Fluid-pressure and analogous brake systems – Speed-controlled – Odd condition or device detection
Reexamination Certificate
1998-07-17
2001-07-24
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Odd condition or device detection
C303S163000, C303S191000, C303S194000
Reexamination Certificate
active
06264292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wheel condition estimating apparatus, and more particularly to a wheel condition estimating apparatus for estimating a wheel condition from an output response or the like of a wheel resonance system on the basis of a vibration model of the wheel resonance system including a frictional characteristic between a tire and a road surface.
2. Description of the Related Art
In recent years, in accordance with an increase in efforts to improve the safety of automotive vehicles, preventative safety techniques have been researched and developed. An antilock brake systems (ABS), which are a representative safety apparatus, have already been used in many vehicles.
ABS control on the basis of a new principle which pays attention to the resonance phenomenon of the tire has been proposed, and the study thereof continues (Japanese Patent Application No. 7-220920 and the like). This technique is such that a micro vibration having a frequency component equal to a resonance frequency when the tire grips a road is applied to the brake pressure, and the average brake pressure is controlled on the basis of a resonance gain (micro amplitude of wheel speed at the resonance frequency/vibration amplitude of brake pressure) of a tire resonance system at that time.
It is known that the resonance gain is a physical quantity related to the gradient of a coefficient of friction &mgr; with respect to a slip ratio S (hereinafter referred to as a &mgr; gradient) of a coefficient &mgr; of friction in a so-called S-&mgr; characteristic (a changing curve of a coefficient of friction &mgr; with respect to a Slip ratio S). It is expected that a frictional characteristic, which relates to ease of slipping between a tire and a road surface at a time of braking, can be estimated on the basis of the resonance gain.
However, since the prior art mentioned above presupposes that the resonance frequency of the tire resonance system is known, there is a problem that it cannot immediately respond in the case that the resonance frequency changes due to the tire being replaced or the air pressure in the tire changing. For example, when the air pressure in the tire falls, the resonance frequency at the time when the tire grips the road surface changes to a lower side. Therefore, the value of the resonance gain becomes small, and the accuracy of detecting whether the current state is a state immediately before a peak &mgr; value by comparison with a predetermined reference gain deteriorates.
Further, in the above-described prior art, the brake pressure is minutely vibrated at a time of calculating the resonance gain. However, because the micro vibration can be applied only at a time of braking due to the structure of a brake portion, there is a problem that the opportunity to estimate the road surface condition is limited to the time of braking in the case of a vehicle having the brake portion of this type. Still further, there are cases in which micro vibration of the brake pressure is not preferable such as a time of driving, a time of steady running and the like.
SUMMARY OF THE INVENTION
The present invention has been achieved by taking the facts mentioned above into consideration, and an object of the present invention is to provide a wheel condition estimating apparatus which can estimate a road surface condition equally in various running conditions such as braking, driving, steady running and the like, and which can always estimate with high precision a frictional characteristic which relates to ease of slipping between a tire and a road surface regardless of variations in a resonance frequency due to replacement of a tire or changes in air pressure of a tire, and which enables highly-accurate ABS control on the basis of the frictional characteristic.
In order to realize the aforementioned object, in accordance with a first aspect of a present invention, there is provided a wheel condition estimating apparatus for estimating a wheel condition in a wheel resonance system including a frictional characteristic between a tire and a road surface, comprising: detecting means for detecting an output response with respect to a vibration input to the wheel resonance system; and estimating means for expressing a transfer characteristic of the wheel resonance system from the vibration input to the output response by a vibration model including, at least a physical quantity relating to ease of a slipping between the tire and the road surface as an unknown component of a wheel condition, and for estimating at least the unknown component which substantially satisfies the output response detected by the detecting means on the basis of the vibration model.
Further, in accordance with a second aspect of the present invention, the wheel condition estimating apparatus of the first aspect further comprises modifying means for modifying the vibration model on the basis of the output response detected by the detecting means.
Still further, in accordance with a third aspect of the present invention, in the wheel condition estimating apparatus of the first aspect or the second aspect, the vibration model further includes, a physical quantity relating to a constant of a torsion spring of the tire as an unknown component of the wheel condition.
Furthermore, in accordance with a fourth aspect of the present invention, the wheel condition estimating apparatus of any of the first aspect to the third aspect further comprises vibrating means for applying a vibration input to the wheel resonance system.
Moreover, in accordance with a fifth aspect of the present invention, the wheel condition estimating apparatus of the fourth aspect further comprises vibration input detecting means for detecting the vibration input applied to the wheel resonance system by the vibrating means.
Further, in accordance with a sixth aspect of the present invention, the wheel condition estimating apparatus of any of the first to the fifth aspects further comprises calculating means for calculating a determining value for determining whether or not the output response detected by the detecting means is a periodical output on the basis of the output response, and selecting means for selecting the output to be delivered to the estimating means among the output responses detected by the detecting means on the basis of the determining value calculated by the calculating means, wherein the estimating means uses the output selected by the selecting means at a time of estimating the unknown component.
Still further, in accordance with a seventh aspect of the present invention, in the wheel condition estimating apparatus of the sixth aspect, the calculating means calculates a correlation coefficient between the output response detected by the detecting means and a converted value obtained by converting the output response such that the periodical portion of the output response changes in correspondence to the change of the output response, as the determining value.
(Principles of the Present Invention)
Principles of the present invention will be described below with reference to
FIGS. 1
to
3
. Here,
FIG. 1
shows an equivalent dynamic model of a wheel resonance system,
FIG. 2
shows a frictional characteristic between a tire and a road surface, which defines a transfer characteristic of the wheel resonance system shown in
FIG. 1
, and
FIG. 3
shows an example of a vibration model from a vibration input to an output response in the transfer characteristic of the wheel resonance system shown in FIG.
1
.
First, as shown in
FIG. 1
, a vibration phenomenon in a wheel when a vehicle runs at a vehicle speed V (an angular velocity xv), that is, a vibration phenomenon of a wheel resonance system formed by at least a wheel and a road surface, is considered by referring to a dynamic model which is obtained by equivalent modeling by using a wheel rotational axis. The various quantities shown in
FIG. 1
are as follows.
J
1
: moment of inertia at rim
J
2
: moment of inertia at belt
K: constant of tor
Asano Katsuhiro
Ono Eiichi
Sugai Masaru
Umeno Takaji
Yamaguchi Hiroyuki
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oberleitner Robert J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sy Mariano
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