Abstract:
A fuel pump system for pumping fuel to an engine in a vehicle includes a pump motor having a carbon-based commutator and brushes in a position exposed to fuel, resulting in a tendency to form a film between the commutator and brushes that can reduce pump performance by increasing the electrical resistance of the brush-commutator interface. The pump motor has a nominal voltage rating. A power circuit is coupled to the pump motor for selectably providing an operating voltage and a boost voltage, wherein the boost voltage is greater than the nominal voltage rating. A controller selecting the operating voltage during an ordinary run cycle and selects the boost voltage during a clean-up cycle. The controller selects the clean-up cycle for a limited time that is sufficiently short to avoid damage to the pump motor from exceeding the nominal voltage rating and sufficiently long to create arcing between the commutator and brushes that reverses formation of the film.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 11/142,587, filed Jun. 1, 2005, entitled “Fuel Pump Boost System.” 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to electric fuel pumps, and, more specifically, to reducing films that build-up on carbon-based commutators and brushes during exposure to fuel. 
     One conventional type of automotive fuel pump uses an electric motor immersed in the fuel inside a pump housing to drive an impeller or a roller mechanism to pump fuel from a fuel tank to an engine in a vehicle. Fuel flowing through the motor advantageously cools the motor during operation. By not sealing the motor components from the fuel, a more inexpensive and compact pump design is achieved. 
     The pump motor typically comprises a DC motor having a commutator and brushes for coupling current to armature coils. Efficient coupling of current between the brushes and commutator depends on maintaining robust contact between them. The contact of fuel with the brush-commutators, however, results in the buildup of various high resistance materials on the brush-commutator interface referred to as filming. The increased resistance of the connection between the brushes and commutator reduces current flow to the armature thereby reducing the flow rate through the pump. The reduced flow rate impacts engine performance and may require a pump to be replaced. 
     The rate at which filming occurs may vary depending upon the type of fuel present. Modern vehicles are typically exposed to various grades and types of fuel. Ethanol/gasoline blends such as E10 fuel may have a particularly high rate of filming. As these fuels are increasingly used, the problem of filming is becoming more urgent. 
     The rate of filming also depends upon the material used for constructing the brush and the commutator. One traditional commutator material has been copper. Although copper is less susceptible to film formation than some other materials, the surface of the copper wears away at an undesirably high rate. While the wearing away of the copper surface is probably responsible for the lower amount of filming, the premature wearing away of the commutator provides a shortened service life of the pump motor. Thicker commutator pads could provide greater lifetime, but would undesirably increase the length and mass of the armature thereby decreasing efficiency. Fuel pump brushes typically have been and continue to be made of carbon and carbon-based materials. 
     More recently, carbon-based materials have been used for commutators because of their increased wear resistance. These carbon-based materials may include sintered carbon or carbon mixed with resins or other materials. A disadvantage of the carbon-based materials is an increased susceptibility to buildup of a filming layer. One solution has been to apply various coatings to the commutator and/or brush comprising a material more resistant to buildup of the filming layer. However, these measures have resulted in significantly increased costs of materials and cost of manufacture. Therefore, it would be desirable to reduce filming without requiring special materials or manufacturing processes. 
     SUMMARY OF THE INVENTION 
     The present invention avoids the lowering of pump performance and the increase of impedance from brush-commutator filming by operating the pump motor at a voltage boost over its nominal voltage rating for brief periods to clear the film as a result of arcing. 
     In one aspect of the invention, a fuel pump system pumps fuel to an engine in a vehicle. A pump motor includes a carbon-based commutator and brushes in a position exposed to fuel, resulting in a film forming between the commutator and brushes. The pump motor has a nominal voltage rating. A power circuit is coupled to the pump motor for selectably providing an operating voltage and a boost voltage, wherein the boost voltage is greater than the nominal voltage rating. A controller selects the operating voltage during an ordinary run cycle and selects the boost voltage during a clean-up cycle. The controller selects the clean-up cycle for a limited time that is sufficiently short to avoid damage to the pump motor from exceeding the nominal voltage rating and sufficiently long to create arcing between the commutator and brushes that reverses formation of the film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of certain elements of a fuel pump system according to one aspect of the invention. 
         FIG. 2  is a front plan view of the commutator shown in  FIG. 1 . 
         FIG. 3  is a side view of the commutator of  FIG. 2  with the presence of filming. 
         FIG. 4  plots voltage supplied to a pump motor in one embodiment of the invention during an ordinary run cycle and a clean-up cycle. 
         FIG. 5  is a block diagram of one embodiment of the invention utilizing a powertrain controller to control the timing of the clean-up cycle. 
         FIG. 6  is a block diagram of a logic circuit for controlling the clean-up cycle according to another embodiment. 
         FIG. 7  is a flowchart showing yet another method of controlling the clean-up cycle. 
         FIG. 8  is a block diagram according to another embodiment wherein a controller may be integrated with a DC-DC converter to supply appropriate voltages to the pump motor. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , an electric fuel pump  10  has an inlet  11  for receiving fuel within a fuel tank and an outlet  12  for connecting to a fuel line to a fuel rail or fuel injectors of a vehicle engine. A pumping chamber  13  containing an impeller is connected to a motor armature  14 . A commutator  16  is mounted to the opposite end of armature  14  and has commutator bars  17  disposed thereon. Commutator bars  17  are in mechanical contact with brushes  18  under the influence of springs  19  for maintaining the close contact of brushes  18  with commutators  17 . Brushes  18  are electrically connected to a power circuit  20 . Power circuit  20  receives electrical power at terminals  21  and operates according to a control signal received from a controller  22 . 
       FIG. 2  shows a front view of commutator bars  17  on commutator  16 .  FIG. 3  is a side view showing a filming layer  25  that has built up between commutator bars  17  and brushes  18 . 
     In accordance with the present invention, it has been found that boosting the voltage supplied to the fuel pump motor to a sufficiently high voltage can reverse (i.e., either reduce or remove) the filming action. The boosted voltage results in electrical arcing between the commutator bars and brushes which removes the film and restores their electrical conductivity. Since the higher voltage level to be used is greater than what is desirable for typical pump operation, the present invention employs a clean-up cycle that is periodically initiated for very limited times so that the filming is minimized to a sufficient extent. 
       FIG. 4  shows a voltage waveform  26  which is applied to a fuel pump motor according to one preferred embodiment of the invention. The pump motor has a nominal voltage rating dictated by its particular design. The nominal voltage rating is indicated on the vertical axis in  FIG. 4  and may have a value of about 13 volts for a typical automotive fuel pump. Waveform  26  shows that at time t=0 which coincides with the vehicle being started (i.e., turning on of an ignition key), the pump voltage rises from zero to a normal operating voltage, wherein the normal operating voltage is less than or equal to about the nominal voltage rating of the motor. The power circuit provides this normal operating voltage to the pump motor to implement an ordinary run cycle of the pump for providing normal pump output. The ordinary run cycle could also include operating regimes wherein the motor voltage is modulated to lower levels in order to reduce the amount of fuel flow, as is known in the art. 
     In order to periodically reverse the filming on the brush-commutator interface, one or more clean-up cycles are provided wherein a boosted voltage is supplied to the pump motor by the power circuit. The boost voltage is greater than the nominal voltage rating and may preferably be in the range from about 16 to 20 volts. The power circuit provides the boost voltage during a clean-up cycle for a limited time that is sufficiently short to avoid damage to the pump motor from exceeding the nominal voltage rating and is sufficiently long to create arcing at the brush-commutator interface that reverses formation of the film. The actual boost voltage level and the length of time that the voltage is boosted can be optimized for different brush and commutator materials, different pump speeds, different motor currents, types of vehicle operation, type of fuel, and other factors. By way of example, a pump having a nominal voltage rating of 13 volts that has been operated in E10 fuel for 1,000 hours can have the resulting film almost completely removed by running the pump motor at 16 volts for about 90 seconds. 
     There are many potential ways of obtaining an appropriate frequency of clean-up cycles to keep filming in check while simultaneously avoiding motor damage from excessive boost voltages. For example, the clean-up cycle may occur once during each time a vehicle is operated (i.e., between engine starting and stopping) and have a duration of about 90 seconds. Alternatively, the clean-up cycle may occur several times during a driving session such that each individual clean-up cycle may have a duration between about 5 to 10 seconds. To minimize the risk of motor damage, it may be preferable to limit the occurrence of boost cycles during any particular intervals (e.g., one driving session or a period of 24 hours) to less than or equal to about 90 seconds. 
     One concern related to fuel pump operation at a higher voltage concerns the increased noise output from the fuel pump that may be audible to occupants of the vehicle. In order to mask the added noise, it may be preferable to conduct the clean-up cycle during times of other increased noise from the engine such as during a hard acceleration. Accordingly,  FIG. 5  illustrates an embodiment wherein pump motor  30  is driven by either an operating voltage or a boost voltage as provided by a DC-DC converter  31 . A powertrain control module (PCM)  32  is connected to DC-DC converter  31  for selecting either the normal operating voltage or the boost voltage as appropriate. PCM  32  is connected to an ignition switch  33  for determining when the key of the vehicle is on (i.e., in the accessory, run, or start position). PCM  32  is also connected to many other sensors and input control elements such as a throttle for determining engine operation. When the key is on, PCM  32  activates DC-DC converter  31  to convert a regulated vehicle system voltage +V to the normal operating voltage of pump motor  30 . One known typical pump motor has a nominal voltage rating of 13.2 volts, in which case the regulated vehicle voltage of about 14 volts may be converted by DC-DC converter  31  to an operating voltage of about 13.2 volts. 
     In response to information relating to the throttle position and other factors, PCM  32  detects whether a sufficiently large acceleration of the vehicle is taking place so that sufficient engine noise is present to mask the added fuel pump noise to conduct a clean-up cycle. In response to detection of such an acceleration event, PCM  32  commands DC-DC converter  31  to generate the boost voltage which may be in the range of about 16-20 volts. 
       FIG. 6  shows in greater detail a control circuit for generating a control signal to limit the times that a clean-up cycle may be performed during any particular time interval (such as a 24 hour period). An acceleration event signal as determined by the PCM is provided to a timer  35  for measuring the limited time for an individual clean-up cycle, preferably less than about 10 seconds. A high logic level signal from timer  35  determining the limited time for an individual clean-up cycle is provided to one input of an AND gate  36 . The timer output signal is also provided to an input of an accumulator  37  which keeps a running total of the durations of clean-up cycles over a predetermined interval. The predetermined interval is defined by consecutive reset signals provided to accumulator  37 . The reset signal may be obtained from a clock in the PCM for measuring a predetermined interval such as 24 hours, for example. The accumulated total time of all clean-up cycles during the current interval is provided from accumulator  37  to an inverting input of a comparator  38 . The non-inverting input of comparator  38  receives a threshold signal defining a maximum amount of time for conducting clean-up cycles during the predetermined interval. The maximum threshold and the predetermined interval between reset signals are coordinated in order to insure that the limited time for the clean-up cycles are sufficiently short during the predetermined interval to avoid damage to the pump motor while being sufficiently long to reverse formation of the film. For example, a maximum threshold of 90 seconds during a predetermined interval of 24 hours may be appropriate depending upon brush and commutator size, dimension, and materials and other factors. Each individual clean-up cycle is sufficiently short (e.g., less than 10 seconds) in order to prevent obsessive heating or other stresses when operating the motor over its nominal voltage rating. 
     The output of inverter  38  provides a high logic level signal to the remaining input of AND gate  36  unless the accumulated amount exceeds the maximum. Thus, AND gate  36  functions as a transmission gate for the timer signal until the repeated periods of the clean-up cycle have accumulated to the maximum during the predetermined interval. 
     A method according to another embodiment is shown in  FIG. 7 . In this embodiment, the predetermined interval corresponds with a driving cycle from the time a vehicle is started, driven, and turned off. When the ignition key is turned on, the accumulated time is reset in step  40 . In step  41 , the pump motor is run in its ordinary run cycle at its normal operating voltage. A check is made in step  42  to determine whether an acceleration event is in progress. If not, then the pump motor continues to run in the ordinary run cycle in step  41 . If an acceleration event is detected, then a check is made in step  43  to determine whether the accumulated time is greater than or equal to the maximum allowed time. If it is, then a return is made to step  41  for continuing to run the pump motor in its ordinary run cycle. Otherwise, the pump motor is put into its clean-up cycle at the boost voltage in step  41  for a predetermined number seconds (designated as x seconds). In step  45 , the amount x is added to the accumulated time and after the current clean-up cycle time expires a return is made to step  41  to return the pump motor to its ordinary run cycle. 
       FIG. 8  shows yet another embodiment for generating clean-up cycles. This embodiment does not depend upon a connection with a powertrain control or engine control module. Pump motor  30  is driven by a DC-DC converter system  50  that receives system voltage (i.e., the regulated voltage from the voltage regulator such as 14 volts). A converter circuit  51  which may comprise an integrated circuit has an input receiving the system voltage and an output for providing either an operating voltage (e.g., 12 volts) or a boost voltage (e.g., 18 volts) to pump motor  30 . Converter circuit  51  has a SELECT input receiving a control signal from a controller  52 . Controller  52  receives the system voltage in order to be able to detect the key-on status of the vehicle and to coordinate the occurrence of a clean-up cycle or cycles during a particular driving cycle. For example, a clean-up cycle may be conducted at a fixed time interval after the key-on signal is received. A clean-up cycle could be conducted a few seconds after receiving system voltage or could be a longer delay in order to wait until engine operation and the electrical system voltage have stabilized. Alternatively, the clean-up cycle could be initiated at key-off when the system voltage drops back to zero, provided there is sufficient stored energy in the DC-DC converter or provision is made to provide additional power to the DC-DC converter. System voltage may typically be provided through a fuel pump relay as is known in the art. 
     The pump motor of the present invention may be sized for efficient operation at the normal operating voltage of the vehicle electrical system. For example, the pump motor may be run directly off of the vehicle system voltage so that the DC-DC converter is only activated during the clean-up cycle in order to provide the boost voltage. Therefore, the pump motor design may be optimized for its ordinary run cycle. Nevertheless, the pump motor may be safely operated at a boost voltage greater than the motor&#39;s nominal voltage rating by limiting the time of the clean-up cycles by any suitable method including but not limited to the methods shown herein.