This invention relates to a vibration isolator assembly, i.e., an assembly that absorbs vibrations and dampens relative movement between two structures. Examples of such assemblies include isolator mounts, bushing assemblies, cradle mount assemblies, etc. More particularly, this application is directed to a preloaded engine bushing mount and will be described with reference thereto. It will be appreciated, however, that the invention may have application in other vibration isolator assemblies or structures that encounter the same problems.
A vibration isolator assembly typically includes an external housing and an internal mounting shaft joined by an isolator formed from a vibration damping material such as a molded elastomer (e.g., rubber). The elastomer provides vibration isolation between the housing and the mounting shaft. Normally, the elastomer is molded to the housing shaft in a high-temperature molding operation. This provides a desirable bond between the elastomer and the housing shaft.
The inner mounting shaft is usually a rigid material, generally steel or aluminum, and the rubber isolator is received within the housing. Since it is often desirable to impart a degree of pre-compression onto the rubber isolator, the shapes and dimensions of the isolator and the housing are designed such that the isolator can be retained within the housing during service, and without the use of adhesives or other similar materials. Thus the pre-compression retains the rubber isolator within the housing, provides desired spring rate characteristics, and also improves durability.
In some arrangements, the housing is designed as a two-piece assembly. The isolator is placed within a first portion of the housing and the second portion of the housing is assembled and secured to the first housing portion, providing the desired pre-compression. In other instances, it is deemed more economical to design the housing as a one-piece component. In such a case, the rubber isolator is assembled through a window or opening in the housing. As the rubber isolator is larger than the opening in the housing, the opening is limited as to how much smaller it may be than the rubber before the process or assembly, or forcing the rubber through a smaller opening, imparts damage to the rubber.
The size of the opening in the housing also serves to limit the maximum displacement of the isolator shaft of the assembled bushing. This travel limiting feature is important, particularly in motor vehicle applications where packaging space under the hood is limited and a particular design requires that a travel limit be established. Usually the limit of travel is fixed by the inner mounting shaft movement relative to the wall defining the opening of the housing.
For design and tuning flexibility, significant variation in the spring rate characteristics of the isolators may be required. For example, in certain designs, it is desirable to reduce the dynamic rates and soften the mounts. To achieve this, it is common knowledge that a higher volume of rubber is needed in the isolator. This is often achieved by merely scaling up the isolator, that is, enlarging the components in a scaled-up version which results in a greater amount of rubber in the assembly. Because the isolator is necessarily larger, it becomes necessary to enlarge the opening in the housing and likewise the interior dimensions of the housing. The rubber is molded separately from the housing and then inserted into the housing window or opening to assemble and retain the isolator therein.
Merely enlarging the structure results in an extended travel excursion of the power train when mounted to the isolators. As noted above, the extent of travel limit relates to the inner metal shaft piece bottoming out on a rim of the housing opening. Thus, if the design maintains the same size shaft from the original bushing mount assembly for use with the scaled-up rubber isolator in order to incorporate extra rubber into the assembly, the resultant tradeoff is that extra travel of the power train will result. This, of course, could be an issue where only a limited amount of travel is permitted by the design.
One proposed solution was to expand the shaft size. This is perhaps best represented by
In
As noted with respect to
A vibration isolator assembly is provided that satisfactorily incorporates additional rubber into the isolator while limiting travel excursion of the shaft.
A preferred embodiment of the vibration isolator assembly includes a rubber isolator received around the shaft and a housing having a cavity with first and second different windows or openings at opposite ends thereof.
The first and second openings are preferably different sizes.
In the preferred arrangement, the openings are similarly configured.
The rubber isolator is dimensioned to be inserted through the enlarged, first opening and advanced toward the smaller, second opening. The housing is sized relative to rubber isolator to impart a pre-compression to the isolator.
The vibration isolator assembly is also preferably oriented so that the first and second openings are arranged to counteract dislodging forces exerted thereon.
A primary benefit of the invention is the ability to incorporate additional rubber into the isolator while still controlling relative travel of the shaft with respect to the housing.
Another benefit is offered by orienting the bushing/isolator so that outside forces tend to push the isolator toward the smaller opening.
Still another feature of the invention is the ability to pre-compress the isolator, add additional rubber, control the travel limit, and do so in a cost effective manner.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.
With the above description of
For ease of illustration and understanding, the primary distinction between the dimensions of the large and small windows is related to the height of the internal sidewalls. This is represented in
On the other hand, dimension 66 in
Nevertheless, by providing the enlarged opening, additional rubber 80 that is bonded to the mounting shaft 70 (
The rubber isolator and a portion of the housing are both scaled up to the desired larger size needed to achieve the technical goals of rate characteristics and/or durability. The entire housing, though, is not increased or scaled up. That is, the opening on one side is suitably enlarged or scaled up to permit ease of assembly of the rubber isolator. The opening on the opposite side is maintained at a smaller size to limit maximum travel of the isolator shaft to the desired level. In the end, the housing design having unequally sized openings, a large one for assembly, and a smaller one for travel restriction, is obtained while incorporating a greater amount of rubber into the assembly.
The smaller opening in the housing also advantageously addresses design problems that might otherwise occur with the embodiments of
It will be appreciated by one skilled in the art that the openings in the housing and likewise the configuration of the rubber isolator may adopt different profiles or shapes. It is not as desirable to provide small openings on both sides of the housing since it then would be difficult to pre-compress the bushing during assembly. Thus, the different openings at opposite ends of the housing also facilitate assembly.
The housing is preferably a stamped material such as steel or aluminum. It can also be a cast structure while the metal shaft (steel or aluminum) is typically bonded to the elastomeric isolator or rubber. In this arrangement, the rubber is not bonded to the outer housing so that the isolator can be preloaded during insertion or installation into the housing.
The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon reading and understanding this specification. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof