Temperature compensating mount

Abstract: To accommodate differential thermal growth of a component and its support, a pair of temperature responsive mounts are provided. Each mount comprises a rigid, bowed beam having lugs at each end affixed to the component and an intermediate lug affixed to the case. Thermal expansions of the beams and the component load the beams in compression, causing flexures thereof in directions to produce motions of the third lugs that track the thermal growth of the support.

Description: The present invention relates to temperature compensating structures for maintaining the requisite mounted positions of components despite changes in temperature and to minimize stresses at the points of mounting attachment due to differential thermal coefficients of expansion. Background of the Invention The mounting of components to support structures in operating environments of wide variations in temperature requires prudent engineering design when materials of different thermal coefficients of expansion are involved. Differential thermal growths of the component and the support structure can create significant mechanical stresses at their points of attachment and ultimate fatigue failure when the parts undergo frequent thermal cycling. Another important design consideration in many applications is maintaining the mounted component in a fixed position relative to the support structure despite wide variations in temperature. An application where both fatigue failure and positioning considerations are of critical importance is the mounting of transmission operating components to the transmission case. Transmissions, such as hydromechanical steering transmissions in military vehicles, e.g., tanks, are subjected to temperatures cycling over a wide range. From cold starts in sub-zero temperatures, a tank transmission can heat up to several hundred degrees Fahenheit in service. The transmission operating components are typically made of steel, while the mounting case is typically aluminum to save weight. The different coefficients of expansion of steel and aluminum result in different thermal growths at the common points of mounting attachment between the component and case. With repeated thermal cycling, the stresses generated at these attachment points can ultimately lead to fatigue failure of one of the parts, most typically the aluminum case. Moreover, this different thermal growth can alter the crucial alignment between transmission operating components, causing undue bearing and gear wear and other adverse consequences. FR-A-2315056 shows a mounting arrangement for a machine having a horizontal axis. In this arrangement a number of parallel levers are connected between the machine and the foundation on which it is mounted. The levers are mounted in an axial plane or a plane parallel thereto and are either articulated or flexible such that thermal expansion of the machine in a radial direction is taken up by an axial movement of the machine so as to avoid stresses developing between the machine and its foundation. However, such an arrangement is unsuitable for application where the axial movement used to compensate for differences in expansion between the machine and its foundation are not acceptable or undesirable as is the case, for example, with transmission. Summary of the Invention The present invention accordingly seeks to provide a temperature compensating mount for mounting a component to a support. The invention further seeks to provide a temperature compensation mount of the above-character which accommodates differential thermal growth of the component and support. In accordance with the present invention, there is provided a temperature compensating arrangement comprising in combination a component, a support and a temperature compensating mount for rigidly mounting the component to the support, wherein the component and the support have different thermal coefficients of expansion, said mount comprising, in combination: A. a beam bowed in the direction of elongation and having a generally concave side facing the component and a generally convex side facing away from the component; B. a first lug provided at a first end of said beam for affixing to the component at a first attachment point; C. a second lug provided at a second end of said beam for affixation to the component at a second attachment point; and D. a third lug laterally extending from said generally convex side of said beam at a location intermediate said first and second lugs for affixation to the support at a third attachment point; E. the mount being of a material having a higher thermal coefficient of expansion than the component whereby, under rising temperature conditions, thermal expansion of the component and said beam loads said beam in compression, causing flexure thereof in a direction to produce movement of said third attachment point at said third lug, the dimensions and geometry of the mount and its thermal coefficient of expansion relative to the component and support materials being such that said third attachment point on the third lug tracks the movement of said third attachment point at the support produced by thermal expansion of the support. Brief Description of the Drawings The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: FIGURE 1 is an end view, partially broken away, of a prior art approach to mounting a transmission component to a transmission case; FIGURE 2 is an end view, partially broken away, of temperature compensating mounts constructed in accordance with the present invention for mounting a transmission component to a transmission case; and FIGURE 3 is an enlarged end view of one of the temperature compensating mounts of FIGURE 2. Corresponding reference numerals refer to like parts throughout the several views of the drawings. Detailed Description The assembly of transmission operating components of a transmission has typically called for mounting the components directly to the transmission case. Thus, as seen in FIGURE 1, the prior art approach has been to provide an operating component 10, such as a hydrostatic drive unit of a hydromechanical steering transmission, with opposed laterally extending ears or lugs 12 which rest on platform mounting surfaces 14 of ribs 16 integrally formed with a transmission case 18. The assembly is secured using bolts 20. Unfortunately, component 10 and case 18 are typically formed of dissimilar metals having different thermal coefficients of expansion. To save weight, the transmission case is aluminum, while the operating component is typically steel. Aluminum has a greater thermal coefficient of expansion than steel. Consequently, under the widely varying temperature conditions encountered in service, the common attachment points 22 of the component and case attempt to move at different rates as these parts thermally grow and shrink. Relative movements of the component and case attachments points are obviously constrained by bolts 20, and thus stresses are generated at these attachments. With repeated thermal cycling, shearing forces parallel to platform surfaces 14 develop cracks in ribs 16 surrounding the tapped bolt holes, leading to ultimate fatigue failure of the weaker aluminum case material. In accordance with the present invention and as seen in FIGURE 2, operating component 10 is mounted to transmission case 18 via a pair of intermediary, temperature compensating mounts, generally indicated at 24. The component is reconfigured to remove lugs 12 seen in FIGURE 1 to accommodate mounts 24 in flanking relation. Each mount includes an outwardly curved or bowed (relative to component) support beam 26 terminating at its ends in upper and lower lugs 28 and 30, respectively. These lugs are affixed to component 10 by bolts 32, to establish pairs of upper 34 and lower 36 attachment points. At a central location between lugs 28 and 30, an ear or lug 38 extends laterally outward from the convex side of each support beam 26. These lugs rest on platform mounting surfaces 14 and are clamped to ribs 16 via bolts 20 to establish common attachment points 22. The mounts are formed of a metal having a higher thermal coefficient of expansion than steel component 10. To describe the temperature compensating action of mounts 24, reference is made to the enlarged view of one of the mounts seen in FIGURE 3. When the transmission is non-operating and the component and case are at the ambient temperature of the environment, the only stresses on the attachment points 22, 34 and 36 are those imposed by the component weight. The loading on ribs 16 are compression forces normal to platform surfaces 14, which the aluminum case can readily withstand. As the component, case and mount heat up during transmission operating, support beam 26 grows at a faster rate than the transmission component. As a consequence, component 10 loads the support beam in compression, causing it to flex outwardly, as indicated by dash lines 26a. This action produces outwardly motion of attachment point 22 of lug 38. The attachment point 22 of case rib 16 also moves outwardly as case 18 experiences thermal growth. By structuring mounts 24 with appropriate dimensions and geometry and of a material having the proper thermal coefficient of expansion relationship with the component and case materials, the attachment points 22 of the lugs 38 and case ribs 16 are caused to move at the same rate, i.e., track each other, during thermal cycling of these parts. Absent forces attempting to produce relative movement between the mount lugs and the case ribs at platform surfaces 14, lateral shearing stresses at the common attachment points 22 are effectively eliminated. Fatigue failure of the transmission case due to temperature variations is thus avoided. By virtue of the designed curvature of support beams 26, the direction and degree of flexure are predetermined and controllable. It will be appreciated that flexure of the beams is effective in avoiding excessive shearing stresses at attachment points 34 and 36 between the component and the mounts. Since the actions of the mounts are duplicated at each side of the component, the positional relationship between the component and the case is not disturbed during thermal cycling. Duplication of mount reaction to temperature variations is assured in the illustrated embodiment in FIGURES 2 and 3, wherein attachment points 22 are aligned with horizontal centerline 40 of component 10, and wherein attachment points 34 and 36 are vertically aligned and located equidistance above and below centerline 40. Also, when the mounts are installed, the radius of curvature 42 of beams 26 is centered on the axis 44 of component 10. Since other transmission operating components are also mounted by case 18, their alignments with component 10 are also preserved. It will be appreciated that beams 26 are of a sufficient cross section to constitute rigid support members, and thus the mounting of the component to the case is rigid in character at all temperatures. Thus, flexure of the beams occurs only in response to variations in temperature and not in response to vibration or mechanical shock incident with transmission operation. It should be understood that attachment points 22, 34 and 36 are used herein as a matter of convenience in describing the reactions of the parts of variations in temperature. These attachment points correspond to points located at the geometrical centers of the areas of interfacial contact between the lugs and the component and case. While the temperature compensating mount of the present invention has been disclosed in its application to mounting transmission components, it will be appreciated that the teachings herein are applicable to mounting any object to a support, wherein differential thermal growth of the object and support with variations in temperature jeopardizes support integrity and alignment. It is seen from the foregoing that the objects set forth above, including those made apparent from the preceding Detailed Description, are efficiently attained, and, since certain changes may be made in the construction set forth without departing from the scope of the invention as defined by the claims, it is intended that matters of detail be taken as illustrative and not in a limiting sense.

Claims: A temperature compensating arrangement comprising in combination a component (10), a support (18) and a temperature compensating mount for rigidly mounting the component (10) to the support (18), wherein the component (10) and the support (18) have different thermal coefficients of expansion, said mount comprising, in combination: A. a beam (26) bowed in the direction of elongation and having a generally concave side (27) facing the component (10) and a generally convex side (29) facing away from the component (10); B. a first lug (28) provided at a first end of said beam (26) for affixing to the component (10) at a first attachment point (34); C. a second lug (30) provided at a second end of said beam (26) for affixation to the component (10) at a second attachment point (36); and D. a third lug (38) laterally extending from said generally convex side of said beam (26) at a location intermediate said first and second lugs (28,30) for affixation to the support (18) at a third attachment point (22); E. the mount being of a material having a higher thermal coefficient of expansion than the component (10) whereby, under rising temperature conditions, thermal expansion of the component (10) and said beam (26) loads said beam in compression, causing flexure thereof in a direction to produce movement of said third attachment point (22) at said third lug (38), the dimensions and geometry of the mount and its thermal coefficient of expansion relative to the component and support materials being such that said third attachment point on the third lug tracks the movement of said third attachment point (22) at the support (18) produced by thermal expansion of the support (18). The arrangement defined in claim 1, wherein said first second and third lugs (28,30,38) are integrally formed with said beam (26). The arrangement defined in claim 1 or 2, wherein said third attachment point (22) is equally spaced from said first and second attachment points (28,30). The arrangement defined in any one of claims 1 to 3, wherein a pair of said mounts are affixed to the component (10) and support (18) in opposed relation at opposite sides of the component (10). The arrangement defined in any one of claims 1 to 4, further comprising a second temperature compensating mount (24) disposed at an opposite side of said component (10) to said first mount (24), said second mount (24) comprising, in combination: A. a beam (26) permanently bowed in the direction of elongation and having a generally concave side (27) facing the component (10) and a convex side (29); B. a first lug (28) provided at a first end of said beam (26) and affixed to the component at a first attachment point (34); C. a second lug (30) provided at a second end of said beam (26) and affixed to said component (10) at a second attachment point (36); and D. a third lug (38) laterally extending from the convex side (24) of said beam (26) and affixed to the support at a third attachment point (22); E. the mount being of a material having a higher thermal coefficient of expansion than the component (10), whereby thermal expansion of the component (10) and said beams (26) under rising temperature conditions loads said beams (26) in compression, causing flexures of said beams (26) in directions away from the component (10) to produce movements of said third attachment points (22) at said third lugs (38) the dimensions and geometry of the mount and its thermal coefficient of expansion relative to the component and support materials being such that said third attachment points on the third lugs (38) track the movements of said third attachment points (22) at the support (18) produced by thermal expansion of the support (18). The arrangement defined in claim 5, wherein said third common attachment points (22) at said third lugs (38) of each said mount are substantially aligned with a horizontal centerline (40) of the component (10). The arrangement defined in claim 6, wherein said first and second attachment points (34,38) at said first and second lugs (28,30), respectively, of each said mount are in substantial vertical alignment. The arrangement defined in claim 7, wherein said first and second attachment points (36,38) are located equidistance above and below the horizontal centerline (40). The mounts defined in claim 8, wherein said beams (26) are bowed along a curve having a radius of curvature substantially centered at an axis (44) of the component (10). The arrangement as defined in any preceding claim, wherein the component is a transmission or a transmission operating component and the support is a transmission case.

Inventors: DAVIS DOUGLAS FAIRFIELD, GROSSENBACHER ERNEST JR, KOWALCZYK THOMAS ANTHONY, DAVIS, DOUGLAS FAIRFIELD, GROSSENBACHER, ERNEST, JR., KOWALCZYK, THOMAS ANTHONY
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1991
Main classification: F16M7
IPC codes: F16M7, B23Q11, F41H7, B23Q1, B60K17