The present invention relates to a face of tensioner arm, guide or snubber, and more specifically to a unique pattern applied to the face of the tensioner arm, guide or snubber to influence chain system noise, vibration harshness (NVH).
A chain or toothed belt drive is subjected to oscillating excitations. For example, a chain or toothed belt drive can be used between an engine crankshaft and camshaft. The oscillating excitation could be the torsional vibrations of the crankshaft and/or fluctuating torque loads from the valve train and/or a fuel pump.
Chain applications, either timing or drivetrain can require contact between the back of the chain and the face of a tensioner guide, arm or snubber to control chain motion. The contact between the chain and the face can result in engagement noise which can increase NVH, reducing perceived performance of the chain system. In particular, the chain-to-face contact forces can align with chain related orders, such as pitch frequency, causing additional excitations and unacceptable performance. Orders related to the number of events per shaft revolution is the number of events per unit of time.
NVH of the chain system is often caused by pitch orders, which is the noise associated with engagement of each link of the chain with sprockets and tensioners as well as the engagement differences which occur at half pitch and twice pitch orders due to the engagement differences from the links in guide row to the links in the non-guide row or flanks transitions along the teeth of the chain links of the chain. Pitch order equals the number of teeth on the drive sprocket. Therefore, if a drive sprocket has 40 teeth, then one sprocket revolution equals the 40th order and is referred to as the pitch order. Frequency (Hz) can then be expressed as: (order number×rpm)/60.
A torsion spring 66 is present between the mounting bracket 62 and acts to bias the arm 68 in a direction. One end 68a of the spring 66 is grounded relative to the mounting bracket 62 and the second end 66b of the spring 66 contacts the arm 68 to provide the bias force.
Other prior art includes dimples or slits to provide oil to a chain sliding surface to reduce friction between the chain links and the tensioner face or to guide the chain as the chain slides along the chain sliding surface. The prior art does not constitute any pattern that is actively controlling the alignment with the backs of the chain to decrease engagement at specific chain related orders to decrease NVH or to increase overall noise to obscure chain related orders that increase NVH.
According to one embodiment of the present invention, a unique pattern is applied to the face of the tensioner arm, guide or snubber to intentionally break up the chain contact force between the back of the chain and the tensioner arm, guide or snubber face to prevent alignment with the chain related orders which are causing NVH within the chain system.
According to another embodiment of the present invention, the pattern applied to the face of the tensioner arm, guide or snubber face is applied to intentionally excite non-chain related orders of lesser noise magnitudes, therefore increasing the overall noise level to mask or obscure the orders causing significant NVH.
The non-engagement portion 175 of the second surface 183 does not engage with the chain strands 8a, 8b and extends into the boss portion 185 which defines a hole 186 for rotatably receiving the pivot axle 164.
In alternate embodiments, the body 178 of the arm 168 can be manufactured from multiple pieces.
The unique pattern and associated groove pattern spacing is preferably calculated using equation 1.1 and 1.2 shown below. The pattern engagement dimension is the width of the spacers between grooves.
Pattern Engagement Dimension≠pn (1.1)
Pattern Engagement Dimension≠p(1/n)(1.2)
Equations 1.1 and 1.2 are removing the pitch orders which are causing NVH of the chain system due to engagement of each link 7, and engagement differences from the guide to the non-guide row or flank transitions of links 7 of the chain 8 of the chain system.
or p(0.5). In other words, the spacing between the groove 180 is set as 0.5×pitch of the chain. As shown in the half pitch NVH metric shown in
or p(0.4). Using 0.4×pitch results in a tensioner torque content of 0.1 Nm, which is less NVH than the continuous face and 0.5×pitch.
A torsion spring 166 is present between the mounting bracket 162 and the boss portion of the arm 185, adjacent to the non-engagement portion 174 of the second surface 183 and acts upon the arm 168 to bias the arm 168 towards the chain 8. One end 166a of the spring 166 is grounded relative to the mounting bracket 162 and the second end 166b of the spring 166 is grounded relative to the shaft 165. The coils 166c of the spring 166 are wrapped around the pivot axle 164 and present between the boss portion 185, the bracket 162 and second end 183b of the tensioner arm 168.
A stop 169 is present on the shaft 165 which can interact with the boss portion 185 of the arm 168 if the arm 168 pivots too far.
The pivot axle 164 receives an arm 168 formed of a body 178 having a first end 178a and a second end 178b, a first surface 188 and a second surface 183, opposite the first surface 188. The second surface 183 is defined by a first end 183a, a second end 183b, a first side 183c, a second side 183d and an arcuate boss portion 185. The second surface 183 includes, from a first end 178a to a second end 178b, a chain sliding surface 274, a non-engagement surface 175, and a boss portion 185. The chain sliding surface 274 has a unique pattern of grooves 280 and spacers 281 which engage with or interact with the backs 5 of the chain links 7 of each of the chain strands 8a, 8b. The pattern includes a plurality of radial grooves 280 separated by a spacer 281 of a width w. The unique pattern and associated groove pattern spacing is preferably calculated using equation 1.1 and 1.2. In this embodiment, the width w of the spacer 281 is constant through the pattern. The grooves 280 extend between the first and the second side 183c, 183d and are angled, such that the grooves 280 are not at 90 degrees relative to the first side 183c or the second side 183d. The minimum angle allows for the entire chain width to pass over a given groove during its contact with the tensioner. This angle can be calculated from the tensioner contact length (x) and the width of the chain (y) as tan−1(y/x). The number of grooves 280 and spacers 281 can vary. The width (w) of the spacers 281 spacing the grooves 280 apart and the number of grooves 280 intentionally break up the chain contact force between the back 5 of the chain links 7 of the chain strand 8a, 8b and the chain sliding face 174 of the tensioner arm 168 to prevent alignment with the chain related orders which are causing NVH within the chain system.
The non-engagement portion 175 of the second surface 181 does not engage with the chain strands 8a, 8b and extends into the boss portion 185 which defines a hole 186 for rotatably receiving the pivot axle 164.
A stop 169 is present on the shaft 165 which can interact with the boss portion 185 of the arm 168 if the arm 168 pivots too far.
In a first step, chain related orders at which NVH occurs within the chain system are determined (step 502). The chain related orders can be determined through computer simulation or through testing of the chain system itself.
Based on the determined chain related orders which cause NVH issues, a pattern is created for application to the face of the tensioner arm, guide or snubber of a plurality of grooves and spacers (step 506). The specific geometry of the grooves can be determined through simulation, testing, or a combination thereof. This process is iterative through experimentation. Groove geometry should be selected to avoid diminishing that lines up with known chain related orders as identified in equations 1.1. and 1.2.
The pattern is then applied to chain sliding face of the tensioner arm, guide or snubber (step 508) and the method ends.
In
Instead of having grooves and spacers that extend between the sides of the chain sliding face, extending from first side 383c to the second side 383d of the second surface 383 of the arm 320 are three different axial paths. Each axial path has a series of protrusions and depressions placed at different points, such that the chain contacts different protrusions and retrusions of each axial path as the tensioner tensions the chain strand. The protrusions and depressions are placed such that the chain related orders are broken up, similar to grooved embodiments discussed above. Again, dimensionality of these protrusions are governed by equations 1.1 and 1.2.
The examples of a pattern for application to the chain sliding face are shown as being applied to a tensioner arm, but could also be applied to the chain sliding face of a guide or snubber without deviating from the scope of the invention.
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.