TORSIONAL VIBRATION ISOLATOR AND METHOD

Abstract: An apparatus and method by which possibly destructive stress of torsion vibration in a rotating crankshaft/flywheel system of a multicylinder internal combustion engine is avoided by effectively isolating the flywheel (11) from the crankshaft (10) for torsional vibration considerations. The flywheel (11) and crankshaft (10) are coupled by a resilient coupling (12) which accommodates angular movement between the components and which has a torsional spring rate which is relatively low compared to the torsional spring rate of a conventional crankshaft/flywheel system. The coupling (12) reduces the natural frequency of torsional vibration of the system to a frequency well below the normal operating range of the engine in terms of revolution per minute, thereby substantially eliminating the effects of torsional vibration in the normal operating range of the engine.

Description: TORSIONAL VIBRATION ISOLATOR AND METHOD Field and Background of Invention This invention relates to multicylinder internal combustion engines and particularly to such engines having provision for protecting the rotating system formed by a crankshaft and a flywheel from stress other¬ wise induced by torsional vibration. It has long been recognized that the crankshaft and flywheel of a multicylinder internal combustion engine form a rotating system which has, because of the moments of inertia and coupling of the components, a natural or resonant frequency of torsional vibration. The pulsating forces applied to a crankshaft as a result of the firing of the cylinders of an engine give rise to such vibration and will, at certain rotational speeds, impose stress which will cause a crankshaft or the bearings supporting the crankshaft to fail. As is indicated in an important reference in the field of this invention (S.A.F. Paper SP-445 presented by Robert C. Fre er, Jr. at the West Coast International Meeting in Portland, Oregon, August 5-9, 1979), the usual approach in dealing with torsional vibration and stress in the environment of this invention is to analyze a crankshaf /flywheel system as if it were a simple torsional oscillator. In one approach to such an analysis, the moments of inertia of the components are re-solved about the crankpin closest to the flywheel and the system is treated as if the pin were a spring con- necting the portion of the crankshaft forward of the pin with the flywheel. The system may then be viewed as two masses (the crankshaft _and the flywheel) j oined by a springy connector (the pin) which has a torsional spring rate which determines the natural frequency of torsional vib ration of the system. The system may then be analyzed for harmonic f requencies which fall into the operating range of the engine (in revolutions per minute) or which combine with other frequencies in such a way as to generate stres s and pos s ibly become destructive. As such frequencies are found, dampers are designed for mounting on the end of the crankshaft remote from the flywheel for the purpose of damping out or reducing the vibration by dissipating energy. While such an approach has achieved some success, as evidenced by the commercially produced engines and vehicles which employ this technology, signif icant difficulty has been encountered in attempting to apply the technology to engines which have a wide range of operating speeds, and therefore encounter a wider range of possibly dangerous operating conditions . Brief Description of Invention With the foregoing in mind, it is an obj ect of this invention to avoid possibly destructive stress of tors ional vibration in a rotating crankεhaft/f lywheel system by effectively isolating the flywheel from the crankshaft ' for torsional vibration considerations. In realizing this object of the invention, the flywheel and crankshaft are coupled by a resilient coupling means which accommodates angular movement between the components and which has a torsional spring rate which is relatively low compared to the torsional spring rate of a conventional crankshaft/flywheel system. Yet a further object of this invention is to reduce the possibility of damaging stress in an engine having a crankshaft/fl heel system of the type described by reducing the natural frequency of torsional vibration of the system to a frequency well below the normal operating range of the engine in terms of revolutions per minute. Tn realizing this object of the present invention, the separation of the crankshaft and flywheel by the coupling mentioned hereinabove, and the selection of the spring rate for the coupling, enables selection of the frequency so as to substantially eliminate the effects of torsional vibration in the normal operating range of an engine. Brief Description of Drawings Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which: Figure 1 is an elevation view of components of a multicylinder internal co bustion engine and illustrating the present invention; Figure 2 is an enlarged elevation view of a coupling element used in the apparatus of Figure 1; Figure 3 is a perspective view of the element of Figure 2 ; and Figure 4 is an enlarged elevation view, partly in section, of certain of components of Figure 1. Detailed Description-of Invention While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosu re di rected to persons of skill in the appropriate arts, and not as limiting upon the present invention . Re f e r r ing n ow mo r e pa rt i c ul a r ly t o t he accompanying draw ings , a multicyl inde r internal combustion engine has a numbe r of elements which cooperate to enable the engine to operate, as is well known to skilled mechanics. Fo r purposes of simplifying the drawings, only certain elements have been shown or suggested, and it is left to the knowledge of the skilled person to understand the simplification which has been made for purposes of clarity. Those elements of signif icance to this invention are the crankshaft generally indicated at 10 in Figure 1 and the - 5 - flywheel generally indicated at I]. Conventionally, the flywheel is attached to the end of the crankshaft adjacent a clutch, transmission and starter (none of which are shown) and remote from such accessories as a belt driven water pump and fan. In many conventional engines, and particularly in high performance engines used for such purposes as auto¬ motive racing, marine applications and aviation, the flywheel serves few if any useful purposes beyond per- mitting engagement of the engine with a starter and with a clutch. The more conventional reasons for having a flywheel, relating to providing an inertial mass, are simply irrelevant. However, the problems created by the presence of the inertial mass, and particularly those relating to the effects of torsional vibration, remain. Further, the conventional approach described above and relying on the use of dampers to absorb energy is not capable of avoiding catastrophic failure of engines. The present invention provides an alternative which is successful in such an environment, and is also of more general utility. More particularly, in a multicylinder internal combustion engine having a rotatable crankshaft 10 and a rotatable flywheel 11, the improvement of this invention facilitates avoiding destructive effects on the crankshaft of stress induced by torsional vibration by providing a resilient coupling means generally indicated at 12 which is interposed between the crankshaft 10 and flywheel 11 (Figure 2 through 4) for coupling the crankshaft and flywheel together for rotation of the flywheel with the crankshaft. In accordance with an important feature of this invention, the resilient coup- ling means has a low torsional spring rate effective for isolating the rotating inertia of the flywheel from the rotating inertia of the crankshaft for purposes of torsional vibration considerations. In particular, the coupling means takes the form of an annulus of resilient material, preferably an elastomer such as rubber, opera- tively interposed between the crankshaft and flywheel and having a low torsional spring rate effective for reducing the natural frequency of torsional vibration of the rotating system defined by the crankshaft and fly- wheel to a predetermined low frequency. In one opera¬ ting embodiment in accordance with this invention, the resilient material annulus has a torsional spring rate of less than 20,000 in-lb/radian and is effective to reduce the natural frequency of torsional vibration of the rotating system defined by the crankshaft and fly¬ wheel to a frequency below fifty Hertz. In order to accomplish coupling of the crankshaft and flywheel, the crankshaft and flywheel are provided with means for permitting coupling thereof while accommodating relative rotation therebetween. The crankshaft 11 has means defining a driving flange 14 and a bearing surface 15, while the flywheel has means defining a bearing 16 for engaging the bearing surface of the crankshaft. Both the crankshaft 10 and flywheel 11 have a plurality of lugs, with the crankshaft having a plurality of driving lugs 18 extending from the driving flange at predetermined locations encircling the axis of rotation of the crankshaft and the flywheel having a plurality of driven lugs 19 extending therefrom at pre¬ determined locations encircling the axis of rotation of the flywheel. The resilient material annulus encircles the bearing surface 15 and the bearing 16 and is enclosed by the driving flange 14 and flywheel 11. The annulus or coupling means 12 has a plurality of openings or holes therein sized to fit snugly onto the lugs 18, 19. Thus, by means of the bearing surface and bearing and the resilient connection established by the coupling means 12, the flywheel and crankshaft are in driving relation one to another while having a substantial degree of relative rotation possible therebetween, against the spring force of the coupling means. In operation, the coupling means has sufficient rigidity to accommodate starting of the engine by a starter engaging the flywheel and transmission of driving force to a load. However, the coupling means has sufficient resilience that an analysis of the rotating system, for torsional vibration considerations, proceeds on the basis that the inertial mass of the crankshaft taken as a whole is coupled to the inertial mass of the flywheel taken as a whole through a component with a significantly lower torsional spring rate than has heretofore been the case. Thus, as the natural frequency of torsional vibration is a known factor of the moments of inertia of the two masses of a torsional oscillator and the spring rate through which they are coupled (equal to the square root of a value . determined by dividing the product of the spring rate times the sum of the moments by the product of the moments), decreasing the spring rate decreases the natural frequency and accomplishes a lowering to a range effectively below the operating range of the engine. For example, a natural frequency below 50 Hertz corresponds to an engine speed below 3000 revolutions per minute, which is below the operating speed of many engines with which this invention finds utility. Conversely, the ability to control the natural frequency of a crankshaft/flywheel system opens the possibility of adapting the teaching of this invention to engines of other types, sizes, and ranges. In use, the isolation of the flywheel from the crankshaft for torsional vibration considerations, and the arrangement as described hereinabove, permits the flywheel to rotate relative to the crankshaft in such a way that the excursion or angular difference between the rotational positions of those elements may be several degrees, depending upon forces being transmitted and the particular spring constant being used. Such an excursion, in the present invention, is advantageous as assuring that the rotating system is being properly protected from the otherwise possibly adverse effects of torsional vibration, and is not deemed disadvantageous. In the drawings and specifications there has been set forth a preferred embodiment of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation.

Claims: What is claimed is: 1. In a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel, an improvement which facilitates avoiding destructive effects on the crankshaft of stress induced by torsional vibration and comprising resilient coupling means inter¬ posed between the crankshaft and flywheel for coupling the crankshaft and flywheel together for rotation of the flywheel with the crankshaft, said resilient coupling means having a low torsional spring rate effective to permit substantial angular displacement between the flywheel and the crankshaft for isolating the rotating inertia of the flywheel from the rotating inertia of the crankshaft after engine startup for purposes of avoiding damping while preventing torsional vibration from being transferred between the flywheel and the crankshaft. 2. In a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel, an improvement which facilities avoiding destructive effects on the crankshaft of stress induced by torsional vibration and comprising resilient coupling means inter¬ posed between the crankshaft and flywheel for coupling the crankshaft and flywheel together for rotation of the flywheel with the crankshaft, said resilient coupling means having a low torsional spring rate effective to permit substantial angular displacement between the flywheel and the crankshaft for isolating the rotating inertia of the flywheel from the rotating inertia of the crankshaft after engine startup for purposes of avoiding damping while preventing torsional vibration from being transferred between the flywheel and the crankshaft and reducing the natural frequency of torsional vibration the rotating system defined by the crankshaft and fly¬ wheel to a predetermined low frequency. 3. Apparatus according to one of Claim 1 and Claim 2 wherein the crankshaft and flywheel together define a rotating inertial system subject to torsional vibration and further wherein said coupling means comprises an annulus of resilient material operatively interposed between the crankshaft and flywheel for coupling the crankshaft and flywheel together. 4. Apparatus according to Claim 3 wherein the crankshaft has means defining a driving flange and a bearing surface, the flyv/heel has means defining a bearing for engaging the bearing surface of the crankshaft, and said resilient material annulus encircles the bearing surface and the bearing and is enclosed by the driving flange and flywheel. 5. Apparatus according to Claim 4 wherein the crankshaft has a plurality of driving lugs extending from the driving flange at predetermined locations encircling the axis of rotation of the crankshaft for engaging said resilient material annulus and the flywheel has a plurality of driven lugs extending therefrom at predetermined locations encircling the axis of rotation of the flywheel for engagement with said resilient material annulus. 6. Apparatus according to Claim 4 wherein said resilient material annulus is of an elastomeric material. 7. Apparatus according to Claim 6 wherein said resilient material annulus has a torsional spring rate of less than 20,000 in-lb/radian. 8. Apparatus according to Claim 2 wherein said resilient material annulus is effective to reduce the natural frequency of torsional vibration of the rotating system defined by the crankshaft and flywheel to a predetermined low frequency below fifty Hertz. 9. In a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel which together define a rotating inertial system subject to torsional vibration, an improvement which facilitates avoiding destructive effects on the crankshaft of stress induced by torsional vibration and comprising the crankshaft having means defining a driving flange and a bearing surface and a plurality of driving lugs extending from the driving flange at predetermined locations encircling the axis of rotation of the crankshaft, the flywheel having means defining a bearing for engaging the bearing surface of the crankshaft and a plurality of driven lugs extending from the flywheel at predetermined locations encircling the axis of rotation of the flywheel, and an annulus of elastomeric material operatively interposed between the crankshaft and flywheel and engaging said driving and driven lugs for coupling the crankshaft and flywheel together for rotation of the flywheel with the crankshaft, said elastomeric material annulus having a torsional spring rate of less than 20,000 in-lb/radian and being effective for reducing the natural frequency of torsional vibration of the rotating system defined by the crankshaft and flywheel to a predetermined low frequency below fifty Hertz. 10. A method of protecting the components of a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel against destructive effects on the crankshaft of stress induced by torsional vibration and comprising the steps of mounting the flywheel for rotation relative to the crankshaft, and interconnecting the crankshaft and flywheel with a coupling which joins the crankshaft and flywheel together for rotation of the flywheel with the crankshaft while isolating the rotating inertia of the flywheel from the rotating inertia of the crankshaft for purposes of torsional vibration considerations. 11. A method of protecting the components of a multicylinder internal combustion engine having a rotatable crankshaft and a rotatable flywheel against destructive effects on the crankshaft of stress induced by torsional vibration and comprising the steps of mounting the flywheel for rotation relative to the crankshaft, and interconnecting the crankshaft and flywheel with a coupling which joins the crankshaft and flywheel together for rotation of the flywheel with the crankshaft while reducing the natural frequency of torsional vibration of the rotating system defined by the crankshaft, coupling and flywheel to a predetermined low frequency. . 12. A method according to one of Claims 10 and 11 wherein said step of interconnecting the crankshaft and flywheel comprises selecting a coupling which is an annulus of a resilient elastomeric material. 13. A method according to Claim 12 wherein said step of selecting a coupling further comprises selecting a resilient material annulus which has a torsional spring rate of less than 20,000 in-lb/radian. 14. A method according to Claim 12 wherein said step of selecting a coupling further comprises selecting a resilient material annulus which is effective to reduce the natural frequency of torsional vibration of the rotating system defined by the crankshaft and flywheel to a predetermined low frequency below fifty Hertz.

Applicants: KNITTED SLEEVE OVERSEAS LTD, KNITTED SLEEVE (OVERSEAS) LTD.
Application year: 1986
Main classification: F16D3
IPC codes: F16D3, F16F15