Road surface friction coefficient estimation device

Abstract

To provide a road surface friction coefficient estimating device capable of estimating the maximum road surface friction coefficient between a wheel and a road surface regardless of whether the wheel is spinning.SOLUTION: A road surface friction coefficient estimating device 10 selects, as the maximum road surface friction coefficient μP, a model maximum road surface friction coefficient μP_md estimatingly calculated by a μP model estimating unit 13, when a friction state between a wheel and a road surface is in an adhesive state not reaching the maximum road surface friction coefficient μP. On the other hand, when the friction state between the wheel and the road surface is in a spinning state exceeding the maximum road surface friction coefficient μP, the road surface friction coefficient estimating device 10 selects, as the maximum road surface friction coefficient μP, a peak hold maximum road surface friction coefficient μP_ph estimatingly calculated by a peak hold estimating unit 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a road surface friction coefficient estimation device capable of estimating the maximum road surface friction coefficient between a wheel and a road surface.

Background Art

[0002] For example, Patent Document 1 discloses a vehicle ground contact surface friction state estimation device that uses the detection value ratio of the current tire force and the current slip ratio as a reference value ratio and refers to a tangential gradient correlation map to obtain the slope of the tangent corresponding to the reference value ratio as a grip characteristic parameter indicating the grip characteristics of the wheel. This obtained grip characteristic parameter indicates the grip characteristics of the tire, such as the margin with respect to the friction limit of the tire.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the vehicle ground contact surface friction state estimation device described in Patent Document 1 above, it is shown that the friction limit of the road surface can be estimated by estimating the friction limit of the tire grip force according to the magnitude of the obtained slope of the tangent of the engagement.

[0005] However, in the vehicle ground contact surface friction state estimation device of Patent Document 1 above, an effective tangent slope for estimating the friction limit of the road surface can be obtained only when the tire is not spinning.

[0006] The present disclosure has been made in view of the above points, and an object thereof is to provide a road surface friction coefficient estimation device capable of estimating the maximum road surface friction coefficient between a wheel and a road surface regardless of whether the wheel is spinning or not.

Means for Solving the Problems

[0007] In order to achieve the above object, the road surface friction coefficient estimation device (10) according to the present disclosure includes: Vehicle, a slip ratio calculation unit (11) that calculates a slip ratio of at least one wheel; a road surface friction coefficient calculation unit (12) that calculates a road surface friction coefficient between the wheel and a road surface based on a force acting in a rotational direction of the wheel and a ground load; a determination unit (17) that determines a slip state of the wheel based on a polarity of a change over time in the slip ratio calculated by the slip ratio calculation unit and a polarity of a change over time in the road surface friction coefficient calculated by the road surface friction coefficient calculation unit; a first calculation unit (13) that estimates and calculates a maximum road friction coefficient between the wheel and the road surface by using a first calculation method based on a slip ratio and a road friction coefficient; a second calculation unit (14) that estimates and calculates a maximum road friction coefficient between the wheels and the road surface using a second calculation method that is different from the first calculation method and is based on a road friction coefficient; a selection unit (18) that selects either the maximum road surface friction coefficient estimated and calculated by the first calculation unit or the maximum road surface friction coefficient estimated and calculated by the second calculation unit according to a result of the determination of the slip state of the wheel by the determination unit, The determination unit is Based on the polarity of the change in the slip ratio over time and the polarity of the change in the road surface friction coefficient over time, At least, the slippage of the wheels and the friction between the wheels and the road surface are determined by the road surface friction coefficient. Maximum of The adhesion is not yet reached or the road friction coefficient of Determine whether the maximum value has been exceeded and whether the wheel is in a spinning state. The selection unit is configured to select the maximum road friction coefficient to be estimated and calculated by the first calculation unit when the judgment unit judges that the vehicle is in a sticky state, and to select the maximum road friction coefficient to be estimated and calculated by the second calculation unit when the judgment unit judges that the vehicle is in a spinning state.

[0008] As described above, according to the road surface friction coefficient estimation device of the present disclosure, the maximum road surface friction coefficient estimated by the first calculation unit or the maximum road surface friction coefficient estimated by the second calculation unit is selected according to the slip state of the wheel determined based on the polarity of the change in the slip ratio and the polarity of the change in the road surface friction coefficient. Maximum of If the adhesion state does not reach the road surface friction coefficient, the maximum road surface friction coefficient estimated and calculated by the first calculation unit is selected, and the friction state between the wheel and the road surface is determined to be equal to or greater than the road surface friction coefficient Maximum of In this way, when the wheel slip rate exceeds the road friction coefficient, the maximum road friction coefficient estimated by the second calculation unit is selected. Maximum of Since the calculation method for the maximum road friction coefficient is switched depending on whether the slip ratio is less than the slip ratio corresponding to the maximum road friction coefficient, it is possible to appropriately estimate and calculate the maximum road friction coefficient of the road surface on which the vehicle is traveling, regardless of the magnitude of the wheel slip ratio, that is, regardless of whether the wheels are spinning or not.

[0009] The reference numbers in parentheses above are merely an example of a correspondence with a specific configuration in an embodiment described below, in order to facilitate understanding of the present disclosure, and are not intended to limit the scope of the present disclosure in any way.

[0010] In addition to the above-mentioned features, the technical features described in each claim of the claims will become clear from the following description of the embodiments and the accompanying drawings. [Brief description of the drawings]

[0011] [Figure 1] 1 is a configuration diagram showing an example of the configuration of a road surface friction coefficient estimating device according to a first embodiment. [Diagram 2] 1. FIG. 4 is an explanatory diagram for explaining a method in which the μP model estimating unit in FIG. 1 estimates and calculates a model maximum road surface friction coefficient μ_md. [Diagram 3]This is an explanatory diagram to explain four states classified as wheel slip states: a sticky state, a spinning state, a first transition state (high μ → low μ) in which a high μ road is switched to a low μ road, and a second transition state (low μ → high μ) in which a low μ road is switched to a high μ road. [Figure 4] 4 is a flowchart showing a process for estimating and calculating a maximum road surface friction coefficient μP executed in the road surface friction coefficient estimation device according to the first embodiment. [Diagram 5] 10 is a flowchart showing a part of a process for estimating and calculating a maximum road surface friction coefficient μP executed in the road surface friction coefficient estimation device according to the second embodiment. [Figure 6] 13 is a flowchart showing a part of a process for estimating and calculating a maximum road surface friction coefficient μP executed in the road surface friction coefficient estimation device according to the third embodiment. [Figure 7] FIG. 13 is an explanatory diagram for explaining a method for selecting one of the model maximum road surface friction coefficient μP_md and the peak hold maximum road surface friction coefficient μP_ph in the road surface friction coefficient estimation device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the road surface friction coefficient estimating device according to the present disclosure will be described in detail with reference to the drawings.

[0013] (First embodiment) FIG. 1 shows a configuration diagram illustrating an example of the configuration of a road surface friction coefficient estimation device 10 according to the first embodiment. In the example shown in FIG. 1, the road surface friction coefficient estimation device 10 is applied to a driving force control system that controls the driving force acting on the tires (wheels) of a vehicle 22. The driving force control system controls the maximum road surface friction coefficient μ P However, the road friction coefficient estimation device 10 is applied to a braking force control system that controls the braking force acting on each wheel, and the braking force control system controls the driving force based on the maximum road friction coefficient μ P The braking force acting on each wheel may be controlled based on the above.

[0014] As shown in FIG. 1, the driving force control system includes a driving force limiting unit 20, a driving force control unit 21, a vehicle 22 including a motor generator (MG), and a detection unit 23.

[0015] The driving force limiting unit 20 generates and outputs a driving force command value in response to the accelerator pedal operation of the driver of the vehicle 22. However, the driving force limiting unit 20 determines whether the driving force command value is greater than the maximum road friction coefficient μ estimated by the road friction coefficient estimation device 10. P If the driving force is greater than the maximum driving force set based on the above, a driving force command value limited to the maximum driving force is generated and output.

[0016] The driving force limiting unit 20 is configured to limit the maximum road friction coefficient μ P Based on this, the wheel slip ratio s is the maximum road friction coefficient μ P The maximum value of the driving force command value is set so as not to exceed the slip ratio corresponding to the maximum road friction coefficient μ P Even if the driver of the vehicle 22 depresses the accelerator pedal heavily while the vehicle 22 is traveling on a road surface with a relatively low friction coefficient, the driving force command value is limited to a set maximum value or less. In this way, the driving force control system controls the wheel slip rate to be equal to or less than the maximum road friction coefficient μ P Therefore, it is possible to suppress the slip ratio from exceeding the slip ratio corresponding to the vehicle 22, thereby supporting stable running of the vehicle 22.

[0017] The driving force control unit 21 outputs an MG drive signal to the motor generator of the vehicle 22 so that the motor generator generates an MG torque corresponding to the driving force command value output by the driving force limiting unit 20. In this embodiment, since the motor generator is used as the driving force source of the vehicle 22, the driving force control unit 21 outputs an MG drive signal to the motor generator. However, in addition to or instead of the motor generator, the vehicle 22 may be equipped with another driving force source such as an engine.

[0018] The detection unit 23 includes a sensor for detecting the MG torque generated by the motor generator of the vehicle 22, a sensor for detecting the speed of each wheel of the vehicle 22, a sensor for detecting the ground load of each wheel of the vehicle 22, etc. Detection signals by each sensor of the detection unit 23 are input to the road surface friction coefficient estimation device 10.

[0019] As shown in FIG. 1, the road surface friction coefficient estimation device 10 includes a slip ratio (s) calculation unit 11, a road surface friction coefficient (μ) estimated value calculation unit 12, and a maximum road surface friction coefficient (μ P ) model estimation unit 13 and peak hold estimation unit 14.

[0020] The s calculation unit 11 calculates the slip ratio s of at least one driving wheel based on the detection result of the speed of each wheel of the vehicle 22. For example, the s calculation unit 11 can calculate the slip ratio s of at least one driving wheel from the ratio of the wheel speed to the average of the speeds of the wheels. Alternatively, when the vehicle 22 includes driving wheels on which a driving force acts and driven wheels that simply roll, the wheel slip ratio s may be calculated from the ratio of the speed of the driving wheels to the speed of the driven wheels. Furthermore, a sensor that detects the ground speed of the vehicle 22 may be separately provided, and the slip ratio s may be calculated from the ratio of the wheel speed of at least one driving wheel to the detected ground speed of the vehicle 22.

[0021] The μ estimated value calculation unit 12 calculates the μ estimated value based on the MG torque detected by the detection unit 23, the wheel speed of the wheel for which the slip ratio has been calculated, and the ground contact load of the wheel. For example, when the motor generator is connected to the wheels via a drive train (propeller shaft, differential, etc.), the μ estimated value calculation unit 12 can calculate the road surface friction coefficient μ by the following Equation 1.

number

[0022] Furthermore, when the motor generator is an in-wheel motor, the μ estimated value calculation unit 12 can calculate the road surface friction coefficient μ by the following Equation 2.

number

[0023] Alternatively, the μ estimation value calculation unit 12 may calculate the μ estimation value by using the wheel radius r and the MG torque T M The road friction coefficient μ may be calculated simply by dividing the driving force determined by the ground load Fz.

[0024] μ P The model estimation unit 13 receives the wheel slip ratio s calculated by the s calculation unit 11 and the μ estimated value calculated by the μ estimated value calculation unit 12, and calculates the model maximum road friction coefficient μ using a predetermined tire model. P_md For example, μ P The model estimation unit 13 may include the configuration shown in Fig. 2. In the configuration shown in Fig. 2, the tire model 30 derives a model road surface friction coefficient μ from an input slip ratio s by using a model formula shown in Equation 3, for example. _md Calculate.

number

[0025] The model road friction coefficient μ _mdand the μ estimated value calculated by the μ estimated value calculation unit 12 is input to an adaptation mechanism 31. The adaptation mechanism 31 calculates the model road surface friction coefficient μ according to an optimization algorithm such as a least mean squares (LMS) algorithm or a recursive least squares (RLS) algorithm. _md The parameters of the first to third terms of the tire model shown in Equation 3 are adapted so that the difference Δμ between the estimated μ value and the tire speed Δμ is minimized.

[0026] In this manner, when each term of the parameters of the tire model shown in Equation 3 is adjusted, the model maximum road friction coefficient μ P_md More specifically, μ P The model estimation unit 13 calculates the model maximum road friction coefficient μ by using the first and second terms of the parameters in Equation 3, as shown in Equation 4 below. P_md can be calculated.

number

[0027] The peak hold estimation unit 14 receives the μ estimated value calculated by the μ estimated value calculation unit 12 and holds the μ maximum value in the time-dependent change of the input μ estimated value. The peak hold estimation unit 14 then calculates the held μ maximum value as the peak hold maximum road friction coefficient μ P_ph The output is as follows:

[0028] In this way, in the road surface friction coefficient estimation device 10 according to the present embodiment, two types of maximum road surface friction coefficients (model maximum road surface friction coefficient μ P_md and peak hold maximum road friction coefficient μ P_ph) is calculated. Either one of these two types of maximum road friction coefficient is selected as appropriate depending on the slip state of the wheels. The method of selecting the two types of maximum road friction coefficient is described below.

[0029] As shown in FIG. 3, in this embodiment, the slip state of the wheel is classified into four states: a sticking state in which the friction state between the wheel and the road surface has not reached the maximum road friction coefficient; a spinning state in which the friction state exceeds the maximum road friction coefficient; a first transition state (high μ→low μ) in which the wheel has transitioned from a high friction road surface to a low friction road surface; and a second transition state (low μ→high μ) in which the wheel has transitioned from a low friction road surface to a high friction road surface.

[0030] In the adhesion state, the wheel slip ratio s varies from zero to the maximum road friction coefficient μ P In this adhesive state, as shown in Figure 3, if the slip ratio s increases, the road friction coefficient μ also increases (section (1) of the "adhesive state" in Figure 3), and if the slip ratio s decreases, the road friction coefficient μ also decreases (section (2) of the "adhesive state" in Figure 3). In other words, in the adhesive state, the polarity of the change in the slip ratio s and the polarity of the change in the road friction coefficient μ match.

[0031] Therefore, conversely speaking, if the polarity of the change in slip ratio s over time and the polarity of the change in road surface friction coefficient μ over time match, the wheel slip state can be determined to be an adhesion state. P The model maximum road friction coefficient μ calculated by the model estimation unit 13 P_md The maximum road friction coefficient μ between the wheel and the road surface is P Therefore, when the slip state of the wheels is determined to be an adhesion state, the maximum road friction coefficient μ P Model maximum road friction coefficient μ P_md is selected.

[0032] In the spinning state, the slip ratio s of the wheel increases with time due to the maximum road friction coefficient μ P The slip ratio s of the wheel changes beyond the maximum road friction coefficient μP As shown in FIG. 3, in the range exceeding the slip ratio s corresponding to, when the slip ratio s increases, the road friction coefficient μ decreases slightly (section (2) of the "spinning state" in FIG. 3), and when the slip ratio s decreases, the road friction coefficient μ increases slightly (section (3) of the "adhesive state" in FIG. 3). In this embodiment, when the change in the road friction coefficient μ falls between a predetermined negative threshold value and a positive threshold value, the change in the road friction coefficient μ is considered to be zero. For this reason, in the "spinning state" column in FIG. 3, the change in the road friction coefficient μ in sections (2) and (3) is shown to be zero.

[0033] Therefore, if the polarity of the change in slip ratio s over time and the polarity of the change in road surface friction coefficient μ over time do not match, and the change in road surface friction coefficient μ over time relative to the change in slip ratio s over time is within a range that can be considered to be zero, it can be determined that the wheel is in a slipping state. In this slipping state, the peak hold maximum road surface friction coefficient μ output by the above-mentioned peak hold estimation unit 14 is P_ph The maximum road friction coefficient μ between the wheel and the road surface is P Therefore, when the slip state of the wheels is determined to be a spin state, the maximum road friction coefficient μ P Peak hold maximum road friction coefficient μ P_ph is selected.

[0034] In the first transition state (high μ → low μ) when moving from a high friction road surface (high μ road) to a low friction road surface (low μ road), as shown in Figure 3, the wheel slip state transitions from a change that follows the characteristic curve of slip ratio - road friction coefficient of a high μ road to a change that follows the characteristic curve of slip ratio - road friction coefficient of a low μ road. In this case, the wheel slip ratio s increases significantly, while the road friction coefficient μ decreases significantly (section (2) of "high μ → low μ" in Figure 3). After that, when the slip ratio s decreases significantly, the road friction coefficient μ increases slightly (section (3) of "high μ → low μ" in Figure 3).

[0035] Therefore, if the polarity of the change in slip ratio s over time and the change in road friction coefficient μ over time do not match, and the polarity of the change in slip ratio s over time is positive while the polarity of the change in road friction coefficient μ over time is negative, it can be determined that the wheel slip state is in the first transition state. In this first transition state, the data on the road friction coefficient μ obtained during the transition from the change in accordance with the characteristic curve of slip ratio-road friction coefficient of a high μ road to the change in accordance with the characteristic curve of slip ratio-road friction coefficient of a low μ road does not correspond to the road friction coefficient μ of the low μ road after the transition. For this reason, the data on the road friction coefficient μ and slip ratio s obtained during the transition from a high μ road to a low μ road (section (2) of "high μ → low μ" in Figure 3) corresponds to the maximum road friction coefficient μ P After the vehicle has moved onto the low μ road, the peak-hold maximum road friction coefficient μ output by the peak-hold estimation unit 14 is removed from the data for calculating the peak-hold maximum road friction coefficient μ P_ph The maximum road friction coefficient μ between the wheel and the road surface is P Therefore, when the slip state of the wheel is determined to be the first transition state, the maximum road friction coefficient μ P The data on the road surface friction coefficient μ and slip rate s during the transition from the high μ road to the low μ road are excluded, and the peak hold maximum road surface friction coefficient μ based on the road surface friction coefficient μ obtained after transitioning to the low μ road is calculated. P_ph is selected.

[0036] In the second transition state (low μ → high μ) when moving from a low μ road to a high μ road, as shown in Figure 3, the wheel slip state transitions from a change that follows the characteristic curve of slip ratio - road friction coefficient of a low μ road to a change that follows the characteristic curve of slip ratio - road friction coefficient of a high μ road. In this case, while the wheel slip ratio s decreases, the road friction coefficient μ increases slightly (section (2) of "low μ → high μ" in Figure 3). After that, as the slip ratio s decreases, the road friction coefficient μ also decreases (section (3) of "low μ → high μ" in Figure 3).

[0037] Therefore, if the polarity of the change in slip ratio s over time does not match the polarity of the change in road friction coefficient μ over time, and the polarity of the change in slip ratio s over time is negative while the polarity of the change in road friction coefficient μ over time is zero or greater, the wheel slip state can be determined to be the second transition state. In this second transition state, the data on the road friction coefficient μ and slip ratio s obtained during the transition from the change in accordance with the characteristic curve of slip ratio-road friction coefficient of a low μ road to the change in accordance with the characteristic curve of slip ratio-road friction coefficient of a high μ road do not correspond to the road friction coefficient μ of the high μ road after the transition. For this reason, the data on the road friction coefficient μ and slip ratio s obtained during the transition from a low μ road to a high μ road (section (2) of "low μ → high μ" in Figure 3) corresponds to the maximum road friction coefficient μ P After the road surface is changed to a high μ road, the above-mentioned μ is calculated in the same manner as in the case of the adhesion state. P The model maximum road friction coefficient μ output by the model estimation unit 13 P_md Therefore, when the slip state of the wheel is determined to be the second transition state, the maximum road friction coefficient μ P The data on the road surface friction coefficient μ and slip rate s during the transition from the low μ road to the high μ road are excluded, and the model maximum road surface friction coefficient μ P_md is selected.

[0038] In order to realize the above-mentioned two types of maximum road friction coefficient selection methods, the road friction coefficient estimation device (10) according to this embodiment includes a road friction coefficient (μ) time change polarity determination unit 15, a slip ratio (s) time change polarity determination unit 16, a slip state determination unit 17, and a selection unit 18, as shown in FIG. 1.

[0039] The μ time change polarity determination unit 15 determines the polarity of the time change of the μ estimated value calculated by the μ estimated value calculation unit 12. Specifically, if the magnitude of the time change of the μ estimated value is greater than a predetermined positive threshold, the μ time change polarity determination unit 15 determines that the polarity of the time change of the μ estimated value is positive. If the magnitude of the time change of the μ estimated value is equal to or less than a predetermined positive threshold and equal to or more than a predetermined negative threshold, the μ time change polarity determination unit 15 determines that the polarity of the time change of the μ estimated value is zero. Furthermore, if the magnitude of the time change of the μ estimated value is smaller than a predetermined negative threshold, the μ time change polarity determination unit 15 determines that the polarity of the time change of the μ estimated value is negative. The μ time change polarity determination unit 15 can obtain the time change of the μ estimated value from the time derivative of the μ estimated value (the magnitude of change per unit time).

[0040] The s time change polarity determination unit 16 determines the polarity of the change over time of the slip ratio s calculated by the s calculation unit 11. Specifically, if the magnitude of the change over time of the slip ratio s is greater than a predetermined positive threshold, the s time change polarity determination unit 16 determines that the polarity of the change over time of the slip ratio s is positive. If the magnitude of the change over time of the slip ratio s is equal to or less than a predetermined positive threshold and equal to or greater than a predetermined negative threshold, the s time change polarity determination unit 16 determines that the polarity of the change over time of the slip ratio s is zero. Furthermore, if the magnitude of the change over time of the slip ratio s is smaller than a predetermined negative threshold, the s time change polarity determination unit 16 determines that the polarity of the change over time of the slip ratio s is negative. However, the s time change polarity determination unit 16 may simply determine whether the polarity of the change over time of the slip ratio s is positive or negative. The s time change polarity determining unit 16 can determine the change in the slip ratio s over time from the time derivative of the slip ratio s.

[0041] The slip state determination unit 17 determines the slip state of the wheel based on the polarity of the time-dependent change in the μ estimated value determined by the μ time-dependent change polarity determination unit 15 and the polarity of the time-dependent change in the slip ratio s determined by the s time-dependent change polarity determination unit 16. Specifically, as described above, the slip state determination unit 17 determines whether the wheel is in a slip state when the friction state between the wheel and the road surface is greater than or equal to the maximum road surface friction coefficient μP Adhesion state not yet reached, maximum road friction coefficient μ P It is determined whether the state is a spinning state exceeding the threshold, a first transition state in which the vehicle has transitioned from a high μ road to a low μ road (high μ → low μ), or a second transition state in which the vehicle has transitioned from a low μ road to a high μ road (low μ → high μ).

[0042] Then, when the slip state determination unit 17 determines that the slip state of the wheels is an adhesive state, it outputs to the selection unit 18 the model maximum road friction coefficient μ P_md Furthermore, when the slip state determination unit 17 determines that the wheel slip state is a free-spin state, it instructs the selection unit 18 to select the peak hold maximum road surface friction coefficient μ P_ph Instruct the user to select

[0043] Furthermore, when the slip state determination unit 17 determines that the wheel slip state is the first transition state (high μ → low μ), it instructs the peak hold estimation unit 14 to exclude data related to the road surface friction coefficient μ obtained while transitioning from a high μ road to a low μ road (section (2) of "high μ → low μ" in FIG. 3), for example, to reset the peak value. Furthermore, the slip state determination unit 17 instructs the selection unit 18 to select the peak hold maximum road surface friction coefficient μ P_ph Instruct the user to select

[0044] On the other hand, when the slip state determination unit 17 determines that the wheel slip state is the second transition state (low μ → high μ), it instructs the peak hold estimation unit 14 to exclude data related to the road surface friction coefficient μ and the slip rate s obtained while the vehicle is transitioning from a low μ road to a high μ road (the section (2) of “low μ → high μ” in FIG. 3 ). P Alternatively, the slip state determination unit 17 determines whether the data on the road surface friction coefficient μ and the slip ratio s when the slip state of the wheel is determined to be the second transition state (low μ→high μ) is μ PIt is also possible to configure so that the model maximum road friction coefficient μ is not input to the model estimation unit 13. Furthermore, the slip state determination unit 17 instructs the peak hold estimation unit 14 to exclude data relating to the road friction coefficient μ obtained while switching from a high μ road to a low μ road (section (2) of "low μ → high μ" in FIG. 3), for example to reset the peak value. Furthermore, the slip state determination unit 17 instructs the selection unit 18 to exclude the model maximum road friction coefficient μ P_md Instruct the user to select

[0045] In this manner, the road surface friction coefficient estimation device 10 according to the present embodiment estimates the friction state between the wheel and the road surface based on the maximum road surface friction coefficient μ P When the adhesion state does not reach the maximum road friction coefficient μ P As, μ P The model maximum road surface friction coefficient μ estimated and calculated by the model estimation unit 13 P_md On the other hand, the road friction coefficient estimation device 10 selects the maximum road friction coefficient μ P When the slippage exceeds the maximum road friction coefficient μ P The peak hold maximum road friction coefficient μ P_ph In this way, the wheel slip ratio s is selected as the maximum road friction coefficient μ P Depending on whether the slip ratio is less than the maximum road friction coefficient μ P Since the calculation method is switched, the maximum road friction coefficient μ of the road surface on which the vehicle 22 is traveling can be calculated regardless of the magnitude of the wheel slip ratio. P It becomes possible to appropriately estimate and calculate the above.

[0046] Next, the maximum road friction coefficient μ P The process for estimating and calculating the following will be described with reference to the flowchart of Fig. 4. Note that the process shown in the flowchart of Fig. 4 is repeatedly executed at a predetermined interval, for example.

[0047] In step S100, a μ estimated value is calculated based on the MG torque, the wheel speed, and the wheel ground load. In step S110, a time derivative dμ / dt of the μ estimated value that changes over time is calculated. In step S120, the polarity of the time derivative dμ / dt of the μ estimated value is determined. In this polarity determination, if the time derivative dμ / dt of the μ estimated value is greater than a predetermined positive threshold, the polarity of the time derivative dμ / dt of the μ estimated value is determined to be positive in step S130. If the magnitude of the time derivative dμ / dt of the μ estimated value is equal to or less than a predetermined positive threshold and equal to or greater than a predetermined negative threshold, the polarity of the time derivative dμ / dt of the μ estimated value is determined to be zero in step S140. Furthermore, if the magnitude of the time derivative dμ / dt of the μ estimated value is smaller than a predetermined negative threshold, the polarity of the time derivative dμ / dt of the μ estimated value is determined to be negative in step S150.

[0048] In step S160, the slip ratio s of at least one driving wheel is calculated based on, for example, the detection results of the speeds of each wheel of the vehicle 22. In step S170, the time derivative ds / dt of the slip ratio s, which changes over time, is calculated. In step S180, the polarity of the time derivative ds / dt of the slip ratio s is determined. In this polarity determination, if the time derivative ds / dt of the slip ratio s is greater than a predetermined positive threshold, in step S190, the polarity of the time derivative ds / dt of the slip ratio s is determined to be positive. If the magnitude of the time derivative ds / dt of the slip ratio s is equal to or less than a predetermined positive threshold and equal to or greater than a predetermined negative threshold, in step S200, the polarity of the time derivative ds / dt of the slip ratio s is determined to be zero. Furthermore, if the magnitude of the time derivative ds / dt of the slip ratio s is smaller than a predetermined negative threshold, the polarity of the time derivative ds / dt of the slip ratio s is determined to be negative in step S210. As described above, the polarity of the time derivative ds / dt of the slip ratio s may simply be determined to be positive or negative.

[0049] In step S220, the slip state of the wheel is judged based on the polarity of the time derivative dμ / dt of the judged μ estimated value and the polarity of the time derivative ds / dt of the slip ratio s. Specifically, if the polarity of the time derivative dμ / dt of the μ estimated value matches the polarity of the time derivative ds / dt of the slip ratio s, in step S230, the slip state of the wheel is judged to be the maximum road friction coefficient μ P If the polarity of the time derivative dμ / dt of the μ estimated value is negative and the polarity of the time derivative ds / dt of the slip ratio s is positive, then in step S240, the wheel slip state is determined to be a first transition state (high μ → low μ) in which the wheel has transitioned from a high μ road to a low μ road. If the polarity of the time derivative dμ / dt of the μ estimated value is zero or greater and the polarity of the time derivative ds / dt of the slip ratio s is negative, then in step S250, the wheel slip state is determined to be a second transition state (low μ → high μ) in which the wheel has transitioned from a low μ road to a high μ road. Furthermore, if the polarity of the time derivative dμ / dt of the μ estimated value is zero and the polarity of the time derivative ds / dt of the slip ratio s is positive, then in step S260, the wheel slip state is determined to be a second transition state (low μ → high μ) in which the wheel has transitioned from a low μ road to a high μ road. P It is determined that the wheel is in a spin state exceeding the limit.

[0050] When determining that the wheel slip state is one of the first transition state, the second transition state, and the spin state, the judgment may be made taking into consideration not only the combination pattern of the polarity of the time derivative dμ / dt of the μ estimated value and the time derivative ds / dt of the slip rate in section (2) of each state in Figure 3, but also the combination pattern of the polarity of the time derivative dμ / dt of the μ estimated value and the time derivative ds / dt of the slip rate in section (3).

[0051] In step S270, it is determined whether the result of the wheel slippage is an adhesion state, a spinning state, a first transition state (high μ→low μ), or a second transition state (low μ→high μ). In this determination process, if the result of the wheel slippage is determined to be an adhesion state, in step 280, the maximum road friction coefficient μ PAs, μ P Model maximum road friction coefficient μ estimated by model P_md Then, in step S290, the peak value held in the peak hold estimation is reset. This allows at least the model maximum road friction coefficient μ P_md Peak hold maximum road friction coefficient μ P_ph You can reset the held peak value before switching the selection to

[0052] In step S270, the result of the determination of the wheel slip state is Idle If it is determined that the state is 300 In the above, the peak-hold maximum road friction coefficient μP_ph estimated by the peak-hold estimation is selected as the maximum road friction coefficient μP.

[0053] If it is determined in step S270 that the wheel slip state is the first transition state (high μ → low μ) or the second transition state (low μ → high μ), then in step 310 the μ estimated value and slip rate s obtained while transitioning from a high μ road to a low μ road or from a low μ road to a high μ road are discarded. Furthermore, in step S290, the peak value held in the peak hold estimation is reset. In this way, particularly when the road surface on which the vehicle 22 is traveling changes from a high μ road to a low μ road, the maximum value of the road surface friction coefficient μ can be determined based on the μ estimated value obtained on the low μ road, and an appropriate peak hold maximum road surface friction coefficient μ can be determined by the peak hold estimation. P_ph It is possible to determine the peak value by distinguishing between the first transition state and the second transition state and resetting the peak value only when the transition state is determined to be the first transition state.

[0054] In addition, when the vehicle 22 starts traveling on a low μ road or a high μ road after the first transfer state or the second transfer state, the maximum road friction coefficient μ P is estimated and calculated in step S300 or S280 described above.

[0055] Second embodiment Next, a second embodiment of the road surface friction coefficient estimation device 10 according to the present disclosure will be described with reference to the drawings. The road surface friction coefficient estimation device 10 according to the first embodiment described above determines the polarity of the change over time of the μ estimated value from the polarity of the time derivative of the μ estimated value, and determines the polarity of the change over time of the slip ratio s from the polarity of the time derivative of the slip ratio s.

[0056] In contrast, the road surface friction coefficient estimation device 10 according to the second embodiment obtains the polarity of the change over time of the μ estimated value from the polarity of the difference between the road surface friction coefficients μ of the front and rear wheels, and obtains the polarity of the change over time of the slip ratio s from the polarity of the difference between the slip ratios s of the front and rear wheels. However, since this embodiment is based on the premise that acceleration slip occurs in the front and rear wheels of the vehicle 22, this embodiment is applied to an all-wheel drive vehicle.

[0057] 5 is a flowchart showing the process in which the road friction coefficient estimation device 10 according to this embodiment calculates the polarity of the difference between the road friction coefficient μ and the slip rate s of the front and rear wheels, and judges the slip state of the wheels from the combination pattern of the polarities. Note that the process after the determination of the slip state of the wheels is the same as the process in the flowchart of FIG. 4, and is therefore not shown in the figure.

[0058] In step S105, the μ estimated values ​​of the front and rear wheels are calculated based on the MG torque, the wheel speed, and the wheel ground load. In step S115, the difference μ between the μ estimated values ​​of the front and rear wheels is calculated. dif In step S125, the difference μ of the μ estimate value is calculated. dif In this polarity determination, the difference μ of the μ estimate value is dif If is greater than the predetermined positive threshold, in step S135, the difference μ of the μ estimate dif The polarity of is determined to be positive. dif If the magnitude of is equal to or smaller than a predetermined positive threshold and equal to or larger than a predetermined negative threshold, in step S145, the difference μ of the μ estimate value is dif The polarity of is determined to be zero. Furthermore, the difference μ of the μ estimate difIf the magnitude of is smaller than a predetermined negative threshold, in step S155, the difference μ of the μ estimate value is dif The polarity of is determined to be negative.

[0059] In step S165, the slip ratios s of the front and rear wheels are calculated. In step S175, the difference s between the slip ratios s of the front and rear wheels is calculated. dif In step S185, the difference s of the slip ratio s is calculated. dif In this polarity determination, the difference s of the slip ratio s is dif is greater than the predetermined positive threshold, in step S195, the difference s of the slip ratio s is calculated. dif The polarity of is determined to be positive. The difference s of the slip ratio s dif If the magnitude of is equal to or smaller than a predetermined positive threshold and equal to or larger than a predetermined negative threshold, in step S205, the difference s of the slip ratio s is calculated. dif The polarity of is determined to be zero. Furthermore, the difference s of the slip ratio s dif If the magnitude of is smaller than the predetermined negative threshold, in step S215, the difference s of the slip ratio s is dif The polarity of is determined to be negative.

[0060] In step S225, the difference μ of the determined μ estimate value is calculated. dif The polarity of and the difference in slip ratio s dif The slip state of the wheels is determined based on the polarity of the estimated μ. dif The difference between the polarity of and the slip ratio s dif If the polarities of are both zero, that is, if there is no substantial difference between the μ estimated value and the slip ratio s of the front and rear wheels, in step S230, the slip state of the wheels is determined to be equal to or greater than the maximum road friction coefficient μ P It is judged as a state of adhesion that does not reach the above level.

[0061] In the determination process of step S225, the difference μ of the μ estimated value difIf the polarity of is negative, i.e., if the estimated μ value of the front wheels is smaller than the estimated μ value of the rear wheels, the slip state of the wheels is determined to be the first transition state (high μ → low μ) in which the wheels have transitioned from a high μ road to a low μ road in step S240. dif If the polarity of is positive, i.e., if the estimated μ value of the front wheels is greater than the estimated μ value of the rear wheels, in step S250, it is determined that the wheel slip state is a second transition state (low μ → high μ) in which the wheel has transitioned from a low μ road to a high μ road.

[0062] Furthermore, in the determination process of step S225, the difference μ of the μ estimated value dif The polarity of is zero and the difference in slip ratio s is s dif If the polarity of is positive, i.e., the estimated μ values ​​for the front and rear wheels are equivalent, but the slip ratio s of the front wheels is greater than the slip ratio s of the rear wheels, then in step S260, the wheel slip state is determined to be greater than the maximum road friction coefficient μ P This is because when the vehicle 22 accelerates, a spin state is likely to occur in the front wheels due to a so-called squat.

[0063] In this way, the polarity of the change over time in the road friction coefficient μ of the wheel and the polarity of the change over time in the slip ratio s can be obtained from the polarity of the difference between the μ estimated values ​​and the slip ratio s of the front and rear wheels. Furthermore, the slip state of the wheels can be appropriately determined from the polarity of the difference between the μ estimated values ​​and the slip ratio s of the front and rear wheels.

[0064] Third embodiment Next, a third embodiment of the road surface friction coefficient estimation device 10 according to the present disclosure will be described with reference to the drawings. The road surface friction coefficient estimation device 10 according to the first embodiment described above determines the slip state of the wheels based on the polarity of the time-dependent change in the μ estimated value and the polarity of the time-dependent change in the slip ratio s, and calculates the maximum road surface friction coefficient μ from the determined slip state of the wheels. P As the model maximum road friction coefficient μ P_md and peak hold maximum road friction coefficient μ P_ph The choice was between the two.

[0065] In contrast, the road surface friction coefficient estimation device 10 according to the present embodiment calculates the road surface friction coefficient by the following steps as shown in the flowchart of FIG. P Model maximum road friction coefficient μ estimated by model P_md and the peak-hold maximum road friction coefficient μ P_ph Which is the maximum road friction coefficient μ P It is determined by statistical processing which is more likely as the above. For this reason, the flowchart in Fig. 6 includes step S325 for performing statistical processing. Note that the flowchart in Fig. 6 shows only the processing related to the characteristic part of this embodiment, and other processing is omitted.

[0066] In the statistical processing of step S325, for example, μ P Model maximum road friction coefficient μ estimated by model P_md The magnitude of the fluctuation range of and the peak-hold maximum road friction coefficient μ P_ph Then, the maximum road friction coefficient μ P_md Fluctuation range and peak hold maximum road friction coefficient μ P_ph The maximum road friction coefficient μ P is the model maximum road friction coefficient μ with a smaller fluctuation range P_md , or peak hold maximum road friction coefficient μ P_ph For example, the maximum road friction coefficient μ P is the model maximum road friction coefficient μ with a smaller fluctuation range P_md , or peak hold maximum road friction coefficient μ P_ph It can be calculated as the most frequent value, average value, median, etc.

[0067] For example, FIG. 7(a) shows a plurality of model maximum road friction coefficients μ estimated based on the μ estimated value and the slip ratio s obtained when the wheel slip state is in an adhesive state. P_md The fluctuation range of the road friction coefficient μ P_phIn the case shown in Fig. 7(a), multiple model maximum road friction coefficients μ P_md The fluctuation range of multiple peak hold maximum road friction coefficient μ P_ph Since the fluctuation range is smaller than the maximum road friction coefficient μ P is the maximum road friction coefficient μ P_md is determined based on:

[0068] On the other hand, FIG. 7(b) shows multiple model maximum road friction coefficients μ estimated based on the μ estimated value and the slip ratio s obtained when the wheel slip state is in a freewheeling state. P_md The fluctuation range of the road friction coefficient μ P_ph In the case shown in Fig. 7(b), multiple model maximum road friction coefficients μ P_md The fluctuation range of multiple peak hold maximum road friction coefficient μ P_ph Since the fluctuation range of the maximum road friction coefficient μ P is the peak hold maximum road friction coefficient μ P_ph is determined based on:

[0069] Although several preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms without departing from the spirit and scope of the present disclosure.

[0070] For example, the statistical processing in the third embodiment described above is the same as that in the first or second embodiment, except that the maximum road friction coefficient μ P For example, the maximum road friction coefficient μ selected based on the wheel slip state may be combined with the selection method of P When the fluctuation range of the estimation calculation result of the first estimation calculation is clearly larger than the fluctuation range of the other estimation calculation result, the estimation calculation result by the statistical processing may be given priority in selection. [Explanation of symbols]

[0071] 10: Road surface friction coefficient estimation device, 11: Slip ratio calculation unit, 12: Road surface friction coefficient estimated value calculation unit, 13: Maximum road surface friction coefficient model estimation unit, 14: Peak hold estimation unit, 15: Road surface friction coefficient time change polarity determination unit, 16: Slip ratio time change polarity determination unit, 17: Slip state determination unit, 18: Selection unit, 20: Driving force limiting unit, 21: Driving force control unit, 22: Vehicle, 23: Detection unit, 30: Tire model, 31: Adaptation mechanism

Claims

1. A slip ratio calculation unit (11) that calculates a slip ratio of at least one wheel of a vehicle; a road surface friction coefficient calculation unit (12) that calculates a road surface friction coefficient between the wheel and a road surface based on a force acting in a rotational direction of the wheel and a ground load; a determination unit (17) that determines a slip state of the wheel based on a polarity of the change over time of the slip ratio calculated by the slip ratio calculation unit and a polarity of the change over time of the road surface friction coefficient calculated by the road surface friction coefficient calculation unit; a first calculation unit (13) that estimates and calculates a maximum road friction coefficient between the wheel and a road surface using a first calculation method based on the slip ratio and the road friction coefficient; a second calculation unit (14) that estimates and calculates a maximum road friction coefficient between the wheel and a road surface using a second calculation method that is different from the first calculation method and is based on the road friction coefficient; a selection unit (18) that selects either the maximum road surface friction coefficient estimated and calculated by the first calculation unit or the maximum road surface friction coefficient estimated and calculated by the second calculation unit according to a result of the determination of the slip state of the wheel by the determination unit, the determination unit determines, based on the polarity of the change in the slip ratio over time and the polarity of the change in the road surface friction coefficient over time, at least whether the slip state of the wheel is an adhesion state in which the friction state between the wheel and the road surface has not reached a maximum value of the road surface friction coefficient, or a spin state in which the friction state has exceeded the maximum value of the road surface friction coefficient; The road surface friction coefficient estimation device, wherein the selection unit selects the maximum road surface friction coefficient to be estimated and calculated by the first calculation unit when the determination unit determines that a sticking state is present, and selects the maximum road surface friction coefficient to be estimated and calculated by the second calculation unit when the determination unit determines that a spinning state is present.

2. 2. The road surface friction coefficient estimation device according to claim 1, wherein the determination unit calculates a time derivative of the slip ratio and the road surface friction coefficient of at least one of the wheels, and determines a polarity of a change in the slip ratio over time and a polarity of a change in the road surface friction coefficient over time from a polarity of each of the calculated time derivatives.

3. The slip ratio calculation unit calculates slip ratios of front wheels and rear wheels of the vehicle as the wheels, the road surface friction coefficient calculation unit calculates road surface friction coefficients of front wheels and rear wheels of the vehicle, 2. The road surface friction coefficient estimation device according to claim 1, wherein the determination unit calculates differences between the slip ratio and the road surface friction coefficient of the front and rear wheels of the vehicle, and determines a polarity of a change in the slip ratio over time and a polarity of a change in the road surface friction coefficient over time from polarities of the calculated differences.

4. the determination unit determines whether the friction state between the wheel and the road surface is in an adhesive state in which the maximum value of the road surface friction coefficient has not been reached, a spinning state in which the maximum value of the road surface friction coefficient has been exceeded, a first transition state in which the vehicle has transitioned from a high friction road surface to a low friction road surface, or a second transition state in which the vehicle has transitioned from a low friction road surface to a high friction road surface, based on the polarity of the change over time in the slip ratio calculated by the slip ratio calculation unit and the polarity of the change over time in the road surface friction coefficient calculated by the road surface friction coefficient calculation unit; 4. The road surface friction coefficient estimation device according to claim 1, wherein when the determination unit determines that the vehicle is in the first transition state or the second transition state, the first calculation unit and the second calculation unit estimate and calculate a maximum road surface friction coefficient by excluding the slip ratio and the road surface friction coefficient calculated when the vehicle transfers between road surfaces having different friction coefficients.

5. the first calculation unit estimates and calculates a maximum road surface friction coefficient by using a tire model equation that defines a relationship between the slip ratio and the road surface friction coefficient, 5. The road surface friction coefficient estimation device according to claim 1, wherein the second calculation unit estimates and calculates a maximum road surface friction coefficient from a peak value of the road surface friction coefficient calculated by the road surface friction coefficient calculation unit.

6. 6. The road surface friction coefficient estimation device according to claim 5, wherein the peak value of the road surface friction coefficient is reset at least before the selection unit switches the selection from the maximum road surface friction coefficient estimated and calculated by the first calculation unit to the maximum road surface friction coefficient estimated and calculated by the second calculation unit.

7. The first calculation unit is capable of calculating the road surface friction coefficient corresponding to the slip ratio by using the tire model equation, 6. The road surface friction coefficient estimation device according to claim 5, wherein the first calculation unit has: an adaptation mechanism (31) that adjusts parameters of the tire model equation so that an error between a road surface friction coefficient calculated by the road surface friction coefficient calculation unit and a road surface friction coefficient determined from the slip ratio using the tire model equation is minimized; and a maximum road surface friction coefficient calculation unit that calculates the maximum road surface friction coefficient from the parameters adjusted by the adaptation mechanism.

8. The vehicle further comprises a statistical processing unit (S325) for performing statistical processing on a plurality of maximum road friction coefficients estimated by the first calculation unit and a plurality of maximum road friction coefficients estimated by the second calculation unit to determine a more probable maximum road friction coefficient; The road surface friction coefficient estimating device according to claim 1 , wherein the determination by the statistical processing unit takes precedence over the selection by the selection unit.

9. 9. The road surface friction coefficient estimation device according to claim 8, wherein the statistical processing unit selects a plurality of maximum road surface friction coefficients having a smaller fluctuation range based on the magnitude of the fluctuation range of the plurality of maximum road surface friction coefficients estimated and calculated by the first calculation unit and the second calculation unit, respectively, and determines a more likely maximum road surface friction coefficient from the selected plurality of maximum road surface friction coefficients.

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