Brake control device

Abstract

To provide a brake control device capable of improving controllability of brake force imparted to a wheel.SOLUTION: A brake control device controls brake force given to a wheel, on the basis of target brake force or a target physical amount. The brake control device functions as a superposed signal generating part M15 for superimposing a vibration signal SGE on a target brake force basic value FbA or a basic signal SGB exhibiting a basic value of a target physical amount, and thereby generating a superposed signal SGS, an output signal generating part M19 for generating an output signal SGO indicating the brake force given to the wheel or a physical amount related to the brake force, and a basic value adjustment part M11 for adjusting the target brake force basic value FbA or the basic value of the target physical amount, on the basis of a calculated value of an inner product within a predetermined period of a first function corresponding to the output signal and a second function corresponding to the vibration signal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a braking control device that controls the braking force applied to a wheel. [Background technology]

[0002] Patent Document 1 discloses a braking control device that adjusts the braking force applied to a wheel according to the slip ratio of the wheel. More specifically, the braking control device adjusts the braking force applied to the wheel according to a target braking force on which a vibration signal indicating a predetermined vibration component is superimposed. The target braking force before the vibration signal is superimposed is defined as a target braking force base value. At this time, when the direction of change of the target braking force on which the vibration signal is superimposed coincides with the direction of change of the slip ratio of the wheel, the braking control device increases the target braking force base value. On the other hand, when the direction of change of the target braking force on which the vibration signal is superimposed differs from the direction of change of the slip ratio, the braking control device decreases the target braking force base value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 46-2864 Summary of the Invention [Problem to be solved by the invention]

[0004] The slip ratio of the wheels is calculated using the vehicle speed. Generally, the vehicle speed is calculated based on a detection signal of a wheel speed sensor. When braking the vehicle, the calculated vehicle speed is likely to deviate from the actual vehicle speed. Therefore, the slip ratio calculated value, which is the slip ratio calculated using the vehicle speed, may deviate from the actual slip ratio. The above braking control device derives a target braking force base value and a target braking force using the slip ratio calculated value. Then, the braking control device adjusts the braking force applied to the wheels based on the target braking force. As a result, a deviation occurs between the actual braking force value and the target braking force. In other words, the above braking control device has room for improvement in terms of improving the controllability of the braking force applied to the wheels. [Means for solving the problem]

[0005] A braking control device for solving the above problem is a device that controls a braking force based on a target braking force that is a target value of a braking force applied to a wheel of a vehicle, or a target physical quantity that is a target value of a physical quantity correlated to the braking force. The braking control device includes a superimposed signal generating unit that generates a superimposed signal by superimposing an excitation signal that is a signal indicating a predetermined vibration component on a base signal indicating a base value of the target braking force or a base value of the target physical quantity, an output signal generating unit that generates an output signal indicating the braking force applied to the wheel or a physical quantity correlated to the braking force, and a base value adjusting unit that adjusts the base value of the target braking force or the base value of the target physical quantity based on a calculated value of an inner product, within a predetermined period, of a first function corresponding to the output signal and a second function corresponding to the excitation signal. Effect of the Invention

[0006] The braking control device described above has an effect of improving the controllability of the braking force applied to the wheels. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a vehicle equipped with a brake control device according to an embodiment. [Diagram 2]FIG. 2 is a block diagram showing a functional configuration of a processing circuit included in the braking control device of FIG. [Diagram 3] FIG. 3 is a graph showing the base signal, the excitation signal, and the superimposed signal. [Figure 4] FIG. 4 is a graph showing the relationship between the amplitude of the output signal and the frequency of the excitation signal, and the relationship between the phase delay amount of the output signal relative to the excitation signal and the frequency of the excitation signal. [Diagram 5] FIG. 5 is a graph showing the relationship between the wheel slip ratio and the actual braking force. [Figure 6] FIG. 6 is a flowchart showing a series of processes executed by the braking control device of FIG. [Figure 7] FIG. 7 is a flowchart showing a series of processes executed by the braking control device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, one embodiment of the brake control device will be described with reference to Figs. 1 illustrates a vehicle 10 equipped with a brake control device 50. The vehicle 10 further includes a brake operating member 11, a plurality of wheels 13, a plurality of friction brakes 20, a brake device 30, and a plurality of sensors. The brake operating member 11 is a member that is operated by the driver to adjust the braking force or deceleration of the vehicle 10. One example of the brake operating member 11 is a brake pedal.

[0009] <Friction brake> Each of the multiple friction brakes 20 applies a braking force to the corresponding wheel 13. For example, the friction brake 20 has a wheel cylinder 21, a rotating body 22, and a friction portion 23. The rotating body 22 rotates integrally with the wheel 13. Therefore, a braking force is applied to the wheel 13 by pressing the friction portion 23 against the rotating body 22. The hydraulic pressure in the wheel cylinder 21 is called the "WC pressure." At this time, the higher the WC pressure, the greater the force pressing the friction portion 23 against the rotating body 22. Therefore, the friction brake 20 can apply a greater braking force to the wheel 13 as the WC pressure is higher. The sum of the braking forces applied to the multiple wheels 13 is called the "vehicle braking force."

[0010] <Brake device> The braking device 30 adjusts the braking force applied to the multiple wheels 13 by operating the multiple friction brakes 20. In this embodiment, the braking device 30 adjusts the braking force applied to the multiple wheels 13 by controlling the WC pressure of the multiple wheel cylinders 21. The braking device 30 has an electric pump or an electric cylinder as a pressure source 31 that supplies brake fluid to the multiple wheel cylinders 21. The braking device 30 is configured to be able to individually control the WC pressure of the multiple wheel cylinders 21.

[0011] <Multiple sensors> The multiple sensors output signals according to the detection results to the braking control device 50. The multiple sensors include a brake sensor 101, multiple wheel speed sensors 102, and an acceleration sensor 103. The brake sensor 101 detects operation-related information related to the operation of the brake operating member 11 by the driver. The brake sensor 101 may be a stroke sensor that detects the amount of operation of the brake operating member 11 by the driver as the operation-related information, or may be a sensor that detects the operating force of the brake operating member 11 by the driver as the operation-related information. The wheel speed sensor 102 outputs a signal according to the rotation speed of the corresponding wheel 13. The acceleration sensor 103 acquires the longitudinal acceleration of the vehicle 10.

[0012] The rotation speed of the wheels 13 based on the detection signal of the wheel speed sensor 102 is referred to as the "wheel speed VW." The acceleration of the vehicle 10 based on the detection signal of the acceleration sensor 103 is referred to as the "longitudinal acceleration GX."

[0013] <Brake control device> The braking control device includes a processing circuit 51. One example of the processing circuit 51 is an electronic control device. In this case, the processing circuit 51 includes a CPU 52 and a memory 53. The memory 53 stores a control program executed by the CPU 52. The CPU 52 executes the control program, whereby the processing circuit 51 controls the operation of the braking device 30. That is, the processing circuit 51 controls the braking force applied to the wheels 13 based on a target braking force FbTr, which is a target of the braking force applied to the wheels 13, or a target physical quantity, which is a target of a physical quantity correlated with the braking force applied to the wheels 13.

[0014] The physical quantity correlated with the braking force applied to the wheels 13 is a vehicle state quantity corresponding to a change in the braking force applied to the wheels 13. The WC pressure of the wheel cylinder 21 is an example of such a physical quantity.

[0015] <Functional configuration of the processing circuit> The functional configuration of the processing circuit 51 will be described with reference to FIGS. The CPU 52 executes the control program in the memory 53, whereby the processing circuit 51 functions as a plurality of functional units. The plurality of functional units includes a base value adjustment unit M11, a vibration signal generation unit M13, a superimposed signal generation unit M15, a control unit M17, an output signal generation unit M19, a compensation unit M21, a signal correction unit M23, and a correlation value calculation unit M25.

[0016] <Basal Value Adjustment Section> The base value adjustment unit M11 adjusts the target braking force base value FbA or the target physical quantity base value. The base value adjustment unit M11 adjusts the target braking force base value FbA or the target physical quantity base value for each of the multiple wheels 13. The target braking force base value FbA is a base value of the target braking force FbTr. The target physical quantity base value is a base value of the target physical quantity and is a value correlated with the target braking force base value FbA. An example of the "target physical quantity" here is the target value of the WC pressure of the wheel cylinder 21. In this case, the target physical quantity base value is a value obtained by converting the target braking force base value FbA into the WC pressure.

[0017] In this embodiment, the base value adjustment unit M11 adjusts the target braking force base value FbA. The adjustment process of the target braking force base value FbA will be described later. The signal indicating the transition of the target braking force base value FbA is referred to as the "base signal SGB indicating the target braking force base value FbA."

[0018] There is a certain degree of correlation between the braking force Fb applied to the wheels 13 and the WC pressure of the wheel cylinder 21. Therefore, the base value adjustment unit M11 may adjust the target value of the WC pressure as the target physical quantity base value.

[0019] <Excitation signal generator> The excitation signal generating unit M13 generates an excitation signal SGE which is a signal indicating a predetermined vibration component. The excitation signal SGE is a signal whose signal value oscillates at a predetermined period. The frequency of the excitation signal SGE generated by the excitation signal generating unit M13 will be described later.

[0020] <Superimposed signal generator> The superimposed signal generating unit M15 generates a superimposed signal SGS by superimposing the excitation signal SGE on the base signal SGB indicating the target braking force base value FbA. The process of superimposing the excitation signal SGE on the base signal SGB is also referred to as a "signal superimposition process." For example, the superimposed signal generating unit M15 performs the signal superimposition process when a predetermined braking control is being executed. The predetermined braking control is a control in which the target braking force base value FbA is repeatedly increased and decreased, as shown in FIG. 3(A). An example of such a predetermined braking control is antilock brake control.

[0021] In the signal superposition process, the superposed signal generation unit M15 superposes the vibration signal SGE shown in Fig. 3(B) on the basic signal SGB shown in Fig. 3(A). As a result, the superposed signal generation unit M15 generates the superposed signal SGS as shown in Fig. 3(C). The signal value of this superposed signal SGS corresponds to the target braking force FbTr. In other words, the superposed signal SGS can be said to be a signal indicating the transition of the target braking force FbTr. In other words, the superposed signal generation unit M15 can be said to be a target braking force derivation unit that derives the target braking force FbTr.

[0022] On the other hand, when the superimposition signal generating unit M15 does not execute the signal superimposition process, it derives the target braking force base value FbA as the target braking force FbTr. In addition, when the base value adjustment unit M11 derives the target physical quantity base value, the superimposed signal generation unit M15 derives a superimposed signal indicating the target physical quantity by superimposing the vibration signal SGE on the base signal indicating the target physical quantity base value in a signal superimposition process.

[0023] <Control Unit> Returning to FIG. 2, the control unit M17 controls the braking force Fb applied to the wheels 13 based on the target braking force FbTr or the target physical quantity. In this embodiment, since the superimposed signal generating unit M15 derives the target braking force FbTr, the control unit M17 controls the braking force Fb based on the target braking force FbTr. For example, when the target braking force FbTr increases, the control unit M17 operates the braking device 30 so that the braking force Fb increases. On the other hand, when the target braking force FbTr decreases, the control unit M17 operates the braking device 30 so that the braking force Fb decreases.

[0024] When the superposition signal generator M15 derives the target physical quantity, the controller M17 controls the braking force Fb applied to the wheels 13 based on the target physical quantity. For example, when the target physical quantity increases, the controller M17 operates the brake device 30 so that the braking force Fb increases. On the other hand, when the target physical quantity decreases, the controller M17 operates the brake device 30 so that the braking force Fb decreases.

[0025] <Output signal generation section> The output signal generating unit M19 acquires the braking force Fb applied to the wheel 13 or a physical quantity correlated to the braking force Fb as an output value. Then, the output signal generating unit M19 generates an output signal SGO indicating the acquired output value. In this embodiment, the output signal generating unit M19 acquires the longitudinal acceleration GX as the physical quantity correlated to the braking force Fb applied to the wheel 13. That is, the longitudinal acceleration GX corresponds to the output value. In this case, the output signal generating unit M19 generates a signal indicating a change in the longitudinal acceleration GX as the output signal SGO.

[0026] The output signal generating unit M19 may obtain the wheel acceleration as a physical quantity correlated with the braking force Fb applied to the wheel 13. The wheel acceleration is a value obtained by differentiating the wheel speed VW with respect to time. In this case, the output signal generating unit M19 generates a signal indicating the transition of the wheel acceleration as an output signal.

[0027] <Compensation Department> The compensation unit M21 compensates for the excitation signal SGE generated by the excitation signal generation unit M13. For example, the compensation unit M21 generates a corrected excitation signal SGEA, which is a signal obtained by delaying the phase of the excitation signal SGE according to a predetermined phase delay amount PHLA.

[0028] Here, the predetermined phase delay amount PHLA will be described with reference to (B) of Fig. 4. (B) of Fig. 4 illustrates the relationship between the frequency of the excitation signal SGE and the phase delay amount PHL of the output signal SGO relative to the excitation signal SGE.

[0029] When the braking force Fb applied to the wheel 13 is controlled in accordance with the target braking force FbTr indicated by the superimposed signal SGS on which the vibration signal SGE is superimposed, the output signal SGO generated by the output signal generating unit M19 includes a fluctuation component corresponding to the vibration signal SGE.

[0030] Due to the characteristics of the configuration of the vehicle 10, the braking device 30, and the friction brake 20, the output signal SGO has a phase lag with respect to the vibration signal SGE, which is an input signal. The present inventors have conducted various experiments and simulations, and have obtained the following findings. Specifically, as shown in FIG. 4B, when the frequency of the vibration signal SGE is changed, the phase lag amount PHL of the output signal SGO with respect to the vibration signal SGE changes according to the vehicle speed VS.

[0031] In (B) of FIG. 4, the solid line shows the relationship between the frequency of the vibration signal SGE and the phase delay amount PHL when the vehicle speed VS is a first vehicle speed VS1. The dashed line shows the relationship between the frequency of the vibration signal SGE and the phase delay amount PHL when the vehicle speed VS is a second vehicle speed VS2. The second vehicle speed VS2 is smaller than the first vehicle speed VS1. The two-dot chain line shows the relationship between the frequency of the vibration signal SGE and the phase delay amount PHL when the vehicle speed VS is a third vehicle speed VS3. The third vehicle speed VS3 is smaller than the second vehicle speed VS2. The one-dot chain line shows the relationship between the frequency of the vibration signal SGE and the phase delay amount PHL when the vehicle speed VS is a fourth vehicle speed VS4. The fourth vehicle speed VS4 is smaller than the third vehicle speed VS3.

[0032] As is clear from FIG. 4B, when the frequency of the excitation signal SGE is the specified frequency FRA, the phase delay amount PHL is the same regardless of the vehicle speed VS. Therefore, the specified frequency FRA is set as the frequency of the excitation signal SGE. Also, the phase delay amount PHL when the frequency is the specified frequency FRA is set as a predetermined phase delay amount PHLA. The specified frequency FRA is determined by the specifications of the vehicle 10, etc.

[0033] <Signal correction section> 2, the signal corrector M23 corrects the output signal SGO in accordance with the vehicle speed VS. The corrected output signal SGO is referred to as a "corrected output signal SGOA."

[0034] FIG. 4A illustrates the relationship between the frequency of the excitation signal SGE and the amplitude AM of the output signal SGO. In detail, in FIG. 4A, the solid line illustrates the relationship between the frequency of the excitation signal SGE and the amplitude AM of the output signal SGO when the vehicle speed VS is a first vehicle speed VS1. The dashed line illustrates the relationship between the frequency of the excitation signal SGE and the amplitude AM of the output signal SGO when the vehicle speed VS is a second vehicle speed VS2. The two-dot chain line illustrates the relationship between the frequency of the excitation signal SGE and the amplitude AM of the output signal SGO when the vehicle speed VS is a third vehicle speed VS3. The dashed dot chain line illustrates the relationship between the frequency of the excitation signal SGE and the amplitude AM of the output signal SGO when the vehicle speed VS is a fourth vehicle speed VS4.

[0035] As is clear from FIG. 4A, when the frequency of the vibration signal SGE is the specified frequency FRA, the amplitude AM of the output signal SGO increases as the vehicle speed VS decreases. In order to prevent the amplitude ratio, which is the amplitude of the output signal SGO to the amplitude of the vibration signal SGE, from changing significantly depending on the vehicle speed VS, it is preferable to correct the amplitude of the output signal SGO depending on the vehicle speed VS.

[0036] Therefore, the signal correction unit M23 generates the corrected output signal SGOA by correcting the output signal SGO such that the correction amount of the amplitude of the output signal SGO increases as the vehicle speed VS increases. For example, the signal correction unit M23 generates the corrected output signal SGOA by correcting the output signal SGO such that the amplitude of the corrected output signal SGOA is constant regardless of the vehicle speed VS.

[0037] <Correlation value calculation section> Returning to Fig. 2, the correlation value calculation unit M25 calculates a friction coefficient slope correlation value XT, which is the increase in the friction coefficient between the wheel 13 and the road surface in response to an increase in the slip rate SLP of the wheel 13. The friction coefficient slope correlation value XT is also simply referred to as a "slope correlation value XT." If the friction coefficient increases in response to an increase in the slip rate SLP, the slope correlation value XT will be a positive value. On the other hand, if the friction coefficient decreases in response to an increase in the slip rate SLP, the slope correlation value XT will be a negative value.

[0038] FIG. 5 shows the relationship between the slip ratio SLP of the wheel 13 and the actual braking force Fbf. The actual braking force Fbf is the braking force that is actually generated between the wheel 13 and the road surface. The larger the friction coefficient, the larger the actual braking force Fbf. In other words, the actual braking force Fbf corresponds to the friction coefficient. When the slip ratio SLP gradually increases from 0 (zero), the actual braking force Fbf and the friction coefficient increase as the slip ratio SLP increases. When the slip ratio SLP reaches the boundary slip ratio SLPL, the grip force of the wheel 13 becomes maximum. Therefore, when the slip ratio SLP becomes larger than the boundary slip ratio SLPL, the actual braking force Fbf and the friction coefficient decrease as the slip ratio SLP increases. In other words, the actual braking force Fbf when the slip ratio SLP is the boundary slip ratio SLPL is the extreme value Fbfmax of the braking force.

[0039] The correlation value calculation unit M25 calculates a value that correlates with the slope of the solid line shown in Fig. 5 at the slip ratio SLP at that time as a slope correlation value XT. That is, the correlation value calculation unit M25 calculates the inner product of a first function corresponding to the output signal and a second function corresponding to the vibration signal within a predetermined period TM as a slope correlation value XT. The slope correlation value XT is the calculated value of the inner product within the predetermined period TM. The function corresponding to the signal is a function that represents the transition of the magnitude of the signal. The inner product of such functions is the integral of the function.

[0040] Here, it will be explained below that the gradient, which is the amount of increase in the actual braking force Fbf relative to the increase in the slip ratio SLP, is approximately equivalent to the calculated value J of the inner product of the output signal and the vibration signal. The following relational expressions (D2) and (D3) are derived on the premise of a single tire model shown in the following relational expression (D1). In addition, in this derivation, the nonlinear state equation is linearized under the condition that a constant brake input and a constant slip ratio are maintained. Furthermore, by treating it in a very short time, the equation is transformed on the premise that various parameters do not change with time.

[0041]

number

[0042] From the relations (D1), (D2), and (D3), it can be seen that the slope "ΔFx / ΔSx", which is the increase in braking force relative to an increase in slip ratio, is approximately equivalent to the calculated value J of the inner product of the output signal and the vibration signal.

[0043] Therefore, the calculated value J of the inner product of a first function corresponding to the output signal corresponding to the actual braking force Fbf and a second function corresponding to the vibration signal superimposed on the target braking force FbTr is a value that correlates with the slope of the relationship between the slip ratio SLP and the actual braking force Fbf.

[0044] As described above, when a predetermined braking control is executed in which the target braking force base value FbA is repeatedly increased and decreased, the target braking force FbTr is generated with the excitation signal SGE superimposed thereon. Here, the predetermined period TM is N fluctuation periods of the excitation signal SGE. N is an integer equal to or greater than 1. An example of N is 1.

[0045] The relationship between the inner product of the first function and the second function within the predetermined period TM and the above-mentioned friction coefficient gradient will be described. As described above, the slope "δFx / δSx" corresponding to the increase in the actual braking force Fbf with respect to the increase in the slip ratio SLP is approximately equivalent to the calculated value J of the dot product of the output signal and the vibration signal. Therefore, in the first region RG1 shown in FIG. 5, the slope corresponding to the increase in the actual braking force Fbf with respect to the increase in the slip ratio SLP is positive, so the calculated value J of the dot product is also a positive value. On the other hand, in the second region RG2 shown in FIG. 5, the slope corresponding to the increase in the actual braking force Fbf with respect to the increase in the slip ratio SLP is negative, so the calculated value J of the dot product is also a negative value. Furthermore, the magnitude of the calculated value J of the dot product is a value according to the above slope.

[0046] From the above, the correlation value calculation unit M25 calculates the inner product of the first function corresponding to the output signal and the second function corresponding to the vibration signal within a predetermined period TM as the gradient correlation value XT. In detail, the correlation value calculation unit M25 calculates the inner product of the first function corresponding to the corrected output signal SGOA and the second function corresponding to the corrected vibration signal SGEA within a predetermined period TM as the gradient correlation value XT.

[0047] 6, a series of processes executed by the processing circuit 51 when the braking device 30 is actuated to apply the braking force Fb to the wheels 13 will be described. When there is a braking request, the processing circuit 51 repeatedly executes the series of processes.

[0048] In step S11, the processing circuit 51 adjusts the target braking force base value FbA. That is, the processing of step S11 is an adjustment processing of the target braking force base value FbA. When the above-mentioned predetermined braking control is not being executed, for example, the processing circuit 51 derives a value according to the detection signal of the brake sensor 101 as the target braking force base value FbA. Also, for example, the processing circuit 51 derives a value according to a required value of the vehicle deceleration from another control device as the target braking force base value FbA. On the other hand, when the above-mentioned predetermined braking control is being executed, a signal value of a superimposed signal SGS generated by superimposing the vibration signal SGE on the base signal SGB of the target braking force base value FbA is derived as the target braking force FbTr. Therefore, the processing circuit 51 adjusts the target braking force base value FbA based on the previous value of the target braking force base value FbA and the slope correlation value XT. The previous value of the target braking force base value FbA is the target braking force base value FbA derived at the time of the previous execution of the series of processing shown in FIG. 6. At this time, the processing circuit 51 derives the target braking-force base value FbA as shown below. For example, when the slope correlation value XT is a positive value, the processing circuit 51 derives a value larger than the previous value of the target braking-force base value FbA as the latest value of the target braking-force base value FbA. When the slope correlation value XT is a negative value, the processing circuit 51 derives a value smaller than the previous value of the target braking-force base value FbA as the latest value of the target braking-force base value FbA. When the slope correlation value XT is 0 (zero), the processing circuit 51 derives a value equal to the previous value of the target braking-force base value FbA or a value slightly smaller than the previous value as the latest value of the target braking-force base value FbA.

[0049] In the next step S13, the processing circuit 51 determines whether or not the execution condition for the signal superimposition process is satisfied. For example, if the predetermined braking control is being executed, the execution condition is deemed to be satisfied. On the other hand, if the predetermined braking control is not being executed, the execution condition is deemed to be not satisfied. If the processing circuit 51 determines that the execution condition is satisfied (S13: YES), the processing circuit 51 shifts the processing to step S15. On the other hand, if the processing circuit 51 determines that the execution condition is not satisfied (S13: NO), the processing circuit 51 shifts the processing to step S17.

[0050] In step S15, the processing circuit 51 derives the target braking force FbTr by executing a signal superposition process. Specifically, the processing circuit 51 generates a superposition signal SGS by superposing the vibration signal SGE on the output signal SGO indicating the target braking force base value FbA. Then, the processing circuit 51 derives the signal value of the superposition signal SGS as the target braking force FbTr. That is, it can be said that the processing circuit 51 derives the sum of the target braking force base value FbA and the signal value of the vibration signal SGE as the target braking force FbTr. After deriving the target braking force FbTr, the processing circuit 51 transitions to step S19.

[0051] In step S17, the processing circuit 51 derives the target braking force FbTr without performing a signal superposition process. Specifically, the processing circuit 51 derives the target braking force base value FbA as the target braking force FbTr. Then, the processing circuit 51 shifts the process to step S19.

[0052] In step S19, the processing circuit 51 operates the braking device 30 based on the target braking force FbTr to control the braking force Fb applied to the wheels 13. After that, the processing circuit 51 temporarily ends a series of processes.

[0053] In this embodiment, the processing circuitry 51 executes the process of step S11 by functioning as the base value adjustment unit M11. The processing circuitry 51 executes the processes of steps S13, S15, and S17 by functioning as the superposition signal generation unit M15. The processing circuitry 51 executes the process of step S19 by functioning as the control unit M17.

[0054] A series of processes executed by the processing circuit 51 when deriving the slope correlation value XT will be described with reference to FIG. 7. When the signal superimposition process is being executed, the processing circuit 51 repeatedly executes the series of processes for each of the above-mentioned predetermined periods TM. The length of the predetermined period TM is set as the predetermined time. In this case, if the time of the base processing step is shorter than the predetermined time, it is preferable to derive the slope correlation value XT for each of the base processing steps using each piece of information going back a predetermined time. This is because the slope correlation value XT can be updated at a cycle shorter than the predetermined time.

[0055] In step S31, the processing circuit 51 generates a corrected vibration signal SGEA by correcting the phase of the vibration signal SGE. In the following step S35, the processing circuit 51 generates a corrected output signal SGOA by correcting the amplitude of the output signal SGO indicating the longitudinal acceleration GX in accordance with the vehicle speed VS.

[0056] In the next step S37, the processing circuit 51 calculates the inner product of the first function corresponding to the corrected output signal SGOA and the second function corresponding to the corrected vibration signal SGEA within a predetermined period TM as the gradient correlation value XT. After that, the processing circuit 51 temporarily ends a series of processes.

[0057] In this embodiment, the processing circuit 51 executes the process of step S31 by functioning as the compensation unit M21. The processing circuit 51 executes the process of step S35 by functioning as the signal correction unit M23. The processing circuit 51 executes the process of step S37 by functioning as the correlation value calculation unit M25.

[0058] <Actions and Effects of the Present Embodiment> (1) When a braking force is applied to the wheel 13, there is a possibility that deceleration slip is occurring in the wheel 13. In this case, when the vehicle speed VS is calculated based on the detection signal of the wheel speed sensor 102, there is a possibility that a deviation occurs between the vehicle speed VS and the actual value of the vehicle speed. In other words, the slip ratio SLP using the vehicle speed VS may deviate from the actual value of the slip ratio of the wheel 13. When controlling the braking force Fb applied to the wheel 13 using such a slip ratio SLP, it is difficult to say that the control accuracy of the braking force Fb is high.

[0059] As described above, the inner product of the first function corresponding to the output signal and the second function corresponding to the vibration signal within a predetermined period TM correlates with the friction coefficient slope, which is the increase in the friction coefficient relative to the increase in the slip ratio SLP. Furthermore, the inner product can be calculated without using the slip ratio SLP.

[0060] Therefore, the braking control device 50 calculates the slope correlation value XT by using the inner product within the above-mentioned predetermined period TM. In other words, the braking control device 50 can estimate the relationship between the slip ratio SLP and the actual braking force Fbf without using the slip ratio SLP, which is difficult to say has high calculation accuracy. Then, the braking control device 50 uses the slope correlation value XT calculated in this way to derive the target braking force base value FbA and the target braking force FbTr, and operates the braking device 30 based on the target braking force FbTr. Therefore, the braking control device 50 can improve the controllability of the braking force Fb applied to the wheels 13.

[0061] (2) When the predetermined braking control is being executed, the braking control device 50 adjusts the braking force Fb applied to the wheel 13 using the slope correlation value XT. Specifically, when the slope correlation value XT is a positive value, the braking control device 50 increases the target braking force base value FbA. On the other hand, when the slope correlation value XT is a negative value, the braking control device 50 decreases the target braking force base value FbA. In this way, the braking control device 50 can bring the actual braking force Fbf closer to the extreme value Fbfmax while suppressing the occurrence of deceleration slip in the wheel 13.

[0062] (3) As described above, the slope correlation value XT is correlated with the friction coefficient slope, which is the increase in the friction coefficient relative to the increase in the slip ratio SLP. Therefore, the braking control device 50 can estimate the extreme value Fbfmax of the braking force applied to the wheel 13 based on the slope correlation value XT.

[0063] (4) When the braking force Fb applied to the wheels 13 is controlled based on the target braking force FbTr superimposed with the vibration signal SGE, a phase shift occurs between the output signal SGO indicating the longitudinal acceleration GX and the vibration signal SGE.

[0064] As described above, the frequency of the excitation signal SGE is set to the specified frequency FRA. The specified frequency FRA is a frequency at which the response delay amount PHL of the output signal SGO in response to the excitation signal SGE becomes a constant value with respect to the vehicle speed VS. In other words, the response delay amount PHL is maintained at a predetermined phase delay amount PHLA shown in FIG. 4B.

[0065] The braking control device 50 calculates the slope correlation value XT using a second function corresponding to the corrected vibration signal SGEA, which is the vibration signal SGE whose phase is delayed according to a predetermined phase delay amount PHLA. This increases the correlation between the slope correlation value XT and the actual braking force Fbf. Therefore, the braking control device 50 can further increase the controllability of the braking force Fb by controlling the braking force Fb applied to the wheels 13 using this slope correlation value XT.

[0066] Here, a comparative example will be described in which a frequency different from the specified frequency FRA is set as the frequency of the excitation signal. In this comparative example, when the vehicle speed VS changes, the response delay amount PHL of the output signal SGO with respect to the excitation signal SGE changes. Therefore, when generating a corrected excitation signal with a delayed phase, the device of the comparative example varies the delay amount of the phase of the excitation signal according to the vehicle speed VS. As a result, in the device of the comparative example, it is possible to increase the correlation between the gradient correlation value XT and the actual braking force Fbf by calculating the gradient correlation value XT using a second function corresponding to such a corrected excitation signal. However, in the device of the comparative example, the control load increases due to varying the phase delay amount according to the vehicle speed VS.

[0067] In this regard, in the braking control device 50, the frequency of the vibration signal SGE is set to the specified frequency FRA. Therefore, the braking control device 50 does not need to vary the amount of phase delay according to the vehicle speed VS. Therefore, the braking control device 50 can increase the correlation between the slope correlation value XT and the actual braking force Fbf while suppressing an increase in the control load.

[0068] (5) When the specified frequency FRA is set as the frequency of the vibration signal SGE, the amplitude AM of the output signal SGO changes according to the vehicle speed VS. If the amplitude AM changes according to the vehicle speed VS in this way, the calculation accuracy of the gradient correlation value XT may be reduced.

[0069] In this regard, the braking control device 50 corrects the output signal SGO so that the amount of correction of the amplitude increases as the vehicle speed VS increases. As a result, the amplitude of the corrected output signal SGOA, which is the output signal after the correction, does not change much even if the vehicle speed VS changes. The braking control device 50 calculates the slope correlation value XT using a first function corresponding to such a corrected output signal SGOA. As a result, the braking control device 50 can suppress changes in the calculation accuracy of the slope correlation value XT according to changes in the vehicle speed VS.

[0070] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0071] The predetermined period TM may be N fluctuation periods of the excitation signal SGE. For example, N may be an integer of 2 or more. The signal correction unit M23 may be located as shown in FIG. 2, or may be located between the correlation value calculation unit M25 and the base value adjustment unit M11.

[0072] Even when the predetermined braking control is not being executed, the processing circuit 51 may generate the superimposed signal SGS by superimposing the excitation signal SGE on the base signal SGB indicating the target braking force base value FbA. In this case, even when the predetermined braking control is not being executed, the processing circuit 51 derives the signal value of the superimposed signal SGS as the target braking force FbTr.

[0073] The processing circuit 51 may execute the following process to adjust the target braking force base value FbA based on the slope correlation value XT. That is, the processing circuit 51 derives the target braking force base value FbA by feedback control using the deviation between the slope correlation value XT and the target value of the slope correlation value as an input. It is preferable to set 0 (zero) or a positive value slightly larger than 0 (zero) as the target value of the slope correlation value. Even in this case, the processing circuit 51 can bring the braking force Fb applied to the wheels 13 closer to the extreme value Fbfmax.

[0074] However, when the slope correlation value XT transitions from a positive value to a negative value, the slip ratio of the wheel 13 increases suddenly. Therefore, when the processing circuit 51 derives the target braking force base value FbA by the above-mentioned feedback control, it is preferable that the processing circuit 51 increases the gain of the feedback control when the slope correlation value XT transitions from a positive value to a negative value. This allows the slip ratio of the wheel 13 to be reduced quickly. Note that, when the slope correlation value XT transitions from a positive value to a negative value under circumstances in which the target braking force base value FbA is derived by the above-mentioned feedback control, the processing circuit 51 may stop the feedback control and significantly reduce the target braking force base value FbA.

[0075] The frequency of the vibration signal SGE may be different from the specified frequency FRA. In this case, the phase shift amount between the vibration signal SGE and the output signal SGO differs depending on the vehicle speed VS. Therefore, when generating a corrected vibration signal with a delayed phase, it is preferable that the processing circuit 51 varies the delay amount of the phase of the vibration signal depending on the vehicle speed VS.

[0076] The processing circuitry 51 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for performing at least some of the various processes, or a combination of these. An example of the dedicated hardware is an application specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., the storage medium, includes any available medium accessible by a general purpose or dedicated computer.

[0077] <Other technical ideas> Next, the technical ideas that can be understood from the above embodiment and modified examples will be described. [Appendix 1] A signal correction unit is provided that corrects the amplitude of the output signal so that the amount of correction of the amplitude increases as the vehicle speed increases, It is preferable that the correlation value calculation unit calculates an inner product of the first function and the second function within the specified period, which corresponds to the output signal corrected by the signal correction unit, as the correlation value of the friction coefficient slope.

[0078] [Additional Note 2] It is preferable that the base value adjustment unit adjusts the base value of the target braking force or the base value of the target physical quantity so that the correlation value of the friction coefficient gradient approaches a target value. [Appendix 3] It is preferable that the superimposed signal generation unit superimposes the vibration signal on the base signal when braking control is being executed in which an increase and decrease in a base value of the target braking force or a base value of the target physical quantity is repeated.

[0079] [Appendix 3] A superposition signal generating unit that generates a superposition signal by superimposing an excitation signal, which is a signal indicating a predetermined vibration component, on a base signal indicating a base value of a target braking force, which is a target value of a braking force to be applied to a wheel of a vehicle, or a base signal indicating a base value of a target physical quantity, which is a target value of a physical quantity correlated with the braking force; a control unit that controls a braking force applied to a wheel of a vehicle based on the target braking force or the target physical quantity, which is a signal value of the superimposed signal; an output signal generating unit that generates an output signal indicative of a braking force applied to the wheel or a physical quantity correlated to the braking force; a slope correlation value calculation unit that calculates an inner product of a first function corresponding to the output signal and a second function corresponding to the vibration signal within a predetermined period as a correlation value of a friction coefficient slope, which is an increase in a friction coefficient between the wheel and a road surface with respect to an increase in a slip rate of the wheel, A braking control device that estimates an extreme value of the braking force to be applied to the wheel based on the correlation value of the friction coefficient gradient.

[0080] The term "at least one" used herein means "one or more" of the desired options. As an example, the term "at least one" used herein means "only one option" or "both of two options" if the number of options is two. As another example, the term "at least one" used herein means "only one option" or "any combination of two or more options" if the number of options is three or more. [Explanation of symbols]

[0081] 10…Vehicle 13...Wheel 20...Friction brake 30...braking device 50...Brake control device 51... Processing circuit 102...Wheel speed sensor 103...Acceleration sensor M11…Base value adjustment section M15: Superimposed signal generator M17…Control section M19…Output signal generation section M21…compensation section M23: Signal correction section M25: Correlation value calculation section

Claims

1. 1. A braking control device that controls a braking force applied to a wheel of a vehicle based on a target braking force, which is a target value of the braking force, or a target physical quantity, which is a target value of a physical quantity correlated to the braking force, comprising: a superposition signal generating unit that generates a superposition signal by superposing a vibration signal, which is a signal indicating a predetermined vibration component, on a base signal indicating a base value of the target braking force or a base value of the target physical quantity; an output signal generating unit that generates an output signal indicative of a braking force applied to the wheel or a physical quantity correlated to the braking force; a base value adjusting unit that adjusts a base value of the target braking force or a base value of the target physical quantity based on a calculated value of an inner product of a first function corresponding to the output signal and a second function corresponding to the excitation signal within a predetermined period. A braking control device comprising:

2. a frequency of the vibration component of the excitation signal is set to a specified frequency at which a phase delay amount of the output signal with respect to the excitation signal is a constant value with respect to the vehicle speed; The second function is a function corresponding to the excitation signal whose phase is delayed according to the phase delay amount.

2. The braking control device according to claim 1.

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