1. Field of the Invention
The present invention relates in general to the field of information handling system cooling, and more particularly to a system and method for information handling system cooling fan operation with reduced audible noise.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems typically give off heat as a byproduct of powering electrical components. Generally, as information handling system components have grown more powerful, the amount of heat given off has increased. In order to remove excess heat, information handling systems generally include cooling subsystems, such as a cooling fan that circulates a cooling airflow through the information handling system chassis. The more powerful components included in information handling systems have led to the use of more and more powerful cooling fans in order to ensure that an adequate cooling airflow is available. The use of more powerful cooling fans generally results in two difficulties for information handling system design: greater power consumption and increased acoustic noise. Generally, to address these difficulties, cooling fan operations are regulated based on internal chassis temperature so that a cooling fan operates at a minimal speed that will keep the internal temperature below a designed maximum level. Nonetheless, cooling fans must still have the capability of providing a minimal level of cooling airflow so that the increasing level of heat provided as a byproduct of information handling system operation has generally required increased capability from cooling fans included in information handling systems.
Generally, brushless DC electric motors are used to turn information handling system cooling fans. Brushless DC electric motors operate in a manner similar to DC electric motors that have brushes except that a microcontroller in a brushless DC electric motor performs the application of current to coils instead of the interaction between the brushes and the coils. Brushless DC electric motors also tend to be more reliable, efficient and quiet that motors that use brushes. A brushless DC electric motor has a permanent magnet formed in a cylindrical shape around a coil and microcontroller assembly. As current is applied to the coils, the magnetic force generated by the coils interacts with the permanent magnet to cause the permanent magnet to turn. A common method for manufacture of the permanent magnet is curl a flat strip of material into a cylinder shape having an axial seam or split where the two ends of the original flat strip meet. For a typical 4-pole motor with two positive poles and 2 negative poles, the magnetic field of the permanent magnet is a sine-like wave. The seam in the permanent magnet where the folded over material meets introduces a discontinuity or disturbance in the magnetic field which, during operation of the motor, can cause an audible tone at the pole-passing frequency and harmonics. Similar audible tones are reduced in motors having a rotor constructed of stacked laminations by skewing the rotor slots, which reduces the cogging torque. However, in order to remove the discontinuity introduced by the seam of a cylindrical magnet, the magnet is typically formed from cylindrical stock instead of sheet stock. This tends to increase the cost of the magnet and, thus, the motor.
Therefore a need has arisen for a system and method which reduces the effect of a DC brushless motor permanent magnet discontinuity on operation of the motor.
In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for providing cooling airflow to an information handling system. A seam formed in a permanent magnet of a brushless DC electric motor is skewed relative to the rotational axis of the permanent magnet to moderate discontinuity introduced by the seam to the magnetic field of a coil.
More specifically, an information handling system has plural processing components to process information and a cooling fan to remove excess heat from the processing components. The cooling fan has a brushless DC electric motor with a cylinder-shaped permanent magnet rotating about coils on a rotational axis. A controller applies current to the coils to create a magnetic field within the cylinder shape that interacts with the permanent magnet to rotate the permanent magnet about the rotational axis. The permanent magnet is formed from a sheet of magnetic material having a parallelogram shape. The parallelogram is curled into the cylinder shape so that opposing sides of the parallelogram meet at a seam. The seam is skewed at the angle of the parallelogram relative to the rotational axis so that discontinuity introduced to the magnetic field of the permanent magnet by the seam is distributed across the magnetic field of the coil as the permanent magnet rotates.
The present invention provides a number of important technical advantages. One example of an important technical advantage is that a brushless DC electric motor operates more quietly by moderating the effect of a discontinuity throughout the rotation of a permanent magnet. Forming the permanent magnet from a sheet of magnetic material so that the seam is skewed or not parallel relative to the rotational axis of the coil offers a moderated effect from the discontinuity of the seam which extends through a predetermined amount of rotation of the magnet without a substantial increase in the cost of the magnet.
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
Information handling system brushless DC electric cooling fan operation has reduced acoustics by skewing a permanent magnet seam from the rotation axis of the permanent magnet. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components.
Referring now to
Referring now to
In order to reduce the effect of the discontinuity introduced by seam 32 on the operation of cooling fan 22, seam 32 is skewed relative to rotation axis 34 so that the effect of the discontinuity is distributed through a portion of the rotation of permanent magnet portion 26. In the example embodiment of
Referring now to
Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.