JP2017082715A - Circumscription gear type fuel pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low pressure fuel pump capable of attaining both assurance of lubricating characteristic and a restriction against reduction of pump efficiency even if DME fuel is applied as lubricant oil.SOLUTION: A low pressure fuel pump is provided with a plurality of oil grooves 61, 62 extending in a radial direction in such a way that each of gear side surfaces of a pair of gears and each of plate contact surfaces 51, 52 of a pair of side plates 11, 12 may not be contacted to each other over one circumference. Further, there are provided oil grooves 63, 64 crossing with the plurality of oil grooves 61, 62 and connecting the plurality of oil grooves 61, 62 in a peripheral direction to cause DME fuel to fulfill the entire surface. With this arrangement as above, it is possible to increase lubricating characteristics at the contact part and to restrict reduction of pump efficiency even in the case that DME fuel is applied as lubricant oil since a discharging side space 45 and a suction side space 44 are communicated to each other by the plurality of oil grooves 61 to 64 through bearing holes 46, 47.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an external gear type fuel pump that sucks fuel having a viscosity lower than that of light oil, boosts the pressure, and feeds the fuel to an engine side.

2. Description of the Related Art Conventionally, an external gear type fuel pump that pressurizes fuel sucked from a fuel tank and supplies oil to the engine side has been proposed (see, for example, Patent Document 1).
The fuel pump includes a pair of gears that mesh with each other and rotate, a pair of side plates that are installed on both sides of the pair of gears in the rotation axis direction, and a gear chamber that is formed between the pair of side plates. .
A space on the discharge side of the fuel pump and a space on the suction side of the fuel pump are formed in the gear chamber. A pair of gears are rotatably accommodated in the gear chamber.
At least one side plate is pressed against each side surface of the pair of gears from both sides in the axial direction by an elastic member. As a result, the side surfaces of the pair of gears rotate and slide on the contact surfaces of the pair of side plates.

Here, Patent Document 1 discloses a fuel pump in which an oil groove that communicates a discharge side space and a suction side space is provided on a contact surface of a side plate. The fuel pump is configured to flow fuel from a discharge side space to a suction side space to improve lubricity at a contact portion between a pair of gears and a pair of side plates.
However, when a DME fuel having a viscosity lower than that of light oil is used as the lubricating oil, the DME fuel leaking from the discharge side space to the suction side space increases more than the light oil. For this reason, since the boosting efficiency for boosting the DME fuel by the fuel pump is lowered, there is a problem that the pump efficiency is lowered.
Therefore, when DME fuel is used as a lubricating oil, there is a demand for an external gear type fuel pump that can improve lubricity at the contact portion and suppress a decrease in pump efficiency.

JP 11-082323 A

  The present invention has been made in view of the above problems, and the purpose thereof is to improve the lubricity at the contact portion even when a fuel having a viscosity lower than that of light oil is used as a lubricating oil, and to provide a pump. It is an object of the present invention to provide an external gear type fuel pump capable of suppressing a decrease in efficiency.

According to the first aspect of the present invention, the low-viscosity fuel is partially communicated with the pair of gears and the pair of side plates by communicating the discharge side space in the fuel pump and the suction side space in the fuel pump. When each groove depth in the plurality of oil grooves to be supplied is h,
The relationship of 5 μm ≦ h ≦ 10 μm is satisfied.
Here, if each groove depth in the plurality of oil grooves is smaller than 5 μm, the amount of low-viscosity fuel leaking from the discharge side space to the suction side space is small, and the lubricity at the contact portion cannot be maintained.
When each groove depth in the plurality of oil grooves is larger than 10 μm, the amount of low-viscosity fuel flowing through the oil grooves is large and the pump efficiency is lowered.
Therefore, even when a fuel having a viscosity lower than that of light oil is used as the lubricating oil, it is possible to improve the lubricity at the contact portion and to suppress a decrease in pump efficiency.

1 is a cross-sectional view showing a circumscribed gear type fuel pump (Embodiment 1). It is II-II sectional drawing of FIG. 1 (Embodiment 1). It is the front view which showed the contact surface of the side plate (Embodiment 1). 5 is a graph showing the amount of fuel leakage and the groove area / total contact area (Embodiment 1). (A) is explanatory drawing which showed the contact surface of the side plate of condition 1, (b) is sectional drawing of (a), (c) is explanatory drawing which showed the contact surface of the side plate of condition 2, (D) is sectional drawing of (c) (Embodiment 1). It is the front view which showed the contact surface of the side plate (Embodiment 2). It is the front view which showed the contact surface of the side plate (Embodiment 3). It is the front view which showed the contact surface of the side plate (Embodiment 4). It is the front view which showed the contact surface of the side plate (Embodiment 5). FIG. 10 is an explanatory diagram showing the flow of fuel (Embodiment 5).

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.

[Configuration of Embodiment 1]
1 to 5 show Embodiment 1 to which the present invention is applied.

The fuel supply device of the present embodiment is mainly composed of dimethyl ether, which has a viscosity lower than that of light oil and contains a component that vaporizes under atmospheric pressure, as a fuel for a traveling engine (hereinafter referred to as an engine) mounted on an automobile. DME fuel is used.
DME fuel is a liquid fuel having a kinematic viscosity at 25 ° C. of 0.27 cst.
The fuel supply device includes an external gear type low-pressure fuel pump 1 that sucks DME fuel from a fuel tank (not shown) and boosts the pressure, and a high-pressure fuel pump that pressurizes DME fuel fed from the low-pressure fuel pump 1 ( (Not shown). The fuel supply device further includes a common rail (not shown) into which DME fuel is introduced from the high-pressure fuel pump, and a plurality of fuel injection valves (not shown) to which DME fuel is distributed and supplied from the common rail. .

The high-pressure fuel pump has a known configuration, pressurizes and pressurizes the DME fuel sucked into the pressurizing chamber by reciprocating the plunger in the cylinder, and discharges it to the engine side.
The common rail has a known configuration and has a pressure accumulating chamber for accumulating DME fuel.
The plurality of fuel injection valves have a known configuration, and inject the DME fuel accumulated in the pressure accumulation chamber into the cylinder of the engine.

[Features of Embodiment 1]
The low-pressure fuel pump 1 is installed in the fuel tank. The low pressure fuel pump 1 may be installed outside the fuel tank.
The low-pressure fuel pump 1 increases the pressure of the sucked DME fuel and feeds it toward the high-pressure fuel pump. The low-pressure fuel pump 1 includes an electric motor 2 energized and controlled by an electronic control unit (hereinafter referred to as ECU) and a pair of gears (hereinafter referred to as a drive gear 4 and a driven gear 5) that are rotationally driven by a drive shaft 3 of the electric motor 2. And.

The low-pressure fuel pump 1 includes a pump case 7 attached to the bracket 6 of the electric motor 2 and a pair of side plates 11 arranged on both sides of the drive gear 4 in the direction of the rotation axis RL1 and on both sides of the driven gear 5 in the direction of the rotation axis RL2. , 12 and clearance adjustment screws 13 and 14 for eliminating clearances between the drive gear 4 and the driven gear 5 and the side plates 11 and 12.
When the electric motor 2 is supplied with electric power, the electric motor 2 generates rotational power for driving the drive gear 4 to rotate. The electric motor 2 is electrically connected to a battery (not shown) via a motor drive circuit electronically controlled by the ECU.

The drive gear 4 is made of metal. The drive gear 4 rotates in a predetermined rotation direction about the rotation axis RL1 shown in FIG.
Further, the drive gear 4 is fixed to the outer periphery on the tip end side of the drive shaft 3 via a key 15. Further, the drive gear 4 is connected to the drive shaft 3 so as to be integrally rotatable.
On both sides of the drive gear 4 in the direction of the rotation axis RL1, gear side surfaces 21 and 22 are formed that can rotate and slide with respect to the side plates 11 and 12, respectively. The drive gear 4 includes a cylindrical sleeve 24 in which a through hole 23 extending in the axial direction is formed, and an annular tooth forming portion 25 that protrudes radially outward from the outer peripheral surface of the sleeve 24. Yes.
The distal end side of the drive shaft 3 is inserted into the sleeve 24. The sleeve 24 is rotatably supported on the motor side of the tooth forming portion 25 via a bearing 26. The sleeve 24 is rotatably supported on the opposite side to the motor side of the tooth forming portion 25 via a bearing 27.
A plurality of gear tooth portions 28 that mesh with the driven gear 5 in the entire circumferential direction are provided on the outer periphery of the tooth forming portion 25.

The driven gear 5 is made of metal. The driven gear 5 rotates in a predetermined rotation direction about the rotation axis RL2 shown in FIG.
On both sides of the driven gear 5 in the direction of the rotation axis RL2, gear side surfaces 31 and 32 are formed which can rotate and slide with respect to the side plates 11 and 12, respectively. The driven gear 5 includes a cylindrical sleeve 34 in which a through hole 33 extending in the axial direction is formed, and an annular tooth forming portion 35 that protrudes radially outward from the outer peripheral surface of the sleeve 34. Yes.
The sleeve 34 is hollow inside. The sleeve 34 is rotatably supported on the motor side of the tooth forming portion 35 via a bearing 36. Further, the sleeve 34 is rotatably supported on the opposite side to the motor side of the tooth forming portion 35 via a bearing 37. On the outer periphery of the tooth forming portion 35, a plurality of gear tooth portions 38 that mesh with the plurality of gear tooth portions 28 are provided in the entire circumferential direction.

The bracket 6 is integrally attached to the front side of the electric motor 2. The bracket 6 fastens and fixes a flange (not shown) of the pump case 7 using a plurality of screws (not shown). Further, a coupling end surface for coupling the pump case 7 is formed on the pump side end surface of the bracket 6. The bracket 6 is formed with a bearing hole 41 through which the drive shaft 3 slides rotatably.
The pump case 7 forms a pump chamber 42 between the end face of the bracket 6 on the pump side.
In this pump chamber 42, the drive gear 4 and the driven gear 5 are rotatably accommodated. Further, side plates 11 and 12 are accommodated in the pump chamber 42.

The side plates 11 and 12 are made of metal.
A gear chamber 43 that accommodates the drive gear 4 and the driven gear 5 is formed between the side plates 11 and 12. The side plates 11 and 12 are disposed to face each other with the gear chamber 43 interposed therebetween.
The pump chamber 42 has a suction side space 44 in the low pressure fuel pump 1 and a discharge side space 45 in the low pressure fuel pump 1.
DME fuel is sucked into the suction side space 44 from the fuel tank via a suction passage (not shown) formed in the pump case 7. The suction side space 44 communicates with the gear chamber 43 through a fuel suction passage 44a.
DME fuel is sent to the high-pressure fuel pump into the discharge side space 45 via a discharge passage (not shown) formed in the pump case 7. The discharge side space 45 communicates with the gear chamber 43 through the fuel discharge passage 45a.

Here, the DME fuel that has reached the suction side of the pump chamber 42 from the suction side space 44 through the fuel suction passage 44a is rotated by the drive gear 4 about the rotation shaft RL1. Inhaled between the surface and the inner peripheral surface of the gear chamber 43. Then, the outer peripheral side of the drive gear 4 is sent in the gear rotation direction and reaches the discharge side of the pump chamber 42.
Further, the DME fuel that has reached the suction side of the pump chamber 42 is located between each tooth surface of the plurality of gear tooth portions 38 and the inner peripheral surface of the gear chamber 43 when the driven gear 5 rotates about the rotation shaft RL2. Inhaled. Then, the outer peripheral side of the driven gear 5 is sent in the gear rotation direction and reaches the discharge side of the pump chamber 42.
The DME fuel that has reached the discharge side of the pump chamber 42 merges with the DME fuel that has passed through the outer peripheral side of the drive gear 4, and then reaches the discharge side space 45 through the fuel discharge passage 45a. Then, the DME fuel that has reached the discharge side space 45 is sent from the low pressure fuel pump 1 to the high pressure fuel pump.

The side plates 11 and 12 are formed with a bearing hole 46 for bearing the outer peripheral surface of the sleeve 24 via bearings 26 and 27 and a bearing hole 47 for bearing the outer peripheral surface of the sleeve 34 via bearings 36 and 37. Yes.
The side plates 11 and 12 have plate contact surfaces 51 to 53 that are in sliding contact with the drive gear 4 and the driven gear 5, respectively.
The plate contact surfaces 51 are in sliding contact with the gear side surfaces 31 and 32 of the drive gear 4. Each plate contact surface 51 is formed in an annular shape so as to surround each bearing hole 46 in the circumferential direction.
Each plate contact surface 52 is in sliding contact with the gear side surfaces 31 and 32 of the driven gear 5. Each plate contact surface 52 is formed in an annular shape so as to surround each bearing hole 47 in the circumferential direction.

Each plate contact surface 53 is in sliding contact with each side surface of the meshing portion of the plurality of gear tooth portions 28 and the plurality of gear tooth portions 38. Each plate contact surface 53 connects each plate contact surface 51 and each plate contact surface 52.
Here, as shown in FIG. 3, when the major axis CL direction of the side plates 11 and 12 is the vertical direction, and the direction perpendicular to the vertical direction is the horizontal direction, each plate contact surface 51 corresponds to each plate. The plate contact surfaces 52 are disposed above the contact surfaces 53, and the plate contact surfaces 52 are disposed below the plate contact surfaces 53.
Further, the right side of the long axis CL of the side plates 11 and 12 is the suction side of the pump chamber 42 and the gear chamber 43, and the left side of the long axis CL is the discharge side of the pump chamber 42 and the gear chamber 43. .

A plurality of oil grooves 61 to 64 that connect the discharge side space 45 of the pump chamber 42 and the suction side space 44 of the pump chamber 42 are formed in each plate contact surface 51, 52. These oil grooves 61 to 64 supply a part of the DME fuel to the contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52.
The plurality of oil grooves 61 are radial oil grooves extending in the radial direction on each plate contact surface 51. These oil grooves 61 are provided so as to extend radially on each plate contact surface 51 with each bearing hole 46 as the center.
The plurality of oil grooves 62 are radial oil grooves extending in the radial direction on each plate contact surface 52. The oil grooves 62 are provided so as to extend radially on the plate contact surfaces 52 around the bearing holes 47.

  The oil groove 63 is provided on the radially outer side of each plate contact surface 51 so as to extend in the circumferential direction. The oil groove 63 intersects each oil groove 61 so as to connect the oil grooves 61. The oil groove 64 is provided on the radially outer side of each plate contact surface 52 so as to extend in the circumferential direction. The oil groove 64 intersects each oil groove 62 so as to connect the oil grooves 62. The groove widths and groove depths of the plurality of oil grooves 61 and 62 are constant in the radial direction of the plate contact surfaces 51 and 52. Further, the groove width and depth of the oil grooves 63 and 64 are constant in the circumferential direction of the plate contact surfaces 51 and 52.

Here, when each groove depth in the plurality of oil grooves 61 to 64 is h,
It is provided so as to satisfy the relationship of 5 μm ≦ h ≦ 10 μm.
In addition, when each groove depth (h) in the plurality of oil grooves 61 to 64 is shallower than 5 μm, the gear side surfaces 21 and 22, the gear side surfaces 31 and 32, and the plate contact surfaces 51 and 52 Although the DME fuel hardly flows in the contact portion and the pump efficiency can be prevented from being lowered, the lubricity in the contact portion tends to be lowered.
Further, when each groove depth (h) in the plurality of oil grooves 61 to 64 is deeper than 10 μm, a large amount is supplied from the discharge side space 45 to the suction side space 44 via the plurality of oil grooves 61 to 64. Since DME fuel leaks, the lubricity at the contact portion can be ensured, but the pump efficiency tends to decrease.

An arithmetic expression showing the relationship between the fuel leak amount (Q) leaking from the discharge side space 45 to the suction side space 44 and each groove depth (h) is shown in the following equation (1).
[Equation 1]
Q = {(b · h ³ ) ÷ (12 · μ · L)} × ΔP
Where μ is the kinematic viscosity of the liquid fuel, L is the linear distance between the discharge side space 45 and the suction side space 44, b is the width of each of the plurality of oil grooves 61 to 64, and h is the plurality of oil grooves 61. Each groove depth at ˜64. ΔP is a pressure difference between the fuel pressure in the suction side space 44 and the fuel pressure in the discharge side space 45.

[Effect of Embodiment 1]
As described above, in the low-pressure fuel pump 1 according to the present embodiment, the gear side surfaces 21 and 22, the gear side surfaces 31 and 32, and the plate contact surfaces 51 and 52 are not brought into contact with each other. The plurality of oil grooves 61 and 62 are provided so as to extend in the radial direction. Further, oil grooves 63 and 64 that cross the plurality of oil grooves 61 and 62 and connect the plurality of oil grooves 61 and 62 in the circumferential direction are provided so as to extend in the circumferential direction so that the DME fuel spreads over the entire surface. .

  As a result, the discharge side space 45 and the suction side space 44 communicate with each other through the bearing holes 46 and 47 through the plurality of oil grooves 61 to 64, so that the flow of the DME fuel into the plurality of oil grooves 61 to 64. Is always formed. As a result, heat is generated by local sliding resistance between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52, and the DME fuel in the plurality of oil grooves 61 to 64 is locally generated. Even when the gas is vaporized automatically, the vaporized fuel can be quickly discharged to the suction side space 44. Therefore, it is possible to prevent seizure at the contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52.

Here, in Patent Document 1, an oil groove for ensuring slidability between each gear side surface of the pair of gears and each contact surface of the pair of side plates is provided with a discharge side space and a suction side space in the fuel pump. A configuration that does not communicate is also disclosed.
However, when DME fuel having a low boiling point is used as the lubricating oil, heat may be generated due to sliding resistance between each gear side surface and each contact surface. In this case, since the saturated vapor pressure increases as the temperature of the DME fuel rises, a part of the DME fuel supplied in a liquid state in the oil groove may be vaporized.
Therefore, since the fuel pump of Patent Document 1 adopts a configuration in which the oil groove is not communicated, the DME fuel in the oil groove is not replaced, and the DME fuel in the gas phase may be left as it is. . For this reason, the lubrication of the region where the DME fuel is in the gas phase state is extremely lowered, the sliding resistance is increased, and the contact portion between each gear side surface and each contact surface may be seized.

Therefore, in the low-pressure fuel pump 1 of the present embodiment, for the purpose of lubricating the contact portion, oil grooves 61 to 64 that connect the discharge side space 45 and the suction side space 44 are provided, and these oil grooves 61 to 64 are provided. A DME fuel in a liquid state always flows through the inside. Thereby, the lubricity in a contact part can be improved.
Moreover, each groove depth h in the oil grooves 61 to 64 is made extremely shallow, such as 10 μm or less. Desirably, each groove depth h is as shallow as 5 to 10 μm, so that the amount of DME fuel flowing out from the discharge side space 45 through the oil grooves 61 to 64 to the suction side space 44 is minimized. Thereby, the fall of pump efficiency can be suppressed.

[Experimental Results of Embodiment 1]
Next, an experiment in which the amount of fuel leaking from the discharge-side space 45 to the suction-side space 44 in the low-pressure fuel pump 1 is changed by variously changing the groove area / total contact area will be described.
In the experiment, the groove area / the total area of the contact portion was changed, and the amount of fuel leakage was investigated. The result of the experiment is shown in the graph of FIG.

As shown in FIG. 4 and FIGS. 5A and 5B, the condition j1 of Comparative Example 1 is that the oil groove width b in the plurality of oil grooves 65 and 66 is 0.8 mm, and the oil groove depth (= Clearance h is 15 μm.
Condition j2 of Comparative Example 1 is that, as shown in FIGS. 4 and 5C and 5D, the oil groove width b in the plurality of oil grooves 65 and 66 is 1.7 mm, and the oil groove depth (= Clearance h is 15 μm.
As shown in FIG. 4, the condition J1 of Example 1 is that the oil groove width b in the plurality of oil grooves 65 and 66 is 0.8 mm, and the oil groove depth (= clearance) h is 8 μm.
As shown in FIG. 4, the condition J2 of Example 1 is that the oil groove width b in the plurality of oil grooves 65 and 66 is 1.7 mm, and the oil groove depth (= clearance) h is 8 μm.

As can be confirmed from the graph of FIG. 4, in Comparative Example 1 in which the groove depth h is 15 μm, the groove area / total area of the contact portion is gradually changed from the condition j2 to the condition j1. The amount of fuel leak decreases as it decreases. However, it can be seen that in Comparative Example 1, the amount of fuel leakage is larger than the target value that can suppress the reduction in pump efficiency even when the groove area / total contact area is changed up to the condition j1.
On the other hand, in Example 1 where the groove depth h is 8 μm, when the groove area / total contact area is gradually changed from the condition J2 to the condition J1, the amount of fuel leakage decreases as the groove area decreases. In addition, it can be seen that the fuel leak amount in Example 1 is smaller than the target value that can suppress the reduction in pump efficiency even under the condition J2.

Further, the fuel leak amount (Q) decreases in inverse proportion to the cube of each groove depth h in the plurality of oil grooves 61 to 64, as shown in Equation 1 above. That is, the smaller the groove depth h, the smaller the fuel leak amount (Q).
Therefore, the discharge side space 45 and the suction side space 44 are communicated with each other by the plurality of oil grooves 61 to 64 through the bearing holes 46 and 47, and each groove depth h in the plurality of oil grooves 61 to 64 is 5 μm. As described above, by setting the thickness to 10 μm or less, it is possible to ensure both lubricity at the contact portion and suppression of reduction in pump efficiency even when DME fuel is used as the lubricating oil.

[Configuration of Embodiment 2]
FIG. 6 shows a second embodiment to which the present invention is applied.
Here, the same reference numerals as those in the first embodiment indicate the same configuration or function, and a description thereof will be omitted.

In the plate contact surfaces 51 and 52 of the present embodiment, a plurality of DME fuels are supplied to contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52. Oil grooves 71 to 74 are formed.
Here, the major axis CL direction of the side plates 11 and 12 is defined as the vertical direction, and the minor axis direction perpendicular to the vertical direction is defined as the horizontal direction.
In this case, the plurality of oil grooves 71 to 74 are a plurality of oil grooves 71 and 72 that are vertical grooves extending in the vertical direction on the plate contact surfaces 51 and 52, and the vertical grooves extending in the left and right directions on the plate contact surfaces 51 and 52. A plurality of oil grooves 73 and 74 which are grooves are provided.

The plurality of oil grooves 71 intersect each oil groove 73 perpendicularly so as to connect each oil groove 73 on each plate contact surface 51.
The plurality of oil grooves 72 intersect each oil groove 74 perpendicularly so as to connect each oil groove 74 at each plate contact surface 52.
As described above, the low-pressure fuel pump 1 of the present embodiment has the same effects as those of the first embodiment.

[Configuration of Embodiment 3]
FIG. 7 shows a third embodiment to which the present invention is applied.
Here, the same reference numerals as those in Embodiments 1 and 2 indicate the same configuration or function, and the description thereof will be omitted.

In the plate contact surfaces 51 and 52 of the present embodiment, a plurality of DME fuels are supplied to contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52. Oil grooves 81 to 84 are formed.
The plurality of oil grooves 81 are radial oil grooves extending in the radial direction on each plate contact surface 51. These oil grooves 81 are inclined by a predetermined angle in the gear rotation direction indicated by the arrow RD1 in FIG.

The plurality of oil grooves 82 are radial oil grooves extending in the radial direction on each plate contact surface 52. These oil grooves 82 are inclined by a predetermined angle in the gear rotation direction indicated by the arrow RD2 in FIG.
The oil groove 83 is provided on the radially outer side of each plate contact surface 51 so as to extend in the circumferential direction. The oil groove 83 intersects each oil groove 81 so as to connect the oil grooves 81. The oil groove 84 is provided on the radially outer side of each plate contact surface 52 so as to extend in the circumferential direction. The oil groove 84 intersects each oil groove 82 so as to connect the oil grooves 82. As described above, the low-pressure fuel pump 1 of the present embodiment has the same effects as those of the first and second embodiments.

[Configuration of Embodiment 4]
FIG. 8 shows a fourth embodiment to which the present invention is applied.
Here, the same reference numerals as those in the first to third embodiments indicate the same configuration or function, and a description thereof will be omitted.

In the plate contact surfaces 51 and 52 of the present embodiment, a plurality of DME fuels are supplied to contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52. Oil grooves 85 to 88 are formed.
The plurality of oil grooves 85 are radial oil grooves extending in the radial direction on each plate contact surface 51. These oil grooves 85 are inclined in the gear rotation direction indicated by the arrow RD1 in FIG. Further, the plurality of oil grooves 85 are gradually narrowed from the radially outer side toward the bearing hole 46 side.

The plurality of oil grooves 86 are radial oil grooves extending in the radial direction on each plate contact surface 52. These oil grooves 86 are inclined in the gear rotation direction indicated by the arrow RD2 in FIG. Further, the plurality of oil grooves 86 have a groove width that gradually decreases from the radially outer side toward the bearing hole 47 side.
The oil groove 87 is provided on the radially outer side of each plate contact surface 51 so as to extend in the circumferential direction. The oil groove 87 intersects each oil groove 85 so as to connect the oil grooves 85. The oil groove 88 is provided on the radially outer side of each plate contact surface 52 so as to extend in the circumferential direction. The oil groove 88 intersects each oil groove 85 so as to connect the oil grooves 85.

Here, since the speed is faster on the radially outer side than the radially inner side of the drive gear 4 and the driven gear 5, the groove widths of the plurality of oil grooves 85, 86 are set to the same diameter as the oil grooves 81, 82 of FIG. 7. If the direction is constant, the oil grooves 85 and 86 are likely to stay on the radially outer peripheral side. For this reason, the retention of the DME fuel due to the difference in speed can be prevented by making the groove width of the plurality of oil grooves 85 and 86 wider on the radially outer circumferential side than on the radially inner circumferential side. This facilitates the flow of DME fuel from the discharge side space 45 toward the suction side space 44 through the oil grooves 85 to 88.
As described above, the low-pressure fuel pump 1 of the present embodiment has the same effects as those of the first to third embodiments.

[Configuration of Embodiment 5]
FIG. 9 and FIG. 10 show Embodiment 5 to which the present invention is applied.
Here, the same reference numerals as those in the first to fourth embodiments indicate the same configuration or function, and a description thereof will be omitted.

In the plate contact surfaces 51 and 52 of the present embodiment, a plurality of DME fuels are supplied to contact portions between the gear side surfaces 21 and 22 and the gear side surfaces 31 and 32 and the plate contact surfaces 51 and 52. Oil grooves 91 to 94 are formed.
The plurality of oil grooves 91 are radial oil grooves extending in the radial direction on each plate contact surface 51. Further, the plurality of oil grooves 91 are gradually narrowed from the radially outer side toward the bearing hole 46 side.

The plurality of oil grooves 92 are radial oil grooves extending in the radial direction on each plate contact surface 52. Further, the plurality of oil grooves 92 have a groove width that gradually decreases from the radially outer side toward the bearing hole 47 side.
The oil groove 93 is provided on the radially outer side of each plate contact surface 51 so as to extend in the circumferential direction. The oil groove 93 intersects each oil groove 91 so as to connect the oil grooves 91. The oil groove 94 is provided on the radially outer side of each plate contact surface 52 so as to extend in the circumferential direction. The oil groove 94 intersects each oil groove 92 so as to connect the oil grooves 92.

Here, the oil groove 91 from the discharge side closest to the discharge side space 45 to the suction side closest to the suction side space 44 may be referred to as oil grooves 91a to 91g in order. Further, the oil groove 92 from the discharge side closest to the discharge side space 45 to the suction side closest to the suction side space 44 may be referred to as oil grooves 92a to 92g in order.
In the low pressure fuel pump 1 of the present embodiment, DME fuel leaks from the discharge side space 45 having a relatively high pressure to the suction side space 44 having a relatively low pressure.

However, if the groove widths and depths of the oil grooves 91 and 92 are constant as in the oil grooves 61 and 62 in FIG. 3, the DME fuel F is discharged from the discharge-side oil grooves 91 a and 92 a closest to the discharge-side space 45. Inflow. The DME fuel F flowing in from the oil grooves 91a and 92a passes through the oil grooves 93 and 94, the oil grooves 91b and 92b, and the oil grooves 91c and 92c, and the suction-side oil grooves 91g and 92g closest to the suction-side space 44. (See FIG. 10).
In this case, when the DME fuel F flowing in from the oil grooves 91a and 92a flows out of the oil grooves 91g and 92g through the bearing holes 46 and 47, a relatively short lubrication flow path is obtained. When the amount of DME fuel passing through this lubricating flow path is large, there is a risk that the fuel supply to the other oil grooves 91d to 91f and 92d to 92f will be insufficient.

Therefore, in order to spread the DME fuel over the entire oil grooves 91 to 94 in each plate contact surface 51, 52, the groove width of the plurality of oil grooves 91 is increased from the radially outer side to the radially inner side of each plate contact surface 51. The groove shape gradually becomes thinner. Similarly, the groove widths of the plurality of oil grooves 92 are gradually narrowed from the radially outer side of each plate contact surface 52 toward the radially inner side.
By the plurality of groove-shaped oil grooves 91 and 92, a lubricating flow path through which sufficient DME fuel flows is formed at the inlets of the oil grooves 91a and 92a. As a result, the groove width gradually decreases from the oil grooves 91a and 92a toward the bearing holes 46 and 47, so that the amount of DME fuel flowing through the oil grooves 91a and 92a is smaller than when the groove width and groove depth are constant. It can be reduced. Further, since the DME fuel can be supplied to the other oil grooves 91b to 91f and 92b to 92f to the extent that the lubricating oil is satisfied, the DME fuel can be supplied to the entire oil grooves 91 to 94.

As described above, the low-pressure fuel pump 1 of the present embodiment has the same effects as those of the first to fourth embodiments.
As the oil grooves 91 and 92 of the present embodiment, the oil grooves 91 and 52 have the same function as that of the groove width that gradually decreases from the radially outer side to the radially inner side of the plate contact surfaces 51 and 52, respectively. Even when the groove depth of the oil grooves 91 and 92 is made shallower as the groove depth of 92 is closer to the radial inner side of each plate contact surface 51 and 52, that is, closer to the bearing holes 46 and 47, this embodiment The same effect can be obtained.

[Modification]
In this embodiment, a DME fuel having a kinematic viscosity of 0.27 cst at 25 ° C. is used as a liquid fuel having a lower viscosity than that of light oil. However, a kinematic viscosity at 25 ° C. of a liquid fuel having a viscosity lower than that of light oil is used. A liquid fuel having a viscosity higher than 0.27 cst may be used. Desirably, a liquid fuel having a kinematic viscosity at 25 ° C. of 1 cst or less is used.
Any liquid fuel of propane, isobutane, butane, butene, and propylene may be used as engine fuel and lubricating oil (hereinafter also referred to as fuel used). Alternatively, a mixed fuel obtained by mixing any two of DME, propane, isobutane, butane, butene, and propylene may be used as the fuel used.
Moreover, you may use the mixed fuel which mixed any one or more of propane, isobutane, butane, butene, and propylene, and light oil in arbitrary ratios as a use fuel.
Moreover, you may use the high concentration DME mixed fuel which mixed DME and light oil in arbitrary ratios, or DME100% fuel as a use fuel.
Further, LPG may be used as the fuel used. Moreover, you may use gasoline oil as a use fuel.

In the present embodiment, as the fuel pump of the present invention, the low-pressure fuel pump 1 that pressurizes the liquid fuel sucked from the fuel tank and feeds the fuel toward the high-pressure fuel pump is adopted, but as the fuel pump of the present invention, You may employ | adopt the fuel pump which pressurizes the liquid fuel suck | inhaled from the fuel tank, and sends oil toward the engine side. For example, a fuel pump that feeds liquid fuel toward the fuel injection valve may be employed.
In the present embodiment, a plurality of oil grooves 61-64, 71-74, 81-88, 91-94 are provided on the plate contact surfaces 51, 52 of the pair of side plates 11, 12, but the drive gear 4 and A plurality of oil grooves 61 to 64, 71 to 74, 81 to 88, and 91 to 94 may be provided on the gear side surfaces 21 and 22 of the driven gear 5.
Further, instead of the gap adjusting screws 13 and 14, an elastic member such as a spring that generates an urging force in a direction in which the side plates 11 and 12 are pressed against the side surfaces of the drive gear 4 and the driven gear 5 may be installed. good. As a result, it is possible to eliminate gaps between the drive gear 4 and the driven gear 5 and the side plates 11 and 12. Alternatively, it is possible to minimize the gap.
The present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

1 Low Pressure Fuel Pump 4 Drive Gear 5 Driven Gear 11 Side Plate 12 Side Plate 61 Oil Groove (Diameter Oil Groove)
62 Oil groove (radial oil groove)
63 Oil groove (circumferential oil groove)
64 oil groove (circumferential oil groove)

Claims (7)

In the external gear type fuel pump (1) that sucks fuel having a viscosity lower than that of light oil, boosts the pressure, and discharges the fuel to the engine side.
A pair of gears (4, 5) rotating in mesh with each other;
A pair of side plates (11, 12) disposed on both sides in the direction of the rotation shaft (RL1, RL2) of the pair of gears,
The pair of gears have gear side surfaces (31, 32) formed on both sides in the rotation axis direction, respectively.
Each of the pair of side plates has a contact surface (51, 52) on which each gear side surface of the pair of gears is slidably contacted,
A discharge side space (45) in the fuel pump and a suction side space (44) in the fuel pump are provided on either one of the gear side surfaces of the pair of gears or the contact surfaces of the pair of side plates. A plurality of oil grooves (61-66, 71-74, 81-88, 91-94) that communicate and supply a part of the low-viscosity fuel to contact portions between the pair of gears and the pair of side plates Is formed,
When each groove depth in the plurality of oil grooves is h,
An external gear type fuel pump characterized by satisfying a relationship of 5 μm ≦ h ≦ 10 μm. The external gear type fuel pump according to claim 1,
The external gear type fuel pump according to claim 1, wherein the fuel having a viscosity lower than that of the light oil is a DME fuel mainly composed of dimethyl ether. In the external gear type fuel pump according to claim 1 or 2,
The external gear type fuel pump characterized in that the fuel having a viscosity lower than that of the light oil is a liquid fuel having a kinematic viscosity at 25 ° C. of 1 cst or less. The external gear type fuel pump according to any one of claims 1 to 3,
The plurality of oil grooves have a plurality of radial oil grooves (61, 62, 81, 82, 85, 86, 91, 92) extending in the radial direction. . The external gear type fuel pump according to claim 4,
The circumscribed gear type fuel pump, wherein the plurality of radial oil grooves have a groove width that gradually decreases from the radially outer side toward the radially inner side. In the external gear type fuel pump according to claim 4 or 5,
The plurality of oil grooves have circumferential oil grooves (63, 64, 83, 84, 87, 88, 93, 94) extending in the circumferential direction,
The circumscribed gear type fuel pump characterized in that the circumferential oil groove intersects the plurality of radial oil grooves and connects the plurality of radial oil grooves. The external gear type fuel pump according to any one of claims 1 to 6,
When the major axis (CL) direction of the pair of side plates is the vertical direction, and the minor axis direction perpendicular to the vertical direction is the horizontal direction,
The plurality of oil grooves have a plurality of vertical grooves (71, 72) extending in the vertical direction and a plurality of horizontal grooves (73, 74) extending in the left-right direction,
The external gear type fuel pump according to claim 1, wherein the plurality of vertical grooves intersect the plurality of horizontal grooves perpendicularly to connect the plurality of horizontal grooves.

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