Vehicle braking system

Abstract

To provide a brake device for vehicle which reduces electric current of a dynamo-electric brake while avoiding deterioration of feeling due to discrepancy between actual brake force and required brake force.SOLUTION: A relationship between electric current and brake force in a dynamo-electric brake has hysteresis characteristic. The brake force increases along a positive efficiency line when the electric current increases. The brake force is retained constantly when the electric current decreases from a turning value which turns from increase to decrease to a retention critical value. The brake force decreases along a reverse efficiency line when the electric current decreases from the retention critical value. A period which increases actual brake force along the positive efficiency line is defined as "increase period", and a period which retains the actual brake force constantly is defined as "retention period". A brake force control part switches a period from the increase period to the retention period when the actual brake force increases and reaches target brake force which is set based upon the required brake force, and switches a period from the retention period to the increase period when a target difference Δtgt which is a difference between the actual brake force and the target brake force reaches a prescribed target difference threshold value Δs.SELECTED DRAWING: Figure 5

Description

【Technical Field】 【0001】 The present invention relates to a braking device for a vehicle. 【Background Art】 【0002】 Conventionally, in an electric braking device for a vehicle, a technique for reducing power consumption during braking is known. 【0003】 For example, the electric braking device disclosed in Patent Document 1 performs braking by converting the output of a motor into a pressing force. When increasing the motor torque, the pressing force increases by positive efficiency operation, and when decreasing the motor torque, a hysteresis characteristic is shown in that the pressing force does not change until it reaches a certain torque. This electric braking device aims to reduce the motor current by limiting the ratio of the positive efficiency operation time within a predetermined time to a predetermined value or less. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent No. 6505896 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 In the electric braking device of Patent Document 1, the time ratio between the increase period in which positive efficiency operation is performed to increase the braking force and the holding period in which positive efficiency operation is not performed and the braking force is held is managed to be a predetermined value. Since the increase period and the holding period alternate every predetermined time regardless of the change amount of the required braking force during the holding period, the difference between the actual braking force and the required braking force during the holding period cannot be managed. When the required braking force rapidly increases during the holding period, the actual braking force and the required braking force deviate from each other, which causes deterioration of the driver's braking feeling. 【0006】 This invention was created in view of the above-mentioned points, and its purpose is to provide a vehicle braking device that reduces the current of the electric brake while avoiding deterioration of the feeling due to the discrepancy between the actual braking force and the required braking force. [Means for solving the problem] 【0007】 The vehicle braking system of the present invention is mounted on a vehicle (900) in which a plurality of electric brakes (61-64) that generate braking force on the corresponding wheels (91-94) are provided on each wheel. The vehicle braking system includes a braking force control unit (40) that controls the braking force generated by each electric brake based on a requested braking force commanded from an external source. 【0008】 The relationship between current and braking force in electric brakes exhibits hysteresis characteristics. When the current increases, the braking force increases along the positive efficiency curve. When the current decreases from the turning point where it begins to decrease to the holding critical value, the braking force is maintained at a constant level. When the current decreases from the holding critical value, the braking force decreases along the negative efficiency curve. 【0009】 The period during which the actual braking force, which is the braking force actually output by the electric brake, is increased along the positive efficiency curve is defined as the "increase period," and the period during which the actual braking force is kept constant while the current is reduced from the turning value to the holding critical value is defined as the "holding period." If the vehicle does not meet the prescribed exemption requirements and the required braking force is increasing, the braking force control unit performs the following control. 【0010】 The braking force control unit [1] switches from the increase period to the holding period when the actual braking force increases and reaches the target braking force set based on the required braking force. [2] When the target difference (Δtgt), which is the difference between the actual braking force and the target braking force, reaches a predetermined target difference threshold (Δs, Δp), it switches from the holding period to the increase period. 【0011】 In the present invention, the braking force control unit does not manage the time ratio between the increase period and the holding period as in the prior art described in Patent Document 1, but rather switches from the holding period to the increase period when the target difference reaches the target difference threshold during the holding period. This makes it possible to reduce the electric brake current and heat generated by energization while avoiding deterioration of the feeling due to the discrepancy between the actual braking force and the required braking force. [Brief explanation of the drawing] 【0012】 [Figure 1] A diagram showing the configuration of a vehicle equipped with the vehicle braking system of this embodiment. [Figure 2] A diagram showing the hysteresis characteristics between electric brake current and braking force. [Figure 3] A diagram illustrating the challenges of conventional technology. [Figure 4] A time chart showing the braking force holding switching process according to the first embodiment. [Figure 5] Enlarged view of section [I] to [IV] in Figure 4. [Figure 6] Flowchart for the braking force retention switching process. [Figure 7] A flowchart for determining whether an exemption condition is met. [Figure 8] A time chart showing the braking force retention switching process according to the second embodiment. [Figure 9] A time chart showing the braking force retention switching process according to the third embodiment. [Figure 10] A time chart showing the braking force retention switching process according to the fourth embodiment. [Figure 11] A time chart showing the braking force retention switching process according to the fifth embodiment. [Figure 12] A time chart showing the braking force retention switching process according to a modified example of the fifth embodiment. [Figure 13] A time chart showing the braking force retention switching process according to the sixth embodiment. [Modes for carrying out the invention] 【0013】 Hereinafter, a vehicle braking device according to an embodiment of the present invention will be described based on the drawings. The vehicle braking device of this embodiment is mounted on a vehicle in which a plurality of electric brakes for generating braking force are provided for corresponding wheels. The vehicle braking device includes a braking force control unit that controls the braking force generated by each electric brake. "This embodiment" includes the following First to Sixth Embodiments. In the First to Sixth Embodiments, the configuration of the vehicle braking device itself is the same, and the processing by the braking force control unit is different. 【0014】 (First Embodiment) Referring to FIGS. 1 to 7, the common matters of each embodiment and the First Embodiment will be described. First, referring to FIG. 1, the configuration of a vehicle 900 on which a vehicle braking device 30 is mounted will be described. The vehicle 900 is a four-wheeled vehicle having two rows of left and right paired wheels 91, 92, 93, 94 in the front-rear direction. In this specification, the wheels 91, 92 are also referred to as the front-row left and right wheels FL, FR. Also, the wheels 93, 94 are also referred to as the rear-row left and right wheels RL, RR. 【0015】 A plurality (four in this example) of electric brakes 61, 62, 63, 64 are provided corresponding to each of the wheels 91, 92, 93, 94. Hereinafter, four consecutive reference numerals will be appropriately abbreviated as, for example, "wheels 91-94" and "electric brakes 61-64". The same applies to the "electric brake temperatures Temp1-Temp4" described later. 【0016】 The electric brakes 61-64 generate braking force on the corresponding wheels 91-94 by pressing a friction pad against a brake rotor by the forward movement of an electric actuator composed of a motor or the like. Also, the braking force is released by the friction pad moving away from the brake rotor due to the operation of the electric actuator. Since the mechanical structure of such electric brakes 61-64 is well-known technology, a detailed description thereof will be omitted. 【0017】 The vehicle braking system 30 includes a braking force control unit 40 that controls the braking force generated by each electric brake 61-64 on the corresponding wheels 91-94 based on a requested braking force commanded from an external source. Specifically, the requested braking force is commanded by the driver's brake operation or a braking signal from a driver assistance system. The braking force control unit 40 individually controls the current supplied to each electric brake 61-64 and the timing of the energization. 【0018】 As shown by the dashed line, the braking force control unit 40 may also obtain the vehicle speed V from the vehicle speed sensor 97, or obtain the electric brake temperatures Temp1-Temp4 from each electric brake 61-64. The electric brake temperatures Temp1-Temp4 are detected, for example, by a temperature sensor. Alternatively, if the influence of ambient temperature and vehicle exhaust heat is similar for each electric brake 61-64, the electric brake temperatures Temp1-Temp4 may be calculated based on the accumulated power values ​​of each electric brake 61-64. 【0019】 Vehicle speed V and electric brake temperatures Temp1-Temp4 are mentioned in the description of the exemption requirements, referencing Figure 7. If not used to determine the exemption requirements, the braking force control unit 40 does not need to acquire vehicle speed V or electric brake temperatures Temp1-Temp4. 【0020】 Next, referring to Figure 2, the relationship between the current supplied to the electric brakes 61-64 and the braking force will be explained. As shown in Figure 2, the relationship between the current and the braking force of the electric brakes 61-64 exhibits hysteresis characteristics. Figure 2 corresponds to Figure 5 of Patent Document 1 (Japanese Patent No. 6505896). However, while Patent Document 1 assumes that the actuator of the electric brake is a motor and describes the horizontal axis as torque, Figure 2 does not limit the actuator of the electric brake to a motor and generally describes it as "current". For example, an electric linear actuator may be used. Regarding the vertical axis, while Patent Document 1 specifically describes it as the pressing force of the friction pad, Figure 2 generally describes it as "braking force". 【0021】 The arrows in Figure 2 indicate the direction of hysteresis. In section (A), when the current increases, the braking force increases along the positive efficiency line. The value at which the current changes from increasing to decreasing is called the "turning point Iconv". The process of decreasing current can be divided into two sections, (B) and (C). In section (B), when the current decreases from the turning point Iconv to the holding critical value Icr, the braking force is maintained at a constant holding braking force Br_H. In section (C), when the current decreases from the holding critical value Icr, the braking force decreases along the negative efficiency line. 【0022】 When the current changes from decreasing to increasing, as indicated by arrow (D), the system moves to section (A) along the positive efficiency line while maintaining the braking force at that point. To clarify, the switching value Iconv and the holding braking force Br_H are not fixed values, but change each time the current increases or decreases. That is, as shown by the dashed arrow in Figure 2, each time the current increases and decreases, the system moves back and forth along a constant braking force line between the positive efficiency line and the negative efficiency line. Power consumption is high in section (A), but in section (B), the current can be reduced while maintaining the braking force by utilizing friction. 【0023】 Hereinafter, the braking force actually output by the electric brakes 61-64 will be referred to as the "actual braking force." The period during which the actual braking force is increased along the positive efficiency line will be defined as the "increase period." The period during which the actual braking force is kept constant while decreasing the current from the turning value Iconv to the holding critical value Icr will be defined as the "holding period." During the increase period, the braking force control unit 40 controls the energization of the electric brakes 61-64 at the operating point on the positive efficiency line. During the holding period, the braking force control unit 40 controls the energization of the electric brakes 61-64 at the operating point on the negative efficiency line. 【0024】 Figure 3 shows the change in pressing force, or braking force, over time, based on Figure 2(A) of Patent Document 1. In the prior art of Patent Document 1, the time ratio between the increase period Ta, in which the braking force is increased by performing positive efficiency operation, and the holding period Tb, in which the braking force is maintained without performing positive efficiency operation, is managed to be a predetermined value. Regardless of the amount of change in the required braking force during the holding period, the increase period Ta and the holding period Tb alternate at predetermined time intervals, so it is not possible to manage the difference between the actual braking force and the required braking force during the holding period Tb. As shown in the (*) section, if the required braking force increases rapidly during the holding period Tb, the actual braking force and the required braking force will diverge, causing the driver's braking feeling to deteriorate. 【0025】 Therefore, this embodiment aims to reduce the electric brake current while avoiding deterioration of the feeling due to the discrepancy between the actual braking force and the required braking force during the holding period. To this end, the braking force control unit 40 assumes, in principle, that "the vehicle does not meet the predetermined exemption requirements and the required braking force commanded from an external source is increasing," and performs a "braking force holding switching process" that switches between the increase period and the holding period according to predetermined rules. 【0026】 However, as an exception, if the vehicle meets the exemption requirements, or if the required braking force is constant or decreasing, the braking force control unit 40 will not perform the braking force holding switching process. The exemption requirements will be described later with reference to Figures 6 and 7. 【0027】 Next, the braking force holding switching process according to this embodiment will be described. First, Figure 4 shows a model of the change in required braking force. In this model, the required braking force increases in two stages from 0 to the maximum value, and then decreases in two stages from the maximum value to 0. The horizontal axis shows the whole divided into 7 intervals. As shown by the dashed line, the required braking force increases in the interval [I] from time t0 to t1, remains constant in the interval [II] from time t1 to t2, and increases again in the interval [III] from time t2 to t3. In the interval [IV] from time t3 to t4, the required braking force becomes constant at the maximum value. Furthermore, the required braking force decreases in the interval [V] from time t4 to t5, remains constant in the interval [VI] from time t5 to t6, and decreases in the interval [VII] from time t6 to t7. 【0028】 In response to this required braking force, the actual braking force obtained through the braking force holding switching process in the first embodiment changes as shown by the solid line. First, common to all embodiments, when the required braking force decreases in the section [V] to [VII], the braking force holding switching process is not performed, and the actual braking force changes in accordance with the required braking force. From now on, we will omit further mention of the period when the required braking force decreases. 【0029】 On the other hand, with reference to Figure 5, which shows an enlarged view of the intervals [I] to [IV] in which the required braking force intermittently increases, the braking force holding switching process of the first embodiment will be described. The braking force control unit 40 sets an internal control target value, the "target braking force," based on the required braking force commanded from the outside. In the first embodiment, the "target braking force set based on the required braking force" is set to the same value as the required braking force. In other words, "required braking force = target braking force." 【0030】 Furthermore, the difference between the actual braking force (solid line) and the target braking force (dashed line) is defined as the "target difference Δtgt". In the first embodiment, the target difference threshold Δs, which is compared to the target difference Δtgt, is set to a fixed value. Hereinafter, this type of target difference threshold Δs will be referred to as the "fixed target difference threshold". The symbol "Δs" is derived from 'stationary'. 【0031】 The braking force control unit 40 switches from the increasing period to the holding period when the actual braking force increases and reaches the target braking force, that is, when the target difference Δtgt becomes 0. Also, the braking force control unit 40 switches from the holding period to the increasing period when the target difference Δtgt reaches the target difference threshold Δs. Therefore, in the intervals [I] and [III] in which the required braking force increases monotonically, the actual braking force increases in a stepwise manner. 【0032】 The braking force control unit 40 does not manage the time ratio between the increase period and the holding period as in the prior art described in Patent Document 1, but rather switches from the holding period to the increase period when the target difference Δtgt reaches the target difference threshold Δs during the holding period. This makes it possible to reduce the electric brake current and heat generated by energization while avoiding deterioration of the feeling due to the discrepancy between the actual braking force and the required braking force. 【0033】 The braking force holding switching process according to this embodiment will be explained with reference to the flowchart in Figure 6. In the flowchart, the symbol "S" represents a step. In S20, it is determined whether the vehicle 900 meets the exemption requirements. In situations where the benefits of current reduction are small, or where responsiveness to the required braking force takes precedence over current reduction, it may be better not to perform the braking force holding switching process. The requirements for determining such cases are defined as exemption requirements. Specific examples of exemption requirements will be described later with reference to Figure 7. 【0034】 If the answer in S20 is NO, i.e., the exemption requirements are not met, then in S30 it is determined whether the required braking force is currently increasing. If the answer in S20 is YES or in S30 is NO, then in S26 the braking force control unit 40 controls the energization of the electric brakes 61-64 as normal control, so that the actual braking force follows the required braking force with each control cycle. 【0035】 In general, when we say "to make the actual braking force follow the required braking force," it is interpreted as meaning to make it follow the required braking force with each control cycle. In other words, looking at it on a microscopic time axis, in normal control, the actual braking force increases stepwise in discrete values ​​with each control cycle. In contrast, the holding period for one holding period in the braking force holding switching process of this embodiment is sufficiently long compared to the control cycle. It is precisely because a certain amount of time is secured for each holding period that the benefit of current reduction is obtained. Therefore, the braking force holding switching process of this embodiment is clearly based on a different technical concept from normal control which is performed with each control cycle. 【0036】 If the answer is NO in S20 and YES in S30, then in S40, the braking force control unit 40 switches from the holding period to the increasing period when the target difference Δtgt reaches the target difference threshold Δs. In the second embodiment and others, the symbol for the target difference threshold is replaced with "Δp". 【0037】 Referring to the flowchart in Figure 7, an example of determining whether the exemption requirements are met will be explained. In this example, the success or failure of the four requirements is determined sequentially in S21 to S24. If at least one of S21 to S24 is judged as YES, then in S25 it is determined that the exemption requirements are met. 【0038】 In S21, it is determined whether the required braking force is below a predetermined braking force threshold. In the low-current region, the benefit of reducing the current is small, so it is sufficient to energize the system so that the actual braking force follows the required braking force with each control cycle. Also, as a prerequisite for determining emergency braking in S22, in the low-current region, by applying the maximum current without using a braking force holding section, it becomes easier to avoid response delays until emergency braking is determined. 【0039】 In S22, it is determined whether the fluctuation in the required braking force is greater than a predetermined braking force fluctuation threshold. If the answer in S22 is YES, i.e., in the case of "emergency braking", response speed takes precedence over current reduction. Therefore, it is preferable to make the actual braking force follow the required braking force with high response speed. 【0040】 In S23, it is determined whether the temperatures Temp1-Temp4 of the electric brakes 61-64 are below a predetermined temperature threshold. If the answer in S23 is YES, the benefit of reducing heat by reducing current is small. In S24, it is determined whether the vehicle speed V is greater than a predetermined vehicle speed threshold. If the answer in S24 is YES, it is preferable to make the actual braking force follow the required braking force with high responsiveness. 【0041】 Next, each embodiment that differs from the first embodiment in the switching configuration from the holding period to the increasing period will be described in order with reference to the time charts in Figures 8 to 13, which correspond to Figure 5. In Figures 8 to 13, the dashed lines indicating the required braking force are the same as in Figure 5. In the second and fifth embodiments, as in the first embodiment, the required braking force becomes the target braking force. In the third, fourth, and sixth embodiments, as will be described later, the target braking force is a switching upper limit that is greater than the required braking force. 【0042】 (Second Embodiment) In the second embodiment shown in Figure 8, the target difference threshold Δp is set to a value correlated with the current required braking force. In a typical example, the target difference threshold Δp is set to a value proportional to the current required braking force. The symbol "Δp" is derived from "proportional". In Figure 8, the lower limit value calculated as "required braking force × α" with α (0 < α < 1) as the proportionality constant is represented by the dashed line. The difference between the lower limit value and the required braking force at the switching time is the target difference threshold Δp. When the target difference Δtgt reaches the target difference threshold Δp during the holding period, the braking force control unit 40 switches from the holding period to the increasing period. In this way, in the second embodiment, the actual braking force can be controlled so that the target difference Δtgt is within a predetermined ratio of the required braking force. 【0043】 Incidentally, if the target differential threshold Δp is proportional to the required braking force, the target differential threshold Δp is a small value close to 0 in the section immediately after the required braking force rises from 0, which may cause control hunting. To prevent this, for example, it is preferable not to perform the braking force holding switching process in the rising section [-], as indicated by the exclusion requirement "required braking force is less than a predetermined braking force threshold Br_th" shown in S21 of Figure 6. Alternatively, a fixed target differential threshold Δs may be used when the required braking force is less than the braking force threshold Br_th, and then switched to a target differential threshold Δp proportional to the required braking force when the required braking force reaches the braking force threshold Br_th. 【0044】 The target difference threshold Δp in the second embodiment is not limited to a simple proportionality, but may also be defined as a linear function represented by the sum of a proportional term and a constant term of the required braking force, or as a quadratic function including a squared term of the required braking force. Including these examples, the target difference threshold Δp according to the concept of the second embodiment is called the "target difference threshold of the required braking force correlation equation." 【0045】 (Third embodiment) In the third embodiment shown in Figure 9, the braking force control unit 40 sets a switching upper limit (single dashed line) and a switching lower limit (double dashed line) with a difference corresponding to a fixed target difference threshold Δs, above and below the required braking force. The braking force control unit 40 uses the switching upper limit as the target braking force and controls the actual braking force between the switching lower limit and the switching upper limit. 【0046】 For example, a value obtained by adding half of the target difference threshold Δs to the required braking force is set as the switching upper limit value. In this case, a value obtained by subtracting half of the target difference threshold Δs from the required braking force becomes the switching lower limit value, and the switching upper limit value and the switching lower limit value are set equally above and below with the required braking force sandwiched therebetween. The actual braking force in FIG. 9 is obtained by offsetting the actual braking force in FIG. 5 upward by half of the target difference threshold Δs, and the average value of the actual braking force approaches the required braking force. However, the switching upper limit value and the switching lower limit value may be set unevenly above and below with the required braking force sandwiched therebetween. Assuming 0 < h < 1, generally, "switching upper limit value = required braking force + h×Δs = target braking force" is expressed. 【0047】 (Fourth Embodiment) In the fourth embodiment shown in FIG. 10, the braking force control unit 40 sets a switching upper limit value and a switching lower limit value having a difference corresponding to the target difference threshold Δp of the required braking force correlation formula above and below with the required braking force sandwiched therebetween. Similar to the third embodiment, the braking force control unit 40 controls the actual braking force between the switching lower limit value and the switching upper limit value with the switching upper limit value as the target braking force. 【0048】 When the target difference threshold Δp is proportional to the required braking force, assuming 0 < β < 1 and 1 < γ, the switching lower limit value is calculated as "required braking force × β", and the switching upper limit value is calculated as "required braking force × γ". When "γ - β = 1 - α" with respect to the proportionality constant α in FIG. 8, the switching upper limit value and the switching lower limit value in FIG. 10 have a difference corresponding to the target difference threshold Δp in FIG. 8. Further, when "β + γ = 2", the switching upper limit value and the switching lower limit value are set equally above and below with the required braking force sandwiched therebetween. 【0049】 (Fifth Embodiment) In the fifth and sixth embodiments, the difference between the actual braking force and the required braking force is defined as "required difference Δreq". The fifth embodiment shown in FIG. 11 has a different switching configuration in section [II] compared to the first embodiment in FIG. 5. Since the required braking force is constant in section [II], the required difference Δreq in the holding period started immediately before section [II] is also constant. If section [II] continues for a long time, the braking force deviation due to the required difference Δreq will remain for a long time. 【0050】 Therefore, the braking force control unit 40 stops holding the actual braking force and adjusts the actual braking force to match the required braking force if the required difference Δreq at time t1c, when the holding period has elapsed for a predetermined duration Tc, is greater than or equal to the required difference threshold Δc. The required difference threshold Δc is set to a value smaller than the target difference threshold Δs. In the fifth embodiment, since the target braking force is equal to the required braking force, the actual braking force also appears to match the target braking force. The symbols "Tc" and "Δc" are derived from 'continue'. This prevents the braking force deviation from remaining for a long period of time. 【0051】 When transitioning from section [II] to section [III], the required braking force increases again. In the example shown in Figure 11, the actual braking force before the elapsed time t1c of the duration Tc is reset, and the target difference threshold Δs is reset based on the actual braking force at the start of section [III]. Thereafter, each time the target difference Δtgt in section [III] reaches the target difference threshold Δs, the system switches from a holding period to an increasing period. 【0052】 On the other hand, in the modified example of the fifth embodiment shown in Figure 12, the actual braking force before the elapsed time t1c of the duration Tc is stored, and even after the start of section [III], a target difference threshold Δs based on the previous actual braking force is used. Thus, the method for restarting the braking force holding switching process after the elapsed duration Tc may be set as appropriate. 【0053】 (Sixth Embodiment) The sixth embodiment shown in Figure 13 applies the discontinuation of holding the actual braking force when a duration Tc has elapsed, in addition to the fourth embodiment which uses switching upper and lower limits. In section [II], the braking force control unit 40 discontinues holding the actual braking force and adjusts the actual braking force to match the required braking force if the required difference Δreq at time t1c, when the holding period has elapsed for a predetermined duration Tc, is greater than or equal to the required difference threshold Δc. The required difference threshold Δc is set to a value smaller than the target difference threshold Δp. In the sixth embodiment, it is clear that the control target value of the actual braking force is the required braking force. 【0054】 When transitioning from section [II] to section [III], the required braking force increases again. In the example shown in Figure 13, the actual braking force before the elapsed time t1c of the duration Tc is reset, and the target difference threshold Δp is reset. In addition to this example, a target difference threshold Δp based on the previous actual braking force may be used, similar to the modification of the fifth embodiment. 【0055】 (Other embodiments) (a) The vehicle on which the vehicle braking device of the present invention is installed is not limited to a four-wheeled vehicle having two rows of left and right pairs of wheels in the longitudinal direction of the vehicle, but may also be a six-wheeled or more vehicle having three or more rows of wheels in the longitudinal direction of the vehicle. 【0056】 (b) In the above embodiment, the braking force retention switching process for the electric brakes 61-64 corresponding to each wheel 91-94 is described as independent. However, for example, the switching method and threshold values ​​for the braking force retention switching process for the front wheels 91 and 92 and the braking force retention switching process for the rear wheels 93 and 94 may be distinguished, or the processes may be linked together. 【0057】 (c) The exemption criteria may include cases where it is assumed that the likelihood of a sudden increase in required braking force due to road conditions, weather, etc., is low. For example, when driving on an uneven road or when there is a strong headwind, braking is enhanced, so the exemption criteria may be considered met. 【0058】 The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit. 【0059】 The invention of "a vehicle braking device according to claim 1, wherein, when at least one of the above-mentioned exclusion requirements is met, the braking force control unit controls the energization of the electric brake so that the actual braking force follows the required braking force in each control cycle," may be specified by reference to any one of the claims from claim 1 to the immediately preceding claim, where the description requirements are permitted. 【0060】 The braking force control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. Alternatively, the braking force control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, the braking force control unit and its method described herein may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to perform one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium. [Explanation of symbols] 【0061】 30. Vehicle braking systems, 40. Braking force control unit, 61, 62, 63, 64... Electric brakes, 900...vehicles, 91, 92, 93, 94...wheels.

Claims

[Claim 1] A vehicle braking system mounted on a vehicle (900) in which multiple electric brakes (61-64) that generate braking force on the corresponding wheels (91-94) are provided on each wheel, The system includes a braking force control unit (40) that controls the braking force generated by each of the electric brakes based on a requested braking force commanded from an external source. The relationship between current and braking force in the aforementioned electric brake has a hysteresis characteristic in which, as the current increases, the braking force increases along the positive efficiency curve; as the current decreases from the turning point where it changes from increasing to decreasing to the holding critical value, the braking force is maintained at a constant level; and as the current decreases from the holding critical value, the braking force decreases along the negative efficiency curve. If we define the period during which the actual braking force, which is the braking force actually output by the electric brake, is increased along the positive efficiency curve as the increase period, and define the period during which the actual braking force is kept constant while decreasing the current from the turning value to the holding critical value as the holding period, If the vehicle does not meet the specified exemption requirements and the required braking force has increased, The aforementioned braking force control unit, When the actual braking force increases and reaches the target braking force set based on the required braking force, the system switches from the increase period to the holding period. A vehicle braking device that switches from the holding period to the increasing period when the target difference (Δtgt), which is the difference between the actual braking force and the target braking force, reaches a predetermined target difference threshold (Δs, Δp). [Claim 2] The vehicle braking device according to claim 1, wherein the target difference threshold (Δs) is set to a fixed value. [Claim 3] The vehicle braking device according to claim 1, wherein the target difference threshold (Δp) is set to a value that correlates with the current required braking force. [Claim 4] The braking force control unit sets a switching upper limit and a switching lower limit having a difference corresponding to the target difference threshold, above and below the requested braking force, and controls the actual braking force between the switching lower limit and the switching upper limit, with the switching upper limit as the target braking force. [Claim 5] The braking device for a vehicle according to claim 2 or 3, wherein the braking force control unit discontinues holding the actual braking force and adjusts the actual braking force to match the required braking force if the required difference (Δreq), which is the difference between the actual braking force and the required braking force at the time when the holding period has elapsed for a predetermined duration (Tc), is greater than or equal to a required difference threshold (Δc) which is smaller than the target difference threshold. [Claim 6] The aforementioned exemption requirements include, The required braking force of the vehicle is less than a predetermined braking force threshold. If the vehicle's required braking force fluctuates more than a predetermined braking force fluctuation threshold, The temperature of the electric brake is below a predetermined temperature threshold. The vehicle speed is greater than the predetermined vehicle speed threshold. When at least one of the following requirements is met, The vehicle braking device according to claim 1, wherein the braking force control unit controls the energization of the electric brake so that the actual braking force follows the required braking force at each control cycle.

Images