Abstract:
A motor is disclosed that has the capability of detecting the rotary motion of the motor and to generate electrical signals that are indicative of the speed of operation of the motor. The motor has a magnet that is embedded within the molded resin of the commutator or other parts of an armature and a Hall effect sensor is positioned in close proximity to the rotating magnet to thereby provide an electrical signal that is proportional to the rotating speed of the motor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to electrical motors and more particularly to a motor having the capability to detect its rotational movement. 
     Electric motors are primarily used to drive fans for engine cooling systems in motor vehicles at the present time and most modem vehicles have a sophisticated in-board engine control unit microprocessor (ECU) that is used to monitor and control the operation of the motor vehicle engine. With the increased sophistication in the operation and control of motor vehicles, it is very desirable to provide an input signal that is indicative of the speed of operation of an engine cooling fan to the ECU so that a diagnostic monitoring and control can be accomplished. The speed of an engine cooling fan can be determinative of an overload condition that may cause a stall of the cooling fan that in turn can cause damage to the cooling fan motor. Such an overload condition can be caused by any number of outside agencies, such as ice or snow pack, or a stick or other debris interfering with the rotation of the fan. It is therefore desirable to monitor the speed of operation of the engine cooling fan in a reliable manner that is not detrimentally affected by large temperature variations. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the present invention to provide an improved motor that has rotational movement detection capability that is easily implemented, inexpensive and reliable in its operation 
     A corollary object lies in the provision of the apparatus not requiring any appreciable redesign of motor components or significant changes in the manufacturing process of such motors. 
     Another object is to provide such an improved motor that utilizes a small unobtrusive magnet that can be placed at various locations on the armature assembly, including the commutator of the motor without affecting the design of the armature or other components of the motor. The motor also includes a sensor that can be easily installed on the brush card that is installed within the housing of the motor near the commutator thereof. 
     Still another object of the present invention lies in the provision of using a conventional Hall effect sensor that is attached to the brush card and which can be positioned in close proximity to a magnet installed on the armature at one of various locations and which is adapted to produce a single pulse per revolution that can be forwarded to the ECU indicating the speed of operation of the fan. 
     Another object of the present invention lies in the provision for setting the small magnet in the resin during the resin molding process of the commutator. 
     These and other objects will become apparent upon reading the following detailed description, while referring to the attached drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view with portions cut away of an electric motor with the magnet embedded in the resin compound of the commutator and a stationary sensor attached to the motor brush card in accordance with the preferred embodiment of the present invention; 
     FIG. 2 is a side view with portions cut away of an electric motor showing the location of the magnet located inside a plastic ring located between the commutator and the armature core; 
     FIG. 3 is a side view with portions cut away of an electric motor showing the location of a magnet attached to the armature winding with a sensor being attached to the brush card; and, 
     FIG. 4 is a partial front view of an engine cooling fan system showing placement of sensor on the fan or guide housing or shroud and the magnet attached to the fan band. 
    
    
     DETAILED DESCRIPTION 
     Broadly stated, the present invention is directed to a motor having the capability for sensing rotary movement, with the motor being of the type which is used in driving an engine cooling fan or the like. The motor is adapted to generate an electrical signal that is indicative of its rotational speed of the motor during operation and such signal can be forwarded to the vehicle&#39;s ECU for diagnostic purposes. The motor preferably includes a small magnet which, in several embodiments, is mounted at various locations within the armature and a Hall sensor device which is preferably mounted to and carried by the brush card of the motor. During operation, the movement of the magnet past the Hall effect sensor is sensed by the Hall effect sensor and produces a pulse during every revolution of the motor and this pulse is communicated to an in-board microprocessor or engine control unit (ECU) which can then be used to provide diagnostic or status information of the operation of the engine cooling fan. Such information can then be used to determine if the system is operating properly or if an overload or other fault condition exists which can be used to create alarms and the like so that damage to the fan motor and other components can be prevented. 
     Turning now to the drawings and particularly FIG. 1, a fan motor is shown generally at  10  and includes an armature, indicated generally at  12 , that comprises a lamination core stack  14  and windings  16  which are connected to a commutator  18  through winding portions  20 . The commutator  18  is generally cylindrical and has a resin molded portion  22  that is molded during the manufacturing process and is fitted over a shaft  24 . The commutator  18  has an outer cylindrical sheath that is preferably made of copper. The inside of the cylindrical sheath is filled with resin during a molding process, and the copper cylinder is then cut into a plurality of bars  26  that are oriented in a direction that is parallel to the axis of the shaft. Lower portions of the commutator bars are bent back to form tangs  28  that loop around the winding portions  20  so as to electrically and mechanically attach them to the individual bars, of which there are preferably  16 . It should be understood that the construction of the commutator, in and of itself, is not a part of the present invention and is of conventional construction. 
     When the resin is molded to the commutator, a small magnet  30  is placed in the commutator preferably slightly below the bottom of the tangs  28  as shown in FIG.  1 . By locating the magnet during the molding process at a location that is nearer the laminated core stack  14 , it is physically distanced away from the commutator bars where the most heat is produced due to the physical contact of the brushes with the commutator bars. This can result in more reliable operation through a greater temperature range which may extend from approximately −40° C. to approximately +150° C. 
     It should also be understood that the position of the magnet  30  maybe raised to a position near the top of the commutator and in such position would be coextensive with, but inside of or behind the bars  26 . It is preferred that the magnet be relatively small and lightweight, and it has been found that a magnet having dimensions of approximately 8 mm×6 mm×3-½ mm is sufficient to enable in a Hall effect sensor to sense the magnet and generate a pulse, which is shown at  32  as being connected to a brush card  34 . The brush card is a part, preferably made of plastic or the like, which carries the commutator brushes and provides an electrical path to side harnesses that are connected to a power source for powering the motor. The sensor  32  is a Hall effect sensor that is adapted to generate a pulse whenever the magnet comes in close proximity to it during rotation of the commutator  18 . The entire construction of the motor is located within a motor enclosure or case  36  in which stator magnets  38  are located. 
     In an alternative embodiment and referring to FIG. 2, a magnet  40  may be embedded in a resin ring that is preferably fit onto the shaft  24  slightly above the laminated stack  14  and below the commutator  18 . A Hall effect sensor  32  is again provided and is carried by and mounted to the brush card  34 . In another embodiment and referring to FIG. 3, a magnet  41  may be attached to one of the windings  16  and a second magnet or weight balancing object  42  may be provided at the opposite winding from the magnet  41  so that rotational vibration that may otherwise be experienced can be minimized. The sensor  32  is again carried by and connected to the brush card  34 . 
     In yet another embodiment and referring to FIG. 4, the magnet  20  may be connected to a band  44  of a fan construction having a hub  46 , a circular center portion  48  that is attached to blades  50 , and the sensor  34  may be connected to a fan air guide housing portion  52 . In another embodiment that is not shown, the magnet may be placed on the underside of the fan at approximate location  54  on the portion  48  near the hub  46 , and the sensor  32  can be located on the brush card of the motor. 
     From the foregoing, it should be understood that a motor having the capability for detecting rotation of a motor has been shown and described which has many desirable attributes. The detection capability involves only a few parts, is easily incorporated into the manufacture of the motor, provides reliable operation and is inexpensive. Because the magnet and sensor are located within the housing  36  of the motor, except for those embodiments shown in FIG. 4, neither component is directly exposed to outside elements and is reliable in its operation over an extended temperature range. 
     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims. 
     Various features of the invention are set forth in the appended claims.