Abstract:
A switchable hydraulic bushing ( 10 ) is provided in which a secondary chamber ( 60 ) is sealed so as to be air-tight and is provided with a bleed passage ( 38 ) for allowing for the free flow of air into and out of the secondary air chamber ( 60 ). A closure device ( 40 ) is provided for closing off the bleed passage ( 38 ) for sealing off the air-tight secondary chamber ( 60 ) to alter the flexibility characteristics of the walls ( 58 ) of the compensation chambers ( 52 ) and effectively turn off the hydraulic damping function of the hydraulic bushing ( 10 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/492,918, filed on Aug. 6, 2003. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to hydraulic bushings and more particularly to a switchable hydraulic bushing.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hydraulic bushings or mounts are used to dampen and reduce vibrations transmitted between an engine and a chassis in vehicles. Generally, a hydraulic engine mount includes an inner core connected to an inner support structure, commonly known as an inner ring, by an elastomeric material to form an assembly. The assembly is received in a housing. The housing is mounted to an engine and a chassis. A hydraulic fluid is provided in a chamber formed between the assembly and the housing. When the engine or chassis receives a vibration, hydraulic fluid in the engine mount is displaced into desired chambers to dampen the vibration and reduce its transmission. Although the hydraulic damping provided by the hydraulic bushing is desirable for most modes of operation, there are certain modes of operation (i.e. vibration frequencies) for which the hydraulic damping is not desirable.  
       SUMMARY OF THE INVENTION  
       [0004]     Accordingly, the present invention provides a switchable hydraulic bushing which is provided with a system for deactivating the hydraulic damping effect of the hydraulic bushing. In particular, the present invention provides a switchable hydraulic bushing mount including a housing, a core disposed in the housing and an elastomeric member bonded to an outer surface of the core and disposed in the housing. The elastomeric member combines with the housing for defining a pumping chamber and at least one compensation chamber fluidly interconnect to one another by an inertia track extending along a periphery of the elastomeric member. The compensation chamber is defined by an interior wall surface of the housing and a flexible wall portion of the elastomeric member. The flexible wall portion of the compensation chamber also defines a portion of a secondary chamber adjacent to the compensation chamber with the secondary chamber being air-tight and including a bleed passage communicating thereto. A closure device is operable for closing the bleed passage in order to seal off the secondary chamber and thereby reduce the ability of the flexible wall portion to flex and provide hydraulic damping for the hydraulic bushing.  
         [0005]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0007]      FIG. 1  is a cross-sectional view of the switchable hydraulic mount according to the principles of the present invention;  
         [0008]      FIG. 2  is a perspective view of the elastomeric member utilized in the switchable hydraulic mount according to the principles of the present invention;  
         [0009]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  of  FIG. 2 ; and  
         [0010]      FIG. 4  is a perspective view of an inner support structure of the elastomeric member according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0012]     With reference to  FIGS. 1 and 3 , a hydraulic bushing or mount  10  is shown. The switchable hydraulic mount  10  is particularly adapted for use as an engine mount in a vehicle. However, the switchable hydraulic mount can also be utilized in other automotive applications and non-automotive applications. The hydraulic engine mount  10  includes a housing  12  commonly referred to as a can having an elastomeric member  14  received therein. The elastomeric member  14  is bonded to the outer surface of a core  16 . The core  16  is mounted to a first support structure  18  by a threader fastener  20 . The housing  12  is mounted to a bracket  24  which is mounted to a second support structure  26 . It should be understood that the switchable hydraulic mount  10  according to the principles of the present invention can be mounted between any support members  18 ,  26  as is desired. In a particular application, for use as an engine mount, the support structure  18  can be fastened to an engine  22  of a vehicle while the support structure  26  can be part of a vehicle frame or body.  
         [0013]     The housing  12  includes a cup-shaped can  30  that receives the elastomeric member  14 . The can is received in the bracket  24 . The can  30  includes a base portion  32  and a cylindrical side wall portion  34  extending from the base portion  32 . The cylindrical side wall portion  34  has an open end with the edge  36  of the cylindrical side wall being crimped inwardly in order to retain the elastomeric member  14  therein. The can  30  includes an aperture defining a bleed passage  38  in the base portion  32  of the can  30 . A closure device  40  is provided for closing off the bleed passage  38  in the can  30 . The closure device  40  can include an electronic solenoid  42  which can be activated to cause a valve member  44  to engage the valve seat surface  46  surrounding the bleed passage  38 .  
         [0014]     The elastomeric member  14  as illustrated  FIGS. 1 and 2  include a pumping chamber  50  and a pair of compensation chambers  52  which are in fluid communication with the pumping chamber  50  via an inertia track  54  which extends around a perimeter of the elastomeric  14 . In particular, as illustrated in  FIG. 1 , the pumping chamber  50  communicates with the inertia track  54  via an axially extending channel (not shown) that extends axially from the pumping chamber  50  to the inertia track  54 . As illustrated in  FIG. 2 , the inertia track  54  communicates with at least one of the compensation chambers  52  via an axially extending channel  56  as illustrated in  FIG. 2 .  
         [0015]     As is known in the art, the pumping chamber  50  and compensation chambers  52  are provided with hydraulic fluid therein that provides a damping function when the core element  16  is moved relative to the housing  12  thereby causing compression of the pumping chamber  50  which results in hydraulic fluid being forced through the inertia track  54  towards the compensation chambers  52 . The compensation chambers have a flexible wall portion  58  as best illustrated in  FIG. 3  that is capable of flexing in spring-like manner in order to absorb vibrations via the pulsing of the hydraulic fluid within the hydraulic bushing  10 .  
         [0016]     A secondary air chamber  60  is provided is provided adjacent to the flexible wall portion  58  of the compensation chamber  52  as best illustrated in  FIGS. 2 and 3 . The secondary chamber  60  is an air-tight chamber which communicates with the bleed passage  38  provided in the housing  12 . The bleed passage  38  is intended to remain normally open to allow the free flow of air in and out of the secondary chamber  60  so that the hydraulic bushing  10  functions to properly provide a hydraulic damping function. When it is desired to switch off the hydraulic damping function, the closure device  40  is operable to close off the bleed passage  38  so as to seal the air within the secondary chamber  60 . With the secondary chamber  60  sealed, the flexible wall portions  58  disposed between the compensation chambers  52  and the secondary chamber  60  have limited flexibility due to the compression of air within the secondary chamber  60  thereby limiting the motion of the flexible wall portion  58 . Thus, the hydraulic damping function of the hydraulic bushing  10  is effectively switched off.  
         [0017]     The switchable hydraulic bushing  10  of the present invention has the ability to select coupled or decoupled behavior including the presence or lack of hydraulic damping. The ability to tune and possibly to modulate the switching behavior and extent of damping is thus provided by control of the closure device  40 . The switchable hydraulic bushing  10  of the present invention provides the ability to switch, via an electronically controllable switch, for several possible control situations. The system of the present invention provides a relatively low-cost implementation for providing the added switchability in the hydraulic bushing  10 . Furthermore, the system provides low complexity and high manufacturing reliability.  
         [0018]     The elastomeric member  14  according to the principles of the present invention is provided with an interior support structure  70  as best illustrated in  FIGS. 1, 3 , and  4 . The inner support structure includes a first ring  72  having an annular wall  72   a  and an outer end wall  72   b  and an inner end wall  72   c . The inner support structure  70  also includes a second ring  74  including an annular wall  74   a and an outer end wall  74   b  and an inner end wall  74   c . A plurality of legs  76 A-C are formed between the first and second rings  72 ,  74 . The plurality of legs  76 A-C of the inner support structure  70  include a first pair of legs,  76 A,  76 B that are disposed on opposite sides of the pumping chamber  50 . In addition, a third leg  76 C is provided between the first and second compensation chambers  52 . In addition, the outer end wall  72 B and inner end wall  72 C of the inner support structure  70  are provided on opposite sides of the inertia track  54  to provide support thereto.  
         [0019]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.