ROAD SURFACE FRICTIONAL COEFFICIENT ESTIMATING APPARATUS

• US 20100211256A1
• Filed: 02/11/2010
• Published: 08/19/2010
• Est. Priority Date: 02/16/2009
• Status: Active Grant

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Inventors: Urabe, Hiroyuki, Mori, Yoshihiro, Yano, Osamu, Ushimura, Tomoya, Takenaka, Toru
• Granted Patent: US 8,315,758 B2
• Time in Patent Office: Days
• US Class Current: 701/29
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2270/86 Optimizing braking by using ESP vehicle or tire model
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• CPC Class Codes: B60W 40/068 Road friction coefficient
• CPC Class Codes: B62D 6/006 using a measured or estimated road friction coefficient
• CPC Class Codes: Y10T 152/10792 Structure where each bias angle reinforcing cord ply has no opposingly angled ply

Abstract

A road surface frictional coefficient estimating apparatus has a device for determining a first estimated value of a yaw moment Mnsp_estm generated at an NSP of a vehicle due to the resultant force of road surface reaction forces acting on each wheel by using, for example, a frictional coefficient estimated value that has been determined, and a device for determining a second estimated value of a yaw moment Mnsp_sens generated at the NSP from the observed value of motional state amounts defining an inertial force moment at the NSP. The increasing/decreasing manipulated variable of the frictional coefficient estimated value is sequentially determined on an error (Mnsp_sens−Mnsp_estm) such that the error is converged to zero, and the road surface frictional coefficient is updated on the basis of the increasing/decreasing manipulated variable.

Claims

1. A road surface frictional coefficient estimating apparatus which estimates a frictional coefficient of a road surface, on which a vehicle is traveling, while updating the frictional coefficient, comprising:

first estimating means of a neutral steer point (hereinafter referred to as “

NSP”

) yaw moment which determines a first estimated value of the NSP yaw moment, which is an external force moment generated about a yaw axis at the NSP of the vehicle by the resultant force of road surface reaction forces acting on each wheel of the vehicle from a road surface, by using a friction characteristic model indicating a relationship between a slip between a wheel of the vehicle and the road surface and a road surface reaction force, an estimated value of a frictional coefficient already determined, and an observed value of a predetermined type of amount to be observed, which is related to a behavior of the vehicle;

an acceleration sensor which generates an output based on a lateral acceleration of the vehicle;

second estimating means of an NSP yaw moment which determines a value of an external force moment that balances out an inertial force moment from an observed value of a motional state amount of the vehicle that defines the inertial force moment produced about a yaw axis at the NSP by a motion of the vehicle, the observed value of the motional state amount including an observed value of an acceleration indicated by an output of the acceleration sensor, and then obtains the determined value of the external force moment as a second estimated value of the NSP yaw moment;

frictional coefficient increasing/decreasing manipulated variable determining means which determines an increasing/decreasing manipulated variable of an estimated value of the frictional coefficient of the road surface on the basis of at least a difference between the first estimated value and the second estimated value or a difference between a first estimated filtering value obtained by passing the first estimated value through a first filter for frequency component adjustment and a second estimated filtering value obtained by passing the second estimated value through a second filter for frequency component adjustment, such that the difference is converged to zero; and

frictional coefficient estimated value updating means which determines a new estimated value of a frictional coefficient by updating the estimated value of the frictional coefficient of a road surface on the basis of the increasing/decreasing manipulated variable.

2. The road surface frictional coefficient estimating apparatus according to claim 1,

wherein the first estimating means of the NSP yaw moment estimates at least a lateral force of the road surface reaction force acting on each wheel of the vehicle on the basis of the friction characteristic model, the estimated value of the frictional coefficient of the road surface that has already been determined, and the observed value of the amount to be observed, then determines the first estimated value of the NSP yaw moment by using the estimated value of the lateral force.

3. The road surface frictional coefficient estimating apparatus according to claim 2,

wherein the first estimating means of the NSP yaw moment has vehicle motion/road surface reaction force estimating means which estimates at least the lateral force of the road surface reaction force acting on each wheel while estimating at least a side slip motional state amount of the motional state amount of the vehicle generated by the resultant force of the road surface reaction forces acting on each wheel of the vehicle,

the vehicle motion/road surface reaction force estimating means includes:

means which determines the estimated value of a side slip angle as the slip of each wheel of the vehicle by using the observed value of the amount to be observed and the estimated value of the side slip motional state amount of the vehicle that has already been determined;

means which inputs at least the estimated value of the side slip angle of each wheel and the estimated value of the frictional coefficient of the road surface that has been already determined to the friction characteristic model so as to determine the estimated value of the lateral force acting on each wheel by the friction characteristic model, and

means which determines a new estimated value of the side slip motional state amount of the vehicle by using a dynamic relationship between the resultant force of road surface reaction forces including at least the lateral force acting on each wheel and the side slip motional state amount of the vehicle and the estimated value of the lateral force acting on each wheel.

4. The road surface frictional coefficient estimating apparatus according to claim 1,

wherein the first estimating means of the NSP yaw moment estimates a driving/braking force and a lateral force of the road surface reaction force acting on each wheel of the vehicle on the basis of the already determined estimated value of the road surface frictional coefficient, the friction characteristic model, and the observed value of the amount to be observed, and then uses the estimated value of the driving/braking force and the estimated value of the lateral force to determine the first estimated value of the NSP yaw moment.

5. The road surface frictional coefficient estimating apparatus according to claim 4,

wherein the first estimating means of the NSP yaw moment comprises vehicle motion/road surface reaction force estimating means which estimates the driving/braking force and the lateral force of a road surface reaction force acting on each wheel while estimating at least the side slip motional state amount among the state amount of a motion of the vehicle produced by the resultant force of the road surface reaction forces acting on each wheel of the vehicle,

the vehicle motion/road surface reaction force estimating means comprises:

means which determines the estimated values of a slip rate and a side slip angle indicative of the slip of each wheel of the vehicle by using the observed value of the amount to be observed and the estimated value of the side slip motional state amount of the vehicle that has already been determined,

means which inputs at least the estimated values of the slip rate and the side slip angle of each wheel and the estimated value of the frictional coefficient of the road surface which has already been determined into the friction characteristic model so as to determine the estimated values of the driving/braking force and the lateral force acting on each wheel by the friction characteristic model, and

means which determines the new estimated value of the side slip motional state amount of the vehicle by using a dynamic relationship between the resultant force of the road surface reaction forces, including at least a driving/braking force and a lateral force acting on each wheel, and the side slip motional state amount of the vehicle and the estimated values of the driving/braking force and the lateral force acting on each wheel.

6. The road surface frictional coefficient estimating apparatus according to claim 2,

wherein the friction characteristic model includes a model which represents a relationship among at least the slip rate of each wheel of the vehicle or the driving/braking force of a road surface reaction force acting on the wheel, the lateral force of the road surface reaction force, the side slip angle of the wheel, and the frictional coefficient of the road surface.

7. The road surface frictional coefficient estimating apparatus according to claim 4,

wherein the friction characteristic model includes a first model which represents a relationship among the slip rate of each wheel of the vehicle, the driving/braking force of a road surface reaction force acting on the wheel, the side slip angle of the wheel, and the frictional coefficient of a road surface and a second model which represents a relationship among the slip rate of each wheel of the vehicle or the driving/braking force of a road surface reaction force acting on the wheel, the lateral force of the road surface reaction force, the side slip angle of the wheel, and the frictional coefficient of a road surface.

8. The road surface frictional coefficient estimating apparatus according to claim 1,

wherein the second estimating means of the NSP yaw moment uses, as the observed values of the motional state amounts, the observed value of a state amount related to the rotational motion about the yaw axis of the vehicle and the value of the lateral acceleration of the vehicle indicated by an output of the acceleration sensor.

9. The road surface frictional coefficient estimating apparatus according to claim 1, further comprising μ

sensitivity calculating means which determines the value of a μ

sensitivity, which is the ratio of an incremental amount of the NSP yaw moment relative to an incremental amount of the frictional coefficient of a road surface by linearly combining the observed value of a steering angle of a steering control wheel among the wheels of the vehicle and the observed value of the yaw rate of the vehicle,

wherein the frictional coefficient increasing/decreasing manipulated variable determining means determines the increasing/decreasing manipulated variable on the basis of the difference between the first estimated value and the second estimated value or the difference between the first estimated filtering value and the second estimated filtering value and the value of the μ

sensitivity.

10. The road surface frictional coefficient estimating apparatus according to claim 9,

wherein the frictional coefficient increasing/decreasing manipulated variable determining means determines the increasing/decreasing manipulated variable on the basis of the product of a difference and a μ

sensitivity, that is, the product of the difference between the first estimated value and the second estimated value or the difference between the first estimated filtering value and the second estimated filtering value and the value of the μ

sensitivity or a μ

sensitivity dependent value obtained by passing the value of the μ

sensitivity through one or both of a third filter for frequency component adjustment and a saturation characteristic element.

11. The road surface frictional coefficient estimating apparatus according to claim 10,

wherein the frictional coefficient increasing/decreasing manipulated variable determining means determines the increasing/decreasing manipulated variable on the basis of the product of the difference and the μ

sensitivity such that the increasing/decreasing manipulated variable is proportional to the product of the difference and the μ

sensitivity.

12. The road surface frictional coefficient estimating apparatus according to claim 9,

wherein the μ

sensitivity calculating means sets at least one of a weighting factor applied to the observed value of the steering angle and a weighting factor applied to the observed value of the yaw rate in the linear coupling according to the observed value of a vehicle speed such that the mutual ratio of both weighting factors changes according to the vehicle speed of the vehicle, and uses the set weighting factors to carry out the calculation of the linear coupling.

13. The road surface frictional coefficient estimating apparatus according to claim 9,

wherein the μ

sensitivity calculating means determines the value of the μ

sensitivity according to expression 01 given below from the observed value of the steering angle of a steering control wheel among the wheels of the vehicle (δ

f_sens), the observed value of a yaw rate of the vehicle (γ

_sens), and the observed value of the vehicle speed of the vehicle (Vgx_estm).

μ

sensitivity=A1(Vgx_—

estm)*γ

_—

sens+A2*δ

f_—

sens 

 

Expression 01

where A1(Vgx_estm)=Iz*(a22−

(a21/a11)*a12s)/Vgx_estm, A2=(b2−

(a21/a11)*b1), a11=−

2*(CPf0+CPr0)/m, a12s=−

2*(Lf*CPf0−

Lr*CPr0)/m, a21=−

2*(Lf*CPf0−

Lr*CPr0)/Iz, a22=−

2*(Lf*Lf*CPf0+Lr*Lr*CPr0)/Iz, b1=2*CPf0/m, CPf0;

Cornering power per wheel of the front wheels of the vehicle (steering control wheels) on a road surface where frictional coefficient=1, CPr0;

Cornering power per wheel of the rear wheels of the vehicle on a road surface where frictional coefficient=1, Lf;

Distance between the center of gravity of the vehicle and the axle of the front wheels, Lr;

Distance between the center of gravity of the vehicle and the axle of rear wheels, m;

Mass of the vehicle, and Iz;

Inertial moment about the yaw axis of the vehicle.

14. The road surface frictional coefficient estimating apparatus according to claim 9,

wherein the linear coupling carried out by the μ

sensitivity calculating means is configured to be linear coupling in which the value of the μ

sensitivity is determined such that the value of the μ

sensitivity is proportional to the value of the NSP yaw moment identified using a linear two-wheeled vehicle model from the observed value of the steering angle of a steering control wheel among the wheels of the vehicle, the observed value of the yaw rate of the vehicle, and the observed value of the vehicle speed of the vehicle in the case where the frictional coefficient of a road surface takes a constant value, the linear two-wheel vehicle model being adapted t approximately represent a side slip motion and a rotational motion about the yaw axis of an actual vehicle as a behavior of a model vehicle having one front wheel as a steering control wheel and one rear wheel as a non-steering control wheel.