Abstract:
A dual motor configuration  10  is provided for driving two fans for moving air to cool an engine. The dual motor configuration includes a primary brushless motor  18  constructed and arranged to be electronically controlled to drive a first fan  16  over a range of speeds. A secondary brush motor  24  is constructed and arranged to be electronically controlled to drive a second fan  22  over a range of speeds. The secondary brush motor includes an electronic switching device  26  associated therewith for receiving a pulse width modulated signal for controlling speed of the secondary brush motor. Thus, different combinations of speeds of the first and second motors can be selectively chosen to meet cooling requirements.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to electric motors for automobile engine cooling applications and, more particularly, to a dual motor configuration having a primary brushless motor and a secondary brush motor with integrated speed control.  
           [0002]    In engine cooling applications, there is a need for dual engine cooling fans. Conventionally, this has been achieved using dual brush motors. Wound field-type motors generally 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. With these types of motors, however, the number of speeds available is limited.  
           [0003]    Accordingly, there is a need to provide a dual motor configuration for an engine cooling application whereby different combinations of speeds of first and second motors can be selectively chosen to meet cooling requirements of an engine.  
         SUMMARY OF THE INVENTION  
         [0004]    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 a dual motor configuration for driving two fans for moving air to cool an engine. The dual motor configuration includes a primary brushless motor constructed and arranged to be electronically controlled to drive a first fan over a range of speeds. A secondary brush motor is constructed and arranged to be electronically controlled to drive a second fan over a range of speeds. The secondary brush motor includes an electronic switching device associated therewith for receiving a pulse width modulated signal for controlling speed of the secondary brush motor, whereby different combinations of speeds of the first and second motors can be selectively chosen to meet cooling requirements  
           [0005]    In accordance with another aspect of the invention, a method is provided for controlling a dual motor configuration for driving first and second fans for moving air to cool an engine. The dual motor configuration includes a primary brushless motor for driving the first fan, and a secondary brush motor for driving the second fan. The secondary brush motor includes an electronic switching device associated therewith. According to the method, a control signal is received at the primary brushless motor to control operation of the primary brushless motor. A pulse width modulated control signal is received at the electronic switching device to control operation of the secondary brush motor, such that different combinations of speeds of the first and second motors can be selectively chosen to meet cooling requirements of an engine.  
           [0006]    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  
       [0007]    Preferred embodiments of the invention are described in greater detail herein below with reference to the drawings wherein:  
         [0008]    [0008]FIG. 1A is schematic illustration of a dual motor configuration provided in accordance with the principles of a first embodiment of the present invention, showing a secondary motor being controlled and powered through a primary motor.  
         [0009]    [0009]FIG. 1B is schematic illustration of a dual motor configuration provided in accordance with the principles of a second embodiment of the present invention, showing a secondary motor being controlled through a primary motor with the primary motor and secondary motor being powered separately.  
         [0010]    [0010]FIG. 1C is schematic illustration of a dual motor configuration provided in accordance with the principles of a third embodiment of the present invention, showing a primary motor and a secondary motor being controlled and powered separately.  
         [0011]    [0011]FIG. 2 is a schematic illustration of a circuit of the secondary motor of FIG. 3 shown electrically coupled to an electronic control unit of a vehicle.  
         [0012]    [0012]FIG. 3 is a schematic view of an end of the secondary motor of the invention showing a MOSFET coupled thereto.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Referring to the drawings wherein like numerals identify similar or like elements through the several views, FIG. 1A illustrates a first embodiment of a dual motor cooling configuration, generally indicated at  10 , for cooling an engine (not shown) of a vehicle. The cooling configuration  10  includes a shroud structure  12  having a first opening  14  therethrough receiving a first fan  16 . A primary, conventional d.c. brushless motor  18  is mounted with resect to the shroud structure  12  and is electronically controlled to drive the first fan  16  at a variety of different speeds, for example, 0 to 4000 rpm. The primary brushless motor  18  may be of the type, and controlled, as disclosed in U.S. Pat. No. 5,744,921, the entire contents of which is hereby incorporated by reference into present specification.  
         [0014]    A second opening  20  is provided through the shroud structure  12  is adjacent to first opening  14 . The second opening receives a second fan  22 . A secondary, integrated speed control motor  24  is mounted with resect to the shroud structure  12  and is electronically controlled to drive the second fan  16  at a variety of different speeds, for example 0 to 4000 rpm. The secondary motor  24  is a permanent magnet, brush-type motor including an electronically controlled switching device  26  associated therewith. The switching device  26  may be a MOSFET, SCR, IGBT, GTO or even a relay. In the embodiment, a MOSFET is shown. The secondary motor  24  is preferably of the type disclosed in commonly owned, co-pending U.S. application Ser. No. 09/113,415, entitled, “Pulse Width Modulated Engine Cooling Fan Motor With Integrated MOSFET”, the entire content of which is hereby incorporated into the present specification by reference.  
         [0015]    With reference to FIG. 3, the switching device or MOSFET  26  is shown to be mounted directly to the end cap  28  or other housing portion of the secondary motor  24 . The MOSFET  26  need not be mounted on the secondary motor  24  but can be provided in a location so as to be electrically connected between the secondary motor  24  and a controller, such as an engine control unit (ECU)  30 . As discussed more fully below, if the secondary motor is controlled by the primary motor  18 , the MOSFET may be electrically connected between the primary motor  18  and the secondary motor  24 .  
         [0016]    With reference to the embodiment FIG. 1A, the secondary motor  24  derives its control and power from the primary motor  18 . Thus, the primary motor  18  is powered by a positive lead  32  and a negative lead  34 , which also provide power to the secondary motor  24 . A control signal is provided from the ECU  30  to the primary motor  18  via line  36 . Secondary motor  24  receives a control signal from the primary motor  18  via line  38 . In this manner, the primary motor  18  interprets the signal from the ECU  30  and gives the appropriate output signal to the secondary motor  24 . Control of the motors can be based on sensed engine temperature.  
         [0017]    [0017]FIG. 1B shows a second embodiment of a cooling configuration of the invention, generally indicated at  10 ′. The components of configuration  10 ′ are the same as disclosed above with resect to the configuration  10  of FIG. 1A, however, the primary motor  18  and the secondary motor  24  are powered individually. Thus, power leads  40  and  42  power the secondary motor  24  separate from power leads  32  and  34  of the primary motor  18 . The primary motor  18  interprets the signal from the ECU  30  and gives the appropriate output signal to the secondary motor  24 .  
         [0018]    For the embodiments of FIGS. 1A and 1B, fault handling can be made in the following manner. For over voltage protection, the primary motor  18  is capable of sensing the system voltage and enable or signal the secondary motor  24  accordingly. In addition, the primary motor  18  is capable of sensing stall conditions from itself or the secondary motor  24  and of tailoring cooling operation accordingly. If, for example, the secondary motor  24  is stalled, the primary motor  18  can obtain a stall diagnostic from the secondary motor  24  and signal the vehicle ECU  30  and increase the speed of the primary motor  18  compensate from the loss of cooling from the secondary motor  24 . In a similar manner, if the primary motor  18  is stalled, the primary motor  18  can signal the ECU  30  and cause the secondary motor  24  to operate at a faster speed.  
         [0019]    [0019]FIG. 1C shows a third embodiment of a cooling configuration of the invention, generally indicated at  10 ″. The components of configuration  10 ′ are the same as disclosed above with resect to the configuration  10  of FIG. 1A, however, the primary motor  18  and the secondary motor  24  are powered and controlled individually. Thus, power leads  40  and  42  power the secondary motor  24  separate from power leads  32  and  34  of the primary motor  18 . In addition, a control signal, e.g., from the ECU  30 , is received by the secondary motor  24  though separate line  44 . As seen in FIGS. 2 and 3, the negative lead  42  is secured to a metal end cap  46  of the secondary motor  24 . Only three lead wires stem from the motor  24 : positive lead  40 , negative lead  42  and control signal lead  44 . The MOSFET drain terminal D is connected to a negative brush card assembly lead of the motor  24  via a lead wire  48 . 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  30 . The ECU  30  is constructed and arranged to generate a varying PWM signal based on the load requirement of the motor  24  that is sent directly to the gate terminal G. This allows a multiple of motor speed operations for the secondary motor  24 .  
         [0020]    In the embodiment of FIG. 1C and FIG. 3, a zener diode  50  is provided between the gate G and drain D of the MOSFET  26  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  52  is provided between the positive and negative terminals of the motor  24 . The zener diode  50 , resistor R and free-wheeling diode  52  can be mounted on the brush card assembly of the motor  24 , or provided in a separate structure. 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.  
         [0021]    The motor  24  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.  
         [0022]    The low frequency PWM signal can be delivered to the motor  24  using the output of the ECU  30  or, if full speed operation of the motor  24  is desired, the speed input to the motor  24  can be achieved using temperature sensors.  
         [0023]    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.  
         [0024]    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  26  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  24 .  
         [0025]    In all of the embodiments, the primary motor  18  contains stall protection and over current detection. The primary motor  18  also contains its own commutation logic and can be controlled by an 8 bit or 16-bit processor.  
         [0026]    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.