TIMING DRIVE TENSIONER ASSEMBLY WITH PRE-LOAD AND METHOD

Abstract

A tensioner assembly for an engine timing drive includes a tensioner with a tensioner body having a fastener opening and defining a cavity with a plunger opening. A plunger is disposed in the cavity and a removable pin restrains the plunger in the cavity. The plunger is configured to be biased out of the plunger opening when the pin is removed. A protuberance extends outward from the tensioner body and is adapted to receive an applied torque. The tensioner body is configured to pivot about a center axis of the fastener opening in response to a predetermined torque applied to the protuberance. A method of assembling an engine timing drive includes applying a predetermined torque to a protuberance of a tensioner that is pivotably mounted to a cylinder block to rotate the tensioner toward a rotatable device such that the tensioner applies a predetermined load to the rotatable device.

Claims

1. A tensioner assembly for an engine timing drive, the tensioner assembly comprising: a tensioner including: a tensioner body having a fastener opening and defining a cavity with a plunger opening; a plunger disposed in the cavity and a removable pin restraining the plunger in the cavity, wherein the plunger is configured to be biased out of the plunger opening when the pin is removed; and a protuberance extending outward from the tensioner body and adapted to receive an applied torque; wherein the tensioner body is configured to pivot about a center axis of the fastener opening when fixed at the fastener opening in response to a predetermined torque applied to the protuberance.

2. The tensioner assembly of claim 1, wherein the tensioner body includes a slot extending through the tensioner body with the protuberance between the fastener opening and the slot.

3. The tensioner assembly of claim 2, further comprising: a shoulder bolt extending through the fastener opening; and a locking bolt extending through the slot; wherein the locking bolt interferes with the tensioner body at an end of the slot to limit a range of motion of the tensioner body about the shoulder bolt in response to the predetermined torque applied to the protuberance.

4. The tensioner assembly of claim 2, wherein: a first flange extends in a first direction from the tensioner body; the fastener opening is in the first flange; a second flange extends in a second direction from the tensioner body opposite to the first direction; and the slot is in the second flange.

5. The tensioner assembly of claim 1, wherein a side surface of the protuberance is hexagonal.

6. The tensioner assembly of claim 1, wherein the protuberance extends from an outer side of the tensioner body; and wherein an inner side of the tensioner body opposite from the outer side is generally planar.

7. The tensioner assembly of claim 1 in combination with a tensioner arm having a convex surface; wherein a distal end of the plunger extending out of the cavity has a convex distal surface configured to be engaged with the convex surface of the tensioner arm when the tensioner body is pivoted about the center axis of the fastener opening toward the tensioner arm in response to the predetermined torque applied to the protuberance.

8. An engine assembly comprising: a cylinder block; a cylinder head supported on the cylinder block; a crankshaft rotatably mounted on the cylinder block; at least one camshaft mounted on the cylinder head; and a timing drive for controlling a relative angular orientation of the crankshaft and the at least one camshaft, the timing drive including: a rotatable device operatively engaged with the crankshaft and the camshafts; wherein the rotatable device is one of a chain or a belt; a tensioner arm pivotably secured to one of the cylinder block and the cylinder head and configured to direct the rotatable device; a tensioner assembly comprising: a tensioner body having a fastener opening and defining a cavity with a plunger opening; a plunger disposed in the cavity; a removable pin restraining the plunger in the cavity, wherein the plunger is configured to be biased out of the plunger opening when the pin is removed; and a protuberance extending outward from the tensioner body and adapted to receive an applied torque; wherein the tensioner body is pivotably secured at the fastener opening to the cylinder block adjacent to the tensioner arm and is configured to pivot relative to the cylinder block toward the tensioner arm in response to a predetermined torque applied to the protuberance such that the tensioner applies a predetermined load to the rotatable device via the tensioner arm.

9. The engine assembly of claim 8, wherein the tensioner body includes a slot extending through the tensioner body with the protuberance between the fastener opening and the slot, and further comprising: a locking bolt secured to the cylinder block and extending through the slot; wherein the locking bolt interferes with the tensioner body at an end of the slot to limit a range of motion of the tensioner body in response to the torque applied to the protuberance.

10. The engine assembly of claim 9, wherein: a first flange extends in a first direction from the tensioner body; the fastener opening is in the first flange; a second flange extends in a second direction from the tensioner body opposite to the first direction; and the slot is in the second flange.

11. The engine assembly of claim 8, wherein the protuberance extends from an outer side of the tensioner body away from the cylinder block; and wherein an inner side of the tensioner body confronting the cylinder block is generally planar.

12. The engine assembly of claim 8, wherein the tensioner arm has an outer surface facing the tensioner; wherein a distal end of the plunger has a convex distal surface configured to be engaged with the outer surface of the tensioner arm when the tensioner body is pivoted toward the tensioner arm in response to the predetermined torque applied to the protuberance; and wherein the outer surface of the tensioner arm is curved.

13. The engine assembly of claim 12, wherein the outer surface of the tensioner arm and the distal surface of the plunger are both convex.

14. A method of assembling an engine timing drive, the method comprising: applying a predetermined torque to a protuberance of a tensioner that is pivotably mounted to a cylinder block to rotate the tensioner toward a rotatable device such that the tensioner applies a predetermined load to the rotatable device; wherein the rotatable device is one of a chain or a belt placed around a crankshaft sprocket and around at least one camshaft phaser; tightening a bolt securing the at least one camshaft phaser to the camshaft; removing the predetermined torque from the protuberance of the tensioner; and tightening a locking bolt to secure the tensioner to the cylinder block.

15. The method of claim 14, further comprising: releasing a locking pin on the tensioner such that a plunger of the tensioner is biased toward the rotatable device.

16. The method of claim 14, further comprising: prior to applying the predetermined torque, mounting the tensioner to the cylinder block with a shoulder bolt such that the tensioner pivots about the shoulder bolt when the predetermined torque is applied.

17. The method of claim 14, further comprising: prior to applying the predetermined torque and prior to tightening the locking bolt, extending the locking bolt through a slot in the tensioner into the cylinder block; and wherein the locking bolt abuts an end of the slot when the predetermined torque is applied.

18. The method of claim 14, further comprising: prior to applying the predetermined torque, placing the rotatable device around the crankshaft sprocket and the at least one camshaft phaser.

19. The method of claim 17, further comprising: prior to applying the predetermined torque, locking the crankshaft at a predetermined angular position relative to the cylinder block such that the crankshaft remains at the angular position when the predetermined torque is applied.

20. The method of claim 17, further comprising: prior to applying the predetermined torque, locking the camshaft at a predetermined position relative to a cylinder head mounted on the cylinder block to prevent rotation of the at least one camshaft phaser relative to the cylinder block.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a schematic illustration in fragmentary perspective view of an engine assembly with a timing drive having a tensioner assembly within the scope of the present disclosure.

[0018] FIG. 2 is a schematic illustration in perspective view of an engine-facing side of the timing drive and tensioner assembly of FIG. 1.

[0019] FIG. 3 is a schematic illustration in fragmentary perspective view of the engine assembly with the timing drive and tensioner assembly of FIG. 1, showing the tensioner assembly prior to application of an applied torque.

[0020] FIG. 4 is a schematic illustration in fragmentary perspective view of the engine assembly with the timing drive and tensioner assembly of FIG. 3, showing a torque wrench in phantom applying torque to a torque-receiving feature of the tensioner assembly.

[0021] FIG. 5 is a schematic illustration in perspective view of the tensioner assembly of FIG. 1.

[0022] FIG. 6 is a schematic fragmentary illustration in front end view of the tensioner secured to the cylinder block and with a plunger removed.

[0023] FIG. 7 is a flowchart of a method of assembling an engine timing drive.

DETAILED DESCRIPTION

[0024] Referring to the drawings, wherein like reference numbers refer to like components throughout the views, FIG. 1 shows an engine assembly 10, with a timing drive 12 that includes a tensioner assembly 13 with a tensioner 15. The engine assembly 10 includes a cylinder block 14, and a cylinder head 16 supported on the cylinder block 14. A crankshaft 18 is rotatably mounted on the cylinder block 14. At least one camshaft is mounted on the cylinder head 16. In the embodiment shown, there is an intake camshaft 20A and an exhaust camshaft 20B configured to open and close intake and exhaust valves, respectively.

[0025] The timing drive 12 controls the relative angular orientation of the crankshaft 18 and the camshafts 20A, 20B. The timing drive 12 includes a rotatable device 22 operatively engaged with the crankshaft 18 and the camshafts 20A, 20B. The rotatable device 22 may be a chain or a belt. The rotatable device 22 may be referred to herein as a chain for purposes of discussion; however, it should be understood that the rotatable device 22 may be a belt. The chain 22 is operatively engaged with a crankshaft sprocket 24 that is fixedly mounted to the crankshaft 18 with one or more crank bolts 26 so that the sprocket 24 rotates with the crankshaft 18. The chain 22 is operatively engaged with cam sprockets 28A, 28B that are integral with camshaft phasers 27A, 27B, respectively. The camshaft phasers 27A, 27B are mounted to the camshafts 20A, 20B, respectively, each with one or more camshaft phaser bolts such as bolts 30A, 30B. The camshaft phasers 27A, 27B are controlled by an engine controller (not shown) via oil pressure or otherwise to vary the angular position of the camshafts 20A, 20B relative to the respective sprockets 28A, 28B. This changes the timing of intake and/or exhaust valve opening relative to the crankshaft position.

[0026] Other timing drive components include one or more chain guides 36 and a tensioner assembly 13 including a tensioner arm 32 (also referred to as a tensioner guide) that directs the chain 22 and is pivotably secured to the cylinder head 16 with a bolt 34 or other fastener such that the tensioner arm 32 pivots about a pivot axis P1 and is configured to direct the chain 22 as well as direct the plunger 52 of the tensioner assembly 13 to act on the chain 22 as discussed herein. The tensioner arm 32 pivots about its pivot axis P1, moving toward the chain guide 36 as the tensioner 15 loads the chain 22 via the tensioner arm 32, thereby resulting in a load (i.e., a tensile force) in the chain 22. The tensioner arm 32 thus guides the chain 22 between the crankshaft sprocket 24 and the camshaft sprocket 28B. Although shown mounted to the cylinder head 16, in other embodiments, the tensioner arm 32 could be shorter, and mounted to the cylinder block 14 instead of the cylinder head 16.

[0027] Another chain guide 36 is fixed to the cylinder head 16 with a bolt 38, and is also fixed to the cylinder block 14 with a bolt 40. The chain guide 36 guides the chain 22 between the camshaft sprocket 28A and the crankshaft sprocket 24.

[0028] It should be understood that bolts or other fasteners described herein as operable to mount components to the cylinder block 14 or to the cylinder head 16 interfit with corresponding fastener openings in the cylinder block 14 or the cylinder head 16, and may or may not be threaded.

[0029] The tensioner assembly 13 is configured to allow the chain 22 to be preloaded during engine assembly with a load applied to the chain 22 by the tensioner 15 via the tensioner arm 32 that is substantially equal to the load applied by tightening the camshaft phaser bolts 30A and 30B. The magnitude of this load is a function of the The substantially equal magnitude preload prevents chain slack from being introduced during assembly, and ensures that assembly of the engine and timing drive components best achieves the desired timing.

[0030] With reference to FIGS. 5 and 6, the tensioner 15 includes a tensioner body 44 having a first flange 45 with a fastener opening 46 extending therethrough. A shoulder bolt 48 extends through the fastener opening 46 and has an end that may be threaded and that secures to the cylinder block 14 to pivotably secure the tensioner body 44 to the cylinder block 14. Stated differently, the tensioner body 44 can pivot relative to the cylinder block 14 about the shoulder bolt 48 (i.e., about the center axis 47 of the fastener opening 46).

[0031] The tensioner body 44 also defines a cavity 55 with a plunger opening 50 that generally faces toward the chain 22 as can be determined from FIGS. 1 and 6 when taken together. A generally cylindrical plunger 52 is disposed in the cavity 55. A removable locking pin 42 shown in FIG. 3 restrains the plunger 52 in the cavity 55 to prevent the plunger 52 from being biased further outward from the opening 46 by a biasing feature such as pressurized oil and/or a spring disposed in the cavity 55. When the locking pin 42 is removed, the biasing force of the biasing feature urges the plunger 52 further outward from the opening 50 and against the adjacent tensioner arm 32, applying a predetermined force on the arm 32 resulting in a predetermined load L in the chain 22 as described herein.

[0032] The tensioner body 44 includes a protuberance 54 that extends outward from an outer side 56 of the tensioner body 44 away from the cylinder block 14. An inner side 57 of the tensioner body 44 is generally planar and is visible in FIGS. 2 and 6. The inner side 57 is configured to confront the cylinder block 14 when the tensioner 15 is secured to the cylinder block 14, as best indicated in FIG. 6.

[0033] The protuberance 54 is adapted to receive an applied torque from a torque applying tool. For example, as shown in FIG. 5, the protuberance 54 has a hexagonal side surface 60 that is adapted to interfit with a torque wrench 62 represented in phantom applying the predetermined torque T to the protuberance 54 in FIG. 4. The tensioner body 44 pivots relative to the cylinder block 14 toward the tensioner arm 32 in response to a predetermined torque T applied to the protuberance 54 such that the tensioner 15 (and more specifically, the plunger 52) applies a predetermined force F on the chain 22 via the tensioner arm, resulting in the predetermined tensile load L on the chain 22. The predetermined force F results in a predetermined load L (i.e., tensile load L in the chain 22, also referred to as tensile force L, represented in FIG. 4). The magnitude of the predetermined load is a function of the friction between the camshaft phaser bolts 30A, 30B and the camshaft phaser 28A, 28B and between the camshaft phaser and the camshaft 20A, 20B and can be determined by testing. The pivoting of the tensioner body 44 is evident by comparing the position of the tensioner body 44 in FIG. 3 relative to the position in FIG. 4. The position of the tensioner body 44 prior to application of the predetermined torque is indicated by the angle A1 of the center axis C of the plunger 52 and of the cavity 55 to horizontal H. The position of the tensioner body 44 under application of the predetermined torque T is indicated by the angle A2 of the center axis C of the plunger 52 and of the cavity 55 to horizontal H.

[0034] With reference to FIGS. 5 and 6, the tensioner body 44 includes a second flange 63 extending in a second direction D2 from the tensioner body 44 and with a slot 64 extending therethrough. The protuberance 54 is between the fastener opening 46 and the slot 64. The tensioner assembly 13 includes a locking bolt 66 secured to the cylinder block 14 and extending through the slot 64. The second direction D2 is opposite from the first direction D1 in which the first flange 45 extends. For example, the first direction D1 is generally downward and the second direction D2 is generally upward when the tensioner 15 is mounted to the cylinder block 14. The first direction D1 is orthogonal to the center axis C of the plunger 52 and of the cavity 55 in a generally downward direction, and the second direction D2 is orthogonal to the center axis C of the plunger 52 and of the cavity 55 in a generally upward direction. A center axis 49 of the protuberance 54 extends orthogonally to the center axis C of the plunger 52 and the cavity 55, orthogonally to the first direction D1 of the first flange 45, and orthogonally to the second direction D2 of the second flange 63. Accordingly, the center axis 47 of the first opening 46 and of the shoulder bolt 48, the center axis 49 of the protuberance 54, and the center axis 51 of the locking bolt are parallel.

[0035] As best shown in FIG. 2, the slot 64 is elongated relative to the diameter of the portion of the locking bolt 66 extending through the slot 64. When the torque T is applied as described, and assuming the locking bolt 66 is not yet tightened so that the second flange 63 is not held tightly between the locking bolt 66 and the cylinder block 14, the tensioner body 44 can move relative to the stationary locking bolt 66. More specifically, the length of the slot 64 allows a range of motion of the tensioner body 44 between a first position in FIG. 3, prior to application of the applied torque T, and a second position of FIG. 4 when the torque T is applied. The first position of FIG. 3 is determined by the interference of the shank portion of the locking bolt 66 with a first end 70 (shown in FIG. 4) of the slot 64 (i.e., a proximal end nearest the chain 22). The second position of FIG. 4 is determined by interference of the shank portion of the locking bolt 66 with the second end 72 (shown in FIG. 3) of the slot 64 (i.e., a distal end further from the chain 22). The locking bolt 66 thus interferes with the tensioner body 44 at either end of the slot 64 to limit a range of motion of the tensioner body 44 in response to the torque applied to the protuberance 54.

[0036] The plunger 52 and the tensioner arm 32 are cooperatively configured so that their interface does not obstruct the ability of the tensioner body 44 to pivot under the applied torque T. For example, the interfacing surfaces may be curved to minimize friction during pivoting of the tensioner 15. As shown in FIG. 3, the tensioner arm 32 has a convex outer surface 74 facing the tensioner 15. As shown in FIGS. 3 and 5, a distal end 76 of the plunger 52 has a convex distal surface 78. The distal surface 78 is configured to be engaged with the convex outer surface 74 of the tensioner arm 32 both when the tensioner body 44 is secured to the cylinder block 14 prior to application of the applied torque T (i.e., in the first position of FIG. 3), and when the tensioner body 44 is pivoted toward the tensioner arm 32 in response to the predetermined torque T applied to the protuberance 54 (i.e., in the second position of FIG. 4). This allows the two surfaces 74, 78 to interface over an entire range of motion of the tensioner 15, as the plunger 52 applies the predetermined force F to the tensioner arm 32. The two convex surfaces 74, 78 confront one another over the range of motion of the tensioner body 44, preventing abrupt impact on the tensioner arm 32 due to pivoting of the tensioner body 44.

[0037] The tensioner body 44 may be held in the pivoted position of FIG. 4 by the torque wrench 62 while assembly of other timing drive components is completed. In this manner, the chain 22 is pre-loaded during assembly of the timing drive 12 with the tension in the chain 22 during assembly thereby being substantially equal to the tension in the chain 22 during subsequent engine use. Final tightening of the timing drive components will thus not introduce slack in the chain 22 which could otherwise make it more difficult to ensure that desired relative rotational positions of the crankshaft sprocket 24 and the camshaft phasers 27A, 27B are maintained during a net build process.

[0038] In accordance with the tensioner 15 and timing drive 12 described above, FIG. 7 shows a flowchart illustrating a method 100 of assembling an engine timing drive 12. The method 100 begins with several actions that occur prior to the pre-loading of the chain 22. For example, in block 102, the crankshaft 18 is locked at a predetermined rotational position. Those skilled in the art understand a variety of ways to lock a crankshaft. For example, an indicator mark on the crankshaft 18 may be aligned with an indicator mark on the cylinder block 14 to ensure a predetermined rotational position, such as top dead center. Locking the crankshaft 18 may then be accomplished by extending a tool such as a pin through an access opening in a bell housing surrounding a flex plate so that the tool rests against the flex plate that is mounted on the crankshaft 18.

[0039] Similarly, in block 104, the camshafts 20A, 20B are each locked in a predetermined rotational position, such as by aligning indicator marks on the camshafts 20A, 20B with indicator marks on the cylinder head 16, and then extending a respective tool such as a pin through an opening in each camshaft 20A, 20B. The tool will abut the cylinder head 16 or other non-rotatable member to prevent rotation of the camshafts 20A, 20B.

[0040] Next, in block 106, the camshaft phasers 27A, 27B and the tensioner 15 are loosely assembled, such as by mounting the camshaft phasers 27A, 27B with the cam sprockets 28A, 28B on the camshafts 20A, 20B, without fully tightening the bolts 30A, 30B. Similarly, block 106 may include mounting the tensioner 15 to the cylinder block 14 also loosely, without fully tightening the shoulder bolt 48 to a final, pre-specified torque. For example, each of the mounting tasks in block 106 may be accomplished by hand tightening.

[0041] Next, in block 108, the locking bolt 66 may be extended through the slot 64 in the tensioner body 44 and into the cylinder block 14, but without fully tightening the locking bolt 66 so that the tensioner body 44 can be pivoted relative to the cylinder block 14 and the shoulder bolt 48 as described herein.

[0042] In block 110, the timing drive components can be assembled such as by mounting the tensioner arm 32 to the cylinder head 16, mounting the chain guide 36 to the cylinder head 16 and to the cylinder block 14, mounting the crankshaft sprocket 24 to the crankshaft 18, and placing the chain 22 around the camshaft sprockets 28A, 28B and the crankshaft sprocket 24.

[0043] In block 112, the tensioner 13 can then be located, such as by placing the tensioner body 44 in the first position of FIG. 3 with the locking bolt 66 at the end 70 of the slot 64. The shoulder bolt 48 can then be tightened in block 114. Even with the shoulder bolt 48 fully tightened to the cylinder block 14, the tensioner body 44 can be pivoted about the shoulder bolt 48

[0044] The timing drive 12 is now ready for pre-loading the chain 22 in block 116 by applying the predetermined torque T to the protuberance 54 with the torque wrench 62 to rotate the tensioner 15 toward the chain 22 such that the tensioner 15 applies the predetermined load L to the chain 22 (via the plunger 52 interfacing with the tensioner arm 32). Next, in block 118, the camshaft phaser bolts 30A, 30B are tightened one at a time, or together using a multi-axis tool. Due to the pre-load on the chain 22, tightening the bolts 30A, 30B will not cause slack in the chain that would otherwise need to be accounted for in accurately assembling the relative rotational positions of the crankshaft 18 and the camshafts 20A, 20B.

[0045] The locking bolt 66 is then tightened in block 120 to secure the tensioner 15 to the cylinder block 14. Once the camshaft phaser bolts 30A, 30B and the locking bolt 66 are tightened, in block 122, the predetermined torque T is removed from the protuberance 54 of the tensioner body 44 by removing the torque wrench 62. The locking pin 42 can then be released (i.e., removed) in block 124 such that the biasing feature within the tensioner 13 biases the plunger 52 toward the chain 22. The camshafts 20A, 20B and the crankshaft 18 are then unlocked so that they can rotate, and will do so at the desired relative timing.

[0046] While the best modes for carrying out the disclosure have been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and embodiments for practicing the disclosure within the scope of the appended claims.