Abstract:
A fuel system control method may include determining when an engine transitions from an engine on condition to an engine off condition. The method further includes determining a first fuel pressure in a fuel system of the engine a predetermined time after the determined engine off condition. A fuel injector of the fuel system may be actuated during the engine off condition when the first determined fuel pressure is above a first predetermined pressure limit to bleed fuel from the fuel system and reduce pressure within the fuel system.

Description:
FIELD 
     The present disclosure relates to fuel system control strategies. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Engines may include fuel pressure sensors to determine and control operating pressures therein. After engine shutdown, high pressure fuel systems may bleed fuel from the system through clearances in the fuel injectors. However, some fuel types may have difficulty leaking through the fuel injectors after engine shutdown. This may hinder service of the fuel system due to high pressure being maintained after engine shutdown. Additionally, this may result in longer than expected leak times and may set a false error indicating a pressure sensor failure. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A fuel system control method may include determining when an engine transitions from an engine on condition to an engine off condition. The method further includes determining a first fuel pressure in a fuel system of the engine a predetermined time after the determined engine off condition. A fuel injector of the fuel system may be actuated during the engine off condition when the first determined fuel pressure is above a first predetermined pressure limit to bleed fuel from the fuel system and reduce pressure within the fuel system. 
     The method may additionally include determining a second fuel pressure in the fuel system after the actuating and indicating a system fault when the second fuel pressure is above a second predetermined pressure limit. 
     A control module may include an engine operating condition evaluation module, a fuel pressure determination module, and a fuel injector actuation module. The engine operating condition evaluation module may determine when an engine transitions from an on condition to an off condition. The fuel pressure determination module may be in communication with the engine operating condition evaluation module and may determine a first fuel pressure in a fuel system of the engine a predetermined time after the determined engine off condition. The fuel injector actuation module may be in communication with the fuel pressure determination module and may actuate a fuel injector of the fuel system during the engine off condition when the first determined fuel pressure is above a first predetermined pressure limit to bleed fuel from the fuel system and reduce pressure within the fuel system. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic illustration of an engine assembly according to the present disclosure; 
         FIG. 2  is a schematic illustration of a control module of the engine assembly of  FIG. 1 ; and 
         FIG. 3  is an illustration of control logic for operation of the engine assembly of  FIG. 1 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term “module” refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring to  FIG. 1 , an exemplary engine assembly  10  is schematically illustrated. The engine assembly  10  may include an engine  12  in communication with a fuel system  14  and a control module  16 . The engine  12  may include an engine block  18  defining a plurality of cylinders  20  in communication with the fuel system  14 . 
     The fuel system  14  may include a fuel tank  22 , a fuel pump  24 , a fuel line  26 , a fuel rail  28 , fuel injectors  30 , and a pressure sensor  32 . The fuel injectors  30  may be in direct communication with the cylinders  20 , forming a direct injection arrangement. More specifically, the engine  12  may be a diesel engine and the fuel tank  22  may store a supply of diesel fuel. The fuel injectors  30  may be solenoid actuated, each including a solenoid  34  in communication with the control module  16  and selectively displacing a valve member (not shown) in the fuel injector  30  to provide a pressurized fuel flow to the cylinders  20 . However, while described with respect to a diesel engine, it is understood that the present disclosure is not limited to diesel applications. 
     During operation, the fuel pump  24  may provide a pressurized fuel flow from the fuel tank  22  to the fuel rail  28  via the fuel line  26 . The fuel line  26  and the fuel rail  28  may define a fuel volume (V) between the fuel pump  24  and the fuel injectors  30 . During engine operation, the fuel volume (V) may be maintained at a pressure greater than 30 megapascal (MPa). For example, the pressure within the fuel volume (V) during engine idle conditions may be greater than 30 MPa. The pressure sensor  32  may be in communication with the fuel volume (V) to monitor the fuel pressure. In the present example, the pressure sensor  32  is in communication with the fuel rail  28  and monitors the fuel pressure therein. 
     Referring now to  FIG. 2 , the control module  16  may include an engine operating condition evaluation module  36 , a fuel injector actuation module  38 , a fuel pressure determination module  40 , and a fuel system fault determination module  42 . The engine operating condition evaluation module  36  may be in communication with the fuel injector actuation module  38  and the fuel pressure determination module  40  and may determine an engine on/off condition. An engine on condition may generally correspond to pistons within the cylinders  20  being driven by combustion events within the cylinders  20 . The engine off condition may generally correspond to the pistons within the cylinders  20  being stationary. The engine operating condition evaluation module  36  may provide a signal to the fuel injector actuation module  38  and the fuel pressure determination module  40  indicative of the engine on/off condition. 
     The fuel injector actuation module  38  and the fuel pressure determination module  40  may be in communication with one another. The fuel pressure determination module  40  may additionally be in communication with the fuel pressure sensor  32  and may determine an operating fuel pressure within the fuel volume (V). The fuel pressure determination module  40  may provide a signal to the fuel injector actuation module  38  indicative of the operating fuel pressure and the fuel injector actuation module  38  may provide a signal to the fuel pressure determination module  40  indicating when the fuel injectors  30  have been actuated. The fuel pressure determination module  40  may additionally be in communication with the fuel system fault determination module  42 . The fuel system fault determination module  42  may determine a system fault based on the operating fuel pressure as discussed below. 
     Referring now to  FIG. 3 , control logic  110  is illustrated for fuel system control. Control logic  110  may begin at block  112  where the engine operating condition is evaluated by the engine operating condition evaluation module  36 . If the engine  12  is on, control may return to block  112 . If the engine  12  is off, control logic  110  may proceed to block  114  and wait a predetermined time (t). Control logic  110  may then proceed to block  116  where fuel pressure determination module  40  determines the fuel pressure (P) within the fuel volume (V). Control logic  110  may then proceed to block  118  where the fuel pressure (P) is evaluated by fuel injector actuation module  38 . If the fuel pressure (P) is below a first predetermined pressure limit (LIMIT 1 ), control logic  110  may terminate. Otherwise, control logic  110  may proceed to block  120  where at least one of the fuel injectors  30  is actuated by the fuel injector actuation module  38 . The fuel injectors  30  may be actuated for 100 microseconds or more at block  120 . The control logic  110  may actuate as few as one and as many as all of the fuel injectors  30  at block  120 . Control logic  110  may then proceed to block  122 . 
     Fuel pressure determination module  40  may again determine the fuel pressure (P) within the fuel volume (V) at block  122 . Control logic  110  may then proceed to block  124  where the fuel pressure (P) is evaluated by fuel system fault determination module  42 . If the fuel pressure (P) is above a second predetermined pressure limit (LIMIT 2 ), control logic  110  may proceed to block  126  where a fault is indicated. The fault may generally indicate a faulty pressure sensor  32 . Control logic  110  may then terminate. If the fuel pressure (P) is below the second predetermined pressure limit (LIMIT 2 ), control logic  110  may terminate after block  124 . The first predetermined pressure limit (LIMIT 1 ) and the second predetermined pressure limit (LIMIT 2 ) may be equal to one another and may be less than or equal to 5 MPa. 
     After the engine  12  is shut down, the pressure within the fuel volume (V) may gradually be reduced via leakage through the fuel injectors  30 . The predetermined time (t) may correspond to an expected pressure drop (ΔP e ) producing the first and second predetermined pressure limits (LIMIT 1 , LIMIT 2 ) in the fuel volume (V) after engine shutdown. The predetermined time (t) may be empirically derived and may vary based on a given engine application. However, by way of non-limiting example, the predetermined time may be greater than 15 seconds, and more specifically greater than 30 seconds. The expected pressure drop (ΔP e ) may generally correspond to a pressure drop from an engine idle condition immediately prior to shutdown. For example, the fuel volume (V) may be operating at approximately 30 MPa at idle and the expected pressure after time (t) may be less than 5 MPa. Therefore, in the present example, the expected pressure drop (ΔP e ) may be approximately equal to 25 MPa. 
     Different fuel types may have difficulty leaking through the fuel injectors  30  after engine shutdown, maintaining a high pressure within the fuel volume (V). For example, biodiesel and contaminated fuel may have difficulty leaking through the fuel injectors  30 . Therefore, fuel pressure within the fuel volume (V) may remain high after engine shutdown. Actuation of the fuel injectors  30  after engine shutdown may generally alleviate any high pressure condition maintained due to the issues described about with respect to fuel leak rates. However, high pressure readings may still occur even after the actuation of the fuel injectors  30  due to a faulty pressure sensor  32 .