Fuel systems for internal combustion engines

Abstract

A fuel system (10) includes a low pressure fuel delivery unit (20) and a high pressure fuel delivery unit (22), the high pressure fuel delivery unit having a low pressure zone (30) and a high pressure zone (32), such that the low pressure zone (30) supplies fuel to the high pressure zone (32), and the high pressure zone (32) supplies fuel to a plurality of high pressure fuel injectors (16). A low pressure fuel rail (56) supplies fuel to the low pressure fuel injectors (18). A low pressure fuel injector line (54) is directly connected to the high pressure fuel delivery unit (22) at a first end and receives fuel from the low pressure zone (30), and is directly connected to the low pressure fuel rail (56) at a second end to provide fluid communication from the low pressure zone (30) to the low pressure fuel rail (56). Devices (58a, 58b, 58c, 58d) are located between the low pressure zone (30) and the low pressure fuel rail (56) and reduce fuel pressure pulsations.

Description

[0001] Cross-references to related patent applications

[0002] This patent application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 078,720, filed on September 15, 2020, the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates to a fuel system for an internal combustion engine; more particularly, to a fuel system including a portion that delivers fuel directly to a combustion chamber of the internal combustion engine at a relatively high pressure and a portion that delivers fuel upstream of the combustion chamber at a relatively low pressure; and more particularly, to a fuel system in which a high-pressure fuel delivery unit can be cooled and lubricated even when little or no fuel is delivered directly to the combustion chamber. Background Art

[0004] Fuel systems for modern internal combustion engines typically employ 1) port fuel injection (PFI), in which fuel is injected into the intake manifold or other combustion air passages of the internal combustion engine at a relatively low pressure (typically less than about 500 kPa) and subsequently delivered to the combustion chambers of the internal combustion engine, or 2) gasoline direct injection (GDi), in which fuel is injected directly into the combustion chambers of the internal combustion engine at a relatively high pressure (typically greater than about 14 MPa). However, some fuel systems that employ both PFI and GDi have been developed to take advantage of operating modes in which PFI provides operating advantages and operating modes in which GDi provides operating advantages. Thus, only PFI may be utilized under certain operating conditions, while only GDi may be utilized under other operating conditions. An example of a fuel system that employs both PFI and GDi is described in U.S. Patent No. 7,263,973 to Akita et al.; however, a disadvantage of Akita et al.'s system is that when only the PFI system is used, the high-pressure fuel pump used to pressurize the fuel in the GDi system continues to be recycled by the camshaft of the internal combustion engine. This circulation, coupled with the proximity of the high pressure fuel pump to the internal combustion engine, causes the fuel in the high pressure fuel pump to increase in temperature and may create vapor in the GDi system, which is undesirable for the high pressure fuel pump and may prevent fueling when the GDi system is used.

[0005] Hoefner et al., U.S. Patent No. 8,973,556, describes another fuel system that uses both PFI and GDi. Hoefner et al. provide an arrangement whereby the fuel for both the PFI system and the GDi system is first supplied to the drive section of the high-pressure fuel pump. Thus, when only the PFI system is used, the fuel flows through the drive section of the high-pressure fuel pump, thereby providing lubrication and cooling to the high-pressure fuel pump. However, the PFI system of Hoefner et al. may be susceptible to pressure pulsations.

[0006] What is needed is a fuel system that minimizes or eliminates one or more of the disadvantages discussed above and provides an alternative to the fuel systems discussed above. Summary of the invention

[0007] Briefly described, a fuel system for an internal combustion engine is provided, which includes: a low-pressure fuel delivery unit; a high-pressure fuel delivery unit having a low-pressure zone and a high-pressure zone, such that the low-pressure zone supplies fuel to the high-pressure zone, and the high-pressure zone pressurizes the fuel and supplies the fuel pressurized by the high-pressure zone to a plurality of high-pressure fuel injectors; a low-pressure fuel rail, which supplies fuel to a plurality of low-pressure fuel injectors; a low-pressure fuel injector line, which 1) is directly connected to the high-pressure fuel delivery unit at its first end and receives fuel from the low-pressure zone, and 2) is directly connected to the low-pressure fuel rail at its second end, thereby providing fluid communication from the low-pressure zone to the low-pressure fuel rail; and a device for reducing fuel pressure pulses, the device for reducing fuel pressure pulses being located between the low-pressure zone and the low-pressure fuel rail. A fuel system with a device for reducing fuel pressure pulsations allows the high-pressure fuel delivery unit to be lubricated and cooled even when only low-pressure fuel injectors are used to supply fuel to the internal combustion engine. Furthermore, objectionable audible noise, cylinder-to-cylinder fuel delivery variations, and other adverse effects caused by pressure pulses between the high pressure fuel delivery unit and the low pressure fuel rail are minimized. Further features and advantages of the present invention will become more apparent upon reading the following detailed description of preferred embodiments of the invention given by way of non-limiting example only and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be further described with reference to the accompanying drawings, in which:

[0009] Figure 1-4 is a schematic diagram of a fuel system according to the present disclosure. DETAILED DESCRIPTION

[0010] According to the preferred embodiment of the present disclosure and with reference to Figure 1, a fuel system 10 for an internal combustion engine 12 is shown. The fuel system 10 generally includes: a fuel tank 14 that holds a volume of fuel to be supplied to the internal combustion engine 12 for operation thereof; a plurality of high-pressure fuel injectors 16 that inject fuel directly into various combustion chambers (not shown) of the internal combustion engine 12; a plurality of low-pressure fuel injectors 18 that inject fuel into an intake manifold or other combustion air passage (not shown) of the internal combustion engine 12, where the fuel mixes with air and then passes into the combustion chambers through various intake valves (not shown); a low-pressure fuel delivery unit 20; and a high-pressure fuel delivery unit 22, where the low-pressure fuel delivery unit 20 draws fuel from the fuel tank 14 and increases the pressure of the fuel for delivery to the high-pressure fuel delivery unit 22 and the low-pressure fuel injectors 18, and where the high-pressure fuel delivery unit 22 further increases the pressure of the fuel for delivery to the high-pressure fuel injectors 16. As a non-limiting example only, the low-pressure fuel delivery unit 20 can increase the pressure of the fuel to about 500 kilopascals (kPa) or less, while the high-pressure fuel delivery unit 22 can increase the pressure of the fuel to about 14 megapascals (MPa) or more. Depending on the operating conditions and the required performance, it can be selected to deliver fuel to the combustion chamber through the high-pressure fuel injector 16 or the low-pressure fuel injector 18. It is also conceivable that fuel is delivered to the combustion chamber by both the high-pressure fuel injector 16 and the low-pressure fuel injector 18 at the same time. Although four high-pressure fuel injectors 16 and four low-pressure fuel injectors 18 have been shown, it should be understood that the respective numbers of the high-pressure fuel injectors 16 and the low-pressure fuel injectors 18 can be less or more. The various elements of the fuel system 10 will be described in more detail in the following paragraphs.

[0011] As shown, the low pressure fuel delivery unit 20 may be disposed within the fuel tank 14, however, the low pressure fuel delivery unit 20 may alternatively be disposed outside the fuel tank 14. The low pressure fuel delivery unit 20 may be an electric fuel pump. The low pressure fuel supply passage 24 provides fluid communication from the low pressure fuel delivery unit 20 to the high pressure fuel delivery unit 22. A fuel pressure regulator 26 may be provided such that the fuel pressure regulator 26 returns a portion of the fuel supplied by the low pressure fuel delivery unit 20 to the fuel tank 14 through a fuel return passage 28, thereby maintaining a substantially uniform pressure within the low pressure fuel supply passage 24. Although the fuel pressure regulator 26 has been shown in the low pressure fuel supply passage 24 outside the fuel tank 14, it should be understood that the fuel pressure regulator 26 may be located within the fuel tank 14 and may be integrated with the low pressure fuel delivery unit 20.

[0012] The high pressure fuel delivery unit 22 includes a low pressure region 30 and a high pressure region 32. The high pressure fuel delivery unit 22 may be a plunger pump that is mechanically driven by the internal combustion engine 12, such that the low pressure region 30 includes a pumping plunger 34 that reciprocates within a plunger bore 36 by a rotating camshaft 38 of the internal combustion engine 12. The high pressure region 32 includes an inlet valve 40, a pump chamber 42, and an outlet valve 44. The low pressure region 30 includes all portions of the high pressure fuel delivery unit 22 that are in fluid communication with the low pressure fuel supply passage 24 when the inlet valve 40 is closed. The fuel within the pump chamber 42 is pressurized by the reciprocating motion of the pumping plunger 34, and when the pressure within the pump chamber 42 is sufficiently high, the outlet valve 44 is caused to open. The fuel that leaves the high pressure fuel delivery unit 22 through the outlet valve 44 is communicated to a high pressure fuel rail 46 via a high pressure fuel passage 45, with each high pressure fuel injector 16 being in fluid communication with the high pressure fuel rail 46. By way of non-limiting example, the inlet valve 40 may be a solenoid operated valve controlled by a controller 48. The controller 48 may receive input from a pressure sensor 50 that provides a signal indicative of the pressure of the fuel supplied to the high pressure fuel injector 16. Although the pressure sensor 50 is shown as being used to read the fuel pressure within the high pressure fuel rail 46, it should be understood that the pressure sensor 50 may be positioned at other locations that indicate the pressure of the fuel supplied to the high pressure fuel injector 16. The controller 48 sends a signal to the inlet valve 40 to open and close the inlet valve 40 as necessary to achieve a desired fuel pressure at the pressure sensor 50, which may be determined by current and anticipated engine operating requirements. When the inlet valve 40 is opened, while the pumping plunger 34 moves to increase the volume of the pump chamber 42, fuel from the low pressure fuel supply passage 24 is allowed to flow into the pump chamber 42.

[0013] The low pressure fuel injector supply passage 54 is directly connected at one end to the high pressure fuel delivery unit 22, particularly to the low pressure zone 30, and even more particularly to the portion of the low pressure zone 30 surrounding the pumping plunger 34, and at its other end directly to the low pressure fuel rail 56, with which each low pressure fuel injector 18 is in fluid communication. The low pressure fuel injector supply passage 54 provides fluid communication from the high pressure fuel delivery unit 22 to the low pressure fuel rail 56. However, it is important to note that the low pressure fuel injector supply passage 54 receives fuel from the high pressure fuel delivery unit 22 without the fuel passing through the pump chamber 42. In this way, the fuel passes through the low pressure zone 30 without being further pressurized, thereby allowing the fuel to be supplied to the low pressure fuel rail 56 and the low pressure fuel injectors 18 at an appropriate pressure, while assisting in the cooling and lubrication of the high pressure fuel delivery unit 22, because new, relatively cool fuel from the fuel tank 14 passes through the low pressure zone 30 even when high pressure fuel is not being supplied to the high pressure fuel rail 46 and the high pressure fuel injectors 16.

[0014] If not mitigated, fuel pressure pulsations induced by injection events (opening and closing of the high pressure fuel injector 16 or opening and closing of the low pressure fuel injector 18) or by pump operation events (filling, overflowing, and pumping of the high pressure fuel delivery unit 22) can result in objectionable audible noise, cylinder-to-cylinder fuel delivery variations, and other adverse effects. As used herein, filling is understood to be the filling of the pump chamber 42 with fuel when the pumping plunger 34 moves to expand the pump chamber 42, while overflowing is the flow of fuel from the pump chamber 42 back into the low pressure fuel supply passage 24 and / or the low pressure region 30 when the pumping plunger 34 moves to reduce the volume of the pump chamber 42 and the inlet valve 40 is open (this is done to provide a desired fuel output from the high pressure fuel delivery unit 22). In order to minimize or eliminate one or more of these results, a device for reducing fuel pressure pulsations is provided in the low pressure fuel injector supply passage 54 between the high pressure fuel delivery unit 22 and the low pressure fuel rail 56, wherein the fuel pressure pulsations are reduced by the fuel pressure pulsations. Figure 1 In the figure, it is indicated by reference numeral 58a. Figure 1 As shown, the device 58a for reducing fuel pressure pulsations may take the form of a fixed or variable orifice or restriction. The orifice or restriction inhibits the propagation of pressure pulsations within the low pressure fuel injector supply passage 54. Figure 2 In the illustrated alternative, the means for reducing fuel pressure pulsations is indicated by reference numeral 58b and takes the form of a check valve that allows fuel to flow from the high pressure fuel delivery unit 22 to the low pressure fuel rail 56 but prohibits fuel flow in the opposite direction. Similar to an orifice or restriction, the check valve provides a restriction or obstruction to flow that inhibits the propagation of pressure pulsations within the low pressure fuel injector supply passage 54. Figure 3 In the alternative case shown, the device for reducing fuel pressure pulsations is represented by reference numeral 58c, which takes the form of a chamber or accumulator that includes an enlarged cross-sectional area within the low pressure fuel injector supply passage 54. The chamber or accumulator provides an enlarged volume within which pressure pulsations can be naturally reflected and reduced in amplitude. A pulsation dampener 60 can be located within the chamber or accumulator such that the pulsation dampener 60 has flexible and elastic properties to absorb pressure pulsations. The pulsation dampener 60 can take the form of an imperforate hollow flexible shell that is pressurized with gas. Pressure pulsations cause the shell of the pulsation dampener 60 to bend inwardly, and the pressurized gas restores the shell to its original shape, thereby reducing the pressure pulsations. An example of a suitable pulsation dampener is described in Lucas' U.S. Patent No. 8,727,752, the disclosure of which is incorporated herein by reference in its entirety. Alternatively, the walls defining the chamber or accumulator are flexible in response to fuel pressure pulsations so as to mitigate fuel pressure pulsations by flexing outwardly, with or without the presence of the pulsation dampener 60 therein. Figure 4In another embodiment shown in , the device for reducing fuel pressure pulsation includes Figure 1 Restrictions or openings, Figure 2 Check valve and Figure 3 Two or more of the chambers or accumulators of the present invention may be arranged in series. Although all three of these devices are shown, it should be understood that one may be omitted. It should also be understood that some duplications of certain devices may also be additionally included. In addition, although these devices are shown as being arranged in series, it should be understood that parallel arrangements or combinations of series and parallel arrangements may be utilized. By selecting the most effective orifice or restriction size, flow rate and opening pressure of the check valve, and volume and curvature characteristics of the chamber or accumulator, the application of the particular fuel system may be optimized. By way of non-limiting example only, such optimization may be achieved through empirical testing or computer simulation.

[0015] In operation, when only the high pressure fuel injectors 16 are used to supply fuel to the combustion chambers of the internal combustion engine 12, the low pressure fuel delivery unit 20 draws fuel from the fuel tank 14 and passes the fuel to the high pressure fuel delivery unit 22 through the low pressure fuel supply passage 24. When the pumping plunger 34 moves to expand the volume of the pump chamber 42, the inlet valve 40 is opened by the controller 48 to draw fuel into the pump chamber 42. The inlet valve 40 is then closed by the controller 48, allowing the fuel in the pump chamber 42 to be compressed when the pumping plunger 34 moves to reduce the volume of the pump chamber 42. When the fuel pressure in the pump chamber 42 is high enough, the fuel pressure causes the outlet valve 44 to open and communicate the pressurized fuel to the high pressure fuel rail 46, where the high pressure fuel injectors 16 can receive the pressurized fuel and inject the fuel directly into the combustion chambers of the internal combustion engine 12. Since the high pressure fuel delivery unit 22 is supplying fuel to the high pressure fuel injectors 16 , new, relatively cool fuel is continuously supplied from the fuel tank 14 to the high pressure fuel delivery unit 22 , thereby providing lubrication and cooling to the high pressure fuel delivery unit 22 .

[0016] In operation, when only the low pressure fuel injectors 18 are used to supply fuel to the combustion chambers of the internal combustion engine 12, the low pressure fuel delivery unit 20 draws fuel from the fuel tank 14 and passes the fuel to the high pressure fuel delivery unit 22 through the low pressure fuel supply passage 24. The fuel supplied to the high pressure fuel delivery unit 22 passes through the low pressure region 30 and exits the high pressure fuel delivery unit 22 through the low pressure fuel injector supply passage 54. The fuel then passes into the low pressure fuel rail 56 and is subsequently distributed therein to the low pressure fuel injectors 18. Thus, the high pressure fuel delivery unit 22 is lubricated and cooled even when only the low pressure fuel injectors 18 are used to supply fuel to the combustion chambers of the internal combustion engine 12, or when the low pressure fuel injectors 18 are used to provide fuel to the combustion chambers of the internal combustion engine 12 while the high pressure fuel injectors 16 are supplying fuel to the combustion chambers at a low rate.

[0017] While the present invention has been described with respect to the embodiments thereof, it is not intended to be so limited but rather to the scope set forth in the following claims.

Claims

1. A fuel system (10) for an internal combustion engine (12), the fuel system (10) comprising: A low pressure fuel delivery unit (20); a high-pressure fuel delivery unit (22) having a low-pressure region (30) and a high-pressure region (32), so that the low-pressure region (30) supplies fuel to the high-pressure region (32), and so that the high-pressure region (32) pressurizes the fuel and supplies the fuel pressurized by the high-pressure region (32) to a plurality of high-pressure fuel injectors (16); a low pressure fuel rail (56) that supplies fuel to a plurality of low pressure fuel injectors (18); a low pressure fuel injector line (54) directly connected at a first end thereof to the high pressure fuel delivery unit (22) and receiving fuel from the low pressure region (30) and directly connected at a second end thereof to the low pressure fuel rail (56) thereby providing fluid communication from the low pressure region (30) to the low pressure fuel rail (56); and a device for reducing fuel pressure pulsation, the device for reducing fuel pressure pulsation being located between a high pressure fuel delivery unit (22) and the low pressure fuel rail (56), The means (58a) for reducing fuel pressure pulsations comprises a chamber (58c) providing an enlarged volume, and the walls of the chamber (58c) are flexible in response to the fuel pressure pulsations.

2. The fuel system (10) according to claim 1, characterized in that The device for reducing fuel pressure pulsation further includes a restriction member (58a).

3. The fuel system (10) according to claim 1 or 2, characterized in that The device for reducing fuel pressure pulsation further includes a check valve (58b) that allows fuel to flow from the low pressure area (30) to the low pressure fuel rail (56) and prevents fuel from flowing from the low pressure fuel rail (56) to the low pressure area (30).

4. The fuel system (10) according to claim 1, characterized in that The device for reducing fuel pressure pulsation includes a pulsation damper (60) which is flexible and elastic to suppress pressure pulsation, such that the pulsation damper is located within the chamber (58c).

5. The fuel system (10) according to claim 1, characterized in that The low-pressure fuel injector line (54) provides a path for fuel to flow from the high-pressure fuel delivery unit (22) to the low-pressure fuel rail (56) without passing through the high-pressure fuel delivery unit (22) again.

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