Patent Grant
9273688
The present invention relates to a pump rotor formed by combining an inner rotor (external gear) and an outer rotor (internal gear) between which a difference in the number of teeth is one, and to an internal gear pump formed by fitting the pump rotor within a housing.
Internal gear pumps are used as, for example, pumps for lubricating engines and automatic transmissions (AT) in vehicles. One known type of such an internal gear pump is formed by combining an inner rotor and an outer rotor, between which a difference in the number of teeth is one, and disposing the rotors eccentrically relative to each other. Furthermore, in another known pump of this type, the tooth profile of the rotors is formed by using a trochoidal curve, which is known for good volume efficiency, low noise, and low drive torque.
A tooth profile formed by using this trochoidal curve is formed in the following manner. First, as shown in
In a pump having a tooth profile using such a trochoidal curve, an amount E of eccentricity between the center of the inner rotor and the center of the outer rotor is regulated for ensuring the face width and for designing the tooth profile. Therefore, an increase in the tooth height is limited, making it difficult to fulfill demands for increasing the discharge rate. The present applicant has made a proposition in Patent Literature 2 below in which the tooth height can be freely set in a pump rotor of the aforementioned type.
PTL 1: Japanese Unexamined Patent Application Publication No. 61-201892
PTL 2: Japanese Unexamined Patent Application Publication No. 2010-151068
In the internal gear pump having the rotors in Patent Literature 2, the capacity of a pump chamber formed between the teeth of the inner rotor and the outer rotor can be increased by increasing the tooth height of the rotors. Although this achieves high discharge performance, noise caused by, for example, gear rattling increases.
The inner rotor whose tooth profile is formed based on the method according to claim 2 in the same literature has narrow addenda. Thus, addendum abrasion tends to occur easily.
An object of this invention is to reduce noise and suppress addendum abrasion in the pump proposed in Patent Literature 2 by devising the method for forming the tooth profile of the inner rotor.
In order to achieve the aforementioned object, in an internal gear pump according to the present invention that is forming by combining an inner rotor having n teeth and an outer rotor having (n+1) teeth, the rotors are formed in the following manner.
Specifically, when a rolling circle having a diameter d1 is rolled along a base circle having a diameter d without slipping and a trochoidal curve is drawn by a point distant from a center of the rolling circle by a distance e, a tooth profile of the inner rotor is formed by an envelope of a group of circular arcs of a locus circle having a diameter d2 and having a center on the trochoidal curve. The diameter d2 of the locus circle is constant until one point between an addendum point and a dedendum point of the inner rotor and changes from the one point such that a diameter d2B at the dedendum point becomes larger than a diameter d2T at the addendum point.
The diameter d2 of the locus circle (C) may change so as to satisfy the following expression:
d2θ=d2T+(d2B−d2T)×(θ−θs)/(θe−θs) Expression (1)
where θ denotes an angle between the addendum point and the center of the locus circle,
d2θ denotes a diameter of the locus circle C at the angle θ,
d2T denotes a diameter of the locus circle C at the addendum point of the inner rotor,
d2B denotes a diameter of the locus circle C at the dedendum point of the inner rotor,
θe denotes an angle between the addendum point and the dedendum point of the inner rotor and is determined from 180°/n, and
θs denotes an angle from the addendum point of the inner rotor to a position where the diameter d2 of the locus circle C begins to change (θe≠θs).
A ratio of a diameter d2T of the locus circle C at the addendum point of the inner rotor to a diameter d2B at the dedendum point preferably satisfies a condition d2T/d2B>0.9.
Furthermore, the angle θs is preferably set between 5% and 40% of an angle θe between the addendum point and the dedendum point of the inner rotor.
The present invention also provides an internal gear pump formed by accommodating a pump rotor within a rotor chamber provided in a housing. The pump rotor is formed by combining an inner rotor having the aforementioned tooth profile with an outer rotor whose tooth profile is formed by an envelope of a group of tooth-profile curves of the inner rotor, the envelope of the group of tooth-profile curves being formed by revolving a center of the inner rotor around a circle having a diameter (2E+t) and coaxial with a center of the outer rotor, and rotating the inner rotor 1/n times while the center of the inner rotor makes one revolution around the circle.
In the above description, E denotes an amount of eccentricity between the inner rotor and the outer rotor, t denotes a maximum clearance (tip clearance) between addenda of the outer rotor and the inner rotor pressed against the outer rotor, and n denotes the number of teeth of the inner rotor. The amount E of eccentricity between the inner rotor and the outer rotor is as follows: E=e+(d2B−d2T)/4.
The present invention can reduce noise and suppress addendum abrasion by devising the method for forming the tooth profile of the inner rotor.
An embodiment of a pump rotor 1 according to this invention will be described below with reference to
The inner rotor 2 has a tooth profile that is formed by an envelope described with reference to
As shown in
Accordingly, a tooth height h of the inner rotor 2 is larger than the tooth height of teeth formed based on the method in
The diameter d2 of the locus circle C changes as expressed by the following expression (1):
d2θ=d2T+(d2B−d2T)×(θ−θs)/(θe−θs) Expression (1)
where θ denotes an angle between the addendum point and the center of the locus circle,
d2θ denotes a diameter of the locus circle C at the angle θ,
d2T denotes a diameter of the locus circle C at the addendum point of the inner rotor,
d2B denotes a diameter of the locus circle C at the dedendum point of the inner rotor,
θe denotes an angle between the addendum point and the dedendum point of the inner rotor and is determined from 180°/n, and
θs denotes an angle from the addendum point of the inner rotor to a position where the diameter d2 of the locus circle C begins to change (θe≠θs).
With regard to a ratio of the diameter d2T at the addendum point of the locus circle C to the diameter d2B at the dedendum point (d2T/d2B), a smaller value thereof allows for a larger tooth height. However, since this leads to louder gear rattling noise, the ratio may be set such that the condition d2T/d2B>0.9 is satisfied.
Furthermore, in the tooth profile formed based on the method described in claim 2 of Patent Literature 2 mentioned above, the face width of the inner rotor 2 decreases with decreasing ratio of d2T/d2B. In the rotor according to this invention, the diameter d2 of the locus circle C based on Expression (1) changes from a position displaced from the addendum by a certain angle. Thus, even if the ratio of d2T/d2B is small to a certain extent, a narrow addendum is suppressed.
In this case, as described above, the angle θs from the addendum to the position where the diameter d2 of the locus circle C begins to change may be set between 5% and 40% of the angle θe between the addendum point and the dedendum point of the inner rotor (referred to as “half tooth angle” hereinafter), or more preferably, between about 10% and 20% thereof.
By setting the angle θs to 5% or higher of the half tooth angle θe, an advantage of suppressing addendum abrasion can be satisfactorily achieved. Furthermore, by setting the angle θs to 40% or lower of the half tooth angle θe, an advantage of suppressing a rapid increase in the clearance at each addendum does not need to be sacrificed. In view of the balance between the addendum-abrasion suppression effect and the noise prevention effect, an appropriate numerical value may be selected for the angle θs from a preferred range.
The outer rotor 3 used has one tooth more than the inner rotor 2. The tooth profile of the outer rotor 3 is formed as shown in
In this case, E denotes an amount of eccentricity between the inner rotor and the outer rotor, t denotes a maximum clearance (=tip clearance) between the addenda of the outer rotor and the inner rotor pressed against the outer rotor, and n denotes the number of teeth of the inner rotor. The relationship between the amount E of eccentricity and the tentative amount e of eccentricity is as follows: E=e+(d2B−d2T)/4.
As shown in
The pump rotor 1 is formed by combining the inner rotor 2 and the outer rotor 3 described above and disposing them eccentrically relative to each other. Then, as shown in
In the internal gear pump 9, a drive shaft (not shown) is fitted through the shaft hole 2c of the inner rotor 2, and the inner rotor 2 rotates by receiving a drive force from the drive shaft. In this case, the outer rotor 3 is driven and rotated. This rotation causes the capacity of the pump chamber 4 formed between the two rotors to increase or decrease so that a liquid, such as oil, is injected or discharged.
An internal gear pump having the specifications shown in Table I is designed. In sample 1 in Table I, the diameter of the locus circle C for forming the tooth profile of the inner rotor is changed from the addendum as in the rotor according to Patent Literature 2 (i.e., θs=0°), and the aforementioned ratio of d2T/d2B is set to 0.9. Moreover, the tentative amount e of eccentricity (i.e., amount of eccentricity in design) is slightly smaller than that in sample 2.
In sample 2, d2T/d2B=0.99, and the angle from the addendum to the position where the diameter of the locus circle begins to change is set such that θs=2.5°.
The tooth profile of the outer rotor to be combined with the inner rotor is formed based on the method described with reference to
Next, each sample is fitted into a housing so as to form a pump. The pump is driven under the following conditions to check the occurrence of noise. The test results obtained are shown in Table II and Table III.
From these test results, it can be confirmed that it is advantageous to set the diameter of the locus circle, for forming the tooth profile of the inner rotor, constant until one point between the addendum point and the dedendum point of the inner rotor and then to change the diameter of the locus circle such that the diameter d2B at the dedendum point becomes larger than the diameter d2T at the addendum point. With this configuration, for example, a rapid increase in tooth-to-tooth clearance is suppressed, whereby noise is reduced.
Furthermore, when forming the tooth profile of the inner rotor, the diameter of the locus circle is made to change from a position displaced from the addendum point by a certain angle. Thus, the addenda of the inner rotor are thicker than those of the rotor according to Patent Literature 2 described above, thereby suppressing addendum abrasion.
Next, an internal gear rotor with an inner rotor 2 having eight teeth and an outer rotor 3 having nine teeth is designed. The design specifications are shown in Table IV.
In each sample, d2T/d2B=0.983. The angle θs from the addendum point of the inner rotor to the position where the diameter d2 of the locus circle C begins to change is changed.
The tooth profile of the outer rotor to be combined with the inner rotor is formed based on the method described with reference to
Next, each sample is fitted into a housing so as to form a pump. The pump is driven under the following conditions to check the occurrence of noise. The test results obtained are shown in Table V.
From these test results, it can be confirmed that it is advantageous to set the diameter of the locus circle, for forming the tooth profile of the inner rotor, constant until one point between the addendum point and the dedendum point of the inner rotor and then to change the diameter of the locus circle such that the diameter d2B at the dedendum point becomes larger than the diameter d2T at the addendum point. With this configuration, for example, a rapid increase in the tooth-to-tooth clearance is suppressed, whereby noise is reduced.
The embodiment disclosed this time is merely an example in all aspects and should not be considered as being limitative. The scope of this invention is intended to include all modifications that are defined within the scope of the claims or within a scope equivalent to the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-093767 | Apr 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/055271 | 2/28/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/157306 | 10/24/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5772419 | Hansen et al. | Jun 1998 | A |
| 20100209276 | Uozumi et al. | Aug 2010 | A1 |
| 20120177525 | Uozumi et al. | Jul 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 1442615 | Sep 2003 | CN |
| 1816694 | Aug 2006 | CN |
| 101627209 | Jan 2010 | CN |
| 101821510 | Sep 2010 | CN |
| 0779432 | Jun 1997 | EP |
| 2206923 | Jul 2010 | EP |
| 61-201892 | Sep 1986 | JP |
| 2008138601 | Jun 2008 | JP |
| 2010-151068 | Jul 2010 | JP |
| 2005005835 | Jan 2005 | WO |
| 2008111270 | Sep 2008 | WO |
| 2010016473 | Feb 2010 | WO |
| Entry |
|---|
| European Office Action for related European Application No. 13777471.7—1608 dated Jun. 16, 2015, 6 pages. |
| International Search Report of corresponding International Application PCT/JP2013/055271, dated May 21, 2013, 1 page. |
| Chinese Office Action for related Chinese Patent Application No. 201380003081.4 dated Sep. 25, 2015, 17 Pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20140341769 A1 | Nov 2014 | US |
