Abstract:
A fuel filter assembly incorporates a BLDC motor and control circuit configured to operate at a first rotational speed upon startup and switch to a second rotational speed when measured variables indicate that the filter assembly is filled with fuel. The first rotational speed is initiated as a default when power is applied to the control circuit. If the filter assembly has been serviced, it must be primed before resuming normal operation. The first rotational speed is significantly higher than the second rotational speed to reduce the amount of time necessary to prime the filter assembly. The control circuit is arranged to monitor a variable which corresponds to the torque necessary to drive the pump. When the pump is filled with air prior to priming, lower torque is required to drive the pump, which corresponds to lower current draw and power consumption at the BLDC motor.

Description:
BACKGROUND 
       [0001]    The disclosure relates to fuel filter assemblies and in particular to fuel filter assemblies that include a motor driven pump to move fuel through the filter assembly. 
         [0002]    Fuel filter assemblies are configured to condition fuel prior to delivery to systems that consume the fuel, such as internal combustion engines. Fuel filter assemblies define a housing that routes fuel through one or more filter media configured to remove particulates and separate water from the fuel. The filter assembly may include a motor-driven pump that moves fuel through the assembly. The motor for driving the pump may be a brushed or brushless motor. Brushless motors are referred to as BLDC motors and require a drive circuit to generate the rotating magnetic field that drives the motor. Power consumed by a BLDC motor will be proportional to the torque needed to rotate the pump to which the motor is connected. 
         [0003]    The filter media in a filter assembly must be periodically replaced to maintain the removal of particulates and water. Filter media may be contained within a disposable housing, which may be referred to as a filter cartridge, or may be supported on a filter element that is placed into a re-usable housing that may be opened for this purpose. When the filter media is replaced, and the filter assembly housing is closed, a large volume of air remains in the housing and must be displaced by fuel prior to resuming normal system operation. The process of displacing fuel with air is called “priming” the filter assembly. Various manual pumps have been proposed for this purpose. It has also been proposed to provide a separate pump which rotates in a first direction to empty the filter housing and operates in a reverse direction to prime the filter housing after a service event. These prior art approaches complicate the filter assembly by requiring additional components, connections and hardware. 
         [0004]    There is a need in the art for a self-priming fuel filter assembly that does not require additional components. 
       SUMMARY OF THE INVENTION 
       [0005]    The disclosed fuel filter assembly incorporates a BLDC motor and control circuit configured to operate at a first rotational speed upon startup and switch to a second rotational speed when measured variables indicate that the filter assembly is filled with fuel. The first rotational speed is initiated as a default when power is applied to the control circuit. If the filter assembly has been serviced, it must be primed before resuming normal operation. The first rotational speed is significantly higher than the second rotational speed to reduce the amount of time necessary to prime the filter assembly. The control circuit is arranged to monitor a variable which corresponds to the torque necessary to drive the pump. When the pump is filled with air prior to priming, lower torque is required to drive the pump, which corresponds to lower current draw and power consumption at the BLDC motor. Variables such as current draw and power consumption can be monitored at the control circuit and a threshold value can be used to switch from the initial priming speed to the second, lower, operational speed. Variables such as fluid pressure at the filter assembly outlet may also be employed for this purpose. In a simplified alternative, the priming speed may be set to a pre-determined time, with excess fuel bled off by a mechanical regulator when the filter assembly is full of fuel. 
         [0006]    When the threshold variable value is reached, the control circuit switches from the high initial priming rotational speed to the lower steady state operational speed. According to aspects of the disclosure, the control circuit may be configured to maintain the steady state rotational speed even if the measured variable falls below the threshold variable value. 
         [0007]    In one embodiment, a motor control circuit is programmed to operate a fuel filter pump at a first, priming rotational speed at power up that is higher than a steady state operational speed. 
         [0008]    In one embodiment, a motor control circuit is programmed to operate a fuel filter pump at a default rotational speed that is higher than a steady state rotational speed of the pump. 
         [0009]    In one embodiment, a motor control circuit is programmed to switch driving a fuel filter pump at a first, priming rotational speed to a second, steady state rotational speed when current consumed by a motor driving the pump exceeds a pre-determined threshold. 
         [0010]    In one embodiment, a motor control circuit is programmed to switch driving a fuel filter pump at a first, priming rotational speed to a second, steady state rotational speed when power consumed by a motor driving the pump exceeds a pre-determined threshold. 
         [0011]    Alternative embodiments of the disclosed brushless DC motor control may incorporate one or more of the features set forth in the detailed description below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a sectional view through a filter assembly according to aspects of the disclosure; 
           [0013]      FIG. 2  illustrates variables relevant to the disclosed filter assembly and methods during system startup after a service event with the filter housing and assembly drained of fuel; 
           [0014]      FIG. 3  illustrates variables relevant to the disclosed filter assembly and methods during system startup when the filter housing and assembly are full of fuel; 
           [0015]      FIG. 4  illustrates variables relevant to the disclosed filter assembly and methods during system startup after a service event with the filter housing and assembly drained of fuel; and 
           [0016]      FIG. 5  is a simplified operational block diagram illustrating aspects of the disclosed method. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is a sectional view through a filter assembly  10  incorporating a brushless DC motor (BLDC motor)  12  and integrated pump  14  according to aspects of the disclosure. A control board  16  is arranged on the side of the pump housing  18  in a compartment  20  defined partially by the housing  18  and partially by a cover  22  secured to the housing. Together, the housing  18  and cover  22  provide a sealed enclosure for the control board  16  and electronic control circuit  17  that drive the BLDC motor  12 . The control circuit for a BLDC motor is generally known to those skilled in the art and typically includes a programmable microcontroller and components necessary to generate the rotating magnetic field that drives the BLDC motor  12 . Power delivered to the BLDC motor may be controlled using pulse width modulation (PWM) to vary the duty cycle of the power transmitted to the motor  12 . Power is transmitted from the control board  16  to the BLDC motor  12  through conductive studs  24  (one of three is shown) that pass through the wall of the housing  18 . The BLDC motor  12  and pump  14  are arranged at the clean fuel outlet  26  of the filter assembly  10  and pull fuel through fuel delivery conduits from a fuel reservoir (not shown), through the filter cartridge  30  and deliver the fuel to downstream engine assemblies such as high pressure fuel pumps and fuel injection systems (not shown) via outlet  26 . 
         [0018]    In the disclosed embodiment, the pump  14  coupled to the BLDC motor  12  is a gerotor pump that will pump air or liquid. Other pump configurations may be compatible with the disclosed filter assemblies and methods. The pump  14  is connected in fluid communication with an outlet  32  of the housing  34  surrounding a filter element  36 , placing the filter housing and filter element on the suction side of the pump  14 . Alternatively, the pump  14  may be connected to push fluid through the filter housing and filter media. A gerotor pump is an example of a “positive displacement” pump, in which the volume of fluid pumped is the same for each rotation of the pump, regardless of pressure. 
         [0019]    The disclosed filter assembly  10  is of the type where the replaceable filter component carries its own housing  34  and is typically referred to as a filter cartridge  30 . Alternative filter assembly configurations employ a permanent housing that can be opened to remove and replace a filter element. In either form of filter assembly, replacement of a spent filter cartridge or filter element results in a large pocket of air in the filter assembly. The air must be displaced by fuel to re-fill the filter assembly  10  before the fuel delivery system can be returned to service. The process of filling a filter assembly with fuel after a service event or loss of fuel in the assembly is called “priming” the assembly. 
         [0020]    In the disclosed filter assembly  10 , the control board  16  includes control circuitry  17  configured to operate the BLDC motor  12  to drive the pump  14  to maintain a constant flow of pressurized fuel to downstream engine assemblies (not shown). The control circuitry  17  includes a microcontroller that runs firmware implementing the disclosed methods of operating a filter assembly. The filter assembly  10  includes a mechanical regulator  27  to regulate pressure of fuel leaving the filter assembly, which simplifies the filter assembly and motor control software. In one disclosed embodiment, the motor control circuit  17  is set to drive the BLDC motor  12  at a fixed rotational speed, where the BLDC motor  12  and pump  14  are configured to provide enough fuel to meet maximum demand from the engine to which the filter assembly  10  is connected. In the disclosed embodiment, during periods of non-peak demand for fuel, excess fuel is bled off by the mechanical regulator  27  and returned to the inlet  28  of the filter assembly  10  where it is recirculated through the filter media  36  to the outlet  32  of the filter housing  34 . In the disclosed filter assembly  10 , the fixed rotational speed of the motor during normal operation is approximately 3600 rpm, with the motor consuming between 50 and 60 watts of power. In the disclosed filter assembly  10 , the BLDC motor  12  draws approximately 8 amps of current during steady state operation and generates outlet pressure of approximately 5 bar (72 psi). 
         [0021]    As shown in the block diagram of  FIG. 5 , when the fuel filter assembly  10  is powered up after a service event, most of the filter assembly is filled with air, and in this condition the drag on the pump  14  coupled to the BLDC motor  12  is low compared to when the pump  14  is filled with fuel. The air needs to be displaced with fuel for the connected engine to resume operation. In the disclosed embodiment, the control circuit is programmed to drive the BLDC motor at 6500 rpm while the filter assembly is being primed with fuel. Running the BLDC motor and pump at a higher rotational speed reduces the time needed to prime the filter assembly with fuel. The BLDC motor consumes between 19 and 21 watts of power to drive the BLDC motor at 6500 rpm when pumping air out of the filter assembly. The BLDC motor draws approximately 2 amps when pumping air at 6500 rpm during priming. 
         [0022]      FIG. 2  illustrates measurements taken from the disclosed embodiment of a filter assembly while priming the filter assembly. The test was started with a new dry filter cartridge and the system plumbing had been drained of fuel. From power on it took 49 seconds to fill the filter assembly with fuel, which included lifting the fuel the equivalent of 8 vertical feet. As the filter assembly  10  fills with fuel, the pressure at the outlet  26  accumulates and the BLDC motor  12  begins to draw more current. Testing has proven that when the priming is essentially complete, the current drawn by the BLDC motor  12  exceeds 5 amps. The disclosed control circuit  17  is programmed to monitor the current draw of the BLDC motor  10  and when the current exceeds 5 amps, then the control circuit  17  reduces the motor rotational speed to 3600 rpm, which is maintained during operation of the engine to which the disclosed filter assembly is connected. 
         [0023]      FIG. 3  illustrates a start sequence where the filter assembly  10  already filled with fuel, as in a normal start up in the absence of a service event. It took less than 2 seconds for the system pressure to rise and the BLDC motor  12  to begin consuming more than 5 amps, triggering the switch to the 3600 rpm operating speed.  FIG. 3  illustrates the disclosed filter assembly operation during a normal start of the equipment. 
         [0024]      FIG. 4  illustrates a startup sequence with the filter assembly configured to raise fuel the equivalent of 10 vertical feet, starting with a new dry filter cartridge and the filter assembly drained of fuel. It took the disclosed filter assembly 52 seconds to complete priming and cause the BLDC motor  12  to exceed 5 amps of current draw, triggering the switch to the lower 3600 rpm operating speed. The maximum inlet vacuum observed during this test was 0.26 bar (3.7 psi) (7.6 in-Hg). 
         [0025]    After the disclosed filter assembly  10  has been powered off and then turned back on, the control circuit  17  will automatically default to a motor speed of 6500 rpm. 6500 rpm exceeds the normal operating speed of the pump by more than 40%, and may approach the maximum operating rotational speed of the hardware. The high initial rotational speed of the BLDC motor  12  is selected to maximize the priming capabilities of the disclosed filter assembly. Once the current drawn by the BLDC motor  12  reaches 5 A, the control circuit  17  switches to the normal operating speed of 3600 rpm, and as long as power is maintained to the filter assembly, the motor speed will be maintained at 3600 rpm even if current drawn by the BLDC motor  12  drops below the 5 A threshold. When power has been turned off, the control circuit  17  will default to the 6500 rpm speed, but will almost immediately drop to 3600 rpm if fuel is already present in the system, as shown in  FIG. 2 . 
         [0026]    Monitoring current drawn by the BLDC motor serves as a proxy for monitoring power consumed by the BLDC motor. An alternative control method may monitor power consumed by the BLDC motor and switch from the first, (higher) rotational speed to the second (lower) operational speed upon detection of power consumed by the BLDC motor  12  that exceeds a power threshold indicating that the fuel filter assembly  10  has completed priming and is filled with fuel. In the disclosed embodiment, when power consumed by the BLDC motor  12  exceeds approximately 40 watts, the filter assembly  10  is filled with fuel and the BLDC motor  12  can then be driven at the second rotational speed, which corresponds to steady state operation of the filter assembly. 
         [0027]    In a further alternative control method, a pressure sensor (not shown) may be arranged at the outlet  26  of the filter assembly  10  and used to monitor when the assembly has completed priming. Other control inputs may be employed to trigger the shift from a high priming rotational speed to a lower steady state rotational speed. It is also possible to program the control circuit to start up at a high priming speed for a pre-determined time interval, with excess fuel returned to the filter assembly inlet when the filter assembly is filled with fuel.