Patent Application
20080234080
The invention relates to a wheel isolator, and more particularly, to a motorcycle wheel isolator comprising resilient members having relief features and projecting bending mode members.
Isolators are used in motorcycle rear wheel drives in order to reduce the noise, vibration and harness (NVH) that may otherwise be transmitted to the rider.
Representative of the art is U.S. Pat. No. 6,516,912 B2 which discloses a power transmission mechanism into which a driven flange is assembled, the power transmission mechanism producing no metal contact noises. A driven flange is divided into an engine side flange and a wheel side flange. The engine side flange may be formed of a steel forging and the wheel side flange may be formed of an aluminum forging. The engine side flange is spline-fitted in a final gear integrally rotated with a bevel gear. Furthermore, openings are formed in the wheel side flange at equal intervals and blocks having a threaded hole therein are pressed into the openings. In addition, the engine side flange, the wheel side flange, and the blocks are integrally connected together with bolts.
What is needed is a motorcycle wheel isolator comprising resilient members having relief features and projecting bending mode members. The present invention meets this need.
The primary aspect of the invention is to provide a motorcycle wheel isolator comprising resilient members blocks having relief features and projecting bending mode members.
Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.
The invention comprises a motorcycle wheel isolator comprising a first sprocket member, the first sprocket member having a first projecting member, a second hub member, the second hub member having a second projecting member, at least one first projecting member disposed between two second projecting members, whereby a receiving portion is defined, at least one resilient isolator having a first portion and a second portion connected by a connecting member, the resilient isolator disposed in the receiving portion, an edge of each first portion and second portion having a chamfer disposed adjacent either the first projecting member or second projecting member, each first portion and second portion having a projecting member disposed on an outer surface of each first portion and second portion such that a compressive force applied to the first portion and second portion causes a bending mode in each first portion and second portion, and each first portion and second portion having a relief portion disposed on an outer surface of each first portion and second portion such that the first portion and second portion may expand under the compressive force.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.
a) and 1(b) illustrate the prior art.
a), 2(b) and 2(c) illustrate the compound bending mode, where the three-point bending is achieved in the width direction (W) and two-point bending in the length direction (L).
a), 3(b) and 3(c) shows simple two-point bending mode in the length direction L.
The inventive motorcycle rear wheel isolator filters or reduces torsional vibration and torsional impact load during motorcycle operation and gear shifting. The benefit of the isolator is best illustrated during the dynamic transient events, namely transmission speed shifting, such as high speed downshifting and hard launch. In those events, the impact shock load (torque) can be absorbed by the soft rubber cushion blocks. However, the difficulty of proper isolator design is its competing targets, namely, the low torsional stiffness and low axial force.
Since the rubber elastomeric material is substantially incompressible, a low torsional stiffness implies a large axial displacement under high impact torque. In this condition, the rubber isolator is compressed in the tangential direction and will flow to expand in the other dimensions, i.e., radial and axial directions. Expansion in the axial direction will be detrimental to the axle bearing life. This is because the isolator bearing is selected mainly to undertake the hubload induced by the belt tension (tangential load), while its axial force limit is relative low. The axial load is oriented parallel to a wheel axis. An improper isolator design will typically lead to premature axle bearing failure due to excessive axial force.
The other requirement is durability. In the case of a soft (low modulus) rubber isolator, rubber deformation and strain will be significant, resulting in a shorter operating life. For example, conventional isolator design places locating pins P1 and P2 adjacent to each other, as schematically shown in
The principle of the inventive isolator is to switch the axial force from the compression mode into a bending mode since the force created by the bending moment is much less than its compression counterpart.
a), 2(b) and 2(c) illustrate the compound bending mode where the three-point bending is achieved in the width direction (W) and two-point bending in the length direction (L). This configuration is the most effective means to reduce the axial force where the overall length L dimension is limited.
a), 3(b) and 3(c) shows simple two-point bending mode in the length direction L. Although this arrangement increases the stability of the rubber isolator part it requires somewhat more space in the length direction than the mode in
Up to a 50% axial force reduction can be achieved by using the bending mode approach described in this specification. The axial force operates along axis A-A in each of
An important aspect of the inventive isolator is how the projecting members come into contact with the resilient element 10 under compressive load. This is in addition to the bending mode and relief features described herein. The prior design has a drawback that the projecting member edge will cut into resilient block under a compressive load, ultimately leading to a crack in blocks 100, 200. To avoid this, the inventive isolator has three solutions.
First, in order to prevent pinching the bottom corners of each block 100, 200, a chamfer 175, 176 is used to prevent bottom edge contact with projecting member 300 or projecting member 401, see
Recess 301 is disposed at the top of each projecting member 300 to form a drop bridge. Connector member 150 is situated between first block 100 and second block 200. Connector member 150 joins first block 100 to second block 200 by extending through the recess 301. Connector member 150 comprises the same material as block 100 and block 200.
Blocks 100, 200 compositions may comprise suitable natural or synthetic rubbers, including the following or a combination of two or more.
(1) Traditional diene elastomers such as NR, BR, SBR, IIR, CR and NBR. As is known in the art, they are generally vulcanized by means of heat-activated cure systems comprising sulfur and sulfur-based cure accelerators. However, rubber formulated with these elastomers are limited in terms of heat resistance and ozone resistance; or,
(2) Higher performance elastomers such as EPM, EPDM, HNBR, AEM, fluoro- and silicone rubbers. EPM and EPDM, members of the ethylene-alpha-olefin family of elastomers, are desirable for vibration isolators because of their high heat resistance, ease of incorporating fillers, and relatively low cost.
The elastomer compounds may also include reinforcement additives, such as carbon black fillers, antioxidants, internal lubricants to lower compound friction co-efficiency and curatives, each is known in the art. Curatives may include sulfur-based cure accelerators, peroxides or metal oxides.
Concave recesses 101, 201, 203 extend substantially normal to a radius R originating at a center of curvature C. Concave recesses 101, 201, 203 provide a means by which block 200 may expand when subjected to a compressive load, for example, during a downshift. Further, the pair concave recesses 201, 203 on the second block 200 creates two separated loading paths that minimizes the force transferred in the middle section of second block 200 thereby reducing the block material flow under a compressive load.
By combining recess 301 with the connector member 150, the projecting member 300 extends beyond the full width of the block contact area. Hence, bottom corner pinching of each block 100 and 200 seen in prior art isolators is eliminated.
An alternate embodiment is shown in
The concave recesses 101, 203 are also omitted. The width dimension W1 of the projecting member 300 is slightly greater than the width W2 of first block 100 prevent pinching block 100 and block 200 between adjacent metal paddles.
Under the full torque condition, each relief feature 40 is “filled” by the material of blocks 100, 200 as each block 100, 200 expands under the compression. The detail shape of each relief feature may be further refined based upon the maximum torque and the overall geometry cavity created between the wheel and the sprocket. This technique reduces the isolator torsional stiffness thereby making the isolator more efficient and durable.
Projecting members 204 and 205 allows block 200 to “stand-off” from the receiving portion 601 compartment sides. Projecting members 103 and 104 allow block 100 to “stand-off” from the receiving portion 601 compartment sides. Each of the projecting members 204, 205, 103, 104 and the position of each causes each block 100 and block 200 to be subjected to a bending moment as described in
Wheel hub 400 is fastened to a wheel (not shown) using fasteners 402. Fasteners 402 comprise bolts. Sprocket 600 is engaged with wheel hub 400 only by engagement of each isolator 10 and projecting members 300 and 401. Projecting members 300 and projecting members 401 interengage in an alternating manner. Receiving portions 601 are disposed within sprocket 600. Blocks 100, 200 occupy the receiving portions 601.
Torque is transmitted from sprocket 600 to wheel hub 400 through compression of isolators 10 as each isolator bears upon projecting members 300 and projecting members 401.
Axle 500 is connected to a motorcycle frame swingarm (not shown) in a manner known in the art using mounting nuts 501 and 502. Sprocket 600 rotates about axle 500 on sprocket bearing 700. A toothed belt B engages belt bearing surface 602.
In operation torque is transmitted from the engine transmission to sprocket 600 through belt B. Belt B applies a tangential force to sprocket surface 602. The tangential force compresses blocks 100 through projecting members 300. Blocks 100 in turn press upon projecting members 401 which drive wheel hub 400. In the downshift mode torque is transmitted from the wheel to the engine through blocks 200, thereby allowing engine compression braking.
Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.
