Patent Application
20140271313
1. Field of Invention
This invention relates generally to gear pumps used for liquids, and more particularly, to positive displacement gear pumps that emulate characteristics of lobe pumps.
2. Description of Related Art
Typical spur gear pumps used for pumping hydraulic fluids generally use a drive gear and an idler gear that mesh proximate inlet and outlet openings of the pump. As the drive and idler gears rotate, hydraulic fluid fills the gaps between adjacent spur teeth and is transferred from the inlet through an intermediate transition zone to the outlet. Each of the rotors has a plurality of radially extending, circumferentially-spaced spur teeth with recesses between the teeth. The teeth on each rotor intermesh with the teeth of the other rotor in sealing contact with the recesses of rotors therebetween. The drive gear and idler gear are mounted for rotation on spaced parallel axis with the gears or rotors typically enclosed in a housing or casing in sealing relationship with pumping chamber walls thereof. When there is rotational action of the spur tooth rotors and displacement of fluid by the mating teeth thereof, the pump is considered a positive displacement gear pump.
Spur gear pumps are well known. For example, U.S. Pat. No. 3,272,140, titled “Metering Pump”, to Curry, et al., discloses a split spur gear pump using rotors with radially arrayed spur teeth projections that drive one another with inter-projection pockets between the spur teeth transferring fluid from the inlet to the outlet. However, spur pumps subject the spurs to fluid milling action that produces high shearing stress and high pressures. This milling action is detrimental to shear sensitive liquids, such as delicate food substances (e.g., salsa, relish, mayonnaise, pasta sauce, soup).
For shear sensitive liquids, lobed pumps may be preferred, with lobed rotors that mesh in opposite direction defining cavities or pockets between adjacent lobes that can trap and transport liquid from the inlet port to the outlet port of the pump with a more gentle pumping action and avoid damage resulting from excessive agitation. U.S. Pat. No. 5,755,566, titled “Self-Driving Fluid Pump”, to Marsillo, et al., discloses an exemplary lobed pump for delicate fluids with inter-lobe pockets that can transport relatively large volumes of product at a time and thus avoid the excessive milling action arising under spur gear pumps with relatively small inter-spur tooth pockets. The lobes are significantly larger than teeth of spur gear pumps to include larger inter-lobe pockets and thereby provide the ability to better handle shear sensitive liquids.
However, it would be even more beneficial to provide larger volume pockets that are available with typical lobe gear pumps to even better handle shear sensitive liquids. The invention described herein by example aims to provide such a benefit as the inventor has realized the benefit to provide even larger volume pockets in a gear pump.
All references cited herein are incorporated herein by reference in their entireties.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify central features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.
In accordance with an example of the invention, a pump is provided with a housing having an internal cavity that defines a pumping chamber, an inlet port adapted to allow a fluid into the pumping chamber, and an outlet port adapted to discharge the fluid from the pumping chamber. The pump also includes a gearbox located in the pumping chamber. The gearbox has a plurality of driving rotors including first and second spur toothed gears, each having a plurality of spur shaped teeth, and first and second lobed gears, each having lobes wider than the spur teeth. The first toothed gear and the first lobed gear may be a first gear set with the first toothed gear mounted to one of a first rotational axis and a second rotational axis in the pumping chamber adjacent the first rotational axis, and the first lobed gear mounted to the other one of the first rotational axis and the second rotational axis in the pumping chamber. The second toothed gear and said second lobed gear may be a second gear set with the second toothed gear mounted to one of the first rotational axis and the second rotational axis in the pumping chamber, and the second lobed gear mounted to the other one of the first rotational axis and the second rotational axis in the pumping chamber.
In another example of the invention, a gearbox of a pump is provided, with the pump having a housing with an internal cavity that defines a pumping chamber, an inlet port adapted to allow fluid into the pumping chamber, and an outlet port adapted to discharge the fluid from the pumping chamber. The gearbox may be located in the pumping chamber of the housing. The gearbox includes a plurality of driving rotors including first and second spur toothed gears, each having a plurality of spur shaped teeth, and first and second lobed gears, each having a plurality of lobes wider than the teeth. The first toothed gear and the first lobed gear may be a first gear set with the first toothed gear mounted to one of a first rotational axis and a second rotational axis in the pumping chamber adjacent the first rotational axis, and the first lobed gear mounted to the other one of the first rotational axis and the second rotational axis in the pumping chamber. The second toothed gear and said second lobed gear may be a second gear set with the second toothed gear mounted to one of the first rotational axis and the second rotational axis in the pumping chamber, and the second lobed gear mounted to the other one of the first rotational axis and the second rotational axis in the pumping chamber.
The spur tooth gears may be rotatably mounted in angularly offset about a first rotational axis in the pumping chamber. The lobed gears may be rotatably mounted and angularly offset about a second rotational axis in the pumping chamber adjacent and preferably substantially parallel to the first rotational axis. The first spur toothed gear is intermeshed with the first lobed gear in a driving relationship therebetween. The second spur toothed gear is intermeshed with the second lobed gear in a driving engagement therebetween. While not being limited to a particular theory, the teeth of the spur toothed gears and the lobes of the lobed gears may have an involute-shaped profile to provide continuously rolling contact and a fixed pressure angle between the teeth and lobes during the driving engagement. Preferably one of the first rotational axis and the second rotational axis is a drive shaft.
The second gear set may be engaged in the driving relationship therebetween when the first gear set is disengaged between the first toothed gear and the first lobed gear. Similarly, the first gear set may be engaged in the driving relationship therebetween when the second gear set is disengaged between the second toothed gear and the second lobed gear. The teeth of the first toothed gear may be angularly offset with relation to the teeth of the second toothed gear such that a tooth of the first toothed gear is axially aligned between two teeth of the second toothed gear.
The toothed gears or lobed gears can be mounted on either the drive shaft or the idler shaft, with the drive shaft being one of the first or second rotational axes and the idler shaft being the other one of the rotational axes. In some examples of the invention, the first toothed gear and the second lobed gear may be mounted to the first rotational axis. In other examples, the first toothed gear and the first lobed gear may be mounted to the first rotational axis. In yet other examples, the first toothed gear and the first lobed gear may be mounted to the second rotational axis. In still other examples, the first toothed gear and the second lobed gear may be mounted to the second rotational axis.
The examples of the invention may include a partition wall extending orthogonally to the first and second rotational axes between the first gear set and the second gear set for hydraulic isolation of the fluid. The examples may also include radial vanes extending from the teeth to seal circumferential liquid slip paths between the toothed gears and the housing and to seal slip paths between the toothed gears and the lobed gears. The examples may further include radial vanes extending from the lobes to seal circumferential liquid slip paths between the lobed gears and the housing and to seal slip paths between the toothed gears and the lobed gears.
The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:
The exemplary embodiments of the pump are described with reference to
The profile of the spur gear rotors and the lobe gear rotors can be made as an improvement from standard spur and helical gear designs, for example, by omitting alternate teeth on the standard spur rotors and filling in corresponding gaps on the mating standard lobed rotors. In some cases, depending upon gear geometry, this approach allows the gears to become disengaged from one another as they rotate. To solve this problem, additional spur toothed and lobed rotors are added in tandem to the shafts and circumferentially offset to provide driving tooth engagement between at least one pair of the spur toothed and lobed rotors at every point around the rotational circumference of the rotors. With this configuration, the rotor sets directly drive one another, and thus do not require a separate gearbox with driving/synchronizing gears.
Accordingly, tandem gears overcome the problem of gear disengagement that previously would require an additional gearbox. As can be seen in the figures, a spur toothed gear and matching lobe gear may become completely disengaged in certain rotational positions. Placing another pair of matching spur and lobed gears in tandem behind the first pair, with a rotational offset between the pairs that may be equal to half of the angle between the spurs or lobes on the rotors, and keying them all to the shafts to lock the rotational offset provides teeth in mesh in at least one of the pairs of rotors at all times.
According to examples of the invention, there is provided a self-driving fluid pump having male (e.g., spur toothed) and female (e.g., lobed) rotary members mounted for rotation on spaced parallel axis. The rotors can be enclosed in a housing or casing in sealing relationship with cylindrically curved parts thereof, or they may be mounted on open framework for operation while immersed in a fluid medium. Each of the male rotors has a plurality of radially extending circumferentially spaced spur shaped teeth with recesses between the teeth. Each of the female rotors has a plurality of radially descending pockets that define circumferentially spaced lobes, with the pockets forming recesses between the lobes. The spur teeth on each male rotor intermeshed with the lobes of the female rotor in sealing contact. Preferably, each of the rotors has flat parallel sides, although the invention is not limited by shape of the sides.
The rotors may rotate in the housing in sealing contact with opposite interval sides or walls of the housing that define the pumping chamber thereof. The housing includes two communication compartments. One compartment may serve as an inlet bore or port to receive fluid from an external conduit connected to the housing. The other compartment may serve as an outlet bore or port to expel fluid under pressure to a discharge conduit as the rotors rotate in the housing.
A first set of in tandem rotors may serve as drive rotors driven by a powered shaft connected to the rotors. Other tandem rotors intermeshed with the first set of tandem rotors, then serve as driven rotors coupled to the idler shaft. The rotors are connected to their respective shafts and rotationally locked to their shaft via locking pins that extend into and between the rotors and shafts for locked engagement therebetween. As the spur teeth of a rotor enter the recesses of its matching lobed rotor, fluid is pumped between the rotors and out of the outlet compartment. While the examples of the invention depicted in the figures and discussed below concentrate on spur gears, it is understood that the invention covers at least both spur gears and helical gears. In other words, the tooth gears and lobe gears may be helical within the scope of the invention, that is, with gear teeth and lobes at some angle relative to the shaft centerlines.
Other advantages, characteristics and details of the invention will emerge from the explanatory description below with reference to the attached drawings and examples, however, it should be understood that the present invention is not deemed to be limited thereto. To that end,
Referring to
In the examples depicted by the drawings, the gearbox 14 includes at least two pairs of meshed gears with each pair including a spur tooth gear 28 and a lobe gear 32. For example, a first pair of meshed gears includes a first lobed gear 36 adjacent a first spur tooth gear 38 and intermeshed in a driving engagement therebetween. Continuing, a second pair of meshed gears includes a second lobed gear 40 adjacent a second spur toothed gear 42 intermeshed in a driving engagement therebetween. The form of the spur teeth and lobes may be involute-shaped to provide continuously rolling contact and a fixed pressure angle between the spur teeth and lobes during the intermeshed driving engagement. It is understood that additional gear sets (e.g., pairs of tooth and lobe gears), including third, fourth and fifth sets may be placed in tandem with the first and second gear sets.
Still referring to
The lobed gears 36, 40 preferably are rotationally locked against the first shaft 44, which is shown by example as a drive shaft. Similarly, the male spur toothed gears 38, 42 preferably are rotationally locked to the second shaft 46, which is shown by example as an idler shaft. Between the shafts 44, 46, preferably one of the shafts is the drive shaft and the other shaft is the idler shaft. It is understood that the current invention is not limited to either configuration, as the pump apparatus 10 works equally well regardless of which shaft is the drive shaft or the idler shaft. The gears 36, 38, 40, 42 are keyed to their respective shaft 44, 46 with pins 48 slip-fitted into matching channels of the gears and shafts to at least rotationally lock the gears to the shafts, as would readily be understood by a skilled artisan.
While the examples of the invention depict the lobed gears as coupled to the first shaft 44 and the spur toothed gears coupled to the second shaft 46, it is understood that the invention is not limited to the placement of any lobed gear or any spur toothed gear on any one particular shaft. For example, the spur toothed and lobed gears may alternatively be placed on either one of the shafts 44, 46 as long as one of each corresponding spur toothed gear and lobed gear are placed to form a pair of rotors, with one spur toothed gear and one lobed gear in a meshed relationship therebetween. In other words, a spur toothed gear 28 and a lobed gear 32 may be mounted in tandem to the first shaft 44, with each gear intermeshed with a corresponding lobed gear 32 and a spur toothed gear 28 mounted in tandem to the second shaft 46.
While not being limited to a particular theory, the spur teeth 30 of the toothed gears 28 and the lobes 34 of the lobed gears 32 have an involute-shaped profile to provide continuously rolling contact and a fixed pressure angle between the teeth and lobes during the driving engagement. With teeth of other shapes, the relative speeds and forces rise and fall as successive teeth engage, resulting in vibration, noise and excessive wear. The exemplary embodiments of the invention preferably use teeth and lobes having the involute shape so that the relative rates of rotation are constant while the teeth and lobes are engaged, and further, the engaging gears always make contact along a single steady line of force.
The exemplary embodiments depicted by the figures show each gear having either three spur teeth 30 or three lobes 34. However, it is understood that the gears of the invention are not limited to any specific number of teeth/lobes. In some cases, depending upon gear geometry, gears may become disengaged from one another as they rotate. For example, in
Still referring to
Preferably, the housing, gears, shafts, wear plate, vanes and springs discussed by example herein are made of metal or other hard, durable material, as readily understood by a skilled artisan. For example, the housing, gears, wear plate, shafts, vanes and springs are preferably made of steel, cast iron, bronze, ceramic, or some combination thereof. The wear plate and vanes may also be made of a resin, rubber or polypropylene. It should be understood that the springs may most preferably be formed of a material capably strong and resilient to function as a biasing member.
During operation, fluid is drawn from the inlet port 16 into an increasing volume defined by the pumping chamber 26, the gears and any wear plate that may be included within the gearbox. After entering the inlet port, the fluid is transported circumferentially around the outside of the rotors in the pockets formed by the gear 28, 32 and the housing bore walls. The transported fluid is then displaced by the teeth and lobes coming into mesh and discharged through the outlet port 18 and out of the housing 12. During the rotation of the gears, the vanes 84 are extended, preferably to the bore walls of the pumping chamber 26 to help seal radial clearance slip paths, and during intermeshing, the vanes 84 are extended to compress against centrifugal force and/or a biasing member into the surface of the meshed gear.
It is understood that the spur toothed/lobed gear pump described and shown are exemplary indications of preferred embodiments of the invention, and are given by way of illustration only. In other words, the concept of the present invention may be readily applied to a variety of preferred embodiments, including those disclosed herein. While the invention has been described in detail and with reference to specific examples thereof, it would be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and the scope thereof. For example, the number and material of the spur or helical teeth, lobes, gears, wear plate and vanes described may be altered without departing from the scope of the invention. Without further elaboration, the foregoing will so fully illustrate the invention that others may, by applying current and future knowledge, readily adapt the same for use under various conditions of service.
