GB1574846A

GB1574846A - Torsional vibration dampers

Info

Publication number: GB1574846A
Application number: GB246077A
Authority: GB
Original assignee: Wallace Murray Corp
Current assignee: Wallace Murray Corp
Priority date: 1977-01-12
Filing date: 1977-01-21
Publication date: 1980-09-10
Also published as: DE2700936A1

Description

(54) IMPROVEMENTS IN AND RELATING TO TORSIONAL VIBRATION DAMPERS (71) We, WALLACE MURRAY CORPORATION, a corporation organized and existing under the laws of the State of Delaware, whose principal place of business is 299 Park Avenue, New York, State of New York, United States of America, (assignee of Robert Charles Bremer, Jr.), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to torsional vibration dampers having a hub secured to an outer inertia member by an elastomer annulus.

The invention exhibits particular utility to the damping of torsional vibrations in internal combustion engines. Such dampers are well known. Torsional vibrations may be considered as back-and-forth twistings of the crankshaft of an internal combustion engine, super-imposed upon the main, unidirectional rotation of the crankshaft. Unless controlled, such torsional vibrations will often lead to failure of the crankshaft, as well as contributing to failure in other parts of the engine or its cooling system. According to present theory of elastomer vibration dampers, the torsional vibrational energy transmitted to the crankshaft by the action of the pistons is converted into heat in the elastomer. The elastomer may accordingly be considered as a drain or sump which continually receives a portion of the energy of the torsional vibrations. The theory and performance of such vibration dampers is assumed to be known to the reader and further discussion will accordingly not be offered.

According to this invention, there is provided a torsional vibration damper having a hub coupled to a concentric outer inertia member by an annular elastomer member, the outer periphery of the hub and the inner periphery of the inertia member both being concave in axial cross-section, the extent of the concave portions in an axial direction, being that of the axial thickness of the hub and the inertia mem ber, said concave portions facing each other in a radial direction and the elastomer member having a radial thickness in its undeformed state which is greater than the maximum radial distance of the annular gap between the hub and the outer inertia member whereby the elastomer member is compressed upon insertion into the annular gap so that the member is deformed the greatest in a radial direction at its axial ends and the least in a radial direction between its ends, the hub and inertia member being each of a one-piece construction. One advantage of this construction is that the elastomer which is radially deformed the greatest is that portion of the elastomer in which most of the heat is generated and, being adjacent each axial face, the heat is more readily dissipated to atmosphere.

The prior art is aware of generally similar constructions. For example, in U.S. Patent No. 2,779,211 to Henrich, a construction is illustrated employing a one-piece hub con struction and a one-piece inertia ring con struction, with the inner periphery of the inertia member being concave and elastom er in the zone between these two members.

However, an assembly radius at an axial face is necessary in order to permit lateral pushing of the inertia ring over or across the prepositioned elastomer annulus which is on the hub. The presence of such assembly radius is undesirable because the rubber adjacent the assembly radius is not radially deformed, rather, it tends to spread out.

Such dampers often fail in a manner com mencing with the loss of chunks of elastom er flying off, elastomer eroding from that portion adjacent the assembly radius. Furth er, the method of assembly required in a construction such as Henrich results in the annular elastomer member having a tendency to roll and thereby set up permanent strains in the assembled state, the strains being non-uniform and accordingly not easily controlled.

Another prior art construction employing a one-piece hub and a one-piece inertia ring is shown in U.S. Patent No. 2,722,138 to Neher. The elastomer annulus is fitted over the periphery of the inertia member. A sheet metal flange, connected to and extending axially from the hub, is bent over the elastomer. The sheet metal must be deformed to complete the assembly of the damper and the problem of springback control of sheet metal is inherently present.

A further disadvantage of such a construction is the inherent weakness of the sheet metal flange or sleeve which surrounds the elastomer and inertia members.

U.S. Patents 2,898,777, issued to Boehm, and 2,556,999, issued to Hardy, also show generally similar constructions. In these two assemblies, however, either the hub member or the inertia member must be of'two parts in order to effect assembly. Clearly, a vibration damper requiring only three elements (as with the present invention) is generally superior to one requiring four elements.

Other constructions, such as U.S. Patents 3,088,332, issued to Aunt; 1,928,763, issued to Rosenberg; 2,972,904, issued to Troyer; and 2,992.569, issued to Katzenberger, also show somewhat similar devices. In the Rosenberg construction, variable radial deformation of an elastomer annulus is present to inhibit axial movement of a gear, but the greatest radial deformation is at the axial center of the hub-gear assembly. The tendency of the elastomer is to squirm laterally out in both axial directions and to hence cause high central tensile stresses.

Advantageously, the damper of this invention may be assembled by laterally pushing an elastomer annulus into the zone between the hub and inertia member by means of a pusher assembly and an assem bly tool.

The invention is described further, by way of example. with reference to the accom panying drawings wherein: Figure 1 is an axial cross-section of the upper half of the torsional vibration damper according to the practice of this invention.

Figure 2 is a partial elevational view looking at the right face of the damper of Figure 1.

Figure 3 is a partial axial upper half cross-section illustrating the apparatus and method of assembly of the torsional vibra tion damper of this invention in one axial position of assembly.

Figure 4 is a partial axial upper half cross-section illustrating the apparatus and method of assembly of the torsional vibration damper of this invention in another, later axial position of assembly.

Figure 5 is a partially schematic illustration of a typical prior art construction.

Referring now to Figures 1 and 2 of the drawings, the numeral 10 denotes generally a torsional vibration damper of this invention and includes an outer inertia ring 12 concentric with a hub member 14, the two members being joined by an annular elastomer denoted by the numeral 16. The surfaces 12a and 14a which face each other are both concave in axial cross-section as shown, and the extent of the concave surfaces in an axial direction is that of the axial thickness of the hub member 14 and the inertia ring 12. The angle theta denotes the angle between either face of the hub assembly and either of the concave surfaces 12a and 14a. Both upper angles theta between the axial ends of surface 12a and the two faces of the ring 12 are the same, as is the case with the corresponding lower two angles theta. They may, however, be different and are a function of the design axial radial rubber deformation gradient. However, it is only necessary that theta be less than 90". The numeral 18 indicates the axis of rotation of the completed damper assembly.

In practice, the axis 18 may coincide with the axis of rotation of the crankshaft of an internal combustion engine.

Reference now to Figures 3 and 4 of the drawings illustrates the mode of assembly of the damper. The numeral 30 denotes a two-part annular assembly fixture formed of, for example, cast iron. The outer half of assembly fixture 30 is positioned on the outermost part of inertia ring 12. The inner half is located on a convenient inside surface of the hub member 14 such as the bore as shown. The completed assembly thus forms an annular channel 31 of uniform radial dimension extending completely around the fixture 30. The left portion of fixture 30 includes an adjacent continuous annular channel 32 of the indicated shape, i.e., both facing surfaces of the channel 32 are convex.

The numeral 34 denotes a continuous annular pusher ring having a main portion slidably disposed in annular cavity 31. The left axial face thereof is provided with a continuous. axially extending rib 36 of generally rectangular configuration in crosssection. The numeral 38 denotes an auxiliary elastomer pusher plug member and of continuous annular configuration. In the undistorted state, the plug is of a radial dimension only slightly less than that of annular channel 31. The numeral 40 denotes the left face of pusher elastomer annulus 38 and it is seen that this face abuts the right axial face of elastomer annulus 16. Numeral 42 denotes the right axial face of pusher elastomer annulus 38. Preferably, adhesive is applied to the right face 42, and also within the annular depression of pusher 38 which receives rib 36, such that movement to the right of piston ring 34 will cause following motion of pusher elastomer 38.

To prepare the assembly apparatus the outer and inner fixture portions of 30 are located on the ring and on the hub, respectively. The two portions are then radially aligned with pusher element 34. The elastomer annulus 16 is inserted until its left face abuts surfaces 32. The pusher elements 34 and 38 are now inserted until the two elastomer elements abut each other.

The inertia and hub members 14 are now positioned as indicated at Figure 3. In this position, the continuous annular cavity between members 12 and 14 is aligned with the left portion of the annular cavity of surfaces 32. Thus, there is a smooth transition from the cavity of surfaces 32 to the cavity between the damper hub and inertia members. The annular elastomer element 16 is pushed laterally from right to left through annular cavity 31 of assembly fixture 30.

Prior to assembly, the annular elastomer member which forms element 16 of the completed assembly is in axial cross-section rectangular and is in the general form of a ring. Its radial thickness prior to assembly is slightly less than that of annular chamber 31, but is greater than the maximum radial thickness of the annular cavity between members 12 and 14. The annulus 16 is pushed in until its left face initially abuts the curved surfaces 32. The annular piston 34, which carries pusher elastomer bushing 38, is in a position so that its left face 40 abuts the right face of annular elastomer member 16. Preferably, a suitable lubricant is provided on those surfaces of the elastomer and metal which will be in sliding engagement.

The annular piston 34 is now pushed towards the left by any suitable mechanism, such as a fluid motor, for applying force to the right face of piston 34. With continued leftward motion of elastomer ring 16, pusher element 38, and piston 34, elastomer annulus 16 is radially and axially deformed and passes through the narrowest portion of the cavity surrounded by surfaces 32 and thence into the annular cavity between elements 12 and 14. Figure 3 illustrates the assembly process just after commencement, while Figure 4 illustrates the assembly process when approximately three-fourths complete. At the conclusion of the assembly process elastomer ring 16 will be positioned completely within the cavity between elements 12 and 14, as indicated in Figure 1.

Piston 34 is now moved in the opposite direction, i.e., towards the right, and by virtue of the adhesive bond between the right face of pusher annular elastomer 30 and the left face of piston 34 strengthened by the additional bond area produced by annular rib 36, the pusher elastomer is also drawn to the right and finally the piston is removed completely from the assembly fixture 30 and is ready for another damper assembly operation.

An advantage of the assembly apparatus shown at Figures 3 and 4 over the device shown at the noted Tarbox patent is that withdrawal of annular pusher piston 34 will bring with it the pusher elastomer, i.e., will withdraw the pusher elastomer from the annular cavity in assembly fixture 30. The maximum radial thickness of elastomer 16 at the central portion of the completed damper is somewhat smaller than its original radial thickness and accordingly its axial extent when assembled will be greater than its axial extent prior to assembly. If desired with certain types of elastomer, any bulge of elastomer 16 beyond the axial faces of the damper may be removed as by cutting.

One example of the utility of the damper of this invention over those commonly encountered in the prior art may be seen by reference to Figure 5. The left portion of Figure 5 illustrates a typical prior art construction and shows a portion only of a hub and an inertia ring. An assembly radius indicated by R is analogous to the assembly radius denoted by the numeral 23 in the noted patent to Henrich. The right portion of Figure 5 indicates the strain of the elastomer when the inertia ring and hub undergo an angular displacement relative to each other. The longest curve (straight line) indicates the corresponding strain on the right face A-A, while the shorter curve indicates a strain at the narrowest portion, i.e., at section B-B. The relatively short axial distance between the maximum compression at section B-B and zero compression at the face A-A causes a severe local strain gradient on the elastomer while the damper is responding to a vibration. In addition, the axial transition of the elastomer to the uncompressed state at A-A produces high static tensile stresses in the general position shown by C. In the present construction, the total strain, i.e., total radial deformation of the elastomer, may be as great as in prior art constructions, however, it is uniform, extending from the axial faces of the damper assembly to the center thereof.

The damper of the invention requires, by nature of the geometry of the elastomer annulus, that radial compression or deformation of the elastomer member be accomplished external to the confines of the annulus formed by the damper hub and inertia member. The external compression method of assembly is desirable both be cause of a lessening of the force required to mechanically cause compression, and because of a resultant higher structural integrity of the assembled damper. Both of these benefits arise because the assembly tooling can be designed to produce low friction characteristics in the compression section of the annulus, a characteristic that is not desirable in a damper that must resist inertial and external torques on the elastomer member.

The reader will note that the surface 12a, being the interface between the inertia ring and the elastomer annulus, is uniformly concave from one axial face to the other axial face of the ring. The exact shape of this interface 12 may be (in the illustrated axial cross-section) circular, parabolic, or a portion of a sine curve. The property of being uniformly concave and facing radially inwardly is equivalent to the property that the second derivative of the cruve (12a as shown at Figure 1) is continuous and of negative algebraic sign throughout the axial extent of the interface. The same mathematical property is exhibited by the other radial interface 14a which is between the hub and the elastic annulus. The only difference is that the algebraic sign of its second derivative is positive, to indicate a concave radially outwardly facing interface curve 14a. The mathematical reference system for these two second derivatives is the common Cartesian coordinate system, with the positive X-axis corresponding to the rightextending axis of rotation 18 of Figure 1.

WHAT WE CLAIM IS: 1. A torsional vibration damper having a hub coupled to a concentric outer inertia member by an annular elastomer member, the outer periphery of the hub and the inner periphery of the inertia member both being concave in axial cross-section, the extent of the concave portions in an axial direction being that of the axial thickness of the hub and the inertia member, said concave portions facing each other in a radial direction and the elastomer member having a radial thickness in its undeformed state which is greater than the maximum radial distance of the annular gap between the hub and the outer inertia member whereby the elastomer member is compressed upon insertion into the annular gap so that the member is deformed the greatest in a radial direction at its axial ends and the least in a radial direction between its ends, the hub and inertia member being each of a one-piece construction.

2. A damper as claimed in Claim 1 wherein the anglc. in axial cross-section between the concave surface and the axial end faces of the inertia member is an acute angle.

3. A damper as claimed in Claim 1 or Claim 2 wherein the angle, in axial crosssection between the concave surface and the axial end faces of the hub is an acute angle.

4. A damper as claimed in any of the preceding claims wherein nowhere within the annular cavity defined between the total axial extent of the outer surface of the hub and the total axial extent of the inner surface of the inertia member and containing the elastomer member in the assembled state is the elastomer member in an uncompressed state.

5. A damper as claimed in any of the preceding claims wherein the annular elastomer member is rectangular in axial crosssection prior to its assembly in the damper.

6. A damper as claimed in any of claims 1 to 5 wherein the axial cross-sectional shape of the interface between the said inertia member and the said elastomer annulus is such that the second derivative of the radius to the interface with respect to axial position is continuous and is negative, and wherein the axial cross-sectional shape of the interface between the said hub and the said elastomer annulus is such that the second derivative of the radius to that interface with respect to axial position is continuous and is positive, such derivatives referenced to a co-ordinate system in the plane of the section wherein the ordinate is radius, with zero at the axis of rotation of the damper, and the abscissa is axial position along the axis of rotation of the damper.

7. A torsional vibration damper constructed substantially as herein particularly described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cause of a lessening of the force required to mechanically cause compression, and because of a resultant higher structural integrity of the assembled damper. Both of these benefits arise because the assembly tooling can be designed to produce low friction characteristics in the compression section of the annulus, a characteristic that is not desirable in a damper that must resist inertial and external torques on the elastomer member. The reader will note that the surface 12a, being the interface between the inertia ring and the elastomer annulus, is uniformly concave from one axial face to the other axial face of the ring. The exact shape of this interface 12 may be (in the illustrated axial cross-section) circular, parabolic, or a portion of a sine curve. The property of being uniformly concave and facing radially inwardly is equivalent to the property that the second derivative of the cruve (12a as shown at Figure 1) is continuous and of negative algebraic sign throughout the axial extent of the interface. The same mathematical property is exhibited by the other radial interface 14a which is between the hub and the elastic annulus. The only difference is that the algebraic sign of its second derivative is positive, to indicate a concave radially outwardly facing interface curve 14a. The mathematical reference system for these two second derivatives is the common Cartesian coordinate system, with the positive X-axis corresponding to the rightextending axis of rotation 18 of Figure 1. WHAT WE CLAIM IS:

1. A torsional vibration damper having a hub coupled to a concentric outer inertia member by an annular elastomer member, the outer periphery of the hub and the inner periphery of the inertia member both being concave in axial cross-section, the extent of the concave portions in an axial direction being that of the axial thickness of the hub and the inertia member, said concave portions facing each other in a radial direction and the elastomer member having a radial thickness in its undeformed state which is greater than the maximum radial distance of the annular gap between the hub and the outer inertia member whereby the elastomer member is compressed upon insertion into the annular gap so that the member is deformed the greatest in a radial direction at its axial ends and the least in a radial direction between its ends, the hub and inertia member being each of a one-piece construction.