The disclosure of Japanese Patent Application Nos. 2001-328425 filed on Oct. 25, and 2002-232195 filed on Aug. 9, 2002 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
1. Field of the Invention
The invention relates to a motor-driven type fuel pump for a vehicle to be accommodated in a fuel tank for a vehicle, and more particularly to a motor-type fuel pump for a vehicle to reliably prevent entry of a fuel compressed by a compression stroke of a pump into an intake side as vapor, and further to allow a single hole to serve both as positioning pin for executing positioning when assembling a housing and a cover and as a pressure relief hole for releasing pressure in a pump chamber.
2. Description of Related Art
Recently, as a fuel pump for supplying fuel to a vehicle engine, an in-tank type motor-driven fuel pump which is installed in a fuel tank is used. Among them, a fuel pump suspending from a flange member secured to an opening of an upper wall of the fuel tank is widely used. Further, a unit-type fuel pump incorporating a filter or the like thereinto has also been used.
In such fuel pumps, a pump body portion is structured by combining a housing 42 formed with a pump chamber 41 therein and a cover 43 abutting against a lower surface of the housing 42 so as to cover the pump chamber 41, as shown for example in a sectional view of the pump portion in FIG. 9. The pump chamber 41 is provided, as a pump member, with an inner rotor 44 of a trochoid-gear type or the like. The inner rotor 44 is rotated by a rotation axis 46 of a motor 45, and a fuel in the fuel tank is sucked through an intake port 47 formed on the cover 43 and discharged through a discharge hole 48 into a motor chamber 50. Next, the fuel passing through the motor chamber 50 is pressurized, and supplied through an exhaust hole, not shown, on the upper portion of the pump body to a fuel injection system and the like.
In a fuel pump like this, particularly when the fuel temperature is increased, there are some cases where the fuel pressurized inside the pump generates vapor from the inside of the pump and deteriorates pump performance. Therefore, as shown in FIG. 9B, a pressure relief hole 54 communicated with the outside of the pump is formed piercing the cover 43 at a position between the intake port 47 and the discharge hole 48 at an end portion of a place at which a high-pressure area of the pump is formed.
FIGS. 10A and 10B show this state in more detail. Particularly, as shown in FIG. 10B, which is a sectional view taken along line XBxe2x80x94XB portion in FIG. 10A, an internal tooth gear-like pump chamber outer peripheral surface is formed on an inner peripheral surface 56 of the pump chamber portion in an outer rotor 60 rotatably disposed in the housing 42. Inside the internal tooth gear-like pump chamber outer peripheral surface, rotatably provided is an external tooth gear-like inner rotor 44, capable of meshing with the pump chamber outer peripheral surface in a manner of the trochoid-gear type, and having a small diameter and a smaller number of teeth than the aforementioned internal teeth. Then, the inner rotor 44 is rotated by the rotation axis 46 driven by the motor 45 as above, and pump action is carried out.
At this time, in accordance with rotation of the inner rotor 44 in a direction shown in arrow R in the figure, the fuel sucked through the intake port 47 is sucked via an intake groove 57 formed on the upper surface of the cover 43 into a chamber portion at an intake stroke side in the pump chamber. After that, the chamber at the intake stroke side is closed and the fuel is compressed, the chamber is communicated with a discharge groove 58 formed at a discharge port 48 side, and the fuel is discharged through the discharge port 48 to the inside of the motor body.
When the inner rotor 44 is further rotated, the external teeth of the inner rotor 44 mesh with the internal teeth formed on the inner surface of the outer rotor 60, thereby forming a high-pressure closed chamber portion P in the figure. After that, when the high-pressure closed chamber is communicated with the intake groove 57 caused by the rotation of the inner rotor 44, a high-pressure fuel enters a low-pressure fuel through the intake hole 47. Since the pressure is released, liquid inside carries out vacuum boiling and vaporizes. Therefore, vapor contaminates the fuel at the intake side in the pump chamber, causing a vapor lock state in which the fuel is unable to be compressed sufficiently. This may sometimes deteriorate pump performance remarkably.
As a countermeasure, for example, as shown in FIGS. 9A, 9B, 10A and 10B, the pressure relief hole 54 is formed at a position where a high-pressure area of the pump is formed. The pressure relief hole 54, for example, as shown in FIG. 10B, is provided on the cover 43 between a front edge portion of the intake groove 57 and a rear edge portion of the discharge groove so as to pierce the cover toward below the pump. Owing to this, the high-pressure fuel is introduced from a portion of the highest pressure shown as point P in the figure to the pressure relief hole 54, through a narrow gap between opposite wall surfaces of the cover 43 and the housing 42. Then, the fuel is released from the pressure relief hole 54 into the fuel tank.
A problem of generation of vapor lock due to entry of the high-pressure fuel at the discharge side into the intake side in the fuel pump as above occurs not only in a trochoid-gear type positive-displacement fuel pump as shown in the figure but also in other positive-displacement fuel pumps. Further, as well as in positive-displacement fuel pumps, similar problems occur in various non-positive-displacement fuel pumps of wesco type or the like.
In the meantime, when assembling the housing 42 and the cover 43 as above, in order to easily perform a precise relative positioning between the intake port 47 portion formed on the cover 43 and the discharge hole 48 portion formed on the housing 42 or the like, a positioning pin 52 is inserted into a positioning pin insertion hole 59 at the housing 42 side and fixed in advance so as to protrude toward the cover 43 side, which is then inserted into the positioning pin insertion hole 59 formed in the cover 43. Alternatively, the positioning pin 52 is inserted into the positioning pin insertion hole 59 of the cover 43 and fixed so as to protrude toward the housing 42 side, which is then inserted into the positioning pin insertion hole 59 formed on the housing 42.
Accordingly, when assembling this fuel pump, for example, in a case where the positioning pin 52 is fixed at the housing 42 side in advance, a tip of the positioning pin 52 is fitted into the pin insertion hole 53 of the cover 43 so as to combine the both in a state where a pump member 44 is disposed in the pump chamber 41 of the housing 42. The combined one is incorporated into a tip of the rotation axis 46 of the motor 45, and the tip and the rotation axis are bonded by an external casing 55, so as to provide an integrated fuel pump unit as a whole. Note that, an example of the positioning pin 52 to be used includes a C-type pin in cross section or the like.
In a fuel pump like this, in order to prevent generation of vapor lock caused by entry of the fuel across the boundary area from the high-pressure discharge side to the low-pressure intake side in the pump, the pressure relief hole 54 for communicating the boundary area with the outside of the pump was provided. However, as the pressure relief hole is provided at one point of the area, namely in a point-like manner, pressure relief was not always carried out sufficiently. Thus, effects of preventing generation of vapor lock is not sufficient.
Further, in a fuel pump as above, it was necessary to form the positioning pin insertion hole 53 in the cover 43 through which the positioning pin 52 passes, and further the pressure relief hole 54 as above. Therefore, since it was necessary to form these holes separately in the cover 43 or the like of the pump, man-hours are increased and the pump becomes expensive.
Therefore, it is a first object of the invention to prevent with reliability generation of vapor lock caused by entry of high-pressure fuel at a discharge side of a pump chamber into an intake side thereof. It is a second object of the invention to eliminate the necessity of forming a positioning pin press fitting hole and a pressure relief hole separately, allow a single hole to serve as both holes. Further, it is a third object of the invention to achieve the first and second objects by using the same means.
In order to achieve the first object, a motor-type fuel pump for a vehicle according to a first aspect of the invention is provided with a pressure relief portion extended along a boundary area portion between a high-pressure portion and a low-pressure portion, which be communicated with a pressure chamber so as to reduce a pressure in the pressure chamber
Note that, in a case of a trochoid-gear type pump as shown in the figure, the xe2x80x9chigh-pressure portionxe2x80x9d of the pump refers to a high-pressure portion in which a sucked fuel is compressed due to reduced volume of a pump chamber in accordance with rotation of an inner rotor and an outer rotor, and xe2x80x9clow-pressure portionxe2x80x9d refers to a low-pressure portion in which the fuel is sucked and secured due to increased volume of the pump chamber in accordance with rotation of the inner rotor and the outer rotor. Note that, a problem like this occurs not only in a trochoid-gear type pump like this, but also in other positive-displacement fuel pumps. Further, it also occurs in various non-positive-displacement fuel pumps of a wesco type or the like as well as postivie-displacement fuel pumps. In those pumps, there are also a xe2x80x9chigh-pressure portionxe2x80x9d which is a compression side, and a xe2x80x9clow-pressure portionxe2x80x9d which is an intake side. The problem like this can be solved by using the aforementioned means for solving the problem.
Further, a fuel pump according to the invention may have a structure in which, at a boundary area portion between the high-pressure portion and the low-pressure portion of the pump, a groove or a slit is formed extending along the boundary area portion, so that the groove or the slit communicates the chamber with the outside of the fuel pump.
Further, in order to achieve the second object, a motor-type fuel pump for a vehicle according to a second aspect of the invention, is provided with a pressure relief hole which both positions a housing that accommodates the pump therein and a cover formed with a fuel intake hole with a positioning pin and releases pressure in a pump chamber. The motor-type fuel pump is structured such that the positioning pin is inserted into the aforementioned pressure relief hole and a pressure relief passage can be secured in the aforementioned pressure relief hole when inserting the positioning pin.
Further, in order to achieve the aforementioned first and second objects by the same method, a fuel pump according to the second aspect of the present invention may be structured such that the aforementioned pressure relief hole may be communicated with the boundary area portion between the high-pressure portion and the low-pressure portion by means of a opening, such as a pressure relief groove, extending along the boundary area portion.