Inlet air preheater with good insulativity
By employing an insulation design using mica sheets and Teflon insulation layers in the intake preheater, the problems of short circuits and corrosion in the intake preheater are solved, insulation and durability are improved, and service life is extended.
Patent Information
- Application Number
- CN202520586509.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2026-02-03
- Estimated Expiration
- 2035-03-31
AI Technical Summary
Existing air intake preheaters lack a robust insulation structure, which can easily lead to short circuits and corrosion, affecting their service life and performance.
It employs insulation designs such as mica sheets and insulating coatings, and isolates the heating element and preheater base through the insulated connection of the terminal block and heating tape to prevent electrical short circuits. It also uses a Teflon insulation layer to interrupt current flow and prevent electro-corrosion.
It improves the insulation and corrosion resistance of the intake preheater, extends its service life, avoids electrical short circuits and corrosion problems, and ensures the reliability and environmental adaptability of the product.
Smart Images
Figure CN223868087U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to the field of air intake preheater, especially to an air intake preheater with good insulation. BACKGROUND
[0002] The existing air intake preheater is usually used to heat the intake air during cold start, reduce the engine start wear and tear and improve the combustion efficiency. The traditional air intake preheater does not have a good stable insulation structure, and after long-term use, for example, it is easy to cause short circuit after wear or deformation, which seriously affects the service life of the product.
[0003] In addition, the current preheater product has no protection, and corrosion occurs during use, affecting the product performance.
[0004] Therefore, in view of the above-mentioned technical problems, it is necessary to provide a new technical scheme. UTILITY MODEL CONTENT
[0005] In order to at least solve one of the technical problems existing in the prior art, the utility model provides an air intake preheater with good insulation, which is designed by cleverly matching, and sets mica sheets, insulation coatings and the like, which can play a good insulation isolation, avoid causing short circuit and improve the service life of the product. The specific technical scheme is as follows:
[0006] On the one hand, the utility model provides an air intake preheater with good insulation, which comprises a preheater seat, an electric heating band and at least two terminal posts;
[0007] The preheater seat is provided with a containing cavity, and the containing cavity has at least one opening. The surface of the preheater seat is provided with at least two through holes, and the two through holes are communicated with the containing cavity;
[0008] The electric heating band is fixedly arranged in the containing cavity, and the two ends of the electric heating band are provided with mounting holes. The electric heating band is mounted on the corresponding terminal post through the mounting holes;
[0009] The terminal post comprises a first bolt, a first insulation sleeve, a first mica sheet, a first flat gasket and a first nut. The mounting hole of the end of the electric heating band is sleeved on the corresponding first bolt;
[0010] The first bolt sleeved with the electric heating band is sleeved with the first insulation sleeve, then passes through the through hole and extends out of the preheater seat. The first bolt is insulated from the preheater seat through the first insulation sleeve. The first mica sheet, the first flat gasket and the first nut are sequentially sleeved on the extending end of the first bolt. The first nut is configured to fix the first bolt on the preheater seat.
[0011] As a preferred scheme of the air intake preheater, the electric heating band comprises a plurality of electric heating sheets, the plurality of electric heating sheets are arranged in parallel in the accommodating cavity, a plurality of fixing holes are arranged on the electric heating sheets at intervals, a plurality of fixing columns are arranged in the accommodating cavity at intervals, the electric heating sheets are fixedly sleeved on the fixing columns through the fixing holes, a spacer is sleeved on the fixing column, the spacer is configured to separate two adjacent electric heating sheets, and the electric heating sheets are sequentially electrically connected in head-tail mode along the current flowing direction.
[0012] As a preferred scheme of the air intake preheater, a first mounting hole is formed in the bottom wall of the accommodating cavity in a penetrating mode, and a threaded hole is formed in the top wall of the accommodating cavity.
[0013] The fixing column comprises a fixing bolt, a second flat washer, a second mica sheet, a second insulating sleeve, a mica sleeve, the spacer and a mica washer; the fixing bolt is sequentially sleeved with the second flat washer, the second mica sheet, the second insulating sleeve and the mica sleeve, the fixing bolt is inserted into the first mounting hole from outside the preheater base and extends into the accommodating cavity, the second flat washer and the second mica sheet are stopped outside the preheater base, the second insulating sleeve is accommodated in the first mounting hole, the mica sleeve is located in the accommodating cavity, the spacer and the electric heating sheet are sequentially sleeved on the mica sleeve, the electric heating sheet is isolated from the bottom wall of the accommodating cavity through the spacer, the electric heating sheets are isolated from each other through the spacer, the mica washer is sleeved on the fixing bolt, the mica washer is located on the side of the mica sleeve away from the second insulating sleeve, and one end of the fixing bolt is screwed into the threaded hole.
[0014] As a preferred scheme of the air intake preheater, the electric heating sheet is not electrically connected at the head-tail position, the spacer comprises a mica sheet and a metal gasket, the mica sheet and the metal gasket are sleeved on the fixing column, and two adjacent electric heating sheets are separated by the mica sheet and the metal gasket; at the head-tail position of the electric heating sheet, the spacer is a metal gasket, and the metal gasket is sleeved between the two adjacent electric heating sheets.
[0015] As a preferred scheme of the air intake preheater, one end of each of the two electric heating sheets is electrically connected with a connecting band, a mounting hole is formed in the connecting band, one connecting band is fixedly installed on one terminal post through the mounting hole, and the other connecting band is fixedly installed on the other terminal post through the mounting hole.
[0016] As a preferred scheme of the air intake preheater, the first bolt is a conductive bolt, and the fixing bolt is a conductive bolt.
[0017] As a preferred scheme of the air intake preheater, a Teflon insulating layer is arranged on the surface of the preheater base.
[0018] As a preferred scheme of the air intake preheater, the thickness of the Teflon insulating layer is 0.019mm-0.051mm.
[0019] As a preferred embodiment of the air intake preheater described in this utility model, the fixing column further includes an insulating cover, which covers the bolt head of the fixing bolt.
[0020] As a preferred embodiment of the air intake preheater described in this utility model, one terminal is installed on the upper part of the preheater base, and the other terminal is installed on the bottom of the preheater base, with the two terminals arranged correspondingly above and below each other.
[0021] Compared with the prior art, the technical solution of this utility model has at least one or more of the following beneficial effects:
[0022] The heating tape formed by the metal heating element is connected to the power source through the electrode (i.e., the first bolt on the terminal block), forming a predetermined current path to ensure uniform heating of the heating tape. The electrode is isolated from the preheater base through the first mica sheet and Teflon insulation layer to prevent electrical short circuits.
[0023] The heating elements are separated by mica sheets and metal gaskets and fixed by bolts passing through them, which avoids localized heating problems, ensures its reliability, and improves the service life of the product.
[0024] During operation, after the engine starts, the intake preheater located in the intake manifold begins to work and gradually heats up. If the surface of the preheater housing is not coated with a Teflon insulating layer, an electrolyte will form when the preheater housing comes into contact with the incoming gas (such as oil vapor, moisture, dust, or sulfides and chlorides in other pollutants). The preheater housing itself contains elements such as copper and iron, and there will be a potential difference between different metal materials, causing current to flow between the two materials. When the current flows, atoms on the anode material will lose electrons (oxidation), forming ions that dissolve into the electrolyte and undergo a metal reaction, causing initial corrosion. In humid conditions, the heating creates a high-temperature and high-humidity environment, and the electrolyte adhering to the surface of the preheater housing is more likely to accelerate metal oxidation, thereby affecting circuit performance and the mechanical properties of components, and in severe cases, may even cause a short circuit. The Teflon insulation layer, applied to the preheater base, interrupts current flow and prevents the formation of a potential difference, thus combating electro-corrosion caused by high temperature and humidity environments. Furthermore, the extremely low surface energy of the Teflon insulation layer reduces contaminant adhesion, and its excellent chemical resistance provides strong resistance to most chemicals. The superior corrosion resistance, impermeability, water swelling resistance, and shock resistance of the Teflon insulation layer significantly extend the service life and operating environment of the preheater base after coating it with the Teflon insulation layer.
[0025] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0026] To more clearly illustrate the technical solution of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of the main structure of the air intake preheater described in this patent;
[0028] Figure 2 yes Figure 1 A cross-sectional view of the air intake preheater in the position of a fixed column;
[0029] Figure 3 yes Figure 1 A partially enlarged three-dimensional structural diagram of the air intake preheater;
[0030] Figure 4 This is an electron microscope schematic diagram of the Teflon insulation layer on the surface of the preheater seat described in this patent;
[0031] Figure 5 This is an electron microscope schematic diagram of the Teflon insulation layer on the surface of the preheater seat described in this patent.
[0032] Among them, 1-preheater base, 2-heating tape, 3-terminal, 11-receiving cavity, 12-Teflon insulation layer, 13-fixing post, 131-fixing bolt, 132-second flat washer, 133-second mica sheet, 134-second insulating sleeve, 135-mica sleeve, 136-mica washer, 137-insulating cover, 21-heating element, 22-connecting strip, 31-first bolt, 32-first insulating sleeve, 33-first mica sheet, 34-first flat washer, 35-first nut. Detailed Implementation
[0033] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.
[0034] In the description of this utility model, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this utility model. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0035] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "provided with," "equipped with," "connected," "installed," "sleeved," "opened," and "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.
[0036] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
[0037] Please refer to Figures 1-5 .like Figures 1-5 As shown, this utility model provides an intake preheater with good insulation, which is mainly used in automobile intake pipes, but this patent is not limited thereto. The intake preheater includes a preheater base 1, an electric heating tape 2, and at least two terminals 3;
[0038] The preheater base 1 has a receiving cavity 11, the receiving cavity 11 has at least one opening, and the surface of the preheater base 1 has at least two through holes, both of which are connected to the receiving cavity 11.
[0039] The electric heating tape 2 is fixedly housed in the receiving cavity 11. Both ends of the electric heating tape 2 are provided with mounting holes, and the electric heating tape 2 is installed on the corresponding terminal block 3 through the mounting holes.
[0040] The terminal block 3 includes a first bolt 31, a first insulating sleeve 32, a first mica sheet 33, a first flat washer 34 and a first nut 35, and the mounting hole at the end of the heating tape 2 is fitted onto the corresponding first bolt 31;
[0041] After the first insulating sleeve 32 is fitted onto the first bolt 31, it passes through the through hole and extends out of the preheater base 1. The first bolt 31 is insulated from the preheater base 1 by the first insulating sleeve 32. The first mica sheet 33, the first flat washer 34, and the first nut 35 are sequentially fitted onto the protruding end of the first bolt 31. The first nut 35 is configured to fix the first bolt 31 onto the preheater base 1. In this example, the first bolt 31 is a conductive hexagonal head bolt.
[0042] In the example, the first nut 35 is a hexagonal flange nut, wherein the flange face of the hexagonal flange nut is close to the first flat washer 34.
[0043] In the example, openings are provided on both sides of the receiving cavity 11.
[0044] In the example, at least one of the two terminals 3 is the positive terminal and the other is the negative terminal.
[0045] In a preferred embodiment, such as Figure 1 As shown, the heating tape 2 includes multiple heating elements 21, which are arranged in parallel within the receiving cavity 11. Multiple fixing holes are spaced apart on the heating elements 21, and multiple fixing posts 13 are spaced apart within the receiving cavity 11. The heating elements 21 are fixedly sleeved onto the fixing posts 13 through the fixing holes. Spacers are sleeved on the fixing posts 13, and the spacers are configured to separate at least two adjacent heating elements 21. The heating elements are electrically connected end to end along the direction of current flow.
[0046] Specifically, such as Figure 3As shown, the bottom wall of the receiving cavity 11 has a through first mounting hole, and the top wall of the receiving cavity 11 has a threaded hole; the fixing column 13 includes a fixing bolt 131, a second flat washer 132, a second mica sheet 133, a second insulating sleeve 134, a mica sleeve 135, a spacer, and a mica washer 136; the fixing bolt 131 is sequentially fitted with the second flat washer 132, the second mica sheet 133, the second insulating sleeve 134, and the mica sleeve 135, and the fixing bolt 131 is inserted from outside the preheater seat 1 into the first mounting hole and extends into the receiving cavity 11, the second... A flat washer 132 and a second mica sheet 133 are positioned outside the preheater base 1. A second insulating sleeve 134 is housed within the first mounting hole. A mica sleeve 135 is located within the receiving cavity 11. A spacer and a heating element 21 are sequentially threaded onto the mica sleeve 135. The heating element is isolated from the bottom wall of the receiving cavity by a spacer, and the heating elements are also isolated from each other by spacers. A mica washer 136 is fitted onto the fixing bolt 131. The mica washer 136 is located on the side of the mica sleeve 135 away from the second insulating sleeve 134. One end of the fixing bolt 131 is screwed into a threaded hole. In this example, the second mica sheet 133 is configured to insulate the fixing bolt 131 from the preheater base 1, the second insulating sleeve 134 is configured to insulate the fixing bolt 131 from the first mounting hole of the preheater base 1, and the mica sleeve 135 is configured to insulate the heating element 21 from the fixing bolt 131. In the example, the fixing bolt 131 is a conductive internal hexagon socket head cap screw. In the example, the lowermost heating element is also separated from the bottom wall of the receiving cavity by a spacer.
[0047] In a further preferred embodiment, the fixing post 13 also includes an insulating cover 137, which covers the bolt head of the fixing bolt 131.
[0048] In the example, at the non-terminal electrical connection points of the heating elements, the spacers consist of mica sheets and metal gaskets, which are fitted onto the fixing posts. Adjacent heating elements are separated by these spacers. At the terminal electrical connection points, the spacers are metal gaskets, fitted between adjacent heating elements. Corrugated metal heating elements are separated from each other by mica and metal gaskets, and secured by bolts passing through them, preventing localized overheating, ensuring reliability, and extending product lifespan.
[0049] In a preferred embodiment, each of the two heating elements 21 is electrically connected to a connecting strip 22 at one end. The connecting strip 22 has mounting holes. One connecting strip 22 is fixedly mounted to a terminal 3 through the mounting holes, and the other connecting strip 22 is fixedly mounted to another terminal 3 through the mounting holes. In this example, the heating elements that are in direct electrical contact with the connecting strips are preferably located on either side of the heating strip. In this example, the heating element 21 is a corrugated heating element, and the direction of the corrugation of the heating element 21 is consistent with the length direction of the fixing post. Preferably, the thickness of the heating element 21 is greater than or equal to 0.8 mm. More preferably, the thickness of the corrugated heating element 21 is between 1.0 mm and 1.2 mm. In this example, the connecting strip 22 and its corresponding heating element 21 are electrically connected by being sleeved on the fixing post.
[0050] This patent utilizes a corrugated heating element, improving the product's durability and reliability. During the cold start phase, the temperature of the preheater gradually increases along the flow direction, especially at the center of the corrugated metal element, while the temperature on the outer side of the preheater base gradually decreases. In the absence of ventilation, the center of the corrugated metal element can reach a maximum temperature of 1200℃. Therefore, the use of a corrugated heating element mitigates thermal expansion and contraction during heating, with the corrugations acting as a buffer to prevent deformation and failure of the heated metal element. This also reduces post-assembly stress and increases the product's lifespan.
[0051] In a preferred embodiment, such as Figures 4-5 As shown, a Teflon insulating layer 12 is provided on the surface of the preheater base 1. Preferably, the thickness of the Teflon insulating layer 12 is 0.019 mm to 0.051 mm. In the example, both the inner and outer surfaces of the preheater base 1) are coated with the Teflon insulating layer.
[0052] During operation, after the engine starts, the intake preheater located in the intake manifold begins to work and gradually heats up. If the surface of the preheater housing is not coated with a Teflon insulating layer, an electrolyte will form when the preheater housing comes into contact with the incoming gas (such as oil vapor, moisture, dust, or sulfides and chlorides in other pollutants). The preheater housing itself contains elements such as copper and iron, and there will be a potential difference between different metal materials, causing current to flow between the two materials. When the current flows, atoms on the anode material will lose electrons (oxidation), forming ions that dissolve into the electrolyte and undergo a metal reaction, causing initial corrosion. In humid conditions, the heating creates a high-temperature and high-humidity environment, and the electrolyte adhering to the surface of the preheater housing is more likely to accelerate metal oxidation, thereby affecting circuit performance and the mechanical properties of components, and in severe cases, may even cause a short circuit. The Teflon insulation layer, applied to the preheater base, interrupts current flow and prevents the formation of a potential difference, thus combating electro-corrosion caused by high temperature and humidity environments. Furthermore, the extremely low surface energy of the Teflon insulation layer reduces contaminant adhesion, and its excellent chemical resistance provides strong resistance to most chemicals. The superior corrosion resistance, impermeability, water swelling resistance, and shock resistance of the Teflon insulation layer significantly extend the service life and operating environment of the preheater base after coating it with the Teflon insulation layer.
[0053] In a preferred example, one terminal 3 is installed on the upper side of the preheater base 1, and the other terminal 3 is installed on the bottom side of the preheater base 1, with the two terminals 3 arranged correspondingly above and below each other.
[0054] The heating tape formed by the metal heating element is connected to the power source through the electrode (i.e., the first bolt on the terminal block), forming a predetermined current path to ensure uniform heating of the heating tape. The electrode is isolated from the preheater base through the first mica sheet and Teflon insulation layer to prevent electrical short circuits.
[0055] It should be noted that, unless otherwise specified, all features in the above embodiments or embodiments described herein can be combined arbitrarily.
[0056] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "yet another embodiment," "another embodiment," "other embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.
[0057] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications and variations to the above embodiments within the scope of the present invention.
Claims
1. An inlet preheater with good insulation, characterized in that, It includes a preheater base (1), an electric heating tape (2), and at least two terminals (3); The preheater seat (1) has a receiving cavity (11) with at least one opening. The surface of the preheater seat (1) has at least two through holes, both of which are connected to the receiving cavity (11). The electric heating tape (2) is fixedly housed in the receiving cavity (11). Both ends of the electric heating tape (2) are provided with mounting holes. The electric heating tape (2) is installed on the corresponding terminal block (3) through the mounting holes. The terminal block (3) includes a first bolt (31), a first insulating sleeve (32), a first mica sheet (33), a first flat washer (34) and a first nut (35), and the mounting hole at the end of the heating tape (2) is fitted onto the corresponding first bolt (31); After the first insulating sleeve (32) is fitted onto the first bolt (31) which is fitted with the electric heating tape, it passes through the through hole and extends out to the outside of the preheater base (1). The first bolt (31) is insulated from the preheater base (1) by the first insulating sleeve (32). The first mica sheet (33), the first flat washer (34) and the first nut (35) are fitted onto the extended end of the first bolt (31) in sequence. The first nut (35) is configured to fix the first bolt (31) onto the preheater base (1).
2. The intake preheater according to claim 1, characterized in that, The heating tape (2) includes multiple heating elements (21), which are arranged in parallel within the receiving cavity (11). Multiple fixing holes are spaced apart on the heating elements (21), and multiple fixing posts (13) are spaced apart within the receiving cavity (11). The heating elements (21) are fixedly fitted onto the fixing posts (13) through the fixing holes. Spacers are fitted onto the fixing posts (13), and the spacers are configured to separate adjacent heating elements (21) from each other. The heating elements are electrically connected end to end along the direction of current flow.
3. The intake preheater according to claim 2, characterized in that, The bottom wall of the receiving cavity (11) is provided with a through first mounting hole, and the top wall of the receiving cavity (11) is provided with a threaded hole; The fixing column (13) includes a fixing bolt (131), a second flat washer (132), a second mica sheet (133), a second insulating sleeve (134), a mica sleeve (135), a spacer, and a mica washer (136); the fixing bolt (131) is sequentially fitted with the second flat washer (132), the second mica sheet (133), the second insulating sleeve (134), and the mica sleeve (135); the fixing bolt (131) is inserted into the first mounting hole from outside the preheater seat (1) and extends into the receiving cavity (11); the second flat washer (132) and the second mica sheet (133) are... The stop is placed outside the preheater seat (1), the second insulating sleeve (134) is housed in the first mounting hole, the mica sleeve (135) is located in the receiving cavity (11), the spacer and the heating element (21) are sequentially sleeved on the mica sleeve (135), the heating element is isolated from the bottom wall of the receiving cavity by the spacer, the heating element is isolated from each other by the spacer, the fixing bolt (131) is fitted with a mica washer (136), the mica washer (136) is located on the side of the mica sleeve (135) away from the second insulating sleeve (134), and one end of the fixing bolt (131) is screwed into the threaded hole.
4. The intake preheater according to any one of claims 1-3, characterized in that, At the non-head-to-tail electrical connection of the heating element, the spacer includes a mica sheet and a metal gasket. The mica sheet and the metal gasket are sleeved on the fixed post, and adjacent heating elements are separated by the mica sheet and the metal gasket. At the head-to-tail electrical connection of the heating element, the spacer is a metal gasket, which is sleeved between adjacent heating elements.
5. The intake preheater according to claim 2, characterized in that, Two of the heating elements (21) are electrically connected to a connecting strip (22) at one end. The connecting strip (22) has a mounting hole. One connecting strip (22) is fixedly installed on one of the terminals (3) through the mounting hole, and the other connecting strip (22) is fixedly installed on the other terminal (3) through the mounting hole.
6. The intake preheater according to claim 3, characterized in that, The first bolt (31) is a conductive bolt, and the fixing bolt (131) is a conductive bolt.
7. The intake preheater according to claim 1, characterized in that, The surface of the preheater base (1) is provided with a Teflon insulation layer (12).
8. The intake preheater according to claim 7, characterized in that, The thickness of the Teflon insulation layer (12) is 0.019 mm to 0.051 mm.
9. The intake preheater according to claim 3, characterized in that, The fixing post (13) also includes an insulating cover (137) that covers the bolt head of the fixing bolt (131).
10. The intake preheater according to claim 1, characterized in that, One terminal (3) is installed on the upper part of the preheater base (1), and the other terminal (3) is installed on the bottom of the preheater base (1). The two terminals (3) are set up correspondingly above and below each other.