Abstract:
A hydraulic mount provides active control of dip rate performance through use of an orifice track connecting a primary pumping chamber of the mount to a secondary fluid chamber having a movable wall, and an actuator for regulating pressure applied to the movable wall for controlling movement of the movable wall. With little or no pressure applied to the movable wall, the mount provides significant isolation and very little damping in a predetermined and designed frequency range. As pressure is applied to the movable wall, the stiffness of the mount is increased significantly, to thereby provide substantial damping.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to resilient mounts of the type used in motor vehicles, and more particularly to resilient mounts using a hydraulic fluid.  
         BACKGROUND OF THE INVENTION  
         [0002]    It has long been the practice in motor vehicles, such as automobiles and trucks, to suspend engines and other heavy components that generate vibrations when operating on resilient mounts that isolate and damp the vibration from reaching the passenger compartment of the vehicle. It is desirable in such circumstances to provide a mount that is relatively soft for low amplitude higher frequency vibrations, such as those produced while an engine is operating at idle speed or at a constant speed while the vehicle is cruising along on a smooth road. Making the mount too soft, however, results in a structure that may not be capable of damping the motion of a heavy mass, such as the engine, when the vehicle is traveling over a bumpy road.  
           [0003]    The competing requirements for a mount that is soft enough to isolate low amplitude vibrations generated by an engine at idle, and yet is robust enough to damp and limit the movement of an engine relative to the vehicle chassis when the vehicle is encountering a bumpy road surface, have caused the designers of resilient mounts to employ hydraulic fluid flowing between multiple chambers within the mount, together with judiciously sized orifice tracks and fluid valve arrangements providing fluid communication between the chambers, to provide mounts that exhibit different damping performance dependent upon the magnitude and frequency of the vibratory input to the mount, without any active external control of fluid flow between the various chambers. Such mounts are known as passive rate dip mounts.  
           [0004]    Ideally, a rate dip mount would provide vibration isolation with almost no damping during idle or constant engine speed operation, so that the mount would transmit very little vibration from the engine to the vehicle chassis at idle or constant engine operation. An ideal mount would, however, provide significant damping for controlling engine bounce induced during events such as driving over a bump. These competing requirements for mount performance make designing a passive rate dip mount offering acceptable performance under all driving conditions a challenging task. As a result, compromises must be made which have resulted in prior rate dip mounts that do not provide optimum performance. In addition, prior mounts had to be designed for use in a given application, and could not be readily applied, or tuned, for use in other applications or under operating conditions other than those used in designing the mount.  
           [0005]    What is needed, therefore, is an improved hydraulic rate dip mount, offering better overall performance than prior mounts. It is also desirable that the improved mount incorporate features which allow the operating characteristics of the mount to be tuned for use in multiple applications and adjusted to match changing driving conditions.  
         SUMMARY OF THE INVENTION  
         [0006]    Our invention provides an improved hydraulic mount through use of an orifice track connecting a primary pumping chamber of the mount to a secondary fluid chamber having a movable wall, and an actuator for regulating pressure applied to the movable wall to control movement of the movable wall. With little or no pressure applied to the movable wall, the mount provides significant isolation and very little damping. As pressure is applied to the movable wall, the stiffness of the mount is increased significantly, to thereby provide substantial damping.  
           [0007]    In one form of our invention, a hydraulic mount includes a resilient hollow body and an actuator. The resilient hollow body defines a primary fluid chamber and a secondary fluid chamber, separated by a partition, and connected in fluid communication by an orifice track passing through the partition. The secondary fluid chamber includes a movable wall thereof having an inner and an outer surface with the inner surface of the movable wall being in fluid communication with the secondary fluid chamber. The actuator regulates pressure acting against the outer surface of the movable wall.  
           [0008]    The resilient hollow body may further define a pressure regulating chamber separated from the secondary fluid chamber by the movable wall and having a pressure regulating orifice passing into the pressure regulating chamber. The pressure regulating chamber is separated from the secondary fluid chamber by the movable wall and is partially bounded by the outer surface of the movable wall. The actuator regulates fluid flow through the pressure regulating orifice.  
           [0009]    The mount may further include a fluid reservoir, separate from the primary, secondary, and pressure regulating fluid chambers, and a first orifice track providing fluid communication between the primary fluid chamber and the reservoir. In this form of our invention, the orifice track between the primary fluid chamber and the secondary fluid chamber defines a second orifice track of the mount.  
           [0010]    Our invention may also take the form of a method for operating a hydraulic mount having a resilient hollow body defining a primary fluid chamber, a reservoir, a secondary chamber having a movable wall, a first orifice track providing fluid communication between the primary chamber and the reservoir, and a second orifice track providing fluid communication between the primary chamber and the secondary chamber, by regulating pressure acting against the movable wall from outside of the secondary chamber, to thereby control stiffness and damping characteristics of the mount. Where the resilient hollow body further defines a pressure regulating chamber separated from the secondary fluid camber by the movable wall for containing a fluid within the pressure regulating chamber, a method according to our invention may further include regulating the pressure of a fluid contained in the pressure regulating chamber.  
           [0011]    The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary 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]    [0012]FIG. 1 is a cross section, showing a first exemplary embodiment of a hydraulic mount, according to our invention; and  
         [0013]    [0013]FIG. 2 is a cross section, showing a second exemplary embodiment of a hydraulic mount according to our invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 illustrates an exemplary embodiment of a hydraulic mount  10 , according to our invention. The hydraulic mount  10  includes a resilient hollow body  12  defining a primary fluid chamber  14 , a reservoir  16 , and a secondary chamber  18  having a movable wall in the form of a flexible diaphragm  20 . A first orifice track  22  provides fluid communication between the primary fluid chamber  14  and the reservoir  16 . A second orifice track  24  provides fluid communication between the primary chamber  14  and the secondary chamber  18 . An actuator  26  regulates pressure acting against the movable wall  20 , from outside of the secondary chamber  18 , for regulating stiffness of the mount  10 , in a manner described in more detail below.  
         [0015]    The resilient hollow body  12  of the mount  10  includes a partition  28  formed by an upper partition plate  30  and a lower partition plate  32 . The upper and lower partition plates  30 ,  32  have complimentary shaped elements on faying surfaces thereof, that form the first orifice track  22 , and the secondary fluid chamber  18 , when the upper and lower partition plates  30 ,  32  are joined together. The partition plate  28  also separates the primary fluid chamber  14  from the reservoir  16 . The reservoir  16  is also partially defined by a second movable wall, in the form of a second flexible diaphragm  34  attached to, and extending from, the partition  28 .  
         [0016]    The first track  22  includes an inlet  36  opening in to the primary fluid chamber  14 , and an outlet  38  opening into the reservoir  16 , connected by a groove  40  in the lower partition plate  32 . The groove  40  extends generally around a central mount axis  42 . The shape, length, and size of the groove  40 , together with the physical characteristics of the inlet and outlet openings  36 ,  38  of the first orifice track  22  are selected to provide a desired stiffness and damping characteristic of the mount  10 .  
         [0017]    The upper plate  30  further defines the second orifice track  24 . In the embodiment shown in FIG. 1, the second orifice track  24  extends vertically along the mount axis  42 . The second orifice track includes an inlet  44  opening into the primary fluid chamber  14 , and an outlet  46  opening into the secondary fluid chamber  18 , connected by a bore  48  in the upper partition plate  30 .  
         [0018]    [0018]FIG. 2 shows a second embodiment of a mount  10 , according to our invention, having a second orifice track  24  of a different shape than the second orifice track  24  shown in FIG. 1. The second orifice track  24  of FIG. 2 includes an inlet  44  opening in to the primary fluid chamber  14 , and an outlet  46  opening into the secondary fluid chamber  18 , connected by a groove  48  in a third partition plate  50  attached to the upper partition plate  30 . The groove  48 , in the embodiment of FIG. 2, extends generally around the central mount axis  42 .  
         [0019]    The shape, length, and size of the bore or groove  48 , together with the physical characteristics of the inlet and outlet  44 ,  46  of the second orifice track  24 , in either the embodiment of FIG. 1 or FIG. 2, are judiciously selected to provide a particular operating characteristic of the mount  10 .  
         [0020]    The partition  28  further defines a pressure regulating chamber  52  separated from the secondary fluid chamber  18  by the first diaphragm  20 , and a pressure regulating orifice  54  passing through the lower plate  32  of the partition  28  into the pressure regulating chamber  52 . The pressure regulating chamber  52  is separated from the secondary fluid chamber  18  by the diaphragm  20  and is partially bounded by the outer surface  56  of the diaphragm  20 .  
         [0021]    The mount  10  includes a cup-shaped base plate  58  attached to the partition  28 , and having a lower mount attachment stud  60  extending from the base plate along the axis mount  42 . The mount  10  also includes an upper mounting stud  62  extending along the mount axis  42  from the upper end of the mount  10 . The upper mounting stud  62  extends from a base  63  attached to the partition  28  by a flexible element  64  made from natural rubber or a similar material.  
         [0022]    The actuator  26  includes a movable valve poppet  66  for regulating fluid flow through the pressure regulating orifice  54 . The poppet  66  in the exemplary embodiments takes the form of a stopper  66  of resilient material that deforms slightly when forced against the lower partition plate  32  around the pressure regulating orifice  54 , to close off and seal the pressure regulating orifice  54 .  
         [0023]    The resilient stopper  66  is attached to the end of a movable armature  68  of a solenoid  70 . The solenoid  70  also includes an electro-magnetic coil  72  that generates an electro-magnetic field acting on the armature  68  of the solenoid  70 , when the coil  72  is connected to a source of electrical current, to generate a corresponding force on the armature  68  for moving the resilient stopper  66  in and out of engagement with the lower plate  32  of the partition  28 .  
         [0024]    A return spring  74 , in the form or a helical compression spring, a wavy washer, or a Bellville washer, between the armature  68  and the coil  72  provides a return force for moving the armature  68  into contact with the lower plate  32  when the solenoid  70  is not energized. In the embodiment of our invention shown in FIG. 1, the actuator  26  is mounted in a cup-shaped actuator mount  76  attached to the base-plate  58  of the mount  10 . In the embodiment of the mount  10  shown in FIG. 2, the actuator  26  is mounted in an actuator mount  78  attached to the partition  28 . The actuator mount  78  includes one or more openings  80  extending through the actuator mount  78  to allow air inside the base-plate  58  to flow through the openings  80  to enter or be exhausted from the pressure regulating chamber  18  through the pressure regulating orifice  54 .  
         [0025]    When the mount  10  is operating in a vibration isolating mode, the actuator  26  is energized to pull the armature  68  and poppet  66  away from the partition  28 , to thereby open the pressure regulating orifice  54 . With the pressure regulating orifice  54  open, the pressure regulating chamber  52  is exposed to and operates at atmospheric air pressure. The diaphragm  20  can move freely to accommodate fluid flow through the second track  22 , and in and out of the secondary fluid chamber  18 .  
         [0026]    When it is desired to increase the stiffness of the mount  10  to provide significant damping, the actuator  26  is de-energized. The return spring  74  urges the armature  68  and poppet  66  into contact with the partition  28 , to thereby block the pressure regulating orifice  54  and create a trapped pocket of air in the pressure regulating chamber  52 . For fluid to flow through the second orifice track  24 , while the pressure regulating orifice  54  is blocked, the air trapped in the pressure regulating chamber  52  must be compressed. This need to compress the trapped air causes fluid to flow through the orifice track  40 . As a result, the mount generates damping and higher dynamic stiffness at a lower frequency of interest  
         [0027]    Those skilled in the art will recognize that the actuator  26  can be energized at any time or frequency, to change the performance of the mount  10 . Because actuation of the secondary orifice track  24  is done actively, rather than passively as in prior passive rate dip mounts, a mount  10  according to our invention offers greater flexibility of operation.  
         [0028]    It will also be recognized, that although the embodiments disclosed herein use a simple two-state operation of the actuator  26  to completely open, or alternatively to completely close the pressure regulating orifice  54 , in other embodiments of our invention it may be desirable to utilize the actuator  26  and poppet  66  for modulating flow through the pressure regulating orifice  54 , to thereby provide continuously variable control of the mount characteristics. We contemplate that in other embodiments of our invention, it may be desirable to control the actuator  26  with a technique such as pulse width modulation, or to configure the poppet  66  and actuator  26  to modulate flow through a partially open pressure regulating orifice  54 .  
         [0029]    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.  
         [0030]    For example, although the exemplary embodiments expressly disclosed herein utilize an electrically activated actuator  26 , other types of actuators using power sources such as fluid pressure, vacuum, or mechanical force may also be used in practicing our invention. The movable wall  20  may also take many forms other than the flexible diaphragm disclosed herein, such as a piston or a bellows.  
         [0031]    The various elements and aspects of the invention may also be used independently from one another, or in different combinations or orientations than are described above and in the drawing with regard to the exemplary embodiment. The first and second attachment devices  60 ,  62  may take many other forms, and can be oriented at an angle to one another and/or the mount axis  42  to facilitate use of the invention in a wide range of applications. The invention may be practiced in mounts providing resilient support of a wide variety of masses, in addition to the automotive engine mounts described herein.  
         [0032]    The scope of the invention is indicated in the appended claims. All changes or modifications within the meaning and range of equivalents are embraced by the claims.