VIBRATION ATTENUATING MEANS

Abstract: Vibration attenuating means, particularly for use in engine mountings and vehicle suspensions, is arranged to attenuate the vibrations of a vibrating body (5). There is provided a lever (2) having a mass or weight (1) at one end and connected to one of the bodies (5) through a connection (6) located at an intermediate position along the lever. The other of the bodies (7) is attached to the lever (2) through a connection (3, 4) towards the end remote from the mass (1) and at least one of the connections (3, 4, 6) is an elastic connection. The arrangement enables a tunable resonant system to be formed within the assembly and attenuation occurs at frequencies above the resonant frequency of the system.

Description: Vibration Attenuating Means This invention relates to vibration attenuating means whereby, in connecting a vibrating body to another body the transmission of vibrations to the other body is reduced. Vibration attenuating means in the form of flexible or elastic mountings or connecting devices are commonly employed to reduce the transmission of vibrations from one body to another, for example in mounting a vehicle on its wheels and in mounting engines on vehicles. Often such devices use simple elastic connections with little inherent damping, the elements having such a stiffness or rigidity as to avoid resonance between the bodies within the range of likely disturbing frequencies. To reduce vibration transmissions still further at a particular frequency a dynamic absorber is sometimes used in addition to the elastic devices but such absorbers may require heavy absorber masses to be effective. In the connection between two bodies it is usually required to provide a given static stiffness having regard to the application. An object of the invention is to reduce the transmission of vibration forces from one body to the other above a chosen vibration frequency whilst maintaining the desired static stiffness. According to one aspect the invention provides vibration attenuating means for connecting two bodies, a first of which is subject to vibration and the second of which is to be attached to the first through means whereby the transmission of the vibrational movements of the first body is attenuated in its connection to the second body, wherein the attenuating means comprises a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever and connecting the first or second body to the lever, and a second connection connecting the lever to the second or first body respectively at an intermediate position on the lever remote from said mass, wherein at least one of said two connections is elastic. According to another aspect the invention provides a vehicle suspension system comprising a wheel constituting a first body which is subject to vibration, and a vehicle body constituting a second body, the wheel to be attached to the vehicle body through vibration attenuating means by which the transmission of vibrations from the wheel to the body is attenuated, the vibration attenuating means comprising a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever to the first body, and a second connection connecting the lever to the second body at an intermediate position on the lever remote from said mass, wherein at least one of said two connections is elastic. According to a third aspect the invention provides an engine mounting comprising an engine constituting a first body which is subject to vibration, and a frame constituting a second body, the engine to be mounted on the frame through vibration attenuating means by which the transmission of vibrations of the engine to the frame is attenuated, the vibration attenuating means comprising a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever to the first body, and a second connection connecting the lever to the second body at an intermediate position on the lever remote from said mass, wherein at least one of said two connections is elastic. Preferably there is provided a third connection which connects the lever to the same body as the second connection; the second and third connections being displaced from one another along the lever, and in which at least two of the first, second and third connections are elastic. Conveniently the first and second connections are elastic, the third connection is rigid and the lever is of rigid construction. Alternatively the first connection is rigid and the second and third connections are elastic. Alternatively the second connection may be a torsion spring acting as an elastic connection. In the vibration attenuating means the combined mass and polar moment of inertia of the mass, the stiffness/elasticity of the lever and its connections and the centre distances from the mass to the connections are located and selected according to the desired resonant frequency, attenuation characteristics and static stiffness. In one arrangement the lever, over at least part of its length, is elastic, the second connection is rigid, the first connection is elastic and any third connection is elastic or rigid. The second connection at one end of the lever may be a pivot connected to a first body which is subject to vibration; the first connection to the other body being elastic and the third connection to the first body may then be elastic. If the pivot incorporates a torsion spring the third connection may be omitted. Elastic connections may be formed of any suitable elastomeric material such as rubber and may be bonded to metal or otherwise secured. The elastomeric material may be loaded in tension, compression or in shear. Further features of the invention will appear from the following description of various embodiments of the invention given by way of example only and in which: Figs. 1A, IB and 1C are schematic diagrams of three embodiments of the invention, Fig. 2 is a side elevation of a practical embodiment of the invention for use in a vehicle suspension system. Fig. 3 is a plan view of the embodiment of Fig. 2, Fig. 4 is a side elevation of the rear suspension of a motor vehicle having a suspension damper mounting means similar to that illustrated in Figs. 2 and 3, Fig. 5 is a side elevation of an engine mounting means. Fig. 6 is a side elevation of an alternative form of engine mounting means. Fig. 7 is a graph showing the vibrational characteristics of the Fig. 4 embodiment compared with a conventional suspension, and Fig. 8 is a graph showing the characteristics of the embodiments of Figs. 5 and 6 in comparison with those of a conventional mounting. Referring to the drawings and firstly to Fig. 1A, there is shown an arrangement in which two bodies 5 and 7 are interconnected by vibration attenuating means comprising a lever 2 on one end of which is carried a mass or weight 1. The lever 2 is connected to the body 7 through a rigid connection 6 and the connection 6 is located part way along the lever 2. The body 5 is connected to the lever 2 through elastic connections 3 and 4 which are located displaced from the connection of the body 7 to lever 2 towards the end remote from the mass 1. In this arrangement the body 7 may be subject to vibrations and the body 5 insulated from such vibrations, or vice versa. Referring now to Fig. IB there is shown a similar arrangement to that of Fig. 1A in which the same reference numerals are used for similar parts. In this arrangement the body 5 is subject to vibrations and one of the elastic connections 3 and 4 of Fig. 1A is replaced by a rigid connection 4. Moreover the rigid connection 6 of Fig. 1A is replaced by a elastic connection. The body 7 is insulated from the vibrations of body 5. Referring to Fig. IC, the lever 2 is in this case elastic in the plane of the drawing, as shown, along its whole length or, alternatively, over that portion of the lever 2 including the connections 3, 4 and 6. The connection 4 is rigid as is the connection 6, the elasticity of the arm 2 providing the overall elasticity required. Alternatively the connection 4 and/or the connection 6 may be elastic. Either the body 5 or the body 7 is subject to vibration. Referring now to Figs. 2 and 3 in which the same reference numbers are used for equivalent parts, the connections 3 and 4 are elastic and comprise conventional bonded rubber units having linear and torsional elasticity in the vertical plane. The connections 3 and 4 are attached to the body 5 by means of a bracket 8. The lever 2 is rigid. The connection 6 may be a suspension damper unit connected to a body 7 which is subject to vibration, and the body 5 is to be insulated from such vibration. Fig. 4 shows an embodiment of the invention incorporated into the rear suspension of a motor vehicle, a wheel 13 constituting a vibrating body. Similar parts have the same reference numbers as in the previous embodiments. A connection 6 between the arm 2 and the wheel 13 and a wheel hub 14 is a suspension damper of known form. Conventional suspension springs 12 are also provided between the body 5 and a suspension lever 15 pivotally attached to the vehicle body in known manner. Vibration attenuating means is located between the damper 6 and the body 5 by the provision of the lever arm 2, mass 1 and elastic connecting means 3 and 4, all as previously described. The connecting means 3 and 4 may be of the form shown in Figs. 2 and 3 to give the desired static stiffness in combination with the desired attenuation characteristics. High road excited forces are normally transmitted to the vehicle body by the suspension damper 6 especially when vertical resonance of the unsprung mass of the tyre occurs. These forces are usually most apparent at road excited frequencies above 6Hz, and therefore attenuation above that frequency is desirable. Also the mounting characteristics must ensure that the damper is fully effective in damping the vertical resonance of the unsprung mass at about 14Hz. Referring now to Fig. 7 this shows for the Fig. 4 embodiment the vertical acceleration of the vehicle body measured at rear axle centre line, excitation being a vertical input under the rear tyres of 0.25 centimetres sinusoidal amplitude. Curve 1 shows the vertical response of a car having conventional rear damper mountings, and curve 2 is that of the same vehicle fitted with assembly according to Fig. 4 showing attenuation above 6Hz. It will be seen that the arrangement of Fig. 4 could also be adapted to connect the front dampers of a vehicle to the body. Referring now to Figs. 5 and 6 there is shown another embodiment of the invention particularly for use in mounting an engine in a motor vehicle. In Fig. 5 the body 5 is the vehicle engine which is subject to vibration. A body 7 is the vehicle body which is connected to the lever 2 through a rigid connection 6 and the lever 2 is also rigid. The lever 2 carries a mass or weight 1 at one end and towards the opposite end the lever 2 is connected to the engine 5 through elastic connections 3 and 4. In an alternative arrangement the connection 6 may be elastic. Referring to Fig. 6 the body 7 is the vehicle body which is connected to the lever 2 through an elastic connection 6. The lever 2 is connected to the engine 5 through an elastic connection 3 towards the end of the lever opposite to the mass 1 and through a pivotal connection 4, the pivot of the connection 4 being rigidly carried on the engine 5. In this arrangement the connection 6 may be rigid. In an alternative arrangement the pivotal connection 4 is an elastic connection which may include a torsion spring whereby pivoting is resiliently resisted. If a torsion spring arrangement is utilised the elastic connection 3 may be omitted. The connection 6 is, in the latter arrangement, elastic. Referring now to Fig 8 there is shown curves plotting a comparison of the force transmitted from the engine to the body for a simple conventional mounting, as shown at curve 1, and for the arrangement shown in Fig. 6, shown as curve 2. The static stiffnesses of both types of mounting are similar, as are their damping coefficients, in order to make a fair comparison. Curve 2 shows that at frequencies above 90Hz there is considerable attenuation, the frequency of 90Hz being the chosen resonant frequency of the mounting system. In each of the described embodiments the combined mass and polar moments of inertia of the mass 1 and the lever 2, the rigidity/elasticity of the lever 2 and of its connections, and the centre distances from the mass 1 to each of the connections all affect the resonant frequency of the assembly and the attenuation characteristics of the device. It is also necessary to have regard to the desired static stiffness of the device. These characteristics are optimised by computer simulation in order to obtain the desired attenuation characteristics for the application. Such simulation is within the scope of a person practised in the field of vibration dynamics.

Claims: Claims 1. Vibration attenuating means for connecting two bodies, a first of which is subject to vibration and the second of which is to be attached to the first through means whereby the transmission of the vibrational movements of the first body is attenuated in its connection to the second body, wherein the attenuating means comprises a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever and connecting the first or second body to the lever, and a second connection connecting the lever to the second or first body respectively at an intermediate position on the lever remote from said mass, wherein at least one of said two connections is elastic. 2. A vehicle suspension system comprising a wheel constituting a first body which is subject to vibration, and a vehicle body constituting a second body, the wheel to be attached to the vehicle body through vibration attenuating means by which the transmission of vibrations from the wheel to the body is attenuated, the vibration attenuating means comprising a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever to the first body, and a second connection connecting the lever to the second body at an intermediate position on the lever remote from said mass, wherein at least one of said two connections is elastic. 3. An engine mounting comprising an engine constituting a first body which is subject to vibration, and a frame constituting a second body, the engine to be mounted on the frame through vibration attenuating means by which the transmission of vibrations of the engine to the frame is attenuated, the vibration attenuating means comprising a lever having at or towards one end a mass or weight, a first connection located at an intermediate position along the lever to the first body, and a second connection connecting the lever to the second body at an intermediate position on the lever remote from said mass, wherein at least one said two connections is elastic. 4. The invention according to Claim 1, 2 or 3 wherein there is provided a third connection which connects the lever to the same body as the second connection; the second and third connections being displaced from one another along the lever, and in which at least two of the first, second and third connections are elastic. 5. The invention according to Claim 4 wherein the first and second connections are elastic, the third connection is rigid and the lever is of rigid construction. 6. The invention according to Claim 4 wherein the first connection is rigid and the second and third connections are elastic, and the first connection is constituted by a vehicle damper. 7. The invention according to any one of the preceding claims wherein the second connection includes a torsion spring acting as an elastic connection. 8. The invention according to any one of the preceding claims wherein the lever over at least part of its length is elastic, the second connection is rigid, the first connection is elastic and any third connection is elastic or rigid. 9. The invention according to any one of the preceding claims wherein the elastic connections or one of them includes elastomeric material to provide flexibility. 10. The invention according to any one of the preceding claims wherein the combined mass and polar moment of inertia of the mass and the lever, the elasticity/stiffness of the lever and its connections and the centre distances from the mass to each of the connections are located and selected according to the desired resonant frequency, attenuation characteristics and static stiffness.

Inventors: KNIGHT ROBERT JOSEPH, KNIGHT, ROBERT, JOSEPH
Applicants: KNIGHT ROBERT JOSEPH, KNIGHT, ROBERT, JOSEPH
Application year: 1991
Main classification: B60G13
IPC codes: B60G13, B60G15, B60K5, F16F7