This application is based on Japanese Patent Application No. 2017-173796 filed on Sep. 11, 2017, the disclosure of which is incorporated herein by reference.
The present disclosure relates to a screw pump for pressurizing and pumping out working fluid by use of rotation of screw members.
The screw pump is known in the art, for example, as disclosed in Japanese Patent Publication No. 2004-36547. In the screw pump, working fluid is pressurized and pumped out by rotation of multiple screw members. A radial gap between the screw members as well as a radial gap between the screw member and a pump housing is generally very small, for example, several ten micro-meters (μm). In a case that extraneous material enters a working chamber of the screw pump, the extraneous material may enter the radial gap and may be wedged between the respective parts.
In the screw pump of the above prior art (JP2004-36547), a suction port is formed at a side wall of the pump housing in such a way that the suction port is opened to the working chamber in a direction perpendicular to a rotational axis of the screw member, so as to avoid a situation that the extraneous material may directly drop into the working chamber. In addition, a trap member of a groove shape is provided at a position neighboring to the suction port in order to accumulate the extraneous material.
In the screw pump of the above prior art, since the extraneous material is trapped by use of its gravity, it is difficult to completely trap the extraneous material when suction speed of the working fluid is high. In such a case, the extraneous material may enter the working chamber of the screw pump and may be wedged between the screw members. When the screw pump is thereby locked and prevented from its operation, reliability is decreased. In addition, since the trap member is formed at the side wall of the pump housing, it is a problem that a size of the screw pump becomes larger.
The present disclosure is made in view of the above problem. It is an object of the present disclosure to provide a screw pump, which can prevent an operation stop of the screw pump caused by break-in of the extraneous material.
According to a feature of the present disclosure, the screw pump comprises;
a male screw member and a female screw member, one of which forms a driving-side screw member and the other of which forms a driven-side screw member;
a driving-side convex portion of a spiral shape formed at an outer peripheral surface of the driving-side screw member, which is rotatable about a first rotational axis; and
a driven-side convex portion of a spiral shape formed at an outer peripheral surface of the driven-side screw member, which is rotatable about a second rotational axis together with the driving-side screw member,
wherein the driving-side screw member and the driven-side screw member are operatively engaged with each other and rotated together in order to pressurize working fluid from a suction port of a low pressure side and to pump out the working fluid from a discharge port of a high pressure side.
The screw pump further comprises;
(i) a pump housing;
(ii) a driving-side screw accommodation hole formed in the pump housing and movably accommodating the driving-side screw member;
(iii) a driven-side screw accommodation hole formed in the pump housing and movably accommodating the driven-side screw member; and
(iv) a lock-prevention portion for preventing a locked condition of the driving-side screw member and the driven-side screw member, which is caused by extraneous material entering the driving-side screw accommodation hole and/or the driven-side screw accommodation hole.
The lock-prevention portion is formed at least in one of the following portions,
(iv-a) the driving-side screw accommodation hole,
(iv-b) the driven-side screw accommodation hole, and
(iv-c) a screw engagement portion of the driving-side and/or the driven-side screw members, at which the driving-side screw member and the driven-side screw member are engaged with each other.
According to the above feature of the present disclosure, it is possible to avoid the locked condition of the screw pump, in which the extraneous material is wedged between the driving-side screw member and the driven-side screw member. Since an operation stop of the screw pump can be prevented, the reliability of the screw pump can be increased. In addition, since it is not necessary to provide the lock-prevention mechanism at a position outside of the pump housing, an increase of a size of the screw pump can be avoided.
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:
The screw pump of the present disclosure will be explained hereinafter by way of multiple embodiments and/or modifications with reference to the drawings. The same reference numerals are given to the same or similar structures and/or portions in order to avoid repeated explanation.
At first, an entire structure of a fuel supply system 90, to which a screw pump 101 is applied, as well as a detailed structure of the screw pump 101 will be explained with reference to
As shown in
As shown in
The high pressure pump 96 further pressurizes the fuel F from the screw pump 101 so as to supply high pressure fuel to the fuel injection device 97. The fuel injection device 97 includes a fuel injection valve (an injector) and an electronic control unit for controlling fuel injection to be carried out from the injector. The injector injects the high pressure fuel into a combustion chamber or an intake-air passage of the engine 98. The screw pump 101 is provided as one of components of the fuel supply system 90 and located in the fuel tank 91. In a conventional fuel supply system, a fuel pump of an impeller type is provided at a place of the screw pump 101.
As shown in
In the present embodiment, the male screw member 4 is driven to rotate about a first rotational axis “P” in a clockwise direction Rm, as shown in
A male convex portion 41 of a spiral shape is formed at an outer peripheral surface of the male screw member 4. A female convex portion 51 of a spiral shape is likewise formed at an outer peripheral surface of the female screw member 5. The male convex portion 41 corresponds to a driving-side convex portion, while the female convex portion 51 corresponds to a driven-side convex portion.
In the male screw member 4, an axial length “W1” of the male convex portion 41 in an axial direction of the screw pump 101 is smaller than an axial length of a groove 43 between the neighboring male convex portions 41. In the female screw member 5, an axial length “W2” of the female convex portion 51 in the axial direction is equal to an axial length of a groove between the neighboring female convex portions 51. In the present disclosure, each of the axial length “W1” and “W2” in the axial direction is also referred to as a tooth width. The tooth width “W1” of the male screw member 4 is smaller than the tooth width “W2” of the female screw member 5. The male screw member 4 is engaged with the groove of the female screw member 5. In the present embodiment, the male screw member 4 is formed as a double thread screw, while the female screw member 5 is formed as a triple-thread screw. Each of the male screw member 4 and the female screw member 5 is made of iron, for example, high carbon-chromium steel.
When the male screw member 4 and the female screw member 5 are engaged with each other and rotated, the screw pump 101 pressurizes the low pressure fuel sucked from the suction port 11 and pumps out the high pressure fuel from the discharge port 32. In the present disclosure, a lower-side end of the screw pump 101 is referred to as a suction-port side or a low-pressure side. An upper-side end of the screw pump 101 is referred to as a discharge-port side or a high-pressure side.
The suction port 11 is formed in the lower-side cover 1 and the supporting plate 12 is provided between the pump housing 201 and the lower-side cover 1. A fuel suction passage (not shown) is formed in the supporting plate 12 for communicating the suction port 11 to a housing hole 21.
The supporting plate 12 is located at a position on an axial forward end side of the male screw member 4 and the female screw member 5. The supporting plate 12 extends in a horizontal direction perpendicular to each of the first and the second rotational axes “P” and “Q”. The horizontal direction corresponds to a radial direction of the screw pump 101. The supporting plate 12 rotatably supports each of an axial forward end 42 of the male screw member 4 and an axial forward end 52 of the female screw member 5. Each of the axial forward ends 42 and 52 is formed in a conical shape, so that each of the axial forward ends 42 and 52 is in a point contact with the supporting plate 12.
A journal accommodation space 26 is formed in the pump housing 201 at its upper-side end surface 34 (that is, a surface on a side closer to the electric motor 6). A communication passage (not shown) is formed in the pump housing 201 for communicating the housing hole 21 to a discharge chamber 31 formed in the upper-side cover 3. The communication passage is formed at a position different from that of the journal accommodation space 26.
In the upper-side cover 3, the discharge chamber 31 and the discharge port 32 are formed. The discharge chamber 31 accumulates the fuel supplied from the communication passage and the discharge port 32 discharges the fuel from the discharge chamber 31 to an outside of the screw pump 101. The electric motor 6 is accommodated in the upper-side cover 3.
The electric motor 6 includes a stator 62 and a rotor 63. A coil 61 is wound on the stator 62 so as to generate rotational magnetic field. The rotor 63 has permanent magnets in such a way that N-poles and S-poles are alternately arranged in a circumferential direction thereof, so that the rotor 63 is rotated depending on the rotational magnetic field generated by the stator 62. An upper-side end 65 of a shaft of the rotor 63 is rotatably supported by a shaft holding portion 33 of the upper-side cover 3. A lower-side end of the shaft of the rotor 63 forms the output shaft 64, which is connected to the journal 7.
The journal 7 is integrally formed with and formed at a position between the output shaft 64 and the male screw member 4. The journal 7 is made of iron, for example, high-speed tool steel (SKH51). The journal 7 is made of the material having a higher hardness than that of the male screw member 4.
In the present embodiment, a part of the pump housing 201 is formed as a bearing portion 8. The journal accommodation space 26 is connected to the housing hole 21. The journal 7 is accommodated in the journal accommodation space 26. A grinding finish processing is carried out for an inside surface of the journal accommodation space 26 in such a way that surface roughness becomes lower and thereby an oil film can be easily formed. According to the above structure, the part of the pump housing 201 surrounding the journal accommodation space 26 is formed as the bearing portion 8.
The pump housing 201, in particular, a relationship between the housing hole 21 and the screw members 4 and 5 will be explained more in detail. As shown in
In the housing hole 21 of the peanut shape, there are two inwardly projecting portions respectively formed between the male screw accommodation hole 22 and the female screw accommodation hole 23. Each of the inwardly projecting portions extends in the axial direction of the pump housing 201. One of the inwardly projecting portions, which is located at a forward side of a rotation of the male screw member 4, is referred to as a forward-side boundary portion 24. The other of the inwardly projecting portions, which is located at a backward side of the rotation of the male screw member 4, is referred to as a backward-side boundary portion 25. The radial cross section of the housing hole 21 is symmetrically formed with respect to a virtual plane V extending in the axial direction. The virtual plane V is also referred to as a reference plane V.
As shown in
Pressure of the fuel flowing in the groove of a rotational backward side is higher than pressure of the fuel flowing in the groove of a rotational forward side, when compared them at the same axial height of the screw pump 101. In other words, the fuel pressure in the backward-side engagement area is higher than the fuel pressure in the forward-side engagement area. As a result, in the screw engagement area, a radial force Fr is generated in a direction from the rotational backward side to the rotational forward side, that is, from the backward-side engagement area to the forward-side engagement area.
The boundary portion between the male screw accommodation hole 22 and the female screw accommodation hole 23, which is located at a position of the rotational forward side in the screw engagement area, corresponds to the forward-side boundary portion 24.
A small radial gap of several ten microns (several ten pm) is formed in the radial direction of the screw pump 101 between an inner peripheral wall of the housing hole 21 and each radial-outward end of the male convex portion 41 and the female convex portion 51 of the screw members 4 and 5. A seal structure is thereby formed at the small radial gap. A working chamber 27 is formed between the inner peripheral wall of the housing hole 21 and each of the screw members 4 and 5 so as to compress the fuel F sucked from the suction port 11, as shown in
As shown in
An operation of the screw pump 101 will be explained. When the male screw member 4 and the female screw member 5 are rotated by the electric motor 6, the fuel F is sucked into the working chamber 27 via the suction port 11. In this operation, the working chamber 27 is moved in the axial-upward direction from the lower-side cover 1 to the upper-side cover 3 in accordance with the rotation of the male screw member 4 and the female screw member 5.
When each of the male screw member 4 and the female screw member 5 is rotated by a predetermined angle, the working chamber 27 is communicated to the discharge port 32. Then, since an operational condition of the working chamber 27 is changed from a closed condition to an opened condition, the fuel Fin the working chamber 27 is discharged from the working chamber 27 to the outside of the screw pump 101 via the discharge port 32.
In the present embodiment, when any extraneous material, for example, sand or the like, enters the working chamber 27 during the operation of the screw pump 101, the female screw member 5 can move in a direction away from the male screw member 4 to the female screw accommodation hole 23, which has the female-side clearance “CLf” larger than the male-side clearance “CLm” of the male screw accommodation hole 22. Therefore, it is possible to prevent a locked condition of the screw members 4 and 5, which may be caused by the extraneous material wedged in a space between the male screw member 4 and the female screw member 5. In other words, the female-side clearance “CLf”, which is made to be larger than the male-side clearance “CLm”, works as an escape portion for the female screw member 5. The female-side clearance “CLf”, which is made to be larger than the male-side clearance “CLm”, is also referred to as “a clearance-enlarged portion”. The female screw accommodation hole 23, for which the female-side clearance “CLf” is enlarged, corresponds to “a lock-prevention portion” for preventing the locked condition of the screw members 4 and 5, which would be caused by the extraneous material wedged between the screw members 4 and 5 and in which the screw members 4 and 5 are interlocked with each other.
In the screw pump of the above prior art (JP 2004-36547), the trap member is provided at the position of the side wall of the pump housing, in order to prevent the extraneous material from entering the screw pump. On the other hand, in the present embodiment, the lock-prevention portion is formed at the small radial gap in the housing hole 21. When compared the present embodiment with the screw pump of the prior art having the trap member, a size of the screw pump can be made to be smaller in the present embodiment.
Since it is not necessary in the present embodiment to provide a separate part, it is possible to reduce cost of the screw pump without increasing a number of parts. In addition, since the lock-prevention portion can be formed by simply increasing the inner diameter of the female screw accommodation hole 23, a manufacturing process of a hole drilling can be easily done.
In addition, in the present embodiment, the tooth width “W2” of the female screw member 5 is larger than the tooth width “W1” of the male screw member 4. The small radial gap (the female-side clearance “CLf”) is made larger on a side of the female screw member 5, in which a sealing length is larger than that in the male screw member 4. It is thereby possible to make leakage loss smaller, when compared with a case in which the small radial gap (the male-side clearance “CLm”) is made larger on a side of the male screw member 4.
A screw pump 102 according to a second embodiment will be explained with reference to
As shown in
The small radial gap between the female screw member 5 and the inner peripheral wall of the female screw accommodation hole 232 in the second inner surface area (which is formed between the stepped portion 28 and the backward-side boundary portion 25) is referred to as a second female-side clearance “CLf2”. The first female-side clearance “CLf1” is made to be larger than the second female-side clearance “CLf2”. The second female-side clearance “CLf2” is equal to the male-side clearance “CLm”. Each of the second female-side clearance “CLf2” and the male-side clearance “CLm” is set at such a value, with which a sealing performance can be sufficiently maintained between the screw member and the inner peripheral wall of the housing hole 21.
In the present embodiment, apart of the inner peripheral wall of the female screw accommodation hole 232 which has the first female-side clearance “CLf1”, that is, a radial gap portion in the first inner surface area between the forward-side boundary portion 24 and the stepped portion 28, works as the escape portion for the female screw member 5. The first female-side clearance “CLf1” is formed in the first inner surface area from the forward-side boundary portion 24 to the stepped portion 28, which is an intermediate point between the forward-side boundary portion 24 and the backward-side boundary portion 25. A center angle “θ” of the first female-side clearance “CLf1” is almost 120 degrees. In the first embodiment, the clearance-enlarged portion (the female-side clearance “CLf”) is formed for an entire inner surface area of the female screw accommodation hole 23 in the circumferential direction. On the other hand, in the second embodiment, the clearance-enlarged portion (the first female-side clearance “CLf1”) is formed for a limited inner surface area of the female screw accommodation hole 232 in the circumferential direction.
In the present embodiment, since the female screw member 5 is formed as the triple-thread screw, the first female-side clearance “CLf1” is formed for the circumferential portion of the inner peripheral wall of the female screw accommodation hole 232 having the center angle “θ” of 120 degrees. Ina case that the female screw member 5 was formed as an N-thread screw, the first female-side clearance “CLf1” will be formed for a limited circumferential portion of the inner peripheral wall of the female screw accommodation hole 232 having the center angle “θ” of 360/N degrees.
In the second embodiment, the same advantages to those of the first embodiment can be obtained. Since the first female-side clearance “CLf1”, which is the clearance-enlarged portion working as the escape portion, is formed in the limited circumferential portion of the female screw accommodation hole 232, it is possible to reduce the leakage loss, which would be generated by making larger the radial gap between the screw member and the inner peripheral wall of the housing hole. As above, it is possible in the present embodiment to increase efficiency of the screw pump. In addition, the first female-side clearance “CLf1” is formed at the forward side of the rotation of the female screw member 5, at which the interlock of the screw members caused by the extraneous material is likely to occur. As a result, the female screw member 5 can smoothly move to the first female-side clearance “CLf1”, when the extraneous material is going to be wedged between the male screw member 4 and the female screw member 5.
A screw pump 103 according to a third embodiment will be explained with reference to
In
As shown in
Even in the present embodiment, the same advantages to those of the second embodiment can be obtained. Since the radial gap between the female screw member 5 and the inner peripheral wall of the female screw accommodation hole 233 is gradually reduced in the first inner surface area (the clearance-enlarged portion), it is possible to further reduce the leakage loss.
A screw pump 104 according to a fourth embodiment will be explained with reference to
In
In the present embodiment, a surface of a groove 53 of the female screw member 50 is further recessed in a radial-inward direction of the female screw member 50 from the reference line “L”. A radial clearance between the surface of the groove 53 and the reference line “L” is set at a value “CLf3” at maximum.
As above, the groove 53 is so formed that the radial-outward end of the male convex portion 41 is not brought into contact with a bottom end of the groove 53, when the screw engagement portion 60 of the male convex portion 41 is engaged with the groove 53 of the female screw member 50. In other words, a space surrounded by the surface of the groove 53 and the reference line “L” works as the escape portion for the extraneous material. The groove 53 having the escape portion corresponds to the lock-prevention portion.
The interlock of the screw members 4 and 5 is likely to occur at such a portion, at which the radial-outward end of the male convex portion 41 is brought into contact with the groove 53, that is, at a portion neighboring to the reference line “L”. However, in the present embodiment, the escape portion is formed in the groove 53 of the female screw member 50, so as to reduce probability of the interlock and to increase reliability of the screw pump.
A screw pump 105 according to a fifth embodiment will be explained with reference to
In
As shown in
In the present embodiment, since the escape portion is made smaller than that of the fourth embodiment, it is possible to further reduce the leakage loss and correspondingly improve the efficiency of the screw pump.
In the forward-side groove area, the extraneous material is more easily wedged between the screw members. However, since the escape portion for the extraneous material is formed at such a portion at which the interlock is likely to occur, the leakage loss can be reduced.
A screw pump 106 according to a sixth embodiment will be explained with reference to
As shown in
In the normal operation of the screw pump 106 in which no extraneous material enters, the low-rigidity layer 29 exists as it is. However, in a case that the extraneous material enters the screw pump 106 and the extraneous material is going to be wedged in the radial gap between the female screw member 5 and the inner peripheral wall of the female screw accommodation hole 232, a part of the low-rigidity layer 29 is chipped off by the female screw member 5.
As above, a high efficiency of the screw pump 106 can be maintained in the normal operation. The low-rigidity layer 29 works as the lock-prevention portion when the extraneous material enters the screw pump 106.
(Further Embodiments and/or Modifications)
In the above embodiments, the lock-prevention portion of each embodiment can be combined to one another.
For example, not only the female-side clearance “CLf” is formed between the female screw member 5 and the female screw accommodation hole 23 as the clearance-enlarged portion, as shown in the first embodiment (
In the above third embodiment (
In the above fourth and fifth embodiments (
In the above sixth embodiment (
In the above first to third embodiments (
In the above embodiments, the male screw member 4 is formed as the double-thread screw and the female screw member 5 (50, 500) is formed as the triple-thread screw. However, the type of the screw is not limited to the double-thread or the triple-thread screw.
In the above embodiments, the screw pump 101 (102, 103, 104, 105, 106) has one driving-side screw member and one driven-side screw member. However, it may be so modified that multiple driven-side screw members are provided around one driving-side screw member.
In the above embodiments, the female screw member may be used as the driving-side screw member and the male screw member may be used as the driven-side screw member.
A rotational-type actuator, which is operated by oil pressure or air pressure, may be used as the driving portion instead of the electric motor 6. The driving portion may be provided at a position outside of the upper-side cover.
The screw pump may be used as a pumping device for any fluid other than the fuel, for example, air.
The present disclosure is not limited to the above embodiments and/or the modifications but can be further modified in various manners without departing from a spirit of the present disclosure.
Number | Date | Country | Kind |
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2017-173796 | Sep 2017 | JP | national |