Related Application Data

This application claims priority to U.S. Provisional Patent Application Serial No. 61/949,414, filed on March 7, 2014, the content of which is

incorporated here by reference.

Field of Invention

The present application relates generally to fluid pump systems, and more particularly to fluid pump systems and multi-gear configurations for fluid pump systems configured for use with low viscosity fluids.

Background

Pump systems for low viscosity fluids are used in numerous applications. For example, low viscosity oils are commonly used in various diesel engine systems for construction and transportation vehicles. Methanol or ethanol based fuel systems, including for example jet fuel systems and high performance vehicle systems, also incorporate pumps in their fuel systems. Pump efficiency is particularly significant for low viscosity fluids such as those utilized in the referenced exemplary applications. Low viscosity fluids tend to flow more readily, and thus can leak or otherwise flow into undesirable areas of the system if not pumped efficiently. The advantage of the three-gear pump in improving volumetric efficiency by reducing leakage is described in US2008/0056926 A1 . This problem is exacerbated when high outlet pressure is required of the pump.

Low-viscosity fluid pump systems, as referenced above, commonly are used in vehicle and transportation systems. Pumps in such applications therefore must be compact. It is difficult to design a pump that is sufficiently compact, and yet still handle the loads associated with the high pressures and flows particularly required for low-viscosity fluid applications.

Multi-gear pumps may be utilized in such systems, which have an advantage of reduced gear facewidth per unit of displacement, so as to permit a lower shaft load per gear at a given pump displacement and running speed. Many conventional configurations use a two-gear pump, including a drive gear and a driven gear. Three-gear pumps have been employed, in which a center or drive gear drives two opposite driven gears to pump the fluid. Such three-gear pumps have an advantage in that the drive gear load tends to be balanced by two high-pressure and two low-pressure ports located diagonally opposite to each other adjacent the driven gears. This configuration enhances the load carrying capability of the pump, but supporting loads on the two driven gears is still of concern.

In addition, for efficient operation it is required to build up a hydrodynamic journal film over the journals or shafts of the pump gears at the running

conditions of the pump. The film results in minimal direct surface-to-surface contact of the pump components, and particularly the gear journals against the corresponding bearings, which reduces friction and wear. Maintaining a hydrodynamic journal film is more difficult for low viscosity fluids, which flow more readily out of the journal areas of the pump. Increasing the running speeds of the driven gear or gears can enhance the creation of the hydrodynamic journal film.

Summary of Invention

In view of the deficiencies of conventional low viscosity fluid pump systems, a need exists in the art for an improved three-gear pump system that is compact, while accommodating the requisite bearing structures. The present invention is a three-gear pump system in which the driven gears have an enhanced bearing structure, and the center or drive gear need not have a robust bearing support structure. As a result, the bearing structures supporting the driven gears can be enlarged relative to conventional configurations, which permits higher bearing loads to be carried.

An aspect of the invention, therefore, is a three-gear pump system. In exemplary embodiments, the three-gear pump system includes a housing and a three-gear configuration within the housing that pumps fluid from one or two fluid inlets to one or two fluid outlets. The three-gear configuration includes a center drive gear, a first driven gear and a second driven gear positioned on opposite sides of the drive gear. The drive gear meshes with the driven gears to drive the driven gears, and the driven gears are radially supported within the housing by a bearing structure for rotation of the driven gears about respective axes. The balanced radial loads on the drive gear eliminate the need for bearing support of the drive gear, which is free to float relative to the driven gears.

The drive gear may have a larger diameter and a greater number of gear teeth as compared to the driven gears. The pump system may include a pump head that houses the three-gear configuration, a motor, and a magnetic coupling that transmits torque from the motor to a drive shaft that drives the drive gear. The three-gear pump system particularly is suitable for pumping a low viscosity fluids at high pressures and running speeds.

These and further features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. Rather, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments. Brief Description of the Drawings

Fig. 1 is a drawing that depicts an exemplary conventional two-gear arrangement of gears for a two-gear pump system.

Fig. 2 is a drawing that depicts an exemplary three-gear arrangement of gears for a three-gear pump system in accordance with embodiments of the present invention.

Fig. 3 is a drawing that depicts a first exemplary three-gear configuration for a three-gear pump system in accordance with embodiments of the present invention.

Fig. 4 is a drawing that depicts a second exemplary three-gear

configuration for a three-gear pump system in accordance with embodiments of the present invention.

Fig. 5 is a drawing that depicts a third exemplary three-gear configuration for a three-gear pump system in accordance with embodiments of the present invention.

Fig. 6 is a drawing that depicts a first exemplary assembly of a three-gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention.

Fig. 7 is a drawing that depicts a second exemplary assembly of a three- gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention.

Fig. 8 is a drawing that depicts a third exemplary assembly of a three-gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention.

Fig. 9 is a drawing that depicts an exemplary three-gear configuration for a three-gear pump system in accordance with embodiments of the present invention, in which the drive gear has a larger outer diameter than the driven gears.

Fig. 10 is a drawing that depicts an exemplary three-gear arrangement of gears for a three-gear pump system from a gear facing view in accordance with embodiments of the present invention, in which the drive gear has a larger outer diameter than the outer diameters of the driven gears.

Fig. 1 1 is drawing that depicts an isometric view of the an exemplary three-gear pump system in accordance with embodiments of the present invention.

Fig. 12 is a drawing that depicts a cross-sectional view of the exemplary three-gear pump system of Fig. 1 1 .

Detailed Description

Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale.

Fig. 1 is a drawing that depicts an exemplary conventional two-gear arrangement 10 of gears for a two-gear pump system. Fig. 1 depicts the limitations of a two-gear configuration with respect to bearing size and the resultant bearing load capability. As seen in Fig. 1 , a first gear 12 may be a drive gear that drives a second or driven gear 14. The gears may be spur gears by which the drive gear drives the driven gear via interacting or meshing gear teeth as is known in the art. As is commonly a referred to in the art, a center distance is deemed to be the distance between the rotating axes of the gears. In addition, as denoted in Fig. 1 by the parallel lines and arrows, a wall thickness is a distance between the bearing pockets of the two gears. With such a configuration, a maximum thickness of a bearing to support the gear shafts or journals is the difference between the center distance and the wall thickness. If ball bearings are employed as the bearing structure, the maximum distance would correspond to a maximum outer diameter of the ball bearings. The resultant maximum distance or outer ball bearing diameter is less than the pitch diameter of the gears in the two-gear arrangement of Fig. 1 . Fig. 2 is a drawing that depicts an exemplary three-gear arrangement 20 of gears for a three-gear pump system in accordance with embodiments of the present invention. Fig. 2 demonstrates that an enlarged bearing size can be utilized with a three-gear arrangement as compared to a two-gear arrangement. With the enlarged bearing size, bearings are capable of carrying higher loads. Referring to Fig. 2, the three-gear arrangement 20 includes a center drive gear 22 that drives a first driven gear 24 and a second driven gear 26. The two driven gears are positioned on opposite sides of the drive gear such that the axes of rotation of the three gears are aligned. As in the two-gear configuration, the gears in the three-gear configuration may be spur gears by which the drive gear drives the driven gears via interacting or meshing gear teeth as is known in the art. In the case of a three-gear arrangement, the maximum thickness of the bearings for the driven gears (the maximum thickness being the maximum outer diameter when ball bears are employed) is equal to twice the difference of the center distance between the axes of rotation of the drive gear and the driven gears, minus the drive shaft outer diameter and the wall thickness (again denoted by the parallel lines and arrows in Fig. 2), as set forth in Equation (1 ):

Eq. (1 ): Maximum Thickness = 2 ^* (C.D.- Drive Shaft O.D. - wall thickness),

where CD. is the center distance and O.D. refers to the outer diameter of the drive shaft that drives the center gear. The result of Equation (1 ) is that the maximum bearing thickness, or in the case of ball bearings the maximum ball bearing outer diameter, is slightly larger than the outer diameter of the driven gears, which also is significantly larger than the maximum bearing thickness calculated for the two-gear configuration of Fig. 1 .

In accordance with the present invention, therefore, a three-gear pump system configuration is provided in which the driven gears are each supported by a bearing structure having a thickness up to the maximum as determined by Equation (1 ). In addition, the load on the center or drive gear is balanced to near zero by the positioning of the two driven gears. The drive gear acts as an overhung load driven by a drive shaft mechanism, such as for example a keyway or spline. Accordingly, the drive gear can rotate freely between the driven gears without any separate bearing structure for the drive gear. As referred to herein, because the drive gear is free to float radially relative to the driven gears without a separate or independent bearing structure, it is said to be a "floating drive gear" between the driven gears. With a floating drive gear, the thicknesses of the bearing structures for the driven gears can be increased to the maximum permitted by Equation (1 ), without any potential interference by a separate bearing structure for the drive gear. In the present invention, therefore, the bearing structures for the driven gears are further enhanced as compared to conventional configurations in which the drive gear typically is provided with its own support bearing.

In exemplary embodiments, a three-gear pump system includes a housing and a three-gear configuration within the housing that pumps fluid from a fluid inlet to a fluid outlet. The three-gear configuration includes a center drive gear, and a first driven gear and a second driven gear positioned on opposite sides of the drive gear. The drive gear meshes with the driven gears to drive the driven gears, and the driven gears are radially supported within the housing by a bearing structure for rotation of the driven gears about respective axes. The drive gear is free to float radially relative to the driven gears.

Fig. 3 is a drawing that depicts a first exemplary three-gear configuration 30 for a three-gear pump system in accordance with embodiments of the present invention. Fig. 3 is taken at a side view of the three-gear configuration. Similarly to the configuration depicted in Fig. 2, the three-gear configuration 30 includes a center drive gear 32 that drives a first driven gear 34 and a second driven gear 36. The two driven gears are positioned on opposite sides of the drive gear such that the axes of rotation of the three gears are parallel and aligned. The drive gear 32 is driven by a drive shaft 38 that ultimately is driven by a motor (not shown). The drive gear 32 in turn drives the driven gears 34 and 36, which rotate respectively in conjunction with gear shafts 40 and 42. The rotation of the gears causes displacement of the fluid so as to pump fluid from an inlet side 44 to an outlet side 46.

The three-gear configuration 30 further has a bearing structure that includes bearings 48 and 50 positioned respectively adjacent to the driven gears 34 and 36. In the embodiment of Fig. 3, the bearing structures 48 and 50 are configured as a plurality of sleeve bearings that radially support the journals or gear shafts of the driven gears for rotation of the driven gears about respective axes. The plurality of sleeve bearings may be configured as sleeve bearing pairs, in which one sleeve bearing is positioned on portions of the gear shafts 40 and 42 on opposite sides of the driven gears. In the embodiment of Fig. 3, the sleeve bearings may be pressed into a surrounding pump housing of the pump system. In such embodiment, therefore, the sleeve bearings remain fixed and thus do not rotate, with the shafts of the driven gears rotating relative to the sleeve bearings.

In exemplary embodiments, the gears may be formed of a rigid metallic material, such as stainless steel or other suitable metals. The sleeve bearings may be formed of a rigid polymer or any suitable bearing grade plastic material as are known in the art. As such, the bearings tend to be softer than the gears, and bearing wear is a concern. Bearing wear changes the shape of the bearing edges to more of an oval curvature.

In addition, as referenced above, the drive gear 32 is configured as a floating drive gear as it rotates to drive the driven gears. In other words, because the load on the drive gear is balanced by the positioning of the drive gear between the driven gears, the drive gear is free to float radially relative to the driven gears. There is no separate or independent bearing structure associated with radially supporting the drive gear. Such configuration permits the thickness of the sleeve bearings to be increased up to the maximum permitted by Equation (1 ), as the spaces between the drive shaft 38 and gear shafts 40 and 42 need not be allotted to providing a separate bearing structure for the drive gear. Figs. 4-8 are drawings depicting alternative configurations of the three- gear configuration 30 of Fig. 3. Accordingly, like structures are afforded the same reference numerals in Figs. 4-8 as in Fig. 3.

Fig. 4 is a drawing that depicts a second exemplary three-gear

configuration for a three-gear pump system in accordance with embodiments of the present invention. The embodiment of Fig. 4 differs in the nature of the bearing structures provided for radially supporting the driven gears 34 and 36 for rotation of the driven gears about respective axes. In particular, the three-gear configuration of Fig. 4 includes bearing structures 52 and 54 positioned respectively adjacent to the driven gears 34 and 36. In the embodiment of Fig. 4, the bearing structures 52 and 54 are configured as sleeve bearing pairs, in which one sleeve bearing is provided on portions of the gear shafts 40 and 42 on opposite sides of the driven gear.

In the embodiment of Fig. 4, in contrast to the embodiment of Fig. 3, the sleeve bearings 52 and 54 are fixed to the gears shafts 40 and 42. In such embodiment, therefore, the sleeve bearings rotate with the gears shafts as a unit relative to the pump housing structure. The configuration of Fig. 4 may be particularly suitable in applications when the housing is made of a non-metallic or other material that would tend to be softer than the gear material. With such configuration, the bearings rotate relative to the softer housing material, which results in less bearing wear than would tend to occur if the harder gear material rotated relative to the softer bearing material, as in the configuration of Fig. 3. The drive gear 32 of Fig. 4 also is configured as a floating drive gear as it rotates to drive the driven gears. In other words, the load on the drive gear is balanced and the drive gear is free to float radially relative to the driven gears. There again is no separate or independent bearing structure associated with radially supporting the drive gear.

Fig. 5 is a drawing that depicts a third exemplary three-gear configuration for a three-gear pump system in accordance with embodiments of the present invention. The embodiment of Fig. 5 differs in the nature of the bearing structure provided for radailly supporting the driven gears 34 and 36. In particular, in the three-gear configuration of Fig. 5, the bearing structure has bearings 56 and 58 positioned respectively adjacent to the driven gears 34 and 36. In the

embodiment of Fig. 5, the bearing structures 56 and 58 are configured as a plurality of ball bearings that radially support the journals or gear shafts of the driven gears for rotation of the driven gears about respective axes. The ball bearings may be configured as ball bearing pairs, in which one ball bearing is provided on portions of the gear shafts 40 and 42 on opposite sides of the driven gear. Each ball bearing rotates within a ball bearing housing 60 or 61 . The drive gear 32 of Fig. 5 also has a balanced load and is configured as a floating drive gear as it rotates to drive the driven gears. With such configuration, the outer diameters of the ball bearings may extend into spaces adjacent the drive gear 32 in accordance with Equation (1 ) to permit greater bearing loads.

Figs. 6-8 are drawings that depict exemplary assemblies of a three-gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention. As in the previous embodiments, the assemblies of Figs. 6-8 include bearing structures adjacent to or associated with the driven gears, and a balanced load drive gear with no independent bearing structure. Accordingly, like structures are afforded the same reference numerals in Figs. 6-8 as in Figs. 3-5. In addition, for illustrative purposes, the assemblies of Figs. 6-8 are depicted with bearing structures comparable to those of Fig. 3. It will be appreciated, however, that any of the bearing structures of Figs. 3-5 may be employed in the assemblies of Figs. 6-8.

Fig. 6 is a drawing that depicts a first exemplary assembly of a three-gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention. The drive shaft 38 has a first end portion 62 that extends in a direction of a motor (not shown) that drives the drive shaft, and a driving portion 64 that extends into and drives the drive gear 32. In exemplary embodiments, the driving portion 64 is a spline portion that drives the drive gear, although alternative driving mechanisms, such as a keyway, may be employed. The driving or spline portion 64 cooperates with a reciprocal portion of the drive gear 32 to drive the drive gear. The drving portion 64 has a step configuration relative to the first end portion 62, such that the driving portion has a smaller outer diameter than the first end portion. The drive gear 32 has a reciprocal reverse step configuration for receiving the step configuration of the drive shaft. In this manner, the step configurations of the drive shaft and the drive gear act as a locator for easier positioning of the drive shaft properly with respect to the drive gear.

Fig. 7 is a drawing that depicts a second exemplary assembly of a three- gear configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention. In the embodiment of Fig. 7, the locator function is enhanced by providing a pin 66. The pin 66 may be pressed or otherwise fixed into the pump housing, and extends into the reverse step portion of the drive gear 32. Because the pin is fixed into the pump housing, the pin does not rotate, and the drive gear rotates relative to the pin. The pin extends into the reverse step portion of the drive gear to locate the drive gear within the pump housing. In addition, for proper positioning of the drive shaft 38, the drive shaft is inserted through the pin 66 such that the driving portion 64 extends into the drive gear. In this manner, the pin 66 operates to properly locate the drive gear within the pump housing, and locate the drive shaft relative to the drive gear. The ease of installation is thus significantly enhanced. The configuration of Fig. 7 may not work effectively in a conventional two-gear configuration, as both the drive and driven gear shafts would carry radial loads. Supporting a drive gear shaft on a pin may result in excessive wear in a low viscosity fluid that is incapable of hydrodynamically supporting the loads on the pin.

Fig. 8 is a drawing that depicts a third exemplary assembly of a three-gea configuration and drive shaft for a three-gear pump system, in accordance with embodiments of the present invention. In the configuration of Fig. 8, the driving function of the driving portion (spline) 64 and the locator functions are separated In this embodiment, a pin 68 is pressed or fixed into the pump housing. The pin and the cooperating reverse step portion of the drive gear 32 are positioned on an opposite side of the drive gear relative to the drive shaft 38. In this configuration, the pin 68 extends into the reverse step portion of the drive gear to properly locate the drive gear within the pump housing. In addition, the driving portion 64 of the drive shaft acts as a self-locating element of the drive shaft to properly locate the drive shaft relative to the drive gear.

Fig. 9 is a drawing that depicts an exemplary three-gear configuration 70 for a three-gear pump system in accordance with embodiments of the present invention, in which the drive gear has a larger diameter than a diameter of the driven gears. As in the previous embodiments, the three-gear configuration of Fig. 9 includes bearing structures adjacent to or associated with the driven gears, and a floating drive gear having a balanced load with no independent bearing structure. Accordingly, like structures are afforded the same reference numerals in Fig. 9 as in the previous figures. In addition, for illustrative purposes, the three-gear configuration of Fig. 9 is depicted with bearing structures comparable to those of Fig. 3. It will be appreciated, however, that any of the bearing structures of Figs. 3-5 may be employed in the three-gear configuration of Fig. 9.

Fig. 9 is taken at a side view of the three-gear configuration 70. Similarly to the configuration depicted in the previous figures the three-gear configuration 70 includes a center drive gear 72 that drives a first driven gear 34 and a second driven gear 36. The two driven gears are positioned on opposite sides of the drive gear 72 such that the axes of rotation of the three gears are parallel and aligned. The drive gear 72 is driven by the input shaft 38 that ultimately is driven by a motor (not shown). The drive gear 72 in turn drives the driven gears 34 and 36, which rotate respectively in conjunction with gear shafts 40 and 42. As in the previous embodiments, the rotation of the gears causes displacement of the fluid so as to pump fluid from an inlet side 44 to an outlet side 46.

In the embodiment of Fig. 9, the drive gear 72 has an outer diameter that is greater than an outer diameter of the driven gears 34 and 36, as indicated by the lines/arrow in Fig. 9. This configuration may be contrasted with the

configuration of the previous embodiments, in which the drive gear 32 has the same outer diameter as the driven gears. An advantage of the greater drive gear diameter is that the permissible thickness or diameter of the bearings for the driven gears is increased. Specifically, the larger outer diameter of the center drive gear 72 in the embodiment of Fig. 9 increases the center distance value in Equation (1 ) above, which results in a greater maximum thickness of the bearings.

Relatedly, in view of the greater outer diameter, the drive gear 72 also may have a greater number of gear teeth than the driven gears 34 and 36. In general, because the center drive gear teeth interact with the gear teeth of both driven gears, the gear teeth of the drive gear are subject to more wear than the gear teeth of the driven gears. For example, when the number of gear teeth on the drive gear equals the number of teeth on the driven gears, there are twice as many interactions by the drive gear teeth so the drive gear teeth may wear twice as much as the driven gear teeth. By increasing the outer diameter and number of teeth of the drive gear, the number of interactions of the drive gear teeth is reduced, which commensurately reduces the amount of wear of the drive gear teeth relative to the amount of wear of the driven gear teeth.

Fig. 10 is a drawing that depicts an exemplary three-gear arrangement that can be employed in the three-gear configuration of 70 of Fig. 9. In the example of Fig. 10, the center gear 72 has twelve gear teeth as compared to the nine gear teeth of the driven gears 34 and 36. It will be appreciated that Fig. 10 illustrates one non-limiting example, and the precise number of gear teeth in the drive and/or driven gears may be varied. In one embodiment, the drive gear has twice as many gear teeth as the driven gears. Such configuration tends to equalize the gear teeth wear in the drive gear versus the driven gears by equalizing the number of gear teeth interactions.

Another advantage of the increased drive gear diameter is in control of the running speed. For a given drive gear running speed, a larger diameter drive gear will drive the driven gears at a higher running speed as compared to a smaller diameter drive gear. The higher speeds may result in an increased likelihood of building a hydrodynamic film to support loads on the driven gears. Stated in another way, to maintain a given running speed of the driven gears, a drive gear running speed may be reduced for a larger diameter drive gear as compared to a smaller diameter drive gear. Reducing the running speed of the drive gear is particularly suitable for pump systems employing a brushless direct current (DC) electric motor as is known in the art, which are common in automotive and similar vehicle applications. Accordingly, the three-gear configuration in which the drive gear has a greater outer diameter than the driven gears provides a degree of flexibility in the control of the gear running speeds.

The various embodiments of the three-gear configurations described above may be employed in a pump system, and a low-viscosity fluid pump system in particular. Fig. 1 1 is drawing that depicts an isometric view of an exemplary three-gear pump system 80 in accordance with embodiments of the present invention. Fig. 12 is a drawing that depicts a cross-sectional view of the exemplary three-gear pump system 80 of Fig. 1 1 .

Referring first to Fig. 1 1 , the pump system 80 includes a motor 82, a magnetic coupling 84, and a pump head 86 that includes or acts as a housing for the three-gear configurations. The motor may be a brushless DC electric motor as referenced above, although any suitable motor may be employed. The magnetic coupling 84 couples the pump head 86 to the motor 82, and the magnetic coupling further provides a barrier that prevents fluid from flowing from the pump head into the motor components. The pump head 86 includes an inlet 88 for receiving fluid being pumped, and an outlet 90 through which the pump fluid exits the pump head. The components of the three-gear configurations described above are housed within the pump head 86.

The cross-sectional view of Fig. 12 further depicts components of the pump system 80, including the motor 82, magnetic coupling 84, and pump head 86. An exemplary three-gear configuration is shown as being enclosed within and/or housed within a housing 92 of the pump head 86. The pump head includes a center or drive gear 94 that is driven by a drive shaft 96 that drives the drive gear. At an end opposite the drive gear, the drive shaft 96 extends into the magnetic coupling 84. The magnetic coupling 84 is located between the motor 82 and the pump head 86, and transmits torque from the motor to the drive shaft 96 so as to drive the drive gear 94. The drive gear 94 in turn drives the driven gears 98 and 100. Although in the example of Fig. 12 the drive gear and driven gears have essentially the same outer diameter, configurations comparable to the embodiments of Figs. 9 and 10 may be employed, in which the drive gear has a greater diameter than the driven gears.

Journal bearing structures 102 and 104 are provided adjacent to or otherwise associated with the journals or shafts of the driven gears 98 and 100. In the example of Fig. 12, the bearing structure configuration is shown to have a sleeve bearing configuration. It will be appreciated that the configuration of Fig. 12 is an example, and any of the bearing structure configurations comparable to any of the embodiments of Figs. 3-5 may be employed. Similarly, the drive shaft 96 may be located and positioned relative to the drive gear 94 utilizing any of the structural components and configurations comparable to any of the embodiments the assemblies of Figs. 6-8. The pump head 86 also may include a plate 106 located between the gears and the outlet 90, and enclosed by the housing 92. The plate 106 operates to provide axial pressure balance across the gears.

In accordance with the above, an aspect of the invention is a three-gear pump system. In exemplary embodiments, the three-gear pump system includes a housing, and a three-gear configuration within the housing that pumps fluid from a fluid inlet to a fluid outlet. The three-gear configuration includes a center drive gear, a first driven gear, and a second driven gear positioned on opposite sides of the drive gear, and the drive gear meshes with the driven gears to drive the driven gears. The driven gears are radially supported within the housing by a bearing structure for rotation of the driven gears about respective axes, wherein the drive gear is free to float radially relative to the driven gears.

In an exemplary embodiment of the three-gear pump system, the bearing structure comprises a plurality of sleeve bearings that support gear shafts of the driven gears. In an exemplary embodiment of the three-gear pump system, the plurality of sleeve bearings comprises sleeve bearing pairs positioned on portions of the gear shafts on opposite sides of the driven gears.

In an exemplary embodiment of the three-gear pump system, the sleeve bearings are pressed into a pump housing and the driven gear shafts rotate relative to the sleeve bearings.

In an exemplary embodiment of the three-gear pump system, the sleeve bearings are fixed to the gear shafts of the driven gears and the gear shafts and sleeve bearings rotate as a unit.

In an exemplary embodiment of the three-gear pump system, a maximum thickness of each sleeve bearing is set forth by the equation:

Maximum Thickness = 2 ^* (C.D.- Drive Shaft O.D. - wall thickness), wherein CD. is a center distance between axes of rotation of the drive gear and the driven gears, and O.D. is an outer diameter of the drive shaft that drives the center gear.

In an exemplary embodiment of the three-gear pump system, the bearing structure comprises a plurality of ball bearings that support gear shafts of the driven gears.

In an exemplary embodiment of the three-gear pump system, the plurality of ball bearings comprises ball bearing pairs positioned on portions of the gear shafts on opposite sides of the driven gears.

In an exemplary embodiment of the three-gear pump system, each ball bearing rotates within a ball bearing housing.

In an exemplary embodiment of the three-gear pump system, each ball bearing has an outer diameter that extends into a space adjacent the drive gear.

In an exemplary embodiment of the three-gear pump system, a maximum outer diameter of each ball bearing is set forth by the equation:

Maximum Outer Diameter = 2 ^* (C.D.- Drive Shaft O.D. - wall thickness), where CD. is a center distance between axes of rotation of the drive gear and the driven gears, and O.D. is an outer diameter of the drive shaft that drives the center gear.

In an exemplary embodiment of the three-gear pump system, the system further includes a drive shaft that has a driving portion that drives the drive gear.

In an exemplary embodiment of the three-gear pump system, the driving portion of the drive shaft has a step configuration that acts as a locator to position the drive shaft relative to a reciprocal reverse step configuration of the drive gear.

In an exemplary embodiment of the three-gear pump system, the system further includes a pin that is pressed into a housing of the pump system and extends into the reverse step configuration of the drive gear to locate the drive gear within the pump housing, and the drive shaft is inserted through the pin to locate the drive shaft relative to the drive gear.

In an exemplary embodiment of the three-gear pump system, the system further includes a pin that is pressed into a housing of the pump system, and the pin extends into a reverse step configuration of the drive gear to locate the drive gear within the pump housing.

In an exemplary embodiment of the three-gear pump system, the drive gear has a larger diameter than a diameter of the driven gears.

In an exemplary embodiment of the three-gear pump system, the drive gear has a greater number of gear teeth than the driven gears.

In an exemplary embodiment of the three-gear pump system, the drive gear has twice as many gear teeth as the driven gears.

In an exemplary embodiment of the three-gear pump system, the system includes a pump head including the housing that houses the three-gear configuration and includes the fluid inlet and the fluid outlet, a drive shaft that drives the drive gear, a motor, and a magnetic coupling that is located between the motor and the pump head and transmits torque from the motor to the drive shaft.

In an exemplary embodiment of the three-gear pump system, the sytem includes a housing, and a three-gear configuration within the housing that pumps fluid from a fluid inlet to a fluid outlet. The three-gear configuration includes a center drive gear, a first driven gear, and a second driven gear positioned on opposite sides of the drive gear, and the drive gear meshes with the driven gears to drive the driven gears. The driven gears are radially supported within the housing by a bearing for rotation of the driven gears about respective axes, wherein the drive gear has a larger diameter than a diameter of the driven gears.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.