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FIELD OF THE INVENTION 
     The disclosed invention is directed generally to front end loader vehicles with an accessory, particularly an accessory for clearing snow, manure, etc., and more particularly apparatus for protecting the vehicle and driver when the scraping edge of the accessory strikes an immovable object when the scraping edge is sliding along the ground. 
     BACKGROUND 
     Commercial snow plows, front end loaders and snow blowers have a long history of use in removing snow from streets and highways. Over the past several decades the use of snow plows on light and medium duty trucks has become commonplace. Snow plows work well for clearing snow from roadways, particularly in open places and in areas where yearly snowfall totals are such that the snow can be readily pushed off the roadway. In densely populated urban areas, where real estate is at a premium, and in areas with large annual snowfalls, there is a need to be able to lift snow over snowbanks for deposit into large piles. Alternately, the snow is often lifted into dump trucks to be hauled and deposited elsewhere, or dumped into snow melting machines. In addition, snow blowers are widely used by people in clearing snow from their yards and sidewalks. 
     One of the issues related to the use of these snow clearing machines is that a great amount of stress is imparted to the structural components when plowing in areas such as those prone to frost heaving where manhole covers, and other relatively fixed objects, are struck by the moving scraping edge of the machine&#39;s clearing accessory. Not only do such encounters with immovable objects greatly shorten the life of these snow clearing machines, but they are also quite jarring to the machine operator and pose an enhanced risk of injury to the machine operator as well as others in the vicinity of the machines that are in operation. 
     Several devices have been developed for use with snow clearing machines, particularly, snow plows, whereby either the whole plow blade, or just a portion of it, pivots back up to about 90 degrees upon encountering a fixed object in the road (see for example U.S. Pat. Nos. 6,701,646 and 5,697,172, respectively). Such devices, while effective for some of the snow plow blades, are not compatible with some other snow clearing machines. For example, due to the different geometry of a loader bucket, the bucket&#39;s longitudinal depth combined with the required rear pivotal connections for lifting and dumping prevent such a pivoting back since such pivoting generally requires a pivot point on an angle greater than 45 degrees up from the leading edge. Also, since such buckets typically have a leading edge attached to the horizontal structure of the bucket bottom, the tilting back solutions are impractical because this would require tilting the whole bucket backwards by around 180 degrees. Consequently, there is a need for a device which allows the scraping edge of snow clearing machines to ride up over fixed objects upon impacting them, which thereby reduces the wear and tear on snow clearing machines while also enhancing the safety of the machine operator and the public at large. 
     BRIEF SUMMARY 
     The disclosed invention is directed to an apparatus connecting between a clearing accessory and a vehicle. In this context, “vehicle” means a structure comprising a body, wheels, and a means for self propulsion. Examples of the type of vehicles to which the invention may be most appropriately attached include all-terrain vehicles (ATVs), farm tractors, skid loaders, and pickup trucks. It is understood that the clearing accessory may be used for snow or other accumulations, such as, for example, manure. The inventive apparatus as attached to such vehicle provides for the scraping edge of clearing accessories to rise up and pass over fixed objects, rather than tilt backwards as in the prior art. 
     The accessory of interest has a scraping edge and a heel, and the apparatus includes a linkage assembly attachable to the vehicle. The linkage assembly has first and second pivot axes pivotally connecting with the accessory. The first pivot axis is beneath the second pivot axis. The linkage assembly has first and second configurations: the first configuration includes the first axis located in a first position horizontally relative to the second axis, the second configuration includes the first axis located in a second position horizontally relative to the second axis. The second position is horizontally separated in a direction toward the accessory relative to the first position. When the scraping edge of the accessory strikes an immovable object, the linkage assembly moves from the first to the second configuration. When the linkage assembly is in the first configuration, the scraping edge and the heel of the accessory are both resting on ground. When the linkage assembly is in the second configuration, the heel of the accessory is on the ground and the scraping edge is elevated to allow the scraping edge to ride up and over the immovable object. 
     In another embodiment, the linkage assembly has a frame assembly including a pair of downwardly projecting legs which at an end attach to a bucket at a first pivot axis. A member, preferably in the form of a hydraulic cylinder attaches between the frame assembly and the bucket at a location forwardly of the downwardly projecting legs. The hydraulic cylinder is pivotally attached to the bucket to form a second pivot axis and also to the frame assembly near the top of the downwardly projecting legs at a third pivot axis. The frame assembly is further attachable to the vehicle. In one alternative embodiment, the present invention has a sensor and control mechanism for determining when the distance between the first pivot axis and the attachment to the vehicle contracts thereby signaling that the bucket has met an immovable object. When a threshold level is reached, a control mechanism causes the bucket to pivot at the first pivot axis, tilt up, and slide over the immovable object. The bucket and framework are thereby spared from bending and breaking, and the vehicle operator is less likely to be injured. 
     In another alternative embodiment, there are hinged joints in each of the projecting legs, and a biasing mechanism in the form of a spring or elastomeric member, or a hydraulic or pneumatic cylinder, or a flexible fluid-filled container which provide a biasing force which maintains the bucket edge along the ground. When the bucket strikes an immovable object and generates a force sufficient to overcome the biasing force, the hinged joints allow the bucket to pivot at the first and second pivot axes so that the bucket can tilt and ride over the immovable object. Once past the object, the biasing mechanism causes the hinged joint to close so that the bucket pivots back to its original scraping position. 
     In a further embodiment, the biasing force provided by the biasing mechanism may be adjusted directly through various mechanical, hydraulic, or pneumatic means of control so that the impact-force threshold beyond which tilting of the bucket occurs may be set by the vehicle operator. For instance, the vehicle driver may set the biasing force at one setting for plowing dirt roads, and at another level when plowing city streets having protruding manhole covers. 
     In yet another embodiment, lower portions of downwardly projecting legs are split into top portions and bottom portions with the bottom portion connected to the top portion through the use of guiding means and a hydraulic cylinder which can extend the overall length of the lower portion of the downwardly projecting leg so that the amount of bucket tipping is amplified by the extension. 
     Additionally, an adjustable threshold impact level may be set through the use of sensors incorporated into an electromechanical control circuit, or mechanically through the use of shear pins or a mechanical nipple and détente assembly. For example, when a bucket strikes an immovable object with a force sufficient to cause a nipple and détente assembly to disengage, the hinged joints allow the bucket to pivot at the first and second pivot axes so that the bucket can tilt and ride over the immovable object. The biasing mechanism then causes the hinged joint to close and the nipple and détente assembly to reset, so that the bucket pivots back to its original scrapping position. 
     In still another embodiment, the linkage accessory is a quadrilateral linkage having a front plate that connects to an accessory bucket and a rear plate that connects to the loader vehicle. The front plate connects to a first pair of arms at first pivot points and second pair of arms at second pivot points. The rear plate connects to the second pair of arms at third pivot points and the first pair of arms at fourth pivot points. The first pair of arms is non-parallel to the second pair of arms. 
     The quadrilateral linkage has an activated state and an inactivated state. In the inactivated state, the linkage is held together by a bias member, such as a spring. The linkage is activated when the scraping edge of the bucket strikes an immovable object. During this process, the elastomeric force of the spring is overcome and the linkage is compressed. The first pivot axis moves forwardly toward the bucket relative to the second pivot axis so that the bucket is tilted at its heel and the scraping edge is elevated and rides up and over the immovable object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate schematically in side view an embodiment of the present invention, including a sensor and bucket tilt control system.  FIG. 1A  shows the bucket riding over a flat surface;  FIG. 1B  shows the bucket riding up over a fixed object which it initially struck. 
         FIG. 2  is a side view of another embodiment of the present invention. 
         FIG. 3  is an enlarged plan view of the lower bucket assembly as shown in  FIG. 2  taken along auxiliary line  3 - 3 . 
         FIG. 4A  is a sectional view of the lower bucket assembly as shown in  FIG. 3 , taken along section line  4 - 4 , showing the assembly in the undeflected position. 
         FIG. 4B  is a sectional view of the lower bucket assembly as shown in  FIG. 3 , taken along section line  4 - 4 , showing the assembly in the deflected position as the bucket rides up over a fixed object. 
         FIG. 5A  is a side view of the lower bucket assembly, which includes a nipple and détente mechanism, showing the assembly in the undeflected position. 
         FIG. 5B  is a side view of the lower bucket assembly, which includes a nipple and détente mechanism, showing the assembly in the deflected position. 
         FIG. 6  is a sectional view of the lower bucket assembly of a further embodiment as shown generally in  FIG. 3 , taken along section line  4 - 4 , showing the assembly in the undeflected position. 
         FIG. 7  is a side view of the lower bucket assembly of still another embodiment of the present invention, showing the assembly in the undeflected position. 
         FIG. 8  is an enlarged plan view of the lower bucket assembly as shown in  FIG. 7  taken along auxiliary line  8 - 8 . 
         FIG. 9  is a sectional view of the lower bucket assembly as shown generally in  FIG. 8 , taken along section line  9 - 9 , showing the assembly in the undeflected position. 
         FIG. 10A  is a sectional view of the lower bucket assembly as shown in  FIG. 8 , taken along section line  10 - 10 , showing the nipple and détente mechanism when the assembly is in the undeflected position. 
         FIG. 10B  is a sectional view of the lower bucket assembly as shown in  FIG. 8 , taken along section line  10 - 10 , showing the nipple and détente mechanism when the assembly is in the deflected position. 
         FIG. 11A  is a partial side view of the lower bucket assembly of yet another embodiment as shown in  FIG. 2 , showing a divided lower portion of a downwardly projecting leg, and a hydraulic cylinder (and associated hydraulic circuit) which controls its overall length, in the undeflected position. 
         FIG. 11B  is a partial side view of the lower bucket assembly of the embodiment of  FIG. 11A  as shown in  FIG. 2 , showing a divided lower portion of a downwardly projecting leg, and a hydraulic cylinder (and associated hydraulic circuit) which controls its overall length, in the deflected position. 
         FIG. 12A  is a side view of a loader with a quadrilateral linkage connecting a bucket to the loader, when the quadrilateral linkage is not activated. 
         FIG. 12B  is a side view of a loader with a quadrilateral linkage connecting a bucket to the loader, when the quadrilateral linkage is activated. 
         FIG. 13A  is an enlarged side view of the quadrilateral linkage of  FIG. 12  A, when the quadrilateral linkage is not activated. 
         FIG. 13B  is an enlarged side view of the quadrilateral linkage of  FIG. 12B , when the quadrilateral linkage is activated. 
         FIG. 14  is a top view of the quadrilateral linkage. 
         FIG. 15  is a sectional view of the quadrilateral linkage as shown in  FIG. 13A , taken along section line  15 - 15 , showing the rear plate. 
         FIG. 16  is a sectional view of the quadrilateral linkage as shown in  FIG. 13A , taken along section line  16 - 16 , showing the front plate. 
         FIG. 17A  is a side sectional view of the quadrilateral linkage including a nipple and détente assembly, as shown in  FIG. 15 , taken along section line  17 - 17 , when the quadrilateral linkage is not activated. 
         FIG. 17B  is a side sectional view of the quadrilateral linkage including the nipple and détente assembly, when the quadrilateral linkage is activated. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure relates to an apparatus for attaching an accessory having a scraping edge and a heel to a vehicle and includes a linkage assembly attachable to the vehicle. The linkage assembly has first and second pivot axes pivotally connecting with the accessory. The first pivot axis is beneath the second pivot axis. The linkage assembly has first and second configurations: the first configuration includes the first axis located in a first position horizontally relative to the second axis, the second configuration includes the first axis located in a second position horizontally relative to the second axis. The second position is horizontally separated in a direction toward the accessory relative to the first position. When the scraping edge of the accessory strikes an immovable object, the linkage assembly moves from the first to the second configuration. When the linkage assembly is in the first configuration, the scraping edge and the heel of the accessory are both resting on ground. When the linkage assembly is in the second configuration, the heel of the accessory is on the ground and the scraping edge is elevated to allow the scraping edge to ride over the immovable object. 
     In one embodiment, the linkage assembly is mounted to a front end loader apparatus. Referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to  FIGS. 1A and 1B , the front end loader apparatus in accordance with the present invention is designated generally by the numeral  10 . Designations such as front, back, top, bottom, right side and left side are to be referenced to the vehicle, particularly from the perspective of the vehicle driver. Apparatus  10  includes a frame assembly  12  attached to the vehicle (not shown). Frame assembly  12  includes a pair of downwardly projecting legs  16  which are pivotally attached at first pivot points  18  to bucket  20 . Hydraulic cylinders  22  are pivotally attached at second pivot points  24  to bucket  20  and also to frame assembly  12  near the top of downwardly projecting legs  16  at third pivot points  26 . The frame assembly  12  is pivotally attached at vehicle attachment pivot points  14 . In the first embodiment, the hydraulic cylinders  22  are part of a mechanism  28  controlled by control system  30 , which in conjunction with sensor  32 , causes the bucket  20  to tip back upon striking an immovable object  34  as shown in  FIG. 1(B) . Sensor  32  senses a change in distance between first and vehicle attachment pivot points  18  and  14  or, alternatively, a change in velocity of bucket  20  or an impact deceleration of bucket  20 . That is, when bucket  20  has met immovable object  34 , sensor  32  sends a signal to control system  30  which determines if a threshold value of the parameter measured has been reached. If the threshold value has been met, control system  30  actuates a contraction of hydraulic cylinders  22  so that bucket  20  tips appropriately up at the scraping edge and rides up and over the immovable object  34 . 
     In another embodiment as shown in  FIGS. 2-5(B) , there are two downwardly projecting legs  16 ′ which have hinged joints  36  which allow bucket  20  to tip relative to frame assembly  12 ′. Each downwardly projecting leg  16 ′ has upper and lower portions  38 ,  40  separated at a break location  42 . The two upper portions  38  are rigidly connected by a first cross member  60  as shown in  FIG. 3 . The two lower portions  40  are rigidly connected by a second cross member  41 . The upper portions  38  and lower portions  40  of each of the downwardly projecting legs  16 ′ are rotatably fastened together at fourth pivot point  44 . Pivot points  44  have axes lying parallel and located rearwardly of break locations  42 . A lever arm  46  is fixedly attached to the lower portion  40  of each of the downwardly projecting legs  16 ′. Alternatively, lever arm  46  could be a unitary part of the lower portion  40  of the downwardly projecting leg  16 ′. A mating leg  48  extends rearwardly from each of the upper portions  38  of downwardly projecting legs  16 ′ so that the rearward end of lever arm  46  and mating leg  48  are pivotally attached together at the fourth pivot point  44 . The lower portions  40  of the downwardly projecting legs  16 ′ are attached to bucket  20  at first pivot points  18 . 
     Working in conjunction with hinged joints  36  are hinged joint closing devices  50 . With respect to  FIGS. 4A and 4B , a hinged joint closing device  50  includes a coil spring  52 . One end  54  of the spring  52  is attached to a forwardly extending portion  56  of lever arm  46 . The other end  58  of the spring  52  is attached to the first cross member  60  which rigidly connects the upper portions  38  of the downwardly projecting legs  16 ′. As shown in  FIG. 3 , there are similar hinged joint closing devices  50  associated with each of the downwardly projecting legs  16 ′. 
     In use, apparatus  10  is positioned so that the bottom  62  of bucket  20  is flat on the ground so that the front edge  64  scrapes, for example, snow and ice appropriately along the ground. When front edge  64  strikes an immovable object  34  as shown in  FIG. 4B , the lower portions  40  of the downwardly projecting legs  16 ′ pivot backward about the fourth pivot points  44 . As the lower portion of the downwardly projecting legs  40  pivot backward, the bucket  20  pivots about the second pivot points  24  and first pivot points  18  thereby allowing the front scraping edge  64  of the bucket  20  to lift up and over the immovable object  34 . The heel of the bucket remains on the ground. Hydraulic cylinder  22  maintains a constant length during these operations. The impact force of the immovable object  34  is counteracted by the hinged joint closing device  50 , or more particularly, springs  52 . When the impact force of the immovable object  34  overcomes the counteracting spring force, which is determined by the spring constant, as well as the length of the lever arm  46  relative to the fourth pivot points  44 , the front scraping edge  64  of the bucket  20  will lift up and over the immovable object  34  as shown in  FIG. 4B . Once the immovable object  34  has been cleared, the springs  52  will pivot the lower portion  40  of the downwardly projecting legs  16 ′ about the fourth pivot points  44  so that the upper portions  38  and the lower portions  40  lie directly adjacent one another in the area of break locations  42 , thereby resetting the hinged joint closing device  50 . 
     In a further embodiment of apparatus  10  as shown in  FIGS. 5A and 5B , a sensor in the form of a mechanical nipple/détente assembly  82  is disclosed. Nipple/détente assembly  82  includes a détente member  84  pivotally attached to both the right and left sides of the lower portion  40  of each downwardly projecting leg  16 ′ at pivot point  86 . The detent member  84  additionally provides a stop which prevents the over-rotation of the lower portion  40  of the downwardly projecting leg  16 ′. A nipple sub-assembly  88  is pivotally attached to the inside of the upper portion  38  of each downwardly projecting leg  16 ′. Nipple sub-assembly  88  includes a pair of plates  94 , on either side of détente member  84 , held together with a bolt  96  and nut  98 . A coil spring  100  is provided on bolt  96  between nut  98  and one of plates  94 . The combination of nut and bolt  98 ,  96  and spring  100  provides a force adjustment for nipple/détente assembly  82 . That is, if nut  98  is tightened against spring  100 , it takes more force to separate plates  94  and allow détente member to pull away and further allow hinged joints  36  to open. Protuberance nipples  102  are provided on each of the plates  94 , while indention détentes  104  are located to receive nipples  102  when hinged joints  36  are closed. It is preferred that nipple/détente assembly  82  be a part of appropriate embodiments above. 
     In use, when an immovable object  34  is struck, if a force is generated above the preset threshold to which spring  100  is adjusted, détente member  84  overcomes the force of the compression spring  100  thereby releasing détente member  84  which allows lower portion  40  to rotate so that the hinge joints  36  open as depicted in  FIG. 5B . Once the hinged joints  36  close, nipple/détente assembly  82  resets as in  FIG. 5A . 
     The use of nipple/détente assembly  82  is readily tailored to snowplowing conditions, and may even provide a mechanism for locking out the bucket tilting function during activities such as excavating soil and the like for the front-end loader vehicle. 
     In still another embodiment as shown in  FIG. 6 , springs  52  of the embodiment of  FIGS. 2-5B  are replaced by fluid-filled (pneumatic or hydraulic) cylinders  66 . The rest of the apparatus is as disclosed. As shown in broken lines, a fluid-filled cylinder  66  includes a piston  68  having first and second chambers  70 ,  72  on either side of piston  68 . When bottom  62  of bucket  20  is sliding along the ground at a level orientation, the first chambers  70  are maintained at a greater pressure than the pressure in the second chambers  72  such that the fluid-filled cylinders  66  provide a biasing force to the end of the lever arms  46 . 
     When front scraping edge  64  strikes an immovable object  34 , as similarly shown in  FIG. 5B , the lower portions  40  of the downwardly projecting legs  16 ′ pivot backward about the fourth pivot points  44 . As the lower portions of the downwardly projecting legs  40  pivot backward, the bucket  20  pivots about the second pivot points  24  and first pivot points  18  thereby allowing the front edge  64  of the bucket  20  to lift up and over the immovable object  34 . The first pivot points  18  move in the direction toward bucket  20  relative to the second pivot points  24 . Hydraulic cylinder  22  maintains a constant length during these operations. The impact force of the immovable object  34  is counteracted by the hinged joint closing device  50 , or more particularly fluid-filled cylinders  66 . When the impact force of the immovable object  34  overcomes the counteracting force provided by the fluid-filled cylinders, the front edge  64  of the bucket  20  will lift up and over the immovable object  34 . Once the immovable object  34  has been cleared, the fluid-filled cylinders  66  will pivot the lower portion  40  of the downwardly projecting legs  16 ′ about the pivot points  44  so that the upper portions  38  and the lower portions  40  lie directly adjacent to one another in the area of break locations  42 , thereby resetting the hinged joint closing device  50 . 
     In the embodiment as shown in  FIGS. 7-10B , a different type of fluid-filled or elastomeric device is used. A lever arm  74  is solidly attached to the second cross member  41 ′ near its midpoint. The top end portion  76  of lever arm  74  includes a bumper member  78  comprising a volume-constrained fluid-filled bag, or an elastomeric member, which presses against a bumper coupler member  106  which is attached to a first cross member  60 ′ near its midpoint. When bucket  20  strikes an immovable object  34  causing hinged joint  36  to open, lever arm  74  presses the bumper member  78  against the bumper coupler member  106  thereby causing it to deform. This deformation stores energy in the bumper member  78  as either increased fluid pressure in the case of the volume-constrained bag, or as stored elastic energy in the case of an elastomeric member. The deformation of the bumper member  78  opposes the opening of hinged joints  36  and urges them closed. As this occurs, bucket  20  rides over immovable object  34  as discussed earlier. 
     In the embodiment as shown in  FIGS. 11A and 11B , a lower portion of a downwardly projecting leg  40 ′ is divided into a top portion  108  and a bottom portion  110 . The top portion  108  is slidably connected to the bottom portion  110  with a bearing member  126  there between, and a hydraulic cylinder  112  is attached to the top portion  108  at top hydraulic cylinder coupling  114 , and to the bottom portion  110  at bottom hydraulic cylinder coupling  116 . The hydraulic cylinder  112  contains a hydraulic cylinder piston  118  and a hydraulic cylinder piston rod  120 . An upper cavity  122  is located in the hydraulic cylinder  112  above the piston  118 , and a lower cavity  124  exists below the piston  118 . A hydraulic circuit  150  activates the hydraulic cylinder  112 . The hydraulic circuit  150  includes a reservoir  138 , a hydraulic pump  136 , a check valve  134 , a fast-acting gas-filled accumulator  132 , and a solenoid valve  130 . A sensor  140  is connected to the solenoid  130  and determines its position. In one embodiment, the sensor  140  comprises a switch  142 ,  144 , located across break location  42 . 
     In use, the lower portions of the downwardly projecting legs appear as in  FIG. 11A . The hydraulic pump  136  supplies pressurized hydraulic fluid  146  through check valve  134  to the fast-acting gas-filled accumulator  132 . Solenoid valve  130  is in a position which supplies the hydraulic pressure from the hydraulic pump  136  and fast-acting gas-filled accumulator  132 , preferably nitrogen accumulator, to the lower cavity  124  of the hydraulic cylinder  112  which maintains the lower portion of the downwardly projecting leg  40 ′ in its shortest configuration. When an immovable object is struck by the bucket  20 , the break location  42  opens up sufficiently to cause sensor  140  to send a signal to the solenoid valve  130 , causing it to switch to the location depicted in  FIG. 11B . When the solenoid valve  130  shuttles its position, hydraulic fluid  146  immediately rushes to the upper cavity  122  of the hydraulic cylinder  112 , thereby causing the hydraulic cylinder piston  118  to move downward, thus pushing the bottom portion of the lower portion of the downwardly projecting leg  110  to move away from the top portion of the lower portion of the downwardly projecting leg  108 . This extension causes the bucket  20  to tilt upwardly about the first pivot point  18  and the second pivot point  24 . Furthermore, the mechanics of elongating the lower portion of the downwardly projecting leg  40 ′ are such that the degree of upward tilting of the bucket  20  is amplified by this increased length. 
     The mechanism of this embodiment is preferably used as a safety device in cases where the magnitude of the collision impulse is large, e.g. where large immovable objects are struck by the bucket  20 , such as in the case when a curb is struck with the bucket  20 . The threshold of sensor  140  or switch  142 ,  144  would be set so that this mechanism is activated only upon hitting an immovable object large enough or rigid enough so as to cause a large impulse to the loader and its occupant(s). After such a jarring collision, the mechanism would be reset by the operator of the vehicle, after inspecting the vehicle for damage. By amplifying the amount of rotation which bucket  20  may make in the case of extreme collisions injury to the occupant(s) and damage to the loader can be prevented. 
     In yet a further embodiment as shown in  FIGS. 12A-17B , the linkage assembly  200  includes a quadrilateral linkage  210  and connects a clearing accessory and a vehicle. It will be appreciated that the vehicle may be ATVs, farm tractors, skid loaders, pickup trucks, or other vehicles and that the clearing accessory may clear snow, manure or other material. 
     The linkage assembly  200  includes a front plate  260  that connects conventionally to the bucket  220  of the loader vehicle  264  and a rear plate  212  that connects conventionally to the vehicle. With respect to the quadrilateral linkage  210 , the front plate  260  connects at braces  304  to a first pair of arms  216  at first pivot points  218  and to a second pair of arms  222  at second pivot points  224 . The rear plate  212  connects at braces  302  to the second pair of arms  222  at third pivot points  226  and the first pair of arms  216  at fourth pivot points  214 . The first pair of arms  216  is shorter than and non-parallel to the second pair of arms  222 . Pins forming the various pivot points or axes are bolts and nuts or other appropriate fasteners (not shown). 
     The linkage assembly  200  has an inactivated state or first configuration as shown in  FIG. 13A  and an activated state or second configuration as shown in  13 B. In the inactivated state, the linkage assembly  200  is urged to its designed limit by a bias member, such as a spring  252 . The linkage assembly  200  is activated when a scraping edge  266  of the bucket  220  strikes an immovable object  234 . During this process, the spring  252  is compressed and the quadrilateral linkage  210  is likewise compressed. The first pivot axis  218  moves in the direction of the bucket  220  relative to the second pivot axis  224  so that the bucket  220  is tilted at its heel  268  and the scraping edge  266  is elevated and rides up and over the immovable object  234 . 
     The linkage assembly  200  may also include a first stopper device  270  to prevent over compression in the activated state and a second stopper device  274  to determine the design limit of the inactivated state. Stopper device  270  is attached to a brace  302  and extends forwardly toward plate  260  and when there is a hard impact stopper device  270  contacts plate  260  and solidifies linkage assembly  200 . There could be more than one stopper device  270 . Stopper device  274  is located to contact one of the front and rear plates  260 , 212  and one of the first and second pair of arms  216 , 222  when linkage assembly  200  is in the inactivated state. Likewise, there could be more than one stopper device  274 . The linkage assembly  200  may also include a mechanical nipple and détente assembly  282 . As similarly described with respect to an earlier embodiment, the nipple and détente assembly  282  includes a détente member  284  pivotally attached to the rear plate  212  at pivot point  272  (shown attached to rear plate  212  at brace  302 ) and a nipple sub-assembly  306  pivotally attached to the front plate  260  at a pivot point  286  (shown attached to front plate  260  at brace  304 ). It will be appreciated that the nipple and détente assembly  282  can be attached anywhere between the front and rear plates  260  and  212  in any appropriate position, for example, attaching the détente member  284  to the front plates  260  and attaching the nipple sub-assembly  306  to the rear plate  212 . The nipple sub-assembly  306  includes a pair of plates  308 , on either side of détente member  284 , which are held together at one end with a bolt  296  and nut  298 . A bracket  310  is pivotally attached at the pivot point  286  and plates  308  are pivotally attached to bracket  310  at the other end of plates  308 . A coil spring  300  is provided on bolt  296  between nut  298  and one of plates  308 . The combination of nut and bolt  298 ,  296  and spring  300  provides a force adjustment for nipple/détente assembly  282 . That is, if nut  298  is tightened against spring  300 , it takes more force to separate plates  308  and allow détente member to pull away and further allow the quadrilateral linkage  210  to activate. Protuberance nipples  312  are provided on each of the plates  308 , while indention détentes  314  are located to receive nipples  312  when linkage  210  is inactivated. The nipple and détente assembly  282  provides an extra retention mechanism in addition to the elastomeric force provided by the spring  252  for any impact force to overcome caused by the scraping edge striking an immovable object. 
     In use, the loader vehicle operator operates the hook  262  to scoop the rear plate  212  of the quadrilateral linkage  210  and then uses the front plate  260  of the linkage  210  to scoop the bucket  220 . In the inactivated state, the linkage  210  is urged to its designed limit by the spring  252  against stopper device  274 . The linkage  210  is activated when the scraping edge  266  of the bucket  220  strikes an immovable object  234 . During this process, the spring  252  is compressed and the quadrilateral linkage  210  is likewise compressed. The first pivot axis  216  moves in the direction of the bucket  220  relative to the second pivot axis  224  so that the bucket  220  is tilted at its heel  268  and the scraping edge  266  is elevated and rides up and over the immovable object  234 . In the case of a heavy impact, plate  260  may contact stopper device  270 . 
     In an embodiment where a nipple/détente assembly  282  appears, when an immovable object  234  is struck and a force is generated above the preset threshold force, the détente member  284  overcomes the force of the spring  300  thereby releasing détente member  284  which allows the front plate  260  to be compressed toward the rear plate  212  as depicted in  FIG. 17B . Once linkage  210  is urged back to the inactivated state, the nipple and détente assembly  282  resets as in  FIG. 17A . 
     Thus, preferred embodiments of apparatus in accordance with the present invention have been described in detail. It is understood, however, that equivalents to the disclosed invention are possible. Therefore, it is further understood that changes made, especially in matter of shape, size and arrangement to the full extent extended by the general meaning of the terms in which the appended claims are expressed, are within the principle of the invention.

Summary:
A mounting apparatus for a bucket of a front end loader vehicle. The mounting system allows the bucket to pivot up and over fixed objects when the leading edge of the bucket strikes an immovable object for the purpose of protecting the loader assembly, vehicle, and operator.