Abstract:
A switchable locking torque strut assembly and associated method are provided. The strut assembly is interposed between an associated vehicle chassis and an associated vehicle powertrain to provide high elastomeric rate resistance during start-up and/or shutdown of an associated internal combustion engine (ICE) and low elastomeric rate resistance during idle and/or driving events. The strut assembly includes a housing and a shaft at least partially received in the housing and operatively mounted for selective relative movement relative to the housing. A locking assembly is interposed between the strut and the housing for selectively locking the strut relative to the housing in response to start-up and/or shutdown of the ICE.

Description:
This application claims the priority benefit of U.S. provisional application 61/589,621, filed 23 Jan. 2012. 
    
    
     BACKGROUND 
     In order to make vehicles more fuel efficient, many manufacturers are implementing “Start/Stop” technology, where the engine is shut off when the vehicle comes to a stop and is restarted when acceleration is required. With the engine starting and stopping so frequently, reducing the occupant vibrations during these events is paramount. 
     The issue this disclosure is trying to solve is to control the high displacement vibrations generated during start-up and shut-down of ICE engines. This is an issue with most internal combustion engines, regardless of whether they are gas, diesel or hybrid (although some hybrids have a generator/motor that may reduce or prevent these vibrations). 
     Start-up is generally the bigger of the two issues, as the ignition cycle causes the powertrain to displace violently. The large displacement vibrations from this event cause noise and unwanted excitations in the passenger compartment. Shutdown typically does not create as high excitations (as it is not being driven by the combustion cycle), although shutdown can still create noise and unwanted excitations in the passenger compartment. When the ignition is shut off, the engine slows and RPMs drop, and as this occurs self-generated frequencies or engine orders excite low frequency rigid body modes in both the powertrain and chassis. This creates natural frequency oscillations which can intrude into the passenger compartment, disturbing the occupants. 
     Therefore a need exists for an inexpensive, reliable solution to address these oscillations. 
     SUMMARY 
     A switchable locking torque strut assembly is interposed between an associated vehicle chassis and an associated vehicle powertrain that provides high elastomeric rate resistance during start-up and/or shutdown of an associated internal combustion engine (ICE) and low elastomeric rate resistance during idle and/or driving events. The strut assembly includes a housing and a shaft at least partially received in the housing and operatively mounted for selective relative movement relative to the housing. A locking assembly is interposed between the shaft and the housing for selectively locking the shaft relative to the housing in response to start-up and/or shutdown of the ICE. 
     The locking assembly includes an expander and a generally annular collet that is selectively increased in dimension by the expander. 
     The expander and the collet each include cooperating surfaces that selectively increase and decrease a diameter of the collet as the expander and collet are moved relative to one another. 
     The locking assembly includes one of a solenoid or a motor/screw assembly that advances and retracts the collet by advancing and retracting the expander relative to the collet. 
     An elastomeric member and the expander are operatively connected to the associated vehicle and the shaft that expands the elastomeric member into engagement between the shaft and the housing. 
     In one embodiment, the locking assembly includes a motor and a drive screw operatively connected to the motor and to the expander for selectively advancing the expander relative to the elastomeric member that expands the elastomeric member into operative engagement with the housing and retracts the expander relative to the elastomeric member. 
     In another embodiment, the locking assembly includes a solenoid operatively connected to the expander for directly advancing and retracting the expander, and the elastomeric member is a rubber coating on at least a portion of the collet. 
     A biasing member urges the expander and the collet apart. 
     A method of selectively providing high elastomeric rate resistance between a chassis and a powertrain and low elastomeric rate resistance therebetween is provided. The method includes providing a strut having first and second ends between the chassis and the powertrain. The method further includes selectively locking the first end of the strut from moving relative to the second end, and selectively unlocking the first end of the strut to move relative to the second end. 
     The method includes configuring an elastomeric member as a part of the strut whereby the elastomeric member locks the first and second ends from moving relative to one another. 
     The method includes expanding the elastomeric member to radially lock the first and second ends. 
     The selectively locking step includes expanding the elastomeric member during start-up and/or shutdown of an associated internal combustion engine (ICE). 
     The selectively unlocking step occurs during idle and/or driving events. 
     One advantage of the present disclosure is the ability to control the motion of an internal combustion engine (ICE) during start-up and shut-down events, as an aid to the existing powertrain mounting system. 
     Another advantage is the provision of high elastomeric rate resistance during start-up and shutdown to control powertrain motion thereby reducing vibration excitations to the occupant during start/stop events. 
     Yet another benefit is the ability to switch to a low elastomeric rate state during idle and drive events for improved powertrain isolation. 
     A further benefit resides in the simple construction and method of operation. 
     Still other benefits and advantages will become apparent to those skilled in the art upon reading and understanding the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a strut assembly. 
         FIG. 2  is an exploded perspective view of the strut assembly of  FIG. 1 . 
         FIG. 3  is a longitudinal, cross-sectional view in perspective of the assembled strut assembly of  FIG. 1 . 
         FIG. 4  is a an exploded perspective view of an alternative strut assembly. 
         FIG. 5  is a longitudinal, cross-sectional view in perspective of the alternative assembled strut assembly of  FIG. 4 . 
         FIG. 6  is a perspective view of another alternative strut assembly. 
         FIG. 7  is a longitudinal, cross-sectional view in perspective of the alternative assembled strut assembly of  FIG. 6 . 
         FIG. 8  is an enlarged longitudinal, cross-sectional view of the alternative strut assembly of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     This strut works in a very simple fashion. One end is fastened through the isolator to the chassis (or cradle) and the other end is fastened through the isolator to the powertrain. The strut locks during the start-up and shutdown cycles, allowing only the rubber isolators to move, generating a high elastomeric rate along the axis of the strut. Positioned in the direction of greatest excitation of the engine, this will reduce the displacement of the powertrain, thereby reducing the vibration and noise perceived by the vehicle occupants. Once start-up or shutdown is complete, the strut is unlocked, and the shaft is allowed to travel in and out of the outer housing, providing little resistance to this motion, and isolating any incoming vibrations regardless of the shaft position relative to the housing. 
     This strut provides high elastomeric rate resistance during start-up and shutdown to control powertrain motion thereby reducing vibration excitations to the occupant during start/stop events, and switches to a low elastomeric rate state during idle and drive events for improved powertrain isolation. 
     In a first exemplary embodiment shown in  FIGS. 1-3 , strut assembly  100  includes a first portion or housing  102  at a first end of the strut assembly that at least partially receives a second portion or shaft  104  that forms a second end of the strut assembly. Each end of the strut assembly includes an eyelet  110 . The housing  102  includes an eyelet  110  and the shaft includes an eyelet  112 . Each eyelet  110 ,  112  receives a rubber isolator or bushing  120  that includes a central metal shaft  122 . The eyelets  110 ,  112 , with the rubber bushing  120  received therein, provide for attachment to the chassis or cradle (not shown) and the powertrain (not shown). An expander  130  has a threaded inner diameter which engages with a threaded outer diameter of the drive screw  140 . A motor  150  (which can be either a basic DC motor or stepper motor, for example) rotates or spins the drive screw  140  thereby moving the expander  130  along the axis of the drive screw. As the expander  130  is drawn toward the motor  150 , a tapered outer diameter of the expander presses against a tapered inside diameter of a collet  160  received on one end of the shaft  104 . Drawing the expander  130  into the collet  160  expands the collet radially outward against the inside diameter surface of the housing  102 . This binds the collet  160  to the inside of the housing  102 , preventing the shaft  104  from moving with respect to the housing. This is the locked state of the strut assembly, i.e., the first end (housing  102 ) and the second end (shaft  104 ) of the strut assembly  100  are locked against relative movement with respect to one another when the expander  130  is received within the collet  160  and expands the collet radially outward into engagement with the housing  102 . 
     When the motor  150  is operated or run in the reverse direction, the expander  130  is forced away from the motor and thereby collapses the collet  160 . This allows the shaft  104  to slide freely within the housing  102 . This is the unlocked state of the strut assembly  100 . 
     In a second exemplary embodiment ( FIGS. 4-5 ), like elements are identified by like reference numerals in the “ 200 ” series (e.g., housing  102  is now referred to as housing  202 ), and new components are identified by new reference numerals. Thus, strut assembly  200  includes a first portion or housing  202  that at least partially receives a second portion or shaft  204 . Each of the housing  202  and shaft  204  includes an eyelet  210 ,  212 , respectively, that receives a rubber isolator or bushing  220  that includes a metal shaft  222  along its inner diameter. This allows opposite ends of the strut assembly  200  to be secured to the chassis/cradle and the powertrain, respectively. An expander  230  has a threaded inner diameter which engages with a threaded outer diameter of a drive screw  240 . A motor  250  (which can be either a basic DC motor or stepper motor, for example) rotates or spins the drive screw  240  thereby moving the expander  230  along the axis of the drive screw. As the expander  230  is drawn toward the motor  250 , the expander compresses a rubber member or compressible grommet such as a rubber grommet  270 , forcing the grommet to expand against an inside diameter surface of a housing  202 . More particularly, the rubber grommet  270  is compressed between the expander  230  and a shaft end cap  272  when the expander  230  is drawn toward the motor  250  as the motor rotates in a first direction. This compresses the grommet  270  axially between the expander  230  and the shaft end cap  272 , and radially expands the grommet against the inside of the housing, preventing the shaft  204  from moving with respect to the housing  202 . This is the locked state of the strut. 
     When the motor  250  is run in the reverse direction, the expander  230  is forced away from the motor allowing the compressed rubber grommet  270  to withdraw from the inside diameter surface of the housing  202 , and allowing the shaft  204  to slide freely within the housing. This is the unlocked state. 
     Still another embodiment is illustrated in  FIGS. 6-8 . Again, for ease of understanding and purposes of brevity, like elements are identified by like reference numerals in the “ 300 ” series (housing  102  or  202  from the first and second embodiments of  FIGS. 2 and 4 , respectively, is now referred to as housing  302 ) while new components are identified by new reference numerals. This version of the electrically switchable torque strut assembly  300  eliminates use of a stepper motor or a DC motor to operate the drive screw and to pull an expander. Instead, the strut assembly  300  uses a solenoid  350  that is directly connected to expander  330  at one end. The expander  330  is selectively received in collet  360 . Preferably, the collet  360  is coated in elastomer or rubber to increase friction between the collet and the inner surface of housing  302  in the locked state. The increased friction likewise results in increased stiffness of the torque strut  300  in the locked state when compared with a locked collet without the rubber coating that could potentially slide if sufficient force is imposed thereon. Thus, the rubber on the collet  360  increases the sliding force considerably. The solenoid  350  directly pulls the expander  330  to the locked position and expands the collet  360  into frictional engagement with the housing  302 . When the strut  300  is electrically switched, a return spring  380  returns the expander  332  to the unlocked position (in the left-hand direction of  FIGS. 6-8 ) so that the collet  360  decreases in radial dimension in the housing  302 , whereby the housing and shaft  304  move relative to one another in the unlocked state. 
     The electrical wiring  390  extends through a sheath  392  to provide protection for the wiring as the wiring leads from an electronic control unit (ECU) (not shown) to the shaft or second portion  304  of the strut assembly where the wiring connects with the solenoid  350 . Another difference between the embodiment of  FIGS. 6-8  and the earlier embodiments is that the eyelets  310 ,  312  at opposite ends of the strut assembly  300  are disposed 90° relative to one another. 
     The disclosure is designed to function in temperature ranges from −40° C. to 125° C. The strut housing can be a plastic (likely glass reinforced nylon) or metal (most likely aluminum). The isolator on either end will be a rubber. The total mass of an exemplary embodiment of the disclosure as shown is about 200 g to 300 g, has a length of approximately 240 mm long in its nominal position, and a diameter of approximately 46 mm. The strut is designed to travel +/−30 mm in the preferred embodiment. However, one skilled in the art will recognize that these numerical values are exemplary only and the mass, size, and travel can all be changed and scaled to meet different application requirements. 
     This strut can be used with all powertrains (gas, diesel, or hybrid) that require control during start-up and shutdown. 
     Unlike, fluid filled struts, the strut of the present disclosure does not create undesired fluid resonances and creates little to no damping or rate resistance when in the unlocked state. The strut requires power only to switch between lock and unlock states, thereby conserving energy. 
     The locking and unlocking feature of this strut allows for a significant change in elastomeric rate between the two states. The strut can be locked, power removed, and the strut will hold the locked position. This is advantageous as this feature consumes no energy in the locked state, so that the strut can be locked during shutdown and will remain locked while the powertrain is off, until after the next start-up where power is applied and the strut unlocked for idle and drive conditions. 
     One end is fastened through the isolator to the Chassis (or Cradle) and the other is fastened through the isolator to the powertrain. The strut assembly locks during the start-up and shutdown cycles, allowing only the rubber isolators to move, generating a high elastomeric rate along the axis of the strut. Positioned in the direction of greatest excitation of the engine, this will reduce the displacement of the powertrain, thereby reducing the vibration and noise perceived by the vehicle occupants. Once start-up or shutdown is complete, the strut is unlocked, and the shaft is allowed to travel in and out of the outer housing, providing little resistance to this motion, and isolating any incoming vibrations regardless of the shaft position relative to the housing. 
     This strut provides high elastomeric rate resistance during start-up and shutdown to control powertrain motion thereby reducing vibration excitations to the occupant during start/stop events, and switches to a low elastomeric rate state during idle and drive events for improved powertrain isolation.