BACKGROUND

[0001] The invention pertains to the field of hydraulic tensioners. More particularly, the invention pertains to hydraulic tensioners venting through radial holes in a high pressure bore.

[0002] In tensioners which are mounted in a nose (piston) down orientation, when the engine is not operating, oil can drain out of the tensioner. When the engine is started oil will be supplied to the tensioner, but the air can be trapped in the tensioner, posing problems in operation. Preferably, the air can be purged within a few seconds of startup, but some systems rattle for several minutes after a dry start until the air is purged from the tensioner.

[0003] Figures 1-4 show a first prior art hydraulic tensioner. The hydraulic tensioner 1 has a body 10 which is mounted via bolts received in bolt holes 12 to an engine in a piston nose down position. The cylindrical bore 11 having a first open end 11a and a second end 1 lb in fluid connection with a supply inlet 16.

[0004] The cylindrical bore 11 slidable receives a hollow piston 14. The hollow piston 14 has a first nose end 14a and a second end 14b separated by a length 14c. Along the length 14c of the hollow piston near the first nose end 14a is a circlip groove 14d which receives a shipping pin (not shown) which is used to maintain the tensioner in position during shipping. The hollow piston 14 has an inner circumference 14e. The first nose end 14a also includes a nose vent passage 14f. A clearance between the piston 14 and the walls of the cylindrical bore 11 is typically within a range of about 0.015 mm to 0.075 mm, and most would be in the range of 0.025 mm to 0.065 mm range. A “loose” fit between the piston 14 and the cylindrical bore 11 is approximately 0.065 mm of diametrical clearance.

[0005] A hydraulic pressure chamber 36 is defined by the inner circumference 14e of the hollow piston 14, the cylindrical bore 11, and a check valve assembly 18. Hydraulic fluid in the hydraulic pressure chamber 36 and compression spring 17 bias the piston 14 away from the body 10 of the tensioner 1. [0006] Within the inner circumference 14e of the hollow piston 14 near the first nose end 14a is, a volume reducer 24 to aid in venting and purging air from within the inner circumference 14e of the hollow piston 14 and the hydraulic pressure chamber 36.

[0007] Referring to Figure 4, the volume reducer 24 has a first end 24a with a cap 60, a second end 24b and an extended body 24c. The cap 60 has a top surface 62, a bottom surface 61, opposite the top surface 62, and an outer circumference 63. The top surface 62 has a restrictive circular groove 26 with a first end 26a and a second end 26b in communication with a flat 27 along the outer circumference 63 of the cap 61. The flat 27 extends across the entire width of the outer circumference 63. The width of the outer circumference 63 includes a diameter portion 29 adjacent the bottom surface 61 and a reduced diameter portion 28 adjacent the top surface 62 in communication with the flat 27 and the second end 26b of the restrictive circular groove 26. Air or oil flow path from the high pressure chamber 36 to the nose vent line 14f is as follows. Fluid and/or air flows from the high pressure chamber 36 through flat 27. From flat 27, fluid and/or air enters the restrictive circular groove 26 and then flows to the central opening 25. From the central opening 25, fluid flows to the nose vent line 14f and atmosphere. When the volume reducer 24 is installed within the inner circumference 14e, the central opening 25 is aligned with the nose vent line 14f. Restrictive circular groove 26 sets the oil flow rate out of the tensioner to achieve the desired level of damping.

[0008] The check valve assembly 18 is located at the second end 1 lb of the cylindrical bore 11 between the inlet 16 and the hydraulic pressure chamber 36. Although any check valve assembly 18 known in the art could be used, the check valve assembly 18 in the figures includes a retainer 35, a spring 22, a ball 19, a check valve seat 21, and a seal 23 and operates to allow fluid to flow from the supply inlet 16 into the hydraulic pressure chamber 36 and prevents fluid from the hydraulic pressure chamber 36 from exiting through the supply inlet 16.

[0009] Oil pressure from the supply inlet 16 acts to push the hollow piston 14 outward to tension a chain or belt (not shown), and pulses in the chain or belt which might momentarily force the hollow piston 14 inward are resisted by the inability of the relatively incompressible oil to flow backward through the check valve assembly 18. If air is trapped in the cylindrical bore 11 behind the hollow piston 14, then the compressibility of the air will allow the hollow piston 14 to move or “chatter” in the cylindrical bore 11. One possible leak path that allows the oil to eventually drain to the lowest point in the bore opening 11a is the flow between the piston 14 to cylindrical bore 11 clearance.

[0010] Line 66 in Figure 2 represents the oil level in the hydraulic tensioner 1 after rest. Oil leaks down through the restrictive circular groove 26 and through nose passage 14f. Nose passage 14f defines the lowest point for draining to atmosphere. With the venting of the high pressure chamber 36 to atmosphere through the nose passage 14f of the piston 14, there is significant oil draining.

[0011] Line 65 in Figure 3 represents the oil level after rest if the tensioner 1 were to be mounted piston up. Again, oil leaks down to the lowest opening in the piston to bore clearance, assuming that the supply inlet reservoir is well sealed.

[0012] Figures 5-8 show an alternate conventional hydraulic tensioner 70. Hydraulic tensioner 70, in comparison to hydraulic tensioner 1 does not contain a nose vent 14f and instead has an optional air line 50 from reservoir 52 to atmosphere for venting.

[0013] The hydraulic tensioner 70 has a body 10 which is mounted via bolts received in bolt holes 12 to an engine in a piston nose down position. The cylindrical bore 11 having a first open end 11a and a second end lib in fluid connection with a supply inlet 16.

[0014] The cylindrical bore 11 slidable receives a hollow piston 14. The hollow piston 14 has a first nose end 14a and a second end 14b separated by a length 14c. Along the length 14c of the hollow piston at the first nose end 14a is a circlip groove 14d which receives a shipping pin (not shown) used for maintaining tensioner piston during shipping. The hollow piston 14 has an inner circumference 14e.

[0015] A hydraulic pressure chamber 36 is defined by the inner circumference 14e of the hollow piston 14, the cylindrical bore 11, and a vent disk 40. The vent disk 40 controls oil flow out during compression to tune damping. As most reservoirs 52 do not have a reservoir vent 50, there is no way for the air to escape the tensioner through passage 46b. Air is instead shuttled back and forth between the hydraulic pressure chamber 36 and the reservoir 52. With the only way for the air to escape being through the piston to bore clearance, the time associated with the air purge is long. Hydraulic fluid in the hydraulic pressure chamber 36 and compression spring 17 bias the piston 14 away from the body 10 of the tensioner 1.

[0016] Within the inner circumference 14e of the hollow piston 14 near the first nose end 14a is a volume reducer 24 to reduce compressibility of the tensioner by reducing the total volume of fluid contained in the hydraulic pressure chamber 36. The volume reducer 24 can be the same volume reducer as shown in Figure 4 and described above.

[0017] The vent disk 40 is located at the second end 1 lb of the cylindrical bore 11 between the inlet 16 and the hydraulic pressure chamber 36. Referring to Figure 8, the vent check 40 has a top surface 40a, a bottom surface 40b defined by projecting legs 40d and a cavity 40c (see Figure 6). A central opening 45 passes from the top surface 40a through to the bottom surface 40b. Along the top surface 40a is a restrictive circular groove 46 with a first end 46a in communication with a central opening 45 and a second end 46b in communication with a flat 47 along the outer circumference 49 of the vent disk 40. The flat 47 extends across the entire width of the outer circumference 49.

[0018] Oil flows in through the supply inlet 16 and central opening 45 of vent disk 40. From central opening 45, oil flows through check valve assembly 18. From the check valve assembly 18, fluid flows into hydraulic pressure chamber 36. When the chain or belt forces the piston 14 in towards the second end lib of the cylindrical bore 11, the check valve assembly 18 closes to prevent oil from flowing back towards the inlet supply 16 via central opening 45. Instead, oil flows from the hydraulic pressure chamber 36 through flat 47 and the restrictive circular groove 46 of vent disk 40 to the supply inlet 16. The restrictive circular groove 46 restricts the flow rate to achieve the desired amount of damping. Air that gets pushed out through the restrictive circular groove moves into the reservoir 52 through the supply inlet 16. The air is pulled back into the tensioner again unless the air escapes the tensioner through the reservoir vent 50 which is optionally present. Line 71 in Figure 6 represents the oil level in the hydraulic tensioner 70 after rest.

[0019] The conventional options for venting tensioners, for example through a vent passage in the piston tip as shown in Figures 1-4, through a passage in the base of the tensioner that communicates back to the oil source as shown in Figures 5-8, or simply allowing oil to leak through the piston to bore clearance are not optimal, as none of these options work well for purging air from some tensioners with a nose down orientation. SUMMARY

[0020] According to one embodiment of the present invention, a hydraulic tensioner used for chain or belt drives is vented to atmosphere through a radial hole in the high-pressure chamber. The venting hole may be one hole or a plurality of holes to achieve the desired flow characteristics. The hole may be created by any process, but laser drilling is the envisioned process for creating the small diameter holes that are likely to be needed. The preferred location for the venting hole is at the highest achievable point in the high- pressure chamber when the tensioner is in the position it will be installed in the application. The preferred mounting condition is the highest location in the bore where the hole will not be covered by the piston during normal operation.

[0021] Embodiments of the present invention vent the high pressure chamber directly to atmosphere with a resting drain level that requires less draining than prior art solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 shows a top down view of a conventional hydraulic tensioner.

[0023] Fig. 2 shows a sectional view along line 2-2 of Figure 1.

[0024] Fig. 3 shows an alternate sectional view of Figure 1 mounted in a nose up orientation.

[0025] Fig. 4 shows an isometric view of a volume reducer.

[0026] Fig. 5 shows a top down view of another conventional hydraulic tensioner. [0027] Fig. 6 shows a sectional view along line 6-6 of Figure 2.

[0028] Fig. 7 shows an alternate sectional view of Figure 5.

[0029] Fig. 8 shows an isometric of a check vent.

[0030] Fig. 9 shows a top down view of a hydraulic tensioner of a first embodiment. [0031] Fig. 10 shows a sectional view along line 10-10 of Figure 9.

[0032] Fig. 11 shows a sectional view along line 11-11 of Figure 10. [0033] Fig. 12 shows a top down view of a hydraulic tensioner of a second embodiment.

[0034] Fig. 13 shows a sectional view along line 13-13 of Figure 12.

[0035] Fig. 14 shows a sectional view along line 14-14 of Figure 13.

[0036] Fig. 15 shows a top down view of a hydraulic tensioner of a third embodiment.

[0037] Fig. 16 shows a sectional view along line 16-16 of Figure 15.

[0038] Fig. 17 shows a sectional view along line 17-17 of Figure 16.

[0039] Fig. 18a shows a graph of the engine crankshaft speed versus time with a dry tensioner of an embodiment of the present invention during a 20 second interval.

[0040] Fig. 18b shows a graph of the engine crankshaft speed versus time with a dry tensioner of an embodiment of the present invention for 150 seconds.

[0041] Fig. 19a shows a graph of the engine crankshaft speed versus time with a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention during a twenty second interval.

[0042] Fig. 19b shows a graph of the engine crankshaft speed versus time with a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention for 150 seconds.

[0043] Fig. 20a shows a graph of the engine crankshaft speed versus running time for a prior art tensioner with a check valve vent or check vent for a twenty second increment.

[0044] Fig. 20b shows a graph of the engine crankshaft speed versus running time for a prior art tensioner with a check valve vent or check vent for 600 seconds.

[0045] Fig. 21a shows a graph of the engine crankshaft speed versus running time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for a twenty second increment.

[0046] Fig. 21b shows a graph of the engine crankshaft speed versus running time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for 600 seconds. [0047] Fig. 22a shows a graph of engine oil pressure versus time for a dry tensioner of an embodiment of the present invention for a twenty second interval.

[0048] Fig. 22b shows a graph of engine oil pressure versus time for a dry tensioner of an embodiment of the present invention for 160 seconds. [0049] Fig. 23a shows a graph of engine oil pressure versus time for a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention for a twenty second interval.

[0050] Fig. 23b shows a graph of engine oil pressure versus time for a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention for 160 seconds.

[0051] Fig. 24a shows a graph of engine oil pressure versus time for a prior art tensioner which a check valve vent or check vent for a twenty second increment.

[0052] Fig. 24b shows a graph of engine oil pressure versus time for a prior art tensioner which a check valve vent or check vent for 600 seconds. [0053] Fig. 25a shows a graph of engine oil pressure versus time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for a twenty second increment.

[0054] Fig. 25b shows a graph of engine oil pressure versus time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for 600 seconds.

[0055] Fig. 26a shows a graph of tensioner piston motion during engine start versus time for a dry tensioner of an embodiment of the present invention for a twenty second interval.

[0056] Fig. 26b shows a graph of tensioner piston motion during engine start versus time for a dry tensioner of an embodiment of the present invention for 150 seconds. [0057] Fig. 27a shows a graph of tensioner piston motion during engine start versus time for a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention for a twenty second interval.

[0058] Fig. 27b shows a graph of tensioner piston motion during engine start versus time for a wet tensioner in which the engine has sat in rest state for ten days after running long enough to purge air of an embodiment of the present invention for 150 seconds.

[0059] Fig. 28a shows a graph of tensioner piston motion during engine start versus time for a prior art tensioner with a check valve vent or check vent for a twenty second increment.

[0060] Fig. 28b shows a graph of tensioner piston motion during engine start versus time for a prior art tensioner with a check valve vent or check vent for 600 seconds.

[0061] Fig. 29a shows a graph of tensioner piston motion during engine start versus time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for a twenty second increment.

[0062] Fig. 29b shows a graph of tensioner piston motion during engine start versus time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for 600 seconds.

DETAILED DESCRIPTION

[0063] Figures 9-11 show a hydraulic tensioner of a first embodiment. The hydraulic tensioner 100 has a body 110 which is mounted via bolts received in bolt holes 112 to an engine in a piston nose down position. The cylindrical bore 111 having a first open end 111a and a second end 11 lb in fluid connection with a supply inlet 116.

[0064] The cylindrical bore 111 slidable receives a hollow piston 114. The hollow piston 114 has a first nose end 114a and a second end 114b separated by a length 114c. Along the length 114c of the hollow piston 114 near the first nose end 114a is a circlip groove 114d which receives a shipping pin (not shown) and is used to maintain the tensioner in position during shipping. The hollow piston 114 has an inner circumference 114e.

[0065] A hydraulic pressure chamber 136 is defined by the inner circumference 114e of the hollow piston 114, the cylindrical bore 111, and a check valve assembly 18. Hydraulic fluid in the hydraulic pressure chamber 136 and compression spring 117 bias the hollow piston 114 away from the body 110 of the tensioner 100.

[0066] Within the inner circumference 114e of the hollow piston 114 near the first nose end 114a is a volume reducer 24 to decrease compressibility by lowering the fluid volume present in hydraulic pressure chamber 136. The volume reducer 24 can be conventional, as described and shown in Figure 4.

[0067] The check valve assembly 18 is located at the second end 11 lb of the cylindrical bore 111 between the supply inlet 116 and the hydraulic pressure chamber 136. Although any check valve assembly 18 known in the art could be used, the check valve assembly 18 in the figures includes a retainer 35, a spring 22, a ball 19, a check valve seat 21, and a seal 23 and operates to allow fluid to flow from the supply inlet 116 into the hydraulic pressure chamber 136 and prevents fluid from the hydraulic pressure chamber 136 from exiting through the supply inlet 116.

[0068] A single radial vent line 150 with a single radial hole 152 is present within the body 110 and in communication with a body hole 153. Body hole 153 is in communication with atmosphere. The single radial hole 152 and vent line 150 may be created by any manufacturing process. In one embodiment, the single radial hole 150 is created by laser drilling. The single radial hole 152 and vent line 150 are placed in communication with the high pressure chamber 136 of the cylindrical bore 111. The single radial hole 152 is preferably placed at the highest achievable point in the cylindrical bore 111 when the hydraulic tensioner 100 is in the position it is installed in the engine which allows the most air to be purged before the oil level covers the vent hole. The single radial hole 152 is any orientation orthogonal to centerline C-C and is therefore placed perpendicular relative to the cylindrical bore 111. A center of the radial hole 152 is preferably aligned with any radius drawn from the center to the outer diameter of the cylindrical bore 111. The radial hole 152 and the associated body hole 153 pass through the body 110, such that the single radial vent line 150 intersects with cylindrical bore 111 at a high point in the high pressure chamber 136 and is not covered by the piston 114 during normal use.

[0069] In this embodiment, the diameter of the single radial hole 152 is preferably between 0.08 mm to 1.35 mm yielding flow rates of approximately 0.5 cc/sec to 100 cc/sec respectively. A preferred hole size for most systems is between 0.08 mm and 0.7mm yielding 0.5 cc/sec to 28 cc/sec respectively. Any stated flow rates are approximate with a pressure drop of 700 psi and a fluid viscosity of 18.4cST (centi-Stoke) which is equivalent to approximately 5W30 at 76.6°C (170°F).

[0070] The single radial hole 152 and radial vent line 150 provides a path for air to escape the hydraulic tensioner 100 during startup and after oil has leaked out the pressure chamber 136 during a period of rest. Additionally, the single radial hole 152 provides a path for oil to exit the hydraulic tensioner 100, providing damping during use. The diameter and associated flow area of the single radial hole 152 can be altered to match the required dampening for any application in which the hydraulic tensioner 100 is used. The single radial hole 152 can be the only tuning device used to define the oil flow out of the high pressure bore 136, or used in conjunction with other flow devices at traditional locations in the tensioner, such as piston vents as shown in prior art Figures 2-4, check valve venting as shown in Figures 6-8, and increased clearance present between the piston and the cylindrical bore.

[0071] Oil pressure from the supply inlet 116 acts to push the hollow piston 114 outward to tension a chain or belt (not shown), and pulses in the chain or belt which might momentarily force the hollow piston 114 inward are resisted by the inability of the relatively incompressible oil to flow backward through the check valve assembly 18.

[0072] Line 109 in Figure 10 represents the oil level in the hydraulic tensioner 100 after rest. Oil leaks down to the lowest opening the in the cylindrical bore 11.

[0073] Figures 12-14 show a hydraulic tensioner of a second embodiment. The cylindrical bore 111 slidable receives a hollow piston 114. The hollow piston 114 has a first nose end 114a and a second end 114b separated by a length 114c. Along the length 114c of the hollow piston 114 near the first nose end 114a is a circlip groove 114d which receives a shipping pin (not shown) which is used to maintain the tensioner in position during shipping. The hollow piston 114 has an inner circumference 114e.

[0074] A hydraulic pressure chamber 136 is defined by the inner circumference 114e of the hollow piston 114, the cylindrical bore 111, and a check valve assembly 18. Hydraulic fluid in the hydraulic pressure chamber 136 and compression spring 117 bias the hollow piston 114 away from the body 110 of the tensioner 200.

[0075] Within the inner circumference 114e of the hollow piston 114 near the first nose end 114a is a volume reducer 24 to decrease compressibility by decreasing the fluid volume in the hydraulic pressure chamber 136. The volume reducer 24 can be conventional, as described and shown in Figure 4.

[0076] The check valve assembly 18 is located at the second end 11 lb of the cylindrical bore 111 between the supply inlet 116 and the hydraulic pressure chamber 136. Although any check valve assembly 18 known in the art could be used, the check valve assembly 18 in the figures includes a retainer 35, a spring 22, a ball 19, a check valve seat 21, and a seal 23 and operates to allow fluid to flow from the supply inlet 116 into the hydraulic pressure chamber 136 and prevents fluid from the hydraulic pressure chamber 136 from exiting through the supply inlet 116.

[0077] A plurality of radial vent lines 162, 164, 166, 168 each with a single radial hole

163, 165, 167, 169 is present within the body and in communication with a body hole 160. The plurality of radial vent lines 162, 164, 166, 168, associated radial holes 163, 165, 167, 169 and vent line 160 may be created by any manufacturing process. In one embodiment, the plurality of radial holes 163, 165, 167, 169 are created by laser drilling. Each of the plurality of radial vent lines 162, 164, 166, 168 are in fluid communication with the high pressure chamber 136 of the cylindrical bore 111. The plurality of radial vent lines 162,

164, 166, 168 and associated radial holes 163, 165, 167, 169 are preferably placed at the highest achievable point in the cylindrical bore 111 when the hydraulic tensioner 100 is in the position it is installed in the engine which allows the most air to be purged before the oil level covers the vent hole and is therefore placed radially relative to the cylindrical bore 111 and a centerline of the cylindrical bore 111 and the piston 114. The plurality of radial vent lines 162, 164, 166, 168, associated radial holes 163, 165, 167, 169, and radial vent line 160 provides multiple paths for air to escape the hydraulic tensioner 200 during startup and after oil has leaked out the pressure chamber 136 during a period of rest.

[0078] In this embodiment, the plurality of radial holes are 0.08 mm to 0.66 mm in diameter yielding a combined flow rate of approximately 2 cc/sec to 100 cc/sec. Any stated flow rates are approximate with a pressure drop of 700 psi and a fluid viscosity of 18.4cST (centi-Stoke) which is equivalent to approximately 5W30 at 76.6°C (170°F).

[0079] Additionally, the plurality of radial holes 163, 165, 167, 169 provide a path for oil to exit the hydraulic tensioner 200, providing damping during use. The diameter and associated flow area of each of the plurality of radial holes 163, 165, 167, 169 can be altered to match the required dampening for any application in which the hydraulic tensioner 200 is used. The diameter of the plurality of radial holes 163, 165, 167, 169 can be the same or different. The plurality of radial holes 163, 165, 167, 169 can be the only tuning device used to define the oil flow out of the high pressure bore 136, or used in conjunction with other flow devices at traditional locations in the tensioner, such as piston vents as shown in prior art Figures 2-4, valve venting as shown in Figures 6-8, and increased clearance present between the piston and the cylindrical bore.

[0080] Oil pressure from the supply inlet 116 and the force from spring 117 acts to push the hollow piston 114 outward to tension a chain or belt (not shown), and pulses in the chain or belt which might momentarily force the hollow piston 114 inward are resisted by the inability of the relatively incompressible oil to flow backward through the check valve assembly 18.

[0081] Line 109 in Figure 13 represents the oil level in the hydraulic tensioner 200 after rest. Oil leaks down to the lowest opening the in the cylindrical bore 11.

[0082] In one embodiment, the plurality of radial holes 163, 165, 167, 169 are placed at an arbitrary orientation relative to centerline C-C. A center of the each of the plurality of radial holes 163, 165, 167, 169 is preferably perpendicular to a radius drawn from the centerline C-C

[0083] Figures 15-17 show a hydraulic tensioner of a third embodiment. The difference between the hydraulic tensioner 100 in Figures 9-11 and the hydraulic tensioner 300 of this embodiment is the placement of the single vent hole and single vent line relative to the cylindrical bore. While hydraulic tensioner 100 had the single vent line 150 and single vent hole 152 being perpendicular to the cylindrical bore 111, the single vent line 170 and the single vent hole 172 in tensioner 300 are placed at the highest achievable point in the cylindrical bore 111 when the hydraulic tensioner 100 is in the position it is installed in the engine which allows the most air to be purged before the oil level covers the vent hole.

The single radial hole 172 is placed at an arbitrary orientation relative to centerline C-C. A center of the radial hole 172 is preferably perpendicular to a radius drawn from the centerline C-C.

[0084] As in the first embodiment, the single radial hole 172 and radial vent line 170 provides a path for air to escape the hydraulic tensioner 300 during startup and after oil has leaked out the pressure chamber 136 during a period of rest. Additionally, the single radial hole 172 provides a path for oil to exit the hydraulic tensioner 300, providing damping during use. The diameter and associated flow area of the single radial hole 172 can be altered to match the required dampening for any application in which the hydraulic tensioner 300 is used. In one embodiment, the single radial hole has a diameter of 0.08 mm to 1.35 mm yielding flow rates of approximately 0.5 cc/sec to 100 cc/sec. Any stated flow rates are approximate with a pressure drop of 700 psi and a fluid viscosity of 18.4cST (centi-Stoke) which is equivalent to approximately 5W30 at 76.6°C (170°F).

[0085] The single radial hole 172 can be the only tuning device used to define the oil flow out of the high pressure bore 136, or used in conjunction with other flow devices at traditional locations in the tensioner, such as piston vents as shown in prior art Figures 2-4, check valve venting as shown in Figures 6-8, and increased clearance present between the piston and the cylindrical bore.

[0086] Therefore, by placing one or more air vent holes at the highest point in the cylindrical bore allows the most air to be purge before the oil level covers the one or more vent holes. Additionally, placing the one or more vent holes at the highest point also prevents the one or more vent holes from becoming a drain path for oil to exit the tensioner when not in use. This purge feature would be most beneficial for tensioners that install at any angle from horizontal to the tensioner piston pointing down. The one or more vent holes also provide a path for oil to exit the tensioner to provide damping during use. The flow area of the one or more vent holes are chosen to match the required damping for any specific application. The one or more radial vent holes could be the singular tuning device used to define oil flow out of the high pressure bore, or it could be used in conjunction with other flow devices at traditional locations in the tensioner. [0087] In the drawings, while a hollow piston is shown, a solid piston may also be used with a spring and high pressure chamber between the end of the solid piston and cylindrical bore.

[0088] In regards to Figures 18a- 29b, a “dry tensioner” is defined as tensioner that does not currently have any oil present in the tensioner prior to running of the engine. A “wet tensioner” is defined as a tensioner which was run on the engine long enough to purge oil prior to the start of the test without disassembly that would allow oil to leak out. For the test conducted, a dry tensioner was assembled, the dry tensioner was run on an engine to purge oil, and then the engine was shut down and the tensioner was allowed to sit for 10 days to allow the oil to drain. For example, the oil preferably drained from the pressure chamber 136 to line 109 indicated in Figure 10. The engine was then started while recording data for the “wet tensioner”.

[0089] The tests of Figures 18a-29b were conducted on a double overhead cam (DOHC) V6 engine with the tensioner of the present invention tensioning a new chain at a temperature of approximately 20°C. The tensioners, both prior art and tensioner of embodiments of the present invention were all oriented in a nose-down orientation within the engine. The prior art tensioner was similar to the tensioner shown in Figure 6 without the optional reservoir vent, but including the restrictive path 46 that had an equivalent flow rate to a 0.1 mm hole. The tensioner of an embodiment of the present invention which was tested included a single 0.1mm diameter hole.

[0090] The “0” seconds indicated in the graphs represents a first crankshaft motion during engine start. Furthermore, the twenty second intervals shown are always captured within the longer time period shown in associated graphs.

[0091] Fig. 18a shows a graph of the engine crankshaft speed during engine start with a dry tensioner of an embodiment of the present invention concentrating on a 20 sec interval and Fig. 18b shows a graph of the engine crankshaft speed during engine start with a dry tensioner of an embodiment of the present invention for 150 seconds. It is noted that the 20 second interval of Fig. 18a is present within the 150 seconds of Fig. 18b.

[0092] As shown in Figs. 18a- 18b, 0 seconds represents a first crankshaft motion during start with the engine firing at approximately 2.5 seconds. [0093] Fig. 19a shows a graph of the engine crankshaft speed during engine start with a wet tensioner that has drained of hydraulic fluid for 10 days of an embodiment of the present invention during a 20 sec interval and Fig. 19b shows a graph of the engine crankshaft speed during engine start with a wet tensioner that has drained of hydraulic fluid for 10 days of an embodiment of the present invention for 150 seconds.

[0094] As shown in Figs. 19a-19b, 0 seconds represents a first crankshaft motion during start with the engine firing at approximately 3 seconds.

[0095] Therefore, figures 18 and 19 show the running conditions that existed for each test, providing a crankshaft speed profile. [0096] Figs. 20a and 20b show graphs of the engine crankshaft speed versus time for a prior art tensioner in a twenty second increment and a 600 second increment, respectively.

[0097] For the prior art tensioner of Figure 6 which has a check valve 18 with a vent 40, but not reservoir vent 50, the engine fires at about 2.5 seconds and the engine idles at about 4 seconds. The idling speed ranges betweenl400-2100 revolutions per minute (RPM). In Figure 20b, the spikes shown between 400 and 500 seconds are manual throttle opening events to try and help the prior art tensioner purge air. The gap between 500 and 600 seconds represents a gap in which the engine continues to idle while the recorder is not running.

[0098] Figs. 21a and 21b show graphs of the engine crankshaft speed versus time for a tensioner with a radial vent through the high pressure bore of an embodiment of the present invention for a twenty second increment and a 600 second increment, respectively.

[0099] The engine fired at about 2.5 seconds and reaches an idle speed at 4.5 seconds. The engine idles between 1250 to 1700 RPM before setting at 1200 RPM near the end of the recording. [00100] Figs. 22a and 22b shows graphs of engine oil pressure versus time for a dry tensioner of an embodiment of the present invention. The engine oil gallery pressure during the engine start rises at about 2.5 seconds from the first crankshaft motion of the engine start. The engine oil gallery pressure is controlled by the engine oil pump to be about 80 psi and then to 30 psi for the remainder of the recording. [00101] Figs. 23a and 23b show graphs of engine oil pressure versus time for a wet tensioner of an embodiment of the present invention. The engine oil gallery pressure during engine start rises at about 3 seconds from the first crankshaft motion of the engine start. The engine oil gallery pressure is controlled by the engine oil pump to be about 80 psi and then to 30 psi for the remainder of the recording.

[00102] Figs 24a and 24b show the engine oil pressure following an engine start for a prior art tensioner, for example the prior art tensioner of Figure 6. The engine oil gallery pressure during the engine start rises at about 3 seconds from the first crankshaft motion of the engine start. The engine oil gallery pressure is controlled by the engine oil pump to be about 80 psi and then to 30 psi for the remainder of the recording. The manual throttle events are shown in Fig. 24b to encourage the air purge from the tensioner. The manual throttle events are also shown in Fig. 20b.

[00103] Figs. 25a and 25b show the engine oil pressure following an engine start for a tensioner with a radial vent which the high pressure chamber of the bore of an embodiment of the present invention. The engine oil gallery pressure during the engine start rises at about 2.8 seconds from the first crankshaft motion of the engine start. The engine oil gallery pressure is controlled by the engine oil pump to be about 80 psi or slightly less and then to 30 psi for the remainder of the recording.

[00104] Figs. 26a and 26b show graphs of piston motion versus time from the first crankshaft motion of engine start for a dry tensioner of a tensioner of an embodiment of the present invention. In a dry tensioner, high piston motion of approximately 7.3 mm peak to peak is present during cranking and until oil pressure builds. Air is purged from the tensioner at approximately 6.8 seconds. The peak to peak motion of less than 1mm starts at 6.8 seconds, the same time as the tensioner finished purging air. The small step down in mean position and slight increase in peak to peak motion observed at 8 seconds is the active oil pump switching from 80 psi down to 30 psi (see Figures 22a and 23a).

[00105] Figs. 27a and 27b show graphs of piston motion versus time from the first crankshaft motion of engine start for a wet tensioner after being allowed to drain for ten days of a tensioner of an embodiment of the present invention. In the wet tensioner, high piston motion of approximately 5 mm peak to peak is present during cranking and until oil pressure builds. Air is purged from the tensioner at approximately 4 seconds. The peak to peak motion of less than 1 mm starts at 4 seconds, the same time as the tensioner finished purging air. The small step down in mean position and slight increase in peak to peak motion observed at 8.5 seconds is the active oil pump switching from 80 psi down to 30 psi (see Figures 22a and 23a).

[00106] The significantly shorter time for the wet tensioner to purge air shows that the tensioner was able to retain a significant amount of oil after resting for 10 days. The reduced time required to purge air was caused by less air volume needing to be purged during the wet start when compared to the dry start of the tensioner of an embodiment of the present invention.

[00107] Figs. 28a and 28b show graphs of the piston motion versus time from the first crankshaft motion of engine start for a prior art tensioner, for example the prior art tensioner of Figure 6. The high piston motion of the prior art tensioner is approximately 7.3 mm initially and then to 6 mm peak to peak during cranking and until oil pressure builds. Manual throttle motions were used to attempt to get the piston to purge air, but normal piston motion of less than 1 mm did not occur during the recording as some air was still present.

[00108] Fig. 29a and 29b show graphs of the piston motion versus time from the first crankshaft motion of engine start for a tensioner with a vent in the high pressure chamber of the bore of an embodiment of the present invention. The high piston motion of the tensioner is approximately 7.3 mm peak to peak during cranking and until oil pressure builds. Air is purged from the tensioner at approximately 6.3 seconds and normal piston motion of less than 1 mm occurs at 6.3 seconds from the first crankshaft motion during engine start.

[00109] From the testing discussed above, the prior art tensioner which includes a check vent does not purge air well in a nose-down orientation, resulting in a time delay from the first crankshaft motion during engine start before achieving normal piston motion. The tensioners of present invention, whether started as dry tensioner or a wet tensioner were able to reduce piston motion required at startup and purge air in a short period of time.

[00110] Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.