Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-07-12
2004-10-12
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06802226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a physical amount estimating apparatus, a road surface friction condition estimating apparatus, a steering angle neutral point estimating apparatus and a tire air pressure reduction estimating apparatus, and particularly to a physical amount estimating apparatus for estimating a physical amount based on a corrected value with a hysteresis characteristic removed therefrom, a road surface friction condition estimating apparatus for calculating a corrected value with a hysteresis characteristic, caused by influence from viscous friction of Coulomb friction, removed therefrom, using an estimated value of self aligning torque (SAT) and estimating a road surface friction condition based on the calculated corrected value, a steering angle neutral point estimating apparatus for estimating a neutral point of a steering angle based on a corrected value with a hysteresis characteristic removed therefrom and a steering angle, and an air pressure reduction estimating apparatus of a tire for estimating a reduction in air pressure of a tire based on a corrected value with a hysteresis characteristic removed therefrom and an SAT reference value.
2. Description of the Related Art
Japanese Patent Application Laid-open (JP-A) No. 11-287749 discloses technology for detecting a steering angle and steering torque of a tire, calculating a characteristic of the steering torque with regard to the steering angle and calculating a friction coefficient &mgr; (road surface &mgr;) of a road surface on which a tire is grounded.
According to the related art, the road surface &mgr;, which constitutes a physical amount in correspondence with a grip state, is calculated as an amount of change of the steering torque with regard to an amount of change of the steering angle, and therefore the resulting estimating method is liable to be affected by noise. That is, calculation of an amount of change signifies carrying out differentiation, which amplifies noise, and therefore the estimated value becomes a value that includes a large amount of noise.
Further, according to the related art, the road surface &mgr; is estimated only when the steering angle is increased in order to steer. Thus, at a maximum steering angle, at which a load applied to the tire is maximized, the steering angle cannot be increased in order to steer, and therefore the friction coefficient cannot be estimated. Inherently, if the road surface &mgr; is estimated when the load applied to the tire is maximized, that is, near a limit, or in other words, when limit road surface &mgr; is estimated, accuracy of the estimation is promoted. According to the related art, however, there is a problem in that the road surface &mgr; cannot be estimated at the maximum steering angle and the road surface &mgr; can be estimated only before reaching the maximum steering angle.
Meanwhile, a hysteresis characteristic is caused by twisting of a tire tread, Coulomb friction in a power steering apparatus, or the like, between SAT and a slip angle or a steering angle. Therefore, the characteristic differs when increasing the steering angle and when decreasing the steering angle, and according to the related art, in which attention is paid to a change in SAT with regard to a change in the slip angle or the steering angle, a dispersion in the estimated value is caused.
Further, when a driver reduces steering torque to the point of not moving the steering wheel when steering is maintained, although there is no change in the slip angle or the steering angle, as a result of reducing SAT, there is a possibility of erroneously determining that a “reduction in grip” has occurred. That is, according to the above-described related art, although such an erroneous determination is avoided and the dispersion in the estimated value is reduced by carrying out the estimation only when the steering angle is increased, as a result, there is a problem in that a road surface friction condition of the grip state or the like cannot be estimated when decreasing or maintaining the steering angle.
Further, that the road surface friction condition cannot be estimated when decreasing or maintaining the steering angle, signifies that when the tire shifts from a low &mgr; road to a high &mgr; road while maintaining the steering angle, or when the grip state is changed by shifting from a high &mgr; road to a low &mgr; road, at the time of the change, the road surface friction condition and the grip state cannot be estimated until the steering angle is subsequently increased. Therefore, the estimated value of the grip state according to the related art cannot be utilized as a control parameter for switching a characteristic of a power steering apparatus or ABS, which require swift adaptability in accordance with the grip state.
Further, JP-A Nos. 11-334634 and 11-59466, disclose technology in which reference steering torque, which is set based on a steering angle and vehicle speed, is compared with steering torque, and when a state in which the steering torque is greater than the reference steering torque continues for a certain period of time, it is determined that a reduction in air pressure of a tire has occurred.
In the above-described related art, the steering torque, which includes friction of a steering system, is utilized, and therefore there is a problem in that a change in the steering torque with regard to air pressure is influenced by the friction. As a result, the change cannot accurately be detected and a reduction in air pressure cannot be estimated with high accuracy due to the influence of the friction.
Further, the relationship between the steering angle and the steering torque is also influenced by movement of the vehicle, which is a dynamic characteristic, aside from the friction of the steering system. Therefore, there is a concern that the accuracy of estimation is deteriorated when fast steering is carried out.
As a countermeasure against the above-described problem, according to the related art, a condition is added that the state in which the steering torque is greater than the reference steering torque must continue for a certain period of time or longer, and due to the condition, the problem of deterioration in accuracy is alleviated. As a result of the condition, however, chances to carry out estimation are decreased, and there is a new problem in that estimation time is delayed.
SUMMARY OF THE INVENTION
The invention has been carried out in order to resolve the above-described problem and it is an object thereof to provide a physical amount estimating apparatus capable of estimating a highly accurate physical amount by removing a hysteresis characteristic such that a dispersion is not caused in an estimated value, a road surface friction condition estimating apparatus capable of accurately estimating a road surface friction condition without steering to increase a steering angle, a steering angle neutral point estimating apparatus capable of accurately estimating a neutral point of a steering angle and an air pressure reduction estimating apparatus of tire capable of estimating reduction in the pressure of tire.
In order to achieve the above-described object, a physical amount estimating apparatus of the invention is constituted by including first outputting means for outputting a first physical amount which is not provided with a hysteresis characteristic, second outputting means for outputting a second physical amount which has a predetermined physical relationship with the first physical amount and has a hysteresis characteristic, hysteresis removing means for calculating a corrected value removed of the hysteresis characteristic based on the second physical amount, and estimating means for estimating a third physical amount based on a physical relationship between the first physical amount and the corrected value.
According to the invention, the hysteresis characteristic is removed based on the physical amount having the predetermined physical relationship with the first physical a
Asano Katsuhiro
Miyashita Masanori
Muragishi Yuji
Ono Eiichi
Watanabe Yoshitoshi
Kabushiki Kaisha Toyota Chuo Kenkyusho
Noori Max
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