An excavator bucket top assembly can be completed as an assembly before being attached to other components to form an excavator bucket. The top assembly includes a flat bottom plate and a top plate with two bends, each having relatively simple geometry for ease of manufacturing. Two hinge plates penetrate through the top plate and are joined to both the bottom plate and the top plate. The top assembly includes strategically positioned, continuous weld joints to avoid weld starts and stops that create stress risers. The top assembly produces a torque tube which is stiff and resistant to fatigue.

This application claims priority to U.S. Provisional Patent Application No. 61/021,736 filed Jan. 17, 2008. 
    
    
     TECHNICAL FIELD 
     The field of this invention is excavator buckets, and more specifically top assemblies or hinge assemblies for excavator buckets. 
     BACKGROUND 
     Excavators, such as the one illustrated in U.S. Pat. No. 6,865,464, can be used in a wide variety of applications: in the construction industry to prepare building sites, in mining to load ore-laden material into trucks or onto conveyors, in road building to make cuts through hillsides for new road beds, in pipe laying and utility work to dig trenches. In all of these operations, excavators employ buckets to penetrate into material in the ground or in a pile, to scoop the material, and then to dump it. The bucket is the implement at the center of performing these tasks. 
     Excavator buckets are subjected to extreme loads and wear. An excavator bucket on a large excavator could be used to penetrate into extremely hard and dense material such as loosely shot or fractured granite. For this kind of duty, an excavator bucket requires high performance steels and a specialized construction to withstand both the high shock loads, and the extreme abrasive wear. Besides withstanding these maximum load cases and the abrasive environment, an excavator bucket must also be strong enough to endure many thousands, or in some cases, millions of cycles. (A cycle is each repetition of penetrating into the material, scooping, and dumping.) So an excavator bucket also requires resistance to fatigue wear and failure. 
     If an excavator bucket fails, replacement of the bucket can amount to a great expense in parts and labor. In addition, replacing a bucket will cause the excavator to sit idle and its productivity to decline, resulting in further costs. Besides idling the excavator, a bucket failure can also idle other machines in an integrated operation, such as haul trucks and crushers, further increasing the losses. Thus, a reliable excavator bucket that lasts through many cycles without breaking can be an important requirement for owners of excavator machines. 
     An excavator bucket can be expensive and difficult to manufacture because of its size and weight and other factors. Excavator buckets are typically constructed as weldments of more than a dozen pieces of plate steel. A bucket for a large, 60 metric ton excavator, for example, can be about 2 meters tall and 2 meters wide, weighing about 5 metric tons. Manipulating these large and heavy pieces of plate steel to align them to one another, and then correctly performing the welds can be a difficult and expensive task. A bucket design which requires a large number of pieces and multiple welds can add to the costs. 
     Thus, there are many demands affecting the design of an excavator bucket. The design must result in a bucket which exhibits the appropriate performance characteristics of resistance to high loads, abrasion, and fatigue, and which can also be manufactured in an economical manner. To produce a competitive bucket design, a designer must identify design features and techniques to satisfy and balance all of these demands. 
     SUMMARY 
     This invention relates to an improved design of a top assembly for an excavator bucket, which satisfies performance and manufacturability demands on the design, resulting in a bucket that is both resistant to failure, and economical to manufacture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of an excavator bucket with an embodiment of the new top assembly. 
         FIG. 2  is the same as  FIG. 1 , but with the top plate of the top assembly removed to reveal more of the torque tube construction details. 
         FIG. 3  is a sectional view taken through one of the hinge plates. 
         FIG. 4  is a section view taken through the centerline of the bucket. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  depict an excavator bucket  10  having a bottom section  20  and a curved heel section  30 . Normal to the bottom section  20  and heel section  30  are two side sections  40  and  50 . The bottom section  20  includes a base edge  21  on which are mounted several adapters, tips, and base edge protectors, which are commonly referred to as ground engaging tools, or GET. One or more steel plates forming a part of the bottom section  20  may be joined to a wrapper  31  which forms a part of the heel section  30 . Each side section  40 ,  50  includes a side plate  41 ,  51 , a side bar  42 ,  52 , and a side wear plate  43 ,  53 . Different basic bucket elements and structure may be used to form the bucket  10 , as will be apparent to those of ordinary skill in this art. 
     Joining the heel section  30  and the side sections  40 ,  50  is the top assembly (sometimes called hinge assembly)  100 . The top assembly includes a top plate  110 , a bottom plate  120 , and a pair of hinge plates  130 ,  140 . 
       FIG. 1  depicts the top assembly  100  in an assembled state and joined with the rest of the bucket  10 . In this view, the top plate  110  and hinge plates  130 ,  140  are visible, but the top plate  110  obscures the view of the remaining top assembly  100  structure. In  FIG. 2 , the top plate  110  has been removed to reveal the underlying structure.  FIG. 3  is a sectional view taken through one of the hinge plates  130 ,  140 .  FIG. 4  is a sectional view taken through the center of the bucket  10 . 
     The hinge plate  130  includes two bores  131  and  132 . Likewise, hinge plate  140  includes two bores  141  and  142 . Bores  131  and  141  are axially aligned and will support a stick pin that passes through the stick of the excavator. Bores  132  and  142  are axially aligned and will support a linkage pin that passes through the power link of the excavator which causes the bucket's curling motion about the stick pin. Thus, the hinge plates  130 ,  140  form two sets of two axially aligned bores ( 131  and  141  form a first set of two axially aligned bores, and  132  and  142  form a second set of two axially aligned bores). 
     Elements of the top assembly  100  cooperate to form a torque tube  150 . Torque tube  150  is designed to transfer torque from its middle section to its ends. The torque tube  150  functions to transfer “curling” torque about the center of the stick pin created by the power link and linkage pin, to the side sections  40 ,  50  and the rest of the bucket  10 . When the bucket base edge  21  penetrates into material, the force propelling the base edge is transferred to the base edge in part by this torsional force created about the stick pin by the power link. In addition to torque, a variety of other load paths exist through the torque tube  150 . The torque tube  150  must be capable of transferring all of these large sustained and shock loads and torques. The torque tube is formed in part through joining the top plate  110 , bottom plate  120 , and hinge plates  130 ,  140  to form a rigid, tube-like structure. 
     The top plate  110  defines a top surface  111 , a bottom surface  112 , a front edge  113 , and a rear edge  114 . The bottom plate  120  defines a top surface  121 , a bottom surface  122 , a front edge  123 , and a rear edge  124 . The bottom surface  112  and the top surface  121  are part of the inside surfaces of the generally enclosed torque tube  150 . The top surface  111  and the bottom surface  122  are part of the outside surfaces of the torque tube  150 . 
     The bottom plate  120  is formed from flat steel plate stock. For ease of manufacturing, the bottom plate  120  may not include any bends, nor any relatively complex cuts or shapes formed in it. 
     The top plate  110  is also formed from flat steel plate stock. The top plate  110  may include two bends, with a first bend having an included angle of approximately 105-125°, and more specifically approximately 115°, and a second bend having an included angle of approximately 100-120°, and more specifically approximately 110°. Each bend is approximately parallel to the front edge  113  of the top plate  110 . Each of the included angles faces toward the bottom plate  120  when assembled to help form the enclosed, tube-like structure of torque tube  150 . The outside surface profile of torque tube  150  created by these bends in top plate  110  helps the torque tube to be effectively positioned relative to certain existing, traditional quick couplers which may be used to attach bucket  10  to an excavator. The top plate  110  may easily be formed by first cutting its shape from plate stock, and then by creating the bends in a brake press or other type of press. Although the top plate may include two bends, it is still relatively easy to manufacture because it does not require any complex shapes or machining. 
     The assembly of top assembly  100  can begin by attaching hinge plates  130 ,  140  to bottom plate  120  so that the hinge plates are parallel to one another and normal to the bottom plate. Each of the hinge plates includes a flat bottom edge  133 ,  143  which butts against and is welded to the top surface  121  of bottom plate  120 . One of these weld joints is illustrated in  FIG. 4  with the reference character A. Each of the flat bottom edges  133 ,  143  is approximately the same length as the distance between the front edge  123  to the rear edge  124 . Thus, the hinge plate  130 ,  140  to bottom plate  120  butt joint extends approximately from the front edge  123  to the rear edge  124 . Advantageously, the butt joint need not extend beyond the rear edge  124  (as it does in some prior art designs where the hinge plates  130 ,  140  also are joined to the wrapper  31 ) in order to permit joining the hinge plates  130 ,  140  to bottom plate  120  in an assembly which can be fully completed before being joined to the rest of bucket  10 . 
     Optional rib or ribs  160  may be included between hinge plates  130 ,  140  and bottom plate  120 . The rib  160  may reinforce the connection between the hinge plates  130 ,  140  and the bottom plate  120 , add stiffness to the torque tube  150 , as well as aid in maintaining alignment during welding and assembly. Both the hinge plates  130 ,  140  and the rib  160  may include a slot cut in each—a portion of the rib fitting into the slot in each hinge plate, and vise versa—forming an interlocking halved joint therebetween. The rib  160  may be welded to the hinge plates  130 ,  140  and to the bottom plate  120  around the same time as welding between the hinge plates and the bottom plate. 
     Hinge plates  130 ,  140  may pass through and divide the top plate  110 . This allows hinge plates  130 ,  140  to be welded to the bottom plate  120  as well as the top plate  110 , forming a stronger and stiffer torque tube  150 . Some prior art designs do not have hinge plates which are welded to both a top plate and a bottom plate, having instead hinge plates which are only welded to a top plate, which results in a weaker torque tube. Hinge plates  130 ,  140  may divide the top plate  110  into three separate segments  110   a ,  110   b , and  110   c . Segments  110   a  and  110   c  are outboard of the hinge plates, meaning they are between one of the hinge plates and one of the sides of the bucket  10 . Segment  110   b  is inboard of the hinge plates, or between the two hinge plates in the middle of the bucket  10 . The hinge plates  120 ,  130  and segments  110   a ,  110   b , and  110   c  are welded at a weld joint formed at their intersection and along the top surface  111 . One of these weld joints is illustrated in  FIG. 4  with the reference character B. 
     Top plate  110  and bottom plate  120  are joined to each other along a first and a second weld joint. A first weld joint may be formed at the intersection of the rear edge  114  of top plate  110  and the bottom plate  120 , along the top surface  121 . This weld joint is illustrated in  FIG. 4  with the reference character C. The bottom plate  120  may overlap the top plate  110  (i.e. the bottom plate extends further than the intersection of the top plate and bottom plate, and the top plate terminates at the intersection) to permit this joint. Because the rear edge  114  is joined to the bottom plate  120 , and does not extend further to intersect or join with wrapper  31 , the assembly between the top plate  110  and bottom plate  120  can be completed before the top assembly  100  is joined to the remainder of bucket  10 . 
     A second weld joint may be formed at the intersection of the front edge  123  with the top plate  110 , along the bottom surface  112 . This weld joint is illustrated in  FIG. 4  with the reference character D. In order to make this joint, the top plate  110  may overlap the bottom plate  120 . This construction advantageously permits this weld joint to be made with a continuous, non-interrupted welding pass from one end of torque tube  150  to the other. In other prior art designs where the bottom plate  120  overlaps the top plate  110 , this weld joint is formed at this intersection but on the top surface  121 , and the weld joint is segmented or broken because it is interrupted by the hinge plates. It has been determined by the inventors that the breaks in this second weld joint result in weak areas, or stress risers, which are an important cause of bucket failures. By eliminating the weld starts and stops in this second weld joint, the stress risers are minimized and the bucket is stronger. This second weld joint resides in a high load path region of the torque tube  150 , so minimizing stress risers in this region is very beneficial. 
     The foregoing construction of the top assembly  100  permits it to be completely assembled as an independent module before attaching to the remaining components of the bucket. Constructing the top assembly  100  as an independent module can present several advantages. The many welds in the top assembly  100  can all be performed before attaching the remaining components of bucket  10 . The top assembly  100  is smaller and lighter than the entire bucket  10  so the top assembly is easier to move around and position, making these welds simpler to perform. 
     Bores  131 ,  132 ,  141 , and  142  formed in hinge plates  130 ,  140 , typically require tight tolerances. Traditionally, these bores are formed through machining after the hinge plates have been fixed to the bucket. Because hinge plates  130 ,  140  are completely assembled into the top assembly  100 , these bores  131 ,  132 ,  141 , and  142  can be machined after top assembly  100  is assembled, but before top assembly  100  is joined to the rest of the bucket. Positioning top assembly  100  on a boring machine for making these bores can be a much simpler task than positioning the entire bucket  10  on a boring machine, and a smaller boring machine may be used. 
     For manufacturing workflow, the top assembly  100  can be completed and then wait for the remaining components to be gathered together for assembly into the final bucket  10 . The top assembly  100  can even be designed to work as a top assembly for more than one size and/or type of bucket. So a single top assembly  100  can be constructed and then fit to different remaining components to form a variety of buckets. 
     After the top assembly  100  is assembled, it can be attached to the heel section  30  and side sections  40 ,  50 . The wrapper  31  is welded to the bottom plate  120 . The side bars  42 ,  52  include ears  44 ,  54 , which overlap the ends of the torque tube  150 . The ends of torque tube  150  are welded to these ears  44 ,  54 . A fully assembled bucket  10  is illustrated in  FIG. 1 . 
     INDUSTRIAL APPLICABILITY 
     The foregoing excavator bucket top assembly may be used in the construction of excavator buckets for use in many industries including construction and mining.