High Slip Prime Mover For Pumpjack Apparatus

Abstract

Pumpjack apparatus for reciprocatingly driving a plunger comprising a low slip electric motor connected to a gear reduction assembly by a torque converter, with the gear reducer cranking a walking beam so as to effect reciprocatory motion thereof. The combination of a low slip motor and a torque converter provides more slip than can be attained with a conventional high slip electrical motor, and also imposes less peak torque loads upon the gear reduction system.

Description

BACKGROUND OF THE INVENTION

Above surface pumping apparatus of varied design are employed for effecting artificial lift so that sub-terranean oil may be pumped to the surface of the ground. A common and universally accepted pumping system is found in a pumpjack. The pumpjack is generally comprised of a walking beam suitably journaled and supported in overhanging relationship to the borehole so that a string of sucker rod can be attached to a reciprocating end of the walking beam, while a driving means is connected to a crank which in turn is interconnected to the walking beam by a pitman.

Throughout the vast desolate region of West Texas, as well as in other geographical locations of the United States of America where oil is produced, it sometimes happens that production declines over the years until further production becomes uneconomical. As production declines, the producer usually will economize by replacing the original large pump-jack, reduction gears, and high-slip motors with smaller, less expensive pumpjack apparatus.

Man has cleverly devised a technique called "water flooding" in order to stimulate production of the depleted reservoirs. Should a reservoir favorably respond to the water flooding, the producer is faced with the agreeable task of pumping a large quantity of oil, whereas over the several preceeding years, he was faced with progressively declining productivity.

Electrical motors, when used as a prime mover for powering the reduction gears of a pumpjack, are universally of a type identified as a "high slip motor" because the motor in driving the massive counterweights and walking beam must be of a design which enables it to cyclicly speed-up and slow-down each pumping cycle or stroke of the pump. A high slip motor is more expensive, more comlex, and less efficient as compared to a similar size of low slip motor. A high slip motor imposes less torque upon a pumping unit reduction gear assembly because as the torque imposed upon the motor during each pumping cycle increases, the high slip motor, together with the rotating masses of the pumpjack unit, slow down or decelerate.

On the other hand, a low slip motor is designed to run at a constant speed and accordingly, it cannot be satisfactorily substituted for a high slip motor of a pumpjack unit because as the masses of a pumpjack unit give up their kinetic energy during each pumping cycle, the motor is forced to labor because it is forced to run at a speed substantially below its designed operating speed, and therefore, it rapidly overheats and ultimately, if it is of a reasonable size for its expected duty, it will burn up.

The torque required to drive the rod string of a pumpjack unit can be divided between two source: (1) the prime mover; and (2) the rotating masses which are decelerating. The rotating masses yield kinetic energy and torque during the process of decelerating. The torque obtained aids in driving the rod string. The torque delivered from the rotating masses to the rod string is not transmitted through the reducer, thus the reducer does not need to be large enough to transmit the total torque required to drive the rod string. The reducer needs to be only large enough to transmit that portion of the torque being delivered from the motor to the rod string, and not that portion of the torque supplied by the rotating masses, that is, the portion of the torque which does not pass through the reducer.

During each pump cycle there are periods of peak torque demand. It is desirable that the rotating masses supply as large a portion of the required torque as is possible. This is accomplished in accordance with the present invention by increasing the slip of the prime mover while allowing the rotating masses to decelerate more rapidly, because the torque yielded by the rotating masses increases as the rate of deceleration increases. This expedient enables considerable reduction in the designed load of the reduction gear box to be effected, and since the peak rod stresses are reduced, the life span of the rod string is considerably elongated.

The provision of a high slip mover used in accordance with the present invention also enables the use of a smaller size gear reducer as well as effecting a savings in the initial cost of the induction motor used therewith.

Accordingly, in new water flood areas, where heretofore it has been necessary to replace pumping units with much larger ones, it is now possible to increase the capacity of a small pumping unit by adding thereto a high slip prime mover made in accordance with the present invention.

SUMMARY OF THE INVENTION

A pumping unit having a driving means connected to reciprocate a walking beam of a pumpjack, comprising a high slip prime mover connected to the reduction gear assembly of the pumping unit. The high slip prime mover is in the form of a torque converter and a low slip electric motor connected together so that the motor drives the torque converter which in turn drives the reduction gear assembly, thereby inducing reciprocatory motion into the walking beam by means of the usual pitman and crank assembly.

Accordingly, a primary object of the present invention is the provision of means by which pumpjack units may be increased in efficiency.

Another object of the invention is to provide improvements in methods for driving a pumpjack unit.

A further object of this invention is the provision of new and useful methods and apparatus by which a high slip prime mover can be connected to the gear box of a pumpjack unit.

A still further object of this invention is the provision of apparatus for reducing the peak loads in a rod string of a pumpjack unit while at the same time increasing the production capability of the assembly.

Another and still further object is the provision of means for reducing the peak torque loads generally encountered in the reduction gear of a pumpjack unit.

Another object of this invention is the provision of improvements in a combination motor, motor mount assembly, torque converter, and gear reduction assembly for a pumpjack unit.

Still another object of this invention is the provision of a high slip prime mover assembly which enables a low slip induction motor to be used in driving a pumpjack unit.

These and various other objects and advantages of the invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings.

The above objects are attained in accordance with the present invention by the provision of a combination of elements which are fabricated in a manner substantially as described in the above abstract and summary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a pumpjack unit having a drive means made in accordance with the present invention;

FIG. 2 is an enlarged side view of one embodiment of the drive means disclosed in FIG. 1;

FIG. 3 is an opposite side view of the apparatus disclosed in FIG. 2;

FIG. 4 is an end view of the drive means employed in conjunction with apparatus disclosed in FIG. 3;

FIG. 5 is a side elevational view of another embodiment of a drive means made in accordance with the present invention;

FIG. 6 is a graphical illustrative of the torque and the loads encountered during a cycle of operation of a pumpjack unit; and

FIG. 7 is a diagrammatical representation of the operation involved in a pumpjack unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is disclosed a pumping unit 10 having a driving means 11 connected thereto with the apparatus being suitably supported from a ground supported base 12.

A Samson post 13 supports a walking beam 14 which is suitably pivotally affixed thereto by the illustrated saddle 15 which forms a journal means.

The walking beam has a horse-head attachment 16 at one end thereof so that a cable 17 can be connected at 18 to a polish rod 19, thereby enabling a rod string located downhole in the well bore 20 to be reciprocated, which in turn imparts reciprocatory motion into a pump located deep down-hole within the borehole.

The remaining end 21 of the walking beam is journaled at 22 to a pitman or connecting rod 23, while the remaining end of the connecting rod is affixed to a crank 24 by means of journal 25. The crank is affixed to a power output drive 26 of a reduction gear assembly 27. Counterbalance 28 is generally affixed along a marginal free end portion of the crank.

The gear reducer is set upon a support means 29, which in turn is bottom supported from the before mentioned base. Driven gear 30 is attached by means of belts or chains 31 to drive gear 32 which in turn is supported at 33 from a base 34. A torque converter 35 is affixed to a fluid reservoir 36 with the reservoir being supported from the last named base. An electrical motor 37 having low slip characteristics is adjustably mounted by hinge means 38 to the before mentioned reservoir. Control box 39 contains the necessary relays, starters, and circuitry for properly controlling the flow of current to the motor in a manner known to those skilled in the art.

As best seen in FIGS. 2 - 4, the low slip electric motor drives sheave 40 which is attached to a shaft in the usual manner. The shaft is journaled at 41 to an end wall of the reservoir, and includes a free depending end having a propeller (not shown) affixed thereto so as to provide for forced circulation through hydraulic fluid radiator 42.

The opposed wall of the reservoir abuttingly receives flange 43 thereagainst, with the flange providing a bolt circle so that the torque converter can be removably affixed thereto. The torque converter is bottom supported to member 33 by means of mount member 44. The output shaft 45 of the torque converter is provided with the drive pulley 32 of FIG. 1.

As seen in FIG. 3, in conjunction with FIGS. 2 and 4, hydraulic hoses 46 and 47 provide a flow path between the radiator and the torque converter, with conventional fluid couplings being employed in a known manner.

The hinge means 38 is comprised of a fixed plate 48 which is journaled in a pivotal manner to a movable plate 49 by hinge means 50. Hinge pin 51 enables the movable plate to be removed from the assembly. Spaced bolts 52 threadedly engage the movable plate and have a free end which bears against the fixed plate so that the bolts can cause relative adjustable movement to be effected between the contiguous plates. Lock nuts are provided in the illustrated manner. The fixed plate is bottom supported by the spaced beams 53.

Looking now to the details of the embodiment of FIG. 5, wherein there is disclosed a motor 137 (3 phase 60 cycle 50 hp 1800 rpm pefc squirrel cage induction motor) which has the drive shaft 54 thereof connected to drive shaft 55 of a torque converter 135 by means of coupling member 56 (number 80 Koppers elastomeric coupling).

The reservoir 136 (O.I.M.E. adapter) has the before mentioned input shaft 55 extending in journaled relationship from one wall thereof, with the output shaft of the torque converter (6f1307 "Twin Disk" converter ms280) 135 being axially aligned with the input shaft of the motor. The output shaft is attached to coupling 57 which in turn is mounted to spaced pillow block bearings 58, 59, with the sheave 132 being interposed therebetween.

In FIG. 6, the curve 60 illustrates the well load torque, which goes through two opposite peak loads each pumping cycle. Curve 61 illustrates an idealized constant torque effected at output shaft 45 or 54 of the low slip motor 37 or 137. Curve 62 illustrates the energy storage and dissipation of the rotating mass. The three curves are displaced from one another for clarity, while in reality, curve 61 plus curve 62 less heat losses would equal curve 60.

FIG. 7 is a diagrammatic representation of the operation of the invention showing the relative position of the walking beam, crank and pitmans, and crankshaft.

Throughout this disclosure, the term "torque converter" refers to any hydraulic coupling apparatus having an input shaft which is driven at a substantially constant speed and torque while the output shaft delivers a substantially constant torque at various speeds.

Throughout this disclosure the term "high slip motor" refers to an induction motor specifically constructed to operate at continuous duty under cyclic speeds of rotation; for example, a N.E.M.A. rated Class D motor. The term "low slip motor" refers to an induction motor constructed to run at a substantially constant speed, such as the usual squirrel-cage induction motor for industrial purposes, and classified by N.E.M.A. as Class A, for example.

In operation, the low slip electric motor 37 drives the torque converter with the motor being sized relative to the torque converter and to the expected well load so that the constant output of power from the motor is an optimum value respective of its maximum horsepower. The torque converter output shaft 45 provides a torque which is proportional to the torque provided by the motor, for all speeds of the converter shaft. The output shaft of the torque converter drives the input shaft of the gear reducer, which in turn drives the crank. The crank is connected to the walking beam by the usual pittman and reciprocates the polish rod 19 in the usual manner.

Accordingly, the torque required to drive the rod string is divided between the high slip prime mover assembly and the rotating masses which are accelerating and decelerating each pumping cycle. The torque delivered from the rotating masses to the rod string is not transmitted through the gear reducer because of the presence of the torque converter which continuously provides a force which tends to accelerate the rotating masses during the entire pump cycle. Therefore, the only consideration of the size of the reducer is that it needs to be large enough to transmit the constant flow of torque provided by the output shaft of the torque converter. That portion of the torque applied by the rotating masses and not passing through the reducer need not be considered in selecting the size of the gear reducer.

It is preferred that the rotating masses supply as large a portion of the required torque as is possible. Since the torque converter permits the low slip electric motor to run at a substantially constant speed and power input, the amount of slip available between the gear reducer and the electric motor is substantially 100 percent. This value is at least three times that of prior art high slip motors.

In one specific installation, a size "4" high slip motor in the low torque mode; that is, the highest possible slip; will slow down 1 rpm for each 6.6 inches pounds increase in torque. On the other hand, a torque converter driven by a 50 hp low slip motor, in accordance with the present invention, will slow down 1 rpm for each 2.9 inches pounds increase in torque. Accordingly, the torque converter allows the rotating masses to decelerate 2.3 times faster (6.6/2.9=2.3) than the high slip motor in the low torque mode and 5.6 times faster than the same motor in the high torque mode.

In carrying out the preferred form of the present invention, the torque converter is bolted onto the reservoir with the output shaft extending at 45 in opposed relationship to the input shaft journal seen at 41. Hydraulic oil coolant radiator 42 is disposed adjacent to the illustrated shrouded fan assembly. The fan propeller is directly driven by the input shaft of the torque converter, which also carries sheave 40.

The low slip induction motor 37 is mounted above the torque converter by utilizing the hydraulic fluid reservoir for carrying the pivoted plate member seen at 38. The tension of the illustrated drive belt assembly is controlled by moving the spaced bolts 52, which in turn pivots the plate member 49 about the hinge means. Hence, the spaced bolts form an adjustable stop means for controlling the angular disposition of the motor relative to the base which is supported by the spaced beams 53.

This packaged unit provides a high slip prime mover assembly which can be directly substituted for a prior art high slip induction motor of a pumpjack apparatus by merely lifting the old motor from the base 34, and setting the packaged unit in the same space previously occupied by the motor.

One unexpected advantage of a high-slip prime-mover assembly made in accordance with the present invention lies in the reduction of the peak rod stresses. Peak rod stresses often occur simultaneously with the peak torque. As the prime mover output shaft decelerates during periods of peak torque, the upward acceleration of the rod string is reduced, resulting in lower stresses applied thereto. The present invention substantially equalizes the net torque level applied to the crank shaft of the reduction assembly during the pumping cycle of the pumping unit. Accordingly, the driving means of the present invention has the unexpected advantage of the capability of handling extra well loads of a pumping unit and hence additional fluid can be lifted and delivered to ground level each stroke by employment of the present invention.

It has been found that employment of a high-slip motor makes possible the use of one size smaller reducer than is normally required with conventional low-slip motors. On the other hand, the present invention enables a low-slip motor to be utilized in lieu of the same size high-slip motor while permitting still a smaller reducer to be employed because of the above unexpected advantages. In new water flood areas it is often necessary to replace small pumping units of the prior art with larger prior art units because of the larger anticipated loads. By the practice of the present invention it is possible to increase the pumping capacity of a small pumping unit by adding a torque converter and low slip motor in accordance with this invention. The unforseen advantages gained with the higher slip provided by the torque converter makes it possible to substitute the high-slip prime mover assembly disclosed in FIG. 2 for the existing high slip electric motor of the prior art and to achieve the added advantages as pointed out above.

Assuming that the indicated variables of FIG. 7 have been properly adjusted; that is, the counterweights positioned at the optimum angular location relative to the crank 25', with the pivot 26' being ideally positioned relative to vertical line 63, and with the crank radius R being properly selected; those skilled in the art, having digested this entire disclosure, will be able to calculate with exactness the horsepower requirements of the instant high slip prime mover apparatus for lifting a specified fluid load each pump cycle.

Claims

I claim:

1. In a pumping unit having a driving means connected to a crank, with the crank being connected to a walking beam, wherein the driving means effects rocking motion into the walking beam, the improvement comprising:

said driving means includes a reduction gear assembly, an electric induction motor, and a torque converter, a belt drive means by which said motor is connected to drive said torque converter;

said reduction gear assembly having a power output drive connected to rotate the crank and having a power input drive, said torque converter having a power output shaft connected to said power input drive;

said torque converter includes a fluid reservoir, a radiator, and a converter housing; said housing being affixed to said reservoir with said torque converter shafts being received through the reservoir;

a base, hinge means by which said motor can be pivoted towards and away from said base, means for controlling the angular disposition of the motor relative to the base so that the tension of the belt drive means can be controlled;

whereby said motor delivers a relatively steady flow of power to said torque converter while said torque converter delivers a relatively unsteady flow of power to said reduction gear assembly.

2. The driving means of claim 1 wherein said induction motor is fabricated in a manner to impart the motor with low slip characteristics.

3. A pumpjack apparatus for reciprocatingly driving a plunger comprising a Samson post, a walking beam pivotally connected in journaled relationship to said Samson post; a reduction gear assembly having a power input drive and a power output drive; a crank connected to said power output drive and swingable about the axis of said power output drive;

a pitman having opposed end portions with one end portion thereof being journaled to said walking beam and another end portion thereof journaled to said crank so that the crank effects reciprocating movement in the walking beam;

a low slip induction motor, a torque converter having a power input shaft and a power output shaft, a belt drive means connecting said motor to said power input shaft for effecting torque at said output shaft of said torque converter;

a base, means by which said motor is mounted for movement towards and away from said base, adjustable stop means for controlling the relative disposition of the motor relative to the base, so that the tension of the belt drive means is controlled by the position of the motor relative to the base.

4. In a pumping unit having a driving means connected to a crank, with the crank being connected to a walking beam, wherein the driving means effects reciprocatory motion into the walking beam, the improvement comprising:

said driving means including a reduction gear assembly, and a high slip prime mover means, said prime mover means includes an electric low slip induction motor and a torque converter, means by which said motor is connected to drive said torque converter;

said reduction gear assembly having a power output drive connected to rotate the crank and having a power input drive, said high slip prime mover means having a power output shaft connected to said power input drive;

a base, means by which said motor can be moved towards and away from said base, adjustable stop means for controlling the disposition of the motor relative to the base;

said means by which said motor is connected to drive said torque converter includes a belt drive means arranged so that the tension of the belt drive means is controlled by the position of the motor relative to the base;

whereby; said motor of said prime mover means delivers a relatively steady flow of power to said torque converter while said torque converter delivers a relatively unsteady flow of power to said reduction gear assembly.

5. The apparatus of claim 4 wherein said torque converter includes a fluid reservoir, a radiator, and a converter housing; said housing being affixed to said reservoir with the shaft thereof being received through the reservoir.

6. A pumpjack apparatus for reciprocatingly driving a plunger comprising a Samson post, a walking beam pivotally connected in journaled relationship to said Samson post; a reduction gear assembly having a power input drive and a power output drive; a crank connected to said power output drive and swingable about the axis of said power output drive;

a pitman having opposed end portions with one end portion thereof being journaled to said walking beam and another end portion thereof journaled to said crank so that the crank effects reciprocating movement in the walking beam;

a low slip induction motor, a torque converter having a power input shaft and a power output shaft, a base by which said motor is mounted in overlying relationship to said torque converter; means including a belt drive connecting said motor to said power input shaft for effecting torque at said output shaft of said torque converter;

means connecting said output shaft to said power input drive for effecting torque at said output drive;

hinge means by which said motor can be pivoted towards and away from said base, adjustable stop means for controlling the angular disposition of the motor relative to the base so that the tension of said belt drive means is controlled by the position of the motor relative to the base.