Tire inflation pressure monitoring apparatus

• US 5,469,136 A
• Filed: 08/31/1994
• Issued: 11/21/1995
• Est. Priority Date: 08/31/1993
• Status: Expired due to Fees

• Current Assignee: NHK Spring Company Limited
• Original Assignee: NHK Spring Company Limited
• Inventors: Matsubara, Kousuke, Fukumura, Takeo
• Primary Examiner(s): Ball, Michael W.
• Assistant Examiner(s): Lorin, Francis J.
• Application Number:
  US08/298,830
• Time in Patent Office: 447 Days
• Field of Search: 152/415, 152/427, 152/429, 152/431, 73/146.4, 340/445, 340/444, 364/558, 200/61.25
• US Class Current: 340/445
• CPC Class Codes: B60C 23/0425 Means comprising permanent magnets, e.g. Hall-effect or Reed-switches

Abstract

A tire inflation pressure monitoring apparatus comprises a reference magnet fixed to a wheel, a movable magnet whose position shifts depending on the inflation pressure of a tire, and a magnetic sensor for detecting the magnetism of the magnets. The reference magnet can be moved in the axial direction of the wheel by means of a position adjusting mechanism. Thus, a relative distance from the reference magnet to the movable magnet can be adjusted to a fixed value (e.g., zero) at the time of calibration. An electric circuit section is stored with a computation formula or a map indicative of the relationships between outputs of the magnetic sensor and minimum distances from the magnets to the magnetic sensor. In detecting the inflation pressure of the tire, data associated with the minimum distances from the magnetic sensor to the magnets are obtained according to the computation formula or map on the basis of the outputs obtained by means of the magnetic sensor. Based on these data, the inflation pressure of the tire is obtained according to a pressure computation formula or a map indicative of the relationship between the tire inflation pressure and the distance between the magnets.

Claims

1. A tire inflation pressure monitoring apparatus for detecting the inflation pressure of a tire attached to a wheel, comprising:

reference means including a reference magnet fixed to the wheel;

a transducer attached to the wheel and including a movable magnet whose position shifts for a distance corresponding to the inflation pressure of the tire in the axial direction of the wheel;

a stationary-side member facing the wheel at a distance therefrom in the axial direction thereof;

a magnetic sensor attached to the stationary-side member, the sensor being situated in a position such that the sensor can detect the magnetism of the reference magnet and the movable magnet when the wheel rotates and adapted to generate outputs of magnitudes corresponding to the minimum distance from the reference magnet and the minimum distance from the movable magnet as the wheel rotates;

means for storing a previously obtained computation formula or map indicative of the relationships between the outputs of the magnetic sensor and the minimum distances from the magnets to the magnetic sensor;

electric circuit means for obtaining data associated with the minimum distances from the magnetic sensor to the magnets according to the computation formula or map on the basis of the outputs obtained by means of the magnetic sensor in detecting the inflation pressure of the tire, and obtaining the tire inflation pressure according to a pressure computation formula or map indicative of the relationship between the tire inflation pressure and the distance between the magnets on the basis of the obtained data; and

notifying means for notifying of information relating to the tire inflation pressure obtained by said electric circuit means.

2. A tire inflation pressure monitoring apparatus according to claim 1, wherein said reference means includes a position adjusting mechanism capable of moving the reference magnet in the axial direction of the wheel and fixing the reference magnet in a desired position.

3. A tire inflation pressure monitoring apparatus according to claim 2, wherein said position adjusting mechanism of the reference means includes a bracket fixed to the wheel, a tapped hole formed in the bracket and extending along the axial direction of the wheel, a rod screwed in the tapped hole and fitted with the reference magnet, and locking means for fixing the rod to the bracket.

4. A tire inflation pressure monitoring apparatus for detecting the inflation pressure of a tire attached to a wheel, comprising:

reference means including a reference magnet attached to the wheel and a position adjusting mechanism capable of moving the reference magnet in the axial direction of the wheel;

a transducer attached to the wheel and including a movable magnet whose position shifts for a distance corresponding to the inflation pressure of the tire in the axial direction of the wheel;

a stationary-side member facing the wheel at a distance therefrom in the axial direction thereof;

a magnetic sensor attached to the stationary-side member, the sensor being situated in a position such that the sensor can detect the magnetism of the reference magnet and the movable magnet when the wheel rotates and adapted to generate outputs of magnitudes corresponding to the minimum distance from the reference magnet and the minimum distance from the movable magnet as the wheel rotates;

computing means for obtaining the tire inflation pressure in accordance with the outputs of the magnetic sensor obtained individually when the reference magnet and the movable magnet pass by the magnetic sensor; and

notifying means for notifying of information relating to the tire inflation pressure obtained by said computing means.

5. A tire inflation pressure monitoring apparatus according to claim 4, wherein said position adjusting mechanism of the reference means includes a bracket fixed to the wheel, a tapped hole formed in the bracket and extending along the axial direction of the wheel, a rod screwed in the tapped hole and fitted with the reference magnet, and locking means for fixing the rod to the bracket.

6. A tire inflation pressure monitoring apparatus according to claim 4, wherein said transducer includes a body fixed to the wheel, a closed air chamber fed with the inflation pressure of the tire, a movable shaft movable in the axial direction of the wheel and urged in a first direction by means of the inflation pressure in the air chamber, the movable magnet attached to the movable shaft, a spring for urging the movable shaft in a second direction opposite to the first direction, a metallic bellows having two opposite ends and capable of extension and contraction in the axial direction of the movable shaft, one and the other ends of the bellows being airtightly connected to the body and the movable shaft, respectively.

7. A tire inflation pressure monitoring apparatus according to claim 4, wherein said computing means includes means for storing a previously obtained computation formula or map indicative of the relationships between the outputs of the magnetic sensor and the minimum distances from the magnets to the magnetic sensor, and means for obtaining data associated with the minimum distances from the magnetic sensor to the magnets according to the computation formula or map on the basis of the outputs obtained by means of the magnetic sensor in detecting the inflation pressure of the tire, and obtaining the tire inflation pressure according to a pressure computation formula or map indicative of the relationship between the tire inflation pressure and the distance between the magnets on the basis of the obtained data.