Coaxial reverse paddle double-impeller driving type breeze generator

Abstract

According to the coaxial reverse paddle double-impeller driving type breeze generator, the two laminated wind gathering type impellers with the opposite rotation directions are adopted to drive the coaxial reverse paddle driving integrated power generation module to generate power, the diameter of the impellers can be greatly reduced under the same power / working condition, and the manufacturing conditions and manufacturing cost of the impellers can be reduced; the wind gathering ring of the wind gathering type impeller is used as an enhanced structure main body of the main blade, so that the main blade can be optimized to obtain a larger windward area and better light weight; the wind gathering ring gathers low-speed airflow and disordered airflow penetrating through the area according to the duct-like principle to form vortex airflow to push the auxiliary blades to do work so as to improve the low-wind-speed starting performance and the power generation stability. The integrated wind gathering type impeller composed of the propeller hub, the main blades, the wind gathering ring and the auxiliary blades is higher in overall structural strength and high in damage resistance. The economical efficiency of micro wind power generation can be further improved, emission of greenhouse gases such as carbon dioxide can be effectively reduced, and environmental protection and sustainable development are facilitated.

Description

Technical Field

[0001] This invention belongs to the technical field of wind power generation devices, and relates to a coaxial counter-rotating dual-blade driven micro wind generator. Background Technology

[0002] Wind power generation is a method of generating electricity by converting wind turbines into electrical energy. Wind power is a widely distributed, free, clean, and renewable energy source with the advantages of maintaining environmental balance and improving energy efficiency. Conventional low-elevation micro-wind generators typically use an L-type three (or more) blade horizontal axis power generation method. Specifically, ① in low-elevation / low-wind-speed applications, the low wind-catching efficiency of multi-bladed impellers with a radial aerodynamic structure centered on the impeller hub axis results in poor low-wind-speed start-up performance and insufficient stability of power generation in turbulent airflow at low elevations, further reducing the economic indicators of micro-wind power generation equipment; ② the generator is driven by a single multi-bladed impeller, and the small overall windward area of ​​a single multi-bladed impeller necessitates the use of longer blades (i.e., larger diameter impellers). Longer and lighter blades require high-quality materials and manufacturing processes, resulting in higher costs; ③ the long blades with cantilever structures are easily damaged in extreme weather conditions, and repair is difficult and costly. In summary, existing methods for micro-wind power generation using L-type three (or more) blade horizontal axis generators suffer from several drawbacks. The radial aerodynamic structure of the impeller exhibits poor low-wind-speed start-up performance, insufficient stability in power generation under turbulent airflow at low elevations, and requires stringent manufacturing conditions and incurs high costs for individual large-diameter impellers. Furthermore, the long, cantilevered blades are susceptible to damage under extreme weather conditions, and repair is difficult and costly. Therefore, addressing these issues—poor low-wind-speed start-up performance of radial aerodynamic structure impellers, insufficient stability in power generation under turbulent airflow at low elevations, high manufacturing conditions and costs for individual large-diameter impellers, and the vulnerability and costly repair of long, cantilevered blades under extreme weather conditions—is a critical technical challenge that requires expertise in the field. Summary of the Invention

[0003] To address the above technical problems, this invention provides a coaxial counter-rotating dual-impeller driven micro wind generator.

[0004] To achieve the above objectives, the present invention provides the following solution: Specifically, a coaxial reverse-propeller dual-impeller driven micro wind turbine is composed of a coaxial reverse-propeller integrated power generation module, a wind-gathering impeller, and a support / automatic yaw and power transmission assembly. The coaxial reverse-propeller integrated power generation module consists of a generator, a housing, a long main shaft, a hollow input shaft, a driven gear, a large transmission gear, a small transmission gear, a turntable, an internal gear ring, and a short shaft. The wind-gathering impeller consists of a hub, main blades, a wind-gathering ring, and auxiliary blades. The support / automatic yaw and power transmission assembly consists of a fairing, a conductive slip ring, a column, a slewing support, connecting cable I, connecting cable II, a controller, a lower hollow shaft, and a wind direction control tail fin.

[0005] More specifically, the front end of the generator is fixedly connected to the rear end of the casing at a corresponding position; inside the casing, a driven gear is fixedly installed at a corresponding position on the long main shaft of the generator, coaxial with the main shaft; the outer ring of the hollow shaft is rotatably connected to the casing via bearings at a corresponding position, and the inner ring of the hollow shaft is rotatably connected to the long main shaft via bearings at a corresponding position; the large and small transmission gears are fixedly connected coaxially; a short shaft is fixedly installed at a corresponding position on the front end of the generator, and the large and small transmission gears are rotatably connected to the short shaft via bearings; the rear end of the hollow shaft is fixedly connected coaxially to the turntable at a corresponding position, and the rear end of the turntable is fixedly connected coaxially to the internal gear ring at a corresponding position; the internal gear ring meshes with the large transmission gear. The transmission pinion meshes with the driven gear; the inner hole of the hub of the forward-rotating wind-gathering impeller is fixedly connected to the corresponding position of the long main shaft, and the inner hole of the hub of the reverse-rotating wind-gathering impeller is fixedly connected to the corresponding position of the hollow shaft; the front end of the connecting rod of the wind direction control tail fin is fixedly installed to the corresponding position of the rear end of the generator; the corresponding position of the rear side of the fairing is fixedly connected to the corresponding position of the front side of the hub of the forward-rotating wind-gathering impeller; a lower hollow shaft is fixedly installed at the corresponding position on the generator base, coaxial with the lower hollow shaft; the movable end of the slewing support is fixedly connected to the corresponding position on the generator base, and the fixed end of the slewing support is fixedly connected to the corresponding position of the top of the column; the movable end of the conductive slip ring is fixedly connected to the corresponding position of the lower hollow shaft, and the fixed end of the conductive slip ring is fixedly connected to the corresponding position of the column.

[0006] The blade roots of the main blades are fixedly connected to the corresponding positions on the outer ring of the blade hub, and the blade tips of the main blades are fixedly connected to the corresponding positions on the inner ring of the wind-gathering ring. Auxiliary blades are fixedly installed at the corresponding positions on the inner ring of the wind-gathering ring. The inner ring of the wind-gathering ring, the auxiliary blades, and the corresponding areas of the blade tip sections of the main blades form a spiral through-type wind channel structure with spacing and staggered sequence.

[0007] The speed ratio between the internal gear ring and the large transmission gear is 3:1, the speed ratio between the driven gear and the small transmission gear is 3:1, and the speed ratio between the large transmission gear and the small transmission gear is 2:1.

[0008] The front row of concentrator impellers rotates in the opposite direction to the rear row of concentrator impellers; the front row of concentrator impellers and the rear row of concentrator impellers are arranged sequentially and stacked.

[0009] One end of connecting cable I is electrically connected to the corresponding output terminal of the generator, and the other end of connecting cable I is electrically connected to the corresponding input terminal of the controller. One end of corresponding connecting cable II is electrically connected to the corresponding output terminal of the controller, and the other end of corresponding connecting cable II passes through the lower hollow shaft and is electrically connected to the corresponding input terminal of the conductive slip ring. One end of corresponding connecting cable II is electrically connected to the corresponding output terminal of the conductive slip ring, and the other end of corresponding connecting cable II is led out from the column and connected to the power grid or other electrical loads.

[0010] The basic operating mode of this coaxial reverse-rotor dual-impeller driven micro wind turbine is as follows: Supported by a column, a slewing support provides active support and hold for the coaxial reverse-rotor driven integrated power generation module, the front-row concentrating impeller, the rear-row concentrating impeller, and the wind direction control tail fin. Continuous micro-wind airflow drives the coaxial reverse-rotor driven integrated power generation module through the wind direction control tail fin, ensuring that the front and rear concentrating impellers are aligned with the wind direction and maintain stable yaw rotation. During this process, the continuous micro-wind airflow first passes through the front-row concentrating impeller. The micro-wind airflow in the central area directly drives the front-row main impeller to generate a positive rotational torque. Simultaneously, the micro-wind airflow in the outer area and the radially diffused airflow aerodynamically pushed out by the front-row main impeller are collected / aggregated by the front-row concentrating ring, forming a vortex airflow that drives the front-row auxiliary impeller to generate a positive rotational auxiliary torque. In other words, the main rotation is formed by the front-row main impeller, the front-row concentrating ring, and the front-row auxiliary impeller. The combined torque and auxiliary torque drive the long main shaft to rotate forward through the front rotor hub. Simultaneously, the continuous airflow that completes one power stroke passes through the rear concentrator impeller. The airflow in the central region directly drives the rear main blades to generate a reverse-rotating main torque. At the same time, the airflow in the outer region and the radially diffused airflow aerodynamically pushed out by the rear main blades are collected / gathered by the rear concentrator ring to form a vortex airflow that drives the rear auxiliary blades to generate a reverse-rotating auxiliary torque. That is, the reverse-rotating main torque and the reverse-rotating auxiliary torque generated by the rear main blades, the rear concentrator ring, and the rear auxiliary blades are combined and then drive the hollow input shaft, turntable, internal gear ring, large transmission gear, small transmission gear, and driven gear through the rear rotor hub to drive the long main shaft to rotate forward. The rotating long main shaft drives the generator to generate electricity. The generator outputs power through connecting cable I, controller, corresponding connecting cable II, conductive slip ring, and corresponding connecting cable II.

[0011] The present invention achieves the following technical effects compared to the prior art: This invention discloses a coaxial counter-rotating dual-impeller driven micro wind turbine, comprising a coaxial counter-rotating integrated power generation module, a wind-concentrating impeller, a support / automatic yaw system, and a power transmission assembly. It utilizes two coaxial, counter-rotating wind-concentrating impellers (front and rear) to drive the coaxial counter-rotating integrated power generation module to generate electricity. Under the same power / operating conditions, the impeller diameter can be significantly reduced, thereby lowering the impeller's manufacturing requirements and costs. The wind-concentrating ring of the wind-concentrating impeller primarily serves as a reinforcing structural element for the main impeller blades, allowing for optimization of the main impeller blades. This invention achieves a larger windward area and better weight reduction. Simultaneously, the wind-gathering ring, using a duct-like principle, concentrates low-speed and turbulent airflow passing through the area to form vortex airflow that drives the auxiliary blades, further improving the impeller's wind-catching efficiency. Compared to the method of using a single large-diameter radial aerodynamic structure impeller in an L-type three (or more)-bladed horizontal axis generator for micro-wind power generation, this invention provides a coaxial counter-rotating dual-impeller driven micro-wind generator, consisting of a coaxial counter-rotating integrated power generation module, a wind-gathering impeller, and a support structure. The automatic yaw and power transmission components are combined, using two coaxial, oppositely rotating wind-concentrating impellers to drive a coaxial counter-rotating propeller integrated power generation module. Under the same power / operating conditions, the impeller diameter can be significantly reduced, thus lowering the impeller's manufacturing requirements and costs. The wind-concentrating ring of the wind-concentrating impeller serves as the main reinforcing structure for the main blades, allowing for optimized larger windward area and better weight reduction. Simultaneously, the wind-concentrating ring, using a duct-like principle, regulates low-speed and turbulent airflow passing through the area. The converging airflow creates a vortex that drives the auxiliary blades to perform work. The high wind-catching efficiency of the converging impeller improves the low-wind-speed start-up performance of the micro wind generator and enhances the stability of power generation in turbulent airflow at low elevations. Furthermore, the integrated converging impeller, composed of a hub, main blades, wind-catching ring, and auxiliary blades, has a higher overall structural strength and is more resistant to damage in extreme weather conditions. It can further improve the economics of micro wind power generation, more effectively reduce the emission of greenhouse gases such as carbon dioxide, and is beneficial to environmental protection and sustainable development. Attached Figure Description

[0012] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

[0013] Figure 1 This is a schematic diagram of the overall structure from the right side of an embodiment of the present invention; Figure 2 This is a frontal view of the overall structure of an embodiment of the present invention; Figure 3 This is an embodiment of the present invention. Figure 2 Enlarged structural diagram of region A in the middle; Figure 4This is a right-side view of the overall structure of an embodiment of the present invention, excluding the wind-gathering impeller, wind direction control tail fin, and fairing. Figure 5 This is a frontal view of the overall structure of an embodiment of the present invention without including the wind-gathering impeller, wind direction control tail fin, and fairing. Figure 6 This is a front view schematic diagram of the overall structure of the wind-gathering impeller according to an embodiment of the present invention; Figure 7 This is an electrical schematic diagram of an embodiment of the present invention; Explanation of reference numerals in the attached figures: 1-Generator; 2-Casing; 3-Long main shaft; 4-Hollow input shaft; 5-Drive gear; 6-Large transmission gear; 7-Small transmission gear; 8-Turntable; 9-Internal gear ring; 10-Short shaft; 11-Lower hollow shaft; 12-Wind direction control tail fin; 13-Buzzer; 14-Main blade; 15-Wind concentrator ring; 16-Auxiliary blade; 17-Fairing; 18-Conductive slip ring; 19-Column; 20-Slewing support; 21-Connecting cable I; 22-Connecting cable II; 23-Controller; Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by other people skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] refer to Figures 1-7 As shown, the arrow points forward, illustrating a coaxial counter-rotating dual-impeller driven micro wind generator provided in this embodiment of the invention.

[0017] Specifically, a coaxial counter-rotating dual-impeller driven micro wind turbine is composed of a coaxial counter-rotating integrated power generation module, a wind-gathering impeller, and a support / automatic yaw and power transmission assembly. The coaxial counter-rotating integrated power generation module consists of a generator 1, a housing 2, a long main shaft 3, a hollow input shaft 4, a driven gear 5, a large transmission gear 6, a small transmission gear 7, a turntable 8, an internal gear ring 9, and a short shaft 10. The wind-gathering impeller consists of a hub 13, main blades 14, a wind-gathering ring 15, and auxiliary blades 16. The support / automatic yaw and power transmission assembly consists of a fairing 17, a conductive slip ring 18, a column 19, a slewing support 20, connecting cable I 21, connecting cable II 22, a controller 23, a lower hollow shaft 11, and a wind direction control tail fin 12.

[0018] More specifically, viewed from the front and right, the front end of generator 1 is fixedly connected to the rear end of housing 2 at the corresponding position; inside housing 2, a driven gear 5 is fixedly installed at the corresponding position of the long main shaft 3 of generator 1, coaxial with the long main shaft 3; the outer ring of hollow input shaft 4 is rotatably connected to housing 2 via bearings at the corresponding position, and the inner ring of hollow input shaft 4 is rotatably connected to long main shaft 3 via bearings at the corresponding position; the large transmission gear 6 and small transmission gear 7 are fixedly connected coaxially; a short shaft 10 is fixedly installed at the front end of generator 1, and the large transmission gear 6 and small transmission gear 7 are rotatably connected to short shaft 10 via bearings; the rear end of hollow input shaft 4 is fixedly connected coaxially to turntable 8, and the rear end of turntable 8 is fixedly connected coaxially to the corresponding position of internal gear ring 9; the internal gear ring 9 meshes with the large transmission gear 6, transmitting... The driving pinion 7 meshes with the driven gear 5; the inner hole of the hub 13 of the forward-rotating wind-gathering impeller is fixedly connected to the corresponding position of the long main shaft 3, and the inner hole of the hub 13 of the reverse-rotating wind-gathering impeller is fixedly connected to the corresponding position of the hollow shaft 4; the front end of the connecting rod of the wind direction control tail fin 12 is fixedly connected to the corresponding position of the rear end of the generator 1; the corresponding position of the rear side of the fairing 17 is fixedly connected to the corresponding position of the front side of the hub 13 of the forward-rotating wind-gathering impeller; a lower hollow shaft 11 is fixedly installed at the corresponding position of the generator 1 base, coaxial with the lower hollow shaft 11; the movable end of the slewing support 20 is fixedly connected to the corresponding position of the generator 1 base, and the fixed end of the slewing support 20 is fixedly connected to the corresponding position of the top of the column 19; the movable end of the conductive slip ring 18 is fixedly connected to the corresponding position of the lower hollow shaft 11, and the fixed end of the conductive slip ring 18 is fixedly connected to the corresponding position of the column 19.

[0019] The blade roots of the main blade 14 are fixedly connected to the corresponding positions of the outer ring of the blade hub 13, and the blade tips of the main blade 14 are fixedly connected to the corresponding positions of the inner ring of the wind-gathering ring 15. Auxiliary blades 16 are fixedly installed at the corresponding positions of the inner ring of the wind-gathering ring 15. The inner ring of the wind-gathering ring 15, the auxiliary blades 16, and the corresponding areas of the blade tip sections of the main blade 14 form a spiral through-type wind channel structure with spacing and staggered sequence.

[0020] The speed ratio between the internal gear ring 9 and the large transmission gear 6 is 3:1, the speed ratio between the driven gear 5 and the small transmission gear 7 is 3:1, and the speed ratio between the large transmission gear 6 and the small transmission gear 7 is 2:1.

[0021] The front row of concentrator impellers rotates in the opposite direction to the rear row of concentrator impellers; the front row of concentrator impellers and the rear row of concentrator impellers are arranged sequentially and stacked.

[0022] One end of connecting cable I 21 is electrically connected to the corresponding output terminal of generator 1, and the other end of connecting cable I 21 is electrically connected to the corresponding input terminal of controller 23. One end of corresponding connecting cable II 22 is electrically connected to the corresponding output terminal of controller 23, and the other end of corresponding connecting cable II 22 passes through the lower hollow shaft 11 and is electrically connected to the corresponding input terminal of conductive slip ring 18. One end of corresponding connecting cable II 22 is electrically connected to the corresponding output terminal of conductive slip ring 18, and the other end of corresponding connecting cable II 22 is led out from column 19 and connected to the power grid or other electrical loads.

[0023] The basic operating mode of this coaxial reverse-propeller dual-impeller driven micro wind turbine is as follows: Supported by the column 19, the slewing support 20 provides support and stability to the coaxial reverse-propeller driven integrated power generation module, the front-row wind-gathering impeller, the rear-row wind-gathering impeller, and the wind direction control tail fin 12. Continuous micro-wind airflow drives the coaxial reverse-propeller driven integrated power generation module through the wind direction control tail fin 12, ensuring that the front and rear wind-gathering impellers are aligned with the wind direction and maintain stable yaw rotation. A continuous, gentle airflow first passes through the front-row concentrator impeller. The airflow in the central area directly drives the main blades 14 in the front row to generate a positive rotational torque. Simultaneously, the airflow in the outer area and the radially diffused airflow aerodynamically pushed out by the main blades 14 are collected / aggregated by the concentrator ring 15 in the front row, forming a vortex airflow that drives the auxiliary blades 16 in the front row to generate a positive rotational auxiliary torque. That is, the main torque and auxiliary torque generated by the main blades 14, the concentrator ring 15, and the auxiliary blades 16 in the front row are superimposed. The front rotor hub 13 drives the long main shaft 3 to rotate in the forward direction; simultaneously, the continuous airflow that has completed one work cycle passes through the rear concentrator impeller. The airflow in the central region directly drives the rear main rotor blades 14 to generate a main torque that rotates in the opposite direction. At the same time, the airflow in the outer region and the radially diffused airflow aerodynamically pushed out by the rear main rotor blades 14 are collected / gathered by the rear concentrator ring 15 to form a vortex airflow that drives the rear auxiliary rotor blades 16 to generate an auxiliary torque that rotates in the opposite direction. That is, the rear main rotor blades 14 and the rear... The main torque and auxiliary torque generated by the wind-gathering ring 15 and the rear auxiliary blades 16 are superimposed and drive the hollow input shaft 4, turntable 8, internal gear ring 9, transmission large gear 6, transmission small gear 7, and driven gear 5 through the rear blade hub 13. At the same time, the long main shaft 3 is driven to rotate in the forward direction. The rotating long main shaft 3 drives the generator 1 to do work and generate electricity. The generator 1 outputs power through the connecting cable I 21, controller 23, corresponding connecting cable II 22, conductive slip ring 18, and corresponding connecting cable II 22.

[0024] This specification uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

[0025] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A coaxial counter-rotating dual-impeller driven micro wind generator, characterized in that: It is composed of a coaxial counter-rotating propeller integrated power generation module, a wind-gathering impeller, and a support / automatic yaw and power transmission assembly. The coaxial counter-rotating propeller integrated power generation module consists of a generator (1), a housing (2), a long main shaft (3), a hollow input shaft (4), a driven gear (5), a large transmission gear (6), a small transmission gear (7), a turntable (8), an internal gear ring (9), and a short shaft (10). The wind-gathering impeller consists of a hub (13), a main blade (14), a wind-gathering ring (15), and an auxiliary blade (16). The support / automatic yaw and power transmission assembly consists of a fairing (17), a conductive slip ring (18), a column (19), a slewing support (20), connecting cable I (21), connecting cable II (22), a controller (23), a lower hollow shaft (11), and a wind direction control tail fin (12).

2. The coaxial counter-rotating dual-impeller driven micro wind generator according to claim 1, characterized in that: The front end of the generator (1) is fixedly connected to the rear end of the casing (2); inside the casing (2), a driven gear (5) is fixedly installed at the corresponding position of the long main shaft (3) of the generator (1), coaxial with the long main shaft (3) of the generator (1); the outer ring of the hollow shaft (4) is rotatably connected to the casing (2) through a corresponding bearing, and the inner ring of the hollow shaft (4) is rotatably connected to the long main shaft (3) through a corresponding bearing; the large transmission gear (6) and the small transmission gear (7) are fixedly connected coaxially; a short shaft (10) is fixedly installed at the corresponding position of the front end of the generator (1), and the large transmission gear (6) and the small transmission gear (7) are connected through a corresponding bearing. The corresponding bearing is rotatably connected to the short shaft (10); the corresponding position of the rear end of the hollow input shaft (4) is fixedly connected to the turntable (8) coaxially, and the corresponding position of the rear end of the turntable (8) is fixedly connected to the corresponding position of the internal gear ring (9) coaxially; the internal gear ring (9) meshes with the transmission large gear (6), and the transmission small gear (7) meshes with the driven gear (5); the inner hole of the hub (13) of the forward-rotating wind-gathering impeller is fixedly connected to the corresponding position of the long main shaft (3), and the inner hole of the hub (13) of the reverse-rotating wind-gathering impeller is fixedly connected to the corresponding position of the hollow input shaft (4); the front end of the connecting rod of the wind direction control tail fin (12) is fixedly connected to the corresponding position of the rear end of the generator (1).

3. A coaxial counter-rotating dual-impeller driven micro wind generator according to claim 1, characterized in that: The blade roots of the main blade (14) are fixedly connected to the corresponding positions of the outer ring of the hub (13), and the blade tips of the main blade (14) are fixedly connected to the corresponding positions of the inner ring of the wind-gathering ring (15). Auxiliary blades (16) are fixedly installed at the corresponding positions of the inner ring of the wind-gathering ring (15). The inner ring of the wind-gathering ring (15), the auxiliary blades (16), and the corresponding areas of the blade tip section of the main blade (14) form a spiral through-type wind channel structure with spacing and staggered sequence.

4. A coaxial counter-rotating dual-impeller driven micro wind generator according to claim 1, characterized in that: The speed ratio between the internal gear ring (9) and the transmission large gear (6) is 3:1, the speed ratio between the driven gear (5) and the transmission small gear (7) is 3:1, and the speed ratio between the transmission large gear (6) and the transmission small gear (7) is 2:

1.

5. A coaxial counter-rotating dual-impeller driven micro wind generator according to claim 1, characterized in that: The front row of concentrating impellers rotates in the opposite direction to the rear row of concentrating impellers; the front row of concentrating impellers and the rear row of concentrating impellers are arranged sequentially and stacked.

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