Abstract:
An electric motor  10  includes a motor housing  12  defining an internal cavity  15.  A brush card assembly  24 , a commutator  26  and an armature assembly  18  are provided in the cavity  15.  The commutator  26  cooperates with the brush card assembly  24  to resupply electric current to the armature assembly  18.  Permanent magnet structure  44  is provided in the housing  12  to generate a magnetic field to cause rotation of the armature assembly  18.  A FET  52  is mounted with respect to the housing  16  so as to be in heat exchange relation therewith. A gate terminal G of the FET is constructed and arranged to receive pulse width modulation output from an electronic control unit  64  which is remote from the motor so as to enable able the motor to operate at more than one speed. A method of integrating a FET in a motor is also provided.

Description:
This invention is based on and claims the benefit of U.S. Provisional Application No. 60/134,654, filed on May 18, 1999, and U.S. Provisional Application No. 60/164,160, filed on Nov. 8, 1999, and U.S. Provisional Patent Application No. 60/183,914 filed Feb. 22, 2000 the content of which is incorporated into the present specification by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to electric motors for automobile applications and, more particularly, to permanent magnet, brush-type, direct current motors which utilize pulse width modulation for speed control. 
     A significant challenge of permanent magnet, brush-type, direct current motors is to achieve different speeds of operation. Wound field-type motors generally can have speed controlled by altering the field flux. This is done by changing the current or the number of coil turns in the field winding. Since permanent magnet motors have a constant field flux, they cannot achieve speed control by field flux variation. 
     Often, permanent magnet motors used in automotive applications require the use of more than one speed, usually requiring a lower speed for general purpose operation and a maximum speed for worst case operation. Typically, multiple speeds have been achieved in permanent magnet motors by adding a resistor in series with the motor, switching out brushes (lap wound motor), adding a third brush (short-out coils) or using external electronic control such as analog devices or pulse width modulation. 
     U.S. Pat. No. 5,119,466 uses pulse width modulation to control the speed of a permanent magnet dc motor. A speed control circuit is carried by a circuit board disposed within the motor. The circuit board includes a motor control signal converter which receives a motor control signal from a vehicles electronic control unit (ECU) and sends a pulse width modulated signal to a field effect transistor (FET), which is also mounted on the circuit board and joined to a projection of the case of the motor. However, the requirement of the circuit board having a signal converter and FET mounted thereon increases the motor cost and the dissipation of heat created by the FET can be improved. 
     Another known arrangement provides a FET in a separate housing for modulating power to the motor based on a PWM signal from the ECU. However, this arrangement introduces another component mounted in an already crowded engine compartment. 
     Accordingly, there is a need to provide a direct current permanent magnet motor which utilizes pulse width modulation for speed control and has a metal oxide semiconductor FET (MOSFET) integrated therewith, without requiring a speed control circuit board within the motor. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing an electric motor including a motor housing defining an internal cavity. A brush card assembly, a commutator and an armature assembly are provided in the cavity. The commutator cooperates with the brush card assembly to supply electric current to the armature assembly. Permanent magnet structure is provided in the housing to generate a magnetic field to cause rotation of the armature assembly. A FET is mounted with respect to the housing and the FET has a gate terminal constructed and arranged to receive a pulse width modulated output directly from an electronic control unit which is remote from the motor so as to enable able the motor to operate at more than one speed. 
     In accordance with another aspect of the invention, a method of controlling speed of an electric motor is provided. The motor comprises a motor housing defining an internal cavity. A brush card assembly, a commutator and an armature assembly is provided in the cavity. The commutator cooperates with the brush card assembly to supply electric current to the armature assembly. Permanent magnet structure is provided in the housing to generate a magnetic field to cause rotation of the armature assembly. A FET is mounted with respect to the housing so as to be in heat exchange relation therewith. The method includes connecting a drain terminal of the FET to a negative lead of the brush card assembly. A source terminal of the FET is connected to a ground terminal or a negative terminal of the motor. A gate terminal of the FET is connected to a pulse width modulated output of an electronic control unit which is remote from the motor. A pulse width modulated signal is sent directly from the electronic control unit to the FET to control a speed of the motor. 
     In accordance with yet another aspect of the invention, a method of integrating a FET into a motor includes: providing a direct current motor comprising a motor housing defining an internal cavity; a brush card assembly, a commutator and an armature assembly being disposed in the cavity. The commutator cooperates with the brush card assembly to supply electric current to the armature assembly. Permanent magnet structure in the housing generates a magnetic field to cause rotation of the armature assembly. A connector structure is connected to the motor. The connector structure has a mounting surface. Spring structure is associated with the mounting surface. The FET is placed on the spring structure such that the spring structure is disposed between a surface of the FET and the mounting surface. The FET is electrically connected to the motor. An end cap is secured to the motor to close the cavity, with the spring structure forcing a surface of the FET into contact with a surface of the end cap such that heat generated by the FET is transferred directly to the end cap. 
     Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described in greater detail herein below with reference to the drawings wherein: 
     FIG. 1 is a side cross-sectional view of an electric motor having a MOSFET mounted on an end cap in accordance with the principles of the present invention; 
     FIG. 2 is a schematic illustration of a circuit of the motor of FIG. 1 shown electrically coupled to an electronic control unit of a vehicle; 
     FIG. 3 is a schematic view of an end cap of a motor of the invention showing a MOSFET coupled thereto; 
     FIG. 4 is a end view of a motor of a second embodiment of the invention showing connector structure with integrated MOSFET; 
     FIG. 5 is an enlarged view of the connector structure of FIG. 4; and 
     FIG. 6 is a side view, partially in section, of the motor of FIG.  4 . 
     FIG. 7 is a end view of a motor of a third embodiment of the invention showing a heat sink with integrated MOSFET; and 
     FIG. 8 is a side view, partially in section, of the motor of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In general, the electric motor of the present invention may be adapted for a number of different automotive applications including heat, ventilation, air conditioning systems, radiator engine cooling fans, etc. 
     Referring now in detail to the drawings wherein like numerals identify similar or like elements through the several views, FIG. 1 illustrates an electric motor, generally indicated at  10 , provided in accordance with principles of the present invention. 
     The motor  10  includes a housing  12  defining an internal cavity  14  and having open end  15 . An end cap  16  of the housing  12  is mounted to the rear end of the housing  12  to close the open end  15 . An armature assembly, generally indicated at  18 , is supported for rotational movement within the housing  12  by front and rear bearing structures  20  and  22 . Motor  10  further includes a brush card assembly, generally indicated at  24 , mounted adjacent to the end cap  16 , and a commutator  26  which cooperates with the brush card assembly  24  to supply electric current to the armature assembly  18 . A mounting flange  28  is coupled to the housing  12  for mounting the motor  10  to a supporting portion of a vehicle. The end cap  16  includes a cut-out portion  30  which corresponds with the housing  12  to accommodate an electrical connector  32 . 
     With reference to FIG. 1, the armature assembly  18  includes a shaft  34  and an armature  36  mounted about the shaft  34 . The shaft  34  consists of shaft end sections  38  and  40 , supported by bearing structures  20  and  22 , and an intermediate shaft section  42 . Armature  36  may be any conventional armature and consists of an armature core having a number of stacked laminations with insulation-coated wire windings wound thereabout. The laminations may he treated with inductive heating if desired. Armature  36  is coaxially mounted about shaft  34 . A mounting plate (not shown) may be provided for structural connection of the armature core and windings to the intermediate shaft section  42 . Armature  36  is in electrical contact with commutator  26  and rotates in response to a magnetic field generated by permanent magnets  44  mounted within housing  12 . Armature  36  may be axially centered relative to the magnets  44  or may be off-center with respect to the magnets  44  whereby the armature  36  is pre-loaded to one side. 
     The brush card assembly  24  includes a brush support member  46  having a pair of mounting posts  48  extending therefrom. The brush support member  46 , preferably made of plastic, is coupled to the end cap  16 . A brush assembly  50  is carried by a respective mounting post  48 . In the illustrated embodiment, each brush assembly  50  includes a brush positioned to be in contact with the commutator  26  in the conventional manner. 
     In accordance with the invention and with reference to FIGS. 1 and 3, a heat transfer surface of a MOSFET  52  is mounted directly to the end cap  16  or other housing portion of the motor which is disposed substantially transverse with respect to a rotational axis of the armature assembly  18 . In the embodiment of FIG. 1, the MOSFET  52  is mounted to the outside surface of the end cap  16 . A pop-rivet  54  is used to secure the MOSFET  52  to the end cap  16 . Alternatively, the MOSFET  52  can be mounted via a screws, a clip and/or with adhesive. Preferably, a thermal compound  53  is provided between the MOSFET  52  and the end cap  16 , to promote heat transfer from the MOSFET  52  to the end cap  16 . 
     As seen in FIGS. 2 and 3, the negative motor lead  55  is secured to the metal end cap  16 . Only three lead wires stem from the motor  10 : positive lead  56 , negative lead  55  and control signal lead  60 . The MOSFET drain terminal D is connected to the negative brush card assembly lead of the motor  10  via a lead wire  62 . The MOSFET source terminal S is connected to ground or the negative motor terminal. The MOSFET gate terminal G is connected to a PWM output from the vehicle&#39;s ECU  64 . The ECU  64  is constructed and arranged to generate a varying PWM signal based on the load requirement of the motor which is sent directly to the gate terminal G. This allows not only two speed motor operation, but a multiple of motor speed operations are available. 
     With reference to FIG. 3, a zener diode  66  is provided between the gate G and drain D of the MOSFET  52  to protect the MOSFET from over-voltage transients when the MOSFET is switched under a heavy load. A resistor R is provided in series with the MOSFET gate G to protect the ECU output stage from failure due to rapid charging and discharging of the MOSFET gate G. A free-wheeling diode  68  is provided between the positive and negative terminals of the motor  10 . The zener diode  66 , resistor R and free-wheeling diode  68  can be mounted on the brush card assembly  24  of the motor  10 , or provided in a separate connector structure as will be described with regard to a second embodiment of the invention. It can be appreciated that no relays or switches are required since the MOSFET acts as the switch applying current to the motor windings based on the PWM signal received. 
     The motor  10  can be controlled by a low frequency PWM signal (50 to 400 HZ typical). The switching frequency, however, is not limited to lower frequencies. If the control circuitry and the heatsinking of the MOSFET are modified, higher frequencies could be used. 
     The low frequency PWM signal can be delivered to the motor using the output of the ECU or, if full speed operation of the motor is desired, the speed input to the motor can be achieved using temperature and/or temperature sensors. 
     The low frequency PWM signal can be modulated in such a manner to avoid mechanical resonance. For example, if the fundamental PWM frequency is 50 Hz, the PWM frequency can be modulated 5 Hz on either side of 50 Hz in a random, or pseudo random fashion. 
     For starting conditions, a soft feature can be implemented by ramping up the PWM duty cycle from 0% to the desired PWM duty cycle. In order to ensure a gradual increase in current through the switching device, a capacitor C (FIG. 2) can be connected from the gate of the MOSFET to ground. The capacitor, in addition to the series resistor R, acts as a low pass filter in series with the MOSFET gate G. If the PWM frequency is high enough, the linear increase in the MOSFET gate voltage would result in a gradual increase in the MOSFET drain current. This increase in the MOSFET drain current would occur until the motor back EMF is built-up to the desired running speed, at which point the motor switches to a lower frequency PWM signal to control the speed of the motor. 
     A second embodiment of the invention is shown in FIGS. 4-6 which enables the assembly of the MOSFET  52  with respect to the end cap  16  to be made easily. The motor  10 ′ of the second embodiment of the invention includes a commutator, armature, and permanent magnets in the manner disclosed with regard to the motor of FIG.  1 . Thus, these components are not shown in FIGS. 4-6. With reference to FIGS. 4 and 6, the motor  10 ′ includes connector structure  70  disposed within end cap  16  and coupled to the brush card assembly  24  via tab  72 . In the broadest aspect of the invention, the connector structure  70  may be considered to be part of the end cap  16 . A surface of the connector structure  70  includes recesses  74  and  76  therein defining mounting surfaces for receiving the MOSFET  52  and free-wheeling diode  68 , respectively. Spring structure in the form of a wave washer  78  is provided between the diode  68  and a mounting surface of the recess  76  and between the MOSFET  52  and a mounting surface of recess  74 , the function of which will be explained below. 
     As best shown in FIG. 5, the connector structure  70  includes a bus bar support  82  which supports controller bus bar  84 . The connector structure  70  carries an RFI capacitor  85 , resistor  86 , capacitor C, resistor R, and zener diode  66 . The connector structure  70  also includes a positive terminal  87 , a negative terminal  88 , and ground/negative terminal  55 , which is connected to the end cap  16  (FIG.  4 ). As best shown in FIG. 4, once the MOSFET  52  end diode  68  are inserted into the associated recess and electrically connected in the manner as shown in FIG. 2, the negative terminal  88  is connected to the negative bus bar  92  of the brush card assembly  24 , and the positive terminal  87  is connected to the positive bus bar  94  of the brush card assembly  24 . Power to the motor is provided to the positive motor terminal  102  and negative motor terminal  104  of the connector structure  70 . 
     As shown in FIGS. 4 and 6, a generally L-shaped partition  96  is provided to physically separate the MOSFET  52  from the diode  68 . The partition  96  extends past an opening in the end cap  16  and thus divides the end cap  16  into two separate heat exchange zones: one zone being associated with the diode  68  and the other zone being associated with the MOSFET  52 . 
     In the embodiment of FIG. 4, the MOSFET  52  is disposed inside of the end cap  16 . A thin, electrically insulating thermal compound or film (not shown) is provided between the inside surface of the end cap  16  and the heat exchange surfaces  98  and  100  of the MOSFET  52  and diode  68 , respectively. 
     Thus, an integrated assembly is achieved by placing the MOSFET  52  and diode  68  into the associated recesses  74  and  76  of the connector structure  70 . This placement eliminates additional component locating devices and positions the diode  68  and MOSFET  52  terminals on the connector bus bars  92  and  94 , as well as on the controller bus bar  84 . When assembled, the wave washers  78  maintain a constant pressure of the heat exchange surfaces  98  and  100  of the MOSFET  52  and diode  68 , respectively, on the inside surface of the end cap  16 . Thus, heat of the diode  68  and MOSFET  52  is transferred to the body of the motor end cap  16 . 
     A third embodiment of the invention is shown in FIGS. 7 and 8 which can be employed in motors which operate from about 400 to 600 Watts. The motor  10 ″ of the third embodiment of the invention includes a commutator, armature, and permanent magnets in the manner disclosed with regard to the motor of FIG.  1 . Thus, these components are not shown in FIGS. 7 and 8. With reference to FIGS. 7 and 8, the motor  10 ″ includes a heat sink  106  which is coupled to an electrical connector  108  by slipping a portion of the heat sink  106  into grooves in the electrical connector  108 . This eliminates the need for an additional heat sink locating device. The heat sink  106  includes a mounting portion  110  including a pair of recesses  112 . A heat conducting surface of a MOSFET  114  is mounted to a surface defining one recess  112  via heat conducting and electrically insulating adhesive  113 . Further, a heat conducting surface of a free-wheeling diode  116  is coupled to a surface defining the other recess  112  via the same heat conducting and electrically insulating adhesive  113 . A printed circuit board  118  is mounted with respect to the mounting portion  110  of the heat sink  106 . In the illustrated embodiment, brackets or tabs  120  space the circuit board from the mounting portion  110  of the heat sink  106 . The dashed line  122  in FIG. 8 shows the extent of the components mounted on the circuit board  118 . A ground terminal  124 , a positive terminal  126  and a negative terminal  128  are carried by the circuit board  118 . The circuit board  118  also carries resistors  130 ,  132 , an RFI capacitor,  134 , a zener diode,  136  and a capacitor  138 . The MOSFET  114  and free wheeling diode  116  are also electrically connected to the circuit board  118 . The positive terminal  126  is electrically connected to the positive bus bar  140  of the brush card assembly  24  (FIG. 8) and the negative terminal  128  is coupled to the negative bus bar  142  of the brush card assembly  24 . Three electrical leads  144  extend from the circuit board  118  to the connector  108 . Two leads are used to power the motor  10 ′ and one lead is used to receive the pulse width modulated control signal from the ECU to be sent to the MOSFET  114 . 
     The motor  10 ″ is constructed and arranged to operate a cooling fan of a vehicle. Thus, with reference to FIG. 8, the heat sink includes fins  146  which are coupled to the heat sink mounting portion  110  and which extends from the motor housing  148 . The fins  146  are thus positioned to be in the airflow stream of the fan (not shown) so as to be cooled by the airflow. Thus, heat generated by the MOSFET  114  and free-wheeling diode  116  is transferred to the heat sink mounting portion  110  and the heat is transferred to the fins  146 . 
     The motors  10 ′ and  10 ′ operate in the same manner as the motor  10  of FIG. 1 in that a PWM signal from a remotely located engine control unit is sent to the gate terminal of the MOSFET  52  to control the speed of the motors  10 ′ and  10 ″. 
     The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.