This application is based on Japanese Patent Application No. 2015-170680 filed on Aug. 31, 2015, the disclosure of which is incorporated herein by reference.
The present disclosure relates to a screw pump which pumps a fluid by rotating a screw.
A fluid pump in the related art pumps a fluid by rotationally driving an impeller or the like. For example, a water pump disclosed in Patent Literature 1 pumps a coolant by rotating an electric motor and thereby rotationally driving an impeller attached to a rotor of the electric motor. The rotor is rotatably supported on a casing at both ends in an axial direction via dynamic bearings.
Patent Literature 1: JP2003-328986A
In the water pump of Patent Literature 1, one rotor is supported on sliding bearings in a rotatable manner. Besides an impeller pump, a structure of the sliding bearings is also applicable to a screw pump which pumps a fluid by rotating a male screw and a female screw in mesh with each other. However, when the structure of Patent Literature 1 is merely applied to a screw pump, an outcome is a simple configuration in which a sliding bearing is provided only to a drive screw (for example, a male screw) and no bearing is provided to a driven screw (for example, a female screw).
In the screw pump of such a configuration, a position of the driven screw is determined by meshing with the drive screw. Hence, a meshing contact force and a fluid pressure give rise to vibrations and friction is produced due to vibration contact between the drive screw and the driven screw. In addition, because a position of the driven screw is not settled, leakage of pumped fuel increases, which may possibly deteriorate pump efficiency.
It is an object of the present disclosure is to provide a screw pump reducing friction between a drive screw and a driven screw and reducing leakage.
According an aspect of the present disclosure, the screw pump pumps a fluid from an inlet port on a low-pressure side to a discharge port on a high-pressure side by rotating one drive screw constituted by one of a male screw and a female screw and at least one driven screw constituted by the other one of the male screw and the female screw which mesh with each other. The screw pump includes the drive screw, the driven screw, a drive journal, a driven journal, a case and a bearing member.
The drive screw is rotatable about a drive rotation shaft by a torque transmitted from a drive device. The driven screw is driven by the drive screw and is rotatable about a driven rotation shaft. The drive journal is provided coaxially with the drive screw and rotates integrally with the drive screw. The driven journal is provided coaxially with the driven screw and rotates integrally with the driven screw while making contact with the drive journal along a contact line between the drive rotation shaft and the driven rotation shaft. The case includes a cylinder that receives the drive screw and the driven screw. The bearing member rotatably supports the drive journal and the driven journal.
In contrast to the related art in which a bearing is provided only to the drive screw, the journal and the bearing member are provided not only to the drive screw but also to the driven screw in the screw pump of the present disclosure. The drive journal and the driven journal are rotatable while making contact with each other along the contact line. The drive journal and the driven journal are fluid-lubricated with a fluid flowing into a fitting clearance between the respective journals and the bearing member. A structure of a sliding bearing is thus obtained.
As the above configuration, a relative position of the driven screw to the drive screw is maintained. Hence, friction caused by vibration contact between the drive screw and the driven screw can be reduced. In addition, an area of fuel-passing clearances between the drive screw and the driven screw and between the respective screws and an inner wall of the cylinder can be maintained constant. Hence, leakage can be reduced.
The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
Hereinafter, screw pumps of several embodiments will be described according to the drawings. Substantially same configurations in the respective embodiments below are labelled with same reference numerals and a description is not repeated.
A screw pump of a first embodiment will be described with reference to
Firstly, reference is made to
The screw pump 101 draws in the fuel F in the fuel tank 91 from an inlet port 21 after the fuel F is filtered by the suction filter 93, and discharges the fuel F from a discharge port 42 after raising a pressure of the fuel F. The discharged fuel F is pumped to the high-pressure pump 96 by way of the fuel filter 94. A discharge pressure is adjusted by returning the fuel F for an extra pressure to the fuel tank 91 through the pressure regulator 95 provided to a branched path after the fuel filter 94.
The high-pressure pump 96 further raises a pressure of fuel pumped from the screw pump 101 and pumps the fuel to the fuel injection device 97. The fuel injection device 97 includes a fuel injection valve and a control device controlling fuel injection, and injects high-pressure fuel into a cylinder and an intake passage of the engine 98.
As has been described above, the screw pump 101 of the present embodiment is provided in the fuel tank 91 constituting the fuel supply system 90, and performs a function which have been performed by, for example, an impeller fuel pump in the related art.
Reference is made to
As is shown in
The male screw 5 of the present embodiment corresponds to a drive screw rotatable by a torque transmitted from the motor 8. The female screw 6 of the present embodiment corresponds to a driven screw driven to rotate by the drive screw.
The male journal 57 corresponds to a drive journal provided coaxially with the male screw 5 to rotate integrally with the male screw 5. The female journal 67 corresponds to a driven journal provided coaxially with the female screw 6 to rotate integrally with the female screw 6.
In the following, the male screw 5 and the female screw 6 are referred to collectively also as the screws 5 and 6, and the male journal 57 and the female journal 67 are referred to collectively also as the journals 57 and 67.
A configuration of the screw pump common in the respective embodiments will be described first.
The male screw 5 is driven to rotate about a drive rotation shaft P in a rotation direction Rm, which is a counterclockwise direction when viewed from the motor 8. The female screw 6 driven by the male screw 5 rotates about a driven rotation shaft Q in a rotation direction Rf, which is a clockwise direction when viewed from the motor 8.
In the male screw 5, crests are narrower than roots whereas crests are wider than roots in the male screw 6. The crests of the female screw 6 mesh with the roots of the male screw 5. In the present embodiment, the male screw 5 is a double thread screw and the female screw 6 is a triple thread screw.
When the male screw 5 and the female screw 6 rotate in mesh with each other, the screw pump 101 raises a pressure of low-pressure fuel drawn in from the inlet port 21 and discharges the fuel from the discharge port 42. Regarding directions specified by a phrase, “a first side and a second side in the axial direction of the screw pump 101”, referred to in the following, the first side of
The lower cover 2 has the inlet port 21 opening at one end and includes a backup plate 22 between the case 30 and the inlet port 21. The backup plate 22 supports a tip end 52 of the male screw 5 and a tip end 62 of the female screw 6. The backup plate 22 includes an inlet passage 23 allowing the inlet port 21 and a cylinder 34 in the case 30 to communicate.
The cylinder 34 in which to receive the screws 5 and 6 penetrates through the case 30 in the axial direction. In a radial cross section of
A virtual straight line passing an intersection of a pitch circle Cm of the male screw 5 and a pitch circle Cf of the female screw 6 and parallel to the drive rotation shaft P and the driven rotation shaft Q is given as a contact line C. The contact line C passes a point at which an interval between the drive rotation shaft P and the driven rotation shaft Q is internally divided by a ratio of the number of threads of the male screw 5 to the female screw 6. When the male screw 5 is a double tread screw and the female screw 6 is a triple thread screw, the contact line C passes a point at which the interval between the drive rotation shaft P and the driven rotation shaft Q is internally divided by a ratio of two to three.
The upper cover 4 includes a discharge chamber 41 in which to store fuel fed from a communication path (first storage portion) 35, and the discharge port 42 from which to discharge fuel in the discharge chamber 41 to an outside. The motor 8 is provided inside the upper cover 4.
The motor 8 has a stator 81 and a rotor 83. A coil 82 is wound around the stator 81 and generates a rotating field. The rotor 83 has N poles and S poles of permanent magnets disposed alternately in a circumferential direction, and rotates in response to the rotating field generated by the stator 81. An end of a shaft of the rotor 83 on a side of the discharge port 42 is rotatably supported on a shaft holding portion 48 of the upper cover 4. An output shaft 85, which is an end of the shaft of the rotor 83 on a side of the inlet port 21, is coupled to the male screw 5. A torque of the motor 8 is transmitted from the output shaft 85 to the male screw 5.
A radial load generated when fuel is pumped will now be described with reference to
In a portion near the contact line C where the male screw 5 and the female screw 6 mesh with each other, an upper side of the reference plane S in
A pressure of pumped fuel is relatively low on the inlet side and relatively high on the discharge side. Hence, the radial load Fr rises toward the discharge port 42. Due to such a pressure distribution, the male screw 5 and the female screw 6 are forced to incline in a direction of the radial load Fr, respectively, about the tip end 52 and the tip end 62 as supporting points.
Friction may possibly be produced when the screws 5 and 6 collide with each other or the screws 5 and 6 make contact with an inner wall of the cylinder 34 due to the radial load Fr and vibrations generated when the screw pump 101 is in operation. In addition, leakage may occur due to a variance in area of a fuel-passing clearance.
According to a technique in the related art disclosed in, for example, Patent Literature 1 (JP2003-328986A), it is anticipated that a sliding bearing is provided only to the male screw 5 in a drive region. When configured in such a manner, a position of the female screw 6 in a driven region is determined by meshing with the male screw 5. Hence, a meshing contact force and a fluid pressure give rise to vibrations, and friction is produced as well due to vibration contact between the male screw 5 and the female screw 6. Because the position of the female screw 6 is not settled, an area of a fuel-passing clearance varies. Consequently, leakage of pumped fuel increases, which may possibly deteriorate pump efficiency.
By contrast, in the screw pump 101 of the first embodiment, the journals 57 and 67 and the bearing member 71 are provided not only to the male screw 5 in the drive region but also to the female screw 6 in the driven region. A configuration of a sliding bearing adopted herein is to rotatably support outer peripheral walls of the drive and driven journals 57 and 67 by the bearing member 71 while the drive and driven journals 57 and 67 are fluid-lubricated.
A characteristic configuration of the screw pump 101 of the first embodiment will now be described.
The journals 57 and 67 are made of a steel material, for example, high carbon-chromium bearing steel.
As has been described, the male journal 57 is provided coaxially with the male screw 5 to rotate integrally with the male screw 5, and the female journal 67 is provided coaxially with the female screw 6 to rotate integrally with the female screw 6. The male journal 57 and the female journal 67 are of a cylindrical shape and the outer peripheral walls make contact with each other along the contact line C. A ratio of diameters of the male journal 57 to the female journal 67 is two to three, which is a ratio of the number of threads of the male screw 5 to the female screw 6.
A clearance between the respective journals 57 and 67 and the inner wall of the cylinder 34 is set to several μm and the respective journals 57 and 67 are fluid-lubricated when fuel flows in.
A reference is now made to
In the first embodiment, as is shown in
More specifically, an inner periphery of the bearing member 71 is shaped by linking an outer peripheral circle of the male journal 57 to an outer peripheral circle of the female journal 67 with a common external tangent 710. A portion enclosed by the outer peripheral circle of the male journal 57, the outer peripheral circle of the female journal 67, and the common external tangent 710 and communicating with the cylinder 34 defines a journal passage (passage between journals) 37.
The outer peripheral wall of the male journal 57 on an opposite side to the contact line C is denoted as an outermost peripheral wall D, and the outer peripheral wall of the female journal 67 on an opposite side to the contact line C is denoted as an outermost peripheral wall E. For ease of illustration, the outermost peripheral walls D and E are represented by points D and E in
Side passages 775 and 776 are provided, respectively, to a portion facing the outermost peripheral wall D of the male journal 57 and a portion facing the outermost peripheral wall E of the female journal 67. The side passages 775 and 776 directly allow communication between the cylinder 34 and the discharge chamber 41. Hence, the side passages 775 and 776 communicate with the inlet port 21 and the discharge port 42.
Pumped fuel flows by passing the journal passage 37 and the side passages 775 and 776 to be discharged. Basically, the side passages 775 and 776 are secondary channels. However, by adjusting a ratio of areas of the respective passages, a distribution ratio of a flow rate can be adjusted.
As is shown in
The bearing member 71 that is an annular shape includes a flange portion 711 and a press-fit portion 712 in a step shape in the axial direction. By press-fitting the press-fit portion 712 into the second storage hole 32, the bearing member 71 is positioned with respect to the case 30, in particular, to the cylinder 34. The flange portion 711 is inserted into the first storage hole 31 and fitted with clearance.
Advantages of the screw pump 101 of the first embodiment configured as above will now be described.
(1) In the configuration of the related art in which bearings are provided only to the male screw 5 in the drive region, a shaft position of the female screw 6 in the driven region is not maintained. The shaft of the female screw 6 may be independently supported at a base end. However, it is still difficult to secure a relative position of the female screw 6 with respect to the male screw 5 with high accuracy.
By contrast, in the first embodiment, the journals 57 and 67 are rotatably supported on the bearing member 71, respectively, on the both sides of the male screw 5 and the female screw 6. It should be noted that the bearing member 71 is positioned with respect to the cylinder 34 in which the screws 5 and 6 are received.
Owing to the configuration as above, a relative position of the female screw 6 to the male screw 5 is maintained. Hence, friction caused by vibration contact between the screws 5 and 6 can be reduced. In addition, an area of fuel-passing clearances between the screws 5 and 6 and between the respective screws 5 and 6 and the inner wall of the cylinder 34 can be maintained constant. Hence, leakage can be reduced.
(2) In the first embodiment, the male journal 57 and the female journal 67 are of a cylindrical shape and the outer peripheral walls make contact with each other along the contact line C. Also, a ratio of diameters of the male journal 57 to the female journal 67 is set to two to three, which is a ratio of the number of threads of the male screw 5 to the female screw 6. Hence, the journals 57 and 67 are of a simple shape and easily machined. Accuracy in dimension and accuracy in surface roughness can be thus ensured. Consequently, positions of the screws 5 and 6 can be settled more securely by eliminating slip between the screws 5 and 6.
(3) In the first embodiment, the side passages 775 and 776 communicating with the inlet port 21 and the discharge port 42 are provided, respectively, to a portion facing the outermost peripheral wall D of the male journal 57 and a portion facing the outermost peripheral wall E of the female journal 67. A force in a direction heading to the contact line C acts on the male journal 57 and the female journal 67 due to a pressure of pumped fuel flowing in the side passages 775 and 776 to be discharged. Hence, a relative position of the female screw 6 to the male screw 5 can be maintained by bringing the male journal 57 and the female journal 67 into contact with each other in a more reliable manner.
(4) In the first embodiment, the bearing member 71 is provided separately from the case 30. Hence, the cylinder 34 can be readily provided to penetrate through the case 30, that is, the case 30 is easily machined. The bearing member 71 is also easily machined while ensuring accuracy of the inner periphery of a bearing portion and the outer periphery of the press-fit portion 712.
(5) In the first embodiment, the single common bearing member 71 that is configured to commonly support the male journal 57 and the female journal 67 is provided. When the bearing member 71 is machined, accuracy in shaft position of the arc inner wall supporting the male journal 57 and the female journal 67, accuracy in inner diameter dimension, and accuracy in roundness are particularly crucial. However, by machining the common bearing member 71 out of a single material, such crucial accuracy in machining can be readily ensured.
In the first embodiment of the present disclosure, the male journal 57 and the female journal 67 are of a cylindrical shape and the outer peripheral walls make contact with each other along the contact line. A ratio of diameters of the male journal to the female journal is set to be equal to a ratio of the number of threads of the male screw 5 to the female screw 6. In such a case, it is preferable to provide the bearing member 71 separately from the case 30.
A screw pump of a second embodiment will be described with reference to
The bearing member 725 supports an outer peripheral wall of the male journal 57 on a side opposite to a contact line C. The bearing member 726 supports an outer peripheral wall of the female journal 67 on a side opposite to the contact line C. The bearing member 725 and the bearing member 726 are provided oppositely to each other with the contact line C in between.
The bearing member 725 corresponds to a drive bearing member and the bearing member 726 corresponds to a driven bearing member.
On a front side in a rotation direction, inner peripheral portions 727 and 728 of the bearing members 725 and 726, respectively, extend in a direction nearing the contact line C. That is, the bearing members 725 and 726 are provided asymmetric with respect to a reference plane S. Such a configuration allows the bearing members 725 and 726 to suitably receive a radial load Fr acting on the front side in the rotation direction.
The bearing members 725 and 726 are provided, respectively, with the side passages 775 and 776 same as the counterparts of the first embodiment above.
As has been described, in the second embodiment, the journals 57 and 67 are supported intensively on a side in high need of support in a circumferential direction by using the isolated bearing members 725 and 726, respectively. Owing to the configuration as above, a total of volumes of the two bearing members 725 and 726 can be smaller than a volume of the bearing member 71. Hence, a product weight can be reduced. In addition, a material size can be reduced.
Further, the second embodiment can achieve advantages same as the advantages (1) through (4) of the first embodiment above.
A screw pump of a third embodiment will be described with reference to
A screw pump 103 of the third embodiment is different from the counterparts of the first and second embodiments above in shapes of a male journal and a female journal. The screw pump 103 of the third embodiment is different in that an independent bearing member is not required and a cylinder in a case functions also as the bearing member. A male journal 58 and a female journal 68 of the third embodiment correspond to a drive journal and a driven journal, respectively.
As is shown in
A contact line C is set on pitch circles Cm and Cf. It is obvious from
A case 38 includes the cylinder 34 in which to receive the male screw 5 and the female screw 6, and also functions as a bearing member. In short, the bearing member is provided integrally with the case 38 where the cylinder 34 is provided.
A portion of the case 38 functioning as the bearing member is in a same shape as an inner peripheral shape of the cylinder 34. In other words, a portion of the cylinder 34 on a mouth side rotatably supports outer peripheral walls of the male journal 58 and the female journal 68 as the bearing member.
In the third embedment of the present disclosure, the male journal 58 and the female journal 68 are of pillar shapes meshed with each other and defined by moving the shapes of the male screw 5 and the female screw 6 in radial cross section in a direction parallel to the axial direction, respectively, and the contact line is set on the pitch circles. The bearing member is of a same shape as the inner peripheral shape of the cylinder and provided integrally with the case 38.
The male journal 58 and the female journal 68 mesh with each other, and the male journal 58 drives the female journal 68 to rotate. Hence, the male journal 58 and the female journal 68 also function to transmit a drive torque between the screws 5 and 6. Accordingly, as is shown in
In the third embodiment, the male journal 58 and the female journal 68 of shapes same as shapes, respectively, of the screws 5 and 6 in radial cross section rotate while making contact with each other along the contact line C. Also, the male journal 58, the female journal 68, and the inner periphery of the case 38 functioning also as the bearing member are liquid-lubricated. In short, the case 38 functions as a sliding bearing. Hence, the third embodiment achieves an advantage same as the advantage (1) of the first embodiment above.
In the third embodiment, an independent bearing member is not required and the cylinder 34 in the case 38 functions also as the bearing member. Hence, the number of components can be reduced.
For example, in the first embodiment above, the bearing member 71 is provided separately from the case 30. Hence, it is necessary to machine the press-fit portion 712 of the bearing member 71 and the second storage hole 32 of the case 30 with accuracy to position the bearing member 71 with respect to the case 30. By contrast, the bearing member is provided integrally with the case 38 in the third embodiment. Hence, a positioning configuration is not required.
In the third embodiment, by providing the male screw 5 and the female screw 6 to be rotatable without making contact with each other, friction between the screws 5 and 6 can be reduced. Also, leakage can be reduced by reducing expansion of a clearance caused by a variance in position of the screws 5 and 6.
(A) A screw pump 104 of another embodiment shown in
(B) A screw pump 105 of still another embodiment shown in
(C) Shapes and sizes of the side passages 775 and 776 in the first and second embodiments above are not limited to shapes and sizes specified in
(D) In the first and second embodiments above, the bearing member may be provided integrally with the case when machining is feasible.
(E) The screw pumps of the respective embodiments above include one drive screw and one driven screw. However, more than one driven screw may be provided around one drive screw in another embodiment.
(F) A female screw may be a drive screw and a male screw may be a driven screw in an opposite manner to the respective embodiments above. In such a case, a journal and a bearing member on a female screw side correspond to a drive journal and a drive bearing member, and a journal and a bearing member on a male screw side correspond to a driven journal and a driven bearing member.
(G) A drive device may be a rotating actuator operating on a hydraulic pressure, an air pressure or the like instead of the electric motor. The drive device may be provided outside of an upper cover.
(H) Configurations of the screw pump of the present disclosure as to shapes, locations, and the number of the journals and the bearing members may be changed from the configurations of the embodiments above as needed.
A fluid to which the screw pumps of the present disclosure are applied is not limited to fuel, and the present disclosure is also applicable to a liquid other than fuel and a gas, such as air.
The present disclosure is not limited to the embodiments mentioned above, and can be changed and modified to various embodiments which are also within the spirit and scope of the present disclosure.
While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.
Number | Date | Country | Kind |
---|---|---|---|
2015-170680 | Aug 2015 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2016/003112 | 6/29/2016 | WO | 00 |