Main branch offset exhaust pipe structure of multi-cylinder engine and construction method of main branch offset exhaust pipe structure

Abstract

The invention discloses a main branch offset exhaust pipe structure of a multi-cylinder engine and a construction method thereof, and belongs to the technical field of internal combustion power, the main branch offset exhaust pipe structure comprises a main exhaust pipe and an exhaust manifold, the horizontal plane where the axis of the main exhaust pipe is located and the horizontal plane where the axis of the exhaust manifold is located are arranged in different planes, the horizontal height difference between the main exhaust pipe and the exhaust manifold is d, the inner diameter of the exhaust manifold is D, and 0.25 < = d / D < = 0.5. When exhaust gas of an engine is exhausted and converged into the main exhaust pipe from the branch exhaust manifolds, relatively stable longitudinal vortex structures with the same rotation direction and a turbine shaft parallel to the axis of the main pipe can be generated, the negative influence of exhaust gas of a downstream manifold on upstream flow is reduced, and the exhaust gas flow condition of the engine is improved.

Description

Technical Field

[0001] This invention belongs to the field of internal combustion power and relates to the main manifold offset exhaust pipe structure of a multi-cylinder engine and its construction method. Background Technology

[0002] In multi-cylinder engines, the exhaust pipe is typically a main manifold structure. The exhaust manifold collects exhaust gases from each cylinder into the main exhaust pipe, which then transports the exhaust gases to downstream components such as the turbocharger or aftertreatment system. Currently, most engine exhaust pipes employ a coplanar arrangement of the main and manifolds, ensuring that the manifold axis is coplanar with the main pipe axis near the connection point. However, in multi-cylinder engines, each cylinder exhausts gas in turn. With this coplanar arrangement, downstream cylinder exhaust can easily cause higher pressure than upstream cylinders, leading to stagnation or backflow of the working fluid upstream, ultimately resulting in increased repulsion losses and excessively high exhaust pressure.

[0003] Currently, one common solution is to increase the velocity component of the manifold exhaust velocity downstream of the main pipe by changing the main manifold angle, thereby reducing the manifold's influence on the upstream flow field. However, in a coplanar arrangement of the main and manifolds, the main manifold angle is constrained by the overall engine design, making it difficult to significantly reduce the angle to weaken the manifold's influence on the upstream flow field. In practical applications, whether or not the manifold exhausts gas still has a significant impact on the flow characteristics within the main pipe, making it difficult to fully address issues such as high pipe losses and high exhaust pressure. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention proposes a main manifold offset exhaust pipe structure and its construction method for a multi-cylinder engine. Addressing the technical issues in the prior art, the exhaust manifold axis and the exhaust main pipe axis are spatially opposite in the horizontal direction. This allows the exhaust forces of each exhaust manifold to generate a stable longitudinal vortex structure within the main pipe, with the vortex axis parallel to the main pipe axis. On one hand, the longitudinal vortex structure utilizes its ability to store kinetic energy through circumferential rotation under high adverse pressure gradients and its stable development along the flow direction, reducing the impact of whether or not exhaust is present in each manifold on the flow characteristics within the main pipe, thereby achieving the goal of reducing repulsion losses and improving flow stability within the main pipe. On the other hand, the low-pressure vortex core construction capability of the longitudinal vortex structure enables the main pipe to actively entrain the working fluid within the manifold, thereby achieving the goal of reducing exhaust pressure and improving engine operating conditions.

[0005] The main manifold offset exhaust pipe structure of a multi-cylinder engine includes an exhaust main pipe and an exhaust manifold. The horizontal plane containing the axis of the exhaust main pipe is opposite to the horizontal plane containing the axis of the exhaust manifold, and the difference in their horizontal height is d. The inner diameter of the exhaust manifold is D, and 0.25≤d / D≤0.5.

[0006] Furthermore, the horizontal plane where the axis of the exhaust manifold is located is higher than the horizontal plane where the axis of the exhaust main pipe is located, and the horizontal plane where the upper end of the exhaust manifold is located is higher than the horizontal plane where the uppermost end of the exhaust main pipe is located, forming a low-pressure vortex core of a longitudinal vortex structure, which enables the exhaust main pipe to actively entrain the working fluid in the exhaust manifold and reduce the exhaust pressure.

[0007] Furthermore, the inner diameter of the exhaust manifold is not greater than the inner diameter of the exhaust main pipe, and the horizontal plane at the top of the exhaust manifold is not lower than the horizontal plane at the top of the exhaust main pipe.

[0008] Furthermore, the axis of the exhaust main pipe is set at an angle β with the axis of the exhaust manifold. Along the direction of gas flow, the angle β formed at the convergence point is an acute angle, which makes the exhaust from each exhaust manifold form a stable longitudinal vortex structure in the exhaust main pipe with the vortex axis parallel to the axis of the exhaust main pipe.

[0009] Furthermore, the longitudinal vortex structure stores kinetic energy through circumferential rotation under a high adverse pressure gradient, flows along the flow direction, reduces the gas flow in the main exhaust pipe by reducing the gas flow in each exhaust manifold, reduces repulsion losses, and stabilizes the gas flow in the main exhaust pipe.

[0010] Furthermore, the exhaust manifold deforms and transitions into the exhaust main pipe to form a transition section, and the curved surfaces at each connection point between the transition section and the exhaust main pipe are second-order continuous.

[0011] Furthermore, the outer contour of the transition section is controlled by a styling reference surface, which is the plane containing the shortest distance between the exhaust manifold axis and the exhaust main axis in the perpendicular direction. The outer contour generatrix of the transition section is projected as a spiral line on the styling reference surface.

[0012] Furthermore, multiple styling constraint surfaces with equal phase differences are included. The shape of the transition section is controlled by the cross-sectional shape of the transition section on each constraint surface. The initial constraint surface is the plane containing the line connecting the exhaust manifold axis and the shortest distance perpendicular to the exhaust manifold axis. Furthermore, it also includes a termination constraint surface, the phase difference between the termination constraint surface and the starting constraint surface being [0.25π, π].

[0013] Furthermore, there are two exhaust manifolds, which converge to form a main exhaust pipe, forming a Y-shaped structure. The axes of the two exhaust manifolds are located on opposite horizontal planes, and the exhaust from the two exhaust manifolds forms a stable longitudinal vortex structure within the main exhaust pipe, with the vortex axis parallel to the axis of the main exhaust pipe.

[0014] The method for constructing the main manifold offset exhaust pipe structure of a multi-cylinder engine includes the following steps: S1. The axis of the exhaust main pipe is set at an angle β to the axis of the exhaust manifold, and the two are set on opposite sides in the horizontal direction. S2. Establish a styling reference surface control, wherein the styling reference surface is the plane containing the exhaust manifold axis and the line connecting the shortest distance perpendicular to the exhaust manifold axis and the exhaust main axis. S3. Establish multiple styling constraint surfaces with equal phase difference. The starting constraint surface is the plane containing the shortest distance between the exhaust manifold axis and the exhaust main axis in the perpendicular direction. The phase difference between the ending constraint surface and the starting constraint surface is [0.25π, π]. S4. The exhaust manifold transforms into the exhaust main pipe to form a transition section. The outer contour generatrix of the transition section is projected as a spiral on the modeling reference surface. By controlling the cross-sectional shape of the transition section on each constraint surface and controlling the shape of the transition section, the exhaust from each exhaust manifold forms a stable longitudinal vortex structure in the exhaust main pipe with the vortex axis parallel to the exhaust main pipe axis, thus stabilizing the gas flow in the exhaust main pipe. S5. Determine the three-dimensional shape of the transition section to ensure that the surfaces at each connection point between the transition section and the exhaust main pipe, and at each connection point between the transition section and the exhaust manifold, are continuous in two orders.

[0015] Compared with the prior art, the main manifold offset exhaust pipe structure and its construction method for the multi-cylinder engine described in this application have the following advantages: (1) Based on the conventional coplanar arrangement of the main exhaust manifold, this application arranges the exhaust manifold axis and the exhaust main pipe axis in a horizontally parallel manner in space, so that the exhaust force of each exhaust manifold generates a stable longitudinal vortex structure in the main pipe with the vortex axis parallel to the main pipe axis. On the one hand, by utilizing the flow characteristics of the longitudinal vortex structure, which can store kinetic energy by circumferential rotation under high adverse pressure gradient and exist and develop stably along the flow direction, the influence of whether each manifold exhausts or not on the flow characteristics in the main pipe is reduced, thereby achieving the goal of reducing repulsion loss and improving the flow stability in the main pipe; on the other hand, by utilizing the low-pressure vortex core construction capability of the longitudinal vortex structure, the main pipe can actively entrain the working fluid in the manifold, thereby achieving the goal of reducing exhaust pressure and improving the engine operating condition.

[0016] (2) The exhaust manifold of this application is deformed and transitioned to the exhaust main pipe to form a transition section. The curved surfaces at each connection between the transition section and the exhaust main pipe are second-order continuous. From the perspective of gas flow, the second-order continuous inner wall of the pipeline can minimize the flow resistance. From the perspective of hardware structure, stress concentration will be greatly reduced, thereby improving the fatigue life and structural reliability of the pipeline.

[0017] (3) The outer contour of the transition section in this application is controlled by the modeling reference surface. The generatrix of the outer contour line of the transition section is projected as a spiral on the modeling reference surface, so that the shape of the transition section is smooth. By controlling the cross-sectional shape of the transition section on each constraint surface, the modeling details of the transition section are controlled, so that the cross-section of the transition section is infinitely close to a circular arc, and the overall second-order continuity is completely smooth. Under the condition of satisfying the second-order continuity, the preferred scheme is that the cross-section of the transition section on the modeling constraint surface is close to a circle. After completion, the entire structure is continuous and smooth, which helps the smoothness of the exhaust process and the formation of the process described in the first point above. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the structure when the exhaust main pipe and exhaust manifold are vertically arranged according to this application; Figure 2 This is a schematic diagram of the structure when the exhaust main pipe and exhaust manifold of this application are set at an acute angle; Figure 3 This is a schematic diagram of the structure in this application where a vortex is formed when the gas enters the main exhaust pipe from the exhaust manifold. Figure 4 This is a structural schematic diagram of the shape reference surface and shape constraint surface in this application; Figure 5 This is a perspective view of the main manifold offset exhaust pipe structure of the multi-cylinder engine in this application; Figure 6 This is a front view of the main manifold offset exhaust pipe structure of the multi-cylinder engine in this application; Figure 7 For this application Figure 6 AA section view; Figure 8 For this application Figure 6 BB cross-sectional view; Figure 9 This is a frontal structural diagram of Embodiment 2 in this application; Figure 10 This is a schematic diagram of the structure of Embodiment 2 of this application, showing the two exhaust manifolds offset in opposite directions from the rear. Figure 11 This is a schematic diagram of the structure of two exhaust manifolds in Embodiment 2 of this application, which are offset to the same side and viewed from opposite rear views.

[0019] Explanation of reference numerals in the attached figures: 1. Exhaust main pipe; 2. Exhaust manifold; 3. Design reference surface; 4. Starting constraint surface; 5. Ending constraint surface; 6. Transition section. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0021] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0022] like Figures 1-8 As shown, the main manifold offset exhaust pipe structure of a multi-cylinder engine includes an exhaust main pipe 1 and an exhaust manifold 2. The horizontal plane containing the axis of the exhaust main pipe 1 is opposite to the horizontal plane containing the axis of the exhaust manifold 2, and the difference in their horizontal height is d. The inner diameter of the exhaust manifold 2 is D, and 0.25≤d / D≤0.5 is set with a certain parameter ratio to ensure the formation of vortex during the subsequent gas emission process.

[0023] Preferably, the horizontal plane where the axis of the exhaust manifold 2 is located is higher than the horizontal plane where the axis of the exhaust main pipe 1 is located, and the horizontal plane where the upper end of the exhaust manifold 2 is located is higher than the horizontal plane where the uppermost end of the exhaust main pipe 1 is located, forming a longitudinal vortex structure low-pressure vortex core, so that the exhaust main pipe 1 actively entrains the working fluid in the exhaust manifold 2, reducing the exhaust pressure.

[0024] Preferably, the inner diameters of the exhaust main pipe 1 and the exhaust manifold 2 are the same. In actual application, the two inner diameters can also be different. The inner diameter of the exhaust manifold 2 is less than or equal to the inner diameter of the exhaust main pipe 1. It is necessary to maintain the existence of the horizontal height difference d between the two, and at the same time ensure that the horizontal plane at the upper end of the exhaust manifold 2 is not lower than the horizontal plane at the uppermost end of the exhaust main pipe 1, which is conducive to the formation of the low-pressure vortex core in the future.

[0025] Preferably, the axis of the exhaust main pipe 1 is set at an angle β with the axis of the exhaust manifold 2. Along the direction of gas flow, the angle β formed at the converging point is an acute angle, preferably 30-60 degrees, so that the exhaust from each exhaust manifold 2 forms a stable longitudinal vortex structure in the exhaust main pipe 1 with the vortex axis parallel to the axis of the exhaust main pipe 1.

[0026] Preferably, the longitudinal vortex structure stores kinetic energy by rotating circumferentially under a high adverse pressure gradient and flows along the flow direction. By reducing the gas flow in the main exhaust pipe 1, it reduces the gas repulsion loss and stabilizes the gas flow in the main exhaust pipe 1.

[0027] Preferably, the exhaust manifold 2 deforms and transitions into the exhaust main pipe 1 to form a transition section 6, and the surfaces at each connection point between the transition section 6 and the exhaust main pipe 1 are second-order continuous. Second-order continuous surfaces mean that the surfaces at the connection point between the exhaust main pipe 1 and the exhaust manifold 2 are not only smoothly connected, but also have completely consistent bending trends without abrupt transitions. That is, the tangent directions and curvatures of the two surfaces at the connection point are the same. For the exhaust structure in this application, from a gas flow perspective, the second-order continuous inner wall of the pipe can minimize flow resistance. From a hardware structural perspective, stress concentration is greatly reduced, improving the fatigue life and structural reliability of the pipe.

[0028] Throughout the construction process, to ensure second-order continuity, surfaces are constructed using curves such as splines or curvature-continuous transition curves (such as clothoid spirals), so that the curvature changes continuously from the starting point to the ending point, eliminating any abrupt changes.

[0029] Preferably, the outer contour of the transition section 6 is controlled by the styling reference surface 3. The styling reference surface 3 is the plane containing the shortest distance between the axis of the exhaust manifold 2 and the axis of the exhaust main pipe 1 in the perpendicular direction. The generatrix of the outer contour line of the transition section 6 is projected as a spiral line on the styling reference surface 3, so that the shape of the transition section 6 is smooth.

[0030] Preferably, the design includes multiple styling constraint surfaces with equal phase differences. The shape of the transition segment 6 on each constraint surface controls the styling details of the transition segment 6, making it infinitely close to a circular arc, achieving complete smoothness of the overall second-order continuity. It is necessary to ensure the smoothness of the profile of the cross section itself, as well as the smooth and natural change rules of the cross section's posture along the path (such as torsional control). The starting constraint surface 4 is the plane containing the shortest distance between the axis of the exhaust manifold 1 and the axis of the exhaust manifold 2 perpendicular to the axis of the exhaust manifold 1. The phase difference between the ending constraint surface 5 and the starting constraint surface 4 is [0.25π, π]. The cross section of the transition segment 6 on the multiple styling constraint surfaces should be as smooth as possible to ensure the overall smoothness. Adjustments and corrections are made according to the actual cross section situation until second-order continuity is satisfied. Under the condition of satisfying second-order continuity, it is preferable that the cross section of the transition segment 6 on the styling constraint surface is close to a circle. The smoother the connection, the better it is for the smoothness of exhaust and the higher the stability.

[0031] The method for constructing the main manifold offset exhaust pipe structure of a multi-cylinder engine includes the following steps: S1. The axis of the exhaust main pipe 1 is set at an angle β with the axis of the exhaust manifold 2, and the two are set on opposite sides in the horizontal direction. S2. Establish the shape reference plane 3 for control. The shape reference plane 3 is the plane containing the shortest distance between the axis of exhaust manifold 2 and the axis of exhaust main pipe 1 in the perpendicular direction. S3. Establish multiple styling constraint surfaces with equal phase difference. The starting constraint surface 4 is the plane where the shortest distance between the axis of exhaust manifold 1 and the axis of exhaust manifold 2 perpendicular to the axis of exhaust manifold 1 is located. The phase difference between the ending constraint surface 5 and the starting constraint surface 4 is [0.25π, π]. S4. The exhaust manifold 2 deforms and transitions to the exhaust main pipe 1 to form a transition section 6. The outer contour generatrix of the transition section 6 is projected as a spiral line on the modeling reference surface 3. By controlling the cross-sectional shape of the transition section 6 on each constraint surface and making the shape of the transition section 6 close to a circular arc, the exhaust of each exhaust manifold 2 forms a stable longitudinal vortex structure in the exhaust main pipe 1 with the vortex axis parallel to the axis of the exhaust main pipe 1, thus stabilizing the gas flow in the exhaust main pipe 1. S5. Determine the three-dimensional shape of the transition section 6 to ensure that the surfaces of the transition section 6 at each connection point with the exhaust main pipe 1 and with the exhaust manifold 2 are continuous at the second order.

[0032] The smooth transition between the exhaust main pipe and the exhaust manifold, formed strictly according to the steps, along with the non-planar arrangement structure, solves problems such as high pipe loss and high exhaust pressure. In addition to its application in exhaust structures, it can also be applied to similar structures such as heating and water supply systems.

[0033] Example 2: Unlike Example 1, the pipeline system does not have an upstream main pipe. Instead, multiple exhaust manifolds converge at the same location to form the main pipe. The multiple exhaust manifolds are arranged horizontally, and the exhaust main pipe is also arranged horizontally. Taking the case of two exhaust manifolds as an example, by controlling the transition form in which the two exhaust manifolds converge to form the exhaust main pipe, a stable vortex structure is formed within the exhaust main pipe.

[0034] After being assembled, the front view shows a Y-shaped structure, as shown below. Figure 9 As shown in the side view, the axes of the two exhaust manifolds are positioned on opposite horizontal planes. The junction of the two exhaust manifolds and the main exhaust pipe forms a circumferentially evenly distributed structure. The exhaust gas from the two manifolds forms a stable, longitudinally swirling structure within the main exhaust pipe, with its vortex axis parallel to the main exhaust pipe axis. Specifically, the two exhaust manifolds can be arranged in two different ways, such as... Figure 10 As shown in the side view, the two exhaust manifolds are offset to the left and right respectively. After being offset in opposite directions, their axes are positioned on opposite horizontal planes. Figure 11As shown in the side view, the two exhaust manifolds are offset to the same side, and their axes are located on opposite horizontal planes. If the section perpendicular to the main exhaust flow direction of the transition section between the exhaust manifold and the main exhaust pipe is defined as the transition section, then the velocity vector projections of the working fluids in the two exhaust manifolds on the transition section are not coaxial. This results in the mixed working fluids within the transition section having a non-zero initial velocity circulation, i.e., a rotational component. The motion directions at each point are inconsistent, which is the basis for generating vortices. This induces the working fluid in the downstream exhaust pipe to form a stable longitudinal vortex structure with the vortex axis along the main flow direction. Regardless of the structure, both can solve problems such as high pipe losses and high exhaust pressure.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0036] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A main manifold offset exhaust pipe structure for a multi-cylinder engine, characterized in that: It includes an exhaust main pipe and at least one exhaust manifold. The horizontal plane containing the axis of the exhaust main pipe is opposite to the horizontal plane containing the axis of the exhaust manifold, and the difference in their horizontal height is d. The inner diameter of the exhaust manifold is D, and 0.25≤d / D≤0.

5.

2. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 1, characterized in that: The horizontal plane where the axis of the exhaust manifold is located is higher than the horizontal plane where the axis of the exhaust main pipe is located, and the horizontal plane where the upper end of the exhaust manifold is located is higher than the horizontal plane where the uppermost end of the exhaust main pipe is located, forming a longitudinal vortex structure low-pressure vortex core, which enables the exhaust main pipe to actively entrain the working fluid in the exhaust manifold and reduce the exhaust pressure.

3. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 1, characterized in that: The inner diameter of the exhaust manifold is not greater than the inner diameter of the exhaust main pipe, and the horizontal plane at the top of the exhaust manifold is not lower than the horizontal plane at the top of the exhaust main pipe.

4. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 1, characterized in that: The axis of the exhaust main pipe is set at an angle β with the axis of the exhaust manifold. Along the direction of gas flow, the angle β formed at the converging point is an acute angle, which makes the exhaust from each exhaust manifold form a stable longitudinal vortex structure in the exhaust main pipe with the vortex axis parallel to the axis of the exhaust main pipe.

5. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 4, characterized in that: The longitudinal vortex structure stores kinetic energy by rotating circumferentially under high adverse pressure gradients and flows along the flow direction. It reduces the gas flow in the main exhaust pipe by reducing the gas flow in each exhaust manifold, thereby reducing repulsion losses and stabilizing the gas flow in the main exhaust pipe.

6. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 1, characterized in that: The exhaust manifold deforms and transitions into the exhaust main pipe to form a transition section, and the curved surfaces at each connection point between the transition section and the exhaust main pipe are second-order continuous.

7. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 6, characterized in that: The outer contour of the transition section is controlled by a styling reference surface, which is the plane containing the shortest distance between the exhaust manifold axis and the exhaust main axis in the perpendicular direction. The outer contour line generatrix of the transition section is projected as a spiral line on the styling reference surface.

8. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 6, characterized in that: It includes multiple styling constraint surfaces with equal phase difference. The transition section shape is controlled by the transition section cross-sectional shape on each constraint surface. The starting constraint surface is the plane where the shortest distance between the exhaust manifold axis and the exhaust main axis and the exhaust manifold axis in the perpendicular direction is located. It also includes a termination constraint surface. The phase difference between the termination constraint surface and the starting constraint surface is [0.25π, π].

9. The main manifold offset exhaust pipe structure for a multi-cylinder engine according to claim 1, characterized in that: The number of exhaust manifolds is two. The two exhaust manifolds converge to form an exhaust main pipe, forming a Y-shaped structure. The horizontal planes containing the axes of the two exhaust manifolds are set at opposite angles. The exhaust from the two exhaust manifolds forms a stable longitudinal vortex structure in the exhaust main pipe, with the vortex axis parallel to the axis of the exhaust main pipe.

10. A method for constructing a main manifold offset exhaust pipe structure for a multi-cylinder engine, characterized in that: Based on the main manifold offset exhaust pipe structure of the multi-cylinder engine according to any one of claims 1-6, the following steps are included: S1. The axis of the exhaust main pipe is set at an angle β to the axis of the exhaust manifold, and the two are set on opposite sides in the horizontal direction. S2. Establish a styling reference surface control, wherein the styling reference surface is the plane containing the exhaust manifold axis and the line connecting the shortest distance perpendicular to the exhaust manifold axis and the exhaust main axis. S3. Establish multiple styling constraint surfaces with equal phase difference. The starting constraint surface is the plane containing the shortest distance between the exhaust manifold axis and the exhaust main axis in the perpendicular direction. The phase difference between the ending constraint surface and the starting constraint surface is [0.25π, π]. S4. The exhaust manifold transforms into the exhaust main pipe to form a transition section. The outer contour generatrix of the transition section is projected as a spiral on the modeling reference surface. By controlling the cross-sectional shape of the transition section on each constraint surface and controlling the shape of the transition section, the exhaust from each exhaust manifold forms a stable longitudinal vortex structure in the exhaust main pipe with the vortex axis parallel to the exhaust main pipe axis, thus stabilizing the gas flow in the exhaust main pipe. S5. Determine the three-dimensional shape of the transition section to ensure that the surfaces at each connection point between the transition section and the exhaust main pipe, and at each connection point between the transition section and the exhaust manifold, are continuous in two orders.

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