Abstract:
A system and method for avoiding loss of prime in a primed fuel system of a diesel engine ( 10 ) that propels a motor vehicle. With the engine running, a control system ( 14 ) shuts down the engine when a fuel level sender ( 20 ) indicates an incipient risk of the fuel system losing its prime due to insufficient fuel in the tank ( 16 ). In one embodiment, the engine cannot be re-started until more fuel is added to the tank. Another feature allows engine re-starting and limited running after a shut-down by first turning the ignition switch ( 48 ) to OFF.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to motor vehicles that are powered by diesel engines, in particular to a system and method for avoiding loss of prime in the fuel system when the fuel supply approaches empty.  
       BACKGROUND OF THE INVENTION  
       [0002]     When a motor vehicle engine runs out of fuel, the engine stops and cannot be restarted until the fuel supply is replenished. The fuel systems in larger vehicles like cars and trucks typically have electronically controlled fuel injectors that inject fuel into engine cylinders under pressure. Because a fuel tank is typically located outside an engine compartment, a pump is needed to move fuel from the tank to the fuel injection system at the engine, and once the fuel has been moved, the pressure still needs to boosted to one that is high enough for diesel injection.  
         [0003]     If the fuel tank is pumped dry, a pump begins to cavitate and is prone to losing prime. The injection system may also be affected.  
         [0004]     The very nature of a diesel engine, and diesel fuel as well, tend to make re-priming the engine difficult, especially in cold weather. Consequently, regular drivers of commercial trucks are usually careful enough to keep fuel in their tanks from running too low.  
         [0005]     That may not be the case for trucks that are rented from rental fleets. Because such trucks may not be rented to regular drivers, it is believed that there is a greater risk that a rented commercial truck may run out of diesel fuel. Such an event may incur the expense of having to call a service technician to the location where the truck ran out of fuel, or even that of having the truck towed to a service facility.  
         [0006]     Some motor vehicles are equipped with low-fuel warning systems that issue visible and/or audible warnings when the in-tank fuel supply reaches at level suggesting that the driver needs to re-fill fairly soon. For whatever reason, such a warning may on occasion be ignored, sometimes without adverse consequence, but at other times with the consequence of running out of fuel when no fuel is readily available, and the further consequence of causing the fuel system to lose its prime.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention relates to a system and method for avoiding loss of prime before the fuel supply level drops so low that the fuel system is at risk of losing prime.  
         [0008]     According to one generic aspect, the invention relates to a motor vehicle comprising a diesel engine that propels the vehicle and comprises a fuel system that has been primed. A sender indicates the level of diesel fuel in a tank that holds a supply of diesel fuel for the engine. An engine control system that provides control of the engine including control of engine fueling is effective, with the engine running, to shut down the engine when the sender indicates an incipient risk of the fuel system losing its prime due to insufficient fuel in the tank.  
         [0009]     According to another generic aspect, the invention relates to a method of avoiding loss of prime in a primed fuel system of a diesel engine that propels a motor vehicle having a fuel tank for holding diesel fuel for the engine and a sender for indicating the level of diesel fuel in the tank. With the engine running, a control system shuts down the engine when the sender indicates an incipient risk of the fuel system losing its prime due to insufficient fuel in the tank.  
         [0010]     The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram illustrating a portion of a motor vehicle engine and fuel system relevant to an understanding of principles of the present invention.  
         [0012]      FIG. 2  is a schematic diagram illustrating additional detail 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     A motor vehicle, such as a truck, is powered by a diesel engine  10  disposed in an engine compartment of the vehicle. A fuel system for engine  10  comprises a fuel injection system  12  whose operation is controlled by an engine control system  14 .  
         [0014]     Control system  14  comprises one or more processors for processing data from various sources to control various fueling parameters such as injection control pressure, injection timing, and injection quantity.  
         [0015]     The fuel system further includes one or more tanks, such as tank  16 , for carrying diesel fuel for engine  10 . Fuel is moved from tank  16  to the engine compartment by a pump  18  that may be disposed internal or external to tank  16 .  
         [0016]     A sender  20  is disposed in tank  16  for indicating the amount of fuel in the tank. A common type of sender comprises a body  20 A that is mounted in any suitably appropriate way and a float arm  22  that carries a float  24  that seeks the level of fuel in the tank. As float  24  moves vertically with changes in fuel level, float arm  22  is correspondingly positioned on body  20 A to operate a device such as a variable resistor that is connected to a circuit providing a signal for informing the driver of the vehicle of the amount of fuel in the tank.  
         [0017]     In accordance with principles of the invention, the signal from sender  20  is also utilized by engine control system  12 . When the signal indicates a fuel level corresponding to an incipient risk of the fuel system losing its prime due to insufficient fuel in tank  16 , control system  12  shuts down engine  10 . In that way, the fuel system retains its prime. Once it has shut down engine  12  in this way, the control system does not allow the engine to be re-started until fuel has been added to tank  16  to bring the fuel level to one that is higher than the one that caused the shutdown.  
         [0018]     The vehicle also has a warning system  26  for issuing a low-fuel warning, either visibly and/or audibly. System  26  will first issue a low-fuel warning at an indicated fuel level in advance of the level indicating an incipient risk of the fuel system losing its prime due to insufficient fuel in the tank. That warning is typical of known warning systems in that it is intended to alert the driver of a need to re-fuel fairly soon, but it is not indicative of an imminent engine shutdown due to incipient risk of loss of fuel system prime.  FIG. 1  shows a fuel level  28  representing that at which the low-fuel warning might be given.  
         [0019]      FIG. 1  also shows a lower fuel level  30 . It is when fuel level in tank  16  drops to level  30  that warning system  26  issues an imminent shutdown warning because sender  20  is indicating an incipient risk of the fuel system losing its prime due to insufficient fuel in the tank. Some margin of time for allowing the driver to move the vehicle off the road or to park the vehicle is thereafter provided before actual shutdown occurs.  
         [0020]     For purposes of improved accuracy, sender  20  may be of the type that includes a bottom reference feature that references the signal to tank bottom as sensed by a member, such as member  32  in  FIG. 1 , being forced against the bottom wall of the tank. This feature accounts for slight dimensional differences in sender mounting location from tank-to-tank in mass-produced vehicles due principally to dimensional tolerances to the bottom wall, and to any deformation that may occur in the bottom wall.  
         [0021]     Accuracy is also improved by processing the signal from the sender according to an algorithm to attenuate the effect of fuel slosh in the tank.  
         [0022]     The additional detail included in  FIG. 2  shows an embodiment where the motor vehicle has a body control module  40  with which a driver display  42  is associated. The fuel level sender contained in tank  16  provides a signal to body control module  40  indicating the level of fuel in the tank.  
         [0023]     Body control module  40  is an on-board electronic system that is for the most part associated with components and devices in the cab or body of the vehicle, such as -driver display  42 . Module  40  also interfaces with other modules, such as engine control module  14  that corresponds to engine control system  14  in  FIG. 1 . The interfacing typically occurs via a data link  44 .  
         [0024]     To avoid loss of prime, body control module  40  can signal engine control module  14  via data link  44  to shut off engine  10  when the fuel level sensed by the in-tank sender reaches a level corresponding to level  30  in  FIG. 1 . Advance warning of shut-down can be given by module  40  to display  42 .  
         [0025]     If an engine shut-down actually occurs, a feature shown in  FIG. 2  allows the engine to be re-started and operated for a limited time. This features allows the vehicle to be moved to a more favorable location if shut-down occurs in a less favorable one. The feature involves the use of the vehicle&#39;s ignition switch  48 , which is typically associated with body control module  40 .  
         [0026]     When a shut-down occurs in order to avoid loss of prime, the fuel level that triggers shut-down is chosen to allow some small amount of additional fuel consumption before prime is lost so that the vehicle can be driven to a more favorable location.  
         [0027]     Shut-down would be expected to occur with ignition switch  48  in ON position. If the switch is thereafter turned to OFF position, the signaling of OFF position to body control module  40  resets the body and/or engine control module, as appropriate, to a condition that allows the engine to be cranked and re-started and then to run either for a limited amount of time, or until some small additional amount of fuel has been consumed.  
         [0028]      FIG. 2  also shows a “hard-wired” connection  46  from body control module  40  to engine control module  14  that can -be used to directly interrupt fueling instead of having engine control module  14  process data from module  40  via data link  44  in order to stop the fueling.  
         [0029]     While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.