BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention belongs to the technical field of trochoid pumps which are
used, for example, in vehicles.
Description of the Related Art
[0002] It is known to use trochoid pumps as fuel pumps for feeding fuel to an engine of
a vehicle. One known pump structure includes a trochoid gear in which outer teeth
of an inner rotor engage inner teeth of an outer rotor. The number of outer teeth
on the inner rotor is different from the number of inner teeth on the outer rotor.
The capacity of a pump space formed between the teeth of the two rotors gradually
changes as the outer rotor rotates in response to the rotation of the inner rotor.
The pump has a rotor casing against which one side surface of the trochoid gear is
rotatably engaged. The rotor casing has a suction port formed opposite to one half
section of the side where the capacity of the pump space gradually increases to bring
about a pressure-reduced state, and a discharge port formed opposite to the other
half section at the side where the capacity of the pump space gradually decreases
to bring about a pressurized state. Fuel sucked in through the suction port in response
to a gradual increase in the pump space capacity as the rotors rotate, is discharged
through a discharge port in response to a gradual decrease in the capacity of the
pump space, wherein a pumping action can be thus carried out as described above.
[0003] Although respective pump spaces are filled with fuel, low boiling point constituents
of the fuel are vaporized as the fuel temperature rises with continuous operations
of the pump, and this can lead to cavitation. If such cavitation occurs, the capacity
of liquid fuel is decreased in the pump spaces, and there is a problem in that the
fuel flow is decreased, and furthermore the amount of discharge becomes zero, that
is, a vapor lock phenomenon is brought about. Therefore, conventionally, for example,
as shown in Fig. 7, a structure has been proposed, in which a trochoid gear T comprising
of an inner rotor 17 and an outer rotor 18 is rotatably accommodated in a recess grooved
section 16 of a rotor casing, and, on the bottom surface 16a of the recessed groove
section 16 of the rotor casing with which one side surface of the trochoid gear T
is brought into contact, a long curved hole-shaped suction portion 16b, which is located
at the above-described one half section and communicates with the outside is formed
like a through-hole, is formed. A long curved hole-shaped discharge port 16c located
at the other half section and provided with a guide way communicating with the open
side of the rotor casing 16 is formed in the manner of a recessed groove, to provide
a deaerating hole 16d communicating with the outside at the recess bottom section
of the discharge port 16c, and deaerating is carried out through the deaerating hole
16d. In this structure, utilizing high pressurization in the pump space PR formed
between gear teeth 17a and 18a of the respective rotors 17 and 18 in response to a
gradual decrease in the capacity of the pump space PR, evaporated fuel is forcibly
exhausted through the deaerating hole 16d.
[0004] Thus, in this arrangement, because the deaerating hole 16d is formed in the groove
bottom section of the discharge port 16c formed facing the high pressure side, even
if fuel has a normal temperature and is in a normal use condition in which no cavitation
occurs, fuel is forcibly exhausted to the outside through the deaerating hole 16d.
As a result, the pump performance may be worsened by an amount corresponding to the
above-described exhausted fuel. In such a case, in order to obtain necessary pump
capacity of discharge the trochoid pump has to be operated at higher power, which
results in the problems that high electric consumption is needed or the pump has to
be made larger in size. The present invention attempts to solve this problem.
[0005] Additionally, since the deaerating hole 16d is provided at the side that is subjected
to high pressure, the diameter of the deaerating hole 16d greatly influences the pump
efficiency. Therefore another problem arises in that, if the accuracy of the port
diameter is lost, unevenness occurs in pump performance, resulting in a deterioration
in the reliability of the product. These and other problems can be solved by the invention.
SUMMARY OF THE INVENTION
[0006] According to the present invention there is provided a trochoid pump comprising;
a trochoid gear having an inner rotor with outer teeth which engage inner teeth of
an outer rotor, the number of teeth on the inner rotor being different from the number
of teeth of the outer rotor, variable capacity pump spaces being formed between said
teeth of said rotors as the rotation of the outer rotor follows rotation of the inner
rotor; and
a rotor casing against which one side surface of said trochoid gear is rotatably abutted,
said casing having a suction port formed opposite to one half section at a region
where the capacity of said pump spaces gradually increases, and a discharge port formed
opposite to the other half section at a region where the capacity of the pump spaces
gradually decreases;
wherein, a deaerating hole is formed in said rotor casing to exhaust vaporized fuel
in said pump spaces, said deaerating hole being located on the rear side of said discharge
port in the rotor turning direction, and at a position where said deaerating hole
is capable of communicating a pump space at a timing when a pump space, which is at
its maximum capacity, commences decreasing its capacity.
[0007] With such a structure, fuel vaporized by being subjected to high temperatures can
be very efficiently exhausted.
[0008] In such a structure, the above-described suction port formed in one half section
of the above-described rotor casing may interrupt its communication with the above-described
pump space at a timing when the pump space enters its maximum capacity.
[0009] Further, in such a structure, the above-described deaerating hole may be positioned
and formed at the outer diametrical portion of said inner rotor.
The invention will be described now by way of example only, with particular reference
to the accompanying drawings. In the drawings:
Fig. 1 is a side view partly in section of a trochoid pump;
Fig. 2(A) is a front elevational view of Fig. 1, and Fig. 2(B) is a rear elevational
view thereof;
Fig. 3(A) is a rear elevational view of a rotor casing, and Fig. 3(B) is a cross-sectional
view taken along the line X-X of Fig. 3(A);
Fig. 4(A) is a front elevational view of a trochoid gear, and Fig. (B) is a cross-sectional
view taken along the line X-X in Fig. 4(A);
Figs. 5(A), (B) and (C) are schematic views explaining the relationship between a
deaerating hole and a state of fluctuation of a pump based on rotations of the trochoid
gear;
Fig. 6 is a graph showing the relationship between the fuel temperature and the quantity
of fuel discharged both for a prior art trochoid pump and a trochoid pump in accordance
with the present embodiment; and
Fig. 7 is a schematic view explaining the deaerating hole in a prior art trochoid
gear.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] A description is given of an embodiment of the invention with reference to the accompanying
drawings, Fig. 1 through Fig. 5.
[0011] In the drawings, a trochoid pump 1 is provided in a fuel tank as a fuel pump. A motor
section M and a pump section P disposed at the other end side from the motor section
M are mounted internally in a cylindrical housing 2 of the trochoid pump 1. The motor
section M includes motor shaft 3 which is disposed coaxially with the housing 2. One
end section of the shaft 3 is rotatably supported by a cover body 4, which is fixed
so as to cover the one end side opening, at the above-described one end side opening
of the housing 2. The other end of the motor shaft 3 is rotatably supported so that
it can pass through a through-hole 5a in a partitioning plate 5 which is non-rotatably
mounted on the inner circumferential surface of the housing 2. The partition plate
5 divides the motor section M from the pump section P. The other end of the motor
shaft 3 extends toward the pump section P. An armature core 6, on which a coil is
wound, is disposed integrally with the motor shaft 3, and a disk-shaped commutator
7 is fixed at and attached to the motor shaft 3 at one end side of the armature core
6. A plurality of commutator elements 7a are fixed at and attached to one end side
of the commutator 7. A protruding end of a brush 8, which is disposed so as to protrude
and retreat in the direction of the motor shaft 3 is set so that it can be resiliently
brought into sliding contact with the cover body 4. Further, an external lead-out
terminal 8a for feeding power to the brush 8 is provided on the cover body 4, and
a fuel discharge port 4a to be described later is arranged so as to communicate with
the outside. A permanent magnet 9 that forms a magnetic field is fixed at and attached
to the inner circumferential surface of the housing 2, wherein the motor shaft 3 is
set so as to rotate integrally with the armature core 6 when power is fed to the commutator
7 via the brush 8.
[0012] A rotor casing 10 that forms part of the pump section P acts as a cover body that
covers the opening at the other end side of the housing 2. The casing 10 has a disk-shaped
outer circumferential edge portion 10a that fits internally to the opening at the
other end side of the housing 2, and is sealed relative to the housing 2 by caulking
the housing 2 at the internally fitted position thereof. A disk-shaped recessed groove
section 10b is formed on the inner side (one end side) of the rotor casing 10. The
groove center G of the recessed groove section 10b is formed so that it is offset
from the circle center R of the rotor casing 10. A cam ring 11 is fixed integrally
to the groove side face of the recessed groove section 10b so as to be internally
fitted thereto, and a trochoid gear T is rotatably accommodated on the inner circumference
of the cam ring 11. A bearing section 10d is formed so that it is recessed at the
other end on the groove bottom face 10c of the recessed groove section 10b and is
concentric with the circle center R of the rotor casing 10. The other end portion
of the motor shaft 3 that protrudes from the partitioning plate 5 to the pump section
P side is axially supported in the bearing portion 10d and abuts against it.
[0013] A long curved hole-shaped suction port 10e is positioned at the right half section
(corresponding to one half part of the invention) of the center line M, which is common
to the center lines of the rotor casing 10 and the recessed groove section 10b in
Fig. 3, and is formed at the groove bottom face 10c of the recessed groove part of
the rotor casing 10. The suction port 10e is formed in the groove bottom face 10c
as a through-hole and provides a communication between the inside and outside of the
rotor casing 10. Fuel in the fuel tank can communicate with the inside of the trochoid
pump 1 via the suction port 10e.
[0014] A discharge port 10f recessed like a long curved hole is formed on the groove bottom
face 10c that is located at the left half part (corresponding to the other half part
of the pump) of the above-described center line M. A guide way 10g to the outer diametrical
side of the cam ring 11 is recessed integrally with the outer diametrical side of
the discharge port 10f. A funnel-shaped fuel guide body 10h is formed in the outer
surface (the other end face) of the suction port 10e so as to protrude therefrom,
in order to guide fuel to the rotor casing suction port 10e.
[0015] A plurality of outer teeth 12a are formed on the outer periphery of the inner rotor
12 that constitutes the trochoid gear T. In the present embodiment, six teeth are
formed around the circumference of the gear. The inner rotor 12 is accommodated in
the recessed groove part 10b in such a way that the other end side thereof rotatably
contacts the groove bottom face 10c of the rotor casing, and the other end part of
the motor shaft 3, which protrudes to the pump section P side is fixed (like a key
fitted into the key-hole) at the center of rotation so that it is prevented from turning.
The inner rotor 12 can rotate integrally and concentrically with the motor shaft 3
centering around the circle center R of the rotor casing 10. In addition, a plurality
of inner teeth 13a are formed on the inner periphery of the outer rotor 13. Seven
teeth are formed around the circumference of the rotor 13 in the present embodiment.
The outer rotor 13 is internally fitted to the recessed groove part 10b in such a
way that the other end side thereof rotatably contacts the groove bottom part 10c,
whereby the outer rotor 13 can rotate centering around the groove center G of the
recessed groove part 10b that is biased from the motor shaft 3 (the inner rotor 12).
The outer teeth 12a of the inner rotor 12 and the inner teeth 13a of the outer rotor
13 are engaged with each other at the lower half section in Fig. 3 and Fig. 4(A),
whereby when the inner rotor 12 rotates, the outer rotor 13 rotates following the
inner rotor 12.
[0016] A sealing plate 14 that extends to the outer circumference of the outer rotor 13
is disposed at one end side of the inner and outer rotors 12 and 13 (Trochoid gear
T), which are accommodated in the recessed groove part 10b, so that it abuts against
the one end side thereof, wherein, by means of a spring 15 disposed between the sealing
plate 14 and the partitioning plate 5, the trochoid gear T is urged towards the groove
bottom face 10c of the rotor casing 10. As a result, six pump spaces PR, both sides
of which are enclosed by the groove bottom face 10c of the outer rotor and the sealing
plate 14, are formed in the circumferential direction between the inner and outer
teeth 12a and 13a. The arrangement is such that as the trochoid gear T rotates the
respective pump spaces PR turn and move and their capacities vary gradually with respect
to both of the sides.
[0017] That is, these pump spaces PR are set to vary so that the capacity of any one of
the respective pump spaces PR is roughly zero (the minimum capacity state) when it
is positioned at the lower end position in Fig. 4(A) and so that the capacity is a
maximum when it is positioned at the upper end position. In this embodiment, the trochoid
gear T is designed so that it rotates in the counterclockwise direction in Fig. 4(A),
whereby the right half section facing the drawing of the recessed groove part 10b
is a pressure-reduced area where the capacity of the pump space PR gradually increases
in line with rotations of the trochoid gear T. As the trochoid gear rotates fuel in
a fuel tank is caused to flow in the respective pump spaces PR facing the area through
the suction port 10e, whereby the fuel capacity of the pump spaces PR is gradually
increased. The left half section facing the drawing of the recessed groove part 10b
is a highly pressurized area where the capacity of the pump space PR gradually decreases
as the trochoid gear T rotates, whereby the trochoid gear T rotates while the respective
pump spaces PR are discharging fuel through the discharge portions 10f, and the fuel
capacity of the pump space PR is gradually decreased. The fuel discharged from the
pump space PR is guided to the outer diametrical side at one end side (the partitioning
plate 5 side) of the rotor casing 10 via the guide way 10g that communicates with
the discharge portion 10f, and is caused to flow into the motor section M side via
an opening 5b secured on the disk plate of the partitioning plate 5 like a through-hole.
The fuel flowing in the motor section M side is discharged or supplied from the trochoid
pump 1 to an engine (a target to which fuel is supplied) via a fuel discharge port
4a formed integrally with the cover body.
[0018] A description is now given with reference to Fig. 5(A) of the relationship between
the positions of the inner and outer rotors 12 and 13 and the positions where the
above-described suction port 10e and discharge port 10f are formed. Fig. 5(A) shows
a state of maximum capacity, where any one of the pump spaces PR is located at the
upper end part and the capacity of the pump space PR is maximized. In this state,
the description is based on the assumption that the pump chamber which is in this
state of maximum capacity is the first pump space PR1, and subsequent pump spaces
are the second, third, fourth, fifth, sixth and seventh pump spaces, PR2, PR3, PR4,
PR5, PR6 and PR7 in compliance with the direction of rotation. In this state of maximum
capacity, the suction port 10e faces the fifth and sixth pump spaces PR and is formed
to have a size so that it is not faced to the first and fourth pump spaces PR1 and
PR4, and the tip end edge part of the suction portion 10e in the direction of rotation
of both rotors 12 and 13 extends between the sixth pump space PR6 and the first pump
space PR1, and set to so as to open until the pump space PR reaches maximum capacity.
Thus in this condition, the communication of the suction port 10e with an optional
pump space PR is interrupted at a timing corresponding to that at which the capacity
of the optional pump space PR is maximized, whereby the inside of the first pump space
PR1 does not enter a pressure-reduced state.
[0019] The discharge port 10f faces the second, third and fourth pump spaces PR2, PR3 and
PR4. The rear side edge portion of the discharge port 10f in the direction of rotation
is formed to a size that reaches the central portion of the second pump space PR2,
whereby an optional pump space PR whose capacity is maximized is set so that the pump
space PR communicates with the discharge port 10f, after elapse of an appointed period
of time from the pump space PR commencing a reduction in capacity until the pump space
facing the discharge port 10f before reaching the facing position of the second pump
space PR2.
[0020] The deaerating hole H is formed on the groove bottom face 10c of the rotor casing
10 so that it extends through to the outside. It is located at a position that is
closed by the rear side edge of any one of the inner and outer teeth 12a and 13a of
the inner and outer rotors 12 and 13 in the direction of rotation, which constitute
the first pump space PR1 in the above-described state of maximum capacity. Although
the deaerating hole H is small in diameter it is opened at a time when the trochoid
gear T slightly rotates from the above-described state of maximum capacity. That is,
it is set so that it can communicate with an optional pump space PR at a time at which
the optional pump space PR, which has been in the state of maximum capacity, comes
to reduce its capacity (See Fig. 5(B)).
[0021] In this connection, in the present embodiment, the deaerating hole H is formed at
a position of the groove bottom face 10c that is closed by the vicinity of the contacting
portions of the tooth tip of the inner tooth 13a with the tooth tip of the outer tooth
12a at the tip end side in the direction of rotation, which constitutes the pump space
PR in the state of maximum capacity, that is to say the position that roughly corresponds
to the outer diametrical end portion of the outer teeth 12a of the inner rotor. Further,
the deaerating hole H is located at the rear side of the discharge port 10f in the
direction of rotation, and is formed in a state where an appointed interval is secured
between the deaerating hole H and the discharge port 10f.
[0022] Therefore, in a case where vaporized fuel is deposited in the pump space PR, the
vaporized fuel is exhausted from the deaerating hole H. At this time, since the deaerating
hole H is caused to communicate with the pump space PR in a state where the pump space
PR reaches a high-pressurized state in which the pump space PR reduces its capacity,
the vaporized fuel is exhausted from the pump space PR in a state where it is subjected
to pressure for attempting to reduce the capacity, wherein the exhausting performance
of vaporized fuel from the deaerating hole H is set to be increased. In addition,
the deaerating hole H according to the present embodiment is located on the rear side
in the direction of rotation of the discharge port 10f that is formed at the high
pressurized area being the left half section of the groove bottom face 10c, whereby
an appointed interval is secured therebetween. Thus, the trochoid gear T rotates from
the state of the maximum capacity as described above, and it rotates while maintaining
a state of communication between only the pump space PR and deaerating hole H for
an appointed period of time after the pump space PR communicates with the deaerating
hole H. After that, the pump space PR communicates with the discharge 10f (See Fig.
5(C)), wherein the exhaust through the deaerating hole H is suppressed. Thereby, it
is possible to ensure there is a selected interval of time during which the deaerating
hole H effectively carries out its exhausting function, wherein the vaporized air
can be securely exhausted from the deaerating hole H.
[0023] It is possible to adequately establish the selected interval of time by adjusting
the distance between the deaerating hole H and the rear edge side of the discharge
port 10f in the direction of rotation.
[0024] In the embodiment of the invention, which is constructed as described above, the
trochoid pump 1 causes fuel in a fuel tank to flow into the pump spaces PR through
the suction port 10e of the rotor casing 10 by rotations of the trochoid gear T in
line with the rotations of the motor section M, and fuel in the pump spaces PR to
be exhausted to the motor section M side through the discharge port 10f and the opening
5b of the partitioning plate 5, wherein the fuel is exhausted to the outside through
the fuel exhaust port 4a that is formed at the cover body 4 of the trochoid pump 1,
whereby the fuel is supplied by the trochoid pump 1. With such a structure, in a case
where the fuel reaches a high temperature through continuous operations of the trochoid
pump 1 and is vaporized, vaporized fuel is generated in respective pump spaces PR.
However, the corresponding vaporized fuel is exhausted through the deaerating hole
H that is attempted to be opened at a timing when the pump space PR attempts to reduce
its capacity after entering the state of maximum capacity. Therefore, since the exhaust
from the pump space PR is carried out at the beginning stage of the highly pressurized
area where the pump space PR attempts to reduce its capacity, the exhaust capacity
can be increased. As a result, it is possible to efficiently exhaust the vaporized
fuel, and to reduce generation of cavitation.
[0025] In the embodiment according to the invention, the suction port 10e faces an optional
pump space PR until the optional pump space PR reaches the state of maximum capacity,
whereby it is possible to prevent the inside of the pump space PR from entering a
pressure-reduced state. As a result, when an attempt is made to reduce the capacity
of the pump space PR, there is no case where the exhaust of the vaporized fuel is
lost due to the occurrence of a pressure-reduced state in the pump space PR.
[0026] In addition, in such an embodiment, a selected interval exists between the discharge
port 10f and the deaerating hole H and a state is secured for an appointed period
of time, in which communication between the pump space PR and the deaerating hole
H ensures to be continued. On the other hand, since the deaerating hole H is caused
to communicate with the pump space PR at a stage where a pump space that enters the
state of maximum capacity commences reduction in its capacity as described above,
there is no case where deaerating is forcibly carried out in a highly pressurized
state, wherein, where the fuel temperature is normal, the amount of fuel that is discharged
from the deaerating hole H can be decreased. And it is not necessary to still further
increase the power in order to secure high pump efficiency, and it is not necessary
to still further increase the accuracy of the deaerating port. Therefore, it is possible
to provide a trochoid pump having high reliability at low cost, and the loss of fuel
can be minimized.
[0027] In this connection, Fig. 6 shows the results of having measured the amounts of discharge
with respect to fuel temperatures, using the above-described prior art trochoid pump
and a trochoid pump 1 on the basis of the above-described first embodiment. According
to the results, although it can be observed in both pumps that the amount of discharge
is lowered as the temperature rises, after a state exceeding approx. 45°C, the ratio
of lowering in the case of the trochoid pump according to the present embodiment can
be made almost half the ratio of lowering in the case of the prior art trochoid pump.
Moreover, the lowering corresponds to that due to vaporization incidental to a temperature
rise of the fuel in the case where the temperature is approx. 60°C, wherein it can
be confirmed that the amount of discharge is not lowered on the basis of the trochoid
pump 1 itself.
[0028] Also, it will be appreciated that the invention is not limited to the above-described
embodiment. The deaerating hole may be formed at any position that communicates with
the pump space at a timing when the pump space in the state of maximum capacity commences
reduction of its capacity. In Fig. 5(A), the deaerating hole may be formed at any
point of portions along the circumference edge portion, on the rear side in the direction
of rotation, of the inner and outer teeth of the inner and outer rotors at the tip
end side in the direction of rotation, which constitute the pump space that has entered
maximum capacity.