ROLLER HYDRAULIC VALVE LIFTER BEARING

Abstract

A roller hydraulic valve lifter includes a body having a longitudinal central axis and an interior area defined by an inside surface which has a pair of flat surfaces opposite one another and connected by a pair of walls. A first bore, essentially perpendicular to the longitudinal axis, extends through the flat surfaces. A bearing is disposed partially in the interior area. The bearing includes an outer ring having substantially cylindrical exterior and interior bearing surfaces. A shaft extends through the first bore and the outer ring and between the pair of flat surfaces. A plurality of needle rollers is disposed between and rollingly engage the shaft and the cylindrical inner bearing surface. The shaft and the plurality of needle rollers are manufactured from an AISI 52100 alloy steel that is carbo-nitrided. The shaft and the plurality of needle rollers have a surface hardness of a minimum of HRc 65.

Claims

1. A roller hydraulic valve lifter comprising: a body having a longitudinal central axis and an interior area defined by an inside surface, the inside surface, comprising a first flat surface and a second flat surface opposite the first flat surface the first flat surface and the second flat surface being connected by a pair of connecting walls, a first bore extending through the first flat surface and the second flat surface, the first bore being substantially perpendicular to the longitudinal central axis; a bearing disposed partially in the interior area, the bearing comprising: an outer ring having a substantially cylindrical exterior bearing surface, and a substantially cylindrical inner bearing surface that defines second bore; a shaft extending through the first bore and the second bore, the shaft extending between the first flat surface and the second flat surface; a plurality of needle rollers disposed between and rollingly engaging the shaft and the cylindrical inner bearing surface; the shaft and the plurality of needle rollers are manufactured from an AISI 52100 alloy steel that is carbo-nitrided and the shaft and plurality of needle rollers having a surface hardness of a minimum of HRc 65; the shaft and the plurality of needle rollers each have an exterior surface that is in compression and each have exterior surfaces treated by a mass finishing process; and the shaft and the plurality of needle rollers each have a microstructure having less than 12 volumetric percent retained austenite.

2. The roller hydraulic valve lifter of claim 1, wherein the shaft and the plurality of needle rollers each have a minimum carbo-nitrided case depth of 0.25 mm.

3. The roller hydraulic valve lifter of claim 1, wherein the shaft and the plurality of needle rollers each have a core hardness of HRc 59 to HRc 65.

4. A method of increasing a life of a roller hydraulic valve lifter, the method comprising: providing a first roller hydraulic valve lifter comprising a body having a predetermined set of dimensions and a first shaft mounted in the body, the first shaft having a first outside diameter; providing a first bearing comprising an outer ring having a second outside diameter, a first inside diameter and an axial length; providing a plurality of first needle rollers each having a third outside diameter and an axial length, the plurality of first needle rollers being disposed between and in rolling engagement with the first shaft and the outer ring, the first shaft and the plurality of first needle rollers being manufactured from an AISI 52100 alloy steel having a surface hardness of less than HRc 65; and creating a second roller hydraulic valve lifter that has a life of at least 1.5 times that of the first roller hydraulic valve lifter, the second roller hydraulic valve lifter being created by substituting at least the first shaft and the plurality of first needle rollers with a second shaft and a plurality of second needle rollers, the second shaft having the first outside diameter, and the plurality of second needle rollers each having the third outside diameter and the axial length, utilizing the body having the predetermined set of dimensions and utilizing the outer ring having the second outside diameter, the first inside diameter and the axial length; the plurality of second needle rollers being disposed between and in rolling engagement with the second shaft and the outer ring, and wherein the second shaft and the plurality of the second rollers are manufactured from an AISI 52100 alloy steel that is carbo-nitrided and the second shaft and plurality of second needle rollers having a surface hardness of a minimum of HRc 65.

5. The method of claim 4, wherein the second shaft and the plurality of second needle rollers each have a minimum carbo-nitrided case depth of 0.25 mm.

6. The method of claim 4, wherein the second shaft and the plurality of second needle rollers each have an exterior surface that is in compression.

7. The method of claim 4, further comprising treating the exterior surface with a mass finishing process.

8. The method of claim 4, wherein the second shaft and the plurality of second needle rollers each have a core hardness of HRc 59 to HRc 65.

9. The method of claim 4, further comprising cooling the second shaft and the plurality of the second rollers to 84 C. and establishing a microstructure having less than 12 volumetric percent retained austenite.

10. A method for manufacturing a shaft and rollers for a roller hydraulic valve lifter, the method comprising the following steps in the order presented: providing an AISI 52100 alloy steel; carbonitriding the AISI 52100 alloy steel; oil quenching the AISI 52100 alloy steel; tempering the AISI 52100 alloy steel at 149 C.; and cooling the AISI 52100 alloy steel to 84 C.

11. The method of claim 10, wherein the carbonitriding is performed at 829 C.

12. The method of claim 10, wherein another tempering is performed at 177 C. after the cooling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a schematic view of a cam-in-block engine valvetrain with a prior art roller hydraulic valve lifter;

[0018] FIG. 2 is a perspective view of the roller hydraulic valve lifter of the present invention;

[0019] FIG. 3 is a perspective view of a bearing for the roller hydraulic valve lifter of FIG. 2 shown with a temporary plug therein for retaining the needle rollers therein prior to installation in a roller hydraulic valve lifter;

[0020] FIG. 4 is a perspective view of the shaft of the roller hydraulic valve lifter of FIG. 2;

[0021] FIG. 5 is a cross sectional view of the roller hydraulic valve lifter of FIG. 2 taken across section 5-5;

[0022] FIG. 6 is a bottom view of the roller hydraulic valve lifter of FIG. 2;

[0023] FIG. 7 is a cross sectional view of the roller hydraulic valve lifter of FIG. 2 taken across section 7-7;

[0024] FIG. 8 is a graph of a carbo-nitriding heat treatment process of the present invention; and

[0025] FIG. 9 is a graph of a prior art carbo-nitriding heat treatment process.

DETAILED DESCRIPTION

[0026] As shown in FIG. 2, a roller hydraulic valve lifter of the present invention is generally designated by the numeral 10. As shown in FIGS. 2 and 5, the roller hydraulic valve lifter 10 includes a generally cylindrical body 12 having a longitudinal central axis L. The body 12 has an interior area 12A defined by an inside surface 12B (see FIG. 5). As shown in FIGS. 5-7, the inside surface 12A includes a first flat surface 13A and a second flat surface 13B opposite the first flat surface 13A. The first flat surface 13A and the second flat surface 13B are connected by a pair of connecting walls 14A and 14B (see FIGS. 6 and 7). In one embodiment, the connecting walls 14A and 14B are arcuate (e.g., a section of a cylinder). A first bore 15 extends through the first flat surface 13A and the second flat surface 13B and entirely through the body 12. The first bore 15 is substantially perpendicular to the longitudinal axis L.

[0027] As shown in FIGS. 2, 3 and 5-7 the roller hydraulic valve lifter 10 includes a bearing 20 disposed partially in the interior area 12A. Thus, a portion of the bearing 20 extends axially out of the interior area 12A of the roller hydraulic valve lifter 10 by a distance P1, as shown in FIG. 5. The bearing 20 includes an outer ring 22 that has a substantially cylindrical exterior bearing surface 22E and a substantially cylindrical inner bearing 22F surface that defines a second bore 23. The exterior bearing surface 22E defines an outside diameter D2 and the inner bearing surface 22F defines an inside diameter D3, as shown in FIG. 5. The outer ring 22 has an axial length L2 (depicted in FIG. 7).

[0028] As shown in FIG. 5, the hydraulic piston 4 engages a pushrod seat 3K of a pushrod 3 that extends into the interior area 12A. The hydraulic piston 4 is a damper that absorbs shock and takes up clearance between all of the components of the valve train to reduce clatter and other noise. An inner biasing member 5 holds valve 6 in place against one end of the piston 4. The inner biasing member 5 and valve 6 sit within damper cup 8, which is held against the piston 4 by outer biasing member 7. In other embodiments, the valve 6 is a ball valve or a check valve with a different structure.

[0029] As shown in FIGS. 2 and 4-7, a shaft 30 extends through the first bore 15 and the second bore 23. The shaft 30 extends through the first bore 15 a length L1 and between the first flat surface 13A and the second flat surface 13B. The shaft 30 is substantially cylindrical and has an outside diameter D1.

[0030] As shown in FIGS. 3, 4, 5 and 7, a plurality of needle rollers 40 are disposed between and rollingly engage an exterior surface 30E of the shaft 30 and the cylindrical inner bearing surface 22F. Each of the plurality of needle rollers 40 is substantially cylindrical and has an axial length L3. Prior to installation of the bearing 20 in the roller hydraulic valve lifter 10, the plurality of needle rollers 40 are temporarily held in position by a plug 29 (e.g., a plastic plug), as shown in FIG. 3. During installation of the bearing 20 in the roller hydraulic valve lifter 10, the shaft 30 is pressed through the bore 15 to displace the plug 29 and hold the plurality of needle rollers 40 in position around the shaft 30. The shaft 30 pushes the plug 29 out of the bore 15. The plurality of needle rollers 40 rollingly engage a portion of the shaft 30 along a length of the shaft about equal to the length L3 of the needle rollers, between the first flat surface 13A and the second flat surface 13B. The plurality of needle rollers 40 are retained axially by and maintain an axial position between the first flat surface 13A and the second flat surface 13B

[0031] The shaft 30 and the plurality of needle rollers 40 are manufactured from an AISI 52100 alloy steel that is carbo-nitrided such that the shaft 30 and the plurality of needle rollers 40 each have a surface hardness of a minimum of HRc 65. In one embodiment, the shaft 30 has a surface hardness of HRc 65 to HRc 69. In one embodiment, the plurality of rollers 40 each has a surface hardness of HRc 65 to HRc 69. The shaft 30 and the plurality of needle rollers 40 each have a minimum carbo-nitrided case depth of 0.25 mm. In one embodiment, the shaft 30 and the plurality of needle rollers 40 each have a case depth of 0.25 mm to 0.50 mm.

[0032] The shaft 30 and each of the plurality of needle rollers 40 each have an exterior surface that is in compression (e.g., has a residual compressive stress). In one embodiment, the exterior surface is treated by a mass finishing process (e.g., barrel finishing, vibratory finishing, tumbling, or the like to help obtain the compression of the exterior surface. In one embodiment, the shaft 30 and each of the plurality of needle rollers 40 each have a core hardness of HRc 59 to HRc 65.

[0033] AISI 52100 is also referred to as GCr15, SUJ2 and 100Cr6 which are the Chinese, Japanese and German versions, respectively and has the following chemical composition, wherein the percentages are given in weight percent.

TABLE-US-00001 Chemical Compoisition % C Mn P S Si Ni Cr Cu Mo Steel 0.93- 0.500 0.030 0.025 0.15- 0.300 1.30- 0.300 0.100 1.10 0.35 1.65 Max Max Max Max Max Max

[0034] The shaft 30 and each of the plurality of needle rollers 40 each have an exterior surface that is in compression, for example, a compressed surface treatment created by a mass finishing process. The shaft 30 and each of the plurality of needle rollers 40 each have a microstructure that has less than 12 percent by volume retained austenite for improved dimensional stability, higher hardness (i.e., greater than HRc 65) and improved wear resistance.

[0035] There is also disclosed herein a method of increasing the life of a prior art roller hydraulic valve lifter 105, as illustrated in FIG. 1. The method includes providing a first roller hydraulic valve lifter 105 that includes the body having a predetermined set of dimensions (e.g., outside diameter of the body, clearances between the exterior surface of the bearing 109 and the interior area of the body; clearances between the axial ends of the needle rollers and interior area of the body; and clearances between the axial ends of the bearing 109 and the interior area of the body). The method also includes providing a first shaft 111 mounted in the body. The first shaft 111 has a first outside diameter D1, dimensionally similar to that shown in FIG. 4 for the second shaft 30. The roller hydraulic valve lifter 105 includes a first bearing 109 that has an outer ring which has a second outside diameter D2, a first inside diameter D3 and an axial length L2, dimensionally similar to that shown in FIGS. 5 and 7 for the second bearing 20. The roller hydraulic valve lifter 105 includes a plurality of first needle rollers each having a third outside diameter D4 and an axial length L3, dimensionally similar to that shown in FIG. 7 for the plurality of second needle rollers 40. The plurality of first needle rollers is disposed between and in rolling engagement with the first shaft 111 and the outer ring of the first bearing 109. The first shaft 111 and the plurality of first needle rollers are manufactured from an AISI 52100 alloy steel and have a surface hardness of less than HRc 65.

[0036] The method includes creating a second roller hydraulic valve lifter 10 (e.g., by retrofitting the first roller hydraulic valve lifter 105) that has a life of at least 1.5 times that of the first roller hydraulic valve lifter 105. The second roller hydraulic valve lifter 10 is created by substituting the first shaft 111 and the plurality of first needle rollers in the first roller hydraulic valve lifter 105, with a second shaft 30 and a plurality of second needle rollers 40. The second shaft 30 has essentially the same dimension as the first shaft 111 of the first roller hydraulic valve lifter 105. For example, the first and second shafts 111 and 30 both have first outside diameters D1 of the same magnitude. The plurality of second needle rollers 40 each has essentially the same dimensions as the plurality of needle rollers of the first roller hydraulic valve lifter 105. For example, each of the plurality of second needle rollers 40 has a third outside diameter D4 and an axial length L3 of a same magnitude as the plurality of first needle rollers of the first roller hydraulic valve lifter 105. The method includes utilizing the body 12 having the predetermined set of dimensions essentially the same as the body of the first roller hydraulic valve lifter 105. The method also includes utilizing the outer ring 22 having a second outside diameter D2, a first inside diameter D3 and an axial length L2 of essentially the same magnitude compared to the respective dimensions of the outer ring of the bearing 109 of the first roller hydraulic valve lifter 105. The plurality of second needle rollers 40 is disposed between and in rolling engagement with the second shaft 30 and the outer ring 22. The second shaft 30 and the plurality of the second needle rollers 40 are manufactured from an AISI 52100 alloy steel that is carbo-nitrided. The second shaft 30 and plurality of second needle rollers 40 have a surface hardness of a minimum of HRc 65.

[0037] In one embodiment, the second shaft 30 and the plurality of second needle rollers 40 each have a minimum carbo-nitrided case depth of 0.25 mm. In one embodiment, the second shaft 30 and the plurality of second needle rollers 40 each have an exterior surface that is in compression. In one embodiment, the exterior surface is treated by a mass finishing process to help enhance the surface compression. In one embodiment, the second shaft 30 and the plurality of second needle rollers 40 each have a core hardness of HRc 59 to HRc 65.

[0038] There is also disclosed herein a method for manufacturing (e.g., heat treating 70, per FIG. 8) the shaft 30 and rollers 40 for a roller hydraulic valve lifter 10 of the present invention. The method includes the following steps in the order presented. An AISI 52100 alloy steel is provided. Step 1carbonitriding the AISI 52100 alloy steel; Step 2oil quenching the AISI 52100 alloy steel; Step 3tempering the AISI 52100 alloy steel at 149 C.; and Step 4cooling the AISI 52100 alloy steel to -84 C. In one embodiment, the method includes Step 5another tempering step that is performed at 177 C. after the cooling.

[0039] Carbo-nitriding, as used herein refers to heating the parts (e.g., the shaft 30 and the plurality of needle rollers 40) to an austenitizing temperature in a nitrogen rich atmosphere. For example, the gas concentrations in the furnace atmosphere are 0.85%+/0.05% carbon and 3.00% ammonia+/0.15 m.sup.3 per hour ammonia flow rate. As shown in FIG. 8, a heat treatment process (i.e., for an AISI 52100 alloy steel) of the present invention is generally designated by the numeral 70. The heat treatment process 70 includes carbo-nitriding (Step 1) the shaft 30 and the plurality of needle rollers 40 that are manufactured from AISI alloy steel by heating in a furnace at 1525 F.+/25 F. (829 C.) in an atmosphere are 0.85%+/0.05% carbon and 3.00% ammonia+/0.15 m.sup.3 per hour ammonia flow rate. After Step 1, the shaft 30 and the plurality of needle rollers 40 are oil quenched (Step 2) to ambient temperature. After Step 2, the shaft 30 and the plurality of needle rollers 40 are tempered (Step 3) for example, snap tempered at 300 F.+/10 F. (149 C.). After Step 3, the shaft 30 and the plurality of needle rollers 40 are cooled (Step 4) to 120 F.+/10 F. (84 C.). The temperature for step 4 is chosen to balance the cost against the reduction in retained austenite. In one embodiment, after Step 4, the shaft 30 and the plurality of needle rollers 40 are tempered (Step 5) at 350 F.+/15 F. (177 C.). As shown in FIG. 8, the shaft 30 and the plurality of needle rollers 40 are not heated or tempered between Step 1 and Step 2. As shown in FIG. 8, the heat treatment process 70 includes only one quenching step, namely Step 2. The term quenching, as used herein means, the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. Quenching prevents undesired low-temperature processes, such as phase transformations, from occurring. The snap temper referred to in Step 3 is used to stress relieve the part prior to sub-zero cooling. During quenching or rapid cooling, stresses are induced in the steal. Cooling to 120 F. directly after quenching adds more stress and can potentially lead to cracking. The snap temper step relieves some of the internal stresses from quenching, reducing the chance of cracking during sub-zero cooling. The heat treatment process 70 results in the shaft 30 and each of the plurality of needle rollers 40 each having a microstructure that has less than 12 percent by volume retained austenite for improved dimensional stability, higher hardness (i.e., greater than HRc 65) and improved wear resistance. The part is less dimensionally stable with more retained. Austenite can change to martensite under stress and temperature changes. Martensite occupies more volume than austenite so the part can grow in volume. Typically, not all the austenite changes to martensite so the actual growth is difficult to predict; however, it does not take much change in volume to reduce the clearance in the bearings if both the shaft and needles are heat treated with this process. Additionally, excessive retained austenite can reduce the surface hardness. Austenite is a softer constituent than martensite or carbides and nitrides that are present. The process is designed to obtain the hardest surface to reduce wear and increase bearing life without being prohibitively expensive.

Example 1

[0040] Over ten load tests of the roller hydraulic valve lifter bearings 20 of the present invention with the shaft 30 and the plurality of needle rollers 40 manufactured from an AISI 52100 alloy steel that is carbo-nitrided; and the shaft and the plurality of rollers each having a surface hardness of a minimum of HRc 65, with high loads and speeds. On average, the roller hydraulic valve lifter bearings 20 did not fail until over 4.8 million revolutions. Whereas, on average, for tests with the same high loads and speeds, the prior art roller hydraulic valve lifter bearings of the prior art roller hydraulic valve lifters 105 with the first shaft and the plurality of first needle rollers manufactured from an AISI 52100 alloy steel having a surface hardness of less than HRc 65 failed at 2.9 million revolutions. Thus, the roller hydraulic valve lifter bearings 20 of the present invention had an increased life of 1.68 times greater than the life of the prior art roller hydraulic valve lifter bearings.

[0041] Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended claims.