High-capacity air-cooled battery plug-in box

Abstract

The invention relates to the technical field of energy storage batteries, and provides a high-capacity air-cooled battery subrack which comprises a shell and battery modules, the battery modules comprise a first group, a second group, a third group and a fourth group which are connected in series side by side, and a first gap is formed between the second group and the third group; second gaps are formed between the first group and the second group and between the third group and the fourth group, each group in the battery module comprises a plurality of battery cells, the plurality of battery cells are sequentially connected in series along the thickness direction, and a harmonica-shaped tube plate is arranged between every two adjacent battery cells; the shell comprises a first heat dissipation structure arranged on the side wall, a second heat dissipation structure arranged on the bottom wall and an exhaust fan arranged corresponding to the first gap, the airflow comprises a first path of airflow and a second path of airflow, the first path of airflow enters the plug-in box from the first heat dissipation structure, flows through the battery cell along the harmonica-shaped tube plate and flows to the first gap, and the second path of airflow flows to the second gap; and the second path of airflow flows into the second gap from the second heat dissipation structure, flows through the battery cell along the harmonica-shaped tube plate and is converged with the first path of airflow, and the airflow is discharged out of the plug-in box by the exhaust fan.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage batteries, and in particular relates to a large-capacity air-cooled battery plug-in box. Background Art

[0002] At present, most energy storage products can be divided into air cooling, liquid cooling, phase change heat dissipation and other forms according to the cooling method. Air-cooled energy storage products are widely used due to the advantages of simple heat dissipation structure, low design difficulty and low cost. However, the air flow method directly affects the heat dissipation effect of the air-cooled battery, which in turn determines the life, reliability and safety of the entire product.

[0003] Most of the batteries currently used in large-capacity energy storage products are square lithium batteries, which are grouped into battery modules consisting of multiple batteries, and then into battery plug-ins consisting of 2 to 3 modules. Then, different numbers of battery plug-ins form a battery cluster, and finally, multiple battery clusters form energy storage products of different capacities. The current mainstream air-cooled battery plug-in box consists of 16 cells, and a small number of companies design and produce plug-ins consisting of 24 or 32 cells. With the development of the energy storage industry, there are increasingly higher requirements for the energy density of products. At present, the competitiveness of plug-in boxes with 16 cells is insufficient. Plug-ins consisting of more cells have become an inevitable trend and direction of industry design. However, the increase in the number of cells will bring challenges to the overall heat dissipation and temperature uniformity of single batteries.

[0004] In order to solve the above technical problems, the present invention designs a large-capacity air-cooled battery plug-in box. Summary of the invention

[0005] The invention provides a large-capacity air-cooled battery plug-in box, aiming to solve the problems of poor overall heat dissipation and poor temperature uniformity of the large-capacity air-cooled battery plug-in box.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a large-capacity air-cooled battery plug-in box, comprising a shell and a battery module, the battery module comprising a first group, a second group, a third group and a fourth group arranged in parallel in series, a first gap is provided between the second group and the third group, a second gap is provided between the first group and the second group and between the third group and the fourth group, each group in the battery module comprises a plurality of battery cells, the plurality of battery cells are arranged in series in sequence along the thickness direction, a harmonica tube plate is provided between two adjacent battery cells, the shell comprises a first heat dissipation structure provided on the side wall, a second heat dissipation structure provided on the bottom wall and an exhaust fan provided corresponding to the first gap, wherein the airflow comprises a first airflow and a second airflow, the first airflow enters the plug-in box from the first heat dissipation structure, flows through the battery cells along the harmonica tube plate and flows to the first gap, the second airflow flows into the second gap from the second heat dissipation structure, flows through the battery cells along the harmonica tube plate and merges with the first airflow, and the airflow is discharged from the plug-in box by the exhaust fan.

[0007] Based on the above technical solution, the number of battery cells in the first group, the second group, the third group and the fourth group is greater than or equal to 6.

[0008] Based on the above technical solution, the first heat dissipation structure includes a first air inlet, and the number of the first air inlets is multiple, and the multiple first air inlets are arranged in sequence and spaced apart along the battery cell arrangement direction.

[0009] Based on the above technical solution, the multiple first air inlets are arranged in one-to-one correspondence with the harmonica tube plates and extend along the height direction of the battery core.

[0010] Based on the above technical solution, the air inlet area of ​​the first air inlet is adapted to the internal air flow rate.

[0011] Based on the above technical solution, the second heat dissipation structure includes a second air inlet, an air duct and an air outlet slot, the second air inlet is arranged at the connection between the side wall and the bottom wall of the outer shell, the air duct is arranged inside the bottom wall, and the air outlet slot extends along the arrangement direction of the battery cells and is arranged toward the second gap, wherein the second airflow flows into the air duct from the second air inlet, flows out from the air outlet slot to the second gap, and then flows through the battery cells along the harmonica tube plate to the first gap.

[0012] Based on the above technical solution, the shell is provided with a first baffle and a second baffle, the first baffle is arranged in the first gap and opposite to the exhaust fan, and the second baffle is arranged at the four corners of the shell.

[0013] Based on the above technical solution, the housing is further provided with a third baffle, and the number of the third baffle is multiple, and the multiple third baffles are relatively arranged at two ends of the second gap.

[0014] On the basis of the above technical solution, the large-capacity air-cooled battery box also includes a cover plate, which includes a first cover plate, a second cover plate, a third cover plate and a fourth cover plate, which are respectively covered on the first group, the second group, the third group and the fourth group, each of the cover plates has a flange extending downward in the circumferential direction, and the second cover plate and the third cover plate are provided with a first notch at the flanges at both ends along the direction of arrangement of the battery cells.

[0015] Based on the above technical solution, the flanges of the second cover plate and the third cover plate close to the first gap are provided with second notches, and there are multiple second notches, which are evenly spaced.

[0016] On the basis of the above technical solution, a heat insulating gasket is provided between the battery module and the bottom wall of the shell, and the heat insulating gasket is provided with an opening, and the opening is arranged corresponding to the air outlet slot.

[0017] Compared with the related art, the beneficial effects of the present invention are as follows: The present invention sets a first heat dissipation structure so that a first airflow can enter the plug-in box through the first heat dissipation structure, and can take away the heat generated by two adjacent battery cells in the battery module when they are working when flowing through the battery cells along the harmonica tube plate. Then the first airflow flows to the first gap and can be discharged from the plug-in box by the exhaust fan. In this way, the heat dissipation effect of the battery cells in the battery module can be improved. By setting a second heat dissipation structure, a second airflow can enter the plug-in box through the second heat dissipation structure and flow to the second gap. Then the harmonica tube plates of the second and third groups flow through the battery cells and can take away the heat generated by the adjacent battery cells in the second and third groups when they are working. Then the second airflow flows to the first gap and is discharged from the plug-in box by the exhaust fan. In this way, the heat dissipation effect of the battery cells of the second and third groups near the middle of the battery plug-in box can be further improved, which is beneficial to improving the temperature uniformity between the battery cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0019] Figure 1 This is a schematic diagram of the exploded structure of a large-capacity air-cooled battery plug-in box provided by the present invention; Figure 2 It is a schematic structural diagram of a shell of a large-capacity air-cooled battery plug-in box provided by the present invention; Figure 3 It is a schematic diagram of the internal airflow direction of a large-capacity air-cooled battery plug-in box provided by the present invention; Figure 4 It is a structural schematic diagram of a cover plate of a large-capacity air-cooled battery plug-in box provided by the present invention; Figure 5 It is a structural schematic diagram of a battery module of a large-capacity air-cooled battery plug-in box provided by the present invention; Figure 6 It is a structural schematic diagram of a battery module of another large-capacity air-cooled battery plug-in box provided by the present invention; Figure 7 It is a schematic diagram of simulated surface temperature distribution of a battery module provided by the present invention; Figure 8 is a schematic diagram of simulated air flow velocity of a battery module provided by the present invention; Fig. 9 It is a schematic diagram of simulated airflow direction of a battery module provided by the present invention.

[0020] In the figure: 1. shell; 11. first baffle; 12. second baffle; 13. third baffle; 2. battery module; 21. first group; 22. second group; 23. third group; 24. fourth group; 25. first gap; 26. second gap; 27. battery cell; 271. harmonica tube plate; 272. end plate; 273. steel belt; 274. aluminum bar; 275. copper bar; 3. first heat dissipation structure; 31. first air inlet; 4. second heat dissipation structure; 41. second air inlet; 42. air duct; 43. air outlet; 5. exhaust fan; 6. cover plate; 61. first cover plate; 62. second cover plate; 63. third cover plate; 64. fourth cover plate; 65. first notch; 66. second notch. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and examples: Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0022] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0024] Combination Figure 1-3As shown, the embodiment of the present disclosure provides a large-capacity air-cooled battery plug-in box, including a housing 1 and a battery module 2, wherein the battery module 2 includes a first group 21, a second group 22, a third group 23 and a fourth group 24 arranged in parallel in series, a first gap 25 is provided between the second group 22 and the third group 23, a second gap 26 is provided between the first group 21 and the second group 22 and between the third group 23 and the fourth group 24, each group in the battery module 2 includes a plurality of battery cells 27, and the plurality of battery cells 27 are sequentially arranged in series along the thickness direction, and two adjacent battery cells 27 are connected in series. A harmonica tube plate 271 is provided between the battery cells 27, and the housing 1 includes a first heat dissipation structure 3 provided on the side wall, a second heat dissipation structure 4 provided on the bottom wall, and an exhaust fan 5 provided corresponding to the first gap 25, wherein the airflow includes a first airflow and a second airflow, the first airflow enters the plug-in box from the first heat dissipation structure 3, flows through the battery cells 27 along the harmonica tube plate 271 and flows to the first gap 25, the second airflow flows from the second heat dissipation structure 4 into the second gap 26, flows through the battery cells 27 along the harmonica tube plate 271 and merges with the first airflow, and the airflow is discharged from the plug-in box by the exhaust fan 5.

[0025] The large-capacity air-cooled battery plug-in box provided by the embodiment of the present disclosure is adopted. By setting the first heat dissipation structure 3, the first airflow can enter the plug-in box through the first heat dissipation structure 3. When flowing through the battery cells 27 along the harmonica tube plate 271, the first airflow can take away the heat generated by the two adjacent battery cells 27 in the battery module 2 when they are working. Then the first airflow flows to the first gap 25 and can be discharged from the plug-in box by the exhaust fan 5. In this way, the heat dissipation effect of the battery cells 27 in the battery module 2 can be improved. By setting the second heat dissipation structure 4, the second airflow can enter the plug-in box through the second heat dissipation structure 4 and flow to the second gap 26. Then the harmonica tube plates 271 of the second group 22 and the third group 23 flow through the battery cells 27 and can take away the heat generated by the adjacent battery cells 27 in the second group 22 and the third group 23 when they are working. Then the second airflow flows to the first gap 25 and is discharged from the plug-in box by the exhaust fan 5. In this way, the heat dissipation effect of the battery cells 27 of the second group 22 and the third group 23 near the middle of the battery plug-in box can be further improved, which is conducive to improving the temperature uniformity between each battery cell 27.

[0026] Based on the above technical solution, the number of the battery cells 27 in the first group 21, the second group 22, the third group 23 and the fourth group 24 is greater than or equal to 6. Preferably, the number of the battery cells 27 in the first group 21, the second group 22, the third group 23 and the fourth group 24 can be 6 to 13.

[0027] Compared with most traditional battery boxes consisting of 16 battery cells 27, the air-cooled battery box provided in the present application consists of at least 24 battery cells 27, and can also be composed of 28, 32, 36, 40, 44, 48 or 52 battery cells 27, which increases the number of battery cells 27 and improves the energy density of the battery box, while still being able to ensure the overall heat dissipation effect and temperature uniformity.

[0028] Based on the above technical solution, Figure 1 and Figure 2 As shown, the first heat dissipation structure 3 includes a first air inlet 31 , and the number of the first air inlet 31 is multiple, and the multiple first air inlets 31 are sequentially spaced apart along the arrangement direction of the battery cells 27 .

[0029] On the basis of the above technical solution, the plurality of first air inlets 31 are arranged in one-to-one correspondence with the harmonica tube plates 271 , and extend along the height direction of the battery core 27 .

[0030] Multiple first air inlets 31 are arranged along the arrangement direction of the battery cells 27, and are respectively arranged corresponding to the harmonica tube plates 271 between the battery cells 27. In this way, after the airflow flows into the battery compartment from the outside, it can enter the corresponding harmonica tube plates 271 more quickly, which can improve the heat dissipation efficiency to a certain extent.

[0031] Based on the above technical solution, the air inlet area of ​​the first air inlet 31 is adapted to the internal air flow rate.

[0032] Specifically, the size of each first air inlet 31 is different, and the size of each first air inlet 31 is adjusted according to the air flow rate inside the housing 1. When the exhaust fan 5 is arranged at the housing 1 at one end of the first gap 25, the air flow rate inside the housing 1 will have a certain difference as the distance from the exhaust fan 5 is different. Therefore, the air inlet area of ​​each first air inlet 31 is adjusted according to the air flow rate, so that the air flow rates at multiple first air inlets 31 are similar, thereby improving the temperature uniformity between multiple battery cells 27 and improving the temperature uniformity of the battery box as a whole.

[0033] Based on the above technical solution, Figure 1-3 As shown, the second heat dissipation structure 4 includes a second air inlet 41, an air duct 42 and an air outlet slot 43, the second air inlet 41 is arranged at the connection between the side wall and the bottom wall of the outer shell 1, the air duct 42 is arranged inside the bottom wall, and the air outlet slot 43 extends along the arrangement direction of the battery cells 27 and is arranged toward the second gap 26, wherein the second airflow flows into the air duct 42 from the second air inlet 41, flows out from the air outlet slot 43 to the second gap 26, and then flows through the battery cells 27 along the harmonica tube plate 271 to the first gap 25.

[0034] Specifically, after the second airflow flows to the second gap 26, it will flow through the harmonica tube plates 271 between multiple adjacent battery cells 27 to reach the first gap 25, which can have a cooling effect on the adjacent battery cells 27. The second airflow flows through the harmonica tube plates 271 between the battery cells 27 in the second group 22 and the third group 23. Since the second group 22 and the third group 23 are arranged between the first group 21 and the fourth group 24, the temperature of the battery cells 27 in the second group 22 and the third group 23 is higher than that of the first group 21 and the fourth group 24. By setting the second air inlet 41, the air duct 42 and the air outlet slot 43, the second airflow directly enters the second gap 26, and then flows through the battery cells 27 of the second group 22 and the third group 23 at the same time on the basis of the first airflow, which can further improve the heat dissipation effect of the battery cells 27 of the second group 22 and the third group 23 near the middle of the battery compartment, which is beneficial to improving the temperature uniformity between each battery cell 27.

[0035] On the basis of the above technical solution, a heat insulating gasket is provided between the battery module 2 and the bottom wall of the housing 1 , and the heat insulating gasket is provided with an opening, and the opening is arranged corresponding to the air outlet slot 43 .

[0036] The second air flow flows into the air duct 42 from the second air inlet 41, and flows out from the air outlet slot 43 to the second gap 26. The provision of the thermal insulation gasket can ensure that when the air flow flows through the air duct 42, the air flow temperature is not affected by the temperature of the battery cell 27, thereby avoiding the phenomenon of temperature increase after the air flow flows through the air duct 42, and ensuring the subsequent heat dissipation effect of the air flow.

[0037] Based on the above technical solution, Figure 2 As shown, the housing 1 is provided with a first baffle 11 and a second baffle 12 . The first baffle 11 is provided in the first gap 25 and is arranged opposite to the exhaust fan 5 . The second baffle 12 is provided at the four corners of the housing 1 .

[0038] Based on the above technical solution, Figure 2 As shown, the housing 1 is further provided with a third stop bar 13 , and the number of the third stop bars 13 is multiple, and the multiple third stop bars 13 are relatively arranged at two ends of the second gap 26 .

[0039] The arrangement of the first baffle 11 , the second baffle 12 and the third baffle 13 can block the airflow entering the battery compartment to a certain extent, so that the airflow can flow along a predetermined route, thereby ensuring the heat dissipation effect at each position and facilitating improving the temperature uniformity between each battery cell 27 .

[0040] Based on the above technical solution, Figure 4As shown, the large-capacity air-cooled battery plug-in box also includes a cover plate 6, which includes a first cover plate 61, a second cover plate 62, a third cover plate 63 and a fourth cover plate 64, which are respectively covered on the first group 21, the second group 22, the third group 23 and the fourth group 24, each of the cover plates 6 has a flange extending downward in the circumferential direction, and the second cover plate 62 and the third cover plate 63 are provided with a first notch 65 at the flanges at both ends along the arrangement direction of the battery cells 27.

[0041] Based on the above technical solution, Figure 4 As shown, the flanges of the second cover plate 62 and the third cover plate 63 close to the first gap 25 are provided with second notches 66 , and there are multiple second notches 66 , which are evenly spaced.

[0042] Since the second group 22 and the third group 23 are arranged between the first group 21 and the fourth group 24, the temperature of the cells 27 in the second group 22 and the third group 23 is higher than that in the first group 21 and the fourth group 24. The corresponding second cover plate 62 and the third cover plate 63 are provided with first notches 65 at the flanges at both ends along the arrangement direction of the cells 27, so that the airflow in this direction is larger and the flow rate is faster, thereby improving the heat dissipation effect. The corresponding second cover plate 62 and the third cover plate 63 are provided with second notches 66 at the flanges close to the first gap 25, so that the airflow at the top of the second group 22 and the third group 23 is facilitated to flow, so that the overall temperature uniformity is better.

[0043] Based on the above scheme, if Figure 5 and Figure 6 As shown, end plates 272 are provided at both ends along the arrangement direction of the battery cells 27, and the battery module 2 also includes a steel belt 273, which is circumferentially bundled to the battery cells 27 and the end plates 272, and the positive and negative electrodes of two adjacent battery cells 27 are sequentially connected through the aluminum bar 274, and the positive and negative electrodes of the first group 21, the second group 22, the third group 23 and the fourth group 24 are sequentially connected through the copper bar 275, forming a series system. In addition, the end plates 272 can be set at the ends of each group of battery cells 27, with a number of eight, or can be set at the ends of two groups of battery cells 27 at the same time, with a number of four. In this way, the end plates 272 can also play the role of the third stop bar 13, so that the third stop bar 13 can be removed from the housing 1.

[0044] In order to verify the temperature uniformity of the large-capacity air-cooled battery plug-in box provided in this application, the surface temperature distribution of the battery module was simulated using fluid dynamics (CFD) simulation software. The simulated surface temperature diagram obtained is as follows: Figure 7 As shown, Figure 7To simulate the surface temperature distribution of the first group 21 and the second group 22 of battery cells 27, the temperature difference between each battery cell 27 ranges from 2°C to 3°C. Compared with the traditional battery module, the temperature difference is greatly reduced, thus indicating that the large-capacity air-cooled battery box improves the temperature uniformity between the battery cells.

[0045] In order to verify the effects of the first heat dissipation structure 3 and the second heat dissipation structure 4 of the large-capacity air-cooled battery plug-in box provided in the present application on heat dissipation and temperature uniformity, the airflow speed and direction between the battery modules 2 were simulated using CFD simulation software. Figure 8 is a cloud diagram of the air flow velocity between the battery modules 2. It can be seen that the air flow velocity at the first gap 25 and the second gap 26 is significantly greater than that at other positions. Fig. 9 is the airflow direction between the battery modules 2. It can be seen that there is obvious airflow entering the first gap 25 and the second gap 26 to exchange heat with the battery cells 27 to improve the overall temperature uniformity.

[0046] The present invention is described above by way of examples, but the present invention is not limited to the above specific embodiments, and any changes or modifications made based on the present invention belong to the scope of protection claimed by the present invention.

Claims

1. A large-capacity air-cooled battery box, characterized in that: It comprises a shell and a battery module, wherein the battery module comprises a first group, a second group, a third group and a fourth group which are arranged in parallel in series, a first gap is provided between the second group and the third group, a second gap is provided between the first group and the second group and between the third group and the fourth group, each group in the battery module comprises a plurality of battery cells, the plurality of battery cells are arranged in series in sequence along the thickness direction, a harmonica tube plate is provided between two adjacent battery cells, the shell comprises a first heat dissipation structure provided on the side wall, a second heat dissipation structure provided on the bottom wall and an exhaust fan provided corresponding to the first gap, wherein the airflow comprises a first airflow and a second airflow, the first airflow enters the plug-in box from the first heat dissipation structure, flows through the battery cells along the harmonica tube plate and flows to the first gap, the second airflow flows into the second gap from the second heat dissipation structure, flows through the battery cells along the harmonica tube plate and merges with the first airflow, and the airflow is discharged from the plug-in box by the exhaust fan.

2. The large-capacity air-cooled battery plug-in box according to claim 1 is characterized in that: The number of battery cells in the first group, the second group, the third group and the fourth group is greater than or equal to 6.

3. The large-capacity air-cooled battery plug-in box according to claim 1, characterized in that: The first heat dissipation structure includes a plurality of first air inlets, and the plurality of first air inlets are sequentially spaced apart along the direction in which the battery cells are arranged.

4. The large-capacity air-cooled battery plug-in box according to claim 3 is characterized in that: The multiple first air inlets are arranged one by one corresponding to the harmonica tube plates and extend along the height direction of the battery core.

5. The large-capacity air-cooled battery plug-in box according to claim 3, characterized in that: The air inlet area of ​​the first air inlet is adapted to the internal air flow rate.

6. The large-capacity air-cooled battery plug-in box according to any one of claims 1 to 5, characterized in that: The second heat dissipation structure includes a second air inlet, an air duct and an air outlet slot, the second air inlet is arranged at the connection between the side wall and the bottom wall of the outer shell, the air duct is arranged inside the bottom wall, and the air outlet slot extends along the arrangement direction of the battery cells and is arranged toward the second gap, wherein the second airflow flows into the air duct from the second air inlet, flows out from the air outlet slot to the second gap, and then flows through the battery cells along the harmonica tube plate to the first gap.

7. The large-capacity air-cooled battery plug-in box according to any one of claims 1 to 5, characterized in that: The housing is provided with a first baffle and a second baffle, wherein the first baffle is arranged in the first gap and is arranged opposite to the exhaust fan, and the second baffle is arranged at four corners of the housing.

8. The large-capacity air-cooled battery plug-in box according to claim 7, characterized in that: The housing is further provided with a third stopper, and the number of the third stopper is multiple, and the multiple third stoppers are relatively arranged at two ends of the second gap.

9. The large-capacity air-cooled battery plug-in box according to any one of claims 1 to 5, characterized in that: It also includes a cover plate, which includes a first cover plate, a second cover plate, a third cover plate and a fourth cover plate, which are respectively covered on the first group, the second group, the third group and the fourth group, each of the cover plates has a flange extending downward in the circumferential direction, and the second cover plate and the third cover plate have first notches at the flanges at both ends along the direction of arrangement of the battery cells.

10. The large-capacity air-cooled battery plug-in box according to claim 9, characterized in that: The flanges of the second cover plate and the third cover plate close to the first gap are provided with second notches, and there are a plurality of the second notches, which are evenly spaced.

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