Abstract:
A drive system comprises a shaft in rotational engagement with a crankshaft of an engine, the shaft including a first cam having a first quantity of lobes; and a second cam having a second quantity of lobes greater than the first quantity of lobes; and a selection mechanism to selectively engage a follower to one of the first cam or the second cam. A method comprises rotating a shaft having a first cam and a second cam; monitoring operating parameters of a vehicle; operating a fuel pump of the vehicle at a desired capacity based on the monitoring, including selectively engaging the fuel pump to one of the first cam and the second cam.

Description:
FIELD 
     The present disclosure relates to fuel pumps in vehicles, and more specifically, to high pressure fuel pumps in vehicles. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Vehicles may utilize a fuel pump to provide fuel to be combusted during operation of an engine. A fuel pump used to provide fuel to an engine may be a piston pump. The piston pump may be driven by a crankshaft output through a chain gear and cam. 
     In some vehicle operating conditions a requested fuel supply may exceed the capacity of a fuel pump configuration. For example, at vehicle cold start it may be desired to provide additional fuel to the combustion chamber. Increased fuel at cold start may be used with fuels such as ethanol blends, an example of which is an 85% blend of ethanol (E85). Another example of an operating condition requiring an increased fuel supply may be a heavy load where more fuel is required to power the engine. 
     In some vehicle operating conditions, the piston pump operation may not be optimal. For example, at high engine speeds the piston and cam may fail to engage properly. In such a “no-follow” condition the piston of the fuel pump may not stroke properly. 
     SUMMARY 
     A drive system comprises a shaft in rotational engagement with a crankshaft of an engine, the shaft including a first cam having a first quantity of lobes; and a second cam having a second quantity of lobes greater than the first quantity of lobes; and a selection mechanism to selectively engage a follower to one of the first cam or the second cam. 
     A method comprises rotating a shaft having a first cam and a second cam; monitoring operating parameters of a vehicle; operating a fuel pump of the vehicle at a desired capacity based on the monitoring, including selectively engaging the fuel pump to one of the first cam and the second cam. 
     A control module comprises an operating mode determination module monitoring operating parameters of a vehicle and determining a capacity of a fuel pump; and a fuel pump mode selection module in communication with the operating mode determination module to selectively engage the fuel pump to one of a first cam and a second cam. 
     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 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. The present teachings will be become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an exemplary powertrain; 
         FIG. 2  is a schematic illustration of a two-step cam follower mechanism; 
         FIG. 3  is a profile view of a four-lobe cam; 
         FIG. 4  is a profile view of a two-lobe cam; 
         FIG. 5  is a block diagram of a control module for a vehicle; and 
         FIG. 6  is a flow diagram describing the steps in high pressure pump actuation in a vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the present teachings, applications, or uses. For purposes of clarity, the same reference numbers may 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 combination of logic circuits, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary vehicle  10  is schematically illustrated. Vehicle  10  may include engine  12 , which may be in communication with fuel system  14 , intake system  30 , ignition system  34 , exhaust system  32 , coupling  28  and transmission  26 . Fuel system  14  may include fuel pump  16 , fuel rail  18 , injection system  20 , two-step cam mechanism  22 , and fuel line  36 . Two-step cam mechanism  22  may be in communication with coupling  28 . Control module  24  may be in communication with engine  12 , fuel pump  16 , fuel rail  18 , injection system  20 , intake system  30 , and ignition system  34 . Engine  12  may be a spark ignition direct injection (SIDI) engine. A SIDI engine  12  may require high pressure fuel for direct injection. Although the following description includes a SIDI engine, it should be recognized that this description may apply to any engine  12  that utilizes a fuel pump  16 . 
     Engine  12  may have access points through which fuel may be injected into a combustion chamber of engine  12 . Fuel may be provided by fuel system  14  and intake system  30  may provide air to engine  12 . The location of the fuel injection points may allow engine  12  to operate with a lean fuel-to-air mixture in comparison to conventional engines without direct fuel injection. Ignition system  34  may provide a spark to ignite the fuel and air mixture in engine  12 . When operated in this manner, engine  12  may produce an output power equivalent to conventional engine while using less fuel. 
     Coupling  28  may engage two-step cam mechanism  22  to the crankshaft (not pictured) of engine  12 . Alternatively, the two-step cam mechanism  22  may be directly driven by the engine camshaft (not pictured) or by placing the pump cam actuation cams on an engine camshaft (not pictured). Coupling  28  may be any system that transfers rotational energy to two-step cam mechanism  22  from the crankshaft or camshaft of engine  12 . Two-step cam mechanism  22  may be a shaft having two or more cams with two or more lobe profiles, as will be described in more detail below. Two-step cam mechanism  22  or fuel pump  16  may include a cam follower that may selectively engage a cam of two-step cam mechanism  22  to provide power to fuel pump  16 , which may be a piston pump. Fuel pump  16  may provide high pressure fuel to fuel rail  18  through fuel line  36 . Fuel rail  18  may deliver the high pressure fuel to injection system  20  at the direct injection inputs of engine  12 . Injection system  20  may provide fuel directly to the engine combustion chamber such as in an atomized spray. 
     Intake system  30  may provide air to engine  12  and ignition system  34  may provide a spark for ignition of the air-fuel mixture in a combustion chamber of engine  12 . Combustion of the air-fuel mixture in engine  12  may produce exhaust which may exit engine  12  through exhaust system  32 . Combustion of the air-fuel mixture in engine  12  may also provide power that is transferred to transmission  26 . 
     Control module  24  may monitor, control and communicate with components of vehicle  10  including engine  12 , fuel system  14 , intake system  30  and ignition system  34 . Control module  24  may receive measurements and status indicators, and may provide commands that control the operation of components of vehicle  10 . 
     Referring now to  FIG. 2 , two-step cam mechanism  22  and fuel pump  16  are depicted in more detail. Two-step cam mechanism  22  may include shaft  46 , outer cams  40  and  44 , and inner cam  42 . Cam follower  48  may be integral to fuel pump  16  or may be coupled to fuel pump  16 . Cam follower  48  may include selection mechanism  50 , inner follower  52 , outer follower  54 , inner spring  56  and outer spring  58 . Although two-step cam mechanism  22  is depicted with two outer cams  40  and  44 , and inner cam  42 , it should be recognized that two-step cam mechanism  22  will operate properly with any shaft  46  having at least two cams. Shaft  46  may be drivingly engaged with coupling  28  (not shown) that transfers power from a crankshaft of engine  12  to shaft  46 . Alternatively, shaft  46  may be integral with a camshaft of engine  12  or driven directly by a camshaft of engine  12 . Cams  40 ,  42  and  44  may be affixed about shaft  46  such that cams  40 ,  42 , and  44  rotate with shaft  46 . 
     Follower  48  may be selectively engaged with one or more of cams  40 ,  42  and  44 . Although follower  48  is depicted, it should be recognized that numerous follower mechanisms may be operable to select one or more of cams  40 ,  42 , and  44 . The other end of follower  48  may be engaged with a piston of fuel pump  16 . Selection mechanism  50  may be a conventional hydraulic mechanism that may selectively lock inner follower  52  within outer follower  54 , as depicted in  FIG. 2 . When inner follower  52  is locked within outer follower  54 , follower  48  may translate motion to a piston of fuel pump  16  relative to the rotation of outer cams  40  and  44 . When inner follower  52  is not locked within outer follower  54 , follower  48  may translate motion to a piston of fuel pump  16  relative to the rotation of inner cam  42 . Outer cams  40  and  44  may have a lobe profile with four lobes while inner cam  42  may have a lobe profile with two lobes. When shaft  46  rotates, follower  48  may be displaced relative to the lobe profile of the cam that follower  48  is engaged with such that a piston of fuel pump  16  completes a stroke for each lobe. 
     Referring now to  FIG. 3 , a profile view of outer cams  40  and  44  about shaft  46  is depicted. Outer cams  40  and  44  may have a 4-lobe profile with each set of opposing lobes having a generally oval shape. When in communication with outer cams  40  and  44 , follower  48  may be fully displaced to stroke a piston of fuel pump  48  four times for each revolution of shaft  46 . 
     Referring now to  FIG. 4 , a profile view of inner cam  42  about shaft  46  is depicted. Inner cam  42  may have a generally oval shape. A follower  48  in communication with inner cam  42  with a 2-lobe profile may be fully displaced to stroke a piston of fuel pump  16  twice for each revolution of shaft  46 . In this manner, the differing lobe profiles of outer cams  40  and  44 , and inner cam  42  may allow the capacity of fuel pump  16  to vary based on the selected cam. It should be recognized that the 4-lobe profile may be the inner cam while the 2-lobe profile may be the outer cams. It should also be recognized that different numbers of lobes and different lobe profiles may be used to stroke a piston of fuel pump  16 . 
     Referring now to  FIG. 5 , control module  24  may include engine control module  60 , operating mode determination module  62 , and fuel pump mode selection module  64 . Engine control module  60  may include ignition system control module  70 , intake system control module  72 , and fuel system control module  74 . Operating mode determination module  62  may be in communication with fuel pump mode selection module  64  and engine control module  60 . Operating mode determination module  62  may monitor or receive parameters from engine control module  60  or other components of vehicle  10  that may be in communication with control module  24 . Based on the status of monitored or received parameters, operating mode determination module  62  may communicate an operating mode status to fuel pump mode selection module  64  and engine control module  60 . 
     Fuel pump mode selection module  64  may receive an operating mode status from operating mode determination module  62  and may be in communication with selection mechanism  50  and fuel pump  16  to select a mode for fuel pump  16 . Engine control module  60  may be in communication with engine  12 , ignition system control module  70  may be in communication with ignition system  34 , intake system control module  72  may be in communication with intake system  30 , and fuel system control module  74  may be in communication with fuel system  14  and components thereof such as fuel pump  16 , fuel rail  18  and injection system  20 . Engine control module  60 , ignition system control module  70 , intake system control module  72 , and fuel system control module  74  may provide fuel, air, and ignition to engine  12  based on driver inputs, monitored and received parameters from components of vehicle  10 , and an operating mode as determined by operating mode determination module  62 . 
     Referring now to  FIG. 6 , a flowchart illustrates control logic  100 . At block  102 , engine control module  60  may determine the engine speed. Control logic  100  may then continue to block  104 . At block  104 , operating mode determination module  62  may receive the determined engine speed and may compare the determined engine speed to a 4-lobe limit. A 4-lobe limit may be based on an engine speed at which a no-follow condition may occur such that 4-lobe outer cams  40  and  44  and follower  48  may not engage properly. For example, outer spring  58  may not provide enough force when the outer cams  40  and  44  are rotating at a high speed. For example, the 4-lobe limit may be based on an engine speed at which a no-follow condition occurs, such as 2500 rpm or greater. If operating mode determination module  62  determines that the measured engine speed exceeds the 4-lobe limit, control logic  100  may continue to block  118 . If the measured engine speed does not exceed the 4-lobe of limit, control logic  100  may continue to block  106 . 
     At block  106 , engine control module  60  may determine from monitored or measured engine parameters whether a vehicle cold start condition exists and communicate that information to operating mode determination module  62 . A cold start condition may include when engine  12  has not been started for an extended period of time. If a cold start condition exists, control logic  100  may continue to block  112 . If a cold start condition does not exist, control logic  100  may continue to block  108 . 
     At block  112 , engine control module  60  may determine a coolant temperature based on monitored or received perimeters. Control logic  100  may then continue to block  114 . At block  114 , operating mode determination module  62  may receive a coolant temperature from engine control module  60  and determine whether the temperature measured at block  112  exceeds a 4-lobe limit. A 4-lobe limit may be based on a coolant temperature that indicates that the engine  12  is not in a cold-start condition. If operating mode determination module  62  determines that the coolant temperature does not exceed the 4-lobe limit, the control logic  100  may continue to block  116 . If operating mode determination module  62  determines that the coolant temperature does exceed the 4-lobe limit, control logic  100  may continue to block  118 . 
     If at block  106  engine control module  60  has determined that a cold start condition does not exist, control logic  100  may continue to block  108  where engine control module  60  and/or fuel system control module  74  may determine a requested fuel flow from monitored or received perimeters. Control logic  100  may continue to block  110  where operating mode control module  62  may determine whether the amount of fuel requested for operation of engine  12  exceeds the capacity of 2-lobe inner cam  42 . If operating mode determination module  62  determines that the fuel requested exceeds the 2-lobe capacity, control logic  100  may continue to block  116 . If operating mode determination module  62  determines that the requested fuel does not exceed the 2-lobe capacity, control logic  100  may continue to block  118 . 
     Based on the operation of control logic  100 , block  118  may be reached if the engine speed exceeds the 4-lobe limit at block  104 , if a cold start condition exists at block  106  but the coolant temperature exceeds a 4-lobe limit at block  114 , or if a cold start condition does not exist at block  106  and the requested fuel does not exceed a 2-lobe capacity at block  110 . 
     At block  118  operating mode determination module  62  may communicate that 2-lobe operation is enabled to fuel pump mode selection module  64  and engine control module  60 . Fuel pump mode selection module  64  may communicate with fuel pump  16  such that selection mechanism  50  may allow inner follower  52  of follower  48  to engage 2-lobe inner cam  42 . Follower  48  may be displaced to fully stroke the piston of fuel pump  16  twice per revolution of shaft  46  and 2-lobe inner cam  42 . 
     Engine control module  60 , ignition system control module  70 , intake system control module  72 , and fuel system control module  74  may control engine  12 , ignition system  34 , intake system  30  and fuel system  14  to operate based on a fuel pump capacity for 2-lobe operation. Once 2-lobe operation is enabled at block  118 , control logic  100  may end. 
     Control logic  100  may reach block  116  if the measured engine speed does not exceed the four-lobe limit at block  104 , and a requested fuel flow exceeds the 2-lobe capacity at block  110  in a non-cold start condition from block  106 , or if a cold start condition exists at block  106  and the coolant temperature does not exceed a 4-lobe limit at block  114 . 
     At block  116  operating mode determination module  62  may communicate that four-lobe operation is enabled to engine control module  60  and fuel pump mode selection module  64 . Fuel pump mode selection module  64  may communicate with fuel pump  16  such that selection mechanism  50  may allow outer follower  54  of follower  48  to engage 4-lobe outer cams  40  and  44 . Follower  48  may be displaced to fully stroke the piston of fuel pump  16  four times per revolution of the 4-lobe outer cams  40  and  44 . 
     Engine control module  60 , ignition system control module  70 , intake system control module  72 , and fuel system control module  74  may control engine  12 , ignition system  34 , intake system  30  and fuel system  14  to operate based on a fuel pump capacity for 4-lobe operation. Once 4-lobe operation is enabled at block  116 , control logic  100  may end. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of this disclosure should not be so limited since other modification will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.