Patent Application
20090272366
The present disclosure relates generally to fuel pumps and installation strategies for fuel pumps in internal combustion engine systems, and relates more particularly to setting an asynchronous timing between a fuel pump and an engine during installation of the fuel pump on the engine.
It is typically desirable to set different components of an internal combustion engine system at specified timings relative to one another. For instance, engine operating strategies often dictate a certain timing between an engine crankshaft and one or more camshafts. If the timing is not set as specified, certain engine events may take place at a timing relative to other engine events which is inappropriate. These concerns may be particularly acute in some fuel systems for internal combustion engines.
It has become commonplace for internal combustion engines, and in particular diesel engines, to utilize a mechanism known in the art as a common rail. A typical common rail fuel system includes a rail which contains fuel at a relatively high pressure. The rail is connected with a plurality of fuel injectors, associated one with each of a plurality of engine cylinders. When fuel injection into one of the engine cylinders is desired, one of the fuel injectors coupled with the common rail may be actuated to spray fuel into the corresponding engine cylinder. A fuel pump is typically driven via engine rotation and replenishes fuel as it is consumed from the common rail. One goal associated with many common rail fuel systems is maintaining a fuel pressure within the rail at a stable level. To this end, engineers have experimented with a wide variety of strategies for maintaining and controlling rail pressure. Common strategies have included attempts to set a timing of the fuel pump relative to an engine timing such that fuel pressure drops in the rail are compensated for via pumping strokes of the fuel pump. In other words, many strategies attempt to set the fuel pump in phase with certain engine events. Regardless of the specific approach, to successfully maintain or control common rail pressure, it is typically necessary to time the fuel pump with relatively great precision relative to a timing of the engine.
When an internal combustion engine system is assembled and set up for initial service, an appropriate timing between an engine and a fuel pump for the engine is typically set. Over the course of the many years of an engine's service life, it may be necessary to remove a fuel pump from the engine for servicing or for installing replacement parts, upgraded parts, etc., also requiring the timing to be set. In either of these instances, technicians are often expected to undertake a relatively laborious process of timing the fuel pump relative to the engine. One conventional strategy is to lock the fuel pump at a given orientation, remove the fuel pump from the engine, service the engine, then reinstall the fuel pump at the locked orientation. Other strategies attempt to use relatively unwieldy and specialized tools to set the fuel pump at a specific timing which corresponds to a known timing state of the engine. In either case, fuel pump installation and timing set-up in many internal combustion engine systems could be improved.
U.S. Pat. No. 5,845,397 to Reedy et al. is directed to one timing strategy for use in heavy duty diesel engines. In the strategy proposed by Reedy et al., a crankshaft and camshaft are locked into predetermined rotational positions to set a desired timing between the crankshaft and camshaft. The camshaft is stated to be locked into its predetermined rotational position using a camshaft timing member positioned between a flat portion on an outer surface of the camshaft and an adjacent portion of the engine, such as the cylinder head. Positioning the camshaft as described via the timing member purportedly locks the camshaft into a desired rotational position for setting its timing with respect to the crankshaft. While the proposal set forth in Reedy et al. may have certain applications, it requires specialized hardware and is relatively labor intensive.
In one aspect, a method of setting up a common rail internal combustion engine system for operation includes a step of setting a fuel pump for a common rail of the engine system at a pump configuration where a camshaft of the fuel pump is rotationally stable. The method further includes the steps of placing an engine of the engine system at an engine timing state which is accordant with the pump configuration, and installing the fuel pump on the engine when the fuel pump is in the pump configuration and the engine is at the engine timing state. The method still further includes a step of setting a timing between the engine and the fuel pump at an asynchronous timing at least in part via the installing step.
In another aspect, an electronically controlled variable displacement fuel pump for a common rail fuel system of an internal combustion engine includes a housing having a fuel inlet and a fuel outlet, and a metering valve associated with the housing and configured to vary an output of the fuel pump to a common rail. The fuel pump further includes a camshaft having a plurality of cams, a plurality of plungers and a plurality of biasers each biasing one of the plurality of plungers toward interaction with one of the plurality of cams. The fuel pump has a pump configuration where the camshaft is rotationally stable, and the fuel pump further includes an installation assist mechanism which includes the plurality of biasers and the plurality of cams and is configured to bias the fuel pump toward the pump configuration.
In still another aspect, a method of reducing timing errors of a fuel pump in a common rail engine system includes the steps of biasing the fuel pump toward a pump configuration where a camshaft of the fuel pump is rotationally stable, and placing an engine at an engine timing state which is accordant with the pump configuration. The method further includes the steps of installing the fuel pump on the engine when the fuel pump is in the pump configuration and the engine is at the engine timing state, and setting a timing between the engine and the fuel pump at an asynchronous timing at least in part via the installing step.
FIG. 3is a graph illustrating engine phasing versus pump phasing, according to one embodiment.
Referring to
In one embodiment, fuel pump 12 may include a reciprocating fuel pump which is actuated via rotation of a camshaft 16 coupled with pump gear 28. Camshaft 16 may include a plurality of cams, including a first cam 40a and a second cam 40b. A first lifter-roller assembly 34a is associated with first cam 40a, and a second lifter-roller assembly 34b is associated with second cam 40b. Rotation of camshaft 16 can actuate lifter-roller assemblies 34a and 34b to reciprocate a first plunger 30a and a second plunger 30b, respectively. Fuel pump 12 may further include a pump housing 32 which includes a fuel inlet 48 connecting with low pressure fuel supply 50, and a fuel outlet 46 which connects with common rail 14 in a conventional manner. Housing 32 may further define a first pump chamber 58a and a second pump chamber 58b, and plungers 30a and 30b may be reciprocable at least partially within pump chambers 58a and 58b, respectively, to pressurize fuel therein for supplying to common rail 14.
Turning now to
In one embodiment, pump 12 may include a first spill valve assembly 60a associated with first pump portion 12a, and a second spill valve assembly 60b associated with second pump portion 12b. Spill valve assemblies 60a and 60b may be identical in one embodiment. Fuel pump 12 may be an outlet metered pump. To this end, fuel pump 12 may include metering valves 54a and 54b, which are configured to fluidly connect a corresponding one of pump chambers 58a and 58b with outlet 46 to supply pressurized fuel to common rail 14. In certain embodiments, outlet 46 might be one outlet for one of pump portions 12a and 12b, and fuel pump 12 could include another fuel outlet for the other of pump portions 12a and 12b. Each spill valve assembly 60a and 60b may include an electrical actuator 62 which is configured to move plunger 64 to selectively block fluid communications between fuel inlet 48 and the corresponding pump chamber 58a and 58b. This general operating principle for an outlet metered pump is known in the art.
Fuel pump 12 may further include an installation assist mechanism 56 which includes lifter springs 36a and 36b, and also includes cams 40a and 40b. In one embodiment, installation assist mechanism 56 is configured to bias fuel pump 12 toward a pump configuration which is rotationally stable. It has been discovered that for certain types of fuel pumps, of which fuel pump 12 is one example, camshaft 16 will tend to always seek a position of balanced moments about axis of rotation Z when no external rotation force is acting on camshaft 16. This phenomenon may be leveraged to assist in timing pump 12 for installation on engine 18. It may be noted that fuel pump 12 is free from fixture interaction surfaces and the like, such as are used in other pumps to enable a fixture to engage with and lock a fuel pump camshaft or other components at a given orientation. Installation assist mechanism 56 enables fuel pump 12 to be installed without the need for interaction with a fixture to lock a position of camshaft 16, and without the need for specialized installation tools. Thus, the term “installation assist mechanism” as used herein should be understood to refer only to features or components of a fuel pump which are not used to interact with a fixture, timing tool, etc. For example, a fuel pump having a threaded bore in its camshaft for engaging with a set screw would, without more, not fairly be said to include an installation assist mechanism as contemplated herein.
It may further be noted that each of cams 40a and 40b has a symmetrical profile. Each of cams 40a and 40b may further be identical to one another, but positioned in fuel pump 12 about 180° out of phase relative to one another. As a consequence of the relative phasing, when one of plungers 30a and 30b is at a maximum lift position, the other of plungers 30a and 30b is at a minimum lift position. In other words, when one plunger is ascending, the other plunger 30a, 30b is descending. Each plunger 30a and 30b is reciprocated via a motion of the corresponding lifter-roller assembly 34a and 34b. Each lifter-roller assembly 34a and 34b is biased against the corresponding cam 40a and 40b via spring loads of lifter springs 36a and 36b, respectively. Rollers 38a and 38b contact cams 40a and 40b, respectively, to react this load. Since cams 40a and 40b have symmetrical profiles and are about 180° out of phase, the point at which moments about camshaft 16 sum to zero, or are balanced, is a point where one of rollers 38a and 38b exerts a force on its corresponding cam 40a and 40b at a location which is balanced by a force exerted by the other of rollers 38a and 38b at a different location on its corresponding cam 40a and 40b, as further described herein.
In the illustration of
As mentioned above, fuel pump 12 has a rotationally balanced configuration, corresponding to the balanced moment configuration approximately as shown in
As alluded to above, the described self locating feature of fuel pump 12 may be leveraged to ensure that installation on engine 18 occurs at an appropriate timing between fuel pump 12 and engine 18. A typical process of setting up engine system 10 for operation, either during factory installation of fuel pump 12, or after fuel pump 12 has been removed for servicing engine system 10 and is to be reinstalled on engine 18, may begin by setting fuel pump 12 at a pump configuration for installation.
When camshaft 16 is rotationally stable, an angular location of camshaft 16, or one of a plurality of angular configurations where camshaft 16 is rotationally stable, may be known. In other words, since fuel pump 12 will tend to always self-adjust via forces of lifter springs 36a and 36b, the camshaft angle corresponding to a rotationally stable configuration of camshaft 16 is ascertainable. In the case of fuel pump 12, two rotationally stable configurations about 180° of camshaft angle from one another may exist. For purposes of phasing fuel pump 12 relative to engine 18, these two rotationally stable configurations may be considered equivalent. When set at the pump configuration where camshaft 16 is rotationally stable, pump gear 28 may be fixed at a desired timing angle relative to camshaft 16, for example by using a fixture or the like to rotate or set pump gear 28 at a desired timing angle. In many engine systems, a desired timing precision of a camshaft relative to an engine crankshaft may be a precision which is greater than the precision available by coupling gear teeth of a pump gear with the engine geartrain. In other words, it may be desirable to fix pump gear 28 with camshaft 16 within a range of angles which is finer than the angle between adjacent gear teeth on pump gear 28.
Once pump gear 28 is fixed at a desired timing angle relative to camshaft 16, with fuel pump 12 in a pump configuration where camshaft 16 is rotatably stable, engine 18 may be placed at an engine timing state which is accordant with the pump configuration. In other words, setting up engine system 10 for operation may include placing engine 18 at an engine timing state which is compatible with the pump configuration where camshaft 16 is rotationally stable. It will be recalled that setting a timing between fuel pump 12 and engine 18 may establish a relative timing of certain engine events relative to certain fuel pump events. Placing engine 18 at the engine timing state which is accordant with the rotationally stable pump configuration should be understood to mean that engine 18 is placed at an engine timing state where engine events which take place at the engine timing state will not interfere with or compromise operation of fuel pump 12 or otherwise result in undesired operation of engine system 10. For instance, it may be desirable to set the relative timing between fuel pump 12 and engine 18 such that supplying fuel from fuel pump 12 to common rail 14 occurs only when none of fuel injectors 23 is injecting fuel. Thus, placing engine 18 at a crank angle which would result in supplying fuel to common rail 14 during a fuel injection event would be an example of an engine timing state which is not accordant with the pump configuration where camshaft 16 is rotationally stable.
With engine 18 at the accordant engine timing state and fuel pump 12 in the pump configuration where camshaft 16 is rotationally stable, fuel pump 12 may be installed on engine 18. Installing fuel pump 12 on engine 18 may set a timing between engine 18 and fuel pump 12, since coupling pump gear 28 with geartrain 26 may effectively fix the relative positions between camshaft 16 and crankshaft 24. In one embodiment, the timing set between engine 18 and fuel pump 12 may be an asynchronous timing, where at least one of pistons 20 is out of phase relative to each of plungers 30a and 30b. In one further embodiment, engine 18 may be located at an engine timing state such that at least one of pistons 20 is located about 90° out of phase with respect to each of plungers 30a and 30b.
Setting up engine system 10 for operation according to the present disclosure may take place at the factory when engine system 10 is prepared for initial service. In addition, the self timing feature of fuel pump 12 may be used when installing fuel pump 12 as a replacement part for another fuel pump in an engine system, and may also be used when fuel pump 12 needs to be removed from engine 18 for servicing, then reinstalled. Installation of fuel pump 12 to engine 18 in the manner described herein is contemplated to reduce timing errors between fuel pump 12 and engine 18 during installation. By biasing fuel pump 12 via installation assist mechanism 56 toward its pump configuration where camshaft 16 is rotationally stable, and placing engine 18 at an engine timing state which is accordant with the pump configuration where camshaft 16 is rotationally stable, it may be unnecessary to utilize a secondary means for timing fuel pump 12. In other words, the unwieldy, inconvenient and labor intensive hardware and timing methods of earlier timing strategies may be dispensed with.
Turning now to
Numerous crank angles may exist where at least one piston 20 is out of phase with respect to each of plungers 30a and 30b. Numerous crank angles may also exist where more than one of pistons 20 is out of phase with respect to each of plungers 30a and 30b. For purposes of convenience and reliability and repeatability of the installation procedure, it may be desirable to select an easily ascertainable crank angle. In one embodiment, engine 18 may be set for installation of fuel pump 12 at a crank angle where the piston 20 associated with a first one of cylinders 22 (cylinder “I”) is at a top dead center position. In
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects and features will be apparent upon an examination of the attached drawings and appended claims.
