Oil pump rotor

Abstract

Provided is an oil pump rotor capable of improving a volume efficiency and a quietness. When a diameter of a base circle bi of an inner rotor is bi; a diameter of a first outer rolling circle Di is Di; a diameter of a first inner rolling circle di is di; a diameter of a base circle bo of an outer rotor is bo; a diameter of a second outer rolling circle Do is Do; a diameter of a second inner rolling circle do is do; and an eccentricity amount between the inner rotor and the outer rotor is e, bi=n.Math.( Di+ di) and bo=(n+1).Math.( Do+ do) hold; either Di+ di=2e or Do+ do=2e holds; and Do> Di and di> do hold. When a clearance between the inner rotor and the outer rotor is t, 0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6 holds, provided that Di+ di=2e; or 0.3(( Do+ do)( Di+ di)).Math.n/t0.6 holds, provided that Do+ do=2e.

Claims

1. An oil pump rotor for use in an oil pump transferring a fluid by drawing in and discharging said fluid as volumes of cells formed between tooth surfaces of two rotors that change when said two rotors rotate while being engaged with each other, said oil pump rotor comprising: an inner rotor having n (n is a natural number) external teeth, said inner rotor exhibiting a tooth tip shape established by an epicycloid curve that is generated by a first outer rolling circle Di externally tangent to and rolling on a base circle bi of said inner rotor without slipping and a tooth groove shape established by a hypocycloid curve that is generated by a first inner rolling circle di internally tangent to and rolling within said base circle bi without slipping; an outer rotor having n+1 internal teeth, said outer rotor exhibiting a tooth groove shape established by an epicycloid curve that is generated by a second outer rolling circle Do externally tangent to and rolling on a base circle bo of said outer rotor without slipping and a tooth tip shape established by a hypocycloid curve that is generated by a second inner rolling circle do internally tangent to and rolling within said base circle bo without slipping; and a casing having an intake port for drawing in a fluid and a discharge port for discharging the fluid, wherein the inner and outer rotors are formed to satisfy:
bi=n( Di+ di), bo=(n+1).Math.( Do+ do);
Di+ di=2e;
Do> Di, di> do, ( Di+ di)<( Do+ do),
and,
0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6;
or,
bi=n.Math.( Di+ di), bo=(n+1).Math. Do+ do)
Do+ do=2e
Do> Di, di> do, ( Di+ di)<( Do+ do)
and,
0.3(( Do+ do)( Di+ di)).Math.n/t0.6 where bi, Di, di, bo, Do, do, e, and t respectively indicate a diameter of said base circle bi, a diameter of said first outer rolling circle Di, a diameter of said first inner rolling circle di, a diameter of said base circle bo, a diameter of said second outer rolling circle Do, a diameter of a second inner rolling circle do, an eccentricity amount between said inner rotor and a said outer rotor and a clearance between said inner rotor and said outer rotor.

2. The oil pump rotor according to claim 1, wherein said external teeth of said inner rotor and said internal teeth of said outer rotor exhibit there between a minimum inter-tooth clearance with a deviation of not larger than 10 m, at all locations where said external teeth of said inner rotor and said internal teeth of said outer rotor are adjacent to one another.

3. The oil pump rotor according to claim 2, wherein said minimum inter-tooth clearance is 35 to 45 m.

4. The oil pump rotor according to claim 1, wherein said deviation of said minimum inter-tooth clearance is not larger than 5 m.

5. The oil pump rotor according to claim 4, wherein said minimum inter-tooth clearance is 37.5 to 42.5 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein like designations denote like elements in the various views, and wherein:

(2) FIG. 1 is a plane view of an oil pump rotor of a first embodiment of the present invention.

(3) FIG. 2 is an enlarged view of an engaged section of the oil pump rotor of the first embodiment shown in FIG. 2.

(4) FIG. 3 is a plane view of the oil pump rotor of the first embodiment, in which locations of minimum intertooth clearances are shown.

(5) FIG. 4 is a graph showing correlations between rotor revolution and sound pressure with regard to an oil pump of the present invention and an oil pump of the second example of conventional arts.

(6) FIG. 5 is a graph comparing the minimum intertooth clearances of the oil pump rotor of the present invention and the oil pump rotors of the first and second examples of conventional arts.

(7) FIG. 6 is a graph showing a correlation between the minimum intertooth clearances and angles of rotation of an inner rotor.

(8) FIG. 7 is a plane view of an oil pump rotor of the second example of conventional arts.

(9) FIG. 8 is an enlarged view of an engaged section of an oil pump of the second example of conventional arts shown in FIG. 7.

(10) FIG. 9 is a graph showing a correlation between intertooth clearances and angles of rotation of an inner rotor of the second example of conventional arts.

(11) FIG. 10 is a graph showing the correlation between intertooth clearances and angles of rotation of the inner rotor of the second example of conventional arts, in which the displacement velocities of the intertooth clearances are diagrammatically indicated by arrows.

(12) FIG. 11 is a graph showing the correlation between intertooth clearances and angles of rotation of the inner rotor of the second example of conventional arts, in which diagrammatically indicated are ranges of minute deceleration, acceleration and then minute deceleration of an outer rotor of the second example of conventional arts.

(13) FIG. 12 is a graph showing the correlation between intertooth clearances and angles of rotation of the inner rotor of the second example of conventional arts, in which engagement intervals I and VI are diagrammatically indicated.

(14) FIG. 13 is a plane view of an oil pump rotor of the first example of conventional arts.

(15) FIG. 14 is an enlarged view of an engaged section of an oil pump of the first example of conventional arts shown in FIG. 13.

(16) FIG. 15 is an enlarged view of the engaged section of the oil pump of the first example of conventional arts, showing an engaged state of a tooth tip of an outer rotor and a tooth groove of an inner rotor.

DETAILED DESCRIPTION OF THE INVENTION

(17) Preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. However, the embodiments shown hereunder shall not limit the contents of the present invention that are described in this application. Further, not all elements described hereunder are essential to the present invention. Since each embodiment employs an unconventional oil pump rotor, an unconventional oil pump rotor is obtained. This oil pump rotor is disclosed hereunder.

(18) First Embodiment

(19) A first embodiment of the present invention is described in detail with reference to the accompanying drawings. Here, elements identical to those of examples of conventional arts are given identical symbols in the following description. As shown in FIG. 1 to FIG. 3, an oil pump rotor includes: an inner rotor 10 having n external teeth (n is a natural number; n=7 in this embodiment); and an outer rotor 20 having n+1 (8 in this embodiment) internal teeth engageable with the external teeth. The inner rotor 10 and the outer rotor 20 are received in a casing 50.

(20) Here, a plurality of cells C are formed between the tooth surfaces of the inner rotor 10 and the outer rotor 20 in a manner such that the cells C are actually provided along rotational directions of the rotors 10, 20. In a forward and backward rotational directions of the rotors 10, 20, each cell C is individually established as a result of allowing external teeth 11 of the outer rotor 10 and internal teeth 21 of the outer rotor 20 to come into contact with one another; and both sides of this cell C are surrounded by the casing 50. In this way, there are formed individual fluid transfer chambers. Moreover, the cells C rotate as the rotors 10, 20 rotate, in a manner such that each cell C repeatedly exhibits an increase and decrease in its volume within each rotational cycle as one cycle.

(21) The inner rotor 10 is attached to a rotary shaft, and is rotatably supported thereby around a shaft center Oi. The shape of each tooth tip of the inner rotor 10 is established by an epicycloid curve that is generated by a first outer rolling circle Di externally tangent to and rolling on a base circle bi of the inner rotor 10 without slipping. The shape of each tooth groove of the inner rotor 10 is established by a hypocycloid curve that is generated by a first inner rolling circle di internally tangent to and rolling within the base circle bi without slipping.

(22) The outer rotor 20 whose shaft center is Oo is eccentrically disposed with respect to the shaft center Oi of the inner rotor 10 (eccentricity amount: e), and is rotatably supported within the casing 50 about the shaft center Oo. The shape of each tooth groove of the outer rotor 20 is established by an epicycloid curve that is generated by a second outer rolling circle Do externally tangent to and rolling on a base circle bo of the outer rotor 20 without slipping. The shape of each tooth tip of the outer rotor 20 is established by a hypocycloid curve that is generated by a second inner rolling circle do internally tangent to and rolling within the base circle bo without slipping.

(23) The following relational expressions hold between the inner rotor 10 and the outer rotor 20, provided that a diameter of the base circle bi of the inner rotor 10 is bi; a diameter of the first outer rolling circle Di is Di; a diameter of the first inner rolling circle di is di; a diameter of the base circle bo of the outer rotor 20 is bo; a diameter of the second outer rolling circle Do is Do; and a diameter of the second inner rolling circle do is do. Here, mm (millimeter) is used as the measurement unit.

(24) As for the inner rotor 10, rolling distances of the first outer rolling circle Di and the first inner rolling circle di should add up to one cycle. That is, the rolling distances of the first outer rolling circle Di and the first inner rolling circle di should altogether be equal to the circumference of the base circle bi.
bi=n.Math.( Di+ di) (Ia)
Likewise, as for the outer rotor 20, rolling distances of the second outer rolling circle Do and the second inner rolling circle do should altogether be equal to the circumference of the base circle bo.
bo=(n+1).Math.( Do+ do) (Ib)

(25) Further, as for the shapes of the tooth tips of the inner rotor 10 that are established by the first outer rolling circle Di and correspond to the shapes of the tooth grooves of the outer rotor 20 which are established by the second outer rolling circle Do; and as for the shapes of the tooth tips of the outer rotor 20 that are established by the second inner rolling circle do and correspond to the shapes of the tooth grooves of the inner rotor 10 which are established by the first inner rolling circle di, the following relational expressions have to hold such that backlashes between the tooth surfaces of the two rotors 10 and 20 can be secured in a large magnitude during an engagement process.
Do> Di, and di> do

(26) Here, the backlashes refer to clearances that are formed, during the engagement process, between the tooth surfaces of the outer rotor 20 and the tooth surfaces of the inner rotor 10, the tooth surfaces of the inner rotor 10 in such case being the tooth surfaces opposite to those subjected to loads.

(27) Further, in order for the inner rotor and the outer rotor to engage with each other, either one of Di+ di=2 e and Do+ do=2 e has to hold.

(28) In the present invention, in order for the inner rotor 10 to successfully rotate inside the outer rotor 20; the magnitude of the backlashes to be optimized, and an engagement resistance to be reduced, while securing tip clearances, the diameter of the base circle bo of the outer rotor 20 is formed large such that the base circle bi of the inner rotor 10 and the base circle bo of the outer rotor 20 will not come into contact with each other at an engagement point of the inner rotor 10 and the outer rotor 20. That is, a relational expression (n+1).Math. bi<n.Math. bo holds.

(29) Obtained from this expression, expressions (Ia) and (Ib) is
( Di+ di)<( Do+ do).

(30) Particularly, the aforementioned engagement point refers to a point where, as shown in FIG. 2, a tooth groove of an internal tooth 21 of the outer side directly faces a tooth tip of an external tooth 11 of the inner side.

(31) Moreover, the inner rotor 10 and the outer rotor 20 are so configured that when a clearance between the inner rotor and the outer rotor is t,
0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6 (Ic),
provided that Di+ di=2e; or
0.3(( Do+ do)( Di+ di)).Math.n/t0.6 (Ic),
provided that Do+ do=2e holds

(32) (( Do+ do)( Di+ di)) is referred to, hereunder, as a difference in tooth depth between the internal tooth 21 of the outer rotor 20 and the external tooth 11 of the inner rotor 10). Particularly, in (expression Ic), the unit of clearance t is mm (millimeter). Further, the tooth depth refers to the dimension of each tooth in the normal direction.

(33) Further, a minimum intertooth clearance ts between the internal tooth 21 of the outer rotor 20 and the external tooth 11 of the inner rotor 10 at the engagement point shown in FIG. 2 (the lowermost part in FIG. 1) where the tooth groove and the tooth tip directly face each other, serves as a side clearance formed on both sides of the internal tooth 21 and external tooth 11 in the rotational directions thereof. Here, since the internal tooth 21 also has an intertooth clearance formed in a direction opposite to the rotational direction thereof, the smaller clearance is referred to as the minimum intertooth clearance in the description of the present embodiment.

(34) FIG. 3 shows the locations of the minimum intertooth clearances ts. When rotationally driving the inner rotor 10 in the counterclockwise direction, a minimum intertooth clearance ts is formed on the rotational direction side of the external tooth 11 and a counter-rotational direction side of the internal tooth 21 at the location where the volume of the cell C increases (the right side in FIG. 3); a minimum intertooth clearance ts is formed on the counter-rotational direction side of the external tooth 11 and the rotational direction side of the internal tooth 21 at the location where the volume of the cell C decreases (the left side in FIG. 3); and a minimum intertooth clearance ts is formed between the tip of the external tooth 11 and the tip of the internal tooth 21 at a nonengagement point where the tooth tips directly face each other (the uppermost part in FIG. 1), the minimum intertooth clearance ts being substantially the size of the clearance t.

(35) Further, since the aforementioned (expression Ic) holds, as shown in FIG. 3, at all locations where the external teeth 11 of the inner rotor 10 and the internal teeth 21 of the outer rotor 20 are adjacent to one another (e.g. the engagement points where the tooth grooves and the tooth tips directly face each other, the locations where the volumes of the cells C increase and decrease and the locations where the tooth tips directly face each other), the minimum intertooth clearances ts between the external teeth 11 of the inner rotor 10 and the internal teeth 21 of the outer rotor 20 can be formed substantially identical to one another. In the present embodiment, the minimum intertooth clearances ts in all locations are set to be 40 m, whereas a deviation of the minimum intertooth clearance ts to the value thus set is 10 m, preferably in a range of not larger than 5 m. The deviations of the minimum intertooth clearances ts of all locations to the set minimum intertooth clearance ts are each within the range of not larger than 5 m.

(36) However, in the present embodiment, the inner rotor 10 (base circle bi, bi=44.8 mm; first outer rolling circle Di, Di=3.60 mm; first inner rolling circle di, di=2.80 mm; teeth number n=7) and the outer rotor 20 (outer diameter 65.0 mm; base circle bo, bo=51.24 mm; second outer rolling circle Do, Do=3.625 mm; second inner rolling circle do, do=2.78 mm) are combined at an eccentricity amount of e=3.20 mm so as to compose the oil pump rotor. Further, in the present embodiment, a tooth width (dimension in a rotary shaft direction) of both the rotors is set to be 13.2 mm. Thus, a difference in tooth depth is 0.005 mm. Furthermore, the clearance t is t=0.08 mm (80 m); the minimum intertooth clearance ts is ts=0.037 to 0.041 mm (37 to 41 m); and a value obtained with the expression (Ic) is 0.5. In this way, the minimum intertooth clearance ts is substantially of the clearance t, and the deviation is not larger than 5 m.

(37) As for the casing 50, among the cells C that are formed between the tooth surfaces of both the rotors 10 and 20, formed along a cell C whose volume is in the process of increasing is an arc-shaped intake port (not shown), whereas formed along a cell C whose volume is in the process of decreasing is an arc-shaped discharge port (not shown).

(38) The cells C are so configured that after the volume of a cell C has reached its minimum level during the process of engaging an external tooth 11 with an internal tooth 21, this cell C shall suck in a fluid by enlarging its volume when moving along the intake port; and that after the volume of this cell C has reached its maximum level, the corresponding cell C shall then discharge the fluid by decreasing its volume when moving along the discharge port.

(39) The aforementioned expression (Ic) involves a value obtained by multiplying the difference in tooth depth by the teeth number n of the inner rotor 10 or by the teeth number (n+1) of the outer rotor 20; and then diving by the clearance t. The expression (Ic) defines a range in which not only the minimum intertooth clearances ts of all locations can be set to be small; but the deviations of the minimum intertooth clearances ts can also be small. When the teeth number n is large, it is necessary to reduce the difference in tooth depth. In contrast, when the teeth number n is small, it is then necessary to make the difference in tooth depth large. That is, the difference in tooth depth that changes as the teeth number n increases or decreases and the clearance t bear a proportionate relationship to each other within a given range.

(40) In this way, since 0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6 when Di+ di=2 e, or since 0.3(( Do+ do)( Di+ di)).Math.n/t0.6 when Do+ do=2 e, the minimum intertooth clearances ts can be equalized and shrunk such that engagement noises or the like may be reduced and a volume efficiency may be improved. If not exceeding 0.3 or if exceeding 0.6, it becomes difficult to equalize the minimum intertooth clearances ts.

(41) FIG. 5 shows a graph comparing: the intertooth clearance at each angle of rotation of an inner rotor used in an oil pump rotor of a conventional technique 1 (Japanese Patent No. 3734617) (dashed line in FIG. 5); the intertooth clearance at each angle of rotation of an inner rotor used in an oil pump rotor of a conventional technique 2 (Japanese Patent No. 4485770) (dashed-dotted line in FIG. 5); and the intertooth clearance at each angle of rotation of the inner rotor used in the oil pump rotor of the present embodiment (continuous line in FIG. 5). According to this graph, the oil pump rotor of the present embodiment which is the invention makes it possible for the minimum intertooth clearances of all locations to be formed small and substantially equalized. Therefore, while the conventional techniques bore a problem where a variation in tooth shape could have led to tooth interferences in regions with small intertooth clearances, the developed product is capable of securing appropriate intertooth clearances, thereby making it possible to easily avoid the aforementioned problem and realize a smooth rotation. Here, in FIG. 5, the reason that only the intertooth clearances at the angles of rotation of 0 to 180 are denoted is because changes in intertooth clearance from 180 to 360 (0) are similar to that from 180 to 0 shown in FIG. 5, thus omitting the description thereof.

(42) Further, FIG. 6 shows a graph obtained by applying the graphs of FIG. 9 to FIG. 12 of the examples of conventional arts to the invention. As indicated by the symbols YI, YVI in FIG. 6, since the displacement velocities are synchronized, engagement at the location of VI can start to take place smoothly, thus making it possible to restrict tooth contact noises. Moreover, a difference in intertooth clearance between the locations of I and VI at/beyond an engagement switching point is small (deviation of not larger than 5 m, 1 to 3 m in FIG. 6), thus making it possible to improve a contact ratio and restrict engagement mechanical noises. In addition, since the outer rotor 20 does not accelerate or decelerate, rotational noises of the outer rotor 20 can be restricted, thereby improving quietness as a whole.

(43) Here, shown in FIG. 4 are correlations between rotor revolution and sound pressure with regard to the oil pump of the present invention and the conventional oil pump, from which it is understood that the present invention is capable of improving quietness.

(44) Further, the minimum intertooth clearances is between the external teeth 11 of the inner rotor 10 and the internal teeth 21 of the outer rotor 2 are substantially equalized at all locations where the external teeth 11 of the inner rotor 10 and the internal teeth 21 of the outer rotor 20 are adjacent to one another (engagement points where the tooth grooves and tooth tips directly face one another; locations where the volumes of the cells C increase and decrease; and locations where the tooth tips directly face one another). Therefore, for the purpose of improving volume efficiency, since the minimum intertooth clearances at the locations where the cells C reach their maximum levels are reduced, the minimum intertooth clearance at each tooth shall not be exceedingly small even when attempting to improve fluid tightness. For this reason, appropriate intertooth clearances can be secured, thus making it possible to prevent the teeth from interfering with one another and restrict noises.

(45) In this way, the oil pump rotor of the present embodiment described above includes: the inner rotor having n (n is a natural number) external teeth; the outer rotor having n+1 internal teeth engageable with the external teeth; and the casing having the intake port for a fluid to be drawn thereinto and the discharge port for the fluid to be discharged therefrom. Particularly, this oil pump rotor is used in an oil pump transferring a fluid by drawing in and discharging the same as the volumes of the cells formed between the tooth surfaces of the two rotors change when the two engaged rotors rotate.

(46) As for the aforementioned inner rotor, the shape of each tooth tip of the inner rotor is established by the epicycloid curve that is generated by the first outer rolling circle Di externally tangent to and rolling on the base circle bi of the inner rotor without slipping. The shape of each tooth groove of the inner rotor is established by the hypocycloid curve that is generated by the first inner rolling circle di internally tangent to and rolling within the base circle bi without slipping.

(47) As for the aforementioned outer rotor, the shape of each tooth groove of the outer rotor is established by the epicycloid curve that is generated by the second outer rolling circle Do externally tangent to and rolling on the base circle bo of the outer rotor without slipping. The shape of each tooth tip of the outer rotor is established by the hypocycloid curve that is generated by the second inner rolling circle do internally tangent to and rolling within the base circle bo without slipping.

(48) When the diameter of the base circle bi of the inner rotor is bi; the diameter of the first outer rolling circle Di is Di; the diameter of the first inner rolling circle di is di; the diameter of the base circle bo of the outer rotor is bo; the diameter of the second outer rolling circle Do is Do; the diameter of the second inner rolling circle do is do; and the eccentricity amount between the inner rotor and the outer rotor is e, the expression bi=n.Math.( Di+ di) and the expression bo=(n+1).Math.( Do+ do) hold; the expression Di+ di=2 e or Do+ do=2 e holds;

(49) and the expressions Do> Di, di> do and ( Di+ di)<( Do+ do) hold.

(50) Here, the inner rotor and the outer rotor are also configured in a manner such that when Di+ di=2 e, the expression 0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6 holds, or that when Do+ do=2 e, the expression 0.3(( Do+ do)( Di+ di)).Math.n/t0.6 holds, provided that the clearance between the inner rotor and the outer rotor is t.

(51) For this reason, there can be obtained an oil pump with a superior quietness. Especially, since the minimum intertooth clearances ts can be equalized, contact noises, vibration sounds and engagement mechanical noises at the engagement switching point can be prevented from occurring such that not only the quietness of the oil pump rotor can be reliably achieved, but the volume efficiency can be improved as a result of improving the sealability. Particularly, the deviation of the minimum intertooth clearance ts is set to be 10 m, preferably in the range of not larger than 5 m.

(52) Further, as an effect of the embodiment, since the deviation of each intertooth clearance ts to the inner rotor is constantly 10 m, preferably not larger than 5 m, under the condition in which when Di+ di=2 e, the expression 0.3(( Do+ do)( Di+ di)).Math.(n+1)/t0.6 holds; or the condition in which when Do+ do=2 e, the expression 0.3(( Do+ do)( Di+ di)).Math.n/t0.6 holds, the minimum intertooth clearances ts which are the appropriate clearance gaps can be secured at engaged sections even when the clearance t is formed small. Therefore, it is possible to avoid the interferences between the external teeth 11 and the internal teeth 12 by absorbing variation in part accuracy, thereby realizing a smooth rotation, thus improving mechanical efficiency. Moreover, by making the minimum intertooth clearances ts small, e.g., as small as 35 to 45 m, preferably 37.5 to 42.5 m, the sealability between the external teeth 11 and the internal teeth 21 at where the volumes of the cells reach their maximum levels increases, thereby making it possible to improve volume efficiency.

(53) However, the present invention is not limited to the aforementioned embodiment. In fact, various modified embodiments are possible.

DESCRIPTION OF THE SYMBOLS

(54) 10 inner rotor

(55) 11 external teeth

(56) 20 outer rotor

(57) 21 internal teeth

(58) 50 casing

(59) Di outer rolling circle of inner rotor (first outer rolling circle)

(60) Do outer rolling circle of outer rotor (second outer rolling circle)

(61) di inner rolling circle of inner rotor (first inner rolling circle)

(62) do inner rolling circle of outer rotor (second inner rolling circle)

(63) C cell

(64) bi base circle of inner rotor

(65) bo base circle of outer rotor

(66) Oi shaft center of inner rotor

(67) Oo shaft center of outer rotor

(68) t clearance

(69) ts minimum intertooth clearance