Abstract:
A progressing cavity stator and a method for fabricating such a stator are disclosed. Exemplary embodiments of the progressing cavity stator include a plurality of rigid longitudinal stator sections concatenated end-to-end in a stator tube. The stator sections are rotationally aligned so that each of the internal lobes extends in a substantially continuous helix from one end of the stator to the other. The stator further includes an elastomer liner deployed on an inner surface of the concatenated stator sections. Exemplary embodiments of this invention include a comparatively rigid stator having high torque output and are relatively simple and inexpensive to manufacture as compared to prior art rigid stators.

Description:
RELATED APPLICATIONS  
       [0001]     None.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to positive displacement progressing cavity drilling motors, typically for downhole use. This invention more specifically relates to a progressing cavity stator having a plurality of cast longitudinal sections.  
       BACKGROUND OF THE INVENTION  
       [0003]     Progressing cavity hydraulic motors and pumps (also known in the art as Moineau style motors and pumps) are well known in subterranean drilling and artificial lift applications, such as for oil and/or gas exploration. Such progressing cavity motors make use of hydraulic power from drilling fluid to provide torque and rotary power, for example, to a drill bit assembly. The power section of a typical progressing cavity motor includes a helical rotor disposed within the helical cavity of a corresponding stator. When viewed in circular cross section, a typical stator shows a plurality of lobes in the helical cavity. In most conventional Moineau style power sections, the rotor lobes and the stator lobes are preferably disposed in an interference fit, with the rotor including one fewer lobes than the stator. Thus, when fluid, such as a conventional drilling fluid, is passed through the helical spaces between rotor and stator, the flow of fluid causes the rotor to rotate relative to the stator (which may be coupled, for example, to a drill string). The rotor may be coupled, for example, through a universal connection and an output shaft to a drill bit assembly. Alternatively, in pump applications, the rotor may be driven by, for example, electric power, in which case fluid may be caused to flow through the progressing cavities.  
         [0004]     Conventional stators typically include a helical cavity component bonded to an inner surface of a steel tube. The helical cavity component in such conventional stators typically includes an elastomer (e.g., rubber) and provides a resilient surface with which to facilitate the interference fit with the rotor. Many stators are known in the art in which the helical cavity component is made substantially entirely of a single elastomer layer.  
         [0005]     It has been observed that during operations, the elastomer portions of conventional stator lobes are subject to considerable cyclic deflection, due at least in part to the interference fit with the rotor and reactive torque from the rotor. Such cyclic deflection is well known to cause a significant temperature rise in the elastomer. The temperature rise is known to degrade and embrittle the elastomer, eventually causing cracks, cavities, and other types of failure in the lobes. Such elastomer degradation is known to reduce the expected operational life of the stator and necessitate premature replacement thereof. Moreover, the cyclic deflection is also known to reduce torque output and drilling efficiency in subterranean drilling applications. One solution to this problem has been to increase the length of power sections utilized in such subterranean drilling applications. However, increasing stator length tends to increase fabrication complexity and may also tend to increase the distance between the drill bit and downhole logging sensors. It is generally desirable to locate logging sensors as close as possible to the drill bit, since they are intended to monitor at-bit conditions, and they tend to monitor conditions that are remote from the bit when located distant from the bit.  
         [0006]     Stators including a comparatively rigid helical cavity component have been developed to address these problems. For example, U.S. Pat. No. 5,171,138 to Forrest and U.S. Pat. No. 6,309,195 to Bottos et al. disclose stators having helical cavity components in which a thin elastomer liner is deployed on the inner surface of a rigid, metallic stator former. The &#39;138 patent discloses a rigid, metallic stator former deployed in a stator tube. The &#39;195 patent discloses a “thick walled” stator having inner and outer helical stator profiles. The use of such rigid stators is disclosed to preserve the shape of the stator lobes during normal operations (i.e., to prevent lobe deformation) and therefore to improve stator efficiency and torque transmission. Moreover, such metallic stators are also disclosed to provide greater heat dissipation than conventional stators including elastomer lobes.  
         [0007]     While comparatively rigid stators have been disclosed to improve the performance of downhole power sections (e.g., to improve torque output), fabrication of such rigid stators is complex and expensive as compared to that of the above described conventional elastomer stators. Most fabrication processes utilized to produce long, internal, multi-lobed helixes are tooling intensive (such as helical broaching) and/or slow (such as electric discharge machining). As such, rigid stators of the prior art are often only used in demanding applications in which the added expense is acceptable.  
         [0008]     Various attempts have been made to address the above-mentioned difficulties associated with rigid stator fabrication. For example, U.S. Pat. No. 6,543,132 to Krueger et al. discloses methods for forming a rigid stator about an inner mandrel having a helical outer surface. The mandrel is then removed leaving a longitudinal member having an inner profile defined by the outer profile of the mandrel. U.S. Pat. No. 5,832,604 to Johnson et al. discloses a rigid stator formed of a plurality of duplicate disks including an inner cavity having a plurality of lobes. The discs are assembled into the form of a stator by stacking on a mandrel such that the discs are progressively rotationally offset from one another. The stack is then deployed in a stator tube. U.S. Pat. No. 6,241,494 to Pafitis et al. discloses a non elastomeric stator including a plurality of stainless steel sections that are aligned and welded together to form a stator of conventional length. Nevertheless, despite these efforts, there exists a need for yet further improved stators for progressing cavity drilling motors, and in particular improved rigid stators and methods for fabricating such rigid stators.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention addresses one or more of the above-described drawbacks of prior art Moineau style motors and/or pumps (also referred to as progressing cavity motors and pumps). Aspects of this invention include a progressing cavity stator for use in such motors and/or pumps, such as in a downhole drilling assembly. Progressive cavity stators embodiments of this invention include at least one longitudinal stator section deployed in an outer stator tube. In exemplary embodiments, the stator includes a plurality of substantially identical longitudinal stator sections concatenated end-to-end in a stator tube. In such exemplary embodiments, the stator sections are rotationally aligned with one another in the stator tube such that a plurality of helical lobes extend in a substantially continuous helix from one end of the stator to the other. Exemplary stator embodiments further include a resilient elastomer liner deployed on an inner surface of comparatively rigid stator sections.  
         [0010]     Exemplary embodiments of the present invention advantageously provide several technical advantages. For example, exemplary embodiments of this invention include a rigid stator having high torque output. Moreover, exemplary embodiments of this invention are relatively simple and inexpensive to manufacture as compared to prior art rigid stators. Various embodiments of this invention may also promote field service flexibility. For example, worn or damaged stator sections may be replaced in the field at considerable savings of time and expense. Alternatively, stator sections may be replaced, for example, to optimize power section performance (e.g., with respect to speed and power).  
         [0011]     In one aspect, this invention includes a progressing cavity stator. The stator includes an outer stator tube having a longitudinal axis and a helical cavity component deployed substantially coaxially in the stator tube. The helical cavity component includes a plurality of rigid longitudinal stator sections concatenated end-to-end in the stator tube. Each of the stator sections provides an internal helical cavity and includes a plurality of internal lobes. The stator sections are rotationally aligned with one another so that each of the internal lobes extends in a substantially continuous helix from one longitudinal end of the stator to an opposing longitudinal end of the stator. The stator sections are rotationally restrained to substantially prevent relative rotation thereof about the longitudinal axis. Moreover, the stator sections are further retained by and secured in the stator tube to substantially prevent rotation of the stator sections about the longitudinal axis relative to the stator tube. The helical cavity component further includes an elastomer liner deployed on an inner surface of the concatenated stator sections.  
         [0012]     In another aspect, this invention includes a progressive cavity stator. The stator includes an outer stator tube having a longitudinal axis and a helical cavity component deployed substantially coaxially in the stator tube. The helical cavity component includes first and second longitudinal portions. The first longitudinal portion includes at least one rigid longitudinal stator section deployed in the stator tube, the at least one stator section retained by and secured in the stator tube to substantially prevent rotation of the at least one stator section about the longitudinal axis relative to the stator tube. The at least one stator section reinforces an elastomer liner, which is deployed on an internal helical surface of the at least one stator section. The second portion of the helical cavity component includes an elastomer layer deployed in and retained by the stator tube. The elastomer liner in the first portion is substantially continuous with the elastomer layer in the second portion such that the helical cavity component provides an internal helical cavity and such that the helical cavity component includes a plurality of lobes, each of which extends in a substantially continuous helix from one longitudinal end of the stator to another longitudinal end of the stator.  
         [0013]     In still another aspect, this invention includes a method for fabricating a progressing cavity stator. The method includes casting a plurality of stator sections, the stator sections providing an internal helical cavity and including a plurality of internal helical lobes. The method further includes concatenating the stator sections end-to-end in a stator tube such that each of the internal helical lobes extends in a substantially continuous helix from one longitudinal end of the stator to an opposing longitudinal end of the stator and rotationally restraining the stator sections to substantially prevent relative rotation the stator sections. The method still further includes securing the stator sections in the stator tube to substantially prevent rotation of the stator sections relative to the stator tube and deploying an elastomer liner on an inner surface of the stator sections.  
         [0014]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0016]      FIG. 1  depicts a conventional drill bit coupled to a progressing cavity motor utilizing an exemplary stator embodiment of the present invention including a plurality of stator sections.  
         [0017]      FIG. 2  depicts a portion of the stator shown on  FIG. 1  in longitudinal cross section.  
         [0018]      FIG. 3A  depicts first and second cast stator sections in longitudinal cross-section.  
         [0019]      FIG. 3B  is an axial view of the stator section  120 A shown on  FIG. 3A .  
         [0020]      FIGS. 4A and 4B  depict an alternative embodiment of a stator according to this invention including a thin elastomer layer between the stator sections and the stator tube.  
         [0021]      FIGS. 4C and 4D  depict longitudinal and circular cross sections of stator section  220 A shown on  FIG. 4A .  
         [0022]      FIG. 5  depicts another alternative embodiment of a stator according to this invention in which the stator sections include an axial spline, the spline sized and shaped to engage an axial groove on the stator tube.  
         [0023]      FIG. 6  depicts still another alternative embodiment of a stator according to this invention.  
     
    
     DETAILED DESCRIPTION  
       [0024]      FIG. 1  illustrates one exemplary embodiment of a progressing cavity power section  100  according to this invention in use in a downhole drilling motor  60 . Drilling motor  60  includes a helical rotor  150  deployed in the helical cavity of progressing cavity stator  105 . In the embodiment shown on  FIG. 1 , drilling motor  60  is coupled to a drill bit assembly  50  in a configuration suitable, for example, for drilling a subterranean borehole, such as in an oil and/or gas bearing formation. It will be understood that the progressing cavity stator  105  of this invention, while shown coupled to a drill bit assembly in  FIG. 1 , is not limited to downhole applications, but rather may be utilized in substantially any application in which progressing cavity hydraulic motors and/or pumps are used.  
         [0025]     Turning now to  FIG. 2 , a portion of stator  105  is shown in longitudinal cross section. Progressing cavity stator  105  includes an outer stator tube  140  (e.g., a steel tube) retaining a comparatively rigid (preferably metallic) helical cavity component  110 . Helical cavity component  110  is shaped to define a plurality of helical lobes  160  (and grooves) on an inner surface thereof. In the embodiment shown on  FIG. 2 , helical cavity component  110  further includes a resilient elastomer liner  112  deployed on inner surface  116  thereof.  
         [0026]     As further shown on  FIG. 2 , helical cavity component  110  includes a plurality of longitudinal sections  120 A,  120 B,  120 C, and  120 D, which are referred to collectively as  120 A-D, deployed end-to-end in the stator tube  140 . In the exemplary embodiment illustrated on  FIG. 2 , the sections  120 A-D are substantially identical and are rotationally aligned with one another in the tube  140  such that the helical lobes  160  extend substantially continuously from one end of the stator  105  to the other. It will be appreciated, however, that the invention is not limited to substantially identical sections  120 A-D. Other embodiments may include, for example, a series of sections, which, while not substantially identical, may be concatenated in predetermined fashion into a desired stator. Returning to the embodiment of  FIG. 2 , stator  105  may include substantially any suitable number of sections  120 A-D. In exemplary embodiments in which the concatenated sections  120 A-D extend from substantially one longitudinal end of the stator  105  to the other, the stator typically includes from about 5 to about 20 sections  120 A-D. As described in more detail below with respect to  FIG. 6 , the invention is not limited to stator embodiments in which a plurality of concatenated stator sections extend from one longitudinal end of the stator to the other. Sections  120 A-D may also have substantially any suitable length, but typically have a length in the range from about 15 to about 60 centimeters (6 to 24 inches). For example, in one serviceable embodiment, a two and a half turn power section configured for subterranean drilling applications includes 10 sections each having a length of about 28 centimeters (11 inches) and an internal helical angle of 90 degrees.  
         [0027]     Turning now to  FIG. 3A , stator sections  120 A and  120 B are shown in an exploded longitudinal cross section. As described above, stator sections  120 A and  120 B include a plurality of helical lobes  160  formed in the inner surface  116  thereof. Exemplary stator sections  120 A and  120 B further include a plurality of holes  124  formed in the axial faces  122  thereof. For example only, as shown on  FIG. 3B , which depicts an end view of stator section  120 A, stator sections  120 A and  120 B include holes  124  formed in three of the lobes in each axial face  122 . The holes  124  are sized and shaped to receive dowel pins  126  upon end-to-end deployment of the stator sections  120 A and  120 B. The use of such dowel pins  126  advantageously enables the stator sections  120 A and  120 B to be rotationally aligned with one another to form continuous helical lobes  160 . Moreover, the dowel pins  126  are further intended to substantially prevent rotation of one or more of the stator sections with respect to others. It will be understood that the use of dowel pins and corresponding holes in some embodiments as described herein is exemplary, and that in such embodiments, other types of conventional keys and rotational locators may be substituted with equivalent effect. Moreover, in the exemplary embodiment shown on  FIG. 3B , stator sections  120 A and  120 B include five helical lobes  160 . It will be appreciated that this depiction is purely for illustrative purposes only, and that the present invention is in no way limited to any particular number of helical lobes  160 .  
         [0028]     While this invention is not limited to the use of any particular techniques used for the fabrication of the stator sections, the use of cast stator sections has been found to advantageously reduce manufacturing costs. In certain advantageous embodiments, stator sections (e.g., stator sections  120 A-D shown on  FIG. 2 ) are preferably cast from a steel or aluminum alloy, for example, using conventional investment casting techniques. In such embodiments, the outer surface of the cast stator sections may be ground (or machined) to predetermined dimensions and tolerances prior to final stator assembly. The stator sections may then be deployed and secured in a stator tube, for example, as described in more detail below. In certain embodiments, such as those in which a positive interference stator is desirable, an elastomer liner is then deployed on the inner surface of the stator. To form the elastomer liner a helical stator core may be deployed substantially coaxially in the stator sections and a suitable elastomer material injected into the helical cavity between the stator core and the stator sections. Elastomer injection is described in more detail below for one exemplary embodiment of this invention.  
         [0029]     Referring again to  FIG. 2 , stator sections  120 A-D are sufficiently secured in the stator tube  140  in order to support the high torques typically experienced in downhole power section applications. In one suitable embodiment, the stator tube  140  may be shrunk fit about the stator sections  120 A-D. To construct such an embodiment, the stator sections  120 A-D are typically first concatenated end-to-end (e.g., as shown for sections  120 A and  120 B on  FIG. 4 ) and then deployed in a preheated stator tube (e.g., a stator tube heated to a temperature in the range from about 300 to about 400 degrees C.). To facilitate deployment of the stator sections in the stator tube, the stator sections  120 A-D may be advantageously slid down an incline into the stator tube  140 , although the invention is not limited in this regard. Moreover, it will be appreciated that the outer surface of the stator sections may be coated with a lubricant. Upon cooling, the stator tube  140  contracts about the stator sections  120 A-D, thereby forming a tight shrink fit and securing the stator sections  120 A-D in place in the stator tube  140 .  
         [0030]     It has been found that stator sections may alternatively be secured in a stator tube by a thin elastomer layer injected between the stator sections and the stator tube. Referring now to  FIGS. 4A and 4B , one alternative stator embodiment  205  according to this invention is shown. Stator  205  is similar to stator  105  (shown on  FIG. 2 ) with an exception that it includes a thin elastomer layer  230  ( FIG. 4B ) formed between an outer surface the stator sections  220 A,  220 B,  220 C, and  220 D (referred to collectively as  220 A-D) and the stator tube  240 . Elastomer layer  230  is typically formed and cured simultaneously with that of elastomer liner  212 . As stated above, elastomer liner  212  may be formed by deploying a helical stator core coaxially in the concatenated stator sections and a suitable elastomer material injected into the helical cavity between the stator core and the concatenated stator sections. In one exemplary embodiment, stator sections  220 A-D include small ports  228  (shown on  FIGS. 4C and 4D  for stator section  220 A) disposed to promote flow of the injected elastomer from the helical cavity between the stator core and the stator sections  220 A-D to a thin annular cavity located between the stator sections  240 A-D and the stator tube  240 . It will be appreciated that the inner surface of stator tube  240  and the outer surfaces of stator sections  220 A-D may be coated with a bonding compound (e.g., an adhesive) prior to injection of the elastomer material to promote bonding between the elastomer and stator tube  240  and between the elastomer and the stator sections  220 A-D. Suitable bonding compounds include, for example, Lord Chemical Products Chemlock 250 or Chemlock 252×. In certain embodiments it may be advantageous to utilize aqueous based adhesives, such as Lord Chemical Products 8007, 8110, or 8115 or Rohm and Haas 516EF or Robond® L series adhesives.  
         [0031]     It will be appreciated that elastomer layer  230  is thin relative to the other components in stator  205  (e.g., relative to elastomer liner  212 ). In one exemplary embodiment stator sections  220 A-D are sized and shaped to be slidably received in the stator tube  240 , with elastomer layer  230  being formed therebetween. In such embodiments, elastomer layer  230  typically has an average thickness in the range of from about 0.1 to about 1 millimeter (about 4 to about 40 thousands of an inch), although the invention is not limited in this regard. It will also be appreciated that there is a tradeoff in selecting an optimum elastomer layer  230  thickness (or thickness range). On one hand, if the annular cavity between the stator sections  220 A-D and the stator tube  240  is too thin, the elastomer material (which is typically somewhat viscous) may not completely fill the cavity. The elastomer layer may then tend to acquire voids, cracks, and/or other defects and thus not support high torque. On the other hand, if the elastomer layer  230  is too thick it may be too resilient to adequately support high torque.  
         [0032]     Referring now to  FIG. 5 , in another alternative embodiment, one or more stator sections  320 A and  320 B (referred to collectively as  320 A-B) may be secured in stator tube  340  by at least one axial spline  370 A and  370 B, formed on the outer surface of each of the corresponding stator sections  320 A-B, and corresponding axial grooves  342  formed on the inner surface of the stator tube  340 . Axial splines  370 A and  370 B may be formed, for example, during casting of the stator sections  320 A-B, while axial grooves may be formed via machining the inner surface of stator tube  340 , however the invention is not limited in these regards. Stator sections  320 A-B are deployed in stator tube  340  such that splines  370 A and  370 B engage grooves  342 , thereby substantially preventing stator sections  320 A-B from rotating relative to one another and to the stator tube  340 . The stator sections  320 A-B may then be held in place in stator tube  340 , for example, via a threaded end cap (not shown) or some other suitable arrangement. Exemplary embodiments of stator  305  advantageously enable stator sections  320 A-B to be removed from stator tube  340  as shown at  331 . In the event of elastomeric degradation, for example, one or more of the stator sections  320 A-B may be removed from the stator tube  340  and replaced with other similar stator sections  320 A-B in the field (e.g., at a drilling rig) typically providing significant savings in time and expense.  
         [0033]     Stator  305  is similar to stators  105  ( FIG. 2 ) and  205  ( FIG. 4 ) in that it includes an elastomer liner (not shown) deployed on an inner surface of the helical cavity component (inner surface  316  of stator sections  320 A-B in the embodiment shown on  FIG. 5 ). In the exemplary embodiment shown on  FIG. 5 , an elastomer liner may be deployed as described above via known elastomer injection and curing techniques after deployment of the stator sections  320 A-B in stator tube  340 . Alternatively, each stator section  320 A-B may be fitted with an elastomer liner (not shown on  FIG. 5 ) on the inner surface thereof prior to deployment in the stator tube  340 .  
         [0034]     Turning now to  FIG. 6 , another alternative embodiment of a stator  405  according to this invention is illustrated. Stator  405  is similar to stators  105 ,  205 , and  305  (described above with respect to  FIGS. 2 through 5 ) in that it includes at least one longitudinal stator section  420  deployed in a stator tube  440 . Moreover, the at least one stator section  420  is similar to stator sections  120 A-D,  220 A-D, and  320 A-B (also described above with respect to  FIGS. 2 through 5 ) in that it includes a plurality of helical lobes  460  formed in the inner surface  416  thereof. Stator  405  differs from those described above in that the stator sections do not extend from one longitudinal end of the stator  405  to the other. Rather, in the exemplary embodiment shown, stator  405  includes a single stator section  420  deployed at one end  407  of the stator  405  (e.g., the downhole hole end). It will be appreciated that this invention is not limited to stator embodiments including only a single stator section  420 , but that stator  405  may also include a plurality of concatenated stator sections deployed at one end thereof. Moreover, stator  405  may alternatively include one or more stator sections  420  deployed at each longitudinal end of the stator.  
         [0035]     With continued reference to  FIG. 6 , stator  405  includes an outer stator tube  440  retaining a helical cavity component  410 . Helical cavity component  410  includes at least one rigid stator section  420 . In the exemplary embodiment shown, stator section  420  reinforces a first portion  410 ′ of the helical cavity component  410  while a second portion  410 ″ of the helical cavity component  410  is of an all elastomer construction as shown at  452 . Stator  405  further includes an elastomer liner  412  deployed on internal surface  416  of stator section  420 . The elastomer liner  412  is continuous with elastomer layer  452  such that the stator  405  includes a plurality of stator lobes  462  extending substantially continuously from one longitudinal end of the stator  405  to the other.  
         [0036]     Exemplary embodiments of stator  405  may be fabricated, for example, as described above with respect to stators  105 ,  205 , and  305 . In one suitable embodiment, the stator tube  440  may be shrunk fit about the at least one stator section  420 . In exemplary embodiments including a plurality of stator sections, the sections may first be concatenated end-to-end (as described above) prior to deployment in the stator tube  440 . Stator tube  440  may advantageously include a shoulder  442  against which the at least one stator section  420  is deployed. After deployment of section  420  in the stator tube  440 , a stator core may be deployed substantially coaxially in the stator tube  440  and elastomer injected into the helical cavity between the core and the stator tube  440 . The stator core is then removed and the elastomer cured, e.g., in a steam autoclave.  
         [0037]     With further reference to  FIG. 6 , stator  405  may be advantageous for various applications in that it provides a relatively cost effective rigid reinforcement to a portion of helical cavity component  410  (as compared to providing rigid reinforcement along the entire length of the stator). For example only, in some downhole drilling applications, conventional stators having an all elastomer helical cavity component are known to fail frequently at the downhole end of the stator. Such failures tend to characterize, in some applications, a “zone of high stress” at the downhole end of the stator. This “zone of high stress” may result, for example, from increased loads on the stator due to the eccentric path of the rotor at the downhole end thereof. Moreover, the pressure drop of the drilling fluid per stator stage is also known to be greatest in some applications at or near the downhole end of the stator. It will be appreciated that exemplary embodiments of stator  405  are configured to provide additional rigidity and reinforcement at the above-described “zone of high stress” of stators in such applications (e.g., at or near the downhole end of the stator). Exemplary embodiments of stator  405  may thus provide a cost effective approach for improving torque output and/or stator longevity. It will also be appreciated that in other applications, additional stator rigidity and reinforcement may be advantageous at other locations along the stator (e.g., at the uphole end and/or at some other location between the two stator ends).  
         [0038]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.