Oil pump

The present invention provides an oil pump in which eroding of the inside of the pump due to cavitation and erosion is prevented by minimizing the pressure change in a fluid when inter-tooth spaces formed by an inner rotor and an outer rotor transport the fluid from the intake port to the discharge port. The oil pump comprises: an inner rotor; an outer rotor; an intake port; a discharge port; a transfer side partition part formed between a terminal end of the intake port and a leading end of the discharge port; and a shallow groove which is formed in the transfer side partition part, and which communicates with the discharge port but does not communicate with the intake port. The shallow groove does not intersect with the cell on the transfer side partition part, and is positioned farther inward than the circular locus of the gear bottom parts of the inner rotor. The shallow groove communicates with the cell through a side clearance between the transfer side partition part and the rotor side surfaces of the inner rotor and the outer rotor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil pump which is an internal contact gear pump, wherein each inter-tooth space formed by an inner rotor and an outer rotor transports a fluid from an intake port to a discharge port while minimizing and smoothing the change in pressure of the fluid enclosed in the inter-tooth space and preventing eroding of the inside of the pump due to cavitation and erosion, while having an extremely simple construction.

2. Description of the Related Art

There many types of pumps with inter-tooth chambers formed by an inner rotor and outer rotor equipped with trochoidal teeth, which discharge a fluid from a discharge port by moving the inter-tooth chamber filled with fluid from an intake port with a maximum volume condition to a reduced volume stroke. With these pumps, when the inter-tooth chamber carries fluid from an intake port to a discharge port, the volume of the inter-tooth chamber, which has a trochoidal tooth structure, will gradually change. In other words, the volume of the inter-tooth space will increase and decrease while moving from the intake port to the discharge port, so the pressure of the fluid in the inter-tooth chamber will vary.

Furthermore, when the inter-tooth chamber reaches the discharge port, the fluid enclosed at high pressure in the inter-tooth chamber will abruptly enter the discharge port, causing loud and unusual noises. In order to prevent the fluid from abruptly flowing into the discharge port in this manner, a pump with a small port formed on the discharge port side has been disclosed in U.S. Pat. No. 2,842,450. This small port is a shallow groove formed from the leading edge of the discharge port to the intake port side.

Therefore, a small amount of the high-pressure fluid in the inter-tooth chamber will be discharged into the discharge port through the small port before the inter-tooth chamber reaches the discharge port, because the inter-tooth chamber intersects with the small port and communicates with the discharge port through the small port. Therefore when the inter-tooth chamber reaches the discharge port, the fluid in the inter-tooth chamber will not abruptly flow into the discharge port, and pump noise can be prevented.

According to the referenced patent (U.S. Pat. No. 2,842,450), the high-pressure fluid in the inter-tooth chamber which moves from the intake port to the discharge port is prevented from abruptly flowing into the discharge port and the generation of large noise can be prevented. However, as described above, the inter-tooth chamber increases and decreases in volume during the process of moving the fluid from the intake port to the discharge port, and the pressure of the fluid enclosed inside will vary. This change in fluid pressure causes cavitation where vapor bubbles are formed in the fluid. The vapor bubbles created by cavitation will congregate on the gear bottom side on the inner rotor side of the inter-tooth chamber.

Furthermore, the small port disclosed in the referenced patent (U.S. Pat. No. 2,842,450) will directly intersect with the inter-tooth chamber which moves toward the discharge port side, and at the moment when communicated with the inter-tooth chamber, pressure variation will occur at the small port, and there is a possibility that the vapor bubbles collected at the gear bottom parts of the inner rotor will abruptly collapse (destruct). At this time, the small port will not be able to accommodate the change in hydraulic pressure, and there is a possibility of erosion where the vapor bubbles caused by cavitation will abruptly collapse (destruct).

Because of this erosion phenomenon, the momentary generation and collapse (destruct) of a plurality of vapor bubbles will cause impact scarring on the inner rotor, outer rotor, and housing or the like, the pump efficiency will be negatively affected, and maintaining a predetermined pump performance will be difficult. In other words, even though the fluid which is in the inter-tooth chamber which transports the fluid to the discharge port can be prevented from abruptly flowing into the discharge port, eroding cannot be prevented, and there is a possibility that erosion will occur.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simple construction which can suppress erosion by controlling sudden pressure variation inside the inter-tooth chamber which transports fluid from the intake port to the discharge port.

The invention of claim1resolves these problems using an oil pump, comprising: an inner rotor; an outer rotor which rotates with the inner rotor while forming a cell; an intake port; a discharge port; a transfer side partition part formed between the terminal end of the intake port and the leading end of the discharge port; and a shallow groove which is formed in the transfer side partition part, and which does not communicate with the intake port but communicates with the discharge port, wherein the shallow groove does not intersect with the cell on the transfer side partition part and is positioned toward the inside of the circular locus of the gear bottom parts of the inner rotor, a side clearance is established between the transfer side partition part and the rotor side surfaces of the inner rotor and the outer rotor, and the shallow groove communicates with the cell through this side clearance.

The invention of claim2resolves these problems using an oil pump with the aforementioned construction, wherein a gap of approximately1mm or less is established between the outside edge of the shallow groove in the groove width direction and the circular locus of the gear bottom parts formed by the rotation of the inner rotor. The invention of claim3resolves these problems using an oil pump with the aforementioned construction, wherein, in the transport side partition part, an outer shallow groove is formed positioned farther to the outside, from the center of rotation of the inner rotor, than the location where the shallow groove is formed, with the outer shallow groove communicating with the discharge port while not communicating with the intake port, and wherein the outer shallow groove communicates and intersects with the cell.

The invention of claim4resolves these problems using an oil pump with the aforementioned construction, wherein the length of the outer shallow groove in the longitudinal direction is formed to be shorter than that of the shallow groove. The invention of claim5resolves these problems using an oil pump with the aforementioned construction wherein the transport side partition part in which the shallow groove is formed is established on both sides of the inner rotor and the outer rotor.

With the invention of claim1, the inside of the cell which moves along the transfer side partition part from the intake port to the discharge port is communicated with the shallow groove through the side clearance. Furthermore, the volume of the cell will increase by the process where the cell moves along the transfer side partition part from the intake port to the discharge port, the fluid pressure will drop, and vapor bubbles will occur because of cavitation. At this time, the flow of fluid into the cell will be very slow and gradual because the fluid is supplemented through the side clearance from the shallow groove, and therefore the pressure in the cell will gradually and smoothly rise, so the vapor bubbles generated will not abruptly collapse (destruct), but rather the vapor bubbles can be gradually eliminated by the smoothly increasing pressure. In this manner, vapor bubbles formed by cavitation will not abruptly collapse (destruct) because of the change in pressure, erosion will be prevented, and therefore the durability of the pump can be increased and pump life extended.

With the invention of claim2, the flow of fluid from the shallow groove to the cell will be favorable, and the fluid in the cell can easily be supplemented because of the gap between the outside edge of the shallow groove in the groove width direction and the circular locus of the gear bottom parts formed by the rotation of the inner rotor, is approximately1mm or less. With the invention of claim3, an outer shallow groove is established in addition to the shallow groove, so vapor bubbles which occur in the fluid in the cell can more positively be eliminated.

With the invention of claim4, the pressure variation caused by the shallow groove can be minimized and vapor bubbles which occur can be eliminated during the initial movement phase to the middle movement phase of the cell along the transfer side partition part, and extremely good pump performance can be obtained because the fluid will be gradually discharged to the discharge port side through the outer shallow groove, from the final movement phase of the cell. Next, with the invention of claim5, the supplementary fluid can relatively rapidly flow with good balance into the cell, vapor bubbles can be eliminated, and stable pump performance can be achieved because of the shallow grooves on both sides and the side clearance to both sides of the transfer side partition part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below based on the drawings. As shown inFIG. 1A, the oil pump of the present invention contains an inner rotor7and an outer rotor8with trochoidal teeth in a rotor chamber1formed in a housing A.FIG. 2is a front view drawing of the main components of the housing body A1of the housing A, and as shown inFIG. 2A, an intake port2and a discharge port3are formed in the rotor chamber near the outer circumference in the circumferential direction thereof. The intake port2and the discharge port3are asymmetrically formed on the left and right of the rotor chamber1. Alternatively, the intake port2and the discharge port3may be formed with left and right symmetry.

As shown inFIG. 1A, the inner rotor7has one fewer tooth than the outer rotor8, creating a relationship where when the inner rotor7makes one rotation, the rotation of the outer rotor8will be delayed. Therefore, the inner rotor7will have teeth7awhich protrude outward and gear bottom parts7bwhich are recessed inward, and similarly, the outer rotor8will have protruding teeth8aand recessed gear bottom parts8bcloser to the center side than the inner circumferential side. Inter-tooth spaces are formed by the combination of these teeth7a,8aand these gear bottom parts7b,8bby the rotation of the inner rotor7and the outer rotor8, and these inter-tooth spaces are referred to as cells S.

In the intake port2, the edge of the intake port2where the cell S formed by the rotation of the inner rotor7and the outer rotor8moves and first reaches the intake port2is referred to as the leading edge2aof the intake port2, and the edge where the cell S leaves the intake port2because of rotation is referred to as the terminal end2bof the intake port2. Similarly, in the discharge port3, the edge of the discharge port3where the cell S formed by the rotation of the inner rotor7and the outer rotor8moves and first reaches the discharge port3is referred to as the leading edge3aof the discharge port3, and the edge where the cell S leaves the discharge port3because of the rotation of the cell S is referred to as the terminal end3bof the discharge port3(Refer toFIG. 3).

As shown inFIG. 2A,FIG. 3A, andFIG. 4, a transfer side partition part4is formed between the terminal end2bof the intake port2and the leading edge3aof the discharge port3in order to partition the intake port2and the discharge port3. The transfer side partition part4is the region enclosed by the double dotted broken line inFIG. 2A, and the region shown by the double dotted broken line hatch marks inFIG. 3andFIG. 4. The transfer side partition part4is formed to be a flat surface. Furthermore, the transfer side partition part4acts to form a closed chamber in the process where the fluid from the intake port2drawn into the cell S formed by the inner rotor7and the outer rotor8is transported to the discharge port3(Refer toFIG. 1B). Incidentally, the inner rotor7and the outer rotor8rotate in a clockwise direction. Furthermore, if the intake port2and the discharge port3are formed on the opposite left and right sides, the inner rotor7and the outer rotor8will rotate in a counterclockwise direction.

The housing A is comprising a housing body A1and a cover A2, and a rotor chamber1is formed in the housing body A1(Refer toFIG. 3A). Furthermore, the transfer side partition parts4are formed on both sides of the housing body A1and the cover A2(Refer toFIG. 1BandFIG. 2B). Furthermore, the cell S formed by the inner rotor7and the outer rotor8contained in the rotor chamber1is enclosed in a near closed condition by both rotor side surfaces because of both of the transfer side partition parts4,4(Refer toFIG. 1BandFIG. 2B).

A side clearance C is established between the rotor side surface7sof the inner rotor7and the transfer side partition part4. Furthermore, similarly a side clearance C may also be established between the rotor side surface8sof the outer rotor8and the transfer side partition part4. Herein, the rotor side surface7sof the inner rotor7and the rotor side surface8sof the outer rotor8are the surfaces perpendicular to the outer circumferential surface.

Therefore, if the inner rotor7and the outer rotor8are trochoidal tooth shaped rotors, then the outer circumferential surface of the inner rotor7will be the tooth surface and the inner circumferential surface of the outer rotor8will be the circumferential side surface. This side clearance C allows fluid to flow between the cell S located above the transfer side partition part4and the shallow groove5which will be discussed later. The width of this side clearance C is appropriately set by the width and depth or the like of the shallow groove5which will be discussed later, and each of these dimensions are not restricted.

Therefore, the clearance which is always between the rotor side surface8sof the outer rotor8and the rotor side surface7sof the inner rotor7and the inside of the housing A (housing body A1and cover A2) in order to allow smooth rotation of the inner rotor7and the outer rotor8inside the rotor chamber1of the housing A may be used as this side clearance C. Furthermore, the side clearance C is a clearance with larger gap dimensions than a normal clearance.

In actuality, the difference between a normal clearance and a clearance with larger gap dimensions may be extremely minimal. Furthermore, the side clearance C allows fluid from the shallow groove5which will be discussed later, but only an extremely small quantity of fluid must gradually be set to the cell S. Therefore, a normal clearance that exists between the housing and the rotor in a standard pump with built-in rotor, is included in the side clearance C. This normal clearance is the clearance necessary for the rotor to rotate smoothly.

Next, as shown inFIG. 3andFIG. 4or the like, a shallow groove5is formed in the transfer side partition part4. The shallow groove5is formed on the transfer side partition part4with a near linear or near stirated configuration extending from the leading edge3aof the discharge port3to the terminal end2bof the intake port2. The shallow groove5is communicated with the discharge port3, but is not communicated with the intake port2. Furthermore, the shallow groove5is formed at a location inside of the circular locus Q formed by the gear bottom part points7bwhen the inner rotor7is rotated, and the shallow groove5does not protrude outside of this circular locus Q. Furthermore, the shallow groove5is formed to be substantially parallel to the arc of the circular locus Q along the inside side of the circular locus Q (Refer toFIG. 2A,FIG. 3,FIG. 4and the like).

Herein, the circular locus Q is defined as the circular locus for the movement of the deepest point7b1of the gear bottom parts7bby the rotation of inner rotor7(Refer toFIG. 1AandFIG. 2A). Furthermore, the shallow groove5does not intersect with the cell S which moves the transfer side partition part4(Refer toFIG. 1andFIG. 2). In other words, the shallow groove5does not enter into the region where the cell S is formed in the transfer side partition part4. Incidentally, the center of the circular locus Q is the center of the boss hole1awhich axially supports the drive shaft9of the inner rotor7. The boss hole1ais formed in the housing A.

As previously stated and as shown inFIG. 2B, the cell S and the shallow groove5are communicated only by the side clearance C, and the fluid is able to flow from the shallow groove5through the side clearance C into the cell S. The outer edge5aon the outside edge of the shallow groove5in the widthwise direction is formed on the inside of the circular locus Q close to the circular locus Q (Refer toFIG. 2A). Therefore, the outer edge5ais formed along the longitudinal direction (direction from the leading edge3aof the discharge port3to the terminal end2bof the intake port2) of the shallow groove5, and the interval to the deepest point7b1of the gear bottom parts7bof the inner rotor7is set to be extremely small.

Specifically, this interval is only a few millimeters, and preferably is less than approximately 1 mm. Therefore the gap dimension of the side clearance C is minimized, and for instance, normally even with a clearance of minimum gap width, the interval between the shallow groove5and the circular locus Q of the gear bottom parts of the inner rotor7which forms the cell S is extremely short, so fluid will reach the cell S relatively quickly and the fluid can be replenished.

Incidentally, the interval between the circular locus Q and the outer edge5ain the widthwise direction of the shallow groove5is not restricted to the aforementioned values, and may be 1 mm or greater depending on the size of the inner rotor7and outer rotor8as well as the gap dimensions of the side clearance C, and these values may be set as appropriate. Furthermore, the shape of the shallow groove5in the longitudinal direction is formed to be a circular arc, but a linear shape is also acceptable. Furthermore, the shallow groove5may be formed by either a cutting operation or aluminum diecast forming.

The leading edge of the shallow groove5in the longitudinal direction is extremely close to the terminal end2bof the intake port2, and when the cell S reaches the transfer side partition part4, the cell S communicates with the shallow groove5through the side clearance C from the initial condition where the side surface of the cell S is enclosed by the transfer side partition part4. The side clearance C is the gap between the transfer side partition part4and the inner rotor7and the outer rotor8, and this gap is extremely small, so the flow of fluid into the cell S from the side clearance C through the shallow groove5will be minimal. However, the fluid transported in the shallow groove5will flow substantially consistently and simultaneously into the cell S along the longitudinal direction of the shallow groove5, and the pressure of the fluid in the cell S will smoothly rise to precisely the proper level (Refer toFIG. 5andFIG. 6).

Furthermore, in the process where the cell S moves from the intake port2side to the discharge port3side on the transfer side partition part4, fluid from the shallow groove5will gradually be transported in minute quantities to the cell S. Therefore, as the cell S moves along the transfer side partition part4, fluid in the discharge port3will be replenished from the shallow groove5depending on the pressure of the fluid which changes pressure in conjunction with the increase or decrease in volume, and this replenishing will gradually transport a minute quantity of fluid, so the pressure rise will be smooth, the plurality of vapor bubbles v which are generated in the fluid will not abruptly collapse (destruct), but rather will gradually shrink and be eliminated.

Therefore, eroding can be prevented, and erosion to the housing A, inner rotor7, and outer rotor8can be prevented. As previously mentioned, the cell S increases in volume and reaches maximum volume while moving the transfer side partition part4from the intake port2side to the discharge port3side, and then decreases in volume, but, through the shallow grove5and the side clearance C, fluid has been gradually flowing into and replenishing the cell S since the internal fluid inside the cell S became a negative pressure prior to reaching the maximum volume (Refer toFIG. 5).

Incidentally, the shallow groove5is usually formed in the transfer side partition part4on the housing body A1side, but if necessary, a construction where the shallow groove5is also formed on the transfer side partition part4on the side where the cover A2is formed is also acceptable. In other words, shallow grooves5,5may be formed on both transfer side partition parts4,4which are formed on both the housing body A1side and the cover A2side, and therefore this construction will allow fluid to flow from both side surfaces of the cell S through both side clearances C, C and both shallow grooves5,5(Refer toFIG. 9). Furthermore, it is also possible that a shallow groove5is not formed on the transfer side partition part4on the housing body A1side, but a shallow groove5is formed on the transfer side partition part4on the cover A2side.

Next, as shown inFIG. 3andFIG. 4, an outer shallow groove6is formed in the transfer side partition part4. The outer shallow groove6is formed on the transfer side partition part4to extend from the leading edge3aof the intake port3to the terminal end2bof the intake port2. The outer shallow groove6is located farther from the rotational center of the inner rotor than the location where the shallow groove5is formed, and the outer groove6is communicated with the discharge port3but not communicated with the intake port2. The outer groove6, on the transfer side partition part, directly intersects and communicates with the region forming the cell S as the cell S approaches the discharge port3(Refer toFIG. 5C).

Furthermore, liquid is discharged from the outer groove6to the discharge port3as the volume of the cell S decreases as the cell S moves along the transfer side partition part4from the intake port2side to the discharge port3side, and the pressure of the fluid enclosed therein rises. Therefore, when the cell S reaches the discharge port3, the fluid in the cell S will not abruptly flow into the discharge port3.

Furthermore, the outer shallow groove6differs in length in the longitudinal direction towards the intake port2side as compared to the shallow groove5, and is formed to be shorter than the longitudinal length of the shallow groove5(Refer toFIG. 1A,FIG. 3A, andFIG. 4). In other words, the shallow groove5and the outer shallow groove6are made to begin functioning at different times, and the construction is such that as the cell S moves along the transfer side partition part4, the fluid will first flow from the shallow groove5through the side clearance C, and later the fluid in the cell S will gradually be discharged from the outer shallow groove6.

Next, the process where the negative pressure of the fluid smoothly increases as the cell S moves along the transfer side partition part4from the intake port2side to the discharge port3side, will be described based onFIG. 5andFIG. 6. First, a suitable cell S reaches the transfer side partition part4and a closed condition is created when both side surfaces of the cell S are enclosed by both transfer side partition parts4, lowering the pressure than that of the fluid on the discharge port side3. The internal fluid becomes negatively pressured, so vapor bubbles v occur because of cavitation and collect at the gear bottom parts7bof the inner rotor7which forms the cell S (Refer toFIG. 5AandFIG. 6A). The fluid pressure inside the cell S is negative, so the fluid in the shallow groove5will enter the cell S through the side clearance C (Refer toFIG. 5B). Furthermore, as the cell S moves to the discharge port3side, the fluid pressure in the cell S which was negative will gradually rise, and the vapor bubbles v will gradually shrink and be eliminated without abruptly collapsing (destructing) (Refer toFIG. 5CandFIG. 6B).

Next, the aforementioned process will be described using the graph ofFIG. 8. First, point (1) on the graph represents the point with negative pressure PI where both sides of the cell S are closed by the transfer side partition part4. At point (1), the shallow groove5and the cell S are communicated through the side clearance C, and fluid gradually flows into the cell S from the shallow groove5through the side clearance C, and the pressure of the fluid in the cell S smoothly rises up to an appropriate pressure P2(Refer to the gradually rising bold line).

Next, point (3) represents the location where the cell S which had been closed by the transfer side partition part4becomes communicated with the outer shallow groove6, and the vapor bubbles v are gradually reduced (without abruptly collapsing (destructing)) because of the smooth pressure rise (between points (1) and (3)), and the collapsing force (impact of destruction) of the vapor bubbles v created by cavitation can be reduced. Incidentally, a plurality of vapor bubbles v which have collected around the gear bottom parts of the inner rotor7are eliminated in between points (1) and (3).

The dotted line in the figure represents the pressure change attributed to the shallow groove5and the outer shallow groove6. At point (2), the cell S which is communicated with the shallow groove5through the side clearance C at the transfer side partition part4becomes communicated with the outer shallow groove6through the side clearance C as the cell S approaches the outer shallow groove6. At this time, the cell S will be communicated with the outer shallow groove6after the fluid pressure in the cell S has been gradually increased because of the shallow groove5, and therefore the cell S can be communicated with the outer shallow groove6without an abrupt pressure change (P3) at point (3).

The present invention provides a shallow groove5in order to relieve an abrupt rise in fluid pressure, prevents cavitation collapse (destruction), and can increase the durability of the pump. With the present invention, vapor bubbles v caused by cavitation can be eliminated even by using only the shallow groove5. Furthermore, by using the shallow groove5together with an outer shallow groove6, vapor bubbles v which occur in the fluid inside the cell S can more positively be eliminated.

Incidentally, the outer shallow groove6is preferably formed in the transfer side partition part4to intersect with the gear bottom parts of the outer rotor8, and is preferably formed as far to the outside as possible from the location of the gear bottom parts of the inner rotor7, or in other words the circular locus Q. Furthermore, when the cell S is communicated with the outer shallow groove6, replenishing of fluid from the shallow groove5is not necessary, so the shallow groove5is not required to be in a position close to the gear bottom circle of the inner rotor7in the transport path of the cell S.

If the fluid is discharged by the outer shallow groove6, the shape of the shallow groove5may be as shown below. FirstFIG. 7Ashows an embodiment where the shallow groove5gradually separates from the circular locus Q when approaching the leading edge3aof the discharge port3.FIG. 7Bshows an embodiment where the shallow groove5moves away from the circular locus Q as the shallow groove5approaches the leading edge3aof the discharge port3and the region which is moving away is linear.FIG. 7Cshows an embodiment where the shallow groove5moves away from the circular locus Q as the shallow groove5approaches the leading edge3aof the discharge port3, and particularly the region which is moving away is shortened.

Furthermore, with the present invention, the transfer side partition part4was disclosed to be located at a lagging angle, but this is not an absolute restriction. Furthermore, the shallow groove5is communicated with the cell S through the side clearance C when the cell S is closed by the transfer side partition part4, but the invention also includes the case where the cell S is communicated with the shallow groove5when the cell S is at the maximum partitioned volume.

A comparison of the present invention and conventional technology is shown inFIG. 10andFIG. 11.FIG. 10shows the present invention, andFIG. 11shows the conventional technology. With the present invention, as shown inFIG. 10A, the cell S and the shallow groove5do not intersect. On the other hand, with the conventional technology, as shown inFIG. 11A, the inside of the cell and the shallow groove do intersect and are directly communicated. Furthermore, with the present invention, as shown inFIG. 10B, the inside of the cell S is communicated with the shallow groove5through the side clearance C, so the pressurized fluid from the discharge port3will gradually flow from the shallow groove5through the side clearance C in with the internal fluid at negative pressure.

Furthermore, the negative pressure of the internal fluid (−P) will gradually and smoothly change to become positive pressure (+P). Therefore, as shown inFIG. 10C, the vapor bubbles v will gradually become pressurized by the surrounding fluid, and will eventually disappear. With the conventional technology, as shown inFIG. 11B, a local pressure change will occur the moment the cell intersects with the shallow groove, and the negative pressure (−P) of the internal fluid will abruptly change to positive pressure (+P).

Therefore, as shown inFIG. 11C, the vapor bubbles v will abruptly be pressurized by the fluid and will collapse (destruct), and this impact will create erosion which causes impact scarring on the rotors and the inside of the housing. In this manner, the present invention can prevent erosion by gradually eliminating the vapor bubbles v formed because of cavitation, but the conventional technology can not prevent erosion from occurring.