FIELD OF THE INVENTIONS
This specification relates generally to the field of railroad locomotives and more generally to a common rail fuel system for a diesel engine of a railroad locomotive.
BACKGROUND OF THE INVENTIONS
Fuel injection systems are widely used on internal combustion engines, including spark ignition engines and compression ignition (diesel) engines for automobiles, trucks, marine and stationary engines. One such fuel injection system is described in U.S. Pat. No. 6,357,421. A common rail fuel system utilizes a fuel accumulator (rail) that is maintained at a high pressure (typically 1,000 bar) by one or more high-pressure fuel pumps. The fuel injectors associated with cylinders of the engine receive fuel from the fuel rail, with the delivery of the fuel being controlled by a solenoid valve disposed between the fuel rail and the injection nozzle.
U.S. Pat. No. 5,394,851 describes a fuel injection system commonly used on the large displacement, turbocharged, medium speed diesel engines of railroad locomotives provided by the present assignee. Such engines include a plurality of unitized power assemblies each containing a cylinder, a cylinder head, cam-driven intake and exhaust valves, and a fuel injection system including a fuel pump, a fuel injection control solenoid and a fuel injection nozzle. Each fuel pump is driven by a fuel lobe located on the respective camshaft of the engine.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a multi-cylinder diesel locomotive engine incorporating a common rail fuel injection apparatus.
FIG. 2 is a perspective illustration of the camshafts used in the engine of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have recognized certain benefits associated with utilizing a high-pressure common rail fuel system for fuel delivery to a multi-cylinder diesel engine in a locomotive application. Such benefits result from the ability to control fuel delivery to each cylinder with more precision and flexibility than is possible with other systems. However, the present inventors have also recognized certain limitations of prior art common rail fuel systems that are particularly problematic for locomotive applications. For example, a fuel rail is normally positioned close to its associated cylinders in order to minimize fuel pressure fluctuations at the fuel injection nozzles. For engines containing two banks of cylinders, such as are common for locomotive applications, two separate rails are typically provided to supply fuel independently to the two banks of cylinders, such as is illustrated in U.S. Pat. No. 5,133,645. In the event of a failure of the fuel supply to either of the two rails, half of the cylinders of such an engine become inoperative, which has not been recognized as a significant problem in prior art truck applications. However, the application of known common rail fuel systems to a locomotive application would leave the locomotive vulnerable to a failure mode that could disable a train due to the inability of the engine to provide enough motive force to keep the train moving along an inclined track. Such a failure mode is highly undesirable in the rail industry.
FIG. 1 illustrates an improved fuel injection apparatus 1 that facilitates the exploitation of the benefits of common rail fueling technology in a multi-bank, multi-cylinder, diesel locomotive engine application. FIG. 1 is a schematic illustration of a locomotive engine 10 including twelve cylinders 12. Each cylinder 12 may be part of a power assembly that includes the cylinder, a cylinder head, a piston, intake and exhaust valves, and a fuel flow control apparatus 14. The fuel flow control apparatus 14 may include a fuel injection nozzle and a solenoid valve controlling the delivery of fuel to the fuel injection nozzle. The cylinders 12 are grouped into a left bank 16 and a right bank 18. The terms left bank and right bank are commonly used in the art as an engine naming convention and should not be construed herein as being limiting.
A fuel injection apparatus left bank common fuel rail 20 is disposed proximate the left bank of cylinders 16 and a right bank common fuel rail 22 is disposed proximate the right bank of cylinders 18. The rails 20, 22 are advantageously located as close to the cylinders 12 as practical so that high pressure fuel supply lines 24 delivering high pressure fuel from the respective rail 20, 22 to the flow control apparatus 14 are kept as short as practical. A low pressure fuel supply 26 includes a fuel tank 28 containing a supply of fuel 30, and a low pressure fuel pump 32 delivering the fuel 30 from the tank 28 to one or more high pressure fuel pumps 34 through a flow metering valve 36. The pressure in the fuel rails 20, 22 is maintained within a desired pressure range by controlling the delivery of fuel 30 through valve 36 using any known closed-loop control arrangement (not shown).
Advantageously, a fluid cross connection 38 is provided for the conveyance of fuel 30 between the left bank common rail 20 and the right bank common rail 22. While other arrangements may be envisioned in other embodiments, the three high-pressure pumps 34 of FIG. 1 are all disposed proximate the left common rail 20 and are connected to provide fuel to the left common rail 20 via high pressure supply lines 40. One skilled in the art may appreciate that one or more such high pressure pumps 34 may be provided in other applications to deliver fuel 30 to the right common rail 22. For example, in one V-16 diesel engine application, two high pressure fuel pumps may be used to provide fuel to the left rail and two high pressure fuel pumps may be used to provide fuel to the right rail. In the embodiment of FIG. 1, high pressure fuel is provided from the left common rail 20 to the right common rail 22 via the cross connection 38. Other embodiments may have more than one fluid cross connection between the fuel rails such as may be desired to optimize the mechanical and fluid design of the fuel injection apparatus 1. The plurality of high pressure pumps 34 and the fluid cross connection 38 cooperate to enable delivery of fuel 30 for continued operation of all of the cylinders 12 in the event of a failure of one of the high pressure pumps 34. The location of the cross connection 38 is illustrated schematically in FIG. 1, and one skilled in the art may appreciate that it may be located closer to the high pressure pumps 34 in other embodiments.
The fuel injection apparatus 1 of FIG. 1 may be designed to provide for continued full power operation, or a selected reduced power level of operation with one of the high-pressure pumps 34 being inoperative. The fluid capacity of the each high pressure pump 34 may be selected to be approximately 50% of the total engine fuel flow requirement at full power operation, for example. In this manner, should one of the three high pressure fuel pumps 34 fail, the remaining two operating pumps 34 remain capable of providing full fuel flow to all cylinders 12 at full power operating conditions. Because of the functionality of the cross connection 38, this capability exists with the high pressure pumps 34 all providing fuel into only the left rail 20, as illustrated, or in other embodiments where one, two or three of the high pressure pumps 34 provide fuel 30 into the right rail 22.
The fuel injection apparatus 1 of FIG. 1 may be installed as original equipment on a new engine 10, or it may be back-fitted into an existing engine that originally utilized a fuel injection apparatus such as illustrated in U.S. Pat. No. 5,394,851. Such prior art systems include a cam-driven mechanical fuel pump mounted onto the strongback (mounting bracket) of each power assembly unit of the engine. When modifying such a twelve-cylinder engine to include the improved fuel injection apparatus 1 of FIG. 1, the twelve original fuel pumps are removed and the three high-pressure fuel pumps 34 are mounted onto the respective strongbacks in the place of three of the original pumps. Openings through the strongbacks that do not receive a high-pressure pump 34 may need to be sealed. For a bank of cylinders 12 where the high-pressure pumps 34 are installed, such as the left bank 16 of FIG. 1, a change in camshaft design may be required. Some of the original cam sections may be used in the modified engine. The present inventors have innovatively exploited the need for a change in camshaft design to further extend the advantages of the present fuel injection apparatus 1, as described more fully in the following paragraphs with reference made to FIG. 2.
FIG. 2 is a perspective view of camshafts 50, 52 as may be used in one embodiment of the engine 10 of FIG. 1. Left camshaft 50 is used in conjunction with the left bank 16 of cylinders 12 and right camshaft 52 is used in conjunction with the right bank 18 of cylinders 12. Each camshaft 50, 52 includes a drive gear 54, 56 at a driven end 58 and an opposed idler end 60. Torque is transferred from the drive gears 54, 56 to provide mechanical energy to respective valve lobes 62 for motivating the intake and exhaust valves (not shown) of each power assembly. Torque is also transferred from drive gear 54 to provide mechanical energy to respective fuel lobes 64 for powering the respective high-pressure fuel pumps 34. The camshafts 50, 52 are assembled by joining a plurality of cam sections, with each cam section being associated with one cylinder 12/power assembly of the engine 10. Left camshaft 50 includes cam sections 50a, 50b, 50c, 50d, 50e and 50f. Every cam section includes valve lobes 62 for the intake and exhaust valves of the respective power assembly. The cam sections alternatively include a fuel lobe 64 or do not include a fuel lobe 64. Cam sections 50a, 50b and 50c of FIG. 1 include fuel lobes 64. The lobes 64 may be angularly displaced relative to each other, such as by 40 degrees in one embodiment, in order to provide a more constant fuel supply pressure to the fuel rail 20. Advantageously, each of the sections 50a, 50b and 50c including a fuel lobe 64 are located proximate the driven end 58 of the camshaft 50, and no cam section that does not include a fuel lobe is located between the drive gear 54 and any section(s) including a fuel lobe 64. Thus, the adjoined sections most proximate the gear driven end 58 of the camshaft 50 may include a fuel lobe 64 and the adjoined sections most remote from the gear driven end 58 do not include a fuel lobe 64. In this manner, a torque value transmitted through the sections 50d, 50e, 50f not including a fuel lobe 64 is less than the torque value transmitted through the camshaft sections 50a, 50b, 50c that include a fuel lobe 64. This allows the camshaft sections not including a fuel lobe to be designed to have a smaller load-carrying capability than the section that include a fuel lobe. This may be accomplished by designing them with a smaller shaft diameter or by utilizing a material having a strength value (such as tensile or shear strength, for examples) lower than a corresponding strength value of a material of the camshaft sections including a fuel lobe. Thus, the cost of manufacturing camshaft sections not including a fuel lobe may be lower than the cost of manufacturing sections that do include a fuel lobe and/or lower than the cost of a prior art camshaft section that does include a fuel lobe. For a back-fit application utilizing the embodiment of FIG. 1, the original right camshaft may be left in place, and only the cam sections of the left camshaft that are associated with pumps need be replaced to assemble the camshaft 50 of FIG. 2. The replacement camshaft may be a completely new unit or it may be assembled using sections of the replaced camshaft.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Patent Application
20070012294
