Drive shaft for vehicles

Abstract

The present disclosure provides a propeller shaft for a vehicle. In this propeller shaft, a tube yoke is connected to a main tube via an adapter, and tapered splines are formed at the contact area between the tube yoke and the main tube to transmit power output from the transmission to the rear wheels. The tube yoke and the main tube move relative to each other at the tapered splines to break the adapter. By breaking the adapter, the tube yoke and the main tube separate, effectively absorbing impact energy.

Description

Technical Field

[0001] The present disclosure relates to a propeller shaft for a vehicle, and more particularly, to a propeller shaft for a vehicle in which a tube yoke and a main tube are connected to each other through an adapter while contacting each other through surface splines, thereby improving performance in absorbing impact energy. Background Art

[0002] The recent trend is to widely develop high-performance vehicles with excellent driving performance. Most of these high-performance vehicles employ rear-wheel drive to enhance handling and sporty performance. Rear-wheel drive systems inevitably require a propeller shaft to transmit power from the transmission to the rear-wheel drive shaft. In addition to rear-wheel drive or high-performance vehicles, propeller shafts are also used in vehicles that optionally incorporate four-wheel drive into a basic front-wheel drive system for stable driving on rough roads.

[0003] Because the propeller shaft is subject to strong rotational and torsional forces during power transmission, it must be made of materials that can withstand these forces. In particular, since the propeller shaft extends along the length of the vehicle body, it must be manufactured to absorb impact energy while shortening its length to reduce injuries to passengers in the event of a vehicle collision.

[0004] The assembly structure of a conventional transmission shaft and the structure for absorbing shock will now be described. Figure 1 FIG. 2 shows a transmission shaft for a vehicle according to the prior art. Figure 1 As shown, a conventional drive shaft 10 includes: a tube yoke 11, connected to the output side of the transmission; a front main pipe 12, connected to the rear of the tube yoke 11; a rear main pipe 14, connected to the input side of a differential gear device for distributing power to a rear wheel drive shaft; and a constant velocity joint (CVJ) 13, disposed between and connected to the front main pipe 12 and the rear main pipe 14.

[0005] For reference, a constant velocity joint is employed to ensure the propeller shaft's power transmission function and enhance the support rigidity of the central portion of the propeller shaft as the vehicle length increases. In the event of a vehicle collision, the propeller shaft 10 could be severely deformed by the impact energy applied in the vehicle's fore-aft direction, potentially damaging peripheral components or injuring passengers. Therefore, the propeller shaft 10 has a structure that can absorb impact energy in the event of a collision.

[0006] like Figure 1As shown, for example, the front main pipe 12 has a small diameter portion 12-1 at the front and a large diameter portion 12-2 at the rear that are integrally connected to each other. Therefore, when the impact energy caused by a collision is transmitted to the front main pipe 12, the impact energy can be absorbed while the small diameter portion 12-1 is pushed into the large diameter portion 12-2.

[0007] Furthermore, when the impact energy caused by a collision is transmitted to the front main pipe 12, the impact energy can be absorbed while the connection portion between the small diameter portion 12-1 and the large diameter portion 12-2 is bent. However, when the front main pipe 12 includes the small diameter portion 12-1 and the large diameter portion 12-2, the strength required for power transmission, which is the main function of the front main pipe 12, is reduced due to the reduction in the outer diameter of the small diameter portion 12-1.

[0008] Although the reduction in strength required for power transmission can be prevented by increasing the overall diameter of the front main pipe 12 including the small diameter portion 12-1 and the large diameter portion 12-2, this is disadvantageous for the layout and the weight is excessively increased, so the front main pipe 12 cannot effectively perform compressive deformation according to the impact energy.

[0009] In addition, even when the front main pipe 12 includes the small-diameter portion 12-1 and the large-diameter portion 12-2, the impact energy caused by the vehicle collision cannot be properly transmitted along the length direction of the front main pipe 12, so the small-diameter portion 12-1 may not be fully pushed into the large-diameter portion 12-2. Instead, the front main pipe 12 may hit the floor of the vehicle body while bending, thereby increasing damage to the vehicle and injury to passengers in the vehicle.

[0010] In addition, if Figure 1 As shown, since the connection portion between the tube yoke 11 and the front main pipe 12, that is, the connection portion between the rear end of the tube yoke 11 and the front end of the small diameter portion 12-1 of the front main pipe 12 is formed integrally by friction welding, the tube yoke 11 and the front main pipe 12 are not completely separated from each other by the impact energy caused by the collision of the vehicle, so that the connection portion between the tube yoke 11 and the front main pipe 12 does not absorb the impact energy.

[0011] Furthermore, a structure for absorbing impact energy is also employed within the constant velocity joint 13. For example, a partition wall (not shown) can be formed within the constant velocity joint 13 so that the partition wall collapses in response to the impact energy caused by a vehicle collision, thereby absorbing the impact energy. However, since only the partition wall within the constant velocity joint 13 collapses in response to the impact energy caused by the vehicle collision, and the separation and deformation of the various components of the constant velocity joint are limited, the impact energy absorption effect is negligible.

[0012] The above information disclosed in this section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Summary of the Invention

[0013] The present disclosure provides a drive shaft for a vehicle, in which a tube yoke can be connected to a main tube by an adapter and a tapered spline can be formed in a contact area between the tube yoke and the main tube to more easily transmit power output from a transmission to the rear wheels, and in which the tube yoke and the main tube can move relative to each other at the tapered spline to break the adapter, so that the tube yoke and the main tube can be separated from each other by the breaking of the adapter to effectively absorb impact energy.

[0014] In one aspect, the present disclosure provides a propeller shaft for a vehicle. The propeller shaft may include: an adapter having a front end coupled to the inner surface of a tube yoke and a rear end coupled to the inner surface of a main tube, with a fracture-inducing notch formed at a predetermined position between the front and rear ends of the adapter; a first tapered spline formed at the rear end of the tube yoke; and a second tapered spline formed at the front end of the main tube and alternately engaged with the first tapered spline to transmit power. In particular, the fracture-inducing notch is fractured due to the impact force generated when the first tapered spline of the tube yoke moves relative to the second tapered spline of the main tube due to impact energy caused by a vehicle collision.

[0015] In an exemplary embodiment, the inner surface of the tube yoke may include an internal thread, and the front end of the adapter may include an external thread for threaded engagement with the internal thread of the tube yoke. Additionally, the inner surface of the main tube may include a locking groove, and the rear end of the adapter may include a plurality of spring clips for coupling to the locking groove. The rear end of each of the plurality of spring clips may be integrally formed with a hook that bends outward to fit into the locking groove.

[0016] The transmission shaft may further include an O-ring fitted into a fracture induction cutout in the adapter to prevent foreign matter from penetrating. The rear surface of the first tapered spline and the front surface of the second tapered spline may have tapered surfaces whose inclined surfaces contact each other.

[0017] In particular, the first tapered spline may include a plurality of first teeth and a plurality of first tooth grooves arranged circumferentially and alternately, and a rear surface of each of the plurality of first teeth and the plurality of first tooth grooves may be formed as a first tapered surface that is inclined outward from the inner surface to the outer surface of the tube yoke. The second tapered spline may include a plurality of second teeth and a plurality of second tooth grooves arranged circumferentially and alternately, and a front surface of each of the plurality of second teeth and the plurality of second tooth grooves may be formed as a second tapered surface that is inclined inward from the outer surface to the inner surface of the main tube.

[0018] In another exemplary embodiment, the first tapered spline may include a plurality of first teeth and a plurality of first tooth grooves arranged circumferentially and alternately, and a rear surface of each of the plurality of first teeth and the plurality of first tooth grooves may be formed as a first tapered surface that is inclined inwardly from the outer surface of the tube yoke to the inner surface of the tube yoke. The second tapered spline may include a plurality of second teeth and a plurality of second tooth grooves arranged circumferentially and alternately, and a front surface of each of the plurality of second teeth and the plurality of second tooth grooves may be formed as a second tapered surface that is inclined outwardly from the inner surface of the main tube to the outer surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments of the disclosure illustrated in the accompanying drawings, which are given hereinafter by way of illustration only and therefore not limiting of the present disclosure, and in which:

[0020] Figure 1 is a diagram showing a propeller shaft for a vehicle according to the prior art;

[0021] Figure 2 is a partially sectional exploded perspective view of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure;

[0022] Figures 3 to 5 is a partial cross-sectional perspective view illustrating an assembly process of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure;

[0023] Figures 6 to 8 is a diagram illustrating an example of tapered splines formed on a tube yoke and a main tube of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure; and

[0024] Figures 9 to 11 is a diagram illustrating another example of tapered splines formed on a tube yoke and a main tube of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure.

[0025] It should be understood that the drawings are not necessarily drawn to scale and present a somewhat simplified representation of various exemplary features of the basic principles of the present disclosure. Specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, positions, and shapes, will depend in part on the specific intended application and use environment. In the drawings, reference numerals designate identical or equivalent components throughout the several figures of the drawing. DETAILED DESCRIPTION

[0026] It should be understood that the term "vehicle" or "vehicular" or other similar terms used herein generally include motor vehicles, for example, passenger automobiles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, and watercraft including various boats and ships, aircraft, etc., including hybrid vehicles, electric vehicles, internal combustion engine vehicles, plug-in hybrid vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum).

[0027] The terms used in this document are intended only to describe specific embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" used in this document are intended to include the plural forms as well. It will be further understood that when the terms "include" and / or "including" are used in this specification, the presence of the stated features, wholes, steps, operations, elements and / or components is specified, but the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or groups thereof is not excluded. The term "and / or" used in this document includes any and all combinations of one or more of the relevant listed items.

[0028] Unless otherwise specified or apparent from the context, the term "about" as used herein should be understood to mean within the normal tolerance range in the art, such as within 2 standard deviations of the mean. "About" can be understood to mean within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term "about."

[0029] Hereinafter, reference will now be made in detail to various exemplary embodiments of the present disclosure, examples of which are shown in the accompanying drawings and described below. Although the present disclosure will be described in conjunction with the exemplary embodiments, it will be understood that this description is not intended to limit the present disclosure to those exemplary embodiments. On the contrary, the present disclosure is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents or other exemplary embodiments, which may be included within the spirit and scope of the present disclosure as defined by the appended claims.

[0030] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Figure 2 is a partially sectional exploded perspective view of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure. Figures 3 to 5 1 is a partial cross-sectional perspective view illustrating an assembly process of a propeller shaft for a vehicle according to an exemplary embodiment of the present disclosure. In the drawings, reference numeral 100 denotes an adapter.

[0031] Adapter 100 can connect a tube yoke 110 connected to the output side of the transmission in a drive shaft assembly to a main tube 120 extending to the input side of the differential gear device and arranged along the length direction of the vehicle. In other words, adapter 100 can have a cylindrical shape, and the front end of adapter 100 can be coupled to the inner surface of tube yoke 110 and the rear end of adapter 100 can be coupled to the inner surface of main tube 120 to connect tube yoke 110 to main tube 120.

[0032] For this reason, Figure 3 and Figure 4 As shown, the adapter 100 may include an external threaded portion 101 at the front end of the adapter 100 and a plurality of elastic clips 103 at the rear end of the adapter 100, with a fracture inducing notch 102 formed between the front and rear ends of the adapter 100. More specifically, the external threaded portion 101 may be formed in the outer surface of the front end of the adapter 100, and the plurality of elastic clips 103 may be circumferentially arranged at regular intervals at the rear end of the adapter 100 and protrude rearward. The fracture inducing notch 102 may be formed in the outer surface of the adapter 100 between the front and rear ends of the adapter 100 and have a "V"-shaped cross-section.

[0033] Each of the elastic clips 103 may be integrally provided at its rear end with a hook 104 that is bent outward to couple with the main tube 120. Specifically, the inner surface of the tube yoke 110 may be formed with an internal threaded portion 111 with which the external threaded portion 101 of the adapter 100 may be threadedly coupled, and the inner surface of the main tube 120 may be formed with a locking groove 121 into which the hook 104 formed on the elastic clip 103 of the adapter 100 may be fitted.

[0034] Therefore, if Figure 3 and Figure 4 As shown, when the external thread portion 101 of the adapter 100 is threadedly coupled with the internal thread portion of the tube yoke 110 and the main tube 120 is pushed toward the rear end of the adapter 100, the elastic clip 103 can be assembled into the main tube 120 while being bent inwardly, and then the hook 104 of the elastic clip 103 can be moved outward by the elastic restoring force and can be locked in the locking groove 121, thereby, as shown in FIG. Figure 5 As shown, the tube yoke 110 is integrally connected to the main tube 120 via the adapter 100 .

[0035] In particular, before the tube yoke 110 is connected to the main tube 120 through the adapter 100, an O-ring 105 may be assembled into the fracture inducing cutout 102 to prevent foreign matter, moisture, etc. from penetrating into the inside of the tube yoke 100 and the main tube 120. The tube yoke 110 may include a first tapered spline 130 at the rear end of the tube yoke 110, and the main tube 120 may include a second tapered spline 140 at the front end of the main tube 120, the second tapered spline 140 being alternately coupled with the first tapered spline 130 and the inclined surfaces of the second tapered spline 140 and the first tapered spline 130 being in contact with each other.

[0036] The rear surface of first tapered spline 130 and the front surface of second tapered spline 140 may have respective tapered surfaces, and thus, the inclined surfaces of the rear surface of first tapered spline 130 and the front surface of second tapered spline 140 may contact each other. Therefore, when first tapered spline 130 of tube yoke 110 and second tapered spline 140 of main tube 120 move relative to each other in the area where the inclined surfaces contact due to the impact energy caused by a vehicle collision, first tapered spline 130 or second tapered spline 140 strikes fracture inducing notch 102 of adapter 100 and fractures at fracture inducing notch 102, thereby separating adapter 100 into two sections.

[0037] In one exemplary embodiment for achieving this, Figure 6 As shown, the first tapered spline 130 may include a plurality of first teeth 131 and a plurality of first tooth grooves 132, which are circumferentially and alternately arranged at the rear end of the tube yoke 110, and the rear surface of each of the first teeth 131 and the first tooth grooves 132 may have a first tapered surface 133, which is inclined outward from the inner surface to the outer surface of the tube yoke 110. In addition, as shown in FIG. Figure 6 As shown, the second tapered spline 140 may include a plurality of second teeth 141 and a plurality of tooth grooves 142, which are circumferentially and alternately arranged at the front end of the main pipe 120, and the front surface of each of the second teeth 141 and the second tooth grooves 142 may have a second tapered surface 143, which is inclined inward from the outer surface to the inner surface of the main pipe 120.

[0038] Therefore, if Figure 7As shown, when the tube yoke 110 and the main tube 120 are connected to each other via the adapter 100, the first teeth 131 of the first tapered spline 130 can be fitted into and engaged with the second tooth grooves 142 in the second tapered spline 140, and the first teeth 141 of the second tapered spline 140 can be fitted into and engaged with the first tooth grooves 132 in the first tapered spline 130, so that the inclined surfaces of the first tapered surface 133 of the first tapered spline 130 and the second tapered surface 143 of the second tapered spline 140 contact each other. Since the first tooth grooves 132 and the first teeth 131 of the first tapered spline 130 are respectively engaged with the second teeth 141 and the second tooth grooves 142 of the second tapered spline 140, the rotational force output from the transmission can be transmitted to the differential gear device, which is configured to distribute the rotational force to the rear wheel drive shaft through the tube yoke 110 and the main tube 120.

[0039] Meanwhile, when the impact energy caused by the vehicle collision is transmitted to the tube yoke 110, since the inclined surfaces of the first tapered surface 133 of the first tapered spline 130 and the second tapered surface 143 of the second tapered spline 140 contact each other, as shown in FIG. Figure 8 As indicated by the arrow in FIG, first tapered splines 130 of tube yoke 110 may move outward, while second tapered splines 140 of main tube 120 may move inward, thereby causing first tapered splines 130 to move relative to second tapered splines 140. Simultaneously, second tapered splines 140 may strike and push fracture inducing notches 102 of adapter 100 while moving inward, causing fracture at fracture inducing notches 102. As a result, the front and rear portions of adapter 100 may be separated from each other.

[0040] In particular, since the adapter 100 connecting the tube yoke 110 to the main tube 120 is separated into the front and rear portions, the tube yoke 110 screwed to the front end of the adapter 100 and the main tube 120 connected to the rear end of the adapter 100 by the elastic clip 103 can be separated from each other. In addition, since the front and rear portions of the adapter 100 are separated from each other and thus the tube yoke 110 and the main tube 120 are also separated from each other by the impact energy caused by the vehicle collision, the impact energy caused by the vehicle collision can be effectively absorbed.

[0041] Even when the impact energy caused by a vehicle collision is not properly transmitted along the length of the propeller shaft, first tapered splines 130 and second tapered splines 140 can strike and break off cutouts 102 in adapter 100 while moving relative to each other, allowing tube yoke 110 and main tube 120 to reliably separate from each other and absorb the impact energy caused by the vehicle collision. Furthermore, even when first tapered surface 133 of first tapered spline 130 and second tapered surface 143 of second tapered spline 140 are formed in opposite directions, the impact energy absorption effect can be achieved.

[0042] In another exemplary embodiment for achieving this, Figure 9 and Figure 10 As shown, the first tapered spline 130 may include a plurality of first teeth 131 and a plurality of first tooth grooves 132, which are circumferentially and alternately arranged at the rear end of the tube yoke 110, and the rear surface of each of the first teeth 131 and the first tooth grooves 132 may be formed as a first tapered surface 133, which is inclined inward from the outer surface of the tube yoke 110 to the inner surface.

[0043] In addition, if Figure 9 and Figure 10 As shown, the second tapered spline 140 may include a plurality of second teeth 141 and a plurality of second tooth grooves 142, which are circumferentially and alternately arranged at the front end of the main pipe 120, and the front surface of each of the second teeth 141 and the second tooth grooves 142 may be formed as a second tapered surface 143, which is inclined outward from the inner surface of the main pipe 120 to the outer surface.

[0044] Therefore, when the impact energy caused by the vehicle collision is transmitted to the tube yoke 110, since the inclined surfaces of the first tapered surface 133 of the first tapered spline 130 and the second tapered surface 143 of the second tapered spline 140 contact each other, as shown in FIG. Figure 11 As indicated by the arrows in the figure, first tapered splines 130 of yoke 110 can move inward, while second tapered splines 140 of main tube 120 can move outward, thereby causing first tapered splines 130 to move relative to second tapered splines 140. Simultaneously, first tapered splines 130 can strike and push against fracture inducing notches 102 of adapter 100 while moving inward, causing fracture at notches 102. Consequently, the front and rear portions of adapter 100 can be separated from each other. Specifically, yoke 110, which is threadedly coupled to the front end of adapter 100, and main tube 120, which is connected to the rear end of adapter 100 via spring clip 103, can also be separated from each other.

[0045] As described above, even when the first tapered surface 133 of the first tapered spline 130 and the second tapered surface 143 of the second tapered spline 140 are formed in opposite manners, the front and rear portions of the adapter 100 can be separated from each other and the tube yoke 110 and the main tube 120 can also be separated from each other by the impact energy caused by the vehicle collision, thereby effectively absorbing the impact energy caused by the vehicle collision.

[0046] Through the above-described configuration, the present disclosure provides the following effects.

[0047] First, the tapered splines formed at the contact point between the tube yoke and the main tube allow transmission power from the transmission to be transmitted to the rear wheels. Furthermore, since the tube yoke and main tube can move relative to each other, breaking at the cutouts in the adapter due to the impact energy caused by a vehicle collision, the tube yoke and main tube can be separated by the adapter breaking, effectively absorbing the impact energy.

[0048] Second, even when the impact energy caused by a vehicle collision is mistakenly transmitted along the length direction of the drive shaft, that is, regardless of the direction of the impact energy transmission, the tube yoke and the main tube can move relative to each other at the tapered spline to hit and break the cutout in the adapter, so that the tube yoke and the main tube can be reliably separated from each other to absorb the impact energy caused by the vehicle collision.

[0049] Third, the use of an adapter including a threaded portion and a clamp makes it easier to assemble the pipe yoke and the main pipe.

[0050] Fourth, since the O-ring is installed in the cutout in the adapter, it can prevent foreign matter from penetrating into the inside of the drive shaft, thereby ensuring a watertight structure in normal times.

[0051] The present disclosure has been described in detail with reference to the exemplary embodiments of the present disclosure. However, it will be appreciated by those skilled in the art that changes can be made in these exemplary embodiments without departing from the principles and ideas of the present disclosure, the scope of the present disclosure being defined in the appended claims and their equivalents.

Claims

1. A propeller shaft for a vehicle, comprising: an adapter having a front end coupled to an inner surface of the pipe yoke and a rear end coupled to an inner surface of the main pipe, a fracture inducing notch formed at a predetermined position between the front and rear ends of the adapter; a first tapered spline formed at a rear end of the tube yoke; and a second tapered spline formed at the front end of the main pipe and alternately combined with the first tapered spline to transmit power; wherein, due to the impact energy caused by a vehicle collision causing the first tapered spline of the tube yoke to move relative to the second tapered spline of the main tube, fracture occurs at the fracture inducing notch; wherein the first tapered spline has a thickness that decreases toward a rear end of the tube yoke, and the second tapered spline has a thickness that decreases toward a front end of the main tube, and Wherein, the first tapered spline and the second tapered spline match each other.

2. The transmission shaft according to claim 1, wherein: An inner surface of the tube yoke includes an internal thread portion, and a front end of the adapter includes an external thread portion for threaded engagement with the internal thread portion of the tube yoke.

3. The transmission shaft according to claim 1, wherein: An inner surface of the main pipe includes a locking groove, and a rear end of the adapter includes a plurality of elastic clips for coupling to the locking groove.

4. The transmission shaft according to claim 3, wherein: A rear end of each of the plurality of elastic clips is integrally formed with a hook that is bent outward to fit into the locking groove.

5. The transmission shaft according to claim 1, further comprising: An O-ring is fitted into the fracture-inducing cutout in the adapter to prevent penetration of foreign matter.

6. The transmission shaft according to claim 1, wherein A rear surface of the first tapered spline and a front surface of the second tapered spline have tapered surfaces, inclined surfaces of which contact each other.

7. The transmission shaft according to claim 6, wherein: The first conical spline includes a plurality of first teeth and a plurality of first tooth grooves arranged circumferentially and alternately, and a rear surface of each of the plurality of first teeth and the plurality of first tooth grooves is formed as a first conical surface, which is inclined outward from the inner surface to the outer surface of the tube yoke.

8. The transmission shaft according to claim 6, wherein: The second tapered spline includes a plurality of second teeth and a plurality of second tooth grooves that are circumferentially and alternately arranged, and a front surface of each of the plurality of second teeth and the plurality of second tooth grooves is formed as a second tapered surface that is inclined inwardly from an outer surface toward an inner surface of the main pipe.

9. The transmission shaft according to claim 6, wherein: The first conical spline includes a plurality of first teeth and a plurality of first tooth grooves arranged circumferentially and alternately, and a rear surface of each of the plurality of first teeth and the plurality of first tooth grooves is formed as a first conical surface, which is inclined inward from the outer surface to the inner surface of the tube yoke.

10. The transmission shaft according to claim 6, wherein The second tapered spline includes a plurality of second teeth and a plurality of second tooth grooves that are circumferentially and alternately arranged, and a front surface of each of the plurality of second teeth and the plurality of second tooth grooves is formed as a second tapered surface that is inclined outward from the inner surface to the outer surface of the main pipe.

Images