Method and apparatus for real time estimation of road surface friction coefficient

An apparatus for estimation of a road surface friction coefficient for vehicle stability control, comprising:

• a vehicle stability control system comprising at least one of brake force actuators and torque control actuators;
• sensors for detecting data for deriving vehicle operating parameters, the sensors comprising at least a speed sensor for detecting vehicle speed Vx,, a steer angle sensor for detecting vehicle steer angle δ, a yaw rate sensor for detecting yaw rate r, and a lateral acceleration sensor for detecting lateral acceleration ay;
• at least one non-transitory memory device storing programming for estimating a road surface friction coefficient, the programming comprising processor-executable instructions to:
• determine whether the following enabling criteria are met:
• Vx,MIN≦Vx≦Vx,MAX,
• δMIN≦δ≦δMAX,
• rMIN≦r≦rMAX, and
• ay,MIN≦ay≦ay,MAX,
• in which Vx,MIN, and Vx,max are predetermined minimum and maximum values of vehicle speed, δMIN and δMAX are predetermined minimum and maximum values for steer angle, rMIN and rMAX are predetermined minimum and maximum values of yaw rate, and ay,MIN and ay,MIN are predetermined minimum and maximum values of the lateral acceleration;
• when the enabling criteria are met, calculate a lookup value based on the vehicle parameters and an recursive least square estimation;
• retrieve a road surface friction coefficient from a stored lookup table by matching the calculated lookup value to the road surface friction coefficient;
• calculate adjustments to the vehicle using the road surface friction coefficient;
• and
• output the adjustments to the vehicle control system for implementation;
• and
• at least one processor in communication with the sensors and the at least one memory device, the at least one processor configured to:
• receive and execute the instructions;
• and
• receive the detected vehicle parameters,
• wherein, when the adjustments are output to the vehicle control system for implementation, the actuators adjust the at least one brake force actuators or torque control actuators.

An apparatus for estimation of a road surface friction coefficient for vehicle stability control, comprising:

• a vehicle stability control system comprising at least one of brake force actuators and torque control actuators;
• sensors for detecting data for deriving vehicle operating parameters, the operating parameters comprising at least a vehicle speed Vx, a steer angle δ , a yaw rate r, and a lateral acceleration ay;
• at least one non-transitory memory device storing programming for estimating a road surface friction coefficient, the programming comprising processor-executable instructions to:
• calculate a lookup value based on the vehicle operating parameters and an recursive least square estimation, wherein the lookup value is calculated utilizing instructions for calculating a partial derivative of the measured yaw rate over an estimated yaw rate rEST, and the estimated yaw rate rEST is calculated according to the equation:
• r
• EST
• =
• V
• x
• ⁢
• δ
• ⁢
• /
• ⁢
• (
• L
• +
• k
• us
• ⁢
• V
• x
• 2
• g
• )
• ,
• in which L is a wheelbase length, kus is a vehicle understeer gradient, and g is a gravitational constant;
• retrieve a road surface friction coefficient from a stored lookup table by matching the calculated lookup value to the road surface friction coefficient;
• calculate adjustments to the vehicle using the road surface friction coefficient;
• and
• output the adjustments to the vehicle control system for implementation;
• and
• at least one processor in communication with the sensors and the at least one memory device, the at least one processor configured to:
• receive and execute the instructions;
• and
• receive the detected vehicle operating parameters,
• wherein, when the adjustments are output to the vehicle control system for implementation, the actuators adjust the at least one brake force actuators or torque control actuators.

An apparatus for estimation of a road surface friction coefficient for vehicle stability control, comprising:

• a vehicle stability control system comprising at least one of brake force actuators and torque control actuators;
• sensors for detecting data for deriving vehicle operating parameters, the vehicle operating parameters comprising at least a vehicle speed VX, a vehicle steer angle δ, a yaw rate r, and a lateral acceleration ay;
• at least one non-transitory memory device storing programming for estimating a road surface friction coefficient, the programming comprising processor-executable instructions to:
• calculate a lookup value based on the vehicle operating parameters and an recursive least square estimation, wherein the lookup value is calculated utilizing instructions for calculating a partial derivative of a normalized lateral force ψ on front and rear tires over vehicle steer angle, and the normalized lateral force ψ , is calculated according to the equation
• ψ
• =
• F
• f
• +
• F
• r
• V
• x
• =
• ma
• y
• +
• V
• x
• ⁢
• mr
• V
• x
• ,
• in which m is the mass of the vehicle, Ff is front tire lateral force, and Fr is rear tire lateral force;
• retrieve a road surface friction coefficient from a stored lookup table by matching the calculated lookup value to the road surface friction coefficient;
• calculate adjustments to the vehicle using the road surface friction coefficient;
• and
• output the adjustments to the vehicle control system for implementation;
• and
• at least one processor in communication with the sensors and the at least one memory device, the at least one processor configured to:
• receive and execute the instructions;
• and
• receive the vehicle operating parameters,
• wherein, when the adjustments are output to the vehicle control system for implementation, the actuators adjust the at least one brake force actuators or torque control actuators.