Patent Application
20140209063
The present disclosure relates generally to a valve assembly in an internal combustion engine fuel system, and relates more particularly to a multi-layer coating on impacting parts of the valve assembly having a harder metal nitride base layer and a softer metal nitride outer layer.
Various fuel system components in modern internal combustion engine fuel systems are subjected to harsh operating conditions. High fuel pressures, debris particles, and repetitively impacting components tend to require the hardware used in such systems to be robust. If not addressed, various in-service and break-in wear phenomena can lead to performance degradation and potentially system failure. Hardening of materials, coating of certain components, and exacting manufacturing tolerances are techniques which have all been used in various forms to prolong fuel system service life.
Commonly owned and co-pending U.S. patent application Ser. No. 11/863,777 to Taylor, et al., now U.S. Pat. No. ______, is directed to a method for coating fuel system components. Taylor, et al. teach provision of a substrate and a coating, where the substrate comprises steel and the coating comprises a metal nitride, for use in production of a fuel system component. The strategy in Taylor, et al. appears to result in components resistant to wear. Despite the advantages offered by Taylor, et al., there remains room for improvement.
In one aspect, a valve assembly for a fuel system in an internal combustion engine includes a valve body having therein a valve seat located fluidly between a first fluid passage and a second fluid passage and being formed of a first metal substrate. The valve assembly further includes a valve member movable within the valve body between a first position at which the valve member contacts the valve seat and blocks fluid communication between the first and second fluid passages, and a second position at which the fluid communication is open, the valve member being formed of a second metal substrate. The valve seat and the valve member each include a multi-layer coating positioned within a sealing interface formed by the contact at the first position, and having a metal nitride base layer adherent to the corresponding first or second metal substrate, and a metal nitride outer layer. The metal nitride base layer has a greater hardness, such that the metal nitride base layer is relatively incompliant to impacts between the valve member and the valve seat at the first position and limits wear of the valve member and the valve seat during service of the valve assembly in the fuel system. The metal nitride outer layer has a lesser hardness, such that the metal nitride outer layer is relatively compliant to the impacts and is thereby deformable to enlarge the sealing interface during break-in of the valve assembly in the fuel system.
In another aspect, a fuel system for an internal combustion engine includes a housing defining a first fuel passage and a second fuel passage, and having a valve seat formed of a first metal substrate and positioned fluidly between the first and second fuel passages. The fuel system further includes a valve assembly positioned at least partially within the housing and configured to control a flow of fuel between the first and second fuel passages, and including a valve member formed of a second metal substrate. The valve member is movable between a first position at which the valve member contacts the valve seat and blocks fluid communication between the first and second fuel passages, and a second position at which the fluid communication is open. The valve seat and the valve member each include a multi-layer coating positioned within a sealing interface formed by the contact at the first position, and having a metal nitride base layer adherent to the corresponding first or second metal substrate, and a metal nitride outer layer. The metal nitride base layer has a greater hardness, such that the metal nitride base layer is relatively incompliant to impacts between the valve member and valve seat at the first position and limits wear of the valve member and the valve seat during service of the valve assembly in the fuel system. The metal nitride outer layer has a lesser hardness, such that the metal nitride outer layer is relatively compliant to the impacts and is thereby deformable to enlarge the sealing interface during break-in of the valve assembly in the fuel system.
In still another aspect, a method of limiting valve damage during breaking-in a valve assembly in a fuel system of an internal combustion engine includes moving a valve member of the valve assembly from a first position at which a first fuel passage and a second fuel passage in the fuel system are in fluid communication via a valve seat, to a second position at which the valve member contacts the valve seat to block the fluid communication. The method further includes transmitting a force of impact of the valve member on the valve seat at the second position from a softer outer layer of a metal nitride coating on at least one of the valve member and the valve seat to a harder base layer of the metal nitride coating adherent to a metal substrate of the at least one of the valve member and the valve seat. The method further includes preventing failure of the harder base layer in response to the transmission of the force via deforming the softer outer layer in response to the impact.
Referring to
Referring now to
As noted above, valve assembly 36 may include a control valve assembly for outlet check 40. Valve assembly 36 may include a valve body 52, which may be considered a part of housing 34, and having therein a valve seat 54 located fluidly between a first fluid passage such as first fuel passage 46 and a second fluid passage, such as second fuel passage 48 or second fuel passage 49. Each of passages 46, 48 and 49 may be understood to be formed in and defined by valve body 52, and similarly understood to be formed in and defined by housing 34 since valve body 52 may be considered a part thereof. Any of passages 46, 48 and 49 might further be understood as a first fluid passage or a first fuel passage, and likewise understood as a second fluid passage or second fuel passage, or as a third fluid passage or third fuel passage. It will thus be appreciated that the labels “first,” “second,” and “third,” may be variously applied, depending upon perspective. In the embodiment shown, valve assembly 36 includes a three-way valve assembly, varying fluid communications among passages 46, 48 and 49, and operably coupled with outlet check 40. In alternative fuel injector design strategies, as well as in other fuel system components, a valve assembly according to the present disclosure might be designed as a two-way valve assembly. Valve assembly 38 may be one such two-way valve assembly design. As a three-way valve assembly implementation, valve body 52 may include therein a second valve seat 56, which can be similarly understood to be located fluidly between first and second fluid or fuel passages.
Valve assembly 36 further includes a valve member 58 movable within valve body 52 between a first position at which valve member 58 contacts valve seat 54 and blocks fluid communication between first and second fluid passages, and a second position at which the fluid communication is open. At the second position, valve member 58 may contact valve seat 56 and block fluid communication between one or both of the first and second fluid passages and a third fluid passage formed within valve body 52. The third fluid passage may be in fluid communication with the first passage at the first position of valve member 58, and valve member 58 being in contact with second valve seat 56 at the second position such that the fluid communication between the first and third passages is blocked. An electrical actuator 50 is coupled with valve member 58 to move it between the first and second positions, in a conventional manner.
Referring now to
Referring also now to
As noted above, a unique strategy of coating valve components according to the present disclosure is considered to prolong service life. To this end, each of valve seats 54 and 56 and valve member 58 may include a multi-layer coating 64 positioned within sealing interface 66 formed by the contact at the first position, and within an analogous sealing interface formed by contact between valve member 58 and valve seat 56 at the second position. A contacting valve seat and valve member in valve assembly 38 may be analogously coated. Valve body 52 may be formed of a first metal substrate 60, and valve member 58 may be formed of a second metal substrate 62. In one embodiment, substrates 60 and 62 may consist of the same material, which may be a hardened steel material having a Rockwell hardness of about 55 (HRC scale) or greater. Multi-layer coating 64 may have a metal nitride base layer 68 adherent to the corresponding first or second metal substrates 60 or 62, and a metal nitride outer layer 70. A surface finish on each of substrates 60 and 62 to which base layer 68 is adherent may have a roughness average (Ra) of about 0.0001 mm, as determined by deflection of a stylus in a conventional manner. As used herein, the term “about” may be understood in the context of conventional rounding to a consistent number of significant digits. Thus, “about 55” means from 54.5 to 55.4, “about 0.1” means from 0.05 to 0.14. As to ratios, “about 1:1” means a ratio from 0.5 to 1, to 1.4 to 1.
Base layer 68 may have a greater hardness, such that base layer 68 is relatively incompliant to impacts between valve member 58 and valve seat 54 at the first position and limits wear of valve member 58 and valve seat 54 during service of valve assembly 36 in fuel system 12. Wear of valve seat 56 is analogously limited. Outer layer 70 may have a lesser hardness, such that outer layer 70 is relatively compliant to the impacts, and is thereby deformable to enlarge sealing interface 66 during break-in of valve assembly 36 in fuel system 12. The sealing interface at valve seat 56 will be analogously enlarged. In a practical implementation strategy, a thickness of coating 64 on valve member 58 and valve seat 54 is from about 0.005 mm to about 0.020 mm, and a ratio of a thickness of base layer 68 to a thickness of outer layer 70 is from about 1:1 to about 1:10.
The greater hardness of base layer 68 may be uniform throughout base layer 68, and the lesser hardness of outer layer 70 may be non-uniform throughout outer layer 70, and such that outer layer 70 is hardest at an inward location adjacent base layer 68 and transitions to softest at an exposed outward location spaced from base layer 68. A number of layers greater than two might be used in certain embodiments. The steel of first and second substrates 60 and 62 may have a hardness less than the lesser hardness of outer layer 70 at the outward location. The hardness of outer layer 70 may be about three times the hardness of substrate materials 60 and 62, at the softest part of outer layer 70, although the present disclosure is note thereby limited. Hardness of coating 64 may be from about 13 giga-Pascals (GPa) to about 30 giga-Pascals. Given these general parameters, it may be understood that substrates 60 and 62 are relatively hard, outer layer 70 is relatively harder, and hardest adjacent and typically adjoining base layer 68 and softest at its outermost exposed location. Base layer 68 is hardest of all. These general features are considered to allow the materials of valve member 58 and valve body 52 to function as a system, with resistance to various forms of damage during service as further discussed herein. Deposition of coating(s) 64 may take place via physical vapor deposition, in a single batch, with the parameters varied for deposition of the different layers.
In practical implementation strategies, each of base layer 68 and outer layer 70 is formed of a transition metal nitride, and a transition metal content of base layer 68 may be less than a transition metal content of outer layer 70. Outer and softer layer 70 may be inversely graduated in hardness as noted above, and graduated in the transition metal content from the inward location adjacent base layer 68 to the outward location to obtain this property. The transition metal nitride forming base layer 68 and outer layer 70 may include chromium nitride. A ratio of chromium to nitrogen in base layer 68 may be about 2:1, or less, and a ratio of chromium to nitrogen in outer layer 70 may be about 9:1, or less. Other metals, and in particular transition metals, may provide differing properties than chromium nitride, such as adhesion to the metal substrate, but may nevertheless fall within the scope of the present disclosure.
As noted above, the teachings of the present disclosure may be applied to limit valve damage in a valve assembly in a fuel system of an internal combustion engine. Limiting the valve damage may occur during service in the fuel system, and also occur during breaking-in a valve assembly. Many wear resistant, hard coatings and the like tend to be brittle. It has been observed that during break-in of certain valve assemblies coated with hard material coatings, cracking and/or de-lamination of the relatively brittle coating material can occur, resulting in metal on metal contact between a valve member and a valve seat. As a result, the metal substrate of at least one of the valve member and the valve seat can be unduly packed via post-delamination impacts between the valve member and the valve seat, resulting in an increase in valve member travel distance, leading to performance degradation and/or failure. De-lamination of protective coatings can also have the unsurprising result of subjecting the metal substrates to erosion via hard debris particles as well as deformation from such debris particles being pounded into the metal substrate. Erosion and deformation caused by debris can result in valve sealing problems, or raise other concerns.
The present disclosure is considered to address these and other concerns, by way of the unique coatings disclosed herein. To this end, outer layer 70 may be relatively more metal-like or ductile and serve as a buffer layer against impacts by debris trapped between the contacting valve surfaces. This tends to have the desirable effect of inhibiting crack initiation and propagation in the relatively harder and wear resistant base layer. In addition, the outer layer will tend to be plastically deformable to transition the sealing interface between the valve components from a knife-edge or line contact pattern to an enlarged band or surface contact pattern, spreading out the force of subsequent impacts.
Referring generally now to
In
It may also be noted that a plurality of cracks 100 have formed in base layer 68 on valve member 58 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, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
