Combination bearing and electronic water pump adopting combination bearing
By injection molding an engineering plastic wear-resistant contact layer onto a copper bushing substrate, a combined bearing structure was developed, which solved the problem of oilless bearing failure at high temperatures and high speeds, enabling stable use and cost reduction under special working conditions.
Patent Information
- Application Number
- CN202423144874.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-19
- Publication Date
- 2025-12-23
- Estimated Expiration
- 2034-12-19
AI Technical Summary
Existing oilless bearings are prone to failure under high temperature, high speed and high torque conditions. Traditional materials cannot meet the requirements under special working conditions and have high production costs.
The bearing adopts a combined structure of copper bushing base and wear-resistant contact layer. The copper bushing base is integrally formed by sintered honeycomb copper, and the wear-resistant contact layer is formed by injection molding of engineering plastic onto the inner ring sidewall of the copper bushing base to form a wear-resistant contact surface. The combination of protrusions and holes improves the bonding strength and reduces the coefficient of thermal expansion.
Under conditions without lubrication, the combined bearing can maintain a low coefficient of expansion at high speed and high temperature, meeting the requirements of various working conditions, reducing production costs, and is suitable for electronic water pumps.
Smart Images
Figure CN223707937U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the technical field of rotary connection, and in particular to a combined bearing and an electronic water pump using the same. Background Technology
[0002] Oilless bearings are indispensable in the transmission fields of various mechanical equipment. Traditional oilless bearings can be broadly categorized into three types: The first type uses a steel bushing coated with PTFE / PEEK. However, due to the limited formulation of the surface coating material, this type cannot meet the operating conditions under special environments with high temperature, high speed, and high torque. The second type uses pure graphite and graphite composite materials. Pure graphite bearings are relatively expensive and can only be manufactured through machining to achieve their structure and dimensions, resulting in a limited manufacturing process and making it impossible to produce complex structures. The third type uses composite material bearings. The disadvantage of this type is that the material has a high coefficient of thermal expansion under high speed and high temperature, making it prone to seizing and causing bearing failure. Utility Model Content
[0003] To overcome the above-mentioned defects, this utility model provides a combined bearing and an electronic water pump using the same. The combined bearing has the characteristics of simple structure, corrosion resistance and low coefficient of thermal expansion. The electronic water pump using the combined bearing can dry rub for more than 30 minutes without lubricating medium and can be used in special working conditions.
[0004] The technical solution adopted by this utility model to solve its technical problem is: a combined bearing, including a copper sleeve base and a wear-resistant contact layer, wherein the wear-resistant contact layer formed of engineering plastic is fixedly composited on the inner ring side wall surface of the copper sleeve base, and the inner side surface of the wear-resistant contact layer forms the sliding contact surface of the bearing.
[0005] As a further improvement of this utility model, the copper sleeve substrate is a sintered honeycomb copper integral molding structure, which forms a number of holes on the surface of the copper sleeve substrate and inside the material. The outer circumferential surface of the wear-resistant contact layer has a number of connecting protrusions that extend into the holes on the inner ring sidewall of the copper sleeve substrate.
[0006] As a further improvement of this utility model, the wear-resistant contact layer is an engineering plastic integrally molded onto the surface of the inner ring sidewall of the copper sleeve substrate by injection molding.
[0007] As a further improvement of this utility model, the wear-resistant contact layer is a PEEK, PAI and PPS material layer integrally formed on the surface of the inner ring sidewall of the copper sleeve substrate.
[0008] As a further improvement of this utility model, the copper sleeve substrate is a T-shaped sleeve with one end having a larger outer diameter than the other end, and the wear-resistant contact layer is fixedly covered on the inner ring side wall surface of the copper sleeve substrate and the end face with the larger diameter.
[0009] An electronic water pump includes a pump housing, a motor, a drive shaft, a sliding block, an upper thrust bearing, a lower thrust bearing, a first combined bearing, and a second combined bearing. The motor is fixedly installed inside one end of the pump housing, and a chamber is formed inside the other end of the pump housing. The chamber has an inlet channel communicating with an inlet pipe and an outlet channel communicating with an outlet pipe, spaced apart. The drive shaft is rotatable circumferentially but axially stopped, inserted into the pump housing. One end of the drive shaft is connected to the motor's power output end, and the other end of the drive shaft passes through the chamber with a dynamic seal. The sliding block is fixedly sleeved on the outside of the drive shaft and rotates with the drive shaft. The system can continuously supply water from the inlet channel of the chamber to the outlet channel of the chamber. The upper thrust bearing and the lower thrust bearing are respectively fixedly installed in the axial ends of the chamber, and the sliding contact surfaces of the upper thrust bearing and the lower thrust bearing respectively contact the axial end faces of the sliding block to provide axial support. The first combined bearing and the second combined bearing are respectively fixedly installed in the axial ends of the chamber. The other end of the drive shaft is rotatably inserted into the first combined bearing and the second combined bearing. The wear-resistant contact layer formed by engineering plastic on the inner side of the first combined bearing and the second combined bearing contacts the outer circumferential surface of the other part of the drive shaft to provide rotational support.
[0010] As a further improvement of this utility model, a first support block and a second support block are fixedly installed at intervals inside one end of the pump body shell. The motor is fixedly accommodated in the space between the first support block and the second support block. A third combined bearing and a fourth combined bearing are fixedly installed in the first support block and the second support block, respectively. A section of the transmission shaft passes sequentially through the third combined bearing, the inner hole of the motor, and the fourth combined bearing. The wear-resistant contact layer formed by engineering plastic on the inner side of the third combined bearing and the fourth combined bearing contacts the outer circumferential surface of a section of the transmission shaft to provide rotational support.
[0011] As a further improvement of this utility model, one end of the drive shaft has a radially contracted first end, and the other end of the drive shaft has a diameter-expanding second end. A first limiting block is fixedly installed on one end of the second support block. A T-shaped limiting hole with one end inner diameter smaller than the other end inner diameter is formed in the first limiting block. One end of the drive shaft is inserted into the T-shaped limiting hole of the first limiting block, and the stepped surface formed by the first end of the drive shaft stops on the inner step of the T-shaped limiting hole of the first limiting block. A countersunk structure is provided on the other end face of the chamber. A second limiting block is inserted in the countersunk structure. A T-shaped groove is formed in the second limiting block. The other end of the drive shaft is inserted into the T-shaped groove of the limiting block, and the end of the other end of the drive shaft stops on the inner step of the T-shaped groove of the limiting block.
[0012] As a further improvement of this utility model, a limiting sleeve is fixedly sleeved on the outer side of the middle section of the transmission shaft between the first support block and the chamber. A limiting thrust bearing is installed on the end face of the chamber facing the first support block. The end face of the limiting sleeve facing the chamber contacts and limits the sliding contact surface of the limiting thrust bearing.
[0013] As a further improvement of this utility model, the pump body shell includes a shell body, a chamber bottom plate, and a chamber plug. The shell body is a cylindrical structure with one end having a smaller inner diameter than the other end. The chamber bottom plate is circumferentially inserted into the end of the shell body with the larger inner diameter. A radially expanding stepped ring is formed on the outer circumference of the chamber bottom plate. The stepped ring is in sealing contact with the inner surface of the shell body and stops on the stepped surface formed between the two ends of the shell body. The end face of the chamber bottom plate facing the other end of the pump body shell is in close contact with the axial end face of the lower thrust bearing. A water inlet hole is formed on the wall, and a water inlet channel extending radially and axially is formed inside the stepped ring. One end of the water inlet channel is connected to the water inlet hole on the side wall of the outer shell body, and the other end of the water inlet channel can be intermittently connected to the water passage on the sliding block. The chamber plug is fixedly installed on the other end of the outer shell body by a threaded structure. The end face of the chamber plug at one end is tightly abutted against the other end face of the thrust bearing axially. A water outlet channel is formed inside the chamber plug. The water outlet channel is intermittently connected to the water passage on the sliding block, and the water passage on the sliding block is alternately connected to the water supply channel and the water outlet channel.
[0014] The beneficial effects of this utility model are as follows: This utility model uses in-mold injection molding to form a wear-resistant contact layer of special engineering plastic material on the inner ring surface of the sintered honeycomb copper sleeve matrix. The wear-resistant contact layer is firmly bonded to the copper sleeve matrix and is not easy to fall off after long-term use. Moreover, by utilizing the material stability of the sintered honeycomb copper sleeve matrix, the wear-resistant contact layer can maintain a low coefficient of expansion under high speed and high temperature conditions. Furthermore, by utilizing the properties of special engineering plastics, this type of bearing can meet the needs of various working conditions. In addition, this type of bearing has a simple structure, can be mass-produced, and reduces the production cost of the bearing. Compared with pure graphite bearings, it has a significant cost advantage. When this bearing is applied to an electronic water pump, this type of combined bearing provides rotational support for the drive shaft of the electronic water pump. Even without a lubricating medium, it can withstand dry friction for more than 30 minutes without damage, making this type of electronic water pump suitable for various special working conditions. Attached Figure Description
[0015] Figure 1 This is a front view of the combined bearing of this utility model;
[0016] Figure 2 This is a top view of the combined bearing of this utility model.
[0017] Figure 3 for Figure 2 Sectional view along line AA;
[0018] Figure 4 This is a front view of the electronic water pump of this utility model;
[0019] Figure 5 for Figure 4 Sectional view along the BB direction;
[0020] Figure 6 for Figure 5 Enlarged view of section C. Detailed Implementation
[0021] Example: A composite bearing includes a copper bushing base 1 and a wear-resistant contact layer 2. The wear-resistant contact layer 2, formed of engineering plastic, is fixedly bonded to the inner ring sidewall surface of the copper bushing base 1. The inner surface of the wear-resistant contact layer 2 forms the sliding contact surface of the bearing.
[0022] The material stability of the copper bushing substrate 1 allows the wear-resistant contact layer 2 to maintain a low coefficient of expansion under high speed and high temperature conditions. By utilizing the properties of special engineering plastics, it can meet the needs of various working conditions. Moreover, this structure can be mass-produced, reducing the production cost of the bearing and giving it a significant cost advantage compared to pure graphite bearings.
[0023] The copper sleeve substrate 1 is a sintered honeycomb copper integral molding structure. This structure creates a plurality of porous structures 101 on the surface and inside the material of the copper sleeve substrate 1. The outer circumferential surface of the wear-resistant contact layer 2 has a plurality of bonding protrusions extending into the porous structures 101 on the inner ring sidewall of the copper sleeve substrate 1. The sintered honeycomb copper has numerous honeycomb-shaped porous structures 101 inside and on the surface. When the engineering plastic molded wear-resistant contact layer 2 is bonded to the inner ring surface of the copper sleeve substrate 1, the bonding protrusions and porous structures 101 can interact to improve the bonding strength between the wear-resistant contact layer 2 and the copper sleeve substrate 1. Long-term use will not cause the wear-resistant contact layer 2 to detach. Furthermore, this type of copper sleeve substrate 1 has a lower coefficient of thermal expansion and higher stability in use.
[0024] The wear-resistant contact layer 2 is an engineering plastic integrally molded onto the inner ring sidewall surface of the copper sleeve substrate 1 by injection molding. This structure can ensure the bonding strength between the wear-resistant contact layer 2 and the copper sleeve substrate 1, and has high molding precision, high production efficiency, and low production cost. It can be molded from various engineering plastics to meet various working conditions.
[0025] The wear-resistant contact layer 2 is a layer of PEEK, PAI, and PPS materials integrally molded on the inner ring sidewall surface of the copper sleeve substrate 1. This type of engineering plastic has good wear resistance and material stability.
[0026] The copper sleeve substrate 1 is a T-shaped sleeve with one end having a larger outer diameter than the other end. The wear-resistant contact layer 2 is fixedly covered on the inner ring sidewall surface of the copper sleeve substrate 1 and the end face with the larger diameter.
[0027] An electronic water pump includes a pump housing, a motor 4, a drive shaft 5, a sliding block 6, an upper thrust bearing 7, a lower thrust bearing 8, a first combined bearing 9, and a second combined bearing 10. The motor 4 is fixedly installed inside one end of the pump housing, and a chamber is formed inside the other end of the pump housing. The chamber has an inlet channel 11 communicating with an inlet pipe and an outlet channel 12 communicating with an outlet pipe, which are spaced apart. The drive shaft 5 is rotatable in the circumferential direction and axially stopped, and is inserted into the pump housing. One end of the drive shaft 5 is connected to the power output end of the motor 4, and the other end of the drive shaft 5 passes through the chamber in a dynamic seal. The sliding block 6 is fixedly sleeved on the outside of the drive shaft 5 and rotates with the drive shaft 5. Water from the inlet channel 11 of the chamber is continuously fed into the outlet channel 12 of the chamber. The upper thrust bearing 7 and the lower thrust bearing 8 are respectively fixedly installed in the axial ends of the chamber, and the sliding contact surfaces of the upper thrust bearing 7 and the lower thrust bearing 8 respectively contact the axial end faces of the sliding block 6 to provide axial support. The first combined bearing 9 and the second combined bearing 10 are respectively fixedly installed in the axial ends of the chamber. The other end of the drive shaft 5 is rotatably inserted into the first combined bearing 9 and the second combined bearing 10, and the wear-resistant contact layer 2 formed of engineering plastic on the inner side of the first combined bearing 9 and the second combined bearing 10 contacts the other circumferential outer side of the drive shaft 5 to provide rotational support.
[0028] During operation, motor 4 drives transmission shaft 5 to rotate continuously, which in turn drives sliding block 6 to rotate. The rotation of sliding block 6 continuously discharges water from inlet channel 11 into outlet channel 12. The drainage principle of sliding block 6 can be varied. For example, multiple blades can be formed on sliding block 6, which continuously push water as sliding block 6 rotates. Sliding block 6 can also be an eccentric or non-circular structure, with several radially elastically extending blades evenly spaced on it. The ends of the blades dynamically seal against the inner wall of the cavity. A moving arc-shaped sealing cavity is formed between the outer circumference of sliding block 6, the inner wall of the cavity, the upper thrust bearing 7, and the lower thrust bearing 8. This arc-shaped sealing cavity first contacts the inlet channel as it rotates. The water inlet channel 11 is connected to the water outlet channel 12. After the water inlet channel 11 is drawn in, the sliding block 6 continues to rotate at a certain angle, and the arc-shaped sealing cavity is connected to the water outlet channel 12. The water in the arc-shaped sealing cavity is discharged into the water outlet channel 12 to achieve water discharge. The sliding block 6 is driven by the drive shaft 5 to rotate continuously, thus realizing continuous water pumping. During the rotation of the drive shaft 5, it is supported by the combined bearing. Through testing, it has been proven that when this structure is used in the electronic water pump of new energy vehicles, the drive shaft 5 can be dry-rubbed for more than 30 minutes without damage, even without lubrication medium. Therefore, this type of electronic water pump with combined bearing for rotational support can be used in various special operating conditions.
[0029] A first support block 13 and a second support block 14 are fixedly installed at intervals inside one end of the pump body shell. The motor 4 is fixedly accommodated in the space between the first support block 13 and the second support block 14. A third combined bearing 15 and a fourth combined bearing 16 are fixedly installed in the first support block 13 and the second support block 14, respectively. A section of the drive shaft 5 passes sequentially through the third combined bearing 15, the inner hole of the motor 4, and the fourth combined bearing 16. The wear-resistant contact layer 2 formed of engineering plastic on the inner side of the third combined bearing 15 and the fourth combined bearing 16 contacts the outer circumferential surface of a section of the drive shaft 5 to provide rotational support. The motor 4 is accommodated in the gap between the first support block 13 and the second support block 14. The first support block 13 and the second support block 14 are preferably sealed to the pump body shell, which can achieve a sealing and waterproof effect, effectively protecting the motor 4. At the same time, the third combined bearing 15 and the fourth combined bearing 16 in the first support block 13 and the second support block 14 provide effective rotational support for a section of the drive shaft 5, ensuring smooth rotation of the drive shaft 5.
[0030] One end of the drive shaft 5 has a radially contracting first end 51, and the other end has a second end 52 with an outwardly expanding diameter. A first limiting block 17 is fixedly installed on one end of the second support block 14. A T-shaped limiting hole with one end having a smaller inner diameter than the other end is formed within the first limiting block 17. One end of the drive shaft 5 is inserted into the T-shaped limiting hole of the first limiting block 17, and the stepped surface formed by the first end 51 of the drive shaft 5 stops on the inner step of the T-shaped limiting hole of the first limiting block 17. A countersunk structure is provided on the other end face of the chamber, and a second limiting block 18 is inserted into the countersunk structure. A T-shaped groove is formed within the second limiting block 18, and the other end of the drive shaft 5 is inserted into the T-shaped groove of the limiting block, stopping on the inner step surface of the T-shaped groove of the limiting block. This structure achieves axial stopping and positioning of the drive shaft 5, is simple in structure, provides precise positioning of the drive shaft 5, and is easy to assemble.
[0031] A limiting sleeve 19 is fixedly fitted on the outer side of the intermediate section of the drive shaft 5 between the first support block 13 and the chamber. A limiting thrust bearing 20 is installed on the end face of the chamber facing the first support block 13. The end face of the limiting sleeve 19 facing the chamber contacts the sliding contact surface of the limiting thrust bearing 20 for limiting. The limiting sleeve 19 can be fixed to the drive shaft 5 by a threaded connection, which facilitates the adjustment of the axial position of the limiting sleeve 19, ensures the accurate position of the sliding block 6, and also effectively protects and strengthens the drive shaft 5, preventing bending and deformation. The end of the limiting sleeve 19 that contacts the limiting thrust bearing 20 should ideally have a structure with an increased radial dimension to ensure the contact area.
[0032] The pump housing includes a housing body 3, a chamber bottom plate 21, and a chamber plug 22. The housing body 3 is a cylindrical structure with one end having a smaller inner diameter than the other. The chamber bottom plate 21 is circumferentially inserted into the end of the housing body 3 with the larger inner diameter. A radially expanding stepped ring is formed on the outer circumference of the chamber bottom plate 21. The stepped ring is in sealing contact with the inner side of the housing body 3 and stops on the stepped surface formed between the two ends of the housing body 3. The end face of the chamber bottom plate 21 facing the other end of the pump housing is in close contact with the axial end face of the lower thrust bearing 8. A water inlet hole 31 is formed on the side wall of the housing body 3. A water inlet channel 11 extending radially and axially is formed within the stepped ring. One end of the water inlet channel 11 communicates with the water inlet hole 31 on the side wall of the outer shell body 3, and the other end of the water inlet channel 11 can intermittently communicate with the water passage on the sliding block 6. The chamber plug 22 is fixedly installed at the other end of the outer shell body 3 by a threaded structure, with one end face of the chamber plug 22 tightly abutting against the other end face of the upper thrust bearing 7 axially. A water outlet channel 12 is formed inside the chamber plug 22, and the water outlet channel 12 intermittently communicates with the water passage on the sliding block 6. The water passage on the sliding block alternately communicates with the water supply channel and the water outlet channel 12. The pump body outer shell adopts a split assembly structure, which is convenient for manufacturing and assembly.
Claims
1. A composite bearing, characterized in that: It includes a copper bushing substrate (1) and a wear-resistant contact layer (2). The wear-resistant contact layer, formed of engineering plastic, is fixedly bonded to the inner ring sidewall surface of the copper bushing substrate. The inner side of the wear-resistant contact layer forms the sliding contact surface of the bearing.
2. The combined bearing according to claim 1, characterized in that: The copper sleeve substrate is a sintered honeycomb copper integral molding structure, which forms a number of hole structures (101) on the surface of the copper sleeve substrate and inside the material. The wear-resistant contact layer has a number of connecting protrusions on the outer circumference of the outer surface of the outer surface of the outer surface of the outer surface of the outer surface of the outer surface of the copper sleeve substrate that extend into the hole structure on the inner ring sidewall of the outer surface ...
3. The combined bearing according to claim 1 or 2, characterized in that: The wear-resistant contact layer is an engineering plastic integrally molded onto the inner ring sidewall surface of the copper sleeve substrate by injection molding.
4. The combined bearing according to claim 3, characterized in that: The wear-resistant contact layer is a PEEK, PAI and PPS material layer integrally formed on the inner ring sidewall surface of the copper sleeve substrate.
5. The combined bearing according to claim 1, characterized in that: The copper sleeve substrate is a T-shaped sleeve with one end having a larger outer diameter than the other end. The wear-resistant contact layer is fixedly covered on the inner ring sidewall surface of the copper sleeve substrate and the end face with the larger diameter.
6. An electronic water pump, characterized in that: The combined bearing according to claim 1 includes a pump housing, a motor (4), a drive shaft (5), a sliding block (6), an upper thrust bearing (7), a lower thrust bearing (8), a first combined bearing (9), and a second combined bearing (10). The motor is fixedly installed inside one end of the pump housing, and a chamber is formed inside the other end of the pump housing. The chamber has an inlet channel (11) connected to the inlet pipe and an outlet channel (12) connected to the outlet pipe, which are spaced apart. The drive shaft is rotatable in the circumferential direction and axially stopped, and one end of the drive shaft is connected to the power output end of the motor. The other end of the drive shaft passes through the chamber in a dynamic seal. The sliding block is fixed. Sleeveted on the outside of the drive shaft, the sliding block rotates with the drive shaft to continuously deliver water from the inlet channel of the chamber to the outlet channel of the chamber. The upper thrust bearing and the lower thrust bearing are respectively fixedly installed in the axial ends of the chamber, and the sliding contact surfaces of the upper thrust bearing and the lower thrust bearing respectively contact the axial end faces of the sliding block to provide axial support. The first combined bearing and the second combined bearing are respectively fixedly installed in the axial ends of the chamber. The other end of the drive shaft is rotatably inserted into the first combined bearing and the second combined bearing, and the wear-resistant contact layer formed by engineering plastic on the inner side of the first combined bearing and the second combined bearing contacts the outer circumferential surface of the other part of the drive shaft to provide rotational support.
7. The electronic water pump according to claim 6, characterized in that: The pump body housing is also fixedly installed with a first support block (13) and a second support block (14) at intervals. The motor is fixedly housed in the space between the first support block and the second support block. The first support block and the second support block are respectively fixedly installed with a third combined bearing (15) and a fourth combined bearing (16). A section of the drive shaft passes sequentially through the third combined bearing, the inner hole of the motor and the fourth combined bearing. The wear-resistant contact layer formed by engineering plastic on the inner side of the third combined bearing and the fourth combined bearing contacts the outer circumferential surface of a section of the drive shaft to provide rotational support.
8. The electronic water pump according to claim 7, characterized in that: One end of the drive shaft has a radially contracted first end (51), and the other end of the drive shaft has a diameter-expanding second end (52). A first limiting block (17) is fixedly installed on one end of the second support block. A T-shaped limiting hole with an inner diameter smaller than that of the other end is formed in the first limiting block. One end of the drive shaft is inserted into the T-shaped limiting hole of the first limiting block, and the stepped surface formed by the first end of the drive shaft stops on the inner step of the T-shaped limiting hole of the first limiting block. A countersunk structure is provided on the other end face of the chamber. A second limiting block (18) is inserted in the countersunk structure. A T-shaped groove is formed in the second limiting block. The other end of the drive shaft is inserted into the T-shaped groove of the limiting block, and the end of the other end of the drive shaft stops on the inner step of the T-shaped groove of the limiting block.
9. The electronic water pump according to claim 8, characterized in that: A limiting sleeve (19) is fixedly sleeved on the outer side of the middle section of the drive shaft between the first support block and the chamber. A limiting thrust bearing (20) is installed on the end face of the chamber facing the first support block. The end face of the limiting sleeve facing the chamber contacts and limits the sliding contact surface of the limiting thrust bearing.
10. The electronic water pump according to claim 6, characterized in that: The pump body housing includes a housing body (3), a chamber bottom plate (21), and a chamber plug (22). The housing body is a cylindrical structure with one end having a smaller inner diameter than the other end. The chamber bottom plate is circumferentially inserted into the end of the housing body with the larger inner diameter. A radially expanding stepped ring is formed on the outer circumference of the chamber bottom plate. The stepped ring is in sealed contact with the inner surface of the housing body and is stopped on the stepped surface formed between the two ends of the housing body. The end face of the chamber bottom plate facing the other end of the pump body housing is in close contact with the axial end face of the lower thrust bearing. A ring is formed on the side wall of the housing body. There is a water inlet hole (31), and a water inlet channel extending radially and axially is formed in the stepped ring. One end of the water inlet channel is connected to the water inlet hole on the side wall of the outer shell body, and the other end of the water inlet channel can be intermittently connected to the water passage on the sliding block. The chamber plug is fixedly installed on the other end of the outer shell body by a threaded structure. The end face of the chamber plug at one end is tightly abutted against the other end face of the upper thrust bearing axially. A water outlet channel is formed in the chamber plug. The water outlet channel is intermittently connected to the water passage on the sliding block, and the water passage on the sliding block is alternately connected to the water supply channel and the water outlet channel.