Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
1997-07-10
2001-02-06
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S207250, C310S049540, C310S168000
Reexamination Certificate
active
06184678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in a rotor to be used in combination with a wheel speed sensor which forms part of an anti-lock brake system or a traction control system for an automotive vehicle, and more particularly to the improvements in the structure of the rotor to raise a detection precision of the rotational speed of a road wheel of an automotive vehicle.
2. Description of the Prior Art
An anti-lock brake system (ABS) for an automotive vehicle includes a wheel speed detecting device for detecting rotational speeds of a road wheel. The wheel speed detecting device includes a ring-shaped rotor which is press-fitted around a hub at the side of an axle shaft on which the road wheel is mounted. A wheel speed sensor is disposed facing the rotor, in which magnetic field is developed around the wheel speed sensor and extends throughout the thickness of the rotor. The rotor is formed with a plurality of holes which are aligned at equal intervals in the peripheral direction thereof, so that the peripheral surface of the rotor is formed uneven to take a generally gear shape,. When the uneven peripheral surface of the rotor traverses the magnetic field from the wheel speed sensor, the magnetic flux density is changed so as to develop an electromotive force at the coil of the wheel speed sensor, thereby causing a change in voltage. This voltage change is output as an wheel speed signal to a ABS control unit for effecting an anti-lock brake to the road wheel.
A variety of shapes of the rotors have been proposed and put into practical use. One of them is formed of a ring-shaped sheet metal strip having a plurality of generally rectangular holes which are formed by being punched out. Another one is formed by cutting gear on the peripheral portion of a ring-shaped member. A further one is disclosed in Japanese Utility Model Provisional Publication No. 6-37766 and has a generally ]-shaped cross-section so as to include inner and outer flange sections each of which is formed with a plurality of holes which are formed by punching out each flange section. A still further one is disclosed in Japanese Patent Publication No. 6-14058 and formed by fitting inner and outer rings to each other in which the outer ring is generally comb-shaped. Of these rotors, one produced by punching out the sheet metal strip to form the generally rectangular holes seems to be the most advantageous form the view points of production cost lowering and weight-lightening.
However, drawbacks have been encountered in such a conventional rotor which is produced by punching out the sheet metal strip to form the generally rectangular holes. That is, it is usual that the width dimension of the rotor is generally equal to or slightly smaller than the width dimension of the sensor head section of the wheel speed sensor since the width dimension of the sensor head is usually restricted in connection with the locational relationship between it and other parts around the wheel speed sensor device. Under such a situation, when each hole of the rotor passes by the sensor head section, flat parts located at the opposite sides of each hole simultaneously pass by the sensor head section. As a result, the difference in magnetic flux density or output voltage in the wheel speed sensor is small between a time when the hole with the flat parts pass by the sensor head section and another time when each axially extending flat section located between the adjacent holes passes by the sensor head section. As a result, precision of detection for rotational speed of the road wheel has been unavoidably suppressed at a relatively low level.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved rotor for a wheel speed sensor, which can effectively overcome drawbacks encountered in conventional rotors to be used in combination of a wheel speed sensor.
Another object of the present invention is to provide an improved rotor for a wheel speed sensor, which is high in detection precision of wheel speed as compared with the conventional rotors.
A further object of the present invention is to provide an improved rotor for a wheel speed sensor, by which a difference in magnetic flux density or output voltage becomes large between a time when each hole in the rotor passes by a sensor head section of the wheel speed sensor and a time when a part other than the holes passes by the sensor head section even in case the width dimension of the rotor is restricted relative to the width dimension of the sensor head section, as compared with the conventional rotors.
An aspect of the present invention resides in a rotor to be used in combination with a wheel speed sensor. The rotor comprises an annular axial central section formed of a magnetic material. First and second annular axial end sections are coaxial and integral with the central section. The first and second annular axial end sections are formed of the magnetic material and arranged such that the annular axial central section is located between the first and second annular axial end sections. A plurality of holes are formed in the annular axial central section. The holes are arranged at equal intervals in the peripheral direction of the annular central section. Additionally, first and second depressed surfaces are located radially inward of a radially outward surface of the annular axial central section. The first and second depressed surfaces are respectively formed in the first and second axial end sections and contiguous with each hole.
Another aspect of the present invention resides in a rotor to be used in combination with a wheel speed sensor. The rotor comprises an annular axial central section formed of a magnetic material. First and second annular axial end sections are coaxial and integral with the central section. The first and second annular axial end sections are formed of the magnetic material and arranged such that the annular axial central section is located between the first and second annular axial end sections. A plurality of holes are formed in the annular axial central section. The holes are arranged at equal intervals in the peripheral direction of the annular axial central section. A plurality of first and second depressions are respectively formed in the first and second axial end sections. A pair of the first and second depressions are respectively located opposite to each other and connected with each hole.
According to this aspect, by virtue of the depressions formed in each of the opposite annular axial end sections, the gap between each end section and the sensor head section is large similarly to the gap between each hole and the sensor head section when each hole passes by the sensor head section in case that the width dimension of the rotor is generally equal to or smaller than that of the sensor head section, so that each depression at the end section substantially functions like each hole. As a result, the difference in magnetic flux density or output voltage becomes larger between a time when each hole passes by the sensor head section and a time when a part other than the holes passes by the sensor head section, than that in case of using conventional rotors. This largely improves a detection precision of the wheel speed. As a matter of course, a further larger difference in output voltage can be obtained in case that the width dimension of the rotor is larger than that of the sensor head section.
A further aspect of the present invention resides in a rotor to be used in combination with a wheel speed sensor. The rotor comprises a rotor main body formed of a sheet made of a magnetic material. The rotor main body is arranged as follows: An annular axial central section is projected radially outwardly. First and second annular axial end sections are coaxial and integral with the central section. The first and second annular axial end sections are formed of the magnetic material and arranged such that the annular axial central section is located between the first an
Hayasaka Masanobu
Kumamoto Yukio
Nagami Ikuo
Suzuki Masayuki
McDermott & Will & Emery
Nissan Motor Co,. Ltd.
Snow Walter E.
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