Measuring and testing – Frictional resistance – coefficient or characteristics
Reexamination Certificate
2002-04-19
2003-08-05
Willams, Hezron (Department: 2855)
Measuring and testing
Frictional resistance, coefficient or characteristics
C701S080000, C702S148000
Reexamination Certificate
active
06601435
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and device for estimating a friction coefficient between a tire and a road surface, and more particularly, to a method and a device for estimating a friction coefficient between a tire and a road surface that may be used in obtaining a safety distance for an adaptive vehicle.
BACKGROUND OF THE INVENTION
In general, a running vehicle has to maintain a predetermined separation from a vehicle ahead thereof as a provision against an emergency situation such as an abrupt stop of the preceding vehicle. For this reason, recent vehicles are equipped with a system calculating a proper safety distance with respect to the preceding vehicle and a system for maintaining the calculated safety distance between the two vehicles.
In a prior art longitudinal vehicle motion control system, the safety distance between the vehicles has been calculated by means of the following Equation 1:
[Equation 1]
safety distance between vehicles=speed of a vehicle being controlled X headway time
The resulting safety distance found by such equation is a value obtained without taking into consideration the characteristics of the road surface on which the vehicle runs. Accordingly, the same safety distance is applied to the vehicle regardless of factors of an environment surrounding the vehicle, e.g., conditions of the road surface. In other words, the safety distance applied to a vehicle running on a road surface under normal conditions is identical to that applied to a vehicle on a slippery road covered with snow. This leads to an increase of the possibility of an accident to the latter vehicle, i.e., the vehicle running on the slippery road.
SUMMARY OF THE INVENTION
The present invention provides a method and a device for estimating a friction coefficient between a tire and a road surface that may be used in obtaining a safety distance for an adaptive vehicle, by only using RPM sensors normally equipped on vehicles. According to a preferred embodiment of the present invention, a method for estimating a friction coefficient between a tire of a vehicle and a road surface comprises (a) obtaining state variable data representing conditions of the vehicle by using RPM sensors equipped on the vehicle; (b) correcting part of the state variable data including noise by means of a Kalman Filter; (c) obtaining a turbine torque by means of mathematical modeling having the state variable data as input data; (d) estimating a driving torque based on the turbine torque and the state variable data; (e) calculating a slip ratio based on the state variable data; and (f) estimating the friction coefficient based on the state variable data, the slip ratio, and the driving torque as input data. The state variable data include an angular velocity of an engine, an angular velocity of a transmission carrier, an angular velocity of a front wheel, and an angular velocity of a rear wheel.
In accordance with another aspect of the present invention, there is provided a device for estimating a friction coefficient between a tire of a vehicle and a road surface. In a preferred embodiment, a state variable input section obtains state variable data representing conditions of the vehicle by using RPM sensors equipped on the vehicle. A friction coefficient estimator estimates the friction coefficient by using the state variable data. A friction coefficient value storage or memory stores the estimated friction coefficient. A braking/steering monitoring section monitors the braking action and steering action of the vehicle and generates signals when either of the braking action or the steering action are applied. Further, a control section receives the signals from the braking/steering monitoring section and outputs the friction coefficient stored in the friction coefficient value storage when both or either of the braking action and the steering action are applied. The control section also outputs the friction coefficient estimated by the friction coefficient estimator when the braking action and the steering action are not applied to the vehicle.
Preferably, the friction coefficient estimator includes a Kalman Filter for correcting part of the state variable data including noise. A torque converter modeling section is also included to obtain a turbine torque by means of mathematical modeling based on the state variable data as input data. A drive shaft torque calculator estimates a driving torque based on the turbine torque and the state variable data. A slip ratio calculator calculates a slip ratio based on the state variable data, and a friction coefficient calculator calculates the friction coefficient based on the state variable data, the slip ratio and the driving torque as input data.
In a further preferred embodiment, a method for estimating a friction coefficient between a tire of a vehicle and a road surface comprises generating at least one vehicle state variable data signal representative of the vehicle operational state; selectively filtering noise from said at least one data signal; mathematically modeling turbine torque based on said at least one data signal; estimating driving torque based on said modeled turbine torque and said at least one data signal; calculating a vehicle slip ratio based on said at least one data signal; and estimating the friction coefficient based on said slip ratio, driving torque and at least one data signal. Preferably, the at least one data signal contains information representative of revolution speed of selected vehicle components, including signals representative of engine angular velocity, transmission carrier angular velocity, front wheel angular velocity and rear wheel angular velocity. Also preferably, the selectively filtering comprises Kalman filtering the transmission carrier angular velocity and front and rear wheel angular velocity signals.
According to yet another aspect of the invention, an apparatus for estimating and outputting a friction coefficient between a tire of a vehicle and a road surface for use in safety distance calculations in an adaptive vehicle is provided. In a preferred embodiment, the apparatus comprises at least one processor communicating with plural vehicle sensors to receive signals representative of the vehicle operational state. The processor is preferably programmed to execute a number of functions, including to mathematically model turbine torque based the data signals; estimate driving torque based on the modeled turbine torque and selected data signals; calculate a vehicle slip ratio based on selected data signals; and estimate the friction coefficient based on the slip ratio, driving torque and data signals. In a preferred embodiment, the data signals comprise at least signals representative of engine angular velocity, transmission carrier angular velocity, front wheel angular velocity and rear wheel angular velocity. Preferably the at least one processor is programmed to Kalman filter the transmission carrier angular velocity and front and rear wheel angular velocity signals.
In a further preferred embodiment, the estimated friction coefficient is stored in a memory for later output. The data signals preferably comprise signals representative of applied braking functions and steering control functions and the at least one processor is further programmed to output the stored friction coefficient when one or both of the braking and steering functions are employed, and to estimate a new friction coefficient when no braking or steering functions are employed. Thus, the at least one processor may be further programmed to calculate an effective safety distance in part on the output friction coefficient.
REFERENCES:
patent: 4212063 (1980-07-01), Hardmark
patent: 5198982 (1993-03-01), Kobayashi
patent: 6266600 (2001-07-01), Miyazaki
patent: 6427519 (2002-08-01), Ueda et al.
Hyundai Motor Company
Jenkins Jermaine
Pennie & Edmonds LLP
Willams Hezron
LandOfFree
Method and device for estimating a friction coefficient... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for estimating a friction coefficient..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for estimating a friction coefficient... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3116644