Road-surface friction coefficient estimating device and road-surface friction coefficient estimating method

1. A road-surface friction coefficient estimating device for estimating a road-surface friction coefficient by updating the road-surface friction coefficient with time lapse by using an estimated present value of the road-surface friction coefficient as a standard for a next estimation of the road-surface friction coefficient, comprising:

a specifying unit for specifying the road-surface friction coefficient based on road-surface information detected by a road-side infrastructure in a traveling direction of a vehicle when the road-surface information is acquired; and

an estimating unit for setting the specified road-surface friction coefficient as an initial value, resetting the estimated present value of the road-surface friction coefficient to the initial value and then starting next estimation of the road-surface friction coefficient with the initial value as a standard for a next estimation of the road-surface friction coefficient,

wherein the specifying unit previously stores plural road-surface friction coefficients corresponding to plural pieces of road-surface information, and

wherein the specifying unit specifies the road-surface friction coefficient corresponding to the acquired road-surface information from the plural road-surface friction coefficients associated with the plural pieces of road-surface information.

2. The road-surface friction coefficient estimating device as claimed in claim 1 , further comprising:

an acquiring device for acquiring service information that includes the road-surface information from the road-side infrastructure; and

a computer for outputting the road-surface information to the specifying unit in synchronization with an arrival timing at which the vehicle arrives at a point corresponding to the road-surface information specified by the acquired service information.

3. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein the estimating unit estimates cornering power based on a dynamic equation of the vehicle by using a vehicle speed, a steering angle and a yaw rate, and estimating the present value of the road-surface friction coefficient based on cornering power of front and rear wheels regarding a predetermined road-surface friction coefficient and the cornering power of the front and rear wheels thus estimated.

4. The road-surface friction coefficient estimating device as claimed in claim 3 , wherein the specifying unit specifies the road-surface friction coefficient corresponding to the acquired road-surface information from plural road-surface friction coefficients associated with plural pieces of road-surface information.

5. The road-surface friction coefficient estimating device as claimed in claim 3 , further comprising:

an acquiring device for acquiring service information that includes the road-surface information from the road-side infrastructure; and

a computer for outputting the road-surface information to the specifying unit in synchronization with an arrival timing at which the vehicle arrives at a point corresponding to the road-surface information specified by the acquired service information.

6. The road-surface friction coefficient estimating device as claimed in claim 1 , further comprising:

an acquiring device for acquiring service information that includes the road-surface information from the road-side infrastructure; and

a computer for outputting the road-surface information to the specifying unit in synchronization with an arrival timing at which the vehicle arrives at a point corresponding to the road-surface information specified by the acquired service information.

7. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein said road-surface friction coefficient is estimated based on a vehicle speed, a steering angle, and a yaw rate.

8. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein the road surface information comprises information related to at least one of a dry condition, a wet condition, a water film condition, a snow condition, and an ice condition.

9. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein the estimating unit gives the initial value with interruption.

10. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein said estimating unit receives said road-surface information from the road-side infrastructure and detections signals from at least one on-vehicle sensor.

11. The road-surface friction coefficient estimating device as claimed in claim 10 , wherein said at least one on-vehicle sensor detects a vehicle speed, a steering angle, and a yaw rate.

12. The road-surface friction coefficient estimating device as claimed in claim 10 , wherein said estimating unit receives actuating signals from at least one of a traction controlling unit, an anti-lock brake controlling unit, a brake-force controlling unit, a skid detecting unit, and a transmission controlling unit.

13. The road-surface friction coefficient estimating device as claimed in claim 12 , wherein the transmission controlling unit inputs a signal indicating a selected one of a plurality of travel patterns, the plurality of travel patterns including a normal pattern and a pattern having a broader travel area than the normal pattern under a low gear.

14. The road-surface friction coefficient estimating device as claimed in claim 1 , wherein said road-surface friction coefficient is estimated based on cornering powers of wheels of the vehicle.

15. A road-surface friction coefficient estimating method for estimating a road-surface friction coefficient by updating the road-surface friction coefficient with time lapse by using an estimated present value of the road-surface friction coefficient as a standard for a next estimation of the road-surface friction coefficient, comprising:

specifying the road-surface friction coefficient based on road-surface information detected by a road-side infrastructure in a traveling direction of a vehicle when the road-surface information is acquired; and

setting the specified road-surface friction coefficient as an initial value, resetting the estimated present value of the road-surface friction coefficient to the initial value and then starting next estimation of the road-surface friction coefficient with the initial value as a standard for a next estimation of the road-surface friction coefficient,

wherein plural road-surface friction coefficients corresponding to plural pieces of road-surface information are previously stored, and

wherein the road-surface friction coefficient is specified corresponding to the acquired road-surface information from the plural road-surface friction coefficients associated with the plural pieces of road-surface information.

16. The method according to claim 15 , wherein said setting is performed with interruption.

17. A road-surface friction coefficient estimating method, comprising:

setting a specified road-surface friction coefficient as an initial value of the road-surface friction coefficient;

resetting a present value of the road-surface friction coefficient to the initial value; and

estimating the road-surface friction coefficient with the initial value as a standard for a next estimation of the road-surface friction coefficient.

18. The method according to claim 17 , wherein said setting is performed with interruption.

19. A road-surface friction coefficient estimating device for estimating a road-surface friction coefficient by updating the road-surface friction coefficient with a time lapse by using an estimated present value of the road-surface friction coefficient, comprising:

a specifying unit for specifying the road-surface friction coefficient based on road-surface information detected by a road-side infrastructure in a traveling direction of a vehicle when the road-surface information is acquired; and

an estimating unit for estimating a present value of the road-surface friction coefficient based on an estimated previous value of the road-surface friction coefficient when the road-surface information is not acquired, and for estimating the present value of the road-surface friction coefficient as a specified road-surface friction coefficient when the road-surface information is acquired.