Abstract:
A hydraulic mount having first and second fluid tracks, and a decoupler functioning as an air spring with two remotely selectable settings. The settings allow tailoring of the air spring characteristics to provide mount damping for differing engine operating states, such as engine idle. A solenoid is used to select a smaller or larger air volume to control the characteristics of the air spring and, in turn, the dynamic response of the hydraulic mount. An integral controller provides switched operation of the solenoid and compensates for variations in temperature and input voltage, as well as minimizing electrical noise generated by the solenoid when it is energized.

Description:
TECHNICAL FIELD 
     The present invention pertains generally to a hydraulic mount for vibration damping and, more particularly, a hydraulic mount assembly including a decoupler that functions as an air spring to provide remotely selectable damping characteristics to match the characteristics of the input vibration. 
     BACKGROUND OF THE INVENTION 
     Hydraulic mounts are used in many situations where it is desired to isolate sources of vibration, or to protect sensitive equipment from shock and vibration. Examples include, but are not limited to: industrial equipment and machinery isolators; industrial robotics; building, bridge and ship isolators; military weapons systems; agricultural equipment; and construction equipment. Hydraulic mounts are also often used with vehicle powertrains to control movement of the powertrain in response to forces, such as reaction torque and vibration. The mounts serve a second function, that of isolating the engine from the body of the vehicle. A well-known type of hydraulic vibration damping mount generates damping in a predetermined frequency range of vibrations by pumping a hydraulic fluid through an orifice track of predetermined dimensions. The dimensions of the orifice track are typically such that the hydraulic fluid resonates at certain frequencies of input vibration, which maximizes the damping of the mount. At vibration frequencies above the track resonance the dynamic rate of the mount increases, reducing the isolative properties of the mount. Hydraulic mounts may also be provided with devices known as decouplers, which are disposed in a space formed within the mount orifice plate, for example, and allowed limited free travel within the space to “short circuit” the fluid from flowing through the orifice track, thus generating a low magnitude of dynamic stiffness necessary to provide isolation of certain vibrations. When the input vibration to the mount exceeds the allowable limit of the free motion of the decoupler, the hydraulic fluid flows through the orifice track, thereby generating the mount damping characteristics. 
     For optimum isolation, the dynamic rate of the mount at the input vibration or “disturbance” frequency should be as low as possible. Since the resonant frequency of the hydraulic damping mount is fixed by the dimensions of the orifice track, prior art mounts must be designed to cover as broad a range of vibration characteristics as possible, or to damp the most prevalent vibration frequencies, to provide effective damping. This necessarily results in a tradeoff or compromise in the performance of the mount. For example, a vehicle&#39;s powertrain exhibits varying vibration characteristics as the engine changes from an idle state, where the engine is operating at a low rate (typically measured in revolutions per minute or “RPM”), to an operating state, where the engine operates at a higher RPM. These changing input vibration frequencies are imposed upon the mount. However, due to the fixed physical properties of the mount, the mount&#39;s effectiveness at damping the vibration will be greater or lesser, depending upon the mismatch between the disturbance frequency and the resonant frequency of the mount. Accordingly, there is a need for a hydraulic damping mount that provides improved performance over a broader range of disturbance frequencies. 
     SUMMARY OF THE INVENTION 
     The present invention is a bi-state hydraulic mount that provides improved damping performance over a broader range of input vibration frequencies by means of a first hydraulic fluid track, a second hydraulic fluid track and a decoupler functioning as an air spring having two remotely selectable settings. The characteristics of the air spring can thus be tailored to provide mount damping compatible with a particular engine operating state. For example, a first setting of the air spring may reduce the dynamic rate of the mount during engine idle conditions for improved isolation. The second air spring setting may be tuned to provide mount damping tailored to the disturbances generated by the engine when it is operating at RPMs above idle. 
     The air spring is formed by an elastomeric decoupler that is held captive in an orifice plate assembly and encloses a selectable volume of air. The characteristics of the air spring are controlled by the volume of air. An integral solenoid is used to select either a first air cavity alone, or the first cavity in combination with a second air cavity. When the solenoid is not energized, a spring-actuated plunger seals an orifice between the first and second air cavities, limiting the volume of air enclosed by the decoupler to the first cavity and increasing the compliance of the decoupler. The relatively high stiffness of the decoupler does not allow hydraulic fluid to easily pass into the first fluid track, forcing the fluid to flow into the second fluid track to control vibration from the engine, such as when the engine is operating above idle. When the engine is at idle, the solenoid may be actuated, moving the plunger away from the orifice and allowing communication between the first and second air cavities. The resulting increased volume of air enclosed by the decoupler reduces the compliance of the decoupler, allowing resonance in the first fluid track such that the dynamic rate of the mount is reduced for improved isolation during engine idle conditions. 
     An integral controller is used to energize the solenoid. The controller allows low-level logic control of the solenoid, reducing the electrical load placed on powertrain control components. The controller also compensates for variations in temperature and operating voltage. In addition, the controller limits the actuation rate of the solenoid so as to reduce noise during actuation. 
    
    
     
       SUMMARY OF THE DRAWING 
       Further features of the present invention will become apparent to those skilled in the art to which the present embodiments relate from reading the following specification and claims, with reference to the accompanying drawing, in which  FIG. 1  is a longitudinal central section view of a hydraulic mount in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description which follows, like parts are marked throughout the specification and drawing with the same reference numerals. The drawing figure is not necessarily to scale in the interest of clarity and conciseness. 
       FIG. 1  shows a hydraulic mount, generally designated  10 , embodying the invention. The mount  10  includes a generally cylindrical, cup-shaped base  12  suitably secured to a mounting member or bracket assembly  14  by any conventional means, such as by molding, adhesives, press fit, welding and fasteners. The base  12  may be made from any suitable material, such as formed metal, and includes a peripheral side wall  16  and a circumferential, radially outwardly projecting flange  18 . The base  12  may also include a key  41  to orient the mount  10  to an external bracket or brace (not shown) during installation and prevent the mount from rotating after being installed. The mount  10  is further characterized by a generally cylindrical molded elastomer body  20 , which is reinforced by a suitable core part  22  made from any suitable material, such as metal, plastic or composites. The body  20  is molded to a central metal hub member  24 , which supports a mounting member  26  for connecting the mount  10  to an engine assembly or the like. 
     The elastomer body  20  includes a central, generally cylindrical depending portion  28  that, in the position shown, is engageable with an orifice plate assembly  32  comprising an upper, generally cylindrical orifice plate  34  and a lower, generally cylindrical orifice plate  36 . The upper orifice plate  34  further comprises an annular opening  35 , which defines a first fluid track  33 . The lower orifice plate  36  further comprises an orifice  38 . Upper and lower orifice plates  34 , 36  are shown in assembly to define an annular passage or second fluid track  42  which opens through a first port  44  to a pumping chamber  46 . A circumferentially spaced second port  48  communicates hydraulic fluid between second fluid track  42  and a second fluid chamber or reservoir  50  defined by a generally cup-shaped flexible diaphragm  62 . 
     Lower orifice plate  36  also defines a generally cylindrical recess  51  that receives an elastomeric, cylindrical, disk-shaped decoupler member  40 . A first air cavity  52  is defined by a peripheral outer wall  54  and a reduced-diameter, generally planar bottom wall surface  56 , which is relieved to provide a space between bottom wall surface  56  and the decoupler  40 , as shown. The decoupler  40  is also characterized by a circumferential rim part  58  that is trapped in fluid-tight sealing engagement between the upper orifice plate  34  and the lower orifice plate  36 . However, a major part of the body  60  of the decoupler  40  radially inward of the rim  58  may be annularly recessed and allowed limited space within the recess  51  between the bottom surface  56  and the decoupler  40 . Upper orifice plate  34  is also provided with a relieved cylindrical wall surface  37  to provide space between decoupler  40  and orifice plate  34  except at the rim  58 . 
     A second air cavity  70 , defined by lower orifice plate  36  and bottom wall surface  56 , is in communication with first air cavity  52  via orifice  38 . In this regard, the first and second air cavities may be filled with air or a suitable inert gas. A solenoid  64  having a plunger  66  and a spring  68  is mounted to the lower orifice plate  36  such that an actuating tip or end  67  of the plunger is aligned with orifice  38 . The action of the solenoid  64  is such that the tip  67  of plunger  66  is held away from orifice  38  when the solenoid is energized, allowing communication between first air cavity  52  and second air cavity  70 . When the solenoid is unenergized, tip  67  is held against orifice  38  by spring  68 , effectively blocking communication between first air cavity  52  and second air cavity  70 . An integral controller  72 , mounted to lower orifice plate  36  within mount  10 , is electrically connected to solenoid  64 . The integral controller  72  provides switched electrical power to energize solenoid  64  upon command, and also provides compensation for variations in temperature and source voltage. Further, the controller  72  controls the energization rate of the solenoid  64  to reduce the generation of electrical noise by the solenoid. In addition, controller  72  accepts low-power logical control signals, reducing the electrical load placed on powertrain control components. An electrical connector  74  is mounted to the lower orifice plate  36  and sealed from internal exposure to the hydraulic fluid within the mount  10 . The electrical connector  74  provides an external interface for electrical power and logical control to the integral controller  72 . 
     In a first embodiment of the present invention, the second fluid track  42  is tuned to provide the desired dynamic rate to provide engine control during operation above idle. Movement of the elastomer body  20  causes fluid movement between the pumping chamber  46  and the reservoir  50 , which are in communication via first and second ports  44 , 48  and second fluid track  42 . Solenoid  64  is unenergized in this state, causing the first air cavity  52  and second air cavity  70  to be blocked from communication by virtue of tip  67  of plunger  66  closing off orifice  38 . The air volume of only the first air cavity  52  in communication with decoupler  40  increases the compliance of decoupler. The decoupler  40  functions as an air spring supported by the first air cavity  52  to damp relatively low amplitude vibrations. The relative stiffness of the decoupler  40  does not allow fluid to easily pass into the first fluid track  33 , forcing the fluid to flow into the second fluid track  42  to damp vibration. When the engine is at idle, the solenoid is actuated, causing tip  67  of plunger  66  to move away from orifice  38  and allowing first and second air cavities  52 , 70  to communicate. The increased air volume resulting from the communication of air cavities  52 , 70  with decoupler  40  lowers the compliance of the decoupler, allowing resonance in the first fluid track  33  and generating a reduction in the dynamic response of the mount to better match the disturbance frequencies of the engine at idle. 
     In an alternate embodiment of the present invention, the first fluid track  33  is configured to provide dynamic response reductions at two different frequency ranges. One example would be to provide a reduction in the dynamic rate of the mount  10  during warm idle and cold idle engine states for improved isolation. A second example is to provide reduction in the dynamic rate of the mount  10  at several structural resonant frequencies. The volume of first air cavity  52  is sized for a dynamic response reduction at a first desired frequency range. When solenoid  64  is unenergized, first air cavity  52  generates a decoupler compliance for resonance of first fluid track  33  at the first desired frequency range. When the solenoid  64  is energized and the first and second air cavities  52 , 70  are in communication with decoupler  40 , the compliance of the decoupler will be reduced due to the increased volume of air in communication with decoupler  40 , lowering the resonant point of the first fluid track  33  to a second, lower desired frequency range. The second frequency range is determined by the combined volume of the first and second cavities  52 , 70 . The second fluid track  42  is tuned to provide the desired dynamic rate to provide engine control during operation above idle. 
     The present invention provides a simple method for assembling a controllable hydraulic mount. A diaphragm  62  is placed onto the orifice plate assembly  32 . The diaphragm  62  and orifice plate assembly  32  are then placed inside the base  12 . The elastomer body  20  is placed over the base  12 , and the elastomer body is then crimped around the base. The mount is filled with hydraulic fluid by any conventional means, such as fill ports, plugs, caps, seals, and the like. The hydraulic fluid (referred to herein generally as “fluid”) may be any compatible fluid, such as a mixture of water and ethylene glycol. 
     The various embodiments have been described in detail with respect to specific embodiments thereof, but it will be apparent that numerous variations and modifications are possible without departing from the spirit and scope of the embodiments as defined by the following claims.