Abstract:
A liquefied petroleum gas (LPG) fuel assembly may include a fuel rail and a flow control mechanism. The fuel rail may have an inlet in communication with a pressurized LPG fuel source, an injection passageway in communication with the inlet and a fuel injector that provides fuel to a combustion chamber of an engine, and an outlet in communication with the fuel injection passageway. The flow control mechanism may be in communication with the outlet of the fuel rail and a LPG fuel tank and may be operable in first and second modes. The second mode may provide a greater flow restriction than the first mode to control a fuel flow from the outlet of the fuel rail to the fuel tank.

Description:
FIELD 
       [0001]    The present disclosure relates to engine assemblies, and more specifically to liquefied petroleum gas engine assemblies with fuel flow control. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Liquefied petroleum gas (LPG) engine assemblies may include a fuel rail attached to fuel injectors that inject liquid fuel into a combustion chamber or into an injection port in communication with the combustion chamber. LPG engine assemblies may also include a pump that circulates fuel from a fuel tank through the fuel rail. In warm conditions, fuel in the fuel rail may be heated to a vapor state. Thus, the pump may circulate fuel through the fuel rail prior to engine startup to purge vapor fuel in the fuel rail. This purge of vapor fuel in the fuel rail increases the time required for engine startup. 
         [0004]    During engine operation, the pump may pressurize fuel supplied to the fuel rail to maintain fuel in the fuel rail in a liquid state. Operating the pump may increase fuel consumption and cause noise. 
       SUMMARY 
       [0005]    An engine assembly may include an engine structure defining a combustion chamber and a liquefied petroleum gas (LPG) fuel assembly including a fuel tank, a fuel pump, a fuel rail, a fuel injector, and a flow control mechanism. The fuel tank may contain LPG fuel and the fuel pump may be in communication with the LPG fuel. The fuel rail may have an inlet in communication with the fuel pump, an injection passageway in communication with the inlet, and an outlet in communication with the fuel injection passageway. The fuel injector may be in communication with the fuel injection passageway and the combustion chamber. The flow control mechanism may be in communication with the outlet of the fuel rail and the fuel tank and may be operable in first and second modes. The second mode may provide a greater flow restriction from the fuel rail to the fuel tank than the first mode to control a fuel flow from the outlet of the fuel rail to the fuel tank. 
         [0006]    A method of controlling LPG fuel supply may include providing pressurized LPG fuel to an inlet of a fuel rail, distributing the LPG fuel to a fuel injector through an injection passageway of the fuel rail that is in communication with the inlet, controlling LPG fuel flow exiting the fuel rail through a fuel rail outlet via a flow control mechanism in communication with the outlet of the fuel rail and a fuel tank in first and second modes, the second mode providing a greater flow restriction than the first mode to control a fuel flow from the outlet of the fuel rail to the fuel tank. 
         [0007]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0008]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0009]      FIG. 1  is a schematic illustration of an engine assembly according to the present disclosure; and 
           [0010]      FIG. 2  is a flowchart illustrating operation of the engine assembly according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0012]    Referring now to  FIG. 1 , an exemplary engine assembly  10  is schematically illustrated. The engine assembly  10  may form a liquefied petroleum gas (LPG) engine assembly including an engine structure  12  defining cylinder bores  14  and injection ports  16 , pistons  18 , an intake manifold  20 , an exhaust manifold  22 , and a fuel assembly  23 . The engine structure  12  may include an engine block that defines the cylinder bores  14  and a cylinder head that defines the injection ports  16 . While the engine assembly  10  is illustrated as including an inline four cylinder engine, it is understood that the present disclosure applies equally to engines having any number of cylinders and arrangements including, but not limited to, inline and V-engines. 
         [0013]    The pistons  18  may be disposed within the cylinder bores  14  for reciprocal displacement therein. The intake manifold  20  may be in communication with the cylinder bores  14  to provide airflow (indicated by arrow A) into the cylinder bores  14 . The exhaust manifold  22  may be in communication with the cylinder bores  14  to transport exhaust gases (indicated by arrow E) away from the cylinder bores  14 . 
         [0014]    The fuel assembly  23  may form a LPG fuel assembly including a fuel tank  24 , a fuel pump  26 , a motor  28 , a fuel supply line  30 , a fuel rail  32 , fuel injectors  34 , a fuel return line  44 , and a flow control mechanism  45 . The fuel pump  26  and the motor  28  may be located in the fuel tank  24 . The fuel tank  24  may form an LPG tank and may store LPG therein. The fuel pump  26  may be driven by the motor  28  and may generate a fuel flow (indicated by arrow F) from the fuel tank  24  through the fuel supply line  30 . 
         [0015]    The fuel rail  32  may include an inlet  38  in communication with the fuel supply line  30 , and injection passageways  40  in communication with the inlet  38  and an outlet  42  of the fuel rail  32 . The fuel injectors  34  may be in communication with the injection passageways  40 . The fuel rail  32  may receive fuel flow from the fuel pump  26  and distribute fuel to the fuel injectors  34 . The fuel injectors  34  may provide fuel to the cylinder bores  14 . By way of non-limiting example, the fuel injectors  34  may inject fuel directly into the cylinder bores  14 . Alternatively, the fuel injectors  34  may inject fuel into the injection ports  16  and reciprocal movement of the pistons  18  within the cylinder bores  14  may create a vacuum that draws the fuel from injection ports  36  into the cylinder bores  14 . 
         [0016]    The fuel return line  44  may be in communication with the outlet  42  and the fuel tank  24  and may return fuel from the fuel rail  32  to the fuel tank  24 . The flow control mechanism  45  may be in communication with and located between the outlet  42  and the fuel tank  24 . By way of non-limiting example, the flow control mechanism  45  may be located between the outlet  42  and the fuel return line  44 , between the fuel return line  44  and the fuel tank  24 , or within the fuel return line  44 . 
         [0017]    By way of non-limiting example, the flow control mechanism  45  may include a variable orifice and may provide a variable flow restriction between the outlet  42  and the fuel tank  24 . The variable flow restriction may be varied between no restriction, complete restriction (i.e., no flow), and any restriction therebetween. 
         [0018]    The engine assembly  10  may further include a control module  46 , a coolant temperature sensor  48 , an oil temperature sensor  50 , a fuel rail pressure sensor  52 , a fuel tank temperature sensor  54 , and a fuel tank pressure sensor  56 . 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, and/or other suitable components that provide the described functionality. The control module  46  may control operation of the motor  28  and the flow control mechanism  45 . By way of non-limiting example, the control module  46  may control operation of the motor  28  and the flow control mechanism  45  via pulse width modulation (PWM) of signals sent thereto. 
         [0019]    The coolant temperature sensor  48  and the oil temperature sensor  50  may provide signals to the control module  46  that respectively indicate the temperature of oil in the engine structure  12  and the temperature of coolant in the engine structure  12 . The fuel rail pressure sensor  52 , the fuel tank temperature sensor  54 , and the fuel tank pressure sensor  56  may provide signals to the control module  46  that respectively indicate the pressure of fuel in the fuel rail  32 , the temperature of fuel in the fuel tank  24 , and the pressure of fuel in the fuel tank  24 . 
         [0020]    Operation of the fuel assembly  23  is illustrated in the control logic shown in  FIG. 2 . Control module  46  may determine when engine startup is initiated in step  100  based on a signal received from an ignition system. Engine startup may be initiated when a driver turns an ignition key to a start position. Control module  46  may activate the motor  28  to drive the fuel pump  26  in step  102  when engine startup is initiated and provide fuel flow to the fuel rail  32  via the fuel supply line  30 . In turn, the fuel flow may travel through the fuel rail  32 , the flow control mechanism  45 , and the return line  44 . 
         [0021]    Control module  46  may determine whether the temperature of the fuel rail  32  is greater than a temperature threshold in step  104 . The temperature threshold may be a temperature at which fuel in the fuel rail  32  transitions from liquid to vapor. The temperature threshold may be a predetermined value based on the pressure in the fuel rail  32  received from the fuel rail pressure sensor  52 . 
         [0022]    Control module  46  may determine the temperature of the fuel rail  32  based on the coolant temperature from the coolant temperature sensor  48 , the oil temperature from the oil temperature sensor  50 , and an engine-off period. The engine-off period may be a period of time during which the engine assembly  10  is shutoff. Control module  46  may determine the temperature of the fuel rail  32  based on a predetermined relationship between the coolant and oil temperatures when the engine assembly  10  is initially shut off, the engine-off period, and the temperature of the fuel rail  32 . 
         [0023]    Control module  46  may operate the flow control mechanism  45  in a first mode in step  106  when the temperature of the fuel rail  32  is greater than the temperature threshold. In step  108 , the flow control mechanism  45  may adjust to a first position to provide a first flow restriction. By way of non-limiting example, the first position may be a fully open position (e.g., 100 percent open), a partially open position (e.g., 95 percent open), and any position therebetween. The first flow restriction may provide limited or no restriction of the fuel flow traveling through the flow control mechanism  45 . 
         [0024]    Control module  46  may continue to operate the flow control mechanism  45  in the first mode when the temperature of the fuel rail  32  is greater than the temperature threshold. In this manner, the LPG engine assembly of the present disclosure may minimize the time required to purge a rail of vapor LPG during a hot start (i.e., engine startup when outside temperatures are hot) and during a short soak restart (i.e., engine startup following a short engine-off period). In turn, the time required for engine startup during hot start or short soak restart may be minimized. 
         [0025]    Control module  46  may operate the flow control mechanism  45  in a second mode in step  110  when the temperature of the fuel rail  32  is less than or equal to the temperature threshold. In the second mode, the flow control mechanism  45  may adjust to a second position to provide a second flow restriction that is greater than the first flow restriction. By way of non-limiting example, the second position may be a fully closed position (e.g., 0 percent open), a partially closed position (e.g., 90 percent open), and any position therebetween. The second flow restriction may partially or completely restrict the fuel flow traveling through the flow control mechanism  45 , thereby limiting fuel flow from the fuel rail  32  to the fuel tank  24 , which increases the pressure in the fuel rail  32 . 
         [0026]    Control module  46  may determine whether a difference between the pressure in the fuel rail  32  and the pressure in the fuel tank  24  is less than a desired pressure difference in step  112 . The difference between the pressure in the fuel tank  24  and the pressure in the fuel rail  32  may be referred to as a system pressure head. The desired pressure difference may be predetermined to maintain the fuel flow traveling through the fuel rail  32  in a liquid state. 
         [0027]    Control module  46  may determine the pressure in the fuel rail  32  and the pressure in the fuel tank  24  based on the signals received from the fuel rail pressure sensor  52  and the fuel tank pressure sensor  56 , respectively. Alternatively, the pressure in the fuel rail  32  may be determined based on the coolant temperature from the coolant temperature sensor  48 , the oil temperature from the oil temperature sensor  50 , and the engine-off period using the methods discussed above in reference to determining the temperature of the fuel rail  32 . In addition, the pressure in the fuel tank  24  may be a predetermined value based on a fuel temperature and a type of fuel. By way of non-limiting example, the pressure in the fuel tank  24  may range from 350 kPa to 1400 kPa when the fuel temperature ranges from −10 degrees Celsius to 40 degrees Celsius and the type of fuel contained in the fuel tank  24  is propane. The fuel temperature may be determined based on an ambient temperature. 
         [0028]    Control module  46  may decrease a work output of the fuel pump  26  and/or adjust the flow control mechanism  45  to decrease a restriction of the fuel flow in step  114  when the system pressure head is greater than the desired pressure difference. Control module  46  may adjust the work output of the fuel pump  26  by adjusting the duty cycle of the signal sent to the motor  28 . The work output of the fuel pump  26  and/or the restriction of the fuel flow traveling through the flow control mechanism  45  may be decreased to decrease the pressure in the fuel rail  32 . The pressure in the fuel rail  32  may be decreased until the system pressure head is greater than the desired pressure difference. 
         [0029]    Control module  46  may determine whether the work output of the fuel pump  26  is equal to a maximum work output in step  116  when the system pressure head is less than desired. The work output of the fuel pump  26  may be equal to the maximum work output when a duty cycle of a PWM signal sent to the motor  28  is 100 percent. Control module  46  may increase the work output of the fuel pump  26  by increasing the duty cycle of the PWM signal sent to the motor  28  in step  118  when the work output of the fuel pump  26  is less than the maximum work output. In addition, control module  46  may maintain the flow control mechanism  45  in the fully open position, the partially open position, or positions therebetween when the work output of the fuel pump  26  is less than the maximum work output. 
         [0030]    The flow control mechanism  45  may be adjusted to the partially closed position or the fully closed position in step  120  when the work output of the fuel pump  26  is equal to the maximum work output. Control module  46  may continue to restrict the fuel flow traveling through the flow control mechanism  45  until the system pressure head is greater than or equal to the desired pressure difference. 
         [0031]    In this manner, an increased system pressure head may be achieved for a fuel pump. Increasing the achievable system pressure head may be desirable during certain conditions such as post purge (i.e., period after rail purge and before engine startup) and normal driving (i.e., engine operating). This minimizes the amount of pump work necessary to achieve a system pressure head that maintains liquid LPG in a rail, which reduces fuel consumption and eliminates noise. 
         [0032]    In addition, an increased system pressure head may be beneficial during post purge to reliably start an engine. The LPG engine assembly of the present disclosure provides the ability to maximize the system pressure head and to minimize the time required to achieve the increase system pressure head. In turn, the reliability of engine startup may be improved and the time required for engine startup may be reduced. 
         [0033]    Moreover, locating a flow control device adjacent to an outlet end of a fuel rail minimizes the length of fuel line to be purged, which minimizes the fuel to be purged. This further reduces the period required for engine startup.