Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1999-11-18
2001-10-23
Martin, David S. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S286000, C388S907200
Reexamination Certificate
active
06307337
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dc motor assembly and, more particularly, to a compact and efficient brushless dc motor assembly.
BACKGROUND OF THE INVENTION
Permanent magnet brushless dc motors are widely used in a variety of applications due to their simplicity of design, high efficiency, and low noise. These motors operate by electronic commutation of stator windings rather than the conventional mechanical commutation accomplished by the pressing engagement of brushes against a rotating commutator. To achieve electronic commutation, brushless dc motor designs usually include an electronic controller for controlling the excitation of the stator winding(s). Advantageously, electronic commutation allows for specific, user-controlled motor operating characteristics.
Given the relative simplicity of design for permanent magnet brushless dc motors, however, prior art designs have failed to satisfactorily achieve a reliable design which may be produced at a minimized cost. For example, prior art brushless dc motor designs generally control motor operating characteristics using relatively complicated microprocessor-based electronics. Incorporation of a microprocessor into the control board is expensive and time-consuming from a production standpoint. In addition, the more components that are incorporated into the control electronics, the more likely it is that operational malfunctions will occur as a result of damaged or improperly installed electronics.
Also, elaborate mounting mechanisms have been developed in the prior art for mounting hall effect sensors adjacent the rotor to sense rotor rotational position. The hall effect sensors are typically connected to the control board via separate wires to provide a feedback signal for controlling motor operation through the electronics. Typically, the electronics are also mounted to the assembly using a separate bracket or other mechanism which further complicates and adds costs to the production process.
Accordingly, there is a long-felt need in the art for a brushless dc motor which is capable of achieving user-controlled operating characteristics, and which is efficient, compact, and cost-effective.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention is to provide a brushless dc motor having control electronics for allowing variable speed, user-controlled motor operation in an efficient, cost-effective, and reliable design.
Yet another object of the invention is to provide a permanent magnet, brushless dc motor having control electronics mounted to a control board, wherein the control board is secured directly to a bearing bracket of the motor for eliminating cumbersome manufacturing steps and reducing the size of the motor assembly.
Yet another object of the invention is to provide a permanent magnet, brushless dc motor having control electronics mounted to a control board which is secured directly to a bearing bracket of the motor, wherein hall devices are mounted directly to the control board in a position adjacent the rotor to eliminate the need for a separate mounting mechanism for the hall devices and reduce the size of the motor assembly.
Another object of the present invention is to provide a reliable and efficient brushless dc motor which may be efficiently manufactured, thereby reducing the consumer cost of such motors.
These and other objects of the present invention will become apparent from a review of the description provided below.
SUMMARY OF THE INVENTION
The present invention is organized about the concept of providing an efficient, reliable brushless dc motor which is of a simple and cost-efficient design. The motor includes control electronics for allowing variable speed, user-controlled motor operation. The control electronics are connected to a control board which is mounted directly to the motor bearing bracket. Hall devices for providing rotor rotational position information to the electronics are connected directly to the control board and extend therefrom to a position adjacent the rotor.
Specifically, the brushless dc motor of the present invention includes: a stator assembly having a stator winding thereon and a rotor opening formed therein; and a control board having control electronics connected thereto for receiving an electrical input and establishing current in the stator winding for generating a rotating magnetic field in the stator assembly. A rotor assembly of the motor has a rotor shaft, a rotor core fixed to the rotor shaft, and first and second bearings secured to the rotor shaft on opposite sides of the rotor core. The rotor core is disposed at least partially within the rotor opening in the stator with the first and second bearings positioned on opposite sides of the stator assembly.
A bearing bracket assembly secures the rotor in position relative the stator assembly, provides bearing surfaces for the bearings, and provides means for mounting the control board. The bearing bracket assembly includes a first bearing bracket for receiving the first bearing and a second bearing bracket for receiving the second bearing. The first and second bearing brackets each have at least one bore formed therein which aligns with a corresponding bore formed through the stator assembly. At least one fastener passes through the at least one bore in the first bearing bracket, the corresponding bore in the stator assembly, and the at least one bore in the second bearing bracket. The fastener thereby secures the first and second bearing brackets to the stator assembly with the first and second bearings received at least partially within the first and second bearing brackets, respectively.
The control board has at least one bore therein which aligns with the at least one bore in the second bearing bracket. Advantageously, the fastener extends through the second bearing bracket and through the at least one bore in the control board for securing the control board to the bearing bracket assembly. With this construction, the control board may be efficiently assembled to the motor assembly without the need for a separate mounting bracket or other mechanism.
Also, the control electronics include at least one hall effect device, and preferably two hall effect devices. The hall effect device has leads connected (soldered) directly to the control board and a sensor portion for establishing an output on at least one of the leads which is representative of a rotational position of the rotor core. Advantageously, no separate mounting mechanism for the hall effect device(s) is necessary since the hall device(s) extends directly from the control board toward the rotor core so that the sensor portion is positioned adjacent the rotor core. Where two hall effect devices are used, as in the preferred embodiment, they are secured to the control board so that the sensor portions thereof are positioned adjacent the rotor core at approximately 180 degrees apart relative to the circumference of the rotor opening.
In the preferred embodiment, production efficiency is also achieved by forming the rotor-core as a single-piece, permanent magnet. Preferably, the rotor core is cylindrical with a central bore formed therein. The rotor core is secured to the shaft with the shaft extending through the central bore. Also, in the preferred embodiment, operating efficiency is achieved by forming a pair of radially inward extending teeth on an inner surface of the rotor opening at approximately 180 degrees apart. The teeth form magnetic poles on the stator which provide starting orientation of the permanent magnet rotor assembly relative to the hall effect devices and cause a magnetic attraction during motor operation.
Also, in the preferred embodiment, the motor assembly is formed as a C-frame motor having a C-frame portion, an I-bar portion, and a bobbin around which the stator winding is formed. The I-bar portion extends through a central opening in the bobbin and is secured to the C-frame portion to complete the stator assembly. Although a C-frame motor construction is preferred, the features a
Andrus Sceales Starke & Sawall LLP
Fasco Industries, Inc.
Martin David S.
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