Patent Publication Number: US-2003234477-A1

Title: Hydraulic mount with compliant element in fluid chamber

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001] This invention relates to powertrain mounts for motor vehicles, and more particularly to a powertrain mount having a compliant element in the fluid chamber.  
       BACKGROUND OF THE INVENTION  
       [0002] It is desirable to provide motor vehicles with improved operating smoothness by damping and/or isolating powertrain vibrations of the vehicle. A variety of mount assemblies are presently available to inhibit such engine and transmission vibrations. Many of these mount assemblies combine the advantageous properties of elastomeric materials with hydraulic fluids. A hydraulic mount assembly of this type typically includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is separated into two chambers by a plate. The chambers are in fluid communication through a relatively large central orifice in the plate. The first or primary chamber is formed between the partition plate and the body. The secondary chamber is formed between the plate and the diaphragm.  
       [0003] A decoupler may be positioned in the central passage of the plate to reciprocate in response to the vibrations. The decoupler movement alone accommodates small volume changes in the two chambers. When, for example, the decoupler moves in a direction toward the diaphragm, the volume of the portion of the decoupler cavity in the primary chamber increases and the volume of the portion in the secondary chamber correspondingly decreases, and vice-versa. In this way, for certain small vibratory amplitudes and generally higher frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, this decoupler is a passive tuning device.  
       [0004] In addition to the relatively large central passage, an orifice track with a smaller, restricted flow passage is provided extending around the perimeter of the orifice plate. Each end of the track has an opening; one opening communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the decoupler, provides at least three distinct dynamic operating modes. The particular operating mode is primarily determined by the flow of fluid between the two chambers.  
       [0005] More specifically, small amplitude vibrating input, such as from relatively smooth engine idling or the like, produces no damping due to the action of the decoupler, as explained above. In contrast, large amplitude vibrating inputs, such as large suspension inputs, produce high velocity fluid flow through the orifice track, and an accordingly high level of damping force and desirable control and smoothing action. A third or intermediate operational mode of the mount occurs during medium amplitude inputs experienced in normal driving and resulting in lower velocity fluid flow through the orifice track.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention is a mount for a powertrain component of a motor vehicle. The mount comprises a primary chamber and a secondary chamber. An orifice track is in fluid communication between the primary chamber and the secondary chamber, and a compliant element is disposed in the primary chamber.  
       [0007] Accordingly, it is an object of the present invention to provide an improved hydraulic mount overcoming the limitations and disadvantages of the prior art.  
       [0008] Another object of the present invention is to provide a hydraulic mount of the type described above which has a relatively low dynamic rate with the ability to tune the dynamic rate at a selected frequency.  
       [0009] Still another object of the present invention is to provide an improved hydraulic mount of the type described above having a compliant element disposed in the primary chamber.  
       [0010] Still another object of the present invention is to provide an improved hydraulic mount of the type described above having a compliant element disposed in communication with the primary chamber.  
       [0011] The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012]FIG. 1 is a cross-sectional view of a powertrain mount according to the present invention for a motor vehicle;  
     [0013]FIG. 2 is a cross-sectional view of the mount taken along line  2 — 2  in FIG. 1; and  
     [0014]FIG. 3 is a cross-sectional view similar to FIG. 2 and showing an alternative embodiment of the mount. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT  
     [0015]FIGS. 1 and 2 shows an improved hydraulic mount assembly  10  according to the present invention. The mount assembly  10  is particularly adapted for mounting an internal combustion engine and/or transmission to a frame in a vehicle. The mount assembly  10  includes a generally cylindrical body  18 . An inner insert  20 , preferably formed of metal or plastic, is supported inside the body  18  by one or more elastomeric legs  22 . The inner insert  20  includes a bore  24  through which a fastener may extend to fasten the mount assembly  10  to the powertrain component or to the frame, as is well known. An outer insert  26  is disposed at least partially around the inner insert  20 . The outer insert  26  may be formed from aluminum, steel, or plastic.  
     [0016] A pumping or primary chamber  30  is formed by the rubber legs  22 . An elastomeric diaphragm  36  of natural or synthetic rubber partially defines a secondary chamber  32 . The pumping chamber  30  is in fluid communication with the secondary chamber  32  through an orifice track  34 . A finger  38  extends from the inner insert  20  into the pumping chamber  30 . The finger  38  is covered with an elastomeric skin, and a compliant element  40  is attached around the skin of the finger so as to be disposed in the pumping chamber  30 .  
     [0017] The chambers  30  and  32 , and the orifice track  34 , are filled with a damping liquid such as a glycol-based solution. In a preferred embodiment, the compliant element  40  is a closed-cell foam or a self-contained gas spring. The compliant element  40  is more compliant than the bulge stiffness of the elastomeric legs  22 , which allows the mount assembly to accommodate the volume changes associated with small amplitude motions and results in a lower rate. Under large amplitude motion, the compliance of the foam is exceeded and it cannot accommodate the volume change. In this condition, fluid is forced through the orifice track  34 , creating damping for motion control. In particular, the operating characteristics of the mount can be varied by changing the volume and/or density of the trapped air or foam comprising the compliant element  40 .  
     [0018]FIG. 3 shows an alternative embodiment of the mount assembly in which one or more cavities  41  are formed in communication with the pumping chamber  30 . A compliant element  42 , similar to the compliant element  40  discussed above with respect to FIGS. 1 and 2, is positioned in each of the cavities  41 . In all other respects, the embodiment shown in FIG. 3 operates similarly to the embodiment of FIGS. 1 and 2.  
     [0019] While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.