Combined start bypass and safety pressure relief valve for a fuel system

Abstract: A high pressure fuel system (10) includes a combination bypass and safety pressure release valve (24) across the high pressure fuel pump (22). The combination valve (24) allows the feed pump to directly provide fuel to the system before the high pressure pump reaches full output pressure. The valve (80) also releases overpressure in the system when the high pressure pump is deadheaded. The combination valve includes a check ball (88) which allows fuel to flow from its input to its output when the pressure is greater at its input than at its output.

Description: Field of the Invention The present invention relates generally to a fuel system for an engine, and more particularly to a method and apparatus for providing fuel to an engine in a high pressure fuel injection system. Background of the Invention High pressure fuel injection systems typically include positive displacement pumps such as a swash plate pump or cam ring piston pump to provide highly pressurized fuel (e.g., 30-150 bar system pressure) to fuel injectors in an engine. The positive displacement pump or high pressure pump is mechanically coupled to the engine via a belt, gear, or clutch drive which turns the pump at a ratio of the engine speed. Thus, the performance of the high pressure pump is dependent on the speed of cranking, rotating, or turning of the engine. Generally, the high pressure pump, which is driven by the engine, is not able to provide full or operating pressure at its output until the engine has been started. Providing the fuel at the operating pressure is necessary for the fuel injectors in the high pressure fuel system to provide proper atomization and high delivery rates. High pressure fuel systems are typically equipped with a feed pump or conventional low pressure pump in the fuel tank which supplies the fuel to the high pressure pump in the engine compartment. The output of the low pressure pump is generally coupled to the input of the high pressure pump. The low pressure pumps are often electric pumps such as a vane pump, turbine pump, or roller pump and cannot create high system pressures required for atomization and high delivery rates. However, these pumps are able to relatively quickly provide low pressure fuel from the tank independent of engine revolutions. The low pressure pumps provide the fuel at the specified low pressure as soon as the electrical system of the vehicle or other engine system is turned on. Generally, fuel cannot be directly provided by the low pressure pump through the high pressure pump to the engine because restrictive clearances in the pistons of the high pressure pump prevent fuel flow through the high pressure pump. Heretofore, starting an engine equipped with a high pressure pump is an objectively slow process because the high pressure pump is not able to provide the fuel until the engine has been started, or cranked (e.g., turned over) a significant number of times. Another problem associated with high pressure pumps involves the generation of extremely high output pressures when the high pressure pump is deadhead, such as when the high pressure fuel system becomes a closed system due to a system failure. If the regulator or other parts of the high pressure fuel system malfunction, the high pressure pump can be deadheaded (e.g., have no path back to the fuel tank) and can generate extremely high pressures at the output of the pump. The high pressures may even exceed the proof pressure of the system, resulting in catastrophic failure of hoses or seals in the high pressure fuel system of the engine. Japanese patent No. 62-21056 (JP'056) discloses a fuel supply device for an internal combustion engine in which a mechanical pump that is driven by the output of the engine and an electrically operated pump that is driven independently of this mechanical pump are arranged in series in a fuel supply passage. In JP'056 the mechanical pump is provided with a fuel passage connecting an inlet passage and an outlet passage and in this fuel passage there is provided a bypass valve body that is opened in the direction such as to allow passage of fuel from the inlet passage to the outlet passage in the condition that the pressure of said inlet passage has become more than a set value. JP'056 further show the bypass valve body integrally assembled with a relief valve body that is capable of valve opening in a direction such as to permit return of fuel from this outlet passage to the inlet passage in the condition that the pressure of said outlet passage has become more than a prescribed value. Thus, there is a need for a high pressure fuel system which quickly supplies fuel to the engine as the engine is started. Further, there is a need for a high pressure fuel injection system which allows the feed pump to directly provide fuel to the engine. Additionally, there is a need for a high pressure fuel system which includes overpressure protection. Summary of the Invention The present invention relates to an integral start bypass and pressure relief valve for use in a fuel system having a high pressure pump with a pump inlet and a pump outlet, the valve comprising a housing ; a valve inlet in said housing coupled to the pump inlet; a valve outlet in said housing coupled to the pump outlet; a first bypass valve means disposed in said housing between said valve inlet and said valve outlet to allow the fuel to flow from said valve inlet to said valve outlet when a fluid pressure difference across said valve inlet and said valve outlet exceeds a first limit, thereby allowing the fuel to bypass the high pressure pump when the high pressure pump is not providing highly pressurized fuel at the pump outlet; a second bypass valve means disposed in said housing between said valve outlet and said valve inlet, said valve allowing the fuel to flow from the pump outlet to the pump inlet when the fluid pressure difference across said valve inlet and said valve outlet reaches a second limit; said integral bypass valve further comprises a stepped bore section in said housing extending between said valve inlet and said valve outlet and said bore section having a cylindrical section and a chamfer section connecting said cylindrical section with said valve inlet; a bypass valve body located in said cylindrical section, said valve body sealed within said cylindrical section by sealing means circumferentially around one end; a relief spring in said chamfer section in contact with said valve body; and wherein said bypass valve body is movable in said cylindrical section against said relief spring and said sealing means able to enter said chamfer section, thereby allowing the fuel to flow from said pump outlet to said pump inlet around said valve body when the pressure difference exceeds said second limit. The bypass valve thereby allows the fuel at the first pressure to bypass the high pressure pump. The second limit may be representative of an overpressure condition for the fuel system. The first bypass valve may include a check ball disposal in said valve body between said valve inlet and valve outlet and a check valve spring biasing the check ball within said valve body. The present invention also relates to a method of providing fuel in a fuel system from a tank to an engine as the engine is started. The fuel system includes a feed pump in fluid communication with the tank, a high pressure pump having a pump inlet and a pump outlet. The feed pump has a feed output in fluid communication with the pump inlet and a pump outlet. The feed pump has a feed output in fluid communication with the pump inlet. The fuel system also includes an integral start bypass and pressure relief valve which comprises a housing, a valve body, a valve inlet in fluid communication with the pump inlet, a valve outlet in fluid communication with the pump outlet, a first bypass valve means disposed in said housing between said valve inlet and said valve outlet, and a second bypass valve means disposed in said housing between said valve outlet and said valve inlet. The integral start bypass and pressure relief valve also comprises a stepped bore section in said housing extending between said valve inlet and said valve outlet. The bore section has a cylindrical section and a chamfer section connecting said cylindrical section with said valve inlet. The valve body is located in said cylindrical section and valve body is sealed within said cylindrical section by sealing means circumferentially around one end. A relief spring in said chamfer section is in contact with said valve body. The valve body is movable in said cylindrical section against said relief spring and said sealing means is able to enter said chamfer section. The feed pump provides fuel at a first pressure and the high pressure pump provides the fuel at a second pressure, the second pressure being greater than the first pressure under normal conditions. The method is characterised by the steps of operating the feed pump to provide the fuel at a first pressure to the pump inlet; arranging the first and second bypass value means to allow the fuel at the first pressure to flow from the valve inlet to the valve outlet through the valve and prevent the fuel from flowing through the valve from the valve outlet to the valve inlet as the engine is started; operating the high pressure pump to provide the fuel at a second pressure at the pump outlet; and further arranging the first and second bypass means to prevent the fuel at the first pressure from flowing from the valve inlet through the valve to the valve outlet after the engine is started and to allow the fuel to flow from the pump outlet around the valve body to the pump inlet when the second pressure reaches an overpressure threshold. In one exemplary aspect of the present invention, an integral start bypass and safety pressure relief valve can be provided across a high pressure pump in a high pressure gasoline fuel injection system. The valve advantageously provides a bypass for the low pressure fuel before the high pressure pump reaches operating pressure. Once the high pressure pump reaches operating pressure, the valve is closed and prevents fuel from flowing across the high pressure pump. Additionally, the valve can provide a relief outlet for the high pressure system when the high pressure fuel system reaches an overpressure condition such as when the high pressure pump is deadheaded. The integral start bypass and safety pressure release valve advantageously reduces the amount of time to start an engine by providing low pressure fuel to the fuel system with a low pressure pump until the high pressure pump is driven by the engine. The high pressure pump may reach operating pressure during the cranking of the engine. The valve also advantageously returns fuel to the pump inlet without need for an added line to the fuel tank in the event of an overpressure condition. A relief mechanism in the valve is preferably a spring and piston relief assembly. The relief assembly is held closed until the force of an overpressure condition moves the assembly against the spring and opens a relief output. Brief Description of the Drawings The invention will hereafter be described with reference to the accompanying drawings wherein like referenced numerals denote like elements, and: Figure 1 is a simplified schematic block diagram of a high pressure fuel system including a check and relief valve for use with an engine in accordance with an exemplary embodiment of the present invention; and Figure 2 is a cross-sectional view along the centerline of the cylindrical check and relief valve illustrated in Figure 1. Detailed Description of the Preferred Exemplary Embodiment Referring generally to the schematic block diagram of Figure 1, a high pressure fuel system 10 is coupled to fuel injectors 12 of an engine 14. Engine 14 may be a gasoline powered automobile engine or other combustion motor which utilizes fuel. High pressure fuel system 10 supplies fuel to fuel injectors 12 of engine 14. The fuel is provided at a high pressure such as 30 to 150 bar. The pressure of the fuel must be high enough for proper atomization and high delivery rates for engine 14. High pressure fuel system 10 includes a fuel tank 16 having an in-tank electric pump or low pressure pump 18, a fuel filter 20, a positive displacement pump or high pressure pump 22, a combination check and relief valve 24, a high pressure regulator 28, a solenoid 33, a fuel rail 30, a regulator control circuit 36, an electronic control circuit 38, an injector driver circuit 40, and a pressure sensor 42. Low pressure fuel pump 18 is in fluid communication with fuel 15 in tank 16. Fuel 15 is preferably gasoline. Fuel pump 18 is a feed pump and has a feed outlet 29 coupled through fuel filter 20 to a pump input or inlet 44 of high pressure pump 22. Pump inlet 44 is coupled to a valve input or inlet 46 of valve 24, and a pump output or outlet 47 of high pressure pump 22 is coupled to a valve output or outlet 48 of valve 24. Pump outlet 47 is also coupled to a regulator input 49 of regulator 28. Regulator 28 includes a tank outlet 52 coupled to tank 16 and a fuel rail output 54 coupled to fuel rail 30. Fuel rail 30 provides fuel to fuel injectors 12 at outputs 56. Fuel rail 30 is also in fluid communication with pressure sensor 42. Low pressure pump 18 also includes electrical inputs 58 which receive electrical power for driving pump 18. Pump 18 is turned on by providing the electrical power to inputs 58. Electronic control circuit 38 receives a pressure signal from sensor 42 via a conductor 61 and provides electronic system control signals to regulator control circuit 36 and injector driver circuit 40 in response to the pressure signal on conductor 61 as well as other control criteria. Similarly, regulator control circuit 36 receives the pressure signal on conductor 61 and provides regulator control signals to solenoid 33 in response to the system control signals from electronic control circuit 38 and the pressure signal on conductor 61. Solenoid 33 controls regulator 28 in response to the regulator control signals. Electronic driver circuit 40 is coupled to injectors 12 and provides drive signals to injectors 12 which control the distribution of the fuel to engine 14. Electronic control circuit 38 can cause driver circuit 40 to adjust the drive signals to compensate for different pressures and conditions in system 10. For example, the pulse widths of the drive signals can be increased to compensate for lower pressures in system 10. High pressure fuel pump 22 is mechanically coupled to engine 14 via a valve, gear, or clutch (e.g., dog) drive (not shown). Pump 22 may be a swash plate or cam ring piston pump which is mechanically coupled to engine 14 to rotate at a slower rate than engine 14. Low pressure pump 18 may be a vain pump, turbine pump, or roller pump which provides low pressure fuel at feed output or outlet 29 in response to the electrical power at inputs 58. Preferably, the electrical power at inputs 58 is provided as soon as electrical control system 38 is turned ON such as when an ignition key (not shown) is placed in the ignition (not shown) of engine 14. The operation of high pressure fuel system 10 is discussed generally below as follows. Before engine 14 is started or cranked, a key is placed in the ignition (not shown) and the electrical power is provided on electrical inputs 58 to low pressure fuel pump 18. Low pressure fuel pump 18 pumps fuel 15 from tank 16 at a low pressure through fuel filter 20 to pump inlet 44 of high pressure pump 22. Before engine 14 is started, high pressure pump 22 does not pump the fuel provided by pump 18 because engine 14 has not begun rotating, turning over, or cranking. High pressure pump 22 begins pumping when engine 14 begins cranking and does not provide highly pressured fuel at pump outlet 47 until engine 14 has rotated many times such as after engine 14 has been started. Alternatively, high pressure pump 22 may be configured to provide the highly pressurized fuel at outlet 47 during the cranking or starting of engine 14. However, high pressure pump 22 is not able to provide the fuel at full pressure or rated output until engine 14 has been rotated or cranked a significant number of times. High pressure pump 22 prevents the fuel at pump inlet 22 from reaching pump outlet 47 because restrictive clearances in the pistons (not shown) of high pressure pump 22 block the path from inlet 44 to outlet 47. As engine 14 is started and high pressure pump 22 is unable to provide fuel at pump outlet 47 due to insufficient turns of engine 14, the fuel is provided to valve inlet 46 of combination check and relief valve 24. If the pressure at pump outlet 47 is less than the pressure at pump inlet 44, valve 24 allows fuel to flow from valve inlet 46 to valve outlet 48 so the fuel reaches regulator 28. The fuel provided at feed outlet 29 to pump inlet 44 generally exceeds the pressure of fuel provided at pump outlet 47 when engine 14 is initially started. Valve 24 is also configured to prevent fuel from flowing from valve outlet 48 to valve inlet 46. When high pressure pump 22 provides the fuel at pump outlet 47 at a higher pressure than the fuel at pump inlet 44 (e.g., after engine 14 is started), valve 24 is closed and the fuel is prevented from flowing from valve inlet 46 to valve outlet 48. Additionally, the fuel is always preventing from flowing from valve outlet 48 to valve inlet 46 under normal conditions. Therefore, the fuel is able to bypass high pressure pump 22 when engine 14 is initially started or before pump 22 provides the fuel at full pressure. The fuel is essentially directly provided by low pressure pump 18 to engine 14 before engine 14 is completely started. Combination check and relief valve 24 also advantageously provides a path from valve outlet 48 to valve inlet 46 when the pressure at pump outlet 47 reaches a predetermined threshold representative of an overpressure condition. The predetermined threshold is generally a pressure threshold below the proof pressure of the high pressure fuel system 10 and above the full pressure of pump 22. If high pressure pump 22 is deadheaded (e.g., pressure pump 22 is pumping into a closed system) due to a malfunction of regulator 28 or other portion of system 10, pump 22 can generate significant pressures at pump outlet 47. The pressures can exceed the proof pressure of system 10. When the pressure at pump outlet 47 reaches the predetermined threshold or overpressure threshold (e.g., preferably slightly above the full pressure or normal operating pressure of pump 22), valve 24 provides a path from valve outlet 48 to valve inlet 46 so that the fuel at outlet 47 is returned to tank 16, thereby preventing catastrophic failure of system 10. The configuration of valve 24 advantageously returns the fuel to tank 16 during an overpressure condition without the need for an additional fuel line or path to tank 16. Figure 2 is a cross-sectional view along the centerline of combination check and relief valve 24. Check and relief valve 24 is preferably a cylindrical valve integrated within a stepped bore 70 in a housing 72 of high pressure fuel pump 22 (Figure 1). Bore 70 includes a cylindrical section 74 and a chamfered section 76. A floating valve body 80 is seated within cylindrical section 74 of stepped bore 70. Valve body 80 is sealed within cylindrical section 74 by an O-ring 82. Preferably, cylindrical section 74, valve body 80, and O-ring 82 are sized to prevent leakage from valve inlet 46 to valve outlet 48. Valve 24 includes a bypass assembly 86 and a relief assembly 92. Bypass assembly 86 is disposed within valve body 80 and includes a check ball 88, a check spring 90, and a body inlet 91. Check spring 90 biases check ball 88 against a body inlet 91. Body inlet 91 is in fluid communication with valve inlet 46 via chamfered section 76. Relief assembly 92 includes a relief spring 96, floating valve body 80, O-ring 82, and a fuel inlet fitting 99. Fuel inlet fitting 99 is threaded and engaged with threads 98 of chamfered section 76 to prove a leak proof seal. Relief spring 96 is disposed between valve body 80 and fitting 99 and biases valve body 80 in cylindrical section 74. Valve 24 also includes valve inlet 46 and valve outlet 48. Valve inlet 46 is in fluid communication with chamfered section 76. Valve outlet 48 is in fluid communication with pump outlet 47. Valve inlet 46 is in fluid communication with pump inlet 44 via chamfered section 76. The operation of valve 24 is discussed in more detail with reference to Figure 2. When the pressure at valve inlet 46 exceeds the pressure at valve outlet 48 as when engine 14 is initially started, check ball 88 in bypass assembly 86 is moved against spring 90 and the fuel flows from valve inlet 46 through body inlet 91 to valve outlet 48. When the pressure of the fuel at valve outlet 48 exceeds the pressure of the fuel at valve outlet 46 as when engine 14 has been cranked or rotated many times or when high pressure pump 22 provides the rated pressure (e.g., pressure during normal operation of engine 14) at outlet 47, check ball 88 is forced against body inlet 91, thereby preventing fuel flow from valve inlet 46 and to valve outlet 48 and valve outlet 48 to valve inlet 46. If an overpressure condition exists such as when high pressure pump 22 is deadheaded, excessive pressure builds at valve output 48. If the pressure is above a predetermined threshold below the proof pressure of system 10, floating valve body 80 is moved against relief spring 96. As body 80 is moved against relief spring 96 in relief assembly 92, O-ring 82 enters chamfered section 76 and the fuel is able to flow from valve outlet 48 around valve body 80 into chamfered section 76 and to valve inlet 46. Preferably, relief assembly 92 is designed so that the preload force of relief spring 96 is equal to the force on valve body 80 when the pressure at valve outlet 48 is at the predetermined threshold. When the pressure at valve outlet 48 returns to normal conditions, relief spring 96 pushes valve body 80 back into cylindrical section 74 for normal operation of valve 24. Preferably, the preload force of relief spring 96 is chosen so that it corresponds to a pressure slightly above the normal operating pressure. Such a configuration ensures that valve body 80 is stationary during normal operation to protect valve body 80 and O-ring 82 from excessive wear. The distance from the nominal position of O-ring 82 when valve body 80 is seated within cylindrical section 74 to the position of O-ring 82 where it loses compression (e.g., an overpressure condition) is chosen so that relief spring 96 is compressed the proper distance by the pressure difference between operating pressure of pump 22 and the predetermined threshold. It is understood that, while the detailed specific examples, and particular shapes given describe a preferred exemplary embodiment of the present invention, they are for the purposes of illustration only. The apparatus and method of the invention is not limited to the precise details and conditions disclosed. For example, although a gasoline fuel system 10 is shown, other types of fuel systems may be utilized. Also, although the preferred exemplary embodiment includes a check ball 88, other types of bypass valves may be utilized. Thus, various changes may be made to the details disclosed without departing from the spirit of the invention which is defined by the following claims.

Claims: An integral start bypass and pressure relief valve (24) for use in a fuel system (10) having a high pressure pump (22) with a pump inlet (44) and a pump outlet (47), the valve (24) comprising: a housing (72); a valve inlet (46) in said housing (72) coupled to the pump inlet (44): a valve outlet (48) in said housing (72) coupled to the pump outlet (47); a first bypass valve means (86) disposed in said housing (72) between said valve inlet (46) and said valve outlet (48) to allow the fuel to flow from said valve inlet (46) to said valve outlet (48) when a fluid pressure difference across said valve inlet (46) and said valve outlet (48) exceeds a first limit, thereby allowing the fuel to bypass the high pressure pump (22) when the high pressure (22) pump is not providing highly pressurized fuel at the pump outlet (47); and a second bypass valve means (92) disposed in said housing (72) between said valve outlet (48) and said valve inlet (46), said valve (92) allowing the fuel to flow from the pump outlet (47) to the pump inlet (44) when the fluid pressure difference across said valve inlet (46) and said valve outlet (48) reaches a second limit; characterised in that said bypass valve (24) further comprises; a stepped bore section (70) in said housing (72) extending between said valve inlet (46) and said valve outlet (48) and said bore section (70) having a cylindrical section (74) and a chamfer section (76) connecting said cylindrical section (74) with said valve inlet (46); a bypass valve body (80) located in said cylindrical section (74), said valve body (80) sealed within said cylindrical section (74) by sealing means (82) circumferentially around one end; a relief spring (96) in said chamfer section (76) in contact with said valve body (80); and wherein said bypass valve body (80) is movable in said cylindrical section (74) against said relief spring (96) and said sealing means (82) able to enter said chamfer section (76), thereby allowing the fuel to flow from said pump outlet (47) to said pump inlet (44) around said valve body (80) when the pressure difference exceed said second limit. The integral bypass valve of claim 1, wherein said second limit is representative of an overpressure condition for the fuel system (10). The integral bypass valve of claims 1 or 2, wherein the first bypass valve (86) includes a check ball (88) disposed in said valve body (80) between said valve inlet (46) and valve outlet (48) and a check valve spring (90) biasing the check ball (88) within said valve body (80). The integral bypass valve of claims 1-3, wherein said sealing means (82) is an O-ring. A method of providing fuel in a fuel system (10) from a tank (16) to an engine (14) as the engine is started, the fuel system including a feed pump (18) in fluid communication with the tank, a high pressure pump (22) having a pump inlet (44) and a pump outlet (47), the feed pump (18) having a feed output, the feed output being in fluid communication with the pump inlet (44), and an integral start bypass and pressure relief valve (24) including a housing (72), a valve body (80), a valve inlet (46) in fluid communication with the pump inlet (44), a valve outlet (48) in fluid communication with the pump outlet (47), a first bypass valve means (86) disposed in said housing (72) between said valve inlet (46) and said valve outlet (48), and a second bypass valve means (92) disposed in said housing (72) between said valve outlet (48) and said valve inlet (46), the feed pump (18) providing fuel at a first pressure, the high pressure pump (22) providing the fuel at a second pressure, the second pressure being greater than the first pressure under normal conditions, said bypass valve (24) further comprises; a stepped bore section (70) in said housing (72) extending between said valve inlet (46) and said valve outlet (48) and said bore section (70) having a cylindrical section (74) and a chamfer section (76) connecting said cylindrical section (74) with said valve inlet (46); said valve body (80) being located in said cylindrical section (74), said valve body (80) being sealed within said cylindrical section (74) by sealing means (82) circumferentially around one end; a relief spring (96) in said chamfer section (76) in contact with said valve body (80); and wherein said valve body (80) is movable in said cylindrical section (74) against said relief spring (96) and said sealing means (82) is able to enter said chamfer section (76), the method characterised by the steps of: operating the feed pump (18) to provide the fuel at a first pressure to the pump inlet (44); arranging the first and second bypass valve means (86; 92) to allow the fuel at the first pressure to flow from the valve inlet (46) to the valve outlet (48) through the valve (24) and prevent the fuel from flowing through the valve (24) from the valve outlet (48) to the valve inlet (46) as the engine is started; operating the high pressure pump (22) to provide the fuel at a second pressure at the pump outlet (47); and further arranging the first and second bypass means to prevent the fuel at the first pressure from flowing from the valve inlet (46) through the valve (24) to the valve outlet (48) after the engine is started and to allow the fuel to flow from the pump outlet (47) around the valve body (80) to the pump inlet (44) when the second pressure reaches an overpressure threshold.

Inventors: WAKEMAN RUSSELL J, WAKEMAN, RUSSELL J.
Applicants: SIEMENS AUTOMOTIVE CORP LP, SIEMENS AUTOMOTIVE CORPORATION
Application year: 1996
Main classification: F02M55
IPC codes: F02M63, F02M55, F02M51, F02M69