Road surface friction estimation device

Abstract

To obtain an estimate friction maximum value which is the maximum value of a friction coefficient to be estimated between a road surface and a tire of a vehicle, by suppressing an adverse effect of a non-periodic disturbance.SOLUTION: A range determination unit 16 defines a determination range Rj which contains an average value μpmdav, on the basis of the average value μpmdav obtained from repeatedly calculated plural tentative friction maximum values μpmd, and a standard deviation σpmd. When the tentative friction maximum values μpmd fall within the determination range Rj, a second estimation unit 22 determines the tentative friction maximum values μpmd as estimate friction maximum values μp. On the other hand, when the tentative friction maximum values μpmd fall outside the determination range Rj, the second estimation unit 22 determines a correction value which falls within the determination range Rj, as the estimate friction maximum value μp. Accordingly, when the tentative friction maximum values μpmd non-periodically vary, since the correction value is adopted as the estimate friction maximum value μp, the estimate friction maximum value μp can be obtained by suppressing an adverse effect of a non-periodic disturbance.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a road surface friction estimation device that estimates a maximum value of a friction coefficient between a road surface and a vehicle tire. [Background technology]

[0002] Patent Document 1 describes a driving assistance system equipped with a control device that performs vehicle driving control to control the driving of a vehicle. The control device of the driving assistance system estimates the maximum value of the friction coefficient between the road surface and the vehicle's tires, and calculates the upper limit acceleration at which the tires do not spin based on the estimated maximum value of the friction coefficient. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-124998 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the driving assistance system of Patent Document 1, the maximum value of the friction coefficient is estimated, but the estimated maximum friction value, which is the maximum value of the estimated friction coefficient, is calculated based on various physical quantities obtained while the vehicle is traveling. Since the physical quantities on which the estimated maximum friction value is based are affected by disturbances, the estimated maximum friction value obtained by the driving assistance system of Patent Document 1 is also calculated while being affected by disturbances.

[0005] However, if the estimated maximum friction value is calculated while being affected by a non-periodic disturbance, the variation in the estimated maximum friction value becomes excessively large when the estimated maximum friction value is used for vehicle driving control, etc. As a result of detailed studies by the inventors, the above was found. Note that examples of non-periodic disturbances include the vehicle's tires running over pebbles and the vehicle's tires falling into a depression in the road surface.

[0006] In view of the above, an object of the present disclosure is to provide a road surface friction estimating device that can obtain an estimated maximum friction value while suppressing the influence of non-periodic disturbances. [Means for solving the problem]

[0007] In order to achieve the above object, a road friction estimation device according to one aspect of the present disclosure includes: A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) travels and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of an estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between a road surface and tires and detected while the vehicle is traveling; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value based on an average value (μpmdav) and a standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; and a second estimation unit (22) that determines the provisional maximum friction value as an estimated maximum friction value if the provisional maximum friction value is within the judgment range, and determines a modified value, which is a value within the judgment range, as the estimated maximum friction value if the provisional maximum friction value is outside the judgment range.

[0008] In this way, if the provisional maximum friction value varies non-periodically, the second estimator determines the above-mentioned corrected value from which the non-periodic variation has been removed as the estimated maximum friction value, and therefore it is possible to obtain the estimated maximum friction value while suppressing the effects of non-periodic disturbances.

[0009] Further, a road surface friction estimation device according to another aspect of the present disclosure includes: A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) travels and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of an estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between a road surface and tires and detected while the vehicle is traveling; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value based on an average value (μpmdav) and a standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; and a second estimation unit (22) that determines the provisional maximum friction value as an estimated maximum friction value if the provisional maximum friction value is within the judgment range, and determines the median (μpmid) of the multiple provisional maximum friction values ​​on which the average value is based as the estimated maximum friction value if the provisional maximum friction value is outside the judgment range.

[0010] In this way, when the provisional maximum friction value varies non-periodically, the second estimator determines the median value, in which the influence of the non-periodic variation of the provisional maximum friction value is reduced, as the estimated maximum friction value. Therefore, the estimated maximum friction value can be obtained while suppressing the influence of non-periodic disturbances.

[0011] In addition, in each section of the application documents, each element may be given a reference number in parentheses. In this case, the reference number merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment described later. Therefore, the present disclosure is not limited in any way by the description of the reference number. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic diagram of a vehicle equipped with a road surface friction estimating device in a first embodiment. [Diagram 2] 1 is a block diagram showing a functional configuration of a road surface friction estimating device in a first embodiment. [Diagram 3] 4 is a flowchart showing a control process executed by the road surface friction estimating device in the first embodiment. [Figure 4]4 is a flowchart showing a subroutine executed in step S103 of FIG. 3. [Diagram 5] 4 is a friction coefficient map used to calculate a provisional maximum friction value in step S101 of FIG. 3. [Figure 6] 3 is a block diagram showing a functional configuration of a range determination unit in FIG. 2 in the first embodiment. [Figure 7] FIG. 10A is a time chart showing a schematic diagram of provisional maximum friction values ​​repeatedly calculated at a predetermined calculation period in the first embodiment, and FIG. 10B is a schematic diagram showing the occurrence frequency distribution of multiple provisional maximum friction values ​​repeatedly calculated. [Figure 8] FIG. 4 is a diagram illustrating the process of step S105 in FIG. 3 in the first embodiment, using a time chart of an estimated maximum friction value. [Figure 9] FIG. 4 is a diagram illustrating the process of step S106 in FIG. 3 in the first embodiment, using a time chart of an estimated maximum friction value. [Figure 10] 5 is a time chart for explaining the control process of FIG. 3 and FIG. 4 in the first embodiment. [Figure 11] 10 is a flowchart showing a control process executed by a road surface friction estimating device in a second embodiment, and corresponds to FIG. 3. [Figure 12] FIG. 14 is a flowchart showing a subroutine executed in step S111 of FIG. 11 in the second embodiment, and corresponds to FIG. [Figure 13] FIG. 7 is a block diagram showing a functional configuration of the range determination unit in FIG. 2 in the second embodiment, and corresponds to FIG. 6. [Figure 14] 13 is a time chart for explaining an average value of provisional maximum friction values ​​that is successively updated in the control process of FIG. 11 and FIG. 12 in the second embodiment. [Figure 15] FIG. 14 is a flowchart showing a subroutine executed in step S111 of FIG. 11 in the third embodiment, and corresponds to FIG. [Figure 16]16 is a time chart for explaining an average value of provisional maximum friction values ​​updated in the control processing of FIG. 11 and FIG. 15 in the third embodiment. [Figure 17] FIG. 17 is a time chart for explaining the control process of FIGS. 11 and 15 in the third embodiment, and corresponds to FIG. 10. [Figure 18] 13 is a flowchart showing a control process executed by a road surface friction estimating device in a fourth embodiment, and corresponds to FIG. 3. [Figure 19] FIG. 17 is a time chart for explaining the control process of FIGS. 15 and 18 in the fourth embodiment, and corresponds to FIG. 10. [Figure 20] FIG. 11 is a block diagram showing a functional configuration of a road surface friction estimating device in a fifth embodiment, and corresponds to FIG. 2. [Figure 21] 13 is a flowchart showing a control process executed by a road surface friction estimating device in a fifth embodiment, and corresponds to FIG. 3. [Figure 22] FIG. 24 is a flowchart showing a subroutine executed in step S111 of FIG. 21 in the fifth embodiment, and corresponds to FIG. 12. [Diagram 23] FIG. 27 is a time chart for explaining the control process of FIGS. 21 and 22 in the fifth embodiment, and corresponds to FIG. 10. [Figure 24] FIG. 13 is a block diagram showing a functional configuration of a road surface friction estimating device in a sixth embodiment, and corresponds to FIG. 2. [Diagram 25] 13 is a time chart for explaining a problem that may occur in a comparative example compared to the sixth embodiment. [Figure 26] FIG. 27 is a time chart illustrating how the sixth embodiment solves the problems that may occur in the comparative example, and corresponds to FIG. 25. [Figure 27] 12 is a flowchart showing a control process executed by a road surface friction estimating device in a sixth embodiment, and corresponds to FIG. 11. [Figure 28]FIG. 28 is a flowchart showing a subroutine executed in step S111 of FIG. 27 in the sixth embodiment, and corresponds to FIG. 15. [Figure 29] FIG. 23 is a block diagram illustrating a schematic functional configuration of a road surface determination unit in the sixth embodiment. [Diagram 30] FIG. 18 is a time chart illustrating a control process executed in the comparative example compared with the sixth embodiment, and corresponds to FIG. 17. [Diagram 31] FIG. 31 is a time chart for explaining the control process of FIGS. 27 and 28 in the sixth embodiment, and corresponds to FIG. 30. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, each embodiment will be described with reference to the drawings. In the following embodiments, the same reference numerals are given to parts that are the same or equivalent to each other.

[0014] (First embodiment) As shown in Fig. 1, a road surface friction estimation device 10 of this embodiment is mounted on a vehicle 80, for example an electric vehicle, and is used in a vehicle control system that controls the traveling of the vehicle 80. Note that each of the double-ended arrows in Fig. 1 indicates the orientation of the vehicle 80 on which the road surface friction estimation device 10 is mounted. That is, in Fig. 1, a vehicle longitudinal direction DR1 that is the front-rear direction of the vehicle 80 and a vehicle vertical direction DR2 that is the up-down direction of the vehicle 80 are each indicated by a double-ended arrow.

[0015] As shown in Fig. 2, the road surface friction estimation device 10 is an electronic control device configured as an on-board microcomputer equipped with a CPU, RAM, ROM, non-volatile rewritable memory, etc. (not shown). That is, the road surface friction estimation device 10 reads and executes a computer program stored in a ROM or non-volatile rewritable memory, which is a non-transient substantial recording medium. By executing this computer program, a method corresponding to the computer program is performed. For example, the road surface friction estimation device 10 executes various control processes such as the control process in Fig. 3 described later, in accordance with the computer program.

[0016] 1 and 2, the road surface friction estimation device 10 estimates a maximum value μmx (see FIG. 5 described later) of a friction coefficient μ between a road surface 84 on which a vehicle 80 travels and tires 81 which are drive wheels of the vehicle 80, and obtains the estimated maximum value μmx of the friction coefficient μ as an estimated maximum friction value μp. To this end, the road surface friction estimation device 10 includes a first estimation unit 11, a range determination unit 16, and a second estimation unit 22. The first estimation unit 11 includes a slip calculation unit 12, a friction calculation unit 13, and a provisional value calculation unit 14.

[0017] The road surface friction estimating device 10 is electrically connected to a detection unit SR composed of a plurality of sensors, and is capable of obtaining various physical quantities detected by the detection unit SR. Although the vehicle 80 has a plurality of drive wheels, in this embodiment, the road surface friction estimating device 10 calculates the estimated maximum friction value μp for each of the tires 81, which are the drive wheels.

[0018] The detection unit SR is a group of sensors that detect various information related to the friction between the road surface 84 and the tires 81 when the vehicle 80 travels on the road surface 84, among information related to the behavior of the vehicle 80, and is provided on the vehicle 80. Specifically, the detection unit SR has a vehicle speed sensor that detects the vehicle speed, which is the speed of the vehicle 80, a wheel speed sensor that detects the drive wheel speed, which is the rotation speed of the tires 81, and a steering angle sensor that detects the steering angle, which is the rotation angle of the steering wheel. The detection unit SR also has a yaw rate sensor that detects the yaw rate, which is the rotation angular velocity of the vehicle 80 in the yaw direction, and an acceleration sensor that detects the acceleration of the vehicle 80. Furthermore, the detection unit SR has a torque sensor that detects the motor torque, which is the output torque of the driving motor, and a load sensor that detects the tire load, which is the vertical load generated on the tires 81. The detection unit SR transmits detection signals corresponding to the detection values ​​detected by these various sensors to the road surface friction estimation device 10.

[0019] The road surface friction estimating device 10 repeatedly executes the control process of Fig. 3 at a predetermined calculation period Tc while the vehicle is traveling, thereby successively calculating the estimated maximum friction value μp. Fig. 3 is a flowchart showing the control process executed by the road surface friction estimating device 10. Fig. 4 is a flowchart showing the subroutine executed in step S103 of Fig. 3.

[0020] In step S101 of FIG. 3, first, the slip calculation unit 12 and the friction calculation unit 13 obtain, from various sensors of the detection unit SR, related physical quantities Xa and Xb, which are physical quantities related to friction between the road surface 84 and the tire 81 and detected during the running of the vehicle 80. Then, the slip calculation unit 12 calculates a slip ratio S between the tire 81 and the road surface 84 based on the related physical quantity Xa, and the friction calculation unit 13 calculates a friction coefficient μ between the tire 81 and the road surface 84 based on the related physical quantity Xb. The slip ratio S calculated by the slip calculation unit 12 is called a calculated slip ratio Sc, and the friction coefficient μ calculated by the friction calculation unit 13 is called a calculated friction coefficient μc. The slip ratio S is the degree to which the rotating tire 81 slips against the road surface 84.

[0021] Specifically, the relevant physical quantity Xa obtained by the slip calculation unit 12 is the vehicle speed, the driving wheel speed, the steering angle, the yaw rate of the vehicle 80, and the acceleration of the vehicle 80. The relevant physical quantity Xb obtained by the friction calculation unit 13 is the motor torque, the tire load, and the acceleration of the vehicle 80.

[0022] In this embodiment, the calculated slip ratio Sc and the calculated friction coefficient μc are calculated taking into account the lateral slip of the vehicle 80. Therefore, the related physical quantity Xa obtained by the slip calculation unit 12 includes the steering angle, the yaw rate of the vehicle 80, and the acceleration of the vehicle 80, and the related physical quantity Xb obtained by the friction calculation unit 13 includes the acceleration of the vehicle 80. In addition, for example, the motor torque obtained from the detection unit SR is converted into a driving wheel torque applied to one tire 81 and then used to calculate the calculated friction coefficient μc.

[0023] Also, in step S101, when the calculated slip ratio Sc and the calculated friction coefficient μc are calculated, the provisional value calculation unit 14 calculates a provisional maximum friction value μpmd, which is a provisional value of the estimated maximum friction value μp, based on the calculated slip ratio Sc and the calculated friction coefficient μc.

[0024] There are various possible methods for calculating the provisional maximum friction value μpmd, but the provisional value calculation unit 14 of this embodiment calculates the provisional maximum friction value μpmd using a friction coefficient map MPm in Fig. 5. The friction coefficient map MPm in Fig. 5 is a map obtained by experimentally measuring in advance the relationship between the slip ratio S and the friction coefficient μ in various road surface conditions. The friction coefficient map MPm is expressed in a coordinate system with the slip ratio S and the friction coefficient μ as the coordinate axes, and is configured to include a large number of relationship curves Lm that indicate the relationship between the slip ratio S and the friction coefficient μ. The large number of relationship curves Lm are obtained from mutually different road surface conditions, and each of them indicates a mutually different maximum value μmx of the friction coefficient μ.

[0025] For example, when the provisional value calculation unit 14 calculates the calculated slip ratio Sc and the calculated friction coefficient μc, the provisional value calculation unit 14 identifies a relation point Pc indicating the calculated slip ratio Sc and the calculated friction coefficient μc in the friction coefficient map MPm. Then, the provisional value calculation unit 14 identifies on which of the multiple relation curves Lm the relation point Pc is located, and calculates the maximum value μmx of the friction coefficient μ indicated by the relation curve Lm on which the relation point Pc is located as the provisional maximum friction value μpmd.

[0026] For example, as illustrated in Fig. 5, when a relation point Pc indicating the calculated slip ratio Sc and the calculated friction coefficient μc is located on a relation curve L1m among a large number of relation curves Lm, the maximum value μmx of the friction coefficient μ indicated by the relation curve L1m is calculated as the provisional maximum friction value μpmd. After step S101 in Fig. 3, the process proceeds to step S102.

[0027] In step S102, the range determination unit 16 determines whether or not the average value μpmdav and the standard deviation σpmd of the provisional maximum friction value μpmd have already been calculated in steps S204 and S205 of Fig. 4 described below. In short, the range determination unit 16 determines whether or not the average value μpmdav and the standard deviation σpmd have already been calculated.

[0028] For example, if steps S204 and S205 have not yet been executed since the start of the flowchart in Fig. 3, the range determination unit 16 determines that the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd have not been calculated. In contrast, if steps S204 and S205 have already been executed since the start of the flowchart, the range determination unit 16 determines that the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd have already been calculated.

[0029] In step S102, if it is determined that the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd have not been calculated, the process proceeds to step S103. On the other hand, if it is determined that the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd have already been calculated, the process proceeds to step S104.

[0030] In step S103, range determination unit 16 executes the subroutine of Fig. 4. And, as shown in Fig. 6, range determination unit 16 has storage device 17 which is a memory used in the subroutine of Fig. 4. Storage device 17 is constituted by, for example, a flash memory or a RAM, and functions as a data storage unit which sequentially stores the provisional maximum friction value μpmd each time provisional value calculation unit 14 calculates the provisional maximum friction value μpmd in step S101.

[0031] 4 is executed in step S103, and when the subroutine ends and the process returns to the flowchart of Fig. 3, the flowchart of Fig. 3 ends. Then, the flowchart of Fig. 3 starts again from step S101.

[0032] In step S201 of FIG. 4, the range determination unit 16 shifts the memory data, which is the provisional maximum friction value μpmd already stored in the storage device 17, by one data address toward the old memory data side.

[0033] 6, the storage device 17 is configured to be able to store N provisional maximum friction values ​​μpmd as memory data, and a data address is assigned to the storage location of each piece of memory data. That is, the storage device 17 has N storage locations for the memory data.

[0034] The temporary maximum friction values ​​μpmd are stored in the storage device 17 in chronological order. 1 , D 2 , ,D NEach of D represents memory data that is the stored provisional maximum friction value μpmd. The subscripts "1, 2, ..., N" of D represent data addresses, and the smaller the subscript value, the newer the provisional maximum friction value μpmd that is stored.

[0035] Since the storage device 17 has such a configuration, by executing step S201 in FIG. 4, for example, memory data D N-1 is memory data D N and the memory data D 2 is memory data D 3 and the memory data D 1 is memory data D 2 Then, the memory data D 1 The memory location of becomes empty. Note that the initial state of the memory device 17 is a state in which no provisional maximum friction value μpmd is stored, and when the memory device 17 is in the initial state, the range determination unit 16 does not perform anything in step S201 because shifting the memory data is meaningless. After step S201 in FIG. 4, the process proceeds to step S202.

[0036] In step S202, the range determination unit 16 stores the provisional maximum friction value μpmd calculated in step S101 of Fig. 3 in the storage device 17. In detail, the provisional maximum friction value μpmd calculated in step S101 is stored in the storage location of the most recent provisional maximum friction value μpmd among a plurality of storage locations in the storage device 17. That is, the provisional maximum friction value μpmd calculated in step S101 is stored in the memory data D 1 and stored in the storage device 17. After step S202 in FIG.

[0037] In step S203, the range determination unit 16 determines whether or not the provisional maximum friction values ​​μpmd have been stored in all of the memory locations of the memory device 17. In other words, as shown in Fig. 6, the memory device 17 has N memory locations, so the range determination unit 16 determines whether or not N provisional maximum friction values ​​μpmd have been stored in the memory device 17.

[0038] In step S203, if it is determined that the provisional maximum friction value μpmd has been stored in all of the memory locations of the memory device 17, the process proceeds to step S204. On the other hand, if it is determined that the provisional maximum friction value μpmd has not been stored in all of the memory locations of the memory device 17 and there is still free space in the memory locations of the memory device 17, the subroutine in Fig. 4 ends and returns to the flowchart in Fig. 3.

[0039] As shown in Fig. 6, the range determination unit 16 includes, in addition to the above-mentioned storage device 17, an average value calculation unit 18 and a standard deviation calculation unit 19. In step S204 of Fig. 4, the average value calculation unit 18 calculates the memory data D 1 ~D N Based on the above, the average value μpmdav of the provisional maximum friction values ​​μpmd is calculated from the following formula F1. 1 ~D N The average value μpmdav is calculated.

number

[0040] In the next step S205, the standard deviation calculation unit 19 calculates the memory data D, which is a plurality of temporary maximum friction values ​​μpmd stored in the storage device 17. 1 ~D N Based on the average value μpmdav calculated from the above formula F1, the standard deviation σpmd of the provisional maximum friction value μpmd is calculated from the following formula F2. 1 ~D N Calculate the standard deviation σpmd.

number

[0041] The variable i in the above formula F1 and formula F2 indicates the data address of the storage device 17. That is, the variable i indicates the subscripts "1, 2, . . . , N" of the memory data D in FIG. 6. Therefore, the provisional maximum friction value μpmd in the above formula F1 and formula F2 is i is set as the provisional maximum friction value μpmd stored in the storage device 17. The same applies to later-described calculation formulas equivalent to the above formula F1 or F2, for example, formulas F9 and F10, which will be described later. After step S205 in FIG. 4, the process proceeds to step S206.

[0042] In step S206, the range determination unit 16 determines a judgment range Rj of the provisional maximum friction value μpmd based on the average value μpmdav of the provisional maximum friction value μpmd calculated in step S204 and the standard deviation σpmd of the provisional maximum friction value μpmd calculated in step S205. This judgment range Rj is used as shown in Fig. 7(b) for the provisional maximum friction value μpmd that varies as shown in Fig. 7(a) due to periodic disturbances and non-periodic disturbances. Then, this judgment range Rj is formed as a range that includes the average value μpmdav within the judgment range Rj.

[0043] For example, in this embodiment, the judgment range Rj is set to the range of "μpmdav±3·σpmd." Therefore, in step S206, the range determination unit 16 calculates the upper limit value μpp of the judgment range Rj from the following formula F3, and calculates the lower limit value μmp of the judgment range Rj from the following formula F4. μpp=μpmdav+3·σpmd ···(F3) μmp=μpmdav-3·σpmd ···(F4)

[0044] When step S206 is completed, the subroutine in FIG. 4 ends and the process returns to the flowchart in FIG.

[0045] Returning to Fig. 3, in step S104, the second estimation unit 22 determines whether or not the provisional maximum friction value μpmd calculated in step S101 is within the judgment range Rj. In other words, the second estimation unit 22 determines whether or not the following inequality F5 is satisfied. If the following inequality F5 is satisfied, the second estimation unit 22 determines that the provisional maximum friction value μpmd is within the judgment range Rj. On the other hand, if the following inequality F5 is not satisfied, the second estimation unit 22 determines that the provisional maximum friction value μpmd is outside the judgment range Rj. μmp≦μpmd≦μpp (F5)

[0046] In step S104, if it is determined that the provisional maximum friction value μpmd is within the judgment range Rj, the process proceeds to step S105. On the other hand, if it is determined that the provisional maximum friction value μpmd is outside the judgment range Rj, the process proceeds to step S106.

[0047] For example, the idea is that the range within the judgment range Rj is the range of fluctuation of the provisional maximum friction value μpmd caused by periodic disturbances, and the range outside the judgment range Rj is the range of fluctuation of the provisional maximum friction value μpmd caused by non-periodic disturbances, and the range of fluctuation of the provisional maximum friction value μpmd is separated.

[0048] In step S105, the second estimator 22 determines the provisional maximum friction value μpmd as the estimated maximum friction value μp. For example, as shown in Fig. 8, in step S105, since the provisional maximum friction value μpmd is within the judgment range Rj, the estimated maximum friction value μp is set to be the same value as the provisional maximum friction value μpmd.

[0049] In step S106, the second estimation unit 22 determines a correction value, which is a value within the judgment range Rj, as the estimated maximum friction value μp. In this embodiment, the correction value is set to the previous value of the estimated maximum friction value μp, which is repeatedly determined as the flowchart in FIG. 3 is repeatedly executed.

[0050] For example, as shown in Fig. 9, in step S106, the provisional maximum friction value μpmd is outside the judgment range Rj, so the provisional maximum friction value μpmd is not adopted. The estimated maximum friction value μp determined in this step S106, in other words, the current value of the estimated maximum friction value μp shown at point Pa in Fig. 9, is made the same value as the previous value of the estimated maximum friction value μp shown at point Pb.

[0051] When step S105 or step S106 ends, the flowchart in Fig. 3 ends. Then, the flowchart in Fig. 3 starts again from step S101. As the flowchart in Fig. 3 is repeatedly executed in this manner, the second estimator 22 repeatedly determines the estimated maximum friction value μp in step S105 or step S106 every time the provisional maximum friction value μpmd is calculated in step S101.

[0052] The second estimation unit 22 also outputs the estimated maximum friction value μp determined in step S105 or step S106 to an external control device. Examples of the external control device include a traction control device and an ABS control device. ABS is an abbreviation for Anti-lock Brake System.

[0053] 3 and 4 constitute functional units that realize the respective functions. This also applies to the flowcharts described later.

[0054] Next, the control processes of Figures 3 and 4 will be described with reference to the time chart of Figure 10. In the time chart of Figure 10, values ​​obtained at each calculation period Tc of the control process of Figure 3 are indicated by black dots.

[0055] Note that both the periodic disturbance and the non-periodic disturbance shown in Fig. 10 are disturbances that affect the calculated provisional maximum friction value μpmd. For example, when the motor torque fluctuates due to a disturbance as shown in Fig. 10, the detected values ​​of the physical quantities on which the calculated friction coefficient μc and the calculated slip ratio Sc are calculated also fluctuate, and therefore the calculated friction coefficient μc and the calculated slip ratio Sc also fluctuate.

[0056] An example of a periodic disturbance is a repeated change in the road surface 84 when driving on a gravel road or a sandy beach. An example of a non-periodic disturbance is a tire 81 of the vehicle 80 running over a pebble or a tire 81 of the vehicle 80 falling into a depression in the road surface 84.

[0057] 10, a plurality of provisional maximum friction values ​​μpmd obtained within an accumulation period PDx prior to time ta1 are sequentially stored and accumulated in the memory device 17. Then, based on the plurality of provisional maximum friction values ​​μpmd stored in the memory device 17, the average value μpmdav and the standard deviation σpmd of the provisional maximum friction values ​​μpmd are calculated.

[0058] At time ta1 in Fig. 10, the judgment result of step S102 in Fig. 3 has switched from a judgment that the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd have not been calculated to a judgment that the average value μpmdav and standard deviation σpmd have already been calculated. As a result, after time ta1, the judgment of step S104 in Fig. 3, that is, a judgment of whether or not the provisional maximum friction value μpmd is within the judgment range Rj, is performed.

[0059] For example, at times ta2, ta3, and ta4, it is determined in step S104 in Fig. 3 that the provisional maximum friction value μpmd is outside the determination range Rj. As a result, the provisional maximum friction value μpmd is not adopted as the estimated maximum friction value μp, and the previous value of the estimated maximum friction value μp is maintained as is.

[0060] As described above, according to this embodiment, the range determination unit 16 determines a judgment range Rj including the average value μpmdav based on the average value μpmdav and standard deviation σpmd obtained from a plurality of repeatedly calculated provisional maximum friction values ​​μpmd. If the provisional maximum friction value μpmd is within the judgment range Rj, the second estimation unit 22 determines the provisional maximum friction value μpmd as the estimated maximum friction value μp. On the other hand, if the provisional maximum friction value μpmd is outside the judgment range Rj, the second estimation unit 22 determines a modified value, which is a value within the judgment range Rj, as the estimated maximum friction value μp.

[0061] Therefore, when the provisional maximum friction value μpmd varies non-periodically, the second estimator 22 determines the above-mentioned corrected value from which the non-periodic variation has been removed as the estimated maximum friction value μp. Therefore, the estimated maximum friction value μp can be obtained while suppressing the influence of non-periodic disturbances. As a result, it is possible to avoid malfunction of the traction control, etc., even when traveling on a gravel road or the like where non-periodic disturbances are likely to occur.

[0062] (1) Furthermore, according to this embodiment, the second estimator 22 repeatedly determines the estimated maximum friction value μp each time the provisional maximum friction value μpmd is calculated. In short, the second estimator 22 repeatedly determines the estimated maximum friction value μp as time passes. The above-mentioned correction value is the previous value of the estimated maximum friction value μp. Therefore, the estimated maximum friction value μp can be determined by temporarily storing the previous value of the estimated maximum friction value μp, which makes it easy to conserve memory. Also, since the previous value of the estimated maximum friction value μp has already been calculated and no calculation load is incurred to obtain the above-mentioned correction value, high-speed calculation is possible.

[0063] (2) Furthermore, according to this embodiment, the first estimator 11 calculates the friction coefficient μ and the slip ratio S of the tire 81 based on the related physical quantities Xa and Xb, and calculates the provisional maximum friction value μpmd based on the calculated friction coefficient μ and slip ratio S. Therefore, the related physical quantities Xa and Xb on which the provisional maximum friction value μpmd is calculated can be obtained from sensors that are generally provided on the vehicle 80.

[0064] Second embodiment Next, a second embodiment will be described. In this embodiment, differences from the first embodiment will be mainly described. Also, parts that are the same as or equivalent to the above-mentioned embodiment will be omitted or simplified. This also applies to the following embodiments.

[0065] In this embodiment, the flowchart of Fig. 3 in the first embodiment is replaced with a flowchart of Fig. 11, and the flowchart of Fig. 4 in the first embodiment is replaced with a flowchart of Fig. 12. In this embodiment, similarly to the first embodiment, the road surface friction estimating device 10 repeatedly executes the control process of Fig. 11 at a predetermined calculation period Tc while the vehicle is traveling, thereby sequentially calculating the estimated maximum friction value μp.

[0066] In the flowchart of Fig. 11, step S103 in Fig. 3 is not included, and instead, step S111 is provided between step S101 and step S102. Therefore, step S101 in Fig. 11 is followed by step S111.

[0067] In step S111 of Fig. 11, the range determination unit 16 executes the subroutine of Fig. 12. Then, in step S111, the subroutine of Fig. 12 is executed, and when the subroutine ends and the process returns to the flowchart of Fig. 11, the process proceeds from step S111 to step S102.

[0068] As described above, the flowchart in Fig. 11 does not include step S103 in Fig. 3. Therefore, if it is determined in step S102 in Fig. 11 that the average value μpmdav and standard deviation σpmd of the provisional maximum friction values ​​μpmd have not been calculated, the flowchart in Fig. 11 ends and starts again from step S101.

[0069] 12, the range determination unit 16 shifts the memory data, which is the provisional maximum friction value μpmd already stored in the storage device 17, by one data address toward the old memory data side. In this respect, step S211 in FIG. 12 is similar to step S201 in FIG. 4.

[0070] Here, in the first embodiment, once the provisional maximum friction value μpmd is stored in all of the memory locations of the memory device 17, steps S201 and S202 in Fig. 4 are not executed thereafter. In contrast, in this embodiment, even if the provisional maximum friction value μpmd is stored in all of the memory locations of the memory device 17, steps S211 and S202 in Fig. 12 may be executed thereafter.

[0071] Therefore, in step S211 of FIG. 12, unlike step S201 of FIG. 4, the range determination unit 16 selects the oldest memory data D among the multiple memory locations of the storage device 17 as shown in FIG. N The range determination unit 16 deletes the provisional maximum friction value μpmd stored in the memory location D from the memory device 17. N The deletion of data from the memory location is performed together with the shifting of the memory data to the old memory data side.

[0072] Therefore, by executing step S211 in FIG. 12, for example, the oldest memory data D N is deleted from the storage device 17, and the memory data D N-1 is memory data D N and the memory data D 2 is memory data D 3 and the memory data D 1 is memory data D 2 Then, the memory data D 1 The memory location becomes free.

[0073] Except for what has been described above, step S211 in FIG. 12 is similar to step S201 in FIG.

[0074] Since the provisional maximum friction values ​​μpmd are stored sequentially in the memory device 17 as described above, once the memory device 17 reaches a state in which the provisional maximum friction values ​​μpmd are stored in all of the memory locations of the memory device 17, this state is maintained as long as the control processes of Figures 11 and 12 continue. Therefore, once it is determined in step S203 that the provisional maximum friction values ​​μpmd have been stored in all of the memory locations of the memory device 17, this result of determination will be maintained as long as the control processes of Figures 11 and 12 continue.

[0075] In this embodiment, the control process of Fig. 11 is executed repeatedly, and so as shown in Fig. 13 and Fig. 14, the range determination unit 16 sequentially stores and accumulates a plurality of provisional maximum friction values ​​μpmd obtained within an accumulation period PDx, which is a predetermined period, in the storage device 17. Then, the accumulation period PDx shifts toward the time elapsing side Atp each time a provisional maximum friction value μpmd is calculated.

[0076] 12, the range determination unit 16 determines a judgment range Rj of the provisional maximum friction value μpmd based on the average value μpmdav and standard deviation σpmd obtained from the multiple provisional maximum friction values ​​μpmd calculated within the accumulation period PDx each time the provisional maximum friction value μpmd is calculated. In this way, the range determination unit 16 updates the judgment range Rj of the provisional maximum friction value μpmd each time the provisional maximum friction value μpmd is calculated.

[0077] The road surface friction estimating device 10 of this embodiment provides the following operational effects.

[0078] (1) According to this embodiment, each time the provisional maximum friction value μpmd is calculated, the judgment range Rj of the provisional maximum friction value μpmd is repeatedly determined based on the average value μpmdav and the standard deviation σpmd obtained from the provisional maximum friction values ​​μpmd calculated within the accumulation period PDx. Then, each time the provisional maximum friction value μpmd is calculated, the accumulation period PDx shifts toward the time-elapsed side Atp. In other words, the accumulation period PDx shifts toward the time-elapsed side Atp as time passes.

[0079] Therefore, it is possible to continue updating the judgment range Rj of the provisional maximum friction value μpmd to one based on the latest provisional maximum friction value μpmd, while avoiding a sudden change in the judgment range Rj that accompanies the update of the judgment range Rj.

[0080] Except for the points described above, this embodiment is similar to the first embodiment. In this embodiment, the same effects as those of the first embodiment can be obtained from the configuration common to the first embodiment.

[0081] Third embodiment Next, a third embodiment will be described. In this embodiment, differences from the first embodiment will be mainly described.

[0082] In this embodiment, the flowchart of Fig. 3 in the first embodiment is replaced with a flowchart of Fig. 11, and the flowchart of Fig. 4 in the first embodiment is replaced with a flowchart of Fig. 15. In this embodiment, similarly to the first embodiment, the road surface friction estimating device 10 repeatedly executes the control process of Fig. 11 at a predetermined calculation period Tc while the vehicle is traveling, thereby successively calculating the estimated maximum friction value μp.

[0083] The flowchart of Fig. 11 employed in this embodiment is the flowchart described in the above-mentioned second embodiment. In this embodiment, unlike the second embodiment, in step S111 of Fig. 11, the range determination unit 16 executes the subroutine of Fig. 15. Except for this, the flowchart of Fig. 11 in this embodiment is as described in the second embodiment.

[0084] In the flowchart of Fig. 15 of this embodiment, steps S227 and S228 are added to the flowchart of Fig. 4 of the first embodiment. Note that the configuration of the range determination unit 16 of this embodiment is as shown in Fig. 6, similar to the first embodiment.

[0085] When step S206 of the flowchart in FIG. 15 is completed, the process proceeds to step S227. Then, in step S227 of FIG. 15, the range determination unit 16 executes memory data clear for the storage device 17 of FIG. 6. That is, the range determination unit 16 deletes the provisional maximum friction value μpmd stored in all the storage locations of the storage device 17. This causes the storage device 17 to return from a state in which the provisional maximum friction value μpmd is stored in all the storage locations of the storage device 17 to an initial state in which no provisional maximum friction value μpmd is stored at all. Therefore, in the next step S203 in which the storage device 17 has returned to the initial state, it is determined again that there is still free space in the storage locations of the storage device 17. When step S227 is completed, the subroutine in FIG. 15 is completed, and the process returns to the flowchart in FIG. 11.

[0086] In step S203 of FIG. 15, if it is determined that the temporary maximum friction value μpmd is not stored in all the memory locations of the memory device 17 and there is still free space in the memory locations of the memory device 17, the process proceeds to step S228.

[0087] Then, in step S228, if the average value μpmdav, standard deviation σpmd, and judgment range Rj of the provisional maximum friction value μpmd have already been calculated or determined, the range determination unit 16 maintains the average value μpmdav, standard deviation σpmd, and judgment range Rj as they are. Also, if the average value μpmdav, standard deviation σpmd, and judgment range Rj of the provisional maximum friction value μpmd have not yet been calculated or determined, the range determination unit 16 maintains the state in which they have not been calculated or determined. In short, the range determination unit 16 does nothing in this step S228. When step S228 ends, the subroutine in FIG. 15 ends, and the process returns to the flowchart in FIG. 11.

[0088] 11 is executed repeatedly, and as shown in Figures 6 and 16, the range determination unit 16 updates the average value μpmdav, standard deviation σpmd, and judgment range Rj of the provisional maximum friction value μpmd every time the provisional maximum friction value μpmd is stored a predetermined number of calculations Nc in the storage device 17. Then, the updated average value μpmdav, standard deviation σpmd, and judgment range Rj are calculated or determined based on the provisional maximum friction value μpmd stored in the storage device 17 at the time of the update.

[0089] Incidentally, the above-mentioned predetermined number of calculations Nc is equal to the number of storage locations of the storage device 17, so "number of calculations Nc=N."

[0090] Furthermore, since the provisional maximum friction value μpmd is stored in the storage device 17 in sequence at a prescribed calculation period Tc, the prescribed number of calculations Nc can be converted into time. Therefore, the above-mentioned "every time the provisional maximum friction value μpmd is stored in the storage device 17 for the prescribed number of calculations Nc" can be rephrased as every accumulation period PDx corresponding to the prescribed number of calculations Nc. In this case, the accumulation period PDx in this embodiment is defined as a prescribed period during which the provisional maximum friction value μpmd is continuously accumulated in the storage device 17.

[0091] Furthermore, after updating the average value μpmdav, the standard deviation σpmd, and the judgment range Rj, the range determination unit 16 erases all of the provisional maximum friction values ​​μpmd stored in the storage device 17, and then starts storing the provisional maximum friction values ​​μpmd again in the storage device 17. Therefore, as shown in Fig. 16, the accumulation period PDx described above shifts toward the time-elapsed side Atp as time passes.

[0092] Next, the control processes of Figures 11 and 15 will be described using the time chart of Figure 17. In the time chart of Figure 17, values ​​obtained for each calculation cycle Tc of the control process of Figure 11 are indicated by black dots. Note that the time chart of Figure 17 corresponds to the time chart of Figure 10 described above, and similarly to Figure 10, an example is shown in which periodic disturbances and non-periodic disturbances that affect the provisional maximum friction value μpmd occur.

[0093] At time tb1 in Fig. 17, in step S203 in Fig. 15, it is determined for the first time since the start of the control process in Fig. 11 and Fig. 15 that the provisional maximum friction value μpmd has been stored in all of the memory locations of the memory device 17. As a result, the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd are calculated, and the judgment range Rj is determined based on these. The average value μpmdav, standard deviation σpmd and judgment range Rj at time tb1 are maintained until just before the next update time point, time tb5, and are updated at time tb5.

[0094] Also, for example, at times tb2, tb3, and tb4 in the time chart of Fig. 17, it is determined in step S104 of Fig. 11 that the provisional maximum friction value μpmd is outside the determination range Rj. As a result, the provisional maximum friction value μpmd is not adopted as the estimated maximum friction value μp, and the previous value of the estimated maximum friction value μp is held as is.

[0095] The road surface friction estimating device 10 of this embodiment provides the following operational effects.

[0096] (1) According to this embodiment, the storage device 17 sequentially stores the provisional maximum friction value μpmd each time the provisional value calculation unit 14 calculates the provisional maximum friction value μpmd in step S101. The range determination unit 16 updates the average value μpmdav, standard deviation σpmd, and judgment range Rj of the provisional maximum friction value μpmd each time the provisional maximum friction value μpmd is stored in the storage device 17 a predetermined number of calculations Nc. The updated average value μpmdav, standard deviation σpmd, and judgment range Rj are calculated or determined based on the provisional maximum friction value μpmd stored in the storage device 17 at the time of the update. Furthermore, after updating the average value μpmdav, standard deviation σpmd, and judgment range Rj, the range determination unit 16 starts storing the provisional maximum friction value μpmd for the calculation number Nc again in the storage device 17.

[0097] In other words, each time the provisional maximum friction value μpmd is stored in the memory device 17 a predetermined number of calculations Nc, the range determination unit 16 determines the judgment range Rj based on the average value μpmdav and standard deviation σpmd obtained from the multiple provisional maximum friction values ​​μpmd stored in the memory device 17 for the above-mentioned calculation number Nc.

[0098] Therefore, the computational load can be reduced compared to when the judgment range Rj is updated each time the provisional maximum friction value μpmd is calculated, and the judgment range Rj can be updated appropriately so as not to carry over the influence of older provisional maximum friction value μpmd calculated in the past.

[0099] Except for the points described above, this embodiment is similar to the first embodiment. In this embodiment, the same effects as those of the first embodiment can be obtained from the configuration common to the first embodiment.

[0100] (Fourth embodiment) Next, a fourth embodiment will be described. In this embodiment, differences from the third embodiment will be mainly described.

[0101] In this embodiment, the flowchart of Fig. 11 of the third embodiment is replaced with a flowchart of Fig. 18. As in the third embodiment, the road surface friction estimating device 10 in this embodiment repeatedly executes the control process of Fig. 18 at a predetermined calculation period Tc while the vehicle is traveling, thereby sequentially calculating the estimated maximum friction value μp. In addition, in this embodiment, the flowchart of Fig. 15, which is the same as in the third embodiment, is adopted as the subroutine executed in step S111 of Fig. 18.

[0102] In the flowchart of Fig. 18 of this embodiment, step S106 in the flowchart of Fig. 11 of the third embodiment is replaced with step S136. Therefore, if it is determined in step S104 of Fig. 18 that the provisional maximum friction value μpmd is outside the determination range Rj, the process proceeds to step S136.

[0103] In step S136, the second estimation unit 22 determines a correction value, which is a value within the judgment range Rj, as the estimated maximum friction value μp. In this embodiment, the correction value is set to the average value μpmdav of the provisional maximum friction values ​​μpmd calculated in step S204 of FIG.

[0104] When step S136 ends, the flow chart of FIG. 18 ends and starts again from step S101.

[0105] Next, the control processes of Fig. 15 and Fig. 18 will be described using the time chart of Fig. 19. In the time chart of Fig. 19, values ​​obtained at each calculation period Tc of the control process of Fig. 18 are indicated by black dots. Note that the time chart of Fig. 19 corresponds to the time chart of Fig. 17 described above.

[0106] At time tc1 in FIG. 19, similarly to time tb1 in FIG. 17, the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd are calculated, and the judgment range Rj is determined based on them.

[0107] Furthermore, at times tc2, tc3, and tc4 in the time chart of Figure 19, it is determined in step S104 of Figure 18 that the provisional maximum friction value μpmd is outside the judgment range Rj, just as at times tb2, tb3, and tb4 in Figure 17.

[0108] As a result, the provisional maximum friction value μpmd is not adopted as the estimated maximum friction value μp at times tc2, tc3, and tc4 in the time chart of Fig. 19. This is similar to times tb2, tb3, and tb4 in Fig. 17. However, unlike times tb2, tb3, and tb4 in Fig. 17, the average value μpmdav of the provisional maximum friction values ​​μpmd is adopted as the estimated maximum friction value μp at times tc2, tc3, and tc4 in Fig. 19, respectively.

[0109] The road surface friction estimating device 10 of this embodiment provides the following operational effects.

[0110] (1) According to this embodiment, in step S136 in FIG. 18, the second estimator 22 determines the average value μpmdav of the provisional maximum friction values ​​μpmd calculated in step S204 in FIG. 15 as the estimated maximum friction value μp.

[0111] Here, for example, if the periodic disturbance is large, the fluctuation of the motor torque becomes large as shown in range B1 in Fig. 19, and as a result, the variation in the provisional maximum friction value μpmd also becomes large as shown by arrow B2 in Fig. 19. In such a case, for example, if a value within the judgment range Rj of the provisional maximum friction value μpmd but near the end of the judgment range Rj continues to be used as the estimated maximum friction value μp, the disturbance removal effect of removing the disturbance from the estimated maximum friction value μp will be weakened.

[0112] In contrast to this, in this embodiment, the average value μpmdav becomes the estimated maximum friction μp in step S136 as described above, so that a value near the end of the judgment range Rj is unlikely to continue as the estimated maximum friction μp. Therefore, compared to a case where the previous value of the estimated maximum friction μp is maintained as is, for example, it is possible to determine the estimated maximum friction μp while reducing the influence of a large variation in the provisional maximum friction μpmd. Note that, as an example of a case where the periodic disturbance becomes large, a case where the road surface 84 on which the vehicle 80 is traveling is a rough gravel road or a road covered with fresh snow, etc., is assumed.

[0113] Except for the points described above, this embodiment is similar to the third embodiment. In this embodiment, the same effects as those of the third embodiment can be obtained from the configuration common to the third embodiment.

[0114] It should be noted that although this embodiment is a modification based on the third embodiment, this embodiment can also be combined with the first or second embodiment described above.

[0115] Fifth embodiment Next, a fifth embodiment will be described. In this embodiment, differences from the second embodiment will be mainly described.

[0116] In this embodiment, the block diagram of FIG. 2 in the second embodiment is replaced with the block diagram of FIG. 20, the flowchart of FIG. 11 in the second embodiment is replaced with the flowchart of FIG. 21, and the flowchart of FIG. 12 in the second embodiment is replaced with the flowchart of FIG. 22.

[0117] In this embodiment, similarly to the second embodiment, the road surface friction estimating device 10 repeatedly executes the control process of FIG. 21 at a predetermined calculation period Tc while the vehicle is traveling, thereby sequentially calculating the estimated maximum friction value μp. In addition, in this embodiment, the subroutine executed in step S111 of FIG. 21 is the flowchart of FIG. 22. In addition, the configuration of the storage device 17 of this embodiment is similar to that of the storage device 17 of the second embodiment shown in FIG. 13.

[0118] In the flowchart of Fig. 22, step S206 is followed by step S247. The range determination unit 16 of Fig. 20 has a median calculation unit 161, and the median calculation unit 161 calculates memory data D 1 ~D N The median value μpmid of the plurality of temporary maximum friction values ​​μpmd stored in the storage device 17 is calculated. 1 ~D N In other words, these are the multiple provisional maximum friction values ​​μpmd on which the average value μpmdav calculated in step S204 is based.

[0119] When step S247 is completed, the subroutine of FIG. 22 ends and the process returns to the flowchart of FIG.

[0120] In the flowchart of Fig. 21 of this embodiment, step S106 in the flowchart of Fig. 11 of the second embodiment is replaced with step S146. Therefore, if it is determined in step S104 of Fig. 21 that the provisional maximum friction value μpmd is outside the determination range Rj, the process proceeds to step S146.

[0121] In step S146, the second estimator 22 determines the median value μpmid of the provisional maximum friction values ​​μpmd calculated in step S247 in Fig. 22 as the estimated maximum friction value μp. In other words, the estimated maximum friction value μp is set to the median value μpmid of the provisional maximum friction values ​​μpmd.

[0122] When step S146 is completed, the flow chart of FIG. 21 ends and starts again from step S101.

[0123] Next, the control process of Fig. 21 and Fig. 22 will be described with reference to the time chart of Fig. 23. This time chart of Fig. 23 corresponds to Fig. 19 of the fourth embodiment. In the time chart of Fig. 23, values ​​obtained at each calculation period Tc of the control process of Fig. 21 are indicated by black dots.

[0124] At time td1 in FIG. 23, similarly to time tc1 in FIG. 19, the average value μpmdav and standard deviation σpmd of the provisional maximum friction value μpmd are calculated, and the judgment range Rj is determined based on them.

[0125] 19. At time td2 in the time chart of FIG. 23, like time tc2 in FIG. 19, it is determined in step S104 of FIG. 21 that the provisional maximum friction value μpmd is outside the determination range Rj.

[0126] As a result, at time td2 in the time chart of Fig. 23, the provisional maximum friction value μpmd is not adopted as the estimated maximum friction value μp. This is similar to time tc2 in Fig. 19. However, unlike time tc2 in Fig. 19, at time td2 in Fig. 23, the median value μpmid of the provisional maximum friction values ​​μpmd is adopted as the estimated maximum friction value μp in step S146 in Fig. 21.

[0127] The road surface friction estimating device 10 of this embodiment provides the following operational effects.

[0128] (1) According to this embodiment, in step S146 in FIG. 21, the second estimator 22 determines the median value μpmid of the provisional maximum friction values ​​μpmd calculated in step S247 in FIG. 22 as the estimated maximum friction value μp.

[0129] Therefore, when the provisional maximum friction value μpmd varies non-periodically, the second estimator 22 determines the above-mentioned median value μpmid, in which the influence of the non-periodic variation of the provisional maximum friction value μpmd is weakened, as the estimated maximum friction value μp. Therefore, the estimated maximum friction value μp can be obtained while suppressing the influence of non-periodic disturbances.

[0130] Here, for example, immediately after a non-periodic disturbance is superimposed, such as the vehicle 80 experiencing a headwind while traveling at high speed, the motor torque may temporarily fluctuate significantly as shown in range B3 in Fig. 23, and the average value μpmdav may be strongly affected by the disturbance as shown by arrow B4. Also, if a value within the judgment range Rj of the provisional maximum friction value μpmd but near the end of the judgment range Rj continues to be used as the estimated maximum friction value μp, the disturbance removal effect of removing the disturbance from the estimated maximum friction value μp will be weakened.

[0131] Therefore, in this embodiment, as described above, in step S146 in Fig. 21, the estimated maximum friction μp is set to the median value μpmid of the provisional maximum friction μpmd. This makes it possible to reduce the temporary effect of a non-periodic disturbance on the estimated maximum friction μp immediately after the disturbance is superimposed, compared to when the estimated maximum friction μp is set to, for example, the previous value of the estimated maximum friction μp or the average value μpmdav of the provisional maximum friction μpmd. Note that the range B5 shown in Fig. 23 indicates the judgment range Rj of the provisional maximum friction μpmd obtained when there is no non-periodic disturbance, or after a while after the non-periodic disturbance has subsided.

[0132] Except for the points described above, this embodiment is similar to the second embodiment. In this embodiment, the same effects as those of the second embodiment can be obtained from the configuration common to the second embodiment.

[0133] It should be noted that although this embodiment is a modification based on the second embodiment, this embodiment can also be combined with the above-described first or third embodiment.

[0134] Sixth embodiment Next, a sixth embodiment will be described. In this embodiment, differences from the third embodiment will be mainly described.

[0135] In this embodiment, the judgment range Rj of the provisional maximum friction value μpmd is determined taking into account the change in the road surface 84 on which the vehicle 80 is traveling. Therefore, as shown in Fig. 24, the road surface friction estimation device 10 of this embodiment includes a road surface judgment unit 24 that judges whether or not a change in the road surface 84 has occurred.

[0136] For comparison with this embodiment, a road surface friction estimating device of a comparative example is assumed that does not include the road surface determining unit 24 of FIG. 24 and does not take into account changes in the road surface 84 on which the vehicle 80 is traveling.

[0137] For example, as shown in Fig. 25, if the road surface 84 changes at time tx while the vehicle 80 is traveling, the distribution of the provisional maximum friction value μpmd will be as shown in distribution map DSa in a first period PD1 before the time tx. Then, in a second period PD2 spanning the time tx, the distribution of the provisional maximum friction value μpmd will be as shown in distribution map DSb, and in a third period PD3 after the time tx, the distribution of the provisional maximum friction value μpmd will be as shown in distribution map DSc.

[0138] In the above comparative example, since the change in road surface 84 is not taken into consideration, even if a plurality of provisional maximum friction values ​​μpmd has a distribution with a plurality of occurrence frequency peaks as in the distribution map DSb of the second period PD2, the average value μpmdav and the standard deviation σpmd are calculated based on the plurality of provisional maximum friction values ​​μpmd. When this happens, an inappropriate judgment range Rj of the provisional maximum friction values ​​μpmd is temporarily set. That is, in the above comparative example, the calculation process for determining the judgment range Rj becomes temporarily erroneous.

[0139] In contrast to this, in this embodiment, as shown in Fig. 26, at time txa immediately after time tx when the road surface 84 changed, the road surface determination unit 24 determines that a change in the road surface 84 has occurred. In this embodiment, based on this determination, the average value μpmdav and the standard deviation σpmd are calculated based on one or more provisional maximum friction values ​​μpmd excluding the provisional maximum friction value μpmd obtained before the change in the road surface 84 occurred.

[0140] In the example of FIG. 26, the second period PD2 in FIG. 25 is a combination of the exclusion period PDn and the adoption period PDy. The exclusion period PDn includes the tx time, but the adoption period PDy does not include the tx time, and is a period that starts after the tx time. In this embodiment, the provisional maximum friction value μpmd of the exclusion period PDn in the second period PD2 is not used to calculate the average value μpmdav and the standard deviation σpmd, and the provisional maximum friction value μpmd of the adoption period PDy is used to calculate the average value μpmdav and the standard deviation σpmd. As a result, the distribution of the provisional maximum friction value μpmd of the second period PD2 used to calculate the average value μpmdav and the standard deviation σpmd becomes similar to that after the change of the road surface 84 as shown in the distribution diagram DSby, so that it is possible to avoid temporarily setting an inappropriate judgment range Rj.

[0141] In order to perform the above-mentioned processing, in this embodiment, the flowchart of Fig. 11 of the third embodiment is replaced with the flowchart of Fig. 27, and the flowchart of Fig. 15 of the third embodiment is replaced with the flowchart of Fig. 28. Note that, in this embodiment, as in the third embodiment, the road surface friction estimating device 10 repeatedly executes the control processing of Fig. 27 at a predetermined calculation period Tc while the vehicle is traveling, thereby sequentially calculating the estimated maximum friction value μp. Also, in this embodiment, the subroutine executed in step S111 of Fig. 27 is the flowchart of Fig. 28.

[0142] In the flowchart of Fig. 27 of this embodiment, steps S151 to S156 are provided between step S101 and step S111. Therefore, in the flowchart of Fig. 27, step S101 is followed by step S151.

[0143] In step S151 in Fig. 27, the road surface judgment unit 24 first calculates a time differential value dμc / dt of the calculated friction coefficient μc calculated in step S101 and a time differential value dSc / dt of the calculated slip ratio Sc, as shown in Fig. 29. Then, the road surface judgment unit 24 calculates a judgment parameter μdiff from the following formula F6. μdiff=dμc / dSc=(dμc / dt) / (dSc / dt) ···(F6)

[0144] When the road surface judgment unit 24 calculates the judgment parameter μdiff, the road surface judgment unit 24 stores the judgment parameter μdiff in a judgment storage device 241 included in the road surface judgment unit 24. This judgment storage device 241 basically has the same configuration as the storage device 17 in Fig. 13. In detail, the judgment storage device 241 differs from the storage device 17 in Fig. 13 in that the memory data stored in the judgment storage device 241 is the judgment parameter μdiff and that the number of storage locations for the memory data is NN, but otherwise has the same configuration as the storage device 17 in Fig. 13.

[0145] Therefore, a plurality of judgment parameters μdiff are stored in the judgment storage device 241 in chronological order. 1 , D 2 , ,D NN Each of D represents memory data that is a stored decision parameter μdiff. The subscripts of D, “1, 2, . . . , NN”, represent data addresses, and the smaller the subscript value, the newer the stored decision parameter μdiff is.

[0146] For example, memory data D 1 is updated to the latest one of the sequentially calculated decision parameters μdiff every time the decision parameter μdiff is calculated. NN is the memory data D 1 The determination parameter μdiff is updated every time it is calculated so that it becomes the determination parameter μdiff calculated a certain time before the calculation point of μdiff. After step S151 in FIG. 27, the process proceeds to step S152.

[0147] In step S152, the road surface determination unit 24 first calculates a determination parameter difference Δμdiff from the following formula F7 using the determination parameter μdiff stored in the determination storage device 241, as shown in FIG. Δμdiff=┃(μdiff[NN]-μdiff[1])┃ (F7)

[0148] Here, μdiff[1] in the above formula F7 is the judgment parameter μdiff stored in the first memory location of the judgment storage device 241, that is, the most recent judgment parameter μdiff stored in the judgment storage device 241. This μdiff[1] is the memory data D 1 In addition, μdiff[NN] in the above formula F7 is the judgment parameter μdiff stored in the NNth memory location of the judgment storage device 241, that is, the oldest judgment parameter μdiff stored in the judgment storage device 241. This μdiff[NN] is represented by the memory data D NN It is expressed as:

[0149] As shown in Fig. 27 and Fig. 29, when the judgment parameter difference Δμdiff is calculated in step S152, the road surface judgment unit 24 judges whether or not the judgment parameter difference Δμdiff is larger than a predetermined road surface change judgment value μdiffth. In this way, the road surface judgment unit 24 judges whether or not a change in the state of the road surface 84 has occurred in which the frictional state between the road surface 84 and the tire 81 changes beyond a predetermined limit, in other words, whether or not the road surface 84 on which the vehicle 80 is traveling has changed. That is, the road surface change judgment value μdiffth is set in accordance with the above-mentioned predetermined limit for the above-mentioned frictional state, and is experimentally set in advance so as to be able to determine the change in the road surface 84 during traveling.

[0150] In step S152, if it is determined that the determination parameter difference Δμdiff is greater than the road surface change determination value μdiffth, the process proceeds to step S154. On the other hand, if it is determined that the determination parameter difference Δμdiff is equal to or smaller than the road surface change determination value μdiffth, the process proceeds to step S153.

[0151] 27 is started, there is a period during which μdiff[NN] in the above formula F7 is not determined. Therefore, from the start of the control process in FIG. 27 until the determination parameter μdiff is stored in all memory locations of the determination storage device 241, no determination is made in step S152, and the process proceeds to step S153 immediately after step S152.

[0152] In step S153 in Fig. 27, the road surface determination unit 24 sets the flag variable Rmem to "Rmem = 0" as shown in Fig. 27 and Fig. 29. On the other hand, in step S154 in Fig. 27, the road surface determination unit 24 sets the flag variable Rmem to "Rmem = 1". After step S153 or step S154, the process proceeds to step S155.

[0153] In step S155 of Fig. 27, the road surface determination unit 24 determines whether the flag variable Rmem has switched from "Rmem = 0" to "Rmem = 1". The switch of the flag variable Rmem from "Rmem = 0" to "Rmem = 1" means that the frictional state between the road surface 84 and the tires 81 has changed beyond a predetermined limit, that is, the above-mentioned change in state of the road surface 84 has occurred. In other words, the case where the flag variable Rmem has switched from "Rmem = 0" to "Rmem = 1" is the case where the previous value of the flag variable Rmem was 0 and the current value of the flag variable Rmem is 1.

[0154] If it is determined in step S155 that the flag variable Rmem has switched from "Rmem=0" to "Rmem=1", the process proceeds to step S156. On the other hand, if it is determined that the flag variable Rmem has not switched from "Rmem=0" to "Rmem=1", the process proceeds to step S111. Note that a case in which the flag variable Rmem has not switched from "Rmem=0" to "Rmem=1" refers to a case in which the flag variable Rmem remains at "Rmem=0" or "Rmem=1", or a case in which the flag variable Rmem has switched from "Rmem=1" to "Rmem=0".

[0155] In step S156 in Fig. 27, the road surface judgment unit 24 first reads the number Nyt of vacant memory locations in which the provisional maximum friction value μpmd has not yet been stored among all memory locations in the memory device 17 in Fig. 6, that is, the remaining number of memory locations Nyt. Then, the road surface judgment unit 24 determines the number M of calculation targets from the following formula F8 based on the remaining number Nyt of memory locations. When compared with N, which is the total number of memory locations in the memory device 17, this number M of calculation targets is always "M≦N". M=Nyt-1 (F8)

[0156] The number of calculation targets M is a variable used in equation F9 (to be described later) for calculating the average value μpmdav of the provisional maximum friction values ​​μpmd, and equation F10 (to be described later) for calculating the standard deviation σpmd. The initial value of the number of calculation targets M is set to N, which is the total number of storage locations for memory data in the storage device 17. Therefore, unless step S156 is executed, the number of calculation targets M is maintained as "M=N". After step S156, the process proceeds to step S111.

[0157] In the flowchart of Fig. 28 of this embodiment, step S204 in the flowchart of Fig. 15 of the third embodiment is replaced with step S254, and step S205 in the flowchart of Fig. 15 is replaced with step S255. Also, in the flowchart of Fig. 28, step S257 is added to the flowchart of Fig. 15, and step S257 is provided as the next step after step S227.

[0158] In step S254, the average value calculation unit 18 calculates the average value μpmdav of the provisional maximum friction values ​​μpmd from the following formula F9, based on the multiple provisional maximum friction values ​​μpmd stored in the memory device 17. In the following step S255, the standard deviation calculation unit 19 calculates the standard deviation σpmd of the provisional maximum friction values ​​μpmd from the following formula F10, based on the multiple provisional maximum friction values ​​μpmd stored in the memory device 17 and the average value μpmdav calculated from the following formula F9. After step S255 in Figure 28, the process proceeds to step S206.

number

number

[0159] Here, the above formula F9 is obtained by replacing the constant N in the above formula F1 with the number of calculation objects M, and is otherwise the same as the above formula F1. Also, the above formula F10 is obtained by replacing the constant N in the above formula F2 with the number of calculation objects M, and is otherwise the same as the above formula F2. Note that if the number of calculation objects M is "M≦0", the above formulas F9 and F10 cannot be calculated, so that in steps S254 and S255, for example, the average value μpmdav and standard deviation σpmd are not updated and are maintained at the previous values.

[0160] Therefore, if the number of calculation objects M remains at the initial value N, in this embodiment as in the third embodiment, the average value μ pmdav and the standard deviation σ pmd are calculated based on the memory data D, which is all the provisional maximum friction values ​​μ pmd stored in the storage device 17, as shown in FIG. 1 ~D N In short, in this case, in step S254, the memory data D 1 ~D N The average value μpmdav of the memory data D is calculated from the above formula F9. 1 ~D N The standard deviation σpmd of is calculated from the above formula F10.

[0161] On the other hand, when the number of calculation targets M is set to "M < N" in step S156 of FIG. 27, the average value μpmdav and the standard deviation σpmd are calculated based on all the memory data D stored in the storage device 17 1 ~D N Among them, the memory data D on the newer side in time series 1 ~D M is calculated based on. And, for the calculation of the average value μpmdav and the standard deviation σpmd, the memory data D 1 ~D N Among them, the memory data D on the older side in time series M+1 ~D N is not used. In short, in this case, in step S254, the average value μpmdav of the memory data D 1 ~D M is calculated from the above formula F9, and in step S255, the standard deviation σpmd of the memory data D 1 ~D M is calculated from the above formula F10.

[0162] In step S257 following step S227 of FIG. 28, the road surface determination unit 24 sets the number of calculation targets M to "M = N". In short, the road surface determination unit 24 returns the number of calculation targets M to N, which is the initial value. When step S257 ends, the subroutine of FIG. 28 ends, and the process returns to the flowchart of FIG. 27.

[0163] Next, in order to explain the operation and effect of the present embodiment, the control process in the above comparative example in which the determination range Rj is determined without considering the switching of the traveling road surface 84 will be described using the time chart of FIG. 30. This comparative example is the same as the present embodiment except that it is determined whether or not the road surface 84 has switched without determining the determination range Rj. In the example of FIG. 30 and the example of FIG. 31 described later, N, which is the total number of storage locations in the storage device 17, is "N = 8".

[0164] As shown in FIG. 30, in the comparative example, the average value μpmdav of the provisional maximum friction value μpmd is calculated at the time te1 based on a plurality of provisional maximum friction values ​​μpmd calculated during the accumulation period PDx spanning the time tx, which is the time when the road surface 84 is changed, and accumulated in the storage device 17. That is, the average value μpmdav adopted from the time te1 is calculated based on the provisional maximum friction value μpmd obtained before the time tx and the provisional maximum friction value μpmd obtained after the time tx. Therefore, the deviation between the average value μpmdav and the maximum value μmx of the actual friction coefficient μ on the road surface 84 during travel becomes large due to the change in the road surface 84, and the deviation state continues until the average value μpmdav is updated next time. The transition of the maximum value μmx of the actual friction coefficient μ is indicated by the dashed line Lmx in FIG. 30.

[0165] Next, the control process in this embodiment, that is, the control process in Figs. 27 and 28, will be described with reference to the time chart in Fig. 31. As shown in Figs. 31 and 28, the judgment range Rj of the provisional maximum friction value μpmd in this embodiment is repeatedly determined based on the average value μpmdav and standard deviation σpmd obtained from a plurality of provisional maximum friction values ​​μpmd calculated within an accumulation period PDx as a predetermined period. This allows the judgment range Rj to be updated successively. This is the same in the above comparative example and the third embodiment described above. Note that the plurality of provisional maximum friction values ​​μpmd calculated within an accumulation period PDx is memory data D in Fig. 6. 1 ~D N and may be abbreviated to "multiple provisional values ​​within the period."

[0166] Unlike the comparative example, the road surface friction estimation device 10 of this embodiment includes a road surface determination unit 24 that determines whether or not a change in the state of the road surface 84 has occurred during travel. Therefore, in this embodiment, as shown in Fig. 31, at time tf1 immediately after time tx, which is the time point when the road surface 84 changes, the flag variable Rmem switches from "Rmem = 0" to "Rmem = 1", and as a result, it is determined in step S155 of Fig. 27 that a change in the state of the road surface 84 has occurred during travel.

[0167] As a result of this determination, in step S156 of Fig. 27, the number of calculation objects M is determined according to the above formula F8. Specifically, at time tf1 in Fig. 31, the remaining number of memory locations Nyt obtained in step S156 is "Nyt = 4", so from the above formula F8, the number of calculation objects M is determined as "M = 4 - 1 = 3". This calculation result of "M = 3" is maintained until the number of calculation objects M is subsequently set to "M = N" in step S257 of Fig. 28.

[0168] Therefore, the average value μpmdav of the provisional maximum friction values ​​μpmd calculated at time tf2 in Figure 31 is calculated in accordance with the above formula F9 in step S254 in Figure 28 with "M = 3" as described above. And the standard deviation σpmd of the provisional maximum friction values ​​μpmd calculated at time tf2 is calculated in accordance with the above formula F10 in step S255 in Figure 28 with "M = 3".

[0169] That is, the average value μpmdav and the standard deviation σpmd are the three provisional friction maximum values ​​μpmd on the new side in the time series stored in the storage device 17 of FIG. 6, which are the memory data D 1 ~D 3 The memory data D 1 ~D 3 In terms of FIG. 31, these correspond to the three provisional maximum friction values ​​μ pmd calculated during the adoption period PDy of the accumulation period PDx spanning the tx time point in FIG. 31. In addition, the average value μ pmdav and the standard deviation σ pmd at the time point tf2 are calculated using the memory data D 4 ~D 8 The memory data D is not used. 4 ~D 8 In terms of Fig. 31, these correspond to the five provisional maximum friction values ​​μpmd calculated in the excluded period PDn of the accumulation period PDx spanning the time tx in Fig. 31. The five provisional maximum friction values ​​μpmd in the excluded period PDn include the provisional maximum friction values ​​μpmd obtained before the time tx at which a change in the state of the road surface 84 occurs.

[0170] Then, at time tf2, the judgment range Rj of the provisional maximum friction value μpmd is determined based on the average value μpmdav and standard deviation σpmd obtained from the three provisional maximum friction values ​​μpmd calculated in the adoption period PDy.

[0171] In this way, when it is determined within a certain accumulation period PDx that a change in the condition of the road surface 84 has occurred, the mean value μpmdav and standard deviation σpmd are calculated based on the provisional maximum friction value μpmd within the adopted period PDy, which is obtained by excluding the five provisional maximum friction values ​​μpmd within the exclusion period PDn from the above-mentioned multiple provisional values ​​within a period. Then, based on the mean value μpmdav and standard deviation σpmd obtained from the provisional maximum friction values ​​μpmd within the adopted period PDy, a determination range Rj of the provisional maximum friction value μpmd is determined.

[0172] Therefore, in this embodiment, it is possible to suppress, more than in the above comparative example, the average value μpmdav of the provisional maximum friction value μpmd from deviating from the maximum value μmx of the actual friction coefficient μ indicated by the dashed dotted line Lmx in Fig. 31. That is, it is possible to suppress, more than in the above comparative example, the inappropriate judgment range Rj of the provisional maximum friction value μpmd from being temporarily set due to a change in the road surface 84. Note that, in the example of Fig. 31, the number of calculations of the provisional maximum friction value μpmd within the adoption period PDy is three, but depending on the size of the number of calculation targets M, it may be one.

[0173] Except for the points described above, this embodiment is similar to the third embodiment. In this embodiment, the same effects as those of the third embodiment can be obtained from the configuration common to the third embodiment.

[0174] It should be noted that although this embodiment is a modification based on the third embodiment, this embodiment can also be combined with any of the second, fourth, and fifth embodiments described above.

[0175] (Other embodiments) (1) In each of the above-described embodiments, the vehicle 80 on which the road surface friction estimation device 10 in Fig. 1 is mounted is, for example, an electric vehicle that does not have an engine and uses a traction motor as a driving force source, but this is just one example. The vehicle 80 may be a hybrid vehicle or an engine vehicle that does not have a traction motor.

[0176] (2) In each of the above-described embodiments, the road surface friction estimation device 10 calculates the estimated maximum friction value μp for each tire 81, which is a driving wheel, but this is just one example. For example, the road surface friction estimation device 10 may calculate the estimated maximum friction value μp for all of the multiple tires 81 together, or for a pair of left and right tires 81 together.

[0177] (3) In each of the above-described embodiments, the calculated slip ratio Sc is calculated based on the vehicle body speed, the driving wheel speed, the steering angle, the yaw rate of the vehicle 80, and the acceleration of the vehicle 80, as shown in FIG. 2, but this is only one example. The physical quantities on which the calculated slip ratio Sc is calculated are not limited to these, and may be selected as appropriate. The same is true for the physical quantities on which the calculated friction coefficient μc is calculated, and the physical quantities on which the calculated friction coefficient μc is calculated are not limited to those shown in FIG. 2, and may be selected as appropriate.

[0178] Furthermore, the method of calculating the provisional maximum friction value μpmd is not limited to the method disclosed in the above-mentioned first embodiment, and the provisional maximum friction value μpmd may be calculated without using the friction coefficient map MPm in Fig. 5. For example, a tire model formula may be set in advance by computer simulation, and the provisional maximum friction value μpmd may be calculated according to the tire model formula. Furthermore, the provisional maximum friction value μpmd may be calculated based on other parameters without using the slip ratio S or the friction coefficient μ in the calculation of the provisional maximum friction value μpmd.

[0179] (4) In each of the above-described embodiments, the judgment range Rj of the provisional maximum friction value μpmd is set to the range of "μpmdav±3 σpmd", as shown in Fig. 4, but this is just one example. For example, the judgment range Rj may be the range of "μpmdav±σpmd" or the range of "μpmdav±2 σpmd".

[0180] (5) In the sixth embodiment described above, the number of calculation objects M is calculated from the above formula F8 in step S156 in Fig. 27, but this is just an example. For example, the number of calculation objects M may be "M = Nyt".

[0181] (6) In the sixth embodiment described above, as shown in Fig. 27, the determination as to whether or not a change in the state of the road surface 84 has occurred is made using the difference in "dμc / dSc", but this is just one example. For example, the determination may be made based on an image captured by an in-vehicle camera capturing an image of the road surface 84, without using the difference in "dμc / dSc".

[0182] (7) In each of the above-described embodiments, as shown in FIG. 2, for example, the road surface friction estimation device 10 is described as an independent device. However, it may be a control unit included in an on-board electronic control device as a functional part of the electronic control device.

[0183] (8) The present disclosure is not limited to the above-described embodiment, and can be implemented in various modified forms. The above-described embodiments are not unrelated to each other, and can be appropriately combined, except in cases where the combination is clearly impossible.

[0184] In each of the above embodiments, the elements constituting the embodiment are not necessarily essential, unless otherwise specified as essential or considered to be obviously essential in principle. In each of the above embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when specified as essential or when they are obviously limited to a specific number in principle. In each of the above embodiments, when the materials, shapes, positional relationships, etc. of the components are mentioned, they are not limited to the materials, shapes, positional relationships, etc., except when specified as essential or when they are obviously limited to a specific material, shape, positional relationship, etc. in principle.

[0185] The control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Also, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions to be executed by a computer. The road friction estimation device 10 of each embodiment corresponds to the above control unit.

[0186] (In view of the present disclosure) The present disclosure described above can be understood from the following viewpoints, for example. [First viewpoint] A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) travels and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of the estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between the road surface and the tires and detected while the vehicle is traveling; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value (μpmdav) and standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; a second estimation unit (22) that determines the provisional maximum friction value as the estimated maximum friction value if the provisional maximum friction value is within the judgment range, and determines a modified value, which is a value within the judgment range, as the estimated maximum friction value if the provisional maximum friction value is outside the judgment range. [Second viewpoint] The second estimation unit repeatedly determines the estimated maximum friction value over time, The road surface friction estimating device according to a first aspect, wherein the correction value is a previous value of the estimated maximum friction value. [Third Perspective] The road surface friction estimating device according to a first aspect, wherein the correction value is the average value. [Fourth viewpoint] A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) travels and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of the estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between the road surface and the tires and detected while the vehicle is traveling; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value (μpmdav) and standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; a second estimation unit (22) that determines the provisional maximum friction value as the estimated maximum friction value if the provisional maximum friction value is within the judgment range, and determines the median (μpmid) of the multiple provisional maximum friction values ​​on which the average value is based as the estimated maximum friction value if the provisional maximum friction value is outside the judgment range. [Fifth viewpoint] the range determination unit determines the judgment range based on the average value and the standard deviation obtained from a plurality of the provisional maximum friction values ​​calculated within a predetermined period (PDx) each time the provisional maximum friction value is calculated; The road surface friction estimating device according to any one of first to fourth aspects, wherein the predetermined period of time is shifted toward the time elapsed side (Atp) every time the provisional maximum friction value is calculated. [Sixth viewpoint] The range determination unit is a data storage unit (17) that stores the provisional maximum friction value every time the first estimation unit calculates the provisional maximum friction value, The road surface friction estimation device according to any one of the first to fourth aspects, wherein the judgment range is determined based on the average value and the standard deviation obtained from the plurality of provisional maximum friction values ​​stored in the data storage unit each time the provisional maximum friction value is stored in the data storage unit a predetermined number of calculations (Nc). [Seventh viewpoint] a road surface determination unit (24) for determining whether or not a change in the state of the road surface has occurred in which the frictional condition between the road surface and the tire has changed beyond a predetermined limit; The range determination unit repeatedly determines the judgment range based on the average value and the standard deviation obtained from a plurality of provisional values ​​within a period, which are the provisional maximum friction values ​​calculated within a predetermined period (PDx) that shifts over time toward the time elapsed side (Atp); A road surface friction estimation device according to any one of the first to fourth aspects, wherein, when the road surface determination unit determines that a change in the road surface condition has occurred, the range determination unit determines the determination range based on the average value and the standard deviation obtained from one or more provisional maximum friction values ​​obtained by excluding the provisional maximum friction value obtained before the change in the road surface condition occurred from the multiple provisional values ​​within the period. [Eighth viewpoint] The road surface friction estimation device according to any one of the first to seventh aspects, wherein the first estimation unit calculates the friction coefficient and a slip ratio (S) of the tire based on the physical quantity, and calculates the provisional maximum friction value based on the friction coefficient and the slip ratio. [Explanation of symbols]

[0187] 11 First estimation part 16 Range determination section 22 Second estimation part 81 Tires 84 Road surface Rj Judgment range μp Estimated maximum friction μpmd Provisional maximum friction value μpmdav Mean value of provisional maximum friction σpmd Standard deviation of provisional maximum friction value

Claims

1. A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) runs and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of the estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between the road surface and the tires and detected during traveling of the vehicle; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value (μpmdav) and standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; a second estimation unit (22) that determines the provisional maximum friction value as the estimated maximum friction value if the provisional maximum friction value is within the judgment range, and determines a modified value that is a value within the judgment range as the estimated maximum friction value if the provisional maximum friction value is outside the judgment range.

2. The second estimation unit repeatedly determines the estimated maximum friction value over time, The road surface friction estimating device according to claim 1 , wherein the correction value is a previous value of the estimated maximum friction value.

3. The road friction estimating device according to claim 1 , wherein the correction value is the average value.

4. A road surface friction estimation device that estimates a maximum value (μmx) of a friction coefficient (μ) between a road surface (84) on which a vehicle (80) runs and a tire (81) of the vehicle, and obtains the estimated maximum value of the friction coefficient as an estimated maximum friction value (μp), a first estimation unit (11) that repeatedly calculates a provisional maximum friction value (μpmd), which is a provisional value of the estimated maximum friction value, based on physical quantities (Xa, Xb) related to friction between the road surface and the tires and detected during traveling of the vehicle; a range determination unit (16) that determines a judgment range (Rj) of the provisional maximum friction value including the average value (μpmdav) and standard deviation (σpmd) of the provisional maximum friction values ​​obtained from the plurality of provisional maximum friction values ​​calculated by the first estimation unit; a second estimating unit (22) that determines the provisional maximum friction value as the estimated maximum friction value when the provisional maximum friction value is within the judgment range, and determines the median (μpmid) of the multiple provisional maximum friction values ​​on which the average value is based as the estimated maximum friction value when the provisional maximum friction value is outside the judgment range.

5. the range determination unit determines the judgment range based on the average value and the standard deviation obtained from a plurality of the provisional maximum friction values ​​calculated within a predetermined period (PDx) each time the provisional maximum friction value is calculated; 5. The road surface friction estimating device according to claim 1, wherein the predetermined period is shifted toward the time elapsing side (Atp) every time the provisional maximum friction value is calculated.

6. The range determination unit is a data storage unit (17) that stores the provisional maximum friction value every time the first estimation unit calculates the provisional maximum friction value, 5. The road surface friction estimation device according to claim 1, wherein the judgment range is determined based on the average value and the standard deviation obtained from the plurality of provisional maximum friction values ​​stored in the data storage unit each time the provisional maximum friction value is stored in the data storage unit a predetermined number of calculations (Nc).

7. a road surface determination unit (24) for determining whether or not a change in the state of the road surface has occurred in which the frictional condition between the road surface and the tire has changed beyond a predetermined limit; the range determination unit repeatedly determines the judgment range based on the average value and the standard deviation obtained from a plurality of provisional values ​​within a period, which are the provisional maximum friction values, calculated within a predetermined period (PDx) that shifts over time toward the time lapse side (Atp); 5. A road surface friction estimation device as described in any one of claims 1 to 4, wherein, when the road surface determination unit determines that a change in the road surface condition has occurred, the range determination unit determines the determination range based on the average value and the standard deviation obtained from one or more provisional friction maximum values ​​obtained by excluding the provisional friction maximum value obtained before the change in the road surface condition occurred from the multiple provisional values ​​within the period.

8. 5. The road surface friction estimation device according to claim 1, wherein the first estimation unit calculates the friction coefficient and a slip ratio (S) of the tire based on the physical quantity, and calculates the provisional maximum friction value based on the friction coefficient and the slip ratio.

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