Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-06-01
2001-12-04
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000, C318S599000, C417S044100
Reexamination Certificate
active
06326748
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-11-161775 filed on Jun. 9, 1999, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brushless motor driven by a DC power source such as a battery, and more particularly to a brushless motor that drives a device mounted on an automotive vehicle such as a fuel pump.
2. Description of Related Art
A brushless motor is composed of a magnet rotor and a stator having a multi-phase armature winding and is driven by sequentially switching power supply to each phase winding of the armature winding. The power supply timing is controlled based on a rotational position of the magnet rotor detected by a rotor position detector such as a hall-effect element or by induction voltage of the armature winding. A rotational speed of the brushless motor (referred to as a motor speed) is dependent on a power source voltage, i.e., the motor speed decreases as the power source voltage decreases. It is therefore desirable to keep the power source voltage constant to drive the brushless motor at a constant speed.
However, when the power source is an on-board battery, its voltage varies according to various conditions. For example, the battery voltage decreases when the battery is exhausted, and especially it considerably drops when a stator motor is operated. If the motor speed decreases due to the battery voltage drop, a required power cannot be obtained from the motor. To cope with this problem, JP-B2-2560855 proposes to use a voltage stabilizer or a pulse-width modulation control circuit. Such a device, however, is costly and does not meet a cost level required.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved brushless motor in which the rotational speed decrease due to the battery voltage decrease is alleviated in a cost effective manner.
The brushless motor is composed of a cylindrical stator having a multi-phase armature winding and a rotor having plural permanent magnet poles. A drive-control circuit having switching elements is connected between a DC power source such as a battery and the armature winding. Electric current is supplied to the armature winding from the battery through the drive-control circuit. The switching elements in the drive-control circuit are sequentially and selectively turned on and off to generate a rotating magnetic field in the stator. The switch-timing of the switching elements is determined based on a rotational position of the rotor and a battery voltage detected by a voltage detector.
When the battery voltage is normal, i.e., the battery voltage is higher than a predetermined level, the switch-timing is set to an optimum point so that an efficiency of the brushless motor becomes maximum. On the other hand, when the battery voltage drops, i.e., the battery voltage becomes lower than the predetermined level, the switch-timing is advanced to secure a required rotational speed of the brushless motor. The amount of switch-timing advance may be a fixed amount or an amount determined according to the detected battery voltage.
Preferably, the multi-phase armature winding of the stator is connected in a star-connection forming a neutral point. The rotor position is detected based on a voltage induced in a phase winding to which current is not supplied, the induced voltage being determined from a voltage at the neutral point. The brushless motor may be integrated with a fuel pump for supplying fuel to an internal combustion engine to provide a compact fuel pump assembly.
According to the present invention, a required motor speed is secured even when the battery voltage becomes low by advancing the switch-timing of the switching elements, without using an additional voltage stabilezer or a pulse-width modulating controller. Moreover, the brushless motor can be operated with the highest efficiency when the battery voltage is normal.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.
REFERENCES:
patent: 4403177 (1983-09-01), Weber et al.
patent: 4740734 (1988-04-01), Takeuchi et al.
patent: 4950968 (1990-08-01), Ogura
patent: 4955790 (1990-09-01), Nakanishi et al.
patent: 5115174 (1992-05-01), Masuda et al.
patent: A-57-25196 (1982-02-01), None
patent: B2-2560855 (1996-09-01), None
Ito Motoya
Moroto Kiyonori
Dang Khanh
Denso Corporation
Nixon & Vanderhye P.C.
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