Apparatus and method for estimating road friction coefficient

Abstract

A device and method for estimating a road friction coefficient, and more particularly to a device for estimating a road friction coefficient, the device including: an additional power control module that, when it is determined that a driving state of a vehicle is an inertia driving state, arbitrarily adds a braking force that causes a wheel speed difference to a braking force application axis of the vehicle, and adds a driving force that cancels the braking force to a driving force application axis of the vehicle; and a road friction coefficient estimation module that estimates a road friction coefficient from the wheel speed difference caused by the newly added braking force.

Claims

1. An apparatus for estimating the coefficient of friction of a road surface, comprising: The driving state determination module is configured to determine the driving state of the vehicle by collecting information for understanding the driving state of the vehicle, and to determine whether to estimate the road friction coefficient based on the determination result of the driving state of the vehicle. An additional power control module is configured to, when the driving state determination module determines that the driving state of the vehicle is an inertial driving state, arbitrarily add the braking force that causes the wheel speed difference to the braking force application shaft of the vehicle, and also add the driving force that counteracts the braking force to the driving force application shaft of the vehicle. as well as The road surface friction coefficient estimation module is configured to estimate the state of the road surface friction coefficient by means of the wheel speed difference caused by arbitrarily added braking force; The road surface friction coefficient estimation module includes a wheel speed difference calculation device, which is configured as follows: The wheel speeds of the vehicle are obtained from the wheels coupled to the braking force application axle and the wheels coupled to the driving force application axle, and Determine the magnitude of the wheel speed difference between the wheel speeds; The road surface friction coefficient estimation module further includes a wheel speed difference correction device, which is configured as follows: Based on the magnitude of the target driving torque acting on the driving force application shaft, the wheel speed difference determined by the wheel speed difference calculation device is multiplied by a predetermined correction coefficient to determine the corrected wheel speed difference index value.

2. The apparatus according to claim 1, wherein, The driving state determination module includes a signal processing device, which is configured to: At least one of the longitudinal acceleration and wheel speed of the vehicle is obtained to estimate the speed of the moving vehicle. Obtain at least one of the vehicle's lateral acceleration, steering angle, steering angular velocity, and yaw rate to determine whether the vehicle is driving in a straight line; as well as The value of the motor torque is obtained to determine the static driving state of the vehicle.

3. The apparatus according to claim 2, wherein, The driving status determination module also includes: A vehicle speed estimation device is configured to estimate the speed of the moving vehicle by using data obtained from the signal processing device; and The wheel torque estimation device is configured to estimate the wheel torque applied to each of the front and rear wheels of the currently moving vehicle.

4. The apparatus according to claim 2, wherein, The driving status determination module also includes: A straight-line driving determination device is configured to determine whether the vehicle is currently driving in a straight line based on data obtained through the signal processing device.

5. The apparatus according to claim 4, wherein, The driving status determination module also includes: A static driving determination device is configured to determine whether the vehicle is in the static driving state by comparing the current wheel torque value of the vehicle being driven with a predetermined reference value.

6. The apparatus according to claim 1, wherein, The additional power control module includes: The final braking force setting device is configured to set the value of the final braking force acting on the braking force application shaft for braking of the moving vehicle.

7. The apparatus according to claim 6, wherein, The additional power control module also includes: A target braking force calculation device is configured to determine a target braking force to be added to the braking force application axis, such that the final braking force is configured to take effect by overcoming the current driving force applied to the vehicle; and A target driving force calculation device is configured to determine a driving force of magnitude equal to the target braking force and applied in a direction opposite to the direction of the target braking force as a target driving force to be added to the driving force application axis, such that the vehicle speed is maintained by counteracting the target braking force.

8. The apparatus according to claim 7, wherein, The additional power control module also includes: The target wheel torque calculation device is configured to determine the target braking torque by multiplying the target braking force by the radius of each tire disposed on the braking force application axle, and to determine the target driving torque by multiplying the target driving force by the radius of each tire disposed on the driving force application axle.

9. The apparatus according to claim 8, wherein, The additional power control module also includes: A brake pressure calculation device is configured to determine a target brake pressure to be achieved in the braking system of the vehicle by dividing the target brake torque by the brake gain and the effective tire radius; and The motor torque calculation device is configured to determine the target motor torque to be achieved in the electric motor of the vehicle by dividing the target drive torque by the drive torque gear ratio and the drive torque distribution ratio.

10. The apparatus according to claim 1, wherein, The wheel speed difference correction device is configured to: determine the wheel speed difference index value by applying a relatively higher correction coefficient among correction coefficients between 0 and 1 when the value of the final drive torque, which is the sum of the drive torques applied to the drive force application shaft, is less than a predetermined value; and determine the wheel speed difference index value by applying a relatively lower correction coefficient among correction coefficients between 0 and 1 when the value of the final drive torque is greater than the predetermined value.

11. The apparatus according to claim 1, wherein, The road surface friction coefficient estimation module also includes: The road surface friction coefficient estimation device is configured to determine whether the road surface on which the vehicle is traveling is in a low friction state or a high friction state by comparing the wheel speed difference index value with a predetermined road surface friction coefficient threshold.

12. A method for estimating the coefficient of road surface friction, the method comprising: The driving status determination module collects information from sensors installed in the vehicle to determine the vehicle speed. The driving state determination module determines whether to estimate the road surface friction coefficient by determining whether the vehicle is in an inertial driving state based on the collected information. When the driving state determination module determines that the vehicle is in an inertial driving state, the module arbitrarily adds the braking force that causes the wheel speed difference to the vehicle's braking force application axis, and also adds the driving force that counteracts the braking force to the vehicle's driving force application axis; and The driving state determination module estimates the state of the road surface friction coefficient by using the wheel speed difference caused by arbitrarily added braking force. The estimation of the road surface friction coefficient includes: The vehicle's wheel speed is received from the wheel coupled to the braking force application shaft and the wheel coupled to the driving force application shaft. Determine the magnitude of the wheel speed difference between the stated wheel speeds; The estimation of the road surface friction coefficient also includes: Based on the magnitude of the target driving torque acting on the shaft where the driving force is applied, the wheel speed difference determined when determining the magnitude of the wheel speed difference is multiplied by a predetermined correction factor to determine the corrected wheel speed difference index value.

13. The method according to claim 12, wherein, The collection of the information includes: The wheel torque value applied to each of the front and rear wheels of the vehicle is determined by the drive source torque, which is the motor torque collected from sensors installed in the vehicle.

14. The method according to claim 12, wherein, Determining whether to estimate the road surface friction coefficient includes: Based on the collected information, determine whether the vehicle is currently driving in a straight line; and When it is determined that the vehicle is driving in a straight line, it is determined whether the vehicle is in a static driving state by comparing the current wheel torque value of the vehicle with a predetermined reference value.

15. The method according to claim 12, wherein, Adding the braking force includes: Set the final braking force that ultimately acts on the braking force application shaft for braking of the moving vehicle; A target braking force to be added to the braking force application axis is determined such that the set final braking force is configured to take effect, and a target driving force to be added to the driving force application axis is determined such that the vehicle speed is maintained by counteracting the target braking force. When the target braking force is added to the braking force application shaft and the target driving force is added to the driving force application shaft, the target braking torque and target driving torque applied to each of the front and rear wheels of the vehicle are determined as the target wheel torque.

16. The method according to claim 15, wherein, Adding the aforementioned braking force also includes: Determine the target braking pressure to be applied to the braking device as a control quantity to achieve the target braking torque; and The target motor torque is determined as the control quantity to be applied to the electric motor of the vehicle to achieve the target drive torque.

17. The method according to claim 12, wherein, The estimation of the road surface friction coefficient also includes: The wheel speed difference index value is compared with a predetermined road surface friction coefficient threshold. When the wheel speed difference index value is greater than the road surface friction coefficient threshold, the road surface friction coefficient is estimated to be in a low friction state; and When the wheel speed difference index value is less than the road surface friction coefficient threshold, the road surface friction coefficient is estimated to be in a high friction state.

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