Abstract:
A cooling fan module for a heat exchanger or the like, has a motor, a fan driven by the motor and a speed controller connected between the motor and a power supply. The speed controller is configured to operate the motor in a high speed mode and a low speed mode. The speed controller includes a high speed branch and a low speed branch connected in parallel. The low speed branch includes a pulse width modulation circuit configured to reduce an average voltage by a fixed duty ratio to achieve a low speed operation of the motor. By eliminating the conventional voltage dropping resistor, the speed controller reduces the power consumption, thus increasing the efficiency of the module, in the low speed mode of operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201510003977.3 filed in The People&#39;s Republic of China on Jan. 5, 2015, the entire contents of which are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a cooling fan module for a heat exchanger of a vehicle or the like and in particular, to a cooling fan module having a speed controller. 
       BACKGROUND OF THE INVENTION 
       [0003]    A cooling fan module comprises a fan driven by an electric motor. Cooling fan modules are used, for example in vehicles to cool the radiator of the engine of a conventional vehicle or the battery of an electric vehicle. 
         [0004]    The motor drive circuit of a conventional two speed cooling fan module has a high-speed branch and a low-speed branch which are connected in parallel. When the high-speed branch is turned on, the motor runs at a high speed. When the low-speed branch is turned on and the high-speed branch is turned off, the motor runs at a low speed. Generally, power is directly connected to an input terminal (for example, a positive electrode) of the motor through the high-speed branch, and the low-speed branch outputs power to the motor terminal at a reduced voltage via a voltage dropping resistor. In this case, if the motor is running at a low speed, the voltage dropping resistor generates a lot of heat, which causes a great loss. 
         [0005]    As known to those skilled in the art, a Pulse Width Modulation (PWM) circuit has an adjustable duty ratio, and the average value of an output voltage may be changed by adjusting the duty ratio of the PWM circuit. An improved variable speed cooling fan module is provided, in which the PWM circuit with an adjustable duty ratio is used to replace the conventional high-speed branch and low-speed branch. 
         [0006]    In a vehicle radiator cooling system, the PWM circuit is connected to an Engine Control Unit (ECU) of the vehicle through a control terminal, and the duty ratio changes in response to instructions from the ECU in a real-time manner, thus the output voltage is adjusted and the motor is provided with various voltages to operate at different speeds in a low speed range. For example, where the duty ratio is  100 %, the PWM circuit is equivalent to the conventional high-speed branch, the motor runs at a high speed; or where the duty ratio is smaller than  100 %, the motor runs at a lower speed. 
         [0007]    The loss of the PWM circuit described above is smaller than that of the convention circuit with the voltage dropping resistor. However, the overall cost is greatly increased because an additional control circuit (for example, a circuit for adjusting the duty ratio) is included in the PWM circuit. Besides, the conventional high-speed branch and low-speed branch connected in parallel are replaced by a power supply branch in the PWM circuit and the PWM circuit has an additional control terminal, which means that the interface of the cooling fan module adopting the PWM circuit is incompatible with the conventional interface. In the vehicle industry, different components are provided by different providers, hence, the incompatibility of the interface has a serious impact on sales of the cooling fan module adopting the PWM circuit and applications of the cooling fan module. 
         [0008]    Therefore, an improved technical solution is desired. 
       SUMMARY OF THE INVENTION 
       [0009]    Hence there is a desire for a cooling fan module having an improved efficiency in a low speed operating mode. 
         [0010]    Accordingly, in one aspect thereof, the present invention provides a cooling fan module comprising: a motor, a fan driven by the motor and a speed controller connected in series between the motor and a power supply for the motor, wherein the speed controller comprises a high speed branch and a low speed branch which are connected in parallel, the low speed branch comprises a pulse width modulation circuit connected in series, and the pulse width modulation circuit is configured to reduce an average voltage by a fixed duty ratio to achieve a low speed operation of the motor. 
         [0011]    Preferably, the low speed branch further comprises a voltage modulation circuit connected in series, and the voltage modulation circuit is configured to disconnect the low speed branch via the pulse width modulation circuit where an input voltage is higher than a preset high voltage threshold or lower than a preset low voltage threshold. 
         [0012]    Preferably, the low speed branch further comprises a current protection circuit, the current protection circuit comprises a current measurement resistor and a switch circuit connected in series and the current protection circuit is configured to control the switch circuit to adjust the current to be within a preset current threshold via the pulse width modulation circuit, when a current flowing through the current measurement resistor is larger than the preset current threshold. 
         [0013]    Preferably, the switch circuit comprises a gate drive and a MOS transistor, an output signal of the pulse width modulation circuit is inputted to an input terminal of the gate drive and an output signal of the gate drive is inputted to the MOS transistor. 
         [0014]    Preferably, the low speed branch further comprises a temperature detection circuit configured to measure a temperature. 
         [0015]    Preferably, the speed controller comprises a printed circuit board supporting the pulse width modulation circuit. 
         [0016]    Preferably, the speed controller comprises a shell and a heat sink which are fitted together to form an outer shell of the speed controller, and the printed circuit board is installed inside the outer shell and heat is dissipated through the heat sink. 
         [0017]    Preferably, the heat sink comprises several fingers extending outwardly to increase heat dissipation. 
         [0018]    Preferably, inductors and capacitors are installed on the printed circuit board, the inductors and the capacitors protrude from the printed circuit board in a direction towards the heat sink, and the heat sink has a cavity to accommodate the inductors and the capacitors. 
         [0019]    Preferably, the heat sink comprises fingers extending outwardly from a back of the cavity to increase heat dissipation. 
         [0020]    In the cooling fan module according to embodiments of the present invention, by replacing the conventional voltage dropping resistor for the low speed operation by a fixed duty ratio PWM circuit, the efficiency of the module is significantly increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0022]      FIG. 1  illustrates a cooling fan module according to a preferred embodiment of the invention; 
           [0023]      FIG. 2  illustrates assembly of a speed controller onto the cooling fan module of  FIG. 1 ; 
           [0024]      FIG. 3  illustrates the speed controller of  FIG. 2 ; 
           [0025]      FIG. 4  is a partially exploded view of the speed controller; 
           [0026]      FIG. 5  is a partially exploded view of the speed controller with a shell and heat sink removed; 
           [0027]      FIG. 6  is a block circuit diagram of the speed controller; 
           [0028]      FIG. 7  is a schematic circuit diagram of a pulse width modulation circuit and switch circuit illustrated in  FIG. 6 ; 
           [0029]      FIG. 8  is a schematic circuit diagram of a voltage modulation circuit and a temperature detection circuit illustrated in  FIG. 6 ; and 
           [0030]      FIG. 9  is a schematic circuit diagram of a current protection circuit illustrated in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]      FIG. 1  illustrates a cooling fan module  100  according to the present invention, which includes a fan shroud  21 , a motor  27  installed on the fan shroud  21 , a fan  29  installed on a shaft of the motor  27  and a speed controller  30  installed on the fan shroud  21 . The fan shroud  21  has a large vent and several spokes  23  stretching toward the center of the vent, and a hub  25  fixed to the ends of the spokes  23 . The motor  27  is installed on the hub  25 . The motor  27  and the fan  29  are disposed in the vent. 
         [0032]    Referring to  FIG. 2 , the fan shroud  21  has a cut-out or recess  22  in which the speed controller  30  is installed. As for circuit connections, the speed controller  30  is connected in series between a power and the motor  27 , and is configured to change the speed of the motor by changing the output voltage applied to the motor. 
         [0033]    Referring to  FIGS. 3 and 4 , the speed controller  30  includes a shell  31  and a heat sink  36  which are snapped together, and a printed circuit board  41  installed inside the shell  31 . Preferably, the shell  31  and the heat sink  36  are of half-shell structures which are joined together with bolts  33  to form a full shell. A PWM circuit which includes components such as inductors  42  and capacitors  43 , is formed on the printed circuit board  41 . The components which generate heat such as the inductors  42  and the capacitors  43  are arranged on a side of the printed circuit board  41  facing the heat sink  36 . The heat sink  36  has a cavity  37  to accommodate the heat generating components, to better dissipate the heat from these components. Heat dissipation fingers  38  protrude from a surface of the main body of the heat sink  36 , to increase the heat dissipation area of the heat sink  36 . Preferably, a wall  39  of the cavity  37  also protrudes from the surface of the main body of the heat sink. 
         [0034]    Referring to  FIGS. 4 and 5 , a connector  32  is arranged on the shell  31 , four input terminals  34 , i.e.,  34   a,    34   b,    34   c  and  34   d,  are installed inside a connector  32  and are for receiving a input voltage. Preferably, positions and functions of the four input terminals  34   a  to  34   d  are the same as those of conventional connectors. For example, the input terminal  34   a  is connected to a negative electrode of an external power, the input terminal  34   c  is connected to a positive electrode of the external power to operate the motor at low speed, the input terminal  34   d  is connected to the positive of the external power to operate the motor at high speed, and the input terminal  34   b  is a reservation terminal. 
         [0035]    The printed circuit board  41  has four terminals, i.e.,  44   a,    44   b,    44   c  and  44   d . The terminal  44   a  is connected to the input terminal  34   a  to be connected to the negative electrode of the external power, the terminal  44   d  is connected to the input terminal  34   c  to be connected to the positive electrode of the external power, and the terminal  44   d  is connected to the input terminal  34   d  to be connected to the positive electrode of the external power. The two terminals  44   a  and  44   c  in the middle are input terminals and electrically connected to the terminals  34   a  and  34   c  of the connector  32 , respectively. The two terminals  44   b  and  44   d  are output terminals and connected to two output cables  35   a  and  35   b,  respectively. In the embodiment, the output cables  35  extends out of the shell  31  and is connected to the motor  27 . 
         [0036]    Referring to the block diagram of  FIG. 6 , as for circuit connections, the speed controller  30  is connected in series between the power and the motor  27 . In the embodiment, the input terminal  34   a  is connected to the negative electrode of the power, and the input terminals  34   c  and  34   d  are connected to the positive electrode of the power supply. When the input terminal  34   d  is turned on via a switch K 1 , the motor operates at high speed. Where the input terminal  34   c  is turned on via a switch K 2  and the input terminal  34   d  is not turned on via the switch K 1 , the motor operates at low speed. In addition, where both K 1  and K 2  are switched on, the motor operates at high speed because the power supply still supplies power to the motor via the switch K 1 . A voltage modulation circuit  56  is connected in series between the input terminal  34   c  and a pulse width modulation circuit  55 . Once it is detected that the voltage is not within a normal threshold range, for example, the voltage is higher than a preset high voltage value or lower than a preset low voltage value, the voltage modulation circuit  56  controls the pulse width modulation circuit  55  to stop the motor. Assumed that the normal threshold range is from 9V to 16V, the pulse width modulation circuit  55  stops the motor when the voltage of the power supply is lower than 9V or higher than 16V. 
         [0037]    In the embodiment, the low speed operation of the motor is achieved in a way of pulse width modulation. The input terminal  34   c  is connected in series to the pulse width modulation circuit  55  and then connected to the motor  27 , and the pulse width modulation circuit  55  reduces the voltage and current supplied to the motor by a preset duty ratio, and thus the low speed operation of the motor is achieved. Compared with the conventional solution of connecting a voltage dropping resistor in series, the solution of connecting the pulse width modulation circuit  55  in series is used according to the present invention, to achieve the low speed operation of the motor with a lower loss and a higher efficiency. 
         [0038]      FIG. 7  is a schematic circuit diagram of the pulse width modulation circuit  55  and a switch circuit  57  according to an embodiment of the invention. A voltage signal V pwm  with a fixed duty ratio is generated by comparing a continuous triangular wave generated by a triangular wave oscillator with a direct current control signal Vcon. The gate drive in the switch circuit  57  is configured to convert the voltage signal V pwm  into V g  to drive a high-side MOS transistor Q 2 , and a voltage, lower than the voltage from the input terminal  34   c,  is supplied to the motor through Q 2 . 
         [0039]    Furthermore, reference is made to  FIG. 8 , which illustrates the voltage modulation circuit  56  and a temperature detection circuit  58  according to an embodiment of the invention. The final output of the voltage modulation circuit  56  is usually a fixed voltage provided by the circuit  56   c,  and is also the direct current control signal Vcon inputted to the pulse width modulation circuit  55 . The under-voltage protection circuit  56   a  above is configured to manage the under-voltage state, and Vcc is a voltage from the input terminal  34   c.  When Vcc is too low, the comparator U 1 D outputs a high voltage to turn Q 4  on, so that the direct current signal inputted to the pulse width modulation circuit  55  is interrupted. On the other hand, when the voltage value of Vcc is larger than 9V, the comparator provides zero voltage for Q 4  to turn Q 4  off, and thus the signal Vcon may be kept at a fixed level. The over-voltage protection circuit  56   b  below is configured to manage the over-voltage state. Where the voltage Vcc is too high, the comparator U 1 C interrupts the signal Vcon. On the other hand, after the voltage Vcc is restored under 16V, the comparator U 1 C restores the signal Vcon to a normal level. The temperature detection circuit  58  is connected in series between the input terminal  34   c  and the motor  27 . The temperature detection circuit  58  includes a temperature sensor which is configured to sense the temperature of the printed circuit board  41  and the environment temperature. When the detected temperature is higher than a preset temperature threshold, the voltage modulation circuit  56  is controlled to stop operating to disconnect the low-speed branch, thereby achieving the function of temperature protection. For example, when the temperature of the printed circuit board is higher than 130 degrees Celsius, the temperature sensor controls the voltage modulation circuit  56  to stop operating to disconnect the low-speed branch. As illustrated in  FIG. 8 , the temperature detection circuit  58  is a voltage divider, and a negative temperature coefficient thermistor is used to generate a temperature-related voltage and affect the under-voltage protection circuit  56   a.  If the temperature is too high, V temp  may decrease and the comparator UM may turn Vcon to zero, and thus the motor stops operating. 
         [0040]    Furthermore, referring to  FIG. 9 , a current protection circuit  53  is connected in series between the input terminal  34   b  and the motor  27 . The current protection circuit  53  includes a current measurement resistor R 1  which is connected in series between the pulse width modulation circuit  55  and the motor  27  and configured to measure an input current of the motor. The current signal detected by the current measurement resistor R 1  is amplified by an amplification circuit  53   a,  and then an output signal V I  is compared with a predetermined threshold V th  in an error compensation circuit  53   c,  to compensate the pulse width modulation circuit  55  with the current signal Vcon. By comparing V I  and V th  cyclically using such a negative feedback circuit, the current threshold of the motor in an over-current state may be limited. Therefore, the motor can still be driven where the current is larger than a threshold (for example, under the circumstance of locked rotor), and the motor can be restored to be in a normal operating state once it is detected that the current of the motor is smaller than the threshold. 
         [0041]    An input terminal of the switch circuit  57  is connected to the positive electrode of the power and an output terminal of the pulse width modulation circuit  55 , and an output terminal of the switch circuit  57  is connected to an input terminal of the current protection circuit  53 . The switch circuit  57  is configured to prevent the circuit voltage from being too large or too small, or prevent the circuit from being damaged due to a reversion of the voltage. 
         [0042]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item or feature but do not preclude the presence of additional items or features. 
         [0043]    It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. 
         [0044]    The embodiments described above are provided by way of example only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined by the appended claims.