Abstract:
A mount is provided with a pair of spaced apart support members. One of the support members includes a stop. A vibration isolation member is connected to both support members. The vibration isolation member has a rubber block for absorbing unwanted vibrations. A restraint member is connected to the rubber block to reduce the mass of the vibrating components so as to prevent reducing the resonant frequency of the device. The restraint member has a first portion and a second portion. The design is compact and does not permit the stop to extend above the restraint member in order to permit unrestrained travel of the first support member toward the second support member when the mount is in a compression mode. The second portion engages the stop to limit the stretch of the rubber block away from the support member and provides a heat shield for the rubber block and stop.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Provisional Patent Application No. 60/127,066, filed Mar. 31, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a vibration isolating device for use in vehicle power train mounting systems and more particularly to a rubber vibration isolating apparatus which limits the axial travel of the device and provides a heat shield. 
     DESCRIPTION OF THE PRIOR ART 
     Many isolating devices permit unrestrained axial or longitudinal travel of the damping device, either in tension and/or in compression. Normally, axial or longitudinal travel in the compression mode does not seriously affect the life of the device. However, stretching or axial tension in the rubber device can cause elongation of the rubber and ultimately failure of the rubber component. 
     This is especially important in hydraulic isolation or damping devices which have a pair of supporting members which are secured to a vibrating body in a frame. A rubber block is disposed between supporting members and the concave surface of the rubber block and a rubber diaphragm which is joined to the rubber block, together define a liquid chamber filled with a damping fluid, such as glycol or a similar fluid. A partition defines the liquid chamber which is divided into a main liquid chamber and an auxiliary liquid chamber. The partition has an opening which is closed with an elastic rubber wall. The partition is also provided with a throttle passageway which communicates with both the main liquid chamber and the auxiliary liquid chamber. 
     High frequency, low amplitude vibration is imparted into the main liquid chamber which absorbs most of the vibration. Low frequency, high damping forces cause the liquid in the main chamber to move into the auxiliary liquid chamber and thereby absorb the large amplitudes and axial forces. In the process, particularly in the low vibration, high damping modes, the rubber block may be subjected to large axial or longitudinal travel which imposes high compression and alternatively high tension forces in the rubber block. These high tension forces in the rubber block can lead to its premature failure. 
     Several devices have been proposed to solve this problem, such as U.S. Pat. No. 4,842,258, U.S. Pat. No. 5,178,374, and U.S. Pat. No. 5,501,433. All of these devices seek to limit both the axial stretching mode and the axial compression mode in the rubber block. However, all of these devices are complicated and costly to make. 
     Thus, none of these devices provides a vibration device that limits axial stretching of the rubber mount, and at the same time provides a heat shield to protect the rubber block from temperature extremes and is simple, compact and inexpensive to make. 
     SUMMARY OF THE INVENTION 
     The present invention therefore sets out to solve the problems thus posed above by eliminating these drawbacks. To this end, a vibration damping device in accordance with the present invention is characterized by a pair of support members, one of the support members having a stop. A vibration isolation member is connected to the pair of support members. The vibration isolation member has a rubber block which defines an axis. The block stretches along the axis. A restraint member is connected to the rubber block. The restraint member has a first portion extending along the axis and a second portion attached to the front portion. The second portion engages the stop member to limit the axial travel of the rubber block away from the other of the pair of support assemblies. Additionally, the restraint member forms a heat shield to protect the rubber block. 
     It is an object of the present invention to provide a damping device with a resilient member where the stretch of elastic rubber block is limited, thus improving useful life for the damping device, is simple, easy to make and does not contribute to the critical core mass. 
     It is another object of the present invention to provide a damping device with an elastic rubber block which has an axial stretch restraint which also acts as a heat shield to prevent deterioration of the rubber due to temperature. 
     It is another object of the present invention to attach the stop to one of the support members so that the stop does not contribute to the critical core mass and thus does not deteriorate the resonance performance of the mount. 
     It is still another object of the present invention to provide a mount which locates the stop so as not to extend below the restraint member but yet permits unrestrained travel of the core toward the chassis side of the mount during its compressive mode and this provides a compact mount device. 
     It is a further object of the present invention to provide a tension restraint which is attached to one of the support members so as not to cause unwanted resonant effects in the working fluid chamber. 
     These and other features of the present invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings all of which form part of the specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the damping device according to the present invention; 
     FIG. 2 is a top view of the damping device according to the present invention; 
     FIG. 3 is a cross sectional view of the preferred embodiment of the damp device in accordance with the present invention; and 
     FIG. 4 is a partial cross sectional view of the elastomeric member of circle  4  in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A mount is utilized to locate and support a vehicle powertrain assembly as well as isolate powertrain induced vibration from the chassis of the vehicle. A powertrain is defined as an energy conversion device or similar device which converts chemical energy into mechanical or electrical energy and includes a transmission which can be a mechanical, hydraulic or electrical device to provide motive power for a vehicle. Those skilled in the art will recognize that a chemical energy conversion device is preferably a heat engine, including gasoline fueled, diesel fueled, gas turbine, sterling engine or similar devices. The heat engine can also include battery powered, fuel cell powered or similar devices. Preferably, the energy conversion device is a gasoline fueled engine. The chassis can also transmit road induced vibration levels back to the powertrain assembly which can over time create harmful interactions in the powertrain assembly. The damping mount acts to provide a vibration isolation device to control harmful powertrain motion. 
     As shown in FIGS. 1-3, in order to connect the mount  100 , according to the invention, to the powertrain assembly (not shown), a threaded bolt  1  is pressed, riveted or cast into an upper core  2  member of the mount  100 . The upper core  2  is a preferably round member which is attached by the bolt  1  to the engine bracket  17 . The core  2  may also be square, rectangular or any other similar, suitable shape. The opposite side of the core  2  is connected to a concave shaped rubber or elastomeric isolator  3  by rubber to metal bonding as is well known in the prior art. The isolator  3  or resilient member is also bonded at its periphery to a metal support ring  4 . The support ring  4  is crimped to a cap  5 . The cap  5  is attached to the chassis through a threaded bolt  6 . The bolt  1  and bolt  6  define a longitudinal axis  25  for the mount  100 . Bolt  1  connects the powertrain assembly (not shown) and bolt  6  connects the chassis (not shown). The mount  100 , in response to vibrations from the chassis and/or powertrain assembly, moves along the longitudinal axis  25 . The support ring  4  which is crimped to the cap  5  also rigidly holds two nozzle plates  7  together. The nozzle plates  7  form two separate fluid filled chambers  8 ,  9  respectively. On the engine side, or powertrain side, a working chamber  8  is formed and is bounded by the interior surface of the rubber isolator  3  and the nozzle plates  7 . On the chassis side, a compensation chamber  9  is formed and bounded to the nozzle plates  7  and a flexible membrane or bellows  10 . The nozzle plates  7  form a long and slender fluid filled channel  11  between the working chamber  8  and compensation chamber  9 . The channel  11  is oriented tangentially around the bottom portion of the working chamber  8 . The geometry and the relationship of the cross-section and length of the chamber  11  are important factors for the achievement of isolation and damping performance of the mount  100 . 
     The nozzle plates  7  also have short nozzles  13  which are parallel to the longitudinal axis  25  of the engine mount  100  motion from the powertrain assembly. The short nozzles  13  are located adjacent to the periphery of the diaphragm  12 . A diaphragm  12  separates the working chamber  8  and the compensation chamber  9 . The soft compliance of an elastomeric diaphragm  12  allows the generally incompressible fluid in the working chamber  8  to isolate small movements and vibrations that are generated by the powertrain. This mechanism creates the primary isolation function for the powertrain generated vibration. The nozzle plates  7  also function to limit the soft compliant movement of the diaphragm  12  within certain limits. Furthermore, the nozzle plates  7  serve as a fluid restriction to force fluid through the channel  11  and create the desired vibration damping performance. In order to achieve high resonance frequencies in the powertrain bracket  17 , it is desirable to reduce the weight of the mount components which are directly attached to the bracket. A stop or energy absorption member  15  is located on the core  2  and the tension restraint member  14  is attached to the support ring  4 , preferably by crimping. Those skilled in the art will recognize that any other suitable connecting method known in the art is acceptable. The flange  18  of the member  14  is crimped to ring  4  by rolling over the end  19  over the flange  18 . In this way, the components, such as the restraint member  14 , flange  18  or ring  4  prevent deterioration of the resonance performance of the mount  100  by minimizing the mass being subjected to vibration. 
     Those skilled in the art will recognize that the mount damping performance can also be achieved with the engine mount oriented in the reverse condition at installation. However, installation with the lighter side of the mount attached to the powertrain bracket is preferable since it provides better vibration isolation characteristics by reducing the weight on the powertrain bracket which adds to the vibration mass. Any additional weight reduces the resonant frequency of the bracket, requiring stiffer brackets and engine block attachments and would be detrimental to the isolation characteristics of the mount. In many known designs, the core side of the mount is the lighter side. For this reason, aluminum and composite materials are preferably utilized to manufacture the core  2 . In addition to the beneficial isolation or vibration attenuation performance results of such an installation, the endurance of the rubber components of the isolation device must also be taken into consideration. The rubber components such as the rubber isolator  3  and rubber member or stop  15 , because of packaging considerations, are generally located near the engine block or powertrain assembly (not shown) and exhaust pipes (not shown). This exposes the elastomeric or rubber components to radiated and convective heat. Two primary factors which contribute to early deterioration of elastomeric properties are heat exposure and tension or stretch loads. In the present invention, the rubber isolator  3  and rubber member  15  are shielded from the radiated heat by a spaced apart but closely packaged tension restraint member  14  that interrupts the line of sight between the heat source such as the exhaust manifolds and the rubber isolator components. The tension restraint member  14  is generally a cylindrically shaped element that is located with the open side down around the powertrain mount or isolator  100  when viewed as shown in FIGS. 1 and 2. The member  14  also has a radially extending flange  20  which extends from the cylindrical portion  21  towards but spaced away from the threaded bolt  1 , as shown in FIG.  3 . The flange  20  cooperates with rubber member  15  to provide a limit in the tension direction  36  of the core  2  relative to the flange  20  of the member  14 . 
     Access to attach the engine or powertrain bracket  17  to the isolator  100  is provided through the angular or cut-out section  30  that is cut away from the member  14  and is preferably oriented towards the powertrain assembly. The cut-out section  30  has a radial portion  31  and an axial portion  33 . The attachment of the tension restraint member  14  to the support ring  4  allows tight packaging of the tension restraint member  14  to the powertrain bracket  17  thereby eliminating tolerance stack-ups between the various components which make up the mount  100 . Thus, the radial axis and longitudinal axis travel limitations designed into the core  2  and tension restraint member  14  interface can be tightly matched by the clearance between the powertrain bracket  17  and tension restraint member  14 , and good shielding from radiated heat sources is also provided. Additionally, the cut-out  30  and the flange  20  of the tension restraint member  14  permit the overall assembly height of the mount  100  to be compact since the bracket  17  can be attached to the bolt  1  through the cut-out section  30 . Because of this compact design, the core  2  does not extend below the restraint member  14  in the tension direction  36  and yet permits unrestrained travel of the bracket  17  toward the threaded bolt  6  connected to the chassis in the compression direction  37  of the mount  100 . The unrestrained travel of the bracket  17  and the core  2  in the compression direction  37  is defined as travel which is unrestrained by the geometry of the mount  100  and is only limited to the elastomeric properties of the isolator  3 . 
     As stated earlier, the tension restraint member  14  provides a limitation to excessive tension or stretch loads in the rubber isolator  3  by providing a travel limit to the core  2  along the longitudinal axis  25  which is within the partial cavity formed by the restraint member  14  and rubber isolator  3 . This provides a very compact design which is critical for tightly packaged powertrain installation in current motor vehicles. The core  2  may also be radially displaced relative to the tension restraint member  14  in the direction of movement for the typical tension loads introduced by the powertrain assembly. The core  2  has a rubber member  15  molded on the surface of the core  2  to provide low impact load absorption into the restraint member  14  and to avoid metal to metal contact of the bracket  17  to the core  2  due to angular movement of the powertrain assembly. As stated previously, the restraint member  14  is crimped or solidly attached to the support ring  4  and thus does not contribute to the critical core side mass. This prevents the restraint  14  and stop  15  from deteriorating the resonance performance of the engine bracket mount  17 . This also alleviates the negative effects of internal tension restraints. Many currently known internal tension restraint systems include vibrating components near the fluid working chamber which often cause unwanted resonance effects significantly decreasing the isolation performance of known engine mounts. 
     The tension restraint member  14  and the support ring  4  have multiple openings  16  in the crimp section to allow for drainage of fluids and solid contaminants which may enter from the outside of isolator surface. 
     The rubber member or stop  15  and rubber isolator  3  may be made of Natural Rubber, Ethylene Propylene Diene, Hydrogenated Nitrile, Nitrile, Butyl, Ethylene Acrylate, Polyisoprene, Polybutadiene, Styrene Butadiene, or Fluorocarbon Polymers or other similar materials. Optionally, the stop  15  may be made of a different elastomer than the isolator  3 . Butyl rubber is preferably used to make the stop  15  for high damping performance and Natural Rubber is preferably used to make the rubber isolator  3 . The rubber member  15  may be optionally separately attached or fastened to the core  2  to permit tailoring of the engine mount spring rate. Preferably the rubber member  15  is between 1 to 10 mm thick. An elastomer member  15  on the core  2  which facilitates a gradual and even force distribution is preferable. The spring rate of the rubber member  15  can be modified by molding a plurality of beads of different height, ribs, cylindrical or conical risers, voids in the rubber surface, or other similar shapes used in the rubber industry. Preferably, the rubber member  15  has three concentric rings of rubber beads. The outer most rubber bead  22  projects away from the core  2  at the greatest height, the inner most rubber bead  24  projects away from the core  2  at the least height and the middle rubber bead  23  projects away from the core  2  at a height between the outer most bead and the inner most bead, as shown in FIG.  4 . This permits a gradual load absorption as the restraint member  14  moves along the longitudinal axis  25  to contact the stop  15 . 
     The tension restraint member  14  is designed for occasional impact due to excessive powertrain motion or chassis motion. The material thickness therefore ranges from 1 mm to 5 mm. Light metals with high strength to weight ratios are preferable such as aluminum and magnesium. Strength enhancing design features such as using ribs on the outside of the restraint member  14  can achieve similar effects. The preferable tension or stretch range limitation of the rubber isolator mount  100  is 5 o 20 mm from a loaded height of the mount that is when the mount is inserted between the bracket  17  and the chassis (not shown). Any metal to metal interference between the core  2  and bracket  17  must be limited to allow reliable function of the mount  100 . However, some small plastic deformation is acceptable. Interference ranges from 300 mm 2  or larger were found to be acceptable. 
     Those skilled in art will also recognize that while the preferred embodiment has been described with a hydromount design, any rubber or elastomeric vibration absorbing mount or bushing as is well known in the art or similar isolation devices, can be employed with the described invention. 
     While it will be apparent that the preferred embodiment of the disclosed invention fulfills the objectives and benefits of the invention, it will be appreciated that the invention is susceptible to modification without departing from the proper scope of the appended claims.