Initial correction factor determining device and device utilizin

Details Initial correction factor determining device and device utilizin Initial correction factor determining device and device utilizin

1997-11-13

2000-05-09

Shah, Kamini

Data processing: measuring, calibrating, or testing

Calibration or correction system

For mechanical system

701 71, 701 78, 701 70, G01P 356

Patent

active

060616423

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to an initial correction factor determining device applied to detection of the drop in air pressure of a tire, for example, for finding an initial correction factor for eliminating the effect of a relative difference in effective rolling radius, depending on an initial difference between tires, on the rotational velocity. Further, it relates to a slip factor calculating device applied to detection of a drop in air pressure of a tire, for example, for calculating the slip factor of a driving tire. Furthermore, it relates to a tire pressure drop detecting device for detecting a drop in air pressure of a tire utilizing the rotational velocity corrected using the initial correction factor found by the initial correction factor determining device.
2. Background Art
In recent years, as an example of a safety device of a four-wheel vehicle such as an automobile or a truck, devices for detecting a drop in air pressure of a tire have been developed, and some of them have been put to practical use.
An example of a method of detecting a drop in air pressure of a tire is a method utilizing the differences among the respective rotational velocities F.sub.1, F.sub.2, F.sub.3, and F.sub.4 of four tires W.sub.1, W.sub.2, W.sub.3, and W.sub.4 mounted on a vehicle. The tires W.sub.1 and W.sub.2 are right and left front tires. The tires W.sub.3 and W.sub.4 are right and left rear tires.
In this detecting method, the rotational velocity F.sub.i of each of the tires W.sub.i (i=1, 2, 3, 4) is detected for each predetermined sampling period on the basis of a signal outputted from a wheel speed sensor associated with the tire W.sub.i.
The detected rotational velocities F.sub.i are equal if all of the effective rolling radii of the respective tires W.sub.1 are the same, and the vehicle is traveling linearly. The effective rolling radius is the distance the tire W.sub.i freely rolling in a loaded state (rolling in a state where both the slip angle and the slip factor are zero) moves by one rotation divided by 2.pi..
On the other hand, the effective rolling radius of each of the tires W.sub.i changes with changes in air pressure in the tire W.sub.i, for example. That is, when the air pressure in the tire W.sub.i drops, the effective rolling radius thereof is smaller than that at a time of normal internal pressure. Consequently, the rotational velocity F.sub.i of the tire W.sub.i whose air pressure drops is higher than that at a time of normal internal pressure. Therefore, the reduced pressure of the tire W.sub.i can be judged on the basis of differences among the rotational velocities F.sub.i.
An equation used in detecting the drop in air pressure in the tire W.sub.i on the basis of differences among the rotational velocities F.sub.i is the following equation (1), for example (see Japanese Patent Laid-Open (KOKAI) No. 305011/1988, Japanese Patent Laid-Open (KOKAI) No. 212609/1992, etc.). ##EQU1##
If the effective rolling radii of the tires W.sub.i are the same, the respective rotational velocities F.sub.i are the same (F.sub.1 =F.sub.2 =F.sub.3 =F.sub.4). Consequently, the judged value D is zero. Therefore, threshold values D.sub.TH1 and D.sub.TH2 (where D.sub.TH1, D.sub.TH2 >0) are set. When conditions indicated by the following expression (2) are satisfied, it is judged that there is a tire W.sub.i whose air pressure has dropped. When the conditions are not satisfied, it is judged that all the tires W.sub.i have normal internal pressure:
The effective rolling radii of the actual tires W.sub.i include variations within the production standard occurring at the time of fabricating the tires W.sub.i (hereinafter referred to as an "an initial difference"). That is, even if the four tires W.sub.i have normal internal pressure, the effective rolling radii of the four tires W.sub.i differ due to the initial difference. Correspondingly, the rotational velocities F.sub.i of the tires W.sub.i vary. As a result, the judged value D may be a value

REFERENCES:
patent: 5299131 (1994-03-01), Haas et al.
patent: 5453942 (1995-09-01), Wood et al.
patent: 5490070 (1996-02-01), Kiryu et al.
Helmut Mayer; "Comparative Diagnosis Of Tyre Pressures"; Institute For Industrial Information Systems; pp. 627-632 vol. 1; Aug. 24, 1994.

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