Variable pressure regulator for gaseous fuel

Abstract

A system for a gaseous fuel-powered engine comprises the following: a gaseous fuel tank; a first pressure regulator comprising: a high-pressure chamber coupled to the gaseous fuel tank, a low-pressure chamber coupled to a fuel distributor of the engine, and a reference chamber; a second pressure regulator coupled to the reference chamber; a first valve controlling the flow of fuel from the gaseous fuel tank to the fuel distributor of the engine; a second valve controlling the flow of fuel from the second pressure regulator to the reference chamber; and a controller containing a memory with instructions to adjust the valves based on a fuel distributor setpoint pressure.In this way, the system allows for at least two different fuel distributor pressures, so that peak fuel demands can be met without maintaining a peak fuel distributor pressure at all times.

Description

[0001] Alternative fuels have been developed to alleviate the rising costs of conventional fuels and to reduce exhaust emissions. Gaseous fuels, such as natural gas, are emerging as attractive alternative fuels. For automotive applications, natural gas can be compressed and stored at a high pressure as a gas in cylinders. A pressure regulator can then be used to deliver the compressed natural gas (CNG) at lower pressures to an engine intake port or an engine combustion chamber. The pressure regulator can deliver this gaseous fuel to the engine at a fixed, constant pressure or can be a variable-pressure regulator that can deliver the gaseous fuel to the engine at varying pressures.

[0002] Fixed-pressure regulators are generally used in gaseous-fuel vehicles, but have several disadvantages. Delivering fuel at a fixed, constant pressure limits the dynamic range of the associated fuel injector. As such, the amount of injected fuel remains the same even during low fuel demands. This causes the fuel injector to be subjected to high pressures throughout operation, affecting injector durability. Using a variable-pressure regulator, in contrast, the dynamic range (or turndown ratio) of the injector can be increased. Providing fuel at a lower pressure during a low fuel demand allows for a longer fuel injection pulse width, which in turn enables injections of a lower repeatable mass.Furthermore, varying the gaseous fuel pressure allows for the use of a lower gaseous fuel pressure during engine cold start-up, when only a minimal voltage may be available to open the injectors. Furthermore, varying the pressure can allow rare fuel peak demands to be met without subjecting the injector to the durability challenge of injecting gaseous fuel at high pressure at all times.

[0003] Despite these potential advantages, known variable-pressure regulators are expensive and prone to instability. In some systems, for example, variable-pressure control is achieved by exposing the regulator's reference chamber to intake manifold pressure. However, this dependence on intake manifold pressure limits the pressure regulator's operability if the intake manifold vacuum is not within a certain range. In other systems, pressure variability is achieved by varying the reference pressure from the high-pressure source via a valve. As another example, a known variable-pressure regulator varies the gaseous fuel pressure through the duty cycle of a main valve between the regulator and the fuel rail.However, systems that rely on a single valve to perform pressure control, where the valve is subjected to a high-pressure flow of gaseous fuel, may not be sufficiently robust. Furthermore, such systems require electronic pressure feedback to activate the valve.

[0004] US 5 117 798 A describes a fuel supply system of a gas engine, comprising a tank for gaseous fuel; a first pressure regulator having a high-pressure chamber coupled to the tank and a low-pressure chamber coupled to a fuel rail of the engine; a second pressure regulator coupled to a reference chamber; and a controller.

[0005] In one example, some of the above issues may be addressed by a system for a gaseous fuel-powered engine, including: a gaseous fuel tank; a first pressure regulator including: a high-pressure chamber coupled to the gaseous fuel tank, a low-pressure chamber coupled to an engine fuel rail, and a reference chamber; a second pressure regulator coupled to the reference chamber; a first valve controlling fuel flow from the gaseous fuel tank to the engine fuel rail; a second valve controlling fuel flow from the second pressure regulator to the reference chamber; and a controller including memory with instructions therein to adjust the valves based on a desired fuel rail pressure.In this way, the first valve can be operated to supply the gaseous fuel to the engine fuel rail at a pressure determined by the characteristics of the first pressure regulator. Then, in response to an increase in the desired fuel rail pressure, the second valve can be operated. Operating the second valve allows the gaseous fuel to flow through the second pressure regulator into the reference chamber, thereby increasing the pressure of the reference chamber and the low-pressure chamber to a pressure determined by the characteristics of the second pressure regulator. Consequently, the system allows for at least two different fuel rail pressures so that the peak fuel demand can be met without maintaining the peak fuel rail pressure at all times.

[0006] In another example, some of the above problems may be addressed by a method for regulating the pressure of gaseous fuel in an engine, comprising: increasing a control pressure in a low-pressure chamber of a first pressure regulator by controllably increasing the flow of gaseous fuel via a second pressure regulator into a reference chamber of the first pressure regulator. In this way, a plurality of different fuel rail pressures may be set by changing the pressure in the reference chamber of the first pressure regulator. The flow of gaseous fuel may be controlled by valves in response to changes in a desired fuel rail pressure without relying on mechanical pressure feedback to operate or deactivate the valves.

[0007] In yet another example, some of the above issues may be addressed by a method for cold starting the engine, comprising closing a valve coupling a gaseous fuel tank to a high-pressure chamber of a first gaseous fuel regulator, and opening a valve coupling a fuel rail, via a second gaseous fuel regulator, to a reference chamber of the first gaseous fuel regulator. In this way, the gaseous fuel already present in the fuel rail may be used to establish a low injection pressure, which may be used when a slight voltage is available to open the fuel injectors, since a lower injection pressure requires a lower opening voltage of the fuel injectors.

[0008] The above advantages and other advantages and features of the present description will be readily appreciated from the following detailed description when taken alone or in conjunction with the accompanying drawings.

[0009] It should be understood that the above summary is provided to introduce, in a simplified form, a selection of the concepts further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is clearly defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that eliminate all of the disadvantages noted above or in any part of this disclosure. Fig. 1 shows a schematic representation of an engine system configured to operate with a gaseous fuel. Fig. Figure 2A shows a schematic representation of a pressure control system for controlling the pressure of a gaseous fuel distributor. Fig. Figure 2B shows a schematic representation of a pressure control system for controlling the pressure of a gaseous fuel distributor. Fig. Figure 3 shows an example high-level flow chart for controlling the valves of the pressure control system according to the Fig. 2A-B. Fig. Figure 4 shows exemplary time diagrams showing the relationship between the various parameters of the pressure control system according to the Fig. 2A-B regarding time. Fig. Figure 5A shows a schematic representation of a pressure control system for controlling the pressure of a gaseous fuel distributor. Fig. Figure 5B shows a schematic representation of a pressure control system for controlling the pressure of a gaseous fuel distributor. Fig. Figure 6 shows an example high-level flow chart for controlling the valves of the pressure control system according to the Fig. 5A-B. Fig. Figure 7 shows exemplary time diagrams showing the relationship between the various parameters of the pressure control system according to the Fig. 5A-B with respect to time.

[0010] Systems and methods for a variable pressure regulator for controlling the pressure of gaseous fuel in a fuel rail of a gaseous fuel vehicle, such as the vehicle of Fig. 1. The variable pressure regulator may comprise one or more gas pressure regulators coupled to one or more valves, as shown in the Fig. 2A-2B and 5A-5B. A controller may be configured to execute a control routine, such as that shown in the Fig. 3 and Fig. 6. Example timing diagrams for the implementations of such systems and control routines are shown in the Fig. 4 and Fig. 7. In this way, multiple fuel injection pressures can be achieved by mechanical means at low cost.

[0011] Fig. 1 shows a schematic representation of a vehicle system 6. The vehicle system 6 includes an engine system 8, a control system 14, and a fuel system 18. The engine system 8 may include an engine 10 having a plurality of cylinders 30. The engine 10 includes an engine intake 23 and an engine exhaust 25. The engine intake 23 includes a throttle valve 62 fluidly coupled to the engine intake manifold 44 via an intake passage 42. The engine exhaust 25 includes an exhaust manifold 48 leading to an exhaust passage 35 that directs exhaust gas to the atmosphere after passing through an emission control device 70. The engine 10 may further include a crankcase 79 enclosing a crankshaft (not shown), the crankshaft being driven by the movement of the pistons of the cylinders 30.It is recognized that additional components may be included in the engine, such as various valves and sensors.

[0012] The control system 14 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). As one example, the sensors 16 may include MAP and MAF sensors 124 and 125 in the intake, an exhaust gas sensor 126 and a temperature sensor 127 located in the exhaust, a temperature sensor 128 located in the engine, a pressure sensor 33 coupled to a gaseous fuel conduit, a pressure sensor 102 coupled to a gaseous fuel manifold, etc. Other sensors, such as pressure, temperature, fuel level, air / fuel ratio, and composition sensors, may be coupled to various locations in the vehicle system 6.As another example, the actuators may include a fuel pump 21, a fuel injector 66, a throttle valve 62, a fuel tank valve 32, and the valves of the pressure control system 34. Examples of the pressure control systems are described below with respect to . Fig. 2A-2B and the Fig. 5A-5B. The control system 14 may include a controller 12. The controller may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on an instruction or code programmed therein according to one or more routines. Example control routines are described herein with respect to the Fig. 3 and Fig. 6 described.

[0013] The fuel system 18 may include one or more fuel tanks. In the depicted example, the fuel system is a dual-fuel system including a high-pressure fuel tank 20 configured to supply a gaseous fuel to a fuel rail 52 via a pressure control system 34. The fuel tank 20 may be configured to store a gaseous fuel at a high pressure and supply the fuel to the engine 10 via the high-pressure fuel line 94, the pressure control system 34, and the fuel line 50 at a regulated pressure. The gaseous fuel may be, for example, compressed natural gas (CNG), liquefied petroleum gas (LPG), adsorbed natural gas (ANG), or hydrogen fuel. The fuel tank 20 can contain the gaseous fuel in a pressure range of 10-700 bar (e.g. 0-100+ psi for LNG fuel, 500 psi for ANG fuel, 3600 psi or 250 bar for CNG fuel and 5000-10.000 psi for hydrogen fuel).

[0014] The fuel tank 20 may be filled with gaseous fuel via a fuel fill port 54. A check valve 55 (or two check valves in series for redundancy) may be coupled between the fuel tank 20 and the fuel fill port 54 to ensure proper fuel flow. Fuel may be delivered from the fuel tank 20 to the injectors of the engine 10, such as injector 66, via the fuel rail 52. While only a single injector coupled to the fuel rail 52 is shown, it will be appreciated that additional injectors are provided for each cylinder 30. In an example where the fuel system 18 includes a direct fuel injection system, the injector 66 may be configured as a direct fuel injector.In an alternative embodiment, fuel system 18 may include a port fuel injection system, where injector 66 may be configured as a port fuel injector. In still further embodiments, each cylinder may include one or more injectors, including a direct fuel injector and a port fuel injector.

[0015] The fuel tank 20 may be coupled to a fuel tank valve 32 for regulating a pressure of the gaseous fuel supplied to the fuel line 94. The fuel tank valve 32 may be configured to supply the gaseous fuel to the fuel line 94 at a pressure similar to the tank pressure. Alternatively, even if a high fuel injection pressure is desired, the fuel tank valve may be activated, and a pressure regulation system downstream of the valve may be controlled to ensure that the fuel rail pressure is regulated to a sufficiently high pressure. Such operation may be preferred in examples where high-pressure flow of the gaseous fuel through various components that may be included in the fuel line 94 (e.g., filters, valves, etc.) would degrade the components.

[0016] The fuel tank 20 may further be coupled to a pressure control system 34 to enable gaseous fuel to be provided to the fuel rail 52 and from there to the injector 66 at different pressures. In one example, the fuel tank 20 may store gaseous fuel in a pressure range of 10-700 bar, while the pressure control system 34 may regulate the fuel rail pressure to a variable range of 2 to 40 bar (e.g., 2 to 10 bar for CNG fuel). As discussed below with respect to Fig. 2A-2B and the Fig. 5A-5B, the pressure control system 34 may be coupled to a pressure relief line 92. The pressure relief line 92 may couple the reference chamber to the intake manifold, the crankcase, the fuel vapor canister, the injector vacuum, the vacuum pump vacuum, and / or the atmosphere.

[0017] The fuel system 18 may also include a fuel tank 22 configured to supply a fuel having chemical and physical properties different from the gaseous fuel (e.g., a liquid fuel) to the fuel rail 53. While the illustrated example includes separate fuel rails for the two different fuels, in some examples, a common fuel rail may be used. The fuel tank 22 may store liquid fuel, such as gasoline, fuel with a range of alcohol concentrations, various gasoline-ethanol fuel blends (e.g., E10, E85), and / or combinations thereof. As shown, the fuel tank 22 may be coupled to a fuel pump 21 to pressurize the fuel supplied to the fuel rail 53.The fuel tank 22 may include a pressure sensor 114 and may also include a fuel fill port 83 that may be used to refill the fuel tank 22 with liquid fuel.

[0018] The fuel rail 53 may be coupled to a fuel injector 67. Fuel may be delivered from the fuel tank 22 to the injector 67 via the fuel rail 53. While only a single injector coupled to each fuel rail is illustrated, it will be appreciated that additional injectors are provided for each cylinder 30. In one example where the fuel system 18 includes a direct injection system, the injector 67 may be configured as a direct fuel injector. In an alternative embodiment, the fuel system 18 may include a port injection system, where the injector 67 may be configured as a port fuel injector. In still other embodiments, each cylinder may include one or more injectors, including a direct injector and a port injector.

[0019] Pump 21 may not pump fuel from the fuel tank 22 to the fuel rail 53 during conditions when the supply of liquid fuel to the engine is not desired (e.g., during engine off conditions or during conditions when the supply of gaseous fuel only to the engine is desired). A fuel rail pressure sensor 103 in the fuel rail 53 may be configured to sample the current fuel rail pressure and provide the sampled value to the controller 12 of the control system 14. In some examples, pump 21 may be controlled based on the fuel rail pressure sensed by sensor 103 and / or based on other parameter values.Further, in some embodiments, a check valve (not shown) may be positioned between the fuel tank 22 and the fuel rail 53 to ensure proper flow of fuel from the fuel tank 22.

[0020] The Fig. 2A and Fig. 2B show detailed schematic drawings of exemplary pressure control systems, such as the pressure control system 34 shown in Fig. 1. Further examples are shown in the Fig. 5A and Fig. 5B and are discussed further below. The pressure control system 34 includes a high-pressure regulator 200 and a low-pressure regulator 201. The high-pressure regulator 200 includes a high-pressure chamber 84 that receives gaseous fuel from the fuel tank 20 via the fuel line 94, a low-pressure chamber 86 that provides a regulated-pressure gaseous fuel to the fuel rail 52 via a regulated fuel line 50, and a reference chamber 88. Similar to a mechanical pressure regulator, the high-pressure regulator 200 includes a diaphragm 98 and a valve 100. A position of the valve 100 relative to an opening in the wall 104 separating the high-pressure chamber 84 and the low-pressure chamber 86 determines the flow rate of gas from the high-pressure chamber 84 to the low-pressure chamber 86.The position of the valve 100 depends on the pressures in the reference chamber 88 and the low-pressure chamber 86 and on a spring force provided by a spring 96 coupled at one end to a bottom of the pressure regulator 38 and at the other end to a bottom of the diaphragm 98. As the pressure in the reference chamber increases, a greater pressure is required in the low-pressure chamber 86 to achieve any given position of the valve 100. For example, the high-pressure chamber may communicate with the low-pressure chamber via the orifice when a pressure in the reference chamber exceeds a threshold, where the threshold corresponds to a pressure at which the diaphragm moves the valve 100 beyond the wall 104. As the pressure in the reference chamber decreases, a lower pressure is required in the low-pressure chamber 86 to achieve a force balance.

[0021] However, unlike mechanical pressure regulators that control a reference chamber pressure to a fixed, constant pressure to achieve a fixed, constant control pressure in a low-pressure chamber, the pressure control system 34 couples the low-pressure chamber 201 to the reference chamber 88, allowing the reference chamber pressure to be varied, with the reference chamber pressure in turn varying the control pressure in the low-pressure chamber 86.

[0022] Under most conditions, when the gaseous fuel tank 20 is fluidly coupled to the pressure control system 34, the high-pressure chamber 84 contains a gaseous fuel at a higher pressure than the gaseous fuel contained in the low-pressure chamber 86. The gaseous fuel stored at high pressure in the gaseous fuel tank 20 flows to the high-pressure chamber 84 via the high-pressure fuel line 94. A quantity of the gaseous fuel in the high-pressure chamber 84 may then be directed through the valve 100 to the low-pressure chamber 86 such that the pressure of the gaseous fuel in the low-pressure chamber 86 is lower than the pressure of the gaseous fuel in the high-pressure chamber 84.In this way, a gaseous fuel at a pressure significantly lower than the fuel pressure in the high pressure fuel line 94 and the gaseous fuel tank 20 can be directed to a regulated fuel line 50 and on to the fuel rail 52.

[0023] In the in the Fig. 2A and Fig. 2B, the pressure regulation system 34 includes a primary valve 205. In these examples, the pressure regulation system 34 includes a secondary fuel line 210. The low-pressure regulator 201 and the secondary valve 215 are shown coupled to the secondary fuel line 210. The pressure relief line 92 is also shown coupled to the secondary fuel line 210. The pressure relief line 92 may include an orifice 220. The orifice 220 may be an orifice with a fixed or variable opening. In some examples, the orifice 220 may be replaced with a controllable valve.

[0024] The low pressure regulator 201 may include ports for the inlet pressure, the outlet pressure, and a reference pressure. As shown in the Fig. 2A and Fig. 2B, a conduit may connect a reference chamber of the low-pressure regulator to atmosphere. In further examples, the low-pressure regulator 201 may have a self-connected reference pressure. In these examples, a pressure relief conduit providing a constant leak point may not be required, as the low-pressure regulator may be capable of both increasing and decreasing the pressure downstream in the reference chamber 88.

[0025] In the Fig. In the example illustrated in Figure 2A, the primary valve 205 is shown coupled to the high-pressure fuel line 94 upstream of the secondary fuel line branch 210. The primary valve 205 can be activated or deactivated via signals from the controller 12. When the primary valve 205 is commanded open, the gaseous fuel in the high-pressure fuel line 94 can flow to the high-pressure chamber 84 of the high-pressure regulator 200, and can also flow to the low-pressure regulator 201 via the secondary fuel line 210.

[0026] In the Fig. In the example illustrated in Figure 2A, the secondary valve 215 is coupled to the secondary fuel line 210 downstream of the low-pressure regulator 201. While the primary valve 205 is open, if the secondary valve 215 is open, the gaseous fuel from the low-pressure regulator can flow into the reference chamber 88 of the high-pressure regulator 200. In this way, the pressure in the reference chamber can be increased. The increased pressure in the reference chamber increases the pressure of the fuel in the low-pressure chamber 86 (the regulation pressure) due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel being directed to the regulated fuel line 50 and downstream to the fuel rail 52. If the secondary valve 215 is then closed, the gaseous fuel can be vented from the reference chamber to the pressure relief line 92 via the opening 220.In this way, the reference chamber returns to the steady-state pressure, thereby reducing the control pressure in the low-pressure chamber 86. This, in turn, reduces the pressure of the fuel being directed to the regulated fuel line 50 and downstream to the fuel rail 52. The gaseous fuel purged from the reference chamber via the closure of the secondary valve 215 may be directed via the pressure relief line 92 to the engine system 8, e.g., to the intake manifold 44, the crankcase 79, the injector vacuum or the vacuum pump vacuum, or to the fuel tank storage canister 27. Alternatively, the purged gaseous fuel may be vented to the atmosphere.

[0027] In the Fig. 2B, the primary valve 205 is coupled to the regulated fuel line 50 upstream of the high-pressure regulator 200. The primary valve 205 can be activated or deactivated via signals from the controller 12. When coupled to the regulated fuel line, the primary valve 205 can function as a fuel rail isolation valve, wherein it can be closed to prevent communication between the pressure control system 34 and the fuel rail 52 during conditions when the delivery of gaseous fuel to the engine is not desired (e.g., during engine-off conditions or during conditions where the delivery of liquid fuel alone to the engine is desired). Otherwise, the primary valve 205 can be opened so that fuel from the pressure control system 34 can be delivered to the fuel rail 52.Unlike the valves in the systems that vary the fuel rail pressure across the duty cycle of a valve between a pressure regulator and a fuel rail, the primary valve 205 may be a simple valve that is only controllable to a fully open or fully closed state and is not used to vary the pressure of the fuel delivered to the fuel rail. However, in other examples, the pressure control system 34 may cycle the primary valve 205 based on feedback from the fuel rail pressure sensor, such that the valve operates in conjunction with other pressure control mechanisms of the systems or replaces the other pressure control mechanisms of the systems during selected operating conditions.

[0028] In the Fig. In the example illustrated in Figure 2B, the secondary valve 215 is coupled to the secondary fuel line 210 upstream of the low-pressure regulator 201. While the primary valve 205 is open, if the secondary valve 215 is open, gaseous fuel can flow from the fuel tank to the low-pressure regulator and further into the reference chamber 88 of the high-pressure regulator 200. In this way, the pressure in the reference chamber can be increased. The increased pressure in the reference chamber increases the pressure of the fuel in the low-pressure chamber 86 (the regulation pressure) due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52. If the secondary valve 215 is then closed, the gaseous fuel from the reference chamber can be vented via the opening 220 to the pressure relief line 92.In this manner, the reference chamber returns to the steady-state pressure, thereby reducing the control pressure in the low-pressure chamber 86. This, in turn, reduces the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52. Closing valve 215 ceases the filling of the reference chamber 88, equilibrating the reference chamber 88 to the same pressure as seen through line 92. The gaseous fuel purged from the reference chamber 88 via the pressure relief line 92 may be directed to the engine system 8, e.g., to the intake manifold 44, the crankcase 79, the manifold vacuum, the vacuum pump vacuum, or the fuel tank storage canister 27. Alternatively, the purged gaseous fuel may be vented to the atmosphere.

[0029] It should be understood that the terms "high-pressure regulator" and "low-pressure regulator" (and / or "higher pressure regulator" and "lower pressure regulator") are used herein to describe the regulators in terms of the relative pressures of the gaseous fuel exiting the regulators. In other words, under most circumstances, the gaseous fuel exiting the high-pressure regulator is regulated to a higher pressure than the gaseous fuel exiting the low-pressure regulator. In one example, the high-pressure regulator may be a 7-bar regulator and the low-pressure regulator may be a 3-bar regulator. In the Fig. 2A and Fig. In the examples shown in Figure 2B, if the primary valve 205 is open and the secondary valve 215 is closed, the gaseous fuel exiting the low-pressure chamber 86 exits at a pressure of 7 bar. If the secondary valve 215 is then open, the gaseous fuel flows into the reference chamber 88 at a pressure of 3 bar. The gaseous fuel exiting the low-pressure chamber 86 exits at a pressure of 10 bar.

[0030] The pressure control system 34 may control the fuel rail pressure based on electronic feedback from the fuel rail. The fuel rail pressure sensor 102 may be configured to sample the current fuel rail pressure and provide the sampled value to the controller 12 of the control system 14. If the current fuel rail pressure is not within a range of a desired fuel rail pressure determined based on the engine operating conditions, the controller may control the valves 205 and 215 to achieve the desired fuel rail pressure. An example control routine for the example pressure control systems shown in the Fig. 2A and Fig. 2B is shown in Fig. 3 shown.

[0031] Both the Fig. 2A and Fig. 2B shown regulator for a variable pressure (as well as the ones shown in the Fig. 5A and Fig. 5B) may enable a system for a gaseous fuel-powered engine, comprising: a gaseous fuel tank; a first pressure regulator comprising: a high-pressure chamber coupled to the gaseous fuel tank, a low-pressure chamber coupled to an engine fuel rail, and a reference chamber; a second pressure regulator coupled to the reference chamber; a first valve controlling the flow of fuel from the gaseous fuel tank to the engine fuel rail; a second valve controlling the flow of fuel from the second pressure regulator to the reference chamber; and a controller including memory with instructions therein to adjust the valves based on a desired fuel rail pressure.In some examples, the first pressure regulator is a higher pressure regulator and the second pressure regulator is a lower pressure regulator. The system may further include a first fuel line coupling the gaseous fuel tank to the high-pressure chamber and a second fuel line coupling the gaseous fuel tank to the reference chamber via the second pressure regulator and the second valve, and may further include a pressure relief line coupled to the second fuel line downstream of the second pressure regulator and the second valve and upstream of the reference chamber.The controller may further include a memory having instructions therein for, when the first valve is energized, energizing the second valve in response to an increase in the desired fuel rail pressure, and may further include a memory having instructions therein for, when the first and second valves are energized, de-energizing the second valve in response to a decrease in the desired fuel rail pressure.

[0032] In some examples, the fuel vented from the reference chamber through the pressure relief line is routed to the engine for combustion. The system may further include a first fuel line coupling the low-pressure chamber to the engine fuel rail, a second fuel line coupling the engine fuel rail to the reference chamber via the second pressure regulator and second valve, and may further include a pressure relief line coupled to the second fuel line downstream of the second pressure regulator and second valve and upstream of the reference chamber.The controller may further include a memory having instructions therein to operate the second valve in response to an increase in the desired fuel rail pressure, and may further include a memory having instructions therein to decommission the second valve in response to a decrease in the desired fuel rail pressure.

[0033] In this way, the first valve may be operated to supply gaseous fuel to the engine fuel rail at a pressure determined by the characteristics of the first pressure regulator. Then, in response to an increase in the desired fuel rail pressure, the second valve may be operated. Operating the second valve allows gaseous fuel to flow through the second pressure regulator into the reference chamber, thereby increasing the pressure of the reference chamber and the low-pressure chamber to a pressure determined by the characteristics of the second pressure regulator. Consequently, the system allows for at least two different fuel rail pressures so that the peak fuel demand can be met without maintaining the peak fuel rail pressure at all times.

[0034] Fig. 3 shows a high-level flow diagram for an example method 350 for a gas pressure regulator for a gaseous fuel system, such as that shown in Fig. 1, which includes a pressure regulator for gaseous fuel, such as the pressure control system 34 as shown in the Fig. 2A and Fig. 2B. Method 350 may be performed by controller 12 and may be performed when the vehicle is operating or upon a key-on event. Method 350 may begin at 355 by determining engine operating conditions. Engine operating conditions may be measured, estimated, or inferred and may include various vehicle conditions, such as vehicle speed, as well as various engine operating conditions, such as engine operating mode, engine speed, engine temperature, exhaust temperature, boost level, MAP, MAF, torque request, horsepower request, etc.

[0035] Method 350 may further include determining at 360 whether the vehicle is in a gaseous fuel mode of operation or whether the vehicle is about to enter a gaseous fuel mode. The gaseous fuel mode may include a gaseous fuel only mode, a bifuel mode of operation, a gaseous fuel hybrid electric mode, or another mode of operation in which gaseous fuel is injected into at least one combustion cylinder.

[0036] If the vehicle is not operating in a gaseous fuel mode and the vehicle is not about to enter a gaseous fuel mode, method 350 may proceed to 365. At 365, method 350 may include opening and closing the primary and secondary gaseous fuel valves (e.g., primary gaseous fuel valve 205 and secondary gaseous fuel valve 215, as shown in FIGS. Fig. 2A and Fig. 2B). If either or both valves are open, the controller 12 may operate the valves closed, decoupling the gaseous fuel tank 20 from the gaseous fuel manifold 52. Method 350 may then end.

[0037] If the vehicle is in a gaseous fuel mode or about to enter a gaseous fuel mode, method 350 may proceed to 370. At 370, method 350 may include opening the primary gaseous fuel valve 205. Opening the primary gaseous fuel valve 205 couples the gaseous fuel tank 20 to the gaseous fuel manifold 52 and allows gaseous fuel to enter the regulated fuel line 50 at a pressure determined by the high-pressure regulator 200.

[0038] At 375, method 350 may include determining whether the desired fuel rail pressure is greater than a threshold. The desired fuel rail pressure may be calculated or estimated based on engine operating conditions, such as engine mode, available fuel levels, engine torque request, engine power request, etc. The threshold fuel rail pressure may be a predetermined value or may be calculated as a function of current engine conditions. If the desired fuel rail pressure is not greater than the threshold pressure, method 350 may proceed to 380.

[0039] At 380, method 350 may include closing or maintaining closed the secondary gaseous fuel valve 215. In this way, the low-pressure regulator 201 is decoupled from the reference chamber 88. If gaseous fuel has been directed into the reference chamber 88, the fuel may then flow out of the reference chamber 88 via the opening 220 through the pressure relief line 92. In this way, the reference chamber 88 maintains a pressure substantially equal to atmospheric pressure. This, in turn, causes the pressure in the low-pressure chamber 86 to drop due to the movement of the diaphragm 98 away from the wall 104. The gaseous fuel entering the regulated fuel line 50 and on to the fuel rail 52 is, in turn, delivered at a pressure substantially equal to the predetermined value for the high-pressure regulator 200. Method 350 may then end.

[0040] If the desired fuel rail pressure is greater than the threshold pressure, method 350 may proceed to 385. At 385, method 350 may include opening or maintaining open the secondary gaseous fuel valve 215. In this way, the low-pressure regulator 201 is coupled to the reference chamber 88. Fuel from the gaseous fuel tank 20 may enter the low-pressure regulator 201 via the secondary fuel line 210. This, in turn, causes the pressure in the reference chamber 88 to increase by an amount substantially equal to the predetermined value for the low-pressure regulator 201. This further increases the pressure in the low-pressure chamber 86 due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52.The pressure of the fuel delivered to the regulated fuel line 50 and downstream to the fuel rail 52 may be substantially equal to the sum of the predetermined values ​​of the high-pressure regulator 200 and the low-pressure regulator 201. Method 350 may then end.

[0041] Method 350 may further include determining whether the desired fuel rail pressure remains above the threshold pressure. If the desired fuel rail pressure remains above the threshold pressure, method 350 may include maintaining the primary and secondary gaseous fuel valves in an open configuration. Then, method 350 may end. If the desired fuel rail pressure has fallen below the threshold, method 350 may include closing the secondary gaseous fuel valve 215. In this way, the low-pressure regulator 201 is decoupled from the reference chamber 88. Gaseous fuel may then flow out of the reference chamber 88 via the opening 220 through the pressure relief line 92. In this way, the reference chamber 88 maintains a pressure substantially equal to atmospheric pressure or the pressure seen through the relief line 92.This, in turn, causes the pressure in the low-pressure chamber 86 to drop due to the movement of the diaphragm 98 away from the wall 104. The gaseous fuel entering the regulated fuel line 50 and further into the fuel rail 52 is again supplied at a pressure substantially equal to the predetermined value for the high-pressure regulator 200. Method 350 may then end.

[0042] Both the Fig. 3 (as well as the high-level flow chart shown in the Fig. 6 and Fig. 8) may enable one or more methods. In one example, a method for regulating the pressure of gaseous fuel in an engine includes increasing a control pressure in a low-pressure chamber of a first pressure regulator by controllably increasing the flow of gaseous fuel via a second pressure regulator into a reference chamber of the first pressure regulator. In some examples, increasing the control pressure in the low-pressure chamber of the first pressure regulator further increases the pressure of gaseous fuel in a fuel rail of the engine. The method may further include decreasing a control pressure in the low-pressure chamber of the first pressure regulator by closing a first valve coupling the reference chamber to a gaseous fuel tank via the second pressure regulator.In some examples, reducing a control pressure in the low-pressure chamber of the first pressure regulator further comprises purging the gaseous fuel from the reference chamber through a pressure relief line. In some examples, the reference chamber and the second pressure regulator are coupled to the fuel rail via a second valve. The method may further include adjusting the control pressure in the low-pressure chamber based on a fuel rail target pressure. In some examples, the second valve couples the second pressure regulator and the reference chamber to the pressure relief line.

[0043] In this way, several different fuel rail pressures can be set by changing the pressure in the reference chamber of the first pressure regulator. The flow of gaseous fuel can be controlled by valves in response to changes in the fuel rail target pressure, without relying on mechanical pressure feedback to activate or deactivate the valves.

[0044] Fig. Figure 4 shows an exemplary timing diagram 400 illustrating the relationship between the various parameters of the pressure control system according to the Fig. 2A-B with respect to time. The timing diagram may be representative of an exemplary pressure control routine, such as the one shown in Fig. 3. The timing diagram 400 includes the current fuel rail pressure graphical representation 410, the desired fuel rail pressure graphical representation 420, the primary valve state graphical representation 430, and the secondary valve state graphical representation 440.

[0045] Before t0, the engine may be off or running in a mode that does not require gaseous fuel injection. At t0, the desired fuel rail pressure increases from 0 to a value less than threshold 425. In response to this increase in desired fuel rail pressure, a primary gaseous fuel valve is activated, as shown by plot 430. As shown by plot 410, activation of the primary valve causes the fuel rail pressure to increase to the desired fuel rail pressure. In this example, activation of the primary valve is equivalent to opening the valve at a 100% duty cycle. In some examples, the valve may be opened at different duty cycles to further control the fuel rail pressure.

[0046] At t1, the desired fuel rail pressure increases to a value greater than threshold 425. This may be due to a change in operating conditions, such as an increased engine torque request. In response to the increase in the desired fuel rail pressure, a secondary gaseous fuel valve is activated, as shown by plot 440. Concurrently, the primary gaseous fuel valve is maintained open. As shown by plot 410, activation of the secondary valve causes the fuel rail pressure to increase to the desired fuel rail pressure. In this example, activation of the secondary valve is equivalent to opening the valve at a 100% duty cycle. In some examples, the valve may be opened at various duty cycles to further control the fuel rail pressure.As above with reference to . Fig. 2, the activation of the secondary valve causes gaseous fuel to flow into the reference chamber of the high pressure fuel regulator, which increases the pressure of the gaseous fuel entering the fuel rail.

[0047] At time t2, the desired fuel rail pressure decreases to a value less than the threshold 425. This may be due to a change in operating conditions, e.g., a reduced engine torque request. In response to the decrease in the desired fuel rail pressure, the secondary gaseous fuel valve is closed, as shown by plot 440. Simultaneously, the primary gaseous fuel valve is maintained open. As shown by plot 410, closing the secondary valve causes the fuel rail pressure to decrease to the desired fuel rail pressure. As described above with reference to Fig. As described in Figure 2, closing the secondary valve causes the gaseous fuel to flow from the reference chamber of the high-pressure fuel regulator through a pressure relief line. This reduces the pressure of the gaseous fuel entering the fuel rail.

[0048] At time t3, the target fuel rail pressure decreases to 0. This may be due to a change in operating conditions, such as a key-off event or switching operating modes. In response to the decrease in the target fuel rail pressure, the primary gaseous fuel valve is closed, as shown by plot 430. Closing the primary gaseous fuel valve decouples the gaseous fuel tank from the gaseous fuel manifold. As shown by plot 410, closing the primary gaseous fuel valve causes the fuel rail pressure to decrease to 0.

[0049] The Fig. 5A and Fig. 5B show detailed schematic drawings of alternative exemplary pressure control systems, such as the one shown in Fig. 1 shown pressure control system 34. As regards the Fig. 2A and Fig. 2B, the pressure control system 34 includes a high-pressure regulator 300 and a low-pressure regulator 301. The high-pressure regulator 300 includes a high-pressure chamber 84 that receives gaseous fuel from the fuel tank 20 via the fuel line 94, a low-pressure chamber 86 that provides gaseous fuel at a regulated pressure to the fuel rail 52 via the regulated fuel line 50, and a reference chamber 88. The high-pressure regulator 300 includes a diaphragm 98 and a valve 100. A position of the valve 100 relative to an opening in the wall 104 separating the high-pressure chamber 84 and the low-pressure chamber 86 determines the flow rate of gas from the high-pressure chamber 84 to the low-pressure chamber 86.The position of the valve 100 depends on the pressures in the reference chamber 88 and the low-pressure chamber 86 and a spring force provided by a spring 96 coupled at one end to a bottom of the pressure regulator 38 and at the other end to a bottom of the diaphragm 98. As the pressure in the reference chamber increases, a greater pressure in the low-pressure chamber 86 is required to achieve any given position of the valve 100. In these examples, the pressure control system 34 couples the low-pressure regulator 301 to the reference chamber 88, allowing the pressure of the reference chamber to be varied, with the reference chamber pressure, in turn, varying the control pressure in the low-pressure chamber 86.

[0050] As above regarding the Fig. 2A and Fig. 2B, under most conditions, when the gaseous fuel tank 20 is fluidly coupled to the fuel pressure control system 34, the high pressure chamber 84 contains gaseous fuel at a higher pressure than the gaseous fuel contained in the low pressure chamber 86. The gaseous fuel stored at high pressure in the gaseous fuel tank 20 flows into the high pressure chamber 84 via the high pressure fuel line 94. A quantity of the gaseous fuel in the high pressure chamber 84 may then be directed through the valve 100 to the low pressure chamber 86 such that the pressure of the gaseous fuel in the low pressure chamber 86 is lower than the pressure of the gaseous fuel in the high pressure chamber 84.In this way, the gaseous fuel can be delivered to the regulated fuel line 50 and on to the fuel rail 52 at a pressure that is significantly lower than the fuel pressure in the high pressure fuel line 94 and the gaseous fuel tank 20.

[0051] In the Fig. In the example shown in Figure 5A, the pressure regulation system 34 includes a primary valve 305. In this example, the pressure regulation system 34 includes a secondary fuel line 310. The low-pressure regulator 301 and the secondary valve 315 are shown coupled to the secondary fuel line 310. The pressure relief line 92 is also shown coupled to the secondary fuel line 310. The pressure relief line 92 may include an orifice 320. The orifice 320 may be an orifice with a fixed or variable opening. In some examples, the orifice 320 may be replaced with a controllable valve.

[0052] The low pressure regulator 301 may include ports for the inlet pressure, the outlet pressure, and a reference pressure. As shown in the Fig. 5A and Fig. 5B, a conduit may connect a reference chamber of the low-pressure regulator to atmosphere. In further examples, the low-pressure regulator 301 may have a self-connected reference pressure. In these examples, a pressure relief line providing a constant leak point may not be required, as the low-pressure regulator may be capable of both increasing and decreasing the pressure downstream in the reference chamber 88.

[0053] In the in the Fig. 5A and Fig. In the examples illustrated in Figure 5B, the primary valve 305 is shown coupled to the high-pressure fuel line 94 upstream of the high-pressure regulator 300. The primary valve 305 may be enabled and disabled via signals from the controller 12. When the primary valve 305 is commanded open, the gaseous fuel in the high-pressure fuel line 94 may flow to the high-pressure chamber 84 of the high-pressure regulator 300. The primary valve 305 may function as a fuel rail isolation valve, and may be closed to prevent communication between the pressure regulation system 34 and the fuel rail 52 during conditions when the delivery of gaseous fuel to the engine is not desired (e.g., during engine-off conditions or during conditions where the delivery of liquid fuel alone to the engine is desired).Otherwise, the primary valve 305 may be open so that fuel from the pressure control system 34 can be delivered to the fuel rail 52. Unlike the valves in the systems that vary the fuel rail pressure via the duty cycle of a valve between a pressure regulator and a fuel rail, the primary valve 305 may be a simple valve that is only controllable to a fully open or fully closed state and that does not serve to vary the pressure of the fuel delivered to the fuel rail. However, in other examples, the pressure control system 34 may cycle the primary valve 205 based on feedback from the fuel rail pressure sensor so that the valve operates in conjunction with other pressure control mechanisms of the systems or replaces the other pressure control mechanisms of the systems during selected operating conditions.

[0054] In dem in Fig. 5A, the secondary valve 315 is coupled to the secondary fuel line 310 downstream of the low-pressure regulator 301. When the secondary valve 315 is open, gaseous fuel can flow from the fuel rail through the low-pressure regulator 301 into the reference chamber 88 of the high-pressure regulator 300. In this way, the pressure in the reference chamber can be increased. The increased pressure in the reference chamber increases the pressure of the fuel in the low-pressure chamber 86 (the regulation pressure) due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel being directed to the regulated fuel line 50 and downstream to the fuel rail 52. Closing the valve 315 stops the filling of the reference chamber 88, equilibrating the reference chamber 88 to the same pressure as seen through line 92.The gaseous fuel vented from the reference chamber 88 via the pressure relief line 92 may be directed to the engine system 8, e.g., to the intake manifold 44, the crankcase 79, the manifold vacuum, the vacuum pump vacuum, or the fuel tank storage canister 27. Alternatively, the vented gaseous fuel may be vented to the atmosphere.

[0055] In this way, the Fig. 5A can use the fuel rail pressure to adjust the pressure in the reference chamber. By controlling the position of valves 305 and 315, the pressure in the regulated fuel line 50 can, in turn, be controlled. If the primary valve 305 is closed and the secondary valve 315 is also closed, there is no net flow of gaseous fuel to the regulated fuel line 50 or to the fuel rail 52. If the primary valve 305 is closed and the secondary valve 315 is open, the gaseous fuel can flow from the fuel rail 52 via the secondary fuel line 310 to the reference chamber 88. In this way, the gaseous fuel passes through the low-pressure regulator 301. This, in turn, increases the pressure in the reference chamber 88, which increases the pressure of the low-pressure chamber 86.Increasing the pressure of the low-pressure chamber 86 results in increased pressure of the gaseous fuel in the regulated fuel line 50 and further in the fuel rail 52 to a pressure substantially equal to the set value for the low-pressure regulator 301. This configuration, with the primary valve 305 closed and the secondary valve 315 open, can result in a first, low-pressure setting that can be selected in situations involving low fuel rail pressure operation, such as extreme cold-start situations.

[0056] In another scenario, the reference chamber 88 is equilibrated to atmospheric pressure if the primary valve 305 is open and the secondary valve 315 is closed. Gaseous fuel flows from the fuel tank to the high-pressure chamber 84, with the gaseous fuel flowing from the low-pressure chamber to the regulated fuel line 50 and on to the fuel rail 52 at a pressure substantially equal to the set value for the high-pressure regulator 300. This configuration, with the primary valve 305 open and the secondary valve 315 closed, may result in a second, default pressure setting that may be selected under normal operating conditions.

[0057] In another scenario, if the primary valve 305 is open and the secondary valve 315 is open, gaseous fuel flows from the fuel tank to the high-pressure chamber 84, and gaseous fuel flows from the fuel rail via the secondary fuel line 310 to the reference chamber 88, passing through the low-pressure regulator 301. This, in turn, increases the pressure in the reference chamber 88, which increases the pressure of the low-pressure chamber 86. Increasing the pressure of the low-pressure chamber 86 results in an increased pressure of the gaseous fuel in the regulated fuel line 50 and further into the fuel rail 52 to a pressure substantially equal to the sum of the set values ​​for the high-pressure regulator 300 and the low-pressure regulator 301.

[0058] In the Fig. 5B, the secondary valve 325 is coupled to the secondary fuel line 310 downstream of the low-pressure regulator 301. In this example, the secondary valve 325 is a three-way valve coupled to both the secondary fuel line 310 and the pressure relief line 92. For the purposes of this example, the secondary valve 325 is described as a three-way valve switchable between a first and a second position; however, it should be recognized that numerous other valve configurations may be used without departing from the scope of this disclosure. The secondary valve 325 may be positioned in accordance with commands received from the controller 12.

[0059] The secondary valve 325 may be arranged in a first position in which a first valve opening is aligned with the inlet of the pressure relief line 92, a second valve opening is aligned with a portion of the secondary fuel line 310 such that the gaseous fuel can flow from the reference chamber 88 through the secondary valve 325, and a third valve opening is not aligned with an opening in the secondary fuel line 310 such that the gaseous fuel cannot flow from the low-pressure regulator 301 to the reference chamber 88. This may be functionally equivalent to the closed position described for the secondary valve 315, as in Fig. 5A is shown.

[0060] For example, if the secondary valve 325 moves to the first position, the gaseous fuel can be vented from the reference chamber via the opening 220 to the pressure relief line 92. In this way, the reference chamber returns to the steady-state pressure, thereby reducing the regulated pressure in the low-pressure chamber 86. This, in turn, reduces the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52. By energizing the valve 325, the filling of the reference chamber 88 ceases, equilibrating the reference chamber 88 to the same pressure as seen through line 92. The gaseous fuel vented from the reference chamber 88 via the pressure relief line 92 can be directed to the engine system 8, e.g.to the intake manifold 44, the crankcase 79, the injector vacuum, the vacuum pump vacuum, or the fuel vapor storage canister 27. Alternatively, the purged gaseous fuel may be vented to the atmosphere.

[0061] The secondary valve 325 may be arranged in a second position in which a first valve opening is aligned with an inlet in the secondary fuel line 310 and a second valve opening is aligned with an outlet in the secondary fuel line 310, so that gaseous fuel can flow from the low-pressure regulator 301 to the reference chamber 88. This may result in the open position described for the secondary valve 315, as in Fig. 5A, may be functionally equivalent, although the pressure relief line 92 may be blocked. In this arrangement, the gaseous fuel can flow from the fuel rail through the low-pressure regulator 301 into the reference chamber 88 of the high-pressure regulator 300. In this way, the pressure in the reference chamber can be increased. The increased pressure in the reference chamber increases the pressure of the fuel in the low-pressure chamber 86 (the regulation pressure) due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52.In this scenario, if the primary valve 305 is open while the secondary valve 325 is in the second position, gaseous fuel flows from the fuel tank to the high-pressure chamber 84, and gaseous fuel flows from the fuel rail via the secondary fuel line 310 to the reference chamber 88, passing through the low-pressure regulator 301. This, in turn, increases the pressure in the reference chamber 88, which increases the pressure of the low-pressure chamber 86. Increasing the pressure of the low-pressure chamber 86 results in an increased pressure of the gaseous fuel in the regulated fuel line 50 and further into the fuel rail 52 to a pressure substantially equal to the sum of the set values ​​for the high-pressure regulator 300 and the low-pressure regulator 301.

[0062] If the primary valve 305 is closed and the secondary valve 325 is in the second position, gaseous fuel can flow from the fuel rail 52 via the secondary fuel line 310 to the reference chamber 88. In this way, the gaseous fuel passes through the low-pressure regulator 301. This, in turn, increases the pressure in the reference chamber 88, which increases the pressure of the low-pressure chamber 86. Increasing the pressure of the low-pressure chamber 86 results in an increased pressure of the gaseous fuel in the regulated fuel line 50 and further into the fuel rail 52 to a pressure substantially equal to the set value for the low-pressure regulator 301. This configuration, with the primary valve 305 closed and the secondary valve 325 in the second position, can result in a first, low-pressure setting, which is useful in situations involving low fuel rail pressure operation, e.g.extreme cold start situations.

[0063] As in Fig. 5B, the pressure control system 34 may further include a combining filter 330 coupled to the regulated fuel line 50.

[0064] It should be understood that the terms "high-pressure regulator" and "low-pressure regulator" (and / or "higher pressure regulator" and "lower pressure regulator") are used herein to describe the regulators in terms of the relative pressures of the gaseous fuel exiting the regulators. In other words, under most circumstances, the gaseous fuel exiting the high-pressure regulator is regulated to a higher pressure than the gaseous fuel exiting the low-pressure regulator. In one example, the high-pressure regulator may be a 7-bar regulator and the low-pressure regulator may be a 3-bar regulator. In the Fig. In the example illustrated in Figure 5A, if the primary valve 305 is open and the secondary valve 315 is closed, the gaseous fuel exiting the low-pressure chamber 86 exits at a pressure of 7 bar. If the secondary valve 315 is then open, the gaseous fuel flows into the reference chamber 88 at a pressure of 3 bar. The gaseous fuel exiting the low-pressure chamber 86, in turn, exits at a pressure of 10 bar. In the scenario where the primary valve 305 is closed and the secondary valve 315 is open, the gaseous fuel flows into the reference chamber 88 at a pressure of 3 bar and exits the low-pressure chamber 86 at a pressure of 3 bar, thereby increasing the pressure of the gaseous fuel in the fuel rail in a closed-loop control circuit.

[0065] The pressure control system 34 may control the fuel rail pressure based on electronic feedback from the fuel rail. The fuel rail pressure sensor 102 may be configured to sample the current fuel rail pressure and provide the sampled value to the controller 12 of the control system 14. If the current fuel rail pressure is not within a range of a desired fuel rail pressure determined based on the engine operating conditions, the controller may control the valves 305 and 315 to achieve the desired fuel rail pressure. An example control routine for the example pressure control systems shown in FIGS. Fig. 5A and Fig. 5B is shown in Fig. 6 shown.

[0066] Fig. 6 shows a high-level flow diagram for an example method 600 for a gas pressure regulator for a gaseous fuel system, such as that shown in Fig. 1, which includes a pressure regulator for gaseous fuel, such as the pressure control system 34 as shown in Fig. 5A. Method 600 may be performed by controller 12 and may be performed when the vehicle is operating or upon a key-on event. Method 600 may begin at 605 by determining engine operating conditions. Engine operating conditions may be measured, estimated, or inferred and may include various vehicle conditions, such as vehicle speed, as well as various engine operating conditions, such as engine operating mode, engine speed, engine temperature, exhaust temperature, boost level, MAP, MAF, torque request, horsepower request, etc.

[0067] Method 600 may further include determining at 610 whether the vehicle is in a gaseous fuel operating mode or whether the vehicle is about to enter a gaseous fuel operating mode. The gaseous fuel operating mode may include a gaseous fuel only mode, a bifuel operating mode, a gaseous fuel hybrid electric mode, or another operating mode in which gaseous fuel is injected into at least one combustion cylinder.

[0068] If the vehicle is not operating in a gaseous fuel mode and the vehicle is not about to enter a gaseous fuel mode, method 600 may proceed to 615. At 615, method 600 may include opening and closing the primary and secondary gaseous fuel valves (e.g., primary gaseous fuel valve 305 and secondary gaseous fuel valve 315, as shown in Fig. 5A) or to keep it closed. For the Fig. In the system illustrated in FIG. 5B, this may include setting the secondary gaseous fuel valve 315 to a first decompression position. If either or both valves are open, the controller 12 may operate the valves closed, decoupling the gaseous fuel tank 20 from the gaseous fuel manifold 52. Method 600 may then end.

[0069] If the vehicle is in a gaseous fuel mode or about to enter a gaseous fuel mode, method 600 may proceed to 620. At 620, method 600 may include determining whether the vehicle is currently in a cold start condition. This may include evaluating the engine operating conditions assessed at 605 and may include determining the voltage available for fuel injection. If no cold start routine is in progress, method 600 may proceed to 630. If a cold start routine is in progress, method 600 may proceed to 625. At 625, method 600 may include opening a secondary gaseous fuel valve, such as secondary gaseous fuel valve 315, as shown in Fig. 5A. For the Fig. 5B, this may include placing the secondary gaseous fuel valve 315 in a second, allowable position. A primary gaseous fuel valve, such as the primary gaseous fuel valve 305, or another isolation valve on the high-pressure side of the high-pressure regulator 300, may be closed simultaneously with the opening of the secondary gaseous fuel valve 315, or may be maintained closed. As described above, in this arrangement, gaseous fuel may flow from the fuel rail 52 via the secondary fuel line 310 to the reference chamber 88. In this manner, the gaseous fuel passes through the low-pressure regulator 301. This, in turn, increases the pressure in the reference chamber 88, which increases the pressure of the low-pressure chamber 86.Increasing the pressure of the low-pressure chamber 86 results in increased gaseous fuel pressure in the regulated fuel line 50 and further into the fuel rail 52 to a pressure substantially equal to the set value for the low-pressure regulator 301. This may result in a low-pressure setting that enables low-pressure fuel injection for cold start or other scenarios where minimal voltage is available for gaseous fuel injection.

[0070] At 630, method 600 may include determining whether the desired fuel rail pressure is greater than a first threshold. The first threshold may be a predetermined fuel rail pressure or may be a function of the current engine operating conditions. If this determination is made after a cold-start condition, there may be a predetermined period of time or a predetermined sequence of events after the cold-start condition that may elapse before comparing the fuel rail pressure to the first threshold. If the desired fuel rail pressure is not greater than a first threshold, method 600 may proceed to 635. At 635, method 600 may include closing or maintaining the primary gaseous fuel valve closed. Then, method 600 may end.

[0071] If the desired fuel rail pressure is greater than a first threshold, method 600 may proceed to 640. At 640, method 600 may include closing or maintaining the closed state of the secondary gaseous fuel valve and opening the primary gaseous fuel valve and coupling the gaseous fuel tank 20 to the gaseous fuel manifold 52. For the Fig. 5B, this may include setting the secondary gaseous fuel valve 315 to a first, decompression position. As discussed above with respect to Fig. 5A, in this arrangement, the reference chamber 88 is equilibrated to atmospheric pressure. The gaseous fuel flows from the fuel tank to the high-pressure chamber 84, with the gaseous fuel flowing from the low-pressure chamber to the regulated fuel line 50 and on to the fuel rail 52 at a pressure substantially equal to the set value for the high-pressure regulator 300. This may result in a primary or default pressure setting that allows a fuel rail pressure to be selected under most operating conditions.

[0072] Method 600 may continue to 645, including determining whether the desired fuel rail pressure is greater than a second threshold, where the second threshold is greater than the first threshold. The desired fuel rail pressure may be calculated or estimated based on engine operating conditions, such as engine mode, available fuel levels, engine torque request, engine power request, etc. The threshold fuel rail pressure may be a predetermined value or may be calculated as a function of current engine conditions. If the desired fuel rail pressure is not greater than the second threshold pressure, method 600 may continue to 650.

[0073] At 650, the method 600 may include closing or maintaining the secondary gaseous fuel valve 315 closed. For the Fig. 5B, this may include placing the secondary gaseous fuel valve 315 in a first, decompression position. In this way, the low-pressure regulator 301 is decoupled from the reference chamber 88. If gaseous fuel has been directed into the reference chamber 88, the fuel may then flow out of the reference chamber 88 via the orifice 320 through the pressure relief line 92. In this way, the reference chamber 88 maintains a pressure substantially equal to atmospheric pressure. This, in turn, causes the pressure in the low-pressure chamber 86 to drop due to the movement of the diaphragm 98 away from the wall 104. The gaseous fuel entering the regulated fuel line 50 and onward to the fuel rail 52 is, in turn, delivered at a pressure substantially equal to the predetermined value for the high-pressure regulator 300. Method 600 may then end.

[0074] If the desired fuel rail pressure is greater than the threshold pressure, method 600 may proceed to 655. At 655, method 600 may include opening or maintaining open the secondary gaseous fuel valve 315. For the Fig. 5B, this may include placing the secondary gaseous fuel valve 315 in a second, allowable position. In this way, the low-pressure regulator 301 is coupled to the reference chamber 88. Fuel from the gaseous fuel tank 20 may enter the low-pressure regulator 301 via the secondary fuel line 310. This, in turn, causes the pressure in the reference chamber 88 to increase by an amount substantially equal to the predetermined value for the low-pressure regulator 301. This further increases the pressure in the low-pressure chamber 86 due to the movement of the diaphragm 98 toward the wall 104. This, in turn, increases the pressure of the fuel directed to the regulated fuel line 50 and downstream to the fuel rail 52.The pressure of the fuel delivered to the regulated fuel line 50 and downstream to the fuel rail 52 may be substantially equal to the sum of the predetermined values ​​of the high-pressure regulator 300 and the low-pressure regulator 301. Then, the method 600 may end.

[0075] Method 600 may further include determining whether the desired fuel rail pressure remains above the second threshold pressure. If the desired fuel rail pressure remains above the second threshold pressure, method 600 may include maintaining the primary and secondary gaseous fuel valves in an open configuration. Then, method 600 may end. If the desired fuel rail pressure has fallen below the threshold, method 600 may include closing the secondary gaseous fuel valve 315. For the Fig. 5B, this may include placing the secondary gaseous fuel valve 315 in a first, decompression position. In this way, the low-pressure regulator 301 is decoupled from the reference chamber 88. The gaseous fuel can then flow out of the reference chamber 88 via the opening 320 through the pressure relief line 92. In this way, the reference chamber 88 maintains a pressure substantially equal to atmospheric pressure. This, in turn, causes the pressure in the low-pressure chamber 86 to drop due to the movement of the diaphragm 98 away from the wall 104. The gaseous fuel entering the regulated fuel line 50 and further into the fuel rail 52 is again supplied at a pressure substantially equal to the predetermined value for the high-pressure regulator 300. Method 600 may then end.

[0076] The Fig. The high-level flowchart shown in Figure 6 may enable one or more methods. In one example, a method for an engine cold start includes closing a valve coupling a gaseous fuel tank to a high-pressure chamber of a first gaseous fuel regulator and opening a valve coupling a fuel rail, via a second gaseous fuel regulator, to a reference chamber of the first gaseous fuel regulator. In this way, the gaseous fuel already present in the fuel rail may be used to establish a low injection pressure, which may be used when slight voltage is available to open the fuel injectors, since lower injection pressure requires lower fuel injector opening voltage.

[0077] Fig. 7 shows an exemplary timing diagram 700 illustrating the relationship between the various parameters of the pressure control system according to Fig. 5A with respect to time. The timing diagram may be representative of an exemplary pressure control routine, such as the one shown in Fig. 6. The timing diagram 700 includes the current fuel rail pressure graphical representation 710, the target fuel rail pressure graphical representation 720, the primary valve state graphical representation 730, and the secondary valve state graphical representation 740. The secondary valve state graphical representation 740 shows a first and a second position for the secondary valve. As described above, for the Fig. 5A, the secondary valve 315 may be set to a first, closed position or a second, open position. For the system shown in Fig. In the system illustrated in Figure 5B, the secondary valve 325 can be set to a first, decompression position or a second, open position. For both valves 315 and 325, the first position decouples the low-pressure regulator 301 from the reference chamber 88, while the second position couples the low-pressure regulator 301 to the reference chamber 88. In this example, the default or decommissioning position is the first position, while the commissioning position is the second position.

[0078] Before t0, the engine may be off or running in a mode that does not require gaseous fuel injection. At t0, the desired fuel rail pressure increases from 0 to a value less than the first threshold 725. In response to this increase in the desired fuel rail pressure, a secondary gaseous fuel valve is set to a second position, as shown by plot 740. As shown by plot 720, commissioning of the secondary valve causes the fuel rail pressure to increase to the desired fuel rail pressure. In this example, commissioning the secondary valve is equivalent to opening the valve at a 100% duty cycle. In some examples, the valve may be opened at different duty cycles to further control the fuel rail pressure.

[0079] At t1, the desired fuel rail pressure increases to a value greater than the primary threshold 725 but less than the secondary threshold 726. In response to this increase in the desired fuel rail pressure, a primary gaseous fuel valve is activated, as shown by graphical representation 730. Simultaneously, the secondary gaseous fuel valve is set to the first position, as shown by graphical representation 740. As shown by graphical representation 710, energizing the primary valve and simultaneously de-energizing the secondary valve causes the fuel rail pressure to increase to the desired fuel rail pressure. In this example, energizing the primary valve is equivalent to opening the valve at a 100% duty cycle.In some examples, the valve may be opened at different duty cycles to further control fuel rail pressure.

[0080] At t2, the desired fuel rail pressure increases to a value greater than the second threshold 726. This may be due to a change in operating conditions, e.g., an increased engine torque request. In response to the increase in the desired fuel rail pressure, a secondary gaseous fuel valve is activated, as shown by plot 740. Concurrently, the primary gaseous fuel valve is maintained open. As shown by plot 710, activation of the secondary valve causes the fuel rail pressure to increase to the desired fuel rail pressure. In this example, activation of the secondary valve is equivalent to opening the valve at a 100% duty cycle. In some examples, the valve may be opened at different duty cycles to further control the fuel rail pressure.As above with reference to the . Fig. 5A and Fig. 5B, the activation of the secondary valve causes gaseous fuel to flow into the reference chamber of the high pressure fuel regulator, which increases the pressure of the gaseous fuel entering the fuel rail.

[0081] At time t3, the desired fuel rail pressure decreases to a value that is less than threshold 726 but greater than threshold 725. This may be due to a change in operating conditions, e.g., a reduced engine torque request. In response to the decrease in the desired fuel rail pressure, the secondary gaseous fuel valve is decommissioned, as shown by plot 740. Simultaneously, the primary gaseous fuel valve is maintained open. As shown by plot 710, decommissioning the secondary valve causes the fuel rail pressure to decrease to the desired fuel rail pressure. As described above with reference to the Fig. 5A and Fig.As described in Figure 5B, deactivation of the secondary valve causes gaseous fuel to flow from the reference chamber of the high-pressure fuel regulator through a pressure relief line. This reduces the pressure of the gaseous fuel entering the fuel rail.

[0082] At time t4, the desired fuel rail pressure decreases to 0. This may be due to a change in operating conditions, such as a key-off event or switching engine modes. In response to the decrease in the desired fuel rail pressure, the primary gaseous fuel valve is closed, as shown by plot 730. Closing the primary gaseous fuel valve decouples the gaseous fuel tank from the gaseous fuel manifold. As shown by plot 710, closing the primary gaseous fuel valve causes the fuel rail pressure to decrease to 0.

[0083] It is understood that the configurations and methods disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, as numerous variations are possible. For example, the above technique may be applied to V-6, I-4, I-6, V-12, horizontally opposed four, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0084] The following claims particularly set forth certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to include the inclusion of one or more such elements and neither require nor exclude two or more such elements. Further combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application.Such claims, whether broader in scope than, narrower than, equal to, or different in scope from the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] A system for a gaseous fuel-powered engine (10) comprising: a tank (20) for gaseous fuel; a first pressure regulator comprising: a high-pressure chamber (84) coupled to the gaseous fuel tank (20), a low-pressure chamber (86), coupled to a fuel rail (52) of the engine (10), and a reference chamber (88); a second pressure regulator coupled to the reference chamber (88); a first valve (205) that controls the flow of gaseous fuel from the gaseous fuel tank (20) to the fuel rail (52) of the engine (10); a second valve (215) controlling the flow of gaseous fuel from the second pressure regulator to the reference chamber (88); and a controller (12) including a memory with instructions therein to adjust the first (205) and second valves (215) based on a desired fuel rail pressure. [2] The system of claim 1, wherein the first pressure regulator is a higher pressure regulator (200, 300) and the second pressure regulator is a lower pressure regulator (201, 301). [3] The system of claim 2, further comprising a first fuel line coupling the gaseous fuel tank (20) to the high pressure chamber (84) and a second fuel line (210, 310) coupling the gaseous fuel tank (20) to the reference chamber (88) via the second pressure regulator and the second valve (215). [4] The system of claim 3, further comprising a pressure relief line (92) coupled to the second fuel line (210, 310) downstream of the second pressure regulator and the second valve (215) and upstream of the reference chamber (88). [5] The system of claim 3, wherein the controller (12) further includes a memory having instructions therein for, when the first valve (205) is operative, operatively operating the second valve (215) in response to an increase in the desired fuel rail pressure. [6] The system of claim 4, wherein the controller (12) further includes a memory having instructions therein for, when the first (205) and second valves (215) are operative, de-energizing the second valve (215, 315) in response to a decrease in the desired fuel rail pressure. [7] The system of claim 4, wherein the fuel emptied from the reference chamber (88) through the pressure relief line (92) is directed to the engine (10) for combustion. [8] The system of claim 2, further comprising a first fuel line coupling the low pressure chamber (86) to the fuel rail (52) of the engine (10), and a second fuel line (210) coupling the fuel rail (52) of the engine (10) to the reference chamber (88) via the second pressure regulator and the second valve (215, 315). [9] The system of claim 8, further comprising a pressure relief line (92) coupled to the second fuel line (210) downstream of the second pressure regulator and the second valve (215, 315) and upstream of the reference chamber (88). [10] The system of claim 8, wherein the controller (12) further includes a memory having instructions therein to operate the second valve (215, 315) in response to an increase in the desired fuel rail pressure. [11] The system of claim 9, wherein the controller (12) further includes a memory having instructions therein to deactivate the second valve (215, 315) in response to a decrease in the desired fuel rail pressure. [12] The system of claim 9, wherein the fuel evacuated from the reference chamber (88) through the pressure relief line (92) is directed to the engine (10) for combustion. [13] A method for regulating a pressure of a gaseous fuel in an engine (10), comprising: Increasing a control pressure in a low-pressure chamber (86) of a first pressure regulator by controllably increasing a flow of the gaseous fuel via a second pressure regulator into a reference chamber (88) of the first pressure regulator. [14] The method of claim 13, wherein increasing the control pressure in the low pressure chamber (86) of the first pressure regulator further increases a pressure of the gaseous fuel in a fuel rail (52) of the engine (10). [15] The method of claim 13, further comprising reducing a control pressure in the low pressure chamber (86) of the first pressure regulator by closing a first valve (205) coupling the reference chamber (88) to a gaseous fuel tank (20) via the second pressure regulator. [16] The method of claim 15, wherein reducing a control pressure in the low pressure chamber (86) of the first pressure regulator further comprises emptying the gaseous fuel from the reference chamber (88) through a pressure relief line (92). [17] The method of claim 16, wherein the reference chamber (88) and the second pressure regulator are coupled to a fuel rail (52) of the engine (10) via a second valve (215, 315). [18] The method of claim 15, further comprising adjusting the control pressure in the low pressure chamber (86) based on a desired fuel rail pressure. [19] The method of claim 17, wherein the second valve (215, 315) couples the second pressure regulator and the reference chamber (88) to the pressure relief line (92). [20] A method for cold starting an engine (10), comprising: Closing a valve coupling a gaseous fuel tank (20) to a high-pressure chamber (84) of a first gaseous fuel regulator, and Opening a valve coupling a fuel rail (52) via a second gaseous fuel regulator to a reference chamber (88) of the first gaseous fuel regulator.

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