Oil pump

A rotor-type oil pump for supplying lubricating oil to an automotive internal combustion engine. The oil pump is comprised of inner and outer rotors which are rotatably disposed inside a pump casing. The inner rotor is formed with an external gear partly in mesh with an internal gear of the outer rotor. The inner rotor is fixedly mounted on a drive shaft forming part of an engine crankshaft and formed at its inner peripheral surface with at least three flat surface portions which are located at equal intervals in the peripheral direction. The at least three flat surface portions of the inner rotor are fittingly contactable respectively with at least three flat surface portions formed at the peripheral surface of the drive shaft, thereby preventing the inner rotor from shifting radially upon receiving a biasing force (due to a pressure differential) directing to an oil inlet chamber side.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improvements in an oil pump for supplying oil, 
and more particularly to an oil pump for supplying lubricating oil to 
necessary parts in an automotive engine. 
2. Description of the Prior Art 
A variety of oil pumps have been proposed and put into practical use. A 
typical one of them is disclosed in Japanese Utility Model Publication No. 
1-76582, in which inner and outer cylindrical rotors are rotatably 
disposed inside a pump casing. The inner rotor is fixedly mounted on one 
end section of a drive shaft and formed with an external gear which is in 
mesh with an internal gear of the outer rotor. The drive shaft is formed 
at the peripheral surface of its one end section with two flat surface 
portions which are parallel with and spaced from each other. During 
operation of the oil pump, the torque from the drive shaft is transmitted 
through the two flat surface portions to the inner rotor. 
Additionally, Japanese Utility Model Provisional Publication No. 63-126506 
discloses an oil pump similar to the above-discussed one. In this oil 
pump, an annular drive spacer is interposed between a drive shaft and an 
inner rotor. The drive spacer is formed with the two parallel flat surface 
portions and fixed to the drive shaft by means of a key. 
However, drawbacks have been encountered in all of the above-discussed 
conventional oil pumps. That is to say, since driving of the inner rotor 
is carried out through the two parallel flat surface portions, the inner 
rotor is unavoidably pushed and moved toward an oil inlet chamber side 
under oil discharge pressure at an oil outlet chamber side when the two 
parallel flat surface portions come to a position to extend in the 
direction connecting the oil inlet and outlet chambers. As a result, the 
external gear of the inner rotor and the internal gear of the outer rotor 
interfere with each other thereby generating gear noise. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved oil pump 
which effectively solves the above-discussed drawbacks encountered in the 
conventional oil pumps. 
Another object of the present invention is to provide an improved oil pump 
which effectively suppresses noise generation due to interference of the 
external gear of an inner rotor and the internal gear of an outer rotor. 
A further object of the present invention is to provide an improved oil 
pump arrangement in which an inner rotor partly meshed with an outer rotor 
can be effectively prevented from shifting toward an oil inlet chamber 
side even upon being subjected to a pressure difference between oil inlet 
and outlet chambers. 
An oil pump of the present invention is comprised of a pump casing. A 
generally annular outer rotor is rotatably disposed in the pump casing and 
has an internal gear. A generally annular inner rotor is rotatably 
disposed inside the outer rotor and has an external gear which is partly 
in mesh with the internal gear of the outer rotor. The inner rotor is 
formed at its inner peripheral surface with at least three flat surface 
portions which are peripherally separate from each other. The extensions 
of the respective flat surface portions intersect each other. 
Additionally, a drive shaft is provided in such a manner that the inner 
rotor is coaxially and fixedly mounted thereon. The drive shaft is formed 
at its peripheral surface with at least three flat surface portions which 
are respectively contactable with the at least three flat surface portions 
of the inner rotor. The at least three flat surfaces of the drive shaft 
are parallel respectively with the at least three flat surface portions of 
the inner rotor. 
Accordingly, even when the inner rotor is biased radially under oil 
discharge pressure during driving of the inner rotor, at least one of the 
three flat surface portions of the drive shaft resists against the biasing 
force, thereby preventing the inner rotor from shifting toward an oil 
inlet chamber side. Thus, the behavior of the inner rotor within the pump 
casing is stabilized, thereby reducing gear noise in the oil pump.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1 and 2 of the drawings, an embodiment of an oil 
pump arrangement according to the present invention is illustrated by the 
reference character P. The oil pump P of this embodiment is for 
pressurizing oil from an oil reservoir or pan (not shown) of an automotive 
vehicle to supply the oil into a variety of oil-requiring parts in an 
engine, though not shown. 
The oil pump P is comprised of a pump casing 1 which is formed with a 
generally flat cylindrical depression 1A. A generally cylindrical or 
annular outer rotor 3 is slidably rotatably disposed in the flat 
cylindrical depression 1A of the pump casing 1. The outer rotor 3 has a 
smooth cylindrical outer peripheral surface in slidable contact with the 
smooth surface of the cylindrical depression 1A, and is formed with an 
annular internal gear 3a defining a central opening (not identified). A 
generally cylindrical inner rotor 2 is rotatably disposed inside or in the 
central opening of the outer rotor 3 and formed with an annular external 
gear 2a which is partly in mesh with the internal gear 3a of the outer 
rotor 3 because the inner rotor 2 is eccentric to the outer rotor 3. It 
will be understood that an axial dimension of the inner rotor 2 is the 
same as that of the outer rotor 3, and nearly the same as the that of the 
flat cylindrical depression 1A. 
A pump cover 4 is fixedly secured to the pump casing 1 by bolts or the like 
(not shown) in a manner to cover the flat cylindrical depression 1A, 
confining the inner and outer rotors 2, 3 within the flat cylindrical 
depression 1A. A drive shaft 5 is provided to pierce the pump casing 1 and 
the pump cover 4, maintaining an oil-tight seal between it and each of the 
pump casing and cover 1, 4. The inner rotor 2 is securely fittingly and 
coaxially mounted on the drive shaft 5 so that the axes of them are 
generally aligned with each other. The inner peripheral surface of the 
inner rotor 2 is in fitting contact with the outer peripheral surface of 
the drive shaft 5. In this embodiment, the drive shaft 5 is an end section 
of a crankshaft of the engine, so that the inner rotor is driven to rotate 
in relation to engine revolution. 
The drive shaft 5 is formed at its peripheral surface with three outer flat 
surface portions A1, A2, A3 which lie within a generally cylindrical 
region R facing the inner peripheral surface of the inner rotor 2. The 
outer flat surface portions A1, A2, A3 are peripherally spaced from each 
other and located at equal intervals along the periphery of the drive 
shaft 5. In other words, the flat surface portions A1, A2, A3 are located 
at equal angular intervals in a cross-section to which the axis of the 
drive shaft is perpendicular as shown in FIG. 1. Additionally, the flat 
surface portions A1, A2, A3 are the same in peripheral length. It will be 
understood that the surfaces of the flat surface portions A1, A2, A3 are 
not parallel with each other so that the extensions (not shown) of the 
surfaces of the respective flat surface portions A1, A2, A3 angularly 
intersect each other. 
In connection with the above, the inner rotor 2 is formed at its inner 
peripheral surface with three inner flat surface portions B1, B2, B3 which 
are located corresponding respectively to the three outer flat surface 
portions A1, A2, A3 of the drive shaft 5, so that the flat surface 
portions B1, B2, B3 face and are contactable with the flat surface 
portions A1, A2, A3, respectively. The inner rotor 2 and the drive shaft 5 
are fitted with each other, forming a slight clearance therebetween so as 
to allow a relative movement therebetween in the axial direction. 
As shown in FIG. 1, the teeth of the inner rotor external gear 2a and the 
outer rotor internal gear 3a are partly out of mesh so as to leave a 
plurality of spaces or volume chambers 10 which are filled with oil drawn 
from an oil inlet chamber 6. The oil inlet chamber 6 is communicated 
through an oil inlet port 7 with the oil reservoir. The oil filling the 
volume chambers 10 is discharged to an oil outlet chamber 8 which is 
communicated through an oil outlet port 9 to the oil-requiring parts in 
the engine. 
The manner of operation of the oil pump arrangement P will be discussed 
along with advantageous effects. 
As the engine runs rotating the crankshaft including the drive shaft 5, the 
inner rotor 2 is driven to rotate in the direction of an arrows indicated 
in FIG. 1. Then, the inner rotor 2 rotates causing the outer rotor 3 to 
rotate, in which the gears 2a, 3a of the inner and outer rotors 2, 3 
partly mesh with each other and partly come out of mesh from each other. 
Accordingly, oil introduced to the oil inlet chamber 6 is carried through 
the volume chambers 10 to the oil outlet chamber 8, accomplishing a 
pumping action of the oil. During such pumping action, as usual, the oil 
outlet chamber 8 becomes higher in oil pressure than the oil inlet chamber 
6, so that the inner and outer rotors 2, 3 receive a force directed from 
the side of the oil outlet chamber 8 to the side of the oil inlet chamber 
6. 
During driving rotation of the drive shaft 5, the torque of the drive shaft 
5 is transmitted from each outer flat surface portion A1, A2, A3 of the 
drive shaft 5 to each inner flat surface portion B1, B2, B3 of the inner 
rotor 2. More specifically, such torque transmission is made through a 
line at which the end of each outer flat surface portion A1, A2, A3 
contacts the corresponding inner flat surface portion B1, B2, B3 of the 
inner rotor 2 as shown in FIG. 1, because there is the slight clearance 
between the peripheral surface of the drive shaft 5 and the inner 
peripheral surface of the inner rotor 2. At this time, even when the 
biasing force (due to the pressure differential) directed from the side of 
the oil outlet chamber 8 to the side of the oil inlet chamber 6 is applied 
to the inner rotor 2, movement of the inner rotor 2 is resisted by at 
least one of the outer flat surface portions A1, A2, A3 of the drive shaft 
5, thereby effectively preventing the inner rotor 2 from shifting toward 
the side of the oil inlet chamber 6. 
In contrast, according to the conventional oil pumps in which torque of the 
drive shaft is transmitted through the two parallel flat surface portions 
to the inner rotor, there are two moments at which no resistance force is 
produced against the movement of the inner rotor, during one rotation of 
the drive shaft. 
While the three flat surface portions A1, A2, A3 and B1, B2, B3 have been 
shown and described as being formed in the inner rotor 2 and the drive 
shaft 5, it will be understood that the number of the flat surface 
portions A1, A2, A3 and B1, B2, B3 may be increased (for example, five, 
seven and eight) over three, maintaining a relationship in which all the 
flat surface portions are not parallel with each other. 
FIGS. 3 and 4 illustrate another embodiment of the oil pump arrangement 
according to the present invention, which is similar to the embodiment of 
FIGS. 1 and 2 except for provision of a drive spacer 15. In this 
embodiment, the cylindrical drive spacer 15 is interposed between the 
drive shaft 5 and the inner rotor 2. The drive shaft 5 in this embodiment 
is formed with no flat surface portion, so that the drive spacer 15 is 
peripherally fixed to the drive shaft 5 by means of a key 16 disposed in 
key grooves (not identified) formed in the drive spacer 15 and the drive 
shaft 5. 
The drive spacer 15 is formed at its peripheral surface with three outer 
flat surface portions A1', A2', A3' which are located corresponding and 
facing respectively to the three inner flat surface portions B1, B2, B3 of 
the inner rotor 2. Thus, the outer flat surface portions A1', A2', A3' of 
this embodiment correspond respectively to those A1, A2, A3 of the drive 
shaft 5 in the embodiment of FIGS. 1 and 2. It will be understood that 
this embodiment can offer the same advantageous effects as those in the 
embodiment of FIG. 1 and 2. 
It will be appreciated that, in the above embodiments, the inner rotor can 
be prevented from shifting in a radial direction, and therefore it has 
been made possible to omit a conventional cylindrical flange portion (not 
shown) formed in an inner rotor and inserted in the central opening of a 
pump casing. Accordingly, the inner rotor 2 of the embodiments is 
rectangular in cross-section. This omits a power loss generated due to the 
existence of the flange portion, thereby reducing power consumption in the 
oil pump.