Sealing transmission shaft assembly of screw drill

Abstract

The utility model discloses a sealing transmission shaft assembly of a screw drill, which overcomes the technical defect that the sealing pressure of sealing elements in an upper sealing assembly and a lower sealing assembly in the sealing transmission shaft assembly of the screw drill cannot be adjusted. Which comprises a bearing lubrication cavity and sealing combination structures located at the two ends of the bearing lubrication cavity, and is characterized in that each sealing combination structure comprises a pressing ring and a V-shaped combination sealing ring assembly, and the V-shaped combination sealing ring assemblies are arranged between a bearing inner sleeve and a bearing shell and are in dynamic sealing fit; the pressing ring is connected with the bearing shell in a threaded fit mode and abuts against the V-shaped combined sealing ring assembly. V-shaped combined sealing rings and pressing rings are designed at the two ends of a sealing cavity of the screw drill. The elastic deformation of the V-shaped combined sealing ring can be adjusted through the supporting ring and the pressing ring.

Description

Technical Field

[0001] The utility model relates to the technical field of screw drill sealing transmission shaft assemblies. Background Art

[0002] The existing conventional screw drill drive shaft assembly can be divided into open drive shaft assembly and sealed drive shaft assembly according to the sealing structure. In the open drive shaft assembly, the TC bearing and thrust bearing are lubricated and cooled by mud, but the mud contains impurities with strong abrasive properties such as fine sand. Therefore, the internal parts of the drive shaft are easily eroded and corroded by the mud, and the life of the drive shaft is relatively short.

[0003] The sealed transmission shaft assembly is to set a sealing component on the outside of the TC bearing and the thrust bearing group. For example, the patent application document 201811520305.X discloses a screw drill transmission shaft assembly, which clearly states that the transmission shaft and the lower housing, upper housing, upper sealing assembly, lower sealing assembly, lower sleeve, and upper sleeve are combined to form a closed space, wherein the upper sealing assembly is composed of an upper piston, a shaft seal, a hole seal, and an O-ring; the lower sealing assembly is composed of a lower piston, a shaft seal, a hole seal, and an O-ring. That is, by setting the upper sealing assembly and the lower sealing assembly, sand-containing mud is prevented from entering the above-mentioned closed space, so that the TC bearing and the thrust bearing group can be protected.

[0004] Similar patent documents include 201110261917.3, which also introduces a screw drill drive shaft assembly.

[0005] In summary, the search of relevant patent documents mainly introduces the sealing mechanisms of different sealing forms, but none of them mentions the adjustable sealing pressure function. In other words, there is no clear record as to whether the sealing performance of the seals in the upper sealing assembly and the lower sealing assembly is adjustable. Utility Model Content

[0006] In order to solve the deficiencies of the prior art, the utility model provides a screw drill sealing transmission shaft assembly, which mainly solves the technical defect that the sealing pressure of the sealing components in the upper sealing assembly and the lower sealing assembly in the screw drill sealing transmission shaft assembly cannot be adjusted.

[0007] The technical solution adopted by the utility model to solve its technical problems is:

[0008] The screw drill sealed transmission shaft assembly includes a bearing lubrication cavity and a sealing combination structure located at both ends of the bearing lubrication cavity, and is characterized in that: the sealing combination structure includes a clamping ring and a V-shaped combined sealing ring assembly, wherein the V-shaped combined sealing ring assembly is arranged between the bearing inner sleeve and the bearing shell and performs dynamic sealing cooperation; the sealing clamping ring is connected to the bearing shell through threaded cooperation, and abuts against the V-shaped combined sealing ring assembly, and the sealing of the sealing combination structure is adjusted by torque.

[0009] The V-shaped combined sealing ring assembly comprises a pressure ring at both ends, a support ring and a rubber ring between the pressure ring and the support ring. The hardness of the pressure ring and the support ring is greater than that of the rubber ring.

[0010] The rubber ring is composed of a plurality of sub-bodies with V-shaped cross sections, and the V-shaped matching surface of each sub-body faces the opposite direction of the bearing lubrication cavity.

[0011] A C-shaped notch is arranged at the V-shaped matching surface.

[0012] The sealing assembly structure comprises an upper sealing assembly structure and a lower sealing assembly structure, which are arranged at two ends of the bearing lubrication cavity.

[0013] An elastic compensation element is arranged between the clamping ring and the V-shaped combined sealing ring assembly.

[0014] The bearing in the bearing lubrication cavity is a combination of a TC bearing, a thrust bearing or / and a ball bearing.

[0015] The bearing lubrication cavity is provided with an oil filling port and a sealing screw seal.

[0016] The beneficial effects of the utility model are:

[0017] In the newly designed screw drill seal transmission shaft assembly with adjustable sealing pressure, the seals in the upper and lower sealing combination structures are changed to V-type combination sealing rings, that is, by designing V-type combination sealing rings, pressure rings, support rings and clamping rings at both ends of the screw drill seal cavity, the elastic deformation of the V-type combination sealing ring can be adjusted. Among them, the V-type combination sealing ring assembly is molded from rubber, and the rubber material generally uses NBR (nitrile rubber). The pressure ring and support ring are generally pressed with hard plastic. The combination of soft and hard can provide good stability and good wear resistance, and can prevent the sealing ring from being squeezed into the gap. Even under harsh conditions, such as axial or radial vibration, sudden pressure, temperature changes, etc., it can still provide the best sealing effect.

[0018] Specific components in the sealing combination structure, such as the upper bearing shell and the lower bearing shell, are designed with oil filling holes, which can fill the gaps of TC bearings, thrust bearings, etc. with lubricating oil, and the sealing cavity where the bearing is located maintains internal and external pressure balance through lubricating oil filling, which not only avoids erosion of bearings and other parts caused by the entry of sand-containing mud, but also provides a lubricating environment to keep the bearings in the best lubrication state. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a full cross-sectional view of the first embodiment.

[0020] Figure 2 for Figure 1 Partial view of the upper middle section.

[0021] Figure 3 for Figure 1 Partial view of the middle section.

[0022] Figure 4 for Figure 1 Partial view of the lower middle section.

[0023] Figure 5 It is a cross-sectional view of the upper radial bearing sleeve.

[0024] Figure 6 A cross-sectional view of the lower bearing shell.

[0025] Figure 7 This is a cross-sectional view of the lower seal adjustment clamping ring.

[0026] Figure 8 A cross-sectional view of the upper bearing shell.

[0027] Fig. 9 A half-section view of the main axis.

[0028] Fig.10 This is the first local structural scheme of the sealing section in the second embodiment.

[0029] Fig.11 This is the second local structural scheme of the sealing section in the second embodiment.

[0030] Fig.12 This is the third local structural scheme of the sealing section in the second embodiment. DETAILED DESCRIPTION

[0031] Embodiment 1

[0032] In conjunction with the instruction manual Figure 1 To Attachment Fig. 9 This embodiment is described in detail.

[0033] The screw drill seal transmission shaft assembly has a main shaft 100 located in the center, and the upper and lower ends of the main shaft 100 are connection ends. Figure 1 and Fig. 9 In the figure, the top of the main shaft 100 is the tail, which is provided with a first threaded section 101, and the tail is used to install a water cap (not shown in the figure), the head is an enlarged structure 103, the middle is a stepped shaft, and a second threaded section 102 is provided in the middle section, and the steps are arranged step by step from top to bottom. In the art, this is also the normal form of the main shaft in the art.

[0034] Near the head of the spindle 110, an annular spindle gasket 110 is sleeved from top to bottom. The spindle gasket is a circular ring-type component. In terms of structural features, the cross-section of the annular spindle gasket 110 is a Z-shaped, and the upper part of the spindle gasket fits the spindle, that is, a conventional mechanical transition fit. The lower end face of the spindle gasket 110 is an annular plane, and effectively abuts against the head end face of the spindle, that is, the enlarged end face of the head is matched with the spindle gasket through the annular surface, which is a transition support component.

[0035] Above the spindle gasket 110 and sleeved on the spindle is a lower sealing assembly consisting of a lower radial bearing inner sleeve 210, a lower bearing shell 220, a lower sealing adjustment clamping ring 230, and a V-shaped combined sealing ring assembly 240, which constitutes a lower section sealing assembly structure. The lower sealing assembly is located at the lower end of the sealing cavity. Among them, the lower radial bearing inner sleeve 210 and the lower bearing shell 220 are arranged in pairs, the lower radial bearing inner sleeve 210 is located on the inner side, and the lower bearing shell 220 is located on the outer side, and the two have the same size in the length direction. The lower radial bearing inner sleeve 210 is a cylindrical structure with equal cross-sections above and below, that is, the wall thickness is designed with equal thickness. The carcass of the lower radial bearing inner sleeve 210 is a cemented carbide material, and the outer surface is covered with a wear-resistant layer, for example, a wear-resistant layer can be a tungsten carbide surface layer (composite material). In this embodiment, the tungsten carbide surface layer is a through-covering on the carcass, which is an integrated structure. Optimally, in this embodiment, the tungsten carbide surface layer runs through the lower radial bearing inner sleeve 210, specifically along the length direction. Unlike the lower radial bearing inner sleeve, the lower bearing shell 220 is designed with a non-uniform cross-section. Figure 6, although the lower bearing shell 220 is a cylindrical structure as a whole. According to the functional division, the lower bearing shell 220 can be divided into a tungsten carbide surface section 221, a transition section 222 and a sealing section 223 in the upper, middle and lower parts. The so-called tungsten carbide surface section 221 means that the inner surface of the lower bearing shell in this section is covered with a layer of tungsten carbide surface layer. After assembly, this section forms a clearance fit with the above-mentioned lower radial bearing inner sleeve. The clearance fit is filled with lubricating oil. When the two (lower radial bearing inner sleeve and lower bearing shell) rotate relative to each other (high speed or low speed), a lubricating oil film can be formed at the fitting clearance, and this part constitutes an essential TC bearing fit. The inner diameter of the transition section 222 is slightly larger than the inner diameter of the tungsten carbide surface section. The transition section is designed so that an annular lubricating oil channel I224 is formed between the inner surface of the transition section and the outer surface of the above-mentioned lower radial bearing inner sleeve. The best, exemplary lubricating oil passage I of this embodiment has a gap size of 0.5 mm, which is sufficient to allow the lubricating oil to pass through and continuously supply lubricating oil to the upper tungsten carbide surface section 221 mating surface. The sealing section 223 is used to install the lower seal adjustment clamping ring 230 and the V-type combined seal ring assembly 240, wherein the lower seal adjustment clamping ring 230 is an annular thin-walled cylinder, including a threaded section 231 and a non-threaded section 232. Further, the outer surface of the threaded section of the lower seal adjustment clamping ring 230 has an external thread, and correspondingly, the lower bearing shell inner surface of the sealing section 223 is partially provided with an internal thread 225 for installing the lower seal adjustment clamping ring 230, and the lower seal adjustment clamping ring 230 is installed and fixed in the lower bearing shell by a mechanical connection method of threaded matching, and the lower seal adjustment clamping ring 230 is used to clamp the V-type combined seal ring assembly 240, that is, to achieve axial fixation. A tightening tool operating structure is provided on the lower seal adjustment clamping ring 230, and the relative position of the lower seal adjustment clamping ring in the lower bearing shell can be adjusted by rotation, strictly speaking, the relative position in the axial direction, so as to realize the pressure adjustment function of the lower seal adjustment clamping ring 230 on the V-type combined seal ring assembly 240. The non-threaded section 232 has a smooth outer surface and is slidably matched with the lower bearing shell. After installing the lower seal adjustment clamping ring 230, a sealing installation cavity is formed between the lower seal adjustment clamping ring 230, the lower radial bearing inner sleeve 210 and the lower bearing shell 220, and the V-type combined seal ring assembly 240 is installed in the installation cavity. The V-type combined seal ring assembly 240 is manufactured by a rubber molding manufacturing process, and according to different materials, includes a pressure ring 241 at both ends, a support ring 242 and a rubber ring 243 between the pressure ring and the support ring. The middle rubber ring 243 is composed of a plurality of sub-bodies with V-shaped cross-sections, the number of which can be increased or decreased according to design requirements. The rubber material of the middle rubber ring 243 is generally NBR (nitrile rubber).The pressure ring 241 and the support ring 242 are generally pressed with hard plastic and are located at both ends, wherein the pressure ring 241 cooperates with the lower seal adjustment clamping ring 230, and the support ring 242 cooperates with the step in the lower bearing shell 220. It is easy to understand that by adjusting the preload force of the lower seal adjustment clamping ring 230, the slight deformation of the rubber ring 243 can be adjusted, and then the deformation of the rubber ring can be adjusted, so that the best sealing effect can be provided here under harsh conditions, such as axial or radial vibration, sudden pressure, temperature change, etc.

[0036] Furthermore, a plurality of oil filling ports are provided on the lower bearing shell corresponding to the lubricating oil passage I 224 for replenishing the lubricating oil, and a sealing screw 226 is used to seal the oil filling port.

[0037] Furthermore, a C-shaped notch 244 is provided at the V-shaped mating surfaces of the pressure ring, support ring and rubber ring. The C-shaped notch 244 is used to compensate for the axial deformation caused by the axial extrusion and improve the fitting effect of the rubber ring.

[0038] Furthermore, in this embodiment, the V-shaped mating surface faces the lower end of the main shaft 100, that is, toward the outside of the drill pipe, that is, the opposite direction of the bearing lubrication cavity, so as to block the external mud and sand in a reverse setting.

[0039] The sealing process here is: when the drill pipe is working, if it is in a non-pressure or low-pressure state, the sealing can be achieved by relying on the interference of the V-shaped combined sealing ring assembly 240, so the inner and outer lips of the sealing ring have a self-sealing effect; when used at high pressure, the V-shaped combined sealing ring assembly 240 fully acts on the pressure surface with the help of the mud working pressure, so that the working sealing lip is better expanded, and the sealing surfaces on both sides are pressed tightly to achieve the purpose of high-pressure sealing. The V-shaped mating surface faces the lower end of the main shaft, so that the possibility of mud entering the lubricating oil channel in reverse is suppressed.

[0040] Generally speaking, the more rubber rings there are in the V-shaped combined sealing ring assembly 240, the better the sealing performance. Even if the main shaft has a slight eccentric movement, it will not affect the sealing effect.

[0041] In addition, according to different geological conditions and under different operating pressures, the deformation of the V-shaped combined sealing ring assembly 240 can be adjusted by adjusting the torque of the lower sealing adjustment clamping ring 230, thereby adjusting the sealing effect. The sealing structure in this embodiment achieves the goal of adjustable sealing effect.

[0042] The upper section of the outer surface of the lower bearing shell 220 is a threaded section and a sealing section, wherein the threaded section is mechanically connected to the upper bearing shell through a threaded connection, and an annular groove is provided at the sealing section for installing an O-type rubber sealing ring 227, which realizes a static seal between the lower bearing shell and the upper bearing shell. The static seal and mechanical connection with the upper bearing shell are completed through the above structure.

[0043] The lower fixing nut 310 and the thrust ring 320 are adjacent to and arranged above the lower sealing assembly, which are a pair of transition parts. Among them, the lower fixing nut 310 is installed on the main shaft 100 through a threaded connection, that is, the main shaft is partially provided with an external thread, and the external thread is used to install the lower fixing nut 310. After the lower fixing nut is tightened, the lower radial bearing inner sleeve 210 and the main shaft gasket 110 in the lower sealing assembly are firmly fixed (axially), that is, the lower fixing nut forms an axial limit and tightening. The lower fixing nut does not contact the lower bearing shell, that is, the two are in a non-contact state. The thrust ring 320 is sleeved on the outside of the lower fixing nut, and the two are designed at the same height. After installation, an annular lubricating oil channel II330 is formed between the thrust ring and the lower fixing nut, which can also be understood as a narrow oil storage chamber, which has the function of temporarily storing a small amount of lubricating oil. The above-mentioned thrust ring 320 contacts the lower bearing shell 230, that is, it is in a relatively static state together with the contact of the lower bearing shell. The outer side of the thrust ring 320 is the upper bearing shell, and the two are conventionally mechanically matched.

[0044] Immediately adjacent to the lower fixing nut and the upper part of the thrust ring is a thrust bearing 400. In this embodiment, five thrust bearings are provided. This number is not a limitation of the utility model. Under known circumstances, the number of thrust bearings 400 can be obtained according to engineering mechanics design. The outer ring of the thrust bearing 400 is abutted and connected with the thrust ring, and the inner ring is abutted and connected with the lower fixing nut. The thrust bearing in this embodiment is preferably a standard bearing.

[0045] The thrust bearing 400 described above may be equivalently replaced by other types of bearings depending on different design schemes, which is also within the protection scope of the present utility model.

[0046] Immediately above the thrust bearing 400 is a combination of an upper radial bearing outer sleeve 520 and an upper radial bearing inner sleeve 510, wherein the upper radial bearing inner sleeve 510 is a long cylindrical structure, which is similar to the lower radial bearing inner sleeve, and is a cylindrical structure with equal sections from top to bottom, and has a length, and the long length is designed based on mechanical considerations. The matrix of the upper radial bearing inner sleeve is a cemented carbide material, and the outer surface is covered with a tungsten carbide surface layer, which is a composite material, and the tungsten carbide surface layer is covered in the length direction. In this embodiment, the tungsten carbide surface layer is covered on the matrix through. The upper radial bearing outer sleeve 520 is a non-equal section design, and the length is about half of the upper radial bearing inner sleeve. The tungsten carbide surface layer on the inner surface of the upper radial bearing outer sleeve 520 forms a clearance fit with the above-mentioned upper radial bearing inner sleeve after assembly, and the clearance fit is filled with lubricating oil. When the two (the upper radial bearing inner sleeve and the upper radial bearing outer sleeve) rotate relative to each other (high speed or low speed), a lubricating oil film can be formed.

[0047] The upper bearing shell 600 is sleeved on the outside from top to bottom and covers the upper assembly, the lower assembly and the thrust bearing assembly. The upper bearing shell 600 is divided from top to bottom into: a dynamic seal section 610, an oil injection section 620, a shell section 630 and a connection section 640, wherein the connection section 640 is threadedly connected to the lower bearing shell and statically sealed. The shell section 630 refers to the outer shell part that protects the thrust bearing and its auxiliary structures at both ends. The oil injection section 620 is an annular protrusion pointing to the inner side. The lubricating oil channel III 650 is formed between the annular protrusion and the inner sleeve of the upper radial bearing 6, and a hole is drilled on the upper bearing shell where the annular protrusion is located. The best, the gap size of the lubricating oil channel III given in this embodiment is 0.5 mm, and the gap of the lubricating oil channel I is sufficient to allow the lubricating oil to pass through and continuously supply the lubricating oil to the mating surface of the tungsten carbide surface section below.

[0048] Theoretically, the above-mentioned lubricating oil passages I, II, and III are interconnected, that is, they constitute a bearing lubricating cavity, in which the TC bearing and the thrust bearing are continuously lubricated. Lubricating oil is injected through the oil filling port to lubricate the bearing, and the injection of lubricating oil keeps the pressure of the lubricating oil passage and the outer side of the assembly balanced.

[0049] The dynamic seal section 610 is used to install the upper seal adjustment clamping ring 660 and the V-type combined seal ring assembly 240, wherein the upper seal adjustment clamping ring 660 is an annular thin-walled cylinder, including a threaded section and a non-threaded section. To be more specific, the outer surface of the threaded section of the upper seal adjustment clamping ring has an external thread, and correspondingly, the inner surface of the upper bearing shell of the dynamic seal section is provided with an internal thread. The upper seal adjustment clamping ring is installed and fixed in the upper bearing shell 600 through a mechanical connection method of thread matching. A fastening tool operating structure is provided on the upper seal adjustment clamping ring, and the relative position of the upper seal adjustment clamping ring in the upper bearing shell can be adjusted by rotation, strictly speaking, the relative position in the axial direction. The non-threaded section has a smooth outer surface and is slidably matched with the inner surface of the upper bearing shell. After installing the upper seal adjustment clamping ring, a sealing installation cavity is formed between the upper seal adjustment clamping ring, the upper radial bearing inner sleeve and the upper bearing shell, and the V-type combined seal ring assembly 240 is installed in the installation cavity. The structure of the V-shaped combined sealing ring assembly 240 is the same as the structure of the above-mentioned V-shaped combined sealing ring assembly, but the setting direction is opposite, that is, the V-shaped opening in the V-shaped combined sealing ring assembly here is set upward. The above-mentioned structure constitutes an upper sealing combined structure. The above-mentioned upper sealing combined structure and the lower sealing combined structure are used in pairs.

[0050] The upper fixing nut 700 is arranged above the upper radial bearing inner sleeve. The upper fixing nut is fixed to the upper neck of the main shaft through threaded cooperation to achieve axial compression and position limiting of the upper radial bearing inner sleeve. Through the implementation of this structure, the upper radial bearing inner sleeve and the thrust bearing below it are in a compressed state. A threaded section is also arranged on the main shaft above the upper fixing nut, and the threaded section is used to install a water cap (not shown in the figure).

[0051] The structural advantages of this embodiment are:

[0052] When there is no pressure or low pressure, the sealing ring can be pre-pressed by the interference fit and the upper and lower sealing clamping rings to achieve sealing, so the inner and outer lips of the sealing ring have a self-sealing effect; when used under high pressure, the sealing ring uses the mud working pressure to fully act on the pressure surface, so that the working sealing lip can be well expanded and the sealing surfaces on both sides can be pressed to achieve the purpose of high-pressure sealing.

[0053] Secondly, the more sealing rings there are, the greater the sealing pressure; if the main shaft has a slight eccentric movement, it will not affect the sealing effect.

[0054] In addition, the upper and lower sealing clamping rings are used to clamp the two sides of the V-type combined seal respectively. Under different working pressures, the torque of the clamping ring (230, 660) is adjusted to enable the sealing ring to obtain a greater sealing pressure.

[0055] Embodiment 2

[0056] refer to Figures 10 to 12 The three views show three improved situations respectively. An elastic compensation element is added between the clamping ring and the V-type combined sealing ring assembly. Take the following segment sealing combination structure as an example. Specifically, Fig.10 In the embodiment, a disc spring 01 is added between the lower seal adjustment clamping ring 230 and the V-type combined seal ring assembly 240. Its function is that when the rubber material in the V-type combined seal ring assembly produces a slight wear, the disc spring can produce a slight compensation, so that the rubber seal ring is in the best sealing state. Fig.11 In the embodiment, the corrugated elastic sheet 02 is used as the elastic compensation element, which has the same technical effect as the above-mentioned disc spring. Fig.12 In the embodiment, compression spring 03 is used as an elastic compensation element, which has the same technical effect as the above-mentioned disc spring.

[0057] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements to the present invention by relevant technical personnel in the field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A screw drill sealed transmission shaft assembly, comprising a bearing lubrication cavity and a sealing assembly structure located at both ends of the bearing lubrication cavity, characterized in that: The sealing combination structure includes a clamping ring and a V-shaped combined sealing ring assembly, wherein the V-shaped combined sealing ring assembly is arranged between the bearing inner sleeve and the bearing shell and performs dynamic sealing cooperation; the clamping ring is connected to the bearing shell through threaded cooperation and abuts against the V-shaped combined sealing ring assembly.

2. The screw drill seal transmission shaft assembly according to claim 1, characterized in that: The V-shaped combined sealing ring assembly comprises a pressure ring at both ends, a support ring and a rubber ring between the pressure ring and the support ring. The hardness of the pressure ring and the support ring is greater than that of the rubber ring.

3. The screw drill seal transmission shaft assembly according to claim 2, characterized in that: The rubber ring is composed of a plurality of sub-bodies with V-shaped cross sections, and the V-shaped matching surface of each sub-body faces the opposite direction of the bearing lubrication cavity.

4. The screw drill seal transmission shaft assembly according to claim 3, characterized in that: A C-shaped notch is arranged at the V-shaped matching surface.

5. The screw drill seal transmission shaft assembly according to claim 1, characterized in that: The sealing assembly structure comprises an upper sealing assembly structure and a lower sealing assembly structure.

6. The screw drill seal transmission shaft assembly according to claim 1, characterized in that: An elastic compensation element is arranged between the clamping ring and the V-shaped combined sealing ring assembly.

7. The screw drill seal transmission shaft assembly according to claim 1, characterized in that: The bearing in the bearing lubrication cavity is a combination of a TC bearing, a thrust bearing or / and a ball bearing.

8. The screw drill seal transmission shaft assembly according to claim 1, characterized in that: The bearing lubrication cavity is provided with an oil filling port and a sealing screw, and the sealing screw is sealedly connected to the oil filling port.

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