Road surface friction coefficient calculation device, vehicle, and road surface friction coefficient calculation method

Abstract

A road surface friction coefficient calculation device according to one aspect of the present disclosure is provided with a determination unit capable of determining a road surface state in front of a vehicle by performing a majority vote on a plurality of road surface states on the basis of n pieces of sensor data obtained by a sensor. The determination unit sets different road surface friction coefficients for the plurality of road surface states, respectively, and determines a road surface friction coefficient in front of the vehicle on the basis of the road surface friction coefficient corresponding to the road surface state determined by the majority vote.

Description

Road surface friction coefficient calculation device, vehicle, and road surface friction coefficient calculation method

[0001] The present disclosure relates to a road surface friction coefficient calculation device, a vehicle, and a road surface friction coefficient calculation method.

[0002] In order to further improve driving safety, it may be important to accurately determine in advance the road surface condition in the direction of travel of a vehicle. For example, the road surface friction coefficient may be used to determine the road surface condition. Techniques for estimating the road surface friction coefficient using a non-contact method are disclosed in, for example, Patent Documents 1 and 2.

[0003] JP 2006-046936 A JP 2010-164521 A

[0004] A road friction coefficient calculation device according to one aspect of the present disclosure includes a determination unit capable of determining a road surface condition ahead of a vehicle by conducting a majority vote for a plurality of road surface conditions based on n sensor data obtained by sensors. The determination unit sets different road surface friction coefficients for the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote.

[0005] A vehicle according to one aspect of the present disclosure includes a control unit that controls the operation of the vehicle. The control unit has a determination unit that determines a road surface condition ahead of the vehicle by conducting a majority vote for a plurality of road surface conditions based on n pieces of sensor data obtained by sensors. The determination unit sets different road surface friction coefficients for the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote.

[0006] A road surface friction coefficient calculation method according to one aspect of the present disclosure includes the following three steps: (A) setting different road surface friction coefficients for each of a plurality of road surface conditions; (B) performing a majority vote for the plurality of road surface conditions based on n pieces of sensor data obtained by sensors; and (C) determining the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote.

[0007] The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate one embodiment and, together with the description, serve to explain the principles of the disclosure.

[0008] Fig. 1 is a diagram illustrating an example of a schematic configuration of a vehicle equipped with a road surface friction coefficient calculation device according to an embodiment of the present disclosure. Fig. 2 is a diagram for explaining the data set of Fig. 1. Fig. 3 is a diagram for explaining an example of a calculation procedure for a road surface friction coefficient in the vehicle of Fig. 1. Fig. 4 is a diagram illustrating a modified example of the data set of Fig. 2. Fig. 5 is a diagram for explaining a modified example of the calculation procedure for a road surface friction coefficient in the vehicle of Fig. 1.

[0009] In estimating the road friction coefficient, errors may occur due to the influence of noise contained in the detection signal of the sensor. It is desirable to provide a road friction coefficient calculation device, a vehicle, and a road friction coefficient calculation method that are capable of estimating the road friction coefficient robust against external disturbances.

[0010] Some exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that the following description illustrates one specific example of the present disclosure and should not be construed as limiting the present disclosure. For example, each element, including numerical values, shapes, materials, parts, the position of each part, and the connection method of each part, is merely an example and should not be construed as limiting the present disclosure. Furthermore, in the following exemplary embodiments, components not described in independent claims based on the highest concept of the present disclosure are optional and may be provided as needed. The drawings are schematic and are not intended to be drawn to scale. Throughout this specification and the drawings, components having substantially the same function and configuration are designated by the same reference numerals, and redundant description will be omitted. Furthermore, components not directly related to one embodiment of the present disclosure are not shown in the drawings.

[0011] 1. Embodiment [Configuration Example] Fig. 1 shows a schematic configuration example of a vehicle 100 equipped with a road surface friction coefficient calculation device according to an embodiment of the present disclosure. As shown in Fig. 1, the vehicle 100 includes, for example, a sensor unit 10, a memory unit 20, a mode input unit 30, an inter-vehicle communication unit 40, a control unit 50, a drive unit 60, and a navigation system 70. The control unit 50 corresponds to a specific example of a "road surface friction coefficient calculation device" of the present disclosure.

[0012] The sensor unit 10 includes various sensors mounted on the vehicle 100. The sensor unit 10 includes, for example, a state quantity sensor and a light receiving sensor.

[0013] The state quantity sensors are capable of detecting vehicle state quantities, which are information indicating the state of the vehicle 100. The state quantity sensors are capable of detecting, as vehicle state quantities, for example, the speed of the vehicle 100 (vehicle speed), the lateral acceleration applied to the vehicle 100, and the yaw acceleration. The state quantity sensors are capable of outputting data on the detected vehicle state quantities (vehicle state quantity data) to the control unit 50. The speed of the vehicle 100 (vehicle speed) can be detected by a vehicle speed sensor. The lateral acceleration and yaw acceleration can be detected by an acceleration sensor.

[0014] The light-receiving sensor includes, for example, a light source unit (e.g., a light-emitting diode or a semiconductor laser) that emits near-infrared light containing three wavelengths, and a light-receiving unit (e.g., a photodiode) that receives the near-infrared light containing the three wavelengths. The light-receiving unit is capable of receiving the near-infrared light containing the three wavelengths that is reflected from the road surface in front of the vehicle when the near-infrared light containing the three wavelengths is emitted from the light-emitting diode or the semiconductor laser. The light-receiving sensor is capable of outputting data (light-receiving data) corresponding to the amount of reflected light detected by the light-receiving unit to the control unit 50.

[0015] Here, the near-infrared light containing three wavelengths consists of, for example, light of a first wavelength (e.g., 980 nm) that is relatively little affected by water, light of a second wavelength (1370 to 1450 nm) that is poorly absorbed by ice but easily absorbed by water (i.e., the effect of water is great and the effect of ice is small), and light of a third wavelength (1470 to 1550 nm) that is easily absorbed by ice but poorly absorbed by water (i.e., the effect of water is small and the effect of ice is large).

[0016] The light receiving sensor is a non-contact sensor that is capable of periodically acquiring n pieces of sensor data (light receiving data).

[0017] The memory unit 20 is configured with a known updatable recording medium, such as a solid state drive (SSD), a hard disk drive (HDD), a USB flash drive, a storage device, etc. The memory unit 20 stores a data set 21, for example, as shown in FIG.

[0018] The data set 21 is a data set in which a road surface friction coefficient and a threshold value are associated with each road surface condition, for example, as shown in Fig. 2. In the data set 21, the road surface conditions include, for example, four conditions (DRY, WET, SNOW, ICE) as shown in Fig. 2. The number and contents of the road surface conditions are not limited to those described above.

[0019] In the data set 21, the road friction coefficient has an upper limit value and a lower limit value for each road surface condition, for example, as shown in Fig. 2. In other words, a range of the road friction coefficient is set for each road surface condition, for example, as shown in Fig. 2. In the data set 21, each road friction coefficient (range of road friction coefficient) differs from one another for each road surface condition.

[0020] The data set 21 is further associated with a count value for each road surface condition. Each of the n pieces of sensor data input from the sensor unit 10 to the control unit 50 during a predetermined period is assigned to one of a plurality of road surface conditions defined in the data set 21. For example, a numerical range of the sensor data is set for each road surface condition, and each of the n pieces of sensor data is assigned to the road surface condition corresponding to the corresponding numerical range. The number of sensor data assigned to each road surface condition becomes the count value. The n pieces of sensor data are, for example, data obtained during a predetermined period from the light receiving sensor of the sensor unit 10, and are parameters resulting from the road surface friction coefficient.

[0021] In the data set 21, the threshold value is a value that is compared with the count value. If there is one road surface condition for which the count value is equal to or greater than the threshold value, that road surface condition is estimated to be the current road surface condition ahead of the vehicle 100. If there are two or more road surface conditions for which the count value is equal to or greater than the threshold value, the road surface condition determined in accordance with a predetermined decision rule is estimated to be the current road surface condition ahead of the vehicle 100. If there is no road surface condition for which the count value is equal to or greater than the threshold value, the road surface condition determined in accordance with the predetermined decision rule is estimated to be the current road surface condition ahead of the vehicle 100. The count value is reset at predetermined intervals. In the data set 21, the threshold value is set to a relatively smaller value as the corresponding road friction coefficient becomes relatively smaller.

[0022] The mode input unit 30 is an interface capable of accepting a driving mode setting from the user. Examples of driving modes include an urban driving mode, a highway driving mode, a sports driving mode, a rainy weather driving mode, and a snowy road driving mode. The mode input unit 30 is configured, for example, with a touch panel, a voice input device, or the like. The mode input unit 30 is capable of outputting data regarding the driving mode input by the user to the control unit 50, for example.

[0023] The vehicle-to-vehicle communication unit 40 is an interface capable of communicating with vehicles (hereinafter also referred to as "other vehicles") traveling around the vehicle 100. The vehicle-to-vehicle communication unit 40 of the host vehicle (vehicle 100) and the vehicle-to-vehicle communication unit 40 of the other vehicle (vehicle 100) are connected to a network 200. The network 20 may be an in-vehicle communication network conforming to any standard, such as a Controller Area Network (CAN), a Local Interconnect Network (LIN), a Local Area Network (LAN), or FlexRay (registered trademark). The vehicle-to-vehicle communication unit 40 includes, for example, a receiver capable of receiving sensor data acquired by a sensor unit (a device corresponding to the sensor unit 10) of the other vehicle, and a transmitter capable of transmitting the sensor data acquired by the sensor unit 10 to the other vehicle.

[0024] The control unit 50 includes, for example, a CPU (Central Processing Unit) and is capable of executing, for example, a program stored in the memory unit 20. The control unit 50 is capable of controlling the entire vehicle 100. The control unit 50 is capable of executing, for example, a series of procedures described in the program.

[0025] The control unit 50 includes, for example, a driving control unit 51 as shown in Fig. 1. The driving control unit 51 is capable of controlling the driving of the vehicle 100 (for example, the torque of the drive unit 60). The driving control unit 51 includes, for example, a torque control unit 54 as shown in Fig. 1.

[0026] The torque control unit 54 is capable of deriving a required torque according to an acceleration request. The acceleration request refers to the depression of the accelerator pedal or a variation in the amount of depression of the accelerator pedal. The acceleration request may be made by the driver during manual driving, or by the cruise control unit 51 during automated driving. The torque control unit 54 is capable of deriving the amount of torque (required torque) that the drive unit 60 should generate based on accelerator position data obtained from the accelerator position sensor.

[0027] The torque control unit 54 is capable of controlling the torque of the drive unit 60 based on the required torque. The drive unit 60 is configured to drive the steered wheels of the vehicle 100, and drives the steered wheels of the vehicle 100 in accordance with the required torque. The drive unit 60 is configured to include, for example, at least one of an engine and an electric motor. The drive unit 60 is capable of driving at least one of the engine and the electric motor in accordance with control from the control unit 50, for example.

[0028] The navigation system 70 is a known navigation system that sets a driving route to a destination input by the driver and notifies the driver of the driving route. The navigation system 70 has a GPS (Global Positioning System) sensor and map data, receives satellite signals from GPS satellites via the GPS sensor, and acquires position data of the vehicle 100 on the map data. The navigation system 70 has a display panel that displays the acquired position data superimposed on the map data. Instead of a GPS sensor, the navigation system 70 may have an antenna that receives satellite signals from other satellite systems that identify the position of the vehicle 100.

[0029] The control unit 50 includes, for example, a road surface condition determining section 52 and a road surface μ determining section 53 as shown in FIG.

[0030] The road surface condition determination unit 52 is capable of determining the road surface condition ahead of the vehicle by taking a majority vote for the plurality of road surface conditions in the data set 21 based on the n pieces of sensor data (e.g., light reception data) obtained by the sensor unit 10. The road surface condition determination unit 52 is capable of setting a range of road surface friction coefficients for each of the plurality of road surface conditions in the data set 21. The road surface condition determination unit 52 is capable of setting a road surface friction coefficient and a threshold value for each of the plurality of road surface conditions in the data set 21, setting the threshold value to a relatively smaller value as the road surface friction coefficient becomes relatively smaller, and taking a majority vote using the threshold value as a determination criterion.

[0031] When the count number for any of a plurality of road surface conditions is equal to or greater than a threshold as a result of majority vote, the road surface condition determination unit 52 can determine the road surface condition for which the count number is equal to or greater than the threshold as the road surface condition ahead of the vehicle. The road surface condition determination unit 52 can determine which of a plurality of road surface conditions the road surface condition ahead of the vehicle corresponds to based on sensor data (e.g., light reception data), and perform majority vote by incrementing the count number corresponding to the determined road surface condition.

[0032] The road surface condition determination unit 52 assigns each of the n pieces of sensor data (e.g., light reception data) input from the sensor unit 10 to the control unit 50 during a predetermined period to one of a plurality of road surface conditions defined in the data set 21. For example, the road surface condition determination unit 52 sets a numerical range of the sensor data (e.g., light reception data) for each road surface condition, and assigns each of the n pieces of sensor data to a road surface condition corresponding to the corresponding numerical range. The number of sensor data assigned to each road surface condition becomes the count value.

[0033] When the majority decision shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the road surface condition determination unit 52 may determine the road surface condition with the smallest road surface friction coefficient among the plurality of road surface conditions as the road surface condition ahead of the vehicle. When the majority decision shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the road surface condition determination unit 52 may not determine the road surface condition and may shift processing to the road surface μ determination unit 53. When the majority decision shows that the count number is equal to or greater than the threshold value for two or more road surface conditions among the plurality of road surface conditions, the road surface condition determination unit 52 may not determine the road surface condition and may shift processing to the road surface μ determination unit 53.

[0034] The road surface μ determination unit 53 is capable of determining the road surface friction coefficient ahead of the vehicle based on, for example, the road surface friction coefficient corresponding to the road surface conditions determined by majority vote. The road surface μ determination unit 53 may be configured to determine the road surface friction coefficient ahead of the vehicle based on, for example, a range of road surface friction coefficients corresponding to the road surface conditions determined by majority vote. The road surface μ determination unit 53 may be configured to set the median of the road surface friction coefficients corresponding to the road surface conditions determined by majority vote as the road surface friction coefficient ahead of the vehicle.

[0035] When the result of the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the road surface μ determination unit 53 may, for example, perform the following process. The road surface μ determination unit 53 may, for example, determine the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient (e.g., a range of road surface friction coefficients) corresponding to the road surface condition with the smallest road surface friction coefficient among the plurality of road surface conditions. The road surface μ determination unit 53 may, for example, weight the road surface friction coefficients (e.g., a range of road surface friction coefficients) of each road surface condition according to the count number, and determine the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficients (e.g., a range of road surface friction coefficients). The road surface μ determination unit 53 may, for example, weight the road surface friction coefficient (e.g., range of road surface friction coefficient) for each road surface condition according to the magnitude of the road surface friction coefficient (e.g., range of road surface friction coefficient) (DRY<WET<SNOW<ICE), and determine the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficient (e.g., range of road surface friction coefficient).

[0036] The road surface μ determination unit 53 may be configured to perform, for example, the following processing when, as a result of the majority vote, the count number is equal to or greater than a threshold value for two or more of the multiple road surface conditions. The road surface μ determination unit 53 may be configured to determine the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of two or more road surface conditions for which the count number is equal to or greater than the threshold value. The road surface μ determination unit 53 may be configured to weight the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of each road surface condition for which the count number is equal to or greater than the threshold value according to the count number, and determine the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficients (e.g., ranges of road surface friction coefficients). The road surface μ determination unit 53 may be configured to set the median of the medians of the ranges of road surface friction coefficients of each road surface condition for which the count number is equal to or greater than the threshold value as the road surface friction coefficient ahead of the vehicle.

[0037] [Calculation of Road Surface μ] Next, a procedure for calculating the road surface friction coefficient in the vehicle 100 according to an embodiment of the present disclosure will be described. Fig. 3 shows an example of a procedure for calculating the road surface friction coefficient in the vehicle 100.

[0038] The control unit 50 first determines whether the drive unit 60 has started (step S101). If it is determined that the drive unit 60 has started (step S101; Y), the control unit 50 starts sensing using the sensor unit 10 (step S102). The control unit 50 then determines whether the vehicle 100 has started traveling (step S103). If it is determined that the vehicle 100 has started traveling (step S103; Y), the control unit 50 periodically acquires various sensor data from the sensor unit 10 (step S104).

[0039] The control unit 50 determines which of a plurality of road surface conditions the road surface condition ahead of the vehicle corresponds to based on the sensor data (e.g., light reception data), and increments the count number corresponding to the determined road surface condition (step S105). The control unit 50 performs this process for all n pieces of sensor data (e.g., light reception data). When the control unit 50 has completed processing for the n pieces of sensor data (e.g., light reception data) (step S106; Y), it performs a majority vote using a threshold value and thereby determines the road surface condition (step S107).

[0040] When the count number for any of a plurality of road surface conditions is equal to or greater than a threshold as a result of majority voting, the control unit 50 determines that the road surface condition for which the count number is equal to or greater than the threshold is the road surface condition ahead of the vehicle. For example, let n = 10, the DRY threshold = 9, the WET threshold = 7, the SNOW threshold = 5, and the ICE threshold = 3. In this case, when the DRY count value = 9, the WET count value = 0, the SNOW count value = 1, and the ICE count value = 0, the control unit 50 determines the road surface condition as DRY. On the other hand, when the DRY count value = 0, the WET count value = 5, the SNOW count value = 1, and the ICE count value = 4, the control unit 50 determines the road surface condition as ICE.

[0041] Note that, when the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 may determine that the road surface condition with the smallest road surface friction coefficient among the plurality of road surface conditions is the road surface condition ahead of the vehicle. For example, let n = 10, the DRY threshold value = 9, the WET threshold value = 7, the SNOW threshold value = 5, and the ICE threshold value = 3. In this case, when the DRY count value = 0, the WET count value = 0, the SNOW count value = 5, and the ICE count value = 5, the control unit 50 determines that the road surface condition is ICE.

[0042] If the result of the majority vote shows that the count number is not equal to or greater than the threshold for any of the multiple road surface conditions, the control unit 50 may proceed to step S108 without immediately determining the road surface condition. For example, let n = 10, the DRY threshold = 9, the WET threshold = 7, the SNOW threshold = 5, and the ICE threshold = 3. In this case, if the DRY count value = 6, the WET count value = 3, the SNOW count value = 0, and the ICE count value = 0, the control unit 50 proceeds to step S108 without immediately determining the road surface condition.

[0043] If the result of the majority vote shows that the count numbers for two or more of the multiple road surface conditions are equal to or greater than the thresholds, the control unit 50 may proceed to step S108 without immediately determining the road surface condition. For example, let n = 10, the DRY threshold = 9, the WET threshold = 7, the SNOW threshold = 5, and the ICE threshold = 3. In this case, if the DRY count value = 0, the WET count value = 4, the SNOW count value = 6, and the ICE count value = 3, the control unit 50 proceeds to step S108 without immediately determining the road surface condition.

[0044] The control unit 50 reads the sensor data 21 from the memory unit 20 and determines the road friction coefficient (e.g., a range of road friction coefficients) corresponding to the road surface condition determined by majority vote, and determines the road friction coefficient ahead of the vehicle based on the read road friction coefficient (e.g., a range of road friction coefficients) (step S108). For example, when one road surface condition is determined as a result of majority vote, the control unit 50 determines the road friction coefficient ahead of the vehicle based on the road friction coefficient (e.g., a range of road friction coefficients) corresponding to that road surface condition. For example, when one road surface condition is determined as a result of majority vote, the control unit 50 may determine the median of the road friction coefficients corresponding to that road surface condition as the road friction coefficient ahead of the vehicle.

[0045] When the result of the majority vote indicates that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 may perform, for example, the following process. The control unit 50 may determine the road friction coefficient ahead of the vehicle based on, for example, the road friction coefficient (e.g., a range of road friction coefficients) corresponding to the road surface condition with the smallest road friction coefficient among the plurality of road surface conditions. The control unit 50 may, for example, weight the road friction coefficients (e.g., a range of road friction coefficients) of each road surface condition according to the count number, and determine the road friction coefficient ahead of the vehicle based on the weighted road friction coefficients (e.g., a range of road friction coefficients). The control unit 50 may, for example, weight the road friction coefficients (e.g., a range of road friction coefficients) of each road surface condition according to the magnitude of the road friction coefficient (e.g., a range of road friction coefficients) (DRY < WET < SNOW < ICE), and determine the road friction coefficient ahead of the vehicle based on the weighted road friction coefficients (e.g., a range of road friction coefficients).

[0046] When the majority vote results in the count number being equal to or greater than a threshold value for two or more of the multiple road surface conditions, the control unit 50 may perform, for example, the following process. The control unit 50 may, for example, determine the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of the two or more road surface conditions for which the count number is equal to or greater than the threshold value. The road surface μ determination unit 53 may, for example, weight the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of each road surface condition for which the count number is equal to or greater than the threshold value according to the count number, and determine the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficients (e.g., ranges of road surface friction coefficients). The control unit 50 may, for example, determine the road surface friction coefficient ahead of the vehicle to be the median of the medians of the ranges of road surface friction coefficients for each road surface condition for which the count number is equal to or greater than the threshold value.

[0047] The control unit 50 determines whether the vehicle 100 has stopped traveling (step S109). If it determines that the vehicle 100 has stopped traveling (step S109; Y), the control unit 50 ends sensing by the sensor unit 10 (step S110). In this manner, the road friction coefficient of the vehicle 100 is calculated.

[0048] [Effects] Next, effects of the vehicle 100 according to the embodiment of the present disclosure will be described.

[0049] In this embodiment, the road surface condition ahead of the vehicle is determined by majority voting for a plurality of road surface conditions based on n pieces of sensor data (e.g., light reception data) obtained by the sensor unit 10. Furthermore, different road surface friction coefficients are set for the plurality of road surface conditions, and the road surface friction coefficient ahead of the vehicle is determined based on the road surface friction coefficient corresponding to the road surface condition determined by majority voting. As a result, even if the sensor detection signal contains noise, it is possible to estimate the road surface friction coefficient more robust to external disturbances than when the road surface friction coefficient is estimated directly from the sensor data.

[0050] In this embodiment, a range of road friction coefficients is set for each of a plurality of road surface conditions, and the road friction coefficient ahead of the vehicle is determined based on the range of frontal friction coefficients corresponding to the road surface condition determined by majority vote. This makes it possible to estimate the road friction coefficient more robust to disturbances than when the road friction coefficient is estimated directly from sensor data, even when noise is included in the sensor detection signal.

[0051] In this embodiment, a road friction coefficient and a threshold are set for each of a plurality of road surface conditions, the threshold is set to a relatively smaller value as the road friction coefficient becomes relatively smaller, and a majority vote is performed using the threshold as a judgment criterion. This makes it possible to estimate the road friction coefficient more robust to disturbances than when the road friction coefficient is estimated directly from sensor data, even if the detection signal from the sensor contains noise.

[0052] In this embodiment, when the majority vote shows that the count is not equal to or greater than the threshold value for any of the road surface conditions, the road friction coefficient ahead of the vehicle is determined based on the road surface friction coefficient corresponding to the road surface condition with the smallest road surface friction coefficient among the road surface conditions, thereby making it possible to avoid vehicle control that induces slippage.

[0053] Furthermore, in this embodiment, when the result of the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the road friction coefficient for each road surface condition is weighted according to the count number, and the road friction coefficient ahead of the vehicle is determined based on the weighted road friction coefficients. As a result, even if the detection signal of the sensor contains noise, it is possible to estimate the road friction coefficient more robustly against disturbances than when the road friction coefficient is estimated directly from the sensor data.

[0054] Furthermore, in this embodiment, when the majority vote results in the count being equal to or greater than the threshold value for two or more of the multiple road surface conditions, the road friction coefficient ahead of the vehicle is determined based on the road friction coefficients for the two or more road surface conditions for which the count is equal to or greater than the threshold value. This makes it possible to estimate the road friction coefficient more robust to disturbances than when the road friction coefficient is estimated directly from the sensor data, even when noise is included in the sensor detection signal.

[0055] In this embodiment, the road surface condition ahead of the vehicle is determined based on the sensor data to be one of a plurality of road surface conditions, and a majority vote is performed by incrementing the count number corresponding to the determined road surface condition. This makes it possible to estimate the road surface friction coefficient more robust to disturbances than when the road surface friction coefficient is estimated directly from the sensor data, even when the sensor detection signal contains noise.

[0056] In this embodiment, the road friction coefficient corresponding to the road surface conditions determined by majority vote is read from the data set 21 in the memory unit 20, and the road friction coefficient ahead of the vehicle is determined based on the read road friction coefficient. As a result, even if the detection signal from the sensor contains noise, it is possible to estimate the road friction coefficient more robustly against disturbances than when the road friction coefficient is estimated directly from the sensor data.

[0057] In this embodiment, n pieces of sensor data are periodically acquired from the sensor unit 10 of the vehicle (vehicle 100). This allows the road friction coefficient to be estimated in real time. Furthermore, compared to when n pieces of sensor data are acquired from an external device, the road friction coefficient can be estimated without being affected by the communication environment.

[0058] 2. Modifications The present disclosure has been described above by giving embodiments, but the present disclosure is not limited to these embodiments and various modifications are possible.

[0059] [Variation A] In the data set 21 of the above embodiment, for example, as shown in FIG. 4A, only one value may be defined as the road friction coefficient for each road surface condition. Alternatively, in the data set 21 of the above embodiment, for example, as shown in FIG. 4B, two values ​​may be defined as the road friction coefficient for each road surface condition. Alternatively, in the data set 21 of the above embodiment, for example, as shown in FIG. 4C, a function with a predetermined physical quantity as a parameter (X) may be defined as the road friction coefficient for each road surface condition. The parameter (X) may be, for example, data obtained from the sensor unit 10 (e.g., water film thickness). Even in this case, as in the above embodiment, it is possible to estimate the road friction coefficient more robustly against external disturbances than when the road friction coefficient is estimated directly from sensor data.

[0060] [Variation B] In the above embodiment and variations thereof, the control unit 50 determines the road surface conditions ahead of the vehicle by performing a majority vote on multiple road surface conditions based on n pieces of sensor data (e.g., light reception data) obtained from the sensor unit 10 of the host vehicle (vehicle 100). However, in the above embodiment and Variation A, the control unit 50 may also acquire n pieces of sensor data (e.g., light reception data) obtained from the sensor unit 10 of another vehicle (vehicle 100) traveling ahead of the host vehicle (vehicle 100) via the vehicle-to-vehicle communication unit 40. In this case, the vehicle-to-vehicle communication unit 40 may have, for example, a receiver capable of periodically receiving n pieces of sensor data obtained by a sensor unit (a device corresponding to the sensor unit 10) of the other vehicle (vehicle 100) traveling ahead. In this case, the control unit 50 may calculate the road surface friction coefficient by, for example, executing the procedure shown in FIG. 5.

[0061] FIG. 5 shows an example of a procedure for calculating the road surface friction coefficient in the vehicle 100 according to this modified example.

[0062] The control unit 50 first determines whether the drive unit 60 has started (step S201). As a result, if it is determined that the drive unit 60 has started (step S201; Y), the control unit 50 starts sensing by the sensor unit 10 (step S202). The control unit 50 determines whether the host vehicle (vehicle 100) has started traveling (step S203). As a result, if it is determined that the host vehicle (vehicle 100) has started traveling (step S203; Y), the control unit 50 periodically acquires various sensor data from the sensor unit 10 (step S204).

[0063] The control unit 50 transmits the acquired various sensor data to the rear vehicle (vehicle 100) via the vehicle-to-vehicle communication unit 40 (step S205). The control unit 50 acquires n pieces of sensor data (e.g., light reception data) obtained from the sensor unit 10 of the other vehicle (vehicle 100) traveling in front of the host vehicle (vehicle 100) via the vehicle-to-vehicle communication unit 40 (step S206).

[0064] The control unit 50 determines which of a plurality of road surface conditions the road surface condition ahead of the vehicle corresponds to based on sensor data (e.g., light reception data) acquired from another vehicle (vehicle 100), and increments the count number corresponding to the determined road surface condition (step S207). The control unit 50 performs this process for all n pieces of sensor data (e.g., light reception data). When the control unit 50 has completed processing for the n pieces of sensor data (e.g., light reception data) (step S208; Y), it performs a majority vote using a threshold value and thereby determines the road surface condition (step S209).

[0065] When the majority vote results in the count number being equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 determines that the road surface condition for which the count number is equal to or greater than the threshold value is the road surface condition ahead of the vehicle. Note that when the majority vote results in the count number not being equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 may determine that the road surface condition with the smallest road surface friction coefficient among the plurality of road surface conditions is the road surface condition ahead of the vehicle.

[0066] If the result of the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 may proceed to step S210 without immediately determining the road surface condition. If the result of the majority vote shows that the count number is equal to or greater than the threshold value for two or more road surface conditions out of the plurality of road surface conditions, the control unit 50 may proceed to step S210 without immediately determining the road surface condition.

[0067] The control unit 50 reads the sensor data 21 from the memory unit 20 and determines the road friction coefficient (e.g., a range of road friction coefficients) corresponding to the road surface condition determined by majority vote, and determines the road friction coefficient ahead of the vehicle based on the read road friction coefficient (e.g., a range of road friction coefficients) (step S210). For example, when one road surface condition is determined as a result of majority vote, the control unit 50 determines the road friction coefficient ahead of the vehicle based on the road friction coefficient (e.g., a range of road friction coefficients) corresponding to that road surface condition. For example, when one road surface condition is determined as a result of majority vote, the control unit 50 may determine the median of the road friction coefficients corresponding to that road surface condition as the road friction coefficient ahead of the vehicle.

[0068] When the result of the majority vote indicates that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the control unit 50 may perform, for example, the following process. The control unit 50 may determine the road friction coefficient ahead of the vehicle based on, for example, the road friction coefficient (e.g., a range of road friction coefficients) corresponding to the road surface condition with the smallest road friction coefficient among the plurality of road surface conditions. The control unit 50 may, for example, weight the road friction coefficients (e.g., a range of road friction coefficients) of each road surface condition according to the count number, and determine the road friction coefficient ahead of the vehicle based on the weighted road friction coefficients (e.g., a range of road friction coefficients). The control unit 50 may, for example, weight the road friction coefficients (e.g., a range of road friction coefficients) of each road surface condition according to the magnitude of the road friction coefficient (e.g., a range of road friction coefficients) (DRY < WET < SNOW < ICE), and determine the road friction coefficient ahead of the vehicle based on the weighted road friction coefficients (e.g., a range of road friction coefficients).

[0069] When the majority vote results in the count number being equal to or greater than a threshold value for two or more of the multiple road surface conditions, the control unit 50 may perform, for example, the following process. The control unit 50 may, for example, determine the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of the two or more road surface conditions for which the count number is equal to or greater than the threshold value. The road surface μ determination unit 53 may, for example, weight the road surface friction coefficients (e.g., ranges of road surface friction coefficients) of each road surface condition for which the count number is equal to or greater than the threshold value according to the count number, and determine the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficients (e.g., ranges of road surface friction coefficients). The control unit 50 may, for example, determine the road surface friction coefficient ahead of the vehicle to be the median of the medians of the ranges of road surface friction coefficients for each road surface condition for which the count number is equal to or greater than the threshold value.

[0070] The control unit 50 determines whether the host vehicle (vehicle 100) has finished traveling (step S211). As a result, when it is determined that the host vehicle (vehicle 100) has finished traveling (step S211; Y), the control unit 50 ends sensing by the sensor unit 10 (step S212). In this way, the road surface friction coefficient of the vehicle 100 is calculated.

[0071] In this modification, n pieces of sensor data are periodically acquired from the sensor unit 10 of the forward vehicle (vehicle 100). As a result, even if the detection signal of the sensor contains noise, it is possible to estimate the road friction coefficient more robustly against disturbances than when the road friction coefficient is estimated directly from the sensor data.

[0072] [Variation C] In the above embodiment and its variations, the control unit 50 may be configured to change at least one of the multiple threshold values ​​set for multiple road surface conditions in accordance with the mode set in the mode input unit 30. In this case, for example, in a rainy weather driving mode or a snowy road driving mode, a threshold value can be set that suppresses slippage. Also, for example, in a sporty driving mode, it is possible to prevent the driver from feeling poor acceleration.

[0073] [Variation D] In the above embodiment and its variations, the control unit 50 may be configured to set the number of sensor data used for majority voting to a smaller number as the vehicle speed increases. When the vehicle speed is high, the traveling distance required to acquire n pieces of sensor data also becomes long. By setting the number of sensor data used for majority voting to a smaller number as the vehicle speed increases, the traveling distance required to acquire n pieces of sensor data can be made appropriate. As a result, even when the vehicle speed is high, it is possible to estimate the road friction coefficient in a manner that is robust against external disturbances.

[0074] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0075] The present disclosure may further take the following forms. (1) A road friction coefficient calculation device including a determination unit capable of determining a road surface condition ahead of a vehicle by conducting a majority vote for a plurality of road surface conditions based on n pieces of sensor data obtained by sensors, wherein the determination unit sets different road surface friction coefficients for each of the plurality of road surface conditions and determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. (2) The road friction coefficient calculation device described in (1), wherein the determination unit sets a range for the road surface friction coefficient for each of the plurality of road surface conditions and determines the road surface friction coefficient ahead of the vehicle based on the range of the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. (3) The road friction coefficient calculation device described in (1), wherein the determination unit sets a function for the road surface friction coefficient for each of the plurality of road surface conditions and determines the road surface friction coefficient ahead of the vehicle based on the function of the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. (4) The road surface friction coefficient calculation device described in (1), wherein the determination unit sets one or more values ​​as the road surface friction coefficient for each of the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. (5) The road surface friction coefficient calculation device described in any one of (1) to (4), wherein the determination unit sets the road surface friction coefficient and a threshold for each of the plurality of road surface conditions, sets the threshold to a relatively smaller value as the road surface friction coefficient becomes relatively smaller, and performs the majority vote using the threshold as a judgment criterion. (6) The road surface friction coefficient calculation device described in any one of (1) to (5), wherein the determination unit sets the number of sensor data used for the majority vote to a smaller number as the vehicle speed increases. (7) The road surface friction coefficient calculation device described in any one of (1) to (5), wherein the determination unit changes at least one value of the plurality of thresholds set for the plurality of road surface conditions according to a set mode.(8) The road surface friction coefficient calculation device described in any one of (1) to (5), wherein when the result of the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the determination unit determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition with the smallest road surface friction coefficient among the plurality of road surface conditions. (9) The road surface friction coefficient calculation device described in any one of (1) to (5), wherein when the result of the majority vote shows that the count number is not equal to or greater than the threshold value for any of the plurality of road surface conditions, the determination unit weights the road surface friction coefficients of each of the road surface conditions according to the count number, and determines the road surface friction coefficient ahead of the vehicle based on the weighted road surface friction coefficients. (10) The road surface friction coefficient calculation device according to any one of (1) to (5), wherein, when the count number is equal to or greater than the threshold value in two or more of the plurality of road surface conditions as a result of the majority vote, the determination unit determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficients of the two or more road surface conditions for which the count number is equal to or greater than the threshold value. (11) The road surface friction coefficient calculation device according to any one of (8) to (10), wherein the determination unit determines which of the plurality of road surface conditions the road surface condition ahead of the vehicle corresponds to based on the sensor data, and performs the majority vote by incrementing the count number corresponding to the determined road surface condition. (12) The road surface friction coefficient calculation device according to any one of (1) to (11), further comprising a memory in which a data set in which the road surface friction coefficient is associated with each of the road surface conditions is stored, wherein the determination unit reads out from the memory the road surface friction coefficient corresponding to the road surface condition determined by the majority vote, and determines the road surface friction coefficient ahead of the vehicle based on the read out road surface friction coefficient.(13) A vehicle comprising: a control unit that controls operation of the vehicle, the control unit having a determination unit that determines a road surface condition ahead of the vehicle by taking a majority vote for a plurality of road surface conditions based on n pieces of sensor data obtained by sensors, the determination unit setting different road surface friction coefficients for the plurality of road surface conditions, and determining the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. (14) The vehicle according to (13), further comprising: the sensor that periodically acquires the n pieces of sensor data, the sensor being a non-contact sensor. (15) The vehicle according to (13), further comprising: a communication unit that periodically acquires the n pieces of sensor data from a forward vehicle. (16) A road surface friction coefficient calculation method including: setting different road surface friction coefficients for each of a plurality of road surface conditions; taking a majority vote for the plurality of road surface conditions based on n pieces of sensor data obtained by sensors; and determining a road surface friction coefficient ahead of a vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote.

[0076] The control unit 50 shown in FIG. 1 can be implemented by circuitry including at least one semiconductor integrated circuit, such as at least one processor (e.g., a central processing unit (CPU)), at least one application-specific integrated circuit (ASIC), and / or at least one field-programmable gate array (FPGA). The at least one processor can be configured to perform all or a portion of the various functions of the control unit 50 shown in FIG. 1 by reading instructions from at least one non-transitory, tangible computer-readable medium. Such media can take various forms, including, but not limited to, various magnetic media such as hard disks, various optical media such as CDs or DVDs, and various semiconductor memories (i.e., semiconductor circuits) such as volatile or non-volatile memories. Volatile memories can include DRAM and SRAM. Non-volatile memories can include ROM and NVRAM. An ASIC is an integrated circuit (IC) specialized to perform all or a portion of the various functions of the control unit 50 shown in FIG. 1. An FPGA is an integrated circuit designed to be configurable after manufacture to perform all or part of the various functions of the control unit 50 shown in FIG.

Claims

1. A vehicle driving method comprising: a determining unit capable of determining road surface conditions ahead of a vehicle by taking a majority vote on multiple road surface conditions based on n pieces of sensor data periodically obtained by specific sensors during a predetermined period; The determination unit sets different road surface friction coefficients for the plurality of road surface conditions, and determines a road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. Road surface friction coefficient calculation device.

2. The determination unit sets a range for the road surface friction coefficient for each of the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the range of the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. The road surface friction coefficient calculation device according to claim 1 .

3. The determination unit sets a function as the road surface friction coefficient for each of the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the function of the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. The road surface friction coefficient calculation device according to claim 1 .

4. The determination unit sets one or more values ​​as the road surface friction coefficient for each of the plurality of road surface conditions, and determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. The road surface friction coefficient calculation device according to claim 1 .

5. The determination unit sets the road surface friction coefficient and a threshold value for each of the plurality of road surface conditions, sets the threshold value to a relatively smaller value as the road surface friction coefficient becomes relatively smaller, and performs the majority decision using the threshold value as a judgment criterion. The road surface friction coefficient calculation device according to claim 1 .

6. The determination unit sets the number of the sensor data used in the majority decision to a smaller number as the vehicle speed increases. The road surface friction coefficient calculation device according to claim 1 .

7. The determination unit changes at least one value of the plurality of threshold values ​​set for the plurality of road surface conditions in accordance with a set mode. The road surface friction coefficient calculation device according to claim 5.

8. When the count number is not equal to or greater than the threshold value in any of the plurality of road surface conditions as a result of the majority decision, the determination unit determines the road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition having the smallest road surface friction coefficient among the plurality of road surface conditions. The road surface friction coefficient calculation device according to claim 5.

9. When the count number is not equal to or greater than the threshold value in any of the plurality of road surface conditions as a result of the majority decision, the determination unit weights the road surface friction coefficients of each of the road surface conditions according to the count number, and determines a road surface friction coefficient ahead of the vehicle based on each of the weighted road surface friction coefficients. The road surface friction coefficient calculation device according to claim 5.

10. When the count number becomes equal to or greater than the threshold value in two or more of the road surface conditions among the plurality of road surface conditions as a result of the majority decision, the determination unit determines a road surface friction coefficient ahead of the vehicle based on the road surface friction coefficients of the two or more road surface conditions in which the count number becomes equal to or greater than the threshold value. The road surface friction coefficient calculation device according to claim 5.

11. The determination unit determines which of the plurality of road surface conditions a road surface condition ahead of the vehicle corresponds to based on the sensor data, and performs the majority decision by incrementing the count number corresponding to the determined road surface condition. The road surface friction coefficient calculation device according to any one of claims 8 to 10.

12. A memory storing a data set in which the road surface friction coefficient is associated with each of the road surface conditions, The determination unit reads out from the memory the road surface friction coefficient corresponding to the road surface condition determined by the majority vote, and determines the road surface friction coefficient ahead of the vehicle based on the read out road surface friction coefficient. The road surface friction coefficient calculation device according to claim 1 .

13. A control unit for controlling an operation of the vehicle is provided, the control unit has a determination unit that determines a road surface condition ahead of the vehicle by taking a majority vote for a plurality of road surface conditions based on n pieces of sensor data periodically obtained by a specific sensor during a predetermined period, The determination unit sets different road surface friction coefficients for the plurality of road surface conditions, and determines a road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote. vehicle.

14. The sensor further includes a sensor that periodically acquires the n pieces of sensor data. The sensor is a non-contact sensor.

14. A vehicle as claimed in claim 13.

15. The vehicle further includes a communication unit that periodically acquires the n pieces of sensor data from a forward vehicle.

14. A vehicle as claimed in claim 13.

16. Setting different road surface friction coefficients for each of a plurality of road surface conditions; performing majority voting for a plurality of road surface conditions based on n pieces of sensor data periodically obtained by specific sensors during a predetermined period; determining a road surface friction coefficient ahead of the vehicle based on the road surface friction coefficient corresponding to the road surface condition determined by the majority vote; Includes Method for calculating road surface friction coefficient.