Abstract:
The present invention features an insulator unit for supporting a suspension arrangement on a chassis or the like. The main elastomeric body of the insulator is arranged to have sufficient rigidity as to limit the displacement of the suspension with respect to the chassis. The device further includes a vibratory mass or masses which upon being excited cancel vibrations which would otherwise be transmitted through the main elastomeric member.

Description:
BACKGROUND OF THE PRESENT INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a suspension such as that used in an automotive vehicle and more specifically to an insulator or bush arrangement therefor which simultaneously provides good rigidity and vibration damping characteristics. 
     2. Description of the Prior Art 
     In nearly all suspension arrangements (for example see Nissan Service Weekly Vol. 401 November 1979 page 98), a problem is encountered in that elastomeric bushes interposed between members subject to vibration and a chassis or base which is to be isolated from the vibrations, such as the chassis of an automotive vehicle, are required to simultaneously support large weights (e.g. a vehicle chassis) and absorb relatively high frequency vibration. However, in order to provide the required rigidity and therefore support (viz., resistance to displacement), the insulator is required to be relatively hard. However, in order to absorb relatively high frequency vibration the elastomer used in the insulator should be relatively soft. Accordingly, in view of this conflict it is quite difficult to provide an arrangement which will adequately provide both functions. 
     One attempt to acheive the required characteristics is disclosed in Nissan Service Weekly issued in June 1980. This arrangement features the provision of a dynamic vibration damping device which is attached to a member of the suspension subject to vibration. This device upon being excited by vibration produces a similar vibration but with a 180 degree phase difference. The vibration produced by the dynamic damper and that which excites same, neutralize each other. This arrangement while proving effective undesirably increases the complexity and weight of the vehicle or device to which it is applied. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an insulator for a suspension which is simple and which simultaneously provides adequate rigidity and good vibration damping characteristics via the inclusion of a dynamic damping mechanism therein. 
     In brief, the above object is fullfilled by a insulator arrangement wherein the main elastomeric member is sufficiently rigid to limit displacement and which is provided with a vibratory or vibratile mass or masses which upon vibrating cancel vibrations which would otherwise be transmitted through the main elastomeric body. 
     More specifically, the present invention takes the form of a insulator for supporting a structural member subject to vibration on a chassis comprising: a first member connected to one of the structural member and the chassis a second member connected to the other of the structural member and the chassis, a first elastomeric body interconnecting the first and second members, a mass and a second elastomeric body which interconnects the mass and one of the first and second members, the mass being arranged to vibrate and suppress the transmission of vibration from the structural member to the chassis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the arrangement of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a sectional view of a first embodiment of the present invention; 
     FIG. 2 is a section taken along section line II--II of FIG. 1; 
     FIG. 3 is a partial plan view of a suspension member of a semi trailing arm type suspension which is connected to a chassis via insulators according the present invention; 
     FIG. 4 is a graph showing in terms of vibration reduction produced by the dynamic damping vibratory masses and the weight of the masses, the performance characteristics obtained with the present invention when the mass of the vibratory masses are varied; and 
     FIG. 5 is a graph showing in terms of the vibration reduction provided by the vibratory masses and the displacement of the masses from the end of the suspension member to which the insulator according to the present invention is applied the performance characteristics obtained with the present invention when the mass of the vibratory masses is held constant and the displacement thereof with respect to the ends of the previously mentioned suspension member is varied. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show an embodiment of the present invention. In this arrangement coaxially arranged tubular inner and outer members 10, 12 are interconnected by a main elastomeric body 14. This body 14, as shown, includes pairs of plates 16 which are arranged parallel to each other and the axis about which the inner and outer members are coaxially arranged. The elastomeric body 14 is so shaped as to define spaces 18 within the outer tubular member 12. Masses 20 are disposed within the spaces 18 and connected with the outer tubular member 12 by auxiliary elastomeric members 22. The masses 20 are preferably arranged diametrically opposite one another in a symmetrical manner and so as to be sufficiently spaced from the inner and outer tubular members 10, 12 and the main elastomeric body 14 so that upon vibration they do not contact either the main elastomeric body 14 or the outer tubular member 12. The masses 20 may be formed of any material having a high density but are preferably selected from materials which can be securely bonded or vulcanized to the auxiliary elastomeric members 22. 
     FIG. 3 shows one of the above described insulators in a semi trailing arm type suspension. In this arrangement the insulators are disposed in suitable recepticle-like arrangements formed at each end of a suspension member 24 which extends laterally across the vehicle chassis (not shown). In this arrangement the inner tubular members 10 are connected to the chassis by bolts. The insulators are arranged to suspend the suspension member 24 in a manner that displacement of the suspension member 24 in the fore-and-aft direction of the vehicle shears the main elastomeric member 14 while left-right lateral movement compresses same. 
     By suitably selecting the mass of the masses 20 and the elastomer constituting the auxiliary elastomeric bodies 22, it is possible to endow on the system resonance characteristics which cause the masses 20 to vibrate at frequencies at which the main elastomeric member 14 fails to provide the desired characteristics but with a 180 degree phase difference. With this, vibration which excites the masses is neutralized by the vibration produced by same. 
     It should be noted that with the above described suspension arrangement, as the insulators are disposed at each end of the suspension member 24, the load applied to the vehicle body due to the primary sympathetic bending vibration can be effectively reduced. 
     There are two distinct moments produced by each of the masses 20. The first is defined between the center of mass of each mass 20 and the resilent center of each auxiliary elastomeric body 22. The second is defined between the center of the shaft which is disposed through the inner tubular member 10 and the center of mass of each mass 20. However, as each of the masses 20 in the illustrated embodiment are symmetrically arranged with respect to the aformentioned connecting shaft center, the moments mutually cancel each other and thus the device is able to effectively damp vibration in the direction &#34;X&#34; indicated by the arrow in FIG. 2. 
     FIG. 4 shows the variation in damping characteristics which occurs as the mass of the masses 20 are varied (other variables being held constant). From this graph it is possible to select the appropriate mass for the particular vibration which is required to be damped. 
     FIG. 5 is a graph plotted in terms of the vibration reduction provided by the invention and the distance of each mass from the end of the suspension member 24 and wherein the mass of the masses are held constant (at one 1 Kgm for example). 
     As will be apparent from the above graphs the present invention may provide satisfactory vibration damping characteristics simply by being provided at each end of a suspension member and without detrimental effect by the smallness of the vibratable masses per se. 
     Although the masses 20 of the above embodiment are disclosed as having identical vibrational characteristics, it is possible to arrange the masses 20 to each have a different mass and the elastomers constituting each of the auxiliary elastomeric bodies to have different spring characteristics. This makes it possible for each insulator to have at least two vibrational damping frequencies and thus be effective over a wider vibrational frequency range. However, with this kind of arrangement it is desirable to arrange same so that the sum of the respective moments is not excessively large. Furthermore, it is possible to connect the vibratory masses 20 to the inner member 10 or to the exterior of the outer tubular member 12 so long as the masses 20 may be permitted to move without interference from adjacent elements. 
     Thus, with the present invention it is possible to provide a single insulator unit wherein the main elastomeric body is sufficiently rigid as to provide the desired displacement limiting functions but which due to the provision of the resonating masses therein is able to damp the transmission of vibration which would otherwise be permitted to reach the chassis of the vehicle or the like.