Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
  • F16H55/02—Toothed members; Worms
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2/00—Rotary-piston machines or pumps
  • F04C2/08—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C2/10—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member
  • F04C2/102—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member the two members rotating simultaneously around their respective axes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2/00—Rotary-piston machines or pumps
  • F04C2/08—Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C2/082—Details specially related to intermeshing engagement type machines or pumps
  • F04C2/084—Toothed wheels

Definitions

• the present invention relates to an internal gear, and more particularly, to a tooth profile of an internal gear in which the number of teeth of an outer gear is greater than the number of teeth of an inner gearby one, to a structure in which an addendum part of the outer gear tooth profile comes into contact with an addendum part of the inner gear tooth profile continuously while the gears are rotating and to a tooth profile of the internal gear employed to a fluid pump, a reducer, a fluid motor and so on.
• An internal gear pump is largely employed to an oil pump of an internal combustion engine or an automatic transmission due to advantages of simple structure and low noise. And there are various kinds of tooth profiles of the internal gear pump.
• a gerotor is a type of obtaining a tooth profile described by a circle moving along an extended epicycloid curve but has a disadvantage that a diameter of an inner gear should be large in order to ensure a radius of curvature of a tooth profile of the internal gear.
• addendum and dedendum tooth profiles of inner and outer gears may consist of an epicycloid which is described by a point on a small circle rolling externally upon a pitch circle and a hypocycloid which is described by a point on a small circle rolling internally upon the pitch circle.
• a diameter of the internal gear can be minimized by minimizing a diameter of the rolling circle which describes the epicycloid curve but there is a limitation of occurrence of durability problem since the smaller the diameter of the rolling circle is, the smaller a radius of curvature of the inner gear is. Because the tooth profile curve is fixed once a size of a pitch circle and a size of rolling circle are determined, a degree of freedom of tooth profile design is low and there is a limitation to adjust the radius of curvature as a designing intention.
• the present invention is to provide a novel method which is different from the prior tooth profile forming method and it is an object of the present invention to provide a method for designing a tooth profile which increases a degree of freedom of the tooth profile design to overcome the limitation in the prior art and to allow design optimization of tooth profile required by an internal gear.
• the present invention provides a tooth profile of an internal gear with a high degree of freedom in design, wherein, when a pitch circle of an outer gear and a pitch circle of an inner gear are rolled to each other, a rotation angle of one period is segmented in an arbitrary method; an addendum tooth profile of the inner gear consists of total gathering of partial curves of a plurality of extended epicycloids having different fixed points at every segmented rotation angle; an addendum tooth profile of the outer gear consists of total gathering of partial curves of a plurality of extended hypocycloids having different fixed points at every segmented rotation angle; an end point of each partial curve of the cycloids is used as a fixed point; and the tooth profile varies as a size and a method of segmenting total rotation angle.
• An extended epicyclod is a trace curve which is described on the inner gear by an arbitrary fixed point placed at a position deviated from the pitch circle of the outer gear and fixed to the outer gear when the pitch circle of the outer gear rolls and touches with the outside of the pitch circle of the inner gear.
• An extended hypocycloid is a trace curve which is described on the outer gear by arbitrary one fixed point placed at a position deviated from the pitch circle of the inner gear and fixed to the inner gear when the pitch circle of the inner gear rolls and touches with the inside of the pitch circle of the outer gear.
• the addendum tooth profiles of the outer and inner gears of the present invention are characterized in that they are formed using the method of forming the extended epicycloid and extended hypocycloid curves as mentioned above however the fixed point is not fixed to a position but varies at every unit rotation angle.
• the fixed point describing the trace curve when the outer and inner gears roll to each other on the base of each pitch circle thereof, is not fixed to one position but a fixed point of the extended epicycloid and a fixed point of the extended hypocycloid move respectively to complete the entire trace curve.
• the outer gear is fixed to a space and entire rotation angle of one period of rolling is segmented into an arbitrary size when the pitch circle of the inner gear rolls upon the pitch circle of the outer gear and the size of the segmented rotation angle maybe large or small or it may be segmented in equiangular or non-equiangular.
• the segmentation method is not limited to a specific method, the size of the segmented angle is also not limited and it may be laid in a scope of the present invention even though the size of each segmented rotation angle is the same or different.
• Half of the segmented rotation angles corresponding to odd number of total number is used to obtain a partial trace curve of the inner gear (or the outer gear) and half of the segmented rotation angles corresponding to even number of total number is used to obtain a partial trace curve of the outer gear (or the inner gear).
• a first fixed point of the outer gear is fixed to the outer gear and the fixed point describes a first partial trace curve on the inner gear while the inner gear rolls upon the outer gear by a first segmented rotation angle
• an end point of the first partial trace curve of the inner gear becomes a first fixed point of the inner gear
• the first fixed point of the inner gear describes a first partial trace curve on the outer gear while the inner gear rolls upon the outer gear by a second segmented rotation angle.
• Tangential directions of the partial trace curves adjacent to each other are not correspond to each other at their boundary if a size of the segmented rotation angle is large, however the tangential directions of adjacent partial trace curves approach to be correspond to each other if the size of the segmented rotation angle is small enough.
• the segmented rotation angle desirably, is small enough and thus the number of the segmentation in relation to the rolling rotation angle of entire one period is more than 10. In a practical embodiment, it is preferable that the segmented rotation angle is less than 1 degree, however a case that the segmented rotation angle is larger than 1 degree is also laid in the scope of the present invention.
• kl is applied to the first part of the segmented angles
• k2 is applied to the second part of the segmented angles
• k3 is applied to the third part of the segmented angles
• kn is applied to the nth part of the segmented angles, wherein n is natural number and one or more of kl,k2,k3,...,kn may be the same value as another of kl,k2,k3,...,kn. That is, k has a variable value corresponding to the segmented rotation angles.
• a part of the addendum tooth profile is constituted according to the method of the present invention and another part consists of an arc, a part of an ellipse, a part of a parabola or a part of epicycloid or hypocycloid, etc. and the tangents thereof are correspond to each other at the boundary therebetween.
• the addendum tooth profiles of the outer and inner gears are constituted according to the method of the present invention and a recess for noise improvement is provided to a part of the dedendum tooth profile.
• a backlash should be provided in order that the internal gear is practically implemented.
• an eccentricity is e and the number of teeth of the inner gear is N
• an addendum tooth profile of the inner gear is selected from the method of obtaining the tooth profiles of the outer and inner gears regardless of considering the backlash b and a dedendum tooth profile of the inner gear is obtained from the addendum tooth profile of the outer gear by kinematical calculation
• FIG. 1 is a structural view of an oil pump which employs a tooth profile according to the present invention
• FIG. 2 is a schematic view for explaining a pitch circle and a fixed point
• FIG. 3 is an explanation view in which the fixed point is laid in an inner gear and a tooth profile is drawn on an outer gear;
• FIG. 4 is an enlarged view for explaining FIG. 3.
• FIG. 5 is an explanation view in which the fixed point is laid in an outer gear and a tooth profile is drawn on an inner gear;
• FIG. 6 is a view of a result to which the tooth profile design according to the present invention is applied;
• FIG. 7 is a view of another result according to the present invention.
• FIG. 8 is an explanation view of an embodiment with an optimized radius of curvature.
• a tooth profile according to the present invention may be employed to a hydraulic motor, a reducer, a hydraulic pump and so on and the following description is based on an oil pump employing the tooth profile according to the present invention.
• FIG. 1 is an example of an oil pump and an outer gear 2 and an inner gear 3 are engaged with each other to be assembled in an oil pump housing 1.
• An addendum 2a of the outer gear 2 and an addendum 3 a of the inner gear 3 come into contact with each other continuously while the gear rotates 360 degrees in a clockwise direction.
• the number of teeth of the inner gear is N
• a center 02 of the inner gear is eccentric by an eccentricity e from a center Ol of the outer gear
• FIG. 4 is an enlarged view of the trace 9 and an end point Pl of the trace 9 is fixed to the outer gear 2.
• a trace 10 which is described on the inner gear 3 by the point Pl while the inner gear 3 rotates around the center 02 in a counterclockwise direction by an arbitrary rotation angle dTl and the outer gear 2 rotates around the center Ol in a counterclockwise direction by dTl*N/(N+l), constitutes a part of the addendum 3a of the inner gear 3.
• a dedendum tooth profile 2d of the outer gear 2 is obtained as an arbitrary tooth profile which does not interfere with the addendum tooth profile 3 a of the inner gear and, for example, a tooth profile of the outer gear 2, which is processed when a gear teeth cutting tool having the same shape as the addendum tooth profile 3a is rotated in a state of being engaged with the outer gear 2, can be used as the dedendum tooth profile 2d.
• a dedendum 3d of the inner gear 3 can be obtained from the addendum 2a.
• Sizes of the arbitrary rotation angles dSl, dS2, dS3, dTl, dT2, dT3, etc. may be defined arbitrarily. In cases, a specific segmental rotation angle may be 0.0.
• the tooth profile curves of the addendums 2a and 3 a are designed differently according to segmental size of the rotation angle.
• a radius of curvature of the tooth profile varies as the value of dSi/dTi, and the radius of curvature of the tooth profile of the outer gear is relatively small and the radius of curvature of the inner gear is relatively large when the value is less than 1.0.
• the radius of curvature of the tooth profile of the outer gear is relatively large and the radius of curvature of the inner gear is relatively small when the value is greater than 1.0.
• the radiuses of curvature should be large in order to minimize a contact stress of the gears, however they should be optimized because when the radius of curvature of the inner gear tooth profile is enlarged, the radius of curvature of the outer gear tooth profile becomes correspondingly small. [64] In addition, because the radius of curvature is small at a vicinity of a boundary of the addendum profile with the dedendum, it should be maximized.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Rotary Pumps (AREA)

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Cited By (7)

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Citations (4)

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• 2006
  • 2006-09-03 KR KR1020060084453A patent/KR100812754B1/ko active IP Right Grant
• 2007
  • 2007-08-24 WO PCT/KR2007/004071 patent/WO2008030004A1/en active Application Filing

Patent Citations (4)

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