Patent Application
20100282212
The present disclosure relates generally to pressure control in common rail fuel systems, and more particularly to a means for controlling rail pressure in low static leak fuel systems.
Common rail fuel systems typically include a fuel source and fuel delivery components for supplying fuel directly into cylinders of an internal combustion engine by way of a common rail. Fuel within the common rail may be pressurized to a relatively high pressure using one or more pumps, and may be delivered to fuel injectors through a plurality of individual fuel supply passages. A control system may be associated with the fuel system to monitor and control operation of one or more of the fuel system components. Specifically, for example, the control system may be configured to control the high-pressure pump and each of the fuel injectors to control pressurization rates and injection, thus improving performance and control of the engine. Typically, such fuel systems also include some means to protect the system against gross over-pressurization, which may occur due to one or more of an operational, control, or component problem. Often, this protection is provided through the use of a pressure relief valve, which may be mechanically or electronically actuated when rail pressure is above a predetermined maximum operating pressure.
Engineers are constantly seeking improved performance and expanded capabilities for such fuel systems. For example, a low static leak fuel system may provide minimal leakage and, as a result, may improve the overall efficiency, reliability, and durability of common rail fuel systems. However, the lack of static leakage from the fuel system may present a previously unrecognized performance challenge, such that when a reduction in rail pressure is required, the pressure may not be reduced at a desired rate. More specifically, conventionally designed fuel systems, which may allow a tolerable amount of leakage, may increase a reduction rate, or decay rate, of pressure within the rail, whereas the low static leak fuel system may not. As a result, for example, the settle time required for an operational engine having a low static leak fuel system to go from a high load condition, during which relatively high rail pressures are used, to a low load or idle condition, during which relatively low rail pressures are used, may be compromised.
As introduced above, a variety of mechanical and electronic means for preventing over-pressurization within common rail fuel systems are generally known. For example, U.S. Pat. No. 7,392,792 teaches a pressure relief valve that may fluidly connect the common rail to the fuel tank via a fluid passageway to relieve pressure from the fuel system. Although the commonly owned reference is directed to a method for dynamically detecting fuel leakage, a pressure relief valve that may be actuated when rail pressure exceeds a biasing spring force and/or when a solenoid is energized is described. While the reference may effectively reduce or prevent over-pressurization from occurring, it does not recognize a need for controlling rail pressure in low static leak fuel systems.
The present disclosure is directed to one or more of the problems set forth above.
In one aspect, a pressure relief valve includes a valve body having a valve seat fluidly positioned between an inlet and an outlet. A valve member is movable among a first position, a second position, and a thud position. The valve member is in contact with the valve seat and fluidly blocks the inlet from the outlet at the first position. At the second position of the valve member, the inlet is fluidly connected to the outlet via a small flow area. The inlet is fluidly connected to the outlet via a large flow area when the valve member is at the third position. An electrical actuator is attached to the valve body and is operably coupled to move the valve member when energized. The valve member includes an opening hydraulic surface exposed to fluid pressure in the inlet when at the first position. A first spring is operably positioned to bias the valve member toward the second position when the valve member is at the third position.
In another aspect, an engine system includes a low static leak fuel system. The low static leak fuel system includes a common rail and a plurality of fuel injectors fluidly connected to the common rail via individual branch passages. A variable delivery high-pressure pump includes an outlet fluidly connected to an inlet of the common rail. The low static leak fuel system also includes a fuel tank and a fuel transfer pump having an inlet fluidly connected to the fuel tank and an outlet fluidly connected to an inlet of the variable delivery high-pressure pump. A pressure relief subsystem includes an electrical actuator and has a first configuration, a second configuration, and a third configuration. In the first configuration, fluid communication between the common rail and the fuel tank is closed. In the second configuration, the common rail is in fluid communication with the fuel tank via a small flow area. In the third configuration, the common rail is in fluid communication with the fuel tank via a large flow area. The pressure relief subsystem is hydraulically moved from the first configuration to the third configuration in response to fluid pressure in the common rail exceeding a predetermined pressure that is greater than a predetermined maximum operating pressure of the fuel system. An electronic controller is in individual control communication with each of the pressure relief subsystem, the variable delivery high pressure pump, and the plurality of fuel injectors, and is configured to communicate a pressure decay control signal to the electrical actuator to move the pressure relief subsystem from the first configuration to the second configuration and then back to the first configuration in response to an engine load reduction determination.
In yet another aspect, a method of operating an engine having a low static leak fuel system includes supplying fuel to a common rail by operating a variable delivery high-pressure pump. Fuel is supplied from the common rail to a plurality of fuel injectors via individual branch passages. Fuel is injected from the plurality of fuel injectors directly into respective engine cylinders, and is ignited within the respective engine cylinders. The engine is transitioned from a first high engine load to a first low engine load. This transitioning step including opening and then closing a fluid connection between the common rail and a fuel tank.
a-9d are graphs of actuator voltage, valve position, flow area schedule, and rail pressure versus time for an exemplary engine operation, according to one embodiment of the present disclosure.
Referring to
The engine system 10 may also include a low static leak fuel system 26, also referred to as a common rail fuel system, for supplying fuel into each of the combustion chambers 18 dining operation of the internal combustion engine 12. The low static leak fuel system 26, as described herein, may be characterized as such based on a pressure decay from a predetermined maximum operating pressure to a predetermined minimum operating pressure in a particular time. For example, the low static leak fuel system 26 may include a fuel system that transitions from the maximum operating pressure to the minimum operating pressure in greater than about two seconds. As should be appreciated, fuel systems that transition from maximum operating pressure to minimum operating pressure in less than about two seconds may not generally be characterized as exhibiting low static leakage.
The low static leak fuel system 26 may include a fuel tank 28 configured to hold a supply of fuel, and a fuel pumping arrangement 30 configured to pressurize the fuel and direct the pressurized fuel to a plurality of fuel injectors 32 by way of a common rail 34. The fuel pumping arrangement 30 may include one or more pumping devices that function to increase the pressure of the fuel and direct one or more pressurized streams of fuel to the common rail 34 using fuel lines 36. For example, the fuel pumping arrangement 30 may include a fuel transfer pump 38 having an inlet 38a fluidly connected to the fuel tank 28, and an outlet 38b fluidly connected to an inlet 40a of a variable delivery high-pressure pump 40. The variable delivery high-pressure pump 40, which may increase the pressure of the fuel to a range of about 30-300 MPa, may have an outlet 40b that is fluidly connected to an inlet 34a of the common rail 34. One or both of the fuel transfer pump 38 and the variable delivery high-pressure pump 40 may be operably connected to the internal combustion engine 12 and driven by the crankshaft 22. For example, the variable delivery high-pressure pump 40 may be connected to the crankshaft 22 through a gear train 42.
The fuel injectors 32 may be disposed within a portion of the cylinder block 14, as shown, and may be connected to the common rail 34 via a plurality of individual branch passages 44. Each fuel injector 32 may be operable to inject an amount of pressurized fuel into an associated combustion chamber 18 at predetermined timings, fuel pressures, and fuel flow rates. The timing of fuel injection into the combustion chambers 18 may be synchronized with the motion of the pistons 20. For example, fuel may be injected as piston 20 nears a top-dead-center position in a compression stroke to allow for compression-ignited combustion of the injected fuel. Alternatively, fuel may be injected as piston 20 begins the compression stroke heading towards a top-dead-center position for homogenous charge compression ignition operation. As shown, fuel injectors 32 may also be fluidly connected to fuel tank 28 via one or more drain lines 45.
A control system 46 may be associated with low static leak fuel system 26 and/or engine system 10 to monitor and control the operations of the fuel pumping arrangement 30, fuel injectors 32, and various other components of the fuel system 26. In particular, and according to the exemplary embodiment, the control system 46 may include an electronic controller 48 in communication with the variable delivery high-pressure pump 40 and each of the fuel injectors 32 via communication lines 50. For example, the electronic controller 48 may be configured to control pressurization rates and injection, thus improving performance and control of the internal combustion engine 12. Although a particular embodiment is shown, it should be appreciated that the control system 46 may be configured to provide any desired level of control, and may include any number of components and/or devices, such as, for example, sensors, useful in providing the desired control.
The electronic controller 48 may be of standard design and may generally include a processor, such as for example a central processing unit, a memory, and an input/output circuit that facilitates communication internal and external to the electronic controller 48. The central processing unit may control operation of the electronic controller 48 by executing operating instructions, such as, for example, programming code stored in memory, wherein operations may be initiated internally or externally to the electronic controller 48. A control scheme may be utilized that monitors outputs of systems or devices, such as, for example, sensors, actuators or control units, via the input/output circuit to control inputs to various other systems or devices. For instance, the electronic controller 48 may be in control communication with each of the fuel injectors 32 or, more specifically, actuators thereof via communication lines 50 to deliver the required amount of fuel at the correct time. Further, the electronic controller 48 may communicate control signals to variable delivery high-pressure pump 40 via communication lines 50 to control pressure and output of the high-pressure pump 40 to common rail 34.
The engine system 10 or, more particularly, the low static leak fuel system 26 may also include a pressure relief subsystem 52. The pressure relief subsystem 52, generally speaking, may include a means for opening and closing a fluid connection between the common rail 34 and the fuel tank 28, or other drain. According to one embodiment, the pressure relief subsystem 52 may include a two-stage pressure relief valve 54, which may receive electronic control signals from electronic controller 48. The two-stage pressure relief valve 54, shown in a first configuration in
According to one embodiment, an electrical actuator 80 may be attached to the valve body 70 and operably coupled to move the valve member 78 when energized. The electrical actuator 80 may include a solenoid 84 with an armature 86 that is coupled to move the valve member 78 toward the first position when the solenoid 84 is energized. Specifically, the solenoid 84 may be energized to move valve member 78 into the first position against a spring force provided by a second spring 88, which may be considered a weak spring relative to a first spring 92. Alternatively, or additionally, the solenoid 84 may be energized to urge the valve member 78 against an opening force acting on an opening hydraulic surface 90 of the valve member 78. Further, such movement may effectively decouple the valve member 78 from a first spring 92, which may be considered a strong spring relative to second or weak spring 88, and is discussed later in greater detail. Although the electrical actuator 80 is depicted as including a solenoid 84 and armature 86, it should be appreciated that the electrical actuator 80 may include any of a variety of known actuators. For example, the electrical actuator 80 may include a piezo electrical actuator having a piezo stack that changes in length in response to control signals, or voltages, received on communication lines 50 from electronic controller 48.
Turning now to
A third configuration of the two-stage pressure relief valve 54 is shown generally in
Alternatively, as shown in
It should be appreciated that the pressure relief subsystem 54 may include a number of additional or alternative valve configurations, without deviating from the scope of the present disclosure. Although “leaking” pressure relief valves have been shown in
As should be appreciated, the overtravel mechanism 130 may allow the armature pin 124 to travel beyond its positions effected by the electrical actuator 128 so that the armature pin 124 does not limit movement of the valve member 126. Although a particular embodiment is shown, it should be appreciated that alternative overtravel mechanisms may be used with pressure relief valve 120, or alternative pressure relief valves. For example, as shown in
According to yet another alternative embodiment, shown in
It should also be appreciated that actuation of the electrical actuator 80 may be controlled via control signals communicated from the electronic controller 48. Such control signals may be generated responsive to conditions of the low static leak fuel system 26 and/or the engine system 10. For example, control signals may be communicated to the two-stage pressure relief valve 54 in response to sensors or load determinations. For example, a pressure sensor (not shown) may be configured to sense a pressure of fuel within the common rail 34. In addition, sensors may be configured to sense one or more different or additional parameters of the fuel, such as, for example, temperature, viscosity, flow rate, or any other parameter known in the an. Sensors, or other devices, may similarly be provided to detect conditions or parameters of the engine system 10. Such information may be communicated to the electronic controller 48 and used to monitor and/or control operation of the engine system 10 and/or low static leak fuel system 26.
Referring generally to the graphs of
As current rail pressure 180 quickly approaches the desired rail pressure 182 near time t2, the two-stage pressure relief valve 54 may be moved into the second configuration of
Between times t3 and t6, the internal combustion engine 12 may transition from a high load condition to a low load condition. When this occurs, as shown at time t4, the desired rail pressure 182 may drop well below the current rail pressure 180. To more quickly reduce the current rail pressure 180, the electronic controller 48 may communicate a pressure decay control signal, or parasitic loss control signal, to the electrical actuator 80 to move the valve member 78 from the first position to the second position, and then back to the first position, in response to the engine load reduction determination. As described above, when the electrical actuator 80 is briefly de-energized, the two-stage pressure relief valve 54 may fluidly connect the common rail 34 and fuel tank 28 via a small flow area to reduce the current rail pressure 180. According to the alternative embodiment of
As shown near time t5, current rail pressure 180 may increase above a predetermined maximum operating pressure 184 in the common rail 34. Such a gross over-pressurization may occur due to one or more of an operational, control, or component issue. To protect the low static leak fuel system 26 from damage, in such an over-pressurized state, the two-stage pressure relief valve 54 may be moved to the third configuration of
The large flow area, as should be appreciated, may be greater than the flow area opened in the second configuration of the two-stage pressure relief valve 54. Precise dimensions of both flow areas, as should be appreciated, may be selected based on desired performance of the two-stage pressure relief valve 54. For example, if the small flow area is too large, the valve 54 may not provide the desired rail pressure control. If, however, the small flow area is too small, the valve 54 may not provide the ability to precisely control rail pressure within desired times. Alternatively, the large flow area may be configured to quickly dump rail pressure, rather than provide a more controlled leakage.
At time t6, the internal combustion engine 12 may be shut down, thus reducing the desired rail pressure 182, as shown. To relieve rail pressure from the low static leak fuel system 26 when the internal combustion engine 12 is shut down, the electronic controller 48 may communicate a depressurization control signal to the electrical actuator 80 to move the valve member 78 from the first position to the second position in response to an engine off determination. As a result, the two-stage pressure relief valve 54 may be opened to drain pressure from the fuel system 26 toward a predetermined minimum operating pressure 186. By relieving the low static leak fuel system 26 of the current pressure, maintenance or repair of the fuel system 26, when the internal combustion engine 12 is off, may be more safely performed.
Although the pressure relief subsystem 52 is exemplified as including the two-stage pressure relief valve 54 (or valves 100, 120, 140, or 160), it should be appreciated that the functions described herein with respect to the two-stage pressure relief valve 54 may be performed using two or more pressure control components. For example, the pressure relief subsystem 52 may include a first valve that may be configured to provide pressure relief to reduce over-pressurization in the fuel system 26, such as by opening the first valve in response to rail pressure exceeding a maximum operating pressure. The pressure relief subsystem 52 may also include a second valve, which may be electronically controlled to vent rail pressure at certain desired times, such as in some of the situations described above, to assist in rail pressure control. Specifically, the second valve may provide fast action and precise operation to allow development and exploitation of comprehensive fuel control algorithms, particularly for use with low static leak fuel system 26. For example, by monitoring rail pressure, engine conditions, and other parameters, such an electronically controlled pressure relief device may be used to more quickly and precisely synchronize the current rail pressure 180 with the desired rail pressure 182.
The present disclosure may find potential application to fuel systems for internal combustion engines, and especially to fuel systems for compression ignition engines. Further, the present disclosure may be particularly applicable to common rail fuel systems exhibiting low static leakage. Yet further, the present disclosure may be applicable to low static leak fuel systems that require acceptable fuel pressure settle times.
Referring generally to
The low static leak fuel system 26 may provide minimal leakage and, as a result, may improve the overall efficiency, reliability, and durability of the common rail fuel system 26. However, the lack of static leakage may present a previously unrecognized performance challenge, such that when a reduction in rail pressure is required, the pressure may not be reduced at a desired rate. More specifically, conventionally designed fuel systems, which allow a tolerable amount of leakage, may increase a reduction rate, or decay rate, of pressure within the rail, whereas the low static leak fuel system 26 may not. As a result, for example, the settle time required for an operational engine utilizing low static leak fuel system 26 to go from a high load condition, during which relatively high rail pressures are used, to a low load or idle condition, during which relatively low rail pressures are used, may be compromised.
The pressure relief subsystem 52 described herein, which may include a two-stage pressure relief valve 54, may provide passive pressure relief to protect common rail fuel system 26 from over-pressurization, and/or may provide an electrical actuation strategy and means for selectively venting rail pressure at certain desired times to assist in rail pressure control. For example, to protect the low static leak fuel system 26 from damage, in an over-pressurized state, the two-stage pressure relief valve 54 may be moved to an opened configuration, as shown in
Further, during operation of the engine system 10, the internal combustion engine 12 may be transitioned from a first high engine load to a first low engine load. In response, a fluid connection between the common rail 34 and fuel tank 28 may be briefly opened and then closed. Specifically, to more quickly reduce the current rail pressure 180, the electronic controller 48 may communicate a pressure decay control signal, or parasitic loss control signal, to the electrical actuator 80 to move the valve member 78 from the first position to the second position, and then back to the first position, in response to the engine load reduction determination. When the electrical actuator 80 is de-energized, the two-stage pressure relief valve 54 may fluidly connect the common rail 34 and fuel tank 28 via a small flow area to reduce the current rail pressure 180. In addition, when the internal combustion engine 12 is stopped, the fluid connection between the common rail 34 and fuel tank 28 may be opened and then closed to relieve pressure within the low static leak fuel system 26.
Also, during operation, the internal combustion engine 12 may be transitioned from a second low engine load to a second high engine load. In response, the fluid connection between the common rail 34 and fuel tank 28 may be briefly opened and then closed, such as by energizing and then de-energizing the electrical actuator 80, as described above, to dampen an overshoot. Although only a few examples have been provided, it should be appreciated that the pressure relief subsystem 52, which may or may not include a passive over-pressurization relief aspect, may provide control of rail pressure within the low static leak fuel system 26 throughout operation of the internal combustion engine 12. Such precise control may reduce settle times in a variety of operational transitions, such as those described above.
In addition, such a pressure relief subsystem 52 may provide desired “limp home” capabilities. For example, the two-stage pressure relief valve 54, which, when de-energized, may include a biased open position, may maintain a desired reduced rail pressure for operating under such “limp home” conditions. In addition, alternative pressure relief valve 120, which may be biased to a closed position, may facilitate suitable rail pressure for “limp home” conditions. Of course, in such conditions, it is assumed that suitable control of the fuel pumping arrangement 30 and fuel injectors 32 is maintained.
Further, the pressure relief subsystem 52 may be used to reduce torque reversals, and resulting noise, in a gear train 42 powering the variable delivery high-pressure pump 40. Specifically, when operating the internal combustion engine 12 at an idle condition, the variable delivery high-pressure pump 40 may be required to provide a limited amount of fuel. In some circumstances, this may require non-pumping movement of the one or more pistons of the variable delivery high-pressure pump 40. Shortly thereafter, when pumping resumes, torque reversal may result. Such torque reversals may be reduced by pumping fuel to the common rail 34 in excess of a combined fuel injection quantity of the plurality of fuel injectors 32, thus allowing at least one piston to continue pumping. The excess fuel may be returned to the fuel tank 28 by opening the fluid connection between the common rail 34 and the fuel tank 28. As should be appreciated, such control may only be necessary when a low, or minimum, operating pressure is required.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
