1. Field of the Invention
The present invention relates to a motor for driving a blower fan that is used, for example, for driving to rotate a blower fan of a car air conditioner which air-conditions the inside of the car.
2. Description of the Related Art
A car air conditioner comprises a blower fan disposed on the upstream end of a duct that is mounted with an evaporator for cooling air and a heater core for heating the same. The car air conditioner conditions air, which is taken in from the inside of a car or the outside of the car through an intake provided on the upstream end of the duct, to be a predetermined temperature by means of at least one of the evaporator and heater core, and then blows the air into the car.
A centrifugal multiblade fan is generally used as the abovedescribed blower fan, and the centrifugal multiblade fan is driven to rotate by a motor. Such a motor for driving a blower fan generally comprises a case body cylindrically formed of an iron based magnetic material and a pair of stators (permanent magnets) are supported and fixed at two positions on opposite sides in the diametrical direction of the middle portion in the axial direction of the inner circumferential surface of the case body. In addition, a rear end plate is bound and fixed on a rear end opening portion of the case body and a front end plate is bound and fixed on a front end opening portion of the same.
Then, a rotary drive shaft is inserted into the central portion of the case body and the rear end portion of the rotary drive shaft is supported on the rear end plate and the forward middle portion thereof is supported on the front end plate to be rotated freely by means of a bearing, respectively. A rotor is fixed at a portion opposed to the inner circumferential surfaces of the pair of stators of the middle portion of the rotary drive shaft, and a commutator for conducting a current to said rotor is fixed at a portion apart from the rotor of the same. Also, a brush is supported on a portion opposed to the outer circumferential surface of the commutator of the inside the case body so as to be freely displaced in the diametrical direction of the commutator. Then, the inner end face of the brush is elastically urged to the outer circumferential surface of the commutator.
The blower fan is fixed on the portion projected from the front of the front end plate of the front end portion of the rotary drive shaft. When the motor of the blower fan comprised as mentioned above is incorporated in a car air conditioner, the motor excluding its front end portion is stored and supported in a cylindrical attachable bracket with a bottom made of a synthetic resin. Then, the attachable bracket is fixed on the outer wall of the upstream end portion of the duct by means of an attaching flange provided on the outer circumferential surface of the middle portion.
When the car air conditioner is used, by conducting a current through the brush and commutator to the rotor, the blower fan is driven to rotate via the rotary drive shaft. As a result, air for air harmonization flows from the upstream end opening of the duct toward the downstream end opening. Herein, a part of the air is sent into the attachable bracket through an air-supply hose connected to the attachable bracket and sent further into the case body. Then, the air flows from the rear end side to the front end side in the case body, cools components of the motor for driving a blower fan, and is then discharged outside the motor via an exhaust hole provided on the front end plate. Thereafter, the air joins air sent from the upstream end opening of the duct and flows in said duct toward the downstream end opening.
The rotor composing the motor for driving a blower fan is formed by winding coils, respectively, around slots provided at a plurality of spots (for example, six spots) in the circumferential direction of the outer circumferential surface of a core made of laminated steel plates. Then, the rotary drive shaft is rotated by a magnetic suction and magnetic repulsive force which occur between magnetic fields that occur around each coil by conduction of a current to each coil and magnetic fields that exist at the portion of the pair of stators. Herein, since the coils are provided intermittently in the circumferential direction of the rotor, the magnetic suction and magnetic repulsive force are increase and decrease according to the rotation of the rotor. However, said rotor and the rotary drive shaft continue to rotate at an almost uniform speed due to the inertia of the rotor and rotary drive shaft.
However, in the motor for driving a blower fan which is structured and effects as mentioned above, according to the rotation of the rotary drive shaft, the magnetic suction and magnetic repulsive force alternately effect respective portions of each stator in terms of the diametrical direction of the case body. Therefore, each stator vibrates in the diametrical direction of the case body and the case body having the stators fixed on the inner circumferential surface thereof vibrates similarly. Such vibration of the case body is transmitted to the duct via the attachable bracket and there arises a possibility that noise in the car caused by the duct vibration becomes so loud as to make a driver uncomfortable. In order to prevent the noise that occurs due to such causes, suppression of the vibration of the case body by increasing the thickness of the whole plate members composing the case body can be considered. However, such a measure causes a substantially increased weight and cost of the motor for driving a blower fan, and hence is not preferable.