is performed. Furthermore, the order of the determinations in S1 to S3 does not matter.

[0063] In S1, the holding operation execution determiner 44 determines whether or not at least one of the following (a) to (d) has continued for a determination time Tj or more. * is the "correlation amount of the required braking force", and the actual load F is the "correlation amount of the actual braking force".

[0064] (a) Load command value F * Time rate of change (dF * / dt) is the rate of change threshold (dF * / dt)thU. (b) Load command value F * The difference RF between the maximum and minimum values ​​in a given period Tr * is the range threshold RF * (c) Load command value F * The absolute value of the load deviation |ΔF| between the actual load F and the load command value F is smaller than the deviation threshold value ΔFthU. (d) Load command value F * is the demand threshold F * A state larger than thL.

[0065] In S2, the holding operation execution determiner 44 determines whether the state in which the electric brake temperature Temp is higher than the temperature threshold value Temp_thL has continued for the determination time Tj or more. In S3, the holding operation execution determiner 44 determines whether the state in which the vehicle speed V is lower than the vehicle speed threshold value VthU has continued for the determination time Tj or more.

[0066] In an embodiment in which determinations S1 to S3 are made, if all of S1, S2, and S3 are YES, the holding operation execution determiner 44 determines in S4 to perform the current reduction holding operation. If any one of S1, S2, and S3 is NO, the holding operation execution determiner 44 determines in S5 to perform the fixed current supply operation. Note that, for example, in an embodiment in which only determination S1 is made, the holding operation execution determiner 44 determines to perform the current reduction holding operation if S1 is YES, and determines to perform the fixed current supply operation if S1 is NO. In this way, the holding operation execution determiner 44 switches between the current reduction holding operation and the fixed current supply operation depending on the vehicle state, etc., and can reduce the current as much as possible when the vehicle's braking performance is not impaired.

[0067] (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.

[0068] (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 position command value and the actual position may be used as the "correlation amount of the required braking force" and the "correlation amount of the actual braking force" in determining whether to perform the current reduction and maintaining operation.

[0069] (c) Information on the electric brake temperature Temp or the vehicle speed V does not have to be used in determining whether or not to perform the current reduction and maintenance operation. Furthermore, for example, in areas where the influence of air temperature is greater than the influence of heat generated by current flow on the electric brake temperature Temp, the air temperature may be regarded as the electric brake temperature Temp and processed accordingly.

[0070] 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.

[0071] 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]

[0072] 30. Vehicle braking device, 400: Braking force control unit; 44: Holding operation execution determiner; 81-84···Electric brake, 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 to generate braking forces on corresponding wheels (91-94), a braking force control unit (400) that controls the braking force generated by each of the electric brakes based on a required braking force commanded from an external source; The relationship between current and braking force in the electric brake has a hysteresis characteristic in which, when the current increases, the braking force increases along a positive efficiency line, when the current decreases from a turning value where the current changes from increasing to decreasing to a holding critical value, the braking force is maintained constant, and when the current decreases from the holding critical value, the braking force decreases along an inverse efficiency line, The braking force control unit a holding operation execution determiner (44) for determining, when the required braking force is constant, whether to perform a current reduction and holding operation for holding the braking force while reducing the current at an operating point closer to the inverse efficiency line than the positive efficiency line, or to perform a fixed current supply operation for supplying a constant current at an operating point on the positive efficiency line, The holding operation execution determiner, in a current result or a future prediction, (a) a state in which the time rate of change (dF* / dt) of the required braking force (F*) or the correlation amount of the required braking force is smaller than a change rate threshold; (b) a state in which the difference (RF*) between the maximum and minimum values ​​of the required braking force or the correlation amount of the required braking force in a predetermined period is smaller than a range threshold value; (c) a state in which the absolute value of the deviation between the required braking force and the actual braking force (F), which is the braking force actually output by the electric brake, or the absolute value (|ΔF|) of the deviation between the correlation amount of the required braking force and the correlation amount of the actual braking force is smaller than a deviation threshold value; (d) a state in which the required braking force or the correlation amount of the required braking force is greater than a required amount threshold value; and determining that the current reduction and maintenance operation should be performed when at least one of the above conditions continues for a determination time or longer.

2. 2. The vehicle braking system according to claim 1, wherein the holding operation execution determiner changes one or more of the change rate threshold, the range threshold, the deviation threshold, and the demand amount threshold in accordance with at least one of a temperature of the electric brake and a vehicle speed.

3. A vehicle braking device mounted on a vehicle (900) in which a plurality of electric brakes (81-84) are provided on each wheel to generate braking forces on corresponding wheels (91-94), a braking force control unit (400) that controls the braking force generated by each of the electric brakes based on a required braking force commanded from an external source; The relationship between current and braking force in the electric brake has a hysteresis characteristic in which, when the current increases, the braking force increases along a positive efficiency line, when the current decreases from a turning value where the current changes from increasing to decreasing to a holding critical value, the braking force is maintained constant, and when the current decreases from the holding critical value, the braking force decreases along an inverse efficiency line, The braking force control unit a holding operation execution determiner (44) for determining, when the required braking force is constant, whether to perform a current reduction and holding operation for holding the braking force while reducing the current at an operating point closer to the inverse efficiency line than the positive efficiency line, or to perform a fixed current supply operation for supplying a constant current at an operating point on the positive efficiency line, The holding operation execution determiner, in a current result or a future prediction, The vehicle braking system determines to perform the current reduction and maintenance operation when it is determined that the temperature (Temp1-Temp4) of the electric brake is higher than a temperature threshold value for a determination time or longer.

4. A vehicle braking device mounted on a vehicle (900) in which a plurality of electric brakes (81-84) are provided on each wheel to generate braking forces on corresponding wheels (91-94), a braking force control unit (400) that controls the braking force generated by each of the electric brakes based on a required braking force commanded from an external source; The relationship between current and braking force in the electric brake has a hysteresis characteristic in which, when the current increases, the braking force increases along a positive efficiency line, when the current decreases from a turning value where the current changes from increasing to decreasing to a holding critical value, the braking force is maintained constant, and when the current decreases from the holding critical value, the braking force decreases along an inverse efficiency line, The braking force control unit a holding operation execution determiner (44) for determining, when the required braking force is constant, whether to perform a current reduction and holding operation for holding the braking force while reducing the current at an operating point closer to the inverse efficiency line than the positive efficiency line, or to perform a fixed current supply operation for supplying a constant current at an operating point on the positive efficiency line, The holding operation execution determiner, in a current result or a future prediction, The vehicle braking device determines to perform the current reduction and maintenance operation when it is determined that the vehicle speed (V) continues to be lower than a vehicle speed threshold for a determination time or longer.

5. The vehicle is equipped with an automatic driving controller (200), The vehicle braking system according to any one of claims 1 to 4, wherein the holding operation execution determiner acquires at least a portion of prediction information used to determine whether to execute the current reduction holding operation from the automatic driving controller.

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