Abstract:
A fluid-filled type vibration-damping device having a movable rubber plate housed within a partition member partitioning a pressure-receiving chamber and an equilibrium chamber from each other. The movable rubber plate is moved owing to the pressure difference between the two chambers. The movable rubber plate comprises the movable rubber plate formed of a generally disk shaped rubber elastic body having formed thereon in alternating fashion concave grooves and convex ribs each extending in a circumferential direction about a same center axis, the convex ribs have tapered cross section gradually narrowing in width towards an distal end thereof, and the concave grooves and convex ribs are disposed at the same locations in a diametrical direction on either face of the movable rubber plate so that the thickness of the movable rubber plate is varied in the circumferential direction.

Description:
INCORPORATED BY REFERENCE 
   The disclosure of Japanese Patent Application No. 2005-077975 filed on Mar. 17, 2005 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a fluid-filled type vibration-damping device designed to produce vibration damping effect on the basis of flow action of a non-compressible fluid sealed within its interior; and more particularly to a fluid-filled type vibration-damping device having a flexible plate as a fluid pressure absorbing mechanism. 
   2. Description of the Related Art 
   Rubber vibration dampers comprising a first mounting member and a second mounting member connected by a main rubber elastic body are widely employed in a variety of fields as vibration-damped connectors or vibration-damped supports installed between components that make up a vibration transmission system. As one type of rubber vibration damper of this kind, there have been proposed fluid-filled type vibration-damping devices that utilize resonance or other flow action of a non-compressible fluid sealed within the device. As one such vibration-damping device, there is known a fluid-filled type vibration-damping device that typically comprises: a first mounting member and a second mounting member attached respectively to a vibration-damped member and a vibrating member and connected together by a main rubber elastic body; a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body and that gives rise to pressure fluctuations when vibration is input; an equilibrium chamber whose wall is partially constituted by a flexible film and which allows change in volume; a non-compressible fluid sealed within the pressure-receiving chamber and the equilibrium chamber; and an orifice passage interconnecting the two chambers. 
   Vibration damping effect based on resonance of the non-compressible fluid induced to flow through the orifice passage is achieved only in the specific frequency range to which the device has been pre-tuned. Accordingly, in order to improve vibration damping ability, while avoiding markedly high dynamic spring constant exhibited particularly when vibration of a higher frequency range than the tuning frequency of the orifice passage is input, there has been proposed a fluid pressure absorbing mechanism, which employs a movable plate. The fluid pressure absorbing mechanism is typically constructed by forming a housing space in the partition member that divides the pressure-receiving chamber and the equilibrium chamber, and disposing a movable plate housed within this housing space so as to permit minute displacement thereof. The housing space connects with the pressure-receiving chamber and the equilibrium chamber via through-holes, and pressure in the pressure-receiving chamber is exerted on one face of the movable plate, while pressure in the equilibrium chamber is exerted on the other face. 
   Displacement of the movable plate based on a pressure differential between the pressure-receiving chamber and the equilibrium chamber enables minute pressure fluctuations produced in the pressure-receiving chamber during input of vibration in the high-frequency range to escape into and be absorbed in the equilibrium chamber. During input of vibration of the low-frequency range to which the orifice passage has been tuned, on the other hand, due to the large amplitude of the vibration, the movable plate is forced into contact against the inside face of the housing space, and in a state of being juxtaposed or superimposed against it substantially blocks off the through-hole. Consequently, absorption of pressure of the pressure-receiving chamber by the fluid pressure absorbing mechanism is avoided, so that the relative pressure fluctuations are produced effectively in the pressure-receiving chamber and the equilibrium chamber, ample fluid flow through the orifice passage between the two chambers is assured, and vibration damping action is produced by the orifice passage. 
   In this kind of fluid pressure absorbing mechanism, when sharp pressure fluctuations are produced in the pressure-receiving chamber by input of large-amplitude vibration, the movable plate is caused to strike forcefully against the inside wall of the housing space. A resultant problem is that the impact of the movable plate striking against the inside wall of the housing space tends to produce noise and vibration. For example, where employed as an automotive engine mount, noise that is audible to the driver can be produced during engine cranking or when driving over bumps, which poses the risk of contributing to diminished drive feel. 
   To address such problems, it has been proposed, for example in JP-Y2-4-33478, to fabricate the movable plate from a rubber elastic plate, and to integrally form a small projection of rib form on the surface thereof, whereby the impact of striking can be absorbed by this small projection. However, while such a small projection has been found effective against striking at relatively low energy, in the event of a sudden large pressure fluctuation in the pressure-receiving chamber, adequate effectiveness is not readily achieved, making further improvement desirable. 
   SUMMARY OF THE INVENTION 
   It is therefore one object of this invention to provide a fluid-filled type vibration-damping device furnished with a movable plate of novel construction able to consistently and effectively prevent noise from occurring when the movable rubber plate comes into contact with the partition member. 
   The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. The following modes and/or elements employed in each mode of the invention may be adopted at any possible optional combinations. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety. 
   A first mode of the invention provide A fluid-filled type vibration-damping device for elastically connecting two components making up a vibration transmission system in a vibration damping fashion, the device comprising: a first mounting member adapted to be attached to one of the two components; a second mounting member adapted to be attached to an other one of the two components; a main rubber elastic body elastically connecting the first and second mounting members; a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body having a non-compressible fluid sealed therein, and into which vibration is input; an equilibrium chamber having the non-compressible fluid sealed therein, whose wall is partially constituted by a flexible film that readily permits change in volume of the equilibrium chamber; a partition member supported by the second mounting member and positioned such that the pressure-receiving chamber and the auxiliary fluid chamber are disposed on either side thereof; an orifice passage through which the pressure-receiving chamber and the equilibrium chamber communicate with each other; and a movable rubber plate is housed within a housing space provided in the partition member, the housing space formed with through-holes for connecting the housing space to the pressure-receiving chamber and the equilibrium chamber respectively so that the pressure in the pressure-receiving chamber is exerted on a first face of the movable rubber plate while pressure in the equilibrium chamber is exerted on an other face so that small pressure fluctuations produced in the pressure-receiving chamber during vibration input escape to and are absorbed by the equilibrium chamber via the movable rubber plate, wherein the movable rubber plate is formed of a generally disk shaped rubber elastic body, and has at least one concave groove and at least one convex rib formed in alternating fashion on each of the first face and the other face of the movable rubber plate, extending in a circumferential direction about a same center axis, and wherein each of the convex ribs has tapered cross section gradually narrowing in width towards an distal end thereof, and the at least one concave groove and convex rib on the first face and the at least one concave groove and convex rib on the other face are disposed at the same locations in a diametrical direction, respectively, so that the thickness of the movable rubber plate is varied in the circumferential direction. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, the distal end of the convex ribs formed on either side of the movable rubber plate have tapered cross section that gradually narrows in width towards the distal end. Accordingly, in the event that the convex ribs undergo elastic deformation due to pressure resulting from the movable rubber plate contacting the housing space wall during input of large-amplitude vibration, the area of contact between the movable rubber plate and the housing space wall increases gradually. Consequently, it becomes possible to prevent a sharp rise in pressure due to the movable rubber plate striking the housing space inside wall when vibration is input, and to effectively prevent striking noise from occurring due to the sharp rise in pressure. 
   By forming the convex ribs so as to extend in the circumferential direction, when convex ribs are caused to undergo elastic deformation as the movable rubber plate comes into contact against the housing space inside wall, the convex ribs will be consistently caused to undergo compressive deformation without producing bending or other unwanted deformation, whereby impact absorbing effect may be achieved in a highly reliable manner. 
   By means of appropriately establishing the slope angle and curvature of the sloping faces and curving faces making up the convex ribs, or the projecting height thereof, it is possible to readily adjust the pressure produced when the partition member and the movable rubber plate come into contact, and to establish, in accordance with the required tuning accuracy, the level of absorption of the energy of contact associated with elastic deformation of the movable rubber plate. 
   On the front and back faces of the movable rubber plate, the concave grooves are situated at the same locations in the diametrical direction, and the convex ribs are situated at the same locations in the diametrical direction. Consequently, the convex ribs of the movable rubber plate reliably undergo compression and elastic deformation in the axial direction by means of the pressure created when the movable rubber plate strikes against the housing space, thus assuring highly consistent suppressing effect against striking noise. 
   A second mode of the invention provide a fluid-filled type vibration-damping device according to the first mode, wherein on each of the first and other faces, a plurality of the concave grooves extending in the circumferential direction are formed in a concentric arrangement, and the convex rib is formed diametrically between neighboring concave grooves, so as to extend in the circumferential direction. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, there are formed a plurality of concave grooves, and convex ribs extending in the circumferential direction are formed diametrically between neighboring concave grooves. With this arrangement, bulging deformation of the convex ribs in the diametrical direction of the movable rubber plate is permitted by means of the concave grooves that are located to either side of each convex rib in the diametrical direction of the movable rubber plate. Consequently, compressive deformation in the projection direction of the convex ribs in association with bulging deformation thereof in the diametrical direction of the movable rubber plate is readily permitted, and it is possible to advantageously absorb pressure fluctuations that cause noise of the movable rubber plate striking against the housing space during vibration input. 
   A third mode of the invention provides a fluid-filled type vibration-damping device according to the first or second mode, wherein each of the convex ribs is formed extending in the circumferential direction with a generally triangular cross section, and a slope angle: α of sloping faces making up side walls of each of the concave grooves is such that 45&lt;α&lt;90°. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, by imparting triangular shape to the cross section of the convex ribs, contact pressure which can produce noise when coming into contact against the housing space inside wall can be dispersed successfully through elastic deformation, whereby striking noise can be prevented. With the movable rubber plate in a state of initial contact having come into contact against the housing space, the projecting distal ends of the convex ribs come into linear contact against the housing space, and thus the area of contact can be made extremely small, and high impact absorbing action can be achieved during the initial contact period. Additionally, by establishing the slope angle: a of the sloping faces making up the side walls of the concave grooves such that 45°&lt;α&lt;90°, an adequate angle at the projecting distal end of the convex rib may be assured, whereby bending of the projecting distal end due to pressure at the time of contact can be advantageously prevented, and excellent shock absorbing effect can be consistently achieved. 
   A fourth mode of the invention provides a fluid-filled type vibration-damping device according to any of the first to third modes, wherein a projecting distal end of each of the convex ribs has a curving face. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, by constituting the projecting distal end of the convex rib as a curving face, it is possible to more advantageously avoid bending deformation of the projecting distal ends of the convex ribs when the movable rubber plate comes into contact with the housing space inside wall, and to consistently prevent the occurrence of noise. Additionally, when the movable rubber plate and the housing space come into contact, the zones of contact of the movable rubber plate with the housing space are linear, and the area of contact is extremely small. Consequently, excellent impact absorbing ability can be realized immediately upon contact. 
   A fifth mode of the invention provides a fluid-filled type vibration-damping device according to any of the first to fourth modes, wherein each of the concave grooves is formed so as to extend continuously in the circumferential direction with a generally V shaped cross section. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, by forming the concave groove with a generally V shaped cross section extending continuously in the circumferential direction, a sufficient level of elastic deformation of the convex ribs is permitted while assuring adequate rigidity of the movable rubber plate as a whole, making it possible to achieve stable operation. 
   A sixth mode of the invention provides a fluid-filled type vibration-damping device according to any one of the first to fifth modes, further comprising a positioning member for positioning the movable rubber plate with respect to the partition member such that the movable rubber plate is positioned within the housing space so that at a minimum the through-holes are positioned over the concave groove. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, the movable rubber plate is arranged so that by means of the positioning member, it is positioned within the housing space in such a way that, at a minimum, the through-hole is positioned over the concave groove, whereby in the event that the side walls of the concave groove undergo elastic deformation in association with elastic deformation of the convex rib when vibration is input, the non-compressible fluid located within the concave groove will escape out through-hole and into the pressure-receiving chamber or the equilibrium chamber. Consequently, bulging deformation of the convex ribs in the diametrical direction of the movable rubber plate produced in association with compressive deformation of the convex ribs in the direction of projection can be achieved unhindered by non-compressible fluid sealed within the concave groove, and impact force produced when the movable rubber plate is forced into contact with the housing space can be more advantageously absorbed through elastic deformation of the convex ribs. 
   A seventh mode of the invention provides a fluid-filled type vibration-damping device according to the sixth mode, wherein the positioning member comprises a mating portion of irregular shape for positioning the movable rubber plate with respect to the partition member that is situated at an approximate diametrical center of the movable rubber plate. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, by constituting the positioning member of a mating portion situated in the diametrical center, it is possible to advantageously assure a gap between the movable rubber plate and the housing space in the diametrical direction, and to permit an adequate level of elastic deformation of the convex rib situated outmost on the movable rubber plate in the diametrical direction thereof, whereby the effect of suppressing striking noise through elastic deformation of the convex ribs can be advantageously achieved. Additionally, since a sufficient gap is assured between the outside peripheral face of the movable rubber plate and the housing space side wall during production, control of the diametrical size of the movable rubber plate can be carried out easily. 
   An eighth mode of the invention provides a fluid-filled type vibration-damping device according to any of the first to seventh modes wherein the first face of the movable rubber plate is identical in shape to the other face. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, there is no need to distinguish between front and back of the movable rubber plate when assembling the movable rubber plate to the partition member, thereby preventing misassembly during the assembly operation, making for a more efficient assembly operation. 
   A ninth mode of the invention provides a fluid-filled type vibration-damping device according to any one of the first to eighth modes wherein the through-holes are formed only to a diametrical inner peripheral side from a location of the convex rib formed most outwardly in the diametric direction of the movable rubber plate. 
   In the fluid-filled type vibration-damping device constructed in accordance with this mode, during input of low-frequency, large-amplitude vibration, all of the through-holes are substantially blocked off by means of the movable rubber plate coming into contact with the housing space inside wall, whereby fluid flow between the pressure-receiving chamber and the equilibrium chamber through the housing space can be blocked off. Consequently, in the event of input of vibration in the low-frequency range to which the orifice passage has been tuned, relative pressure fluctuations of the pressure-receiving chamber and the equilibrium chamber are advantageously assured, and high vibration damping capability can be achieved. 
   As will be apparent from the preceding description, in the fluid-filled type vibration-damping device constructed in accordance with the invention, the planar area of the portions at which the distal ends of the convex ribs formed on the movable rubber plate are in contact with the partition member expands gradually with an increase in pressure, whereby it is possible to suppress or avoid striking noise due to a sharp rise in contact pressure in association with a sharp increase in the contact area. 
   Additionally, the concave groove formed between neighboring convex ribs permits bulging deformation of the convex ribs in the diametrical direction, so that compressive deformation in the axial direction is unhindered. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The forgoing and/or other objects features and advantages of the invention will become more apparent from the following description of a preferred embodiment with reference to the accompanying drawings in which like reference numerals designate like elements and wherein: 
       FIG. 1  is an elevational view in axial or vertical cross section of a fluid-filled engine mount in the form of an engine mount of construction according to a first embodiment of the invention; and 
       FIG. 2  is an elevational view in axial or vertical cross section of an engine mount of construction according to a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring first to  FIG. 1 , there is shown an automotive engine mount  10  as a first embodiment of the invention. The engine mount  10  comprises a first mounting member  12  of metal and a second mounting member  14  of metal, and a main rubber elastic body  16  elastically connecting the first and second mounting members  12 ,  14 . The engine mount  10 , in cooperation with another engine mount not shown in the drawings, supports the power unit on the body in a vibration damped manner, by means of attaching the first mounting member  12  to the power unit side and the second mounting member  14  to the body side. In the installed state, the engine mount  10 , in association with elastic deformation of the main rubber elastic body  16  due to input of the distributed load of the power unit, undergoes relative displacement of the first mounting member  12  and the second mounting member  14  so that these move closer to one another by a prescribed amount in the vertical direction in  FIG. 1 . The principal vibration to be damped is input across the first mounting member  12  and the second mounting member  14 , in the approximately vertical direction in  FIG. 1 . With the engine mount  10  of this embodiment in the installed state, as depicted in  FIG. 1 , the center axis of the engine mount  10  (the center axes of the first and second mounting members  12 ,  14 ) lies in the approximately vertical direction, and thus in the description hereinbelow the vertical direction in  FIG. 1  shall be designated as the vertical direction. 
   To describe in greater detail, the first mounting member  12  has a generally circular block shape, and an upwardly extending fastener bolt  18  is formed on its center axis. The fastener bolt  18  is threaded into a bolt hole (not shown) formed in a bracket or other such mounting member on the power unit (not shown), thereby attaching the first mounting member  12  to the power unit side. 
   The second mounting member  14  has a thick, generally annular disk shape overall, and includes an upper mounting member  20  and lower mounting member  22 . The upper mounting member  20  is formed of metal of generally annular disk shape overall, and has an elastic body anchoring portion  24  extending axially upward formed on its diametrical inside peripheral edge. The elastic body anchoring portion  24  is of generally annular shape and has a tapered face  26  on an inside peripheral side of its axial upper end forming a gradually sloping face that gradually widens out going upward. On the lower face of the diametrically inside peripheral portion there is formed a press fitting groove  28  extending in the circumferential direction. The lower face located peripherally inward from this press fitting groove  28  is constituted as a fastening fixture support portion  30  situated axially upward by slight extent from the lower face located peripherally outward from the press fitting groove  28 . A partition fitting support portion  32  of stepped shape is positioned axially above the fastening fixture support portion  30  by slight extent, on the inside peripheral edge of the upper mounting member  20 . 
   The lower mounting member  22  is thinner than the upper mounting member  20 , but the inside diameter dimension and outside diameter dimension thereof are approximately the same as those of the upper mounting member  20 . The upper mounting member  20  and the lower mounting member  22  are superimposed top and bottom on the same center axis, to form the second mounting member  14  having thick, generally annular disk shape overall. The diametrically medial portion of the second mounting member  14  is perforated by several bolt holes  34  spaced apart from one another in the circumferential direction. The second mounting member  14  is press-fit into a bracket fitting (not shown), and the bolt holes  34  are fastened to the bracket fitting by means of mounting bolts (not shown) to fasten the second mounting member  14  to the bracket fitting. 
   The second mounting member  14  is then attached to a tubular bracket fitting (not shown) and the bracket fitting is mounted onto the vehicle body side to fasten it to the vehicle body. The first mounting member  12  is positioned spaced apart above the second mounting member  14  on approximately the same center axis therewith, with the main rubber elastic body  16  disposed between the first mounting member  12  and the second mounting member  14 . 
   The main rubber elastic body  16  has a large-diameter, generally frustoconical shape, and is provided with a large-diameter recess  36  of generally inverted conical shape opening onto its large-diameter end face. With the first mounting member  12  inserted downward in the axial direction from the small-diameter end face of the main rubber elastic body  16 , it is bonded by vulcanization to the main rubber elastic body  16  while positioned coaxially therewith. The outside peripheral face of the large-diameter end of the main rubber elastic body  16  is bonded by vulcanization to the tapered face  26  formed in the upper mounting member  20  which makes up the second mounting member  14 . That is, the main rubber elastic body  16  is formed as an integrally vulcanization molded component with the first mounting member  12  and the second mounting member  14 . With this arrangement, the first mounting member  12  and the second mounting member  14  are positioned approximately coaxially on a center axis extending in the principal direction of input of vibration to be damped, while positioned spaced apart from one another and elastically connected by means of the main rubber elastic body  16 . The second mounting member  14  is affixed to the main rubber elastic body  16 , whereby the opening at one end of the second mounting member  14  (the upper end in  FIG. 1 ) is sealed off fluid-tightly by the main rubber elastic body  16 . A zone on the inside peripheral face of the upper mounting member  20 , situated below the inside peripheral edge of the tapered face  26  and above the caulking portion of the partition member  50 , is covered in its entirety by a seal rubber layer  38  integrally formed with the main rubber elastic body  16 . 
   At the opening on the other end (the lower end in  FIG. 1 ) of the second mounting member  14 , there is attached a diaphragm  40  serving as a flexible film. The diaphragm  40  is constituted by a readily deformable, thin rubber elastic film of generally disk shape imparted with sufficient slack in its center portion. To the outside peripheral edge portion of the diaphragm  40  is bonded by vulcanization a fastener fitting  42  of large-diameter, generally hollow cylindrical shape. The fastener fitting  42  has a step portion  44  disposed in its upper portion. The portion further above the step portion  44  serves as a large-diameter press fitting portion  46 , and the portion below the step portion  44  has smaller diameter than the press fitting portion  46  and serves as a film anchoring portion  48  having the diaphragm  40  joined to its inside peripheral wall. 
   The press fitting portion  46  of the fastener fitting  42  is press-fit into the press fitting groove  28  formed in the lower face of the upper mounting member  20 , while the upper face of the step portion  44  of the fastener fitting  42  is superimposed against the fastening fixture support portion  30  formed on the lower face of the upper mounting member  20  and the lower face of the step portion  44  is superimposed against the upper inside peripheral edge of the lower mounting member  22 , so as to be sandwiched between the superimposed faces of the upper mounting member  20  and the lower mounting member  22  which are bolted together. By so doing the fastener fitting  42  is fastened to the second mounting member  14 , with the lower opening of the second mounting member  14  covered fluid-tightly by the diaphragm  40 . 
   With this arrangement, the zone between the opposed faces of the main rubber elastic body  16  and the diaphragm  40  is sealed off from the outside, and by sealing a non-compressible fluid within this zone, a sealed liquid zone is defined. As the non-compressible fluid sealed within the sealed liquid zone it is possible to use water, an alkylene glycol, a polyalkylene glycol, silicone oil or the like. In terms of effectively achieving vibration damping action on the basis of flow action such as resonance action of the fluid, it is preferable to use a low-viscosity fluid having viscosity of 0.1 Pa·s or lower. Sealing of the non-compressible fluid is accomplished, for example, by performing assembly of the diaphragm  40  to the integrally vulcanization molded component of the main rubber elastic body  16  with the first and second mounting members  12 ,  14 , while immersed in the non-compressible fluid. 
   The integrally vulcanization molded component of the main rubber elastic body  16  with the first and second mounting members  12 ,  14  additionally has a partition member  50  attached to the second mounting member  14 . The partition member  50  is constituted to include an upper partition fitting  52  and a lower partition fitting  54 . 
   The upper partition fitting  52  has a thin, generally disk shape in plan view. In the center portion of the upper partition fitting  52 , by means of pressing or other working process, there is integrally formed a hollow circular convex portion  56  that projects upward in a generally flat circular shape. The upper base portion of this circular convex portion  56  is perforated by a mating hole  58  situated in its diametrical center portion as well as having a number of communication holes  60  consisting of small circular holes bored in the diametrical medial portion. In the outside peripheral portion of the upper partition fitting  52  there is formed an annular convex portion  62  that extends a prescribed distance in the circumferential direction with a groove-shaped cross section that opens downward. 
   The lower partition fitting  54 , on the other hand, has a thin, generally disk shape, and like the upper partition fitting  52  has a mating hole  64  formed in its diametrical center portion, and a number of communication holes  66  consisting of small circular holes bored in its diametrical medial portion. The communication holes  60  and the communication holes  66  make up the through-holes in this embodiment. 
   The upper partition fitting  52  and the lower partition fitting  54  are superimposed on the same center axis in the axial direction in order to construct the partition member  50 . The partition member  50  is positioned with the upper outside peripheral edge portion thereof superimposed against the partition fitting support portion  32  formed on the lower face of the inside peripheral edge of the upper mounting member  20  making up the second mounting member  14  with the lower outside peripheral edge portion thereof superimposed against the fastener fitting  42  affixed to the outside peripheral edge of the diaphragm  40 . With this arrangement, the partition member  50  is fixedly supported clasped between the upper mounting member  20  and the lower mounting member  22  via the fastener fitting  42 . 
   With this arrangement, the sealed fluid zone is divided in two top to bottom by means of the partition member  50  disposed extending in the axis-perpendicular direction in the interior thereof. In association with this, there is formed to one side of the partition member  50  in the axial direction (the upper side in  FIG. 1 ) a pressure-receiving chamber  68  a portion of whose wall is constituted by the main rubber elastic body  16  and that gives rise to pressure fluctuations in association with elastic deformation of the main rubber elastic body  16  when vibration is input across the first mounting member  12  and the second mounting member  14 . To the other side of the partition member  50  in the axial direction (the lower side in  FIG. 1 ) there is formed an equilibrium chamber  70  a portion of whose wall is constituted by the diaphragm  40  and that readily permits change in volume on the basis of elastic deformation of the diaphragm  40 . 
   The opening on the lower side of the annular convex portion  62  formed in the outside peripheral portion of the upper partition fitting  52  is covered by the outside peripheral portion of the lower partition fitting  54 , thereby forming between the opposing faces of the upper partition fitting  52  and the lower partition fitting  54  a fluid flow passage constituting an orifice passage  72 . 
   This fluid flow passage extends a predetermined distance in the circumferential direction, with one end thereof connecting to the pressure-receiving chamber  68  through a pressure-receiving chamber-side communication hole  74  formed perforating the upper mounting member  20 , and the other end connecting to the equilibrium chamber  70  through an equilibrium chamber-side communication hole  76  formed perforating the portion of the lower partition fitting  54  that covers the opening of the annular convex portion  62 . With this arrangement, the pressure-receiving chamber  68  and the equilibrium chamber  70  communicate with one another by means of the orifice passage  72  which includes the fluid flow passage, thus permitting flow of fluid through the orifice passage  72  between the two chambers  68 ,  70 . 
   In this embodiment in particular, the resonance frequency of the fluid caused to flow through the orifice passage  72  is tuned so as to produce effective vibration damping performance (high attenuating effect) of vibration in a low frequency range of about 10 Hz corresponding to engine shake and the like, on the basis of resonance action of the fluid. Tuning of the orifice passage  72  can be carried out, for example, by adjusting the passage length and passage cross sectional area of the orifice passage  72 . In consideration of the spring rigidity (a characteristic value equivalent to the pressure change required to produce a given change in unit volume) of the walls of the pressure-receiving chamber  68  and the equilibrium chamber  70 . Typically, the frequency at which the phase of pressure fluctuations transmitted through the orifice passage  72  changes, producing an approximately resonant state is understood to be the tuning frequency of the orifice passage  72 . 
   The lower opening of the circular convex portion  56  formed in the upper partition fitting  52  is covered by the center portion of the lower partition fitting  54 , thereby forming a housing zone  78  as a housing space between the opposing faces of the upper partition fitting  52  and the lower partition fitting  54  at the diametrical center. 
   An elastic rubber plate  80  serving as the movable rubber plate is disposed in the housing zone  78 . The elastic rubber plate  80  has a generally disk shape overall, and on the center axis thereof are formed mating convex portions  82  that project axially upward and downward, respectively. The mating convex portions  82  extend in the axial direction with a circular cross section of outside diameter slightly smaller than the inside diameter of the mating holes  58 ,  64  respectively formed in the center portions of the upper and lower partition fittings  52 ,  54 ; by passing the mating convex portions  82  through these mating holes  58 ,  64  respectively formed in the upper and lower partition fittings  52 ,  54 , axial displacement of the elastic rubber plate  80  within the housing zone  78  is permitted while limiting the extent of displacement of the elastic rubber plate  80  in the diametrical direction within the housing zone  78 . That is, the mating portion in this embodiment is composed of the mating convex portions  82  and the mating holes  58 ,  64 . The elastic rubber plate  80  is formed with a diameter dimension smaller than the diameter dimension of the housing zone  78 , thus forming between the opposing elastic rubber plate  80  outside peripheral face and the housing zone  78  side wall inside face a gap which serves as a fluid flow zone  84 . 
   At the diametrical center portion of the elastic rubber plate  80 , there are formed center convex portions  86  of generally conical shape projecting axially upward and downward, respectively. At the outside peripheral edge portion of the elastic rubber plate  80 , there are formed outside peripheral convex ribs  88  in the form of convex ribs of generally annular shape that project axially upward and downward, respectively. Between these center convex portions  86  and outside peripheral convex ribs  88  in the diametrical direction there are formed medial circumferential grooves  90  serving as concave grooves that extend in the circumferential direction. A center thick portion  92  is formed by the center convex portions  86  and an outside peripheral thick portion  94  is formed by the outside peripheral convex ribs  88 , while a medial thin portion  96  is formed by the medial circumferential grooves  90 , with these thick and thin portions being situated in alternating fashion across the diameter of the elastic rubber plate  80 . 
   The center convex portions  86  have a generally frustoconical shape gradually narrowing in diameter towards the distal end, and are formed in the center on each face of the elastic rubber plate  80 . The projecting height of the center convex portions  86  is established so as to be sufficiently shorter than the projecting height of the mating convex portions  82 , with the mating convex portions  82  being formed so as to project axially upward and downward from the diametrical center portion of the center convex portions  86 . The projecting height of the center convex portions  86  is established such that the projecting distal ends of the center convex portions  86 ,  86  respectively formed on the top and bottom of the elastic rubber plate  80  do not come into simultaneous contact with the inside wall of the housing zone  78 . That is, the distance between the projecting distal ends of the center convex portions  86 ,  86  respectively formed on each side of the elastic rubber plate  80  is smaller than the axial dimension of the housing zone  78 . Consequently, at any given time the center convex portion  86  formed on at least one face will be positioned away from the inside wall of the housing zone  78 . 
   The outside peripheral convex ribs  88 , on the other hand, are formed at the outside peripheral portion the elastic rubber plate  80 , and take the form of convex ribs extending in the circumferential direction with a generally triangular cross section. The projecting height of the outside peripheral convex ribs  88  is approximately the same as that of the center convex portions  86 , and in the event that the elastic rubber plate  80  undergoes displacement in the axial direction, the center convex portions  86  and the outside peripheral convex ribs  88  will come into approximately simultaneous contact against the inside wall of the housing zone  78 . 
   In this embodiment in particular, the slope angle: a of the sloping face  97  constituting the inside peripheral side wall of the outside peripheral convex rib  88  is set within the range 45°&lt;α&lt;90°. The slope angle of the sloping face  97  refers to the angle between center axis of the elastic rubber plate  80  and a line extended from the structural line indicating the sloping face  97  in longitudinal cross section in an arbitrary radial direction, as shown in  FIG. 1 . In this embodiment, the angle: a between center axis of the elastic rubber plate  80  and a line extended from the structural line indicating the sloping face  97  has an alternate angle or corresponding angle relationship to the angle: β of the projecting distal end of the outside peripheral convex ribs  88 , with the angle: β of the projecting distal end outside peripheral convex ribs  88  being equal to the slope angle: α of the sloping face  97 . 
   Returning now to the medial circumferential grooves  90 , these are concave grooves situated diametrically between the center convex portions  86  and the outside peripheral convex ribs  88 , and extending in the circumferential direction; in this embodiment in particular, the medial circumferential groove  90  is constituted by a curving face smoothly connecting the side wall of the center convex portion  86  with the insider peripheral side wall of the outside peripheral convex rib  88 . As will be understood from the fact that the medial circumferential grooves  90  are formed diametrically between the center convex portions  86  and the outside peripheral convex ribs  88 , these are formed respectively on each face of the elastic rubber plate  80 , with the medial circumferential grooves  90 ,  90  on the faces being situated at the same location in the diametrical direction. The communication holes  60 ,  66  formed respectively in the upper partition fitting  52  and the lower partition fitting  54  are aligned so as to be positioned over the medial circumferential grooves  90 . 
   In the automotive engine mount  10  of construction described above, when shake or other low-frequency, large-amplitude vibration is input, active fluid flow is produced between the pressure-receiving chamber  68  and the equilibrium chamber  70  through the orifice passage  72  which has been pre-tuned to vibration in the low-frequency range, such as shake. When low-frequency, large-amplitude vibration is input, displacement of the elastic rubber plate  80  is unable to follow, and the elastic rubber plate  80  becomes forced against the inside wall of the housing zone  78  thus impeding absorption of fluid pressure through displacement of the elastic rubber plate  80 . Additionally, at least one of set of holes from among the communication holes  60 ,  66  formed respectively in the upper partition fitting  52  and the lower partition fitting  54  become blocked off by elastic rubber plate  80 , thereby preventing flow of fluid between the two chambers  68 ,  70  through the communication holes  60 ,  66  and the housing zone  78 . With this arrangement, pressure fluctuation in the pressure-receiving chamber  68  is advantageously assured, ample flow of fluid induced to flow between the two chambers  68 ,  70  through the orifice passage  72  is advantageously achieved, and vibration damping action based on resonance of fluid induced to flow through the orifice passage  72  is effectively realized. 
   Here, striking noise caused by impact force when the elastic rubber plate  80  contacts the inside wall of the housing zone  78  when low-frequency, large-amplitude vibration is input can tend to become a problem. However, with the engine mount  10  constructed in accordance with this embodiment, it is possible to effectively reduce the impact force during contact, and thus to reduce or avoid the occurrence of noise due to impact force during contact. 
   Specifically, in the event that the elastic rubber plate  80  is induced to undergo displacement in the axial direction and comes into contact with the wall of the housing zone  78 , with the elastic rubber plate  80  of the engine mount  10  pertaining to this embodiment, the center convex portions  86  and the outside peripheral convex ribs  88  initially come into contact with the partition member  50  making up the wall of the housing zone  78 . In this embodiment in particular, the center convex portions  86  and the outside peripheral convex ribs  88  are formed with approximately identical projecting height so as to come into contact with the partition member  50  approximately simultaneously, while the center convex portions  86  are frustoconical in shape and the outside peripheral convex ribs  88  have generally triangular cross section gradually narrowing in width towards the projecting distal end. Accordingly, immediately upon contact the elastic rubber plate  80  and the partition member  50  are placed in linear contact, so that the impact force of initial contact is effectively dispersed and mitigated. 
   As the elastic rubber plate  80  is urged further against the partition member  50  by the relative pressure differential between the pressure-receiving chamber  68  and the equilibrium chamber  70 , the center convex portion  86  and the distal end of the outside peripheral convex rib  88  are become compressed in the axial direction and undergo elastic deformation so as to collapse. Here, the center convex portion  86  and the outside peripheral convex rib  88  caused to undergo compressive deformation in the axial direction are induced thereby to undergo bulging deformation in the diametrical direction, but since the medial circumferential groove  90  has been formed diametrically between the center convex portion  86  and the outside peripheral convex rib  88 , this bulging deformation is permitted, and compressive deformation of the center convex portion  86  and the outside peripheral convex rib  88  in the axial direction is advantageously achieved. By means of this, as pressure acts on the elastic rubber plate  80  forcing it against the partition member  50  with greater force, the center convex portion  86  and the outside peripheral convex rib  88  are induced to undergo gradual elastic deformation, whereby it is possible to prevent a sharp rise in contact pressure, and to reduce or avoid striking noise caused by a sudden pressure fluctuation during contact. The cross sectional area of the medial circumferential groove  90  becomes smaller due to compressive deformation of the center convex portion  86  and the outside peripheral convex rib  88  in the axial direction. However, since the communication holes  60 ,  66  are formed opening onto the location where the circumferential groove  90  is formed, the non-compressible fluid within the medial circumferential groove  90  escapes into the pressure-receiving chamber  68  or the equilibrium chamber  70  in association with the elastic deformation of the elastic rubber plate  80 , so that impaired elastic deformation of the elastic rubber plate  80  due to non-compressible fluid being sealed within the medial circumferential groove  90  can be effectively avoided. 
   Additionally, the projecting distal end of the center convex portion  86  becomes gradually smaller in diameter, and the width dimension of the outside peripheral convex rib  88  gradually decreases towards its projecting distal end. As these elements undergo gradual elastic deformation in association with increasing pressure acting on the elastic rubber plate  80  due to contact, the contact area of the elastic rubber plate  80  with the partition member  50  increases gradually. Consequently, the occurrence of noise due to a sharp increase in contact force produced by a sudden increase in contact area can be effectively prevented. 
   The cross sectional area of the outside peripheral convex rib  88  in a reference plane which is a plane that passes through the deepest location of the medial circumferential groove  90  and extends in the axis-perpendicular direction of the elastic rubber plate  80  is established so as to be equivalent to at least 30% but no more than 70% of the cross sectional area of the medial circumferential groove  90  in a reference plane which is a plane that passes through the location of the projecting distal end of the outside peripheral convex rib  88  and extends in the axis-perpendicular direction of the elastic rubber plate  80 . In preferred practice, the cross sectional area of the outside peripheral convex rib  88  will be equivalent to at least 40% but no more than 60% of the cross sectional area of the medial circumferential groove  90 , and more preferably the cross sectional area of the outside peripheral convex rib  88  will be 50% of the cross sectional area of the medial circumferential groove  90 . 
   If the cross sectional area of the outside peripheral convex rib  88  is too small relative to the cross sectional area of the medial circumferential groove  90 , while the initial impact force of contact can be absorbed, as compressive deformation is induced by increasing contact pressure, the outside peripheral convex rib  88  will collapse within a relatively short time so that sufficient cushioning action subsequent to elastic deformation is not achieved. If on the other hand the cross sectional area of the outside peripheral convex rib  88  is too large relative to the cross sectional area of the medial circumferential groove  90 , the medial circumferential groove  90  will not be endowed with adequate width and will not accommodate an adequate level of bulging deformation in the diametrical direction in association with compressive deformation of the outside peripheral convex rib  88  in the axial direction, and thus will not readily permit effective compressive deformation, with the risk that impact absorbing effect through elastic deformation in the axial direction will not be sustained at its initial level. 
   From this viewpoint, it is clear that, in order to achieve both cushioning performance immediately after contact and sustained cushioning performance after the outside peripheral convex rib  88  has been induced to undergo elastic deformation, it is effective for the cross sectional area of the outside peripheral convex rib  88  relative to the cross sectional area of the medial circumferential groove  90  to be established within the range given above, and by so doing to more effectively reduce or avoid the occurrence of noise. 
   When running booming noise or similar high-frequency, small-amplitude vibration is input to the automotive engine mount  10 , the orifice passage  72 , which is tuned to a lower frequency range than the input vibration, assumes markedly higher fluid flow resistance due to anti-resonance action, and becomes substantially closed off. 
   Meanwhile, due to small-amplitude pressure fluctuations produced in the pressure-receiving chamber  68  by input of high-frequency, small-amplitude vibration, the elastic rubber plate  80  is induced to undergo minute displacement in the axial direction within the housing zone  78 . By means of this, pressure fluctuations in the pressure-receiving chamber  68  are effectively transmitted to the equilibrium chamber  70 , and the pressure fluctuations produced in the pressure-receiving chamber  68  are absorbed by the equilibrium chamber  70  which permits change in volume. Additionally, due to the flow of fluid between the pressure-receiving chamber  68  and the equilibrium chamber  70  through the communication holes  60  formed in the upper partition fitting  52  and the communication holes  66  formed in the lower partition fitting  54 , fluid pressure within the pressure-receiving chamber  68  escapes into the equilibrium chamber  70 . Thus, a marked rise in dynamic spring constant caused by the orifice passage  72  becoming substantially closed off is avoided, and good vibration damping effect (vibration insulating effect based on low dynamic spring characteristics) against high-frequency, small-amplitude vibration is achieved. 
   In the engine mount  10  constructed according to this embodiment, impact force produced by the elastic rubber plate  80  coming into contact against the partition member  50  when large-amplitude vibration is input is effectively absorbed through cooperation on the part of the center convex portions  86 , the medial circumferential grooves  90 , and the outside peripheral convex ribs  88  formed on the elastic rubber plate  80 , and the occurrence of noise caused by such impact force can be effectively reduced or avoided. 
   By forming the outside peripheral convex ribs  88  as convex ribs of annular shape extending in the circumferential direction, it is possible to achieve consistent elastic deformation during contact, and to reliably reduce or avoid noise. Additionally, since the outside peripheral convex ribs  88  are formed extending about the entire circumference at the outermost peripheral edge of the elastic rubber plate  80 , when the elastic rubber plate  80  is forced into contact against the partition member  50  during input of large-amplitude vibration, flow of fluid between the pressure-receiving chamber  68  and the equilibrium chamber  70  through the communication holes  60 ,  66  is immediately obstructed by the outside peripheral convex rib  88 , advantageously ensuring that pressure fluctuations are produced within the pressure-receiving chamber  68 . Consequently, fluid flow through the orifice passage  72  can be adequately assured, and vibration damping action based on resonance of the fluid can be exhibited effectively. 
   By positioning the mating convex portions  82  in the center of the elastic rubber plate  80  so that they are engaged by the mating holes  58 ,  64  formed in the center of the partition member  50 , the elastic rubber plate  80  is positioned in the axial direction with respect to the partition member  50 . Consequently, the fluid flow zone  84  formed to the outside in the diametrical direction is consistently assured, and during input of small-amplitude vibration, fluid pressure absorbing action is effectively realized by means of permitting fluid flow between the pressure-receiving chamber  68  and the equilibrium chamber  70 . 
   Turning next to  FIG. 2 , there is shown an elastic rubber plate  98  in an engine mount according to a second embodiment of the invention. In the following description, components and areas substantially identical to those in the first embodiment described previously are assigned identical symbols in the drawings, and are not described in any detail. 
   More specifically, the elastic rubber plate  98  is of generally disk shape having medial convex ribs  100  in portions of its diametrically medial section. The medial convex ribs  100  are convex ribs of unchanging, generally triangular cross section extending all the way around in the circumferential direction. By forming a medial convex rib  100  on each side of the elastic rubber plate  98 , there is formed a medial thick portion  102 . In this embodiment in particular, one medial convex rib  100  is formed on each of the two faces of the elastic rubber plate  98 , situated about the same center axis approximately midway in the diametrical direction between the center convex portions  86  and the outside peripheral convex ribs  88 . In this embodiment, the medial convex ribs  100  and the outside peripheral convex ribs  88  constitute the convex ribs. 
   Also, the angle: γ of the projecting distal end of the medial convex rib  100  in cross section is an obtuse angle such that 90°&lt;γ&lt;180°, and the narrow zone at the distal end is constituted by a slightly bowing face. The projecting height of the medial convex rib  100  is about the same as the projecting height of the center convex portion  86  and the outside peripheral convex rib  88 . The cross sectional area of the medial convex rib  100  is approximately double the cross sectional area of the outside peripheral convex rib  88 , and the angle: γ of the projecting distal end of the medial convex rib  100  is approximately double the angle: β of the projecting distal end of the outside peripheral convex rib  88 . Additionally, the slope angle of the sloping face  103  of the medial convex rib  100  is equal to the slope angle of the sloping face  97  of the outside peripheral convex rib  88 . The slope angle of the sloping face  103  of the medial convex rib  100  refers to the angle: a between center axis of the elastic rubber plate  98  and a line extended from the sloping face  103  constituting a side wall of the medial convex rib  100 , in longitudinal cross section in an arbitrary radial direction. That is, in this embodiment, the angle: a between center axis of the elastic rubber plate  80  and a line extended from the structural line indicating the sloping face  97  is one-half the size of the angle: γ of the projecting distal end of the outside peripheral convex rib  88 . 
   On each face of the elastic rubber plate  98  in this embodiment are formed a total of two medial circumferential grooves  104 ,  104 , i.e. one between the center convex portion  86  and the medial convex rib  100 , and one between the medial convex rib  100  and the outside peripheral convex rib  88 . The medial circumferential grooves  104 ,  104  take the form of concave grooves of generally rectangular cross section, with slightly bowing faces at their deepest part. 
   The cross sectional area of the medial convex rib  100  in a reference plane which is a plane passing through the deepest location of the medial circumferential groove  104  and extending in the axis-perpendicular direction of the elastic rubber plate  98  is established so as to be equivalent to at least 60% but no more than 140% of the cross sectional area of the medial circumferential groove  104  in a reference plane which is a plane that passes through the location of the projecting distal end of the medial convex rib  100  and extends in the axis-perpendicular direction of the elastic rubber plate  98 . In preferred practice, the cross sectional area of the medial convex rib  100  will be equivalent to at least 80% but no more than 120% of the cross sectional area of the medial circumferential groove  104 , and more preferably the cross sectional area of the medial convex rib  100  will be 100% of the cross sectional area of the medial circumferential groove  104 . 
   Specifically, if the cross sectional area of the medial convex rib  100  is too small relative to the cross sectional area of the medial circumferential groove  104 , while the initial impact force of contact can be absorbed, as compressive deformation is induced by increasing contact pressure, the medial convex rib  100  will collapse within a relatively short time so that sufficient cushioning action subsequent to elastic deformation is not achieved. If on the other hand the cross sectional area of the medial convex rib  100  is too large relative to the cross sectional area of the medial circumferential groove  104 , the medial circumferential groove  104  will not be endowed with adequate width and will not accommodate an adequate level of bulging deformation in the diametrical direction in association with compressive deformation of the medial convex rib  100  in the axial direction, and thus will not readily permit effective compressive deformation, with the risk that impact absorbing effect through elastic deformation in the axial direction will not be sustained at its initial level. 
   This clearly shows that in order to achieve both cushioning performance immediately after contact and sustained cushioning performance after the medial convex rib  100  has been induced to undergo elastic deformation, it is effective for the cross sectional area of the medial convex rib  100  relative to the cross sectional area of the medial circumferential groove  104  to be established within the range given above, and by so doing to more effectively reduce or avoid the occurrence of noise. 
   By means of the above, the elastic rubber plate  98  in this embodiment is composed, in order from the diametrical center, of center convex portions  86 , first medial circumferential grooves  104 , medial convex ribs  100 , second medial circumferential grooves  104 , and outside peripheral convex ribs  88 , disposed concentrically about the same axis, with the convex ribs in this embodiment being constituted by the medial convex ribs  100  and the outside peripheral convex ribs  88 , and with the concave grooves being constituted by the medial circumferential grooves  104 ,  104 . 
   The elastic rubber plate  98  described above may be installed in the housing zone  78  in place of the elastic rubber plate  80  described in the preceding first embodiment. 
   In the engine mount furnished with the elastic rubber plate  98  of this embodiment, by means of forming medial convex ribs  100 , contact pressure can be dispersed more advantageously, and cushioning action achieved more effectively. Consequently, sharp rise in pressure which can cause striking noise can be more effectively suppressed, so that the occurrence of noise can be suppressed. 
   By imparting an obtuse angle to the projecting distal end of the medial convex rib  100 , it is possible to advantageously prevent the projecting distal end from undergoing bending deformation due to pressure during contact, and to reliably achieve a gentle increase in pressure by causing it to undergo gradual collapse, and thus to effectively prevent the occurrence of noise due to a sharp rise in pressure. Additionally, by imparting curving faces to the projecting distal ends of the medial convex ribs  100  and the outside peripheral convex ribs  88 , it is possible to more effectively prevent bending deformation immediately after contact, so as to avoid a sudden change in pressure, and so as to more effectively reduce or avoid the occurrence of noise. 
   While the present invention has been described in detail in its presently preferred embodiments, for illustrative purpose only, it is to be understood that the invention is by no means limited to the details of the illustrated embodiment, but may be otherwise embodied. It is also to be understood that the present invention may be embodied with various changes, modifications and improvements which may occur to those skilled in the art, without departing from the spirit and scope of the invention. 
   For instance, the cross sectional shape of the elastic rubber plates  80 ,  98  in the illustrated first and second embodiments are just preferred example, and the principle of the present invention is not limited to the illustrated embodiments. More specifically, it is possible to employ two or more medial convex ribs  100  so as to disperse contact pressure, making it possible to further enhance impact noise suppression effect. For the same reason, the medial convex rib  100 , the outside peripheral convex ribs  88 , the medial circumferential grooves  90 ,  104  may be suitably adjusted in their shape. More specifically, the medial convex rib  100  may have a cross sectional shape of generally semi-elliptical shape or trapezoid shape. 
   While the mating convex portions  82  are formed at the diametrically medial portion of the elastic rubber plates  80 ,  98  in the illustrated first and second embodiments, the mating convex portions  82  are not essential to practice the present invention. Likewise, the mating holes  58 ,  64  formed through the upper and lower partition fittings  52 ,  54  are not essential. 
   In the illustrated first embodiment, the partition member  50  is formed of metal, but it may be formed of rigid resin material, if appropriate. 
   The shape, size, structure, position, numbers of the orifice passage  72  may be suitably changed depending upon required damping performance or fabrication utility. 
   It is also to be understood that the present invention may be embodied with various other changes, modifications and improvements, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the following claims.