Abstract:
A slant hole pumping unit includes a base mounting a support structure. A drive system is mounted on the support structure and is connected to a bridle strap assembly for reciprocating same. A constraint link assembly includes a lower end pivotally connected to the base and an upper end engaging the bridle strap assembly for constraining the movement thereof to an arc defined by the pivotal movement of the bridle strap assembly.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/056,592, filed Aug. 20, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to well head pumping units and in particular to a pumping unit with a constrained bridle strap. 
     2. Description of the Prior Art 
     Well head pumping units are placed over wells for operating down-hole pumps whereby oil, water, etc. are extracted and brought to the earth&#39;s surface. The Pauls U.S. Pat. No. 4,631,970 discloses a pumping unit with a bridle strap connecting the drive system thereof with a rod string. The flexible bridle strap transfers the reciprocating motion of the pumping unit drive system to a vertically reciprocating motion of the rod string. However, the equalizer beam which connects the drive system to the bridle strap assembly in this pumping unit is unconstrained. Thus, the equalizer beam can damage other components of the pumping unit if tension is released, e.g., if the rod string breaks. The pumping unit shown in the aforementioned Pauls &#39;970 patent is designed to equally divide the rotation of the drive system between the upstroke and downstroke of the rod string, i.e. 180°/180°. However, in many applications different upstroke/downstroke ratios are preferred. For example, relatively high viscosity oil and/or slant hole applications often necessitate a slower downstroke in order to maintain tension on the bridle strap assembly. 
     The present invention addresses the shortcomings of the prior art. Heretofore there has not been available a slant hole pumping unit with the advantages and features of the present invention. 
     SUMMARY OF THE INVENTION 
     In the practice of the present invention, a slant hole pumping unit is provided which includes a base, a support structure mounted on the base and a drive system mounted on the support structure. Crank arms are driven by the drive system and are connected to a bridle strap assembly through a pitman arm assembly. The bridle strap assembly is also connected to a rod string. A post assembly includes a lower end mounted on the base and the support structure and an upper end mounting a post strap guide. A constraint link includes a lower end pivotally connected to the base and an upper end engaging the bridle strap assembly for constraining the movement thereof through a pivotal arc defined by the bridle strap assembly. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     The principal objects and advantages of the present invention include: providing a pumping unit for well head applications; providing such a pumping unit which is adapted for slant hole pumping applications; providing such a pumping unit which constrains movement of a bridle strap; providing such a pumping unit which permits adjustment of the upstroke and downstroke portions of a drive system cycle; providing such a pumping unit which can increase reliability in the field; and providing such a pumping unit which is economical to manufacture, efficient in operation and particularly well adapted for the proposed usage thereof. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a pumping unit embodying the present invention. 
     FIG. 2 is a side elevational view of the pumping unit showing upstroke positions thereof. 
     FIG. 3 is a side elevational view of the pumping unit showing downstroke positions thereof. 
     FIG. 4 is a side elevational view showing a comparison of constrained and unconstrained equalizer beam paths of movement and positions. 
     FIG. 5 is a side elevational view of a constraint link assembly of the pumping unit. 
     FIG. 6 is a front elevational view of the constraint link assembly. 
     FIG. 7 is a side elevational view of the pumping unit shown mounted on a trailer in an operating position thereof. 
     FIG. 8 is a side elevational view of the pumping unit shown mounted on a tractor trailer unit in a transport position thereof. 
     FIG. 9 is a side elevational view of a pumping unit comprising a first modified embodiment of the present invention. 
     FIG. 10 is a side elevational view of a pumping unit comprising a second modified embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. Introduction and Environment 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Referring to the drawings in more detail, the reference numeral 2 generally designates a pumping unit embodying the present invention. The pumping unit 2 uses a bridle strap assembly 24 and other components which are similar to those shown in U.S. Pat. No. 4,631,970, which is incorporated herein by reference. 
     II. Pumping Unit 2 
     The pumping unit 2 includes a base 4 which mounts a support structure 6 extending upwardly therefrom. The support structure mounts a drive system 8 with counterweights 7. The drive system 8 rotates a pair of crank arms 10. A pair of pitman arms 12 have proximate ends 12a connected to the crank arms 10 and distal ends 12b. The base can be supported on any suitable foundation, such as the piers 5. The base can also comprise or be mounted on a vehicle, such as a trailer or truck bed. 
     A post assembly 14 includes a length-adjustable rear post leg 16 with a proximate end 16a pivotally connected to the support structure 6 and a distal end 16b. The post assembly 14 also includes a front post leg 18 with a proximate end 18a pivotally connected to the base 4 in proximity to a base front 4a and a distal end 18b. The post leg distal ends 16b, 18b mount a strap guide assembly 20 which comprises a roller 22 rotatable on a horizontal, transverse rotational axis. A bridle strap assembly 24 includes proximate and distal ends 24a,b and is placed over the roller 22. 
     A constraint link assembly 26 includes a lower end 26a pivotally mounted on the base 4 adjacent to its front end 4a and an upper end 26b pivotally connected to the pitman arm distal ends 12b and to the bridle strap assembly proximate end 24a. The constraint link assembly 26 has a generally triangular configuration as shown in FIG. 6 with a pair of side members 26c, a equalizer beam 26d at its upper end 26b and a brace 26e extending between and connected to the side members 26c. 
     III. Operation 
     In operation, the pumping unit 2 functions in a manner similar to the pumping unit disclosed in U.S. Pat. No. 4,631,970, except that the constraint link assembly 26 constrains the equalizer beam 26d to a predetermined arc of movement 28 defined by the pivoting motion of the constraint link assembly 26. FIG. 4 shows an equalizer beam 26d path of movement describing an arc 28 when constrained by the constraint link assembly 26 with various equalizer beam 26d positions designated 26p. Positions of the equalizer beam 26d if it were not so constrained are designated 26p&#39;. 
     By adjusting the length and end locations of the constraint link assembly 26 with respect to the other components of the pumping unit 2, a variety of stroke profiles can be accommodated for particular applications. In particular, the division between upstroke and downstroke can be adjusted to ratios of, such as 208°/152°. For example, lower upstroke speeds may be desirable to reduce power requirements and reduce the acceleration forces on the rod string. The downstroke can have a faster speed, which increases the leverage of the counterweights 7 and reduces the counterbalance weight required on the crank arm to achieve the necessary counterbalance effect on the rod string. 
     Faster upstroke and slower downstroke can be accomplished by reversing the rotational direction of the crank arms 10. Such operating characteristics may be desirable to compensate for relatively slow rod string fall (downstroke) speed, which can result from relatively high viscosity liquids (e.g., oil) being pumped or a slant hole well configuration. 
     The pumping unit 2 can be mounted on a trailer 30b of a tractor-trailer rig 30 for towing by a tractor unit 30a. (FIGS. 7 &amp; 8). 
     IV. First Modified Embodiment Pumping Unit 102 
     A first modified embodiment pumping unit 102 is shown in FIG. 9 and includes the bridle strap assembly proximate end 24a being connected to the base 4 with the equalizer beam 26d functioning as a constraint link assembly guide roller. Greater stroke length, i.e. up to twice the crank arm swing diameter, can be achieved with this configuration. 
     V. Second Modified Embodiment Pumping Unit 202 
     FIG. 10 shows a pumping unit 202 comprising a second modified embodiment of the present invention wherein the pitman arm distal ends 12b are connected to the constraint link assembly 26 intermediate its lower and upper ends 26a,b. Stroke amplification is thus achieved based upon a ratio defined by the placement of the bridle strap assembly proximate end 24a with respect to the constraint link assembly lower and upper ends 26a,b. In this configuration the second modified embodiment pumping unit 202 functions as a four bar linkage system. 
     It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.