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Axial flow fan

Axial flow fan description/claims

1. Field of the Invention

The present invention relates to an electric axial flow fan used for sending air.

2. Description of the Related Art

Axial flow fans are conventionally used in electronic devices for sending air to cool heat-generating electronic components so as to suppress temperature rise in the devices. Such an axial flow fan creates an air flow by rotating a plurality of rotor vanes by an electric motor. In order to deal with the increase in the amount of heat generation attendant on the performance improvement of electronic devices, demand is growing for high-speed rotation of such motors.

On the other hand, drive current must be increased in order to rotate the motor at high speeds. This causes increase in the amount of rise in temperature of electronic components on the circuit board or coils of the armature inside the motor, which may affect the performance of the electronic components and the operation of the motor. For high-speed rotation of the motor, a circuit which can suppress heat generation or a circuit for reducing current, such as a current limiting circuit for the motor (a circuit that prevents the current at or above a predetermined current value from passing through the circuit), is provided on the circuit board, for example. In addition, a large locked rotor current (a current that flows through the circuit and coil when the motor is locked) flows at the time of motor lock in the case where the motor is run at a high speed; therefore, also available is the method for reducing current by arranging a lock protection circuit (a circuit that reduces the value of current that flows through the coil by increasing an on-to-off ratio of energization during motor lock time) to reduce the locked rotor current value.

Ever higher output is required for modern axial flow fans in many cases. In conventional axial flow fans, two-phase unipolar driven motors or single-phase bipolar driven motors have mainly been used. With the increase in motor output, three-phase bipolar driven motors have started to be frequently used, and the number of electronic components to be mounted on the circuit board has increased accordingly. Since the three-phase bipolar drive requires a large number of Hall elements and FETs (field effect transistors) to be mounted, the number of electronic components to be mounted inevitably becomes larger than that for the single-phase bipolar drive or the two-phase unipolar drive.

Also, while complex control over motor rotation using e.g. PWM (pulse width modulation) circuits and temperature sensors has conventionally been performed outside the motors, these features are incorporated in the modern motors. For this reason, the number of electronic components to be mounted on the circuit board in the motor becomes large.

Due to these factors, more electronic components are mounted on the circuit board in the motors today than in the conventional motors. With the sizes of the conventional circuit boards, however, it is not possible to ensure sufficient space for mounting electronic components to be necessitated in responding to the future demand, for the mounting space for the electronic components is too small.

An axial flow fan according to a preferred embodiment of the present invention includes a base portion, a circuit board, an armature, an impeller cup portion, a field-generating magnet, a bearing portion, and a plurality of rotor vanes. The base portion is hollow and has an open end at its top end. The circuit board is mounted to axially face the base portion. The armature is disposed above the circuit board. The impeller cup portion is hollow and approximately cylindrical about the central axis, and has an open end at its bottom. The open end of the impeller cup portion faces the open end of the base portion. The field-generating magnet is fixed on the inner side surface of the impeller cup portion for developing torque centered on the central axis, with the armature. The bearing portion supports the impeller cup portion relative to the base portion in a rotatable manner about the central axis. The plurality of rotor vanes radiate from the outer surface of the impeller cup portion, and rotate with the impeller cup portion in a predetermined rotation direction to produce an air flow in an axial direction.

In an axial flow fan according to a preferred embodiment of the present invention, the distance between the central axis and the outer surface of the circuit board is approximately the same as or larger than the distance between the central axis and the outer side surface of a sidewall of the base portion.

In an axial flow fan according to a preferred embodiment of the present invention, a plurality of locking portions may be circumferentially arranged on the top of the sidewall of the base portion, so that the circuit board can be fixed at its outer peripheral edge by these locking portions.

In an axial flow fan according to a preferred embodiment of the present invention, a plurality of stationary vanes may be provided in a radiating manner from the outer surface of the base portion, with each stationary vane slanting in an opposite direction to the rotation direction. The stationary vanes each include projecting portions that project toward the rotor vanes to a higher level than the upper surface of the sidewall of the base portion.

The outer surface of the circuit board has a portion in contact with an enveloping surface that is defined by the inner surfaces of the projecting portions.

With the structure of the axial flow fan according to preferred embodiments of the present invention, the area of the circuit board can be increased, and thus an increased number of electronic components can be mounted thereon.

Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

FIG. 1 is a cross-sectional view of an axial flow fan according to a first preferred embodiment of the present invention.

FIG. 2 is a perspective view of the axial flow fan according to the first preferred embodiment.

• Provisional Patent
• Utility Patent

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