In an engine timing drive, a rotatable element, such as a chain or belt, is engaged with a crankshaft sprocket and camshaft sprockets to enable the drive power of the crankshaft to turn the camshafts. The angular positions of the camshafts relative to the angular position of the crankshaft ensures intake and exhaust valve opening and closing occurs at desired crankshaft positions. Additionally, camshafts may be controlled by phasers to vary the angular position of the camshafts relative to the crankshaft, and thereby vary the timing of the valve opening and closing. Proper timing is maintained in part via a timing drive tensioner, which provides tension despite expected wear of the chain or belt.
Achieving desired valve timing is also dependent upon the engine assembly process. In an index build assembly of the timing drive, the crankshaft and the camshafts are locked in known positions (e.g., positions associated with top dead center), and the timing drive components are then assembled. Tension from the timing drive tensioner is introduced only after the timing drive components such as the camshaft phasers, crankshaft sprocket, chain guides and chain are assembled. The tension in the chain, however, influences the final cam timing.
A tensioner assembly for an engine timing drive and a method of assembling an engine enable the chain or belt to be preloaded to a tension that mitigates the slack introduced by the tightening of the camshaft phaser bolts, thereby helping to ensure timing requirements are achieved. A tensioner assembly for an engine timing drive comprises a tensioner that has a tensioner body. The tensioner body has a fastener opening and defines a cavity with a plunger opening. A plunger is disposed in the cavity, and a removable pin restrains the plunger in the cavity. When the pin is removed, the plunger is configured to be biased out of the plunger opening. The tensioner assembly also includes a protuberance that 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 when fixed at the fastener opening in response to a predetermined torque applied to the protuberance.
In an aspect of the disclosure, the tensioner body includes a slot extending through the tensioner body with the protuberance between the fastener opening and the slot. The tensioner assembly may further include a shoulder bolt extending through the fastener opening, and a locking bolt extending through the slot. 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.
For example, the protuberance may have a side surface, such as but not limited to a hexagonal side surface, that is adapted to interfit with a torque wrench. A torque wrench may be applied to the protuberance, and rotated to apply a predetermined torque on the tensioner body, causing the tensioner body to pivot about the shoulder bolt and apply the predetermined load to an adjacent rotatable device, such as a timing chain or a timing belt. The predetermined torque may be selected so that the resulting predetermined load is substantially equal to a load that prevents rotation of the camshaft phasers as camshaft phaser bolts are tightened. The magnitude of the predetermined load is a function of the friction between the camshaft phaser bolts and the camshaft phaser and between the camshaft phaser and the camshaft and can be determined by testing. The tensioner body may be held in the pivoted position while assembly of the timing drive is completed. In this manner, the rotatable device is pre-loaded during assembly of the timing drive with the tension in the rotatable device during assembly thereby being consistent with the tension during engine operation. Final tightening of the timing drive components will thus not cause slack in the rotatable device which could otherwise make it more difficult to ensure that desired relative rotational positions of the crankshaft sprocket and the camshaft phasers, for example, are maintained during a net build process.
In an aspect of the disclosure, a first flange extends in a first direction from the tensioner body, such as downward. 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, such as upward. The slot is in the second flange.
In an aspect of the disclosure, the protuberance extends from an outer side of the tensioner body, and an inner side of the tensioner body opposite from the outer side is generally planar. For example, the inner side may be adapted to confront a cylinder block of the engine assembly.
In an aspect of the disclosure, the tensioner assembly may be in combination with a tensioner arm having a convex surface. A distal end of the plunger extending out of the cavity may have 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. The two convex surfaces may confront one another over the range of motion of the tensioner body as the tensioner body is pivoted when the predetermined torque is applied to the protuberance, preventing abrupt impact on the tensioner arm due to pivoting of the tensioner body.
In an aspect of the disclosure, an engine assembly comprises a cylinder block, a cylinder head supported on the cylinder block, and a crankshaft rotatably mounted on the cylinder block. The engine assembly includes 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 includes a rotatable device operatively engaged with the crankshaft and the camshaft. The rotatable device is one of a chain or a belt. A tensioner arm is pivotably secured to one of the cylinder block and the cylinder head and is configured to direct the rotatable device. The engine assembly also includes a tensioner assembly. The tensioner assembly comprises a tensioner body having a fastener opening. The tensioner assembly body has a cavity with a plunger opening, and a plunger is disposed in the cavity. 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 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.
In an aspect of the disclosure, the tensioner body includes a slot extending through the tensioner body with the protuberance between the fastener opening and the slot. The tensioner body includes a locking bolt secured to the cylinder block and extending through the slot. 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.
In an aspect of the disclosure, 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. The slot is in the second flange.
In an aspect of the disclosure, the protuberance extends from an outer side of the tensioner body away from the cylinder block. An inner side of the tensioner body confronts the cylinder block and is generally planar. The tensioner arm may have an outer surface facing the tensioner. 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. The outer surface of the tensioner arm may be curved. For example, both the outer surface of the tensioner arm and the distal surface of the plunger may be convex. This allows the two surfaces to interface over an entire range of motion of the tensioner, as the plunger applies the predetermined force to the tensioner arm resulting in the predetermined load in the rotatable device.
A method of assembling an engine timing drive comprises 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. The rotatable device is one of a chain or a belt placed around a crankshaft sprocket and around at least one camshaft phaser. The method further comprises tightening a bolt that secures the at least one camshaft phaser to the camshaft. Once the bolt is tightened, the method comprises removing the predetermined torque from the protuberance of the tensioner. A locking bolt may then be tightened to secure the tensioner to the cylinder block. The predetermined load is that required to prevent rotation of the at least one camshaft phaser as the bolt is tightened.
For example, in an aspect of the disclosure, the method may further include releasing a locking pin on the tensioner such that a plunger of the tensioner is biased toward the rotatable device to apply the predetermined load to the rotatable device.
Several additional aspects of the method may occur prior to applying the predetermined torque. For example, 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, and 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 may both occur prior to applying the predetermined load. The method may include placing the rotatable device around the crankshaft sprocket and the at least one camshaft phaser. Furthermore, the method may include 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. Additionally, also prior to applying the predetermined torque and prior to tightening the locking bolt, the method may include extending the locking bolt through a slot in the tensioner into the cylinder block. The slot and locking bolt are configured so that the locking bolt abuts an end of the slot when the predetermined torque is applied. In one example, an assembler (or robot) that applies the predetermined torque to the tensioning bolt may first perform these actions. Alternatively, the engine assembly may be shipped to a final assembly destination where the torque is to be applied to the protuberance with one or more of these actions already performed.
The above features and advantages and other features and advantages of the present disclosure are readily apparent from the following detailed description of the best modes for carrying out the disclosure when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the views,
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.
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.
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.
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.
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.
With reference to
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
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
The protuberance 54 is adapted to receive an applied torque from a torque applying tool. For example, as shown in
With reference to
As best shown in
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
The tensioner body 44 may be held in the pivoted position of
In accordance with the tensioner 15 and timing drive 12 described above,
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.
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.
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.
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.
In block 112, the tensioner 13 can then be located, such as by placing the tensioner body 44 in the first position of
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.
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.
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.