US patent application number 10/372,533, filed on 21 February 2003, is incorporated herein by reference.

In the US this is a continuation-in-part of US patent application number 10/372,533, filed on 21 February 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable REFERENCE TO A"MICROFICHE APPENDIX" Not applicable BACKGROUND 1. Field The present invention relates to oil well pumps. More particularly, the present invention relates to a downhole oil well pump apparatus that can use a circulating working fluid to drive a specially configured pump that is operated by the working fluid and wherein the pump transmits oil from the well to the surface by commingling the pumped oil with the working fluid, oil and the working fluid being separated at the wellhead or earth's surface. Even more particularly, the present invention can relate to an oil well pump that is operated in a downhole cased, production pipe environment that utilizes a pump having a single pump shaft that has gerotor devices at each end of the pump shaft, one of the gerotor devices being driven by the working fluid, the other gerotor device pumping the oil to be retrieved.

2. General Background In the pumping of oil from wells, various types of pumps are utilized, the most

common of which is a surface mounted pump that reciprocates between lower and upper positions. Examples include the common oil well pumpj ack, and the Ajusta pump. Such pumps reciprocate sucker rods that are in the well and extend to the level of producing formation. One of the problems with pumps is the maintenance and repair that must be performed from time to time.

SUMMARY The present invention provides an improved pumping system from pumping oil from a well that provides a downhole pump apparatus that can be operated with a working fluid that operates a specially configured pumping arrangement that includes a common shaft. One end portion of the shaft can be a gerotor that is driven by the working fluid.

The other end portion of the shaft can have a gerotor that pumps oil from the well. In this arrangement, both the oil being pumped and the working fluid commingle as they are transmitted to the surface. A separator can be used at the earth's surface to separate the working fluid (for example, water) and the oil.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein: Figures 1A, 1B, 1C are a sectional elevation view of a preferred embodiment, wherein the drawing 1A matches to the drawing 1B at match lines A-A and the drawing 1B matches to the drawing 1C at match lines B-B; Figure 2 is a partial exploded perspective body of a preferred embodiment of Figures 1A-lC showing some of the pumping components; Figure 3 is an enlarged fragmentary sectional view of the geroter illustrating the pumping components; Figure 4 is a sectional view taken along lines 4-4 of figure 3; Figure5 is a sectional view taken along lines 5-5 of figure 3; Figure 6 is a section view taken along lines 6-6 of figure 3 ; Figures 7A-7B are perspective views of a preferred embodiment of the apparatus of the present invention wherein the match line AA of figure 7A matches the match line AA of 7B ;

Figure 8 is a fragmentary, top view of illustrating one of the filtered disks; Figure 9 is a fragmentary plan view illustrating a filter disk spacer; Figures 10A-10E are sequential illustrations that show various positions of the gerotor devices for both the upper and lower gerotors ; Figure 11 A is a schematic diagram showing operation of the apparatus and method of the present invention in a pumping position ; Figure 11B is a schematic diagram showing operation of the apparatus and method of the present invention in a retrieval position; Figure 11 C is a schematic diagram showing operation of the apparatus and method of the present invention in a neutral position; Figure 12 is an exploded view of an alternative construction for the pump housing.

Figure 13 shows a tool for inserting a plate into the pump housing; Figure 14 shows the plate tool inserting the plate into the pump housing; Figure 15 shows the plate tool after the plate has been inserted into the pump housing; Figure 16 shows a biasing member for maintaining a pressure on the plate when contained in the pump housing ; Figure 17 shows a tool for inserting a retainer into the pump housing; Figure 18 shows the retainer tool inserting the retainer into the pump housing; Figure 19 shows the retainer tool after the retainer has been inserted into the pump housing; and Figure 20 shows the retainer in its final position after being inserted int the pump housing.

DETAILED DESCRIPTION Oil well pump apparatus 10 as shown in the sectional elevation view of figures 1A, 1B and 1C are in the lines A-A in figures 1A and 1B are match lines and the lines B-B in figures 1B and 1C are match lines. Oil well pump 10 can be used in a well casing 11 that surrounds production tubing 12. A packer 13 can be set in between casing 11 and production tubing 12 as shown in figure 1 C. Landing nipple 14 is positioned above packer 13. The landing nipple 14 receives the lower end portion 17 of tool body 15 as shown in figure 1 C. Tool body 15 can be pumped hydraulically (Figure 114 or lowered into the

production tubing 12 bore 18 using a work string (not shown) that grips neck portion 32 at tool body 15 upper end 16.

The apparatus 10 of the present invention provides an oil well pump 10 that has a tool body 15 that is elongated to fit inside of the bore 18 of production tubing 12 as shown in figures 1A-1C. A well annulus 19 is that space in between casing 11 and production tubing 12. During use, a working fluid such as water, "lease" water, or an oil water mixture can be used to power pump mechanism 26. This working fluid follows the path that is generally designated by the arrows 20,21, 22 and 23 in figures lA-lB. The working fluid is pumped from the wellhead area 120 using a prime mover 121 as shown in figure 11A and indicated by arrows 20.

Prime mover 121 (Figure 11) can be a commercially available pump that receives working fluid via flowline 122 from reservoir 123. Reservoir 123 is supplied with the working fluid such as water via flowline 124 that exits oil/water separator 125.

As the working fluid is pumped by prime mover 121 in the direction of arrows 20 through production tubing 12, the working fluid enters tee-shaped passage 34 as indicated by arrows 21. The working fluid then travels in sleeve bore 36 of sleeve 35 as indicated by arrows 22 until it reaches connector 60 and its flow passages 67. Arrows 23 indicate the flow of the working fluid from the passages 67 to retainer 111 and its passageways 112,113. At this point, the working fluid enters pump mechanism 26 (see figures 1B, 2, and 3-6). A check valve 25 is provided that prevents oil from flowing in a reverse direction. This check valve 25 has a spring 50 that is overcome by the pressure of working fluid that flows through passageway 51 in the direction of arrows 20,21, 22,23. The working fluid exits tool body 15 via passageway 137 and working fluid discharge port 65 (see arrow 24).

The pump mechanism 26 is driven by the working fluid. The pump mechanism 26 also pumps oil from the well in the direction of oil flow arrows 27 as shown in figures 1B, 1C and 11A. Connector 68 attaches to the lower end of pump mechanism housing 63.

Connector 68 provides upper and lower external threads 69,70 and flow passages 71 that enable oil to be produced to reach lower filter 31, suction ports 133,134 of retainer 132 and lower gerotor device 151 so that the oil can be pumped by lower gerotor device 151 via passageway 135 to produced oil discharge port 66. At discharge port 66, the produced oil enters production tubing bore IS where it commingles with the working fluid, the

commingled mixture flowing into annulus 19 via perforations 114.

Oil that flows from the producing formation in to the tool body (see arrows 27) flows upwardly via bore 86 of seating nipple 14. The lower end portion 17 of tool body 15 has a tapered section 84 that is shaped to fit seating nipple 14 as seen in figure 1C. An o-ring 87 on lower end 17 of tool body 15 can form a fluid seal between tool body 15 and seating nipple 14. Above passageway S6, oil is filtered with lower filter 31. Of similar construction to filter 30, filter 31 can be of alternating disks 76 and spacers 108 (figures 8-9). Filter disk 76 can be secured to connector 68 with shaft 72 having threaded connection 73 attaching to connector 68 while retainer plate 74 and bolt 75 hold filter disks 76 to shaft 72 (see figure 1B, 7B and 8-9). Connector 68 attaches to pump mechanism body 3 at threaded connection 78. Connector 68 attaches to sleeve 80 and its internal threads 82 at threaded connection 79. Sleeve 80 has bore 81 occupied by lower filter 31 (see figures 1B and 7B). Seating nipple 14 attaches to the lower end of sleeve 80 with threaded connection 83. Seating nipple 14 has bore 86 and external threads 85 that connect to sleeve 80 at threaded connection 83.

The oil producing formation is below packer 13 and check valve 88. The producing oil enters the production tubing bore 18 via perforations (not shown) as is known in the art for oil wells. Check valve 88 and its spring 89 prevent the working fluid from flowing into the formation that contains oil. The check valve 88 is overcome by the pump 26 pressure as oil is pumped upwardly in the direction of arrows 27. Pump 26 can include two central impellers or rotors 94,95. The upper central rotor 94 and outer rotor 98 are driven by the working fluid. The lower central rotor 95 and outer rotor 99 are connected to the upper rotor 94 with shaft 91 so that the lower central rotor 95 rotates when the upper rotor 95 is driven by the working fluid. Thus, driving the upper rotor 94 with the working fluid simultaneously drives the lower rotor 95 so that it pumps oil from the well production bore 18. The oil that is pumped mixes with the working fluid at perforations 114 in the production tubing as indicated schematically by the arrows 28, 29 in figures 1A, 1B. The arrows 29 indicate the return of the oil/water mix in the annulus 19 that is in between casing 11 and production tubing 12. To create a bearing effect shaft 91 can be of a different material than pump housing 63. Additionally, seals such as o-rings can be placed at upper and lower positions of shaft 91.

In figure 11A, the oil, water (or other working fluid) mix is collected in flowline

126 and flows into oil/water separator 125 as indicated by arrows 127. Oil is then removed from the separator in flowline 128 as indicated by arrows 129 in figure 11 A. The working fluid (e. g. , water) is separated and flows via flowline 124 back into reservoir 123 for reuse as the working fluid.

As an alternate means to lower the tool body 15 into the well (if not using pumping of figure l 1A), a neck section 32 is provided having an annular shoulder 33. This is common type of connector that is known in the oil field for lowering down hole tools into a well bore or as an alternate means of retrieval.

An upper filter 30 is provided for filtering the working fluid before it enters the pump mechanism 26. A lower filter 31 is provided for filtering oil before it enters the pump mechanism 26.

Tool body 15 can include a sleeve 35 that can be attached with a threaded connection 38 to the lower end portion of neck section 32 as shown in figure 1A. A pair of swab cups 37,40 are attached to sleeve section 35 at spacer sleeve 42. The swab cup 37 provides an annular socket 39. The swab cup 40 provides an annular socket 41. The spacer sleeve 42 has a bore 43 that has an internal diameter that closely conforms to the outer surface of sleeve 35. The sleeve 35 provides bore 36 through which working fluid can flow as shown in figures 1A and 1B. A third swab cup 44 can be positioned just above valve housing 48 as shown in figure 1B. The swab cup 44 has an annular socket 47. A spacer sleeve 45 with bore 46 is sized to closely fit over sleeve 35 as shown in figure 1B.

Valve housing 48 has external threads that enable a threaded connection 49 to be formed with sleeve 52 at its bore 53 that is provided with internally threaded portions. The bore 53 of sleeve 52 carries filter 30 which is preferably in the form of a plurality of filter disks 54 separated by spacers 108 (see figures 1B, 8-9). As shown in 7A, the filtered disks 54 of filter 30 are held in position upon shaft 57 with retainer plate 55 and bolt 56. Shaft 57 has an internally threaded portion 58 for receiving bolt 56 as shown in figures 1B and 7A. A threaded connection 59 is formed between the lower end portion of shaft 57 and connector 60. The connector 60 has externally threaded portion 61,62 and a plurality of longitudinally extending flow passages 71 as shown in figure 1B and 7A.

Pump mechanism 26 (see figures 1B, 2,3) can include a pump housing 63 that is attached using a threaded connection to the bottom of connector 60 at thread 62. The pump housing 63 in figure 7B has internal threads 64 that enable connection with

connector 60.

Housing 63 can have a working fluid discharge port 65 and an oil discharge port 66 (see figure 3). Pump housing 63 can carry shaft 91. The shaft 91 (see figures 2 and 3) has keyed end portions 92,93. Each rotor 94,95 can be provided with a correspondingly shaped opening so that it fits tightly to a keyed end portion 92 or 93 of shaft 91. In figure 2, the upper rotor 94 has a shaped opening 96 that fits the keyed end portion 92 of shaft 91. The rotor 95 has a shaped opening 97 that fits the keyed end portion 93 of shaft 91.

Each of the central rotors 94,95 can fit an outer rotor 98, 99 that has a star shaped chamber 109, 110. In figures 2 and 3, upper rotor 94 fits the star shaped chamber 109 of rotor 98. Similarly, the lower rotor 95 fits the star shaped chamber 110 of rotor 99.

Each rotor 94,95 can have multiple lobes (e. g. , four as shown). The upper rotor 94 can have lobes or gear teeth 100, 101, 102,103. The lower rotor 95 can have lobes or gear teeth 104,105, 106,107. This configuration of a star shaped inner or central rotor rotating in a star shaped chamber of an outer rotor having one more lobe than the central or inner rotor is a per se known pumping device known as a"gerotor". Gerotor pumps are disclosed, for example, in U. S. patents 3,273, 501 ; 4,193, 746,4, 540,347 ; 4,986, 739; and 6,113, 360 each hereby incorporated herein by reference.

Working fluid that flows downwardly in the direction of arrow 23 enters the enlarged chamber 113 part of passageway 112 of retainer 111 so that the working fluid can enter any part of the star shaped chamber 109 of upper disk 98. An influent plate 115 is supported above upper disk 98 and provides a shaped opening 116. When the working fluid is pumped from enlarged section 113 into the star shaped chamber 109 that is occupied by upper rotor 94, both rotors 94 and 98 rotate as shown in figures 10A-lOE to provide an upper gerotor device 150. Figures 10A-lOE show a sequence of operation during pumping of the upper central rotor 94 in relation to upper outer rotor 98 and its star shaped chamber 109. In figure 1 osa, the opening 116 is shown in position relative to rotors 94 and 98. The two reference dots 140,141 are aligned in the starting position of figure 10A. Arrow 118 indicates the direction of rotation of rotor 94. Arrow 119 indicates the direct of rotation of upper disk 98. By inspecting the position of the reference dots 14 0, 141 in each of the views 10A-1 OE, the pumping sequence can be observed.

The two gerotor devices 150,151 provided at the keyed end portions 92,93 of shaft 91 can each utilize an inner and outer rotors. At shaft upper end 92, upper inner rotor

94 can be mounted in star shaped chamber 109 of peripheral rotor 98. As the inner, central rotor 94 rotates, the outer rotor 98 also rotates, both being driven by the working fluid that is pumped under pressure to this upper gerotor 150.

The rotor or impeller 94 rotates shaft 92 and lower inner rotor or impeller 95. As rotor 95 rotates with shaft 92, outer peripheral rotor 99 also rotates, pulling oil upwardly in the direction of arrows 27. Each inner, central rotor 94, 95 can have one less tooth or lobe than its associated outer rotor 98, 99 respectively as shown in figures 2 and 10A-10E.

While figures 10A-10E show upper rotors 94, 98, the same configuration of figures 1 osa- 10E can apply for lower rotors 95, 99. An eccentric relationship can be established by the parallel but nonconcentric axes of rotation of rotors 94, 98 so that full tooth or lobe engagement between rotors 94,98 occurs at a single point only (see figures 10A-10E).

As working fluid flows through passageways 112, 113 into star shaped chamber 109 and shaped opening 116, rotors 94,98 rotate as do rotors 95,99. Oil to be produced is drawn through suction ports 133,134 of retainer 132 to shaped opening 136 of effluent plate 117 and then into star shaped chamber 110 of outer rotor 99. The rotating rotors 95, 99 transmit the oil to be pumped via passageway 135 to oil discharge port 66.

At discharge port 66, oil to be produced can mix with the working fluid and exit perforations 114 in production tubing 12 as indicated by arrows 28 in figure 1B.

In the pumping mode of figure 1 lA, working fluid (e. g. , water or oil) moves from the reservoir 123 to the prime mover 121. The prime mover 121 can be a positive displacement pump that pumps the working fluid through three way valve 130. In the pumping mode, three way valve 130 handle 131 is in the down position as shown in figure 11A, allowing the working fluid or power fluid into the tubing 12. The working fluid pumps the tool body 15 into the seating nipple 14 and then the lower swab cups 40,44 flare outwardly sealing against the tubing 12 causing the power fluid to then enter the ports or channel 34 at the upper end 16 of the tool body 15. The working fluid travels through the center of the stacked disk upper filter 30 into the uppermost gerotor motor 150 causing the upper gerotor 150 to rotate and, in turn, causing the shaft 91 to rotate which causes the lower gerotor 151 to turn.

When the lower gerotor 151 turns, it pumps produced oil into the casing annulus 19 so that it commingles (arrows 28) with the working fluid and returns to the surface. At the surface or wellhead 120, the oil/water separator 125 separates produced oil into a

selected storage tank and recirculates the power fluid into the reservoir to complete the cycle.

In the retrieval mode of figure 11B, working fluid moves from the reservoir 123 to the prime mover 121. The positive displacement prime mover 121 pumps the working fluid through the three way valve 130. In the retrieval mode, the three way valve handle 131 is in an upper position (as shown in figure 11B) that allows the working fluid to enter the casing annulus 19. The working fluid enters the perforated production tubing 12 at perforations 114 but does not pass the packer 13. This working fluid that travels in the annulus 19 flares the upper swab cup 37 against the production tubing 12 causing a seal.

A check valve 88 can be provided to prevent circulation of the working fluid through the tool body 15 to the oil producing formation that is below valve 88 and packer 13. This arrangement causes the tool body 15 to lift upward and return to the wellhead 120 where it can be removed using an overshot. In figure 11B, the tool body 15 can thus be pumped to the surface or wellhead area 120 for servicing or replacement. The power fluid or working fluid circulates through the three way valve 130 to the oil separator 125 and then to the reservoir 123 completing the cycle.

In figure 11 C, a neutral mode is shown. When the tool body 15 is captured with an overshot, for example, the three way valve 130 is placed in a middle or neutral position as shown in figure 11 C. The figure 11 C configuration causes the power fluid or working fluid to circulate through the three way valve 130 and directly to the separator 125 and then back to the reservoir 123. The configuration of figure 11A produces zero pressure on the tubing 12. A hammer union can be loosened to remove the tool body 15 and release the overshot. The tool body 15 can be removed for servicing or replacement. A replacement pump can then be placed in the tubing 12 bore 18. A well operator then replaces the hammer union and places the handle 131 of the three way valve 130 in the down position of figure 11A. The tool body 15 is then pumped to the seating nipple 14 as shown in figure 11 A, seating in the seating nipple 14 so that oil production can commence.

Figures 12-20 show an alternative embodiment for pump housing 63. Figure 12 is an exploded view of an alternative construction for pump housing 63. From top to bottom is shown retainer 111A, biasing member 210, influent plate 115A, and pump housing 63. Retainer 111A can comprise a plurality of holes 200 (as will be explained

later) and passageway 112. Biasing member 210 can be a spring or other elastic member.

Influent plate 115A can comprise shaped opening 116A, threaded bore 260, seat 220, track 235, and hole 230. Seat 220 can be used to seat a sealing member such as an o-ring. Hole 230 can be used to line up shaped opening 116A with star shaped chamber 109. Opening 116A can be positioned by inserting hole 230 over pin 250. Track 235 can be used to assist in lining up hole 230 over pin 250. Track 235 is preferably circular to assist lining hole 230 with pin 250.

Figure 13 shows tool 300 for inserting influent plate 115A into pump housing 63.

Tool 300 can comprise handle 310, base 330, and screw 320. Figure 14 shows tool 300 inserting influent plate 115A into pump housing 63. Screw 320 can be threaded into threaded bore 260 thereby attaching tool 300 to plate 115A. By pushing in the direction of arrow 315, handle 310 can be used to insert influent plate 115A into bore 63A. One object is to line up hole 230 with pin 250 thus ensuring that shaped opening 116A is properly aligned for gerotor operation. Track 235 can be used to assist in lining up hole 230 with pin 250. Influent plate 115A can be worked in the direction of arrow 315 until plate 115A rests on face 270 of pump housing 63 as shown in figure 15. Thread 320 can be reverse threaded to allow rotation in a counterclockwise direction without tending to separate tool 300 from plate 115A.

Figure 15 shows plate tool 300 after influent plate 115A has been inserted into pump housing 63. Also shown is pin 250 lining up with bore 230. O-ring 225 is shown sealingly engaging sidewall 280. Shaped opening 116A is shown properly lined up with outer rotor 98. To remove tool 300 handle 310 should be turned in a clockwise rotation and pulled upwardly.

Figure 16 shows a biasing member 210 for maintaining pressure on influent plate 115A when plate 115 A is assembled in pump housing 63.

Figure 17 shows a tool 400 for inserting retainer 111 A into pump housing 63. Tool 400 can comprise handle 410, base 420, space 430, and pins 440. Pins 440 can be constructed so that they mate with holes 200 of retainer 11 lA.

Figure 18 shows retainer tool 400 inserting retainer 111A into pump housing 63.

Retainer 111A can include external threads which mate with threaded portion 290 of pump housing 63. To insert retainer 111 A, handle 410 should be turned in the direction of arrow 440. Handle 410 is turned in the direction of arrow 440 until lower surface 425 contacts

upper face 285 of pump housing. Spacer 430 can ensure that retainer 11 lA is inserted to a proper position for compressing biasing member 210. This position is shown in Figure 19. Tool 400 is removed by pulling it out of bore 63A.

Figure 20 shows retainer 11 lA in its final position after being inserted into pump housing 63. Biasing member 210 has been compressed by retainer 111A maintaining a downward forced on influent plate 115A. Pin 250 resists rotational movement of influent plate 115A. O-ring 250 sealingly engages sidewall 280. As shown in Figure 3, 0-ring 500 can also be used to sealingly engage retainer 111 with influent plate 115.

Accordingly, a single path for fluid flow is allowed--passageway 112A to enlarged section 113A ; to shaped opening 116A ; to star shaped chamber 109; and to passageway 137. Even where retainer 111 A backs out somewhat during use biasing member 210 tends to push influent plate 115A towards face 270 and maintaining a fluid tight seal and proper position of influent plate 115A.

PARTS LIST The following is a list of suitable parts and materials for the various elements of the preferred embodiment of the present invention.

10 oil well pump 11 casing 12 production tubing 13 packer 14 seating nipple 15 tool body 16 upper end portion 17 lower end portion 18 bore 19 annulus 20 arrow 21 arrow 22 arrow 23 arrow

24 arrow 25 check valve 26 pump mechanism 27 oil flow arrow 28 oil mix flow arrow 29 return flow arrow 30 filter, upper 31 filter, lower 32 neck section 33 annular shoulder 34 channel 35 sleeve 36 sleeve bore 37 swab cup 38 threaded connection 39 annular socket 40 swab cup 41 annular socket 42 spacer sleeve 43 bore 44 swab cup 45 spacer sleeve 46 bore 47 annular socket 48 valve housing 49 threaded connection 50 spring 51 passageway 52 sleeve 53 bore 54 filter disk 55 retainer plate

56 bolt 57 shaft 58 internal threads 59 threaded connection 60 connector 61 external threads 62 external threads 63 pump mechanism housing 63A bore 64 internal threads 65 working fluid discharge port 66 produced oil discharge port 67 flow passage 68 connector 69 external threads 70 external threads 71 flow passage 72 shaft 73 threaded connection 74 retainer plate 75 bolt 76 filler disk 78 threaded connection 79 threaded connection 80 sleeve 81 bore 82 internal threads 83 threaded connection 84 tapered section 85 external threads 86 bore 87 o-ring

88 check valve 89 spring 90 internal threads 91 shaft 92 keyed portion 93 keyed portion 94 upper rotor 95 lower rotor 96 shaped opening 97 shaped opening 98 outer rotor 99 outer rotor 100 lobe 101 lobe 102 lobe 103 lobe 104 lobe 105 lobe 106 lobe 107 lobe 108 spacer 109 star shaped chamber 110 star shaped chamber 111 retainer 112 passageway 113 enlarged section 114 perforations 115 influent plate 116 shaped opening 117 effluent plate 118 arrow 119 arrow

120 wellhead area 121 prime mover 122 flowline 123 reservoir 124 Bowline 125 separator 126 flowline 127 arrow 128 Bowline 129 arrow 130 three way valve 131 handle 132 retainer 133 suction port 134 suction port 135 passageway 136 shaped opening 137 passageway 140 reference dot 141 reference dot 150 upper gerotor device 151 lower gerotor device 200 holes 210 biasing member 220 seat 225 o-ring 230 hole for pin 235 track 240 line 250 pin 260 bore 262 upper face

270 face 280 sidewall 285 upper face 290 threaded portion 300 tool for plate 310 handle 315 arrow 320 screw 330 base 400 tool for retainer 410 handle 420 base 425 lower surface of base 430 spacer 440 pins 440 arrow The foregoing embodiments are presented by way of example only ; the scope of the present invention is to be limited only by the following claims.