End wall positioning and sealing structure of rotary adjustable guide vane of supercharger

Abstract

The invention discloses an end wall positioning and sealing structure of a rotary adjustable guide vane of a supercharger, and belongs to the technical field of supercharging power systems, the end wall positioning and sealing structure comprises an adjustable vane and a lower end wall which are matched with each other, the lower end wall is used as a fixed part, and the adjustable vane rotates relative to the lower end wall; a guide inclined surface is arranged between the adjustable blade and the lower end wall and is used for restraining coaxial positioning of a rotating shaft of the adjustable blade relative to a mounting hole in the lower end wall, so that the guide blade slides up and down relative to the lower end wall when the thermal expansion and cold contraction state of a shaft hole is changed due to temperature difference change of the blade and the lower end wall, and clamping stagnation of a contact surface caused by thermal expansion and cold contraction is avoided; and a gap is formed between the lower edge and the lower end wall of the adjustable blade to form a non-contact labyrinth channel which is matched with the guide inclined surface to prevent waste gas leakage. The coaxial sealing device is high in coaxial precision, good in sealing performance, capable of avoiding clamping stagnation and high in stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercharged power systems, and in particular relates to an end wall positioning and sealing structure of a supercharger rotary adjustable guide vane. Background Art

[0002] Turbocharging is a common technology used to increase the intake pressure of a power system. In a turbocharger, the turbine's primary task is to convert the energy of high-temperature exhaust gases into mechanical energy and perform external work. Rotating adjustable guide vanes are a technical approach to improving the dynamic response of the turbocharger and reducing the boost lag effect. However, in a rotating adjustable guide vane turbocharger, on the one hand, it is necessary to limit the impact of high-temperature combustion gases on components such as the transmission mechanism outside the end wall, suppressing leakage flow within the gap between the nozzle vanes and the nozzle end wall; on the other hand, it is necessary to support the nozzle vanes to rotate stably and smoothly relative to the end wall to ensure the nozzle's variable geometry flow regulation function; and on the other hand, it is necessary to deal with a series of mating and blocking issues caused by the large thermal load state gap between the nozzle vanes and the nozzle end wall in most operating conditions and the asynchronous thermal expansion and contraction of the two components. Summary of the Invention

[0003] In order to solve the above-mentioned problems existing in the prior art, the present invention proposes an end wall positioning sealing structure for a supercharger rotary adjustable guide vane. In response to the technical problems existing in the background technology, a guide bevel is used to constrain the adjustable blade rotation axis to be strictly coaxial with the lower end wall mounting hole, thereby avoiding the adjustable blade from skewing. At the same time, the guide bevel is used to allow the blade and the end wall shaft hole to slide up and down relative to each other when the expansion and contraction are inconsistent, thereby avoiding contact surface jamming. Further, a complex non-contact maze channel is used to strengthen the gas sealing on both sides of the lower end wall, ultimately supporting the stable adjustment of the rotary adjustable guide vane.

[0004] The end wall positioning sealing structure of the supercharger rotary adjustable guide vane includes an adjustable vane and a lower end wall that are arranged in a coordinated manner. The lower end wall serves as a fixed part, and the adjustable vane rotates relative to the lower end wall. A guide slope is provided between the adjustable blade and the lower end wall. The guide slope is used to constrain the coaxial positioning of the rotating axis of the adjustable blade relative to the mounting hole on the lower end wall. When the temperature difference between the blade and the lower end wall causes the thermal expansion and contraction state of the shaft hole to change, the guide blade slides up and down relative to the lower end wall to avoid contact surface stagnation caused by thermal expansion and contraction. A gap is provided between the lower edge of the adjustable blade and the lower end wall to form a non-contact labyrinth passage, which cooperates with the guide slope to prevent exhaust gas leakage.

[0005] Furthermore, the included angle between the guide slope and the horizontal plane is no greater than 30 degrees.

[0006] Furthermore, the non-contact maze channel includes at least five channel turns with an angle no greater than 90° and forms at least one "concave" channel.

[0007] Furthermore, the structural dimensions of the walls on both sides of the non-contact maze channel are selected according to the maximum positive and negative temperature difference and the limit deformation between the guide vane and the end wall, so as to ensure that the various mating surfaces of the non-contact maze channel are clearance-fitted, thereby avoiding jamming caused by contact between the walls of the non-contact maze channel under thermal expansion and contraction.

[0008] Furthermore, the thickness of the non-contact maze channel is 0.2-0.3 mm.

[0009] Furthermore, the upper end and / or lower end surface of the guide slope is provided with an oil storage microstructure for lubrication.

[0010] Furthermore, the upper end and / or lower end surface of the guide slope is coated with a low-resistance material layer for anti-wear and resistance reduction.

[0011] Furthermore, when the expansion degree of the rotating shaft of the adjustable blade is greater than or the contraction degree is smaller than the mounting hole of the lower end wall, the guide bevel acts to constrain the adjustable blade to slide along the rotating shaft toward the side away from the lower end wall; when the expansion degree of the blade shaft is less than or the contraction degree is greater than the mounting hole of the lower end wall, the guide bevel constrains the adjustable blade to slide along the rotating shaft toward the side close to the lower end wall.

[0012] Furthermore, the non-contact maze channels are uniformly thick.

[0013] Furthermore, outside the non-contact labyrinth channel, the distance between the lower end surface of the adjustable blade and the upper end surface of the lower end wall is H, and H is greater than the thickness setting of the non-contact labyrinth channel.

[0014] Compared with the prior art, the end wall positioning and sealing structure of the supercharger rotary adjustable guide vane described in this application has the following beneficial effects: (1) This application uses a guide bevel to constrain the adjustable blade's rotating axis to be strictly coaxial with the lower end wall mounting hole to prevent the adjustable blade from tilting. At the same time, the guide bevel allows the blade and the end wall shaft hole to slide up and down relative to each other when the expansion and contraction are inconsistent to avoid contact surface jamming. The complex non-contact maze channel is further used to strengthen the gas seal on both sides of the lower end wall, ultimately supporting the stable adjustment of the rotary adjustable guide vane.

[0015] (2) The non-contact labyrinth channel of the present application is provided with at least five bends to form a concave structure. When the gas flows through multiple bends, the pressure decreases, which is the result of viscous dissipation and flow separation. The principle of continuous loss of fluid mechanical energy (pressure energy, kinetic energy) due to friction, eddy currents and momentum changes is utilized to achieve better and more stable sealing.

[0016] (3) This application sets a guide slope, which cooperates with the non-contact maze channel to achieve sealing, ensure coaxiality, and realize up and down adjustment, achieving higher precision and better stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings: Figure 1 It is a structural schematic diagram of the exhaust gas flow direction in the variable-section turbocharger structure; Figure 2 This is a schematic structural diagram of the variable-geometry turbocharger of this application; Figure 3 This is a half-section schematic diagram of the adjustable blades and the lower end wall after being matched in Example 1 of the present application; Figure 4 This is a half-section schematic diagram of the adjustable blades after being matched with the lower end wall in Example 2 of the present application; Figure 5 This is a half-section schematic diagram of the adjustable blades after being matched with the lower end wall in Example 3 of the present application.

[0018] Description of reference numerals: 1. Adjustable guide vane; 2. Lower end wall; 3. Rotation axis; 4. Mounting hole; 5. Guide slope; 6. First turning channel; 7. Second turning channel; 8. Third turning channel; 9. Fourth turning channel; 10. Fifth turning channel; 11. Sixth turning channel. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0020] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should have the usual meanings understood by people with ordinary skills in the field to which this application belongs. The "first", "second" and similar words used in the embodiments of the present application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like 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.

[0021] In this application, the term "supercharger" refers to a variable geometry turbocharger (VGT), also known as a variable nozzle turbocharger (VNT). This type of turbocharger achieves efficient boosting across all operating conditions by dynamically adjusting the turbine cross-section. It is primarily used in gasoline and diesel engines. The core component of the entire structure is the guide vanes, whose angle is adjusted in real time by an electronic control system to alter the exhaust gas flow and velocity. At low rpm, the flow path cross-section is reduced, increasing air velocity for faster turbine response (for example, the Volkswagen EA888 engine achieves 400 Nm of torque at 1700 rpm). At high rpm, the cross-section is expanded to reduce backpressure and prevent turbine overspeed. Compared to traditional turbochargers, this significantly improves low-speed response time and acceleration. Gasoline engines using variable turbine cross-section technology are significantly more efficient across the entire speed range than current standard blow-off valve turbochargers. Consequently, fuel efficiency is further improved across the entire speed range.

[0022] The working principle of the variable nozzle turbocharger is: it uses movable nozzle ring blades, which can rotate together around their respective axes. As the angle of the nozzle ring blades changes, the minimum flow cross-sectional area of ​​the turbine and the angle and speed of the exhaust gas entering the turbine will change, thereby changing the turbine speed and the boost pressure at the compressor outlet.

[0023] When the engine is running at low speed, the cross-sectional area of ​​the nozzle ring decreases, the turbine speed increases, and the boost pressure increases, ensuring the boost pressure and intake volume at low speed; when the engine is running at high speed, the cross-sectional area of ​​the nozzle ring increases, the turbine speed decreases, and the supercharger overspeed is prevented. When the engine accelerates, in order to improve the response speed of the supercharger, the cross-sectional area of ​​the nozzle ring can be reduced and the supercharger speed can be increased, thereby increasing the boost pressure and intake volume to meet the intake requirements during transient operation. For an introduction to this structure, please refer to the following video link.

[0024] In existing technical solutions, guide vanes are referred to as guide vanes and are usually fixed to the turbine housing through the following structure. The lower end wall and the turbine housing are cast as an integral structure. In this application, the cooperation between the guide vanes and the lower end wall can also be described as the cooperation between the guide vanes and the turbine housing. After the two are rotatably connected, it is ensured that the guide vanes can rotate and adjust the angle while maintaining sealing and stability. There are two main fixing methods: Rotating shaft design: There is a short shaft at the bottom of each guide vane, which is inserted into the corresponding shaft hole of the turbine housing. There may be a bushing (high temperature resistant material such as bronze or ceramic coating) in the shaft hole to reduce friction and allow the blade to rotate freely.

[0025] Ring linkage mechanism: The top or bottom of all blades are connected by a unison ring. The rotation of the unison ring will synchronously drive all blades to rotate around their respective axes to ensure consistent angles.

[0026] Attention should be paid to sealing and clearance control. A very small gap (usually 0.05~0.1mm) must be maintained between the edge of the guide vane and the turbine housing to prevent exhaust gas leakage. In high-temperature environments, the thermal expansion of the material must be calculated in advance to avoid sticking. For example, the materials used are nickel-based alloy blades and cast iron housings.

[0027] The guide vane drive system needs to work reliably in a high temperature and high vibration environment. Common drive solutions are as follows: 1. Pneumatic drive (vacuum / air pressure): The vacuum diaphragm valve (Vacuum Actuator) is connected to the linkage ring through a connecting rod.

[0028] The ECU controls the vacuum level of the vacuum pump or the engine intake manifold to move the diaphragm. It is characterized by low cost and is commonly used in early diesel engines, such as the Bosch system. It has a slow response speed and limited control accuracy.

[0029] 2. Electric drive (servo motor): A small stepper motor or DC servo motor drives the linkage ring through gears or connecting rods.

[0030] The motor has a built-in position sensor (such as a Hall sensor) that feeds back the blade angle to the ECU. It is characterized by precise control (such as the Toyota D4-ST gasoline engine) and fast response, and requires a high-temperature resistant motor design (the motor is usually external and transmits power through the shaft).

[0031] Hydraulic drive: Utilizes engine oil pressure or a dedicated hydraulic pump to push the piston, which in turn drives the linkage ring. This system requires high-pressure seals and oil control valves. It features high thrust and is suitable for large turbines (such as those in commercial vehicles). However, the system is complex and has high maintenance costs.

[0032] The detailed workflow taking electric drive as an example is as follows: ECU command: Calculate target blade angle based on engine operating conditions; Motor action: The servo motor rotates and pushes the linkage ring through the reduction gear; Synchronous adjustment: The linkage ring drives all guide vanes to rotate around the axis, changing the cross-sectional area of ​​the exhaust gas channel; Feedback closed loop: The position sensor monitors the angle in real time, and the ECU dynamically corrects the error.

[0033] The end wall refers to the annular structural surface inside the turbine housing that fits tightly with the two ends of the guide vanes. It is the key boundary of the exhaust gas flow channel. The guide vanes are distributed radially along the turbine shaft, and the two ends (top and bottom) are respectively close to two parallel annular end walls. The upper end wall refers to the side close to the turbine housing cover, and the lower end wall refers to the side close to the turbine impeller (that is, the rotor blades impacted by the exhaust gas). The end wall is essentially the "ceiling" and "floor" of the exhaust gas flow channel, and its design directly affects the energy conversion efficiency of the airflow. In the end wall structure, the exhaust gas flow direction is shown as follows Figure 1 as follows.

[0034] Structurally, the end wall provides a mounting base for the rotating shaft of the guide vane. The shaft hole is located in the lower end wall to withstand the impact and vibration of the airflow. The gap between the end wall and the two ends of the guide vane is extremely small, forming a sealed airflow channel to prevent leakage of high-pressure exhaust gas and ensure that all airflow is used to drive the turbine. The end wall and the guide vane together form a contracting or expanding flow channel to guide the direction of the airflow and control the flow trajectory and speed of the exhaust gas, similar to the nozzle effect.

[0035] The connection method between the end wall and other parts is as follows: the blade rotating shaft is inserted into the shaft hole of the lower end wall, and the hole is lined with self-lubricating material (such as graphite bronze) to ensure flexible rotation; the linkage ring is located on the outside of the end wall, and the blade is connected by a connecting rod passing through the slot on the lower end wall to avoid contact with the exhaust gas during driving; the lower end wall directly faces the turbine impeller, and its profile affects the angle at which the exhaust gas enters the impeller and the energy transfer efficiency. During the cooperation between the end wall and the guide vane, gap management and dynamic sealing are required, that is, a constant gap must be maintained when the blade rotates to avoid thermal expansion jamming, such as using a "thermal gap compensation" structure; at the same time, surface treatment is performed, and the end wall contact surface is sprayed with a wear-resistant coating (such as alumina ceramic) to reduce blade friction and wear.

[0036] During operation, large amounts of exhaust gas are discharged for a long time, which is prone to carbon accumulation and blockage. Exhaust gas particles accumulate in the end wall gap, causing the blades to get stuck, and then the boost response is delayed. At the same time, long-term friction between the blades and the end wall causes the gap to increase, causing exhaust gas leakage and a drop in boost pressure.

[0037] like Figure 2-5 As shown, the end wall positioning sealing structure of the supercharger rotary adjustable guide vane includes an adjustable blade and a lower end wall that are arranged in a coordinated manner. The lower end wall serves as a fixed part, and the adjustable blade rotates relative to the lower end wall. In actual application, the lower end wall and the lower end wall can be cast into an integral structure as a core static component. A guide bevel is provided between the adjustable blade and the lower end wall, and the guide bevel is used to constrain the coaxial positioning of the rotating shaft of the adjustable blade relative to the mounting hole on the lower end wall, so that when the temperature difference between the blade and the lower end wall causes the thermal expansion and contraction state of the shaft hole to change, the guide blade slides up and down relative to the lower end wall to avoid thermal expansion and contraction causing the contact surface to become stuck; preferably, the thickness of the non-contact maze channel is 0.1-0.5mm, more preferably 0.2-0.3mm, and the two are matched to reserve expansion and contraction space. If this gap is too large, there will be air leakage problems, and there will be a lot of air leakage. In different situations, there will also be smoke leakage. During application, the gas diffuses, and other parts are not resistant to high temperatures and are prone to malfunctions, which reduces the overall service life and even causes control failure after high temperature. If the matching gap between the two is too small, during thermal expansion, When the shrinkage exceeds the budget value, it will get stuck directly and malfunction. The structure of this application and the reserved gap solve the sealing problem, avoid omissions, and avoid getting stuck. Furthermore, the wall structure dimensions on both sides of the non-contact maze channel are selected according to the maximum positive and negative temperature difference and the limit deformation between the guide vane and the end wall to ensure that the various mating surfaces of the non-contact maze channel are clearance-matched to avoid jamming caused by contact of the wall of the non-contact maze channel under thermal expansion and contraction. Under the test state, the temperature difference value range is 0-750 degrees. The test temperature range can also be adjusted according to different application conditions. For example, the minimum temperature value can also be set to -25 degrees or other temperature values ​​to determine the amount of expansion and contraction, the structure and gap before and after expansion, and the hot test is performed in the cold state to achieve the maximum temperature difference without getting stuck.

[0038] Preferably, a gap is provided between the lower edge of the adjustable blade and the lower end wall to form a non-contact maze channel, which cooperates with the guide slope to prevent exhaust gas leakage. More preferably, the non-contact maze channel includes at least five channel turns of no more than 90° and at least one "concave" channel slope contact for sealing, and space for up and down movement can be reserved, which cooperates with the non-contact maze channel to reduce air pressure and improve the stability of the seal.

[0039] Preferably, the angle between the guide slope and the horizontal plane is not greater than 30 degrees. It can be a guide slope less than 30 degrees with the horizontal plane in the first quadrant, or it can be a guide slope less than 30 degrees with the horizontal plane in the second quadrant. This horizontal plane is specific to the present application, which can be the lower end wall and the blade assembly plane or the lower end wall on the side of the blade. In the present application, the coordination between the guide slope and the non-contact maze channel is diverse. It can be set at one end of the non-contact maze channel close to the mounting hole, or it can be set at the other end away from the mounting hole. Both can achieve the technical effect of the present application. There is appropriate displacement space on both sides of the contact line of the guide slope, and sufficient adjustment space is reserved.

[0040] Preferably, the upper and / or lower end surfaces of the guide slope are provided with an oil storage microstructure, which may be an oil storage pit structure, for anti-wear and drag reduction after lubrication, ensuring that the adjustable blades can be driven by the control system to rotate stably and smoothly relative to the lower end wall in the slope contact state.

[0041] Preferably, the upper and / or lower end surfaces of the guide slope are coated with a low-resistance material layer for anti-wear and drag reduction, such as a low-resistance ceramic layer, to ensure that the adjustable blades can be driven by the control system to rotate stably and smoothly relative to the lower end wall in the slope contact state.

[0042] During actual application, when the expansion degree of the rotating shaft of the adjustable blade is greater than or the contraction degree is smaller than the mounting hole of the lower end wall, the guide bevel constrains the adjustable blade to slide along the rotating shaft to the side away from the lower end wall; when the expansion degree of the blade shaft is less than or the contraction degree is greater than the mounting hole of the lower end wall, the guide bevel constrains the adjustable blade to slide along the rotating shaft to the side close to the lower end wall.

[0043] Preferably, the non-contact maze channel is set to be uniformly thick, and the airflow is smoother; more preferably, outside the non-contact maze channel, the distance between the lower end surface of the adjustable blade and the upper end surface of the lower end wall is H, and H is greater than the thickness setting of the non-contact maze channel to avoid contact interference.

[0044] Example 1: The guide slope is arranged on the side close to the mounting hole, the first turning path, the second turning path, the third turning path, the fourth turning path, the fifth turning path and the sixth turning path constitute a non-contact maze channel, and the sixth turning path is connected to the outside.

[0045] Example 2: A sixth turning channel connected to the mounting hole is provided on the side close to the mounting hole, and a guide slope is provided on the side of the sixth turning channel away from the mounting hole. The first turning channel, the second turning channel, the third turning channel, the fourth turning channel and the fifth turning channel constitute a non-contact maze channel, and the fifth turning channel is connected to the outside.

[0046] Example 3: The guide slope is arranged on the side away from the mounting hole, the first turning path, the second turning path, the third turning path, the fourth turning path, the fifth turning path and the sixth turning path constitute a non-contact maze channel, and the sixth turning path is connected to the mounting hole.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

[0048] The embodiments of the present 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 the present application should be included in the scope of protection of this application.

Claims

1. The end wall positioning sealing structure of the supercharger rotary adjustable guide vane is characterized by: It includes an adjustable blade and a lower end wall that are matched together, the lower end wall serves as a fixed part, and the adjustable blade rotates relative to the lower end wall; A guide slope is provided between the adjustable blade and the lower end wall. The guide slope is used to constrain the coaxial positioning of the rotating axis of the adjustable blade relative to the mounting hole on the lower end wall. When the temperature difference between the blade and the lower end wall causes the thermal expansion and contraction state of the shaft hole to change, the guide blade slides up and down relative to the lower end wall to avoid contact surface stagnation caused by thermal expansion and contraction. A gap is provided between the lower edge of the adjustable blade and the lower end wall to form a non-contact labyrinth passage, which cooperates with the guide slope to prevent exhaust gas leakage.

2. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The included angle between the guide slope and the horizontal plane is no greater than 30 degrees.

3. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The non-contact maze channel includes at least five channel turns with an angle of no more than 90° and forms at least one "concave" channel.

4. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The structural dimensions of the walls on both sides of the non-contact labyrinth channel are selected according to the maximum positive and negative temperature difference and the limit deformation between the guide vane and the end wall to ensure that the mating surfaces of the non-contact labyrinth channel are clearance-fitted and to avoid jamming caused by wall contact of the non-contact labyrinth channel under thermal expansion and contraction.

5. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The non-contact maze channels are uniformly arranged.

6. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The thickness of the non-contact maze channel is 0.2-0.3 mm.

7. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The upper end and / or lower end surface of the guide inclined surface is provided with an oil storage microstructure for lubrication.

8. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: The upper end and / or lower end surface of the guide slope is coated with a low-resistance material layer for anti-wear and resistance reduction.

9. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: When the expansion degree of the rotating shaft of the adjustable blade is greater than or the contraction degree is smaller than the mounting hole of the lower end wall, the guide bevel constrains the adjustable blade to slide along the rotating shaft toward the side away from the lower end wall; when the expansion degree of the blade shaft is less than or the contraction degree is greater than the mounting hole of the lower end wall, the guide bevel constrains the adjustable blade to slide along the rotating shaft toward the side close to the lower end wall.

10. The end wall positioning and sealing structure of the supercharger rotary adjustable guide vane according to claim 1, characterized in that: Outside the non-contact labyrinth channel, the distance between the lower end surface of the adjustable blade and the upper end surface of the lower end wall is H, and H is greater than the thickness setting of the non-contact labyrinth channel.

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