Stove with downdraft exhaust

Abstract

The stove (1) includes: a support surface (2) for supporting one or more cooking pots (P); an exhaust duct (4) extending through the support surface (2); and a ventilation system (6) disposed below the support surface (2) and fluidly connected to the exhaust duct (4) for drawing air downward above the support surface (2), wherein the exhaust duct (4) includes an inlet end (4a), an outlet end (4b) and a raised inner surface (8) extending between the inlet end (4a) and the outlet end (4b).

Description

Technical Field

[0001] This invention relates to a stove that includes a downdraft exhaust fan or ventilator. Background Technology

[0002] US Patent Application US 2018 / 0073745 A1 discloses a household appliance including a heating element located on the upper surface of the appliance and a variable-height downdraft vent assembly movable relative to the upper surface. The vent assembly includes a duct defining a flow passage between its upper and lower ends. The duct is movable in a vertical direction relative to the upper surface of the appliance. A drive assembly is provided for engaging the duct to position the upper end of the duct at a user-selected variable height relative to the upper surface of the appliance. The movable duct includes an inner tube and an outer tube, wherein the inner tube has an upper end, a lower end, and an internal passage extending between the upper and lower ends. A plurality of openings are formed at the upper end of the inner tube and fluidly communicate with the passage. The outer tube is disposed around the inner tube and axially aligned therewith. The outer tube includes an upper end and a lower end. A plurality of openings are formed at the upper end of the outer tube, and air is drawn from a region near the upper end of the movable duct through the plurality of openings in the outer tube, through the plurality of openings in the inner tube, and along the passage in the inner tube.

[0003] As described above, downdraft vent assemblies are often affected by high and unpleasant noise levels and moisture / grease buildup that limits ventilation / exhaust efficiency during operation. The increased noise level is typically caused by turbulent airflow as air enters the duct and passes through multiple openings, which further reduces the ventilation / exhaust efficiency of the downdraft vent assembly. Summary of the Invention

[0004] This invention seeks to provide a cooktop with improved downdraft exhaust / ventilation, wherein the downdraft exhaust produces a significantly lower noise level and exhibits higher exhaust efficiency and / or higher cooking steam capture efficiency. Furthermore, the cooktop provides improved handling of moisture, grease, and other contaminants, and minimizes uncontrolled internal contamination.

[0005] According to the present invention, a stove of the type mentioned in the foregoing preamble is provided, wherein the stove includes: an exhaust duct extending through a support surface; and a ventilation system disposed below the support surface and fluidly connected to the exhaust duct for drawing air downward from above the support surface, wherein the exhaust duct includes an inlet end, an outlet end, and a raised inner surface extending between the inlet end and the outlet end.

[0006] By providing a raised inner surface to the exhaust duct, turbulent airflow is allowed to be significantly reduced as air above the support surface converges into the exhaust duct in a smoother manner, thereby reducing noise and increasing the efficiency of the (downdraft) ventilation system.

[0007] In an advantageous embodiment, the raised inner surface is an airfoil-shaped inner surface, which provides a smoother convergence of air entering the exhaust duct and prevents premature surface separation. In an exemplary embodiment, the inlet end of the exhaust duct includes the leading edge of the airfoil-shaped inner surface, and the outlet end includes the trailing edge of the airfoil-shaped inner surface. In this embodiment, the air drawn into the exhaust duct flows from the leading edge to the trailing edge and is prevented from separating prematurely from the inner surface, resulting in maintaining laminar airflow within the exhaust duct, thereby reducing turbulence and noise. Attached Figure Description

[0008] The invention will now be discussed in more detail with reference to the accompanying drawings, in which:

[0009] Figure 1 A cross-sectional view of a stove with a downdraft exhaust duct according to an embodiment of the present invention is shown.

[0010] Figure 2 A top view of a stove with a downdraft exhaust duct according to an embodiment of the present invention is shown.

[0011] Figure 3 A cross-sectional view of a stove with a downdraft exhaust duct according to another embodiment of the present invention is shown.

[0012] Figure 4A and Figure 4B Simulations of the streamline and noise level of the air duct of the downdraft exhaust fan according to the first embodiment of the present invention are shown respectively.

[0013] Figure 5A and Figure 5B Simulations of the streamline and noise level of the air duct of the downdraft exhaust fan according to the second embodiment of the present invention are shown respectively.

[0014] Figure 6 A cross-sectional view of a stove with a fan motor according to an embodiment of the present invention is shown. Detailed Implementation

[0015] Figure 1 and 2Cross-sectional and top views of a stove 1 with a downdraft exhaust duct 4 according to an embodiment of the present invention are shown. In the illustrated embodiment, the stove 1 includes a support surface 2 for supporting one or more cooking pots "P". The downdraft exhaust duct 4, hereinafter simply referred to as exhaust duct 4, is provided and extends through the support surface 2. A ventilation or suction system 6 is arranged below the support surface 2 and fluidly connected to the exhaust duct 4 for drawing air, cooking steam, etc., downward from above the support surface 2. The exhaust duct 4 includes an inlet end 4a and an outlet end 4b, and in an exemplary embodiment, the inlet end 4a extends through the support surface 2.

[0016] As further described, the exhaust duct 4 includes a (smooth) raised inner surface 8 extending between the inlet end 4a and the outlet end 4b. The raised inner surface 8 can be viewed as a circumferentially inwardly arched or curved wall surface of the exhaust duct 4, which provides the exhaust duct 4 with an inner diameter / width “D” that varies from the inlet end 4a to the outlet end 4b, wherein a minimum internal width is provided at some point between the inlet end 4a and the outlet end 4b.

[0017] According to the invention, the circumferentially raised inner surface 8 facilitates the smoothing of airflow entering the inlet end 4a, passing through the exhaust duct 4, and exiting the exhaust duct 4 at the outlet end 4b. When the (downdraft) ventilation system 6 is in operation, the smooth airflow provided by the raised inner surface 8 is essentially laminar, resulting in minimized turbulence, leading to more efficient flow and less noise. As another advantage, the raised inner surface 8 improves the ventilation / extraction efficiency of the ventilation system 6 due to lower airflow resistance.

[0018] from Figure 2 In the top view, the exhaust duct 4 does not necessarily have to be circular or cylindrical. For example, in one set of embodiments, the exhaust duct 4 can be rectangular, square, elliptical, or circular, so that the shape of the exhaust duct 4 can be selected according to the specific requirements / needs of the stove 1. For example, in the case where the exhaust duct 4 is substantially rectangular, the raised inner surface 8 includes two different widths D1 and D2 from the inlet end 4a to the outlet end 4b.

[0019] In addition, grilles, screens, or blades can be applied to the exhaust duct 4, for example, in the holes formed by the inlet end 4a.

[0020] It should also be noted that, according to the requirements of stove 1, the exhaust duct 4 can be arranged at any position P1 or P2 on the support surface 2 as shown in the figure.

[0021] In one embodiment, the raised inner surface 8 may include an airfoil-shaped inner surface. The airfoil-shaped inner surface provides improved laminar flow through the exhaust duct 4 when the separation of the airflow from the airfoil-shaped inner surface occurs closer to the outlet end 4b of the exhaust duct 4 than to the inlet end 4b. In a particularly advantageous embodiment, the inlet end 4a of the exhaust duct 4 includes the leading edge of the airfoil-shaped inner surface 8, and the outlet end 4b includes the trailing edge of the airfoil-shaped inner surface 8. In this embodiment, the airfoil-shaped inner surface 8 completely spans between the inlet end 4a and the outlet end 4b, such that laminar airflow is provided substantially throughout the entire length of the exhaust duct 4, wherein the separation of the airflow from the airfoil-shaped inner surface 8 is delayed and occurs as close as possible to the outlet end 4b of the exhaust duct 4.

[0022] like Figure 1 and Figure 2 As further shown, in an embodiment, the exhaust duct 4 may include an internally arranged (e.g., centrally arranged) duct wall 10 extending from the inlet end 4a to the outlet end 4b, providing exhaust channels 12 on either side of the duct wall 10. This allows for directional air extraction from both sides of the exhaust duct 4, such as when the exhaust duct 4 is arranged between two cooking pots P on the support surface 2. The internally arranged duct wall 10 can further reduce turbulence in the central portion of the exhaust duct 4 to minimize noise and ventilation / extraction inefficiencies. In the illustrated embodiment, the exhaust channels 12 on either side of the duct wall 10 are symmetrically arranged, resulting in substantially symmetrical air / steam extraction with minimal noise and turbulence.

[0023] In this embodiment, the duct wall 10 widens from the inlet end 4a of the exhaust duct 4 toward the outlet end 4b, i.e., it narrows outward, thereby reducing the airflow resistance when air / steam is drawn into the exhaust duct 4.

[0024] exist Figure 3 The image depicts a cross-sectional view of a stove 1 with a downdraft exhaust duct 4 according to another embodiment of the invention. In the illustrated embodiment, the exhaust duct 4 extends through the support surface 2 and is in an elevated position relative to the support surface 2, thereby raising the inlet end 4b higher (and thus also raising the relevant low-pressure area) to facilitate steam extraction when using a higher cooking pot P. In principle, except that the inlet end 4b of the exhaust duct 4 further extends above the support surface 2 to a height "H", but the outlet end 4b remains below the support surface 2, Figure 3 The implementation methods described herein are similar to Figure 1 The implementation method is the same.

[0025] Note that, as Figure 1The inlet end 4a shown does not need to be flush with the support surface 2. In particular, an advantageous embodiment is envisioned in which the inlet end 4a is raised slightly above the support surface 2 and flush with the overflow barrier 2a (i.e., the raised surface portion of the support surface 2 to prevent overflow that may enter the exhaust duct 4 during cooking).

[0026] according to Figure 1 and Figure 3 In an advantageous embodiment, the exhaust duct 4 can be movably arranged, for example, in a vertical direction, such as... Figure 1 The reduced construction shown is as follows Figure 3 The elevated structures depicted herein. To this end, an exemplary embodiment is provided in which the duct wall 10 is connected to an actuation system for moving (e.g., raising and lowering) the exhaust duct 4 relative to the support surface 2. By allowing the exhaust duct 4, particularly its inlet end 4a, to rise and fall relative to the support surface 2, optimal air / steam extraction is facilitated for various cooking pots P. In an alternative embodiment, the exhaust duct 4 may be connected to an actuation system without the duct wall 10. Note that the actuation system may be a manual or automatic actuation system.

[0027] As previously described, according to the present invention, the raised inner surface 8 facilitates the smoothing of airflow entering the inlet end 4a, through the exhaust duct 4, and exiting the exhaust duct 4 at the outlet end 4b. When the ventilation system 6 is operating, the smoothed airflow provided by the raised inner surface 8 is substantially laminar in nature, thereby minimizing the generation of turbulence and noise. Furthermore, the raised inner surface 8 improves the overall efficiency of the ventilation system 6 due to the lower flow resistance.

[0028] Figure 4A and Figure 4B Each example shows a simulation of the streamline and noise level of the exhaust duct 4 according to an embodiment of the present invention. Figure 4A As shown, the raised inner surface 8 of the exhaust duct 4 induces substantially parallel (curved) streamlines representing laminar flow near the raised inner surface 8. The airflow remains attached to the raised inner surface 8 for almost the entire length from the inlet end 4a to the outlet end 4b, thus reducing turbulence and minimizing noise. Figure 4B The system does indeed contain and indicates a louder air noise zone N1, where the noise level is highest (54.64 dB in this particular example). Noise zone N1 begins approximately where the inner diameter / width D of the exhaust duct 4 begins to widen towards the outlet end 4b.

[0029] exist Figure 4A and Figure 4BIn the illustrated embodiment, the raised inner surface 8 includes an airfoil, wherein the inlet end 4a includes the leading edge 8a of the airfoil inner surface 8, and wherein the outlet end 4b includes the trailing edge 8b of the airfoil inner surface 8. Figure 4A The depicted streamlines indicate that the airflow remains attached to the inner surface 8 of the airfoil until the trailing edge 8b, where the airflow separates and forms a trailing recirculation zone R1, which is a source of turbulence and noise. However, the area of ​​maximum noise is indicated as zone N1.

[0030] Note that flow separation occurs when the boundary layer on the raised inner surface 8 travels far enough against the unfavorable pressure gradient that its velocity becomes almost zero. Typically, an unfavorable pressure gradient occurs when the static pressure within the exhaust duct 4 increases along the flow direction (i.e., from inlet end 4a to outlet end 4b), which may be due to the widening of the inner diameter / width “D” as described above. When flow separation occurs, a backflow zone tends to form, which can negatively impact noise and performance.

[0031] When the exhaust duct 4 is in an elevated configuration / position relative to the support surface 2, a wall backflow zone can be formed at the location where the exhaust duct 4 meets the support surface 2 or the overflow baffle 2a (if present).

[0032] Even if Figure 4A and Figure 4B The raised inner surface 8 (e.g., an airfoil-shaped inner surface) depicted in the paper significantly reduces turbulence and noise compared to existing downdraft exhaust systems, but can further reduce turbulence and noise.

[0033] Therefore, referring to Figure 5A and Figure 5B The diagrams illustrate the streamlines and noise level simulations of an exhaust duct 4 according to another embodiment of the present invention. In the illustrated embodiment, the exhaust duct 4 includes an outer surface 14 and a plurality of circumferentially distributed slots / channels 16, each slot / channel 16 extending from a raised inner surface 8 (e.g., an airfoil-shaped inner surface) to the outer surface 14. These slots / channels 16 allow secondary airflow to be provided when the exhaust duct 4 is in an elevated position, thereby virtually eliminating the aforementioned wall backflow zone. Furthermore, as... Figure 5B The noise zone N1 described is compared to Figure 4B The noise zone N1 is much smaller, and the sound is much quieter (48.51 dB in the example shown). Therefore, multiple slots / channels 16 allow for further reduction of the recirculation zone and noise generated by the exhaust duct 4.

[0034] In this implementation, multiple slots 16 may be located between the minimum inner diameter / width D of the exhaust duct 4 and its outlet end 4b. This also applies to the location of the slots / channels 16 on the airfoil inner surface 8.

[0035] In an advantageous embodiment, each of the plurality of slots 16 may be oriented downward at an acute / oblique angle relative to the outer surface 14. This allows each slot 16 to provide an outlet opening in the raised inner surface 8 closer to the outlet end 4b of the exhaust duct 4, while providing an inlet opening in the outer surface 14 closer to the inlet end 4a. These outlet openings ensure that the airflow remains attached to the raised inner surface 8 below the outlet opening, while providing sufficient secondary airflow through the outer surface 14 to minimize backflow at the wall recirculation zone. To allow for an improved, smoother secondary airflow through the plurality of slots 16, an embodiment in which each slot is curved is provided.

[0036] Return to reference Figure 1 and Figure 3 In one embodiment, the stove 1 may further include a fluid collector housing 18 disposed below the support surface 2, which fluidly connects the exhaust duct 4 to the ventilation system 6. The fluid collector housing 18 includes two recessed air deflector walls 22a, 22b extending downwards from a apex 20 of the fluid collector 18 in a mirror image, wherein the apex 20 is centrally disposed below the exhaust duct 4. As the drawn-out air exits the outlet end 4b of the exhaust duct 4, the recessed air deflector walls 22a, 22b allow the airflow A1, A2 to be smoothly deflected laterally into the separate, laterally extending housing channels C1, C2. Note that the housing channels C1, C2 allow for a reduction in the overall height of the fluid collector housing 18, thereby freeing up more space below the support surface 2 for kitchen storage. Furthermore, by laterally deflecting the airflow A1, A2, moisture, condensed water droplets, grease, dirt, etc., are allowed to be captured by the deflector walls 22a, 22b rather than the ventilation system 6. Therefore, the recessed air deflector walls 22a and 22b serve as water vapor and grease collectors.

[0037] Note that, viewed from the inside of the fluid collector housing 18, the recessed air deflector walls 22a, 22b are outwardly curved or arched deflector walls, each of the recessed air deflector walls 22a, 22b including a apex 20 connecting to the highest point / part of the other deflector wall. Therefore, the recessed air deflector walls 22a, 22b and apex 20 can be conceived as forming a conical bottom of the fluid collector housing 18, centrally located below the exhaust duct 4, with apex 20 near the outlet end 4b of the exhaust duct 4.

[0038] As further depicted, in one embodiment, the aforementioned duct wall 10 may extend through the apex 20 of the fluid collector housing 18. In another embodiment, the duct wall 10 extends movably through the apex 20 of the fluid collector housing 1, so that when the exhaust duct 4 can be in place... Figure 1 The lowered position described in the text is similar to... Figure 3When moving between the elevated positions depicted, the duct wall 10 can be configured to move the exhaust duct 4.

[0039] Figure 1 and Figure 3 It is also shown that, in one embodiment, the duct wall 10 may extend beyond the outlet end 4b of the exhaust duct 4 into the fluid collector housing 18. This further facilitates the easy connection of the duct wall 10 to, for example, an actuation system for raising and lowering the exhaust duct 4 relative to the support surface 2.

[0040] The airflows A1 and A2, deflected by the recessed air deflector walls 22a and 22b, typically contain water vapor, oil / grease droplets, etc. To reduce internal contamination of the entire fluid collector housing 18, an embodiment is provided in which the lowest points / parts of the two recessed air deflector walls 22a and 22b include leakage discs 24a and 24b. The leakage discs 24a and 24b allow water vapor, oil, grease, etc., to move downwards along the deflector walls 22a and 22b and be trapped within them, thereby preventing further diffusion through the fluid collector housing 18.

[0041] Preferably, the ventilation system 6 should be kept as clean as possible to maintain efficiency and prevent over-cleaning. To this end, an embodiment is provided in which the fluid collector housing 18 includes two internally arranged filter members 26a, 26b, such as rectangular filter members, each of which is arranged adjacent to and downstream of one of the two air deflector walls 22a, 22b, and forms an acute / oblique angle (outward) (α) with the longitudinal axis L of the exhaust duct 4. The depicted obliquely arranged filter members 26a, 26b allow space for the recessed air deflector walls 22a, 22b, such as lateral space, and optionally allow space for the leak discs 24a, 24b, ensuring that each of the filter members 26a, 26b remains substantially invisible through the inlet end 4a of the exhaust duct 4. Furthermore, the inclined arrangement of the filter components 26a and 26b allows water vapor, oil, grease, etc., to easily leak toward the recessed air deflection walls 22a and 22b, especially the leakage discs 24a and 24b (when present).

[0042] In one embodiment, each of the two filter components 26a, 26b includes an upper edge and a lower edge, wherein the upper edge engages or extends toward the exhaust duct 4, and wherein the lower edge engages or extends toward the outermost edge of one of the leak discs 24a, 24b. This ensures that each of the filter components 26a, 26b will be positioned at the aforementioned tilted / angled (α) position relative to the longitudinal axis L of the exhaust duct 4. In an exemplary embodiment, the lower edge of each filter component 26a, 26b may be supported by the outermost edge of one of the leak discs 24a, 24b.

[0043] from Figure 1 and Figure 3 It can also be seen that, in the embodiment, the ventilation system 6 may include two fan motors 28a, 28b, each of which is connected to a fluid collector housing 18 adjacent to and downstream of one of the two filter components 26a, 26b, and wherein each fan motor 28a, 28b includes a rotation shaft O1, O2 arranged at an acute angle / oblique angle (outward) (β) relative to the longitudinal axis L.

[0044] The inclined arrangement of the rotation shafts O1 and O2 of each fan motor 28a and 28b provides advantages for flow performance and noise generation. In particular, due to the inclined arrangement of the fan motors 28a and 28b, the protruding area of ​​the inlet openings 30a and 30b of each fan motor 28a and 28b facing the filter components 26a and 26b is increased, and as a result, the flow area of ​​each of the housing channels C1 and C2 facing the fan motors 28a and 28b is kept as large as possible, thereby reducing the velocity of the airflow A1 and A2 through the housing channels C1 and C2 and reducing pressure loss.

[0045] Figure 6 A cross-sectional side view of a stove 1 having one of two fan motors 28a, 28b, according to an embodiment of the present invention, is shown. As indicated by the embodiment, each of the two fan motors 28a, 28b may include a scroll housing 32a that extends / bends out of a plane perpendicular to the rotation axes O1, O2, such that the scroll housing 32a bends / deviates from the aforementioned plane along a bend B indicated by arrow "B". This bent scroll housing 32a allows for a compact design in which the outlet end 34a of each fan motor 28a, 28b can be conveniently connected to a vertical suction pipe 36, for example located behind a kitchen drawer 38 of a kitchen cabinet K. The bent scroll housing 32a allows each fan motor 28a, 28b to be arranged at any desired acute angle β while keeping the ventilation system 6 compact. Furthermore, the curved vortex shell 32a of each fan motor 28a, 28b still allows for large-volume flow and minimizes turbulence and pressure loss, while achieving a compact connection with the vertical downpipe 36.

[0046] The invention has been described above with reference to several exemplary embodiments shown in the accompanying drawings. Modifications and substitutions of some components or elements are possible and are included within the scope of protection defined by the appended claims.

Claims

1. A stove (1), comprising: Support surface (2) for supporting one or more cooking pots (P); The exhaust duct (4) extends through the supporting surface (2) and is movably arranged between the lowered structure and the raised structure; and A ventilation system (6), arranged below the support surface (2) and fluidly connected to the exhaust duct (4), is used to draw air downward from above the support surface (2) through the exhaust duct (4). The exhaust duct (4) includes an inlet end (4a), an outlet end (4b), and a raised inner surface (8) extending between the inlet end (4a) and the outlet end (4b). The raised inner surface (8) is a circumferentially arranged, inwardly curved wall surface of the exhaust duct (4), providing the exhaust duct (4) with an internal width (D) that varies from the inlet end (4a) to the outlet end (4b), and wherein a minimum internal width is provided between the inlet end (4a) and the outlet end (4b). The protruding inner surface (8) includes an airfoil-shaped inner surface, and The inlet end (4a) of the exhaust duct (4) includes the leading edge of the airfoil inner surface, and the outlet end (4b) includes the trailing edge of the airfoil inner surface. The exhaust duct (4) includes an outer surface (14) and a plurality of circumferentially distributed slots (16), each of the plurality of slots (16) extending from the airfoil inner surface to the outer surface (14) to provide secondary airflow when the exhaust duct (4) is in the elevated configuration.

2. The stove according to claim 1, wherein, The exhaust duct (4) includes an internally arranged duct wall (10) extending from the inlet end (4a) to the outlet end (4b), providing an exhaust passage (12) on either side of the duct wall (10).

3. The stove according to claim 2, wherein, The duct wall (10) widens from the inlet end (4a) of the exhaust duct (4) toward the outlet end (4b).

4. The stove according to claim 2 or 3, wherein, The duct wall (10) is connected to an actuation system for moving the exhaust duct (4) up or down relative to the support surface (2).

5. The stove according to any one of claims 1 to 3, wherein, Each of the plurality of slots (16) is oriented downward at an acute angle relative to the outer surface (14).

6. The stove according to any one of claims 1 to 3, wherein, Each of the plurality of slots (16) is a downwardly curved slot.

7. The stove according to any one of claims 1 to 3 further includes a fluid collector housing (18) disposed below the support surface (2) and fluidly connecting the exhaust duct (4) to the ventilation system (6). in, The fluid collector housing (18) includes two recessed air deflection walls (22a, 22b) extending downward in a mirror manner from the apex (20) of the fluid collector housing (18), wherein the apex (20) is centrally located below the exhaust duct (4).

8. The stove according to claim 7, wherein, The exhaust duct (4) includes an internally arranged duct wall (10) extending from the inlet end (4a) to the outlet end (4b), providing an exhaust passage (12) on either side of the duct wall (10), wherein the duct wall (10) is connected to an actuation system for moving the exhaust duct (4) upward or downward relative to the support surface (2), wherein the duct wall (10) extends through the apex (20) of the fluid collector housing (18).

9. The stove according to claim 7, wherein, The lowest point of each of the two air deflection walls (22a, 22b) includes a leaking disc (24a, 24b).

10. The stove according to claim 7, wherein, The fluid collector housing (18) includes two internally arranged filter components (26a, 26b), each of which is arranged adjacent to and downstream of one of the two air deflection walls (22a, 22b) and forms an acute angle with the longitudinal axis (L) of the exhaust duct (4).

11. The stove according to claim 10, wherein, The lowest point of each of the two air deflection walls (22a, 22b) includes a leak disc (24a, 24b), wherein each of the two filter components (26a, 26b) includes an upper edge and a lower edge, wherein the upper edge engages with the exhaust duct (4), and wherein the lower edge engages with the outermost edge of one of the leak discs (24a, 24b).

12. The stove according to claim 10, wherein, The ventilation system (6) can include two fan motors (28a, 28b), each of which is connected to the fluid collector housing (18) adjacent to and downstream of one of the two filter components (26a, 26b), and wherein each fan motor (28a, 28b) includes a rotating shaft (O1, O2) arranged at an acute angle (β) relative to the longitudinal axis (L).

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