Abstract:
A method of providing variable pumping rate from a piston type pump at a constant drive speed, comprising providing a connecting rod connected to the throw of a crankshaft on one end and to a connecting pin on the other end, constraining said connecting pin to move reciprocally generally in a first direction when said crankshaft rotates, a piston connected to said connecting pin which is mounted in a head and moves reciprocally in a second direction, and varying the angle between said first direction and said second direction to vary the volume being pumped by said pump.

Description:
BACKGROUND OF THE INVENTION 
     The field of this invention of that of crankshaft driven pumps which are used to produce pressurized fluid, typically at relatively high pressures. A conventional crankshaft driven pump has a crankshaft, connecting rod, and piston very much like an automotive engine. It will typically have an intake valve for each cylinder to draw fluid into the cylinder area on the “down stroke” of the piston, or the portion of the stroke when the volume of the cylinder area is increasing. On the returning “up stroke” or the portion of the stroke when the volume of the cylinder area is decreasing, the fluids will be forced out the cylinder through another valve. This can happen on a cylinder or any number of cylinders. A triplex pump is one with three cylinders and is a very common combination in oilfield operations. 
     As the piston moves up and down due to the rotation of the crankshaft, the up and the down position of the piston are typically very well defined. This means that the pump will pump a very predictable volume of fluid, or will have a positive displacement for each rotation of the crankshaft. 
     When the pump is driven by a single speed electric motor, the total volume pumped will simply be the positive displacement for each rotation of the crankshaft times the number of revolutions per minute. 
     There are occasions when it is desirable to have different flow rates from the pump. This is conventionally achieved by getting a variable speed motor or by having intermediate components which change the single speed of a motor to a variable speed for the pump. The variable speed motor always seems like a simple solution, but especially in high horsepower applications and applications in explosive environments the motors become very expensive. 
     The intermediate components to achieve variable flow also tend to be complex. One solution is to install a gear box, but this is complex and can require that the system be stopped to change gears. Alternately a variable displacement hydraulic pump and a hydraulic motor can be installed between the electric motor and the triplex pump. This is space consuming, expensive and prone to need maintenance. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a piston type pump which has a variable displacement at a given revolutions per minute speed. 
     A second object of the present invention is to provide a piston type pump on which the pressure differential between the piston area and the crankshaft area is shared among a number of individual seals. 
     A third object of the present invention is to provide an extension of the inlet check which causes a circulation of cooling water within the piston to cool the piston seals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section of the pump of this invention while pumping and the piston at mid stroke. 
         FIG. 2  is a section of the pump cylinder head enlarged for details. 
         FIG. 3  is a section of the pump of this invention with the cylinder head rotated 90 degrees to the non-pumping position. 
         FIG. 4  is a section of the pump of this invention at 90 degrees to the section of  FIG. 3 . 
         FIG. 5  is a section of the pump of this invention through the crankshaft. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
       FIG. 1  shows pump  1  with a housing  3  and a lid  5 . A crankshaft  8  with a throw or eccentric portion  10  is shown which rotates about a center of rotation shown at  12 . Bearings are shown at  14 , a connecting rod at  16  and an intermediate link at  18 . Connecting pin  20  connects connecting rod  16  to intermediate link  18 , and also connects wag rod or second link  22  to the connecting rod  16  and the intermediate link  18 . Wag rod or second link  22  rotates about bearings  24  which are mounted on shaft  26  which has a fixed axis of rotation. 
     When the crankshaft  8  rotates about the center of rotation  12 , the eccentric location of the throw  10  causes the bearing  14  and therefore the end  28  of the connecting rod  16  to move in a circular fashion. Because of the connection to pin  20  and the wag rod or second link  22 , the connecting pin  20  and therefore the end  30  of the connecting rod  16  are constrained to move about the locus of points indicated at  32  between ends  34  and  36 . 
     The movement of connecting pin  20  along the path indicated at  32  is transmitted to pin  40  which moves piston  42  a corresponding distance within cylinder head  46 . 
     Referring now to  FIG. 2 , an enlarged view of the cylinder head  46  is shown with an inlet port  50 , and inlet check valve  52 , and an inlet check valve extension  54 . The inlet check valve extension  54  partially fits within a recess  56  of the piston  42  to cause circulation of the fluid being pumped into the top of piston for cooling. Outlet port  60  is provided with outlet check valve  62 . 
     A multiplicity of piston seals  70 ,  72 , and  74  are provided for sealing between the high pressure differential between the pumping chamber  76  and the atmosphere at  78 . The intermittent high pressure in the pumping chamber  76  is communicated along hole  80  to the back of compensating pistons  82  and  84  which have differing pressure areas on opposite ends. The pressure areas of the compensating pistons are manufactured to deliver ⅔ of the chamber  76  pressure to the area between seals  70  and  72  via port  86  and ⅓ of the chamber  76  pressure to the area between seals  72  and  74 . In this manner each of the seals  70 ,  72 , and  74  are only required to withstand the wear and stress of ⅓ of the full differential of the pressure pumping chamber  76 , thereby extending the service life of the seals. 
     Port  90  is shown connecting to port  88  through a check valve. Port  90  is supplied with a constant low pressure supply of fluid to make sure that an operational amount of liquid is in port  88  at all times. A similar supply of liquid is provided for port  86  also. 
     Referring now to  FIG. 3 , the cylinder head  46  has been rotated through a 90° arc by a mechanical or hydraulic means illustrated by the ball screw  100 . The ball screw  100  is comprised of a long screw  102  and a ball housing  104 . Rotation of the ball housing  102  will cause its translation, and with attachment to the cylinder head  46 , it will cause the cylinder head  46  to be pivoted about a center at  110 . The center  110  is manufactured to be at the center of the path  32  as indicated above. The centerline of one end of the wag rod or second link  22  and the intermediate link  18  will be in the same place due to common connection of pin  20 , and the centerline of the other end of the wag rod or second link  22  and the intermediate link  18  will be in the same place due to the 90° movement. At this time as the crankshaft  8  rotates and the connection pin  20  moves along the path  32 , the pin  40  and therefore the piston  42  do not move at all. Even though the motor is driving the crankshaft at a high rate of speed, there is no pumping occurring. We have changed the pump from a full flow rate in  FIG. 1  to a no flow rate in  FIG. 3 . Any position between the position of  FIG. 1  and the position of  FIG. 3  will yield a varying output, depending on the angle. In this way, by varying the angle of the cylinder head  46 , we can vary the flow of the pump. 
     Referring now to  FIG. 4  which is section “ 4 — 4 ” from  FIG. 3 , center  110  is shown as centerlines  112  and  114  of swivels  116  and  118  respectively. Swivel  116  is the inlet swivel from the supply tank and swivel  118  is the high pressure outlet swivel. In the position as shown in  FIG. 3  in mid stroke, the connecting pin  20  shown here as pins  20 A,  20 B, and  20 C is concentric with the centerlines  112  and  114 . In reality, only one of pins  20 A,  20 B, and  20 C will be concentric with the centerlines at any time. The other two would be either in a position into or out of the page. Pin  40  shown here as pins  40 A,  40 B, and  40 C are concentric with shaft  26 . In this configuration, pins  20 A,  20 B, and  20 C can reciprocate into and out of the plane of the page without causing any movement of pins  40 A,  40 B, and  40 C or any flow from the attached pistons. The movement of wag rod or second link  22  is somewhat like a dog wagging its tail, hence the name wag rod. 
     Three separate piston/cylinder combinations are shown, making the unit a triplex pump. Any number of cylinders can be used to supply the appropriate flow rates. 
     Referring now to  FIG. 5 , a section “ 5 — 5 ” from  FIG. 3  is shown through the crankshaft with the eccentrics visible at  10  and  130 . At  132 , the eccentric will exist, but the position of the throw is drawn at the midpoint and is not visible at this point in the rotation. End  134  of the crankshaft  8  is shown going through seal  136  and has preparation  138  for receipt of a single speed motor for rotational power. 
     The preferred embodiment discussed has the piston and head rotating about a centerline to allow for variation in the flow rate. In like manner, the piston and head portion can remain stationary and the crankshaft area can be rotated to achieve the same results. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.