Systems in which a fluid is pumped can be found in a variety of applications such as heavy and industrial machines, chemical industry, food industry, medical industry, commercial applications, and residential applications to name just a few. Because the specifics of the pump system can vary depending on the application, for brevity, the background of the invention will be described in terms of a generalized hydraulic system application typically found in heavy and industrial machines. In such machines, hydraulic systems can be used in applications ranging from small to heavy load applications, e.g., excavators, front-end loaders, cranes, and hydrostatic transmissions to name just a few. Depending on the type of system, a conventional machine with a hydraulic system usually includes many parts such as a hydraulic actuator (e.g., a hydraulic cylinder, hydraulic motor, or another type of actuator that performs work on an external load), a hydraulic pump (including a motor and gear assembly), and a fluid reservoir. The motor drives the gear assembly to provide pressurized fluid from the fluid reservoir to the hydraulic actuator, in a predetermined manner. For example, when the hydraulic actuator is a hydraulic cylinder, the hydraulic fluid from the pump causes the piston rod of the cylinder to move within the body of the cylinder. In a case where the hydraulic actuator is a hydraulic motor, the hydraulic fluid from the pump causes the hydraulic motor to, e.g., rotate and drive an attached load. Typically, the hydraulic circuits in such conventional machines are open-loop hydraulic systems in that the pump draws the hydraulic fluid from the fluid reservoir and the hydraulic fluid is sent back to the reservoir after performing work on the hydraulic actuator. That is, the hydraulic fluid output from the hydraulic actuator is not sent directly to the inlet of the pump as in a closed-loop system. In these types of systems, the motor that drives the hydraulic pump is often run at constant speed, typically at a high speed, which builds up temperature in the hydraulic fluid. Thus, the reservoir also acts to keep the average fluid temperature down by increasing the fluid volume in the system. To control the flow in the system, a variable-displacement hydraulic pump and/or a directional flow control valve (or another type of flow control device) can be added to the system. However, these hydraulic systems can be relatively large and complex. In addition, the various components are often located spaced apart from one another. To interconnect these parts, various additional components like connecting shafts, hoses, pipes, and/or fittings are used in a complicated manner. Moreover, these components are susceptible to damage or degradation in harsh working environments, thereby causing increased machine downtime and reduced reliability of the machine.
In addition, conventional external gear pumps, which are typically used in the above-described conventional systems, are configured to have a drive gear and a driven gear in a casing that has an inlet and an outlet (driver-driven configuration). Fluid is transferred from the inlet to the outlet due to the meshing of the two gears. That is, there is an interlock between the drive gear and the driven gear such that, when the drive gear is rotatably driven, the driven gear is rotated by the force produced from the mechanical contact with the drive gear. The drive gear is integral with a shaft that extends outside the casing to connect to an external power source such as an electric motor. The electric motor disposed outside the casing is typically housed in a separate housing. However, these extended shaft and separate housing take up a significant amount of space and increase the weight of the pump. In addition, the pumps may be susceptible to contamination due to components that extend outside the pump casing and/or fluid system. For example, dirt and other contaminates may be able to enter the pump through clearances in the shaft seals or through some other means. Further, the extended shaft may require extra bearing(s) that need proper lubrication, which could increase structural complexity in the gear pump design. Thus, known pumps and systems have undesirable drawbacks with respect to compactness, complexity and reliability of the systems.
Further limitation and disadvantages of conventional, traditional, and proposed approaches will become apparent to one skilled in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present disclosure with reference to the drawings.