US20140345557A1

US20140345557A1 - Thermal Spray Coated Engine Valve for Increased Wear Resistance

Info

Publication number: US20140345557A1
Application number: US13/900,892
Authority: US
Inventors: Mark D. Veliz; Daniel J. Sordelet; Ondrej Racek; M. Brad Beardsley
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2013-05-23
Filing date: 2013-05-23
Publication date: 2014-11-27
Also published as: WO2014190043A1

Abstract

A valve for use in an internal combustion engine is disclosed. The valve includes a stem connected to a fillet disposed between the stem and a seat face. A port receives the stem and accommodates a seat insert that engages the seat face when the valve is in a closed position. The seat insert is fabricated from a non-cobalt-based alloy or an iron-based alloy and the seat face is coated with a cobalt-based alloy or a nickel-based alloy. The coating may be applied using a thermal spray process, such as HVOF.

Description

TECHNICAL FIELD

This disclosure relates to valves coated with a wear-resistant thermal spray coating and internal combustion engines incorporating the same.

BACKGROUND

Internal combustion engines are used in many different applications. For example, intake valves of such engines are positioned in an intake port disposed between the air intake and the combustion chamber. During an air intake stroke, a cam or rocker arm pushes the intake valve open and allows the fuel mixture to enter the combustion chamber. Further, exhaust valves are positioned in an exhaust port disposed between the combustion chamber and an exhaust flow passage. During an exhaust stroke, the cam or rocker arm pushes the exhaust valve open and combustion gases are expelled from the chamber.
The seal that the valve makes with the port is important to engine performance and efficiency. If the valve leaks, the pressure in the combustion chamber decreases and the engine generates considerably less power. Engine manufacturers over the last few decades have dedicated substantial efforts in designing valves that can form a tight seal between the seat insert of the port and the seating face or the seat face of the fillet.
Both the seat insert and the seat face are important for the reliability of the valve. For example, it is well-known that corrosion or wear of either the seat insert or seat face can cause the valve to leak when the valve is closed, which results in “burn through.” To prevent burn through, the seat insert and the seat face on the valve fillet have been made with increasingly harder materials that are also corrosion resistant.
The seat face may be hardened by applying a hard cladding layer followed by machining to form the seat face with the desired dimensions. The hard cladding makes the seat face more wear-resistant. Hard cladding can also reduce the formation of dent marks. Examples of materials that are frequently used for seat face materials are metal alloys having cobalt and nickel. As an alternative to applying hard cladding to the seat face, hard cladding may also be applied to seat inserts. Because of the high cost, hard cladding is typically not applied to both the seat insert and the seat face. Regardless, in almost all cases, the advantages of using hard cladding for either the seat insert or the seat face may not be sufficient to offset the increase in price over softer metals such as iron-based alloys.
While hardened seat faces last longer, the means by which the seat faces are hardened is problematic. Specifically, plasma transferred arc (PTA) cladding, also known in the art as hard facing, is routinely used on valves in the engine manufacturing industry. Unfortunately, PTA cladding requires that the deposition of a thick layer and high heat input, which causes the base material of the valve to degrade because of microstructural degradation or from residual stress. As a result, there is an increased tendency for fatigue failures. To improve the durability of seat inserts disposed in the port, additional nitriding or thin-film coatings have been used. Nitriding is typically not an option for outlet or exhaust ports as the alloys used for the outlet ports are not responsive to nitriding.
Cobalt-based materials have been used to coat seat inserts as well as seat faces via PTA cladding. It is widely recognized in the art that if a cobalt-based material is used to coat the seat face, a cobalt material may be used to coat the seat insert for improved performance. In other words, it is widely recognized that cobalt based materials, when used as wear-resistant coatings, may be “self-mated,” or both parts that engage one another should be coated with cobalt-based materials. However, cobalt-based materials may be expensive and using a cobalt-based material to clad the seat face and/or to coat the seat insert may result in a costly assembly.
When wear occurs on the seat face or the seat insert of an automobile or truckvalve, the geometry and the gap between the stem and the rocker are no longer optimized, and therefore adjustments need to be made, which are referred to as lash adjustments. Performing lash adjustments manually requires a vehicle to be taken out of service, which is an expense and a nuisance to the operator. Some vehicles are equipped with hydraulic lash adjusters (HLA or lifters or tappets) that automatically adjust the gap between the stem tip and the rocker to maintain proper sealing and seating velocities. Heavy-duty diesel engines do not typically have HLA because of the high valve train loads. Therefore, lash adjustments for most heavy duty diesel engines must be made manually, thereby requiring the machine to be taken out of service.
Thus, there is a need for improved seat faces and as seat inserts that are cost-effective and that provide sufficient wear resistance to extend the time between lash resets.

SUMMARY

In one aspect, a valve for use in an internal combustion engine is disclosed. The valve may include a stem connected to a fillet that connects the stem to a seat face. The stem may be received in a port that accommodates a seat insert that engages the seat face when the valve is in a closed position. The seat insert may be fabricated from a non-cobalt-based alloy and the seat face may be coated with a cobalt-based alloy or a nickel-based alloy.
In another aspect, an internal combustion engine is disclosed. The engine may include a cylinder block that may include at least one combustion chamber. The engine may further include at least one passage in communication with to the at least one combustion chamber and defining a port configured to receive a valve. The valve may be positioned within the port for selectively opening and closing the port. The valve may include a stem connected to a fillet that connects the stem to a seat face. The seat face may be coated with a cobalt-based alloy or a nickel-based alloy. Further, in the case of an intake valve, the port may accommodate a seat insert. The seat insert may be fabricated from an iron-based alloy.
In yet another aspect, a method of improving the durability of an engine valve is disclosed. The method may include providing a valve that may include a stem connected to a fillet that connects the stem to a seat face. The method may further include providing an engine port for receiving the stem and the seat face when the valve is in a closed position. In the case of an intake valve, the port may accommodate an iron-based seat insert that engages the seat face when the valve is in the closed position. The method may further include thermal spray coating the seat face with a cobalt-based alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front plan view of a disclosed valve.

FIG. 2 is a partial sectional view of a disclosed internal combustion engine showing a disclosed valve in a closed position and in contact with a port disposed between an air intake and a combustion chamber.

FIG. 3 is an enlarged partial view of the contact between a seat insert that is accommodated in the port shown in FIG. 2 and the seat face shown in FIGS. 1-2.

FIG. 4 graphically illustrates the improved wear performance of cobalt-based alloys (STELLITE® 6, TRIBALOY® T-400 and STELLITE® 1) versus other cobalt-based and non-cobalt-based alloys shown to the left in FIG. 4 (TRIBALOY® T-800, CoNiCrAlY, NiCrAlY) at an operating temperature of 800° C.

FIG. 5 graphically illustrates the improved performance of cobalt-based alloys (STELLITE® 6, TRIBALOY® T-400 and STELLITE® 1) versus other cobalt-based and non-cobalt based alloys (TRIBALOY® T-800, CoNiCrAlY, NiCrAlY) when used to coat a seat face on a fillet of a valve operating at a temperature of 550° C.

FIG. 6 illustrates, graphically, the improved total wear performance of STELLITE® 1 versus TRIBALOY® 400, a NiCrAlY alloy and no seat face coating at all as well as the improved performance of the iron-based alloy J130 for the seat insert versus the iron-based alloy J10. Further, FIG. 6 also illustrates the increased wear that occurs at an operating temperature of 800° C. versus an operating temperature of 550° C.

FIG. 7 illustrates, graphically, the improved percent valve wear performance of STELLITE® 1 versus TRIBALOY® 400, a NiCrAlY alloy and no seat face coating at all as well as the improved performance of the iron-based alloy J130 for the seat insert versus the iron-based alloy J10. Further, FIG. 7 also illustrates the increased wear that occurs at an operating temperature of 800° C. versus an operating temperature of 550° C.

FIG. 8 illustrates, graphically, the improved performance of using a thermal spray coating process (HVOF) versus a cladding process (PTA) for STELLITE® 1 for coating the seat face as well as no coating at all at an operating temperature of 550° C. and using the iron based alloy J3 for the seat insert.

FIG. 9 illustrates, graphically, the improved performance of thermal spray coating (HVOF) STELLITE® 1 on the seat face versus using a cladding process (PTA) and comparing the performance of J3 versus J130 as the seat inserts for HVOF applied STELLITE® 1 at an operating temperature of 800° C.

FIG. 10 is a photograph of a seat face coated with a cobalt-based alloy via a thermal spray process (e.g., HVOF).

FIG. 11 is a photograph of a cobalt-based alloy that has been applied to a seat insert via a cladding process (e.g., PTA).

DESCRIPTION

FIG. 1 illustrates a valve 20, that may serve as an intake valve or an exhaust valve. The valve 20 may include a stem 21 that may be connected to a fillet 22. The fillet 22 may connect the stem 21 to a seat face 23. The seat face 23 may be disposed between the fillet 22 and a margin 24. The margin 24 may be disposed between the seat face 23 and a combustion face 19.
Turning to FIG. 2, one valve 20 may be installed in a cylinder head 25 that may define an air intake 26 that terminates at an intake port 27. The intake port 27 may lead to a combustion chamber 28, which may slidably accommodate a piston 29 (only partially shown in FIG. 2). The valve 20 may be biased into the closed position shown in FIG. 2 by a spring or other biasing element 31. The stem 21 may extend upward through said biasing element 31 to be engaged by an actuator in the form of a rocker arm or cam (not shown in FIG. 2). As shown in FIG. 2, the seat face 23 may engage a seat insert 32 in the closed position. As noted above, it is important to reduce the wear incurred by the seat face 23 and/or the seat insert 32 to extend the time between lash resets. An enlarged view of the contact between the seat insert 32 and a coating 33 disposed on the seat face 23 is shown in FIG. 3. Also shown in FIG. 2 is another valve 20′ installed in the cylinder head 25 that also defines an exhaust passage 41 and an exhaust port 42. Typically, the exhaust port 42 will not be equipped with a seat insert 32. However, the the valve 20′ may also include a seat face 23′ that may be coated in a manner similar to the seat face 23 of the valve 20.
As noted above, it is widely recognized that seat faces and seat inserts or cobalt-based wear resistant coatings on seat faces and seat inserts perform well when they are “self-mated” or when both mating components (i.e., a seat insert and a seat face) are either made from the same cobalt-based alloy or similar cobalt-based alloys or coated with the same cobalt-based coating or similar cobalt-based coatings. However, surprisingly, it has been found that a cobalt-based alloy may be used for the coating 33 on the seat face 23 while the seat insert 32 may be fabricated from a non-cobalt-based alloy or a non-cobalt based alloy may be used for the coating 33 on the seat face 23 while the seat insert 32 may be fabricated from a non-cobalt-based alloy, such as an iron-based alloy. Further, it has been found that nickel chromium aluminum yttrium (NiCrAlY) may also be used for the coating 33 on the seat face 23 and still provide good wear resistance when the seat insert is fabricated from a cobalt-based alloy or a non-cobalt-based alloy such as an iron-based alloy. The seat face 23′ may also be coated with either a cobalt-based coating or a non-cobalt based alloy.
The data graphically illustrated in FIGS. 4-5 was attained using a seat insert 32 made from a cobalt-based alloy, J3, available from L. E. Jones Company (www.lejones.com/). In FIG. 4, the operating temperature or the temperature to the combustion face 19 (FIG. 1) was 800° C. The left column of FIG. 4 serves as a base line as the seat face 23 was uncoated and therefore the left column recites the alloy used to make the valve, PYROMET® 31V (P31V), which is an iron-based alloy (www.cartech.com). The other six alloys that were tested for wear in FIGS. 4-5 include: TRIBALOY® T-800 (T-800), which is a cobalt based alloy manufactured by Deloro Stellite (www.steliite.com); a cobalt nickel chromium aluminum yttrium alloy sold under the trademark DIAMALLOY® 4700 (CoNiCrAlY), manufactured by Sulzer Metco; a nickel chromium aluminum yttrium alloy sold under the designation NI343 by Praxair (NiCrAlY); STELLITE® 6, another cobalt based alloy; TRIBALOY® T-400 (T-400), another cobalt based alloy; and STELLITE® 1, which is another cobalt based alloy. Thus, the only non-cobalt based alloy evaluated in FIGS. 4-5 are the NiCrAlY alloy (NI343) and the P31V, the iron-based alloy used to fabricate the valve. All of the alloys used for a coating on the seat face were coated using an HVOF thermal spray process except, of course, the uncoated valve shown at the left in FIGS. 4-5, which leaves exposed P31V, the iron-based alloy used to fabricate the valve.
At 800° C. operating temperature, the cobalt-based alloy, STELLITE® 1 exhibited the least amount of wear after 200 hours of operation. Similarly, at an operating temperature of 550° C. and after 200 hundred hours of operation, the STELLITE® 1, TRIBALOY® 400, TRIBALOY® 800 and the NiCrAlY (NI343) alloys all performed the best, when used with the cobalt-based insert (J3). The results for the NiCrAlY alloy are surprising because, as noted above, it is well known in the art that cobalt-based alloys show better wear results when the two wear surfaces are fabricated from the same alloy or the same type of alloy (i.e., both wear surfaces are fabricated from the same or different cobalt-based alloys or are “self-mated”).
In another test graphically illustrated in FIGS. 6-7, the seat insert material was changed to another L.E. Jones cobalt-based alloy J10 and an iron-based alloy J130. As shown in FIG. 6, the cobalt-based alloy, STELLITE® 1 had less wear then the TRIBALOY® 400 and NiCrAlY (NI343) alloys, although the NiCrAlY (NI343) and TRIBALOY® 400 alloys did very well. Further, it appears that the non-cobalt, iron-based J130alloy performed slightly better than the J10 alloy, which is surprising as J130 is an iron-based alloy, which worked very well with STELLITE® 1, a cobalt-based alloy. FIG. 6 graphically illustrates the total wear while FIG. 7 graphically illustrates the percentage of valve wear. In FIG. 7, STELLITE® 1 performed better than TRIBALOY® 400, NiCrAlY, and the insert alloys, J10 and J130 performed comparably. FIGS. 6-7 show that the STELLITE® 1 as a seat face coating, an inexpensive cobalt-based alloy, does not need to be matched with a seat insert fabricated from or coated with a cobalt-based alloy. Further, FIGS. 6-7 show that the combination of the iron-based J130 alloy for the seat insert and STELLITE® 1 as the coating for the seat face provide excellent wear resistance results.
Turning to FIGS. 8-9, the use of a STELLITE® 1 coating deposited via a thermal spray process (HVOF) or a cladding process (PTA) was compared at 550° C. (FIG. 8) and at 800° C. (FIG. 9). The seat insert was made from the J3 cobalt-based alloy, except where noted in FIG. 9. The tests were carried out over a 200 hour period. Surprisingly, at 800° C., the use of cladding (PTA) proved to be inferior to no coating at all. In any event, the application of STELLITE® 1 by HVOF was far superior to the cladding method (PTA). At 800° C., a further improvement was made using the iron-based J130 alloy for the insert instead of the cobalt-based J3 seat insert, which is surprising given the fact that STELLITE® 1 is a cobalt-based alloy. Thus, an effective combination is the application of a wear resistant coating in the form of STELLITE® 1 alloy applied to the seat face via a thermal spray process, such as HVOF, or another thermal spray process as will be apparent to those skilled in the art. Further, an effective combination is the STELLITE® 1 alloy for the protective coating on the seat face 23 and the use of the iron-based alloy J130 for the seat insert 32.
Finally, turning to FIGS. 10-11, the wear resistant coating 33 was applied to the seat face 23 shown in FIG. 10 via a thermal spray process, such as HVOF. The thickness of the coating 33 may range from about 0.05 mm to about 2 mm.
In contrast, a cladding process (PTA) was used to harden the seat face 23 in FIG. 11 and the degradation of the base material of the valve 20 is clearly shown which may explain, in part, the poor performance of the PTA treated seat face at the 800° C. operating temperature as shown in FIG. 9.

INDUSTRIAL APPLICABILITY

Improved valves for internal combustion engines are provided. The valves may include a stem connected to a fillet. The fillet may be disposed between the stem and a seat face that is coated with a cobalt-based alloy or a NiCrAlY alloy. While cobalt-based seat face coatings in combination with readily available iron-based alloy seat inserts provide superior performance, NiCrAlY alloys may provide a lower cost alternative although the wear resistant properties of NiCrAlY alloys may be somewhat inferior to the cobalt-based alloys, particularly STELLITE® 1, TRIBALOY® 400 and TRIBALOY® 800. The seat inserts which engage the seat face disposed on the fillet may be made of readily-available iron based alloys as discussed above. The result is an improved valve that is both cost effective and provides excellent wear resistance.

Claims

1. A valve for use in an internal combustion engine, the valve comprising:

a stem connected to a fillet, the fillet connecting the stem to a seat face;

a port that receives the stem and accommodates a seat insert that engages the seat face when the valve is in a closed position;

the seat insert being fabricated from a non-cobalt-based alloy; and

the seat face being coated with a cobalt-based alloy or a nickel-based alloy.

2. The valve of claim 1 wherein the cobalt-based alloy covers the seat face and not the fillet.

3. The valve of claim 1 wherein the seat face is disposed between the fillet and a margin, the cobalt-based alloy covering the seat face and not the fillet or the margin.

4. The valve of claim 1 wherein the cobalt-based alloy is coated onto the seat face using a thermal spray process.

5. The valve of claim 4 wherein the thermal spray process is high velocity oxygen fuel (HVOF) process.

6. The valve of claim 1 wherein the non-cobalt-based alloy is an iron-based alloy.

7. The valve of claim 1 wherein the non-cobalt-based alloy is J130.

8. The valve of claim 1 wherein the nickel-based alloy is a NiCrAlY alloy.

9. The valve of claim 1 wherein the cobalt-based alloy is STELLITE® 1.

10. The valve of claim 1 wherein the cobalt-based alloy is selected from the group consisting of STELLITE® 1, STELLITE® 3, STELLITE® 4, STELLITE® 6, STELLITE® 6B, STELLITE® 12, STELLITE® 21, STELLITE® 25, STELLITE® 31, STELLITE® 190, STELLITE® 694, STELLITE® 706, STELLITE® 712, STELLITE® F, STELLITE® Star 3, TRIBALOY® 400, TRIBALOY® 400C, TRIBALOY® 800, TRIBALOY® 900 and combinations thereof.

11. The valve of claim 1 wherein the cobalt-based alloy is STELLITE® 1 and the iron-based alloy is J130.

12. The valve of claim 1 wherein the cobalt-based alloy is coated onto the seat face with a thickness ranging from about 0.05 mm to about 2 mm.

13. An internal combustion engine including the valve as defined in claim 1.

14. An internal combustion engine, comprising:

a cylinder block including at least one combustion chamber;

at least one air intake leading into the least one combustion chamber and defining a port configured to receive a valve;

the valve positioned within the at least one port for selectively opening and closing the port, the valve including a stem connected to a fillet that is connects the stem to a seat face, the seat face being coated with a cobalt-based alloy or a nickel-based alloy; and

the port accommodating a seat insert, the seat insert being fabricated from an iron-based alloy.

15. The engine of claim 14 wherein the nickel-based alloy is a NiCrAlY alloy.

16. The engine of claim 14 wherein the seat face is coated using a thermal spray process.

17. The engine of claim 14 wherein the cobalt-based alloy is selected from the group consisting of STELLITE® 1, STELLITE® 3, STELLITE® 4, STELLITE® 6, STELLITE® 6B, STELLITE® 12, STELLITE® 21, STELLITE® 25, STELLITE® 31, STELLITE® 190, STELLITE® 694, STELLITE® 706, STELLITE® 712, STELLITE® F, STELLITE® Star 3, TRIBALOY® 400, TRIBALOY® 400C, TRIBALOY® 800, TRIBALOY® 900 and combinations thereof.

18. The engine of claim 14 wherein the cobalt-based alloy is STELLITE® 1 and the non-cobalt based alloy is J130.

19. The engine of claim 14 wherein the cobalt-based alloy is coated onto the seat face with a thickness ranging from about 0.05 mm to about 2 mm.

20. A method of improving the durability of an engine valve, comprising: providing a valve including a stem connected to a fillet that connects the stem to a seat face;

providing an engine port for receiving the stem, wherein the port accommodates an iron-based seat insert that engages the seat face when the valve is in a closed position; and

thermal spray coating the seat face with a cobalt-based alloy or a NiCrAlY alloy.