CN219826700U

CN219826700U - Screw vibration reduction transmission shaft assembly

Info

Publication number: CN219826700U
Application number: CN202320793271.1U
Authority: CN
Inventors: 田玉栋; 柳贡慧; 齐悦; 李军; 路彩虹
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2023-04-11
Filing date: 2023-04-11
Publication date: 2023-10-13
Anticipated expiration: 2033-04-11

Abstract

The utility model relates to a screw vibration reduction transmission shaft assembly, which comprises a shell structure, wherein a transmission main shaft and a drill bit shaft are arranged in the shell structure in a penetrating way, and a first end of the drill bit shaft is inserted into a first end of the transmission main shaft in a sliding way; a guide rail sleeve is arranged between the drill bit shaft and the shell structure, a first end of the guide rail sleeve is fixedly connected with a first end of the transmission main shaft, an axial elastic unit is arranged between the drill bit shaft and the guide rail sleeve, a vibration reduction connecting structure is arranged between the drill bit shaft and the guide rail sleeve, the vibration reduction connecting structure comprises a convex guide rail unit arranged on the outer wall of the drill bit shaft and a groove guide groove unit arranged on the inner wall of the guide rail sleeve, and the convex guide rail unit can spirally ascend or descend along the groove guide groove unit; the outer wall of the drill bit shaft is connected with a hanging block capable of axially limiting the drill bit shaft. The vibration reduction system is arranged in the conventional transmission shaft, so that the axial and radial impact loads can be absorbed simultaneously, the working state of the screw drilling tool bearing is improved, and the service life of the screw drilling tool is prolonged.

Description

Screw vibration reduction transmission shaft assembly

Technical Field

The utility model relates to an underground drilling tool in the field of petroleum development, in particular to a screw vibration reduction transmission shaft assembly.

Background

With the development of drilling technology, screw drilling tools are increasingly used, and the tool utilizes the hydraulic energy of drilling fluid to generate rotary cutting torque to drive a drill bit to rotate, so that rock breaking is realized. The screw drilling tool is a volumetric underground power drilling tool which uses drilling fluid as power and converts the pressure energy of the drilling fluid into mechanical energy. When mud pumped by the mud pump flows through the bypass valve to enter the motor, a certain pressure difference is formed between the inlet and the outlet of the motor, the rotor is pushed to rotate around the axis of the stator, and the rotating speed and the torque are transmitted to the drill bit through the universal shaft and the transmission shaft, so that the drilling operation is realized.

In the screw drilling tool, the screw drilling tool mainly comprises a bypass valve assembly, a motor assembly, a universal joint assembly and a transmission shaft assembly. Wherein the drive shaft assembly is operative to transmit torque generated by the upper motor to the drill bit, which is required to bear the upper axial and radial loads. Meanwhile, the lower end of the transmission shaft assembly is generally directly connected with the drill bit, namely vibration generated by cutting rock by the drill bit directly acts on the transmission shaft assembly, so that the use environment of the transmission shaft assembly is severe. Conventional drive shaft assemblies are internally provided with multiple thrust bearings, including ball bearings and PDC bearings. Among them, the ball bearing is relatively inexpensive, so that it is applied more. Taking a ball bearing as an example, the bearing needs to bear the weight on bit, that is, the weight on bit needs to be transmitted to the bit through a ball in the middle of the ball bearing, and meanwhile, the shell of the transmission shaft assembly and the transmission shaft in the transmission shaft assembly need to rotate relatively. Typically the bearing portion of the drive shaft assembly is of an open architecture, i.e. allowing drilling fluid containing certain solid particles to flow into the interior of the bearing. The working environment of the ball bearing makes this part a weak link in the drive shaft assembly, and once the bearing wears too much, the screw drilling tool needs to replace the bearing. In practical use of the screw drilling tool, it is generally determined whether the screw needs maintenance by measuring the wear amount of the bearing.

Another common failure mode of bearings in drive shafts is chipping of balls in the bearings, which once present exacerbates wear of the bearings, causing complete failure of the drive shaft in a short period of time. Ball chipping in the ball bearing is an important factor limiting the life of the screw drilling tool, and thus it is desirable to avoid this situation as much as possible in the use of the screw drilling tool.

The main reason for ball fracture in bearings is the severe vibration that occurs, i.e. the ball is subjected to a large impact load, and the instantaneous and very large impact peak causes ball fracture. The severe vibration of the part mainly originates from the fluctuation of the load generated by the rock breaking of the drill bit, which is unavoidable due to the uncertainty of the downhole environment and is difficult to predict, so that the vibration is difficult to be damped in an active way. When severe vibration is generated at the drill bit, the vibration is finally transmitted to the ball of the bearing, and the vibration impact load can cause great threat to the service life of the screw drilling tool due to the fact that the conventional screw drilling tool does not have any vibration reduction structure.

In order to further increase the service life of the screw drilling tool, it is necessary to absorb the shock impact load near the drill bit by designing a new drive shaft structure.

Therefore, the inventor provides a screw vibration reduction transmission shaft assembly by virtue of experience and practice of related industries for many years so as to overcome the defects of the prior art.

Disclosure of Invention

The utility model aims to provide a screw vibration reduction transmission shaft assembly, which solves the technical problems that a screw drilling tool transmission shaft is not resistant to vibration and impact and the like in the prior art.

The utility model aims to achieve the purpose, and the screw vibration reduction transmission shaft assembly comprises a shell structure, wherein a transmission main shaft and a drill bit shaft which are sequentially connected are arranged in the shell structure in a penetrating manner, the first end of the drill bit shaft can be slidably inserted into the first end of the transmission main shaft, and a central flow passage is arranged on the transmission main shaft and the drill bit shaft in a penetrating manner along the axial direction;

a guide rail sleeve is arranged between the drill bit shaft and the shell structure, a first end of the guide rail sleeve is fixedly connected with a first end of the transmission main shaft, an axial elastic unit is arranged between the drill bit shaft and the guide rail sleeve, a vibration reduction connecting structure is arranged between the drill bit shaft and the guide rail sleeve, the vibration reduction connecting structure comprises a convex guide rail unit arranged on the outer wall of the drill bit shaft and a groove guide rail unit arranged on the inner wall of the guide rail sleeve, and the convex guide rail unit can spirally ascend or descend along the groove guide rail unit; and a hanging block which can axially limit the drill bit shaft is connected to the outer wall of the drill bit shaft and is positioned below the vibration reduction connecting structure.

In a preferred embodiment of the present utility model, the housing structure includes a transmission shaft housing, a middle TC bearing stator ring and a lower TC bearing stator ring connected in sequence; the transmission spindle is arranged in the transmission shaft shell in a penetrating manner, the drill bit shaft is arranged in the middle TC bearing static ring and the lower TC bearing static ring in a penetrating manner, a middle TC bearing moving ring is arranged between the middle TC bearing static ring and the transmission spindle, and a lower static cylinder and a lower TC bearing moving ring are arranged between the lower TC bearing static ring and the drill bit shaft.

In a preferred embodiment of the present utility model, the raised guide rail unit has a multi-start external thread structure, the groove guide rail unit has a multi-start internal thread structure, and a gap is formed between the raised guide rail unit and the groove guide rail unit.

In a preferred embodiment of the present utility model, the cross sections of the raised guide rail unit and the recessed guide rail unit are arranged in a trapezoid shape.

In a preferred embodiment of the present utility model, the axial elastic unit is a disc spring.

In a preferred embodiment of the present utility model, the hanging blocks are half-moon rings, and the number of the hanging blocks is two; the side wall of the drill bit shaft is provided with a connecting groove, each hanging block is in interference fit connection with the connecting groove, and each hanging block is in clearance fit with the middle TC bearing static ring.

In a preferred embodiment of the present utility model, the transmission shaft housing is screwed with the middle TC bearing stator, and the middle TC bearing stator is screwed with the lower TC bearing stator; the middle TC bearing moving coil is connected with the transmission main shaft through interference fit, and the middle TC bearing moving coil and the middle TC bearing static coil are arranged in clearance fit.

In a preferred embodiment of the utility model, a centralizing bearing sleeve assembly is arranged at the second end of the transmission main shaft, the centralizing bearing sleeve assembly comprises an upper TC bearing moving coil, an upper moving cylinder, an upper static cylinder and an upper TC bearing static coil which are arranged from inside to outside, and the centralizing bearing sleeve assembly is axially fixed on the transmission main shaft through a shaft sleeve; the upper TC bearing moving coil is connected with the transmission main shaft through threads, the upper moving cylinder is connected with the upper TC bearing moving coil through interference fit, and the upper TC bearing static coil is connected with the transmission shaft shell through interference fit.

In a preferred embodiment of the present utility model, an upper static ring sleeve is arranged between the upper TC bearing static ring and the transmission shaft housing; and a bearing inner ring, balls and a bearing outer ring are arranged between the transmission main shaft and the transmission shaft shell, and a spacer bush is arranged between the bearing outer ring and the middle TC bearing static ring.

In a preferred embodiment of the present utility model, the lower TC bearing moving coil is connected to the drill bit shaft by a screw thread, the lower stationary barrel is connected to the lower TC bearing stationary coil by an interference fit, and the lower stationary barrel and the lower TC bearing moving coil are disposed in a clearance fit.

From the above, the screw vibration reduction transmission shaft assembly has the following beneficial effects:

the screw vibration reduction transmission shaft assembly solves the technical problems that a screw drilling tool transmission shaft is not resistant to vibration and impact and the like in the prior art, and the screw vibration reduction transmission shaft assembly is arranged in a conventional transmission shaft assembly, so that axial and radial impact loads can be absorbed simultaneously, the working state of a screw drilling tool bearing is improved, and the service life of the screw drilling tool is prolonged.

Drawings

The following drawings are only for purposes of illustration and explanation of the present utility model and are not intended to limit the scope of the utility model. Wherein:

fig. 1: the external appearance diagram of the screw vibration reduction transmission shaft assembly is provided.

Fig. 2: is a sectional view B-B in FIG. 1.

Fig. 3: is a cross-sectional view A-A in fig. 2.

Fig. 4: is a schematic view of the drill bit shaft of the present utility model.

In the figure:

1. a transmission main shaft; 2. a shaft sleeve; 3. a TC bearing moving coil is arranged; 4. an upper moving cylinder; 5. a TC bearing static ring is arranged; 6. a static cylinder is arranged on the upper part; 7. a drive shaft housing; 8. an upper static ring sleeve; 9. a bearing inner ring; 10. a bearing outer ring; 11. a ball; 12. a spacer bush; 13. a middle TC bearing moving coil; 14. middle TC bearing static ring; 15. a guide rail sleeve; 151. groove guide groove units; 16. a drill bit shaft; 161. a protruding guide rail unit; 17. a disc spring; 18. a hanging block; 19. a lower TC bearing static ring; 20. a lower static cylinder; 21. and a lower TC bearing moving coil.

Detailed Description

For a clearer understanding of technical features, objects, and effects of the present utility model, a specific embodiment of the present utility model will be described with reference to the accompanying drawings.

The specific embodiments of the utility model described herein are for purposes of illustration only and are not to be construed as limiting the utility model in any way. Given the teachings of the present utility model, one of ordinary skill in the related art will contemplate any possible modification based on the present utility model, and such should be considered to be within the scope of the present utility model. It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "mounted," "connected," "coupled," and "connected" are to be construed broadly, and may be, for example, mechanically or electrically connected, may be in communication with each other in two elements, may be directly connected, or may be indirectly connected through an intermediary, and the specific meaning of the terms may be understood by those of ordinary skill in the art in view of the specific circumstances. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this utility model belongs. The terminology used herein in the description of the utility model is for the purpose of describing particular embodiments only and is not intended to be limiting of the utility model. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

As shown in fig. 1, 2, 3 and 4, the utility model provides a screw vibration damping transmission shaft assembly, which comprises a shell structure, wherein a transmission main shaft 1 and a drill bit shaft 16 which are sequentially connected are arranged in the shell structure in a penetrating way, the first end of the drill bit shaft 16 can be slidably inserted into the first end of the transmission main shaft 1, and central flow passages are arranged on the transmission main shaft 1 and the drill bit shaft 16 in a penetrating way along the axial direction;

a guide rail sleeve 15 is arranged between the drill bit shaft 16 and the shell structure, a first end of the guide rail sleeve 15 is fixedly connected (in threaded connection) with a first end of the transmission main shaft 1, an axial elastic unit is arranged between the drill bit shaft 16 and the guide rail sleeve 15, a vibration reduction connecting structure is arranged between the drill bit shaft 16 and the guide rail sleeve 15, the vibration reduction connecting structure comprises a convex guide rail unit 161 arranged on the outer wall of the drill bit shaft 16 and a groove guide groove unit 151 arranged on the inner wall of the guide rail sleeve 15, and the convex guide rail unit 161 can ascend or descend along the groove guide groove unit 151 in a spiral manner; a suspension block 18 capable of axially limiting the bit shaft is connected to the outer wall of the bit shaft 16 below the vibration reduction connection structure.

In the screw vibration reduction transmission shaft assembly, when the screw vibration reduction transmission shaft assembly is in an initial state, the bit shaft 16 is positioned at the lowest end (the lower end in fig. 2), the suspension block 18 ensures that the bit shaft 16 cannot fall off from the shell structure, the first end of the bit shaft 16 is positioned at the lowest position of the transmission main shaft 1, and the bit shaft 16 can move a certain distance in the axial direction; when in use, the drill bit is connected to the lower end of the drill bit shaft 16, and under the matched connection of the convex guide rail unit 161 and the concave guide rail unit 151, the rotation moment of the transmission main shaft 1 is transmitted to the drill bit through the guide rail sleeve 15 and the drill bit shaft 16 to drive the drill bit to drill; when the drill bit hits harder things, the drill bit shaft 16 receives upward axial force, and under the cooperation of the convex guide rail units 161 and the concave guide groove units 151, the drill bit shaft 16 spirally ascends and slides in the guide rail sleeve 15, and meanwhile, axial and radial impact loads are absorbed; meanwhile, the axial elastic unit gradually enters a compression state, stores energy, further absorbs axial impact load, and achieves the purpose of axial vibration reduction.

Further, as shown in fig. 1 and 2, the housing structure includes a transmission shaft housing 7, a middle TC bearing stator ring 14 and a lower TC bearing stator ring 19 which are sequentially connected; a transmission main shaft 1 (the transmission main shaft 1 can use a traditional screw transmission shaft) is penetrated in the transmission shaft shell 7, and a drill bit shaft 16 is penetrated in the middle TC bearing static ring 14 and the lower TC bearing static ring 19; a middle TC bearing moving coil 13 is arranged between the middle TC bearing static coil 14 and the transmission main shaft 1, and a lower static cylinder 20 and a lower TC bearing moving coil 21 are arranged between the lower TC bearing static coil 19 and the drill bit shaft 16; the second end of the bit shaft 16 is restrained from rocking in the circumferential direction by the lower TC bearing moving coil 21 and the lower TC bearing static coil 19 so as to ensure the positioning accuracy of output.

Screw drilling tools are one of the most widely used downhole power tools in petroleum drilling. TC bearings are located in the drive section thereof and are critical components affecting the life of the screw drilling tool. The TC bearing is divided into an inner bearing sleeve and an outer bearing sleeve (a static ring and a moving ring), the inner shaft sleeve is matched with a transmission shaft and locked, the outer shaft sleeve is assembled with a casing of the underground power drilling tool, the inner shaft sleeve and the outer shaft sleeve are matched to form a working surface, and the working surface is mainly used for transmitting the torque and the rotating speed of a motor to a drill bit. In the working process, the TC bearing is subjected to axial and radial forces of the universal bearing and the drill bit, and the inner sleeve has eccentric movement trend around the outer sleeve.

Further, as shown in fig. 2, 3 and 4, the raised guide rail unit 161 has a multi-head external thread structure, the groove guide rail unit 151 has a multi-head internal thread structure, the multi-head external thread structure is in screw connection with the multi-head internal thread structure, and a gap is formed between the raised guide rail unit 161 and the groove guide rail unit 151.

For ease of assembly and fitting, the cross sections of the raised rail unit 161 and the recessed channel unit 151 are arranged in a trapezoidal shape.

Further, as shown in fig. 2, the axial elastic unit is a disc spring 17, the initial state of the disc spring 17 is a compressed state, and when the bit shaft 16 receives an upward axial force of the bit, the disc spring 17 compresses and buffers. The lower end of the bit shaft 16 needs to be connected with a drill bit, when the drill bit hits harder things, the bit shaft 16 slides in the trapezoidal groove guide groove unit 151 in the guide rail sleeve 15 through the convex guide rail unit 161, so that the disc spring 17 is further compressed, and energy is stored.

Further, as shown in fig. 2, the hanging blocks 18 are half-moon rings, and the number of the hanging blocks is two; the side wall of the drill bit shaft 16 is provided with a connecting groove, each hanging block 18 is connected with the connecting groove in an interference fit mode, and each hanging block 18 is in clearance fit with the middle TC bearing static ring 14. The hanging block 18 limits the distance of up and down movement of the bit shaft 16 and prevents the bit shaft 16 from falling down.

Further, as shown in fig. 2, the transmission shaft housing 7 is connected with the middle TC bearing stator ring 14 through threads, and the middle TC bearing stator ring 14 is connected with the lower TC bearing stator ring 19 through threads; the middle TC bearing moving coil 13 is connected with the transmission main shaft 1 through interference fit, and the middle TC bearing moving coil 13 and the middle TC bearing static coil 14 are arranged in clearance fit.

Further, as shown in fig. 2, a centralizing bearing sleeve assembly is arranged at the second end of the transmission main shaft 1, the centralizing bearing sleeve assembly comprises an upper TC bearing moving coil 3, an upper moving cylinder 4, an upper static cylinder 6 and an upper TC bearing static coil 5 which are arranged from inside to outside, and the centralizing bearing sleeve assembly is axially fixed on the transmission main shaft 1 through a shaft sleeve 2. The second end (upper end in fig. 1) of the drive spindle 1 is restrained from circumferential wobble by a righting bearing assembly.

Further, as shown in fig. 2, an upper static ring sleeve 8 is arranged between the upper TC bearing static ring 5 and the transmission shaft shell 7; a bearing inner ring 9, balls 11 and a bearing outer ring 10 are arranged between the transmission main shaft 1 and the transmission shaft shell 7, and a spacer 12 is arranged between the bearing outer ring 10 and a middle TC bearing static ring 14.

Further, as shown in fig. 2, the upper TC bearing moving coil 3 is connected with the transmission main shaft 1 through threads, the upper moving cylinder 4 is connected with the upper TC bearing moving coil 3 through interference fit, and the upper TC bearing static coil 5 is connected with the transmission shaft housing 7 through interference fit.

Further, as shown in fig. 2, the lower TC bearing moving coil 21 is screwed with the bit shaft 16, the lower stationary barrel 20 is connected with the lower TC bearing stationary coil 19 by interference fit, and the lower stationary barrel 20 and the lower TC bearing moving coil 21 are disposed in clearance fit.

The working principle of the utility model is as follows:

as shown in fig. 1, the lower end of the screw vibration reduction transmission shaft assembly of the present utility model is connected with a drill bit, the upper end is connected with a motor (prior art) for providing power, the power is transmitted to the transmission main shaft 1 through a screw structure, the first end (lower end in fig. 1) of the transmission main shaft 1 is connected with the guide rail sleeve 15 through screw threads, the power is transmitted to the guide rail sleeve 15, the guide rail sleeve 15 and the drill bit shaft 16 are connected with the cooperation of the groove guide groove unit 151 through the trapezoidal convex guide rail unit 161, the power is transmitted to the drill bit shaft 16 through the guide rail sleeve 15, finally, the drill bit shaft 16 and the transmission main shaft 1 synchronously rotate, and the drill bit shaft 16 can rotate in the circumferential direction and keep axially moving through the cooperation of the convex guide rail unit 161 and the groove guide groove unit 151 due to a certain distance left between the drill bit shaft 16 and the axial direction of the transmission main shaft 1. The second end (upper end in fig. 1) of the drive spindle 1 has a righting bearing to restrict its circumferential movement. When the drill bit connected with the drill bit shaft 16 contacts a harder object, the drill bit shaft 16 is subjected to upward force in order to protect the drill bit and maintain the mechanical rotation speed, and due to the cooperation of the convex guide rail unit 161 and the concave guide rail unit 151, a sufficient axial distance is left between the transmission main shaft 1 and the drill bit shaft 16 and the existence of a disc spring, and the drill bit shaft 16 can move up and down in the middle TC bearing static ring 14, so that the pressure of the rolling balls 11 in the rolling bearing on the transmission main shaft 1 is shared.

The foregoing is illustrative of the present utility model and is not to be construed as limiting the scope of the utility model. Any equivalent changes and modifications can be made by those skilled in the art without departing from the spirit and principles of this utility model, and are intended to be within the scope of this utility model.

Claims

1. The screw vibration reduction transmission shaft assembly is characterized by comprising a shell structure, wherein a transmission main shaft and a drill bit shaft which are sequentially connected are arranged in the shell structure in a penetrating manner, the first end of the drill bit shaft can be slidably inserted into the first end of the transmission main shaft, and a central flow passage is arranged on the transmission main shaft and the drill bit shaft in a penetrating manner along the axial direction;

2. The screw vibration-damped drive shaft assembly of claim 1, wherein said housing structure comprises a drive shaft housing, a center TC bearing stator ring and a lower TC bearing stator ring connected in sequence; the transmission spindle is arranged in the transmission shaft shell in a penetrating manner, the drill bit shaft is arranged in the middle TC bearing static ring and the lower TC bearing static ring in a penetrating manner, a middle TC bearing moving ring is arranged between the middle TC bearing static ring and the transmission spindle, and a lower static cylinder and a lower TC bearing moving ring are arranged between the lower TC bearing static ring and the drill bit shaft.

3. The screw vibration reduction transmission shaft assembly according to claim 1 or 2, wherein the raised guide rail unit has a multi-start external thread structure, the groove guide rail unit has a multi-start internal thread structure, and a gap is formed between the raised guide rail unit and the groove guide rail unit.

4. A screw vibration-damping drive shaft assembly as claimed in claim 3, wherein said raised rail units and said recessed channel units are trapezoidal in cross section.

5. The screw vibration-damped drive shaft assembly of claim 1 or 2, wherein said axially resilient unit is a disc spring.

6. The screw vibration-damping drive shaft assembly of claim 2, wherein the suspension blocks are half-moon rings, two in number; the side wall of the drill bit shaft is provided with a connecting groove, each hanging block is in interference fit connection with the connecting groove, and each hanging block is in clearance fit with the middle TC bearing static ring.

7. The screw vibration-damped drive shaft assembly of claim 2, wherein said drive shaft housing is threadably connected to said center TC bearing retainer ring, said center TC bearing retainer ring being threadably connected to said lower TC bearing retainer ring; the middle TC bearing moving coil is connected with the transmission main shaft through interference fit, and the middle TC bearing moving coil and the middle TC bearing static coil are arranged in clearance fit.

8. The screw vibration-damping transmission shaft assembly according to claim 2, wherein a second end of the transmission main shaft is provided with a centralizing bearing sleeve assembly, the centralizing bearing sleeve assembly comprises an upper TC bearing moving coil, an upper moving cylinder, an upper static cylinder and an upper TC bearing static coil which are arranged from inside to outside, and the centralizing bearing sleeve assembly is axially fixed on the transmission main shaft through a shaft sleeve; the upper TC bearing moving coil is connected with the transmission main shaft through threads, the upper moving cylinder is connected with the upper TC bearing moving coil through interference fit, and the upper TC bearing static coil is connected with the transmission shaft shell through interference fit.

9. The screw vibration dampening drive shaft assembly of claim 8, wherein an upper static ring sleeve is disposed between the upper TC bearing static ring and the drive shaft housing; and a bearing inner ring, balls and a bearing outer ring are arranged between the transmission main shaft and the transmission shaft shell, and a spacer bush is arranged between the bearing outer ring and the middle TC bearing static ring.

10. The screw vibration reduction transmission shaft assembly according to claim 2, wherein the lower TC bearing moving coil is in threaded connection with the drill bit shaft, the lower stationary barrel is connected with the lower TC bearing stationary coil through interference fit, and the lower stationary barrel and the lower TC bearing moving coil are disposed in clearance fit.